NFSv4 T. Haynes
Internet-Draft D. Noveck
Intended status: Standards Track Editors
Expires: April 24, 2011 October 21, 2010
NFS Version 4 Protocol
draft-ietf-nfsv4-rfc3530bis-05.txt
Abstract
The Network File System (NFS) version 4 is a distributed filesystem
protocol which owes heritage to NFS protocol version 2, RFC 1094, and
version 3, RFC 1813. Unlike earlier versions, the NFS version 4
protocol supports traditional file access while integrating support
for file locking and the mount protocol. In addition, support for
strong security (and its negotiation), compound operations, client
caching, and internationalization have been added. Of course,
attention has been applied to making NFS version 4 operate well in an
Internet environment.
This document, together with the companion XDR description document,
replaces RFC 3530 as the definition of the NFS version 4 protocol.
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].
Status of this Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
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This Internet-Draft will expire on April 24, 2011.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 8
1.1. Changes since RFC 3530 . . . . . . . . . . . . . . . . . 8
1.2. Changes since RFC 3010 . . . . . . . . . . . . . . . . . 8
1.3. NFS Version 4 Goals . . . . . . . . . . . . . . . . . . 10
1.4. Inconsistencies of this Document with the companion
document NFS Version 4 Protocol . . . . . . . . . . . . 10
1.5. Overview of NFS version 4 Features . . . . . . . . . . . 11
1.5.1. RPC and Security . . . . . . . . . . . . . . . . . . 11
1.5.2. Procedure and Operation Structure . . . . . . . . . 11
1.5.3. Filesystem Model . . . . . . . . . . . . . . . . . . 12
1.5.4. OPEN and CLOSE . . . . . . . . . . . . . . . . . . . 14
1.5.5. File Locking . . . . . . . . . . . . . . . . . . . . 14
1.5.6. Client Caching and Delegation . . . . . . . . . . . 14
1.6. General Definitions . . . . . . . . . . . . . . . . . . 15
2. Protocol Data Types . . . . . . . . . . . . . . . . . . . . . 17
2.1. Basic Data Types . . . . . . . . . . . . . . . . . . . . 17
2.2. Structured Data Types . . . . . . . . . . . . . . . . . 18
3. RPC and Security Flavor . . . . . . . . . . . . . . . . . . . 24
3.1. Ports and Transports . . . . . . . . . . . . . . . . . . 24
3.1.1. Client Retransmission Behavior . . . . . . . . . . . 25
3.2. Security Flavors . . . . . . . . . . . . . . . . . . . . 25
3.2.1. Security mechanisms for NFS version 4 . . . . . . . 26
3.3. Security Negotiation . . . . . . . . . . . . . . . . . . 28
3.3.1. SECINFO . . . . . . . . . . . . . . . . . . . . . . 28
3.3.2. Security Error . . . . . . . . . . . . . . . . . . . 28
3.3.3. Callback RPC Authentication . . . . . . . . . . . . 29
4. Filehandles . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.1. Obtaining the First Filehandle . . . . . . . . . . . . . 31
4.1.1. Root Filehandle . . . . . . . . . . . . . . . . . . 31
4.1.2. Public Filehandle . . . . . . . . . . . . . . . . . 31
4.2. Filehandle Types . . . . . . . . . . . . . . . . . . . . 32
4.2.1. General Properties of a Filehandle . . . . . . . . . 32
4.2.2. Persistent Filehandle . . . . . . . . . . . . . . . 33
4.2.3. Volatile Filehandle . . . . . . . . . . . . . . . . 33
4.2.4. One Method of Constructing a Volatile Filehandle . . 35
4.3. Client Recovery from Filehandle Expiration . . . . . . . 35
5. File Attributes . . . . . . . . . . . . . . . . . . . . . . . 36
5.1. REQUIRED Attributes . . . . . . . . . . . . . . . . . . 37
5.2. RECOMMENDED Attributes . . . . . . . . . . . . . . . . . 37
5.3. Named Attributes . . . . . . . . . . . . . . . . . . . . 38
5.4. Classification of Attributes . . . . . . . . . . . . . . 39
5.5. Set-Only and Get-Only Attributes . . . . . . . . . . . . 40
5.6. REQUIRED Attributes - List and Definition References . . 40
5.7. RECOMMENDED Attributes - List and Definition
