NFSv4 S. Shepler
Internet-Draft M. Eisler
Intended status: Standards Track D. Noveck
Expires: August 1, 2008 Editors
January 29, 2008
NFS Version 4 Minor Version 1
draft-ietf-nfsv4-minorversion1-19.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This Internet-Draft describes NFS version 4 minor version one,
including features retained from the base protocol and protocol
extensions made subsequently. Major extensions introduced in NFS
version 4 minor version one include: Sessions, Directory Delegations,
and parallel NFS (pNFS).
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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 described in RFC 2119 [1].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 11
1.1. The NFS Version 4 Minor Version 1 Protocol . . . . . . . 11
1.2. Scope of this Document . . . . . . . . . . . . . . . . . 11
1.3. NFSv4 Goals . . . . . . . . . . . . . . . . . . . . . . 11
1.4. NFSv4.1 Goals . . . . . . . . . . . . . . . . . . . . . 12
1.5. General Definitions . . . . . . . . . . . . . . . . . . 12
1.6. Overview of NFSv4.1 Features . . . . . . . . . . . . . . 15
1.6.1. RPC and Security . . . . . . . . . . . . . . . . . . 15
1.6.2. Protocol Structure . . . . . . . . . . . . . . . . . 15
1.6.3. File System Model . . . . . . . . . . . . . . . . . 16
1.6.4. Locking Facilities . . . . . . . . . . . . . . . . . 18
1.7. Differences from NFSv4.0 . . . . . . . . . . . . . . . . 18
2. Core Infrastructure . . . . . . . . . . . . . . . . . . . . . 19
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 19
2.2. RPC and XDR . . . . . . . . . . . . . . . . . . . . . . 19
2.2.1. RPC-based Security . . . . . . . . . . . . . . . . . 19
2.3. COMPOUND and CB_COMPOUND . . . . . . . . . . . . . . . . 22
2.4. Client Identifiers and Client Owners . . . . . . . . . . 23
2.4.1. Upgrade from NFSv4.0 to NFSv4.1 . . . . . . . . . . 26
2.4.2. Server Release of Client ID . . . . . . . . . . . . 27
2.4.3. Resolving Client Owner Conflicts . . . . . . . . . . 27
2.5. Server Owners . . . . . . . . . . . . . . . . . . . . . 28
2.6. Security Service Negotiation . . . . . . . . . . . . . . 29
2.6.1. NFSv4.1 Security Tuples . . . . . . . . . . . . . . 29
2.6.2. SECINFO and SECINFO_NO_NAME . . . . . . . . . . . . 29
2.6.3. Security Error . . . . . . . . . . . . . . . . . . . 30
2.7. Minor Versioning . . . . . . . . . . . . . . . . . . . . 33
2.8. Non-RPC-based Security Services . . . . . . . . . . . . 36
2.8.1. Authorization . . . . . . . . . . . . . . . . . . . 36
2.8.2. Auditing . . . . . . . . . . . . . . . . . . . . . . 36
2.8.3. Intrusion Detection . . . . . . . . . . . . . . . . 36
2.9. Transport Layers . . . . . . . . . . . . . . . . . . . . 36
2.9.1. REQUIRED and RECOMMENDED Properties of Transports . 37
2.9.2. Client and Server Transport Behavior . . . . . . . . 37
2.9.3. Ports . . . . . . . . . . . . . . . . . . . . . . . 39
2.10. Session . . . . . . . . . . . . . . . . . . . . . . . . 39
2.10.1. Motivation and Overview . . . . . . . . . . . . . . 39
2.10.2. NFSv4 Integration . . . . . . . . . . . . . . . . . 40
2.10.3. Channels . . . . . . . . . . . . . . . . . . . . . . 42
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2.10.4. Trunking . . . . . . . . . . . . . . . . . . . . . . 43
2.10.5. Exactly Once Semantics . . . . . . . . . . . . . . . 46
2.10.6. RDMA Considerations . . . . . . . . . . . . . . . . 58
2.10.7. Sessions Security . . . . . . . . . . . . . . . . . 61
2.10.8. The SSV GSS Mechanism . . . . . . . . . . . . . . . 66
2.10.9. Session Mechanics - Steady State . . . . . . . . . . 70
2.10.10. Session Mechanics - Recovery . . . . . . . . . . . . 71
2.10.11. Parallel NFS and Sessions . . . . . . . . . . . . . 75
3. Protocol Constants and Data Types . . . . . . . . . . . . . . 75
3.1. Basic Constants . . . . . . . . . . . . . . . . . . . . 75
3.2. Basic Data Types . . . . . . . . . . . . . . . . . . . . 76
3.3. Structured Data Types . . . . . . . . . . . . . . . . . 78
4. Filehandles . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.1. Obtaining the First Filehandle . . . . . . . . . . . . . 87
4.1.1. Root Filehandle . . . . . . . . . . . . . . . . . . 87
4.1.2. Public Filehandle . . . . . . . . . . . . . . . . . 88
4.2. Filehandle Types . . . . . . . . . . . . . . . . . . . . 88
4.2.1. General Properties of a Filehandle . . . . . . . . . 89
4.2.2. Persistent Filehandle . . . . . . . . . . . . . . . 89
4.2.3. Volatile Filehandle . . . . . . . . . . . . . . . . 90
4.3. One Method of Constructing a Volatile Filehandle . . . . 91
4.4. Client Recovery from Filehandle Expiration . . . . . . . 91
5. File Attributes . . . . . . . . . . . . . . . . . . . . . . . 92
5.1. REQUIRED Attributes . . . . . . . . . . . . . . . . . . 94
5.2. RECOMMENDED Attributes . . . . . . . . . . . . . . . . . 94
5.3. Named Attributes . . . . . . . . . . . . . . . . . . . . 94
5.4. Classification of Attributes . . . . . . . . . . . . . . 96
5.5. REQUIRED Attributes - List and Definition References . . 97
5.6. RECOMMENDED Attributes - List and Definition
References . . . . . . . . . . . . . . . . . . . . . . . 97
5.7. Attribute Definitions . . . . . . . . . . . . . . . . . 99
5.7.1. Definitions of REQUIRED Attributes . . . . . . . . . 99
5.7.2. Definitions of Uncategorized RECOMMENDED
Attributes . . . . . . . . . . . . . . . . . . . . . 101
5.8. Interpreting owner and owner_group . . . . . . . . . . . 107
5.9. Character Case Attributes . . . . . . . . . . . . . . . 109
5.10. Directory Notification Attributes . . . . . . . . . . . 109
5.11. pNFS Attribute Definitions . . . . . . . . . . . . . . . 110
5.12. Retention Attributes . . . . . . . . . . . . . . . . . . 112
6. Security Related Attributes . . . . . . . . . . . . . . . . . 114
6.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . 114
6.2. File Attributes Discussion . . . . . . . . . . . . . . . 115
6.2.1. Attribute 12: acl . . . . . . . . . . . . . . . . . 115
6.2.2. Attribute 58: dacl . . . . . . . . . . . . . . . . . 130
6.2.3. Attribute 59: sacl . . . . . . . . . . . . . . . . . 130
6.2.4. Attribute 33: mode . . . . . . . . . . . . . . . . . 131
6.2.5. Attribute 74: mode_set_masked . . . . . . . . . . . 131
6.3. Common Methods . . . . . . . . . . . . . . . . . . . . . 132
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6.3.1. Interpreting an ACL . . . . . . . . . . . . . . . . 132
6.3.2. Computing a Mode Attribute from an ACL . . . . . . . 133
6.4. Requirements . . . . . . . . . . . . . . . . . . . . . . 134
6.4.1. Setting the mode and/or ACL Attributes . . . . . . . 134
6.4.2. Retrieving the mode and/or ACL Attributes . . . . . 136
6.4.3. Creating New Objects . . . . . . . . . . . . . . . . 136
7. Single-server Namespace . . . . . . . . . . . . . . . . . . . 140
7.1. Server Exports . . . . . . . . . . . . . . . . . . . . . 140
7.2. Browsing Exports . . . . . . . . . . . . . . . . . . . . 141
7.3. Server Pseudo File System . . . . . . . . . . . . . . . 141
7.4. Multiple Roots . . . . . . . . . . . . . . . . . . . . . 142
7.5. Filehandle Volatility . . . . . . . . . . . . . . . . . 142
7.6. Exported Root . . . . . . . . . . . . . . . . . . . . . 142
7.7. Mount Point Crossing . . . . . . . . . . . . . . . . . . 143
7.8. Security Policy and Namespace Presentation . . . . . . . 143
8. State Management . . . . . . . . . . . . . . . . . . . . . . 144
8.1. Client and Session ID . . . . . . . . . . . . . . . . . 145
8.2. Stateid Definition . . . . . . . . . . . . . . . . . . . 145
8.2.1. Stateid Types . . . . . . . . . . . . . . . . . . . 146
8.2.2. Stateid Structure . . . . . . . . . . . . . . . . . 147
8.2.3. Special Stateids . . . . . . . . . . . . . . . . . . 148
8.2.4. Stateid Lifetime and Validation . . . . . . . . . . 150
8.2.5. Stateid Use for I/O Operations . . . . . . . . . . . 153
8.3. Lease Renewal . . . . . . . . . . . . . . . . . . . . . 153
8.4. Crash Recovery . . . . . . . . . . . . . . . . . . . . . 155
8.4.1. Client Failure and Recovery . . . . . . . . . . . . 155
8.4.2. Server Failure and Recovery . . . . . . . . . . . . 156
8.4.3. Network Partitions and Recovery . . . . . . . . . . 159
8.5. Server Revocation of Locks . . . . . . . . . . . . . . . 164
8.6. Short and Long Leases . . . . . . . . . . . . . . . . . 165
8.7. Clocks, Propagation Delay, and Calculating Lease
Expiration . . . . . . . . . . . . . . . . . . . . . . . 165
8.8. Vestigial Locking Infrastructure From V4.0 . . . . . . . 166
9. File Locking and Share Reservations . . . . . . . . . . . . . 167
9.1. Opens and Byte-range Locks . . . . . . . . . . . . . . . 167
9.1.1. State-owner Definition . . . . . . . . . . . . . . . 167
9.1.2. Use of the Stateid and Locking . . . . . . . . . . . 168
9.2. Lock Ranges . . . . . . . . . . . . . . . . . . . . . . 171
9.3. Upgrading and Downgrading Locks . . . . . . . . . . . . 171
9.4. Blocking Locks . . . . . . . . . . . . . . . . . . . . . 172
9.5. Share Reservations . . . . . . . . . . . . . . . . . . . 173
9.6. OPEN/CLOSE Operations . . . . . . . . . . . . . . . . . 174
9.7. Open Upgrade and Downgrade . . . . . . . . . . . . . . . 174
9.8. Parallel OPENs . . . . . . . . . . . . . . . . . . . . . 175
9.9. Reclaim of Open and Byte-range Locks . . . . . . . . . . 176
10. Client-Side Caching . . . . . . . . . . . . . . . . . . . . . 176
10.1. Performance Challenges for Client-Side Caching . . . . . 177
10.2. Delegation and Callbacks . . . . . . . . . . . . . . . . 178
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10.2.1. Delegation Recovery . . . . . . . . . . . . . . . . 180
10.3. Data Caching . . . . . . . . . . . . . . . . . . . . . . 182
10.3.1. Data Caching and OPENs . . . . . . . . . . . . . . . 182
10.3.2. Data Caching and File Locking . . . . . . . . . . . 183
10.3.3. Data Caching and Mandatory File Locking . . . . . . 185
10.3.4. Data Caching and File Identity . . . . . . . . . . . 185
10.4. Open Delegation . . . . . . . . . . . . . . . . . . . . 187
10.4.1. Open Delegation and Data Caching . . . . . . . . . . 189
10.4.2. Open Delegation and File Locks . . . . . . . . . . . 190
10.4.3. Handling of CB_GETATTR . . . . . . . . . . . . . . . 191
10.4.4. Recall of Open Delegation . . . . . . . . . . . . . 194
10.4.5. Clients that Fail to Honor Delegation Recalls . . . 195
10.4.6. Delegation Revocation . . . . . . . . . . . . . . . 196
10.4.7. Delegations via WANT_DELEGATION . . . . . . . . . . 197
10.5. Data Caching and Revocation . . . . . . . . . . . . . . 197
10.5.1. Revocation Recovery for Write Open Delegation . . . 198
10.6. Attribute Caching . . . . . . . . . . . . . . . . . . . 199
10.7. Data and Metadata Caching and Memory Mapped Files . . . 201
10.8. Name and Directory Caching without Directory
Delegations . . . . . . . . . . . . . . . . . . . . . . 203
10.8.1. Name Caching . . . . . . . . . . . . . . . . . . . . 203
10.8.2. Directory Caching . . . . . . . . . . . . . . . . . 205
10.9. Directory Delegations . . . . . . . . . . . . . . . . . 205
10.9.1. Introduction to Directory Delegations . . . . . . . 206
10.9.2. Directory Delegation Design . . . . . . . . . . . . 207
10.9.3. Attributes in Support of Directory Notifications . . 208
10.9.4. Directory Delegation Recall . . . . . . . . . . . . 208
10.9.5. Directory Delegation Recovery . . . . . . . . . . . 208
11. Multi-Server Namespace . . . . . . . . . . . . . . . . . . . 209
11.1. Location Attributes . . . . . . . . . . . . . . . . . . 209
11.2. File System Presence or Absence . . . . . . . . . . . . 209
11.3. Getting Attributes for an Absent File System . . . . . . 211
11.3.1. GETATTR Within an Absent File System . . . . . . . . 211
11.3.2. READDIR and Absent File Systems . . . . . . . . . . 212
11.4. Uses of Location Information . . . . . . . . . . . . . . 213
11.4.1. File System Replication . . . . . . . . . . . . . . 213
11.4.2. File System Migration . . . . . . . . . . . . . . . 214
11.4.3. Referrals . . . . . . . . . . . . . . . . . . . . . 215
11.5. Location Entries and Server Identity . . . . . . . . . . 217
11.6. Additional Client-side Considerations . . . . . . . . . 217
11.7. Effecting File System Transitions . . . . . . . . . . . 218
11.7.1. File System Transitions and Simultaneous Access . . 219
11.7.2. Simultaneous Use and Transparent Transitions . . . . 220
11.7.3. Filehandles and File System Transitions . . . . . . 223
11.7.4. Fileids and File System Transitions . . . . . . . . 223
11.7.5. Fsids and File System Transitions . . . . . . . . . 224
11.7.6. The Change Attribute and File System Transitions . . 225
11.7.7. Lock State and File System Transitions . . . . . . . 226
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11.7.8. Write Verifiers and File System Transitions . . . . 229
11.7.9. Readdir Cookies and Verifiers and File System
Transitions . . . . . . . . . . . . . . . . . . . . 230
11.7.10. File System Data and File System Transitions . . . . 230
11.8. Effecting File System Referrals . . . . . . . . . . . . 231
11.8.1. Referral Example (LOOKUP) . . . . . . . . . . . . . 232
11.8.2. Referral Example (READDIR) . . . . . . . . . . . . . 236
11.9. The Attribute fs_locations . . . . . . . . . . . . . . . 238
11.10. The Attribute fs_locations_info . . . . . . . . . . . . 240
11.10.1. The fs_locations_server4 Structure . . . . . . . . . 244
11.10.2. The fs_locations_info4 Structure . . . . . . . . . . 249
11.10.3. The fs_locations_item4 Structure . . . . . . . . . . 250
11.11. The Attribute fs_status . . . . . . . . . . . . . . . . 252
12. Parallel NFS (pNFS) . . . . . . . . . . . . . . . . . . . . . 256
12.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 256
12.2. pNFS Definitions . . . . . . . . . . . . . . . . . . . . 257
12.2.1. Metadata . . . . . . . . . . . . . . . . . . . . . . 258
12.2.2. Metadata Server . . . . . . . . . . . . . . . . . . 258
12.2.3. pNFS Client . . . . . . . . . . . . . . . . . . . . 258
12.2.4. Storage Device . . . . . . . . . . . . . . . . . . . 258
12.2.5. Storage Protocol . . . . . . . . . . . . . . . . . . 258
12.2.6. Control Protocol . . . . . . . . . . . . . . . . . . 258
12.2.7. Layout Types . . . . . . . . . . . . . . . . . . . . 259
12.2.8. Layout . . . . . . . . . . . . . . . . . . . . . . . 259
12.2.9. Layout Iomode . . . . . . . . . . . . . . . . . . . 260
12.2.10. Device IDs . . . . . . . . . . . . . . . . . . . . . 260
12.3. pNFS Operations . . . . . . . . . . . . . . . . . . . . 262
12.4. pNFS Attributes . . . . . . . . . . . . . . . . . . . . 263
12.5. Layout Semantics . . . . . . . . . . . . . . . . . . . . 263
12.5.1. Guarantees Provided by Layouts . . . . . . . . . . . 263
12.5.2. Getting a Layout . . . . . . . . . . . . . . . . . . 264
12.5.3. Layout Stateid . . . . . . . . . . . . . . . . . . . 265
12.5.4. Committing a Layout . . . . . . . . . . . . . . . . 266
12.5.5. Recalling a Layout . . . . . . . . . . . . . . . . . 269
12.5.6. Revoking Layouts . . . . . . . . . . . . . . . . . . 276
12.5.7. Metadata Server Write Propagation . . . . . . . . . 276
12.6. pNFS Mechanics . . . . . . . . . . . . . . . . . . . . . 276
12.7. Recovery . . . . . . . . . . . . . . . . . . . . . . . . 278
12.7.1. Recovery from Client Restart . . . . . . . . . . . . 278
12.7.2. Dealing with Lease Expiration on the Client . . . . 279
12.7.3. Dealing with Loss of Layout State on the Metadata
Server . . . . . . . . . . . . . . . . . . . . . . . 280
12.7.4. Recovery from Metadata Server Restart . . . . . . . 280
12.7.5. Operations During Metadata Server Grace Period . . . 282
12.7.6. Storage Device Recovery . . . . . . . . . . . . . . 283
12.8. Metadata and Storage Device Roles . . . . . . . . . . . 283
12.9. Security Considerations for pNFS . . . . . . . . . . . . 284
13. PNFS: NFSv4.1 File Layout Type . . . . . . . . . . . . . . . 285
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13.1. Client ID and Session Considerations . . . . . . . . . . 285
13.2. File Layout Definitions . . . . . . . . . . . . . . . . 287
13.3. File Layout Data Types . . . . . . . . . . . . . . . . . 288
13.4. Interpreting the File Layout . . . . . . . . . . . . . . 292
13.4.1. Determining the Stripe Unit Number . . . . . . . . . 292
13.4.2. Interpreting the File Layout Using Sparse Packing . 292
13.4.3. Interpreting the File Layout Using Dense Packing . . 294
13.4.4. Sparse and Dense Stripe Unit Packing . . . . . . . . 297
13.5. Data Server Multipathing . . . . . . . . . . . . . . . . 298
13.6. Operations Sent to NFSv4.1 Data Servers . . . . . . . . 299
13.7. COMMIT Through Metadata Server . . . . . . . . . . . . . 302
13.8. The Layout Iomode . . . . . . . . . . . . . . . . . . . 303
13.9. Metadata and Data Server State Coordination . . . . . . 303
13.9.1. Global Stateid Requirements . . . . . . . . . . . . 303
13.9.2. Data Server State Propagation . . . . . . . . . . . 304
13.10. Data Server Component File Size . . . . . . . . . . . . 306
13.11. Layout Revocation and Fencing . . . . . . . . . . . . . 307
13.12. Security Considerations for the File Layout Type . . . . 308
14. Internationalization . . . . . . . . . . . . . . . . . . . . 309
14.1. Stringprep profile for the utf8str_cs type . . . . . . . 310
14.2. Stringprep profile for the utf8str_cis type . . . . . . 311
14.3. Stringprep profile for the utf8str_mixed type . . . . . 313
14.4. UTF-8 Capabilities . . . . . . . . . . . . . . . . . . . 314
14.5. UTF-8 Related Errors . . . . . . . . . . . . . . . . . . 314
15. Error Values . . . . . . . . . . . . . . . . . . . . . . . . 315
15.1. Error Definitions . . . . . . . . . . . . . . . . . . . 315
15.1.1. General Errors . . . . . . . . . . . . . . . . . . . 317
15.1.2. Filehandle Errors . . . . . . . . . . . . . . . . . 319
15.1.3. Compound Structure Errors . . . . . . . . . . . . . 320
15.1.4. File System Errors . . . . . . . . . . . . . . . . . 322
15.1.5. State Management Errors . . . . . . . . . . . . . . 324
15.1.6. Security Errors . . . . . . . . . . . . . . . . . . 325
15.1.7. Name Errors . . . . . . . . . . . . . . . . . . . . 326
15.1.8. Locking Errors . . . . . . . . . . . . . . . . . . . 326
15.1.9. Reclaim Errors . . . . . . . . . . . . . . . . . . . 328
15.1.10. pNFS Errors . . . . . . . . . . . . . . . . . . . . 328
15.1.11. Session Use Errors . . . . . . . . . . . . . . . . . 330
15.1.12. Session Management Errors . . . . . . . . . . . . . 331
15.1.13. Client Management Errors . . . . . . . . . . . . . . 331
15.1.14. Delegation Errors . . . . . . . . . . . . . . . . . 332
15.1.15. Attribute Handling Errors . . . . . . . . . . . . . 333
15.1.16. Obsoleted Errors . . . . . . . . . . . . . . . . . . 333
15.2. Operations and their valid errors . . . . . . . . . . . 334
15.3. Callback operations and their valid errors . . . . . . . 350
15.4. Errors and the operations that use them . . . . . . . . 352
16. NFSv4.1 Procedures . . . . . . . . . . . . . . . . . . . . . 366
16.1. Procedure 0: NULL - No Operation . . . . . . . . . . . . 366
16.2. Procedure 1: COMPOUND - Compound Operations . . . . . . 367
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17. Operations: REQUIRED, RECOMMENDED, or OPTIONAL . . . . . . . 377
18. NFSv4.1 Operations . . . . . . . . . . . . . . . . . . . . . 380
18.1. Operation 3: ACCESS - Check Access Rights . . . . . . . 380
18.2. Operation 4: CLOSE - Close File . . . . . . . . . . . . 383
18.3. Operation 5: COMMIT - Commit Cached Data . . . . . . . . 384
18.4. Operation 6: CREATE - Create a Non-Regular File Object . 387
18.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting
Recovery . . . . . . . . . . . . . . . . . . . . . . . . 390
18.6. Operation 8: DELEGRETURN - Return Delegation . . . . . . 391
18.7. Operation 9: GETATTR - Get Attributes . . . . . . . . . 391
18.8. Operation 10: GETFH - Get Current Filehandle . . . . . . 393
18.9. Operation 11: LINK - Create Link to a File . . . . . . . 394
18.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 396
18.11. Operation 13: LOCKT - Test For Lock . . . . . . . . . . 400
18.12. Operation 14: LOCKU - Unlock File . . . . . . . . . . . 402
18.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 403
18.14. Operation 16: LOOKUPP - Lookup Parent Directory . . . . 405
18.15. Operation 17: NVERIFY - Verify Difference in
Attributes . . . . . . . . . . . . . . . . . . . . . . . 406
18.16. Operation 18: OPEN - Open a Regular File . . . . . . . . 407
18.17. Operation 19: OPENATTR - Open Named Attribute
Directory . . . . . . . . . . . . . . . . . . . . . . . 426
18.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 427
18.19. Operation 22: PUTFH - Set Current Filehandle . . . . . . 428
18.20. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 429
18.21. Operation 24: PUTROOTFH - Set Root Filehandle . . . . . 431
18.22. Operation 25: READ - Read from File . . . . . . . . . . 431
18.23. Operation 26: READDIR - Read Directory . . . . . . . . . 434
18.24. Operation 27: READLINK - Read Symbolic Link . . . . . . 437
18.25. Operation 28: REMOVE - Remove File System Object . . . . 438
18.26. Operation 29: RENAME - Rename Directory Entry . . . . . 441
18.27. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 444
18.28. Operation 32: SAVEFH - Save Current Filehandle . . . . . 445
18.29. Operation 33: SECINFO - Obtain Available Security . . . 446
18.30. Operation 34: SETATTR - Set Attributes . . . . . . . . . 449
18.31. Operation 37: VERIFY - Verify Same Attributes . . . . . 452
18.32. Operation 38: WRITE - Write to File . . . . . . . . . . 453
18.33. Operation 40: BACKCHANNEL_CTL - Backchannel control . . 458
18.34. Operation 41: BIND_CONN_TO_SESSION . . . . . . . . . . . 459
18.35. Operation 42: EXCHANGE_ID - Instantiate Client ID . . . 462
18.36. Operation 43: CREATE_SESSION - Create New Session and
Confirm Client ID . . . . . . . . . . . . . . . . . . . 478
18.37. Operation 44: DESTROY_SESSION - Destroy existing
session . . . . . . . . . . . . . . . . . . . . . . . . 487
18.38. Operation 45: FREE_STATEID - Free stateid with no
locks . . . . . . . . . . . . . . . . . . . . . . . . . 489
18.39. Operation 46: GET_DIR_DELEGATION - Get a directory
delegation . . . . . . . . . . . . . . . . . . . . . . . 490
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18.40. Operation 47: GETDEVICEINFO - Get Device Information . . 494
18.41. Operation 48: GETDEVICELIST - Get All Device Mappings
for a File System . . . . . . . . . . . . . . . . . . . 496
18.42. Operation 49: LAYOUTCOMMIT - Commit writes made using
a layout . . . . . . . . . . . . . . . . . . . . . . . . 498
18.43. Operation 50: LAYOUTGET - Get Layout Information . . . . 501
18.44. Operation 51: LAYOUTRETURN - Release Layout
Information . . . . . . . . . . . . . . . . . . . . . . 505
18.45. Operation 52: SECINFO_NO_NAME - Get Security on
Unnamed Object . . . . . . . . . . . . . . . . . . . . . 510
18.46. Operation 53: SEQUENCE - Supply per-procedure
sequencing and control . . . . . . . . . . . . . . . . . 511
18.47. Operation 54: SET_SSV - Update SSV for a Client ID . . . 517
18.48. Operation 55: TEST_STATEID - Test stateids for
validity . . . . . . . . . . . . . . . . . . . . . . . . 519
18.49. Operation 56: WANT_DELEGATION - Request Delegation . . . 521
18.50. Operation 57: DESTROY_CLIENTID - Destroy existing
client ID . . . . . . . . . . . . . . . . . . . . . . . 525
18.51. Operation 58: RECLAIM_COMPLETE - Indicates Reclaims
Finished . . . . . . . . . . . . . . . . . . . . . . . . 525
18.52. Operation 10044: ILLEGAL - Illegal operation . . . . . . 528
19. NFSv44.1 Callback Procedures . . . . . . . . . . . . . . . . 528
19.1. Procedure 0: CB_NULL - No Operation . . . . . . . . . . 529
19.2. Procedure 1: CB_COMPOUND - Compound Operations . . . . . 529
20. NFSv4.1 Callback Operations . . . . . . . . . . . . . . . . . 533
20.1. Operation 3: CB_GETATTR - Get Attributes . . . . . . . . 533
20.2. Operation 4: CB_RECALL - Recall an Open Delegation . . . 534
20.3. Operation 5: CB_LAYOUTRECALL - Recall Layout from
Client . . . . . . . . . . . . . . . . . . . . . . . . . 535
20.4. Operation 6: CB_NOTIFY - Notify directory changes . . . 539
20.5. Operation 7: CB_PUSH_DELEG - Offer Delegation to
Client . . . . . . . . . . . . . . . . . . . . . . . . . 543
20.6. Operation 8: CB_RECALL_ANY - Keep any N delegations . . 544
20.7. Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal
Resources for Recallable Objects . . . . . . . . . . . . 546
20.8. Operation 10: CB_RECALL_SLOT - change flow control
limits . . . . . . . . . . . . . . . . . . . . . . . . . 547
20.9. Operation 11: CB_SEQUENCE - Supply backchannel
sequencing and control . . . . . . . . . . . . . . . . . 548
20.10. Operation 12: CB_WANTS_CANCELLED - Cancel Pending
Delegation Wants . . . . . . . . . . . . . . . . . . . . 550
20.11. Operation 13: CB_NOTIFY_LOCK - Notify of possible
lock availability . . . . . . . . . . . . . . . . . . . 551
20.12. Operation 14: CB_NOTIFY_DEVICEID - Notify device ID
changes . . . . . . . . . . . . . . . . . . . . . . . . 553
20.13. Operation 10044: CB_ILLEGAL - Illegal Callback
Operation . . . . . . . . . . . . . . . . . . . . . . . 555
21. Security Considerations . . . . . . . . . . . . . . . . . . . 555
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22. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 557
22.1. Named Attribute Definitions . . . . . . . . . . . . . . 557
22.2. ONC RPC Network Identifiers (netids) . . . . . . . . . . 557
22.3. Defining New Notifications . . . . . . . . . . . . . . . 558
22.4. Defining New Layout Types . . . . . . . . . . . . . . . 559
22.5. Path Variable Definitions . . . . . . . . . . . . . . . 560
22.5.1. Path Variable Values . . . . . . . . . . . . . . . . 560
22.5.2. Path Variable Names . . . . . . . . . . . . . . . . 561
23. References . . . . . . . . . . . . . . . . . . . . . . . . . 561
23.1. Normative References . . . . . . . . . . . . . . . . . . 561
23.2. Informative References . . . . . . . . . . . . . . . . . 562
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 564
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 566
Intellectual Property and Copyright Statements . . . . . . . . . 567
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1. Introduction
1.1. 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 described in [21]. It generally follows the
guidelines for minor versioning model listed in Section 10 of RFC
3530. However, it diverges from guidelines 11 ("a client and server
that supports minor version X must support minor versions 0 through
X-1"), and 12 ("no features may be introduced as mandatory in a minor
version"). These divergences are due to the introduction of the
sessions model for managing non-idempotent operations and the
RECLAIM_COMPLETE operation. These two new features are
infrastructural in nature and simplify implementation of existing and
other new features. Making them anything but REQUIRED would add
undue complexity to protocol definition and implementation. NFSv4.1
accordingly updates the Minor Versioning guidelines (Section 2.7).
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.
1.2. Scope of this Document
This document describes the NFSv4.1 protocol. With respect to
NFSv4.0, this document does not:
o describe the NFSv4.0 protocol, except where needed to contrast
with NFSv4.1.
o modify the specification of the NFSv4.0 protocol.
o clarify the NFSv4.0 protocol.
1.3. NFSv4 Goals
The NFSv4 protocol is a further revision of the NFS protocol defined
already by NFSv3 [22]. It retains the essential characteristics of
previous versions: easy recovery; independence of transport
protocols, operating systems and file systems; simplicity; and good
performance. NFSv4 has the following goals:
o Improved access and good performance on the Internet.
The protocol is designed to transit firewalls easily, perform well
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where latency is high and bandwidth is low, and scale to very
large numbers of clients per server.
o Strong security with negotiation built into the protocol.
The protocol builds on the work of the ONCRPC working group in
supporting the RPCSEC_GSS protocol. Additionally, the NFSv4.1
protocol provides a mechanism to allow clients and servers the
ability to negotiate security and require clients and servers to
support a minimal set of security schemes.
o Good cross-platform interoperability.
The protocol features 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.
o Designed for protocol extensions.
The protocol is designed to accept standard extensions within a
framework that enable and encourages backward compatibility.
1.4. NFSv4.1 Goals
NFSv4.1 has the following goals, within the framework established by
the overall NFSv4 goals.
o To correct significant structural weaknesses and oversights
discovered in the base protocol.
o To add clarity and specificity to areas left unaddressed or not
addressed in sufficient detail in the base protocol. However, as
stated in Section 1.2, it is not a goal to clarify the NFSv4.0
protocol in the NFSv4.1 specification.
o To add specific features based on experience with the existing
protocol and recent industry developments.
o To provide protocol support to take advantage of clustered server
deployments including the ability to provide scalable parallel
access to files distributed among multiple servers.
1.5. General Definitions
The following definitions are provided for the purpose of providing
an appropriate context for the reader.
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Byte This document defines a byte as an octet, i.e. a datum exactly
8 bits in length.
Client The "client" is the entity that accesses the NFS server's
resources. The client may be an application which contains the
logic to access the NFS server directly. The client may also be
the 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 file 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 crash or failure recovery for those
locks it manages.
Note that multiple clients may share the same transport and
connection and multiple clients may exist on the same network
node.
Client ID A 64-bit quantity used as a unique, short-hand reference
to a client supplied Verifier and client owner. The server is
responsible for supplying the client ID.
Client Owner The client owner is a unique string, opaque to the
server, which identifies a client. Multiple network connections
and source network addresses originating from those connections
may share a client owner. The server is expected to treat
requests from connnections with the same client owner as coming
from the same client.
File System The collection of objects on a server (as identified by
the major identifier of a Server Owner, which is defined later in
this section), that share the same fsid attribute (see
Section 5.7.1.9).
Lease An interval of time defined by the server for which the client
is irrevocably granted a lock. At the end of a lease period the
lock may be revoked if the lease has not been extended. The lock
must be revoked if a conflicting lock has been granted after the
lease interval.
All leases granted by a server have the same fixed interval. Note
that the fixed interval was chosen to alleviate the expense a
server would have in maintaining state about variable length
leases across server failures.
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Lock The term "lock" is used to refer to record (byte-range) locks,
share reservations, delegations, or layouts unless specifically
stated otherwise.
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 and minor identifier. When
the client has two connections each to a peer with the same major
identifier, the client assumes both peers are the same server (the
server namespace is the same via each connection), and assumes and
lock state is sharable across both connections. When each peer
has both the same major and minor identifier, the client assumes
each connection might be associatable with the same session.
Stable Storage NFSv4.1 servers must be able to recover without data
loss from multiple power failures (including cascading power
failures, that is, several power failures in quick succession),
operating system failures, and hardware failure of components
other than the storage medium itself (for example, disk,
nonvolatile RAM).
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 128-bit quantity returned by a server that uniquely
defines the open and locking state provided by the server for a
specific open or lock owner for a specific file and type of lock.
Verifier A 64-bit quantity generated by the client that the server
can use to determine if the client has restarted and lost all
previous lock state.
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1.6. Overview of NFSv4.1 Features
To provide a reasonable context for the reader, 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 that 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 XDR and RPC protocols as described
in [2] and [3]. 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
added in minor version one from those present in the base protocol
but will treat NFSv4.1 as a unified whole. See Section 1.7 for a
summary of the differences between NFSv4.0 and NFSv4.1.
1.6.1. 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 [2] and [3]. To meet end-to-end
security requirements, the RPCSEC_GSS framework [4] will be used to
extend the basic RPC security. With the use of RPCSEC_GSS, various
mechanisms can be provided to offer authentication, integrity, and
privacy to the NFSv4 protocol. Kerberos V5 will be used as described
in [5] to provide one security framework. The LIPKEY and SPKM-3 GSS-
API mechanisms described in [6] will be used to provide for the use
of user password and client/server public key certificates by the
NFSv4 protocol. With the use of RPCSEC_GSS, other mechanisms may
also be specified and used for NFSv4.1 security.
To enable in-band security negotiation, the NFSv4.1 protocol has
operations which provide the client a method of querying the server
about its policies regarding which security mechanisms must be used
for access to the server's file system resources. With this, the
client can securely match the security mechanism that meets the
policies specified at both the client and server.
1.6.2. Protocol Structure
1.6.2.1. Core Protocol
Unlike NFSv3, which used a series of ancillary protocols (e.g. NLM,
NSM, MOUNT), within all minor versions of NFSv4 a single RPC protocol
is used to make requests to the server. Facilities that had been
separate protocols, such as locking, are now integrated within a
single unified protocol.
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1.6.2.2. Parallel Access
Minor version one supports high-performance data access to a
clustered server implementation by enabling a separation of metadata
access and data access, with the latter 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.
1.6.3. File System Model
The general file system model used for the NFSv4.1 protocol is the
same as previous versions. The server file system is hierarchical
with the regular files contained within being treated as opaque byte
streams. In a slight departure, file and directory names are encoded
with UTF-8 to deal with the basics of internationalization.
The NFSv4.1 protocol does not require 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
provides any necessary pseudo file systems to bridge any gaps that
arise due to unexported gaps between exported file systems.
1.6.3.1. Filehandles
As in previous versions of the NFS protocol, opaque filehandles are
used to identify individual files and directories. Lookup-type and
create operations are used to go from file and directory names to the
filehandle which is then used to identify the object to subsequent
operations.
The NFSv4.1 protocol provides support for persistent filehandles,
guaranteed to be valid for the lifetime of the file system object
designated. In addition it provides support to servers to provide
filehandles with more limited validity guarantees, called volatile
filehandles.
1.6.3.2. File Attributes
The NFSv4.1 protocol has a rich and extensible attribute structure.
Only a small set of the defined attributes are REQUIRED to be
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provided by all server implementations. The other attributes are
known as RECOMMENDED attributes.
The acl, sacl, and dacl attributes are a significant set of file
attributes that make up the Access Control List (ACL) of a file.
These attributes provide for directory and file access control beyond
the model used in NFSv3. The ACL definition allows for specification
of specific sets of permissions for individual users and groups. In
addition, ACL inheritance allows propagation of access permissions
and restriction down a directory tree as file system objects are
created.
One other type of attribute is the named attribute. A named
attribute is an opaque byte stream that is associated with a
directory or file and referred to by a string name. Named attributes
are meant to be used by client applications as a method to associate
application-specific data with a regular file or directory. NFSv4.1
modifies named attributes relative to NFSv4.0 by tightening the
allowed operations in order to prevent the development of non-
interoperable implementation. See Section 5.3 for details.
1.6.3.3. 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 non-disruptive transfer of support for individual file systems
between servers. They are all based upon attributes that allow one
file system to specify alternate or new locations for that file
system.
These attributes may be used together with the concept of absent file
systems, which provide specifications for additional locations but no
actual file system content. This allows a number of important
facilities:
o Location 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.
o Location attributes may be provided for present file systems to
provide the locations of alternate file system instances or
replicas to be used in the event that the current file system
instance becomes unavailable.
o Location attributes may be provided when a previously present file
system becomes absent. This allows non-disruptive migration of
file systems to alternate servers.
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1.6.4. Locking Facilities
As mentioned previously, NFS v4.1 is a single protocol which 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:
o Share reservations as established by OPEN operations.
o Byte-range locks.
o 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.
o Directory delegations, which are recallable delegations that
assure the holder that inconsistent directory modifications cannot
occur so long as the delegation is held.
o 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 inconsistent with
that access may be made so long as the layout is held.
All 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 leases are not promptly renewed locks are
subject to revocation. In the event of server reboot, clients have
the opportunity to safely reclaim their locks within a special grace
period.
1.7. Differences from NFSv4.0
The following summarizes the differences between minor version one
and the base protocol:
o Implementation of the sessions model.
o Support for parallel access to data.
o Addition of the RECLAIM_COMPLETE operation to better structure the
lock reclamation process.
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o Support for delegations on directories and other file types in
addition to regular files.
o Operations to re-obtain a delegation.
o Support for client and server implementation id's.
2. Core Infrastructure
2.1. Introduction
NFSv4.1 relies on core infrastructure common to nearly every
operation. This core infrastructure is described in the remainder of
this section.
2.2. 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 [3] and [2].
2.2.1. RPC-based Security
Previous NFS versions have been thought of as having a host-based
authentication model, where the NFS server authenticates the NFS
client, and trust the client to authenticate all users. Actually,
NFS has always depended on RPC for authentication. The first form of
RPC authentication which required a host-based authentication
approach. NFSv4.1 also depends on RPC for basic security services,
and mandates RPC support for a user-based authentication model. The
user-based authentication model has user principals authenticated by
a server, and in turn the server authenticated by user principals.
RPC provides some basic security services which are used by NFSv4.1.
2.2.1.1. RPC Security Flavors
As described in section 7.2 "Authentication" of [3], RPC security is
encapsulated in the RPC header, via a security or authentication
flavor, and information specific to the specification of the security
flavor. Every RPC header conveys information used to identify and
authenticate a client and server. As discussed in Section 2.2.1.1.1,
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, MAY be implemented as well.
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2.2.1.1.1. RPCSEC_GSS and Security Services
RPCSEC_GSS ([4]) uses the functionality of GSS-API [7]. This allows
for the use of various security mechanisms by the RPC layer without
the additional implementation overhead of adding RPC security
flavors.
2.2.1.1.1.1. Identification, Authentication, Integrity, Privacy
Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate
users on clients to servers, and servers to users. It can also
perform integrity checking on the entire RPC message, including the
RPC header, and the arguments or results. Finally, privacy, usually
via encryption, is a service available with RPCSEC_GSS. Privacy is
performed on 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 [4] 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.
2.2.1.1.1.2. Security mechanisms for NFSv4.1
RPCSEC_GSS, via GSS-API, normalizes access to mechanisms that provide
security services. Therefore NFSv4.1 clients and servers MUST
support three security mechanisms: Kerberos V5, SPKM-3, and LIPKEY.
The use of RPCSEC_GSS requires selection of: mechanism, quality of
protection (QOP), and service (authentication, integrity, privacy).
For the mandated security mechanisms, NFSv4.1 specifies that a QOP of
zero (0) is used, leaving it up to the mechanism or the mechanism's
configuration to use an appropriate level of protection that QOP zero
maps to. Each mandated mechanism specifies minimum set of
cryptographic algorithms for implementing integrity and privacy.
NFSv4.1 clients and servers MUST be implemented on operating
environments that comply with the REQUIRED cryptographic algorithms
of each REQUIRED mechanism.
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2.2.1.1.1.2.1. Kerberos V5
The Kerberos V5 GSS-API mechanism as described in [5] MUST be
implemented with the RPCSEC_GSS services as specified in the
following table:
column descriptions:
1 == number of pseudo flavor
2 == name of pseudo flavor
3 == mechanism's OID
4 == RPCSEC_GSS service
5 == NFSv4.1 clients MUST support
6 == NFSv4.1 servers MUST support
1 2 3 4 5 6
------------------------------------------------------------------
390003 krb5 1.2.840.113554.1.2.2 rpc_gss_svc_none yes yes
390004 krb5i 1.2.840.113554.1.2.2 rpc_gss_svc_integrity yes yes
390005 krb5p 1.2.840.113554.1.2.2 rpc_gss_svc_privacy no yes
Note that the number and name of the pseudo flavor is presented here
as a mapping aid to the implementor. Because the NFSv4.1 protocol
includes a method to negotiate security and it understands the GSS-
API mechanism, the pseudo flavor is not needed. The pseudo flavor is
needed for the NFSv3 since the security negotiation is done via the
MOUNT protocol as described in [23].
2.2.1.1.1.2.2. LIPKEY
The LIPKEY V5 GSS-API mechanism as described in [6] MUST be
implemented with the RPCSEC_GSS services as specified in the
following table:
1 2 3 4 5 6
------------------------------------------------------------------
390006 lipkey 1.3.6.1.5.5.9 rpc_gss_svc_none yes yes
390007 lipkey-i 1.3.6.1.5.5.9 rpc_gss_svc_integrity yes yes
390008 lipkey-p 1.3.6.1.5.5.9 rpc_gss_svc_privacy no yes
2.2.1.1.1.2.3. SPKM-3 as a security triple
The SPKM-3 GSS-API mechanism as described in [6] MUST be implemented
with the RPCSEC_GSS services as specified in the following table:
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1 2 3 4 5 6
------------------------------------------------------------------
390009 spkm3 1.3.6.1.5.5.1.3 rpc_gss_svc_none yes yes
390010 spkm3i 1.3.6.1.5.5.1.3 rpc_gss_svc_integrity yes yes
390011 spkm3p 1.3.6.1.5.5.1.3 rpc_gss_svc_privacy no yes
2.2.1.1.1.3. 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, LIPKEY, and SPKM-3, the
following form is RECOMMENDED:
nfs/hostname
2.3. 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
operations. For example, multi-component lookup 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.
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NFSv4.1 also contains a considerable set of callback operations in
which the server makes an RPC directed at the client. Callback RPC's
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, 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 reply protection for non-idempotent
requests.
2.4. Client Identifiers and Client Owners
For each operation that obtains or depends on locking state, the
specific client must 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 2.10) 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
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 lock, share
reservation, layout state, and where the server is not supporting the
CLAIM_DELEGATE_PREV claim type, all delegation state associated with
the same client with the same identity. For discussion of delegation
state recovery, see Section 10.2.1. For discussion of layout state
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recovery see Section 12.7.1.
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 8.3)
and the new client will need to wait for such state to be removed, if
it makes conflicting lock requests.
Client identification is encapsulated in the following Client Owner
structure:
struct client_owner4 {
verifier4 co_verifier;
opaque co_ownerid<NFS4_OPAQUE_LIMIT>;
};
The first field, co_verifier, is a client incarnation verifier. 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 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:
o 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
canceled.
o 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 implementor 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.
o 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
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paths as described in Section 2.10.4. (Note: the precise opposite
was advised in the NFSv4.0 specification [21].)
o 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:
o If applicable, the client's statically assigned network address.
o 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 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).
* A true random number. However since this number ought to be
the same between client incarnations, this shares the same
problem as that of the using the timestamp of the software
installation.
o 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.
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In the event of a server restart, a client may find out that its
current client ID is no longer valid when it receives a
NFS4ERR_STALE_CLIENTID error. The precise circumstances depend on
the characteristics of the sessions involved, specifically whether
the session is persistent (see Section 2.10.5.5), 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 must 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 reboot. 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 must 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.
When NFS4ERR_STALE_CLIENTID is received in either of these
situations, the client must 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 8.4.2).
See the detailed descriptions of EXCHANGE_ID (Section 18.35 and
CREATE_SESSION (Section 18.36) for a complete specification of these
operations.
2.4.1. Upgrade from NFSv4.0 to NFSv4.1
To facilitate upgrade from NFSv4.0 to NFSv4.1, a server may compare a
client_owner4 in an EXCHANGE_ID with an nfs_client_id4 established
using SETCLIENTID using NFSv4.0, so that an NFSv4.1 client is not
forced to delay until lease expiration for locking state established
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by the earlier client using minor version 0. This requires the
client_owner4 be constructed the same way as the nfs_client_id4. If
the latter's contents included the server's network address, 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.
2.4.2. Server Release of Client ID
NFSv4.1 introduces a new operation called DESTROY_CLIENTID
(Section 18.50) which the client SHOULD use 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 (including sessions, opens, locks, delegations,
layouts, and wants), the server may choose to unilaterally release
the client ID. The server may make this choice for an inactive
client so that resources are not consumed by those intermittently
active clients. If the client contacts the server after this
release, the server must ensure the client receives the appropriate
error so that it will use the EXCHANGE_ID/CREATE_SESSION sequence to
establish a new identity. It should be clear that the server must 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. 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 2.10.10.1.4 for discussion on releasing
inactive sessions.
2.4.3. 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 are
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true:
o The principal that created the client ID for the client owner is
the same as the principal that is issuing the EXCHANGE_ID. Note
that if the client ID was created with SP4_MACH_CRED protection
(Section 18.35), 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.
o The client ID was established with SP4_SSV protection
(Section 18.35, Section 2.10.7.3) and the client sends the
EXCHANGE_ID with the security flavor set to RPCSEC_GSS using the
GSS SSV mechanism (Section 2.10.8).
o The client ID was established with SP4_SSV protection. Because
the SSV might not persist 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, it deletes state (once CREATE_SESSION
confirms the client ID) if the co_verifier in the EXCHANGE_ID differs
from the co_verifier used when the client ID was created. If the
co_verifier values are the same, then the client is either updating
properties of the client ID (Section 18.35), or possibly attempting
trunking (Section 2.10.4) and the server MUST NOT delete state.
2.5. Server Owners
The Server Owner is similar to a Client Owner (Section 2.4), but
unlike the Client Owner, there is no shorthand serverid. The Server
Owner is defined in the following structure:
struct server_owner4 {
uint64_t so_minor_id;
opaque so_major_id<NFS4_OPAQUE_LIMIT>;
};
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The Server Owner is returned from EXCHANGE_ID. When the so_major_id
fields are the same in two EXCHANGE_ID results, the connections each
EXCHANGE_ID are sent over can be assumed to address the same Server
(as defined in Section 1.5). If the so_minor_id fields are also the
same, then not only do both connections connect to the same server,
but the session and other state 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 Section 2.10.4 and
Section 18.35.
The considerations for generating a so_major_id are similar to that
for generating a co_ownerid string (see Section 2.4). 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 2.10.4).
2.6. Security Service Negotiation
With the NFSv4.1 server potentially offering multiple security
mechanisms, the client needs a method to determine or negotiate which
mechanism is to be used for its communication with the server. The
NFS server may have multiple points within its file system namespace
that are available for use by NFS clients. These points can be
considered security policy boundaries, and in some NFS
implementations are tied to NFS export points. In turn the NFS
server may be configured such that each of these security policy
boundaries may have different or multiple security mechanisms in use.
The security negotiation between client and server must be done with
a secure channel to eliminate the possibility of a third party
intercepting the negotiation sequence and forcing the client and
server to choose a lower level of security than required or desired.
See Section 21 for further discussion.
2.6.1. NFSv4.1 Security Tuples
An NFS server can assign one or more "security tuples" to each
security policy boundary in its namespace. Each security tuple
consists of a security flavor (see Section 2.2.1.1), and if the
flavor is RPCSEC_GSS, a GSS-API mechanism OID, a GSS-API quality of
protection, and an RPCSEC_GSS service.
2.6.2. SECINFO and SECINFO_NO_NAME
The SECINFO and SECINFO_NO_NAME operations allow the client to
determine, on a per filehandle basis, what security tuple is to be
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used for server access. In general, the client will not have to use
either operation except during initial communication with the server
or when the client crosses security policy boundaries at the server.
However, the server's policies may also change at any time and force
the client to negotiate a new security tuple.
Where the use of different security tuples would affect the type of
access that would be allowed if a request was sent over the same
connection used for the SECINFO or SECINFO_NO_NAME operation (e.g.
read-only vs. read-write) access, security tuples that allow greater
access should be presented first. Where the general level of access
is the same and different security flavors limit the range of
principals whose privileges are recognized (e.g. allowing or
disallowing root access), flavors supporting the greatest range of
principals should be listed first.
2.6.3. Security Error
Based on the assumption that each NFSv4.1 client and server must
support a minimum set of security (i.e., LIPKEY, SPKM-3, and
Kerberos-V5 all under RPCSEC_GSS), the NFS client will initiate file
access to the server with one of the minimal security tuples. During
communication with the server, the client may receive an NFS error of
NFS4ERR_WRONGSEC. This error allows the server to notify the client
that the security tuple currently being used contravenes the server's
security policy. The client is then responsible for determining (see
Section 2.6.3.1) what security tuples are available at the server and
choosing one which is appropriate for the client.
2.6.3.1. Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME
This section explains of the mechanics of NFSv4.1 security
negotiation. The term "put filehandle operation" refers to
PUTROOTFH, PUTPUBFH, PUTFH, and RESTOREFH.
2.6.3.1.1. Put Filehandle Operation + SAVEFH
The client is saving a filehandle for a future RESTOREFH. The server
MUST NOT return NFS4ERR_WRONGSEC to either the put filehandle
operation or SAVEFH.
2.6.3.1.2. 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 series of operations, and the second in the series of operations is
not a put filehandle operation. For example if the server received
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PUTFH, PUTROOTFH, LOOKUP, then the PUTFH is ignored for
NFS4ERR_WRONGSEC purposes, and the PUTROOTFH, LOOKUP subseries is
processed as according to Section 2.6.3.1.3.
2.6.3.1.3. Put Filehandle Operation + LOOKUP (or OPEN by Name)
This situation also applies to a put filehandle operation followed by
a LOOKUP or an OPEN operation that specifies a component name.
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 that of its
parent directory.
b) sec_policy_child ^ sec_policy_parent != {} (^ for intersection,
{} for the empty set). This means that the 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 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.
For a server to support approach (b) (when client chooses a flavor
that is not a member of sec_policy_parent) and (c), the put
filehandle operation must NOT return NFS4ERR_WRONGSEC when there is a
security tuple mismatch. Instead, it should be returned from the
LOOKUP (or OPEN by 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.
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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.
2.6.3.1.4. 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 2.6.3.1.3, 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.
2.6.3.1.5. 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 the
either 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 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.
2.6.3.1.6. Put Filehandle Operation + Nothing
The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC.
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2.6.3.1.7. Put Filehandle Operation + Anything Else
"Anything Else" includes OPEN by filehandle.
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 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).
2.6.3.1.8. Operations after SECINFO and SECINFO_NO_NAME
Placing an operation that uses the current filehandle after SECINFO
or SECINFO_NO_NAME seemingly introduces a issue with what error to
return when security tuple of the request is not allowed for the
operation that uses the current filehandle. For example, suppose a
client sends a COMPOUND procedure containing the series SEQUENCE,
PUTFH, SECINFO_NONAME, READ, and suppose the security tuple used does
not match that required for the target file. By rule (see
Section 2.6.3.1.5), neither PUTFH nor SECINFO_NO_NAME can return
NFS4ERR_WRONGSEC. By rule (see Section 2.6.3.1.7), READ cannot
return NFS4ERR_WRONGSEC. The issue is resolved by the fact that
SECINFO and SECINFO_NO_NAME consume the current filehandle. This
leaves no current filehandle for READ to use, and READ returns
NFS4ERR_NOFILEHANDLE.
2.7. Minor Versioning
To address the requirement of an NFS protocol that can evolve as the
need arises, the NFSv4.1 protocol contains the rules and framework to
allow for future minor changes or versioning.
The base assumption with respect to minor versioning is that any
future accepted minor version must follow the IETF process and be
documented in a standards track RFC. Therefore, each minor version
number will correspond to an RFC. Minor version zero of the NFSv4
protocol is represented by [21], and minor version one is represented
by this document [[Comment.1: RFC Editor: change "document" to "RFC"
when we publish]]. The COMPOUND and CB_COMPOUND procedures support
the encoding of the minor version being requested by the client.
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The following items represent the basic rules for the development of
minor versions. Note that a future minor version may decide to
modify or add to the following rules as part of the minor version
definition.
1. Procedures are not added or deleted
To maintain the general RPC model, NFSv4 minor versions will not
add to or delete procedures from the NFS program.
2. Minor versions may add operations to the COMPOUND and
CB_COMPOUND procedures.
The addition of operations to the COMPOUND and CB_COMPOUND
procedures does not affect the RPC model.
* Minor versions may append attributes to the bitmap4 that
represents sets of attributes and the fattr4 that represents
sets of attribute values.
This allows for the expansion of the attribute model to allow
for future growth or adaptation.
* Minor version X must append any new attributes after the last
documented attribute.
Since attribute results are specified as an opaque array of
per-attribute XDR encoded results, the complexity of adding
new attributes in the midst of the current definitions would
be too burdensome.
3. Minor versions must not modify the structure of an existing
operation's arguments or results.
Again the complexity of handling multiple structure definitions
for a single operation is too burdensome. New operations should
be added instead of modifying existing structures for a minor
version.
This rule does not preclude the following adaptations in a minor
version.
* adding bits to flag fields such as new attributes to
GETATTR's bitmap4 data type and providing corresponding
variants of opaque arrays, such as a notify4 used together
with such bitmaps.
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* adding bits to existing attributes like ACLs that have flag
words
* extending enumerated types (including NFS4ERR_*) with new
values and
4. Minor versions may not modify the structure of existing
attributes.
5. Minor versions may not delete operations.
This prevents the potential reuse of a particular operation
"slot" in a future minor version.
6. Minor versions may not delete attributes.
7. Minor versions may not delete flag bits or enumeration values.
8. Minor versions may declare an operation MUST NOT be implemented.
Specifying an operation MUST NOT be implemented is equivalent to
obsoleting an operation. For the client, it means that the
operation should not be sent to the server. For the server, an
NFS error can be returned as opposed to "dropping" the request
as an XDR decode error. This approach allows for the
obsolescence of an operation while maintaining its structure so
that a future minor version can reintroduce the operation.
1. Minor versions may declare an attribute MUST NOT be
implemented.
2. Minor versions may declare a flag bit or enumeration value
MUST NOT be implemented.
9. Minor versions may downgrade features from REQUIRED to
RECOMMENDED, or RECOMMENDED to OPTIONAL.
10. Minor versions may upgrade features from OPTIONAL to RECOMMENDED
or RECOMMENDED to REQUIRED.
11. A client and server that supports minor version X should support
minor versions 0 (zero) through X-1 as well.
12. Except for infrastructural changes, no new features may be
introduced as REQUIRED in a minor version.
This rule allows for the introduction of new functionality and
forces the use of implementation experience before designating a
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feature as REQUIRED. On the other hand, some classes of
features are infrastructural and have broad effects. Allowing
such features to not be REQUIRED complicates implementation of
the minor version.
13. A client MUST NOT attempt to use a stateid, filehandle, or
similar returned object from the COMPOUND procedure with minor
version X for another COMPOUND procedure with minor version Y,
where X != Y.
2.8. Non-RPC-based Security Services
As described in Section 2.2.1.1.1.1, NFSv4.1 relies on RPC for
identification, authentication, integrity, and privacy. NFSv4.1
itself provides additional security services as described in the next
several subsections.
2.8.1. Authorization
Authorization to access a file object via an NFSv4.1 operation is
ultimately determined by the NFSv4.1 server. A client can
predetermine its access to a file object via the OPEN (Section 18.16)
and the ACCESS (Section 18.1) operations.
Principals with appropriate access rights can modify the
authorization on a file object via the SETATTR (Section 18.30)
operation. Attributes that affect access rights include: mode,
owner, owner_group, acl, dacl, and sacl. See Section 5.
2.8.2. Auditing
NFSv4.1 provides auditing on a per file object basis, via the acl and
sacl attributes as described in Section 6. It is outside the scope
of this specification to specify audit log formats or management
policies.
2.8.3. Intrusion Detection
NFSv4.1 provides alarm control on a per file object basis, via the
acl and sacl attributes as described in Section 6. Alarms may serve
as the basis for intrusion detection. It is outside the scope of
this specification to specify heuristics for detecting intrusion via
alarms.
2.9. Transport Layers
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2.9.1. REQUIRED and RECOMMENDED Properties of Transports
NFSv4.1 works over RDMA and non-RDMA_based transports with the
following attributes:
o The transport supports reliable delivery of data, which NFSv4.1
requires but neither NFSv4.1 nor RPC has facilities for ensuring.
[24]
o 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 [3].
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. At the
time this document was written, the only two transports that had the
above attributes were TCP and SCTP. To enhance the possibilities for
interoperability, an NFSv4.1 implementation MUST support operation
over the TCP transport protocol.
