Network File System (NFS) Version 4 Minor Version 1 Protocol
draft-ietf-nfsv4-rfc8881bis-06
| Document | Type | Active Internet-Draft (nfsv4 WG) | |
|---|---|---|---|
| Author | David Noveck | ||
| Last updated | 2026-02-22 | ||
| Replaces | draft-ietf-nfsv4-rfc5661bis | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-nfsv4-rfc8881bis-06
NFSv4 D. Noveck, Ed.
Internet-Draft NetApp
Obsoletes: 8881, 8434 (if approved) 22 February 2026
Updates: 5664, 8154 (if approved)
Intended status: Standards Track
Expires: 26 August 2026
Network File System (NFS) Version 4 Minor Version 1 Protocol
draft-ietf-nfsv4-rfc8881bis-06
Abstract
This document describes the Network File System (NFS) version 4 minor
version 1, including features retained from the base protocol (NFS
version 4 minor version 0, which is specified in RFC 7530) and
protocol extensions made and part of Minor Version 1. The later
minor version has no dependencies on NFS version 4 minor version 0,
and was, until recently, documented as a completely separate
protocol.
This document is part of a set of documents which collectively
obsolete RFCs 8881 and 8434. In addition to many corrections and
clarifications, it will rely on NFSv4-wide documents to substantially
revise the treatment of protocol extension, internationalization, and
security, superseding the descriptions of those aspects of the
protocol appearing in RFCs 5661 and 8881.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 26 August 2026.
Noveck Expires 26 August 2026 [Page 1]
Internet-Draft Draft of rfc88811bis February 2026
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Table of Contents
1. Introduction to this Update . . . . . . . . . . . . . . . . . 16
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 17
1.2. The Changed Role of this Specification . . . . . . . . . 18
1.3. Possibility of Compatibility Issues . . . . . . . . . . . 19
1.3.1. Compatibility issues for RFCTBD10 . . . . . . . . . . 20
1.3.2. Compatibility issues for NFSv4-wide Documents . . . . 23
1.3.3. Compatibility issues for RFCTBD30 . . . . . . . . . . 24
1.4. Addressing Protocol Defects Via XDR Changes . . . . . . . 25
1.5. Incorporation of RFC8434 . . . . . . . . . . . . . . . . 31
2. Introduction to this Minor Version Specification . . . . . . 32
2.1. The NFS Version 4 Minor Version 1 Protocol . . . . . . . 32
2.2. Scope of This Document . . . . . . . . . . . . . . . . . 32
2.3. NFSv4 Goals . . . . . . . . . . . . . . . . . . . . . . . 32
2.4. NFSv4.1 Goals . . . . . . . . . . . . . . . . . . . . . . 33
2.5. General Definitions . . . . . . . . . . . . . . . . . . . 34
2.6. Overview of NFSv4.1 Features . . . . . . . . . . . . . . 37
2.7. RPC and Security . . . . . . . . . . . . . . . . . . . . 37
2.8. Protocol Structure . . . . . . . . . . . . . . . . . . . 37
2.8.1. Core Protocol . . . . . . . . . . . . . . . . . . . . 38
2.8.2. Parallel Access . . . . . . . . . . . . . . . . . . . 38
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2.9. File System Model . . . . . . . . . . . . . . . . . . . . 38
2.9.1. Filehandles . . . . . . . . . . . . . . . . . . . . . 39
2.9.2. Numbered File Attributes . . . . . . . . . . . . . . 39
2.9.3. Named Attributes . . . . . . . . . . . . . . . . . . 42
2.9.4. Multi-Server Namespace . . . . . . . . . . . . . . . 42
3. Locking Facilities . . . . . . . . . . . . . . . . . . . . . 43
4. Differences from NFSv4.0 . . . . . . . . . . . . . . . . . . 44
5. Core Infrastructure . . . . . . . . . . . . . . . . . . . . . 45
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 45
5.2. RPC and XDR . . . . . . . . . . . . . . . . . . . . . . . 45
5.3. RPC-Based Security . . . . . . . . . . . . . . . . . . . 45
5.3.1. RPCSEC_GSS and Security Services . . . . . . . . . . 46
5.4. COMPOUND and CB_COMPOUND . . . . . . . . . . . . . . . . 46
5.5. Client Identifiers and Client Owners . . . . . . . . . . 47
5.5.1. Upgrade from NFSv4.0 to NFSv4.1 . . . . . . . . . . . 51
5.5.2. Server Release of Client ID . . . . . . . . . . . . . 51
5.5.3. Resolving Client Owner Conflicts . . . . . . . . . . 52
5.6. Server Owners . . . . . . . . . . . . . . . . . . . . . . 53
5.7. Transport Layers . . . . . . . . . . . . . . . . . . . . 54
5.7.1. REQUIRED and RECOMMENDED Properties of Transports . . 54
5.7.2. Client and Server Transport Behavior . . . . . . . . 55
5.7.3. Ports . . . . . . . . . . . . . . . . . . . . . . . . 57
6. Security-related Infrastructure . . . . . . . . . . . . . . . 57
6.1. NFSv4.1-specific Recommendations and Requirements Regarding
Security Services . . . . . . . . . . . . . . . . . . . . 58
6.2. NFSv4.1-specific Details of Security Negotiation . . . . 60
6.2.1. Put Filehandle Operations . . . . . . . . . . . . . . 60
6.2.2. LINK and RENAME . . . . . . . . . . . . . . . . . . . 63
7. Session . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.1. Motivation and Overview . . . . . . . . . . . . . . . . . 64
7.2. NFSv4 Integration . . . . . . . . . . . . . . . . . . . . 65
7.2.1. SEQUENCE and CB_SEQUENCE . . . . . . . . . . . . . . 66
7.2.2. Client ID and Session Association . . . . . . . . . . 66
7.3. Channels . . . . . . . . . . . . . . . . . . . . . . . . 67
7.3.1. Association of Connections, Channels, and Sessions . 67
7.4. Server Scope . . . . . . . . . . . . . . . . . . . . . . 68
7.5. Trunking . . . . . . . . . . . . . . . . . . . . . . . . 70
7.5.1. Verifying Claims of Matching Server Identity . . . . 73
7.6. Exactly Once Semantics . . . . . . . . . . . . . . . . . 74
7.6.1. Slot Identifiers and Reply Cache . . . . . . . . . . 76
7.6.2. Retry and Replay of Reply . . . . . . . . . . . . . . 85
7.6.3. Resolving Server Callback Races . . . . . . . . . . . 87
7.6.4. COMPOUND and CB_COMPOUND Construction Issues . . . . 88
7.6.5. Setting Size limits for Sessions . . . . . . . . . . 90
7.7. RDMA Considerations . . . . . . . . . . . . . . . . . . . 91
7.7.1. RDMA Connection Resources . . . . . . . . . . . . . . 91
7.7.2. Flow Control . . . . . . . . . . . . . . . . . . . . 92
7.7.3. Padding . . . . . . . . . . . . . . . . . . . . . . . 92
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7.7.4. Dual RDMA and Non-RDMA Transports . . . . . . . . . . 94
7.8. Session Security . . . . . . . . . . . . . . . . . . . . 94
7.8.1. Session Callback Security . . . . . . . . . . . . . . 94
7.8.2. Backchannel RPC Security . . . . . . . . . . . . . . 94
7.8.3. Protection from Unauthorized State Changes . . . . . 95
7.9. The Secret State Verifier (SSV) GSS Mechanism . . . . . . 99
7.10. Security Considerations for RPCSEC_GSS When Using the SSV
Mechanism . . . . . . . . . . . . . . . . . . . . . . . 104
7.11. Session Mechanics - Steady State . . . . . . . . . . . . 105
7.11.1. Obligations of the Server . . . . . . . . . . . . . 105
7.11.2. Obligations of the Client . . . . . . . . . . . . . 105
7.11.3. Steps the Client Takes to Establish a Session . . . 106
7.12. Session Inactivity Timer . . . . . . . . . . . . . . . . 107
7.13. Session Mechanics - Recovery . . . . . . . . . . . . . . 107
7.13.1. Events Requiring Client Action . . . . . . . . . . . 107
7.13.2. Events Requiring Server Action . . . . . . . . . . . 112
7.14. Parallel NFS and Sessions . . . . . . . . . . . . . . . . 113
8. Persistence . . . . . . . . . . . . . . . . . . . . . . . . . 113
8.1. Need for Feature Respecification . . . . . . . . . . . . 114
8.2. Persistence of Reply Cache . . . . . . . . . . . . . . . 115
8.3. Persistence of Locking State . . . . . . . . . . . . . . 117
8.4. Client Handling of Server Failure When Persistence Can be
Used . . . . . . . . . . . . . . . . . . . . . . . . . . 118
8.5. Client Use of Session-based Persistence . . . . . . . . . 119
8.6. Client Use of Clientid-based Persistence . . . . . . . . 121
9. Protocol Constants and Data Types . . . . . . . . . . . . . . 122
9.1. Basic Constants . . . . . . . . . . . . . . . . . . . . . 122
9.2. Basic Data Types . . . . . . . . . . . . . . . . . . . . 123
9.3. Structured Data Types . . . . . . . . . . . . . . . . . . 126
9.3.1. nfstime4 . . . . . . . . . . . . . . . . . . . . . . 126
9.3.2. time_how4 . . . . . . . . . . . . . . . . . . . . . . 127
9.3.3. settime4 . . . . . . . . . . . . . . . . . . . . . . 127
9.3.4. specdata4 . . . . . . . . . . . . . . . . . . . . . . 127
9.3.5. fsid4 . . . . . . . . . . . . . . . . . . . . . . . . 127
9.3.6. change_policy4 . . . . . . . . . . . . . . . . . . . 127
9.3.7. fattr4 . . . . . . . . . . . . . . . . . . . . . . . 128
9.3.8. change_info4 . . . . . . . . . . . . . . . . . . . . 128
9.3.9. netaddr4 . . . . . . . . . . . . . . . . . . . . . . 128
9.3.10. state_owner4 . . . . . . . . . . . . . . . . . . . . 129
9.3.11. open_to_lock_owner4 . . . . . . . . . . . . . . . . . 129
9.3.12. stateid4 . . . . . . . . . . . . . . . . . . . . . . 129
9.3.13. layouttype4 . . . . . . . . . . . . . . . . . . . . . 130
9.3.14. deviceid4 . . . . . . . . . . . . . . . . . . . . . . 130
9.3.15. device_addr4 . . . . . . . . . . . . . . . . . . . . 131
9.3.16. layout_content4 . . . . . . . . . . . . . . . . . . . 131
9.3.17. layout4 . . . . . . . . . . . . . . . . . . . . . . . 131
9.3.18. layoutupdate4 . . . . . . . . . . . . . . . . . . . . 132
9.3.19. layouthint4 . . . . . . . . . . . . . . . . . . . . . 132
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9.3.20. layoutiomode4 . . . . . . . . . . . . . . . . . . . . 132
9.3.21. nfs_impl_id4 . . . . . . . . . . . . . . . . . . . . 133
9.3.22. threshold_item4 . . . . . . . . . . . . . . . . . . . 133
9.3.23. mdsthreshold4 . . . . . . . . . . . . . . . . . . . . 134
10. Filehandles . . . . . . . . . . . . . . . . . . . . . . . . . 135
10.1. Obtaining the First Filehandle . . . . . . . . . . . . . 135
10.1.1. Root Filehandle . . . . . . . . . . . . . . . . . . 135
10.1.2. Public Filehandle . . . . . . . . . . . . . . . . . 136
10.2. Filehandle Types . . . . . . . . . . . . . . . . . . . . 136
10.2.1. General Properties of a Filehandle . . . . . . . . . 136
10.2.2. Persistent Filehandle . . . . . . . . . . . . . . . 137
10.2.3. Volatile Filehandle . . . . . . . . . . . . . . . . 137
10.3. One Method of Constructing a Volatile Filehandle . . . . 139
10.4. Client Recovery from Filehandle Expiration . . . . . . . 139
11. File Attributes . . . . . . . . . . . . . . . . . . . . . . . 140
11.1. Categorization of File Attributes . . . . . . . . . . . 140
11.2. Changes in the Categorization of File Attributes . . . . 141
11.3. Categorization of Authorization-related Attributes . . . 142
11.4. REQUIRED Attributes . . . . . . . . . . . . . . . . . . 143
11.5. OPTIONAL Attributes . . . . . . . . . . . . . . . . . . 143
11.6. Experimental Attributes . . . . . . . . . . . . . . . . 144
11.7. Named Attributes . . . . . . . . . . . . . . . . . . . . 144
11.8. Classification of Attributes . . . . . . . . . . . . . . 147
11.9. Set-Only and Get-Only Attributes . . . . . . . . . . . . 148
11.10. REQUIRED Attributes - List and Definition References . . 148
11.11. OPTIONAL Attributes - List and Definition References . . 149
11.12. Attribute Definitions . . . . . . . . . . . . . . . . . 154
11.12.1. Definitions of REQUIRED Attributes . . . . . . . . 154
11.12.2. Definitions of Uncategorized OPTIONAL Attributes . 156
11.13. Interpreting owner and owner_group . . . . . . . . . . . 163
11.14. Character Case Attributes . . . . . . . . . . . . . . . 164
11.15. Directory Notification Attributes . . . . . . . . . . . 164
11.15.1. Attribute 56: dir_notif_delay . . . . . . . . . . . 164
11.15.2. Attribute 57: dirent_notif_delay . . . . . . . . . 164
11.16. pNFS Attribute Definitions . . . . . . . . . . . . . . . 164
11.16.1. Attribute 62: fs_layout_type . . . . . . . . . . . 164
11.16.2. Attribute 66: layout_alignment . . . . . . . . . . 165
11.16.3. Attribute 65: layout_blksize . . . . . . . . . . . 165
11.16.4. Attribute 63: layout_hint . . . . . . . . . . . . . 165
11.16.5. Attribute 64: layout_type . . . . . . . . . . . . . 165
11.16.6. Attribute 68: mdsthreshold . . . . . . . . . . . . 165
11.17. Retention Attributes . . . . . . . . . . . . . . . . . . 166
11.17.1. Attribute 69: retention_get . . . . . . . . . . . . 166
11.17.2. Attribute 70: retention_set . . . . . . . . . . . . 167
11.17.3. Attribute 71: retentevt_get . . . . . . . . . . . . 168
11.17.4. Attribute 72: retentevt_set . . . . . . . . . . . . 168
11.17.5. Attribute 73: retention_hold . . . . . . . . . . . 168
11.18. Access Control Attributes . . . . . . . . . . . . . . . 169
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12. Single-Server Namespace . . . . . . . . . . . . . . . . . . . 169
12.1. Server Exports . . . . . . . . . . . . . . . . . . . . . 169
12.2. Browsing Exports . . . . . . . . . . . . . . . . . . . . 170
12.3. Server Pseudo File System . . . . . . . . . . . . . . . 170
12.4. Multiple Roots . . . . . . . . . . . . . . . . . . . . . 171
12.5. Filehandle Volatility . . . . . . . . . . . . . . . . . 171
12.6. Exported Root . . . . . . . . . . . . . . . . . . . . . 171
12.7. Mount Point Crossing . . . . . . . . . . . . . . . . . . 172
12.8. Security Policy and Namespace Presentation . . . . . . . 172
13. State Management . . . . . . . . . . . . . . . . . . . . . . 173
13.1. Client and Session ID . . . . . . . . . . . . . . . . . 174
13.2. Stateid Definition . . . . . . . . . . . . . . . . . . . 174
13.2.1. Stateid Types . . . . . . . . . . . . . . . . . . . 175
13.2.2. Stateid Structure . . . . . . . . . . . . . . . . . 176
13.2.3. Special Stateids . . . . . . . . . . . . . . . . . . 178
13.2.4. Stateid Lifetime and Validation . . . . . . . . . . 179
13.2.5. Stateid Use for I/O Operations . . . . . . . . . . . 182
13.2.6. Stateid Use for SETATTR Operations . . . . . . . . . 183
13.3. Lease Renewal . . . . . . . . . . . . . . . . . . . . . 183
13.4. Crash Recovery . . . . . . . . . . . . . . . . . . . . . 186
13.4.1. Client Failure and Recovery . . . . . . . . . . . . 186
13.4.2. Server Failure and Recovery . . . . . . . . . . . . 187
13.4.3. Network Partitions and Recovery . . . . . . . . . . 193
13.5. Server Revocation of Locks . . . . . . . . . . . . . . . 198
13.6. Short and Long Leases . . . . . . . . . . . . . . . . . 199
13.7. Clocks, Propagation Delay, and Calculating Lease
Expiration . . . . . . . . . . . . . . . . . . . . . . . 199
13.8. Obsolete Locking Infrastructure from NFSv4.0 . . . . . . 200
14. File Locking and Share Reservations . . . . . . . . . . . . . 201
14.1. Opens and Byte-Range Locks . . . . . . . . . . . . . . . 201
14.1.1. State-Owner Definition . . . . . . . . . . . . . . . 201
14.1.2. Use of the Stateid and Locking . . . . . . . . . . . 202
14.2. Lock Ranges . . . . . . . . . . . . . . . . . . . . . . 205
14.3. Upgrading and Downgrading Locks . . . . . . . . . . . . 205
14.4. Stateid Seqid Values and Byte-Range Locks . . . . . . . 206
14.5. Issues with Multiple Open-Owners . . . . . . . . . . . . 206
14.6. Blocking Locks . . . . . . . . . . . . . . . . . . . . . 207
14.7. Share Reservations . . . . . . . . . . . . . . . . . . . 208
14.8. OPEN/CLOSE Operations . . . . . . . . . . . . . . . . . 209
14.9. Open Upgrade and Downgrade . . . . . . . . . . . . . . . 210
14.10. Parallel OPENs . . . . . . . . . . . . . . . . . . . . . 211
14.11. Reclaim of Open and Byte-Range Locks . . . . . . . . . . 211
15. Client-Side Caching for Files . . . . . . . . . . . . . . . . 212
15.1. Performance Challenges for Client-Side Caching . . . . . 214
15.2. Delegation and Callbacks . . . . . . . . . . . . . . . . 215
15.2.1. Delegation Recovery . . . . . . . . . . . . . . . . 217
15.3. Data Caching . . . . . . . . . . . . . . . . . . . . . . 220
15.3.1. Data Caching and OPENs . . . . . . . . . . . . . . . 220
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15.3.2. Data Caching and Files Open for Write . . . . . . . 221
15.3.3. Data Caching and File Locking . . . . . . . . . . . 222
15.3.4. Data Caching and Mandatory File Locking . . . . . . 223
15.3.5. Data Caching and File Identity . . . . . . . . . . . 224
15.4. Open Delegation . . . . . . . . . . . . . . . . . . . . 225
15.4.1. Open Delegation and Data Caching . . . . . . . . . . 227
15.4.2. Open Delegation and File Locks . . . . . . . . . . . 229
15.4.3. Handling of CB_GETATTR . . . . . . . . . . . . . . . 229
15.4.4. Recall of Open Delegation . . . . . . . . . . . . . 232
15.4.5. Clients That Fail to Honor Delegation Recalls . . . 234
15.4.6. Delegation Revocation . . . . . . . . . . . . . . . 235
15.4.7. Delegations via WANT_DELEGATION . . . . . . . . . . 236
15.5. Data Caching and Revocation . . . . . . . . . . . . . . 236
15.5.1. Revocation Recovery for Write Open Delegation . . . 237
15.6. Attribute Caching . . . . . . . . . . . . . . . . . . . 238
15.6.1. Attribute Caching Coherence Between Requesting Client
and Server . . . . . . . . . . . . . . . . . . . . . 239
15.6.2. Attribute Caching Coherence Between Requesting Client
and Other Clients . . . . . . . . . . . . . . . . . . 240
15.6.3. Attribute Caching Coherence Between Requesting Client
and Remote Applications . . . . . . . . . . . . . . . 241
15.7. Data and Metadata Caching and Memory Mapped Files . . . 242
16. Client-side Name and Directory Caching . . . . . . . . . . . 243
16.1. Name and Directory Caching without Directory
Delegations . . . . . . . . . . . . . . . . . . . . . . 243
16.1.1. Name Caching . . . . . . . . . . . . . . . . . . . . 244
16.1.2. Directory Caching . . . . . . . . . . . . . . . . . 245
16.2. Directory Delegations and Notifications . . . . . . . . 246
16.2.1. Motivation for Directory Delegations . . . . . . . . 246
16.2.2. Directory Caching Features . . . . . . . . . . . . . 247
16.2.3. Directory Delegation Notifications . . . . . . . . . 248
16.2.4. Directory Delegation Choices . . . . . . . . . . . . 249
16.2.5. Directory Delegation Mechanics . . . . . . . . . . . 251
16.2.6. Directory Delegation Authorization Extensions . . . 256
16.2.7. Former Authorization Practices and Their Current
Validity . . . . . . . . . . . . . . . . . . . . . . 258
16.2.8. Alternatives to Use of Directory Delegation
Authorization Support . . . . . . . . . . . . . . . . 260
16.2.9. Directory Delegation Authorization Support . . . . . 262
16.2.10. Directory Delegation Feature Version Management . . 264
16.2.11. Directory Content Notifications . . . . . . . . . . 265
16.2.12. Directory Attribute Notifications . . . . . . . . . 269
16.2.13. Directory Delegation Authorization-related
Information . . . . . . . . . . . . . . . . . . . . . 271
16.2.14. Directory Delegation Recall . . . . . . . . . . . . 274
16.2.15. Directory Delegation Recovery . . . . . . . . . . . 275
17. Multi-Server Namespace . . . . . . . . . . . . . . . . . . . 275
17.1. Terminology . . . . . . . . . . . . . . . . . . . . . . 275
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17.1.1. Terminology Related to Trunking . . . . . . . . . . 275
17.1.2. Terminology Related to File System Location . . . . 277
17.2. File System Location Attributes . . . . . . . . . . . . 279
17.3. File System Presence or Absence . . . . . . . . . . . . 280
17.4. Getting Attributes for an Absent File System . . . . . . 281
17.4.1. GETATTR within an Absent File System . . . . . . . . 281
17.4.2. READDIR and Absent File Systems . . . . . . . . . . 283
17.5. Uses of File System Location Information . . . . . . . . 283
17.5.1. Combining Multiple Uses in a Single Attribute . . . 284
17.5.2. File System Location Attributes and Trunking . . . . 285
17.5.3. File System Location Attributes and Connection Type
Selection . . . . . . . . . . . . . . . . . . . . . . 286
17.5.4. File System Replication . . . . . . . . . . . . . . 287
17.5.5. File System Migration . . . . . . . . . . . . . . . 289
17.5.6. Referrals . . . . . . . . . . . . . . . . . . . . . 291
17.5.7. Changes in File System Location Attributes . . . . . 293
17.6. Trunking without File System Location Information . . . 294
17.7. Users and Groups in a Multi-Server Namespace . . . . . . 294
17.8. Additional Client-Side Considerations . . . . . . . . . 295
17.9. Overview of File Access Transitions . . . . . . . . . . 296
17.10. Effecting Network Endpoint Transitions . . . . . . . . . 296
17.11. Effecting File System Transitions . . . . . . . . . . . 297
17.11.1. File System Transitions and Simultaneous Access . . 298
17.11.2. Filehandles and File System Transitions . . . . . . 299
17.11.3. Fileids and File System Transitions . . . . . . . . 300
17.11.4. Fsids and File System Transitions . . . . . . . . . 301
17.11.5. The Change Attribute and File System Transitions . 302
17.11.6. Write Verifiers and File System Transitions . . . . 302
17.11.7. READDIR Cookies and Verifiers and File System
Transitions . . . . . . . . . . . . . . . . . . . . . 302
17.11.8. File System Data and File System Transitions . . . 303
17.11.9. Lock State and File System Transitions . . . . . . 304
17.12. Transferring State upon Migration . . . . . . . . . . . 308
17.12.1. Transparent State Migration and pNFS . . . . . . . 308
17.13. Client Responsibilities When Access Is Transitioned . . 310
17.13.1. Client Transition Notifications . . . . . . . . . . 310
17.13.2. Performing Migration Discovery . . . . . . . . . . 313
17.13.3. Overview of Client Response to NFS4ERR_MOVED . . . 316
17.13.4. Obtaining Access to Sessions and State after
Migration . . . . . . . . . . . . . . . . . . . . . . 318
17.13.5. Obtaining Access to Sessions and State after Network
Address Transfer . . . . . . . . . . . . . . . . . . 320
17.14. Server Responsibilities Upon Migration . . . . . . . . . 320
17.14.1. Server Responsibilities in Effecting State Reclaim
after Migration . . . . . . . . . . . . . . . . . . . 321
17.14.2. Server Responsibilities in Effecting Transparent
State Migration . . . . . . . . . . . . . . . . . . . 322
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17.14.3. Server Responsibilities in Effecting Session
Transfer . . . . . . . . . . . . . . . . . . . . . . 324
17.15. Effecting File System Referrals . . . . . . . . . . . . 326
17.15.1. Referral Example (LOOKUP) . . . . . . . . . . . . . 327
17.15.2. Referral Example (READDIR) . . . . . . . . . . . . 331
17.16. The Attribute fs_locations . . . . . . . . . . . . . . . 333
17.17. The Attribute fs_locations_info . . . . . . . . . . . . 336
17.17.1. The fs_locations_server4 Structure . . . . . . . . 340
17.17.2. The fs_locations_info4 Structure . . . . . . . . . 347
17.17.3. The fs_locations_item4 Structure . . . . . . . . . 348
17.18. The Attribute fs_status . . . . . . . . . . . . . . . . 350
18. Parallel NFS (pNFS) . . . . . . . . . . . . . . . . . . . . . 354
18.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 354
18.2. Layout Types . . . . . . . . . . . . . . . . . . . . . . 357
18.3. Normative Layout Specification Terminology . . . . . . . 357
18.4. pNFS Definitions . . . . . . . . . . . . . . . . . . . . 359
18.4.1. Metadata . . . . . . . . . . . . . . . . . . . . . . 359
18.4.2. Metadata Server . . . . . . . . . . . . . . . . . . 360
18.4.3. pNFS Client . . . . . . . . . . . . . . . . . . . . 360
18.4.4. Data Storage Devices . . . . . . . . . . . . . . . . 360
18.4.5. Data Access Protocol . . . . . . . . . . . . . . . . 360
18.4.6. Control Protocol . . . . . . . . . . . . . . . . . . 360
18.4.7. Layout . . . . . . . . . . . . . . . . . . . . . . . 361
18.4.8. Layout Iomode . . . . . . . . . . . . . . . . . . . 361
18.4.9. Device IDs . . . . . . . . . . . . . . . . . . . . . 362
18.5. pNFS Operations . . . . . . . . . . . . . . . . . . . . 364
18.6. pNFS Attributes . . . . . . . . . . . . . . . . . . . . 365
18.7. Layout Semantics . . . . . . . . . . . . . . . . . . . . 365
18.7.1. Guarantees Provided by Layouts . . . . . . . . . . . 365
18.7.2. Getting a Layout . . . . . . . . . . . . . . . . . . 366
18.7.3. Layout Stateid . . . . . . . . . . . . . . . . . . . 367
18.7.4. Committing a Layout . . . . . . . . . . . . . . . . 371
18.7.5. Recalling a Layout . . . . . . . . . . . . . . . . . 372
18.7.6. Revoking Layouts . . . . . . . . . . . . . . . . . . 380
18.7.7. Metadata Server Write Propagation . . . . . . . . . 380
18.8. pNFS Mechanics . . . . . . . . . . . . . . . . . . . . . 380
18.9. Recovery . . . . . . . . . . . . . . . . . . . . . . . . 382
18.9.1. Recovery from Client Restart . . . . . . . . . . . . 382
18.9.2. Dealing with Lease Expiration on the Client . . . . 383
18.9.3. Dealing with Loss of Layout State on the Metadata
Server . . . . . . . . . . . . . . . . . . . . . . . 384
18.9.4. Recovery from Metadata Server Restart . . . . . . . 384
18.9.5. Operations during Metadata Server Grace Period . . . 386
18.9.6. Storage Device Recovery . . . . . . . . . . . . . . 387
18.10. Metadata and Storage Device Roles . . . . . . . . . . . 387
18.11. Security Issues for pNFS . . . . . . . . . . . . . . . . 388
18.11.1. Security-related Handling for non-RPC Storage
Protocols . . . . . . . . . . . . . . . . . . . . . . 390
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18.11.2. Security-related Handling for RPC Storage Protocols
that are NFSv4 Minor Versions Assisted by Control
Protocols . . . . . . . . . . . . . . . . . . . . . . 391
18.11.3. Security-related Handling for RPC Storage Protocols
using NFS Versions together with Control Protocol
Assistance . . . . . . . . . . . . . . . . . . . . . 392
19. Specification of Layout Types . . . . . . . . . . . . . . . . 393
19.1. Layout Specification Needs . . . . . . . . . . . . . . . 393
19.1.1. Layout Type Interoperability Models . . . . . . . . 394
19.1.2. Layout-Type-Specific Data Types . . . . . . . . . . 395
19.1.3. Control Protocol Layout Management Functions" . . . 396
19.1.4. Other Control Protocol Functions" . . . . . . . . . 396
19.1.5. IO Checking Requirements . . . . . . . . . . . . . . 399
19.1.6. Security-related Requirements" . . . . . . . . . . . 400
19.1.7. Recovery Requirements" . . . . . . . . . . . . . . . 400
19.1.8. Requirements Regarding Committing Layouts . . . . . 400
19.1.9. Requirements Regarding Layout Termination . . . . . 401
19.1.10. Requirements Regarding Feature Interactions" . . . . 402
19.2. Addressing Requirements for Existing Layout Types . . . 402
19.2.1. Blocks Layout Type and Layout Type Requirements . . 403
19.2.2. Scsi Layout Type and Layout Type Requirements . . . 404
19.2.3. Object Layout Type and Layout Type Requirements . . 405
19.2.4. Flexible Files Layout Type and Layout Type
Requirements . . . . . . . . . . . . . . . . . . . . 406
19.2.5. Needed Updates to Layout Specification Documents . . 409
20. The pNFS File Layout Type . . . . . . . . . . . . . . . . . . 409
20.1. Recent Changes to the File Layout Type . . . . . . . . . 411
20.2. File Layout Type Motivation . . . . . . . . . . . . . . 412
20.3. Protocol Feature Support for the Files Layout Type . . . 413
20.4. Storage Protocol for the Files Layout Type . . . . . . . 413
20.5. Client ID and Session Considerations . . . . . . . . . . 415
20.5.1. Sessions Considerations for Data Servers . . . . . . 417
20.6. File Layout Definitions . . . . . . . . . . . . . . . . 418
20.7. File Layout Data Types . . . . . . . . . . . . . . . . . 418
20.7.1. File Layout Hint-related Data Types . . . . . . . . 419
20.7.2. File Layout Content-related Data Types . . . . . . . 421
20.8. Interpreting the File Layout . . . . . . . . . . . . . . 424
20.8.1. Determining the Stripe Unit Number . . . . . . . . . 424
20.8.2. Interpreting the File Layout Using Sparse Packing . 424
20.8.3. Interpreting the File Layout Using Dense Packing . . 427
20.8.4. Sparse and Dense Stripe Unit Packing . . . . . . . . 430
20.9. Multipathing to Data Servers . . . . . . . . . . . . . . 432
20.10. Operations Sent to NFSv4.1 Data Servers . . . . . . . . 434
20.11. COMMIT through Metadata Server . . . . . . . . . . . . . 436
20.12. The Layout Iomode . . . . . . . . . . . . . . . . . . . 437
20.13. LAYOUTCOMMIT on file layouts . . . . . . . . . . . . . . 438
20.14. File Layout Type Control Protocol . . . . . . . . . . . 440
20.14.1. Control Protocol State Coordination . . . . . . . . 441
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20.14.2. Control Protocol Authorization Coordination . . . . 444
20.14.3. Control Protocol Layout Management . . . . . . . . 444
20.14.4. Control Protocol Role in Storage Allocation for File
Layout Type . . . . . . . . . . . . . . . . . . . . . 444
20.14.5. IO Validation for the Files Layout Type . . . . . . 445
20.15. File Attributes . . . . . . . . . . . . . . . . . . . . 445
20.16. Data Server Component File Size . . . . . . . . . . . . 446
20.17. Revocation and Fencing for the Files Layout Type . . . . 447
20.18. Layout/IO Conflicts for the Files Layout Type . . . . . 448
20.19. File Layout MDS-directed IO . . . . . . . . . . . . . . 449
20.20. File Layout Handling of Mandatory Byte-Range Locks . . . 449
20.21. Layout Recall Issues for File Layout Type . . . . . . . 451
20.22. Restrictions on Layout Information Discard for File Layout
Type . . . . . . . . . . . . . . . . . . . . . . . . . 451
20.23. Dealing with Client and Server Failure . . . . . . . . . 452
20.23.1. Dealing with MDS Failure . . . . . . . . . . . . . 453
20.23.2. Dealing with Data Server Failure . . . . . . . . . 455
20.23.3. Dealing with Client Failure . . . . . . . . . . . . 457
20.24. Dealing with Lease Expiration . . . . . . . . . . . . . 457
20.25. Security Issues for the File Layout Type . . . . . . . . 458
20.26. Necessary Changes to the Files Layout Type to Meet Layout
Type Requirements . . . . . . . . . . . . . . . . . . . 459
20.27. The File Layout Type and Layout Type Requirements . . . 460
21. Internationalization . . . . . . . . . . . . . . . . . . . . 462
21.1. UTF-8 Capabilities . . . . . . . . . . . . . . . . . . . 462
22. Error Values . . . . . . . . . . . . . . . . . . . . . . . . 463
22.1. Error Definitions . . . . . . . . . . . . . . . . . . . 463
22.1.1. General Errors . . . . . . . . . . . . . . . . . . . 468
22.1.2. Filehandle Errors . . . . . . . . . . . . . . . . . 471
22.1.3. Compound Structure Errors . . . . . . . . . . . . . 473
22.1.4. File System Errors . . . . . . . . . . . . . . . . . 475
22.1.5. State Management Errors . . . . . . . . . . . . . . 476
22.1.6. Security Errors . . . . . . . . . . . . . . . . . . 477
22.1.7. Name Errors . . . . . . . . . . . . . . . . . . . . 478
22.1.8. Locking Errors . . . . . . . . . . . . . . . . . . . 479
22.1.9. Reclaim Errors . . . . . . . . . . . . . . . . . . . 480
22.1.10. pNFS Errors . . . . . . . . . . . . . . . . . . . . 482
22.1.11. Session Use Errors . . . . . . . . . . . . . . . . . 483
22.1.12. Session Management Errors . . . . . . . . . . . . . 484
22.1.13. Client Management Errors . . . . . . . . . . . . . . 484
22.1.14. Delegation Errors . . . . . . . . . . . . . . . . . 485
22.1.15. Attribute Handling Errors . . . . . . . . . . . . . 486
22.1.16. Obsoleted Errors . . . . . . . . . . . . . . . . . . 486
22.2. Operations and Their Valid Errors . . . . . . . . . . . 488
22.3. Callback Operations and Their Valid Errors . . . . . . . 505
22.4. Errors and the Operations That Use Them . . . . . . . . 508
23. NFSv4.1 Procedures . . . . . . . . . . . . . . . . . . . . . 523
23.1. Procedure 0: NULL - No Operation . . . . . . . . . . . . 523
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23.2. Procedure 1: COMPOUND - Compound Operations . . . . . . 523
24. Operations: REQUIRED, RECOMMENDED, or OPTIONAL . . . . . . . 535
25. NFSv4.1 Operations . . . . . . . . . . . . . . . . . . . . . 541
25.1. Operation 3: ACCESS - Check Access Rights . . . . . . . 541
25.2. Operation 4: CLOSE - Close File . . . . . . . . . . . . 546
25.3. Operation 5: COMMIT - Commit Cached Data . . . . . . . . 547
25.4. Operation 6: CREATE - Create a Non-Regular File
Object . . . . . . . . . . . . . . . . . . . . . . . . 550
25.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting
Recovery . . . . . . . . . . . . . . . . . . . . . . . 553
25.6. Operation 8: DELEGRETURN - Return Delegation . . . . . . 554
25.7. Operation 9: GETATTR - Get Attributes . . . . . . . . . 554
25.8. Operation 10: GETFH - Get Current Filehandle . . . . . . 556
25.9. Operation 11: LINK - Create Link to a File . . . . . . . 557
25.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 560
25.11. Operation 13: LOCKT - Test for Lock . . . . . . . . . . 564
25.12. Operation 14: LOCKU - Unlock File . . . . . . . . . . . 565
25.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 567
25.14. Operation 16: LOOKUPP - Lookup Parent Directory . . . . 568
25.15. Operation 17: NVERIFY - Verify Difference in
Attributes . . . . . . . . . . . . . . . . . . . . . . 570
25.16. Operation 18: OPEN - Open a Regular File . . . . . . . . 571
25.17. Operation 19: OPENATTR - Open Named Attribute
Directory . . . . . . . . . . . . . . . . . . . . . . . 593
25.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File
Access . . . . . . . . . . . . . . . . . . . . . . . . 594
25.19. Operation 22: PUTFH - Set Current Filehandle . . . . . . 596
25.20. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 597
25.21. Operation 24: PUTROOTFH - Set Root Filehandle . . . . . 598
25.22. Operation 25: READ - Read from File . . . . . . . . . . 599
25.23. Operation 26: READDIR - Read Directory . . . . . . . . . 601
25.24. Operation 27: READLINK - Read Symbolic Link . . . . . . 605
25.25. Operation 28: REMOVE - Remove File System Object . . . . 605
25.26. Operation 29: RENAME - Rename Directory Entry . . . . . 610
25.27. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 614
25.28. Operation 32: SAVEFH - Save Current Filehandle . . . . . 615
25.29. Operation 33: SECINFO - Obtain Available Security . . . 616
25.30. Operation 34: SETATTR - Set Attributes . . . . . . . . . 620
25.31. Operation 37: VERIFY - Verify Same Attributes . . . . . 623
25.32. Operation 38: WRITE - Write to File . . . . . . . . . . 624
25.33. Operation 40: BACKCHANNEL_CTL - Backchannel Control . . 629
25.34. Operation 41: BIND_CONN_TO_SESSION - Associate Connection
with Session . . . . . . . . . . . . . . . . . . . . . 631
25.35. Operation 42: EXCHANGE_ID - Instantiate Client ID . . . 634
25.36. Operation 43: CREATE_SESSION - Create New Session and
Confirm Client ID . . . . . . . . . . . . . . . . . . . 652
25.37. Operation 44: DESTROY_SESSION - Destroy a Session . . . 663
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25.38. Operation 45: FREE_STATEID - Free Stateid with No
Locks . . . . . . . . . . . . . . . . . . . . . . . . . 664
25.39. Operation 46: GET_DIR_DELEGATION - Get a Directory
Delegation . . . . . . . . . . . . . . . . . . . . . . 665
25.40. Operation 47: GETDEVICEINFO - Get Device Information . . 671
25.41. Operation 48: GETDEVICELIST - Get All Device Mappings for
a File System . . . . . . . . . . . . . . . . . . . . . 674
25.42. Operation 49: LAYOUTCOMMIT - Commit Writes Made Using a
Layout . . . . . . . . . . . . . . . . . . . . . . . . 675
25.43. Operation 50: LAYOUTGET - Get Layout Information . . . . 680
25.44. Operation 51: LAYOUTRETURN - Release Layout
Information . . . . . . . . . . . . . . . . . . . . . . 691
25.45. Operation 52: SECINFO_NO_NAME - Get Security on Unnamed
Object . . . . . . . . . . . . . . . . . . . . . . . . 695
25.46. Operation 53: SEQUENCE - Supply Per-Procedure Sequencing
and Control . . . . . . . . . . . . . . . . . . . . . . 696
25.47. Operation 54: SET_SSV - Update SSV for a Client ID . . . 702
25.48. Operation 55: TEST_STATEID - Test Stateids for
Validity . . . . . . . . . . . . . . . . . . . . . . . 705
25.50. Operation 57: DESTROY_CLIENTID - Destroy a Client ID . . 709
25.51. Operation 58: RECLAIM_COMPLETE - Indicates Reclaims
Finished . . . . . . . . . . . . . . . . . . . . . . . 710
25.52. Operation 10044: ILLEGAL - Illegal Operation . . . . . . 714
26. NFSv4.1 Callback Procedures . . . . . . . . . . . . . . . . . 715
26.1. Procedure 0: CB_NULL - No Operation . . . . . . . . . . 715
26.2. Procedure 1: CB_COMPOUND - Compound Operations . . . . . 715
27. NFSv4.1 Callback Operations . . . . . . . . . . . . . . . . . 719
27.1. Operation 3: CB_GETATTR - Get Attributes . . . . . . . . 719
27.2. Operation 4: CB_RECALL - Recall a Delegation . . . . . . 720
27.3. Operation 5: CB_LAYOUTRECALL - Recall Layout from
Client . . . . . . . . . . . . . . . . . . . . . . . . 721
27.4. Operation 6: CB_NOTIFY - Notify Client Using Directory
Delegations . . . . . . . . . . . . . . . . . . . . . . 725
27.5. Operation 7: CB_PUSH_DELEG - Offer Previously Requested
Delegation to Client . . . . . . . . . . . . . . . . . 741
27.6. Operation 8: CB_RECALL_ANY - Keep Any N Recallable
Objects . . . . . . . . . . . . . . . . . . . . . . . . 742
27.7. Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal Resources
for Recallable Objects . . . . . . . . . . . . . . . . 745
27.8. Operation 10: CB_RECALL_SLOT - Change Flow Control
Limits . . . . . . . . . . . . . . . . . . . . . . . . 746
27.9. Operation 11: CB_SEQUENCE - Supply Backchannel Sequencing
and Control . . . . . . . . . . . . . . . . . . . . . . 747
27.10. Operation 12: CB_WANTS_CANCELLED - Cancel Pending
Delegation Wants . . . . . . . . . . . . . . . . . . . 750
27.11. Operation 13: CB_NOTIFY_LOCK - Notify Client of Possible
Lock Availability . . . . . . . . . . . . . . . . . . . 751
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27.12. Operation 14: CB_NOTIFY_DEVICEID - Notify Client of Device
ID Changes . . . . . . . . . . . . . . . . . . . . . . 752
27.13. Operation 10044: CB_ILLEGAL - Illegal Callback
Operation . . . . . . . . . . . . . . . . . . . . . . . 755
28. Security Considerations . . . . . . . . . . . . . . . . . . . 755
28.1. Issues with Inherited Security Considerations Section . 755
28.2. Threat Analysis . . . . . . . . . . . . . . . . . . . . 756
28.2.1. Threat Analysis for Use of Persistent Sessions and
Locking State . . . . . . . . . . . . . . . . . . . . 756
28.2.2. Threat Analysis for Use of pNFS . . . . . . . . . . 757
29. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 762
29.1. IANA Actions . . . . . . . . . . . . . . . . . . . . . . 762
29.2. Named Attribute Definitions . . . . . . . . . . . . . . 762
29.2.1. Initial Registry . . . . . . . . . . . . . . . . . . 763
29.2.2. Updating Registrations . . . . . . . . . . . . . . . 763
29.3. Device ID Notifications . . . . . . . . . . . . . . . . 763
29.3.1. Initial Registry . . . . . . . . . . . . . . . . . . 764
29.3.2. Updating Registrations . . . . . . . . . . . . . . . 764
29.4. Object Recall Types . . . . . . . . . . . . . . . . . . 765
29.4.1. Initial Registry . . . . . . . . . . . . . . . . . . 766
29.4.2. Updating Registrations . . . . . . . . . . . . . . . 766
29.5. Layout Types . . . . . . . . . . . . . . . . . . . . . . 766
29.5.1. Initial Registry . . . . . . . . . . . . . . . . . . 767
29.5.2. Updating Registrations . . . . . . . . . . . . . . . 768
29.5.3. IANA-Related Requirements for Layout Type
Specifications . . . . . . . . . . . . . . . . . . . 768
29.6. Path Variable Definitions . . . . . . . . . . . . . . . 768
29.6.1. Path Variables Registry . . . . . . . . . . . . . . 769
29.6.2. Values for the ${ietf.org:CPU_ARCH} Variable . . . . 770
29.6.3. Values for the ${ietf.org:OS_TYPE} Variable . . . . 771
30. References . . . . . . . . . . . . . . . . . . . . . . . . . 771
30.1. Normative References . . . . . . . . . . . . . . . . . . 772
30.2. Informative References . . . . . . . . . . . . . . . . . 776
Appendix A. Nature of the Changes Being Made for This Update . . 779
A.1. Reliance on NFSv4-wide Documents . . . . . . . . . . . . 779
A.2. Adaptation of the NFSv4-wide Security Document to
v4.1-specific Features . . . . . . . . . . . . . . . . . 780
A.3. Changes to Effect Necessary Cleanup and Correction . . . 781
Appendix B. Status of The Changes Being Made in this Update . . 783
B.1. Changes Completed So Far in this Update . . . . . . . . . 783
B.2. Changes Made in this Update to Address NFSv4.1 Errata
Reports . . . . . . . . . . . . . . . . . . . . . . . . . 784
B.3. Changes Being Made Now in this Update . . . . . . . . . . 786
B.4. Changes That Will Need to be Made Later in this Update . 789
Appendix C. Work Done in Various Drafts . . . . . . . . . . . . 789
C.1. Changes Made in 5661bis Draft -00 . . . . . . . . . . . . 790
C.2. Changes Made in 5661bis Draft -01 . . . . . . . . . . . . 790
C.3. Changes Made in 5661bis Draft -02 . . . . . . . . . . . . 792
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C.4. Changes Made in 5661bis Draft -03 . . . . . . . . . . . . 792
C.5. Changes Made in 5661bis Draft -04 . . . . . . . . . . . . 793
C.6. Changes Made in 5661bis Draft -05 . . . . . . . . . . . . 795
C.7. Changes Made in 5661bis Draft -06 . . . . . . . . . . . . 796
C.8. Changes Made in 5661bis Draft -07 . . . . . . . . . . . . 797
C.9. Changes Made in 5661bis Draft -08 . . . . . . . . . . . . 797
C.10. Changes Made in 5661bis Draft -09 . . . . . . . . . . . . 797
C.11. Changes Made in 5661bis Draft -10 . . . . . . . . . . . . 798
C.12. Changes Made in 5661bis Draft -11 . . . . . . . . . . . . 798
C.13. Changes Made in 8881bis Draft -00 . . . . . . . . . . . . 799
C.14. Changes Made in 8881bis Draft -01 . . . . . . . . . . . . 799
C.15. Changes Made in 8881bis Draft -02 . . . . . . . . . . . . 800
C.16. Changes Made in 8881bis Draft -03 . . . . . . . . . . . . 801
C.17. Changes Made in 8881bis Draft -04 . . . . . . . . . . . . 802
C.18. Changes Made in 8881bis Draft -05 . . . . . . . . . . . . 803
C.19. Changes Made in 8881bis Draft -06 . . . . . . . . . . . . 803
Appendix D. Issues Requiring Further Discussion . . . . . . . . 805
D.1. Appropriate Uses of RFC2119 Keywords . . . . . . . . . . 805
D.1.1. Appropriate Use of "SHOULD" and "SHOULD NOT" . . . . 806
D.1.2. Uses of "MUST" and "MUST NOT" that are Problematic . 809
D.1.3. Issues Regarding Use of RFC2119 Keywords
"Sparingly" . . . . . . . . . . . . . . . . . . . . . 812
D.1.4. Going Forward Regarding Use of RFC2119 Keywords . . . 813
D.2. Issues Regarding Proposed and Actual Changes . . . . . . 813
D.2.1. Changes Regarding Request Aborts, Retries, and the
Session Model . . . . . . . . . . . . . . . . . . . . 814
D.2.2. Issues Regarding Directory Delegation that Need to be
Resolved . . . . . . . . . . . . . . . . . . . . . . 816
D.2.3. Changes Regarding Memory Mapping . . . . . . . . . . 824
D.2.4. Issues Regarding Handling of Persistence . . . . . . 825
D.2.5. Changes in Attribute Categorization . . . . . . . . . 830
D.2.6. Changes in Treatment of Attributes for Named Attribute
Directories . . . . . . . . . . . . . . . . . . . . . 831
D.2.7. Changes Made as a Result of REJECTED Errata
Reports . . . . . . . . . . . . . . . . . . . . . . . 832
D.2.8. Changes Made to Address Problems in Description of
REMOVE/RENAME . . . . . . . . . . . . . . . . . . . . 833
D.2.9. Changes Made to Address Lack of Clarity Regarding "The
Forgetful Model" . . . . . . . . . . . . . . . . . . 834
D.2.10. Need for Replacement of RFC8434 . . . . . . . . . . . 836
D.2.11. Remaining Issues for Discussion After Replacement of
RFC8434 . . . . . . . . . . . . . . . . . . . . . . . 837
D.2.12. Layout-Type-Specificity for LAYOUTCOMMIT . . . . . . 839
D.2.13. Layout-Type-Specificity for Layout Termination . . . 840
D.2.14. Possible Generalization Data Server Failure
Handling . . . . . . . . . . . . . . . . . . . . . . 841
D.2.15. Discussion Needed re Status of RFC5663 . . . . . . . 841
D.2.16. Discussion of Possible Additional Access Flags . . . 842
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D.2.17. Discussion of Named Attributes and Their Possible
Relationship with Extended Attributes . . . . . . . . 843
D.2.18. Discussion of Neglected Caching Needs . . . . . . . . 845
D.2.19. Discussion Regarding Ways of Avoiding Cache
Incoherence . . . . . . . . . . . . . . . . . . . . . 847
D.2.20. Discussion Regarding Possible Semantic Changes to
Address Cache Incoherence . . . . . . . . . . . . . . 849
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 852
Acknowledgments for This Update . . . . . . . . . . . . . . . 852
Acknowledgments for Previous Specification Documents . . . . 853
RFC Editor Notes . . . . . . . . . . . . . . . . . . . . . . . 854
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 855
1. Introduction to this Update
This document is intended to be the basis for a revised and updated
specification of NFSv4.1. Unlike [RFC8881], which provided a
limited-function update to [RFC5661], this document has a broader
mandate and will do the following:
* Revise any text known to be wrong or otherwise inappropriate.
Such text will not be retained as it has been merely because it is
outside a limited pre-specified change scope.
This includes changes in some errata reports with the status
REJECTED, where there is a Working Group Consensus that change is
necessary.
* Correct protocol defects, that, by their nature, can and should be
addressed via a limited use of the extension mechanism described
in Section 9 of [RFC8178].
For more discussion of the correction of existing protocol
defects, see Section 1.4. This discussion, which covers protocol
defects addressed in NFSv4-wide documents in addition to this
document, will focus on how compatibility issues are addressed
when defects are corrected. It will also pay attention to the
question of when XDR extensions in a bis document are necessary as
part of providing features already included (albeit incorrectly)
in the current minor version as opposed to deferring such
extensions to later minor versions.
* Incorporate the necessary changes to the description of NFSv4.1
that were published in documents marked as updating [RFC8881], in
this case [RFC8434].
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This incorporation involved a major advance in our understanding
of the structure and benefits of pNFS and the possibilities of its
further extension. See Section 1.5.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as specified in BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
The above differs from the corresponding statement in earlier
specification versions ([RFC5661] and [RFC8881]) which only referred
to [RFC2119]. For further discussion of this change, see
Appendix B.3
In some cases, such keywords will appear in all capitals within
quotations, direct or indirect, from earlier documents. In such
cases, these terms are to be interpreted just as above, except where
it is explicitly noted that such an interpretation is not to be
inferred. In some cases, it might be that this document's approach
to the matter would not use those key words for reasons explained in
the text. Such a shift might cause compatibility issues, if the
previous keyword were actually relied upon but it also possible that
it was not relied upon while the implications of that use were
ignored for various reasons.
The reader should be aware that, as discussed in Appendix D.1, there
are uses of the keywords listed above in RFCs 5661 and 8881 which
might not have been appropriate, even though the interpretation
specified above was intended when the text was written and submitted
for publication. In some cases, the text in this document has been
updated to correct the issue but it should be understood that not all
such questionable uses have been addressed and that this state of
affairs might continue to exist until a later draft of this document
is submitted for publication.
It should not be assumed that all statements that do not include
these keywords are inherently non-normative and can be safely ignored
as constituting implementation advice. In some cases, where
guidelines are given for the specification of future documents, the
intent is normative, as that word is normally used, outside the IETF.
An important example is the specification of layout types, as
described in Section 19. This is important because many aspects of
the pNFS feature depend on the specific layout type(s) implemented,
essentially making pNFS an extensible feature suite. For detailed
discussion, see Section 18.3.
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1.2. The Changed Role of this Specification
Previous specifications for this minor version ([RFC5661], [RFC8881])
have purported to describe the protocol in its entirety, without
reference to features common to all minor versions of NFS Version 4.
In contrast, this update relies on a set of base documents describing
common aspects of the NFSv4 protocol that applies to all minor
versions.
* Rules for extensions and creation of new minor versions appear
only in [RFC8178], unlike previously in which they appeared in the
NFSv4.1 specification. This eliminates the unfortunate situation
in which each minor version was allowed to create its own
extension rules.
* Handling of internationalization-related matters (for all minor
versions) is now discussed in its own document, which is expected
to be an RFC derived from [I-D.ietf-nfsv4-internationalization].
That document, based in large part on the handling of
internationalization for NFSv4 minor version zero outlined in
[RFC7530], has been extended to cover all minor versions and
enhanced to fully support case-insensitive handling of
internationalized file names.
This corrects the unfortunate situation in which
internationalization for minor version one and subsequent minor
versions (in [RFC5661] and [RFC8881]) had never been implemented
and could never have been implemented by NFS Version four clients
and servers.
* Handling of core security-related matters for all NFSv4 minor
versions will be consolidated in a set of documents that are
expected to be RFCs derived from [I-D.dnoveck-nfsv4-security] and
[I-D.ietf-nfsv4-acls-update].
This shift is made necessary by the following issues, many of
which are of long standing and make the continuation of previous
approaches to these issues insupportable:
- The lack of a substantial threat analysis in the Security
Considerations section of any existing minor version
specification.
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- The unfortunate designation of AUTH_SYS an "OPTIONAL means of
authentication" which had the effect of obscuring the severe
security problems with its common use. The use of "OPTIONAL"
suggested that use of AUTH_SYS had no harmful consequences
while the phrase "means of authentication" ignored the fact
that no actual authentication took place.
- The assumption that data confidentiality could be
satisfactorily addressed as an occasionally-used optional
facility.
- The neglect of the need for dependable semantic description of
the protocol's authorization semantics.
Earlier versions of NFS had avoided the need for such
descriptions by relying on POSIX semantics. The addition of
non-POSIX semantic elements, including named attributes and
ACLs, interfered with that approach although the necessity was
not recognized as NFSv4 was being formulated.
The availability of new transport-level security features such as
those provided by RPC-with-TLS [RFC9289] provides a basis to
correct many of the above issues.
In providing that sort of correction, we need to be careful not to
declare existing implementations non-compliant post facto, while
still providing adequate warning of the security consequences of
continuing to use the NFS Version 4 protocol insecurely, as
described in previous specifications.
1.3. Possibility of Compatibility Issues
Because this document or other documents that are part of this
specification update might make changes to matters previously
discussed in [RFC8881], the possibility of compatibility issues
cannot be excluded.
However, the likelihood of such issues arising is expected to be low
because:
* In many cases, descriptions within [RFC8881] differed from the
existing implementations and change was necessary to avoid
directing implementers to create implementations that could not
interoperate with existing implementations.
* There are cases in which attributes were specified to be OPTIONAL
even though there were no good reasons to implement a server that
did not otherwise provide support for them.
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* In some cases, it was necessary to change the definition of
OPTIONAL features that had never been implemented, often because
problems in the existing specification made the features
impossible to implement as defined. In such cases, the absence of
implementations makes it impossible for compatibility problems to
arise.
* In some cases, problems in the protocol as previously are being
corrected as described in Section 9 of [RFC8178], by creating
OPTIONAL protocol extensions. In such cases, implementations
unaware of the extensions will function as they did before, while
others have the option of using the extensions when interacting
with an implementation supporting the extension.
Specific updates are dealt with in the following subsections:
* Updates in RFCTBD10 are addressed in Section 1.3.1.
* Updates in new NFSv4-wide documents are discussed un
Section 1.3.2.
* Updates in RFCTBD30 are addressed in Section 1.3.3.
1.3.1. Compatibility issues for RFCTBD10
This document introduces a number of potential incompatibilities that
either cannot be realized or could only be realized in situations
highly unlikely to exist. For discussion of the reasons such
incompatibilities are highly unlikely to be problematic, see the rest
of this section which also explains the needs for the changes.
One important example concerns the conversion of the attributes mode,
owner, and owner_group from OPTIONAL to REQUIRED. Since the vast
majority of servers support these attributes and the vast majority of
clients use them, any incompatibilities would be very unlikely to
exist.
If there did exist servers not supporting any of these attributes and
clients capable of interacting with them, this unexpected situation
would not result in any incompatibility. The only change would be
that the client and the server would become non-compliant when they
previously had been considered compliant. This change of status has
no consequences for client-server compatibility.
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Overall, the need for this change illustrates previous
specifications' lack of serious attention to security issues, which
it is part of the job of the NFsv4.1 respecification effort to
correct.
Another important class of potential compatibility issues in which we
had to change the specification derives from situations in which the
previous text designate normal, often unavoidable, behavior as non-
compliant:
* Previously, clients were required to wait forever for an RPC
response while many (e.g. Linux) clients stopped waiting in the
event of a control-C. This common behavior, formerly non-
compliant, is now allowed but there is no incompatibility
resulting from this change even though much existing behavior has
gone from non-compliant to compliant.
* Previously the use of RoCE for NFS/RDMA had been disallowed
(formally) but is now allowed. Even so, there are clients and
servers that do this and work together doing so and making them
compliant raises no compatibility issues.
* Previously retries were not allowed ("MUST NOT" was used) unless
there was a connection drop. This was changed to a recommendation
since there us no way this could be a "fundamental requirement of
the specification" given that the reply cache was designed to
avoid any negative consequences of retries. In any case there was
no possibility of an incompatibility since the effect of the
changes is only to make previously non-compliant clients
compliant.
There are also other changes made to make specification text match
the actual implementations. Because care was used in making sure
that the change reflected implementation changes documented in errata
reports, we do not expect compatibility issues to arise. Some
important examples concern changes to pNFS-related operations that
have been documented in errata report and discussed within the group
so that existing implementations all follow the changed approach.
These include the following:
* In LAYOUTCOMMIT4args, loca_offset and loca_length are present but
not used. Previously, they had been used to effect partial layout
commits, which are no longer provided for outside of explicitly
layout-type-specific features.
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* In struct notify_deviceid_change4, ndc_immediate is present but
not used. Previously, this field had been used to indicate
whether or not a device change notification was being done
immediately rather than being delayed.
A number of new features that are highly unlikely to have been
implemented have been respecified so that they are effectively
implementable, Although the Working Group's has limits on its ability
to investigate the matter, in each case, it appears veery unlikely
that implementations exist. See below for details. In the absence
of such implementations, we can expect new implementations to follow
this specification, avoiding compatibility issues.
* The persistent reply cache feature was added to NFSv4.1 in
[RFC5661] but there is good reason to believe it has never been
implemented based on that document or on [RFC8881] Although an
implementer would have no obligation to inform the Working Group
of the existence of any implementation, the nature of the current
description makes it very unlikely that any such implementations
exist.
For reasons discussed in Section 8.1, the feature was essentially
implementable as described, while it is unlikely that any
attempting an approximate implementation would do so without
consulting the Working Group.
As a result, there is no real possibility of compatibility issues
arising.
* The directory delegation feature was added to NFSv4.1 in [RFC5661]
but there has been no discussion of implementations even though
the performance effects of the feature would be of interest to the
Working Group, since this feature was included in NFSv4.1 because
of performance concerns.
As things turned out, there were discussions of NFSv4 performance
on metadata-intensive workloads at Working Group meetings with the
effect of directory delegations not being commented on leading to
a strong belief that no such implementations existed.
When the reasons for the presumed non-implementation were
analyzed, changes were made to the specification of this feature.
While the probability of implementations existing is non-zero,
their possible existence will not give rise to compatibility
issues due to the way in which changes were made.
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All of the XDR changes took the form of extensions to correct
defects as discussed in Section 9 of [RFC8178]. In addition the
added requirement for delegation recall on certain changes to the
directory will not lead to incompatibility since the server is
free to recall delegations as it chooses. In the case of possible
existing servers that fail to recall the delegation in such cases,
they will become non-compliant. However, this fact is not
troublesome as we will be going from a compliant server that does
not work correctly to a non-compliant one, with the non-compliance
being an important cue to fix the server.
1.3.2. Compatibility issues for NFSv4-wide Documents
For these three NFSv4-wide documents, a major implementation area was
respecified because of major problem in the existing NFSv4.1
descriptions of these areas. Because the replacement text was
intended to reflect the actual implementation, the likelihood of
incompatibilities is quite low:
* RFCTBD20 respecified internationalization in a fashion quite
different from the way it is specified in [RFC5661] and [RFC8881].
This major shift did not give rise to compatibility issues because
the approach to internationalization presented in [RFC5661] and
[RFC8881] had never been implemented. We can be sure of this
because any attempt to implement this stringprep-based approach
would have generated comments/questions due to the complexity
involved in, for example, rejecting unassigned code points.
Existing implementations were compatible with the approach
discussed in [RFC7530] and the treatment in RFCTBD20 maintained
that compatibility.
* RFCTBD21 respecified security in a fashion markedly different in
tone from the way it had been discussed in previous
specifications. This included a different approach to the use of
AUTH_SYS, more concern about issues related to the security of
data in flight, and the inclusion of a discussion of authorization
semantics.
Despite these major differences, care has been taken to avoid the
creation of incompatibilities. The new treatment avoided
incompatibilities by avoiding any disallowing of previously
allowed behavior, even in cases in which there might be grounds
for doing so.
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For example, although the use of AUTH_SYS in the clear has enough
associated security issues that saying it MUST NOT or SHOULD NOT
be used, this cannot be done for existing minor versions. To deal
with this situation, its use is not disallowed or recommended
against. However, unlike in previous specifications, implementers
are given appropriate notice of the security issues resulting from
use of AUTH_SYS in the clear.
The addition of discussion of RPC-with-TLS is another important
difference which cannot cause incompatibility issues. Despite the
optionality of the use of this facility, it is important to
discuss in connection with NFSv4 security and its handling of the
security of data in flight.
* The new treatment of ACLs in RFCTBD22, while extensive, does not
give rise to major incompatibilities because of the way we were
forced to adapt to the previous approach while using a clearer
explanatory framework that made the POSIX-oriented subset the
basis of the description and explicitly making the Windows-ACL-
based extensions OPTIONAL.
For the most part, this approach does not generate
incompatibilities in that it moves formerly allowed behaviors
(implicitly optional) to be formally OPTIONAL, without changing
the set of allowed behaviors. However, with the addition of the
OPTIONAL attribute Aclchoice, the client is able to determine what
extensions to the base ACL mode have been implemented.
The one possible formal incompatibility arises from the three ACE
mask bits corresponding to the POSIX R, W, and X bits. support
for these are now REQUIRED whereas previously it had been
suggested that they were effectively optional along with all the
other ACE mask bits. The chance of this being a problem is low
since, we have not heard any discussion of server without support
for all of these bits and the difficulty of adopting to POSIX
semantics, of such implementations existed would certainly have
led to Working Group discussion of the issue.
1.3.3. Compatibility issues for RFCTBD30
These changes can be divided into three groups:
* In many cases, the XDR changes consist of changes in the typedef
naming structure, with no change to the structure of messages
described by the XDR. As a result, compatibility issues are not
expected to arise.
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* Many changes cannot create incompatibilities because the change
consists only of changed names of typedefs. Such changes were
necessary to clarify how naming interpretation rules applied to
various strings. Because all such strings have types that
evaluate to opaque<>;, there can be no incompatibilities
generated.
* In some cases, fields defined in various messages have become
unused. Space is still reserved for these fields but the on-use
is indicated in comments, so there is no XDR change to generate an
incompatibility.
* All substantive XDR changes take the form of XDR extensions as
provided for by Section 9 of [RFC8178]. As a result,
implementations unaware of the change will function as they dis
previously, while those that are aware of extension have the
option of adapting to the support or non-support by the peer
implementation.
1.4. Addressing Protocol Defects Via XDR Changes
This section provides an overview of situations in which it was
necessary to change the protocol XDR to correct specification issues
that needed to be addressed as part of the respecification effort.
Although all these issues can, from today's perspective, be viewed as
arising from mistakes, it is not always clear whether that
description is appropriate given the knowledge available when the
decisions were made. In any case, the fact that we would have done
something different if the decision were made today does not imply
that the bis document should adopt that approach. The following
considerations will often determine if we choose to defer such work
to a later minor version. This is sometimes necessary despite the
fact that the extension technique within [RFC8178] would allow the
same sort of work to be done in a bis document rather than an in
extension.
* The need to avoid adding new features that are substantial, since
they would need a period of review and refinement more easily done
in an extension document.
In general, we would try to avoid adding new attributes or
operations in the bis document to provide additional functionality
not considered during the original protocol development.
* In features structured to be extensible, the XDR is often enhanced
easily to expand the functionality available.
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* If a new attribute is necessary to make a feature usable, that
will make necessary to specify as part of the bis document, rather
than live with a severely compromised feature in a minor version
being respecified.
The correction of protocol defects often gives rise to compatibility
issues and their possible presence will be discussed below. In
addition, the question of when it is appropriate to address such
issues using the protocol extension mechanism described in [RFC8178]
needs to be considered. Section 9 of that document alludes to this
possibility but we have to decide when defects are best addressed in
that way.
These defects can be divided into two groups based on their origin.
* Defects that originated in minor version zero
Many of these defects are addressed in the new NFSv4-wide
documents ([I-D.dnoveck-nfsv4-security],
[I-D.ietf-nfsv4-acls-update], and
[I-D.ietf-nfsv4-internationalization]. For these defects , the
greater change scope require more attention to compatibility
issues. In addition, that greater scope limits the degree to
which protocol extension can be used in providing a correction
since that extension would need to be propagated to two non-
extensible minor versions.
* Defects that originated in minor version one.
A major source of defects was the result of the addition of a set
of OPTIONAL features in v4.1, that have never been implemented,
making it important to eliminate issues in the specification that
have led to this situation.
The presumptive non-implementation of these features will limit
interoperability concerns. However, since we cannot be sure about
the possible existence of implementations under development, we
will try to provide for the possibility of interoperating with
earlier implementations, even if that interoperation is
hypothetical. Only in the case of features whose current
specification makes implementation impossible can we ignore the
possibility of interoperating with such implementations.
The following defects were addressed as part of this update effort:
1: Internationalization is being thoroughly respecified in the
NFSv4-wide document [I-D.ietf-nfsv4-internationalization].
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There were no NFSv4.1 compatibility issues to deal with since
the handling of internationalization approach mandated by
[RFC8881] had never been implemented.
Potential NFSv4.0 compatibility issues were very limited since
the approach followed in [RFC7530] was continued and that
approach had been used by all implementations.
In one particular case, there is a potential compatibility issue
arising from the transition of one potential troubling server
behavior from being discouraged using SHOULD NOT to being
prohibited using MUST NOT. However, in view of the unlikelihood
of ongoing use of the discouraged behavior, this has not been
considered problematic.
The respecification of the fs_charset_cap attribute raises the
possibility of within-NFS4.1 compatibility issues. However the
very limited use of this attribute by clients combine with the
lack of clarity in the previous definition makes it unlikely
that the use of protocol extension to support previous uses
would be justified.
2: Because the Persistent reply cache feature could not be
implemented as described in [RFC8881], the entire area was
respecified in Section 8.
The reasons for this respecification are discussed in
Section 8.1.
Because the existing feature specification was unimplementable
there were no compatibility issues to deal with.
No protocol extensions were needed since the small set of bits
defined for the earlier feature could be coopted.
3: Security for all minor versions is being thoroughly respecified
in the NFSv4-wide document [I-D.dnoveck-nfsv4-security]. In
this discussion, issues related to authorization semantics and
to ACLs are being dealt with separately.
This respecification was made necessary by the lack of threat
analyses for all minor versions, the absence of any discussion
of the security problems associated with the use of AUTH_SYS,
and the half-hearted approach to the security of over-the-wire
transmission in which transmission in the clear was the default
and the provision of secure transmission was an option requiring
per-fs configuration.
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4: As part of the new handling of security, a more serious
treatment of authorization semantics was necessary. As part of
effecting this, the attributes mode, owner, and owner_group
became REQUIRED, as it is impossible to effect security without
them.
This change was not connected to the shift in terminology in
which the attributes incorrectly described as "RECOMMENDED"
became "OPTIONAL".
No significant compatibility issue are expected, since the
existence of servers not supporting these attributes or of
clients interacting with such servers, while possible
theoretically, has to be considered extremely unlikely and none
are known to the working group.
5: A number of gaps in the description of authorization semantics
needed to be addressed. These include the lack of a clear
description of authorization for operations on named attribute
directories and potential use of the "sticky" bit in controlling
authorization of file deletion.
These matters are being addressed within
[I-D.dnoveck-nfsv4-security] where they are being tracked as
Consensus Items #66 and #6 respectively.
Working group consideration of the security document will
involve resolving those two Consensus Items, as well as others.
6: The handling of ACLs for all minor versions is being thoroughly
respecified in the NFSv4-wide document
[I-D.ietf-nfsv4-acls-update].
Such a respecification was made necessary by the profound
underspecification of the ACL feature that arose from a
misguided attempt to support two very different approaches to
the provision of ACLs. The problems posed by the different
semantics of these two were never clearly addressed since it was
erroneously assumed that semantic description could be avoided.
As a result, potential interoperability was compromised since
there was no way for the client to determined what ACL-based
facilities were supported by a particular server, given that the
specification treated these differences as if they were quality-
of-implementation issues.
The development of [I-D.ietf-nfsv4-acls-update] has included a
respecification of the area in which support for a subset of
draft POSIX ACLs, termed UNIX ACLs, was the core and the various
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additions to that core were considered additional OPTIONAL
features. These included the features that motivated the
extensions in the NFSv4 ACL model.
The treatment within [I-D.ietf-nfsv4-acls-update] now makes it
clear that the current ACL model is only one of a set of ACL
formats, implying that future minor versions could define new
ones.
The development of [I-D.ietf-nfsv4-acls-update] has involved use
of protocol extension within NFSv4.1 in addition to necessary
structural changes that did not involve XDR changes.
The development of [I-D.ietf-nfsv4-acls-update] to support the
rfc8881bis effort will most likely be limited to providing
interoperability for those using the facilities within the UNIX
ACL core or within the draft POSIX acl model. Interoperability
for features beyond that set is likely to be delayed to later
ACL bis, while the deletion of unneeded proposed features will
have to wait for a later minor version, e.g., NFSv4.3.
7: It has been necessary to define a new read-only per-fs OPTIONAL
attribute that will allow clients to determine which of the
OPTIONAL extensions to the core UNIX ACL model are supported by
the server.
While this was essential to make the NFSv4 extensions usable, it
also has a critical role in making POSIX ACL support available
within NFSv4, albeit with some client mapping/filtering,
8: The defects described in Appendix D.2.1 needed to be addressed
together, in connection with making it clear that the term
"Exactly-once Semantics" ignored the fact that there were valid
reasons to give up on requests which could leave them
unexecuted.
This change did not give rise to compatibility issues since the
specification was changed to match existing implementations, and
these are expected to remain as they are.
9: The inadvertent prohibition of the use of RoCE in implementing
NFSv4.1 using RPC-over-RDMA was removed.
This is another case in which compatibility issue are not
expected because the spec has been changed to match existing
implementations.
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10: The corrections discussed in Appendix D.2.3 had to be made since
most of the worries expressed within it were the result of
misunderstandings.
Although no compatibility issues are expected we will need to
review the changes and reach consensus on them.
11: There were a number of issues in the earlier specification of
the directory delegation feature that need to be addressed to
enable implementations of this needed feature to be produced.
Given the lack of implementation during the long period since
they were introduced in [RFC5661] many years ago.
While a significant part of the problems could be ascribed to
clarity issues, there were also a set of defects, some of which
required protocol extensions, as provided for in Section 9 of
[RFC8178].
The defects which contributed substantially to this long-lasting
lack of implementation includes the failure to fully address
authorization issues for the use of cached directory data,
implementability issues regarding the maintenance of cached
attribute data, and the assumption that clients could maintain
the cached directory contents only in the same format as used by
the server. For more discussion of these defects, see
Appendix D.2.2.
These issues were addressed by a major rewrite of Section 16.2
in which protocol extension was necessary, including the
addition of new values to the enum notify_type4. In addition,
there are complementary changes made to Section 25.39 and
Section 27.4) and to operations that might result in
notifications being sent.
Although no client and server implementations of this feature
are known to exist, the possibility of them existing cannot be
excluded. As a result, the revised specification takes care to
deal appropriately with such hypothetical implementations, and
to not prohibit their use unless that is necessary to avoid
unacceptable system behavior.
12: Change in the recommendations regarding handling of numeric
strings to represent users and groups.
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Formerly considered troublesome even in the AUTH_SYS case
despite the fact that there is no explanation given as to how to
effect mapping between numeric ids and strings. Instead, it is
assumed that client and server will somehow agree to do this
without the specification making it possible or giving a
convincing reason that such mapping is needed.
Of the above, only the items 7, 8, 9, 10, and 14 required protocol
extension to resolve. All will to be incorporated in RFCTBD30.
1.5. Incorporation of RFC8434
The incorporation of [RFC8434], originally written to clarify the
requirements for new layout types, resulted in a deep and significant
improvement in our understanding of pNFS-related features of the
protocol and how various layout types deal with similar issues.
As a consequence, the original description of pNFS, formerly in
Sections 12 and 13 of [RFC8881] has been restructured as three top-
level sections in the revised NFsv4.1 specification:
* Section 18 is based on Section 12 of [RFC8881] but the material
has undergone considerable revision to fit in the new three-
section organization.
Most previous references to various layout types have been
eliminated except for a few clearly marked as examples. As a
result, this section now makes clear that pNFS is a framework
making deliberate allowance for per-layout-type differences in a
number of areas.
* Section 19 is based on [RFC8434] but the requirements have been
expanded to make clearer the division between the aspects common
to all layout types (the subject of Section 18) and the choices
that individual layout types might make to address the gaps
deliberately left by the treatment in Section 18.
* Section 20 is based on Section 13 of [RFC8881] but the material
has been adapted to meet the requirements of Section 19.
As part of these changes it was necessary to fill in gaps left
previously regarding the validity of layout revocation and how
conflicts arising as a result of server-multipathing could be
addressed by layout/recall and with layouts re-established once
the two targets were again in sync. For details, see
Section 20.1.
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2. Introduction to this Minor Version Specification
2.1. The NFS Version 4 Minor Version 1 Protocol
The NFS version 4 minor version 1 (NFSv4.1) protocol is the second
minor version of the NFS version 4 (NFSv4) protocol. The first minor
version, NFSv4.0, is now described in [RFC7530], as modified by
[RFC7931] and [RFC8587]. Minor version 1 follows the guidelines for
minor versioning presented in [RFC8178].
As a minor version, NFSv4.1 is consistent with the overall goals for
NFSv4, but extends the protocol so as to better meet those goals,
based on experiences with NFSv4.0. In addition, NFSv4.1 has adopted
some additional goals, which motivate some of the major extensions in
NFSv4.1, such as the use of the sessions model.
This minor version adds a considerable number of new operations
including some that are not OPTIONAL and makes a number of NFSv4.0
operations MANDATORY to NOT implement. As a result, the vast
majority of NFSv4.0 requests are not valid in NFSv4.1 and vice versa.
While clients and servers that support both minor versions are
common, such implementations treat the two versions as distinct
protocols sharing a substantial common heritage.
2.2. Scope of This Document
This document describes the NFSv4.1 protocol. With respect to
NFSv4.0, this document does not:
* Describe the NFSv4.0 protocol, except where needed to contrast it
with NFSv4.1.
* Modify the specification of the NFSv4.0 protocol.
* Clarify the NFSv4.0 protocol.
2.3. NFSv4 Goals
The NFSv4 protocol is a further revision of the NFS protocol defined
already by NFSv3 [RFC1813]. It retains the essential characteristics
of previous versions: easy recovery; independence of transport
protocols, operating systems, and file systems; simplicity; and good
performance. NFSv4 had the following goals:
* Improved access and good performance on the Internet.
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The protocol is designed to transit firewalls easily, perform well
where latency is high and bandwidth is low, and scale to very
large numbers of clients per server.
* Strong security with facilities for negotiation of security
handling built into the protocol.
The protocol has been built on the work of the ONCRPC working
group by supporting the RPCSEC_GSS protocol. Additionally, the
NFSv4.1 protocol provides a mechanism to allow clients and servers
the ability to negotiate security and has provisions requiring or
recommending client and server support for a minimal set of
security schemes.
The protocol now takes advantage of the ability of RPC to make
confidentiality available by using TLS-based encryption on
connections to be used for NFSv4.1, which may limit the need for
negotiation regarding facilities such as privacy.
* Good cross-platform interoperability.
The protocol embraces a file system model that provides a useful,
common set of features that does not unduly favor one file system
or operating system over another.
* Designed for protocol extensions via minor versioning.
The protocol is designed to accept standard extensions within a
framework that enables and encourages backward compatibility.
When extensions are OPTIONAL, they can be added to an existing
extensible minor version.
2.4. NFSv4.1 Goals
NFSv4.1 has the following goals, within the framework established by
the overall NFSv4 goals.
* To correct significant structural weaknesses and oversights
discovered in the base protocol.
* To add clarity and specificity to areas left unaddressed or not
addressed in sufficient detail in the base protocol. However, as
stated in Section 2.2, it is not a goal to clarify the NFSv4.0
protocol in the NFSv4.1 specification.
* To add specific features based on experience with the existing
protocol and recent industry developments.
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* To provide protocol support to take advantage of clustered server
deployments including the ability to provide scalable parallel
access to sets of files distributed among multiple servers, using
a range of data access protocols.
This parallel access may involve striping of single files among a
set of servers within the cluster.
Alternatively, parallel access may be provided by distributing
unstriped files within the cluster allowing each client to contact
the server holding each particular file directly.
2.5. General Definitions
The following definitions provide an appropriate context for the
reader.
Byte: In this document, a byte is an octet, i.e., a datum exactly
eight bits in length.
Client: The client is the entity that accesses the NFS server's
resources. The client may be an application that contains the
logic to access the NFS server directly. The client may also be a
traditional operating system client that provides remote file
system services for a set of applications.
A client is uniquely identified by a client owner.
With reference to byte-range locking, the client is also the
entity that maintains a set of locks on behalf of one or more
applications. This client is responsible for providing crash or
failure recovery for those locks it manages, in order to deal with
the possibility of server reboot.
Note that multiple clients may share the same transport and
connection and multiple clients may exist on the same network
node.
Client ID: The client ID is a 64-bit quantity used as a unique,
short-hand reference to a client-supplied client owner, consisting
of a verifier and a client owner id. The server is responsible
for supplying the client ID.
Client Owner: The client owner includes a unique string, the client
owner id, opaque to the server, that identifies a client. It also
includes a verifier to enable successive instances of the same
client to be distinguished. Multiple network connections and
source network addresses originating from those connections may
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share a client owner. The server is expected to treat requests
from connections with the same client owner as coming from the
same client. See Section 5.5 for more detail.
File System: A file system is the collection of objects accessed
using a particular server (as identified by the major identifier
of a server owner, which is defined later in this section) that
share the same value of the fsid attribute (see
Section 11.12.1.9).
Lease: A lease is an interval of time defined by the server for
which the client is granted locks. At the end of a lease period,
unrecallable locks may be revoked if the lease has not been
extended. Such a lock must be revoked if a conflicting lock has
been granted after the lease interval. Revocation of unrecallable
locks within the lease interval is expected to be an unusual event
and clients normally expect such revocations to be rare.
A server grants a client a single lease for all of its associated
locking state. Recallable locks such as layouts and delegations
can be revoked within the lease period and are generally not
affected by the state of the lease.
Lock: The term "lock" is used to refer to byte-range (in UNIX
environments, also known as record) locks, share reservations,
delegations, or layouts unless specifically stated otherwise.
Secret State Verifier (SSV): The SSV is a unique secret key shared
between a client and server. The SSV serves as the secret key for
an internal (that is, internal to NFSv4.1) Generic Security
Services (GSS) mechanism (the SSV GSS mechanism; see Section 7.9).
The SSV GSS mechanism uses the SSV to compute message integrity
code (MIC) and Wrap tokens. See Section 7.8.3 for more details on
how NFSv4.1 uses the SSV and the SSV GSS mechanism.
Server: The Server is the entity responsible for coordinating client
access to a set of file systems and is identified by a server
owner. A server can span multiple network addresses.
Server Owner: The server owner identifies the server to the client.
The server owner consists of a major identifier and a minor
identifier. When the client has two connections each to a peer
with the same major identifier, the client assumes that both peers
are the same server (the server namespace is the same via each
connection) and that lock state is sharable across both
connections. When each peer has both the same major and minor
identifiers, the client assumes that each connection might be
associated with the same session.
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Stable Storage: Stable storage is storage from which data stored by
an NFSv4.1 server can be recovered without data loss from multiple
power failures (including cascading power failures, that is,
several power failures in quick succession), operating system
failures, and/or hardware failure of components other than the
storage medium itself (such as disk, nonvolatile RAM, flash
memory, etc.).
Some examples of stable storage that are allowable for an NFS
server include:
1. Media commit of data; that is, the modified data has been
successfully written to the disk media, for example, the disk
platter.
2. An immediate reply disk drive with battery-backed, on-drive
intermediate storage or uninterruptible power system (UPS).
3. Server commit of data with battery-backed intermediate storage
and recovery software.
4. Cache commit with uninterruptible power system (UPS) and
recovery software.
Stateid: A stateid is a 128-bit quantity returned by a server that
uniquely defines the open and locking states provided by the
server for a specific open-owner or lock-owner/open-owner pair for
a specific file and type of lock.
Verifier: A verifier is a 64-bit quantity that is changed to
indicate that a corresponding change on one of the peers has
occurred requiring the other peer to adjust to possibility of
change. There are a number of 64-bit quantities identified as
verifiers:
* In many cases, a verifier is a 64-bit quantity generated by the
server that the client can use to determine if the client has
restarted and potentially lost writes that had not been
reliably committed to stable storage.
* Another type of verifier is used to indicate whether the server
mapping between directory cookies and directory entries has
changed, requiring the client to restart directory
interrogations that normally may be continued across multiple
READDIR requests.
* As described above, client owners include a verifier, allowing
the server to determine when a client reboot has occurred
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The Secret State Verifier is not a verifier in the sense given in
this definition.
2.6. Overview of NFSv4.1 Features
The major features of the NFSv4.1 protocol will be reviewed in brief.
This will be done to provide an appropriate context for both the
reader who is familiar with the previous versions of the NFS protocol
and the reader who is new to the NFS protocols. For the reader new
to the NFS protocols, there is still a set of fundamental knowledge
that is expected. The reader should be familiar with the External
Data Representation (XDR) and Remote Procedure Call (RPC) protocols
as described in [RFC4506] and [RFC5531]. A basic knowledge of file
systems and distributed file systems is expected as well.
In general, this specification of NFSv4.1 will not distinguish those
features added in minor version 1 from those present in the base
protocol but will treat NFSv4.1 as a unified whole. See Section 4
for a summary of the differences between NFSv4.0 and NFSv4.1.
2.7. RPC and Security
As with previous versions of NFS, the External Data Representation
(XDR) and Remote Procedure Call (RPC) mechanisms used for the NFSv4.1
protocol are those defined in [RFC4506] and [RFC5531], as extended by
[RFC9289]) to provide TLS-based encryption and client-host
authentication. NFSv4.1 security. A description of the basics of
NFv4.1 security will appear in an NFSv4-wide security document, to be
derived from [I-D.dnoveck-nfsv4-security].
NFSv4.1 introduces parallel access (see Section 2.8.2), through the
use of pNFS. The security framework described above is significantly
modified by the introduction of pNFS (see Section 18.11), because of
the addition of additional actors and because data access sometimes
does not rely on RPC for principal identification/authentication.
The appropriate handling depends on the data access protocol used
(see Section 18.4.5) which depends in turn on the layout type (see
Section 18.2.) The sections 18.11.1 through 18.11.3 discuss the
security implications of using different sorts of data access
protocols.
2.8. Protocol Structure
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2.8.1. Core Protocol
Unlike NFSv3, which relied on a series of ancillary protocols (e.g.,
NLM, NSM (Network Status Monitor), MOUNT), within all minor versions
of NFSv4 a single RPC protocol is available to make requests to the
server. Facilities that had used separate protocols, such as
locking, are now integrated within a single unified protocol,
although, to implement pNFS, different data access protocols may also
be used.
2.8.2. Parallel Access
Minor version 1 supports high-performance data access to a clustered
server implementation by enabling a separation of metadata access and
data access, with the latter able to be done to multiple servers in
parallel.
Such parallel data access is controlled by recallable objects known
as "layouts", which are integrated into the protocol locking model.
Clients direct requests for data access to a set of data servers
specified by the layout via a data storage protocol which may be
NFSv4.1 or may be another protocol.
Because the protocols used for parallel data access are not
necessarily RPC-based, the RPC-based security model (Section 2.7) is
impacted (see Section 18.11). The degree of impact varies with the
protocol (see Section 18.4.5) used for data access, and can be as low
as zero for some RPC-based data access protocols (see Section 20.25).
2.9. File System Model
The general file system model used for the NFSv4.1 protocol is the
same as for previous minor versions of NFSv4. The server file system
is hierarchical with the regular files contained within being treated
as opaque byte streams. File names MAY be restricted to UTF-
8-encoded strings of Unicode characters or treated as opaque. In
addition, for some file systems, name handling MAY reflect the UTF-8
canonical equivalence relation, and in some cases, case-based
equivalence relations as well.
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The NFSv4.1 protocol does not rely on a separate protocol to provide
for the initial mapping between path name and filehandle. All file
systems exported by a server are presented as a tree so that all file
systems are reachable from a special per-server global root
filehandle. This allows LOOKUP operations to be used to perform
functions previously provided by the MOUNT protocol. The server is
responsible for providing any necessary pseudo file systems to bridge
any gaps that arise due to unexported portions of the server-local
name space that are between exported file systems.
2.9.1. Filehandles
As in previous versions of the NFS protocol, opaque filehandles are
used to identify individual files and directories. Lookup-type and
create operations translate file and directory names to filehandles,
which are then used to identify objects in subsequent operations.
The NFSv4.1 protocol provides support for persistent filehandles,
guaranteed to be valid for the lifetime of the file system object
designated and bever to be reused after that. In addition, it
provides support to allow servers to provide filehandles with more
limited validity guarantees, referred to as volatile filehandles.
2.9.2. Numbered File Attributes
The NFSv4.1 protocol has a rich and extensible file object attribute
structure in which each attribute is assigned an attribute number.
The set of such attributes can be usefully divided in a number of
ways, in order to provide helpful context for server implementers
choosing to implement or not implement particular attributes which
are not REQUIRED and for client implementers deciding how to deal
with non-support of particular attributes which are not REQUIRED.
* Attributes differ as to their scope, with only a subset applicable
to a particular file object, while others apply to an entire file
system.
As a practical matter, attributes applicable to a single file
object, often require support within the file system proper.
While this functionality is most often provided by a file system
created initially for local access and only later adapted to
remote use through an NFSv4.1 server, there are also file systems
purpose-built for remote access.
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Attributes applicable to an entire file system do not typically
require support within the file system proper. One possible
exception is when such attributes can be set to indicate the
client's desire for some particular feature that inherently
require file system support.
Note that, in all these cases, applications are most likely to be
adapted to features that can be accessed using existing file
access facilities. As a result, implementers are unlikely to
devote efforts to implementation of OPTIONAL features and
attributes which require interactions with applications while
being more open to attributes usable by the client and server to
communicate to optimize data flows without requiring application
involvement.
* Attributes differ as to their mutability characteristics,
including whether the attribute is question can be modified
explicitly by the client and whether the attribute modification
happens as a result of performing other operations, such as
modifying a file or directory
* In this update of the NFSv4.1 specification, the details for
handling authorization-related attributes are the responsibility
of the NFSv4-wide security documents expected to be derived from
[I-D.dnoveck-nfsv4-security] and [I-D.ietf-nfsv4-acls-update].
Although the detailed categorization of such attributes will be
the responsibility of the security documents, this document will,
in Section 11.3, provide a brief summary and make clear that some
of these are more necessary than others, and that they all cannot
be reasonably treated as having the being of the same class
regarding the need for server support.
Attributes are divided into a number of classes based on the
protocol's requirements/recommendations for server implementation and
the client's expected response to a server's non-support of those
attributes. This categorization differs from that appearing
previously for a number of reasons with the specific differences
explained in Section 11.2.
* A significant number of attributes are described as REQUIRED so
that servers MUST provide support for them.
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These include the same set of attributes described in this way in
RFCs [RFC7530] and [RFC8881]. In addition, there are a set of
authorization-related attributes that need to be included in this
group for reasons explained in [I-D.dnoveck-nfsv4-security]. The
inclusion of all these attributes is discussed in more detail in
Section 11.4.
* Many attributes are truly OPTIONAL, even though such attributes
have been erroneously categorized as "RECOMMENDED" in the past.
These attributes are discussed in more detail in Section 11.5.
For a more detailed explanation of these shifts in terminology,
see Section 11.2.
* It appears necessary to designate certain authorization-related
attributes as Experimental.
These attributes are discussed in more detail in Sections 11.3 and
11.6.
Descriptions of each specific attribute appears in the following
places:
* Those which are authorization-related are described in
[I-D.dnoveck-nfsv4-security] and [I-D.ietf-nfsv4-acls-update].
* Others are described sections 11.14 through 11.17.5
These descriptions can be found using the three sources described
below:
* The list of Authorization-related attributes appears in
Section 11.18
* The list of REQUIRED Attributes appears in Table 4 within
Section 11.10.
* The list of attributes which are not REQUIRED) appears in Table 5
within Section 11.11.
"Named attributes", despite this designation, which will be retained,
differ substantially from file attributes per se and are explained in
Section 2.9.3. The entire named attribute feature is OPTIONAL and
such objects, when they exist, are not part of the categorization
above.
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2.9.3. Named Attributes
A named attribute is an opaque byte stream that is associated with a
directory or file and referred to by a string name. The named
attribute feature was originally intended to be used to provide
extended attributes providing more flexibility than is possible for
attributes defined within a standards-track protocol.
Servers providing support for the named attribute feature, which is
OPTIONAL, allow a number of opaque byte streams to be associated with
a directory or a file. This feature allows applications to define
multiple data streams associated with a file object, each of which
can be opened, read, and written just as files are.
This approach to the issue provided a level of functionality beyond
that typically available for extended attributes which typically
restrict the length of such attributes in order to make them
available in the same way that other attributes are. Nevertheless,
despite this mismatch, NFSv4.1 makes these data streams available for
that purpose and they have been used to support extended attribute
functionality. The possible development of extended attribute
protocol support more tailored to that specific application is a
matter to be dealt with in future minor versions.
For further information about the use of named attributes, see
Section 11.7
2.9.4. Multi-Server Namespace
NFSv4.1 contains a number of features to allow implementation of
namespaces that cross server boundaries and that allow and facilitate
a nondisruptive transfer of support for individual file systems
between servers. They are all based upon attributes that allow one
file system to specify alternate, additional, and new location
information that specifies how the client may access that file
system.
These attributes can be used to provide for individual active file
systems:
* Alternate network addresses to access the current file system
instance.
* The locations of alternate file system instances or replicas to be
used in the event that the current file system instance becomes
unavailable.
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These file system location attributes may be used together with the
concept of absent file systems, in which a position in the server
namespace is associated with locations on other servers without there
being any corresponding file system instance on the current server.
For example,
* These attributes may be used with absent file systems to implement
referrals whereby one server may direct the client to a file
system provided by another server. This allows extensive multi-
server namespaces to be constructed.
* These attributes may be provided when a previously present file
system becomes absent. This allows nondisruptive migration of
file systems to alternate servers.
3. Locking Facilities
As mentioned previously, NFSv4.1 is a single protocol that includes
locking facilities. These locking facilities include support for
many types of locks including a number of sorts of recallable locks.
Recallable locks such as delegations allow the client to be assured
that certain events will not occur so long as that lock is held.
When circumstances change, the lock is recalled via a callback
request. The assurances provided by delegations allow more extensive
caching to be done safely when circumstances allow it.
The types of locks are:
* Share reservations as established by OPEN operations.
* Byte-range locks.
* File delegations, which are recallable locks that assure the
holder that inconsistent opens and file changes cannot occur so
long as the delegation is held.
* Directory delegations, which are recallable locks that assure the
holder that inconsistent directory modifications cannot occur so
long as the delegation is held.
* Layouts, which are recallable objects that assure the holder that
direct access to the file data may be performed directly by the
client and that no change to the data's location that is
inconsistent with that access may be made so long as the layout is
held.
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All non-recallable locks for a given client are tied together under a
single client-wide lease. All requests made on sessions associated
with the client renew that lease. When the client's lease is not
promptly renewed, the client's locks are subject to revocation. In
the event of server restart, clients have the opportunity to safely
reclaim their locks within a special grace period.
Recallable locks are subject to revocation irrespective of lease
state. Servers often need to revoke such locks when recalling them
does not result in their prompt return.
4. Differences from NFSv4.0
The following summarizes the major differences between minor version
One and the base protocol:
* Implementation of the sessions model (Section 7).
* Parallel access to data (Section 18).
* Addition of the RECLAIM_COMPLETE operation to better structure the
lock reclamation process (Section 25.51).
* Enhanced delegation support as follows.
- Delegations on directories and other file types in addition to
regular files (Section 25.39, Section 25.49).
- Operations to optimize acquisition of recalled or denied
delegations (Section 25.49, Section 27.5, Section 27.7).
- Notifications of changes to files and directories
(Section 25.39, Section 27.4).
- A method to allow a server to indicate that it is recalling one
or more delegations for resource management reasons, and thus a
method to allow the client to pick which delegations to return
(Section 27.6).
* Attributes can be set atomically during exclusive file create via
the OPEN operation (See the new EXCLUSIVE4_1 creation method in
Section 25.16).
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* Open files can be preserved if removed and the hard link count
("hard link" is defined in an Open Group [hardlink] standard) goes
to zero, thus obviating the need for clients to rename deleted
files to partially hidden names, a technique colloquially called
"silly rename" (See the new OPEN4_RESULT_PRESERVE_UNLINKED reply
flag in Section 25.16).
* Improved compatibility with Microsoft Windows for Access Control
Lists (sacl and dacl attributes, acl inheritance).
* Data retention (Section 11.17).
* Identification of the implementation of the NFS client and server
(Section 25.35).
* Support for notification of the availability of byte-range locks
(See the new OPEN4_RESULT_MAY_NOTIFY_LOCK reply flag in
Section 25.16 and see Section 27.11).
* In NFSv4.1, LIPKEY and SPKM-3 are not required security mechanisms
[RFC2847].
5. Core Infrastructure
5.1. Introduction
NFSv4.1 relies on core infrastructure common to nearly every
operation. This core infrastructure is described in the remainder of
this section.
5.2. RPC and XDR
The NFSv4.1 protocol is a Remote Procedure Call (RPC) application
that uses RPC version 2 and the corresponding eXternal Data
Representation (XDR) as defined in [RFC5531] and [RFC4506]. The
transport-level encryption and client-host authentication facilities
described in [RFC9289] can also be used.
5.3. RPC-Based Security
In addition to the above, as discussed in Section 5.3.1, some
security flavors provide additional security services.
NFSv4.1 clients and servers MUST implement RPCSEC_GSS. (This
requirement to implement is not a requirement to use.) Other
flavors, such as AUTH_NONE and AUTH_SYS, can be implemented as well,
although the security implications of doing so need to be carefully
considered, particularly when the client host is not itself
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authenticated. In particular, it is RECOMMENDED by rpc-tls [RFC9289]
that AUTH_SYS not be used when client host authentication is not in
effect.
5.3.1. RPCSEC_GSS and Security Services
RPCSEC_GSS [RFC2203] uses the functionality of GSS-API [RFC2743].
This allows for the use of various security mechanisms by the RPC
layer without the additional implementation overhead of adding RPC
security flavors.
5.3.1.1. GSS Server Principal
Regardless of what security mechanism under RPCSEC_GSS is being used,
the NFS server MUST identify itself in GSS-API via a
GSS_C_NT_HOSTBASED_SERVICE name type. GSS_C_NT_HOSTBASED_SERVICE
names are of the form:
service@hostname
For NFS, the "service" element is
nfs
Implementations of security mechanisms will convert nfs@hostname to
various different forms. For Kerberos V5, the following form is
RECOMMENDED:
nfs/hostname
5.4. COMPOUND and CB_COMPOUND
A significant departure from the versions of the NFS protocol before
NFSv4 is the introduction of the COMPOUND procedure. For the NFSv4
protocol, in all minor versions, there are exactly two RPC
procedures, NULL and COMPOUND. The COMPOUND procedure is defined as
a series of individual operations and these operations perform the
sorts of functions performed by traditional NFS procedures.
The operations combined within a COMPOUND request are evaluated in
order by the server, without any atomicity guarantees. A limited set
of facilities exist to pass results from one operation to another.
Once an operation returns a failing result, the evaluation ends and
the results of all evaluated operations are returned to the client.
With the use of the COMPOUND procedure, the client is able to build
simple or complex requests. These COMPOUND requests allow for a
reduction in the number of RPCs needed for logical file system
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operations. For example, multi-component look up requests can be
constructed by combining multiple LOOKUP operations. Those can be
further combined with operations such as GETATTR, READDIR, or OPEN
plus READ to do more complicated sets of operation without incurring
additional latency.
NFSv4.1 also contains a considerable set of callback operations in
which the server makes an RPC directed at the client. Callback RPCs
have a similar structure to that of the normal server requests. In
all minor versions of the NFSv4 protocol, there are two callback RPC
procedures: CB_NULL and CB_COMPOUND. The CB_COMPOUND procedure is
defined in an analogous fashion to that of COMPOUND with its own set
of callback operations.
The addition of new server and callback operations within the
COMPOUND and CB_COMPOUND request framework provides a means of
extending the protocol in subsequent minor versions.
Except for a small number of operations needed for session creation,
server requests and callback requests are performed within the
context of a session. Sessions provide a client context for every
request and support robust replay protection, which provides the
original response to the caller in the case of non-idempotent
requests.
5.5. Client Identifiers and Client Owners
For each operation that obtains or depends on locking state, the
specific client needs to be identifiable by the server.
Each distinct client instance is represented by a client ID. A
client ID is a 64-bit identifier representing a specific client at a
given time. The client ID is changed whenever the client re-
initializes, and may change when the server re-initializes. Client
IDs are used to support lock identification and crash recovery.
During steady state operation, the client ID associated with each
operation is derived from the session (See Section 7) on which the
operation is sent. A session is associated with a client ID when the
session is created.
Unlike NFSv4.0, the only NFSv4.1 operations possible before a client
ID is established are those needed to establish the client ID.
A sequence of an EXCHANGE_ID operation followed by a CREATE_SESSION
operation using that client ID (eir_clientid as returned from
EXCHANGE_ID) is required to establish and confirm the client ID on
the server. Establishment of identification by a new incarnation of
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the client also has the effect of immediately releasing any locking
state that a previous incarnation of that same client might have had
on the server. Such released state would include all byte-range
lock, share reservation, layout state. Also, where the server
supports neither the CLAIM_DELEGATE_PREV nor the CLAIM_DELEG_PREV_FH
claim types, all delegation state associated with the same client is
released as well. For discussion of delegation state recovery, see
Section 15.2.1. For discussion of layout state recovery, see
Section 18.9.1.
Releasing such state requires that the server be able to determine
that one client instance is the successor of another. Where this
cannot be done, for any of a number of reasons, the locking state
will remain for a time subject to lease expiration (See Section 13.3)
and the new client will need to wait for such state to be removed, if
it makes conflicting lock requests.
Client identification is encapsulated by the following client owner
data type:
struct client_owner4 {
verifier4 co_verifier;
opaque co_ownerid<NFS4_OPAQUE_LIMIT>;
};
The first field, co_verifier, is a client incarnation verifier,
allowing the server to distinguish successive incarnations (e.g.,
reboots) of the same client. The server will start the process of
canceling the client's leased state if co_verifier is different than
what the server has previously recorded for the identified client (as
specified in the co_ownerid field).
The second field, co_ownerid, contains the client owner id. This is
a variable-length string that uniquely defines the client so that
subsequent instances of the same client bear the same co_ownerid with
a different verifier.
There are several considerations for how the client generates the
co_ownerid string:
* The string should be unique so that multiple clients do not
present the same string. The consequences of two clients
presenting the same string range from one client getting an error
to one client having its leased state abruptly and unexpectedly
cancelled.
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* The string should be selected so that subsequent incarnations
(e.g., restarts) of the same client cause the client to present
the same string. The implementer is cautioned from an approach
that requires the string to be recorded in a local file because
this precludes the use of the implementation in an environment
where there is no local disk and all file access is from an
NFSv4.1 server.
* The string should be the same for each server network address that
the client accesses. This way, if a server has multiple
interfaces, the client can trunk traffic over multiple network
paths as described in Section 7.5. (Note: the precise opposite
was advised in the NFSv4.0 specification [RFC3530].)
* The algorithm for generating the string should not assume that the
client's network address will not change, unless the client
implementation knows it is using statically assigned network
addresses. This includes changes between client incarnations and
even changes while the client is still running in its current
incarnation. Thus, with dynamic address assignment, if the client
includes just the client's network address in the co_ownerid
string, there is a real risk that after the client gives up the
network address, another client, using a similar algorithm for
generating the co_ownerid string, would generate a conflicting
co_ownerid string.
Given the above considerations, an example of a well-generated
co_ownerid string is one that includes:
* If applicable, the client's statically assigned network address.
* Additional information that tends to be unique, such as one or
more of:
- The client machine's serial number (for privacy reasons, it is
best to perform some one-way function on the serial number).
- A Media Access Control (MAC) address (again, a one-way function
should be performed).
- The timestamp of when the NFSv4.1 software was first installed
on the client (though this is subject to the previously
mentioned caution about using information that is stored in a
file, because the file might only be accessible over NFSv4.1).
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- A true random number. However, since this number ought to be
the same between client incarnations, this shares the same
problem as that of using the timestamp of the software
installation.
* For a user-level NFSv4.1 client, it should contain additional
information to distinguish the client from other user-level
clients running on the same host, such as a process identifier or
other unique sequence.
The client ID is assigned by the server (the eir_clientid result from
EXCHANGE_ID) and should be chosen so that it will not conflict with a
client ID previously assigned by the server. This applies across
server restarts.
In the event of a server restart, a client may find out that its
current client ID is no longer valid when it receives an
NFS4ERR_STALE_CLIENTID error. The precise circumstances depend on
the characteristics of the sessions involved, specifically whether
the session is persistent (See Section 8), but in each case the
client will receive this error when it attempts to establish a new
session with the existing client ID and receives the error
NFS4ERR_STALE_CLIENTID, indicating that a new client ID needs to be
obtained via EXCHANGE_ID and the new session established with that
client ID.
When a session is not persistent, the client will find out that it
needs to create a new session as a result of getting an
NFS4ERR_BADSESSION, since the session in question was lost as part of
a server restart. When the existing client ID is presented to a
server as part of creating a session and that client ID is not
recognized, as would happen after a server restart, the server will
reject the request with the error NFS4ERR_STALE_CLIENTID.
In the case of the session being persistent, the client will re-
establish communication using the existing session after the restart.
This session will be associated with the existing client ID but may
only be used to retransmit operations that the client previously
transmitted and did not see replies to. Replies to operations that
the server previously performed will come from the reply cache;
otherwise, NFS4ERR_DEADSESSION will be returned. Hence, such a
session is referred to as "dead". In this situation, in order to
perform new operations, the client needs to establish a new session.
If an attempt is made to establish this new session with the existing
client ID, the server will reject the request with
NFS4ERR_STALE_CLIENTID.
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When NFS4ERR_STALE_CLIENTID is received in either of these
situations, the client needs to obtain a new client ID by use of the
EXCHANGE_ID operation, then use that client ID as the basis of a new
session, and then proceed to any other necessary recovery for the
server restart case (See Section 13.4.2).
See the descriptions of EXCHANGE_ID (Section 25.35) and
CREATE_SESSION (Section 25.36) for a complete specification of these
operations.
5.5.1. Upgrade from NFSv4.0 to NFSv4.1
To facilitate upgrade from NFSv4.0 to NFSv4.1, a server may compare a
value of data type client_owner4 in an EXCHANGE_ID with a value of
data type nfs_client_id4 that was established using the SETCLIENTID
operation of NFSv4.0. A server that does so will allow an upgraded
client to avoid waiting until the lease (i.e., the lease established
by the NFSv4.0 instance client) expires. This requires that the
value of data type client_owner4 be constructed the same way as the
value of data type nfs_client_id4. If the latter's contents included
the server's network address (per the recommendations of the NFSv4.0
specification [RFC3530]), and the NFSv4.1 client does not wish to use
a client ID that prevents trunking, it should send two EXCHANGE_ID
operations. The first EXCHANGE_ID will have a client_owner4 equal to
the nfs_client_id4. This will clear the state created by the NFSv4.0
client. The second EXCHANGE_ID will not have the server's network
address. The state created for the second EXCHANGE_ID will not have
to wait for lease expiration, because there will be no state to
expire.
5.5.2. Server Release of Client ID
NFSv4.1 introduces a new operation called DESTROY_CLIENTID
(Section 25.50), which the client uses to destroy a client ID it no
longer needs. This permits graceful, bilateral release of a client
ID. The operation cannot be used if there are sessions associated
with the client ID, or state with an unexpired lease.
If the server determines that the client holds no associated state
for its client ID (associated state includes unrevoked sessions,
opens, locks, delegations, layouts, and wants), the server MAY choose
to unilaterally release the client ID in order to conserve resources.
If the client contacts the server after this release, the server MUST
ensure that the client receives the appropriate error so that it will
use the EXCHANGE_ID/CREATE_SESSION sequence to establish a new client
ID. The server ought to be very hesitant to release a client ID
since the resulting work on the client to recover from such an event
will be the same burden as if the server had failed and restarted.
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Typically, a server would not release a client ID unless there had
been no activity from that client for many minutes. As long as there
are sessions, opens, locks, delegations, layouts, or wants, the
server MUST NOT release the client ID. See Section 7.13.1.4 for
discussion on releasing inactive sessions.
5.5.3. Resolving Client Owner Conflicts
When the server gets an EXCHANGE_ID for a client owner that currently
has no state, or that has state but the lease has expired, the server
MUST allow the EXCHANGE_ID and confirm the new client ID if followed
by the appropriate CREATE_SESSION.
When the server gets an EXCHANGE_ID for a new incarnation of a client
owner that currently has an old incarnation with state and an
unexpired lease, the server is allowed to dispose of the state of the
previous incarnation of the client owner if one of the following is
true:
* The client ID was created without explicit state protection (i.e.,
SP4_NONE was used) and without client host authentication while
the current EXCHANGE_ID shares those characteristics and the
principals used for client Id creation and the current EXCHANGE_ID
match as well.
* The client ID was created without explicit state protection (i.e.
SP4_NONE was used) and with client host authentication while the
current EXCHANGE_ID shares those characteristics with the
EXCHANGE_ID used to create the client ID while the authenticated
client hosts match as well.
* The principal that created the client ID for the client owner is
the same as the principal that is sending the EXCHANGE_ID
operation. Note that if the client ID was created with
SP4_MACH_CRED state protection (Section 25.35), the principal MUST
be based on RPCSEC_GSS authentication, the RPCSEC_GSS service used
MUST be integrity or privacy, and the same GSS mechanism and
principal MUST be used as that used when the client ID was
created.
* The client ID was established with SP4_SSV protection
(Section 25.35, Section 7.8.3) and the client sends the
EXCHANGE_ID with the security flavor set to RPCSEC_GSS using the
GSS SSV mechanism (Section 7.9).
* The client ID was established with SP4_SSV protection, and under
the conditions described herein, the EXCHANGE_ID was sent with
SP4_MACH_CRED state protection. Because the SSV might not persist
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across client and server restart, and because the first time a
client sends EXCHANGE_ID to a server it does not have an SSV, the
client MAY send the subsequent EXCHANGE_ID without an SSV
RPCSEC_GSS handle. Instead, as with SP4_MACH_CRED protection, the
principal MUST be based on RPCSEC_GSS authentication, the
RPCSEC_GSS service used MUST be integrity or privacy, and the same
GSS mechanism and principal MUST be used as that used when the
client ID was created.
If none of the above situations apply, the server MUST return
NFS4ERR_CLID_INUSE.
If the server accepts the principal and co_ownerid as matching that
which created the client ID, and the co_verifier in the EXCHANGE_ID
differs from the co_verifier used when the client ID was created,
then after the server receives a CREATE_SESSION that confirms the
client ID, the server deletes state. If the co_verifier values are
the same (e.g., the client either is updating properties of the
client ID (Section 25.35) or is attempting trunking (Section 7.5),
the server MUST NOT delete state.
5.6. Server Owners
The server owner is similar to a client owner (Section 5.5), but
unlike the client owner, there is no shorthand server ID. The server
owner is defined in the following data type:
struct server_owner4 {
uint64_t so_minor_id;
opaque so_major_id<NFS4_OPAQUE_LIMIT>;
};
The server owner is returned from EXCHANGE_ID. When the so_major_id
fields are the same in two EXCHANGE_ID results, the connections that
each EXCHANGE_ID were sent over can be assumed to address the same
server (as defined in Section 2.5). If the so_minor_id fields are
also the same, then not only do both connections connect to the same
server, but the session can be shared across both connections. The
reader is cautioned that multiple servers may deliberately or
accidentally claim to have the same so_major_id or so_major_id/
so_minor_id; the reader should examine Sections 7.5 and 25.35 in
order to avoid acting on falsely matching server owner values.
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The considerations for generating an so_major_id are similar to that
for generating a co_ownerid string (see Section 5.5). The
consequences of two servers generating conflicting so_major_id values
are less dire than they are for co_ownerid conflicts because the
client can use RPCSEC_GSS to compare the authenticity of each server
(See Section 7.5).
5.7. Transport Layers
5.7.1. REQUIRED and RECOMMENDED Properties of Transports
NFSv4.1 works over Remote Direct Memory Access (RDMA) and non-RDMA-
based transports with the following attributes:
* The transport supports reliable delivery of data, which NFSv4.1
requires. However the possibility of connections breaking is
addressed in NFSv4.1 by a session-based replay cache to prevent
the spurious re-execution of non-idempotent requests or modifying
idempotent requests.
* The transport delivers data in the order it was sent. Ordered
delivery simplifies detection of transmit errors, and simplifies
the sending of arbitrary sized requests and responses via the
record marking protocol [RFC5531].
Because efficient handling is required when sending large amounts of
data, congestion control facilities are a significant concern.
* When NFSv4.1 is used over an IP-based network protocol, it is
REQUIRED that the transport provide congestion control.
* When NFSv4.1 is used over a non-IP network protocol, it is
RECOMMENDED that the transport provide congestion control.
To enhance the possibilities for interoperability, it is strongly
recommended that NFSv4.1 client and server implementations support
operation over the TCP transport protocol.
It is permissible for a connectionless transport to be used under
NFSv4.1; however, reliable and in-order delivery of data combined
with congestion control by the connectionless transport is REQUIRED.
As a consequence, UDP by itself MUST NOT be used as an NFSv4.1
transport, although transports to be used for NFSv4.1 may be layered
on UDP. NFSv4.1 assumes that a client transport address and server
transport address used to send data over a transport together
constitute a connection, even if the underlying transport eschews the
concept of a connection.
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5.7.2. Client and Server Transport Behavior
[Author Aside]: Section substantially revised to address unjustified
use of RFC2119-defined keywords regarding retries and replace that
with appropriate implementation advice.
When a connection-oriented transport (e.g., TCP) is used, the client
and server are normally expected to maintain the use of connections
already established for a considerable length of time. This is for a
number reasons:
* This will prevent the weakening of the transport's congestion
control mechanisms by the confusion resulting from dispersing a
single burst of network traffic into multiple connections.
* This will improve performance for the WAN environment by
eliminating the need for connection setup handshakes. This is
particularly so given that each new connection requires the re-
establishment of a connection id, as well as setting up new
connections.
* The NFSv4.1 callback model requires the client and server to
maintain a client-created backchannel (See Section 7.3.1) for the
server to use so that any dropping of the connection will
interfere with the use of the backchannel.
Although it is not fatal for a requester to retry without a
disconnect between the request and retry, there are good reasons to
avoid this practice. The retry does consume resources, especially
with RDMA, where each request, retry or not, consumes a credit.
Retries for no reason, especially retries sent shortly after the
previous attempt, are a poor use of network bandwidth and defeat the
purpose of a transport's inherent congestion control system.
There is no situation in which a replier is allowed to silently drop
a request, whether the request is a retry or not. (The silent drop
behavior of RPCSEC_GSS [RFC2203] is not relevant here since this
behavior happens at the RPCSEC_GSS layer, which is at a lower layer
in the request processing.) While the replier MAY disconnect the
connection, if it does not do so, it is obligated to execute the
request or return an appropriate error based on the contents of the
reply cache (see Section 7.6.1).
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When sending a reply, the replier MUST send the reply to the same
full network address (e.g., if using an IP-based transport, the
source port of the requester is part of the full network address)
from which the requester sent the request. If using a connection-
oriented transport, replies MUST be sent on the connection from which
the request was received.
If a connection is dropped after the replier receives the request but
before the replier sends the reply, the replier might have a pending
reply. If a connection is established with the same source and
destination full network address as the dropped connection, then the
replier MUST NOT send the reply until the requester retries the
request. The reason for this prohibition is that the requester MAY
retry a request over a different connection (provided that connection
is associated with the original request's session).
When using RDMA transports, there are other reasons for avoiding
retries over the same connection:
* RDMA transports use "credits" to enforce flow control, where a
credit is a right to a peer to transmit a message. If one peer
were to retransmit a request (or reply), it would consume an
additional credit. If the replier retransmitted a reply, it would
certainly result in an RDMA connection loss, since the requester
would typically only post a single receive buffer for each
request. If the requester retransmitted a request, the additional
credit consumed on the server might lead to RDMA connection
failure unless the client accounted for it and decreased its
available credit, leading to wasted resources.
* RDMA credits present a new issue to the reply cache in NFSv4.1.
The reply cache may be used when a connection within a session is
lost, such as after the client reconnects. Credit information is
a dynamic property of the RDMA connection, and stale values must
not be replayed from the cache. This implies that the reply cache
contents must not be blindly used when replies are sent from it,
and credit information appropriate to the channel must be
refreshed by the RPC layer.
In addition, as described in Section 7.6.2, while a session is
active, an NFSv4.1 requester that ceases to wait for an outstanding
reply MUST take appropriate care to avoid that situation vitiating
guarantees needed to maintain the exactly-once semantics needed for
the successful operation of the session-based reply cache.
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5.7.3. Ports
Historically, NFSv3 servers have listened over TCP port 2049. The
registered port 2049 [RFC3232] for the NFS protocol should be the
default configuration for NFSv4.1, although the port 20049 is used
for NFSv4.1 layered on RPC-over-RDMA.
The use of a reserved port has been common for NFS implementations
and it is expected that this will apply to NFSv4.1 as well. While
the use of RPC binding protocols as described in [RFC1833] is a
possibility, there is no requirement that servers provide support for
such use.
In light of this, a client should avoid this sort of use unless it
has good reason to expect such support to be present on the server,
while accessing NFS services at the appropriate well-known port
depending on the transport to be used.
6. Security-related Infrastructure
NFSv4.1 relies on the Infrastructure described by the NFSv4-wide
security-related documents, currently [I-D.dnoveck-nfsv4-security]
and [I-D.ietf-nfsv4-acls-update]. This infrastructure includes:
* The RPC-based facilities to provide authentication, privacy and
integrity, including facilities provided by the various
authentication flavors and those provided at the transport layer.
* The security negotiation facilities described in section 16 of the
security document, as they have been enhanced to support selection
of transport-layer facilities, as well as authentication flavors
and associated services.
* The authorization facilities described in Sections 5.3, 5.4, and 7
of the security document.
* The audit and alarm facilities described in Section 13 of the
security document.
There are, however, a number of places where the NFSv4-wide treatment
needs to be supplemented to deal with NFSv4.1-specific features,
requirements, and recommendations as discussed below:
* The parallel NFS feature is described in Section 18, with security
for it dealt with in Section 18.11. The case of the file layout
type is described in Section 20 with security for it dealt with in
Section 20.25.
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The security for parallel NFS is dealt with in this specification
even though it relies on the security infrastructure described in
the NFSv4-wide security document. As a result, it will be
discussed in a restructured Section 28.
* The handling of SECINFO and SECINFO_NO_NAME is complicated because
both share the extensions to the negotiation process described in
Section 12 of the NFSv4-wide security document, currently
[I-D.dnoveck-nfsv4-security], while the former operation in
present in all minor versions while the latter is specific to
NFSv4.1.
* The requirements and recommendations regarding associated security
services are discussed in Section 6.1. The discussion had been
modified to include the possibility that encryption at the RPC
transport layer might obviate the need for these services,
although the existing requirements and recommendations still
stand.
[Author Aside]: Further work in this area is likely and there
should be working group discussion of possible changes. Of
particular concern is the use of "SHOULD" in connection with
support for privacy, as it is not clear what might be valid
reasons not to support this. The provision of confidentiality
using transport-based encryption further complicates the matter,
although it needs to be clear that the need that confidentiality
be available in some form is strongly recommended.
6.1. NFSv4.1-specific Recommendations and Requirements Regarding
Security Services
[Author Aside]: Significant revisions have been made to address the
hole created by the fact that the discussion of client support of
data privacy uses the word "SHOULD".
Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate
users on clients to servers, and servers to users. Authentication of
the client itself is not provided but can be provided by RPC
independently of the use of RPCSEC_GSS.
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GSS-API can also perform integrity checking on the entire RPC
message, including the RPC header, and on the arguments or results.
Finally, privacy/confidentiality, usually via encryption, is a
service available with RPCSEC_GSS. Privacy is provided for the
arguments and results. Note that if privacy is selected, integrity,
authentication, and identification are enabled. If privacy is not
selected, but integrity is selected, authentication and
identification are enabled. If integrity and privacy are not
selected, but authentication is enabled, identification is enabled.
RPCSEC_GSS does not provide identification as a separate service.
Although GSS-API has an authentication service distinct from its
privacy and integrity services, GSS-API's authentication service is
not used for RPCSEC_GSS's authentication service. Instead, each RPC
request and response header is integrity protected with the GSS-API
integrity service, and this allows RPCSEC_GSS to offer per-RPC
authentication and identity. See [RFC2203] for more information.
NFSv4.1 client and servers MUST support RPCSEC_GSS's integrity and
authentication service. NFSv4.1 servers MUST support RPCSEC_GSS's
privacy service.
NFSv4.1 clients SHOULD support RPCSEC_GSS's privacy service. Given
that it is has never been made clear, as required by the definition
of "SHOULD in [RFC2119], it has to be assumed that this statement,
appearing in previous specifications has been treated as providing
permission for clients not to support RPCSEC_GSS privacy. In light
of this situation, it needs to be understood that, with regard to the
use of "SHOULD" above, valid reasons to bypass this recommendation
are limited to the reliance of implementors on those previous
specifications and the difficulty of changing them now.
The following consequences need to be kept in mind by those not
providing such support:
* Any data accessed on connections for which rpc-tls support is not
provided will be available, in the clear, to those with the
ability to monitor network traffic on a network segment used to
effect the access.
* The existence of clients without privacy support would make it
difficult or impossible to enforce privacy constraints that would
otherwise be straightforward. The effect is to undercut the
process of security negotiation, which is the only possible way to
provide confidentiality when rpc-tls encryption is not in effect.
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The reader is directed to Section 18.3.1 of
[I-D.dnoveck-nfsv4-security] for a more complete discussion of
security issues regarding data in flight.
6.2. NFSv4.1-specific Details of Security Negotiation
Unlike NFSv4.0, which only has the SECINFO operation, NFSv4.1 has the
SECINFO_NO_NAME operation as well. As a result, many of the details
of performing security negotiation will be different from those in
other minor versions and need to be discussed in this document, in
the sections below.
6.2.1. Put Filehandle Operations
The term "put filehandle operation" refers to PUTROOTFH, PUTPUBFH,
PUTFH, and RESTOREFH. Each of the subsections herein describes how
the server handles a subseries of operations that starts with a put
filehandle operation.
6.2.1.1. Put Filehandle Operation + SAVEFH
The client is saving a filehandle for a future RESTOREFH, LINK, or
RENAME. SAVEFH MUST NOT return NFS4ERR_WRONGSEC. To determine
whether or not the put filehandle operation returns NFS4ERR_WRONGSEC,
the server implementation pretends SAVEFH is not in the series of
operations and examines which of the situations described in the
other subsections of Section 6.2.1 apply.
6.2.1.2. Two or More Put Filehandle Operations
For a series of N put filehandle operations, the server MUST NOT
return NFS4ERR_WRONGSEC to the first N-1 put filehandle operations.
The Nth put filehandle operation is handled as if it is the first in
a subseries of operations. For example, if the server received a
COMPOUND request with this series of operations -- PUTFH, PUTROOTFH,
LOOKUP -- then the PUTFH operation is ignored for NFS4ERR_WRONGSEC
purposes, and the PUTROOTFH, LOOKUP subseries is processed as
according to Section 6.2.1.3.
6.2.1.3. Put Filehandle Operation + LOOKUP (or OPEN of an Existing
Name)
This situation also applies to a put filehandle operation followed by
a LOOKUP or an OPEN operation that specifies an existing component
name.
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In this situation, the client is potentially crossing a security
policy boundary, and the set of security tuples the parent directory
supports may differ from those of the child. The server
implementation may decide whether to impose any restrictions on
security policy administration. There are at least three approaches
(sec_policy_child is the tuple set of the child export,
sec_policy_parent is that of the parent).
(a) sec_policy_child <= sec_policy_parent (<= for subset). This
means that the set of security tuples specified on the security
policy of a child directory is always a subset of its parent
directory.
(b) sec_policy_child ^ sec_policy_parent != {} (^ for intersection,
{} for the empty set). This means that the set of security
tuples specified on the security policy of a child directory
always has a non-empty intersection with that of the parent.
(c) sec_policy_child ^ sec_policy_parent == {}. This means that the
set of security tuples specified on the security policy of a
child directory may not intersect with that of the parent. In
other words, there are no restrictions on how the system
administrator may set up these tuples.
In order for a server to support approaches (b) (for the case when a
client chooses a flavor that is not a member of sec_policy_parent)
and (c), the put filehandle operation cannot return NFS4ERR_WRONGSEC
when there is a security tuple mismatch. Instead, it should be
returned from the LOOKUP (or OPEN by existing component name) that
follows.
Since the above guideline does not contradict approach (a), it should
be followed in general. Even if approach (a) is implemented, it is
possible for the security tuple used to be acceptable for the target
of LOOKUP but not for the filehandles used in the put filehandle
operation. The put filehandle operation could be a PUTROOTFH or
PUTPUBFH, where the client cannot know the security tuples for the
root or public filehandle. Or the security policy for the filehandle
used by the put filehandle operation could have changed since the
time the filehandle was obtained.
Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC in
response to the put filehandle operation if the operation is
immediately followed by a LOOKUP or an OPEN by component name.
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6.2.1.4. Put Filehandle Operation + LOOKUPP
Since SECINFO only works its way down, there is no way LOOKUPP can
return NFS4ERR_WRONGSEC without SECINFO_NO_NAME. SECINFO_NO_NAME
solves this issue via style SECINFO_STYLE4_PARENT, which works in the
opposite direction as SECINFO. As with Section 6.2.1.3, a put
filehandle operation that is followed by a LOOKUPP MUST NOT return
NFS4ERR_WRONGSEC. If the server does not support SECINFO_NO_NAME,
the client's only recourse is to send the put filehandle operation,
LOOKUPP, GETFH sequence of operations with every security tuple it
supports.
Regardless of whether SECINFO_NO_NAME is supported, an NFSv4.1 server
MUST NOT return NFS4ERR_WRONGSEC in response to a put filehandle
operation if the operation is immediately followed by a LOOKUPP.
6.2.1.5. Put Filehandle Operation + SECINFO/SECINFO_NO_NAME
A security-sensitive client is allowed to choose a strong security
tuple when querying a server to determine a file object's permitted
security tuples. The security tuple chosen by the client does not
have to be included in the tuple list of the security policy of
either the parent directory indicated in the put filehandle operation
or the child file object indicated in SECINFO (or any parent
directory indicated in SECINFO_NO_NAME). Of course, the server has
to be configured for whatever security tuple the client selects;
otherwise, the request will fail at the RPC layer with an appropriate
authentication error.
In theory, there is no connection between the security flavor used by
SECINFO or SECINFO_NO_NAME and those supported by the security
policy. But in practice, the client may start looking for strong
flavors from those supported by the security policy, followed by
those in the REQUIRED set.
The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to a put
filehandle operation that is immediately followed by SECINFO or
SECINFO_NO_NAME. The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC
from SECINFO or SECINFO_NO_NAME.
6.2.1.6. Put Filehandle Operation + Nothing
The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC.
6.2.1.7. Put Filehandle Operation + Anything Else
"Anything Else" includes OPEN by filehandle.
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The security policy enforcement applies to the filehandle specified
in the put filehandle operation. Therefore, the put filehandle
operation MUST return NFS4ERR_WRONGSEC when there is a security tuple
mismatch. This avoids the complexity of adding NFS4ERR_WRONGSEC as
an allowable error to every other operation.
A COMPOUND containing the series put filehandle operation +
SECINFO_NO_NAME (style SECINFO_STYLE4_CURRENT_FH) is an efficient way
for the client to recover from NFS4ERR_WRONGSEC.
The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to any operation
other than a put filehandle operation, LOOKUP, LOOKUPP, and OPEN (by
component name).
6.2.1.8. Operations after SECINFO and SECINFO_NO_NAME
Suppose a client sends a COMPOUND procedure containing the series
SEQUENCE, PUTFH, SECINFO_NO_NAME, READ, and suppose the security
tuple used does not match that required for the target file. By rule
(See Section 6.2.1.5), neither PUTFH nor SECINFO_NO_NAME can return
NFS4ERR_WRONGSEC. By rule (See Section 6.2.1.7), READ cannot return
NFS4ERR_WRONGSEC. The issue is resolved by the fact that SECINFO and
SECINFO_NO_NAME consume the current filehandle (note that this is a
change from NFSv4.0). This leaves no current filehandle for READ to
use so that READ returns NFS4ERR_NOFILEHANDLE.
6.2.2. LINK and RENAME
The LINK and RENAME operations use both the current and saved
filehandles. If the security policy of the saved filehandle rejects
the security flavor used in the COMPOUND request's credentials, the
server MAY return NFS4ERR_WRONGSEC from LINK or RENAME. When the
server does so, if there is no intersection between the security
policies of saved and current filehandles, this implies that it will
be impossible for the client to perform the intended LINK or RENAME
operation.
For example, suppose the client sends this COMPOUND request:
SEQUENCE, PUTFH bFH, SAVEFH, PUTFH aFH, RENAME "c" "d", where
filehandles bFH and aFH refer to different directories. Suppose no
common security tuple exists between the security policies of aFH and
bFH. If the client sends the request using credentials acceptable to
bFH's security policy but not aFH's policy, then the PUTFH aFH
operation will fail with NFS4ERR_WRONGSEC. After a SECINFO_NO_NAME
request, the client sends SEQUENCE, PUTFH bFH, SAVEFH, PUTFH aFH,
RENAME "c" "d", using credentials acceptable to aFH's security policy
but not bFH's policy. The server returns NFS4ERR_WRONGSEC on the
RENAME operation.
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To prevent a client from an endless sequence of a request containing
LINK or RENAME, followed by a request containing SECINFO_NO_NAME or
SECINFO, the server MUST detect when the security policies of the
current and saved filehandles have no mutually acceptable security
tuple, and MUST NOT return NFS4ERR_WRONGSEC from LINK or RENAME in
that situation. Instead, the server MUST do one of two things:
* The server can return NFS4ERR_XDEV.
* The server can allow the security policy of the current filehandle
to override that of the saved filehandle, and so return NFS4_OK.
7. Session
NFSv4.1 clients and servers MUST support and MUST use the session
feature as described in this section.
7.1. Motivation and Overview
Previous versions and minor versions of NFS have suffered from the
following:
* Lack of support for Exactly Once Semantics (EOS). This includes
lack of support for EOS through server failure and recovery.
* Limited callback support, including no support for sending
callbacks through firewalls, and races between replies to normal
requests and callbacks.
* Limited trunking over multiple network paths.
* Requiring machine credentials for fully secure operation.
Through the introduction of a session, NFSv4.1 addresses the above
shortfalls with practical solutions:
* EOS is enabled by a reply cache with a bounded size, making it
feasible to keep the cache in persistent storage and enable EOS
through server failure and recovery. One reason than previous
revisions of NFS did not support EOS was because some EOS
approaches often limited parallelism. As will be explained in
Section 7.6, NFSv4.1 supports EOS without unduly limiting
parallelism.
* The NFSv4.1 client (defined in Section 2.5) creates transport
connections and provides them to the server to use for sending
callback requests, thus solving the firewall issue
(Section 25.34). Races between responses from client requests and
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callbacks caused by the requests are detected via the session's
sequencing properties that are a consequence of EOS
(Section 7.6.3).
* The NFSv4.1 client can associate an arbitrary number of
connections with the session, and thus provide trunking
(Section 7.5).
* The NFSv4.1 client and server produce a session key independent of
client and server machine credentials which can be used to compute
a digest for protecting critical session management operations
(Section 7.8.3).
* The NFSv4.1 client can also create secure RPCSEC_GSS contexts for
use by the session's backchannel that do not require the server to
authenticate to a client machine principal (Section 7.8.2).
A session is a dynamically created, long-lived server object created
by a client and used over time from one or more transport
connections. Its function is to maintain the server's state relative
to the connection(s) belonging to a client instance. This state is
entirely independent of the connection itself, and indeed the state
exists whether or not the connection exists. A client may have one
or more sessions associated with it so that client-associated state
may be accessed using any of the sessions associated with that
client's client ID, when connections are associated with those
sessions. When no connections are associated with any of a client
ID's sessions for an extended time, such objects as locks, opens,
delegations, layouts, etc. are subject to expiration. The session
serves as an object representing a means of access by a client to the
associated client state on the server, independent of the physical
means of access to that state.
A single client may create multiple sessions. A single session MUST
NOT serve multiple clients.
7.2. NFSv4 Integration
Sessions are part of NFSv4.1 and not NFSv4.0. Normally, a major
infrastructure change such as sessions would require a new major
version number to an Open Network Computing (ONC) RPC program like
NFS. However, because NFSv4 encapsulates its functionality in a
single procedure, COMPOUND, and because COMPOUND can support an
arbitrary number of operations, sessions have been added to NFSv4.1
with little difficulty. COMPOUND includes a minor version number
field, and for NFSv4.1 this minor version is set to 1. When the
NFSv4 server processes a COMPOUND with the minor version set to 1, it
expects a different set of operations than it does for NFSv4.0.
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NFSv4.1 defines the SEQUENCE operation, which is required for every
COMPOUND that operates over an established session, with the
exception of some session administration operations, such as
DESTROY_SESSION (Section 25.37).
7.2.1. SEQUENCE and CB_SEQUENCE
In NFSv4.1, when the SEQUENCE operation is present, it MUST be the
first operation in the COMPOUND procedure. The primary purpose of
SEQUENCE is to carry the session identifier. The session identifier
associates all other operations in the COMPOUND procedure with a
particular session. SEQUENCE also contains required information for
maintaining EOS (See Section 7.6). Session-enabled NFSv4.1 COMPOUND
requests thus have the form:
+-----+--------------+-----------+------------+-----------+----
| tag | minorversion | numops |SEQUENCE op | op + args | ...
| | (== 1) | (limited) | + args | |
+-----+--------------+-----------+------------+-----------+----
and the replies have the form:
+------------+-----+--------+-------------------------------+--//
|last status | tag | numres |status + SEQUENCE op + results | //
+------------+-----+--------+-------------------------------+--//
//-----------------------+----
// status + op + results | ...
//-----------------------+----
A CB_COMPOUND procedure request and reply has a similar form to
COMPOUND, but instead of a SEQUENCE operation, there is a CB_SEQUENCE
operation. CB_COMPOUND also has an additional field called
"callback_ident", which is superfluous in NFSv4.1 and MUST be ignored
by the client. CB_SEQUENCE has the same information as SEQUENCE, and
also includes other information needed to resolve callback races
(Section 7.6.3).
7.2.2. Client ID and Session Association
Each client ID (Section 5.5) can have zero or more active sessions.
A client ID and associated session are required to perform file
access in NFSv4.1. Each time a session is used (whether by a client
sending a request to the server or the client replying to a callback
request from the server), the state leased to its associated client
ID is automatically renewed.
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State (which can consist of share reservations, locks, delegations,
and layouts (Section 3)) is tied to the client ID. Client state is
not tied to any individual session. Successive state changing
operations from a given state owner MAY go over different sessions,
provided the session is associated with the same client ID. A
callback MAY arrive over a different session than that of the request
that originally acquired the state pertaining to the callback. For
example, if session A is used to acquire a delegation, a request to
recall the delegation MAY arrive over session B if both sessions are
associated with the same client ID. Sections 7.8.1 and 7.8.2 discuss
the security considerations around callbacks.
7.3. Channels
A channel is not a connection. A channel represents a single
direction in which ONC RPC requests are sent as part of a session..
Each session has one or two channels: the fore channel and the
backchannel. Because there are at most two channels per session, and
because each channel has a distinct purpose, channels are not
assigned identifiers.
The fore channel is used for ordinary requests from the client to the
server, and carries COMPOUND requests and responses. A session
always has a fore channel.
The backchannel is used for callback requests from server to client,
and carries CB_COMPOUND requests and responses. Whether or not there
is a backchannel is decided by the client; however, many features of
NFSv4.1 require a backchannel. NFSv4.1 servers MUST support
backchannels.
Each session has resources for each channel, including separate reply
caches (see Section 7.6.1). Note that even the backchannel requires
a reply cache (or, at least, a slot table in order to detect
retries). This is because it is necessary to avoid re-execution of
modifying requests, even if they are idempotent.
7.3.1. Association of Connections, Channels, and Sessions
Each channel is associated with zero or more transport connections
(whether of the same transport protocol or different transport
protocols). A connection can be associated with one channel or both
channels of a session; the client and server negotiate whether a
connection will carry traffic for one channel or both channels via
the CREATE_SESSION (Section 25.36) and the BIND_CONN_TO_SESSION
(Section 25.34) operations. When a session is created via
CREATE_SESSION, the connection that transported the CREATE_SESSION
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request is automatically associated with the fore channel, and
optionally the backchannel. If the client specifies no state
protection (Section 25.35) when the session is created, then when
SEQUENCE is transmitted on a different connection, the connection is
automatically associated with the fore channel of the session
specified in the SEQUENCE operation.
A connection's association with a session is not exclusive. A
connection associated with the channel(s) of one session may be
simultaneously associated with the channel(s) of other sessions
including sessions associated with other client IDs.
It is permissible for connections of multiple transport types to be
associated with the same channel. For example, both TCP and RDMA
connections can be associated with the fore channel. In the event an
RDMA and non-RDMA connection are associated with the same channel, it
is desirable for the maximum number slots to be at least one more
than the total number of RDMA credits (Section 7.6.1). This way, if
all RDMA credits are used, the non-RDMA connection can have at least
one outstanding request. If a server supports multiple transport
types, it MUST allow a client to associate connections from each
transport to a channel.
It is permissible for a connection of one type of transport to be
associated with the fore channel, and a connection of a different
type to be associated with the backchannel.
7.4. Server Scope
Servers each specify a server scope value in the form of an opaque
string eir_server_scope returned as part of the results of an
EXCHANGE_ID operation. The purpose of the server scope is to allow a
group of servers to indicate to clients that a set of servers sharing
the same server scope value has arranged to use distinct values of
opaque identifiers so that the two servers never assign the same
value to two distinct objects. Thus, the identifiers generated by
two servers within that set can be assumed compatible so that, in
certain important cases, identifiers generated by one server in that
set may be presented to another server of the same scope.
The use of such compatible values does not imply that a value
generated by one server will always be accepted by another. In most
cases, it will not. However, a server will not inadvertently accept
a value generated by another server. When it does accept it, it will
be because it is recognized as valid and carrying the same meaning as
on another server of the same scope.
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When servers are of the same server scope, this compatibility of
values applies to the following identifiers:
* Filehandle values. A filehandle value accepted by two servers of
the same server scope denotes the same object. A WRITE operation
sent to one server is reflected immediately in a READ sent to the
other.
* Server owner values. When the server scope values are the same,
server owner value may be validly compared. In cases where the
server scope values are different, server owner values are treated
as different even if they contain identical strings of bytes.
The coordination among servers required to provide such compatibility
can be quite minimal, and limited to a simple partition of the ID
space. The recognition of common values requires additional
implementation, but this can be tailored to the specific situations
in which that recognition is desired.
Clients will have occasion to compare the server scope values of
multiple servers under a number of circumstances, each of which will
be discussed under the appropriate functional section:
* When server owner values received in response to EXCHANGE_ID
operations sent to multiple network addresses are compared for the
purpose of determining the validity of various forms of trunking,
as described in Section 17.5.2.
* When network or server reconfiguration causes the same network
address to possibly be directed to different servers, with the
necessity for the client to determine when lock reclaim should be
attempted, as described in Section 13.4.2.1.
When two replies from EXCHANGE_ID, each from two different server
network addresses, have the same server scope, there are a number of
ways a client can validate that the common server scope is due to two
servers cooperating in a group.
* If both EXCHANGE_ID requests were sent with RPCSEC_GSS ([RFC2203],
[RFC5403], [RFC7861]) authentication and the server principal is
the same for both targets, the equality of server scope is
validated. It is RECOMMENDED that two servers intending to share
the same server scope and server_owner major_id also share the
same principal name. In some cases, this simplifies the client's
task of validating server scope.
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* The client may accept the appearance of the second server in the
fs_locations or fs_locations_info attribute for a relevant file
system. For example, if there is a migration event for a
particular file system or there are locks to be reclaimed on a
particular file system, the attributes for that particular file
system may be used. The client sends the GETATTR request to the
first server for the fs_locations or fs_locations_info attribute
with RPCSEC_GSS authentication. It may need to do this in advance
of the need to verify the common server scope. If the client
successfully authenticates the reply to GETATTR, and the GETATTR
request and reply containing the fs_locations or fs_locations_info
attribute refers to the second server, then the equality of server
scope is supported. A client may choose to limit the use of this
form of support to information relevant to the specific file
system involved (e.g. a file system being migrated).
7.5. Trunking
Trunking is the use of multiple connections between a client and
server in order to increase the speed of data transfer. NFSv4.1
supports two types of trunking: session trunking and client ID
trunking.
In the context of a single server network address, it can be assumed
that all connections are accessing the same server, and NFSv4.1
servers MUST support both forms of trunking. When multiple
connections use a set of network addresses to access the same server,
the server MUST support both forms of trunking. NFSv4.1 servers in a
clustered configuration MAY allow network addresses for different
servers to use client ID trunking.
Clients may use either form of trunking as long as they do not, when
trunking between different server network addresses, violate the
servers' mandates as to the kinds of trunking to be allowed (See
below). With regard to callback channels, the client MUST allow the
server to choose among all callback channels valid for a given client
ID and MUST support trunking when the connections supporting the
backchannel allow session or client ID trunking to be used for
callbacks.
Session trunking is essentially the association of multiple
connections, each with potentially different target and/or source
network addresses, to the same session. When the target network
addresses (server addresses) of the two connections are the same, the
server MUST support such session trunking. When the target network
addresses are different, the server MAY indicate such support using
the data returned by the EXCHANGE_ID operation (See below).
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Client ID trunking is the association of multiple sessions to the
same client ID. Servers MUST support client ID trunking for two
target network addresses whenever they allow session trunking for
those same two network addresses. In addition, a server MAY, by
presenting the same major server owner ID (Section 5.6) and server
scope (Section 7.4), allow an additional case of client ID trunking.
When two servers return the same major server owner and server scope,
it means that the two servers are cooperating on locking state
management, which is a prerequisite for client ID trunking.
Distinguishing when the client is allowed to use session and client
ID trunking requires understanding how the results of the EXCHANGE_ID
(Section 25.35) operation identify a server. Suppose a client sends
EXCHANGE_IDs over two different connections, each with a possibly
different target network address, but each EXCHANGE_ID operation has
the same value in the eia_clientowner field. If the same NFSv4.1
server is listening over each connection, then each EXCHANGE_ID
result MUST return the same values of eir_clientid,
eir_server_owner.so_major_id, and eir_server_scope. The client can
then treat each connection as referring to the same server (subject
to verification; see Section 7.5.1 below), and it can use each
connection to trunk requests and replies. The client's choice is
whether session trunking or client ID trunking applies.
Session Trunking. If the eia_clientowner argument is the same in two
different EXCHANGE_ID requests, and the eir_clientid,
eir_server_owner.so_major_id, eir_server_owner.so_minor_id, and
eir_server_scope results match in both EXCHANGE_ID results, then
the client is permitted to perform session trunking. If the
client has no session mapping to the tuple of eir_clientid,
eir_server_owner.so_major_id, eir_server_scope, and
eir_server_owner.so_minor_id, then it creates the session via a
CREATE_SESSION operation over one of the connections, which
associates the connection to the session. If there is a session
for the tuple, the client can send BIND_CONN_TO_SESSION to
associate the connection to the session.
Of course, if the client does not desire to use session trunking,
it is not required to do so. It can invoke CREATE_SESSION on the
connection. This will result in client ID trunking as described
below. It can also decide to drop the connection if it does not
choose to use trunking.
Client ID Trunking. If the eia_clientowner argument is the same in
two different EXCHANGE_ID requests, and the eir_clientid,
eir_server_owner.so_major_id, and eir_server_scope results match
in both EXCHANGE_ID results, then the client is permitted to
perform client ID trunking (regardless of whether the
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eir_server_owner.so_minor_id results match). The client can
associate each connection with different sessions, where each
session is associated with the same server.
The client completes the act of client ID trunking by invoking
CREATE_SESSION on each connection, using the same client ID that
was returned in eir_clientid. These invocations create two
sessions and also associate each connection with its respective
session. The client is free to decline to use client ID trunking
by simply dropping the connection at this point.
When doing client ID trunking, locking state is shared across
sessions associated with that same client ID. This requires the
server to coordinate state across sessions and the client to be
able to associate the same locking state with multiple sessions.
It is always possible that, as a result of various sorts of
reconfiguration events, eir_server_scope and eir_server_owner values
may be different on subsequent EXCHANGE_ID requests made to the same
network address.
In most cases, such reconfiguration events will be disruptive and
indicate that an IP address formerly connected to one server is now
connected to an entirely different one.
Some guidelines on client handling of such situations follow:
* When eir_server_scope changes, the client has no assurance that
any IDs that it obtained previously (e.g., filehandles) can be
validly used on the new server, and, even if the new server
accepts them, there is no assurance that this is not due to
accident. Thus, it is best to treat all such state as lost or
stale, although a client may assume that the probability of
inadvertent acceptance is low and treat this situation as within
the next case.
* When eir_server_scope remains the same and
eir_server_owner.so_major_id changes, the client can use the
filehandles it has, consider its locking state lost, and attempt
to reclaim or otherwise re-obtain its locks. It might find that
its filehandle is now stale. However, if NFS4ERR_STALE is not
returned, it can proceed to reclaim or otherwise re-obtain its
open locking state.
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* When eir_server_scope and eir_server_owner.so_major_id remain the
same, the client has to use the now-current values of
eir_server_owner.so_minor_id in deciding on appropriate forms of
trunking. This may result in connections being dropped or new
sessions being created.
7.5.1. Verifying Claims of Matching Server Identity
When the server responds using two different connections that claim
matching or partially matching eir_server_owner, eir_server_scope,
and eir_clientid values, the client does not have to trust the
servers' claims. The client may verify these claims before trunking
traffic in the following ways:
* For session trunking, clients SHOULD reliably verify if
connections between different network paths are in fact associated
with the same NFSv4.1 server and usable on the same session, and
servers MUST allow clients to perform reliable verification. When
a client ID is created, the client SHOULD, unless client host
authentication is in effect, specify that BIND_CONN_TO_SESSION is
to be verified according to the SP4_SSV or SP4_MACH_CRED
(Section 25.35) state protection options. For SP4_SSV, reliable
verification depends on a shared secret (the SSV) that is
established via the SET_SSV (see Section 25.47) operation.
When a new connection is associated with the session (via the
BIND_CONN_TO_SESSION operation, see Section 25.34), if the client
specified SP4_SSV state protection for the BIND_CONN_TO_SESSION
operation, the client MUST send the BIND_CONN_TO_SESSION with
RPCSEC_GSS protection, using integrity or privacy, and an
RPCSEC_GSS handle created with the GSS SSV mechanism (See
Section 7.9).
If the client mistakenly tries to associate a connection to a
session of a wrong server, the server will either reject the
attempt because it is not aware of the session identifier of the
BIND_CONN_TO_SESSION arguments, or it will reject the attempt
because the RPCSEC_GSS authentication fails. Even if the server
mistakenly or maliciously accepts the connection association
attempt, the RPCSEC_GSS verifier it computes in the response will
not be verified by the client, so the client will know it cannot
use the connection for trunking the specified session.
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If the client specified SP4_MACH_CRED state protection, the
BIND_CONN_TO_SESSION operation will use RPCSEC_GSS integrity or
privacy, using the same credential that was used when the client
ID was created. Mutual authentication via RPCSEC_GSS assures the
client that the connection is associated with the correct session
of the correct server.
* For client ID trunking, the client has at least two options for
verifying that the same client ID obtained from two different
EXCHANGE_ID operations came from the same server. The first
option is to use RPCSEC_GSS authentication when sending each
EXCHANGE_ID operation. Each time an EXCHANGE_ID is sent with
RPCSEC_GSS authentication, the client notes the principal name of
the GSS target. If the EXCHANGE_ID results indicate that client
ID trunking is possible, and the GSS targets' principal names are
the same, the servers are the same and client ID trunking is
allowed.
The second option for verification is to use SP4_SSV protection.
When the client sends EXCHANGE_ID, it specifies SP4_SSV
protection. The first EXCHANGE_ID the client sends always has to
be confirmed by a CREATE_SESSION call. The client then sends
SET_SSV. Later, the client sends EXCHANGE_ID to a second
destination network address different from the one the first
EXCHANGE_ID was sent to. The client checks that each EXCHANGE_ID
reply has the same eir_clientid, eir_server_owner.so_major_id, and
eir_server_scope. If so, the client verifies the claim by sending
a CREATE_SESSION operation to the second destination address,
protected with RPCSEC_GSS integrity using an RPCSEC_GSS handle
returned by the second EXCHANGE_ID. If the server accepts the
CREATE_SESSION request, and if the client verifies the RPCSEC_GSS
verifier and integrity codes, then the client has proof the second
server knows the SSV, and thus the two servers are cooperating for
the purposes of specifying server scope and client ID trunking.
7.6. Exactly Once Semantics
[Author Aside]: This section, including some subsections, has been
substantially modified from the corresponding section appearing in
previous specifications [RFC5661] [RFC8881] and earlier drafts of
this document. Change has been driven primarily by the incorrect use
of RFC2119-defined keywords, most importantly in the case in which
RPC requests need to be aborted, leading to some related changes to
clarify the appropriate level of checking for the possibility of
false retry. As part of this revised description, it is explained
that, given the possibility of requests being aborted, the term
"Exactly-once semantics" describes an aspiration and that what is
really provided would better be called "at-most-once semantics.
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Also, the description of retry has been revised to properly use
RFC2119 keywords. For more detailed information regarding changes
which have been made, see Appendix D.2.1.
Via the session, NFSv4.1 offers what is termed "exactly once
semantics" (EOS) for requests sent over a channel. EOS is supported
on both the fore channel and backchannel.
Although this term is well-established and will not be changed, it
should be noted that what is actually provided is at-most-once
semantics to accommodate the possibility that the client will need to
abort RPC requests, remaining unsure about whether the requested
actions have been performed one time or not at all.
Each COMPOUND or CB_COMPOUND request that is sent with a leading
SEQUENCE or CB_SEQUENCE operation needs to be executed by the
receiver at most once. This requirement holds regardless of whether
the request is sent with reply caching specified (See
Section 7.6.1.3). The requirement also holds in the case in which
NFSv4.1 is a pNFS data access protocol and the requester is sending
the request over a session created between a pNFS data client and
pNFS data server. To help understand the need for this requirement,
we divide the requests sent to be executed into three categories:
* Non-idempotent requests.
* Idempotent modifying requests.
* Idempotent non-modifying requests.
An example of a non-idempotent request is RENAME. Obviously, if a
replier executes the same RENAME request twice, and the first
execution succeeds, the re-execution will fail. If the replier
returns the result from the re-execution, this result is incorrect.
For this reason, EOS is required for non-idempotent requests and it
is supplemented by returning the original response to the requester.
An example of an idempotent modifying request is a COMPOUND request
containing a WRITE operation. Repeated execution of the same WRITE
has the same effect as execution of that WRITE a single time.
Nevertheless, enforcing EOS for WRITEs and other idempotent modifying
requests is necessary to avoid data corruption, which could result
from executing the same write request multiple times including some
executions that occur after the completion of the first is noted by
the requester.
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Suppose a client sends WRITE A to a noncompliant server that does not
enforce EOS, and receives no response, perhaps due to a network
partition. The client reconnects to the server and re-sends WRITE A.
Now, the server has outstanding two instances of A. The server can
be in a situation in which it executes and replies to the retry of A,
while the first A is still waiting in the server's internal I/O
system for some resource. Upon receiving the reply to the second
attempt of WRITE A, the client believes its WRITE is done so it is
free to send WRITE B, which overlaps the byte-range of A. When the
original A is dispatched from the server's I/O system and executed
(thus, the second time A will have been written), then what has been
written by B can be overwritten and thus corrupted.
An example of an idempotent non-modifying request is a COMPOUND
containing SEQUENCE, PUTFH, READLINK, and nothing else. The re-
execution of such a request will not cause data corruption or produce
an incorrect result. Nonetheless, the session feature's design
provides that the replier MUST enforce EOS for all requests, whether
or not they are idempotent or modifying.
Note that fully complete EOS is not possible unless the server
persists the reply cache in stable storage, and unless the server is
somehow implemented to never require a restart (indeed, if such a
server exists, the distinction between a reply cache kept in stable
storage versus one that is not is one without meaning). See
Section 8 for a discussion of persistence in the reply cache.
Regardless, even if the server does not persist the reply cache, EOS
improves robustness and correctness relative to previous versions of
NFS because the earlier duplicate request/reply caches were based on
the ONC RPC transaction identifier (XID). Section 7.6.1 explains the
shortcomings of the XID as a basis for a reply cache and describes
how NFSv4.1 sessions improve upon the XID.
7.6.1. Slot Identifiers and Reply Cache
The RPC layer provides a transaction ID (XID), which, while required
to be unique, is not convenient for tracking requests for two
reasons. First, the XID is only meaningful to the requester; it
cannot be interpreted by the replier except to test for equality with
previously sent requests. When consulting an RPC-based duplicate
request cache, the opaqueness of the XID requires a computationally
expensive look up (often via a hash that includes XID and source
address). NFSv4.1 requests include a non-opaque slot ID, which can
be used as an index into a slot table, which is far more efficient.
Second, because RPC requests can be executed by the replier in any
order, there is no bound on the number of requests that may be
outstanding at any time. To achieve perfect EOS, using ONC RPC would
require storing all replies in the reply cache. XIDs are 32 bits;
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storing over four billion (2^32) replies in the reply cache is not
practical. In practice, previous versions of NFS have chosen to
store a fixed number of replies in the cache, and to use a least
recently used (LRU) approach to replacing cache entries with new
entries when the cache is full. In NFSv4.1, the number of
outstanding requests is bounded by the size of the slot table, and a
sequence ID per slot is used to tell the replier when it is safe to
delete a cached reply.
In the NFSv4.1 reply cache, when the requester sends a new request,
it selects a slot ID in the range 0..N, where N is the replier's
current maximum slot ID granted to the requester on the session over
which the request is to be sent. The value of N starts out as equal
to ca_maxrequests - 1 (Section 25.36), but can be adjusted by the
response to SEQUENCE or CB_SEQUENCE as described later in this
section. The slot ID must be unused by any of the requests that the
requester already has active on the session. "Unused" here means the
requester has no outstanding request for that slot ID.
A slot contains a sequence ID and the cached reply corresponding to
the request sent with that sequence ID. The sequence ID is a 32-bit
unsigned value and is therefore in the range 0..0xFFFFFFFF (2^32 -
1). The first time a slot is used, the requester MUST specify a
sequence ID of one (Section 25.36). Each time a slot is reused, the
request MUST specify a sequence ID that is one greater than that of
the previous request on the slot. If the previous sequence ID was
0xFFFFFFFF, then the next request for the slot MUST have the sequence
ID set to zero (i.e., (2^32 - 1) + 1 mod 2^32).
The sequence ID accompanies the slot ID in each request. It is for
the critical check at the replier: it used to efficiently determine
whether a request using a certain slot ID is a retransmit or a new,
never-before-seen request. It is not feasible for the requester to
assert that it is retransmitting to implement this, because for any
given request the requester cannot know whether the replier has seen
it unless the replier actually replies. Of course, if the requester
has seen the reply, the requester would not retransmit.
The replier compares each received request's sequence ID with the
last one previously received for that slot ID, to see if the new
request is:
* A new request, in which the sequence ID is one greater than that
previously seen in the slot (accounting for sequence wraparound).
The replier proceeds to execute the new request, and the replier
MUST increase the slot's sequence ID by one.
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* A retransmitted request, in which the sequence ID is equal to that
currently recorded in the slot. If the original request has
executed to completion, the replier returns the cached reply. See
Section 7.6.2 for direction on how the replier deals with retries
of requests that are still in progress.
* A misordered retry, in which the sequence ID is less than
(accounting for sequence wraparound) that previously seen in the
slot. The replier MUST return NFS4ERR_SEQ_MISORDERED (as the
result from SEQUENCE or CB_SEQUENCE).
* A misordered new request, in which the sequence ID is two or more
than (accounting for sequence wraparound) that previously seen in
the slot. Note that because the sequence ID MUST wrap around to
zero once it reaches 0xFFFFFFFF, a misordered new request and a
misordered retry cannot be distinguished. Thus, the replier MUST
return NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
CB_SEQUENCE).
Unlike the XID, the slot ID is always within a specific range; this
has two implications. The first implication is that for a given
session, the replier need only cache the results of a limited number
of COMPOUND requests. The second implication derives from the first,
which is that unlike XID-indexed reply caches (also known as
duplicate request caches - DRCs), the slot ID-based reply cache
cannot be overflowed. Through use of the sequence ID to identify
retransmitted requests, the replier does not need to actually cache
the request itself, reducing the storage requirements of the reply
cache further. These facilities make it practical to maintain all
the required entries for an effective reply cache.
As a result, the slot ID, sequence ID, and session ID take over the
traditional role of the XID and source network address in the
replier's reply cache implementation. This approach is considerably
more portable and completely robust -- it is not subject to the
reassignment of ports as clients reconnect over IP networks. In
addition, the RPC XID is not used in the reply cache, enhancing
robustness of the cache in the face of any rapid reuse of XIDs by the
requester. While the replier does not care about the XID for the
purposes of reply cache management (but the replier MUST return the
same XID that was in the request), nonetheless there are
considerations for the XID in NFSv4.1 that are the same as all other
previous versions of NFS. The RPC XID remains in each message and
needs to be formulated in NFSv4.1 requests as in any other ONC RPC
request. The reasons include:
* The RPC layer retains its existing semantics and implementation.
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* The requester and replier must be able to interoperate at the RPC
layer, prior to the NFSv4.1 decoding of the SEQUENCE or
CB_SEQUENCE operation.
* If an operation is being used that does not start with SEQUENCE or
CB_SEQUENCE (e.g., BIND_CONN_TO_SESSION), then the RPC XID is
needed for correct operation to match the reply to the request.
* The SEQUENCE or CB_SEQUENCE operation may generate an error. If
so, the embedded slot ID, sequence ID, and session ID (if present)
in the request will not be in the reply, and the requester has
only the XID to match the reply to the request.
Given that well-formulated XIDs continue to be required, this raises
the question: why do SEQUENCE and CB_SEQUENCE replies have a session
ID, slot ID, and sequence ID? Having the session ID in the reply
means that the requester does not have to use the XID to look up the
session ID, which would be necessary if the connection were
associated with multiple sessions. Having the slot ID and sequence
ID in the reply means that the requester does not have to use the XID
to look up the slot ID and sequence ID. Furthermore, since the XID
is only 32 bits, it is too small to guarantee the re-association of a
reply with its request (See [rpc_xid_issues]); having session ID,
slot ID, and sequence ID in the reply allows the client to validate
that the reply in fact belongs to the matched request.
The SEQUENCE (and CB_SEQUENCE) operation also carries a
"highest_slotid" value, which carries additional requester slot usage
information. The requester MUST always indicate the slot ID
representing the outstanding request with the highest-numbered slot
value. The requester should in all cases provide the most
conservative value possible, although it can be increased somewhat
above the actual instantaneous usage to maintain some minimum or
optimal level. This provides a way for the requester to yield unused
request slots back to the replier, which in turn can use the
information to reallocate resources.
The replier responds with both a new target highest_slotid and an
enforced highest_slotid, described as follows:
* The target highest_slotid is an indication to the requester of the
highest_slotid the replier wishes the requester to be using. This
permits the replier to withdraw (or add) resources from a
requester that has been found to not be using them, in order to
more fairly share resources among a varying level of demand from
other requesters. The requester must always comply with the
replier's value updates, since they indicate newly established
hard limits on the requester's access to session resources.
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However, because of request pipelining, the requester might have
active requests in flight reflecting prior values; therefore, the
replier cannot immediately require the requester to comply.
* The enforced highest_slotid indicates the highest slot ID the
requester is permitted to use on a subsequent SEQUENCE or
CB_SEQUENCE operation. The replier's enforced highest_slotid
SHOULD be no less than the highest_slotid the requester indicated
in the SEQUENCE or CB_SEQUENCE arguments.
A requester can be intransigent with respect to lowering its
highest_slotid argument to a Sequence operation, i.e. the
requester continues to ignore the target highest_slotid in the
response to a Sequence operation, and continues to set its
highest_slotid argument to be higher than the target
highest_slotid. This can be considered particularly egregious
behavior when the replier knows there are no outstanding requests
with slot IDs higher than its target highest_slotid. When faced
with such intransigence, the replier is free to take more forceful
action, and MAY reply with a new enforced highest_slotid that is
less than its previous enforced highest_slotid. Thereafter, if
the requester continues to send requests with a highest_slotid
that is greater than the replier's new enforced highest_slotid,
the server MAY return NFS4ERR_BAD_HIGH_SLOT, unless the slot ID in
the request is greater than the new enforced highest_slotid and
the request is a retry.
The replier should retain the slots it wants to retire until the
requester sends a request with a highest_slotid less than or equal
to the replier's new enforced highest_slotid.
The requester can also be intransigent with respect to sending
non-retry requests that have a slot ID that exceeds the replier's
highest_slotid. Once the replier has forcibly lowered the
enforced highest_slotid, the requester is only allowed to send
retries on slots that exceed the replier's highest_slotid. If a
request is received with a slot ID that is higher than the new
enforced highest_slotid, and the sequence ID is one higher than
what is in the slot's reply cache, then the server can both retire
the slot and return NFS4ERR_BADSLOT (however, the server MUST NOT
do one and not the other). The reason it is safe to retire the
slot is because by using the next sequence ID, the requester is
indicating it has received the previous reply for the slot.
* The requester is better off using the lowest available slot when
sending a new request. This way, the replier may be able to
retire slot entries faster. However, where the replier is
actively adjusting its granted highest_slotid, it will not be able
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to use only the receipt of the slot ID and highest_slotid in the
request. Neither the slot ID nor the highest_slotid used in a
request may reflect the replier's current idea of the requester's
session limit because the request may have been sent from the
requester before the update was received. Therefore, in the
downward adjustment case, the replier may have to retain a number
of reply cache entries at least as large as the old value of
maximum requests outstanding, until it can infer that the
requester has seen a reply containing the new granted
highest_slotid. The replier can infer that the requester has seen
such a reply when it receives a new request with the same slot ID
as the request replied to and the next higher sequence ID.
7.6.1.1. Caching of SEQUENCE and CB_SEQUENCE Replies
When a SEQUENCE or CB_SEQUENCE operation is successfully executed,
its reply MUST always be cached. Specifically, session ID, sequence
ID, and slot ID MUST be cached in the reply cache. The reply from
SEQUENCE also includes the highest slot ID, target highest slot ID,
and status flags. Instead of caching these values, the server MAY
re-compute the values from the current state of the fore channel,
session, and/or client ID as appropriate. Similarly, the reply from
CB_SEQUENCE includes a highest slot ID and target highest slot ID.
The client MAY re-compute the values from the current state of the
session as appropriate.
Regardless of whether or not a replier is re-computing highest slot
ID, target slot ID, and status on replies to retries, the requester
cannot assume that the values are being re-computed whenever it
receives a reply after a retry is sent, since it has no way of
knowing whether the reply it has received was sent by the replier in
response to the retry or is a delayed response to the original
request. Therefore, it may be the case that highest slot ID, target
slot ID, or status bits may reflect the state of affairs when the
request was first executed. Although acting based on such delayed
information is valid, it may cause the receiver of the reply to do
unneeded work. Requesters MAY choose to send additional requests to
get the current state of affairs or use the state of affairs reported
by subsequent requests, in preference to acting immediately on data
that might be out of date.
7.6.1.2. Errors from SEQUENCE and CB_SEQUENCE
Any time SEQUENCE or CB_SEQUENCE returns an error, the sequence ID of
the slot MUST NOT change. The replier MUST NOT modify the reply
cache entry for the slot whenever an error is returned from SEQUENCE
or CB_SEQUENCE.
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7.6.1.3. Optional Reply Caching
On a per-request basis, the requester can choose to direct the
replier to cache the reply to all operations after the first
operation (SEQUENCE or CB_SEQUENCE) via the sa_cachethis or
csa_cachethis fields of the arguments to SEQUENCE or CB_SEQUENCE.
The reason it needs to direct the replier to cache the entire reply
is that the request contains a non-idempotent operations [Chet].
Caching the reply may offer little benefit. If the reply is too
large (see Section 7.6.4), it may not be cacheable anyway. Even if
the reply to an idempotent request is small enough to cache,
unnecessarily caching the reply slows down the server and increases
RPC latency.
Whether or not the requester requests the reply to be cached has no
effect on the slot processing. If the result of SEQUENCE or
CB_SEQUENCE is NFS4_OK, then the slot's sequence ID MUST be
incremented by one. If a requester does not direct the replier to
cache the reply, the replier MUST do one of following:
* The replier can cache the entire original reply. Even though
sa_cachethis or csa_cachethis is FALSE, the replier is always free
to cache. It may choose this approach in order to simplify
implementation.
* The replier enters into its reply cache a reply consisting of the
original results to the SEQUENCE or CB_SEQUENCE operation, and
with the next operation in COMPOUND or CB_COMPOUND having the
error NFS4ERR_RETRY_UNCACHED_REP. Thus, if the requester later
retries the request, it will get NFS4ERR_RETRY_UNCACHED_REP. If a
replier receives a retried Sequence operation where the reply to
the COMPOUND or CB_COMPOUND was not cached, then the replier,
- MAY return NFS4ERR_RETRY_UNCACHED_REP in reply to a Sequence
operation if the Sequence operation is not the first operation
(granted, a requester that does so is in violation of the
NFSv4.1 protocol).
- MUST NOT return NFS4ERR_RETRY_UNCACHED_REP in reply to a
Sequence operation if the Sequence operation is the first
operation.
* If the second operation is an illegal operation, or an operation
that was legal in a previous minor version of NFSv4 and MUST NOT
be supported in the current minor version (e.g., SETCLIENTID), the
replier MUST NOT ever return NFS4ERR_RETRY_UNCACHED_REP. Instead
the replier MUST return NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR or
NFS4ERR_NOTSUPP as appropriate.
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* If the second operation can result in another error status, the
replier MAY return a status other than NFS4ERR_RETRY_UNCACHED_REP,
provided the operation is not executed in such a way that the
state of the replier is changed. Examples of such error statuses
include NFS4ERR_SEQUENCE_POS,NFS4ERR_REQ_TOO_BIG, and
NFS4ERR_NOTSUPP returned for an operation that is legal but not
REQUIRED in the current minor version and but is not supported by
the replier or its file system.
The discussion above assumes that the retried request matches the
original one. Section 7.6.1.3.1 discusses what the replier might do,
and MUST do when it is aware that original and retried requests do
not match. Since the replier might only cache a small amount of the
information that would be required to determine whether this is a
case of a false retry, the replier may send to the client any of the
following responses:
* The cached reply to the original request. This is sent if users
of the original request and retry match, and there is no evidence
that there is in fact a mismatch between the original request and
retry.
This can occur if the server caches the entire request and
compares it to the retry but also in situations in which only a
limited comparison or no comparison is possible. For details see
Section 7.6.1.3.1
* A reply that consists only of the Sequence operation with the
error NFS4ERR_SEQ_FALSE_RETRY.
This is sent if the users of the original request and putative
retry do not match, or, if they do, the server has sufficient data
to indicate that the supposed retry does not match the original
request.
* A reply consisting of the response to Sequence with the status
NFS4_OK, together with the second operation as it appeared in the
retried request with an error of NFS4ERR_RETRY_UNCACHED_REP or
other error as described above.
* A reply that consists of the response to Sequence with the status
NFS4_OK, together with the second operation as it appeared in the
original request with an error of NFS4ERR_RETRY_UNCACHED_REP or
other error as described above.
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7.6.1.3.1. False Retry
[Author Aside]: Section substantially revised to explain why false
retries can occur, even though EOS is designed to avoid them. This
is used as a basis for explaining the potential need for false retry
detection while avoiding a level of checking that would be a
performance issue.
The mechanisms described in Section 7.6 are designed to ensure that
if a Sequence operation is sent and matches a request in the reply
cache with the same slot ID and sequence ID then, it is a retry of
that original request. However, it is possible, although quite
unlikely, that servers will encounter requests where this is not the
case, in which case the request is considered a "false retry".
* False reties can occur if the client does not implement request
sequencing as described in Section 7.6.
* They can also occur as a result of situations in which large
number of requests are aborted and considered complete, even
though no response has been received by the requester. However,
for this situation to result in a false retry there would have to
be a sequence of over four billion such requests being processed
using the same slot ID with that sequence followed by a long-
delayed transmission of an abandoned request.
If a requester sent a Sequence operation with a slot ID and sequence
ID that are in the reply cache but the replier detects that the
retried request is not the same as the original request, including a
retry that has different operations or different arguments in the
operations from the original and a retry that uses a different
principal in the RPC request's credential field that translates to a
different user, then this is a false retry.
Given the low expected frequency of such false retries, the replier
is not obligated to check for their existence although it is prudent
to do so with requesters whose implementation of EOD is any way
suspect or where the requests are transmitted over a network capable
of delivering a request a very long time after it was sent. When the
replier does detect a false retry, it is permitted (but not always
obligated) to return NFS4ERR_SEQ_FALSE_RETRY in response to the
Sequence operation when it detects a false retry.
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Translations of particularly privileged user values to other users
due to the lack of appropriately secure credentials, as configured on
the replier, should be applied before determining whether the users
are the same or different. If the replier determines the users are
different between the original request and a retry, then the replier
MUST return NFS4ERR_SEQ_FALSE_RETRY.
Regardless of whether such user mismatches do occur, the occurrence
of false retries is an indication that the EOS logic is faulty, has
not been implemented correctly, or that there is an extraordinary
frequency of aborted requests. In light of this fact, there are
practical limits to the information that might be saved in order to
determine whether a particular request is a false retry. In the case
of large requests recording the entire request might not be practical
while a recording a compact form in the form of a checksum might
unacceptably limit performance.
In the case of requests for which the reply is cached, comparing the
operations in the cached response to those in the putative retry can
serve to detect interactions with clients not properly implementing
EOS or aborting requests inappropriately. In other cases, recording
the operation count and the identity of the first non-SEQUENCE
operation can make a simple check for false retry feasible.
If an operation of the retry is an illegal operation, or an operation
that was legal in a previous minor version of NFSv4 and MUST NOT be
supported in the current minor version (e.g., SETCLIENTID), the
replier MAY return NFS4ERR_SEQ_FALSE_RETRY (and MUST do so if the
users of the original request and retry differ). Otherwise, the
replier MAY return NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR or
NFS4ERR_NOTSUPP as appropriate. Note that the handling is in
contrast for how the replier deals with retries requests with no
cached reply. The difference is due to NFS4ERR_SEQ_FALSE_RETRY being
a valid error for only Sequence operations, whereas
NFS4ERR_RETRY_UNCACHED_REP is a valid error for all operations except
illegal operations and operations that MUST NOT be supported in the
current minor version of NFSv4.
7.6.2. Retry and Replay of Reply
Because NFSv4.1 is used on transports providing reliable delivery,
retrying requests within an existing connection is unlikely to be
helpful. Requesters will not normally retry a request, unless the
connection it used to send the request disconnects. The requester
can then reconnect and re-send the request, or it can re-send the
request over a different connection that is associated with the same
session, to deal with the possibility that the original connection is
no longer functioning appropriately.
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If the requester is a server wanting to re-send a callback operation
over the backchannel of a session, the requester of course cannot
reconnect because only the client can associate connections with the
backchannel. The server can re-send the request over another
connection that is bound to the same session's backchannel. If there
is no such connection, the server is forced to indicate that the
session has no backchannel by setting the
SEQ4_STATUS_CB_PATH_DOWN_SESSION flag bit in the response to the next
SEQUENCE operation from the client. The client then has no option
but to associate a new connection with the session (or destroy the
session).
Note that it is not, in general, fatal for a requester to retry
without a disconnect between the request and retry. However, in
order to prevent false retries (see Section 7.6.1.3.1), the requester
MUST NOT retry a request once the slot used to send that request has
been used to send a new request.
Nevertheless, the retry does consume resources, especially with RDMA,
where each request, retry or not, consumes a credit. Retries for no
reason, especially retries sent shortly after the previous attempt,
are a poor use of network bandwidth and defeat the purpose of a
transport's inherent congestion control system.
A requester will normally wait for a reply to a request before using
the slot for another request and MUST do so unless events such as
termination of the issuing process makes it impossible to do so. If
no such situation were to arise, then the protocol design would
ensure no false retry situation could occur (See Section 7.6.1.3.1
for details). When it does not wait for a reply, the requester
cannot be sure that using the next sequence ID for the slot chosen,
as it normally does, will always be accepted. For example, suppose a
requester sends a request with sequence ID 1, and does not wait for
the response. The next time it uses the slot, it sends the new
request with sequence ID 2. If the replier has not seen the request
with sequence ID 1, then the replier is not expecting sequence ID 2,
and rejects the requester's new request with NFS4ERR_SEQ_MISORDERED
(as the result from SEQUENCE or CB_SEQUENCE).
In light of the above, clients that do not wait for a reply before
reusing the slot need to be aware of the possibility of receiving
NFS4ERRR_SEQ_MISORDERED as a result and infer the probable existence
of a request not received by the server. The client will then adjust
the current sequence id sent, using successful execution as an
indication that seqids on that slot are again correctly aligned.
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RDMA fabrics do not guarantee that the memory handles (Steering Tags)
within each RPC/RDMA "chunk" [RFC8166] are valid on a scope outside
that of a single connection. Therefore, handles used by the direct
operations become invalid after connection loss. The server must
ensure that any RDMA operations that must be replayed from the reply
cache use the newly provided handle(s) from the most recent request.
A retry might be sent while the original request is still in progress
on the replier. In this case, the replier SHOULD deal with the issue
by returning NFS4ERR_DELAY as the reply to SEQUENCE or CB_SEQUENCE
operation, but implementations MAY return NFS4ERR_MISORDERED. Since
errors from SEQUENCE and CB_SEQUENCE are never recorded in the reply
cache, this approach allows the results of the execution of the
original request to be properly recorded in the reply cache (assuming
that the requester specified the reply to be cached).
7.6.3. Resolving Server Callback Races
It is possible for server callbacks to arrive at the client before
the reply from related forward channel operations. For example, a
client may have been granted a delegation to a file it has opened,
but the reply to the OPEN (informing the client of the granting of
the delegation) may be delayed in the network. If a conflicting
operation arrives at the server, it will recall the delegation using
the backchannel, which may be on a different transport connection,
perhaps even a different network, or even a different session
associated with the same client ID.
The presence of a session between the client and server alleviates
this issue. When a session is in place, each client request is
uniquely identified by its { session ID, slot ID, sequence ID }
triple. By the rules under which slot entries (reply cache entries)
are retired, the server has knowledge whether the client has "seen"
each of the server's replies. The server can therefore provide
sufficient information to the client to allow it to disambiguate
between an erroneous or conflicting callback race condition.
For each client operation that might result in some sort of server
callback, the server SHOULD keep track of the { session ID, slot ID,
sequence ID } triple of the client request until the slot ID
retirement rules allow the server to determine that the client has,
in fact, seen the server's reply. Until the time the { session ID,
slot ID, sequence ID } request triple can be retired, any recalls of
the associated object MUST carry an array of these referring
identifiers (in the CB_SEQUENCE operation's arguments), for the
benefit of the client. After this time, it is not necessary for the
server to provide this information in related callbacks, since it is
certain that a race condition can no longer occur.
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The CB_SEQUENCE operation that begins each server callback carries a
list of "referring" { session ID, slot ID, sequence ID } triples. If
the client finds the request corresponding to the referring session
ID, slot ID, and sequence ID to be currently outstanding (i.e., the
server's reply has not been seen by the client), it can determine
that the callback has raced the reply, and act accordingly. If the
client does not find the request corresponding to the referring
triple to be outstanding (including the case of a session ID
referring to a destroyed session), then there is no race with respect
to this triple. The server SHOULD limit the referring triples to
requests that refer to just those that apply to the objects referred
to in the CB_COMPOUND procedure.
The client must not simply wait forever for the expected server reply
to arrive before responding to the CB_COMPOUND that won the race,
because it is possible that it will be delayed indefinitely. The
client should assume the likely case that the reply will arrive
within the average round-trip time for COMPOUND requests to the
server, and wait that period of time. If that period of time
expires, it can respond to the CB_COMPOUND with NFS4ERR_DELAY. There
are other scenarios under which callbacks may race replies. Among
them are pNFS layout recalls as described in Section 18.7.5.2.
7.6.4. COMPOUND and CB_COMPOUND Construction Issues
Very large requests and replies may pose both buffer management
issues (especially with RDMA) and reply cache issues. When the
session is created (Section 25.36), for each channel (fore and back),
the client and server negotiate the maximum-sized request they will
send or process (ca_maxrequestsize), the maximum-sized reply they
will return or process (ca_maxresponsesize), and the maximum-sized
reply they will store in the reply cache (ca_maxresponsesize_cached).
For discussion related to the selections of appropriate values for
these quantities, see Section 7.6.5
If a request exceeds ca_maxrequestsize, the reply will have the
status NFS4ERR_REQ_TOO_BIG. A replier MAY return NFS4ERR_REQ_TOO_BIG
as the status for the first operation (SEQUENCE or CB_SEQUENCE) in
the request (which means that no operations in the request executed
and that the state of the slot in the reply cache is unchanged), or
it MAY opt to return it on a subsequent operation in the same
COMPOUND or CB_COMPOUND request (which means that at least one
operation did execute and that the state of the slot in the reply
cache does change). The replier SHOULD set NFS4ERR_REQ_TOO_BIG on
the operation that exceeds ca_maxrequestsize.
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If a reply exceeds ca_maxresponsesize, the reply will have the status
NFS4ERR_REP_TOO_BIG. A replier MAY return NFS4ERR_REP_TOO_BIG as the
status for the first operation (SEQUENCE or CB_SEQUENCE) in the
request, or it MAY opt to return it on a subsequent operation (in the
same COMPOUND or CB_COMPOUND reply). A replier MAY return
NFS4ERR_REP_TOO_BIG in the reply to SEQUENCE or CB_SEQUENCE, even if
the response would still exceed ca_maxresponsesize.
If sa_cachethis or csa_cachethis is TRUE, then the replier MUST cache
a reply except if an error is returned by the SEQUENCE or CB_SEQUENCE
operation (see Section 7.6.1.2). If the reply exceeds
ca_maxresponsesize_cached (and sa_cachethis or csa_cachethis is
TRUE), then the server MUST return NFS4ERR_REP_TOO_BIG_TO_CACHE.