References . . . . . . . . . . . . . . . . . . . . . . . 41
5.8. Attribute Definitions . . . . . . . . . . . . . . . . . 42
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5.8.1. Definitions of REQUIRED Attributes . . . . . . . . . 42
5.8.2. Definitions of Uncategorized RECOMMENDED
Attributes . . . . . . . . . . . . . . . . . . . . . 44
5.9. Interpreting owner and owner_group . . . . . . . . . . . 50
5.10. Character Case Attributes . . . . . . . . . . . . . . . 52
6. Access Control Attributes . . . . . . . . . . . . . . . . . . 53
6.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.2. File Attributes Discussion . . . . . . . . . . . . . . . 54
6.2.1. Attribute 12: acl . . . . . . . . . . . . . . . . . 54
6.2.2. Attribute 33: mode . . . . . . . . . . . . . . . . . 68
6.3. Common Methods . . . . . . . . . . . . . . . . . . . . . 68
6.3.1. Interpreting an ACL . . . . . . . . . . . . . . . . 68
6.3.2. Computing a Mode Attribute from an ACL . . . . . . . 69
6.4. Requirements . . . . . . . . . . . . . . . . . . . . . . 70
6.4.1. Setting the mode and/or ACL Attributes . . . . . . . 71
6.4.2. Retrieving the mode and/or ACL Attributes . . . . . 72
6.4.3. Creating New Objects . . . . . . . . . . . . . . . . 72
7. Multi-Server Namespace . . . . . . . . . . . . . . . . . . . 74
7.1. Location Attributes . . . . . . . . . . . . . . . . . . 74
7.2. File System Presence or Absence . . . . . . . . . . . . 75
7.3. Getting Attributes for an Absent File System . . . . . . 76
7.3.1. GETATTR Within an Absent File System . . . . . . . . 76
7.3.2. READDIR and Absent File Systems . . . . . . . . . . 77
7.4. Uses of Location Information . . . . . . . . . . . . . . 77
7.4.1. File System Replication . . . . . . . . . . . . . . 78
7.4.2. File System Migration . . . . . . . . . . . . . . . 79
7.4.3. Referrals . . . . . . . . . . . . . . . . . . . . . 80
7.5. Location Entries and Server Identity . . . . . . . . . . 80
7.6. Additional Client-Side Considerations . . . . . . . . . 81
7.7. Effecting File System Transitions . . . . . . . . . . . 82
7.7.1. File System Transitions and Simultaneous Access . . 83
7.7.2. Filehandles and File System Transitions . . . . . . 83
7.7.3. Fileids and File System Transitions . . . . . . . . 84
7.7.4. Fsids and File System Transitions . . . . . . . . . 85
7.7.5. The Change Attribute and File System Transitions . . 85
7.7.6. Lock State and File System Transitions . . . . . . . 86
7.7.7. Write Verifiers and File System Transitions . . . . 88
7.7.8. Readdir Cookies and Verifiers and File System
Transitions . . . . . . . . . . . . . . . . . . . . 88
7.7.9. File System Data and File System Transitions . . . . 89
7.8. Effecting File System Referrals . . . . . . . . . . . . 90
7.8.1. Referral Example (LOOKUP) . . . . . . . . . . . . . 90
7.8.2. Referral Example (READDIR) . . . . . . . . . . . . . 94
7.9. The Attribute fs_locations . . . . . . . . . . . . . . . 97
7.9.1. Inferring Transition Modes . . . . . . . . . . . . . 98
8. NFS Server Name Space . . . . . . . . . . . . . . . . . . . . 100
8.1. Server Exports . . . . . . . . . . . . . . . . . . . . . 100
8.2. Browsing Exports . . . . . . . . . . . . . . . . . . . . 100
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8.3. Server Pseudo Filesystem . . . . . . . . . . . . . . . . 100
8.4. Multiple Roots . . . . . . . . . . . . . . . . . . . . . 101
8.5. Filehandle Volatility . . . . . . . . . . . . . . . . . 101
8.6. Exported Root . . . . . . . . . . . . . . . . . . . . . 101
8.7. Mount Point Crossing . . . . . . . . . . . . . . . . . . 102
8.8. Security Policy and Name Space Presentation . . . . . . 102
9. File Locking and Share Reservations . . . . . . . . . . . . . 103
9.1. Locking . . . . . . . . . . . . . . . . . . . . . . . . 104
9.1.1. Client ID . . . . . . . . . . . . . . . . . . . . . 104
9.1.2. Server Release of Clientid . . . . . . . . . . . . . 107