Even if NFSv4.1 is used over a non-IP network protocol, it is
RECOMMENDED that the transport support congestion control.
It is permissible for a connectionless transport to be used under
NFSv4.1, however reliable and in-order delivery of data by the
connectionless transport is still required. 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.
2.9.2. Client and Server Transport Behavior
If a connection-oriented transport (e.g. TCP) is used the client and
server SHOULD use long lived connections for at least three reasons:
1. This will prevent the weakening of the transport's congestion
control mechanisms via short lived connections.
2. This will improve performance for the WAN environment by
eliminating the need for connection setup handshakes.
3. The NFSv4.1 callback model differs from NFSv4.0, and requires the
client and server to maintain a client-created backchannel (see
Section 2.10.3.1) for the server to use.
In order to reduce congestion, if a connection-oriented transport is
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used, and the request is not the NULL procedure,
o A requester MUST NOT retry a request unless the connection the
request was sent over was lost before the reply was received.
o 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 2.10.5.1) or it
MAY disconnect the connection.
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) that the
requester sent the request from. If using a connection-oriented
transport, replies MUST be sent on the same connection the request
was received from.
If a connection is dropped after the replier receives the request but
before the replier sends the reply, the replier might have an 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 client retries the request.
The reason for this prohibition is that the client MAY retry a
request over a different connection than is associated with the
session.
When using RDMA transports there are other reasons for not tolerating
retries over the same connection:
o 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.
o 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,
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and credit information appropriate to the channel must be
refreshed by the RPC layer.
In addition, the NFSv4.1 requester is not allowed to stop waiting for
a reply, as described in Section 2.10.5.2.
2.9.3. Ports
Historically, NFSv3 servers have listened over TCP port 2049. The
registered port 2049 [25] for the NFS protocol should be the default
configuration. NFSv4.1 clients SHOULD NOT use the RPC binding
protocols as described in [26].
2.10. Session
2.10.1. Motivation and Overview
Previous versions and minor versions of NFS have suffered from the
following:
o Lack of support for exactly once semantics (EOS). This includes
lack of support for EOS through server failure and recovery.
o Limited callback support, including no support for sending
callbacks through firewalls, and races between responses from
normal requests, and callbacks.
o Limited trunking over multiple network paths.
o Requiring machine credentials for fully secure operation.
Through the introduction of a session, NFSv4.1 addresses the above
shortfalls with practical solutions:
o 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 that previous
revisions of NFS did not support EOS was because some EOS
approaches often limited parallelism. As will be explained in
Section 2.10.5, NFSv4.1 supports both EOS and unlimited
parallelism.
o The NFSv4.1 client (defined in Section 1.5, Paragraph 2) creates
transport connections and provides them to the server to use for
sending callback requests, thus solving the firewall issue
(Section 18.34). Races between responses from client requests,
and callbacks caused by the requests are detected via the
session's sequencing properties which are a consequence of EOS
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(Section 2.10.5.3).
o The NFSv4.1 client can add an arbitrary number of connections to
the session, and thus provide trunking (Section 2.10.4).
o The NFSv4.1 client and server produces 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 2.10.7.3).
o 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 2.10.7.2).
A session is a dynamically created, long-lived server object created
by a client, 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 the connection exists or not. 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.
2.10.2. 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 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. 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 18.37).
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2.10.2.1. 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 2.10.5). Session-enabled NFSv4.1
COMPOUND requests thus have the form:
+-----+--------------+-----------+------------+-----------+----
| tag | minorversion | numops |SEQUENCE op | op + args | ...
| | (== 1) | (limited) | + args | |
+-----+--------------+-----------+------------+-----------+----
and the reply's structure is:
+------------+-----+--------+-------------------------------+--//
|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 2.10.5.3).
2.10.2.2. Client ID and Session Association
Each client ID (Section 2.4) 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.
State such as share reservations, locks, delegations, and layouts
(Section 1.6.4) 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 from the session that originally
acquired the state pertaining to the callback. For example, if
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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. Section 2.10.7.1 and Section 2.10.7.2
discuss the security considerations around callbacks.
2.10.3. Channels
A channel is not a connection. A channel represents the direction
ONC RPC requests are sent.
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 used for callback requests from server to client, and
carries CB_COMPOUND requests and responses. Whether there is a
backchannel or not is a decision 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 2.10.5.1). Note that even the backchannel
requires a reply cache because some callback operations are
nonidempotent.
2.10.3.1. Association of Connections, Channels, and Sessions
Each channel is associated with zero or more transport connections.
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 18.36) and the BIND_CONN_TO_SESSION (Section 18.34)
operations. When a session is created via CREATE_SESSION, the
connection that transported the CREATE_SESSION request is
automatically associated with the fore channel, and optionally the
backchannel. If the client specifies no state protection
(Section 18.35) 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
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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 a TCP and RDMA
connection can be associated with the fore channel. 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 credits (Section 2.10.5.1. 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.
2.10.4. 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. NFSv4.1 servers MUST support trunking.
Session trunking is essentially the association of multiple
connections, each with a potentially different target network
address, to the same session.
Client ID trunking is the association of multiple sessions to the
same client ID, major server owner ID (Section 2.5), and server scope
(Section 11.7.7). When two servers return the same major server
owner and server scope it means the two servers are cooperating on
locking state management which is a prerequisite for client ID
trunking.
Understanding and distinguishing session and client ID trunking
requires understanding how the results of the EXCHANGE_ID
(Section 18.35) operation identify a server. Suppose a client sends
EXCHANGE_ID over two different connections each with a possibly
different target network address but each EXCHANGE_ID with 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
Paragraph 5 later in this section), and it can use each connection to
trunk requests and replies. The question is whether session trunking
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and/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,
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. Or if the client does
not want to use session trunking, it can invoke CREATE_SESSION on
the connection.
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, but the eir_server_owner.so_minor_id
results do not match then the client is permitted to perform
client ID trunking. The client can associate each connection with
different sessions, where each session is associated with the same
server. Of course, even if the eir_server_owner.so_minor_id
fields do match, the client is free to employ client ID trunking
instead of sessiond trunking. 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 each session.
When doing client ID trunking, locking state is shared across
sessions associated with the same client ID. This requires the
server to coordinate state across sessions.
When two servers over two connections 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:
o 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
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a client ID is created, the client SHOULD specify that
BIND_CONN_TO_SESSION is to be verified according to the SP4_SSV or
SP4_MACH_CRED (Section 18.35) state protection options. For
SP4_SSV, reliable verification depends on a shared secret (the
SSV) that is established via the SET_SSV (Section 18.47)
operation.
When a new connection is associated with the session (via the
BIND_CONN_TO_SESSION operation, see Section 18.34), 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 a
RPCSEC_GSS using the GSS SSV mechanism (Section 2.10.8). The
RPCSEC_GSS handle is created by CREATE_SESSION (Section 18.36).
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.
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.
o 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 issuing each
EXCHANGE_ID. 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 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
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address than the first EXCHANGE_ID was sent with. 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 issuing a CREATE_SESSION 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 the same for the purposes of client ID trunking.
2.10.5. Exactly Once Semantics
Via the session, NFSv4.1 offers exactly once semantics (EOS) for
requests sent over a channel. EOS is supported on both the fore and
back channels.
Each COMPOUND or CB_COMPOUND request that is sent with a leading
SEQUENCE or CB_SEQUENCE operation MUST be executed by the receiver
exactly once. This requirement holds regardless of whether the
request is sent with reply caching specified (see
Section 2.10.5.1.2). The requirement holds even if the requester is
issuing the request over a session created between a pNFS data client
and pNFS data server. To understand the rationale for this
requirement, divide the requests into three classifications:
o Nonidempotent requests.
o Idempotent modifying requests.
o Idempotent non-modifying requests.
An example of a non-idempotent request is RENAME. If is obvious that
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.
Therefore, EOS is required for nonidempotent requests.
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 once. Nevertheless,
enforcing EOS for WRITEs and other idempotent modifying requests is
necessary to avoid data corruption.
Suppose a client sends WRITEs A and B 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
both WRITEs. Now, the server has outstanding two instances of each
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of A and B. The server can be in a situation in which it executes and
replies to the retries of A and B, while the first A and B are still
waiting in the server's I/O system for some resource. Upon receiving
the replies to the second attempts of WRITEs A and B, the client
believes its writes are done so it is free to send WRITE D which
overlaps the range of one or both of A and B. If A or B are
subsequently executed for the second time, then what has been written
by D 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 a such a request will not cause data corruption, or
produce an incorrect result. Nonetheless, to keep the implementation
simple, the replier MUST enforce EOS for all requests whether
idempotent and non-modifying or not.
Note that true and complete EOS is not possible unless the server
persists the reply cache in stable storage, 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 2.10.5.5 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 over previous versions of NFS
because the legacy duplicate request/reply caches were based on the
ONC RPC transaction identifier (XID). Section 2.10.5.1 explains the
shortcomings of the XID as a basis for a reply cache and describes
how NFSv4.1 sessions improve upon the XID.
2.10.5.1. 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 lookup (often via a hash that includes XID and source
address). NFSv4.1 requests use a non-opaque slot id which is 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; 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 use a least recently used (LRU)
approach to replacing cache entries with new entries when the cache
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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 18.36), 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 which the
requester has already 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 (1) (Section 18.36). 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 server: 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 client to
assert that it is retransmitting to implement this, because for any
given request the client cannot know whether the server has seen it
unless the server actually replies. Of course, if the client has
seen the server's reply, the client 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:
o 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.
o 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 2.10.5.2 for direction on how the replier deals with
retries of requests that are stll in progress.
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o 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).
o A misordered new request, in which the sequence id is two or more
than (accounting for sequence wraparound) than that previously
seen in the slot. Note that because the sequence id must
wraparound to zero (0) 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 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.
The slot id and sequence id therefore 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 must be formulated in NFSv4.1 requests as
it any other ONC RPC request. The reasons include:
o The RPC layer retains its existing semantics and implementation.
o 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
o 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.
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o The SEQUENCE or CB_SEQUENCE operation may generate an error. If
so, the embedded slot id, sequence id, and sessionid (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.
Givem that well formulated XIDs continue to be required, this begs
the question why SEQUENCE and CB_SEQUENCE replies have a sessionid,
slot id and sequence id? Having the sessionid in the reply means the
requester does not have to use the XID to lookup the sessionid, which
would be necessary if the connection were associated with multiple
sessions. Having the slot id and sequence id in the reply means
requester does not have to use the XID to lookup the slot id and
sequence id. Furhermore, since the XID is only 32 bits, it is too
small to guarantee the re-association of a reply with its request
([27]); having sessionid, 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 provide a 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:
o 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.
However, because of request pipelining, the requester may have
active requests in flight reflecting prior values, therefore the
replier must not immediately require the requester to comply.
o 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
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SHOULD be no less than the highest_slotid the requester indicated
in the SEQUENCE or CB_SEQUENCE arguments.
If a replier detects the client is being intransigent, i.e. it
fails in a series of requests to honor the target highest_slotid
even though the replier knows there are no outstanding requests a
higher slot ids, it MAY take more forceful action. When faced
with intransigence, the replier 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_HIGHSLOT, unless the slot id in the request is greater
than the new enforced highest_slotid, and the request is a retry.
The replier SHOULD keep slots it wants to retire around until the
requester sends a request with a highest_slotid less than or equal
to the replier's new enforced highest_slotid. Also a request with
a slot that is higher than the new enforced highest_slotid can be
retired if the requester specifies a sequence id that is not equal
what is in the slot's reply cache. In other words, once the
replier has forcibly lowered the enforced highest_slotid, the
requester is only allowed to send retries to the to-be-retired
slots.
o The requester SHOULD use the lowest available slot when issuing 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 not be able 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 requester as seen such a reply when it
receives a new request with the same slotid as the request replied
to and the next higher sequenceid.
2.10.5.1.1. Errors from SEQUENCE and CB_SEQUENCE
Any time SEQUENCE or CB_SEQUENCE return 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
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or CB_SEQUENCE.
2.10.5.1.2. 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
would not direct the replier to cache the entire reply is that the
request is composed of all idempotent operations [24]. Caching the
reply may offer little benefit. If the reply is too large (see
Section 2.10.5.4), it may not be cacheable anyway. Even if the reply
to idempotent request is small enough to cache, unnecessarily caching
the reply slows down the server and increases RPC latency.
Whether the requester requests the reply to be cached or not has no
effect on the slot processing. If the results of SEQUENCE or
CB_SEQUENCE are 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:
o The replier can cache the entire original reply. Even though
sa_cachethis or csa_cachethis are FALSE, the replier is always
free to cache. It may choose this approach in order to simplify
implementation.
o 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.
2.10.5.2. Retry and Replay of Reply
A requester MUST NOT 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.
If the requester is a server wanting to re-send a callback operation
over the backchannel of 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 MUST 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 MUST then associate a connection with the session (or
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destroy the session).
Note that it is not fatal for a client 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.
A client 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 client
does not know what sequence id to use for the slot on its next
request. For example, suppose a client 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 server has
not seen the request with sequence id 1, then the server is not
expecting sequence id 2, and rejects the client's new request with
NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or CB_SEQUENCE).
RDMA fabrics do not guarantee that the memory handles (Steering Tags)
within each RPC/RDMA "chunk" ([8]) 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 which 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. The replier SHOULD deal with the issue by 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
the requester specified the reply to be cached).
2.10.5.3. Resolving Server Callback Races
It is possible for server callbacks to arrive at the client before
the reply from related fore 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
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The presence of a session between client and server alleviates this
issue. When a session is in place, each client request is uniquely
identified by its { sessionid, 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 which might result in some sort of server
callback, the server SHOULD "remember" the { sessionid, 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 { sessionid,
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.
The CB_SEQUENCE operation which begins each server callback carries a
list of "referring" { sessionid, slot id, sequence id } triples. If
the client finds the request corresponding to the referring
sessionid, 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 the referring triple
to be outstanding (including the case of a sessionid 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 pNFS layout recalls, described in Section 12.5.5.2.
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2.10.5.4. 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 18.36), 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).
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 first operation (SEQUENCE or CB_SEQUENCE) in the
request (which means no operations in the request executed, and the
state of the slot in the reply cache is unchanged), or it MAY chose
to return it on a subsequent operation in the same COMPOUND or
CB_COMPOUND request (which means at least one operation did execute
and the state of the slot in reply cache does change). The replier
SHOULD set NFS4ERR_REQ_TOO_BIG on the operation that exceeds
ca_maxrequestsize.
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 first operation (SEQUENCE or CB_SEQUENCE) in the request,
or it MAY chose 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 are TRUE, then the replier MUST
cache a reply except if an error is returned by the SEQUENCE or
CB_SEQUENCE operation (see Section 2.10.5.1.1). If the reply exceeds
ca_maxresponsesize_cached, (and sa_cachethis or csa_cachethis are
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 a operation other than first operation (SEQUENCE or
CB_SEQUENCE), then the reply MUST be cached if sa_cachethis or
csa_cachethis are 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 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.
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A client needs to take care that when sending operations that change
the current filehandle (except for PUTFH, PUTPUBFH, PUTROOTFH and
RESTOREFH) that it 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 18.16),
retry is not always available as an option. The following guidelines
for the handling of filehandle changing operations are advised:
o 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 (for example, 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.
o 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.
o 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.
o 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.
2.10.5.5. Persistence
Since the reply cache is bounded, it is practical for the reply cache
to persist across server restarts. The replier MUST persist the
following information if it agreed to persist the session (when the
session was created; see Section 18.36):
o The sessionid.
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o The slot table including the sequence id and cached reply for each
slot.
The above are sufficient for a replier to provide EOS semantics for
any requests that were sent and executed before the server restarted.
If the replier is a client then there is no need for it to persist
any more information, unless the client will be persisting all other
state across client restart. In which case, the server will never
see any NFSv4.1-level protocol manifestation of a client restart. If
the replier is a server, with just the slot table and sessionid
persisting, any requests the client retries after the server restart
will return the results that are cached in reply cache. and any new
requests (i.e. the sequence id is one (1) greater than the slot's
sequence id) MUST be rejected with NFS4ERR_DEADSESSION (returned by
SEQUENCE). Such a session is considered: dead. A server MAY re-
animate a session after a server restart so that the session will
accept new requests as well as retries. To re-animate a session the
server needs to persist additional information through server
restart:
o The client ID. This is a prerequisite to let the client to create
more sessions associated with the same client ID as the
o The client ID's sequenceid that is used for creating sessions (see
Section 18.35 and Section 18.36. This is a prerequisite to let
the client create more sessions.
o The principal that created the client ID. This allows the server
to authenticate the client when it sends EXCHANGE_ID.
o The SSV, if SP4_SSV state protection was specified when the client
ID was created (see Section 18.35). This lets the client create
new sessions, and associate connections with the new and existing
sessions.
o The properties of the client ID as defined in Section 18.35.
A persistent reply cache places certain demands on the server. The
execution of the sequence of operations (starting with SEQUENCE) and
placement of its results in the persistent cache MUST be atomic. If
a client retries an sequence of operations that was previously
executed on the server the only acceptable outcomes are either the
original cached reply or an indication that 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).
A server could fail and restart in the middle of a COMPOUND procedure
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that contains one or more non-idempotent or idempotent-but-modifying
operations. This creates an even higher challenge for atomic
execution and placement of results in the reply cache. One way to
view the problem is as a single transaction consisting of each
operation in the COMPOUND followed by storing the result in
persistent storage, then finally a transaction commit. If there is a
failure before the transaction is committed, then the server rolls
back the transaction. If server itself fails, then when it restarts,
its recovery logic could roll back the transaction before starting
the NFSv4.1 server.
While the description of the implementation for atomic execution of
the request and caching of the reply is beyond the scope of this
document, an example implementation for NFSv2 [28] is described in
[29].
2.10.6. RDMA Considerations
A complete discussion of the operation of RPC-based protocols over
RDMA transports is in [8]. A discussion of the operation of NFSv4,
including NFSv4.1, over RDMA is in [9]. 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.
2.10.6.1. 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 which would cause a
fatal error on the RDMA connection.
NFSv4.1 manages slots as resources on a per session basis (see
Section 2.10), 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
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a session, then if the total number of credits across all RDMA
connections associated with the session is X, and the number slots in
the session is Y, then the maximum number of outstanding requests is
lesser of X and Y.
2.10.6.2. 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 18.36). These limits then provide
the maxima which each connection associated with the session's
channel(s) must remain within. RDMA connections are managed within
these limits as described in section 3.3 ("Flow Control"[[Comment.2:
RFC Editor: please verify section and title of the RPCRDMA
document]]) of [8]; 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 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 20.8)
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.
2.10.6.3. Padding
Header padding is requested by each peer at session initiation (see
the ca_headerpadsize argument to CREATE_SESSION in Section 18.36),
and subsequently used by the RPC RDMA layer, as described in [8].
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
the negotiated size) so that the "data" field of the NFSv4.1 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
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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 not to overburden the server, and vice- versa.
The payoff of an appropriate padding value is higher performance.
[[Comment.3: RFC editor please keep this diagram on one page.]]
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 which 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.
2.10.6.4. Dual RDMA and Non-RDMA Transports
Some RDMA transports (for example [10]), 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 Section 18.36
and Section 18.34).
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2.10.7. Sessions Security
2.10.7.1. 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 18.34), and subject to the same
firewall and routing checks as the fore channel. The connection
cannot be hijacked by an attacker who connects to the client port
prior to the intended server as is possible with NFSv4.0. At the
client's option (see Section 18.35), connection association is fully
authenticated before being activated (see Section 18.34). Traffic
from the server over the backchannel is authenticated exactly as the
client specifies (see Section 2.10.7.2).
2.10.7.2. 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 unoffered combinations. This way,
the client need not provide a target GSS principal for the
backchannel as it did with NFSv4.0, nor the server have to implement
an RPCSEC_GSS initiator as it did with NFSv4.0 [21].
The CREATE_SESSION (Section 18.36) and BACKCHANNEL_CTL
(Section 18.33) operations allow the client to specify flavor/
principal combinations.
Also note that the SP4_SSV state protection mode (see Section 18.35
and Section 2.10.7.3) has the side benefit of providing SSV-derived
RPCSEC_GSS contexts (Section 2.10.8).
2.10.7.3. 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 sessionid 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.
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Setting a security policy on the file which 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 18.35).
The first (SP4_NONE) is to simply waive state protection.
The other two options (SP4_MACH_CRED and SP4_SSV) share several
traits:
o 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.
o 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.
o 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 (for example
LOCKU, CLOSE, etc.). The server may require that the principal
that removes the state match certain criteria (for example, 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 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 safe guarding the per-machine credential.
Assuming a proper safe guard, using the per-machine credential for
operations like CREATE_SESSION, BIND_CONN_TO_SESSION,
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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. That the system administrator configures a unique, permanent per-
machine credential for one of the mandated GSS mechanisms (for
example, if Kerberos V5 is used, a "keytab" for principal named
after 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 must be allocated at least one session each, so
the approach suffers from lack of economy.
The SP4_SSV protection option uses a Secret State Verifier (SSV)
which is shared between a client and server. The SSV serves as the
secret key for an internal (that is, internal to NFSv4.1) GSS
mechanism that uses the secret key for Message Integrity Code (MIC)
and Wrap tokens (Section 2.10.8). The SP4_SSV protection option is
intended for the client that has multiple users, and the system
administrator does not wish to configure a permanent machine
credential for each client. The SSV is established on the server via
SET_SSV (see Section 18.47). To prevent eavesdropping, a client
SHOULD send SET_SSV via RPCSEC_GSS with the privacy service. 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:
o The arguments to and results of SET_SSV include digests of the old
and new SSV, respectively.
o 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 2.10.8). A client SHOULD send SET_SSV as soon as
a session is created.
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o A SET_SSV 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:
o Suppose Eve is the first user to log into a legitimate client.
Eve's use of an NFSv4.1 file system will cause an SSV to be
created via the legitimate client's NFSv4.1 implementation. The
SET_SSV 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 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
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 following sub-scenarios:
* Let us suppose that from the rogue connection, Eve sent a
SET_SSV with the same slot id and sequence that the legitimate
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client later uses. The server will assume this 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 on the server fails, and it is again apparent to
the client 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.
o 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 by issuing a SET_SSV. The client receives
an error that indicates the session does not exist. When the
client tries to create a new session, this will fail because the
SSV it has does not that the server has, and now the client knows
the session was hijacked. The legitimate client establishes a new
client ID as before.
o 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.
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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 is RECOMMENDED.
If the goal of a counter threat strategy is to prevent a connection
hijacker from making unauthorized state changes, then the
SP4_MACH_CRED protection approach can be used with a client ID per
user (i.e. the aforementioned third scenario for machine credential
state protection). For each unique user, the client invokes
EXCHANGE_ID with the user's credential, specifying SP4_MACH_CRED
protections, and specifying that all operations MUST be protected
with the machine credential. The server will then reject any
subsequent operations on the client ID or its sessions that do not
use RPCSEC_GSS with privacy or integrity and do not use the same
credential that created the client ID.
2.10.8. The SSV GSS Mechanism
The SSV provides the secret key for a mechanism 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 (emitted by GSS_Wrap).
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 mechanisms 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 2.6).
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 four subkeys are calculated by from each of
the valid ssv_subkey4 enumerated values. The calculation uses the
HMAC ([11]), 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 of type ssv_subkey4.
/* 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
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};
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-
MIST2I 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 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 smt_orig_plain is
the input text as passed into GSS_GetMIC().
The PerMsgToken description is based on an XDR definition:
/* 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 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 1 after SET_SSV (Section 18.47) is called
the first time on a client ID. Thereafter, it 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 18.35, 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.
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The SealedMessage description is based on an XDR definition:
/* 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 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 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 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.
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The sspt_ssv_seq field is the same as ssvt_ssv_seq.
The sspt_orig_plain field is the original plaintext as passed to
GSS_Wrap().
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 whether the caller
of GSS_Wrap() requests confidentiality or not, 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.
Effectively there is a single GSS context for a single client ID.
All RPCSEC_GSS handles 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 send periodic SET_SSV operations, 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.
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
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MUST fail.
The SSV mechanism does not support replay detection and sequencing in
its tokens because RPCSEC_GSS does not use those features (See
Section 5.2.2 "Context Creation Requests" in [4]).
2.10.9. Session Mechanics - Steady State
2.10.9.1. 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 2.10.10.2.
2.10.9.2. Obligations of the Client
The client SHOULD honor the following obligations in order to utilize
the session:
o 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.
o Destroy the session when not needed. If a client has multiple
sessions and one of them has no requests waiting for replies, and
has been idle for some period of time, it SHOULD destroy the
session.
o Maintain GSS contexts 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 contexts handed to the server via
BACKCHANNEL_CTL are unexpired.
o 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 the client
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.
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2.10.9.3. 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 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 the server will persist the session reply cache through a
server restarted or not, 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 must 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
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 must 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 must 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.
2.10.10. Session Mechanics - Recovery
2.10.10.1. Events Requiring Client Action
The following events require client action to recover.
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2.10.10.1.1. RPCSEC_GSS Context Loss by Callback Path
If all RPCSEC_GSS contexts granted by the client to the server for
callback use have expired, the client MUST establish a new context
via BACKCHANNEL_CTL. The sr_status_flags field of the SEQUENCE
results indicates when callback contexts are nearly expired, or fully
expired (see Section 18.46.3).
2.10.10.1.2. Connection Loss
If the client loses the last connection of the session, and if wants
to retain the session, then it must 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_CONNN_TO_SESSION
to associate the connection with the session.
If there was a request outstanding at the time the of connection
loss, then if client wants to continue to use the session it MUST
retry the request, as described in Section 2.10.5.2. 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 sessionid, 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
not put recallable state subject to revocation, the client must
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.
2.10.10.1.3. 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 the retain the backchannel and/or not put recallable
state subjection to revocation, the client must use BACKCHANNEL_CTL
to assign new contexts.
2.10.10.1.4. Loss of Session
The replier might lose a record of the session. Causes include:
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o Replier failure and restart
o A catastrophe that causes the reply cache to be corrupted or lost
on the media it was stored on. This applies even if the replier
indicated in the CREATE_SESSION results that it would persist the
cache.
o The server purges the session of a client that has been inactive
for a very extended period of time.
Loss of reply cache is equivalent to loss of session. The replier
indicates loss of session to the requester by returning
NFS4ERR_BADSESSION on the next operation that uses the sessionid that
refers to the lost session.
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 sessionid. Otherwise, it invokes
SEQUENCE. If BIND_CONN_TO_SESSION or SEQUENCE returns
NFS4ERR_BADSESSION, the client knows the session was lost. 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.
When the client detects session loss, it must call CREATE_SESSION to
recover. Any non-idempotent operations that were in progress may
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 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 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,
lock, open, delegation, and layout state. See Section 8.4.2. A
session can survive a server restart, but lock recovery may still be
needed.
It is possible CREATE_SESSION will fail with NFS4ERR_STALE_CLIENTID
(for example 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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2.10.10.2. Events Requiring Server Action
The following events require server action to recover.
2.10.10.2.1. Client Crash and Restart
As described in Section 18.35, a restarted client sends EXCHANGE_ID
in such a way it causes the server to delete any sessions it had.
2.10.10.2.2. 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.
2.10.10.2.3. Extended Network Partition
To the server, the extended network partition may be no different
from a client crash with no restart (see Section 2.10.10.2.2).
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.
2.10.10.2.4. Backchannel Connection Loss
If there were callback requests outstanding at the time of a
connection loss, then the server MUST retry the request, as described
in Section 2.10.5.2. 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
sessionid, 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 reestablished. There are two situations each of which use
different status flags: no connectivity for the session's
backchannel, and no connectivity for any session backchannel of the
client. See Section 18.46 for a description of the appropriate flags
in sr_status_flags.
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2.10.10.2.5. GSS Context Loss
The server SHOULD monitor when the number RPCSEC_GSS contexts
assigned to the backchannel reaches one, and that one context 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 the all of the backchannel's assigned RPCSEC_GSS
contexts have expired in the sr_status_flags field of all SEQUENCE
replies.
2.10.11. 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 13.1 for pNFS
sessions considerations.
3. 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 [2] and RPC RFC1831 [3]
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 [12].
3.1. 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.
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o NFS4_FHSIZE is the maximum size of a filehandle.
o NFS4_VERIFIER_SIZE is the fixed size of a verifier.
o NFS4_OPAQUE_LIMIT is the maximum size of certain opaque
information.
o NFS4_SESSIONID_SIZE is the fixed size of a session identifier.
o NFS4_INT64_MAX is the maximum value of a signed 64 bit integer.
o NFS4_UINT64_MAX is the maximum value of an unsigned 64 bit
integer.
o NFS4_INT32_MAX is the maximum value of a signed 32 bit integer.
o NFS4_UINT32_MAX is the maximum value of an unsigned 32 bit
integer.
o NFS4_MAXFILELEN is the maximum length of a regular file.
o NFS4_MAXFILEOFF is the maximum offset into a regular file.
3.2. 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 definition of change_info |
| 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; |
| | Describes LOCK lengths |
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| mode4 | typedef uint32_t mode4; |
| | Mode attribute data type |
| nfs_cookie4 | typedef uint64_t nfs_cookie4; |
| | Opaque cookie value for READDIR |
| nfs_fh4<NFS4_FHSIZE> | 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 [7] for |
| | details. |
| 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 file 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 case sensitive prefix |
| | and a case insensitive suffix. |
| component4 | typedef utf8str_cs component4; |
| | Represents path name components |
| linktext4 | typedef utf8str_cs linktext4; |
| | Symbolic link contents |
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| pathname4<> | typedef component4 pathname4<>; |
| | Represents path name 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. |
+----------------------+--------------------------------------------+
End of Base Data Types
Table 1
3.3. Structured Data Types
3.3.1. nfstime4
struct nfstime4 {
int64_t seconds;
uint32_t nseconds;
};
The nfstime4 structure gives the number of seconds and nanoseconds
since midnight or 0 hour January 1, 1970 Coordinated Universal Time
(UTC). Values greater than zero for the seconds field denote dates
after the 0 hour January 1, 1970. Values less than zero for the
seconds field denote dates before the 0 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 0 hour January 1, 1970, the
seconds field would have a value of negative one (-1) and the
nseconds fields would have a value of one-half second (500000000).
Values greater than 999,999,999 for nseconds are considered 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
defined, loss of precision can occur. An adjunct time maintenance
protocol is RECOMMENDED to reduce client and server time skew.
3.3.2. time_how4
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
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3.3.3. settime4
union settime4 switch (time_how4 set_it) {
case SET_TO_CLIENT_TIME4:
nfstime4 time;
default:
void;
};
The above definitions are used as the attribute definitions to set
time values. If set_it is SET_TO_SERVER_TIME4, then the server uses
its local representation of time for the time value.
3.3.4. specdata4
struct specdata4 {
uint32_t specdata1; /* major device number */
uint32_t specdata2; /* minor device number */
};
This data type represents additional information for the device file
types NF4CHR and NF4BLK.
3.3.5. fsid4
struct fsid4 {
uint64_t major;
uint64_t minor;
};
3.3.6. chg_policy4
struct change_policy4 {
uint64_t cp_major;
uint64_t cp_minor;
};
The chg_policy4 data type is used for the change_policy RECOMMENDED
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.
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3.3.7. fattr4
struct fattr4 {
bitmap4 attrmask;
attrlist4 attr_vals;
};
The fattr4 structure is used to represent file and directory
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 |
+-----------+-----------+-----------+--
3.3.8. change_info4
struct change_info4 {
bool atomic;
changeid4 before;
changeid4 after;
};
This structure is used with the CREATE, LINK, REMOVE, RENAME
operations to let the client know the value of the change attribute
for the directory in which the target file system object resides.
3.3.9. netaddr4
struct netaddr4 {
/* see struct rpcb in RFC 1833 */
string na_r_netid<>; /* network id */
string na_r_addr<>; /* universal address */
};
The netaddr4 structure is used to identify TCP/IP based endpoints.
The r_netid and r_addr fields are specified in RFC1833 [26], but they
are underspecified in RFC1833 [26] as far as what they should look
like for specific protocols.
For TCP over IPv4 and for UDP over IPv4, the format of r_addr is the
US-ASCII string:
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h1.h2.h3.h4.p1.p2
The prefix, "h1.h2.h3.h4", is the standard textual form for
representing an IPv4 address, which is always four bytes long.
Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
the first through fourth bytes each converted to ASCII-decimal.
Assuming big-endian ordering, p1 and p2 are, respectively, the first
and second bytes each converted to ASCII-decimal. For example, if a
host, in big-endian order, has an address of 0x0A010307 and there is
a service listening on, in big endian order, port 0x020F (decimal
527), then complete universal address is "10.1.3.7.2.15".
For TCP over IPv4 the value of r_netid is the string "tcp". For UDP
over IPv4 the value of r_netid is the string "udp". That this
document specifies the universal address and netid for UDP/IPv6 does
not imply that UDP/IPv4 is a legal transport for NFSv4.1 (see
Section 2.9).
For TCP over IPv6 and for UDP over IPv6, the format of r_addr is the
US-ASCII string:
x1:x2:x3:x4:x5:x6:x7:x8.p1.p2
The suffix "p1.p2" is the service port, and is computed the same way
as with universal addresses for TCP and UDP over IPv4. The prefix,
"x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
representing an IPv6 address as defined in Section 2.2 of RFC2373
[13]. Additionally, the two alternative forms specified in Section
2.2 of RFC2373 [13] are also acceptable.
For TCP over IPv6 the value of r_netid is the string "tcp6". For UDP
over IPv6 the value of r_netid is the string "udp6". That this
document specifies the universal address and netid for UDP/IPv6 does
not imply that UDP/IPv6 is a legal transport for NFSv4.1 (see
Section 2.9).
3.3.10. 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 3.3.10.1 and lock_owner4 Section 3.3.10.2.
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3.3.10.1. open_owner4
This structure is used to identify the owner of open state.
3.3.10.2. lock_owner4
This structure is used to identify the owner of file locking state.
3.3.11. open_to_lock_owner4
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
This structure 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.
3.3.12. stateid4
struct stateid4 {
uint32_t seqid;
opaque other[12];
};
This structure is used for the various state sharing mechanisms
between the client and server. For the client, this data structure
is read-only. The starting value of the seqid field is undefined.
The server is required to increment the seqid field monotonically 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.
3.3.13. layouttype4
enum layouttype4 {
LAYOUT4_NFSV4_1_FILES = 1,
LAYOUT4_OSD2_OBJECTS = 2,
LAYOUT4_BLOCK_VOLUME = 3
};
This data type indicates what type of layout is being used. The file
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server advertises the layout types it supports through the
fs_layout_type file system attribute (Section 5.11.1). A client asks
for layouts of a particular type in LAYOUTGET, and processes those
layouts in its layout-type-specific logic.
The layouttype4 structure 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 22.4; 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 is to be used. The LAYOUT4_OSD2_OBJECTS enumeration
specifies that the object layout, as defined in [30], is to be used.
Similarly, the LAYOUT4_BLOCK_VOLUME enumeration that the block/volume
layout, as defined in [31], is to be used.
3.3.14. deviceid4
const NFS4_DEVICEID4_SIZE = 16;
typedef opaque deviceid4[NFS4_DEVICEID4_SIZE];
Layout information includes device IDs that specify a storage device
through a compact handle. Addressing and type information is
obtained with the GETDEVICEINFO operation. A client must not assume
that device IDs are valid across metadata server reboots. The device
ID is qualified by the layout type and are unique per file system
(FSID). See Section 12.2.10 for more details.
3.3.15. 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 types
of structures to define how they communicate with storage devices.
The opaque da_addr_body field must be interpreted based on the
specified da_layout_type field.
This document defines the device address for the NFSv4.1 file layout
(see Section 13.3), which identifies a storage device by network IP
address and port number. This is sufficient for the clients to
communicate with the NFSv4.1 storage devices, and may be sufficient
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for other layout types as well. Device types for object storage
devices and block storage devices (e.g., SCSI volume labels) will be
defined by their respective layout specifications.
3.3.16. layout_content4
struct layout_content4 {
layouttype4 loc_type;
opaque loc_body<>;
};
The loc_body field must be interpreted based on the layout type
(loc_type). This document defines the loc_body for the NFSv4.1 file
layout type is defined; see Section 13.3 for its definition.
3.3.17. layout4
struct layout4 {
offset4 lo_offset;
length4 lo_length;
layoutiomode4 lo_iomode;
layout_content4 lo_content;
};
The layout4 structure 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.
3.3.18. layoutupdate4
struct layoutupdate4 {
layouttype4 lou_type;
opaque lou_body<>;
};
The layoutupdate4 structure is used by the client to return 'updated'
layout information to the metadata server at LAYOUTCOMMIT time. This
structure provides a channel to pass layout type specific information
(in field lou_body) back to the metadata server. E.g., for block/
volume layout types this could include the list of reserved blocks
that were written. The contents of the opaque lou_body argument are
determined by the layout type and are defined in their context. The
NFSv4.1 file-based layout does not use this structure, thus the
lou_body field should have a zero length.
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3.3.19. layouthint4
struct layouthint4 {
layouttype4 loh_type;
opaque loh_body<>;
};
The layouthint4 structure 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 structure specified by the layout_hint attribute described
in Section 5.11.4. 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 loh_body field is specific to the type of layout
(loh_type). The NFSv4.1 file-based layout uses the
nfsv4_1_file_layouthint4 structure as defined in Section 13.3.
3.3.20. layoutiomode4
enum layoutiomode4 {
LAYOUTIOMODE4_READ = 1,
LAYOUTIOMODE4_RW = 2,
LAYOUTIOMODE4_ANY = 3
};
The iomode specifies whether the client intends to read or write
(with the possibility of reading) the data represented by the layout.
The ANY iomode MUST NOT be used for LAYOUTGET, however, it can be
used for LAYOUTRETURN and CB_LAYOUTRECALL. The ANY iomode specifies
that layouts pertaining to both READ and 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.
3.3.21. nfs_impl_id4
struct nfs_impl_id4 {
utf8str_cis nii_domain;
utf8str_cs nii_name;
nfstime4 nii_date;
};
This structure is used to identify client and server implementation
detail. The nii_domain field is the DNS domain name that the
implementer is associated with. 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
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architecture, machine platforms, revisions, versions, and patch
levels. The nii_date field is the timestamp of when the software
instance was published or built.
3.3.22. threshold_item4
struct threshold_item4 {
layouttype4 thi_layout_type;
bitmap4 thi_hintset;
opaque thi_hintlist<>;
};
This structure 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 vs. the data servers. The hint structure
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
structure is determined by the hintset bitmap. See the mdsthreshold
attribute for more details.
The thi_hintset field is a bitmap of the following values:
+-------------------------+---+---------+---------------------------+
| name | # | Data | Description |
| | | Type | |
+-------------------------+---+---------+---------------------------+
| threshold4_read_size | 0 | length4 | The file size below which |
| | | | it is RECOMMENDED to read |
| | | | data through the MDS. |
| threshold4_write_size | 1 | length4 | The file size below which |
| | | | it is RECOMMENDED to |
| | | | write data through the |
| | | | MDS. |
| threshold4_read_iosize | 2 | length4 | For read I/O sizes below |
| | | | this threshold it is |
| | | | RECOMMENDED to read data |
| | | | through the MDS |
| threshold4_write_iosize | 3 | length4 | For write I/O sizes below |
| | | | this threshold it is |
| | | | RECOMMENDED to write data |
| | | | through the MDS |
+-------------------------+---+---------+---------------------------+
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3.3.23. mdsthreshold4
struct mdsthreshold4 {
threshold_item4 mth_hints<>;
};
This structure holds an array of threshold_item4 structures each of
which is valid for a particular layout type. An array is necessary
since a server can support multiple layout types for a single file.
4. 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.
4.1. 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 [22], 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 path name 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 [32] and RFC2055 [33]. 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 path names to a filehandle. Two
special filehandles will be used as starting points for the NFS
client.
4.1.1. Root Filehandle
The first of the special filehandles is the ROOT filehandle. The
ROOT filehandle is the "conceptual" root of the file system name
space at the NFS server. The client uses or starts with the ROOT
filehandle by employing the PUTROOTFH operation. The PUTROOTFH
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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
name space is in the Section 7.
4.1.2. 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.
4.2. 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 which 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 which may be
used by the client to determine the filehandle types being returned
by the server.
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4.2.1. 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.
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 which might cause
incorrect behavior. Further discussion of filehandle and attribute
comparison in the context of data caching is presented in the
Section 10.3.4.
As an example, in the case that two different path names 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 is used to create two file names which 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 path names traversals.
4.2.2. 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 or reboots 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 name space (i.e. unmounted in a UNIX environment).
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4.2.3. 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
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 case 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 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 which provide volatile filehandles that may expire while open
(i.e. if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if
FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), 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
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deny all RENAME or REMOVE requests during the grace period upon
server restart.
Servers which provide volatile filehandles that may expire while open
require special care as regards handling of RENAMESs 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 not set,
or if a non-readonly 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.
Volatile filehandles are especially suitable for implementation of
the pseudo file systems used to bridge exports. See Section 7.5 for
a discussion of this.
4.3. 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]
o slot is an index in the server volatile filehandle table
o 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 reboots, the table is gone (it is volatile).
If volatile bit is 0, then it is a persistent filehandle with a
different structure following it.
4.4. 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
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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 name space that is still
available or by starting at the root of the server's file system name
space.
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.
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 path name based on the
processing of the rename request. The client can then regenerate the
new filehandle based on the new path name. The client could also use
the compound operation mechanism to construct a set 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.
5. File Attributes
To meet the requirements of extensibility and increased
interoperability with non-UNIX platforms, attributes must be handled
in a flexible manner. The NFSv3 fattr3 structure contains a fixed
list of attributes that not all clients and servers are able to
support or care about. The fattr3 structure can not be extended as
new needs arise and it provides no way to indicate non-support. With
the NFSv4.1 protocol, the client is able query what attributes the
server supports and construct requests with only those supported
attributes (or a subset thereof).
To this end, attributes are divided into three groups: REQUIRED,
RECOMMENDED, and named. Both REQUIRED and RECOMMENDED attributes are
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supported in the NFSv4.1 protocol by a specific and well-defined
encoding and are identified by number. They are requested by setting
a bit in the bit vector sent in the GETATTR request; the server
response includes a bit vector to list what attributes were returned
in the response. New REQUIRED or RECOMMENDED attributes may be added
to the NFS protocol between major revisions by publishing a
standards-track RFC which allocates a new attribute number value and
defines the encoding for the attribute. See Section 2.7 for further
discussion.
Named attributes are accessed by the new OPENATTR operation, which
accesses a hidden directory of attributes associated with a file
system object. OPENATTR takes a filehandle for the object and
returns the filehandle for the attribute hierarchy. The filehandle
for the named attributes is a directory object accessible by LOOKUP
or READDIR and contains files whose names represent the named
attributes and whose data bytes are the value of the attribute. 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 |
+----------+-----------+---------------------------------+
Named attributes are intended for data needed by applications rather
than by an NFS client implementation. NFS implementors are strongly
encouraged to define their new attributes as RECOMMENDED attributes
by bringing them to the IETF standards-track process.
The set of attributes which are classified as REQUIRED is
deliberately small since servers must do whatever it takes to support
them. A server should support as many of the RECOMMENDED attributes
as possible but by their definition, the server is not required to
support all of them. Attributes are deemed REQUIRED if the data is
both needed by a large number of clients and is not otherwise
reasonably computable by the client when support is not provided on
the server.
Note that the hidden directory returned by OPENATTR is a convenience
for protocol processing. The client should not make any assumptions
about the server's implementation of named attributes and whether the
underlying file system at the server has a named attribute directory
or not. Therefore, operations such as SETATTR and GETATTR on the
named attribute directory are undefined.
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5.1. 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 and the client must 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. A client may ask for any of these attributes
to be returned by setting a bit in the GETATTR request and the server
must return their value.
5.2. RECOMMENDED Attributes
These attributes are understood well enough to warrant support in the
NFSv4.1 protocol. However, they may not be supported on all clients
and servers. A client may ask for any of these attributes to be
returned by setting a bit in the GETATTR request but must handle the
case where the server does not return them. A client may ask for the
set of attributes the server supports and should not request
attributes the server does not support. A server should be tolerant
of requests for unsupported attributes and simply not return them
rather than considering the request an error. It is expected that
servers will support all attributes they comfortably can and only
fail to support attributes which are difficult to support in their
operating environments. A server should provide attributes whenever
they don't have to "tell lies" to the client. For example, a file
modification time should be either an accurate time or should not be
supported by the server. This will not always be comfortable to
clients but the client is better positioned decide whether and how to
fabricate or construct an attribute or whether to do without the
attribute.
5.3. Named Attributes
These attributes are not supported by direct encoding in the NFSv4
protocol but are accessed by string names rather than numbers and
correspond to an uninterpreted stream of bytes which are stored with
the file system object. The name space for these attributes may be
accessed by using the OPENATTR operation. The OPENATTR operation
returns a filehandle for a virtual "named attribute directory" and
further perusal and modification of the name space may be done using
operations that work on more typical directories. In particular,
READDIR may be used to get a list of such named attributes and LOOKUP
and OPEN may select a particular attribute. Creation of a new named
attribute may be the result of an OPEN specifying file creation.
Once an OPEN is done, named attributes may be examined and changed by
normal READ and WRITE operations using the filehandles and stateids
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returned by OPEN.
Named attributes and the named attribute directory may have have
their own (non-named) attributes. Each of objects must have all of
the REQUIRED attributes and may have additional RECOMMENDED
attributes. However, the set of attributes for named attributes and
the named attribute directory need not be as large as, and typically
will not be as large as that for other objects in that file system.
Named attributes and the named attribute directory may be the target
of delegations (in the case of the named attribute directory these
will be directory delegations). However, since granting of
delegations or not is within the server's discretion, a server need
not support delegations on named attributes or the named attribute
directory.
It is RECOMMENDED that servers support arbitrary named attributes. A
client should not depend on the ability to store any named attributes
in the server's file system. If a server does support named
attributes, a client which is also able to handle them should be able
to copy a file's data and meta-data with complete transparency from
one location to another; this would imply that names allowed for
regular directory entries are 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 set, but fully adequate to the
feature's goals. In such an environment, clients or applications
might come to depend on non-portable extensions. The restrictions
are:
o 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 no hierarchical structure of named
attributes for a single object is allowed.
o OPENATTR many not be done on a named attribute directory or on a
named attribute. Thus, although these object have attributes,
they may not may named attributes.
o 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.
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o Creating hard links between names 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. See Section 22.1 for further
discussion.
5.4. Classification of Attributes
Each of the REQUIRED and RECOMMENDED attributes can be classified in
one of three categories: per server, per file system, or per file
system object. Note that it is possible that some per file system
attributes may vary within the file system. See the "homogeneous"
attribute for its definition. 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.
o The per server attribute is:
lease_time
o 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
o 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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5.5. REQUIRED Attributes - List and Definition References
+--------------------+----+------------+-----+------------------+
| name | Id | Data Type | Acc | Defined in: |
+--------------------+----+------------+-----+------------------+
| supported_attrs | 0 | bitmap4 | RD | Section 5.7.1.1 |
| type | 1 | nfs_ftype4 | RD | Section 5.7.1.2 |
| fh_expire_type | 2 | uint32_t | RD | Section 5.7.1.3 |
| change | 3 | uint64_t | RD | Section 5.7.1.4 |
| size | 4 | uint64_t | R/W | Section 5.7.1.5 |
| link_support | 5 | bool | RD | Section 5.7.1.6 |
| symlink_support | 6 | bool | RD | Section 5.7.1.7 |
| named_attr | 7 | bool | RD | Section 5.7.1.8 |
| fsid | 8 | fsid4 | RD | Section 5.7.1.9 |
| unique_handles | 9 | bool | RD | Section 5.7.1.10 |
| lease_time | 10 | nfs_lease4 | RD | Section 5.7.1.11 |
| rdattr_error | 11 | enum | RD | Section 5.7.1.12 |
| filehandle | 19 | nfs_fh4 | RD | Section 5.7.1.13 |
| suppattr_exclcreat | 75 | bitmap4 | RD | Section 5.7.1.14 |
+--------------------+----+------------+-----+------------------+
5.6. RECOMMENDED Attributes - List and Definition References
+--------------------+----+----------------+-----+------------------+
| name | Id | Data Type | Acc | Defined in: |
+--------------------+----+----------------+-----+------------------+
| acl | 12 | nfsace4<> | R/W | Section 6.2.1 |
| aclsupport | 13 | uint32_t | RD | Section 6.2.1.2 |
| archive | 14 | bool | R/W | Section 5.7.2.1 |
| cansettime | 15 | bool | RD | Section 5.7.2.2 |
| case_insensitive | 16 | bool | RD | Section 5.7.2.3 |
| case_preserving | 17 | bool | RD | Section 5.7.2.4 |
| change_policy | 60 | chg_policy4 | RD | Section 5.7.2.5 |
| chown_restricted | 18 | bool | RD | Section 5.7.2.6 |
| dacl | 58 | nfsacl41 | R/W | Section 6.2.2 |
| dir_notif_delay | 56 | nfstime4 | RD | Section 5.10.1 |
| dirent_notif_delay | 57 | nfstime4 | RD | Section 5.10.2 |
| fileid | 20 | uint64_t | RD | Section 5.7.2.7 |
| files_avail | 21 | uint64_t | RD | Section 5.7.2.8 |
| files_free | 22 | uint64_t | RD | Section 5.7.2.9 |
| files_total | 23 | uint64_t | RD | Section 5.7.2.10 |
| fs_charset_cap | 76 | uint32_t | RD | Section 5.7.2.11 |
| fs_layout_type | 62 | layouttype4<> | RD | Section 5.11.1 |
| fs_locations | 24 | fs_locations | RD | Section 5.7.2.12 |
| fs_locations_info | 67 | * | RD | Section 5.7.2.13 |
| fs_status | 61 | fs4_status | RD | Section 5.7.2.14 |
| hidden | 25 | bool | R/W | Section 5.7.2.15 |
| homogeneous | 26 | bool | RD | Section 5.7.2.16 |
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| layout_alignment | 66 | uint32_t | RD | Section 5.11.2 |
| layout_blksize | 65 | uint32_t | RD | Section 5.11.3 |
| layout_hint | 63 | layouthint4 | WRT | Section 5.11.4 |
| layout_type | 64 | layouttype4<> | RD | Section 5.11.5 |
| maxfilesize | 27 | uint64_t | RD | Section 5.7.2.17 |
| maxlink | 28 | uint32_t | RD | Section 5.7.2.18 |
| maxname | 29 | uint32_t | RD | Section 5.7.2.19 |
| maxread | 30 | uint64_t | RD | Section 5.7.2.20 |
| maxwrite | 31 | uint64_t | RD | Section 5.7.2.21 |
| mdsthreshold | 68 | mdsthreshold4 | RD | Section 5.11.6 |
| mimetype | 32 | utf8<> | R/W | Section 5.7.2.22 |
| mode | 33 | mode4 | R/W | Section 6.2.4 |
| mode_set_masked | 74 | mode_masked4 | WRT | Section 6.2.5 |
| mounted_on_fileid | 55 | uint64_t | RD | Section 5.7.2.23 |
| no_trunc | 34 | bool | RD | Section 5.7.2.24 |
| numlinks | 35 | uint32_t | RD | Section 5.7.2.25 |
| owner | 36 | utf8<> | R/W | Section 5.7.2.26 |
| owner_group | 37 | utf8<> | R/W | Section 5.7.2.27 |
| quota_avail_hard | 38 | uint64_t | RD | Section 5.7.2.28 |
| quota_avail_soft | 39 | uint64_t | RD | Section 5.7.2.29 |
| quota_used | 40 | uint64_t | RD | Section 5.7.2.30 |
| rawdev | 41 | specdata4 | RD | Section 5.7.2.31 |
| retentevt_get | 71 | retention_get4 | RD | Section 5.12.3 |
| retentevt_set | 72 | retention_set4 | WRT | Section 5.12.4 |
| retention_get | 69 | retention_get4 | RD | Section 5.12.1 |
| retention_hold | 73 | uint64_t | R/W | Section 5.12.5 |
| retention_set | 70 | retention_set4 | WRT | Section 5.12.2 |
| sacl | 59 | nfsacl41 | R/W | Section 6.2.3 |
| space_avail | 42 | uint64_t | RD | Section 5.7.2.32 |
| space_free | 43 | uint64_t | RD | Section 5.7.2.33 |
| space_total | 44 | uint64_t | RD | Section 5.7.2.34 |
| space_used | 45 | uint64_t | RD | Section 5.7.2.35 |
| system | 46 | bool | R/W | Section 5.7.2.36 |
| time_access | 47 | nfstime4 | RD | Section 5.7.2.37 |
| time_access_set | 48 | settime4 | WRT | Section 5.7.2.38 |
| time_backup | 49 | nfstime4 | R/W | Section 5.7.2.39 |
| time_create | 50 | nfstime4 | R/W | Section 5.7.2.40 |
| time_delta | 51 | nfstime4 | RD | Section 5.7.2.41 |
| time_metadata | 52 | nfstime4 | RD | Section 5.7.2.42 |
| time_modify | 53 | nfstime4 | RD | Section 5.7.2.43 |
| time_modify_set | 54 | settime4 | WRT | Section 5.7.2.44 |
+--------------------+----+----------------+-----+------------------+
* fs_locations_info4
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5.7. Attribute Definitions
5.7.1. Definitions of REQUIRED Attributes
5.7.1.1. Attribute 0: supported_attrs
The bit vector which would retrieve all REQUIRED and RECOMMENDED
attributes that are supported for this object. The scope of this
attribute applies to all objects with a matching fsid.
5.7.1.2. Attribute 1: type
Designates the type of an object in terms of one of a number of
special constants:
o NF4REG designates a regular file.
o NF4DIR designates a directory.
o NF4BLK designates a block device special file.
o NF4CHR designates a character device special file.
o NF4LNK designates a symbolic link.
o NF4SOCK designates a named socket special file.
o NF4FIFO designates a fifo special file.
o NF4ATTRDIR designates a named attribute directory.
o NF4NAMEDATTR designates a named attribute.
Within the explanatory text and operation descriptions, the following
phrases will be used with the meanings given below:
o The phrase "is a directory" means that the object is of type
NF4DIR or of type NF4ATTRDIR.
o The phrase "is a special file" means that the object is of one of
the types NF4BLK, NF4CHR, NF4SOCK, or NF4FIFO.
o The phrase "is an ordinary file" means that the object is of type
NF4REG or of type NF4NAMEDATTR.
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5.7.1.3. Attribute 2: fh_expire_type
Server uses this to specify filehandle expiration behavior to the
client. See Section 4 for additional description.
5.7.1.4. 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 can not
be updated more frequently than the resolution of time_metadata.
5.7.1.5. Attribute 4: size
The size of the object in bytes.
5.7.1.6. Attribute 5: link_support
True, if the object's file system supports hard links.
5.7.1.7. Attribute 6: symlink_support
True, if the object's file system supports symbolic links.
5.7.1.8. Attribute 7: named_attr
True, if this object has named attributes. In other words, object
has a non-empty named attribute directory.
5.7.1.9. Attribute 8: fsid
Unique file system identifier for the file system holding this
object. fsid contains major and minor components each of which are of
data type uint64_t.
5.7.1.10. Attribute 9: unique_handles
True, if two distinct filehandles guaranteed to refer to two
different file system objects.
5.7.1.11. Attribute 10: lease_time
Duration of leases at server in seconds.
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5.7.1.12. Attribute 11: rdattr_error
Error returned from getattr during readdir.
5.7.1.13. Attribute 19: filehandle
The filehandle of this object (primarily for readdir requests).
5.7.1.14. Attribute 75: suppattr_exclcreat
The bit vector which would set all REQUIRED and RECOMMENDED
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.
5.7.2. Definitions of Uncategorized RECOMMENDED Attributes
The definitions of most of the RECOMMENDED attributes follow.
Collections that share a common category are defined in other
sections.
5.7.2.1. Attribute 14: archive
True, if this file has been archived since the time of last
modification (deprecated in favor of time_backup).
5.7.2.2. Attribute 15: cansettime
True, if the server able to change the times for a file system object
as specified in a SETATTR operation.
5.7.2.3. Attribute 16: case_insensitive
True, if filename comparisons on this file system are case
insensitive.
5.7.2.4. Attribute 17: case_preserving
True, if filename case on this file system are preserved.
5.7.2.5. 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 fsstat_type field of the fs_status attribute have not changed.
On the other hand, a change in this value does necessarily imply a
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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 3.3.6 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.
5.7.2.6. 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).
5.7.2.7. Attribute 20: fileid
A number uniquely identifying the file within the file system.
5.7.2.8. Attribute 21: files_avail
File slots available to this user on the file system containing this
object - this should be the smallest relevant limit.
5.7.2.9. Attribute 22: files_free
Free file slots on the file system containing this object - this
should be the smallest relevant limit.
5.7.2.10. Attribute 23: files_total
Total file slots on the file system containing this object.
5.7.2.11. Attribute 76: fs_charset_cap
Character set capabilities for this file system. See Section 14.4.
5.7.2.12. 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.
5.7.2.13. Attribute 67: fs_locations_info
Full function file system location.
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5.7.2.14. Attribute 61: fs_status
Generic file system type information.
5.7.2.15. Attribute 25: hidden
True, if the file is considered hidden with respect to the Windows
API.
5.7.2.16. Attribute 26: homogeneous
True, if this object's file system is homogeneous, i.e. are per file
system attributes the same for all file system's objects.
5.7.2.17. Attribute 27: maxfilesize
Maximum supported file size for the file system of this object.
5.7.2.18. Attribute 28: maxlink
Maximum number of links for this object.
5.7.2.19. Attribute 29: maxname
Maximum filename size supported for this object.
5.7.2.20. Attribute 30: maxread
Maximum read size supported for this object.
5.7.2.21. Attribute 31: maxwrite
Maximum write size supported 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.
5.7.2.22. Attribute 32: mimetype
MIME body type/subtype of this object.
5.7.2.23. Attribute 55: mounted_on_fileid
Like fileid, but if the target filehandle is the root of a file
system return 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
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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 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.
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 RECOMMENDED, so the server SHOULD
provide it if possible, and for a UNIX-based server, this is
straightforward. Usually, mounted_on_fileid will be requested during
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.
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5.7.2.24. Attribute 34: no_trunc
True, if a name longer than name_max is used, an error be returned
and name is not truncated.
5.7.2.25. Attribute 35: numlinks
Number of hard links to this object.
5.7.2.26. Attribute 36: owner
The string name of the owner of this object.
5.7.2.27. Attribute 37: owner_group
The string name of the group ownership of this object.