Even if NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for that
matter) is returned on an operation other than the first operation
(SEQUENCE or CB_SEQUENCE), then the reply MUST be cached if
sa_cachethis or csa_cachethis is TRUE. For example, if a COMPOUND
has eleven operations, including SEQUENCE, the fifth operation is a
RENAME, and the tenth operation is a READ for one million bytes, the
server may return NFS4ERR_REP_TOO_BIG_TO_CACHE on the tenth
operation. Since the server executed several operations, especially
the non-idempotent RENAME, the client's request to cache the reply
needs to be honored in order for the correct operation of exactly
once semantics. If the client retries the request, the server will
have cached a reply that contains results for ten of the eleven
requested operations, with the tenth operation having a status of
NFS4ERR_REP_TOO_BIG_TO_CACHE.
A client needs to take care that, when sending operations that change
the current filehandle (except for PUTFH, PUTPUBFH, PUTROOTFH, and
RESTOREFH), it does not exceed the maximum reply buffer before the
GETFH operation. Otherwise, the client will have to retry the
operation that changed the current filehandle, in order to obtain the
desired filehandle. For the OPEN operation (See Section 25.16),
retry is not always available as an option. The following guidelines
for the handling of filehandle-changing operations are advised:
* Within the same COMPOUND procedure, a client SHOULD send GETFH
immediately after a current filehandle-changing operation. A
client MUST send GETFH after a current filehandle-changing
operation that is also non-idempotent (e.g., the OPEN operation),
unless the operation is RESTOREFH. RESTOREFH is an exception,
because even though it is non-idempotent, the filehandle RESTOREFH
produced originated from an operation that is either idempotent
(e.g., PUTFH, LOOKUP), or non-idempotent (e.g., OPEN, CREATE). If
the origin is non-idempotent, then because the client MUST send
GETFH after the origin operation, the client can recover if
RESTOREFH returns an error.
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* A server MAY return NFS4ERR_REP_TOO_BIG or
NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
filehandle-changing operation if the reply would be too large on
the next operation.
* A server SHOULD return NFS4ERR_REP_TOO_BIG or
NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
filehandle-changing, non-idempotent operation if the reply would
be too large on the next operation, especially if the operation is
OPEN.
* A server MAY return NFS4ERR_UNSAFE_COMPOUND to a non-idempotent
current filehandle-changing operation, if it looks at the next
operation (in the same COMPOUND procedure) and finds it is not
GETFH. The server SHOULD do this if it is unable to determine in
advance whether the total response size would exceed
ca_maxresponsesize_cached or ca_maxresponsesize.
7.6.5. Setting Size limits for Sessions
The following issues need to be taken account of in setting the size
limits introduced in Section 7.6.4.
* The primary factor governing the choice of ca_maxrequestsize is
the need to make WRITE requests of sufficient size, so that IO
overhead does not become excessive. In addition. SETATTR
requests may be long and require a high ca_maxrequestsize when
they are used to set attributes such as acl, sacl and dacl, which
can be of substantial size.
In both cases, allowances also needs to be made for smaller
operations that will need to be included in the COMPOUND.
* The primary factor governing the choice of ca_maxresponsesize is
the need to make READ requests of sufficient size, so that IO
overhead does not become excessive. In addition. GETATTR request
may be long and require a high ca_maxresponsesize when they are
used to get the value attributes such as acl, sacl and dacl, which
can be of substantial size.
In both cases, allowances also need to be made for smaller
operation that will need to be included in the COMPOUND.
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* In determining the appropriate value for
ca_maxresponsesize_cached, the response sizes of idempotent
requests such as READ and GETATTR can be ignored unless the client
needs to issue COMPOUNDS that combine non-idempotent operation
together with operations that return long responses. When a
client chooses to do this, a large ca_maxresponsesize_cached is
likely to be needed.
When new operations are proposed the effect on the requirements on
ca_maxresponsesize_cached needs to be considered since it might be
impractical to require large reply caches.
7.7. RDMA Considerations
A complete discussion of the operation of RPC-based protocols over
RDMA transports is in [RFC8166]. A discussion of the operation of
NFSv4, including NFSv4.1, over RDMA is in [RFC8267]. Where RDMA is
considered, this specification assumes the use of such a layering; it
addresses only the upper-layer issues relevant to making best use of
RPC/RDMA.
7.7.1. RDMA Connection Resources
RDMA requires its consumers to register memory and post buffers of a
specific size and number for receive operations.
Registration of memory can be a relatively high-overhead operation,
since it requires pinning of buffers, assignment of attributes (e.g.,
readable/writable), and initialization of hardware translation.
Preregistration is desirable to reduce overhead. These registrations
are specific to hardware interfaces and even to RDMA connection
endpoints; therefore, negotiation of their limits is desirable to
manage resources effectively.
Following basic registration, these buffers must be posted by the RPC
layer to handle receives. These buffers remain in use by the RPC/
NFSv4.1 implementation; the size and number of them must be known to
the remote peer in order to avoid RDMA errors that would cause a
fatal error on the RDMA connection.
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NFSv4.1 manages slots as resources on a per-session basis (See
Section 7), while RDMA connections manage credits on a per-connection
basis. This means that in order for a peer to send data over RDMA to
a remote buffer, it has to have both an NFSv4.1 slot and an RDMA
credit. If multiple RDMA connections are associated with a session,
then if the total number of credits across all RDMA connections
associated with the session is X, and the number of slots in the
session is Y, then the maximum number of outstanding requests is the
lesser of X and Y.
7.7.2. Flow Control
Previous versions of NFS do not provide flow control; instead, they
rely on the windowing provided by transports like TCP to throttle
requests. This does not work with RDMA, which provides no operation
flow control and will terminate a connection in error when limits are
exceeded. Limits such as maximum number of requests outstanding are
therefore negotiated when a session is created (See the
ca_maxrequests field in Section 25.36). These limits then provide
the maxima within which each connection associated with the session's
channel(s) must remain. RDMA connections are managed within these
limits as described in Section 3.3 of [RFC8166]; if there are
multiple RDMA connections, then the maximum number of requests for a
channel will be divided among the RDMA connections. Put a different
way, the onus is on the replier to ensure that the total number of
RDMA credits across all connections associated with the replier's
channel does exceed the channel's maximum number of outstanding
requests.
The limits may also be modified dynamically at the replier's choosing
by manipulating certain parameters present in each NFSv4.1 reply. In
addition, the CB_RECALL_SLOT callback operation (see Section 27.8)
can be sent by a server to a client to return RDMA credits to the
server, thereby lowering the maximum number of requests a client can
have outstanding to the server.
7.7.3. Padding
Header padding is requested by each peer at session initiation (See
the ca_headerpadsize argument to CREATE_SESSION in Section 25.36),
and subsequently used by the RPC RDMA layer, as described in
[RFC8166]. Zero padding is permitted.
Padding leverages the useful property that RDMA preserve alignment of
data, even when they are placed into anonymous (untagged) buffers.
If requested, client inline writes will insert appropriate pad bytes
within the request header to align the data payload on the specified
boundary. The client is encouraged to add sufficient padding (up to
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the negotiated size) so that the "data" field of the WRITE operation
is aligned. Most servers can make good use of such padding, which
allows them to chain receive buffers in such a way that any data
carried by client requests will be placed into appropriate buffers at
the server, ready for file system processing. The receiver's RPC
layer encounters no overhead from skipping over pad bytes, and the
RDMA layer's high performance makes the insertion and transmission of
padding on the sender a significant optimization. In this way, the
need for servers to perform RDMA Read to satisfy all but the largest
client writes is obviated. An added benefit is the reduction of
message round trips on the network -- a potentially good trade, where
latency is present.
The value to choose for padding is subject to a number of criteria.
A primary source of variable-length data in the RPC header is the
authentication information, the form of which is client-determined,
possibly in response to server specification. The contents of
COMPOUNDs, sizes of strings such as those passed to RENAME, etc. all
go into the determination of a maximal NFSv4.1 request size and
therefore minimal buffer size. The client must select its offered
value carefully, so as to avoid overburdening the server, and vice
versa. The benefit of an appropriate padding value is higher
performance.
Sender gather:
|RPC Request|Pad bytes|Length| -> |User data...|
\------+----------------------/ \
\ \
\ Receiver scatter: \-----------+- ...
/-----+----------------\ \ \
|RPC Request|Pad|Length| -> |FS buffer|->|FS buffer|->...
In the above case, the server may recycle unused buffers to the next
posted receive if unused by the actual received request, or may pass
the now-complete buffers by reference for normal write processing.
For a server that can make use of it, this removes any need for data
copies of incoming data, without resorting to complicated end-to-end
buffer advertisement and management. This includes most kernel-based
and integrated server designs, among many others. The client may
perform similar optimizations, if desired.
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7.7.4. Dual RDMA and Non-RDMA Transports
Some RDMA transports (e.g. [RFC5040]) permit a "streaming" (non-RDMA)
phase, where ordinary traffic might flow before "stepping up" to RDMA
mode, commencing RDMA traffic. Some RDMA transports start
connections always in RDMA mode. NFSv4.1 allows, but does not
assume, a streaming phase before RDMA mode. When a connection is
associated with a session, the client and server negotiate whether
the connection is used in RDMA or non-RDMA mode (See Sections 25.36
and 25.34).
7.8. Session Security
7.8.1. Session Callback Security
Via session/connection association, NFSv4.1 improves security over
that provided by NFSv4.0 for the backchannel. The connection is
client-initiated (see Section 25.34) and subject to the same firewall
and routing checks as the fore channel. At the client's option (See
Section 25.35), connection association is fully authenticated before
being activated (See Section 25.34). Traffic from the server over
the backchannel is authenticated exactly as the client specifies (See
Section 7.8.2).
7.8.2. Backchannel RPC Security
When the NFSv4.1 client establishes the backchannel, it informs the
server of the security flavors and principals to use when sending
requests. If the security flavor is RPCSEC_GSS, the client expresses
the principal in the form of an established RPCSEC_GSS context. The
server is free to use any of the flavor/principal combinations the
client offers, but it MUST NOT use combinations not offered. This
way, the client need not provide a target GSS principal for the
backchannel as it did with NFSv4.0, nor does the server have to
implement an RPCSEC_GSS initiator as it did with NFSv4.0 [RFC3530].
The CREATE_SESSION (Section 25.36) and BACKCHANNEL_CTL
(Section 25.33) operations allow the client to specify flavor/
principal combinations.
Also note that the SP4_SSV state protection mode (See Sections 25.35
and 7.8.3) has the side benefit of providing SSV-derived RPCSEC_GSS
contexts (Section 7.9).
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7.8.3. Protection from Unauthorized State Changes
As described to this point in the specification, the state model of
NFSv4.1 is vulnerable to an attacker that sends a SEQUENCE operation
with a forged session ID and with a slot ID that it expects the
legitimate client to use next. When the legitimate client uses the
slot ID with the same sequence number, the server returns the
attacker's result from the reply cache, which disrupts the legitimate
client and thus denies service to it. Similarly, an attacker could
send a CREATE_SESSION with a forged client ID to create a new session
associated with the client ID. The attacker could send requests
using the new session that change locking state, such as LOCKU
operations to release locks the legitimate client has acquired.
Setting a security policy on the file that requires RPCSEC_GSS
credentials when manipulating the file's state is one potential work
around, but has the disadvantage of preventing a legitimate client
from releasing state when RPCSEC_GSS is required to do so, but a GSS
context cannot be obtained (possibly because the user has logged off
the client).
NFSv4.1 provides three options to a client for state protection,
which are specified when a client creates a client ID via EXCHANGE_ID
(Section 25.35).
The first (SP4_NONE) is to simply waive state protection, except for
that provided by client host authentication.
The other two options (SP4_MACH_CRED and SP4_SSV) share several
traits:
* An RPCSEC_GSS-based credential is used to authenticate client ID
and session maintenance operations, including creating and
destroying a session, associating a connection with the session,
and destroying the client ID.
* Because RPCSEC_GSS is used to authenticate client ID and session
maintenance, the attacker cannot associate a rogue connection with
a legitimate session, or associate a rogue session with a
legitimate client ID in order to maliciously alter the client ID's
lock state via CLOSE, LOCKU, DELEGRETURN, LAYOUTRETURN, etc.
* In cases where the server's security policies on a portion of its
namespace require RPCSEC_GSS authentication, a client may have to
use an RPCSEC_GSS credential to remove per-file state (e.g.,
LOCKU, CLOSE, etc.). The server may require that the principal
that removes the state match certain criteria (e.g., the principal
might have to be the same as the one that acquired the state).
However, the client might not have an RPCSEC_GSS context for such
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a principal, and might not be able to create such a context
(perhaps because the user has logged off). When the client
establishes SP4_MACH_CRED or SP4_SSV protection, it can specify a
list of operations that the server MUST allow using the machine
credential (if SP4_MACH_CRED is used) or the SSV credential (if
SP4_SSV is used).
The SP4_MACH_CRED state protection option uses a machine credential
where the principal that creates the client ID MUST also be the
principal that performs client ID and session maintenance operations.
The security of the machine credential state protection approach
depends entirely on safeguarding the per-machine credential.
Assuming a proper safeguard using the per-machine credential for
operations like CREATE_SESSION, BIND_CONN_TO_SESSION,
DESTROY_SESSION, and DESTROY_CLIENTID will prevent an attacker from
associating a rogue connection with a session, or associating a rogue
session with a client ID.
There are at least three scenarios for the SP4_MACH_CRED option:
1. The system administrator configures a unique, permanent per-
machine credential for one of the mandated GSS mechanisms (e.g.,
if Kerberos V5 is used, a "keytab" containing a principal derived
from a client host name could be used).
2. The client is used by a single user, and so the client ID and its
sessions are used by just that user. If the user's credential
expires, then session and client ID maintenance cannot occur, but
since the client has a single user, only that user is
inconvenienced.
3. The physical client has multiple users, but the client
implementation has a unique client ID for each user. This is
effectively the same as the second scenario, but a disadvantage
is that each user needs to be allocated at least one session
each, so the approach suffers from lack of economy.
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The SP4_SSV protection option uses the SSV (Section 2.5), via
RPCSEC_GSS and the SSV GSS mechanism (Section 7.9), to protect state
from attack. The SP4_SSV protection option is intended for the
situation comprised of a client that has multiple active users and a
system administrator who wants to avoid the burden of installing a
permanent machine credential on each client. The SSV is established
and updated on the server via SET_SSV (See Section 25.47). To
prevent eavesdropping, a client SHOULD send SET_SSV via RPCSEC_GSS
with the privacy service or use tls encryption on the connection
making the request. Several aspects of the SSV make it intractable
for an attacker to guess the SSV, and thus associate rogue
connections with a session, and rogue sessions with a client ID:
* The arguments to and results of SET_SSV include digests of the old
and new SSV, respectively.
* Because the initial value of the SSV is zero, therefore known, the
client that opts for SP4_SSV protection and opts to apply SP4_SSV
protection to BIND_CONN_TO_SESSION and CREATE_SESSION MUST send at
least one SET_SSV operation before the first BIND_CONN_TO_SESSION
operation or before the second CREATE_SESSION operation on a
client ID. If it does not, the SSV mechanism will not generate
tokens (Section 7.9). A client SHOULD send SET_SSV as soon as a
session is created.
* A SET_SSV request does not replace the SSV with the argument to
SET_SSV. Instead, the current SSV on the server is logically
exclusive ORed (XORed) with the argument to SET_SSV. Each time a
new principal uses a client ID for the first time, the client
SHOULD send a SET_SSV with that principal's RPCSEC_GSS
credentials, with RPCSEC_GSS service set to RPC_GSS_SVC_PRIVACY.
Here are the types of attacks that can be attempted by an attacker
named Eve on a victim named Bob, and how SP4_SSV protection foils
each attack:
* Suppose Eve is the first user to log into a legitimate client.
Eve's use of an NFSv4.1 file system will cause the legitimate
client to create a client ID with SP4_SSV protection, specifying
that the BIND_CONN_TO_SESSION operation MUST use the SSV
credential. Eve's use of the file system also causes an SSV to be
created. The SET_SSV operation that creates the SSV will be
protected by the RPCSEC_GSS context created by the legitimate
client, which uses Eve's GSS principal and credentials. Eve can
eavesdrop on the network while her RPCSEC_GSS context is created
and the SET_SSV using her context is sent. Even if the legitimate
client sends the SET_SSV with RPC_GSS_SVC_PRIVACY, because Eve
knows her own credentials, she can decrypt the SSV. Eve can
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compute an RPCSEC_GSS credential that BIND_CONN_TO_SESSION will
accept, and so associate a new connection with the legitimate
session. Eve can change the slot ID and sequence state of a
legitimate session, and/or the SSV state, in such a way that when
Bob accesses the server via the same legitimate client, the
legitimate client will be unable to use the session.
The client's only recourse is to create a new client ID for Bob to
use, and establish a new SSV for the client ID. The client will
be unable to delete the old client ID, and will let the lease on
the old client ID expire.
Once the legitimate client establishes an SSV over the new session
using Bob's RPCSEC_GSS context, Eve can use the new session via
the legitimate client, but she cannot disrupt Bob. Moreover,
because the client SHOULD have modified the SSV due to Eve using
the new session, Bob cannot get revenge on Eve by associating a
rogue connection with the session.
The question is how did the legitimate client detect that Eve has
hijacked the old session? When the client detects that a new
principal, Bob, wants to use the session, it SHOULD have sent a
SET_SSV, which leads to the following sub-scenarios:
- Let us suppose that from the rogue connection, Eve sent a
SET_SSV with the same slot ID and sequence ID that the
legitimate client later uses. The server will assume the
SET_SSV sent with Bob's credentials is a retry, and return to
the legitimate client the reply it sent Eve. However, unless
Eve can correctly guess the SSV the legitimate client will use,
the digest verification checks in the SET_SSV response will
fail. That is an indication to the client that the session has
apparently been hijacked.
- Alternatively, Eve sent a SET_SSV with a different slot ID than
the legitimate client uses for its SET_SSV. Then the digest
verification of the SET_SSV sent with Bob's credentials fails
on the server, and the error returned to the client makes it
apparent that the session has been hijacked.
- Alternatively, Eve sent an operation other than SET_SSV, but
with the same slot ID and sequence that the legitimate client
uses for its SET_SSV. The server returns to the legitimate
client the response it sent Eve. The client sees that the
response is not at all what it expects. The client assumes
either session hijacking or a server bug, and either way
destroys the old session.
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* Eve associates a rogue connection with the session as above, and
then destroys the session. Again, Bob goes to use the server from
the legitimate client, which sends a SET_SSV using Bob's
credentials. The client receives an error that indicates that the
session does not exist. When the client tries to create a new
session, this will fail because the SSV it has does not match that
which the server has, and now the client knows the session was
hijacked. The legitimate client establishes a new client ID.
* If Eve creates a connection before the legitimate client
establishes an SSV, because the initial value of the SSV is zero
and therefore known, Eve can send a SET_SSV that will pass the
digest verification check. However, because the new connection
has not been associated with the session, the SET_SSV is rejected
for that reason.
In summary, an attacker's disruption of state when SP4_SSV protection
is in use is limited to the formative period of a client ID, its
first session, and the establishment of the SSV. Once a non-
malicious user uses the client ID, the client quickly detects any
hijack and rectifies the situation. Once a non-malicious user
successfully modifies the SSV, the attacker cannot use NFSv4.1
operations to disrupt the non-malicious user.
Note that neither the SP4_MACH_CRED nor SP4_SSV protection approaches
prevent hijacking of a transport connection that has previously been
associated with a session. If the goal of a counter-threat strategy
is to prevent connection hijacking, the use of IPsec or TLS is
RECOMMENDED.
If a connection hijack occurs, the hijacker could in theory change
locking state and negatively impact the service to legitimate
clients. However, if the server is configured to require the use of
RPCSEC_GSS with integrity or privacy on the affected file objects,
and if EXCHGID4_FLAG_BIND_PRINC_STATEID capability (Section 25.35) is
in force, this will thwart unauthorized attempts to change locking
state.
7.9. The Secret State Verifier (SSV) GSS Mechanism
The SSV provides the secret key for a GSS mechanism internal to
NFSv4.1 that NFSv4.1 uses for state protection. Contexts for this
mechanism are not established via the RPCSEC_GSS protocol. Instead,
the contexts are automatically created when EXCHANGE_ID specifies
SP4_SSV protection. The only tokens defined are the PerMsgToken
(emitted by GSS_GetMIC) and the SealedMessage token (emitted by
GSS_Wrap).
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The mechanism OID for the SSV mechanism is
iso.org.dod.internet.private.enterprise.Michael Eisler.nfs.ssv_mech
(1.3.6.1.4.1.28882.1.1). While the SSV mechanism does not define any
initial context tokens, the OID can be used to let servers indicate
that the SSV mechanism is acceptable whenever the client sends a
SECINFO or SECINFO_NO_NAME operation (see Section 6.2).
The SSV mechanism defines four subkeys derived from the SSV value.
Each time SET_SSV is invoked, the subkeys are recalculated by the
client and server. The calculation of each of the four subkeys
depends on each of the four respective ssv_subkey4 enumerated values.
The calculation uses the HMAC [RFC2104] algorithm, using the current
SSV as the key, the one-way hash algorithm as negotiated by
EXCHANGE_ID, and the input text as represented by the XDR encoded
enumeration value for that subkey of data type ssv_subkey4. If the
length of the output of the HMAC algorithm exceeds the length of key
of the encryption algorithm (which is also negotiated by
EXCHANGE_ID), then the subkey MUST be truncated from the HMAC output,
i.e., if the subkey is of N bytes long, then the first N bytes of the
HMAC output MUST be used for the subkey. The specification of
EXCHANGE_ID states that the length of the output of the HMAC
algorithm MUST NOT be less than the length of subkey needed for the
encryption algorithm (See Section 25.35).
/* Input for computing subkeys */
enum ssv_subkey4 {
SSV4_SUBKEY_MIC_I2T = 1,
SSV4_SUBKEY_MIC_T2I = 2,
SSV4_SUBKEY_SEAL_I2T = 3,
SSV4_SUBKEY_SEAL_T2I = 4
};
The subkey derived from SSV4_SUBKEY_MIC_I2T is used for calculating
message integrity codes (MICs) that originate from the NFSv4.1
client, whether as part of a request over the fore channel or a
response over the backchannel. The subkey derived from
SSV4_SUBKEY_MIC_T2I is used for MICs originating from the NFSv4.1
server. The subkey derived from SSV4_SUBKEY_SEAL_I2T is used for
encryption text originating from the NFSv4.1 client, and the subkey
derived from SSV4_SUBKEY_SEAL_T2I is used for encryption text
originating from the NFSv4.1 server.
The PerMsgToken description is based on an XDR definition:
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/* Input for computing smt_hmac */
struct ssv_mic_plain_tkn4 {
uint32_t smpt_ssv_seq;
opaque smpt_orig_plain<>;
};
/* SSV GSS PerMsgToken token */
struct ssv_mic_tkn4 {
uint32_t smt_ssv_seq;
opaque smt_hmac<>;
};
The field smt_hmac is an HMAC calculated by using the subkey derived
from SSV4_SUBKEY_MIC_I2T or SSV4_SUBKEY_MIC_T2I as the key, the one-
way hash algorithm as negotiated by EXCHANGE_ID, and the input text
as represented by data of type ssv_mic_plain_tkn4. The field
smpt_ssv_seq is the same as smt_ssv_seq. The field smpt_orig_plain
is the "message" input passed to GSS_GetMIC() (See Section 2.3.1 of
[RFC2743]). The caller of GSS_GetMIC() provides a pointer to a
buffer containing the plain text. The SSV mechanism's entry point
for GSS_GetMIC() encodes this into an opaque array, and the encoding
will include an initial four-byte length, plus any necessary padding.
Prepended to this will be the XDR encoded value of smpt_ssv_seq, thus
making up an XDR encoding of a value of data type ssv_mic_plain_tkn4,
which in turn is the input into the HMAC.
The token emitted by GSS_GetMIC() is XDR encoded and of XDR data type
ssv_mic_tkn4. The field smt_ssv_seq comes from the SSV sequence
number, which is equal to one after SET_SSV (Section 25.47) is called
the first time on a client ID. Thereafter, the SSV sequence number
is incremented on each SET_SSV. Thus, smt_ssv_seq represents the
version of the SSV at the time GSS_GetMIC() was called. As noted in
Section 25.35, the client and server can maintain multiple concurrent
versions of the SSV. This allows the SSV to be changed without
serializing all RPC calls that use the SSV mechanism with SET_SSV
operations. Once the HMAC is calculated, it is XDR encoded into
smt_hmac, which will include an initial four-byte length, and any
necessary padding. Prepended to this will be the XDR encoded value
of smt_ssv_seq.
The SealedMessage description is based on an XDR definition:
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/* Input for computing ssct_encr_data and ssct_hmac */
struct ssv_seal_plain_tkn4 {
opaque sspt_confounder<>;
uint32_t sspt_ssv_seq;
opaque sspt_orig_plain<>;
opaque sspt_pad<>;
};
/* SSV GSS SealedMessage token */
struct ssv_seal_cipher_tkn4 {
uint32_t ssct_ssv_seq;
opaque ssct_iv<>;
opaque ssct_encr_data<>;
opaque ssct_hmac<>;
};
The token emitted by GSS_Wrap() is XDR encoded and of XDR data type
ssv_seal_cipher_tkn4.
The ssct_ssv_seq field has the same meaning as smt_ssv_seq.
The ssct_encr_data field is the result of encrypting a value of the
XDR encoded data type ssv_seal_plain_tkn4. The encryption key is the
subkey derived from SSV4_SUBKEY_SEAL_I2T or SSV4_SUBKEY_SEAL_T2I, and
the encryption algorithm is that negotiated by EXCHANGE_ID.
The ssct_iv field is the initialization vector (IV) for the
encryption algorithm (if applicable) and is sent in clear text. The
content and size of the IV MUST comply with the specification of the
encryption algorithm. For example, the id-aes256-CBC algorithm MUST
use a 16-byte initialization vector (IV), which MUST be unpredictable
for each instance of a value of data type ssv_seal_plain_tkn4 that is
encrypted with a particular SSV key.
The ssct_hmac field is the result of computing an HMAC using the
value of the XDR encoded data type ssv_seal_plain_tkn4 as the input
text. The key is the subkey derived from SSV4_SUBKEY_MIC_I2T or
SSV4_SUBKEY_MIC_T2I, and the one-way hash algorithm is that
negotiated by EXCHANGE_ID.
The sspt_confounder field is a random value.
The sspt_ssv_seq field is the same as ssvt_ssv_seq.
The field sspt_orig_plain field is the original plaintext and is the
"input_message" input passed to GSS_Wrap() (See Section 2.3.3 of
[RFC2743]). As with the handling of the plaintext by the SSV
mechanism's GSS_GetMIC() entry point, the entry point for GSS_Wrap()
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expects a pointer to the plaintext, and will XDR encode an opaque
array into sspt_orig_plain representing the plain text, along with
the other fields of an instance of data type ssv_seal_plain_tkn4.
The sspt_pad field is present to support encryption algorithms that
require inputs to be in fixed-sized blocks. The content of sspt_pad
is zero filled except for the length. Beware that the XDR encoding
of ssv_seal_plain_tkn4 contains three variable-length arrays, and so
each array consumes four bytes for an array length, and each array
that follows the length is always padded to a multiple of four bytes
per the XDR standard.
For example, suppose the encryption algorithm uses 16-byte blocks,
and the sspt_confounder is three bytes long, and the sspt_orig_plain
field is 15 bytes long. The XDR encoding of sspt_confounder uses
eight bytes (4 + 3 + 1-byte pad), the XDR encoding of sspt_ssv_seq
uses four bytes, the XDR encoding of sspt_orig_plain uses 20 bytes (4
+ 15 + 1-byte pad), and the smallest XDR encoding of the sspt_pad
field is four bytes. This totals 36 bytes. The next multiple of 16
is 48; thus, the length field of sspt_pad needs to be set to 12
bytes, or a total encoding of 16 bytes. The total number of XDR
encoded bytes is thus 8 + 4 + 20 + 16 = 48.
GSS_Wrap() emits a token that is an XDR encoding of a value of data
type ssv_seal_cipher_tkn4. Note that regardless of whether or not
the caller of GSS_Wrap() requests confidentiality, the token always
has confidentiality. This is because the SSV mechanism is for
RPCSEC_GSS, and RPCSEC_GSS never produces GSS_wrap() tokens without
confidentiality.
There is one SSV per client ID. There is a single GSS context for a
client ID / SSV pair. All SSV mechanism RPCSEC_GSS handles of a
client ID / SSV pair share the same GSS context. SSV GSS contexts do
not expire except when the SSV is destroyed (causes would include the
client ID being destroyed or a server restart). Since one purpose of
context expiration is to replace keys that have been in use for "too
long", hence vulnerable to compromise by brute force or accident, the
client can replace the SSV key by sending periodic SET_SSV
operations, which is done by cycling through different users'
RPCSEC_GSS credentials. This way, the SSV is replaced without
destroying the SSV's GSS contexts.
SSV RPCSEC_GSS handles can be expired or deleted by the server at any
time, and the EXCHANGE_ID operation can be used to create more SSV
RPCSEC_GSS handles. Expiration of SSV RPCSEC_GSS handles does not
imply that the SSV or its GSS context has expired.
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The client MUST establish an SSV via SET_SSV before the SSV GSS
context can be used to emit tokens from GSS_Wrap() and GSS_GetMIC().
If SET_SSV has not been successfully called, attempts to emit tokens
MUST fail.
The SSV mechanism does not support replay detection and sequencing in
its tokens because RPCSEC_GSS does not use those features (see
"Context Creation Requests", Section 5.2.2 of [RFC2203]). However,
Section 7.10 discusses special considerations for the SSV mechanism
when used with RPCSEC_GSS.
7.10. Security Considerations for RPCSEC_GSS When Using the SSV
Mechanism
When a client ID is created with SP4_SSV state protection (See
Section 25.35), the client is permitted to associate multiple
RPCSEC_GSS handles with the single SSV GSS context (See Section 7.9).
Because of the way RPCSEC_GSS (both version 1 and version 2, see
[RFC2203] and [RFC5403]) calculate the verifier of the reply, special
care must be taken by the implementation of the NFSv4.1 client to
prevent attacks by a man-in-the-middle. The verifier of an
RPCSEC_GSS reply is the output of GSS_GetMIC() applied to the input
value of the seq_num field of the RPCSEC_GSS credential (data type
rpc_gss_cred_ver_1_t) (See Section 5.3.3.2 of [RFC2203]). If
multiple RPCSEC_GSS handles share the same GSS context, then if one
handle is used to send a request with the same seq_num value as
another handle, an attacker could block the reply, and replace it
with the verifier used for the other handle.
There are multiple ways to prevent the attack on the SSV RPCSEC_GSS
verifier in the reply. The simplest is believed to be as follows.
* Each time one or more new SSV RPCSEC_GSS handles are created via
EXCHANGE_ID, the client SHOULD send a SET_SSV operation to modify
the SSV. By changing the SSV, the new handles will not result in
the re-use of an SSV RPCSEC_GSS verifier in a reply.
* When a requester decides to use N SSV RPCSEC_GSS handles, it
SHOULD assign a unique and non-overlapping range of seq_nums to
each SSV RPCSEC_GSS handle. The size of each range SHOULD be
equal to MAXSEQ / N (See Section 5 of [RFC2203] for the definition
of MAXSEQ). When an SSV RPCSEC_GSS handle reaches its maximum, it
SHOULD force the replier to destroy the handle by sending a NULL
RPC request with seq_num set to MAXSEQ + 1 (See Section 5.3.3.3 of
[RFC2203]).
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* When the requester wants to increase or decrease N, it SHOULD
force the replier to destroy all N handles by sending a NULL RPC
request on each handle with seq_num set to MAXSEQ + 1. If the
requester is the client, it SHOULD send a SET_SSV operation before
using new handles. If the requester is the server, then the
client SHOULD send a SET_SSV operation when it detects that the
server has forced it to destroy a backchannel's SSV RPCSEC_GSS
handle. By sending a SET_SSV operation, the SSV will change, and
so the attacker will be unavailable to successfully replay a
previous verifier in a reply to the requester.
Note that if the replier carefully creates the SSV RPCSEC_GSS
handles, the related risk of a man-in-the-middle splicing a forged
SSV RPCSEC_GSS credential with a verifier for another handle does not
exist. This is because the verifier in an RPCSEC_GSS request is
computed from input that includes both the RPCSEC_GSS handle and
seq_num (See Section 5.3.1 of [RFC2203]). Provided the replier takes
care to avoid re-using the value of an RPCSEC_GSS handle that it
creates, such as by including a generation number in the handle, the
man-in-the-middle will not be able to successfully replay a previous
verifier in the request to a replier.
7.11. Session Mechanics - Steady State
7.11.1. Obligations of the Server
The server has the primary obligation to monitor the state of
backchannel resources that the client has created for the server
(RPCSEC_GSS contexts and backchannel connections). If these
resources vanish, the server takes action as specified in
Section 7.13.2.
7.11.2. Obligations of the Client
The client SHOULD honor the following obligations in order to utilize
the session:
* Keep a necessary session from going idle on the server. A client
that requires a session but nonetheless is not sending operations
risks having the session be destroyed by the server. This is
because sessions consume resources, and resource limitations may
force the server to cull an inactive session. A server MAY
consider a session to be inactive if the client has not used the
session before the session inactivity timer (Section 7.12) has
expired.
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* Destroy the session when not needed. If a client has multiple
sessions, one of which has no requests waiting for replies, and
has been idle for some period of time, it SHOULD destroy the
session.
* Maintain GSS contexts and RPCSEC_GSS handles for the backchannel.
If the client requires the server to use the RPCSEC_GSS security
flavor for callbacks, then it needs to be sure the RPCSEC_GSS
handles and/or their GSS contexts that are handed to the server
via BACKCHANNEL_CTL or CREATE_SESSION are unexpired.
* Preserve a connection for a backchannel. The server requires a
backchannel in order to gracefully recall recallable state or
notify the client of certain events. Note that if the connection
is not being used for the fore channel, there is no way for the
client to tell if the connection is still alive (e.g., the server
restarted without sending a disconnect). The onus is on the
server, not the client, to determine if the backchannel's
connection is alive, and to indicate in the response to a SEQUENCE
operation when the last connection associated with a session's
backchannel has disconnected.
7.11.3. Steps the Client Takes to Establish a Session
If the client does not have a client ID, the client sends EXCHANGE_ID
to establish a client ID. If it opts for SP4_MACH_CRED or SP4_SSV
protection, in the spo_must_enforce list of operations, it SHOULD at
minimum specify CREATE_SESSION, DESTROY_SESSION,
BIND_CONN_TO_SESSION, BACKCHANNEL_CTL, and DESTROY_CLIENTID. If it
opts for SP4_SSV protection, the client needs to ask for SSV-based
RPCSEC_GSS handles.
The client uses the client ID to send a CREATE_SESSION on a
connection to the server. The results of CREATE_SESSION indicate
whether or not the server undertakes to persist the session reply
cache in which a server restarts, and the client notes this for
future reference.
If the client specified SP4_SSV state protection when the client ID
was created, then it SHOULD send SET_SSV in the first COMPOUND after
the session is created. Each time a new principal goes to use the
client ID, it SHOULD send a SET_SSV again.
If the client wants to use delegations, layouts, directory
notifications, or any other state that requires a backchannel, then
it needs to add a connection to the backchannel if CREATE_SESSION did
not already do so. The client creates a connection, and calls
BIND_CONN_TO_SESSION to associate the connection with the session and
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the session's backchannel. If CREATE_SESSION did not already do so,
the client MUST tell the server what security is required in order
for the client to accept callbacks. The client does this via
BACKCHANNEL_CTL. If the client selected SP4_MACH_CRED or SP4_SSV
protection when it called EXCHANGE_ID, then the client SHOULD specify
that the backchannel use RPCSEC_GSS contexts for security.
If the client wants to use additional connections for the
backchannel, then it needs to call BIND_CONN_TO_SESSION on each
connection it wants to use with the session. If the client wants to
use additional connections for the fore channel, then it needs to
call BIND_CONN_TO_SESSION if it specified SP4_SSV or SP4_MACH_CRED
state protection when the client ID was created.
At this point, the session has reached steady state.
7.12. Session Inactivity Timer
The server MAY maintain a session inactivity timer for each session.
If the session inactivity timer expires, then the server MAY destroy
the session. To avoid losing a session due to inactivity, the client
MUST renew the session inactivity timer. The length of session
inactivity timer MUST NOT be less than the lease_time attribute
(Section 11.12.1.11). As with lease renewal (Section 13.3), when the
server receives a SEQUENCE operation, it resets the session
inactivity timer, and MUST NOT allow the timer to expire while the
rest of the operations in the COMPOUND procedure's request are still
executing. Once the last operation has finished, the server MUST set
the session inactivity timer to expire no sooner than the sum of the
current time and the value of the lease_time attribute.
7.13. Session Mechanics - Recovery
7.13.1. Events Requiring Client Action
The following events require client action to recover.
7.13.1.1. RPCSEC_GSS Context Loss by Callback Path
If all RPCSEC_GSS handles granted by the client to the server for
callback use have expired, the client MUST establish a new handle via
BACKCHANNEL_CTL. The sr_status_flags field of the SEQUENCE results
indicates when callback handles are nearly expired, or fully expired
(See Section 25.46.3).
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7.13.1.2. Connection Loss
If the client loses the last connection of the session and wants to
retain the session, then it needs to create a new connection, and if,
when the client ID was created, BIND_CONN_TO_SESSION was specified in
the spo_must_enforce list, the client MUST use BIND_CONN_TO_SESSION
to associate the connection with the session.
If there was a request outstanding at the time of connection loss,
then if the client wants to continue to use the session, it MUST
retry the request, as described in Section 7.6.2. Note that it is
not necessary to retry requests over a connection with the same
source network address or the same destination network address as the
lost connection. As long as the session ID, slot ID, and sequence ID
in the retry match that of the original request, the server will
recognize the request as a retry if it executed the request prior to
disconnect.
If the connection that was lost was the last one associated with the
backchannel, and the client wants to retain the backchannel and/or
prevent revocation of recallable state, the client needs to
reconnect, and if it does, it MUST associate the connection to the
session and backchannel via BIND_CONN_TO_SESSION. The server SHOULD
indicate when it has no callback connection via the sr_status_flags
result from SEQUENCE.
7.13.1.3. Backchannel GSS Context Loss
Via the sr_status_flags result of the SEQUENCE operation or other
means, the client will learn if some or all of the RPCSEC_GSS
contexts it assigned to the backchannel have been lost. If the
client wants to retain the backchannel and/or not put recallable
state subject to revocation, the client needs to use BACKCHANNEL_CTL
to assign new contexts.
7.13.1.4. Loss of Session
The replier might lose a record of the session. Causes include:
* Replier failure and restart.
* A catastrophe that causes the reply cache to be corrupted or lost
on the media on which it was stored. This applies even if the
replier indicated in the CREATE_SESSION results that it would
persist the cache.
* The server purges the session of a client that has been inactive
for a very extended period of time.
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* As a result of configuration changes among a set of clustered
servers, a network address previously connected to one server
becomes connected to a different server that has no knowledge of
the session in question. Such a configuration change will
generally only happen when the original server ceases to function
for a time.
Loss of reply cache often leads to loss of session. The replier
indicates loss of session to the requester by returning
NFS4ERR_BADSESSION on the next operation that uses the session ID
that refers to the lost session.
Although loss of session is often associated with loss of the
associated clientid and corresponding locking state, this is not
always the case. A session can be lost without loss of the
corresponding clientid-based locking state in the event of clientid
trunking, or when locking state is stored persistently but the reply
cache is not. See Section 8 for details.
In the event of server restart, in the absence of clientid trunking,
the following situations can arise:
* If neither the reply cache nor locking state is being stored
persistently both the session and clientid are lost and new ones
need to be established to continue operation.
* If the reply cache is persistent, it is possible that existing
locking state is available so the existing session id and clientid
can be tried going forward to determine if operation can be
continued with existing locking state or a new clientid needs to
be established and locks reclaimed.
* If the reply cache is not persistent, and the locking state is
available in persistent storage the session is lost and a new
session can be created for the existing clientid.
After an event like a server restart, the client may have lost its
connections. The client assumes for the moment that the session has
not been lost. It reconnects, and if it specified connection
association enforcement when the session was created, it invokes
BIND_CONN_TO_SESSION using the session ID. Otherwise, it invokes
SEQUENCE. If BIND_CONN_TO_SESSION or SEQUENCE returns
NFS4ERR_BADSESSION, the client knows the session is not available to
it when communicating with that network address. If the connection
survives session loss, then the next SEQUENCE operation the client
sends over the connection will get back NFS4ERR_BADSESSION. The
client again knows the session was lost.
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Here is one suggested algorithm for the client when it gets
NFS4ERR_BADSESSION. It is not obligatory in that, if a client does
not want to take advantage of such features as trunking, it may omit
parts of it. However, it is a useful example that draws attention to
various possible recovery issues:
1. If the client has other connections to other server network
addresses associated with the same session, attempt a COMPOUND
with a single operation, SEQUENCE, on each of the other
connections.
2. If the attempts succeed, the session is still alive, and this is
a strong indicator that the server's network address has moved.
The client might send an EXCHANGE_ID on the connection that
returned NFS4ERR_BADSESSION to see if there are opportunities for
client ID trunking (i.e., the same client ID and so_major_id
value are returned). The client might use DNS to see if the
moved network address was replaced with another, so that the
performance and availability benefits of session trunking can
continue.
3. If the SEQUENCE requests fail with NFS4ERR_BADSESSION, then the
session no longer exists on any of the server network addresses
for which the client has connections associated with that session
ID. It is possible that the session is still alive and available
on other network addresses. The client sends an EXCHANGE_ID on
all the connections to see if the server owner is still listening
on those network addresses. If the same server owner is returned
but a new client ID is returned, this is a strong indicator of a
server restart. If both the same server owner and same client ID
are returned, then this is a strong indication that the server
did delete the session, and the client will need to send a
CREATE_SESSION if it has no other sessions for that client ID.
If a different server owner is returned, the client can use DNS
to find other network addresses. If it does not, or if DNS does
not find any other addresses for the server, then the client will
be unable to provide NFSv4.1 service, and fatal errors should be
returned to processes that were using the server. If the client
is using a "mount" paradigm, unmounting the server is advised.
4. If the client knows of no other connections associated with the
session ID and server network addresses that are, or have been,
associated with the session ID, then the client can use DNS to
find other network addresses. If it does not, or if DNS does not
find any other addresses for the server, then the client will be
unable to provide NFSv4.1 service, and fatal errors should be
returned to processes that were using the server. If the client
is using a "mount" paradigm, unmounting the server is advised.
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If there is a reconfiguration event that results in the same network
address being assigned to servers where the eir_server_scope value is
different, it cannot be guaranteed that a session ID generated by the
first will be recognized as invalid by the first. Therefore, in
managing server reconfigurations among servers with different server
scope values, it is necessary to make sure that all clients have
disconnected from the first server before effecting the
reconfiguration. Nonetheless, clients should not assume that servers
will always adhere to this requirement; clients MUST be prepared to
deal with unexpected effects of server reconfigurations. Even where
a session ID is inappropriately recognized as valid, it is likely
either that the connection will not be recognized as valid or that a
sequence value for a slot will not be correct. Therefore, when a
client receives results indicating such unexpected errors, the use of
EXCHANGE_ID to determine the current server configuration is
RECOMMENDED.
A variation on the above is that after a server's network address
moves, there is no NFSv4.1 server listening, e.g., no listener on
port 2049. In this example, one of the following occur: the NFSv4
server returns NFS4ERR_MINOR_VERS_MISMATCH, the NFS server returns a
PROG_MISMATCH error, the RPC listener on 2049 returns PROG_UNVAIL, or
attempts to reconnect to the network address timeout. These SHOULD
be treated as equivalent to SEQUENCE returning NFS4ERR_BADSESSION for
these purposes.
When the client detects session loss, it needs to call CREATE_SESSION
to recover. Any non-idempotent operations that were in progress
might have been performed on the server at the time of session loss.
The client has no general way to recover from this.
Note that loss of session does not imply loss of byte-range lock,
open, delegation, or layout state because locks, opens, delegations,
and layouts are tied to the client ID and depend on the client ID,
not the session. Nor does loss of byte-range lock, open, delegation,
or layout state imply loss of session state, because the session
depends on the client ID; loss of client ID however does imply loss
of session, byte-range lock, open, delegation, and layout state. See
Section 13.4.2. A session can survive a server restart, but lock
recovery may still be needed.
It is possible that CREATE_SESSION will fail with
NFS4ERR_STALE_CLIENTID (e.g., the server restarts and does not
preserve client ID state). If so, the client needs to call
EXCHANGE_ID, followed by CREATE_SESSION.
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7.13.2. Events Requiring Server Action
The following events require server action to recover.
7.13.2.1. Client Crash and Restart
As described in Section 25.35, a restarted client sends EXCHANGE_ID
in such a way that it causes the server to delete any sessions it
had.
7.13.2.2. Client Crash with No Restart
If a client crashes and never comes back, it will never send
EXCHANGE_ID with its old client owner. Thus, the server has session
state that will never be used again. After an extended period of
time, and if the server has resource constraints, it MAY destroy the
old session as well as locking state.
7.13.2.3. Extended Network Partition
To the server, the extended network partition may be no different
from a client crash with no restart (see Section 7.13.2.2). Unless
the server can discern that there is a network partition, it is free
to treat the situation as if the client has crashed permanently.
7.13.2.4. Backchannel Connection Loss
If there were callback requests outstanding at the time of a
connection loss, then the server MUST retry the requests, as
described in Section 7.6.2. Note that it is not necessary to retry
requests over a connection with the same source network address or
the same destination network address as the lost connection. As long
as the session ID, slot ID, and sequence ID in the retry match that
of the original request, the callback target will recognize the
request as a retry even if it did see the request prior to
disconnect.
If the connection lost is the last one associated with the
backchannel, then the server MUST indicate that in the
sr_status_flags field of every SEQUENCE reply until the backchannel
is re-established. There are two situations, each of which uses
different status flags: no connectivity for the session's backchannel
and no connectivity for any session backchannel of the client. See
Section 25.46 for a description of the appropriate flags in
sr_status_flags.
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7.13.2.5. GSS Context Loss
The server SHOULD monitor when the number of RPCSEC_GSS handles
assigned to the backchannel reaches one, and when that one handle is
near expiry (i.e., between one and two periods of lease time), and
indicate so in the sr_status_flags field of all SEQUENCE replies.
The server MUST indicate when all of the backchannel's assigned
RPCSEC_GSS handles have expired via the sr_status_flags field of all
SEQUENCE replies.
7.14. Parallel NFS and Sessions
A client and server can potentially be a non-pNFS implementation, a
metadata server implementation, a data server implementation, or two
or three types of implementations. The EXCHGID4_FLAG_USE_NON_PNFS,
EXCHGID4_FLAG_USE_PNFS_MDS, and EXCHGID4_FLAG_USE_PNFS_DS flags (not
mutually exclusive) are passed in the EXCHANGE_ID arguments and
results to allow the client to indicate how it wants to use sessions
created under the client ID, and to allow the server to indicate how
it will allow the sessions to be used. See Section 20.5 for sessions
considerations regarding the pNFS files layout type.
8. Persistence
[Author Aside]: This is a new top-level section which is based on the
Persistence section previously within the discussion of Exactly-once
Semantics. Essentially, it deletes the feature described in
[RFC8881] which could never be implemented in that form and addresses
the need with a new feature having the same goals.
While file data and metadata are typically stored persistently and
are not affected by server restart, with the exception of certain
optimizations for writing data, there are two sorts of data not
normally stored persistently, that often are affected by server
restart. Since [RFC8881] did not address either of these in a way
that could be implemented, the entire area has been respecified for
reasons discussed in Section 8.1.
For each of these types of data, the protocol provides an OPTIONAL
feature whereby the server can provide persistent storage to
eliminate functional problems when the data is lost or to simplify
the process of reconstructing the data based on the client's
knowledge.
* Reply caches may be stored persistently, as described in
Section 8.2, allowing the same at-most-once semantics (often
called "EOS") provided by the session-based reply cache to be
maintained across server restarts.
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As discussed below, the server may provide a persistent reply
cache allowing EOS across server restarts or fully persistent
sessions that allow the use of existing sessions to be continued
across server restart.
* Per-client locking state may be stored persistently, as described
in Section 8.3, allowing clients to continue after server restart
without the delay caused by interposing a grace period during
which all new lock requests are to be rejected.
If per-client locking state is not stored persistently, a grace
period is provided to allow clients time to reclaim their locks.
When this period is needed, requests to obtain new locks (e.g.
when opening a file) are delayed until all clients have had a
chance to reclaim their locks.
Although the incremental cost of supporting lock persistence is
generally low enough that servers providing persistent sessions would
provide persistent locking state as well, these two features are
independent and the client cannot always assume lock persistence is
available when an associated session is persistent and successfully
recovered. For a discussion of how the client would be able to
determine what state has been stored persistently and continue
operation without unnecessary disruption, see Section 8.4
8.1. Need for Feature Respecification
The original material has been modified substantially and extended in
order address the three items listed below. As a result, the focus
of the section has shifted to include all elements relevant to
persistence across server failure, rather than dealing only with
reply cache issues.
* Eliminate elements of the description that made the feature
essentially unimplementable. These include overbroad requirements
for atomicity and the assumption that all requests needed to be
continued across server restart.
* Appropriately discuss lock persistence and its relation to reply
cache persistence and session persistence.
* Provide new material describing the process by which the client
finds out about the presence of persistence- related features in
the event of server restart.
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8.2. Persistence of Reply Cache
Since the reply cache is bounded, it is possible for the reply cache
to be maintained in persistent storage so that it can be made
available across server restarts. When the server undertakes to
provide this support when the session is created (see Section 25.36
for details), it is uncertain whether what will provided is either:
* Persistence of the reply cache only.
* Persistent of the session including its membership within the
clientid of which it is a part.
The replier needs to persist the following information if it agreed
to provide persistence for the session (when the session was created;
* The session ID.
* The slot table
This need to include the sequence ID and cached reply for each
slot.
* Information about the connection(s) used by the server with is
sufficient to determine whether a client attempting to connect
after a server Restart.
This sort of information can be used to provide either of the two
distinct sorts of session-based persistence. The server provides no
specific commitment to provide either of these, although, as
described in Section 8.4, the client will be able to determine which
form, if any, has actually been provided, and respond appropriately
In describing persistence-related semantics it will be helpful to
define the following two terms:
* An operation is said "reply-caching relevant" if it is either non-
idempotent, modifying, or is the final operation (including the
case of request termination because of an error) of a request that
is specifically requested to be cached (i.e., has a SEQUENCE
operation with sa_cachethis set to true).
* A request is said "reply-caching relevant" if it contains one or
more operations which are non-idempotent or modifying or it is
specifically requested to be cached (i.e., has a SEQUENCE
operation with sa_cachethis set to true).
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Whichever form of session-based persistence is provided by the
server, any requests the client retries after the server restarts
will return the results that are cached in the reply cache, However,
these two forms differ with regard to the handling of new requests
and the possible use of clientid-based persistence facilities:
* If only reply cache persistence is provided, any new requests will
fail with NFS4ERR_DEADSESSION being returned as the result of the
initial SEQUENCE operation.
Because there is no need to use the sequence id to order future
request the server does not need to update persistent storage, if
two successive requests using the same slot are both not reply-
caching relevant, although it does if one or both of the request
is reply-cache relevant.
* If session persistence is provided, the existing session can be
used after connection re-establishment to support the execution of
new requests so that the client will be able to continue just as
it would have if no session restart had occurred.
A persistent reply cache places certain demands on the server.
Although it is not it is not necessary to execute successive
operations within a COMPOUND atomically, the transfer of the results
of a set of operations and their installation in the persistent cache
must immediately follow the execution of any reply-cache relevant
operation so that it is impossible for operations to be executed or
have other visible effects while not appearing in persistent reply
cache.
If a client were to retry a sequence of operations that was issued to
the server, the only acceptable outcomes are:
* an indication that the request is still being processed.
* a cached reply reflecting the completion of the request,
* a cached reply reflecting the interruption of the request due to
server failure.
* an indication that the client ID or session has been lost
(indicating a catastrophic loss of the reply cache or a session
that has been deleted because the client failed to use the session
for an extended period of time).
The possibility exists of situations in which a server could fail and
restart in the middle of a COMPOUND procedure that contains one or
more non-idempotent or idempotent-but-modifying operations. If the
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server allows COMPOUND procedures to be continued after server
failure, it creates significantly greater challenges for the
execution of such requests and the atomic placement of results in the
reply cache.
When a server providing a persistent reply cache does not continue a
COMPOUND procedure that was interrupted by a server failure, the
error NFS4ERR_DEADSESSION is returned on the last operation which was
executed.
8.3. Persistence of Locking State
Servers may make locking state available across a server restart in a
number of ways including the following:
* Data related to the existence of locks and their corresponding
characteristics can be stored in persistent RAM and then used
after restart if the address of that storage can be reliably
obtained after restart.
* The storage of locking-related state can be integrated with the
file system by treating locking state in the same fashion used for
other metadata.
* Locking state information may be periodically logged to block-
based low-latency persistent storage with logging of individual
updates.
Although the details will vary with the means of providing
persistence that is adopted, it is important that locking state made
available across the server restart be consistent with locking state
reflected in the results of requests made by clients.
The simplest part of this is to ensure that all locking state changes
are effectively made available persistently before returning to the
requester. In addition, when lock state additions or deletions are
reflected in the processing of other operations, the state changes
must be available persistently before allowing or denying some
operation done by another client. For example, when opens denying
write prevent file removal, granting such opens or doing
corresponding closes need to be reflected persistently before denying
or allowing corresponding file removal. Similar consideration apply
to doing IO when mandatory byte-range locks are supported
The following facts need to be kept in mind:
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* There is no commitment by the server to provide this persistence
and it may be dropped if for a particular client if unusual
situations make it advisable.
This decision is made separately for each client so that it is
possible there will be server restarts where some, but not all,
clients have persistent locking state available.
* While the fact that a reclaim on a reclaimable lock is part of the
locking state which is to be persistent, the client's state of
awareness of that need not be.
There is thus no need for the reclaiming client to inform the
server that it has completed specific individual reclaims after
receiving the response.
8.4. Client Handling of Server Failure When Persistence Can be Used
When server failure occurs, the connection to the client will be
disconnected and the client can then find out, as described below,
whether server failure has occurred and what steps are necessary to
continue use of the client with minimal disruption to those using the
client.
This process includes the potential use of a persistent reply cache,
as described in Section 8.5. The same process is followed depending
on whether the server provided only a persistent reply cache or full
session persistence.
If the server did not promise any session persistence, the client
instead immediately does an EXCHANGE_ID followed by a CREATE_SESSION.
On the other hand, if there was a possible use of a persistent reply
cache, the use of EXCHANGE_ID/CREATE_SESSION is conditional and only
happens if a new request has been completed with the error
NFS4ERR_STALECLIENTID.
In either case, the next step depends on whether the clientid is the
same as the one before the disconnection. If it is, then recovery is
complete and new requests can be issued. This could happen if there
were no server restart but also could if a combination of session-
based and clientid-based persistence allowed the server failure to be
dealt with essentially transparently.
In the case in which the clientid is different, the client need to
reclaim its locks, as described in Section 8.6.
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Even in the case in which lock persistence is available for a client,
it is still possible that attempts to obtain new locks will fail with
NFS4ERR_GRACE if other clients do not have their locks made available
persistently.
8.5. Client Use of Session-based Persistence
After the connection to the server is re-established, the server will
try to re-establish the connection, as the connection breakage
occurred at a lower layer, without server restart. Although it is
theoretically possible for an intermediary to hide such a
disconnection, it would cause problems if it were to do so and the
client had no knowledge of the server failure The discussion here
assumes that no such disconnection-hiding implementation is in effect
After re-establishing the connection to the server, the client would
initially attempt to continue use of the session, since it has no
knowledge of whether the disconnection was the result of a server
restart. If persistence was not requested when creating the session
or the server indicated it was not present, then the client can
legitimately conclude that EOS semantics was not available across
server restart and needs to operate in that environment.
The continued use of the existing session could include both retries
of requests issued before the disconnection and issuing new requests.
As a result, the discussion below will deal with both type of
requests. Given that context, one needs to note the following:
* Whether a given request is a retry or a new one may be judged
differently by the client and the server.
While it is virtually certain that a new request issued by the
client will be perceived as such by the server, the reverse is not
the case. Retries issued by the client might be perceived as new
requests, if the original requests was lost before it was executed
or its existence was noted in persistent storage.
* Although it might be desirable for a client to obtain information
about existing requests before issuing a new one, the discussion
will not assume that clients take steps to prevent new requests
from being issued.
Since retries, as perceived by the client, may be considered as
new requests by the server, the prevention of new requests by the
client does not ensure that the server will not see and respond to
such requests.
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After re-establishing the connection, the client will be able to
issue requests, including retries of requests already issued before
the disconnection occurred. These retries need to be issued since
there is no way the results of these requests could be communicated
back to the client in the absence of a retry since the connection on
which it was received no longer exists.
When responses to these requests are received, what is to be done
depends primarily about the error, if any, associated with the
response:
* In all the cases except the two special error codes noted in the
bulleted items below, including receiving no error, the client can
conclude that the request was executed to completion as reflected
in the response. By design, the client is not aware of whether
the execution occurred before or after the serve restart, or
whether a server restart, in fact, occurred. However, if
persistence was requested when the session was created and the
server indicated it was present, the client can assume that the
request was executed exactly once with the result reflected in the
response.
When this is the result that is returned for new requests, it can
be because the server has provided full session persistence or
because no server restart has occurred. In the former case, it
must be true that the server has provided persistent storge of
locking state for the d associated clientid since, if it had not,
the error NFS4ERR_STALECLIENTID would have been returned.
* In the case that NFS4ERR_DEADSESSION is returned on the SEQUENCE
operation, the most likely cause is that the request was, from the
server's point of view, a new request and that session persistence
was not provided by the server. In this case, the current request
should be deferred until the results of all retried requests known
to the client have been resolved. Others that are considered new
by the server also need to be deferred until are reply cache
information is obtained.
In the case that NFS4ERR_DEADSESSION is returned on another
operation, the request is one that was discontinued as a result of
server restart. It is most likely that the request was one that
contained more than one non-idempotent or modifying operations,
with the server failing after one had been completed but before
later operations were started. In this case the client has been
informed of a partially complete request and needs to issue a new
request to include the operations that were not performed as part
of the initial request.
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* In the case that the error NFS4ERR_STALECLIENTID is returned, the
server has recognized a new request but was unable to continue its
execution because the locking information it would use has been
destroyed as part of the server restart. This can occur if no
persistence was provided for the session, if the persistence was
limited to the reply cache or if there was session persistence and
client locking state was not maintained persistently.
In this case lock recovery will be required but it will need to be
delayed until all requests that were issued before the
disconnection have been marked completed using the persisted reply
cache.
Once the existing pending requests are disposed of, the client can
proceed to doing new requests, although it might have to do lock
recovery first. This can occur after a persistent reply cache is
used to provide EOS or after it is found that there is no session
persistence provided by the server.
8.6. Client Use of Clientid-based Persistence
At this point, lock recovery needs to begin if a new request is
processed and completes returning the error NFS4ERR_STALECLIENTID.
If no new requests have been issued at this point, the client can
issue a request consisting only of a SEQUENCE operation to provide a
test. If NFS4ERR_STALECLIENTID is not returned then the client will
assume either that there has been no server restart or thar server
restart as been accompanied with the recovery of locking state for
the current clientid. Otherwise, lock recovery can be done as part
of a server-provided grace period. The following three steps need to
be taken:
When lock recovery is necessary, the client need to inform the new
server of the existence of its locks before using stateids it
obtained before the server restart. This process is referred to as
reclaiming the client's locks, which is accomplished using the method
listed below, depending on the type of lock to be reclaimed.
* Opens can generally be reclaimed by doing an OPEN with the claim
type CLAIM_PREVIOUS.
This includes the case of opens associated with delegation. For
details, see Section 15.2.1,
There is no specific way to reclaim delegations that have no
associated open. In such cases, the client can open the file
asking for an associated delegation, and return it immediately
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* To reclaim byte-range locks, a LOCK operation with the reclaim
parameter set to true is used.
The associated open will need to be reclaimed first.
* There is no provision regarding reclaiming of layouts and thus no
way to obtain them during a grace period.
As a result, in case in which locking state is not made available
by the server across a server failure, use of the data server is
not immediately available and the client is best off doing IO
through the MDS until obtaining needed layouts once the rest of
lock reclamation is complete.
Once all reclaimable locks have been reclaimed, the client needs to
do a global RECLAIM_COMPLETE to indicate that process is complete.
The is necessary to allow new locks to be obtained. However, even
after this done, such requests might still be rejected with
NFS4ERR_GRACE if other clients have not completed their lock
reclamations.
9. Protocol Constants and Data Types
The syntax and semantics to describe the data types of the NFSv4.1
protocol are defined in the XDR ([RFC4506]) and RPC ([RFC5531])
documents. The next sections build upon the XDR data types to define
constants, types, and structures specific to this protocol. The full
list of XDR data types is in RFCTBD30.
9.1. Basic Constants
const NFS4_FHSIZE = 128;
const NFS4_VERIFIER_SIZE = 8;
const NFS4_OPAQUE_LIMIT = 1024;
const NFS4_SESSIONID_SIZE = 16;
const NFS4_INT64_MAX = 0x7fffffffffffffff;
const NFS4_UINT64_MAX = 0xffffffffffffffff;
const NFS4_INT32_MAX = 0x7fffffff;
const NFS4_UINT32_MAX = 0xffffffff;
const NFS4_MAXFILELEN = 0xffffffffffffffff;
const NFS4_MAXFILEOFF = 0xfffffffffffffffe;
Except where noted, all these constants are defined in bytes.
* NFS4_FHSIZE is the maximum size of a filehandle.
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* NFS4_VERIFIER_SIZE is the fixed size of a verifier.
* NFS4_OPAQUE_LIMIT is the maximum size of certain opaque
information.
* NFS4_SESSIONID_SIZE is the fixed size of a session identifier.
* NFS4_INT64_MAX is the maximum value of a signed 64-bit integer.
* NFS4_UINT64_MAX is the maximum value of an unsigned 64-bit
integer.
* NFS4_INT32_MAX is the maximum value of a signed 32-bit integer.
* NFS4_UINT32_MAX is the maximum value of an unsigned 32-bit
integer.
* NFS4_MAXFILELEN is the maximum length of a regular file.
* NFS4_MAXFILEOFF is the maximum offset into a regular file.
9.2. Basic Data Types
These are the base NFSv4.1 data types.
+===============+==================================================+
| Data Type | Definition |
+===============+==================================================+
| int32_t | typedef int int32_t; |
+---------------+--------------------------------------------------+
| uint32_t | typedef unsigned int uint32_t; |
+---------------+--------------------------------------------------+
| int64_t | typedef hyper int64_t; |
+---------------+--------------------------------------------------+
| uint64_t | typedef unsigned hyper uint64_t; |
+---------------+--------------------------------------------------+
| attrlist4 | typedef opaque attrlist4<>; |
| | |
| | Used for file/directory attributes. |
+---------------+--------------------------------------------------+
| bitmap4 | typedef uint32_t bitmap4<>; |
| | |
| | Used in attribute array encoding. |
+---------------+--------------------------------------------------+
| changeid4 | typedef uint64_t changeid4; |
| | |
| | Used in the definition of change_info4. |
+---------------+--------------------------------------------------+
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| clientid4 | typedef uint64_t clientid4; |
| | |
| | Shorthand reference to client identification. |
+---------------+--------------------------------------------------+
| count4 | typedef uint32_t count4; |
| | |
| | Various count parameters (READ, WRITE, COMMIT). |
+---------------+--------------------------------------------------+
| length4 | typedef uint64_t length4; |
| | |
| | The length of a byte-range within a file. |
+---------------+--------------------------------------------------+
| mode4 | typedef uint32_t mode4; |
| | |
| | Mode attribute data type. |
+---------------+--------------------------------------------------+
| nfs_cookie4 | typedef uint64_t nfs_cookie4; |
| | |
| | Opaque cookie value for READDIR. |
+---------------+--------------------------------------------------+
| nfs_fh4 | typedef opaque nfs_fh4<NFS4_FHSIZE>; |
| | |
| | Filehandle definition. |
+---------------+--------------------------------------------------+
| nfs_ftype4 | enum nfs_ftype4; |
| | |
| | Various defined file types. |
+---------------+--------------------------------------------------+
| nfsstat4 | enum nfsstat4; |
| | |
| | Return value for operations. |
+---------------+--------------------------------------------------+
| offset4 | typedef uint64_t offset4; |
| | |
| | Various offset designations (READ, WRITE, LOCK, |
| | COMMIT). |
+---------------+--------------------------------------------------+
| qop4 | typedef uint32_t qop4; |
| | |
| | Quality of protection designation in SECINFO. |
+---------------+--------------------------------------------------+
| sec_oid4 | typedef opaque sec_oid4<>; |
| | |
| | Security Object Identifier. The sec_oid4 data |
| | type is not really opaque. Instead, it contains |
| | an ASN.1 OBJECT IDENTIFIER as used by GSS-API in |
| | the mech_type argument to GSS_Init_sec_context. |
| | See [RFC2743] for details. |
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+---------------+--------------------------------------------------+
| sequenceid4 | typedef uint32_t sequenceid4; |
| | |
| | Sequence number used for various session |
| | operations (EXCHANGE_ID, CREATE_SESSION, |
| | SEQUENCE, CB_SEQUENCE). |
+---------------+--------------------------------------------------+
| seqid4 | typedef uint32_t seqid4; |
| | |
| | Sequence identifier used for locking. |
+---------------+--------------------------------------------------+
| sessionid4 | typedef opaque sessionid4[NFS4_SESSIONID_SIZE]; |
| | |
| | Session identifier. |
+---------------+--------------------------------------------------+
| slotid4 | typedef uint32_t slotid4; |
| | |
| | Sequencing artifact for various session |
| | operations (SEQUENCE, CB_SEQUENCE). |
+---------------+--------------------------------------------------+
| utf8string | typedef opaque utf8string<>; |
| | |
| | UTF-8 encoding for strings. |
+---------------+--------------------------------------------------+
| utf8str_cis | typedef utf8string utf8str_cis; |
| | |
| | Case-insensitive UTF-8 string. |
+---------------+--------------------------------------------------+
| utf8str_cs | typedef utf8string utf8str_cs; |
| | |
| | Case-sensitive UTF-8 string. |
+---------------+--------------------------------------------------+
| utf8str_mixed | typedef utf8string utf8str_mixed; |
| | |
| | UTF-8 strings with a domain or host prefix and |
| | an server or file name suffix. Domains can be |
| | internationalized as described in |
| | [I-D.ietf-nfsv4-internationalization]. |
+---------------+--------------------------------------------------+
| utf8pref | typedef opaque utf8pref<>; |
| | |
| | String for which UTF-8 encoding is preferred, |
| | although other encodings can be used, |
+---------------+--------------------------------------------------+
| component4 | typedef utf8pref component4; |
| | |
| | Represents pathname components, which may be |
| | either encoded using UTF-8 or nor, with use of |
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| | UTF-8 needed to support normalization and case- |
| | insensitivity. |
+---------------+--------------------------------------------------+
| linktext4 | typedef opaque linktext4<> |
| | |
| | Symbolic link contents ("symbolic link" is |
| | defined in an Open Group [symlink] standard). |
+---------------+--------------------------------------------------+
| pathname4 | typedef component4 pathname4<>; |
| | |
| | Represents pathname for fs_locations. |
+---------------+--------------------------------------------------+
| verifier4 | typedef opaque verifier4[NFS4_VERIFIER_SIZE]; |
| | |
| | Verifier used for various operations (COMMIT, |
| | CREATE, EXCHANGE_ID, OPEN, READDIR, WRITE) |
| | NFS4_VERIFIER_SIZE is defined as 8. |
+---------------+--------------------------------------------------+
Table 1
End of Base Data Types
9.3. Structured Data Types
9.3.1. nfstime4
struct nfstime4 {
int64_t seconds;
uint32_t nseconds;
};
The nfstime4 data type gives the number of seconds and nanoseconds
since midnight or zero hour January 1, 1970 Coordinated Universal
Time (UTC). Values greater than zero for the seconds field denote
dates after the zero hour January 1, 1970. Values less than zero for
the seconds field denote dates before the zero hour January 1, 1970.
In both cases, the nseconds field is to be added to the seconds field
for the final time representation. For example, if the time to be
represented is one-half second before zero hour January 1, 1970, the
seconds field would have a value of negative one (-1) and the
nseconds field would have a value of one-half second (500000000).
Values greater than 999,999,999 for nseconds are invalid.
This data type is used to pass time and date information. A server
converts to and from its local representation of time when processing
time values, preserving as much accuracy as possible. If the
precision of timestamps stored for a file system object is less than
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defined, loss of precision can occur. An adjunct time maintenance
protocol is RECOMMENDED to reduce skew between client and server
times.
9.3.2. time_how4
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
9.3.3. settime4
union settime4 switch (time_how4 set_it) {
case SET_TO_CLIENT_TIME4:
nfstime4 time;
default:
void;
};
The time_how4 and settime4 data types are used for setting timestamps
in file object attributes. If set_it is SET_TO_SERVER_TIME4, then
the server uses its local representation of time for the time value.
9.3.4. specdata4
struct specdata4 {
uint32_t specdata1; /* major device number */
uint32_t specdata2; /* minor device number */
};
This data type represents the device numbers for the device file
types NF4CHR and NF4BLK.
9.3.5. fsid4
struct fsid4 {
uint64_t major;
uint64_t minor;
};
9.3.6. change_policy4
struct change_policy4 {
uint64_t cp_major;
uint64_t cp_minor;
};
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The change_policy4 data type is used for the change_policy OPTIONAL
attribute. It provides change sequencing indication analogous to the
change attribute. To enable the server to present a value valid
across server re-initialization without requiring persistent storage,
two 64-bit quantities are used, allowing one to be a server instance
ID and the second to be incremented non-persistently, within a given
server instance.
9.3.7. fattr4
struct fattr4 {
bitmap4 attrmask;
attrlist4 attr_vals;
};
The fattr4 data type is used to represent sets of protocol-defined
attributes.
The bitmap is a counted array of 32-bit integers used to contain bit
values. The position of the integer in the array that contains bit n
can be computed from the expression (n / 32), and its bit within that
integer is (n mod 32).
0 1
+-----------+-----------+-----------+--
| count | 31 .. 0 | 63 .. 32 |
+-----------+-----------+-----------+--
9.3.8. change_info4
struct change_info4 {
bool atomic;
changeid4 before;
changeid4 after;
};
This data type is used with the CREATE, LINK, OPEN, REMOVE, and
RENAME operations to let the client know the value of the change
attribute for the directory in which the target file system object
resides.
9.3.9. netaddr4
struct netaddr4 {
/* see struct rpcb in RFC 1833 */
string na_r_netid<>; /* network id */
string na_r_addr<>; /* universal address */
};
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The netaddr4 data type is used to identify network transport
endpoints. The na_r_netid and na_r_addr fields respectively contain
a netid and uaddr. The netid and uaddr concepts are defined in
[RFC5665]. The netid and uaddr formats for TCP over IPv4 and TCP
over IPv6 are defined in [RFC5665], specifically Tables 2 and 3 and
in Sections 5.2.3.3 and 5.2.3.4.
9.3.10. state_owner4
struct state_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
typedef state_owner4 open_owner4;
typedef state_owner4 lock_owner4;
The state_owner4 data type is the base type for the open_owner4
(Section 9.3.10.1) and lock_owner4 (Section 9.3.10.2).
9.3.10.1. open_owner4
This data type is used to identify the owner of OPEN state.
9.3.10.2. lock_owner4
This structure is used to identify the owner of byte-range locking
state.
9.3.11. open_to_lock_owner4
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
This data type is used for the first LOCK operation done for an
open_owner4. It provides both the open_stateid and lock_owner, such
that the transition is made from a valid open_stateid sequence to
that of the new lock_stateid sequence. Using this mechanism avoids
the confirmation of the lock_owner/lock_seqid pair since it is tied
to established state in the form of the open_stateid/open_seqid.
9.3.12. stateid4
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struct stateid4 {
uint32_t seqid;
opaque other[12];
};
This data type is used for the various state sharing mechanisms
between the client and server. The client never modifies a value of
data type stateid. The starting value of the "seqid" field is
undefined. The server is required to increment the "seqid" field by
one at each transition of the stateid. This is important since the
client will inspect the seqid in OPEN stateids to determine the order
of OPEN processing done by the server.
9.3.13. layouttype4
enum layouttype4 {
LAYOUT4_NFSV4_1_FILES = 0x1,
LAYOUT4_OSD2_OBJECTS = 0x2,
LAYOUT4_BLOCK_VOLUME = 0x3
};
This data type indicates what type of layout is being used. The file
server advertises the layout types it supports through the
fs_layout_type file system attribute (Section 11.16.1). A client
asks for layouts of a particular type in LAYOUTGET, and processes
those layouts using layout-type-specific logic.
The layouttype4 data type is 32 bits in length. The range
represented by the layout type is split into three parts. Type 0x0
is reserved. Types within the range 0x00000001-0x7FFFFFFF are
globally unique and are assigned according to the description in
Section 29.5; they are maintained by IANA. Types within the range
0x80000000-0xFFFFFFFF are site specific and for private use only.
The LAYOUT4_NFSV4_1_FILES enumeration specifies that the NFSv4.1 file
layout type, as defined in Section 20, is to be used. The
LAYOUT4_OSD2_OBJECTS enumeration specifies that the object layout, as
defined in [RFC5664], is to be used. Similarly, the
LAYOUT4_BLOCK_VOLUME enumeration specifies that the block/volume
layout, as defined in [RFC5663], is to be used.
9.3.14. deviceid4
const NFS4_DEVICEID4_SIZE = 16;
typedef opaque deviceid4[NFS4_DEVICEID4_SIZE];
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Layout information includes device IDs that specify a storage device
through a compact handle. Addressing and type information is
obtained with the GETDEVICEINFO operation. Device IDs are not
guaranteed to be valid across metadata server restarts. A device ID
is unique per client ID and layout type. See Section 18.4.9 for more
details.
9.3.15. device_addr4
struct device_addr4 {
layouttype4 da_layout_type;
opaque da_addr_body<>;
};
The device address is used to set up a communication channel with the
storage device. Different layout types will require different data
types to define how they communicate with storage devices. The
nominally opaque da_addr_body field is interpreted based on the
specified da_layout_type field. As required by Section 19.1.2, the
layout type specification provides the actual data within this field.
This document defines the device address for the NFSv4.1 file layout
(See Section 20.7.2), which identifies a storage device by network IP
address and port number. Device types for other layout types are
defined by their respective layout specifications.
9.3.16. layout_content4
struct layout_content4 {
layouttype4 loc_type;
opaque loc_body<>;
};
The loc_body field is interpreted based on the layout type
(loc_type). This document defines the loc_body for the NFSv4.1 file
layout type; see Section 20.7 for its definition.
9.3.17. layout4
struct layout4 {
offset4 lo_offset;
length4 lo_length;
layoutiomode4 lo_iomode;
layout_content4 lo_content;
};
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The layout4 data type defines a layout for a file. The layout type
specific data is opaque within lo_content. Since layouts are sub-
dividable, the offset and length together with the file's filehandle,
the client ID, iomode, and layout type identify the layout.
9.3.18. layoutupdate4
struct layoutupdate4 {
layouttype4 lou_type;
opaque lou_body<>;
};
The layoutupdate4 data type is used by the client to return updated
layout information to the metadata server via the LAYOUTCOMMIT
(Section 25.42) operation. This data type provides a channel to pass
layout-type-specific information (in field lou_body) back to the
metadata server. The actual contents of the nominally opaque field
lou_body is the responsibility of the layout type specification for
lou_type. See Section 19.1.8 for details about how this is used by
LAYOUTCOMMIT for individual layout type. For example, for the block/
volume layout type, this could include the list of reserved blocks
that were written.
9.3.19. layouthint4
struct layouthint4 {
layouttype4 loh_type;
opaque loh_body<>;
};
The layouthint4 data type is used by the client to pass in a hint
about the type of layout it would like created for a particular file.
It is the data type specified by the layout_hint attribute described
in Section 11.16.4. The metadata server may ignore the hint or may
selectively ignore fields within the hint. This hint should be
provided at create time as part of the initial attributes within
OPEN. The actual contents loh_body field is specific to the type of
layout (loh_type) and is described by the layout type specification.
9.3.20. layoutiomode4
enum layoutiomode4 {
LAYOUTIOMODE4_READ = 1,
LAYOUTIOMODE4_RW = 2,
LAYOUTIOMODE4_ANY = 3
};
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The iomode specifies whether the client intends to just read or both
read and write the data represented by the layout. While the
LAYOUTIOMODE4_ANY iomode MUST NOT be used in the arguments to the
LAYOUTGET operation, it MAY be used in the arguments to the
LAYOUTRETURN and CB_LAYOUTRECALL operations. The LAYOUTIOMODE4_ANY
iomode specifies that layouts pertaining to both LAYOUTIOMODE4_READ
and LAYOUTIOMODE4_RW iomodes are being returned or recalled,
respectively. The metadata server's use of the iomode may depend on
the layout type being used. The storage devices MAY validate I/O
accesses against the iomode and reject invalid accesses.
9.3.21. nfs_impl_id4
struct nfs_impl_id4 {
utf8str_cis nii_domain;
utf8str_cs nii_name;
nfstime4 nii_date;
};
This data type is used to identify client and server implementation
details. The nii_domain field is the DNS domain name with which the
implementer is associated. The nii_name field is the product name of
the implementation and is completely free form. It is RECOMMENDED
that the nii_name be used to distinguish machine architecture,
machine platforms, revisions, versions, and patch levels. The
nii_date field is the timestamp of when the software instance was
published or built.
9.3.22. threshold_item4
struct threshold_item4 {
layouttype4 thi_layout_type;
bitmap4 thi_hintset;
opaque thi_hintlist<>;
};
This data type contains a list of hints specific to a layout type for
helping the client determine when it should send I/O directly through
the metadata server versus the storage devices. The data type
consists of the layout type (thi_layout_type), a bitmap (thi_hintset)
describing the set of hints supported by the server (they may differ
based on the layout type), and a list of hints (thi_hintlist) whose
content is determined by the hintset bitmap. See the mdsthreshold
attribute for more details.
The thi_hintset field is a bitmap of the following values:
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+=========================+===+=========+===========================+
| name | # | Data | Description |
| | | Type | |
+=========================+===+=========+===========================+
| threshold4_read_size | 0 | length4 | If a file's length is |
| | | | less than the value of |
| | | | threshold4_read_size, |
| | | | then it is RECOMMENDED |
| | | | that the client read |
| | | | from the file via the |
| | | | MDS and not a storage |
| | | | device. |
+-------------------------+---+---------+---------------------------+
| threshold4_write_size | 1 | length4 | If a file's length is |
| | | | less than the value of |
| | | | threshold4_write_size, |
| | | | then it is RECOMMENDED |
| | | | that the client write |
| | | | to the file via the |
| | | | MDS and not a storage |
| | | | device. |
+-------------------------+---+---------+---------------------------+
| threshold4_read_iosize | 2 | length4 | For read I/O sizes |
| | | | below this threshold, |
| | | | it is RECOMMENDED that |
| | | | the client read data |
| | | | using the MDS. |
+-------------------------+---+---------+---------------------------+
| threshold4_write_iosize | 3 | length4 | For write I/O sizes |
| | | | below this threshold, |
| | | | it is RECOMMENDED that |
| | | | the client write data |
| | | | using the MDS. |
+-------------------------+---+---------+---------------------------+
Table 2
9.3.23. mdsthreshold4
struct mdsthreshold4 {
threshold_item4 mth_hints<>;
};
This data type holds an array of elements of data type
threshold_item4, each of which is valid for a particular layout type.
An array is necessary because a server can support multiple layout
types for a single file.
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10. Filehandles
The filehandle in the NFS protocol is a per-server unique identifier
for a file system object. The contents of the filehandle are opaque
to the client. Therefore, the server is responsible for translating
the filehandle to an internal representation of the file system
object.
10.1. Obtaining the First Filehandle
The operations of the NFS protocol are defined in terms of one or
more filehandles. Therefore, the client needs a filehandle to
initiate communication with the server. With the NFSv3 protocol
([RFC1813]), there exists an ancillary protocol to obtain this first
filehandle. The MOUNT protocol, RPC program number 100005, provides
the mechanism of translating a string-based file system pathname to a
filehandle, which can then be used by the NFS protocols.
The MOUNT protocol has deficiencies in the area of security and use
via firewalls. This is one reason that the use of the public
filehandle was introduced in [RFC2054] and [RFC2055]. With the use
of the public filehandle in combination with the LOOKUP operation in
the NFSv3 protocol, it has been demonstrated that the MOUNT protocol
is unnecessary for viable interaction between NFS client and server.
Therefore, the NFSv4.1 protocol will not use an ancillary protocol
for translation from string-based pathnames to a filehandle. Two
special filehandles will be used as starting points for the NFS
client.
10.1.1. Root Filehandle
The first of the special filehandles is the ROOT filehandle. The
ROOT filehandle is the "conceptual" root of the file system namespace
at the NFS server. The client uses or starts with the ROOT
filehandle by employing the PUTROOTFH operation. The PUTROOTFH
operation instructs the server to set the "current" filehandle to the
ROOT of the server's file tree. Once this PUTROOTFH operation is
used, the client can then traverse the entirety of the server's file
tree with the LOOKUP operation. A complete discussion of the server
namespace is in Section 12.
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10.1.2. Public Filehandle
The second special filehandle is the PUBLIC filehandle. Unlike the
ROOT filehandle, the PUBLIC filehandle may be bound or represent an
arbitrary file system object at the server. The server is
responsible for this binding. It may be that the PUBLIC filehandle
and the ROOT filehandle refer to the same file system object.
However, it is up to the administrative software at the server and
the policies of the server administrator to define the binding of the
PUBLIC filehandle and server file system object. The client may not
make any assumptions about this binding. The client uses the PUBLIC
filehandle via the PUTPUBFH operation.
10.2. Filehandle Types
In the NFSv3 protocol, there was one type of filehandle with a single
set of semantics. This type of filehandle is termed "persistent" in
NFSv4.1. The semantics of a persistent filehandle remain the same as
before. A new type of filehandle introduced in NFSv4.1 is the
"volatile" filehandle, which attempts to accommodate certain server
environments.
The volatile filehandle type was introduced to address server
functionality or implementation issues that make correct
implementation of a persistent filehandle infeasible. Some server
environments do not provide a file-system-level invariant that can be
used to construct a persistent filehandle. The underlying server
file system may not provide the invariant or the server's file system
programming interfaces may not provide access to the needed
invariant. Volatile filehandles may ease the implementation of
server functionality such as hierarchical storage management or file
system reorganization or migration. However, the volatile filehandle
increases the implementation burden for the client.
Since the client will need to handle persistent and volatile
filehandles differently, a file attribute is defined that may be used
by the client to determine the filehandle types being returned by the
server.
10.2.1. General Properties of a Filehandle
The filehandle contains all the information the server needs to
distinguish an individual file. To the client, the filehandle is
opaque. The client stores filehandles for use in a later request and
can compare two filehandles from the same server for equality by
doing a byte-by-byte comparison. However, the client MUST NOT
otherwise interpret the contents of filehandles. If two filehandles
from the same server are equal, they MUST refer to the same file.
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Servers SHOULD try to maintain a one-to-one correspondence between
filehandles and files, but this is not required. Clients MUST use
filehandle comparisons only to improve performance, not for correct
behavior. All clients need to be prepared for situations in which it
cannot be determined whether two filehandles denote the same object
and in such cases, avoid making invalid assumptions that might cause
incorrect behavior. Further discussion of filehandle and attribute
comparison in the context of data caching is presented in
Section 15.3.5.
As an example, in the case that two different pathnames when
traversed at the server terminate at the same file system object, the
server SHOULD return the same filehandle for each path. This can
occur if a hard link (See [hardlink]) is used to create two file
names that refer to the same underlying file object and associated
data. For example, if paths /a/b/c and /a/d/c refer to the same
file, the server SHOULD return the same filehandle for both
pathnames' traversals.
10.2.2. Persistent Filehandle
A persistent filehandle is defined as having a fixed value for the
lifetime of the file system object to which it refers. Once the
server creates the filehandle for a file system object, the server
MUST accept the same filehandle for the object for the lifetime of
the object. If the server restarts, the NFS server MUST honor the
same filehandle value as it did in the server's previous
instantiation. Similarly, if the file system is migrated, the new
NFS server MUST honor the same filehandle as the old NFS server.
The persistent filehandle will be become stale or invalid when the
file system object is removed. When the server is presented with a
persistent filehandle that refers to a deleted object, it MUST return
an error of NFS4ERR_STALE. A filehandle may become stale when the
file system containing the object is no longer available. The file
system may become unavailable if it exists on removable media and the
media is no longer available at the server or the file system in
whole has been destroyed or the file system has simply been removed
from the server's namespace (i.e., unmounted in a UNIX environment).
10.2.3. Volatile Filehandle
A volatile filehandle does not share the same longevity
characteristics of a persistent filehandle. The server may determine
that a volatile filehandle is no longer valid at many different
points in time. If the server can definitively determine that a
volatile filehandle refers to an object that has been removed, the
server should return NFS4ERR_STALE to the client (as is the case for
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persistent filehandles). In all other cases where the server
determines that a volatile filehandle can no longer be used, it
should return an error of NFS4ERR_FHEXPIRED.
The REQUIRED attribute "fh_expire_type" is used by the client to
determine what type of filehandle the server is providing for a
particular file system. This attribute is a bitmask with the
following values:
FH4_PERSISTENT The value of FH4_PERSISTENT is used to indicate a
persistent filehandle, which is valid until the object is removed
from the file system. The server will not return
NFS4ERR_FHEXPIRED for this filehandle. FH4_PERSISTENT is defined
as a value in which none of the bits specified below are set.
FH4_VOLATILE_ANY The filehandle may expire at any time, except as
specifically excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).
FH4_NOEXPIRE_WITH_OPEN May only be set when FH4_VOLATILE_ANY is set.
If this bit is set, then the meaning of FH4_VOLATILE_ANY is
qualified to exclude any expiration of the filehandle when it is
open.
FH4_VOL_MIGRATION The filehandle will expire as a result of a file
system transition (migration or replication), in those cases in
which the continuity of filehandle use is not specified by handle
class information within the fs_locations_info attribute. When
this bit is set, clients without access to fs_locations_info
information should assume that filehandles will expire on file
system transitions.
FH4_VOL_RENAME The filehandle will expire during rename. This
includes a rename by the requesting client or a rename by any
other client. If FH4_VOL_ANY is set, FH4_VOL_RENAME is redundant.
Servers that provide volatile filehandles that can expire while open
require special care as regards handling of RENAMEs and REMOVEs.
This situation can arise if FH4_VOL_MIGRATION or FH4_VOL_RENAME is
set, if FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN is not
set, or if a non-read-only file system has a transition target in a
different handle class. In these cases, the server should deny a
RENAME or REMOVE that would affect an OPEN file of any of the
components leading to the OPEN file. In addition, the server should
deny all RENAME or REMOVE requests during the grace period, in order
to make sure that reclaims of files where filehandles may have
expired do not do a reclaim for the wrong file.
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Volatile filehandles are especially suitable for implementation of
the pseudo file systems used to bridge exports. See Section 12.5 for
a discussion of this.
10.3. One Method of Constructing a Volatile Filehandle
A volatile filehandle, while opaque to the client, could contain:
[volatile bit = 1 | server boot time | slot | generation number]
* slot is an index in the server volatile filehandle table
* generation number is the generation number for the table entry/
slot
When the client presents a volatile filehandle, the server makes the
following checks, which assume that the check for the volatile bit
has passed. If the server boot time is less than the current server
boot time, return NFS4ERR_FHEXPIRED. If slot is out of range, return
NFS4ERR_BADHANDLE. If the generation number does not match, return
NFS4ERR_FHEXPIRED.
When the server restarts, the table is gone (it is volatile).
If the volatile bit is 0, then it is a persistent filehandle with a
different structure following it.
10.4. Client Recovery from Filehandle Expiration
If possible, the client SHOULD recover from the receipt of an
NFS4ERR_FHEXPIRED error. The client must take on additional
responsibility so that it may prepare itself to recover from the
expiration of a volatile filehandle. If the server returns
persistent filehandles, the client does not need these additional
steps.
For volatile filehandles, most commonly the client will need to store
the component names leading up to and including the file system
object in question. With these names, the client should be able to
recover by finding a filehandle in the namespace that is still
available or by starting at the root of the server's file system
namespace.
If the expired filehandle refers to an object that has been removed
from the file system, obviously the client will not be able to
recover from the expired filehandle.
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It is also possible that the expired filehandle refers to a file that
has been renamed. If the file was renamed by another client, again
it is possible that the original client will not be able to recover.
However, in the case that the client itself is renaming the file and
the file is open, it is possible that the client may be able to
recover. The client can determine the new pathname based on the
processing of the rename request. The client can then regenerate the
new filehandle based on the new pathname. The client could also use
the COMPOUND procedure to construct a series of operations like:
RENAME A B
LOOKUP B
GETFH
Note that the COMPOUND procedure does not provide atomicity. This
example only reduces the overhead of recovering from an expired
filehandle.
11. File Attributes
To meet the requirements of extensibility and increased
interoperability with non-UNIX platforms, attributes are being
handled in a more flexible manner than NFSv3. The NFSv3 fattr3
structure consists of a fixed list of attributes some of which that
might not all be supported by some potential servers and includes
some attributes that not all clients have an interest in. The fattr3
structure and similar fixed structures cannot be extended as new
needs arise and provide no way to indicate non-support of particular
attributes. Within the NFSv4.1 protocol, the client is able to query
what attributes the server supports and construct requests that deal
only with those supported attributes (or a subset thereof). This
raises the issues, discussed in Sections 11.1 through 11.3 and 11.5
through 11.6, of determining how the non-support of particular
attributes is to be dealt with.
11.1. Categorization of File Attributes
In order to clarify the requirements for server support of particular
attributes, and to provide guidance for clients dealing with non-
support of particular attributes, all NFSv4.1 attributes are divided
into the groups listed below:
All of these attributes are accommodated in the NFSv4.1 protocol by a
specific, well-defined encoding and are identified by a number. They
are interrogated by setting a bit in the bit vector sent in a
GETATTR, request. The server response includes a bit vector to
indicate which attributes were returned in the response.
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The following attribute categories are defined:
* REQUIRED attributes, as discussed in Section 11.4.
* OPTIONAL attributes, as discussed in Section 11.5.
* Experimental attributes, as discussed in Section 11.6.
New attributes of any of these categories may be added to the NFSv4
protocol as part of a new minor version by publishing a Standards
Track RFC that allocates a new attribute number value and defines the
encoding for the attribute. In addition, new minor versions can move
attributes between categories or make formerly OPTIONAL and
Experimental attributes MANDATORY to NOT implement. Similarly,
OPTIONAL attributes may be added to an existing extensible version by
publishing a Standards Track RFC that allocates a new attribute
number value and defines the encoding for the attribute. See
[RFC8178] for further details
11.2. Changes in the Categorization of File Attributes
The categorization of file attributes appearing in this specification
differs from that previously published for a number of reasons:
* The description of the attributes for which support is not
REQUIRED no longer uses the RFC2119 keyword "RECOMMENDED" as this
is not in accord with the definition of that term in [RFC2119].
We now describe such attributes as OPTIONAL, leaving it to server
to decide which are worthy of support and to clients to decide
whether they wish to use servers on which they are not supported.
* The categorization of requirements/recommendation as to support
for authorization-related attributes is now the responsibility of
the NFSv4-wide security documents, to be derived from
[I-D.dnoveck-nfsv4-security] and [I-D.ietf-nfsv4-acls-update].
Currently, given the likely lack of agreement on the semantics of
ACLs, it is likely that acl would best be described as an
Experimental attribute. See Section 11.3 for further discussion.
As one illustration of the new approach to these matters, and its
differences from older approaches, let us consider the following
statement from Section 5.1 of [RFC8881]. Referring to the REQUIRED
attributes, it states:
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The client is expected to be able to function with an attribute
set limited to these attributes. With just the REQUIRED
attributes some client functionality may be impaired or limited in
some ways. In the case of servers not supporting the owner, mode,
or acl-related attributes, there would be no ability to provide
substantial security-related functionality.
This expectation was not a reasonable one when first formulated and
as the NFSv4 protocols have been developed, there have never been any
cases of it being realized. There is no reason to implement a server
without the minimal authorization-related attributes derived from
NFSv3 and no point in working to develop clients capable of
interoperating with it. There is no motivation for the working group
to devote any time to defining how such a combination is to operate
or for implementers to experiment to try to implement remote file
access without any meaningful authorization process.
Further, the above also seems to conflict with the following,
appearing in Section 5.2 of [RFC8881]:
It is expected that servers will support all attributes they
comfortably can and only fail to support attributes that are
difficult to support in their operating environments.
Together, these imply that there are operating environments in which
it difficult to support all of mode, owner, group, and acl
attributes. It is hard to believe that any such environments exist
or that there would be any point in implementing an NFSv4.1 server
using then, if they did exist.
11.3. Categorization of Authorization-related Attributes
This section provides an overview of the issues in involved in
appropriately categorizing the authorization-related attributes,
although the final categorization of these will appear in NFSv4-wide
security documents, expected to be based on
[I-D.dnoveck-nfsv4-security] and [I-D.ietf-nfsv4-acls-update].
Authorization-related attributes that are part of NFSv4.1 can be
divided into those connected to he POSIX-based authorization model
used in NFSv3 and those related to the use of ACLs to provide a more
flexible authorization model. Within the context of NFSv4.1, the
following should be noted:
* The attributes mode, owner, and owner_group need to be considered
REQUIRED, as they are in [I-D.dnoveck-nfsv4-security].
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This is despite the fact that previous specifications have
considered these attributes as OPTIONAL, although the word
"RECOMMENDED" was sometimes used. In any case, the new
categorization in [I-D.ietf-nfsv4-acls-update] has to be
considered dispositive both with regard to NFSv4.1 and other minor
versions.
* The attributes acl, sacl, and dacl, although designated as
OPTIONAL, have never been documented in a manner allowing
effective client-server interoperability, suggesting that they
would more appropriately be designated as "Experimental".
While it is possible that tightening of the specifications being
done in [I-D.dnoveck-nfsv4-security] and
[I-D.ietf-nfsv4-acls-update] as part of the rfc8881bis effort
might allow this to change, that is not yet assured
In any case, efforts to provide a path to interoperability will
continue and might affect this categorization in later minor
versions, even if NFSv4.1 is not affected. See
[I-D.ietf-nfsv4-acls-update] for details,
* The attribute aclsupport is appropriately designated as OPTIONAL,
as it is in [I-D.dnoveck-nfsv4-security].
11.4. REQUIRED Attributes
These MUST be supported by every NFSv4.1 client and server in order
to ensure a minimum level of interoperability. The server MUST store
and return these attributes when requested. A client may ask for the
value of any of these attributes to be returned by setting a bit in
the GETATTR request, and the server MUST return their value.
The client is expected to be able to function with an attribute set
limited to these attributes. With just the REQUIRED attributes some
client functionality may be unavailable or functionally limited .
11.5. OPTIONAL Attributes
These attributes are understood well enough to warrant support in the
NFSv4.1 protocol. However, they might not be supported on all
servers or used by all clients. A client may ask for any of these
attributes to be returned by setting a bit in the GETATTR request but
need to handle the case where the server does not return them. A
client MAY ask for the set of attributes the server supports within a
given file system and has no reason to request attributes the server
does not support. A server is REQUIRED to be deal with requests for
unsupported attributes by not returning values for them rather than
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by considering the request an error.
Previous versions of the NFSv4.1 specification [RFC5661] [RFC8881]
have described these attributes as "RECOMMENDED" even though that
description is not accord with [RFC2119]. The NFSv4.0 specification
[RFC7530] still uses "RECOMMENDED" although explicitly disclaiming
the assumption that the RFC2119 definition applies in this case. The
description of these attribute as OPTIONAL connects them
appropriately to provisions for protocol extension and minor
versioning in which attributes are to be treated as OPTIONAL.
11.6. Experimental Attributes
While the vast majority of attributes are, as described in
Section 11.5, "understood well enough to warrant support in the
NFSv4.1 protocol", it appears to be the case that, for several
attributes, that understanding was never properly recorded in
existing NFSv4.1 specification documents. While it might be possibly
to rectify that issue before eventual publication of this document,
the likely existence of multiple incompatible implementations of such
attributes make that unlikely
Although the existence of such attributes has never been acknowledged
before as part of the categorization of NFSv4 attributes.
Nevertheless, such attributes have existed in all NFSv4 minor
versions and the necessary clarification, if it occurs, is not likely
to be complete for some time.
While the intention has always been that attribute not be included in
Proposed Standards unless they are described adequately to allow
interoperable implementation to be developed. Despite that
intention, such attributes have been included in multiple minor
versions. Given the need to correct that situation, we need to be
clear about the issues that have led to these unfortunate situations,
so that we can, over time, address them.
11.7. Named Attributes
These attributes are not supported by direct encoding in the NFSv4
protocol but are accessed using string names rather than numbers and
each corresponds to an uninterpreted stream of bytes that is stored
in its own file system object. The namespace for these attributes
may be accessed by using the OPENATTR operation as described below.
The OPENATTR operation returns a filehandle for a "named attribute
directory", and further perusal and modification of the namespace may
be done using operations that work on more typical directories,
subject to restrictions discussed below. In particular, READDIR may
be used to get a list of such named attributes, and LOOKUP and OPEN
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may select a particular attribute. Creation of a new named attribute
can be accomplished using an OPEN specifying file creation.
OPENATTR takes a filehandle for the object and returns the filehandle
for the attribute directory. The filehandle for the named attributes
designates a directory object accessible by LOOKUP or READDIR and
contains files whose names identify the named attributes and whose
data bytes are the value of those attributes. For example:
+----------+-----------+---------------------------------+
| LOOKUP | "foo" | ; look up file |
+----------+-----------+---------------------------------+
| GETATTR | attrbits | |
+----------+-----------+---------------------------------+
| OPENATTR | | ; access foo's named attributes |
+----------+-----------+---------------------------------+
| LOOKUP | "x11icon" | ; look up specific attribute |
+----------+-----------+---------------------------------+
| READ | 0,4096 | ; read stream of bytes |
+----------+-----------+---------------------------------+
Table 3
Named attributes are intended for data needed by applications rather
than by NFS client implementations. NFS implementers who wish to
define new attributes need to specify them as OPTIONAL attributes
using the protocol extension facilities specified in [RFC8178].
Once an OPEN is done, named attributes may be examined and changed
using READ and WRITE operations referencing the filehandles and
stateids returned by OPEN.
Named attributes may have their own (non-named) attributes. Each of
these objects MUST have all of the REQUIRED attributes and may have
additional attributes which are not REQUIRED. However, the sets of
supported attributes for named attributes need not be, and typically
will not be, as large as that for other objects in that file system.
Nevertheless, the value of the supported_attrs attribute should
reflect the supported attributes for the file system and will not
reflect the restricted attribute sets for these special objects.
Named attributes and the named attribute directories can be the
target of delegations (in the case of the named attribute directory,
these will be directory delegations). However, since granting of
delegations is at the server's discretion, a server need not support
delegations on named attributes or on named attribute directories.
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Support for named attributes is OPTIONAL and clients need to be
prepared to deal with servers that do not support them. However,
clients are entitled to assume that if OPENATTR is supported, there
will be support for arbitrarily named attributes, rather than support
for a few specific names known to the server. If a server does
support named attributes, a client that is also able to handle them
should be able to copy a file's data and metadata with complete
transparency from one location to another since names allowed for
regular directory entries are expected to be valid for named
attribute names as well.
In NFSv4.1, the structure of named attribute directories is
restricted in a number of ways, in order to prevent the development
of non-interoperable implementations in which some servers support a
fully general hierarchical directory structure for named attributes
while others support a limited, non-hierarchal structure for named
attributes. In such a mixed environment, clients or applications
might come to depend on non-portable extensions. The restrictions
are:
* CREATE is not allowed in a named attribute directory. Thus, such
objects as symbolic links and special files are not allowed to be
named attributes. Further, directories may not be created in a
named attribute directory, so a hierarchical structure of named
attributes for a single object is not allowed.
* If OPENATTR is done on a named attribute directory or on a named
attribute, the server MUST return NFS4ERR_WRONG_TYPE.
* Doing a RENAME of a named attribute to a different named attribute
directory or to an ordinary (i.e., non-named-attribute) directory
is not allowed.
* Creating hard links between named attribute directories or between
named attribute directories and ordinary directories is not
allowed.
Names of attributes will not be controlled by this document or other
IETF Standards Track documents, beyond what is necessary to regulate
the names of files within directories to handle internationalization
and case-insensitivity. See Section 29.2 for further discussion.
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11.8. Classification of Attributes
Each of the protocol-defined attributes can be classified in one of
three categories: per server (i.e., the value of the attribute will
be the same for all file objects that share the same server owner;
see Section 5.6 for a definition of server owner), per file system
(i.e., the value of the attribute will be the same for some or all
file objects that share the same fsid attribute (Section 11.12.1.9)
and server owner), or per file system object. Note that it is
possible that some per file system attributes may vary within the
file system, depending on the value of the "homogeneous"
(Section 11.12.2.16) attribute. Note that the attributes
time_access_set and time_modify_set are not listed in this section
because they are write-only attributes corresponding to time_access
and time_modify, and are used in a special instance of SETATTR.
* The per-server attribute is:
lease_time
* The per-file system attributes are:
supported_attrs, suppattr_exclcreat, fh_expire_type,
link_support, symlink_support, unique_handles, aclsupport,
cansettime, case_insensitive, case_preserving,
chown_restricted, files_avail, files_free, files_total,
fs_locations, homogeneous, maxfilesize, maxname, maxread,
maxwrite, no_trunc, space_avail, space_free, space_total,
time_delta, change_policy, fs_status, fs_layout_type,
fs_locations_info, fs_charset_cap
* The per-file system object attributes are:
type, change, size, named_attr, fsid, rdattr_error, filehandle,
acl, archive, fileid, hidden, maxlink, mimetype, mode,
numlinks, owner, owner_group, rawdev, space_used, system,
time_access, time_backup, time_create, time_metadata,
time_modify, mounted_on_fileid, dir_notif_delay,
dirent_notif_delay, dacl, sacl, layout_type, layout_hint,
layout_blksize, layout_alignment, mdsthreshold, retention_get,
retention_set, retentevt_get, retentevt_set, retention_hold,
mode_set_masked
For quota_avail_hard, quota_avail_soft, and quota_used, see their
definitions below for the appropriate classification.
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11.9. Set-Only and Get-Only Attributes
Some of the protocol-defined attributes are set-only; i.e., they can
be set via SETATTR but not retrieved via GETATTR. Similarly, some
protocol-defined attributes are get-only; i.e., they can be retrieved
via GETATTR but not set via SETATTR. If a client attempts to set a
get-only attribute or get a set-only attributes, the server MUST
return NFS4ERR_INVAL.
11.10. REQUIRED Attributes - List and Definition References
The list of REQUIRED attributes appears in Table 4. The meaning of
the columns of the table are:
Name: The name of the attribute.
Id: The number assigned to the attribute. In the event of conflicts
between the number assigned here and in RFCTBD30, the latter is
likely authoritative, but should be resolved with Errata to this
document and/or RFCTBD30. See [errata] for the Errata process.
Data Type: The XDR data type of the attribute.
Acc: Access allowed to the attribute. R means read-only (GETATTR
may retrieve, SETATTR may not set). W means write-only (SETATTR
may set, GETATTR may not retrieve). R W means read/write (GETATTR
may retrieve, SETATTR may set).
Defined in: The section of this specification that describes the
attribute.
+====================+====+===============+=====+===================+
| Name | Id | Data Type | Acc | Defined in: |
+====================+====+===============+=====+===================+
| supported_attrs | 0 | bitmap4 | R | Section |
| | | | | 11.12.1.1 |
+--------------------+----+---------------+-----+-------------------+
| type | 1 | nfs_ftype4 | R | Section |
| | | | | 11.12.1.2 |
+--------------------+----+---------------+-----+-------------------+
| fh_expire_type | 2 | uint32_t | R | Section |
| | | | | 11.12.1.3 |
+--------------------+----+---------------+-----+-------------------+
| change | 3 | uint64_t | R | Section |
| | | | | 11.12.1.4 |
+--------------------+----+---------------+-----+-------------------+
| size | 4 | uint64_t | R W | Section |
| | | | | 11.12.1.5 |
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+--------------------+----+---------------+-----+-------------------+
| link_support | 5 | bool | R | Section |
| | | | | 11.12.1.6 |
+--------------------+----+---------------+-----+-------------------+
| symlink_support | 6 | bool | R | Section |
| | | | | 11.12.1.7 |
+--------------------+----+---------------+-----+-------------------+
| named_attr | 7 | bool | R | Section |
| | | | | 11.12.1.8 |
+--------------------+----+---------------+-----+-------------------+
| fsid | 8 | fsid4 | R | Section |
| | | | | 11.12.1.9 |
+--------------------+----+---------------+-----+-------------------+
| unique_handles | 9 | bool | R | Section |
| | | | | 11.12.1.10 |
+--------------------+----+---------------+-----+-------------------+
| lease_time | 10 | nfs_lease4 | R | Section |
| | | | | 11.12.1.11 |
+--------------------+----+---------------+-----+-------------------+
| rdattr_error | 11 | enum | R | Section |
| | | | | 11.12.1.12 |
+--------------------+----+---------------+-----+-------------------+
| filehandle | 19 | nfs_fh4 | R | Section |
| | | | | 11.12.1.13 |
+--------------------+----+---------------+-----+-------------------+
| mode | 33 | mode4 | R W | Section |
| | | | | 11.18 |
+--------------------+----+---------------+-----+-------------------+
| owner | 36 | utf8str_mixed | R W | Section |
| | | | | 11.18 |
+--------------------+----+---------------+-----+-------------------+
| owner_group | 37 | utf8str_mixed | R W | Section |
| | | | | 11.18 |
+--------------------+----+---------------+-----+-------------------+
| suppattr_exclcreat | 75 | bitmap4 | R | Section |
| | | | | 11.12.1.14 |
+--------------------+----+---------------+-----+-------------------+
Table 4
11.11. OPTIONAL Attributes - List and Definition References
The OPTIONAL attributes are defined in Table 5. The meanings of the
column headers are the same as Table 4; see Section 11.10 for the
meanings.
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+====================+====+====================+=====+=============+
| Name | Id | Data Type | Acc | Defined in: |
+====================+====+====================+=====+=============+
| acl | 12 | nfsace4<> | R W | Section |
| | | | | 11.18 |
+--------------------+----+--------------------+-----+-------------+
| aclsupport | 13 | uint32_t | R | Section |
| | | | | 11.18 |
+--------------------+----+--------------------+-----+-------------+
| archive | 14 | bool | R W | Section |
| | | | | 11.12.2.1 |
+--------------------+----+--------------------+-----+-------------+
| cansettime | 15 | bool | R | Section |
| | | | | 11.12.2.2 |
+--------------------+----+--------------------+-----+-------------+
| case_insensitive | 16 | bool | R | Section |
| | | | | 11.12.2.3 |
+--------------------+----+--------------------+-----+-------------+
| case_preserving | 17 | bool | R | Section |
| | | | | 11.12.2.4 |
+--------------------+----+--------------------+-----+-------------+
| change_policy | 60 | chg_policy4 | R | Section |
| | | | | 11.12.2.5 |
+--------------------+----+--------------------+-----+-------------+
| chown_restricted | 18 | bool | R | Section |
| | | | | 11.12.2.6 |
+--------------------+----+--------------------+-----+-------------+
| dacl | 58 | nfsacl41 | R W | Section |
| | | | | 11.18 |
+--------------------+----+--------------------+-----+-------------+
| dir_notif_delay | 56 | nfstime4 | R | Section |
| | | | | 11.15.1 |
+--------------------+----+--------------------+-----+-------------+
| dirent_notif_delay | 57 | nfstime4 | R | Section |
| | | | | 11.15.2 |
+--------------------+----+--------------------+-----+-------------+
| fileid | 20 | uint64_t | R | Section |
| | | | | 11.12.2.7 |
+--------------------+----+--------------------+-----+-------------+
| files_avail | 21 | uint64_t | R | Section |
| | | | | 11.12.2.8 |
+--------------------+----+--------------------+-----+-------------+
| files_free | 22 | uint64_t | R | Section |
| | | | | 11.12.2.9 |
+--------------------+----+--------------------+-----+-------------+
| files_total | 23 | uint64_t | R | Section |
| | | | | 11.12.2.10 |
+--------------------+----+--------------------+-----+-------------+
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| fs_charset_cap | 76 | uint32_t | R | Section |
| | | | | 11.12.2.11 |
+--------------------+----+--------------------+-----+-------------+
| fs_layout_type | 62 | layouttype4<> | R | Section |
| | | | | 11.16.1 |
+--------------------+----+--------------------+-----+-------------+
| fs_locations | 24 | fs_locations | R | Section |
| | | | | 11.12.2.12 |
+--------------------+----+--------------------+-----+-------------+
| fs_locations_info | 67 | fs_locations_info4 | R | Section |
| | | | | 11.12.2.13 |
+--------------------+----+--------------------+-----+-------------+
| fs_status | 61 | fs4_status | R | Section |
| | | | | 11.12.2.14 |
+--------------------+----+--------------------+-----+-------------+
| hidden | 25 | bool | R W | Section |
| | | | | 11.12.2.15 |
+--------------------+----+--------------------+-----+-------------+
| homogeneous | 26 | bool | R | Section |
| | | | | 11.12.2.16 |
+--------------------+----+--------------------+-----+-------------+
| layout_alignment | 66 | uint32_t | R | Section |
| | | | | 11.16.2 |
+--------------------+----+--------------------+-----+-------------+
| layout_blksize | 65 | uint32_t | R | Section |
| | | | | 11.16.3 |
+--------------------+----+--------------------+-----+-------------+
| layout_hint | 63 | layouthint4 | W | Section |
| | | | | 11.16.4 |
+--------------------+----+--------------------+-----+-------------+
| layout_type | 64 | layouttype4<> | R | Section |
| | | | | 11.16.5 |
+--------------------+----+--------------------+-----+-------------+
| maxfilesize | 27 | uint64_t | R | Section |
| | | | | 11.12.2.17 |
+--------------------+----+--------------------+-----+-------------+
| maxlink | 28 | uint32_t | R | Section |
| | | | | 11.12.2.18 |
+--------------------+----+--------------------+-----+-------------+
| maxname | 29 | uint32_t | R | Section |
| | | | | 11.12.2.19 |
+--------------------+----+--------------------+-----+-------------+
| maxread | 30 | uint64_t | R | Section |
| | | | | 11.12.2.20 |
+--------------------+----+--------------------+-----+-------------+
| maxwrite | 31 | uint64_t | R | Section |
| | | | | 11.12.2.21 |
+--------------------+----+--------------------+-----+-------------+
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| mdsthreshold | 68 | mdsthreshold4 | R | Section |
| | | | | 11.16.6 |
+--------------------+----+--------------------+-----+-------------+
| mimetype | 32 | utf8str_cs | R W | Section |
| | | | | 11.12.2.22 |
+--------------------+----+--------------------+-----+-------------+
| mode | 33 | mode4 | R W | Section |
| | | | | 11.18 |
+--------------------+----+--------------------+-----+-------------+
| mode_set_masked | 74 | mode_masked4 | W | Section |
| | | | | 11.18 |
+--------------------+----+--------------------+-----+-------------+
| mounted_on_fileid | 55 | uint64_t | R | Section |
| | | | | 11.12.2.23 |
+--------------------+----+--------------------+-----+-------------+
| no_trunc | 34 | bool | R | Section |
| | | | | 11.12.2.24 |
+--------------------+----+--------------------+-----+-------------+
| numlinks | 35 | uint32_t | R | Section |
| | | | | 11.12.2.25 |
+--------------------+----+--------------------+-----+-------------+
| quota_avail_hard | 38 | uint64_t | R | Section |
| | | | | 11.12.2.26 |
+--------------------+----+--------------------+-----+-------------+
| quota_avail_soft | 39 | uint64_t | R | Section |
| | | | | 11.12.2.27 |
+--------------------+----+--------------------+-----+-------------+
| quota_used | 40 | uint64_t | R | Section |
| | | | | 11.12.2.28 |
+--------------------+----+--------------------+-----+-------------+
| rawdev | 41 | specdata4 | R | Section |
| | | | | 11.12.2.29 |
+--------------------+----+--------------------+-----+-------------+
| retentevt_get | 71 | retention_get4 | R | Section |
| | | | | 11.17.3 |
+--------------------+----+--------------------+-----+-------------+
| retentevt_set | 72 | retention_set4 | W | Section |
| | | | | 11.17.4 |
+--------------------+----+--------------------+-----+-------------+
| retention_get | 69 | retention_get4 | R | Section |
| | | | | 11.17.1 |
+--------------------+----+--------------------+-----+-------------+
| retention_hold | 73 | uint64_t | R W | Section |
| | | | | 11.17.5 |
+--------------------+----+--------------------+-----+-------------+
| retention_set | 70 | retention_set4 | W | Section |
| | | | | 11.17.2 |
+--------------------+----+--------------------+-----+-------------+
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| sacl | 59 | nfsacl41 | R W | Section |
| | | | | 11.18 |
+--------------------+----+--------------------+-----+-------------+
| space_avail | 42 | uint64_t | R | Section |
| | | | | 11.12.2.30 |
+--------------------+----+--------------------+-----+-------------+
| space_free | 43 | uint64_t | R | Section |
| | | | | 11.12.2.31 |
+--------------------+----+--------------------+-----+-------------+
| space_total | 44 | uint64_t | R | Section |
| | | | | 11.12.2.32 |
+--------------------+----+--------------------+-----+-------------+
| space_used | 45 | uint64_t | R | Section |
| | | | | 11.12.2.33 |
+--------------------+----+--------------------+-----+-------------+
| system | 46 | bool | R W | Section |
| | | | | 11.12.2.34 |
+--------------------+----+--------------------+-----+-------------+
| time_access | 47 | nfstime4 | R | Section |
| | | | | 11.12.2.35 |
+--------------------+----+--------------------+-----+-------------+
| time_access_set | 48 | settime4 | W | Section |
| | | | | 11.12.2.36 |
+--------------------+----+--------------------+-----+-------------+
| time_backup | 49 | nfstime4 | R W | Section |
| | | | | 11.12.2.37 |
+--------------------+----+--------------------+-----+-------------+
| time_create | 50 | nfstime4 | R W | Section |
| | | | | 11.12.2.38 |
+--------------------+----+--------------------+-----+-------------+
| time_delta | 51 | nfstime4 | R | Section |
| | | | | 11.12.2.39 |
+--------------------+----+--------------------+-----+-------------+
| time_metadata | 52 | nfstime4 | R | Section |
| | | | | 11.12.2.40 |
+--------------------+----+--------------------+-----+-------------+
| time_modify | 53 | nfstime4 | R | Section |
| | | | | 11.12.2.41 |
+--------------------+----+--------------------+-----+-------------+
| time_modify_set | 54 | settime4 | W | Section |
| | | | | 11.12.2.42 |
+--------------------+----+--------------------+-----+-------------+
Table 5
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11.12. Attribute Definitions
11.12.1. Definitions of REQUIRED Attributes
11.12.1.1. Attribute 0: supported_attrs
The bit vector that would retrieve all protocol-defined attributes
that are supported for this object. The scope of this attribute
applies to all objects with a matching fsid.
11.12.1.2. Attribute 1: type
Designates the type of an object in terms of one of a number of
special constants:
* NF4REG designates a regular file.
* NF4DIR designates a directory.
* NF4BLK designates a block device special file.
* NF4CHR designates a character device special file.
* NF4LNK designates a symbolic link.
* NF4SOCK designates a named socket special file.
* NF4FIFO designates a fifo special file.
* NF4ATTRDIR designates a named attribute directory.
* NF4NAMEDATTR designates a named attribute.
Within the explanatory text and operation descriptions, the following
phrases will be used with the meanings given below:
* The phrase "is a directory" means that the object's type attribute
is NF4DIR or NF4ATTRDIR.
* The phrase "is a special file" means that the object's type
attribute is NF4BLK, NF4CHR, NF4SOCK, or NF4FIFO.
* The phrases "is an ordinary file" and "is a regular file" mean
that the object's type attribute is NF4REG or NF4NAMEDATTR.
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11.12.1.3. Attribute 2: fh_expire_type
Server uses this to specify filehandle expiration behavior to the
client. See Section 10 for additional description.
11.12.1.4. Attribute 3: change
A value created by the server that the client can use to determine if
file data, directory contents, or attributes of the object have been
modified. The server may return the object's time_metadata attribute
for this attribute's value, but only if the file system object cannot
be updated more frequently than the resolution of time_metadata.
11.12.1.5. Attribute 4: size
The size of the object in bytes.
11.12.1.6. Attribute 5: link_support
TRUE, if the object's file system supports hard links.
11.12.1.7. Attribute 6: symlink_support
TRUE, if the object's file system supports symbolic links.
11.12.1.8. Attribute 7: named_attr
TRUE, if this object has named attributes. In other words, object
has a non-empty named attribute directory.
11.12.1.9. Attribute 8: fsid
Unique file system identifier for the file system holding this
object. The fsid attribute has major and minor components, each of
which are of data type uint64_t.
11.12.1.10. Attribute 9: unique_handles
TRUE, if two distinct filehandles are guaranteed to refer to two
different file system objects.
11.12.1.11. Attribute 10: lease_time
Duration of the lease at server in seconds.
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11.12.1.12. Attribute 11: rdattr_error
Error returned from an attempt to retrieve attributes during a
READDIR operation.
11.12.1.13. Attribute 19: filehandle
The filehandle of this object (primarily for use by READDIR
requests).
11.12.1.14. Attribute 75: suppattr_exclcreat
The bit vector that would set all protocol-defined attributes that
are supported by the EXCLUSIVE4_1 method of file creation via the
OPEN operation. The scope of this attribute applies to all objects
with a matching fsid.
11.12.2. Definitions of Uncategorized OPTIONAL Attributes
The definitions of most of the OPTIONAL attributes follow.
Collections that share a common category are defined in other
sections.
11.12.2.1. Attribute 14: archive
TRUE, if this file has been archived since the time of last
modification (deprecated in favor of time_backup).
11.12.2.2. Attribute 15: cansettime
TRUE, if the server is able to change the times for a file system
object as specified in a SETATTR operation.
11.12.2.3. Attribute 16: case_insensitive
TRUE, if file name comparisons on this file system are case
insensitive.
11.12.2.4. Attribute 17: case_preserving
TRUE, if file name case on this file system is preserved.
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11.12.2.5. Attribute 60: change_policy
A value created by the server that the client can use to determine if
some server policy related to the current file system has been
subject to change. If the value remains the same, then the client
can be sure that the values of the attributes related to fs location
and the fss_type field of the fs_status attribute have not changed.
On the other hand, a change in this value does necessarily imply a
change in policy. It is up to the client to interrogate the server
to determine if some policy relevant to it has changed. See
Section 9.3.6 for details.
This attribute MUST change when the value returned by the
fs_locations or fs_locations_info attribute changes, when a file
system goes from read-only to writable or vice versa, or when the
allowable set of security flavors for the file system or any part
thereof is changed.
11.12.2.6. Attribute 18: chown_restricted
If TRUE, the server will reject any request to change either the
owner or the group associated with a file if the caller is not a
privileged user (for example, "root" in UNIX operating environments
or, in Windows 2000, the "Take Ownership" privilege).
11.12.2.7. Attribute 20: fileid
A number uniquely identifying the file within the file system.
11.12.2.8. Attribute 21: files_avail
File slots available to this user on the file system containing this
object -- this should be the smallest relevant limit.
11.12.2.9. Attribute 22: files_free
Free file slots on the file system containing this object -- this
should be the smallest relevant limit.
11.12.2.10. Attribute 23: files_total
Total file slots on the file system containing this object.
11.12.2.11. Attribute 76: fs_charset_cap
Character set capabilities for this file system. See Section 21.1.
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11.12.2.12. Attribute 24: fs_locations
Locations where this file system may be found. If the server returns
NFS4ERR_MOVED as an error, this attribute MUST be supported. See
Section 17.16 for more details.
11.12.2.13. Attribute 67: fs_locations_info
Full function file system location. See Section 17.17.2 for more
details.
11.12.2.14. Attribute 61: fs_status
Generic file system type information. See Section 17.18 for more
details.
11.12.2.15. Attribute 25: hidden
TRUE, if the file is considered hidden with respect to the Windows
API.
11.12.2.16. Attribute 26: homogeneous
TRUE, if this object's file system is homogeneous; i.e., all objects
in the file system (all objects on the server with the same fsid)
have common values for all per-file-system attributes.
11.12.2.17. Attribute 27: maxfilesize
Maximum supported file size for the file system of this object.
11.12.2.18. Attribute 28: maxlink
Maximum number of links for this object.
11.12.2.19. Attribute 29: maxname
Maximum file name size supported for this object.
11.12.2.20. Attribute 30: maxread
Maximum amount of data the READ operation will return for this
object.
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11.12.2.21. Attribute 31: maxwrite
Maximum amount of data the WRITE operation will accept for this
object. This attribute SHOULD be supported if the file is writable.
Lack of this attribute can lead to the client either wasting
bandwidth or not receiving the best performance.
11.12.2.22. Attribute 32: mimetype
MIME body type/subtype of this object.
11.12.2.23. Attribute 55: mounted_on_fileid
Like fileid, but if the target filehandle is the root of a file
system, this attribute represents the fileid of the underlying
directory.
UNIX-based operating environments connect a file system into the
namespace by connecting (mounting) the file system onto the existing
file object (the mount point, usually a directory) of an existing
file system. When the mount point's parent directory is read via an
API like readdir(), the return results are directory entries, each
with a component name and a fileid. The fileid of the mount point's
directory entry will be different from the fileid that the stat()
system call returns. The stat() system call is returning the fileid
of the root of the mounted file system, whereas readdir() is
returning the fileid that stat() would have returned before any file
systems were mounted on the mount point.
Unlike NFSv3, NFSv4.1 allows a client's LOOKUP request to cross other
file systems. The client detects the file system crossing whenever
the filehandle argument of LOOKUP has an fsid attribute different
from that of the filehandle returned by LOOKUP. A UNIX-based client
will consider this a "mount point crossing". UNIX has a legacy
scheme for allowing a process to determine its current working
directory. This relies on readdir() of a mount point's parent and
stat() of the mount point returning fileids as previously described.
The mounted_on_fileid attribute corresponds to the fileid that
readdir() would have returned as described previously.
While the NFSv4.1 client could simply fabricate a fileid
corresponding to what mounted_on_fileid provides (and if the server
does not support mounted_on_fileid, the client has no choice), there
is a risk that the client will generate a fileid that conflicts with
one that is already assigned to another object in the file system.
Instead, if the server can provide the mounted_on_fileid, the
potential for client operational problems in this area is eliminated.
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If the server detects that there is no mounted point at the target
file object, then the value for mounted_on_fileid that it returns is
the same as that of the fileid attribute.
The mounted_on_fileid attribute is OPTIONAL, and the server should
provide it if possible. For a UNIX-based server, this is
straightforward. Usually, mounted_on_fileid will be requested as
part of a READDIR operation, in which case it is trivial (at least
for UNIX-based servers) to return mounted_on_fileid since it is equal
to the fileid of a directory entry returned by readdir(). If
mounted_on_fileid is requested in a GETATTR operation, the server
should obey an invariant that has it returning a value that is equal
to the file object's entry in the object's parent directory, i.e.,
what readdir() would have returned. Some operating environments
allow a series of two or more file systems to be mounted onto a
single mount point. In this case, for the server to obey the
aforementioned invariant, it will need to find the base mount point,
and not the intermediate mount points.
11.12.2.24. Attribute 34: no_trunc
If this attribute is TRUE, then if the client uses a file name longer
than name_max, an error will be returned instead of the name being
truncated.
11.12.2.25. Attribute 35: numlinks
Number of hard links to this object.
11.12.2.26. Attribute 38: quota_avail_hard
The value in bytes that represents the amount of additional disk
space beyond the current allocation that can be allocated to this
file or directory before further allocations will be refused. It is
understood that this space may be consumed by allocations to other
files or directories.
11.12.2.27. Attribute 39: quota_avail_soft
The value in bytes that represents the amount of additional disk
space that can be allocated to this file or directory before the user
may reasonably be warned. It is understood that this space may be
consumed by allocations to other files or directories though there is
a rule as to which other files or directories.
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11.12.2.28. Attribute 40: quota_used
The value in bytes that represents the amount of disk space used by
this file or directory and possibly a number of other similar files
or directories, where the set of "similar" meets at least the
criterion that allocating space to any file or directory in the set
will reduce the "quota_avail_hard" of every other file or directory
in the set.
Note that there may be a number of distinct but overlapping sets of
files or directories for which a quota_used value is maintained,
e.g., "all files with a given owner", "all files with a given group
owner", etc. The server is at liberty to choose any of those sets
when providing the content of the quota_used attribute, but should do
so in a repeatable way. The rule may be configured per file system
or may be "choose the set with the smallest quota".
11.12.2.29. Attribute 41: rawdev
Raw device number of file of type NF4BLK or NF4CHR. The device
number is split into major and minor numbers. If the file's type
attribute is not NF4BLK or NF4CHR, the value returned SHOULD NOT be
considered useful.
11.12.2.30. Attribute 42: space_avail
Disk space in bytes available to this user on the file system
containing this object -- this should be the smallest relevant limit.
11.12.2.31. Attribute 43: space_free
Free disk space in bytes on the file system containing this object --
this should be the smallest relevant limit.
11.12.2.32. Attribute 44: space_total
Total disk space in bytes on the file system containing this object.
11.12.2.33. Attribute 45: space_used
Number of file system bytes allocated to this object.
11.12.2.34. Attribute 46: system
This attribute is TRUE if this file is a "system" file with respect
to the Windows operating environment.
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11.12.2.35. Attribute 47: time_access
The time_access attribute represents the time of last access to the
object by a READ operation sent to the server. The notion of what is
an "access" depends on the server's operating environment and/or the
server's file system semantics. For example, for servers obeying
Portable Operating System Interface (POSIX) semantics, time_access
would be updated only by the READ and READDIR operations and not any
of the operations that modify the content of the object [read_atime],
[readdir_atime], [write_atime]. Of course, setting the corresponding
time_access_set attribute is another way to modify the time_access
attribute.
Whenever the file object resides on a writable file system, the
server should make its best efforts to record time_access into stable
storage. However, to mitigate the performance effects of doing so,
and most especially whenever the server is satisfying the read of the
object's content from its cache, the server MAY cache access time
updates and lazily write them to stable storage. It is also
acceptable to give administrators of the server the option to disable
time_access updates.
11.12.2.36. Attribute 48: time_access_set
Sets the time of last access to the object. SETATTR use only.
11.12.2.37. Attribute 49: time_backup
The time of last backup of the object.
11.12.2.38. Attribute 50: time_create
The time of creation of the object. This attribute does not have any
relation to the traditional UNIX file attribute "ctime" or "change
time".
11.12.2.39. Attribute 51: time_delta
Smallest useful server time granularity.
11.12.2.40. Attribute 52: time_metadata
The time of last metadata modification of the object.
11.12.2.41. Attribute 53: time_modify
The time of last modification to the object.
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11.12.2.42. Attribute 54: time_modify_set
Sets the time of last modification to the object. SETATTR use only.
11.13. Interpreting owner and owner_group
The attributes "owner" and "owner_group" (and also users and groups
within the "acl" attribute) are transferred in the form of a UTF-8
string. This string can be used to identify users and groups in
several ways:
* A string of the form "name@domain" can be used to give a user or
group name together with a domain in which those are defined.
This form provides greater degree of extensibility than was
possible in NFSv3 which limited these identifiers to 32-bit
unsigned integers whose values are all centrally administered as
members within a common domain.
* Numeric ids converted to string form.
Using this format maintains the strengths and weaknesses of the
NFSv3 approach.
The following issues are relevant in selected the form to use.
* The use of the form "name@domain" provides greater flexibility,
both with regard to the number of users that can be accommodated
and to the management of multiple sets of users in separate
domains.
Taking advantage of this flexibility often requires extensive work
because of limitations of the API's used to reference users and
groups.
* The use of the form "name@domain" allows clients and servers to
work together even if they have different internal formats for
user and groups.
In many cases, there is no need for such mapping.
Providing this mapping requires extra implementation and raises
potential security issues.
For detailed discussions regarding which of the forms clients and
server are to use for these values, see Section 5.1 of
[I-D.dnoveck-nfsv4-security].
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11.14. Character Case Attributes
With respect to the case_insensitive and case_preserving attributes,
each UCS-4 character (which UTF-8 encodes) can be mapped to an
equivalent character of different case or compared in a case-
insensitive manner. The details vary based on the Unicode version
implemented by the server for the current file system. Details of
the process and how the client can best deal with uncertainty about
the process will be discussed in the NFSv4-wide internationalization
document (See [I-D.ietf-nfsv4-internationalization] for the latest
version)
11.15. Directory Notification Attributes
As described in Section 25.39, the client can request a minimum delay
for notifications of changes to attributes, but the server is free to
ignore what the client requests. The client can determine in advance
what notification delays the server will accept by sending a GETATTR
operation for either or both of two directory notification
attributes. When the client calls the GET_DIR_DELEGATION operation
and asks for attribute change notifications, it should request
notification delays that are no less than the values in the server-
provided attributes.
11.15.1. Attribute 56: dir_notif_delay
The dir_notif_delay attribute is the minimum number of seconds the
server will delay before notifying the client of a change to the
directory's attributes.
11.15.2. Attribute 57: dirent_notif_delay
The dirent_notif_delay attribute is the minimum number of seconds the
server will delay before notifying the client of a change to a file
object that has an entry in the directory.
11.16. pNFS Attribute Definitions
11.16.1. Attribute 62: fs_layout_type
The fs_layout_type attribute (see Section 9.3.13) applies to a file
system and indicates what layout types are supported by the file
system. When the client encounters a new fsid, the client SHOULD
obtain the value for the fs_layout_type attribute associated with the
new file system. This attribute is used by the client to determine
if the layout types supported by the server match any of the client's
supported layout types.
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11.16.2. Attribute 66: layout_alignment
When a client holds layouts on files of a file system, the
layout_alignment attribute indicates the preferred alignment for I/O
to files on that file system. Where possible, the client should send
READ and WRITE operations with offsets that are whole multiples of
the layout_alignment attribute.
11.16.3. Attribute 65: layout_blksize
When a client holds layouts on files of a file system, the
layout_blksize attribute indicates the preferred block size for I/O
to files on that file system. Where possible, the client should send
READ operations with a count argument that is a whole multiple of
layout_blksize, and WRITE operations with a data argument of size
that is a whole multiple of layout_blksize.
11.16.4. Attribute 63: layout_hint
The layout_hint attribute (see Section 9.3.19) may be set on newly
created files to influence the metadata server's choice for the
file's layout. If possible, this attribute is one of those set in
the initial attributes within the OPEN operation. The metadata
server may choose to ignore this attribute. The layout_hint
attribute is a subset of the layout structure returned by LAYOUTGET.
For example, instead of specifying particular devices, this would be
used to suggest the stripe width of a file. The server
implementation determines which fields within the layout will be
used.
11.16.5. Attribute 64: layout_type
This attribute lists the layout type(s) available for a file. The
value returned by the server is for informational purposes only. The
client will use the LAYOUTGET operation to obtain the information
needed in order to perform I/O, for example, the specific device
information for the file and its layout.
11.16.6. Attribute 68: mdsthreshold
This attribute is a server-provided hint used to communicate to the
client when it is more efficient to send READ and WRITE operations to
the metadata server or the data server. The two types of thresholds
described are file size thresholds and I/O size thresholds. If a
file's size is smaller than the file size threshold, data accesses
SHOULD be sent to the metadata server. If an I/O request has a
length that is below the I/O size threshold, the I/O SHOULD be sent
to the metadata server. Each threshold type is specified separately
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for read and write.
The server MAY provide both types of thresholds for a file. If both
file size and I/O size are provided, the client SHOULD reach or
exceed both thresholds before sending its read or write requests to
the data server. Alternatively, if only one of the specified
thresholds is reached or exceeded, the I/O requests are sent to the
metadata server.
For each threshold type, a value of zero indicates no READ or WRITE
should be sent to the metadata server, while a value of all ones
indicates that all READs or WRITEs should be sent to the metadata
server.
The attribute is available on a per-filehandle basis. If the current
filehandle refers to a non-pNFS file or directory, the metadata
server should return an attribute that is representative of the
filehandle's file system. It is suggested that this attribute is
queried as part of the OPEN operation. Due to dynamic system
changes, the client should not assume that the attribute will remain
constant for any specific time period; thus, it should be
periodically refreshed.
11.17. Retention Attributes
Retention is a concept whereby a file object can be placed in an
immutable, undeletable, unrenamable state for a fixed or infinite
duration of time. Once in this "retained" state, the file cannot be
moved out of the state until the duration of retention has been
reached.
When retention is enabled, retention MUST extend to the data of the
file, and the name of file. The server MAY extend retention to any
other property of the file, including any subset of REQUIRED,
OPTIONAL, and named attributes, with the exceptions noted in this
section.
Servers MAY support or not support retention on any file object type.
The five retention attributes are explained in the next subsections.
11.17.1. Attribute 69: retention_get
If retention is enabled for the associated file, this attribute's
value represents the retention begin time of the file object. This
attribute's value is only readable with the GETATTR operation and
MUST NOT be modified by the SETATTR operation (Section 11.9). The
value of the attribute consists of:
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const RET4_DURATION_INFINITE = 0xffffffffffffffff;
struct retention_get4 {
uint64_t rg_duration;
nfstime4 rg_begin_time<1>;
};
The field rg_duration is the duration in seconds indicating how long
the file will be retained once retention is enabled. The field
rg_begin_time is an array of up to one absolute time value. If the
array is zero length, no beginning retention time has been
established, and retention is not enabled. If rg_duration is equal
to RET4_DURATION_INFINITE, the file, once retention is enabled, will
be retained for an infinite duration.
If (as soon as) rg_duration is zero, then rg_begin_time will be of
zero length, and again, retention is not (no longer) enabled.
11.17.2. Attribute 70: retention_set
This attribute is used to set the retention duration and optionally
enable retention for the associated file object. This attribute is
only modifiable via the SETATTR operation and MUST NOT be retrieved
by the GETATTR operation (Section 11.9). This attribute corresponds
to retention_get. The value of the attribute consists of:
struct retention_set4 {
bool rs_enable;
uint64_t rs_duration<1>;
};
If the client sets rs_enable to TRUE, then it is enabling retention
on the file object with the begin time of retention starting from the
server's current time and date. The duration of the retention can
also be provided if the rs_duration array is of length one. The
duration is the time in seconds from the begin time of retention, and
if set to RET4_DURATION_INFINITE, the file is to be retained forever.
If retention is enabled, with no duration specified in either this
SETATTR or a previous SETATTR, the duration defaults to zero seconds.
The server MAY restrict the enabling of retention or the duration of
retention on the basis of the ACE4_WRITE_RETENTION ACL permission.
The enabling of retention MUST NOT prevent the enabling of event-
based retention or the modification of the retention_hold attribute.
The following rules apply to both the retention_set and retentevt_set
attributes.
* As long as retention is not enabled, the client is permitted to
decrease the duration.
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* The duration can always be set to an equal or higher value, even
if retention is enabled. Note that once retention is enabled, the
actual duration (as returned by the retention_get or retentevt_get
attributes; see Section 11.17.1 or Section 11.17.3) is constantly
counting down to zero (one unit per second), unless the duration
was set to RET4_DURATION_INFINITE. Thus, it will not be possible
for the client to precisely extend the duration on a file that has
retention enabled.
* While retention is enabled, attempts to disable retention or
decrease the retention's duration MUST fail with the error
NFS4ERR_INVAL.
* If the principal attempting to change retention_set or
retentevt_set does not have ACE4_WRITE_RETENTION permissions, the
attempt MUST fail with NFS4ERR_ACCESS.
11.17.3. Attribute 71: retentevt_get
Gets the event-based retention duration, and if enabled, the event-
based retention begin time of the file object. This attribute is
like retention_get, but refers to event-based retention. The event
that triggers event-based retention is not defined by the NFSv4.1
specification.
11.17.4. Attribute 72: retentevt_set
Sets the event-based retention duration, and optionally enables
event-based retention on the file object. This attribute corresponds
to retentevt_get and is like retention_set, but refers to event-based
retention. When event-based retention is set, the file MUST be
retained even if non-event-based retention has been set, and the
duration of non-event-based retention has been reached. Conversely,
when non-event-based retention has been set, the file MUST be
retained even if event-based retention has been set, and the duration
of event-based retention has been reached. The server MAY restrict
the enabling of event-based retention or the duration of event-based
retention on the basis of the ACE4_WRITE_RETENTION ACL permission.
The enabling of event-based retention MUST NOT prevent the enabling
of non-event-based retention or the modification of the
retention_hold attribute.
11.17.5. Attribute 73: retention_hold
Gets or sets administrative retention holds, one hold per bit
position.
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This attribute allows one to 64 administrative holds, one hold per
bit on the attribute. If retention_hold is not zero, then the file
MUST NOT be deleted, renamed, or modified, even if the duration on
enabled event or non-event-based retention has been reached. The
server MAY restrict the modification of retention_hold on the basis
of the ACE4_WRITE_RETENTION_HOLD ACL permission. The enabling of
administration retention holds does not prevent the enabling of
event-based or non-event-based retention.
If the principal attempting to change retention_hold does not have
ACE4_WRITE_RETENTION_HOLD permissions, the attempt MUST fail with
NFS4ERR_ACCESS.
11.18. Access Control Attributes
The use of the access control attributes are fully described in
various sections of the NFSv4-wide security documents
[I-D.dnoveck-nfsv4-security] [I-D.ietf-nfsv4-acls-update].
* The mode, mode_set_masked, owner, and owner_group attributes are
described in Sections 5.3.1 though 5.3.4 of
[I-D.dnoveck-nfsv4-security].
* The acl, aclsupport, sacl, and dacl attributes are described in
Sections 3.4, 3.5, 3.6, and 3.8 of [I-D.ietf-nfsv4-acls-update].
12. Single-Server Namespace
This section describes the NFSv4 single-server namespace. Single-
server namespaces may be presented directly to clients, or they may
be used as a basis to form larger multi-server namespaces (e.g.,
site-wide or organization-wide) to be presented to clients, as
described in Section 17.
12.1. Server Exports
On a UNIX server, the namespace describes all the files reachable by
pathnames under the root directory or "/". On a Windows server, the
namespace constitutes all the files on disks named by mapped disk
letters. NFS server administrators rarely make the entire server's
file system namespace available to NFS clients. More often, portions
of the namespace are made available via an "export" feature. In
previous versions of the NFS protocol, the root filehandle for each
export is obtained through the MOUNT protocol; the client sent a
string that identified the export name within the namespace and the
server returned the root filehandle for that export. The MOUNT
protocol also provided an EXPORTS procedure that enumerated the
server's exports.
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12.2. Browsing Exports
The NFSv4.1 protocol provides a root filehandle that clients can use
to obtain filehandles for the exports of a particular server, via a
series of LOOKUP operations within a COMPOUND, to traverse a path. A
common user experience is to use a graphical user interface (perhaps
a file "Open" dialog window) to find a file via progressive browsing
through a directory tree. The client must be able to move from one
export to another export via single-component, progressive LOOKUP
operations.
This style of browsing is not well supported by the NFSv3 protocol.
In NFSv3, the client expects all LOOKUP operations to remain within a
single server file system. For example, the device attribute will
not change. This prevents a client from taking namespace paths that
span exports.
In the case of NFSv3, an automounter on the client can obtain a
snapshot of the server's namespace using the EXPORTS procedure of the
MOUNT protocol. If it understands the server's pathname syntax, it
can create an image of the server's namespace on the client. The
parts of the namespace that are not exported by the server are filled
in with directories that might be constructed similarly to an NFSv4.1
"pseudo file system" (See Section 12.3) that allows the user to
browse from one mounted file system to another. There is a drawback
to this representation of the server's namespace on the client: it is
static. If the server administrator adds a new export, the client
will be unaware of it.
12.3. Server Pseudo File System
NFSv4.1 servers avoid this namespace inconsistency by presenting all
the exports for a given server within the framework of a single
namespace for that server. An NFSv4.1 client uses LOOKUP and READDIR
operations to browse seamlessly from one export to another.
Where there are portions of the server namespace that are not
exported, clients require some way of traversing those portions to
reach actual exported file systems. A technique that servers may use
to provide for this is to bridge the unexported portion of the
namespace via a "pseudo file system" that provides a view of exported
directories only. A pseudo file system has a unique fsid and behaves
like a normal, read-only file system.
Based on the construction of the server's namespace, it is possible
that multiple pseudo file systems may exist. For example,
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/a pseudo file system
/a/b real file system
/a/b/c pseudo file system
/a/b/c/d real file system
Each of the pseudo file systems is considered a separate entity and
therefore MUST have its own fsid, unique among all the fsids for that
server.
12.4. Multiple Roots
Certain operating environments are sometimes described as having
"multiple roots". In such environments, individual file systems are
commonly represented by disk or volume names. NFSv4 servers for
these platforms can construct a pseudo file system above these root
names so that disk letters or volume names are simply directory names
in the pseudo root.
12.5. Filehandle Volatility
The nature of the server's pseudo file system is that it is a logical
representation of file system(s) available from the server.
Therefore, the pseudo file system is most likely constructed
dynamically when the server is first instantiated. It is expected
that the pseudo file system may not have an on-disk counterpart from
which persistent filehandles could be constructed. Even though it is
preferable that the server provide persistent filehandles for the
pseudo file system, the NFS client should expect that pseudo file
system filehandles are volatile. This can be confirmed by checking
the associated "fh_expire_type" attribute for those filehandles in
question. If the filehandles are volatile, the NFS client must be
prepared to recover a filehandle value (e.g., with a series of LOOKUP
operations) when receiving an error of NFS4ERR_FHEXPIRED.
Because it is quite likely that servers will implement pseudo file
systems using volatile filehandles, clients need to be prepared for
them, rather than assuming that all filehandles will be persistent.
12.6. Exported Root
If the server's root file system is exported, one might conclude that
a pseudo file system is unneeded. This is not necessarily so.
Assume the following file systems on a server:
/ fs1 (exported)
/a fs2 (not exported)
/a/b fs3 (exported)
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Because fs2 is not exported, fs3 cannot be reached with simple
LOOKUPs. The server must bridge the gap with a pseudo file system.
12.7. Mount Point Crossing
The server file system environment may be constructed in such a way
that one file system contains a directory that is 'covered' or
mounted upon by a second file system. For example:
/a/b (file system 1)
/a/b/c/d (file system 2)
The pseudo file system for this server may be constructed to look
like:
/ (place holder/not exported)
/a/b (file system 1)
/a/b/c/d (file system 2)
It is the server's responsibility to present the pseudo file system
that is complete to the client. If the client sends a LOOKUP request
for the path /a/b/c/d, the server's response is the filehandle of the
root of the file system /a/b/c/d. In previous versions of the NFS
protocol, the server would respond with the filehandle of directory
/a/b/c/d within the file system /a/b.
The NFS client will be able to determine if it crosses a server mount
point by a change in the value of the "fsid" attribute.
12.8. Security Policy and Namespace Presentation
Because NFSv4 clients possess the ability to change the security
mechanisms used, after determining what is allowed, by using SECINFO
and SECINFO_NO_NAME, the server SHOULD NOT present a different view
of the namespace based on the security mechanism being used by a
client. Instead, it should present a consistent view and return
NFS4ERR_WRONGSEC if an attempt is made to access data with an
inappropriate security mechanism.
If security considerations make it necessary to hide the existence of
a particular file system, as opposed to all of the data within it,
the server can apply the security policy of a shared resource in the
server's namespace to components of the resource's ancestors. For
example:
/ (place holder/not exported)
/a/b (file system 1)
/a/b/MySecretProject (file system 2)
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The /a/b/MySecretProject directory is a real file system and is the
shared resource. Suppose the security policy for /a/b/
MySecretProject is Kerberos with integrity and it is desired to limit
knowledge of the existence of this file system. In this case, the
server should apply the same security policy to /a/b. This allows
for knowledge of the existence of a file system to be secured when
desirable.
For the case of the use of multiple, disjoint security mechanisms in
the server's resources, applying that sort of policy would result in
the higher-level file system not being accessible using any security
flavor. Therefore, that sort of configuration is not compatible with
hiding the existence (as opposed to the contents) from clients using
multiple disjoint sets of security flavors.
In other circumstances, a desirable policy is for the security of a
particular object in the server's namespace to include the union of
all security mechanisms of all direct descendants. A common and
convenient practice, unless strong security requirements dictate
otherwise, is to make the entire the pseudo file system accessible by
all of the valid security mechanisms.
Where there is concern about the security of data on the network,
clients should use strong security mechanisms to access the pseudo
file system in order to prevent man-in-the-middle attacks.
13. State Management
Integrating locking into the NFS protocol necessarily causes it to be
stateful. With the inclusion of such features as share reservations,
file and directory delegations, recallable layouts, and support for
mandatory byte-range locking, the protocol becomes substantially more
dependent on proper management of state than the combination of NFS
and NLM (Network Lock Manager) [xnfs]. used for locking within
previous NFS versions. The new features include expanded locking
facilities, which provide some measure of inter-client exclusion, but
the state also offers features not readily providable using a
stateless model. There are three components to making this state
manageable:
* clear division between client and server
* ability to reliably detect inconsistency in state between client
and server
* simple and robust recovery mechanisms
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In this model, the server owns the state information. The client
requests changes in locks and the server responds with the changes
made. Non-client-initiated changes in locking state are infrequent.
The client receives prompt notification of such changes and can
adjust its view of the locking state to reflect the server's changes.
Individual pieces of state created by the server and passed to the
client at its request are represented by 128-bit stateids. These
stateids may represent a particular open file, a set of byte-range
locks held by a particular owner, or a recallable delegation of
privileges to access a file in particular ways or at a particular
location.
In all cases, there is a transition from the most general information
that represents a client as a whole to the eventual lightweight
stateid used for most client and server locking interactions. The
details of this transition will vary with the type of object but it
always starts with a client ID.
13.1. Client and Session ID
A client must establish a client ID (See Section 5.5) and then one or
more sessionids (See Section 7) before performing any operations to
open, byte-range lock, delegate, or obtain a layout for a file
object. Each session ID is associated with a specific client ID, and
thus serves as a shorthand reference to an NFSv4.1 client.
For some types of locking interactions, the client will represent
some number of internal locking entities called "owners", which
normally correspond to processes internal to the client. For other
types of locking-related objects, such as delegations and layouts, no
such intermediate entities are provided for, and the locking-related
objects are considered to be transferred directly between the server
and a unitary client.
13.2. Stateid Definition
When the server grants a lock of any type (including opens, byte-
range locks, delegations, and layouts), it responds with a unique
stateid that represents a set of locks (often a single lock) for the
same file, of the same type, and sharing the same ownership
characteristics. Thus, opens of the same file by different open-
owners each have an identifying stateid. Similarly, each set of
byte-range locks on a file owned by a specific lock-owner has its own
identifying stateid. Delegations and layouts also have associated
stateids by which they may be referenced. The stateid is used as a
shorthand reference to a lock or set of locks, and given a stateid,
the server can determine the associated state-owner or state-owners
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(in the case of an open-owner/lock-owner pair) and the associated
filehandle. When stateids are used, the current filehandle must be
the one associated with that stateid.
All stateids associated with a given client ID are associated with a
common lease that represents the claim of those stateids and the
objects they represent to be maintained by the server. See
Section 13.3 for a discussion of the lease.
The server may assign stateids independently for different clients.
A stateid with the same bit pattern for one client may designate an
entirely different set of locks for a different client. The stateid
is always interpreted with respect to the client ID associated with
the current session. Stateids apply to all sessions associated with
the given client ID, and the client may use a stateid obtained from
one session on another session associated with the same client ID.
13.2.1. Stateid Types
With the exception of special stateids (See Section 13.2.3), each
stateid represents locking objects of one of a set of types defined
by the NFSv4.1 protocol. Note that in all these cases, where we
speak of guarantee, it is understood there are situations such as a
client restart, or lock revocation, that allow the guarantee to be
voided.
* Stateids may represent opens of files.
Each stateid in this case represents the OPEN state for a given
client ID/open-owner/filehandle triple. Such stateids are subject
to change (with consequent incrementing of the stateid's seqid) in
response to OPENs that result in upgrade and OPEN_DOWNGRADE
operations.
* Stateids may represent sets of byte-range locks.
All locks held on a particular file by a particular owner and
gotten under the aegis of a particular open file are associated
with a single stateid with the seqid being incremented whenever
LOCK and LOCKU operations affect that set of locks.
* Stateids may represent file delegations, which are recallable
guarantees by the server to the client that other clients will not
reference or modify a particular file, until the delegation is
returned. In NFSv4.1, file delegations may be obtained on both
regular and non-regular files.
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A stateid represents a single delegation held by a client for a
particular filehandle.
* Stateids may represent directory delegations, which are recallable
guarantees by the server to the client that other clients will not
modify the directory without appropriate notice to the holder,
until the delegation is returned.
A stateid represents a single delegation held by a client for a
particular directory filehandle.
* Stateids may represent layouts, which are recallable guarantees by
the server to the client that particular files may be accessed via
an alternate data access protocol at specific locations. Such
access is limited to particular sets of byte-ranges and may
proceed until those byte-ranges are reduced or the layout is
returned.
A stateid represents the set of all layouts held by a particular
client for a particular filehandle with a given layout type. The
seqid is updated as the layouts of that set of byte-ranges change,
via layout stateid changing operations such as LAYOUTGET and
LAYOUTRETURN.
13.2.2. Stateid Structure
Stateids are divided into two fields, a 96-bit "other" field
identifying the specific set of locks and a 32-bit "seqid" sequence
value. Except in the case of special stateids (See Section 13.2.3),
a particular value of the "other" field denotes a set of locks of the
same type (for example, byte-range locks, opens, delegations, or
layouts), for a specific file or directory, and sharing the same
ownership characteristics. The seqid designates a specific instance
of such a set of locks, and is incremented to indicate changes in
such a set of locks, either by the addition or deletion of locks from
the set, a change in the byte-range they apply to, or an upgrade or
downgrade in the type of one or more locks.
When such a set of locks is first created, the server returns a
stateid with seqid value of one. On subsequent operations that
modify the set of locks, the server is required to increment the
"seqid" field by one whenever it returns a stateid for the same
state-owner/file/type combination and there is some change in the set
of locks actually designated. In this case, the server will return a
stateid with an "other" field the same as previously used for that
state-owner/file/type combination, with an incremented "seqid" field.
This pattern continues until the seqid is incremented past
NFS4_UINT32_MAX, and one (not zero) is the next seqid value.
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The purpose of the incrementing of the seqid is to allow the server
to communicate to the client the order in which operations that
modified locking state associated with a stateid have been processed
and to make it possible for the client to send requests that are
conditional on the set of locks not having changed since the stateid
in question was returned.
Except for layout stateids (Section 18.7.3), when a client sends a
stateid to the server, it has two choices with regard to the seqid
sent. It may set the seqid to zero to indicate to the server that it
wishes the most up-to-date seqid for that stateid's "other" field to
be used. This would be the common choice in the case of a stateid
sent with a READ or WRITE operation. It also may set a non-zero
value, in which case the server checks if that seqid is the correct
one. In that case, the server is required to return
NFS4ERR_OLD_STATEID if the seqid is lower than the most current value
and NFS4ERR_BAD_STATEID if the seqid is greater than the most current
value. This would be the common choice in the case of stateids sent
with a CLOSE or OPEN_DOWNGRADE. Because OPENs may be sent in
parallel for the same owner, a client might close a file without
knowing that an OPEN upgrade had been done by the server, changing
the lock in question. If CLOSE were sent with a zero seqid, the OPEN
upgrade would be cancelled before the client even received an
indication that an upgrade had happened.
When a stateid is sent by the server to the client as part of a
callback operation, it is not subject to checking for a current seqid
and returning NFS4ERR_OLD_STATEID. This is because the client is not
in a position to know the most up-to-date seqid and thus cannot
verify it. Unless specially noted, the seqid value for a stateid
sent by the server to the client as part of a callback is required to
be zero with NFS4ERR_BAD_STATEID returned if it is not.
In making comparisons between seqids, both by the client in
determining the order of operations and by the server in determining
whether the NFS4ERR_OLD_STATEID is to be returned, the possibility of
the seqid being swapped around past the NFS4_UINT32_MAX value needs
to be taken into account. When two seqid values are being compared,
the total count of slots for all sessions associated with the current
client is used to do this. When one seqid value is less than this
total slot count and another seqid value is greater than
NFS4_UINT32_MAX minus the total slot count, the former is to be
treated as lower than the latter, despite the fact that it is
numerically greater.
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13.2.3. Special Stateids
Stateid values whose "other" field is either all zeros or all ones
are reserved. They may not be assigned by the server but have
special meanings defined by the protocol. The particular meaning
depends on whether the "other" field is all zeros or all ones and the
specific value of the "seqid" field.
The following combinations of "other" and "seqid" are defined in
NFSv4.1:
* When "other" and "seqid" are both zero, the stateid is treated as
a special anonymous stateid, which can be used in READ, WRITE, and
SETATTR requests to indicate the absence of any OPEN state
associated with the request. When an anonymous stateid value is
used and an existing open denies the form of access requested,
then access will be denied to the request. This stateid MUST NOT
be used on operations to data servers (Section 20.10).
* When "other" and "seqid" are both all ones, the stateid is a
special READ bypass stateid. When this value is used in WRITE or
SETATTR, it is treated like the anonymous value. When used in
READ, the server MAY grant access, even if access would normally
be denied to READ operations. This stateid MUST NOT be used on
operations to data servers.
* When "other" is zero and "seqid" is one, the stateid represents
the current stateid, which is whatever value is the last stateid
returned by an operation within the COMPOUND. In the case of an
OPEN, the stateid returned for the open file and not the
delegation is used. The stateid passed to the operation in place
of the special value has its "seqid" value set to zero, except
when the current stateid is used by the operation CLOSE or
OPEN_DOWNGRADE. If there is no operation in the COMPOUND that has
returned a stateid value, the server MUST return the error
NFS4ERR_BAD_STATEID. As illustrated in Figure 6, if the value of
a current stateid is a special stateid and the stateid of an
operation's arguments has "other" set to zero and "seqid" set to
one, then the server MUST return the error NFS4ERR_BAD_STATEID.
* When "other" is zero and "seqid" is NFS4_UINT32_MAX, the stateid
represents a reserved stateid value defined to be invalid. When
this stateid is used, the server MUST return the error
NFS4ERR_BAD_STATEID.
If a stateid value is used that has all zeros or all ones in the
"other" field but does not match one of the cases above, the server
MUST return the error NFS4ERR_BAD_STATEID.
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Special stateids, unlike other stateids, are not associated with
individual client IDs or filehandles and can be used with all valid
client IDs and filehandles. In the case of a special stateid
designating the current stateid, the current stateid value
substituted for the special stateid is associated with a particular
client ID and filehandle, and so, if it is used where the current
filehandle does not match that associated with the current stateid,
the operation to which the stateid is passed will return
NFS4ERR_BAD_STATEID.
13.2.4. Stateid Lifetime and Validation
Stateids must remain valid until either a client restart or a server
restart or until the client returns all of the locks associated with
the stateid by means of an operation such as CLOSE or DELEGRETURN.
If the locks are lost due to revocation, as long as the client ID is
valid, the stateid remains a valid designation of that revoked state
until the client frees it by using FREE_STATEID. Stateids associated
with byte-range locks are an exception. They remain valid even if a
LOCKU frees all remaining locks, so long as the open file with which
they are associated remains open, unless the client frees the
stateids via the FREE_STATEID operation.
It should be noted that there are situations in which the client's
locks become invalid, without the client requesting they be returned.
These include lease expiration and a number of forms of lock
revocation within the lease period. It is important to note that in
these situations, the stateid remains valid and the client can use it
to determine the disposition of the associated lost locks.
An "other" value must never be reused for a different purpose (i.e.,
different filehandle, owner, or type of locks) within the context of
a single client ID. A server may retain the "other" value for the
same purpose beyond the point where it may otherwise be freed, but if
it does so, it must maintain "seqid" continuity with previous values.
One mechanism that may be used to satisfy the requirement that the
server recognize invalid and out-of-date stateids is for the server
to divide the "other" field of the stateid into two fields.
* an index into a table of locking-state structures.
* a generation number that is incremented on each allocation of a
table entry for a particular use.
And then store in each table entry,
* the client ID with which the stateid is associated.
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* the current generation number for the (at most one) valid stateid
sharing this index value.
* the filehandle of the file on which the locks are taken.
* an indication of the type of stateid (open, byte-range lock, file
delegation, directory delegation, layout).
* the last "seqid" value returned corresponding to the current
"other" value.
* an indication of the current status of the locks associated with
this stateid, in particular, whether these have been revoked and
if so, for what reason.
With this information, an incoming stateid can be validated and the
appropriate error returned when necessary. Special and non-special
stateids are handled separately. (See Section 13.2.3 for a
discussion of special stateids.)
Note that stateids are implicitly qualified by the current client ID,
as derived from the client ID associated with the current session.
Note, however, that the semantics of the session will prevent
stateids associated with a previous client or server instance from
being analyzed by this procedure.
If server restart has resulted in an invalid client ID or a session
ID that is invalid, SEQUENCE will return an error and the operation
that takes a stateid as an argument will never be processed.
If there has been a server restart where there is a persistent
session and all leased state has been lost, then the session in
question will, although valid, be marked as dead, and any operation
not satisfied by means of the reply cache will receive the error
NFS4ERR_DEADSESSION, and thus not be processed as indicated below.
When a stateid is being tested and the "other" field is all zeros or
all ones, a check that the "other" and "seqid" fields match a defined
combination for a special stateid is done and the results determined
as follows:
* If the "other" and "seqid" fields do not match a defined
combination associated with a special stateid, the error
NFS4ERR_BAD_STATEID is returned.
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* If the special stateid is one designating the current stateid and
there is a current stateid, then the current stateid is
substituted for the special stateid and the checks appropriate to
non-special stateids are performed.
* If the combination is valid in general but is not appropriate to
the context in which the stateid is used (e.g., an all-zero
stateid is used when an OPEN stateid is required in a LOCK
operation), the error NFS4ERR_BAD_STATEID is also returned.
* Otherwise, the check is completed and the special stateid is
accepted as valid.
When a stateid is being tested, and the "other" field is neither all
zeros nor all ones, the following procedure could be used to validate
an incoming stateid and return an appropriate error, when necessary,
assuming that the "other" field would be divided into a table index
and an entry generation.
* If the table index field is outside the range of the associated
table, return NFS4ERR_BAD_STATEID.
* If the selected table entry is of a different generation than that
specified in the incoming stateid, return NFS4ERR_BAD_STATEID.
* If the selected table entry does not match the current filehandle,
return NFS4ERR_BAD_STATEID.
* If the client ID in the table entry does not match the client ID
associated with the current session, return NFS4ERR_BAD_STATEID.
* If the stateid represents revoked state, then return
NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or NFS4ERR_DELEG_REVOKED,
as appropriate.
* If the stateid type is not valid for the context in which the
stateid appears, return NFS4ERR_BAD_STATEID. Note that a stateid
may be valid in general, as would be reported by the TEST_STATEID
operation, but be invalid for a particular operation, as, for
example, when a stateid that doesn't represent byte-range locks is
passed to the non-from_open case of LOCK or to LOCKU, or when a
stateid that does not represent an open is passed to CLOSE or
OPEN_DOWNGRADE. In such cases, the server MUST return
NFS4ERR_BAD_STATEID.
* If the "seqid" field is not zero and it is greater than the
current sequence value corresponding to the current "other" field,
return NFS4ERR_BAD_STATEID.
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* If the "seqid" field is not zero and it is less than the current
sequence value corresponding to the current "other" field, return
NFS4ERR_OLD_STATEID.
* Otherwise, the stateid is valid and the table entry should contain
any additional information about the type of stateid and
information associated with that particular type of stateid, such
as the associated set of locks, e.g., open-owner and lock-owner
information, as well as information on the specific locks, e.g.,
open modes and byte-ranges.
13.2.5. Stateid Use for I/O Operations
Clients performing I/O operations need to select an appropriate
stateid based on the locks (including opens and delegations) held by
the client and the various types of state-owners sending the I/O
requests. SETATTR operations that change the file size are treated
like I/O operations in this regard.
The following rules, applied in order of decreasing priority, govern
the selection of the appropriate stateid. In following these rules,
the client will only consider locks of which it has actually received
notification by an appropriate operation response or callback. Note
that the rules are slightly different in the case of I/O to data
servers when file layouts are being used (See Section 20.14.1).
* If the client holds a delegation for the file in question, the
delegation stateid SHOULD be used.
* Otherwise, if the entity corresponding to the lock-owner (e.g., a
process) sending the I/O has a byte-range lock stateid for the
associated open file, then the byte-range lock stateid for that
lock-owner and open file SHOULD be used.
* If there is no byte-range lock stateid, then the OPEN stateid for
the open file in question SHOULD be used.
* Finally, if none of the above apply, then a special stateid SHOULD
be used.
Ignoring these rules may result in situations in which the server
does not have information necessary to properly process the request.
For example, when mandatory byte-range locks are in effect, if the
stateid does not indicate the proper lock-owner, via a lock stateid,
a request might be avoidably rejected.
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The server however should not try to enforce these ordering rules and
should use whatever information is available to properly process I/O
requests. In particular, when a client has a delegation for a given
file, it SHOULD take note of this fact in processing a request, even
if it is sent with a special stateid.
13.2.6. Stateid Use for SETATTR Operations
Because each operation is associated with a session ID and from that
the clientid can be determined, operations do not need to include a
stateid for the server to be able to determine whether they should
cause a delegation to be recalled or are to be treated as done within
the scope of the delegation.
In the case of SETATTR operations, a stateid is present. In cases
other than those that set the file size, the client may send either a
special stateid or, when a delegation is held for the file in
question, a delegation stateid. While the server SHOULD validate the
stateid and may use the stateid to optimize the determination as to
whether a delegation is held, it SHOULD note the presence of a
delegation even when a special stateid is sent, and MUST accept a
valid delegation stateid when sent.
13.3. Lease Renewal
Each client/server pair, as represented by a client ID, has a single
lease. The purpose of the lease is to allow the client to indicate
to the server, in a low-overhead way, that it is active, and thus
that the server is to retain the client's locks. This arrangement
allows the server to remove stale locking-related objects that are
held by a client that has crashed or is otherwise unreachable, once
the relevant lease expires. This in turn allows other clients to
obtain conflicting locks without being delayed indefinitely by
inactive or unreachable clients. It is not a mechanism for cache
consistency and lease renewals may not be denied if the lease
interval has not expired.
Since each session is associated with a specific client (identified
by the client's client ID), any operation sent on that session is an
indication that the associated client is reachable. When a request
is sent for a given session, successful execution of a SEQUENCE
operation (or successful retrieval of the result of SEQUENCE from the
reply cache) on an unexpired lease will result in the lease being
implicitly renewed, for the standard renewal period (equal to the
lease_time attribute).
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If the client ID's lease has not expired when the server receives a
SEQUENCE operation, then the server MUST renew the lease. If the
client ID's lease has expired when the server receives a SEQUENCE
operation, the server MAY renew the lease; this depends on whether
any state was revoked as a result of the client's failure to renew
the lease before expiration.
Absent other activity that would renew the lease, a COMPOUND
consisting of a single SEQUENCE operation will suffice. The client
should also take communication-related delays into account and take
steps to ensure that the renewal messages actually reach the server
in good time. For example:
* When trunking is in effect, the client should consider sending
multiple requests on different connections, in order to ensure
that renewal occurs, even in the event of blockage in the path
used for one of those connections.
* Transport retransmission delays might become so large as to
approach or exceed the length of the lease period. This may be
particularly likely when the server is unresponsive due to a
restart; see Section 13.4.2.1. If the client implementation is
not careful, transport retransmission delays can result in the
client failing to detect a server restart before the grace period
ends. The scenario is that the client is using a transport with
exponential backoff, such that the maximum retransmission timeout
exceeds both the grace period and the lease_time attribute. A
network partition causes the client's connection's retransmission
interval to back off, and even after the partition heals, the next
transport-level retransmission is sent after the server has
restarted and its grace period ends.
The client MUST either recover from the ensuing NFS4ERR_NO_GRACE
errors or it MUST ensure that, despite transport-level
retransmission intervals that exceed the lease_time, a SEQUENCE
operation is sent that renews the lease before expiration. The
client can achieve this by associating a new connection with the
session, and sending a SEQUENCE operation on it. However, if the
attempt to establish a new connection is delayed for some reason
(e.g., exponential backoff of the connection establishment
packets), the client will have to abort the connection
establishment attempt before the lease expires, and attempt to
reconnect.
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If the server renews the lease upon receiving a SEQUENCE operation,
the server MUST NOT allow the lease to expire while the rest of the
operations in the COMPOUND procedure's request are still executing.
Once the last operation has finished, and the response to COMPOUND
has been sent, the server MUST set the lease to expire no sooner than
the sum of current time and the value of the lease_time attribute.
A client ID's lease can expire when it has been at least the lease
interval (lease_time) since the last lease-renewing SEQUENCE
operation was sent on any of the client ID's sessions and there are
no active COMPOUND operations on any such sessions.
Because the SEQUENCE operation is the basic mechanism to renew a
lease, and because it must be done at least once for each lease
period, it is the natural mechanism whereby the server will inform
the client of changes in the lease status that the client needs to be
informed of. The client should inspect the status flags
(sr_status_flags) returned by sequence and take the appropriate
action (See Section 25.46.3 for details).
* The status bits SEQ4_STATUS_CB_PATH_DOWN and
SEQ4_STATUS_CB_PATH_DOWN_SESSION indicate problems with the
backchannel that the client may need to address in order to
receive callback requests.
* The status bits SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING and
SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED indicate problems with GSS
contexts or RPCSEC_GSS handles for the backchannel that the client
might have to address in order to allow callback requests to be
sent.
* The status bits SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED,
SEQ4_STATUS_ADMIN_STATE_REVOKED, and
SEQ4_STATUS_RECALLABLE_STATE_REVOKED notify the client of lock
revocation events. When these bits are set, the client should use
TEST_STATEID to find what stateids have been revoked and use
FREE_STATEID to acknowledge loss of the associated state.
* The status bit SEQ4_STATUS_LEASE_MOVE indicates that
responsibility for lease renewal has been transferred to one or
more new servers.
* The status bit SEQ4_STATUS_RESTART_RECLAIM_NEEDED indicates that
due to server restart the client must reclaim locking state.
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* The status bit SEQ4_STATUS_BACKCHANNEL_FAULT indicates that the
server has encountered an unrecoverable fault with the backchannel
(e.g., it has lost track of a sequence ID for a slot in the
backchannel).
13.4. Crash Recovery
A critical requirement in crash recovery is that both the client and
the server know when the other has failed. Additionally, it is
required that a client sees a consistent view of data across server
restarts. All READ and WRITE operations that may have been queued
within the client or network buffers must wait until the client has
successfully recovered the locks protecting the READ and WRITE
operations. Any that reach the server before the server can safely
determine that the client has recovered enough locking state to be
sure that such operations can be safely processed must be rejected.
This will happen because either:
* The state presented is no longer valid since it is associated with
a now invalid client ID. In this case, the client will receive
either an NFS4ERR_BADSESSION or NFS4ERR_DEADSESSION error, and any
attempt to attach a new session to that invalid client ID will
result in an NFS4ERR_STALE_CLIENTID error.
* Subsequent recovery of locks may make execution of the operation
inappropriate (NFS4ERR_GRACE).
13.4.1. Client Failure and Recovery
In the event that a client fails, the server may release the client's
locks when the associated lease has expired. Conflicting locks from
another client may only be granted after this lease expiration. As
discussed in Section 13.3, when a client has not failed and re-
establishes its lease before expiration occurs, requests for
conflicting locks will not be granted.
To minimize client delay upon restart, lock requests are associated
with an instance of the client by a client-supplied verifier. This
verifier is part of the client_owner4 sent in the initial EXCHANGE_ID
call made by the client. The server returns a client ID as a result
of the EXCHANGE_ID operation. The client then confirms the use of
the client ID by establishing a session associated with that client
ID (see Section 25.36.3 for a description of how this is done). All
locks, including opens, byte-range locks, delegations, and layouts
obtained by sessions using that client ID, are associated with that
client ID.
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Since the verifier will be changed by the client upon each
initialization, the server can compare a new verifier to the verifier
associated with currently held locks and determine that they do not
match. This signifies the client's new instantiation and subsequent
loss (upon confirmation of the new client ID) of locking state. As a
result, the server is free to release all locks held that are
associated with the old client ID that was derived from the old
verifier. At this point, conflicting locks from other clients, kept
waiting while the lease had not yet expired, can be granted. In
addition, all stateids associated with the old client ID can also be
freed, as they are no longer reference-able.
Note that the verifier must have the same uniqueness properties as
the verifier for the COMMIT operation.
13.4.2. Server Failure and Recovery
If the server loses locking state (usually as a result of a restart),
it must allow clients time to discover this fact and re-establish the
lost locking state. The client must be able to re-establish the
locking state without having the server deny valid requests because
the server has granted conflicting access to another client.
Likewise, if there is a possibility that clients have not yet re-
established their locking state for a file and that such locking
state might make it invalid to perform READ or WRITE operations. For
example, if mandatory locks are a possibility, the server must
disallow READ and WRITE operations for that file.
A client can determine that loss of locking state has occurred via
several methods.
1. When a SEQUENCE (most common) or other operation returns
NFS4ERR_BADSESSION, this may mean that the session has been
destroyed but the client ID is still valid. The client sends a
CREATE_SESSION request with the client ID to re-establish the
session. If CREATE_SESSION fails with NFS4ERR_STALE_CLIENTID,
the client must establish a new client ID (see Section 13.1) and
re-establish its lock state with the new client ID, after the
CREATE_SESSION operation succeeds (See Section 13.4.2.1).
2. When a SEQUENCE (most common) or other operation on a persistent
session returns NFS4ERR_DEADSESSION, this indicates that a
session is no longer usable for new, i.e., not satisfied from the
reply cache, operations. Once all pending operations are
determined to be either performed before the retry or not
performed, the client sends a CREATE_SESSION request with the
client ID to re-establish the session. If CREATE_SESSION fails
with NFS4ERR_STALE_CLIENTID, the client must establish a new
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client ID (see Section 13.1) and re-establish its lock state
after the CREATE_SESSION, with the new client ID, succeeds
(Section 13.4.2.1).
3. When an operation, neither SEQUENCE nor preceded by SEQUENCE (for
example, CREATE_SESSION, DESTROY_SESSION), returns
NFS4ERR_STALE_CLIENTID, the client MUST establish a new client ID
(Section 13.1) and re-establish its lock state
(Section 13.4.2.1).
13.4.2.1. State Reclaim
When state information and the associated locks are lost as a result
of a server restart, the protocol must provide a way to cause that
state to be re-established. The approach used is to define, for most
types of locking state (layouts are an exception), a request whose
function is to allow the client to re-establish on the server a lock
first obtained from a previous instance. Generally, these requests
are variants of the requests normally used to create locks of that
type and are referred to as "reclaim-type" requests, and the process
of re-establishing such locks is referred to as "reclaiming" them.
Because each client must have an opportunity to reclaim all of the
locks that it has without the possibility that some other client will
be granted a conflicting lock, a "grace period" is devoted to the
reclaim process. During this period, requests creating client IDs
and sessions are handled normally, but locking requests are subject
to special restrictions. Only reclaim-type locking requests are
allowed, unless the server can reliably determine (through state
persistently maintained across restart instances) that granting any
such lock cannot possibly conflict with a subsequent reclaim. When a
request is made to obtain a new lock (i.e., not a reclaim-type
request) during the grace period and such a determination cannot be
made, the server must return the error NFS4ERR_GRACE.
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Once a session is established using the new client ID, the client
will use reclaim-type locking requests (e.g., LOCK operations with
reclaim set to TRUE and OPEN operations with a claim type of
CLAIM_PREVIOUS; see Section 14.11) to re-establish its locking state.
Once this is done, or if there is no such locking state to reclaim,
the client sends a global RECLAIM_COMPLETE operation, i.e., one with
the rca_one_fs argument set to FALSE, to indicate that it has
reclaimed all of the locking state that it will reclaim. Once a
client sends such a RECLAIM_COMPLETE operation, it may attempt non-
reclaim locking operations, although it might get an NFS4ERR_GRACE
status result from each such operation until the period of special
handling is over. See Section 17.11.9 for a discussion of the
analogous handling lock reclamation in the case of file systems
transitioning from server to server.
During the grace period, the server must reject any non-reclaim
locking requests (i.e., other LOCK and OPEN operations) with an error
of NFS4ERR_GRACE, unless it can guarantee that these may be done
safely, as described below. In addition, READ and WRITE requests
that are not associated with a reclaimed OPEN need to be rejected as
well.
The grace period may last until all clients that are known to have
possibly had locks have done a global RECLAIM_COMPLETE operation,
indicating that they have finished reclaiming the locks they held
before the server restart. This means that a client that has done a
RECLAIM_COMPLETE must be prepared to receive an NFS4ERR_GRACE when
attempting to acquire new locks. In order for the server to know
that all clients with possible prior lock state have done a
RECLAIM_COMPLETE, the server must maintain in stable storage a list
clients that may have such locks. The server may also terminate the
grace period before all clients have done a global RECLAIM_COMPLETE.
The server SHOULD NOT terminate the grace period without all expected
RECLAIM_COPLETEs before a time equal to the lease period in order to
give clients an opportunity to find out about the server restart, as
a result of sending requests on associated sessions with a frequency
governed by the lease time. Note that when a client does not send
such requests (or they are sent by the client but not received by the
server), it is possible for the grace period to expire before the
client finds out that the server restart has occurred.
Some additional time in order to allow a client to establish a new
client ID and session and to effect lock reclaims may be added to the
lease time. Note that analogous rules apply to file system-specific
grace periods discussed in Section 17.11.9.
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If the server can reliably determine that granting a non-reclaim
request will not conflict with reclamation of locks by other clients,
the NFS4ERR_GRACE error does not have to be returned even within the
grace period, although NFS4ERR_GRACE must always be returned to
clients attempting a non-reclaim lock request before doing their own
global RECLAIM_COMPLETE. For the server to be able to service READ
and WRITE operations during the grace period, it must again be able
to guarantee that no possible conflict could arise between a
potential reclaim locking request and the READ or WRITE operation.
If the server is unable to offer that guarantee, the NFS4ERR_GRACE
error must be returned to the client.
For a server to provide simple, valid handling during the grace
period, the easiest method is to simply reject all non-reclaim
locking requests and READ and WRITE operations not subsumed within
reclaimed OPENs by returning the NFS4ERR_GRACE error. However, a
server may keep information about granted locks in stable storage.
With this information, the server could determine if a locking
operation, or a READ or WRITE outside a reclaimed OPEN can be safely
processed.
For example, if the server maintained on stable storage summary
information on whether mandatory locks exist, either mandatory byte-
range locks, or share reservations specifying deny modes, many
requests could be allowed during the grace period. If it is known
that no such share reservations exist, OPEN request that do not
specify deny modes can be safely granted. If, in addition, it is
known that no mandatory byte-range locks exist, either through
information stored on stable storage or simply because the server
does not support such locks, READ and WRITE operations may be safely
processed during the grace period. Another important case is where
it is known that no mandatory byte-range locks exist, either because
the server does not provide support for them or because their absence
is known from persistently recorded data. In this case, READ and
WRITE operations specifying stateids derived from reclaim-type
operations may be validly processed during the grace period because
of the fact that the valid reclaim ensures that no lock subsequently
granted can prevent the I/O.
To reiterate, for a server that allows non-reclaim lock and I/O
requests to be processed during the grace period, it MUST determine
that no lock subsequently reclaimed will be rejected and that no lock
subsequently reclaimed would have prevented any I/O operation
processed during the grace period.
Clients should be prepared for the return of NFS4ERR_GRACE errors for
non-reclaim lock and I/O requests. In this case, the client should
employ a retry mechanism for the request. A delay (on the order of
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several seconds) between retries should be used to avoid overwhelming
the server. Further discussion of the general issue is included in
[Floyd]. The client must account for the server that can perform I/O
and non-reclaim locking requests within the grace period as well as
those that cannot do so.