9.1.3. lock_owner and stateid Definition . . . . . . . . . 108
9.1.4. Use of the stateid and Locking . . . . . . . . . . . 109
9.1.5. Sequencing of Lock Requests . . . . . . . . . . . . 111
9.1.6. Recovery from Replayed Requests . . . . . . . . . . 112
9.1.7. Releasing lock_owner State . . . . . . . . . . . . . 113
9.1.8. Use of Open Confirmation . . . . . . . . . . . . . . 113
9.2. Lock Ranges . . . . . . . . . . . . . . . . . . . . . . 114
9.3. Upgrading and Downgrading Locks . . . . . . . . . . . . 115
9.4. Blocking Locks . . . . . . . . . . . . . . . . . . . . . 115
9.5. Lease Renewal . . . . . . . . . . . . . . . . . . . . . 116
9.6. Crash Recovery . . . . . . . . . . . . . . . . . . . . . 116
9.6.1. Client Failure and Recovery . . . . . . . . . . . . 117
9.6.2. Server Failure and Recovery . . . . . . . . . . . . 117
9.6.3. Network Partitions and Recovery . . . . . . . . . . 119
9.7. Recovery from a Lock Request Timeout or Abort . . . . . 123
9.8. Server Revocation of Locks . . . . . . . . . . . . . . . 123
9.9. Share Reservations . . . . . . . . . . . . . . . . . . . 124
9.10. OPEN/CLOSE Operations . . . . . . . . . . . . . . . . . 125
9.10.1. Close and Retention of State Information . . . . . . 126
9.11. Open Upgrade and Downgrade . . . . . . . . . . . . . . . 126
9.12. Short and Long Leases . . . . . . . . . . . . . . . . . 127
9.13. Clocks, Propagation Delay, and Calculating Lease
Expiration . . . . . . . . . . . . . . . . . . . . . . . 127
9.14. Migration, Replication and State . . . . . . . . . . . . 128
9.14.1. Migration and State . . . . . . . . . . . . . . . . 128
9.14.2. Replication and State . . . . . . . . . . . . . . . 129
9.14.3. Notification of Migrated Lease . . . . . . . . . . . 130
9.14.4. Migration and the Lease_time Attribute . . . . . . . 130
10. Client-Side Caching . . . . . . . . . . . . . . . . . . . . . 131
10.1. Performance Challenges for Client-Side Caching . . . . . 131
10.2. Delegation and Callbacks . . . . . . . . . . . . . . . . 132
10.2.1. Delegation Recovery . . . . . . . . . . . . . . . . 134
10.3. Data Caching . . . . . . . . . . . . . . . . . . . . . . 136
10.3.1. Data Caching and OPENs . . . . . . . . . . . . . . . 136
10.3.2. Data Caching and File Locking . . . . . . . . . . . 137
10.3.3. Data Caching and Mandatory File Locking . . . . . . 139
10.3.4. Data Caching and File Identity . . . . . . . . . . . 139
10.4. Open Delegation . . . . . . . . . . . . . . . . . . . . 140
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10.4.1. Open Delegation and Data Caching . . . . . . . . . . 142
10.4.2. Open Delegation and File Locks . . . . . . . . . . . 144
10.4.3. Handling of CB_GETATTR . . . . . . . . . . . . . . . 144
10.4.4. Recall of Open Delegation . . . . . . . . . . . . . 147
10.4.5. Clients that Fail to Honor Delegation Recalls . . . 149
10.4.6. Delegation Revocation . . . . . . . . . . . . . . . 150
10.5. Data Caching and Revocation . . . . . . . . . . . . . . 150
10.5.1. Revocation Recovery for Write Open Delegation . . . 151
10.6. Attribute Caching . . . . . . . . . . . . . . . . . . . 151
10.7. Data and Metadata Caching and Memory Mapped Files . . . 153
10.8. Name Caching . . . . . . . . . . . . . . . . . . . . . . 156
10.9. Directory Caching . . . . . . . . . . . . . . . . . . . 157
11. Minor Versioning . . . . . . . . . . . . . . . . . . . . . . 157
12. Internationalization . . . . . . . . . . . . . . . . . . . . 160
12.1. Use of UTF-8 . . . . . . . . . . . . . . . . . . . . . . 161
12.1.1. Relation to Stringprep . . . . . . . . . . . . . . . 161
12.1.2. Normalization, Equivalence, and Confusability . . . 162
12.2. String Type Overview . . . . . . . . . . . . . . . . . . 165
12.2.1. Overall String Class Divisions . . . . . . . . . . . 165
12.2.2. Divisions by Typedef Parent types . . . . . . . . . 166
12.2.3. Individual Types and Their Handling . . . . . . . . 167