5.7.2.28. Attribute 38: quota_avail_hard
The value in bytes which represent 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.
5.7.2.29. Attribute 39: quota_avail_soft
The value in bytes which 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.
5.7.2.30. Attribute 40: quota_used
The value in bytes which represent the amount of disc 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 but should do so
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in a repeatable way. The rule may be configured per file system or
may be "choose the set with the smallest quota".
5.7.2.31. Attribute 41: rawdev
Raw device identifier. UNIX device major/minor node information. If
the value of type is not NF4BLK or NF4CHR, the value return SHOULD
NOT be considered useful.
5.7.2.32. 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.
5.7.2.33. Attribute 43: space_free
Free disk space in bytes on the file system containing this object -
this should be the smallest relevant limit.
5.7.2.34. Attribute 44: space_total
Total disk space in bytes on the file system containing this object.
5.7.2.35. Attribute 45: space_used
Number of file system bytes allocated to this object.
5.7.2.36. Attribute 46: system
True, if this file is a "system" file with respect to the Windows
API.
5.7.2.37. Attribute 47: time_access
The time_access attribute represents the time of last access to the
object by a read that was satisfied by the server. The notion of
what is an "access" depends on server's operating environment and/or
the server's file system semantics. For example, for servers obeying
POSIX semantics, time_access would be updated only by the READLINK,
READ, and READDIR operations and not any of the operations that
modify the content of the object. 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 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
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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.
5.7.2.38. Attribute 48: time_access_set
Set the time of last access to the object. SETATTR use only.
5.7.2.39. Attribute 49: time_backup
The time of last backup of the object.
5.7.2.40. 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".
5.7.2.41. Attribute 51: time_delta
Smallest useful server time granularity.
5.7.2.42. Attribute 52: time_metadata
The time of last meta-data modification of the object.
5.7.2.43. Attribute 53: time_modify
The time of last modification to the object.
5.7.2.44. Attribute 54: time_modify_set
Set the time of last modification to the object. SETATTR use only.
5.8. Interpreting owner and owner_group
The RECOMMENDED attributes "owner" and "owner_group" (and also users
and groups within the "acl" attribute) are represented in terms of a
UTF-8 string. To avoid a representation that is tied to a particular
underlying implementation at the client or server, the use of the
UTF-8 string has been chosen. Note that section 6.1 of RFC2624 [34]
provides additional rationale. It is expected that the client and
server will have their own local representation of owner and
owner_group that is used for local storage or presentation to the end
user. Therefore, it is expected that when these attributes are
transferred between the client and server that the local
representation is translated to a syntax of the form "user@
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dns_domain". This will allow for a client and server that do not use
the same local representation the ability to translate to a common
syntax that can be interpreted by both.
Similarly, security principals may be represented in different ways
by different security mechanisms. Servers normally translate these
representations into a common format, generally that used by local
storage, to serve as a means of identifying the users corresponding
to these security principals. When these local identifiers are
translated to the form of the owner attribute, associated with files
created by such principals they identify, in a common format, the
users associated with each corresponding set of security principals.
The translation used to interpret owner and group strings is not
specified as part of the protocol. This allows various solutions to
be employed. For example, a local translation table may be consulted
that maps between a numeric id to the user@dns_domain syntax. A name
service may also be used to accomplish the translation. A server may
provide a more general service, not limited by any particular
translation (which would only translate a limited set of possible
strings) by storing the owner and owner_group attributes in local
storage without any translation or it may augment a translation
method by storing the entire string for attributes for which no
translation is available while using the local representation for
those cases in which a translation is available.
Servers that do not provide support for all possible values of the
owner and owner_group attributes, should return an error
(NFS4ERR_BADOWNER) when a string is presented that has no
translation, as the value to be set for a SETATTR of the owner,
owner_group, or acl attributes. When a server does accept an owner
or owner_group value as valid on a SETATTR (and similarly for the
owner and group strings in an acl), it is promising to return that
same string when a corresponding GETATTR is done. Configuration
changes and ill-constructed name translations (those that contain
aliasing) may make that promise impossible to honor. Servers should
make appropriate efforts to avoid a situation in which these
attributes have their values changed when no real change to ownership
has occurred.
The "dns_domain" portion of the owner string is meant to be a DNS
domain name. For example, user@ietf.org. Servers should accept as
valid a set of users for at least one domain. A server may treat
other domains as having no valid translations. A more general
service is provided when a server is capable of accepting users for
multiple domains, or for all domains, subject to security
constraints.
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In the case where there is no translation available to the client or
server, the attribute value must be constructed without the "@".
Therefore, the absence of the @ from the owner or owner_group
attribute signifies that no translation was available at the sender
and that the receiver of the attribute should not use that string as
a basis for translation into its own internal format. Even though
the attribute value can not be translated, it may still be useful.
In the case of a client, the attribute string may be used for local
display of ownership.
To provide a greater degree of compatibility with NFSv3, which
identified users and groups by 32-bit unsigned uid's and gid's, owner
and group strings that consist of decimal numeric values with no
leading zeros can be given a special interpretation by clients and
servers which choose to provide such support. The receiver may treat
such a user or group string as representing the same user as would be
represented by an NFSv3 uid or gid having the corresponding numeric
value. A server is not obligated to accept such a string, but may
return an NFS4ERR_BADOWNER instead. To avoid this mechanism being
used to subvert user and group translation, so that a client might
pass all of the owners and groups in numeric form, a server SHOULD
return an NFS4ERR_BADOWNER error when there is a valid translation
for the user or owner designated in this way. In that case, the
client must use the appropriate name@domain string and not the
special form for compatibility.
The owner string "nobody" may be used to designate an anonymous user,
which will be associated with a file created by a security principal
that cannot be mapped through normal means to the owner attribute.
5.9. Character Case Attributes
With respect to the case_insensitive and case_preserving attributes,
each UCS-4 character (which UTF-8 encodes) has a "long descriptive
name" RFC1345 [35] which may or may not included the word "CAPITAL"
or "SMALL". The presence of SMALL or CAPITAL allows an NFS server to
implement unambiguous and efficient table driven mappings for case
insensitive comparisons, and non-case-preserving storage. For
general character handling and internationalization issues, see
Section 14.
5.10. Directory Notification Attributes
As described in Section 18.39, 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 issuing a GETATTR
for either or both of two directory notification attributes. When
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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.
5.10.1. 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.
5.10.2. 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.
5.11. pNFS Attribute Definitions
5.11.1. Attribute 62: fs_layout_type
The fs_layout_type attribute (data type layouttype4 (Section 3.3.13))
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.
5.11.2. Attribute 66: layout_alignment
When a client has layouts for 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.
5.11.3. Attribute 65: layout_blksize
When a client has layouts for 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.
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5.11.4. Attribute 63: layout_hint
The layout_hint attribute (data type layouthint4 (Section 3.3.19))
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 sub-set 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.
5.11.5. 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.
5.11.6. 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 is below the I/O
size threshold, the I/O should be sent to the metadata server. As
defined, each threshold type is specified separately 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 exceed both
thresholds before issuing its READ or WRITE requests to the data
server. Alternatively, if only one of the specified thresholds is
exceeded, the I/O requests are sent to the metadata server.
For each threshold type, a value of 0 indicates no READ or WRITE
should be sent to the metadata server, while a value of all 1s
indicates 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
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changes, the client should not assume that the attribute will remain
constant for any specific time period, thus it should be periodically
refreshed.
5.12. 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 any
other property of the file, including any subset of REQUIRED,
RECOMMENDED, 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 as follows:
5.12.1. 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 may
not be modified by the SETATTR operation. The value of the attribute
consists of:
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.
5.12.2. 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
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only modifiable via SETATTR operation and may not be read with the
GETATTR operation. 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 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 does not prevent the enabling of event-
based retention nor the modification of the retention_hold attribute.
5.12.3. Attribute 71: retentevt_get
Get 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.
5.12.4. Attribute 72: retentevt_set
Set the event-based retention duration, and optionally enable event-
based retention on the file object. This attribute corresponds to
retentevt_get, 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 the 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 does not prevent
the enabling of non-event-based retention nor the modification of the
retention_hold attribute.
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5.12.5. Attribute 73: retention_hold
Get or set administrative retention holds, one hold per bit position.
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.
6. Security Related Attributes
Access Control Lists (ACLs) are file attributes that specify fine
grained access control. This chapter covers the "acl", "dacl",
"sacl", "aclsupport", "mode", "mode_set_masked" file attributes, and
their interactions. Note that file attributes may apply to any file
system objects.
6.1. Goals
ACLs and modes represent two well established models for specifying
permissions. This chapter specifies requirements that attempt to
meet the following goals:
o If a server supports the mode attribute, it should provide
reasonable semantics to clients that only set and retrieve the
mode attribute.
o If a server supports ACL attributes, it should provide reasonable
semantics to clients that only set and retrieve those attributes.
o On servers that support the mode attribute, if ACL attributes have
never been set on an object, via inheritance or explicitly, the
behavior should be traditional UNIX-like behavior.
o On servers that support the mode attribute, if the ACL attributes
have been previously set on an object, either explicitly or via
inheritance:
* Setting only the mode attribute should effectively control the
traditional UNIX-like permissions of read, write, and execute
on owner, owner_group, and other.
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* Setting only the mode attribute should provide reasonable
security. For example, setting a mode of 000 should be enough
to ensure that future opens for read or write by any principal
fail, regardless of a previously existing or inherited ACL.
o NFSv4.1 may introduce different semantics relating to the mode and
ACL attributes, but it does not render invalid any previously
existing implementations. Additionally, this chapter provides
clarifications based on previous implementations and discussions
around them.
o On servers that support both the mode and the acl or dacl
attributes, the server must keep the two consistent with each
other. The value of the mode attribute (with the exception of the
three high order bits described in Section 6.2.4), must be
determined entirely by the value of the ACL, so that use of the
mode is never required for anything other than setting the three
high order bits. See Section 6.4.1 for exact requirements.
o When a mode attribute is set on an object, the ACL attributes may
need to be modified so as to not conflict with the new mode. In
such cases, it is desirable that the ACL keep as much information
as possible. This includes information about inheritance, AUDIT
and ALARM ACEs, and permissions granted and denied that do not
conflict with the new mode.
6.2. File Attributes Discussion
6.2.1. Attribute 12: acl
The NFSv4.1 ACL attribute contains an array of access control entries
(ACEs) that are associated with the file system object. Although the
client can read and write the acl attribute, the server is
responsible for using the ACL to perform access control. The client
can use the OPEN or ACCESS operations to check access without
modifying or reading data or metadata.
The NFS ACE structure is defined as follows:
typedef uint32_t acetype4;
typedef uint32_t aceflag4;
typedef uint32_t acemask4;
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struct nfsace4 {
acetype4 type;
aceflag4 flag;
acemask4 access_mask;
utf8str_mixed who;
};
To determine if a request succeeds, the server processes each nfsace4
entry in order. Only ACEs which have a "who" that matches the
requester are considered. Each ACE is processed until all of the
bits of the requester's access have been ALLOWED. Once a bit (see
below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
considered in the processing of later ACEs. If an ACCESS_DENIED_ACE
is encountered where the requester's access still has unALLOWED bits
in common with the "access_mask" of the ACE, the request is denied.
When the ACL is fully processed, if there are bits in the requester's
mask that have not been ALLOWED or DENIED, access is denied.
Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE types do
not affect a requester's access, and instead are for triggering
events as a result of a requester's access attempt. Therefore, AUDIT
and ALARM ACEs are processed only after processing ALLOW and DENY
ACEs.
The NFSv4.1 ACL model is quite rich. Some server platforms may
provide access control functionality that goes beyond the UNIX-style
mode attribute, but which is not as rich as the NFS ACL model. So
that users can take advantage of this more limited functionality, the
server may support the acl attributes by mapping between its ACL
model and the NFSv4.1 ACL model. Servers must ensure that the ACL
they actually store or enforce is at least as strict as the NFSv4 ACL
that was set. It is tempting to accomplish this by rejecting any ACL
that falls outside the small set that can be represented accurately.
However, such an approach can render ACLs unusable without special
client-side knowledge of the server's mapping, which defeats the
purpose of having a common NFSv4 ACL protocol. Therefore servers
should accept every ACL that they can without compromising security.
To help accomplish this, servers may make a special exception, in the
case of unsupported permission bits, to the rule that bits not
ALLOWED or DENIED by an ACL must be denied. For example, a UNIX-
style server might choose to silently allow read attribute
permissions even though an ACL does not explicitly allow those
permissions. (An ACL that explicitly denies permission to read
attributes should still be rejected.)
The situation is complicated by the fact that a server may have
multiple modules that enforce ACLs. For example, the enforcement for
NFSv4.1 access may be different from, but not weaker than, the
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enforcement for local access, and both may be different from the
enforcement for access through other protocols such as SMB. So it
may be useful for a server to accept an ACL even if not all of its
modules are able to support it.
The guiding principle with regard to NFSv4 access is that the server
must not accept ACLs that appear to make the file more secure than it
really is.
6.2.1.1. ACE Type
The constants used for the type field (acetype4) are as follows:
const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
const ACE4_ACCESS_DENIED_ACE_TYPE = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE = 0x00000003;
Only the ALLOWED and DENIED bits types may be used in the dacl
attribute, and only the AUDIT and ALARM bits may be used in the sacl
attribute. All four are permitted in the acl attribute.
+------------------------------+--------------+---------------------+
| Value | Abbreviation | Description |
+------------------------------+--------------+---------------------+
| ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW | Explicitly grants |
| | | the access defined |
| | | in acemask4 to the |
| | | file or directory. |
| ACE4_ACCESS_DENIED_ACE_TYPE | DENY | Explicitly denies |
| | | the access defined |
| | | in acemask4 to the |
| | | file or directory. |
| ACE4_SYSTEM_AUDIT_ACE_TYPE | AUDIT | LOG (in a system |
| | | dependent way) any |
| | | access attempt to a |
| | | file or directory |
| | | which uses any of |
| | | the access methods |
| | | specified in |
| | | acemask4. |
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| ACE4_SYSTEM_ALARM_ACE_TYPE | ALARM | Generate a system |
| | | ALARM (system |
| | | dependent) when any |
| | | access attempt is |
| | | made to a file or |
| | | directory for the |
| | | access methods |
| | | specified in |
| | | acemask4. |
+------------------------------+--------------+---------------------+
The "Abbreviation" column denotes how the types will be referred to
throughout the rest of this chapter.
6.2.1.2. Attribute 13: aclsupport
A server need not support all of the above ACE types. This attribute
indicates which ACE types are supported for the current file system.
The bitmask constants used to represent the above definitions within
the aclsupport attribute are as follows:
const ACL4_SUPPORT_ALLOW_ACL = 0x00000001;
const ACL4_SUPPORT_DENY_ACL = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL = 0x00000008;
Servers which support either the ALLOW or DENY ACE type SHOULD
support both ALLOW and DENY ACE types.
Clients should not attempt to set an ACE unless the server claims
support for that ACE type. If the server receives a request to set
an ACE that it cannot store, it MUST reject the request with
NFS4ERR_ATTRNOTSUPP. If the server receives a request to set an ACE
that it can store but cannot enforce, the server SHOULD reject the
request with NFS4ERR_ATTRNOTSUPP.
Support for any of the ACL attributes is optional (albeit,
RECOMMENDED). However, a server that supports either of the new ACL
attributes (dacl or sacl) MUST allow use of the new ACL attributes to
access all of the ACE types which it supports. In other words, if
such a server supports ALLOW or DENY ACEs, then it MUST support the
dacl attribute, and if it supports AUDIT or ALARM ACEs, then it MUST
support the sacl attribute.
6.2.1.3. ACE Access Mask
The bitmask constants used for the access mask field are as follows:
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const ACE4_READ_DATA = 0x00000001;
const ACE4_LIST_DIRECTORY = 0x00000001;
const ACE4_WRITE_DATA = 0x00000002;
const ACE4_ADD_FILE = 0x00000002;
const ACE4_APPEND_DATA = 0x00000004;
const ACE4_ADD_SUBDIRECTORY = 0x00000004;
const ACE4_READ_NAMED_ATTRS = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS = 0x00000010;
const ACE4_EXECUTE = 0x00000020;
const ACE4_DELETE_CHILD = 0x00000040;
const ACE4_READ_ATTRIBUTES = 0x00000080;
const ACE4_WRITE_ATTRIBUTES = 0x00000100;
const ACE4_WRITE_RETENTION = 0x00000200;
const ACE4_WRITE_RETENTION_HOLD = 0x00000400;
const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
Note that some masks have coincident values, for example,
ACE4_READ_DATA and ACE4_LIST_DIRECTORY. The mask entries
ACE4_LIST_DIRECTORY, ACE4_ADD_SUBDIRECTORY, and ACE4_TRAVERSE are
intended to be used with directory objects, while ACE4_READ_DATA,
ACE4_WRITE_DATA, and ACE4_EXECUTE are intended to be used with non-
directory objects.
6.2.1.3.1. Discussion of Mask Attributes
ACE4_READ_DATA
Operation(s) affected:
READ
OPEN
Discussion:
Permission to read the data of the file.
Servers SHOULD allow a user the ability to read the data of the
file when only the ACE4_EXECUTE access mask bit is allowed.
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ACE4_LIST_DIRECTORY
Operation(s) affected:
READDIR
Discussion:
Permission to list the contents of a directory.
ACE4_WRITE_DATA
Operation(s) affected:
WRITE
OPEN
SETATTR of size
Discussion:
Permission to modify a file's data.
ACE4_ADD_FILE
Operation(s) affected:
CREATE
LINK
OPEN
RENAME
Discussion:
Permission to add a new file in a directory. The CREATE
operation is affected when nfs_ftype4 is NF4LNK, NF4BLK,
NF4CHR, NF4SOCK, or NF4FIFO. (NF4DIR is not listed because it
is covered by ACE4_ADD_SUBDIRECTORY.) OPEN is affected when
used to create a regular file. LINK and RENAME are always
affected.
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ACE4_APPEND_DATA
Operation(s) affected:
WRITE
OPEN
SETATTR of size
Discussion:
The ability to modify a file's data, but only starting at EOF.
This allows for the notion of append-only files, by allowing
ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to the same user
or group. If a file has an ACL such as the one described above
and a WRITE request is made for somewhere other than EOF, the
server SHOULD return NFS4ERR_ACCESS.
ACE4_ADD_SUBDIRECTORY
Operation(s) affected:
CREATE
RENAME
Discussion:
Permission to create a subdirectory in a directory. The CREATE
operation is affected when nfs_ftype4 is NF4DIR. The RENAME
operation is always affected.
ACE4_READ_NAMED_ATTRS
Operation(s) affected:
OPENATTR
Discussion:
Permission to read the named attributes of a file or to lookup
the named attributes directory. OPENATTR is affected when it
is not used to create a named attribute directory. This is
when 1.) createdir is TRUE, but a named attribute directory
already exists, or 2.) createdir is FALSE.
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ACE4_WRITE_NAMED_ATTRS
Operation(s) affected:
OPENATTR
Discussion:
Permission to write the named attributes of a file or to create
a named attribute directory. OPENATTR is affected when it is
used to create a named attribute directory. This is when
createdir is TRUE and no named attribute directory exists. The
ability to check whether or not a named attribute directory
exists depends on the ability to look it up, therefore, users
also need the ACE4_READ_NAMED_ATTRS permission in order to
create a named attribute directory.
ACE4_EXECUTE
Operation(s) affected:
READ
OPEN
REMOVE
RENAME
LINK
CREATE
Discussion:
Permission to execute a file.
Servers SHOULD allow a user the ability to read the data of the
file when only the ACE4_EXECUTE access mask bit is allowed.
This is because there is no way to execute a file without
reading the contents. Though a server may treat ACE4_EXECUTE
and ACE4_READ_DATA bits identically when deciding to permit a
READ operation, it SHOULD still allow the two bits to be set
independently in ACLs, and MUST distinguish between them when
replying to ACCESS operations. In particular, servers SHOULD
NOT silently turn on one of the two bits when the other is set,
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as that would make it impossible for the client to correctly
enforce the distinction between read and execute permissions.
As an example, following a SETATTR of the following ACL:
nfsuser:ACE4_EXECUTE:ALLOW
A subsequent GETATTR of ACL for that file SHOULD return:
nfsuser:ACE4_EXECUTE:ALLOW
Rather than:
nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW
ACE4_EXECUTE
Operation(s) affected:
LOOKUP
Discussion:
Permission to traverse/search a directory.
ACE4_DELETE_CHILD
Operation(s) affected:
REMOVE
RENAME
Discussion:
Permission to delete a file or directory within a directory.
See Section 6.2.1.3.2 for information on ACE4_DELETE and
ACE4_DELETE_CHILD interact.
ACE4_READ_ATTRIBUTES
Operation(s) affected:
GETATTR of file system object attributes
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VERIFY
NVERIFY
READDIR
Discussion:
The ability to read basic attributes (non-ACLs) of a file. On
a UNIX system, basic attributes can be thought of as the stat
level attributes. Allowing this access mask bit would mean the
entity can execute "ls -l" and stat. If a READDIR operation
requests attributes, this mask must be allowed for the READDIR
to succeed.
ACE4_WRITE_ATTRIBUTES
Operation(s) affected:
SETATTR of time_access_set, time_backup,
time_create, time_modify_set, mimetype, hidden, system
Discussion:
Permission to change the times associated with a file or
directory to an arbitrary value. Also permission to change the
mimetype, hidden and system attributes. A user having
ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be allowed to set
the times associated with a file to the current server time.
ACE4_WRITE_RETENTION
Operation(s) affected:
SETATTR of retention_set, retentevt_set.
Discussion:
Permission to modify the durations of event and non-event-based
retention. Also permission to enable event and non-event-based
retention. A server MAY behave such that setting
ACE4_WRITE_ATTRIBUTES allows ACE4_WRITE_RETENTION.
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ACE4_WRITE_RETENTION_HOLD
Operation(s) affected:
SETATTR of retention_hold.
Discussion:
Permission to modify the administration retention holds. A
server MAY map ACE4_WRITE_ATTRIBUTES to
ACE_WRITE_RETENTION_HOLD.
ACE4_DELETE
Operation(s) affected:
REMOVE
Discussion:
Permission to delete the file or directory. See
Section 6.2.1.3.2 for information on ACE4_DELETE and
ACE4_DELETE_CHILD interact.
ACE4_READ_ACL
Operation(s) affected:
GETATTR of acl, dacl, or sacl
NVERIFY
VERIFY
Discussion:
Permission to read the ACL.
ACE4_WRITE_ACL
Operation(s) affected:
SETATTR of acl and mode
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Discussion:
Permission to write the acl and mode attributes.
ACE4_WRITE_OWNER
Operation(s) affected:
SETATTR of owner and owner_group
Discussion:
Permission to write the owner and owner_group attributes. On
UNIX systems, this is the ability to execute chown() and
chgrp().
ACE4_SYNCHRONIZE
Operation(s) affected:
NONE
Discussion:
Permission to access file locally at the server with
synchronized reads and writes.
Server implementations need not provide the granularity of control
that is implied by this list of masks. For example, POSIX-based
systems might not distinguish ACE4_APPEND_DATA (the ability to append
to a file) from ACE4_WRITE_DATA (the ability to modify existing
contents); both masks would be tied to a single "write" permission.
When such a server returns attributes to the client, it would show
both ACE4_APPEND_DATA and ACE4_WRITE_DATA if and only if the write
permission is enabled.
If a server receives a SETATTR request that it cannot accurately
implement, it should err in the direction of more restricted access,
except in the previously discussed cases of execute and read. For
example, suppose a server cannot distinguish overwriting data from
appending new data, as described in the previous paragraph. If a
client submits an ALLOW ACE where ACE4_APPEND_DATA is set but
ACE4_WRITE_DATA is not (or vice versa), the server should either turn
off ACE4_APPEND_DATA or reject the request with NFS4ERR_ATTRNOTSUPP.
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6.2.1.3.2. ACE4_DELETE vs. ACE4_DELETE_CHILD
Two access mask bits govern the ability to delete a directory entry:
ACE4_DELETE on the object itself (the "target"), and
ACE4_DELETE_CHILD on the containing directory (the "parent").
Many systems also take the "sticky bit" (MODE4_SVTX) on a directory
to allow unlink only to a user that owns either the target or the
parent; on some such systems the decision also depends on whether the
target is writable.
Servers SHOULD allow unlink if either ACE4_DELETE is permitted on the
target, or ACE4_DELETE_CHILD is permitted on the parent. (Note that
this is true even if the parent or target explicitly denies one of
these permissions.)
If the ACLs in question neither explicitly ALLOW nor DENY either of
the above, and if MODE4_SVTX is not set on the parent, then the
server SHOULD allow the removal if and only if ACE4_ADD_FILE is
permitted. In the case where MODE4_SVTX is set, the server may also
require the remover to own either the parent or the target, or may
require the target to be writable.
This allows servers to support something close to traditional unix-
like semantics, with ACE4_ADD_FILE taking the place of the write bit.
6.2.1.4. ACE flag
The bitmask constants used for the flag field are as follows:
const ACE4_FILE_INHERIT_ACE = 0x00000001;
const ACE4_DIRECTORY_INHERIT_ACE = 0x00000002;
const ACE4_NO_PROPAGATE_INHERIT_ACE = 0x00000004;
const ACE4_INHERIT_ONLY_ACE = 0x00000008;
const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG = 0x00000010;
const ACE4_FAILED_ACCESS_ACE_FLAG = 0x00000020;
const ACE4_IDENTIFIER_GROUP = 0x00000040;
const ACE4_INHERITED_ACE = 0x00000080;
A server need not support any of these flags. If the server supports
flags that are similar to, but not exactly the same as, these flags,
the implementation may define a mapping between the protocol-defined
flags and the implementation-defined flags.
For example, suppose a client tries to set an ACE with
ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE. If the
server does not support any form of ACL inheritance, the server
should reject the request with NFS4ERR_ATTRNOTSUPP. If the server
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supports a single "inherit ACE" flag that applies to both files and
directories, the server may reject the request (i.e., requiring the
client to set both the file and directory inheritance flags). The
server may also accept the request and silently turn on the
ACE4_DIRECTORY_INHERIT_ACE flag.
6.2.1.4.1. Discussion of Flag Bits
ACE4_FILE_INHERIT_ACE
Any non-directory file in any sub-directory will get this ACE
inherited.
ACE4_DIRECTORY_INHERIT_ACE
Can be placed on a directory and indicates that this ACE should be
added to each new directory created.
If this flag is set in an ACE in an ACL attribute to be set on a
non-directory file system object, the operation attempting to set
the ACL SHOULD fail with NFS4ERR_ATTRNOTSUPP.
ACE4_INHERIT_ONLY_ACE
Can be placed on a directory but does not apply to the directory;
ALLOW and DENY ACEs with this bit set do not affect access to the
directory, and AUDIT and ALARM ACEs with this bit set do not
trigger log or alarm events. Such ACEs only take effect once they
are applied (with this bit cleared) to newly created files and
directories as specified by the above two flags.
If this flag is present on an ACE, but neither
ACE4_DIRECTORY_INHERIT_ACE nor ACE4_FILE_INHERIT_ACE is present,
then an operation attempting to set such an attribute SHOULD fail
with NFS4ERR_ATTRNOTSUPP.
ACE4_NO_PROPAGATE_INHERIT_ACE
Can be placed on a directory. This flag tells the server that
inheritance of this ACE should stop at newly created child
directories.
ACE4_INHERITED_ACE
Indicates that this ACE is inherited from a parent directory. A
server that supports automatic inheritance will place this flag on
any ACEs inherited from the parent directory when creating a new
object. Client applications will use this to perform automatic
inheritance. Clients and servers MUST clear this bit in the acl
attribute; it may only be used in the dacl and sacl attributes.
ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
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ACE4_FAILED_ACCESS_ACE_FLAG
The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits may be set only on
ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
(ALARM) ACE types. If during the processing of the file's ACL,
the server encounters an AUDIT or ALARM ACE that matches the
principal attempting the OPEN, the server notes that fact, and the
presence, if any, of the SUCCESS and FAILED flags encountered in
the AUDIT or ALARM ACE. Once the server completes the ACL
processing, it then notes if the operation succeeded or failed.
If the operation succeeded, and if the SUCCESS flag was set for a
matching AUDIT or ALARM ACE, then the appropriate AUDIT or ALARM
event occurs. If the operation failed, and if the FAILED flag was
set for the matching AUDIT or ALARM ACE, then the appropriate
AUDIT or ALARM event occurs. Either or both of the SUCCESS or
FAILED can be set, but if neither is set, the AUDIT or ALARM ACE
is not useful.
The previously described processing applies to ACCESS operations
even when they return NFS4_OK. For the purposes of AUDIT and
ALARM, we consider an ACCESS operation to be a "failure" if it
fails to return a bit that was requested and supported.
ACE4_IDENTIFIER_GROUP
Indicates that the "who" refers to a GROUP as defined under UNIX
or a GROUP ACCOUNT as defined under Windows. Clients and servers
MUST ignore the ACE4_IDENTIFIER_GROUP flag on ACEs with a who
value equal to one of the special identifiers outlined in
Section 6.2.1.5.
6.2.1.5. ACE Who
The "who" field of an ACE is an identifier that specifies the
principal or principals to whom the ACE applies. It may refer to a
user or a group, with the flag bit ACE4_IDENTIFIER_GROUP specifying
which.
There are several special identifiers which need to be understood
universally, rather than in the context of a particular DNS domain.
Some of these identifiers cannot be understood when an NFS client
accesses the server, but have meaning when a local process accesses
the file. The ability to display and modify these permissions is
permitted over NFS, even if none of the access methods on the server
understands the identifiers.
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+---------------+--------------------------------------------------+
| Who | Description |
+---------------+--------------------------------------------------+
| OWNER | The owner of the file |
| GROUP | The group associated with the file. |
| EVERYONE | The world, including the owner and owning group. |
| INTERACTIVE | Accessed from an interactive terminal. |
| NETWORK | Accessed via the network. |
| DIALUP | Accessed as a dialup user to the server. |
| BATCH | Accessed from a batch job. |
| ANONYMOUS | Accessed without any authentication. |
| AUTHENTICATED | Any authenticated user (opposite of ANONYMOUS) |
| SERVICE | Access from a system service. |
+---------------+--------------------------------------------------+
Table 7
To avoid conflict, these special identifiers are distinguished by an
appended "@" and should appear in the form "xxxx@" (with no domain
name after the "@"). For example: ANONYMOUS@.
The ACE4_IDENTIFIER_GROUP flag MUST be ignored on entries with these
special identifiers. When encoding entries with these special
identifiers, the ACE4_IDENTIFIER_GROUP flag SHOULD be set to zero.
6.2.1.5.1. Discussion of EVERYONE@
It is important to note that "EVERYONE@" is not equivalent to the
UNIX "other" entity. This is because, by definition, UNIX "other"
does not include the owner or owning group of a file. "EVERYONE@"
means literally everyone, including the owner or owning group.
6.2.2. Attribute 58: dacl
The dacl, and sacl, attributes are like the acl attribute, but dacl
and sacl each allow only certain types of ACEs. The dacl attribute
allows just ALLOW and DENY ACEs. The dacl and sacl attributes also
support automatic inheritance (see Section 6.4.3.2).
6.2.3. Attribute 59: sacl
The sacl, and dacl, attributes are like the acl attribute, but dacl
and sacl each allow only certain types of ACEs. The sacl attribute
allows just AUDIT and ALARM ACEs. The dacl and sacl attributes also
support automatic inheritance (see Section 6.4.3.2).
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6.2.4. Attribute 33: mode
The NFSv4.1 mode attribute is based on the UNIX mode bits. The
following bits are defined:
const MODE4_SUID = 0x800; /* set user id on execution */
const MODE4_SGID = 0x400; /* set group id on execution */
const MODE4_SVTX = 0x200; /* save text even after use */
const MODE4_RUSR = 0x100; /* read permission: owner */
const MODE4_WUSR = 0x080; /* write permission: owner */
const MODE4_XUSR = 0x040; /* execute permission: owner */
const MODE4_RGRP = 0x020; /* read permission: group */
const MODE4_WGRP = 0x010; /* write permission: group */
const MODE4_XGRP = 0x008; /* execute permission: group */
const MODE4_ROTH = 0x004; /* read permission: other */
const MODE4_WOTH = 0x002; /* write permission: other */
const MODE4_XOTH = 0x001; /* execute permission: other */
Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal
identified in the owner attribute. Bits MODE4_RGRP, MODE4_WGRP, and
MODE4_XGRP apply to principals identified in the owner_group
attribute but who are not identified in the owner attribute. Bits
MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to any principal that does
not match that in the owner attribute, and does not have a group
matching that of the owner_group attribute.
Bits within the mode other than those specified above are not defined
by this protocol. A server MUST NOT return bits other than those
defined above in a GETATTR or READDIR operation, and it MUST return
NFS4ERR_INVAL if bits other than those defined above are set in a
SETATTR, CREATE, OPEN, VERIFY or NVERIFY operation.
6.2.5. Attribute 74: mode_set_masked
The mode_set_masked attribute is a write-only attribute that allows
individual bits in the mode attribute to be set or reset, without
changing others. It allows, for example, the bits MODE4_SUID,
MODE4_SGID, and MODE4_SVTX to be modified while leaving unmodified
any of the nine low-order mode bits devoted to permissions.
In such instances that the nine low-order bits are left unmodified,
then neither the acl nor the dacl attribute should be automatically
modified as discussed in Section 6.4.1.
The mode_set_masked attribute consists of two words each in the form
of a mode4. The first consists of the value to be applied to the
current mode value and the second is a mask. Only bits set to one in
the mask word are changed (set or reset) in the file's mode. All
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other bits in the mode remain unchanged. Bits in the first word that
correspond to bits which are zero in the mask are ignored, except
that undefined bits are checked for validity and can result in
NFS4ERR_INVAL as described below.
The mode_set_masked attribute is only valid in a SETATTR operation.
If it is used in a CREATE or OPEN operation, the server MUST return
NFS4ERR_INVAL.
Bits not defined as valid in the mode attribute are not valid in
either word of the mode_set_masked attribute. The server MUST return
NFS4ERR_INVAL if any of those are on in a SETATTR. If the mode and
mode_set_masked attributes are both specified in the same SETATTR,
the server MUST also return NFS4ERR_INVAL.
6.3. Common Methods
The requirements in this section will be referred to in future
sections, especially Section 6.4.
6.3.1. Interpreting an ACL
6.3.1.1. Server Considerations
The server uses the algorithm described in Section 6.2.1 to determine
whether an ACL allows access to an object. However, the ACL may not
be the sole determiner of access. For example:
o In the case of a file system exported as read-only, the server may
deny write permissions even though an object's ACL grants it.
o Server implementations MAY grant ACE4_WRITE_ACL and ACE4_READ_ACL
permissions to prevent a situation from arising in which there is
no valid way to ever modify the ACL.
o All servers will allow a user the ability to read the data of the
file when only the execute permission is granted (i.e. If the ACL
denies the user the ACE4_READ_DATA access and allows the user
ACE4_EXECUTE, the server will allow the user to read the data of
the file).
o Many servers have the notion of owner-override in which the owner
of the object is allowed to override accesses that are denied by
the ACL. This may be helpful, for example, to allow users
continued access to open files on which the permissions have
changed.
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o Many servers have the notion of a "superuser" that has privileges
beyond an ordinary user. The superuser may be able to read or
write data or metadata in ways that would not be permitted by the
ACL.
6.3.1.2. Client Considerations
Clients SHOULD NOT do their own access checks based on their
interpretation the ACL, but rather use the OPEN and ACCESS operations
to do access checks. This allows the client to act on the results of
having the server determine whether or not access should be granted
based on its interpretation of the ACL.
Clients must be aware of situations in which an object's ACL will
define a certain access even though the server will not enforce it.
In general, but especially in these situations, the client needs to
do its part in the enforcement of access as defined by the ACL. To
do this, the client MAY send the appropriate ACCESS operation prior
to servicing the request of the user or application in order to
determine whether the user or application should be granted the
access requested. For examples in which the ACL may define accesses
that the server doesn't enforce see Section 6.3.1.1.
6.3.2. Computing a Mode Attribute from an ACL
The following method can be used to calculate the MODE4_R*, MODE4_W*
and MODE4_X* bits of a mode attribute, based upon an ACL.
First, for each of the special identifiers OWNER@, GROUP@, and
EVERYONE@, evaluate the ACL in order, considering only ALLOW and DENY
ACEs for the identifier EVERYONE@ and for the identifier under
consideration. The result of the evaluation will be an NFSv4 ACL
mask showing exactly which bits are permitted to that identifier.
Then translate the calculated mask for OWNER@, GROUP@, and EVERYONE@
into mode bits for, respectively, the user, group, and other, as
follows:
1. Set the read bit (MODE4_RUSR, MODE4_RGRP, or MODE4_ROTH) if and
only if ACE4_READ_DATA is set in the corresponding mask.
2. Set the write bit (MODE4_WUSR, MODE4_WGRP, or MODE4_WOTH) if and
only if ACE4_WRITE_DATA and ACE4_APPEND_DATA are both set in the
corresponding mask.
3. Set the execute bit (MODE4_XUSR, MODE4_XGRP, or MODE4_XOTH), if
and only if ACE4_EXECUTE is set in the corresponding mask.
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6.3.2.1. Discussion
Some server implementations also add bits permitted to named users
and groups to the group bits (MODE4_RGRP, MODE4_WGRP, and
MODE4_XGRP).
Implementations are discouraged from doing this, because it has been
found to cause confusion for users who see members of a file's group
denied access that the mode bits appear to allow. (The presence of
DENY ACEs may also lead to such behavior, but DENY ACEs are expected
to be more rarely used.)
The same user confusion seen when fetching the mode also results if
setting the mode does not effectively control permissions for the
owner, group, and other users; this motivates some of the
requirements that follow.
6.4. Requirements
The server that supports both mode and ACL must take care to
synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
ACEs which have respective who fields of "OWNER@", "GROUP@", and
"EVERYONE@" so that the client can see semantically equivalent access
permissions exist whether the client asks for owner, owner_group and
mode attributes, or for just the ACL.
In this section, much is made of the methods in Section 6.3.2. Many
requirements refer to this section. But note that the methods have
behaviors specified with "SHOULD". This is intentional, to avoid
invalidating existing implementations that compute the mode according
to the withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
actual permissions on owner, group, and other.
6.4.1. Setting the mode and/or ACL Attributes
In the case where a server supports the sacl or dacl attribute, in
addition to the acl attribute, the server MUST fail a request to set
the acl attribute simultaneously with a dacl or sacl attribute. The
error to be given is NFS4ERR_ATTRNOTSUP.
6.4.1.1. Setting mode and not ACL
When any of the nine low-order mode bits are subject to change,
either because the mode attribute was set or because the
mode_set_masked attribute was set and the mask included one or more
bits from the nine low-order mode bits, and no ACL attribute is
explicitly set, the acl and dacl attributes must be modified in
accordance with the updated value of those bits. This must happen
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even if the value of the low-order bits is the same after the mode is
set as before.
Note that any AUDIT or ALARM ACEs (hence any ACEs in the sacl
attribute) are unaffected by changes to the mode.
In cases in which the permissions bits are subject to change, the acl
and dacl attributes MUST be modified such that the mode computed via
the method in Section 6.3.2 yields the low-order nine bits (MODE4_R*,
MODE4_W*, MODE4_X*) of the mode attribute as modified by the
attribute change. The ACL attributes SHOULD also be modified such
that:
1. If MODE4_RGRP is not set, entities explicitly listed in the ACL
other than OWNER@ and EVERYONE@ SHOULD NOT be granted
ACE4_READ_DATA.
2. If MODE4_WGRP is not set, entities explicitly listed in the ACL
other than OWNER@ and EVERYONE@ SHOULD NOT be granted
ACE4_WRITE_DATA or ACE4_APPEND_DATA.
3. If MODE4_XGRP is not set, entities explicitly listed in the ACL
other than OWNER@ and EVERYONE@ SHOULD NOT be granted
ACE4_EXECUTE.
Access mask bits other those listed above, appearing in ALLOW ACEs,
MAY also be disabled.
Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do not affect
the permissions of the ACL itself, nor do ACEs of the type AUDIT and
ALARM. As such, it is desirable to leave these ACEs unmodified when
modifying the ACL attributes.
Also note that the requirement may be met by discarding the acl and
dacl, in favor of an ACL that represents the mode and only the mode.
This is permitted, but it is preferable for a server to preserve as
much of the ACL as possible without violating the above requirements.
Discarding the ACL makes it effectively impossible for a file created
with a mode attribute to inherit an ACL (see Section 6.4.3).
6.4.1.2. Setting ACL and not mode
When setting the acl or dacl and not setting the mode or
mode_set_masked attributes, the permission bits of the mode need to
be derived from the ACL. In this case, the ACL attribute SHOULD be
set as given. The nine low-order bits of the mode attribute
(MODE4_R*, MODE4_W*, MODE4_X*) MUST be modified to match the result
of the method Section 6.3.2. The three high-order bits of the mode
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(MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain unchanged.
6.4.1.3. Setting both ACL and mode
When setting both the mode (includes use of either the mode attribute
or the mode_set_masked attribute) and the acl or dacl attributes in
the same operation, the attributes MUST be applied in this order:
mode (or mode_set_masked), then ACL. The mode-related attribute is
set as given, then the ACL attribute is set as given, possibly
changing the final mode, as described above in Section 6.4.1.2.
6.4.2. Retrieving the mode and/or ACL Attributes
This section applies only to servers that support both the mode and
ACL attributes.
Some server implementations may have a concept of "objects without
ACLs", meaning that all permissions are granted and denied according
to the mode attribute, and that no ACL attribute is stored for that
object. If an ACL attribute is requested of such a server, the
server SHOULD return an ACL that does not conflict with the mode;
that is to say, the ACL returned SHOULD represent the nine low-order
bits of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
described in Section 6.3.2.
For other server implementations, the ACL attribute is always present
for every object. Such servers SHOULD store at least the three high-
order bits of the mode attribute (MODE4_SUID, MODE4_SGID,
MODE4_SVTX). The server SHOULD return a mode attribute if one is
requested, and the low-order nine bits of the mode (MODE4_R*,
MODE4_W*, MODE4_X*) MUST match the result of applying the method in
Section 6.3.2 to the ACL attribute.
6.4.3. Creating New Objects
If a server supports any ACL attributes, it may use the ACL
attributes on the parent directory to compute an initial ACL
attribute for a newly created object. This will be referred to as
the inherited ACL within this section. The act of adding one or more
ACEs to the inherited ACL that are based upon ACEs in the parent
directory's ACL will be referred to as inheriting an ACE within this
section.
Implementors should standardize on what the behavior of CREATE and
OPEN must be depending on the presence or absence of the mode and ACL
attributes.
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1. If just the mode is given in the call:
In this case, inheritance SHOULD take place, but the mode MUST be
applied to the inherited ACL as described in Section 6.4.1.1,
thereby modifying the ACL.
2. If just the ACL is given in the call:
In this case, inheritance SHOULD NOT take place, and the ACL as
defined in the CREATE or OPEN will be set without modification,
and the mode modified as in Section 6.4.1.2
3. If both mode and ACL are given in the call:
In this case, inheritance SHOULD NOT take place, and both
attributes will be set as described in Section 6.4.1.3.
4. If neither mode nor ACL are given in the call:
In the case where an object is being created without any initial
attributes at all, e.g. an OPEN operation with an opentype4 of
OPEN4_CREATE and a createmode4 of EXCLUSIVE4, inheritance SHOULD
NOT take place (note that EXCLUSIVE4_1 is a better choice of
createmode4, since it does permit initial attributes). Instead,
the server SHOULD set permissions to deny all access to the newly
created object. It is expected that the appropriate client will
set the desired attributes in a subsequent SETATTR operation, and
the server SHOULD allow that operation to succeed, regardless of
what permissions the object is created with. For example, an
empty ACL denies all permissions, but the server should allow the
owner's SETATTR to succeed even though WRITE_ACL is implicitly
denied.
In other cases, inheritance SHOULD take place, and no
modifications to the ACL will happen. The mode attribute, if
supported, MUST be as computed in Section 6.3.2, with the
MODE4_SUID, MODE4_SGID and MODE4_SVTX bits clear. If no
inheritable ACEs exist on the parent directory, the rules for
creating acl, dacl or sacl attributes are implementation defined.
If either the dacl or sacl attribute is supported, then the
ACL4_DEFAULTED flag SHOULD be set on the newly created
attributes.
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6.4.3.1. The Inherited ACL
If the object being created is not a directory, the inherited ACL
SHOULD NOT inherit ACEs from the parent directory ACL unless the
ACE4_FILE_INHERIT_FLAG is set.
If the object being created is a directory, the inherited ACL should
inherit all inheritable ACEs from the parent directory, those that
have ACE4_FILE_INHERIT_ACE or ACE4_DIRECTORY_INHERIT_ACE flag set.
If the inheritable ACE has ACE4_FILE_INHERIT_ACE set, but
ACE4_DIRECTORY_INHERIT_ACE is clear, the inherited ACE on the newly
created directory MUST have the ACE4_INHERIT_ONLY_ACE flag set to
prevent the directory from being affected by ACEs meant for non-
directories.
When a new directory is created, the server MAY split any inherited
ACE which is both inheritable and effective (in other words, which
has neither ACE4_INHERIT_ONLY_ACE nor ACE4_NO_PROPAGATE_INHERIT_ACE
set), into two ACEs, one with no inheritance flags, and one with
ACE4_INHERIT_ONLY_ACE set. (In the case of a dacl or sacl attribute,
both of those ACEs SHOULD also have the ACE4_INHERITED_ACE flag set.)
This makes it simpler to modify the effective permissions on the
directory without modifying the ACE which is to be inherited to the
new directory's children.
6.4.3.2. Automatic Inheritance
The acl attribute consists only of an array of ACEs, but the sacl
(Section 6.2.3) and dacl (Section 6.2.2) attributes also include an
additional flag field. The flag field applies to the entire sacl or
dacl; three flag values are defined:
const ACL4_AUTO_INHERIT = 0x00000001;
const ACL4_PROTECTED = 0x00000002;
const ACL4_DEFAULTED = 0x00000004;
and all other bits must be cleared. The ACE4_INHERITED_ACE flag may
be set in the ACEs of the sacl or dacl (whereas it must always be
cleared in the acl).
Together these features allow a server to support automatic
inheritance, which we now explain in more detail.
Inheritable ACEs are normally inherited by child objects only at the
time that the child objects are created; later modifications to
inheritable ACEs do not result in modifications to inherited ACEs on
descendents.
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However, the dacl and sacl provide an OPTIONAL mechanism which allows
a client application to propagate changes to inheritable ACEs to an
entire directory hierarchy.
A server that supports this performs inheritance at object creation
time in the normal way, and SHOULD set the ACE4_INHERITED_ACE flag on
any inherited ACEs as they are added to the new object.
A client application such as an ACL editor may then propagate changes
to inheritable ACEs on a directory by recursively traversing that
directory's descendants and modifying each ACL encountered to remove
any ACEs with the ACE4_INHERITED_ACE flag and to replace them by the
new inheritable ACEs (also with the ACE4_INHERITED_ACE flag set). It
uses the existing ACE inheritance flags in the obvious way to decide
which ACEs to propagate. (Note that it may encounter further
inheritable ACEs when descending the directory hierarchy, and that
those will also need to be taken into account when propagating
inheritable ACEs to further descendants.)
The reach of this propagation may be limited in two ways: first,
automatic inheritance is not performed from any directory ACL that
has the ACL4_AUTO_INHERIT flag cleared; and second, automatic
inheritance stops wherever an ACL with the ACL4_PROTECTED flag is
set, preventing modification of that ACL and also (if the ACL is set
on a directory) of the ACL on any of the object's descendants.
This propagation is performed independently for the sacl and the dacl
attributes; thus the ACL4_AUTO_INHERIT and ACL4_PROTECTED flags may
be independently set for the sacl and the dacl, and propagation of
one type of acl may continue down a hierarchy even where propagation
of the other acl has stopped.
New objects should be created with a dacl and a sacl that both have
the ACL4_PROTECTED flag cleared and the ACL4_AUTO_INHERIT flag set to
the same value as that on, respectively, the sacl or dacl of the
parent object.
Both the dacl and sacl attributes are RECOMMENDED, and a server may
support one without supporting the other.
A server that supports both the old acl attribute and one or both of
the new dacl or sacl attributes must do so in such a way as to keep
all three attributes consistent with each other. Thus the ACEs
reported in the acl attribute should be the union of the ACEs
reported in the dacl and sacl attributes, except that the
ACE4_INHERITED_ACE flag must be cleared from the ACEs in the acl.
And of course a client that queries only the acl will be unable to
determine the values of the sacl or dacl flag fields.
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When a client performs a SETATTR for the acl attribute, the server
SHOULD set the ACL4_PROTECTED flag to true on both the sacl and the
dacl. By using the acl attribute, as opposed to the dacl or sacl
attributes, the client signals that it may not understand automatic
inheritance, and thus cannot be trusted to set an ACL for which
automatic inheritance would make sense.
When a client application queries an ACL, modifies it, and sets it
again, it should leave any ACEs marked with ACE4_INHERITED_ACE
unchanged, in their original order, at the end of the ACL. If the
application is unable to do this, it should set the ACL4_PROTECTED
flag. This behavior is not enforced by servers, but violations of
this rule may lead to unexpected results when applications perform
automatic inheritance.
If a server also supports the mode attribute, it SHOULD set the mode
in such a way that leaves inherited ACEs unchanged, in their original
order, at the end of the ACL. If it is unable to do so, it SHOULD
set the ACL4_PROTECTED flag on the file's dacl.
Finally, in the case where the request that creates a new file or
directory does not also set permissions for that file or directory,
and there are also no ACEs to inherit from the parent's directory,
then the server's choice of ACL for the new object is implementation-
dependent. In this case, the server SHOULD set the ACL4_DEFAULTED
flag on the ACL it chooses for the new object. An application
performing automatic inheritance takes the ACL4_DEFAULTED flag as a
sign that the ACL should be completely replaced by one generated
using the automatic inheritance rules.
7. Single-server Namespace
This chapter 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 11.
7.1. Server Exports
On a UNIX server, the namespace describes all the files reachable by
pathnames under the root directory or "/". On a Windows NT 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
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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 server's
exports.
7.2. 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 a NFSv4.1
"pseudo file system" (see Section 7.3) 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.
7.3. 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 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
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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,
/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.
7.4. 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.
7.5. 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.
7.6. Exported Root
If the server's root file system is exported, one might conclude that
a pseudo file system is unneeded. This not necessarily so. Assume
the following file systems on a server:
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/ fs1 (exported)
/a fs2 (not exported)
/a/b fs3 (exported)
Because fs2 is not exported, fs3 cannot be reached with simple
LOOKUPs. The server must bridge the gap with a pseudo file system.
7.7. Mount Point Crossing
The server file system environment may be constructed in such a way
that one file system contains a directory which 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.
7.8. 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_NONAME, 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:
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/ (place holder/not exported)
/a/b (file system 1)
/a/b/MySecretProject (file system 2)
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 desired to prevent
knowledge of the existence of this file system to be very limited.
In this case the server should apply the same security policy to
/a/b. This allows for knowledge the existence of a file system to be
secured in cases where this is 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, which would make the that higher-level file system
inaccessible. 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 should 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 all of the pseudo file system accessible by all
of the valid security mechanisms.
Where there is concern about the security of data on the wire,
clients should use strong security mechanisms to access the pseudo
file system in order to prevent man-in-the-middle-attacks from
directing LOOKUPs within the pseudo file system from compromising the
existence of sensitive data, or getting access to data that the
client is sending by directing the client to send it using weak
security mechanisms.
8. 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 record locking the protocol becomes substantially more
dependent on proper management of state than the traditional
combination of NFS and NLM [XNFS]. These features include expanded
locking facilities, which provide some measure of interclient
exclusion, but the state is also valuable to providing other useful
features not readily providable using a stateless model. There are
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three components to making this state manageable:
o Clear division between client and server
o Ability to reliably detect inconsistency in state between client
and server
o Simple and robust recovery mechanisms
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
and the client receives prompt notification of them 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
which 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.
8.1. Client and Session ID
A client must establish a client ID (see Section 2.4) and then one or
more sessionids (see Section 2.10) before performing any operations
to open, lock, delegate, or obtain a layout for a file object. Each
sessionid 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.
8.2. Stateid Definition
When the server grants a lock of any type (including opens, record
locks, delegations, and layouts) it responds with a unique stateid,
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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
record locks on a file owned by a specific lock-owner and gotten via
an open for a specific open-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 (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 clientid are associated with a
common lease which represents the claim of those stateids and the
objects they represent to be maintained by the server. See
Section 8.3 for a discussion of leases.
The server may assign stateids independently for different clients
and 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.
8.2.1. Stateid Types
With the exception of special stateids, to be discussed later, 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, there is always an implied codicil that any
situation such as a client reboot, or lock revocation, allows the
guarantee to be voided.
o Stateids may represent opens of files.
Each stateid in this case represents the open for a given
clientid/openowner/filehandle triple. Such stateids are subject
to change (with consequent bumping of the seqid) in response to
OPENs that result in upgrade and OPEN_DOWNGRADE operations.
o Stateids may represent sets of byte-range locks.
All locks held on a particular file by a particular owner and all
gotten under the aegis of a particular open file are associated
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with a single stateid with the seqid being bumped as LOCK and
LOCKU operation affect that set of locks.
o Stateids may represent file delegations, which are recallable
guarantees by the server to the client, that other clients will
not reference, or will not modify a particular file, until the
delegation is returned. In NFSv4.1, file delegations may be
obtained on both regular and non-regular files.
A stateid represents a single delegation held by a client for a
particular filehandle.
o Stateids may represent directory delegations, which are recallable
guarantees by the server to the client, that other clients will
not modify the directory, until the delegation is returned.
A stateid represents a single delegation held by a client for a
particular directory filehandle.
o 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 all layouts held by a particular client for a
particular filehandle with a given layout type. The seqid is
updated as the contents of that set changes with LAYOUT
8.2.2. 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, to be discussed
below, 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 which
modify the set of locks the server is required to increment the seqid
field by one (1) whenever it returns a stateid for the same state
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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.
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 12.5.3) 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 canceled before the client even received an
indication that an upgrade had happened.
When a stateid is sent by the server to 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.
8.2.3. 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.
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The following combinations of "other" and "seqid" are defined in
NFSv4.1:
o 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 13.6).
o 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 requests. This stateid MUST NOT be used on
operations to data servers.
o 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 which
has returned a stateid value, the server MUST return the error
NFS4ERR_BAD_STATEID.
o 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 which has all zero 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.
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 current
filehandle does not match that associated with the current stateid,
the operation to which the stateid is passed will return
NFS4ERR_BAD_STATEID.
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8.2.4. Stateid Lifetime and Validation
Stateids must remain valid until either a client reboot or a server
reboot 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 the stateid remains a valid
designation of that revoked state until the client frees it by using
FREE_STATEID. Stateids associated with record 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 does a FREE_STATEID to cause the
stateid to be freed.
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 if forms 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.
o An index into a table of locking-state structures.
o A generation number which is incremented on each allocation of a
table entry for a particular use.
And then store in each table entry,
o The client ID with which the stateid is associated.
o The current generation number for the (at most one) valid stateid
sharing this index value.
o The filehandle of the file on which the locks are taken.
o An indication of the type of stateid (open, record lock, file
delegation, directory delegation, layout).
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o The last "seqid" value returned corresponding to the current
"other" value.
o 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 and
the appropriate error returned when necessary. Special and non-
special stateids are handled separately. (See Section 8.2.3 for a
discussion of special stateids).
Note that stateids are implicitly qualified by the current client ID,
as derived the 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 sessionid
which 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
either.
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:
o If the "other" and "seqid" fields do not match a defined
combination associated with a special stateid, the error
NFS4ERR_BAD_STATEID is returned.
o 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 in performed.
o 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
the error NFS4ERR_BAD_STATEID is also returned.
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o 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 or 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.
o If the table index field is outside the range of the associated
table, return NFS4ERR_BAD_STATEID.
o If the selected table entry is of a different generation than that
specified in the incoming stateid, return NFS4ERR_BAD_STATEID.
o If the selected table entry does not match the current filehandle,
return NFS4ERR_BAD_STATEID.
o If the client ID in the table entry does not match the client ID
associated with the current session, return NFS4ERR_BAD_STATEID.
o If the stateid represents revoked state, then return
NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or NFS4ERR_DELEG_REVOKED,
as appropriate.
o 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 which doesn't represent byte-range locks
is passed to the non-from_open case of LOCK or to LOCKU, or when a
stateid which does not represent an open is passed to CLOSE or
OPEN_DOWNGRADE. In such cases, the server MUST return
NFS4ERR_BAD_STATEID.
o If the "seqid" field is not zero, and it is greater than the
current sequence value corresponding the current "other" field,
return NFS4ERR_BAD_STATEID.
o If the "seqid" field is not zero, and it is less than the current
sequence value corresponding the current "other" field, return
NFS4ERR_OLD_STATEID.
o 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, such as open-owner and lock-owner
information, as well as information on the specific locks, such as
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open modes and byte ranges.
8.2.5. Stateid Use for I/O Operations
Clients performing I/O operations (and SETATTR's modifying the file
size), need to select an appropriate stateid based on the locks
(including opens and delegations) held by the client and the various
types of lock owners issuing the I/O requests.
The following rules, applied in order of decreasing priority, govern
the selection of the appropriate stateid. Note that the rules are
slightly different in the case of I/O to data servers when file
layouts are being used. (See Section 13.9.1).
o If the client holds a delegation for the file in question, the
delegation stateid should be used.
o Otherwise, if the lockowner corresponding entity (e.g. process)
issuing the I/O has a lock stateid for the associated open file,
then the lock stateid for that lockowner and open file should be
used.
o If there is no lock stateid, then the open stateid for the open
file in question is used.
o Finally, if none of the above apply, then a special stateid should
be used.
8.3. Lease Renewal
The purpose of a lease is to provide 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 its 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 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.
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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.
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 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 must
be no active COMPOUND operations on any such session.
Because the SEQUENCE operation is the basic mechanism to renew a
lease, and because if 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 18.46.3 for details).
o The status bits SEQ4_STATUS_CB_PATH_DOWN and
SEQ4_STATUS_CB_PATH_DOWN_SESSION indicate problems with the
backchannel which the the client may need to address in order to
receive callback requests.
o The status bits SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING and
SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED indicates actual problems with
GSS contexts for the backchannel which the client may have to
address to allow callback requests to be sent to it.
o 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.
o The status bit SEQ4_STATUS_LEASE_MOVE indicates that
responsibility for lease renewal has been transferred to one or
more new servers.