A reclaim-type locking request outside the server's grace period can
only succeed if the server can guarantee that no conflicting lock or
I/O request has been granted since restart.
A server may, upon restart, establish a new value for the lease
period. Therefore, clients should, once a new client ID is
established, refetch the lease_time attribute and use it as the basis
for lease renewal for the lease associated with that server.
However, the server must establish, for this restart event, a grace
period at least as long as the lease period for the previous server
instantiation. This allows the client state obtained during the
previous server instance to be reliably re-established.
The possibility exists that, because of server configuration events,
the client will be communicating with a server different than the one
on which the locks were obtained, as shown by the combination of
eir_server_scope and eir_server_owner. This leads to the issue of if
and when the client should attempt to reclaim locks previously
obtained on what is being reported as a different server. The rules
to resolve this question are as follows:
* If the server scope is different, the client should not attempt to
reclaim locks. In this situation, no lock reclaim is possible.
Any attempt to re-obtain the locks with non-reclaim operations is
problematic since there is no guarantee that the existing
filehandles will be recognized by the new server, or that if
recognized, they denote the same objects. It is best to treat the
locks as having been revoked by the reconfiguration event.
* If the server scope is the same, the client should attempt to
reclaim locks, even if the eir_server_owner value is different.
In this situation, it is the responsibility of the server to
return NFS4ERR_NO_GRACE if it cannot provide correct support for
lock reclaim operations, including the prevention of edge
conditions.
The eir_server_owner field is not used in making this determination.
Its function is to specify trunking possibilities for the client (See
Section 7.5) and not to control lock reclaim.
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13.4.2.1.1. Security Issues for State Reclaim
During the grace period, a client can reclaim state that it believes
or asserts it had before the server restarted. Unless the server has
maintained a complete record of all the state the client had, the
server has little choice but to trust the client's requests. (Of
course, if the server maintained a complete record, then there would
be no need to force the client to reclaim state after server
restart.) While the server has to trust the client to tell the
truth, the negative consequences for security are limited to enabling
denial-of-service attacks in situations in which AUTH_SYS,
particularly AUTH_SYS in the clear, is supported. The fundamental
rule for the server when processing reclaim requests is that it MUST
NOT grant the reclaim if an equivalent non-reclaim request would not
be granted during steady state due to access control or access
conflict issues. For example, an OPEN request during a reclaim will
be refused with NFS4ERR_ACCESS if the principal making the request
does not have sufficient access to open the file according to the
acl, dacl, or mode attributes of the file.
Nonetheless, it is possible that a client operating in error or
maliciously could, during reclaim, prevent another client from
reclaiming access to state. For example, an attacker could send an
OPEN reclaim operation with a deny mode that prevents another client
from reclaiming the OPEN state it had before the server restarted.
The attacker could perform the same denial of service during steady
state prior to server restart, as long as the attacker had
permissions. Given that the attack vectors are equivalent, the grace
period does not offer any additional opportunity for denial of
service, and any concerns about this attack vector, whether during
grace or steady state, are addressed in the same way, by using
RPCSEC_GSS for authentication and limiting access to the file only to
principals that the owner of the file trusts.
Note that if prior to restart the server had client IDs with the
EXCHGID4_FLAG_BIND_PRINC_STATEID (Section 25.35) capability set, then
the server SHOULD record in stable storage the client owner id and
the principal that established the client ID via EXCHANGE_ID. If the
server does not do so, then there is a risk a client will be unable
to reclaim state if it does not have a credential for a principal
that was originally authorized to establish the state.
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13.4.3. Network Partitions and Recovery
If the duration of a network partition is greater than the lease
period provided by the server, the server will not have received a
lease renewal from the client. If this occurs, the server may free
all locks held for the client or it may allow the lock state to
remain for a considerable period, subject to the constraint that if a
request for a conflicting lock is made, locks associated with an
expired lease do not prevent such a conflicting lock from being
granted but MUST be revoked as necessary so as to avoid interfering
with such conflicting requests.
If the server chooses to delay freeing of lock state until there is a
conflict, it may either free all of the client's locks once there is
a conflict or it may only revoke the minimum set of locks necessary
to allow conflicting requests. When it adopts the finer-grained
approach, it must revoke all locks associated with a given stateid,
even if the conflict is with only a subset of locks.
When the server chooses to free all of a client's lock state, either
immediately upon lease expiration or as a result of the first attempt
to obtain a conflicting a lock, the server may report the loss of
lock state in a number of ways.
The server may choose to invalidate the session and the associated
client ID. In this case, once the client can communicate with the
server, it will receive an NFS4ERR_BADSESSION error. Upon attempting
to create a new session, it would get an NFS4ERR_STALE_CLIENTID.
Upon creating the new client ID and new session, the client will
attempt to reclaim locks. Normally, the server will not allow the
client to reclaim locks, because the server will not be in its
recovery grace period.
Another possibility is for the server to maintain the session and
client ID but for all stateids held by the client to become invalid
or stale. Once the client can reach the server after such a network
partition, the status returned by the SEQUENCE operation will
indicate a loss of locking state; i.e., the flag
SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED will be set in sr_status_flags.
In addition, all I/O submitted by the client with the now invalid
stateids will fail with the server returning the error
NFS4ERR_EXPIRED. Once the client learns of the loss of locking
state, it will suitably notify the applications that held the
invalidated locks. The client should then take action to free
invalidated stateids, either by establishing a new client ID using a
new verifier or by doing a FREE_STATEID operation to release each of
the invalidated stateids.
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When the server adopts a finer-grained approach to revocation of
locks when a client's lease has expired, only a subset of stateids
will normally become invalid during a network partition. When the
client can communicate with the server after such a network partition
heals, the status returned by the SEQUENCE operation will indicate a
partial loss of locking state
(SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED). In addition, operations,
including I/O submitted by the client, with the now invalid stateids
will fail with the server returning the error NFS4ERR_EXPIRED. Once
the client learns of the loss of locking state, it will use the
TEST_STATEID operation on all of its stateids to determine which
locks have been lost and then suitably notify the applications that
held the invalidated locks. The client can then release the
invalidated locking state and acknowledge the revocation of the
associated locks by doing a FREE_STATEID operation on each of the
invalidated stateids.
When a network partition is combined with a server restart, there are
edge conditions that place requirements on the server in order to
avoid silent data corruption following the server restart. Two of
these edge conditions are known, and are discussed below.
The first edge condition arises as a result of the scenarios such as
the following:
1. Client A acquires a lock.
2. Client A and server experience mutual network partition, such
that client A is unable to renew its lease.
3. Client A's lease expires, and the server releases the lock.
4. Client B acquires a lock that would have conflicted with that of
client A.
5. Client B releases its lock.
6. Server restarts.
7. Network partition between client A and server heals.
8. Client A connects to a new server instance and finds out about
server restart.
9. Client A reclaims its lock within the server's grace period.
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Thus, at the final step, the server has erroneously granted client
A's lock reclaim. If client B modified the object the lock was
protecting, client A will experience object corruption.
The second known edge condition arises in situations such as the
following:
1. Client A acquires one or more locks.
2. Server restarts.
3. Client A and server experience mutual network partition, such
that client A is unable to reclaim all of its locks within the
grace period.
4. Server's reclaim grace period ends. Client A has either no
locks or an incomplete set of locks known to the server.
5. Client B acquires a lock that would have conflicted with a lock
of client A that was not reclaimed.
6. Client B releases the lock.
7. Server restarts a second time.
8. Network partition between client A and server heals.
9. Client A connects to new server instance and finds out about
server restart.
10. Client A reclaims its lock within the server's grace period.
As with the first edge condition, the final step of the scenario of
the second edge condition has the server erroneously granting client
A's lock reclaim.
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Solving the first and second edge conditions requires either that the
server always assumes after it restarts that some edge condition
occurs, and thus returns NFS4ERR_NO_GRACE for all reclaim attempts,
or that the server record some information in stable storage. The
amount of information the server records in stable storage is in
inverse proportion to how harsh the server intends to be whenever
edge conditions arise. The server that is completely tolerant of all
edge conditions will record in stable storage every lock that is
acquired, removing the lock record from stable storage only when the
lock is released. For the two edge conditions discussed above, the
harshest a server can be, and still support a grace period for
reclaims, requires that the server record in stable storage some
minimal information. For example, a server implementation could, for
each client, save in stable storage a record containing:
* the co_ownerid field from the client_owner4 presented in the
EXCHANGE_ID operation.
* a boolean that indicates if the client's lease expired or if there
was administrative intervention (see Section 13.5) to revoke a
byte-range lock, share reservation, or delegation and there has
been no acknowledgment, via FREE_STATEID, of such revocation.
* a boolean that indicates whether the client may have locks that it
believes to be reclaimable in situations in which the grace period
was terminated, making the server's view of lock reclaimability
suspect. The server will set this for any client record in stable
storage where the client has not done a suitable RECLAIM_COMPLETE
(global or file system-specific depending on the target of the
lock request) before it grants any new (i.e., not reclaimed) lock
to any client.
Assuming the above record keeping, for the first edge condition,
after the server restarts, the record that client A's lease expired
means that another client could have acquired a conflicting byte-
range lock, share reservation, or delegation. Hence, the server must
reject a reclaim from client A with the error NFS4ERR_NO_GRACE.
For the second edge condition, after the server restarts for a second
time, the indication that the client had not completed its reclaims
at the time at which the grace period ended means that the server
must reject a reclaim from client A with the error NFS4ERR_NO_GRACE.
When either edge condition occurs, the client's attempt to reclaim
locks will result in the error NFS4ERR_NO_GRACE. When this is
received, or after the client restarts with no lock state, the client
will send a global RECLAIM_COMPLETE. When the RECLAIM_COMPLETE is
received, the server and client are again in agreement regarding
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reclaimable locks and both booleans in persistent storage can be
reset, to be set again only when there is a subsequent event that
causes lock reclaim operations to be questionable.
Regardless of the level and approach to record keeping, the server
MUST implement one of the following strategies (which apply to
reclaims of share reservations, byte-range locks, and delegations):
1. Reject all reclaims with NFS4ERR_NO_GRACE. This is extremely
unforgiving, but necessary if the server does not record lock
state in stable storage.
2. Record sufficient state in stable storage such that all known
edge conditions involving server restart, including the two noted
in this section, are detected. It is acceptable to erroneously
recognize an edge condition and not allow a reclaim, when, with
sufficient knowledge, it would be allowed. The error the server
would return in this case is NFS4ERR_NO_GRACE. Note that it is
not known if there are other edge conditions.
In the event that, after a server restart, the server determines
there is unrecoverable damage or corruption to the information in
stable storage, then for all clients and/or locks that may be
affected, the server MUST return NFS4ERR_NO_GRACE.
A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
outside the scope of this specification, since the strategies for
such handling are very dependent on the client's operating
environment. However, one potential approach is described below.
When the client receives NFS4ERR_NO_GRACE, it could examine the
change attribute of the objects for which the client is trying to
reclaim state, and use that to determine whether to re-establish the
state via normal OPEN or LOCK operations. This is acceptable
provided that the client's operating environment allows it. In other
words, the client implementer is advised to document for his users
the behavior. The client could also inform the application that its
byte-range lock or share reservations (whether or not they were
delegated) have been lost, such as via a UNIX signal, a Graphical
User Interface (GUI) pop-up window, etc. See Section 15.5 for a
discussion of what the client should do for dealing with unreclaimed
delegations on client state.
For further discussion of revocation of locks, see Section 13.5.
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13.5. Server Revocation of Locks
At any point, the server can revoke locks held by a client, and the
client must be prepared for this event. When the client detects that
its locks have been or may have been revoked, the client is
responsible for validating the state information between itself and
the server. Validating locking state for the client means that it
must verify or reclaim state for each lock currently held.
The first occasion of lock revocation is upon server restart. Note
that this includes situations in which sessions are persistent and
locking state is lost. In this class of instances, the client will
receive an error (NFS4ERR_STALE_CLIENTID) on an operation that takes
client ID, usually as part of recovery in response to a problem with
the current session), and the client will proceed with normal crash
recovery as described in the Section 13.4.2.1.
The second occasion of lock revocation is the inability to renew the
lease before expiration, as discussed in Section 13.4.3. While this
is considered a rare or unusual event, the client must be prepared to
recover. The server is responsible for determining the precise
consequences of the lease expiration, informing the client of the
scope of the lock revocation decided upon. The client then uses the
status information provided by the server in the SEQUENCE results
(field sr_status_flags, see Section 25.46.3) to synchronize its
locking state with that of the server, in order to recover.
The third occasion of lock revocation can occur as a result of
revocation of locks within the lease period, either because of
administrative intervention or because a recallable lock (a
delegation or layout) was not returned within the lease period after
having been recalled. While these are considered rare events, they
are possible, and the client must be prepared to deal with them.
When either of these events occurs, the client finds out about the
situation through the status returned by the SEQUENCE operation. Any
use of stateids associated with locks revoked during the lease period
will receive the error NFS4ERR_ADMIN_REVOKED or
NFS4ERR_DELEG_REVOKED, as appropriate.
In all situations in which a subset of locking state may have been
revoked, which include all cases in which locking state is revoked
within the lease period, it is up to the client to determine which
locks have been revoked and which have not. It does this by using
the TEST_STATEID operation on the appropriate set of stateids. Once
the set of revoked locks has been determined, the applications can be
notified, and the invalidated stateids can be freed and lock
revocation acknowledged by using FREE_STATEID.
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13.6. Short and Long Leases
When determining the time period for the server lease, the usual
lease trade-offs apply. A short lease is good for fast server
recovery at a cost of increased operations to effect lease renewal
(when there are no other operations during the period to effect lease
renewal as a side effect). A long lease is certainly kinder and
gentler to servers trying to handle very large numbers of clients.
The number of extra requests to effect lock renewal drops in inverse
proportion to the lease time. The disadvantages of a long lease
include the possibility of slower recovery after certain failures.
After server failure, a longer grace period may be required when some
clients do not promptly reclaim their locks and do a global
RECLAIM_COMPLETE. In the event of client failure, the longer period
for a lease to expire will force conflicting requests to wait longer.
A long lease is practical if the server can store lease state in
stable storage. Upon recovery, the server can reconstruct the lease
state from its stable storage and continue operation with its
clients.
13.7. Clocks, Propagation Delay, and Calculating Lease Expiration
To avoid the need for synchronized clocks, lease times are granted by
the server as a time delta. However, there is a requirement that the
client and server clocks do not drift excessively over the duration
of the lease. There is also the issue of propagation delay across
the network, which could easily be several hundred milliseconds, as
well as the possibility that requests will be lost and need to be
retransmitted.
To take propagation delay into account, the client should subtract it
from lease times (e.g., if the client estimates the one-way
propagation delay as 200 milliseconds, then it can assume that the
lease is already 200 milliseconds old when it gets it). In addition,
it will take another 200 milliseconds to get a response back to the
server. So the client must send a lease renewal or write data back
to the server at least 400 milliseconds before the lease would
expire. If the propagation delay varies over the life of the lease
(e.g., the client is on a mobile host), the client will need to
continuously subtract the increase in propagation delay from the
lease times.
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The server's lease period configuration should take into account the
network distance of the clients that will be accessing the server's
resources. It is expected that the lease period will take into
account the network propagation delays and other network delay
factors for the client population. Since the protocol does not allow
for an automatic method to determine an appropriate lease period, the
server's administrator may have to tune the lease period.
13.8. Obsolete Locking Infrastructure from NFSv4.0
There are a number of operations and fields within existing
operations that no longer have a function in NFSv4.1. In one way or
another, these changes are all due to the implementation of sessions
that provide client context and exactly once semantics as a base
feature of the protocol, separate from locking itself.
The following NFSv4.0 operations MUST NOT be implemented in NFSv4.1.
The server MUST return NFS4ERR_NOTSUPP if these operations are found
in an NFSv4.1 COMPOUND.
* SETCLIENTID since its function has been replaced by EXCHANGE_ID.
* SETCLIENTID_CONFIRM since client ID confirmation now happens by
means of CREATE_SESSION.
* OPEN_CONFIRM because state-owner-based seqids have been replaced
by the sequence ID in the SEQUENCE operation.
* RELEASE_LOCKOWNER because lock-owners with no associated locks do
not have any sequence-related state and so can be deleted by the
server at will.
* RENEW because every SEQUENCE operation for a session causes lease
renewal, making a separate operation superfluous.
Also, there are a number of fields, present in existing operations,
related to locking that have no use in minor version 1. They were
used in minor version 0 to perform functions now provided in a
different fashion.
* Sequence ids used to sequence requests for a given state-owner and
to provide retry protection, now provided via sessions.
* Client IDs used to identify the client associated with a given
request. Client identification is now available using the client
ID associated with the current session, without needing an
explicit client ID field.
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Such vestigial fields in existing operations have no function in
NFSv4.1 and are ignored by the server. Note that client IDs in
operations new to NFSv4.1 (such as CREATE_SESSION and
DESTROY_CLIENTID) are not ignored.
14. File Locking and Share Reservations
To support Win32 share reservations, it is necessary to provide
operations that atomically open or create files. Having a separate
share/unshare operation would not allow correct implementation of the
Win32 OpenFile API. In order to correctly implement share semantics,
the previous NFS protocol mechanisms used when a file is opened or
created (LOOKUP, CREATE, ACCESS) need to be replaced. The NFSv4.1
protocol defines an OPEN operation that is capable of atomically
looking up, creating, and locking a file on the server.
14.1. Opens and Byte-Range Locks
It is assumed that manipulating a byte-range lock is rare when
compared to READ and WRITE operations. It is also assumed that
server restarts and network partitions are relatively rare.
Therefore, it is important that the READ and WRITE operations have a
lightweight mechanism to indicate if they possess a held lock. A
LOCK operation contains the heavyweight information required to
establish a byte-range lock and uniquely define the owner of the
lock.
14.1.1. State-Owner Definition
When opening a file or requesting a byte-range lock, the client must
specify an identifier that represents the owner of the requested
lock. This identifier is in the form of a state-owner, represented
in the protocol by a state_owner4, a variable-length opaque array
that, when concatenated with the current client ID, uniquely defines
the owner of a lock managed by the client. This may be a thread ID,
process ID, or other unique value.
Owners of opens and owners of byte-range locks are separate entities
and remain separate even if the same opaque arrays are used to
designate owners of each. The protocol distinguishes between open-
owners (represented by open_owner4 structures) and lock-owners
(represented by lock_owner4 structures).
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Each open is associated with a specific open-owner while each byte-
range lock is associated with a lock-owner and an open-owner, the
latter being the open-owner associated with the open file under which
the LOCK operation was done. Delegations and layouts, on the other
hand, are not associated with a specific owner but are associated
with the client as a whole (identified by a client ID).
14.1.2. Use of the Stateid and Locking
All READ, WRITE, and SETATTR operations contain a stateid. For the
purposes of this section, SETATTR operations that change the size
attribute of a file are treated as if they are writing the area
between the old and new sizes (i.e., the byte-range truncated or
added to the file by means of the SETATTR), even where SETATTR is not
explicitly mentioned in the text. The stateid passed to one of these
operations must be one that represents an open, a set of byte-range
locks, or a delegation, or it may be a special stateid representing
anonymous access or the special bypass stateid.
If the state-owner performs a READ or WRITE operation in a situation
in which it has established a byte-range lock or share reservation on
the server (any OPEN constitutes a share reservation), the stateid
(previously returned by the server) must be used to indicate what
locks, including both byte-range locks and share reservations, are
held by the state-owner. If no state is established by the client,
either a byte-range lock or a share reservation, a special stateid
for anonymous state (zero as the value for "other" and "seqid") is
used. (See Section 13.2.3 for a description of 'special' stateids in
general.) Regardless of whether a stateid for anonymous state or a
stateid returned by the server is used, if there is a conflicting
share reservation or mandatory byte-range lock held on the file, the
server MUST refuse to service the READ or WRITE operation.
Share reservations are established by OPEN operations and by their
nature are mandatory in that when the OPEN denies READ or WRITE
operations, that denial results in such operations being rejected
with error NFS4ERR_LOCKED. Byte-range locks may be implemented by
the server as either mandatory or advisory, or the choice of
mandatory or advisory behavior may be determined by the server on the
basis of the file being accessed (for example, some UNIX-based
servers support a "mandatory lock bit" on the mode attribute such
that if set, byte-range locks are required on the file before I/O is
possible). When byte-range locks are advisory, they only prevent the
granting of conflicting lock requests and have no effect on READs or
WRITEs. Mandatory byte-range locks, however, prevent conflicting I/O
operations. When they are attempted, they are rejected with
NFS4ERR_LOCKED. When the client gets NFS4ERR_LOCKED on a file for
which it knows it has the proper share reservation, it will need to
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send a LOCK operation on the byte-range of the file that includes the
byte-range the I/O was to be performed on, with an appropriate
locktype field of the LOCK operation's arguments (i.e., READ*_LT for
a READ operation, WRITE*_LT for a WRITE operation).
Note that for UNIX environments that support mandatory byte-range
locking, the distinction between advisory and mandatory locking is
subtle. In fact, advisory and mandatory byte-range locks are exactly
the same as far as the APIs and requirements on implementation. If
the mandatory lock attribute is set on the file, the server checks to
see if the lock-owner has an appropriate shared (READ_LT) or
exclusive (WRITE_LT) byte-range lock on the byte-range it wishes to
READ from or WRITE to. If there is no appropriate lock, the server
checks if there is a conflicting lock (which can be done by
attempting to acquire the conflicting lock on behalf of the lock-
owner, and if successful, release the lock after the READ or WRITE
operation is done), and if there is, the server returns
NFS4ERR_LOCKED.
For Windows environments, byte-range locks are always mandatory, so
the server always checks for byte-range locks during I/O requests.
Thus, the LOCK operation does not need to distinguish between
advisory and mandatory byte-range locks. It is the server's
processing of the READ and WRITE operations that introduces the
distinction.
Every stateid that is validly passed to READ, WRITE, or SETATTR, with
the exception of special stateid values, defines an access mode for
the file (i.e., OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
OPEN4_SHARE_ACCESS_BOTH).
* For stateids associated with opens, this is the mode defined by
the original OPEN that caused the allocation of the OPEN stateid
and as modified by subsequent OPENs and OPEN_DOWNGRADEs for the
same open-owner/file pair.
* For stateids returned by byte-range LOCK operations, the
appropriate mode is the access mode for the OPEN stateid
associated with the lock set represented by the stateid.
* For delegation stateids, the access mode is based on the type of
delegation.
When a READ, WRITE, or SETATTR (that specifies the size attribute)
operation is done, the operation is subject to checking against the
access mode to verify that the operation is appropriate given the
stateid with which the operation is associated.
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In the case of WRITE-type operations (i.e., WRITEs and SETATTRs that
set size), the server MUST verify that the access mode allows writing
and MUST return an NFS4ERR_OPENMODE error if it does not. In the
case of READ, the server may perform the corresponding check on the
access mode, or it may choose to allow READ on OPENs for
OPEN4_SHARE_ACCESS_WRITE, to accommodate clients whose WRITE
implementation may unavoidably do reads (e.g., due to buffer cache
constraints). However, even if READs are allowed in these
circumstances, the server MUST still check for locks that conflict
with the READ (e.g., another OPEN specified OPEN4_SHARE_DENY_READ or
OPEN4_SHARE_DENY_BOTH). Note that a server that does enforce the
access mode check on READs need not explicitly check for conflicting
share reservations since the existence of OPEN for
OPEN4_SHARE_ACCESS_READ guarantees that no conflicting share
reservation can exist.
The READ bypass special stateid (all bits of "other" and "seqid" set
to one) indicates a desire to bypass locking checks. The server MAY
allow READ operations to bypass locking checks at the server, when
this special stateid is used. However, WRITE operations with this
special stateid value MUST NOT bypass locking checks and are treated
exactly the same as if a special stateid for anonymous state were
used.
A lock may not be granted while a READ or WRITE operation using one
of the special stateids is being performed and the scope of the lock
to be granted would conflict with the READ or WRITE operation. This
can occur when:
* A mandatory byte-range lock is requested with a byte-range that
conflicts with the byte-range of the READ or WRITE operation. For
the purposes of this paragraph, a conflict occurs when a shared
lock is requested and a WRITE operation is being performed, or an
exclusive lock is requested and either a READ or a WRITE operation
is being performed.
* A share reservation is requested that denies reading and/or
writing and the corresponding operation is being performed.
* A delegation is to be granted and the delegation type would
prevent the I/O operation, i.e., READ and WRITE conflict with an
OPEN_DELEGATE_WRITE delegation and WRITE conflicts with an
OPEN_DELEGATE_READ delegation.
When a client holds a delegation, it needs to ensure that the stateid
sent conveys the association of operation with the delegation, to
avoid the delegation from being avoidably recalled. When the
delegation stateid, a stateid open associated with that delegation,
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or a stateid representing byte-range locks derived from such an open
is used, the server knows that the READ, WRITE, or SETATTR does not
conflict with the delegation but is sent under the aegis of the
delegation. Even though it is possible for the server to determine
from the client ID (via the session ID) that the client does in fact
have a delegation, the server is not obliged to check this, so using
a special stateid can result in avoidable recall of the delegation.
14.2. Lock Ranges
The protocol allows a lock-owner to request a lock with a byte-range
and then either upgrade, downgrade, or unlock a sub-range of the
initial lock, or a byte-range that overlaps -- fully or partially --
either with that initial lock or a combination of a set of existing
locks for the same lock-owner. It is expected that this will be an
uncommon type of request. In any case, servers or server file
systems may not be able to support sub-range lock semantics. In the
event that a server receives a locking request that represents a sub-
range of current locking state for the lock-owner, the server is
allowed to return the error NFS4ERR_LOCK_RANGE to signify that it
does not support sub-range lock operations. Therefore, the client
should be prepared to receive this error and, if appropriate, report
the error to the requesting application.
The client is discouraged from combining multiple independent locking
ranges that happen to be adjacent into a single request since the
server may not support sub-range requests for reasons related to the
recovery of byte-range locking state in the event of server failure.
As discussed in Section 13.4.2, the server may employ certain
optimizations during recovery that work effectively only when the
client's behavior during lock recovery is similar to the client's
locking behavior prior to server failure.
14.3. Upgrading and Downgrading Locks
If a client has a WRITE_LT lock on a byte-range, it can request an
atomic downgrade of the lock to a READ_LT lock via the LOCK
operation, by setting the type to READ_LT. If the server supports
atomic downgrade, the request will succeed. If not, it will return
NFS4ERR_LOCK_NOTSUPP. The client should be prepared to receive this
error and, if appropriate, report the error to the requesting
application.
If a client has a READ_LT lock on a byte-range, it can request an
atomic upgrade of the lock to a WRITE_LT lock via the LOCK operation
by setting the type to WRITE_LT or WRITEW_LT. If the server does not
support atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP. If the
upgrade can be achieved without an existing conflict, the request
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will succeed. Otherwise, the server will return either
NFS4ERR_DENIED or NFS4ERR_DEADLOCK. The error NFS4ERR_DEADLOCK is
returned if the client sent the LOCK operation with the type set to
WRITEW_LT and the server has detected a deadlock. The client should
be prepared to receive such errors and, if appropriate, report the
error to the requesting application.
14.4. Stateid Seqid Values and Byte-Range Locks
When a LOCK or LOCKU operation is performed, the stateid returned has
the same "other" value as the argument's stateid, and a "seqid" value
that is incremented (relative to the argument's stateid) to reflect
the occurrence of the LOCK or LOCKU operation. The server MUST
increment the value of the "seqid" field whenever there is any change
to the locking status of any byte offset as described by any of the
locks covered by the stateid. A change in locking status includes a
change from locked to unlocked or the reverse or a change from being
locked for READ_LT to being locked for WRITE_LT or the reverse.
When there is no such change, as, for example, when a range already
locked for WRITE_LT is locked again for WRITE_LT, the server MAY
increment the "seqid" value.
14.5. Issues with Multiple Open-Owners
When the same file is opened by multiple open-owners, a client will
have multiple OPEN stateids for that file, each associated with a
different open-owner. In that case, there can be multiple LOCK and
LOCKU requests for the same lock-owner sent using the different OPEN
stateids, and so a situation may arise in which there are multiple
stateids, each representing byte-range locks on the same file and
held by the same lock-owner but each associated with a different
open-owner.
In such a situation, the locking status of each byte (i.e., whether
it is locked, the READ_LT or WRITE_LT type of the lock, and the lock-
owner holding the lock) MUST reflect the last LOCK or LOCKU operation
done for the lock-owner in question, independent of the stateid
through which the request was sent.
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When a byte is locked by the lock-owner in question, the open-owner
to which that byte-range lock is assigned SHOULD be that of the open-
owner associated with the stateid through which the last LOCK of that
byte was done. When there is a change in the open-owner associated
with locks for the stateid through which a LOCK or LOCKU was done,
the "seqid" field of the stateid MUST be incremented, even if the
locking, in terms of lock-owners has not changed. When there is a
change to the set of locked bytes associated with a different stateid
for the same lock-owner, i.e., associated with a different open-
owner, the "seqid" value for that stateid MUST NOT be incremented.
14.6. Blocking Locks
Some clients require the support of blocking locks. While NFSv4.1
provides a callback when a previously unavailable lock becomes
available, this is an OPTIONAL feature and clients cannot depend on
its presence. Clients need to be prepared to continually poll for
the lock. This presents a fairness problem. Two of the lock types,
READW_LT and WRITEW_LT, are used to indicate to the server that the
client is requesting a blocking lock. When the callback is not used,
the server should maintain an ordered list of pending blocking locks.
When the conflicting lock is released, the server may wait for the
period of time equal to lease_time for the first waiting client to
re-request the lock. After the lease period expires, the next
waiting client request is allowed the lock. Clients are required to
poll at an interval sufficiently small that it is likely to acquire
the lock in a timely manner. The server is not required to maintain
a list of pending blocked locks as it is used to increase fairness
and not correct operation. Because of the unordered nature of crash
recovery, storing of lock state to stable storage would be required
to guarantee ordered granting of blocking locks.
Servers may also note the lock types and delay returning denial of
the request to allow extra time for a conflicting lock to be
released, allowing a successful return. In this way, clients can
avoid the burden of needless frequent polling for blocking locks.
The server should take care in the length of delay in the event the
client retransmits the request.
If a server receives a blocking LOCK operation, denies it, and then
later receives a nonblocking request for the same lock, which is also
denied, then it should remove the lock in question from its list of
pending blocking locks. Clients should use such a nonblocking
request to indicate to the server that this is the last time they
intend to poll for the lock, as may happen when the process
requesting the lock is interrupted. This is a courtesy to the
server, to prevent it from unnecessarily waiting a lease period
before granting other LOCK operations. However, clients are not
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required to perform this courtesy, and servers must not depend on
them doing so. Also, clients must be prepared for the possibility
that this final locking request will be accepted.
When a server indicates, via the flag OPEN4_RESULT_MAY_NOTIFY_LOCK,
that CB_NOTIFY_LOCK callbacks might be done for the current open
file, the client should take notice of this, but, since this is a
hint, cannot rely on a CB_NOTIFY_LOCK always being done. A client
may reasonably reduce the frequency with which it polls for a denied
lock, since the greater latency that might occur is likely to be
eliminated given a prompt callback, but it still needs to poll. When
it receives a CB_NOTIFY_LOCK, it should promptly try to obtain the
lock, but it should be aware that other clients may be polling and
that the server is under no obligation to reserve the lock for that
particular client.
14.7. Share Reservations
A share reservation is a mechanism to control access to a file. It
is a separate and independent mechanism from byte-range locking.
When a client opens a file, it sends an OPEN operation to the server
specifying the type of access required (READ, WRITE, or BOTH) and the
type of access to deny others (OPEN4_SHARE_DENY_NONE,
OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or
OPEN4_SHARE_DENY_BOTH). If the OPEN fails, the client will fail the
application's open request.
Pseudo-code definition of the semantics:
if (request.access == 0) {
return (NFS4ERR_INVAL)
} else {
if ((request.access & file_state.deny)) ||
(request.deny & file_state.access)) {
return (NFS4ERR_SHARE_DENIED)
}
return (NFS4ERR_OK);
When doing this checking of share reservations on OPEN, the current
file_state used in the algorithm includes bits that reflect all
current opens, including those for the open-owner making the new OPEN
request.
The constants used for the OPEN and OPEN_DOWNGRADE operations for the
access and deny fields are as follows:
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const OPEN4_SHARE_ACCESS_READ = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH = 0x00000003;
const OPEN4_SHARE_DENY_NONE = 0x00000000;
const OPEN4_SHARE_DENY_READ = 0x00000001;
const OPEN4_SHARE_DENY_WRITE = 0x00000002;
const OPEN4_SHARE_DENY_BOTH = 0x00000003;
14.8. OPEN/CLOSE Operations
To provide correct share semantics, a client MUST use the OPEN
operation to obtain the initial filehandle and indicate the desired
access and what access, if any, to deny. Even if the client intends
to use a special stateid for anonymous state or READ bypass, it must
still obtain the filehandle for the regular file with the OPEN
operation so the appropriate share semantics can be applied. Clients
that do not have a deny mode built into their programming interfaces
for opening a file should request a deny mode of
OPEN4_SHARE_DENY_NONE.
The OPEN operation with the CREATE flag also subsumes the CREATE
operation for regular files as used in previous versions of the NFS
protocol. This allows a create with a share to be done atomically.
The CLOSE operation removes all share reservations held by the open-
owner on that file. If byte-range locks are held, the client SHOULD
release all locks before sending a CLOSE operation. The server MAY
free all outstanding locks on CLOSE, but some servers may not support
the CLOSE of a file that still has byte-range locks held. The server
MUST return failure, NFS4ERR_LOCKS_HELD, if any locks would exist
after the CLOSE.
The LOOKUP operation will return a filehandle without establishing
any lock state on the server. Without a valid stateid, the server
will assume that the client has the least access. For example, if
one client opened a file with OPEN4_SHARE_DENY_BOTH and another
client accesses the file via a filehandle obtained through LOOKUP,
the second client could only read the file using the special read
bypass stateid. The second client could not WRITE the file at all
because it would not have a valid stateid from OPEN and the special
anonymous stateid would not be allowed access.
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14.9. Open Upgrade and Downgrade
When an OPEN is done for a file and the open-owner for which the OPEN
is being done already has the file open, the result is to upgrade the
open file status maintained on the server to include the access and
deny bits specified by the new OPEN as well as those for the existing
OPEN. The result is that there is one open file, as far as the
protocol is concerned, and it includes the union of the access and
deny bits for all of the OPEN requests completed. The OPEN is
represented by a single stateid whose "other" value matches that of
the original open, and whose "seqid" value is incremented to reflect
the occurrence of the upgrade. The increment is required in cases in
which the "upgrade" results in no change to the open mode (e.g., an
OPEN is done for read when the existing open file is opened for
OPEN4_SHARE_ACCESS_BOTH). Only a single CLOSE will be done to reset
the effects of both OPENs. The client may use the stateid returned
by the OPEN effecting the upgrade or with a stateid sharing the same
"other" field and a seqid of zero, although care needs to be taken as
far as upgrades that happen while the CLOSE is pending. Note that
the client, when sending the OPEN, may not know that the same file is
in fact being opened. For reasons clarified later, the above only
applies if both OPENs result in the OPENed object being designated by
the same filehandle.
There are a number of situations in which the open-owner and file are
the same but the upgrade, as described above, is inappropriate:
* If the principal doing the later OPEN is different from the one
doing the preceding OPEN, the upgrade SHOULD NOT be done. The
only valid reason known to allow this recommendation to be
bypassed is that previous specifications including [RFC8881] did
not deal with the issue at all, resulting in implementors doing
the upgrade described above despite the fact the authorization of
IO operation done by these two OPENs becomes confused since
authorization checking for IO done within OPEN needs to allow the
operations authorized by the OPEN.
* When the server chooses to export multiple filehandles
corresponding to the same file object and returns different
filehandles on two different OPENs of the same file object, the
server MUST NOT "OR" together the access and deny bits and
coalesce the two open files. Instead, the server needs to
maintain separate OPENs with separate stateids and will require
separate CLOSEs to free them.
When multiple open files on the client are merged into a single
OPEN file object on the server, the close of one of the open files
(on the client) may necessitate change of the access and deny
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status of the open file on the server. This is because the union
of the access and deny bits for the remaining opens may be smaller
(i.e., a proper subset) than previously. The OPEN_DOWNGRADE
operation is used to make the necessary change and the client
should use it to update the server so that share reservation
requests by other clients are handled properly. The stateid
returned has the same "other" field as that passed to the server.
The "seqid" value in the returned stateid MUST be incremented,
even in situations in which there is no change to the access and
deny bits for the file.
14.10. Parallel OPENs
Unlike the case of NFSv4.0, in which OPEN operations for the same
open-owner are inherently serialized because of the owner-based
seqid, multiple OPENs for the same open-owner may be done in
parallel. When clients do this, they may encounter situations in
which, because of the existence of hard links, two OPEN operations
may turn out to open the same file, with a later OPEN performed being
an upgrade of the first, with this fact only visible to the client
once the operations complete.
In this situation, clients may determine the order in which the OPENs
were performed by examining the stateids returned by the OPENs.
Stateids that share a common value of the "other" field can be
recognized as having opened the same file, with the order of the
operations determinable from the order of the "seqid" fields, mod any
possible wraparound of the 32-bit field.
When the possibility exists that the client will send multiple OPENs
for the same open-owner in parallel, it may be the case that an open
upgrade may happen without the client knowing beforehand that this
could happen. Because of this possibility, CLOSEs and
OPEN_DOWNGRADEs should generally be sent with a non-zero seqid in the
stateid, to avoid the possibility that the status change associated
with an open upgrade is not inadvertently lost.
14.11. Reclaim of Open and Byte-Range Locks
Special forms of the LOCK and OPEN operations are provided when it is
necessary to re-establish byte-range locks or opens after a server
failure.
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* To reclaim existing opens, an OPEN operation is performed using a
CLAIM_PREVIOUS. Because the client, in this type of situation,
will have already opened the file and have the filehandle of the
target file, this operation requires that the current filehandle
be the target file, rather than a directory, and no file name is
specified.
* To reclaim byte-range locks, a LOCK operation with the reclaim
parameter set to true is used.
Reclaims of opens associated with delegations are discussed in
Section 15.2.1.
15. Client-Side Caching for Files
Client-side caching of data, and of file attributes, is essential to
providing good performance with the NFS protocol. Given the
difficulties of providing distributed cache coherence, NFSv4 has
focused on a number of techniques to reduce the need for such
facilities:
* Using the state provided by OPEN to avoid coherence- related
checks, in the common cases in which files are not shared among
client unless all access is read-only.
* Taking advantage of the structure of existing file access API's to
limit the need for inter-file coherence to be limited to that
provided by the name and directory caching described in
Section 16.
* Using share reservation to prevent the sort of sharing which would
require inter-client cache coherence.
Unfortunately, the lack of support for share reservations has led
to caching being used without the coherence support that would
make it effective. As a result, there remans a need that will
need to be addressed in future minor versions to provide ways of
advising clients not to use data and attribute caching in sharing
situations in which coherence would be needed.
In order to deal effectively with the lack of cache coherence,
several NFS client implementation techniques have been used to deal
the problems that a lack of coherence poses for users. These
techniques have not been clearly defined by earlier protocol
specifications, and it is often unclear what is valid or invalid
client behavior.
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Cases in which access to the same file is shared among multiple files
including at least one writer pose particular difficulties given the
absence of cache coherence. In such cases it may be necessary to
avoid caching to deal with the issue. NFSv4.1 has no standard means
to notify clients of the need to avoid such caching although the
possibility of extensions to provide for this case in discussed in
Appendix D.2.19.
The NFSv4.1 protocol uses many techniques similar to those that have
been used in previous protocol versions. The NFSv4.1 protocol does
not provide distributed cache coherence. However, it defines a more
limited set of caching guarantees to allow locks and share
reservations to be used without destructive interference from client-
side caching. This leaves difficulties that have yet to be addressed
satisfactorily for some environments in which share reservations are
not available.
Although numerous forms of caching are dealt within the included
subsections it is important to note how some of these commonly
addressed separately are related in important ways. In particular,
file data caching (discussed in Section 15.3 and attribute caching
(discussed in Section 15.6) are more closely related than might be
thought of at first, since:
* There are an important set of attributes that are modified by IO
operations with access or modify file data.
The possibility of changes to file data and attributes tied to
file data is constrained similarly by the potential existence of
share reservations
In at least one important case, discussion of the rules associated
with data caching is discussed only with regard to their effect on
file attributes. This happens with the treatment of write-behind
caching which has turned out to be quite consequential for many
workloads that are important for NFsv4 to address without the
difficulties result from the use of incoherent caches.
* They are both affected importantly by the existence of file
delegations, as discussed in Section 15.4.
While delegations are helpful in dealing with the common cases in
which sharing is infrequent, problems remain in dealing with files
shared among multiple clients
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15.1. Performance Challenges for Client-Side Caching
Caching techniques used in previous versions of the NFS protocol have
been successful in providing good performance. However, several
scalability challenges can arise when those techniques are used with
very large numbers of clients. This is particularly true when
clients are geographically distributed, which classically increases
the latency for cache revalidation requests.
The previous versions of the NFS protocol repeat their file data
cache validation requests at the time the file is opened. This
behavior can have serious performance drawbacks. A common case is
one in which a file is only accessed by a single client. Therefore,
sharing is infrequent.
In this case, repeated references to the server to find that no
conflicts exist are expensive. A better option with regards to
performance is to allow a client that repeatedly opens a file to do
so without reference to the server. This is done until potentially
conflicting operations from another client actually occur.
A similar situation arises in connection with byte-range locking.
Sending LOCK and LOCKU operations as well as the READ and WRITE
operations necessary to make data caching consistent with the locking
semantics (See Section 15.3.3) can severely limit performance. When
locking is used to provide protection against infrequent conflicts, a
large penalty is incurred. This penalty may discourage the use of
byte-range locking by applications.
The NFSv4.1 protocol provides more aggressive caching strategies with
the following design goals:
* Compatibility with a large range of server semantics.
* Providing the same caching benefits as previous versions of the
NFS protocol when unable to support the more aggressive model.
* Requirements for aggressive caching are organized so that a large
portion of the benefit can be obtained even when not all of the
requirements can be met.
The appropriate requirements for the server are discussed in later
sections in which specific forms of caching are covered (See
Section 15.4).
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15.2. Delegation and Callbacks
Recallable delegation of server responsibilities for a file to a
client improves performance by avoiding repeated requests to the
server in the absence of inter-client conflict. With the use of a
"callback" RPC from server to client, a server recalls delegated
responsibilities when another client engages in sharing of a
delegated file.
A delegation is passed from the server to the client, specifying the
object of the delegation and the type of delegation. There are
different types of delegations, but each type contains a stateid to
be used to represent the delegation when performing operations that
depend on the delegation. This stateid is similar to those
associated with locks and share reservations but differs in that the
stateid for a delegation is associated with a client ID and may be
used on behalf of all the open-owners for the given client. A
delegation is made to the client as a whole and not to any specific
process or thread of control within it.
The backchannel is established by CREATE_SESSION and
BIND_CONN_TO_SESSION, and the client is required to maintain it.
Because the backchannel may be down, even temporarily, correct
protocol operation does not depend on them. Preliminary testing of
backchannel functionality by means of a CB_COMPOUND procedure with a
single operation, CB_SEQUENCE, can be used to check the continuity of
the backchannel. A server avoids delegating responsibilities until
it has determined that the backchannel exists. Because the granting
of a delegation is always conditional upon the absence of conflicting
access, clients MUST NOT assume that a delegation will be granted and
they MUST always be prepared for OPENs, WANT_DELEGATIONs, and
GET_DIR_DELEGATIONs to be processed without any delegations being
granted.
Unlike locks, an operation by a second client to a delegated file
will cause the server to recall a delegation through a callback. For
individual operations, we will describe, under IMPLEMENTATION, when
such operations are required to effect a recall. A number of points
should be noted, however.
* The server is free to recall a delegation whenever it feels it is
desirable and may do so even if no operations requiring recall are
being done.
* Operations done outside the NFSv4.1 protocol, due to, for example,
access by other protocols including other minor version of NFSv4,
or by local access, also need to result in delegation recall when
they make analogous changes to file system data, including the
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delegated file's contents, its attributes and the set of names
linked to that file. What is crucial is if the change would
invalidate the guarantees provided by the delegation. When this
is possible, the delegation needs to be recalled and MUST be
returned or revoked before allowing the operation to proceed.
* The semantics of the file system are crucial in defining when
delegation recall is required. If a particular change within a
specific implementation causes change to a file attribute, then
delegation recall is required, whether that operation has been
specifically listed as requiring delegation recall. Again, what
is critical is whether the guarantees provided by the delegation
are being invalidated.
Despite those caveats, the implementation sections for a number of
operations describe situations in which delegation recall would be
required under some common circumstances:
* For GETATTR, see Section 25.7.4.
* For LINK, see Section 25.9.4.
* For OPEN, see Section 25.16.4.
* For READ, see Section 25.22.4.
* For REMOVE, see Section 25.25.4.
* For RENAME, see Section 25.26.4.
* For SETATTR, see Section 25.30.4.
* For WRITE, see Section 25.32.4.
On recall, the client holding the delegation needs to flush modified
state (such as modified data) to the server and return the
delegation. The conflicting request will not be acted on until the
recall is complete. The recall is considered complete when the
client returns the delegation or the server times its wait for the
delegation to be returned and revokes the delegation as a result of
the timeout. In the interim, the server will either delay responding
to conflicting requests or respond to them with NFS4ERR_DELAY.
Following the resolution of the recall, the server has the
information necessary to grant or deny the second client's request.
At the time the client receives a delegation recall, it may have
substantial state that needs to be flushed to the server. Therefore,
the server should allow sufficient time for the delegation to be
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returned since it may involve numerous RPCs to the server. If the
server is able to determine that the client is diligently flushing
state to the server as a result of the recall, the server may extend
the usual time allowed for a recall. However, the time allowed for
recall completion should not be unbounded.
An example of this is when responsibility to mediate opens on a given
file is delegated to a client (See Section 15.4). The server will
not know what opens are in effect on the client. Without this
knowledge, the server will be unable to determine if the access and
deny states for the file allow any particular open until the
delegation for the file has been returned.
A client failure or a network partition can result in failure to
respond to a recall callback. In this case, the server will revoke
the delegation, which in turn will render useless any modified state
still on the client.
15.2.1. Delegation Recovery
There are three situations that delegation recovery needs to deal
with:
* client restart
* server restart
* network partition (full or backchannel-only)
In the event the client restarts, establishment of a new clientid
associated with the new client instance or failure to renew the lease
will result in the revocation of byte-range locks and share
reservations. Delegations, however, may be treated somewhat
differently. It is also possible for the same sorts of revocation to
occur as a result of lease non-renewal.
There will be situations in which delegations will need to be re-
established after a client restarts. The reason for this is that the
client may have file data stored locally and this data was associated
with the previously held delegations. The client will need to re-
establish the appropriate file state on the server.
To allow for this type of client recovery, the server MAY provide a
special period to allow the clients to recover the delegations
obtained before the restart. This special period will often be
longer the typical lease expiration period. As a result, requests
from other clients that conflict with these delegations would need to
wait. Because the normal recall process may require significant time
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for the client to flush changed state to the server, other clients
need be prepared for delays that occur because of a conflicting
delegation. Such a longer interval would increase the window for
clients to restart and consult stable storage so that the delegations
can be returned after the data is appropriately flushed to the
server.
This special period, although analogous to the grace period used
after server restart, is distinct from it. For OPEN delegations,
such delegations are reclaimed using OPEN with a claim type of
CLAIM_DELEGATE_PREV or CLAIM_DELEG_PREV_FH (See Sections 15.5 and
25.16 f or discussion of OPEN delegation and the details of OPEN,
respectively). Although these types of OPENs are considered reclaim-
type operations they are not, like other sorts of reclaims limited to
the grace period. They are intended for use during the special
delegation recovery period, and are not directly affected by possible
existence of a server grace period.
A server MAY support claim types of CLAIM_DELEGATE_PREV and
CLAIM_DELEG_PREV_FH, and if it does, it MUST NOT remove delegations
upon a CREATE_SESSION that confirm a client ID created by
EXCHANGE_ID. Instead, the server MUST, for a period of time no less
than that of the value of the lease_time attribute, maintain the
client's delegations to allow time for the client to send
CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH requests. The server
that supports CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH MUST
support the DELEGPURGE operation.
When the server restarts, delegations are reclaimed (using the OPEN
operation with CLAIM_PREVIOUS) in a similar fashion to byte-range
locks and share reservations. However, there is a slight semantic
difference. In the normal case, if the server decides that a
delegation should not be granted, it performs the requested action
(e.g., OPEN) without granting any delegation. For reclaim, the
server grants the delegation but a special designation is applied so
that the client treats the delegation as having been granted but
recalled by the server. Because of this, the client has the duty to
write all modified state to the server and then return the
delegation. This process of handling delegation reclaim reconciles
three principles of the NFSv4.1 protocol:
* Upon reclaim, a client reporting resources assigned to it by an
earlier server instance must be granted those resources.
* The server has unquestionable authority to determine whether
delegations are to be granted and, once granted, whether they are
to be continued.
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* The use of callbacks should not be depended upon until the client
has proven its ability to receive them.
When a client needs to reclaim a delegation and there is no
associated open, the client may use the CLAIM_PREVIOUS variant of the
WANT_DELEGATION operation. However, since the server is not required
to support this operation, an alternative is to reclaim via a dummy
OPEN together with the delegation using an OPEN of type
CLAIM_PREVIOUS. The dummy open file can be released using a CLOSE to
re-establish the original state to be reclaimed, a delegation without
an associated open.
When a client has more than a single open associated with a
delegation, state for those additional opens can be established using
OPEN operations of type CLAIM_DELEGATE_CUR. When these are used to
establish opens associated with reclaimed delegations, the server
MUST allow them when made within the grace period.
When a network partition occurs, delegations are subject to freeing
by the server when the lease renewal period expires. This is similar
to the behavior for locks and share reservations. For delegations,
however, the server may extend the period in which conflicting
requests are held off. Eventually, the occurrence of a conflicting
request from another client will cause revocation of the delegation.
A loss of the backchannel (e.g., by later network configuration
change) will have the same effect. A recall request will fail and
revocation of the delegation will result.
A client normally finds out about revocation of a delegation when it
uses a stateid associated with a delegation and receives one of the
errors NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or
NFS4ERR_DELEG_REVOKED. It also may find out about delegation
revocation after a client restart when it attempts to reclaim a
delegation and receives that same error. Note that in the case of a
revoked OPEN_DELEGATE_WRITE delegation, there are issues because data
may have been modified by the client whose delegation is revoked and
separately by other clients. See Section 15.5.1 for a discussion of
such issues. Note also that when delegations are revoked,
information about the revoked delegation will be written by the
server to stable storage (as described in Section 13.4.3). This is
done to deal with the case in which a server restarts after revoking
a delegation but before the client holding the revoked delegation is
notified about the revocation.
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15.3. Data Caching
When applications share access to a set of files, they need to be
implemented so as to take account of the possibility of conflicting
access by another application. This is true whether the applications
in question execute on different clients or reside on the same
client.
Share reservations and byte-range locks are the facilities the
NFSv4.1 protocol provides to allow applications to coordinate access
by using mutual exclusion facilities. The NFSv4.1 protocol's data
caching must be implemented such that it does not invalidate the
assumptions on which those using these facilities depend.
15.3.1. Data Caching and OPENs
In order to avoid invalidating the sharing assumptions on which
applications rely, NFSv4.1 clients should not provide cached data to
applications or modify it on behalf of an application when it would
not be valid to obtain or modify that same data via a READ or WRITE
operation.
Furthermore, in the absence of an OPEN delegation (See Section 15.4),
two additional rules apply. Note that these rules are obeyed in
practice by many NFSv3 clients.
* First, cached data present on a client must be revalidated after
doing an OPEN. Revalidating means that the client fetches the
change attribute from the server, compares it with the cached
change attribute, and if different, declares the cached data (as
well as the cached attributes) as invalid. This is to ensure that
the data for the OPENed file is still correctly reflected in the
client's cache. This validation must be done at least when the
client's OPEN operation includes a deny of OPEN4_SHARE_DENY_WRITE
or OPEN4_SHARE_DENY_BOTH, thus terminating a period in which other
clients may have had the opportunity to open the file with
OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH access. Clients
may choose to do the revalidation more often (i.e., at OPENs
specifying a deny mode of OPEN4_SHARE_DENY_NONE) to parallel the
NFSv3 protocol's practice for the benefit of users assuming this
degree of cache revalidation.
Since the change attribute is updated for data and metadata
modifications, some client implementers may be tempted to use the
time_modify attribute and not the change attribute to validate
cached data, so that metadata changes do not spuriously invalidate
clean data. The implementer is cautioned in this approach. The
change attribute is guaranteed to change for each update to the
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file, whereas time_modify is guaranteed to change only at the
granularity of the time_delta attribute. Use by the client's data
cache validation logic of time_modify and not change runs the risk
of the client incorrectly marking stale data as valid. Thus, any
cache validation approach by the client MUST include the use of
the change attribute.
* Second, modified data must be flushed to the server before closing
a file OPENed for OPEN4_SHARE_ACCESS_WRITE. This is complementary
to the first rule. If the data is not flushed at CLOSE, the
revalidation done after the client OPENs a file is unable to
achieve its purpose. The other aspect to flushing the data before
close is that the data must be committed to stable storage, at the
server, before the CLOSE operation is requested by the client. In
the case of a server restart and a CLOSEd file, it may not be
possible to retransmit the data to be written to the file, hence,
this requirement.
15.3.2. Data Caching and Files Open for Write
When a file is being written, it is possible, because of the lack of
data cache coherence facilities, for otherwise unexceptionable data
caching arrangements to create problems because each client is
unaware of changes made by other clients:
* The provision for write-behind caching discussed in Section 15.6.1
remains of dubious utility and a source of potential difficulty,
even though it is commonly used and cannot be disallowed at this
time.
Fortunately, because there is no longer a performance-based reason
to adopt write-behind caching, clients are free to avoid this,
using a mount option, as they have been doing. It is possible for
the server, using an extension, to provide advice specifying that
this need to be avoided, at least when the file is written by
others.
* Many other instances of read caching become troublesome when used
in situations in which the file is being written unexpectedly,
often by multiple clients.
Although, in theory, this could be prevented by readers opening
with write being denied, the lack of appropriate provisions to
specify this option in many common environments prevents the issue
from being addressed using existing facilities.
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It is possible to address this issue using a client mount option
suppressing write caching or via an extension providing
information about the existence of clients who have the file open
for write. Because of the negative effect of such suppression on
workloads in which the sharing of access to files being written is
rare or non-existent, it is desirable to be able to provide
updates to readers about the existence of file open for write.
15.3.3. Data Caching and File Locking
For those applications that choose to use byte-range locking instead
of share reservations to exclude inconsistent file access, there is
an analogous set of constraints that apply to client-side data
caching. These rules are effective only if the byte-range locking is
used in a way that matches in an equivalent way the actual READ and
WRITE operations executed. This is as opposed to byte-range locking
that is based on pure convention. For example, it is possible to
manipulate a two-megabyte file by dividing the file into two one-
megabyte ranges and protecting access to the two byte-ranges by byte-
range locks on bytes zero and one. A WRITE_LT lock on byte zero of
the file would represent the right to perform READ and WRITE
operations on the first byte-range. A WRITE_LT lock on byte one of
the file would represent the right to perform READ and WRITE
operations on the second byte-range. As long as all applications
manipulating the file obey this convention, they will work on a local
file system. However, they may not work with the NFSv4.1 protocol
unless clients refrain from data caching.
The rules for data caching in the byte-range locking environment are:
* First, when a client obtains a byte-range lock for a particular
byte-range, the data cache corresponding to that byte-range (if
any cache data exists) must be revalidated. If the change
attribute indicates that the file may have been updated since the
cached data was obtained, the client must flush or invalidate the
cached data for the newly locked byte-range. A client might
choose to invalidate all of the non-modified cached data that it
has for the file, but the only requirement for correct operation
is to invalidate all of the data in the newly locked byte-range.
* Second, before releasing a WRITE_LT lock for a byte-range, all
modified data for that byte-range must be flushed to the server.
The modified data must also be written to stable storage.
Note that flushing data to the server and the invalidation of cached
data must reflect the actual byte-ranges locked or unlocked.
Rounding these up or down to reflect client cache block boundaries
will cause problems if not carefully done. For example, writing a
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modified block when only half of that block is within an area being
unlocked may cause invalid modification to the byte-range outside the
unlocked area. This, in turn, may be part of a byte-range locked by
another client. Clients can avoid this situation by synchronously
performing portions of WRITE operations that overlap that portion
(initial or final) that is not a full block. Similarly, invalidating
a locked area that is not an integral number of full buffer blocks
would require the client to read one or two partial blocks from the
server if the revalidation procedure shows that the data that the
client possesses may not be valid.
The data that is written to the server as a prerequisite to the
unlocking of a byte-range must be written, at the server, to stable
storage. The client may accomplish this either with synchronous
writes or by following asynchronous writes with a COMMIT operation.
This is required because retransmission of the modified data after a
server restart might conflict with a lock held by another client.
A client implementation may choose to accommodate applications that
use byte-range locking in non-standard ways (e.g., using a byte-range
lock as a global semaphore) by flushing to the server more data upon
a LOCKU than is covered by the locked range. This may include
modified data within files other than the one for which the unlocks
are being done. In such cases, the client must not interfere with
applications whose READs and WRITEs are being done only within the
bounds of byte-range locks that the application holds. For example,
an application locks a single byte of a file and proceeds to write
that single byte. A client that chose to handle a LOCKU by flushing
all modified data to the server could validly write that single byte
in response to an unrelated LOCKU operation. However, it would not
be valid to write the entire block in which that single written byte
was located since it includes an area that is not locked and might be
locked by another client. Client implementations can avoid this
problem by dividing files with modified data into those for which all
modifications are done to areas covered by an appropriate byte-range
lock and those for which there are modifications not covered by a
byte-range lock. Any writes done for the former class of files must
not include areas not locked and thus not modified on the client.
15.3.4. Data Caching and Mandatory File Locking
Client-side data caching needs to respect mandatory byte-range
locking when it is in effect. The presence of mandatory byte-range
locking for a given file is indicated when the client gets back
NFS4ERR_LOCKED from a READ or WRITE operation on a file for which it
has an appropriate share reservation. When mandatory locking is in
effect for a file, the client must check for an appropriate byte-
range lock for data being read or written. If a byte-range lock
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exists for the range being read or written, the client may satisfy
the request using the client's validated cache. If an appropriate
byte-range lock is not held for the range of the read or write, the
read or write request must not be satisfied by the client's cache and
the request must be sent to the server for processing. When a read
or write request partially overlaps a locked byte-range, the request
should be subdivided into multiple pieces with each byte-range
(locked or not) treated appropriately.
15.3.5. Data Caching and File Identity
When clients cache data, the file data needs to be organized
according to the file system object to which the data belongs. For
NFSv3 clients, the typical practice has been to assume for the
purpose of caching that distinct filehandles represent distinct file
system objects. The client then has the choice to organize and
maintain the data cache on this basis.
In the NFSv4.1 protocol, there is now the possibility to have
significant deviations from a "one filehandle per object" model
because a filehandle may be constructed on the basis of the object's
pathname. Therefore, clients need a reliable method to determine if
two filehandles designate the same file system object. If clients
were simply to assume that all distinct filehandles denote distinct
objects and proceed to do data caching on this basis, caching
inconsistencies would arise between the distinct client-side objects
that mapped to the same server-side object.
By providing a method to differentiate filehandles, the NFSv4.1
protocol alleviates a potential functional regression in comparison
with the NFSv3 protocol. Without this method, caching
inconsistencies within the same client could occur, and this has not
been present in previous versions of the NFS protocol. Note that it
is possible to have such inconsistencies with applications executing
on multiple clients, but that is not the issue being addressed here.
For the purposes of data caching, the following steps allow an
NFSv4.1 client to determine whether two distinct filehandles denote
the same server-side object:
* If GETATTR directed to two filehandles returns different values of
the fsid attribute, then the filehandles represent distinct
objects.
* If GETATTR for any file with an fsid that matches the fsid of the
two filehandles in question returns a unique_handles attribute
with a value of TRUE, then the two objects are distinct.
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* If GETATTR directed to the two filehandles does not return the
fileid attribute for both of the handles, then it cannot be
determined whether the two objects are the same. Therefore,
operations that depend on that knowledge (e.g., client-side data
caching) cannot be done reliably. Note that if GETATTR does not
return the fileid attribute for both filehandles, it will return
it for neither of the filehandles, since the fsid for both
filehandles is the same.
* If GETATTR directed to the two filehandles returns different
values for the fileid attribute, then they are distinct objects.
* Otherwise, they are the same object.
15.4. Open Delegation
When a file is being OPENed, the server may delegate further handling
of opens and closes for that file to the opening client. Any such
delegation is recallable since the circumstances that allowed for the
delegation are subject to change. In particular, if the server
receives a conflicting OPEN from another client, the server must
recall the delegation before deciding whether the OPEN from the other
client may be granted. Making a delegation is up to the server, and
clients should not assume that any particular OPEN either will or
will not result in an OPEN delegation. The following is a typical
set of conditions that servers might use in deciding whether an OPEN
should be delegated:
* The client must be able to respond to the server's callback
requests. If a backchannel has been established, the server will
send a CB_COMPOUND request, containing a single operation,
CB_SEQUENCE, for a test of backchannel availability.
* The client must have responded properly to previous recalls.
* There must be no current OPEN conflicting with the requested
delegation.
* There should be no current delegation that conflicts with the
delegation being requested.
* The probability of future conflicting open requests should be low
based on the recent history of the file.
* The existence of any server-specific semantics of OPEN/CLOSE that
would make the required handling incompatible with the prescribed
handling that the delegated client would apply (See below).
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There are two types of OPEN delegations: OPEN_DELEGATE_READ and
OPEN_DELEGATE_WRITE. An OPEN_DELEGATE_READ delegation allows a
client to handle, on its own, requests to open a file for reading
that do not deny OPEN4_SHARE_ACCESS_READ access to others. Multiple
OPEN_DELEGATE_READ delegations may be outstanding simultaneously and
do not conflict. An OPEN_DELEGATE_WRITE delegation allows the client
to handle, on its own, all opens. Only one OPEN_DELEGATE_WRITE
delegation may exist for a given file at a given time, and it is
inconsistent with any OPEN_DELEGATE_READ delegations.
When a client has either type of open delegation, it is assured that
neither the contents, the attributes (with the exception of
time_access), nor the names of any links to the file will change
without its knowledge, so long as the delegation is held. When a
client has an OPEN_DELEGATE_WRITE delegation, it may modify the file
data locally since no other client will be accessing the file's data.
The client holding an OPEN_DELEGATE_WRITE delegation may only locally
affect file attributes that are intimately connected with the file
data: size, change, time_access, time_metadata, and time_modify. All
other attributes must be reflected on the server.
When a client has an OPEN delegation, it does not need to send OPENs
or CLOSEs to the server. Instead, the client may update the
appropriate status internally. For an OPEN_DELEGATE_READ delegation,
opens that cannot be handled locally (opens that are for
OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH or that deny
OPEN4_SHARE_ACCESS_READ access) must be sent to the server.
When an OPEN delegation is made, the reply to the OPEN contains an
OPEN delegation structure that specifies the following:
* the type of delegation (OPEN_DELEGATE_READ or
OPEN_DELEGATE_WRITE).
* space limitation information to control flushing of data on close
(OPEN_DELEGATE_WRITE delegation only; see Section 15.4.1)
* an nfsace4 specifying read and write permissions
* a stateid to represent the delegation
The delegation stateid is separate and distinct from the stateid for
the OPEN proper. The standard stateid, unlike the delegation
stateid, is associated with a particular lock-owner and will continue
to be valid after the delegation is recalled and the file remains
open.
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When a request internal to the client is made to open a file and an
OPEN delegation is in effect, it will be accepted or rejected solely
on the basis of the following conditions. Any requirement for other
checks to be made by the delegate should result in the OPEN
delegation being denied so that the checks can be made by the server
itself.
* The access and deny bits for the request and the file as described
in Section 14.7.
* The read and write permissions as determined below.
The nfsace4 passed with delegation can be used to avoid frequent
ACCESS calls. The permission check should be as follows:
* If the nfsace4 indicates that the open may be done, then it should
be granted without reference to the server.
* If the nfsace4 indicates that the open may not be done, then an
ACCESS request must be sent to the server to obtain the definitive
answer.
The server may return an nfsace4 that is more restrictive than the
actual ACL of the file. This includes an nfsace4 that specifies
denial of all access. Note that some common practices such as
mapping the traditional user "root" to the user "nobody" (See
Section 11.13) may make it incorrect to return the actual ACL of the
file in the delegation response.
The use of a delegation together with various other forms of caching
creates the possibility that no server authentication and
authorization will ever be performed for a given user since all of
the user's requests might be satisfied locally. Where the client is
depending on the server for authentication and authorization, the
client should be sure authentication and authorization occurs for
each user by use of the ACCESS operation. This should be the case
even if an ACCESS operation would not be required otherwise. As
mentioned before, the server may enforce frequent authentication by
returning an nfsace4 denying all access with every OPEN delegation.
15.4.1. Open Delegation and Data Caching
An OPEN delegation allows much of the message overhead associated
with the opening and closing files to be eliminated. An open when an
OPEN delegation is in effect does not require that a validation
message be sent to the server. The continued endurance of the
"OPEN_DELEGATE_READ delegation" provides a guarantee that no OPEN for
OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH, and thus no write,
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has occurred. Similarly, when closing a file opened for
OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH and if an
OPEN_DELEGATE_WRITE delegation is in effect, the data written does
not have to be written to the server until the OPEN delegation is
recalled. The continued endurance of the OPEN delegation provides a
guarantee that no open, and thus no READ or WRITE, has been done by
another client.
For the purposes of OPEN delegation, READs and WRITEs done without an
OPEN are treated as the functional equivalents of a corresponding
type of OPEN. Although a client SHOULD NOT use special stateids when
an open exists, delegation handling on the server can use the client
ID associated with the current session to determine if the operation
has been done by the holder of the delegation (in which case, no
recall is necessary) or by another client (in which case, the
delegation must be recalled and I/O not proceed until the delegation
is returned or revoked).
With delegations, a client is able to avoid writing data to the
server when the CLOSE of a file is serviced. The file close system
call is the usual point at which the client is notified of a lack of
stable storage for the modified file data generated by the
application. At the close, file data is written to the server and,
through normal accounting, the server is able to determine if the
available file system space for the data has been exceeded (i.e., the
server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT). This accounting
includes quotas. The introduction of delegations requires that an
alternative method be in place for the same type of communication to
occur between client and server.
In the delegation response, the server provides either the limit of
the size of the file or the number of modified blocks and associated
block size. The server must ensure that the client will be able to
write modified data to the server of a size equal to that provided in
the original delegation. The server must make this assurance for all
outstanding delegations. Therefore, the server must be careful in
its management of available space for new or modified data, taking
into account available file system space and any applicable quotas.
The server can recall delegations as a result of managing the
available file system space. The client should abide by the server's
state space limits for delegations. If the client exceeds the stated
limits for the delegation, the server's behavior is undefined.
Based on server conditions, quotas, or available file system space,
the server may grant OPEN_DELEGATE_WRITE delegations with very
restrictive space limitations. The limitations may be defined in a
way that will always force modified data to be flushed to the server
on close.
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With respect to authentication, flushing modified data to the server
after a CLOSE has occurred may be problematic. For example, the user
of the application may have logged off the client, and unexpired
authentication credentials may not be present. In this case, the
client may need to take special care to ensure that local unexpired
credentials will in fact be available. This may be accomplished by
tracking the expiration time of credentials and flushing data well in
advance of their expiration or by making private copies of
credentials to assure their availability when needed.
15.4.2. Open Delegation and File Locks
When a client holds an OPEN_DELEGATE_WRITE delegation, lock
operations are performed locally. This includes those required for
mandatory byte-range locking. This can be done since the delegation
implies that there can be no conflicting locks. Similarly, all of
the revalidations that would normally be associated with obtaining
locks and the flushing of data associated with the releasing of locks
need not be done.
When a client holds an OPEN_DELEGATE_READ delegation, lock operations
are not performed locally. All lock operations, including those
requesting non-exclusive locks, are sent to the server for
resolution.
15.4.3. Handling of CB_GETATTR
The server needs to employ special handling for a GETATTR where the
target is a file that has an OPEN_DELEGATE_WRITE delegation in
effect. The reason for this is that the client holding the
OPEN_DELEGATE_WRITE delegation may have modified the data, and the
server needs to reflect this change to the second client that
submitted the GETATTR. Therefore, the client holding the
OPEN_DELEGATE_WRITE delegation needs to be interrogated. The server
will use the CB_GETATTR operation. The only attributes that the
server can reliably query via CB_GETATTR are size and change.
Since CB_GETATTR is being used to satisfy another client's GETATTR
request, the server only needs to know if the client holding the
delegation has a modified version of the file. If the client's copy
of the delegated file is not modified (data or size), the server can
satisfy the second client's GETATTR request from the attributes
stored locally at the server. If the file is modified, the server
only needs to know about this modified state. If the server
determines that the file is currently modified, it will respond to
the second client's GETATTR as if the file had been modified locally
at the server.
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Since the form of the change attribute is determined by the server
and is opaque to the client, the client and server need to agree on a
method of communicating the modified state of the file. For the size
attribute, the client will report its current view of the file size.
For the change attribute, the handling is more involved.
For the client, the following steps will be taken when receiving an
OPEN_DELEGATE_WRITE delegation:
* The value of the change attribute will be obtained from the server
and cached. Let this value be represented by c.
* The client will create a value greater than c that will be used
for communicating that modified data is held at the client. Let
this value be represented by d.
* When the client is queried via CB_GETATTR for the change
attribute, it checks to see if it holds modified data. If the
file is modified, the value d is returned for the change attribute
value. If this file is not currently modified, the client returns
the value c for the change attribute.
For simplicity of implementation, the client MAY for each CB_GETATTR
return the same value d. This is true even if, between successive
CB_GETATTR operations, the client again modifies the file's data or
metadata in its cache. The client can return the same value because
the only requirement is that the client be able to indicate to the
server that the client holds modified data. Therefore, the value of
d may always be c + 1.
While the change attribute is opaque to the client in the sense that
it has no idea what units of time, if any, the server is counting
change with, it is not opaque in that the client has to treat it as
an unsigned integer, and the server has to be able to see the results
of the client's changes to that integer. Therefore, the server MUST
encode the change attribute in network order when sending it to the
client. The client MUST decode it from network order to its native
order when receiving it, and the client MUST encode it in network
order when sending it to the server. For this reason, change is
defined as an unsigned integer rather than an opaque array of bytes.
For the server, the following steps will be taken when providing an
OPEN_DELEGATE_WRITE delegation:
* Upon providing an OPEN_DELEGATE_WRITE delegation, the server will
cache a copy of the change attribute in the data structure it uses
to record the delegation. Let this value be represented by sc.
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* When a second client sends a GETATTR operation on the same file to
the server, the server obtains the change attribute from the first
client. Let this value be cc.
* If the value cc is equal to sc, the file is not modified and the
server returns the current values for change, time_metadata, and
time_modify (for example) to the second client.
* If the value cc is NOT equal to sc, the file is currently modified
at the first client and most likely will be modified at the server
at a future time. The server then uses its current time to
construct attribute values for time_metadata and time_modify. A
new value of sc, which we will call nsc, is computed by the
server, such that nsc >= sc + 1. The server then returns the
constructed time_metadata, time_modify, and nsc values to the
requester. The server replaces sc in the delegation record with
nsc. To prevent the possibility of time_modify, time_metadata,
and change from appearing to go backward (which would happen if
the client holding the delegation fails to write its modified data
to the server before the delegation is revoked or returned), the
server SHOULD update the file's metadata record with the
constructed attribute values. For reasons of reasonable
performance, committing the constructed attribute values to stable
storage is OPTIONAL.
As discussed earlier in this section, the client MAY return the same
cc value on subsequent CB_GETATTR calls, even if the file was
modified in the client's cache yet again between successive
CB_GETATTR calls. Therefore, the server must assume that the file
has been modified yet again, and MUST take care to ensure that the
new nsc it constructs and returns is greater than the previous nsc it
returned. An example implementation's delegation record would
satisfy this mandate by including a boolean field (let us call it
"modified") that is set to FALSE when the delegation is granted, and
an sc value set at the time of grant to the change attribute value.
The modified field would be set to TRUE the first time cc != sc, and
would stay TRUE until the delegation is returned or revoked. The
processing for constructing nsc, time_modify, and time_metadata would
use this pseudo code:
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if (!modified) {
do CB_GETATTR for change and size;
if (cc != sc)
modified = TRUE;
} else {
do CB_GETATTR for size;
}
if (modified) {
sc = sc + 1;
time_modify = time_metadata = current_time;
update sc, time_modify, time_metadata into file's metadata;
}
This would return to the client (that sent GETATTR) the attributes it
requested, but make sure size comes from what CB_GETATTR returned.
The server would not update the file's metadata with the client's
modified size.
In the case that the file attribute size is different than the
server's current value, the server treats this as a modification
regardless of the value of the change attribute retrieved via
CB_GETATTR and responds to the second client as in the last step.
This methodology resolves issues of clock differences between client
and server and other scenarios where the use of CB_GETATTR break
down.
It should be noted that the server is under no obligation to use
CB_GETATTR, and therefore the server MAY simply recall the delegation
to avoid its use.
15.4.4. Recall of Open Delegation
The following events necessitate recall of an OPEN delegation:
* potentially conflicting OPEN request (or a READ or WRITE operation
done with a special stateid)
* SETATTR sent by another client
* REMOVE request for the file
* RENAME request for the file as either the source or target of the
RENAME
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Whether a RENAME of a directory in the path leading to the file
results in recall of an OPEN delegation depends on the semantics of
the server's file system. If that file system denies such RENAMEs
when a file is open, the recall must be performed to determine
whether the file in question is, in fact, open.
In addition to the situations above, the server may choose to recall
OPEN delegations at any time if resource constraints make it
advisable to do so. Clients should always be prepared for the
possibility of recall.
When a client receives a recall for an OPEN delegation, it needs to
update state on the server before returning the delegation. These
same updates must be done whenever a client chooses to return a
delegation voluntarily. The following items of state need to be
dealt with:
* If the file associated with the delegation is no longer open and
no previous CLOSE operation has been sent to the server, a CLOSE
operation must be sent to the server.
* If a file has other open references at the client, then OPEN
operations must be sent to the server. The appropriate stateids
will be provided by the server for subsequent use by the client
since the delegation stateid will no longer be valid. These OPEN
requests are done with the claim type of CLAIM_DELEGATE_CUR. This
will allow the presentation of the delegation stateid so that the
client can establish the appropriate rights to perform the OPEN.
(See Section 25.16, which describes the OPEN operation, for
details.)
* If there are granted byte-range locks, the corresponding LOCK
operations need to be performed. This applies to the
OPEN_DELEGATE_WRITE delegation case only.
* For an OPEN_DELEGATE_WRITE delegation, if at the time of recall
the file is not open for OPEN4_SHARE_ACCESS_WRITE/
OPEN4_SHARE_ACCESS_BOTH, all modified data for the file must be
flushed to the server. If the delegation had not existed, the
client would have done this data flush before the CLOSE operation.
* For an OPEN_DELEGATE_WRITE delegation when a file is still open at
the time of recall, any modified data for the file needs to be
flushed to the server.
* With the OPEN_DELEGATE_WRITE delegation in place, it is possible
that the file was truncated during the duration of the delegation.
For example, the truncation could have occurred as a result of an
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OPEN UNCHECKED with a size attribute value of zero. Therefore, if
a truncation of the file has occurred and this operation has not
been propagated to the server, the truncation must occur before
any modified data is written to the server.
In the case of OPEN_DELEGATE_WRITE delegation, byte-range locking
imposes some additional requirements. To precisely maintain the
associated invariant, it is required to flush any modified data in
any byte-range for which a WRITE_LT lock was released while the
OPEN_DELEGATE_WRITE delegation was in effect. However, because the
OPEN_DELEGATE_WRITE delegation implies no other locking by other
clients, a simpler implementation is to flush all modified data for
the file (as described just above) if any WRITE_LT lock has been
released while the OPEN_DELEGATE_WRITE delegation was in effect.
An implementation need not wait until delegation recall (or the
decision to voluntarily return a delegation) to perform any of the
above actions, if implementation considerations (e.g., resource
availability constraints) make that desirable. Generally, however,
the fact that the actual OPEN state of the file may continue to
change makes it not worthwhile to send information about opens and
closes to the server, except as part of delegation return. An
exception is when the client has no more internal opens of the file.
In this case, sending a CLOSE is useful because it reduces resource
utilization on the client and server. Regardless of the client's
choices on scheduling these actions, all must be performed before the
delegation is returned, including (when applicable) the close that
corresponds to the OPEN that resulted in the delegation. These
actions can be performed either in previous requests or in previous
operations in the same COMPOUND request.
15.4.5. Clients That Fail to Honor Delegation Recalls
A client may fail to respond to a recall for various reasons, such as
a failure of the backchannel from server to the client. The client
may be unaware of a failure in the backchannel. This lack of
awareness could result in the client finding out long after the
failure that its delegation has been revoked, and another client has
modified the data for which the client had a delegation. This is
especially a problem for the client that held an OPEN_DELEGATE_WRITE
delegation.
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Status bits returned by SEQUENCE operations help to provide an
alternate way of informing the client of issues regarding the status
of the backchannel and of recalled delegations. When the backchannel
is not available, the server returns the status bit
SEQ4_STATUS_CB_PATH_DOWN on SEQUENCE operations. The client can
react by attempting to re-establish the backchannel and by returning
recallable objects if a backchannel cannot be successfully re-
established.
Whether the backchannel is functioning or not, it may be that the
recalled delegation is not returned. Note that the client's lease
might still be renewed, even though the recalled delegation is not
returned. In this situation, servers SHOULD revoke delegations that
are not returned in a period of time equal to the lease period. This
period of time should allow the client time to note the backchannel-
down status and re-establish the backchannel.
When delegations are revoked, the server will return with the
SEQ4_STATUS_RECALLABLE_STATE_REVOKED status bit set on subsequent
SEQUENCE operations. The client should note this and then use
TEST_STATEID to find which delegations have been revoked.
15.4.6. Delegation Revocation
At the point a delegation is revoked, if there are associated opens
on the client, these opens may or may not be revoked. If no byte-
range lock or open is granted that is inconsistent with the existing
open, the stateid for the open may remain valid and be disconnected
from the revoked delegation, just as would be the case if the
delegation were returned.
For example, if an OPEN for OPEN4_SHARE_ACCESS_BOTH with a deny of
OPEN4_SHARE_DENY_NONE is associated with the delegation, granting of
another such OPEN to a different client will revoke the delegation
but need not revoke the OPEN, since the two OPENs are consistent with
each other. On the other hand, if an OPEN denying write access is
granted, then the existing OPEN must be revoked.
When opens and/or locks are revoked, the applications holding these
opens or locks need to be notified. This notification usually occurs
by returning errors for READ/WRITE operations or when a close is
attempted for the open file.
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If no opens exist for the file at the point the delegation is
revoked, then notification of the revocation is unnecessary.
However, if there is modified data present at the client for the
file, the user of the application should be notified. Unfortunately,
it may not be possible to notify the user since active applications
may not be present at the client. See Section 15.5.1 for additional
details.
15.4.7. Delegations via WANT_DELEGATION
In addition to providing delegations as part of the reply to OPEN
operations, servers MAY provide delegations separate from open, via
the OPTIONAL WANT_DELEGATION operation. This allows delegations to
be obtained in advance of an OPEN that might benefit from them, for
objects that are not a valid target of OPEN, or to deal with cases in
which a delegation has been recalled and the client wants to make an
attempt to re-establish it if the absence of use by other clients
allows that.
The WANT_DELEGATION operation may be performed on any type of file
object other than a directory.
When a delegation is obtained using WANT_DELEGATION, any open files
for the same filehandle held by that client are to be treated as
subordinate to the delegation, just as if they had been created using
an OPEN of type CLAIM_DELEGATE_CUR. They are otherwise unchanged as
to seqid, access and deny modes, and the relationship with byte-range
locks. Similarly, because existing byte-range locks are subordinate
to an open, those byte-range locks also become indirectly subordinate
to that new delegation.
The WANT_DELEGATION operation provides for delivery of delegations
via callbacks, when the delegations are not immediately available.
When a requested delegation is available, it is delivered to the
client via a CB_PUSH_DELEG operation. When this happens, open files
for the same filehandle become subordinate to the new delegation at
the point at which the delegation is delivered, just as if they had
been created using an OPEN of type CLAIM_DELEGATE_CUR. Similarly,
this occurs for existing byte-range locks subordinate to an open.
15.5. Data Caching and Revocation
When locks and delegations are revoked, the assumptions upon which
successful caching depends are no longer guaranteed. For any locks
or share reservations that have been revoked, the corresponding
state-owner needs to be notified. This notification includes
applications with a file open that has a corresponding delegation
that has been revoked. Cached data associated with the revocation
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must be removed from the client. In the case of modified data
existing in the client's cache, that data must be removed from the
client without being written to the server. As mentioned, the
assumptions made by the client are no longer valid at the point when
a lock or delegation has been revoked. For example, another client
may have been granted a conflicting byte-range lock after the
revocation of the byte-range lock at the first client. Therefore,
the data within the lock range may have been modified by the other
client. Obviously, the first client is unable to guarantee to the
application what has occurred to the file in the case of revocation.
Notification to a state-owner will in many cases consist of simply
returning an error on the next and all subsequent READs/WRITEs to the
open file or on the close. Where the methods available to a client
make such notification impossible because errors for certain
operations may not be returned, more drastic action such as signals
or process termination may be appropriate. The justification here is
that an invariant on which an application depends may be violated.
Depending on how errors are typically treated for the client-
operating environment, further levels of notification including
logging, console messages, and GUI pop-ups may be appropriate.
15.5.1. Revocation Recovery for Write Open Delegation
Revocation recovery for an OPEN_DELEGATE_WRITE delegation poses the
special issue of modified data in the client cache while the file is
not open. In this situation, any client that does not flush modified
data to the server on each close must ensure that the user receives
appropriate notification of the failure as a result of the
revocation. Since such situations may require human action to
correct problems, notification schemes in which the appropriate user
or administrator is notified may be necessary. Logging and console
messages are typical examples.
If there is modified data on the client, it must not be flushed
normally to the server. A client may attempt to provide a copy of
the file data as modified during the delegation under a different
name in the file system namespace to ease recovery. Note that when
the client can determine that the file has not been modified by any
other client, or when the client has a complete cached copy of the
file in question, such a saved copy of the client's view of the file
may be of particular value for recovery. In another case, recovery
using a copy of the file based partially on the client's cached data
and partially on the server's copy as modified by other clients will
be anything but straightforward, so clients may avoid saving file
contents in these situations or specially mark the results to warn
users of possible problems.
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Saving of such modified data in delegation revocation situations may
be limited to files of a certain size or might be used only when
sufficient disk space is available within the target file system.
Such saving may also be restricted to situations when the client has
sufficient buffering resources to keep the cached copy available
until it is properly stored to the target file system.
15.6. Attribute Caching
This section focuses on the caching of a file's attributes by clients
that do not hold a delegation on the file.
The attributes discussed in this section do not include named
attributes. Individual named attributes are treated similarly to
files, and caching of the data for these files needs to be handled
just as data caching is for ordinary files. Similarly, LOOKUP
results from an OPENATTR directory (as well as the directory's
contents) can be cached on the same basis as other pathnames.
Within this section and included subsections, attributes intimately
connected with the file's data, termed "data-related attributes"
often have a special role and there are useful constraints on the
circumstances allowing these attributes to be changed, beyond those
provided by delegations. These attributes consist of the following:
* Size
* Modify time
* Change
Clients may cache file attributes obtained from the server and use
them to avoid subsequent GETATTR requests. However, except when the
constraints listed below are relevant, the client needs to understand
that because of the lack of a coherence mechanism, such values can
become outdated due to actions requested by other clients.
* The holder of a write delegation is assured that other clients
cannot cause modification of any file attributes.
* The holder of a read delegation is assured that other clients
cannot cause modification of any file attributes other than access
time.
* The client associated with an open denying WRITE is assured that
other clients cannot cause modification of any of the data-related
attributes.
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* Certain attributes, are by their nature, not subject to change.
These include fsid and file_id.
Clients caching attributes need to be aware of the possibility that
cached attributes may become invalid in the common cases in which
none of constraints cited above prevents their modification. This
makes it necessary that it be able to determine whether the cached
attributes are still valid.
A client can validate its cached version of attributes for a file by
fetching both the change and time_access attributes and assuming that
if the change attribute has the same value as it did when the
attributes were cached, then no attributes other than time_access
have changed. The inclusion of time_access is desirable since it is
often costless to add this to the set of attributes being fetched.
In this way, a current value of access_time is made available o deal
with the common case in which it is the only attribute modified.
15.6.1. Attribute Caching Coherence Between Requesting Client and
Server
The caching as discussed above in Section 15.6 proper is write-
through in that modification to file attributes is always done by
means of requests to the server and should not be done locally and
should not be cached. One potential exception to this are
modifications to data-related attributes that occur as a result of
write-behind caching. When this option is used, extending a file by
writing data to the local data cache is reflected immediately in the
size as seen on the client without this change being immediately
reflected on the server or visible to other clients. In this case,
such changes are not propagated directly to the server, but when the
modified data is flushed to the server, corresponding attribute
changes are made on the server. When a write delegation is in held
by the client. the modified attributes may be returned to the server
in response to a CB_RECALL call.
Note that if the full set of attributes to be cached is requested by
READDIR and returned by the server, the results can be cached by the
client on the same basis as attributes obtained via GETATTR.
The client may maintain a cache of modified attributes for those
attributes intimately connected with data of modified regular files
(size, time_modify, and change). Other than those three attributes,
the client MUST NOT maintain a cache of modified attributes.
Instead, attribute changes are immediately sent to the server.
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In some operating environments, the equivalent to time_access is
expected to be implicitly updated by each read of the content of the
file object. If an NFS client is caching the content of a file
object, whether it is a regular file, directory, or symbolic link,
the client SHOULD NOT update the time_access attribute (via SETATTR
or a small READ or READDIR request) on the server with each read that
is satisfied from cache. The reason is that this can defeat the
performance benefits of caching content, especially since an explicit
SETATTR of time_access may alter the change attribute on the server.
If the change attribute changes, clients that are caching the content
will think the content has changed, and will re-read unmodified data
from the server. Nor is the client encouraged to maintain a modified
version of time_access in its cache, since the client either would
eventually have to write the access time to the server with bad
performance effects or never update the server's time_access, thereby
resulting in a situation where an application that caches access time
between a close and open of the same file observes the access time
oscillating between the past and present. The time_access attribute
always means the time of last access to a file by a read that was
satisfied by the server. This way clients will tend to see only
time_access changes that go forward in time.
15.6.2. Attribute Caching Coherence Between Requesting Client and Other
Clients
The changes made by various clients to file attributes is likely to
result in multiple clients having different values for file
attributes Because typical file system application programming
interfaces do not provide means to atomically modify or interrogate
attributes for multiple files at the same time this incoherence can
be dealt with as discussed below. The following guidelines provide
an environment where the potential incoherencies alluded to above can
be reasonably managed. These guidelines are derived from the
practice of previous NFS protocols, modified to deal with the larger
set of NFSv4.1 file attributes.
* A large set of attributes for a given file (not including per-fsid
attributes excepted) are cached as a unit at the client to avoid
non-serializability can arise within the context of a single file.
* An upper time boundary is maintained on how long a client cache
entry can be kept without being refreshed from the server. Actual
refresh is unnecessary if it can be determined that no attributes
have changed
* When operations are performed that change attributes at the
server, the updated attribute set is requested as part of the
containing RPC. This includes directory operations that result in
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the update of attributes This is accomplished by following the
modifying operation with a GETATTR operation and then using the
results of the GETATTR to update the client's cached attributes.
Including the change attribute in this set simplified the client's
task of periodically validating these attributes.
15.6.3. Attribute Caching Coherence Between Requesting Client and
Remote Applications
The return of attributes modified by one client to applications
running on other clients is often problematic because:
* The application or the operating environment might have been
implemented without consideration of the effects of simultaneous
updates by multiple clients.
This includes environments that were defined for local access and
have no support for open deny modes.
* The applications might have been designed and implemented assuming
that certain file attributes could be accessed without worry about
remote access delays in accessing attributes.
Given the above situation, the applications will no have the same
ability to validate attributes that the client does. This makes it
important to prevent the incorporation of outdated value since:
* The client is not likely to be able to validate if they become
outdated.
* Applications, unless special efforts are undertaken, are unlikely
to be aware of the possibility of simultaneous access.
* The normal way to prevent such simultaneous access, the use of
share reservations, might not be available, due to hard-to-address
limitations of the operating environment.
The best alternative is likely to be elimination of attribute caching
in such cases.
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15.7. Data and Metadata Caching and Memory Mapped Files
Some operating environments include the capability for an application
to map a file's content into the application's address space. Each
time the application accesses a memory location that corresponds to a
block that has not been loaded into the address space, a page fault
occurs and the file is read (or if the block does not exist in the
file, the block is allocated and then instantiated in the
application's address space).
As long as each memory-mapped access to the file requires a page
fault, the relevant attributes of the file that are used to detect
access and modification (time_access, time_metadata, time_modify, and
change) will be updated. However, in many operating environments,
when page faults are not required, these attributes will not be
updated on reads or updates to the file via memory access (regardless
of whether the file is local or is accessed remotely). A client or
server MAY fail to update attributes of a file that is being accessed
via memory-mapped I/O. This has several implications:
* If there is an application on the server that has memory mapped a
file that a client is also accessing, the client may not be able
to get a consistent value of the change attribute to determine
whether or not its cache is stale. A server that knows that the
file is memory-mapped could always pessimistically return updated
values for change so as to force the application to always get the
most up-to-date data and metadata for the file. However, due to
the negative performance implications of this, such behavior is
OPTIONAL.
* If the memory-mapped file is not being modified on the server, and
instead is just being read by an application via the memory-mapped
interface, the client will not see an updated time_access
attribute. However, in many operating environments, neither will
any process running on the server. Thus, NFS clients are at no
disadvantage with respect to local processes.
* If there is another client that is memory mapping the file, and if
that client is holding an OPEN_DELEGATE_WRITE delegation, the same
set of issues as discussed in the previous two bullet points
apply. However, it should be noted that it is very unlikely that
such a delegation will be held since it is normally required that
the file be open for read to be mapped into memory. Only if the
file were not open and accessed using a special stateid could the
delegation be retained while the file in question is mapped into
another client's memory. For this reason, such use is highly
undesirable.
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In this situation, when a server does a CB_GETATTR to a file that
the client has modified in its cache, the reply from CB_GETATTR
would not necessarily be accurate, assuming the delegation is not
recalled at this point. As discussed earlier, the client's
obligation is to report that the file has been modified since the
delegation was granted, not whether it has been modified again
between successive CB_GETATTR calls, and the server MUST assume
that any file the client has modified in cache has been modified
again between successive CB_GETATTR calls. Depending on the
nature of the client's memory management system, it might not be
possible to live up to this weak obligation. A client MAY return
stale information in CB_GETATTR whenever the file is memory-
mapped, if another client is accessing the file without opening
it.
16. Client-side Name and Directory Caching
Although there are important parallels, name and directory caching,
discussed in this section as a whole, need to be considered
separately from caching for files, discussed in Section 15 as a
whole. This is because:
* Directories are structured objects with relatively infrequent
entry changes effected on the server, the need for client-side
data storage is reduced, eliminating one important barrier to
effective coherence.
* The directory delegation feature, because of its notification
features is in a better position to provide inter-client
coherence, although achievement of consistency is likely to be
delayed by transfer delays
Although directory notification include facilities for attribute
updates, the delayed character of the notifications and the lack of
directory-oriented constraints on changes implies that these are
provided as a helpful convenience feature that leaves the caching
architecture substantially unchanged.
16.1. Name and Directory Caching without Directory Delegations
The NFSv4.1 directory delegation facility (described in Section 16.2
below) is OPTIONAL for servers to implement. Even where it is
implemented, it may not always be functional because of resource
availability issues or other constraints. Thus, it is important to
understand how name and directory caching are done in the absence of
directory delegations. These topics are discussed in the next two
subsections.
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16.1.1. Name Caching
The results of LOOKUP and READDIR operations may be cached to avoid
the cost of subsequent LOOKUP operations. Just as in the case of
attribute caching, inconsistencies may arise among the various client
caches. To mitigate the effects of these inconsistencies and given
the context of typical file system APIs, an upper time boundary is
maintained for how long a client name cache entry can be kept without
verifying that the entry has not been made invalid by a directory
change operation performed by another client.
When a client is not making changes to a directory for which there
exist name cache entries, the client needs to periodically fetch
attributes for that directory to ensure that it is not being
modified. After determining that no modification has occurred, the
expiration time for the associated name cache entries can be updated
to be the current time plus the name cache staleness bound.
When a client is making changes to a given directory, it needs to
determine whether there have been changes made to the directory by
other clients. It does this by using the change attribute as
reported before and after the directory operation in the associated
change_info4 value returned for the operation. The server is able to
communicate to the client whether the change_info4 data is provided
atomically with respect to the directory operation. If the change
values are provided atomically, the client has a basis for
determining, given proper care, whether other clients are modifying
the directory in question.
The simplest way to enable the client to make this determination is
for the client to serialize all changes made to a specific directory.
When this is done, and the server provides before and after values of
the change attribute atomically, the client can simply compare the
after value of the change attribute from one operation on a directory
with the before value on the subsequent operation modifying that
directory. When these are equal, the client is assured that no other
client is modifying the directory in question.
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When such serialization is not used, and there may be multiple
simultaneous outstanding operations modifying a single directory sent
from a single client, making this sort of determination can be more
complicated. If two such operations complete in a different order
than they were actually performed, that might give an appearance
consistent with modification being made by another client. Where
this appears to happen, the client needs to await the completion of
all such modifications that were started previously, to see if the
outstanding before and after change numbers can be sorted into a
chain such that the before value of one change number matches the
after value of a previous one, in a chain consistent with this client
being the only one modifying the directory.
In either of these cases, the client is able to determine whether the
directory is being modified by another client. If the comparison
indicates that the directory was updated by another client, the name
cache associated with the modified directory is purged from the
client. If the comparison indicates no modification, the name cache
can be updated on the client to reflect the directory operation and
the associated timeout can be extended. The post-operation change
value needs to be saved as the basis for future change_info4
comparisons.
As demonstrated by the scenario above, name caching requires that the
client revalidate name cache data by inspecting the change attribute
of a directory at the point when the name cache item was cached.
This requires that the server update the change attribute for
directories when the contents of the corresponding directory is
modified. For a client to use the change_info4 information
appropriately and correctly, the server must report the pre- and
post-operation change attribute values atomically. When the server
is unable to report the before and after values atomically with
respect to the directory operation, the server must indicate that
fact in the change_info4 return value. When the information is not
atomically reported, the client should not assume that other clients
have not changed the directory.
16.1.2. Directory Caching
The results of READDIR operations may be used to avoid subsequent
READDIR operations. Just as in the cases of attribute and name
caching, inconsistencies may arise among the various client caches.
To mitigate the effects of these inconsistencies, and given the
context of typical file system APIs, the following rules should be
followed:
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* Cached READDIR information for a directory that is not obtained in
a single READDIR operation must always be a consistent snapshot of
directory contents. This is determined by using a GETATTR before
the first READDIR and after the last READDIR that contributes to
the cache.
* An upper time boundary is maintained to indicate the length of
time a directory cache entry is considered valid before the client
must revalidate the cached information.
The revalidation technique parallels that discussed in the case of
name caching. When the client is not changing the directory in
question, checking the change attribute of the directory with GETATTR
is adequate. The lifetime of the cache entry can be extended at
these checkpoints. When a client is modifying the directory, the
client needs to use the change_info4 data to determine whether there
are other clients modifying the directory. If it is determined that
no other client modifications are occurring, the client may update
its directory cache to reflect its own changes.
As demonstrated previously, directory caching requires that the
client revalidate directory cache data by inspecting the change
attribute of a directory at the point when the directory was cached.
This requires that the server update the change attribute for
directories when the contents of the corresponding directory is
modified. For a client to use the change_info4 information
appropriately and correctly, the server must report the pre- and
post-operation change attribute values atomically. When the server
is unable to report the before and after values atomically with
respect to the directory operation, the server must indicate that
fact in the change_info4 return value. When the information is not
atomically reported, the client should not assume that other clients
have not changed the directory.
16.2. Directory Delegations and Notifications
16.2.1. Motivation for Directory Delegations
Directory caching for the NFSv4.1 protocol when directory delegations
are not available, is similar to file and directory caching in
previous versions. Clients typically cache directory information for
a duration determined by the client. At the end of that predefined
period, the client will query the server to see if the directory has
been updated. By caching attributes, clients reduce the number of
GETATTR calls made to the server to validate attributes. As a
result, frequently accessed files and directories, such as the
current working directory, have their attributes cached on the client
so that some NFS operations can be performed without making an RPC
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call. By caching name and attributes information about most recently
looked up entries in a Directory Name Lookup Cache (DNLC), clients
are able to avoid sending LOOKUP/GETATTR calls to the server every
time such files are accessed.
This caching approach works reasonably well at reducing network
traffic in many environments. However, it does not address
environments where there are numerous queries for files that do not
exist. In these cases of "misses", the client sends requests to the
server in order to provide reasonable application semantics and
promptly detect the creation of new directory entries. Examples of
high miss activity are compilation in software development
environments. The current behavior of NFS limits its potential
scalability and wide-area sharing effectiveness in these types of
environments.
Since, other distributed stateful file system architectures such as
AFS and DFS have proven that adding state around directory contents
can greatly reduce network traffic in high-miss environments, it is
sensible to define and implement such facilities in NFSv4.1.
16.2.2. Directory Caching Features
Delegation of directory contents is an OPTIONAL feature of NFSv4.1.
Possession of a delegation can be taken advantage of in a number of
ways:
* It can be used to provide a recallable assurance that the
directory contents have not changed, allowing LOOKUP results
(whether successful or not) and READDIR results to be cached, in
order to enable these operations to be performed locally.
This mode of operation in which directory contents are fixed is
often referred to as the "pure recall" model since any change in
the directory contents results in the delegation being recalled.
This mode of operation is most effectively used on large
directories which are infrequently changed.
* The client can request, as part of requesting a delegation, that
notifications be provided to update the clients view of the
directory contents to match that of the server. See
Section 16.2.11 for details. This mode of operation allows
directory delegations to be effectively used in handling large
directories that experience a significant stream of updates.
* Independently of the mode of operation selected, notifications to
inform the client of attribute changes can be requested. See
Section 16.2.11 for details.
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16.2.3. Directory Delegation Notifications
As discussed below in Section 16.2.5, the caller had the ability to
request various notifications in the form of callbacks (See
Section 27.4
These callbacks aid the client by:
* Providing ways to update the client's view of the directory
contents to match that of the server, instead of recalling the
delegation.
* Provide Information about changes in directory attributes or the
attributes of file objects named by directory entries.
* Provide assistance in authorizing LOOKUPs and READDIRs based on
names cached by the client.
Each notification identifies the directory and delegation with which
it is associated and contains an array of notification elements (each
of type notify4).
Each notify4 is defined in a manner similar to that used for fattr4,
in that the data is presented in XDR as consisting of a number of
opaque elements, that are not actually opaque but are beyond the
capacity of XDR to explicitly describe. In the case of the notify4
there are two nominally opaque arrays.
* The first is a bitmap4 which has an analogous function to the
attrmask in a fattr4.
The bit positions within this mask are selected from the enum
notify_type4.
* The second nominally opaque element is the concatenation of
selected elements corresponding to set bit in the bit mask
described above.
This is analogous to attrlist4 within an fattr4.
The table in Section 27.4.1 indicates the data segment
corresponding to each bit set.
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16.2.4. Directory Delegation Choices
Unlike other forms of delegation, the directory delegation feature
has associated OPTIONAL features that allow clients to maintain
correct local copies of directory contents even in the face of
ongoing changes to the delegated directories. The client has three
basic choices listed below in choosing a system of directory content
change notifications. See Section 16.2.11 for details.
A major consideration for clients in making these choices concerns
the operations to be performed locally using cached data provided by
or assured correct by the directory delegation:
* Local LOOKUP is expected to be always used and is the core
motivation for the feature.
* Local READDIR is an important possibility but is not universally
provided because some clients and severs are not prepared to
maintain client-side images of READDIR response and deal properly
with the ordering of entries and the cookie values associated with
them in order to keep the server and the clients fully in sync.
* Local GETATTR (and READDIR with attributes) is provided for in the
design of directory delegation but is expected to require extra
support facilities to be effective, as described in
Section 16.2.8.
The need for these support facilities arises principally from the
delayed/batched character of directory entry attribute
notifications, while prompt notifications are hard to implement
given the possibility that certain files will be linked to from
multiple directories, making it difficult to promptly generate
attribute change notifications. The usability of this feature
without prompt notification depends on the need for up-to-date
values of various file attributes, which are not currently
standardized.
* To provide for delegation loss as a result of any directory
change.
Delegation recall results from changes to directory contents if
directory content notifications are not requested.
Because recalls halt directory changes until the delegation is
returned, it is often advantageous to request change notifications
(asynchronous) and respond to them by returning the delegation.
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* To receive notifications about changes to directory contents,
considered as an unordered set of names and update the client's
view of the directory in accord with the notification.
This can be used to support both positive and negative name
caching. However, it does not fully support retention of an
accurate client copy in the face of changes because of lack of
support for tracking ordering changes and entry cookie changes.
* To receive notifications about changes to directory contents,
considered as an ordered set with associated identifying cookies.
Because of server-side difficulties in providing some of this
information and client-side difficulties providing it, this choice
might not be available, but, if so, the previous option will
support positive and negative name caching even if repeated
READDIRs cannot be eliminated.
In addition there are possible additional forms of notifications to
aid the client:
* Notifications regarding changes in directory attributes .
Knowledge of such authorization-related attributes can be helpful
to the client in validating the authorization to use cached name
entries or directories on its own instead of using ACCESS
requests.
In some cases, additional facilities are available to simplify the
task of meeting authorization requirements. See Section 16.2.6
for details.
Knowledge of modified-time or the change attribute can be helpful
in potentially keeping a valid view of the directory when dealing
with the consequences of delegation recall. See Section 16.2.11
to see how attribute notifications can be used together with
content notifications to associate a set of directory contents and
the corresponding directory attributes.
* Notification of changes of attributes of objects within the
directory.
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16.2.5. Directory Delegation Mechanics
The GET_DIR_DELEGATION (Section 25.39) operation is used by clients
to request directory delegation. The delegation is read-only and the
client is not provided any means to make changes to the directory
other than by performing NFSv4.1 operations that modify the
directory.
As part of obtaining a delegation, the client specifies, using the
bit numbers within the notify_type4 enum that appears below, its
choices regarding notification of events related to the reporting of
events affecting the delegation. These bits originally specified a
set of notification types but have been extended into a wider set of
flag values specified when delegations are requested and returned
when the are granted:
* Some bits request that particular notifications be provided to the
client, instead of recalling the delegation.
These bits are used to indicate that the requested notifications
will be provided by the server.
* Other bits have no associated notification message and provide
request flags specifying the requested handling of the delegation
and/or response flags indicating useful information about the
handling of the delegation and associated notifications.
It is important to note that this enum is subject to extension and
has been extended relative to the set of bits defined in [RFC8881].
The distinction between bits that were defined earlier and those
added later is important to enable interoperation between clients and
servers when one might have been written based on the earlier
specification. Although no implementations based on the earlier
specification are known, the possibility of their existence cannot be
excluded.
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/*
* Directory notification types and associated flags
*/
enum notify_type4 {
/*
* Present in RFCs 5661, 8881
*/
NOTIFY4_CHANGE_CHILD_ATTRS = 0,
NOTIFY4_CHANGE_DIR_ATTRS = 1,
NOTIFY4_REMOVE_ENTRY = 2,
NOTIFY4_ADD_ENTRY = 3,
NOTIFY4_RENAME_ENTRY = 4,
NOTIFY4_CHANGE_COOKIE_VERIFIER = 5,
/*
* Added in NFSv4.1 bis document
*/
NOTIFY4_GFLAG_EXTEND = 6,
NOTIFY4_AUFLAG_VALID = 7,
NOTIFY4_AUFLAG_USER = 8,
NOTIFY4_AUFLAG_GROUP = 9,
NOTIFY4_AUFLAG_OTHER = 10,
NOTIFY4_CHANGE_AUTH = 11,
NOTIFY4_CFLAG_ORDER = 12,
NOTIFY4_AUFLAG_GANOW = 13,
NOTIFY4_AUFLAG_GALATER = 14,
NOTIFY4_CHANGE_GA = 15,
NOTIFY4_CHANGE_AMASK = 16,
NOTIFY4_ACCFLAG_USER = 17,
NOTIFY4_ACCFLAG_GROUP = 18,
NOTIFY4_ACCFLAG_OTHER = 19,
NOTIFY4_PRAN_CONTENT = 20,
NOTIFY4_PRAN_AUTH = 21
};
The following table summarizes he handling of the bit numbers
specified in the enum above:
The bits within the enum are organized into the following groups:
* Content change notifications which provide updates regarding the
set of directory entries (or sometimes the order of those
entries).
* General flags which affect the process of other in bits in
multiple groups.
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* Attribute notifications which provide updates regarding attributes
of directories objects identified by directory entries.
* Lookup authorization infrastructure which provides the client
assistance in avoiding repeated use of ACCESS in satisfying
requests using name caching.
* Getattr authorization infrastructure which provides the client
assistance in avoiding repeated use of ACCESS in satisfying
requests for cached file attributes.
Such help is made necessary by the existence of possible
restrictions on attribute fetches in the NFSv4 ACL model.
The group has a reference to an appropriate explanatory section and
is followed by the bits included within the group together with, for
each bit:
* The abbreviated bit name.
* The bit number.
* The bit's extension status with "old" indicating something known
to all client and defined in [RFC8881] and "Ext" indicating an
extension added as part of the respecification effort, to correct
a defect.
* The bit type using one of the codes listed below.
* A reference to one or more sections with more detailed
description.
The following types of notifications and flags ae defined.
PrN Prompt Notification -- One sent immediately as part of the event
being reported.
DlN Delayed Notify -- One sent lazily at some later time based on a
associated attribute.
SmN Specially managed notification -- One sent promptly or in
delayed fashion based on factors explained in the detailed
reference.
Bdf Bidirectional flag -- One specified on delegation request and
interrogated in the corresponding response.
RgF Request Flag -- One used as part of the delegation request with
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no corresponding value in the response.
RsF Response Flag -- One having no use as part of the delegation
request while conveying useful information in the response.
+------------------------+------------------------------+-----------+
| Group |Discussion | Ref |
+------------------------+---+---+----+-----------------+ |
| Item |# |Ext|Type| Description | |
+------------------------+---+---+----+-----------------+-----------+
| Content |Content Change Notifies | S. |
| | | 16.2.11 |
+------------------------+---+---+----+-----------------+-----------+
| REMOVE_ENTRY |2 |Old|PrN | Entry Removal | S. 27.4.5 |
| | | | | Ntfy | |
+------------------------+---+---+----+-----------------+-----------+
| ADD_ENTRY |3 |Old|PrN | Entry | S. 27.4.4 |
| | | | | Addition Ntfy | |
+------------------------+---+---+----+-----------------+-----------+
| RENAME_ENTRY |4 |Old|PrN | Entry Rename | S. 27.4.6 |
| | | | | Ntfy | |
+------------------------+---+---+----+-----------------+-----------+
| CHANGE_COOKIE_VERIFIER |5 |Old|PrN | Change Cookie | S. 27.4.9 |
| | | | | Verifier | |
+------------------------+---+---+----+-----------------+-----------+
| Gen Flags |General Flags | S. |
| | | 16.2.10 |
+------------------------+---+---+----+-----------------+-----------+
| GFLAG_EXTEND |6 |Ext|BdF | General | S. |
| | | | | Extension | 16.2.10 |
| | | | | Flag | |
+------------------------+---+---+----+-----------------+-----------+
| Content Flags |Content Description Flags | S. |
| | | 16.2.11.3 |
+------------------------+---+---+----+-----------------+-----------+
| CFLAG_ORDER |12 |Ext|RqF | Controls | S. |
| | | | | Content | 16.2.11.3 |
| | | | | Ordering | |
| | | | | Needs | |
+------------------------+---+---+----+-----------------+-----------+
| Attribute |Attribute Change Notifies | S. |
| | | 16.2.12 |
+------------------------+---+---+----+-----------------+-----------+
| CHANGE_CHILD_ATTRS |0 |Old|DlN | Changes to | S. |
| | | | | Dir Entry | 16.2.12.2 |
| | | | | Attributes | |
+------------------------+---+---+----+-----------------+-----------+
| CHANGE_DIR_ATTRS |1 |Old|SmN | Changes to | S. |
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| | | | | Dir | 16.2.12.1 |
| | | | | Attributes | |
+------------------------+---+---+----+-----------------+-----------+
| CHANGE_AMASK |16 |Ext|PrN | Change to | S. |
| | | | | Attribute | 27.4.10 |
| | | | | Masks | |
+------------------------+---+---+----+-----------------+-----------+
| PRAN_CONTENT |20 |Ext|RsF | Prompt Not. | S. |
| | | | | for Attr. | 16.2.12.1 |
| | | | | Changes with | |
| | | | | Content | |
| | | | | Changes | |
+------------------------+---+---+----+-----------------+-----------+
| PRAN_AUTH |21 |Ext|RsF | Prompt Not. | S. |
| | | | | for Attr. | 16.2.12.1 |
| | | | | Changes re | |
| | | | | Authorization | |
+------------------------+---+---+----+-----------------+-----------+
| Lookup Authorization |Lookup/readdir Authorization | S. |
| |Support | 16.2.13.1 |
+------------------------+---+---+----+-----------------+-----------+
| AUFLAG_VALID |7 |Ext|RsF | Validity of | S. |
| | | | | Authorization | 16.2.13.1 |
| | | | | Flags | |
+------------------------+---+---+----+-----------------+-----------+
| AUFLAG_OWNER |8 |Ext|RsF | Authorization | S. |
| | | | | for Owner | 16.2.13.1 |
+------------------------+---+---+----+-----------------+-----------+
| AUFLAG_GROUP |9 |Ext|RsF | Authorization | S. |
| | | | | for Owning | 16.2.13.1 |
| | | | | Group | |
+------------------------+---+---+----+-----------------+-----------+
| AUFLAG_OTHERS |10 |Ext|RsF | Authorization | S. |
| | | | | for Others | 16.2.13.1 |
+------------------------+---+---+----+-----------------+-----------+
| ACCFLAG_OWNER |17 |Ext|RsF | Need for | S. |
| | | | | ACCESS for | 16.2.13.1 |
| | | | | Owner | |
+------------------------+---+---+----+-----------------+-----------+
| ACCFLAG_GROUP |18 |Ext|RsF | Need for | S. |
| | | | | ACCESS for | 16.2.13.1 |
| | | | | Owning Group | |
+------------------------+---+---+----+-----------------+-----------+
| ACCFLAG_OTHERS |19 |Ext|RsF | Need for | S. |
| | | | | ACCESS for | 16.2.13.1 |
| | | | | Others | |
+------------------------+---+---+----+-----------------+-----------+
| CHANGE_AUTH |11 |Ext|PrN | Changes to | S. |
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| | | | | Lookup | 27.4.11 |
| | | | | Authorization | |
+------------------------+---+---+----+-----------------+-----------+
| Getattr Authorization |Getattr Authorization | S. |
| |Support | 16.2.13.2 |
+------------------------+---+---+----+-----------------+-----------+
| AUFLAG_GANOW |13 |Ext|RsF | Getattr | S. |
| | | | | processing | 16.2.13.2 |
| | | | | now | |
+------------------------+---+---+----+-----------------+-----------+
| AUFLAG_GALATER |14 |Ext|RsF | Getattr | S. |
| | | | | processing | 16.2.13.2 |
| | | | | deferred | |
+------------------------+---+---+----+-----------------+-----------+
| CHANGE_GA |15 |Ext|PrN | Getattr | S. |
| | | | | processing | 27.4.12 |
| | | | | change | |
+------------------------+---+---+----+-----------------+-----------+
Table 6
The holder of a delegation is assured of certain things not being
changed while the directory delegation is held, as described below.
* That the set of entries within the directory not be changed
without sending a requested notification to the client, informing
the client of the change.
* That the order of directory entries or the cookie values
associated with specific directory entry with the client being
informed (via a NOTIFY4_CHANGE_COOKIE_VERIFIER notification) of
the possibility of change.
Delegations can be recalled by the server at any time and are always
recalled before a directory is removed.
16.2.6. Directory Delegation Authorization Extensions
When cached data is used locally in place of LOOKUP, GETATTR, or,
READDIR operations, the authorization constraints that would normally
be imposed by the server have to be applied by the client instead of
by the server. This is because requiring server-based authorization
would undercut the performance benefits that caching is intended to
provide.
The discussion of these matters is complicated by the fact that,
while facilities have been designed to avoid the overhead
requirements of authorization and these are described in this
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document, the treatment of the matter in earlier specifications did
not provide facilities to help the client do this correctly and had
little to say on the issue. As a result, clients were faced with the
choice of:
* ignoring some difficult authorization issues.
* implicitly deciding that certain features of the NFSv4 ACL Model
are not to be implemented within filesystems for which directory
delegation is to be used.
* burdening the implementation of directory delegation with
authorization checking that would undercut the performance
benefits of the feature, when used with filesystems that implement
NFSv4 ACLs, especially where the implementation includes certain
troublesome features.
Of particular concern are ACLs for which AUDIT or ALARM ACEs are
implemented, making it possible that there are directory ACLs
where authorization checking cannot be accomplished by the client
even if the client is willing and able to process ACLs itself in
order to make authorization decisions.
In considering whether the extensions described in Section 16.2.9 are
worth implementing within client and server implementation of
directory delegation, the following factors need to be considered:
* Whether the cached directories are used to prevent remote access
when implementing READDIR and GETATTR, or only when avoiding
LOOKUPs.
* Whether ACLs are implemented making the decision of search
permissions for a given user more complicated than it is when this
decision is based solely on the mode, owner, and owner-group
attributes derived from the POSIX authorization model.
* The support for and use of the ACE mask bit controlling
authorization to read attribute values.
* The preparedness of the client implementer to fetch and interpret
directory ACLs and use them to derive search/ read authorization.
Beyond the reluctance of client implementers to take on this new
task, especially given the uncertain state of the specification of
ACL semantics, the direction in [RFC8881] stating that this
"SHOULD NOT" be done, even though, in the NFSv4.1 bis documents,
this statement will no longer appear.
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As dealt with in this document and related ones, the determination
of search/read authorization for directories is not considered a
troublesome usage to be discouraged. However, efforts will be
made in the definition of the features defined in Section 16.2.9
to accommodate clients that do not have this capability.
When certain combinations of the above issues are present, we will be
faced with a situation in which we need to decide how to deal with
authorization mistakes that implementers might have been encouraged
to make by previous specs, now considered superseded. See
Section 16.2.7 for a discussion of these matters. Note that while
this could be considered analogous to the situation in which
implementers were told that use of AUTH_SYS in the clear, is an
"OPTIONAL means of authentication", with the consequence that such
use needed to be allowed in the future while being cautioned against,
our situation is different in that:
* This disregard of authorization issues was implicit and there was
no statement that they could be ignored.
* We are dealing with a feature that is unlikely to have troublesome
legacy implementations.
* While the previous use of "SHOULD NOT in connections with client
processing of ACLs might have been relied on, there is unlikely to
be specific implementations embodying this approach, so that our
accommodation of implementors not doing this is motivated by
providing an easier implementation path, rather than accommodating
a previous mistaken specification.
16.2.7. Former Authorization Practices and Their Current Validity
There are a number of troubling authorization issues that arise
because of features that were included as OPTIONAL extensions to the
NFSv4 ACL model.
* The potential use of AUDIT and ALARM ACEs, which make the
requirements for a client-side authorization check more
complicated than a single, cacheable, yes-no decision, making it
possible that server-specific implementation is necessary in the
event of successful or failed authorization,
* The appearance of ACE's that include the ACE mask bit controlling
authorization to read attributes of a specified file.
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This feature is unlikely to be supported by servers because it is
outside the scope of the POSIX authorization model. Nevertheless,
there are likely to be servers supporting it, especially if it is
needed by Windows clients.
This feature is not troublesome if the client implementations of
directory delegation do not support client-local provision of
GETATTR or READDIR with associated attributes.
The existence of these features together with the following issues
means that some implementors might need the server-side assistance
described in Section 16.2.9, even when a client could do
authorization checking on its own.
* The potential transfer of NFSv3-based code (which could not deal
with ACLs to an NFSv4 environment and its subsequent incorporation
in a client-side directory delegation implementation.
* The lack of attention to authorization issue in previous
specifications combined with the sense that a client doing its own
authorization checks was to be discouraged.
* The preparedness of the client implementer to fetch and interpret
directory ACLs and use them to derive search authorization.
Beyond the reluctance of a client implementer to take on this new
task, especially given the uncertain state of the specification of
ACL semantics, the direction in [RFC8881] stating that this
"SHOULD NOT" be done, even though, in the NFSv4.1 bis document,
this statement will no longer appear
When, for whatever reason, a client is unwilling to provide this
support. implementation of directory delegations is not practical
unless the facilities described in Section 16.2.9
As a result, we are faced with the issue of how to accommodate
implementations that are now known to have troubling problems that
were not recognized when the feature was first described in a
Proposed Standard. Normally, one tries to accommodate such
situations by recommending against approaches now known to be flawed
while considering, as a valid reason to bypass the recommendation,
the reliance of the implementer on an approved Proposed Standard at
the time. In this case we have a different approach, because of the
following distinctive factors:
* Unlike the case of implementers being told that use of AUTH_SYS in
the clear, is an "OPTIONAL means of authentication" with the
implication that such use does not result in potentially
unacceptable security vulnerabilities, there is no direct
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suggestion that neglecting these difficulties is acceptable.
Instead, while lack of attention to security issues might have led
people astray, they were not specifically asked to adopt a flawed
approach to security but chose to adopt one on their own. As a
result, while we will make certain allowances to accommodate such
early implementations, there is no known paradigm that could be
cited as valid but discouraged.
* The set of implementations involved is likely to be quite small
and might be empty or only consist of experimental implementations
not widely distributed.
The approach we take here is the same one we take to servers that do
not support the extensions described in Section 16.2.13 and to
clients that interact with such servers. It has the following
elements:
* Clients are free in deciding whether to use directory delegations
to take account of the problems with earlier approaches in
deciding whether to use this feature.
* Neglecting the possibility of authorization failure on GETATTR
when directory entry attributes are cached is not to be considered
valid despite the development of code that ignored this issue
based on previous specifications together with the widely held
impression that authorization of GETATTR is not required.
If the server implements this feature, clients, if they implement
this directory delegation have no basis to justify undercutting
it.
* When clients use ACCESS to do authorization checks, as they should
when they have no ability to process ACLs on their own, allowance
needs to be made for them to cache positive and negative results,
since without that ability, you might as well fetch the data over
the wire anyway, negating the value of directory delegation.
When AUDIT and ALARM ACEs are present, there will be situations in
which local processing of the ACL is not sufficient to avoid
remote use of ACCESS.
16.2.8. Alternatives to Use of Directory Delegation Authorization
Support
The need for implementations of the extensions described in
Section 16.2.9 is affected by the following considerations:
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* The willingness/ability of the client to do authorization checking
on its own, including the ability to read and interpret ACLs
fetched from the directory or reported via attribute change
notifications.
* The frequency of encountering ACLs for which local checking is not
possible.
* The ability of the facilities within Section 16.2.9 to avoid
otherwise necessary remote operations.
We will deal separately with the cases of clients prepared or not
prepared to use ACLs locally.
For clients that are not able to process ACLs locally, there are a
number of features that server filesystems might need support to help
clients deal with situations they cannot effectively deal with in
supporting directory delegations. Clints need to either suppress
directory delegation when these situation exist, or rely on the
assistance provided by the authorization support extensions described
in the next session.
* Support of AUDIT and ALARM ACEs. The ACLSUPORT attribute for a
filesystem can be checked to determine if this feature is present.
When it is present and the client is not able to process ACLs,
each LOOKUP would require a remote ACCESS request, effectively
negating the performance benefits of directory delegation.
* When a server and client work together to support local use of
cached attribute data and the filesystem in question supports the
ACE mask bit ACE4_READ_ATTRIBUTES. Each local execution of
GETATTR, using cached data when clients support this, requires
authorization that the client, if it cannot process ACLs, is not
able to do.
The ACLCHOICE attribute, when it is supported, allows the client
to inhibit support for local GETATTR operations using cached data
for filesystems that support suppression of the authorization of
GETATTR. When ACLCHOICE is not supported or this suppression is
possible support for GETATTR cannot be done.
In situations in which these restrictions are not acceptable, the
authorization support features can help the client by allowing it to
distinguish the directories (expected to be common) where these
features do not occur. For example, even when AUDIT and ALARM ACEs
are present within a filesystem, they are unlikely to be associated
with permission to search directories.
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For clients who can process ACLs on their own the situation is
different since the client can check for these troublesome situations
on its own. Nevertheless, the authorization support facilities,
while not necessarily required can optimize the process by avoiding
ACL processing in situations in which it can be avoided for a common
class of requests.
One important class of authorization requests consists of repeated
requests for authorization of the same user, assuming that the
authorization returned will typically not change when successive
requests to the same directory are made. While the client can deal
with this situation on its own by flushing the associated
authorization cache when the directory's metadata is changed, the
authorization support facilities deal with the issue more completely
because:
* Changes that do nor affect permissions to do LOOKUP (and READDIR
where local READDIR is supported) need not flush cached
indications of authorization success or failure.
* When there are such changes, they can be limited in their effects
since certain commonly used classes of users often are not changed
by common sort of ACL changes.
While the client could do that analysis on its own, it is preferable
to rely on the server since the server needs to support these
facilities to allow effective use of directory delegations.
For clients that intend to support local GETATTR, the need for
additional support facilities is not affected by the ability of the
client to read and interpret ACLs on its own. Given the use of
delayed/batched entry attribute change notifications, the important
issues concern whether the attributes returned include those that
require prompt notification when updated.
16.2.9. Directory Delegation Authorization Support
In providing support for authorization of local operations effecting,
using cached data, the equivalents of LOOKUP and READDIR operations,
the following issue needs to be dealt with:
The possibility of change in authorization-related attributes would
make repeated ACCESS calls necessary, unless facilities are provided
to avoid these when possible.
Note that the same issue applies to authorization of GETATTR-
equivalent local operations, but that, in that case, there are the
following additional issues to deal with:
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* The only potential reason to not grant such access derives from
the possible use of the ACE mask bit ACE4_READ_ATTRIBUTES.
Only where that bit is supported in ACLs and used to either deny
access or require audit or alarm on this operation is there any
possibility of not letting this operation be done unconditionally.
* Since permissions would need to be checked for each individual
object rather than for the directory as a whole, it is harder to
avoid unnecessary ACCESS calls in situations where the possibility
of denial exists.
The possible existence of multiply-linked file adds further
difficulty since it is possible that an ACL could be changed for
such an object in case in which the affected directories might not
be known.
* There are very few ACL implementations supporting use of the ACE
mask bit ACE4_READ_ATTRIBUTES and no known uses of it.
As a result we have to be prepared to efficiently deal with the
simple case where sophisticated support is unnecessary, as well as
providing reasonable support to deal with the possibility of it
becoming more widely implemented.
To provide better support for authorization of LOOKUP/READDIR, we do
the following:
* When the delegation is created, the server returns information
about pre-defined sets of users for which explicit authorization
checks can be avoided or for which client-side authorization
cannot validly be done. These sets are a natural division of the
principal space with POSIX authorization semantics, and remain an
appropriate division even though certain other special user groups
might be defined and used within ACLs.
The flags NOTIFY4_AUFLAG_OWNER, NOTIFY4_AUFLAG_GROUP, and
NOTIFY4_AUFLAG_OTHERS indicate the ability to avoid authorization
checks for LOOKUP and READDIR by the owner of the file, other
members of the owning group, and others, respectively. The
presence of each of these flags indicate that all principals in
the corresponding group can be assumed authorized to perform
LOOKUPs, and, when NOTIFY4_CFLAG_ORDER is set, READDIRs as well.
When multiple users are included in a given group, if some could
fail authorization, the corresponding bit will not be set and
authorization needs to be checked using ACCESS, by the client
doing its own authorization check, or by caching the results of a
previous check.
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The flags NOTIFY4_ACCFLAG_OWNER, NOTIFY4_ACCFLAG_GROUP, and
NOTIFY4_ACCFLAG_OTHERS indicate the need to perform an ACCESS
check when the principal performing the operation (LOOKUP and
possibly READDDIR as in the previous paragraph) is within the
corresponding group. The need for such checks, implying a client-
side check is not acceptable, arises from the possible inclusion
of AUDIT and ALARM ACEs which might require server-side processing
of the authorization request in either the successful or
unsuccessful authorization cases.
* When there is a change in one or more of the directory's
authorization-related attributes, the client is notified of the
new authorization handling scheme using the NOTIFY4_CHANGE_AUTH
notification.
The notification provides changes that apply separately to the
owning user, other users in the owning group, and other users.
For each such group, there are separate bits controlling the need
for explicit ACCESS checks for LOOKUP and for READDIR, and
directing the client whether to flush cached results for previous
ACCESS checks.
To provide adequate support for authorization of local GETATTR and
associated attribute caching the facility described in Sections
27.4.12 and 16.2.13.2.
16.2.10. Directory Delegation Feature Version Management
As part work undertaken to respecify NFSv4 minor version one to
reflect implementation experience since the publication of [RFC5661],
it was necessary to make certain protocol extensions in order to
correct problems that had resulted in a lack of implementation of the
Directory Delegation feature in the years since its initial
introduction.
These extensions took the form of additions to the enum notify_type4
as described in [RFC8178]. These new values,
* Provide new notifications including a set focused on providing
authorization support to allow operations to be performed locally
without impacting needed authorization semantics.
Provided a new notification to allow server to deal with excessive
backchannel traffic for attribute updates without delegation
recall.
* Created flags to be sent by the client as part of delegation
request and by the server as part of delegation creation.
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These flags allowed necessary version control, improved
authorization handling and a more flexible approach to the
provision of position information in content update notifications.
These new notifications and flags are described, together with the
older ones, in Sections 16.2.11 through 16.2.13
The flag NOTIFY4_GFLAG_EXTEND has a special role in the management of
versions, in order to support interoperation of implementations
written to conform to [RFC8881] and to the those written to conform
to the updated definition:
* When NOTIFY4_GFLAG_EXTEND is set in a request, the client is
indicating that it is aware of the additional flags and
notifications.
* When NOTIFY4_GFLAG_EXTEND is set in a response, the server is
indicating that it is aware of the additional flags and
notifications. and that the delegation is to be handled in accord
with the updated specification of the feature.
16.2.11. Directory Content Notifications
When a directory delegation is held, it is normally expected to
remain unmodified. However, to avoid the possibility that directory
content changes will force much of the work done in establishing a
delegation to be redone, the user can request notifications be sent
regarding certain changes, allowing the client to update its view of
the directory, while keeping the delegation unrecalled.
Support is present for clients who are interested in the order of
directory entries and for those that are not. While the former will
have the ability to cache and reuse READDIR responses and synthesize
new ones in response to content modification notifications, the
latter only need the ability to maintain positive and negative name
caches for entries in the directory. The need for order-related
information is specified using the flag NOTIFY4_CFLAG_ORDER (only
specifiable when NOTIFY4_GFLAG_EXTEND is specified as well.
16.2.11.1. Core Content Notifications
Notification of directory content changes is requested by requesting
any of the notification types NOTIFY4_ADD_ENTRY,
NOTIFY4_REMOVE_ENTRY, NOTIFY4_RENAME_ENTRY, although typically a
client would request all of these to avoid situations where common
directory changes result in directory recall.
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These notifications are used as follows. For details regarding the
specifics of the relevant notification messages, see the appropriate
subsection of Section 27.4.
* The creation of a new directory entry, as a result of an OPEN
creating a new file, a CREATE operation, or a LINK operation is
signaled using a NOTIFY4_ADD_ENTRY notification.
It is described in Section 27.4.4.
* The deletion of an existing directory entry as a result of a
REMOVE operation, or the deletion of a file renamed-over by a
cross-directory RENAME operation is signaled using a
NOTIFY4_REMOVE_ENTRY notification.
It is described in Section 27.4.5.
In the cross-directory rename-over case, the NOTIFY4_ADD_ENTRY and
NOTIFY4_REMOVE_ENTRY notification are to appear in the same
notify4, with both notification bits set.
* The renaming of a directory entry and the possible deletion of a
renamed-over entry as part of a within-directory RENAME operation
is signaled by a NOTIFY4_RENAME-ENTRY notification.
It is described in Section 27.4.6.
16.2.11.2. Order and Format Choices
Based on the client's preference regarding order information and the
server's choices, there are three forms of content notification that
can be sent:
* The order-agnostic format is used when the client is not concerned
with directory entry order, as indicated by the
NOTIFY4_CFLAG_ORDER being zero when the NOTIFY4_GFLAG_EXTEND flag
is set.
This form is requested by the client if it does not want to
maintain an ordered image of the directory locally and is
unconcerned with directory cookies.
When this format is requested by a client the notification is not
sent to the client that requested the changes, since it is
presumed to be aware of the change, and has no need for the
additional ordering-related information to be provided.
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If the server does not support this option, additional information
can be provided using one of the other forms, with unneeded
information ignored by the client.
* The derived-order format provides a directory entry ordering based
on the cookies associated with the directory entries, it being
assumed by the client that the order of cookies and the order of
directory entries being the same.
A nad_new_entry_cookie of length 1 with the new cookie in it
provides the necessary position for added files. Any
nad_prev_entry is of length 1 with an invalid notify_entry4
indicated by the ne_file component being o of length 0. The
nad_last_entry value conveys and should be ignored.
The presence pf a nad_new_entry not in this form indicates that,
if the client is order-aware, the notification is to be treated as
in the explicit-order format.
If it is ever the case that the cookie order and the entry order
for a directory becomes different, then this format cannot be used
and the change should be signaled using
NOTIFY4_CHANGE_COOKIE_VERIFIER (See Section 16.2.11.3).
* The explicit-order format fully uses and sets cookie values
nad_prev_entry field and nad_last entry flags
The above rules change the actual form of the notifications. even
though the same XDR definitions are used for the structure associated
with the ADD_ENTRY, REMOVE_ENTRY, and RENAME_ENTRY notifications
16.2.11.3. Order-related Content Change Notifications
Notifications of type NOTIFY4_CHANGE_COOKIE_VERIFIER are used to
signal a number of changes in the order of directory entries and
their associated cookies as listed below. The notification are only
sent if the client is concerned with directory entry order. If the
client is concerned with entry order and these notifications are not
requested or cannot be sent for any other reason, then the delegation
is recalled.
The changes requiring these notifications include, in addition to
cookie verifier changes, any of the following:
* Changes in cookies for cached entries.
* Changes in directory entry order that do not arise in connection
with the content changes discussed in Section 16.2.11.1.
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This notification is described in Section 27.4.9.
It is often sent with the old and new verifiers being the same.
16.2.11.4. Associated Directory Attribute Changes"
There a number of attributes that, by their nature, are changed
whenever the directory contents is changed. These attributes are
modified_time and change.
When change notification for any of these attributes are requested,
they are delivered promptly, without regard to the specification of a
delay time in the delegation request.
The notifications appear in the same notify4 providing information
about the corresponding contents change. These include:
* Changes signaled by NOTIFY4_ADD_ENTRY, NOTIFY4_REMOVE_ENTRY, or
NOTIFY4_RENAME_ENTRY notifications.
* Changes due to cross-directory RENAME signaled using a combination
of NOTIFY4_ADD_ENTRY and NOTIFY4_REMOVE_ENTRY notifications.
* Ordering or cookie change signaled by a
NOTIFY4_ADD_CHANGE_VERIFIER notification.
16.2.11.5. Possible Recall Due to Directory Changes"
The implementation sections for a number of operations describe
situations in which notification or delegation recall would be
required under some common circumstances. When these events result
in delegation recall, a set of caveats similar to those listed in
Section 15.2 apply. Note that in these cases, the operation does not
wait for the delegation to be returned or revoked, as it does in
other cases of delegation recall.
* For CREATE, see Section 25.4.4.
* For LINK, see Section 25.9.4.
* For OPEN, see Section 25.16.4.
* For REMOVE, see Section 25.25.4.
* For RENAME, see Section 25.26.4.
* For SETATTR, see Section 25.30.4.
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16.2.12. Directory Attribute Notifications
Those holding directory delegations may be notified of attribute
changes as described below:
* Information about changes to directory attributes are provided via
the NOTIFY4_CHANGE_DIR_ATTRS notification, as discussed in
Section 16.2.12.1.
Most often these changes are provided using a Batch/Deferred
approach, although prompt notification can be requested by
specifying a delay of zero.
Special prompt handling is available for attributes whose values
are inherently tied to directory content changes. See
Section 16.2.11.4 for details.
* Information about changes to attribute of file objects designated
by directory entry are provided by the NOTIFY4_CHANGE_CHILD_ATTRS
notification, as discussed in Section 16.2.12.2.
* When the server finds it unduly burdensome to provide the
notifications requested above, it has the option of recalling the
delegation but also can, if requested, effect a change in
attributes reported when using a notification.
NOTIFY4_CHANGE_AMASK is used to provide updated sets of masks for
the attribute updates being provided. This notification is
described in Section 27.4.10
These notifications, while asynchronous, are not subject to delay
or batching.
This form of notification can be used by the server to reduce or
eliminate child attribute notifications, without delegation
recall.
16.2.12.1. Directory Attribute Change Notifications
When attributes change for a directory for which a directory
delegation is held, the client is notified by a
NOTIFY4_CHANGE_DIR_ATTRS notification as described in Section 27.4.7.
When these notifications are not requested, the client is not
notified and the delegation is not recalled.
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The delivery of such notifications generally uses a batch/delay
paradigm, although prompt notification can be requested by specifying
a gdda_dir_attr_delay value of zero (allowed if the dir_notif_delay
is zero as well).
These prompt notifications are expected to be available in the
following situations:
* Notifications for attributes that are expected to change as part
of directory content modifications are always presented promptly,
if the above condition are met. See Section 16.2.11.4 for
details.
This information can be useful by clients that try to cache
complete directories to allow provision of a local READDIIR
response for APIs which expect it to be present (e.g., as a
directory entry for ".").
* Notifications for changes of directory attributes that affect the
authorization of LOOKUP and READDIR will be presented promptly
when the when the attributes for which changes are requested and
generated are limited to mode, owner, owner_group and ACL.
The prompt reporting of changes to these attributes allows clients
prepared to do the authorization checking locally to do so
reliably, even when the directory attributes are subject to
change. See Section 16.2.8 for further discussion.
Whether prompt notification for the abovementioned changes is
provided is affected by the attributes for which change is requested
and by the delay requested and in effect for attribute notifications.
When such notifications are requested and in effect, the server
signals that fact by the use of response flags:
* PRAN_CONTENT, when set, indicate that prompt notification will be
used in cases in which attribute changes are an inherent
consequence of directory content changes.
* PRAN_AUTH, when set, indicate that prompt notification will be
used in cases in which attribute changes are affecting the
attributes associated with authorizing LOOKUP and READDIR (i.e.,
mode, owner, owner_group, and ACL).
While it might be supposed that prompt notification of changes in
authorization-related attributes could be used in eliminating the
need for a remote invocation of authorization via use of ACCESS,
there are cases in which such server-based checks are needed (e.g.
due to the presence of AUDIT and ALARM ACEs).
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The use of this approach requires that the client be able to fetch
and interpret ACLs locally, a practice formerly discouraged.
16.2.12.2. Entry Attribute Change Notifications
When attributes change for file objects in a directory for which a
directory delegation is held, the client is notified by a
NOTIFY4_CHANGE_DIR_ATTRS notification as described in Section 27.4.8.
These notification are subject to delay and batching so as to provide
reasonably up-to-date attribute caches without excessive network
traffic. While prompt delivery can be requested by specifying a
gdda_child_attr_delay value of zero, server are unlikely to be able
to provide this because of the difficulty of find all the delegated
directories associated with a file whose attributes are being
modified.
16.2.13. Directory Delegation Authorization-related Information
The flag-based indications and notification types discussed below are
used to inform the of the proper approach to use in authorizing
LOOKUP, READDIR, and GETATTR request to be satisfied using cached
data obtained via directory delegation and associated notifications.
Because of the greater complexity of authorization resulting from the
addition of various form of ACLs, it is rarely practical for the
client to make the authorization itself while the prospect of using
an ACCESS request (remote) could have the effect of vitiating the
benefits of caching that the directory delegations feature is
intended to avoid.
We discuss authorization for these operations below:
* Authorization support for LOOKUP is discussed in
Section 16.2.13.1.
In the case in which the client is order-aware
(NOTIFY4_CFLAG_ORDER set or NOTIFY4_GFLAG_EXTEND reset), this
section also provides authorization support for READDIR satisfied
from a local cache.
* Authorization support for GETATTR is discussed in
Section 16.2.13.2.
Because GETATTR is always authorized unless the server supports
NFSv4 ACLs and also supports a separate permission bit for reading
attributes these feature might not be supported, requiring the
client to use ACCESS when satisfying GETATTR requests locally.
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16.2.13.1. Authorization Support for LOOKUP/READDIR
Initial control of LOOKUP authorization is controlled by the setting
of the bit NOTIFY4_AUFLAG_VALID. If the client is order aware, this
bit controls the handling of READDIR authorization as well.
If bit is set, the flags NOTIFY4_AUFLAG_OWNER, NOTIFY4_AUFLAG_GROUP,
and NOTIFY4_AUFLAG_OTHERS allow LOOKUP to proceed without further
authorization for the owner of the directory, the owning group, or
other users, respectively. If the client is order aware, these bits
allow the handling of READDIR without additional authorization.
If the bit is not set, authorization of each user/operation pair must
be done (using ACCESS) and the results can be cached to avoid
repeated ACCESS calls. The applies cases in which the overall bit
was set but use of ACCESS was required for a particular user.
This situation continues until a NOTIFY4_CHANGE_AUTH notification is
received. This notification is described in Section 27.4.11.
This notification is used to modify authorization handling for LOOKUP
(and READDIR if the client is order-aware) for the following reasons:
* There is a need to treat authorization of LOOKUP and READIR
differently for some users.
* There is a changes to the directory's authorization-related
attributes.
The notification contains three fields modifying authorization
handling.
* There is a three-bit field each whose its allow use of LOOKUP
without additional authorization. The bits concern use by the
directory owner, owning group, and others.
* There is another three-bit field each whose its allow use READIR
without additional authorization. The bits concern use by the
directory owner, owning group, and others.
* There are three bits, each of which, when set, requires the
deletion of cached entries allowing or denying authorization of
LOOKUP or READIR for a particular user. The bits control the
directory owner, all users in the owning group, and others.
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16.2.13.2. Authorization Support for GETTATTR
When a directory delegation is granted, the client uses the flags
returned to establish an initial authorization state with regard to
GETATTR as follows:
* If the flag NOTIFY4_AUFLAG_GANOW is set, the client is being told
that GETATTRs can now be done without explicit ACCESS checks.
This status continues until changed by a possible
NOTIFY4_CHANGE_GA notification.
The server can do this if ACE4_READ_ATTRIBUTES is not supported
and also if it has scanned the directory to make sure that no
current ACEs use that mask and that there are no multiple-linked
files that make it possible that such ACEs will be set without the
directory delegation holder being notified.
* Otherwise, if the flag NOTIFY4_AUFLAG_GALATER is set, the client
is being told that GETATTRs now require explicit ACCESS checks,
but that the situation is expected to change and it will notified
of that using a NOTIFY4_CHANGE_GA notification. In this case,
GETATTRs based on cached attributes require explicit authorization
until changed by a possible NOTIFY4_CHANGE_GA notification.
The server can do this to avoid waiting for a scan of the
directory looking for troublesome ACLs or multiply-linked linked
file that might get troublesome ACLs using one of the other links.
The scan can go on with the client being notified of the new
status later.
* If neither of these bits is set, then the server is indicating the
absence of support for avoiding use of ACCESS to check for GETATTR
authorization. In this case, GETATTRs based on cached attributes
require explicit authorization without the possibility of further
change in this situation.
Regardless of the settings of the flags NOTIFY4_AUFLAG_GANOW and
NOTIFY4_AUFLAG_GALATER, accurate reporting of current values of many
attributes associated with directory entries cannot be expected
because directory entry attribute changes can only be delivered on
batched/delayed basis. In order to help ameliorate this situation
the NOTIFY4_CHANGE_GA notification can provide information allowing
full attribute refetch to be avoided in many cases. For this reason
clients that request this notification are well advised to accept
these notifications and use them to optimize processing as described
in Section 27.4.12.
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Once this initial state is set, it can be modified as described
below, as the server's knowledge of the set of files that require
explicit authorization checks changes in response to file system
changes.
* When a file within the directory is assigned an ACL that can
interfere with the client providing cached attributes without
ACCESS checks, the client can be notified of that change of status
using a NOTIFY4_CHANGE_GA notification.
* Similarly, when a file within the directory is becomes reachable
via an additional link, making it possible that it will
subsequently be assigned an ACL without being aware of the
directory delegation, there is also a need for the client to be
notified. Since such an ACL could interfere with the client
providing cached attributes without ACCESS checks, the client is
also notified of that change of status using a NOTIFY4_CHANGE_GA
notification.
16.2.14. Directory Delegation Recall
When necessary the server will recall the directory delegation by
sending a callback to the client. It uses the same callback
procedure as used for recalling file delegations. The server will
recall the delegation in the following situations:
* If there is a need to send a content update notification or an
authorization update and it is not possible to send that type of
notification.
The server will wait for the delegation to be returned or revoked
if the notification was one that needed to be sent synchronously.
* If a client removes a directory for which a delegation has been
granted.
If the server determines the existence of a delegation for a
directory is causing too many notifications to be sent out, it may
decide to not hand out delegations for that directory and/or recall
those already granted. In the case of attribute update
notifications, it also has the option of reducing update frequency or
limiting set of attributes about which the client is to be notified.
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16.2.15. Directory Delegation Recovery
Recovery from client or server restart for state on regular files has
two main goals: avoiding the necessity of breaking application
guarantees with respect to locked files and delivery of updates
cached at the client. Neither of these goals applies to directories
protected by OPEN_DELEGATE_READ delegations and notifications. As a
result, no provision is made for reclaiming directory delegations in
the event of client or server restart. The client needs to establish
a directory delegation in the same fashion as was done initially.
17. Multi-Server Namespace
NFSv4.1 supports attributes that allow a namespace to extend beyond
the boundaries of a single server. It is desirable that clients and
servers support construction of such multi-server namespaces. Use of
such multi-server namespaces is OPTIONAL; however, and for many
purposes, single-server namespaces are perfectly acceptable. The use
of multi-server namespaces can provide many advantages by separating
a file system's logical position in a namespace from the (possibly
changing) logistical and administrative considerations that cause a
particular file system to be located on a particular server via a
single network access path that has to be known in advance or
determined using DNS.
17.1. Terminology
In this section as a whole (i.e., within all of Section 17), the
phrase "client ID" always refers to the 64-bit shorthand identifier
assigned by the server (a clientid4) and never to the structure that
the client uses to identify itself to the server (called an
nfs_client_id4 or client_owner in NFSv4.0 and NFSv4.1, respectively).
The opaque identifier within those structures is referred to as a
"client id string".
17.1.1. Terminology Related to Trunking
It is particularly important to clarify the distinction between
trunking detection and trunking discovery. The definitions we
present are applicable to all minor versions of NFSv4, but we will
focus on how these terms apply to NFS version 4.1.
* Trunking detection refers to ways of deciding whether two specific
network addresses are connected to the same NFSv4 server. The
means available to make this determination depends on the protocol
version, and, in some cases, on the client implementation.
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In the case of NFS version 4.1 and later minor versions, the means
of trunking detection are as described in this document and are
available to every client. Two network addresses connected to the
same server can always be used together to access a particular
server but cannot necessarily be used together to access a single
session. See below for definitions of the terms "server-
trunkable" and "session-trunkable".
* Trunking discovery is a process by which a client using one
network address can obtain other addresses that are connected to
the same server. Typically, it builds on a trunking detection
facility by providing one or more methods by which candidate
addresses are made available to the client, who can then use
trunking detection to appropriately filter them.
Despite the support for trunking detection, there was no
description of trunking discovery provided in [RFC5661] or
[RFC8881], making it necessary to provide those means in this
document.
The combination of a server network address and a particular
connection type to be used by a connection is referred to as a
"server endpoint". Although using different connection types may
result in different ports being used, the use of different ports by
multiple connections to the same network address in such cases is not
the essence of the distinction between the two endpoints used. This
is in contrast to the case of port-specific endpoints, in which the
explicit specification of port numbers within network addresses is
used to allow a single server node to support multiple NFS servers.
Two network addresses connected to the same server are said to be
server-trunkable. Two such addresses support the use of client ID
trunking, as described in Section 7.5.
Two network addresses connected to the same server such that those
addresses can be used to support a single common session are referred
to as session-trunkable. Note that two addresses may be server-
trunkable without being session-trunkable, and that, when two
connections of different connection types are made to the same
network address and are based on a single file system location entry,
they are always session-trunkable, independent of the connection
type, as specified by Section 7.5, since their derivation from the
same file system location entry, together with the identity of their
network addresses, assures that both connections are to the same
server and will return server-owner information, allowing session
trunking to be used.
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17.1.2. Terminology Related to File System Location
Regarding the terminology that relates to the construction of multi-
server namespaces out of a set of local per-server namespaces:
* Each server has a set of exported file systems that may be
accessed by NFSv4 clients. Typically, this is done by assigning
each file system a name within the pseudo-fs associated with the
server, although the pseudo-fs may be dispensed with if there is
only a single exported file system. Each such file system is part
of the server's local namespace, and can be considered as a file
system instance within a larger multi-server namespace.
* The set of all exported file systems for a given server
constitutes that server's local namespace.
* In some cases, a server will have a namespace more extensive than
its local namespace by using features associated with attributes
that provide file system location information. These features,
which allow construction of a multi-server namespace, are all
described in individual sections below and include referrals
(Section 17.5.6), migration (Section 17.5.5), and replication
(Section 17.5.4).
* A file system present in a server's pseudo-fs may have multiple
file system instances on different servers associated with it.
All such instances are considered replicas of one another.
Whether such replicas can be used simultaneously is discussed in
Section 17.11.1, while the level of coordination between them
(important when switching between them) is discussed in Sections
17.11.2 through 17.11.8 below.
* When a file system is present in a server's pseudo-fs, but there
is no corresponding local file system, it is said to be "absent".
In such cases, all associated instances will be accessed on other
servers.
Regarding the terminology that relates to attributes used in trunking
discovery and other multi-server namespace features:
* File system location attributes include the fs_locations and
fs_locations_info attributes.
* File system location entries provide the individual file system
locations within the file system location attributes. Each such
entry specifies a server, in the form of a hostname or an address,
and an fs name, which designates the location of the file system
within the server's local namespace. A file system location entry
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designates a set of server endpoints to which the client may
establish connections. There may be multiple endpoints because a
hostname may map to multiple network addresses and because
multiple connection types may be used to communicate with a single
network address. However, except where explicit port numbers are
used to designate a set of servers within a single server node,
all such endpoints MUST designate a way of connecting to a single
server. The exact form of the location entry varies with the
particular file system location attribute used, as described in
Section 17.2.
The network addresses used in file system location entries
typically appear without port number indications and are used to
designate a server at one of the standard ports for NFS access,
e.g., 2049 for TCP or 20049 for use with RPC-over-RDMA. Port
numbers may be used in file system location entries to designate
servers (typically user-level ones) accessed using other port
numbers. In the case where network addresses indicate trunking
relationships, the use of an explicit port number is inappropriate
since trunking is a relationship between network addresses. See
Section 17.5.2 for details.
* File system location elements are derived from location entries,
and each describes a particular network access path consisting of
a network address and a location within the server's local
namespace. Such location elements need not appear within a file
system location attribute, but the existence of each location
element derives from a corresponding location entry. When a
location entry specifies an IP address, there is only a single
corresponding location element. File system location entries that
contain a hostname are resolved using DNS, and may result in one
or more location elements. All location elements consist of a
location address that includes the IP address of an interface to a
server and an fs name, which is the location of the file system
within the server's local namespace. The fs name can be empty if
the server has no pseudo-fs and only a single exported file system
at the root filehandle.
* Two file system location elements are said to be server-trunkable
if they specify the same fs name and the location addresses are
such that the location addresses are server-trunkable. When the
corresponding network paths are used, the client will always be
able to use client ID trunking, but will only be able to use
session trunking if the paths are also session-trunkable.
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* Two file system location elements are said to be session-trunkable
if they specify the same fs name and the location addresses are
such that the location addresses are session-trunkable. When the
corresponding network paths are used, the client will be able to
able to use either client ID trunking or session trunking.
Discussion of the term "replica" is complicated by the fact that the
term was used in [RFC5661] with a meaning different from that used in
this document. In short, in [RFC5661] each replica is identified by
a single network access path, while in the current document, a set of
network access paths that have server-trunkable network addresses and
the same root-relative file system pathname is considered to be a
single replica with multiple network access paths.
Each set of server-trunkable location elements defines a set of
available network access paths to a particular file system. When
there are multiple such file systems, each of which containing the
same data, these file systems are considered replicas of one another.
Logically, such replication is symmetric, since the fs currently in
use and an alternate fs are replicas of each other. Often, in other
documents, the term "replica" is not applied to the fs currently in
use, despite the fact that the replication relation is inherently
symmetric.
17.2. File System Location Attributes
NFSv4.1 contains attributes that provide information about how a
given file system may be accessed (i.e., at what network address and
namespace position). As a result, file systems in the namespace of
one server can be associated with one or more instances of that file
system on other servers. These attributes contain file system
location entries specifying a server address target (either as a DNS
name representing one or more IP addresses or as a specific IP
address) together with the pathname of that file system within the
associated single-server namespace.
The fs_locations_info attribute allows specification of one or more
file system instance locations where the data corresponding to a
given file system may be found. In addition to the specification of
file system instance locations, this attribute provides helpful
information to do the following:
* Guide choices among the various file system instances provided
(e.g., priority for use, writability, currency, etc.).
* Help the client efficiently effect as seamless a transition as
possible among multiple file system instances, when and if that
should be necessary.
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* Guide the selection of the appropriate connection type to be used
when establishing a connection.
Within the fs_locations_info attribute, each fs_locations_server4
entry corresponds to a file system location entry: the fls_server
field designates the server, and the fl_rootpath field of the
encompassing fs_locations_item4 gives the location pathname within
the server's pseudo-fs.
The fs_locations attribute defined in NFSv4.0 is also a part of
NFSv4.1. This attribute only allows specification of the file system
locations where the data corresponding to a given file system may be
found. Servers SHOULD make this attribute available whenever
fs_locations_info is supported, but client use of fs_locations_info
is preferable because it provides more information.
Within the fs_locations attribute, each fs_location4 contains a file
system location entry with the server field designating the server
and the rootpath field giving the location pathname within the
server's pseudo-fs.
17.3. File System Presence or Absence
A given location in an NFSv4.1 namespace (typically but not
necessarily a multi-server namespace) can have a number of file
system instance locations associated with it (via the fs_locations or
fs_locations_info attribute). There may also be an actual current
file system at that location, accessible via normal namespace
operations (e.g., LOOKUP). In this case, the file system is said to
be "present" at that position in the namespace, and clients will
typically use it, reserving use of additional locations specified via
the location-related attributes to situations in which the principal
location is no longer available.
When there is no actual file system at the namespace location in
question, the file system is said to be "absent". An absent file
system contains no files or directories other than the root. Any
reference to it, except to access a small set of attributes useful in
determining alternate locations, will result in an error,
NFS4ERR_MOVED. Note that if the server ever returns the error
NFS4ERR_MOVED, it MUST support the fs_locations attribute and SHOULD
support the fs_locations_info and fs_status attributes.
While the error name suggests that we have a case of a file system
that once was present, and has only become absent later, this is only
one possibility. A position in the namespace may be permanently
absent with the set of file system(s) designated by the location
attributes being the only realization. The name NFS4ERR_MOVED
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reflects an earlier, more limited conception of its function, but
this error will be returned whenever the referenced file system is
absent, whether it has moved or not.
Except in the case of GETATTR-type operations (to be discussed
later), when the current filehandle at the start of an operation is
within an absent file system, that operation is not performed and the
error NFS4ERR_MOVED is returned, to indicate that the file system is
absent on the current server.
Because a GETFH cannot succeed if the current filehandle is within an
absent file system, filehandles within an absent file system cannot
be transferred to the client. When a client does have filehandles
within an absent file system, it is the result of obtaining them when
the file system was present, and having the file system become absent
subsequently.
It should be noted that because the check for the current filehandle
being within an absent file system happens at the start of every
operation, operations that change the current filehandle so that it
is within an absent file system will not result in an error. This
allows such combinations as PUTFH-GETATTR and LOOKUP-GETATTR to be
used to get attribute information, particularly location attribute
information, as discussed below.
The file system attribute fs_status can be used to interrogate the
present/absent status of a given file system.
17.4. Getting Attributes for an Absent File System
When a file system is absent, most attributes are not available, but
it is necessary to allow the client access to the small set of
attributes that are available, and most particularly those that give
information about the correct current locations for this file system:
fs_locations and fs_locations_info.
17.4.1. GETATTR within an Absent File System
As mentioned above, an exception is made for GETATTR in that
attributes may be obtained for a filehandle within an absent file
system. This exception only applies if the attribute mask contains
at least one attribute bit that indicates the client is interested in
a result regarding an absent file system: fs_locations,
fs_locations_info, or fs_status. If none of these attributes is
requested, GETATTR will result in an NFS4ERR_MOVED error.
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When a GETATTR is done on an absent file system, the set of supported
attributes is very limited. Many attributes, including those that
are normally REQUIRED, will not be available on an absent file
system. In addition to the attributes mentioned above (fs_locations,
fs_locations_info, fs_status), the following attributes SHOULD be
available on absent file systems. In the case of OPTIONAL
attributes, they should be available at least to the same degree that
they are available on present file systems.
change_policy: This attribute is useful for absent file systems and
can be helpful in summarizing to the client when any of the
location-related attributes change.
fsid: This attribute should be provided so that the client can
determine file system boundaries, including, in particular, the
boundary between present and absent file systems. This value must
be different from any other fsid on the current server and need
have no particular relationship to fsids on any particular
destination to which the client might be directed.
mounted_on_fileid: For objects at the top of an absent file system,
this attribute needs to be available. Since the fileid is within
the present parent file system, there should be no need to
reference the absent file system to provide this information.
Other attributes SHOULD NOT be made available for absent file
systems, even when it is possible to provide them. The server should
not assume that more information is always better and should avoid
gratuitously providing additional information.
When a GETATTR operation includes a bit mask for one of the
attributes fs_locations, fs_locations_info, or fs_status, but where
the bit mask includes attributes that are not supported, GETATTR will
not return an error, but will return the mask of the actual
attributes supported with the results.
Handling of VERIFY/NVERIFY is similar to GETATTR in that if the
attribute mask does not include fs_locations, fs_locations_info, or
fs_status, the error NFS4ERR_MOVED will result. It differs in that
any appearance in the attribute mask of an attribute not supported
for an absent file system (and note that this will include some
normally REQUIRED attributes) will also cause an NFS4ERR_MOVED
result.
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17.4.2. READDIR and Absent File Systems
A READDIR performed when the current filehandle is within an absent
file system will result in an NFS4ERR_MOVED error, since, unlike the
case of GETATTR, no such exception is made for READDIR.
Attributes for an absent file system may be fetched via a READDIR for
a directory in a present file system, when that directory contains
the root directories of one or more absent file systems. In this
case, the handling is as follows:
* If the attribute set requested includes one of the attributes
fs_locations, fs_locations_info, or fs_status, then fetching of
attributes proceeds normally and no NFS4ERR_MOVED indication is
returned, even when the rdattr_error attribute is requested.
* If the attribute set requested does not include one of the
attributes fs_locations, fs_locations_info, or fs_status, then if
the rdattr_error attribute is requested, each directory entry for
the root of an absent file system will report NFS4ERR_MOVED as the
value of the rdattr_error attribute.
* If the attribute set requested does not include any of the
attributes fs_locations, fs_locations_info, fs_status, or
rdattr_error, then the occurrence of the root of an absent file
system within the directory will result in the READDIR failing
with an NFS4ERR_MOVED error.
* The unavailability of an attribute because of a file system's
absence, even one that is ordinarily REQUIRED, does not result in
any error indication. The set of attributes returned for the root
directory of the absent file system in that case is simply
restricted to those actually available.
17.5. Uses of File System Location Information
The file system location attributes (i.e., fs_locations and
fs_locations_info), together with the possibility of absent file
systems, provide a number of important facilities for reliable,
manageable, and scalable data access.
When a file system is present, these attributes can provide the
following:
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* The locations of alternative replicas to be used to access the
same data in the event of server failures, communications
problems, or other difficulties that make continued access to the
current replica impossible or otherwise impractical. Provisioning
and use of such alternate replicas is referred to as "replication"
and is discussed in Section 17.5.4 below.
* The network address(es) to be used to access the current file
system instance or replicas of it. Client use of this information
is discussed in Section 17.5.2 below.
Under some circumstances, multiple replicas may be used
simultaneously to provide higher-performance access to the file
system in question, although the lack of state sharing between
servers may be an impediment to such use.
When a file system is present but becomes absent, clients can be
given the opportunity to have continued access to their data using a
different replica. In this case, a continued attempt to use the data
in the now-absent file system will result in an NFS4ERR_MOVED error,
and then the successor replica or set of possible replica choices can
be fetched and used to continue access. Transfer of access to the
new replica location is referred to as "migration" and is discussed
in Section 17.5.4 below.
When a file system is currently absent, specification of file system
location provides a means by which file systems located on one server
can be associated with a namespace defined by another server, thus
allowing a general multi-server namespace facility. A designation of
such a remote instance, in place of a file system not previously
present, is called a "pure referral" and is discussed in
Section 17.5.6 below.
Because client support for attributes related to file system location
is OPTIONAL, a server may choose to take action to hide migration and
referral events from such clients, by acting as a proxy, for example.
The server can determine the presence of client support from the
arguments of the EXCHANGE_ID operation (See Section 25.35.3).
17.5.1. Combining Multiple Uses in a Single Attribute
A file system location attribute will sometimes contain information
relating to the location of multiple replicas, which may be used in
different ways:
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* File system location entries that relate to the file system
instance currently in use provide trunking information, allowing
the client to find additional network addresses by which the
instance may be accessed.
* File system location entries that provide information about
replicas to which access is to be transferred.
* Other file system location entries that relate to replicas that
are available to use in the event that access to the current
replica becomes unsatisfactory.
In order to simplify client handling and to allow the best choice of
replicas to access, the server should adhere to the following
guidelines:
* All file system location entries that relate to a single file
system instance should be adjacent.
* File system location entries that relate to the instance currently
in use should appear first.
* File system location entries that relate to replica(s) to which
migration is occurring should appear before replicas that are
available for later use if the current replica should become
inaccessible.
17.5.2. File System Location Attributes and Trunking
Trunking is the use of multiple connections between a client and
server in order to increase the speed of data transfer. A client may
determine the set of network addresses to use to access a given file
system in a number of ways:
* When the name of the server is known to the client, it may use DNS
to obtain a set of network addresses to use in accessing the
server.
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* The client may fetch the file system location attribute for the
file system. This will provide either the name of the server
(which can be turned into a set of network addresses using DNS) or
a set of server-trunkable location entries. Using the latter
alternative, the server can provide addresses it regards as
desirable to use to access the file system in question. Although
these entries can contain port numbers, these port numbers are not
used in determining trunking relationships. Once the candidate
addresses have been determined and EXCHANGE_ID done to the proper
server, only the value of the so_major_id field returned by the
servers in question determines whether a trunking relationship
actually exists.
When the client fetches a location attribute for a file system, it
should be noted that the client may encounter multiple entries for a
number of reasons, such that when it determines trunking information,
it may need to bypass addresses not trunkable with one already known.
The server can provide location entries that include either names or
network addresses. It might use the latter form because of DNS-
related security concerns or because the set of addresses to be used
might require active management by the server.
Location entries used to discover candidate addresses for use in
trunking are subject to change, as discussed in Section 17.5.7 below.
The client may respond to such changes by using additional addresses
once they are verified or by ceasing to use existing ones. The
server can force the client to cease using an address by returning
NFS4ERR_MOVED when that address is used to access a file system.
This allows a transfer of client access that is similar to migration,
although the same file system instance is accessed throughout.
17.5.3. File System Location Attributes and Connection Type Selection
Because of the need to support multiple types of connections, clients
face the issue of determining the proper connection type to use when
establishing a connection to a given server network address. In some
cases, this issue can be addressed through the use of the connection
"step-up" facility described in Section 25.36. However, because
there are cases in which that facility is not available, the client
may have to choose a connection type with no possibility of changing
it within the scope of a single connection.
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The two file system location attributes differ as to the information
made available in this regard. The fs_locations attribute provides
no information to support connection type selection. As a result,
clients supporting multiple connection types would need to attempt to
establish connections using multiple connection types until the one
preferred by the client is successfully established.
The fs_locations_info attribute includes the FSLI4TF_RDMA flag, which
is convenient for a client wishing to use RDMA. When this flag is
set, it indicates that RPC-over-RDMA support is available using the
specified location entry. A client can establish a TCP connection
and then convert that connection to use RDMA by using the step-up
facility.
Irrespective of the particular attribute used, when there is no
indication that a step-up operation can be performed, a client
supporting RDMA operation can establish a new RDMA connection, and it
can be bound to the session already established by the TCP
connection, allowing the TCP connection to be dropped and the session
converted to further use in RDMA mode, if the server supports that.
17.5.4. File System Replication
The fs_locations and fs_locations_info attributes provide alternative
file system locations, to be used to access data in place of or in
addition to the current file system instance. On first access to a
file system, the client should obtain the set of alternate locations
by interrogating the fs_locations or fs_locations_info attribute,
with the latter being preferred.
In the event that the occurrence of server failures, communications
problems, or other difficulties make continued access to the current
file system impossible or otherwise impractical, the client can use
the alternate locations as a way to get continued access to its data.
The alternate locations may be physical replicas of the (typically
read-only) file system data supplemented by possible asynchronous
propagation of updates. Alternatively, they may provide for the use
of various forms of server clustering in which multiple servers
provide alternate ways of accessing the same physical file system.
How the difference between replicas affects file system transitions
can be represented within the fs_locations and fs_locations_info
attributes, and how the client deals with file system transition
issues will be discussed in detail in later sections.
Although the location attributes provide some information about the
nature of the inter-replica transition, many aspects of the semantics
of possible asynchronous updates are not currently described by the
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protocol, which makes it necessary for clients using replication to
switch among replicas undergoing change to familiarize themselves
with the semantics of the update approach used. Due to this lack of
specificity, many applications may find the use of migration more
appropriate because a server can propagate all updates made before an
established point in time to the new replica as part of the migration
event.
17.5.4.1. File System Trunking Presented as Replication
In some situations, a file system location entry may indicate a file
system access path to be used as an alternate location, where
trunking, rather than replication, is to be used. The situations in
which this is appropriate are limited to those in which both of the
following are true:
* The two file system locations (i.e., the one on which the location
attribute is obtained and the one specified in the file system
location entry) designate the same locations within their
respective single-server namespaces.
* The two server network addresses (i.e., the one being used to
obtain the location attribute and the one specified in the file
system location entry) designate the same server (as indicated by
the same value of the so_major_id field of the eir_server_owner
field returned in response to EXCHANGE_ID).
When these conditions hold, operations using both access paths are
generally trunked, although trunking may be disallowed when the
attribute fs_locations_info is used:
* When the fs_locations_info attribute shows the two entries as not
having the same simultaneous-use class, trunking is inhibited, and
the two access paths cannot be used together.
In this case, the two paths can be used serially with no
transition activity required on the part of the client, and any
transition between access paths is transparent. In transferring
access from one to the other, the client acts as if communication
were interrupted, establishing a new connection and possibly a new
session to continue access to the same file system.
* Note that for two such location entries, any information within
the fs_locations_info attribute that indicates the need for
special transition activity, i.e., the appearance of the two file
system location entries with different handle, fileid, write-
verifier, change, and readdir classes, indicates a serious
problem. The client, if it allows transition to the file system
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instance at all, must not treat any transition as a transparent
one. The server SHOULD NOT indicate that these two entries (for
the same file system on the same server) belong to different
handle, fileid, write-verifier, change, and readdir classes,
whether or not the two entries are shown belonging to the same
simultaneous-use class.
These situations were recognized by [RFC5661], even though that
document made no explicit mention of trunking:
* It treated the situation that we describe as trunking as one of
simultaneous use of two distinct file system instances, even
though, in the explanatory framework now used to describe the
situation, the case is one in which a single file system is
accessed by two different trunked addresses.
* It treated the situation in which two paths are to be used
serially as a special sort of "transparent transition". However,
in the descriptive framework now used to categorize transition
situations, this is considered a case of a "network endpoint
transition" (See Section 17.9).
17.5.5. File System Migration
When a file system is present and becomes inaccessible using the
current access path, the NFSv4.1 protocol provides a means by which
clients can be given the opportunity to have continued access to
their data. This may involve using a different access path to the
existing replica or providing a path to a different replica. The new
access path or the location of the new replica is specified by a file
system location attribute. The ensuing migration of access includes
the ability to retain locks across the transition. Depending on
circumstances, this can involve:
* The continued use of the existing clientid when accessing the
current replica using a new access path.
* Use of lock reclaim, taking advantage of a per-fs grace period.
* Use of Transparent State Migration.
Typically, a client will be accessing the file system in question,
get an NFS4ERR_MOVED error, and then use a file system location
attribute to determine the new access path for the data. When
fs_locations_info is used, additional information will be available
that will define the nature of the client's handling of the
transition to a new server.
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In most instances, servers will choose to migrate all clients using a
particular file system to a successor replica at the same time to
avoid cases in which different clients are updating different
replicas. However, migration of an individual client can be helpful
in providing load balancing, as long as the replicas in question are
such that they represent the same data as described in
Section 17.11.8.
* In the case in which there is no transition between replicas
(i.e., only a change in access path), there are no special
difficulties in using of this mechanism to effect load balancing.
* In the case in which the two replicas are sufficiently coordinated
as to allow a single client coherent, simultaneous access to both,
there is, in general, no obstacle to the use of migration of
particular clients to effect load balancing. Generally, such
simultaneous use involves cooperation between servers to ensure
that locks granted on two coordinated replicas cannot conflict and
can remain effective when transferred to a common replica.
* In the case in which a large set of clients is accessing a file
system in a read-only fashion, it can be helpful to migrate all
clients with writable access simultaneously, while using load
balancing on the set of read-only copies, as long as the rules in
Section 17.11.8, which are designed to prevent data reversion, are
followed.
In other cases, the client might not have sufficient guarantees of
data similarity or coherence to function properly (e.g., the data in
the two replicas is similar but not identical), and the possibility
that different clients are updating different replicas can exacerbate
the difficulties, making the use of load balancing in such situations
a perilous enterprise.
The protocol does not specify how the file system will be moved
between servers or how updates to multiple replicas will be
coordinated. It is anticipated that a number of different server-to-
server coordination mechanisms might be used, with the choice left to
the server implementer. The NFSv4.1 protocol specifies the method
used to communicate the migration event between client and server.
In the case of various forms of server clustering, the new location
may be another server providing access to the same physical file
system. The client's responsibilities in dealing with this
transition will depend on whether a switch between replicas has
occurred and the means the server has chosen to provide continuity of
locking state. These issues will be discussed in detail below.
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Although a single successor location is typical, multiple locations
may be provided. When multiple locations are provided, the client
will typically use the first one provided. If that is inaccessible
for some reason, later ones can be used. In such cases, the client
might consider the transition to the new replica to be a migration
event, even though some of the servers involved might not be aware of
the use of the server that was inaccessible. In such a case, a
client might lose access to locking state as a result of the access
transfer.
When an alternate location is designated as the target for migration,
it must designate the same data (with metadata being the same to the
degree indicated by the fs_locations_info attribute). Where file
systems are writable, a change made on the original file system must
be visible on all migration targets. Where a file system is not
writable but represents a read-only copy (possibly periodically
updated) of a writable file system, similar requirements apply to the
propagation of updates. Any change visible in the original file
system must already be effected on all migration targets, to avoid
any possibility that a client, in effecting a transition to the
migration target, will see any reversion in file system state.
17.5.6. Referrals
Referrals allow the server to associate a file system namespace entry
located on one server with a file system located on another server.
When this includes the use of pure referrals, servers are provided a
way of placing a file system in a location within the namespace
essentially without respect to its physical location on a particular
server. This allows a single server or a set of servers to present a
multi-server namespace that encompasses file systems located on a
wider range of servers. Some likely uses of this facility include
establishment of site-wide or organization-wide namespaces, with the
eventual possibility of combining such together into a truly global
namespace, such as the one provided by AFS (the Andrew File System)
[AFS].
Referrals occur when a client determines, upon first referencing a
position in the current namespace, that it is part of a new file
system and that the file system is absent. When this occurs,
typically upon receiving the error NFS4ERR_MOVED, the actual location
or locations of the file system can be determined by fetching a
locations attribute.
The file system location attribute may designate a single file system
location or multiple file system locations, to be selected based on
the needs of the client. The server, in the fs_locations_info
attribute, may specify priorities to be associated with various file
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system location choices. The server may assign different priorities
to different locations as reported to individual clients, in order to
adapt to client physical location or to effect load balancing. When
both read-only and read-write file systems are present, some of the
read-only locations might not be absolutely up-to-date (as they would
have to be in the case of replication and migration). Servers may
also specify file system locations that include client-substituted
variables so that different clients are referred to different file
systems (with different data contents) based on client attributes
such as CPU architecture.
If the fs_locations_info attribute lists multiple possible targets,
the relationships among them may be important to the client in
selecting which one to use. The same rules specified in
Section 17.5.5 below regarding multiple migration targets apply to
these multiple replicas as well. For example, the client might
prefer a writable target on a server that has additional writable
replicas to which it subsequently might switch. Note that, as
distinguished from the case of replication, there is no need to deal
with the case of propagation of updates made by the current client,
since the current client has not accessed the file system in
question.
Use of multi-server namespaces is enabled by NFSv4.1 but is not
required. The use of multi-server namespaces and their scope will
depend on the applications used and system administration
preferences.
Multi-server namespaces can be established by a single server
providing a large set of pure referrals to all of the included file
systems. Alternatively, a single multi-server namespace may be
administratively segmented with separate referral file systems (on
separate servers) for each separately administered portion of the
namespace. The top-level referral file system or any segment may use
replicated referral file systems for higher availability.
Generally, multi-server namespaces are for the most part uniform, in
that the same data made available to one client at a given location
in the namespace is made available to all clients at that namespace
location. However, there are facilities provided that allow
different clients to be directed to different sets of data, for
reasons such as enabling adaptation to such client characteristics as
CPU architecture. These facilities are described in Section 17.17.3.
Note that it is possible, when providing a uniform namespace, to
provide different location entries to different clients in order to
provide each client with a copy of the data physically closest to it
or otherwise optimize access (e.g., provide load balancing).
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17.5.7. Changes in File System Location Attributes
Although clients will typically fetch a file system location
attribute when first accessing a file system and when NFS4ERR_MOVED
is returned, a client can choose to fetch the attribute periodically,
in which case, the value fetched may change over time.
For clients not prepared to access multiple replicas simultaneously
(see Section 17.11.1), the handling of the various cases of location
change are as follows:
* Changes in the list of replicas or in the network addresses
associated with replicas do not require immediate action. The
client will typically update its list of replicas to reflect the
new information.
* Additions to the list of network addresses for the current file
system instance need not be acted on promptly. However, to
prepare for a subsequent migration event, the client can choose to
take note of the new address and then use it whenever it needs to
switch access to a new replica.
* Deletions from the list of network addresses for the current file
system instance do not require the client to immediately cease use
of existing access paths, although new connections are not to be
established on addresses that have been deleted. However, clients
can choose to act on such deletions by preparing for an eventual
shift in access, which becomes unavoidable as soon as the server
returns NFS4ERR_MOVED to indicate that a particular network access
path is not usable to access the current file system.
For clients that are prepared to access several replicas
simultaneously, the following additional cases need to be addressed.
As in the cases discussed above, changes in the set of replicas need
not be acted upon promptly, although the client has the option of
adjusting its access even in the absence of difficulties that would
lead to the selection of a new replica.
* When a new replica is added, which may be accessed simultaneously
with one currently in use, the client is free to use the new
replica immediately.
* When a replica currently in use is deleted from the list, the
client need not cease using it immediately. However, since the
server may subsequently force such use to cease (by returning
NFS4ERR_MOVED), clients might decide to limit the need for later
state transfer. For example, new opens might be done on other
replicas, rather than on one not present in the list.
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17.6. Trunking without File System Location Information
In situations in which a file system is accessed using two server-
trunkable addresses (as indicated by the same value of the
so_major_id field of the eir_server_owner field returned in response
to EXCHANGE_ID), trunked access is allowed even though there might
not be any location entries specifically indicating the use of
trunking for that file system.
This situation was recognized by [RFC5661], although that document
made no explicit mention of trunking and treated the situation as one
of simultaneous use of two distinct file system instances. In the
explanatory framework now used to describe the situation, the case is
one in which a single file system is accessed by two different
trunked addresses.
17.7. Users and Groups in a Multi-Server Namespace
As in the case of a single-server environment (see Section 11.13),
when an owner or group name of the form "id@domain" is assigned to a
file, there is an implicit promise to return that same string when
the corresponding attribute is interrogated subsequently. In the
case of a multi-server namespace, that same promise applies even if
server boundaries have been crossed. Similarly, when the owner
attribute of a file is derived from the security principal that
created the file, that attribute should have the same value even if
the interrogation occurs on a different server from the file
creation.
Similarly, the set of security principals recognized by all the
participating servers needs to be the same, with each such principal
having the same credentials, regardless of the particular server
being accessed.
In order to meet these requirements, those setting up multi-server
namespaces will need to limit the servers included so that:
* In all cases in which more than a single domain is supported, the
requirements stated in [RFC8000] are to be respected.
* All servers support a common set of domains that includes all of
the domains clients use and expect to see returned as the domain
portion of an owner or group in the form "id@domain". Note that,
although this set most often consists of a single domain, it is
possible for multiple domains to be supported.
* All servers, for each domain that they support, accept the same
set of user and group ids as valid.
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* All servers recognize the same set of security principals. For
each principal, the same credential is required, independent of
the server being accessed. In addition, the group membership for
each such principal is to be the same, independent of the server
accessed.
Note that there is no requirement in general that the users
corresponding to particular security principals have the same local
representation on each server, even though it is most often the case
that this is so.
When AUTH_SYS is used, the following additional requirements must be
met:
* Only a single NFSv4 domain can be supported through the use of
AUTH_SYS.
* The "local" representation of all owners and groups must be the
same on all servers. The word "local" is used here since that is
the way that numeric user and group ids are described in
Section 11.13. However, when AUTH_SYS or stringified numeric
owners or groups are used, these identifiers are not truly local,
since they are known to the clients as well as to the server.
Similarly, when stringified numeric user and group ids are used, the
"local" representation of all owners and groups must be the same on
all servers, even when AUTH_SYS is not used.
17.8. Additional Client-Side Considerations
When clients make use of servers that implement referrals,
replication, and migration, care should be taken that a user who
mounts a given file system that includes a referral or a relocated
file system continues to see a coherent picture of that user-side
file system despite the fact that it contains a number of server-side
file systems that may be on different servers.
One important issue is upward navigation from the root of a server-
side file system to its parent (specified as ".." in UNIX), in the
case in which it transitions to that file system as a result of
referral, migration, or a transition as a result of replication.
When the client is at such a point, and it needs to ascend to the
parent, it must go back to the parent as seen within the multi-server
namespace rather than sending a LOOKUPP operation to the server,
which would result in the parent within that server's single-server
namespace. In order to do this, the client needs to remember the
filehandles that represent such file system roots and use these
instead of sending a LOOKUPP operation to the current server. This
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will allow the client to present to applications a consistent
namespace, where upward navigation and downward navigation are
consistent.