12.3. Errors Related to Strings . . . . . . . . . . . . . . . 168
12.4. Types with Pre-processing to Resolve Mixture Issues . . 169
12.4.1. Processing of Principal Strings . . . . . . . . . . 169
12.4.2. Processing of Server Id Strings . . . . . . . . . . 169
12.5. String Types without Internationalization Processing . . 170
12.6. Types with Processing Defined by Other Internet Areas . 170
12.7. String Types with NFS-specific Processing . . . . . . . 171
12.7.1. Handling of File Name Components . . . . . . . . . . 172
12.7.2. Processing of Link Text . . . . . . . . . . . . . . 181
12.7.3. Processing of Principal Prefixes . . . . . . . . . . 182
13. Error Values . . . . . . . . . . . . . . . . . . . . . . . . 183
13.1. Error Definitions . . . . . . . . . . . . . . . . . . . 183
13.1.1. General Errors . . . . . . . . . . . . . . . . . . . 185
13.1.2. Filehandle Errors . . . . . . . . . . . . . . . . . 186
13.1.3. Compound Structure Errors . . . . . . . . . . . . . 187
13.1.4. File System Errors . . . . . . . . . . . . . . . . . 188
13.1.5. State Management Errors . . . . . . . . . . . . . . 190
13.1.6. Security Errors . . . . . . . . . . . . . . . . . . 191
13.1.7. Name Errors . . . . . . . . . . . . . . . . . . . . 191
13.1.8. Locking Errors . . . . . . . . . . . . . . . . . . . 192
13.1.9. Reclaim Errors . . . . . . . . . . . . . . . . . . . 193
13.1.10. Client Management Errors . . . . . . . . . . . . . . 194
13.1.11. Attribute Handling Errors . . . . . . . . . . . . . 194
13.2. Operations and their valid errors . . . . . . . . . . . 195
13.3. Callback operations and their valid errors . . . . . . . 203
13.4. Errors and the operations that use them . . . . . . . . 203
14. NFS version 4 Requests . . . . . . . . . . . . . . . . . . . 207
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14.1. Compound Procedure . . . . . . . . . . . . . . . . . . . 208
14.2. Evaluation of a Compound Request . . . . . . . . . . . . 208
14.3. Synchronous Modifying Operations . . . . . . . . . . . . 209
14.4. Operation Values . . . . . . . . . . . . . . . . . . . . 210
15. NFS version 4 Procedures . . . . . . . . . . . . . . . . . . 210
15.1. Procedure 0: NULL - No Operation . . . . . . . . . . . . 210
15.2. Procedure 1: COMPOUND - Compound Operations . . . . . . 210
15.3. Operation 3: ACCESS - Check Access Rights . . . . . . . 213
15.4. Operation 4: CLOSE - Close File . . . . . . . . . . . . 216
15.5. Operation 5: COMMIT - Commit Cached Data . . . . . . . . 217
15.6. Operation 6: CREATE - Create a Non-Regular File Object . 219
15.7. Operation 7: DELEGPURGE - Purge Delegations Awaiting
Recovery . . . . . . . . . . . . . . . . . . . . . . . . 222
15.8. Operation 8: DELEGRETURN - Return Delegation . . . . . . 223
15.9. Operation 9: GETATTR - Get Attributes . . . . . . . . . 223
15.10. Operation 10: GETFH - Get Current Filehandle . . . . . . 224
15.11. Operation 11: LINK - Create Link to a File . . . . . . . 225
15.12. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 227
15.13. Operation 13: LOCKT - Test For Lock . . . . . . . . . . 231
15.14. Operation 14: LOCKU - Unlock File . . . . . . . . . . . 232
15.15. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 233
15.16. Operation 16: LOOKUPP - Lookup Parent Directory . . . . 235
15.17. Operation 17: NVERIFY - Verify Difference in
Attributes . . . . . . . . . . . . . . . . . . . . . . . 236
15.18. Operation 18: OPEN - Open a Regular File . . . . . . . . 237
15.19. Operation 19: OPENATTR - Open Named Attribute
Directory . . . . . . . . . . . . . . . . . . . . . . . 246
15.20. Operation 20: OPEN_CONFIRM - Confirm Open . . . . . . . 247
15.21. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 249
15.22. Operation 22: PUTFH - Set Current Filehandle . . . . . . 251
15.23. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 251
15.24. Operation 24: PUTROOTFH - Set Root Filehandle . . . . . 253