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o The status bit SEQ4_STATUS_RESTART_RECLAIM_NEEDED indicates that
due to server restart or reboot the client must reclaim locking
state.
o The status bit SEQ4_STATUS_BACKCHANNEL_FAULT indicates 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).
8.4. 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 or reboots. 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, either because the state presented is no longer valid
(NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID) or because
subsequent recovery of locks may make execution of the operation
inappropriate (NFS4ERR_GRACE).
8.4.1. 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 8.3, when a client has not failed and re-
establishes his 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 18.36.3 for a description how this is done. All
locks, including opens, record locks, delegations, and layouts
obtained by sessions using that client ID are associated with that
client ID.
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
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loss of locking state. As a result, the server is free to release
all locks held which are associated with the old client ID which 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
clientid 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.
8.4.2. Server Failure and Recovery
If the server loses locking state (usually as a result of a restart
or reboot), 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 through the establishment of mandatory locks,
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 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 8.1) and
re-establish its lock state after the CREATE_SESSION, with the
new client ID CREATE_SESSION succeeds, (Section 8.4.2.1).
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
client ID (see Section 8.1) and re-establish its lock state after
the CREATE_SESSION, with the new client ID, succeeds,
(Section 8.4.2.1).
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3. When a 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 8.1) and re-establish its lock state
(Section 8.4.2.1).
8.4.2.1. State Reclaim
When state information and the associated locks are lost as a result
of a server reboot, the protocol must provide a way to cause that
state to be re-established. The approach used is to define, for most
type 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 special period called the "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 is able to<
reliably determine (through state persistently maintained across
reboot 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.
Once a session is established using the new client ID, the client
will use reclaim-type locking requests (e.g. LOCK requests with
reclaim set to true and OPEN operations with a claim type of
CLAIM_PREVIOUS. See Section 9.9) 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 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 may get NFS4ERR_GRACE errors the operations
until the period of special handling is over. See Section 11.7.7 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 READ and WRITE
operations and non-reclaim locking requests (i.e. other LOCK and OPEN
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operations) with an error of NFS4ERR_GRACE, unless it is able to
guarantee that these may be done safely, as described below.
The grace period may last until all clients who are known to possibly
have had locks have done a global RECLAIM_COMPLETE operation,
indicating that they have finished reclaiming the locks they held
before the server reboot. This means that a client which has done a
RECLAIM_COMPLETE must be prepared to receive an NFS4ERR_GRACE when
attempting to acquire new locks. The server is assumed to maintain
in stable storage a list of clients who 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 before a time equal to the lease period in order to give
clients an opportunity to find out about the server reboot. Some
additional time in order to allow time to establish a new client ID
and session and to effect lock reclaims may be added. Note that
analogous rules apply to file system-specific grace periods discussed
in Section 11.7.7.
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 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 regular lock or READ or WRITE operation can be
safely processed.
For example, if the server maintained on stable storage summary
information on whether mandatory locks exist, either mandatory record
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 may be safely granted. If, in addition, it is known that no
mandatory record locks exist, either through information stored on
stable storage or simply because the server does not support such
locks, READ and WRITE requests may be safely processed during the
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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 operation may be
validly processed during the grace period because the fact of 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
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 is able to
perform I/O and non-reclaim locking requests within the grace period
as well as those that can not 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 reboot or 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.
8.4.3. Network Partitions and Recovery
If the duration of a network partition is greater than the lease
period provided by the server, the server will have not 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 not to interfere with
such conflicting requests.
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If the server chooses to delay freeing of lock state until there is a
conflict, it may either free all of the clients 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 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, when the client is able to communicate with
the server, it will receive an NFS4ERR_BADSESSION. Upon attempting
to create a new session, it would get an NFS4ERR_STALE_CLIENTID.
Upon creating the new clientid and new session it would attempt to
reclaim locks not be allowed to do so by the server.
Another possibility is for the server to maintain the session and
clientid but for all stateids held by the client to become invalid or
stale. Once the client is able to reach the server after such a
network partition, the status returned by the SEQUENCE operation will
indicate a loss of locking state. (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.
When the server adopts a finer-grained approach to revocation of
locks when lease have expired, only a subset of stateids will
normally become invalid during a network partition. When the client
is able to communicate with the server after such a network
partition, the status returned by the SEQUENCE operation will
indicate a partial loss of locking state. 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
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invalidated stateids.
When a network partition is combined with a server reboot, there are
edge conditions that place requirements on the server in order to
avoid silent data corruption following the server reboot. 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 lock.
4. Client B acquires a lock that would have conflicted with that of
Client A.
5. Client B releases its lock.
6. Server reboots.
7. Network partition between client A and server heals.
8. Client A connects to new server instance and finds out about
server reboot.
9. Client A reclaims its lock within the server's grace period.
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 reboots.
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.
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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 reboots 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 reboot.
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.
Solving the first and second edge conditions requires that the server
either always assumes after it reboots that some edge condition
occurs, and thus return 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
information some minimal information. For example, a server
implementation could, for each client, save in stable storage a
record containing:
o the co_ownerid field from the client_owner4 presented in the
EXCHANGE_ID operation.
o a boolean that indicates if the client's lease expired or if there
was administrative intervention (see Section 8.5) to revoke a
record lock, share reservation, or delegation and there has been
no acknowledgement, via FREE_STATEID, of such revocation.
o a boolean that indicates whether the client may have locks that it
believes to be reclaimable in situations 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
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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 reboots, the record that client A's lease expired
means that another client could have acquired a conflicting record
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 reboots 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 reboots 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
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, record 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 reboot, including the two noted
in this section, are detected. Erroneously recognizing a edge
condition and not allowing, when, with sufficient knowledge it
would be grantable, acceptable. Note that at this time, it is
not known if there are other edge conditions.
In the event that, after a server reboot, the server determines
that there is unrecoverable damage or corruption to the
information in stable storage, then for all clients and/or locks
which 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.
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When the client receives NFS4ERR_NO_GRACE, it could examine the
change attribute of the objects the client is trying to reclaim state
for, and use that to determine whether to re-establish the state via
normal OPEN or LOCK requests. This is acceptable provided the
client's operating environment allows it. In other words, the client
implementor is advised to document for his users the behavior. The
client could also inform the application that its record lock or
share reservations (whether they were delegated or not) have been
lost, such as via a UNIX signal, a GUI pop-up window, etc. See
Section 10.5 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 8.5.
8.5. 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 reboot or
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_STATEID on an
operation that takes a stateid as an argument or
NFS4ERR_STALE_CLIENTID on an operation that takes a sessionid or
client ID) and the client will proceed with normal crash recovery as
described in the Section 8.4.2.1.
The second occasion of lock revocation is the inability to renew the
lease before expiration, as discussed in Section 8.4.3. 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 18.46.3) 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
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either of these events occur, 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.
8.6. Short and Long Leases
When determining the time period for the server lease, the usual
lease tradeoffs apply. Short leases are 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). Long leases are 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 long leases
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, there can be a
longer period for leases to expire thus forcing conflicting requests
to wait.
Long leases are usable if the server is able to store lease state in
non-volatile memory. Upon recovery, the server can reconstruct the
lease state from its non-volatile memory and continue operation with
its clients and therefore long leases would not be an issue.
8.7. 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
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from lease times (e.g. if the client estimates the one-way
propagation delay as 200 msec, then it can assume that the lease is
already 200 msec old when it gets it). In addition, it will take
another 200 msec to get a response back to the server. So the client
must send a lease renewal or write data back to the server 400 msec
before the lease would expire.
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.
8.8. Vestigial Locking Infrastructure From V4.0
There are a number of operations and fields within existing
operations that no longer have a function in minor version one. In
one way or another, these changes are all due to the implementation
of sessions which provides 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.
o SETCLIENTID since its function has been replaced by EXCHANGE_ID.
o SETCLIENTID_CONFIRM since client ID confirmation now happens by
means of CREATE_SESSION.
o OPEN_CONFIRM because OPENs no longer require confirmation to
establish an owner-based sequence value.
o 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.
o RENEW because every SEQUENCE operation for a session causes lease
renewal, making a separate operation useless.
Also, there are a number of fields, present in existing operations
related to locking that have no use in minor version one. They were
used in minor version zero to perform functions now provided in a
different fashion.
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o Sequence ids used to sequence requests for a given state-owner and
to provide retry protection, now provided via sessions.
o 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.
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.
9. File Locking and Share Reservations
To support Win32 share reservations it is necessary to provide
operations which 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 which looks up or creates a file
and establishes locking state on the server.
9.1. 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
crashes 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 byte-range lock
request contains the heavyweight information required to establish a
lock and uniquely define the lock owner.
9.1.1. State-owner Definition
When opening a file or requesting a record lock, the client must
specify an identifier which 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
which, when concatenated with the current client ID uniquely defines
the owner of lock managed by the client. This may be a thread id,
process id, or other unique value.
Owners of opens and owners of record 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
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(represented by open_owner4 structures) and lock-owners (represented
by lock_owner4 structures).
Each open is associated with a specific open-owner while each record
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.
9.1.2. Use of the Stateid and Locking
All READ, WRITE and SETATTR operations contain a stateid. For the
purposes of this section, SETATTR operations which change the size
attribute of a file are treated as if they are writing the area
between the old and new size (i.e. the 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 these
operation 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 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 record locks and share reservations, are held
by the state-owner. If no state is established by the client, either
record lock or share reservation, a special stateid for anonymous
state (zero as "other" and "seqid") is used. (See Section 8.2.3 for
a description of 'special' stateids in general). Regardless whether
a stateid for anonymous state or a stateid returned by the server is
used, if there is a conflicting share reservation or mandatory record
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. Record 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, record
locks are required on the file before I/O is possible). When record
locks are advisory, they only prevent the granting of conflicting
lock requests and have no effect on READs or WRITEs. Mandatory
record locks, however, prevent conflicting I/O operations. When they
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are attempted, they are rejected with NFS4ERR_LOCKED. When the
client gets NFS4ERR_LOCKED on a file it knows it has the proper share
reservation for, it will need to send a LOCK request on the region of
the file that includes the region the I/O was to be performed on,
with an appropriate locktype (i.e. READ*_LT for a READ operation,
WRITE*_LT for a WRITE operation).
Note that for UNIX environments that support mandatory file locking,
the distinction between advisory and mandatory locking is subtle. In
fact, advisory and mandatory record locks are exactly the same in so
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) or exclusive (write)
record lock on the region it wishes to read 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 is done), and if there is, the server returns
NFS4ERR_LOCKED.
For Windows environments, there are no advisory record locks, so the
server always checks for record locks during I/O requests.
Thus, the NFSv4.1 LOCK operation does not need to distinguish between
advisory and mandatory record locks. It is the NFSv4.1 server's
processing of the READ and WRITE operations that introduces the
distinction.
Every stateid which is validly passed to READ, WRITE or SETATTR, with
the exception of special stateid values, defines an access mode for
the file (i.e. READ, WRITE, or READ-WRITE)
o For stateids associated with opens, this is the mode defined by
the original OPEN which caused the allocation of the open stateid
and as modified by subsequent OPENs and OPEN_DOWNGRADEs for the
same open-owner/file pair.
o For stateids returned by record lock requests, the appropriate
mode is the access mode for the open stateid associated with the
lock set represented by the stateid.
o For delegation stateids the access mode is based on the type of
delegation.
When a READ, WRITE, or SETATTR which specifies the size attribute, 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 which
set size), the server must verify that the access mode allows writing
and 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 WRITE only, 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 specify denial
of READs). Note that a server which does enforce the access mode
check on READs need not explicitly check for conflicting share
reservations since the existence of OPEN for read access guarantees
that no conflicting share reservation can exist.
The read bypass special stateid (all bits of "other" and "seqid" set
to one) stateid 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:
o A mandatory byte range lock is requested with range that conflicts
with the 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.
o A share reservation is requested which denies reading and or
writing and the corresponding is being performed.
o A delegation is to be granted and the delegation type would
prevent the I/O operation, i.e. READ and WRITE conflict with a
write delegation and WRITE conflicts with a read delegation.
When a client holds a delegation, it is particularly important to
make sure that the stateid sent conveys the association of operation
with the delegation, to avoid the delegation from being avoidably
recalled. When the delegation stateid, or a stateid open associated
with that delegation, or a stateid representing byte-range locks
derived form such an open is used, the server knows that the READ,
WRITE, or SETATTR does not conflict with the delegation, but is sent
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under the aegis of the delegation. Even though it is possible for
the server to determine from the clientid (gotten from the sessionid)
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.
9.2. 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. 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 and for reasons related to
the recovery of file locking state in the event of server failure.
As discussed in Section 8.4.2 below, 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.
9.3. Upgrading and Downgrading Locks
If a client has a write lock on a record, it can request an atomic
downgrade of the lock to a read lock via the LOCK request, 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 lock on a record, it can request an atomic
upgrade of the lock to a write lock via the LOCK request 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 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 request 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
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requesting application.
9.4. 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 new lock types are
added, READW and WRITEW, and 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
the lease period 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 needlessly 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 request, 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 requests. However, clients are not
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 server indicates, via the flag OPEN4_RESULT_MAY_NOTIFY_LOCK,
that CB_NOTIFY_LOCK callbacks will 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
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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 polling and the
server is under no obligation to reserve the lock for that particular
client.
9.5. Share Reservations
A share reservation is a mechanism to control access to a file. It
is a separate and independent mechanism from record 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 (deny NONE, READ, WRITE, or 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_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:
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;
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9.6. 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. For
clients that do not have a deny mode built into their open
programming interfaces, deny equal to NONE should be used.
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 record locks are held, the client SHOULD
release all locks before issuing 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 record 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 the client has the least access. For example, a file
opened with deny READ/WRITE using a filehandle obtained through
LOOKUP could only be read using the special read bypass stateid and
could not be written at all because it would not have a valid stateid
and the special anonymous stateid would not be allowed access.
9.7. 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 s single stateid whose "other" values matches that of
the original open. 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 which happen while the CLOSE is pending. Note that
the client, when issuing the OPEN, may not know that the same file is
in fact being opened. The above only applies if both OPENs result in
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the OPENed object being designated by the same filehandle.
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 must 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 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.
9.8. Parallel OPENs
Unlike the case of NFSv4.0, in which OPEN operations for the same
openowner are inherently serialized because of the owner-based seqid,
multiple OPENs for the same openowner 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 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 openowner 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.
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9.9. 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.
o 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.
o 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 10.2.1.
10. Client-Side Caching
Client-side caching of data, of file attributes, and of file names is
essential to providing good performance with the NFS protocol.
Providing distributed cache coherence is a difficult problem and
previous versions of the NFS protocol have not attempted it.
Instead, several NFS client implementation techniques have been used
to reduce 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.
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.
In addition, the NFSv4.1 protocol introduces a delegation mechanism
which allows many decisions normally made by the server to be made
locally by clients. This mechanism provides efficient support of the
common cases where sharing is infrequent or where sharing is read-
only.
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10.1. 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 reference to the server to find that no
conflicts exist is 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 file locking. Sending
file lock and unlock requests to the server as well as the read and
write requests necessary to make data caching consistent with the
locking semantics (see Section 10.3.2 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 file locking by applications.
The NFSv4.1 protocol provides more aggressive caching strategies with
the following design goals:
o Compatibility with a large range of server semantics.
o Providing the same caching benefits as previous versions of the
NFS protocol when unable to support the more aggressive model.
o 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 10.4).
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10.2. 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.
Once granted, a delegation behaves in many ways like a lock. There
is an associated lease that is subject to renewal together with all
of the other leases held by that client.
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.
o 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.
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o Operations done outside the NFSv4 protocol, due to, for example,
access by other protocols, or by local access, also need to result
in delegation recall when they make analogous changes to file
system data. 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.
o 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:
o For GETATTR, see Section 18.7.4.
o For OPEN, see Section 18.16.4.
o For READ, see Section 18.22.4.
o For REMOVE, see Section 18.25.4.
o For RENAME, see Section 18.26.4.
o For SETATTR, see Section 18.30.4.
o For WRITE, see Section 18.32.4.
On recall, the client holding the delegation must 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 NFSERR_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 10.4). 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 state for the file allows 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.
10.2.1. Delegation Recovery
There are three situations that delegation recovery must deal with:
o Client reboot or restart
o Server reboot or restart
o Network partition (full or backchannel-only)
In the event the client reboots or restarts, the failure to renew the
lease will result in the revocation of record locks and share
reservations. Delegations, however, may be treated a bit
differently.
There will be situations in which delegations will need to be
reestablished after a client reboots or restarts. The reason for
this is the client may have file data stored locally and this data
was associated with the previously held delegations. The client will
need to reestablish the appropriate file state on the server.
To allow for this type of client recovery, the server MAY extend the
period for delegation recovery beyond the typical lease expiration
period. This implies that requests from other clients that conflict
with these delegations will need to wait. Because the normal recall
process may require significant time for the client to flush changed
state to the server, other clients need be prepared for delays that
occur because of a conflicting delegation. This longer interval
would increase the window for clients to reboot and consult stable
storage so that the delegations can be reclaimed. For open
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delegations, such delegations are reclaimed using OPEN with a claim
type of CLAIM_DELEGATE_PREV. (See Section 10.5 and Section 18.16 for
discussion of open delegation and the details of OPEN respectively).
A server MAY support a claim type of CLAIM_DELEGATE_PREV, and if it
does, it MUST NOT remove delegations upon a CREATE_SESSION that
confirms a client ID created by EXCHANGE_ID, and instead 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 requests. The server that
supports CLAIM_DELEGATE_PREV MUST support the DELEGPURGE operation.
When the server reboots or restarts, delegations are reclaimed (using
the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to
record 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:
o Upon reclaim, a client reporting resources assigned to it by an
earlier server instance must be granted those resources.
o The server has unquestionable authority to determine whether
delegations are to be granted and, once granted, whether they are
to be continued.
o The use of callbacks is not to 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
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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 NFS4EER_EXPIRED, NFS4ERR_ADMIN_REVOKED, or
MFS4ERR_DELEG_REVOKED. It also may find out about delegation
revocation after a client reboot when it attempts to reclaim a
delegation and receives that same error. Note that in the case of a
revoked write open delegation, there are issues because data may have
been modified by the client whose delegation is revoked and
separately by other clients. See Section 10.5.1 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 8.4.3). This is
done to deal with the case in which a server reboots after revoking a
delegation but before the client holding the revoked delegation is
notified about the revocation.
10.3. 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 record 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
that those using these facilities depend upon.
10.3.1. Data Caching and OPENs
In order to avoid invalidating the sharing assumptions that
applications rely on, 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
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WRITE operation.
Furthermore, in the absence of open delegation (see Section 10.4),
two additional rules apply. Note that these rules are obeyed in
practice by many NFSv3 clients.
o 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 DENY=WRITE or BOTH thus
terminating a period in which other clients may have had the
opportunity to open the file with WRITE access. Clients may
choose to do the revalidation more often (i.e. at OPENs specifying
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 implementors may be tempted to use the
time_modify attribute and not change to validate cached data, so
that metadata changes do not spuriously invalidate clean data.
The implementor is cautioned in this approach. The change
attribute is guaranteed to change for each update to the 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.
o Second, modified data must be flushed to the server before closing
a file OPENed for write. This is complementary to the first rule.
If the data is not flushed at CLOSE, the revalidation done after
client OPENs as 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
reboot or restart and a CLOSEd file, it may not be possible to
retransmit the data to be written to the file. Hence, this
requirement.
10.3.2. Data Caching and File Locking
For those applications that choose to use file 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 file locking is used in a way
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that matches in an equivalent way the actual READ and WRITE
operations executed. This is as opposed to file 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
regions and protecting access to the two regions by file locks on
bytes zero and one. A lock for write on byte zero of the file would
represent the right to do READ and WRITE operations on the first
region. A lock for write on byte one of the file would represent the
right to do READ and WRITE operations on the second region. 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 file locking environment are:
o First, when a client obtains a file lock for a particular region,
the data cache corresponding to that region (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 region. A client might choose to invalidate all
of 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 region.
o Second, before releasing a write lock for a region, all modified
data for that region 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
modified block when only half of that block is within an area being
unlocked may cause invalid modification to the region outside the
unlocked area. This, in turn, may be part of a region 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 which 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 which the
client possesses may not be valid.
The data that is written to the server as a prerequisite to the
unlocking of a region 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.
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This is required because retransmission of the modified data after a
server reboot might conflict with a lock held by another client.
A client implementation may choose to accommodate applications which
use record locking in non-standard ways (e.g. using a record lock as
a global semaphore) by flushing to the server more data upon an 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 record
locks which 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 unlock. 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 record lock and those for which there
are modifications not covered by a record lock. Any writes done for
the former class of files must not include areas not locked and thus
not modified on the client.
10.3.3. Data Caching and Mandatory File Locking
Client side data caching needs to respect mandatory file locking when
it is in effect. The presence of mandatory file locking for a given
file is indicated when the client gets back NFS4ERR_LOCKED from a
READ or WRITE on a file it has an appropriate share reservation for.
When mandatory locking is in effect for a file, the client must check
for an appropriate file lock for data being read or written. If a
lock exists for the range being read or written, the client may
satisfy the request using the client's validated cache. If an
appropriate file 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 region, the request
should be subdivided into multiple pieces with each region (locked or
not) treated appropriately.
10.3.4. 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
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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
which 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:
o If GETATTR directed to two filehandles returns different values of
the fsid attribute, then the filehandles represent distinct
objects.
o 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.
o 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 which 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.
o If GETATTR directed to the two filehandles returns different
values for the fileid attribute, then they are distinct objects.
o Otherwise they are the same object.
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10.4. 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, the server may
receive 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 OPEN
should be delegated:
o The client must be able to respond to the server's callback
requests. The server will use the CB_NULL procedure for a test of
callback ability.
o The client must have responded properly to previous recalls.
o There must be no current open conflicting with the requested
delegation.
o There should be no current delegation that conflicts with the
delegation being requested.
o The probability of future conflicting open requests should be low
based on the recent history of the file.
o 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).
There are two types of open delegations, read and write. A read open
delegation allows a client to handle, on its own, requests to open a
file for reading that do not deny read access to others. Multiple
read open delegations may be outstanding simultaneously and do not
conflict. A write open delegation allows the client to handle, on
its own, all opens. Only one write open delegation may exist for a
given file at a given time and it is inconsistent with any read open
delegations.
When a client has a read open delegation, it is assured that neither
the contents, the attributes, 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 a write open delegation, it may modify the file
data locally since no other client will be accessing the file's data.
The client holding a write delegation may only locally affect file
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attributes which are intimately connected with the file data: size,
time_modify, change. Changes to other attributes must be reflected
on the server.
When a client has an open delegation, it does not send OPENs or
CLOSEs to the server but updates the appropriate status internally.
For a read open delegation, opens that cannot be handled locally
(opens for write or that deny read access) must be sent to the
server.
When an open delegation is made, the response to the OPEN contains an
open delegation structure which specifies the following:
o the type of delegation (read or write)
o space limitation information to control flushing of data on close
(write open delegation only, see Section 10.4.1.
o an nfsace4 specifying read and write permissions
o a stateid to represent the delegation for READ and WRITE
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.
When a request internal to the client is made to open a file and 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 open delegation
being denied so that the checks can be made by the server itself.
o The access and deny bits for the request and the file as described
in Section 9.5.
o 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:
o If the nfsace4 indicates that the open may be done, then it should
be granted without reference to the server.
o 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.
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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" may make it
incorrect to return the actual ACL of the file in the delegation
response.
The use of delegation together with various other forms of caching
creates the possibility that no server authentication 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, the client should be sure authentication 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.
10.4.1. Open Delegation and Data Caching
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 "read open
delegation" provides a guarantee that no OPEN for write and thus no
write has occurred. Similarly, when closing a file opened for write
and if write open delegation is in effect, the data written does not
have to be flushed 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 client SHOULD NOT use special stateids when
an open exists, delegation handling on the server can use the
clientid 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 recalled 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.
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server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT). This accounting
includes quotas. The introduction of delegations requires that a
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
flush 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 write open 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.
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.
10.4.2. Open Delegation and File Locks
When a client holds a write open delegation, lock operations are
performed locally. This includes those required for mandatory file
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 a read open delegation, lock operations are not
performed locally. All lock operations, including those requesting
non-exclusive locks, are sent to the server for resolution.
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10.4.3. Handling of CB_GETATTR
The server needs to employ special handling for a GETATTR where the
target is a file that has a write open delegation in effect. The
reason for this is that the client holding the 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 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.
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 a
write delegation:
o The value of the change attribute will be obtained from the server
and cached. Let this value be represented by c.
o The client will create a value greater than c that will be used
for communicating modified data is held at the client. Let this
value be represented by d.
o 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 in the file's data
or metadata in its cache. The client can return the same value
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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 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 a
write delegation:
o Upon providing a 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.
o 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.
o 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.
o 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
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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:
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.
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10.4.4. Recall of Open Delegation
The following events necessitate recall of an open delegation:
o Potentially conflicting OPEN request (or READ/WRITE done with
"special" stateid)
o SETATTR sent by another client
o REMOVE request for the file
o RENAME request for the file as either source or target of the
RENAME
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 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:
o 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.
o 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 the Section 18.16 which describes the OPEN" operation for
details.)
o If there are granted file locks, the corresponding LOCK operations
need to be performed. This applies to the write open delegation
case only.
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o For a write open delegation, if at the time of recall the file is
not open for write, 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.
o For a write open 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.
o With the write open 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 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 write open delegation, file locking imposes some
additional requirements. To precisely maintain the associated
invariant, it is required to flush any modified data in any region
for which a write lock was released while the write delegation was in
effect. However, because the write open 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
lock has been released while the write open delegation was in effect.
An implementation need not wait until delegation recall (or deciding
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. Only in the case of closing the
open that resulted in obtaining the delegation would clients be
likely to do this early, since, in that case, the close once done
will not be undone. 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.
10.4.5. 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
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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 a write delegation.
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
respond 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 recalled.
10.4.6. 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 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 read-write with 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
no lock inconsistent with that OPEN has been granted. On the other
hand, if an OPEN denying write 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.
If no opens exist for the file at the point the delegation is
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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 10.5.1 for additional
details.
10.4.7. Delegations via WANT_DELEGATION
In addition to providing delegations as part of the response 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 which 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, existing byte-range locks subordinate to an open
which becomes subordinate to a delegation, 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,
for existing byte-range locks subordinate to an open.
10.5. Data Caching and Revocation
When locks and delegations are revoked, the assumptions upon which
successful caching depend are no longer guaranteed. For any locks or
share reservations that have been revoked, the corresponding owner
needs to be notified. This notification includes applications with a
file open that has a corresponding delegation which has been revoked.
Cached data associated with the revocation must be removed from the
client. In the case of modified data existing in the client's cache,
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that data must be removed from the client without it 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 lock
after the revocation of the 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 lock 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 for
this is that an invariant for which an application depends on 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.
10.5.1. Revocation Recovery for Write Open Delegation
Revocation recovery for a write open delegation poses the special
issue of modified data in the client cache while the file is not
open. In this situation, any client which 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 name space 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 file
in question, such a saved copy of the client's view of the file may
be of particular value for recovery. In other case, recovery using a
copy of the file based partially on the client's cached data and
partially on the server copy as modified by other clients, will be
anything but straightforward, so clients may avoid saving file
contents in these situations or mark the results specially to warn
users of possible problems.
Saving of such modified data in delegation revocation situations may
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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.
10.6. Attribute Caching
The attributes discussed in this section do not include named
attributes. Individual named attributes are analogous to files and
caching of the data for these needs to be handled just as data
caching is for ordinary files. Similarly, LOOKUP results from an
OPENATTR directory are to be cached on the same basis as any other
pathnames and similarly for directory contents.
Clients may cache file attributes obtained from the server and use
them to avoid subsequent GETATTR requests. Such caching 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
cached. The exception to this are modifications to attributes that
are intimately connected with data caching. Therefore, 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. Normally such changes are not
propagated directly to the server but when the modified data is
flushed to the server, analogous attribute changes are made on the
server. When open delegation is in effect, the modified attributes
may be returned to the server in the response to a CB_RECALL call.
The result of local caching of attributes is that the attribute
caches maintained on individual clients will not be coherent.
Changes made in one order on the server may be seen in a different
order on one client and in a third order on a different client.
The typical file system application programming interfaces do not
provide means to atomically modify or interrogate attributes for
multiple files at the same time. The following rules provide an
environment where the potential incoherences mentioned above can be
reasonably managed. These rules are derived from the practice of
previous NFS protocols.
o All attributes for a given file (per-fsid attributes excepted) are
cached as a unit at the client so that no non-serializability can
arise within the context of a single file.
o An upper time boundary is maintained on how long a client cache
entry can be kept without being refreshed from the server.
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o 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 update
attributes indirectly. 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.
Note that if the full set of attributes to be cached is requested by
READDIR, the results can be cached by the client on the same basis as
attributes obtained via GETATTR.
A client may validate its cached version of attributes for a file by
fetching just 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 reason why time_access is also fetched is because
many servers operate in environments where the operation that updates
change does not update time_access. For example, POSIX file
semantics do not update access time when a file is modified by the
write system call. Therefore, the client that wants a current
time_access value should fetch it with change during the attribute
cache validation processing and update its cached time_access.
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.
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 this would mean that the
client will either eventually have to write the access time to the
server with bad performance effects, or it would 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
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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.
10.7. 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
whether the file is local file or is being access 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:
o 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 its cache is stale or not. 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.
o 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.
o If there is another client that is memory mapping the file, and if
that client is holding a write delegation, the same set of issues
as discussed in the previous two bullet items apply. So, when a
server does a CB_GETATTR to a file that the client has modified in
its cache, the response from CB_GETATTR will not necessarily be
accurate. As discussed earlier, the client's obligation is to
report that the file has been modified since the delegation was
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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, this weak obligation may not be
possible. A client MAY return stale information in CB_GETATTR
whenever the file is memory mapped.
o The mixture of memory mapping and file locking on the same file is
problematic. Consider the following scenario, where a page size
on each client is 8192 bytes.
* Client A memory maps first page (8192 bytes) of file X
* Client B memory maps first page (8192 bytes) of file X
* Client A write locks first 4096 bytes
* Client B write locks second 4096 bytes
* Client A, via a STORE instruction modifies part of its locked
region.
* Simultaneous to client A, client B executes a STORE on part of
its locked region.
Here the challenge is for each client to resynchronize to get a
correct view of the first page. In many operating environments, the
virtual memory management systems on each client only know a page is
modified, not that a subset of the page corresponding to the
respective lock regions has been modified. So it is not possible for
each client to do the right thing, which is to only write to the
server that portion of the page that is locked. For example, if
client A simply writes out the page, and then client B writes out the
page, client A's data is lost.
Moreover, if mandatory locking is enabled on the file, then we have a
different problem. When clients A and B execute the STORE
instructions, the resulting page faults require a record lock on the
entire page. Each client then tries to extend their locked range to
the entire page, which results in a deadlock. Communicating the
NFS4ERR_DEADLOCK error to a STORE instruction is difficult at best.
If a client is locking the entire memory mapped file, there is no
problem with advisory or mandatory record locking, at least until the
client unlocks a region in the middle of the file.
Given the above issues the following are permitted:
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o Clients and servers MAY deny memory mapping a file they know there
are record locks for.
o Clients and servers MAY deny a record lock on a file they know is
memory mapped.
o A client MAY deny memory mapping a file that it knows requires
mandatory locking for I/O. If mandatory locking is enabled after
the file is opened and mapped, the client MAY deny the application
further access to its mapped file.
10.8. Name and Directory Caching without Directory Delegations
Although NFSv4.1 defines a directory delegation facility, (described
in Section 10.9 below), servers are allowed not to implement that
facility and even where it is implemented, it may not be always be
functional, because of resource availability issues or other
constraints. Because of that, it is important to understand how name
and directory caching are done in the absence of directory
delegations. Those topics are discussed in the next in
Section 10.8.1.
10.8.1. 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 on 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 may 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
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determining, given proper care, whether other clients are modifying
the directory is 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 next subsequent operation modifying that
directory. When these are equal, the client is assured that no other
client is modifying the directory in question.
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, since two such operations which are recognized as
complete in a different order than they were actually performed,
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 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.
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10.8.2. 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:
o Cached READDIR information for a directory which 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 of READDIR that
contributes to the cache.
o 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.
10.9. Directory Delegations
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10.9.1. Introduction to Directory Delegations
Directory caching for the NFSv4.1 protocol, as previously described,
is similar to file caching in previous versions. Clients typically
cache directory information for a duration determined by the client.
At the end of a predefined timeout, 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. Furthermore, 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 having to make an RPC call. By caching name and
inode information about most recently looked up entries in the
Directory Name Lookup Cache (DNLC), clients do not need to send
LOOKUP calls to the server every time these 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 must make RPC calls 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. 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.
Delegation of directory contents is a RECOMMENDED feature of NFSv4.1.
Directory delegations provide similar traffic reduction benefits as
with file delegations. By allowing clients to cache directory
contents (in a read-only fashion) while being notified of changes,
the client can avoid making frequent requests to interrogate the
contents of slowly-changing directories, reducing network traffic and
improving client performance. It can also simplify the task of
determining whether other clients are making changes to the directory
when the client itself is making many changes to the directory and
changes are not serialized.
Directory delegations allow improved namespace cache consistency to
be achieved through delegations and synchronous recalls, in the
absence of notifications. In addition, if time-based consistency is
sufficient, asynchronous notifications can provide performance
benefits for the client, and possibly the server, under some common
operating conditions such as slowly-changing and/or very large
directories.
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10.9.2. Directory Delegation Design
NFSv4.1 introduces the GET_DIR_DELEGATION (Section 18.39) operation
to allow the client to ask for a directory delegation. The
delegation covers directory attributes and all entries in the
directory. If either of these change, the delegation will be
recalled synchronously. The operation causing the recall will have
to wait before the recall is complete. Any changes to directory
entry attributes will not cause the delegation to be recalled.
In addition to asking for delegations, a client can also ask for
notifications for certain events. These events include changes to
directory attributes and/or its contents. If a client asks for
notification for a certain event, the server will notify the client
when that event occurs. This will not result in the delegation being
recalled for that client. The notifications are asynchronous and
provide a way of avoiding recalls in situations where a directory is
changing enough that the pure recall model may not be effective while
trying to allow the client to get substantial benefit. In the
absence of notifications, once the delegation is recalled the client
has to refresh its directory cache which might not be very efficient
for very large directories.
The delegation is read-only and the client may not make changes to
the directory other than by performing NFSv4.1 operations that modify
the directory or the associated file attributes so that the server
has knowledge of these changes. In order to keep the client
namespace synchronized with the server, the server will, if the
client has requested notifications, notify the client holding the
delegation of the changes made as a result. This is to avoid any
need for subsequent GETATTR or READDIR calls to the server. If a
single client is holding the delegation and that client makes any
changes to the directory (i.e. the changes are made via operations
sent though a session associated with the clientid holding the
delegation), the delegation will not be recalled. Multiple clients
may hold a delegation on the same directory, but if any such client
modifies the directory, the server MUST recall the delegation from
the other clients, unless those clients have made provisions to be
notified of that sort of modification.
Delegations can be recalled by the server at any time. Normally, the
server will recall the delegation when the directory changes in a way
that is not covered by the notification, or when the directory
changes and notifications have not been requested. If another client
removes the directory for which a delegation has been granted, the
server will recall the delegation.
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10.9.3. Attributes in Support of Directory Notifications
See Section 5.10 for a description of the attributes associated with
directory notifications.
10.9.4. Directory Delegation Recall
The server will recall the directory delegation by sending a callback
to the client. It will use the same callback procedure as used for
recalling file delegations. The server will recall the delegation
when the directory changes in a way that is not covered by the
notification. However the server need not recall the delegation if
attributes of an entry within the directory change.
If the server notices that handing out a delegation for a directory
is causing too many notifications to be sent out, it may decide not
to hand out delegations for that directory, or recall those already
granted. If a client tries to remove the directory for which a
delegation has been granted, the server will recall all associated
delegations.
The implementation sections for a number of operations describe
situations in which notification or delegation recall would be
required under some common circumstances. In this regard, a similar
set of caveats to those listed in Section 10.2 apply.
o For CREATE, see Section 18.4.4.
o For LINK, see Section 18.9.4.
o For OPEN, see Section 18.16.4.
o For REMOVE, see Section 18.25.4.
o For RENAME, see Section 18.26.4.
o For SETATTR, see Section 18.30.4.
10.9.5. Directory Delegation Recovery
Crash recovery 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 applies to directories protected by read delegations
and notifications. Thus, no provision is made for reclaiming
directory delegations in the event of client or server failure. The
client can simply establish a directory delegation in the same
fashion as was done initially.
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11. Multi-Server Namespace
NFSv4.1 supports attributes that allow a namespace to extend beyond
the boundaries of a single server. It is RECOMMENDED 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 namespace are perfectly acceptable. Use of
multi-server namespaces can provide many advantages, however, by
separating a file system's logical position in a namespace from the
(possibly changing) logistical and administrative considerations that
result in particular file systems being located on particular
servers.
11.1. Location Attributes
NFSv4 contains RECOMMENDED attributes that allow file systems on one
server to be associated with one or more instances of that file
system on other servers. These attributes specify such file system
instances by specifying a server address target (either as a DNS name
representing one or more IP addresses or as a literal IP address)
together with the path of that file system within the associated
single-server namespace.
The fs_locations_info RECOMMENDED attribute allows specification of
one or more file system instance locations where the data
corresponding to a given file system may be found. This attribute
provides to the client, in addition to information about file system
instance locations, significant information about the various file
system instance choices (e.g. priority for use, writability,
currency, etc.). It also includes information to help the client
efficiently effect as seamless a transition as possible among
multiple file system instances, when and if that should be necessary.
The fs_locations RECOMMENDED attribute is inherited from NFSv4.0 and
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 to be preferred.
11.2. File System Presence or Absence
A given location in an NFSv4 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
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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
which 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
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 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 RECOMMENDED file system attribute fs_status can be used to
interrogate the present/absent status of a given file system.
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11.3. 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.
11.3.1. 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.
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 RECOMMENDED
attributes 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 changes.
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 one
which 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.
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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 which 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.
11.3.2. 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:
o 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.
o 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.
o 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.
o 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.
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11.4. Uses of Location Information
The location-bearing attributes (fs_locations and fs_locations_info),
provide, together with the possibility of absent file systems, a
number of important facilities in providing reliable, manageable, and
scalable data access.
When a file system is present, these attributes can provide
alternative locations, 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 file system
impossible or otherwise impractical. Under some circumstances
multiple alternative locations may be used simultaneously to provide
higher performance access to the file system in question. Provision
of such alternate locations is referred to as "replication" although
there are cases in which replicated sets of data are not in fact
present, and the replicas are instead different paths to the same
data.
When a file system is present and becomes absent, clients can be
given the opportunity to have continued access to their data, at an
alternate location. In this case, a continued attempt to use the
data in the now-absent file system will result in an NFS4ERR_MOVED
error and at that point the successor locations (typically only one
but multiple choices are possible) can be fetched and used to
continue access. Transfer of the file system contents to the new
location is referred to as "migration", but it should be kept in mind
that there are cases in which this term can be used, like
"replication", when there is no actual data migration per se.
Where a file system was not previously present, 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. Designation
of such a location, in place of an absent file system, is called
"referral".
Because client support for location-related attributes is OPTIONAL, a
server may (but is not required 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 data
passed in the EXCHANGE_ID operation (See Section 18.35.3).
11.4.1. File System Replication
The fs_locations and fs_locations_info attributes provide alternative
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,
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the client should obtain the value of the set of alternate locations
by interrogating the fs_locations or fs_locations_info attribute,
with the latter being preferred.
In the event that 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 his data. Depending on
specific attributes of these alternate locations, as indicated within
the fs_locations_info attribute, multiple locations may be used
simultaneously, to provide higher performance through the
exploitation of multiple paths between client and target file system.
The alternate locations may be physical replicas of the (typically
read-only) file system data, or they may reflect alternate paths to
the same server or 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 these different modes
of file system transition are 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 below.
Multiple server addresses, whether they are derived from a single
entry with a DNS name representing a set of IP addresses, or from
multiple entries each with its own server address may correspond to
the same actual server. The fact that two addresses correspond to
the same server is shown by a common so_major_id field within the
eir_server_owner field returned by EXCHANGE_ID (see Section 18.35.3).
For a detailed discussion of how server address targets interact with
the determination of server identity specified by the server owner
field, see Section 11.5.
11.4.2. File System Migration
When a file system is present and becomes absent, clients can be
given the opportunity to have continued access to their data, at an
alternate location, as specified by the fs_locations or
fs_locations_info attribute. Typically, a client will be accessing
the file system in question, get an NFS4ERR_MOVED error, and then use
the fs_locations or fs_locations_info attribute to determine the new
location of the data. When fs_locations_info is used, additional
information will be available which will define the nature of the
client's handling of the transition to a new server.
Such migration can be helpful in providing load balancing or general
resource reallocation. The protocol does not specify how the file
system will be moved between servers. It is anticipated that a
number of different server-to-server transfer mechanisms might be
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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.
The new location may be an alternate communication path to the same
server, or, in the case of various forms of server clustering,
another server providing access to the same physical file system.
The client's responsibilities in dealing with this transition depend
on the specific nature of the new access path and how and whether
data was in fact migrated. These issues will be discussed in detail
below.
When multiple server addresses correspond to the same actual server,
as shown by a common value for the so_major_id field of the
eir_server_owner field returned by EXCHANGE_ID, the location or
locations may designate alternate server addresses in the form of
specific server network addresses. These could be used to access the
file system in question at those addresses and when it is no longer
accessible at the original address.
Although a single successor location is typical, multiple locations
may be provided, together with information that allows priority among
the choices to be indicated, via information in the fs_locations_info
attribute. Where suitable clustering mechanisms make it possible to
provide multiple identical file systems or paths to them, this allows
the client the opportunity to deal with any resource or
communications issues that might limit data availability.
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.
11.4.3. Referrals
Referrals provide a way of placing a file system in a location within
the namespace essentially without respect to its physical location on
a given server. This allows a single server or a set of servers to
present a multi-server namespace that encompasses file systems
located on multiple servers. Some likely uses of this include
establishment of site-wide or organization-wide namespaces, or even
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knitting such together into a truly global namespace.
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 that file system is absent. When this occurs,
typically by receiving the error NFS4ERR_MOVED, the actual location
or locations of the file system can be determined by fetching the
fs_locations or fs_locations_info attribute.
The locations-related 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
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 may 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.
When the fs_locations_info attribute indicates that there are
multiple possible targets listed, the relationships among them may be
important to the client in selecting the one to use. The same rules
specified in Section 11.4.1 defining the appropriate standards for
the data propagation, apply to these multiple replicas as well. For
example, the client might prefer a writable 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 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 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. Any segment or the top-level referral file system may use
replicated referral file systems for higher availability.
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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 location.
There are however facilities provided which allow different clients
to be directed to different sets of data, so as to adapt to such
client characteristics as CPU architecture.
11.5. Location Entries and Server Identity
As mentioned above, a single location entry may have a server address
target in the form of a DNS name which may represent multiple IP
addresses, while multiple location entries may have their own server
address targets, that reference the same server. Whether two IP
addresses designate the same server is indicated by the existence of
a common so_major_id field within the eir_server_owner field returned
by EXCHANGE_ID (see Section 18.35.3), subject to further
verification, for details of which see Section 2.10.4.
When multiple addresses for the same server exist, the client may
assume that for each file system in the namespace of a given server
network address, there exist file systems at corresponding namespace
locations for each of the other server network addresses. It may do
this even in the absence of explicit listing in fs_locations and
fs_locations_info. Such corresponding file system locations can be
used as alternate locations, just as those explicitly specified via
the fs_locations and fs_locations_info attributes. Where these
specific addresses are explicitly designated in the fs_locations_info
attribute, the conditions of use specified in this attribute (e.g.
priorities, specification of simultaneous use) may limit the client's
use of these alternate locations.
If a single location entry designates multiple server IP addresses,
the client cannot assume that these addresses are multiple paths to
the same server. In most case they will be, but the client MUST
verify that before acting on that assumption. When two server
addresses are designated by a single location entry and they
correspond to different servers, this normally indicates some sort of
misconfiguration, and so the client should avoid use such location
entries when alternatives are available. When they are not, clients
should pick one of IP addresses and use it, without using others that
are not directed to the same server.
11.6. Additional Client-side Considerations
When clients make use of servers that implement referrals,
replication, and migration, care should be taken so 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
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file system despite the fact that it contains a number of server-side
file systems which 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 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 issuing a LOOKUPP call 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 issuing a LOOKUPP to
the current server. This 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 lookup 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.
11.7. Effecting File System Transitions
Transitions between file system instances, whether due to switching
between replicas upon server unavailability, or in response to
server-initiated migration events are best dealt with together. This
is so even though for the server pragmatic considerations will
normally force different implementation strategies for planned and
unplanned transitions. Even though the prototypical use cases of
replication and migration contain distinctive sets of features, when
all possibilities for these operations are considered, there is an
underlying unity of these operations, from the client's point of
view, that makes treating them together desirable.
A number of methods are possible for servers to replicate data and to
track client state in order to allow clients to transition between
file system instances with a minimum of disruption. Such methods
vary between those that use inter-server clustering techniques to
limit the changes seen by the client, to those that are less
aggressive, use more standard methods of replicating data, and impose
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a greater burden on the client to adapt to the transition.
The NFSv4.1 protocol does not impose choices on clients and servers
with regard to that spectrum of transition methods. In fact, there
are many valid choices, depending on client and application
requirements and their interaction with server implementation
choices. The NFSv4.1 protocol does define the specific choices that
can be made, how these choices are communicated to the client and how
the client is to deal with any discontinuities.
In the sections below, references will be made to various possible
server implementation choices as a way of illustrating the transition
scenarios that clients may deal with. The intent here is not to
define or limit server implementations but rather to illustrate the
range of issues that clients may face.
In the discussion below, references will be made to a file system
having a particular property or of two file systems (typically the
source and destination) belonging to a common class of any of several
types. Two file systems that belong to such a class share some
important aspect of file system behavior that clients may depend upon
when present, to easily effect a seamless transition between file
system instances. Conversely, where the file systems do not belong
to such a common class, the client has to deal with various sorts of
implementation discontinuities which may cause performance or other
issues in effecting a transition.
Where the fs_locations_info attribute is available, such file system
classification data will be made directly available to the client.
See Section 11.10 for details. When only fs_locations is available,
default assumptions with regard to such classifications have to be
inferred. See Section 11.9 for details.
In cases in which one server is expected to accept opaque values from
the client that originated from another server, the servers SHOULD
encode the "opaque" values in big endian byte order. If this is
done, servers acting as replicas or immigrating file systems will be
able to parse values like stateids, directory cookies, filehandles,
etc. even if their native byte order is different from that of other
servers cooperating in the replication and migration of the file
system.
11.7.1. File System Transitions and Simultaneous Access
When a single file system may be accessed at multiple locations,
whether this is because of an indication of file system identity as
reported by the fs_locations or fs_locations_info attributes or
because two file systems instances have corresponding locations on
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server addresses which connect to the same server (as indicated by a
common so_major_id field in the eir_server_owner field returned by
EXCHANGE_ID), the client will, depending on specific circumstances as
discussed below, either:
o The client accesses multiple instances simultaneously, as
representing alternate paths to the same data and metadata.
o The client accesses one instance (or set of instances) and then
transitions to an alternative instance (or set of instances) as a
result of network issues, server unresponsiveness, or server-
directed migration. The transition may involve changes in
filehandles, fileids, the change attribute, and/or locking state,
depending on the attributes of the source and destination file
system instances, as specified in the fs_locations_info attribute.
Which of these choices is possible, and how a transition is effected,
is governed by equivalence classes of file system instances as
reported by the fs_locations_info attribute, and, for file systems
instances in the same location within multiple single-server
namespace as indicated by the so_major_id field in the
eir_server_owner field returned by EXCHANGE_ID.
11.7.2. Simultaneous Use and Transparent Transitions
When two file system instances have the same location within their
respective single-server namespaces and those two server network
addresses designate the same server (as indicated by the same
so_major_id value in the eir_server_owner value returned in response
to EXCHANGE_ID), those file systems instances can be treated as the
same, and either used together simultaneously or serially with no
transition activity required on the part of the client. In this case
we refer to the transition as "transparent" and the client in
transferring access from to the other is acting as it would in the
event that communication is interrupted, with a new connection and
possibly a new session being established to continue access to the
same file system.
Whether simultaneous use of the two file system instances is valid is
controlled by whether the fs_locations_info attribute shows the two
instances as having the same _simultaneous-use_ class. See
Section 11.10.1 for information about the definition of the various
use classes, including the _simultaneous-use_ class.
Note that for two such file systems, 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
instances with different _handle_, _fileid_, _write-verifier_,
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_change_, _readdir_ classes, indicates a serious problem and the
client, if it allows transition to the file system instance at all,
must not treat this as a transparent transition. The server SHOULD
NOT indicate that these instances belong to different _handle_,
_fileid_, _write-verifier_, _change_, _readdir_ classes, whether the
two instances are shown belonging to the same _simultaneous-use_
class or not.
Where these conditions do not apply, a non-transparent file system
instance transition is required with the details depending on the
respective _handle_, _fileid_, _write-verifier_, _change_, _readdir_
classes of the two file system instances and whether the two servers
address in question have the same eir_server_scope value as reported
by EXCHANGE_ID.
11.7.2.1. Simultaneous Use of File System Instances
When the conditions above hold, in either of the following two cases,
the client may use the two file system instances simultaneously.
o The fs_locations_info attribute does not contain separate per-
network-address entries for file systems instances at the distinct
network addresses. This includes the case in which the
fs_locations_info attribute is unavailable. In this case, the
fact that the two server addresses connect to the same server (as
indicated by the two addresses sharing the same the so_major_id
value and subsequently confirmed as described in in
Section 2.10.4) justifies simultaneous use and there is no
fs_locations_info attribute information contradicting that.
o The fs_locations_info attribute indicates that two file system
instances belong to the same _simultaneous-use_ class.
In this case, the client may use both file system instances
simultaneously, as representations of the same file system, whether
that happens because the two network addresses connect to the same
physical server or because different servers connect to clustered
file systems and export their data in common. When simultaneous use
is in effect, any change made to one file system instance must be
immediately reflected in the other file system instance(s). Locks
are treated as part of a common lease, associated with a common
client ID. Depending on the details of the eir_server_owner returned
by EXCHANGE_ID, the two server instances may be accessed by different
sessions or a single session in common.
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11.7.2.2. Transparent File System Transitions
When the conditions above hold and the fs_locations_info attribute
explicitly shows the file system instances for these distinct network
addresses as belonging to different _simultaneous-use_ classes, the
file system instances should not be used by the client
simultaneously, but rather serially with one being used unless and
until communication difficulties, lack of responsiveness, or an
explicit migration event causes another file system instance (or set
of file system instances sharing a common _simultaneous-use_ class)
to be used.
When a change of file system instance is to be done, the client will
use the same client ID already in effect. If it already has
connections to the new server address, these will be used. Otherwise
new connections to existing sessions or new sessions associated with
the existing client ID are established as indicated by the
eir_server_owner returned by EXCHANGE_ID.
In all such transparent transition cases, the following apply:
o Filehandles stay the same if persistent and if volatile are only
subject to expiration, if they would be in the absence of file
system transition.
o Fileid values do not change across the transition.
o The file system will have the same fsid in both the old and new
locations.
o Change attribute values are consistent across the transition and
do not have to be refetched. When change attributes indicate that
a cached object is still valid, it can remain cached.
o Client and state identifiers retain their validity across the
transition, except where their staleness is recognized and
reported by the new server. Except where such staleness requires
it, no lock reclamation is needed. Any such staleness is an
indication that the server should be considered to have rebooted
and is reported as discussed in Section 8.4.2.
o Write verifiers are presumed to retain their validity and can be
used to compare with verifiers returned by COMMIT on the new
server, with the expectation that if COMMIT on the new server
returns an identical verifier, then that server has all of the
data unstably written to the original server and has committed it
to stable storage as requested.
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o Readdir cookies are presumed to retain their validity and can be
presented to subsequent READDIR requests together with the readdir
verifier with which they are associated. When the verifier is
accepted as valid, the cookie will continue the READDIR operation
so that the entire directory can be obtained by the client.
11.7.3. 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 co-operation 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
fh_expire_type attribute and supersedes the specification of
FH4_VOL_MIGRATION bit, which only affects behavior when
fs_locations_info is not available.
When there is co-operation 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 while are
only volatile due to the FH4_VOL_MIGRATION bit) are subject to
expiration on the target server.
11.7.4. 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 will be consistent across the transition while in the
analogous multi-vendor transitions they will 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 API's 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), and the result of this 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,
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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
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.
11.7.5. Fsids and File System Transitions
Since fsids are generally only unique within a per-server basis, it
is likely that they will change during a file system transition. One
exception is the case of transparent transitions, but in that case we
have multiple network addresses that are defined as the same server
(as specified by a common value of the so_major_id field of
eir_server_owner). 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
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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.
11.7.5.1. File System Splitting
When a file system transition is made and the fs_locations_info
indicates that the file system in question may 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 may maintain the fsids passed to existing applications by
mapping all of the fsids for the descendent file systems to the
common fsid used for the original file system.
Splitting a file system may 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.
11.7.6. 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 gotten on refetch no conclusions can 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 as 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.
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11.7.7. Lock State and File System Transitions
In a file system transition, the client needs to handle cases in
which the two servers have cooperated in state management and in
which they have not. Cooperation by two servers in state management
requires coordination of client IDs. Before the client attempts to
use a client ID associated with one server in a request to the server
of the other file system, it must eliminate the possibility that two
non-cooperating servers have assigned the same client ID by accident.
The client needs to compare the eir_server_scope values returned by
each server. If the scope values do not match, then the servers have
not cooperated in state management. If the scope values match, then
this indicates the servers have cooperated in assigning client IDs to
the point that they will reject client IDs that refer to state they
do not know about.
In the case of migration, the servers involved in the migration of a
file system SHOULD transfer all server state from the original to the
new server. When this is done, it must be done in a way that is
transparent to the client. With replication, such a degree of common
state is typically not the case. Clients, however should use the
information provided by the eir_server_scope returned by EXCHANGE_ID
to determine whether such sharing may be in effect, rather than
making assumptions based on the reason for the transition.
This state transfer will reduce disruption to the client when a file
system transition occurs. If the servers are successful in
transferring all state, the client can attempt to establish sessions
associated with the client ID used for the source file system
instance. If the server accepts that as a valid client ID, then the
client may use the existing stateids associated with that client ID
for the old file system instance in connection with that same client
ID in connection with the transitioned file system instance.
When the two servers belong to the same server scope, it does not
mean that when dealing with the transition, the client will not have
to reclaim state. However it does mean that the client may proceed
using his current client ID when establishing communication with the
new server and the new server will either recognize the client ID as
valid, or reject it, in which case locks must be reclaimed by the
client.
File systems co-operating in state management may actually share
state or simply divide the id space so as to recognize (and reject as
stale) each other's stateids and client IDs. Servers which do share
state may not do so under all conditions or at all times. The
requirement for the server is that if it cannot be sure in accepting
a client ID that it reflects the locks the client was given, it must
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treat all associated state as stale and report it as such to the
client.
When the two file system instances are on servers that do not share a
server scope value the client must establish a new client ID on the
destination, if it does not have one already, and reclaim locks if
possible. In this case, old stateids and client IDs should not be
presented to the new server since there is no assurance that they
will not conflict with IDs valid on that server.
In either case, when actual locks are not known to be maintained, the
destination server may establish a grace period specific to the given
file system, with non-reclaim locks being rejected for that file
system, even though normal locks are being granted for other file
systems. Clients should not infer the absence of a grace period for
file systems being transitioned to a server from responses to
requests for other file systems.
In the case of lock reclamation for a given file system after a file
system transition, edge conditions can arise similar to those for
reclaim after server reboot (although in the case of the planned
state transfer associated with migration, these can be avoided by
securely recording lock state as part of state migration). Unless
the destination server can guarantee that locks will not be
incorrectly granted, the destination server should not allow lock
reclaims and avoid establishing a grace period.
Once all locks have been reclaimed, or there were no locks to
reclaim, the client indicates that there are no more reclaims to be
done for the file system in question by issuing a RECLAIM_COMPLETE
operation with the one_fs parameter set to true. Once this has been
done, non-reclaim locking operations may be done, and any subsequent
request to do reclaims will be rejected with the error
NFS4ERR_NO_GRACE.
Information about client identity may be propagated between servers
in the form of client_owner4 and associated verifiers, under the
assumption that the client presents the same values to all the
servers with which it deals.
Servers are encouraged to provide facilities to allow locks to be
reclaimed on the new server after a file system transition. Often,
however, in cases in which the two servers do not share a server
scope value, such facilities may not be available and client should
be prepared to re-obtain locks, even though it is possible that the
client may have his LOCK or OPEN request denied due to a conflicting
lock.
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The consequences of having no facilities available to reclaim locks
on the sew server will depend on the type of environment. In some
environments, such as the transition between read-only file systems,
such denial of locks should not pose large difficulties in practice.
When an attempt to re-establish a lock on a new server is denied, the
client should treat the situation as if his original lock had been
revoked. Note that when the lock is granted, the client cannot
assume that no conflicting lock could have been granted in the
interim. Where change attribute continuity is present, the client
may check the change attribute to check for unwanted file
modifications. Where even this is not available, and the file system
is not read-only, a client may reasonably treat all pending locks as
having been revoked.
11.7.7.1. 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.
In order for the client to schedule renewal of leases where there is
locking state that may have been relocated to the new server, the
client must find out about lease relocation before those leases
expire. To accomplish this, the SEQUENCE operation will return the
status bit SEQ4_STATUS_LEASE_MOVED, if responsibility for any of the
locking state renewed 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, it
should perform an operation on each file system associated with the
server where there is locking state for the current client associated
with the file system in question. The client may choose to reference
all file systems in the interests of simplicity but what is important
is that it must reference all file systems for which there was
locking state where that state moved. Once the client receives an
NFS4ERR_MOVED error for each file system, the SEQ4_STATUS_LEASE_MOVED
indication is cleared. The client can terminate the process of
checking file systems once this indication is cleared, 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
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cause an error in this context. However, it still must do an
operation which receives NFS4ERR_MOVED on each file system, or order
to clear the SEQ4_STATUS_LEASE_MOVED indication is cleared.
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 those leases on
the new server, unless information in 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.