Another issue concerns refresh of referral locations. When referrals
are used extensively, they may change as server configurations
change. It is expected that clients will cache information related
to traversing referrals so that future client-side requests are
resolved locally without server communication. This is usually
rooted in client-side name look up caching. Clients should
periodically purge this data for referral points in order to detect
changes in location information. When the change_policy attribute
changes for directories that hold referral entries or for the
referral entries themselves, clients should consider any associated
cached referral information to be out of date.
17.9. Overview of File Access Transitions
File access transitions are of two types:
* Those that involve a transition from accessing the current replica
to another one in connection with either replication or migration.
How these are dealt with is discussed in Section 17.11.
* Those in which access to the current file system instance is
retained, while the network path used to access that instance is
changed. This case is discussed in Section 17.10.
17.10. Effecting Network Endpoint Transitions
The endpoints used to access a particular file system instance may
change in a number of ways, as listed below. In each of these cases,
the same fsid, client IDs, filehandles, and stateids are used to
continue access, with a continuity of lock state. In many cases, the
same sessions can also be used.
The appropriate action depends on the set of replacement addresses
that are available for use (i.e., server endpoints that are server-
trunkable with one previously being used).
* When use of a particular address is to cease, and there is also
another address currently in use that is server-trunkable with it,
requests that would have been issued on the address whose use is
to be discontinued can be issued on the remaining address(es).
When an address is server-trunkable but not session-trunkable with
the address whose use is to be discontinued, the request might
need to be modified to reflect the fact that a different session
will be used.
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* When use of a particular connection is to cease, as indicated by
receiving NFS4ERR_MOVED when using that connection, but that
address is still indicated as accessible according to the
appropriate file system location entries, it is likely that
requests can be issued on a new connection of a different
connection type once that connection is established. Since any
two non-port-specific server endpoints that share a network
address are inherently session-trunkable, the client can use
BIND_CONN_TO_SESSION to access the existing session with the new
connection.
* When there are no potential replacement addresses in use, but
there are valid addresses session-trunkable with the one whose use
is to be discontinued, the client can use BIND_CONN_TO_SESSION to
access the existing session using the new address. Although the
target session will generally be accessible, there may be rare
situations in which that session is no longer accessible when an
attempt is made to bind the new connection to it. In this case,
the client can create a new session to enable continued access to
the existing instance using the new connection, providing for the
use of existing filehandles, stateids, and client ids while
supplying continuity of locking state.
* When there is no potential replacement address in use, and there
are no valid addresses session-trunkable with the one whose use is
to be discontinued, other server-trunkable addresses may be used
to provide continued access. Although the use of CREATE_SESSION
is available to provide continued access to the existing instance,
servers have the option of providing continued access to the
existing session through the new network access path in a fashion
similar to that provided by session migration (See Section 17.12).
To take advantage of this possibility, clients can perform an
initial BIND_CONN_TO_SESSION, as in the previous case, and use
CREATE_SESSION only if that fails.
17.11. Effecting File System Transitions
There are a range of situations in which there is a change to be
effected in the set of replicas used to access a particular file
system. Some of these may involve an expansion or contraction of the
set of replicas used as discussed in Section 17.11.1 below.
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For reasons explained in that section, most transitions will involve
a transition from a single replica to a corresponding replacement
replica. When effecting replica transition, some types of sharing
between the replicas may affect handling of the transition as
described in Sections 17.11.2 through 17.11.8 below. The attribute
fs_locations_info provides helpful information to allow the client to
determine the degree of inter-replica sharing.
With regard to some types of state, the degree of continuity across
the transition depends on the occasion prompting the transition, with
transitions initiated by the servers (i.e., migration) offering much
more scope for a nondisruptive transition than cases in which the
client on its own shifts its access to another replica (i.e.,
replication). This issue potentially applies to locking state and to
session state, which are dealt with below as follows:
* An introduction to the possible means of providing continuity in
these areas appears in Section 17.11.9 below.
* Transparent State Migration is introduced in Section 17.12. The
possible transfer of session state is addressed there as well.
* The client handling of transitions, including determining how to
deal with the various means that the server might take to supply
effective continuity of locking state, is discussed in
Section 17.13.
* The source and destination servers' responsibilities in effecting
Transparent State Migration of locking and session state are
discussed in Section 17.14.
17.11.1. File System Transitions and Simultaneous Access
The fs_locations_info attribute (described in Section 17.17) may
indicate that two replicas may be used simultaneously, although some
situations in which such simultaneous access is permitted are more
appropriately described as instances of trunking (See
Section 17.5.4.1). Although situations in which multiple replicas
may be accessed simultaneously are somewhat similar to those in which
a single replica is accessed by multiple network addresses, there are
important differences since locking state is not shared among
multiple replicas.
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Because of this difference in state handling, many clients will not
have the ability to take advantage of the fact that such replicas
represent the same data. Such clients will not be prepared to use
multiple replicas simultaneously but will access each file system
using only a single replica, although the replica selected might make
multiple server-trunkable addresses available.
Clients who are prepared to use multiple replicas simultaneously can
divide opens among replicas however they choose. Once that choice is
made, any subsequent transitions will treat the set of locking state
associated with each replica as a single entity.
For example, if one of the replicas become unavailable, access will
be transferred to a different replica, which is also capable of
simultaneous access with the one still in use.
When there is no such replica, the transition may be to the replica
already in use. At this point, the client has a choice between
merging the locking state for the two replicas under the aegis of the
sole replica in use or treating these separately until another
replica capable of simultaneous access presents itself.
17.11.2. Filehandles and File System Transitions
There are a number of ways in which filehandles can be handled across
a file system transition. These can be divided into two broad
classes depending upon whether the two file systems across which the
transition happens share sufficient state to effect some sort of
continuity of file system handling.
When there is no such cooperation in filehandle assignment, the two
file systems are reported as being in different handle classes. In
this case, all filehandles are assumed to expire as part of the file
system transition. Note that this behavior does not depend on the
fh_expire_type attribute and supersedes the specification of the
FH4_VOL_MIGRATION bit, which only affects behavior when
fs_locations_info is not available.
When there is cooperation in filehandle assignment, the two file
systems are reported as being in the same handle classes. In this
case, persistent filehandles remain valid after the file system
transition, while volatile filehandles (excluding those that are only
volatile due to the FH4_VOL_MIGRATION bit) are subject to expiration
on the target server.
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17.11.3. Fileids and File System Transitions
In NFSv4.0, the issue of continuity of fileids in the event of a file
system transition was not addressed. The general expectation had
been that in situations in which the two file system instances are
created by a single vendor using some sort of file system image copy,
fileids would be consistent across the transition, while in the
analogous multi-vendor transitions they would not. This poses
difficulties, especially for the client without special knowledge of
the transition mechanisms adopted by the server. Note that although
fileid is not a REQUIRED attribute, many servers support fileids and
many clients provide APIs that depend on fileids.
It is important to note that while clients themselves may have no
trouble with a fileid changing as a result of a file system
transition event, applications do typically have access to the fileid
(e.g., via stat). The result is that an application may work
perfectly well if there is no file system instance transition or if
any such transition is among instances created by a single vendor,
yet be unable to deal with the situation in which a multi-vendor
transition occurs at the wrong time.
Providing the same fileids in a multi-vendor (multiple server
vendors) environment has generally been held to be quite difficult.
While there is work to be done, it needs to be pointed out that this
difficulty is partly self-imposed. Servers have typically identified
fileid with inode number, i.e. with a quantity used to find the file
in question. This identification poses special difficulties for
migration of a file system between vendors where assigning the same
index to a given file may not be possible. Note here that a fileid
is not required to be useful to find the file in question, only that
it is unique within the given file system. Servers prepared to
accept a fileid as a single piece of metadata and store it apart from
the value used to index the file information can relatively easily
maintain a fileid value across a migration event, allowing a truly
transparent migration event.
In any case, where servers can provide continuity of fileids, they
should, and the client should be able to find out that such
continuity is available and take appropriate action. Information
about the continuity (or lack thereof) of fileids across a file
system transition is represented by specifying whether the file
systems in question are of the same fileid class.
Note that when consistent fileids do not exist across a transition
(either because there is no continuity of fileids or because fileid
is not a supported attribute on one of instances involved), and there
are no reliable filehandles across a transition event (either because
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there is no filehandle continuity or because the filehandles are
volatile), the client is in a position where it cannot verify that
files it was accessing before the transition are the same objects.
It is forced to assume that no object has been renamed, and, unless
there are guarantees that provide this (e.g., the file system is
read-only), problems for applications may occur. Therefore, use of
such configurations should be limited to situations where the
problems that this may cause can be tolerated.
17.11.4. Fsids and File System Transitions
Since fsids are generally only unique on a per-server basis, it is
likely that they will change during a file system transition.
Clients should not make the fsids received from the server visible to
applications since they may not be globally unique, and because they
may change during a file system transition event. Applications are
best served if they are isolated from such transitions to the extent
possible.
Although normally a single source file system will transition to a
single target file system, there is a provision for splitting a
single source file system into multiple target file systems, by
specifying the FSLI4F_MULTI_FS flag.
17.11.4.1. File System Splitting
When a file system transition is made and the fs_locations_info
indicates that the file system in question might be split into
multiple file systems (via the FSLI4F_MULTI_FS flag), the client
SHOULD do GETATTRs to determine the fsid attribute on all known
objects within the file system undergoing transition to determine the
new file system boundaries.
Clients might choose to maintain the fsids passed to existing
applications by mapping all of the fsids for the descendant file
systems to the common fsid used for the original file system.
Splitting a file system can be done on a transition between file
systems of the same fileid class, since the fact that fileids are
unique within the source file system ensure they will be unique in
each of the target file systems.
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17.11.5. The Change Attribute and File System Transitions
Since the change attribute is defined as a server-specific one,
change attributes fetched from one server are normally presumed to be
invalid on another server. Such a presumption is troublesome since
it would invalidate all cached change attributes, requiring
refetching. Even more disruptive, the absence of any assured
continuity for the change attribute means that even if the same value
is retrieved on refetch, no conclusions can be drawn as to whether
the object in question has changed. The identical change attribute
could be merely an artifact of a modified file with a different
change attribute construction algorithm, with that new algorithm just
happening to result in an identical change value.
When the two file systems have consistent change attribute formats,
and this fact is communicated to the client by reporting in the same
change class, the client may assume a continuity of change attribute
construction and handle this situation just as it would be handled
without any file system transition.
17.11.6. Write Verifiers and File System Transitions
In a file system transition, the two file systems might be
cooperating in the handling of unstably written data. Clients can
determine if this is the case by seeing if the two file systems
belong to the same write-verifier class. When this is the case,
write verifiers returned from one system may be compared to those
returned by the other and superfluous writes can be avoided.
When two file systems belong to different write-verifier classes, any
verifier generated by one must not be compared to one provided by the
other. Instead, the two verifiers should be treated as not equal
even when the values are identical.
17.11.7. READDIR Cookies and Verifiers and File System Transitions
In a file system transition, the two file systems might be consistent
in their handling of READDIR cookies and verifiers. Clients can
determine if this is the case by seeing if the two file systems
belong to the same readdir class. When this is the case, readdir
class, READDIR cookies, and verifiers from one system will be
recognized by the other, and READDIR operations started on one server
can be validly continued on the other simply by presenting the cookie
and verifier returned by a READDIR operation done on the first file
system to the second.
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When two file systems belong to different readdir classes, any
READDIR cookie and verifier generated by one is not valid on the
second and must not be presented to that server by the client. The
client should act as if the verifier were rejected.
17.11.8. File System Data and File System Transitions
When multiple replicas exist and are used simultaneously or in
succession by a client, applications using them will normally expect
that they contain either the same data or data that is consistent
with the normal sorts of changes that are made by other clients
updating the data of the file system (with metadata being the same to
the degree indicated by the fs_locations_info attribute). However,
when multiple file systems are presented as replicas of one another,
the precise relationship between the data of one and the data of
another is not, as a general matter, specified by the NFSv4.1
protocol. It is quite possible to present as replicas file systems
where the data of those file systems is sufficiently different that
some applications have problems dealing with the transition between
replicas. The namespace will typically be constructed so that
applications can choose an appropriate level of support, so that in
one position in the namespace, a varied set of replicas might be
listed, while in another, only those that are up-to-date would be
considered replicas. The protocol does define three special cases of
the relationship among replicas to be specified by the server and
relied upon by clients:
* When multiple replicas exist and are used simultaneously by a
client (See the FSLIB4_CLSIMUL definition within
fs_locations_info), they must designate the same data. Where file
systems are writable, a change made on one instance must be
visible on all instances at the same time, regardless of whether
the interrogated instance is the one on which the modification was
done. This allows a client to use these replicas simultaneously
without any special adaptation to the fact that there are multiple
replicas, beyond adapting to the fact that locks obtained on one
replica are maintained separately (i.e., under a different client
ID). In this case, locks (whether share reservations or byte-
range locks) and delegations obtained on one replica are
immediately reflected on all replicas, in the sense that access
from all other servers is prevented regardless of the replica
used. However, because the servers are not required to treat two
associated client IDs as representing the same client, it is best
to access each file using only a single client ID.
* When one replica is designated as the successor instance to
another existing instance after the return of NFS4ERR_MOVED (i.e.,
the case of migration), the client may depend on the fact that all
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changes written to stable storage on the original instance are
written to stable storage of the successor (uncommitted writes are
dealt with in Section 17.11.6 above).
* Where a file system is not writable but represents a read-only
copy (possibly periodically updated) of a writable file system,
clients have similar requirements with regard to the propagation
of updates. They may need a guarantee that any change visible on
the original file system instance must be immediately visible on
any replica before the client transitions access to that replica,
in order to avoid any possibility that a client, in effecting a
transition to a replica, will see any reversion in file system
state. The specific means of this guarantee varies based on the
value of the fss_type field that is reported as part of the
fs_status attribute (See Section 17.18). Since these file systems
are presumed to be unsuitable for simultaneous use, there is no
specification of how locking is handled; in general, locks
obtained on one file system will be separate from those on others.
Since these are expected to be read-only file systems, this is not
likely to pose an issue for clients or applications.
When none of these special situations applies, there is no basis
within the protocol for the client to make assumptions about the
contents of a replica file system or its relationship to previous
file system instances. Thus, switching between nominally identical
read-write file systems would not be possible because either the
client does not use the fs_locations_info attribute, or the server
does not support it.
17.11.9. Lock State and File System Transitions
While accessing a file system, clients obtain locks enforced by the
server, which may prevent actions by other clients that are
inconsistent with those locks.
When access is transferred between replicas, clients need to be
assured that the actions disallowed by holding these locks cannot
have occurred during the transition. This can be ensured by the
methods below. Unless at least one of these is implemented, clients
will not be assured of continuity of lock possession across a
migration event:
* Providing the client an opportunity to re-obtain his locks via a
per-fs grace period on the destination server, denying all clients
using the destination file system the opportunity to obtain new
locks that conflict with those held by the transferred client as
long as that client has not completed its per-fs grace period.
Because the lock reclaim mechanism was originally defined to
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support server reboot, it implicitly assumes that filehandles
will, upon reclaim, be the same as those at open. In the case of
migration, this requires that source and destination servers use
the same filehandles, as evidenced by using the same server scope
(See Section 7.4) or by showing this agreement using
fs_locations_info (See Section 17.11.2 above).
Note that such a grace period can be implemented without
interfering with the ability of non-transferred clients to obtain
new locks while it is going on. As long as the destination server
is aware of the transferred locks, it can distinguish requests to
obtain new locks that contrast with existing locks from those that
do not, allowing it to treat such client requests without
reference to the ongoing grace period.
* Locking state can be transferred as part of the transition by
providing Transparent State Migration as described in
Section 17.12.
Of these, Transparent State Migration provides the smoother
experience for clients in that there is no need to go through a
reclaim process before new locks can be obtained; however, it
requires a greater degree of inter-server coordination. In general,
the servers taking part in migration are free to provide either
facility. However, when the filehandles can differ across the
migration event, Transparent State Migration is the only available
means of providing the needed functionality.
It should be noted that these two methods are not mutually exclusive
and that a server might well provide both. In particular, if there
is some circumstance preventing a specific lock from being
transferred transparently, the destination server can allow it to be
reclaimed by implementing a per-fs grace period for the migrated file
system.
17.11.9.1. Security Issues Related to Reclaiming Lock State after File
System Transitions
Although it is possible for a client reclaiming state to misrepresent
its state in the same fashion as described in Section 13.4.2.1.1,
most implementations providing for such reclamation in the case of
file system transitions will have the ability to detect such
misrepresentations. This limits the ability of unauthenticated
clients to execute denial-of-service attacks in these circumstances.
Nevertheless, the rules stated in Section 13.4.2.1.1 regarding
principal verification for reclaim requests apply in this situation
as well.
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Typically, implementations that support file system transitions will
have extensive information about the locks to be transferred. This
is because of the following:
* Since failure is not involved, there is no need to store locking
information in persistent storage.
* There is no need, as there is in the failure case, to update
multiple repositories containing locking state to keep them in
sync. Instead, there is a one-time communication of locking state
from the source to the destination server.
* Providing this information avoids potential interference with
existing clients using the destination file system by denying them
the ability to obtain new locks during the grace period.
When such detailed locking information, not necessarily including the
associated stateids, is available:
* It is possible to detect reclaim requests that attempt to reclaim
locks that did not exist before the transfer, rejecting them with
NFS4ERR_RECLAIM_BAD (Section 22.1.9.4). SN
* It is possible when dealing with non-reclaim requests, to
determine whether they conflict with existing locks, eliminating
the need to return NFS4ERR_GRACE (Section 22.1.9.2) on non-reclaim
requests.
It is possible for implementations of grace periods in connection
with file system transitions not to have detailed locking information
available at the destination server, in which case, the security
situation is exactly as described in Section 13.4.2.1.1.
17.11.9.2. Leases and File System Transitions
In the case of lease renewal, the client may not be submitting
requests for a file system that has been transferred to another
server. This can occur because of the lease renewal mechanism. The
client renews the lease associated with all file systems when
submitting a request on an associated session, regardless of the
specific file system being referenced.
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In order for the client to schedule renewal of its lease where there
is locking state that may have been relocated to the new server, the
client must find out about lease relocation before that lease expire.
To accomplish this, the SEQUENCE operation will return the status bit
SEQ4_STATUS_LEASE_MOVED if responsibility for any of the renewed
locking state has been transferred to a new server. This will
continue until the client receives an NFS4ERR_MOVED error for each of
the file systems for which there has been locking state relocation.
When a client receives an SEQ4_STATUS_LEASE_MOVED indication from a
server, for each file system of the server for which the client has
locking state, the client should perform an operation. For
simplicity, the client may choose to reference all file systems, but
what is important is that it must reference all file systems for
which there was locking state where that state has moved. Once the
client receives an NFS4ERR_MOVED error for each such file system, the
server will clear the SEQ4_STATUS_LEASE_MOVED indication. The client
can terminate the process of checking file systems once this
indication is cleared (but only if the client has received a reply
for all outstanding SEQUENCE requests on all sessions it has with the
server), since there are no others for which locking state has moved.
A client may use GETATTR of the fs_status (or fs_locations_info)
attribute on all of the file systems to get absence indications in a
single (or a few) request(s), since absent file systems will not
cause an error in this context. However, it still must do an
operation that receives NFS4ERR_MOVED on each file system, in order
to clear the SEQ4_STATUS_LEASE_MOVED indication.
Once the set of file systems with transferred locking state has been
determined, the client can follow the normal process to obtain the
new server information (through the fs_locations and
fs_locations_info attributes) and perform renewal of that lease on
the new server, unless information in the fs_locations_info attribute
shows that no state could have been transferred. If the server has
not had state transferred to it transparently, the client will
receive NFS4ERR_STALE_CLIENTID from the new server, as described
above, and the client can then reclaim locks as is done in the event
of server failure.
17.11.9.3. Transitions and the Lease_time Attribute
In order that the client may appropriately manage its lease in the
case of a file system transition, the destination server must
establish proper values for the lease_time attribute.
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When state is transferred transparently, that state should include
the correct value of the lease_time attribute. The lease_time
attribute on the destination server must never be less than that on
the source, since this would result in premature expiration of a
lease granted by the source server. Upon transitions in which state
is transferred transparently, the client is under no obligation to
refetch the lease_time attribute and may continue to use the value
previously fetched (on the source server).
If state has not been transferred transparently, either because the
associated servers are shown as having different eir_server_scope
strings or because the client ID is rejected when presented to the
new server, the client should fetch the value of lease_time on the
new (i.e., destination) server, and use it for subsequent locking
requests. However, the server must respect a grace period of at
least as long as the lease_time on the source server, in order to
ensure that clients have ample time to reclaim their lock before
potentially conflicting non-reclaimed locks are granted.
17.12. Transferring State upon Migration
When the transition is a result of a server-initiated decision to
transition access, and the source and destination servers have
implemented appropriate cooperation, it is possible to do the
following:
* Transfer locking state from the source to the destination server
in a fashion similar to that provided by Transparent State
Migration in NFSv4.0, as described in [RFC7931]. Server
responsibilities are described in Section 17.14.2.
* Transfer session state from the source to the destination server.
Server responsibilities in effecting such a transfer are described
in Section 17.14.3.
The means by which the client determines which of these transfer
events has occurred are described in Section 17.13.
17.12.1. Transparent State Migration and pNFS
When pNFS is involved, the protocol is capable of supporting:
* Migration of the Metadata Server (MDS), leaving the Data Servers
(DSs) in place.
* Migration of the file system as a whole, including the MDS and
associated DSs.
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* Replacement of one DS by another.
* Migration of a pNFS file system to one in which pNFS is not used.
* Migration of a file system not using pNFS to one in which layouts
are available.
Note that migration, per se, is only involved in the transfer of the
MDS function. Although the servicing of a layout may be transferred
from one data server to another, this not done using the file system
location attributes. The MDS can effect such transfers by recalling
or revoking existing layouts and granting new ones on a different
data server.
Migration of the MDS function is directly supported by Transparent
State Migration. Layout state will normally be transparently
transferred, just as other state is. As a result, Transparent State
Migration provides a framework in which, given appropriate inter-MDS
data transfer, one MDS can be substituted for another.
Migration of the file system function as a whole can be accomplished
by recalling all layouts as part of the initial phase of the
migration process. As a result, I/O will be done through the MDS
during the migration process, and new layouts can be granted once the
client is interacting with the new MDS. An MDS can also effect this
sort of transition by revoking all layouts as part of Transparent
State Migration, as long as the client is notified about the loss of
locking state.
In order to allow migration to a file system on which pNFS is not
supported, clients need to be prepared for a situation in which
layouts are not available or supported on the destination file system
and so direct I/O requests to the destination server, rather than
depending on layouts being available.
Replacement of one DS by another is not addressed by migration as
such but can be effected by an MDS recalling layouts for the DS to be
replaced and issuing new ones to be served by the successor DS.
Migration may transfer a file system from a server that does not
support pNFS to one that does. In order to properly adapt to this
situation, clients that support pNFS, but function adequately in its
absence, should check for pNFS support when a file system is migrated
and be prepared to use pNFS when support is available on the
destination.
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17.13. Client Responsibilities When Access Is Transitioned
For a client to respond to an access transition, it must become aware
of it. The ways in which this can happen are discussed in
Section 17.13.1, which discusses indications that a specific file
system access path has transitioned as well as situations in which
additional activity is necessary to determine the set of file systems
that have been migrated. Section 17.13.2 goes on to complete the
discussion of how the set of migrated file systems might be
determined. Sections 17.13.3 through 17.13.5 discuss how the client
should deal with each transition it becomes aware of, either directly
or as a result of migration discovery.
The following terms are used to describe client activities:
* "Transition recovery" refers to the process of restoring access to
a file system on which NFS4ERR_MOVED was received.
* "Migration recovery" refers to that subset of transition recovery
that applies when the file system has migrated to a different
replica.
* "Migration discovery" refers to the process of determining which
file system(s) have been migrated. It is necessary to avoid a
situation in which leases could expire when a file system is not
accessed for a long period of time, since a client unaware of the
migration might be referencing an unmigrated file system and not
renewing the lease associated with the migrated file system.
17.13.1. Client Transition Notifications
When there is a change in the network access path that a client is to
use to access a file system, there are a number of related status
indications with which clients need to deal:
* If an attempt is made to use or return a filehandle within a file
system that is no longer accessible at the address previously used
to access it, the error NFS4ERR_MOVED is returned.
Exceptions are made to allow such filehandles to be used when
interrogating a file system location attribute. This enables a
client to determine a new replica's location or a new network
access path.
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This condition continues on subsequent attempts to access the file
system in question. The only way the client can avoid the error
is to cease accessing the file system in question at its old
server location and access it instead using a different address at
which it is now available.
* Whenever a client sends a SEQUENCE operation to a server that
generated state held on that client and associated with a file
system no longer accessible on that server, the response will
contain the status bit SEQ4_STATUS_LEASE_MOVED, indicating that
there has been a lease migration.
This condition continues until the client acknowledges the
notification by fetching a file system location attribute for the
file system whose network access path is being changed. When
there are multiple such file systems, a location attribute for
each such file system needs to be fetched. The location attribute
for all migrated file systems needs to be fetched in order to
clear the condition. Even after the condition is cleared, the
client needs to respond by using the location information to
access the file system at its new location to ensure that leases
are not needlessly expired.
Unlike NFSv4.0, in which the corresponding conditions are both errors
and thus mutually exclusive, in NFSv4.1 the client can, and often
will, receive both indications on the same request. As a result,
implementations need to address the question of how to coordinate the
necessary recovery actions when both indications arrive in the
response to the same request. It should be noted that when
processing an NFSv4 COMPOUND, the server will normally decide whether
SEQ4_STATUS_LEASE_MOVED is to be set before it determines which file
system will be referenced or whether NFS4ERR_MOVED is to be returned.
Since these indications are not mutually exclusive in NFSv4.1, the
following combinations are possible results when a COMPOUND is
issued:
* The COMPOUND status is NFS4ERR_MOVED, and SEQ4_STATUS_LEASE_MOVED
is asserted.
In this case, transition recovery is required. While it is
possible that migration discovery is needed in addition, it is
likely that only the accessed file system has transitioned. In
any case, because addressing NFS4ERR_MOVED is necessary to allow
the rejected requests to be processed on the target, dealing with
it will typically have priority over migration discovery.
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* The COMPOUND status is NFS4ERR_MOVED, and SEQ4_STATUS_LEASE_MOVED
is clear.
In this case, transition recovery is also required. It is clear
that migration discovery is not needed to find file systems that
have been migrated other than the one returning NFS4ERR_MOVED.
Cases in which this result can arise include a referral or a
migration for which there is no associated locking state. This
can also arise in cases in which an access path transition other
than migration occurs within the same server. In such a case,
there is no need to set SEQ4_STATUS_LEASE_MOVED, since the lease
remains associated with the current server even though the access
path has changed.
* The COMPOUND status is not NFS4ERR_MOVED, and
SEQ4_STATUS_LEASE_MOVED is asserted.
In this case, no transition recovery activity is required on the
file system(s) accessed by the request. However, to prevent
avoidable lease expiration, migration discovery needs to be done.
* The COMPOUND status is not NFS4ERR_MOVED, and
SEQ4_STATUS_LEASE_MOVED is clear.
In this case, neither transition-related activity nor migration
discovery is required.
Note that the specified actions only need to be taken if they are not
already going on. For example, when NFS4ERR_MOVED is received while
accessing a file system for which transition recovery is already
occurring, the client merely waits for that recovery to be completed,
while the receipt of the SEQ4_STATUS_LEASE_MOVED indication only
needs to initiate migration discovery for a server if such discovery
is not already underway for that server.
The fact that a lease-migrated condition does not result in an error
in NFSv4.1 has a number of important consequences. In addition to
the fact that the two indications are not mutually exclusive, as
discussed above, there are number of issues that are important in
considering implementation of migration discovery, as discussed in
Section 17.13.2.
Because SEQ4_STATUS_LEASE_MOVED is not an error condition, it is
possible for file systems whose access paths have not changed to be
successfully accessed on a given server even though recovery is
necessary for other file systems on the same server. As a result,
access can take place while:
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* The migration discovery process is happening for that server.
* The transition recovery process is happening for other file
systems connected to that server.
17.13.2. Performing Migration Discovery
Migration discovery can be performed in the same context as
transition recovery, allowing recovery for each migrated file system
to be invoked as it is discovered. Alternatively, it may be done in
a separate migration discovery thread, allowing migration discovery
to be done in parallel with one or more instances of transition
recovery.
In either case, because the lease-migrated indication does not result
in an error, other access to file systems on the server can proceed
normally, with the possibility that further such indications will be
received, raising the issue of how such indications are to be dealt
with. In general:
* No action needs to be taken for such indications received by any
threads performing migration discovery, since continuation of that
work will address the issue.
* In other cases in which migration discovery is currently being
performed, nothing further needs to be done to respond to such
lease migration indications, as long as one can be certain that
the migration discovery process would deal with those indications.
See below for details.
* For such indications received in all other contexts, the
appropriate response is to initiate or otherwise provide for the
execution of migration discovery for file systems associated with
the server IP address returning the indication.
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This leaves a potential difficulty in situations in which the
migration discovery process is near to completion but is still
operating. One should not ignore a SEQ4_STATUS_LEASE_MOVED
indication if the migration discovery process is not able to respond
to the discovery of additional migrating file systems without
additional aid. A further complexity relevant in addressing such
situations is that a lease-migrated indication may reflect the
server's state at the time the SEQUENCE operation was processed,
which may be different from that in effect at the time the response
is received. Because new migration events may occur at any time, and
because a SEQ4_STATUS_LEASE_MOVED indication may reflect the
situation in effect a considerable time before the indication is
received, special care needs to be taken to ensure that
SEQ4_STATUS_LEASE_MOVED indications are not inappropriately ignored.
A useful approach to this issue involves the use of separate
externally-visible migration discovery states for each server.
Separate values could represent the various possible states for the
migration discovery process for a server:
* Non-operation, in which migration discovery is not being
performed.
* Normal operation, in which there is an ongoing scan for migrated
file systems.
* Completion/verification of migration discovery processing, in
which the possible completion of migration discovery processing
needs to be verified.
Given that framework, migration discovery processing would proceed as
follows:
* While in the normal-operation state, the thread performing
discovery would fetch, for successive file systems known to the
client on the server being worked on, a file system location
attribute plus the fs_status attribute.
* If the fs_status attribute indicates that the file system is a
migrated one (i.e., fss_absent is true, and fss_type !=
STATUS4_REFERRAL), then a migrated file system has been found. In
this situation, it is likely that the fetch of the file system
location attribute has cleared one of the file systems
contributing to the lease-migrated indication.
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* In cases in which that happened, the thread cannot know whether
the lease-migrated indication has been cleared, and so it enters
the completion/verification state and proceeds to issue a COMPOUND
to see if the SEQ4_STATUS_LEASE_MOVED indication has been cleared.
* When the discovery process is in the completion/verification
state, if other requests get a lease-migrated indication, they
note that it was received. Later, the existence of such
indications is used when the request completes, as described
below.
When the request used in the completion/verification state completes:
* If a lease-migrated indication is returned, the discovery
continues normally. Note that this is so even if all file systems
have been traversed, since new migrations could have occurred
while the process was going on.
* Otherwise, if there is any record that other requests saw a lease-
migrated indication while the request was occurring, that record
is cleared, and the verification request is retried. The
discovery process remains in the completion/verification state.
* If there have been no lease-migrated indications, the work of
migration discovery is considered completed, and it enters the
non-operating state. Once it enters this state, subsequent lease-
migrated indications will trigger a new migration discovery
process.
It should be noted that the process described above is not guaranteed
to terminate, as a long series of new migration events might
continually delay the clearing of the SEQ4_STATUS_LEASE_MOVED
indication. To prevent unnecessary lease expiration, it is
appropriate for clients to use the discovery of migrations to effect
lease renewal immediately, rather than waiting for the clearing of
the SEQ4_STATUS_LEASE_MOVED indication when the complete set of
migrations is available.
Lease discovery needs to be provided as described above. This
ensures that the client discovers file system migrations soon enough
to renew its leases on each destination server before they expire.
Non-renewal of leases can lead to loss of locking state. While the
consequences of such loss can be ameliorated through implementations
of courtesy locks, servers are under no obligation to do so, and a
conflicting lock request may mean that a lock is revoked
unexpectedly. Clients should be aware of this possibility.
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17.13.3. Overview of Client Response to NFS4ERR_MOVED
This section outlines a way in which a client that receives
NFS4ERR_MOVED can effect transition recovery by using a new server or
server endpoint if one is available. As part of that process, it
will determine:
* Whether the NFS4ERR_MOVED indicates migration has occurred, or
whether it indicates another sort of file system access transition
as discussed in Section 17.10 above.
* In the case of migration, whether Transparent State Migration has
occurred.
* Whether any state has been lost during the process of Transparent
State Migration.
* Whether sessions have been transferred as part of Transparent
State Migration.
During the first phase of this process, the client proceeds to
examine file system location entries to find the initial network
address it will use to continue access to the file system or its
replacement. For each location entry that the client examines, the
process consists of five steps:
1. Performing an EXCHANGE_ID directed at the location address. This
operation is used to register the client owner (in the form of a
client_owner4) with the server, to obtain a client ID to be used
subsequently to communicate with it, to obtain that client ID's
confirmation status, and to determine server_owner4 and scope for
the purpose of determining if the entry is trunkable with the
address previously being used to access the file system (i.e.,
that it represents another network access path to the same file
system and can share locking state with it).
2. Making an initial determination of whether migration has
occurred. The initial determination will be based on whether the
EXCHANGE_ID results indicate that the current location element is
server-trunkable with that used to access the file system when
access was terminated by receiving NFS4ERR_MOVED. If it is, then
migration has not occurred. In that case, the transition is
dealt with, at least initially, as one involving continued access
to the same file system on the same server through a new network
address.
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3. Obtaining access to existing session state or creating new
sessions. How this is done depends on the initial determination
of whether migration has occurred and can be done as described in
Section 17.13.4 below in the case of migration or as described in
Section 17.13.5 below in the case of a network address transfer
without migration.
4. Verifying the trunking relationship assumed in step 2 as
discussed in Section 7.5.1. Although this step will generally
confirm the initial determination, it is possible for
verification to invalidate the initial determination of network
address shift (without migration) and instead determine that
migration had occurred. There is no need to redo step 3 above,
since it will be possible to continue use of the session
established already.
5. Obtaining access to existing locking state and/or re-obtaining
it. How this is done depends on the final determination of
whether migration has occurred and can be done as described below
in Section 17.13.4 in the case of migration or as described in
Section 17.13.5 in the case of a network address transfer without
migration.
Once the initial address has been determined, clients are free to
apply an abbreviated process to find additional addresses trunkable
with it (clients may seek session-trunkable or server-trunkable
addresses depending on whether they support client ID trunking).
During this later phase of the process, further location entries are
examined using the abbreviated procedure specified below:
A: Before the EXCHANGE_ID, the fs name of the location entry is
examined, and if it does not match that currently being used, the
entry is ignored. Otherwise, one proceeds as specified by step 1
above.
B: In the case that the network address is session-trunkable with
one used previously, a BIND_CONN_TO_SESSION is used to access
that session using the new network address. Otherwise, or if the
bind operation fails, a CREATE_SESSION is done.
C: The verification procedure referred to in step 4 above is used.
However, if it fails, the entry is ignored and the next available
entry is used.
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17.13.4. Obtaining Access to Sessions and State after Migration
In the event that migration has occurred, migration recovery will
involve determining whether Transparent State Migration has occurred.
This decision is made based on the client ID returned by the
EXCHANGE_ID and the reported confirmation status.
* If the client ID is an unconfirmed client ID not previously known
to the client, then Transparent State Migration has not occurred.
* If the client ID is a confirmed client ID previously known to the
client, then any transferred state would have been merged with an
existing client ID representing the client to the destination
server. In this state merger case, Transparent State Migration
might or might not have occurred, and a determination as to
whether it has occurred is deferred until sessions are established
and the client is ready to begin state recovery.
* If the client ID is a confirmed client ID not previously known to
the client, then the client can conclude that the client ID was
transferred as part of Transparent State Migration. In this
transferred client ID case, Transparent State Migration has
occurred, although some state might have been lost.
Once the client ID has been obtained, it is necessary to obtain
access to sessions to continue communication with the new server. In
any of the cases in which Transparent State Migration has occurred,
it is possible that a session was transferred as well. To deal with
that possibility, clients can, after doing the EXCHANGE_ID, issue a
BIND_CONN_TO_SESSION to connect the transferred session to a
connection to the new server. If that fails, it is an indication
that the session was not transferred and that a new session needs to
be created to take its place.
In some situations, it is possible for a BIND_CONN_TO_SESSION to
succeed without session migration having occurred. If state merger
has taken place, then the associated client ID may have already had a
set of existing sessions, with it being possible that the session ID
of a given session is the same as one that might have been migrated.
In that event, a BIND_CONN_TO_SESSION might succeed, even though
there could have been no migration of the session with that session
ID. In such cases, the client will receive sequence errors when the
slot sequence values used are not appropriate on the new session.
When this occurs, the client can create a new a session and cease
using the existing one.
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Once the client has determined the initial migration status, and
determined that there was a shift to a new server, it needs to re-
establish its locking state, if possible. To enable this to happen
without loss of the guarantees normally provided by locking, the
destination server needs to implement a per-fs grace period in all
cases in which lock state was lost, including those in which
Transparent State Migration was not implemented. Each client for
which there was a transfer of locking state to the new server will
have the duration of the grace period to reclaim its locks, from the
time its locks were transferred.
Clients need to deal with the following cases:
* In the state merger case, it is possible that the server has not
attempted Transparent State Migration, in which case state may
have been lost without it being reflected in the SEQ4_STATUS bits.
To determine whether this has happened, the client can use
TEST_STATEID to check whether the stateids created on the source
server are still accessible on the destination server. Once a
single stateid is found to have been successfully transferred, the
client can conclude that Transparent State Migration was begun,
and any failure to transport all of the stateids will be reflected
in the SEQ4_STATUS bits. Otherwise, Transparent State Migration
has not occurred.
* In a case in which Transparent State Migration has not occurred,
the client can use the per-fs grace period provided by the
destination server to reclaim locks that were held on the source
server.
* In a case in which Transparent State Migration has occurred, and
no lock state was lost (as shown by SEQ4_STATUS flags), no lock
reclaim is necessary.
* In a case in which Transparent State Migration has occurred, and
some lock state was lost (as shown by SEQ4_STATUS flags), existing
stateids need to be checked for validity using TEST_STATEID, and
reclaim used to re-establish any that were not transferred.
For all of the cases above, RECLAIM_COMPLETE with an rca_one_fs value
of TRUE needs to be done before normal use of the file system,
including obtaining new locks for the file system. This applies even
if no locks were lost and there was no need for any to be reclaimed.
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17.13.5. Obtaining Access to Sessions and State after Network Address
Transfer
The case in which there is a transfer to a new network address
without migration is similar to that described in Section 17.13.4
above in that there is a need to obtain access to needed sessions and
locking state. However, the details are simpler and will vary
depending on the type of trunking between the address receiving
NFS4ERR_MOVED and that to which the transfer is to be made.
To make a session available for use, a BIND_CONN_TO_SESSION should be
used to obtain access to the session previously in use. Only if this
fails, should a CREATE_SESSION be done. While this procedure mirrors
that in Section 17.13.4 above, there is an important difference in
that preservation of the session is not purely optional but depends
on the type of trunking.
Access to appropriate locking state will generally need no actions
beyond access to the session. However, the SEQ4_STATUS bits need to
be checked for lost locking state, including the need to reclaim
locks after a server reboot, since there is always a possibility of
locking state being lost.
17.14. Server Responsibilities Upon Migration
In the event of file system migration, when the client connects to
the destination server, that server needs to be able to provide the
client continued access to the files it had open on the source
server. There are two ways to provide this:
* By provision of an fs-specific grace period, allowing the client
the ability to reclaim its locks, in a fashion similar to what
would have been done in the case of recovery from a server
restart. See Section 17.14.1 for a more complete discussion.
* By implementing Transparent State Migration possibly in connection
with session migration, the server can provide the client
immediate access to the state built up on the source server on the
destination server.
These features are discussed separately in Sections 17.14.2 and
17.14.3, which discuss Transparent State Migration and session
migration, respectively.
All the features described above can involve transfer of lock-related
information between source and destination servers. In some cases,
this transfer is a necessary part of the implementation, while in
other cases, it is a helpful implementation aid, which servers might
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or might not use. The subsections below discuss the information that
would be transferred but do not define the specifics of the transfer
protocol. This is left as an implementation choice, although
standards in this area could be developed at a later time.
17.14.1. Server Responsibilities in Effecting State Reclaim after
Migration
In this case, the destination server needs no knowledge of the locks
held on the source server. It relies on the clients to accurately
report (via reclaim operations) the locks previously held, and does
not allow new locks to be granted on migrated file systems until the
grace period expires. Disallowing of new locks applies to all
clients accessing these file systems, while grace period expiration
occurs for each migrated client independently.
During this grace period, clients have the opportunity to use reclaim
operations to obtain locks for file system objects within the
migrated file system, in the same way that they do when recovering
from server restart, and the servers typically rely on clients to
accurately report their locks, although they have the option of
subjecting these requests to verification. If the clients only
reclaim locks held on the source server, no conflict can arise. Once
the client has reclaimed its locks, it indicates the completion of
lock reclamation by performing a RECLAIM_COMPLETE specifying
rca_one_fs as TRUE.
While it is not necessary for source and destination servers to
cooperate to transfer information about locks, implementations are
well advised to consider transferring the following useful
information:
* If information about the set of clients that have locking state
for the transferred file system is made available, the destination
server will be able to terminate the grace period once all such
clients have reclaimed their locks, allowing normal locking
activity to resume earlier than it would have otherwise.
* Locking summary information for individual clients (at various
possible levels of detail) can detect some instances in which
clients do not accurately represent the locks held on the source
server.
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17.14.2. Server Responsibilities in Effecting Transparent State
Migration
The basic responsibility of the source server in effecting
Transparent State Migration is to make available to the destination
server a description of each piece of locking state associated with
the file system being migrated. In addition to client id string and
verifier, the source server needs to provide for each stateid:
* The stateid including the current sequence value.
* The associated client ID.
* The handle of the associated file.
* The type of the lock, such as open, byte-range lock, delegation,
or layout.
* For locks such as opens and byte-range locks, there will be
information about the owner(s) of the lock.
* For recallable/revocable lock types, the current recall status
needs to be included.
* For each lock type, there will be associated type-specific
information. For opens, this will include share and deny mode
while for byte-range locks and layouts, there will be a type and a
byte-range.
Such information will most probably be organized by client id string
on the destination server so that it can be used to provide
appropriate context to each client when it makes itself known to the
client. Issues connected with a client impersonating another by
presenting another client's client id string can be addressed using
NFSv4.1 state protection features, as described in Section 28.
A further server responsibility concerns locks that are revoked or
otherwise lost during the process of file system migration. Because
locks that appear to be lost during the process of migration will be
reclaimed by the client, the servers have to take steps to ensure
that locks revoked soon before or soon after migration are not
inadvertently allowed to be reclaimed in situations in which the
continuity of lock possession cannot be assured.
* For locks lost on the source but whose loss has not yet been
acknowledged by the client (by using FREE_STATEID), the
destination must be aware of this loss so that it can deny a
request to reclaim them.
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* For locks lost on the destination after the state transfer but
before the client's RECLAIM_COMPLETE is done, the destination
server should note these and not allow them to be reclaimed.
An additional responsibility of the cooperating servers concerns
situations in which a stateid cannot be transferred transparently
because it conflicts with an existing stateid held by the client and
associated with a different file system. In this case, there are two
valid choices:
* Treat the transfer, as in NFSv4.0, as one without Transparent
State Migration. In this case, conflicting locks cannot be
granted until the client does a RECLAIM_COMPLETE, after reclaiming
the locks it had, with the exception of reclaims denied because
they were attempts to reclaim locks that had been lost.
* Implement Transparent State Migration, except for the lock with
the conflicting stateid. In this case, the client will be aware
of a lost lock (through the SEQ4_STATUS flags) and be allowed to
reclaim it.
When transferring state between the source and destination, the
issues discussed in Section 7.2 of [RFC7931] must still be attended
to. In this case, the use of NFS4ERR_DELAY may still be necessary in
NFSv4.1, as it was in NFSv4.0, to prevent locking state changing
while it is being transferred. See Section 22.1.1.3 for information
about appropriate client retry approaches in the event that
NFS4ERR_DELAY is returned.
There are a number of important differences in the NFS4.1 context:
* The absence of RELEASE_LOCKOWNER means that the one case in which
an operation could not be deferred by use of NFS4ERR_DELAY no
longer exists.
* Sequencing of operations is no longer done using owner-based
operation sequences numbers. Instead, sequencing is session-
based.
As a result, when sessions are not transferred, the techniques
discussed in Section 7.2 of [RFC7931] are adequate and will not be
further discussed.
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17.14.3. Server Responsibilities in Effecting Session Transfer
The basic responsibility of the source server in effecting session
transfer is to make available to the destination server a description
of the current state of each slot with the session, including the
following:
* The last sequence value received for that slot.
* Whether there is cached reply data for the last request executed
and, if so, the cached reply.
When sessions are transferred, there are a number of issues that pose
challenges in terms of making the transferred state unmodifiable
during the period it is gathered up and transferred to the
destination server:
* A single session may be used to access multiple file systems, not
all of which are being transferred.
* Requests made on a session may, even if rejected, affect the state
of the session by advancing the sequence number associated with
the slot used.
As a result, when the file system state might otherwise be considered
unmodifiable, the client might have any number of in-flight requests,
each of which is capable of changing session state, which may be of a
number of types:
1. Those requests that were processed on the migrating file system
before migration began.
2. Those requests that received the error NFS4ERR_DELAY because the
file system being accessed was in the process of being migrated.
3. Those requests that received the error NFS4ERR_MOVED because the
file system being accessed had been migrated.
4. Those requests that accessed the migrating file system in order
to obtain location or status information.
5. Those requests that did not reference the migrating file system.
It should be noted that the history of any particular slot is likely
to include a number of these request classes. In the case in which a
session that is migrated is used by file systems other than the one
migrated, requests of class 5 may be common and may be the last
request processed for many slots.
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Since session state can change even after the locking state has been
fixed as part of the migration process, the session state known to
the client could be different from that on the destination server,
which necessarily reflects the session state on the source server at
an earlier time. In deciding how to deal with this situation, it is
helpful to distinguish between two sorts of behavioral consequences
of the choice of initial sequence ID values:
* The error NFS4ERR_SEQ_MISORDERED is returned when the sequence ID
in a request is neither equal to the last one seen for the current
slot nor the next greater one.
In view of the difficulty of arriving at a mutually acceptable
value for the correct last sequence value at the point of
migration, it may be necessary for the server to show some degree
of forbearance when the sequence ID is one that would be
considered unacceptable if session migration were not involved.
* Returning the cached reply for a previously executed request when
the sequence ID in the request matches the last value recorded for
the slot.
In the cases in which an error is returned and there is no
possibility of any non-idempotent operation having been executed,
it may not be necessary to adhere to this as strictly as might be
proper if session migration were not involved. For example, the
fact that the error NFS4ERR_DELAY was returned may not assist the
client in any material way, while the fact that NFS4ERR_MOVED was
returned by the source server may not be relevant when the request
was reissued and directed to the destination server.
An important issue is that the specification needs to take note of
all potential COMPOUNDs, even if they might be unlikely in practice.
For example, a COMPOUND is allowed to access multiple file systems
and might perform non-idempotent operations in some of them before
accessing a file system being migrated. Also, a COMPOUND may return
considerable data in the response before being rejected with
NFS4ERR_DELAY or NFS4ERR_MOVED, and may in addition be marked as
sa_cachethis. However, note that if the client and server adhere to
rules in Section 22.1.1.3, there is no possibility of non-idempotent
operations being spuriously reissued after receiving NFS4ERR_DELAY
response.
To address these issues, a destination server MAY do any of the
following when implementing session transfer:
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* Avoid enforcing any sequencing semantics for a particular slot
until the client has established the starting sequence for that
slot on the destination server.
* For each slot, avoid returning a cached reply returning
NFS4ERR_DELAY or NFS4ERR_MOVED until the client has established
the starting sequence for that slot on the destination server.
* Until the client has established the starting sequence for a
particular slot on the destination server, avoid reporting
NFS4ERR_SEQ_MISORDERED or returning a cached reply that contains
either NFS4ERR_DELAY or NFS4ERR_MOVED and consists solely of a
series of operations where the response is NFS4_OK until the final
error.
Because of the considerations mentioned above, including the rules
for the handling of NFS4ERR_DELAY included in Section 22.1.1.3, the
destination server can respond appropriately to SEQUENCE operations
received from the client by adopting the three policies listed below:
* Not responding with NFS4ERR_SEQ_MISORDERED for the initial request
on a slot within a transferred session because the destination
server cannot be aware of requests made by the client after the
server handoff but before the client became aware of the shift.
In cases in which NFS4ERR_SEQ_MISORDERED would normally have been
reported, the request is to be processed normally as a new
request.
* Replying as it would for a retry whenever the sequence matches
that transferred by the source server, even though this would not
provide retry handling for requests issued after the server
handoff, under the assumption that, when such requests are issued,
they will never be responded to in a state-changing fashion,
making retry support for them unnecessary.
* Once a non-retry SEQUENCE is received for a given slot, using that
as the basis for further sequence checking, with no further
reference to the sequence value transferred by the source server.
17.15. Effecting File System Referrals
Referrals are effected when an absent file system is encountered and
one or more alternate locations are made available by the
fs_locations or fs_locations_info attributes. The client will
typically get an NFS4ERR_MOVED error, fetch the appropriate location
information, and proceed to access the file system on a different
server, even though it retains its logical position within the
original namespace. Referrals differ from migration events in that
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they happen only when the client has not previously referenced the
file system in question (so there is nothing to transition).
Referrals can only come into effect when an absent file system is
encountered at its root.
The examples given in the sections below are somewhat artificial in
that an actual client will not typically do a multi-component look
up, but will have cached information regarding the upper levels of
the name hierarchy. However, these examples are chosen to make the
required behavior clear and easy to put within the scope of a small
number of requests, without getting into a discussion of the details
of how specific clients might choose to cache things.
17.15.1. Referral Example (LOOKUP)
Let us suppose that the following COMPOUND is sent in an environment
in which /this/is/the/path is absent from the target server. This
may be for a number of reasons. It may be that the file system has
moved, or it may be that the target server is functioning mainly, or
solely, to refer clients to the servers on which various file systems
are located.
* PUTROOTFH
* LOOKUP "this"
* LOOKUP "is"
* LOOKUP "the"
* LOOKUP "path"
* GETFH
* GETATTR (fsid, fileid, size, time_modify)
Under the given circumstances, the following will be the result.
* PUTROOTFH --> NFS_OK. The current fh is now the root of the
pseudo-fs.
* LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
* LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
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* LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
* LOOKUP "path" --> NFS_OK. The current fh is for /this/is/the/path
and is within a new, absent file system, but ... the client will
never see the value of that fh.
* GETFH --> NFS4ERR_MOVED. Fails because current fh is in an absent
file system at the start of the operation, and the specification
makes no exception for GETFH.
* GETATTR (fsid, fileid, size, time_modify). Not executed because
the failure of the GETFH stops processing of the COMPOUND.
Given the failure of the GETFH, the client has the job of determining
the root of the absent file system and where to find that file
system, i.e., the server and path relative to that server's root fh.
Note that in this example, the client did not obtain filehandles and
attribute information (e.g., fsid) for the intermediate directories,
so that it would not be sure where the absent file system starts. It
could be the case, for example, that /this/is/the is the root of the
moved file system and that the reason that the look up of "path"
succeeded is that the file system was not absent on that operation
but was moved between the last LOOKUP and the GETFH (since COMPOUND
is not atomic). Even if we had the fsids for all of the intermediate
directories, we could have no way of knowing that /this/is/the/path
was the root of a new file system, since we don't yet have its fsid.
In order to get the necessary information, let us re-send the chain
of LOOKUPs with GETFHs and GETATTRs to at least get the fsids so we
can be sure where the appropriate file system boundaries are. The
client could choose to get fs_locations_info at the same time but in
most cases the client will have a good guess as to where file system
boundaries are (because of where NFS4ERR_MOVED was, and was not,
received) making fetching of fs_locations_info unnecessary.
OP01: PUTROOTFH --> NFS_OK
* Current fh is root of pseudo-fs.
OP02: GETATTR(fsid) --> NFS_OK
* Just for completeness. Normally, clients will know the fsid of
the pseudo-fs as soon as they establish communication with a
server.
OP03: LOOKUP "this" --> NFS_OK
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OP04: GETATTR(fsid) --> NFS_OK
* Get current fsid to see where file system boundaries are. The
fsid will be that for the pseudo-fs in this example, so no
boundary.
OP05: GETFH --> NFS_OK
* Current fh is for /this and is within pseudo-fs.
OP06: LOOKUP "is" --> NFS_OK
* Current fh is for /this/is and is within pseudo-fs.
OP07: GETATTR(fsid) --> NFS_OK
* Get current fsid to see where file system boundaries are. The
fsid will be that for the pseudo-fs in this example, so no
boundary.
OP08: GETFH --> NFS_OK
* Current fh is for /this/is and is within pseudo-fs.
OP09: LOOKUP "the" --> NFS_OK
* Current fh is for /this/is/the and is within pseudo-fs.
OP10: GETATTR(fsid) --> NFS_OK
* Get current fsid to see where file system boundaries are. The
fsid will be that for the pseudo-fs in this example, so no
boundary.
OP11: GETFH --> NFS_OK
* Current fh is for /this/is/the and is within pseudo-fs.
OP12: LOOKUP "path" --> NFS_OK
* Current fh is for /this/is/the/path and is within a new, absent
file system, but ...
* The client will never see the value of that fh.
OP13: GETATTR(fsid, fs_locations_info) --> NFS_OK
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* We are getting the fsid to know where the file system
boundaries are. In this operation, the fsid will be different
than that of the parent directory (which in turn was retrieved
in OP10). Note that the fsid we are given will not necessarily
be preserved at the new location. That fsid might be
different, and in fact the fsid we have for this file system
might be a valid fsid of a different file system on that new
server.
* In this particular case, we are pretty sure anyway that what
has moved is /this/is/the/path rather than /this/is/the since
we have the fsid of the latter and it is that of the pseudo-fs,
which presumably cannot move. However, in other examples, we
might not have this kind of information to rely on (e.g.,
/this/is/the might be a non-pseudo file system separate from
/this/is/the/path), so we need to have other reliable source
information on the boundary of the file system that is moved.
If, for example, the file system /this/is had moved, we would
have a case of migration rather than referral, and once the
boundaries of the migrated file system was clear we could fetch
fs_locations_info.
* We are fetching fs_locations_info because the fact that we got
an NFS4ERR_MOVED at this point means that it is most likely
that this is a referral and we need the destination. Even if
it is the case that /this/is/the is a file system that has
migrated, we will still need the location information for that
file system.
OP14: GETFH --> NFS4ERR_MOVED
* Fails because current fh is in an absent file system at the
start of the operation, and the specification makes no
exception for GETFH. Note that this means the server will
never send the client a filehandle from within an absent file
system.
Given the above, the client knows where the root of the absent file
system is (/this/is/the/path) by noting where the change of fsid
occurred (between "the" and "path"). The fs_locations_info attribute
also gives the client the actual location of the absent file system,
so that the referral can proceed. The server gives the client the
bare minimum of information about the absent file system so that
there will be very little scope for problems of conflict between
information sent by the referring server and information of the file
system's home. No filehandles and very few attributes are present on
the referring server, and the client can treat those it receives as
transient information with the function of enabling the referral.
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17.15.2. Referral Example (READDIR)
Another context in which a client may encounter referrals is when it
does a READDIR on a directory in which some of the sub-directories
are the roots of absent file systems.
Suppose such a directory is read as follows:
* PUTROOTFH
* LOOKUP "this"
* LOOKUP "is"
* LOOKUP "the"
* READDIR (fsid, size, time_modify, mounted_on_fileid)
In this case, because rdattr_error is not requested,
fs_locations_info is not requested, and some of the attributes cannot
be provided, the result will be an NFS4ERR_MOVED error on the
READDIR, with the detailed results as follows:
* PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
* LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
* LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
* LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
* READDIR (fsid, size, time_modify, mounted_on_fileid) -->
NFS4ERR_MOVED. Note that the same error would have been returned
if /this/is/the had migrated, but it is returned because the
directory contains the root of an absent file system.
So now suppose that we re-send with rdattr_error:
* PUTROOTFH
* LOOKUP "this"
* LOOKUP "is"
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* LOOKUP "the"
* READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
The results will be:
* PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
* LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
* LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
* LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
* READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
--> NFS_OK. The attributes for directory entry with the component
named "path" will only contain rdattr_error with the value
NFS4ERR_MOVED, together with an fsid value and a value for
mounted_on_fileid.
Suppose we do another READDIR to get fs_locations_info (although we
could have used a GETATTR directly, as in Section 17.15.1).
* PUTROOTFH
* LOOKUP "this"
* LOOKUP "is"
* LOOKUP "the"
* READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
size, time_modify)
The results would be:
* PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
* LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
* LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
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* LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
* READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
size, time_modify) --> NFS_OK. The attributes will be as shown
below.
The attributes for the directory entry with the component named
"path" will only contain:
* rdattr_error (value: NFS_OK)
* fs_locations_info
* mounted_on_fileid (value: unique fileid within referring file
system)
* fsid (value: unique value within referring server)
The attributes for entry "path" will not contain size or time_modify
because these attributes are not available within an absent file
system.
17.16. The Attribute fs_locations
The fs_locations attribute is structured in the following way:
struct fs_location4 {
utf8str_mixed server<>;
pathname4 rootpath;
};
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
The fs_location4 data type is used to represent the location of a
file system by providing a server name and the path to the root of
the file system within that server's namespace. When a set of
servers have corresponding file systems at the same path within their
namespaces, an array of server names may be provided. An entry in
the server array is a UTF-8 string and represents one of a
traditional DNS host name, IPv4 address, IPv6 address, or a zero-
length string. An IPv4 or IPv6 address is represented as a universal
address (See Section 9.3.9 and [RFC5665]), minus the netid, and
either with or without the trailing ".p1.p2" suffix that represents
the port number. If the suffix is omitted, then the default port,
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2049, SHOULD be assumed. A zero-length string SHOULD be used to
indicate the current address being used for the RPC call. It is not
a requirement that all servers that share the same rootpath be listed
in one fs_location4 instance. The array of server names is provided
for convenience. Servers that share the same rootpath may also be
listed in separate fs_location4 entries in the fs_locations
attribute.
The fs_locations4 data type and the fs_locations attribute each
contain an array of such locations. Since the namespace of each
server may be constructed differently, the "fs_root" field is
provided. The path represented by fs_root represents the location of
the file system in the current server's namespace, i.e., that of the
server from which the fs_locations attribute was obtained. The
fs_root path is meant to aid the client by clearly referencing the
root of the file system whose locations are being reported, no matter
what object within the current file system the current filehandle
designates. The fs_root is simply the pathname the client used to
reach the object on the current server (i.e., the object to which the
fs_locations attribute applies).
When the fs_locations attribute is interrogated and there are no
alternate file system locations, the server SHOULD return a zero-
length array of fs_location4 structures, together with a valid
fs_root.
As an example, suppose there is a replicated file system located at
two servers (servA and servB). At servA, the file system is located
at path /a/b/c. At, servB the file system is located at path /x/y/z.
If the client were to obtain the fs_locations value for the directory
at /a/b/c/d, it might not necessarily know that the file system's
root is located in servA's namespace at /a/b/c. When the client
switches to servB, it will need to determine that the directory it
first referenced at servA is now represented by the path /x/y/z/d on
servB. To facilitate this, the fs_locations attribute provided by
servA would have an fs_root value of /a/b/c and two entries in
fs_locations. One entry in fs_locations will be for itself (servA)
and the other will be for servB with a path of /x/y/z. With this
information, the client is able to substitute /x/y/z for the /a/b/c
at the beginning of its access path and construct /x/y/z/d to use for
the new server.
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Note that there is no requirement that the number of components in
each rootpath be the same; there is no relation between the number of
components in rootpath or fs_root, and none of the components in a
rootpath and fs_root have to be the same. In the above example, we
could have had a third element in the locations array, with server
equal to "servC" and rootpath equal to "/I/II", and a fourth element
in locations with server equal to "servD" and rootpath equal to
"/aleph/beth/gimel/daleth/he".
The relationship between fs_root to a rootpath is that the client
replaces the pathname indicated in fs_root for the current server for
the substitute indicated in rootpath for the new server.
For an example of a referred or migrated file system, suppose there
is a file system located at serv1. At serv1, the file system is
located at /az/buky/vedi/glagoli. The client finds that object at
glagoli has migrated (or is a referral). The client gets the
fs_locations attribute, which contains an fs_root of /az/buky/vedi/
glagoli, and one element in the locations array, with server equal to
serv2, and rootpath equal to /izhitsa/fita. The client replaces
/az/buky/vedi/glagoli with /izhitsa/fita, and uses the latter
pathname on serv2.
Thus, the server MUST return an fs_root that is equal to the path the
client used to reach the object to which the fs_locations attribute
applies. Otherwise, the client cannot determine the new path to use
on the new server.
Since the fs_locations attribute lacks information defining various
attributes of the various file system choices presented, it SHOULD
only be interrogated and used when fs_locations_info is not
available. When fs_locations is used, information about the specific
locations should be assumed based on the following rules.
The following rules are general and apply irrespective of the
context.
* All listed file system instances should be considered as of the
same handle class, if and only if, the current fh_expire_type
attribute does not include the FH4_VOL_MIGRATION bit. Note that
in the case of referral, filehandle issues do not apply since
there can be no filehandles known within the current file system,
nor is there any access to the fh_expire_type attribute on the
referring (absent) file system.
* All listed file system instances should be considered as of the
same fileid class if and only if the fh_expire_type attribute
indicates persistent filehandles and does not include the
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FH4_VOL_MIGRATION bit. Note that in the case of referral, fileid
issues do not apply since there can be no fileids known within the
referring (absent) file system, nor is there any access to the
fh_expire_type attribute.
* All file system instances servers should be considered as of
different change classes.
For other class assignments, handling of file system transitions
depends on the reasons for the transition:
* When the transition is due to migration, that is, the client was
directed to a new file system after receiving an NFS4ERR_MOVED
error, the target should be treated as being of the same write-
verifier class as the source.
* When the transition is due to failover to another replica, that
is, the client selected another replica without receiving an
NFS4ERR_MOVED error, the target should be treated as being of a
different write-verifier class from the source.
The specific choices reflect typical implementation patterns for
failover and controlled migration, respectively. Since other choices
are possible and useful, this information is better obtained by using
fs_locations_info. When a server implementation needs to communicate
other choices, it MUST support the fs_locations_info attribute.
See Section 28 for a discussion on the recommendations for the
security flavor to be used by any GETATTR operation that requests the
fs_locations attribute.
17.17. The Attribute fs_locations_info
The fs_locations_info attribute is intended as a more functional
replacement for the fs_locations attribute, which will continue to
exist and be supported. Clients can use it to get a more complete
set of data about alternative file system locations, including
additional network paths to access replicas in use and additional
replicas. When the server does not support fs_locations_info,
fs_locations can be used to get a subset of the data. A server that
supports fs_locations_info MUST support fs_locations as well.
There is additional data present in fs_locations_info that is not
available in fs_locations:
* Attribute continuity information. This information will allow a
client to select a replica that meets the transparency
requirements of the applications accessing the data and to
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leverage optimizations due to the server guarantees of attribute
continuity (e.g., if the change attribute of a file of the file
system is continuous between multiple replicas, the client does
not have to invalidate the file's cache when switching to a
different replica).
* File system identity information that indicates when multiple
replicas, from the client's point of view, correspond to the same
target file system, allowing them to be used interchangeably,
without disruption, as distinct synchronized replicas of the same
file data.
Note that having two replicas with common identity information is
distinct from the case of two (trunked) paths to the same replica.
* Information that will bear on the suitability of various replicas,
depending on the use that the client intends. For example, many
applications need an absolutely up-to-date copy (e.g., those that
write), while others may only need access to the most up-to-date
copy reasonably available.
* Server-derived preference information for replicas, which can be
used to implement load-balancing while giving the client the
entire file system list to be used in case the primary fails.
The fs_locations_info attribute is structured similarly to the
fs_locations attribute. A top-level structure (fs_locations_info4)
contains the entire attribute including the root pathname of the file
system and an array of lower-level structures that define replicas
that share a common rootpath on their respective servers. The lower-
level structure in turn (fs_locations_item4) contains a specific
pathname and information on one or more individual network access
paths. For that last, lowest level, fs_locations_info has an
fs_locations_server4 structure that contains per-server-replica
information in addition to the file system location entry. This per-
server-replica information includes a nominally opaque array,
fls_info, within which specific pieces of information are located at
the specific indices listed below.
Two fs_location_server4 entries that are within different
fs_location_item4 structures are never trunkable, while two entries
within in the same fs_location_item4 structure might or might not be
trunkable. Two entries that are trunkable will have identical
identity information, although, as noted above, the converse is not
the case.
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The attribute will always contain at least a single
fs_locations_server entry. Typically, there will be an entry with
the FS4LIGF_CUR_REQ flag set, although in the case of a referral
there will be no entry with that flag set.
It should be noted that fs_locations_info attributes returned by
servers for various replicas may differ for various reasons. One
server may know about a set of replicas that are not known to other
servers. Further, compatibility attributes may differ. Filehandles
might be of the same class going from replica A to replica B but not
going in the reverse direction. This might happen because the
filehandles are the same, but replica B's server implementation might
not have provision to note and report that equivalence.
The fs_locations_info attribute consists of a root pathname
(fli_fs_root, just like fs_root in the fs_locations attribute),
together with an array of fs_location_item4 structures. The
fs_location_item4 structures in turn consist of a root pathname
(fli_rootpath) together with an array (fli_entries) of elements of
data type fs_locations_server4, all defined as follows.
/*
* Defines an individual server access path
*/
struct fs_locations_server4 {
int32_t fls_currency;
opaque fls_info<>;
utf8str_mixed fls_server;
};
/*
* Byte indices of items within
* fls_info: flag fields, class numbers,
* bytes indicating ranks and orders.
*/
const FSLI4BX_GFLAGS = 0;
const FSLI4BX_TFLAGS = 1;
const FSLI4BX_CLSIMUL = 2;
const FSLI4BX_CLHANDLE = 3;
const FSLI4BX_CLFILEID = 4;
const FSLI4BX_CLWRITEVER = 5;
const FSLI4BX_CLCHANGE = 6;
const FSLI4BX_CLREADDIR = 7;
const FSLI4BX_READRANK = 8;
const FSLI4BX_WRITERANK = 9;
const FSLI4BX_READORDER = 10;
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const FSLI4BX_WRITEORDER = 11;
/*
* Bits defined within the general flag byte.
*/
const FSLI4GF_WRITABLE = 0x01;
const FSLI4GF_CUR_REQ = 0x02;
const FSLI4GF_ABSENT = 0x04;
const FSLI4GF_GOING = 0x08;
const FSLI4GF_SPLIT = 0x10;
/*
* Bits defined within the transport flag byte.
*/
const FSLI4TF_RDMA = 0x01;
/*
* Defines a set of replicas sharing
* a common value of the rootpath
* within the corresponding
* single-server namespaces.
*/
struct fs_locations_item4 {
fs_locations_server4 fli_entries<>;
pathname4 fli_rootpath;
};
/*
* Defines the overall structure of
* the fs_locations_info attribute.
*/
struct fs_locations_info4 {
uint32_t fli_flags;
int32_t fli_valid_for;
pathname4 fli_fs_root;
fs_locations_item4 fli_items<>;
};
/*
* Flag bits in fli_flags.
*/
const FSLI4IF_VAR_SUB = 0x00000001;
typedef fs_locations_info4 fattr4_fs_locations_info;
As noted above, the fs_locations_info attribute, when supported, may
be requested of absent file systems without causing NFS4ERR_MOVED to
be returned. It is generally expected that it will be available for
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both present and absent file systems even if only a single
fs_locations_server4 entry is present, designating the current
(present) file system, or two fs_locations_server4 entries
designating the previous location of an absent file system (the one
just referenced) and its successor location. Servers are strongly
urged to support this attribute on all file systems if they support
it on any file system.
The data presented in the fs_locations_info attribute may be obtained
by the server in any number of ways, including specification by the
administrator or by current protocols for transferring data among
replicas and protocols not yet developed. NFSv4.1 only defines how
this information is presented by the server to the client.
17.17.1. The fs_locations_server4 Structure
The fs_locations_server4 structure consists of the following items in
addition to the fls_server field, which specifies a network address
or set of addresses to be used to access the specified file system.
Note that both of these items (i.e., fls_currency and fls_info)
specify attributes of the file system replica and should not be
different when there are multiple fs_locations_server4 structures,
each specifying a network path to the chosen replica, for the same
replica.
When these values are different in two fs_locations_server4
structures, a client has no basis for choosing one over the other and
is best off simply ignoring both entries, whether these entries apply
to migration replication or referral. When there are more than two
such entries, majority voting can be used to exclude a single
erroneous entry from consideration. In the case in which trunking
information is provided for a replica currently being accessed, the
additional trunked addresses can be ignored while access continues on
the address currently being used, even if the entry corresponding to
that path might be considered invalid.
* An indication of how up-to-date the file system is (fls_currency)
in seconds. This value is relative to the master copy. A
negative value indicates that the server is unable to give any
reasonably useful value here. A value of zero indicates that the
file system is the actual writable data or a reliably coherent and
fully up-to-date copy. Positive values indicate how out-of-date
this copy can normally be before it is considered for update.
Such a value is not a guarantee that such updates will always be
performed on the required schedule but instead serves as a hint
about how far the copy of the data would be expected to be behind
the most up-to-date copy.
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* A counted array of one-byte values (fls_info) containing
information about the particular file system instance. This data
includes general flags, transport capability flags, file system
equivalence class information, and selection priority information.
The encoding will be discussed below.
* The server string (fls_server). For the case of the replica
currently being accessed (via GETATTR), a zero-length string MAY
be used to indicate the current address being used for the RPC
call. The fls_server field can also be an IPv4 or IPv6 address,
formatted the same way as an IPv4 or IPv6 address in the "server"
field of the fs_location4 data type (see Section 17.16).
With the exception of the transport-flag field (at offset
FSLI4BX_TFLAGS with the fls_info array), all of this data defined in
this specification applies to the replica specified by the entry,
rather than the specific network path used to access it. The
classification of data in extensions to this data is discussed below.
Data within the fls_info array is in the form of 8-bit data items
with constants giving the offsets within the array of various values
describing this particular file system instance. This style of
definition was chosen, in preference to explicit XDR structure
definitions for these values, for a number of reasons.
* The kinds of data in the fls_info array, representing flags, file
system classes, and priorities among sets of file systems
representing the same data, are such that 8 bits provide a quite
acceptable range of values. Even where there might be more than
256 such file system instances, having more than 256 distinct
classes or priorities is unlikely.
* Explicit definition of the various specific data items within XDR
would limit expandability in that any extension within would
require yet another attribute, leading to specification and
implementation clumsiness. In the context of the NFSv4 extension
model in effect at the time fs_locations_info was designed (i.e.,
that which is described in [RFC5661]), this would necessitate a
new minor version to effect any Standards Track extension to the
data in fls_info.
The set of fls_info data is subject to expansion in a future minor
version or in a Standards Track RFC within the context of a single
minor version. The server SHOULD NOT send and the client MUST NOT
use indices within the fls_info array or flag bits that are not
defined in Standards Track RFCs.
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In light of the new extension model defined in [RFC8178] and the fact
that the individual items within fls_info are not explicitly
referenced in the XDR, the following practices should be followed
when extending or otherwise changing the structure of the data
returned in fls_info within the scope of a single minor version:
* All extensions need to be described by Standards Track documents.
There is no need for such documents to be marked as updating
[RFC5661], [RFC8881], or this document.
* It needs to be made clear whether the information in any added
data items applies to the replica specified by the entry or to the
specific network paths specified in the entry.
* There needs to be a reliable way defined to determine whether the
server is aware of the extension. This may be based on the length
field of the fls_info array, but it is more flexible to provide
fs-scope or server-scope attributes to indicate what extensions
are provided.
This encoding scheme can be adapted to the specification of multi-
byte numeric values, even though none are currently defined. If
extensions are made via Standards Track RFCs, multi-byte quantities
will be encoded as a range of bytes with a range of indices, with the
byte interpreted in big-endian byte order. Further, any such index
assignments will be constrained by the need for the relevant
quantities not to cross XDR word boundaries.
The fls_info array currently contains:
* Two 8-bit flag fields, one devoted to general file-system
characteristics and a second reserved for transport-related
capabilities.
* Six 8-bit class values that define various file system equivalence
classes as explained below.
* Four 8-bit priority values that govern file system selection as
explained below.
The general file system characteristics flag (at byte index
FSLI4BX_GFLAGS) has the following bits defined within it:
* FSLI4GF_WRITABLE indicates that this file system target is
writable, allowing it to be selected by clients that may need to
write on this file system. When the current file system instance
is writable and is defined as of the same simultaneous use class
(as specified by the value at index FSLI4BX_CLSIMUL) to which the
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client was previously writing, then it must incorporate within its
data any committed write made on the source file system instance.
See Section 17.11.6, which discusses the write-verifier class.
While there is no harm in not setting this flag for a file system
that turns out to be writable, turning the flag on for a read-only
file system can cause problems for clients that select a migration
or replication target based on the flag and then find themselves
unable to write.
* FSLI4GF_CUR_REQ indicates that this replica is the one on which
the request is being made. Only a single server entry may have
this flag set and, in the case of a referral, no entry will have
it set. Note that this flag might be set even if the request was
made on a network access path different from any of those
specified in the current entry.
* FSLI4GF_ABSENT indicates that this entry corresponds to an absent
file system replica. It can only be set if FSLI4GF_CUR_REQ is
set. When both such bits are set, it indicates that a file system
instance is not usable but that the information in the entry can
be used to determine the sorts of continuity available when
switching from this replica to other possible replicas. Since
this bit can only be true if FSLI4GF_CUR_REQ is true, the value
could be determined using the fs_status attribute, but the
information is also made available here for the convenience of the
client. An entry with this bit, since it represents a true file
system (albeit absent), does not appear in the event of a
referral, but only when a file system has been accessed at this
location and has subsequently been migrated.
* FSLI4GF_GOING indicates that a replica, while still available,
should not be used further. The client, if using it, should make
an orderly transfer to another file system instance as
expeditiously as possible. It is expected that file systems going
out of service will be announced as FSLI4GF_GOING some time before
the actual loss of service. It is also expected that the
fli_valid_for value will be sufficiently small to allow clients to
detect and act on scheduled events, while large enough that the
cost of the requests to fetch the fs_locations_info values will
not be excessive. Values on the order of ten minutes seem
reasonable.
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When this flag is seen as part of a transition into a new file
system, a client might choose to transfer immediately to another
replica, or it may reference the current file system and only
transition when a migration event occurs. Similarly, when this
flag appears as a replica in the referral, clients would likely
avoid being referred to this instance whenever there is another
choice.
This flag, like the other items within fls_info, applies to the
replica rather than to a particular path to that replica. When it
appears, a transition to a new replica, rather than to a different
path to the same replica, is indicated.
* FSLI4GF_SPLIT indicates that when a transition occurs from the
current file system instance to this one, the replacement may
consist of multiple file systems. In this case, the client has to
be prepared for the possibility that objects on the same file
system before migration will be on different ones after. Note
that FSLI4GF_SPLIT is not incompatible with the file systems
belonging to the same fileid class since, if one has a set of
fileids that are unique within a file system, each subset assigned
to a smaller file system after migration would not have any
conflicts internal to that file system.
A client, in the case of a split file system, will interrogate
existing files with which it has continuing connection (it is free
to simply forget cached filehandles). If the client remembers the
directory filehandle associated with each open file, it may
proceed upward using LOOKUPP to find the new file system
boundaries. Note that in the event of a referral, there will not
be any such files and so these actions will not be performed.
Instead, a reference to a portion of the original file system now
split off into other file systems will encounter an fsid change
and possibly a further referral.
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Once the client recognizes that one file system has been split
into two, it can prevent the disruption of running applications by
presenting the two file systems as a single one until a convenient
point to recognize the transition, such as a restart. This would
require a mapping from the server's fsids to fsids as seen by the
client, but this is already necessary for other reasons. As noted
above, existing fileids within the two descendant file systems
will not conflict. Providing non-conflicting fileids for newly
created files on the split file systems is the responsibility of
the server (or servers working in concert). The server can encode
filehandles such that filehandles generated before the split event
can be discerned from those generated after the split, allowing
the server to determine when the need for emulating two file
systems as one is over.
Although it is possible for this flag to be present in the event
of referral, it would generally be of little interest to the
client, since the client is not expected to have information
regarding the current contents of the absent file system.
The transport-flag field (at byte index FSLI4BX_TFLAGS) contains the
following bits related to the transport capabilities of the specific
network path(s) specified by the entry:
* FSLI4TF_RDMA indicates that any specified network paths provide
NFSv4.1 clients access using an RDMA-capable transport.
Attribute continuity and file system identity information are
expressed by defining equivalence relations on the sets of file
systems presented to the client. Each such relation is expressed as
a set of file system equivalence classes. For each relation, a file
system has an 8-bit class number. Two file systems belong to the
same class if both have identical non-zero class numbers. Zero is
treated as non-matching. Most often, the relevant question for the
client will be whether a given replica is identical to / continuous
with the current one in a given respect, but the information should
be available also as to whether two other replicas match in that
respect as well.
The following fields specify the file system's class numbers for the
equivalence relations used in determining the nature of file system
transitions. See Sections 17.9 through 17.14 and their various
subsections for details about how this information is to be used.
Servers may assign these values as they wish, so long as file system
instances that share the same value have the specified relationship
to one another; conversely, file systems that have the specified
relationship to one another share a common class value. As each
instance entry is added, the relationships of this instance to
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previously entered instances can be consulted, and if one is found
that bears the specified relationship, that entry's class value can
be copied to the new entry. When no such previous entry exists, a
new value for that byte index (not previously used) can be selected,
most likely by incrementing the value of the last class value
assigned for that index.
* The field with byte index FSLI4BX_CLSIMUL defines the
simultaneous-use class for the file system.
* The field with byte index FSLI4BX_CLHANDLE defines the handle
class for the file system.
* The field with byte index FSLI4BX_CLFILEID defines the fileid
class for the file system.
* The field with byte index FSLI4BX_CLWRITEVER defines the write-
verifier class for the file system.
* The field with byte index FSLI4BX_CLCHANGE defines the change
class for the file system.
* The field with byte index FSLI4BX_CLREADDIR defines the readdir
class for the file system.
Server-specified preference information is also provided via 8-bit
values within the fls_info array. The values provide a rank and an
order (See below) to be used with separate values specifiable for the
cases of read-only and writable file systems. These values are
compared for different file systems to establish the server-specified
preference, with lower values indicating "more preferred".
Rank is used to express a strict server-imposed ordering on clients,
with lower values indicating "more preferred". Clients should
attempt to use all replicas with a given rank before they use one
with a higher rank. Only if all of those file systems are
unavailable should the client proceed to those of a higher rank.
Because specifying a rank will override client preferences, servers
should be conservative about using this mechanism, particularly when
the environment is one in which client communication characteristics
are neither tightly controlled nor visible to the server.
Within a rank, the order value is used to specify the server's
preference to guide the client's selection when the client's own
preferences are not controlling, with lower values of order
indicating "more preferred". If replicas are approximately equal in
all respects, clients should defer to the order specified by the
server. When clients look at server latency as part of their
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selection, they are free to use this criterion, but it is suggested
that when latency differences are not significant, the server-
specified order should guide selection.
* The field at byte index FSLI4BX_READRANK gives the rank value to
be used for read-only access.
* The field at byte index FSLI4BX_READORDER gives the order value to
be used for read-only access.
* The field at byte index FSLI4BX_WRITERANK gives the rank value to
be used for writable access.
* The field at byte index FSLI4BX_WRITEORDER gives the order value
to be used for writable access.
Depending on the potential need for write access by a given client,
one of the pairs of rank and order values is used. The read rank and
order should only be used if the client knows that only reading will
ever be done or if it is prepared to switch to a different replica in
the event that any write access capability is required in the future.
17.17.2. The fs_locations_info4 Structure
The fs_locations_info4 structure, encoding the fs_locations_info
attribute, contains the following:
* The fli_flags field, which contains general flags that affect the
interpretation of this fs_locations_info4 structure and all
fs_locations_item4 structures within it. The only flag currently
defined is FSLI4IF_VAR_SUB. All bits in the fli_flags field that
are not defined should always be returned as zero.
* The fli_fs_root field, which contains the pathname of the root of
the current file system on the current server, just as it does in
the fs_locations4 structure.
* An array called fli_items of fs_locations4_item structures, which
contain information about replicas of the current file system.
Where the current file system is actually present, or has been
present, i.e., this is not a referral situation, one of the
fs_locations_item4 structures will contain an fs_locations_server4
for the current server. This structure will have FSLI4GF_ABSENT
set if the current file system is absent, i.e., normal access to
it will return NFS4ERR_MOVED.
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* The fli_valid_for field specifies a time in seconds for which it
is reasonable for a client to use the fs_locations_info attribute
without refetch. The fli_valid_for value does not provide a
guarantee of validity since servers can unexpectedly go out of
service or become inaccessible for any number of reasons. Clients
are well-advised to refetch this information for an actively
accessed file system at every fli_valid_for seconds. This is
particularly important when file system replicas may go out of
service in a controlled way using the FSLI4GF_GOING flag to
communicate an ongoing change. The server should set
fli_valid_for to a value that allows well-behaved clients to
notice the FSLI4GF_GOING flag and make an orderly switch before
the loss of service becomes effective. If this value is zero,
then no refetch interval is appropriate and the client need not
refetch this data on any particular schedule. In the event of a
transition to a new file system instance, a new value of the
fs_locations_info attribute will be fetched at the destination.
It is to be expected that this may have a different fli_valid_for
value, which the client should then use in the same fashion as the
previous value. Because a refetch of the attribute causes
information from all component entries to be refetched, the server
will typically provide a low value for this field if any of the
replicas are likely to go out of service in a short time frame.
Note that, because of the ability of the server to return
NFS4ERR_MOVED to trigger the use of different paths, when
alternate trunked paths are available, there is generally no need
to use low values of fli_valid_for in connection with the
management of alternate paths to the same replica.
The FSLI4IF_VAR_SUB flag within fli_flags controls whether variable
substitution is to be enabled. See Section 17.17.3 for an
explanation of variable substitution.
17.17.3. The fs_locations_item4 Structure
The fs_locations_item4 structure contains a pathname (in the field
fli_rootpath) that encodes the path of the target file system
replicas on the set of servers designated by the included
fs_locations_server4 entries. The precise manner in which this
target location is specified depends on the value of the
FSLI4IF_VAR_SUB flag within the associated fs_locations_info4
structure.
If this flag is not set, then fli_rootpath simply designates the
location of the target file system within each server's single-server
namespace just as it does for the rootpath within the fs_location4
structure. When this bit is set, however, component entries of a
certain form are subject to client-specific variable substitution so
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as to allow a degree of namespace non-uniformity in order to
accommodate the selection of client-specific file system targets to
adapt to different client architectures or other characteristics.
When such substitution is in effect, a variable beginning with the
string "${" and ending with the string "}" and containing a colon is
to be replaced by the client-specific value associated with that
variable. The string "unknown" should be used by the client when it
has no value for such a variable. The pathname resulting from such
substitutions is used to designate the target file system, so that
different clients may have different file systems, corresponding to
that location in the multi-server namespace.
As mentioned above, such substituted pathname variables contain a
colon. The part before the colon is to be a DNS domain name, and the
part after is to be a case-insensitive alphanumeric string.
Where the domain is "ietf.org", only variable names defined in this
document or subsequent Standards Track RFCs are subject to such
substitution. Organizations are free to use their domain names to
create their own sets of client-specific variables, to be subject to
such substitution. In cases where such variables are intended to be
used more broadly than a single organization, publication of an
Informational RFC defining such variables is RECOMMENDED.
The variable ${ietf.org:CPU_ARCH} is used to denote that the CPU
architecture object files are compiled. This specification does not
limit the acceptable values (except that they must be valid UTF-8
strings), but such values as "x86", "x86_64", and "sparc" would be
expected to be used in line with industry practice.
The variable ${ietf.org:OS_TYPE} is used to denote the operating
system, and thus the kernel and library APIs, for which code might be
compiled. This specification does not limit the acceptable values
(except that they must be valid UTF-8 strings), but such values as
"linux" and "freebsd" would be expected to be used in line with
industry practice.
The variable ${ietf.org:OS_VERSION} is used to denote the operating
system version, and thus the specific details of versioned
interfaces, for which code might be compiled. This specification
does not limit the acceptable values (except that they must be valid
UTF-8 strings). However, combinations of numbers and letters with
interspersed dots would be expected to be used in line with industry
practice, with the details of the version format depending on the
specific value of the variable ${ietf.org:OS_TYPE} with which it is
used.
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Use of these variables could result in the direction of different
clients to different file systems on the same server, as appropriate
to particular clients. In cases in which the target file systems are
located on different servers, a single server could serve as a
referral point so that each valid combination of variable values
would designate a referral hosted on a single server, with the
targets of those referrals on a number of different servers.
Because namespace administration is affected by the values selected
to substitute for various variables, clients should provide
convenient means of determining what variable substitutions a client
will implement, as well as, where appropriate, providing means to
control the substitutions to be used. The exact means by which this
will be done is outside the scope of this specification.
Although variable substitution is most suitable for use in the
context of referrals, it may be used in the context of replication
and migration. If it is used in these contexts, the server must
ensure that no matter what values the client presents for the
substituted variables, the result is always a valid successor file
system instance to that from which a transition is occurring, i.e.,
that the data is identical or represents a later image of a writable
file system.
Note that when fli_rootpath is a null pathname (that is, one with
zero components), the file system designated is at the root of the
specified server, whether or not the FSLI4IF_VAR_SUB flag within the
associated fs_locations_info4 structure is set.
17.18. The Attribute fs_status
In an environment in which multiple copies of the same basic set of
data are available, information regarding the particular source of
such data and the relationships among different copies can be very
helpful in providing consistent data to applications.
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enum fs4_status_type {
STATUS4_FIXED = 1,
STATUS4_UPDATED = 2,
STATUS4_VERSIONED = 3,
STATUS4_WRITABLE = 4,
STATUS4_REFERRAL = 5
};
struct fs4_status {
bool fss_absent;
fs4_status_type fss_type;
utf8str_cs fss_source;
utf8str_cs fss_current;
int32_t fss_age;
nfstime4 fss_version;
};
The boolean fss_absent indicates whether the file system is currently
absent. This value will be set if the file system was previously
present and becomes absent, or if the file system has never been
present and the type is STATUS4_REFERRAL. When this boolean is set
and the type is not STATUS4_REFERRAL, the remaining information in
the fs4_status reflects that last valid when the file system was
present.
The fss_type field indicates the kind of file system image
represented. This is of particular importance when using the version
values to determine appropriate succession of file system images.
When fss_absent is set, and the file system was previously present,
the value of fss_type reflected is that when the file was last
present. Five values are distinguished:
* STATUS4_FIXED, which indicates a read-only image in the sense that
it will never change. The possibility is allowed that, as a
result of migration or switch to a different image, changed data
can be accessed, but within the confines of this instance, no
change is allowed. The client can use this fact to cache
aggressively.
* STATUS4_VERSIONED, which indicates that the image, like the
STATUS4_UPDATED case, is updated externally, but it provides a
guarantee that the server will carefully update an associated
version value so that the client can protect itself from a
situation in which it reads data from one version of the file
system and then later reads data from an earlier version of the
same file system. See below for a discussion of how this can be
done.
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* STATUS4_UPDATED, which indicates an image that cannot be updated
by the user writing to it but that may be changed externally,
typically because it is a periodically updated copy of another
writable file system somewhere else. In this case, version
information is not provided, and the client does not have the
responsibility of making sure that this version only advances upon
a file system instance transition. In this case, it is the
responsibility of the server to make sure that the data presented
after a file system instance transition is a proper successor
image and includes all changes seen by the client and any change
made before all such changes.
* STATUS4_WRITABLE, which indicates that the file system is an
actual writable one. The client need not, of course, actually
write to the file system, but once it does, it should not accept a
transition to anything other than a writable instance of that same
file system.
* STATUS4_REFERRAL, which indicates that the file system in question
is absent and has never been present on this server.
Note that in the STATUS4_UPDATED and STATUS4_VERSIONED cases, the
server is responsible for the appropriate handling of locks that are
inconsistent with external changes to delegations. If a server gives
out delegations, they SHOULD be recalled before an inconsistent
change is made to the data, and MUST be revoked if this is not
possible. Similarly, if an OPEN is inconsistent with data that is
changed (the OPEN has OPEN4_SHARE_DENY_WRITE/OPEN4_SHARE_DENY_BOTH
and the data is changed), that OPEN SHOULD be considered
administratively revoked.
The opaque strings fss_source and fss_current provide a way of
presenting information about the source of the file system image
being present. It is not intended that the client do anything with
this information other than make it available to administrative
tools. It is intended that this information be helpful when
researching possible problems with a file system image that might
arise when it is unclear if the correct image is being accessed and,
if not, how that image came to be made. This kind of diagnostic
information will be helpful, if, as seems likely, copies of file
systems are made in many different ways (e.g., simple user-level
copies, file-system-level point-in-time copies, clones of the
underlying storage), under a variety of administrative arrangements.
In such environments, determining how a given set of data was
constructed can be very helpful in resolving problems.
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The opaque string fss_source is used to indicate the source of a
given file system with the expectation that tools capable of creating
a file system image propagate this information, when possible. It is
understood that this may not always be possible since a user-level
copy may be thought of as creating a new data set and the tools used
may have no mechanism to propagate this data. When a file system is
initially created, it is desirable to associate with it data
regarding how the file system was created, where it was created, who
created it, etc. Making this information available in this attribute
in a human-readable string will be helpful for applications and
system administrators and will also serve to make it available when
the original file system is used to make subsequent copies.
The opaque string fss_current should provide whatever information is
available about the source of the current copy. Such information
includes the tool creating it, any relevant parameters to that tool,
the time at which the copy was done, the user making the change, the
server on which the change was made, etc. All information should be
in a human-readable string.
The field fss_age provides an indication of how out-of-date the file
system currently is with respect to its ultimate data source (in case
of cascading data updates). This complements the fls_currency field
of fs_locations_server4 (See Section 17.17) in the following way: the
information in fls_currency gives a bound for how out of date the
data in a file system might typically get, while the value in fss_age
gives a bound on how out-of-date that data actually is. Negative
values imply that no information is available. A zero means that
this data is known to be current. A positive value means that this
data is known to be no older than that number of seconds with respect
to the ultimate data source. Using this value, the client may be
able to decide that a data copy is too old, so that it may search for
a newer version to use.
The fss_version field provides a version identification, in the form
of a time value, such that successive versions always have later time
values. When the fs_type is anything other than STATUS4_VERSIONED,
the server may provide such a value, but there is no guarantee as to
its validity and clients will not use it except to provide additional
information to add to fss_source and fss_current.
When fss_type is STATUS4_VERSIONED, servers SHOULD provide a value of
fss_version that progresses monotonically whenever any new version of
the data is established. This allows the client, if reliable image
progression is important to it, to fetch this attribute as part of
each COMPOUND where data or metadata from the file system is used.
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When it is important to the client to make sure that only valid
successor images are accepted, it must make sure that it does not
read data or metadata from the file system without updating its sense
of the current state of the image. This is to avoid the possibility
that the fs_status that the client holds will be one for an earlier
image, which would cause the client to accept a new file system
instance that is later than that but still earlier than the updated
data read by the client.
In order to accept valid images reliably, the client must do a
GETATTR of the fs_status attribute that follows any interrogation of
data or metadata within the file system in question. Often this is
most conveniently done by appending such a GETATTR after all other
operations that reference a given file system. When errors occur
between reading file system data and performing such a GETATTR, care
must be exercised to make sure that the data in question is not used
before obtaining the proper fs_status value. In this connection,
when an OPEN is done within such a versioned file system and the
associated GETATTR of fs_status is not successfully completed, the
open file in question must not be accessed until that fs_status is
fetched.
The procedure above will ensure that before using any data from the
file system the client has in hand a newly-fetched current version of
the file system image. Multiple values for multiple requests in
flight can be resolved by assembling them into the required partial
order (and the elements should form a total order within the partial
order) and using the last. The client may then, when switching among
file system instances, decline to use an instance that does not have
an fss_type of STATUS4_VERSIONED or whose fss_version field is
earlier than the last one obtained from the predecessor file system
instance.
18. Parallel NFS (pNFS)
18.1. Introduction
pNFS is an OPTIONAL feature within NFSv4.1. The pNFS feature
provides for the use of multiple layout types within a common
framework. Within this framework, each layout type specification is
obliged to define how the general features of pNFS are to be
addressed within that layout type. The requirements that needed to
be addressed by the specification for each layout type are described
in Section 19.1. The normative character of these obligations is
discussed in Section 18.3
The description of the pNFS-related features are divided multiple
documents and multiple top-level sections in this document:
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* Common aspects of PNFS that apply to all layout types are
described in Section 18.
* The specifics that might vary among different layout types are
discussed in Section 19.
* The files layout type is described in Section 20.
Because the data access protocol for this layout type is a variant
of NFSv4.1, it is described in this document. However, it should
not be assumed that this placement makes this layout type more
important or makes it somehow not optional.
* A number of other layout types made part of NFSv4,1 are described
in separate layout type specification documents (i.e. [RFC5663],
[RFC5664]).
* Additional layout types are part of NFsv4.2 and are described in
their own layout type specification documents. The addition of
further such layout types is provided for in Section 29.5.
Some Layout types allow direct access to file data's location
including the possibility of unmediated access to the storage devices
containing file data. Others allow the direction of IO requests to
the appropriate data server (considered as a type of data storage
device).
When file data for a single NFSv4 server (often referred to as the
metadata server) is stored on multiple and/or higher-throughput
storage devices (compared to the primary server's throughput
capability), these approaches can provide significantly better file
access performance. The relationship among multiple clients, a
single server (assuming the role of a metadata server), and multiple
file storage devices for pNFS (some of which act as data servers by
implementing support for file access protocols), is shown in
Figure 1.
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+-----------+
|+-----------+ +-----------+
||+-----------+ | |
||| | NFSv4.1 + pNFS | |
+|| Clients |<------------------------------>| Server |
+| | | |
+-----------+ | |
||| +-----------+
||| |
||| |
||| Data Access +-------------+ |
||| Protocol |+-------------+ |
||+----------------||+------------+ Control |
|+-----------------||| | Protocol |
+------------------+|| Data |------------+
|| Storage ||
|| Devices ||
+------------+
Figure 1
In this approach, the clients, the metadata server, and data storage
devices work together to provide file data access and to deny it to
those not appropriately authorized. The specifics of the
responsibility of the participants to contribute to that
authorization are defined in the layout type specification for the
layouts used to perform IO operations.
This approach is in contrast to NFSv4 without pNFS, where this is
primarily the server's responsibility while some of this
responsibility may be delegated to the client under strictly
specified conditions.
See Section 18.4.5 for a discussion of the Data Access Protocols.
See Section 18.4.6 for a discussion of Control Protocols which
provide the mechanisms used to coordinate the metadata server and the
data storage devices.
pNFS involves OPTIONAL operations that manage protocol objects called
'layouts' (Section 18.2) that contain a byte-range and location
information. Layouts are managed in a fashion similar to NFSv4.1
data delegations. For example, layouts are leased, recallable, and
revocable. Note that layouts are distinct abstractions and are
manipulated with new operations. When a client holds a layout, it is
granted the ability to directly access the byte-range at the storage
location designated in the layout.
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There are interactions between layouts and other NFSv4.1 abstractions
such as data delegations and byte-range locking. It is the
responsibility of the layout type specification to address these
issues as described in Section 19.1.10
18.2. Layout Types
A layout describes the mapping of a file's data to the file data
devices that hold the data. Each layout is of a particular type
(data type layouttype4, see Section 9.3.13). The existence of
multiple layout type allows for multiple pNFS-based features to
handle different data access protocols, such as those associated with
the various supported layout types. A metadata server that supports
pNFS MUST support at least one layout type. A private sub-range of
the layout type namespace is also defined. Values from the private
layout type range MAY be used for internal testing or experimentation
(See Section 9.3.13).
Requests for pNFS-related operations will often specify a layout
type. Examples of such operations are GETDEVICEINFO and LAYOUTGET.
The response for these operations will include structures such as a
device_addr4 or a layout4, each of which includes a layout type
within it. The layout type sent by the server MUST always be the
same one requested by the client. When a server sends a response
that includes a different layout type, the client SHOULD ignore the
response and behave as if the server had returned an error response.
18.3. Normative Layout Specification Terminology
As described in Section 1.1, the keywords defined by [RFC2119] and
[RFC8174] have special meanings that this document intends to adhere
to. However, due to the nature of Sections Section 19
format="counter"/> and 29.5.3 together with some special
circumstances resulting from the fact that complementations are
described indirectly, there are some complexities thar it is
important to take note of:
* Where this document does not directly specify implementation
requirements, use of these capitalized terms is often not
appropriate since the guidance given in this document does not
directly affect interoperability.
* In this document, what authors of RFCs defining new layout types
need to do is stated without these specialized terms.
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Although it is necessary to follow this guidance to provide
successful pNFS layout type specifications, that sort of necessity
is not of the sort defined as applicable to the use of the
keywords defined in [RFC2119] [RFC8174].
The fact that these capitalized terms are not used should not be
interpreted as indicating that this guidance does not need to be
followed or is somehow not important.
Another way of stating this is that the material in Section 19.1
is "normative",, as that word is normally used> This is so even
though it is often assumed that text not using these terms is non-
normative and that the implementer/author is free to disregard it.
* When one of these upper-case keywords defined in [RFC2119]
[RFC8174]. is used in Section 19.1,' it is in the context of a
rule directed to an implementer of client using a new layout type
or a metadata server or data storage device implementing a new
layout type, or in a quotation, sometimes indirect, from another
document.
Overall, there are three types of normative statements used in
Section 19.1:
* Requirements that applies to implementations.
These are stated using RFC2119-defined keywords.
* Requirements that apply to those defining layout types.
These are stated without using RFC2119-defined keywords.
Nevertheless, they establish expectations that layout type
specification need to satisfy (i.e norms) and are therefore
described as "normative", the common use of that word in other
IETF documents notwithstanding.
* Requirements which are general in that implementations need to
conform to them, with the specific means by which the requirement
is to be met left to layout type specification.
In this case, it is the responsibility of the layout type
specification to clearly provide a description of the means to be
used, the provision of which is obligatory despite the absence of
RFC2119-defined terms.
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18.4. pNFS Definitions
NFSv4.1's pNFS feature provides parallel data access to a file system
that stripes or otherwise divides its content across multiple storage
servers. pNFS separates the file system protocol processing into two
parts: metadata processing and data processing. Data consist of the
contents of regular files that may be divided across storage servers.
Division of data occurs in at least two ways: on a file-by-file basis
and, within sufficiently large files, on a block-by-block basis. In
contrast, divided access to metadata by pNFS clients is not provided
in NFSv4.1, even though the file system back end of a pNFS server
might stripe metadata. Metadata consist of everything other than
file data, including the contents of non-regular files (e.g.,
directories); see Section 18.4.1. The metadata functionality is
implemented by an NFSv4.1 server that supports pNFS and the
operations described in Section 25; such a server is called a
metadata server (Section 18.4.2).
The data functionality is implemented by one or more data storage
devices, each of which is accessed by the client via a file access
protocol. Definition of this protocol is the responsibility of the
layout type specification as discussed in Section 19.1.
New terms are introduced to the NFSv4.1 nomenclature and existing
terms are clarified to allow for the description of the pNFS feature
suite.
18.4.1. Metadata
Information about a file system object, such as its name, location
within the namespace, owner, ACL, and other attributes. Metadata may
also include storage location information, and this will with the
layout type used based on the underlying storage mechanism that is
used.
While many attributes are only known to the metadata server there are
some necessary to appropriately process IO operations and others
affected by executing IO operations. It is the job of the layout
type specification to describe the necessary coordination. See
Section 19.1 for details.
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18.4.2. Metadata Server
An NFSv4.1 server that supports the pNFS feature. A variety of
architectural choices exist for the metadata server and its use of
file system information held at the server. Some servers may contain
metadata only for file objects residing at the metadata server, while
the file data resides on associated storage devices. Other metadata
servers may hold both metadata together with some portion of file
data.
18.4.3. pNFS Client
An NFSv4.1 client that supports pNFS operations and supports at least
one data access protocol for performing I/O to data storage devices.
18.4.4. Data Storage Devices
A data storage device stores a regular file's data, but while
metadata management is done by the metadata server. A data storage
device could be another NFSv4.1 server, an object-based storage
device (OSD), a block device accessed over a System Area Network
(SAN, e.g., either FiberChannel or iSCSI SAN), or some other entity.
18.4.5. Data Access Protocol
As noted in Figure 1, the data access protocol is provided as a
method used by the client to store and retrieve located on data
storage devices.
The NFSv4.1 pNFS feature has been structured to allow a variety of
data access protocols to be defined and used. The one actually used
depends on the type of layout and is specified by the layout type
specification as described in Section 19.1,
To use a particular data access protocol, both the metadata server
and the client must have support for a layout type that uses that
protocol as its data access protocol.
18.4.6. Control Protocol
As illustrated in Figure 1, a control protocol is used between the
metadata server and data storage devices. Specification of such
protocols is outside the scope of the NFSv4.1 protocol. Such control
protocols would be used to control activities such as the allocation
and deallocation of storage, the management of state required by the
data storage devices to perform client access control, and, depending
on the file access protocol, the enforcement of authentication and
authorization so that restrictions that would be enforced by the
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metadata server could also be enforced by the data storage devices.
A particular control protocol is not REQUIRED by NFSv4.1 but
requirements are placed on the control protocol for maintaining
attributes such as modify time, the change attribute, and the end-of-
file (EOF) position. Note that if pNFS is layered over a clustered,
parallel file system (e.g., PVFS [PVFS]), the mechanisms that enable
clustering and parallelism in that file system serve the same role as
a control protocol. The differences in communication approaches
allow these mechanisms to be treated as if they were structured as a
control protocol.
In the flexible files layout [RFC8435], it is often stated that, when
used in the "loose" coupling mode, there is no control protocol,
which is at variance with the way control protocols are treated in
this document, which requires that certain activities described be
done and considers the means that are used to perform them as
constituting a control protocol. In fact, these activities are
performed using the same base protocol as the data access protocol,
albeit in a different mode with greater privileges. In this
document, we describe such arrangements as having no "separate
control protocol.
18.4.7. Layout
A layout defines how a file's data is organized on one or more data
storage devices. There are many potential layout types; each of the
layout types is differentiated by the data access protocol used to
access data and by the aggregation scheme that lays out the file data
on the various data storage devices. A layout is precisely
identified by the tuple <client ID, filehandle, layout type, iomode,
range>, where filehandle refers to the filehandle of the file on the
metadata server.
It is important to define when layouts overlap and/or conflict with
each other. For two layouts with overlapping byte-ranges to actually
conflict, both layouts must be of the same layout type, correspond to
the same filehandle, and meet layout-specific conditions specified by
the layout type specification as discussed in Section 19.1.
18.4.8. Layout Iomode
The layout iomode (data type layoutiomode4, see Section 9.3.20)
indicates to the metadata server the client's intent to perform
either just READ operations or a mixture containing READ and WRITE
operations. For certain layout types, as defined by the layout type
specification, it is appropriate for a client to specify this intent
at the time it sends LAYOUTGET (Section 25.43). For example, for
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block/volume-based protocols, block allocation could occur when a
LAYOUTIOMODE4_RW iomode is specified. A special LAYOUTIOMODE4_ANY
iomode is defined and can only be used for LAYOUTRETURN and
CB_LAYOUTRECALL, not for LAYOUTGET. It specifies that layouts
pertaining to both LAYOUTIOMODE4_READ and LAYOUTIOMODE4_RW iomodes
are being returned or recalled, respectively.
A data storage device can validate I/O for consistency with the
iomode. Whether this happens depends on the layout type
specification. In cases in which this is to be done, if the client's
layout iomode is inconsistent with the I/O being performed, the data
storage device may reject the client's I/O with an error indicating
that a new layout with the correct iomode should be obtained via
LAYOUTGET. For example, if a client gets a layout with a
LAYOUTIOMODE4_READ iomode and performs a WRITE to a data storage
device, the device is allowed to reject that WRITE.
The use of the layout iomode does not conflict with OPEN share modes
or byte-range LOCK operations; open share mode and byte-range lock
conflicts are enforced as they are without the use of pNFS and are
logically separate from issues related to pNFS layouts. Open share
modes and byte-range locks are the preferred method for restricting
user access to data files. For example, an OPEN of
OPEN4_SHARE_ACCESS_WRITE does not conflict with a LAYOUTGET
containing an iomode of LAYOUTIOMODE4_RW performed by another client.
Applications that depend on writing into the same file concurrently
may use byte-range locking to serialize their accesses.
18.4.9. Device IDs
The device ID (data type deviceid4, see Section 9.3.14) identifies a
group of storage devices. The scope of a device ID is the pair
<client ID, layout type>. In practice, a significant amount of
information may be required to fully address a storage device.
Rather than embedding all such information in a layout, layouts embed
device IDs. The NFSv4.1 operation GETDEVICEINFO (Section 25.40) is
used to retrieve the complete address information (including all
device addresses for the device ID) regarding the storage device
according to its layout type and device ID. For example, the address
of an NFSv4.1 data server or of an object-based storage device could
be an IP address and port. The address of a block storage device
could be a volume label.
Clients cannot expect the mapping between a device ID and its storage
device address(es) to persist across metadata server restart. See
Section 18.9.4 for a description of how recovery works in that
situation.
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A device ID is established by referencing it in the result of a
GETDEVICELIST or LAYOUTGET operation and can be deleted by the server
as soon as there are no layouts referring to the device ID.
If the client requested notifications for device ID mappings, the
server SHOULD send CB_NOTIFY_DEVICEID notifications for device ID
deletions or changes to the device-ID-to-device-address mappings to
any client which has used the device-ID in question at least once,
irrespective of whether the client has any layouts currently
referring to it. If the server does not support or the client does
not request notifications for device ID mappings, the client SHOULD
periodically retired unused device IDs.
Given that GETDEVICELIST does not support requesting notifications a
server that implements GETDEVICELIST MUST NOT advertise support for
NOTIFY_DEVICEID4_CHANGE notification in GETDEVICEINFO, and client
using GETDEVICELIST can not rely on NOTIFY_DEVICEID4_CHANGE or
NOTIFY_DEVICEID4_DELETE notifications to work reliably.
Once a device ID is deleted by the server, the server MUST NOT reuse
the device ID for the same layout type and client ID again. This
requirement is feasible because the device ID is 16 bytes long,
leaving sufficient room to store a generation number if the server's
implementation requires most of the rest of the device ID's content
to be reused. This requirement is necessary because otherwise the
race conditions between asynchronous notification of device ID
addition and deletion would be too difficult to sort out.
Device ID to device address mappings are not leased, and can be
changed at any time. (Note that while device ID to device address
mappings are likely to change after the metadata server restarts, the
server is not required to change the mappings.) A server has two
choices for changing mappings. It can recall all layouts referring
to the device ID or it can use a notification mechanism.
The NFSv4.1 protocol has no optimal way to recall all layouts that
referred to a particular device ID (unless the server associates a
single device ID with a single fsid or a single client ID; in which
case, CB_LAYOUTRECALL has options for recalling all layouts
associated with the fsid, client ID pair, or just the client ID).
Via a notification mechanism (See Section 27.12), device ID to device
address mappings can change over the duration of server operation
without recalling or revoking the layouts that refer to device ID.
The notification mechanism can also delete a device ID, but only if
the client has no layouts referring to the device ID. A notification
of a change to a device ID to device address mapping will immediately
or eventually invalidate some or all of the device ID's mappings.
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The server MUST support notifications and the client must request
them before they can be used. For further information about the
notification types, see Section 27.12.
18.5. pNFS Operations
NFSv4.1 has several operations that are needed for pNFS servers,
regardless of layout type or storage protocol. These operations are
all sent to a metadata server and summarized here. While pNFS is an
OPTIONAL feature, if pNFS is implemented, some operations are
REQUIRED in order to comply with pNFS. See Section 24.
These are the fore channel pNFS operations:
GETDEVICEINFO (Section 25.40), as noted previously (Section 18.4.9),
returns the mapping of device ID to storage device address.
GETDEVICELIST (Section 25.41) allows clients to fetch all device IDs
for a specific file system.
LAYOUTGET (Section 25.43) is used by a client to get a layout for a
file.
LAYOUTCOMMIT (Section 25.42) is used to:
* Inform the metadata server of the client's intent to commit
data that has been written to the storage device (the storage
device as originally indicated in the return value of
LAYOUTGET), in situations in which this information needs to be
provided to the metadata server,, as specified by the file
layout type.
* Provide for the updating of metadata server's view of file
attributes that can modified by WRITEs to incorporate WRITEs
effected by using a data storage device. These attributes
include size, modified_time, and change.
LAYOUTRETURN (Section 25.44) is used to return layouts for a file, a
file system ID (FSID), or a client ID.
These are the backchannel pNFS operations:
CB_LAYOUTRECALL (Section 27.3) recalls a layout, all layouts
belonging to a file system, or all layouts belonging to a client
ID.
CB_RECALL_ANY (Section 27.6) tells a client that it needs to return
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some number of recallable objects, including layouts, to the
metadata server.
CB_RECALLABLE_OBJ_AVAIL (Section 27.7) tells a client that a
recallable object that it was denied (in case of pNFS, a layout
denied by LAYOUTGET) due to resource exhaustion is now available.
CB_NOTIFY_DEVICEID (Section 27.12) notifies the client of changes to
device IDs.
18.6. pNFS Attributes
A number of attributes specific to pNFS are listed and described in
Section 11.16.
18.7. Layout Semantics
18.7.1. Guarantees Provided by Layouts
Layouts grant to the client the ability to access data located at a
data storage device using the associated data access protocol. The
client is guaranteed the layout will be recalled when one of two
things occur: either a conflicting layout is requested or the state
encapsulated by the layout becomes invalid (this can happen when an
event directly or indirectly modifies the layout). When a layout is
recalled and returned by the client, the client continues with the
ability to access file data with normal NFSv4.1 operations through
the metadata server. Only the ability to access the file using the
data storage device is affected.
The requirement of NFSv4.1 that all user access rights MUST be
obtained through the appropriate OPEN, LOCK, and ACCESS operations is
not modified with the existence of layouts. Layouts are provided to
NFSv4.1 clients, and user access still follows the rules of the
protocol as if they did not exist. It is a requirement that for a
client to access a data storage device, a layout must be held by the
client. If a device receives an I/O request for a byte-range for
which the client does not hold a layout, the storage device SHOULD
reject that I/O request. Note that the act of modifying a file for
which a layout is held does not necessarily conflict with the holding
of the layout that describes the file being modified. Therefore, it
is the requirement of the data access protocol or layout type that
determines the necessary behavior. For example, block/volume layout
types require that the layout's iomode agree with the type of I/O
being performed.
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Depending upon the layout type and data access protocol in use,
device-specific access permissions may be granted by LAYOUTGET and
may be encoded within the type-specific layout. For an example of
storage device access permissions, see an object-based protocol such
as [OSD-T10]. If access permissions are encoded within the layout,
the metadata server SHOULD recall the layout when those permissions
become invalid for any reason -- for example, when a file becomes
unwritable or inaccessible to a client. Note, clients are still
required to perform the appropriate OPEN, LOCK, and ACCESS operations
as described above. The degree to which it is possible for the
client to circumvent these operations and the consequences of doing
so must be clearly specified by the individual layout type
specifications. In addition, these specifications must be clear
about the requirements and non-requirements for the checking
performed by the server.
In the presence of pNFS functionality, mandatory byte-range locks
MUST behave as they would without pNFS. Therefore, if mandatory file
locks and layouts are provided simultaneously, the storage device
MUST be able to enforce the mandatory byte-range locks. For example,
if one client obtains a mandatory byte-range lock and a second client
accesses the on the data storage device, the device MUST
appropriately restrict I/O for the range of the mandatory byte-range
lock. If the device is incapable of providing this check in the
presence of mandatory byte-range locks, then the metadata server MUST
NOT grant potentially overlapping layouts and mandatory byte-range
locks simultaneously.
18.7.2. Getting a Layout
A client obtains a layout using the LAYOUTGET operation. The
metadata server will grant layouts of a particular type (e.g., block/
volume, object, or file). The client selects an appropriate layout
type that the server supports and the client is prepared to use. The
layout returned to the client might not exactly match the requested
byte-range as described in Section 25.43.3. As needed, a client may
send multiple LAYOUTGET operations. These might result in multiple
overlapping, non-conflicting layouts (see Section 18.4.7).
In order to get a layout, the client must first have opened the file
via the OPEN operation. When a client has no layout on a file, it
MUST present an open stateid, a delegation stateid, or a byte-range
lock stateid in the loga_stateid argument. A successful LAYOUTGET
result includes a layout stateid. The first successful LAYOUTGET
processed by the server using a non-layout stateid as an argument
MUST have the "seqid" field of the layout stateid in the response set
to one. Thereafter, the client MUST use a layout stateid (See
Section 18.7.3) on future invocations of LAYOUTGET on the file, and
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the "seqid" MUST NOT be set to zero. The client MUST serialize
LAYOUTGET operations using a non-layout stateid with any other
operation affecting the layout state on the file, including
CB_LAYOUTRECALL, to allow consistent initialization of the layout
state. Once the layout has been retrieved, it can be held across
multiple OPEN and CLOSE sequences. Therefore, a client may hold a
layout for a file that is not currently open by any user on the
client. This allows for the caching of layouts beyond CLOSE.
The storage protocol used by the client to access the data on the
storage device is determined by the layout's type. The client is
responsible for matching the layout type with an available method to
interpret and use the layout. The method for this layout type
selection is outside the scope of the pNFS functionality.
Although the metadata server is in control of the layout for a file,
the pNFS client can provide hints to the server when a file is opened
or created about the preferred layout type and aggregation schemes.
pNFS introduces a layout_hint attribute (Section 11.16.4) that the
client can set at file creation time to provide a hint to the server
for new files. Setting this attribute separately, after the file has
been created might make it difficult, or impossible, for the server
implementation to comply.
Because the EXCLUSIVE4 createmode4 does not allow the setting of
attributes at file creation time, NFSv4.1 introduces the EXCLUSIVE4_1
createmode4, which does allow attributes to be set at file creation
time. In addition, if the session is created with persistent reply
caches, EXCLUSIVE4_1 is neither necessary nor allowed. Instead,
GUARDED4 both works better and is prescribed. Table 18 in
Section 25.16.3 summarizes how a client is allowed to send an
exclusive create.
18.7.3. Layout Stateid
As with all other stateids, the layout stateid consists of a "seqid"
and "other" field. Once a layout stateid is established, the "other"
field will stay constant unless the stateid is revoked or the client
returns all layouts on the file and the server disposes of the
stateid. The "seqid" field is initially set to one, and is never
zero on any NFSv4.1 operation that uses layout stateids, whether it
is a fore channel or backchannel operation. After the layout stateid
is established, the server increments by one the value of the "seqid"
in each subsequent LAYOUTGET and LAYOUTRETURN response, and in each
CB_LAYOUTRECALL request.
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Given the design goal of pNFS to provide parallelism, the layout
stateid differs from other stateid types in that the client is
expected to send LAYOUTGET and LAYOUTRETURN operations in parallel.
The "seqid" value is used by the client to properly sort responses to
LAYOUTGET and LAYOUTRETURN. The "seqid" is also used to prevent race
conditions between LAYOUTGET and CB_LAYOUTRECALL. Given that the
processing rules differ from layout stateids and other stateid types,
only the pNFS sections of this document should be considered to
determine proper layout stateid handling.
Once the client receives a layout stateid, it MUST use the correct
"seqid" for subsequent LAYOUTGET or LAYOUTRETURN operations. The
correct "seqid" is defined as the highest "seqid" value from
responses of fully processed LAYOUTGET or LAYOUTRETURN operations or
arguments of a fully processed CB_LAYOUTRECALL operation. Since the
server is incrementing the "seqid" value on each layout operation,
the client may determine the order of operation processing by
inspecting the "seqid" value. In the case of overlapping layout
ranges, the ordering information will provide the client the
knowledge of which layout ranges are held. Note that overlapping
layout ranges may occur because of the client's specific requests or
because the server is allowed to expand the range of a requested
layout and notify the client in the LAYOUTRETURN results. Additional
layout stateid sequencing requirements are provided in
Section 18.7.5.2.
The client's receipt of a "seqid" is not sufficient for it to be
passed back to the metadata server. The client needs to fully
process the operation in which the new seqid is seen before using it
in further communication with the metadata server. For LAYOUTGET
results, if the client is recording details of layout ranges received
(See (Section 18.7.3.1 for information about specifics), it MUST
first update its record of what ranges of the file's layout it has
before using the seqid in this way. For LAYOUTRETURN results, the
client MUST eliminate the range from its record of what ranges of the
file's layout it had before using the seqid. For CB_LAYOUTRECALL
arguments, the client MUST send a response to the recall before using
the seqid in a message to the metadata server. The fundamental basis
of these requirements regarding client processing is that the "seqid"
is used to define the order of processing. LAYOUTGET results may be
processed in parallel. LAYOUTRETURN results may be processed in
parallel. LAYOUTGET and LAYOUTRETURN responses may be processed in
parallel as long as their ranges do not overlap. CB_LAYOUTRECALL
request processing MUST be processed in "seqid" order at all times.
Once a client has no more layouts on a file, the layout stateid is no
longer valid and MUST NOT be used. Any attempt to use such a layout
stateid will result in NFS4ERR_BAD_STATEID.
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A client MAY always forget its layout state and associated layout
stateid at any time (See also Section 18.7.3.1). When this happens,
the client MUST use a non-layout stateid on a subsequent LAYOUTGET
operation. Doing so will inform the server that the client has no
more layouts of that layout type on the file and that its respective
layout state can be released before issuing a new layout in response
to LAYOUTGET.
18.7.3.1. Requirements Regarding Retention of Layout Information.
It might reasonably be assumed that pNFS client state (layout ranges
and iomode) for a file would exactly matches that of the pNFS
metadata server for that file. This assumption would imply that any
callback of a layout results in a LAYOUTRETURN or set of
LAYOUTRETURNs that exactly match the range specified in the callback,
since the client and metadata server would necessarily agree about
the details of the state being maintained.
It is important to understand that the above assumption is not a
protocol requirement and that the protocol does allow the client and
metadata server to drop much of this information, in order to limit
the need for additional storage and internode communication that
maintaining the abovementioned assumption would require.
The obligations of the client and metadata server regarding the
retention of layout information are discussed below. It is important
to understand that data servers often need to be aware of the details
of layouts gotten and that individual layout types might impose
requirements regarding their retention by the client and how they
might be used by the specific storge protocol used by the layout
type.
The relevant protocol requirements discussed here are limited to
those necessary to effect cancellation of layouts to prevent multiple
clients using conflicting layouts and to prevent use of layouts when
changes initiated by the metadata server make their further use
incorrect or otherwise inadvisable. The relevant requirements and
non-requirements can be summarized as follows:
* Within the scope of the base pNFS feature, and the use of
LAYOUTRETURN and CB_LAYOUTRECALL, both the client and the metadata
server are free to drop detailed information about layout ranges
and IO modes at any time.
Any restrictions on the client in this regard derive from the
layout type used and its possible need for the client to have such
information in order to effect IO operations.
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The client MAY do so at any time as long as it does not use these
dropped ranges subsequently or drop them while IO operations based
on them are still being processed.
Even with the requirement above applying to the client, it is
possible that I/O requests may be presented to a storage device no
longer allowed to perform them. Since the server does not have
strict control as to when client will return a recalled layout,
the server needs to be able to unilaterally terminate the client's
access to the storage devices as described by the layout. In
terminating access, the server needs to deal with the possibility
of lingering I/O requests, i.e., I/O requests that are still in
flight to storage devices identified the cancelled layout. All
layout type specifications need to specify whether such unilateral
layout revocation by the metadata server is supported; if it is,
the specification needs to also describe how lingering writes are
dealt with. For example, storage devices identified by the
canceled layout could be fenced off from the client that held the
layout or the data server could be instructed to suppress access
that was previously allowed by the cancelled layout. For details,
see Section 19.1.9.
Similarly, the metadata server MAY also discard detailed
information about layout ranges and IO modes. However, in doing
so, it MUST NOT forget that it could have outstanding layouts for
any part of the file so that it is unaware of layouts that might
be retained by the clients. When that knowledge is lost, the
layout MUST be returned or revoked so that it cannot be used
subsequently.
* The freedom to forget layout details referred to above can be
extended to allow the client to eliminate its knowledge of the
existence of a layout for a particular file. In doing so, it must
ensure that no IOs will use that layout subsequently
* Because of clients and server are allowed to independently discard
layouts they were previously jointly aware of, the processing of
layout recalls is more complicated than it would otherwise be.
See Section 18.7.5.1 for further discussion.
The remainder of this section discusses how clients and metadata
servers might deal with cases in which the other party chooses not to
maintain detailed knowledge of layouts that it is aware of and might
recall. For example,
* In situations in which conflicts that require callbacks are very
rare, a server can use a multi-file callback to recover per-client
resources (e.g., via an FSID recall or a multi-file recall within
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a single CB_COMPOUND). In this case, the result may be
significantly less client-server pNFS traffic, although layouts
might be recalled even if there might be no need to do so.
* It might also be useful for servers to maintain information about
what ranges are held by a client on a coarse-grained basis,
leading to the server's layout ranges being beyond those actually
held by the client.
* In one possible extreme case, a server could manage conflicts on a
per-file basis, only sending whole-file callbacks even though
clients may request and be granted sub-file ranges.
18.7.4. Committing a Layout
The pNFS protocol does not require the metadata server and storage
devices to maintain a consistent view of file attributes that can be
modified as a result of IO operations sent to data storage device.
How each layout type provides for these changes to be reflected in
the metadata server's view is described by the layout type
specification, as described in Section 19.1.8
Some layout types also need to coordinate allocation-related data,
including data location mapping which refers to aspects such as which
offsets store data as opposed to storing holes (See Section 20.8.4
for a discussion). Related issues arise for storage protocols where
a layout may hold provisionally allocated blocks where the allocation
of those blocks does not survive a complete restart of both the
client and server. Because of the potential for inconsistency
between the client and the metadata server, it is necessary, in
general, to resynchronize the client with the metadata server and its
storage devices and make any potential changes available to other
clients. This is accomplished by use of the LAYOUTCOMMIT operation.
See the requirements described in Section 19.1.8 for the layout
specification's obligations to describe and provide for the
coordination of such items.
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The LAYOUTCOMMIT operation is responsible for making globally visible
the effects of layout-based file modifications as they affect the
metadata server. The data should be written and committed to the
appropriate storage devices before the LAYOUTCOMMIT occurs. The
scope of data committed by a LAYOUTCOMMIT operation is specific to
the type of layout because that scope depends on the storage protocol
in use. It is important to note that the level of synchronization is
from the point of view of the client that sent the LAYOUTCOMMIT. The
updated state on the metadata server need only reflect the state as
of the client's last operation previous to the LAYOUTCOMMIT. The
metadata server is need not maintain a global view that accounts for
other clients' I/O that may have occurred within the same time frame.
18.7.5. Recalling a Layout
Since a layout protects a client's access to a file via a direct
client-storage-device path, a layout need only be recalled when it is
semantically unable to serve this function. Typically, this occurs
when the layout no longer encapsulates the true location of the file
over the byte-range it represents. Any operation or action, such as
server-driven restriping or load balancing, that changes the layout
will result in a recall of the layout. A layout is recalled by the
CB_LAYOUTRECALL callback operation (See Section 27.3) and returned
with LAYOUTRETURN (See Section 25.44). The CB_LAYOUTRECALL operation
may recall a layout identified by a byte-range, all layouts
associated with a file system ID (FSID), or all layouts associated
with a client ID. Section 18.7.5.2 discusses sequencing issues
surrounding the getting, returning, and recalling of layouts.
An iomode is also specified when recalling a layout. Generally, the
iomode in the recall request must match the layout being returned;
for example, a recall with an iomode of LAYOUTIOMODE4_RW should cause
the client to only return LAYOUTIOMODE4_RW layouts and not
LAYOUTIOMODE4_READ layouts. However, a special LAYOUTIOMODE4_ANY
enumeration is defined to enable recalling a layout of any iomode; in
other words, the client must return both LAYOUTIOMODE4_READ and
LAYOUTIOMODE4_RW layouts.
A REMOVE operation need to make sure that existing layouts cannot be
used access a non-existent or to reclaim. How this is to be done us
defined by the layout type specification for the existing layout.
Some examples follow:
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* In many cases, metadata server MUST recall the layout to prevent
its subsequent use. Since a REMOVE may be delayed until the last
close of the file has occurred, the recall may also be delayed
until this time. After the last reference on the file has been
released and the file has been removed, the client should no
longer be able to perform I/O using the layout.
* In the case of a file-based layout, the data server returns
NFS4ERR_STALE in response to any operation on the removed file,
making prompt recall of the layout unnecessary.
Later recall of the layout might be done later, as part server
cleanup to object unlikely to be referenced.
Once a layout has been returned, the client MUST NOT send IO requests
to the storage devices for the file, byte-range, and iomode
represented by the returned layout. If a client does send an I/O to
a storage device for which it does not hold a layout, the storage
device will reject the I/O. The ability of and requirements for
storage devices
18.7.5.1. Layout recall/return interaction
As noted in Section 18.7.3.1, It may be useful for clients to
"forget" details about what layouts and ranges the client actually
has, leading to the server's layout ranges being beyond those that
the client "thinks" it has.
In light of the above, it is useful for a server to be able to send
callbacks for layout ranges it has not granted to a client, and for a
client to return ranges it does not hold. A pNFS client MUST always
return layouts that comprise the full range specified by the recall.
Note, the full recalled layout range need not be returned as part of
a single operation, but may be returned in portions. This allows the
client to properly stage the flushing of dirty data and commits and
returns of layouts. Also, it indicates to the metadata server that
the client is making progress.
As long as the client does not assume it has layouts that are beyond
what the server has granted, this is a safe practice. When a client
forgets what ranges and layouts it has, and it receives a
CB_LAYOUTRECALL operation, the client follows up with a LAYOUTRETURN
for what the server recalled (even though what was held does not
match what being recalled) or alternatively return the
NFS4ERR_NOMATCHING_LAYOUT error if it has no layout to return in the
recalled range.
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In order to avoid errors, it is vital that a client not assign itself
layout permissions beyond what the server has granted, and that the
server not forget layout permissions that have been granted. On the
other hand, if a server believes that a client holds a layout that
the client does not know about, it is useful for the client to
cleanly indicate completion of the requested recall either by sending
a LAYOUTRETURN operation for the entire requested range (even though
it is not actually being "returned") or by returning an
NFS4ERR_NOMATCHING_LAYOUT error to the CB_LAYOUTRECALL.
In order to ensure client/server convergence with regard to layout
state, the final LAYOUTRETURN operation in a sequence of LAYOUTRETURN
operations for a particular recall MUST specify the entire range
being recalled, echoing the recalled layout type, iomode, recall/
return type (FILE, FSID, or ALL), and byte-range, even if layouts
pertaining to partial ranges were previously returned. In addition,
if the client holds no layouts that overlap the range being recalled,
the client should return the NFS4ERR_NOMATCHING_LAYOUT error code to
CB_LAYOUTRECALL. This allows the server to update its view of the
client's layout state.
Note that, in the case in which FSID or ALL are specified, the client
needs to do a LAYOUTRETURN for all files for which it holds a layout
stateid but need not do so for files for which it does not, even
though the metadata server might be aware of these stateids.
18.7.5.2. Sequencing of Layout Operations
As with other stateful operations, pNFS requires the correct
sequencing of layout operations. pNFS uses the "seqid" in the layout
stateid to provide the correct sequencing between regular operations
and callbacks. It is the server's responsibility to avoid
inconsistencies regarding the layouts provided and the client's
responsibility to properly serialize its layout requests and layout
returns.
18.7.5.3. Layout Recall and Return Sequencing
One critical issue with regard to layout operations sequencing
concerns callbacks. The protocol must defend against races between
the reply to a LAYOUTGET or LAYOUTRETURN operation and a subsequent
CB_LAYOUTRECALL. A client MUST NOT process a CB_LAYOUTRECALL that
implies one or more outstanding LAYOUTGET or LAYOUTRETURN operations
to which the client has not yet received a reply. The client detects
such a CB_LAYOUTRECALL by examining the "seqid" field of the recall's
layout stateid. If the "seqid" is not exactly one higher than what
the client currently has recorded, and the client has at least one
LAYOUTGET and/or LAYOUTRETURN operation outstanding, or if the client
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has a outstanding LAYOUTGET with a non-layout stateid, the client
knows the server sent the CB_LAYOUTRECALL after sending a response to
an outstanding LAYOUTGET or LAYOUTRETURN. The client MUST wait
before processing such a CB_LAYOUTRECALL until it processes all
replies for outstanding LAYOUTGET and LAYOUTRETURN operations for the
corresponding file with seqid less than the seqid given by
CB_LAYOUTRECALL (lor_stateid; see Section 27.3.)
In addition to the seqid-based mechanism, Section 7.6.3 describes the
sessions mechanism for allowing the client to detect callback race
conditions and delay processing such a CB_LAYOUTRECALL. The server
MAY reference conflicting operations in the CB_SEQUENCE that precedes
the CB_LAYOUTRECALL. Because the server has already sent replies for
these operations before sending the callback, the replies may race
with the CB_LAYOUTRECALL. The client MUST wait for all the
referenced calls to complete and update its view of the layout state
before processing the CB_LAYOUTRECALL.
18.7.5.3.1. Get/Return Sequencing
The protocol allows the client to send concurrent LAYOUTGET and
LAYOUTRETURN operations to the server. The protocol does not provide
any means for the server to process the requests in the same order in
which they were created. However, through the use of the "seqid"
field in the layout stateid, the client can determine the order in
which parallel outstanding operations were processed by the server.
Thus, when a layout retrieved by an outstanding LAYOUTGET operation
intersects with a layout returned by an outstanding LAYOUTRETURN on
the same file, the order in which the two conflicting operations are
processed determines the final state of the overlapping layout. The
order is determined by the "seqid" returned in each operation: the
operation with the higher seqid was executed later.
It is permissible for the client to send multiple parallel LAYOUTGET
operations for the same file or multiple parallel LAYOUTRETURN
operations for the same file or a mix of both. It is permissible for
the client to send multiple parallel LAYOUTGET operations for the
same file using the layout stateid or multiple parallel LAYOUTRETURN
operations for the same file or a mix of both.
It is permissible for the client to use the current stateid (see
Section 23.2.3.1.2) for LAYOUTGET operations, for example, when
compounding LAYOUTGETs or compounding OPEN and LAYOUTGETs. It is
also permissible to use the current stateid when compounding
LAYOUTRETURNs.
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It is permissible for the client to use the current stateid when
combining LAYOUTRETURN and LAYOUTGET operations for the same file in
the same COMPOUND request since the server MUST process these in
order. However, if a client does send such COMPOUND requests, it
MUST NOT have more than one outstanding for the same file at the same
time, and it MUST NOT have other LAYOUTGET or LAYOUTRETURN operations
outstanding at the same time for that same file.
18.7.5.3.2. Client Considerations
Consider a pNFS client that has sent a LAYOUTGET, and before it
receives the reply to LAYOUTGET, it receives a CB_LAYOUTRECALL for
the same file with an overlapping range. There are two
possibilities, which the client can distinguish via the layout
stateid in the recall.
1. The server processed the LAYOUTGET before sending the recall, so
the LAYOUTGET must be waited for because it may be carrying
layout information that will need to be returned to deal with the
CB_LAYOUTRECALL.
2. The server sent the callback before receiving the LAYOUTGET. The
server will not respond to the LAYOUTGET until the
CB_LAYOUTRECALL is processed.
If these possibilities cannot be distinguished, a deadlock could
result, as the client must wait for the LAYOUTGET response before
processing the recall in the first case, but that response will not
arrive until after the recall is processed in the second case. Note
that in the first case, the "seqid" in the layout stateid of the
recall is two greater than what the client has recorded, or the
client has an outstanding LAYOUTGET using a non-layout stateid; in
the second case, the "seqid" is one greater than what the client has
recorded. This allows the client to disambiguate between the two
cases. The client thus knows precisely which possibility applies.
In case 1, the client knows it needs to wait for the LAYOUTGET
response before processing the recall (or the client can return
NFS4ERR_DELAY).
In case 2, the client will not wait for the LAYOUTGET response before
processing the recall because waiting would cause deadlock.
Therefore, the action at the client will only require waiting in the
case that the client has not yet seen the server's earlier responses
to the LAYOUTGET operation(s).
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The recall process can be considered completed when the final
LAYOUTRETURN operation for the recalled range is completed. The
LAYOUTRETURN uses the layout stateid (with seqid) specified in
CB_LAYOUTRECALL. If the client uses multiple LAYOUTRETURNs in
processing the recall, the first LAYOUTRETURN will use the layout
stateid as specified in CB_LAYOUTRECALL. Subsequent LAYOUTRETURNs
will use the highest seqid as is the usual case.
18.7.5.3.3. Server Considerations
Consider a race from the metadata server's point of view. The
metadata server has sent a CB_LAYOUTRECALL and receives an
overlapping LAYOUTGET for the same file before the LAYOUTRETURN(s)
that respond to the CB_LAYOUTRECALL. There are three cases:
1. The client sent the LAYOUTGET before processing the
CB_LAYOUTRECALL. The "seqid" in the layout stateid of the
arguments of LAYOUTGET is one less than the "seqid" in
CB_LAYOUTRECALL. The server returns NFS4ERR_RECALLCONFLICT to
the client, which indicates to the client that there is a pending
recall.
2. The client sent the LAYOUTGET after processing the
CB_LAYOUTRECALL, but the LAYOUTGET arrived before the
LAYOUTRETURN and the response to CB_LAYOUTRECALL that completed
that processing. The "seqid" in the layout stateid of LAYOUTGET
is equal to or greater than that of the "seqid" in
CB_LAYOUTRECALL. The server has not received a response to the
CB_LAYOUTRECALL, so it returns NFS4ERR_RECALLCONFLICT.
3. The client sent the LAYOUTGET after processing the
CB_LAYOUTRECALL; the server received the CB_LAYOUTRECALL
response, but the LAYOUTGET arrived before the LAYOUTRETURN that
completed that processing. The "seqid" in the layout stateid of
LAYOUTGET is equal to that of the "seqid" in CB_LAYOUTRECALL.
The server has received a response to the CB_LAYOUTRECALL, so it
returns NFS4ERR_RETURNCONFLICT.
18.7.5.3.4. Wraparound and Validation of Seqid
The rules for layout stateid processing differ from other stateids in
the protocol because the "seqid" value cannot be zero and the
stateid's "seqid" value changes in a CB_LAYOUTRECALL operation. The
non-zero requirement combined with the inherent parallelism of layout
operations means that a set of LAYOUTGET and LAYOUTRETURN operations
may contain the same value for "seqid". The server uses a slightly
modified version of the modulo arithmetic as described in
Section 7.6.1 when incrementing the layout stateid's "seqid". The
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difference is that zero is not a valid value for "seqid"; when the
value of a "seqid" is 0xFFFFFFFF, the next valid value will be
0x00000001. The modulo arithmetic is also used for the comparisons
of "seqid" values in the processing of CB_LAYOUTRECALL events as
described above in Section 18.7.5.3.3.
Just as the server validates the "seqid" in the event of
CB_LAYOUTRECALL usage, as described in Section 18.7.5.3.3, the server
also validates the "seqid" value to ensure that it is within an
appropriate range. This range represents the degree of parallelism
the server supports for layout stateids. If the client is sending
multiple layout operations to the server in parallel, by definition,
the "seqid" value in the supplied stateid will not be the current
"seqid" as held by the server. The range of parallelism spans from
the highest or current "seqid" to a "seqid" value in the past. To
assist in the discussion, the server's current "seqid" value for a
layout stateid is defined as SERVER_CURRENT_SEQID. The lowest
"seqid" value that is acceptable to the server is represented by
PAST_SEQID. And the value for the range of valid "seqid"s or range
of parallelism is VALID_SEQID_RANGE. Therefore, the following holds:
VALID_SEQID_RANGE = SERVER_CURRENT_SEQID - PAST_SEQID. In the
following, all arithmetic is the modulo arithmetic as described
above.
The server MUST support a minimum VALID_SEQID_RANGE. The minimum is
defined as: VALID_SEQID_RANGE = summation over 1..N of
(ca_maxoperations(i) - 1), where N is the number of session fore
channels and ca_maxoperations(i) is the value of the ca_maxoperations
returned from CREATE_SESSION of the i'th session. The reason for "-
1" is to allow for the required SEQUENCE operation. The server MAY
support a VALID_SEQID_RANGE value larger than the minimum. The
maximum VALID_SEQID_RANGE is (2^32 - 2) (accounting for zero not
being a valid "seqid" value).
If the server finds the "seqid" is zero, the NFS4ERR_BAD_STATEID
error is returned to the client. The server further validates the
"seqid" to ensure it is within the range of parallelism,
VALID_SEQID_RANGE. If the "seqid" value is outside of that range,
the error NFS4ERR_OLD_STATEID is returned to the client. Upon
receipt of NFS4ERR_OLD_STATEID, the client updates the stateid in the
layout request based on processing of other layout requests and re-
sends the operation to the server.
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18.7.5.3.5. Bulk Recall and Return
pNFS supports recalling and returning all layouts that are for files
belonging to a particular fsid (LAYOUTRECALL4_FSID,
LAYOUTRETURN4_FSID) or client ID (LAYOUTRECALL4_ALL,
LAYOUTRETURN4_ALL). There are no "bulk" stateids, so detection of
races via the seqid is not possible. The server MUST NOT initiate
bulk recall while another recall is in progress, or the corresponding
LAYOUTRETURN is in progress or pending. In the event the server
sends a bulk recall while the client has a pending or in-progress
LAYOUTRETURN, CB_LAYOUTRECALL, or LAYOUTGET, the client returns
NFS4ERR_DELAY. In the event the client sends a LAYOUTGET or
LAYOUTRETURN while a bulk recall is in progress, the server returns
NFS4ERR_RECALLCONFLICT. If the client sends a LAYOUTGET or
LAYOUTRETURN after the server receives NFS4ERR_DELAY from a bulk
recall, then to ensure forward progress, the server MAY return
NFS4ERR_RECALLCONFLICT.
Once a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL is sent, the server MUST
NOT allow the client to use any layout stateid except for
LAYOUTCOMMIT operations. Once the client receives a CB_LAYOUTRECALL
of LAYOUTRECALL4_FSID, it MUST NOT use any layout stateid except for
LAYOUTCOMMIT operations. Once a LAYOUTRETURN of LAYOUTRETURN4_ALL is
sent, all layout stateids granted to the client ID are freed. The
client MUST NOT use the layout stateids again. It MUST use LAYOUTGET
to obtain new layout stateids.
Once a CB_LAYOUTRECALL of LAYOUTRECALL4_FSID is sent, the server MUST
NOT allow the client to use any layout stateid that refers to a file
with the specified fsid except for LAYOUTCOMMIT operations. Once the
client receives a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL, it MUST NOT
use any layout stateid that refers to a file with the specified fsid
except for LAYOUTCOMMIT operations. Once a LAYOUTRETURN of
LAYOUTRETURN4_FSID is sent, all layout stateids granted to the
referenced fsid are freed. The client MUST NOT use those freed
layout stateids for files with the referenced fsid again.
Subsequently, for any file with the referenced fsid, to use a layout,
the client MUST first send a LAYOUTGET operation in order to obtain a
new layout stateid for that file.
If the server has sent a bulk CB_LAYOUTRECALL and receives a
LAYOUTGET, or a LAYOUTRETURN with a stateid, the server MUST return
NFS4ERR_RECALLCONFLICT. If the server has sent a bulk
CB_LAYOUTRECALL and receives a LAYOUTRETURN with an lr_returntype
that is not equal to the lor_recalltype of the CB_LAYOUTRECALL, the
server MUST return NFS4ERR_RECALLCONFLICT.
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18.7.6. Revoking Layouts
Parallel NFS allow servers to revoke layouts from clients that fail
to respond to recalls and/or fail to renew their lease in time.
Depending on the layout type, the layout type specification might
allow the server to revoke the layout in other situations and
describe the actions to be taken with respect to the client's I/O to
data servers.
18.7.7. Metadata Server Write Propagation
Asynchronous writes written through the metadata server may be
propagated lazily to the storage devices. For data written
asynchronously through the metadata server, a client performing a
read at the appropriate storage device is not guaranteed to see the
newly written data until a COMMIT occurs at the metadata server.
While the write is pending, reads to the storage device may give out
either the old data, the new data, or a mixture of new and old. Upon
completion of a synchronous WRITE or COMMIT (for asynchronously
written data), the metadata server MUST ensure that storage devices
give out the new data and that the data has been written to stable
storage. If the server implements its storage in any way such that
it cannot obey these constraints, then it MUST recall the layouts to
prevent reads being done that cannot be handled correctly. Note that
the layouts MUST be recalled prior to the server responding to the
associated WRITE operations.
18.8. pNFS Mechanics
This section describes the operations flow taken by a pNFS client to
a metadata server and storage device.
When a pNFS client encounters a new FSID, it sends a GETATTR to the
NFSv4.1 server for the fs_layout_type (Section 11.16.1) attribute.
If the attribute returns at least one layout type, and the layout
types returned are among the set supported by the client, the client
knows that pNFS is a possibility for the file system. If, from the
server that returned the new FSID, the client does not have a client
ID that came from an EXCHANGE_ID result that returned
EXCHGID4_FLAG_USE_PNFS_MDS, it MUST send an EXCHANGE_ID to the server
with the EXCHGID4_FLAG_USE_PNFS_MDS bit set. If the server's
response does not have EXCHGID4_FLAG_USE_PNFS_MDS, then contrary to
what the fs_layout_type attribute said, the server does not support
pNFS, and the client will not be able use pNFS to that server; in
this case, the server MUST return NFS4ERR_NOTSUPP in response to any
pNFS operation.
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The client then creates a session, requesting a persistent session,
so that exclusive creates can be done with single round trip via the
createmode4 of GUARDED4. If the session ends up not being
persistent, the client will use EXCLUSIVE4_1 for exclusive creates.
If a file is to be created on a pNFS-enabled file system, the client
uses the OPEN operation. With the normal set of attributes that may
be provided upon OPEN used for creation, there is an OPTIONAL
layout_hint attribute. The client's use of layout_hint allows the
client to express its preference for a layout type and its associated
layout details. The use of a createmode4 of UNCHECKED4, GUARDED4, or
EXCLUSIVE4_1 will allow the client to provide the layout_hint
attribute at create time. The client MUST NOT use EXCLUSIVE4 (See
Table 18). The client is RECOMMENDED to combine a GETATTR operation
after the OPEN within the same COMPOUND. The GETATTR may then
retrieve the layout_type attribute for the newly created file. The
client will then know what layout type the server has chosen for the
file and therefore what storage protocol the client must use.
If the client wants to open an existing file, then it also includes a
GETATTR to determine what layout type the file supports.
The GETATTR in either the file creation or plain file open case can
also include the layout_blksize and layout_alignment attributes so
that the client can determine optimal offsets and lengths for I/O on
the file.
Assuming the client supports the layout type returned by GETATTR and
it chooses to use pNFS for data access, it then sends LAYOUTGET using
the filehandle and stateid returned by OPEN, specifying the range it
wants to do I/O on. The response is a layout, which may be a subset
of the range for which the client asked. It also includes device IDs
and a description of how data is organized (or in the case of
writing, how data is to be organized) across the devices. The device
IDs and data description are encoded in a format that is specific to
the layout type, but the client is expected to understand.
When the client wants to send an I/O, it determines to which device
ID it needs to send the I/O command by examining the data description
in the layout. It then sends a GETDEVICEINFO to find the device
address(es) of the device ID. The client then sends the I/O request
to one of device ID's device addresses, using the storage protocol
defined for the layout type. Note that if a client has multiple I/Os
to send, these I/O requests may be done in parallel.
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If the I/O is a WRITE, then at some point the client will need to use
LAYOUTCOMMIT to commit the modification time and the new size of the
file (if it believes it could have extended the file size) to the
metadata server and, depending on the layout type, the modified data
to the file system.
18.9. Recovery
Recovery is complicated by the distributed nature of the pNFS
protocol. In general, crash recovery for layouts is similar to crash
recovery for delegations in the base NFSv4.1 protocol. However, the
client's ability to perform I/O without contacting the metadata
server introduces subtleties that must be handled correctly if the
possibility of file system corruption is to be avoided.
18.9.1. Recovery from Client Restart
Client recovery for layouts is similar to client recovery for other
lock and delegation state. When a pNFS client restarts, it will lose
all information about the layouts that it previously owned. There
are two methods by which the server can reclaim these resources and
allow otherwise conflicting layouts to be provided to other clients.
The first is through the expiry of the client's lease. If the client
recovery time is longer than the lease period, the client's lease
will expire and the server will know that state may be released. For
layouts, the server may release the state immediately upon lease
expiry or it may allow the layout to persist, awaiting possible lease
revival, as long as no other layout conflicts.
The second is through the client restarting in less time than it
takes for the lease period to expire. In such a case, the client
will contact the server through the standard EXCHANGE_ID protocol.
The server will find that the client's co_ownerid matches the
co_ownerid of the previous client invocation, but that the verifier
is different. The server uses this as a signal to release all layout
state associated with the client's previous invocation. In this
scenario, the data written by the client but not covered by a
successful LAYOUTCOMMIT is in an undefined state; it may have been
written or it may now be lost. This is acceptable behavior, making
it necessary, depending on the layout type, for the client to use
LAYOUTCOMMIT or other means to achieve the desired level of
stability.
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18.9.2. Dealing with Lease Expiration on the Client
If a client has reason to believe its lease has expired, it MUST NOT
send I/O to the storage device until it has validated its lease. The
client can send a SEQUENCE operation to the metadata server. If the
SEQUENCE operation is successful, but sr_status_flag has
SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED, or
SEQ4_STATUS_ADMIN_STATE_REVOKED set, the client MUST NOT use
currently held layouts. The client has two choices to recover from
the lease expiration. First, for all modified but uncommitted data,
the client writes it to the metadata server using the FILE_SYNC4 flag
for the WRITEs, or WRITE and COMMIT. Second, the client re-
establishes a client ID and session with the server and obtains new
layouts and device-ID-to-device-address mappings for the modified
data ranges and then writes the data to the storage devices with the
newly obtained layouts.
If sr_status_flags from the metadata server has
SEQ4_STATUS_RESTART_RECLAIM_NEEDED set (or SEQUENCE returns
NFS4ERR_BAD_SESSION and CREATE_SESSION returns
NFS4ERR_STALE_CLIENTID), then the metadata server has restarted, and
the client SHOULD recover using the methods described in
Section 18.9.4.
If sr_status_flags from the metadata server has
SEQ4_STATUS_LEASE_MOVED set, then the client recovers by following
the procedure described in Section 17.11.9.2. After that, the client
may get an indication that the layout state was not moved with the
file system. The client recovers as in the other applicable
situations discussed in the first two paragraphs of this section.
If sr_status_flags reports no loss of state, then the lease for the
layouts that the client has are valid and renewed, and the client can
once again send I/O requests to the storage devices.
While clients SHOULD NOT send I/Os to storage devices that may extend
past the lease expiration time period, this is not always possible,
for example, an extended network partition that starts after the I/O
is sent and does not heal until the I/O request is received by the
storage device. Thus, the metadata server and/or storage devices are
responsible for protecting themselves from I/Os that are both sent
before the lease expires and arrive after the lease expires. How
this is to be done needs to be addressed by the layout type
specification. See Section 18.9.3 for further discussion of the
layout type specification's obligation in this regard
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18.9.3. Dealing with Loss of Layout State on the Metadata Server
This is a description of the case where all of the following are
true:
* the metadata server has not restarted
* a pNFS client's layouts have been discarded (usually because the
client's lease expired) and are invalid
* an I/O from the pNFS client arrives at the storage device
The metadata server and its storage devices need to address this
situation by fencing the client as described by the layout type
specification In other words, they MUST prevent the execution of I/O
operations from the client to the storage devices after layout state
loss.
The details of how fencing is done are specific to the layout type
and need to be described in the layout specification, as required by
Section 19.1.9. In some cases the control protocol can be used to
effectively revoke the data server's record of the layout allowing it
to be rejected. In other cases, the means available are not limited
to specific layouts and have a force majeure character. However, it
is always necessary in practice to prevent further prohibited access
by the storage device, even it appears unresponsive. The means by
which this is need not explicitly discussed but it should be clear
that drastic action might be necessary to provide the requisite data
integrity
18.9.4. Recovery from Metadata Server Restart
The pNFS client will discover that the metadata server has restarted
via the methods described in Section 13.4.2 and discussed in a pNFS-
specific context in Section 18.9.2, Paragraph 2. The client MUST
stop using layouts and delete the device ID to device address
mappings it previously received from the metadata server. Having
done that, if the client wrote data to the storage device without
committing the layouts via LAYOUTCOMMIT, then the client has
additional work to do in order to have the client, metadata server,
and storage device(s) all synchronized on the state of the data.
* If the client has data still modified and unwritten in the
client's memory, the client has only two choices.
1. The client can obtain a layout via LAYOUTGET after the
server's grace period and write the data to the storage
devices.
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2. The client can WRITE that data through the metadata server
using the WRITE (Section 25.32) operation, and then obtain
layouts as desired.
* If the client asynchronously wrote data to the storage device, but
still has a copy of the data in its memory, then it has available
to it the recovery options listed above in the previous bullet
point. If the metadata server is also in its grace period, the
client has available to it the options below in the next bullet
point.
* The client does not have a copy of the data in its memory and the
metadata server is still in its grace period. The client cannot
use LAYOUTGET (within or outside the grace period) to reclaim a
layout because the contents of the response from LAYOUTGET may not
match what it had previously. The range might be different or the
client might get the same range but the content of the layout
might be different. Even if the content of the layout appears to
be the same, the device IDs may map to different device addresses,
and even if the device addresses are the same, the device
addresses could have been assigned to a different storage device.
The option of retrieving the data from the storage device and
writing it to the metadata server per the recovery scenario
described above is not available because, again, the mappings of
range to device ID, device ID to device address, and device
address to physical device are stale, and new mappings via new
LAYOUTGET do not solve the problem.
The only recovery option for this scenario is to send a
LAYOUTCOMMIT in reclaim mode, which the metadata server will
accept as long as it is in its grace period. The use of
LAYOUTCOMMIT in reclaim mode informs the metadata server that the
layout has changed. It is critical that the metadata server
receive this information before its grace period ends, and thus
before it starts allowing updates to the file system.
To send LAYOUTCOMMIT in reclaim mode, the client sets the
loca_reclaim field of the operation's arguments (Section 25.42.1)
to TRUE. During the metadata server's recovery grace period (and
only during the recovery grace period) the metadata server is
prepared to accept LAYOUTCOMMIT requests with the loca_reclaim
field set to TRUE.
When loca_reclaim is TRUE, the client is attempting to commit
changes to the layout that occurred prior to the restart of the
metadata server. The metadata server applies some consistency
checks on the loca_layoutupdate field of the arguments to
determine whether the client can commit the data written to the
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storage device to the file system. The loca_layoutupdate field is
of data type layoutupdate4 and contains layout-type-specific
content (in the lou_body field of loca_layoutupdate). The layout-
type-specific information that loca_layoutupdate might have is
defined in the layout type specification as described in
Section 19.1.2. If the metadata server's consistency checks on
loca_layoutupdate succeed, then the metadata server MUST commit
the changed data that was written to the storage device within the
scope of the LAYOUTCOMMIT operation. If the metadata server's
consistency checks on loca_layoutupdate fail, the metadata server
rejects the LAYOUTCOMMIT operation and makes no changes to the
file system. However, any time LAYOUTCOMMIT with loca_reclaim
TRUE fails, the pNFS client may have lost all uncommitted data
within the scope of the failed LAYOUTCOMMIT operation. A client
can defend against this risk by caching all data, whether written
synchronously or asynchronously in its memory, and by not
releasing the cached data until a successful LAYOUTCOMMIT. This
condition does not hold true for all layout types; for example,
file-based storage devices need not suffer from this limitation.
* The client does not have a copy of the data in its memory and the
metadata server is no longer in its grace period; i.e., the
metadata server returns NFS4ERR_NO_GRACE. As with the scenario in
the above bullet point, the failure of LAYOUTCOMMIT means the data
in the scope of that LAYOUTCOMMIT may have been lost. The defense
against the risk is the same -- cache all written data on the
client until a successful LAYOUTCOMMIT
18.9.5. Operations during Metadata Server Grace Period
Some of the recovery scenarios thus far noted that some operations
(namely, WRITE and LAYOUTGET) might be permitted during the metadata
server's grace period. The metadata server may allow these
operations during its grace period. For LAYOUTGET, the metadata
server must reliably determine that servicing such a request will not
conflict with an impending LAYOUTCOMMIT reclaim request. For WRITE,
the metadata server must reliably determine that servicing the
request will not conflict with an impending OPEN or with a LOCK where
the file has mandatory byte-range locking enabled.
As mentioned previously, for expediency, the metadata server might
reject some operations (namely, WRITE and LAYOUTGET) during its grace
period, because the simplest correct approach is to reject all non-
reclaim pNFS requests and WRITE operations by returning the
NFS4ERR_GRACE error. However, depending on the storage protocol
(which is specific to the layout type) and metadata server
implementation, the metadata server may be able to determine that a
particular request is safe. For example, a metadata server may save
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provisional allocation mappings for each file to stable storage, as
well as information about potentially conflicting OPEN share modes
and mandatory byte-range locks that might have been in effect at the
time of restart, and the metadata server may use this information
during the recovery grace period to determine that a WRITE request is
safe.
18.9.6. Storage Device Recovery
Recovery from storage device restart dependent upon the layout type
in use. Details need to be provided as described in Section 19.1.7.
Despite the above, there are a few general techniques a client can
use if it discovers a storage device has crashed while holding
modified, uncommitted data that was asynchronously written. First
and foremost, it is important to realize that the client is the only
one that has the information necessary to recover non-committed data
since it holds the modified data and probably nothing else does.
Second, the best solution is for the client to err on the side of
caution and attempt to rewrite the modified data through another
path.
In consequence, the client SHOULD immediately WRITE the data to the
metadata server, with the stable field in the WRITE4args set to
FILE_SYNC4. Once it does this, there is no need to wait for recovery
of access to the original storage device.
18.10. Metadata and Storage Device Roles
If the same physical hardware is used to implement both a metadata
server and storage device, then the same hardware entity is to be
understood to be implementing two distinct roles and it is important
that it be clearly understood on behalf of which role the hardware is
executing at any given time.
Two sub-cases can be distinguished.
1. The storage device uses NFSv4.1 as the storage protocol, i.e.,
the same physical hardware is used to implement both a metadata
and data server. See Section 20.5 for a description of how
multiple roles are handled.
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2. The storage device does not use NFSv4.1 as the storage protocol,
and the same physical hardware is used to implement both a
metadata and storage device. Whether distinct network addresses
are used to access the metadata server and storage device is
immaterial. This is because it is always clear to the pNFS
client and server, from the upper-layer protocol being used
(NFSv4.1 or non-NFSv4.1), to which role the request to the common
server network address is directed.
18.11. Security Issues for pNFS
pNFS separates file system metadata and data and provides access to
both. For security (and other) purposes, data within the NFSv4.1
protocol can be divided as follows:
* Non-pNFS-related metadata, typically accessed and modified by
using non-pNFS operations directed to the primary server aka the
metadata server.
* pNFS-related metadata which provides metadata used to access file
data, potentially on another device or server.
This information, in the form of layouts, is accessed and modified
using special pNFS-related operations directed at the metadata
server.
* File data, typically accessed using a data access protocol, which
might or might not be an NFS protocol, using requests directed at
what are called data servers or data storage devices, depending on
the layout type.
In other cases, data can be accessed just as it would be on a non-
pNFS server, by making READ and WRITE requests directed to the
metadata server.
The combination of components in a pNFS system (See Figure 1) is
required to preserve the security properties of NFSv4.1 with respect
to an entity that is accessing file data from a client, regardless of
whether this access is directed to the metadata server or to data
elsewhere using layouts provided by the primary server.
Despite this important commonality, the ways in which this is done,
depends on the layout type. The layout type affects the data access
protocol used and the way that the activities of the metadata server
and those providing file data access are coordinated
* Security issues for data access protocols not layered on RPC is
discussed in Section 18.11.1.
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* Security issues for data access protocols which are minor versions
of NFSv4 and are supported by a separate control protocol are
discussed in Section 18.11.2.
* Security for data access protocols for versions of NFS without the
support of a separate control protocol is discussed in
Section 18.11.3.
Given the multiple types of entities whose coordinated effort is
required to implement pNFS access, there are a number of inter-entity
communications paths which need to be provided with sufficient
security to resist attack.
Often, this will require authentication of the requester in order to
properly make authorization decisions. When authentication of the
principal making the request is not possible, authentication of
network peers need to be combined with a trust relationship between
the connected peers.
There are a number of possible types of communication paths whose use
is possible in various pNFS configurations, depending on the layout
type and the specific entities involved.
* When an RPC-based communication path is used, the same sorts of
techniques described in the NFSv4-wide security document (expected
to be derived from [I-D.dnoveck-nfsv4-security]), are adequate to
provide the necessary confidentiality and protection against the
execution of unauthorized requests. The details may differ
depending on the specific protocol used.
* In other cases, freedom from unauthorized access can be effected
by physical isolation of the communication path between the two
entities. However, this physical isolation needs to be
supplemented in order to make sure that hostile entities cannot
gain access to either of these endpoint.
One common and effective way of blocking such hostile access, is
by making sure that the entity is configured so as to not be
accessible for general services that can be compromised by
external actors. This is often done if the entity is not
implemented within a general-purpose operating system or is
configured to not to be responsive to general internet traffic.
Where it is not possible to totally block such access, external
authentication of principals is necessary.
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Given the three types of entities whose coordinated effort is
required to implement pNFS access, there are a number of inter-entity
communications path which need to be provided with sufficient
security to resist attack.
* For communication between the client and the metadata server, the
RPC-based security described in the NFSv4-wide security document
(expected to be derived from [I-D.dnoveck-nfsv4-security]), is to
be used as it is when pNFS is not involved. Note that the
associated threat analysis is to be found in that same document.
* For communication between the client and the data storage devices,
there are multiple possibilities to consider, based on the type of
file access protocol used.
For data access protocols not using RPC, in general it is not
possible to determine whether particular request are appropriately
authorized, since there might not be sufficient data present in
the request to authenticate the sender or even identify it.
In such cases, the clients and data storage devices require mutual
authentication and they need to trust one another.
* For communication between the metadata server and stat storage
device, there needs to be authentication of both peers and a trust
relationship between them.
* When there is communication between multiple data storage devices,
it is generally best to rely on the metadata servers
authentication and its trust of each devices.
18.11.1. Security-related Handling for non-RPC Storage Protocols
These include the blocks layout [RFC5663], the SCSI layout [RFC8154],
and the objects layout [RFC5664].
Because these storage protocols do not use RPC, the storage device
has no way of determining the specific user making the request.
Similarly the storage device has no way of determining the specific
open with which a given IO request is associated. As a result, for
these storage protocols, the client has the major responsibility for
making sure that only valid requests are executed, by implementing
the checking of requests to the storage device at the point of issue.
The important role of the client in enforcing these constraints makes
authentication of the client peer (e.g. by the use of tls
authentication) of critical importance. This is true not only in the
case in which AUTH_SYS is used, but also in the RPCSEC_GSS case. In
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that latter case, the credentials assure that we know the user making
the request but we have no knowledge of the client implementation or
any reason to view it as trustworthy in enforcing pNFS rules.
Given the reliance on the client, such storage protocols need to have
some way of dealing with an unresponsive client when layouts need to
be recalled. Typically, this involves some way for the metadata
server to contact storage device directly (e.g. by effecting a
persistent reservation) and locking out the unresponsive client (and
possibly others).
18.11.2. Security-related Handling for RPC Storage Protocols that are
NFSv4 Minor Versions Assisted by Control Protocols
These include not only the use of NFSv4.1 as a storage protocol, as
described in Section 20 but also the use of all NFSv4 minor versions
as data access protocols as described in [RFC8435], in the "tight"
coupling mode.
The use of NFSv4 (with RPC) eliminates the difficulties that apply to
Section 18.11.1:
* Because of the use of RPC, the data server is aware of the user of
whose behalf the request is made so the same sort of checking made
by the metadata server can be done by the data server. When
RPCSEC_GSS is in use, authentication of that user is
unproblematic. On the other hand, when AUTH_SYS is used to access
the data server, authentication of this identity is a serious
concern, especially when client host authentication is not
available. Generally, the use of AUTH_SYS without client host
authentication is to be avoided when accessing the data server,
since you are trusting an unauthenticated client to "authenticate"
a user's identity.
* Because of the use of NFSv4, the data server is aware of the
specific open with which each IO request is associated.
Because, in this sort of environment, the client is not responsible
for checking the validity of IO requests, situations in which a
layout becomes invalid are dealt with the ordinary recall mechanism
used for other recallable locking objects. However, to deal with e
possibility of an unresponsive client, the metadata server will
typically have the option of contacting the data server directly.
Because of the possibility of communication issues, the control
protocol will often use a lease-like mechanism so that, in the
absence of communication, layouts are cancelled, rather than being
kept indefinitely.
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[Author Aside]: Need TH review for the flexible-files case.
18.11.3. Security-related Handling for RPC Storage Protocols using NFS
Versions together with Control Protocol Assistance
These include the use of NFSv3, NFSv4.0, and NFSv4.1 as storage
protocols, as described in [RFC8435], in the "loose" coupling mode.
With regard to the difficulties discussed in Section 18.11.1,
specifics may vary based on the particular storage protocol used and
the possible use of client-host authentication.
* Since loose authentication is only described for the AUTH_SYS
case, we have to assume that RPCSEC_GSS will not be used. As a
result, it is RECOMMENDED that client host authentication be
available to prevent attackers acting as if they were
unauthenticated clients and presenting their requests for
execution. The authentication needed to prevent this is the
authentication of the clients to the data server. When it is not
used, serious security difficulties arise because the clients are
not authenticated to the data server which is executing their
requests.
The authentication of clients to the metadata server can
ameliorate the problem, but the main value of doing so is the
encryption of traffic between the client and the metadata server,
provided by rpc-tls.
When this problem exists, use of RPCSEC_GSS by the clients in
accessing the metadata server, is not, by itself, helpful. The
confidentiality of traffic between the client and the metadata
server is necessary, whether that is provided by RPCSEC_GSS
privacy services or by rpc-tls encryption.
* In the case of NFSv3 as a storage protocol, there is no way for
the data server to determine the open with which each request is
assigned. While it might be possible to make this determination
in the case in which NFSv4 minor versions are used as storage
protocol, it appears that the loose coupling option makes no
provision for this either.
As a result, the situation is quite like that described in
Section 18.11.1 even though the storage protocol is RPC-based, with
clients, rather than data servers responsible for checking request
validity. As a result, similar issues arise when clients do not
respond properly when layouts are recalled. The metadata server has
the ability to make such layouts unusable by changing ownership of
the data files involved.
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[Author Aside]: TH Needs to review this section.
19. Specification of Layout Types
This section describes the required elements of pNFS layout type
specifications. These layout types include the following:
* The files layout type, specified in Section 20.
* The blocks, objects, scsi and flexible files layout types,
described in [RFC5663], [RFC5664], [RFC8154], and [RFC8435]
respectively.
* Future layout types, expected to be specified in standards-track
documents including those defining new minor versions and
extensions to existing minor versions as provided for in
[RFC8178].
What needs to be specified to define such new layout types is
discussed in Section 19.1.
19.1. Layout Specification Needs
Layout type specifications need to provide:
* An understanding of the interoperability model associated with the
layout type.
These models are discussed in Section 19.1.1.
* Description/definition used to the storage access protocol used to
access the storage devices including specifying how information
provided with the layout affects the IO operations performed.
* The types that need to be known by both the metadata server and
client in order to obtain, return, and commit layouts. The
relevant requests are generally defined containing a nominally
opaque item whose realization by particular layout types is
tailored to the specific needs of that layout type.
These types, whose use needs to explained in layout specification
documents, are summarized in Section 19.1.2.
* Information regarding how pNFS requirements in Sections 19.1.3
through 19.1.5 are met needs to be provided by layout type
specifications.
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* In addition, the information described in Sections 19.1.6 through
19.1.10 needs to be provided.
19.1.1. Layout Type Interoperability Models
One component of the required interoperability needs implementation
on the metadata server and client, acting as requester and responder,
although with a different polarity based on the nature of the
requests involved. This applies to all layout types. These consists
of:
* The implementation described in Section 18.
* The functions described Sections 25.40 through 25.44.
All of these need to be supported by the metadata server in the
role of responder. It is up to the layout type specification to
define the circumstance under which the client needs to use these
in the role of requester.
* The function described in Section 27.3.
This needs to be supported by the client in the role of responder.
It is up to the layout type specification to define the
circumstance under which the metadata server is to use these in
the role of requester. As part of this it needs to clearly define
how the absence of a functioning reverse-direction request path.
Note that many of the requests discussed above contain per-layout-
type data types, as discussed in Section 19.1.2. Discussing how
these are used needs to be explained by the layout type
specification.
In addition to the above, within the NFSv4.1 protocol proper, there
is a set of communication requirements involving at least two of
three components involved in performing IO using pNFS. As a result
there are two interoperability choices for layout types to choose:
* Compatibility models requiring the development of a specific
control protocol for use between the metadata server and one or
more data servers.
Such models typically involve the development of file-system-
specific control mechanisms with the metadata server and data
server implementations being developed together.
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In many cases, these control mechanisms take the form of a bespoke
control protocol (in the strict sense). Often such protocols
cannot be published as standards since the implementation might
involve file-system-specific details that raise serious
intellectual property concerns.
* Compatibility in which an existing protocol, such as a storage
protocol is co-opted as a means to effect the required control
mechanisms.
In this case, it is up to the layout type specification to explain
how the existing protocol can be used to how the storage protocol
can be used to ensure that pNFS requirements in Sections 19.1.3
through 19.1.5 are met.
19.1.2. Layout-Type-Specific Data Types
The XDR definitions of the requests and responses for pNFS operations
and callbacks often contain fields best describe as "nominally
opaque". This term is appropriate because:
* These fields are defined within the protocol as variable- length
opaque arrays.
* The actual data within these arrays is not opaque but is defined
by overlay type whose content is established outside the DR
framework.
While this approach differs from the spirit of XDR use, it has been
used within NFSv4 for a long time, first being used in these protocol
as part of the new NFSv4 attribute model.
The nominally opaque fields whose overlay type need to be provided by
the layout type specification include the following:
* The da_addr_body field of the device_addr4 data type.
* The loh_body field of the layouthint4 data type.
* The loc_body field of layout_content4 data type (which in turn is
the lo_content field of the layout4 data type)
* The lou_body field of the layoutupdate4 data type.
* The lrf_body field of the layoutreturn_file4 structure.
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19.1.3. Control Protocol Layout Management Functions"
The following functions need to be addressed:
* Whether revocation of layouts is supported.
* When a layout is revoked, the metadata server MUST effect the
suppression of future access using the revoked layout and ensure
that there are no "lingering" WRITTEs left active after the
revocation completes.
Some ways control protocols might provide support involve requests
made by the metadata server to the data server to eliminate its
record of previously-granted layouts.
* Layout conflicts and other situations that might result in layout
recall or revocation being needed need to be described.
19.1.4. Other Control Protocol Functions"
Whatever control protocol is provided, it needs to support the
implementation of the functions listed below. In this list a
requirement incumbent upon implementation is presented first,
together with examples of how control protocols might provide support
to allow the requirements to be met. With regard to the potential
normative character of these examples, discussed in Section 19.1.9,
these examples are not normative while it the obligation of the
specification to provide some possible means of satisfying the need
to be addressed in defining the layout type that is normative. Those
evaluating the suitability of proposed new layout types are urged to
make sure this obligation is satisfied so that the requirements
imposed on the implementer can be satisfied.
* Because the client MAY still send I/O requests to the metadata
server, even though the metadata server has successfully given the
client a layout, the metadata server needs to be able to perform
IO requests directed at the metadata server, even though the data
is present on a data storage device such as a data server. In
doing so, it MUST perform the same operation as would be required
by the NFSv4.1 protocol, if the operation were directed to an
NFSv4 server when the pNFS feature is not involved.
Some ways control protocols might provide support involve ways for
the metadata server to request execution of the IO request by the
data server on behalf of the client making the original request so
that the results can be returned to the client.
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In some configurations, no inter-server request is necessary,
since the data storage devices might be directly accessed by the
metadata server, in the same way they would be accessed by the
data access protocol.
* IOs sent to data storage devices must be considered authorized
only if the authorization checking is the same as would be done
when they were sent directly to the metadata server or a non-PNFS
data server. When this authorization checking finds the request
not authorized, it MUST NOT be performed.
Generally and as described in [I-D.dnoveck-nfsv4-security],
explicit authorization checking at IO time is not required, since
most IO operations are performed by the principal that opened the
file. However, in the case in which other principals are
performing IO, the layout type specification needs to indicate how
the necessary checking is done.
This can involve use of the control protocol, to do the checking
on the metadata server, or depending on the client to do the
necessary checking. The layout type specification needs to make
clear how this checking is done so that the result is the same as
would have resulted for IOs directed at metadata server. In this
regard, the uncertainty about the authorization semantics
associated with the NFSv4 ACL model needs to be accommodated.
* The values reported by the metadata server as to the value of
attributes such as modify time, the change attribute, and the EOF
position (i.e. the size attribute) MUST reflect the effect of IO
operations directed to data storage devices, except where the
discrepancies indicated below are tolerated for a limited time:
- While the size of a file can be affected by WRITE requests
directed at the metadata server and by WRITE operations
directed to data storage devices, it is not always clear
whether or how any particular operation affects the file size,
when files are divided into multiple pieces (using striping or
other mechanisms) resident on multiple data storage devices.
In such cases the metadata server may not always have the
definitive file size value but it MUST return the correct value
when the attribute is interrogated by GETATTR/(N)VERIFY after a
LAYOUTCOMMIT is done.
It is the obligation of the layout type specification to
explain how that correct value is to be obtained. This can
involve the knowledge that the metadata server might have as to
the location of the server holding the last component, and
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details of the control program whereby the data server keeps
the metadata server aware if extension to the size of the last
component that might need to be propagated to the metadata
server in the event of a LAYOUTCOMMIT.
- Attributes such as modified_time and change are affected by
WRITEs performed at the data storage device. Such changes need
to be reflected at the metadata server as soon as execution of
LAYOUTCOMMIT for the layout associated with the WRITEs.
Situation in which these are propagated without an explicit
LAYOUTCOMMIT need to be documented in the layout type
specification document.
- A LAYOUTCOMMIT requires that changes in attributes resulting
from operations on the storage device using the layout
committed need to be reflected in the attributes available on
the metadata server before the LAYOUTCOMMIT is responded to.
It is the obligation of the layout type specification to make
it clear how this requirement is to be adhered to.
* Operations directed at the metadata server often need to involve
storage allocation, whether the operation involves creating,
deleting, extending, or truncating files.
The storage allocation MUST be the same as would have been done if
the corresponding operation was performed on an NFSv4.1 server for
which pNFS was not active (or active but not used).
The layout type specification needs to explain how this is to be
done. The following approaches are common for existing layout
types:
- The storage allocation is done by the file system component,
whether that resides with the metadata server or another data
server.
In such cases, the client is unaware of the details of storage
allocation since it sees only the file abstraction, which is
designed to hide these details.
- The storage allocation is done by the metadata server with the
client informed of the detail so that it can use the storage
assigned as the source or destination for IO requests
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- The storage allocation is done by a distinct file system
component and the client needs to be aware of the assigned
location as seen by the metadata server and the data storage
device despite the fact that the latter are different from the
physical addresses used by the data server.
19.1.5. IO Checking Requirements
The requirements listed below were introduced by Section 18.7.1 and
do not always require control protocol support. Nevertheless, they
are discussed here because corresponding requirements for the data
storage device might exist for some layout types and these would
require control protocol support.
The client has these obligations when making I/O requests to the
storage devices:
* Clients MUST NOT perform I/O to the storage device if they do not
have layouts for the files in question.
* Clients MUST NOT perform I/O operations outside of the specified
ranges in the layout segment.
* Clients MUST NOT perform I/O operations that would be inconsistent
with the iomode specified in the layout segments it holds.
* Clients MUST NOT perform I/O operations that would not be
authorized if performed by the metadata server.
It is important to understand that the need to make these checks
might make it inappropriate to discard layout information as
discussed in Section 18.7.3.1
The ability of the data storage device to verify that these
requirements are being adhered to varies with the layout type, as
does the potentially normative requirements for the data server to do
this verification and for the layout type specification to describe
the means by which the control protocol provides the data storage
device the means information necessary to effect such verification.
It is not inherently necessary for a layout type specification to
address the question of storage device normative verification
requirement. Nevertheless, if there is no such requirement, the
security consequences need to be addressed. Furthermore, if this
requirement exists, it is incumbent on the layout type to explain how
the data storage device can obtain the information necessary to do
the required verification.
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19.1.6. Security-related Requirements"
A security considerations section needs to be provided by each layout
type specification,. This section needs to explain how the NFSv4.1
authentication and authorization functions are preserved. That is,
if a metadata server would prevent processing of a READ or WRITE
operation, how would a corresponding IO issued using the layout type
being described be prevented.
19.1.7. Recovery Requirements"
The specification needs to describe the methods of recovery from the
following situations:
* Failure and restart for client, metadata server, storage device.
* Lease expiration from perspective of the active client, metadata
server, and possibly the storage device when applicable.
* Loss of layout state resulting in fencing of client access to
storage devices (for an example, see Section 18.9.3).
19.1.8. Requirements Regarding Committing Layouts
While the XDR provided by Section 25.42 provides extensive
flexibility as to how this function is to be provided, it is not
clear how, for particular layout types, flexibility is to be
appropriately used.
As a result, layout type specifications need to provide the following
information:
* Whether the size value presented is always used if it extends the
file or whether there are circumstances in which the metadata
server is not to do so.
This information is necessary because the statement "may use this
information" makes it extremely unclear how a global view of the
file size might be maintained if it is not so used.
* Whether, and under what circumstances, the metadata server might
use a modified time suggestion provided with LAYOUTCOMMIT.
When this is allowed, there needs to be an explanation about how
lack of time synchronization is to be dealt with and how it deals
with necessary checking of suggested values.
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Also needed is a discussion of how acceptance of such suggestions
affects the change attribute.
* While the XDR defining the format of the lou_body field is made
available as part of defining overlays for nominally opaque types,
explanation of the semantics and uses of this information needs to
be provided to make it clear how LAYOUTCOMMIT is to be used.
* The circumstances under which LAYOUTCOMMIT is necessary. Given
the general assumption that this is necessary iff WEITE operations
are done using layouts, this can be addressed by combining
specification of other situations in which LAYOUCOMMIT is required
and discussion of situations which WRITEs are done and
LAYOUTCOMMIT is NOT required.
19.1.9. Requirements Regarding Layout Termination
Layout termination involves the return, recall, and revocation of
layouts, and participants' discarding of layout information.
As a result, layout type specifications need to provide the following
information:
* In the case of layout return, there is not expected to be any
restrictions on clients' ability to return layouts, other than
requiring the client to wait for pending IO's to complete. In the
event such restrictions exist, the layout type specification needs
to describe them.
For layout types in which IO validation is done on data storage
devices, requirements regarding making the device aware of the
termination of the layout (and consequent refusal of further IO
and draining of current ones) need to be clearly stated.
* The case of layout recall is similar in that restrictions, if they
exist, need to be described by the layout type specification.
In cases in which recall needs to be done only for some layout
types (e.g. REMOVE), the requirements need to be clearly stated.
* While layout revocation is always possible due to an unacceptably
delayed layout recall or a failure-like situation such a an
expired lease, some layout types might allow it in other
situations. These need to be described clearly.
Where these situations are described using the term "conflicting
layouts", the meaning of this term needs to be explained clearly.
This is particularly important because [RFC8881] defined this in a
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way that does not apply to the files layout when server-
multipathing is in effect. Also, it need to be made clear whether
non-layout-based IO operations can have the same effect.