11.7.7.2. Transitions and the Lease_time Attribute
In order that the client may appropriately manage its leases in the
case of a file system transition, the destination server must
establish proper values for the lease_time attribute.
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 leases
granted by the source server. Upon transitions in which state is
transferred transparently, the client is under no obligation to re-
fetch 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 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.
11.7.8. Write Verifiers and File System Transitions
In a file system transition, the two file systems may be clustered in
the handling of unstably written data. When this is the case, and
the two file systems belong to the same _write-verifier_ class, write
verifiers returned from one system may be compared to those returned
by the other and superfluous writes avoided.
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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, it should be treated as not equal even when the
values are identical.
11.7.9. Readdir Cookies and Verifiers and File System Transitions
In a file system transition, the two file systems may be consistent
in their handling of READDIR cookies and verifiers. When this is the
case, and the two file systems belong to the same _readdir_ class,
READDIR cookies and verifiers from one system may be recognized by
the other and READDIR operations started on one server may 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.
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 was rejected.
11.7.10. 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 data the same data or data which 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 will be listed
while in another only those that are up-to-date may 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:
o When multiple server addresses correspond to the same actual
server, as indicated by a common so_major_id field within the
eir_server_owner field returned by EXCHANGE_ID, the client may
depend on the fact that changes to data, metadata, or locks made
on one file system are immediately reflected on others.
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o 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, immediately upon the earlier of the
return of the modifying requester or the visibility of that change
on any of the associated replicas. This allows a client to use
these replicas simultaneously without any special adaptation to
the fact that there are multiple replicas. In this case, locks,
whether shared or byte-range, and delegations obtained one replica
are immediately reflected on all replicas, even though these locks
will be managed under a set of client IDs.
o When one replica is designated as the successor instance to
another existing instance after return NFS4ERR_MOVED (i.e. the
case of migration), the client may depend on the fact that all
changes securely made to data (uncommitted writes are dealt with
in Section 11.7.8) on the original instance are made to the
successor image.
o 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 by which this will be prevented varies
based on fs4_status_type reported as part of the fs_status
attribute (See Section 11.11). Since these file systems are
presumed not to be suitable for simultaneous use, there is no
specification of how locking is handled and it generally will be
the case that locks obtained one file system will be separate from
those on others. Since these are going to be read-only file
systems, this is not expected to pose an issue for clients or
applications.
11.8. 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
they happen only when the client has not previously referenced the
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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 lookup,
but will have cached information regarding the upper levels of the
name hierarchy. However, these example are chosen to make the
required behavior clear and easy to put within the scope of a small
number of requests, without getting unduly into details of how
specific clients might choose to cache things.
11.8.1. 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 the case that the file
system has moved, or, it may be the case that the target server is
functioning mainly, or solely, to refer clients to the servers on
which various file systems are located.
o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
o LOOKUP "the"
o LOOKUP "path"
o GETFH
o GETATTR fsid,fileid,size,time_modify
Under the given circumstances, the following will be the result.
o PUTROOTFH --> NFS_OK. The current fh is now the root of the
pseudo-fs.
o LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
o LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
o LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
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o 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.
o GETFH --> NFS4ERR_MOVED. Fails because current fh is in an absent
file system at the start of the operation and the spec makes no
exception for GETFH.
o 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 here that in this example, the client did not obtain filehandles
and attribute information (e.g. fsid) for the intermediate
directories, so that he 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
lookup of "path" succeeded is that the file system was not absent on
that op 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 fs
boundaries are (because of where NFS4ERR_MOVED was gotten and where
not) 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
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OP13: GETATTR(fsid, fs_locations_info) --> NFS_OK
- We are getting the fsid to know where the file system boundaries
are. 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 another reliable source information on the
boundary of the fs which 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 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 which 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 spec 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, by noting where the change of fsid occurred. 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 basically transient information with the
function of enabling the referral.
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11.8.2. Referral Example (READDIR)
Another context in which a client may encounter referrals is when it
does a READDIR on directory in which some of the sub-directories are
the roots of absent file systems.
Suppose such a directory is read as follows:
o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
o LOOKUP "the"
o 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 attributes cannot be
provided, the result will be an NFS4ERR_MOVED error on the READDIR,
with the detailed results as follows:
o PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
o LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
o LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
o LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
o 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, when in fact it is because the
directory contains the root of an absent file system.
So now suppose that we re-send with rdattr_error:
o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
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o LOOKUP "the"
o READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
The results will be:
o PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
o LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
o LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
o LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
o READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
--> NFS_OK. The attributes for "path" will only contain
rdattr_error with the value NFS4ERR_MOVED, together with an fsid
value and a value for mounted_on_fileid.
So suppose we do another READDIR to get fs_locations_info (although
we could have used a GETATTR directly, as in Section 11.8.1).
o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
o LOOKUP "the"
o READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
size, time_modify)
The results would be:
o PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
o LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
o LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
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o LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
o 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 "path" will only contain
o rdattr_error (value: NFS_OK)
o fs_locations_info
o mounted_on_fileid (value: unique fileid within referring fs)
o fsid (value: unique value within referring server)
The attribute entry for "path" will not contain size or time_modify
because these attributes are not available within an absent file
system.
11.9. The Attribute fs_locations
The fs_locations attribute is structured in the following way:
struct fs_location4 {
utf8str_cis 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, or IPv6 address, or an zero-
length string. A null 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
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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 fs_location attribute 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. 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 a 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.
Since 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.
o 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.
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o 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
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.
o 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:
o When the transition is due to migration, that is the client was
directed to new file system after receiving a NFS4ERR_MOVED error,
the target should be treated as being of the same _write-verifier_
class as the source.
o When the transition is due to failover to another replica, that
is, the client selected another replica without receiving and
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 21 for a discussion on the recommendations for the
security flavor to be used by any GETATTR operation that requests the
"fs_locations" attribute.
11.10. The Attribute fs_locations_info
The fs_locations_info attribute is intended as a more functional
replacement for fs_locations which will continue to exist and be
supported. Clients can use it to get a more complete set of
information about alternative file system locations. When the server
does not support fs_locations_info, fs_locations can be used to get a
subset of the information. A server which supports fs_locations_info
MUST support fs_locations as well.
There is additional information present in fs_locations_info, that is
not available in fs_locations:
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o Attribute continuity information to allow a client to select a
location which meets the transparency requirements of the
applications accessing the data and to take advantage of
optimizations that server guarantees as to attribute continuity
may provide (e.g. change attribute).
o File System identity information which 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 multiple paths to the same thing.
o Information which 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.
o 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 root path on their respective servers. The
lower-level structure in turn (fs_locations_item4) contains a
specific pathname and information on one or more individual server
replicas. For that last lowest-level fs_locations_info has a
fs_locations_server4 structure that contains per-server-replica
information in addition to the server name. This per-server-replica
information includes a nominally opaque array, fls_info, in which
specific pieces of information are located at the specific indices
listed below.
The attribute will always contains at least a single
fs_locations_server entry. Typically, this 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 different for various reasons. One
server may know about a set of replicas that are not know to other
servers. Further, compatibility attributes may differ. Filehandles
may by of the same class going from replica A to replica B but not
going in the reverse direction. This may happen because the
filehandles are the same but the server implementation for the server
on which replica B may not have provision to note and report that
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equivalence.
The fs_locations_info attribute consists of a root pathname (just
like fs_locations), together with an array of fs_location_item4
structures. The fs_location_item4 structures in turn consist of a
root pathname together with an array of
/*
* Defines an individual server replica
*/
struct fs_locations_server4 {
int32_t fls_currency;
opaque fls_info<>;
utf8str_cis 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;
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.
*/
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const FSLI4TF_RDMA = 0x01;
/*
* Defines a set of replicas sharing
* a common value of the root path
* with in 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 and it is generally expected that it will be available
for 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.
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11.10.1. The fs_locations_server4 Structure
The fs_locations_server4 structure consists of the following items:
o An indication of file system up-to-date-ness (fls_currency) in
terms of approximate seconds before the present. 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 zero
indicates that 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 serve as a hint about how far the copy of the data would
be expected to be behind the most up-to-date copy.
o 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.
o The server string (fls_server). For the case of the replica
currently being accessed (via GETATTR), a null string MAY be used
to indicate the current address being used for the RPC call.
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.
o The kinds of data in the fls_info array, representing flags, file
system classes and priorities among set of file systems
representing the same data, are such that eight bits provides 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.
o Explicit definition of the various specific data items within XDR
would limit expandability in that any extension within a
subsequent minor version would require yet another attribute,
leading to specification and implementation clumsiness.
o Such explicit definitions would also make it impossible to propose
standards-track extensions apart from a full minor version.
This encoding scheme can be adapted to the specification of multi-
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byte numeric values, even though none are currently defined. If
extensions are made via standards-track RFC's, 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 are constrained so that the relevant quantities will not
cross XDR word boundaries.
The set of fls_info data is subject to expansion in a future minor
version, or in a standard-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 that are not defined in
standards-track RFC's.
The fls_info array contains within it:
o Two 8-bit flag fields, one devoted to general file-system
characteristics and a second reserved for transport-related
capabilities.
o Six 8-bit class values which define various file system
equivalence classes as explained below.
o Four 8-bit priority values which 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:
o FSLI4GF_WRITABLE indicates that this file system target is
writable, allowing it to be selected by clients which 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
client was previously writing, then it must incorporate within its
data any committed write made on the source file system instance.
See Section 11.7.8 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 read-only
file system can cause problems for clients who select a migration
or replication target based on it and then find themselves unable
to write.
o 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.
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o FSLI4GF_ABSENT indicates that this entry corresponds 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 where a file system has been accessed at this
location and has subsequently been migrated.
o 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 and that the 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.
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 to
avoid being referred to this instance whenever there is another
choice.
o 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
simply forget cached filehandles). If the client remembers the
directory filehandle associated with each open file, it may
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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 action will not be performed.
Instead, reference to portions of the original file system split
off into other will encounter an fsid change and possibly a
further referral.
Once the client recognizes that one file system has been split
into two, it could maintain applications running without
disruption by presenting the two file systems as a single one
until a convenient point to recognize the transition, such as a
reboot. This would require a mapping of fsids 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 files on the
split file systems is the responsibility of the server (or servers
working in concert). Note that filehandles could be different for
file systems that tool part in the split form those newly
accessed, allowing the server to determine when the need for such
treatment 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
file system.
o FSLI4TF_RDMA indicates that this file system provides NFSv4.1 file
system 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
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transitions. See Section 11.7 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 which have the
specified relationship to one another share a common class value. A
simple to provide this data assumes that the server has knowledge of
the appropriate set of identity relationships to be encoded. As each
instance entry is added, the relationships of this instance to
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 increment the value of the last class value assigned
for that index.
o The field with byte index FSLI4BX_CLSIMUL defines the
simultaneous-use class for the file system.
o The field with byte index FSLI4BX_CLHANDLE defines the handle
class for the file system.
o The field with byte index FSLI4BX_CLFILEID defines the fileid
class for the file system.
o The field with byte index FSLI4BX_CLWRITEVER defines the write-
verifier class for the file system.
o The field with byte index FSLI4BX_CLCHANGE defines the change
class for the file system.
o 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 client communication characteristics are
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not tightly controlled and 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
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.
o The field at byte index FSLI4BX_READRANK gives the rank value to
be used for read-only access.
o The field at byte index FSLI4BX_READORDER gives the order value to
be used for read-only access.
o The field at byte index FSLI4BX_WRITERANK gives the rank value to
be used for writable access.
o 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.
11.10.2. The fs_locations_info4 Structure
The fs_locations_info4 structure, encoding the fs_locations_info
attribute, contains the following:
o 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 which
are not defined should always be returned as zero.
o 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.
o 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
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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.
o 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 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
which 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 and it is to be expected that
this may have a different valid_for value, which the client should
then use, in the same fashion as the previous value.
The FSLI4IF_VAR_SUB flag within fli_flags controls whether variable
substitution is to be enabled. See Section 11.10.3 for an
explanation of variable substitution.
11.10.3. The fs_locations_item4 Structure
The fs_locations_item4 structure contains a pathname (in the field
fli_rootpath) which 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
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.
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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 with the
part after being a case-insensitive alphanumeric string.
Where the domain is "ietf.org", only variable names defined in this
document or subsequent standards-track RFC's 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 case 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 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 API's 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 the 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) but 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 value of the variable ${ietf.org:OS_TYPE} with which it
is used.
Use of these variable could result in 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
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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, if 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 the FSLI4IF_VAR_SUB flag within the
associated fs_locations_info4 structure is set or not.
11.11. 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.
enum fs4_status_type {
STATUS4_FIXED = 1,
STATUS4_UPDATED = 2,
STATUS4_VERSIONED = 3,
STATUS4_WRITABLE = 4,
STATUS4_ABSENT = 5
};
struct fs4_status {
fs4_status_type fss_type;
utf8str_cs fss_source;
utf8str_cs fss_current;
int32_t fss_age;
nfstime4 fss_version;
};
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The boolean fsstat_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 type value 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
fsstat_absent is set, and the file system was previously present, the
type reflected is that when the file was last present. Five types
are distinguished:
o 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.
o STATUS4_VERSIONED which indicates that the image, like the
STATUS4_UPDATED case, is updated exogenously, 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.
o STATUS4_UPDATED which indicates an image that cannot be updated by
the user writing to it but may be changed exogenously, 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.
o 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.
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o STATUS4_REFERRAL which indicates that the file system is 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 exogenous changes to delegations. If a server
gives out delegations, they SHOULD be returned if a before a change
which is inconsistent is made to data, and MUST be revoked if this is
not possible. Similarly, if an open is inconsistent with data that
is changed (the open denies WRITE and the data is changed), that lock
SHOULD be considered administratively revoked.
The opaque strings source and current provide a way of presenting
information about the source of the file system image being present.
It is not intended that 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 debugging 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.
The opaque string '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 that is 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,
by whom, etc. Making this information available in this attribute in
a human-readable string form will be helpful for applications and
system administrators and also serves to make it available when the
original file system is used to make subsequent copies.
The opaque string 'current' should provide whatever information is
available about the source of the current copy. Such information as
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 form.
The age provides an indication of how out-of-date the file system
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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 11.10) 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 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 version field provides a version identification, in the form of a
time value, such that successive versions always have later time
values. When the file system 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 'source' and 'current'.
When the type is STATUS4_VERSIONED, servers SHOULD provide a value of
version which 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.
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, to avoid the possibility that the
fs_status which the client holds will be one for an earlier image,
and so accept a new file system instance which is later than that but
still earlier than updated data read by the client.
In order to do this reliably, it must do a GETATTR of fs_status 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
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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 it) and
using the last. The client may then, when switching among file
system instances, decline to use an instance which is not of type
STATUS4_VERSIONED or whose version field is earlier than the last one
obtained from the predecessor file system instance.
12. Parallel NFS (pNFS)
12.1. Introduction
pNFS is an OPTIONAL feature within NFSv4.1; the pNFS feature set
allows direct client access to the storage devices containing file
data. When file data for a single NFSv4 server is stored on multiple
and/or higher throughput storage devices (by comparison to the
server's throughput capability), the result can be significantly
better file access performance. The relationship among multiple
clients, a single server, and multiple storage devices for pNFS
(server and clients have access to all storage devices) is shown in
this diagram:
+-----------+
|+-----------+ +-----------+
||+-----------+ | |
||| | NFSv4.1 + pNFS | |
+|| Clients |<------------------------------>| Server |
+| | | |
+-----------+ | |
||| +-----------+
||| |
||| |
||| Storage +-----------+ |
||| Protocol |+-----------+ |
||+----------------||+-----------+ Control |
|+-----------------||| | Protocol|
+------------------+|| Storage |------------+
+| Devices |
+-----------+
Figure 67
In this model, the clients, server, and storage devices are
responsible for managing file access. This is in contrast to NFSv4
without pNFS where it is primarily the server's responsibility; some
of this responsibility may be delegated to the client under strictly
specified conditions.
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pNFS takes the form of OPTIONAL operations that manage protocol
objects called 'layouts' which contain data location information.
The layout is managed in a similar fashion as NFSv4.1 data
delegations are managed. For example, the layout is leased,
recallable and revocable. However, layouts are distinct abstractions
and are manipulated with new operations. When a client holds a
layout, it is granted the ability to access the data location
directly using the location information specified in the layout.
There are interactions between layouts and other NFSv4.1 abstractions
such as data delegations and record locking. Delegation issues are
discussed in Section 12.5.5. Byte range locking issues are discussed
in Section 12.2.9 and Section 12.5.1.
The NFSv4.1 pNFS feature has been structured to allow for a variety
of storage protocols to be defined and used. As noted in the diagram
above, the storage protocol is the method used by the client to store
and retrieve data directly from the storage devices. The NFSv4.1
protocol directly defines one storage protocol, the NFSv4.1 storage
type, and its use.
Examples of other storage protocols that could be used with NFSv4.1's
pNFS are:
o Block/volume protocols such as iSCSI ([36]), and FCP ([37]). The
block/volume protocol support can be independent of the addressing
structure of the block/volume protocol used, allowing more than
one protocol to access the same file data and enabling
extensibility to other block/volume protocols.
o Object protocols such as OSD over iSCSI or Fibre Channel [38].
o Other storage protocols, including PVFS and other file systems
that are in use in HPC environments.
It is possible that various storage protocols are available to both
client and server and it may be possible that a client and server do
not have a matching storage protocol available to them. Because of
this, the pNFS server MUST support normal NFSv4.1 access to any file
accessible by the pNFS feature; this will allow for continued
interoperability between a NFSv4.1 client and server.
12.2. pNFS Definitions
NFSv4.1's pNFS feature partitions the file system protocol into two
parts: metadata and data. Where data is the contents of a file and
metadata is "everything else". The metadata functionality is
implemented by a metadata server that supports pNFS and the
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operations described in (Section 18). The data functionality is
implemented by a storage device that supports the storage protocol.
A subset (defined in Section 13.6) of NFSv4.1 itself is one such
storage protocol. New terms are introduced to the NFSv4.1
nomenclature and existing terms are clarified to allow for the
description of the pNFS feature.
12.2.1. 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 vary based on
the underlying storage mechanism that is used.
12.2.2. Metadata Server
An NFSv4.1 server which supports the pNFS feature. A variety of
architectural choices exists for the metadata server and its use of
what file system information is held at the server. Some servers may
contain metadata only for the file objects that reside at the
metadata server while file data resides on the associated storage
devices. Other metadata servers may hold both metadata and a varying
degree of file data.
12.2.3. pNFS Client
An NFSv4.1 client that supports pNFS operations and supports at least
one storage protocol or layout type for performing I/O to storage
devices.
12.2.4. Storage Device
A storage device stores a regular file's data, but leaves metadata
management to the metadata server. A storage device could be another
NFSv4.1 server, an object storage device (OSD), a block device
accessed over a SAN (e.g., either FiberChannel or iSCSI SAN), or some
other entity.
12.2.5. Storage Protocol
A storage protocol is the protocol used between the pNFS client and
the storage device to access the file data.
12.2.6. Control Protocol
The control protocol is used by the exported file system between the
metadata server and storage devices. Specification of such protocols
is outside the scope of the NFSv4.1 protocol. Such control protocols
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would be used to control activities such as the allocation and
deallocation of storage and the management of state required by the
storage devices to perform client access control.
A particular control protocol is not REQUIRED by NFSv4.1 but
requirements are placed on the control protocol for maintaining
attributes like modify time, the change attribute, and the end-of-
file (EOF) position.
12.2.7. Layout Types
A layout describes the mapping of a file's data to the storage
devices that hold the data. A layout is said to belong to a specific
layout type (data type layouttype4, see Section 3.3.13). The layout
type allows for variants to handle different storage protocols, such
as those associated with block/volume [31], object [30], and file
(Section 13) layout types. A metadata server, along with its control
protocol, MUST support at least one layout type. A private sub-range
of the layout type name space is also defined. Values from the
private layout type range MAY be used for internal testing or
experimentation.
As an example, a file layout type could be an array of tuples (e.g.,
deviceID, file_handle), along with a definition of how the data is
stored across the devices (e.g., striping). A block/volume layout
might be an array of tuples that store <deviceID, block_number, block
count> along with information about block size and the associated
file offset of the block number. An object layout might be an array
of tuples <deviceID, objectID> and an additional structure (i.e., the
aggregation map) that defines how the logical byte sequence of the
file data is serialized into the different objects. Note that the
actual layouts are typically more complex than these simple
expository examples.
12.2.8. Layout
A layout defines how a file's data is organized on one or more
storage devices. There are many potential layout types; each of the
layout types are differentiated by the storage protocol used to
access data and in the aggregation scheme that lays out the file data
on the underlying storage devices. A layout is precisely identified
by the following 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
overlap each other, both layouts must be of the same layout type,
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correspond to the same filehandle, and have the same iomode. Layouts
conflict when they overlap and differ in the content of the layout
(i.e., the storage device/file mapping parameters differ). Note that
differing iomodes do not lead to conflicting layouts. It is
permissible for layouts with different iomodes, pertaining to the
same byte range, to be held by the same client. An example of this
would be copy-on-write functionality for a block/volume layout type.
12.2.9. Layout Iomode
The layout iomode (data type layoutiomode4, see Section 3.3.20)
indicates to the metadata server the client's intent to perform
either just READ operations (Section 18.22) or a mixture of I/O
possibly containing WRITE (Section 18.32) and READ operations. For
certain layout types, it is useful for a client to specify this
intent at LAYOUTGET (Section 18.43) time. For example, block/volume
based protocols, block allocation could occur when a READ/WRITE
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 READ and
READ/WRITE iomodes are being returned or recalled, respectively.
A storage device may validate I/O with regards to the iomode; this is
dependent upon storage device implementation and layout type. Thus,
if the client's layout iomode is inconsistent with the I/O being
performed, the storage device may reject the client's I/O with an
error indicating a new layout with the correct I/O mode should be
fetched. For example, if a client gets a layout with a READ iomode
and performs a WRITE to a storage device, the storage device is
allowed to reject that WRITE.
The iomode does not conflict with OPEN share modes or lock requests;
open mode and lock conflicts are enforced as they are without the use
of pNFS, and are logically separate from the pNFS layout level. As
well, open modes and locks are the preferred method for restricting
user access to data files. For example, an OPEN of read, deny-write
does not conflict with a LAYOUTGET containing an iomode of READ/WRITE
performed by another client. Applications that depend on writing
into the same file concurrently may use record locking to serialize
their accesses.
12.2.10. Device IDs
The device ID (data type deviceid4, see Section 3.3.14) names a group
of storage devices. The scope of a device ID is per pair of client
ID and 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.
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The NFSv4.1 operation GETDEVICEINFO (Section 18.40) 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 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 12.7.4 for a description of how recovery works in that
situation.
A device ID lives as long as there is a layout referring to the
device ID. If there are no layouts referring to the device ID, the
server is free to delete the device ID any time. 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 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 20.12), 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.
The server MUST support notifications and the client must request
them before they can be used. For further information about the
notification types Section 20.12.
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12.3. 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 17.
These are the fore channel pNFS operations:
GETDEVICEINFO. As noted previously (Section 12.2.10), GETDEVICEINFO
(Section 18.40) returns the mapping of device ID to storage device
address.
GETDEVICELIST (Section 18.41), allows clients to fetch all device
IDs for a specific file system.
LAYOUTGET (Section 18.43) is used by a client to get a layout for a
file.
LAYOUTCOMMIT (Section 18.42) is used to inform the metadata server
of the client's intent to commit data which has been written to
the storage device; the storage device as originally indicated in
the return value of LAYOUTGET.
LAYOUTRETURN (Section 18.44) is used to return layouts for a file,
an FSID and for client ID.
These are the backchannel pNFS operations:
CB_LAYOUTRECALL (Section 20.3) recalls a layout or all layouts
belonging to a file system, or all layouts belonging to a client
ID.
CB_RECALL_ANY (Section 20.6), tells a client that it needs to return
some number of recallable objects, including layouts, to the
metadata server.
CB_RECALLABLE_OBJ_AVAIL (Section 20.7) 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 20.12) Notifies the client of changes to
device IDs.
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12.4. pNFS Attributes
A number of attributes specific to pNFS are listed and described in
Section 5.11
12.5. Layout Semantics
12.5.1. Guarantees Provided by Layouts
Layouts grant to the client the ability to access data located at a
storage device with the appropriate storage 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 and 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 storage devices 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 storage device, a layout must be held by the
client. If a storage device receives an I/O 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 storage 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.
Depending upon the layout type and storage protocol in use, storage
device 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 [38].
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 access operations with open, lock and access
as described above. The degree to which it is possible for the
client to circumvent these access operations and the consequences of
doing so must be clearly specified by the individual layout type
specifications. In addition, these specifications must be clear
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about the requirements and non-requirements for the checking
performed by the server.
In the presence of pNFS functionality, mandatory file 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 file locks. For example, if
one client obtains a mandatory lock and a second client accesses the
storage device, the storage device MUST appropriately restrict I/O
for the byte range of the mandatory file lock. If the storage device
is incapable of providing this check in the presence of mandatory
file locks, the metadata server then MUST NOT grant layouts and
mandatory file locks simultaneously.
12.5.2. Getting a Layout
A client obtains a layout with 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 may not exactly align with the requested byte
range. A field within the LAYOUTGET request, loga_minlength,
specifies the minimum length of the layout. The loga_minlength field
should be at least one. As needed a client may make multiple
LAYOUTGET requests; these will result in multiple overlapping, non-
conflicting layouts.
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
presents a stateid as returned by OPEN, 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 uses a layout stateid
(see Section 12.5.3) on future invocations of LAYOUTGET on the file,
and the "seqid" MUST NOT ever be set to zero. 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.
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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 (Section 5.11.4) attribute 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 18.16.3, summarizes how a client is allowed to send an
exclusive create.
12.5.3. Layout Stateid
As with all other stateids, the stateid consists of a "seqid" and
"other" field. Once a layout stateid is changed, 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 fore channel or backchannel operation. After the layout stateid
is established, the "seqid" is incremented by the server in each
subsequent LAYOUTGET and LAYOUTRETURN response, and in each
CB_LAYOUTRECALL request. When the client fully processes the
response to a LAYOUTGET or LAYOUTRETURN, or fully processes the
arguments of a CB_LAYOUTRECALL, it MUST use the seqid of the stateid
of the reply from LAYOUTGET and LAYOUTRETURN, or the seqid of the
stateid in the arguments of CB_LAYOUTRECALL, on subsequent calls to
LAYOUTGET or LAYOUTRETURN. The client and server use the "seqid" of
the layout stateid for the following purposes:
o Permit the client to send parallel LAYOUTGET operations on the
same file. As with parallel opens (see Section 9.8) the use of
the sequence ID allows a client to avoid serializing LAYOUTGET
operations. If LAYOUTGETs were serialized, especially non-
overlapping LAYOUTGETs, then non-overlapping I/Os to storage
devices would in turn be effectively serialized with each other.
In the event parallel LAYOUTGET operations are sent with a non-
layout stateid (because the client does not yet have a layout
stateid), the successful responses MUST have the same "other"
field in the LAYOUTSTATEID, and each response with a unique
"seqid", where the lowest "seqid" is one, and the highest "seqid"
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is equal to the count of parallel LAYOUTGET operations invoked on
the non-layout stateid.
o Allow the client and server to detect race conditions. See
Section 12.5.5.2.
The client MUST always use a "seqid" that was returned by the server
in a reply to a LAYOUTGET or LAYOUTRETURN operation, or sent by the
server in a CB_LAYOUTRECALL operation. It MUST only use such a seqid
after processing the LAYOUTGET and LAYOUTRETURN results, or the
CB_LAYOUTRECALL request. Simply seeing the result or the
CB_LAYOUTRECALL request is not sufficient cause to use the seqid.
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. For LAYOUTRETURN
results, the client MUST delete 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.
12.5.4. Committing a Layout
Allowing for varying storage protocols capabilities, the pNFS
protocol does not require the metadata server and storage devices to
have a consistent view of file attributes and data location mappings.
Data location mapping refers to aspects such as which offsets store
data as opposed to storing holes (see Section 13.4.4 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 this inconsistency, it is necessary to
re-synchronize 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.
The LAYOUTCOMMIT operation is responsible for committing a modified
layout to the metadata server. The data should be written and
committed to the appropriate storage devices before the LAYOUTCOMMIT
occurs. The scope of the LAYOUTCOMMIT operation 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 which 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. It is not REQUIRED to maintain a global view that
accounts for other clients' I/O that may have occurred within the
same time frame.
For block/volume-based layouts, LAYOUTCOMMIT may require updating the
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block list that comprises the file and committing this layout to
stable storage. For file-layouts synchronization of attributes
between the metadata and storage devices primarily the size attribute
is required.
The control protocol is free to synchronize the attributes before it
receives a LAYOUTCOMMIT, however upon successful completion of a
LAYOUTCOMMIT, state that exists on the metadata server that describes
the file MUST be in sync with the state existing on the storage
devices that comprise that file as of the issuing client's last
operation. Thus, a client that queries the size of a file between a
WRITE to a storage device and the LAYOUTCOMMIT may observe a size
that does not reflect the actual data written.
12.5.4.1. LAYOUTCOMMIT and change/time_modify
The change and time_modify attributes may be updated by the server
when the LAYOUTCOMMIT operation is processed. The reason for this is
that some layout types do not support the update of these attributes
when the storage devices process I/O operations. The client is
capable providing a suggested value to the server for time_modify
within the arguments to LAYOUTCOMMIT. Based on layout type, the
provided value may or may not be used. The server should sanity
check the client provided values before they are used. For example,
the server should ensure that time does not flow backwards. The
client always has the option to set time_modify through an explicit
SETATTR operation.
For some layout protocols, the storage device is able to notify the
metadata server of the occurrence of an I/O and as a result the
change and time_modify attributes may be updated at the metadata
server. For a metadata server that is capable of monitoring updates
to the change and time_modify attributes, LAYOUTCOMMIT processing is
not required to update the change attribute; in this case the
metadata server must ensure that no further update to the data has
occurred since the last update of the attributes; file-based
protocols may have enough information to make this determination or
may update the change attribute upon each file modification. This
also applies for the time_modify attribute. If the server
implementation is able to determine that the file has not been
modified since the last time_modify update, the server need not
update time_modify at LAYOUTCOMMIT. At LAYOUTCOMMIT completion, the
updated attributes should be visible if that file was modified since
the latest previous LAYOUTCOMMIT or LAYOUTGET.
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12.5.4.2. LAYOUTCOMMIT and size
The size of a file may be updated when the LAYOUTCOMMIT operation is
used by the client. One of the fields in the argument to
LAYOUTCOMMIT is loca_last_write_offset; this field indicates the
highest byte offset written but not yet committed with the
LAYOUTCOMMIT operation. The data type of lora_last_write_offset is
newoffset4 and is switched on a boolean value, no_newoffset, that
indicates if a previous write occurred or not. If no_newoffset is
FALSE, an offset is not given. A loca_last_write_offset value of
zero means that one byte was written at offset zero.
The metadata server may do one of the following:
1. Update the file's size using the last write offset provided by
the client as either the true file size or as a hint of the file
size. If the metadata server has a method available, any new
value for file size should be sanity checked. For example, the
file must not be truncated if the client presents a last write
offset less than the file's current size.
2. Ignore the client provided last write offset; the metadata server
must have sufficient knowledge from other sources to determine
the file's size. For example, the metadata server queries the
storage devices with the control protocol.
The method chosen to update the file's size will depend on the
storage device's and/or the control protocol's capabilities. For
example, if the storage devices are block devices with no knowledge
of file size, the metadata server must rely on the client to set the
last write offset appropriately.
The results of LAYOUTCOMMIT contain a new size value in the form of a
newsize4 union data type. If the file's size is set as a result of
LAYOUTCOMMIT, the metadata server must reply with the new size;
otherwise the new size is not provided. If the file size is updated,
the metadata server SHOULD update the storage devices such that the
new file size is reflected when LAYOUTCOMMIT processing is complete.
For example, the client should be able to READ up to the new file
size.
If the client wants to explicitly zero-extend or truncate a file, the
SETATTR operation MUST be used; SETATTR use is not required when
simply writing past EOF via WRITE.
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12.5.4.3. LAYOUTCOMMIT and layoutupdate
The LAYOUTCOMMIT argument contains a loca_layoutupdate field
(Section 18.42.1) of data type layoutupdate4 (Section 3.3.18). This
argument is a layout type-specific structure. The structure can be
used to pass arbitrary layout type-specific information from the
client to the metadata server at LAYOUTCOMMIT time. For example, if
using a block/volume layout, the client can indicate to the metadata
server which reserved or allocated blocks the client used or did not
use. The content of loca_layoutupdate (field lou_body) need not be
the same layout type-specific content returned by LAYOUTGET
(Section 18.43.2) in the loc_body field of the lo_content field, of
the logr_layout field. The content of loca_layoutupdate is defined
by the layout type specification and is opaque to LAYOUTCOMMIT.
12.5.5. 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 20.3) and returned
with LAYOUTRETURN Section 18.44. The CB_LAYOUTRECALL operation may
recall a layout identified by a byte range, all the layouts
associated with a file system (FSID), or all layouts associated with
a client ID. Section 12.5.5.2 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 read-only and read/write
layouts.
A REMOVE operation SHOULD cause the metadata server to recall the
layout to prevent the client from accessing a non-existent file and
to reclaim state stored on the client. 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
files based layout, the data server SHOULD return NFS4ERR_STALE in
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response to any operation on the removed file.
Once a layout has been returned, the client MUST NOT send I/Os 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 SHOULD
reject the I/O.
Although pNFS does not alter the file data caching capabilities of
clients, or their semantics, it recognizes that some clients may
perform more aggressive write-behind caching to optimize the benefits
provided by pNFS. However, write-behind caching may negatively
affect the latency in returning a layout in response to a
CB_LAYOUTRECALL; this is similar to file delegations and the impact
that file data caching has on DELEGRETURN. Client implementations
SHOULD limit the amount of unwritten data they have outstanding at
any one time in order to prevent excessively long responses to
CB_LAYOUTRECALL. Once a layout is recalled, a server MUST wait one
lease period before taking further action. As soon as a lease period
has past, the server may choose to fence the client's access to the
storage devices if the server perceives the client has taken too long
to return a layout. However, just as in the case of data delegation
and DELEGRETURN, the server may choose to wait given that the client
is showing forward progress on its way to returning the layout. This
forward progress can take the form of successful interaction with the
storage devices or sub-portions of the layout being returned by the
client. The server can also limit exposure to these problems by
limiting the byte ranges initially provided in the layouts and thus
the amount of outstanding modified data.
12.5.5.1. Layout Recall Callback Robustness
It has been assumed thus far that pNFS client state for a file
exactly matches the pNFS server state for that file and client
regarding layout ranges and iomode. This assumption leads to the
implication that any callback results in a LAYOUTRETURN or set of
LAYOUTRETURNs that exactly match the range in the callback, since
both client and server agree about the state being maintained.
However, it can be useful if this assumption does not always hold.
For example:
o If conflicts that require callbacks are very rare, and a server
can use a multi-file callback to recover per-client resources
(e.g., via a FSID recall, or a multi-file recall within a single
compound), the result may be significantly less client-server pNFS
traffic.
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o It may 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 the extreme, a server could manage conflicts on a per-
file basis, only issuing whole-file callbacks even though clients
may request and be granted sub-file ranges.
o 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 what the client "thinks"
it has. 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 MUST follow up
with a LAYOUTRETURN for what the server recalled, or alternatively
return the NFS4ERR_NOMATCHING_LAYOUT error if it has no layout to
return in the recalled range.
o 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 issuing a LAYOUTRETURN for the entire requested
range or by returning an NFS4ERR_NOMATCHING_LAYOUT error to the
CB_LAYOUTRECALL.
Thus, 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 stage the flushing of dirty data, layout
commits, and returns. Also, it indicates to the metadata server that
the client is making progress.
When a layout is returned, the client MUST NOT have any outstanding
I/O requests to the storage devices involved in the layout.
Rephrasing, the client MUST NOT return the layout while it has
outstanding I/O requests to the storage device.
Even with this requirement for 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 has no strict control as to when the
client will return the layout, the server may later decide to
unilaterally revoke the client's access to the storage devices as
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provided by the layout. In choosing to revoke access, the server
must deal with the possibility of lingering I/O request; those
outstanding I/O requests are still in flight to storage devices
identified by the revoked layout. All layout specifications MUST
define whether unilateral layout revocation by the metadata server is
supported; if it is, the specification must also describe how
lingering writes are processed. For example, storage devices
identified by the revoked layout could be fenced off from the client
that held the layout.
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 overlaps 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.
12.5.5.2. 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.
12.5.5.2.1. Recall/Return Sequencing
Section 2.10.5.3 describes the sessions mechanism for allowing the
client to detect such situations in order to delay processing such a
CB_LAYOUTRECALL. The server MUST reference all conflicting LAYOUTGET
operations in the CB_SEQUENCE that precedes the CB_LAYOUTRECALL. A
zero length array of referenced operations is used by the server to
tell the client that the server does not know of any LAYOUTGET
operations that conflict with the recall.
While referencing conflicting operations in CB_SEQUENCE conveys to
the client that the server is aware of races, one critical issue with
regard to operation 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
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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 one higher than what the client currently has
recorded, and the client has at least one LAYOUTGET and/or
LAYOUTRETURN operation outstanding, the client knows the server sent
the CB_LAYOUTRECALL after the server sent a response to an
outstanding LAYOUTGET or LAYOUTRETURN.
12.5.5.2.1.1. 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 in parallel multiple
LAYOUTGET operations for the same file or multiple LAYOUTRETURN
operations for the same file, and a mix of both.
It is permissible for the client to combine LAYOUTRETURN and
LAYOUTGET operations for the same file in the same COMPOUND request
since the server MUST process these in order. The client uses the
current stateid (see Section 16.2.3.1.2). 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 MUST NOT have
other LAYOUTGET or LAYOUTRETURN operations outstanding at the same
time for that same file.
12.5.5.2.1.2. 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 issuing 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.
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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 and 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).
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.
12.5.5.2.1.3. 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 are three cases:
1. The client sent the LAYOUTGET before processing the
CB_LAYOUTRECALL. The "seqid" in the layout stateid of LAYOUTGET
is two less than that of 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 that of the "seqid" in CB_LAYOUTRECALL. The server
has not received a response to the CB_LAYOUTRECALL, so it returns
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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.
12.5.5.2.1.4. 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 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_ALL, 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 the layout
stateids for files with the referenced fsid again. It MUST use
LAYOUTGET to obtain new layout stateids files with the referenced
fsid.
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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.
12.5.6. Revoking Layouts
Parallel NFS permits servers to revoke layouts from clients that fail
to response to recalls and/or fail to renew their lease in time.
Whether the server revokes the layout or not depends on the layout
type, and what actions are taken with respect to the client's I/O to
data servers is also layout type specific.
12.5.7. 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.
12.6. 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 5.11.1) 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
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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.
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 which device ID
it needs to send the I/O command to 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
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
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to send, these I/O requests may be done in parallel.
If the I/O was a WRITE, then at some point the client may want to use
LAYOUTCOMMIT to commit the modification time and the new size of the
file (if it believes it extended the file size) to the metadata
server and the modified data to the file system.
12.7. 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 subtleties that must be handled correctly if the possibility
of file system corruption is to be avoided. [[Comment.4: mre:
layouts are bound to stateids]]
12.7.1. Recovery from Client Restart
Client recovery for layouts is similar to client recovery for other
lock and delegation state. When an 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 and it is
the client's responsibility to use LAYOUTCOMMIT to achieve the
desired level of stability.
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12.7.2. Dealing with Lease Expiration on the Client
If a client believes 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,
write it to the metadata server using the FILE_SYNC4 flag for the
WRITEs or WRITE and COMMIT. Second, the client reestablishes a
client ID and session with the server and obtain new layouts and
device ID to device address mappings for the modified data ranges and
then write 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_STALE_CLIENTID, 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 12.7.4.
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 11.7.7.1. 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 Paragraph 1 or Paragraph 2 of this section.
If sr_status_flags reports no loss of state, then the lease for the
layouts 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 sent before
the lease expires, but arrive after the lease expires. See
Section 12.7.3.
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12.7.3. Dealing with Loss of Layout State on the Metadata Server
This is a description of the case where all of the following are
true:
o the metadata server has not restarted
o a pNFS client's device ID to layouts have been discarded (usually
because the client's lease expired) and are invalid
o an I/O from the pNFS client arrives at the storage device
The metadata server and its storage devices MUST solve this by
fencing the client. In other words, 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. The solution for NFSv4.1 file-based layouts is described in
(Section 13.11), and for other layout types in their respective
external specification documents.
12.7.4. Recovery from Metadata Server Restart
The pNFS client will discover that the metadata server has restarted
(e.g. rebooted) via the methods described in Section 8.4.2 and
discussed in a pNFS-specific context in Paragraph 2, of
Section 12.7.2. 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.
o 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.
2. The client can write that data through the metadata server
using the WRITE (Section 18.32) operation, and then obtain
layouts as desired.
o 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
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client has available to it the options below in the next bullet
item.
o 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 it
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, 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 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 18.42.1)
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
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
discussed in Section 12.5.4.3. If the metadata server's
consistency checks on loca_layoutupdate succeed, then the metadata
server MUST commit the data (as described by the loca_offset,
loca_length, and loca_layoutupdate fields of the arguments) that
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was written to storage device. 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 has lost all the data in the range
defined by <loca_offset, loca_length>. A client can defend
against this risk by caching all data, whether written
synchronously or asynchronously in its memory and not release the
cached data until a successful LAYOUTCOMMIT. This condition does
not hold true for all layout types; for example, files-based
storage devices need not suffer from this limitation.
o 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 item, the failure of LAYOUTCOMMIT means the data
in the range <loca_offset, loca_length> lost. The defense against
the risk is the same; cache all written data on the client until a
successful LAYOUTCOMMIT.
12.7.5. 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,
it must reliably determine that it will not conflict with an
impending OPEN; or a LOCK where the file has mandatory file locking
enabled.
As mentioned previously, some operations, namely WRITE and LAYOUTGET
may be rejected during the metadata server's grace period, because to
provide simple, valid handling during the grace period, the easiest
method is to simply 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 provisional allocation mappings for each file to
stable storage, as well as information about potentially conflicting
OPEN share modes and mandatory record locks that might have been in
effect at the time of restart, and use this information during the
recovery grace period to determine that a WRITE request is safe.
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12.7.6. Storage Device Recovery
Recovery from storage device restart is mostly dependent upon the
layout type in use. However, 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 who 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 re-write the modified data through another
path.
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 the original storage device.
12.8. 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.
Various sub-cases can be distinguished.
1. The storage device uses NFSv4.1 as the storage protocol. The
same physical hardware is used to implement both a metadata and
data server. If an EXCHANGE_ID operation sent to the metadata
server has EXCHGID4_FLAG_USE_PNFS_MDS set and
EXCHGID4_FLAG_USE_PNFS_DS not set, the role of all sessions
derived from the client ID is metadata server-only. If an
EXCHANGE_ID operation sent to the data server has
EXCHGID4_FLAG_USE_PNFS_DS set and EXCHGID4_FLAG_USE_PNFS_MDS not
set, the role of all sessions derived from the client ID is data
server only. These assertions are true regardless whether the
network addresses of the metadata server and data server are the
same or not.
The client will use the same client owner for both the metadata
server EXCHANGE_ID and the data server EXCHANGE_ID. Since the
client sends one with EXCHGID4_FLAG_USE_PNFS_MDS set, and the
other with EXCHGID4_FLAG_USE_PNFS_DS set, the server will need to
return unique client IDs, as well as server_owners, which will
eliminate ambiguity about dual roles the same physical entity
serves.
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2. The metadata and data server each return EXCHANGE_ID results with
EXCHGID4_FLAG_USE_PNFS_DS and EXCHGID4_FLAG_USE_PNFS_MDS both
set, the server_owner and server_scope results are the same, and
the client IDs are the same, and if RPCSEC_GSS is used, the
server principals are the same. As noted in Section 2.10.4 the
two servers are the same, whether they have the same network
address or not. If the pNFS server is ambiguous in its
EXCHANGE_ID results as to what role a client ID may be used for,
yet still requires the NFSv4.1 request be directed in a manner
specific to a role (e.g. a READ request for a particular offset
directed to the metadata server role might use a different offset
if the READ was intended for the data server role, if the file is
using STRIPE4_DENSE packing, see Section 13.4.4), the pNFS server
may mark the the metadata filehandle differently from the data
filehandle so that operations addressed to the metadata server
can be distinguished from those directed to the data servers.
Marking the metadata and data server filehandles differently (and
this is RECOMMENDED) is possible because the former are derived
from OPEN operations, and the latter are derived from LAYOUTGET
operations.
Note, that it may be the case that while the metadata server and
the storage device are distinct from one client's point of view,
the roles may be reversed according to another client's point of
view. For example, in the cluster file system model a metadata
server to one client, may be a data server to another client. If
NFSv4.1 is being used as the storage protocol, then pNFS servers
need to mark filehandles according to their specific roles.
3. 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 metadata server and storage device is
immaterial, because, it is always clear to the pNFS client and
server, from upper layer protocol being used (NFSv4.1 or non-
NFSv4.1) what role the request to the common server network
address is directed to.
12.9. Security Considerations for pNFS
pNFS separates file system metadata and data and provides access to
both. There are pNFS-specific operations (listed in Section 12.3)
that provide access to the metadata; all existing NFSv4.1
conventional (non-pNFS) security mechanisms and features apply to
accessing the metadata. The combination of components in a pNFS
system (see Figure 67) is required to preserve the security
properties of NFSv4.1 with respect to an entity accessing storage
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device from a client, including security countermeasures to defend
against threats that NFSv4.1 provides defenses for in environments
where these threats are considered significant.
In some cases, the security countermeasures for connections to
storage devices may take the form of physical isolation or a
recommendation not to use pNFS in an environment. For example, it
may be impractical to provide confidentiality protection for some
storage protocols to protect against eavesdropping; in environments
where eavesdropping on such protocols is of sufficient concern to
require countermeasures, physical isolation of the communication
channel (e.g., via direct connection from client(s) to storage
device(s)) and/or a decision to forego use of pNFS (e.g., and fall
back to conventional NFSv4.1) may be appropriate courses of action.
Where communication with storage devices is subject to the same
threats as client to metadata server communication, the protocols
used for that communication need to provide security mechanisms as
strong as or no weaker than those available via RPSEC_GSS for
NFSv4.1.
pNFS implementations MUST NOT remove NFSv4.1's access controls. The
combination of clients, storage devices, and the metadata server are
responsible for ensuring that all client to storage device file data
access respects NFSv4.1's ACLs and file open modes. This entails
performing both of these checks on every access in the client, the
storage device, or both (as applicable; when the storage device is an
NFSv4.1 server, the storage device is ultimately responsible for
controlling access). If a pNFS configuration performs these checks
only in the client, the risk of a misbehaving client obtaining
unauthorized access is an important consideration in determining when
it is appropriate to use such a pNFS configuration. Such layout
types SHOULD NOT be used when client-only access checks do not
provide sufficient assurance that NFSv4.1 access control is being
applied correctly.
13. PNFS: NFSv4.1 File Layout Type
This section describes the semantics and format of NFSv4.1 file-based
layouts for pNFS. NFSv4.1 file-based layouts uses the
LAYOUT4_NFSV4_1_FILES layout type. The LAYOUT4_NFSV4_1_FILES type
defines striping data across multiple NFSv4.1 data servers.
13.1. Client ID and Session Considerations
Sessions are a REQUIRED feature of NFSv4.1, and this extends to both
the metadata server and file-based (NFSv4.1-based) data servers.
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The role a server plays in pNFS is determined by the result it
returns from EXCHANGE_ID. The roles are:
o metadata server (EXCHGID4_FLAG_USE_PNFS_MDS is set in the result
eir_flags),
o data server (EXCHGID4_FLAG_USE_PNFS_DS)
o 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. The server however
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 |
+--------------------------------------------------------+
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
two roles in 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.
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 must 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
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scopes of the data server and metadata server are equal.
In NFSv4.1, the sessionid 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 client ID on a metadata server, and
because the sessionid 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 must become
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.
13.2. File Layout Definitions
The following definitions apply to the LAYOUT4_NFSV4_1_FILES layout
type, and may 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. An 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 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
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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).
13.3. File Layout Data Types
The high level NFSv4.1 layout types are nfsv4_1_file_layouthint4,
nfsv4_1_file_layout_ds_addr4, and nfsv4_1_file_layout4.
The SETATTR operation supports a layout hint attribute
(Section 5.11.4). When the client sets a layout hint (data type
layouthint4) with a layout type of LAYOUT4_NFSV4_1_FILES (the
loh_type field), the loh_body field contains a value of data type
nfsv4_1_file_layouthint4.
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 type layouthint4: */
struct nfsv4_1_file_layouthint4 {
uint32_t nflh_care;
nfl_util4 nflh_util;
count4 nflh_stripe_count;
};
The generic layout hint structure is described in Section 3.3.19.
The client uses the layout hint in the layout_hint (Section 5.11.4)
attribute to indicate the preferred type of layout to be used for a
newly created file. The LAYOUT4_NFSV4_1_FILES layout type-specific
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content for 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 13.4.4), which is
controlled by the value of nflh_util & NFL4_UFLG_DENSE. 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 13.7), 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). 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.
When LAYOUTGET returns a LAYOUT4_NFSV4_1_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 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:
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 (see Section 13.5) data server address which may
serve equally as the target of IO operations. The length of this
array might be different than the stripe count.
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2. nflda_stripe_indices: An array of indexes used to index into
nflda_multipath_ds_list. 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 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 which 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.
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 13.4.1).
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 13.4.4).
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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 issuing an I/O 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 13.4.4.
* If dense packing is being used, number of elements in
nfl_fh_list MUST be the same as the number of elements in
nflda_stripe_indices. Thus when issuing I/O 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
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 13.4.4.
The details on the interpretation of the layout are in Section 13.4.
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13.4. Interpreting the File Layout
13.4.1. Determining the Stripe Unit Number
To find the stripe unit number that corresponds to the client's
logical file offset, the pattern offset must also be used. The i'th
stripe unit (SUi) is:
relative_offset = file_offset - nfl_pattern_offset;
SUi = floor(relative_offset / stripe_unit_size);
13.4.2. 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:
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];
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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 13.5) 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:
nflda_stripe_indices<> = { 2, 0, 1, 0 }
Now suppose the client gets a layout which has a device ID that maps
to the above device address. The initial index,
nfl_first_stripe_index = 2,
and
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]
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= 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 thirteen storage units are:
+-----+------------+--------------+
| 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 |
+-----+------------+--------------+
13.4.3. 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 13.5) 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 which has a device ID that maps
to the above device address. The initial index,
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 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 thirteen storage 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 |
+-----+------------+--------------+
13.4.4. 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_ds_addr4) 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 must 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 issuing READs and WRITEs directly to the metadata server are
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 a 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 request
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.
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If nfl_util & NFL4_UFLG_DENSE is one, this means that 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 must be packed. Using the
example striping pattern and stripe unit size that was used for the
sparse packing example, the corresponding dense packing would have
all stripe units of all data files filled. 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,
and 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 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:
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.
13.5. Data Server Multipathing
The NFSv4.1 file layout supports multipathing to multiple data server
addresses. Data server-level multipathing is used for bandwidth
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scaling via trunking (Section 2.10.4) and for higher availability of
use in the case of a data server failure. Multipathing allows the
client to switch to another data server address which may that of
another data server that is exporting the same data stripe unit,
without having to contact the metadata server for a new layout.
To support data server 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
it being possible 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 fail over, 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 must 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.
Generally 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 client
ID or session trunking (the latter is RECOMMENDED) as defined in
Section 2.10.4, and 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. For example the data could be read-
only, and the data consist of exact replicas.
13.6. 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
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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 consist of management operations
where the current filehandle is not relevant. 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 12.5.1, 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 13.1, any use of operations
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 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 which is ambiguous regarding its personality
assignment. These include 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 meta-data server, all operations in the second class are
within this group unless a stateid used is incompatible with a
data-server personality in that it is a special stateid or has a
non-zero seqid field.
2. An operation which is referable to the data server personality.
These are data-server I/O operations where the filehandle is one
that can only be validly directed to the data-server personality.
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3. An operation which is referable to the non-data-server
personality. These include 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 one that 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.
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
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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 (see Section 12.5.4.2). Section 13.10, describes the
mechanism by which the client is to handle data server files that do
not reflect the metadata server's size.
13.7. 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 preferred 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 files
layout type.
o When the flag is false, COMMIT operations are to be done to the
data server to which the corresponding writes were done. This
approach is most useful when striping of files is implemented as
part of pNFS server, with the individual data servers each
implementing their own file systems.
o When the flag is true, COMMIT operations are done to the metadata
server, rather than to the individual data servers. This approach
is most useful when the pNFS server is implemented on top of a
clustered file system. In such an implementation, sending
COMMIT's to multiple data servers may result in repeated writes of
metadata blocks as each individual COMMIT is executed, to the
detriment of write performance. Sending a single COMMIT to the
metadata server can provide more efficiency when there exists a
clustered file system capable of implementing such a co-ordinated
COMMIT.
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.
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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 is 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
reissuing the WRITEs to the original data server or using another
path to that data if the layout has not been recalled. Another
option the client has is getting a new layout or just rewrite the
data through 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 12.7.6 for recovery options.
13.8. The Layout Iomode
The layout iomode need not be used by the metadata server when
servicing NFSv4.1 file-based layouts, although in some circumstances
it may be useful. For example, if the server implementation supports
reading from read-only replicas or mirrors, it would be useful for
the server to return a layout enabling the client to do so. As such,
the client SHOULD set the iomode based on its intent to read or write
the data. The client may default to an iomode of LAYOUTIOMODE4_RW.
The iomode need not be checked by the data servers when clients
perform I/O. However, the data servers SHOULD still validate that the
client holds a valid layout and return an error if the client does
not.
13.9. Metadata and Data Server State Coordination
13.9.1. Global Stateid Requirements
When the client sends I/O to a data server, the stateid used MUST NOT
be a layout stateid as returned by LAYOUTGET or sent by
CB_LAYOUTRECALL. Permitted stateids are based on one of the
following: an open stateid (the stateid field of data type OPEN4resok
as returned by OPEN), a delegation stateid (the stateid field of data
types open_read_delegation4 and open_write_delegation4 as returned by
OPEN or WANT_DELEGATION, or as sent by CB_PUSH_DELEG), or a stateid
returned by the LOCK or LOCKU operations. The stateid sent to the
data server MUST be sent with the seqid set to zero, indicating the
most current version of that stateid, rather than indicating a
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specific non-zero seqid value. In no case is the use of special
stateid values allowed.
The stateid used for I/O MUST have the same effect and be subject to
the same validation on a data server as it would if the I/O was being
performed on the metadata server itself in the absence of pNFS. This
has the implication that stateids are globally valid on both the
metadata and data servers. This requires the metadata server to
propagate changes in lock and open state to the data servers, so that
the data servers can validate I/O accesses. This is discussed
further in Section 13.9.2. Depending on when stateids are
propagated, the existence of a valid stateid on the data server may
act as proof of a valid layout.
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 lock owners issuing the I/O
requests. The rules for doing so when referencing data servers are
somewhat different from those discussed in Section 8.2.5 which apply
when accessing metadata servers.
The following rules, applied in order of decreasing priority, govern
the selection of the appropriate stateid:
o If the client holds a delegation for the file in question, the
delegation stateid should be used.
o Otherwise, there must be an open stateid for the current
openowner, and that open stateid for the open file in question is
used, unless mandatory locking, prevents that. See below.
o If the data server had previously responded with NFS4ERR_LOCKED to
use of the open stateid, then the client should use the lock
stateid whenever one exists for that open file with the current
lockowner.
o Special stateids should never be used and if used the data server
MUST reject the I/O with a NFS4ERR_BAD_STATEID error.
13.9.2. Data Server State Propagation
Since the metadata server, which handles lock and open-mode state
changes, as well as ACLs, may not be co-located with the data servers
where I/O access are validated, the server implementation MUST take
care of propagating changes of this state to the data servers. Once
the propagation to the data servers is complete, the full effect of
those changes MUST be in effect at the data servers. However, some
state changes need not be propagated immediately, although all
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changes SHOULD be propagated promptly. These state propagations have
an impact on the design of the control protocol, even though the
control protocol is outside of the scope of this specification.
Immediate propagation refers to the synchronous propagation of state
from the metadata server to the data server(s); the propagation must
be complete before returning to the client.
13.9.2.1. Lock State Propagation
If the pNFS server supports mandatory locking, any mandatory locks on
a file MUST be made effective at the data servers before the request
that establishes them returns to the caller. The effect MUST be the
same as if the mandatory lock state were synchronously propagated to
the data servers, even though the details of the control protocol may
avoid actual transfer of the state under certain circumstances.
On the other hand, since advisory lock state is not used for checking
I/O accesses at the data servers, there is no semantic reason for
propagating advisory lock state to the data servers. Since updates
to advisory locks neither confer nor remove privileges, these changes
need not be propagated immediately, and may not need to be propagated
promptly. The updates to advisory locks need only be propagated when
the data server needs to resolve a question about a stateid. In
fact, if record locking is not mandatory (i.e., is advisory) the
clients are advised not to use the lock-based stateids for I/O at
all. The stateids returned by open are sufficient and eliminate
overhead for this kind of state propagation.
If a client gets back an NFS4ERR_LOCKED error from a data server,
this is an indication that mandatory record locking is in force. The
client recovers from this by getting a record lock that covers the
affected range and re-sends the I/O with the stateid of the record
lock.
13.9.2.2. Open and Deny Mode Validation
Open and deny mode validation MUST be performed against the open and
deny mode(s) held by the data servers. When access is reduced or a
deny mode made more restrictive (because of CLOSE or DOWNGRADE) the
data server MUST prevent any I/Os that would be denied if performed
on the metadata server. When access is expanded, the data server
MUST make sure that no requests are subsequently rejected because of
open or deny issues that no longer apply, given the previous
relaxation.
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13.9.2.3. 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.
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 is
necessary to re-synchronize state such as the size attribute, and the
setting of mtime/change/atime. See Section 12.5.4 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.
Any changes to file attributes that control authorization or access
as reflected by ACCESS calls or READs and WRITEs on the metadata
server, MUST be propagated to the data servers for enforcement on
READ and WRITE I/O calls. If the changes made on the metadata server
result in more restrictive access permissions for any user, those
changes MUST be propagated to the data servers synchronously.
The OPEN operation (Section 18.16.4) 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 requires the server's READ
and WRITE operations to perform appropriate access checking. Changes
to ACLs also require new access checking by READ and WRITE on the
server. The propagation of access right changes due to changes in
ACLs may be asynchronous only if the server implementation is able to
determine that the updated ACL is not more restrictive for any user
specified in the old ACL. Due to the relative infrequency of ACL
updates, it is suggested that all changes be propagated
synchronously.
13.10. Data Server Component File Size
A potential problem exists when a component data file on a particular
data server is grown past EOF; the problem exists for both dense and
sparse layouts. Imagine 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 should
receive 0s back as a result of the READ. However, if the READ falls
on a data server other than the one that received client's original
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WRITE, the data server servicing the READ may still believe that the
file's size is at 0 and return no data with the EOF flag set. The
data server can only return 0s if it knows that the file's size has
been extended. This would require the immediate propagation of the
file's size to all data servers, which is potentially very costly.
Therefore, the client that has initiated the extension of the file's
size MUST be prepared to deal with these EOF conditions; the EOF'ed
or short READs will be treated as a hole in the file and the NFS
client will substitute 0s for the data when the offset is less than
the client's view of the file size.
The NFSv4.1 protocol only provides close to open file data cache
semantics; meaning that when the file is closed all modified data is
written to the server. When a subsequent OPEN of the file is done,
the change attribute is inspected for a difference from a cached
value for the change attribute. For the case above, this means that
a LAYOUTCOMMIT will be done at close (along with the data WRITEs) and
will update the file's size and change attribute. Access from
another client after that point will result in the appropriate size
being returned.
13.11. Layout Revocation and Fencing
As described in Section 12.7, the layout type-specific storage
protocol is responsible for handling the effects of I/Os started
before lease expiration, extending through lease expiration. The
LAYOUT4_NFSV4_1_FILES layout type can prevents all I/Os to data
servers from being executed after lease expiration, without relying
on a precise client lease timer and without requiring data servers to
maintain lease timers. However, while LAYOUT4_NFSV4_1_FILES pNFS
server is free to deny the client all access to the data servers,
because it supports revocation of layouts, it is also free to perform
a denial on a per file basis only when revoking a layout.
In addition to lease expiration, the reasons a layout can be revoked
include: client fails to respond to a CB_LAYOUTRECALL, the metadata
server restarts, or administrative intervention. Regardless of the
reason, once a client's layout has been revoked, the pNFS server MUST
prevent the client from issuing I/O for the affected file from and to
all data servers, in other words, it MUST fence the client from the
affected file on the data servers.
Fencing works as follows. As described in Section 13.1, 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
are used to validate that the client has a valid layout for the I/O
being performed, if it does not, the I/O is rejected with
NFS4ERR_PNFS_NO_LAYOUT. The server can simply check the stateid, and
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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 13.3).
Before the metadata server takes any action to invalidate 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 means that a metadata server may not restripe a file
until it has contacted all of the data servers to invalidate the
layouts from the previous instance nor may it give out mandatory
locks that conflict with layouts from the previous instance without
either doing a specific invalidation (as it would have to do anyway)
or doing a global data server invalidation.
13.12. Security Considerations for the File Layout Type
The NFSv4.1 file layout type MUST adhere to the security
considerations outlined in Section 12.9. NFSv4.1 data servers MUST
make all of the required access checks on each READ or WRITE I/O as
determined by the NFSv4.1 protocol. If the metadata server would
deny READ or WRITE operation on a given file due its ACL, mode
attribute, open mode, open deny mode, mandatory 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 Section 13.9.2 for more details.
The methods for authentication, integrity, and privacy for file
layout-based data servers 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.
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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14. Internationalization
The primary issue in which NFSv4.1 needs to deal with
internationalization, or I18N, is with respect to file names and
other strings as used within the protocol. The choice of string
representation must allow reasonable name/string access to clients
which use various languages. The UTF-8 encoding of the UCS as
defined by ISO10646 [14] allows for this type of access and follows
the policy described in "IETF Policy on Character Sets and
Languages", RFC2277 [15].
RFC3454 [16], otherwise know as "stringprep", documents a framework
for using Unicode/UTF-8 in networking protocols, so as "to increase
the likelihood that string input and string comparison work in ways
that make sense for typical users throughout the world." A protocol
must define a profile of stringprep "in order to fully specify the
processing options." The remainder of this Internationalization
section defines the NFSv4.1 stringprep profiles. Much of terminology
used for the remainder of this section comes from stringprep.
There are three UTF-8 string types defined for NFSv4.1: utf8str_cs,
utf8str_cis, and utf8str_mixed. Separate profiles are defined for
each. Each profile defines the following, as required by stringprep:
o The intended applicability of the profile
o The character repertoire that is the input and output to
stringprep (which is Unicode 3.2 for referenced version of
stringprep)
o The mapping tables from stringprep used (as described in section 3
of stringprep)
o Any additional mapping tables specific to the profile
o The Unicode normalization used, if any (as described in section 4
of stringprep)
o The tables from stringprep listing of characters that are
prohibited as output (as described in section 5 of stringprep)
o The bidirectional string testing used, if any (as described in
section 6 of stringprep)
o Any additional characters that are prohibited as output specific
to the profile
Stringprep discusses Unicode characters, whereas NFSv4.1 renders
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UTF-8 characters. Since there is a one-to-one mapping from UTF-8 to
Unicode, when the remainder of this document refers to Unicode, the
reader should assume UTF-8.
Much of the text for the profiles comes from RFC3491 [17].
14.1. Stringprep profile for the utf8str_cs type
Every use of the utf8str_cs type definition in the NFSv4 protocol
specification follows the profile named nfs4_cs_prep.
14.1.1. Intended applicability of the nfs4_cs_prep profile
The utf8str_cs type is a case sensitive string of UTF-8 characters.
Its primary use in NFSv4.1 is for naming components and pathnames.
Components and pathnames are stored on the server's file system. Two
valid distinct UTF-8 strings might be the same after processing via
the utf8str_cs profile. If the strings are two names inside a
directory, the NFSv4.1 server will need to either:
o disallow the creation of a second name if it's post processed form
collides with that of an existing name, or
o allow the creation of the second name, but arrange so that after
post processing, the second name is different than the post
processed form of the first name.
14.1.2. Character repertoire of nfs4_cs_prep
The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
Appendix A.1
14.1.3. Mapping used by nfs4_cs_prep
The nfs4_cs_prep profile specifies mapping using the following tables
from stringprep:
Table B.1
Table B.2 is normally not part of the nfs4_cs_prep profile as it is
primarily for dealing with case-insensitive comparisons. However, if
the NFSv4.1 file server supports the case_insensitive file system
attribute, and if case_insensitive is true, the NFSv4.1 server MUST
use Table B.2 (in addition to Table B1) when processing utf8str_cs
strings, and the NFSv4.1 client MUST assume Table B.2 (in addition to
Table B.1) are being used.
If the case_preserving attribute is present and set to false, then
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the NFSv4.1 server MUST use table B.2 to map case when processing
utf8str_cs strings. Whether the server maps from lower to upper case
or the upper to lower case is an implementation dependency.
14.1.4. Normalization used by nfs4_cs_prep
The nfs4_cs_prep profile does not specify a normalization form. A
later revision of this specification may specify a particular
normalization form. Therefore, the server and client can expect that
they may receive unnormalized characters within protocol requests and
responses. If the operating environment requires normalization, then
the implementation must normalize utf8str_cs strings within the
protocol before presenting the information to an application (at the
client) or local file system (at the server).
14.1.5. Prohibited output for nfs4_cs_prep
The nfs4_cs_prep profile specifies prohibiting using the following
tables from stringprep:
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
14.1.6. Bidirectional output for nfs4_cs_prep
The nfs4_cs_prep profile does not specify any checking of
bidirectional strings.
14.2. Stringprep profile for the utf8str_cis type
Every use of the utf8str_cis type definition in the NFSv4.1 protocol
specification follows the profile named nfs4_cis_prep.
14.2.1. Intended applicability of the nfs4_cis_prep profile
The utf8str_cis type is a case insensitive string of UTF-8
characters. Its primary use in NFSv4.1 is for naming NFS servers.
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14.2.2. Character repertoire of nfs4_cis_prep
The nfs4_cis_prep profile uses Unicode 3.2, as defined in
stringprep's Appendix A.1
14.2.3. Mapping used by nfs4_cis_prep
The nfs4_cis_prep profile specifies mapping using the following
tables from stringprep:
Table B.1
Table B.2
14.2.4. Normalization used by nfs4_cis_prep
The nfs4_cis_prep profile specifies using Unicode normalization form
KC, as described in stringprep.
14.2.5. Prohibited output for nfs4_cis_prep
The nfs4_cis_prep profile specifies prohibiting using the following
tables from stringprep:
Table C.1.2
Table C.2.2
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
14.2.6. Bidirectional output for nfs4_cis_prep
The nfs4_cis_prep profile specifies checking bidirectional strings as
described in stringprep's section 6.
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14.3. Stringprep profile for the utf8str_mixed type
Every use of the utf8str_mixed type definition in the NFSv4.1
protocol specification follows the profile named nfs4_mixed_prep.
14.3.1. Intended applicability of the nfs4_mixed_prep profile
The utf8str_mixed type is a string of UTF-8 characters, with a prefix
that is case sensitive, a separator equal to '@', and a suffix that
is fully qualified domain name. Its primary use in NFSv4.1 is for
naming principals identified in an Access Control Entry.
14.3.2. Character repertoire of nfs4_mixed_prep
The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
stringprep's Appendix A.1
14.3.3. Mapping used by nfs4_cis_prep
For the prefix and the separator of a utf8str_mixed string, the
nfs4_mixed_prep profile specifies mapping using the following table
from stringprep:
Table B.1
For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
specifies mapping using the following tables from stringprep:
Table B.1
Table B.2
14.3.4. Normalization used by nfs4_mixed_prep
The nfs4_mixed_prep profile specifies using Unicode normalization
form KC, as described in stringprep.
14.3.5. Prohibited output for nfs4_mixed_prep
The nfs4_mixed_prep profile specifies prohibiting using the following
tables from stringprep:
Table C.1.2
Table C.2.2
Table C.3
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Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
14.3.6. Bidirectional output for nfs4_mixed_prep
The nfs4_mixed_prep profile specifies checking bidirectional strings
as described in stringprep's section 6.
14.4. UTF-8 Capabilities
const FSCHARSET_CAP4_CONTAINS_NON_UTF8 = 0x1;
const FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 = 0x2;
typedef uint32_t fs_charset_cap4;
Because some operating environments and file systems do not enforce
character set encodings, NFSv4.1 supports the fs_charset_cap
attribute (Section 5.7.2.11) that indicates to the client a file
system's UTF-8 capabilities. The attribute is an integer containing
a pair of flags. The first flag is FSCHARSET_CAP4_CONTAINS_NON_UTF8,
which, if set to one tells the client the file system contains non-
UTF-8 characters, and the server will not convert non-UTF characters
to UTF-8 if the client reads a symlink or directory, nor will
operations that take component names or pathname have the strings
converted to UTF-8. The second flag is
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 which if set to one, indicates that
the server will accept (and generate) only UTF-8 characters on the
file system. If FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set to one,
FSCHARSET_CAP4_CONTAINS_NON_UTF8 MUST be set to zero.
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 SHOULD always be set to one.
14.5. UTF-8 Related Errors
Where the client sends an invalid UTF-8 string, the server should
return an NFS4ERR_INVAL (Table 11) error. This includes cases in
which inappropriate prefixes are detected and where the count
includes trailing bytes that do not constitute a full UCS character.
Where the client supplied string is valid UTF-8 but contains
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characters that are not supported by the server as a value for that
string (e.g. names containing characters that have more than two
bytes on a file system that supports Unicode characters only), the
server should return an NFS4ERR_BADCHAR (Table 11) error.
Where a UTF-8 string is used as a file name, and the file system,
while supporting all of the characters within the name, does not
allow that particular name to be used, the server should return the
error NFS4ERR_BADNAME (Table 11). This includes situations in which
the server file system imposes a normalization constraint on name
strings, but will also include such situations as file system
prohibitions of "." and ".." as file names for certain operations,
and other such constraints.
15. 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.
15.1. Error Definitions
Protocol Error Definitions
+-----------------------------------+--------+-------------------+
| Error | Number | Description |
+-----------------------------------+--------+-------------------+
| NFS4_OK | 0 | Section 15.1.3.1 |
| NFS4ERR_ACCESS | 13 | Section 15.1.6.1 |
| NFS4ERR_ATTRNOTSUPP | 10032 | Section 15.1.15.1 |
| NFS4ERR_ADMIN_REVOKED | 10047 | Section 15.1.5.1 |
| NFS4ERR_BACK_CHAN_BUSY | 10057 | Section 15.1.12.1 |
| NFS4ERR_BADCHAR | 10040 | Section 15.1.7.1 |
| NFS4ERR_BADHANDLE | 10001 | Section 15.1.2.1 |
| NFS4ERR_BADIOMODE | 10049 | Section 15.1.10.1 |
| NFS4ERR_BADLAYOUT | 10050 | Section 15.1.10.2 |
| NFS4ERR_BADNAME | 10041 | Section 15.1.7.2 |
| NFS4ERR_BADOWNER | 10039 | Section 15.1.15.2 |
| NFS4ERR_BADSESSION | 10052 | Section 15.1.11.1 |
| NFS4ERR_BADSLOT | 10053 | Section 15.1.11.2 |
| NFS4ERR_BADTYPE | 10007 | Section 15.1.4.1 |
| NFS4ERR_BADXDR | 10036 | Section 15.1.1.1 |
| NFS4ERR_BAD_COOKIE | 10003 | Section 15.1.1.2 |
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| NFS4ERR_BAD_HIGH_SLOT | 10077 | Section 15.1.11.3 |
| NFS4ERR_BAD_RANGE | 10042 | Section 15.1.8.1 |
| NFS4ERR_BAD_SEQID | 10026 | Section 15.1.16.1 |
| NFS4ERR_BAD_SESSION_DIGEST | 10051 | Section 15.1.12.2 |
| NFS4ERR_BAD_STATEID | 10025 | Section 15.1.5.2 |
| NFS4ERR_CB_PATH_DOWN | 10048 | Section 15.1.16.2 |
| NFS4ERR_CLID_INUSE | 10017 | Section 15.1.13.2 |
| NFS4ERR_CLIENTID_BUSY | 10074 | Section 15.1.13.1 |
| NFS4ERR_COMPLETE_ALREADY | 10054 | Section 15.1.9.1 |
| NFS4ERR_CONN_BINDING_NOT_ENFORCED | 10073 | Section 15.1.12.3 |
| NFS4ERR_CONN_NOT_BOUND_TO_SESSION | 10055 | Section 15.1.11.5 |
| NFS4ERR_DEADLOCK | 10045 | Section 15.1.8.2 |
| NFS4ERR_DEADSESSION | 10078 | Section 15.1.11.4 |
| NFS4ERR_DELAY | 10008 | Section 15.1.1.3 |
| NFS4ERR_DELEG_ALREADY_WANTED | 10056 | Section 15.1.14.1 |
| NFS4ERR_DENIED | 10010 | Section 15.1.8.3 |
| NFS4ERR_DIRDELEG_UNAVAIL | 10084 | Section 15.1.14.2 |
| NFS4ERR_DQUOT | 69 | Section 15.1.4.2 |
| NFS4ERR_ENCR_ALG_UNSUPP | 10079 | Section 15.1.13.3 |
| NFS4ERR_EXIST | 17 | Section 15.1.4.3 |
| NFS4ERR_EXPIRED | 10011 | Section 15.1.5.4 |
| NFS4ERR_FBIG | 27 | Section 15.1.4.4 |
| NFS4ERR_FHEXPIRED | 10014 | Section 15.1.2.2 |
| NFS4ERR_FILE_OPEN | 10046 | Section 15.1.4.5 |
| NFS4ERR_GRACE | 10013 | Section 15.1.9.2 |
| NFS4ERR_HASH_ALG_UNSUPP | 10072 | Section 15.1.13.4 |
| NFS4ERR_INVAL | 22 | Section 15.1.1.4 |
| NFS4ERR_IO | 5 | Section 15.1.4.6 |
| NFS4ERR_ISDIR | 21 | Section 15.1.2.3 |
| NFS4ERR_LAYOUTTRYLATER | 10058 | Section 15.1.10.3 |
| NFS4ERR_LAYOUTUNAVAILABLE | 10059 | Section 15.1.10.4 |
| NFS4ERR_LEASE_MOVED | 10031 | Section 15.1.16.3 |
| NFS4ERR_LOCKED | 10012 | Section 15.1.8.4 |
| NFS4ERR_LOCKS_HELD | 10037 | Section 15.1.8.5 |
| NFS4ERR_LOCK_NOTSUPP | 10043 | Section 15.1.8.6 |
| NFS4ERR_LOCK_RANGE | 10028 | Section 15.1.8.7 |
| NFS4ERR_MINOR_VERS_MISMATCH | 10021 | Section 15.1.3.2 |
| NFS4ERR_MLINK | 31 | Section 15.1.4.7 |
| NFS4ERR_MOVED | 10019 | Section 15.1.2.4 |
| NFS4ERR_NAMETOOLONG | 63 | Section 15.1.7.3 |
| NFS4ERR_NOENT | 2 | Section 15.1.4.8 |
| NFS4ERR_NOFILEHANDLE | 10020 | Section 15.1.2.5 |
| NFS4ERR_NOMATCHING_LAYOUT | 10060 | Section 15.1.10.5 |
| NFS4ERR_NOSPC | 28 | Section 15.1.4.9 |
| NFS4ERR_NOTDIR | 20 | Section 15.1.2.6 |
| NFS4ERR_NOTEMPTY | 66 | Section 15.1.4.10 |
| NFS4ERR_NOTSUPP | 10004 | Section 15.1.1.5 |
| NFS4ERR_NOT_ONLY_OP | 10081 | Section 15.1.3.3 |
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| NFS4ERR_NOT_SAME | 10027 | Section 15.1.15.3 |
| NFS4ERR_NO_GRACE | 10033 | Section 15.1.9.3 |
| NFS4ERR_NXIO | 6 | Section 15.1.16.4 |
| NFS4ERR_OLD_STATEID | 10024 | Section 15.1.5.5 |
| NFS4ERR_OPENMODE | 10038 | Section 15.1.8.8 |
| NFS4ERR_OP_ILLEGAL | 10044 | Section 15.1.3.4 |
| NFS4ERR_OP_NOT_IN_SESSION | 10070 | Section 15.1.3.5 |
| NFS4ERR_PERM | 1 | Section 15.1.6.2 |
| NFS4ERR_PNFS_IO_HOLE | 10075 | Section 15.1.10.6 |
| NFS4ERR_PNFS_NO_LAYOUT | 10080 | Section 15.1.10.7 |
| NFS4ERR_RECALLCONFLICT | 10061 | Section 15.1.14.3 |
| NFS4ERR_RECLAIM_BAD | 10034 | Section 15.1.9.4 |
| NFS4ERR_RECLAIM_CONFLICT | 10035 | Section 15.1.9.5 |
| NFS4ERR_REJECT_DELEG | 10085 | Section 15.1.14.4 |
| NFS4ERR_REP_TOO_BIG | 10066 | Section 15.1.3.6 |
| NFS4ERR_REP_TOO_BIG_TO_CACHE | 10067 | Section 15.1.3.7 |
| NFS4ERR_REQ_TOO_BIG | 10065 | Section 15.1.3.8 |
| NFS4ERR_RESTOREFH | 10030 | Section 15.1.16.5 |
| NFS4ERR_RETRY_UNCACHED_REP | 10068 | Section 15.1.3.9 |
| NFS4ERR_RETURNCONFLICT | 10086 | Section 15.1.10.8 |
| NFS4ERR_ROFS | 30 | Section 15.1.4.11 |
| NFS4ERR_SAME | 10009 | Section 15.1.15.4 |
| NFS4ERR_SHARE_DENIED | 10015 | Section 15.1.8.9 |
| NFS4ERR_SEQUENCE_POS | 10064 | Section 15.1.3.10 |
| NFS4ERR_SEQ_FALSE_RETRY | 10076 | Section 15.1.11.6 |
| NFS4ERR_SEQ_MISORDERED | 10063 | Section 15.1.11.7 |
| NFS4ERR_SERVERFAULT | 10006 | Section 15.1.1.6 |
| NFS4ERR_STALE | 70 | Section 15.1.2.7 |
| NFS4ERR_STALE_CLIENTID | 10022 | Section 15.1.13.5 |
| NFS4ERR_STALE_STATEID | 10023 | Section 15.1.16.6 |
| NFS4ERR_SYMLINK | 10029 | Section 15.1.2.8 |
| NFS4ERR_TOOSMALL | 10005 | Section 15.1.1.7 |
| NFS4ERR_TOO_MANY_OPS | 10070 | Section 15.1.3.11 |
| NFS4ERR_UNKNOWN_LAYOUTTYPE | 10062 | Section 15.1.10.9 |
| NFS4ERR_UNSAFE_COMPOUND | 10069 | Section 15.1.3.12 |
| NFS4ERR_WRONGSEC | 10016 | Section 15.1.6.3 |
| NFS4ERR_WRONG_CRED | 10082 | Section 15.1.6.4 |
| NFS4ERR_WRONG_TYPE | 10083 | Section 15.1.2.9 |
| NFS4ERR_XDEV | 18 | Section 15.1.4.12 |
+-----------------------------------+--------+-------------------+
Table 11
15.1.1. General Errors
This section deals with errors that are applicable to a broad set of
different purposes.
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15.1.1.1. NFS4ERR_BADXDR (Error Code 10036)
The arguments for this op 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 which is not valid for the enum. A replier
may pre-parse all ops for a Compound procedure before doing any
operation execution and return RPC-level XDR errors in that case.
15.1.1.2. NFS4ERR_BAD_COOKIE (Error Code 10003)
Used for ops 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.
15.1.1.3. 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 client should
wait and then try the request with a new slot and sequence value.
Some example of situations that might lead to this situation:
o A server that supports hierarchical storage receives a request to
process a file that had been migrated.
o An operation requires a delegation recall to proceed and waiting
for this delegation recall makes processing this request in a
timely fashion impossible.
In such cases, the error NFS4ERR_DELAY allows these preparatory
operations to proceed without holding up client resources such as a
session slot. The client can then retry the operation in question.
Note that without the ability to return NFS4ERR_DELAY and the
client's willingness to retry when receiving it, deadlock might well
result. 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.
15.1.1.4. NFS4ERR_INVAL (Error Code 22)
The arguments for this op are not valid for some reason, even though
they do match those specified in the XDR definition for the request.
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15.1.1.5. NFS4ERR_NOTSUPP (Error Code 10004)
Operation not supported, either because the operation is an OPTIONAL
one and is not supported by this server or because the operation is
MUST NOT be implemented in the current minor version.
15.1.1.6. NFS4ERR_SERVERFAULT (Error Code 10006)
An error occurred on the server which 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.
15.1.1.7. 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.
15.1.2. 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.
15.1.2.1. NFS4ERR_BADHANDLE (Error Code 10001)
Illegal NFS filehandle for the current server. The current file
handle failed internal consistency checks. Once accepted as valid
(by PUTFH), no subsequent status change can cause the filehandle to
generate this error.
15.1.2.2. NFS4ERR_FHEXPIRED (Error Code 10014)
A current or saved filehandle which is an argument to the current
operation is volatile and has expired at the server.
15.1.2.3. 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
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target of this operation.
15.1.2.4. NFS4ERR_MOVED (Error Code 10019)
The file system which contains the current filehandle object is not
present at the server. It may have been relocated, migrated to
another server or 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 11.2
15.1.2.5. 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).
15.1.2.6. NFS4ERR_NOTDIR (Error Code 20)
The current (or saved) filehandle designates an object which is not a
directory for an operation in which a directory is required.
15.1.2.7. 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.
15.1.2.8. 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.
15.1.2.9. NFS4ERR_WRONG_TYPE (Error Code 10083)
The current (or saved) filehandle designates an object which 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.
15.1.3. Compound Structure Errors
This section deals with errors that relate to overall structure of a
Compound request (by which we mean to include both COMPOUND and
CB_COMPOUND), rather than to particular operations.
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There are a number of basic constraints on the operations that may
appear in a Compound request. Sessions adds to these basic
constraints by requiring a Sequence operation (either SEQUENCE or
CB_SEQUENCE) at the start of the Compound.
15.1.3.1. NFS_OK (Error code 0)
Indicates the operation completed successfully, in that all of the
constituent operations completed without error.
15.1.3.2. 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 must specify a result count of zero.
15.1.3.3. 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. This error
results when that constraint is not met.
15.1.3.4. 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 ops for a Compound procedure before doing any
operation execution, an RPC-level XDR error may be returned in this
case.
15.1.3.5. NFS4ERR_OP_NOT_IN_SESSION (Error Code 10070)
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.
15.1.3.6. NFS4ERR_REP_TOO_BIG (Error Code 10066)
The reply to a Compound would exceed the channel's negotiated maximum
response size.
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15.1.3.7. 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.
15.1.3.8. NFS4ERR_REQ_TOO_BIG (Error Code 10065)
The Compound request exceeds the channel's negotiated maximum size
for requests.
15.1.3.9. NFS4ERR_RETRY_UNCACHED_REP (Error Code 10068)
The requester has attempted a retry of a Compound which it previously
requested not be placed in the reply cache.
15.1.3.10. NFS4ERR_SEQUENCE_POS (Error Code 10064)
A Sequence operation appeared in a position other than the first
operation of a Compound request.
15.1.3.11. NFS4ERR_TOO_MANY_OPS (Error Code 10070)
The Compound request has too many operations, exceeding the count
negotiated when the session was created.
15.1.3.12. 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 changing the
current filehandle which is not followed by a GETFH.
15.1.4. File System Errors
These errors describe situations which occurred in the underlying
file system implementation rather than in the protocol or any NFSv4.x
feature.
15.1.4.1. 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 it is a type not supported by the server, or because it is a
type for which create is not intended such as a regular file or named
attribute, for which OPEN is used to do the file creation.
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15.1.4.2. NFS4ERR_DQUOT (Error Code 19)
Resource (quota) hard limit exceeded. The user's resource limit on
the server has been exceeded.
15.1.4.3. NFS4ERR_EXIST (Error Code 17)
A file of the specified target name (when creating, renaming or
linking) already exists.
15.1.4.4. NFS4ERR_FBIG (Error Code 27)
File too large. The operation would have caused a file to grow
beyond the server's limit.
15.1.4.5. 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.
15.1.4.6. NFS4ERR_IO (Error Code 5)
Indicates that an I/O error occurred for which the file system was
unable to provide recovery.
15.1.4.7. 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.
15.1.4.8. NFS4ERR_NOENT (Error Code 2)
Indicates no such file or directory. The file or directory name
specified does not exist.
15.1.4.9. NFS4ERR_NOSPC (Error Code 28)
Indicates no space left on device. The operation would have caused
the server's file system to exceed its limit.
15.1.4.10. NFS4ERR_NOTEMPTY (Error Code 66)
An attempt was made to remove a directory that was not empty.
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15.1.4.11. NFS4ERR_ROFS (Error Code 30)
Indicates a read-only file system. A modifying operation was
attempted on a read-only file system.
15.1.4.12. 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:
o That between filesystems (where the fsids are different).
o That between different named attribute directories or between a
named attribute directory and an ordinary directory.
o That between regions of a file system that the file system
implementation treats as separate (for example for space
accounting purposes), and where cross-connection between the
regions are not allowed.
15.1.5. 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 revoked locking state. Depending on
the operation, the stateid when valid may designate opens, byte-range
locks, file or directory delegations, layouts, or device maps.
15.1.5.1. 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.
15.1.5.2. NFS4ERR_BAD_STATEID (Error Code 10026)
A stateid does not properly designate any valid state. See
Section 8.2.4 and Section 8.2.3 for a discussion of how stateids are
validated.
15.1.5.3. NFS4ERR_DELEG_REVOKED (Error Code 10056)
A stateid designates recallable locking state of any type that has
been revoked due to the failure of the client to return the lock,
when it was recalled.
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15.1.5.4. 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.
15.1.5.5. NFS4ERR_OLD_STATEID (Error Code 10024)
A stateid with a non-zero seqid value does match the current seqid
for the state designated by the user.
15.1.6. Security Errors
These are the various permission-related errors in NFSv4.1.
15.1.6.1. 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 15.1.6.2), which restricts itself to owner or
privileged user permission failures, and NFS4ERR_WRONG_CRED
(Section 15.1.6.4) which deals with appropriate permission to delete
or modify transient objects, based on the credentials of the user
that created them.
15.1.6.2. 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.
15.1.6.3. 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 retry the
operation. SECINFO and SECINFO_NO_NAME can be used to determine the
appropriate mechanism.
15.1.6.4. NFS4ERR_WRONG_CRED (Error Code 10082)
An operation manipulating state was attempted by a principal that was
not allowed to modify that piece of state.
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15.1.7. Name Errors
Names in NFSv4 are UTF-8 strings. When the strings are not valid
UTF-8 or are of length zero, the error NFS4ERR_INVAL results.
Besides this, there are a number of other errors to indicate specific
problems with names.
15.1.7.1. NFS4ERR_BADCHAR (Error Code 10040)
A UTF-8 string contains a character which is not supported by the
server in the context in which it being used.
15.1.7.2. NFS4ERR_BADNAME (Error Code 10041)
A name string in a request consisted of valid UTF-8 characters
supported by the server but the name is not supported by the server
as a valid name for 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.
15.1.7.3. NFS4ERR_NAMETOOLONG (Error Code 63)
Returned when the filename in an operation exceeds the server's
implementation limit.
15.1.8. Locking Errors
This section deal 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
the next section.
15.1.8.1. NFS4ERR_BAD_RANGE (Error Code 10042)
The range for a LOCK, LOCKT, or LOCKU operation is not appropriate to
the allowable range of offsets for the server. Specifically, this
error results when a server which only supports 32-bit ranges
receives a range that cannot be handled by that server. (See
Section 18.10.3).
15.1.8.2. NFS4ERR_DEADLOCK (Error Code 10045)
The server has been able to determine a file locking deadlock
condition for a blocking lock request.
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15.1.8.3. 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 retry the lock request until
the lock is accepted. See Section 9.4 for a discussion of retry.
15.1.8.4. 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:
o There is a share reservation inconsistent with the I/O being done.
o The range to be read or written intersects an existing mandatory
byte range lock.
15.1.8.5. NFS4ERR_LOCKS_HELD (Error Code 10037)
An operation was prevented by the unexpected presence of locks.
15.1.8.6. NFS4ERR_LOCK_NOTSUPP (Error Code 10043)
A locking request was attempted which would require the upgrade or
downgrade of a lock range already held by the owner when the server
does not support atomic upgrade or downgrade of locks.
15.1.8.7. NFS4ERR_LOCK_RANGE (Error Code 10028)
A lock request is operating on a range that overlaps in part a
currently held lock for the current lock owner and does not precisely
match a single such lock where the server does not support this type
of request, and thus does not implement POSIX locking semantics. See
Section 18.10.4, Section 18.11.4, and Section 18.12.4 for a
discussion of how this applies to LOCK, LOCKT, and LOCKU
respectively.
15.1.8.8. 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 only
for read).
15.1.8.9. NFS4ERR_SHARE_DENIED (Error Code 10015)
An attempt to OPEN a file with a share reservation has failed because
of a share conflict.
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15.1.9. Reclaim Errors
These errors relate to the process of reclaiming locks after a server
restart.
15.1.9.1. NFS4ERR_COMPLETE_ALREADY (Error Code 10054)
The client previously sent a successful RECLAIM_COMPLETE operation.
An additional RECLAIM_COMPLETE operation is not necessary and results
in this error.
15.1.9.2. NFS4ERR_GRACE (Error Code 10013)
The server is in its recovery or grace period which should at least
match the lease period of the server. A locking request other than a
reclaim could not be granted during that period.
15.1.9.3. 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 can occur because the reclaim has been done
outside of the grace period of the server, after the client has done
a RECLAIM_COMPLETE operation, or because previous operations have
created a situation in which the server is not able to determine that
a reclaim-interfering edge condition does not exist.
15.1.9.4. NFS4ERR_RECLAIM_BAD (Error Code 10034)
A reclaim attempted by the client does not match the server's state
consistency checks and has been rejected therefore as invalid.
15.1.9.5. NFS4ERR_RECLAIM_CONFLICT (Error Code 10035)
The reclaim attempted by the client has encountered a conflict and
cannot be satisfied. 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.
15.1.10. pNFS Errors
This section deals with pNFS-related errors including those that are
associated with using NFSv4.1 to communicate with a data server.
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15.1.10.1. NFS4ERR_BADIOMODE (Error Code 10049)
An invalid or inappropriate layout iomode was specified.
15.1.10.2. 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.
15.1.10.3. NFS4ERR_LAYOUTTRYLATER (Error Code 10058)
Layouts are temporarily unavailable for the file. The client should
retry later.
15.1.10.4. NFS4ERR_LAYOUTUNAVAILABLE (Error Code 10059)
Returned when layouts are not available for the current file system
or the particular specified file.
15.1.10.5. 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.
15.1.10.6. 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 the STRIPE4_SPARSE
stripe type. See Section 13.4.4.
15.1.10.7. 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.
15.1.10.8. 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 12.5.5.2.1.3.
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15.1.10.9. NFS4ERR_UNKNOWN_LAYOUTTYPE (Error Code 10062)
The client has specified a layout type which is not supported by the
server.
15.1.11. Session Use Errors
This section deals with errors encountered in using sessions, that
is, in issuing requests over them using the Sequence (i.e. either
SEQUENCE or CB_SEQUENCE) operations.
15.1.11.1. NFS4ERR_BADSESSION (Error Code 10052)
A sessionid was specified which does not exist.
15.1.11.2. 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.
15.1.11.3. NFS4ERR_BAD_HIGH_SLOT (Error Code 10077)
The highest_slot argument in a Sequence operation exceeds the
replier's enforced highest_slotid.
15.1.11.4. NFS4ERR_DEADSESSION (Error Code 10078)
The specified session is a persistent session which 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).
15.1.11.5. 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, in an environment where the
associated client ID specified that connection binding be enforced.
15.1.11.6. 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.
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15.1.11.7. NFS4ERR_SEQ_MISORDERED (Error Code 10063)
The requester sent a Sequence operation with an invalid sequence id.
15.1.12. Session Management Errors
This section deals with errors associated with requests used in
session management.
15.1.12.1. 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.
15.1.12.2. NFS4ERR_BAD_SESSION_DIGEST (Error Code 10051)
The digest used in a SET_SSV or BIND_CONN_TO_SESSION request is not
valid.
15.1.12.3. NFS4ERR_CONN_BINDING_NOT_ENFORCED (Error Code 10073)
The client is made an attempt to use enforced connection association,
when it has disabled enforcement when the client ID was created, in
that it did not opt for SP4_SSV state protection when the client ID
using EXCHANGE_ID.
15.1.13. Client Management Errors
This sections deals with errors associated with requests used to
create and manage client IDs.
15.1.13.1. 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.
15.1.13.2. NFS4ERR_CLID_INUSE (Error Code 10017)
While processing an EXCHANGE_ID operation, the server was presented
with a co_ownerid field matches an existing client with valid leased
state but the principal issuing the EXCHANGE_ID is different than
that establishing the existing client. This indicates a (most likely
due to chance) collision between clients. The client should recover
by changing the co_ownerid and retrying EXCHANGE_ID.
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15.1.13.3. NFS4ERR_ENCR_ALG_UNSUPP (Error Code 10079)
An EXCHANGE_ID was sent which specified state protection via SSV, and
where the set of encryption algorithms presented by the client did
not include any supported by the server.
15.1.13.4. NFS4ERR_HASH_ALG_UNSUPP (Error Code 10072)
An EXCHANGE_ID was sent which specified state protection via SSV, and
where the set of hashing algorithms presented by the client did not
include any supported by the server.
15.1.13.5. 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.
15.1.14. Delegation Errors
This section deals with errors associated with requesting and
returning delegations.
15.1.14.1. NFS4ERR_DELEG_ALREADY_WANTED (Error Code 10056)
The client has requested a delegation when it had already registered
that it wants that same delegation.
15.1.14.2. NFS4ERR_DIRDELEG_UNAVAIL (Error Code 10084)
This error is returned when the server is unable or unwilling to
provide a requested directory delegation.
15.1.14.3. NFS4ERR_RECALLCONFLICT (Error Code 10061)
A recallable object (i.e. a layout, delegation, or device map is
unavailable due to a conflicting recall operation for that object
that is currently in progress.
15.1.14.4. NFS4ERR_REJECT_DELEG (Error Code 10085)
The callback operation invoked to deal with a new delegation has
rejected it.
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15.1.15. Attribute Handling Errors
This section deals with errors specific to attribute handling within
NFSv4.
15.1.15.1. NFS4ERR_ATTRNOTSUPP (Error Code 10032)
An attribute specified is not supported by the server. This error
MUST NOT be returned by the GETATTR operation.
15.1.15.2. NFS4ERR_BADOWNER (Error Code 10039)
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.
15.1.15.3. 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.
15.1.15.4. 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.
15.1.16. Obsoleted Errors
These errors MUST NOT be generated by any NFSv4.1 operation. This
can be for a number of reasons.
o The function provided by the error has been superseded by one of
the status bits returned by the SEQUENCE operation.
o The new session structure and associated change in locking have
made the error unnecessary.
o There has been a restructuring of some errors for NFSv4.1 which
resulted in the elimination of certain of the errors.
15.1.16.1. NFS4ERR_BAD_SEQID (Error Code 10026)
The sequence number in a locking request is neither the next expected
number or the last number processed. These sequence id's are ignored
in NFSv4.1.
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15.1.16.2. NFS4ERR_CB_PATH_DOWN (Error Code 10048)
There is a problem contacting the client via the callback path
15.1.16.3. NFS4ERR_LEASE_MOVED (Error Code 10031)
A lease being renewed is associated with a file system that has been
migrated to a new server
15.1.16.4. NFS4ERR_NXIO (Error Code 5)
I/O error. No such device or address.
15.1.16.5. NFS4ERR_RESTOREFH (Error Code 10030)
The RESTOREFH operation does not have a saved filehandle (identified
by SAVEFH) to operate upon.
15.1.16.6. NFS4ERR_STALE_STATEID (Error Code 10023)
A stateid generated by an earlier server instance was used.
15.2. Operations and their valid errors
This section contains a table which 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:
o The operations which MUST NOT be implemented: OPEN_CONFIRM,
RELEASE_LOCKOWNER, RENEW, SETCLIENTID, and SETCLIENTID_CONFIRM.
o The invalid operation: ILLEGAL.
Valid error returns for each protocol operation
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+----------------------+--------------------------------------------+
| Operation | Errors |
+----------------------+--------------------------------------------+
| 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_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS |
| BACKCHANNEL_CTL | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_INVAL, |
| | NFS4ERR_NOENT, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS |
| BIND_CONN_TO_SESSION | NFS4ERR_BADSESSION, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_SESSION_DIGEST, |
| | NFS4ERR_CONN_BINDING_NOT_ENFORCED, |
| | 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_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_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
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| 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_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, 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_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNSAFE_COMPOUND |
| CREATE_SESSION | NFS4ERR_BADXDR, 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_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_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED |
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| 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, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, 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_SERVERFAULT, |
| | NFS4ERR_STALE_CLIENTID, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED |
| DESTROY_SESSION | NFS4ERR_BACK_CHAN_BUSY, |
| | NFS4ERR_BADSESSION, NFS4ERR_BADXDR, |
| | 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_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_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
| 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_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED |
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| 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_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_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
| GETDEVICEINFO | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_DELAY, NFS4ERR_INVAL, |
| | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, 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_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE |
| GETFH | NFS4ERR_FHEXPIRED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_STALE |
| ILLEGAL | NFS4ERR_BADXDR NFS4ERR_OP_ILLEGAL |
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| LAYOUTCOMMIT | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADIOMODE, |
| | NFS4ERR_BADLAYOUT, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_EXPIRED, NFS4ERR_FBIG, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | 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_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_SYMLINK, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_CRED |
| 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_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_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOOSMALL, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
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| 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_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, |
| | 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_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE, NFS4ERR_XDEV |
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| 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_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, 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_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_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_CRED |
Shepler, et al. Expires August 1, 2008 [Page 341]
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| 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_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, NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, 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_SAME, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
Shepler, et al. Expires August 1, 2008 [Page 342]
Internet-Draft NFSv4.1 January 2008
| 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_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_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED |
Shepler, et al. Expires August 1, 2008 [Page 343]
Internet-Draft NFSv4.1 January 2008
| 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_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_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_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_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC |
Shepler, et al. Expires August 1, 2008 [Page 344]
Internet-Draft NFSv4.1 January 2008
| 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_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, |
| | NFS4ERR_NOT_SAME, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, 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_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
Shepler, et al. Expires August 1, 2008 [Page 345]
Internet-Draft NFSv4.1 January 2008
| 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_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, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, 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_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_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_XDEV |
| RENEW | NFS4ERR_NOTSUPP |
Shepler, et al. Expires August 1, 2008 [Page 346]
Internet-Draft NFSv4.1 January 2008
| 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_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_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_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_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_TOO_MANY_OPS |
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| 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_CONN_BINDING_NOT_ENFORCED, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, 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_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_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
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| VERIFY | 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_NOT_SAME, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, 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_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, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_WRONG_TYPE |
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+----------------------+--------------------------------------------+
Table 12
15.3. Callback operations and their valid errors
This section contains a table which 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.
Valid error returns for each protocol callback operation
+-------------------------+-----------------------------------------+
| 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_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_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
| CB_NOTIFY | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, 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_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
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| 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_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_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, |
| | NFS4ERR_REQ_TOO_BIG, |
| | 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_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_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
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| 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_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, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_TOO_MANY_OPS |
+-------------------------+-----------------------------------------+
Table 13
15.4. 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 |
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| 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 |
| 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 |
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| NFS4ERR_BADXDR | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_ILLEGAL, |
| | CB_LAYOUTRECALL, CB_NOTIFY, |
| | 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, |
| | 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_CLID_INUSE | EXCHANGE_ID |
| NFS4ERR_CLIENTID_BUSY | DESTROY_CLIENTID |
| NFS4ERR_COMPLETE_ALREADY | RECLAIM_COMPLETE |
| NFS4ERR_CONN_BINDING_NOT_ENFORCED | BIND_CONN_TO_SESSION, SET_SSV |
| NFS4ERR_CONN_NOT_BOUND_TO_SESSION | CB_SEQUENCE, DESTROY_SESSION, |
| | SEQUENCE |
| NFS4ERR_DEADLOCK | LOCK |
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| 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, |
| | 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 |
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| NFS4ERR_DELAY | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, 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, 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, LAYOUTRETURN, |
| | LOCK, LOCKU, OPEN, |
| | OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
| NFS4ERR_FBIG | LAYOUTCOMMIT, OPEN, SETATTR, |
| | WRITE |
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| 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, |
| | WRITE |
| NFS4ERR_HASH_ALG_UNSUPP | EXCHANGE_ID |
| NFS4ERR_INVAL | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, CB_PUSH_DELEG, |
| | CB_RECALLABLE_OBJ_AVAIL, |
| | CB_RECALL_ANY, CREATE, |
| | CREATE_SESSION, DELEGRETURN, |
| | EXCHANGE_ID, GETATTR, |
| | GETDEVICEINFO, GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTGET, LAYOUTRETURN, |
| | LINK, LOCK, LOCKT, LOCKU, |
| | LOOKUP, NVERIFY, OPEN, |
| | OPEN_DOWNGRADE, READ, |
| | READDIR, READLINK, |
| | RECLAIM_COMPLETE, REMOVE, |
| | RENAME, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WANT_DELEGATION, |
| | WRITE |
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| 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 |
| 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 |
| 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 |
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| NFS4ERR_NOFILEHANDLE | ACCESS, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, GETATTR, |
| | GETDEVICEINFO, 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_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_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, |
| | LOCK, OPEN, WANT_DELEGATION |
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| 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, CB_GETATTR, |
| | CB_LAYOUTRECALL, CB_NOTIFY, |
| | 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 |
| 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 |
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| NFS4ERR_REP_TOO_BIG | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, 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 |
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| NFS4ERR_REP_TOO_BIG_TO_CACHE | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, 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 |
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| NFS4ERR_REQ_TOO_BIG | ACCESS, BACKCHANNEL_CTL, |
| | BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_LAYOUTRECALL, |
| | CB_NOTIFY, 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_RETRY_UNCACHED_REP | CB_SEQUENCE, SEQUENCE |
| 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 |
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| NFS4ERR_SERVERFAULT | ACCESS, BIND_CONN_TO_SESSION, |
| | CB_GETATTR, CB_NOTIFY, |
| | 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 |
| 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 |
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| 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_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_UNKNOWN_LAYOUTTYPE | CB_LAYOUTRECALL, |
| | GETDEVICEINFO, GETDEVICELIST, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, NVERIFY, |
| | SETATTR, VERIFY |
| NFS4ERR_UNSAFE_COMPOUND | CREATE, OPEN, OPENATTR |
| NFS4ERR_WRONGSEC | LOOKUP, LOOKUPP, OPEN, PUTFH, |
| | PUTPUBFH, PUTROOTFH, |
| | RESTOREFH |
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| 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 |
+-----------------------------------+-------------------------------+
Table 14
16. NFSv4.1 Procedures
16.1. Procedure 0: NULL - No Operation
16.1.1. ARGUMENTS
void;
16.1.2. RESULTS
void;
16.1.3. DESCRIPTION
Standard NULL procedure. Void argument, 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.
16.1.4. ERRORS
None.
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16.2. Procedure 1: COMPOUND - Compound Operations
16.2.1. 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,
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,
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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
};
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;
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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 */
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
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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;
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<>;
};
16.2.2. 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;
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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;
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
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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;
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
opwant_destroy_clientid;
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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<>;
};
16.2.3. DESCRIPTION
The COMPOUND procedure is used to combine one or more of the NFS
operations into a single RPC request. The main NFS RPC program has
two main procedures: NULL and COMPOUND. All other operations use the
COMPOUND procedure as a wrapper.
The COMPOUND procedure is used to combine individual 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 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 2.10.5.4 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. In this case, 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,
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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.
Note that operations, 0 (zero) and 1 (one) are not defined for the
COMPOUND procedure. Operation 2 is not defined but reserved for
future definition and use with minor versioning. If the server
receives a operation array that contains operation 2 and the
minorversion field has a value of 0 (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_RELEASE_LOCKOWNER). 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 set to NFS4ERR_OP_ILLEGAL. The
COMPOUND procedure's return results will also be NFS4ERR_OP_ILLEGAL.
The definition of the "tag" in the request is left to the
implementor. 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.
16.2.3.1. 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.
16.2.3.1.1. Current Filehandle
The current and saved filehandle are used throughout the protocol.
Most operations implicitly use the current filehandle as a argument
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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:
PUTFH fh1 {fh1}
LOOKUP "compA" {fh2}
GETATTR {fh2}
LOOKUP "compB" {fh3}
GETATTR {fh3}
LOOKUP "compC" {fh4}
GETATTR {fh4}
GETFH
Figure 84
In this example, the PUTFH 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.
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 operations 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.
16.2.3.1.2. 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
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does not return a stateid, the current stateid MUST be set to the
all-zeros special stateid. As an example, PUTFH will change the
current server state from {ocfh, osid} to {cfh, 0} while LOCK will
change the current state from {cfh, osid} to {cfh, nsid}. The SAVEFH
and RESTOREFH operations will save and restore both the filehandle
and the stateid as a set.
Any operation which takes as an argument a stateid that is not the
special all-zeros stateid MUST set the current stateid to the all-
zeros value before evaluating the operation. If the argument is the
special all-zeros stateid, the operation is evaluated using the
current stateid.
The following example is the common case of a simple READ operation
with a supplied stateid showing that the PUTFH initializes the
current stateid to zero. The subsequent READ with stateid sid1
replaces the current stateid before evaluating the operation.
PUTFH fh1 - -> {fh1, 0}
READ sid1,0,1024 {fh1, sid1} -> {fh1, sid1}
Figure 85
This next example performs an OPEN with the client provided stateid
sid1 and as a result generates stateid sid2. The next operation
specifies the READ with the special all-zero stateid but the current
stateid set by the previous operation is actually used when the
operation is evaluated, allowing correct interaction with any
existing, potentially conflicting, locks.
PUTFH fh1 - -> {fh1, 0}
OPEN R,sid1,"compA" {fh1, sid1} -> {fh2, sid2}
READ 0,0,1024 {fh2, sid2} -> {fh2, sid2}
CLOSE 0 {fh2, sid2} -> {fh2, sid3}
Figure 86
The final 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.
PUTFH fh1 - -> {fh1, 0}
LOCK W,0,1024,sid1 {fh1, sid1} -> {fh1, sid2}
READ 0,0,1024 {fh1, sid2} -> {fh1, sid2}
LOCKU W,0,1024,0 {fh1, sid2} -> {fh1, sid3}
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Figure 87
16.2.4. 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:
COMPOUND error returns
+------------------------------+------------------------------------+
| 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
17. Operations: REQUIRED, RECOMMENDED, or OPTIONAL
The following tables summarize the operations of the NFSv4.1 protocol
and the corresponding designation of REQUIRED, RECOMMENDED, 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 they MUST NOT be implemented in NFSv4.1. These
operations are limited to those replaced by the Sessions
functionality of NFSv4.1.
For the most part, the REQUIRED, RECOMMENDED, or OPTIONAL designation
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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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
Operations
+----------------------+------------+--------------+----------------+
| Operation | REQ, REC, | Feature | Definition |
| | OPT, or | (REQ, REC, | |
| | MNI | or OPT) | |
+----------------------+------------+--------------+----------------+
| ACCESS | REQ | | Section 18.1 |
| BACKCHANNEL_CTL | REQ | | Section 18.33 |
| BIND_CONN_TO_SESSION | REQ | | Section 18.34 |
| CLOSE | REQ | | Section 18.2 |
| COMMIT | REQ | | Section 18.3 |
| CREATE | REQ | | Section 18.4 |
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| CREATE_SESSION | REQ | | Section 18.36 |
| DELEGPURGE | OPT | FDELG (REQ) | Section 18.5 |
| DELEGRETURN | OPT | FDELG, | Section 18.6 |
| | | DDELG, pNFS | |
| | | (REQ) | |
| DESTROY_CLIENTID | REQ | | Section 18.50 |
| DESTROY_SESSION | REQ | | Section 18.37 |
| EXCHANGE_ID | REQ | | Section 18.35 |
| FREE_STATEID | REQ | | Section 18.38 |
| GETATTR | REQ | | Section 18.7 |
| GETDEVICEINFO | OPT | pNFS (REQ) | Section 18.40 |
| GETDEVICELIST | OPT | pNFS (OPT) | Section 18.41 |
| GETFH | REQ | | Section 18.8 |
| GET_DIR_DELEGATION | OPT | DDELG (REQ) | Section 18.39 |
| LAYOUTCOMMIT | OPT | pNFS (REQ) | Section 18.42 |
| LAYOUTGET | OPT | pNFS (REQ) | Section 18.43 |
| LAYOUTRETURN | OPT | pNFS (REQ) | Section 18.44 |
| LINK | OPT | | Section 18.9 |
| LOCK | REQ | | Section 18.10 |
| LOCKT | REQ | | Section 18.11 |
| LOCKU | REQ | | Section 18.12 |
| LOOKUP | REQ | | Section 18.13 |
| LOOKUPP | REQ | | Section 18.14 |
| NVERIFY | REQ | | Section 18.15 |
| OPEN | REQ | | Section 18.16 |
| OPENATTR | OPT | | Section 18.17 |
| OPEN_CONFIRM | MNI | | N/A |
| OPEN_DOWNGRADE | REQ | | Section 18.18 |
| PUTFH | REQ | | Section 18.19 |
| PUTPUBFH | REQ | | Section 18.20 |
| PUTROOTFH | REQ | | Section 18.21 |
| READ | REQ | | Section 18.22 |
| READDIR | REQ | | Section 18.23 |
| READLINK | OPT | | Section 18.24 |
| RECLAIM_COMPLETE | REQ | | Section 18.51 |
| RELEASE_LOCKOWNER | MNI | | N/A |
| REMOVE | REQ | | Section 18.25 |
| RENAME | REQ | | Section 18.26 |
| RENEW | MNI | | N/A |
| RESTOREFH | REQ | | Section 18.27 |
| SAVEFH | REQ | | Section 18.28 |
| SECINFO | REQ | | Section 18.29 |
| SECINFO_NO_NAME | REC | pNFS files | Section 18.45, |
| | | layout (REQ) | Section 13.12 |
| SEQUENCE | REQ | | Section 18.46 |
| SETATTR | REQ | | Section 18.30 |
| SETCLIENTID | MNI | | N/A |
| SETCLIENTID_CONFIRM | MNI | | N/A |
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| SET_SSV | REQ | | Section 18.47 |
| TEST_STATEID | REQ | | Section 18.48 |
| VERIFY | REQ | | Section 18.31 |
| WANT_DELEGATION | OPT | FDELG (OPT) | Section 18.49 |
| WRITE | REQ | | Section 18.32 |
+----------------------+------------+--------------+----------------+
Callback Operations:
Callback Operations
+-------------------------+-----------+-------------+---------------+
| Operation | REQ, REC, | Feature | Definition |
| | OPT, or | (REQ, REC, | |
| | MNI | or OPT) | |
+-------------------------+-----------+-------------+---------------+
| CB_GETATTR | OPT | FDELG (REQ) | Section 20.1 |
| CB_LAYOUTRECALL | OPT | pNFS (REQ) | Section 20.3 |
| CB_NOTIFY | OPT | DDELG (REQ) | Section 20.4 |
| CB_NOTIFY_DEVICEID | OPT | pNFS (OPT) | Section 20.4 |
| CB_NOTIFY_LOCK | OPT | | Section 20.11 |
| CB_PUSH_DELEG | OPT | FDELG (OPT) | Section 20.5 |
| CB_RECALL | OPT | FDELG, | Section 20.2 |
| | | DDELG, pNFS | |
| | | (REQ) | |
| CB_RECALL_ANY | OPT | FDELG, | Section 20.6 |
| | | DDELG, pNFS | |
| | | (REQ) | |
| CB_RECALL_SLOT | REQ | | Section 20.8 |
| CB_RECALLABLE_OBJ_AVAIL | OPT | DDELG, pNFS | Section 20.7 |
| | | (REQ) | |
| CB_SEQUENCE | OPT | FDELG, | Section 20.9 |
| | | DDELG, pNFS | |
| | | (REQ) | |
| CB_WANTS_CANCELLED | OPT | FDELG, | Section 20.10 |
| | | DDELG, pNFS | |
| | | (REQ) | |
+-------------------------+-----------+-------------+---------------+
18. NFSv4.1 Operations
18.1. Operation 3: ACCESS - Check Access Rights
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18.1.1. 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;
};
18.1.2. RESULTS
struct ACCESS4resok {
uint32_t supported;
uint32_t access;
};
union ACCESS4res switch (nfsstat4 status) {
case NFS4_OK:
ACCESS4resok resok4;
default:
void;
};
18.1.3. 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 supported field will contain only as many values as was
originally sent in the arguments. For example, if the client sends
an ACCESS operation with only the ACCESS4_READ value set and the
server supports this value, the server will return only ACCESS4_READ
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even if it could have reliably checked other values.
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
does 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 or add directory entries.
ACCESS4_DELETE Delete an existing directory entry.
ACCESS4_EXECUTE Execute file (no meaning for a directory).
On success, the current filehandle retains its value.
18.1.4. 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 can not
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 which will result in an access failure. The OPEN
operation provides a point where the server can verify access to the
file object and method to return that information to the client. The
ACCESS operation is still useful for directory operations or for use
in the case the UNIX API "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.
18.2. Operation 4: CLOSE - Close File
18.2.1. ARGUMENTS
struct CLOSE4args {
/* CURRENT_FH: object */
seqid4 seqid;
stateid4 open_stateid;
};
18.2.2. RESULTS
union CLOSE4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 open_stateid;
default:
void;
};
18.2.3. 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
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as a result of this CLOSE is only that associated with the supplied
stateid. State associated with other OPENs is not affected.
If record locks are held, the client SHOULD release all locks before
issuing 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
record 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 principal, security flavor, and
applicable, the GSS mechanism, combination 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 18.35) to send CLOSE.
18.2.4. 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 stated (the "other" value is zero and the "seqid" field is
NFS4_MAXFILELEN).
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.
18.3. Operation 5: COMMIT - Commit Cached Data
18.3.1. ARGUMENTS
struct COMMIT4args {
/* CURRENT_FH: file */
offset4 offset;
count4 count;
};
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18.3.2. RESULTS
struct COMMIT4resok {
verifier4 writeverf;
};
union COMMIT4res switch (nfsstat4 status) {
case NFS4_OK:
COMMIT4resok resok4;
default:
void;
};
18.3.3. DESCRIPTION
The COMMIT operation forces or flushes data to stable storage for the
file specified by the current filehandle. The flushed data is that
which was previously written with a WRITE operation which had the
stable field set to UNSTABLE4.
The offset specifies the position within the file where the flush is
to begin. An offset value of 0 (zero) means to flush data starting
at the beginning of the file. The count specifies the number of
bytes of data to flush. If count is 0 (zero), a flush from 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 or rebooted between the initial WRITE(s) and the
COMMIT. The client does this by comparing the write verifier
returned from the initial writes 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 rebooted; however, other events at the server may result in
uncommitted data loss as well.
On success, the current filehandle retains its value.
18.3.4. IMPLEMENTATION
The COMMIT operation is similar in operation and semantics to the
POSIX fsync(2) system call 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. Like fsync(2), it may be
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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(2) 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 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 0 and count 0, it should do the equivalent of fsync()'ing the
file. Otherwise, it should arrange to have the cached 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 cached data based
on the offset and count, and flushes any metadata associated with the
file. It then returns the status of the flush and the write
verifier. The other 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 0 and
count of 0, 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 by the client with the stable parameter 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 stable parameter 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.
When a response is returned from either a WRITE or a COMMIT operation
and it contains a write verifier that is different than previously
returned by the server, the client will need to retransmit all of the
buffers containing uncommitted cached data to the server. How this
is to be done is up to the implementor. If there is only one buffer
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of interest, then it should probably be sent back over in a WRITE
request with the appropriate stable parameter. If there is more than
one buffer, it might be worthwhile retransmitting all of the buffers
in WRITE requests 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. The timing of these retransmissions is
left to the implementor.
The above description applies to page-cache-based systems as well as
buffer-cache-based systems. In those systems, the virtual memory
system will need to be modified instead of the buffer cache.