Descriptions of how these situations are to be dealt with need to
describe how IO operations using the revoked layouts are prevented
and existing ones drained. In this context, where referring to
"fencing" is stated in a requirement, it needs to be supplemented
by an explanation of how the requirement is dealt with in all
situations. For example, informing a data server of a layout's
termination needs to be supplemented by consideration of the
situation in which the data server cannot be contacted.
* As discussed in Section 18.7.3.1, clients and metadata servers may
discard layout information without worry about the inconsistency
between the MDA and clients thereby created. However, there can
be restrictions on such discarding based on the layout type.
These need to be clearly described.
19.1.10. Requirements Regarding Feature Interactions"
The layout type specifications need to provide information about
OPTIONAL features that are not supported (or for which special
handling for support is required) for particular layout types.
These features can include those defined after publication of the
layout type specification. While it would be appropriate for the
specification of relevant gaps to be the responsibility of the
extension defining the feature, it is often the case that these
issues were not recognized for some new features.
This situation can result in restrictions that are hard to explain
when the features involved are part of Minor Version Two. Mention of
such features is not fully appropriate in this document, but the
prospect for bis documents for the optional feature or the existing
layout types seems too far off to properly advise potential
implementors. For this reason, we will mention such difficulties in
order to provide helpful implementation information in the layout
type specification or in subsections of Section 19.
19.2. Addressing Requirements for Existing Layout Types
Each of the existing layout types is expected to address the
requirements discussed in previous subsections of Section 19.
However, because some of the definitions of these layout types were
published before these requirements were laid out in detail, it might
be that the existing definition might not make it sufficiently clear
how these requirements were addressed.
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In addition, it might be important to note potential difficulties
with OPTIONAL added in a late minor version.
Descriptions of how existing layout types address these requirements
are to be found as described below:
* The definitions of the blocks, objects, and scsi layout types,
were published before [RFC8434] was published and the need for the
layout type requirements was fully recognized. For a discussion
of how the layout type requirements are addressed, see Sections
19.2.1, 19.2.3 and, 19.2.2 respectively.
* The definition of the flexible files layout type was published
after [RFC8434] but before some the necessity for some of the
clarifications provided in this document were recognized. For a
discussion of how the layout type requirements were addressed, see
Section 19.2.4,
* Although the original definition of the files layout type was
published before [RFC8434], the revisions made as part of the
NFSv4.1 respecification effort can reasonably be expected to make
it clear how the layout type requirements were addressed. In any
case, for a discussion how those revision might affect existing
implementation that relied on earlier specifications, see
Section 20.26 for derails.
19.2.1. Blocks Layout Type and Layout Type Requirements
This layout type was described in [RFC5663], before the obligations
of layout type specifications first discussed in [RFC8434] were
understood. While it is has proved possible for these gaps to be
dealt with by implementers involved in the pNFS effort, the need for
wider understanding of the pNFS feature at this stage of protocol
development makes it necessary to fill in these gaps in this section.
One important class of gaps concerns the need to deal with matters
that need to be explained, as provided for in Section 19.1.4,
Although, the answers could be considered obvious, it might not be so
to all readers and it would be helpful if the explanations below were
taken into account when reading [RFC5663]
* It is not made sufficiently clear how IO request authorization is
provided for.
It needs to be clearly stated that this layout type's approach to
authorization checking relies on the checking being done at OPEN
time, and that cases in which this checking is not adequate are
problematic.
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Of particular concern are IO requests to be performed by a
principal different from the one that the opened file. In order
to provide the same authorization results that would be provided
for an IO request sent to the MDS would require the client to use
ACCESS on each such IO but that needs to be stated clearly if that
is to be done.
One likely approach to this issue and some discussed below (e.g.
mandatory byte-range locks) could be addressed as is done in
Section 3 of [RFC8154].
* The role of the control protocol with respect to storage
allocation needs to be clarified.
While [RFC8434] suggests that this is somehow a control protocol
function and [RFC5663] is silent on the matter, it needs to be
made clear that, for this layout type, the control protocol is not
involved in storage allocation and that allocation are performed
by the file system as they are when pNFS is not involved. The
only exception, which is mentioned in [RFC5663], concerns
allocation which occurs as part of granting writable layouts and
their possible role in implementing copy-on-write.
Another important class of gaps concern the need for discussion of
OPTIONAL features which cannot be supported or require special effort
to support when using this layout type.
* Mandatory byte-range locks are not supportable together with
layouts of the layout type.
Servers which do support such locking need to avoid granting
layouts of this type while such locks are active.
Granting of layout of this type cannot be done when such locks are
in effect for the target file.
* When a server supports NFSv4 ACLs and the server supports use of
distinct permissions for extending file and for overwriting
existing bytes, proper authorization cannot be guaranteed, making
it impossible to grant layout on file with ACLs that sometime
allow one of these actins and not the other.
19.2.2. Scsi Layout Type and Layout Type Requirements
This layout type was described in [RFC8154], before the obligations
of layout type specifications first discussed in [RFC8434] were fully
described.
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Nevertheless, these issues appear have been better understood when
this document was written since this document does address many of
the issues noted in Section 19.2.1 in its Section 3 which clarifies
authorization and locking semantics conformance. While it appears
that, given these, improvements, it might be better if [RFC8154]
obsoleted [RFC5663], as things currently stand, [RFC5663], has been
neither updated or obsoleted by [RFC8154], For a discussion of how
this issues is to be addressed, see Appendix D.2.15.
Despite this large improvement, there remain a number of difficulties
with [RFC8154] lack of attention to the specification's requirements
of [RFC8434] and Section 19, including the following.
* The issue with regard to the clarification of storage allocation
noted in Section 19.2.1 applies equally to this layout type.
* The issue with regard to handling of NFSv4 ACLs noted in
Section 19.2.1 applies equally to this layout type.
19.2.3. Object Layout Type and Layout Type Requirements
This layout type was described in [RFC5664], before the obligations
of layout type specifications first discussed in [RFC8434] were
understood. As a result it will be necessary to fill in these gaps
in this section.
The following issues, noted for other similar layout types, need to
be noted:
* This document, like [RFC5663] does not adequately address many of
the issues noted in Section 19.2.1 regarding authorization and
locking semantics.
As in the case of the blocks layout type, the material in
Section 3 of [RFC8154] is helpful.
* The discussion of allocation while it is not explicit as it might
be, is adequate since it clear that, in this case storage
allocation is a control protocol function, since the control
protocol and the storage protocol are the same.
* The issue with regard to handling of NFSv4 ACLs noted in
Section 19.2.1 applies equally to this layout type and needs to be
addressed similarly to this document.
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19.2.4. Flexible Files Layout Type and Layout Type Requirements
Issues relating to the suitability of this for description of a file
layouts with tight coupling are discussed in Section 19.2.4.1.
The following issues, including a number noted for other layout
types, need to be noted:
* Issues related to locking semantics appear to have been adequately
dealt with in Section 2.3 of [RFC8434].
* Issues with regard to authorization, including dealing with IOs
issued by non-opening principals and other matters relating to the
use of NFSv4 ACLs do not appear to be addressed adequately. This
appears to be due primarily to the fact that the working group was
constrained, in dealing with the authorization-related issues
dealt with in [I-D.dnoveck-nfsv4-security] and
[I-D.ietf-nfsv4-acls-update] to allow a wide range of previously
allowed behavior, invalidating apparently reasonable assumptions
made by the authors of [RFC8435].
Because the existing text relating to authorization is different
for the tight and loose cases, this matter will be discussed in
detail in Section 19.2.4.1.
19.2.4.1. Tight Coupling Using the Flex File Layout Type
As this document is currently written, it attempts to describe
support for multiple storage protocols and multiple approaches to the
handling of locking and authorization. While the description of the
tight coupling model is helpful, it cannot, for reasons explained
below, serve simultaneously as the layout type specification for what
are essentially two different ways of providing access to data
storage devices.
To illustrate the problem, let us look at the statement "The
requirements for a control protocol are specified in [RFC5661] and
clarified in [RFC8434]" appearing in the document Introduction. Part
of the clarification provided in [RFC8434] and Section 19 includes
the requirement that certain matters need to be addressed in a
layout-type-specific fashion with the responsibility for explaining
the particulars of many matters left to the layout type specification
for that layout type. This creates the following difficulties for
the approach currently taken in [RFC8435]
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* The differences between tight and loose coupling are so great that
they cannot be addressed in this framework using the same layout
type for both, as many of the layout-type-specific matters are
likely to be different for these two approaches.
When the description of these two models are interspersed, as they
are now, it is difficult to deal simultaneously with situations in
which request verification is the responsibility of two different
parties and fencing has such wide differences in granularity and
disruptiveness.
A related practical difficulty concerns the inability of clients
to know before, receiving a layout, the type of coupling and the
nature of the storage protocol. Given that the client can only
specify the layout type, it has no way of making sure before
requesting a layout, that t is one that it can use or of helping
the MDS to provide one it can use.
* Layout-type-specific matters are addressed in Section 20, where
layout-type-specific descriptions are provided for the file layout
type, since tis section is layout specification for the files
layout type. There appears to be no specification of the tight
flexible file layout type even if a value were assigned for this
purpose.
If it is intended that these all be dealt with identically, there
needs to be document stating this clearly. As it is, we have a
set of remarks, not always correct, about how these issues might
be addressed in various circumstances.
Of particular importance is the very different approaches, to
request validation and fencing taken in the files layout type and
the loose-coupling case. As a result, it needs to e clearly
stated what approach is be taken in the case of tight-coupling of
flex-files layouts.
* The handling of request authorization appear to be different for
the two types of coupling with both different from the handling
specified in Section 20. All of the cases discussed below need to
deal with the cases that have proved difficult to deal with for
other layout types, including IOs issued by principals other than
the opener, potential finer-grained write permissions for NFSv4
ACLs, and the existing underspecification of NFSv4 ACLs.
* Authorization for loose coupling appears to be described by the
third paragraph of the Security Considerations section of
[RFC8434] which is quoted (with interspersed comments) below:
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The metadata server enforces the file access control policy at
LAYOUTGET time. The client should use RPC authorization
credentials for getting the layout for the requested iomode
((LAYOUTIOMODE4_READ or LAYOUTIOMODE4_RW), and the server
verifies the permissions and ACL for these credentials,
possibly returning NFS4ERR_ACCESS if the client is not allowed
the request ed iomode.
Although following the above probably harmless, it considerably
confuses the matter since layouts, like delegations, are of client
scope and can be used by multiple principals doing IO operations
on multiple OPENs of the same file.
If the LAYOUTGET operation succeeds, the client receives, as
part of the layout, a set of credentials allowing it I/O access
to the specified data files corresponding to the requested
iomode.
This is the essence of the loose file authentication approach.
When the client acts on I/O operations on behalf of its local
users, it MUST authenticate and authorize the user by issuing
respective OPEN and ACCESS calls to the metadata server,
similar to having NFSv4 data delegations.
Needs further clarification although it is correct except for the
confusing mention of authentication by ACCESS and OPEN. Suggest
something like the following:
When the client issues IO requests on behalf of local users, it
use the credential provided by LAYOUTGET. However, it need the
authorization provided by a previous OPEN to ensure that the
opening principal can validly perform the operation. In cases
in which IO operations are performed by principals other than
the opener, ACCESS MUST be used to verify the authorization to
perform the IO request.
* The authorization described for the tight coupling case seems to
assume that if the MDS copies the authorization-related attributes
from the MDS to the data server, the authorization will be the
same. While it would be nice if this were the case, the
underspecification of ACL authorization semantics and the liberal
approach to existing variances from POSIX authorization makes it
hard to rely on. This is probably not a practical problem, if, as
seems to be the case, the discussion of tight coupling is
basically exploratory, making it likely that it can be changed
before being used in a standards-track environment
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* For authorization handling in the files layout type, the material
in Section 20.14.2 provides helpful suggestions.
It should be consulted as possibilities for addressing
authorization issues in the context of tight coupling are
considered.
19.2.5. Needed Updates to Layout Specification Documents
As described in Sections 19.2.2 and 19.2.3, there need to be changes
made to [RFC8154] and [RFC5663]
* [RFC5664] needs to incorporate the material in Section 3 of
[RFC8154] and the update regarding ACL handling currently
presented in Section 19.2.1.
* [RFC8154] needs to the update regarding ACL handling currently
presented in Section 19.2.1.
As a result, this draft and subsequent ones will be marked as
updating [RFC8154] and [RFC5664].
There need to be updates to [RFC5664] and [RFC8435]. However,
because of the issues noted below, these will only affect the status
of these documents in later drafts.
* Because of uncertainty about the continuing need for a non-SCSI
block layout type and how that need might be best provided for,
the working group needs to discuss the issues in Appendix D.2.15
and decide on a way forward involving obsoleting or updating
[RFC5663].
* Because of the interaction between authorization issues and the
question of how and when to address questions related to tight
coupling, it is would be best if the working group addresses the
need for changes following the recommendations of the authors of
[RFC8435].
The working group, in deciding on a way to address issues in this
document, will need to accommodate the authors' plans for future
development of this layout type.
20. The pNFS File Layout Type
This section describes the structure and semantics of the file-based
layout type or pNFS. These file-based layouts use the layout type
LAYOUT4_NFSV4_1_FILES and use NFSv4.1 as a Data Access Protocol
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The information required of all layout type specifications by
Section 19 are provided, for the file layout type, in this section
and included subsections.
There a number of noteworthy characteristics of this layout type that
affect many of the specific characteristics that are to be provided
by layout type specification documents. How these issues are dealt
with in the case of the files layout type are effected by the
following salient design characteristics:
* Because the data storage protocol is identical to that used when
pNFS is not present, there is no potential performance benefit, as
there might be with other layout types, from the use of simpler,
more direct means of performing IO operations.
However, there is a corresponding benefit from directing IO
requests to the servers able to support them directly. This IO
direction function can improve performance by eliminating the
overhead associated with request forwarding with clustered
servers,
* Because the data storage device is a data server containing, at
the least, facilities to persistently record, the physical
location and extent of written data, there is no need for this
information to be part of the interaction with the data storage
device, allowing them to use a file-like access paradigm.
As a result, facilities such as the use of LAYOUTCOMMIT can be
dispensed with in many cases and will never require client
estimates of file attributes to be provided to the metadata
server.
* Because data server devices are expected to have significant
intracluster communication facilities that can be used as part of
a control protocol, information can be passed between the metadata
sever and data storage devices, allowing IO checking to be
performed by the data storage device.
This allows extensive changes to the client to be avoided, thereby
eliminating dependence on IO checking being done by the client
with its negative effect on security.
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20.1. Recent Changes to the File Layout Type
In addition to the re-organization made necessary by the
incorporation of the new Section 19, there are a number of changes
made to fill in gaps left in previous descriptions of this layout
type and correct misunderstandings where previous descriptions of
pNFS did not pay adequate attention to important aspects of this
layout type and the need to deal with the possibility of server-
multipathing (See Section 20.9.
The following issues should be noted:
* Although there were previously references to the need for layout
specifications to specify whether those layout types had the
ability to revoke layouts or to do so "unilaterally", there is was
no explicit statement either accepting or forbidding this for the
files layout type.
Given this lack, it is reasonable to suppose this is allowed since
the files layout type, unlike others, has facilities for fine-
grained non-disruptive fencing.
We have adopted the approach of allowing this because there is no
basis to deny it and because of the need to correctly deal with
WRITEs in the server-multipathing case.
* There are some statements regarding the possibility of layout
conflict which seem to be based on experience with and the needs
of block layouts and only apply to file layouts if the possibility
of server-multipathing is not considered.
This has no practical effect, since the MDS is always free to
recall layouts. Nevertheless, to make things clearer, we needed
to explain such conflicts and how they can arise when server
multipathing is possible.
In order to address this issue we limited the core of recognition
of conflicts to cases of range overlaps and made the rest the
responsibility of the layout type (for the file layout type, this
is discussed in Section 20.18.)
* There are some confusing statements allowing clients to not check
IOs for proper values of layout iomode before issuing WRITEs.
It appears that, for the file layout type, which relies on the
data server to do IO checking, iomode is checked for WRITEs as it
should be.
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Making the check obligatory or using "SHOULD" raises compatibility
issues so we are not changing this, since it workable where
server-multipathing is not an issue.
As modified, we state that checking the iomode is not a general
protocol need but that there are situations (e.g. server-
multipathing) that make it advisable.
Section 13.5 of [RFC5661] and [RFC8881] contains the following
statement which appears to be an early and ultimately not very
helpful discussion of what we have come to call server-multipathing.
It is not always necessary for the two data server addresses to
designate the same server with trunking being used. For example,
the data could be read-only, and the data consist of exact
replicas.
As it wow, about sixteen years later appears necessary to deal,
within in the protocol, transitions to and from situations in which
two areas of a file are read-only replicas, the revised discussion of
the files layout type in Section 20. In so doing, the changes
already discussed to revocation, conflicts and the handling of layout
iomode are pretty much essential, even though they would be
justifiable on other grounds.
20.2. File Layout Type Motivation
The compatibility model (see Section 19.1.1 is one which requires the
development of file-system-specific control mechanisms to meet the
requirements laid out in Section 19 and the performance goals of the
layout type, as described below:
* To provide access to the greater IO throughput made available by a
server cluster, without requiring the user to be aware of detailed
file location information,
* To avoid unnecessary request forwarding by directing IO requests
to servers prepared to execute them directly. This IO direction
function often makes it preferable to request IO operations using
file layout rater than using the metadata server as a point of
access.
* To provide the ability to provide greater throughput while
accessing a single file by including facilities for striping data
across multiple NFSv4.1 data servers.
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20.3. Protocol Feature Support for the Files Layout Type
In general, the addition of post-NFSv4.1 OPTIONAL features are
unlikely to cause difficulties for existing implementations of the
files layout type, although some level of control protocol extension
is likely to be necessary. For example, features that involve
storage allocation changes such those providing hole-punching can
generally be accommodated using facilities for remote request
execution on the associated data server(s).
There is one important case in which support for server-multipathing
(See Section 20.9) was not present for previous implementations of
this layout type and the lack of recognition of this as an important
case in [RFC8881] could leads to lack of support for this case, if,
as suggested in previous specification, conformance to iomode was
ignored. For this reason, those who need support for server
multipathing show be aware of the importance of checking for iomode
validity in order to provide support for server multipsthing.
20.4. Storage Protocol for the Files Layout Type
The storage protocol used to perform IO to the storage devices, which
are data servers in this case, is identical in form to that use to
perform IO to the metadata server, or to an NFSv4.1 server operating
outside the PNFS framework.
Despite this general arrangement, the following discussion of
instances of different treatments and for adherence to uniform
treatment are to be adhered to:
* The checking of authorization done on the data server MUST be
identical to that which would be performed if the IO request were
directed to the metadata server.
While, for the most part, the server performing the IO only needs
to explicitly check authorization if the principal performing the
IO is different from the opener, there can be occasions in which
to provide the identical handling required in previous paragraph,
by adapting to the consequences of some unfortunate gaps in the
specification of NFSv4.1 authorization semantics, the data server
might need to adhere to what is now non-standard authorization
checking, matching that of the metadata server.
Because previous specifications (i.e. [RFC3530], [RFC7530],
[RFC5661], [RFC8881]) did not discuss authorization semantics, it
was necessary to fill this gap in [I-D.dnoveck-nfsv4-security]
but, in so doing, previously acceptable behavior could not be
invalidated. In addition, because of ACL underspecification in
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previous documents, [I-D.ietf-nfsv4-acls-update] had to be written
with similar difficulties because of existence of current
implementations with a wide range of semantics implemented.
As a result. because of the possibility of various undocumented
authorization schemes existing, it might not be possible to
appropriately document the necessary control protocol activity in
Sections 20.14.2 and 20.15 while clearly explaining the most
common case, following POSIX, with limited modification to support
that part of NFSv4 ACLs that fits within the POSIX authorization
model. As a result, implementors need to focus on meeting the
requirement regarding identical authorization and are responsible
for effecting it in the control protocol provided for coordination
among servers
* The possibility, within NFSv4 ACLs, of separate ACE mask bits
separately controlling authorization for extending and for
overwriting existing file data, might make it impossible to fully
ascertain write authorization at open time and limit checking to
the case in which principals other than the opener issue IO.
* When stateids are sent to the data server, they are obtained from
the metadata server rather than from the same server used to do
the IO, as is done when pNFS is not involved.
Despite the above, there are restrictions described in
Section 20.10 that limit the stateids that can be used. Only
stateids with a zero seqid are to be used in performing IO
operations using the file layout type and special stateids cannot
be used.
* Since stateids are interpreted based on the associated clientid,
it is necessary that IO operations be done as part of sessions
that are associated with the same clientid associated with the
clientid used to obtained the stateid.
For a discussion of how such a clientid is to be obtained, see
Section 20.5.
This situation, in which multiple sessions share a clientid, is
similar to that that in effect when clientid trunking is in
effect. However, implementation is simpler since in the pNFS
files case since only one session can cause changes to the locking
state, unless clientid trunking is supported as well.
* The file handles used to designate files on which IO is to be done
are likely to be different since the handle established as part of
the layout is to be used.
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* Although the principals are often the same and need to be
compared, their existence in different forms (e.g. name@domain vs.
numeric uids) will require reliable mapping between multiple forms
as is often necessary at the protocol-filesystem interface.
20.5. Client ID and Session Considerations
Sessions are a REQUIRED feature of NFSv4.1, and this requirement for
use applies to both the metadata server and file-based
(NFSv4.1-based) data servers.
The role a server plays in pNFS is determined by the result it
returns from EXCHANGE_ID. The roles are:
* Metadata server (EXCHGID4_FLAG_USE_PNFS_MDS is set in the result
eir_flags).
* Data server (EXCHGID4_FLAG_USE_PNFS_DS).
* Non-metadata server (EXCHGID4_FLAG_USE_NON_PNFS). This is an
NFSv4.1 server that does not support operations (e.g., LAYOUTGET)
or attributes that pertain to pNFS.
The client MAY request zero or more of EXCHGID4_FLAG_USE_NON_PNFS,
EXCHGID4_FLAG_USE_PNFS_DS, or EXCHGID4_FLAG_USE_PNFS_MDS, even though
some combinations (e.g., EXCHGID4_FLAG_USE_NON_PNFS |
EXCHGID4_FLAG_USE_PNFS_MDS) are contradictory. However, the server
MUST only return the following acceptable combinations:
+========================================================+
| Acceptable Results from EXCHANGE_ID |
+========================================================+
| EXCHGID4_FLAG_USE_PNFS_MDS |
+--------------------------------------------------------+
| EXCHGID4_FLAG_USE_PNFS_MDS | EXCHGID4_FLAG_USE_PNFS_DS |
+--------------------------------------------------------+
| EXCHGID4_FLAG_USE_PNFS_DS |
+--------------------------------------------------------+
| EXCHGID4_FLAG_USE_NON_PNFS |
+--------------------------------------------------------+
| EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_NON_PNFS |
+--------------------------------------------------------+
Table 7
As the above table implies, a server can have one or two roles. A
server can be both a metadata server and a data server, or it can be
both a data server and non-metadata server. In addition to returning
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two roles in the EXCHANGE_ID's results, and thus serving both roles
via a common client ID, a server can serve two roles by returning a
unique client ID and server owner for each role in each of two
EXCHANGE_ID results, with each result indicating each role.
In the case of a server with concurrent pNFS roles that are served by
a common client ID, if the EXCHANGE_ID request from the client has
zero or a combination of the bits set in eia_flags, the server result
should set bits that represent the higher of the acceptable
combination of the server roles, with a preference to match the roles
requested by the client. Thus, if a client request has
(EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS |
EXCHGID4_FLAG_USE_PNFS_DS) flags set, and the server is both a
metadata server and a data server, serving both the roles by a common
client ID, the server SHOULD return with
(EXCHGID4_FLAG_USE_PNFS_MDS | EXCHGID4_FLAG_USE_PNFS_DS) set.
In the case of a server that has multiple concurrent pNFS roles, each
role served by a unique client ID, if the client specifies zero or a
combination of roles in the request, the server results SHOULD return
only one of the roles from the combination specified by the client
request. If the role specified by the server result does not match
the intended use by the client, the client should send the
EXCHANGE_ID specifying just the interested pNFS role.
If a pNFS metadata client gets a layout that refers it to an NFSv4.1
data server, it needs a client ID on that data server. If it does
not yet have a client ID from the server that had the
EXCHGID4_FLAG_USE_PNFS_DS flag set in the EXCHANGE_ID results, then
the client needs to send an EXCHANGE_ID to the data server, using the
same co_ownerid as it sent to the metadata server, with the
EXCHGID4_FLAG_USE_PNFS_DS flag set in the arguments. If the server's
EXCHANGE_ID results have EXCHGID4_FLAG_USE_PNFS_DS set, then the
client may use the client ID to create sessions that will exchange
pNFS data operations. The client ID returned by the data server has
no relationship with the client ID returned by a metadata server
unless the client IDs are equal, and the server owners and server
scopes of the data server and metadata server are equal.
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In NFSv4.1, the session ID in the SEQUENCE operation implies the
client ID, which in turn might be used by the server to map the
stateid to the right client/server pair. However, when a data server
is presented with a READ or WRITE operation with a stateid, because
the stateid is associated with a client ID on a metadata server, and
because the session ID in the preceding SEQUENCE operation is tied to
the client ID of the data server, the data server has no obvious way
to determine the metadata server from the COMPOUND procedure, and
thus has no way to validate the stateid. One RECOMMENDED approach is
for pNFS servers to encode metadata server routing and/or identity
information in the data server filehandles as returned in the layout.
If metadata server routing and/or identity information is encoded in
data server filehandles, when the metadata server identity or
location changes, the data server filehandles it gave out will become
invalid (stale), and so the metadata server MUST first recall the
layouts. Invalidating a data server filehandle does not render the
NFS client's data cache invalid. The client's cache should map a
data server filehandle to a metadata server filehandle, and a
metadata server filehandle to cached data.
If a server is both a metadata server and a data server, the server
might need to distinguish operations on files that are directed to
the metadata server from those that are directed to the data server.
It is RECOMMENDED that the values of the filehandles returned by the
LAYOUTGET operation be different than the value of the filehandle
returned by the OPEN of the same file.
Another scenario is for the metadata server and the storage device to
be distinct from one client's point of view, and the roles reversed
from another client's point of view. For example, in the cluster
file system model, a metadata server to one client might be a data
server to another client. If NFSv4.1 is being used as the storage
protocol, then pNFS servers need to encode the values of filehandles
according to their specific roles.
20.5.1. Sessions Considerations for Data Servers
Section 7.11.2 states that a client has to keep its lease renewed in
order to prevent a session from being deleted by the server. If the
reply to EXCHANGE_ID has just the EXCHGID4_FLAG_USE_PNFS_DS role set,
then (as noted in Section 20.10) the client will not be able to
determine the data server's lease_time attribute because GETATTR will
not be permitted. Instead, the rule is that any time a client
receives a layout referring it to a data server that returns just the
EXCHGID4_FLAG_USE_PNFS_DS role, the client can validly assume that
the lease_time attribute from the metadata server that returned the
layout applies to the data server. Thus, the data server MUST be
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aware of the values of all lease_time attributes of all metadata
servers for which it is providing I/O, and it MUST use the maximum of
all such lease_time values as the lease interval for all client IDs
and sessions established on it.
For example, if one metadata server has a lease_time attribute of 20
seconds, and a second metadata server has a lease_time attribute of
10 seconds, then if both servers return layouts that refer to an
EXCHGID4_FLAG_USE_PNFS_DS-only data server, the data server MUST
renew a client's lease if the interval between two SEQUENCE
operations on different COMPOUND requests is less than 20 seconds.
20.6. File Layout Definitions
The following definitions apply to the LAYOUT4_NFSV4_1_FILES layout
type and might be applicable to other layout types.
Unit. A unit is a fixed-size quantity of data written to a data
server.
Pattern. A pattern is a method of distributing one or more equal
sized units across a set of data servers. A pattern is iterated
one or more times.
Stripe. A stripe is a set of data distributed across a set of data
servers in a pattern before that pattern repeats.
Stripe Count. A stripe count is the number of units in a pattern.
Stripe Width. A stripe width is the size of a stripe in bytes. The
stripe width = the stripe count * the size of the stripe unit.
Hereafter, this document will refer to a unit that is a written in a
pattern as a "stripe unit".
A pattern may have more stripe units than data servers. If so, some
data servers will have more than one stripe unit per stripe. A data
server that has multiple stripe units per stripe MAY store each unit
in a different data file (and depending on the implementation, will
possibly assign a unique data filehandle to each data file).
20.7. File Layout Data Types
This sections defines the specific types overlaying the nominally
opaque types listed in Section 19.1.2
The high level NFSv4.1 layout types are:
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* nfsv4_1_file_layouthint4 overlaying the loh_body field of the
layouthint4 data type. This type is described in detail in
Section 20.7.1.
* nfsv4_1_file_layout_ds_addr4 overlaying the da_addr_body field of
the deice_sddr4 data type. This type is described in detail in
Section 20.7.2.
* nfsv4_1_file_layout4 overlaying the loc_body field of the
layout_content4 data type. This type is described in detail in
Section 20.7.2.
* Within the file layout type, there is no layout-type-specific
overlay for the lou_body field of the layouytupdate4 data type or
for the lrf_body field of the layoutreturn_file4 structure.
As a result, this field can have any value with a zero-length
opaque string being most convenient.
20.7.1. File Layout Hint-related Data Types
The SETATTR operation supports a layout hint attribute
(Section 11.16.4). When the client sets a layout hint (data type
layouthint4) with a layout type of LAYOUT4_NFSV4_1_FILES (the
loh_type field), the opaque loh_body field is overlaid by a value of
data type nfsv4_1_file_layouthint4.
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const NFL4_UFLG_MASK = 0x0000003F;
const NFL4_UFLG_DENSE = 0x00000001;
const NFL4_UFLG_COMMIT_THRU_MDS = 0x00000002;
const NFL4_UFLG_STRIPE_UNIT_SIZE_MASK
= 0xFFFFFFC0;
typedef uint32_t nfl_util4;
enum filelayout_hint_care4 {
NFLH4_CARE_DENSE = NFL4_UFLG_DENSE,
NFLH4_CARE_COMMIT_THRU_MDS
= NFL4_UFLG_COMMIT_THRU_MDS,
NFLH4_CARE_STRIPE_UNIT_SIZE
= 0x00000040,
NFLH4_CARE_STRIPE_COUNT = 0x00000080
};
/* Encoded in the loh_body field of data type layouthint4: */
struct nfsv4_1_file_layouthint4 {
uint32_t nflh_care;
nfl_util4 nflh_util;
count4 nflh_stripe_count;
};
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The generic layout hint structure is described in Section 9.3.19.
The client uses the layout hint in the layout_hint (Section 11.16.4)
attribute to indicate the preferred type of layout to be used for a
newly created file. The layout-type-specific contents for the files
layout in the layout hint is composed of three fields. The first
field, nflh_care, is a set of flags indicating which values of the
hint the client cares about. If the NFLH4_CARE_DENSE flag is set,
then the client indicates in the second field, nflh_util, a
preference for how the data file is packed (Section 20.8.4), which is
controlled by the value of the expression nflh_util & NFL4_UFLG_DENSE
("&" represents the bitwise AND operator). If the
NFLH4_CARE_COMMIT_THRU_MDS flag is set, then the client indicates a
preference for whether the client should send COMMIT operations to
the metadata server or data server (Section 20.11), which is
controlled by the value of nflh_util & NFL4_UFLG_COMMIT_THRU_MDS. If
the NFLH4_CARE_STRIPE_UNIT_SIZE flag is set, the client indicates its
preferred stripe unit size, which is indicated in nflh_util &
NFL4_UFLG_STRIPE_UNIT_SIZE_MASK (thus, the stripe unit size MUST be a
multiple of 64 bytes). The minimum stripe unit size is 64 bytes. If
the NFLH4_CARE_STRIPE_COUNT flag is set, the client indicates in the
third field, nflh_stripe_count, the stripe count. The stripe count
multiplied by the stripe unit size is the stripe width.
20.7.2. File Layout Content-related Data Types
When LAYOUTGET returns a files layout (indicated in the loc_type
field of the lo_content field), the loc_body field of the lo_content
field contains a value of data type nfsv4_1_file_layout4. Among
other content, nfsv4_1_file_layout4 has a storage device ID (field
nfl_deviceid) of data type deviceid4. The GETDEVICEINFO operation
maps a device ID to a storage device address (type device_addr4).
When GETDEVICEINFO returns a device address with a layout type of
LAYOUT4_NFSV4_1_FILES (the da_layout_type field), the da_addr_body
field contains a value of data type nfsv4_1_file_layout_ds_addr4.
typedef netaddr4 multipath_list4<>;
/*
* Encoded in the da_addr_body field of
* data type device_addr4:
*/
struct nfsv4_1_file_layout_ds_addr4 {
uint32_t nflda_stripe_indices<>;
multipath_list4 nflda_multipath_ds_list<>;
};
The nfsv4_1_file_layout_ds_addr4 data type represents the device
address. It is composed of two fields:
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1. nflda_multipath_ds_list: An array of lists of data servers, where
each list can be one or more elements, and each element
represents a data server address that may serve equally as the
target of I/O operations (see Section 20.9). The length of this
array might be different than the stripe count.
2. nflda_stripe_indices: An array of indices used to index into
nflda_multipath_ds_list. The value of each element of
nflda_stripe_indices MUST be less than the number of elements in
nflda_multipath_ds_list. Each element of nflda_multipath_ds_list
SHOULD be referred to by one or more elements of
nflda_stripe_indices. The number of elements in
nflda_stripe_indices is always equal to the stripe count.
/*
* Encoded in the loc_body field of
* data type layout_content4:
*/
struct nfsv4_1_file_layout4 {
deviceid4 nfl_deviceid;
nfl_util4 nfl_util;
uint32_t nfl_first_stripe_index;
offset4 nfl_pattern_offset;
nfs_fh4 nfl_fh_list<>;
};
The nfsv4_1_file_layout4 data type represents the layout. It is
composed of the following fields:
1. nfl_deviceid: The device ID that maps to a value of type
nfsv4_1_file_layout_ds_addr4.
2. nfl_util: Like the nflh_util field of data type
nfsv4_1_file_layouthint4, a compact representation of how the
data on a file on each data server is packed, whether the client
should send COMMIT operations to the metadata server or data
server, and the stripe unit size. If a server returns two or
more overlapping layouts, each stripe unit size in each
overlapping layout MUST be the same.
3. nfl_first_stripe_index: The index into the first element of the
nflda_stripe_indices array to use.
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4. nfl_pattern_offset: This field is the logical offset into the
file where the striping pattern starts. It is required for
converting the client's logical I/O offset (e.g., the current
offset in a POSIX file descriptor before the read() or write()
system call is sent) into the stripe unit number (see
Section 20.8.1).
If dense packing is used, then nfl_pattern_offset is also needed
to convert the client's logical I/O offset to an offset on the
file on the data server corresponding to the stripe unit number
(See Section 20.8.4).
Note that nfl_pattern_offset is not always the same as lo_offset.
For example, via the LAYOUTGET operation, a client might request
a layout starting at offset 1000 of a file that has its striping
pattern start at offset zero.
5. nfl_fh_list: An array of data server filehandles for each list of
data servers in each element of the nflda_multipath_ds_list
array. The number of elements in nfl_fh_list depends on whether
sparse or dense packing is being used.
* If sparse packing is being used, the number of elements in
nfl_fh_list MUST be one of three values:
- Zero. This means that filehandles used for each data
server are the same as the filehandle returned by the OPEN
operation from the metadata server.
- One. This means that every data server uses the same
filehandle: what is specified in nfl_fh_list[0].
- The same number of elements in nflda_multipath_ds_list.
Thus, in this case, when sending an I/O operation to any
data server in nflda_multipath_ds_list[X], the filehandle
in nfl_fh_list[X] MUST be used.
See the discussion on sparse packing in Section 20.8.4.
* If dense packing is being used, the number of elements in
nfl_fh_list MUST be the same as the number of elements in
nflda_stripe_indices. Thus, when sending an I/O operation to
any data server in
nflda_multipath_ds_list[nflda_stripe_indices[Y]], the
filehandle in nfl_fh_list[Y] MUST be used. In addition, any
time there exists i and j, (i != j), such that the
intersection of
nflda_multipath_ds_list[nflda_stripe_indices[i]] and
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nflda_multipath_ds_list[nflda_stripe_indices[j]] is not empty,
then nfl_fh_list[i] MUST NOT equal nfl_fh_list[j]. In other
words, when dense packing is being used, if a data server
appears in two or more units of a striping pattern, each
reference to the data server MUST use a different filehandle.
Indeed, if there are multiple striping patterns, as indicated
by the presence of multiple objects of data type layout4
(either returned in one or multiple LAYOUTGET operations), and
a data server is the target of a unit of one pattern and
another unit of another pattern, then each reference to each
data server MUST use a different filehandle.
See the discussion on dense packing in Section 20.8.4.
The details on the interpretation of the layout are in Section 20.8.
20.8. Interpreting the File Layout
20.8.1. Determining the Stripe Unit Number
To find the stripe unit number that corresponds to the client's
logical file offset, the pattern offset will also be used. The i'th
stripe unit (SUi) is:
relative_offset = file_offset - nfl_pattern_offset;
SUi = floor(relative_offset / stripe_unit_size);
20.8.2. Interpreting the File Layout Using Sparse Packing
When sparse packing is used, the algorithm for determining the
filehandle and set of data-server network addresses to write stripe
unit i (SUi) to is:
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stripe_count = number of elements in nflda_stripe_indices;
j = (SUi + nfl_first_stripe_index) % stripe_count;
idx = nflda_stripe_indices[j];
fh_count = number of elements in nfl_fh_list;
ds_count = number of elements in nflda_multipath_ds_list;
switch (fh_count) {
case ds_count:
fh = nfl_fh_list[idx];
break;
case 1:
fh = nfl_fh_list[0];
break;
case 0:
fh = filehandle returned by OPEN;
break;
default:
throw a fatal exception;
break;
}
address_list = nflda_multipath_ds_list[idx];
The client would then select a data server from address_list, and
send a READ or WRITE operation using the filehandle specified in fh.
Consider the following example:
Suppose we have a device address consisting of seven data servers,
arranged in three equivalence (Section 20.9) classes:
{ A, B, C, D }, { E }, { F, G }
where A through G are network addresses.
Then
nflda_multipath_ds_list<> = { A, B, C, D }, { E }, { F, G }
i.e.,
nflda_multipath_ds_list[0] = { A, B, C, D }
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nflda_multipath_ds_list[1] = { E }
nflda_multipath_ds_list[2] = { F, G }
Suppose the striping index array is:
nflda_stripe_indices<> = { 2, 0, 1, 0 }
Now suppose the client gets a layout that has a device ID that maps
to the above device address. The initial index contains
nfl_first_stripe_index = 2,
and the filehandle list is
nfl_fh_list = { 0x36, 0x87, 0x67 }.
If the client wants to write to SU0, the set of valid { network
address, filehandle } combinations for SUi are determined by:
nfl_first_stripe_index = 2
So
idx = nflda_stripe_indices[(0 + 2) % 4]
= nflda_stripe_indices[2]
= 1
So
nflda_multipath_ds_list[1] = { E }
and
nfl_fh_list[1] = { 0x87 }
The client can thus write SU0 to { 0x87, { E } }.
The destinations of the first 13 stripe units are:
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+=====+============+==============+
| SUi | filehandle | data servers |
+=====+============+==============+
| 0 | 87 | E |
+-----+------------+--------------+
| 1 | 36 | A,B,C,D |
+-----+------------+--------------+
| 2 | 67 | F,G |
+-----+------------+--------------+
| 3 | 36 | A,B,C,D |
+-----+------------+--------------+
+-----+------------+--------------+
| 4 | 87 | E |
+-----+------------+--------------+
| 5 | 36 | A,B,C,D |
+-----+------------+--------------+
| 6 | 67 | F,G |
+-----+------------+--------------+
| 7 | 36 | A,B,C,D |
+-----+------------+--------------+
+-----+------------+--------------+
| 8 | 87 | E |
+-----+------------+--------------+
| 9 | 36 | A,B,C,D |
+-----+------------+--------------+
| 10 | 67 | F,G |
+-----+------------+--------------+
| 11 | 36 | A,B,C,D |
+-----+------------+--------------+
+-----+------------+--------------+
| 12 | 87 | E |
+-----+------------+--------------+
Table 8
20.8.3. Interpreting the File Layout Using Dense Packing
When dense packing is used, the algorithm for determining the
filehandle and set of data server network addresses to write stripe
unit i (SUi) to is:
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stripe_count = number of elements in nflda_stripe_indices;
j = (SUi + nfl_first_stripe_index) % stripe_count;
idx = nflda_stripe_indices[j];
fh_count = number of elements in nfl_fh_list;
ds_count = number of elements in nflda_multipath_ds_list;
switch (fh_count) {
case stripe_count:
fh = nfl_fh_list[j];
break;
default:
throw a fatal exception;
break;
}
address_list = nflda_multipath_ds_list[idx];
The client would then select a data server from address_list, and
send a READ or WRITE operation using the filehandle specified in fh.
Consider the following example (which is the same as the sparse
packing example, except for the filehandle list):
Suppose we have a device address consisting of seven data servers,
arranged in three equivalence (Section 20.9) classes:
{ A, B, C, D }, { E }, { F, G }
where A through G are network addresses.
Then
nflda_multipath_ds_list<> = { A, B, C, D }, { E }, { F, G }
i.e.,
nflda_multipath_ds_list[0] = { A, B, C, D }
nflda_multipath_ds_list[1] = { E }
nflda_multipath_ds_list[2] = { F, G }
Suppose the striping index array is:
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nflda_stripe_indices<> = { 2, 0, 1, 0 }
Now suppose the client gets a layout that has a device ID that maps
to the above device address. The initial index contains
nfl_first_stripe_index = 2,
and
nfl_fh_list = { 0x67, 0x37, 0x87, 0x36 }.
The interesting examples for dense packing are SU1 and SU3 because
each stripe unit refers to the same data server list, yet each stripe
unit MUST use a different filehandle. If the client wants to write
to SU1, the set of valid { network address, filehandle } combinations
for SUi are determined by:
nfl_first_stripe_index = 2
So
j = (1 + 2) % 4 = 3
idx = nflda_stripe_indices[j]
= nflda_stripe_indices[3]
= 0
So
nflda_multipath_ds_list[0] = { A, B, C, D }
and
nfl_fh_list[3] = { 0x36 }
The client can thus write SU1 to { 0x36, { A, B, C, D } }.
For SU3, j = (3 + 2) % 4 = 1, and nflda_stripe_indices[1] = 0. Then
nflda_multipath_ds_list[0] = { A, B, C, D }, and nfl_fh_list[1] =
0x37. The client can thus write SU3 to { 0x37, { A, B, C, D } }.
The destinations of the first 13 stripe units are:
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+=====+============+==============+
| SUi | filehandle | data servers |
+=====+============+==============+
| 0 | 87 | E |
+-----+------------+--------------+
| 1 | 36 | A,B,C,D |
+-----+------------+--------------+
| 2 | 67 | F,G |
+-----+------------+--------------+
| 3 | 37 | A,B,C,D |
+-----+------------+--------------+
+-----+------------+--------------+
| 4 | 87 | E |
+-----+------------+--------------+
| 5 | 36 | A,B,C,D |
+-----+------------+--------------+
| 6 | 67 | F,G |
+-----+------------+--------------+
| 7 | 37 | A,B,C,D |
+-----+------------+--------------+
+-----+------------+--------------+
| 8 | 87 | E |
+-----+------------+--------------+
| 9 | 36 | A,B,C,D |
+-----+------------+--------------+
| 10 | 67 | F,G |
+-----+------------+--------------+
| 11 | 37 | A,B,C,D |
+-----+------------+--------------+
+-----+------------+--------------+
| 12 | 87 | E |
+-----+------------+--------------+
Table 9
20.8.4. Sparse and Dense Stripe Unit Packing
The flag NFL4_UFLG_DENSE of the nfl_util4 data type (field nflh_util
of the data type nfsv4_1_file_layouthint4 and field nfl_util of data
type nfsv4_1_file_layout) specifies how the data is packed within the
data file on a data server. It allows for two different data
packings: sparse and dense. The packing type determines the
calculation that will be made to map the client-visible file offset
to the offset within the data file located on the data server.
If nfl_util & NFL4_UFLG_DENSE is zero, this means that sparse packing
is being used. Hence, the logical offsets of the file as viewed by a
client sending READs and WRITEs directly to the metadata server are
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the same offsets each data server uses when storing a stripe unit.
The effect then, for striping patterns consisting of at least two
stripe units, is for each data server file to be sparse or "holey".
So for example, suppose there is a pattern with three stripe units,
the stripe unit size is 4096 bytes, and there are three data servers
in the pattern. Then, the file in data server 1 will have stripe
units 0, 3, 6, 9, ... filled; data server 2's file will have stripe
units 1, 4, 7, 10, ... filled; and data server 3's file will have
stripe units 2, 5, 8, 11, ... filled. The unfilled stripe units of
each file will be holes; hence, the files in each data server are
sparse.
If sparse packing is being used and a client attempts I/O to one of
the holes, then an error MUST be returned by the data server. Using
the above example, if data server 3 received a READ or WRITE
operation for block 4, the data server would return
NFS4ERR_PNFS_IO_HOLE. Thus, data servers need to understand the
striping pattern in order to support sparse packing.
If nfl_util & NFL4_UFLG_DENSE is one, this means that dense packing
is being used, and the data server files have no holes. Dense
packing might be selected because the data server does not
(efficiently) support holey files or because the data server cannot
recognize read-ahead unless there are no holes. If dense packing is
indicated in the layout, the data files will be packed. Using the
same striping pattern and stripe unit size that were used for the
sparse packing example, the corresponding dense packing example would
have all stripe units of all data files filled as follows:
* Logical stripe units 0, 3, 6, ... of the file would live on stripe
units 0, 1, 2, ... of the file of data server 1.
* Logical stripe units 1, 4, 7, ... of the file would live on stripe
units 0, 1, 2, ... of the file of data server 2.
* Logical stripe units 2, 5, 8, ... of the file would live on stripe
units 0, 1, 2, ... of the file of data server 3.
Because dense packing does not leave holes on the data servers, the
pNFS client is allowed to write to any offset of any data file of any
data server in the stripe. Thus, the data servers need not know the
file's striping pattern.
The calculation to determine the byte offset within the data file for
dense data server layouts is:
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stripe_width = stripe_unit_size * N;
where N = number of elements in nflda_stripe_indices.
relative_offset = file_offset - nfl_pattern_offset;
data_file_offset = floor(relative_offset / stripe_width)
* stripe_unit_size
+ relative_offset % stripe_unit_size
If dense packing is being used, and a data server appears more than
once in a striping pattern, then to distinguish one stripe unit from
another, the data server MUST use a different filehandle. Let's
suppose there are two data servers. Logical stripe units 0, 3, 6 are
served by data server 1; logical stripe units 1, 4, 7 are served by
data server 2; and logical stripe units 2, 5, 8 are also served by
data server 2. Unless data server 2 has two filehandles (each
referring to a different data file), then, for example, a write to
logical stripe unit 1 overwrites the write to logical stripe unit 2
because both logical stripe units are located in the same stripe unit
(0) of data server 2.
20.9. Multipathing to Data Servers
The NFSv4.1 file layout supports multipathing to multiple data server
addresses. This can take the form of network multipathing or server
multipathing:
* Network multipathing is used for bandwidth scaling via trunking
(Section 7.5) and for higher availability of use in the event of a
network discontinuity.
* Server Multipathing allows the client to switch to other data
server addresses which may be that of another data server that is
providing access to the same data, without having to contact the
metadata server for a new layout.
Note however, that care needs to be taken when there are WRITEs
involved as users of the two data servers for multiple IOs can
result in data corruption because this situation could result in
formerly pieces of date becoming non-identical, making server-
multipathing inappropriate until the data sets become identical
once again. As a result, layouts based on server-multipathing can
be recalled/revoked due to conflicts arising from writable layouts
or WRITEs performed by the MDS. For details see Section 20.18.
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To support multipathing, each element of the nflda_multipath_ds_list
contains an array of one more data server network addresses. This
array (data type multipath_list4) represents a list of data servers
(each identified by a network address), with the possibility that
some data servers will appear in the list multiple times.
The client is free to use any of the network addresses as a
destination to send data server requests. If some network addresses
are less optimal paths to the data than others, then the MDS SHOULD
NOT include those network addresses in an element of
nflda_multipath_ds_list. If less optimal network addresses exist to
provide failover, the RECOMMENDED method to offer the addresses is to
provide them in a replacement device-ID-to-device-address mapping, or
a replacement device ID. When a client finds that no data server in
an element of nflda_multipath_ds_list responds, it SHOULD send a
GETDEVICEINFO to attempt to replace the existing device-ID-to-device-
address mappings. If the MDS detects that all data servers
represented by an element of nflda_multipath_ds_list are unavailable,
the MDS SHOULD send a CB_NOTIFY_DEVICEID (if the client has indicated
it wants device ID notifications for changed device IDs) to change
the device-ID-to-device-address mappings to the available data
servers. If the device ID itself will be replaced, the MDS SHOULD
recall all layouts with the device ID, and thus force the client to
get new layouts and device ID mappings via LAYOUTGET and
GETDEVICEINFO.
Typically, if two network addresses appear in an element of
nflda_multipath_ds_list, they will designate the same data server,
and the two data server addresses will support the implementation of
client ID or session trunking (the latter is RECOMMENDED) as defined
in Section 7.5. The two data server addresses will share the same
server owner or major ID of the server owner.
It is not always necessary for the two data server addresses to
designate the same server with trunking being used. One example,
consists of situations in which the data could be read-only, and the
data consist of exact replicas. In cases in which these replicas are
subject to change, the occurrence of WRITEs constitute a layout
conflict (see Section 20.18 even if a layout is not used to perform
the WRITE, leading to layout recall and/or revocation (see 20.17 and
20.18).
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20.10. Operations Sent to NFSv4.1 Data Servers
Clients accessing data on an NFSv4.1 data server MUST send only the
NULL procedure and COMPOUND procedures whose operations are taken
only from two restricted subsets of the operations defined as valid
NFSv4.1 operations. Clients MUST use the filehandle specified by the
layout when accessing data on NFSv4.1 data servers.
The first of these operation subsets consists of management
operations. This subset consists of the BACKCHANNEL_CTL,
BIND_CONN_TO_SESSION, CREATE_SESSION, DESTROY_CLIENTID,
DESTROY_SESSION, EXCHANGE_ID, SECINFO_NO_NAME, SET_SSV, and SEQUENCE
operations. The client may use these operations in order to set up
and maintain the appropriate client IDs, sessions, and security
contexts involved in communication with the data server. Henceforth,
these will be referred to as data-server housekeeping operations.
The second subset consists of COMMIT, READ, WRITE, and PUTFH. These
operations MUST be used with a current filehandle specified by the
layout. In the case of PUTFH, the new current filehandle MUST be one
taken from the layout. Henceforth, these will be referred to as
data-server I/O operations. As described in Section 18.7.1, a client
MUST NOT send an I/O to a data server for which it does not hold a
valid layout; the data server MUST reject such an I/O.
Unless the server has a concurrent non-data-server personality --
i.e., EXCHANGE_ID results returned (EXCHGID4_FLAG_USE_PNFS_DS |
EXCHGID4_FLAG_USE_PNFS_MDS) or (EXCHGID4_FLAG_USE_PNFS_DS |
EXCHGID4_FLAG_USE_NON_PNFS) see Section 20.5 -- any attempted use of
operations against a data server other than those specified in the
two subsets above MUST return NFS4ERR_NOTSUPP to the client.
When the server has concurrent data-server and non-data-server
personalities, each COMPOUND sent by the client MUST be constructed
so that it is appropriate to one of the two personalities, and it
MUST NOT contain operations directed to a mix of those personalities.
The server MUST enforce this. To understand the constraints,
operations within a COMPOUND are divided into the following three
classes:
1. An operation that is ambiguous regarding its personality
assignment. This includes all of the data-server housekeeping
operations. Additionally, if the server has assigned filehandles
so that the ones defined by the layout are the same as those used
by the metadata server, all operations using such filehandles are
within this class, with the following exception. The exception
is that if the operation uses a stateid that is incompatible with
a data-server personality (e.g., a special stateid or the stateid
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has a non-zero "seqid" field, see Section 20.14.1), the operation
is in class 3, as described below. A COMPOUND containing
multiple class 1 operations (and operations of no other class)
MAY be sent to a server with multiple concurrent data server and
non-data-server personalities.
2. An operation that is unambiguously referable to the data-server
personality. This includes data-server I/O operations where the
filehandle is one that can only be validly directed to the data-
server personality.
3. An operation that is unambiguously referable to the non-data-
server personality. This includes all COMPOUND operations that
are neither data-server housekeeping nor data-server I/O
operations, plus data-server I/O operations where the current fh
(or the one to be made the current fh in the case of PUTFH) is
only valid on the metadata server or where a stateid is used that
is incompatible with the data server, i.e., is a special stateid
or has a non-zero seqid value.
When a COMPOUND first executes an operation from class 3 above, it
acts as a normal COMPOUND on any other server, and the data-server
personality ceases to be relevant. There are no special restrictions
on the operations in the COMPOUND to limit them to those for a data
server. When a PUTFH is done, filehandles derived from the layout
are not valid. If their format is not normally acceptable, then
NFS4ERR_BADHANDLE MUST result. Similarly, current filehandles for
other operations do not accept filehandles derived from layouts and
are not normally usable on the metadata server. Using these will
result in NFS4ERR_STALE.
When a COMPOUND first executes an operation from class 2, which would
be PUTFH where the filehandle is one from a layout, the COMPOUND
henceforth is interpreted with respect to the data-server
personality. Operations outside the two classes discussed above MUST
result in NFS4ERR_NOTSUPP. Filehandles are validated using the rules
of the data server, resulting in NFS4ERR_BADHANDLE and/or
NFS4ERR_STALE even when they would not normally do so when addressed
to the non-data-server personality. Stateids must obey the rules of
the data server in that any use of special stateids or stateids with
non-zero seqid values must result in NFS4ERR_BAD_STATEID.
Until the server first executes an operation from class 2 or class 3,
the client MUST NOT depend on the operation being executed by either
the data-server or the non-data-server personality. The server MUST
pick one personality consistently for a given COMPOUND, with the only
possible transition being a single one when the first operation from
class 2 or class 3 is executed.
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Because of the complexity induced by assigning filehandles so they
can be used on both a data server and a metadata server, it is
RECOMMENDED that where the same server can have both personalities,
the server assign separate unique filehandles to both personalities.
This makes it unambiguous for which server a given request is
intended.
GETATTR and SETATTR MUST be directed to the metadata server. In the
case of a SETATTR of the size attribute, the control protocol is
responsible for propagating size updates/truncations to the data
servers. In the case of extending WRITEs to the data servers, the
new size must be visible on the metadata server once a LAYOUTCOMMIT
has completed and in some other circumstances (See Section 18.7.4).
Section 20.16 which describes the mechanisms by which the client is
to handle data-server files that do not reflect the metadata server's
size).
20.11. COMMIT through Metadata Server
The file layout provides two alternate means of providing for the
commit of data written through data servers. The flag
NFL4_UFLG_COMMIT_THRU_MDS in the field nfl_util of the file layout
(data type nfsv4_1_file_layout4) is an indication from the metadata
server to the client of the REQUIRED way of performing COMMIT, either
by sending the COMMIT to the data server or the metadata server.
These two methods of dealing with the issue correspond to broad
styles of implementation for a pNFS server supporting the file layout
type.
* When the flag is FALSE, COMMIT operations MUST to be sent to the
data server to which the corresponding WRITE operations were sent.
This approach is sometimes useful when file striping is
implemented within the pNFS server (instead of the file system),
with the individual data servers each implementing their own file
systems.
* When the flag is TRUE, COMMIT operations MUST be sent to the
metadata server, rather than to the individual data servers. This
approach is sometimes useful when file striping is implemented
within the clustered file system that is the backend to the pNFS
server. In such an implementation, each COMMIT to each data
server might result in repeated writes of metadata blocks to the
detriment of write performance. Sending a single COMMIT to the
metadata server can be more efficient when there exists a
clustered file system capable of implementing such a coordinated
COMMIT.
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If nfl_util & NFL4_UFLG_COMMIT_THRU_MDS is TRUE, then in order to
maintain the current NFSv4.1 commit and recovery model, the data
servers MUST return a common writeverf verifier in all WRITE
responses for a given file layout, and the metadata server's
COMMIT implementation must return the same writeverf. The value
of the writeverf verifier MUST be changed at the metadata server
or any data server that is referenced in the layout, whenever
there is a server event that can possibly lead to loss of
uncommitted data. The scope of the verifier can be for a file or
for the entire pNFS server. It might be more difficult for the
server to maintain the verifier at the file level, but the benefit
is that only events that impact a given file will require recovery
action.
Note that if the layout specified dense packing, then the offset used
to a COMMIT to the MDS may differ than that of an offset used to a
COMMIT to the data server.
The single COMMIT to the metadata server will return a verifier, and
the client should compare it to all the verifiers from the WRITEs and
fail the COMMIT if there are any mismatched verifiers. If COMMIT to
the metadata server fails, the client should re-send WRITEs for all
the modified data in the file. The client should treat modified data
with a mismatched verifier as a WRITE failure and try to recover by
resending the WRITEs to the original data server or using another
path to that data if the layout has not been recalled.
Alternatively, the client can obtain a new layout or it could rewrite
the data directly to the metadata server. If nfl_util &
NFL4_UFLG_COMMIT_THRU_MDS is FALSE, sending a COMMIT to the metadata
server might have no effect. If nfl_util & NFL4_UFLG_COMMIT_THRU_MDS
is FALSE, a COMMIT sent to the metadata server should be used only to
commit data that was written to the metadata server. See
Section 18.9.6 for recovery options.
20.12. The Layout Iomode
The layout iomode need not be used in all cases by the metadata
server when servicing NFSv4.1 file-based layouts, although in some
circumstances its use might be necessary. For example, if the server
implementation supports reading from read-only replicas or mirrors,
it is necessary for the server to return a layout enabling the client
to do so. To support cases in which WRITEs need to be prevented to
ensure that data provided by multiple servers is the same (e.g. to
support server-multipathing) the client SHOULD set the iomode based
on its intent to read or write the data. The iomode need not be
checked by all data servers when clients perform I/O. However, the
data servers MUST still validate that the client holds a valid layout
and return an error if the client does not.
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20.13. LAYOUTCOMMIT on file layouts
As discussed in detail below, requirement for the use of LAYOUTCOMMIT
are quite limited, since the control protocol has the ability to
coordinate attribute changes arising from WRITE operations and make
the result visible to the metadata server and clients. This
information, together with the details below, provides the
appropriate file-layout-related information required in
Section 19.1.4.
* There is no need for the client to provide the file size as part
of LAYOUTCOMMIT.
* There is no need for the client to provide a modified time as part
of LAYOUTCOMMIT.
* When LAYOUTCOMMIT is done the resulting change attribute should
reflect either the change value derived from the modified time or
a value treating the LAYOUTCOMMIT as if it were a WRITE.
* There is no provision for additional information to be provided as
part of LAYOUTCOMMIT, as it is for other layout types.
For file layouts, WRITEs to a Data Server that return a stable_how4
value of FILE_SYNC4 guarantee that data and file system metadata are
on stable storage. This implies that a LAYOUTCOMMIT is not needed in
order to make the data and metadata visible to the metadata server
and other clients.
For file layouts, when WRITE to the data server returns UNSTABLE4 or
DATA_SYNC4 and the NFL4_UFLG_COMMIT_THRU_MDS flag is set, the client
MUST send the COMMIT to the metadata server. A successful COMMIT to
the metadata server guarantees that data and file system metadata are
on stable storage. As a result, any time that
NFS4_UFLG_COMMIT_THRU_MDS is set, a LAYOUTCOMMIT (of the byte range
specified by the layout) is not needed.
For file layouts, when NFL4_UFLG_COMMIT_THRU_MDS flag is not set, and
WRITE or COMMIT to the data server return DATA_SYNC4, the client MUST
send the LAYOUTCOMMIT to the metadata server in order to synchronize
file metadata.
The following table summarizes the conditions under which a
LAYOUTCOMMIT is needed, and the effects of a COMMIT to a data server
and metadata server.
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+============+============+============+============+===========+
| NFL4_UFLG_ | WRITE to | Meaning of | Meaning of | LAYOUT |
| COMMIT_ | DS returns | COMMIT to | COMMIT to | COMMIT |
| THRU_MDS | | DS | DS | reequired |
+============+============+============+============+===========+
| Not Set | UNSTABLE | DATA_SYNC4 | Nothing | Yes |
+------------+------------+------------+------------+-----------+
| Not Set | DATA_SYNC4 | Nothing | Nothing | Yes |
+------------+------------+------------+------------+-----------+
| Not Set | FILE_SYNC4 | Nothing | Nothing | NO |
+------------+------------+------------+------------+-----------+
| Set | UNSTABLE | Nothing | FILE_SYNC4 | NO |
+------------+------------+------------+------------+-----------+
| Set | DATA_SYNC4 | Nothing | FILE_SYNC4 | NO |
+------------+------------+------------+------------+-----------+
| Not Set | FILE_SYNC4 | Nothing | Nothing | NO |
+------------+------------+------------+------------+-----------+
Table 10
Note that a client can always demand FILE_SYNC4 or DATA_SYNC4 via
WRITE arguments. Also note that specifying these stability levels
might adversely impact performance.
If a LAYOUTCOMMIT is required, it should be sent before CLOSE to
maintain close-to-open semantics. If required, it should be sent
before LOCKU, OPEN_DOWNGRADE, LAYOUTRETURN, and when the application
issues fsync() [fsync]. Again, if LAYOUTCOMMIT is required, it
should be sent periodically to keep the file size and modification
time approximately up-to-date. This allows the use of commands such
as "tail -f" which copies its input file to the standard output and
updates the output as new lines become available in the input file.
It is the client implementation's choice to determine how frequently
LAYOUTCOMMIT is issued. Possible policies include every N'th COMMIT
to a data server, every N'th unit of time, or after writing a stripe
to a set of data servers.
Even if a required LAYOUTCOMMIT is not issued by the client, the data
server and metadata servers have a set of responsibilities necessary
to provide data consistency:
1) Data servers MUST commit data and synchronize modification and
size attributes with the metadata server before a layout is
revoked as described in section 12.5.4.
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2) Data servers SHOULD commit data and synchronize modification and
size attributes with the metadata server after the metadata
server reboots. In theory the client should commit the data, but
this avoids the problem where both the client and metadata server
crash at the same time.
3) The metadata server MAY periodically poll data servers to
synchronize modification and size attributes.
20.14. File Layout Type Control Protocol
Although the specifics of the control protocol that might be used are
not specified in this document, implementations of the file layout
type need to provide control mechanisms, often in the form of a
control protocol to provide the functions described in Sections
19.1.3 through 19.1.5.
One important function is the coordination of stateid- related
information as described in 20.14.1 and 20.14.2
The functions described by Section 19.1.3 are provided as discussed
below:
* Revocation needs to be supported. One common way of doing this is
integrating the cancellation of the sharing of layout stateids
with sharing mechanisms described in Section 20.14.1.
* Similarly, when layouts are returned, the metadata server needs to
be made aware of their deletion.
This involves the layout management functions described in
Section 20.14.3.
The functions described by Section 19.1.4 are provided as discussed
below:
* Execution of I/O requests directed to the metadata server is
discussed in Section 20.19.
* Appropriate authorization of IO requests sent to data servers are
discussed in Section 20.14.2.
* Information relating to the committing of layouts, used to update
the metadata server's view of attributes that can be changed as a
consequence of IO operations, is provided in Section 20.13.
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* Information relating to the use of the control protocol in
providing needed storage allocation is provided in
Section 20.14.4.
20.14.1. Control Protocol State Coordination
As described in Section 20.4 it is often necessary for the metadata
server and some set of data server to share knowledge about the lock-
related objects denoted by stateids that may be used in IO operations
(i.e. open stateids, lock stateids, and delegation stateids) and
layout stateids. In each case the unique portion of the stateid has
an associated type and a file with which it is associated. Depending
on the type of stateids used with IO operations, the following
additional information needs to be shared if the file in question has
a layout involving one or more data servers.
* For open stateids, the open mode and the opening principal need to
be provided.
Because previous specifications required open-upgrade to be done
even when the principals were different, following this guidance
might make it impossible to correctly provide the principal as
described above. Although Section 14.9 corrects this issue,
implementers need to consider whether doing so (currently
specified as "SHOULD NOT") is still possible in this context even
though it might be possible in non-pNFS contexts.
When these change due to use of OPEN_DOWNGRADE or CLOSEs and
revocations of open state (treated as reducing the open mode to
zero), the client and associated data servers need to be made
aware of the changes of state.
Deny modes do not need to be provided to the data server since IO
operations outside of OPENs are not allowed to be sent data
servers when the file layout type is used. In this situation, the
open mode is always checked and there is no reason for the deny
mode to be accessed during checking.
* For delegation stateids, the type of delegation (read or write)
needs to be provided to the data server.
* For byte-range lock stateids, unless mandatory byte-range locking
is supported, sharing of this information is unnecessary.
Such locks do not affect the processing of IO operation.
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When mandatory byte-range locking is supported, the mode, bounds
and lockowner needs to be made available, unless, as discussed in
Section 20.20, data server support for this feature can be
avoided.
* For layout stateids, the range and IO mode needs to be provided.
If the metadata server chooses not to provide this information for
locking state created when there are no layouts forcing it to be
provided, then it is obliged to provide this information together
with the layout that makes its sharing necessary.
Given the coordination discussed above, the following rules are to be
used in determining the stateids to be used when client send IO
requests to data servers based of file type layouts. They differ
from those in Section 13.2.5.
* If the entity corresponding to the lock-owner (e.g., a process)
sending the I/O has a mandatory byte-range lock stateid for the
associated open file, then the byte-range lock stateid for that
lock-owner and open file SHOULD be used.
* If there is no appropriate mandatory byte-range lock stateid, then
the OPEN stateid for the open file in question SHOULD be used.
Although clients who hold delegations can do the equivalent of
opening files on their own, in such cases there is no MDS assigned
open stateid and the delegation is to be used instead.
* If there is neither an open stateid nor a mandatory byte-range
lock stateid, a delegation stateid, if it exits, SHOULD be used.
* If none of the above are available or there is no associated
layout, the IO MUST be sent to the MDS. See Section 20.19.
There are three basic approaches to sharing that can be used for the
above and for information that needs to be shared for reason
discussed in Section 20.14.2. Control protocols can use one of these
or a workable combination due to workloads and performance
requirements.
* Synchronous Propagation of changes is often used although its
contribution to latency often makes it desirable to find an
alternative.
* Asynchronous Propagation with Verification, when available, can be
used to reduce latency by providing a way for a subsequent
operation to determine whether the necessary change has occurred.
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* Synchronous Interrogation can be used to make it simpler to obtain
the current data directly from the metadata server using the
control protocol.
Because valid IO execution required a layout and a state id to be
sent with the IO request (i.e. an OPEN, delegation, or lock stateid),
the data server will need these only when stateids of both types are
available. This circumstance can be dealt with in a number of ways:
* Both the layouts and IO-request-associated stateids are propagated
independently to the data server. As a result, the data server
will honor an IO request when it has both a layout (including the
associated filehandle sent as part of the layout) and a valid
stateid.
In this case, the propagation of the of the IO stateids need to be
done synchronously while asynchronous propagation with
verification can be used for layout propagation.
Propagating stateid information even when layouts are not present
simplifies the handling of IO requests sent to the MDS. See
Section 20.19 for further discussion.
* Propagation can be limited to cases in which both necessary
elements are present. In this approach, stateids are not sent to
data servers unless a layout exists. As a result, when a layout
is generated, stateid information for a number of stateids will
need to be sent to the data server.
* A synchronous interrogation model can be used to avoid the need to
propagate stateid information other than layouts. Instead, the
MDS, who has the necessary information is interrogate using the
control protocol. Caching of successful interrogation can be used
but it will need to be supplemented layout protocol messages
advising the data server of a change in the associated stateid
set.
In the case of IO directed to the MDS, the same interrogation
paradigm is used locally, on the MDS.
In either of the cases described above, data servers need to be made
of the creation and deletion of layouts. This propagation is
necessary for the files layout type because state changes need to be
shared among three nodes. The consequences are discussed in
Section 20.14.3.
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20.14.2. Control Protocol Authorization Coordination
As provided for in Section 20.14.1, the need to apply the IO
authorization arrived at via OPEN, in the context of use of file
layouts can be addressed by providing data servers that receive
layout information with additional authorization-related data about
the stateids that can be used with those layouts. This information
will generally include identification of the principal that opened
and information about whether the open is for READ, WRITE or both.
While that addresses the common case in which the IO is only
requested by the OPENing principal, there is a need to provide valid
authorization when other principals perform layout-based IO
operations. There are multiple facilities the control protocol can
provide that can serve as part of a suitable facility to check for
valid authorization:
* Provide the ability within the control protocol for the data
server to request that an ACCESS-like operation be provided by the
MDS.
* Provide notification to LAYOUT-handling data servers of changes in
authorization-related attributes. This could used to allow
caching of ACCESS results with flushing of the cache on attribute
changes,
In the case in which IO operations are done using a delegation
stateid, it is the responsibility of the client performing OPENs
locally to check for authorization for the Opening principal locally.
Once this is done, I/O operations are authorized as discussed above
in that I/O performed by the opener are authorized based on the
authorization done at OPEN time, while those done by other principals
on the same client need to be authorized using the control protocol
facilities discussed above.
20.14.3. Control Protocol Layout Management
Due to the structure of implementations of the file layout type the
role of the data server in layout management is limited to responding
to propagation initiated by the MDS. This includes case of layout
creation and layout termination.
20.14.4. Control Protocol Role in Storage Allocation for File Layout
Type
Within the NFSv4.1 protocol there is relatively little need for the
control protocol to concern itself with matters related to storage
allocation, as explained below:
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* Allocation of new storage (and possible deallocation of existing
storage) as a result of WRITEs happen to the data server just as
they would if the WRITE was forwarded by the MDS or performed by
the data server without pNFS involvement.
* In case of file removal or truncation, the necessary storage
deallocation is the responsible of the data server executing a
control program requests issued by the MDS.
20.14.5. IO Validation for the Files Layout Type
IO validation, which needs to be done on the data server consists of
the following elements:
* Check for layout validity including the existence of a layout for
the file accessed by the client and the range of bytes being
within those specified
The validity of the layout iomode need not always be checked but
support for some features (e.g. server multipathing) are not
supported without checking this, so, for configurations in which
such support is needed, WRITEs to read-only layouts cannot be
processed and might cause layout revocation as described in
Section 20.18.
* Checking the validity of the stateid.
This generally requires control protocol support as described in
Section 20.14.1. In addition, if mandatory byte-range locks are
supported without pNFS, they need to be supported when the files
layout type is used as discussed in Section 20.20.
* Checking for proper IO authorization.
This is not necessary the stateid is for an open file and the
principal that opened the file (made available as described in
Section 20.14.1) is performing the IO operation.
20.15. File Attributes
Since the SETATTR operation has the ability to modify state that is
visible on both the metadata and data servers (e.g., the size), care
must be taken to ensure that the resultant state across the set of
data servers is consistent, especially when truncating or growing the
file.
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As described earlier, the LAYOUTCOMMIT operation is used to ensure
that the metadata is synchronized with changes made to the data
servers. For the NFSv4.1-based data storage protocol, it may be
necessary to re-synchronize state such as the size attribute, and the
setting of mtime/change/atime. See Section 18.7.4 for a full
description of the semantics regarding LAYOUTCOMMIT and attribute
synchronization. It should be noted that by using an NFSv4.1-based
layout type, it is possible to synchronize this state before
LAYOUTCOMMIT occurs. For example, the control protocol can be used
to query the attributes present on the data servers.
The OPEN operation (Section 25.16.4) does not impose any requirement
that I/O operations on an open file have the same credentials as the
OPEN itself (unless EXCHGID4_FLAG_BIND_PRINC_STATEID is set when
EXCHANGE_ID creates the client ID), and so it requires the server's
READ and WRITE operations to perform appropriate access checking,
when the principal making the IO request is not the same as that
doing the OPEN. As a result, changes to ACLs and other
authorization-related attributes (i.e. mode, owner, group_owner, or
similar attributes added later) may require effective sharing of the
new attribute values to deal with IO being done by principals other
than the opener, as discussed in Section 20.14.2.
20.16. Data Server Component File Size
A problem can arise when a component data file on a particular data
server has grown past EOF. This problem can occur for both dense and
sparse layouts.
Consider the following scenario: a client creates a new file (size ==
0) and writes to byte 131072; the client then seeks to the beginning
of the file and reads byte 100. The client expects to receive zeroes
back as a result of the READ. However, if the striping pattern
directs the client to send the READ to a data server other than the
one that received the client's original WRITE, the data server
servicing the READ might believe that the file's size is still 0
bytes. In that event, the data server's READ response would contain
zero bytes and an indication of EOF.
The data server is only able to return zeroes if it knows that the
file's size has been extended. While it might be possible to arrange
the control protocol to provide the requisite knowledge, no such
requirement has dealt with this issue in the past, making it possible
that data server could return EOF as discussed above.
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For this reason, when the offset in the arguments to READ is less
than the client's view of the file size and if the READ response
indicates EOF and/or contains fewer bytes than requested, the client
will need to interpret such a response as a hole in the file, and the
NFS client would substitute zeroes for the data.
Once the file is closed and a subsequent OPEN of the file is done,
the change attribute can be inspected for a difference from a cached
value for the change attribute. In cases such as those described
above, this implies that, if LAYOUTCOMMIT is done at close whenever
necessary (See Section 20.13), subsequent READs cannot encounter the
issue.
20.17. Revocation and Fencing for the Files Layout Type
This section provides information regarding the possibility of layout
revocation, as provided for by Section 19.1.3
There are a number of situations in which the implementations of the
file layout type, through its associated control protocol, need to
cancel existing layout and make it impossible for data servers to use
those layouts to execute further I/O operations using those layouts.
When this process is applied to all layouts associated with a client
for a file, the client is said to be "fenced" from access to the file
in question.
The following situations can result in this sort of layout
cancellation:
* Lease expiration for a client's lease to the MDS. In this case
all data server IO for the client is prevented.
* A Metadata sever restart results in all layouts issued by the
previous MDS instance being cancelled.
* A client fails to respond a CB_LAYOUTRECALL, making it necessary
for the MDs to cancel the layout without the client's assent.
* administrative intervention.
* A conflict such as those described in Section 20.18. The include
the issue of conflicting layouts or other IO operations that
invalidate the assumptions under which layout were previously
granted.
Fencing works as follows. As described in Section 20.5, in COMPOUND
procedure requests to the data server, the data filehandle provided
by the PUTFH operation and the stateid in the READ or WRITE operation
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are used to ensure that the client has a valid layout for the I/O
being performed. If it does not have such a layout, the I/O is
rejected with NFS4ERR_PNFS_NO_LAYOUT. The server can simply check
the stateid and, additionally, make the data filehandle stale if the
layout specified a data filehandle that is different from the
metadata server's filehandle for the file (See the nfl_fh_list
description in Section 20.7.2).
The procedure described above eliminate the possibility of execution
of "lingering" WRITEs, since requests that have not reached the data
server cannot be executed. However, it is possible that IO requests
that have passed this check might not complete in a reasonable time.
In this case, the client has the option of ceasing to wait and
considering the request failed or lease expiration might force it to
be discarded. In either case, there is no possibility of the request
being reissued since it will fail the check due to revocation of the
layout.
Before the metadata server takes any action to revoke layout state
given out by a previous instance, it must make sure that all layout
state from that previous instance are invalidated at the data
servers. This has the following implications.
* The metadata server must not restripe a file until it has
contacted all of the data servers to invalidate the layouts from
the previous instance.
* The metadata server must not give out mandatory locks that
conflict with layouts from the previous instance without either
doing a specific layout invalidation (as it would have to do
anyway) or doing a global data server invalidation.
20.18. Layout/IO Conflicts for the Files Layout Type
When the files layout type is used, conflicts between overlapping
layouts can arise in some circumstances when at least one of the
layouts allows WRITEs to be performed.
Such circumstances can arise when server-multipathing (as opposed to
network-multipathing) is in effect. (See Sections 20.9 and 20.12 for
details).
When server-multipathing is in effect, two distinct regions of
storage (or the same regions as mediated by two distinct data server
need to be kept identical. The presence of WRITEs to one or more of
those paths can invalidate this assumption in the ways listed below.
This can happen even when the iomodes are different.
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* If two distinct storage areas are involved an update to one will
result in incorrect data being returned by some READs
* If access to the same storage area is mediated by two different
data servers, caching done by either server will result in
incorrect results. When persistent write caching is used to
acknowledge stable WRITEs before WRITEs to the ultimate storage
location are performed, the problem is exacerbated
* When WRITEs are done to multiple paths, allocation might be done
separately on separate data servers, resulting in data corruption,
unless the two servers coordinate allocation, which they are
rarely in a position to do.
When WRITEs are performed by the MDS, the same sorts of problems
arise. As a result, when server-multipathing is being used to effect
read-sharing, WRITEs, whether issued to the MDS or data servers, need
to cause the revocation of WRITE-capable layouts so that we can
establish a state of affairs in which either multiple read-only
layouts or a single READ-WRITE layout is in effect.
20.19. File Layout MDS-directed IO
When IO requests are directed at a metadata server and the data is
located on a different server, the request is typically sent to the
appropriate data server even if there is no layout in effect that
would support the request being sent to that data server directly.
Despite the existing distribution arrangement which might arise in
the context of a distributed clustered NFSv4 server, there a number
of issues that require special attention.
* Validation of the stateid is often difficult to do on the data
server since stateid creation is an MDS-specific activity.
* Authorization checking, for the case in which the principal
performing the IO is not the opener.
20.20. File Layout Handling of Mandatory Byte-Range Locks
Although mandatory byte range locking is an OPTIONAL feature that is
not commonly used, there will be situations in which it is present
and needs to be accommodated in an environment in which pNFS using
the files layout type needs to be supported. There are multiple
approaches to doing so. These include:
* Those that exclude layouts and byte-range locks on the same files.
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This can be accomplished by recalling layouts associated with a
file before granting a mandatory byte-range lock. As a result IO
operations on such files will be formed by the MDS as describes in
Section 20.19.
Although this approach is not mentioned in [RFC8881] as a way to
support the requirement to honor these locks, it is, in many
environments, a way to take advantage of pNFS while avoiding its
use where it would hurt performance.
* Those that try to accommodate these features on the same file.
We are not considering the possibility of the data server
requesting IO clearance from MDS, since it similar but poorer-
performing than sending the request directly to the MDS.
This would require the propagation of byte-range locks and unlocks
to data servers (usually one but sometimes more) who might perform
IOs overlapping the range specified range. The fact that it is
hard to do this propagation asynchronously makes it a poor choice
in terms of performance when such locking is done.
* Those try to exclude read-write layouts and exclusive mandatory
byte range locks on the same file. This requires recall of write-
capable layouts before granting a request for an exclusive
mandatory byte-range lock.
This allows READs (more common than WRITEs) and shared byte range
locks to avoid the additional overhead resulting from byte-range
locking.
In other cases, the IO can be sent to the MDS or the locks can be
propagated as in the case described above.
The handling (and potential mishandling) of read-only layout needs
to be considered before using this approach. While this and
previous specifications clearly give the responsibility of
enforcing these to the client, the fact that the data server had
previously been given latitude in this area is concerning,, since,
if the client enforced these, server laxity as to enforcement
would never be needed. As a result, those anticipating this
strategy need to be sure that read-only layouts are enforced in
fact for this to work, with the specification's view that this is
possibly non-compliant not improving things.
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20.21. Layout Recall Issues for File Layout Type
Ther are some noteworthy peculiarities regarding layout recalls that
result from file deletion. These include cases in which a file is
deleted because another file is renamed to have the existing name
deleting the original holder of that name.
In such case other layout types will need to arrange for the
reclamation of storage and the recall of associated layouts to
prevent further access to the deleted file. The files layout type is
different in that:
* Although the storage occupied by the file does need to be freed,
this is more appropriately considered apart from storage
allocation facilities such as those used to support file
truncation. It is better to think of this as a remote file
deletion request effected by the control protocol.
* Because of the proceeding item, there is no possibility of the
existing layout being used to access the deleted file. As a
result, immediate layout recall is not needed.
* Since the layout in question cannot be used, it will need to be
cleaned up eventually and this can occur without coordination
between the MDS and the client who can each drop the layout
independently.
20.22. Restrictions on Layout Information Discard for File Layout Type
As discussed in Section 18.7.3.1, clients are allowed to discard
records of existing layouts, it is the obligation of the layout
type's specification to clearly state any restrictions on the ability
of the client and the MDS to do so. Specifically:
* The client cannot use layouts that have been discarded because it
is required to validate IOs sent to the data server.
As a result, it needs to avoid discarding information that is
likely to be needed again.
* Whether the MDS can discard layout information depends on whether
the control protocol supports retrieving it from the data server.
In the case in which it can, it is free to discard such
information, only concerning itself with the likely cost of
retrieving it when necessary.
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* Data servers MUST NOT discard layout information since doing so
would cause them to reject valid IO requests. Such information
can only be dropped in response to layout return or revocation.
20.23. Dealing with Client and Server Failure
This treatment is considerably more flexible than that appearing in
previous NFSv4.1 specifications. This expanded scope derives from
two important considerations:
* The appearance in Section 18.43.3 of [RFC5661] and [RFC8881] of
the clause "If the metadata server is in a grace period, and does
not persist layouts and device ID to device address mappings"
suggesting that the metadata might validly do these things and
respond substantively during the grace period.
Despite the fact that this suggestion is not followed up in
descriptions of pNFS recovery or of the file layout type, we are
exploring the implications of this choice here, referring to the
metadata server making this choice as being "layout-persistent".
* The inclusion, in changes made in [RFC8881], of the possibility of
clientids and their associated state surviving a disruptive event
such as a node restart or inter-node transfer.
We refer to such occasions as being "state-persistent" and assume,
for our purposes, that layouts would be included among the
persistent stateids.
* Because of the change of descriptive approach prompted by
[RFC8434], it is now clearer that that the control protocol has
the option of making a new instance of a data server after restart
aware of layouts and associated stateids held by the previous data
server instance.
In the current descriptive framework, this might seem a necessary
corollary to the control protocols role in providing sharing for
such information, but within the previous descriptive framework
which focused on specific instances of state propagation, the
absence of specific mention could have been interpreted as
foreclosing this possibility.
We refer to the state of affairs in which layout and their
associated stateids are known to a new data server instance as
manifesting "layout continuity", with the understanding that
layout continuity can arise as a result of either layout
persistence or be provided by the control protocol together with
the MDS' uninterrupted existence.
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The OPTIONAL character of these potential choices makes it important
that to deal with clients unaware of their existence so it needs to
be made clear:
* How these choices have dependencies or where they are independent.
* How the client can determine whether they are in effect.
* How a client unaware of these choices could successfully recover,
even if it does so in a more complicated and time-consuming manner
than it would if it were aware of these choices.
We deal with issues related to recovery from MDS, data server, and
client failure in Sections 20.23.1, 20.23.2, and 20.23.3
respectively.
20.23.1. Dealing with MDS Failure
Because no provision is made is made for reclaiming layouts, when a
client sees an MDS restart, it normally needs to do the actions
below. While we will discuss possible checks for state-persistence
or layout-persistence, the discussion of how these situations are
dealt with is deferred to later in the section.
These actions need to performed, independently of the possibility
that the failed node was acting as a data server as well a metadata
sever. In such cases, once recovery from the MDS failure, the
recovery from the data server failure needs to be done, as described
in Section 20.23.2.
Recovery needs to proceed as follows:
* It is appropriate to consider the possibility of state-persistence
at this point.
State-persistence can arise if the client-MDS session is a
persistent one or if, in establishing a new session, it is found
that the original client-MDS clientid is still in existence.
In either case, we deal with the situation as described later in
this section, whether layout-persistence is present or not.
* A new clientid and session is obtained using a sequence of an
EXCHANGE_ID operation followed by a CREATE_SESSION operation using
that client ID (eir_clientid as returned from EXCHANGE_ID) is
required to establish and confirm the client ID on the server.
This clientid serves as the replacement for the clientid
terminated by the MDS restart.
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* Locks other than layouts need to be reclaimed as they for other
(non-pNFS) occasions of server restart. Whether any of these
exist or not, the determination of whether layout-persistence
still needs to be done although it is up to the client when in the
process this happens.
The presence of layout persistence can best be determined by
attempting to use an existing layout to perform a short READ
operation which only succeeds if layout-persistence is in effect.
It is easier to interpret failures if the stateid under which the
READ is to be done is already reclaimed. Once a successful READ
is done, layout persistence is established and stateids, once
reclaimed, can be used together with pre-existing layouts to
continue work delayed by the MDS restart.
* At that point, recovery is complete even though layouts cannot be
used. At this point, RECAIM_COMPLETE can be done.
Once the last such RECAIM_COMPLETE is done, the grace period is
over and LAYOUTGET can be done to obtain new layouts, completing
the recovery process. It is the responsibility of the control
protocol, as described in Section 20.14.1, to provide stateid
information to the data server for files for which a layout is
obtained.
At this point, the basic recovery process, without state-persistence,
is complete.
The rest of this section will discuss the case in which state
persistence is in effect and its presence can allow the recovery
process to be abbreviated. In this case, further handling depends on
the possible presence of layout-persistence which can be determined
by using an existing layout to do a READ using pNFS. If it succeeds,
recovery is done and normal processing can continue.
In the case, layout-persistence is not in effect, the client needs to
re-establish needed layouts once state recovery is complete. Because
other clients may have obtained state from the restarting server,
even if the current client has not, such use can result in failure if
layout-persistence is not in effect until the grace period is over.
Once the grace period is over, replacement layouts can be obtained
and used.
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20.23.2. Dealing with Data Server Failure
There is potential uncertainty about the actions necessary for
recovery from a data server restart because of the way that the
description of the files layout type has been forced to evolve in
response to the creation of [RFC8434] and its incorporation in the
NFSv4.1 respecification effort:
In essence, because earlier specification efforts did not specify how
recovery was to be done, we are forced to speculate based on the
existing specifications regarding the control protocol about how
these might be used to satisfy recovery needs in the case of data
server restart. This creates a number of questions that need to be
addressed.
* In [RFC5661] and [RFC8881] the general pNFS description indicated
this (restart of a storage device) was a layout-type specific
matter but the section on the files layout type did not address
the issue.
This left considerable uncertainty about whether the restarting
data server would have access to lock stateids and layouts
established by the previous instance (possibly provided by the
control protocol).
While one might expect that the control protocol responsible for
propagating this information in other cases could do upon restart,
there is no explicit statement to this effect. Furthermore, the
appearance of specific directives to propagate information in
other situations could be interpreted as allowing the information
not to be propagated in this case.
* The publication of [RFC8434] and its subsequent incorporation in
rfc8881bis changes things in that it focused on the
responsibilities of the control protocol to provide effective
sharing and avoided specifics about how that sharing was to be
done (via information propagation or later cross-node
interrogation).
Even though this new descriptive approach made it natural for the
control protocol to provide the necessary sharing for simpler
recovery, there is no evidence for the existence of
implementations that do so.
* Given the nature of structure of stateids and clientid mandated by
the files layout type, improving recovery in this way is not
expected to be difficult.
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As a result, we have the following possibilities, for the situations
that a client might see after data server restart:
(A) The control protocol, as part of sharing layout information
including information about associated stateids has made this
information available to the new data server instance, once it
is aware of a new instance of the original server owner.
We refer to this situation as manifesting full state-continuity.
(B) As part of implementing an approximation to a "global" stateid
space, making stateids that are part of a given clientid makes
these available (in read-only fashion) to the new instance of
the server s soon as it establishes a connection to the existing
(originally MDS-based) clientid.
Although layout stateids might be propagated, we are assuming,
in this case, that, in the absence of full control protocol
involvement, functional layouts are not immediately available.
We refer to this situation as manifesting limited state-
continuity.
(C) The new data server initializes itself with an empty stateid
set, despite the use of a common clientid with the data server.
This inconsistency might be expected to be troublesome, but it
could exist and it is possible that it resolves itself once new
layouts are gotten, triggering the transfer of associated
stateid information.
We refer to this situation as manifesting state-discontinuity.
(D) The new data server initializes itself with an empty stateid set
and the MDS maintains synchrony between the two nodes by
resetting the shared clientid to have an empty stateid set.
We refer to this situation as manifesting state-destruction.
As a result of limited testing of available client and server
implementations, we have found instances of (D) but no bases of
(A),(B), or (C). While reasonable arguments could be made that these
behaviors are valid and acceptable as defined by [RFC8881], the
current draft will assume (D) that servers will implement that and
that clients can validly assume that server will behave in that way
until and unless the working group decides differently. See
Appendix D.2.14 for further information.
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At this point, we are assuming that (D) is in effect and the
necessary recovery is as described below"
We need to reobtain any locks that we held. It is not clear that
RECLAIM is possible, since the MDS is not in a grace period. As a
result, it is possible the locks might be unavailable due to the
fact that a conflicting lock might be obtained. In either case,
we need to reobtain layouts in order to re-establish pNFS access.
If these are not obtainable, IO can be directed to the MDS, as
described in Section 20.19.
20.23.3. Dealing with Client Failure
There appears nothing layout-type-specific to add to the discussion
in Section 18.9.1
20.24. Dealing with Lease Expiration
Although there are leases associated with the a client connection to
MDS and to data servers, we need to treat each of the following cases
separately:
* There is a lease loss between the client and a node acting as the
MDS.
In this case, the handling described in Section 18.9.2 can be
followed
* There is a lease loss between the client a single node acting as
both MDS and data server.
In this case as well, the handling described in Section 18.9.2 can
be followed since the client has no locks owned by the data
server.
* There is a lease loss between the client and a node acting as a
data server.
In this case, there should be no lease because there are no lock
held on the data server. However, it is possible that a data
sever might treat the lack of session use over the lease period as
amounting to a lease loss. If so, since there are no locks to be
lost, recovery should be trivial.
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20.25. Security Issues for the File Layout Type
All IO performed using file type layouts MUST adhere to the security
considerations outlined in Section 18.11. To effect this
requirement, NFSv4.1 data servers MUST perform the required access
checks for each READ or WRITE operation where the IO has not been not
authorized by a preceding OPEN allowing that IO type.
Because of lax specification practices with regard to authorization,
in previous NFsv4.1 specifications, additional checks, matching those
that would be done in the absence of pNFS might be needed. If the
metadata server would deny a READ or WRITE operation on a file due to
its ACL, mode attribute, open access mode, mandatory byte-range lock
state, or any other attributes and state, the data server MUST also
deny the READ or WRITE operation. This impacts the control protocol
and the propagation of state from the metadata server to the data
servers; see Sections 20.14.1, 20.14.2, and 20.20 for more details,
including explanations of why the deny mode of each Open does not
need to be known by data servers.
The methods for authentication, integrity, and privacy for data
servers based on the LAYOUT4_NFSV4_1_FILES layout type are the same
as those used by metadata servers. Metadata and data servers use ONC
RPC security flavors to authenticate, and SECINFO and SECINFO_NO_NAME
to negotiate the security mechanism and services to be used. Thus,
when using the LAYOUT4_NFSV4_1_FILES layout type, the impact on the
RPC-based security model due to pNFS (as alluded to in Sections 2.7
and 2.8.2) is zero.
For a given file object, a metadata server MAY require different
security parameters (secinfo4 value) than the data server. For a
given file object with multiple data servers, the secinfo4 value
SHOULD be the same across all data servers. If the secinfo4 values
across a metadata server and its data servers differ for a specific
file, the mapping of the principal to the server's internal user
identifier MUST be the same in order for the access-control checks
based on ACL, mode, open and deny mode, and mandatory locking to be
consistent across on the pNFS server.
If an NFSv4.1 implementation supports pNFS and supports NFSv4.1 file
layouts, then the implementation MUST support the SECINFO_NO_NAME
operation on both the metadata and data servers.
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20.26. Necessary Changes to the Files Layout Type to Meet Layout Type
Requirements
This section describes the changes that were made from the treatment
in [RFC8881] to adequately describe the file layout type within the
descriptive framework established in Section 19. These include:
The following changes were needed to provide a layout type
description that meets the requirements specified in Section 19.1.
Although that section was derived from [RFC8434], it is not precisely
the same.
* Changes in the treatment of authorization to deal with previous
inadequacies in the handling of OPEN.
* Changes in the treatment of authorization that ignored possible
difficulties caused by unclear elements of the underspecified
NFSv4 ACL model.
* A previous lack of clarity regarding the possible need for
revocation.
* A lack of attention to the consequences of server-multipathing
(previously alluded to but not recognized as distinct from
network-multipathing) and the potential for WRITEs to result in
conflicts requiring layout revocation.
* The uncertainty and likely confusion arising from non-normative
statements indicating that there is no need to check IO
conformance with the iomode together with the fact that iomode is
often a necessary element in determining whether a conflict exists
This gap and the possible ensuing confusion are of major
importance when the there is a possibility of conflicts arising as
a result of server- multipathing.
The needed changes can be summarized as follows:
* We try to clearly distinguish server-multipathing from network-
multipathing so that we can make clear the issues raised by the
former.
This replaces a situation in which the possibility of server-
multipathing was mentioned if the two data sets were identical but
there was no consideration of the issues that would arise if a
WRITE caused them to cease to be identical.
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* We try to make it clear that there are circumstances that make it
necessary to check iomode conformance, even though there might be
existing implementations, with certain functionality limits, that
work properly despite a lack of such checking
* All the material regarding stateid sharing with the data server
makes clear the important role of authorization of the opening
principal and the lack of need to respond to changes in
authorization-related attributes.
* We mention the troublesome aspects of the NFSv4 ACL model
including the provision of separate bits to control authorization
of extending the file or overwriting existing bytes.
* We make it clear that, given the uncertainty within older
specification of authorization within the NFSv4 protocol, the
focus often needs to be on whether the handling on the data server
matches that that the MDS would provide, rather than the
conformance with previous specification of authorization
semantics.
* We have adapted the treatment of recovery to incorporate the
persistence options made available in [RFC8881] and to a more
general approach to the handling of state sharing by the control
protocol.
20.27. The File Layout Type and Layout Type Requirements
This section surveys how the requirements for layout type
specifications identified in Section 19.1 are addressed, for the
files layout type.
The overall framework for understanding the file layout type is
provided as follows:
* Information regarding the interoperability model (see
Section 19.1.1) is presented in Section 20.2.
* Information regarding layout-specific data types overlaying the
nominally opaque types specified as part of the pNFS feature (See
Section 19.1.2) is presented in Section 20.7.
* The handling of various OPTIONAL features are discussed later in
this section. Currently the, only such troublesome feature is
mandatory byte-range locking.
Features added in NFSv4.2 need to be checked for how they might be
implemented together with the files layout type.
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* The storage protocol for the files layout type (a variant of
NFSv4.1 or subsequent minor versions is discussed in Section 20.4.
The function of the control protocol whose requirements are specified
in Sections 19.1.3 through 19.1.5 are addressed as follows:
* Control program functions related to layout management (discussed
in Section 19.1.3) are addressed in Sections 20.17, 20.18, and
20.14.1.
* The functions of the control protocol related to storage
allocation whose requirements are specified Section 19.1.4 are
discussed in Section 20.14.4
* The functions of the control protocol related to the performance
of IO requests directed to the MDS that are specified in
Section 20.19.
For important background, see Section 20.14.1.
* The functions of the control protocol related to IO request
authorization that are specified in Section 19.1.4 are discussed
in Section 20.14.2.
* The functions of the control protocol related to the maintenance
of attribute values that can be affected by WRITEs that are
specified in Section 19.1.4 are discussed in Section 20.13.
* The functions described by Section 19.1.5 are provided as
described by Section 20.14.5
The layout specific information regarding the termination of layouts
discussed in Section 19.1.9 is provided as follows:
* Although the sharing of information regarding the return of
layouts can be integrated with the sharing of other state
information as described in Section 20.14.1, it can also be
provided independently, as described in Section 20.14.3.
In either case, it is important that client, data server and MDS
all know that a returned layout no longer exists,' although it is
possible that the MDS and client might not be aware of some
existing layouts.
* Information regarding layout-type-specific issues with regard to
layout recall is discussed in Section 20.21.
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* Information regarding layout-type-specific issues with regard to
layout recall is discussed in Section 20.17.
* Information regarding layout-type-specific issues with regard to
layout recall is discussed in Section 20.18.
* Information regard potential layout-type-specific restrictions
regarding the discarding of layout-related information are
discussed in Section 20.22.
The requirements described by Section 19.1.7 are addressed in
Sections 20.23 and 20.24
The requirements described by Section 19.1.6 are addressed, for the
files layout type, in Section 20.25. To provide some guidance in
satisfying these requirements, the following section are helpful:
* Section 20.14.1 provide information about sharing of state
necessary to verify the appropriate locking state (and indirectly
authorization for the opener) to perform IO.
* Section 20.14.2, provides information about IO requests made by
principals other than the opener and IOs using a delegation
stateid.
* Section 20.20 provides information about options that can be use
to support the case of mandatory byte range locks.
21. Internationalization
Internationalization for NFSv4.1 is described in
[I-D.ietf-nfsv4-internationalization], just as it is for other minor
versions. The only NFSv4.1-specific element, the fs_charset_cap
attribute is described in Section 21.1 below.
21.1. UTF-8 Capabilities
const FSCHARSET_CAP4_CONTAINS_NON_UTF8 = 0x1;
const FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 = 0x2;
typedef uint32_t fs_charset_cap4;
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This attribute provides a simple way of determining whether a
particular file system behaves as a UTF-8-only server and rejects
file names which are not valid Unicode strings encoded using UTF-8.
When this attribute is supported and the value returned has the
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 flag set, the error NFS4ERR_INVAL
MUST be returned if any file name argument contains a string which is
not a valid UTF-8-encoded string.
When this attribute is supported and the value returned has the
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 flag clear, the error NFS4ERR_INVAL
will not be returned based on adherence to the rules of UTF-8. While
such file systems are generally UTF-8-unaware, this cannot be
assumed, since server are allowed (in some circumstances; it is a
"SHOULD NOT") to accept non-UTF-8 names while being aware of the
structure of UTF-8-conforming names, for the purposes of determining
canonical equivalence, for example.
With regard to the flag FSCHARSET_CAP4_CONTAINS_NON_UTF8, it has
proved impossible to determine, from existing treatments of this
attribute, any value that might be helpful here. As a result, we are
forced to assume that this flag is always a complement of
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 and that any result in which it is
not is to be ignored, with the appropriate handling being the same as
would apply if the attribute were not supported.
When this attribute is not supported, the client can perform a LOOKUP
using a name not conforming to the rules of UTF-8 and use the error
returned to determine whether names which not UTF-8-encoded Unicode
are accepted.
22. Error Values
NFS error numbers are assigned to failed operations within a Compound
(COMPOUND or CB_COMPOUND) request. A Compound request contains a
number of NFS operations that have their results encoded in sequence
in a Compound reply. The results of successful operations will
consist of an NFS4_OK status followed by the encoded results of the
operation. If an NFS operation fails, an error status will be
entered in the reply and the Compound request will be terminated.
22.1. Error Definitions
+===================================+========+===================+
| Error | Number | Description |
+===================================+========+===================+
| NFS4_OK | 0 | Section 22.1.3.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_ACCESS | 13 | Section 22.1.6.1 |
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+-----------------------------------+--------+-------------------+
| NFS4ERR_ATTRNOTSUPP | 10032 | Section 22.1.15.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_ADMIN_REVOKED | 10047 | Section 22.1.5.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BACK_CHAN_BUSY | 10057 | Section 22.1.12.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADCHAR | 10040 | Section 22.1.7.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADHANDLE | 10001 | Section 22.1.2.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADIOMODE | 10049 | Section 22.1.10.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADLAYOUT | 10050 | Section 22.1.10.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADNAME | 10041 | Section 22.1.7.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADOWNER | 10039 | Section 22.1.15.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADSESSION | 10052 | Section 22.1.11.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADSLOT | 10053 | Section 22.1.11.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADTYPE | 10007 | Section 22.1.4.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BADXDR | 10036 | Section 22.1.1.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BAD_COOKIE | 10003 | Section 22.1.1.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BAD_HIGH_SLOT | 10077 | Section 22.1.11.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BAD_RANGE | 10042 | Section 22.1.8.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BAD_SEQID | 10026 | Section 22.1.16.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BAD_SESSION_DIGEST | 10051 | Section 22.1.12.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_BAD_STATEID | 10025 | Section 22.1.5.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_CB_PATH_DOWN | 10048 | Section 22.1.11.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_CLID_INUSE | 10017 | Section 22.1.13.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_CLIENTID_BUSY | 10074 | Section 22.1.13.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_COMPLETE_ALREADY | 10054 | Section 22.1.9.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_CONN_NOT_BOUND_TO_SESSION | 10055 | Section 22.1.11.6 |
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+-----------------------------------+--------+-------------------+
| NFS4ERR_DEADLOCK | 10045 | Section 22.1.8.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_DEADSESSION | 10078 | Section 22.1.11.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_DELAY | 10008 | Section 22.1.1.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_DELEG_ALREADY_WANTED | 10056 | Section 22.1.14.1 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_DELEG_REVOKED | 10087 | Section 22.1.5.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_DENIED | 10010 | Section 22.1.8.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_DIRDELEG_UNAVAIL | 10084 | Section 22.1.14.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_DQUOT | 69 | Section 22.1.4.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_ENCR_ALG_UNSUPP | 10079 | Section 22.1.13.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_EXIST | 17 | Section 22.1.4.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_EXPIRED | 10011 | Section 22.1.5.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_FBIG | 27 | Section 22.1.4.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_FHEXPIRED | 10014 | Section 22.1.2.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_FILE_OPEN | 10046 | Section 22.1.4.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_GRACE | 10013 | Section 22.1.9.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_HASH_ALG_UNSUPP | 10072 | Section 22.1.13.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_INVAL | 22 | Section 22.1.1.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_IO | 5 | Section 22.1.4.6 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_ISDIR | 21 | Section 22.1.2.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_LAYOUTTRYLATER | 10058 | Section 22.1.10.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_LAYOUTUNAVAILABLE | 10059 | Section 22.1.10.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_LEASE_MOVED | 10031 | Section 22.1.16.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_LOCKED | 10012 | Section 22.1.8.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_LOCKS_HELD | 10037 | Section 22.1.8.5 |
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+-----------------------------------+--------+-------------------+
| NFS4ERR_LOCK_NOTSUPP | 10043 | Section 22.1.8.6 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_LOCK_RANGE | 10028 | Section 22.1.8.7 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_MINOR_VERS_MISMATCH | 10021 | Section 22.1.3.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_MLINK | 31 | Section 22.1.4.7 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_MOVED | 10019 | Section 22.1.2.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NAMETOOLONG | 63 | Section 22.1.7.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOENT | 2 | Section 22.1.4.8 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOFILEHANDLE | 10020 | Section 22.1.2.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOMATCHING_LAYOUT | 10060 | Section 22.1.10.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOSPC | 28 | Section 22.1.4.9 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOTDIR | 20 | Section 22.1.2.6 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOTEMPTY | 66 | Section 22.1.4.10 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOTSUPP | 10004 | Section 22.1.1.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOT_ONLY_OP | 10081 | Section 22.1.3.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NOT_SAME | 10027 | Section 22.1.15.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NO_GRACE | 10033 | Section 22.1.9.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_NXIO | 6 | Section 22.1.16.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_OLD_STATEID | 10024 | Section 22.1.5.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_OPENMODE | 10038 | Section 22.1.8.8 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_OP_ILLEGAL | 10044 | Section 22.1.3.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_OP_NOT_IN_SESSION | 10071 | Section 22.1.3.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_PERM | 1 | Section 22.1.6.2 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_PNFS_IO_HOLE | 10075 | Section 22.1.10.6 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_PNFS_NO_LAYOUT | 10080 | Section 22.1.10.7 |
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+-----------------------------------+--------+-------------------+
| NFS4ERR_RECALLCONFLICT | 10061 | Section 22.1.14.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_RECLAIM_BAD | 10034 | Section 22.1.9.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_RECLAIM_CONFLICT | 10035 | Section 22.1.9.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_REJECT_DELEG | 10085 | Section 22.1.14.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_REP_TOO_BIG | 10066 | Section 22.1.3.6 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_REP_TOO_BIG_TO_CACHE | 10067 | Section 22.1.3.7 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_REQ_TOO_BIG | 10065 | Section 22.1.3.8 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_RESOURCE | 10018 | Section 22.1.16.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_RESTOREFH | 10030 | Section 22.1.16.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_RETRY_UNCACHED_REP | 10068 | Section 22.1.3.9 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_RETURNCONFLICT | 10086 | Section 22.1.10.8 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_ROFS | 30 | Section 22.1.4.11 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_SAME | 10009 | Section 22.1.15.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_SHARE_DENIED | 10015 | Section 22.1.8.9 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_SEQUENCE_POS | 10064 | Section 22.1.3.10 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_SEQ_FALSE_RETRY | 10076 | Section 22.1.11.7 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_SEQ_MISORDERED | 10063 | Section 22.1.11.8 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_SERVERFAULT | 10006 | Section 22.1.1.6 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_STALE | 70 | Section 22.1.2.7 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_STALE_CLIENTID | 10022 | Section 22.1.13.5 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_STALE_STATEID | 10023 | Section 22.1.16.6 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_SYMLINK | 10029 | Section 22.1.2.8 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_TOOSMALL | 10005 | Section 22.1.1.7 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_TOO_MANY_OPS | 10070 | Section 22.1.3.11 |
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+-----------------------------------+--------+-------------------+
| NFS4ERR_UNKNOWN_LAYOUTTYPE | 10062 | Section 22.1.10.9 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_UNSAFE_COMPOUND | 10069 | Section 22.1.3.12 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_WRONGSEC | 10016 | Section 22.1.6.3 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_WRONG_CRED | 10082 | Section 22.1.6.4 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_WRONG_TYPE | 10083 | Section 22.1.2.9 |
+-----------------------------------+--------+-------------------+
| NFS4ERR_XDEV | 18 | Section 22.1.4.12 |
+-----------------------------------+--------+-------------------+
Table 11: Protocol Error Definitions
22.1.1. General Errors
This section deals with errors that are applicable to a broad set of
different purposes.
22.1.1.1. NFS4ERR_BADXDR (Error Code 10036)
The arguments for this operation do not match those specified in the
XDR definition. This includes situations in which the request ends
before all the arguments have been seen. Note that this error
applies when fixed enumerations (these include booleans) have a value
within the input stream that is not valid for the enum. A replier
may pre-parse all operations for a Compound procedure before doing
any operation execution and return RPC-level XDR errors in that case.
22.1.1.2. NFS4ERR_BAD_COOKIE (Error Code 10003)
Used for operations that provide a set of information indexed by some
quantity provided by the client or cookie sent by the server for an
earlier invocation. Where the value cannot be used for its intended
purpose, this error results.
22.1.1.3. NFS4ERR_DELAY (Error Code 10008)
For any of a number of reasons, the replier could not process this
operation in what was deemed a reasonable time. The requester should
wait and then try the request with a new slot and sequence value.
Some examples of situations that might lead to this error being
returned:
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* A server that supports hierarchical storage receives a request to
process a file that had been migrated.
* An operation requires a delegation recall to proceed, but the need
to wait for this delegation to be recalled and returned makes
processing this request in a timely fashion impossible.
* A request is being performed on a session being migrated from
another server as described in Section 17.14.3, and the lack of
full information about the state of the session on the source
makes it impossible to process the request immediately.
In such cases, returning the error NFS4ERR_DELAY allows necessary
preparatory operations to proceed without holding up requester
resources such as a session slot. After delaying for period of time,
the requester can then re-send the operation in question, often as
part of a nearly identical request. Because of the need to avoid
spurious reissues of non-idempotent operations and to avoid acting in
response to NFS4ERR_DELAY errors returned on responses returned from
the replier's reply cache, integration with the session-provided
reply cache is necessary. There are a number of cases to deal with,
each of which requires different sorts of handling by the requester
and replier:
* If NFS4ERR_DELAY is returned on a SEQUENCE operation, the request
is retried in full with the SEQUENCE operation containing the same
slot and sequence values. In this case, the replier MUST avoid
returning a response containing NFS4ERR_DELAY as the response to
SEQUENCE solely because an earlier instance of the same request
returned that error and it was stored in the reply cache. If the
replier did this, the retries would not be effective as there
would be no opportunity for the replier to see whether the
condition that generated the NFS4ERR_DELAY had been rectified
during the time between the original request and the retry.
* If NFS4ERR_DELAY is returned on an operation other than SEQUENCE
that validly appears as the first operation of a request, the
handling is similar. The request can be retried in full without
modification. In this case as well, the replier MUST avoid
returning a response containing NFS4ERR_DELAY as the response to
an initial operation of a request solely on the basis of its
presence in the reply cache. If the replier did this, the retries
would not be effective as there would be no opportunity for the
replier to see whether the condition that generated the
NFS4ERR_DELAY had been rectified during the interim between the
original request and the retry.
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* If NFS4ERR_DELAY is returned on an operation other than the first
in the request, the request when retried MUST contain a SEQUENCE
operation that is different than the original one, with either the
slot ID or the sequence value different from that in the original
request. Because requesters do this, there is no need for the
replier to take special care to avoid returning an NFS4ERR_DELAY
error obtained from the reply cache. When no non-idempotent
operations have been processed before the NFS4ERR_DELAY was
returned, the requester should retry the request in full, with the
only difference from the original request being the modification
to the slot ID or sequence value in the reissued SEQUENCE
operation.
* When NFS4ERR_DELAY is returned on an operation other than the
first within a request and there has been a non-idempotent
operation processed before the NFS4ERR_DELAY was returned,
reissuing the request as is normally done would incorrectly cause
the re-execution of the non-idempotent operation.
To avoid this situation, the requester should reissue the request
without the non-idempotent operation. The request still must use
a SEQUENCE operation with either a different slot ID or sequence
value from the SEQUENCE in the original request. Because this is
done, there is no way the replier could avoid spuriously re-
executing the non-idempotent operation since the different
SEQUENCE parameters prevent the requester from recognizing that
the non-idempotent operation is being retried.
Note that without the ability to return NFS4ERR_DELAY and the
requester's willingness to re-send when receiving it, deadlock might
result. For example, if a recall is done, and if the delegation
return or operations preparatory to delegation return are held up by
other operations that need the delegation to be returned, session
slots might not be available. The result could be deadlock.
22.1.1.4. NFS4ERR_INVAL (Error Code 22)
The arguments for this operation are not valid for some reason, even
though they do match those specified in the XDR definition for the
request.
22.1.1.5. NFS4ERR_NOTSUPP (Error Code 10004)
Operation not supported because the operation is either of the
following:
* an OPTIONAL one and is not supported by this server or the file
system on which it is issued.
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* an operation which MUST NOT be implemented in the current minor
version.
In addition, this error may be returned in certain unsupported
instances of the LINK operation.
22.1.1.6. NFS4ERR_SERVERFAULT (Error Code 10006)
An error occurred on the server that does not map to any of the
specific legal NFSv4.1 protocol error values. The client should
translate this into an appropriate error. UNIX clients may choose to
translate this to EIO.
22.1.1.7. NFS4ERR_TOOSMALL (Error Code 10005)
Used where an operation returns a variable amount of data, with a
limit specified by the client. Where the data returned cannot be fit
within the limit specified by the client, this error results.
22.1.2. Filehandle Errors
These errors deal with the situation in which the current or saved
filehandle, or the filehandle passed to PUTFH intended to become the
current filehandle, is invalid in some way. This includes situations
in which the filehandle is a valid filehandle in general but is not
of the appropriate object type for the current operation.
Where the error description indicates a problem with the current or
saved filehandle, it is to be understood that filehandles are only
checked for the condition if they are implicit arguments of the
operation in question.
22.1.2.1. NFS4ERR_BADHANDLE (Error Code 10001)
Illegal NFS filehandle for the current server. The current
filehandle failed internal consistency checks. Once accepted as
valid (by PUTFH), no subsequent status change can cause the
filehandle to generate this error.
22.1.2.2. NFS4ERR_FHEXPIRED (Error Code 10014)
A current or saved filehandle that is an argument to the current
operation is volatile and has expired at the server.
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22.1.2.3. NFS4ERR_ISDIR (Error Code 21)
The current or saved filehandle designates a directory when the
current operation does not allow a directory to be accepted as the
target of this operation.
22.1.2.4. NFS4ERR_MOVED (Error Code 10019)
The file system that contains the current filehandle object is not
present at the server or is not accessible with the network address
used. It may have been made accessible on a different set of network
addresses, relocated or migrated to another server, or it may have
never been present. The client may obtain the new file system
location by obtaining the fs_locations or fs_locations_info attribute
for the current filehandle. For further discussion, refer to
Section 17.3.
As with the case of NFS4ERR_DELAY, it is possible that one or more
non-idempotent operations may have been successfully executed within
a COMPOUND before NFS4ERR_MOVED is returned. Because of this, once
the new location is determined, the original request that received
the NFS4ERR_MOVED should not be re-executed in full. Instead, the
client should send a new COMPOUND with any successfully executed non-
idempotent operations removed. When the client uses the same session
for the new COMPOUND, its SEQUENCE operation should use a different
slot ID or sequence.
22.1.2.5. NFS4ERR_NOFILEHANDLE (Error Code 10020)
The logical current or saved filehandle value is required by the
current operation and is not set. This may be a result of a
malformed COMPOUND operation (i.e., no PUTFH or PUTROOTFH before an
operation that requires the current filehandle be set).
22.1.2.6. NFS4ERR_NOTDIR (Error Code 20)
The current (or saved) filehandle designates an object that is not a
directory for an operation in which a directory is required.
22.1.2.7. NFS4ERR_STALE (Error Code 70)
The current or saved filehandle value designating an argument to the
current operation is invalid. The file referred to by that
filehandle no longer exists or access to it has been revoked.
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22.1.2.8. NFS4ERR_SYMLINK (Error Code 10029)
The current filehandle designates a symbolic link when the current
operation does not allow a symbolic link as the target.
22.1.2.9. NFS4ERR_WRONG_TYPE (Error Code 10083)
The current (or saved) filehandle designates an object that is of an
invalid type for the current operation, and there is no more specific
error (such as NFS4ERR_ISDIR or NFS4ERR_SYMLINK) that applies. Note
that in NFSv4.0, such situations generally resulted in the less-
specific error NFS4ERR_INVAL.
22.1.3. Compound Structure Errors
This section deals with errors that relate to the overall structure
of a Compound request (by which we mean to include both COMPOUND and
CB_COMPOUND), rather than to particular operations.
There are a number of basic constraints on the operations that may
appear in a Compound request. Sessions add to these basic
constraints by requiring a Sequence operation (either SEQUENCE or
CB_SEQUENCE) at the start of the Compound.
22.1.3.1. NFS_OK (Error code 0)
Indicates the operation completed successfully, in that all of the
constituent operations completed without error.
22.1.3.2. NFS4ERR_MINOR_VERS_MISMATCH (Error code 10021)
The minor version specified is not one that the current listener
supports. This value is returned in the overall status for the
Compound but is not associated with a specific operation since the
results will specify a result count of zero.
22.1.3.3. NFS4ERR_NOT_ONLY_OP (Error Code 10081)
Certain operations, which are allowed to be executed outside of a
session, MUST be the only operation within a Compound whenever the
Compound does not start with a Sequence operation. This error
results when that constraint is not met.
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22.1.3.4. NFS4ERR_OP_ILLEGAL (Error Code 10044)
The operation code is not a valid one for the current Compound
procedure. The opcode in the result stream matched with this error
is the ILLEGAL value, although the value that appears in the request
stream may be different. Where an illegal value appears and the
replier pre-parses all operations for a Compound procedure before
doing any operation execution, an RPC-level XDR error may be
returned.
22.1.3.5. NFS4ERR_OP_NOT_IN_SESSION (Error Code 10071)
Most forward operations and all callback operations are only valid
within the context of a session, so that the Compound request in
question MUST begin with a Sequence operation. If an attempt is made
to execute these operations outside the context of session, this
error results.
22.1.3.6. NFS4ERR_REP_TOO_BIG (Error Code 10066)
The reply to a Compound would exceed the channel's negotiated maximum
response size.
22.1.3.7. NFS4ERR_REP_TOO_BIG_TO_CACHE (Error Code 10067)
The reply to a Compound would exceed the channel's negotiated maximum
size for replies cached in the reply cache when the Sequence for the
current request specifies that this request is to be cached.
22.1.3.8. NFS4ERR_REQ_TOO_BIG (Error Code 10065)
The Compound request exceeds the channel's negotiated maximum size
for requests.
22.1.3.9. NFS4ERR_RETRY_UNCACHED_REP (Error Code 10068)
The requester has attempted a retry of a Compound that it previously
requested not be placed in the reply cache.
22.1.3.10. NFS4ERR_SEQUENCE_POS (Error Code 10064)
A Sequence operation appeared in a position other than the first
operation of a Compound request.
22.1.3.11. NFS4ERR_TOO_MANY_OPS (Error Code 10070)
The Compound request has too many operations, exceeding the count
negotiated when the session was created.
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22.1.3.12. NFS4ERR_UNSAFE_COMPOUND (Error Code 10068)
The client has sent a COMPOUND request with an unsafe mix of
operations -- specifically, with a non-idempotent operation that
changes the current filehandle and that is not followed by a GETFH.
22.1.4. File System Errors
These errors describe situations that occurred in the underlying file
system implementation rather than in the protocol or any NFSv4.x
feature.
22.1.4.1. NFS4ERR_BADTYPE (Error Code 10007)
An attempt was made to create an object with an inappropriate type
specified to CREATE. This may be because the type is undefined,
because the type is not supported by the server, or because the type
is not intended to be created by CREATE (such as a regular file or
named attribute, for which OPEN is used to do the file creation).
22.1.4.2. NFS4ERR_DQUOT (Error Code 69)
Resource (quota) hard limit exceeded. The user's resource limit on
the server has been exceeded.
22.1.4.3. NFS4ERR_EXIST (Error Code 17)
A file of the specified target name (when creating, renaming, or
linking) already exists.
22.1.4.4. NFS4ERR_FBIG (Error Code 27)
The file is too large. The operation would have caused the file to
grow beyond the server's limit.
22.1.4.5. NFS4ERR_FILE_OPEN (Error Code 10046)
The operation is not allowed because a file involved in the operation
is currently open. Servers may, but are not required to, disallow
linking-to, removing, or renaming open files.
22.1.4.6. NFS4ERR_IO (Error Code 5)
Indicates that an I/O error occurred for which the file system was
unable to provide recovery.
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22.1.4.7. NFS4ERR_MLINK (Error Code 31)
The request would have caused the server's limit for the number of
hard links a file may have to be exceeded.
22.1.4.8. NFS4ERR_NOENT (Error Code 2)
Indicates no such file or directory. The file or directory name
specified does not exist.
22.1.4.9. NFS4ERR_NOSPC (Error Code 28)
Indicates there is no space left on the device. The operation would
have caused the server's file system to exceed its limit.
22.1.4.10. NFS4ERR_NOTEMPTY (Error Code 66)
An attempt was made to remove a directory that was not empty.
22.1.4.11. NFS4ERR_ROFS (Error Code 30)
Indicates a read-only file system. A modifying operation was
attempted on a read-only file system.
22.1.4.12. NFS4ERR_XDEV (Error Code 18)
Indicates an attempt to do an operation, such as linking, that
inappropriately crosses a boundary. This may be due to such
boundaries as:
* that between file systems (where the fsids are different).
* that between different named attribute directories or between a
named attribute directory and an ordinary directory.
* that between byte-ranges of a file system that the file system
implementation treats as separate (for example, for space
accounting purposes), and where cross-connection between the byte-
ranges are not allowed.
22.1.5. State Management Errors
These errors indicate problems with the stateid (or one of the
stateids) passed to a given operation. This includes situations in
which the stateid is invalid as well as situations in which the
stateid is valid but designates locking state that has been revoked.
Depending on the operation, the stateid when valid may designate
opens, byte-range locks, file or directory delegations, layouts, or
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device maps.
22.1.5.1. NFS4ERR_ADMIN_REVOKED (Error Code 10047)
A stateid designates locking state of any type that has been revoked
due to administrative interaction, possibly while the lease is valid.
22.1.5.2. NFS4ERR_BAD_STATEID (Error Code 10026)
A stateid does not properly designate any valid state. See Sections
13.2.4 and 13.2.3 for a discussion of how stateids are validated.
22.1.5.3. NFS4ERR_DELEG_REVOKED (Error Code 10087)
A stateid designates recallable locking state of any type (delegation
or layout) that has been revoked due to the failure of the client to
return the lock when it was recalled.
22.1.5.4. NFS4ERR_EXPIRED (Error Code 10011)
A stateid designates locking state of any type that has been revoked
due to expiration of the client's lease, either immediately upon
lease expiration, or following a later request for a conflicting
lock.
22.1.5.5. NFS4ERR_OLD_STATEID (Error Code 10024)
A stateid with a non-zero seqid value is not the most current seqid
for the state.
22.1.6. Security Errors
These are the various permission-related errors in NFSv4.1.
22.1.6.1. NFS4ERR_ACCESS (Error Code 13)
Indicates permission denied. The caller does not have the correct
permission to perform the requested operation. Contrast this with
NFS4ERR_PERM (Section 22.1.6.2), which restricts itself to owner or
privileged-user permission failures, and NFS4ERR_WRONG_CRED
(Section 22.1.6.4), which deals with appropriate permission to delete
or modify transient objects based on the credentials of the user that
created them.
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22.1.6.2. NFS4ERR_PERM (Error Code 1)
Indicates requester is not the owner. The operation was not allowed
because the caller is neither a privileged user (root) nor the owner
of the target of the operation.
22.1.6.3. NFS4ERR_WRONGSEC (Error Code 10016)
Indicates that the security mechanism being used by the client for
the operation does not match the server's security policy. The
client should change the security mechanism being used and re-send
the operation (but not with the same slot ID and sequence ID; one or
both MUST be different on the re-send). SECINFO and SECINFO_NO_NAME
can be used to determine the appropriate mechanism.
22.1.6.4. NFS4ERR_WRONG_CRED (Error Code 10082)
An operation that manipulates state was attempted by a principal that
was not allowed to modify that piece of state.
22.1.7. Name Errors
Names in NFSv4 are typically UTF-8 strings, although it is possible
for servers, when accessing certain file systems, to support other
encodings to support internationalization. When the strings are of
length zero or are not valid UTF-8 encoding in a file system that
only supports UTF-8 encodings, the error NFS4ERR_INVAL results.
Besides this, there are a number of other errors to indicate specific
problems with names.
22.1.7.1. NFS4ERR_BADCHAR (Error Code 10040)
A string contains a character that is not supported by the server in
the context in which it being used.
22.1.7.2. NFS4ERR_BADNAME (Error Code 10041)
A name string in a request consisted of valid characters supported by
the server, but the name is not supported by the server as a valid
name for the current operation. An example might be creating a file
or directory named ".." on a server whose file system uses that name
for links to parent directories.
22.1.7.3. NFS4ERR_NAMETOOLONG (Error Code 63)
Returned when the filename in an operation exceeds the server's
implementation limit.
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22.1.8. Locking Errors
This section deals with errors related to locking, both as to share
reservations and byte-range locking. It does not deal with errors
specific to the process of reclaiming locks. Those are dealt with in
Section 22.1.9.
22.1.8.1. NFS4ERR_BAD_RANGE (Error Code 10042)
The byte-range of a LOCK, LOCKT, or LOCKU operation is not allowed by
the server. For example, this error results when a server that only
supports 32-bit ranges receives a range that cannot be handled by
that server. (See Section 25.10.3.)
22.1.8.2. NFS4ERR_DEADLOCK (Error Code 10045)
The server has been able to determine a byte-range locking deadlock
condition for a READW_LT or WRITEW_LT LOCK operation.
22.1.8.3. NFS4ERR_DENIED (Error Code 10010)
An attempt to lock a file is denied. Since this may be a temporary
condition, the client is encouraged to re-send the lock request (but
not with the same slot ID and sequence ID; one or both MUST be
different on the re-send) until the lock is accepted. See
Section 14.6 for a discussion of the re-send.
22.1.8.4. NFS4ERR_LOCKED (Error Code 10012)
A READ or WRITE operation was attempted on a file where there was a
conflict between the I/O and an existing lock:
* There is a share reservation inconsistent with the I/O being done.
* The range to be read or written intersects an existing mandatory
byte-range lock.
22.1.8.5. NFS4ERR_LOCKS_HELD (Error Code 10037)
An operation was prevented by the unexpected presence of locks.
22.1.8.6. NFS4ERR_LOCK_NOTSUPP (Error Code 10043)
A LOCK operation was attempted that would require the upgrade or
downgrade of a byte-range lock range already held by the owner, and
the server does not support atomic upgrade or downgrade of locks.
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22.1.8.7. NFS4ERR_LOCK_RANGE (Error Code 10028)
A LOCK operation is operating on a range that overlaps in part a
currently held byte-range lock for the current lock-owner and does
not precisely match a single such byte-range lock where the server
does not support this type of request, and thus does not implement
POSIX locking semantics [fcntl]. See Sections 25.10.4, 25.11.4, and
25.12.4 for a discussion of how this applies to LOCK, LOCKT, and
LOCKU respectively.
22.1.8.8. NFS4ERR_OPENMODE (Error Code 10038)
The client attempted a READ, WRITE, LOCK, or other operation not
sanctioned by the stateid passed (e.g., writing to a file opened for
read-only access).
22.1.8.9. NFS4ERR_SHARE_DENIED (Error Code 10015)
An attempt to OPEN a file with a share reservation has failed because
of a share conflict.
22.1.9. Reclaim Errors
These errors relate to the process of reclaiming locks after a server
restart.
22.1.9.1. NFS4ERR_COMPLETE_ALREADY (Error Code 10054)
The client previously sent a successful RECLAIM_COMPLETE operation
specifying the same scope, whether that scope is global or for the
same file system in the case of a per-fs RECLAIM_COMPLETE. An
additional RECLAIM_COMPLETE operation is not necessary and results in
this error.
22.1.9.2. NFS4ERR_GRACE (Error Code 10013)
This error is returned when the server is in its grace period with
regard to the file system object for which the lock was requested.
In this situation, a non-reclaim locking request cannot be granted.
This can occur because either:
* The server does not have sufficient information about locks that
might be potentially reclaimed to determine whether the lock could
be granted.
* The request is made by a client responsible for reclaiming its
locks that has not yet done the appropriate RECLAIM_COMPLETE
operation, allowing it to proceed to obtain new locks.
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In the case of a per-fs grace period, there may be clients (i.e.,
those currently using the destination file system) who might be
unaware of the circumstances resulting in the initiation of the grace
period. Such clients need to periodically retry the request until
the grace period is over, just as other clients do.
22.1.9.3. NFS4ERR_NO_GRACE (Error Code 10033)
A reclaim of client state was attempted in circumstances in which the
server cannot guarantee that conflicting state has not been provided
to another client. This occurs in any of the following situations:
* There is no active grace period applying to the file system object
for which the request was made.
* The client making the request has no current role in reclaiming
locks.
* Previous operations have created a situation in which the server
is not able to determine that a reclaim-interfering edge condition
does not exist.
22.1.9.4. NFS4ERR_RECLAIM_BAD (Error Code 10034)
The server has determined that a reclaim attempted by the client is
not valid, i.e., the lock specified as being reclaimed could not
possibly have existed before the server restart or file system
migration event. A server is not obliged to make this determination
and will typically rely on the client to only reclaim locks that the
client was granted prior to restart. However, when a server does
have reliable information to enable it to make this determination,
this error indicates that the reclaim has been rejected as invalid.
This is as opposed to the error NFS4ERR_RECLAIM_CONFLICT (See
Section 22.1.9.5) where the server can only determine that there has
been an invalid reclaim, but cannot determine which request is
invalid.
22.1.9.5. NFS4ERR_RECLAIM_CONFLICT (Error Code 10035)
The reclaim attempted by the client has encountered a conflict and
cannot be satisfied. This potentially indicates a misbehaving
client, although not necessarily the one receiving the error. The
misbehavior might be on the part of the client that established the
lock with which this client conflicted. See also Section 22.1.9.4
for the related error, NFS4ERR_RECLAIM_BAD.
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22.1.10. pNFS Errors
This section deals with pNFS-related errors including those that are
associated with using NFSv4.1 to communicate with a data server.
22.1.10.1. NFS4ERR_BADIOMODE (Error Code 10049)
An invalid or inappropriate layout iomode was specified. For example
an inappropriate layout iomode, suppose a client's LAYOUTGT operation
specified an iomode of LAYOUTIOMODE4_RW, and the server is neither
able nor willing to let the client send write requests to data
servers; the server can reply with NFS4ERR_BADIOMODE. The client
would then send another LAYOUTGET with an iomode of
LAYOUTIOMODE4_READ.
22.1.10.2. NFS4ERR_BADLAYOUT (Error Code 10050)
The layout specified is invalid in some way. For LAYOUTCOMMIT, this
indicates that the specified layout is not held by the client or is
not of mode LAYOUTIOMODE4_RW. For LAYOUTGET, it indicates that a
layout matching the client's specification as to minimum length
cannot be granted.
22.1.10.3. NFS4ERR_LAYOUTTRYLATER (Error Code 10058)
Layouts are temporarily unavailable for the file. The client should
re-send later (but not with the same slot ID and sequence ID; one or
both MUST be different on the re-send).
22.1.10.4. NFS4ERR_LAYOUTUNAVAILABLE (Error Code 10059)
Returned when layouts are not available for the current file system
or the particular specified file.
22.1.10.5. NFS4ERR_NOMATCHING_LAYOUT (Error Code 10060)
Returned when layouts are recalled and the client has no layouts
matching the specification of the layouts being recalled.
22.1.10.6. NFS4ERR_PNFS_IO_HOLE (Error Code 10075)
The pNFS client has attempted to read from or write to an illegal
hole of a file of a data server that is using sparse packing. See
Section 20.8.4.
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22.1.10.7. NFS4ERR_PNFS_NO_LAYOUT (Error Code 10080)
The pNFS client has attempted to read from or write to a file (using
a request to a data server) without holding a valid layout. This
includes the case where the client had a layout, but the iomode does
not allow a WRITE.
22.1.10.8. NFS4ERR_RETURNCONFLICT (Error Code 10086)
A layout is unavailable due to an attempt to perform the LAYOUTGET
before a pending LAYOUTRETURN on the file has been received. See
Section 18.7.5.3.3.
22.1.10.9. NFS4ERR_UNKNOWN_LAYOUTTYPE (Error Code 10062)
The client has specified a layout type that is not supported by the
server.
22.1.11. Session Use Errors
This section deals with errors encountered when using sessions, that
is, errors encountered when a request uses a Sequence (i.e., either
SEQUENCE or CB_SEQUENCE) operation.
22.1.11.1. NFS4ERR_BADSESSION (Error Code 10052)
The specified session ID is unknown to the server to which the
operation is addressed.
22.1.11.2. NFS4ERR_BADSLOT (Error Code 10053)
The requester sent a Sequence operation that attempted to use a slot
the replier does not have in its slot table. It is possible the slot
may have been retired.
22.1.11.3. NFS4ERR_BAD_HIGH_SLOT (Error Code 10077)
The highest_slot argument in a Sequence operation exceeds the
replier's enforced highest_slotid. Also returned when the
rsa_target_highest_slotid argument in a CB_RECALL_SLOT operation
exceeds maximum enforced slot ID of the session's fore channel.
22.1.11.4. NFS4ERR_CB_PATH_DOWN (Error Code 10048)
There is a problem contacting the client via the callback path. The
function of this error has been mostly superseded by the use of
status flags in the reply to the SEQUENCE operation (See
Section 25.46).
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22.1.11.5. NFS4ERR_DEADSESSION (Error Code 10078)
The specified session is a persistent session that is dead and does
not accept new requests or perform new operations on existing
requests (in the case in which a request was partially executed
before server restart).
22.1.11.6. NFS4ERR_CONN_NOT_BOUND_TO_SESSION (Error Code 10055)
A Sequence operation was sent on a connection that has not been
associated with the specified session, where the client specified
that connection association was to be enforced with SP4_MACH_CRED or
SP4_SSV state protection.
22.1.11.7. NFS4ERR_SEQ_FALSE_RETRY (Error Code 10076)
The requester sent a Sequence operation with a slot ID and sequence
ID that are in the reply cache, but the replier has detected that the
retried request is not the same as the original request. See
Section 7.6.1.3.1.
22.1.11.8. NFS4ERR_SEQ_MISORDERED (Error Code 10063)
The requester sent a Sequence operation with an invalid sequence ID.
22.1.12. Session Management Errors
This section deals with errors associated with requests used in
session management.
22.1.12.1. NFS4ERR_BACK_CHAN_BUSY (Error Code 10057)
An attempt was made to destroy a session when the session cannot be
destroyed because the server has callback requests outstanding.
22.1.12.2. NFS4ERR_BAD_SESSION_DIGEST (Error Code 10051)
The digest used in a SET_SSV request is not valid.
22.1.13. Client Management Errors
This section deals with errors associated with requests used to
create and manage client IDs.
22.1.13.1. NFS4ERR_CLIENTID_BUSY (Error Code 10074)
The DESTROY_CLIENTID operation has found there are sessions and/or
unexpired state associated with the client ID to be destroyed.
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22.1.13.2. NFS4ERR_CLID_INUSE (Error Code 10017)
While processing an EXCHANGE_ID operation, the server was presented
with a co_ownerid field that matches an existing client with valid
leased state, but the principal sending the EXCHANGE_ID operation
differs from the principal that established the existing client.
This indicates a collision (most likely due to chance) between
clients. The client should recover by changing the co_ownerid and
re-sending EXCHANGE_ID (but not with the same slot ID and sequence
ID; one or both MUST be different on the re-send).
22.1.13.3. NFS4ERR_ENCR_ALG_UNSUPP (Error Code 10079)
An EXCHANGE_ID was sent that specified state protection via SSV, and
where the set of encryption algorithms presented by the client did
not include any supported by the server.
22.1.13.4. NFS4ERR_HASH_ALG_UNSUPP (Error Code 10072)
An EXCHANGE_ID was sent that specified state protection via SSV, and
where the set of hashing algorithms presented by the client did not
include any supported by the server.
22.1.13.5. NFS4ERR_STALE_CLIENTID (Error Code 10022)
A client ID not recognized by the server was passed to an operation.
Note that unlike the case of NFSv4.0, client IDs are not passed
explicitly to the server in ordinary locking operations and cannot
result in this error. Instead, when there is a server restart, it is
first manifested through an error on the associated session, and the
staleness of the client ID is detected when trying to associate a
client ID with a new session.
22.1.14. Delegation Errors
This section deals with errors associated with requesting and
returning delegations.
22.1.14.1. NFS4ERR_DELEG_ALREADY_WANTED (Error Code 10056)
The client has requested a delegation when it had already registered
that it wants that same delegation.
22.1.14.2. NFS4ERR_DIRDELEG_UNAVAIL (Error Code 10084)
This error is returned when the server is unable or unwilling to
provide a requested directory delegation.
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22.1.14.3. NFS4ERR_RECALLCONFLICT (Error Code 10061)
A recallable object (i.e., a layout or delegation) is unavailable due
to a conflicting recall operation that is currently in progress for
that object.
22.1.14.4. NFS4ERR_REJECT_DELEG (Error Code 10085)
The callback operation invoked to deal with a new delegation has
rejected it.
22.1.15. Attribute Handling Errors
This section deals with errors specific to attribute handling within
NFSv4.
22.1.15.1. NFS4ERR_ATTRNOTSUPP (Error Code 10032)
An attribute specified is not supported by the server. This error
MUST NOT be returned by the GETATTR operation.
22.1.15.2. NFS4ERR_BADOWNER (Error Code 10039)
This error is returned when an owner or owner_group attribute value
or the who field of an ACE within an ACL attribute value cannot be
translated to a local representation.
22.1.15.3. NFS4ERR_NOT_SAME (Error Code 10027)
This error is returned by the VERIFY operation to signify that the
attributes compared were not the same as those provided in the
client's request.
22.1.15.4. NFS4ERR_SAME (Error Code 10009)
This error is returned by the NVERIFY operation to signify that the
attributes compared were the same as those provided in the client's
request.
22.1.16. Obsoleted Errors
These errors MUST NOT be generated by any NFSv4.1 operation. This
can be for a number of reasons.
* The function provided by the error has been superseded by one of
the status bits returned by the SEQUENCE operation.
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* The new session structure and associated change in locking have
made the error unnecessary.
* There has been a restructuring of some errors for NFSv4.1 that
resulted in the elimination of certain errors.
22.1.16.1. NFS4ERR_BAD_SEQID (Error Code 10026)
The sequence number (seqid) in a locking request is neither the next
expected number or the last number processed. These seqids are
ignored in NFSv4.1.
22.1.16.2. NFS4ERR_LEASE_MOVED (Error Code 10031)
A lease being renewed is associated with a file system that has been
migrated to a new server. The error has been superseded by the
SEQ4_STATUS_LEASE_MOVED status bit (See Section 25.46).
22.1.16.3. NFS4ERR_NXIO (Error Code 6)
I/O error. No such device or address. This error is for errors
involving block and character device access, but because NFSv4.1 is
not a device-access protocol, this error is not applicable.
22.1.16.4. NFS4ERR_RESOURCE (Error Code 10018)
For the processing of the COMPOUND procedure, the server may exhaust
available resources and cannot continue processing operations within
the COMPOUND procedure. This error will be returned from the server
in those instances of resource exhaustion related to the processing
of the COMPOUND procedure.
In NFSv4.1, the need for this general error has been eliminated
because explicit limits on compound sizes are established when the
session is created.
22.1.16.5. NFS4ERR_RESTOREFH (Error Code 10030)
The RESTOREFH operation does not have a saved filehandle (identified
by SAVEFH) to operate upon. In NFSv4.1, this error has been
superseded by NFS4ERR_NOFILEHANDLE.
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22.1.16.6. NFS4ERR_STALE_STATEID (Error Code 10023)
A stateid generated by an earlier server instance was used. This
error is moot in NFSv4.1 because all operations that take a stateid
MUST be preceded by the SEQUENCE operation, and the earlier server
instance is detected by the session infrastructure that supports
SEQUENCE.
22.2. Operations and Their Valid Errors
This section contains a table that gives the valid error returns for
each protocol operation. The error code NFS4_OK (indicating no
error) is not listed but should be understood to be returnable by all
operations with two important exceptions:
* The operations that MUST NOT be implemented: OPEN_CONFIRM,
RELEASE_LOCKOWNER, RENEW, SETCLIENTID, and SETCLIENTID_CONFIRM.
* All illegal (i.e. undefined) operations.
+======================+========================================+
| Operation | Errors |
+======================+========================================+
| Illegal Ops | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL |
+----------------------+----------------------------------------+
| ACCESS | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| BACKCHANNEL_CTL | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_INVAL, |
| | NFS4ERR_NOENT, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
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| BIND_CONN_TO_SESSION | NFS4ERR_BADSESSION, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_SESSION_DIGEST, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_INVAL, NFS4ERR_NOT_ONLY_OP, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| CLOSE | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_LOCKS_HELD, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| COMMIT | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_IO, |
| | NFS4ERR_ISDIR, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| CREATE | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADCHAR, NFS4ERR_BADNAME, |
| | NFS4ERR_BADOWNER, NFS4ERR_BADTYPE, |
| | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_DQUOT, |
| | NFS4ERR_EXIST, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
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| | NFS4ERR_MLINK, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNSAFE_COMPOUND |
+----------------------+----------------------------------------+
| CREATE_SESSION | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_INVAL, NFS4ERR_NOENT, |
| | NFS4ERR_NOT_ONLY_OP, NFS4ERR_NOSPC, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SEQ_MISORDERED, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE_CLIENTID, |
| | NFS4ERR_TOOSMALL, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| DELEGPURGE | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| DELEGRETURN | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_REVOKED, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
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| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| DESTROY_CLIENTID | NFS4ERR_BADXDR, NFS4ERR_CLIENTID_BUSY, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_NOT_ONLY_OP, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE_CLIENTID, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| DESTROY_SESSION | NFS4ERR_BACK_CHAN_BUSY, |
| | NFS4ERR_BADSESSION, NFS4ERR_BADXDR, |
| | NFS4ERR_CB_PATH_DOWN, |
| | NFS4ERR_CONN_NOT_BOUND_TO_SESSION, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_NOT_ONLY_OP, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE_CLIENTID, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| EXCHANGE_ID | NFS4ERR_BADCHAR, NFS4ERR_BADXDR, |
| | NFS4ERR_CLID_INUSE, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_ENCR_ALG_UNSUPP, |
| | NFS4ERR_HASH_ALG_UNSUPP, |
| | NFS4ERR_INVAL, NFS4ERR_NOENT, |
| | NFS4ERR_NOT_ONLY_OP, NFS4ERR_NOT_SAME, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
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+----------------------+----------------------------------------+
| FREE_STATEID | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_LOCKS_HELD, |
| | NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| GET_DIR_DELEGATION | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DIRDELEG_UNAVAIL, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOTDIR, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| GETATTR | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| GETDEVICEINFO | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_INVAL, |
| | NFS4ERR_NOENT, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
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| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_TOOSMALL, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE |
+----------------------+----------------------------------------+
| GETDEVICELIST | NFS4ERR_BADXDR, NFS4ERR_BAD_COOKIE, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOTSUPP, NFS4ERR_NOT_SAME, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE |
+----------------------+----------------------------------------+
| GETFH | NFS4ERR_FHEXPIRED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_STALE |
+----------------------+----------------------------------------+
| LAYOUTCOMMIT | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADIOMODE, NFS4ERR_BADLAYOUT, |
| | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED, |
| | NFS4ERR_EXPIRED, NFS4ERR_FBIG, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_ISDIR NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP, |
| | NFS4ERR_NO_GRACE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_RECLAIM_BAD, |
| | NFS4ERR_RECLAIM_CONFLICT, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_CRED |
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+----------------------+----------------------------------------+
| LAYOUTGET | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADIOMODE, NFS4ERR_BADLAYOUT, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_LAYOUTTRYLATER, |
| | NFS4ERR_LAYOUTUNAVAILABLE, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OPENMODE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_RECALLCONFLICT, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOOSMALL, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| LAYOUTRETURN | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_REVOKED, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
| | NFS4ERR_ISDIR, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP, |
| | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_CRED, NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| LINK | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADNAME, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
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| | NFS4ERR_DQUOT, NFS4ERR_EXIST, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
| | NFS4ERR_ISDIR, NFS4ERR_IO, |
| | NFS4ERR_MLINK, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_NOTDIR, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_SYMLINK, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONGSEC, NFS4ERR_WRONG_TYPE, |
| | NFS4ERR_XDEV |
+----------------------+----------------------------------------+
| LOCK | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_RANGE, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_DEADLOCK, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DENIED, NFS4ERR_EXPIRED, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_ISDIR, |
| | NFS4ERR_LOCK_NOTSUPP, |
| | NFS4ERR_LOCK_RANGE, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OPENMODE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_RECLAIM_BAD, |
| | NFS4ERR_RECLAIM_CONFLICT, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_SYMLINK, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED, NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| LOCKT | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_RANGE, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DENIED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
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| | NFS4ERR_ISDIR, NFS4ERR_LOCK_RANGE, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED, NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| LOCKU | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_RANGE, |
| | NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_LOCK_RANGE, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| LOOKUP | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADNAME, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONGSEC |
+----------------------+----------------------------------------+
| LOOKUPP | NFS4ERR_ACCESS, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE, |
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| | NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONGSEC |
+----------------------+----------------------------------------+
| NVERIFY | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADCHAR, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SAME, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| OPEN | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADNAME, NFS4ERR_BADOWNER, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_ALREADY_WANTED, |
| | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT, |
| | NFS4ERR_EXIST, NFS4ERR_EXPIRED, |
| | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
| | NFS4ERR_ISDIR, NFS4ERR_IO, |
| | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG, |
| | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_NOTDIR, |
| | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_PERM, NFS4ERR_RECLAIM_BAD, |
| | NFS4ERR_RECLAIM_CONFLICT, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
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| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_SHARE_DENIED, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_WRONGSEC, NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| OPEN_CONFIRM | NFS4ERR_NOTSUPP |
+----------------------+----------------------------------------+
| OPEN_DOWNGRADE | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
+----------------------+----------------------------------------+
| OPENATTR | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DQUOT, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| PUTFH | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_MOVED, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
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| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC |
+----------------------+----------------------------------------+
| PUTPUBFH | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC |
+----------------------+----------------------------------------+
| PUTROOTFH | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC |
+----------------------+----------------------------------------+
| READ | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_REVOKED, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
| | NFS4ERR_ISDIR, NFS4ERR_IO, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_PNFS_IO_HOLE, |
| | NFS4ERR_PNFS_NO_LAYOUT, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| READDIR | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_COOKIE, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
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| | NFS4ERR_NOT_SAME, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOOSMALL, NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| READLINK | NFS4ERR_ACCESS, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| RECLAIM_COMPLETE | NFS4ERR_BADXDR, |
| | NFS4ERR_COMPLETE_ALREADY, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED, NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| RELEASE_LOCKOWNER | NFS4ERR_NOTSUPP |
+----------------------+----------------------------------------+
| REMOVE | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADNAME, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_NOTEMPTY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
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| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| RENAME | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADNAME, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DQUOT, NFS4ERR_EXIST, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MLINK, |
| | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG, |
| | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_NOTDIR, |
| | NFS4ERR_NOTEMPTY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONGSEC, NFS4ERR_XDEV |
+----------------------+----------------------------------------+
| RENEW | NFS4ERR_NOTSUPP |
+----------------------+----------------------------------------+
| RESTOREFH | NFS4ERR_DEADSESSION, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC |
+----------------------+----------------------------------------+
| SAVEFH | NFS4ERR_DEADSESSION, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
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| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| SECINFO | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADNAME, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG, |
| | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| SECINFO_NO_NAME | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_MOVED, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| SEQUENCE | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_HIGH_SLOT, |
| | NFS4ERR_CONN_NOT_BOUND_TO_SESSION, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SEQUENCE_POS, |
| | NFS4ERR_SEQ_FALSE_RETRY, |
| | NFS4ERR_SEQ_MISORDERED, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| SET_SSV | NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_SESSION_DIGEST, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
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| | NFS4ERR_INVAL, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| SETATTR | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADOWNER, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT, |
| | NFS4ERR_EXPIRED, NFS4ERR_FBIG, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| SETCLIENTID | NFS4ERR_NOTSUPP |
+----------------------+----------------------------------------+
| SETCLIENTID_CONFIRM | NFS4ERR_NOTSUPP |
+----------------------+----------------------------------------+
| TEST_STATEID | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+----------------------+----------------------------------------+
| VERIFY | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADCHAR, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
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| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOT_SAME, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| WANT_DELEGATION | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_ALREADY_WANTED, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOTSUPP, NFS4ERR_NO_GRACE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_RECALLCONFLICT, |
| | NFS4ERR_RECLAIM_BAD, |
| | NFS4ERR_RECLAIM_CONFLICT, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
| WRITE | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT, |
| | NFS4ERR_EXPIRED, NFS4ERR_FBIG, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_ISDIR, NFS4ERR_LOCKED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OPENMODE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_PNFS_IO_HOLE, |
| | NFS4ERR_PNFS_NO_LAYOUT, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
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| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_SYMLINK, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+----------------------------------------+
Table 12: Valid Error Returns for Each Protocol Operation
22.3. Callback Operations and Their Valid Errors
This section contains a table that gives the valid error returns for
each callback operation. The error code NFS4_OK (indicating no
error) is not listed but should be understood to be returnable by all
callback operations with the exception of CB_ILLEGAL.
+=========================+=======================================+
| Callback Operation | Errors |
+=========================+=======================================+
| CB_GETATTR | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_DELAY, NFS4ERR_INVAL, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, |
+-------------------------+---------------------------------------+
| CB_ILLEGAL | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL |
+-------------------------+---------------------------------------+
| CB_LAYOUTRECALL | NFS4ERR_BADHANDLE, NFS4ERR_BADIOMODE, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DELAY, NFS4ERR_INVAL, |
| | NFS4ERR_NOMATCHING_LAYOUT, |
| | NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
+-------------------------+---------------------------------------+
| CB_NOTIFY | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY, |
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| | NFS4ERR_INVAL, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
| CB_NOTIFY_DEVICEID | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_INVAL, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
| CB_NOTIFY_LOCK | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY, |
| | NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
| CB_PUSH_DELEG | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_DELAY, NFS4ERR_INVAL, |
| | NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REJECT_DELEG, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
+-------------------------+---------------------------------------+
| CB_RECALL | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
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| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
| CB_RECALL_ANY | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_INVAL, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
| CB_RECALLABLE_OBJ_AVAIL | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_INVAL, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
| CB_RECALL_SLOT | NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_HIGH_SLOT, NFS4ERR_DELAY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
| CB_SEQUENCE | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT, |
| | NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_HIGH_SLOT, |
| | NFS4ERR_CONN_NOT_BOUND_TO_SESSION, |
| | NFS4ERR_DELAY, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SEQUENCE_POS, |
| | NFS4ERR_SEQ_FALSE_RETRY, |
| | NFS4ERR_SEQ_MISORDERED, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
| CB_WANTS_CANCELLED | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_NOTSUPP, |
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| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+---------------------------------------+
Table 13: Valid Error Returns for Each Protocol Callback Operation
22.4. Errors and the Operations That Use Them
+===================================+===============================+
| Error | Operations |
+===================================+===============================+
| NFS4ERR_ACCESS | ACCESS, COMMIT, CREATE, |
| | GETATTR, GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LINK, LOCK, LOCKT, LOCKU, |
| | LOOKUP, LOOKUPP, NVERIFY, |
| | OPEN, OPENATTR, READ, |
| | READDIR, READLINK, REMOVE, |
| | RENAME, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_ADMIN_REVOKED | CLOSE, DELEGRETURN, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LOCK, LOCKU, |
| | OPEN, OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_ATTRNOTSUPP | CREATE, LAYOUTCOMMIT, |
| | NVERIFY, OPEN, SETATTR, |
| | VERIFY |
+-----------------------------------+-------------------------------+
| NFS4ERR_BACK_CHAN_BUSY | DESTROY_SESSION |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADCHAR | CREATE, EXCHANGE_ID, LINK, |
| | LOOKUP, NVERIFY, OPEN, |
| | REMOVE, RENAME, SECINFO, |
| | SETATTR, VERIFY |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADHANDLE | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | PUTFH |
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+-----------------------------------+-------------------------------+
| NFS4ERR_BADIOMODE | CB_LAYOUTRECALL, |
| | LAYOUTCOMMIT, LAYOUTGET |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADLAYOUT | LAYOUTCOMMIT, LAYOUTGET |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADNAME | CREATE, LINK, LOOKUP, OPEN, |
| | REMOVE, RENAME, SECINFO |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADOWNER | CREATE, OPEN, SETATTR |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADSESSION | BIND_CONN_TO_SESSION, |
| | CB_SEQUENCE, |
| | DESTROY_SESSION, SEQUENCE |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADSLOT | CB_SEQUENCE, SEQUENCE |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADTYPE | CREATE |
+-----------------------------------+-------------------------------+
| NFS4ERR_BADXDR | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_ILLEGAL, |
| | CB_LAYOUTRECALL, CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, |
| | CB_RECALL_SLOT, CB_SEQUENCE, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, ILLEGAL, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | NVERIFY, OPEN, OPENATTR, |
| | OPEN_DOWNGRADE, PUTFH, READ, |
| | READDIR, RECLAIM_COMPLETE, |
| | REMOVE, RENAME, SECINFO, |
| | SECINFO_NO_NAME, SEQUENCE, |
| | SETATTR, SET_SSV, |
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| | TEST_STATEID, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_BAD_COOKIE | GETDEVICELIST, READDIR |
+-----------------------------------+-------------------------------+
| NFS4ERR_BAD_HIGH_SLOT | CB_RECALL_SLOT, CB_SEQUENCE, |
| | SEQUENCE |
+-----------------------------------+-------------------------------+
| NFS4ERR_BAD_RANGE | LOCK, LOCKT, LOCKU |
+-----------------------------------+-------------------------------+
| NFS4ERR_BAD_SESSION_DIGEST | BIND_CONN_TO_SESSION, |
| | SET_SSV |
+-----------------------------------+-------------------------------+
| NFS4ERR_BAD_STATEID | CB_LAYOUTRECALL, CB_NOTIFY, |
| | CB_NOTIFY_LOCK, CB_RECALL, |
| | CLOSE, DELEGRETURN, |
| | FREE_STATEID, LAYOUTGET, |
| | LAYOUTRETURN, LOCK, LOCKU, |
| | OPEN, OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_CB_PATH_DOWN | DESTROY_SESSION |
+-----------------------------------+-------------------------------+
| NFS4ERR_CLID_INUSE | CREATE_SESSION, EXCHANGE_ID |
+-----------------------------------+-------------------------------+
| NFS4ERR_CLIENTID_BUSY | DESTROY_CLIENTID |
+-----------------------------------+-------------------------------+
| NFS4ERR_COMPLETE_ALREADY | RECLAIM_COMPLETE |
+-----------------------------------+-------------------------------+
| NFS4ERR_CONN_NOT_BOUND_TO_SESSION | CB_SEQUENCE, |
| | DESTROY_SESSION, SEQUENCE |
+-----------------------------------+-------------------------------+
| NFS4ERR_DEADLOCK | LOCK |
+-----------------------------------+-------------------------------+
| NFS4ERR_DEADSESSION | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
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| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, SET_SSV, |
| | TEST_STATEID, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_DELAY | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, |
| | CB_RECALL_SLOT, CB_SEQUENCE, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, SECINFO, |
| | SECINFO_NO_NAME, SEQUENCE, |
| | SETATTR, SET_SSV, |
| | TEST_STATEID, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_DELEG_ALREADY_WANTED | OPEN, WANT_DELEGATION |
+-----------------------------------+-------------------------------+
| NFS4ERR_DELEG_REVOKED | DELEGRETURN, LAYOUTCOMMIT, |
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| | LAYOUTGET, LAYOUTRETURN, |
| | OPEN, READ, SETATTR, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_DENIED | LOCK, LOCKT |
+-----------------------------------+-------------------------------+
| NFS4ERR_DIRDELEG_UNAVAIL | GET_DIR_DELEGATION |
+-----------------------------------+-------------------------------+
| NFS4ERR_DQUOT | CREATE, LAYOUTGET, LINK, |
| | OPEN, OPENATTR, RENAME, |
| | SETATTR, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_ENCR_ALG_UNSUPP | EXCHANGE_ID |
+-----------------------------------+-------------------------------+
| NFS4ERR_EXIST | CREATE, LINK, OPEN, RENAME |
+-----------------------------------+-------------------------------+
| NFS4ERR_EXPIRED | CLOSE, DELEGRETURN, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LOCK, LOCKU, |
| | OPEN, OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_FBIG | LAYOUTCOMMIT, OPEN, SETATTR, |
| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_FHEXPIRED | ACCESS, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, |
| | GETATTR, GETDEVICELIST, |
| | GETFH, GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SETATTR, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_FILE_OPEN | LINK, REMOVE, RENAME |
+-----------------------------------+-------------------------------+
| NFS4ERR_GRACE | GETATTR, GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, NVERIFY, OPEN, READ, |
| | REMOVE, RENAME, SETATTR, |
| | VERIFY, WANT_DELEGATION, |
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| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_HASH_ALG_UNSUPP | EXCHANGE_ID |
+-----------------------------------+-------------------------------+
| NFS4ERR_INVAL | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_PUSH_DELEG, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, CREATE, |
| | CREATE_SESSION, DELEGRETURN, |
| | EXCHANGE_ID, GETATTR, |
| | GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | NVERIFY, OPEN, |
| | OPEN_DOWNGRADE, READ, |
| | READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | SET_SSV, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_IO | ACCESS, COMMIT, CREATE, |
| | GETATTR, GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LINK, LOOKUP, LOOKUPP, |
| | NVERIFY, OPEN, OPENATTR, |
| | READ, READDIR, READLINK, |
| | REMOVE, RENAME, SETATTR, |
| | VERIFY, WANT_DELEGATION, |
| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_ISDIR | COMMIT, LAYOUTCOMMIT, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, OPEN, READ, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_LAYOUTTRYLATER | LAYOUTGET |
+-----------------------------------+-------------------------------+
| NFS4ERR_LAYOUTUNAVAILABLE | LAYOUTGET |
+-----------------------------------+-------------------------------+
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| NFS4ERR_LOCKED | LAYOUTGET, READ, SETATTR, |
| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_LOCKS_HELD | CLOSE, FREE_STATEID |
+-----------------------------------+-------------------------------+
| NFS4ERR_LOCK_NOTSUPP | LOCK |
+-----------------------------------+-------------------------------+
| NFS4ERR_LOCK_RANGE | LOCK, LOCKT, LOCKU |
+-----------------------------------+-------------------------------+
| NFS4ERR_MLINK | CREATE, LINK, RENAME |
+-----------------------------------+-------------------------------+
| NFS4ERR_MOVED | ACCESS, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, |
| | GETATTR, GETFH, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, READ, READDIR, |
| | READLINK, RECLAIM_COMPLETE, |
| | REMOVE, RENAME, RESTOREFH, |
| | SAVEFH, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WANT_DELEGATION, |
| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_NAMETOOLONG | CREATE, LINK, LOOKUP, OPEN, |
| | REMOVE, RENAME, SECINFO |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOENT | BACKCHANNEL_CTL, |
| | CREATE_SESSION, EXCHANGE_ID, |
| | GETDEVICEINFO, LOOKUP, |
| | LOOKUPP, OPEN, OPENATTR, |
| | REMOVE, RENAME, SECINFO, |
| | SECINFO_NO_NAME |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOFILEHANDLE | ACCESS, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, |
| | GETATTR, GETDEVICELIST, |
| | GETFH, GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | READ, READDIR, READLINK, |
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| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SETATTR, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOMATCHING_LAYOUT | CB_LAYOUTRECALL |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOSPC | CREATE, CREATE_SESSION, |
| | LAYOUTGET, LINK, OPEN, |
| | OPENATTR, RENAME, SETATTR, |
| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOTDIR | CREATE, GET_DIR_DELEGATION, |
| | LINK, LOOKUP, LOOKUPP, OPEN, |
| | READDIR, REMOVE, RENAME, |
| | SECINFO, SECINFO_NO_NAME |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOTEMPTY | REMOVE, RENAME |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOTSUPP | CB_LAYOUTRECALL, CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_WANTS_CANCELLED, |
| | DELEGPURGE, DELEGRETURN, |
| | GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, |
| | OPENATTR, OPEN_CONFIRM, |
| | RELEASE_LOCKOWNER, RENEW, |
| | SECINFO_NO_NAME, |
| | SETCLIENTID, |
| | SETCLIENTID_CONFIRM, |
| | WANT_DELEGATION |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOT_ONLY_OP | BIND_CONN_TO_SESSION, |
| | CREATE_SESSION, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, EXCHANGE_ID |
+-----------------------------------+-------------------------------+
| NFS4ERR_NOT_SAME | EXCHANGE_ID, GETDEVICELIST, |
| | READDIR, VERIFY |
+-----------------------------------+-------------------------------+
| NFS4ERR_NO_GRACE | LAYOUTCOMMIT, LAYOUTRETURN, |
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| | LOCK, OPEN, WANT_DELEGATION |
+-----------------------------------+-------------------------------+
| NFS4ERR_OLD_STATEID | CLOSE, DELEGRETURN, |
| | FREE_STATEID, LAYOUTGET, |
| | LAYOUTRETURN, LOCK, LOCKU, |
| | OPEN, OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_OPENMODE | LAYOUTGET, LOCK, READ, |
| | SETATTR, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_OP_ILLEGAL | CB_ILLEGAL, ILLEGAL |
+-----------------------------------+-------------------------------+
| NFS4ERR_OP_NOT_IN_SESSION | ACCESS, BACKCHANNEL_CTL, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, |
| | CB_RECALL_SLOT, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, DELEGPURGE, |
| | DELEGRETURN, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
| | GETDEVICELIST, GETFH, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SETATTR, SET_SSV, |
| | TEST_STATEID, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_PERM | CREATE, OPEN, SETATTR |
+-----------------------------------+-------------------------------+
| NFS4ERR_PNFS_IO_HOLE | READ, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_PNFS_NO_LAYOUT | READ, WRITE |
+-----------------------------------+-------------------------------+
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| NFS4ERR_RECALLCONFLICT | LAYOUTGET, WANT_DELEGATION |
+-----------------------------------+-------------------------------+
| NFS4ERR_RECLAIM_BAD | LAYOUTCOMMIT, LOCK, OPEN, |
| | WANT_DELEGATION |
+-----------------------------------+-------------------------------+
| NFS4ERR_RECLAIM_CONFLICT | LAYOUTCOMMIT, LOCK, OPEN, |
| | WANT_DELEGATION |
+-----------------------------------+-------------------------------+
| NFS4ERR_REJECT_DELEG | CB_PUSH_DELEG |
+-----------------------------------+-------------------------------+
| NFS4ERR_REP_TOO_BIG | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, |
| | CB_RECALL_SLOT, CB_SEQUENCE, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, SET_SSV, |
| | TEST_STATEID, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_REP_TOO_BIG_TO_CACHE | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, |
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| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, |
| | CB_RECALL_SLOT, CB_SEQUENCE, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, SET_SSV, |
| | TEST_STATEID, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_REQ_TOO_BIG | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, |
| | CB_RECALL_SLOT, CB_SEQUENCE, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
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| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, SET_SSV, |
| | TEST_STATEID, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_RETRY_UNCACHED_REP | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, |
| | CB_RECALL_SLOT, CB_SEQUENCE, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, SET_SSV, |
| | TEST_STATEID, VERIFY, |
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| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_ROFS | CREATE, LINK, LOCK, LOCKT, |
| | OPEN, OPENATTR, |
| | OPEN_DOWNGRADE, REMOVE, |
| | RENAME, SETATTR, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_SAME | NVERIFY |
+-----------------------------------+-------------------------------+
| NFS4ERR_SEQUENCE_POS | CB_SEQUENCE, SEQUENCE |
+-----------------------------------+-------------------------------+
| NFS4ERR_SEQ_FALSE_RETRY | CB_SEQUENCE, SEQUENCE |
+-----------------------------------+-------------------------------+
| NFS4ERR_SEQ_MISORDERED | CB_SEQUENCE, CREATE_SESSION, |
| | SEQUENCE |
+-----------------------------------+-------------------------------+
| NFS4ERR_SERVERFAULT | ACCESS, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKU, LOOKUP, LOOKUPP, |
| | NVERIFY, OPEN, OPENATTR, |
| | OPEN_DOWNGRADE, PUTFH, |
| | PUTPUBFH, PUTROOTFH, READ, |
| | READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SETATTR, TEST_STATEID, |
| | VERIFY, WANT_DELEGATION, |
| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_SHARE_DENIED | OPEN |
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+-----------------------------------+-------------------------------+
| NFS4ERR_STALE | ACCESS, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, |
| | GETATTR, GETFH, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, READ, READDIR, |
| | READLINK, RECLAIM_COMPLETE, |
| | REMOVE, RENAME, RESTOREFH, |
| | SAVEFH, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WANT_DELEGATION, |
| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_STALE_CLIENTID | CREATE_SESSION, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION |
+-----------------------------------+-------------------------------+
| NFS4ERR_SYMLINK | COMMIT, LAYOUTCOMMIT, LINK, |
| | LOCK, LOCKT, LOOKUP, |
| | LOOKUPP, OPEN, READ, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_TOOSMALL | CREATE_SESSION, |
| | GETDEVICEINFO, LAYOUTGET, |
| | READDIR |
+-----------------------------------+-------------------------------+
| NFS4ERR_TOO_MANY_OPS | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, |
| | CB_NOTIFY_DEVICEID, |
| | CB_NOTIFY_LOCK, |
| | CB_PUSH_DELEG, CB_RECALL, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, |
| | CB_RECALL_SLOT, CB_SEQUENCE, |
| | CB_WANTS_CANCELLED, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | EXCHANGE_ID, FREE_STATEID, |
| | GETATTR, GETDEVICEINFO, |
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| | GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, SET_SSV, |
| | TEST_STATEID, VERIFY, |
| | WANT_DELEGATION, WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_UNKNOWN_LAYOUTTYPE | CB_LAYOUTRECALL, |
| | GETDEVICEINFO, |
| | GETDEVICELIST, LAYOUTCOMMIT, |
| | LAYOUTGET, LAYOUTRETURN, |
| | NVERIFY, SETATTR, VERIFY |
+-----------------------------------+-------------------------------+
| NFS4ERR_UNSAFE_COMPOUND | CREATE, OPEN, OPENATTR |
+-----------------------------------+-------------------------------+
| NFS4ERR_WRONGSEC | LINK, LOOKUP, LOOKUPP, OPEN, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | RENAME, RESTOREFH |
+-----------------------------------+-------------------------------+
| NFS4ERR_WRONG_CRED | CLOSE, CREATE_SESSION, |
| | DELEGPURGE, DELEGRETURN, |
| | DESTROY_CLIENTID, |
| | DESTROY_SESSION, |
| | FREE_STATEID, LAYOUTCOMMIT, |
| | LAYOUTRETURN, LOCK, LOCKT, |
| | LOCKU, OPEN_DOWNGRADE, |
| | RECLAIM_COMPLETE |
+-----------------------------------+-------------------------------+
| NFS4ERR_WRONG_TYPE | CB_LAYOUTRECALL, |
| | CB_PUSH_DELEG, COMMIT, |
| | GETATTR, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, NVERIFY, OPEN, |
| | OPENATTR, READ, READLINK, |
| | RECLAIM_COMPLETE, SETATTR, |
| | VERIFY, WANT_DELEGATION, |
| | WRITE |
+-----------------------------------+-------------------------------+
| NFS4ERR_XDEV | LINK, RENAME |
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+-----------------------------------+-------------------------------+
Table 14: Errors and the Operations That Use Them
23. NFSv4.1 Procedures
Both procedures, NULL and COMPOUND, MUST be implemented.
23.1. Procedure 0: NULL - No Operation
23.1.1. ARGUMENTS
void;
23.1.2. RESULTS
void;
23.1.3. DESCRIPTION
This is the standard NULL procedure with the standard void argument
and void response. This procedure has no functionality associated
with it. Because of this, it is sometimes used to measure the
overhead of processing a service request. Therefore, the server
SHOULD ensure that no unnecessary work is done in servicing this
procedure.
23.1.4. ERRORS
None.
23.2. Procedure 1: COMPOUND - Compound Operations
23.2.1. ARGUMENTS
enum nfs_opnum4 {
OP_ACCESS = 3,
OP_CLOSE = 4,
OP_COMMIT = 5,
OP_CREATE = 6,
OP_DELEGPURGE = 7,
OP_DELEGRETURN = 8,
OP_GETATTR = 9,
OP_GETFH = 10,
OP_LINK = 11,
OP_LOCK = 12,
OP_LOCKT = 13,
OP_LOCKU = 14,
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OP_LOOKUP = 15,
OP_LOOKUPP = 16,
OP_NVERIFY = 17,
OP_OPEN = 18,
OP_OPENATTR = 19,
OP_OPEN_CONFIRM = 20, /* Mandatory not-to-implement */
OP_OPEN_DOWNGRADE = 21,
OP_PUTFH = 22,
OP_PUTPUBFH = 23,
OP_PUTROOTFH = 24,
OP_READ = 25,
OP_READDIR = 26,
OP_READLINK = 27,
OP_REMOVE = 28,
OP_RENAME = 29,
OP_RENEW = 30, /* Mandatory not-to-implement */
OP_RESTOREFH = 31,
OP_SAVEFH = 32,
OP_SECINFO = 33,
OP_SETATTR = 34,
OP_SETCLIENTID = 35, /* Mandatory not-to-implement */
OP_SETCLIENTID_CONFIRM = 36, /* Mandatory not-to-implement */
OP_VERIFY = 37,
OP_WRITE = 38,
OP_RELEASE_LOCKOWNER = 39, /* Mandatory not-to-implement */
/* new operations for NFSv4.1 */
OP_BACKCHANNEL_CTL = 40,
OP_BIND_CONN_TO_SESSION = 41,
OP_EXCHANGE_ID = 42,
OP_CREATE_SESSION = 43,
OP_DESTROY_SESSION = 44,
OP_FREE_STATEID = 45,
OP_GET_DIR_DELEGATION = 46,
OP_GETDEVICEINFO = 47,
OP_GETDEVICELIST = 48,
OP_LAYOUTCOMMIT = 49,
OP_LAYOUTGET = 50,
OP_LAYOUTRETURN = 51,
OP_SECINFO_NO_NAME = 52,
OP_SEQUENCE = 53,
OP_SET_SSV = 54,
OP_TEST_STATEID = 55,
OP_WANT_DELEGATION = 56,
OP_DESTROY_CLIENTID = 57,
OP_RECLAIM_COMPLETE = 58,
OP_ILLEGAL = 10044
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};
union nfs_argop4 switch (nfs_opnum4 argop) {
case OP_ACCESS: ACCESS4args opaccess;
case OP_CLOSE: CLOSE4args opclose;
case OP_COMMIT: COMMIT4args opcommit;
case OP_CREATE: CREATE4args opcreate;
case OP_DELEGPURGE: DELEGPURGE4args opdelegpurge;
case OP_DELEGRETURN: DELEGRETURN4args opdelegreturn;
case OP_GETATTR: GETATTR4args opgetattr;
case OP_GETFH: void;
case OP_LINK: LINK4args oplink;
case OP_LOCK: LOCK4args oplock;
case OP_LOCKT: LOCKT4args oplockt;
case OP_LOCKU: LOCKU4args oplocku;
case OP_LOOKUP: LOOKUP4args oplookup;
case OP_LOOKUPP: void;
case OP_NVERIFY: NVERIFY4args opnverify;
case OP_OPEN: OPEN4args opopen;
case OP_OPENATTR: OPENATTR4args opopenattr;
/* Not for NFSv4.1 */
case OP_OPEN_CONFIRM: OPEN_CONFIRM4args opopen_confirm;
case OP_OPEN_DOWNGRADE:
OPEN_DOWNGRADE4args opopen_downgrade;
case OP_PUTFH: PUTFH4args opputfh;
case OP_PUTPUBFH: void;
case OP_PUTROOTFH: void;
case OP_READ: READ4args opread;
case OP_READDIR: READDIR4args opreaddir;
case OP_READLINK: void;
case OP_REMOVE: REMOVE4args opremove;
case OP_RENAME: RENAME4args oprename;
/* Not for NFSv4.1 */
case OP_RENEW: RENEW4args oprenew;
case OP_RESTOREFH: void;
case OP_SAVEFH: void;
case OP_SECINFO: SECINFO4args opsecinfo;
case OP_SETATTR: SETATTR4args opsetattr;
/* Not for NFSv4.1 */
case OP_SETCLIENTID: SETCLIENTID4args opsetclientid;
/* Not for NFSv4.1 */
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case OP_SETCLIENTID_CONFIRM: SETCLIENTID_CONFIRM4args
opsetclientid_confirm;
case OP_VERIFY: VERIFY4args opverify;
case OP_WRITE: WRITE4args opwrite;
/* Not for NFSv4.1 */
case OP_RELEASE_LOCKOWNER:
RELEASE_LOCKOWNER4args
oprelease_lockowner;
/* Operations new to NFSv4.1 */
case OP_BACKCHANNEL_CTL:
BACKCHANNEL_CTL4args opbackchannel_ctl;
case OP_BIND_CONN_TO_SESSION:
BIND_CONN_TO_SESSION4args
opbind_conn_to_session;
case OP_EXCHANGE_ID: EXCHANGE_ID4args opexchange_id;
case OP_CREATE_SESSION:
CREATE_SESSION4args opcreate_session;
case OP_DESTROY_SESSION:
DESTROY_SESSION4args opdestroy_session;
case OP_FREE_STATEID: FREE_STATEID4args opfree_stateid;
case OP_GET_DIR_DELEGATION:
GET_DIR_DELEGATION4args
opget_dir_delegation;
case OP_GETDEVICEINFO: GETDEVICEINFO4args opgetdeviceinfo;
case OP_GETDEVICELIST: GETDEVICELIST4args opgetdevicelist;
case OP_LAYOUTCOMMIT: LAYOUTCOMMIT4args oplayoutcommit;
case OP_LAYOUTGET: LAYOUTGET4args oplayoutget;
case OP_LAYOUTRETURN: LAYOUTRETURN4args oplayoutreturn;
case OP_SECINFO_NO_NAME:
SECINFO_NO_NAME4args opsecinfo_no_name;
case OP_SEQUENCE: SEQUENCE4args opsequence;
case OP_SET_SSV: SET_SSV4args opset_ssv;
case OP_TEST_STATEID: TEST_STATEID4args optest_stateid;
case OP_WANT_DELEGATION:
WANT_DELEGATION4args opwant_delegation;
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case OP_DESTROY_CLIENTID:
DESTROY_CLIENTID4args
opdestroy_clientid;
case OP_RECLAIM_COMPLETE:
RECLAIM_COMPLETE4args
opreclaim_complete;
/* Operations not new to NFSv4.1 */
case OP_ILLEGAL: void;
};
struct COMPOUND4args {
utf8str_cs tag;
uint32_t minorversion;
nfs_argop4 argarray<>;
};
23.2.2. RESULTS
union nfs_resop4 switch (nfs_opnum4 resop) {
case OP_ACCESS: ACCESS4res opaccess;
case OP_CLOSE: CLOSE4res opclose;
case OP_COMMIT: COMMIT4res opcommit;
case OP_CREATE: CREATE4res opcreate;
case OP_DELEGPURGE: DELEGPURGE4res opdelegpurge;
case OP_DELEGRETURN: DELEGRETURN4res opdelegreturn;
case OP_GETATTR: GETATTR4res opgetattr;
case OP_GETFH: GETFH4res opgetfh;
case OP_LINK: LINK4res oplink;
case OP_LOCK: LOCK4res oplock;
case OP_LOCKT: LOCKT4res oplockt;
case OP_LOCKU: LOCKU4res oplocku;
case OP_LOOKUP: LOOKUP4res oplookup;
case OP_LOOKUPP: LOOKUPP4res oplookupp;
case OP_NVERIFY: NVERIFY4res opnverify;
case OP_OPEN: OPEN4res opopen;
case OP_OPENATTR: OPENATTR4res opopenattr;
/* Not for NFSv4.1 */
case OP_OPEN_CONFIRM: OPEN_CONFIRM4res opopen_confirm;
case OP_OPEN_DOWNGRADE:
OPEN_DOWNGRADE4res
opopen_downgrade;
case OP_PUTFH: PUTFH4res opputfh;
case OP_PUTPUBFH: PUTPUBFH4res opputpubfh;
case OP_PUTROOTFH: PUTROOTFH4res opputrootfh;
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case OP_READ: READ4res opread;
case OP_READDIR: READDIR4res opreaddir;
case OP_READLINK: READLINK4res opreadlink;
case OP_REMOVE: REMOVE4res opremove;
case OP_RENAME: RENAME4res oprename;
/* Not for NFSv4.1 */
case OP_RENEW: RENEW4res oprenew;
case OP_RESTOREFH: RESTOREFH4res oprestorefh;
case OP_SAVEFH: SAVEFH4res opsavefh;
case OP_SECINFO: SECINFO4res opsecinfo;
case OP_SETATTR: SETATTR4res opsetattr;
/* Not for NFSv4.1 */
case OP_SETCLIENTID: SETCLIENTID4res opsetclientid;
/* Not for NFSv4.1 */
case OP_SETCLIENTID_CONFIRM:
SETCLIENTID_CONFIRM4res
opsetclientid_confirm;
case OP_VERIFY: VERIFY4res opverify;
case OP_WRITE: WRITE4res opwrite;
/* Not for NFSv4.1 */
case OP_RELEASE_LOCKOWNER:
RELEASE_LOCKOWNER4res
oprelease_lockowner;
/* Operations new to NFSv4.1 */
case OP_BACKCHANNEL_CTL:
BACKCHANNEL_CTL4res
opbackchannel_ctl;
case OP_BIND_CONN_TO_SESSION:
BIND_CONN_TO_SESSION4res
opbind_conn_to_session;
case OP_EXCHANGE_ID: EXCHANGE_ID4res opexchange_id;
case OP_CREATE_SESSION:
CREATE_SESSION4res
opcreate_session;
case OP_DESTROY_SESSION:
DESTROY_SESSION4res
opdestroy_session;
case OP_FREE_STATEID: FREE_STATEID4res
opfree_stateid;
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case OP_GET_DIR_DELEGATION:
GET_DIR_DELEGATION4res
opget_dir_delegation;
case OP_GETDEVICEINFO: GETDEVICEINFO4res
opgetdeviceinfo;
case OP_GETDEVICELIST: GETDEVICELIST4res
opgetdevicelist;
case OP_LAYOUTCOMMIT: LAYOUTCOMMIT4res oplayoutcommit;
case OP_LAYOUTGET: LAYOUTGET4res oplayoutget;
case OP_LAYOUTRETURN: LAYOUTRETURN4res oplayoutreturn;
case OP_SECINFO_NO_NAME:
SECINFO_NO_NAME4res
opsecinfo_no_name;
case OP_SEQUENCE: SEQUENCE4res opsequence;
case OP_SET_SSV: SET_SSV4res opset_ssv;
case OP_TEST_STATEID: TEST_STATEID4res optest_stateid;
case OP_WANT_DELEGATION:
WANT_DELEGATION4res
opwant_delegation;
case OP_DESTROY_CLIENTID:
DESTROY_CLIENTID4res
opdestroy_clientid;
case OP_RECLAIM_COMPLETE:
RECLAIM_COMPLETE4res
opreclaim_complete;
/* Operations not new to NFSv4.1 */
case OP_ILLEGAL: ILLEGAL4res opillegal;
};
struct COMPOUND4res {
nfsstat4 status;
utf8str_cs tag;
nfs_resop4 resarray<>;
};
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23.2.3. DESCRIPTION
The COMPOUND procedure is used to combine one or more NFSv4
operations into a single RPC request. The server interprets each of
the operations in turn. If an operation is executed by the server
and the status of that operation is NFS4_OK, then the next operation
in the COMPOUND procedure is executed. The server continues this
process until there are no more operations to be executed or until
one of the operations has a status value other than NFS4_OK.
In the processing of the COMPOUND procedure, the server may find that
it does not have the available resources to execute any or all of the
operations within the COMPOUND sequence. See Section 7.6.4 for a
more detailed discussion.
The server will generally choose between two methods of decoding the
client's request. The first would be the traditional one-pass XDR
decode. If there is an XDR decoding error in this case, the RPC XDR
decode error would be returned. The second method would be to make
an initial pass to decode the basic COMPOUND request and then to XDR
decode the individual operations; the most interesting is the decode
of attributes. In this case, the server may encounter an XDR decode
error during the second pass. If it does, the server would return
the error NFS4ERR_BADXDR to signify the decode error.
The COMPOUND arguments contain a "minorversion" field. For NFSv4.1,
the value for this field is 1. If the server receives a COMPOUND
procedure with a minorversion field value that it does not support,
the server MUST return an error of NFS4ERR_MINOR_VERS_MISMATCH and a
zero-length resultdata array.
Contained within the COMPOUND results is a "status" field. If the
results array length is non-zero, this status must be equivalent to
the status of the last operation that was executed within the
COMPOUND procedure. Therefore, if an operation incurred an error
then the "status" value will be the same error value as is being
returned for the operation that failed.
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Note that operations zero and one are not defined for the COMPOUND
procedure. Operation 2 is not defined and is reserved for future
definition and use with minor versioning. If the server receives an
operation array that contains operation 2 and the minorversion field
has a value of zero, an error of NFS4ERR_OP_ILLEGAL, as described in
the next paragraph, is returned to the client. If an operation array
contains an operation 2 and the minorversion field is non-zero and
the server does not support the minor version, the server returns an
error of NFS4ERR_MINOR_VERS_MISMATCH. Therefore, the
NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
errors.
It is possible that the server receives a request that contains an
operation that is less than the first legal operation (OP_ACCESS) or
greater than the last legal operation (OP_RECLAIM_COMPLETE for
NFSv4.1). In this case, the server's response will encode the opcode
OP_ILLEGAL rather than the illegal opcode of the request. The status
field in the ILLEGAL return results will be set to
NFS4ERR_OP_ILLEGAL. The COMPOUND procedure's return results will
also be NFS4ERR_OP_ILLEGAL. Note that for future minor versions, the
last legal operation might be different but that illegal operations
are dealt with similarly.
The definition of the "tag" in the request is left to the
implementer. It may be used to summarize the content of the Compound
request for the benefit of packet-sniffers and engineers debugging
implementations. However, the value of "tag" in the response SHOULD
be the same value as provided in the request. This applies to the
tag field of the CB_COMPOUND procedure as well.
23.2.3.1. Current Filehandle and Stateid
The COMPOUND procedure offers a simple environment for the execution
of the operations specified by the client. The first two relate to
the filehandle while the second two relate to the current stateid.
23.2.3.1.1. Current Filehandle
The current and saved filehandles are used throughout the protocol.
Most operations implicitly use the current filehandle as an argument,
and many set the current filehandle as part of the results. The
combination of client-specified sequences of operations and current
and saved filehandle arguments and results allows for greater
protocol flexibility. The best or easiest example of current
filehandle usage is a sequence like the following:
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PUTFH fh1 {fh1}
LOOKUP "compA" {fh2}
GETATTR {fh2}
LOOKUP "compB" {fh3}
GETATTR {fh3}
LOOKUP "compC" {fh4}
GETATTR {fh4}
GETFH
Figure 2
In this example, the PUTFH (Section 25.19) operation explicitly sets
the current filehandle value while the result of each LOOKUP
operation sets the current filehandle value to the resultant file
system object. Also, the client is able to insert GETATTR operations
using the current filehandle as an argument.
The PUTROOTFH (Section 25.21) and PUTPUBFH (Section 25.20) operations
also set the current filehandle. The above example would replace
"PUTFH fh1" with PUTROOTFH or PUTPUBFH with no filehandle argument in
order to achieve the same effect (on the assumption that "compA" is
directly below the root of the namespace).
Along with the current filehandle, there is a saved filehandle.
While the current filehandle is set as the result of operations like
LOOKUP, the saved filehandle must be set directly with the use of the
SAVEFH operation. The SAVEFH operation copies the current filehandle
value to the saved value. The saved filehandle value is used in
combination with the current filehandle value for the LINK and RENAME
operations. The RESTOREFH operation will copy the saved filehandle
value to the current filehandle value; as a result, the saved
filehandle value may be used a sort of "scratch" area for the
client's series of operations.
23.2.3.1.2. Current Stateid
With NFSv4.1, additions of a current stateid and a saved stateid have
been made to the COMPOUND processing environment; this allows for the
passing of stateids between operations. There are no changes to the
syntax of the protocol, only changes to the semantics of a few
operations.
A "current stateid" is the stateid that is associated with the
current filehandle. The current stateid may only be changed by an
operation that modifies the current filehandle or returns a stateid.
If an operation returns a stateid, it MUST set the current stateid to
the returned value. If an operation sets the current filehandle but
does not return a stateid, the current stateid MUST be set to the
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all-zeros special stateid, i.e., (seqid, other) = (0, 0). If an
operation uses a stateid as an argument but does not return a
stateid, the current stateid MUST NOT be changed. For example,
PUTFH, PUTROOTFH, and PUTPUBFH will change the current server state
from {ocfh, (osid)} to {cfh, (0, 0)}, while LOCK will change the
current state from {cfh, (osid} to {cfh, (nsid)}. Operations like
LOOKUP that transform a current filehandle and component name into a
new current filehandle will also change the current state to {0, 0}.
The SAVEFH and RESTOREFH operations will save and restore both the
current filehandle and the current stateid as a set.
The following example is the common case of a simple READ operation
with a normal stateid showing that the PUTFH initializes the current
stateid to (0, 0). The subsequent READ with stateid (sid1) leaves
the current stateid unchanged.
PUTFH fh1 - -> {fh1, (0, 0)}
READ (sid1), 0, 1024 {fh1, (0, 0)} -> {fh1, (0, 0)}
Figure 3
This next example performs an OPEN with the root filehandle and, as a
result, generates stateid (sid1). The next operation specifies the
READ with the argument stateid set such that (seqid, other) are equal
to (1, 0), but the current stateid set by the previous operation is
actually used when the operation is evaluated. This allows correct
interaction with any existing, potentially conflicting, locks.
PUTROOTFH - -> {fh1, (0, 0)}
OPEN "compA" {fh1, (0, 0)} -> {fh2, (sid1)}
READ (1, 0), 0, 1024 {fh2, (sid1)} -> {fh2, (sid1)}
CLOSE (1, 0) {fh2, (sid1)} -> {fh2, (sid2)}
Figure 4
This next example is similar to the second in how it passes the
stateid sid2 generated by the LOCK operation to the next READ
operation. This allows the client to explicitly surround a single I/
O operation with a lock and its appropriate stateid to guarantee
correctness with other client locks. The example also shows how
SAVEFH and RESTOREFH can save and later reuse a filehandle and
stateid, passing them as the current filehandle and stateid to a READ
operation.
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PUTFH fh1 - -> {fh1, (0, 0)}
LOCK 0, 1024, (sid1) {fh1, (sid1)} -> {fh1, (sid2)}
READ (1, 0), 0, 1024 {fh1, (sid2)} -> {fh1, (sid2)}
LOCKU 0, 1024, (1, 0) {fh1, (sid2)} -> {fh1, (sid3)}
SAVEFH {fh1, (sid3)} -> {fh1, (sid3)}
PUTFH fh2 {fh1, (sid3)} -> {fh2, (0, 0)}
WRITE (1, 0), 0, 1024 {fh2, (0, 0)} -> {fh2, (0, 0)}
RESTOREFH {fh2, (0, 0)} -> {fh1, (sid3)}
READ (1, 0), 1024, 1024 {fh1, (sid3)} -> {fh1, (sid3)}
Figure 5
The final example shows a disallowed use of the current stateid. The
client is attempting to implicitly pass an anonymous special stateid,
(0,0), to the READ operation. The server MUST return
NFS4ERR_BAD_STATEID in the reply to the READ operation.
PUTFH fh1 - -> {fh1, (0, 0)}
READ (1, 0), 0, 1024 {fh1, (0, 0)} -> NFS4ERR_BAD_STATEID
Figure 6
23.2.4. ERRORS
COMPOUND will of course return every error that each operation on the
fore channel can return (See Table 12). However, if COMPOUND returns
zero operations, obviously the error returned by COMPOUND has nothing
to do with an error returned by an operation. The list of errors
COMPOUND will return if it processes zero operations include:
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+==============================+==================================+
| Error | Notes |
+==============================+==================================+
| NFS4ERR_BADCHAR | The tag argument has a character |
| | the replier does not support. |
+------------------------------+----------------------------------+
| NFS4ERR_BADXDR | |
+------------------------------+----------------------------------+
| NFS4ERR_DELAY | |
+------------------------------+----------------------------------+
| NFS4ERR_INVAL | The tag argument is not in UTF-8 |
| | encoding. |
+------------------------------+----------------------------------+
| NFS4ERR_MINOR_VERS_MISMATCH | |
+------------------------------+----------------------------------+
| NFS4ERR_SERVERFAULT | |
+------------------------------+----------------------------------+
| NFS4ERR_TOO_MANY_OPS | |
+------------------------------+----------------------------------+
| NFS4ERR_REP_TOO_BIG | |
+------------------------------+----------------------------------+
| NFS4ERR_REP_TOO_BIG_TO_CACHE | |
+------------------------------+----------------------------------+
| NFS4ERR_REQ_TOO_BIG | |
+------------------------------+----------------------------------+
Table 15: COMPOUND Error Returns
24. Operations: REQUIRED, RECOMMENDED, or OPTIONAL
The following tables summarize the operations of the NFSv4.1 protocol
and the corresponding designation of REQUIRED, RECOMMENDED, and
OPTIONAL to implement or MUST NOT implement. The designation of MUST
NOT implement is reserved for those operations that were defined in
NFSv4.0 and MUST NOT be implemented in NFSv4.1.
For the most part, the REQUIRED, RECOMMENDED, or OPTIONAL designation
for operations sent by the client is for the server implementation.
The client is generally required to implement the operations needed
for the operating environment for which it serves. For example, a
read-only NFSv4.1 client would have no need to implement the WRITE
operation and is not required to do so.
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The REQUIRED or OPTIONAL designation for callback operations sent by
the server is for both the client and server. Generally, the client
has the option of creating the backchannel and sending the operations
on the fore channel that will be a catalyst for the server sending
callback operations. A partial exception is CB_RECALL_SLOT; the only
way the client can avoid supporting this operation is by not creating
a backchannel.
Since this is a summary of the operations and their designation,
there are subtleties that are not presented here. Therefore, if
there is a question of the requirements of implementation, the
operation descriptions themselves must be consulted along with other
relevant explanatory text within this specification.
The abbreviations used in the second and third columns of the table
are defined as follows.
REQ REQUIRED to implement
REC RECOMMEND to implement
OPT OPTIONAL to implement
MNI MUST NOT implement
For the NFSv4.1 features that are OPTIONAL, the operations that
support those features are OPTIONAL, and the server would return
NFS4ERR_NOTSUPP in response to the client's use of those operations.
If an OPTIONAL feature is supported, it is possible that a set of
operations related to the feature become REQUIRED to implement. The
third column of the table designates the feature(s) and if the
operation is REQUIRED or OPTIONAL in the presence of support for the
feature.
The OPTIONAL features identified and their abbreviations are as
follows:
pNFS Parallel NFS
FDELG File Delegations
DDELG Directory Delegations
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+======================+=============+============+===============+
| Operation | REQ, REC, | Feature | Definition |
| | OPT, or MNI | (REQ, REC, | |
| | | or OPT) | |
+======================+=============+============+===============+
| ACCESS | REQ | | Section 25.1 |
+----------------------+-------------+------------+---------------+
| BACKCHANNEL_CTL | REQ | | Section 25.33 |
+----------------------+-------------+------------+---------------+
| BIND_CONN_TO_SESSION | REQ | | Section 25.34 |
+----------------------+-------------+------------+---------------+
| CLOSE | REQ | | Section 25.2 |
+----------------------+-------------+------------+---------------+
| COMMIT | REQ | | Section 25.3 |
+----------------------+-------------+------------+---------------+
| CREATE | REQ | | Section 25.4 |
+----------------------+-------------+------------+---------------+
| CREATE_SESSION | REQ | | Section 25.36 |
+----------------------+-------------+------------+---------------+
| DELEGPURGE | OPT | FDELG | Section 25.5 |
| | | (REQ) | |
+----------------------+-------------+------------+---------------+
| DELEGRETURN | OPT | FDELG, | Section 25.6 |
| | | DDELG, | |
| | | pNFS (REQ) | |
+----------------------+-------------+------------+---------------+
| DESTROY_CLIENTID | REQ | | Section 25.50 |
+----------------------+-------------+------------+---------------+
| DESTROY_SESSION | REQ | | Section 25.37 |
+----------------------+-------------+------------+---------------+
| EXCHANGE_ID | REQ | | Section 25.35 |
+----------------------+-------------+------------+---------------+
| FREE_STATEID | REQ | | Section 25.38 |
+----------------------+-------------+------------+---------------+
| GETATTR | REQ | | Section 25.7 |
+----------------------+-------------+------------+---------------+
| GETDEVICEINFO | OPT | pNFS (REQ) | Section 25.40 |
+----------------------+-------------+------------+---------------+
| GETDEVICELIST | OPT | pNFS (OPT) | Section 25.41 |
+----------------------+-------------+------------+---------------+
| GETFH | REQ | | Section 25.8 |
+----------------------+-------------+------------+---------------+
| GET_DIR_DELEGATION | OPT | DDELG | Section 25.39 |
| | | (REQ) | |
+----------------------+-------------+------------+---------------+
| LAYOUTCOMMIT | OPT | pNFS (REQ) | Section 25.42 |
+----------------------+-------------+------------+---------------+
| LAYOUTGET | OPT | pNFS (REQ) | Section 25.43 |
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+----------------------+-------------+------------+---------------+
| LAYOUTRETURN | OPT | pNFS (REQ) | Section 25.44 |
+----------------------+-------------+------------+---------------+
| LINK | OPT | | Section 25.9 |
+----------------------+-------------+------------+---------------+
| LOCK | REQ | | Section 25.10 |
+----------------------+-------------+------------+---------------+
| LOCKT | REQ | | Section 25.11 |
+----------------------+-------------+------------+---------------+
| LOCKU | REQ | | Section 25.12 |
+----------------------+-------------+------------+---------------+
| LOOKUP | REQ | | Section 25.13 |
+----------------------+-------------+------------+---------------+
| LOOKUPP | REQ | | Section 25.14 |
+----------------------+-------------+------------+---------------+
| NVERIFY | REQ | | Section 25.15 |
+----------------------+-------------+------------+---------------+
| OPEN | REQ | | Section 25.16 |
+----------------------+-------------+------------+---------------+
| OPENATTR | OPT | | Section 25.17 |
+----------------------+-------------+------------+---------------+
| OPEN_CONFIRM | MNI | | N/A |
+----------------------+-------------+------------+---------------+
| OPEN_DOWNGRADE | REQ | | Section 25.18 |
+----------------------+-------------+------------+---------------+
| PUTFH | REQ | | Section 25.19 |
+----------------------+-------------+------------+---------------+
| PUTPUBFH | REQ | | Section 25.20 |
+----------------------+-------------+------------+---------------+
| PUTROOTFH | REQ | | Section 25.21 |
+----------------------+-------------+------------+---------------+
| READ | REQ | | Section 25.22 |
+----------------------+-------------+------------+---------------+
| READDIR | REQ | | Section 25.23 |
+----------------------+-------------+------------+---------------+
| READLINK | OPT | | Section 25.24 |
+----------------------+-------------+------------+---------------+
| RECLAIM_COMPLETE | REQ | | Section 25.51 |
+----------------------+-------------+------------+---------------+
| RELEASE_LOCKOWNER | MNI | | N/A |
+----------------------+-------------+------------+---------------+
| REMOVE | REQ | | Section 25.25 |
+----------------------+-------------+------------+---------------+
| RENAME | REQ | | Section 25.26 |
+----------------------+-------------+------------+---------------+
| RENEW | MNI | | N/A |
+----------------------+-------------+------------+---------------+
| RESTOREFH | REQ | | Section 25.27 |
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+----------------------+-------------+------------+---------------+
| SAVEFH | REQ | | Section 25.28 |
+----------------------+-------------+------------+---------------+
| SECINFO | REQ | | Section 25.29 |
+----------------------+-------------+------------+---------------+
| SECINFO_NO_NAME | REC | pNFS file | Section |
| | | layout | 25.45, |
| | | (REQ) | Section 20.25 |
+----------------------+-------------+------------+---------------+
| SEQUENCE | REQ | | Section 25.46 |
+----------------------+-------------+------------+---------------+
| SETATTR | REQ | | Section 25.30 |
+----------------------+-------------+------------+---------------+
| SETCLIENTID | MNI | | N/A |
+----------------------+-------------+------------+---------------+
| SETCLIENTID_CONFIRM | MNI | | N/A |
+----------------------+-------------+------------+---------------+
| SET_SSV | REQ | | Section 25.47 |
+----------------------+-------------+------------+---------------+
| TEST_STATEID | REQ | | Section 25.48 |
+----------------------+-------------+------------+---------------+
| VERIFY | REQ | | Section 25.31 |
+----------------------+-------------+------------+---------------+
| WANT_DELEGATION | OPT | FDELG | Section 25.49 |
| | | (OPT) | |
+----------------------+-------------+------------+---------------+
| WRITE | REQ | | Section 25.32 |
+----------------------+-------------+------------+---------------+
Table 16: Operations
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+=========================+=============+============+============+
| Operation | REQ, REC, | Feature | Definition |
| | OPT, or MNI | (REQ, REC, | |
| | | or OPT) | |
+=========================+=============+============+============+
| CB_GETATTR | OPT | FDELG | Section |
| | | (REQ) | 27.1 |
+-------------------------+-------------+------------+------------+
| CB_LAYOUTRECALL | OPT | pNFS (REQ) | Section |
| | | | 27.3 |
+-------------------------+-------------+------------+------------+
| CB_NOTIFY | OPT | DDELG | Section |
| | | (REQ) | 27.4 |
+-------------------------+-------------+------------+------------+
| CB_NOTIFY_DEVICEID | OPT | pNFS (OPT) | Section |
| | | | 27.12 |
+-------------------------+-------------+------------+------------+
| CB_NOTIFY_LOCK | OPT | | Section |
| | | | 27.11 |
+-------------------------+-------------+------------+------------+
| CB_PUSH_DELEG | OPT | FDELG | Section |
| | | (OPT) | 27.5 |
+-------------------------+-------------+------------+------------+
| CB_RECALL | OPT | FDELG, | Section |
| | | DDELG, | 27.2 |
| | | pNFS (REQ) | |
+-------------------------+-------------+------------+------------+
| CB_RECALL_ANY | OPT | FDELG, | Section |
| | | DDELG, | 27.6 |
| | | pNFS (REQ) | |
+-------------------------+-------------+------------+------------+
| CB_RECALL_SLOT | REQ | | Section |
| | | | 27.8 |
+-------------------------+-------------+------------+------------+
| CB_RECALLABLE_OBJ_AVAIL | OPT | DDELG, | Section |
| | | pNFS (REQ) | 27.7 |
+-------------------------+-------------+------------+------------+
| CB_SEQUENCE | REQ | | Section |
| | | | 27.9 |
+-------------------------+-------------+------------+------------+
| CB_WANTS_CANCELLED | OPT | FDELG, | Section |
| | | DDELG, | 27.10 |
| | | pNFS (REQ) | |
+-------------------------+-------------+------------+------------+
Table 17: Callback Operations
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25. NFSv4.1 Operations
25.1. Operation 3: ACCESS - Check Access Rights
25.1.1. ARGUMENTS
const ACCESS4_READ = 0x00000001;
const ACCESS4_LOOKUP = 0x00000002;
const ACCESS4_MODIFY = 0x00000004;
const ACCESS4_EXTEND = 0x00000008;
const ACCESS4_DELETE = 0x00000010;
const ACCESS4_EXECUTE = 0x00000020;
struct ACCESS4args {
/* CURRENT_FH: object */
uint32_t access;
};
25.1.2. RESULTS
struct ACCESS4resok {
uint32_t supported;
uint32_t access;
};
union ACCESS4res switch (nfsstat4 status) {
case NFS4_OK:
ACCESS4resok resok4;
default:
void;
};
25.1.3. DESCRIPTION
ACCESS determines the access rights that a user, as identified by the
credentials in the RPC request, has with respect to the file system
object specified by the current filehandle. The client encodes the
set of access rights that are to be checked in the bit mask "access".
The server checks the permissions encoded in the bit mask. If a
status of NFS4_OK is returned, two bit masks are included in the
response. The first, "supported", represents the access rights for
which the server can verify reliably. The second, "access",
represents the access rights available to the user for the filehandle
provided. On success, the current filehandle retains its value.
Note that the reply's supported and access fields MUST NOT contain
more values than originally set in the request's access field. For
example, if the client sends an ACCESS operation with just the
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ACCESS4_READ value set and the server supports this value, the server
MUST NOT set more than ACCESS4_READ in the supported field even if it
could have reliably checked other values.
The reply's access field MUST NOT contain more values than the
supported field.
The results of this operation are necessarily advisory in nature. A
return status of NFS4_OK and the appropriate bit set in the bit mask
do not imply that such access will be allowed to the file system
object in the future. This is because access rights can be revoked
by the server at any time.
The following access permissions may be requested:
ACCESS4_READ Read data from file or read a directory.
ACCESS4_LOOKUP Look up a name in a directory (no meaning for non-
directory objects).
ACCESS4_MODIFY Rewrite existing file data or modify existing
directory entries.
ACCESS4_EXTEND Write new data to a file as controlled by the ACE
mask bit for appending data or add directory entries (for either
files or sub-directories).
ACCESS4_DELETE Delete an existing directory entry. Often, when this
is done the link count of the referenced object is decremented to
zero and the object itself is deleted when no longer linked- to or
open.
ACCESS4_EXECUTE Execute a regular file (no meaning for a directory).
On success, the current filehandle retains its value.
ACCESS4_EXECUTE is a challenging semantic to implement because NFS
provides remote file access, not remote execution. This leads to the
following:
* Whether or not a regular file is executable ought to be the
responsibility of the NFS client and not the server. And yet the
ACCESS operation is specified to seemingly require a server to own
that responsibility.
* When a client executes a regular file, it has to read the file
from the server. Strictly speaking, the server should not allow
the client to read a file being executed unless the user has read
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permissions on the file. Requiring explicit read permissions on
executable files in order to access them over NFS is not going to
be acceptable to some users and storage administrators.
Historically, NFS servers have allowed a user to READ a file if
the user has execute access to the file.
As a practical example, the UNIX specification [access_api] states
that an implementation claiming conformance to UNIX may indicate in
the access() programming interface's result that a privileged user
has execute rights, even if no execute permission bits are set on the
regular file's attributes. It is possible to claim conformance to
the UNIX specification and instead not indicate execute rights in
that situation, which is true for some operating environments.
Suppose the operating environments of the client and server are
implementing the access() semantics for privileged users differently,
and the ACCESS operation implementations of the client and server
follow their respective access() semantics. This can cause undesired
behavior:
* Suppose the client's access() interface returns X_OK if the user
is privileged and no execute permission bits are set on the
regular file's attribute, and the server's access() interface does
not return X_OK in that situation. Then the client will be unable
to execute files stored on the NFS server that could be executed
if stored on a non-NFS file system.
* Suppose the client's access() interface does not return X_OK if
the user is privileged, and no execute permission bits are set on
the regular file's attribute, and the server's access() interface
does return X_OK in that situation. Then:
- The client will be able to execute files stored on the NFS
server that could be executed if stored on a non-NFS file
system, unless the client's execution subsystem also checks for
execute permission bits.
- Even if the execution subsystem is checking for execute
permission bits, there are more potential issues. For example,
suppose the client is invoking access() to build a "path search
table" of all executable files in the user's "search path",
where the path is a list of directories each containing
executable files. Suppose there are two files each in separate
directories of the search path, such that files have the same
component name. In the first directory the file has no execute
permission bits set, and in the second directory the file has
execute bits set. The path search table will indicate that the
first directory has the executable file, but the execute
subsystem will fail to execute it. The command shell might
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fail to try the second file in the second directory. And even
if it did, this is a potential performance issue. Clearly, the
desired outcome for the client is for the path search table to
not contain the first file.
To deal with the problems described above, the "smart client, stupid
server" principle is used. The client owns overall responsibility
for determining execute access and relies on the server to parse the
execution permissions within the file's mode, acl, and dacl
attributes. The rules for the client and server follow:
* If the client is sending ACCESS in order to determine if the user
can read the file, the client SHOULD set ACCESS4_READ in the
request's access field.
* If the client's operating environment only grants execution to the
user if the user has execute access according to the execute
permissions in the mode, acl, and dacl attributes, then if the
client wants to determine execute access, the client SHOULD send
an ACCESS request with ACCESS4_EXECUTE bit set in the request's
access field.
* If the client's operating environment grants execution to the user
even if the user does not have execute access according to the
execute permissions in the mode, acl, and dacl attributes, then if
the client wants to determine execute access, it SHOULD send an
ACCESS request with both the ACCESS4_EXECUTE and ACCESS4_READ bits
set in the request's access field. This way, if any read or
execute permission grants the user read or execute access (or if
the server interprets the user as privileged), as indicated by the
presence of ACCESS4_EXECUTE and/or ACCESS4_READ in the reply's
access field, the client will be able to grant the user execute
access to the file.
* If the server supports execute permission bits, or some other
method for denoting executability (e.g., the suffix of the name of
the file might indicate execute), it MUST check only execute
permissions, not read permissions, when determining whether or not
the reply will have ACCESS4_EXECUTE set in the access field. The
server MUST NOT also examine read permission bits when determining
whether or not the reply will have ACCESS4_EXECUTE set in the
access field. Even if the server's operating environment would
grant execute access to the user (e.g., the user is privileged),
the server MUST NOT reply with ACCESS4_EXECUTE set in reply's
access field unless there is at least one execute permission bit
set in the mode, acl, or dacl attributes. In the case of acl and
dacl, the "one execute permission bit" MUST be an ACE4_EXECUTE bit
set in an ALLOW ACE.
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* If the server does not support execute permission bits or some
other method for denoting executability, it MUST NOT set
ACCESS4_EXECUTE in the reply's supported and access fields. If
the client set ACCESS4_EXECUTE in the ACCESS request's access
field, and ACCESS4_EXECUTE is not set in the reply's supported
field, then the client will have to send an ACCESS request with
the ACCESS4_READ bit set in the request's access field.
* If the server supports read permission bits, it MUST only check
for read permissions in the mode, acl, and dacl attributes when it
receives an ACCESS request with ACCESS4_READ set in the access
field. The server MUST NOT also examine execute permission bits
when determining whether the reply will have ACCESS4_READ set in
the access field or not.
Note that if the ACCESS reply has ACCESS4_READ or ACCESS_EXECUTE set,
then the user also has permissions to OPEN (Section 25.16) or READ
(Section 25.22) the file. In other words, if the client sends an
ACCESS request with the ACCESS4_READ and ACCESS_EXECUTE set in the
access field (or two separate requests, one with ACCESS4_READ set and
the other with ACCESS4_EXECUTE set), and the reply has just
ACCESS4_EXECUTE set in the access field (or just one reply has
ACCESS4_EXECUTE set), then the user has authorization to OPEN or READ
the file.
25.1.4. IMPLEMENTATION
In general, it is not sufficient for the client to attempt to deduce
access permissions by inspecting the uid, gid, and mode fields in the
file attributes or by attempting to interpret the contents of the ACL
attribute. This is because the server may perform uid or gid mapping
or enforce additional access-control restrictions. It is also
possible that the server may not be in the same ID space as the
client. In these cases (and perhaps others), the client cannot
reliably perform an access check with only current file attributes.
In the NFSv2 protocol, the only reliable way to determine whether an
operation was allowed was to try it and see if it succeeded or
failed. Using the ACCESS operation in the NFSv4.1 protocol, the
client can ask the server to indicate whether or not one or more
classes of operations are permitted. The ACCESS operation is
provided to allow clients to check before doing a series of
operations that will result in an access failure. The OPEN operation
provides a point where the server can verify access to the file
object and a method to return that information to the client. The
ACCESS operation is still useful for directory operations or for use
in the case that the UNIX interface access() is used on the client.
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The information returned by the server in response to an ACCESS call
is not permanent. It was correct at the exact time that the server
performed the checks, but not necessarily afterwards. The server can
revoke access permission at any time.
The client should use the effective credentials of the user to build
the authentication information in the ACCESS request used to
determine access rights. It is the effective user and group
credentials that are used in subsequent READ and WRITE operations.
Many implementations do not directly support the ACCESS4_DELETE
permission. Operating systems like UNIX will ignore the
ACCESS4_DELETE bit if set on an access request on a non-directory
object. In these systems, delete permission on a file is determined
by the access permissions on the directory in which the file resides,
instead of being determined by the permissions of the file itself.
Therefore, the mask returned enumerating which access rights can be
determined will have the ACCESS4_DELETE value set to 0. This
indicates to the client that the server was unable to check that
particular access right. The ACCESS4_DELETE bit in the access mask
returned will then be ignored by the client.
25.2. Operation 4: CLOSE - Close File
25.2.1. ARGUMENTS
struct CLOSE4args {
/* CURRENT_FH: object */
seqid4 seqid;
stateid4 open_stateid;
};
25.2.2. RESULTS
union CLOSE4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 open_stateid;
default:
void;
};
25.2.3. DESCRIPTION
The CLOSE operation releases share reservations for the regular or
named attribute file as specified by the current filehandle. The
share reservations and other state information released at the server
as a result of this CLOSE are only those associated with the supplied
stateid. State associated with other OPENs is not affected.
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If byte-range locks are held, the client SHOULD release all locks
before sending a CLOSE. The server MAY free all outstanding locks on
CLOSE, but some servers may not support the CLOSE of a file that
still has byte-range locks held. The server MUST return failure if
any locks would exist after the CLOSE.
The argument seqid MAY have any value, and the server MUST ignore
seqid.
On success, the current filehandle retains its value.
The server MAY require that the combination of principal, security
flavor, and, if applicable, GSS mechanism that sent the OPEN request
also be the one to CLOSE the file. This might not be possible if
credentials for the principal are no longer available. The server
MAY allow the machine credential or SSV credential (See
Section 25.35) to send CLOSE.
25.2.4. IMPLEMENTATION
Even though CLOSE returns a stateid, this stateid is not useful to
the client and should be treated as deprecated. CLOSE "shuts down"
the state associated with all OPENs for the file by a single open-
owner. As noted above, CLOSE will either release all file-locking
state or return an error. Therefore, the stateid returned by CLOSE
is not useful for operations that follow. To help find any uses of
this stateid by clients, the server SHOULD return the invalid special
stateid (the "other" value is zero and the "seqid" field is
NFS4_UINT32_MAX, see Section 13.2.3).
A CLOSE operation may make delegations grantable where they were not
previously. Servers may choose to respond immediately if there are
pending delegation want requests or may respond to the situation at a
later time.
25.3. Operation 5: COMMIT - Commit Cached Data
25.3.1. ARGUMENTS
struct COMMIT4args {
/* CURRENT_FH: file */
offset4 offset;
count4 count;
};
25.3.2. RESULTS
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struct COMMIT4resok {
verifier4 writeverf;
};
union COMMIT4res switch (nfsstat4 status) {
case NFS4_OK:
COMMIT4resok resok4;
default:
void;
};
25.3.3. DESCRIPTION
The COMMIT operation forces or flushes uncommitted, modified data to
stable storage for the file specified by the current filehandle. The
flushed data is that which was previously written with one or more
WRITE operations that had the "committed" field of their results
field set to UNSTABLE4.
The offset specifies the position within the file where the flush is
to begin. An offset value of zero means to flush data starting at
the beginning of the file. The count specifies the number of bytes
of data to flush. If the count is zero, a flush from the offset to
the end of the file is done.
The server returns a write verifier upon successful completion of the
COMMIT. The write verifier is used by the client to determine if the
server has restarted between the initial WRITE operations and the
COMMIT. The client does this by comparing the write verifier
returned from the initial WRITE operations and the verifier returned
by the COMMIT operation. The server must vary the value of the write
verifier at each server event or instantiation that may lead to a
loss of uncommitted data. Most commonly this occurs when the server
is restarted; however, other events at the server may result in
uncommitted data loss as well.
On success, the current filehandle retains its value.
25.3.4. IMPLEMENTATION
The COMMIT operation is similar in operation and semantics to the
POSIX fsync() [fsync] system interface that synchronizes a file's
state with the disk (file data and metadata is flushed to disk or
stable storage). COMMIT performs the same operation for a client,
flushing any unsynchronized data and metadata on the server to the
server's disk or stable storage for the specified file. When using
pNFS, if a WRITE returned UNSTABLE4 and NFL4_UFLG_COMMIT_THRU_MDS is
not set, then the client MUST COMMIT to the data server. The COMMIT
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may result in flushing the data but not the metadata. In this case,
the metadata MUST be flushed with a subsequent LAYOUTCOMMIT to the
metadata server. A complete set of pNFS rules for flushing data and
metadata is described in Section 20.13 As in the case of fsync(), it
may be that there is some modified data or no modified data to
synchronize. The data may have been synchronized by the server's
normal periodic buffer synchronization activity. COMMIT should
return NFS4_OK, unless there has been an unexpected error.
COMMIT differs from fsync() in that it is possible for the client to
flush a range of the file (most likely triggered by a buffer-
reclamation scheme on the client before the file has been completely
written).
The server implementation of COMMIT is reasonably simple. If the
server receives a full file COMMIT request, that is, starting at
offset zero and count zero, it should do the equivalent of applying
fsync() to the entire file. Otherwise, it should arrange to have the
modified data in the range specified by offset and count to be
flushed to stable storage. In both cases, any metadata associated
with the file must be flushed to stable storage before returning. It
is not an error for there to be nothing to flush on the server. This
means that the data and metadata that needed to be flushed have
already been flushed or lost during the last server failure.
The client implementation of COMMIT is a little more complex. There
are two reasons for wanting to commit a client buffer to stable
storage. The first is that the client wants to reuse a buffer. In
this case, the offset and count of the buffer are sent to the server
in the COMMIT request. The server then flushes any modified data
based on the offset and count, and flushes any modified metadata
associated with the file. It then returns the status of the flush
and the write verifier. The second reason for the client to generate
a COMMIT is for a full file flush, such as may be done at close. In
this case, the client would gather all of the buffers for this file
that contain uncommitted data, do the COMMIT operation with an offset
of zero and count of zero, and then free all of those buffers. Any
other dirty buffers would be sent to the server in the normal
fashion.
After a buffer is written (via the WRITE operation) by the client
with the "committed" field in the result of WRITE set to UNSTABLE4,
the buffer must be considered as modified by the client until the
buffer has either been flushed via a COMMIT operation or written via
a WRITE operation with the "committed" field in the result set to
FILE_SYNC4 or DATA_SYNC4. This is done to prevent the buffer from
being freed and reused before the data can be flushed to stable
storage on the server.
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When a response is returned from either a WRITE or a COMMIT operation
and it contains a write verifier that differs from that previously
returned by the server, the client will need to retransmit all of the
buffers containing uncommitted data to the server. How this is to be
done is up to the implementer. If there is only one buffer of
interest, then it should be sent in a WRITE request with the
FILE_SYNC4 stable parameter. If there is more than one buffer, it
might be worthwhile retransmitting all of the buffers in WRITE
operations with the stable parameter set to UNSTABLE4 and then
retransmitting the COMMIT operation to flush all of the data on the
server to stable storage. However, if the server repeatably returns
from COMMIT a verifier that differs from that returned by WRITE, the
only way to ensure progress is to retransmit all of the buffers with
WRITE requests with the FILE_SYNC4 stable parameter.
The above description applies to page-cache-based systems as well as
buffer-cache-based systems. In the former systems, the virtual
memory systems, the virtual memory system will need to be modified
instead of the buffer cache.
25.4. Operation 6: CREATE - Create a Non-Regular File Object
25.4.1. ARGUMENTS
union createtype4 switch (nfs_ftype4 type) {
case NF4LNK:
linktext4 linkdata;
case NF4BLK:
case NF4CHR:
specdata4 devdata;
case NF4SOCK:
case NF4FIFO:
case NF4DIR:
void;
default:
void; /* server should return NFS4ERR_BADTYPE */
};
struct CREATE4args {
/* CURRENT_FH: directory for creation */
createtype4 objtype;
component4 objname;
fattr4 createattrs;
};
25.4.2. RESULTS
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struct CREATE4resok {
change_info4 cinfo;
bitmap4 attrset; /* attributes set */
};
union CREATE4res switch (nfsstat4 status) {
case NFS4_OK:
/* new CURRENTFH: created object */
CREATE4resok resok4;
default:
void;
};
25.4.3. DESCRIPTION
The CREATE operation creates a file object other than an ordinary
file in a directory with a given name. The OPEN operation MUST be
used to create a regular file or a named attribute.
The current filehandle must be a directory: an object of type NF4DIR.
If the current filehandle is an attribute directory (type
NF4ATTRDIR), the error NFS4ERR_WRONG_TYPE is returned. If the
current filehandle designates any other type of object, the error
NFS4ERR_NOTDIR results.
The objname specifies the name for the new object. The objtype
determines the type of object to be created: directory, symlink, etc.
If the object type specified is that of an ordinary file, a named
attribute, or a named attribute directory, the error NFS4ERR_BADTYPE
results.
If an object of the same name already exists in the directory, the
server will return the error NFS4ERR_EXIST.
For the directory where the new file object was created, the server
returns change_info4 information in cinfo. With the atomic field of
the change_info4 data type, the server will indicate if the before
and after change attributes were obtained atomically with respect to
the file object creation.
If the objname has a length of zero, or if objname does not obey the
UTF-8 definition, the error NFS4ERR_INVAL will be returned.
The current filehandle is replaced by that of the new object.
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The createattrs specifies the initial set of attributes for the
object. The set of attributes may include any writable attribute
valid for the object type. When the operation is successful, the
server will return to the client an attribute mask signifying which
attributes were successfully set for the object.
If createattrs includes neither the owner attribute nor an ACL with
an ACE for the owner, and if the server's file system both supports
and requires an owner attribute (or an owner ACE), then the server
MUST derive the owner (or the owner ACE). This would typically be
from the principal indicated in the RPC credentials of the call, but
the server's operating environment or file system semantics may
dictate other methods of derivation. Similarly, if createattrs
includes neither the group attribute nor a group ACE, and if the
server's file system both supports and requires the notion of a group
attribute (or group ACE), the server MUST derive the group attribute
(or the corresponding owner ACE) for the file. This could be from
the RPC call's credentials, such as the group principal if the
credentials include it (such as with AUTH_SYS), from the group
identifier associated with the principal in the credentials (e.g.,
POSIX systems have a user database [passwd] that has a group
identifier for every user identifier), inherited from the directory
in which the object is created, or whatever else the server's
operating environment or file system semantics dictate. This applies
to the OPEN operation too.
Conversely, it is possible that the client will specify in
createattrs an owner attribute, group attribute, or ACL that the
principal indicated the RPC call's credentials does not have
permissions to create files for. The error to be returned in this
instance is NFS4ERR_PERM. This applies to the OPEN operation too.
If the current filehandle designates a directory for which another
client holds a directory delegation, then, unless the delegation is
such that the situation can be resolved by sending a notification,
the delegation MUST be recalled, and the CREATE operation MUST NOT
proceed until the delegation is returned or revoked. Except where
this happens very quickly, one or more NFS4ERR_DELAY errors will be
returned to requests made while delegation remains outstanding.
When the current filehandle designates a directory for which one or
more directory delegations exist, then, when those delegations
request such notifications, NOTIFY4_ADD_ENTRY will be generated as a
result of this operation.
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25.4.4. IMPLEMENTATION
If the client desires to set attribute values after the create, a
SETATTR operation can be added to the COMPOUND request so that the
appropriate attributes will be set.
25.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery
25.5.1. ARGUMENTS
struct DELEGPURGE4args {
clientid4 clientid;
};
25.5.2. RESULTS
struct DELEGPURGE4res {
nfsstat4 status;
};
25.5.3. DESCRIPTION
This operation purges all of the delegations awaiting recovery for a
given client. This is useful for clients that do not commit
delegation information to stable storage to indicate that conflicting
requests need not be delayed by the server awaiting recovery of
delegation information.
The client is NOT specified by the clientid field of the request.
The client SHOULD set the client field to zero, and the server MUST
ignore the clientid field. Instead, the server MUST derive the
client ID from the value of the session ID in the arguments of the
SEQUENCE operation that precedes DELEGPURGE in the COMPOUND request.
The DELEGPURGE operation should be used by clients that record
delegation information on stable storage on the client. In this
case, after the client recovers all delegations it knows of, it
should immediately send a DELEGPURGE operation. Doing so will notify
the server that no additional delegations for the client will be
recovered allowing it to free resources, and avoid delaying other
clients which make requests that conflict with the unrecovered
delegations. The set of delegations known to the server and the
client might be different. The reason for this is that after sending
a request that resulted in a delegation, the client might experience
a failure before it both received the delegation and committed the
delegation to the client's stable storage.
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The server MAY support DELEGPURGE, but if it does not, it MUST NOT
support CLAIM_DELEGATE_PREV and MUST NOT support CLAIM_DELEG_PREV_FH.
25.6. Operation 8: DELEGRETURN - Return Delegation
25.6.1. ARGUMENTS
struct DELEGRETURN4args {
/* CURRENT_FH: delegated object */
stateid4 deleg_stateid;
};
25.6.2. RESULTS
struct DELEGRETURN4res {
nfsstat4 status;
};
25.6.3. DESCRIPTION
The DELEGRETURN operation returns the delegation represented by the
current filehandle and stateid.
Delegations may be returned voluntarily (i.e., before the server has
recalled them) or when recalled. In either case, the client must
properly propagate state changed under the context of the delegation
to the server before returning the delegation.
The server MAY require that the principal, security flavor, and if
applicable, the GSS mechanism, combination that acquired the
delegation also be the one to send DELEGRETURN on the file. This
might not be possible if credentials for the principal are no longer
available. The server MAY allow the machine credential or SSV
credential (See Section 25.35) to send DELEGRETURN.
25.7. Operation 9: GETATTR - Get Attributes
25.7.1. ARGUMENTS
struct GETATTR4args {
/* CURRENT_FH: object */
bitmap4 attr_request;
};
25.7.2. RESULTS
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struct GETATTR4resok {
fattr4 obj_attributes;
};
union GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
GETATTR4resok resok4;
default:
void;
};
25.7.3. DESCRIPTION
The GETATTR operation will obtain attributes for the file system
object specified by the current filehandle. The client sets a bit in
the bitmap argument for each attribute value that it would like the
server to return. The server returns an attribute bitmap that
indicates the attribute values that it was able to return, which will
include all attributes requested by the client that are attributes
supported by the server for the target file system. This bitmap is
followed by the attribute values ordered lowest attribute number
first.
The server MUST return a value for each attribute that the client
requests if the attribute is supported by the server for the target
file system. If the server does not support a particular attribute
on the target file system, then it MUST NOT return the attribute
value and MUST NOT set the attribute bit in the result bitmap. The
server MUST return an error if it supports an attribute on the target
but cannot obtain its value. In that case, no attribute values will
be returned.
File systems that are absent should be treated as having support for
a very small set of attributes as described in Section 17.4.1, even
if previously, when the file system was present, more attributes were
supported.
All servers MUST support the REQUIRED attributes as specified in
Section 11.10, for all file systems, with the exception of absent
file systems.
On success, the current filehandle retains its value.
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25.7.4. IMPLEMENTATION
Suppose there is an OPEN_DELEGATE_WRITE delegation held by another
client for the file in question and size and/or change are among the
set of attributes being interrogated. The server has two choices.
First, the server can obtain the actual current value of these
attributes from the client holding the delegation by using the
CB_GETATTR callback. Second, the server, particularly when the
delegated client is unresponsive, can recall the delegation in
question. The GETATTR MUST NOT proceed until one of the following
occurs:
* The requested attribute values are returned in the response to
CB_GETATTR.
* The OPEN_DELEGATE_WRITE delegation is returned.
* The OPEN_DELEGATE_WRITE delegation is revoked.
Unless one of the above happens very quickly, one or more
NFS4ERR_DELAY errors will be returned while a delegation is
outstanding.
25.8. Operation 10: GETFH - Get Current Filehandle
25.8.1. ARGUMENTS
/* CURRENT_FH: */
void;
25.8.2. RESULTS
struct GETFH4resok {
nfs_fh4 object;
};
union GETFH4res switch (nfsstat4 status) {
case NFS4_OK:
GETFH4resok resok4;
default:
void;
};
25.8.3. DESCRIPTION
This operation returns the current filehandle value.
On success, the current filehandle retains its value.
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As described in Section 7.6.4, GETFH is REQUIRED or RECOMMENDED to
immediately follow certain operations, and servers are free to reject
such operations if the client fails to insert GETFH in the request as
REQUIRED or RECOMMENDED. Section 25.16.4.1 provides additional
justification for why GETFH MUST follow OPEN.
25.8.4. IMPLEMENTATION
Operations that change the current filehandle like LOOKUP or CREATE
do not automatically return the new filehandle as a result. For
instance, if a client needs to look up a directory entry and obtain
its filehandle, then the following request is needed.
PUTFH (directory filehandle)
LOOKUP (entry name)
GETFH
25.9. Operation 11: LINK - Create Link to a File
25.9.1. ARGUMENTS
struct LINK4args {
/* SAVED_FH: source object */
/* CURRENT_FH: target directory */
component4 newname;
};
25.9.2. RESULTS
struct LINK4resok {
change_info4 cinfo;
};
union LINK4res switch (nfsstat4 status) {
case NFS4_OK:
LINK4resok resok4;
default:
void;
};
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25.9.3. DESCRIPTION
The LINK operation creates an additional newname for the file
represented by the saved filehandle, as set by the SAVEFH operation,
in the directory represented by the current filehandle. The existing
file and the target directory must reside within the same file system
on the server. On success, the current filehandle will continue to
be the target directory. If an object exists in the target directory
with the same name as newname, the server must return NFS4ERR_EXIST.
For the target directory, the server returns change_info4 information
in cinfo. With the atomic field of the change_info4 data type, the
server will indicate if the before and after change attributes were
obtained atomically with respect to the link creation.
If the newname has a length of zero, or if newname does not obey the
UTF-8 definition, the error NFS4ERR_INVAL will be returned.
25.9.4. IMPLEMENTATION
The server MAY impose restrictions on the LINK operation such that
LINK may not be done when the file is open or when that open is done
by particular protocols, or with particular options or access modes.
When LINK is rejected because of such restrictions, the error
NFS4ERR_FILE_OPEN is returned.
If a server does implement such restrictions and those restrictions
include cases of NFSv4 opens preventing successful execution of a
link, the server needs to recall any delegations that could hide the
existence of opens relevant to that decision. The reason is that
when a client holds a delegation, the server might not have an
accurate account of the opens for that client, since the client may
execute OPENs and CLOSEs locally. The LINK operation must be delayed
only until a definitive result can be obtained. For example, suppose
there are multiple delegations and one of them establishes an open
whose presence would prevent the link. Given the server's semantics,
NFS4ERR_FILE_OPEN may be returned to the caller as soon as that
delegation is returned without waiting for other delegations to be
returned. Similarly, if such opens are not associated with
delegations, NFS4ERR_FILE_OPEN can be returned immediately with no
delegation recall being done.
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If the current filehandle designates a directory for which another
client holds a directory delegation, then, unless the delegation is
such that the situation can be resolved by sending a notification,
the delegation MUST be recalled, and the operation cannot be
performed successfully until the delegation is returned or revoked.
Except where this happens very quickly, one or more NFS4ERR_DELAY
errors will be returned to requests made while delegation remains
outstanding.
When the current filehandle designates a directory for which one or
more directory delegations exist, then, when those delegations
request such notifications, instead of a recall, NOTIFY4_ADD_ENTRY
will be generated as a result of the LINK operation.
If the current file system supports the numlinks attribute, and other
clients have delegations to the file being linked, then those
delegations MUST be recalled and the LINK operation MUST NOT proceed
until all delegations are returned or revoked. Except where this
happens very quickly, one or more NFS4ERR_DELAY errors will be
returned to requests made while delegation remains outstanding.
Changes to any property of the "hard" linked files are reflected in
all of the linked files. When a link is made to a file, the
attributes for the file should have a value for numlinks that is one
greater than the value before the LINK operation.
The statement "file and the target directory must reside within the
same file system on the server" means that the fsid fields in the
attributes for the objects are the same. If they reside on different
file systems, the error NFS4ERR_XDEV is returned. This error may be
returned by some servers when there is an internal partitioning of a
file system that the LINK operation would violate.
On some servers, "." and ".." are illegal values for newname and the
error NFS4ERR_BADNAME will be returned if they are specified.
When the current filehandle designates a named attribute directory
and the object to be linked (the saved filehandle) is not a named
attribute for the same object, the error NFS4ERR_XDEV MUST be
returned. When the saved filehandle designates a named attribute and
the current filehandle is not the appropriate named attribute
directory, the error NFS4ERR_XDEV MUST also be returned.
When the current filehandle designates a named attribute directory
and the object to be linked (the saved filehandle) is a named
attribute within that directory, the server may return the error
NFS4ERR_NOTSUPP.
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In the case that newname is already linked to the file represented by
the saved filehandle, the server will return NFS4ERR_EXIST.
Note that symbolic links are created with the CREATE operation.
25.10. Operation 12: LOCK - Create Lock
25.10.1. ARGUMENTS
/*
* For LOCK, transition from open_stateid and lock_owner
* to a lock stateid.
*/
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
/*
* For LOCK, existing lock stateid continues to request new
* file lock for the same lock_owner and open_stateid.
*/
struct exist_lock_owner4 {
stateid4 lock_stateid;
seqid4 lock_seqid;
};
union locker4 switch (bool new_lock_owner) {
case TRUE:
open_to_lock_owner4 open_owner;
case FALSE:
exist_lock_owner4 lock_owner;
};
/*
* LOCK/LOCKT/LOCKU: Record lock management
*/
struct LOCK4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
bool reclaim;
offset4 offset;
length4 length;
locker4 locker;
};
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25.10.2. RESULTS
struct LOCK4denied {
offset4 offset;
length4 length;
nfs_lock_type4 locktype;
lock_owner4 owner;
};
struct LOCK4resok {
stateid4 lock_stateid;
};
union LOCK4res switch (nfsstat4 status) {
case NFS4_OK:
LOCK4resok resok4;
case NFS4ERR_DENIED:
LOCK4denied denied;
default:
void;
};
25.10.3. DESCRIPTION
The LOCK operation requests a byte-range lock for the byte-range
specified by the offset and length parameters, and lock type
specified in the locktype parameter. If this is a reclaim request,
the reclaim parameter will be TRUE.
Bytes in a file may be locked even if those bytes are not currently
allocated to the file. To lock the file from a specific offset
through the end-of-file (no matter how long the file actually is) use
a length field equal to NFS4_UINT64_MAX. The server MUST return
NFS4ERR_INVAL under the following combinations of length and offset:
* Length is equal to zero.
* Length is not equal to NFS4_UINT64_MAX, and the sum of length and
offset exceeds NFS4_UINT64_MAX.
32-bit servers are servers that support locking for byte offsets that
fit within 32 bits (i.e., less than or equal to NFS4_UINT32_MAX). If
the client specifies a range that overlaps one or more bytes beyond
offset NFS4_UINT32_MAX but does not end at offset NFS4_UINT64_MAX,
then such a 32-bit server MUST return the error NFS4ERR_BAD_RANGE.
If the server returns NFS4ERR_DENIED, the owner, offset, and length
of a conflicting lock are returned.
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The locker argument specifies the lock-owner that is associated with
the LOCK operation. The locker4 structure is a switched union that
indicates whether the client has already created byte-range locking
state associated with the current open file and lock-owner. In the
case in which it has, the argument is just a stateid representing the
set of locks associated with that open file and lock-owner, together
with a lock_seqid value that MAY be any value and MUST be ignored by
the server. In the case where no byte-range locking state has been
established, or the client does not have the stateid available, the
argument contains the stateid of the open file with which this lock
is to be associated, together with the lock-owner with which the lock
is to be associated. The open_to_lock_owner case covers the very
first lock done by a lock-owner for a given open file and offers a
method to use the established state of the open_stateid to transition
to the use of a lock stateid.
The following fields of the locker parameter MAY be set to any value
by the client and MUST be ignored by the server:
* The clientid field of the lock_owner field of the open_owner field
(locker.open_owner.lock_owner.clientid). The reason the server
MUST ignore the clientid field is that the server MUST derive the
client ID from the session ID from the SEQUENCE operation of the
COMPOUND request.
* The open_seqid and lock_seqid fields of the open_owner field
(locker.open_owner.open_seqid and locker.open_owner.lock_seqid).
* The lock_seqid field of the lock_owner field
(locker.lock_owner.lock_seqid).
Note that the client ID appearing in a LOCK4denied structure is the
actual client associated with the conflicting lock, whether this is
the client ID associated with the current session or a different one.
Thus, if the server returns NFS4ERR_DENIED, it MUST set the clientid
field of the owner field of the denied field.
If the current filehandle is not an ordinary file, an error will be
returned to the client. In the case that the current filehandle
represents an object of type NF4DIR, NFS4ERR_ISDIR is returned. If
the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
returned. In all other cases, NFS4ERR_WRONG_TYPE is returned.
On success, the current filehandle retains its value.
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25.10.4. IMPLEMENTATION
If the server is unable to determine the exact offset and length of
the conflicting byte-range lock, the same offset and length that were
provided in the arguments should be returned in the denied results.
LOCK operations are subject to permission checks and to checks
against the access type of the associated file. However, the
specific right and modes required for various types of locks reflect
the semantics of the server-exported file system, and are not
specified by the protocol. For example, Windows 2000 allows a write
lock of a file open for read access, while a POSIX-compliant system
does not.
When the client sends a LOCK operation that corresponds to a range
that the lock-owner has locked already (with the same or different
lock type), or to a sub-range of such a range, or to a byte-range
that includes multiple locks already granted to that lock-owner, in
whole or in part, and the server does not support such locking
operations (i.e., does not support POSIX locking semantics), the
server will return the error NFS4ERR_LOCK_RANGE. In that case, the
client may return an error, or it may emulate the required
operations, using only LOCK for ranges that do not include any bytes
already locked by that lock-owner and LOCKU of locks held by that
lock-owner (specifying an exactly matching range and type).
Similarly, when the client sends a LOCK operation that amounts to
upgrading (changing from a READ_LT lock to a WRITE_LT lock) or
downgrading (changing from WRITE_LT lock to a READ_LT lock) an
existing byte-range lock, and the server does not support such a
lock, the server will return NFS4ERR_LOCK_NOTSUPP. Such operations
may not perfectly reflect the required semantics in the face of
conflicting LOCK operations from other clients.
When a client holds an OPEN_DELEGATE_WRITE delegation, the client
holding that delegation is assured that there are no opens by other
clients. Thus, there can be no conflicting LOCK operations from such
clients. Therefore, the client may be handling locking requests
locally, without doing LOCK operations on the server. If it does
that, it must be prepared to update the lock status on the server, by
sending appropriate LOCK and LOCKU operations before returning the
delegation.
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When one or more clients hold OPEN_DELEGATE_READ delegations, any
LOCK operation where the server is implementing mandatory locking
semantics MUST result in the recall of all such delegations. The
LOCK operation may not be granted until all such delegations are
returned or revoked. Except where this happens very quickly, one or
more NFS4ERR_DELAY errors will be returned to requests made while the
delegation remains outstanding.
25.11. Operation 13: LOCKT - Test for Lock
25.11.1. ARGUMENTS
struct LOCKT4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
offset4 offset;
length4 length;
lock_owner4 owner;
};
25.11.2. RESULTS
union LOCKT4res switch (nfsstat4 status) {
case NFS4ERR_DENIED:
LOCK4denied denied;
case NFS4_OK:
void;
default:
void;
};
25.11.3. DESCRIPTION
The LOCKT operation tests the lock as specified in the arguments. If
a conflicting lock exists, the owner, offset, length, and type of the
conflicting lock are returned. The owner field in the results
includes the client ID of the owner of the conflicting lock, whether
this is the client ID associated with the current session or a
different client ID. If no lock is held, nothing other than NFS4_OK
is returned. Lock types READ_LT and READW_LT are processed in the
same way in that a conflicting lock test is done without regard to
blocking or non-blocking. The same is true for WRITE_LT and
WRITEW_LT.
The ranges are specified as for LOCK. The NFS4ERR_INVAL and
NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
for LOCK.
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The clientid field of the owner MAY be set to any value by the client
and MUST be ignored by the server. The reason the server MUST ignore
the clientid field is that the server MUST derive the client ID from
the session ID from the SEQUENCE operation of the COMPOUND request.
If the current filehandle is not an ordinary file, an error will be
returned to the client. In the case that the current filehandle
represents an object of type NF4DIR, NFS4ERR_ISDIR is returned. If
the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
returned. In all other cases, NFS4ERR_WRONG_TYPE is returned.
On success, the current filehandle retains its value.
25.11.4. IMPLEMENTATION
If the server is unable to determine the exact offset and length of
the conflicting lock, the same offset and length that were provided
in the arguments should be returned in the denied results.
LOCKT uses a lock_owner4 rather a stateid4, as is used in LOCK to
identify the owner. This is because the client does not have to open
the file to test for the existence of a lock, so a stateid might not
be available.
As noted in Section 25.10.4, some servers may return
NFS4ERR_LOCK_RANGE to certain (otherwise non-conflicting) LOCK
operations that overlap ranges already granted to the current lock-
owner.
The LOCKT operation's test for conflicting locks SHOULD exclude locks
for the current lock-owner, and thus should return NFS4_OK in such
cases. Note that this means that a server might return NFS4_OK to a
LOCKT request even though a LOCK operation for the same range and
lock-owner would fail with NFS4ERR_LOCK_RANGE.
When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose
(See Section 25.10.4) to handle LOCK requests locally. In such a
case, LOCKT requests will similarly be handled locally.
25.12. Operation 14: LOCKU - Unlock File
25.12.1. ARGUMENTS
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struct LOCKU4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
stateid4 lock_stateid;
offset4 offset;
length4 length;
};
25.12.2. RESULTS
union LOCKU4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 lock_stateid;
default:
void;
};
25.12.3. DESCRIPTION
The LOCKU operation unlocks the byte-range lock specified by the
parameters. The client may set the locktype field to any value that
is legal for the nfs_lock_type4 enumerated type, and the server MUST
accept any legal value for locktype. Any legal value for locktype
has no effect on the success or failure of the LOCKU operation.
The ranges are specified as for LOCK. The NFS4ERR_INVAL and
NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
for LOCK.
The seqid parameter MAY be any value and the server MUST ignore it.
If the current filehandle is not an ordinary file, an error will be
returned to the client. In the case that the current filehandle
represents an object of type NF4DIR, NFS4ERR_ISDIR is returned. If
the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
returned. In all other cases, NFS4ERR_WRONG_TYPE is returned.
On success, the current filehandle retains its value.
The server MAY require that the principal, security flavor, and if
applicable, the GSS mechanism, combination that sent a LOCK operation
also be the one to send LOCKU on the file. This might not be
possible if credentials for the principal are no longer available.
The server MAY allow the machine credential or SSV credential (See
Section 25.35) to send LOCKU.
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25.12.4. IMPLEMENTATION
If the area to be unlocked does not correspond exactly to a lock
actually held by the lock-owner, the server may return the error
NFS4ERR_LOCK_RANGE. This includes the case in which the area is not
locked, where the area is a sub-range of the area locked, where it
overlaps the area locked without matching exactly, or the area
specified includes multiple locks held by the lock-owner. In all of
these cases, allowed by POSIX locking [fcntl] semantics, a client
receiving this error should, if it desires support for such
operations, simulate the operation using LOCKU on ranges
corresponding to locks it actually holds, possibly followed by LOCK
operations for the sub-ranges not being unlocked.
When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose
(See Section 25.10.4) to handle LOCK requests locally. In such a
case, LOCKU operations will similarly be handled locally.
25.13. Operation 15: LOOKUP - Lookup Filename
25.13.1. ARGUMENTS
struct LOOKUP4args {
/* CURRENT_FH: directory */
component4 objname;
};
25.13.2. RESULTS
struct LOOKUP4res {
/* New CURRENT_FH: object */
nfsstat4 status;
};
25.13.3. DESCRIPTION
The LOOKUP operation looks up or finds a file system object using the
directory specified by the current filehandle. LOOKUP evaluates the
component and if the object exists, the current filehandle is
replaced with the component's filehandle.
If the component cannot be evaluated either because it does not exist
or because the client does not have permission to evaluate the
component, then an error will be returned and the current filehandle
will be unchanged.
If the component is a zero-length string or if any component does not
obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
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25.13.4. IMPLEMENTATION
If the client wants to achieve the effect of a multi-component look
up, it may construct a COMPOUND request such as (and obtain each
filehandle):
PUTFH (directory filehandle)
LOOKUP "pub"
GETFH
LOOKUP "foo"
GETFH
LOOKUP "bar"
GETFH
Unlike NFSv3, NFSv4.1 allows LOOKUP requests to cross mountpoints on
the server. The client can detect a mountpoint crossing by comparing
the fsid attribute of the directory with the fsid attribute of the
directory looked up. If the fsids are different, then the new
directory is a server mountpoint. UNIX clients that detect a
mountpoint crossing will need to mount the server's file system.
This needs to be done to maintain the file object identity checking
mechanisms common to UNIX clients.
Servers that limit NFS access to "shared" or "exported" file systems
should provide a pseudo file system into which the exported file
systems can be integrated, so that clients can browse the server's
namespace. The clients view of a pseudo file system will be limited
to paths that lead to exported file systems.
Note: previous versions of the protocol assigned special semantics to
the names "." and "..". NFSv4.1 assigns no special semantics to
these names. The LOOKUPP operator must be used to look up a parent
directory.
Note that this operation does not follow symbolic links. The client
is responsible for all parsing of filenames including filenames that
are modified by symbolic links encountered during the look up
process.
If the current filehandle supplied is not a directory but a symbolic
link, the error NFS4ERR_SYMLINK is returned as the error. For all
other non-directory file types, the error NFS4ERR_NOTDIR is returned.
25.14. Operation 16: LOOKUPP - Lookup Parent Directory
25.14.1. ARGUMENTS
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/* CURRENT_FH: object */
void;
25.14.2. RESULTS
struct LOOKUPP4res {
/* new CURRENT_FH: parent directory */
nfsstat4 status;
};
25.14.3. DESCRIPTION
The current filehandle is assumed to refer to a regular directory or
a named attribute directory. LOOKUPP assigns the filehandle for its
parent directory to be the current filehandle. If there is no parent
directory, an NFS4ERR_NOENT error must be returned. Therefore,
NFS4ERR_NOENT will be returned by the server when the current
filehandle is at the root or top of the server's file tree.
As is the case with LOOKUP, LOOKUPP will also cross mountpoints.
If the current filehandle is not a directory or named attribute
directory, the error NFS4ERR_NOTDIR is returned.
If the requester's security flavor does not match that configured for
the parent directory, then the server SHOULD return NFS4ERR_WRONGSEC
(a future minor revision of NFSv4 may upgrade this to MUST) in the
LOOKUPP response. However, if the server does so, it MUST support
the SECINFO_NO_NAME operation (Section 25.45), so that the client can
gracefully determine the correct security flavor.
If the current filehandle is a named attribute directory that is
associated with a file system object via OPENATTR (i.e., not a sub-
directory of a named attribute directory), LOOKUPP SHOULD return the
filehandle of the associated file system object.
25.14.4. IMPLEMENTATION
An issue to note is upward navigation from named attribute
directories. The named attribute directories are essentially
detached from the namespace, and this property should be safely
represented in the client operating environment. LOOKUPP on a named
attribute directory may return the filehandle of the associated file,
and conveying this to applications might be unsafe as many
applications expect the parent of an object to always be a directory.
Therefore, the client may want to hide the parent of named attribute
directories (represented as ".." in UNIX) or represent the named
attribute directory as its own parent (as is typically done for the
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file system root directory in UNIX).
25.15. Operation 17: NVERIFY - Verify Difference in Attributes
25.15.1. ARGUMENTS
struct NVERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
25.15.2. RESULTS
struct NVERIFY4res {
nfsstat4 status;
};
25.15.3. DESCRIPTION
This operation is used to prefix a sequence of operations to be
performed if one or more attributes have changed on some file system
object. If all the attributes match, then the error NFS4ERR_SAME
MUST be returned.
On success, the current filehandle retains its value.
25.15.4. IMPLEMENTATION
This operation is useful as a cache validation operator. If the
object to which the attributes belong has changed, then the following
operations may obtain new data associated with that object, for
instance, to check if a file has been changed and obtain new data if
it has:
SEQUENCE
PUTFH fh
NVERIFY attrbits attrs
READ 0 32767
Contrast this with NFSv3, which would first send a GETATTR in one
request/reply round trip, and then if attributes indicated that the
client's cache was stale, then send a READ in another request/reply
round trip.
In the case that an OPTIONAL attribute is specified in the NVERIFY
operation and the server does not support that attribute for the file
system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
client.
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When an attribute is a supported one but is one that is not supported
for use in NVERIFY (e.g., rdattr_error or any set-only attribute
(such as time_modify_set)) is specified, the error NFS4ERR_INVAL is
returned to the client.
25.16. Operation 18: OPEN - Open a Regular File
25.16.1. ARGUMENTS
/*
* Various definitions for OPEN
*/
enum createmode4 {
UNCHECKED4 = 0,
GUARDED4 = 1,
/* Deprecated in NFSv4.1. */
EXCLUSIVE4 = 2,
/*
* New to NFSv4.1. If session is persistent,
* GUARDED4 MUST be used. Otherwise, use
* EXCLUSIVE4_1 instead of EXCLUSIVE4.
*/
EXCLUSIVE4_1 = 3
};
struct creatverfattr {
verifier4 cva_verf;
fattr4 cva_attrs;
};
union createhow4 switch (createmode4 mode) {
case UNCHECKED4:
case GUARDED4:
fattr4 createattrs;
case EXCLUSIVE4:
verifier4 createverf;
case EXCLUSIVE4_1:
creatverfattr ch_createboth;
};
enum opentype4 {
OPEN4_NOCREATE = 0,
OPEN4_CREATE = 1
};
union openflag4 switch (opentype4 opentype) {
case OPEN4_CREATE:
createhow4 how;
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default:
void;
};
/* Next definitions used for OPEN delegation */
enum limit_by4 {
NFS_LIMIT_SIZE = 1,
NFS_LIMIT_BLOCKS = 2
/* others as needed */
};
struct nfs_modified_limit4 {
uint32_t num_blocks;
uint32_t bytes_per_block;
};
union nfs_space_limit4 switch (limit_by4 limitby) {
/* limit specified as file size */
case NFS_LIMIT_SIZE:
uint64_t filesize;
/* limit specified by number of blocks */
case NFS_LIMIT_BLOCKS:
nfs_modified_limit4 mod_blocks;
} ;
/*
* Share Access and Deny constants for open argument
*/
const OPEN4_SHARE_ACCESS_READ = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH = 0x00000003;
const OPEN4_SHARE_DENY_NONE = 0x00000000;
const OPEN4_SHARE_DENY_READ = 0x00000001;
const OPEN4_SHARE_DENY_WRITE = 0x00000002;
const OPEN4_SHARE_DENY_BOTH = 0x00000003;
/* new flags for share_access field of OPEN4args */
const OPEN4_SHARE_ACCESS_WANT_DELEG_MASK = 0xFF00;
const OPEN4_SHARE_ACCESS_WANT_NO_PREFERENCE = 0x0000;
const OPEN4_SHARE_ACCESS_WANT_READ_DELEG = 0x0100;
const OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG = 0x0200;
const OPEN4_SHARE_ACCESS_WANT_ANY_DELEG = 0x0300;
const OPEN4_SHARE_ACCESS_WANT_NO_DELEG = 0x0400;
const OPEN4_SHARE_ACCESS_WANT_CANCEL = 0x0500;
const
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OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
= 0x10000;
const
OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
= 0x20000;
enum open_delegation_type4 {
OPEN_DELEGATE_NONE = 0,
OPEN_DELEGATE_READ = 1,
OPEN_DELEGATE_WRITE = 2,
OPEN_DELEGATE_NONE_EXT = 3 /* new to v4.1 */
};
/*
* Includes multiple types of operations:
*
* - Non-reclaim operations valid independent of grace period
* status.
* - Reclaim operations only used during a grace period.
* - Reclaim operations only used during a special delegation
* recovery period.
*/
enum open_claim_type4 {
CLAIM_NULL = 0, /* Non-reclaim operation, */
CLAIM_PREVIOUS = 1, /* Reclaim operation --
grace period only. */
CLAIM_DELEGATE_CUR = 2, /* Non-reclaim operation. */
CLAIM_DELEGATE_PREV = 3, /* Reclaim operation --
special delegation
recovery period only. */
/*
* Beyond this point, all values are new to v4.1.
*/
/*
* Like CLAIM_NULL, but object identified
* by the current filehandle.
*/
CLAIM_FH = 4, /* Non-reclaim operation. */
/*
* Like CLAIM_DELEGATE_CUR, but object identified
* by current filehandle.
*/
CLAIM_DELEG_CUR_FH = 5, /* Non-reclaim operation. */
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/*
* Like CLAIM_DELEGATE_PREV, but object identified
* by current filehandle.
*/
CLAIM_DELEG_PREV_FH = 6 /* Reclaim operation --
special delegation
recovery period
only. */
};
struct open_claim_delegate_cur4 {
stateid4 delegate_stateid;
component4 file;
};
union open_claim4 switch (open_claim_type4 claim) {
/*
* No special rights to file.
* Ordinary OPEN of the specified file.
*/
case CLAIM_NULL:
/* CURRENT_FH: directory */
component4 file;
/*
* Right to the file established by an
* open previous to server reboot. File
* identified by filehandle obtained at
* that time rather than by name.
*/
case CLAIM_PREVIOUS:
/* CURRENT_FH: file being reclaimed */
open_delegation_type4 delegate_type;
/*
* Right to file based on a delegation
* granted by the server. File is
* specified by name.
*/
case CLAIM_DELEGATE_CUR:
/* CURRENT_FH: directory */
open_claim_delegate_cur4 delegate_cur_info;
/*
* Right to file based on a delegation
* granted to a previous boot instance
* of the client. File is specified by name.
*/
case CLAIM_DELEGATE_PREV:
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/* CURRENT_FH: directory */
component4 file_delegate_prev;
/*
* Like CLAIM_NULL. No special rights
* to file. Ordinary OPEN of the
* specified file by current filehandle.
*/
case CLAIM_FH: /* new to v4.1 */
/* CURRENT_FH: regular file to open */
void;
/*
* Like CLAIM_DELEGATE_PREV. Right to file based on a
* delegation granted to a previous boot
* instance of the client. File is identified
* by filehandle.
*/
case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
/* CURRENT_FH: file being opened */
void;
/*
* Like CLAIM_DELEGATE_CUR. Right to file based on
* a delegation granted by the server.
* File is identified by filehandle.
*/
case CLAIM_DELEG_CUR_FH: /* new to v4.1 */
/* CURRENT_FH: file being opened */
stateid4 oc_delegate_stateid;
};
/*
* OPEN: Open a file, potentially receiving an OPEN delegation
*/
struct OPEN4args {
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
open_owner4 owner;
openflag4 openhow;
open_claim4 claim;
};
25.16.2. RESULTS
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struct open_read_delegation4 {
stateid4 stateid; /* Stateid for delegation*/
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim (CLAIM_PREVIOUS) */
nfsace4 permissions; /* Defines users who don't
need an ACCESS call to
open for read */
};
struct open_write_delegation4 {
stateid4 stateid; /* Stateid for delegation */
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfs_space_limit4
space_limit; /* Defines condition that
the client must check to
determine whether the
file needs to be flushed
to the server on close. */
nfsace4 permissions; /* Defines users who don't
need an ACCESS call as
part of a delegated
open. */
};
enum why_no_delegation4 { /* new to v4.1 */
WND4_NOT_WANTED = 0,
WND4_CONTENTION = 1,
WND4_RESOURCE = 2,
WND4_NOT_SUPP_FTYPE = 3,
WND4_WRITE_DELEG_NOT_SUPP_FTYPE = 4,
WND4_NOT_SUPP_UPGRADE = 5,
WND4_NOT_SUPP_DOWNGRADE = 6,
WND4_CANCELLED = 7,
WND4_IS_DIR = 8
};
union open_none_delegation4 /* new to v4.1 */
switch (why_no_delegation4 ond_why) {
case WND4_CONTENTION:
bool ond_server_will_push_deleg;
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case WND4_RESOURCE:
bool ond_server_will_signal_avail;
default:
void;
};
union open_delegation4
switch (open_delegation_type4 delegation_type) {
case OPEN_DELEGATE_NONE:
void;
case OPEN_DELEGATE_READ:
open_read_delegation4 read;
case OPEN_DELEGATE_WRITE:
open_write_delegation4 write;
case OPEN_DELEGATE_NONE_EXT: /* new to v4.1 */
open_none_delegation4 od_whynone;
};
/*
* Result flags
*/
/* Client must confirm open */
const OPEN4_RESULT_CONFIRM = 0x00000002;
/* Type of file locking behavior at the server */
const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
/* Server will preserve file if removed while open */
const OPEN4_RESULT_PRESERVE_UNLINKED = 0x00000008;
/*
* Server may use CB_NOTIFY_LOCK on locks
* derived from this open
*/
const OPEN4_RESULT_MAY_NOTIFY_LOCK = 0x00000020;
struct OPEN4resok {
stateid4 stateid; /* Stateid for open */
change_info4 cinfo; /* Directory Change Info */
uint32_t rflags; /* Result flags */
bitmap4 attrset; /* attribute set for create*/
open_delegation4 delegation; /* Info on any open
delegation */
};
union OPEN4res switch (nfsstat4 status) {
case NFS4_OK:
/* New CURRENT_FH: opened file */
OPEN4resok resok4;
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default:
void;
};
25.16.3. DESCRIPTION
The OPEN operation opens a regular file in a directory with the
provided name or filehandle. OPEN can also create a file if a name
is provided, and the client specifies it wants to create a file.
Specification of whether or not a file is to be created, and the
method of creation is via the openhow parameter. The openhow
parameter consists of a switched union (data type opengflag4), which
switches on the value of opentype (OPEN4_NOCREATE or OPEN4_CREATE).
If OPEN4_CREATE is specified, this leads to another switched union
(data type createhow4) that supports four cases of creation methods:
UNCHECKED4, GUARDED4, EXCLUSIVE4, or EXCLUSIVE4_1. If opentype is
OPEN4_CREATE, then the claim field of the claim field MUST be one of
CLAIM_NULL, CLAIM_DELEGATE_CUR, or CLAIM_DELEGATE_PREV, because these
claim methods include a component of a file name.
Upon success (which might entail creation of a new file), the current
filehandle is replaced by that of the created or existing object.
If the current filehandle is a named attribute directory, OPEN will
then create or open a named attribute file. Note that exclusive
create of a named attribute is not supported. If the createmode is
EXCLUSIVE4 or EXCLUSIVE4_1 and the current filehandle is a named
attribute directory, the server will return EINVAL.
UNCHECKED4 means that the file should be created if a file of that
name does not exist and encountering an existing regular file of that
name is not an error. For this type of create, createattrs specifies
the initial set of attributes for the file. The set of attributes
may include any writable attribute valid for regular files. When an
UNCHECKED4 create encounters an existing file, the attributes
specified by createattrs are not used, except that when createattrs
specifies the size attribute with a size of zero, the existing file
is truncated.
If GUARDED4 is specified, the server checks for the presence of a
duplicate object by name before performing the create. If a
duplicate exists, NFS4ERR_EXIST is returned. If the object does not
exist, the request is performed as described for UNCHECKED4.
For the UNCHECKED4 and GUARDED4 cases, where the operation is
successful, the server will return to the client an attribute mask
signifying which attributes were successfully set for the object.
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EXCLUSIVE4_1 and EXCLUSIVE4 specify that the server is to follow
exclusive creation semantics, using the verifier to ensure exclusive
creation of the target. The server should check for the presence of
a duplicate object by name. If the object does not exist, the server
creates the object and stores the verifier with the object. If the
object does exist and the stored verifier matches the client provided
verifier, the server uses the existing object as the newly created
object. If the stored verifier does not match, then an error of
NFS4ERR_EXIST is returned.
If using EXCLUSIVE4, and if the server uses attributes to store the
exclusive create verifier, the server will signify which attributes
it used by setting the appropriate bits in the attribute mask that is
returned in the results. Unlike UNCHECKED4, GUARDED4, and
EXCLUSIVE4_1, EXCLUSIVE4 does not support the setting of attributes
at file creation, and after a successful OPEN via EXCLUSIVE4, the
client MUST send a SETATTR to set attributes to a known state.
In NFSv4.1, EXCLUSIVE4 has been deprecated in favor of EXCLUSIVE4_1.
Unlike EXCLUSIVE4, attributes may be provided in the EXCLUSIVE4_1
case, but because the server may use attributes of the target object
to store the verifier, the set of allowable attributes may be fewer
than the set of attributes SETATTR allows. The allowable attributes
for EXCLUSIVE4_1 are indicated in the suppattr_exclcreat
(Section 11.12.1.14) attribute. If the client attempts to set in
cva_attrs an attribute that is not in suppattr_exclcreat, the server
MUST return NFS4ERR_INVAL. The response field, attrset, indicates
both which attributes the server set from cva_attrs and which
attributes the server used to store the verifier. As described in
Section 25.16.4, the client can compare cva_attrs.attrmask with
attrset to determine which attributes were used to store the
verifier.
With the addition of persistent sessions and pNFS, under some
conditions EXCLUSIVE4 MUST NOT be used by the client or supported by
the server. The following table summarizes the appropriate and
mandated exclusive create methods for implementations of NFSv4.1:
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+=============+==========+==============+=======================+
| Persistent | Server | Server | Client Allowed |
| Reply Cache | Supports | REQUIRED | |
| Enabled | pNFS | | |
+=============+==========+==============+=======================+
| no | no | EXCLUSIVE4_1 | EXCLUSIVE4_1 (SHOULD) |
| | | and | or EXCLUSIVE4 (SHOULD |
| | | EXCLUSIVE4 | NOT) |
+-------------+----------+--------------+-----------------------+
| no | yes | EXCLUSIVE4_1 | EXCLUSIVE4_1 |
+-------------+----------+--------------+-----------------------+
| yes | no | GUARDED4 | GUARDED4 |
+-------------+----------+--------------+-----------------------+
| yes | yes | GUARDED4 | GUARDED4 |
+-------------+----------+--------------+-----------------------+
Table 18: Required Methods for Exclusive Create
If CREATE_SESSION4_FLAG_PERSIST is set in the results of
CREATE_SESSION, the reply cache is persistent (See Section 25.36).
If the EXCHGID4_FLAG_USE_PNFS_MDS flag is set in the results from
EXCHANGE_ID, the server is a pNFS server (See Section 25.35). If the
client attempts to use EXCLUSIVE4 on a persistent session, or a
session derived from an EXCHGID4_FLAG_USE_PNFS_MDS client ID, the
server MUST return NFS4ERR_INVAL.
With persistent sessions, exclusive create semantics are fully
achievable via GUARDED4, and so EXCLUSIVE4 or EXCLUSIVE4_1 MUST NOT
be used. When pNFS is being used, the layout_hint attribute might
not be supported after the file is created. Only the EXCLUSIVE4_1
and GUARDED methods of exclusive file creation allow the atomic
setting of attributes.
For the target directory, the server returns change_info4 information
in cinfo. With the atomic field of the change_info4 data type, the
server will indicate if the before and after change attributes were
obtained atomically with respect to the link creation.
The OPEN operation provides for Windows share reservation capability
with the use of the share_access and share_deny fields of the OPEN
arguments. The client specifies at OPEN the required share_access
and share_deny modes. For clients that do not directly support
SHAREs (i.e., UNIX), the expected deny value is
OPEN4_SHARE_DENY_NONE. In the case that there is an existing SHARE
reservation that conflicts with the OPEN request, the server returns
the error NFS4ERR_SHARE_DENIED. For additional discussion of SHARE
semantics, see Section 14.7.
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For each OPEN, the client provides a value for the owner field of the
OPEN argument. The owner field is of data type open_owner4, and
contains a field called clientid and a field called owner. The
client can set the clientid field to any value and the server MUST
ignore it. Instead, the server MUST derive the client ID from the
session ID of the SEQUENCE operation of the COMPOUND request.
The "seqid" field of the request is not used in NFSv4.1, but it MAY
be any value and the server MUST ignore it.
In the case that the client is recovering state from a server
failure, the claim field of the OPEN argument is used to signify that
the request is meant to reclaim state previously held.
The "claim" field of the OPEN argument is used to specify the file to
be opened and the state information that the client claims to
possess. There are seven claim types as follows:
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+======================+============================================+
| open type | description |
+======================+============================================+
| CLAIM_NULL, CLAIM_FH | For the client, this is a new OPEN |
| | request and there is no previous state |
| | associated with the file for the |
| | client. With CLAIM_NULL, the file is |
| | identified by the current filehandle |
| | and the specified component name. |
| | With CLAIM_FH (new to NFSv4.1), the |
| | file is identified by just the current |
| | filehandle. |
+----------------------+--------------------------------------------+
| CLAIM_PREVIOUS | The client is claiming basic OPEN |
| | state for a file that was held |
| | previous to a server restart. |
| | Generally used when a server is |
| | returning persistent filehandles; the |
| | client may not have the file name to |
| | reclaim the OPEN. |
+----------------------+--------------------------------------------+
| CLAIM_DELEGATE_CUR, | The client is claiming a delegation |
| CLAIM_DELEG_CUR_FH | for OPEN as granted by the server. |
| | Generally, this is done as part of |
| | recalling a delegation. With |
| | CLAIM_DELEGATE_CUR, the file is |
| | identified by the current filehandle |
| | and the specified component name. |
| | With CLAIM_DELEG_CUR_FH (new to |
| | NFSv4.1), the file is identified by |
| | just the current filehandle. |
+----------------------+--------------------------------------------+
| CLAIM_DELEGATE_PREV, | The client is claiming a delegation |
| CLAIM_DELEG_PREV_FH | granted to a previous client instance; |
| | used after the client restarts. The |
| | server MAY support CLAIM_DELEGATE_PREV |
| | and/or CLAIM_DELEG_PREV_FH (new to |
| | NFSv4.1). If it does support either |
| | claim type, CREATE_SESSION MUST NOT |
| | remove the client's delegation state, |
| | and the server MUST support the |
| | DELEGPURGE operation. |
+----------------------+--------------------------------------------+
Table 19
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For OPEN requests that reach the server during the grace period, the
server returns an error of NFS4ERR_GRACE. The following claim types
are exceptions:
* OPEN requests specifying the claim type CLAIM_PREVIOUS are devoted
to reclaiming opens after a server restart and are typically only
valid during the grace period.
* OPEN requests specifying the claim types CLAIM_DELEGATE_CUR and
CLAIM_DELEG_CUR_FH are valid both during and after the grace
period. Since the granting of the delegation that they are
subordinate to assures that there is no conflict with locks to be
reclaimed by other clients, the server need not return
NFS4ERR_GRACE when these are received during the grace period.
* OPEN requests specifying the claim types CLAIM_DELEGATE_PREV and
CLAIM_DELEG_PREV_FH are valid both during and after the grace
period. They must be don during the special delegation recovery
period which can overlap a grace period.
For any OPEN request, the server may return an OPEN delegation, which
allows further opens and closes to be handled locally on the client
as described in Section 15.4. Note that delegation is up to the
server to decide. The client should never assume that delegation
will or will not be granted in a particular instance. It should
always be prepared for either case. A partial exception is the
reclaim (CLAIM_PREVIOUS) case, in which a delegation type is claimed.
In this case, delegation will always be granted, although the server
may specify an immediate recall in the delegation structure.
The rflags returned by a successful OPEN allow the server to return
information governing how the open file is to be handled.
* OPEN4_RESULT_CONFIRM is deprecated and MUST NOT be returned by an
NFSv4.1 server.
* OPEN4_RESULT_LOCKTYPE_POSIX indicates that the server's byte-range
locking behavior supports the complete set of POSIX locking
techniques [fcntl]. From this, the client can choose to manage
byte-range locking state in a way to handle a mismatch of byte-
range locking management.
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* OPEN4_RESULT_PRESERVE_UNLINKED indicates that the NFSv4.1 server
will preserve the open file if the client (or any other client)
removes the file as long as it remains open. Since the server
cannot be aware of files opened using NFSv3 and the client has no
information regarding this bit for NFSv4.0 opens, the client, in
situations which such opens might exist could find it necessary to
do a silly-rename even when this bit is set for all NFSv4.1 OPENs.
In addition to the basic guarantee above, the server, by returning
this bit, promises to preserve the file through any necessary
grace period after server restart or file system migration,
thereby giving the client the opportunity to reclaim its open.
In cases in which a client knows that this flag is returned for
all NFSv4.1 opens of a particular file, it can avoid the need for
a possible "silly rename" of the file to assure its preservation.
It should be noted the possibility of files being open by NFSv3
and NFSv4.0 clients may make the use of silly-rename if necessary.
See Section 25.25.4 for further details.
* OPEN4_RESULT_MAY_NOTIFY_LOCK indicates that the server may attempt
CB_NOTIFY_LOCK callbacks for locks on this file. This flag is a
hint only, and may be safely ignored by the client.
If the component is of zero length, NFS4ERR_INVAL will be returned.
The component may also be subject to UTF-8, character support, or
other name validity checks. See Section 22.1.7 for further
discussion.
When an OPEN is done and the specified open-owner already has the
resulting filehandle open, the result is to "OR" together the new
share and deny status together with the existing status. In this
case, only a single CLOSE need be done, even though multiple OPENs
were completed. When such an OPEN is done, checking of share
reservations for the new OPEN proceeds normally, with no exception
for the existing OPEN held by the same open-owner. In this case, the
stateid returned as an "other" field that matches that of the
previous open while the "seqid" field is incremented to reflect the
change status due to the new open.
If the underlying file system at the server is only accessible in a
read-only mode and the OPEN request has specified ACCESS_WRITE or
ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a read-
only file system.
As with the CREATE operation, the server MUST derive the owner, owner
ACE, group, or group ACE if any of the four attributes are required
and supported by the server's file system. For an OPEN with the
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EXCLUSIVE4 createmode, the server has no choice, since such OPEN
calls do not include the createattrs field. Conversely, if
createattrs (UNCHECKED4 or GUARDED4) or cva_attrs (EXCLUSIVE4_1) is
specified, and includes an owner, owner_group, or ACE that the
principal in the RPC call's credentials does not have authorization
to create files for, then the server may return NFS4ERR_PERM.
In the case of an OPEN that specifies a size of zero (e.g.,
truncation) and the file has named attributes, the named attributes
are left as is and are not removed.
NFSv4.1 gives more precise control to clients over acquisition of
delegations via the following new flags for the share_access field of
OPEN4args:
OPEN4_SHARE_ACCESS_WANT_READ_DELEG
OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
OPEN4_SHARE_ACCESS_WANT_NO_DELEG
OPEN4_SHARE_ACCESS_WANT_CANCEL
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
If (share_access & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) is not zero,
then the client will have specified one and only one of:
OPEN4_SHARE_ACCESS_WANT_READ_DELEG
OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
OPEN4_SHARE_ACCESS_WANT_NO_DELEG
OPEN4_SHARE_ACCESS_WANT_CANCEL
Otherwise, the client is neither indicating a desire nor a non-desire
for a delegation, and the server MAY or MAY not return a delegation
in the OPEN response.
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If the server supports the new _WANT_ flags and the client sends one
or more of the new flags, then in the event the server does not
return a delegation, it MUST return a delegation type of
OPEN_DELEGATE_NONE_EXT. The field ond_why in the reply indicates why
no delegation was returned and will be one of:
WND4_NOT_WANTED
The client specified OPEN4_SHARE_ACCESS_WANT_NO_DELEG.
WND4_CONTENTION
There is a conflicting delegation or open on the file.
WND4_RESOURCE
Resource limitations prevent the server from granting a
delegation.
WND4_NOT_SUPP_FTYPE
The server does not support delegations on this file type.
WND4_WRITE_DELEG_NOT_SUPP_FTYPE
The server does not support OPEN_DELEGATE_WRITE delegations on
this file type.
WND4_NOT_SUPP_UPGRADE
The server does not support atomic upgrade of an
OPEN_DELEGATE_READ delegation to an OPEN_DELEGATE_WRITE
delegation.
WND4_NOT_SUPP_DOWNGRADE
The server does not support atomic downgrade of an
OPEN_DELEGATE_WRITE delegation to an OPEN_DELEGATE_READ
delegation.
WND4_CANCELED
The client specified OPEN4_SHARE_ACCESS_WANT_CANCEL and now any
"want" for this file object is cancelled.
WND4_IS_DIR
The specified file object is a directory, and the operation is
OPEN or WANT_DELEGATION, which do not support delegations on
directories.
OPEN4_SHARE_ACCESS_WANT_READ_DELEG,
OPEN_SHARE_ACCESS_WANT_WRITE_DELEG, or
OPEN_SHARE_ACCESS_WANT_ANY_DELEG mean, respectively, the client wants
an OPEN_DELEGATE_READ, OPEN_DELEGATE_WRITE, or any delegation
regardless which of OPEN4_SHARE_ACCESS_READ,
OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH is set. If the
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client has an OPEN_DELEGATE_READ delegation on a file and requests an
OPEN_DELEGATE_WRITE delegation, then the client is requesting atomic
upgrade of its OPEN_DELEGATE_READ delegation to an
OPEN_DELEGATE_WRITE delegation. If the client has an
OPEN_DELEGATE_WRITE delegation on a file and requests an
OPEN_DELEGATE_READ delegation, then the client is requesting atomic
downgrade to an OPEN_DELEGATE_READ delegation. A server MAY support
atomic upgrade or downgrade. If it does, then the returned
delegation_type of OPEN_DELEGATE_READ or OPEN_DELEGATE_WRITE that is
different from the delegation type the client currently has,
indicates successful upgrade or downgrade. If the server does not
support atomic delegation upgrade or downgrade, then ond_why will be
set to WND4_NOT_SUPP_UPGRADE or WND4_NOT_SUPP_DOWNGRADE.
OPEN4_SHARE_ACCESS_WANT_NO_DELEG means that the client wants no
delegation.
OPEN4_SHARE_ACCESS_WANT_CANCEL means that the client wants no
delegation and wants to cancel any previously registered "want" for a
delegation.
The client may set one or both of
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL and
OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED. However, they
will have no effect unless one of following is set:
* OPEN4_SHARE_ACCESS_WANT_READ_DELEG
* OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
* OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
If the client specifies
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it wishes
to register a "want" for a delegation, in the event the OPEN results
do not include a delegation. If so and the server denies the
delegation due to insufficient resources, the server MAY later inform
the client, via the CB_RECALLABLE_OBJ_AVAIL operation, that the
resource limitation condition has eased. The server will tell the
client that it intends to send a future CB_RECALLABLE_OBJ_AVAIL
operation by setting delegation_type in the results to
OPEN_DELEGATE_NONE_EXT, ond_why to WND4_RESOURCE, and
ond_server_will_signal_avail set to TRUE. If
ond_server_will_signal_avail is set to TRUE, the server MUST later
send a CB_RECALLABLE_OBJ_AVAIL operation.
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If the client specifies
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_UNCONTENDED, then it wishes
to register a "want" for a delegation, in the event the OPEN results
do not include a delegation. If so and the server denies the
delegation due to contention, the server MAY later inform the client,
via the CB_PUSH_DELEG operation, that the contention condition has
eased. The server will tell the client that it intends to send a
future CB_PUSH_DELEG operation by setting delegation_type in the
results to OPEN_DELEGATE_NONE_EXT, ond_why to WND4_CONTENTION, and
ond_server_will_push_deleg to TRUE. If ond_server_will_push_deleg is
TRUE, the server MUST later send a CB_PUSH_DELEG operation.
If the client has previously registered a want for a delegation on a
file, and then sends a request to register a want for a delegation on
the same file, the server MUST return a new error:
NFS4ERR_DELEG_ALREADY_WANTED. If the client wishes to register a
different type of delegation want for the same file, it MUST cancel
the existing delegation WANT.
25.16.4. IMPLEMENTATION
In absence of a persistent session, the client invokes exclusive
create by setting the how parameter to EXCLUSIVE4 or EXCLUSIVE4_1.
In these cases, the client provides a verifier that can reasonably be
expected to be unique. A combination of a client identifier, perhaps
the client network address, and a unique number generated by the
client, perhaps the RPC transaction identifier, may be appropriate.
If the object does not exist, the server creates the object and
stores the verifier in stable storage. For file systems that do not
provide a mechanism for the storage of arbitrary file attributes, the
server may use one or more elements of the object's metadata to store
the verifier. The verifier MUST be stored in stable storage to
prevent erroneous failure on retransmission of the request. It is
assumed that an exclusive create is being performed because exclusive
semantics are critical to the application. Because of the expected
usage, exclusive CREATE does not rely solely on the server's reply
cache for storage of the verifier. A nonpersistent reply cache does
not survive a crash and the session and reply cache may be deleted
after a network partition that exceeds the lease time, thus opening
failure windows.
An NFSv4.1 server SHOULD NOT store the verifier in any of the file's
OPTIONAL or REQUIRED attributes. If it does, the server SHOULD use
time_modify_set or time_access_set to store the verifier. The server
SHOULD NOT store the verifier in the following attributes:
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acl (it is desirable for access control to be established at
creation),
dacl (ditto),
mode (ditto),
owner (ditto),
owner_group (ditto),
retentevt_set (it may be desired to establish retention at
creation)
retention_hold (ditto),
retention_set (ditto),
sacl (it is desirable for auditing control to be established at
creation),
size (on some servers, size may have a limited range of values),
mode_set_masked (as with mode),
and
time_creation (a meaningful file creation should be set when the
file is created).
Another alternative for the server is to use a named attribute to
store the verifier.
Because the EXCLUSIVE4 create method does not specify initial
attributes when processing an EXCLUSIVE4 create, the server
* SHOULD set the owner of the file to that corresponding to the
credential of request's RPC header.
* SHOULD NOT leave the file's access control to anyone but the owner
of the file.
If the server cannot support exclusive create semantics, possibly
because of the requirement to commit the verifier to stable storage,
it should fail the OPEN request with the error NFS4ERR_NOTSUPP.
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During an exclusive CREATE request, if the object already exists, the
server reconstructs the object's verifier and compares it with the
verifier in the request. If they match, the server treats the
request as a success. The request is presumed to be a duplicate of
an earlier, successful request for which the reply was lost and that
the server duplicate request cache mechanism did not detect. If the
verifiers do not match, the request is rejected with the status
NFS4ERR_EXIST.
After the client has performed a successful exclusive create, the
attrset response indicates which attributes were used to store the
verifier. If EXCLUSIVE4 was used, the attributes set in attrset were
used for the verifier. If EXCLUSIVE4_1 was used, the client
determines the attributes used for the verifier by comparing attrset
with cva_attrs.attrmask; any bits set in the former but not the
latter identify the attributes used to store the verifier. The
client MUST immediately send a SETATTR to set attributes used to
store the verifier. Until it does so, the attributes used to store
the verifier cannot be relied upon. The subsequent SETATTR MUST NOT
occur in the same COMPOUND request as the OPEN.
Unless a persistent session is used, use of the GUARDED4 attribute
does not provide exactly once semantics. In particular, if a reply
is lost and the server does not detect the retransmission of the
request, the operation can fail with NFS4ERR_EXIST, even though the
create was performed successfully. The client would use this
behavior in the case that the application has not requested an
exclusive create but has asked to have the file truncated when the
file is opened. In the case of the client timing out and
retransmitting the create request, the client can use GUARDED4 to
prevent against a sequence like create, write, create (retransmitted)
from occurring.
For SHARE reservations, the value of the expression (share_access &
~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) MUST be one of
OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
OPEN4_SHARE_ACCESS_BOTH. If not, the server MUST return
NFS4ERR_INVAL. The value of share_deny MUST be one of
OPEN4_SHARE_DENY_NONE, OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE,
or OPEN4_SHARE_DENY_BOTH. If not, the server MUST return
NFS4ERR_INVAL.
Based on the share_access value (OPEN4_SHARE_ACCESS_READ,
OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH), the client
should check that the requester has the proper access rights to
perform the specified operation. This would generally be the results
of applying the ACL access rules to the file for the current
requester. However, just as with the ACCESS operation, the client
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should not attempt to second-guess the server's decisions, as access
rights may change and may be subject to server administrative
controls outside the ACL framework. If the requester's READ or WRITE
operation is not authorized (depending on the share_access value),
the server MUST return NFS4ERR_ACCESS.
Note that if the client ID was not created with the
EXCHGID4_FLAG_BIND_PRINC_STATEID capability set in the reply to
EXCHANGE_ID, then the server MUST NOT impose any requirement that
READs and WRITEs sent for an open file have the same credentials as
the OPEN itself, and the server is REQUIRED to perform access
checking on the READs and WRITEs themselves. Otherwise, if the reply
to EXCHANGE_ID did have EXCHGID4_FLAG_BIND_PRINC_STATEID set, then
with one exception, the credentials used in the OPEN request MUST
match those used in the READs and WRITEs, and the stateids in the
READs and WRITEs MUST match, or be derived from the stateid from the
reply to OPEN. The exception is if SP4_SSV or SP4_MACH_CRED state
protection is used, and the spo_must_allow result of EXCHANGE_ID
includes the READ and/or WRITE operations. In that case, the machine
or SSV credential will be allowed to send READ and/or WRITE. See
Section 25.35.
If the component provided to OPEN is a symbolic link, the error
NFS4ERR_SYMLINK will be returned to the client, while if it is a
directory the error NFS4ERR_ISDIR will be returned. If the component
is neither of those but not an ordinary file, the error
NFS4ERR_WRONG_TYPE is returned. If the current filehandle is not a
directory, the error NFS4ERR_NOTDIR will be returned.
The use of the OPEN4_RESULT_PRESERVE_UNLINKED result flag allows a
client to avoid the common implementation practice of renaming an
open file to ".nfs<unique value>" instead of removing the file.
After the server returns OPEN4_RESULT_PRESERVE_UNLINKED for all
NFsv4.1 OPENs and there are no OPENs issued by other protocols to
deal with, if a client sends a REMOVE operation that would reduce the
file's link count to zero, the server will report a value of zero for
the numlinks attribute on the file, when GETATTR can be done on this
file.
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If another client has a delegation of the file being opened that
conflicts with open being done (sometimes depending on the
share_access or share_deny value specified), the delegation(s) MUST
be recalled, and the operation cannot proceed until each such
delegation is returned or revoked. Except where this happens very
quickly, one or more NFS4ERR_DELAY errors will be returned to
requests made while delegation remains outstanding. In the case of
an OPEN_DELEGATE_WRITE delegation, any open by a different client
will conflict, while for an OPEN_DELEGATE_READ delegation, only opens
with one of the following characteristics will be considered
conflicting:
* The value of share_access includes the bit
OPEN4_SHARE_ACCESS_WRITE.
* The value of share_deny specifies OPEN4_SHARE_DENY_READ or
OPEN4_SHARE_DENY_BOTH.
* OPEN4_CREATE is specified together with UNCHECKED4, the size
attribute is specified as zero (for truncation), and an existing
file is truncated.
If OPEN4_CREATE is specified and the file does not exist and the
current filehandle designates a directory for which another client
holds a directory delegation, then, unless the delegation is such
that the situation can be resolved by sending a notification, the
delegation MUST be recalled, and the operation cannot proceed until
the delegation is returned or revoked. Except where this happens
very quickly, one or more NFS4ERR_DELAY errors will be returned to
requests made while delegation remains outstanding.
If OPEN4_CREATE is specified and the file does not exist and the
current filehandle designates a directory for which one or more
directory delegations exist, then, when those delegations request
such notifications, NOTIFY4_ADD_ENTRY will be generated as a result
of this operation.
25.16.4.1. Warning to Client implementers
OPEN resembles LOOKUP in that it generates a filehandle for the
client to use. Unlike LOOKUP though, OPEN creates server state on
the filehandle. In normal circumstances, the client can only release
this state with a CLOSE operation. CLOSE uses the current filehandle
to determine which file to close. Therefore, the client MUST follow
every OPEN operation with a GETFH operation in the same COMPOUND
procedure. This will supply the client with the filehandle such that
CLOSE can be used appropriately.
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Simply waiting for the lease on the file to expire is insufficient
because the server may maintain the state indefinitely as long as
another client does not attempt to make a conflicting access to the
same file.
See also Section 7.6.4.
25.17. Operation 19: OPENATTR - Open Named Attribute Directory
25.17.1. ARGUMENTS
struct OPENATTR4args {
/* CURRENT_FH: object */
bool createdir;
};
25.17.2. RESULTS
struct OPENATTR4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: named attribute
* directory
*/
nfsstat4 status;
};
25.17.3. DESCRIPTION
The OPENATTR operation is used to obtain the filehandle of the named
attribute directory associated with the current filehandle. The
result of the OPENATTR will be a filehandle to an object of type
NF4ATTRDIR. From this filehandle, READDIR and LOOKUP operations can
be used to obtain filehandles for the various named attributes
associated with the original file system object. Filehandles
returned within the named attribute directory will designate objects
of type of NF4NAMEDATTR.
The createdir argument allows the client to signify if a named
attribute directory should be created as a result of the OPENATTR
operation. Some clients may use the OPENATTR operation with a value
of FALSE for createdir to determine if any named attributes exist for
the object. If none exist, then NFS4ERR_NOENT will be returned. If
createdir has a value of TRUE and no named attribute directory
exists, one is created and its filehandle becomes the current
filehandle. On the other hand, if createdir has a value of TRUE and
the named attribute directory already exists, no error results and
the filehandle of the existing directory becomes the current
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filehandle. The creation of a named attribute directory assumes that
the server has implemented named attribute support in this fashion
and is not required to do so by this definition.
If the current filehandle designates an object of type NF4NAMEDATTR
(a named attribute) or NF4ATTRDIR (a named attribute directory), an
error of NFS4ERR_WRONG_TYPE is returned to the client. Named
attributes or a named attribute directory MUST NOT have their own
named attributes.
25.17.4. IMPLEMENTATION
If the server does not support named attributes for file system
objects on the file system associated with the current filehandle, an
error of NFS4ERR_NOTSUPP will be returned to the client.
25.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access
25.18.1. ARGUMENTS
struct OPEN_DOWNGRADE4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
25.18.2. RESULTS
struct OPEN_DOWNGRADE4resok {
stateid4 open_stateid;
};
union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
case NFS4_OK:
OPEN_DOWNGRADE4resok resok4;
default:
void;
};
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25.18.3. DESCRIPTION
This operation is used to adjust the access and deny states for a
given open. This is necessary when a given open-owner opens the same
file multiple times with different access and deny values. In this
situation, a close of one of the opens may change the appropriate
share_access and share_deny flags to remove bits associated with
opens no longer in effect.
Valid values for the expression (share_access &
~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) are OPEN4_SHARE_ACCESS_READ,
OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH. If the client
specifies other values, the server MUST reply with NFS4ERR_INVAL.
Valid values for the share_deny field are OPEN4_SHARE_DENY_NONE,
OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or
OPEN4_SHARE_DENY_BOTH. If the client specifies other values, the
server MUST reply with NFS4ERR_INVAL.
After checking for valid values of share_access and share_deny, the
server replaces the current access and deny modes on the file with
share_access and share_deny subject to the following constraints:
* The bits in share_access SHOULD equal the union of the
share_access bits (not including OPEN4_SHARE_WANT_* bits)
specified for some subset of the OPENs in effect for the current
open-owner on the current file.
* The bits in share_deny SHOULD equal the union of the share_deny
bits specified for some subset of the OPENs in effect for the
current open-owner on the current file.
If the above constraints are not respected, the server SHOULD return
the error NFS4ERR_INVAL. Since share_access and share_deny bits
should be subsets of those already granted, short of a defect in the
client or server implementation, it is not possible for the
OPEN_DOWNGRADE request to be denied because of conflicting share
reservations.
The seqid argument is not used in NFSv4.1, MAY be any value, and MUST
be ignored by the server.
On success, the current filehandle retains its value.
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25.18.4. IMPLEMENTATION
An OPEN_DOWNGRADE operation may make OPEN_DELEGATE_READ delegations
grantable where they were not previously. Servers may choose to
respond immediately if there are pending delegation want requests or
may respond to the situation at a later time.
25.19. Operation 22: PUTFH - Set Current Filehandle
25.19.1. ARGUMENTS
struct PUTFH4args {
nfs_fh4 object;
};
25.19.2. RESULTS
struct PUTFH4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: argument to PUTFH
*/
nfsstat4 status;
};
25.19.3. DESCRIPTION
This operation replaces the current filehandle with the filehandle
provided as an argument. It clears the current stateid.
If the security mechanism used by the requester does not meet the
requirements of the filehandle provided to this operation, the server
MUST return NFS4ERR_WRONGSEC.
See Section 23.2.3.1.1 for more details on the current filehandle.
See Section 23.2.3.1.2 for more details on the current stateid.
25.19.4. IMPLEMENTATION
This operation is used in an NFS request to set the context for file
accessing operations that follow in the same COMPOUND request.
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25.20. Operation 23: PUTPUBFH - Set Public Filehandle
25.20.1. ARGUMENT
void;
25.20.2. RESULT
struct PUTPUBFH4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: public fh
*/
nfsstat4 status;
};
25.20.3. DESCRIPTION
This operation replaces the current filehandle with the filehandle
that represents the public filehandle of the server's namespace.
This filehandle may be different from the "root" filehandle that may
be associated with some other directory on the server.
PUTPUBFH also clears the current stateid.
The public filehandle represents the concepts embodied in [RFC2054],
[RFC2055], and [RFC2224]. The intent for NFSv4.1 is that the public
filehandle (represented by the PUTPUBFH operation) be used as a
method of providing WebNFS server compatibility with NFSv3.
The public filehandle and the root filehandle (represented by the
PUTROOTFH operation) SHOULD be equivalent. If the public and root
filehandles are not equivalent, then the directory corresponding to
the public filehandle MUST be a descendant of the directory
corresponding to the root filehandle.
See Section 23.2.3.1.1 for more details on the current filehandle.
See Section 23.2.3.1.2 for more details on the current stateid.
25.20.4. IMPLEMENTATION
This operation is used in an NFS request to set the context for file
accessing operations that follow in the same COMPOUND request.
With the NFSv3 public filehandle, the client is able to specify
whether the pathname provided in the LOOKUP should be evaluated as
either an absolute path relative to the server's root or relative to
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the public filehandle. [RFC2224]contains further discussion of the
functionality. With NFSv4.1, that type of specification is not
directly available in the LOOKUP operation. The reason for this is
because the component separators needed to specify absolute vs.
relative are not allowed in NFSv4. Therefore, the client is
responsible for constructing its request such that the use of either
PUTROOTFH or PUTPUBFH signifies absolute or relative evaluation of an
NFS URL, respectively.
Note that there are warnings mentioned in [RFC2224] with respect to
the use of absolute evaluation and the restrictions the server may
place on that evaluation with respect to how much of its namespace
has been made available. These same warnings apply to NFSv4.1. It
is likely, therefore, that because of server implementation details,
an NFSv3 absolute public filehandle look up may behave differently
than an NFSv4.1 absolute resolution.
There is a form of security negotiation as described in [RFC2755].
that uses the public filehandle and an overloading of the pathname.
This method is not available with NFSv4.1 as filehandles are not
overloaded with special meaning and therefore do not provide the same
framework as NFSv3. Clients should therefore use the security
negotiation mechanisms described in Section 12 [To be Updated] of the
NFSv4-wide security document, currently
25.21. Operation 24: PUTROOTFH - Set Root Filehandle
25.21.1. ARGUMENTS
void;
25.21.2. RESULTS
struct PUTROOTFH4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: root fh
*/
nfsstat4 status;
};
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25.21.3. DESCRIPTION
This operation replaces the current filehandle with the filehandle
that represents the root of the server's namespace. From this
filehandle, a LOOKUP operation can locate any other filehandle on the
server. This filehandle may be different from the "public"
filehandle that may be associated with some other directory on the
server.
PUTROOTFH also clears the current stateid.
See Section 23.2.3.1.1 for more details on the current filehandle.
See Section 23.2.3.1.2 for more details on the current stateid.
25.21.4. IMPLEMENTATION
This operation is used in an NFS request to set the context for file
accessing operations that follow in the same COMPOUND request.
25.22. Operation 25: READ - Read from File
25.22.1. ARGUMENTS
struct READ4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
count4 count;
};
25.22.2. RESULTS
struct READ4resok {
bool eof;
opaque data<>;
};
union READ4res switch (nfsstat4 status) {
case NFS4_OK:
READ4resok resok4;
default:
void;
};
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25.22.3. DESCRIPTION
The READ operation reads data from the regular file identified by the
current filehandle.
The client provides an offset of where the READ is to start and a
count of how many bytes are to be read. An offset of zero means to
read data starting at the beginning of the file. If offset is
greater than or equal to the size of the file, the status NFS4_OK is
returned with a data length set to zero and eof is set to TRUE. The
READ is subject to access permissions checking.
If the client specifies a count value of zero, the READ succeeds and
returns zero bytes of data again subject to access permissions
checking. The server may choose to return fewer bytes than specified
by the client. The client needs to check for this condition and
handle the condition appropriately.
Except when special stateids are used, the stateid value for a READ
request represents a value returned from a previous byte-range lock
or share reservation request or the stateid associated with a
delegation. The stateid identifies the associated owners if any and
is used by the server to verify that the associated locks are still
valid (e.g., have not been revoked).
If the read ended at the end-of-file (formally, in a correctly formed
READ operation, if offset + count is equal to the size of the file),
or the READ operation extends beyond the size of the file (if offset
+ count is greater than the size of the file), eof is returned as
TRUE; otherwise, it is FALSE. A successful READ of an empty file
will always return eof as TRUE.
If the current filehandle is not an ordinary file, an error will be
returned to the client. In the case that the current filehandle
represents an object of type NF4DIR, NFS4ERR_ISDIR is returned. If
the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
returned. In all other cases, NFS4ERR_WRONG_TYPE is returned.
For a READ with a stateid value of all bits equal to zero, the server
MAY allow the READ to be serviced subject to mandatory byte-range
locks or the current share deny modes for the file. For a READ with
a stateid value of all bits equal to one, the server MAY allow READ
operations to bypass locking checks at the server.
On success, the current filehandle retains its value.
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25.22.4. IMPLEMENTATION
If the server returns a "short read" (i.e., fewer data than requested
and eof is set to FALSE), the client should send another READ to get
the remaining data. A server may return less data than requested
under several circumstances. The file may have been truncated by
another client or perhaps on the server itself, changing the file
size from what the requesting client believes to be the case. This
would reduce the actual amount of data available to the client. It
is possible that the server reduce the transfer size and so return a
short read result. Server resource exhaustion may also occur in a
short read.
If mandatory byte-range locking is in effect for the file, and if the
byte-range corresponding to the data to be read from the file is
WRITE_LT locked by an owner not associated with the stateid, the
server will return the NFS4ERR_LOCKED error. The client should try
to get the appropriate READ_LT via the LOCK operation before re-
attempting the READ. When the READ completes, the client should
release the byte-range lock via LOCKU.
If another client has an OPEN_DELEGATE_WRITE delegation for the file
being read, the delegation must be recalled, and the operation cannot
proceed until that delegation is returned or revoked. Except where
this happens very quickly, one or more NFS4ERR_DELAY errors will be
returned to requests made while the delegation remains outstanding.
Normally, delegations will not be recalled as a result of a READ
operation since the recall will occur as a result of an earlier OPEN.
However, since it is possible for a READ to be done with a special
stateid, the server needs to check for this case even though the
client should have done an OPEN previously.
25.23. Operation 26: READDIR - Read Directory
25.23.1. ARGUMENTS
struct READDIR4args {
/* CURRENT_FH: directory */
nfs_cookie4 cookie;
verifier4 cookieverf;
count4 dircount;
count4 maxcount;
bitmap4 attr_request;
};
25.23.2. RESULTS
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struct entry4 {
nfs_cookie4 cookie;
component4 name;
fattr4 attrs;
entry4 *nextentry;
};
struct dirlist4 {
entry4 *entries;
bool eof;
};
struct READDIR4resok {
verifier4 cookieverf;
dirlist4 reply;
};
union READDIR4res switch (nfsstat4 status) {
case NFS4_OK:
READDIR4resok resok4;
default:
void;
};
25.23.3. DESCRIPTION
The READDIR operation retrieves a variable number of entries from a
file system directory and returns client-requested attributes for
each entry along with information to allow the client to request
additional directory entries in a subsequent READDIR.
The arguments contain a cookie value that represents where the
READDIR should start within the directory. A value of zero for the
cookie is used to start reading at the beginning of the directory.
For subsequent READDIR requests, the client specifies a cookie value
that is provided by the server on a previous READDIR request.
The request's cookieverf field should be set to 0 (zero) when the
request's cookie field is zero (first read of the directory). On
subsequent requests, the cookieverf field must match the cookieverf
returned by the READDIR in which the cookie was acquired. If the
server determines that the cookieverf is no longer valid for the
directory, the error NFS4ERR_NOT_SAME must be returned.
The dircount field of the request is a hint of the maximum number of
bytes of directory information that should be returned. This value
represents the total length of the names of the directory entries and
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the cookie value for these entries. This length represents the XDR
encoding of the data (names and cookies) and not the length in the
native format of the server.
The maxcount field of the request represents the maximum total size
of all of the data being returned within the READDIR4resok structure
and includes the XDR overhead. The server MAY return less data. If
the server is unable to return a single directory entry within the
maxcount limit, the error NFS4ERR_TOOSMALL MUST be returned to the
client.
Finally, the request's attr_request field represents the set of
attributes to be returned for each directory entry supplied by the
server. As in the case of GETATTR, if this set includes unsupported
attributes, they are not included in the returned data and no error
results. Because of the possibility of mount points within a
directory, different sets of attributes might be supported for
different entries since they might be parts of distinct file systems.
A successful reply consists of a list of directory entries. Each of
these entries contains the name of the directory entry, a cookie
value for that entry, and the associated attributes as requested.
The "eof" flag has a value of TRUE if there are no more entries in
the directory.
The cookie value is only meaningful to the server and is used as a
cursor for the directory entry. As mentioned, this cookie is used by
the client for subsequent READDIR operations so that it may continue
reading a directory. The cookie is similar in concept to a READ
offset but MUST NOT be interpreted as such by the client. Ideally,
the cookie value SHOULD NOT change if the directory is modified since
the client may be caching these values.
In some cases, the server may encounter an error while obtaining the
attributes for a directory entry. Instead of returning an error for
the entire READDIR operation, the server can instead return the
attribute rdattr_error (Section 11.12.1.12). With this, the server
is able to communicate the failure to the client and not fail the
entire operation in the instance of what might be a transient
failure. Obviously, the client must request the fattr4_rdattr_error
attribute for this method to work properly. If the client does not
request the attribute, the server has no choice but to return failure
for the entire READDIR operation.
For some file system environments, the directory entries "." and ".."
have special meaning, and in other environments, they do not. If the
server supports these special entries within a directory, they SHOULD
NOT be returned to the client as part of the READDIR response. To
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enable some client environments, the cookie values of zero, 1, and 2
are to be considered reserved. Note that the UNIX client will use
these values when combining the server's response and local
representations to enable a fully formed UNIX directory presentation
to the application.
For READDIR arguments, cookie values of one and two SHOULD NOT be
used, and for READDIR results, cookie values of zero, one, and two
SHOULD NOT be returned.
On success, the current filehandle retains its value.
25.23.4. IMPLEMENTATION
The server's file system directory representations can differ
greatly. A client's programming interfaces may also be bound to the
local operating environment in a way that does not translate well
into the NFS protocol. Therefore, the use of the dircount and
maxcount fields are provided to enable the client to provide hints to
the server. If the client is aggressive about attribute collection
during a READDIR, the server has an idea of how to limit the encoded
response.
If dircount is zero, the server bounds the reply's size based on the
request's maxcount field.
The cookieverf may be used by the server to help manage cookie values
that may become stale. It should be a rare occurrence that a server
is unable to continue properly reading a directory with the provided
cookie/cookieverf pair. The server SHOULD make every effort to avoid
this condition since the application at the client might be unable to
properly handle this type of failure.
The use of the cookieverf will also protect the client from using
READDIR cookie values that might be stale. For example, if the file
system has been migrated, the server might or might not be able to
use the same cookie values to service READDIR as the previous server
used. With the client providing the cookieverf, the server is able
to provide the appropriate response to the client. This prevents the
case where the server accepts a cookie value but the underlying
directory has changed and the response is invalid from the client's
context of its previous READDIR.
Since some servers will not be returning "." and ".." entries as has
been done with previous versions of the NFS protocol, the client that
requires these entries be present in READDIR responses must fabricate
them.
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25.24. Operation 27: READLINK - Read Symbolic Link
25.24.1. ARGUMENTS
/* CURRENT_FH: symlink */
void;
25.24.2. RESULTS
struct READLINK4resok {
linktext4 link;
};
union READLINK4res switch (nfsstat4 status) {
case NFS4_OK:
READLINK4resok resok4;
default:
void;
};
25.24.3. DESCRIPTION
READLINK reads the data associated with a symbolic link. Depending
on the value of the UTF-8 capability attribute (Section 21.1), the
data is encoded in UTF-8. Whether created by an NFS client or
created locally on the server, the data in a symbolic link is not
interpreted (except possibly to check for proper UTF-8 encoding) when
created, but is simply stored.
On success, the current filehandle retains its value.
25.24.4. IMPLEMENTATION
A symbolic link is nominally a pointer to another file. The data is
not necessarily interpreted by the server, just stored in the file.
It is possible for a client implementation to store a pathname that
is not meaningful to the server operating system in a symbolic link.
A READLINK operation returns the data to the client for
interpretation. If different implementations want to share access to
symbolic links, then they must agree on the interpretation of the
data in the symbolic link.
The READLINK operation is only allowed on objects of type NF4LNK.
The server should return the error NFS4ERR_WRONG_TYPE if the object
is not of type NF4LNK.
25.25. Operation 28: REMOVE - Remove File System Object
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25.25.1. ARGUMENTS
struct REMOVE4args {
/* CURRENT_FH: directory */
component4 target;
};
25.25.2. RESULTS
struct REMOVE4resok {
change_info4 cinfo;
};
union REMOVE4res switch (nfsstat4 status) {
case NFS4_OK:
REMOVE4resok resok4;
default:
void;
};
25.25.3. DESCRIPTION
The REMOVE operation removes (deletes) a directory entry which names
a file system object from the directory corresponding to the current
filehandle. If the entry in the directory was the last reference to
the (i.e., there are no other links to that object), the specified
object may be destroyed. In addition, as discussed below, the
destruction of the object can be delayed by its use as an open file.
The directory may be either of type NF4DIR or NF4ATTRDIR.
For the directory where the filename was removed, the server returns
change_info4 information in cinfo. With the atomic field of the
change_info4 data type, the server will indicate if the before and
after change attributes were obtained atomically with respect to the
removal.
If the target has a length of zero, or if the target does not obey
the UTF-8 definition (and the server is enforcing UTF-8 encoding; see
Section 21.1), the error NFS4ERR_INVAL will be returned.
On success, the current filehandle retains its value.
25.25.4. IMPLEMENTATION
In two important respects, the REMOVE operation within NFSv4.1
differs from remove operations for earlier versions of NFS:
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* NFSv3 required a different operator RMDIR for directory removal
and together with REMOVE for non-directory removal. This allowed
clients to skip checking the file type when being passed a non-
directory delete system call (e.g., unlink() [unlink] in POSIX) to
remove a directory, as well as the converse (e.g., a rmdir() on a
non-directory) because they knew the server would check the file
type. NFSv4.1 REMOVE can be used to delete any directory entry
irrespective of its file type.
The implementer of an NFSv4.1 client's entry points from the
unlink() and rmdir() system calls should first check the file type
against the types the system call is allowed to remove before
sending a REMOVE operation. Alternatively, the implementer can
produce a COMPOUND call that includes a LOOKUP/VERIFY sequence of
operations to verify the file type before a REMOVE operation in
the same COMPOUND call.
* In order to deal with removal of open files in a manner consistent
with local file system semantics, the server has the option of
returning the flag OPEN4_RESULT_PRESERVE_UNLINKED, to indicate to
the client that the file will be preserved as long has it has an
outstanding NFSv4.1 open (See Section 25.16) that returned this
flag.
Regardless of the state of OPEN4_RESULT_PRESERVE_UNLINKED, which
controls the continued existence of the object to be deleted, it
is unwise for the client to rely on the availability of disk space
due to the REMOVE. This is because server file space allocation
policies may differ.
If there is an OPEN preventing writing the file (i.e one specifying
OPEN4_SHARE_DENY_WRITE or OPEN4_SHARE_DENY_BOTH) the server SHOULD
reject the removal operation (i.e a REMOVE or a removal that occurs
as part of RENAME when a file is renamed-over).
In addition, the server MAY implement its own restrictions on removal
of a file while it is open. The server might disallow such a removal
operation. The conditions that influence the restrictions on removal
of a file while it is still open include:
* Whether certain access protocols (i.e., those other than NFS) are
holding the file open.
* Whether particular options or policies on the server are enabled.
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If a file has an outstanding OPEN and this prevents the removal of
the file's directory entry, the error NFS4ERR_FILE_OPEN is returned.
This applies to both rejection because of an OPEN preventing writing
the file and to that due to the server's own policies.
The case of a removal operation being done by a client that holds a
write delegation presents important issues that allows the server to
proceed to process the remove without the delegation being recalled,
since the client is presumed aware of the existence of OPENs that
were sent by it previously or never sent to the server because the
delegation holder can process OPENs on its own. Although the server
has considerable freedom in determining the OPENs that might prevent
a successful removal operation, the server may omit the recall in
this case, unless the server is aware of OPENs performed by other
access protocols or because options or policies are in effect that
might prevent the removal operation independent of the existence of
OPENs with deny modes specified.
To deal efficiently with the common case of servers whose policies
are such that only the potential existence of OPENs denying READ and/
or WRITE, such situations can be dealt with as follows:
* The client doing the removal operation and holding the delegation
needs to make the server aware of the existence of such OPENs
without necessarily returning the delegations.
* The server, using the knowledge that he has about any such OPENs
proceeds to make its decision using only the OPENs it is aware of,
without recalling the delegation.
In cases in which the recall can be dispensed with:
* If the removal operation succeeds, the server may treat the
associate write delegation as effectively canceled just as if it
had recalled and returned.
* If the removal operation returns successfully, the client can
simply forget about the delegation, as if it had been returned.
* If the removal operation returns successfully, the client can
client can avoid flushing pending data to be written to the file
being removed.
* If the removal operation returns successfully, the client can
simply forget about opens the server is unaware of/ These open
cannot have any active deny modes specified.
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Where the determination above cannot be made definitively because
delegations are being held by other clients they MUST be recalled to
allow processing of the removal operation to continue. When such a
delegation is held, the server has no reliable knowledge of the
status of OPENs for that client, so unless there are files opened
with the particular deny modes by clients without delegations other
than the client doing the removal operation, the determination cannot
be made until all such delegations are recalled, and the operation
cannot proceed until each sufficient delegation has been returned or
revoked to allow the server to make a correct determination.
If the current filehandle designates a directory for which another
client holds a directory delegation, then, unless the situation can
be resolved by sending a notification, the directory delegation MUST
be recalled, and the operation MUST NOT proceed until the delegation
is returned or revoked. Except where this happens very quickly, one
or more NFS4ERR_DELAY errors will be returned to requests made while
delegation remains outstanding.
When the current filehandle designates a directory for which one or
more directory delegations exist, then, when those delegations
request such notifications, NOTIFY4_REMOVE_ENTRY will be generated as
a result of this operation.
Note that when a remove occurs as a result of a RENAME,
NOTIFY4_REMOVE_ENTRY will only be generated if the removal happens as
a separate operation. In the case in which the removal is integrated
and atomic with RENAME, the notification of the removal is integrated
with notification for the RENAME. See the discussion of the
NOTIFY4_RENAME_ENTRY notification in Section 27.4.
In all cases in which delegations are recalled, the server is likely
to return one or more NFS4ERR_DELAY errors while delegations remain
outstanding.
The handling of the REMOVE operation, when it not rejected as
described above involves the following activities:
A): The elimination of the directory entry identified by the REMOVE
parameters.
B): The reduction of the link count associated with the file being
removed.
C): The deletion of the file data and its eventual re-use to
accommodate newly-written data.
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This last item need only be done when the link count decremented
as part of item B reaches the value zero. In addition, this
last state transition, will, under certain circumstances. be
deferred as long as the file is known by the server to be open.
See below for details.
Items A and B are done in sequence but there is no atomicity
requirement so that other request may see A having been done without
B occurring. The execution of C is often delayed until the link
count reaches zero and, in many cases, until the file is no longer
open.
* If the reply from the OPEN had the flag
OPEN4_RESULT_PRESERVE_UNLINKED set, the server is obligated to
maintain access to the removed object (using a filehandle) until
the last OPEN is closed.
This obligation continues across reboots and grace periods, so the
file is preserved through the grace period and only considered
closed, if it is not reclaimed during the grace period.
When all of the directory entries within a directory are deleted,
it is subject to deletion itself, despite the fact that there
still might be files actively used by their filehandles, even
though they were once referred by directory entries since removed.
* If a client does not have support for the
OPEN4_RESULT_PRESERVE_UNLINKED flag, it will ignore the value and
behave as if it were not set.
* If the reply from the OPEN did not have the flag
OPEN4_RESULT_PRESERVE_UNLINKED set, the client has the option, as
it did in NFSv3 and NFSv4.0, of renaming the file instead of
removing it (referred to as "silly rename")
25.26. Operation 29: RENAME - Rename Directory Entry
25.26.1. ARGUMENTS
struct RENAME4args {
/* SAVED_FH: source directory */
component4 oldname;
/* CURRENT_FH: target directory */
component4 newname;
};
25.26.2. RESULTS
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struct RENAME4resok {
change_info4 source_cinfo;
change_info4 target_cinfo;
};
union RENAME4res switch (nfsstat4 status) {
case NFS4_OK:
RENAME4resok resok4;
default:
void;
};
25.26.3. DESCRIPTION
The RENAME operation renames the object identified by oldname in the
source directory corresponding to the saved filehandle, as set by the
SAVEFH operation, to newname in the target directory corresponding to
the current filehandle. The operation is required to be atomic to
the client. Source and target directories MUST reside on the same
file system on the server. On success, the current filehandle will
continue to be the target directory.
If the target directory already contains an entry with the name
newname, the source object MUST be compatible with the target: either
both are non-directories or both are directories and the target MUST
be empty. If compatible, the existing target is removed before the
rename occurs or, preferably, the target is removed atomically as
part of the rename. See Section 25.25.4 for client and server
actions whenever a target is removed. Note however that when the
removal is performed atomically with the rename, certain parts of the
removal described there are integrated with the rename. For example,
notification of the removal will not be via a NOTIFY4_REMOVE_ENTRY
but will be indicated as part of the NOTIFY4_ADD_ENTRY or
NOTIFY4_RENAME_ENTRY generated by the rename.
If the source object and the target are not compatible or if the
target is a directory but not empty, the server will return the error
NFS4ERR_EXIST.
If oldname and newname both refer to the same file (e.g., they might
be hard links of each other), then, unless the file is open (see
Section 23.26.4), RENAME MUST perform no action and return NFS4_OK.
For both directories involved in the RENAME, the server returns
change_info4 information. With the atomic field of the change_info4
data type, the server will indicate if the before and after change
attributes were obtained atomically with respect to the rename.
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If oldname refers to a named attribute and the saved and current
filehandles refer to different file system objects, the server will
return NFS4ERR_XDEV just as if the saved and current filehandles
represented directories on different file systems.
If oldname or newname has a length of zero, or if oldname or newname
does not obey the UTF-8 definition in the case of a Unicode- aware
file system, the error NFS4ERR_INVAL will be returned.
25.26.4. IMPLEMENTATION
The server MAY impose restrictions on the RENAME operation such that
RENAME may not be done when the file being renamed is open or when
that open is done by particular protocols, or with particular options
or access modes. Similar restrictions may be applied when a file
exists with the target name and is open. When RENAME is rejected
because of either of the above restrictions, the error
NFS4ERR_FILE_OPEN is returned.
When oldname and rename refer to the same file and that file is open
in a fashion such that RENAME would normally be rejected with
NFS4ERR_FILE_OPEN if oldname and newname were different files, then
RENAME SHOULD be rejected with NFS4ERR_FILE_OPEN.
When the restrictions regarding open files apply to an open file with
the target name and the client has a write delegation for that file,
delegation recalls can be avoided in the same fashion as described in
Section 25.25.4.
If a server does implement such restrictions and those restrictions
include cases of NFSv4 opens preventing successful execution of a
rename, the server needs to recall any delegations that could hide
the existence of opens relevant to that decision. This is because
when a client holds a delegation, the server might not have an
accurate account of the opens for that client, since the client may
execute OPENs and CLOSEs locally. The RENAME operation need only be
delayed until a definitive result can be obtained. For example, if
there are multiple delegations and one of them establishes an open
whose presence would prevent the rename, given the server's
semantics, NFS4ERR_FILE_OPEN may be returned to the caller as soon as
that delegation is returned without waiting for other delegations to
be returned. Similarly, if such opens are not associated with
delegations, NFS4ERR_FILE_OPEN can be returned immediately with no
delegation recall being done.
If the current filehandle or the saved filehandle designates a
directory for which another client holds a directory delegation,
then, unless the situation can be resolved by sending a notification,
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the delegation MUST be recalled, and the operation cannot proceed
until the delegation is returned or revoked. Except where this
happens very quickly, one or more NFS4ERR_DELAY errors will be
returned to requests made while delegation remains outstanding.
When the current and saved filehandles are the same and they
designate a directory for which one or more directory delegations
exist, then, when those delegations request such notifications, a
notification of type NOTIFY4_RENAME_ENTRY will be generated as a
result of this operation. When oldname and rename refer to the same
file, no notification is generated (because, as Section 25.26.3
states, the server MUST take no action). When a file is removed
because it has the same name as the target, if that removal is done
atomically with the rename, a NOTIFY4_REMOVE_ENTRY notification will
not be generated. Instead, the deletion of the file will be reported
as part of the NOTIFY4_RENAME_ENTRY notification.
When the current and saved filehandles are not the same:
* If the current filehandle designates a directory for which one or
more directory delegations exist, then, when those delegations
request such notifications, NOTIFY4_ADD_ENTRY will be generated as
a result of this operation. When a file is removed because it has
the same name as the target, if that removal is done atomically
with the rename, a NOTIFY4_REMOVE_ENTRY notification will not be
generated. Instead, the deletion of the file will be reported as
part of the NOTIFY4_ADD_ENTRY notification.
* If the saved filehandle designates a directory for which one or
more directory delegations exist, then, when those delegations
request such notifications, NOTIFY4_REMOVE_ENTRY will be generated
as a result of this operation.
If the object being renamed has file delegations held by clients
other than the one doing the RENAME, the delegations MUST be
recalled, and the operation cannot proceed until each such delegation
is returned or revoked. Note that in the case of multiply linked
files, the delegation recall requirement applies even if the
delegation was obtained through a different name than the one being
renamed. In all cases in which delegations are recalled, the server
is likely to return one or more NFS4ERR_DELAY errors while the
delegation(s) remains outstanding, although it might not do that if
the delegations are returned quickly.
The direct modification resulting from the RENAME operation must be
atomic to the client. However, any necessary changes to the link
count attributes for the file involved and the eventual deletion of
the file's data in the case of a file deleted because it is renamed
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over need not be atomic. In addition, the delay of deletion until
last close functions in the renamed over case behaves as indicated in
Section 25.25.4.
The statement "source and target directories MUST reside on the same
file system on the server" means that the fsid fields in the
attributes for the directories are the same. If they reside on
different file systems, the error NFS4ERR_XDEV is returned.
Based on the value of the fh_expire_type attribute for the object,
the filehandle may or may not expire on a RENAME. However, server
implementers are strongly encouraged to attempt to keep filehandles
from expiring in this fashion.
On some servers, the file names "." and ".." are illegal as either
oldname or newname, and will result in the error NFS4ERR_BADNAME. In
addition, on many servers the case of oldname or newname being an
alias for the source directory will be checked for. Such servers
will return the error NFS4ERR_INVAL in these cases.
If either of the source or target filehandles are not directories,
the server will return NFS4ERR_NOTDIR.
25.27. Operation 31: RESTOREFH - Restore Saved Filehandle
25.27.1. ARGUMENTS
/* SAVED_FH: */
void;
25.27.2. RESULTS
struct RESTOREFH4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: value of saved fh
*/
nfsstat4 status;
};
25.27.3. DESCRIPTION
The RESTOREFH operation sets the current filehandle and stateid to
the values in the saved filehandle and stateid. If there is no saved
filehandle, then the server will return the error
NFS4ERR_NOFILEHANDLE.
See Section 23.2.3.1.1 for more details on the current filehandle.
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See Section 23.2.3.1.2 for more details on the current stateid.
25.27.4. IMPLEMENTATION
Operations like OPEN and LOOKUP use the current filehandle to
represent a directory and replace it with a new filehandle. Assuming
that the previous filehandle was saved with a SAVEFH operator, the
previous filehandle can be restored as the current filehandle. This
is commonly used to obtain post-operation attributes for the
directory, e.g.,
PUTFH (directory filehandle)
SAVEFH
GETATTR attrbits (pre-op dir attrs)
CREATE optbits "foo" attrs
GETATTR attrbits (file attributes)
RESTOREFH
GETATTR attrbits (post-op dir attrs)
25.28. Operation 32: SAVEFH - Save Current Filehandle
25.28.1. ARGUMENTS
/* CURRENT_FH: */
void;
25.28.2. RESULTS
struct SAVEFH4res {
/*
* If status is NFS4_OK,
* new SAVED_FH: value of current fh
*/
nfsstat4 status;
};
25.28.3. DESCRIPTION
The SAVEFH operation saves the current filehandle and stateid. If a
previous filehandle was saved, then it is no longer accessible. The
saved filehandle can be restored as the current filehandle with the
RESTOREFH operator.
On success, the current filehandle retains its value.
See Section 23.2.3.1.1 for more details on the current filehandle.
See Section 23.2.3.1.2 for more details on the current stateid.
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25.28.4. IMPLEMENTATION
25.29. Operation 33: SECINFO - Obtain Available Security
Although this is an existing NFSv4.1 operation and appropriately
described in this document, much of the detail regarding the values
returned and their role in security negotiation is described in
Section 16 of the NFSv4-wide security document, currently
[I-D.dnoveck-nfsv4-security]. This adaptation has been necessary
since connection characteristics are now an appropriate subject of
negotiation, where previously negotiation only concerned the choice
of appropriate auth flavors on existing connection.
25.29.1. ARGUMENTS
struct SECINFO4args {
/* CURRENT_FH: directory */
component4 name;
};
25.29.2. RESULTS
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/*
* From RFC 2203
*/
enum rpc_gss_svc_t {
RPC_GSS_SVC_NONE = 1,
RPC_GSS_SVC_INTEGRITY = 2,
RPC_GSS_SVC_PRIVACY = 3
};
struct rpcsec_gss_info {
sec_oid4 oid;
qop4 qop;
rpc_gss_svc_t service;
};
/* RPCSEC_GSS has a value of '6' - See RFC 2203 */
union secinfo4 switch (uint32_t flavor) {
case RPCSEC_GSS:
rpcsec_gss_info flavor_info;
default:
void;
};
typedef secinfo4 SECINFO4resok<>;
union SECINFO4res switch (nfsstat4 status) {
case NFS4_OK:
/* CURRENTFH: consumed */
SECINFO4resok resok4;
default:
void;
};
25.29.3. DESCRIPTION
The SECINFO operation is used by the client to obtain a list of valid
RPC authentication flavors for a specific directory filehandle, file
name pair. SECINFO should apply the same access methodology used for
LOOKUP when evaluating the name. Therefore, if the requester does
not have the appropriate access to LOOKUP the name, then SECINFO MUST
behave the same way and return NFS4ERR_ACCESS.
The result will contain an array that represents the security
mechanisms available, with an order corresponding to the server's
preferences, the most preferred being first in the array. The client
is free to pick whatever security mechanism it both desires and
supports, or to pick in the server's preference order the first one
it supports. The array entries are represented by the secinfo4
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structure. The field 'flavor' will contain a value of AUTH_NONE,
AUTH_SYS (as defined in RFC 5531 [RFC5531]), or RPCSEC_GSS (as
defined in RFC 2203 [RFC2203]). The field flavor can also be any
other security flavor registered with IANA.
For the flavors AUTH_NONE and AUTH_SYS, no additional security
information is returned. The same is true of many (if not most)
other security flavors, including AUTH_DH. For a return value of
RPCSEC_GSS, a security triple is returned that contains the mechanism
object identifier (OID, as defined in RFC 2743 [RFC2743]), the
quality of protection (as defined in RFC 2743 [RFC2743]), and the
service type (as defined in RFC 2203 [RFC2203]). It is possible for
SECINFO to return multiple entries with flavor equal to RPCSEC_GSS
with different security triple values.
On success, the current filehandle is consumed (see Section 6.2.1.8),
and if the next operation after SECINFO tries to use the current
filehandle, that operation will fail with the status
NFS4ERR_NOFILEHANDLE.
If the name has a length of zero, or if the name does not obey the
UTF-8 definition (assuming UTF-8 capabilities are enabled; see
Section 21.1), the error NFS4ERR_INVAL will be returned.
See Section 16 of [I-D.dnoveck-nfsv4-security] for additional
information on the use of SECINFO.
25.29.4. IMPLEMENTATION
The SECINFO operation is expected to be used by the NFS client when
the error value of NFS4ERR_WRONGSEC is returned from another NFS
operation. This signifies to the client that the server's security
policy is different from what the client is currently using. At this
point, the client is expected to obtain a list of possible security
flavors and choose what best suits its policies.
As mentioned, the server's security policies will determine when a
client request receives NFS4ERR_WRONGSEC. See Table 14 for a list of
operations that can return NFS4ERR_WRONGSEC. In addition, when
READDIR returns attributes, the rdattr_error (Section 11.12.1.12) can
contain NFS4ERR_WRONGSEC. Note that CREATE and REMOVE MUST NOT
return NFS4ERR_WRONGSEC. The rationale for CREATE is that unless the
target name exists, it cannot have a separate security policy from
the parent directory, and the security policy of the parent was
checked when its filehandle was injected into the COMPOUND request's
operations stream (for similar reasons, an OPEN operation that
creates the target MUST NOT return NFS4ERR_WRONGSEC). If the target
name exists, while it might have a separate security policy, that is
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irrelevant because CREATE MUST return NFS4ERR_EXIST. The rationale
for REMOVE is that while that target might have a separate security
policy, the target is going to be removed, and so the security policy
of the parent trumps that of the object being removed. RENAME and
LINK MAY return NFS4ERR_WRONGSEC, but the NFS4ERR_WRONGSEC error
applies only to the saved filehandle (See Section 6.2.2). Any
NFS4ERR_WRONGSEC error on the current filehandle used by LINK and
RENAME MUST be returned by the PUTFH, PUTPUBFH, PUTROOTFH, or
RESTOREFH operation that injected the current filehandle.
With the exception of LINK and RENAME, the set of operations that can
return NFS4ERR_WRONGSEC represents the point at which the client can
inject a filehandle into the "current filehandle" at the server. The
filehandle is either provided by the client (PUTFH, PUTPUBFH,
PUTROOTFH), generated as a result of a name-to-filehandle translation
(LOOKUP and OPEN), or generated from the saved filehandle via
RESTOREFH. As Section 6.2.1.1 states, a put filehandle operation
followed by SAVEFH MUST NOT return NFS4ERR_WRONGSEC. Thus, the
RESTOREFH operation, under certain conditions (See Section 6.2.1), is
permitted to return NFS4ERR_WRONGSEC so that security policies can be
honored.
The READDIR operation will not directly return the NFS4ERR_WRONGSEC
error. However, if the READDIR request included a request for
attributes, it is possible that the READDIR request's security triple
did not match that of a directory entry. If this is the case and the
client has requested the rdattr_error attribute, the server will
return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.
To resolve an error return of NFS4ERR_WRONGSEC, the client does the
following:
* For LOOKUP and OPEN, the client will use SECINFO with the same
current filehandle and name as provided in the original LOOKUP or
OPEN to enumerate the available security triples.
* For the rdattr_error, the client will use SECINFO with the same
current filehandle as provided in the original READDIR. The name
passed to SECINFO will be that of the directory entry (as returned
from READDIR) that had the NFS4ERR_WRONGSEC error in the
rdattr_error attribute.
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* For PUTFH, PUTROOTFH, PUTPUBFH, RESTOREFH, LINK, and RENAME, the
client will use SECINFO_NO_NAME { style =
SECINFO_STYLE4_CURRENT_FH }. The client will prefix the
SECINFO_NO_NAME operation with the appropriate PUTFH, PUTPUBFH, or
PUTROOTFH operation that provides the filehandle originally
provided by the PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH
operation.
NOTE: In NFSv4.0, the client was required to use SECINFO, and had
to reconstruct the parent of the original filehandle and the
component name of the original filehandle. The introduction in
NFSv4.1 of SECINFO_NO_NAME obviates the need for reconstruction.
* For LOOKUPP, the client will use SECINFO_NO_NAME { style =
SECINFO_STYLE4_PARENT } and provide the filehandle that equals the
filehandle originally provided to LOOKUPP.
See Section 28 for a discussion on the recommendations for the
security flavor used by SECINFO and SECINFO_NO_NAME.
25.30. Operation 34: SETATTR - Set Attributes
25.30.1. ARGUMENTS
struct SETATTR4args {
/* CURRENT_FH: target object */
stateid4 stateid;
fattr4 obj_attributes;
};
25.30.2. RESULTS
struct SETATTR4res {
nfsstat4 status;
bitmap4 attrsset;
};
25.30.3. DESCRIPTION
The SETATTR operation changes one or more of the attributes of a file
system object. The new attributes are specified with a bitmap and
the attributes that follow the bitmap in bit order.
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The stateid argument for SETATTR is used to provide locking context
that is necessary for SETATTR requests that set the size attribute.
Since setting the size attribute modifies the file's data, it has the
same locking requirements as a corresponding WRITE. The area between
the old end-of-file and the new end-of-file is considered to be
modified just as would have been the case had the area in question
been specified as a result:
* Any SETATTR that sets the size attribute is incompatible with a
share reservation that specifies OPEN4_SHARE_DENY_WRITE.
* The target of WRITE, for the purpose of checking conflicts with
mandatory byte-range locks, when a server is implementing
mandatory byte-range locking.
A valid stateid needs to be specified when the size attributed is
said so that the server can determine, when writing is being denied,
whether the size modification is allowed under an open allowing
writing. When the file size attribute is not set, the special
stateid consisting of all bits equal to zero MAY be passed.
On either success or failure of the operation, the server will return
the attrsset bitmask to represent what (if any) attributes were
successfully set. The attrsset in the response is a subset of the
attrmask field of the obj_attributes field in the argument.
On success, the current filehandle retains its value.
25.30.4. IMPLEMENTATION
If the request specifies the owner attribute to be set, the server
SHOULD allow the operation to succeed if the current owner of the
object matches the value specified in the request. Some servers may
be implemented in a way as to prohibit the setting of the owner
attribute unless the requester has privilege to do so. If the server
is lenient in this one case of matching owner values, the client
implementation may be simplified in cases of creation of an object
(e.g., an exclusive create via OPEN) followed by a SETATTR.
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The file size attribute is used to request changes to the size of a
file. A value of zero causes the file to be truncated, a value less
than the current size of the file causes data from new size to the
end of the file to be discarded, and a size greater than the current
size of the file causes logically zeroed data bytes to be added to
the end of the file. Servers are free to implement this using
unallocated bytes (holes) or allocated data bytes set to zero.
Clients should not make any assumptions regarding a server's
implementation of this feature, beyond that the bytes in the affected
byte-range returned by READ will be zeroed. Servers MUST support
extending the file size via SETATTR.
SETATTR is not guaranteed to be atomic. A failed SETATTR may
partially change a file's attributes, hence the reason why the reply
always includes the status and the list of attributes that were set.
If the object whose attributes are being changed has a file
delegation that is held by a client other than the one doing the
SETATTR, the delegation(s) must be recalled, and the operation cannot
proceed to actually change an attribute until each such delegation is
returned or revoked. In all cases in which delegations are recalled,
the server is likely to return one or more NFS4ERR_DELAY errors while
the delegation(s) remains outstanding, although it might not do that
if the delegations are returned quickly.
If the object whose attributes are being set is a directory and
another client holds a directory delegation for that directory, then
if enabled, asynchronous notifications will be generated when the set
of attributes changed has a non-null intersection with the set of
attributes for which notification is requested. Notifications of
type NOTIFY4_CHANGE_DIR_ATTRS will be sent to the appropriate
client(s), but the SETATTR is not delayed by waiting for these
notifications to be sent.
If the object whose attributes are being set is a member of the
directory for which another client holds a directory delegation, then
asynchronous notifications will be generated when the set of
attributes changed has a non-null intersection with the set of
attributes for which notification is requested. Notifications of
type NOTIFY4_CHANGE_CHILD_ATTRS will be sent to the appropriate
clients, but the SETATTR is not delayed by waiting for these
notifications to be sent.
Changing the size of a file with SETATTR indirectly changes the
time_modify and change attributes. A client must account for this as
size changes can result in data deletion.
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The attributes time_access_set and time_modify_set are write-only
attributes constructed as a switched union so the client can direct
the server in setting the time values. If the switched union
specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
be used for the operation. If the switch union does not specify
SET_TO_CLIENT_TIME4, the server is to use its current time for the
SETATTR operation.
If server and client times differ, programs that compare client time
to file times can break. A time synchronization protocol should be
used to limit client/server time skew.
Use of a COMPOUND containing a VERIFY operation specifying only the
change attribute, immediately followed by a SETATTR, provides a means
whereby a client may specify a request that emulates the
functionality of the SETATTR guard mechanism of NFSv3. Since the
function of the guard mechanism is to avoid changes to the file
attributes based on stale information, delays between checking of the
guard condition and the setting of the attributes have the potential
to compromise this function, as would the corresponding delay in the
NFSv4 emulation. Therefore, NFSv4.1 servers SHOULD take care to
avoid such delays, to the degree possible, when executing such a
request.
If the server does not support an attribute as requested by the
client, the server SHOULD return NFS4ERR_ATTRNOTSUPP.
A mask of the attributes actually set is returned by SETATTR in all
cases. That mask MUST NOT include attribute bits not requested to be
set by the client. If the attribute masks in the request and reply
are equal, the status field in the reply MUST be NFS4_OK.
25.31. Operation 37: VERIFY - Verify Same Attributes
25.31.1. ARGUMENTS
struct VERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
25.31.2. RESULTS
struct VERIFY4res {
nfsstat4 status;
};
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25.31.3. DESCRIPTION
The VERIFY operation is used to verify that attributes have the value
assumed by the client before proceeding with the following operations
in the COMPOUND request. If any of the attributes do not match, then
the error NFS4ERR_NOT_SAME must be returned. The current filehandle
retains its value after successful completion of the operation.
25.31.4. IMPLEMENTATION
One possible use of the VERIFY operation is the following series of
operations. With this, the client is attempting to verify that the
file being removed will match what the client expects to be removed.
This series can help prevent the unintended deletion of a file.
PUTFH (directory filehandle)
LOOKUP (file name)
VERIFY (filehandle == fh)
PUTFH (directory filehandle)
REMOVE (file name)
This series does not prevent a second client from removing and
creating a new file in the middle of this sequence, but it does help
avoid the unintended result.
In the case that a OPTIONAL attribute is specified in the VERIFY
operation and the server does not support that attribute for the file
system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
client.
When the attribute specified is supported but is one for which use of
VERIFY is inappropriate (e.g. rdattr_error or any set-only attribute
(such as time_modify_set)), the error NFS4ERR_INVAL is returned to
the client.
25.32. Operation 38: WRITE - Write to File
25.32.1. ARGUMENTS
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enum stable_how4 {
UNSTABLE4 = 0,
DATA_SYNC4 = 1,
FILE_SYNC4 = 2
};
struct WRITE4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
stable_how4 stable;
opaque data<>;
};
25.32.2. RESULTS
struct WRITE4resok {
count4 count;
stable_how4 committed;
verifier4 writeverf;
};
union WRITE4res switch (nfsstat4 status) {
case NFS4_OK:
WRITE4resok resok4;
default:
void;
};
25.32.3. DESCRIPTION
The WRITE operation is used to write data to a regular file. The
target file is specified by the current filehandle. The offset
specifies the offset where the data should be written. An offset of
zero specifies that the write should start at the beginning of the
file. The count, as encoded as part of the opaque data parameter,
represents the number of bytes of data that are to be written. If
the count is zero, the WRITE will succeed and return a count of zero
subject to permissions checking. The server MAY write fewer bytes
than requested by the client.
The client specifies with the stable parameter the method of how the
data is to be processed by the server. If stable is FILE_SYNC4, the
server MUST commit the data written plus all file system metadata to
stable storage before returning results. This corresponds to the
NFSv2 protocol semantics. Any other behavior constitutes a protocol
violation. If stable is DATA_SYNC4, then the server MUST commit all
of the data to stable storage and enough of the metadata to retrieve
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the data before returning. The server implementer is free to
implement DATA_SYNC4 in the same fashion as FILE_SYNC4, but with a
possible performance drop. If stable is UNSTABLE4, the server is
free to commit any part of the data and the metadata to stable
storage, including all or none, before returning a reply to the
client. There is no guarantee whether or when any uncommitted data
will subsequently be committed to stable storage. The only
guarantees made by the server are that it will not destroy any data
without changing the value of writeverf and that it will not commit
the data and metadata at a level less than that requested by the
client.
Except when special stateids are used, the stateid value for a WRITE
request represents a value returned from a previous byte-range LOCK
or OPEN request or the stateid associated with a delegation. The
stateid identifies the associated owners if any and is used by the
server to verify that the associated locks are still valid (e.g.,
have not been revoked).
Upon successful completion, the following results are returned. The
count result is the number of bytes of data written to the file. The
server may write fewer bytes than requested. If so, the actual
number of bytes written starting at location, offset, is returned.
The server also returns an indication of the level of commitment of
the data and metadata via committed. Per Table 20,
* The server MAY commit the data at a stronger level than requested.
* The server MUST commit the data at a level at least as strong as
that requested.
+============+===================================+
| stable | committed |
+============+===================================+
| UNSTABLE4 | FILE_SYNC4, DATA_SYNC4, UNSTABLE4 |
+------------+-----------------------------------+
| DATA_SYNC4 | FILE_SYNC4, DATA_SYNC4 |
+------------+-----------------------------------+
| FILE_SYNC4 | FILE_SYNC4 |
+------------+-----------------------------------+
Table 20: Valid Combinations of the Fields
Stable in the Request and Committed in the
Reply
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The final portion of the result is the field writeverf. This field
is the write verifier and is a cookie that the client can use to
determine whether a server has changed instance state (e.g., server
restart) between a call to WRITE and a subsequent call to either
WRITE or COMMIT. This cookie MUST be unchanged during a single
instance of the NFSv4.1 server and MUST be unique between instances
of the NFSv4.1 server. If the cookie changes, then the client MUST
assume that any data written with an UNSTABLE4 value for committed
and an old writeverf in the reply has been lost and will need to be
recovered.
If a client writes data to the server with the stable argument set to
UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or
UNSTABLE4, the client will follow up some time in the future with a
COMMIT operation to synchronize outstanding asynchronous data and
metadata with the server's stable storage, barring client error. It
is possible that due to client crash or other error that a subsequent
COMMIT will not be received by the server.
For a WRITE with a stateid value of all bits equal to zero, the
server MAY allow the WRITE to be serviced subject to mandatory byte-
range locks or the current share deny modes for the file. For a
WRITE with a stateid value of all bits equal to 1, the server MUST
NOT allow the WRITE operation to bypass locking checks at the server
and otherwise is treated as if a stateid of all bits equal to zero
were used.
On success, the current filehandle retains its value.
25.32.4. IMPLEMENTATION
It is possible for the server to write fewer bytes of data than
requested by the client. In this case, the server SHOULD NOT return
an error unless no data was written at all. If the server writes
less than the number of bytes specified, the client will need to send
another WRITE to write the remaining data.
It is assumed that the act of writing data to a file will cause the
time_modified and change attributes of the file to be updated.
However, these attributes SHOULD NOT be changed unless the contents
of the file are changed. Thus, a WRITE request with count set to
zero SHOULD NOT cause the time_modified and change attributes of the
file to be updated.
Stable storage is persistent storage that survives:
1. Repeated power failures.
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2. Hardware failures (of any board, power supply, etc.).
3. Repeated software crashes and restarts.
This definition does not address failure of the stable storage module
itself.
The verifier is defined to allow a client to detect different
instances of an NFSv4.1 protocol server over which cached,
uncommitted data may be lost. In the most likely case, the verifier
allows the client to detect server restarts. This information is
required so that the client can safely determine whether the server
could have lost cached data. If the server fails unexpectedly and
the client has uncommitted data from previous WRITE requests (done
with the stable argument set to UNSTABLE4 and in which the result
committed was returned as UNSTABLE4 as well), the server might not
have flushed cached data to stable storage. The burden of recovery
is on the client, and the client will need to retransmit the data to
the server.
A suggested verifier would be to use the time that the server was
last started (if restarting the server results in lost buffers).
The reply's committed field allows the client to do more effective
caching. If the server is committing all WRITE requests to stable
storage, then it SHOULD return with committed set to FILE_SYNC4,
regardless of the value of the stable field in the arguments. A
server that uses an NVRAM accelerator may choose to implement this
policy. The client can use this to increase the effectiveness of the
cache by discarding cached data that has already been committed on
the server.
Some implementations may return NFS4ERR_NOSPC instead of
NFS4ERR_DQUOT when a user's quota is exceeded.
In the case that the current filehandle is of type NF4DIR, the server
will return NFS4ERR_ISDIR. If the current file is a symbolic link,
the error NFS4ERR_SYMLINK will be returned. Otherwise, if the
current filehandle does not designate an ordinary file, the server
will return NFS4ERR_WRONG_TYPE.
If mandatory byte-range locking is in effect for the file, and the
corresponding byte-range of the data to be written to the file is
READ_LT or WRITE_LT locked by an owner that is not associated with
the stateid, the server MUST return NFS4ERR_LOCKED. If so, the
client MUST check if the owner corresponding to the stateid used with
the WRITE operation has a conflicting READ_LT lock that overlaps with
the byte-range that was to be written. If the stateid's owner has no
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conflicting READ_LT lock, then the client SHOULD try to get the
appropriate write byte-range lock via the LOCK operation before re-
attempting the WRITE. When the WRITE completes, the client SHOULD
release the byte-range lock via LOCKU.
If the stateid's owner had a conflicting READ_LT lock, then the
client has no choice but to return an error to the application that
attempted the WRITE. The reason is that since the stateid's owner
had a READ_LT lock, either the server attempted to temporarily
effectively upgrade this READ_LT lock to a WRITE_LT lock or the
server has no upgrade capability. If the server attempted to upgrade
the READ_LT lock and failed, it is pointless for the client to re-
attempt the upgrade via the LOCK operation, because there might be
another client also trying to upgrade. If two clients are blocked
trying to upgrade the same lock, the clients deadlock. If the server
has no upgrade capability, then it is pointless to try a LOCK
operation to upgrade.
If one or more other clients have delegations for the file being
written, those delegations MUST be recalled, and the operation cannot
proceed until those delegations are returned or revoked. Except
where this happens very quickly, one or more NFS4ERR_DELAY errors
will be returned to requests made while the delegation remains
outstanding. Normally, delegations will not be recalled as a result
of a WRITE operation since the recall will occur as a result of an
earlier OPEN. However, since it is possible for a WRITE to be done
with a special stateid, the server needs to check for this case even
though the client should have done an OPEN previously.
25.33. Operation 40: BACKCHANNEL_CTL - Backchannel Control
25.33.1. ARGUMENT
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typedef opaque gsshandle4_t<>;
struct gss_cb_handles4 {
rpc_gss_service_t gcbp_service; /* RFC 2203 */
gsshandle4_t gcbp_handle_from_server;
gsshandle4_t gcbp_handle_from_client;
};
union callback_sec_parms4 switch (uint32_t cb_secflavor) {
case AUTH_NONE:
void;
case AUTH_SYS:
authsys_parms cbsp_sys_cred; /* RFC 5531 */
case RPCSEC_GSS:
gss_cb_handles4 cbsp_gss_handles;
};
struct BACKCHANNEL_CTL4args {
uint32_t bca_cb_program;
callback_sec_parms4 bca_sec_parms<>;
};
25.33.2. RESULT
struct BACKCHANNEL_CTL4res {
nfsstat4 bcr_status;
};
25.33.3. DESCRIPTION
The BACKCHANNEL_CTL operation replaces the backchannel's callback
program number and adds (not replaces) RPCSEC_GSS handles for use by
the backchannel.
The arguments of the BACKCHANNEL_CTL call are a subset of the
CREATE_SESSION parameters. In the arguments of BACKCHANNEL_CTL, the
bca_cb_program field and bca_sec_parms fields correspond respectively
to the csa_cb_program and csa_sec_parms fields of the arguments of
CREATE_SESSION (Section 25.36).
BACKCHANNEL_CTL MUST appear in a COMPOUND that starts with SEQUENCE.
If the RPCSEC_GSS handle identified by gcbp_handle_from_server does
not exist on the server, the server MUST return NFS4ERR_NOENT.
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If an RPCSEC_GSS handle is using the SSV context (See Section 7.9),
then because each SSV RPCSEC_GSS handle shares a common SSV GSS
context, there are security considerations specific to this situation
discussed in Section 7.10.
25.34. Operation 41: BIND_CONN_TO_SESSION - Associate Connection with
Session
25.34.1. ARGUMENT
enum channel_dir_from_client4 {
CDFC4_FORE = 0x1,
CDFC4_BACK = 0x2,
CDFC4_FORE_OR_BOTH = 0x3,
CDFC4_BACK_OR_BOTH = 0x7
};
struct BIND_CONN_TO_SESSION4args {
sessionid4 bctsa_sessid;
channel_dir_from_client4
bctsa_dir;
bool bctsa_use_conn_in_rdma_mode;
};
25.34.2. RESULT
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enum channel_dir_from_server4 {
CDFS4_FORE = 0x1,
CDFS4_BACK = 0x2,
CDFS4_BOTH = 0x3
};
struct BIND_CONN_TO_SESSION4resok {
sessionid4 bctsr_sessid;
channel_dir_from_server4
bctsr_dir;
bool bctsr_use_conn_in_rdma_mode;
};
union BIND_CONN_TO_SESSION4res
switch (nfsstat4 bctsr_status) {
case NFS4_OK:
BIND_CONN_TO_SESSION4resok
bctsr_resok4;
default: void;
};
25.34.3. DESCRIPTION
BIND_CONN_TO_SESSION is used to associate additional connections with
a session. It MUST be used on the connection being associated with
the session. It MUST be the only operation in the COMPOUND
procedure. If SP4_NONE (Section 25.35) state protection is used, any
principal, security flavor, or RPCSEC_GSS context MAY be used to
invoke the operation. If SP4_MACH_CRED is used, RPCSEC_GSS MUST be
used with the integrity or privacy services, using the principal that
created the client ID. If SP4_SSV is used, RPCSEC_GSS with the SSV
GSS mechanism (Section 7.9) and integrity or privacy MUST be used.
If, when the client ID was created, the client opted for SP4_NONE
state protection, the client is not required to use
BIND_CONN_TO_SESSION to associate the connection with the session,
unless the client wishes to associate the connection with the
backchannel. When SP4_NONE protection is used, simply sending a
COMPOUND request with a SEQUENCE operation is sufficient to associate
the connection with the session specified in SEQUENCE.
The field bctsa_dir indicates whether the client wants to associate
the connection with the fore channel or the backchannel or both
channels. The value CDFC4_FORE_OR_BOTH indicates that the client
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wants to associate the connection with both the fore channel and
backchannel, but will accept the connection being associated to just
the fore channel. The value CDFC4_BACK_OR_BOTH indicates that the
client wants to associate with both the fore channel and backchannel,
but will accept the connection being associated with just the
backchannel. The server replies in bctsr_dir which channel(s) the
connection is associated with. If the client specified CDFC4_FORE,
the server MUST return CDFS4_FORE. If the client specified
CDFC4_BACK, the server MUST return CDFS4_BACK. If the client
specified CDFC4_FORE_OR_BOTH, the server MUST return CDFS4_FORE or
CDFS4_BOTH. If the client specified CDFC4_BACK_OR_BOTH, the server
MUST return CDFS4_BACK or CDFS4_BOTH.
See the CREATE_SESSION operation (Section 25.36), and the description
of the argument csa_use_conn_in_rdma_mode to understand
bctsa_use_conn_in_rdma_mode, and the description of
csr_use_conn_in_rdma_mode to understand bctsr_use_conn_in_rdma_mode.
Invoking BIND_CONN_TO_SESSION on a connection already associated with
the specified session has no effect, and the server MUST respond with
NFS4_OK, unless the client is demanding changes to the set of
channels the connection is associated with. If so, the server MUST
return NFS4ERR_INVAL.
25.34.4. IMPLEMENTATION
If a session's channel loses all connections, depending on the client
ID's state protection and type of channel, the client might need to
use BIND_CONN_TO_SESSION to associate a new connection. If the
server restarted and does not keep the reply cache in stable storage,
the server will not recognize the session ID. The client will
ultimately have to invoke EXCHANGE_ID to create a new client ID and
session.
Suppose SP4_SSV state protection is being used, and
BIND_CONN_TO_SESSION is among the operations included in the
spo_must_enforce set when the client ID was created (Section 25.35).
If so, there is an issue if SET_SSV is sent, no response is returned,
and the last connection associated with the client ID drops. The
client, per the sessions model, MUST retry the SET_SSV. But it needs
a new connection to do so, and MUST associate that connection with
the session via a BIND_CONN_TO_SESSION authenticated with the SSV GSS
mechanism. The problem is that the RPCSEC_GSS message integrity
codes use a subkey derived from the SSV as the key and the SSV may
have changed. While there are multiple recovery strategies, a
single, general strategy is described here.
* The client reconnects.
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* The client assumes that the SET_SSV was executed, and so sends
BIND_CONN_TO_SESSION with the subkey (derived from the new SSV,
i.e., what SET_SSV would have set the SSV to) used as the key for
the RPCSEC_GSS credential message integrity codes.
* If the request succeeds, this means that the original attempted
SET_SSV did execute successfully. The client re-sends the
original SET_SSV, which the server will reply to via the reply
cache.
* If the server returns an RPC authentication error, this means that
the server's current SSV was not changed (and the SET_SSV was
likely not executed). The client then tries BIND_CONN_TO_SESSION
with the subkey derived from the old SSV as the key for the
RPCSEC_GSS message integrity codes.
* The attempted BIND_CONN_TO_SESSION with the old SSV should
succeed. If so, the client re-sends the original SET_SSV. If the
original SET_SSV was not executed, then the server executes it.
If the original SET_SSV was executed but failed, the server will
return the SET_SSV from the reply cache.
25.35. Operation 42: EXCHANGE_ID - Instantiate Client ID
The EXCHANGE_ID operation exchanges long-hand client and server
identifiers (owners) and provides access to a client ID, creating one
if necessary. This client ID becomes associated with the connection
on which the operation is done, so that it is available when a
CREATE_SESSION is done or when the connection is used to issue a
request on an existing session associated with the current client.
25.35.1. ARGUMENT
const EXCHGID4_FLAG_SUPP_MOVED_REFER = 0x00000001;
const EXCHGID4_FLAG_SUPP_MOVED_MIGR = 0x00000002;
const EXCHGID4_FLAG_BIND_PRINC_STATEID = 0x00000100;
const EXCHGID4_FLAG_USE_NON_PNFS = 0x00010000;
const EXCHGID4_FLAG_USE_PNFS_MDS = 0x00020000;
const EXCHGID4_FLAG_USE_PNFS_DS = 0x00040000;
const EXCHGID4_FLAG_MASK_PNFS = 0x00070000;
const EXCHGID4_FLAG_UPD_CONFIRMED_REC_A = 0x40000000;
const EXCHGID4_FLAG_CONFIRMED_R = 0x80000000;
struct state_protect_ops4 {
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bitmap4 spo_must_enforce;
bitmap4 spo_must_allow;
};
struct ssv_sp_parms4 {
state_protect_ops4 ssp_ops;
sec_oid4 ssp_hash_algs<>;
sec_oid4 ssp_encr_algs<>;
uint32_t ssp_window;
uint32_t ssp_num_gss_handles;
};
enum state_protect_how4 {
SP4_NONE = 0,
SP4_MACH_CRED = 1,
SP4_SSV = 2
};
union state_protect4_a switch(state_protect_how4 spa_how) {
case SP4_NONE:
void;
case SP4_MACH_CRED:
state_protect_ops4 spa_mach_ops;
case SP4_SSV:
ssv_sp_parms4 spa_ssv_parms;
};
struct EXCHANGE_ID4args {
client_owner4 eia_clientowner;
uint32_t eia_flags;
state_protect4_a eia_state_protect;
nfs_impl_id4 eia_client_impl_id<1>;
};
25.35.2. RESULT
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struct ssv_prot_info4 {
state_protect_ops4 spi_ops;
uint32_t spi_hash_alg;
uint32_t spi_encr_alg;
uint32_t spi_ssv_len;
uint32_t spi_window;
gsshandle4_t spi_handles<>;
};
union state_protect4_r switch(state_protect_how4 spr_how) {
case SP4_NONE:
void;
case SP4_MACH_CRED:
state_protect_ops4 spr_mach_ops;
case SP4_SSV:
ssv_prot_info4 spr_ssv_info;
};
struct EXCHANGE_ID4resok {
clientid4 eir_clientid;
sequenceid4 eir_sequenceid;
uint32_t eir_flags;
state_protect4_r eir_state_protect;
server_owner4 eir_server_owner;
opaque eir_server_scope<NFS4_OPAQUE_LIMIT>;
nfs_impl_id4 eir_server_impl_id<1>;
};
union EXCHANGE_ID4res switch (nfsstat4 eir_status) {
case NFS4_OK:
EXCHANGE_ID4resok eir_resok4;
default:
void;
};
25.35.3. DESCRIPTION
The client uses the EXCHANGE_ID operation to register a particular
instance of that client with the server, as represented by a
client_owner4. However, when the client_owner4 has already been
registered by other means (e.g., Transparent State Migration), the
client may still use EXCHANGE_ID to obtain the client ID assigned
previously.
The client ID returned from this operation will be associated with
the connection on which the EXCHANGE_ID is received and will serve as
a parent object for sessions created by the client on this connection
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or to which the connection is bound. As a result of using those
sessions to make requests involving the creation of state, that state
will become associated with the client ID returned.
In situations in which the registration of the client_owner has not
occurred previously, the client ID must first be used, along with the
returned eir_sequenceid, in creating an associated session using
CREATE_SESSION.
If the flag EXCHGID4_FLAG_CONFIRMED_R is set in the result,
eir_flags, then it is an indication that the registration of the
client_owner has already occurred and that a further CREATE_SESSION
is not needed to confirm it. Of course, subsequent CREATE_SESSION
operations may be needed for other reasons.
The value eir_sequenceid is used to establish an initial sequence
value associated with the client ID returned. In cases in which a
CREATE_SESSION has already been done, there is no need for this
value, since sequencing of such request has already been established,
and the client has no need for this value and will ignore it.
EXCHANGE_ID MAY be sent in a COMPOUND procedure that starts with
SEQUENCE. However, when a client communicates with a server for the
first time, it will not have a session, so using SEQUENCE will not be
possible. If EXCHANGE_ID is sent without a preceding SEQUENCE, then
it MUST be the only operation in the COMPOUND procedure's request.
If it is not, the server MUST return NFS4ERR_NOT_ONLY_OP.
The eia_clientowner field is composed of a co_verifier field and a
co_ownerid string. As noted in Section 5.5, the co_ownerid
identifies the client, and the co_verifier specifies a particular
incarnation of that client. An EXCHANGE_ID sent with a new
incarnation of the client will lead to the server removing lock state
of the old incarnation. On the other hand, when an EXCHANGE_ID sent
with the current incarnation and co_ownerid does not result in an
unrelated error, it will potentially update an existing client ID's
properties or simply return information about the existing client_id.
The latter would happen when this operation is done to the same
server using different network addresses as part of creating trunked
connections.
A server MUST NOT provide the same client ID to two different
incarnations of an eia_clientowner.
In addition to the client ID and sequence ID, the server returns a
server owner (eir_server_owner) and server scope (eir_server_scope).
The former field is used in connection with network trunking as
described in Section 7.5. The latter field is used to allow clients
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to determine when client IDs sent by one server may be recognized by
another in the event of file system migration (See Section 17.11.9 of
the current document).
The client ID returned by EXCHANGE_ID is only unique relative to the
combination of eir_server_owner.so_major_id and eir_server_scope.
Thus, if two servers return the same client ID, the onus is on the
client to distinguish the client IDs on the basis of
eir_server_owner.so_major_id and eir_server_scope. In the event two
different servers claim matching server_owner.so_major_id and
eir_server_scope, the client can use the verification techniques
discussed in Section 7.5.1 to determine if the servers are distinct.
If they are distinct, then the client will need to note the
destination network addresses of the connections used with each
server and use the network address as the final discriminator.
The server, as defined by the unique identity expressed in the
so_major_id of the server owner and the server scope, needs to track
several properties of each client ID it hands out. The properties
apply to the client ID and all sessions associated with the client
ID. The properties are derived from the arguments and results of
EXCHANGE_ID. The client ID properties include:
* The capabilities expressed by the following bits, which come from
the results of EXCHANGE_ID:
- EXCHGID4_FLAG_SUPP_MOVED_REFER
- EXCHGID4_FLAG_SUPP_MOVED_MIGR
- EXCHGID4_FLAG_BIND_PRINC_STATEID
- EXCHGID4_FLAG_USE_NON_PNFS
- EXCHGID4_FLAG_USE_PNFS_MDS
- EXCHGID4_FLAG_USE_PNFS_DS
These properties may be updated by subsequent EXCHANGE_ID
operations on confirmed client IDs though the server MAY refuse to
change them.
* The state protection method used, one of SP4_NONE, SP4_MACH_CRED,
or SP4_SSV, as set by the spa_how field of the arguments to
EXCHANGE_ID. Once the client ID is confirmed, this property
cannot be updated by subsequent EXCHANGE_ID operations.
* For SP4_MACH_CRED or SP4_SSV state protection:
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- The list of operations (spo_must_enforce) that MUST use the
specified state protection. This list comes from the results
of EXCHANGE_ID.
- The list of operations (spo_must_allow) that MAY use the
specified state protection. This list comes from the results
of EXCHANGE_ID.
Once the client ID is confirmed, these properties cannot be
updated by subsequent EXCHANGE_ID requests.
* For SP4_SSV protection:
- The OID of the hash algorithm. This property is represented by
one of the algorithms in the ssp_hash_algs field of the
EXCHANGE_ID arguments. Once the client ID is confirmed, this
property cannot be updated by subsequent EXCHANGE_ID requests.
- The OID of the encryption algorithm. This property is
represented by one of the algorithms in the ssp_encr_algs field
of the EXCHANGE_ID arguments. Once the client ID is confirmed,
this property cannot be updated by subsequent EXCHANGE_ID
requests.
- The length of the SSV. This property is represented by the
spi_ssv_len field in the EXCHANGE_ID results. Once the client
ID is confirmed, this property cannot be updated by subsequent
EXCHANGE_ID operations.
There are REQUIRED and RECOMMENDED relationships among the
length of the key of the encryption algorithm ("key length"),
the length of the output of hash algorithm ("hash length"), and
the length of the SSV ("SSV length").
o key length MUST be <= hash length. This is because the keys
used for the encryption algorithm are actually subkeys
derived from the SSV, and the derivation is via the hash
algorithm. The selection of an encryption algorithm with a
key length that exceeded the length of the output of the
hash algorithm would require padding, and thus weaken the
use of the encryption algorithm.
o hash length SHOULD be <= SSV length. This is because the
SSV is a key used to derive subkeys via an HMAC, and it is
recommended that the key used as input to an HMAC be at
least as long as the length of the HMAC's hash algorithm's
output (See Section 3 of [RFC2104]).
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o key length SHOULD be <= SSV length. This is a transitive
result of the above two invariants.
o key length SHOULD be >= hash length / 2. This is because
the subkey derivation is via an HMAC and it is recommended
that if the HMAC has to be truncated, it should not be
truncated to less than half the hash length (See Section 4
of [RFC2104]).
- Number of concurrent versions of the SSV the client and server
will support (See Section 7.9). This property is represented
by spi_window in the EXCHANGE_ID results. The property may be
updated by subsequent EXCHANGE_ID operations.
* The client's implementation ID as represented by the
eia_client_impl_id field of the arguments. The property may be
updated by subsequent EXCHANGE_ID requests.
* The server's implementation ID as represented by the
eir_server_impl_id field of the reply. The property may be
updated by replies to subsequent EXCHANGE_ID requests.
The eia_flags passed as part of the arguments and the eir_flags
results allow the client and server to inform each other of their
capabilities as well as indicate how the client ID will be used.
Whether a bit is set or cleared on the arguments' flags does not
force the server to set or clear the same bit on the results' side.
Bits not defined above cannot be set in the eia_flags field. If they
are, the server MUST reject the operation with NFS4ERR_INVAL.
The EXCHGID4_FLAG_UPD_CONFIRMED_REC_A bit can only be set in
eia_flags; it is always off in eir_flags. The
EXCHGID4_FLAG_CONFIRMED_R bit can only be set in eir_flags; it is
always off in eia_flags. If the server recognizes the co_ownerid and
co_verifier as mapping to a confirmed client ID, it sets
EXCHGID4_FLAG_CONFIRMED_R in eir_flags. The
EXCHGID4_FLAG_CONFIRMED_R flag allows a client to tell if the client
ID it is trying to create already exists and is confirmed.
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set in eia_flags, this means
that the client is attempting to update properties of an existing
confirmed client ID (if the client wants to update properties of an
unconfirmed client ID, it MUST NOT set
EXCHGID4_FLAG_UPD_CONFIRMED_REC_A). If so, it is RECOMMENDED that
the client send the update EXCHANGE_ID operation in the same COMPOUND
as a SEQUENCE so that the EXCHANGE_ID is executed exactly once.
Whether the client can update the properties of client ID depends on
the state protection it selected when the client ID was created, and
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the principal and security flavor it used when sending the
EXCHANGE_ID operation. The situations described in items 6, 7, 8, or
9 of the second numbered list of Section 25.35.4 below will apply.
Note that if the operation succeeds and returns a client ID that is
already confirmed, the server MUST set the EXCHGID4_FLAG_CONFIRMED_R
bit in eir_flags.