18.4. Operation 6: CREATE - Create a Non-Regular File Object
18.4.1. 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;
};
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18.4.2. RESULTS
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;
};
18.4.3. 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 directory must be 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 file handle designate
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 typename is that of an ordinary file, a named attribute, or a
named attribute directory, the error NFS4ERR_WRONG_TYPE 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 0 (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.
The createattrs specifies the initial set of attributes for the
object. The set of attributes may include any writable attribute
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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 (for
e.g., POSIX systems have a passwd database that has the group
identifier for every user identifier), inherited from directory the
object is created in, or whatever else the server's operating
environment or file system semantics dictate. This applies to the
OPEN operation too.
Conversely, it is possible the client will specify in createattrs an
owner attribute or 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 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 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.
If the capability FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set
(Section 14.4), and a symbolic link is being created, then the
content of the symbolic link MUST be in UTF-8 encoding.
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18.4.4. 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.
18.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery
18.5.1. ARGUMENTS
struct DELEGPURGE4args {
clientid4 clientid;
};
18.5.2. RESULTS
struct DELEGPURGE4res {
nfsstat4 status;
};
18.5.3. DESCRIPTION
Purges all of the delegations awaiting recovery for a given client.
This is useful for clients which 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.
This operation should be used by clients that record delegation
information on stable storage on the client. In this case,
DELEGPURGE should be sent immediately after doing delegation recovery
on all delegations known to the client. 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 who make requests that conflict with the unrecovered
delegations. The set of delegations known to the server and the
client may be different. The reason for this is that a client may
fail after making a request which resulted in delegation but before
it received the results and committed them to the client's stable
storage.
The server MAY support DELEGPURGE, but if it does not, it MUST NOT
support CLAIM_DELEGATE_PREV.
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18.6. Operation 8: DELEGRETURN - Return Delegation
18.6.1. ARGUMENTS
struct DELEGRETURN4args {
/* CURRENT_FH: delegated object */
stateid4 deleg_stateid;
};
18.6.2. RESULTS
struct DELEGRETURN4res {
nfsstat4 status;
};
18.6.3. DESCRIPTION
Returns the delegation represented by the current filehandle and
stateid.
Delegations 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 delegation
to the server before returning the delegation.
The server MAY require that the principal, security flavor, and
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 18.35) to send DELEGRETURN.
18.7. Operation 9: GETATTR - Get Attributes
18.7.1. ARGUMENTS
struct GETATTR4args {
/* CURRENT_FH: object */
bitmap4 attr_request;
};
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18.7.2. RESULTS
struct GETATTR4resok {
fattr4 obj_attributes;
};
union GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
GETATTR4resok resok4;
default:
void;
};
18.7.3. 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 which it was able to return, which
will include all attributes requested by the client which 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 which are absent should be treated as having support for
a very small set of attributes as described in GETATTR Within an
Absent File System (Section 5), even if previously, when the file
system was present, more attributes were supported.
All servers MUST support the REQUIRED attributes as specified in File
Attributes (Section 11.3.1), for all file systems, with the exception
of absent file systems.
On success, the current filehandle retains its value.
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18.7.4. IMPLEMENTATION
When there is write delegation held by another client for file in
question and the set of attributes being interrogated includes the
size of change attributes. the server needs to obtain the actual
current value of these attributes from the client holding the
delegation by using the CB_GETATTR callback. The server,
particularly, when the delegated client is unresponsive, choose
instead to recall the delegation in question. The GETATTR may not,
in this case proceed until of the following occurs:
o The requested attribute values are returned in the response to
CB_GETATTR.
o The write delegation is returned.
o The write delegation is revoked.
Except where one of these happens very quickly, one or more
NFS4ERR_DELAY errors will be returned to requests made while
delegation remains outstanding.
18.8. Operation 10: GETFH - Get Current Filehandle
18.8.1. ARGUMENTS
/* CURRENT_FH: */
void;
18.8.2. RESULTS
struct GETFH4resok {
nfs_fh4 object;
};
union GETFH4res switch (nfsstat4 status) {
case NFS4_OK:
GETFH4resok resok4;
default:
void;
};
18.8.3. DESCRIPTION
This operation returns the current filehandle value.
On success, the current filehandle retains its value.
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18.8.4. 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 lookup a directory entry and obtain
its filehandle then the following request is needed.
PUTFH (directory filehandle)
LOOKUP (entry name)
GETFH
18.9. Operation 11: LINK - Create Link to a File
18.9.1. ARGUMENTS
struct LINK4args {
/* SAVED_FH: source object */
/* CURRENT_FH: target directory */
component4 newname;
};
18.9.2. RESULTS
struct LINK4resok {
change_info4 cinfo;
};
union LINK4res switch (nfsstat4 status) {
case NFS4_OK:
LINK4resok resok4;
default:
void;
};
18.9.3. 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.
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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 0 (zero), or if newname does not obey
the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
18.9.4. 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 which could hide the
existence of opens relevant to that decision. This is because of the
fact that when a client holds a delegation, the server need not have
accurate picture 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, if
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.
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, NOTIFY4_ADD_ENTRY will be generated as a
result of this operation.
If the current file system supports the numlinks attribute, and other
clients have delegations to the file being linked, then those
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delegations must be recalled and the operation may 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 server when there is an internal partitioning of a
file system which the LINK operation would violate.
On some servers, the filenames, "." and "..", are illegal as 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.
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.
18.10. Operation 12: LOCK - Create Lock
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18.10.1. 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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18.10.2. 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;
};
18.10.3. DESCRIPTION
The LOCK operation requests a record lock for the byte range
specified by the offset and length parameters. The lock type is also
specified to be one of the nfs_lock_type4s. 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 with all bits set to 1 (one). If the length is zero,
or if a length which is not all bits set to one is specified, and
length when added to the offset exceeds the maximum 64-bit unsigned
integer value, the error NFS4ERR_INVAL will result.
32 bit servers are servers that support locking for byte offsets that
fit within 32 bits (i.e. less than or equal to 0xFFFFFFFF). If the
client specifies a range that overlaps one or more bytes beyond
offset 0xFFFFFFFF, but does not end at the maximum 64 bit offset
(i.e. 0xFFFFFFFFFFFFFFFF), such a 32-bit server MUST return the error
NFS4ERR_BAD_RANGE.
If the server returns NFS4ERR_DENIED, 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 request. The locker4 structure is a switched union that
indicates whether the client has already created record locking state
associated with the current open file and lock owner. In the case in
which it has, the argument is just a stateid for the set of locks
associated with that open file and lock owner, together with a
lock_seqid value which MAY be any value and MUST be ignored by the
server. In the case where no such 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 which 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 client field of the lock owner, and all seqid values in the
arguments MAY be any value and MUST be ignored by the server. The
client ID with which all owners and stateids are associated is the
client ID associated with the session on which the request was sent.
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.
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.
18.10.4. 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
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 type 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, while a POSIX-compliant system does
not.
When the client makes a lock request that corresponds to a range that
the lockowner has locked already (with the same or different lock
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type), or to a sub-region of such a range, or to a region which
includes multiple locks already granted to that lockowner, 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 makes a lock request that amounts to upgrading (changing from
a read lock to a write lock) or downgrading (changing from write lock
to a read lock) an existing record 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 requests from other clients.
When a client holds a write delegation, the client holding that
delegation is assured that there are no opens by other clients.
Thus, there can be no conflicting LOCK requests 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 doing
appropriate LOCK and LOCKU requests before returning the delegation.
When one or more clients hold read delegations, any LOCK request
where the server is implementing mandatory locking semantics, must
result in the recall of all such delegations. The LOCK request may
not be granted until all such delegations are return or revoked.
Except where this happens very quickly, one or more NFS4ERR_DELAY
errors will be returned to requests made while delegation remains
outstanding.
18.11. Operation 13: LOCKT - Test For Lock
18.11.1. ARGUMENTS
struct LOCKT4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
offset4 offset;
length4 length;
lock_owner4 owner;
};
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18.11.2. RESULTS
union LOCKT4res switch (nfsstat4 status) {
case NFS4ERR_DENIED:
LOCK4denied denied;
case NFS4_OK:
void;
default:
void;
};
18.11.3. 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 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.
The client ID field of the owner should be specified as zero. The
client ID used for ownership comparisons is that associated with the
session on which the request is sent. If the client ID field is
other than zero, the server MUST return the error NFS4ERR_INVAL.
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.
18.11.4. 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.
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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 may not be
available.
The test for conflicting locks should exclude locks for the current
lockowner. Note that since such locks are not examined the possible
existence of overlapping ranges may not affect the results of LOCKT.
If the server does examine locks that match the lockowner for the
purpose of range checking, NFS4ERR_LOCK_RANGE may be returned.. In
the event that it returns NFS4_OK, clients may do a LOCK and receive
NFS4ERR_LOCK_RANGE on the LOCK request because of the flexibility
provided to the server.
When a client holds a write delegation, it may choose (See
Section 18.10.4) to handle LOCK requests locally. In such a case,
LOCKT requests will similarly be handled locally.
18.12. Operation 14: LOCKU - Unlock File
18.12.1. ARGUMENTS
struct LOCKU4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
stateid4 lock_stateid;
offset4 offset;
length4 length;
};
18.12.2. RESULTS
union LOCKU4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 lock_stateid;
default:
void;
};
18.12.3. DESCRIPTION
The LOCKU operation unlocks the record 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
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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
applicable, the GSS mechanism, combination that sent a LOCK request
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 18.35) to send LOCKU.
18.12.4. IMPLEMENTATION
If the area to be unlocked does not correspond exactly to a lock
actually held by the lockowner 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 lockowner. In all of
these cases, allowed by POSIX locking 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 requests for the sub-
ranges not being unlocked.
When a client holds a write delegation, it may choose (See
Section 18.10.4) to handle LOCK requests locally. In such a case,
LOCKU requests will similarly be handled locally.
18.13. Operation 15: LOOKUP - Lookup Filename
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18.13.1. ARGUMENTS
struct LOOKUP4args {
/* CURRENT_FH: directory */
component4 objname;
};
18.13.2. RESULTS
struct LOOKUP4res {
/* New CURRENT_FH: object */
nfsstat4 status;
};
18.13.3. DESCRIPTION
This operation LOOKUPs 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.
18.13.4. IMPLEMENTATION
If the client wants to achieve the effect of a multi-component
lookup, 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
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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 "shares" 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
name space. 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 lookup 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 lookup 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.
18.14. Operation 16: LOOKUPP - Lookup Parent Directory
18.14.1. ARGUMENTS
/* CURRENT_FH: object */
void;
18.14.2. RESULTS
struct LOOKUPP4res {
/* new CURRENT_FH: parent directory */
nfsstat4 status;
};
18.14.3. 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.
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As for 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 new SECINFO_NO_NAME operation, so that the client can gracefully
determine the correct security flavor. See the discussion of the
SECINFO_NO_NAME operation for a description.
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.
18.14.4. 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 typically done for the file
system root directory in UNIX).
18.15. Operation 17: NVERIFY - Verify Difference in Attributes
18.15.1. ARGUMENTS
struct NVERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
18.15.2. RESULTS
struct NVERIFY4res {
nfsstat4 status;
};
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18.15.3. 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.
18.15.4. 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:
PUTFH (public)
LOOKUP "foobar"
NVERIFY attrbits attrs
READ 0 32767
In the case that a RECOMMENDED 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.
When the attribute rdattr_error or any write-only attribute (e.g.
time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
the client.
18.16. Operation 18: OPEN - Open a Regular File
18.16.1. 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.
*/
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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;
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:
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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
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 */
};
enum open_claim_type4 {
/*
* Not a reclaim.
*/
CLAIM_NULL = 0,
CLAIM_PREVIOUS = 1,
CLAIM_DELEGATE_CUR = 2,
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CLAIM_DELEGATE_PREV = 3,
/*
* Not a reclaim.
*
* Like CLAIM_NULL, but object identified
* by the current filehandle.
*/
CLAIM_FH = 4, /* new to v4.1 */
/*
* Like CLAIM_DELEGATE_CUR, but object identified
* by current filehandle.
*/
CLAIM_DELEG_CUR_FH = 5, /* new to v4.1 */
/*
* Like CLAIM_DELEGATE_PREV, but object identified
* by current filehandle.
*/
CLAIM_DELEG_PREV_FH = 6 /* new to v4.1 */
};
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
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* 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:
/* 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
* 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
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*/
struct OPEN4args {
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
open_owner4 owner;
openflag4 openhow;
open_claim4 claim;
};
18.16.2. RESULTS
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,
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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_CANCELED = 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;
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;
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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;
default:
void;
};
18.16.3. 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 whether a file is be created or not, 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 (sic) MUST be
one of CLAIM_NULL, CLAIM_DELEGATE_CUR, or CLAIM_DELEGATE_PREV,
because these claim methods include a component of a file name.
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
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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, an error of NFS4ERR_EXIST is returned as the
status. 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.
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 5.7.1.14) 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. The client can
logically AND 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 the
server. The following table summarizes the appropriate and mandated
exclusive create methods for implementations of NFSv4.1:
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Required methods for exclusive create
+--------------+--------+-----------------+-------------------------+
| Persistent | pNFS | Server REQUIRED | Client Allowed |
| Reply Cache | server | | |
+--------------+--------+-----------------+-------------------------+
| no | no | EXCLUSIVE4_1 | EXCLUSIVE4_1 (SHOULD) |
| | | and EXCLUSIVE4 | or EXCLUSIVE4 (SHOULD |
| | | | NOT) |
| no | yes | EXCLUSIVE4_1 | EXCLUSIVE4_1 |
| yes | no | GUARDED4 | GUARDED4 |
| yes | yes | GUARDED4 | GUARDED4 |
+--------------+--------+-----------------+-------------------------+
Table 18
If CREATE_SESSION4_FLAG_PERSIST is set in the results of
CREATE_SESSION the reply cache is persistent. If the
EXCHGID4_FLAG_USE_PNFS_MDS flag is set in the results from
EXCHANGE_ID, the server is a pNFS server. If the client attempts to
use EXCLUSIVE4 on a persistent session, or a session derived from a
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.
Upon successful creation, the current filehandle is replaced by that
of the new object.
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 DENY_NONE. In the
case that there is a existing SHARE reservation that conflicts with
the OPEN request, the server returns the error NFS4ERR_SHARE_DENIED.
For each OPEN, the client must provide a value for the owner field
for the OPEN argument. The client ID associated with the owner is
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not derived from the client field of the owner parameter but is
instead the client ID associated with the session on which the
request is sent. If the client ID field of the owner parameter is
not zero, the server MUST return an NFS4ERR_INVAL error. For
additional discussion of SHARE semantics see Section 9.5.
The seqid value 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 which the client claims to
possess. There are seven claim types as follows:
+----------------------+--------------------------------------------+
| open type | description |
+----------------------+--------------------------------------------+
| CLAIM_NULL, CLAIM_FH | For the client, this is a new OPEN request |
| | and there is no previous state associate |
| | 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 reboot. 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 for |
| CLAIM_DELEG_CUR_FH | 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. |
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| CLAIM_DELEGATE_PREV, | The client is claiming a delegation |
| CLAIM_DELEG_PREV_FH | granted to a previous client instance; |
| | used after the client reboots. The server |
| | MAY support CLAIM_DELEGATE_PREV or |
| | CLAIM_DELEG_PREV_FH (new to NFSv4.1). If |
| | it does support either open type, |
| | CREATE_SESSION MUST NOT remove the |
| | client's delegation state, and the server |
| | MUST support the DELEGPURGE operation. |
+----------------------+--------------------------------------------+
For OPEN requests whose claim type is other than CLAIM_PREVIOUS (i.e.
requests other than those devoted to reclaiming opens after a server
reboot) that reach the server during its grace or lease expiration
period, the server returns an error of NFS4ERR_GRACE.
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 10.4. 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.
o OPEN4_RESULT_CONFIRM is deprecated and MUST NOT be returned by an
NFSv4.1 server.
o OPEN4_RESULT_LOCKTYPE_POSIX indicates the server's file locking
behavior supports the complete set of Posix locking techniques.
From this the client can choose to manage file locking state in a
way to handle a mis-match of file locking management.
o OPEN4_RESULT_PRESERVE_UNLINKED indicates the server will preserve
the open file if the client (or any other client) removes the file
as long as it is open. Furthermore, the server promises to
preserve the file through the grace period after server reboot,
thereby giving the client the opportunity to reclaim his open.
o 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.
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The component is also subject to the normal UTF-8, character support,
and name checks. See Section 14.5 for further discussion.
When an OPEN is done and the specified lockowner 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 lockowner. 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
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, or 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 a OPEN which specifies a size of zero (e.g.
truncation) and the file has named attributes, the named attributes
are left as is. They 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
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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 indicating no desire for a delegation and the
server MAY or MAY not return a delegation in the OPEN response.
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. od_whynone 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 write
delegations on this file type.
WND4_NOT_SUPP_UPGRADE The server does not support atomic upgrade of
a read delegation to a write delegation.
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WND4_NOT_SUPP_DOWNGRADE The server does not support atomic downgrade
of a write delegation to a 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
a read, write, or any delegation regardless which of
OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
OPEN4_SHARE_ACCESS_BOTH is set. If the client has a read delegation
on a file, and requests a write delegation, then the client is
requesting atomic upgrade of its read delegation to a write
delegation. If the client has a write delegation on a file, and
requests a read delegation, then the client is requesting atomic
downgrade to a 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 than the
delegation type the client currently has, indicates successful
upgrade or downgrade. If it does not support atomic delegation
upgrade or downgrade, then od_whynone will be WND4_NOT_SUPP_UPGRADE
or WND4_NOT_SUPP_DOWNGRADE.
OPEN4_SHARE_ACCESS_WANT_NO_DELEG means the client wants no
delegation.
OPEN4_SHARE_ACCESS_WANT_CANCEL means 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 are set:
o OPEN4_SHARE_ACCESS_WANT_READ_DELEG
o OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
o OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
If the client specifies
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it wishes
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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.
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 insufficient resources, the server MAY later inform
the client, via the CB_PUSH_DELEG operation, that the resource
limitation 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_RECALLABLE_OBJ_AVAIL 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.
18.16.4. 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 meta-data 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
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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
RECOMMENDED 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: 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 named attribute to store the verifier.
Because the EXCLUSIVE4 create method does not specify initial
attributes, when processing an EXCLUSIVE4 create, the server
o SHOULD set the owner of the file to that corresponding to the
credential of request's RPC header.
o 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.
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, any attribute set in attrset was
used for the verifier. If EXCLUSIVE4_1 was used, the client
determines the attributes used for the verifier by comparing attrset
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with cva_attrs.attrmask; any bits set in former but not the latter
identify the attributes used store the verifier. The client MUST
immediately send a SETATTR on 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 client must specify a value for
share_access that is one of READ, WRITE, or BOTH. For share_deny,
the client must specify one of NONE, READ, WRITE, or BOTH. If the
client fails to do this, the server must return NFS4ERR_INVAL.
Based on the share_access value (READ, WRITE, or 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
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 is not
authorized to READ or WRITE (depending on the share_access value),
the server must return NFS4ERR_ACCESS. Note that since the NFSv4.1
protocol does not impose any requirement that READs and WRITEs sent
for an open file have the same credentials as the OPEN itself, the
server still must do appropriate access checking on the READs and
WRITEs themselves.
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. 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 avoid the common implementation practice of renaming an open
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file to ".nfs<unique value>" after it removes the file. After the
server returns OPEN4_RESULT_PRESERVE_UNLINKED, if a client sends a
REMOVE operation that would reduce the file's link count to zero, the
server SHOULD report a value of zero for the numlinks attribute on
the file.
If another client has a delegation of the file being opened that
conflicts with open being done (sometimes depending of 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 a
write delegation, any open by a different client will conflict, while
for a read delegation only opens with one of the following
characteristics will be considered conflicting:
o The value of share_access includes the bit
OPEN4_SHARE_ACCESS_WRITE.
o The value of share_deny specifies READ or BOTH.
o 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.
18.16.4.1. WARNING TO CLIENT IMPLEMENTORS
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
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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.
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.
18.17. Operation 19: OPENATTR - Open Named Attribute Directory
18.17.1. ARGUMENTS
struct OPENATTR4args {
/* CURRENT_FH: object */
bool createdir;
};
18.17.2. RESULTS
struct OPENATTR4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: named attribute
* directory
*/
nfsstat4 status;
};
18.17.3. 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
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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
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 file handle 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. Name
attributes or a named attribute directory may have their own named
attributes.
18.17.4. IMPLEMENTATION
If the server does not support named attributes for the current
filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
client.
18.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access
18.18.1. ARGUMENTS
struct OPEN_DOWNGRADE4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
18.18.2. 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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18.18.3. DESCRIPTION
This operation is used to adjust the share_access and share_deny bits
for a given open. This is necessary when a given lockowner opens the
same file multiple times with different share_access and share_deny
flags. 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.
The share_access and share_deny bits specified in this operation
replace the current ones for the specified open file. The
share_access and share_deny bits specified must be exactly equal to
the union of the share_access and share_deny bits specified for some
subset of the OPENs in effect for current openowner on the current
file. If that constraint is not respected, the server may return the
error NFS4ERR_INVAL. Since share_access and share_deny bits are
subsets of those already granted, it is not possible for this 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.
18.18.4. IMPLEMENTATION
An OPEN_DOWNGRADE operation may make 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.
18.19. Operation 22: PUTFH - Set Current Filehandle
18.19.1. ARGUMENTS
struct PUTFH4args {
nfs_fh4 object;
};
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18.19.2. RESULTS
struct PUTFH4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: argument to PUTFH
*/
nfsstat4 status;
};
18.19.3. DESCRIPTION
Replaces the current filehandle with the filehandle provided as an
argument.
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.
18.19.4. IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
18.20. Operation 23: PUTPUBFH - Set Public Filehandle
18.20.1. ARGUMENT
void;
18.20.2. RESULT
struct PUTPUBFH4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: public fh
*/
nfsstat4 status;
};
18.20.3. DESCRIPTION
Replaces the current filehandle with the filehandle that represents
the public filehandle of the server's name space. This filehandle
may be different from the "root" filehandle which may be associated
with some other directory on the server.
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The public filehandle represents the concepts embodied in RFC2054
[32], RFC2055 [33], RFC2224 [39]. 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 public filehandle MUST be a
descendant of the root filehandle.
18.20.4. IMPLEMENTATION
Used as the first operator in an NFS request to set the context for
following operations.
With the NFSv3 public filehandle, the client is able to specify
whether the path name provided in the LOOKUP should be evaluated as
either an absolute path relative to the server's root or relative to
the public filehandle. RFC2224 [39] 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 are used to signify absolute or relative
evaluation of an NFS URL respectively.
Note that there are warnings mentioned in RFC2224 [39] 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. It is
likely, therefore that because of server implementation details, an
NFSv3 absolute public filehandle lookup may behave differently than
an NFSv4.1 absolute resolution.
There is a form of security negotiation as described in RFC2755 [40]
that uses the public filehandle a method of employing SNEGO. 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 this RFC.
18.20.5. ERRORS
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18.21. Operation 24: PUTROOTFH - Set Root Filehandle
18.21.1. ARGUMENTS
void;
18.21.2. RESULTS
struct PUTROOTFH4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: root fh
*/
nfsstat4 status;
};
18.21.3. DESCRIPTION
Replaces the current filehandle with the filehandle that represents
the root of the server's name space. From this filehandle a LOOKUP
operation can locate any other filehandle on the server. This
filehandle may be different from the "public" filehandle which may be
associated with some other directory on the server.
18.21.4. IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
18.22. Operation 25: READ - Read from File
18.22.1. ARGUMENTS
struct READ4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
count4 count;
};
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18.22.2. RESULTS
struct READ4resok {
bool eof;
opaque data<>;
};
union READ4res switch (nfsstat4 status) {
case NFS4_OK:
READ4resok resok4;
default:
void;
};
18.22.3. 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 0 (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 0 (zero) and eof is set to
TRUE. The READ is subject to access permissions checking.
If the client specifies a count value of 0 (zero), the READ succeeds
and returns 0 (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 record 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 request, if offset + count is equal to the size of the file), or
the read request 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
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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 0, the server MAY allow
the READ to be serviced subject to mandatory file locks or the
current share deny modes for the file. For a READ with a stateid
value of all bits 1, the server MAY allow READ operations to bypass
locking checks at the server.
On success, the current filehandle retains its value.
18.22.4. IMPLEMENTATION
It is possible for the server to return fewer than count bytes of
data. If the server returns less than the count 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 may back off the transfer size and reduce
the read request return. Server resource exhaustion may also occur
necessitating a smaller read return.
If mandatory file locking is in effect for the file, and if the
region corresponding to the data to be read from file is write locked
by an owner not associated the stateid, the server will return the
NFS4ERR_LOCKED error. The client should try to get the appropriate
read record lock via the LOCK operation before re-attempting the
READ. When the READ completes, the client should release the record
lock via LOCKU.
If another client has a 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.
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18.23. Operation 26: READDIR - Read Directory
18.23.1. ARGUMENTS
struct READDIR4args {
/* CURRENT_FH: directory */
nfs_cookie4 cookie;
verifier4 cookieverf;
count4 dircount;
count4 maxcount;
bitmap4 attr_request;
};
18.23.2. RESULTS
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;
};
18.23.3. 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
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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 0 (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 cookieverf value should be set to 0 (zero) when the cookie value
is 0 (zero) (first directory read). On subsequent requests, it
should be a cookieverf as returned by the server. The cookieverf
must match that 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 portion of the argument is a hint of the maximum number
of bytes of directory information that should be returned. This
value represents the length of the names of the directory entries and
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 value of the argument is the maximum number of bytes for
the result. This maximum size represents 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 will be returned to the client.
Finally, attr_request represents the list of attributes to be
returned for each directory entry supplied by the server.
On successful return, the server's response will provide 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
"bookmark" 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 should 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
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attributes for a directory entry. Instead of returning an error for
the entire READDIR operation, the server can instead return the
attribute 'fattr4_rdattr_error'. 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 may 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
enable some client environments, the cookie values of 0, 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 1 and 2 should not be used
and for READDIR results cookie values of 0, 1, and 2 should not be
returned.
On success, the current filehandle retains its value.
18.23.4. 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 allow the client the ability to
provide guidelines 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. The dircount field provides a hint on
the number of entries based solely on the names of the directory
entries. Since it is a hint, it may be possible that a dircount
value is zero. In this case, the server is free to ignore the
dircount value and return directory information based on the
specified maxcount value.
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 may not be able to
properly handle this type of failure.
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The use of the cookieverf will also protect the client from using
READDIR cookie values that may be stale. For example, if the file
system has been migrated, the server may or may 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 may accept 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.
18.24. Operation 27: READLINK - Read Symbolic Link
18.24.1. ARGUMENTS
/* CURRENT_FH: symlink */
void;
18.24.2. RESULTS
struct READLINK4resok {
linktext4 link;
};
union READLINK4res switch (nfsstat4 status) {
case NFS4_OK:
READLINK4resok resok4;
default:
void;
};
18.24.3. DESCRIPTION
READLINK reads the data associated with a symbolic link. The data is
a UTF-8 string that is opaque to the server. That is, whether
created by an NFS client or created locally on the server, the data
in a symbolic link is not interpreted when created, but is simply
stored.
On success, the current filehandle retains its value.
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18.24.4. 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 path name 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.
18.25. Operation 28: REMOVE - Remove File System Object
18.25.1. ARGUMENTS
struct REMOVE4args {
/* CURRENT_FH: directory */
component4 target;
};
18.25.2. RESULTS
struct REMOVE4resok {
change_info4 cinfo;
};
union REMOVE4res switch (nfsstat4 status) {
case NFS4_OK:
REMOVE4resok resok4;
default:
void;
};
18.25.3. DESCRIPTION
The REMOVE operation removes (deletes) a directory entry named by
filename from the directory corresponding to the current filehandle.
If the entry in the directory was the last reference to the
corresponding file system object, the object may be destroyed. The
directory may be either of type NF4DIR or NF4ATTRDIR.
For the directory where the filename was removed, the server returns
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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 0 (zero), or if target does not obey
the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
On success, the current filehandle retains its value.
18.25.4. IMPLEMENTATION
NFSv3 required a different operator RMDIR for directory removal and
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() 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 independent of its file type. The
implementor 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 issuing a REMOVE.
Alternatively, the implementor can produce a COMPOUND call that
includes a LOOKUP/VERIFY sequence to verify the file type before a
REMOVE operation in the same COMPOUND call.
The concept of last reference is server specific. However, if the
numlinks field in the previous attributes of the object had the value
1, the client should not rely on referring to the object via a
filehandle. Likewise, the client should not rely on the resources
(disk space, directory entry, and so on) formerly associated with the
object becoming immediately available. Thus, if a client needs to be
able to continue to access a file after using REMOVE to remove it,
the client should take steps to make sure that the file will still be
accessible. The usual mechanism used is to RENAME the file from its
old name to a new hidden name.
If the server finds that the file is still open when the REMOVE
arrives:
o The server SHOULD NOT delete the file's directory entry if the
file was opened with OPEN4_SHARE_DENY_WRITE or
OPEN4_SHARE_DENY_BOTH.
o If the file was not opened with OPEN4_SHARE_DENY_WRITE or
OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's
directory entry. However, until last CLOSE of the file, the
server MAY continue to allow access to the file via its
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filehandle.
The server MAY choose to implement its own restrictions on removal of
files while they are open such that REMOVE or a removal that occurs
as part of RENAME may not be done when the file being removed is if
the open is done by particular protocols, or with particular options
or access modes. In all cases in which a decision is made to not
allow the file's directory entry be removed because of an open, the
error NFS4ERR_FILE_OPEN is returned.
Where the determination above cannot be made definitively because
delegations are being held, they must be recalled to allow processing
of the REMOVE to continue. When a delegation is held, the server's
knowledge of the status of opens for that client is not to be relied
on, so that unless there are files opened with the particular deny
modes by clients without delegations, the determination cannot be
made until delegations are recalled, and the operation cannot proceed
until each sufficient delegations have been returned or revoked to
allow the server to make a correct determination.
When a REMOVE is successfully processed, in that it will remove a
directory entry, whether that is the last reference to the object or
not, and another client holds a delegation for that object, the
delegation(s) must be recalled, the operation cannot proceed 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 error while the delegation(s) remains outstanding,
although it may, if the returns happen quickly, not do that.
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 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, this notification will only be generated if the
removal happens as a separate operation. In the case in which the
removal is integrated with RENAME and is atomic with it, notification
of the removal is integrated with notification for the RENAME.
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18.26. Operation 29: RENAME - Rename Directory Entry
18.26.1. ARGUMENTS
struct RENAME4args {
/* SAVED_FH: source directory */
component4 oldname;
/* CURRENT_FH: target directory */
component4 newname;
};
18.26.2. RESULTS
struct RENAME4resok {
change_info4 source_cinfo;
change_info4 target_cinfo;
};
union RENAME4res switch (nfsstat4 status) {
case NFS4_OK:
RENAME4resok resok4;
default:
void;
};
18.26.3. 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 as part of the rename and atomic with it.
See Section 18.25.4 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
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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 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.
If the 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 the oldname or newname has a length of 0 (zero), or if oldname or
newname does not obey the UTF-8 definition, the error NFS4ERR_INVAL
will be returned.
18.26.4. 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 such restrictions, the error NFS4ERR_FILE_OPEN is
returned.
When oldname and rename refer to the same file and that file is open
is such a fashion that RENAME would normally be rejected with
NFS4ERR_FILE_OPEN, it SHOULD be rejected and the error returned in
the same way as would have been done if oldname and newname did not
refer to the same file.
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 which could hide
the existence of opens relevant to that decision. This is because of
the fact that when a client holds a delegation, the server need not
have accurate picture of the opens for that client, since the client
may execute OPENs and CLOSEs locally. The RENAME operation must be
delayed only until a definitive result can be obtained. For example,
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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 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.
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, it is not required that such a notification be generated. 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:
o 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.
o 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 a file delegation which is held by a
client other than the one doing the RENAME, the delegation(s) must be
recalled, and the operation cannot proceed until each such delegation
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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 error while the
delegation(s) remains outstanding, although it may, if the returns
happen quickly, not do that.
The RENAME operation must be atomic to the client. 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
implementors 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.
18.27. Operation 31: RESTOREFH - Restore Saved Filehandle
18.27.1. ARGUMENTS
/* SAVED_FH: */
void;
18.27.2. RESULTS
struct RESTOREFH4res {
/*
* If status is NFS4_OK,
* new CURRENT_FH: value of saved fh
*/
nfsstat4 status;
};
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18.27.3. DESCRIPTION
Set the current filehandle to the value in the saved filehandle. If
there is no saved filehandle then return the error NFS4ERR_RESTOREFH.
18.27.4. IMPLEMENTATION
Operations like OPEN and LOOKUP use the current filehandle to
represent a directory and replace it with a new filehandle. Assuming
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)
18.27.5. ERRORS
18.28. Operation 32: SAVEFH - Save Current Filehandle
18.28.1. ARGUMENTS
/* CURRENT_FH: */
void;
18.28.2. RESULTS
struct SAVEFH4res {
/*
* If status is NFS4_OK,
* new SAVED_FH: value of current fh
*/
nfsstat4 status;
};
18.28.3. DESCRIPTION
Save the current filehandle. 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.
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On success, the current filehandle retains its value.
18.28.4. IMPLEMENTATION
18.29. Operation 33: SECINFO - Obtain Available Security
18.29.1. ARGUMENTS
struct SECINFO4args {
/* CURRENT_FH: directory */
component4 name;
};
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18.29.2. RESULTS
/*
* 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;
};
18.29.3. 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 which represents the security
mechanisms available, with an order corresponding to the server's
preferences, the most preferred being first in the array. The client
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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
structure. The field 'flavor' will contain a value of AUTH_NONE,
AUTH_SYS (as defined in RFC1831 [3]), or RPCSEC_GSS (as defined in
RFC2203 [4]). The field flavor can also 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 id (as defined in RFC2743 [7]), the quality of protection (as
defined in RFC2743 [7]) and the service type (as defined in RFC2203
[4]). 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 2.6.3.1.8), 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 0 (zero), or if name does not obey the
UTF-8 definition, the error NFS4ERR_INVAL will be returned.
18.29.4. 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. The operations which may
receive this error are: LINK, LOOKUP, LOOKUPP, OPEN, PUTFH, PUTPUBFH,
PUTROOTFH, RESTOREFH, RENAME, and indirectly READDIR. LINK and
RENAME will only receive this error if the security used for the
operation is inappropriate for saved filehandle. With the exception
of READDIR, these operations represent the point at which the client
can instantiate a filehandle into the "current filehandle" at the
server. The filehandle is either provided by the client (PUTFH,
PUTPUBFH, PUTROOTFH) or generated as a result of a name to filehandle
translation (LOOKUP and OPEN). RESTOREFH is different because the
filehandle is a result of a previous SAVEFH. Even though the
filehandle, for RESTOREFH, might have previously passed the server's
inspection for a security match, the server will check it again on
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RESTOREFH to ensure that the security policy has not changed.
If the client wants to resolve an error return of NFS4ERR_WRONGSEC,
the following will occur:
o 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.
o For LINK, PUTFH, PUTROOTFH, PUTPUBFH, RENAME, and RESTOREFH, 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, or for
the failed LINK or RENAME, the SAVEFH.
o 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.
o For LOOKUPP, the client will use SECINFO_NO_NAME { style =
SECINFO_STYLE4_PARENT } and provide the filehandle with equals the
filehandle originally provided to LOOKUPP.
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.
See Section 21 for a discussion on the recommendations for security
flavor used by SECINFO and SECINFO_NO_NAME.
18.30. Operation 34: SETATTR - Set Attributes
18.30.1. ARGUMENTS
struct SETATTR4args {
/* CURRENT_FH: target object */
stateid4 stateid;
fattr4 obj_attributes;
};
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18.30.2. RESULTS
struct SETATTR4res {
nfsstat4 status;
bitmap4 attrsset;
};
18.30.3. 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.
The stateid argument for SETATTR is used to provide file 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.
Any SETATTR that sets the size attribute is incompatible with a share
reservation that specifies DENY_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
the target of WRITE, for the purpose of checking conflicts with
record locks, for those cases in which a server is implementing
mandatory record locking behavior. A valid stateid should always be
specified. When the file size attribute is not set, the special
stateid consisting of all bits zero should 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
bitmap4 that is part of the obj_attributes in the argument.
On success, the current filehandle retains its value.
18.30.4. 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
followed by a SETATTR.
The file size attribute is used to request changes to the size of a
file. A value of 0 (zero) causes the file to be truncated, a value
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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 holes or actual zero data bytes. Clients should not make any
assumptions regarding a server's implementation of this feature,
beyond that the bytes returned will be zeroed. Servers must support
extending the file size via SETATTR.
SETATTR is not guaranteed atomic. A failed SETATTR may partially
change a file's attributes.
If the object whose attributes are being changed has a file
delegation which 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 error while
the delegation(s) remains outstanding, although it may, if the
returns happen quickly, not do that.
If the object whose attributes are being set is a directory and
another client holds a directory delegation for that directory, 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_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 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
client(s), 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. A client must account for this as size changes can
result in data deletion.
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
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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 maintenance 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 attributes bits not requested to
be set by the client, and must be equal to the mask of attributes
requested to be set only if the SETATTR completes without error.
18.31. Operation 37: VERIFY - Verify Same Attributes
18.31.1. ARGUMENTS
struct VERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
18.31.2. RESULTS
struct VERIFY4res {
nfsstat4 status;
};
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18.31.3. DESCRIPTION
The VERIFY operation is used to verify that attributes have a value
assumed by the client before proceeding with 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.
18.31.4. IMPLEMENTATION
One possible use of the VERIFY operation is the following compound
sequence. With this the client is attempting to verify that the file
being removed will match what the client expects to be removed. This
sequence 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 sequence 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 RECOMMENDED 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 rdattr_error or any write-only attribute (e.g.
time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
the client.
18.32. Operation 38: WRITE - Write to File
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18.32.1. ARGUMENTS
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<>;
};
18.32.2. RESULTS
struct WRITE4resok {
count4 count;
stable_how4 committed;
verifier4 writeverf;
};
union WRITE4res switch (nfsstat4 status) {
case NFS4_OK:
WRITE4resok resok4;
default:
void;
};
18.32.3. 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
0 (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 0 (zero), the WRITE will succeed and return
a count of 0 (zero) subject to permissions checking. The server may
choose to write fewer bytes than requested by the client.
Part of the write request is a specification of how the write is to
be performed. The client specifies with the stable parameter the
method of how the data is to be processed by the server. If stable
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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 the data before returning. The server
implementor 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 verf 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 record 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).
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. If the server committed all
data and metadata to stable storage, committed should be set to
FILE_SYNC4. If the level of commitment was at least as strong as
DATA_SYNC4, then committed should be set to DATA_SYNC4. Otherwise,
committed must be returned as UNSTABLE4. If stable was FILE4_SYNC,
then committed must also be FILE_SYNC4: anything else constitutes a
protocol violation. If stable was DATA_SYNC4, then committed may be
FILE_SYNC4 or DATA_SYNC4: anything else constitutes a protocol
violation. If stable was UNSTABLE4, then committed may be either
FILE_SYNC4, DATA_SYNC4, or UNSTABLE4.
The final portion of the result is the write verifier. The write
verifier is a cookie that the client can use to determine whether the
server has changed instance (boot) state between a call to WRITE and
a subsequent call to either WRITE or COMMIT. This cookie must be
consistent during a single instance of the NFSv4.1 protocol service
and must be unique between instances of the NFSv4.1 protocol server,
where uncommitted data may be lost.
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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 0, the server MAY allow
the WRITE to be serviced subject to mandatory file locks or the
current share deny modes for the file. For a WRITE with a stateid
value of all bits 1, the server MUST NOT allow the WRITE operation to
bypass locking checks at the server and are treated exactly the same
as if a stateid of all bits 0 were used.
On success, the current filehandle retains its value.
18.32.4. 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 should 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 of the file to be updated. However, the time_modified
of the file should not be changed unless the contents of the file are
changed. Thus, a WRITE request with count set to 0 should not cause
the time_modified of the file to be updated.
The definition of stable storage has been historically a point of
contention. The following expected properties of stable storage may
help in resolving design sends in the implementation. Stable storage
is persistent storage that survives:
1. Repeated power failures.
2. Hardware failures (of any board, power supply, etc.).
3. Repeated software crashes, including reboot cycle.
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
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allows the client to detect server reboots. 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) it may 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
booted or the time the server was last started (if restarting the
server without a reboot results in lost buffers).
The committed field in the results 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 file locking is on for the file, and corresponding
record of the data to be written file is read or write locked by an
owner that is not associated with the stateid, the server will 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 lock that overlaps with the region that was to be
written. If the stateid's owner has no conflicting read lock, then
the client should try to get the appropriate write record lock via
the LOCK operation before re-attempting the WRITE. When the WRITE
completes, the client should release the record lock via LOCKU.
If the stateid's owner had a conflicting read 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 lock, the server either attempted to temporarily
effectively upgrade this read lock to a write lock, or the server has
no upgrade capability. If the server attempted to upgrade the read
lock and failed, it is pointless for the client to re-attempt the
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upgrade via the LOCK operation, because there might be another client
also trying to upgrade. If two clients are blocked trying 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.
18.33. Operation 40: BACKCHANNEL_CTL - Backchannel control
Control aspects of the backchannel
18.33.1. ARGUMENT
typedef opaque gsshandle4_t<>;
struct gss_cb_handles4 {
rpc_gss_svc_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 1831 */
case RPCSEC_GSS:
gss_cb_handles4 cbsp_gss_handles;
};
struct BACKCHANNEL_CTL4args {
uint32_t bca_cb_program;
callback_sec_parms4 bca_sec_parms<>;
};
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18.33.2. RESULT
struct BACKCHANNEL_CTL4res {
nfsstat4 bcr_status;
};
18.33.3. DESCRIPTION
The BACKCHANNEL_CTL operation replaces the backchannel's callback
program number and adds (not replaces) RPCSEC_GSS contexts for use by
the backchannel.
The arguments of the BACKCHANNEL_CTL call are a subset of the
CREATE_SESSION parameters. In the arguments to BACKCHANNEL_CTL, the
bca_cb_program field and bca_sec_parms fields correspond respectively
to the csa_cb_program and csa_sec_parms of the arguments to
CREATE_SESSION (Section 18.36).
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 will return NFS4ERR_NOENT.
18.34. Operation 41: BIND_CONN_TO_SESSION
18.34.1. 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;
};
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18.34.2. RESULT
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;
};
18.34.3. 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 18.35) state protection is used, any
principal, security flavor, or RPCSEC_GSS context can 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 2.10.8) 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 with a SEQUENCE operation that is sufficient to associate
the connnection with the session specified in SEQUENCE.
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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 the client wants to
associate 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 the client wants to associate with both
the fore and backchannel, but will accept the connection being
associated with 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 18.36), 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 SHOULD respond
with NFS4_OK.
18.34.4. IMPLEMENTATION
If a session's channel loses all connections, the client needs to use
BIND_CONN_TO_SESSION to associate a new connection. If the server
rebooted and does not keep the reply cache in stable storage, the
server will not recognize the sessionid. The client will ultimately
have to invoke EXCHANGE_ID to create a new client ID and session.
Assuming SP4_SSV state protection is being used, there is an issue if
SET_SSV is sent, no response is returned, and the last connection
associated with the client ID disconnects. The client, per the
sessions model, needs to retry the SET_SSV. But it needs a new
connection to do so, and needs to 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. First the client
reconnects. The client assumes the SET_SSV was executed, and so
sends BIND_CONN_TO_SESSION with the subkey derived from new SSV used
as key for the message integrity code in the RPCSEC_GSS credential
message integrity codes. If the server returns an RPC authentication
error, this means the server's current SSV was not changed, and the
SET_SSV was not executed. The client then tries BIND_CONN_TO_SESSION
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with the subkey derived from the old SSV as the key for the
RPCSEC_GSS message integrity code. This should not return an RPC
authentication error. If it does, an implementation error has
occurred on either the client or server, and the client has to create
a new client ID.
18.35. Operation 42: EXCHANGE_ID - Instantiate Client ID
Exchange long hand client and server identifiers (owners), and create
a client ID
18.35.1. ARGUMENT
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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 {
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>;
};
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18.35.2. RESULT
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;
};
18.35.3. DESCRIPTION
The client uses the EXCHANGE_ID operation to register a particular
client owner with the server. The client ID returned from this
operation will be necessary for requests that create state on the
server and will serve as a parent object to sessions created by the
client. In order to confirm the client ID it must first be used,
along with the returned eir_sequenceid, as arguments to
CREATE_SESSION. If the flag EXCHGID4_FLAG_CONFIRMED_R is set in the
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result, eir_flags, then eir_sequenceid MUST be ignored, as it has no
relevancy.
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 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 2.4, the co_ownerid describes
the client, and the co_verifier is the incarnation of the client. An
EXCHANGE_ID sent with a new incarnation of the client will lead to
the server removing lock state of the old incarnation. Whereas an
EXCHANGE_ID sent with the current incarnation and co_ownerid will
result in an error or an update of the client ID's properties,
depending on the arguments to EXCHANGE_ID.
A server MUST NOT use the same client ID for two different
incarnations of an eir_clientowner.
In addition to the client ID and sequence id, the server returns a
server owner (eir_server_owner) and eir_server_scope. The former
field is used for network trunking as described in Section 2.10.4.
The latter field is used to allow clients to determine when clientids
sent by one server may be recognized by another in the event of file
system migration (see Section 11.7.7).
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 server's claim matching server_owner.so_major_id and
eir_server_scope, the client can use the verification techniques
discussed in Section 2.10.4 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 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:
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o 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 requests
on confirmed client IDs though the server MAY refuse to change
them.
o 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 requests.
o For SP4_MACH_CRED or SP4_SSV state protection:
* The list of operations that MUST use the specified state
protection: spo_must_enforce, which come from the results of
EXCHANGE_ID.
* The list of operations that MAY use the specified state
protection: spo_must_allow, which come from the results of
EXCHANGE_ID.
Once the client ID is confirmed, these properties cannot be
updated by subsequent EXCHANGE_ID requests.
o 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
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requests.
* The length of the SSV. This property is represented by the
spi_ssv_len in the EXCHANGE_ID results. Once the client ID is
confirmed, this property cannot be updated by subsequent
EXCHANGE_ID requests. The length of SSV MUST be equal to the
length of the key used by the negotiated encryption algorithm.
* Number of concurrent versions of the SSV the client and server
will support (Section 2.10.8). This property is represented by
spi_window, in the EXCHANGE_ID results. The property may be
updated by subsequent EXCHANGE_ID requests.
o 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 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 should not 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
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 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 the
principal and security flavor it uses when sending the EXCHANGE_ID
request. The situations described in Sub-Paragraph 6, Sub-
Paragraph 7, Sub-Paragraph 8, or Sub-Paragraph 9, of Paragraph 6 in
Section 18.35.4 will apply. Note that if the operation succeeds and
returns a client ID that is already confirmed, the server MUST set
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the EXCHGID4_FLAG_CONFIRMED_R bit in eir_flags.
If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in eia_flags, this
means the client is trying to establish a new client ID; it is
attempting to trunk data communication to the server
(Section 2.10.4); or it is attempting to update properties of an
unconfirmed client ID. The situations described in Sub-Paragraph 1,
Sub-Paragraph 2, Sub-Paragraph 3, Sub-Paragraph 4, or Sub-Paragraph 5
of Paragraph 6 in Section 18.35.4) 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.
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 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
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.
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Existing stateids (and all stateids with 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 13.1 and
convey roles the client ID is to be used for in a pNFS environment
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 state from
unauthorized changes (Section 2.10.7.3):
o 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.
o SP4_MACH_CRED. This choice is only valid if the client sent the
request with RPCSEC_GSS as the security flavor, and with a service
of RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY. 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.
o SP4_SSV. This choice is only valid if the client sent the request
with RPCSEC_GSS as the security flavor, and with a service of
RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY. This choice
indicates the client wants to use the SSV to protect 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.
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When a client specifies SP4_MACH_CRED or SP4_SSV, it also provides
two lists of operations (each expressed as a bit map). 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 the server will require
SP4_MACH_CRED or SP4_SSV protection for. Normally the server's
result equals the client's argument, but the result MAY be different.
The second list is spo_must_allow and consists of those operations
the client wants to have the option of issuing 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 it has to 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:
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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 [18]. 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. 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.
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 [19]. 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.
ssp_window:
This is the number of SSV versions the client wants the server to
maintain (i.e. each 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 (1). Any requests
on the backchannel or forechannel 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 (Section 2.10.8). 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
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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 (0);
the client can create more handles with another EXCHANGE_ID call.
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.
An example use for implementation identifiers would be diagnostic
software that extract 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 interoperational behavior of the implementation.
The reason is that if clients and servers did such a thing, they
might use fewer capabilities of the protocol than the peer can
support, or the client and server might refuse to interoperate.
Because it is possible some implementations will violate the protocol
specification and interpret the identity information, implementations
MUST allow the users of the NFSv4 client and server to set the
contents of the sent nfs_impl_id structure to any value.
18.35.4. 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
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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 a 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.
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.
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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 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 server MUST authorize EXCHANGE_IDs
with the SSV principal in addition to the principal that created the
client ID.
1. New Owner ID
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.
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{ 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 }
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 Paragraph 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 }
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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 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 do to a retry, or perhaps due to 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 the properties of old_clientid_ret are
different than those specified in the current EXCHANGE_ID.
Whether the properties are being updated or not, 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 which has
restarted.
{ ownerid_arg, old_verifier_arg, principal_arg,
old_clientid_ret, confirmed }
Since the previous incarnation of the same client will no
longer be making requests, once the new client ID is confirmed
by CREATE_SESSION, lock 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
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the client had maintained that information across restart,
this request would not have been sent. If the server does not
support the CLAIM_DELEGATE_PREV claim type, associated
delegations should be purged as well; otherwise, delegations
are retained and recovery proceeds according to
Section 10.2.1.
After processing, clientid_ret is returned to the client and
the client record is replaced with:
{ ownerid_arg, verifier_arg, principal_arg, clientid_ret,
unconfirmed }
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.
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
an previous client incarnation.
{ ownerid_arg, old_verifier_arg, *, clientid_ret, confirmed }
The server returns NFS4ERR_NOT_SAME and leaves the client
record intact.
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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.
18.36. Operation 43: CREATE_SESSION - Create New Session and Confirm
Client ID
Start up session and confirm client ID.
18.36.1. ARGUMENT
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<>;
};
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18.36.2. 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;
};
18.36.3. 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 is not, the server MUST return
NFS4ERR_NOT_ONLY_OP.
In addition to creating a session, CREATE_SESSION has the following
effects:
o 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.
o The connection CREATE_SESSION is sent over is associated with the
session's fore channel.
The arguments and results of CREATE_SESSION are described as follows:
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csa_clientid:
This is the client ID the new session will be associated with.
The corresponding result is csr_sessionid, sessionid of the new
session.
csa_sequence:
Each client ID serializes CREATE_SESSION via a per client ID
sequence number. See Section 18.36.4. The corresponding result
is csr_sequence, which MUST be equal to to csa_sequence.
In the next three arguments, the client offers a value that is to be
a property of the session. 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
uses (which will be either what the client offered, or what the
server is insisting on). return the value used to the client. These
parameters have the following interpretation.
csa_flags:
The csa_flags field contains a list of the following flag bits:
CREATE_SESSION4_FLAG_PERSIST:
If CREATE_SESSION4_FLAG_PERSIST is set, the client desires
server support for 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 12.5.2 it SHOULD support
CREATE_SESSION4_FLAG_PERSIST if it supports the layout_hint
(Section 5.11.4) 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 server use the connection
CREATE_SESSION is called over for the backchannel as well as
the fore channel. The server sets
CREATE_SESSION4_FLAG_CONN_BACK_CHAN in the result field
csr_flags if it agrees. If CREATE_SESSION4_FLAG_CONN_BACK_CHAN
is not set in csa_flags, then
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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, the
connection CREATE_SESSION is called over is currently in non-
RDMA mode, but has the capability to operate in RDMA mode, then
client is requesting the server agree to "step up" to RDMA mode
on the connection. The server sets
CREATE_SESSION4_FLAG_CONN_RDMA in the result field csr_flags if
it agrees. 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 ([8]).
csa_fore_chan_attrs:
csa_back_chan_attrs:
The csa_fore_char_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:
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. The replier should reply in ca_headerpadsize with
its preferred value, or zero if padding is not in use. The
replier 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
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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 2.10.5.4.
ca_maxresponsesize:
The maximum size of a COMPOUND or CB_COMPOUND reply that the
replier will accept from the requester including RPC headers
(see the ca_maxrequestsize definition). The NFSv4.1 server
MUST NOT increase the value of this parameter in the
CREATE_SESSION results. 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 to in the CREATE_SESSION reply. 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 2.10.5.4.
ca_maxresponsesize_cached:
Like ca_maxresponsesize, but the maximum size of a reply that
will be stored in the reply cache (Section 2.10.5.1). If the
reply to CREATE_SESSION has ca_maxresponsesize_cached less than
ca_maxresponsesize, then this is an indication to the requester
on the channel that it needs to be selective about which
replies it directs the replier to cache; for example large
replies from nonidempotent operations (e.g. COMPOUND requests
with a READ operation), should not be cached. The requester
decides which replies to cache via an argument to the SEQUENCE
(the sa_cachethis field, see Section 18.46) or CB_SEQUENCE (the
csa_cachethis field, see Section 20.9) operations. 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_TO_CACHE, per the description in
Section 2.10.5.4.
ca_maxoperations:
The maximum number of operations the replier will accept in a
COMPOUND or CB_COMPOUND. The server MUST NOT increase
ca_maxoperations in the reply to CREATE_SESSION. If the
requester sends a COMPOUND or CB_COMPOUND with more operations
than ca_maxoperations, the replier MUST return
NFS4ERR_TOO_MANY_OPS.
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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 0 to ca_maxrequests - 1 inclusive.
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).
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 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 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 Section 5.2.3.1, "Context
Creation Response - Successful Acceptance" of [4].
The first RPCSEC_GSS handle, gcbp_handle_from_server, is the fore
handle the server returned to the client (in the handle field of
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data type rpc_gss_init_res) when the RPCSEC_GSS context was
created on the server. The second handle,
gcbp_handle_from_client, is the back handle the client will map
the RPCSEC_GSS context to. The server can immediately use the
value of gcbp_handle_from_client in the RPCSEC_GSS credential in
callback RPCs. I.e., the value in gcbp_handle_from_client can be
used as the value of the the field "handle" in data type
rpc_gss_cred_t (see Section 5, "Elements of the RPCSEC_GSS
Security Protocol" of [4]) in callback RPCs. The server must use
the RPCSEC_GSS security service specified in gcbp_service, i.e. it
must set the the "service" field of the rpc_gss_cred_t data type
in RPCSEC_GSS credential to the value of gcbp_service (see Section
5.3.1, "RPC Request Header", of [4]).
If the RPCSEC_GSS handle identified by gcbp_handle_from_server
does not exist on the server, the server will return
NFS4ERR_NOENT.
Note that while the GSS context state is shared between the fore
and back RPCSEC_GSS contexts, 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 Section 5 and of Section 5.3.1, "RPC Request Header", of
[4]).
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
server MUST return NFS4ERR_SEQ_MISORDERED.
18.36.4. 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 must consider
the possibility that retries may occur as a result of a client
reboot, network partition, malfunctioning router, etc. For each
client ID created by EXCHANGE_ID, the server maintains a separate
reply cache similar to the session reply cache used for SEQUENCE
operations, with two distinctions.
o First this is a reply cache just for detecting and processing
CREATE_SESSION requests for a given client ID.
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o 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.
When a client sends a successful EXCHANGE_ID and it is returned an
unconfirmed client ID, the client is also returned eir_sequenceid,
and the client is expected to set the value of csa_sequenceid in the
client ID confirming CREATE_SESSION it sends with that client ID to
the value of eir_sequenceid. After EXCHANGE_ID, the server
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
slot thus initialized, the processing of the CREATE_SESSION operation
is divided into four phases:
1. Client record lookup. 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 MUST use a
csa_sequence that is one greater than last successfully used.
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
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If the server has the following unconfirmed record, then
this is the expected confirmation of an unconfirmed record.
{ *, *, principal_arg, clientid_arg, unconfirmed }
The record is replaced with:
{ *, *, principal_arg, clientid_arg, confirmed }
The processing of the operation continues to session
creation.
* 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 are 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.
5. 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. For each slot in the reply cache, the
server sets the sequence id to zero (0), and records an entry
containing a COMPOUND reply with a zero operations and the error
of NFS4ERR_SEQ_MISORDERED. This way, if the first SEQUENCE
request sent has a sequenceid equal to zero, the server can
simply return what is in the reply cache: NFS4ERR_SEQ_MISORDERED.
The 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.
6. If the session state is created successfully, the server
associates the session with the client ID provided by the client.
7. 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
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in non-RDMA mode. If properties of the new connection are
different enough that the arguments to CREATE_SESSION must
change, then a non-retry MUST be sent. The server will
eventually dispose of any session that was created.
On the backchannel, the client and server might wish to have many
slots, in some cases perhaps more that the fore channel in 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 server.
Implementing RPCSEC_GSS callback support requires the client and
server change their RPCSEC_GSS implementations. One possible set of
changes includes:
o Adding a data structure that wraps the GSS-API context with a
reference count.
o 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.
o 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.
o Adding a function to map an existing RPCSEC_GSS handle to a
pointer to the wrapper data structure. The reference count would
be incremented.
o Adding a function to create a new RPCSEC_GSS handle from a pointer
to the wrapper data structure. The reference count would be
incremented.
o Replacing calls from RPCSEC_GSS that free GSS-API contexts, with
calls to decrement the reference count on the wrapper data
structure.
18.37. Operation 44: DESTROY_SESSION - Destroy existing session
Destroy existing session.
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18.37.1. ARGUMENT
struct DESTROY_SESSION4args {
sessionid4 dsa_sessionid;
};
18.37.2. RESULT
struct DESTROY_SESSION4res {
nfsstat4 dsr_status;
};
18.37.3. DESCRIPTION
The DESTROY_SESSION operation closes the session and discards the
session's its reply cache, if any. Any remaining connections
associated with the session are immediately disassociated and it not
associated with out sessions, 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 2.10.8) MUST be
used, with integrity or privacy.
If the COMPOUND request starts with SEQUENCE, and if the sessions
referred to by SEQUENCE and DESTROY_SESSION are the same, then
o DESTROY_SESSION MUST be the final operation in the COMPOUND
request.
o It is advisable to not place DESTROY_SESSION in a COMPOUND request
with other state-modifying operations, because the DESTROY_SESSION
will destroy reply cache.