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in eia_flags, this
means that the client is trying to establish a new client ID; it is
attempting to trunk data communication to the server (See
Section 7.5); or it is attempting to update properties of an
unconfirmed client ID. The situations described in items 1, 2, 3, 4,
or 5 of the second numbered list of Section 25.35.4 below will apply.
Note that if the operation succeeds and returns a client ID that was
previously confirmed, the server MUST set the
EXCHGID4_FLAG_CONFIRMED_R bit in eir_flags.
When the EXCHGID4_FLAG_SUPP_MOVED_REFER flag bit is set, the client
indicates that it is capable of dealing with an NFS4ERR_MOVED error
as part of a referral sequence. When this bit is not set, it is
still legal for the server to perform a referral sequence. However,
a server may use the fact that the client is incapable of correctly
responding to a referral, by avoiding it for that particular client.
It may, for instance, act as a proxy for that particular file system,
at some cost in performance, although it is not obligated to do so.
If the server will potentially perform a referral, it MUST set
EXCHGID4_FLAG_SUPP_MOVED_REFER in eir_flags.
When the EXCHGID4_FLAG_SUPP_MOVED_MIGR is set, the client indicates
that it is capable of dealing with an NFS4ERR_MOVED error as part of
a file system migration sequence. When this bit is not set, it is
still legal for the server to indicate that a file system has moved,
when this in fact happens. However, a server may use the fact that
the client is incapable of correctly responding to a migration in its
scheduling of file systems to migrate so as to avoid migration of
file systems being actively used. It may also hide actual migrations
from clients unable to deal with them by acting as a proxy for a
migrated file system for particular clients, at some cost in
performance, although it is not obligated to do so. If the server
will potentially perform a migration, it MUST set
EXCHGID4_FLAG_SUPP_MOVED_MIGR in eir_flags.
When EXCHGID4_FLAG_BIND_PRINC_STATEID is set, the client indicates
that it wants the server to bind the stateid to the principal. This
means that when a principal creates a stateid, it has to be the one
to use the stateid. If the server will perform binding, it will
return EXCHGID4_FLAG_BIND_PRINC_STATEID. The server MAY return
EXCHGID4_FLAG_BIND_PRINC_STATEID even if the client does not request
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it. If an update to the client ID changes the value of
EXCHGID4_FLAG_BIND_PRINC_STATEID's client ID property, the effect
applies only to new stateids. Existing stateids (and all stateids
with the same "other" field) that were created with stateid to
principal binding in force will continue to have binding in force.
Existing stateids (and all stateids with the same "other" field) that
were created with stateid to principal not in force will continue to
have binding not in force.
The EXCHGID4_FLAG_USE_NON_PNFS, EXCHGID4_FLAG_USE_PNFS_MDS, and
EXCHGID4_FLAG_USE_PNFS_DS bits are described in Section 20.5 and
convey roles the client ID is to be used for in a pNFS environment.
The server MUST set one of the acceptable combinations of these bits
(roles) in eir_flags, as specified in that section. Note that the
same client owner/server owner pair can have multiple roles.
Multiple roles can be associated with the same client ID or with
different client IDs. Thus, if a client sends EXCHANGE_ID from the
same client owner to the same server owner multiple times, but
specifies different pNFS roles each time, the server might return
different client IDs. Given that different pNFS roles might have
different client IDs, the client may ask for different properties for
each role/client ID.
The spa_how field of the eia_state_protect field specifies how the
client wants to protect its client, locking, and session states from
unauthorized changes (Section 7.8.3):
* SP4_NONE. The client does not request the NFSv4.1 server to
enforce state protection. The NFSv4.1 server MUST NOT enforce
state protection for the returned client ID.
* SP4_MACH_CRED. If spa_how is SP4_MACH_CRED, then the client MUST
send the EXCHANGE_ID operation with RPCSEC_GSS as the security
flavor, and with a service of RPC_GSS_SVC_INTEGRITY or
RPC_GSS_SVC_PRIVACY. If SP4_MACH_CRED is specified, then the
client wants to use an RPCSEC_GSS-based machine credential to
protect its state. The server MUST note the principal the
EXCHANGE_ID operation was sent with, and the GSS mechanism used.
These notes collectively comprise the machine credential.
After the client ID is confirmed, as long as the lease associated
with the client ID is unexpired, a subsequent EXCHANGE_ID
operation that uses the same eia_clientowner.co_owner as the first
EXCHANGE_ID MUST also use the same machine credential as the first
EXCHANGE_ID. The server returns the same client ID for the
subsequent EXCHANGE_ID as that returned from the first
EXCHANGE_ID.
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* SP4_SSV. If spa_how is SP4_SSV, then the client MUST send the
EXCHANGE_ID operation with RPCSEC_GSS as the security flavor, and
with a service of RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY.
If SP4_SSV is specified, then the client wants to use the SSV to
protect its state. The server records the credential used in the
request as the machine credential (as defined above) for the
eia_clientowner.co_owner. The CREATE_SESSION operation that
confirms the client ID MUST use the same machine credential.
When a client specifies SP4_MACH_CRED or SP4_SSV, it also provides
two lists of operations (each expressed as a bitmap). The first list
is spo_must_enforce and consists of those operations the client MUST
send (subject to the server confirming the list of operations in the
result of EXCHANGE_ID) with the machine credential (if SP4_MACH_CRED
protection is specified) or the SSV-based credential (if SP4_SSV
protection is used). The client MUST send the operations with
RPCSEC_GSS credentials that specify the RPC_GSS_SVC_INTEGRITY or
RPC_GSS_SVC_PRIVACY security service. Typically, the first list of
operations includes EXCHANGE_ID, CREATE_SESSION, DELEGPURGE,
DESTROY_SESSION, BIND_CONN_TO_SESSION, and DESTROY_CLIENTID. The
client SHOULD NOT specify in this list any operations that require a
filehandle because the server's access policies MAY conflict with the
client's choice, and thus the client would then be unable to access a
subset of the server's namespace.
Note that if SP4_SSV protection is specified, and the client
indicates that CREATE_SESSION must be protected with SP4_SSV, because
the SSV cannot exist without a confirmed client ID, the first
CREATE_SESSION MUST instead be sent using the machine credential, and
the server MUST accept the machine credential.
There is a corresponding result, also called spo_must_enforce, of the
operations for which the server will require SP4_MACH_CRED or SP4_SSV
protection. Normally, the server's result equals the client's
argument, but the result MAY be different. If the client requests
one or more operations in the set { EXCHANGE_ID, CREATE_SESSION,
DELEGPURGE, DESTROY_SESSION, BIND_CONN_TO_SESSION, DESTROY_CLIENTID
}, then the result spo_must_enforce MUST include the operations the
client requested from that set.
If spo_must_enforce in the results has BIND_CONN_TO_SESSION set, then
connection binding enforcement is enabled, and the client MUST use
the machine (if SP4_MACH_CRED protection is used) or SSV (if SP4_SSV
protection is used) credential on calls to BIND_CONN_TO_SESSION.
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The second list is spo_must_allow and consists of those operations
the client wants to have the option of sending with the machine
credential or the SSV-based credential, even if the object the
operations are performed on is not owned by the machine or SSV
credential.
The corresponding result, also called spo_must_allow, consists of the
operations the server will allow the client to use SP4_SSV or
SP4_MACH_CRED credentials with. Normally, the server's result equals
the client's argument, but the result MAY be different.
The purpose of spo_must_allow is to allow clients to solve the
following conundrum. Suppose the client ID is confirmed with
EXCHGID4_FLAG_BIND_PRINC_STATEID, and it calls OPEN with the
RPCSEC_GSS credentials of a normal user. Now suppose the user's
credentials expire, and cannot be renewed (e.g., a Kerberos ticket
granting ticket expires, and the user has logged off and will not be
acquiring a new ticket granting ticket). The client will be unable
to send CLOSE without the user's credentials, which is to say the
client has to either leave the state on the server or re-send
EXCHANGE_ID with a new verifier to clear all state, that is, unless
the client includes CLOSE on the list of operations in spo_must_allow
and the server agrees.
The SP4_SSV protection parameters also have:
ssp_hash_algs:
This is the set of algorithms the client supports for the purpose
of computing the digests needed for the internal SSV GSS mechanism
and for the SET_SSV operation. Each algorithm is specified as an
object identifier (OID). The REQUIRED algorithms for a server are
id-sha1, id-sha224, id-sha256, id-sha384, and id-sha512 [RFC4055].
Due to known weaknesses in id-sha1, it is RECOMMENDED that the
client specify at least one algorithm within ssp_hash_algs other
than id-sha1.
The algorithm the server selects among the set is indicated in
spi_hash_alg, a field of spr_ssv_prot_info. The field
spi_hash_alg is an index into the array ssp_hash_algs. Because of
known the weaknesses in id-sha1, it is RECOMMENDED that it not be
selected by the server as long as ssp_hash_algs contains any other
supported algorithm.
If the server does not support any of the offered algorithms, it
returns NFS4ERR_HASH_ALG_UNSUPP. If ssp_hash_algs is empty, the
server MUST return NFS4ERR_INVAL.
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ssp_encr_algs:
This is the set of algorithms the client supports for the purpose
of providing privacy protection for the internal SSV GSS
mechanism. Each algorithm is specified as an OID. The REQUIRED
algorithm for a server is id-aes256-CBC. The RECOMMENDED
algorithms are id-aes192-CBC and id-aes128-CBC [CSOR_AES]. The
selected algorithm is returned in spi_encr_alg, an index into
ssp_encr_algs. If the server does not support any of the offered
algorithms, it returns NFS4ERR_ENCR_ALG_UNSUPP. If ssp_encr_algs
is empty, the server MUST return NFS4ERR_INVAL. Note that due to
previously stated requirements and recommendations on the
relationships between key length and hash length, some
combinations of RECOMMENDED and REQUIRED encryption algorithm and
hash algorithm either SHOULD NOT or MUST NOT be used. Table 21
summarizes the illegal and discouraged combinations.
ssp_window:
This is the number of SSV versions the client wants the server to
maintain (i.e., each successful call to SET_SSV produces a new
version of the SSV). If ssp_window is zero, the server MUST
return NFS4ERR_INVAL. The server responds with spi_window, which
MUST NOT exceed ssp_window and MUST be at least one. Any requests
on the backchannel or fore channel that are using a version of the
SSV that is outside the window will fail with an ONC RPC
authentication error, and the requester will have to retry them
with the same slot ID and sequence ID.
ssp_num_gss_handles:
This is the number of RPCSEC_GSS handles the server should create
that are based on the GSS SSV mechanism (See Section 7.9). It is
not the total number of RPCSEC_GSS handles for the client ID.
Indeed, subsequent calls to EXCHANGE_ID will add RPCSEC_GSS
handles. The server responds with a list of handles in
spi_handles. If the client asks for at least one handle and the
server cannot create it, the server MUST return an error. The
handles in spi_handles are not available for use until the client
ID is confirmed, which could be immediately if EXCHANGE_ID returns
EXCHGID4_FLAG_CONFIRMED_R, or upon successful confirmation from
CREATE_SESSION.
While a client ID can span all the connections that are connected
to a server sharing the same eir_server_owner.so_major_id, the
RPCSEC_GSS handles returned in spi_handles can only be used on
connections connected to a server that returns the same the
eir_server_owner.so_major_id and eir_server_owner.so_minor_id on
each connection. It is permissible for the client to set
ssp_num_gss_handles to zero; the client can create more handles
with another EXCHANGE_ID call.
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Because each SSV RPCSEC_GSS handle shares a common SSV GSS
context, there are security considerations specific to this
situation discussed in Section 7.10.
The seq_window (See Section 5.2.3.1 of [RFC2203]) of each
RPCSEC_GSS handle in spi_handle MUST be the same as the seq_window
of the RPCSEC_GSS handle used for the credential of the RPC
request of which the EXCHANGE_ID operation was sent as a part.
+======================+===========================+===============+
| Encryption Algorithm | MUST NOT be combined with | SHOULD NOT be |
| | | combined with |
+======================+===========================+===============+
| id-aes128-CBC | | id-sha384, |
| | | id-sha512 |
+----------------------+---------------------------+---------------+
| id-aes192-CBC | id-sha1 | id-sha512 |
+----------------------+---------------------------+---------------+
| id-aes256-CBC | id-sha1, id-sha224 | |
+----------------------+---------------------------+---------------+
Table 21
The arguments include an array of up to one element in length called
eia_client_impl_id. If eia_client_impl_id is present, it contains
the information identifying the implementation of the client.
Similarly, the results include an array of up to one element in
length called eir_server_impl_id that identifies the implementation
of the server. Servers MUST accept a zero-length eia_client_impl_id
array, and clients MUST accept a zero-length eir_server_impl_id
array.
A possible use for implementation identifiers would be in diagnostic
software that extracts this information in an attempt to identify
interoperability problems, performance workload behaviors, or general
usage statistics. Since the intent of having access to this
information is for planning or general diagnosis only, the client and
server MUST NOT interpret this implementation identity information in
a way that affects how the implementation interacts with its peer.
The client and server are not allowed to depend on the peer's
manifesting a particular allowed behavior based on an implementation
identifier but are required to interoperate as specified elsewhere in
the protocol specification.
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Because it is possible that some implementations might violate the
protocol specification and interpret the identity information,
implementations MUST provide facilities to allow the NFSv4 client and
server to be configured to set the contents of the nfs_impl_id
structures sent to any specified value.
25.35.4. IMPLEMENTATION
A server's client record is a 5-tuple:
1. co_ownerid:
The client identifier string, from the eia_clientowner structure
of the EXCHANGE_ID4args structure.
2. co_verifier:
A client-specific value used to indicate incarnations (where a
client restart represents a new incarnation), from the
eia_clientowner structure of the EXCHANGE_ID4args structure.
3. principal:
The principal that was defined in the RPC header's credential
and/or verifier at the time the client record was established.
4. client ID:
The shorthand client identifier, generated by the server and
returned via the eir_clientid field in the EXCHANGE_ID4resok
structure.
5. confirmed:
A private field on the server indicating whether or not a client
record has been confirmed. A client record is confirmed if there
has been a successful CREATE_SESSION operation to confirm it.
Otherwise, it is unconfirmed. An unconfirmed record is
established by an EXCHANGE_ID call. Any unconfirmed record that
is not confirmed within a lease period SHOULD be removed.
The following identifiers represent special values for the fields in
the records.
ownerid_arg:
The value of the eia_clientowner.co_ownerid subfield of the
EXCHANGE_ID4args structure of the current request.
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verifier_arg:
The value of the eia_clientowner.co_verifier subfield of the
EXCHANGE_ID4args structure of the current request.
old_verifier_arg:
A value of the eia_clientowner.co_verifier field of a client
record received in a previous request; this is distinct from
verifier_arg.
principal_arg:
The value of the RPCSEC_GSS principal for the current request.
old_principal_arg:
A value of the principal of a client record as defined by the RPC
header's credential or verifier of a previous request. This is
distinct from principal_arg.
clientid_ret:
The value of the eir_clientid field the server will return in the
EXCHANGE_ID4resok structure for the current request.
old_clientid_ret:
The value of the eir_clientid field the server returned in the
EXCHANGE_ID4resok structure for a previous request. This is
distinct from clientid_ret.
confirmed:
The client ID has been confirmed.
unconfirmed:
The client ID has not been confirmed.
Since EXCHANGE_ID is a non-idempotent operation, we must consider the
possibility that retries occur as a result of a client restart,
network partition, malfunctioning router, etc. Retries are
identified by the value of the eia_clientowner field of
EXCHANGE_ID4args, and the method for dealing with them is outlined in
the scenarios below.
The scenarios are described in terms of the client record(s) a server
has for a given co_ownerid. Note that if the client ID was created
specifying SP4_SSV state protection and EXCHANGE_ID as the one of the
operations in spo_must_allow, then the server MUST authorize
EXCHANGE_IDs with the SSV principal in addition to the principal that
created the client ID.
1. New Owner ID
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If the server has no client records with
eia_clientowner.co_ownerid matching ownerid_arg, and
EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in the EXCHANGE_ID,
then a new shorthand client ID (let us call it clientid_ret) is
generated, and the following unconfirmed record is added to the
server's state.
{ ownerid_arg, verifier_arg, principal_arg, clientid_ret,
unconfirmed }
Subsequently, the server returns clientid_ret.
2. Non-Update on Existing Client ID
If the server has the following confirmed record, and the request
does not have EXCHGID4_FLAG_UPD_CONFIRMED_REC_A set, then the
request is the result of a retried request due to a faulty router
or lost connection, or the client is trying to determine if it
can perform trunking.
{ ownerid_arg, verifier_arg, principal_arg, clientid_ret,
confirmed }
Since the record has been confirmed, the client must have
received the server's reply from the initial EXCHANGE_ID request.
Since the server has a confirmed record, and since
EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, with the possible
exception of eir_server_owner.so_minor_id, the server returns the
same result it did when the client ID's properties were last
updated (or if never updated, the result when the client ID was
created). The confirmed record is unchanged.
3. Client Collision
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and if the
server has the following confirmed record, then this request is
likely the result of a chance collision between the values of the
eia_clientowner.co_ownerid subfield of EXCHANGE_ID4args for two
different clients.
{ ownerid_arg, *, old_principal_arg, old_clientid_ret, confirmed
}
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If there is currently no state associated with old_clientid_ret,
or if there is state but the lease has expired, then this case is
effectively equivalent to the New Owner ID case of
Section 25.35.4, Paragraph 7, Item 1. The confirmed record is
deleted, the old_clientid_ret and its lock state are deleted, a
new shorthand client ID is generated, and the following
unconfirmed record is added to the server's state.
{ ownerid_arg, verifier_arg, principal_arg, clientid_ret,
unconfirmed }
Subsequently, the server returns clientid_ret.
If old_clientid_ret has an unexpired lease with state, then no
state of old_clientid_ret is changed or deleted. The server
returns NFS4ERR_CLID_INUSE to indicate that the client should
retry with a different value for the eia_clientowner.co_ownerid
subfield of EXCHANGE_ID4args. The client record is not changed.
4. Replacement of Unconfirmed Record
If the EXCHGID4_FLAG_UPD_CONFIRMED_REC_A flag is not set, and the
server has the following unconfirmed record, then the client is
attempting EXCHANGE_ID again on an unconfirmed client ID, perhaps
due to a retry, a client restart before client ID confirmation
(i.e., before CREATE_SESSION was called), or some other reason.
{ ownerid_arg, *, *, old_clientid_ret, unconfirmed }
It is possible that the properties of old_clientid_ret are
different than those specified in the current EXCHANGE_ID.
Whether or not the properties are being updated, to eliminate
ambiguity, the server deletes the unconfirmed record, generates a
new client ID (clientid_ret), and establishes the following
unconfirmed record:
{ ownerid_arg, verifier_arg, principal_arg, clientid_ret,
unconfirmed }
5. Client Restart
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and if the
server has the following confirmed client record, then this
request is likely from a previously confirmed client that has
restarted.
{ ownerid_arg, old_verifier_arg, principal_arg, old_clientid_ret,
confirmed }
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Since the previous incarnation of the same client will no longer
be making requests, once the new client ID is confirmed by
CREATE_SESSION, byte-range locks and share reservations should be
released immediately rather than forcing the new incarnation to
wait for the lease time on the previous incarnation to expire.
Furthermore, session state should be removed since if the client
had maintained that information across restart, this request
would not have been sent. If the server supports neither the
CLAIM_DELEGATE_PREV nor CLAIM_DELEG_PREV_FH claim types,
associated delegations should be purged as well; otherwise,
delegations are retained and recovery proceeds according to
Section 15.2.1.
After processing, clientid_ret is returned to the client and this
client record is added:
{ ownerid_arg, verifier_arg, principal_arg, clientid_ret,
unconfirmed }
The previously described confirmed record continues to exist, and
thus the same ownerid_arg exists in both a confirmed and
unconfirmed state at the same time. The number of states can
collapse to one once the server receives an applicable
CREATE_SESSION or EXCHANGE_ID.
* If the server subsequently receives a successful
CREATE_SESSION that confirms clientid_ret, then the server
atomically destroys the confirmed record and makes the
unconfirmed record confirmed as described in Section 25.36.3.
* If the server instead subsequently receives an EXCHANGE_ID
with the client owner equal to ownerid_arg, one strategy is to
simply delete the unconfirmed record, and process the
EXCHANGE_ID as described in the entirety of Section 25.35.4.
6. Update
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server has
the following confirmed record, then this request is an attempt
at an update.
{ ownerid_arg, verifier_arg, principal_arg, clientid_ret,
confirmed }
Since the record has been confirmed, the client must have
received the server's reply from the initial EXCHANGE_ID request.
The server allows the update, and the client record is left
intact.
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7. Update but No Confirmed Record
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server has
no confirmed record corresponding ownerid_arg, then the server
returns NFS4ERR_NOENT and leaves any unconfirmed record intact.
8. Update but Wrong Verifier
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server has
the following confirmed record, then this request is an illegal
attempt at an update, perhaps because of a retry from a previous
client incarnation.
{ ownerid_arg, old_verifier_arg, *, clientid_ret, confirmed }
The server returns NFS4ERR_NOT_SAME and leaves the client record
intact.
9. Update but Wrong Principal
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server has
the following confirmed record, then this request is an illegal
attempt at an update by an unauthorized principal.
{ ownerid_arg, verifier_arg, old_principal_arg, clientid_ret,
confirmed }
The server returns NFS4ERR_PERM and leaves the client record
intact.
25.36. Operation 43: CREATE_SESSION - Create New Session and Confirm
Client ID
25.36.1. ARGUMENT
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struct channel_attrs4 {
count4 ca_headerpadsize;
count4 ca_maxrequestsize;
count4 ca_maxresponsesize;
count4 ca_maxresponsesize_cached;
count4 ca_maxoperations;
count4 ca_maxrequests;
uint32_t ca_rdma_ird<1>;
};
const CREATE_SESSION4_FLAG_PERSIST = 0x00000001;
const CREATE_SESSION4_FLAG_CONN_BACK_CHAN = 0x00000002;
const CREATE_SESSION4_FLAG_CONN_RDMA = 0x00000004;
struct CREATE_SESSION4args {
clientid4 csa_clientid;
sequenceid4 csa_sequence;
uint32_t csa_flags;
channel_attrs4 csa_fore_chan_attrs;
channel_attrs4 csa_back_chan_attrs;
uint32_t csa_cb_program;
callback_sec_parms4 csa_sec_parms<>;
};
25.36.2. RESULT
struct CREATE_SESSION4resok {
sessionid4 csr_sessionid;
sequenceid4 csr_sequence;
uint32_t csr_flags;
channel_attrs4 csr_fore_chan_attrs;
channel_attrs4 csr_back_chan_attrs;
};
union CREATE_SESSION4res switch (nfsstat4 csr_status) {
case NFS4_OK:
CREATE_SESSION4resok csr_resok4;
default:
void;
};
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25.36.3. DESCRIPTION
This operation is used by the client to create new session objects on
the server.
CREATE_SESSION can be sent with or without a preceding SEQUENCE
operation in the same COMPOUND procedure. If CREATE_SESSION is sent
with a preceding SEQUENCE operation, any session created by
CREATE_SESSION has no direct relation to the session specified in the
SEQUENCE operation, although the two sessions might be associated
with the same client ID. If CREATE_SESSION is sent without a
preceding SEQUENCE, then it MUST be the only operation in the
COMPOUND procedure's request. If it is not, the server MUST return
NFS4ERR_NOT_ONLY_OP.
In addition to creating a session, CREATE_SESSION has the following
effects:
* The first session created with a new client ID serves to confirm
the creation of that client's state on the server. The server
returns the parameter values for the new session.
* The connection CREATE_SESSION that is sent over is associated with
the session's fore channel.
The arguments and results of CREATE_SESSION are described as follows:
csa_clientid: This is the client ID with which the new session will
be associated. The corresponding result is csr_sessionid, the
session ID of the new session.
csa_sequence: Each client ID serializes CREATE_SESSION via a per-
client ID sequence number (see Section 25.36.4). The
corresponding result is csr_sequence, which MUST be equal to
csa_sequence.
In the next three arguments, the client offers a value that is to be
a property of the session. Except where stated otherwise, it is
RECOMMENDED that the server accept the value. If it is not
acceptable, the server MAY use a different value. Regardless, the
server MUST return the value the session will use (which will be
either what the client offered, or what the server is insisting on)
to the client.
csa_flags: The csa_flags field contains a list of the following flag
bits:
CREATE_SESSION4_FLAG_PERSIST:
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If CREATE_SESSION4_FLAG_PERSIST is set, the client wants the
server to provide a persistent reply cache. For sessions in
which only idempotent operations will be used (e.g., a read-
only session), clients SHOULD NOT set
CREATE_SESSION4_FLAG_PERSIST. If the server does not or cannot
provide a persistent reply cache, the server MUST NOT set
CREATE_SESSION4_FLAG_PERSIST in the field csr_flags.
If the server is a pNFS metadata server, for reasons described
in Section 18.7.2 it SHOULD support
CREATE_SESSION4_FLAG_PERSIST if it supports the layout_hint
(Section 11.16.4) attribute.
CREATE_SESSION4_FLAG_CONN_BACK_CHAN:
If CREATE_SESSION4_FLAG_CONN_BACK_CHAN is set in csa_flags, the
client is requesting that the connection over which the
CREATE_SESSION operation arrived be associated with the
session's backchannel in addition to its fore channel. If the
server agrees, it sets CREATE_SESSION4_FLAG_CONN_BACK_CHAN in
the result field csr_flags. If
CREATE_SESSION4_FLAG_CONN_BACK_CHAN is not set in csa_flags,
then CREATE_SESSION4_FLAG_CONN_BACK_CHAN MUST NOT be set in
csr_flags.
CREATE_SESSION4_FLAG_CONN_RDMA:
If CREATE_SESSION4_FLAG_CONN_RDMA is set in csa_flags, and if
the connection over which the CREATE_SESSION operation arrived
is currently in non-RDMA mode but has the capability to operate
in RDMA mode, then the client is requesting that the server
"step up" to RDMA mode on the connection. If the server
agrees, it sets CREATE_SESSION4_FLAG_CONN_RDMA in the result
field csr_flags. If CREATE_SESSION4_FLAG_CONN_RDMA is not set
in csa_flags, then CREATE_SESSION4_FLAG_CONN_RDMA MUST NOT be
set in csr_flags. Note that once the server agrees to step up,
it and the client MUST exchange all future traffic on the
connection with RPC RDMA framing and not Record Marking
([RFC8166]).
csa_fore_chan_attrs, csa_back_chan_attrs: The csa_fore_chan_attrs
and csa_back_chan_attrs fields apply to attributes of the fore
channel (which conveys requests originating from the client to the
server), and the backchannel (the channel that conveys callback
requests originating from the server to the client), respectively.
The results are in corresponding structures called
csr_fore_chan_attrs and csr_back_chan_attrs. The results
establish attributes for each channel, and on all subsequent use
of each channel of the session. Each structure has the following
fields:
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ca_headerpadsize:
The maximum amount of padding the requester is willing to apply
to ensure that write payloads are aligned on some boundary at
the replier. For each channel, the server
* will reply in ca_headerpadsize with its preferred value, or
zero if padding is not in use, and
* MAY decrease this value but MUST NOT increase it.
ca_maxrequestsize:
The maximum size of a COMPOUND or CB_COMPOUND request that will
be sent. This size represents the XDR encoded size of the
request, including the RPC headers (including security flavor
credentials and verifiers) but excludes any RPC transport
framing headers. Imagine a request coming over a non-RDMA TCP/
IP connection, and that it has a single Record Marking header
preceding it. The maximum allowable count encoded in the
header will be ca_maxrequestsize. If a requester sends a
request that exceeds ca_maxrequestsize, the error
NFS4ERR_REQ_TOO_BIG will be returned per the description in
Section 7.6.4. For each channel, the server MAY decrease this
value but MUST NOT increase it.
ca_maxresponsesize:
The maximum size of a COMPOUND or CB_COMPOUND reply that the
requester will accept from the replier including RPC headers
(see the ca_maxrequestsize definition). For each channel, the
server MAY decrease this value, but MUST NOT increase it.
However, if the client selects a value for ca_maxresponsesize
such that a replier on a channel could never send a response,
the server SHOULD return NFS4ERR_TOOSMALL in the CREATE_SESSION
reply. After the session is created, if a requester sends a
request for which the size of the reply would exceed this
value, the replier will return NFS4ERR_REP_TOO_BIG, per the
description in Section 7.6.4.
ca_maxresponsesize_cached:
Like ca_maxresponsesize, but the maximum size of a reply that
will be stored in the reply cache (Section 7.6.1). For each
channel, the server MAY decrease this value, but MUST NOT
increase it. If, in the reply to CREATE_SESSION, the value of
ca_maxresponsesize_cached of a channel is less than the value
of ca_maxresponsesize of the same channel, then this is an
indication to the requester that it needs to be selective about
which replies it directs the replier to cache; for example,
large replies from non-idempotent operations (e.g., COMPOUND
requests with a READ operation) should not be cached. The
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requester decides which replies to cache via an argument to the
SEQUENCE (the sa_cachethis field, see Section 25.46) or
CB_SEQUENCE (the csa_cachethis field, see Section 27.9)
operations. After the session is created, if a requester sends
a request for which the size of the reply would exceed
ca_maxresponsesize_cached, the replier will return
NFS4ERR_REP_TOO_BIG_TO_CACHE, per the description in
Section 7.6.4.
ca_maxoperations:
The maximum number of operations the replier will accept in a
COMPOUND or CB_COMPOUND. For the backchannel, the server MUST
NOT change the value the client offers. For the fore channel,
the server MAY change the requested value. After the session
is created, if a requester sends a COMPOUND or CB_COMPOUND with
more operations than ca_maxoperations, the replier MUST return
NFS4ERR_TOO_MANY_OPS.
ca_maxrequests:
The maximum number of concurrent COMPOUND or CB_COMPOUND
requests the requester will send on the session. Subsequent
requests will each be assigned a slot identifier by the
requester within the range zero to ca_maxrequests - 1
inclusive. For the backchannel, the server MUST NOT change the
value the client offers. For the fore channel, the server MAY
change the requested value.
ca_rdma_ird:
This array has a maximum of one element. If this array has one
element, then the element contains the inbound RDMA read queue
depth (IRD). For each channel, the server MAY decrease this
value, but MUST NOT increase it.
csa_cb_program This is the ONC RPC program number the server MUST
use in any callbacks sent through the backchannel to the client.
The server MUST specify an ONC RPC program number equal to
csa_cb_program and an ONC RPC version number equal to 4 in
callbacks sent to the client. If a CB_COMPOUND is sent to the
client, the server MUST use a minor version number of 1. There is
no corresponding result.
csa_sec_parms The field csa_sec_parms is an array of acceptable
security credentials the server can use on the session's
backchannel. Three security flavors are supported: AUTH_NONE,
AUTH_SYS, and RPCSEC_GSS. If AUTH_NONE is specified for a
credential, then this says the client is authorizing the server to
use AUTH_NONE on all callbacks for the session. If AUTH_SYS is
specified, then the client is authorizing the server to use
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AUTH_SYS on all callbacks, using the credential specified
cbsp_sys_cred. If RPCSEC_GSS is specified, then the server is
allowed to use the RPCSEC_GSS context specified in cbsp_gss_parms
as the RPCSEC_GSS context in the credential of the RPC header of
callbacks to the client. There is no corresponding result.
The RPCSEC_GSS context for the backchannel is specified via a pair
of values of data type gsshandle4_t. The data type gsshandle4_t
represents an RPCSEC_GSS handle, and is precisely the same as the
data type of the "handle" field of the rpc_gss_init_res data type
defined in "Context Creation Response - Successful Acceptance",
Section 5.2.3.1 of [RFC2203].
The first RPCSEC_GSS handle, gcbp_handle_from_server, is the fore
handle the server returned to the client (either in the handle
field of data type rpc_gss_init_res or as one of the elements of
the spi_handles field returned in the reply to EXCHANGE_ID) when
the RPCSEC_GSS context was created on the server. The second
handle, gcbp_handle_from_client, is the back handle to which the
client will map the RPCSEC_GSS context. The server can
immediately use the value of gcbp_handle_from_client in the
RPCSEC_GSS credential in callback RPCs. That is, the value in
gcbp_handle_from_client can be used as the value of the field
"handle" in data type rpc_gss_cred_t (See "Elements of the
RPCSEC_GSS Security Protocol", Section 5 of [RFC2203]) in callback
RPCs. The server MUST use the RPCSEC_GSS security service
specified in gcbp_service, i.e., it MUST set the "service" field
of the rpc_gss_cred_t data type in RPCSEC_GSS credential to the
value of gcbp_service (see "RPC Request Header", Section 5.3.1 of
[RFC2203]).
If the RPCSEC_GSS handle identified by gcbp_handle_from_server
does not exist on the server, the server will return
NFS4ERR_NOENT.
Within each element of csa_sec_parms, the fore and back RPCSEC_GSS
contexts MUST share the same GSS context and MUST have the same
seq_window (See Section 5.2.3.1 of RFC 2203 [RFC2203]). The fore
and back RPCSEC_GSS context state are independent of each other as
far as the RPCSEC_GSS sequence number (See the seq_num field in
the rpc_gss_cred_t data type of Sections 5 and 5.3.1 of
[RFC2203]).
If an RPCSEC_GSS handle is using the SSV context (See
Section 7.9), then because each SSV RPCSEC_GSS handle shares a
common SSV GSS context, there are security considerations specific
to this situation discussed in Section 7.10.
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Once the session is created, the first SEQUENCE or CB_SEQUENCE
received on a slot MUST have a sequence ID equal to 1; if not, the
replier MUST return NFS4ERR_SEQ_MISORDERED.
25.36.4. IMPLEMENTATION
To describe a possible implementation, the same notation for client
records introduced in the description of EXCHANGE_ID is used with the
following addition:
clientid_arg: The value of the csa_clientid field of the
CREATE_SESSION4args structure of the current request.
Since CREATE_SESSION is a non-idempotent operation, we need to
consider the possibility that retries may occur as a result of a
client restart, network partition, malfunctioning router, etc. For
each client ID created by EXCHANGE_ID, the server maintains a
separate reply cache (called the CREATE_SESSION reply cache) similar
to the session reply cache used for SEQUENCE operations, with two
distinctions.
* First, this is a reply cache just for detecting and processing
CREATE_SESSION requests for a given client ID.
* Second, the size of the client ID reply cache is of one slot (and
as a result, the CREATE_SESSION request does not carry a slot
number). This means that at most one CREATE_SESSION request for a
given client ID can be outstanding.
As previously stated, CREATE_SESSION can be sent with or without a
preceding SEQUENCE operation. Even if a SEQUENCE precedes
CREATE_SESSION, the server MUST maintain the CREATE_SESSION reply
cache, which is separate from the reply cache for the session
associated with a SEQUENCE. If CREATE_SESSION was originally sent by
itself, the client MAY send a retry of the CREATE_SESSION operation
within a COMPOUND preceded by a SEQUENCE. If CREATE_SESSION was
originally sent in a COMPOUND that started with a SEQUENCE, then the
client SHOULD send a retry in a COMPOUND that starts with a SEQUENCE
that has the same session ID as the SEQUENCE of the original request.
However, the client MAY send a retry in a COMPOUND that either has no
preceding SEQUENCE, or has a preceding SEQUENCE that refers to a
different session than the original CREATE_SESSION. This might be
necessary if the client sends a CREATE_SESSION in a COMPOUND preceded
by a SEQUENCE with session ID X, and session X no longer exists.
Regardless, any retry of CREATE_SESSION, with or without a preceding
SEQUENCE, MUST use the same value of csa_sequence as the original.
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After the client received a reply to an EXCHANGE_ID operation that
contains a new, unconfirmed client ID, the server expects the client
to follow with a CREATE_SESSION operation to confirm the client ID.
The server expects value of csa_sequenceid in the arguments to that
CREATE_SESSION to be to equal the value of the field eir_sequenceid
that was returned in results of the EXCHANGE_ID that returned the
unconfirmed client ID. Before the server replies to that EXCHANGE_ID
operation, it initializes the client ID slot to be equal to
eir_sequenceid - 1 (accounting for underflow), and records a
contrived CREATE_SESSION result with a "cached" result of
NFS4ERR_SEQ_MISORDERED. With the client ID slot thus initialized,
the processing of the CREATE_SESSION operation is divided into four
phases:
1. Client record look up. The server looks up the client ID in its
client record table. If the server contains no records with
client ID equal to clientid_arg, then most likely the client's
state has been purged during a period of inactivity, possibly due
to a loss of connectivity. NFS4ERR_STALE_CLIENTID is returned,
and no changes are made to any client records on the server.
Otherwise, the server goes to phase 2.
2. Sequence ID processing. If csa_sequenceid is equal to the
sequence ID in the client ID's slot, then this is a replay of the
previous CREATE_SESSION request, and the server returns the
cached result. If csa_sequenceid is not equal to the sequence ID
in the slot, and is more than one greater (accounting for
wraparound), then the server returns the error
NFS4ERR_SEQ_MISORDERED, and does not change the slot. If
csa_sequenceid is equal to the slot's sequence ID + 1 (accounting
for wraparound), then the slot's sequence ID is set to
csa_sequenceid, and the CREATE_SESSION processing goes to the
next phase. A subsequent new CREATE_SESSION call over the same
client ID MUST use a csa_sequenceid that is one greater than the
sequence ID in the slot.
3. Client ID confirmation. If this would be the first session for
the client ID, the CREATE_SESSION operation serves to confirm the
client ID. Otherwise, the client ID confirmation phase is
skipped and only the session creation phase occurs. Any case in
which there is more than one record with identical values for
client ID represents a server implementation error. Operation in
the potential valid cases is summarized as follows.
* Successful Confirmation
If the server has the following unconfirmed record, then
this is the expected confirmation of an unconfirmed record.
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{ ownerid, verifier, principal_arg, clientid_arg,
unconfirmed }
As noted in Section 25.35.4, the server might also have the
following confirmed record.
{ ownerid, old_verifier, principal_arg, old_clientid,
confirmed }
The server schedules the replacement of both records with:
{ ownerid, verifier, principal_arg, clientid_arg, confirmed
}
The processing of CREATE_SESSION continues on to session
creation. Once the session is successfully created, the
scheduled client record replacement is committed. If the
session is not successfully created, then no changes are
made to any client records on the server.
* Unsuccessful Confirmation
If the server has the following record, then the client has
changed principals after the previous EXCHANGE_ID request,
or there has been a chance collision between shorthand
client identifiers.
{ *, *, old_principal_arg, clientid_arg, * }
Neither of these cases is permissible. Processing stops
and NFS4ERR_CLID_INUSE is returned to the client. No
changes are made to any client records on the server.
4. Session creation. The server confirmed the client ID, either in
this CREATE_SESSION operation, or a previous CREATE_SESSION
operation. The server examines the remaining fields of the
arguments.
The server creates the session by recording the parameter values
used (including whether the CREATE_SESSION4_FLAG_PERSIST flag is
set and has been accepted by the server) and allocating space for
the session reply cache (if there is not enough space, the server
returns NFS4ERR_NOSPC). For each slot in the reply cache, the
server sets the sequence ID to zero, and records an entry
containing a COMPOUND reply with zero operations and the error
NFS4ERR_SEQ_MISORDERED. This way, if the first SEQUENCE request
sent has a sequence ID equal to zero, the server can simply
return what is in the reply cache: NFS4ERR_SEQ_MISORDERED. The
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client initializes its reply cache for receiving callbacks in the
same way, and similarly, the first CB_SEQUENCE operation on a
slot after session creation MUST have a sequence ID of one.
If the session state is created successfully, the server
associates the session with the client ID provided by the client.
When a request that had CREATE_SESSION4_FLAG_CONN_RDMA set needs
to be retried, the retry MUST be done on a new connection that is
in non-RDMA mode. If properties of the new connection are
different enough that the arguments to CREATE_SESSION need to
change, then a non-retry MUST be sent. The server will
eventually dispose of any session that was created on the
original connection.
On the backchannel, the client and server might wish to have many
slots, in some cases perhaps more that the fore channel, in order to
deal with the situations where the network link has high latency and
is the primary bottleneck for response to recalls. If so, and if the
client provides too few slots to the backchannel, the server might
limit the number of recallable objects it gives to the client.
Implementing RPCSEC_GSS callback support requires changes to both the
client and server implementations of RPCSEC_GSS. One possible set of
changes includes:
* Adding a data structure that wraps the GSS-API context with a
reference count.
* New functions to increment and decrement the reference count. If
the reference count is decremented to zero, the wrapper data
structure and the GSS-API context it refers to would be freed.
* Change RPCSEC_GSS to create the wrapper data structure upon
receiving GSS-API context from gss_accept_sec_context() and
gss_init_sec_context(). The reference count would be initialized
to 1.
* Adding a function to map an existing RPCSEC_GSS handle to a
pointer to the wrapper data structure. The reference count would
be incremented.
* Adding a function to create a new RPCSEC_GSS handle from a pointer
to the wrapper data structure. The reference count would be
incremented.
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* Replacing calls from RPCSEC_GSS that free GSS-API contexts, with
calls to decrement the reference count on the wrapper data
structure.
25.37. Operation 44: DESTROY_SESSION - Destroy a Session
25.37.1. ARGUMENT
struct DESTROY_SESSION4args {
sessionid4 dsa_sessionid;
};
25.37.2. RESULT
struct DESTROY_SESSION4res {
nfsstat4 dsr_status;
};
25.37.3. DESCRIPTION
The DESTROY_SESSION operation closes the session and discards the
session's reply cache, if any. Any remaining connections associated
with the session are immediately disassociated. If the connection
has no remaining associated sessions, the connection MAY be closed by
the server. Locks, delegations, layouts, wants, and the lease, which
are all tied to the client ID, are not affected by DESTROY_SESSION.
DESTROY_SESSION MUST be invoked on a connection that is associated
with the session being destroyed. In addition, if SP4_MACH_CRED
state protection was specified when the client ID was created, the
RPCSEC_GSS principal that created the session MUST be the one that
destroys the session, using RPCSEC_GSS privacy or integrity. If
SP4_SSV state protection was specified when the client ID was
created, RPCSEC_GSS using the SSV mechanism (Section 7.9) MUST be
used, with integrity or privacy.
If the COMPOUND request starts with SEQUENCE, and if the sessionids
specified in SEQUENCE and DESTROY_SESSION are the same, then
* DESTROY_SESSION MUST be the final operation in the COMPOUND
request.
* It is advisable to avoid placing DESTROY_SESSION in a COMPOUND
request with other state-modifying operations, because the
DESTROY_SESSION will destroy the reply cache.
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* Because the session and its reply cache are destroyed, a client
that retries the request may receive an error in reply to the
retry, even though the original request was successful.
If the COMPOUND request starts with SEQUENCE, and if the sessionids
specified in SEQUENCE and DESTROY_SESSION are different, then
DESTROY_SESSION can appear in any position of the COMPOUND request
(except for the first position). The two sessionids can belong to
different client IDs.
If the COMPOUND request does not start with SEQUENCE, and if
DESTROY_SESSION is not the sole operation, then server MUST return
NFS4ERR_NOT_ONLY_OP.
If there is a backchannel on the session and the server has
outstanding CB_COMPOUND operations for the session which have not
been replied to, then the server MAY refuse to destroy the session
and return an error. If so, then in the event the backchannel is
down, the server SHOULD return NFS4ERR_CB_PATH_DOWN to inform the
client that the backchannel needs to be repaired before the server
will allow the session to be destroyed. Otherwise, the error
NFSERR_BACK_CHAN_BUSY SHOULD be returned to indicate that there are
CB_COMPOUNDs that need to be replied to. The client SHOULD reply to
all outstanding CB_COMPOUNDs before re-sending DESTROY_SESSION.
25.38. Operation 45: FREE_STATEID - Free Stateid with No Locks
25.38.1. ARGUMENT
struct FREE_STATEID4args {
stateid4 fsa_stateid;
};
25.38.2. RESULT
struct FREE_STATEID4res {
nfsstat4 fsr_status;
};
25.38.3. DESCRIPTION
The FREE_STATEID operation is used to free a stateid that no longer
has any associated locks (including opens, byte-range locks,
delegations, and layouts). This may be because of client LOCKU
operations or because of server revocation. If there are valid locks
(of any kind) associated with the stateid in question, the error
NFS4ERR_LOCKS_HELD will be returned, and the associated stateid will
not be freed.
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When a stateid is freed that had been associated with revoked locks,
by sending the FREE_STATEID operation, the client acknowledges the
loss of those locks. This allows the server, once all such revoked
state is acknowledged, to allow that client again to reclaim locks,
without encountering the edge conditions discussed in Section 13.4.2.
Once a successful FREE_STATEID is done for a given stateid, any
subsequent use of that stateid will result in an NFS4ERR_BAD_STATEID
error.
25.39. Operation 46: GET_DIR_DELEGATION - Get a Directory Delegation
25.39.1. ARGUMENT
typedef nfstime4 attr_notice4;
struct GET_DIR_DELEGATION4args {
/* CURRENT_FH: delegated directory */
bool gdda_signal_deleg_avail;
bitmap4 gdda_notification_types;
attr_notice4 gdda_child_attr_delay;
attr_notice4 gdda_dir_attr_delay;
bitmap4 gdda_child_attributes;
bitmap4 gdda_dir_attributes;
};
The values to be set for the following arguments need to set as
described below:
* gdda_child_attr_delay indicate an acceptable delay between an
child attribute change and the sending of a corresponding
notification.
If it is zero, prompt notification is requested. It is likely
that this request will be denied because of the difficulty of
providing such notification in the presence of multiply-linked
files.
If the value is below the value returned in the dirent_notif_delay
attribute the request is ignored and no NOTIFY4_CHILD_ATTR
notifications will be generated.
* gdda_dir_attr_delay indicate an acceptable delay between a
directory attribute change and the sending of a corresponding
notification.
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If it is zero, prompt notification is requested. Not that prompt
notification is always used for attributes tied to directory
content notification. See the description of gdda_dir_attributes
below for details.
* gdda_child_attributes indicates the set of attributes for which
notifications (mostly in the form of NOTIFY4_CHILD_ATTR
notifications) are requested.
Note that a specific set of attributes which are not subject to
change are handled separately. These are creation_time, fileid,
fsid, and file_handle. These attributes, which are not subject to
change, are presented as part of the attributes field of
notify4_entry structure reporting on new and deleted files rather
than in a separate notification as a result of change.
* gdda_dir_attributes indicates the set of attributes for which
notifications (in the form of NOTIFY4_DIR_ATTR notifications) are
requested.
Attributes whose update is inherently tied to content
modifications are treated specially. These include modified_time
and change. These are always delivered promptly, regardless of
the value of gdda_dir_attr_delay.
The generation of notifications for these special attributes is
not controlled by NOTIFY4_DIR_ATTR bit in gdda_notification_types.
Instead they are generated (or not) based on the content
notification to which they would be appended.
25.39.2. RESULT
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struct GET_DIR_DELEGATION4resok {
verifier4 gddr_cookieverf;
/* Stateid for get_dir_delegation */
stateid4 gddr_stateid;
/* Which notifications can the server support */
bitmap4 gddr_notification;
bitmap4 gddr_child_attributes;
bitmap4 gddr_dir_attributes;
};
enum gddrnf4_status {
GDD4_OK = 0,
GDD4_UNAVAIL = 1
};
union GET_DIR_DELEGATION4res_non_fatal
switch (gddrnf4_status gddrnf_status) {
case GDD4_OK:
GET_DIR_DELEGATION4resok gddrnf_resok4;
case GDD4_UNAVAIL:
bool gddrnf_will_signal_deleg_avail;
};
union GET_DIR_DELEGATION4res
switch (nfsstat4 gddr_status) {
case NFS4_OK:
GET_DIR_DELEGATION4res_non_fatal gddr_res_non_fatal4;
default:
void;
};
25.39.3. DESCRIPTION
The GET_DIR_DELEGATION operation is used by a client to request a
directory delegation. The directory is represented by the current
filehandle. The client also specifies whether it wants the server to
notify it when the directory changes in certain ways by setting one
or more bits in a bitmap. The server may refuse to grant the
delegation. In that case, the server will return
NFS4ERR_DIRDELEG_UNAVAIL. If the server decides to hand out the
delegation, it will return a cookie verifier for that directory. If
the cookie verifier changes when the client is holding the
delegation, the delegation will be recalled unless the client has
asked for notification for this event.
The server will also return a directory delegation stateid,
gddr_stateid, as a result of the GET_DIR_DELEGATION operation. This
stateid will appear in callback messages related to the delegation,
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such as notifications and delegation recalls. The client will use
this stateid to return the delegation voluntarily or upon recall. A
delegation is returned by calling the DELEGRETURN operation.
The server might not be able to support notifications of certain
events. If the client asks for such notifications, the server MUST
inform the client of its inability to do so as part of the
GET_DIR_DELEGATION reply by not setting the appropriate bits in the
supported notifications bitmask, gddr_notification, contained in the
reply. The server MUST NOT add bits to gddr_notification that the
client did not request.
The GET_DIR_DELEGATION operation can be used for both normal and
named attribute directories.
If client sets gdda_signal_deleg_avail to TRUE, then it is
registering with the client a "want" for a directory delegation. If
the delegation is not available, and the server supports and will
honor the "want", the results will have
gddrnf_will_signal_deleg_avail set to TRUE and no error will be
indicated on return. If so, the client should expect a future
CB_RECALLABLE_OBJ_AVAIL operation to indicate that a directory
delegation is available. If the server does not wish to honor the
"want" or is not able to do so, it returns the error
NFS4ERR_DIRDELEG_UNAVAIL. If the delegation is immediately
available, the server SHOULD return it with the response to the
operation, rather than via a callback.
When a client makes a request for a directory delegation while it
already holds a directory delegation for that directory (including
the case where it has been recalled but not yet returned by the
client or revoked by the server), the server MUST reply with the
value of gddr_status set to NFS4_OK, the value of gddrnf_status set
to GDD4_UNAVAIL, and the value of gddrnf_will_signal_deleg_avail set
to FALSE. The delegation the client held before the request remains
intact, and its state is unchanged. The current stateid is not
changed (See Section 23.2.3.1.2 for a description of the current
stateid).
25.39.4. IMPLEMENTATION
Directory delegations provide the benefit of improving cache
consistency of namespace information. This is done through
synchronous callbacks. A server must support synchronous callbacks
in order to support directory delegations. In addition to that,
notifications, which can be either synchronous or asynchronous,
provide a way to reduce network traffic as well as improve client
performance under certain conditions.
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The bitmap gdda_notification_types allows the client to request
sending of particular notification types and to inform the server of
other information relevant to the provision of notifications. For
detailed description of the notification, see the appropriate
subsection of Section 27.4. The bits, which are defined in
Section 16.2.5, can be classified as follows:
* Content update notifications can be requested to allow the client
to maintain directory information in accord with that on the
server, despite ongoing changes on the server.
The client can ask for notifications on addition of entries to a
directory (by setting the bit NOTIFY4_ADD_ENTRY), notifications on
entry removal (NOTIFY4_REMOVE_ENTRY), and renames
(NOTIFY4_RENAME_ENTRY).
If a client is interested in directory entry caching or negative
name caching, it can set the gdda_notification_types appropriately
to its particular need and the server will notify it of all
changes that would otherwise invalidate its name cache. The kind
of notification a client asks for may depend on the directory
size, its rate of change, and the applications being used to
access that directory. The enumeration of the conditions under
which a client might ask for a notification is out of the scope of
this specification.
In addition, the client can ask for notification of other sorts of
directory change by setting NOTIFY4_CHANGE_COOKIE_VERIFIER. These
include changes to cookie verifiers, cookies within the directory,
or the order of directory entries.
* The client can ask for notification of attribute changes by
setting either NOTIFY4_CHANGE_DIR_ATTRIBUTE (for changes to
directory attributes) or NOTIFY4_CHANGE_CHILD_ATTRIBUTE (for
change to attributes of objects associated with the entries within
the directory)
For attribute notifications, the client will set bits in the
gdda_dir_attributes bitmap to indicate which attributes it wants
to be notified of. If the server does not support notifications
for changes to a certain attribute, it SHOULD NOT set that
attribute in the supported attribute bitmap specified in the reply
(gddr_dir_attributes). The client will also set in the
gdda_child_attributes bitmap the attributes of directory entries
it wants to be notified of, and the server will indicate in
gddr_child_attributes which attributes of directory entries it
will notify the client of.
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The client will also let the server know if it wants to get the
notification as soon as the attribute change occurs or after a
certain delay by setting a delay factor; gdda_child_attr_delay is
for attribute changes to directory entries and gdda_dir_attr_delay
is for attribute changes to the directory. If this delay factor
is set to zero, that indicates to the server that the client wants
to be notified of any attribute changes as soon as they occur. If
the delay factor is set to N seconds, the server will make a best-
effort guarantee that attribute updates are synchronized within N
seconds. If the client asks for a delay factor that the server
does not support or that may cause significant resource
consumption on the server by causing the server to send a lot of
notifications, the server should not commit to sending out
notifications for attributes and therefore must not set the
appropriate bit in the gddr_child_attributes and
gddr_dir_attributes bitmaps in the response.
* Authorization notifications are use to inform the client of
information useful to determine when the local equivalents of
LOOKUP, READDIR, and GETATTR can be considered authorized with the
use of ACCESS to check for authorization. These notifications are
discussed in Section 16.2.13.
NOTIFY4_CHANGE_AUTH is used to inform the client of a necessary
change in the handling of authorization for the local equivalents
of LOOKUP and READDIR operations. The structure of this
notification is described in Section 27.4.11.
NOTIFY4_CHANGE_AUTH is used to inform the client of a necessary
change in the handling of for the local equivalents of GETATTR
operations. The structure of this notification is described in
Section 27.4.12.
* In addition to requesting particular types of notifications some
of the bits in gdda_notification_types are used as flags to inform
the server of notification-related choices that the client can
make. These include NOTIFY4_GFLAG_EXTEND and NOTIFY4_CFLAG_ORDER.
The bitmap gddr_notification_types allows the server to indicate that
particular notification types will be sent when necessary and to
inform the client of other information useful in connection with the
provision of notifications. The bits, which are defined in
Section 16.2.5, can be classified as follows:
* For bits that have associated notifications, the bit is zero if
that notification was not requested and only set to one if that
notification was requested and the server undertook to send it
when necessary.
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These notifications are discussed in Sections 16.2.11 through
16.2.13.
The client MUST use security policy that the directory or its
applicable ancestor (Section 6.2) is exported with. If not, the
server MUST return NFS4ERR_WRONGSEC to the operation that both
precedes GET_DIR_DELEGATION and sets the current filehandle (See
Section 6.2).
The directory delegation covers all the entries in the directory
except the parent entry. That means if a directory and its parent
both hold directory delegations, any changes to the parent will not
cause a notification to be sent for the child even though the child's
parent entry points to the parent directory.
25.40. Operation 47: GETDEVICEINFO - Get Device Information
25.40.1. ARGUMENT
struct GETDEVICEINFO4args {
deviceid4 gdia_device_id;
layouttype4 gdia_layout_type;
count4 gdia_maxcount;
bitmap4 gdia_notify_types;
};
25.40.2. RESULT
struct GETDEVICEINFO4resok {
device_addr4 gdir_device_addr;
bitmap4 gdir_notification;
};
union GETDEVICEINFO4res switch (nfsstat4 gdir_status) {
case NFS4_OK:
GETDEVICEINFO4resok gdir_resok4;
case NFS4ERR_TOOSMALL:
count4 gdir_mincount;
default:
void;
};
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25.40.3. DESCRIPTION
The GETDEVICEINFO operation returns pNFS storage device address
information for the specified device ID. The client identifies the
device information to be returned by providing the gdia_device_id and
gdia_layout_type that uniquely identify the device. The client
provides gdia_maxcount to limit the number of bytes for the result.
This maximum size represents all of the data being returned within
the GETDEVICEINFO4resok structure and includes the XDR overhead. The
server may return less data. If the server is unable to return any
information within the gdia_maxcount limit, the error
NFS4ERR_TOOSMALL will be returned. However, if gdia_maxcount is
zero, NFS4ERR_TOOSMALL MUST NOT be returned.
The da_layout_type field of the gdir_device_addr returned by the
server MUST be equal to the gdia_layout_type specified by the client.
If it is not equal, the client SHOULD ignore the response as invalid
and behave as if the server returned an error, even if the client
does have support for the layout type returned.
The client also provides a notification bitmap, gdia_notify_types,
for the device ID mapping notification for which it is interested in
receiving; the server must support device ID notifications for the
notification request to have affect. The notification mask is
composed in the same manner as the bitmap for file attributes
(Section 9.3.7). The numbers of bit positions are listed in the
notify_device_type4 enumeration type (Section 27.12). Only two
enumerated values of notify_device_type4 currently apply to
GETDEVICEINFO: NOTIFY_DEVICEID4_CHANGE and NOTIFY_DEVICEID4_DELETE
(See Section 27.12).
The notification bitmap applies only to the specified device ID. If
a client sends a GETDEVICEINFO operation on a deviceID multiple
times, the last notification bitmap is used by the server for
subsequent notifications. If the bitmap is zero or empty, then the
device ID's notifications are turned off.
If the client wants to just update or turn off notifications, it MAY
send a GETDEVICEINFO operation with gdia_maxcount set to zero. In
that event, if the device ID is valid, the reply's da_addr_body field
of the gdir_device_addr field will be of zero length.
If an unknown device ID is given in gdia_device_id, the server
returns NFS4ERR_NOENT. Otherwise, the device address information is
returned in gdir_device_addr. Finally, if the server supports
notifications for device ID mappings, the gdir_notification result
will contain a bitmap of which notifications it will actually send to
the client (via CB_NOTIFY_DEVICEID, see Section 27.12).
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If NFS4ERR_TOOSMALL is returned, the results also contain
gdir_mincount. The value of gdir_mincount represents the minimum
size necessary to obtain the device information.
25.40.4. IMPLEMENTATION
Aside from updating or turning off notifications, another use case
for gdia_maxcount being set to zero is to validate a device ID.
The client SHOULD request a notification for changes or deletion of a
device ID to device address mapping so that the server can allow the
client gracefully use a new mapping, without having pending I/O fail
abruptly, or force layouts using the device ID to be recalled or
revoked.
It is possible that GETDEVICEINFO (and GETDEVICELIST) will race with
CB_NOTIFY_DEVICEID, i.e., CB_NOTIFY_DEVICEID arrives before the
client gets and processes the response to GETDEVICEINFO or
GETDEVICELIST. The analysis of the race leverages the fact that the
server MUST NOT delete a device ID that is referred to by a layout
the client has.
* CB_NOTIFY_DEVICEID deletes a device ID. If the client believes it
has layouts that refer to the device ID, then it is possible that
layouts referring to the deleted device ID have been revoked. The
client should send a TEST_STATEID request using the stateid for
each layout that might have been revoked. If TEST_STATEID
indicates that any layouts have been revoked, the client must
recover from layout revocation as described in Section 18.7.6. If
TEST_STATEID indicates that at least one layout has not been
revoked, the client should send a GETDEVICEINFO operation on the
supposedly deleted device ID to verify that the device ID has been
deleted.
If GETDEVICEINFO indicates that the device ID does not exist, then
the client assumes the server is faulty and recovers by sending an
EXCHANGE_ID operation. If GETDEVICEINFO indicates that the device
ID does exist, then while the server is faulty for sending an
erroneous device ID deletion notification, the degree to which it
is faulty does not require the client to create a new client ID.
If the client does not have layouts that refer to the device ID,
no harm is done. The client should mark the device ID as deleted,
and when GETDEVICEINFO or GETDEVICELIST results are received that
indicate that the device ID has been in fact deleted, the device
ID should be removed from the client's cache.
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* CB_NOTIFY_DEVICEID indicates that a device ID's device addressing
mappings have changed. The client should assume that the results
from the in-progress GETDEVICEINFO will be stale for the device ID
once received, and so it should send another GETDEVICEINFO on the
device ID.
25.41. Operation 48: GETDEVICELIST - Get All Device Mappings for a File
System
25.41.1. ARGUMENT
struct GETDEVICELIST4args {
/* CURRENT_FH: object belonging to the file system */
layouttype4 gdla_layout_type;
/* number of deviceIDs to return */
count4 gdla_maxdevices;
nfs_cookie4 gdla_cookie;
verifier4 gdla_cookieverf;
};
25.41.2. RESULT
struct GETDEVICELIST4resok {
nfs_cookie4 gdlr_cookie;
verifier4 gdlr_cookieverf;
deviceid4 gdlr_deviceid_list<>;
bool gdlr_eof;
};
union GETDEVICELIST4res switch (nfsstat4 gdlr_status) {
case NFS4_OK:
GETDEVICELIST4resok gdlr_resok4;
default:
void;
};
25.41.3. DESCRIPTION
This operation is used by the client to enumerate all of the device
IDs that a server's file system uses.
The client provides a current filehandle of a file object that
belongs to the file system (i.e., all file objects sharing the same
fsid as that of the current filehandle) and the layout type in
gdia_layout_type. Since this operation might require multiple calls
to enumerate all the device IDs (and is thus similar to the READDIR
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(Section 25.23) operation), the client also provides gdia_cookie and
gdia_cookieverf to specify the current cursor position in the list.
When the client wants to read from the beginning of the file system's
device mappings, it sets gdla_cookie to zero. The field
gdla_cookieverf MUST be ignored by the server when gdla_cookie is
zero. The client provides gdla_maxdevices to limit the number of
device IDs in the result. If gdla_maxdevices is zero, the server
MUST return NFS4ERR_INVAL. The server MAY return fewer device IDs.
The successful response to the operation will contain the cookie,
gdlr_cookie, and the cookie verifier, gdlr_cookieverf, to be used on
the subsequent GETDEVICELIST. A gdlr_eof value of TRUE signifies
that there are no remaining entries in the server's device list.
Each element of gdlr_deviceid_list contains a device ID.
25.41.4. IMPLEMENTATION
An example of the use of this operation is for pNFS clients and
servers that use LAYOUT4_BLOCK_VOLUME layouts. In these environments
it may be helpful for a client to determine device accessibility upon
first file system access.
25.42. Operation 49: LAYOUTCOMMIT - Commit Writes Made Using a Layout
25.42.1. ARGUMENT
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union newtime4 switch (bool nt_timechanged) {
case TRUE:
nfstime4 nt_time;
case FALSE:
void;
};
union newoffset4 switch (bool no_newoffset) {
case TRUE:
offset4 no_offset;
case FALSE:
void;
};
struct LAYOUTCOMMIT4args {
/* CURRENT_FH: file */
offset4 loca_offset; /* Unused */
length4 loca_length; /* Unused */
bool loca_reclaim;
stateid4 loca_stateid;
newoffset4 loca_last_write_offset;
newtime4 loca_time_modify;
layoutupdate4 loca_layoutupdate;
};
25.42.2. RESULT
union newsize4 switch (bool ns_sizechanged) {
case TRUE:
length4 ns_size;
case FALSE:
void;
};
struct LAYOUTCOMMIT4resok {
newsize4 locr_newsize;
};
union LAYOUTCOMMIT4res switch (nfsstat4 locr_status) {
case NFS4_OK:
LAYOUTCOMMIT4resok locr_resok4;
default:
void;
};
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25.42.3. DESCRIPTION
The LAYOUTCOMMIT operation commits changes made using the layout
represented by the current filehandle, client ID (derived from the
session ID in the preceding SEQUENCE operation), and stateid.
Because of important differences among layout types in handling of
storage allocation and possible server- coordination facilities, this
operation is inherently layout-type-specific, even though all layout
types share a common function and a core set of parameters. Despite
this shared core, many aspects of the functioning of LAYOUTCOMMIT,
including the circumstances when it is required, are defined by the
specification of the layout type. See Section 19.1.8 for details
relating to places where the layout type specification is referred to
below.
In general, LAYOUTCOMMIT commits the entire layout; layout type-
specific data (loca_layoutupdate) may specify a smaller scope of data
that is to be committed. It is the responsibility of the
specification of the layout type involved to specify the possible
forms an effects of such limits. including any restrictions as to
layouts that need to be held by the client, if these are affected by
limits presented by the layout-type-specific data).
The loca_offset and loca_length arguments are no longer used. The
client should set both loca_offset and loca_length to 0. The server
is to ignore the loca_offset and loca_length arguments. The client
MUST hold the layout designated by loca_stateid, having it previously
been granted via LAYOUTGET (Section 25.43), with an iomode of
LAYOUTIOMODE4_RW. For the case where the client does not hold the
specified layout, the server MUST return the error
NFS4ERR_BAD_LAYOUT. Otherwise, where the specified layout does not
have an iomode of LAYOUTIOMODE4_RW, the server MUST return the error
NFS4ERR_BAD_IOMODE.
The LAYOUTCOMMIT operation indicates that the client has completed
writes using a layout obtained by a previous LAYOUTGET. The client
may have only written a subset of the data range it previously
requested. For layout types for which provisional allocation is
valid, as defined by the layout type specification, LAYOUTCOMMIT
allows it to commit or discard provisionally allocated space and to
update the server with a new end-of-file. The layout referenced by
LAYOUTCOMMIT is still valid after the operation completes and can be
continued to be referenced using the same the client ID, filehandle,
byte-range, layout type, and stateid.
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If the loca_reclaim field is set to TRUE, this indicates that the
client is attempting to commit changes to a layout after the restart
of the metadata server during the metadata server's recovery grace
period (See Section 18.9.4). This type of request may be necessary
when the client has uncommitted writes to provisionally allocated
byte-ranges of a file that were sent to the storage devices before
the restart of the metadata server. In this case, the layout
provided by the client MUST be a subset of a writable layout that the
client held immediately before the restart of the metadata server.
The value of the field loca_stateid MUST be a value that the metadata
server returned before it restarted. The metadata server is free to
accept or reject this request based on its own internal metadata
consistency checks. If the metadata server finds that the layout
provided by the client does not pass its consistency checks, it MUST
reject the request with the status NFS4ERR_RECLAIM_BAD. The
successful completion of the LAYOUTCOMMIT request with loca_reclaim
set to TRUE does NOT provide the client with a layout for the file.
It simply commits the changes to the layout specified in the
loca_layoutupdate field. To obtain a layout for the file, the client
must send a LAYOUTGET request to the server after the server's grace
period has expired. If the metadata server receives a LAYOUTCOMMIT
request with loca_reclaim set to TRUE when the metadata server is not
in its recovery grace period, it MUST reject the request with the
status NFS4ERR_NO_GRACE.
Setting the loca_reclaim field to TRUE is required if and only if the
committed layout was acquired before the metadata server restart. If
the client is committing a layout that was acquired during the
metadata server's grace period, it MUST set the "reclaim" field to
FALSE.
The loca_stateid is a layout stateid value as returned by previously
successful layout operations (See Section 18.7.3).
The loca_last_write_offset field specifies the offset of the last
byte written by the client previous to the LAYOUTCOMMIT. Note that
this value is never equal to the file's size (at most it is one byte
less than the file's size) and MUST be less than or equal to
NFS4_MAXFILEOFF. The metadata server uses this information to
determine whether the file's size needs to be updated. If the
metadata server updates the file's size as the result of the
LAYOUTCOMMIT operation, it must return the new size
(locr_newsize.ns_size) as part of the results.
The loca_time_modify field provide a way for the client to suggest a
modification time it would like the metadata server to set, whether
this facility is allowed is specified by the layout type
specification. The metadata server can, subject to the layout type
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specification, use the suggestion but if not it will use the time of
the LAYOUTCOMMIT operation to set the modification time. If the
metadata server uses the client-provided modification time, it need
to ensure that time does not flow backwards, either immediately or as
a consequence of accepting a time in the future resulting in time
flowing backward once it is set to the time of the LAYOUTCOMMIT
later. In any case, layout type specifications allowing this need to
address issues related to the lack of synchronization of client and
MDS clocks.
The handling of the change attribute is similar, For file systems
that derive the change attribute from the modified time, the same
procedure should be used for modified times deriving from
LAYOUTCOMMIT. In other cases, the same approach used for WRITEs to
the MDS should be followed for LAYOUTCOMMITs.
If the client wants to force the metadata server to set an exact
time, the client should use a SETATTR operation in a COMPOUND right
after LAYOUTCOMMIT. See Section 18.7.4 for more details. If the
client desires the resultant modification time or change attribute,
it should construct the COMPOUND so that a GETATTR follows the
LAYOUTCOMMIT.
The loca_layoutupdate argument to LAYOUTCOMMIT provides a mechanism
for a client to provide layout-specific updates to the metadata
server. For example, the layout update can describe what byte-ranges
of the original layout have been used and what byte-ranges can be
deallocated.
The layout information is more verbose for block devices than for
objects and files because the latter two hide the details of block
allocation behind their storage protocols. At the minimum, the
client needs to communicate changes to the end-of-file location back
to the server, and, if desired, its view of the file's modification
time. For block/volume layouts, it needs to specify precisely which
blocks have been used.
If the layout identified in the arguments does not exist, the error
NFS4ERR_BADLAYOUT is returned. The layout being committed will also
be rejected if it does not correspond to an existing layout with an
iomode of LAYOUTIOMODE4_RW.
On success, the current filehandle retains its value and the current
stateid retains its value.
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25.42.4. IMPLEMENTATION
The client MAY also use LAYOUTCOMMIT with the loca_reclaim field set
to TRUE to convey hints to modified file attributes or to report
layout-type specific information such as I/O errors for object-based
storage layouts, as normally done during normal operation. Doing so
may help the metadata server to recover files more efficiently after
restart. For example, some file system implementations may require
expansive recovery of file system objects if the metadata server does
not get a positive indication from all clients holding a
LAYOUTIOMODE4_RW layout that they have successfully completed all
their writes. Sending a LAYOUTCOMMIT (if required) and then
following with LAYOUTRETURN can provide such an indication and allow
for graceful and efficient recovery.
If loca_reclaim is TRUE, the metadata server is free to either
examine or ignore the value in the field loca_stateid. The metadata
server implementation might or might not encode in its layout stateid
information that allows the metadata server to perform a consistency
check on the LAYOUTCOMMIT request.
25.43. Operation 50: LAYOUTGET - Get Layout Information
25.43.1. ARGUMENT
struct LAYOUTGET4args {
/* CURRENT_FH: file */
bool loga_signal_layout_avail;
layouttype4 loga_layout_type;
layoutiomode4 loga_iomode;
offset4 loga_offset;
length4 loga_length;
length4 loga_minlength;
stateid4 loga_stateid;
count4 loga_maxcount;
};
25.43.2. RESULT
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struct LAYOUTGET4resok {
bool logr_return_on_close;
stateid4 logr_stateid;
layout4 logr_layout<>;
};
union LAYOUTGET4res switch (nfsstat4 logr_status) {
case NFS4_OK:
LAYOUTGET4resok logr_resok4;
case NFS4ERR_LAYOUTTRYLATER:
bool logr_will_signal_layout_avail;
default:
void;
};
25.43.3. DESCRIPTION
The LAYOUTGET operation requests a layout from the metadata server
for reading or writing the file given by the filehandle at the byte-
range specified by offset and length. Layouts are identified by the
client ID (derived from the session ID in the preceding SEQUENCE
operation), current filehandle, layout type (loga_layout_type), and
the layout stateid (loga_stateid). The use of the loga_iomode field
depends upon the layout type, but should reflect the client's data
access intent.
If the metadata server is in a grace period, and does not persist
layouts and device ID to device address mappings, then it MUST return
NFS4ERR_GRACE (See Section 13.4.2.1).
The LAYOUTGET operation returns layout information for the specified
byte-range: a layout. The client actually specifies two ranges, both
starting at the offset in the loga_offset field. The first range is
between loga_offset and loga_offset + loga_length - 1 inclusive.
This range indicates the desired range the client wants the layout to
cover. The second range is between loga_offset and loga_offset +
loga_minlength - 1 inclusive. This range indicates the required
range the client needs the layout to cover. Thus, loga_minlength
MUST be less than or equal to loga_length.
When a length field is set to NFS4_UINT64_MAX, this indicates a
desire (when loga_length is NFS4_UINT64_MAX) or requirement (when
loga_minlength is NFS4_UINT64_MAX) to get a layout from loga_offset
through the end-of-file, regardless of the file's length.
The following rules govern the relationships among, and the minima
of, loga_length, loga_minlength, and loga_offset.
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* If loga_length is less than loga_minlength, the metadata server
MUST return NFS4ERR_INVAL.
* If loga_minlength is zero, this is an indication to the metadata
server that the client desires any layout at offset loga_offset or
less that the metadata server has "readily available". Readily is
subjective, and depends on the layout type and the pNFS server
implementation. For example, some metadata servers might have to
pre-allocate stable storage when they receive a request for a
range of a file that goes beyond the file's current length. If
loga_minlength is zero and loga_length is greater than zero, this
tells the metadata server what range of the layout the client
would prefer to have. If loga_length and loga_minlength are both
zero, then the client is indicating that it desires a layout of
any length with the ending offset of the range no less than the
value specified loga_offset, and the starting offset at or below
loga_offset. If the metadata server does not have a layout that
is readily available, then it MUST return NFS4ERR_LAYOUTTRYLATER.
* If the sum of loga_offset and loga_minlength exceeds
NFS4_UINT64_MAX, and loga_minlength is not NFS4_UINT64_MAX, the
error NFS4ERR_INVAL MUST result.
* If the sum of loga_offset and loga_length exceeds NFS4_UINT64_MAX,
and loga_length is not NFS4_UINT64_MAX, the error NFS4ERR_INVAL
MUST result.
After the metadata server has performed the above checks on
loga_offset, loga_minlength, and loga_offset, the metadata server
MUST return a layout according to the rules in Table 22.
Acceptable layouts based on loga_minlength. Note: u64m =
NFS4_UINT64_MAX; a_off = loga_offset; a_minlen = loga_minlength.
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+===========+============+==========+==========+===================+
| Layout | Layout | Layout | Layout | Layout length of |
| iomode of | a_minlen | iomode | offset | reply |
| request | of request | of reply | of reply | |
+===========+============+==========+==========+===================+
| _READ | u64m | MAY be | MUST be | MUST be >= file |
| | | _READ | <= a_off | length - layout |
| | | | | offset |
+-----------+------------+----------+----------+-------------------+
| _READ | u64m | MAY be | MUST be | MUST be u64m |
| | | _RW | <= a_off | |
+-----------+------------+----------+----------+-------------------+
| _READ | > 0 and < | MAY be | MUST be | MUST be >= |
| | u64m | _READ | <= a_off | MIN(file length, |
| | | | | a_minlen + a_off) |
| | | | | - layout offset |
+-----------+------------+----------+----------+-------------------+
| _READ | > 0 and < | MAY be | MUST be | MUST be >= a_off |
| | u64m | _RW | <= a_off | - layout offset + |
| | | | | a_minlen |
+-----------+------------+----------+----------+-------------------+
| _READ | 0 | MAY be | MUST be | MUST be > 0 |
| | | _READ | <= a_off | |
+-----------+------------+----------+----------+-------------------+
| _READ | 0 | MAY be | MUST be | MUST be > 0 |
| | | _RW | <= a_off | |
+-----------+------------+----------+----------+-------------------+
| _RW | u64m | MUST be | MUST be | MUST be u64m |
| | | _RW | <= a_off | |
+-----------+------------+----------+----------+-------------------+
| _RW | > 0 and < | MUST be | MUST be | MUST be >= a_off |
| | u64m | _RW | <= a_off | - layout offset + |
| | | | | a_minlen |
+-----------+------------+----------+----------+-------------------+
| _RW | 0 | MUST be | MUST be | MUST be > 0 |
| | | _RW | <= a_off | |
+-----------+------------+----------+----------+-------------------+
Table 22
If loga_minlength is not zero and the metadata server cannot return a
layout according to the rules in Table 22, then the metadata server
MUST return the error NFS4ERR_BADLAYOUT. If loga_minlength is zero
and the metadata server cannot or will not return a layout according
to the rules in Table 22, then the metadata server MUST return the
error NFS4ERR_LAYOUTTRYLATER. Assuming that loga_length is greater
than loga_minlength or equal to zero, the metadata server SHOULD
return a layout according to the rules in Table 23.
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Desired layouts based on loga_length. The rules of Table 22 MUST be
applied first. Note: u64m = NFS4_UINT64_MAX; a_off = loga_offset;
a_len = loga_length.
+===============+==========+==========+==========+================+
| Layout iomode | Layout | Layout | Layout | Layout length |
| of request | a_len of | iomode | offset | of reply |
| | request | of reply | of reply | |
+===============+==========+==========+==========+================+
| _READ | u64m | MAY be | MUST be | SHOULD be u64m |
| | | _READ | <= a_off | |
+---------------+----------+----------+----------+----------------+
| _READ | u64m | MAY be | MUST be | SHOULD be u64m |
| | | _RW | <= a_off | |
+---------------+----------+----------+----------+----------------+
| _READ | > 0 and | MAY be | MUST be | SHOULD be >= |
| | < u64m | _READ | <= a_off | a_off - layout |
| | | | | offset + a_len |
+---------------+----------+----------+----------+----------------+
| _READ | > 0 and | MAY be | MUST be | SHOULD be >= |
| | < u64m | _RW | <= a_off | a_off - layout |
| | | | | offset + a_len |
+---------------+----------+----------+----------+----------------+
| _READ | 0 | MAY be | MUST be | SHOULD be > |
| | | _READ | <= a_off | a_off - layout |
| | | | | offset |
+---------------+----------+----------+----------+----------------+
| _READ | 0 | MAY be | MUST be | SHOULD be > |
| | | _READ | <= a_off | a_off - layout |
| | | | | offset |
+---------------+----------+----------+----------+----------------+
| _RW | u64m | MUST be | MUST be | SHOULD be u64m |
| | | _RW | <= a_off | |
+---------------+----------+----------+----------+----------------+
| _RW | > 0 and | MUST be | MUST be | SHOULD be >= |
| | < u64m | _RW | <= a_off | a_off - layout |
| | | | | offset + a_len |
+---------------+----------+----------+----------+----------------+
| _RW | 0 | MUST be | MUST be | SHOULD be > |
| | | _RW | <= a_off | a_off - layout |
| | | | | offset |
+---------------+----------+----------+----------+----------------+
Table 23
The loga_stateid field specifies a valid stateid. If a layout is not
currently held by the client, the loga_stateid field represents a
stateid reflecting the correspondingly valid open, byte-range lock,
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or delegation stateid. Once a layout is held on the file by the
client, the loga_stateid field MUST be a stateid as returned from a
previous LAYOUTGET or LAYOUTRETURN operation or provided by a
CB_LAYOUTRECALL operation (See Section 18.7.3).
The loga_maxcount field specifies the maximum layout size (in bytes)
that the client can handle. If the size of the layout structure
exceeds the size specified by maxcount, the metadata server will
return the NFS4ERR_TOOSMALL error.
The returned layout is expressed as an array, logr_layout, with each
element of type layout4. If a file has a single striping pattern,
then logr_layout SHOULD contain just one entry. Otherwise, if the
requested range overlaps more than one striping pattern, logr_layout
will contain the required number of entries. The elements of
logr_layout MUST be sorted in ascending order of the value of the
lo_offset field of each element. There MUST be no gaps or overlaps
in the range between two successive elements of logr_layout. The
lo_iomode field in each element of logr_layout MUST be the same.
Table 22 and Table 23 both refer to a returned layout iomode, offset,
and length. Because the returned layout is encoded in the
logr_layout array, more description is required.
iomode The value of the returned layout iomode listed in Table 22
and Table 23 is equal to the value of the lo_iomode field in each
element of logr_layout. As shown in Table 22 and Table 23, the
metadata server MAY return a layout with an lo_iomode different
from the requested iomode (field loga_iomode of the request). If
it does so, it MUST ensure that the lo_iomode is more permissive
than the loga_iomode requested. For example, this behavior allows
an implementation to upgrade LAYOUTIOMODE4_READ requests to
LAYOUTIOMODE4_RW requests at its discretion, within the limits of
the layout type specific protocol. A lo_iomode of either
LAYOUTIOMODE4_READ or LAYOUTIOMODE4_RW MUST be returned.
offset The value of the returned layout offset listed in Table 22
and Table 23 is always equal to the lo_offset field of the first
element logr_layout.
length When setting the value of the returned layout length, the
situation is complicated by the possibility that the special
layout length value NFS4_UINT64_MAX is involved. For a
logr_layout array of N elements, the lo_length field in the first
N-1 elements MUST NOT be NFS4_UINT64_MAX. The lo_length field of
the last element of logr_layout can be NFS4_UINT64_MAX under some
conditions as described in the following list.
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* If an applicable rule of Table 22 states that the metadata
server MUST return a layout of length NFS4_UINT64_MAX, then the
lo_length field of the last element of logr_layout MUST be
NFS4_UINT64_MAX.
* If an applicable rule of Table 22 states that the metadata
server MUST NOT return a layout of length NFS4_UINT64_MAX, then
the lo_length field of the last element of logr_layout MUST NOT
be NFS4_UINT64_MAX.
* If an applicable rule of Table 23 states that the metadata
server SHOULD return a layout of length NFS4_UINT64_MAX, then
the lo_length field of the last element of logr_layout SHOULD
be NFS4_UINT64_MAX.
* When the value of the returned layout length of Table 22 and
Table 23 is not NFS4_UINT64_MAX, then the returned layout
length is equal to the sum of the lo_length fields of each
element of logr_layout.
Once a LAYOUTGET operation returns with logr_return_on_close set to
TRUE for a given file, then all subsequent LAYOUTGET requests by that
client for the same file and layout type, MUST reply with
logr_return_on_close set to TRUE until the client returns all its
open state for that file using CLOSE and DELEGRETURN. Note that
return_on_close also applies retroactively to all layout segments
retrieved by the client for that file and layout type.
After the client has closed all open stateids and returned the
delegation stateids for a file for which logr_return_on_close was set
to TRUE, the server MUST invalidate all layout segments that were
issued to the client for that file. The client MUST NOT attempt to
use that layout or the layout stateid.
If the server needs to revoke all open stateids and delegation
stateids owned by the client for a file for which
logr_return_on_close was set to TRUE, then it MUST also revoke all
layout segments of type loga_layout_type that were issued for that
file to that client, and take action to fence the access to the DSes
The logr_stateid stateid is returned to the client for use in
subsequent layout related operations. See Sections 13.2, 18.7.3, and
18.7.5.2 for a further discussion and requirements.
The format of the returned layout (lo_content) is specific to the
layout type. The value of the layout type (lo_content.loc_type) for
each of the elements of the array of layouts returned by the metadata
server (logr_layout) MUST be equal to the loga_layout_type specified
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by the client. If it is not equal, the client SHOULD ignore the
response as invalid and behave as if the metadata server returned an
error, even if the client does have support for the layout type
returned.
If neither the requested file nor its containing file system support
layouts, the metadata server MUST return NFS4ERR_LAYOUTUNAVAILABLE.
If the layout type is not supported, the metadata server MUST return
NFS4ERR_UNKNOWN_LAYOUTTYPE. If layouts are supported but no layout
matches the client provided layout identification, the metadata
server MUST return NFS4ERR_BADLAYOUT. If an invalid loga_iomode is
specified, or a loga_iomode of LAYOUTIOMODE4_ANY is specified, the
metadata server MUST return NFS4ERR_BADIOMODE.
If the layout for the file is unavailable due to transient
conditions, e.g., file sharing prohibits layouts, the metadata server
MUST return NFS4ERR_LAYOUTTRYLATER.
If the layout request is rejected due to an overlapping layout
recall, the metadata server MUST return NFS4ERR_RECALLCONFLICT. See
Section 18.7.5.2 for details.
If the layout conflicts with a mandatory byte-range lock held on the
file, and if the storage devices have no method of enforcing
mandatory locks, other than through the restriction of layouts, the
metadata server SHOULD return NFS4ERR_LOCKED.
If client sets loga_signal_layout_avail to TRUE, then it is
registering with the client a "want" for a layout in the event the
layout cannot be obtained due to resource exhaustion. If the
metadata server supports and will honor the "want", the results will
have logr_will_signal_layout_avail set to TRUE. If so, the client
should expect a CB_RECALLABLE_OBJ_AVAIL operation to indicate that a
layout is available.
On success, the current filehandle retains its value and the current
stateid is updated to match the value as returned in the results.
25.43.4. IMPLEMENTATION
Typically, LAYOUTGET will be called as part of a COMPOUND request
after an OPEN operation and results in the client having location
information for the file. This requires that loga_stateid be set to
the special stateid that tells the metadata server to use the current
stateid, which is set by OPEN (See Section 23.2.3.1.2). A client may
also hold a layout across multiple OPENs. The client specifies a
layout type that limits what kind of layout the metadata server will
return. This prevents metadata servers from granting layouts that
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are unusable by the client.
As indicated by Table 22 and Table 23, the specification of LAYOUTGET
allows a pNFS client and server considerable flexibility. A pNFS
client can take several strategies for sending LAYOUTGET. Some
examples are as follows.
* If LAYOUTGET is preceded by OPEN in the same COMPOUND request and
the OPEN requests OPEN4_SHARE_ACCESS_READ access, the client might
opt to request a _READ layout with loga_offset set to zero,
loga_minlength set to zero, and loga_length set to
NFS4_UINT64_MAX. If the file has space allocated to it, that
space is striped over one or more storage devices, and there is
either no conflicting layout or the concept of a conflicting
layout does not apply to the pNFS server's layout type or
implementation, then the metadata server might return a layout
with a starting offset of zero, and a length equal to the length
of the file, if not NFS4_UINT64_MAX. If the length of the file is
not a multiple of the pNFS server's stripe width (See Section 20.6
for a formal definition), the metadata server might round up the
returned layout's length.
* If LAYOUTGET is preceded by OPEN in the same COMPOUND request, and
the OPEN requests OPEN4_SHARE_ACCESS_WRITE access and does not
truncate the file, the client might opt to request a _RW layout
with loga_offset set to zero, loga_minlength set to zero, and
loga_length set to the file's current length (if known), or
NFS4_UINT64_MAX. As with the previous case, under some conditions
the metadata server might return a layout that covers the entire
length of the file or beyond.
* This strategy is as above, but the OPEN truncates the file. In
this case, the client might anticipate it will be writing to the
file from offset zero, and so loga_offset and loga_minlength are
set to zero, and loga_length is set to the value of
threshold4_write_iosize. The metadata server might return a
layout from offset zero with a length at least as long as
threshold4_write_iosize.
* A process on the client invokes a request to read from offset
10000 for length 50000. The client is using buffered I/O, and has
buffer sizes of 4096 bytes. The client intends to map the request
of the process into a series of READ requests starting at offset
8192. The end offset needs to be higher than 10000 + 50000 =
60000, and the next offset that is a multiple of 4096 is 61440.
The difference between 61440 and that starting offset of the
layout is 53248 (which is the product of 4096 and 15). The value
of threshold4_read_iosize is less than 53248, so the client sends
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a LAYOUTGET request with loga_offset set to 8192, loga_minlength
set to 53248, and loga_length set to the file's length (if known)
minus 8192 or NFS4_UINT64_MAX (if the file's length is not known).
Since this LAYOUTGET request exceeds the metadata server's
threshold, it grants the layout, possibly with an initial offset
of zero, with an end offset of at least 8192 + 53248 - 1 = 61439,
but preferably a layout with an offset aligned on the stripe width
and a length that is a multiple of the stripe width.
* This strategy is as above, but the client is not using buffered I/
O, and instead all internal I/O requests are sent directly to the
server. The LAYOUTGET request has loga_offset equal to 10000 and
loga_minlength set to 50000. The value of loga_length is set to
the length of the file. The metadata server is free to return a
layout that fully overlaps the requested range, with a starting
offset and length aligned on the stripe width.
* Again, a process on the client invokes a request to read from
offset 10000 for length 50000 (i.e. a range with a starting offset
of 10000 and an ending offset of 69999), and buffered I/O is in
use. The client is expecting that the server might not be able to
return the layout for the full I/O range. The client intends to
map the request of the process into a series of thirteen READ
requests starting at offset 8192, each with length 4096, with a
total length of 53248 (which equals 13 * 4096), which fully
contains the range that client's process wants to read. Because
the value of threshold4_read_iosize is equal to 4096, it is
practical and reasonable for the client to use several LAYOUTGET
operations to complete the series of READs. The client sends a
LAYOUTGET request with loga_offset set to 8192, loga_minlength set
to 4096, and loga_length set to 53248 or higher. The server will
grant a layout possibly with an initial offset of zero, with an
end offset of at least 8192 + 4096 - 1 = 12287, but preferably a
layout with an offset aligned on the stripe width and a length
that is a multiple of the stripe width. This will allow the
client to make forward progress, possibly sending more LAYOUTGET
operations for the remainder of the range.
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* An NFS client detects a sequential read pattern, and so sends a
LAYOUTGET operation that goes well beyond any current or pending
read requests to the server. The server might likewise detect
this pattern, and grant the LAYOUTGET request. Once the client
reads from an offset of the file that represents 50% of the way
through the range of the last layout it received, in order to
avoid stalling I/O that would wait for a layout, the client sends
more operations from an offset of the file that represents 50% of
the way through the last layout it received. The client continues
to request layouts with byte-ranges that are well in advance of
the byte-ranges of recent and/or read requests of processes
running on the client.
* This strategy is as above, but the client fails to detect the
pattern, but the server does. The next time the metadata server
gets a LAYOUTGET, it returns a layout with a length that is well
beyond loga_minlength.
* A client is using buffered I/O, and has a long queue of write-
behinds to process and also detects a sequential write pattern.
It sends a LAYOUTGET for a layout that spans the range of the
queued write-behinds and well beyond, including ranges beyond the
filer's current length. The client continues to send LAYOUTGET
operations once the write-behind queue reaches 50% of the maximum
queue length.
Once the client has obtained a layout referring to a particular
device ID, the metadata server MUST NOT delete the device ID until
the layout is returned or revoked.
CB_NOTIFY_DEVICEID can race with LAYOUTGET. One race scenario is
that LAYOUTGET returns a device ID for which the client does not have
device address mappings, and the metadata server sends a
CB_NOTIFY_DEVICEID to add the device ID to the client's awareness and
meanwhile the client sends GETDEVICEINFO on the device ID. This
scenario is discussed in Section 25.40.4. Another scenario is that
the CB_NOTIFY_DEVICEID is processed by the client before it processes
the results from LAYOUTGET. The client will send a GETDEVICEINFO on
the device ID. If the results from GETDEVICEINFO are received before
the client gets results from LAYOUTGET, then there is no longer a
race. If the results from LAYOUTGET are received before the results
from GETDEVICEINFO, the client can either wait for results of
GETDEVICEINFO or send another one to get possibly more up-to-date
device address mappings for the device ID.
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25.44. Operation 51: LAYOUTRETURN - Release Layout Information
25.44.1. ARGUMENT
/* Constants used for LAYOUTRETURN and CB_LAYOUTRECALL */
const LAYOUT4_RET_REC_FILE = 1;
const LAYOUT4_RET_REC_FSID = 2;
const LAYOUT4_RET_REC_ALL = 3;
enum layoutreturn_type4 {
LAYOUTRETURN4_FILE = LAYOUT4_RET_REC_FILE,
LAYOUTRETURN4_FSID = LAYOUT4_RET_REC_FSID,
LAYOUTRETURN4_ALL = LAYOUT4_RET_REC_ALL
};
struct layoutreturn_file4 {
offset4 lrf_offset;
length4 lrf_length;
stateid4 lrf_stateid;
/* layouttype4 specific data */
opaque lrf_body<>;
};
union layoutreturn4 switch(layoutreturn_type4 lr_returntype) {
case LAYOUTRETURN4_FILE:
layoutreturn_file4 lr_layout;
default:
void;
};
struct LAYOUTRETURN4args {
/* CURRENT_FH: file */
bool lora_reclaim;
layouttype4 lora_layout_type;
layoutiomode4 lora_iomode;
layoutreturn4 lora_layoutreturn;
};
25.44.2. RESULT
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union layoutreturn_stateid switch (bool lrs_present) {
case TRUE:
stateid4 lrs_stateid;
case FALSE:
void;
};
union LAYOUTRETURN4res switch (nfsstat4 lorr_status) {
case NFS4_OK:
layoutreturn_stateid lorr_stateid;
default:
void;
};
25.44.3. DESCRIPTION
This operation returns from the client to the server one or more
layouts represented by the client ID (derived from the session ID in
the preceding SEQUENCE operation), lora_layout_type, and lora_iomode.
When lr_returntype is LAYOUTRETURN4_FILE, the returned layout is
further identified by the current filehandle, lrf_offset, lrf_length,
and lrf_stateid. If the lrf_length field is NFS4_UINT64_MAX, all
bytes of the layout, starting at lrf_offset, are returned. When
lr_returntype is LAYOUTRETURN4_FSID, the current filehandle is used
to identify the file system and all layouts matching the client ID,
the fsid of the file system, lora_layout_type, and lora_iomode are
returned. When lr_returntype is LAYOUTRETURN4_ALL, all layouts
matching the client ID, lora_layout_type, and lora_iomode are
returned and the current filehandle is not used. After this call,
the client MUST NOT use the returned layout(s) and the associated
storage protocol to access the file data.
If the set of layouts designated in the case of LAYOUTRETURN4_FSID or
LAYOUTRETURN4_ALL is empty, then no error results. In the case of
LAYOUTRETURN4_FILE, the byte-range specified is returned even if it
is a subdivision of a layout previously obtained with LAYOUTGET, a
combination of multiple layouts previously obtained with LAYOUTGET,
or a combination including some layouts previously obtained with
LAYOUTGET, and one or more subdivisions of such layouts. When the
byte-range does not designate any bytes for which a layout is held
for the specified file, client ID, layout type and mode, no error
results. See Section 18.7.5.3.5 for considerations with "bulk"
return of layouts.
The layout being returned may be a subset or superset of a layout
specified by CB_LAYOUTRECALL. However, if it is a subset, the recall
is not complete until the full recalled scope has been returned.
Recalled scope refers to the byte-range in the case of
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LAYOUTRETURN4_FILE, the use of LAYOUTRETURN4_FSID, or the use of
LAYOUTRETURN4_ALL. There must be a LAYOUTRETURN with a matching
scope to complete the return even if all current layout ranges have
been previously individually returned.
For all lr_returntype values, an iomode of LAYOUTIOMODE4_ANY
specifies that all layouts that match the other arguments to
LAYOUTRETURN (i.e., client ID, lora_layout_type, and one of current
filehandle and range; fsid derived from current filehandle; or
LAYOUTRETURN4_ALL) are being returned.
In the case that lr_returntype is LAYOUTRETURN4_FILE, the lrf_stateid
provided by the client is a layout stateid as returned from previous
layout operations. Note that the "seqid" field of lrf_stateid MUST
NOT be zero. See Sections 13.2, 18.7.3, and 18.7.5.2 for a further
discussion and requirements.
Return of a layout or all layouts does not invalidate the mapping of
storage device ID to a storage device address. The mapping remains
in effect until specifically changed or deleted via device ID
notification callbacks. Of course if there are no remaining layouts
that refer to a previously used device ID, the server is free to
delete a device ID without a notification callback, which will be the
case when notifications are not in effect.
If the lora_reclaim field is set to TRUE, the client is attempting to
return a layout that was acquired before the restart of the metadata
server during the metadata server's grace period. When returning
layouts that were acquired during the metadata server's grace period,
the client MUST set the lora_reclaim field to FALSE. The
lora_reclaim field MUST be set to FALSE also when lr_layoutreturn is
LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL. See LAYOUTCOMMIT
(Section 25.42) for more details.
Layouts may be returned when recalled or voluntarily (i.e., before
the server has recalled them). In either case, the client must
properly propagate state changed under the context of the layout to
the storage device(s) or to the metadata server before returning the
layout.
If the client returns the layout in response to a CB_LAYOUTRECALL
where the lor_recalltype field of the clora_recall field was
LAYOUTRECALL4_FILE, the client should use the lor_stateid value from
CB_LAYOUTRECALL as the value for lrf_stateid. Otherwise, it should
use logr_stateid (from a previous LAYOUTGET result) or lorr_stateid
(from a previous LAYRETURN result). This is done to indicate the
point in time (in terms of layout stateid transitions) when the
recall was sent. The client uses the precise lora_recallstateid
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value and MUST NOT set the stateid's seqid to zero; otherwise,
NFS4ERR_BAD_STATEID MUST be returned. NFS4ERR_OLD_STATEID can be
returned if the client is using an old seqid, and the server knows
the client should not be using the old seqid. For example, the
client uses the seqid on slot 1 of the session, receives the response
with the new seqid, and uses the slot to send another request with
the old seqid.
If a client fails to return a layout in a timely manner, then the
metadata server SHOULD use its control protocol with the storage
devices to fence the client from accessing the data referenced by the
layout. See Section 18.7.5 for more details.
If the LAYOUTRETURN request sets the lora_reclaim field to TRUE after
the metadata server's grace period, NFS4ERR_NO_GRACE is returned.
If the LAYOUTRETURN request sets the lora_reclaim field to TRUE and
lr_returntype is set to LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL,
NFS4ERR_INVAL is returned.
If the client sets the lr_returntype field to LAYOUTRETURN4_FILE,
then the lrs_stateid field will represent the layout stateid as
updated for this operation's processing; the current stateid will
also be updated to match the returned value. If the last byte of any
layout for the current file, client ID, and layout type is being
returned and there are no remaining pending CB_LAYOUTRECALL
operations for which a LAYOUTRETURN operation must be done,
lrs_present MUST be FALSE, and no stateid will be returned. In
addition, the COMPOUND request's current stateid will be set to the
all-zeroes special stateid (See Section 23.2.3.1.2). The server MUST
reject with NFS4ERR_BAD_STATEID any further use of the current
stateid in that COMPOUND until the current stateid is re-established
by a later stateid-returning operation.
On success, the current filehandle retains its value.
If the EXCHGID4_FLAG_BIND_PRINC_STATEID capability is set on the
client ID (See Section 25.35), the server will require that the
principal, security flavor, and if applicable, the GSS mechanism,
combination that acquired the layout also be the one to send
LAYOUTRETURN. This might not be possible if credentials for the
principal are no longer available. The server will allow the machine
credential or SSV credential (See Section 25.35) to send LAYOUTRETURN
if LAYOUTRETURN's operation code was set in the spo_must_allow result
of EXCHANGE_ID.
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25.44.4. IMPLEMENTATION
The final LAYOUTRETURN operation in response to a CB_LAYOUTRECALL
callback MUST be serialized with any outstanding, intersecting
LAYOUTRETURN operations. Note that it is possible that while a
client is returning the layout for some recalled range, the server
may recall a superset of that range (e.g., LAYOUTRECALL4_ALL); the
final return operation for the latter must block until the former
layout recall is done.
Returning all layouts in a file system using LAYOUTRETURN4_FSID is
typically done in response to a CB_LAYOUTRECALL for that file system
as the final return operation. Similarly, LAYOUTRETURN4_ALL is used
in response to a recall callback for all layouts. It is possible
that the client already returned some outstanding layouts via
individual LAYOUTRETURN calls and the call for LAYOUTRETURN4_FSID or
LAYOUTRETURN4_ALL marks the end of the LAYOUTRETURN sequence. See
Section 18.7.3.1 for more details.
Once the client has returned all layouts referring to a particular
device ID, the server MAY delete the device ID.
25.45. Operation 52: SECINFO_NO_NAME - Get Security on Unnamed Object
Although this is a new NFSv4.1 operation and appropriately described
in this document, much of the detail regarding the values returned
and their role in security negotiation is described in Section 16 of
the NFSv4-wide security document, currently
[I-D.dnoveck-nfsv4-security]. This adaptation has been necessary
since connection characteristics are now an appropriate subject of
negotiation, where previously negotiation only concerned the choice
of appropriate auth flavors on existing connection.
25.45.1. ARGUMENT
enum secinfo_style4 {
SECINFO_STYLE4_CURRENT_FH = 0,
SECINFO_STYLE4_PARENT = 1
};
/* CURRENT_FH: object or child directory */
typedef secinfo_style4 SECINFO_NO_NAME4args;
25.45.2. RESULT
/* CURRENTFH: consumed if status is NFS4_OK */
typedef SECINFO4res SECINFO_NO_NAME4res;
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25.45.3. DESCRIPTION
Like the SECINFO operation, SECINFO_NO_NAME is used by the client to
obtain a list of valid RPC authentication flavors and transport
characteristics for a specific file object. Unlike SECINFO,
SECINFO_NO_NAME only works with objects that are accessed by
filehandle.
There are two styles of SECINFO_NO_NAME, as determined by the value
of the secinfo_style4 enumeration. If SECINFO_STYLE4_CURRENT_FH is
passed, then SECINFO_NO_NAME is querying for the required security
for the current filehandle. If SECINFO_STYLE4_PARENT is passed, then
SECINFO_NO_NAME is querying for the required security of the current
filehandle's parent, where the current filehandle MUST be that of
directory (an object of type NF4DIR). If the style selected is
SECINFO_STYLE4_PARENT, then SECINFO should apply the same access
methodology used for LOOKUPP when evaluating the traversal to the
parent directory. Therefore, if the requester does not have the
appropriate access to LOOKUPP the parent, then SECINFO_NO_NAME must
behave the same way and return NFS4ERR_ACCESS.
If PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH returns NFS4ERR_WRONGSEC,
then the client resolves the situation by sending a COMPOUND request
that consists of PUTFH, PUTPUBFH, or PUTROOTFH immediately followed
by SECINFO_NO_NAME, style SECINFO_STYLE4_CURRENT_FH. See Section 6.2
for instructions on dealing with NFS4ERR_WRONGSEC error returns from
PUTFH, PUTROOTFH, PUTPUBFH, or RESTOREFH.
If SECINFO_STYLE4_PARENT is specified and there is no parent
directory, SECINFO_NO_NAME MUST return NFS4ERR_NOENT.
On success, the current filehandle is consumed (See Section 6.2.1.8),
and if the next operation after SECINFO_NO_NAME tries to use the
current filehandle, that operation will fail with the status
NFS4ERR_NOFILEHANDLE.
Everything else about SECINFO_NO_NAME is the same as SECINFO. See
the discussion of SECINFO in Section 12.5 of the NFSv4-wide security
document.
25.45.4. IMPLEMENTATION
See the discussion on SECINFO in Section 12.5.4.2 of the NFSv4-wide
security document, currently [I-D.dnoveck-nfsv4-security].
25.46. Operation 53: SEQUENCE - Supply Per-Procedure Sequencing and
Control
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25.46.1. ARGUMENT
struct SEQUENCE4args {
sessionid4 sa_sessionid;
sequenceid4 sa_sequenceid;
slotid4 sa_slotid;
slotid4 sa_highest_slotid;
bool sa_cachethis;
};
25.46.2. RESULT
const SEQ4_STATUS_CB_PATH_DOWN = 0x00000001;
const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING = 0x00000002;
const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED = 0x00000004;
const SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED = 0x00000008;
const SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED = 0x00000010;
const SEQ4_STATUS_ADMIN_STATE_REVOKED = 0x00000020;
const SEQ4_STATUS_RECALLABLE_STATE_REVOKED = 0x00000040;
const SEQ4_STATUS_LEASE_MOVED = 0x00000080;
const SEQ4_STATUS_RESTART_RECLAIM_NEEDED = 0x00000100;
const SEQ4_STATUS_CB_PATH_DOWN_SESSION = 0x00000200;
const SEQ4_STATUS_BACKCHANNEL_FAULT = 0x00000400;
const SEQ4_STATUS_DEVID_CHANGED = 0x00000800;
const SEQ4_STATUS_DEVID_DELETED = 0x00001000;
struct SEQUENCE4resok {
sessionid4 sr_sessionid;
sequenceid4 sr_sequenceid;
slotid4 sr_slotid;
slotid4 sr_highest_slotid;
slotid4 sr_target_highest_slotid;
uint32_t sr_status_flags;
};
union SEQUENCE4res switch (nfsstat4 sr_status) {
case NFS4_OK:
SEQUENCE4resok sr_resok4;
default:
void;
};
25.46.3. DESCRIPTION
The SEQUENCE operation is used by the server to implement session
request control and the reply cache semantics.
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SEQUENCE MUST appear as the first operation of any COMPOUND in which
it appears. The error NFS4ERR_SEQUENCE_POS will be returned when it
is found in any position in a COMPOUND beyond the first. Operations
other than SEQUENCE, BIND_CONN_TO_SESSION, EXCHANGE_ID,
DESTROY_CLIENTID, CREATE_SESSION, and DESTROY_SESSION, MUST NOT
appear as the first operation in a COMPOUND. Such operations MUST
yield the error NFS4ERR_OP_NOT_IN_SESSION if they do appear at the
start of a COMPOUND.
If SEQUENCE is received on a connection not associated with the
session via CREATE_SESSION or BIND_CONN_TO_SESSION, and connection
association enforcement is enabled (See Section 25.35), then the
server returns NFS4ERR_CONN_NOT_BOUND_TO_SESSION.
The sa_sessionid argument identifies the session to which this
request applies. The sr_sessionid result MUST equal sa_sessionid.
The sa_slotid argument is the index in the reply cache for the
request. The sa_sequenceid field is the sequence number of the
request for the reply cache entry (slot). The sr_slotid result MUST
equal sa_slotid. The sr_sequenceid result MUST equal sa_sequenceid.
The sa_highest_slotid argument is the highest slot ID for which the
client has a request outstanding; it could be equal to sa_slotid.
The server returns two "highest_slotid" values: sr_highest_slotid and
sr_target_highest_slotid. The former is the highest slot ID the
server will accept in future SEQUENCE operation, and SHOULD NOT be
less than the value of sa_highest_slotid (but see Section 7.6.1 for
an exception). The latter is the highest slot ID the server would
prefer the client use on a future SEQUENCE operation.
If sa_cachethis is TRUE, then the client is requesting that the
server cache the entire reply in the server's reply cache; therefore,
the server MUST cache the reply (See Section 7.6.1.3). The server
MAY cache the reply if sa_cachethis is FALSE. If the server does not
cache the entire reply, it MUST still record that it executed the
request at the specified slot and sequence ID.
The response to the SEQUENCE operation contains a word of status
flags (sr_status_flags) that can provide to the client information
related to the status of the client's lock state and communications
paths. Note that any status bits relating to lock state MAY be reset
when lock state is lost due to a server restart (even if the session
is persistent across restarts; session persistence does not imply
lock state persistence) or the establishment of a new client
instance.
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SEQ4_STATUS_CB_PATH_DOWN
When set, indicates that the client has no operational backchannel
path for any session associated with the client ID, making it
necessary for the client to re-establish one. This bit remains
set on all SEQUENCE responses on all sessions associated with the
client ID until at least one backchannel is available on any
session associated with the client ID. If the client fails to re-
establish a backchannel for the client ID, it is subject to having
recallable state revoked.
SEQ4_STATUS_CB_PATH_DOWN_SESSION
When set, indicates that the session has no operational
backchannel. There are two reasons why
SEQ4_STATUS_CB_PATH_DOWN_SESSION may be set and not
SEQ4_STATUS_CB_PATH_DOWN. First is that a callback operation that
applies specifically to the session (e.g., CB_RECALL_SLOT, see
Section 27.8) needs to be sent. Second is that the server did
send a callback operation, but the connection was lost before the
reply. The server cannot be sure whether or not the client
received the callback operation, and so, per rules on request
retry, the server MUST retry the callback operation over the same
session. The SEQ4_STATUS_CB_PATH_DOWN_SESSION bit is the
indication to the client that it needs to associate a connection
to the session's backchannel. This bit remains set on all
SEQUENCE responses of the session until a connection is associated
with the session's a backchannel. If the client fails to re-
establish a backchannel for the session, it is subject to having
recallable state revoked.
SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING
When set, indicates that all GSS contexts or RPCSEC_GSS handles
assigned to the session's backchannel will expire within a period
equal to the lease time. This bit remains set on all SEQUENCE
replies until at least one of the following are true:
* All SSV RPCSEC_GSS handles on the session's backchannel have
been destroyed and all non-SSV GSS contexts have expired.
* At least one more SSV RPCSEC_GSS handle has been added to the
backchannel.
* The expiration time of at least one non-SSV GSS context of an
RPCSEC_GSS handle is beyond the lease period from the current
time (relative to the time of when a SEQUENCE response was
sent)
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SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED
When set, indicates all non-SSV GSS contexts and all SSV
RPCSEC_GSS handles assigned to the session's backchannel have
expired or have been destroyed. This bit remains set on all
SEQUENCE replies until at least one non-expired non-SSV GSS
context for the session's backchannel has been established or at
least one SSV RPCSEC_GSS handle has been assigned to the
backchannel.
SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED
When set, indicates that the lease has expired and as a result the
server released all of the client's locking state. This status
bit remains set on all SEQUENCE replies until the loss of all such
locks has been acknowledged by use of FREE_STATEID (See
Section 25.38), or by establishing a new client instance by
destroying all sessions (via DESTROY_SESSION), the client ID (via
DESTROY_CLIENTID), and then invoking EXCHANGE_ID and
CREATE_SESSION to establish a new client ID.
SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED
When set, indicates that some subset of the client's locks have
been revoked due to expiration of the lease period followed by
another client's conflicting LOCK operation. This status bit
remains set on all SEQUENCE replies until the loss of all such
locks has been acknowledged by use of FREE_STATEID.
SEQ4_STATUS_ADMIN_STATE_REVOKED
When set, indicates that one or more locks have been revoked
without expiration of the lease period, due to administrative
action. This status bit remains set on all SEQUENCE replies until
the loss of all such locks has been acknowledged by use of
FREE_STATEID.
SEQ4_STATUS_RECALLABLE_STATE_REVOKED
When set, indicates that one or more recallable objects have been
revoked without expiration of the lease period, due to the
client's failure to return them when recalled, which may be a
consequence of there being no working backchannel and the client
failing to re-establish a backchannel per the
SEQ4_STATUS_CB_PATH_DOWN, SEQ4_STATUS_CB_PATH_DOWN_SESSION, or
SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED status flags. This status bit
remains set on all SEQUENCE replies until the loss of all such
locks has been acknowledged by use of FREE_STATEID.
SEQ4_STATUS_LEASE_MOVED
When set, indicates that responsibility for lease renewal has been
transferred to one or more new servers. This condition will
continue until the client receives an NFS4ERR_MOVED error and the
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server receives the subsequent GETATTR for the fs_locations or
fs_locations_info attribute for an access to each file system for
which a lease has been moved to a new server. See
Section 17.11.9.2.
SEQ4_STATUS_RESTART_RECLAIM_NEEDED
When set, indicates that due to server restart, the client must
reclaim locking state. Until the client sends a global
RECLAIM_COMPLETE (Section 25.51), every SEQUENCE operation will
return SEQ4_STATUS_RESTART_RECLAIM_NEEDED.
SEQ4_STATUS_BACKCHANNEL_FAULT
The server has encountered an unrecoverable fault with the
backchannel (e.g., it has lost track of the sequence ID for a slot
in the backchannel). The client MUST stop sending more requests
on the session's fore channel, wait for all outstanding requests
to complete on the fore and back channel, and then destroy the
session.
SEQ4_STATUS_DEVID_CHANGED
The client is using device ID notifications and the server has
changed a device ID mapping held by the client. This flag will
stay present until the client has obtained the new mapping with
GETDEVICEINFO.
SEQ4_STATUS_DEVID_DELETED
The client is using device ID notifications and the server has
deleted a device ID mapping held by the client. This flag will
stay in effect until the client sends a GETDEVICEINFO on the
device ID with a null value in the argument gdia_notify_types.
The value of the sa_sequenceid argument relative to the cached
sequence ID on the slot falls into one of three cases.
* If the difference between sa_sequenceid and the server's cached
sequence ID at the slot ID is two (2) or more, or if sa_sequenceid
is less than the cached sequence ID (accounting for wraparound of
the unsigned sequence ID value), then the server MUST return
NFS4ERR_SEQ_MISORDERED.
* If sa_sequenceid and the cached sequence ID are the same, this is
a retry, and the server replies with what is recorded in the reply
cache. The lease is possibly renewed as described below.
* If sa_sequenceid is one greater (accounting for wraparound) than
the cached sequence ID, then this is a new request, and the slot's
sequence ID is incremented. The operations subsequent to
SEQUENCE, if any, are processed. If there are no other
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operations, the only other effects are to cache the SEQUENCE reply
in the slot, maintain the session's activity, and possibly renew
the lease.
If the client reuses a slot ID and sequence ID for a completely
different request, the server MAY treat the request as if it is a
retry of what it has already executed. The server MAY however detect
the client's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.
If SEQUENCE returns an error, then the state of the slot (sequence
ID, cached reply) MUST NOT change, and the associated lease MUST NOT
be renewed.
If SEQUENCE returns NFS4_OK, then the associated lease MUST be
renewed (See Section 13.3), except if
SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED is returned in sr_status_flags.
25.46.4. IMPLEMENTATION
The server MUST maintain a mapping of session ID to client ID in
order to validate any operations that follow SEQUENCE that take a
stateid as an argument and/or result.
If the client establishes a persistent session, then a SEQUENCE
received after a server restart might encounter requests performed
and recorded in a persistent reply cache before the server restart.
In this case, SEQUENCE will be processed successfully, while requests
that were not previously performed and recorded are rejected with
NFS4ERR_DEADSESSION.
Depending on which of the operations within the COMPOUND were
successfully performed before the server restart, these operations
will also have replies sent from the server reply cache. Note that
when these operations establish locking state, it is locking state
that applies to the previous server instance and to the previous
client ID, even though the server restart, which logically happened
after these operations, eliminated that state. In the case of a
partially executed COMPOUND, processing may reach an operation not
processed during the earlier server instance, making this operation a
new one and not performable on the existing session. In this case,
NFS4ERR_DEADSESSION will be returned from that operation.
25.47. Operation 54: SET_SSV - Update SSV for a Client ID
25.47.1. ARGUMENT
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struct ssa_digest_input4 {
SEQUENCE4args sdi_seqargs;
};
struct SET_SSV4args {
opaque ssa_ssv<>;
opaque ssa_digest<>;
};
25.47.2. RESULT
struct ssr_digest_input4 {
SEQUENCE4res sdi_seqres;
};
struct SET_SSV4resok {
opaque ssr_digest<>;
};
union SET_SSV4res switch (nfsstat4 ssr_status) {
case NFS4_OK:
SET_SSV4resok ssr_resok4;
default:
void;
};
25.47.3. DESCRIPTION
This operation is used to update the SSV for a client ID. Before
SET_SSV is called the first time on a client ID, the SSV is zero.
The SSV is the key used for the SSV GSS mechanism (Section 7.9)
SET_SSV MUST be preceded by a SEQUENCE operation in the same
COMPOUND. It MUST NOT be used if the client did not opt for SP4_SSV
state protection when the client ID was created (See Section 25.35);
the server returns NFS4ERR_INVAL in that case.
The field ssa_digest is computed as the output of the HMAC [RFC2104]
using the subkey derived from the SSV4_SUBKEY_MIC_I2T and current SSV
as the key (See Section 7.9 for a description of subkeys), and an XDR
encoded value of data type ssa_digest_input4. The field sdi_seqargs
is equal to the arguments of the SEQUENCE operation for the COMPOUND
procedure that SET_SSV is within.
The argument ssa_ssv is XORed with the current SSV to produce the new
SSV. The argument ssa_ssv SHOULD be generated randomly.
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In the response, ssr_digest is the output of the HMAC using the
subkey derived from SSV4_SUBKEY_MIC_T2I and new SSV as the key, and
an XDR encoded value of data type ssr_digest_input4. The field
sdi_seqres is equal to the results of the SEQUENCE operation for the
COMPOUND procedure that SET_SSV is within.
As noted in Section 25.35, the client and server can maintain
multiple concurrent versions of the SSV. The client and server each
MUST maintain an internal SSV version number, which is set to one the
first time SET_SSV executes on the server and the client receives the
first SET_SSV reply. Each subsequent SET_SSV increases the internal
SSV version number by one. The value of this version number
corresponds to the smpt_ssv_seq, smt_ssv_seq, sspt_ssv_seq, and
ssct_ssv_seq fields of the SSV GSS mechanism tokens (See
Section 7.9).
25.47.4. IMPLEMENTATION
When the server receives ssa_digest, it MUST verify the digest by
computing the digest the same way the client did and comparing it
with ssa_digest. If the server gets a different result, this is an
error, NFS4ERR_BAD_SESSION_DIGEST. This error might be the result of
another SET_SSV from the same client ID changing the SSV. If so, the
client recovers by sending a SET_SSV operation again with a
recomputed digest based on the subkey of the new SSV. If the
transport connection is dropped after the SET_SSV request is sent,
but before the SET_SSV reply is received, then there are special
considerations for recovery if the client has no more connections
associated with sessions associated with the client ID of the SSV.
See Section 25.34.4.
Clients SHOULD NOT send an ssa_ssv that is equal to a previous
ssa_ssv, nor equal to a previous or current SSV (including an ssa_ssv
equal to zero since the SSV is initialized to zero when the client ID
is created).
Clients SHOULD send SET_SSV with RPCSEC_GSS privacy. Servers MUST
support RPCSEC_GSS with privacy for any COMPOUND that has { SEQUENCE,
SET_SSV }.
A client SHOULD NOT send SET_SSV with the SSV GSS mechanism's
credential because the purpose of SET_SSV is to seed the SSV from
non-SSV credentials. Instead, SET_SSV SHOULD be sent with the
credential of a user that is accessing the client ID for the first
time (Section 7.8.3). However, if the client does send SET_SSV with
SSV credentials, the digest protecting the arguments uses the value
of the SSV before ssa_ssv is XORed in, and the digest protecting the
results uses the value of the SSV after the ssa_ssv is XORed in.
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25.48. Operation 55: TEST_STATEID - Test Stateids for Validity
25.48.1. ARGUMENT
struct TEST_STATEID4args {
stateid4 ts_stateids<>;
};
25.48.2. RESULT
struct TEST_STATEID4resok {
nfsstat4 tsr_status_codes<>;
};
union TEST_STATEID4res switch (nfsstat4 tsr_status) {
case NFS4_OK:
TEST_STATEID4resok tsr_resok4;
default:
void;
};
25.48.3. DESCRIPTION
The TEST_STATEID operation is used to check the validity of a set of
stateids. It can be used at any time, but the client should
definitely use it when it receives an indication that one or more of
its stateids have been invalidated due to lock revocation. This
occurs when the SEQUENCE operation returns with one of the following
sr_status_flags set:
* SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED
* SEQ4_STATUS_EXPIRED_ADMIN_STATE_REVOKED
* SEQ4_STATUS_EXPIRED_RECALLABLE_STATE_REVOKED
The client can use TEST_STATEID one or more times to test the
validity of its stateids. Each use of TEST_STATEID allows a large
set of such stateids to be tested and avoids problems with earlier
stateids in a COMPOUND request from interfering with the checking of
subsequent stateids, as would happen if individual stateids were
tested by a series of corresponding by operations in a COMPOUND
request.
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For each stateid, the server returns the status code that would be
returned if that stateid were to be used in normal operation.
Returning such a status indication is not an error and does not cause
COMPOUND processing to terminate. Checks for the validity of the
stateid proceed as they would for normal operations with a number of
exceptions:
* There is no check for the type of stateid object, as would be the
case for normal use of a stateid.
* There is no reference to the current filehandle.
* Special stateids are always considered invalid (they result in the
error code NFS4ERR_BAD_STATEID).
All stateids are interpreted as being associated with the client for
the current session. Any possible association with a previous
instance of the client (as stale stateids) is not considered.
The valid status values in the returned status_code array are
NFS4ERR_OK, NFS4ERR_BAD_STATEID, NFS4ERR_OLD_STATEID,
NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, and NFS4ERR_DELEG_REVOKED.
25.48.4. IMPLEMENTATION
See Sections 13.2.2 and 13.2.4 for a discussion of stateid structure,
lifetime, and validation.
25.49. Operation 56: WANT_DELEGATION - Request Delegation
25.49.1. ARGUMENT
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union deleg_claim4 switch (open_claim_type4 dc_claim) {
/*
* No special rights to object. Ordinary delegation
* request of the specified object. Object identified
* by filehandle.
*/
case CLAIM_FH: /* new to v4.1 */
/* CURRENT_FH: object being delegated */
void;
/*
* Right to file based on a delegation granted
* to a previous boot instance of the client.
* File is specified by filehandle.
*/
case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
/* CURRENT_FH: object being delegated */
void;
/*
* Right to the file established by an open previous
* to server reboot. File identified by filehandle.
* Used during server reclaim grace period.
*/
case CLAIM_PREVIOUS:
/* CURRENT_FH: object being reclaimed */
open_delegation_type4 dc_delegate_type;
};
struct WANT_DELEGATION4args {
uint32_t wda_want;
deleg_claim4 wda_claim;
};
25.49.2. RESULT
union WANT_DELEGATION4res switch (nfsstat4 wdr_status) {
case NFS4_OK:
open_delegation4 wdr_resok4;
default:
void;
};
25.49.3. DESCRIPTION
Where this description mandates the return of a specific error code
for a specific condition, and where multiple conditions apply, the
server MAY return any of the mandated error codes.
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This operation allows a client to:
* Get a delegation on all types of files except directories.
* Register a "want" for a delegation for the specified file object,
and be notified via a callback when the delegation is available.
The server MAY support notifications of availability via
callbacks. If the server does not support registration of wants,
it MUST NOT return an error to indicate that, and instead MUST
return with ond_why set to WND4_CONTENTION or WND4_RESOURCE and
ond_server_will_push_deleg or ond_server_will_signal_avail set to
FALSE. When the server indicates that it will notify the client
by means of a callback, it will either provide the delegation
using a CB_PUSH_DELEG operation or cancel its promise by sending a
CB_WANTS_CANCELLED operation.
* Cancel a want for a delegation.
The client SHOULD NOT set OPEN4_SHARE_ACCESS_READ and SHOULD NOT set
OPEN4_SHARE_ACCESS_WRITE in wda_want. If it does, the server MUST
ignore them.
The meanings of the following flags in wda_want are the same as they
are in OPEN, except as noted below.
* OPEN4_SHARE_ACCESS_WANT_READ_DELEG
* OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
* OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
* OPEN4_SHARE_ACCESS_WANT_NO_DELEG. Unlike the OPEN operation, this
flag SHOULD NOT be set by the client in the arguments to
WANT_DELEGATION, and MUST be ignored by the server.
* OPEN4_SHARE_ACCESS_WANT_CANCEL
* OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
* OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
The handling of the above flags in WANT_DELEGATION is the same as in
OPEN. Information about the delegation and/or the promises the
server is making regarding future callbacks are the same as those
described in the open_delegation4 structure.
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The successful results of WANT_DELEGATION are of data type
open_delegation4, which is the same data type as the "delegation"
field in the results of the OPEN operation (See Section 25.16.3).
The server constructs wdr_resok4 the same way it constructs OPEN's
"delegation" with one difference: WANT_DELEGATION MUST NOT return a
delegation type of OPEN_DELEGATE_NONE.
If ((wda_want & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) &
~OPEN4_SHARE_ACCESS_WANT_NO_DELEG) is zero, then the client is
indicating no explicit desire or non-desire for a delegation and the
server MUST return NFS4ERR_INVAL.
The client uses the OPEN4_SHARE_ACCESS_WANT_CANCEL flag in the
WANT_DELEGATION operation to cancel a previously requested want for a
delegation. Note that if the server is in the process of sending the
delegation (via CB_PUSH_DELEG) at the time the client sends a
cancellation of the want, the delegation might still be pushed to the
client.
If WANT_DELEGATION fails to return a delegation, and the server
returns NFS4_OK, the server MUST set the delegation type to
OPEN4_DELEGATE_NONE_EXT, and set od_whynone, as described in
Section 25.16. Write delegations are not available for file types
that are not writable. This includes file objects of types NF4BLK,
NF4CHR, NF4LNK, NF4SOCK, and NF4FIFO. If the client requests
OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG without
OPEN4_SHARE_ACCESS_WANT_READ_DELEG on an object with one of the
aforementioned file types, the server must set
wdr_resok4.od_whynone.ond_why to WND4_WRITE_DELEG_NOT_SUPP_FTYPE.
25.49.4. IMPLEMENTATION
A request for a conflicting delegation is not normally intended to
trigger the recall of the existing delegation. Servers may choose to
treat some clients as having higher priority such that their wants
will trigger recall of an existing delegation, although that is
expected to be an unusual situation.
Servers will generally recall delegations assigned by WANT_DELEGATION
on the same basis as those assigned by OPEN. CB_RECALL will
generally be done only when other clients perform operations
inconsistent with the delegation. The normal response to aging of
delegations is to use CB_RECALL_ANY, in order to give the client the
opportunity to keep the delegations most useful from its point of
view.
25.50. Operation 57: DESTROY_CLIENTID - Destroy a Client ID
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25.50.1. ARGUMENT
struct DESTROY_CLIENTID4args {
clientid4 dca_clientid;
};
25.50.2. RESULT
struct DESTROY_CLIENTID4res {
nfsstat4 dcr_status;
};
25.50.3. DESCRIPTION
The DESTROY_CLIENTID operation destroys the client ID. If there are
sessions (both idle and non-idle), opens, locks, delegations, and/or
wants (Section 25.49) associated with the unexpired lease of the
client ID, the server MUST return NFS4ERR_CLIENTID_BUSY.
DESTROY_CLIENTID MAY be preceded with a SEQUENCE operation as long as
the client ID derived from the session ID of SEQUENCE is not the same
as the client ID to be destroyed. If the client IDs are the same,
then the server MUST return NFS4ERR_CLIENTID_BUSY.
If DESTROY_CLIENTID is not prefixed by SEQUENCE, it MUST be the only
operation in the COMPOUND request (otherwise, the server MUST return
NFS4ERR_NOT_ONLY_OP). If the operation is sent without a SEQUENCE
preceding it, a client that retransmits the request may receive an
error in response, because the original request might have been
successfully executed.
25.50.4. IMPLEMENTATION
DESTROY_CLIENTID allows a server to immediately reclaim the resources
consumed by an unused client ID, and also to forget that it ever
generated the client ID. By forgetting that it ever generated the
client ID, the server can safely reuse the client ID on a future
EXCHANGE_ID operation.
25.51. Operation 58: RECLAIM_COMPLETE - Indicates Reclaims Finished
25.51.1. ARGUMENT
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struct RECLAIM_COMPLETE4args {
/*
* If rca_one_fs TRUE,
*
* CURRENT_FH: object in
* file system reclaim is
* complete for.
*/
bool rca_one_fs;
};
25.51.2. RESULTS
struct RECLAIM_COMPLETE4res {
nfsstat4 rcr_status;
};
25.51.3. DESCRIPTION
A RECLAIM_COMPLETE operation is used to indicate that the client has
reclaimed all of the locking state that it will recover using
reclaim-type operation used to re-establish locking state during a
server grace period. It is not used in connection with the special
delegation recovery period used after client restart.
It does so when it is recovering state due to either a server restart
or the migration of a file system to another server. There are two
types of RECLAIM_COMPLETE operations:
* When rca_one_fs is FALSE, a global RECLAIM_COMPLETE is being done.
This indicates that recovery of all locks that the client held on
the previous server instance has been completed. The current
filehandle need not be set in this case.
* When rca_one_fs is TRUE, a file system-specific RECLAIM_COMPLETE
is being done. This indicates that recovery of locks for a single
fs (the one designated by the current filehandle) due to the
migration of the file system has been completed. Presence of a
current filehandle is required when rca_one_fs is set to TRUE.
When the current filehandle designates a filehandle in a file
system not in the process of migration, the operation returns
NFS4_OK and is otherwise ignored.
Once a RECLAIM_COMPLETE is done, there can be no further reclaim
operations for locks whose scope is defined as having completed
recovery. Once the client sends RECLAIM_COMPLETE, the server will
not allow the client to do subsequent reclaims of locking state for
that scope and, if these are attempted, will return NFS4ERR_NO_GRACE.
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Whenever a client establishes a new client ID as a result of one of
server restart and before it does the first non-reclaim operation
that obtains a lock, it MUST send a RECLAIM_COMPLETE with rca_one_fs
set to FALSE, even if there are no locks to reclaim. If non-reclaim
locking operations are done before the RECLAIM_COMPLETE, an
NFS4ERR_GRACE error will be returned.
Similarly, when the client accesses a migrated file system on a new
server, before it sends the first non-reclaim operation that obtains
a lock on this new server, it MUST send a RECLAIM_COMPLETE with
rca_one_fs set to TRUE and current filehandle within that file
system, even if there are no locks to reclaim. If non-reclaim
locking operations are done on that file system before the
RECLAIM_COMPLETE, an NFS4ERR_GRACE error will be returned.
It should be noted that there are situations in which a client needs
to issue both forms of RECLAIM_COMPLETE. An example is an instance
of file system migration in which the file system is migrated to a
server for which the client has no clientid. As a result, the client
needs to obtain a clientid from the server (incurring the
responsibility to do RECLAIM_COMPLETE with rca_one_fs set to FALSE)
as well as RECLAIM_COMPLETE with rca_one_fs set to TRUE to complete
the per-fs grace period associated with the file system migration.
These two may be done in any order as long as all necessary lock
reclaims have been done before issuing either of them.
Any locks not reclaimed at the point at which RECLAIM_COMPLETE is
done become non-reclaimable. The client MUST NOT attempt to reclaim
them, either during the current server instance or in any subsequent
server instance, or on another server to which responsibility for
that file system is transferred. If the client were to do so, it
would be violating the protocol by representing itself as owning
locks that it does not own, and so has no right to reclaim. See
Section 8.4.3 of [RFC5661] for a discussion of edge conditions
related to lock reclaim.
By sending a RECLAIM_COMPLETE, the client indicates readiness to
proceed to do normal non-reclaim locking operations. The client
should be aware that such operations may temporarily result in
NFS4ERR_GRACE errors until the server is ready to terminate its grace
period.
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25.51.4. IMPLEMENTATION
Servers will typically use the information as to when reclaim
activity is complete to reduce the length of the grace period. When
the server maintains in persistent storage a list of clients that
might have had locks, it is able to use the fact that all such
clients have done a RECLAIM_COMPLETE to terminate the grace period
and begin normal operations (i.e., grant requests for new locks)
sooner than it might otherwise.
Latency can be minimized by doing a RECLAIM_COMPLETE as part of the
COMPOUND request in which the last lock-reclaiming operation is done.
When there are no reclaims to be done, RECLAIM_COMPLETE should be
done immediately in order to allow the grace period to end as soon as
possible.
RECLAIM_COMPLETE should only be done once for each server instance or
occasion of the transition of a file system. If it is done a second
time, the error NFS4ERR_COMPLETE_ALREADY will result. Note that
because of the session feature's retry protection, retries of
COMPOUND requests containing RECLAIM_COMPLETE operation will not
result in this error.
When a RECLAIM_COMPLETE is sent, the client effectively acknowledges
any locks not yet reclaimed as lost. This allows the server to re-
enable the client to recover locks if the occurrence of edge
conditions, as described in Section 13.4.3, had caused the server to
disable the client's ability to recover locks.
Because previous descriptions of RECLAIM_COMPLETE were not
sufficiently explicit about the circumstances in which use of
RECLAIM_COMPLETE with rca_one_fs set to TRUE was appropriate, there
have been cases in which it has been misused by clients who have
issued RECLAIM_COMPLETE with rca_one_fs set to TRUE when it should
have not been. There have also been cases in which servers have, in
various ways, not responded to such misuse as described above, either
ignoring the rca_one_fs setting (treating the operation as a global
RECLAIM_COMPLETE) or ignoring the entire operation.
While clients SHOULD NOT misuse this feature, and servers SHOULD
respond to such misuse as described above, implementers need to be
aware of the following considerations as they make necessary trade-
offs between interoperability with existing implementations and
proper support for facilities to allow lock recovery in the event of
file system migration.
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* When servers have no support for becoming the destination server
of a file system subject to migration, there is no possibility of
a per-fs RECLAIM_COMPLETE being done legitimately, and occurrences
of it SHOULD be ignored. However, the negative consequences of
accepting such mistaken use are quite limited as long as the
client does not issue it before all necessary reclaims are done.
* When a server might become the destination for a file system being
migrated, inappropriate use of per-fs RECLAIM_COMPLETE is more
concerning. In the case in which the file system designated is
not within a per-fs grace period, the per-fs RECLAIM_COMPLETE
SHOULD be ignored, with the negative consequences of accepting it
being limited, as in the case in which migration is not supported.
However, if the server encounters a file system undergoing
migration, the operation cannot be accepted as if it were a global
RECLAIM_COMPLETE without invalidating its intended use.
25.52. Operation 10044: ILLEGAL - Illegal Operation
25.52.1. ARGUMENTS
void;
25.52.2. RESULTS
struct ILLEGAL4res {
nfsstat4 status;
};
25.52.3. DESCRIPTION
This operation is a placeholder for encoding a result to handle the
case of the client sending an operation code within COMPOUND that is
not supported. See the COMPOUND procedure description for more
details.
The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
25.52.4. IMPLEMENTATION
A client will probably not send an operation with code OP_ILLEGAL but
if it does, the response will be ILLEGAL4res just as it would be with
any other invalid operation code. Note that if the server gets an
illegal operation code that is not OP_ILLEGAL, and if the server
checks for legal operation codes during the XDR decode phase, then
the ILLEGAL4res would not be returned.
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26. NFSv4.1 Callback Procedures
The procedures used for callbacks are defined in the following
sections. In the interest of clarity, the terms "client" and
"server" refer to NFS clients and servers, despite the fact that for
an individual callback RPC, the sense of these terms would be
precisely the opposite.
Both procedures, CB_NULL and CB_COMPOUND, MUST be implemented.
26.1. Procedure 0: CB_NULL - No Operation
26.1.1. ARGUMENTS
void;
26.1.2. RESULTS
void;
26.1.3. DESCRIPTION
CB_NULL is the standard ONC RPC NULL procedure, with the standard
void argument and void response. Even though there is no direct
functionality associated with this procedure, the server will use
CB_NULL to confirm the existence of a path for RPCs from the server
to client.
26.1.4. ERRORS
None.
26.2. Procedure 1: CB_COMPOUND - Compound Operations
26.2.1. ARGUMENTS
enum nfs_cb_opnum4 {
OP_CB_GETATTR = 3,
OP_CB_RECALL = 4,
/* Callback operations new to NFSv4.1 */
OP_CB_LAYOUTRECALL = 5,
OP_CB_NOTIFY = 6,
OP_CB_PUSH_DELEG = 7,
OP_CB_RECALL_ANY = 8,
OP_CB_RECALLABLE_OBJ_AVAIL = 9,
OP_CB_RECALL_SLOT = 10,
OP_CB_SEQUENCE = 11,
OP_CB_WANTS_CANCELLED = 12,
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OP_CB_NOTIFY_LOCK = 13,
OP_CB_NOTIFY_DEVICEID = 14,
OP_CB_ILLEGAL = 10044
};
union nfs_cb_argop4 switch (unsigned argop) {
case OP_CB_GETATTR:
CB_GETATTR4args opcbgetattr;
case OP_CB_RECALL:
CB_RECALL4args opcbrecall;
case OP_CB_LAYOUTRECALL:
CB_LAYOUTRECALL4args opcblayoutrecall;
case OP_CB_NOTIFY:
CB_NOTIFY4args opcbnotify;
case OP_CB_PUSH_DELEG:
CB_PUSH_DELEG4args opcbpush_deleg;
case OP_CB_RECALL_ANY:
CB_RECALL_ANY4args opcbrecall_any;
case OP_CB_RECALLABLE_OBJ_AVAIL:
CB_RECALLABLE_OBJ_AVAIL4args opcbrecallable_obj_avail;
case OP_CB_RECALL_SLOT:
CB_RECALL_SLOT4args opcbrecall_slot;
case OP_CB_SEQUENCE:
CB_SEQUENCE4args opcbsequence;
case OP_CB_WANTS_CANCELLED:
CB_WANTS_CANCELLED4args opcbwants_cancelled;
case OP_CB_NOTIFY_LOCK:
CB_NOTIFY_LOCK4args opcbnotify_lock;
case OP_CB_NOTIFY_DEVICEID:
CB_NOTIFY_DEVICEID4args opcbnotify_deviceid;
case OP_CB_ILLEGAL: void;
};
struct CB_COMPOUND4args {
utf8str_cs tag;
uint32_t minorversion;
uint32_t callback_ident;
nfs_cb_argop4 argarray<>;
};
26.2.2. RESULTS
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union nfs_cb_resop4 switch (unsigned resop) {
case OP_CB_GETATTR: CB_GETATTR4res opcbgetattr;
case OP_CB_RECALL: CB_RECALL4res opcbrecall;
/* new NFSv4.1 operations */
case OP_CB_LAYOUTRECALL:
CB_LAYOUTRECALL4res
opcblayoutrecall;
case OP_CB_NOTIFY: CB_NOTIFY4res opcbnotify;
case OP_CB_PUSH_DELEG: CB_PUSH_DELEG4res
opcbpush_deleg;
case OP_CB_RECALL_ANY: CB_RECALL_ANY4res
opcbrecall_any;
case OP_CB_RECALLABLE_OBJ_AVAIL:
CB_RECALLABLE_OBJ_AVAIL4res
opcbrecallable_obj_avail;
case OP_CB_RECALL_SLOT:
CB_RECALL_SLOT4res
opcbrecall_slot;
case OP_CB_SEQUENCE: CB_SEQUENCE4res opcbsequence;
case OP_CB_WANTS_CANCELLED:
CB_WANTS_CANCELLED4res
opcbwants_cancelled;
case OP_CB_NOTIFY_LOCK:
CB_NOTIFY_LOCK4res
opcbnotify_lock;
case OP_CB_NOTIFY_DEVICEID:
CB_NOTIFY_DEVICEID4res
opcbnotify_deviceid;
/* Not new operation */
case OP_CB_ILLEGAL: CB_ILLEGAL4res opcbillegal;
};
struct CB_COMPOUND4res {
nfsstat4 status;
utf8str_cs tag;
nfs_cb_resop4 resarray<>;
};
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26.2.3. DESCRIPTION
The CB_COMPOUND procedure is used to combine one or more of the
callback procedures into a single RPC request. The main callback RPC
program has two main procedures: CB_NULL and CB_COMPOUND. All other
operations use the CB_COMPOUND procedure as a wrapper.
During the processing of the CB_COMPOUND procedure, the client may
find that it does not have the available resources to execute any or
all of the operations within the CB_COMPOUND sequence. Refer to
Section 7.6.4 for details.
The minorversion field of the arguments MUST be the same as the
minorversion of the COMPOUND procedure used to create the client ID
and session. For NFSv4.1, minorversion MUST be set to 1.
Contained within the CB_COMPOUND results is a "status" field. This
status MUST be equal to the status of the last operation that was
executed within the CB_COMPOUND procedure. Therefore, if an
operation incurred an error, then the "status" value will be the same
error value as is being returned for the operation that failed.
The "tag" field is handled the same way as that of the COMPOUND
procedure (See Section 23.2.3).
Illegal operation codes are handled in the same way as they are
handled for the COMPOUND procedure.
26.2.4. IMPLEMENTATION
The CB_COMPOUND procedure is used to combine individual operations
into a single RPC request. The client interprets each of the
operations in turn. If an operation is executed by the client and
the status of that operation is NFS4_OK, then the next operation in
the CB_COMPOUND procedure is executed. The client continues this
process until there are no more operations to be executed or one of
the operations has a status value other than NFS4_OK.
26.2.5. ERRORS
CB_COMPOUND will of course return every error that each operation on
the backchannel can return (See Table 13). However, if CB_COMPOUND
returns zero operations, obviously the error returned by COMPOUND has
nothing to do with an error returned by an operation. The list of
errors CB_COMPOUND will return if it processes zero operations
includes:
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+==============================+==================================+
| Error | Notes |
+==============================+==================================+
| NFS4ERR_BADCHAR | The tag argument has a character |
| | the replier does not support. |
+------------------------------+----------------------------------+
| NFS4ERR_BADXDR | |
+------------------------------+----------------------------------+
| NFS4ERR_DELAY | |
+------------------------------+----------------------------------+
| NFS4ERR_INVAL | The tag argument is not in UTF-8 |
| | encoding. |
+------------------------------+----------------------------------+
| NFS4ERR_MINOR_VERS_MISMATCH | |
+------------------------------+----------------------------------+
| NFS4ERR_SERVERFAULT | |
+------------------------------+----------------------------------+
| NFS4ERR_TOO_MANY_OPS | |
+------------------------------+----------------------------------+
| NFS4ERR_REP_TOO_BIG | |
+------------------------------+----------------------------------+
| NFS4ERR_REP_TOO_BIG_TO_CACHE | |
+------------------------------+----------------------------------+
| NFS4ERR_REQ_TOO_BIG | |
+------------------------------+----------------------------------+
Table 24: CB_COMPOUND Error Returns
27. NFSv4.1 Callback Operations
27.1. Operation 3: CB_GETATTR - Get Attributes
27.1.1. ARGUMENT
struct CB_GETATTR4args {
nfs_fh4 fh;
bitmap4 attr_request;
};
27.1.2. RESULT
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struct CB_GETATTR4resok {
fattr4 obj_attributes;
};
union CB_GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
CB_GETATTR4resok resok4;
default:
void;
};
27.1.3. DESCRIPTION
The CB_GETATTR operation is used by the server to obtain the current
modified state of a file that has been OPEN_DELEGATE_WRITE delegated.
The size and change attributes are the only ones guaranteed to be
serviced by the client. See Section 15.4.3 for a full description of
how the client and server are to interact with the use of CB_GETATTR.
If the filehandle specified is not one for which the client holds an
OPEN_DELEGATE_WRITE delegation, an NFS4ERR_BADHANDLE error is
returned.
27.1.4. IMPLEMENTATION
The client returns attrmask bits and the associated attribute values
only for the change attribute, and attributes that it may change
(time_modify, and size).
27.2. Operation 4: CB_RECALL - Recall a Delegation
27.2.1. ARGUMENT
struct CB_RECALL4args {
stateid4 stateid;
bool truncate;
nfs_fh4 fh;
};
27.2.2. RESULT
struct CB_RECALL4res {
nfsstat4 status;
};
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27.2.3. DESCRIPTION
The CB_RECALL operation is used to begin the process of recalling a
delegation and returning it to the server.
The truncate flag is used to optimize recall for a file object that
is a regular file and is about to be truncated to zero. When it is
TRUE, the client is freed of the obligation to propagate modified
data for the file to the server, since this data is irrelevant.
If the handle specified is not one for which the client holds a
delegation, an NFS4ERR_BADHANDLE error is returned.
If the stateid specified is not one corresponding to an OPEN
delegation for the file specified by the filehandle, an
NFS4ERR_BAD_STATEID is returned.
27.2.4. IMPLEMENTATION
The client SHOULD reply to the callback immediately. Replying does
not complete the recall except when the value of the reply's status
field is neither NFS4ERR_DELAY nor NFS4_OK. The recall is not
complete until the delegation is returned using a DELEGRETURN
operation.
27.3. Operation 5: CB_LAYOUTRECALL - Recall Layout from Client
27.3.1. ARGUMENT
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/*
* NFSv4.1 callback arguments and results
*/
enum layoutrecall_type4 {
LAYOUTRECALL4_FILE = LAYOUT4_RET_REC_FILE,
LAYOUTRECALL4_FSID = LAYOUT4_RET_REC_FSID,
LAYOUTRECALL4_ALL = LAYOUT4_RET_REC_ALL
};
struct layoutrecall_file4 {
nfs_fh4 lor_fh;
offset4 lor_offset;
length4 lor_length;
stateid4 lor_stateid;
};
union layoutrecall4 switch(layoutrecall_type4 lor_recalltype) {
case LAYOUTRECALL4_FILE:
layoutrecall_file4 lor_layout;
case LAYOUTRECALL4_FSID:
fsid4 lor_fsid;
case LAYOUTRECALL4_ALL:
void;
};
struct CB_LAYOUTRECALL4args {
layouttype4 clora_type;
layoutiomode4 clora_iomode;
bool clora_changed;
layoutrecall4 clora_recall;
};
27.3.2. RESULT
struct CB_LAYOUTRECALL4res {
nfsstat4 clorr_status;
};
27.3.3. DESCRIPTION
The CB_LAYOUTRECALL operation is used by the server to recall layouts
from the client; as a result, the client will begin the process of
returning layouts via LAYOUTRETURN. The CB_LAYOUTRECALL operation
specifies one of three forms of recall processing with the value of
layoutrecall_type4. The recall is for one of the following: a
specific layout of a specific file (LAYOUTRECALL4_FILE), an entire
file system ID (LAYOUTRECALL4_FSID), or all file systems
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(LAYOUTRECALL4_ALL).
The behavior of the operation varies based on the value of the
layoutrecall_type4. The value and behaviors are:
LAYOUTRECALL4_FILE
For a layout to match the recall request, the values of the
following fields must match those of the layout: clora_type,
clora_iomode, lor_fh, and the byte-range specified by lor_offset
and lor_length. The clora_iomode field may have a special value
of LAYOUTIOMODE4_ANY. The special value LAYOUTIOMODE4_ANY will
match any iomode originally returned in a layout; therefore, it
acts as a wild card. The other special value used is for
lor_length. If lor_length has a value of NFS4_UINT64_MAX, the
lor_length field means the maximum possible file size. If a
matching layout is found, it MUST be returned using the
LAYOUTRETURN operation (See Section 25.44). An example of the
field's special value use is if clora_iomode is LAYOUTIOMODE4_ANY,
lor_offset is zero, and lor_length is NFS4_UINT64_MAX, then the
entire layout is to be returned.
The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
client does not hold layouts for the file or if the client does
not have any overlapping layouts for the specification in the
layout recall.
LAYOUTRECALL4_FSID and LAYOUTRECALL4_ALL
If LAYOUTRECALL4_FSID is specified, the fsid specifies the file
system for which any outstanding layouts MUST be returned. If
LAYOUTRECALL4_ALL is specified, all outstanding layouts MUST be
returned. In addition, LAYOUTRECALL4_FSID and LAYOUTRECALL4_ALL
specify that all the storage device ID to storage device address
mappings in the affected file system(s) are also recalled. The
respective LAYOUTRETURN with either LAYOUTRETURN4_FSID or
LAYOUTRETURN4_ALL acknowledges to the server that the client
invalidated the said device mappings. See Section 18.7.5.3.5 for
considerations with "bulk" recall of layouts.
The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
client does not hold layouts and does not have valid deviceid
mappings.
In processing the layout recall request, the client also varies its
behavior based on the value of the clora_changed field. This field
is used by the server to provide additional context for the reason
why the layout is being recalled. A FALSE value for clora_changed
indicates that no change in the layout is expected and the client may
write modified data to the storage devices involved; this must be
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done prior to returning the layout via LAYOUTRETURN. A TRUE value
for clora_changed indicates that the server is changing the layout.
Examples of layout changes and reasons for a TRUE indication are the
following: the metadata server is restriping the file or a permanent
error has occurred on a storage device and the metadata server would
like to provide a new layout for the file. Therefore, a
clora_changed value of TRUE indicates some level of change for the
layout and the client SHOULD NOT write and commit modified data to
the storage devices. In this case, the client writes and commits
data through the metadata server.
See Section 18.7.3 for a description of how the lor_stateid field in
the arguments is to be constructed. Note that the "seqid" field of
lor_stateid MUST NOT be zero. See Sections 13.2, 18.7.3, and
18.7.5.2 for a further discussion and requirements.
27.3.4. IMPLEMENTATION
The client's processing for CB_LAYOUTRECALL is similar to CB_RECALL
(recall of file delegations) in that the client responds to the
request before actually returning layouts via the LAYOUTRETURN
operation. While the client responds to the CB_LAYOUTRECALL
immediately, the operation is not considered complete (i.e.,
considered pending) until all affected layouts are returned to the
server via the LAYOUTRETURN operation.
Before returning the layout to the server via LAYOUTRETURN, the
client should wait for the response from in-process or in-flight
READ, WRITE, or COMMIT operations that use the recalled layout.
If the client is holding modified data that is affected by a recalled
layout, the client has various options for writing the data to the
server. As always, the client may write the data through the
metadata server. In fact, the client may not have a choice other
than writing to the metadata server when the clora_changed argument
is TRUE and a new layout is unavailable from the server. However,
the client may be able to write the modified data to the storage
device if the clora_changed argument is FALSE; this needs to be done
before returning the layout via LAYOUTRETURN. If the client were to
obtain a new layout covering the modified data's byte-range, then
writing to the storage devices is an available alternative. Note
that before obtaining a new layout, the client must first return the
original layout.
In the case of modified data being written while the layout is held,
the client must use LAYOUTCOMMIT operations at the appropriate time;
as required LAYOUTCOMMIT must be done before the LAYOUTRETURN. If a
large amount of modified data is outstanding, the client may send
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LAYOUTRETURNs for portions of the recalled layout; this allows the
server to monitor the client's progress and adherence to the original
recall request. However, the last LAYOUTRETURN in a sequence of
returns MUST specify the full range being recalled (See
Section 18.7.3.1 for details).
If a server needs to delete a device ID and there are layouts
referring to the device ID, CB_LAYOUTRECALL MUST be invoked to cause
the client to return all layouts referring to the device ID before
the server can delete the device ID. If the client does not return
the affected layouts, the server MAY revoke the layouts.
27.4. Operation 6: CB_NOTIFY - Notify Client Using Directory
Delegations
27.4.1. ARGUMENT
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/* Changed entry information. */
struct notify_entry4 {
component4 ne_file;
fattr4 ne_attrs;
};
/* Previous entry information */
struct prev_entry4 {
notify_entry4 pe_prev_entry;
/* what READDIR returned for this entry */
nfs_cookie4 pe_prev_entry_cookie;
};
struct notify_remove4 {
notify_entry4 nrm_old_entry;
nfs_cookie4 nrm_old_entry_cookie;
};
/*
* Objects of types defined below are encoded within
* notifylist4, depending on the associated bit map,
* in a fashion similar to the way that attributes
* are presented within an attrlist4 in a fattr4.
*/
typedef opaque notifylist4<>;
struct notify4 {
/* composed from notify_type4 or notify_deviceid_type4 */
bitmap4 notify_mask;
notifylist4 notify_vals;
};
struct CB_NOTIFY4args {
stateid4 cna_stateid;
nfs_fh4 cna_fh;
notify4 cna_changes<>;
};
cna_stateid designates the associated directory delegation while
cna_fh designates the directory for which the delegation is held.
Each element of cna_changes provides a relevant notification with
type based on notify_mask and associated data, with associated
information in a format that depends on the type, within a nominally
opaque array. The elements are processed in sequence.
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The bitmap notify_mask contains bits whose indices are derived from
the enum notify_type4 defined in Section 16.2.5. The following
issues need to be noted:
* Many of bits defined in notify_type4 are flags which do not have
an associated notification message, as explained in
Section 16.2.5.
If any such bits are set in notify mask, the callback is invalid
and NFS4ERR_INVAL is to be returned.
* If the mask contains and bits in positions not defined as valid
elements of the enum notify_type4, the callback is invalid and
NFS4ERR_INVAL is to be returned.
* If the bitmask contains no bits set or more that one bit set, the
callback is invalid and NFS4ERR_INVAL is to be returned.
When an element is found to be invalid, there is no processing of
further elements.
27.4.2. RESULT
struct CB_NOTIFY4res {
nfsstat4 cnr_status;
};
27.4.3. DESCRIPTION
The CB_NOTIFY operation is used by the server to send notifications
to clients about events related to the maintenance of cached
information regarding delegated directories that is used to locally
satisfy needs for information normally provided by the use of LOOKUP,
READDIR, and GETATTR requests.
The registration of notifications occurs when the delegation is
established using GET_DIR_DELEGATION. As a result, these
notifications are sent over the backchannel, when certain events
occur that affect the directory, the files within it, or the
delegation itself. Most notifications are sent asynchronously but
the sending of some pf these is initiated promptly, as part of
operations making changes, while others are subject to delay and
might be sent periodically, Those sent promptly need to be responded
to before the generated operation proceeds but are unlike recalls in
that the operation does not await any completing request from the
client before proceeding. Those subject to delay can be sent some
time after the motivating change occurs. This choice is shown in the
Modes column in Table 25.
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These notifications are used in providing the following functions:
* Notifications relating to the updating of directory contents, as
discussed in Section 16.2.11.
* Notifications relating to the updating of attributes for
directories and objects within them, as discussed in
Section 16.2.12.
* Notifications relating to authorization for use of cached
information in locally satisfying requests, as discussed in
Section 16.2.13.
The notifications are sent as list of pairs of bitmaps and values
with each bitmap consisting of a single bit selected from the enum
notify_type, defined in Section 16.2.5 which identifies the specific
type of notification being sent. Although the description in
Section 9.3.7 is relevant, these bitmaps each have only a single bit
set so that the contents of the accompanying opaque array is
described by the notification structure associated with that
notification type. The individual types are shown in Table 25 with
the Modes used in that table defined as follows:
Synch:
Notifications are sent synchronously in the context of the
operation causing the change that the client needs to be informed
about.
When there is a situation in which the notification is to be sent
but the client has not requested that type of notification, the
delegation is recalled and needs to be returned or revoked before
the operation proceeds.
Ordered:
Notification are sent promptly in the context of the operation
causing the change that the client needs to be informed about.
There is a potential need to order such notifications since
processing some notifications in an order different from that in
which events occurred can confuse the client. Normally this
ordering is provided by putting a number of notifications in the
same CB_NOTIFY so that they are processed in order
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In case in which a server has more notifications than can fit in a
single CB_COMPOUND request, enforcing appropriate ordering will
involve serializing multiple CB_COMPOUND requests. This can
involve waiting for responses before sending new callbacks or
sending all callbacks associated with a given delegation using the
same slot of the session.
When there is a situation in which the notification is to be sent
but the client has not requested that type of notification, the
delegation is recalled but processing of the operation proceeds
without waiting for a client response.
Prompt:
Requests sent promptly as in the case of Ordered notifications but
without need for ordering support outside of the context of
particular notification types.
The functions of such notifications are either inherently order-
independent (e.g., two request to purge a cache are effectively
the same as one, independent of the order) or where state is
updated protected by an ascending sequence value to prevent
difficulties with out-of-order updates.
When there is a situation in which the notification is to be sent
but the client has not requested that type of notification, the
delegation is recalled but processing of the operation proceeds
without waiting for a client response.
Batched:
Sent outside the context of the change, with substantial delays
and with no commitment to deliver changes in the order made. Such
updates can be sent periodically with sufficient delays between
updates to eliminate misordering issues.
When there is a situation in which the notification is to be sent
but the client has not requested that type of notification,
processing of the operation proceeds normally
Note that for many notifications normally sent batched and
described that way in the table below, there are situations in
which the client can ask for them be sent using the Ordered
approach and the server can undertake to do so. This apples to
attribute notifications when the delay of zero is chosen by the
client and agreed to by the server,
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+=================+===============+=========+=======+=======+=======+
|Name | Function |Data |Mode |Desc. |Disc. |
+=================+===============+=========+=======+=======+=======+
|ADD_ENTRY | Add dir. |notify_ |Ordered|S. |S. |
| | entry |add4 | |27.4.4 |16.2.11|
+-----------------+---------------+---------+-------+-------+-------+
|REMOVE_ENTRY | Remove dir. |notify4_ |Ordered|S. |S. |
| | entry |remove | |27.4.5 |16.2.11|
+-----------------+---------------+---------+-------+-------+-------+
|RENAME_ENTRY | Rename dir. |notify_ |Ordered|S. |S. |
| | entry |rename4 | |27.4.6 |16.2.11|
+-----------------+---------------+---------+-------+-------+-------+
|CHANGE_CHILD_ATTR| Update dir |notify4_ |Batched|S. |S. |
| | entry attr. |chattr | |27.4.8 |16.2.12|
+-----------------+---------------+---------+-------+-------+-------+
|CHANGE_DIR_ATTR | Update dir |notify4_ |Batched|S. |S. |
| | attr. |dattr | |27.4.7 |16.2.12|
+-----------------+---------------+---------+-------+-------+-------+
|CHANGE_COOKIE | Update dir. |notify_ |Prompt |S. |S. |
|_VERIFIER | contents |verifier4| |27.4.9 |16.2.11|
+-----------------+---------------+---------+-------+-------+-------+
|CHANGE_AMASK | Update |notify_ |Prompt |S. |S. |
| | Attribute |changeam | |27.4.10|16.2.12|
| | Masks | | | | |
+-----------------+---------------+---------+-------+-------+-------+
|CHANGE_AUTH | Update |notify_ |Prompt |S. |S. |
| | Authorization |changeu4 | |27.4.11|16.2.13|
+-----------------+---------------+---------+-------+-------+-------+
|CHANGE_GA | Update |notify_ |Prompt |S. |S. |
| | getattr |changega4| |27.4.12|16.2.13|
| | processing | | | | |
+-----------------+---------------+---------+-------+-------+-------+
Table 25: Notification Types
27.4.4. NOTIFY4_ADD_ENTRY
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struct notify_add4 {
/*
* Information on object possibly renamed over.
* zero-length array if none.
*/
notify_remove4 nad_old_entry<1>;
/*
* Information on new object with requested values of
* unmodifiable attributes.
*/
notify_entry4 nad_new_entry;
/*
* What READDIR would return for this entry.
*
* Will be invalid (length zero) if client is
* order-unaware.
*/
nfs_cookie4 nad_new_entry_cookie<1>;
/*
* Ordering information.
*
* Invalid/ignored if client is order-unaware.
*
* zero-length nad_prev_entry if this is the
* first entry.
*
* if nad_prev_entry is length one and contains
* zero-length name prev_entry is not provided,
* as happens in the order-unaware and cookie-derived
* order cases.
*/
prev_entry4 nad_prev_entry<1>;
bool nad_last_entry;
};
When this notification is sent, the associated data will be in the
form of a notify_add4, as defined above.
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The server will send information about the new directory entry being
created. If the client is known to be interested in the order of the
entries, the cookie for that entry is also sent. The entry
information (data type notify_add4) includes the component name of
the entry and unmodifiable attributes. These attributes will be the
ones specified by the client when the delegation is created, which
are not modifiable (type, fileid, fsid, creation_time, and
file_handle).
The server will send this type of entry when a file is actually being
created, when an entry is being added to a directory as a result of a
rename across directories (See below), and when a hard link is being
created to an existing file.
If the client is known to be interested in the order of the entries,
additional information to place the new entry as provided as
described in the rest of this paragraph. If this entry is added to
the end of the directory, the server will set the nad_last_entry flag
to TRUE. If the file is added such that there is at least one entry
before it, the server will also return the previous entry information
(nad_prev_entry, a variable-length array of up to one element. If
the array is of zero length, there is no previous entry), along with
its cookie. This is to help clients find the right location in their
file name caches and directory caches where this entry should be
cached. If the new entry's cookie is available, it will be in the
nad_new_entry_cookie (another variable-length array of up to one
element) field.
If the addition of the entry causes another entry to be deleted
(which can only happen in the rename case) atomically with the
addition, then information on this entry is reported in
nad_old_entry.
27.4.5. NOTIFY4_REMOVE_ENTRY
typedef notify4_remove notify_remove4;
When this notification is sent, the associated data will be in the
form of a notify4_remove, as defined in Section 27.4.1
The server will send information about the directory entry being
deleted. If the client is order-aware, the server will send the
cookie value as part of this.
27.4.6. NOTIFY4_RENAME_ENTRY
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struct notify_rename4 {
notify_remove4 nrn_old_entry;
notify_add4 nrn_new_entry;
};
When this notification is sent, the associated data will be in the
form of a notify_rename4, as defined above.
The server will send information about both the old entry and the new
entry. This includes the name and attributes for each entry. In
addition, if the rename causes the deletion of an entry (i.e., the
case of a file renamed over), then this is reported in
nrn_new_new_entry.nad_old_entry. This notification is only sent if
both entries are in the same directory. If the rename is across
directories, the server will send a remove notification to one
directory and an add notification to the other directory, assuming
both have a directory delegation.
27.4.7. Directory Attribute Update Notifications
typedef fattr4 notify4_dattr;
The fattr4 identifies the attributes being changed together with the
new value for each such attribute.
For most attributes, this notification is sent in a batched or prompt
fashion as requested by the delay specified when the delegation is
created.
For the attributes modified_time and change, notification is always
prompt and is part of the same notiff4 as:
* An associated add, remove, or rename notification.
* A combination of add and remove notifications used to signal the
results of a cross-directory RENAME which deletes an existing
renamed-over file.
* An associated change-verifier notification.
27.4.8. Child Attribute Update Notifications
struct notify4_chattr {
notify_entry4 na_changed_entry;
};
When this notification is sent, the associated notify_entry4 will
contain two fields:
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* ne_file identifies the entry whose attributes are being reported.
* ne_attrs provides the changes attribute values.
The client will specify an attribute mask to inform the server of
attributes for which it wants to receive notifications. This change
notification can be requested for changes the attributes of any file
in the directory. The client cannot ask for change attribute
notification for a specific file. One attribute mask covers all the
files in the directory. Upon any attribute change, the server will
send back the values of changed attributes. Notifications might not
make sense for some file system-wide attributes, and it is up to the
server to decide which subset it wants to support. The client can
negotiate the frequency of attribute notifications by letting the
server know how often it wants to be notified of an attribute change.
The server will return supported notification frequencies or an
indication that no notification is permitted for directory or child
attributes by setting the dir_notif_delay and dir_entry_notif_delay
attributes, respectively.
Certain attributes are unmodifiable during the life of the file
system object. These include creation_time, fileid, fsid, and
file_handle. Although these attributes cannot appear in a
notify4_chattr, their inclusion in the mask will cause them to be
provided as part of the ne_attrs for notify_entry4 structure
appearing in content modification notifications.
27.4.9. NOTIFY4_CHANGE_COOKIE_VERIFIER
struct notify_verifier4 {
verifier4 nv_old_cookieverf;
verifier4 nv_new_cookieverf;
};
When this notification is sent, the associated data will be in the
form of a notify_verifier4, as defined above.
The holder is informed via this notification of a number of potential
events:
* When the cookie verifier changes, the client is informed of the
new value.
* When there is any change in the cookie assigned to an existing
directory entry, the client is informed of the change even if the
verifier has remained the same.
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This is necessary because servers are free to not change cookie
verifiers in many cases in which a cookie is changed.
* If there is a change in the order of directory entries and the
client has previously indicated concern with keeping its order in
sync with that of the server by using the NOTIFY4_CFLAG_ORDER
flag. The notification is sent even if there is no corresponding
change in directory entry cookies.
In this case as well, the message can be sent without a verifier
change.
Upon receiving this notification, the client can invalidate its
cookies and re-send a READDIR to get the new set of entries presented
in the server's order together with up-to-date cookies.
27.4.10. Attribute Mask Change Notifications
struct notify_changeam4 {
uint32_t ncam_order;
bitmap4 ncam_damask;
bitmap4 ncam_chmask;
bitmap4 ncam_flags;
};
When this notification is sent, the associated data will be in the
form of a notify_changem4, as defined above.
This notification is sent whenever the server wishes to change the
set of attributes for which updates are to be sent. This includes
the case in which one or both the masks is set to indicate an empty
attribute mask. This enables to respond to excessive attribute
notification traffic without recalling the delegation.
The fields in the notification are used as follows;
* ncam_order is used to protect against the potential effects of
notification misordering. The responder need to compare the
ncam_order value received to the last such value received and only
modify the attribute masks if the new value is greater than the
last one received.
* ncam_damask is a bit mask identifying the set of attributes of the
delegated directory that will be included in subsequent
NOTIFY4_CHANGE_DIR_ATTR notifications.
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* ncam_chmask is a bit mask identifying the set of attributes for
objects identified in entries within the delegated directory that
will be included in subsequent NOTIFY4_CHANGE_CHILD_ATTR
notifications.
* ncam_flags contains new values for flags originally returned as
part of the response to the request to create a directory
delegation but might have been changed because the attribute masks
are being changed.
The values for the flags NOTIFY4_PRAN_CONTENT and
NOTIFY4_PRAN_AUTH need to be used to determine whether prompt
notification for various classes or attribute notifications is
present since it is possible a change of masks might have caused
the discontinuance of prompt notifications or their new presence
when previously not in effect.
27.4.11. Change of Authorization Notifications
const NCAU_OWNER = 1;
const NCAU_GROUP = 2;
const NCAU_OTHERS = 4;
typedef uint32_t usetmask4;
struct notify_upair {
usetmask4 nusp_ok;
usetmask4 nusp_acc;
};
struct notify_changeau4 {
uint32_t ncau_order;
utf8str_mixed ncau_owner:
utf8str_mixed ncau_group:
notify_uspair ncau_lookup;
notify_uspair ncau_readdir;
usetmask4 ncau_flush;
};
The notify_uspair structure used to encode ncau_lookup and
ncau_readdir has a special arrangement including two usermask4s as
described below:
* nsup_ok defines the sets of users for which an authorization check
is unnecessary so that, if the covered operation is to be
performed locally, the client can be certain that the operation is
authorized, without actually performing the checks,
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When a local check is necessary, the result can be cached, subject
to later flushing as directed by later notifications' ncau_flush
values.
* nsup_acc defines the set of users for which an authorization
requires that a (remote) ACCESS call be done. The ACCESS check
cannot be replaced by a local authorization check since the
authorization result is not motivating this need. Instead, there
might be a need for special server-side processing mandated by
AUDIT or ALARM ACEs.
When processing a request involving a user within one of the
specified groups, the result cannot be cached, since the check
needs to be done irrespective of any cached result.
When this notification is sent, the associated data will be in the
form of a notify_changeu4, as defined above.
This notification is used to inform the client of necessary changes
in the appropriate means of authorization of the local equivalents of
LOOKUP and READDIR operations.
The fields in the notification are used as described below. Many of
the fields are in the form of a usetmask4 which defines the handling
of a set of users by including or excluding the directory owner, set
of users in the owning group but excluding the directory owner, and
all other users, with one bit used for each of those sets.
* ncau_order is a numeric value used to avoid mistakes when
notifications are processed in an unexpected order. The value
incremented each time such a notification is sent for a given
directory delegation and the client can check for ascending values
as discussed below.
For the fields ncau_owner, ncau_group, ncau_lookup, and
ncau_readdir, the specified changes are to be used to update the
client's state only if the ncau_order is greater than the last one
received.
The field ncau_flush is to be acted on unconditionally, regardless
of the value of ncau_order. Such actions are not qualified by
ordering since flushing a cache is an idempotent operation.
* ncau_owner and ncau_group provide the updated values of the
directory owner and directory owning group to be used in
classifying requests for authorization and in the caching of
results from those authorization checks.
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* ncau_lookup provides, for each of the three group of users
specified in a usetmask4, whether requests to lookup a file by
users in that group can be granted without an explicit
authorization check or whether an ACCESS check is always needed
and cannot be foreclosed by a client-side check.
* ncau_readdir provides, for each of the three group of users
specified in a usetmask4, whether requests to read the directory
by users in that group can be granted without an explicit
authorization check or whether an ACCESS check is always needed
and cannot be foreclosed by a client-side check.
* ncau_flush indicates, for each of the three group of users
specified in a usetmask4, whether the cache of ACCESS check
results for users of that class is to be flushed.
Such cache flushing is necessary when changes in the mode or ACL-
related attributes make previous results unreliable and when
changes in the owning user or group affect the categorization of
users.
27.4.12. Change of GETATTR Processing Notifications
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enum ncga_astate4 {
NCGAAS_NO = 1,
NCGAAS_ALLOK = 2,
NCGAAS_MOSTOK = 3
};
enum ncga_fstate4 {
NCGFS_FETCH = 0,
NCGFS_COND = 1
};
enum ncga_ftype4 {
NCGAT_RESET = 0,
NCGAT_SET = 1,
NCGAT_ADD = 2
};
union ncga_finfo4 switch(ncga_fstate f) {
case NCGFS_COND:
changeid4 chval;
fattr4_fileid idc;
default:
fattr4_fileid idd;
};
struct notify_changega4 {
uint32_t ncga_order;
ncga_ftype4 ncga_ftype;
ncga_astate ncga_astate
ncga_finfo4 ncga_finf<>;
};
When this notification is sent, the associated data will be in the
form of a notify_changega4, as defined above.
The purpose of this notification is to inform the client of the need
to make changes in the handling local equivalents of the GETATTR
operation using cached data. The potential changes concern:
* The need for explicit authorization checks for the local
equivalents of GETATTR.
* The need for explicit refetching of attributes, as opposed to
using a previously cached value or making the fetch conditional on
knowledge of a particular change id value for the object in
question.
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At any time, the handling is as directed by the client's current
value of its GETATTR authorization state that is represented by one
of the three values below.
* NCGAS_NO indicates that explicit ACCESS checks are always
necessary.
* NCGAS_ALLOK indicates that explicit ACCESS checks are never
necessary, since the operation is known to be authorized a priori.
* NCGAS_SOMEOK that explicit ACCESS checks are necessary only for
use of a specific set of files identified by fileid.
The set of files mentioned above includes the following additional
information for each entry:
* The fileid of the designated file.
* An indication whether the current file attributes need always to
be explicitly fetched or are to be fetched conditionally, based on
the client's current knowledge of the object's change attribute.
* A change attribute to compare to the one in the currently cached
attribute.
The approach allows multiple entry changes to be resolved using a
single READDIR and could be compatible with later delegation
changes that allowed entry changes to trigger a prompt
notification of directory attribute changes (but probably only
when the directory holds no multiply-linked files).
Transition between these states are effected depending on the value
of the ncga_type field of the notification, as described below.
* NCGAT_RESET causes the state to be set to NCGAS_NO and resets the
list of exceptions to empty. In addition all entries will be
treated as if a new attribute fetch was always required.
* NCGAT_SET causes the state to be set to NCGAS_ALLOK or
NCGAS_SOMEOK, depending on whether the list of fileids to be set
as exceptions is empty or not. In either case, attribute fetch is
specified within the new list while requiring a refetch is the
default for fileids not mentioned.
* NCGAT_ADD adds to the list fileids to be used as exceptions and
set the state to NCGAS_SOMEOK if it is currently NCGAS_ALLOK.
Fetching of entries whose fileids are already in the list are
updated as specified in the new list.
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The notify_changega4 contains the following fields:
* ncga_order is a numeric value used to prevent problems when
notifications are received by the client in an order different
from the one in which they are sent.
Every notification carries the current value maintained on the
server. The value is incremented for every notification of type
NCGAT_RESET that is sent.
For notifications of type NCGAT_RESET, the notification is only
acted upon if the order value sent is greater than the last one
received of that type that is acted upon.
For notifications of other types, the notification is only acted
upon if the order value sent is equal the last one received of
type NCGAT_RESET that is acted upon.
* ncga_ftype defines the type of state transition, as described
above.
* ncga_astate indicates the new authorization state as described
above.
* ncga_finf contains set of fileids of object within the directory
which are to be added to the list of objects for which the local
equivalent of GETATTR requires explicit ACCESS checks. In
addition, information relevant to the need to fetch attributes is
included, as described above.
27.5. Operation 7: CB_PUSH_DELEG - Offer Previously Requested
Delegation to Client
27.5.1. ARGUMENT
struct CB_PUSH_DELEG4args {
nfs_fh4 cpda_fh;
open_delegation4 cpda_delegation;
};
27.5.2. RESULT
struct CB_PUSH_DELEG4res {
nfsstat4 cpdr_status;
};
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27.5.3. DESCRIPTION
CB_PUSH_DELEG is used by the server both to signal to the client that
the delegation it wants (previously indicated via a want established
from an OPEN or WANT_DELEGATION operation) is available and to
simultaneously offer the delegation to the client. The client has
the choice of accepting the delegation by returning NFS4_OK to the
server, delaying the decision to accept the offered delegation by
returning NFS4ERR_DELAY, or permanently rejecting the offer of the
delegation by returning NFS4ERR_REJECT_DELEG. When a delegation is
rejected in this fashion, the want previously established is
permanently deleted and the delegation is subject to acquisition by
another client.
27.5.4. IMPLEMENTATION
If the client does return NFS4ERR_DELAY and there is a conflicting
delegation request, the server MAY process it at the expense of the
client that returned NFS4ERR_DELAY. The client's want will not be
cancelled, but MAY be processed behind other delegation requests or
registered wants.
When a client returns a status other than NFS4_OK, NFS4ERR_DELAY, or
NFS4ERR_REJECT_DELAY, the want remains pending, although servers may
decide to cancel the want by sending a CB_WANTS_CANCELLED.
27.6. Operation 8: CB_RECALL_ANY - Keep Any N Recallable Objects
27.6.1. ARGUMENT
const RCA4_TYPE_MASK_RDATA_DLG = 0;
const RCA4_TYPE_MASK_WDATA_DLG = 1;
const RCA4_TYPE_MASK_DIR_DLG = 2;
const RCA4_TYPE_MASK_FILE_LAYOUT = 3;
const RCA4_TYPE_MASK_BLK_LAYOUT = 4;
const RCA4_TYPE_MASK_OBJ_LAYOUT_MIN = 8;
const RCA4_TYPE_MASK_OBJ_LAYOUT_MAX = 9;
const RCA4_TYPE_MASK_OTHER_LAYOUT_MIN = 12;
const RCA4_TYPE_MASK_OTHER_LAYOUT_MAX = 15;
struct CB_RECALL_ANY4args {
uint32_t craa_objects_to_keep;
bitmap4 craa_type_mask;
};
27.6.2. RESULT
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struct CB_RECALL_ANY4res {
nfsstat4 crar_status;
};
27.6.3. DESCRIPTION
The server may decide that it cannot hold all of the state for
recallable objects, such as delegations and layouts, without running
out of resources. In such a case, while not optimal, the server is
free to recall individual objects to reduce the load.
Because the general purpose of such recallable objects as delegations
is to eliminate client interaction with the server, the server cannot
interpret lack of recent use as indicating that the object is no
longer useful. The absence of visible use is consistent with a
delegation keeping potential operations from being sent to the
server. In the case of layouts, while it is true that the usefulness
of a layout is indicated by the use of the layout when storage
devices receive I/O requests, because there is no mandate that a
storage device indicate to the metadata server any past or present
use of a layout, the metadata server is not likely to know which
layouts are good candidates to recall in response to low resources.
In order to implement an effective reclaim scheme for such objects,
the server's knowledge of available resources must be used to
determine when objects must be recalled with the clients selecting
the actual objects to be returned.
Server implementations may differ in their resource allocation
requirements. For example, one server may share resources among all
classes of recallable objects, whereas another may use separate
resource pools for layouts and for delegations, or further separate
resources by types of delegations.
When a given resource pool is over-utilized, the server can send a
CB_RECALL_ANY to clients holding recallable objects of the types
involved, allowing it to keep a certain number of such objects and
return any excess. A mask specifies which types of objects are to be
limited. The client chooses, based on its own knowledge of current
usefulness, which of the objects in that class should be returned.
A number of bits are defined. For some of these, ranges are defined
and it is up to the definition of the storage protocol to specify how
these are to be used. There are ranges reserved for object-based
storage protocols and for other experimental storage protocols. An
RFC defining such a storage protocol needs to specify how particular
bits within its range are to be used. For example, it may specify a
mapping between attributes of the layout (read vs. write, size of
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area) and the bit to be used, or it may define a field in the layout
where the associated bit position is made available by the server to
the client.
RCA4_TYPE_MASK_RDATA_DLG
The client is to return OPEN_DELEGATE_READ delegations on non-
directory file objects.
RCA4_TYPE_MASK_WDATA_DLG
The client is to return OPEN_DELEGATE_WRITE delegations on regular
file objects.
RCA4_TYPE_MASK_DIR_DLG
The client is to return directory delegations.
RCA4_TYPE_MASK_FILE_LAYOUT
The client is to return layouts of type LAYOUT4_NFSV4_1_FILES.
RCA4_TYPE_MASK_BLK_LAYOUT
See [RFC5663] for a description.
RCA4_TYPE_MASK_OBJ_LAYOUT_MIN to RCA4_TYPE_MASK_OBJ_LAYOUT_MAX
See [RFC5664] for a description.
RCA4_TYPE_MASK_OTHER_LAYOUT_MIN to RCA4_TYPE_MASK_OTHER_LAYOUT_MAX
This range is reserved for telling the client to recall layouts of
experimental or site-specific layout types (See Section 9.3.13).
When a bit is set in the type mask that corresponds to an undefined
type of recallable object, NFS4ERR_INVAL MUST be returned. When a
bit is set that corresponds to a defined type of object but the
client does not support an object of the type, NFS4ERR_INVAL MUST NOT
be returned. Future minor versions of NFSv4 may expand the set of
valid type mask bits.
CB_RECALL_ANY specifies a count of objects that the client may keep
as opposed to a count that the client must return. This is to avoid
a potential race between a CB_RECALL_ANY that had a count of objects
to free with a set of client-originated operations to return layouts
or delegations. As a result of the race, the client and server would
have differing ideas as to how many objects to return. Hence, the
client could mistakenly free too many.
If resource demands prompt it, the server may send another
CB_RECALL_ANY with a lower count, even if it has not yet received an
acknowledgment from the client for a previous CB_RECALL_ANY with the
same type mask. Although the possibility exists that these will be
received by the client in an order different from the order in which
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they were sent, any such permutation of the callback stream is
harmless. It is the job of the client to bring down the size of the
recallable object set in line with each CB_RECALL_ANY received, and
until that obligation is met, it cannot be cancelled or modified by
any subsequent CB_RECALL_ANY for the same type mask. Thus, if the
server sends two CB_RECALL_ANYs, the effect will be the same as if
the lower count was sent, whatever the order of recall receipt. Note
that this means that a server may not cancel the effect of a
CB_RECALL_ANY by sending another recall with a higher count. When a
CB_RECALL_ANY is received and the count is already within the limit
set or is above a limit that the client is working to get down to,
that callback has no effect.
Servers are generally free to deny recallable objects when
insufficient resources are available. Note that the effect of such a
policy is implicitly to give precedence to existing objects relative
to requested ones, with the result that resources might not be
optimally used. To prevent this, servers are well advised to make
the point at which they start sending CB_RECALL_ANY callbacks
somewhat below that at which they cease to give out new delegations
and layouts. This allows the client to purge its less-used objects
whenever appropriate and so continue to have its subsequent requests
given new resources freed up by object returns.
27.6.4. IMPLEMENTATION
The client can choose to return any type of object specified by the
mask. If a server wishes to limit the use of objects of a specific
type, it should only specify that type in the mask it sends. Should
the client fail to return requested objects, it is up to the server
to handle this situation, typically by sending specific recalls
(i.e., sending CB_RECALL operations) to properly limit resource
usage. The server should give the client enough time to return
objects before proceeding to specific recalls. This time should not
be less than the lease period.
27.7. Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal Resources for
Recallable Objects
27.7.1. ARGUMENT
typedef CB_RECALL_ANY4args CB_RECALLABLE_OBJ_AVAIL4args;
27.7.2. RESULT
struct CB_RECALLABLE_OBJ_AVAIL4res {
nfsstat4 croa_status;
};
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27.7.3. DESCRIPTION
CB_RECALLABLE_OBJ_AVAIL is used by the server to signal the client
that the server has resources to grant recallable objects that might
previously have been denied by OPEN, WANT_DELEGATION, GET_DIR_DELEG,
or LAYOUTGET.
The argument craa_objects_to_keep means the total number of
recallable objects of the types indicated in the argument type_mask
that the server believes it can allow the client to have, including
the number of such objects the client already has. A client that
tries to acquire more recallable objects than the server informs it
can have runs the risk of having objects recalled.
The server is not obligated to reserve the difference between the
number of the objects the client currently has and the value of
craa_objects_to_keep, nor does delaying the reply to
CB_RECALLABLE_OBJ_AVAIL prevent the server from using the resources
of the recallable objects for another purpose. Indeed, if a client
responds slowly to CB_RECALLABLE_OBJ_AVAIL, the server might
interpret the client as having reduced capability to manage
recallable objects, and so cancel or reduce any reservation it is
maintaining on behalf of the client. Thus, if the client desires to
acquire more recallable objects, it needs to reply quickly to
CB_RECALLABLE_OBJ_AVAIL, and then send the appropriate operations to
acquire recallable objects.
27.8. Operation 10: CB_RECALL_SLOT - Change Flow Control Limits
27.8.1. ARGUMENT
struct CB_RECALL_SLOT4args {
slotid4 rsa_target_highest_slotid;
};
27.8.2. RESULT
struct CB_RECALL_SLOT4res {
nfsstat4 rsr_status;
};
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27.8.3. DESCRIPTION
The CB_RECALL_SLOT operation requests the client to return session
slots, and if applicable, transport credits (e.g., RDMA credits for
connections associated with the operations channel) of the session's
fore channel. CB_RECALL_SLOT specifies rsa_target_highest_slotid,
the value of the target highest slot ID the server wants for the
session. The client MUST then progress toward reducing the session's
highest slot ID to the target value.
If the session has only non-RDMA connections associated with its
operations channel, then the client need only wait for all
outstanding requests with a slot ID > rsa_target_highest_slotid to
complete, then send a single COMPOUND consisting of a single SEQUENCE
operation, with the sa_highestslot field set to
rsa_target_highest_slotid. If there are RDMA-based connections
associated with operation channel, then the client needs to also send
enough zero-length "RDMA Send" messages to take the total RDMA credit
count to rsa_target_highest_slotid + 1 or below.
27.8.4. IMPLEMENTATION
If the client fails to reduce highest slot it has on the fore channel
to what the server requests, the server can force the issue by
asserting flow control on the receive side of all connections bound
to the fore channel, and then finish servicing all outstanding
requests that are in slots greater than rsa_target_highest_slotid.
Once that is done, the server can then open the flow control, and any
time the client sends a new request on a slot greater than
rsa_target_highest_slotid, the server can return NFS4ERR_BADSLOT.
27.9. Operation 11: CB_SEQUENCE - Supply Backchannel Sequencing and
Control
27.9.1. ARGUMENT
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struct referring_call4 {
sequenceid4 rc_sequenceid;
slotid4 rc_slotid;
};
struct referring_call_list4 {
sessionid4 rcl_sessionid;
referring_call4 rcl_referring_calls<>;
};
struct CB_SEQUENCE4args {
sessionid4 csa_sessionid;
sequenceid4 csa_sequenceid;
slotid4 csa_slotid;
slotid4 csa_highest_slotid;
bool csa_cachethis;
referring_call_list4 csa_referring_call_lists<>;
};
27.9.2. RESULT
struct CB_SEQUENCE4resok {
sessionid4 csr_sessionid;
sequenceid4 csr_sequenceid;
slotid4 csr_slotid;
slotid4 csr_highest_slotid;
slotid4 csr_target_highest_slotid;
};
union CB_SEQUENCE4res switch (nfsstat4 csr_status) {
case NFS4_OK:
CB_SEQUENCE4resok csr_resok4;
default:
void;
};
27.9.3. DESCRIPTION
The CB_SEQUENCE operation is used to manage operational accounting
for the backchannel of the session on which a request is sent. The
contents include the session ID to which this request belongs, the
slot ID and sequence ID used by the server to implement session
request control and exactly once semantics, and exchanged slot ID
maxima that are used to adjust the size of the reply cache. In each
CB_COMPOUND request, CB_SEQUENCE MUST appear once and MUST be the
first operation. The error NFS4ERR_SEQUENCE_POS MUST be returned
when CB_SEQUENCE is found in any position in a CB_COMPOUND beyond the
first. If any other operation is in the first position of
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CB_COMPOUND, NFS4ERR_OP_NOT_IN_SESSION MUST be returned.
See Section 25.46.3 for a description of how slots are processed.
If csa_cachethis is TRUE, then the server is requesting that the
client cache the reply in the callback reply cache. The client MUST
cache the reply (See Section 7.6.1.3).
The csa_referring_call_lists array is the list of COMPOUND requests,
identified by session ID, slot ID, and sequence ID. These are
requests that the client previously sent to the server. These
previous requests created state that some operation(s) in the same
CB_COMPOUND as the csa_referring_call_lists are identifying. A
session ID is included because leased state is tied to a client ID,
and a client ID can have multiple sessions. See Section 7.6.3.
The value of the csa_sequenceid argument relative to the cached
sequence ID on the slot falls into one of three cases.
* If the difference between csa_sequenceid and the client's cached
sequence ID at the slot ID is two (2) or more, or if
csa_sequenceid is less than the cached sequence ID (accounting for
wraparound of the unsigned sequence ID value), then the client
MUST return NFS4ERR_SEQ_MISORDERED.
* If csa_sequenceid and the cached sequence ID are the same, this is
a retry, and the client returns the CB_COMPOUND request's cached
reply.
* If csa_sequenceid is one greater (accounting for wraparound) than
the cached sequence ID, then this is a new request, and the slot's
sequence ID is incremented. The operations subsequent to
CB_SEQUENCE, if any, are processed. If there are no other
operations, the only other effects are to cache the CB_SEQUENCE
reply in the slot, maintain the session's activity, and when the
server receives the CB_SEQUENCE reply, renew the lease of state
related to the client ID.
If the server reuses a slot ID and sequence ID for a completely
different request, the client MAY treat the request as if it is a
retry of what it has already executed. The client MAY however detect
the server's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.
If CB_SEQUENCE returns an error, then the state of the slot (sequence
ID, cached reply) MUST NOT change. See Section 7.6.1.3 for the
conditions when the error NFS4ERR_RETRY_UNCACHED_REP might be
returned.
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The client returns two "highest_slotid" values: csr_highest_slotid
and csr_target_highest_slotid. The former is the highest slot ID the
client will accept in a future CB_SEQUENCE operation, and SHOULD NOT
be less than the value of csa_highest_slotid (but see Section 7.6.1
for an exception). The latter is the highest slot ID the client
would prefer the server use on a future CB_SEQUENCE operation.
27.10. Operation 12: CB_WANTS_CANCELLED - Cancel Pending Delegation
Wants
27.10.1. ARGUMENT
struct CB_WANTS_CANCELLED4args {
bool cwca_contended_wants_cancelled;
bool cwca_resourced_wants_cancelled;
};
27.10.2. RESULT
struct CB_WANTS_CANCELLED4res {
nfsstat4 cwcr_status;
};
27.10.3. DESCRIPTION
The CB_WANTS_CANCELLED operation is used to notify the client that
some or all of the wants it registered for recallable delegations and
layouts have been cancelled.
If cwca_contended_wants_cancelled is TRUE, this indicates that the
server will not be pushing to the client any delegations that become
available after contention passes.
If cwca_resourced_wants_cancelled is TRUE, this indicates that the
server will not notify the client when there are resources on the
server to grant delegations or layouts.
After receiving a CB_WANTS_CANCELLED operation, the client is free to
attempt to acquire the delegations or layouts it was waiting for, and
possibly re-register wants.
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27.10.4. IMPLEMENTATION
When a client has an OPEN, WANT_DELEGATION, or GET_DIR_DELEGATION
request outstanding, when a CB_WANTS_CANCELLED is sent, the server
may need to make clear to the client whether a promise to signal
delegation availability happened before the CB_WANTS_CANCELLED and is
thus covered by it, or after the CB_WANTS_CANCELLED in which case it
was not covered by it. The server can make this distinction by
putting the appropriate requests into the list of referring calls in
the associated CB_SEQUENCE.
27.11. Operation 13: CB_NOTIFY_LOCK - Notify Client of Possible Lock
Availability
27.11.1. ARGUMENT
struct CB_NOTIFY_LOCK4args {
nfs_fh4 cnla_fh;
lock_owner4 cnla_lock_owner;
};
27.11.2. RESULT
struct CB_NOTIFY_LOCK4res {
nfsstat4 cnlr_status;
};
27.11.3. DESCRIPTION
The server can use this operation to indicate that a byte-range lock
for the given file and lock-owner, previously requested by the client
via an unsuccessful LOCK operation, might be available.
This callback is meant to be used by servers to help reduce the
latency of blocking locks in the case where they recognize that a
client that has been polling for a blocking byte-range lock may now
be able to acquire the lock. If the server supports this callback
for a given file, it MUST set the OPEN4_RESULT_MAY_NOTIFY_LOCK flag
when responding to successful opens for that file. This does not
commit the server to the use of CB_NOTIFY_LOCK, but the client may
use this as a hint to decide how frequently to poll for locks derived
from that open.
If an OPEN operation results in an upgrade, in which the stateid
returned has an "other" value matching that of a stateid already
allocated, with a new "seqid" indicating a change in the lock being
represented, then the value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag
when responding to that new OPEN controls handling from that point
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going forward. When parallel OPENs are done on the same file and
open-owner, the ordering of the "seqid" fields of the returned
stateids (subject to wraparound) are to be used to select the
controlling value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag.
27.11.4. IMPLEMENTATION
The server MUST NOT grant the byte-range lock to the client unless
and until it receives a LOCK operation from the client. Similarly,
the client receiving this callback cannot assume that it now has the
lock or that a subsequent LOCK operation for the lock will be
successful.
The server is not required to implement this callback, and even if it
does, it is not required to use it in any particular case.
Therefore, the client must still rely on polling for blocking locks,
as described in Section 14.6.
Similarly, the client is not required to implement this callback, and
even it does, is still free to ignore it. Therefore, the server MUST
NOT assume that the client will act based on the callback.
27.12. Operation 14: CB_NOTIFY_DEVICEID - Notify Client of Device ID
Changes
27.12.1. ARGUMENT
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/*
* Device notification types.
*/
enum notify_deviceid_type4 {
NOTIFY_DEVICEID4_CHANGE = 1,
NOTIFY_DEVICEID4_DELETE = 2
};
/* For NOTIFY4_DEVICEID4_DELETE */
struct notify_deviceid_delete4 {
layouttype4 ndd_layouttype;
deviceid4 ndd_deviceid;
};
/* For NOTIFY4_DEVICEID4_CHANGE */
struct notify_deviceid_change4 {
layouttype4 ndc_layouttype;
deviceid4 ndc_deviceid;
bool ndc_immediate; /* Unused */
};
struct CB_NOTIFY_DEVICEID4args {
notify4 cnda_changes<>;
};
27.12.2. RESULT
struct CB_NOTIFY_DEVICEID4res {
nfsstat4 cndr_status;
};
27.12.3. DESCRIPTION
The CB_NOTIFY_DEVICEID operation is used by the server to send
notifications to clients about changes to pNFS device IDs. The
registration of device ID notifications is optional and is done via
GETDEVICEINFO. These notifications are sent over the backchannel
once the original request has been processed on the server. The
server will send an array of notifications, cnda_changes, as a list
of pairs of bitmaps and values. See Section 9.3.7 for a description
of how NFSv4.1 bitmaps work.
As with CB_NOTIFY (Section 27.4.3), it is possible the server has
more notifications than can fit in a CB_COMPOUND, thus requiring
multiple CB_COMPOUNDs. Unlike CB_NOTIFY, serialization is not an
issue because unlike directory entries, device IDs cannot be re-used
after being deleted (Section 18.4.9).
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All device ID notifications contain a device ID and a layout type.
The layout type is necessary because two different layout types can
share the same device ID, and the common device ID can have
completely different mappings for each layout type.
The server will send the following notifications:
NOTIFY_DEVICEID4_CHANGE
A previously provided device-ID-to-device-address mapping has
changed and the client uses GETDEVICEINFO to obtain the updated
mapping. The notification is encoded in a value of data type
notify_deviceid_change4. This data type contains an unused
boolean field, ndc_immediate, which provides no useful information
to the client. The client is permitted to finish outstanding I/O
that references the previously provided device-ID-to-device-
address mapping. Before requesting new layouts, the client needs
to replace the previously provided device-ID-to-device-address
mapping using a GETDEVINFO operation. All outstanding layouts
remain valid after a notification of type NOTIFY_DEVICEID4_CHANGE.
If the device-ID-to-device-address mapping changed in an
incompatible way, that would invalidate outstanding layouts, the
server MUST recall all outstanding layouts and send a
NOTIFY_DEVICEID4_DELETE notification instead
NOTIFY4_DEVICEID_DELETE
Deletes a device ID from the mappings. This notification MUST NOT
be sent if the client has a layout that refers to the device ID.
In other words, if the server is sending a delete device ID
notification, one of the following is true for layouts associated
with the layout type:
* The client never had a layout referring to that device ID.
* The client has returned all layouts referring to that device
ID.
* The server has revoked all layouts referring to that device ID.
The notification is encoded in a value of data type
notify_deviceid_delete4. After a server deletes a device ID, it
MUST NOT reuse that device ID for the same layout type until the
client ID is deleted.
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27.13. Operation 10044: CB_ILLEGAL - Illegal Callback Operation
27.13.1. ARGUMENT
void;
27.13.2. RESULT
/*
* CB_ILLEGAL: Response for illegal operation numbers
*/
struct CB_ILLEGAL4res {
nfsstat4 status;
};
27.13.3. DESCRIPTION
This operation is a placeholder for encoding a result to handle the
case of the server sending an operation code within CB_COMPOUND that
is not defined in the NFSv4.1 specification. See Section 26.2.3 for
more details.
The status field of CB_ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
27.13.4. IMPLEMENTATION
A server will probably not send an operation with code OP_CB_ILLEGAL,
but if it does, the response will be CB_ILLEGAL4res just as it would
be with any other invalid operation code. Note that if the client
gets an illegal operation code that is not OP_ILLEGAL, and if the
client checks for legal operation codes during the XDR decode phase,
then an instance of data type CB_ILLEGAL4res will not be returned.
28. Security Considerations
The majority of the Security Considerations relevant to NFS Version
4.1 will appear in the corresponding section of the document devoted
to the security of NFS Version 4 as a whole
[I-D.dnoveck-nfsv4-security]. Some Security considerations relating
to the use of pNFS and other NFSv4.1-specific features will be dealt
with in subsections of this section.
28.1. Issues with Inherited Security Considerations Section
The following significant issues need to be addressed in a new
Security Considerations section for NFSv4 in whatever document it
appears:
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* The absence of a threat analysis.
* The lack of attention to the security consequences of transmission
of user data in the clear.
* The treatment of AUTH_SYS as OPTIONAL without any discussion of
the security consequences of using it.
It is anticipated that such a revised Security Considerations section
will appear in the NFSV4-wide security document and that the
corresponding section will deal with Security Considerations
(including a threat analysis) for NFSv4.1-specific features such as
parallel NFS.
28.2. Threat Analysis
Possible additional threats raised by new features in NFSv4.1 will be
dealt as follows:
* There do not appear to be additional threats arising from the use
of sessions per se. State protection, originally discussed, as
part NFSv4.1, in now dealt with in NFSv4-wide security document,
rather than in this one.
Threats related to the persistent storage of session state and
locking state are dealt with in Section 28.2.1.
* Threats related to the use of pNFS will be dealt with in
Section 28.2.2 and its subsections.
28.2.1. Threat Analysis for Use of Persistent Sessions and Locking
State
Locking state can be transferred between two different client-server
associations as a result of server restart. This raises the
possibility that the transfer might be made inappropriately if a
hostile client presents itself as the owner of existing persistently-
preserved locking state created before the server restart.
In order to prevent any such misuse, servers that implement
persistent sessions or locking state MUST do the following:
* Limit the persistent storage of state to situations in which the
client peer owning that state is identifiable (e.g. by the use of
client-peer identification together with use of RPC-with-tls).
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* Persistently store the client identification together with the
locking or reply state being maintained across potential server
restart.
* Only restore persisted state when the successor client peer
securely identifies itself with identification matching that
stored when the state was created.
* Mark such persisted state as having been restored to prevent it
being used by a second client peer instance.
It should be noted that there are similar situations in which state
created by one client peer might be incorrectly accessed by another
with current specifications taking a laxer approach as described in
[I-D.dnoveck-nfsv4-security]. For various reasons, it was not
possible for these older features to require the level of strictness
applied above to persisted locking state:
28.2.2. Threat Analysis for Use of pNFS
The threat analysis is divided based on layout type and coupling
mode. Although most layout types only support a single coupling
mode, the flexible files layout is designed to support multiple
coupling modes with the result that its use with tight and loose
coupling need to be dealt with separately.
* For layout types that use RPC for data access and rely on the
support of a separate control protocol (i.e. The files layout type
described in Section 20 and the flexible files layout described in
[RFC8435] when used in tight coupling mode.), the material in
Section 18.11.2 provides a general picture of the security issues
while the corresponding threat analysis appears in
Section 28.2.2.3.
* For layout types that use RPC for data access and have no separate
control protocol (i.e. The flexible files layout described in
[RFC8435] when used in loose coupling mode.), the material in
Section 18.11.3 provides a general picture of the security issues
while the corresponding threat analysis appears in
Section 28.2.2.2.
* For layout types that do not use RPC for data access and have a
separate control protocol (e.g. the blocks layout [RFC5663], the
SCSI layout [RFC8154], and the objects layout [RFC5664]), the
material in Section 18.11.1 provides a general picture of the
security issues while the corresponding threat analysis appears in
Section 28.2.2.1.
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28.2.2.1. Threat Analysis for pNFS Layout Types Involving non-RPC Data
Access
Because data is accessed using non-RPC protocols, there might be no
provision for authenticating or even identifying the requester asking
for data to be read or written. In such situations, every client
whose data access requests are executed has to be trusted to make
such requests only in cases in which they would be authorized if pNFS
were not used.
Clients that make IO requests in such environments have the ability
to access or modify data when they are not authorized to do so. This
provides a means whereby hostile clients can compromise data
security.
Servers can address such threats by limiting use of non-RPC data
access to clients who can be trusted to only make data access
requests that would be authorized in the non-pNFS case. The client-
peer authentication provided by RPC-with-TLS can be helpful in this
regard while the use of such data access without such authentication
gives rise likely compromise of necessary data security.
28.2.2.2. Threat Analysis for Layout Types Using NFS versions as Data
Access Protocols without Control Protocol Assistance
Although RPC is used for data access in this case, it is not used
identify or authenticate the principal making the data access
request. Instead, AUTH_SYS is used and the requesting principal is
specified by the layout. As a result, the situation, in terms of
threats to data integrity, is similar to that described in
Section 28.2.2.1.
[Author Aside]: TH Needs to review this section.
28.2.2.3. Threat Analysis for pNFS Layout Types using NFSv4.1 as a Data
Access Protocol Together with Control Protocol Assistance
Here we need to look at each of the possible pairs of communicating
entities individually:
* For communication between the clients and either the metadata
server to data storage devices (aka data servers), RPC should be
used and the threat analysis in the NFSv4-wide security applies
just as it does in the non-pNFS case. There will be no separate
threat analysis in this document.
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* For communication between the data storage devices and the
metadata server or between two data storage devices, it is
necessary that the communicating peers mutually authenticate and
there needs to be a trust relationship between the peers. See
Section 28.2.2.4 for an analysis of inter-component trust
relationships for the various layout types.
28.2.2.4. pNFS and Inter-component Trust Relationships.
When pNFS is not involved, there are only two actors involved in file
access: the server and the client. There are two possibilities
regarding trust relationships:
* With authenticated principals (e.g. RPCSEC_GSS), there is no need
for the server to trust the client or the user.
The client does need to trust the server to obey the protocol and
not provide information about its requests to others
* When AUTH_SYS is used, the server has to trust the client to
correctly authenticate user principals. To deal with the
possibility that clients might take advantage of this situation to
cause the server to execute unauthenticated requests, RPC-with-tls
can be used together with client peer authentication to limit the
set of clients whose unauthenticated requests are accepted or to
limit the set of principals that can be identified in this way.
At a minimum, acceptance of requests identified as made by root
would be limited.
When pNFS is involved, the situation is potentially more complicated
in that there are three sorts of actors and six potential trust
relationships.
* The interactions between the client and the metadata server are as
described above.
* The interactions between client and data server will vary
depending on the layout type.
For the cases described in Section 28.2.2.3, interactions between
client and data server follows the same model as that between the
client and metadata server. This case, when principals are
authenticated on both the MDS and the data server (i.e., when
RPC_SECGSS is used) is the only one in which the client does not
have to be specially trusted
Other mapping types will be discussed below.
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* Trust relationships between metadata server and data servers need
to exist, although, depending on the details of the mapping type,
the client might not be aware of this distinction, and consider
both servers together as a unified entity.
How this issue is addressed for various mapping types are
discussed below.
Unlike the cases in which tight coupling is provided, for other
mapping types we have no way of authenticating IO requesters and need
to trust the client to determine when IO operations are authorized.
The resulting situation is similar to that in which AUTH_SYS is used.
As is the case when AUTH_SYS is used, the client peer needs to
identify itself so that the server can use this identity to avoid a
case in which hostile node represents itself as having the ability to
individually authorize IO requests given a layout obtained when file
was opened.
Because layouts are per-client, rather than per-principal, objects,
IO authorization needs to checked for each request, as would be the
case if pNFS were not used. Of particular concern is the case in
which the principal performing the IO is not the same as the one
opening the file.
* In the case of such layout types as block or object, RPC is not
used so thee is no opportunity to identify the principal making
the request to the data server.
In the case in which the principal making the IO request is not
the opener, the client need to use ACCESS to ascertain the
authorization for the IO request.
* In the case of the flexible files layout in the loose coupling
mode, the issues are similar, even though RPC is used. Although,
the principal identification could be sent, this mapping type
specifies that a different unrelated principal identified in the
layout is to be passed. As a result, the principal issuing the
request is not identified in the RPC request.
Just as with mapping types that do not use RPC, in the case in
which the principal making the IO request is not the opener, the
client need to use ACCESS to ascertain the authorization for the
IO request. The principal can be authenticated at this point if
the metadata server is accessed using RPC_SECGSS.
Issues regarding trust relationships between the metadata server and
data servers are discussed below:
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* In implementing the file layout and, one assumes, in the case of
the flexible files layout in tight coupling mode, there is
necessarily a (two-way) trust relationship between metadata server
and data server. However, because the nature of their
relationship requires adherence to an undocumented control
protocol, those outside of the two servers are not in a position
to verify or understand the mutual requirements of the two
servers.
For all practical purposes, the client considers the two server
interfaces as a unified whole and has a trust relationship with
those two server interfaces considered together.
In particular, authorization decisions for IO requests are to have
the same results whether the data server or metadata server and is
the responsibility of the two servers to appropriately coordinate
to ensure that, just as it needs to coordinate locking globally.
* For layout types such as block and object there is no special
control protocol but the data access protocol is a subset of the
data device's protocol while the control protocol has access to a
different (usually larger) subset of that same data device
protocol.
For the clients to be assured that their data is safe, there need
to be restrictions on the use of the data device's protocol to
prevent hostile clients getting access to data without
authorization by the metadata sever.
* When the flexible files layout type is used in the loose coupling
mode, the situation is similar to those in which block or object
protocols are used. Just as in those cases, the data device's
protocol is NFSv3 but the data access protocol uses a restricted
subset with special constraints about how authorization is
determined. The metadata server has access to essentially the
full NFSv3 protocol.
Although clients are unlikely to be aware of the details, the
safety of their data depends on limiting access by additional
clients to data servers that are not restricted to the NFSv3
subset to be used by data servers. In order to effect the
necessary limiting, the use of client peer authentication is
needed to prevent use by hostile clients that are not prepared to
implement the equivalent of the metadata server's authorization
decisions. The potential damage is expanded if such hostile
clients have access to the full NFSv3 protocol.
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29. IANA Considerations
This section uses terms that are defined in [RFC8126].
29.1. IANA Actions
This update does not require any modification of, or additions to,
registry entries or registry rules associated with NFSv4.1. However,
since this document obsoletes RFC 8881, IANA is presumed to have
updated all registry entries and registry rules references that point
to RFC 8881 to point to this document instead.
Previous actions by IANA related to NFSv4.1 are listed in the
remaining subsections of Section 29.
29.2. Named Attribute Definitions
IANA has created a registry called the "NFSv4 Named Attribute
Definitions Registry". It has not been used and there is
considerable doubt about whether it ever will be.
The NFSv4.1 protocol supports the association of a file with zero or
more named attributes. The identifiers for these attributes are
defined as string names. The protocol does not define the specific
assignment of the namespace for these file attributes. The IANA
registry was intended to promote interoperability where common
interests exist but that approach now seems ill-advised for the
following reasons:
* Since the feature creates a virtual directory, there is no more
reason for users to register their names than there is for any
other directory. The fact that the feature is referred to as
"named attributes" doesn't change that.
* There is no point in registering this as part of the protocol,
since, when it is used there are similar names in the local
filesystem and for access by SMB that are outside the scope of
what the IETF can and should control.
As a result, specification of a naming standard that applies to
NFSv4 only when these named data streams are accessed using NFSv4
needs to be avoided.
While application developers are allowed to define and use attributes
as needed, they were previously encouraged to register the attributes
with IANA. However, as discussed above, the fact that the names
apply to file systems other than those accessed by NFSv4 implies that
it is not an appropriate way to promote interoperability.
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The registry was specified as being maintained using the
Specification Required policy as defined in Section 4.6 of [RFC8126].
The registry of named attributes was defined a list of assignments,
each containing three fields for each assignment.
1. A US-ASCII string name that is the actual name of the attribute.
This name must be unique. This string name can be 1 to 128 UTF-8
characters long.
2. A reference to the specification of the named attribute. The
reference can consume up to 256 bytes (or more if IANA permits).
3. The point of contact of the registrant. The point of contact can
consume up to 256 bytes (or more if IANA permits).
29.2.1. Initial Registry
There is no initial registry.
29.2.2. Updating Registrations
The registrant is always permitted to update the point of contact
field. Any other change was expected to require Expert Review or
IESG Approval.
29.3. Device ID Notifications
IANA created a registry called the "NFSv4 Device ID Notifications
Registry".
The potential exists for new notification types to be added to the
CB_NOTIFY_DEVICEID operation (See Section 27.12). This can be done
via changes to the operations that register notifications, or by
adding new operations to NFSv4. This requires a new minor version of
NFSv4, and requires a Standards Track document from the IETF.
Another way to add a notification is to specify a new layout type
(See Section 29.5).
Hence, all assignments to the registry are made on a Standards Action
basis per Section 4.6 of [RFC8126], with Expert Review required.
The registry is a list of assignments, each containing five fields
per assignment.
1. The name of the notification type. This name must have the
prefix "NOTIFY_DEVICEID4_". This name must be unique.
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2. The value of the notification. IANA will assign this number, and
the request from the registrant will use TBD1 instead of an
actual value. IANA MUST use a whole number that can be no higher
than 2^32-1, and should be the next available value. The value
assigned must be unique. A Designated Expert must be used to
ensure that when the name of the notification type and its value
are added to the NFSv4.1 notify_deviceid_type4 enumerated data
type in the NFSv4.1 XDR description [RFC5662], the result
continues to be a valid XDR description.
3. The Standards Track RFC(s) that describe the notification. If
the RFC(s) have not yet been published, the registrant will use
RFCTBD20, RFCTBD21, etc. instead of an actual RFC number.
4. How the RFC introduces the notification. This is indicated by a
single US-ASCII value. If the value is N, it means a minor
revision to the NFSv4 protocol. If the value is L, it means a
new pNFS layout type. Other values can be used with IESG
Approval.
5. The minor versions of NFSv4 that are allowed to use the
notification. While these are numeric values, IANA will not
allocate and assign them; the author of the relevant RFCs with
IESG Approval assigns these numbers. Each time there is a new
minor version of NFSv4 approved, a Designated Expert should
review the registry to make recommended updates as needed.
29.3.1. Initial Registry
The initial registry is in Table 26. Note that the next available
value is zero.
+=========================+=======+==========+=====+================+
| Notification Name | Value | RFC | How | Minor Versions |
+=========================+=======+==========+=====+================+
| NOTIFY_DEVICEID4_CHANGE | 1 | RFC | N | 1 |
| | | 8881 | | |
+-------------------------+-------+----------+-----+----------------+
| NOTIFY_DEVICEID4_DELETE | 2 | RFC | N | 1 |
| | | 8881 | | |
+-------------------------+-------+----------+-----+----------------+
Table 26: Initial Device ID Notification Assignments
29.3.2. Updating Registrations
The update of a registration will require IESG Approval on the advice
of a Designated Expert.
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29.4. Object Recall Types
IANA created a registry called the "NFSv4 Recallable Object Types
Registry".
The potential exists for new object types to be added to the
CB_RECALL_ANY operation (see Section 27.6). This can be done via
changes to the operations that add recallable types, or by adding new
operations to NFSv4. This requires a new minor version of NFSv4, and
requires a Standards Track document from IETF. Another way to add a
new recallable object is to specify a new layout type (See
Section 29.5).
All assignments to the registry are made on a Standards Action basis
per Section 4.9 of [RFC8126], with Expert Review required.
Recallable object types are 32-bit unsigned numbers. There are no
Reserved values. Values in the range 12 through 15, inclusive, are
designated for Private Use.
The registry is a list of assignments, each containing five fields
per assignment.
1. The name of the recallable object type. This name must have the
prefix "RCA4_TYPE_MASK_". The name must be unique.
2. The value of the recallable object type. IANA will assign this
number, and the request from the registrant will use TBD1 instead
of an actual value. IANA MUST use a whole number that can be no
higher than 2^32-1, and should be the next available value. The
value must be unique. A Designated Expert must be used to ensure
that when the name of the recallable type and its value are added
to the NFSv4 XDR description [RFC5662], the result continues to
be a valid XDR description.
3. The Standards Track RFC(s) that describe the recallable object
type. If the RFC(s) have not yet been published, the registrant
will use RFCTBD2, RFCTBD3, etc. instead of an actual RFC number.
4. How the RFC introduces the recallable object type. This is
indicated by a single US-ASCII value. If the value is N, it
means a minor revision to the NFSv4 protocol. If the value is L,
it means a new pNFS layout type. Other values can be used with
IESG Approval.
5. The minor versions of NFSv4 that are allowed to use the
recallable object type. While these are numeric values, IANA
will not allocate and assign them; the author of the relevant
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RFCs with IESG Approval assigns these numbers. Each time there
is a new minor version of NFSv4 approved, a Designated Expert
should review the registry to make recommended updates as needed.
29.4.1. Initial Registry
The initial registry is in Table 27. Note that the next available
value is five.
+===============================+=======+======+=====+==========+
| Recallable Object Type Name | Value | RFC | How | Minor |
| | | | | Versions |
+===============================+=======+======+=====+==========+
| RCA4_TYPE_MASK_RDATA_DLG | 0 | RFC | N | 1 |
| | | 8881 | | |
+-------------------------------+-------+------+-----+----------+
| RCA4_TYPE_MASK_WDATA_DLG | 1 | RFC | N | 1 |
| | | 8881 | | |
+-------------------------------+-------+------+-----+----------+
| RCA4_TYPE_MASK_DIR_DLG | 2 | RFC | N | 1 |
| | | 8881 | | |
+-------------------------------+-------+------+-----+----------+
| RCA4_TYPE_MASK_FILE_LAYOUT | 3 | RFC | N | 1 |
| | | 8881 | | |
+-------------------------------+-------+------+-----+----------+
| RCA4_TYPE_MASK_BLK_LAYOUT | 4 | RFC | L | 1 |
| | | 8881 | | |
+-------------------------------+-------+------+-----+----------+
| RCA4_TYPE_MASK_OBJ_LAYOUT_MIN | 8 | RFC | L | 1 |
| | | 8881 | | |
+-------------------------------+-------+------+-----+----------+
| RCA4_TYPE_MASK_OBJ_LAYOUT_MAX | 9 | RFC | L | 1 |
| | | 8881 | | |
+-------------------------------+-------+------+-----+----------+
Table 27: Initial Recallable Object Type Assignments
29.4.2. Updating Registrations
The update of a registration will require IESG Approval on the advice
of a Designated Expert.
29.5. Layout Types
IANA created a registry called the "pNFS Layout Types Registry".
All assignments to the registry are made on a Standards Action basis,
with Expert Review required.
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Layout types are 32-bit numbers. The value zero is Reserved. Values
in the range 0x80000000 to 0xFFFFFFFF inclusive are designated for
Private Use. IANA will assign numbers from the range 0x00000001 to
0x7FFFFFFF inclusive.
The registry is a list of assignments, each containing five fields.
1. The name of the layout type. This name must have the prefix
"LAYOUT4_". The name must be unique.
2. The value of the layout type. IANA will assign this number, and
the request from the registrant will use TBD1 instead of an
actual value. The value assigned must be unique. A Designated
Expert must be used to ensure that when the name of the layout
type and its value are added to the NFSv4.1 layouttype4
enumerated data type in the NFSv4.1 XDR description [RFC5662],
the result continues to be a valid XDR description.
3. The Standards Track RFC(s) that describe the notification. If
the RFC(s) have not yet been published, the registrant will use
RFCTBD2, RFCTBD3, etc. instead of an actual RFC number.
Collectively, the RFC(s) must adhere to the requirements listed
in Section 29.5.3 and 19.1
4. How the RFC introduces the layout type. This is indicated by a
single US-ASCII value. If the value is N, it means a minor
revision to the NFSv4 protocol. If the value is L, it means a
new pNFS layout type. Other values can be used with IESG
Approval.
5. The minor versions of NFSv4 that are allowed to use the
notification. While these are numeric values, IANA will not
allocate and assign them; the author of the relevant RFCs with
IESG Approval assigns these numbers. Each time there is a new
minor version of NFSv4 approved, a Designated Expert should
review the registry to make recommended updates as needed.
29.5.1. Initial Registry
The initial registry is in Table 28.
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+=======================+=======+==========+=====+================+
| Layout Type Name | Value | RFC | How | Minor Versions |
+=======================+=======+==========+=====+================+
| LAYOUT4_NFSV4_1_FILES | 0x1 | RFC 8881 | N | 1 |
+-----------------------+-------+----------+-----+----------------+
| LAYOUT4_OSD2_OBJECTS | 0x2 | RFC 5664 | L | 1 |
+-----------------------+-------+----------+-----+----------------+
| LAYOUT4_BLOCK_VOLUME | 0x3 | RFC 5663 | L | 1 |
+-----------------------+-------+----------+-----+----------------+
Table 28: Initial Layout Type Assignments
29.5.2. Updating Registrations
The update of a registration will require IESG Approval on the advice
of a Designated Expert.
29.5.3. IANA-Related Requirements for Layout Type Specifications
Specification of new layout types takes the form Standards-track
RFCs. Relevant requirements for these specifications are defined in
Section 19.
In addition, the specification needs to include an IANA
considerations section, which will in turn include:
* A request to IANA for a new layout type per Section 29.5.
* A list of requests to IANA for any new recallable object types for
CB_RECALL_ANY; each entry is to be presented in the form described
in Section 29.4.
* A list of requests to IANA for any new notification values for
CB_NOTIFY_DEVICEID; each entry is to be presented in the form
described in Section 29.3.
29.6. Path Variable Definitions
This section deals with the IANA considerations associated with the
variable substitution feature for location names as described in
Section 17.17.3. As described there, variables subject to
substitution consist of a domain name and a specific name within that
domain, with the two separated by a colon. There are two sets of
IANA considerations here:
1. The list of variable names.
2. For each variable name, the list of possible values.
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Thus, there will be one registry for the list of variable names, and
possibly one registry for listing the values of each variable name.
29.6.1. Path Variables Registry
IANA created a registry called the "NFSv4 Path Variables Registry".
29.6.1.1. Path Variable Values
Variable names are of the form "${", followed by a domain name,
followed by a colon (":"), followed by a domain-specific portion of
the variable name, followed by "}". When the domain name is
"ietf.org", all variables names must be registered with IANA on a
Standards Action basis, with Expert Review required. Path variables
with registered domain names neither part of nor equal to ietf.org
are assigned on a Hierarchical Allocation basis (delegating to the
domain owner) and thus of no concern to IANA, unless the domain owner
chooses to register a variable name from his domain. If the domain
owner chooses to do so, IANA will do so on a First Come First Serve
basis. To accommodate registrants who do not have their own domain,
IANA will accept requests to register variables with the prefix
"${FCFS.ietf.org:" on a First Come First Served basis. Assignments
on a First Come First Basis do not require Expert Review, unless the
registrant also wants IANA to establish a registry for the values of
the registered variable.
The registry is a list of assignments, each containing three fields.
1. The name of the variable. The name of this variable must start
with a "${" followed by a registered domain name, followed by
":", or it must start with "${FCFS.ietf.org". The name must be
no more than 64 UTF-8 characters long. The name must be unique.
2. For assignments made on Standards Action basis, the Standards
Track RFC(s) that describe the variable. If the RFC(s) have not
yet been published, the registrant will use RFCTBD1, RFCTBD2,
etc. instead of an actual RFC number. Note that the RFCs do not
have to be a part of an NFS minor version. For assignments made
on a First Come First Serve basis, an explanation (consuming no
more than 1024 bytes, or more if IANA permits) of the purpose of
the variable. A reference to the explanation can be substituted.
3. The point of contact, including an email address. The point of
contact can consume up to 256 bytes (or more if IANA permits).
For assignments made on a Standards Action basis, the point of
contact is always IESG.
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29.6.1.1.1. Initial Registry
The initial registry is in Table 29.
+========================+==========+==================+
| Variable Name | RFC | Point of Contact |
+========================+==========+==================+
| ${ietf.org:CPU_ARCH} | RFC 8881 | IESG |
+------------------------+----------+------------------+
| ${ietf.org:OS_TYPE} | RFC 8881 | IESG |
+------------------------+----------+------------------+
| ${ietf.org:OS_VERSION} | RFC 8881 | IESG |
+------------------------+----------+------------------+
Table 29: Initial List of Path Variables
IANA has created registries for the values of the variable names
${ietf.org:CPU_ARCH} and ${ietf.org:OS_TYPE}. See Sections 29.6.2 and
29.6.3.
For the values of the variable ${ietf.org:OS_VERSION}, no registry is
needed as the specifics of the values of the variable will vary with
the value of ${ietf.org:OS_TYPE}. Thus, values for
${ietf.org:OS_VERSION} are on a Hierarchical Allocation basis and are
of no concern to IANA.
29.6.1.1.2. Updating Registrations
The update of an assignment made on a Standards Action basis will
require IESG Approval on the advice of a Designated Expert.
The registrant can always update the point of contact of an
assignment made on a First Come First Serve basis. Any other update
will require Expert Review.
29.6.2. Values for the ${ietf.org:CPU_ARCH} Variable
IANA created a registry called the "NFSv4 ${ietf.org:CPU_ARCH} Value
Registry".
Assignments to the registry are made on a First Come First Serve
basis. The zero-length value of ${ietf.org:CPU_ARCH} is Reserved.
Values with a prefix of "PRIV" are designated for Private Use.
The registry is a list of assignments, each containing three fields.
1. A value of the ${ietf.org:CPU_ARCH} variable. The value must be
1 to 32 UTF-8 characters long. The value must be unique.
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2. An explanation (consuming no more than 1024 bytes, or more if
IANA permits) of what CPU architecture the value denotes. A
reference to the explanation can be substituted.
3. The point of contact, including an email address. The point of
contact can consume up to 256 bytes (or more if IANA permits).
29.6.2.1. Initial Registry
There is no initial registry.
29.6.2.2. Updating Registrations
The registrant is free to update the assignment, i.e., change the
explanation and/or point-of-contact fields.
29.6.3. Values for the ${ietf.org:OS_TYPE} Variable
IANA created a registry called the "NFSv4 ${ietf.org:OS_TYPE} Value
Registry".
Assignments to the registry are made on a First Come First Serve
basis. The zero-length value of ${ietf.org:OS_TYPE} is Reserved.
Values with a prefix of "PRIV" are designated for Private Use.
The registry is a list of assignments, each containing three fields.
1. A value of the ${ietf.org:OS_TYPE} variable. The value must be 1
to 32 UTF-8 characters long. The value must be unique.
2. An explanation (consuming no more than 1024 bytes, or more if
IANA permits) of what CPU architecture the value denotes. A
reference to the explanation can be substituted.
3. The point of contact, including an email address. The point of
contact can consume up to 256 bytes (or more if IANA permits).
29.6.3.1. Initial Registry
There is no initial registry.
29.6.3.2. Updating Registrations
The registrant is free to update the assignment, i.e., change the
explanation and/or point of contact fields.
30. References
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30.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4506] Eisler, M., Ed., "XDR: External Data Representation
Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
2006, <https://www.rfc-editor.org/info/rfc4506>.
[RFC5531] Thurlow, R., "RPC: Remote Procedure Call Protocol
Specification Version 2", RFC 5531, DOI 10.17487/RFC5531,
May 2009, <https://www.rfc-editor.org/info/rfc5531>.
[RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, DOI 10.17487/RFC2203, September
1997, <https://www.rfc-editor.org/info/rfc2203>.
[hardlink] The Open Group, "Section 3.191 of Chapter 3 of Base
Definitions of The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version",
ISBN 1931624232, 2004, <https://www.opengroup.org>.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743,
DOI 10.17487/RFC2743, January 2000,
<https://www.rfc-editor.org/info/rfc2743>.
[RFC5040] Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
Garcia, "A Remote Direct Memory Access Protocol
Specification", RFC 5040, DOI 10.17487/RFC5040, October
2007, <https://www.rfc-editor.org/info/rfc5040>.
[RFC5403] Eisler, M., "RPCSEC_GSS Version 2", RFC 5403,
DOI 10.17487/RFC5403, February 2009,
<https://www.rfc-editor.org/info/rfc5403>.
[RFC5662] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
External Data Representation Standard (XDR) Description",
RFC 5662, DOI 10.17487/RFC5662, January 2010,
<https://www.rfc-editor.org/info/rfc5662>.
[symlink] The Open Group, "Section 3.372 of Chapter 3 of Base
Definitions of The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version",
ISBN 1931624232, 2004, <https://www.opengroup.org>.
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[RFC5665] Eisler, M., "IANA Considerations for Remote Procedure Call
(RPC) Network Identifiers and Universal Address Formats",
RFC 5665, DOI 10.17487/RFC5665, January 2010,
<https://www.rfc-editor.org/info/rfc5665>.
[read_atime]
The Open Group, "Section 'read()' of System Interfaces of
The Open Group Base Specifications Issue 6 IEEE Std
1003.1, 2004 Edition, HTML Version", ISBN 1931624232,
2004, <https://www.opengroup.org>.
[readdir_atime]
The Open Group, "Section 'readdir()' of System Interfaces
of The Open Group Base Specifications Issue 6 IEEE Std
1003.1, 2004 Edition, HTML Version", ISBN 1931624232,
2004, <https://www.opengroup.org>.
[write_atime]
The Open Group, "Section 'write()' of System Interfaces of
The Open Group Base Specifications Issue 6 IEEE Std
1003.1, 2004 Edition, HTML Version", ISBN 1931624232,
2004, <https://www.opengroup.org>.
[fcntl] The Open Group, "Section 'fcntl()' of System Interfaces of
The Open Group Base Specifications Issue 6 IEEE Std
1003.1, 2004 Edition, HTML Version", ISBN 1931624232,
2004, <https://www.opengroup.org>.
[fsync] The Open Group, "Section 'fsync()' of System Interfaces of
The Open Group Base Specifications Issue 6 IEEE Std
1003.1, 2004 Edition, HTML Version", ISBN 1931624232,
2004, <https://www.opengroup.org>.
[passwd] The Open Group, "Section 'getpwnam()' of System Interfaces
of The Open Group Base Specifications Issue 6 IEEE Std
1003.1, 2004 Edition, HTML Version", ISBN 1931624232,
2004, <https://www.opengroup.org>.
[unlink] The Open Group, "Section 'unlink()' of System Interfaces
of The Open Group Base Specifications Issue 6 IEEE Std
1003.1, 2004 Edition, HTML Version", ISBN 1931624232,
2004, <https://www.opengroup.org>.
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[RFC4055] Schaad, J., Kaliski, B., and R. Housley, "Additional
Algorithms and Identifiers for RSA Cryptography for use in
the Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile", RFC 4055,
DOI 10.17487/RFC4055, June 2005,
<https://www.rfc-editor.org/info/rfc4055>.
[CSOR_AES] National Institute of Standards and Technology, "Computer
Security Objects Register", May 2016,
<https://csrc.nist.gov/projects/computer-security-objects-
register/algorithm-registration>.
[RFC7861] Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
November 2016, <https://www.rfc-editor.org/info/rfc7861>.
[RFC8000] Adamson, A. and N. Williams, "Requirements for NFSv4
Multi-Domain Namespace Deployment", RFC 8000,
DOI 10.17487/RFC8000, November 2016,
<https://www.rfc-editor.org/info/rfc8000>.
[RFC8166] Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
Memory Access Transport for Remote Procedure Call Version
1", RFC 8166, DOI 10.17487/RFC8166, June 2017,
<https://www.rfc-editor.org/info/rfc8166>.
[RFC8267] Lever, C., "Network File System (NFS) Upper-Layer Binding
to RPC-over-RDMA Version 1", RFC 8267,
DOI 10.17487/RFC8267, October 2017,
<https://www.rfc-editor.org/info/rfc8267>.
[RFC8154] Hellwig, C., "Parallel NFS (pNFS) Small Computer System
Interface (SCSI) Layout", RFC 8154, DOI 10.17487/RFC8154,
May 2017, <https://www.rfc-editor.org/info/rfc8154>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8178] Noveck, D., "Rules for NFSv4 Extensions and Minor
Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
<https://www.rfc-editor.org/info/rfc8178>.
[RFC8276] Naik, M. and M. Eshel, "File System Extended Attributes in
NFSv4", RFC 8276, DOI 10.17487/RFC8276, December 2017,
<https://www.rfc-editor.org/info/rfc8276>.
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[RFC8435] Halevy, B. and T. Haynes, "Parallel NFS (pNFS) Flexible
File Layout", RFC 8435, DOI 10.17487/RFC8435, August 2018,
<https://www.rfc-editor.org/info/rfc8435>.
[RFC8587] Lever, C., Ed. and D. Noveck, "NFS Version 4.0 Trunking
Update", RFC 8587, DOI 10.17487/RFC8587, May 2019,
<https://www.rfc-editor.org/info/rfc8587>.
[RFC8881] Noveck, D., Ed. and C. Lever, "Network File System (NFS)
Version 4 Minor Version 1 Protocol", RFC 8881,
DOI 10.17487/RFC8881, August 2020,
<https://www.rfc-editor.org/info/rfc8881>.
[RFC9289] Myklebust, T. and C. Lever, Ed., "Towards Remote Procedure
Call Encryption by Default", RFC 9289,
DOI 10.17487/RFC9289, September 2022,
<https://www.rfc-editor.org/info/rfc9289>.
[I-D.ietf-nfsv4-internationalization]
Noveck, D., "Internationalization for the NFSv4
Protocols", Work in Progress, Internet-Draft, draft-ietf-
nfsv4-internationalization-14, 15 February 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-nfsv4-
internationalization-14>.
[BCP09] Best Current Practice 9,
<https://www.rfc-editor.org/info/bcp9>.
At the time of writing, this BCP comprises the following:
Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
<https://www.rfc-editor.org/info/rfc2026>.
Kolkman, O., Bradner, S., and S. Turner, "Characterization
of Proposed Standards", BCP 9, RFC 7127,
DOI 10.17487/RFC7127, January 2014,
<https://www.rfc-editor.org/info/rfc7127>.
Dusseault, L. and R. Sparks, "Guidance on Interoperation
and Implementation Reports for Advancement to Draft
Standard", BCP 9, RFC 5657, DOI 10.17487/RFC5657,
September 2009, <https://www.rfc-editor.org/info/rfc5657>.
Housley, R., Crocker, D., and E. Burger, "Reducing the
Standards Track to Two Maturity Levels", BCP 9, RFC 6410,
DOI 10.17487/RFC6410, October 2011,
<https://www.rfc-editor.org/info/rfc6410>.
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Resnick, P., "Retirement of the "Internet Official
Protocol Standards" Summary Document", BCP 9, RFC 7100,
DOI 10.17487/RFC7100, December 2013,
<https://www.rfc-editor.org/info/rfc7100>.
Dawkins, S., "Increasing the Number of Area Directors in
an IETF Area", BCP 9, RFC 7475, DOI 10.17487/RFC7475,
March 2015, <https://www.rfc-editor.org/info/rfc7475>.
30.2. Informative References
[RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
Beame, C., Eisler, M., and D. Noveck, "Network File System
(NFS) version 4 Protocol", RFC 3530, DOI 10.17487/RFC3530,
April 2003, <https://www.rfc-editor.org/info/rfc3530>.
[RFC1813] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
Version 3 Protocol Specification", RFC 1813,
DOI 10.17487/RFC1813, June 1995,
<https://www.rfc-editor.org/info/rfc1813>.
[RFC2847] Eisler, M., "LIPKEY - A Low Infrastructure Public Key
Mechanism Using SPKM", RFC 2847, DOI 10.17487/RFC2847,
June 2000, <https://www.rfc-editor.org/info/rfc2847>.
[Chet] Juszczak, C., "Improving the Performance and Correctness
of an NFS Server", USENIX Conference Proceedings, June
1990.
[RFC3232] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced
by an On-line Database", RFC 3232, DOI 10.17487/RFC3232,
January 2002, <https://www.rfc-editor.org/info/rfc3232>.
[RFC1833] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, DOI 10.17487/RFC1833, August 1995,
<https://www.rfc-editor.org/info/rfc1833>.
[rpc_xid_issues]
Werme, R., "RPC XID Issues", USENIX Conference
Proceedings, February 1996.
[RFC5664] Halevy, B., Welch, B., and J. Zelenka, "Object-Based
Parallel NFS (pNFS) Operations", RFC 5664,
DOI 10.17487/RFC5664, January 2010,
<https://www.rfc-editor.org/info/rfc5664>.
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[RFC5663] Black, D., Fridella, S., and J. Glasgow, "Parallel NFS
(pNFS) Block/Volume Layout", RFC 5663,
DOI 10.17487/RFC5663, January 2010,
<https://www.rfc-editor.org/info/rfc5663>.
[RFC2054] Callaghan, B., "WebNFS Client Specification", RFC 2054,
DOI 10.17487/RFC2054, October 1996,
<https://www.rfc-editor.org/info/rfc2054>.
[RFC2055] Callaghan, B., "WebNFS Server Specification", RFC 2055,
DOI 10.17487/RFC2055, October 1996,
<https://www.rfc-editor.org/info/rfc2055>.
[errata] IESG, "IESG Processing of RFC Errata for the IETF Stream",
July 2008,
<https://www.ietf.org/about/groups/iesg/statements/
processing-rfc-errata/>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[xnfs] The Open Group, "Protocols for Interworking: XNFS, Version
3W", ISBN 1-85912-184-5, February 1998.
[Floyd] Floyd, S. and V. Jacobson, "The Synchronization of
Periodic Routing Messages", IEEE/ACM Transactions on
Networking, 2(2), pp. 122-136, April 1994.
[OSD-T10] Weber, R.O., "Object-Based Storage Device Commands (OSD)",
ANSI/INCITS, 400-2004, July 2004,
<https://www.t10.org/drafts.htm>.
[PVFS] Carns, P. H., Ligon III, W. B., Ross, R. B., and R.
Thakur, "PVFS: A Parallel File System for Linux
Clusters.", Proceedings of the 4th Annual Linux Showcase
and Conference, 2000.
[access_api]
The Open Group, "The Open Group Base Specifications Issue
6, IEEE Std 1003.1, 2004 Edition", 2004,
<https://www.opengroup.org>.
[RFC2224] Callaghan, B., "NFS URL Scheme", RFC 2224,
DOI 10.17487/RFC2224, October 1997,
<https://www.rfc-editor.org/info/rfc2224>.
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[RFC2755] Chiu, A., Eisler, M., and B. Callaghan, "Security
Negotiation for WebNFS", RFC 2755, DOI 10.17487/RFC2755,
January 2000, <https://www.rfc-editor.org/info/rfc2755>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[AFS] Spasojevic, M. and M. Satayanarayanan, "An Empirical Study
of a Wide-Area Distributed File System", ACM Transactions
on Computer Systems, Vol. 14, No. 2, pp. 200-222,
DOI 10.1145/227695.227698, May 1996,
<https://doi.org/10.1145/227695.227698>.
[RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
<https://www.rfc-editor.org/info/rfc5661>.
[RFC7530] Haynes, T., Ed. and D. Noveck, Ed., "Network File System
(NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
March 2015, <https://www.rfc-editor.org/info/rfc7530>.
[RFC7931] Noveck, D., Ed., Shivam, P., Lever, C., and B. Baker,
"NFSv4.0 Migration: Specification Update", RFC 7931,
DOI 10.17487/RFC7931, July 2016,
<https://www.rfc-editor.org/info/rfc7931>.
[RFC8434] Haynes, T., "Requirements for Parallel NFS (pNFS) Layout
Types", RFC 8434, DOI 10.17487/RFC8434, August 2018,
<https://www.rfc-editor.org/info/rfc8434>.
[RFC3010] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
Beame, C., Eisler, M., and D. Noveck, "NFS version 4
Protocol", RFC 3010, DOI 10.17487/RFC3010, December 2000,
<https://www.rfc-editor.org/info/rfc3010>.
[I-D.dnoveck-nfsv4-security]
Noveck, D., "Security for the NFSv4 Protocols", Work in
Progress, Internet-Draft, draft-dnoveck-nfsv4-security-13,
16 November 2025, <https://datatracker.ietf.org/doc/html/
draft-dnoveck-nfsv4-security-13>.
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[I-D.ietf-nfsv4-acls-update]
Noveck, D., "ACLs within the NFSv4 Protocols", Work in
Progress, Internet-Draft, draft-ietf-nfsv4-acls-update-03,
9 February 2026, <https://datatracker.ietf.org/doc/html/
draft-ietf-nfsv4-acls-update-03>.
[I-D.dnoveck-nfsv4-rfc5662bis]
Noveck, D., "Network File System (NFS) Version 4 Minor
Version 1 External Data Representation Standard (XDR)
Description", Work in Progress, Internet-Draft, draft-
dnoveck-nfsv4-rfc5662bis-06, 23 May 2025,
<https://datatracker.ietf.org/doc/html/draft-dnoveck-
nfsv4-rfc5662bis-06>.
Appendix A. Nature of the Changes Being Made for This Update
A large number of changes being made in this document are made to
effect corrections to previous NFS Version 4.1 specifications. These
include changes to address errata reports connected with those
specifications, including some that were assigned the status
REJECTED. In addition, similar changes are being made without
explicit errata reports.
It is important to note that there are also a number of important
organizational changes discussed below that will be made in this
updated specification. As work on this document progresses, the
status of those changes, together with other necessary changes, will
be summarized in Appendix B.
* The updated specification will depend on a number of NFSv4-wide
documents, as described in Appendix A.1, rather than trying to
deal with every aspect of the protocol description itself.
In the case of security, there will have to be decisions on how
v4.1-specific security-related features will be addressed. See
Appendix A.2 for details.
A.1. Reliance on NFSv4-wide Documents
In many cases, matters previously described within the NFSv4.1
specification, will be addressed in separate NFSv4-wide documents.
* The process of protocol extension and creation of new minor
versions is described in a separate NFSv4-wide document,
[RFC8178], dealing with the issue for the NFSv4 protocols as a
whole.
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* Internationalization will be described in a separate document
describing internationalization for all of the NFSv4 protocols,
currently [I-D.ietf-nfsv4-internationalization]. The only
v4.1-specific feature is the fs_charset_cap attribute, which is
described in the current document rather than the
internationalization document, although that document does discuss
our choices in the matter.
* Security will also be described in a separate document applying to
all minor versions. The handling is different because there is a
wider range of security-relevant features within v4.1, despite the
fact that the fundamental approach is the same for all minor
versions. As a result, for some features, the security document
will have the lead role while, for others, the v4.1 specification
will be the main source of information about the feature, although
the basic security functionality will be as defined by the
NFSv4-wide security document.
A.2. Adaptation of the NFSv4-wide Security Document to v4.1-specific
Features
The v4.1-specific security-related features are dealt with as
described below:
* Security issues regarding pNFS will be the responsibility of this
v4.1 specification document. In doing this, we will rely, where
we can, on the security facilities described in the NFSv4-wide
security document.
This is necessary because some layout types will access data
without using the RPC-based facilities that are discussed in the
security document. In addition, the requirements for security-
related coordination between data server and metadata server are
best dealt with in this document, including cases in which RPC is
used by both the data server and the metadata server, in which the
necessary coordination requirements are defined by the layout type
specification document.
* The description of the SECINFO_NO_NAME operation, will remain in
the v4.1 specification, even though the description of SECINFO
pseudo-flavors will be consolidated in the security. document.
This approach is necessary because the description of SECINFO
pseudo-flavors needs to be augmented to allow negotiation of
security-related transport characteristics in addition to auth-
flavors, associated mechanisms and RPCSEC_GSS services.
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* The description of the MACH_CRED and SSV features will remain in
the v4.1 specification document and will only be mentioned in
passing in the security document.
Instead, the focus with regard to state protection will be on
client-peer authentication which applies to all minor versions.
A.3. Changes to Effect Necessary Cleanup and Correction
The review of the existing specification text has discovered a set of
areas that require clarification or correction, even though the
problems had not been noticed as part of the pre-publication review
of [RFC8881] and no errata reports have yet been filed.
In the following cases, it was necessary to make revisions to make
the use of certain terms uniform throughout the document or to
clarify the definitions which have come to disagree with the initial
definitions.
* The treatment of the term "client owner" has been clarified to
deal with the fact that previous specifications were inconsistent
about whether the verifier was part of the client owner or added
to it.
In this draft, a "client owner" always includes a verifier. When
it is necessary to refer to the opaque string within it, the term
"client owner id" is used.
These changes appear in Sections 2.5 and 5.5.
* The definition of "verifier" has needed to substantially revised
to reflect the fact that there multiple verifiers within the
protocol, each with its own use.
These changes appear in Section 2.5
* There has been a set of changes motivated by a need to clarify the
circumstances under which delegation might be revoked.
This involved parallel changes in the description of leases where
existing text was confusing because it was sometimes assumed that
all locks were included rather than non-recallable ones, which
obscures discussion of delegation/layout recall and revocation.
These changes appear in Sections 2.5 and 3.
A large set of changes were made to address issues within
Section 7.6. These include:
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* The requirement to wait forever for a response before reusing a
slot has been modified to allow such waits to be terminated
because of extraordinary circumstances such as termination of the
task issuing the request.
That had to be changed because clients were unable to conform and
because of the weakness of the proposed justification for the
prohibition, i.e., that it resulted in a choice as to the next
sequence value to be used.
The replacement makes clear why the sequence number is to be
advanced, which is useful in reducing the probability of false
retries.
* The prohibition on request retry was changed from a normative
requirement to implementation guidance because it was clearly not
a "fundamental requirement of the specification". Also the
justification for a strict prohibition was undercut by work done
in NFSv4.1 to implement Exactly-One Semantics, whose goal was to
avoid negative consequences due to retries.
The replacement text clearly indicates why such retries are
useless and best avoided, which is consistent with current
practice. However it was necessary, in order to limit the
occasions in which false retries could occur to use MUST NOT to
forbid issuing of retries for abandoned requests once the slot had
been used to send a later request.
* The discussion of false retries had to be extensively revised to
make it clear that, while there were requirements to report
certain false retries when detected, there were not corresponding
requirements to check for this possibility. Instead situations in
which such checking might be prudent are provided.
In the revised section, it is clear that false retries cannot
occur if requests are never abandoned without a response and the
protocol is implemented correctly. In addition, it is made clear
how unlikely such false retries are if such request retries are
constrained as required by the text related to valid reasons for
request abandonment.
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Appendix B. Status of The Changes Being Made in this Update
Like all internet drafts, this document is a work in progress. In
this particular case, that designation is particularly appropriate
since there are specific changes that need to be made and either have
not made or have been started but not completed. Information
regarding changes made or to be made in this update is to be found in
Appendices B.1 through B.4.
The current form in which the material is presented is designed for
internal use within the working group, in order to help track the
document's progress towards its goals.
Ultimately, the material regarding these changes will be re-organized
in an eventual RFC.
B.1. Changes Completed So Far in this Update
Work on the necessary changes discussed below has already been
completed, although necessary review might not yet have occurred. At
least for a while, changes made in later drafts of the working group
document (i.e. those beyond -00) will not be reflected in this
section and will be found within a subsection of Appendix C
The discussion of minor versioning has been updated to refer to
[RFC8178], instead of the former approach which allowed each minor
version to make its own versioning rules.
There are issues that have been addressed regarding how retried
requests are to be terminated, including the fact the most common
client handling of this situation violates a "MUST" in the existing
specification. This took form of a revised Section 7.6.2, as
discussed in Appendix D.2.1.
The document has been updated to eliminate the current (erroneous)
treatment of internationalization, derived from earlier NFSv4.1
specifications [RFC5661], [RFC8881]. The section dealing with
internationalization has been deleted, since it was never
implemented. In its place, the specification has been modified to
reference an external document which is to define the appropriate
handling for internationalization for the NFSv4 protocols as a whole.
Currently, that document is the I-D draft-ietf-
nfsv4-internationalization [I-D.ietf-nfsv4-internationalization]. In
addition, the treatment of the fs_charset_cap attribute has been
revised to reflect the analysis presented in the internationalization
document.
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Despite the completion of the internationalization work within this
document, there remains work to do, most of which involves the
completion of review for the NFSv4-wide internationalization document
* The new document was based on the treatment of
internationalization within [RFC7530], which served as a useful
starting point, since implementation of all NFSv4 minor version
followed the same approach to internationalization issues.
However the following issues still needed to be addressed:
* There was a need to update the treatment within RFC7530 to reflect
IDNA changes made soon after the document was published.
* There was a need to deal better with client name-caching issues,
especially in the context of case-insensitive file systems. Text
has been written and submitted but review is needed.
* There was a need to address more fully the provision of
representation-independent name lookup, which maps all canonically
equivalent name strings in a directory to the same file.
However, these issues are being addressed in the context of the
internationalization document, rather than the NFSv4.1 specification.
B.2. Changes Made in this Update to Address NFSv4.1 Errata Reports
Work has been done to deal with errata reports associated previous
NFSv4.1 specifications. These include a large set of errata reports
associated with RFC5661 and a few associated with RFC8881. This work
can be categorized as follows:
* The following errata reports associated with RFC5661 were dealt
with in RFC8881, either because their substance related to issues
to be dealt with in RFC8881 or because the simplicity of the
needed change and its non-controversial nature made it simple to
address the report as part of the RFC editing process for RFC8881:
2062, 2280, 2324, 2330, 2548, 3558, 5212.
* Work needed to be done to address many errata reports relevant to
RFC 5661 that were not addressed in RFC8881, because the change
was too large or too potentially too controversial to address in
the context of RFC editing for RFC881.
* There are a number of errata reports associated with RFC8881, that
also had to be addressed.
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* A few of the existing errata reports might have implications for
RFC5662 and would need to be addressed by an eventual rfc5662bis
RFC.
The errata reports that remain and that are being addressed in this
document include reports currently assigned a range of statuses in
the errata reporting system, including reports marked Verified, Hold
for Document Update, and Rejected. These statuses are relevant to
the processing of the associated errata but not in a way as direct as
might be anticipated since errata reports marked Rejected might be
addressed, as a result of a justified change in working group
consensus.
* The following errata reports associated with RFC5661, have already
been addressed in this document draft, in some cases by splitting
out the associated change, if still necessary, into a related
document: 2005, 2006, 2249, 2291, 2299, 2326, 2327, 2328, 2505,
2722, 3064, 3065, 3066, 3068, 3208, 3379, 3653, 3714, 3901, 4119,
4215, 4492, 4572, 4711, 4712, 4914, 5040, 5417, 5467, 5476, 6015,
6324.
* The following errata reports associated with RFC8881 already been
incorporated into this document draft: 6308, 6337, 6865, 6611,
8705.
* The following errata reports associated with RFC5661 had not
previously been addressed but will be resolved with publication of
this draft as described in Appendix C.5: 2751, 3067, 4118, 5982.
The following issues need to be discussed with the errata report
authors and the rest of the working group to enable the issues raised
to be addressed in the resulting RFC:
* Errata reports 2751 and 3067 are related as both have to do with
LAYOUTCOMMIT on the file layout type. As a result they are best
discussed together.
The current status of 2751 is REJECTED which is justified given
the scope of the proposed change. Nevertheless, it seems the
working group needs to address this area, if not necessarily using
the current proposed text for this report.
These reports need further working group discussion before the
necessary changes are made in the document proper.
* Errata report 4118 has a current status of DEFER and for the most
part appears unproblematic.
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The proposed text uses the RFC2119-defined keyword "SHOULD" in a
way that is not in accord with its definition and adds confusion
to the proposal.
Once agreement is reached on the details of the replacement text,
this issue should be easy to address.
* Errata report 5982 has current status of REJECTED. After further
consideration of the issues, the proposer decided that the
proposed replacement text addressed the wrong issue and so will be
dropped.
Material related to the issues which this report was intended to
address are being dealt with as described in Appendix D.2.1.
The only reports that still need to be addressed are 2751, 3067, and
4118.
B.3. Changes Being Made Now in this Update
Work on the necessary changes discussed below has started but is not
yet complete. This includes cases in which work to be completed is
not within this document, but in a document referred to by this
document. In such cases, matters formerly dealt within the NFSv4.1
specification, in the form of a single document, need to be addressed
in a number of documents, each dealing with all NFSv4 minor versions
together.
As noted previously, there are significant problems with the
treatment of security within previous NFSv4.1 specifications
[RFC3530], [RFC5661], and within other current NFSv4 specifications
(e.g. [RFC7530], [RFC8881]). These are listed in Section 28.1.
Work has started on these issues, although it is not as advanced as
that for internationalization, since many important decisions need to
be made. There is now a security I-D [I-D.dnoveck-nfsv4-security]
which will serve as a guide to the decisions that will need to be
made to guide the further work to arrive at a Proposed Standard
discussing security for all the NFSv4 protocols, which rfc56661bis
will refer to normatively.
Work is being done incorporate the material within [RFC8434], which
establishes the requirements for parallel NFS (pNFS) layout types,
which were not clearly specified in RFC 5661, leading to confusion.
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There are a number of issues that are being addressed regarding the
treatment of Directory Delegations. Although preliminary changes
have been made, there might not be a clear consensus as to how
existing issues should be addressed in this minor version. As a
result further working group discussion will be needed. See
Appendix D.2.2. for details.
Work has been done in Sections 2.7 and 5.3 to make the presentation
more suitable to an environment in which RPC makes transport-level
encryption and client-host authentication available. However, there
is a need for some working group decisions to be made before
completion of the transition to a security framework that fully
embraces these new elements. In addition, the writing of a new
Security Considerations section will require substantial progress on
a standards-track security document for NFSv4 as a whole. Once that
work is done, there will need to be a re-organization of those
sections and their role will primarily be to refer to the standards-
track security document.
In addition, work has been done to address security issues for
NFSv4.1-specific features:
* Significant work has been done to clarify security implications of
pNFS.
This work has primarily consisted of a major revision of
Section 18.11 although there are significant updates to Sections
2.7 and 2.8.2.
It has been made clear that the only cases in which there are
essentially no security consequences from the use of pNFS, are
those in which RPC is used by the storage protocol, correcting
text in previous specifications which gives a contrary impression.
The text has been revised to take account of the existence of
services provided by rpc-tls including encryption and client host
authentication.
There has been a re-organization of Section 18.11, including
separate subsections dealing with non-RPC-based storage protocols
and RPC-based storage protocols with either loose or tight
coupling between storage server and metadata server.
* Significant work has been done to provide rpc-tls-based state
protection which can be taken advantage even by clients who have
not implemented SP4_MACH_CRED or SP4_SSV or who are using
AUTH_SYS.
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The Section 5.5.3 has been revised to allow, when SP4_NONE is
used, client host authentication to be used for state protection.
It is made clear in Section 7.8.3 that the use of SP4_NONE, when
host-client authentication is active, provides state protection
against other clients rather than waiving state protection.
For many of the changes mentioned above, the definitive treatment
will appear in the NFSv4-wide security document and there might
also be a temporary references to the preliminary security I-D.
Further changes along these lines will most likely be necessary
wherever in the document the SP4_* values are referred to.
There are a number of issues relating to the use of the key words
defined in [RFC2119]. While the issues below could be treated
individually and distributed among Sections B.1 through B.4, for now,
we will treat them together.
* A shift has been made from only citing [RFC2119] to citing
[RFC8174]. While it is sometimes said that, in the absence of
RFC8174, "must" and "MUST" are to be considered synonymous, the
working group has never interpreted RFC2119 in that way, although
the clarification provided by RFC8174 was helpful. In light of
this, it might be considered that all the necessary work has been
done, apart from necessary review. However, given the working
group discussion about this issue in connection with RFC8881, it
appears that the working group will need to further discuss this
issue soon after this document becomes a working group document.
That would enable us to consider this aspect of the work complete.
* The use of the term "RECOMMENDED" to describe NFSv4 attributes
which are not REQUIRED as been addressed by switching to the term
"OPTIONAL", since "RECOMMENDED" is not in accord with [RFC2119].
This work is considered complete.
* There is ongoing work to deal with what appears to be a
misclassification of protocol-defined attributes, making a number
of attributes OPTIONAL, when the practical difficulties for
clients in dealing with the absence of server support, makes this
an inappropriate choice.
The security-related attributes owner, owner_group, and mode have
been made REQUIRED, both in this document and in
[I-D.dnoveck-nfsv4-security].
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The working group needs to review existing OPTIONAL attributes to
see if similar changes need to be made for other attributes
derived from NFSv3.
* For many of the existing uses of the terms "SHOULD" and "SHOULD
NOT", it is not clear that the meaning is compatible with RFC2119.
The difficulty is compounded by uncertainty left as to the proper
use of these terms, about which there may be disagreement within
the working group. See Appendix D.1.1 for a detailed discussion
of issues that need to be resolved. Some work has started on this
area by adjusting text in certain sections but the work cannot be
completed until there is agreement about the proper use of these
terms in this document.
These issues have been addressed by changes in Sections 5.7.2,
5.7.3, and 7.6.1). In addition, similar changes will be made in
[I-D.dnoveck-nfsv4-security].
* There are some cases in which the terms "MUST" and "MUST NOT" have
essentially been ignored by implementations or there are other
reasons to believe that these terms may have been used
inappropriately. See Appendix D.1.2 for a detailed discussion.
Some work has been done toward addressing these issues but it is
not complete, because further discussion is needed regarding
changes to be made in Section 7.6.2.
These issues have been addressed by changes in Sections 5.7.1 and
5.7.2.
B.4. Changes That Will Need to be Made Later in this Update
Although this section is currently empty, one show be aware that
* There may be reasons to add new items discovered as on the
document progresses.
* There is still significant work listed in Appendix B.3.
* Much work already done still needs discussion and review.
Appendix C. Work Done in Various Drafts
The work in the subsections below cover changes made in various
drafts of draft-ietf-nfsv4-rfc{5661,8881}bis and does not cover
changes made in drafts of draft-dnoveck-nfsv4-rfc5661bis. As a
result all such changes appear in Appendix C.1.
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C.1. Changes Made in 5661bis Draft -00
This draft made major organizational changes in the text inherited
from [RFC8881] and started the work to clean up many of the
troublesome issues discussed in Appendices D.1 and D.2.1.
The organizational changes included the following:
* Creating a new top-level section describing the reasons for this
update.
* Moving most of the security-related material into its own
NFSv4-wide document.
* Deleting the existing treatment of internationalization and
referring the reader to the new NFSv4-wide internationalization
document.
* Creating the initial versions of Appendices A, B, and D to track
and explain changes needed and made.
C.2. Changes Made in 5661bis Draft -01
Beyond limited editorial changes, this section lists the work done in
draft -01.
The toc depth has been returned to the default value of three, with
exclusions for subsections of operations and callbacks. The value of
two left too many important third-level sections that did not appear
the table of contents.
A large part of the changes consist of the changes described in in
more detail in Appendix A.3.
* The re-organization of the description of client owner
* The revised explanation of the term "verifier".
* The enhanced description of delegation revocation.
* The set of changes made to address issues regarding EOS, retry and
false retry, made to Section 7.6.
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An interrelated set of changes were made in the pNFS area in order to
clarify and re-organize the treatment if pNFS security, with some of
it being the responsibility of the security document and to revise
the material to clearly address the issues dealt with RFC8434 which
is now obsoleted by this document. The following specific changes
were made:
* Changes were made in terminology so that the general description
of pNFS is consistent both with the files layout type and the
layout types that appropriately deal with "storage devices.
The general term "data access protocol" refers both storage
protocol and the use of file protocol to access a data server.
* The treatment of the term "control protocol" has been revised so
as to avoid a contradiction between the presentation in RFC8881,
which implied there was always a control protocol and RFC8435
which claimed it covered cases in which there was no control
protocol.
* The section on pNFS security has been substantially revised for
greater clarity and generality.
* A start has been made organizing the portions of the threat
analysis that are to reside in rfc8881bis proper.
A new section for issues that need discussion was added as
Appendix D.2.4. It deals with the following issues:
* A lack of clarity regarding possible persistence of lock state.
* A number of issues in the description of reply cache persistence
that either make the feature difficult to implement or
unnecessarily suggest that it needs to do things that are
inherently difficult or impossible.
A new section (Appendix D.2.3) was added regarding issues raised by
the discussion of memory-mapped files, now in Section 15.7. In
addition, that section has been revised, in this draft to address the
following issues:
* A neglect of the expected role of opening files for read, which
would have caused delegation recall, rendering many of the issues
worried about irrelevant.
* An unjustified expectation that, with mandatory locking in effect
IO operations would result in obtaining locks making deadlock
likely.
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* An unjustified assumption that locking issues present in the last
of mandatory locking apply as well in the case of advisory
locking.
C.3. Changes Made in 5661bis Draft -02
A number of changes related to the classification of attributes have
been made:
* Attributed described as "Recommended", which previously has been
described (incorrectly) as RECOMMENDED, were described as
OPTIONAL, in accord with [RFC2119].
* The attributes Mode, Owner, Owner_group, previously OPTIONAL,
although referred to as "Recommended", have been made REQUIRED.
This change parallels similar changes in the NFSv4-wide security
document [I-D.dnoveck-nfsv4-security].
C.4. Changes Made in 5661bis Draft -03
A number of changes have been made to adapt to the splitting of ACL-
related material from the security document and its presentation in a
separate document devoted to ACLs [I-D.ietf-nfsv4-acls-update].
* Many reference to the security document have been updated to
include the acls document as well [I-D.ietf-nfsv4-acls-update].
* Many reference to specific sections of the security document have
been updated to reflect changes to that document.
Some of these have been modified to reference sections that are
now in the acls document [I-D.ietf-nfsv4-acls-update].
In addition, a number of changes were made regarding the handling of
various security-related attributes, introducing the topic with the
understanding that the full treatment of the associated issues will
be done within the NFSv4-wide security document
[I-D.dnoveck-nfsv4-security].
* The paragraph regarding GETATTR and SETATTR of the name attribute
directory has been rewritten to eliminate the dubious logic even
though the protocol has not been changed, leaving a gap that still
need to be addressed separately for POSIX authorization and ACLs.
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* The section regarding the interpretation of owner and owner-group
strings has been rewritten to introduce the possible choices,
leaving the policy issues to the NFSv4-wide security document.
Further work was done on the issues discussed in Appendix D.2.1
including addressing issues originally intended to be dealt with a
part of errata report 5982.
The description of the errata report status has been revised making
it clear that only three reports still need to be addressed
We have created new per-draft Appendices C.1, C.2, and C.4 to keep
track of specification changes.
There has been considerable work within Appendix D.2 including the
following:
* Reorganization of the listing of the statuses of Appendix D.2
subsections according to the drafting of corresponding changes
* Considering Appendix D.2.1 Complete and ready for review.
* Creation of Appendices D.2.5 and D.2.6.
C.5. Changes Made in 5661bis Draft -04
Major revision have been made to Section 8 and Appendix D.2.4 in
order to:
* update the description of persistence-related issues to reflect
recent discoveries.
* provide an updated description of a persistence that has a good
chance of being implemented and that could eliminate most grace
period delays in the event of server restart.
* Clarify how a client becomes aware of persistence cross a server
restart.
Considerable work was done in line with the suggestions in
Appendix D.2.2. The following issues were addressed:
* The uncertainty about what assumptions could be made about the
stability of cookie values and directory entry ordering by a
directory delegation holder.
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* The potential confusion about the effect of batching and delays of
notifications needed to be addressed by making it clearer that
these only applies to updates of attribute of file in the
directory, rather than to the directory contents.
As a consequence of this work, the drafting associated with the
various subsections of Appendix D.2 reached completion and it was
necessary to revise Appendix D.2 proper to guide the necessary
working group discussion of those changes.
There was considerable work clarifying the handling of
CLAIM_DELEG_PREV. This includes:
* Distinguishing the special period allowed after client restart
from the grace period used as part of server restart.
* Defining use of DELEG_PREV claim types as reclaim-type operations
while making it clear that they have no relation to the grace
period or RECLAIM_COMPLETE
Completed all necessary errata-based changes for this document by
making the changes listed below:
* Errata report 2751, although rejected, has been incorporated into
this draft.
The proposed changes were followed fairly closely, although the
proposed new section has been moved from the pNFS chapter to the
pNFS file chapter.
* Errata report 3067 has been incorporated into this draft.
The only divergence from the proposed text were the deletion of
the word "deprecated" which was replaced by "are no longer used".
Some incorrect uses of RFC2119-defined keywords were made lower-
case.
* Errata report 4118 has been incorporated into this draft.
The only divergence from the proposed text were the deletion of
the phrase "SHOULD be ignored" and its replacement by a statement
that the field has no use. According to the author's reading of
[RFC2119], "no harm, no 'SHOULD' applies here.
* Errata report 5982, which was rejected, has not been incorporated
into this draft.
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The change proposed, mentioning XID in connection with the false
retry discussion turned out to be inadvisable and was dropped.
Despite that, other changes, discussed above, were made to satisfy
the original motivation of this errata report, to make it clearer
why extensive checking to detect false retry is not likely to be
done, an issue which has needed to be addressed for a while.
Appendix D.2.7 was created to track discussion of errata that had
been rejected.
C.6. Changes Made in 5661bis Draft -05
Changes to make it clearer when a change in the link count made by
anyone other than the delegation holder cause a recall of a
delegation. In particular, the case of changes done by NFSv4.0
clients needed clarification as did the rules for write delegations.
Added a discussion of the defects fixed as part of the rfc8881bis
effort, focusing on the possibility of compatibility issues and the
limited use of protocol extension, as provided for in Section 9 of
[RFC8178]. This work included:
* Adding a summary of the work done to correct existing protocol
defects in a new Section 1.4
* Extension of the notification enum to enable changes discussed
below to enable implementation of directory delegations.
* Preliminary discussion of a new OPTIONAL attribute aclchoices to
avoid having to wait for v4.2 to implement an aclfeatures
attribute, as previously anticipated.
Made a series of changes to the discussion of directory delegations
in Appendix D.2.2 and elsewhere. This work was prompted by
suggestions from Rick Macklem and others.
* Additions to Appendix D.2.2 discussing reasons to provide a more
flexible approach to the provision of position information within
content update notifications.
* Adding of new Appendices D.2.2.2 and D.2.2.3 discussing how that
flexibility might be provided
* Adding of a new Appendix D.2.2.5 together with corresponding work
in Section 16.2
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In addition to the above work within the Appendices, a number of
changes were made to the specification proper to create new
facilities to deal with issues discussed above and to incorporate
Rick's suggestions to make the discussion directory delegations
clearer. The changes included the following:
* Creating a new top-level section (now Section 16.2) explaining the
directory delegation feature.
* A major revision of Section 25.39 to explain the use of the input
and result notification bitmaps.
* A major rework/restructuring of Section 27.4 providing separate
subsections for notification types.
Additional work was done in material first discussed in
Appendix D.2.1 in order more clarity about the motivation for the
changes and the connection to the probability of false retries.
These changes were made in response to Olga Kornievskaia's review of
version of this work appearing in the -04 rfc56661bis drafts. The
changes include the following:
* Made a number of small changes to various subsection of
Section 7.6. One of the most importance of these is connected to
the use of retry without disconnection, formerly normatively
prohibited but now a just a pointless, useless exercise. A
normative prohibition was added about retries of requests that had
been abandoned which was necessary to further limit the
possibility of false retries.
* Major changes were made to Section 7.6.1.3.1 to make it clear
that, while there were some requirements regarding the reporting
of false retries that came to the replier's attention, there were
no requirements regarding the work that replier's needed to do to
make sure these would be found, if they occurred.
In addition, it was made clear why it was quite unlikely for these
to occur, if the requirements laid out in Section 7.6 are
followed.
* Description of the changes and their motivations were added to
Appendix A.3.
C.7. Changes Made in 5661bis Draft -06
Significant additions were made to Section 1.3, adding new items to
the existing list.
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* In item 7, description of a new OPTIONAL attribute defining what
extensions of the core UNIX ACL model are supported by the server.
* In item 8, discussion of a new ACE flag to support differences in
handling of partial ACE satisfaction for draft-POSIX ACLs,
* In Item 9, discussion of a new ACE flag to support implementation
of "default" ACLs as provided for by draft-POSIX ACLs.
C.8. Changes Made in 5661bis Draft -07
The following changes were made:
* A new item (#10) was added to the list in Section 1.3.
This new item mentions the definition of GROUPNOTOWNER@ and
OTHERS@ to be used to translate reverse-slope modes where DENY
ACLs are not supported.
* Added definition of utf8pref to be used for components, since use
of UTF8 is preferred but not required for these.
C.9. Changes Made in 5661bis Draft -08
The following changes were made in this draft:
* Moved Kerberos-specific material from 61bis to the security
document.
* Moved SECINFO description back to this document.
C.10. Changes Made in 5661bis Draft -09
The following changes were made in this draft:
* Changes were made to clarify the role of the grace period as
described in Section 13.4.2.
It appears that changes made in connection with the addition of
RECLAIM_COMPLETE seemed to make it necessary to delay all IO until
completion of the grace period rather than the acquiring of new
(i.e. not reclaimed) locks. This increased the negative effects
of server recovery on clients, particularly if there were clients
whose lock reclaim processing were delayed.
* Major additions were made to complete Section 28.2.
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These included writing Sections 28.2.1, 28.2.2.3, 28.2.2.1,
28.2.2.2, and 28.2.2.4.
C.11. Changes Made in 5661bis Draft -10
The following changes were made in this draft:
* After-the-fact additions of "Changes made in Draft" section for
-06, -07.
* Creation of a new section for RFC Editor Notes containing
definitions of RFCs to replace the strings RFCTBD{10,20,21,22,30}
in the final published document.
Use of these strings to simplify discussions of the relationships
among documents that are part of the rfc56661bis effort.
* Create a new section 1.3 dealing with Compatibility Issues.
* Remove outdated material from the current Section 1.4 (previously
1.3).
List items 8-10 were removed because these had become unnecessary
due to the change of approach to draft-POSIX ACLs. Instead of
enhancing NFSv4 ACLs to support their semantics, it is now
intended that support will be available via an NFSv4.2 extension.
* Work was done to clarify the description regarding returning
NFS4ERR_INVAL when inappropriate attributes are specified for
(N)VERIFY.
C.12. Changes Made in 5661bis Draft -11
A number of changes were necessary to clarify/correct issues with the
text in [RFC8881] in response to Working Group questions. These
questions did not arise as part of the rfc8881bis effort, but suggest
areas where the current specification is inadequate.
* Deal more thoroughly with situation regarding the interactions of
delegation and REMOVE where the suggested recall can be safely
dispensed with.
* Clarify/correct the semantics of PRESERVED_UNLINKED to be POSIX-
compatible, avoiding a gratuitous "MUST NOT".
* Restructure/revise the Implementation description sections for the
REMOVE and RENAME operations.
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This involved a reorganization of REMOVE to treat possible
rejections first and a clear separation of the various REMOVE-
induced file system changes.
RENAME was clarified to refer to REMOVE regarding the handling of
files removed because they were renamed-over. This addresses
issues regarding delegation non-recall and handling of deletion
upon last close.
In addition, Appendix D.2.8 was created to provide helpful background
for the review of the above changes.
C.13. Changes Made in 8881bis Draft -00
This document as been renamed as rfc8881bis since RFC8881 is
obsoleted by it, despite the fact that the issues it addresses were
introduced in RFC5661.
In addition, a number of small clarification/corrections were made in
this draft.
* It needed to be made clearer how unsupported attributes are dealt
with when requested by READDIR. Unfortunately, [RFC8881] says
very little about the attribute fetch feature, leading to
confusion about the case in which the set of supported attributes
changes as result of crossing a mount point.
* In the discussion of pNFS, the text is not clear as to the
client's and server's responsibilities with regard to shared state
and did not provide normative guidance, substituting
implementation advice in its place.
* Some work was done regarding pNFS terminology, following Tom
Haynes' suggestions.
* A discussion of expected work with regard to [RFC8434] has been
added to Appendix D.2.10
C.14. Changes Made in 8881bis Draft -01
The primary change made in this draft involves the creation of
Section 19 as a replacement for [RFC8434] and the redesignation of
this draft as obsoleting that RFC. Associated with these changes are
the following:
* Corrections within Section 20 to make it a valid layout type
specification according to Section 19.
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* Changes to existing layout type specifications discussed in
Section 19.2 and summarized in Section 19.2.5
Additional changes include the following:
* Updates within the Appendices B.1 through B.4 to reflect status
changes made in recent drafts.
Quite important was moving [RFC8434]-related work and material
related to directory delegations from Appendix B.4 to B.3.
Also important was moving the work regarding termination of RPC
requests from Appendix B.4 to B.1.
* Appendix B.4 was rewritten to reflect the fact that it is, for
now, empty.
* A lot of material relating to the revisions of Sections 18 through
18 was discussed in Appendix D.2.
Discussion of the issues raised in Appendices D.2.10 through
D.2.13 is important to validate the changes made in this area.
* Some work as done to clarify and reorganize the description of
directory delegations and associated notifications.
In additions, a few substantive changes were made regarding the
presentation of attribute changes, with special handling for some
child attributes that can never be changed and directory
attributes inherently tied to associated content modifications.
To support the latter, the structure of a notify4 was explained as
similar to a fattr4, and the document was explicit about
combination of notifications that happen at the same time being
presented within a single notify4.
C.15. Changes Made in 8881bis Draft -02
A number of changes were made to reflect a basic problem in the
discussion of open-upgrade that dates back, at least to [RFC3010]:
* Significant revisions were made to Section 14.9 to correct
confusion about IO authorization that would arise if open upgrade
were done when the two principals doing the successive OPENs are
different
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* Changes were made to Section 20.14.1 to deal with the special
challenges that these erroneous open-upgrades pose for the file
layout type.
In addition, there were minor changes to correct omissions found when
defining new layout types for an NFSv4.2 extension:
* Changes to Section 19.1.2 to include lrf_body among the nominally
opaque fields that might have a layout-type-specific overlay
* Changes to Section 20.7 to explicitly indicate that there is no
layout-type-specific overlay for lrf_body within the files layout
type.
C.16. Changes Made in 8881bis Draft -03
A major focus number of changes were made in this draft related to
the ACCESS operation. These were made necessary because of a failure
to keep ACCESS fully aligned with the finer-grained authorization
model introduced by the NFSv4 ACL model. The changs listed below
include some which cannot be completed immediately for a number of
reasons including the current uncertainty about the semantics of the
ACE append bit, and the need to decide whether desirable additions
are reasonably defined as "defects" which might be address in a bis
document or need to wait to be added in an extension to a later minor
version.
* Making it clear that for files, the semantics of EXTEND bit needs
to match that of the ACE mask bit for append.
The need for this match is made clear in this document but the
substance of those semantics will need to be addressed later in
co-ordination with work on the ACL document and the other issues
discussed in Appendix D.2.16.
* Clarifying the discussion of the addition of directory entries,
taking into account the fact the NFSv4 ACL model has separate ACE
mask bits controlling the additions of subdirectories and other
file system objects.
* Possible access bits covering the authorization for the creation
of (and possibly the scanning or modification of) the named
attribute directory associated with a filesystem object.
This issues need to be coordinated with further work on the ACLs
document, which needs change in the current description of related
ACE bits appearing in the -00 draft of
[I-D.ietf-nfsv4-acls-update].
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In addition, the following changes were necessary:
* Updates of references to reflect the promotion and consequent
renaming of the acl document.
* A number of clarifications were necessary in Sections 19.9.6 and
15.9.7 to clarify the needs that led to authorization support
extensions for directory delegations and the possible alternatives
to their use. The result was to restructure the material into
Sections 16.2.6 through 16.2.9.
During the restructuring, it was discovered that some substantive
changes were needed. These reflected the ability, previously
discouraged, for the client to make authorization decisions on its
own and the need to deal with AUDIT and ALARM ACEs that makes that
impossible.
These changes resulted in flags to be added to the response to a
request to create a directory delegation and significant
functional additions to the handling of local GETATTR with respect
to both authorization and caching.
C.17. Changes Made in 8881bis Draft -04
These include a number of related changes made to deal issues
related, direct or indirectly, to the handling of large ACLs.
* Creation of a new Section 7.6.5 that discusses the constraints of
suitable values of ca_maxrequestsize, ca_maxresponsesize, and
ca_maxresponsesize-cached.
* A number of changes to make clear that while EOS is needed for
modifying requests, caching of the reply is only needed for non-
idempotent requests.
This previously was not as clear as it should have been/
* Associated additions to Acknowledgments.
In addition, text was added to address the issue discussed in errata
report 8705, in which [RFC8881] identified the last legal operation
code incorrectly.
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C.18. Changes Made in 8881bis Draft -05
Significant changes were made with regard to the discussion of
corrections of protocol defects in bis documents. These concerned
cases in which the size of the extension is important in deciding
whether the extension is appropriately added to a bis document rather
than being addressed in an extension to a late minor version
Work was done to make clear order-agnostic content notifications do
not need to be sent to client responsible for initiating content
changes.
A number of changes was made to further clarify Named Attributes,
their previous uses, and discuss their possible connections with
future work related to extended attributes:
* A major revision to Section 2.9.3 to clarify the relationship
between named attributes and extended attributes.
* Substantial revisions to Section 29.2 to explain why the creation
of this registry was ill-advised and to make it clearer why it has
never been used and is unlikely to be used in the future.
* Creation of a new Appendix D.2.17 to deal with issues related to
our future handling of extended attributes taking into account the
desire for a unified approach to the problem for both Windows and
POSIX, the difficulties of accommodating both in the same feature,
and the need for compatibility with previous implementations using
the ADS-based approach.
As our unfortunate experience with ACLs suggests, the need to
accommodate both traditions must be approached with caution so
that inconvenient semantic differences are not ignored, despite
the important advantages of a common approach.
C.19. Changes Made in 8881bis Draft -06
A number of changes were made related to attribute caching prompted
by discussion of potential new caching-related advice, to be provided
in later extensions:
* Restructuring of the section dealing with client-side caching into
two sections, dealing with file and attribute caching (still
Section 15 and with name and directory caching (a new Section 16.
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This change was not made to correct a problem with [RFC8881]. It
addresses the fact I should have done this when incorporating
discussion of directory delegations and notification and that
recent developments have made that poor choice insupportable going
forward.
This division provides the opportunity, in Section 15, to discuss
the important connections between file and attribute caching and
their common interaction with file delegation and share
reservations.
Similarly, this division provides, in Section 16, the opportunity
to discuss directory caching and its differences from other forms
of caching with regard to the issue of cache coherence.
* Creation of a new Section 15.3.2, acknowledging the previously
ignored difficulties in sharing files, including those being
written, without effective cache-coherence features.
* A major revision of Section 15.6 discussed below.
* Revisions to Section 25.30.3 to make clearer the necessary
connection between changing size and opens for WRITE.
* Creation of new Appendices D.2.18, D.2.19, and D.2.20 to provide
for necessary working group discussions of the suitability and
adequacy of the changes made to the presentation of data and
attribute caching, their relationship to ongoing work to address
these issues, and the possibility of further work to address the
issues that Tom Haynes has brought to the Working Group's
attention.
Note that, in this context, the approach Tom has proposed, that of
providing for the elimination of caching is considered one way of
avoiding cache incoherence and is therefore dealt with in
Appendix D.2.19.
Work on the revised Section 15.6 has included the following:
* The reorganization of Section 15.6 into multiple subsections
including Sections 15.6.1 through 15.6.3 dealing with,
respectively, coherence between a change-requesting client and the
server, coherence among clients, and coherence between the
requesting client and remote applications.
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* Effecting a distancing from previous ways of treating write-behind
caching, which tended, unfortunately to encourage its use. The
new treatment stresses that it may be used while giving
appropriate non-normative guidance about troubles it might cause
in some environments.
* Revising the unrealistic desire to cache all attributes which was
probably unrealistic when written and certainly unrealistic now.
* Converting the "rules" for sharing attributes to "guidelines"
since these have never been understood well enough to form
verifiable rules and we cannot promise that they work but know
only they have been used successfully in the past.
Appendix D. Issues Requiring Further Discussion
This Appendix discusses issues that the working group needs to
discuss before making decisions regarding potentially necessary
specification changes. Despite the need for working group decisions
on certain policy matters, some of the specific examples cited have
already been addressed by revised text within the draft specification
proper.
D.1. Appropriate Uses of RFC2119 Keywords
Although, as stated in Section 1.1, this document intends to use
these keywords as described in RFC2119, there are a number of issues
that have resulted due to uses of these keywords in RFC5661 and
RFC8881 that may not be clearly in accord with these definitions,
possibly requiring some corrective action, once the working group has
reached a consensus regarding the appropriate path forward.
* Because of a lack of clarity within RFC2119, there is considerable
uncertainty about appropriate situations in which to use "SHOULD"
and "SHOULD NOT", resulting in a number of cases in which they are
inappropriately used or in which it is unclear whether particular
uses are appropriate.
The working group needs to discuss these examples (see
Appendix D.1.1) so that these terms can be used consistently in
this specification and within the boundaries established by
RFC2119, even if those boundaries have some level of uncertainty
surrounding them.
The use of the related term "RECOMMENDED" in connection with file
attributes is not included in the above discussion, since it is
already clearly understood that this use is incorrect.
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* Although RFC2119 is appropriately clear, there are a number of
cases in which uses of "MUST" and "MUST NOT" are problematic,
since they are used in RFCs 5661 and 8881 in ways not in accord
with their definition while the existence of clients and servers
that ignore such statements gives one reason to doubt whether
these are truly required for successful interoperation.
The working group needs to discuss these examples (see
Appendix D.1.2) so that such uses are corrected and to reduce the
probability of similar occurrences in the future.
* Even apart from the definitions of these keywords, there is the
further statement in RFC2119 that these terms are to be used
"sparingly". Given the size of the v4.1 specification, it is
desirable that all contributors adopt a common approach to issues
about where these terms are appropriately used.
The working group needs to discuss the issues described in
Appendix D.1.3) so that the new specification has a consistent
approach to these matters.
D.1.1. Appropriate Use of "SHOULD" and "SHOULD NOT"
RFC2119 defines "SHOULD" as follows, with the definition of "SHOULD
NOT" paralleling it.
This word, or the adjective "RECOMMENDED", means that there may
exist valid reasons in particular circumstances to ignore a
particular item, but the full implications must be understood and
carefully weighed before choosing a different course.
This definition makes it clear how "SHOULD" differs from "MUST" but
the specific difference with "MAY", while these terms are clearly
intended to be distinct, is left unclear. Since it would not
normally be expected for the other peer to be able to judge the
validity of the reasons chosen by the SHOULD-using peer (or even
whether the full implications of the choice made have been understood
and carefully weighed by the peer's implementer), the other peer is
in the same position as it would have been if "MAY" had been used.
It needs to be prepared for the "SHOULD" to be followed or not
followed, as the SHOULD-directed peer chooses.
Although one gets the sense that not following "SHOULD" or "SHOULD
NOT" is in some way disapproved of, since one does not to have "valid
reasons" to either follow or not follow a "MAY". However, this
leaves a great deal of uncertainty remaining as to when "SHOULD" is
justified, especially given the indication within RFC2119 that these
terms are to be used "sparingly".
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One class of cases in which "SHOULD" is appropriately used, since not
following such a directive might have the ability to cause harm, has
to with situations in which security is an issue and some uses of
"SHOULD" in the existing NFSv4.1 specifications fit this model.
However a survey of the NFSv4.1 specifications shows many uses that
take different approaches, some of which are clearly wrong and others
which we need group discussion to establish a specification-wide
policy:
* The statement "the client and server SHOULD use long-lived
connections for at least three reasons" appearing in Section 2.9.1
of [RFC8881] raises a number of issues that make use of "SHOULD"
questionable.
There is no clear definition of "long-lived connections", making
it hard to determine, in any particular case, whether the "SHOULD"
has been adhered to or not. As a result, it might not be clear
whether a particular implementation's connections are long-lived
leaving it unclear whether the "SHOULD" is being adhered to, so
that the full implications of not adhering to it might not be
obvious to those implementations not very clear about whether they
are adhering to the guidance or not.
It is hard to imagine what might valid reasons to ignore the
reasons given, which are valid and worth mentioning, although
there might be implementation considerations which cause
connection lifetimes to be shorter than they would be otherwise.
Overall this seems like useful implementation advice and could
appropriately use the word "should" or a synonym.
* The statement "Instead, the replier SHOULD return an appropriate
error (see Section 2.10.6.1 [Appears in this document as
Section 7.6.1]), or it MAY disconnect the connection" appearing in
Section 2.9.1 of [RFC8881] raises a number of important issues.
It is hard to imagine what might be valid reasons to either return
an inappropriate error or no error.
The intention behind the "MAY" seems clear but given the
definition of "SHOULD", it isn't clear exactly what item is to be
ignored or what sort of knowledge of the implications would be
necessary if that item were to be ignored.
If the construction were reordered to clarify it and so take
disconnection off the table immediately, then it would be unclear
how the "SHOULD" could be validly ignored, since it is stated
elsewhere that the replier "MUST NOT" silently drop the request
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Possible replacement text is discussed elsewhere in connection
with an adjacent "MUST NOT" which is dubious as well.
* The statement "NFSv4.1 clients SHOULD NOT use the RPC binding
protocols as described in RFC1833" appearing in Section 2.9.3 of
[RFC8881] is confusing and appears not to be in accord with our
understanding of RFC2119.
Unlike other cases of "SHOULD", it does not seem that the server,
unaware of the possibly valid reasons to ignore the "SHOULD", is
being asked to essentially treat this as it would a "MAY".
Perhaps something like the following would be needed to give
appropriate guidance to the client and server implementers without
use of RFC2119 keywords.
The use of a reserved port has been common for NFS
implementations and it is expected that this will apply to
NFSv4.1 as well. While the use of RPC binding protocols as
described in RFC1833 [RFC1833] is a possibility, there is no
requirement that servers provide support for it. In light of
this, a client should avoid such use unless it has good reason
to expect such support to be present.
* The statement "In the event an RDMA and non-RDMA connection are
associated with the same channel, the maximum number of slots
SHOULD be at least one more than the total number of RDMA credits
(Section 7.6.1). This way, if all RDMA credits are used, the non-
RDMA connection can have at least one outstanding request"
appearing in Section 2.10.3.1 of [RFC8881] presents another
interesting use of "SHOULD" that the working group should consider
as it decides how this term is to be used in the NFSv4.1
specification.
The second sentence, indicates a generally desirable outcome, but
its nature raises considerable doubts as to whether this is
anything other than helpful implementation advice.
The fact that the RDMA credits are subject to change and that the
client and server may have different views of this quantity make
is hard to understand what exactly is being recommended and part
of the implementation would be responsible for its implementation.
Overall, "should" seems a valid replacement , although rewriting
the sentence to use the phrase "it would be helpful if" also seems
possible.
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D.1.2. Uses of "MUST" and "MUST NOT" that are Problematic
While the definitions of "MUST" and "MUST NOT" are quite clear, there
are still instances within the existing specifications in which it
not clear that particular uses are appropriate or in which common
client and servers do not follow the offered direction while
interoperating successfully.
Some interesting examples from RFC8881 [RFC8881]) follow. Note that,
unlike the case in Appendix D.1.1 which looked at each instance of
the target terms in a given section of the document, here we only
look at a subset of uses which appear ,in some way, spurious or
otherwise questionable.
* There are reasons to question to use of "MUST" in the following
statement appearing in Section 5.7.1 of RFC8881:
Where an NFSv4.1 implementation supports operation over the IP
network protocol, any transport used between NFS and IP MUST be
among the IETF-approved congestion control transport protocols.
This statement would make invalid the use of NFSv4.1 using RPC-
over-RDMA when the RDMA connection is implemented using RoCE while
allowing it for Infiniband and iWARP.
Although the peer might depend on operating together with an
implementation having adequate congestion control, there is no
basis for requiring that specific protocols (i.e. SCTP and TCP) be
used, particularly since RFC2119 indicates that these keywords not
be used "to try to impose a particular method on implementers
where the method is not required for interoperability".
Regardless of ones judgment of the propriety of using "MUST" in
this context, the working group needs to discuss and decide, by
consensus, how to address the issue of RoCE use in supporting
NFSV4.1 using RPC-over-RDMA.
* There are reasons to question to use of "MUST NOT" in the
following statement appearing in Section 5.7.2 of this document
and the similar statement appearing in Section 7.6.2.
A requester MUST NOT retry a request unless the connection the
request was sent over was lost before the reply received.
Given that the text states that this is to "reduce congestion", it
is hard to see how the mandated behavior is an "absolute
requirement of the specification."
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The following statement appearing in Section 7.6.2, phased as
implementation advice, provides a positive explanation of the
motivation, without making the use of "MUST" or similar terms,
resulting in a shift between a normative introduction and the
implementation advice providing the underlying substance:
Note that it is not fatal for a requester to retry without a
disconnect between the request and retry. However, the retry
does consume resources, especially with RDMA, where each
request, retry or not, consumes a credit. Retries for no
reason, especially retries sent shortly after the previous
attempt, are a poor use of network bandwidth and defeat the
purpose of a transport's inherent congestion control system.
Not mentioned in this section but one possible motivation for such
a restriction is the potential need to simplify the work discussed
in Section 7.6.1.3 particularly the possible need of the server to
checksum data to be written to detect false retry, possibly
undercutting the performance benefits of RDMA, as discussed in
Appendix D.2.1.
If the issues relating to limiting the work necessary to detect
false retries is not an appropriate basis for this prohibition, it
seems better to avoid a shift between a normative introduction and
later implementation advice by saying something like the
following:
Given that NFSv4.1 uses transport providing reliable delivery,
there is little point retrying a request, except in cases in
which the occurrence of a connection disconnect leaves the
requester uncertain as to whether the initial request was
successfully delivered. The session-based reply cache allows
the replier to deal correctly with retries after reconnect
whether the initial request was delivered and executed or not.
* The following statement, appearing in Section 5.7.2 RFC8881,
leaves one uncertain about whether the use of "MUST NOT" is
justified, since it gives no clear explanation of why the
prohibited behavior is troublesome.
A replier MUST NOT silently drop a request, even if the request
is a retry. (The silent drop behavior of RPCSEC_GSS [4] does
not apply because this behavior happens at the RPCSEC_GSS
layer, a lower layer in the request processing.) Instead, the
replier SHOULD return an appropriate error (See
Section 3.9.6.1), or it MAY disconnect the connection.
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This uncertainty is exacerbated by the introduction which states,
incorrectly, that this is "to reduce congestion" and that it is
paired in a bulleted list with the previous statement using "MUST
NOT" where its use is also problematic.
It should be considered whether the explanation would be clearer
if the focus is on the responsibilities of the replier in the
session model, rather than on one particular case of the replier
ignoring those responsibilities. One possible approach:
The replier MUST attempt to obtain and send a reply each
compound request received. This applies with equal force to
the case in which the request is a retry, with the instructions
in Section 7.6.1.3 followed in generating the reply which the
replier needs to send to the requester in all cases, except
where a disconnection event makes this impossible
* The following statement, appearing in Section 5.7.2 of RFC8881,
requires further analysis since the justification provided for the
prohibition merely cites a possible difficulty, without
consideration of whether this difficulty could be resolved without
this prohibition.
A requester MUST wait for a reply to a request before using the
slot for another request. If it does not wait for a reply,
then the requester does not know what sequence ID to use for
the slot on its next request. For example, suppose a requester
sends a request with sequence ID 1, and does not wait for the
response. The next time it uses the slot, it sends the new
request with sequence Is 2. If the replier has not seen the
request with sequence ID 1, then the replier is not expecting
sequence ID 2, and rejects the requester's new request with
NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
CB_SEQUENCE).
Beyond the problem with the justification provided, is the fact,
that many clients, including those most commonly used, essentially
ignore the "MUST NOT", yet successfully interoperate with most
servers. This essentially makes the "MUST NOT" untenable.
There are two problems with the current justification:
- Only a single value is assumed as the sequence value to be
chosen for the next request (i.e. two) while the possibility of
the alternative choice (i.e. one) is not addressed at all.
- The occurrence of an error is treated as disposing of the
matter, without consideration of potential recovery approaches.
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It appears likely that whichever value is used as the next
sequence, the resulting error is not fatal, making use of "MUST
NOT" inappropriate. Possible replacement approaches will be
discussed in Appendix D.2.1 and explored in a modified Section 7.6
D.1.3. Issues Regarding Use of RFC2119 Keywords "Sparingly"
RFC2119 contains the following statement:
Imperatives of the type defined in this memo must be used with
care and sparingly. In particular, they MUST only be used where
it is actually required for interoperation or to limit behavior
which has potential for causing harm (e.g., limiting
retransmissions) For example, they must not be used to try to
impose a particular method on implementers where the method is not
required for interoperability.
The following issues make this statement difficult to interpret.
* In fact, none of the terms defined in this RFC is an "imperative".
They range among adjectives, participles, and modal auxiliaries,
making it hard to determine which terms are being referred to.
* The terms "MUST", "MUST NOT", SHALL", and "REQUIRED might be
thought of loosely as imperatives, since they are directing
implementers to do something or to not do something.
* Although the terms "SHOULD", "SHOULD NOT", and "RECOMMENDED" do
not have the sense of imperatives, they might be thought of as
fundamentally carrying an imperative message, albeit one with a
rather unclear provision for the recognition of exceptions.
* The terms "MAY" and "OPTIONAL", cannot reasonably be considered
imperatives. Furthermore, the final sentences of the paragraph do
not really make sense when applied to uses of these terms.
* Although the paragraph would normally be read assuming that the
subject of the first sentence (i.e. "imperatives of the type
defined in this memo") and "they" as used in the final two
sentences, designate the same group of terms, that may not be
possible since "MAY" and "OPTIONAL", do not make sense in the
final sentences while is hard to believe that the author really
meant that these terms did not need to be used with care. The
case of "sparingly" is not as clear cut but it is hard to conclude
that only the first two classes of terms need to be used
sparingly.
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If these terms are to be used "sparingly", whether terms like "MAY"
are included or not, a meaningful distinction must be made between
things that are "an absolute requirement of the protocol" and the far
more numerous set of things that simply describe how the protocol
works. While it is required for interoperability that the client and
server agree on the XDR for operations and results, and the actions
to be performed for each operation, it is not clear how one could
decide which of those interoperability requirements is "an absolute
requirement of the protocol" meriting use the word "MUST", since
deciding that they all do would not use these terms "sparingly" and
is likely to result in an unreadable specification as well.
At times in the past there has been inconclusive working group
discussion of the possible use the word "MUST" in connection with the
need to return certain errors. While it was clear that the need for
interoperability meant that this was a requirement within the
definition of "MUST", there was concern about what that did to the
style of explanation since returning errors, like setting appropriate
operation parameters and results and performing the requested
operations, are simply "the way the protocol works", and not an
"absolute requirement of the specification" assuming those can be
distinguished from ordinary requirements of implementing the
protocol. The possible need to use such terms "sparingly" adds
additional weight to this concern.
In any case, there seems to be a need for the working group to
discuss and come to some consensus regarding the routine use of the
word "MUST" even when the situation is not one which the question to
be addressed is whether the definition of the word is adhered to, as
discussed in Appendix D.1.2.
D.1.4. Going Forward Regarding Use of RFC2119 Keywords
Although many of the specific issue discussed here have been
addressed, the working group needs further discussion in order to
arrive at a consensus regarding policies to be followed on these
issues in general.
D.2. Issues Regarding Proposed and Actual Changes
The subsections within this appendix each concern a set of changes
that have been made to address various issues in the existing
specification for NFSv4.1 [RFC8881] which are discussed in Appendices
D.2.1 through D.2.8. Some, although not all of these, relate to
matters raised in Appendix D.1.
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Each of these require further working group discussion, although The
nature of the discussion may vary, based on the nature of work to
address the cited issues and the possibility that further related
work might be required. The author assumes that, all these cases,
leaving the material in the form it had in [RFC8881] would not be
acceptable.
* For sub-sections in which the changes already been made in the
current draft, if correct, fully address the issues now known, The
necessary discussion will involve discussion of the proposed
changes, in the form suggested in this draft in an attempt to move
to a working group consensus on their correctness, adequacy, and
clarity.
These sub-sections includes Appendices D.2.1, D.2.3, D.2.4, D.2.5,
D.2.7 and D.2.8 changes have already been drafted and appear in
the current document draft.
* For some other sub-sections, the author is unsure whether the
changes made so far, even if correctly done, fully address the
underlying issue. In these cases, the working group discussion of
the proposed changes will need to be combined with a discussion of
whether further changes are necessary and possible in the context
of the current document.
These sub-sections includes Appendices D.2.2 and D.2.6,
D.2.1. Changes Regarding Request Aborts, Retries, and the Session Model
This issues discussed in this section have been dealt with by a set
of changes to the document proper in Sections 7.6 and 7.6.1.3.1.
These changes have been made in multiple drafts as described below
and now need working group review to make sure that the changes made
are adequate to deal with the problems in the existing text in
[RFC8881]
* Previously, the question had been whether and how to deal with the
misuse of RFC2119-defined keywords and the problem that the
ability to terminate RPC requests, required by many client
implementations, was inconsistent with exactly-once semantics,
since zero times is not "exactly once".
* Now that there is an alternate approach available for
consideration, the relevant question is whether that approach is
adequate and how it might need to be changed. For more detail on
the changes made, see Appendix A.3.
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We deal here with three related issues that are connected, in some
way, with the new session feature and the associated reply cache
logic;
1. The potential need, as might be inferred from the discussion in
Section 7.6.1.3 of [RFC8881], to checksum request data,
particularly data to be written in order to eliminate the
possibility of not actually acting on a request which is a "false
retry", potentially resulting in data corruption.
2. The prohibition, discussed in Appendix D.1.2 on reissuing a
request without the occurrence of a disconnection of the
connection on which the request as issued.
3. The prohibition, discussed in Appendix D.1.2 on ceasing to wait
for a response without actually receiving the response.
These issues have been addressed together since considering them in
the context of the design of the sessions feature sheds light on the
troublesome issues mentioned above. Specifically, we are looking at
the possibility that we have arrived at a suitable framework to
discuss these issues so that:
* This framework provides a more realistic and convincing
explanation for any necessary prohibitions and/or recommendations.
* This framework allows such prohibitions to be safely downgraded to
recommendations or implementation advice
* This framework might encourage client implementations to implement
EOS without allowing the possibility of false retries, making it
advisable for server implementations to avoid extensive recording
of request contents or the checksumming of requests in order to
prevent the undetected occurrence of false retries.
The issues and the changes made to address them in rfc5661bis drafts
can be summarized as follows:
* The use of "MUST" in Section 7.6 and force clients to wait for
responses for all requests needed to be adjusted because many
clients were unable to comply when tasks were terminated,
rendering the requirement useless.
In draft-01, the text was modified to make it clear that,
realistically, there were situations in which the client could not
wait forever and that real goal of the EOS logic was at-most-once
semantics. In addition, the discussion now covers the possibility
of getting SEQ_MISORDERED in this situation.
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* The use of "MUST NOT" in Section 5.7.2 to prohibit retransmissions
needed to be revised since sending such retries while undesirable
does not cause the kinds of harm that use of the RFC2119-defined
term implies exist.
In draft-00, we eliminated the prohibition regarding retry and
replaced it with implementation advice indicating why there is
little reason for retries without clear motivation and explaining
the unfortunate consequence of such retries.
* The text in Section 7.6.1.3.1 needed revision to make it clear
when checks for false retries were either required or desirable
and to make clearer how they could arise given the implementation
of Exactly-once semantics.
In draft-01, added an initial paragraph indicated reasons that
checks for false retry result from implementation problems and
that there are practical limits as to when they will be done.
In draft-03, extensive changes were made to explain the situations
in which false retry was a real concern and suggesting approaches
to checking that can realistically be implemented. This includes
addressing issues that were intended to be addressed by errata
report 5982.
D.2.2. Issues Regarding Directory Delegation that Need to be Resolved
Directory delegations and notifications were added to NFSv4.1 but
have never been implemented using the specification in [RFC8881].
During working group discussions of NFSv4 performance issues with
regard to directory handling and later discussions with those working
on implementations, it was discovered that there are a number of
issues with regard to handling of directory delegations that need to
be addressed, including cases where the design is adequate but
substantial clarification is needed.:
* It was assumed that clients holding a delegation would maintain
locally an image of the server directory, that needed to match
that of the server with regard to directory entry order and the
values of directory cookies.
As implementation efforts proceeded, it became apparent that this
assumption was unduly limiting and needed to be addressed. In
addition, this approach made it unduly difficult to use the
feature for file systems in which sets of distinct characters are
treated as equivalent (i.e those supporting normalization-related
processing or case- insensitivity.
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As a result, it was decided that allowance be made for clients
using a different approach to caching, as described in
Appendix D.2.2.2
* In addition, for clients that were prepared to maintain a local
directory image, there were important gaps in the explanation that
resulted in a lack of clarity regarding the ability of the
notification scheme to allow the client image of the directory to
be kept in sync with that of the server. It is not made as
explicit as it might be that server support for continuation of
directory delegations requires that the information provided in
directory notifications is adequate to provide to the client the
information needed to appropriately update the client's image of
the directory to so that it can serve in place of a READDIR to the
server. This includes the ability to maintain a directory
ordering matching that on the server and READDIR cookies that
match those held on the server. In situations in which the
changes to the directory are of such a nature that this sort of
update cannot be done based on a directory notification, the
directory delegation needs to be recalled and returned. With the
clarified, the value of directory delegations in avoiding the need
to refetch large directories because of a small number of
directory changes, would be more obvious. See Appendix D.2.2.1
for some suggestions in that regard.
While it is unusual for CREATEs, RENAMEs, and REMOVEs to cause
wholesale changes in the directory entry ordering or READDIR
cookie values, there has previously been no way for the client to
be sure that no such changes are being made, even when no other
client is changing the directory. As a result, many clients are
accustomed to refetch directories when they are changed, despite
the consequent negative effect on performance.
As a result, it has seemed to many that there is little value in
implementing directory delegations and notifications, leaving
concerns about directory performance unaddressed.
* In addition, there is uncertainty as to whether a client making a
change to a directory will receive timely notice of the details of
the changes that will be made to the modified directory. The
means by which notification is typically provided, using an
asynchronous callback with provision for notification delay and
batching of notifications was primarily directed to cases in which
another client is making the modifications and the client
receiving the notifications needs to sheltered from excessive
notifications. This requires two issues to be addressed.
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* It needs to made clearer that the batching and delay of
notifications apply only to the notifications of directory
attribute changes and not to those notifying the client of changes
in directory contents.
Although this might ultimately require a major rework of the text
of Section 16.2, some useful suggestions can be found in
Appendix D.2.2.4
* Since the notification model for changes in directory contents is
an asynchronous one, it needs to be made clearer how clients
making changes to directory contents can use these notifications
can avoid refetching directory contents.
Some suggestions regarding useful change in this area can be found
in Appendix D.2.2.1
* Although improvements have been made to deal with support for
local equivalents of GETATTR using cached data provided using
directory delegations, further work might need to be done as
discussed in Appendix D.2.2.6.
Changes might be possible to respond to difficulties arising from
the lack of prompt notifications of attribute changes for
directory entries.
D.2.2.1. Clarifying the Role of Directory Delegations and Notifications
in Avoiding the Need to Refetch Directory Contents
The first step is to clearly define the problem that content
notifications address. This could be addressed by adding the
following new paragraph to the end of Section 16.1.2:
Even when a client is certain that no other client is modifying a
cached directory, there still might be a need to refetch the
directory contents to satisfy additional READDIR requests. This
is because there is no way to determine the modified ordering of
the directory or the associated cookie entries using the knowledge
of the directory changes requested and the corresponding
responses. For a discussion of how directory delegation together
with directory content updates can avoid the need to refetch
directory contents, see Section 16.2.11.
In addition the following paragraphs need to be added at an
appropriate place within Section 16.2.
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When a directory delegation is held and notifications of changes
of directory content updates are provided, the need to refetch the
directory contents to satisfy READDIR requests can be avoided.
This is of considerable benefit when the directories are large.
Although the directory content updates provided are asynchronous,
they are not batched or delayed for considerable periods of time.
Because of this, clients can keep track of the set of pending
updates expected to avoid refetching directories when a content
update is likely to enable the client to avoid the extra work.
D.2.2.2. Dealing with Various Client Caching Schemes
As a result of discussions with those involved in working on
directory delegation implementations, it was discovered that:
* There are a significant set of clients that want to be aware of
directory content changes but have no need for the position
information currently provided since they either do not try to
avoid repeated READDIRs by means of caching previous ones or
synthesize READDIR results from cached contents without depending
on the server's choice of directory entry order or directory entry
cookies.
While the client is free to ignore position information provided,
the effort to provide it where it is not needed might be a
significant barrier to implementation.
* Some servers could produce useful position information with less
difficulty if the directory cookies were defined so as to be
acceptable to clients who do want to replicate the server's
directory entry order and cookie values.
* Also relevant are those clients who do wish to provide cached
READDIR results conforming to the server's order (not formally
required but shuffling these might not be accepted by some users).
Addressing these issues requires providing the server more
flexibility in the form of notifications used to inform clients of
directory content changes while respecting client needs, which might
be different for different clients. One way of doing so which has
already been explored would allow three forms of content update
notifications, such as are listed below:
(A): Provision of position information in the way defined in
[RFC8881].
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(B): Provision of position information in a simplified fashion using
directory cookies only and avoiding the need to provide the
names of nearby entries.
This approach is valuable for use in the large class of servers
for which the entry cookie value is monotonically increasing as
successive directory entries are transmitted as part of
READDIR.
(C): Omission of position information i content update
notifications.
This approach is only useful to clients that do not try to
maintain the server's directory order but are only interested
maintaining the set of entries, independent of their order.
Selection of the proper format for any given update requires a new
mechanism for the client server to arrive at the chosen format based
on client needs and server capabilities. This mechanism is described
in Appendix D.2.2.3. Because existing operations were specified
without any provision for such selection, certain desirable options
will only be available once a v4.2-based extension is available.
However, as discussed below, there will be opportunities to avoid the
Procrustean approach currently described in [RFC8881] in which only
(A) is allowed.
In addition to the matters discussed above, the issues raised in
Appendices D.2.2.5 D.2.2.7 need to be addressed.
D.2.2.3. Version Control and Extension
We need an mechanism that is acceptable in the v4.1 context to allow
some limited extension of the approach to directory delegation
specified in [RFC8881]. This needed to:
* Provide a way of including more substantial authorization support
using additional notifications.
* Allow selection of the form of position information in content
update notifications and to decide on the necessity of certain
recalls based on the following factors:
- Certain clients are concerned about the order of directory
while other might not care.
- There are clients concerned about entry order who want to have
knowledge about server directory cookies, while there might be
other that do not.
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- There are servers that maintain directory cookies so they are
always monotonically increasing with directory position while
there others where that connection cannot be relied upon.
- There might be servers and clients written based on the
approach of [RFC8881] rather than the more flexible one
described in this document.
We need to deal with this possibility even though there are
good reason to believe that no such implementations exist.
Until [RFC8881] is obsoleted, which could take a while, we have
no way of tracking ongoing development activities.
Dealing with all of the above, in a general way, requires a general
extension mechanism, the overall structure of which will be discussed
below, while the details will be decided in later extension document.
As pat of this effort, we will need a way to provide greater
flexibility, if possible, in an NFSv4.1 context, while interoperating
correctly with client and server's using the [RFC8881] approach.
This requires some way of distinguishing implementations without
excessive XDR additions.
Regarding the selection of extension mechanism, it appears that the
best approach is to generalize the use of the existing argument and
result notification bitmaps. This requires only very limited XDR
changes that follow the approach laid out in Section 9 of [RFC8178].
Bits can be defined without corresponding notifications and allowing
other interface changes to be inferred from the presence or absence
of particular bits.
For distinguishing new and old implementations, it seems the best
approach is to rely on the notification bitmaps. Inclusion of an
extension could signal client awareness of the extension with the
appearance of the bit in the response signaling the server's
knowledge of the extensions.
D.2.2.4. Clearly Separating Directory Content Updates from Other
Notifications
Although an extensive set of small changes to clearly split content
notifications from attribute notifications is probably necessary, to
begin the clarification of this issue, Section 11.15 needs a
clarifying final paragraph, to read as follows:
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Note that these attributes apply only to directory attribute
notifications and not to directory content updates, which,
although asynchronous are not subject to batching or explicit
delays.
Also important are the following replacement paragraphs for the first
two paragraphs of the IMPLEMENTATION section of GET_DIR_DELEGATION,
Section 25.39.4.
Directory delegations provide the benefit of improving cache
consistency of namespace information. This is done through
synchronous callbacks. A server must support synchronous
callbacks in order to support directory delegations. In addition
to that asynchronous notifications provide a way to provide a
client a way to maintain an accurate client-side image of a
changing directory (through client content updates) and to reduce
network traffic as well (through both sorts of notifications)
Directory update notifications are specified in terms of potential
changes to the directory. A client can ask to be notified of
events by setting one or more bits in gdda_notification_types.
The client can ask for notifications on addition of entries to a
directory (by setting the NOTIFY4_ADD_ENTRY in
gdda_notification_types), notifications on entry removal
(NOTIFY4_REMOVE_ENTRY), and renames (NOTIFY4_RENAME_ENTRY).
Cookie verifier changes, although not directory content updates,
can be obtained by setting NOTIFY4_CHANGE_COOKIE_VERIFIER
gdda_notification_types field. All of these notifications are
asynchronous but they are not, like directory attribute
notifications, subject to batching or time-based delays.
Directory attribute changes are requested using the notification
type NOTIFY4_CHANGE_DIR_ATTRIBUTES), with the specific attributes
that require notifications specified by gddr_dir_attributes. Like
the child attribute notifications discussed below, these
notifications are subject to matching and time-based delay in
order to limit network traffic.
D.2.2.5. Directory Delegations and Permissions
It appears that Section 16.2 was written without sufficient attention
to authorization issues that arise when LOOKUP, READDIR, GETATTR, and
ACCESS operations are satisfied from cached data.
As a result, significant work will need to be done in related
subsections to address that gap. This will inevitably, have to
involve consideration of the increased difficulty of dealing with
situations in the presence of ACLs. Given the current uncertain
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state of ACLs, this will require, at least for NFSv4.1, steps
prohibit or give permission to the server to prohibit use of
directory delegations in situations in which their existence might
compromise needed authorization restrictions.
D.2.2.6. Possible improvements in Support for Local GETATTR
Given that the protocol already has taken significant steps to deal
with the following issues, the rest of this section will focus on the
difficulties that result from the lack of prompt notification of
directory entry attribute changes, the difficulties in providing such
support and how limited server support for prompt notification might
allow significantly more efficient client implementations.
* Handling AUDIT and ALARM ACE entries.
The server can scan the directory for such ACEs and inform the
client of their non-existence using the CHANGE_GA notification.
* Handling ACLs denying ACE4_READ_ATTRBUTES (expected to be
unusual).
The server can scan the directory for such ACLs and inform the
client of their non-existence using the CHANGE_GA notification.
The same scan, we could be done in the background, can address
both issues.
Turning back to the possibility of prompt notification, we need to
consider:
* The possibility that such notifications might slow down attribute
changes making it a net performance loss despite the benefits of
local GETATTR.
* The difficulty of implementing such notification for multiply-
linked file given that filesystems that can find all directories
referencing a file are quite rare with those that can do so
quickly rarer still.
Given the above issues we should consider the possibility of
specially managed notifications that are sometimes provided promptly,
but have a useful fallback path allowing efficient local GETATTR in
unusual situations. The following list is worth considering:
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* In each case in which a requested attribute (e.g. change) can no
longer be provided, the client is guaranteed prompt notification
of that fact through use of existing facilities within a CHANGE_GA
notification.
* This guarantee is presumed negated whenever the directory entry in
question is multiply linked or becomes so.
The existence of files with high link counts can be addressed in
the same asynchronous scan used to find troublesome ACLs.
Transfer of a multiply-linked file into an existing directory for
which a delegation is held, whether as the result of a cross-
directory RENAME or a LINK can trigger the CHANGE_GA since the
target directories identified and the delegation-related
information can be found from that.
* Where significant number of attribute changes, the server is free
to cancel the promise of prompt notification.
Low-frequency asynchronous scans would be free to re-establish the
promise using CHANGE_GA.
D.2.2.7. Going Forward Regarding Directory Delegations
The material in this section should provide a suitable basis for
working group discussion, in the hope that it will enable those
changes to be moved into the specification proper in a later draft
revision.
Once that work is done, the working group will be able to decide;
* Whether, with implementation of directory delegations, NFSv4.1
still has a directory performance problem that needs to be
addressed
* Whether there is a need for extensions to improve directory
delegations (synchronous notifications).
* Whether additional directory performance features are worth
pursuing.
D.2.3. Changes Regarding Memory Mapping
It has been necessary to make major changes to material currently
dealt with in Section 10.7 of RFC8881. The replacement is
Section 15.7. Extensive changes have been necessary for the
following reasons:
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* The previous text consistently ignores the need for those reading
and writing files to open them.
As a result, many the problems the previous section was concerned
with, regarding a concurrently held write delegation only apply in
the unusual case of files being read using special stateids.
* There had been assumption that CB_GETATTR would always be used
when attributes are interrogated, ignoring the possibility of the
delegation being recalled.
This ignored the fact that CB_GETATTR is an OPTIONAL feature and
that there is no requirement for clients implementing to use it
for access and modified time.
* In citing byte-range locking, there was no consideration of the
fact that none of the cited issues poses any difficulty in the
case if advisory byte-range lock.
* The treatment of mandatory byte-range locking assume, incorrectly
that it requires as part a each IO, that a lock be obtained to
enable that operation.
In fact, mandatory byte-range locking only requires that no
inconsistent lock be held by another process performing IO.
As a result most of the potential issues cited do not exist for
NFSv4.1 and if they did, they would apply to local IO as well,
making this sort of locking untenable.
D.2.4. Issues Regarding Handling of Persistence
There are a number of important issues relating to persistence that
need working group discussion and corresponding specification
changes. These involve both reply cache persistence and the
potential persistence of locking state to allow lock reclaim to be
avoided.
The treatment of issues related to the persistence of protocol data
shared by the client and server needs substantial remedial work, as
described below. Without such remedial work, we would be stuck with
a confusing description of a hypothetical feature that has never been
implemented and has no prospect of being implemented, whose
description is unusable due to confusion about the handling of
locking state persistence. The issues to be addressed include the
following;
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* The excessive demands as to request atomicity and continuation
across server restart, leading to a feature which cannot be
implemented, as described in Appendix D.2.4.2.
* Ambiguity about the possibility of transparent state recovery and
the means by which the client might be informed of its existence,
as described in Appendix D.2.4.1.
* The confusion about the role of the clientid in connection with
session recovery as described in Appendix D.2.4.3.
An alternative approach to these issues is presented in
Appendix D.2.4.4. and will be the basis for a revised Section 8.
D.2.4.1. Ambiguity Regarding Locking State Persistence
As to the potential persistence of locking state, current
specifications are unclear, mostly due to different handling of the
issue in different sections and undue focus on what the server will
provide with no attention to the question of how the client finds out
about persistence or the lack thereof and deals appropriately with
the situation.
First of all, the section entitled "Client Identifiers and Client
Owners"(Section 2.4 in [RFC8881] and 5.5 in this document) gives the
impression that, in the event of a server restart, the client will
inevitably find out, by getting an NFS4ERR_BAD_CLIENTID error that
locking state has been lost. While there is no explicit statement to
this effect, the presentation of expected sequences of events (there
are separate discussions of this for the cases of persistent and non-
persistent sessions) leads one to suppose alternatives are not
anticipated.
On the other hand, the section entitled "Loss of Session" (
Section 2.10.13.1.4 in [RFC8881] and 7.13.1.4 in this document
strongly suggests that the NFS4ERR_BAD_CLIENTID is not inevitable,
opening the way for locking state to be persisted across a server
reboot, even though there is no explicit statement allowing servers
to do so.
Given this divergence, it makes sense to determine which of these
approaches is correct and make explicit descriptions of recovery make
clear how clients are to deal with servers that do maintain state
across reboot and avoid reclaim just as they do in the event of
migration. A part of that discussion will concern potential
compatibility issues which are not troublesome if clients do follow
the approach laid out in the loss-of-session section
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Adding to the existing confusion are occasional references to the
possibility of certain forms of state persistence, with no discussion
of how the client might find out about this potentially persistent
state. For example, Section 25.43.3 contains the following
paragraph:
If the metadata server is in a grace period, and does not persist
layouts and device ID to device address mappings, then it MUST
return NFS4ERR_GRACE (See Section 13.4.2.1).
While this strongly implies that metadata servers could persist
layouts across server failure, given the existing confusion it is
hard to see how clients could effectively use this functionality or
why server might provide it other than by providing a general lock
persistence.
D.2.4.2. Implementability of Persistent Reply Cache as Currently
Described
Another important topic of discussion concerns a number of statements
in the section entitled "Persistence" (Section 2.10.6.5 in [RFC8881]
and 8 in this document, which make implementation of persistent reply
caches significantly harder than it needs to be or give the reader
the impression that it is nearly unimplementable. This might have
led to lack of implementation effort as part of a vicious spiral,
that might result in the loss of this helpful feature, that needs
implementation to take advantage the availability of lower-latency
persistent storage. The following issues need to be addressed:
* One concern is that the statement "The execution of the sequence
of operations (starting with SEQUENCE) and placement of its
results in the persistent cache MUST be atomic" might convince the
reader that the execution of each COMPOUND needs to be atomic as
well, making conformance difficult and would seriously undercut
any attempt to provide file system parallelism.
This might not have been the author's intention, even though it is
the most natural reading of the sentence in question
There are necessary atomicity guarantees required but they have to
be more limited and explicit to make implementation possible.
* Even more troubling is the issue raised in the statement "A server
could fail and restart in the middle of a COMPOUND procedure that
contains one or more non-idempotent or idempotent-but-modifying
operations". The text goes on to say, as mildly as possible,
"This creates an even higher challenge for atomic execution and
placement of results in the reply cache.", but the indicating that
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this is a greater challenge is likely to convince most reader that
the feature is essentially unimplementable. The rest of the
paragraph gives no reason to expect something workable except in
special environments in which implementing this feature is the
only goal.
Fortunately, the essential unimplementability derives, not from
the feature but from the assumption that COMPOUNDs be executed
atomically across a server restart rather than being terminated as
part of the termination of the previous server instance, which
this paragraph assume will never happen.
There needs to be a way to terminate CONPOUNDs still active at the
time of server reboot, if there is no way to forbid execution of
such troublesome COMPOUNDs.
* The final paragraph does nothing to correct this impression of
unimplementability.
First, it says the following which would be unexceptionable for
features for which there is at least one way to implement them:
"While the description of the implementation for atomic execution
of the request and caching of the reply is beyond the scope of
this document".
Following this, it drives the final nail into the coffin of this
feature by saying "An example implementation for NFSv2 [45] is
described in [46]". The important fact here is that NFSv2 does
not have COMPOUND, allowing the troublesome atomicity and cross-
server-instance request continuity issues dealt with in the first
two paragraphs to be bypassed, making this citation in this
context inapposite.
D.2.4.3. Confusion about Clientid Role in Persistent Reply Cache
The existing discussion of reply cache persistence describes two
possible variants that primarily differ as to the persistent storage
of clientid-related information, with each variant deficient in some
important way. This leads us to conclude that confusion about the
role of the clientid and clientid-scoped state information and its
persistent storage was not taken into account when this arrangement
was arrived at. For example:
* While the persistent recording of some clientid-related
information is presented as part of the second option given, there
is no mention whatsoever of clientid-scoped locking state and its
persistent storage.
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Given the lack of explicit discussion of these matters, it is hard
to tell whether it was expected that the server would or could
persist this state.
* If clientid-related information is not saved (i.e. the first
option), then the persistent reply cache does provide EOS across
the server failure but does not allow the existing session to be
used for new requests.
While this is a valid use case for clients worried about the
possibility of EOS problems across server failures, the fact that
there is no locking state persistence means that server failure
will disrupt operation by requiring a grace period before, for
example, opening a file. However, giving this limited benefit, it
is troubling that the existing spec, dure to confusion about
clientid state, requires persistent recording of idempotent non-
modifying operations (e.g. READs) with no real benefit because
taking advantage of that benefit would require issuing new
requests and checking their sequence ids against a persistent
sored sequence id.
D.2.4.4. Replacement Approach to Persistence in the Case of Server
Failure
Regardless of the original intent with regard how to how these two
aspects of data persistence were to be tied together, it seems that
these need to be defined as independent features. Even if one could
determine that these were intended to be tied together, which seems
unlikely it is not possible to tie these two aspects of data
persistence, each with its own scope, together at this point. Making
that choice now would undercut the adaptation of NFSv4 to more
available low-latency persistent storage in a number of ways:
* Since the amount of locking state is not bounded, there would need
to be accommodations to the situation in which a surfeit of
locking state makes use of persistent storage impossible. If
these two sets of state were tied together, such situations would
unnecessarily interfere with the a need to provide EOS semantics
across server failure.
* In the context of clustered servers, the loci for the update of
session-related and clientid-related data might be different,
especially where clientid trunking is used. In such situations,
there will inevitably be occasions where only one of these two
forms of persistence is implemented.
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* Given that the flow of locking operations is often a small part of
the total and likely to be below the total of non-idempotent and
modifying operations well, for many server implementors it would
have a higher priority for implementation and use, As a result, it
reasonable to expect servers that implement it without
implementing reply cache persistence even after the issues
discussed in Appendix D.2.4.2 are successfully addressed
If persistence of locking state is to be made available as its own
feature, allowing clientids to persist across server failure, then it
is necessary to decide how to deal appropriately with the existing
two options for session-based state persistence, once the issue of
clientid-based state persistence is put aside.
* Persistence of the reply cache (only) will still be a viable
useful option, not providing session continuation across server
failure.
In defining this as a possible choice, it needs to be stressed
that servers aiming to provide this functionality to not need to
persistently store changes in sequence ids that would not be
perceivable by a reconnecting client.
* Full session persistence would remain an option, even though there
would be no need to persist data beyond the reply cache, current
sequence id array and clientid.
Actual use of a persistent session would require persistence of
the associated clientid-based locking state information. However,
the server would not commit itself to maintain this information at
session creation time and would find out if full session
continuation was available, at the point at which the first new
requests were issued
D.2.5. Changes in Attribute Categorization
The following changes in the categorization of attributes have been
completed in 5661bis draft -03 but need to be further discussed by
the working group. That discussion might involve other documents in
addition to this one.
* The detailed description of authorization-related attributes has
been moved to the documents [I-D.dnoveck-nfsv4-security] and
[I-D.ietf-nfsv4-acls-update].
In line with this shift, the attribute categorizations have been
made the province of [I-D.dnoveck-nfsv4-security] with that
controlling in the event of any conflict.
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* The attributes mode, owner, and owner_group have been made
REQUIRED rather than RECOMMENDED (with the meaning OPTIONAL)
* The attributes acl, sacl, and dacl have been described as
"Experimental" in NFSv4.1, since, unlike other OPTIONAL
attributes, the existing specifications do not describe the
attribute sufficiently to allow interoperable client and server
implementations to be developed.
D.2.6. Changes in Treatment of Attributes for Named Attribute
Directories
Previous specification were self-contradictory in that:
* There were statements that made SETATTR and GETATTR on named
attribute directories were undefined operations.
The explanation offered for this exclusion did not make sense.
For an explanation of why this text was eventually removed See
Author Aside #66a in Section 5.3.5 of
[I-D.dnoveck-nfsv4-security].
* There were other statements saying that named attribute
directories could have attribute and stating that they were to
include all the REQUIRED ones.
Changes have been made to eliminate this contradiction, as described
below:
* The statement regarding SETATTR and GETATTR on named attribute
directories being undefined operations was retained although the
text "explaining" this exclusion was deleted.
Since this material had been moved to
[I-D.dnoveck-nfsv4-security], the replacement appears in
Section 5.3,5 of that document.
* The statements about the ability to have (non-named) attributes
for the named attribute directory in Section 11.7 have been
deleted.
Discussion of these changes needs to continue to address the
following issues:
* Even though the contradiction has been resolved, it is not certain
why the exclusion is justified, given the inadequacy of the
existing explanation.
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Providing the ability to access and modify the attributes
associated with named attribute directories might address some of
the authorization issues discussed below, but could be expected to
add additional complexity.
Leaving this as it is in the current set of documents would avoid
additional complexity but still make it possible to reference
named attribute directory attributes as part of dealing with
authorization of operation involving the named attribute
directory.
* There is no existing discussion of POSIX-based authentication of
operations involving the named attribute directory, leaving a gap
that needs to be filled.
Using the mode, owner and owner_group attributes of the base
object in place of those for the named attribute directory runs
into troublesome issues since the X bit, controlling exec
privileges for a (non-directory) base file controls lookup for the
named attribute directory.
Any necessary changes will be made as part of Consensus Item #66
in [I-D.dnoveck-nfsv4-security].
* There exist ACE mask bits devoted to control of named attribute
directories but it is clear that some changes need to be made.
As currently defined, these bits only control access to and
creation of a named attribute directory, while allowing creation
of new named attributes without authorization controls. Cleaning
this up will be easier when we know how implementations behave but
so far, none have been found.
Any necessary changes will be made as part of Consensus Item #100
in [I-D.ietf-nfsv4-acls-update].
D.2.7. Changes Made as a Result of REJECTED Errata Reports
Changes were made in response to the errata reports listed below,
each of which was assigned a REJECTED status. The author, based on
his own sense of the working group's need and wants, has addressed
those errata reports. Even though there is no reason to suppose
these reports do not need to be addressed, their rejection needs to
be addressed by establishing that their is a working group consensus
to make the change.
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* Errata report 2722, reported by Ricardo Labiaga, was an editorial
change that was rejected for reasons that are not clear. In
addition, it is also unclear why this report was retracted.
In any case, the author addressed the troublesome area in way he
feels satisfactory without necessarily following the text in the
retracted report. The rejection, whatever its motivation implies
we need a working group consensus as to the acceptability of the
change made.
* Errata report 2751, reported by Ricardo Labiaga, was a technical
change that was rejected because it proposed a substantive change
in the handling of LAYOUTCOMMIT. Despite this justified
rejection, it appears that implementation adopted the suggested
approach, making it necessary that we, even at this late date, to
adjust the specification so that implementation and specification
no longer differ.
This specification draft has adopted the proposed changes without
major changes except in one respect: The proposed new section,
slated to be part of pNFS chapter will be done as part of the
chapter devoted to the pNFS files layout. In addition, the
presentation of changes in the form of text replacement
complicated the process by requiring decompilation of the changes
into xml. While the author did as well as he could, the
complexity of the process calls for extra review.
In any case, further review of these change is necessary to make
sure that the resultant text has working group consensus.
* Errata report 5982, reported by David Noveck was a technical
change that was rejected. As things turned out the proposed text
was misguided and was dropped.
Although other changes were made with same ultimate motivation and
do need review, no special review is needed based on the rejection
of the errata report.
D.2.8. Changes Made to Address Problems in Description of REMOVE/RENAME
In addition to the restructurings/clarifications discussed in
Appendix C.12, there are a number of substantive changes for which a
consensus needs to be arrived at. These include changes in which the
change is arguably substantive because ambiguities in the existing
text makes it hard to determine whether the existing text is or is
not compatible with the new treatment.
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* A change of approach to the PRSERVE_UNLINKED flag, making it only
apply to the OPEN which returned it. This avoids dealing with the
possibility of it being returned differently for successive opens
and makes it clear why it does not apply to NFSv3 or NFSv4.0
OPENs.
* Providing rules allowing the recall of delegations help by a
client doing a REMOVE can be dispensed with, depending on the
nature of the server's restrictions regarding REMOVE of open
files.
This includes a requirement for the client holding the delegation
and doing a REMOVE to make the server aware of any OPENs denying
READ or WRITE.
There are also a set of potential changes that might be made once it
is clear whether or not compatibility issues would prevent any
substantive change.
* Making it explicit that the restrictions regarding removal of a
renamed-over file are identical to those removed using REMOVE.
* Applying similar logic regarding the non-recall of delegations for
OPENs of the file being removed.
It is important to note that the need for s write-delegation-holding
client to make the server aware of OPENs denying write before doing a
removal operation potentially raises compatibility issues. However,
the practical problems arising are likely to be small since:
* A large portion of existing clients do not issue OPENs denying
read or write.
* For those that do issue them, the complexity cost of doing so
locally is likely to inhibit broad use of this technique. If a
client were to do this locally, it would be taking on the work of
the server in dealing with multiple processes doing such OPENs and
corresponding CLOSEs, and detecting conflicts. This is unlikely
to be worth doing since the benefit is likely to be quite small.
D.2.9. Changes Made to Address Lack of Clarity Regarding "The Forgetful
Model"
Section 12.5.3 of [RFC8881] (and Section 18.7.3 of the previous draft
this document) contains the following statement;
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The client must fully process the operations before the "seqid"
can be used. For LAYOUTGET results, if the client is not using
the forgetful model (Section 12.5.5.1/>), it MUST first update its
record of what ranges of the file's layout it has before using the
seqid.
This statement raises the following issues/questions:
* There is no explanation of what "using the forgetful model" means
and how it might differ from a presumably more persistent model.
* There is no explanation of how a client might choose a particular
model and how a server might be affected by the client's choice of
model.
* The sentence fragment "if the client is not using the forgetful
model (Section 12.5.5.1), it MUST" is hard to understand since
"MUST", according to [RFC2119] is used to introduce "a fundamental
requirement of the specification". Given that definition, it is
hard to understand how or why a client not following this
requirement might be excused due to following this model.
* The section referenced in the troublesome text (i.e.,
Section 12.5.5.1), does not define "forgetful model"
* The title of the referenced section, referring to "Recall
Robustness" seems to make its use where recalls are not involved,
confusing.
In order to address the existing confusion and provide suitable
normative text regarding the layout sequencing requirements and
server and client requirements regarding obligations to retain layout
information (independent of a presumed model choice), we are doing
the following:
* Rename the sections so it is clear that it is about possible
protocol requirements (and non-requirements).
* Re-organizing the section so that we are clear that what was
previously referred to as an "assumption" which was not always the
case is now explicitly a non-requirement.
* Put all the normative requirements together near the start of the
section.
* Retain the useful implementation suggestion but make it clearer
that this material is non-normative.
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* Divide the previous ancillary section regarding recall robustness
into two sections, one about retention requirements and another
about recall/return interaction.
D.2.10. Need for Replacement of RFC8434
Discussion of recent drafts has made it clear thar further work is
needed to provide an up-to-date replacement for [RFC8434]. For that
reason, draft-00 of rfc8881bis is not marked as obsoleting RFC8434,
while it is intended to renew that designation in a later draft.
Overall, it seems best if most of the material in this RFC is placed
in a new section after the pNFS Section and before the pNFS files
Section.
The new placement, the passage of time and existence of new layout
types leads to a number of issues that will need to be addressed when
this new section is added.
* The use of RFC2119-defined keywords within [RFC8434] needs further
discussion because these keywords are defined as applying to
implementations rather than to possible future documents.
The Working Group faced a similar issue in the drafting of
[RFC8178]. During discussion of that document some group members
argued that each working group was free to specify things as it
might choose and it was inappropriate for one Working Group to
foreclose what a future working group might do.
As a result, we adopted the approach documented in Section 2.1 of
[RFC8178], which can be adopted in a replacement for [RFC8434]
* The nature of this respecification means that we can no longer
assume that the new section updates rfc8881bis, since it is part
of rfc8881bis.
As a result there is no longer a meaningful distinction between
Sections 3.1 and 3.2 of [RFC8434]
Although Section 4.2 and 4.3 still make sense, section 4.1 makes
more sense in the pNFS files section. With regard to flexible
files, it should only need a brief reference to [RFC8435].
Remaining issue that still need to be addressed are discussed
Appendix D.2.11.
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D.2.11. Remaining Issues for Discussion After Replacement of RFC8434
The following work done as part of replacing [RFC8434] needs Working
Group review:
* Making substantial revisions to Section 18 to take advantage of
the more substantial role of layout types introduced by [RFC8434]
This enabled deletion of the confusing practice of referring to
specific layout types in this section, which led to an unclear
expansion path and an undue attention to unusual features of those
layout types, with the placement of the file layout specification
being misunderstood as applying to pNFS as a whole.
* Creating a new top-level Section 19.
While the material was derived from [RFC8434], its new placement
(between Sections 18 20) clarified the relationship between
individual layout type and PNFS as a whole.
* Revising and retitling Section 29.5.3 to focus on IANA-related
requirements only.
* The addition of subsections 20.4, 20.26, and 20.27 to Section 20.
The following choices to change/restructure things as part of this
replacement will need to be discussed:
* The change from using RFC2119-defined keywords to describe the
obligations of layout type specifications to describing these, as
[RFC8178] did, as normative despite the lack of these keywords.
* The reorganization of these requirements from one section (now
Section 29.5.3 in [RFC5661] to two sections (19 and 29.5.3) in the
bis document.
* There are good reasons to change the prohibition of the use of
all-zero and all-one stateids that appears using the phrase "MUST
NOT"".
I can see no good reason for this prohibition, let alone any
reason to consider this restriction "a fundamental requirement of
the specification. On the other hand, it is difficult to change
at this point given that this assumption may have affected
implementations in ways that are difficult to change now.
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* The treatment of authorization-checking needs a major rework
because of the following issues in the way this is dealt with in
Section 19.9.2.3 of [RFC8881]:
- This treatment essentially ignores the access checking done by
OPEN with troublesome negative effects on performance and
requiring a functional divergence from the on-metadata-server
approach that many versions of NFS have needed to deal with to
prevent the authorization checking done by OPEN from being
invalidated post facto.
- It treats ACLs differently from other authorization-related
attributes, adding complexity and possible confusion..
It contradicts what should be the main focus pf the
requirements, making handling on data servers and the metadata
server as nearly identical as possible.
The new treatment in Sections 20.15 and 20.14.2 takes a different
approach:
- It limits the need for post-OPEN access checking to case in
which the requester is different from the opener, as provided
for by POSIX authorization semantics
Requiring this checking be redone on all IOs is a performance
problem and functional problem if it applies to all IO and a
troublesome difference if it applies only to data-server-
directed IO.
- The needed sharing is not limited to ACLs, but applies to all
changes of authorization-related attributes.
- Rather than assuming attribute propagation is always needed,
the new treatment, integrated to discussion of sharing of
locking information, allowing various form of propagation or
remote interrogation as chosen by the implementer.
- Because of the previous uncertainty regarding authorization and
the likely inability to suitably restrict the semantics of
NFSv4 ACLs in the near future, the identity behavior is made
the primary requirement, potentially overriding what is said in
Section 20.15. See Section 20.14.2
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* In a number of areas within existing NFSv4.1 specifications of
pNFS, there are situations where explicit use of per-layout-type
approach would be helpful but, because the text was written before
the concepts behind RFC8434 were understood are dealt with in
unsatisfactory ways:
- the differences are addressed by referring to the needs of
specific layout types, presented as examples.
This results in uncertain handling regarding layout types not
yet defined.
- The need for different sorts of handling is addressed as if it
were implementation advice, even where there is no way that a
particular layout type could do anything other than what is
presented.
- The implementation is allowed to choose its handling (through
use of "MAY") in circumstances in which this is inappropriate
since the choice is better tied to the layout type used.
For the following areas, we have addressed additional case in
which choices need to be made explicitly layout-type-specific.
These are discussed in Appendices D.2.12 and D.2.13.
Aa a result of the need for extensive changes in these areas, Working
Group review of the changes discussed above is necessary to make sure
we have not inadvertently restricted needed implementation freedom or
invalidated an implementations.
D.2.12. Layout-Type-Specificity for LAYOUTCOMMIT
The handling of attribute coordination/synchronization needed to be
addressed by making more of the handing of LAYOUTCOMMIT layout-type-
specific, as discussed below:
* As far as arriving at a global modified-time/change attribute, it
is hard to arrive at a justification for the variation/complexity
allowed in how the MDS's value is to be arrived at. One approach
explicitly allowed the MDS to use the time of the LAYOUTCOMMIT as
the new modified time and proceeding along similar lines for the
change attribute. This avoids a lot of unnecessary complexity int
the treatment within [RFC8881] regarding possible clock
synchronization issues, discussion of possible estimates and how
they might be used or "sanity-checked".
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While a more radical simplification of this might be possible, we
have made the matter layout-type-specific so that, if there is a
justification for this complex treatment, it needs to be made in
the context of a layout type that needs it.
* The change attribute is not explicitly deal with although a global
value needs to be arrived at. The approach taken needs to be tied
together with the layout-type-specific approach to setting of the
modified time.
* As far arriving at a global size attribute at the MDS, the issues
are similar and there seems no case for variation beyond making
the choice layout-type-specific.
* Although there are indications within [RFC8881] that LAYOUTCOMMIT
is not always required where one might expect it to be, the
discussion is separated from other aspects of the description of
LAYOUYCOMMIT as part of a general description of a layout type
(files). Description of any situation in which the requirements
are different is now a necessary as part of the layout type
specifications for all layout types.
* Similarly, there had been within Section 18.9 material that
suggested that LAYOUTCOMMIT would always be necessary, The section
has now been rewritten to make it clear that this requirement is
always layout-type-specific.
D.2.13. Layout-Type-Specificity for Layout Termination
The handling of layout recall, return revocation, and the discarding
of layout-related information needs to be layout-type-specific for a
number of reasons. In the new treatment, they are addressed together
in Section 19.1.9 as discussed below:
* In the case of layout return, any restrictions other than
requiring waiting for the completion of pending IOs, if they
exist, need to be clearly explained in the layout type
specification. These include the potential need to make the data
storage device aware of the change in layout status.
* The case of layout recall is similar in that restrictions, if they
exist, need to be described by the layout type specification. In
cases in which recall needs to be done for some layout types (e.g.
REMOVE), the requirements need to be clearly stated with a
explanation as to how layout types that do not have such
requirements prevent erroneous access to unused storage.
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* While layout revocation is always possible due to an unacceptably
delayed layout recall or a failure-like situation such a an
expired lease, some layout types might allow it in other
situations. These need to be described clearly.
Where these situations are described using the term "conflicting
layouts", the meaning of this term needs to be explained clearly.
This is particularly important because [RFC8881] defined this in a
way that does not apply to the files layout when server multi-
pathing was in effect. Also, it needs to be made clear whether
non-layout-based IO operations can gave the same effect.
Descriptions of how these situations are to be dealt with need to
explain how IO operations using the revoked layouts are prevented
and existing one drained. In this context, it needs to be clear
that referring to "fencing" is stating a requirement which needs
to be supplemented by an explanation of how the requirement is
dealt with in all situations. For example, informing a data
server of a layouts termination needs to be supplemented by
consideration of the situation in which the data sever cannot be
contacted.
* As discussed in Section 18.7.3.1, clients and metadata servers may
discard layout information without worry about the inconsistency
between the MDA and clients thereby created. However, there can
be restrictions on such discarding based on the layout type.
These need to be clearly described.
D.2.14. Possible Generalization Data Server Failure Handling
As discussed in Section 20.23.2, it is possible to generalize
recovery to allow server implementations more freedom to maintain
lock continuity across data server failures. This might become
necessary if servers exist that manifest these behaviors.
D.2.15. Discussion Needed re Status of RFC5663
In light of the discussion in Section 19.2.1, there are reasons to
either update or obsolete [RFC5663]. These problems arise because we
now have a situation in which we have two different block layout
types with corresponding specification documents:
* [RFC5663] was published with some troublesome problems in its
handling of locking semantics and authorization. In addition, it
indicated a need for fencing but remained unclear on how that need
was to be dealt with.
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* Later [RFC8154] was published to provide a clear description of
how fencing was to be implemented. This document substantially
improved the handling of locking semantics and authorization but
these changes, unrelated to the fencing clarification which
motivated the new document, were not backported to [RFC5663].
As a result, we now have two closely related documents describing
block layout types. Given the effort to maintain these two, we need
to decide:
* Whether we need to maintain a separate non-scsi block layout type.
* If we do want that, what is the best available way to provide for
that?
Normally, to deal with such situations, we put the maintenance
effort into the base specification and make the extension (in this
case the SCSI handling of fencing_ a small update but that option
is no longer available to us.
The working group has the following options to address this situation
and might have others.
* Update [RFC5663] in the same way that [RFC5664] is being update
and mark it as updated by the bis document wen approved.
This leaves us with the job of maintaining these two for an
indefinite period.
* Consider [RFC5663] as superseded by [RFC8154] and mark it as
obsoleted by the bis document when approved.
* Write a statement within this document explaining support for the
BLOCKS Layout type stating that is to follow [RFC8154] except that
the scsi-related facilities are not necessarily available.
Mark [RFC5663] as obsoleted by the bis document when approved
D.2.16. Discussion of Possible Additional Access Flags
Discussion is needed to clarify the needs for further control bits
for the ACCESS operation and the appropriate relationship between
these bits and the corresponding ACE mask bits. Although there gas
some additions to these bits to reflect the finer-grained permission
model introduced by NFSv4 ACLs, we need to understand whether these
need to be brought into closer alignment, and, if we do not do so,
how to deal with the differences we leave.
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In earlier specifications in which the client's was discouraged from
making its own authorization decisions, it might have seemed
essential for ACCESS to made of equal or finer granularity than the
ACE mask, this is no longer the case, leaving us to make a number of
specific decisions listed below:
* Whether, given that we have separate ACE bits controlling adding
of files and directories, ACCESS need to follow suite.
* Whether we need ACCESS bit corresponding to the ACE mask bits
controlling access to and modification of the named attributes
directory
If we choose not to do the above, the description of ACCESS needs to
explain why not and how to determine authorization in these
situations.
Another possibility is the definition of a new operation similar to
ACCESS that returns an ACE mask word.
D.2.17. Discussion of Named Attributes and Their Possible Relationship
with Extended Attributes
The following elements of the handling of extended attributes within
NFSv4 so far makes it necessary for the Working Group to discuss and
decide on an appropriate way forward for extended attributes:
* NFSv4.2 contains an XATTR extension oriented solely toward Linux
extended attributes, which, while outside the scope of POSIX, are
commonly available in POSIX-oriented clients and servers.
* The named attribute feature has been used to provide support for
Windows extended attributes, despite the troubling performance
issues, and the fact that named attribute functionality is far
beyond what is necessary to support extended attributes.
This use presents the Working Group with an important
compatibility issue that would need to be addressed by any new
approach to support of Windows extended attributes.
* Although the significance of this fact is unclear, it appears that
there has been, during the evolution of NFSv4, a "deprecation" of
the use of the use of multiple data stream within Windows in favor
of a model closer to that of Linux XATTRs although the exact
differences remain unclear.
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In any case, the working Group now has three possible choices to
consider, identified below by "A" through "C". In analyzing these
choices, we will need to refer to similar issues that arose in the
handling of ACLs. While the desire to avoid a repeat of that
unfortunate situation is part of our motivation, there are important
differences between the two cases. Nevertheless, the similarities
make it useful to use what we have learned from the ACL case in this
analogous situation regarding extended attributes.
The three choice we have to select from are as follows:
A: Maintain the status quo in NFsv4.2 going forward.
Important advantages of this approach are that there is no work
to do and no compatibility issue to address.
One important disadvantage is that we wind up with two different
features to address extended attributes in Linux and Windows.
Beyond the unsatisfactoriness of this approach from an
architectural point of view, it seems that these two feature will
contribute to the further separate evolution of Windows-oriented
and Linux-oriented variants of NFSv4, undercutting the important
value provided by unifying these in a single protocol.
While it might be reasonably assumed that this would make it
difficult to transfer files including, between servers supporting
the two distinct modes of extended attributes, this is only
portly true. While Windows XATTRs would not be representable on
server filesystems without support for multiple data streams
(i.e., almost all Linux filesystems), the reverse is not the case
since the Linux XATTR extension could be easily supported.
B: Create a separate XATTR extension oriented toward the extended
attributes implemented in Windows systems, similar to wat has
already been done in v4.2 for XATTRs in Linux systems.
While this approach shares the architectural issues discussed
above for "A", the file transfer issue discussed there is fully
addressed. The situation is similar to the handling of ACL
transfers in the proposed draft-POSIX ACL extensions in which a
server can support storage of both forms while making a separate
choice as to which attribute(s) to use for authorization. The
XATTR case is simpler because the filesystem does not actually
use the extended attributes.
C: Extend the XATTR feature described in [RFC8276] so that it
supports Window Extended attributes as well.
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This approach. while architecturally more satisfying, requires
extra work to deal with compatibility for servers using the named
attribute approach. Proposals to adopt this approach need to be
evaluated to ensure that they deal satisfactorily with
filesystems that have stored extended attributes in this form and
clients built to store them in this form.
The most important potential disadvantage of this approach is our
current uncertainty as to the semantic requirements for Windows
extended attributes and the possibility, as occurred with ACLs
that neither the Windows nor the POSIX-oriented approach is a
struct subset of the other. Although it is easy and helpful to
assume that this is the case, if it is not true in practice, we
would be putting ourselves in a situation similar to that which
occurred in the ACLs case, which we have no desire to repeat.
The decision as to the appropriate approach will occur with the
analysis of proposed extensions. This is better than trying to
select "A", "B", or "C" in a vacuum, and then look for a proposal in
the selected class. Fortunately, we have time to make this choice,
as we can continue with "A", until a B-style or C-style proposal is
prepared, adopted, and published.
D.2.18. Discussion of Neglected Caching Needs
This section has two major functions:
* To provide a basis for a discussion of the adequacy of the changes
made to the treatment of caching made within Section 15 as a way
of contributing to addressing the troublesome issues that Tom
Haynes' work with workloads including access to files wit multiple
writers as exposed.
This discussion will be limited to work that could be done in
context of the NFSv4.1 respecification effort.
Given that anticipated extensions will probably make reference to
the same issue WG discussion (and presumably assent) to these
changes will provide preparation for discussion of the needed
extensions even though the extensions will be published before
completing the rfc8881bis effort.
* To introduce possible ways of dealing, in later minor versions, of
a range of possible ways to address the difficulties in handling
cases in which a file is accessed by multiple clients including at
least one writer.
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We need to address situations in which a cache coherence mechanism
is needed but might not, in practical terms be implementable.
Complicating the situation is the fact that the protocol's method
of preventing unwanted inter-client interactions, share
reservations is not implemented in many client environments and
there is no easy way to change this.
We will consider ways of directly avoiding cache incoherence
including by eliminating caching as discussed in Appendix D.2.19.
Other alternatives in which we try to avoid difficult sharing that
provides no value by targeted semantic changes, or provide
coordination to deal with sharing more effectively will be
explored in Appendix D.2.20.
As we begin this discussion, I need to make clear how the issues we
need to deal with, and how that view differs from that of others who
might well agree on the means to fix them, at least in part. I think
it is important to be clear about differences as we work to address
the pressing issues that have been identified for sharing in
situations in which cache incoherence is a troubling problem, despite
the usefulness of caching for many other workloads.
In my view, the existence of these problems, decades after the basic
decisions were made as for NFSv4 points to a troubling pattern of
neglect in which the need to deal appropriately, with shared access
to files that are not read-only was simply ignored. This happened
because the only facility available to control such sharing, share
reservations, was not widely implemented in many important
environments. This happened because the needed feature was outside
the POSIX file access framework and no alternatives were provided or
even thought about. It is now time to correct this situation, which
will take considerable time. Luckily, Tom has provided an
expeditious means of surviving this delay, even though it might not
be the right long-term solution from an architectural point of view.
With this in mind we need to proceed as follows:
* Verify that we have done all that we can reasonably to address the
problem as part of the respecification effort, even if it is of no
practical value. However, even if that is the case, we need to be
aware that there is a problem to be addressed, even if we have a
likely partial solution that can be made available in the
immediate NFSv4.2 time-frame.
* Discuss the strengths and weakness of possible mechanisms of
caching elimination, as discussed in Appendix D.2.19.
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These need to address the immediate needs for an expeditious
solution together with the longer term needs for a finer-grained
approach.
* Discuss other alternative semantics to address sharing issues as
discussed in Appendix D.2.20.
D.2.19. Discussion Regarding Ways of Avoiding Cache Incoherence
As noted above, an important way of avoiding the problems associated
with cache incoherency is simply to avoid caching when such problems
are likely to arise. Because caching is so important in other
environments, it is desirable to limit this avoidance to situations
in which it is actually needed.
Given this situation the work already done in specifying the
"uncacheable" attributes needs to be made realizable as quickly
despite possible concerns, which I share, about its coarse- grained
nature. As we note the progress that has been made so far, the
important advance is the recognition, in later drafts, of the
advisory nature of the attribute,, although the prominent use of the
word "uncacheable" sometimes makes it hard to see this properly.
Despite this progress, there are a number of remaining issues that
need to be addressed before a more current version is submitted (and
adopted if necessary) and we prepare to move toward a successful
WGLC.
* Although there has been considerable discussion of the
relationship between advising against caching of files and of
directories, it seems that additional discussion is needed in this
area.
Although the approach taken in discussion is that these are
unrelated is probably correct, the draft needs to make this
clearer and we need an explanation of what problems might cause
the server (or one of the clients ?) to advise clients to avoid
directory caching.
Although the author of these drafts is concerned about the
possibilities of inconsistencies and believes that caching
elimination for files and data needs to done together, the lack of
connection between the file-related caching advice and the
directory-related caching advice seems to be inconsistent with
that.
Apart from issues regarding the number of attributes or documents,
it appears that there is no obvious motivation for elimination of
directory caching, as there is for file and attribute caching.
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If the justification for directory caching elimination is, as one
suspect it is, access-based enumeration, the document needs t say
so, In my view, however, it would be better to enhance NFS to
support ABE in an NFSv4 extension rather than letting each server
do this in its own way.
* Although the switch to a model of advising clients whether to
cache has been successful, there are some unresolved issues left
from the original model in which much of the guidance was stated
with normative text or an approximation thereof.
Part of this is that the word "uncacheable" seems to imply a
mandate rather than helpful advice. More important is a lack of
clarity about the basis for this advice.
This problem is compounded by the specification of this attribute
as writable since the server is in a better position to decide on
such advice on the basis of sharing patterns.
* If, as might be reasonably expected, the advice is conditional on
the sharing pattern, the issue of notification promptness needs to
be addressed.
* The issue of advice granularity needs to be addressed. Although
making this per-file is satisfactory, there are suggestions, given
the description, that something more coarse-grained is likely. to
be implemented. If so, much of the description about the basis
for the server's advice to avoid caching is hard to understand
since the sharing patterns for each file are likely to be
different.
Assuming we can quickly achieve a useful coarse-grained solution, we
need to prepare for a more fine-grained approach that can, unlike the
prototypes already done, be useable in all environments because it
does not suppress caching when there is no need to do so
One way of providing a more fine-grained approach to the problem of
inter-client file sharing involves the extension of file delegations
in a manner similar to the way they are used in directory delegation.
In this case, sharing would result in a notification of the new
sharing pattern rater than revocation of the delegation. Such
notifications would allow the client to avoid revocation while
updating its handling of the open file to respond to current sharing
conditions:
* When the file transitions to a state in which it is shared, with
on or more writers, to cease data caching.
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* When the file transitions to a state in which any sharing is read-
only. to enable use of data and attribute caching.
* n When the file transitions to a state in which it is shared, with
more than one writer, to apply any special coordination measures
to deal with that situation, in addition to refraining from use of
data and attribute caching.
Within such a framework, the initial sharing state could be provided
as part of the OPEN response or as an initial pro forma notification
of the initial sharing state.
D.2.20. Discussion Regarding Possible Semantic Changes to Address Cache
Incoherence
It appears we have a range of issues that arise from the fact share
reservations are the architecturally correct solution to such
unneeded sharing but that we have nearly zero chance of having them
adopted widely in a reasonable time frame. As a result, we will look
at ways to provide facility to avoid unwanted use of incoherent
caching that do not involve changes to the signature of the POSIX
OPEN operation.
Given the current state of affairs, it appears that a large part of
the cases involving troublesome inter-client interactions are
inadvertent because client applications have no means to prevent
them.
Given this troubling situation, the approaches discussed so far,
which suppresses caching in order to prevent cache incoherence,
appears to be the correct solution to a problem that would be
unnecessary, if the sharing is actually not needed.
In this section we will look at alternatives to unwanted sharing that
can be used as defaults if the client-side API cannot be adapted to
prevent unneeded sharing. We will deal separately with:
* Undesirable sharing between a single writer and one or more
readers.
It seems that a considerable portion of such interactions are
inadvertent and only happen because share reservations are
unavailable or not used.
While caching suppression is desirable here, it does not address
all the problems that result from such inadvertent sharing. For
detail regarding how to address this see the discussion below
regarding the single-writer case.
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* Undesirable sharing among multiple writers and possibly some
readers as well.
Where the sharing is inadvertent, the same techniques used for the
single-writer case are useful as well.
For other cases, we separately address the interacting writer and
non-interacting writer cases below.
Although the desire to avoid changes to OPEN leads us to focus on
providing default mechanism that could be selected by things like
mount options, there will be cases in which needs for more extensive
co-ordination can be addressed by API additions that do not modify
OPEN. Because of the difficulty of changing OPEN, we will focus on
function that could be invoked after completion of the OPEN
operation.
There are a number of changes that are likely to be needed for all of
the cases discussed below:
* Creation of a default-DENY flag to be used when no denial mode is
specified.
This is particularly useful for operating environments in which
the user is unable to specify a particular deny mode. However, it
will also be useful if the default depends, as it should, on
actual sharing including also the possibility of caching
elimination or the change deferral mechanism mentioned below.
* Providing for a sort of delegation-like object such as that
described in Appendix D.2.19 that provides sharing-mode updated
without necessarily implying revocation.
* Interfaces to file system facilities to delay visibility of
changes until close or other synchronizing event.
The single-writer-case can be addressed as follows by allowing the
open to proceed (unlike the case with share reservations) and
allowing the client to respond to the existence of sharing, whether
it discovers the sharing, whether this happens as a result of the
OPEN response, or via a later notification when the sharing starts.
In either case, the client will have the following options with a
client-based default selected if he does not make a choice;
* Elimination of caching to avoid reliance on caching that does not
provide coherence.
* Delay of changes by the writer until there are no readers.
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In this case existing readers will see the old copy, most likely
stored persistently as a spares file with later modification of
the existing file happening by modification of the files block
mapping when all the readers are gone.
* The current default of continuing to cache. This is a poor
default but it should be selectable by those who want it.
The case of multiple writers requires distinguishing between
interacting and non-interacting writers. Where both are possible,
use of sharing based defaults is inadequate since the application
would need to signal its need for the less-used handling (probably
the interacting-write case) explicitly, If this is done after the
OPEN, when the existence of multiple-writer sharing is established,
implementers can avoid the difficult work of providing difficult-to-
justify extensions to the OPEN API.
Given the above:
* It appears that noninteracting writers can be dealt with by
multiple instances of the single-writer approach although it is
likely that a different default will be chosen for this case.
Such cases are likely to involve uses of distinct portions of the
file by different clients, as would be likely for local files
modified by multiple processes.
* The interacting-write case would require a range of co-ordination
facilities that are not provided but could be added without
needing changes in OPEN. The client should have the option of
obtaining access to these coordination facilities whenever it is
founnd out that the file is being shared my multiple writers.
These facilities are likely to require some form of mandatory
byte-range locks adapted to provide inter-client coordination
facilities to support multi-client write-sharing of open files.
The development of further extensions might be necessary if uses
of this form becomes more common. Likely developments include the
provisions of atomic block swaps.
Although NFSv4 currently has mandatory byte-range locking as an
OPTONAL feature but there are a number of potential weaknesses that
will need to be resolved:
* The ability to select mandatory or advisory byte-range locking as
opposed to the current server-chosen one-size-fits-all all
approach.
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* More detailed discussion of deadlock detection and recovery
therefrom.
* Some consideration of the relationship between byte-range locking
and caching and how the guarantee provided by the former might
allow routine use of the latter.
Writers should probable have the ability to atomically swap a set of
blocks existing blocks and replacements. Compare and swap of such
block sets should be considered as well. Although byte-ranges might
seem more natural, it is probably not worth the additional
implementation complexity.
Acknowledgments
Acknowledgments for This Update
The author wishes to thank Tom Haynes of Hammerspace for drawing the
working group's attention to the fact that internationalization and
security might best be handled in documents dealing with these
individual protocol areas, addressing those issues as they apply to
all NFSv4 minor versions.
The author wishes to thank Rick Macklem for his help in resolving the
previous confusion regarding the proper timing for use of the
PREV_DELEG claim types.
The author wishes to thank Rick Macklem and Trond Myklebust of
Hammerspace for their helpful discussion of issues related to the
existing text regarding REMOVE and RENAME.
The author wishes to thank Olga Kornievskaia of Red Hat for her
insights regarding the existing prohibition on ceasing to wait for a
request that has not yet been replied to.
The author wishes to thank Tom Haynes of Hammerspace for his helpful
insights and suggestions regarding the incorporation of material
formerly in [RFC8434].
The author wishes to thank Tom Haynes of Hammerspace for drawing his
attention to the weaknesses in previous specifications in dealing
with file and attribute caching as part of his work to address new
sorts of NFS workloads involving open file sharing.
The author wishes to thank all those who contributed corrections/
suggestions to drafts of this specification, including Chuck Lever of
Oracle and Yang Jing of HuaWei.
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The Author wishes to thank Rick Macklem and Pali Rohar for their help
in providing discussion of issues related to limits on the size of
ACLs.
The author wishes to thank Pali Rohar, Cedric Blancher, and Martin
Wege for their helpful perspectives regarding the future of extended
attributes in NFSv4.
Acknowledgments for Previous Specification Documents
In addition to the authors/editors, the following people made
important contributions to RFC 5661:
* The initial text for the SECINFO extensions were edited by Mike
Eisler with contributions from Peng Dai, Sergey Klyushin, and Carl
Burnett.
* The initial text for the SESSIONS extensions were edited by Tom
Talpey, Spencer Shepler, Jon Bauman with contributions from
Charles Antonelli, Brent Callaghan, Mike Eisler, John Howard, Chet
Juszczak, Trond Myklebust, Dave Noveck, John Scott, Mike
Stolarchuk, and Mark Wittle.
* Initial text relating to multi-server namespace features,
including the concept of referrals, were contributed by Dave
Noveck, Carl Burnett, and Charles Fan with contributions from Ted
Anderson, Neil Brown, and Jon Haswell.
* The initial text for the Directory Delegations support were
contributed by Saadia Khan with input from Dave Noveck, Mike
Eisler, Carl Burnett, Ted Anderson, and Tom Talpey.
* The initial text for the ACL explanations were contributed by Sam
Falkner and Lisa Week.
* The pNFS work was inspired by the NASD and OSD work done by Garth
Gibson. Gary Grider has also been a champion of high-performance
parallel I/O. Garth Gibson and Peter Corbett started the pNFS
effort with a problem statement document for the IETF that formed
the basis for the pNFS work in NFSv4.1.
* The initial text for the parallel NFS support was edited by Brent
Welch and Garth Goodson. Additional authors for those documents
were Benny Halevy, David Black, and Andy Adamson. Additional
input came from the informal group that contributed to the
construction of the initial pNFS drafts; specific acknowledgment
goes to Gary Grider, Peter Corbett, Dave Noveck, Peter Honeyman,
and Stephen Fridella.
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* Fredric Isaman found several errors in draft versions of the ONC
RPC XDR description of the NFSv4.1 protocol.
* Audrey Van Belleghem provided, in numerous ways, essential
coordination and management of the process of editing the
specification documents.
The following contributions regarding work done in RFC8881 need to be
acknowledged:
* The important role of Andy Adamson of Netapp in clarifying the
need for trunking discovery functionality, and exploring the role
of the file system location attributes in providing the necessary
support.
* The work of Xuan Qi of Oracle with NFSv4.1 client and server
prototypes of Transparent State Migration functionality.
* The comments of Trond Myklebust of Primary Data related to
trunking helped to clarify the role of DNS in trunking discovery.
* Rick Macklem's comments brought attention to problems in the
handling of the per-fs version of RECLAIM_COMPLETE.
It is important to take note of work of Tom Haynes of Hammerspace in
writing [RFC8434], which enabled a truly transformational advance in
our understanding of the pNFS feature.
RFC Editor Notes
[RFC Editor: please remove this section prior to publishing this
document as an RFC]
[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the
RFC number of this document]
[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD20 with RFCyyyy where yyyy is the
RFC number of the document providing descriptions of NFSv4
internationalization, currently expected to result from completion of
the document referenced in [I-D.ietf-nfsv4-internationalization] or a
document replacing that one.
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[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD21 with RFCyyyy where yyyy is the
RFC number of the document providing an overall description of NFSv4
security, currently expected to result from completion of the
document referenced in [I-D.dnoveck-nfsv4-security] or a document
replacing that one.
[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD22 with RFCyyyy where yyyy is the
RFC number of the document providing descriptions of ACLs, currently
expected to result from completion of the document referenced in
[I-D.ietf-nfsv4-acls-update] or a document replacing that one.
[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD20 with RFCyyyy where yyyy is the
RFC number of the document providing updated XDR for NFSv4.1,
currently expected to result from completion of the document
referenced in [I-D.dnoveck-nfsv4-rfc5662bis] or a document replacing
that one.
Author's Address
David Noveck (editor)
NetApp
201 Jones Road
Waltham, MA 02451
United States of America
Phone: +1-781-572-8038
Email: davenoveck@gmail.com
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