DESTROY_SESSION MAY be the only operation in a COMPOUND request.
Because the session is destroyed, a client that retries the request
may receive an error in reply to the retry, even though the original
request was successful.
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If there is a backchannel on the session and the server has
outstanding CB_SEQUENCE operations, then the server MAY refuse to
destroy the session and return NFS4ERR_BACK_CHAN_BUSY. In the event
the backchannel is down, the server should instead return
NFS4ERR_CB_PATH_DOWN to inform the client that the backchannel needs
to repaired before the server will allow the session to be destroyed.
The client SHOULD reply to all outstanding CB_COMPOUNDs before re-
issuing DESTROY_SESSION.
18.38. Operation 45: FREE_STATEID - Free stateid with no locks
Free a single stateid.
18.38.1. ARGUMENT
struct FREE_STATEID4args {
stateid4 fsa_stateid;
};
18.38.2. RESULT
struct FREE_STATEID4res {
nfsstat4 fsr_status;
};
18.38.3. DESCRIPTION
The FREE_STATEID operation is used to free a stateid which no longer
has any associated locks (including opens, record locks, delegations,
layouts). This may be because of client unlock 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.
When a stateid is freed which had been associated with revoked locks,
the client, by doing the FREE_STATEID 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 8.4.2.
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.
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18.38.4. IMPLEMENTATION
No discussion at this time.
18.39. Operation 46: GET_DIR_DELEGATION - Get a directory delegation
Obtain a directory delegation.
18.39.1. 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;
};
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18.39.2. RESULT
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;
};
18.39.3. 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 choose not 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.
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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,
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 may 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 should 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 may return it with the response to the
operation, rather than via a callback.
18.39.4. IMPLEMENTATION
Directory delegation provides 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 reduce network traffic as
well as improve client performance in certain conditions.
Notifications would not be requested when the goal is just cache
consistency.
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), renames (NOTIFY4_RENAME_ENTRY),
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directory attribute changes (NOTIFY4_CHANGE_DIR_ATTRIBUTES), and
cookie verifier changes (NOTIFY4_CHANGE_COOKIE_VERIFIER) by setting
one or more corresponding bits in the gdda_notification_types field.
The client can also ask for notifications of changes to attributes of
directory entries (NOTIFY4_CHANGE_CHILD_ATTRIBUTES) in order to keep
its attribute cache up to date. However any changes made to child
attributes do not cause the delegation to be recalled. 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.
However, the conditions under which a client might ask for a
notification, is out of the scope of this specification.
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.
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 not out of sync by more than 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.
The client should use a security flavor that the file system is
exported with. If it uses a different flavor, the server should
return NFS4ERR_WRONGSEC to the operation that precedes
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GET_DIR_DELEGATION and sets the current filehandle.
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.
18.40. Operation 47: GETDEVICEINFO - Get Device Information
18.40.1. ARGUMENT
struct GETDEVICEINFO4args {
deviceid4 gdia_device_id;
layouttype4 gdia_layout_type;
count4 gdia_maxcount;
bitmap4 gdia_notify_types;
};
18.40.2. 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;
};
18.40.3. DESCRIPTION
Returns 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 address. 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 the information within the gdia_maxcount
limit, the error NFS4ERR_TOOSMALL will be returned. However, if
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gdia_maxcount is zero, NFS4ERR_TOOSMALL MUST NOT be 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 3.3.7). The numbers of bit positions are listed in the
notify_device_type4 enumeration type (Section 20.12). Only two
enumerated values of notify_device_type4 currently apply to
GETDEVICEINFO: NOTIFY_DEVICEID4_CHANGE and NOTIFY_DEVICEID4_DELETE
(see Section 20.12).
The notification bitmap applies only to the specified device ID. If
a client issues GETDEVICEINFO 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
issue GETDEVICEINFO with gdia_maxcount set to zero. In that event,
if the device ID is valid, the 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 server (via CB_NOTIFY_DEVICEID, see Section 20.12).
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.
18.40.4. 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
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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.
o CB_NOTIFY_DEVICEID deletes a device ID. If the client believes it
has layouts that refer to the device ID, then it is possible the
layouts 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 any layouts have been revoked,
the client must recover from layout revocation as described in
Section 12.5.6. If TEST_STATEID indicates at least one layout has
not been revoked, the client should send a GETDEVICEINFO on the
device ID to verify that the device ID has been deleted. If
GETDEVICEINFO indicates the device ID does not exist, the client
then assumes the server is broken, and recovers issuing
EXCHANGE_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 the GETDEVICEINFO or GETDEVICELIST results
are finally received for the device ID, delete the device ID from
client's cache.
o CB_NOTIFY_DEVICEID indicates 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 a GETDEVICEINFO on the device
ID.
18.41. Operation 48: GETDEVICELIST - Get All Device Mappings for a File
System
18.41.1. 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;
};
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18.41.2. 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;
};
18.41.3. DESCRIPTION
This operation is used by the client to enumerate all of the device
IDs 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 may require multiple calls to
enumerate all the device IDs (and is thus similar to the READDIR
(Section 18.23) operation), the client also provides gdia_cookie and
gdia_cookieverf to specify the current cursor position in the list.
The client provides gdla_maxdevices to limit the number of device IDs
in the result. The server MAY return fewer device IDs.
The successful response to the operation will contain the cookie,
gdlr_cookie, and 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.
18.41.4. 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.
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18.42. Operation 49: LAYOUTCOMMIT - Commit writes made using a layout
18.42.1. ARGUMENT
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;
length4 loca_length;
bool loca_reclaim;
stateid4 loca_stateid;
newoffset4 loca_last_write_offset;
newtime4 loca_time_modify;
layoutupdate4 loca_layoutupdate;
};
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18.42.2. 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;
};
18.42.3. DESCRIPTION
Commits changes in the layout represented by the current filehandle,
client ID (derived from the sessionid in the preceding SEQUENCE
operation), byte range, and stateid. Since layouts are sub-
dividable, a smaller portion of a layout, retrieved via LAYOUTGET,
may be committed. The region being committed is specified through
the byte range (loca_offset and loca_length).
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. 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 by the client ID,
filehandle, byte range, layout type, and stateid.
If the loca_reclaim field is set to TRUE, this indicates that the
client is attempting to commit changes to a layout after the reboot
of the metadata server during the metadata server's recovery grace
period. This type of request may be necessary when the client has
uncommitted writes to provisionally allocated regions of a file which
were sent to the storage devices before the reboot 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 reboot of the metadata server. The metadata server is free to
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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 reboot. 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 12.5.3).
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 may use 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 allows the client to suggest a
modification time it would like the metadata server to set. The
metadata server may use the suggestion or it may use the time of the
LAYOUTCOMMIT operation to set the modification time. If the metadata
server uses the client provided modification time, it should ensure
time does not flow backwards. 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 12.5.4
for more details. If the client desires the resultant modification
time 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 regions of
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the original layout have been used and what regions can be
deallocated. There is no NFSv4.1 file layout-specific layoutupdate4
structure.
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 may 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.
18.42.4. 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
reboot. 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 write 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.
18.43. Operation 50: LAYOUTGET - Get Layout Information
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18.43.1. 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;
};
18.43.2. RESULT
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;
};
18.43.3. DESCRIPTION
Requests a layout from the metadata server for reading or writing
(and reading) 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 sessionid in the preceding SEQUENCE operation),
current filehandle, layout type (loga_layout_type), and the layout
stateid (loga_stateid). The use of the loga_iomode 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 8.4.2.1).
The LAYOUTGET operation returns layout information for the specified
byte range: a layout. To get a layout from a specific offset through
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the end-of-file, regardless of the file's length, a loga_length field
with all bits set to 1 (one) should be used. If loga_length is zero,
or if a loga_length which is not all bits set to one is specified,
and loga_length when added to loga_offset exceeds the maximum 64-bit
unsigned integer value, the error NFS4ERR_INVAL will result.
The loga_minlength field specifies the minimum length of layout the
server MUST return. If this requirement cannot be met, no layout
must be returned; the error NFS4ERR_BADLAYOUT will be returned.
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, record lock, or
delegation stateid. Once a layout is held by the client for the
file, the loga_stateid field is a stateid as returned from a previous
LAYOUTGET or LAYOUTRETURN operation or provided by a CB_LAYOUTRECALL
operation (see Section 12.5.3).
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 an array, logr_layout, of type
layout4. If a file has a single striping pattern, then logr_layout
will contain just one entry. Otherwise, if the requested range
overlaps more than one striping pattern, logr_layout will contain the
required number of entries. Each element of logr_layout MUST have
the same iomode. The elements of logr_layout MUST be sorted in
ascending order of the value of lo_offset field of each element.
There MUST be no gaps in the range between two successive elements of
logr_layout. The lo_iomode field in each element of logr_layout MUST
be the same.
The metadata server may adjust the range of the returned layout based
on the usage implied by the loga_iomode. The client must be prepared
to get a layout that does not align exactly with its request. The
lo_length field in each element of logr_layout SHOULD be at least as
long as loga_minlength or the server SHOULD reject the request. See
Section 12.5.2 for more details.
The metadata server may also return a layout with an lo_iomode other
than that requested by the client. 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 read-
only requests to read/write 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.
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The logr_return_on_close result field is a directive to return the
layout before closing the file. When the server sets this return
value to TRUE, it must be prepared to recall the layout in the case
the client fails to return the layout before close. For the server
that knows a layout must be returned before a close of the file, this
return value can be used to communicate the desired behavior to the
client and thus removing one extra step from the client's and
server's interaction.
The logr_stateid, as with all stateid processing, is returned to the
client for use in subsequent layout related operations. See
Section 8.2 for a further discussion.
The format of the returned layout (lo_content) is specific to the
layout type.
If layouts are not supported for the requested file or its containing
file system the server SHOULD return NFS4ERR_LAYOUTUNAVAILABLE. If
the layout type is not supported, the metadata server should return
NFS4ERR_UNKNOWN_LAYOUTTYPE. If layouts are supported but no layout
matches the client provided layout identification, the server should
return NFS4ERR_BADLAYOUT. If an invalid loga_iomode is specified, or
a loga_iomode of LAYOUTIOMODE4_ANY is specified, the server should
return NFS4ERR_BADIOMODE.
If the layout for the file is unavailable due to transient
conditions, e.g. file sharing prohibits layouts, the server must
return NFS4ERR_LAYOUTTRYLATER.
If the layout request is rejected due to an overlapping layout
recall, the server must return NFS4ERR_RECALLCONFLICT. See
Section 12.5.5.2 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 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.
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18.43.4. IMPLEMENTATION
Typically, LAYOUTGET will be called as part of a compound RPC after
an OPEN operation and results in the client having location
information for the file; a client may also hold a layout across
multiple OPENs. The client specifies a layout type that limits what
kind of layout the server will return. This prevents servers from
issuing layouts that are unusable by the client.
Once the client has obtained a layout referring to a particular
device ID, the 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 the client does not have device
address mappings for, and the 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 18.40.4. 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 LAYTOUTGET, 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.
18.44. Operation 51: LAYOUTRETURN - Release Layout Information
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18.44.1. 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;
};
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18.44.2. RESULT
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;
};
18.44.3. DESCRIPTION
This operation returns one or more layouts represented by the client
ID (derived from the sessionid 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 is all 1s, 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, 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 12.5.5.2.1.4 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
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is not complete until the full recalled scope has been returned.
Recalled scope refers to the byte range in the case of
LAYOUTRETURN4_FILE, 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. Although the precise value returned (with a non-
zero seqid) may be used, it is generally best to use the same "other"
value and set the seqid to zero.
Return of a layout or all layouts does not invalidate the mapping of
storage device ID to storage device address which remains in effect
until specifically recalled or changed via notification callbacks.
The lora_reclaim field set to TRUE in a LAYOUTRETURN request
specifies that the client is attempting to return a layout that was
acquired before the reboot of the metadata server during the metadata
server's grace period. When returning layouts that were acquired
during the metadata server's grace period 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 18.42) 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 is returning the layout in response to a
CB_LAYOUTRECALL where the lor_recalltype was LAYOUTRECALL4_FILE, the
client should include use 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 must use the precise lora_recallstateid value and not set the
seqid to zero. Otherwise NFS4ERR_BAD_STATEID will be returned.
NFS4ERR_OLD_STATEID can be returned if the client is using an old
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seqid, and the server knows the client should not be using the old
seqid. E.g. the client uses the seqid on slot 1 of the session,
received 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 12.5.5 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 operation specified lr_returntype of LAYOUTRETURN4_FILE, then
the lorr_stateid 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 not remaining pending CB_LAYOUTRECALL operations for which a
LAYOUTRETURN operation must be done as a completing operation, this
stateid value may be the special stateid consisting of all zeros.
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 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
MAY allow the machine credential or SSV credential (see
Section 18.35) to send LAYOUTRETURN.
18.44.4. 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 - when its corresponding final return operation is
replied.
Returning all layouts in a file system using LAYOUTRETURN4_FSID is
typically done in response to a CB_LAYOUTRECALL for that file system
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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 12.5.5.1 for more details.
Once the client has returned all layouts referring to a particular
device ID, the server MAY delete the device ID.
18.45. Operation 52: SECINFO_NO_NAME - Get Security on Unnamed Object
Obtain available security mechanisms with the use of the parent of an
object or the current filehandle.
18.45.1. 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;
18.45.2. RESULT
/* CURRENTFH: consumed if status is NFS4_OK */
typedef SECINFO4res SECINFO_NO_NAME4res;
18.45.3. DESCRIPTION
Like the SECINFO operation, SECINFO_NO_NAME is used by the client to
obtain a list of valid RPC authentication flavors for a specific file
object. Unlike SECINFO, SECINFO_NO_NAME only works with objects 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
filehandles's parent. 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
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appropriate access to LOOKUPP the parent then SECINFO_NO_NAME must
behave the same way and return NFS4ERR_ACCESS.
Note that if PUTFH, PUTPUBFH, or PUTROOTFH return NFS4ERR_WRONGSEC,
this is tantamount to the server asserting that the client will have
to guess what the required security is, because there is no way to
query. Therefore, the client must iterate through the security
triples available at the client and reattempt the PUTFH, PUTROOTFH or
PUTPUBFH operation. In the unfortunate event none of the REQUIRED
security triples are supported by the client and server, the client
SHOULD try using others that support integrity. Failing that, the
client can try using other forms (e.g. AUTH_SYS and AUTH_NONE), but
because such forms lack integrity checks, this puts the client at
risk.
The server implementor should pay particular attention to Section 2.6
for instructions on avoiding 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 2.6.3.1.8), 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 on SECINFO (Section 18.29.3).
18.45.4. IMPLEMENTATION
See the discussion on SECINFO (Section 18.29.4).
18.46. Operation 53: SEQUENCE - Supply per-procedure sequencing and
control
Supply per-procedure sequencing and control
18.46.1. ARGUMENT
struct SEQUENCE4args {
sessionid4 sa_sessionid;
sequenceid4 sa_sequenceid;
slotid4 sa_slotid;
slotid4 sa_highest_slotid;
bool sa_cachethis;
};
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18.46.2. 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;
const SEQ4_STATUS_DEVID_DELETED_ALL = 0x00002000;
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;
};
18.46.3. DESCRIPTION
The SEQUENCE operation is used by the server to implement session
request control and the reply cache semantics.
This operation 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,
CREATE_SESSION, and DESTROY_SESSION, may 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.
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If SEQUENCE is received on a connection not associated with the
session via CREATE_SESSION or BIND_CONN_TO_SESSION, and the client
specified connecting association enforcement when the session was
created (see Section 18.36), then the server returns
NFS4ERR_CONN_NOT_BOUND_TO_SESSION.
The sa_sessionid argument identifies the session this request applies
to. 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 the client has
a request outstanding for; 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 the value of sa_highest_slotid. (but see
Section 2.10.5.1 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 2.10.5.1.2). 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 reboot (even if the session
is persistent across reboots; session persistence does not imply lock
state persistence) or the establishment of a new client instance.
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 a backchannel for the client ID, it is subject to
having recallable state revoked.
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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 20.8) 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 the client received the
callback operation or not, 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 on
the session until a backchannel on the session the path is
available. If the client fails to re-establish a 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 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
the expiration time of at least one context is beyond the lease
period from the current time (relative to the time of when a
SEQUENCE response was sent) or until all GSS contexts for the
session's backchannel have expired.
SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED
When set, indicates all GSS contexts assigned to the session's
backchannel have expired. This bit remains set on all SEQUENCE
replies until at least one non-expired context for the session's
backchannel has been established.
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 18.38), 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 request. This status bit
remains set on all SEQUENCE replies until the loss of all such
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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 backchanel and the client
failing to reestablish 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
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 11.7.7.1.
SEQ4_STATUS_RESTART_RECLAIM_NEEDED
When set indicates that due to server restart or reboot the client
must reclaim locking state. Until the client sends a global
RECLAIM_COMPLETE (Section 18.51, 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
GETDEVICELIST or GETDEVICEINFO.
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SEQ4_STATUS_DEVID_DELETED
The server has removed a device ID mapping as held by the client.
This flag will stay in affect until the client either sends a
DELEGRETURN or uses GETDEVICELIST to refresh all mappings.
SEQ4_STATUS_DEVID_DELETED_ALL
The server has deleted all device ID mappings; this flag will stay
present until the client sends the appropriate DELEGRETURN.
The value of sa_sequenceid argument relative to to the cached
sequence id on the slot falls into one of three cases.
o 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.
o If sa_sequenceid and the cached sequence id are the same, this is
a retry, and the server replies with the COMPOUND reply that is
stored the reply cache. The lease is possibly renewed.
o 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
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 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 8.3), except if
SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED is returned in sr_status_flags.
18.46.4. IMPLEMENTATION
The server MUST maintain a mapping of sessionid to client ID in order
to validate any operations that follow SEQUENCE that take a stateid
as an argument and/or result.
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If the client establishes a persistent session, then a SEQUENCE done
after a server reboot may encounter requests performed and recorded
in a persistent reply cache before the server reboot. In this case,
SEQUENCE will be processed successfully, while requests which were
not processed previously are rejected with NFS4ERR_DEADSESSION.
Depending on the operations within the COMPOUND successfully
performed before the server reboot, 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 reboot, 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.
18.47. Operation 54: SET_SSV - Update SSV for a Client ID
18.47.1. ARGUMENT
struct ssa_digest_input4 {
SEQUENCE4args sdi_seqargs;
};
struct SET_SSV4args {
opaque ssa_ssv<>;
opaque ssa_digest<>;
};
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18.47.2. 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;
};
18.47.3. 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 (0).
The SSV is the key used for the SSV GSS mechanism (Section 2.10.8)
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 18.35);
the server returns NFS4ERR_CONN_BINDING_NOT_ENFORCED in that case.
ssa_digest is computed as the output of the HMAC RFC2104 [11] using
the subkey derived from the SSV4_SUBKEY_MIC_I2T and current SSV as
the key (See Section 2.10.8 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.
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 18.35, 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 (1)
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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 counter by one (1). The value of this version number
corresponds to the smpt_ssv_seq, smt_ssv_seq, sspt_ssv_seq, and
ssct_ssv_seq fields for the SSV GSS mechanism tokens (see
Section 2.10.8).
18.47.4. 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 issuing SET_SSV 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 18.34.4.
Clients SHOULD NOT send an ssa_ssv that is equal to a previous
ssa_ssv, nor equal to a previous 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 2.10.7.3). 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.
18.48. Operation 55: TEST_STATEID - Test stateids for validity
Test a series of stateids for validity.
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18.48.1. ARGUMENT
struct TEST_STATEID4args {
stateid4 ts_stateids<>;
};
18.48.2. RESULT
struct TEST_STATEID4resok {
nfsstat4 tsr_status_codes<>;
};
union TEST_STATEID4res switch (nfsstat4 tsr_status) {
case NFS4_OK:
TEST_STATEID4resok tsr_resok4;
default:
void;
};
18.48.3. 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:
o SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED
o SEQ4_STATUS_EXPIRED_ADMIN_STATE_REVOKED
o 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 allows problems with earlier
stateids not to interfere with checking of subsequent ones as would
happen if individual stateids are tested by operation in a COMPOUND.
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:
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o There is no check for the type of stateid object, as would be the
case for normal use of a stateid.
o There is no reference to the current filehandle.
o 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 errors which are validly returned within the status_code array
are: NFS4ERR_OK, NFS4ERR_BAD_STATEID, NFS4ERR_OLD_STATEID,
NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, and NFS4ERR_DELEG_REVOKED.
[[Comment.5: _LAYOUT_REVOKED]].
18.48.4. IMPLEMENTATION
See Section 8.2.2 and Section 8.2.4 for a discussion of stateid
structure, lifetime, and validation.
18.49. Operation 56: WANT_DELEGATION - Request Delegation
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18.49.1. ARGUMENT
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 */
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;
};
18.49.2. RESULT
union WANT_DELEGATION4res switch (nfsstat4 wdr_status) {
case NFS4_OK:
open_delegation4 wdr_resok4;
default:
void;
};
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18.49.3. 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.
This operation allows a client to
o get a delegation on all types of files except directories. The
server MAY support this operation. If the server does not support
this operation, it MUST return NFS4ERR_NOTSUPP.
o 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. When the server
indicates that it will notify the server 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.
o 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:
o OPEN4_SHARE_ACCESS_WANT_READ_DELEG
o OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
o OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
o OPEN4_SHARE_ACCESS_WANT_NO_DELEG
o OPEN4_SHARE_ACCESS_WANT_CANCEL
o OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
o 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
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described in the open_delegation4 structure.
The successful results of WANT_DELEG are of type open_delegation4
which is the same type as the "delegation" field in the results of
the OPEN operation. (See Section 18.16.3). 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) is zero then the
client is indicating no desire for a delegation and the server MUST
return NFS4ERR_INVAL.
The client uses the OPEN4_SHARE_ACCESS_WANT_NO_DELEG 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 18.16. Write delegations are not available for file types
that are not writeable. 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
WND4_WRITE_DELEG_NOT_SUPP_FTYPE.
18.49.4. 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.
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18.50. Operation 57: DESTROY_CLIENTID - Destroy existing client ID
Destroy existing client ID.
18.50.1. ARGUMENT
struct DESTROY_CLIENTID4args {
clientid4 dca_clientid;
};
18.50.2. RESULT
struct DESTROY_CLIENTID4res {
nfsstat4 dcr_status;
};
18.50.3. DESCRIPTION
The DESTROY_CLIENTID operation destroys the client ID. If there are
sessions (both idle and non-idle), opens, locks, delegations,
layouts, and wants (Section 18.49) 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 sessionid 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.
18.50.4. 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 it ever generated the client
ID the server can safely reuse the client ID on a future EXCHANGE_ID
operation.
18.51. Operation 58: RECLAIM_COMPLETE - Indicates Reclaims Finished
Indicate transition between reclaim and non-reclaim locking.
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18.51.1. ARGUMENT
struct RECLAIM_COMPLETE4args {
/*
* If rca_one_fs TRUE,
*
* CURRENT_FH: object in
* filesystem reclaim is
* complete for.
*/
bool rca_one_fs;
};
18.51.2. RESULTS
struct RECLAIM_COMPLETE4res {
nfsstat4 rcr_status;
};
18.51.3. DESCRIPTION
A RECLAIM_COMPLETE operation must be used to indicate that the client
has reclaimed all of the locking state that it will recover, when it
is recovering state due to either a server restart or the transfer of
a file system to another server. There are two types of
RECLAIM_COMPLETE operations:
o When 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 have been completed.
o When 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 a file
system transition have been completed. Presence of a current
filehandle is only required when one_fs is true.
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 will return NFS4ERR_NO_GRACE, if these are attempted.
Whenever a client establishes a new client ID and before it does the
first non-reclaim operation that obtains a lock, it MUST do a global
RECLAIM_COMPLETE, even if there are no locks to reclaim. If non-
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reclaim locking operations are done before the RECLAIM_COMPLETE, a
NFS4ERR_GRACE will be returned.
Similarly, when the client accesses a file system on a new server,
before it sends the first non-reclaim operation that obtains a lock
on this new server, it must do a RECLAIM_COMPLETE with one_fs 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, a NFS4ERR_GRACE will be
returned.
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 for a discussion of edge conditions related to lock
reclaim.
Once the client has done a RECLAIM_COMPLETE, it 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.
18.51.4. 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 a list of clients that may have locks in
persistent storage, it is in a position 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, an 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
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result in this error.
When a RECLAIM_COMPLETE is done, the client effectively acknowledges
any locks not yet reclaimed as lost. This allows the server to again
mark this client as able to subsequently recover locks if it had been
prevented from doing so, be by logic to prevent the occurrence of
edge conditions, as described in Section 8.4.3.
18.52. Operation 10044: ILLEGAL - Illegal operation
18.52.1. ARGUMENTS
void;
18.52.2. RESULTS
struct ILLEGAL4res {
nfsstat4 status;
};
18.52.3. 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.
18.52.4. 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.
19. NFSv44.1 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.
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19.1. Procedure 0: CB_NULL - No Operation
19.1.1. ARGUMENTS
void;
19.1.2. RESULTS
void;
19.1.3. DESCRIPTION
Standard NULL procedure. Void argument, 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 server to client.
19.1.4. ERRORS
None.
19.2. Procedure 1: CB_COMPOUND - Compound Operations
19.2.1. 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,
OP_CB_NOTIFY_LOCK = 13,
OP_CB_NOTIFY_DEVICEID = 14,
OP_CB_ILLEGAL = 10044
};
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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<>;
};
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19.2.2. RESULTS
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;
};
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struct CB_COMPOUND4res {
nfsstat4 status;
utf8str_cs tag;
nfs_cb_resop4 resarray<>;
};
19.2.3. 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.
In 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. This is discussed
in Section 2.10.5.4.
The minorversion field of the arguments MUST be the same as the
minorversion of the COMPOUND procedure used to created 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 equivalent 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.
For a description of the "tag" field, see Section 16.2.3 where the
corresponding forward channel procedure is described.
Illegal operation codes are handled in the same way as they are
handled for the COMPOUND procedure.
19.2.4. 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.
19.2.5. ERRORS
CB_COMPOUND will of course return every error that each operation on
the backchannel can return (see Table 13). However if CB_COMPOUND
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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
include:
CB_COMPOUND error returns
+------------------------------+------------------------------------+
| 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 20
20. NFSv4.1 Callback Operations
20.1. Operation 3: CB_GETATTR - Get Attributes
20.1.1. ARGUMENT
struct CB_GETATTR4args {
nfs_fh4 fh;
bitmap4 attr_request;
};
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20.1.2. RESULT
struct CB_GETATTR4resok {
fattr4 obj_attributes;
};
union CB_GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
CB_GETATTR4resok resok4;
default:
void;
};
20.1.3. DESCRIPTION
The CB_GETATTR operation is used by the server to obtain the current
modified state of a file that has been write delegated. The
attributes size and change are the only ones guaranteed to be
serviced by the client. See Section 10.4.3 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 a
write open delegation, an NFS4ERR_BADHANDLE error is returned.
20.1.4. 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).
20.2. Operation 4: CB_RECALL - Recall an Open Delegation
20.2.1. ARGUMENT
struct CB_RECALL4args {
stateid4 stateid;
bool truncate;
nfs_fh4 fh;
};
20.2.2. RESULT
struct CB_RECALL4res {
nfsstat4 status;
};
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20.2.3. DESCRIPTION
The CB_RECALL operation is used to begin the process of recalling an
open delegation and returning it to the server.
The truncate flag is used to optimize recall for a file which is
about to be truncated to zero. When it is set, the client is freed
of 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 an open
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.
20.2.4. IMPLEMENTATION
The client should reply to the callback immediately. Replying does
not complete the recall except when an error was returned. The
recall is not complete until the delegation is returned using a
DELEGRETURN.
20.3. Operation 5: CB_LAYOUTRECALL - Recall Layout from Client
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20.3.1. ARGUMENT
/*
* 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;
};
20.3.2. RESULT
struct CB_LAYOUTRECALL4res {
nfsstat4 clorr_status;
};
20.3.3. 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 with LAYOUTRETURN. The CB_LAYOUTRECALL operation
specifies one of three forms of recall processing with the value of
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layoutrecall_type4. The recall is either for a specific layout (by
file), for an entire file system (FSID), or for all file systems
(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 following fields
must match in value with 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 LAYOUTIOMODE4_ANY will match any value
originally returned in a layout; therefore it acts as a wild card
for iomode. The other special value used is for lor_length. If
lor_length has a value of NFS4_MAXFILELEN, 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 18.44. 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_MAXFILELEN, 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 12.5.5.2.1.4
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 on the value of the clora_changed field. This field is used
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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 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:
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 12.5.3 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.
20.3.4. IMPLEMENTATION
The client's processing for CB_LAYOUTRECALL is similar to CB_RECALL
(recall of file delegations) in that straightforward processing of
the layout recall done and the client responds to the request before
actually returning layouts with 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 with the LAYOUTRETURN
operation.
Before returning the layout to the server with 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 which is effected 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 with LAYOUTRETURN. If the client were to
obtain a new layout covering the modified data's 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.
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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
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 12.5.5.1 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 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.
20.4. Operation 6: CB_NOTIFY - Notify directory changes
Tell the client of directory changes.
20.4.1. ARGUMENT
/*
* Directory notification types.
*/
enum notify_type4 {
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
};
/* 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 {
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notify_entry4 nrm_old_entry;
nfs_cookie4 nrm_old_entry_cookie;
};
struct notify_add4 {
/*
* Information on object
* possibly renamed over.
*/
notify_remove4 nad_old_entry<1>;
notify_entry4 nad_new_entry;
/* what READDIR would have returned for this entry */
nfs_cookie4 nad_new_entry_cookie<1>;
prev_entry4 nad_prev_entry<1>;
bool nad_last_entry;
};
struct notify_attr4 {
notify_entry4 na_changed_entry;
};
struct notify_rename4 {
notify_remove4 nrn_old_entry;
notify_add4 nrn_new_entry;
};
struct notify_verifier4 {
verifier4 nv_old_cookieverf;
verifier4 nv_new_cookieverf;
};
/*
* Objects of type notify_<>4 and
* notify_device_<>4 are encoded in this.
*/
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<>;
};
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20.4.2. RESULT
struct CB_NOTIFY4res {
nfsstat4 cnr_status;
};
20.4.3. DESCRIPTION
The CB_NOTIFY operation is used by the server to send notifications
to clients about changes to delegated directories The registration of
notifications for the directories occurs when the delegation is
established using GET_DIR_DELEGATION. These notifications are sent
over the backchannel. The notification is sent once the original
request has been processed on the server. The server will send an
array of notifications for changes that might have occurred in the
directory. The notifications are sent as list of pairs of bitmaps
and values. See Section 3.3.7 for a description of how NFSv4.1
bitmaps work.
If the server has more notifications then can fit in the CB_COMPOUND
request, it SHOULD send a sequence of serial CB_COMPOUND requests so
that the client's view of the directory does not become confused.
E.g. If the server indicates a file named "foo" is added, and that
the file "foo" is removed, the order it which the client receives
these notifications are processed needs to be the same as the order
in which corresponding operations occurred on the server.
If the client holding the delegation makes any changes in the
directory that cause files or sub directories to be added or removed,
the server will notify that client of the resulting change(s). If
the client holding the delegation is making attribute or cookie
verifier changes only, the server does not need to send notifications
to that client. The server will send the following information for
each operation:
NOTIFY4_ADD_ENTRY
The server will send information about the new directory entry
being created along with the cookie for that entry. The entry
information (data type notify_add4) includes the component name of
the entry and attributes. 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 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
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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 DNLC or
directory caches where this entry should be cached. If the new
entry's cookie is available, it will be in nad_new_entry_cookie
(another variable length array of up to one element). 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.
NOTIFY4_REMOVE_ENTRY
The server will send information about the directory entry being
deleted. The server will also send the cookie value for the
deleted entry so that clients can get to the cached information
for this entry.
NOTIFY4_RENAME_ENTRY
The server will send information about both the old entry and the
new entry. This includes 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.
NOTIFY4_CHANGE_CHILD_ATTRS/NOTIFY4_CHANGE_DIR_ATTRS
The client will use the attribute mask to inform the server of
attributes for which it wants to receive notifications. This
change notification can be requested for both changes to the
attributes of the directory as well as changes to any file's
attributes in the directory by using two separate attribute masks.
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.
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NOTIFY4_CHANGE_COOKIE_VERIFIER
If the cookie verifier changes while a client is holding a
delegation, the server will notify the client so that it can
invalidate its cookies and re-send a READDIR to get the new set of
cookies.
20.5. Operation 7: CB_PUSH_DELEG - Offer Delegation to Client
Offers a previously requested delegation to the client.
20.5.1. ARGUMENT
struct CB_PUSH_DELEG4args {
nfs_fh4 cpda_fh;
open_delegation4 cpda_delegation;
};
20.5.2. RESULT
struct CB_PUSH_DELEG4res {
nfsstat4 cpdr_status;
};
20.5.3. DESCRIPTION
CB_PUSH_DELEG is used by the server to both signal to the client that
the delegation it wants 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.
The server MUST send in cpda_delegation a delegation which satisfies
a request made in an OPEN or WANT_DELEGATION operation.
20.5.4. 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 typically
not be cancelled, but MAY processed behind other delegation requests
or registered wants.
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When a client returns a status other than NFS4_OK, NFSERR_DELAY, or
NFS4ERR_REJECT_DELAY, the want remains pending, although servers may
decide to cancel the want by sending a CB_WANTS_CANCELLED.
20.6. Operation 8: CB_RECALL_ANY - Keep any N delegations
Notify client to return delegation and keep N of them.
20.6.1. 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_MIN = 4;
const RCA4_TYPE_MASK_BLK_LAYOUT_MAX = 7;
const RCA4_TYPE_MASK_OBJ_LAYOUT_MIN = 8;
const RCA4_TYPE_MASK_OBJ_LAYOUT_MAX = 11;
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;
};
20.6.2. RESULT
struct CB_RECALL_ANY4res {
nfsstat4 crar_status;
};
20.6.3. 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, it is free to recall individual
objects to reduce the load but this would be far from optimal.
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 may be the result of a
large number of potential operations eliminated. In the case of
layouts, the layout will be used explicitly but the meta-data server
does not have direct knowledge of such use.
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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.
For NFSv4.1, 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 for blocks-based
storage protocols, for object-based storage protocols and a reserved
range for other experimental storage protocols. The 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 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.
When an undefined bit is set in the type mask, NFS4ERR_INVAL should
be returned. If a client does not support an object of the specified
type, if the bit is defined, NFS4ERR_INVAL should 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
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 it has not yet received an
acknowledgement from the client for a previous CB_RECALL_ANY with the
same type mask. Although the possibility exists that these will be
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received by the client in a order different from the order in which
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 canceled or modified by any
subsequent CB_RECALL_ANY for the same type mask. Thus if the server
sends two CB_RECALL_ANY's, 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 not to give out 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 issuing 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.
20.6.4. IMPLEMENTATION
The client can choose to return any type of object specified by the
mask. If a server wishes to limit use of objects of a specific type,
it should only specify that type in the mask sent. The client may
not return requested objects and it is up to the server to handle
this situation, typically by doing specific recalls 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.
20.7. Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal Resources for
Recallable Objects
Signals that resources are available to grant recallable objects.
20.7.1. ARGUMENT
typedef CB_RECALL_ANY4args CB_RECALLABLE_OBJ_AVAIL4args;
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20.7.2. RESULT
struct CB_RECALLABLE_OBJ_AVAIL4res {
nfsstat4 croa_status;
};
20.7.3. 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, 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.
20.8. Operation 10: CB_RECALL_SLOT - change flow control limits
Change flow control limits
20.8.1. ARGUMENT
struct CB_RECALL_SLOT4args {
slotid4 rsa_target_highest_slotid;
};
20.8.2. RESULT
struct CB_RECALL_SLOT4res {
nfsstat4 rsr_status;
};
20.8.3. 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) to the server.
CB_RECALL_SLOT specifies rsa_target_highest_slotid, the target
highest_slot the server wants for the session. The client, should
then work toward reducing the highest_slot to the target.
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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 slotid > rsa_target_highest_slotid to
complete, then send a single COMPOUND consisting of a single SEQUENCE
operation, with the sa_highslot 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 Sends to take the total RDMA credit count to
rsa_target_highest_slotid + 1 or below.
20.8.4. 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.
20.9. Operation 11: CB_SEQUENCE - Supply backchannel sequencing and
control
Sequence and control
20.9.1. ARGUMENT
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<>;
};
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20.9.2. 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;
};
20.9.3. 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 to which this request belongs, slot id
and sequence id used by the server to implement session request
control and exactly once semantics, and exchanged slot maximums which
are used to adjust the size of the reply cache. This operation MUST
appear once as the first operation in each CB_COMPOUND request or a
protocol error must result. See Section 18.46.3 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 2.10.5.1.2).
The csa_referring_call_lists array is the list of COMPOUND requests,
identified by sessionid, slot id and sequencid. These are requests
that the client previously sent to the server. These previous
requests created state that some operation(s) in the in the same
CB_COMPOUND as the csa_referring_call_lists is identifying. A
sessionid is included because leased state is tied to a client ID,
and a client ID can have multiple sessions. See Section 2.10.5.3.
The value of csa_sequenceid argument relative to to the cached
sequence id on the slot falls into one of three cases.
o 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
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wraparound of the unsigned sequence id value), then the client
MUST return NFS4ERR_SEQ_MISORDERED.
o 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.
o 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 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.
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 2.10.5.1 for an exception). The latter is the highest slot
id the client would prefer the server use on a future CB_SEQUENCE
operation.
20.9.4. IMPLEMENTATION
20.10. Operation 12: CB_WANTS_CANCELLED - Cancel Pending Delegation
Wants
Retracts promise to signal delegation availability.
20.10.1. ARGUMENT
struct CB_WANTS_CANCELLED4args {
bool cwca_contended_wants_cancelled;
bool cwca_resourced_wants_cancelled;
};
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20.10.2. RESULT
struct CB_WANTS_CANCELLED4res {
nfsstat4 cwcr_status;
};
20.10.3. DESCRIPTION
The CB_WANTS_CANCELLED operation is used to notify the client that
the some or all wants it registered for recallable delegations and
layouts have been canceled.
If cwca_contended_wants_cancelled is TRUE, this indicates 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 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.
20.10.4. 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.
20.11. Operation 13: CB_NOTIFY_LOCK - Notify of possible lock
availability
Notify client of possible byte-range lock availability.
20.11.1. ARGUMENT
struct CB_NOTIFY_LOCK4args {
nfs_fh4 cnla_fh;
lock_owner4 cnla_lock_owner;
};
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20.11.2. RESULT
struct CB_NOTIFY_LOCK4res {
nfsstat4 cnlr_status;
};
20.11.3. DESCRIPTION
The server can use this operation to indicate that a lock for the
given file and lockowner, previously requested by the client via an
unsuccessful LOCK request, 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 which has been polling for a blocking 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 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
going forward. When parallel OPENs are done on the same file and
openowner, the ordering of the "seqid" field of the returned stateid
(subject to wraparound) are to be used to select the controlling
value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag.
20.11.4. IMPLEMENTATION
The server must not grant the lock to the client unless and until it
receives an actual lock request from the client. Similarly, the
client receiving this callback cannot assume that it now has the
lock, or that a subsequent request 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 9.4.
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.
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20.12. Operation 14: CB_NOTIFY_DEVICEID - Notify device ID changes
Tell the client of deviceID changes.
20.12.1. ARGUMENT
/*
* 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;
};
struct CB_NOTIFY_DEVICEID4args {
notify4 cnda_changes<>;
};
20.12.2. RESULT
struct CB_NOTIFY_DEVICEID4res {
nfsstat4 cndr_status;
};
20.12.3. 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 occurs when the device
mapping stateid is established using GETDEVICEINFO or GETDEVICELIST.
These notifications are sent over the backchannel. The notification
is sent once the original request has been processed on the server.
The server will send an array of notifications, cnda_changes, as a
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list of pairs of bitmaps and values. See Section 3.3.7 for a
description of how NFSv4.1 bitmaps work.
As with CB_NOTIFY (Section 20.4.3), 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 12.2.10).
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 or GETDEVICELIST to
obtain the updated mapping. The notification is encoded in a
value of data type notify_deviceid_change4. This data type also
contains a boolean field, ndc_immediate, which if TRUE indicates
that the change will be enforced immediately, and so the client
might not be able to complete any pending I/O to the device ID.
If ndc_immediate is FALSE, then for an indefinite time, the client
can complete pending I/O. After pending I/O is complete, the
client SHOULD get the new device ID to device address mappings
before issuing new I/O to the device ID.
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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20.13. Operation 10044: CB_ILLEGAL - Illegal Callback Operation
20.13.1. ARGUMENT
void;
20.13.2. RESULT
/*
* CB_ILLEGAL: Response for illegal operation numbers
*/
struct CB_ILLEGAL4res {
nfsstat4 status;
};
20.13.3. 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 CB_ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
20.13.4. 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 the CB_ILLEGAL4res would not be returned.
21. Security Considerations
NFS has historically used a model where, from an authentication
perspective, the client was the entire machine, or at least the
source network address of the machine. The NFS server relied on the
NFS client to make the proper authentication of the end-user. The
NFS server in turn shared its files only to specific clients, as
identified by the client's source network address. Given this model,
the AUTH_SYS RPC security flavor simply identified the end-user using
the client to the NFS server. When processing NFS responses, the
client ensured that the responses came from the same network address
and port number that the request was sent to. While such a model is
easy to implement and simple to deploy and use, it is certainly not a
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safe model. Thus, NFSv4.1 implementations are REQUIRED to support a
security model that uses end to end authentication, where an end-user
on a client mutually authenticates (via cryptographic schemes that do
not expose passwords or keys in the clear on the network) to a
principal on an NFS server. Consideration should also be given to
the integrity and privacy of NFS requests and responses. The issues
of end to end mutual authentication, integrity, and privacy are
discussed Section 2.2.1.1.1.
Note that while NFSv4.1 mandates an end to end mutual authentication
model, the "classic" model of machine authentication via network
address checking and AUTH_SYS identification can still be supported
with the caveat that the AUTH_SYS flavor is neither REQUIRED nor
RECOMMENDED by this specification, and so interoperability via
AUTH_SYS is not assured.
For reasons of reduced administration overhead, better performance
and/or reduction of CPU utilization, users of NFSv4.1 implementations
may opt to not use security mechanisms that enable integrity
protection on each remote procedure call and response. The use of
mechanisms without integrity leaves the user vulnerable to an
attacker in the middle of the NFS client and server that modifies the
RPC request and/or the response. While implementations are free to
provide the option to use weaker security mechanisms, there are three
operations in particular that warrant the implementation overriding
user choices.
The first two such operations are SECINFO SECINFO_NO_NAME. It is
RECOMMENDED that the client send the either operation such that it is
protected with a security flavor that has integrity protection, such
as RPCSEC_GSS with either the rpc_gss_svc_integrity or
rpc_gss_svc_privacy service. Without integrity protection
encapsulating SECINFO and SECINFO_NO_NAME and their results, an
attacker in the middle could modify results such that the client
might select a weaker algorithm in the set allowed by server, making
the client and/or server vulnerable to further attacks.
The second operation that should definitely use integrity protection
is any GETATTR for the fs_locations attribute. The attack has two
steps. First the attacker modifies the unprotected results of some
operation to return NFS4ERR_MOVED. Second, when the client follows
up with a GETATTR for the fs_locations attribute, the attacker
modifies the results to cause the client migrate its traffic to a
server controlled by the attacker.
Relative to previous NFS versions, NFSv4.1 has additional security
considerations for pNFS (see Section 12.9 and Section 13.12), locking
and session state (see Section 2.10.7.3).
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22. IANA Considerations
22.1. Named Attribute Definitions
The NFSv4.1 protocol provides for the association of named attributes
to files. The name space identifiers for these attributes are
defined as string names. The protocol does not define the specific
assignment of the name space for these file attributes. Even though
the name space is not specifically controlled to prevent collisions,
an IANA registry has been created for the registration of NFSv4.1
named attributes. Registration will be achieved through the
publication of an Informational RFC and will require not only the
name of the attribute but the syntax and semantics of the named
attribute contents; the intent is to promote interoperability where
common interests exist. While application developers are allowed to
define and use attributes as needed, they are encouraged to register
the attributes with IANA.
Such registered named attributes are presumed to apply to all minor
versions of NFSv4, including those defined subsequently to the
registration. Where the named attribute is intended to be limited
with regard to the minor versions for which they are not be used, the
Informational RFC must clearly state the applicable limits.
22.2. ONC RPC Network Identifiers (netids)
Section 3.3.9) discussed the r_netid field and the corresponding
r_addr field within a netaddr4 structure. The NFSv4 protocol depends
on the syntax and semantics of these fields to effectively
communicate callback information between client and server.
Therefore, an IANA registry has been created to include the values
defined in this document and to allow for future expansion based on
transport usage/availability. Additions to this ONC RPC Network
Identifier registry must be done with the publication of an RFC.
The initial values for this registry are as follows (some of this
text is replicated from Section 3.3.9 for clarity):
The Network Identifier (or r_netid for short) is used to specify a
transport protocol and associated universal address (or r_addr for
short). The syntax of the Network Identifier is a US-ASCII string.
The initial definitions for r_netid are:
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"tcp" - TCP over IP version 4
"udp" - UDP over IP version 4
"tcp6" - TCP over IP version 6
"udp6" - UDP over IP version 6
Note: the '"' marks are used for delimiting the strings for this
document and are not part of the Network Identifier string.
For the "tcp" and "udp" Network Identifiers the Universal Address or
r_addr (for IPv4) is a US-ASCII string and is of the form:
h1.h2.h3.h4.p1.p2
The prefix, "h1.h2.h3.h4", is the standard textual form for
representing an IPv4 address, which is always four octets long.
Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
the first through fourth octets each converted to ASCII-decimal.
Assuming big-endian ordering, p1 and p2 are, respectively, the first
and second octets each converted to ASCII-decimal. For example, if a
host, in big-endian order, has an address of 0x0A010307 and there is
a service listening on, in big endian order, port 0x020F (decimal
527), then complete universal address is "10.1.3.7.2.15".
For the "tcp6" and "udp6" Network Identifiers the Universal Address
or r_addr (for IPv6) is a US-ASCII string and is of the form:
x1:x2:x3:x4:x5:x6:x7:x8.p1.p2
The suffix "p1.p2" is the service port, and is computed the same way
as with universal addresses for "tcp" and "udp". The prefix, "x1:x2:
x3:x4:x5:x6:x7:x8", is the standard textual form for representing an
IPv6 address as defined in Section 2.2 of RFC2373 [13].
Additionally, the two alternative forms specified in Section 2.2 of
RFC2373 [13] are also acceptable.
As mentioned, the registration of new Network Identifiers will
require the publication of an Informational RFC with similar detail
as listed above for the Network Identifier itself and corresponding
Universal Address.
22.3. Defining New Notifications
New notification types may be added to the CB_NOTIFY_DEVICEID
operation Section 20.12. This can be done via changes to the
operations that register notifications, or by adding new operations
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to NFSv4. This requires a new minor version of NFSv4, and requires a
standards track document from IETF. Another way to add a
notification is to specify a new layout type. Notifications for new
layout types would be requested via GETDEVICELIST (Section 18.41) and
GETDEVICEINFO (Section 18.40). See Section 22.4).
22.4. Defining New Layout Types
New layout type numbers will be requested from IANA. IANA will only
provide layout type numbers for Standards Track RFCs approved by the
IESG, in accordance with Standards Action policy defined in RFC2434
[20].
The author of a new pNFS layout specification must follow these steps
to obtain acceptance of the layout type as a standard:
1. The author devises the new layout specification.
2. The new layout type specification MUST, at a minimum:
* Define the contents of the layout-type-specific fields of the
following data types:
+ 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;
* Describe or define the storage access protocol used to access
the data servers
* Describe whether revocation of layouts is supported.
* At a minimum, describe the methods of recovery from:
1. Failure and restart for client, server, storage device.
2. Lease expiration from perspective of the active client,
server, storage device.
3. Loss of layout state resulting in fencing of client access
to storage devices (for an example, see Section 12.7.3).
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* A list of any new notification values for CB_NOTIFY_DEVICEID.
* Include an IANA considerations section.
* Include a security considerations section.
3. The author documents the new layout specification as an Internet
Draft.
4. The author submits the Internet Draft for review through the IETF
standards process as defined in "Internet Official Protocol
Standards" (STD 1). The new layout specification will be
submitted for eventual publication as a standards track RFC.
5. The layout specification progresses through the IETF standards
process; the new option will be reviewed by the NFSv4 Working
Group (if that group still exists), or as an Internet Draft not
submitted by an IETF working group.
22.5. Path Variable Definitions
This section deals with the IANA considerations associated the the
variable substitution feature for location names as described in
Section 11.10.3. As described there, variables subject to
substitution consist of a domain name and a specific name within that
domain, with two separated by a colon.
22.5.1. Path Variable Values
For names with the domain "ietf.org" only three specific names are
currently defined and additional names will only be created via
standards-track RFC's.
For the variable names ${ietf.org:CPU_ARCH} and ${ietf.org:OS_TYPE},
IANA will have to create a registry of values to be used for that
variable. Applications for such values must contain the variable
name, the proposed value of that variable, and a brief (one or two
paragraphs) explanation of what is indicated by that specific value.
Such requests should be reviewed by nfsv4@ietf.org and a Designated
Expert.
For the name ${ietf.org:OS_VERSION}, no such registry need be created
as the specifics of the values will vary with the value of
${ietf.org:OS_TYPE}.
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22.5.2. Path Variable Names
IANA needs to set up a registry to help make generally available
information about variables of the form ${domain:var}, where domain
is something other than "ietf.org".
Applications for the addition of variables to this registry should
contain the name of the variable and a brief (one or a few
paragraphs) explanation of the purpose of the variable. No review of
these applications by IANA is necessary.
23. References
23.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", March 1997.
[2] Eisler, M., "XDR: External Data Representation Standard",
STD 67, RFC 4506, May 2006.
[3] Srinivasan, R., "RPC: Remote Procedure Call Protocol
Specification Version 2", RFC 1831, August 1995.
[4] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, September 1997.
[5] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos Version
5 Generic Security Service Application Program Interface (GSS-
API) Mechanism Version 2", RFC 4121, July 2005.
[6] Eisler, M., "LIPKEY - A Low Infrastructure Public Key Mechanism
Using SPKM", RFC 2847, June 2000.
[7] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[8] Talpey, T. and B. Callaghan, "RDMA Transport for ONC RPC - A
Work in Progress", Internet Draft draft-ietf-nfsv4-rpcrdma-05,
May 2007.
[9] Talpey, T. and B. Callaghan, "NFS Direct Data Placement - A
Work in Progress", Internet
Draft draft-ietf-nfsv4-nfsdirect-05, May 2007.
[10] Recio, P., Metzler, B., Culley, P., Hilland, J., and D. Garcia,
"A Remote Direct Memory Access Protocol Specification",
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RFC 5040, October 2007.
[11] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[12] Shepler, S., Eisler, M., and D. Noveck, "NFSv4 Minor Version 1
XDR Description A Work in Progress", Internet
Draft draft-ietf-nfsv4-minorversion1-dot-x-02.txt,
December 2007.
[13] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[14] International Organization for Standardization, "Information
Technology - Universal Multiple-octet coded Character Set (UCS)
- Part 1: Architecture and Basic Multilingual Plane",
ISO Standard 10646-1, May 1993.
[15] Alvestrand, H., "IETF Policy on Character Sets and Languages",
BCP 18, RFC 2277, January 1998.
[16] Hoffman, P. and M. Blanchet, "Preparation of Internationalized
Strings ("stringprep")", RFC 3454, December 2002.
[17] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile
for Internationalized Domain Names (IDN)", RFC 3491,
March 2003.
[18] 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, June 2005.
[19] National Institute of Standards and Technology, "Cryptographic
Algorithm Object Registration", December 2005.
[20] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
23.2. Informative References
[21] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame,
C., Eisler, M., and D. Noveck, "Network File System (NFS)
version 4 Protocol", RFC 3530, April 2003.
[22] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS Version 3
Protocol Specification", RFC 1813, June 1995.
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[23] Eisler, M., "NFS Version 2 and Version 3 Security Issues and
the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5",
RFC 2623, June 1999.
[24] Juszczak, C., "Improving the Performance and Correctness of an
NFS Server", USENIX Conference Proceedings , June 1990.
[25] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
line Database", RFC 3232, January 2002.
[26] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, August 1995.
[27] Werme, R., "RPC XID Issues", USENIX Conference Proceedings ,
February 1996.
[28] Nowicki, B., "NFS: Network File System Protocol specification",
RFC 1094, March 1989.
[29] Bhide, A., Elnozahy, E., and S. Morgan, "A Highly Available
Network Server", USENIX Conference Proceedings , January 1991.
[30] Halevy, B., Welch, B., and J. Zelenka, "Object-based pNFS
Operations", September 2007, <ftp://www.ietf.org/
internet-drafts/draft-nfsv4-pnfs-obj-04.txt>.
[31] Black, D., Fridella, S., and J. Glasgow, "pNFS Block/Volume
Layout", November 2007, <ftp://www.ietf.org/internet-drafts/
draft-ietf-nfsv4-pnfs-block-05.txt>.
[32] Callaghan, B., "WebNFS Client Specification", RFC 2054,
October 1996.
[33] Callaghan, B., "WebNFS Server Specification", RFC 2055,
October 1996.
[34] Shepler, S., "NFS Version 4 Design Considerations", RFC 2624,
June 1999.
[35] Simonsen, K., "Character Mnemonics and Character Sets",
RFC 1345, June 1992.
[36] Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E.
Zeidner, "Internet Small Computer Systems Interface (iSCSI)",
RFC 3720, April 2004.
[37] Snively, R., "Fibre Channel Protocol for SCSI, 2nd Version
(FCP-2)", ANSI/INCITS 350-2003, Oct 2003.
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[38] Weber, R., "Object-Based Storage Device Commands (OSD)", ANSI/
INCITS 400-2004, July 2004,
<http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf>.
[39] Callaghan, B., "NFS URL Scheme", RFC 2224, October 1997.
[40] Chiu, A., Eisler, M., and B. Callaghan, "Security Negotiation
for WebNFS", RFC 2755, January 2000.
Appendix A. Acknowledgments
The initial drafts for the SECINFO extensions were edited by Mike
Eisler with contributions from Peng Dai, Sergey Klyushin, and Carl
Burnett.
The initial drafts 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 drafts 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 drafts 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 drafts for the ACL explanations were contributed by Sam
Falkner and Lisa Week.
The initial drafts for the parallel NFS support were 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 which contributed to the construction of the
initial pNFS drafts; specific acknowledgement goes to Gary Grider,
Peter Corbett, Dave Noveck, Peter Honeyman, and Stephen Fridella The
pNFS work was inspired by the NASD and OSD work done by Garth Gibson.
Gary Grider of the national labs (LANL) has also been a champion of
high-performance parallel I/O.
Fredric Isaman found several errors in draft versions of the ONC RPC
XDR description of the NFSv4.1 protocol.
Audrey Van Bellingham provided, in numerous ways, essential co-
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ordination and management of the process of editing the specification
drafts.
Richard Jernigan gave feedback on the file layout's striping pattern
design.
Several formal inspection teams were formed to review various areas
of the protocol. All the inspections found significant errors and
room for improvement. NFSv4.1's inspection teams were:
o ACLs, with the following inspectors: Sam Falkner, Bruce Fields,
Rahul Iyer, Saadia Khan, Dave Noveck, Lisa Week, Mario Wurzl, and
Alan Yoder.
o Sessions, with the following inspectors: William Brown, Tom
Doeppner, Robert Gordon, Benny Halevy, Fredric Isaman, Rick
Macklem, Trond Myklebust, Dave Noveck, Karen Rochford, John Scott,
and Peter Shah.
o Initial pNFS inspection, with the following inspectors: Andy
Adamson, David Black, Mike Eisler, Marc Eshel, Sam Falkner, Garth
Goodson, Benny Halevy, Rahul Iyer, Trond Myklebust, Spencer
Shepler, and Lisa Week.
o Global namespace, with the following inspectors: Mike Eisler, Dan
Ellard, Craig Everhart, Fred Isaman, Trond Myklebust, Dave Noveck,
Theresa Raj, Spencer Shepler, Renu Tewari, and Robert Thurlow.
o NFSv4.1 file layout type, with the following inspectors: Andy
Adamson, Marc Eshel, Sam Falkner, Garth Goodson, Rahul Iyer, Trond
Myklebust, and Lisa Week.
o NFSv4.1 locking and directory delegations, with the following
inspectors: Mike Eisler, Pranoop Erasani, Robert Gordon, Saadia
Khan, Eric Kustarz, Dave Noveck, Spencer Shepler, and Amy Weaver.
o EXCHANGE_ID and DESTROY_CLIENTID, with the following inspectors:
Mike Eisler, Pranoop Erasani, Robert Gordon, Benny Halevy, Fred
Isaman, Saadia Khan, Rick Macklem, Spencer Shepler, and Brent
Welch.
o Final pNFS inspection, with the following inspectors: Andy
Adamson, Mike Eisler, Sam Falkner, Mark Eshel, Jason Glasgow,
Garth Goodson, Robert Gordon, Benny Halevy, Dean Hildebrand, Rahul
Iyer, Suchit Kaura, Trond Myklebust, Anatoly Pinchuk, Spencer
Shepler, Renu Tewari, Lisa Week, and Brent Welch.
A review team worked together to generate the tables of assignments
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of error sets to operations and make sure that each such assignment
had two or more people validating it. Participating in the process
were: Andy Adamson, Mike Eisler, Sam Falkner, Garth Goodson, Robert
Gordon, Trond Myklebust, Dave Noveck Spencer Shepler, Tom Talpey, Amy
Weaver, and Lisa Week.
Authors' Addresses
Spencer Shepler
Sun Microsystems, Inc.
7808 Moonflower Drive
Austin, TX 78750
USA
Phone: +1-512-401-1080
Email: spencer.shepler@sun.com
Mike Eisler
NetApp
5765 Chase Point Circle
Colorado Springs, CO 80919
USA
Phone: +1-719-599-9026
Email: email2mre-@yahoo.com
URI: Insert ietf2 between the - and @ symbols in the above address
David Noveck
NetApp
1601 Trapelo Road, Suite 16
Waltham, MA 02454
USA
Phone: +1-781-768-5347
Email: dnoveck@netapp.com
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