15.25. Operation 25: READ - Read from File . . . . . . . . . . 253
15.26. Operation 26: READDIR - Read Directory . . . . . . . . . 255
15.27. Operation 27: READLINK - Read Symbolic Link . . . . . . 259
15.28. Operation 28: REMOVE - Remove Filesystem Object . . . . 260
15.29. Operation 29: RENAME - Rename Directory Entry . . . . . 262
15.30. Operation 30: RENEW - Renew a Lease . . . . . . . . . . 264
15.31. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 265
15.32. Operation 32: SAVEFH - Save Current Filehandle . . . . . 266
15.33. Operation 33: SECINFO - Obtain Available Security . . . 266
15.34. Operation 34: SETATTR - Set Attributes . . . . . . . . . 269
15.35. Operation 35: SETCLIENTID - Negotiate Clientid . . . . . 272
15.36. Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid . . 275
15.37. Operation 37: VERIFY - Verify Same Attributes . . . . . 279
15.38. Operation 38: WRITE - Write to File . . . . . . . . . . 280
15.39. Operation 39: RELEASE_LOCKOWNER - Release Lockowner
State . . . . . . . . . . . . . . . . . . . . . . . . . 284
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15.40. Operation 10044: ILLEGAL - Illegal operation . . . . . . 285
16. NFS version 4 Callback Procedures . . . . . . . . . . . . . . 286
16.1. Procedure 0: CB_NULL - No Operation . . . . . . . . . . 286
16.2. Procedure 1: CB_COMPOUND - Compound Operations . . . . . 287
16.2.6. Operation 3: CB_GETATTR - Get Attributes . . . . . . 288
16.2.7. Operation 4: CB_RECALL - Recall an Open Delegation . 289
16.2.8. Operation 10044: CB_ILLEGAL - Illegal Callback
Operation . . . . . . . . . . . . . . . . . . . . . 290
17. Security Considerations . . . . . . . . . . . . . . . . . . . 291
18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 293
18.1. Named Attribute Definition . . . . . . . . . . . . . . . 293
18.2. ONC RPC Network Identifiers (netids) . . . . . . . . . . 293
19. References . . . . . . . . . . . . . . . . . . . . . . . . . 294
19.1. Normative References . . . . . . . . . . . . . . . . . . 294
19.2. Informative References . . . . . . . . . . . . . . . . . 295
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 297
Appendix B. RFC Editor Notes . . . . . . . . . . . . . . . . . . 297
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 297
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1. Introduction
1.1. Changes since RFC 3530
This document, together with the companion XDR description document
[2], obsoletes RFC 3530 [11] as the authoritative document describing
NFSv4. It does not introduce any over-the-wire protocol changes, in
the sense that previously valid requests requests remain valid.
However, some requests previously defined as invalid, although not
generally rejected, are now explicitly allowed, in that
internationalization handling has been generalized and liberalized.
The main changes from RFC 3530 are:
o The XDR definition has been moved to a companion document [2]
o Updates for the latest IETF intellectual property statements
o There is a restructured and more complete explanation of multi-
server namespace features. In particular, this explanation
explicitly describes handling of inter-server referrals, even
where neither migration nor replication is involved.
o More liberal handling of internationalization for file names and
user and group names, with the elimination of restrictions imposed
by stringprep, with the recognition that rules for the forms of
these name are the province of the receiving entity.
o Updating handling of domain names to reflect IDNA.
o Restructuring of string types to more appropriately reflect the
reality of required string processing.
o LIPKEY SPKM/3 has been moved from being REQUIRED to OPTIONAL.
o Some clarification on a client re-establishing callback
information to the new server if state has been migrated
1.2. Changes since RFC 3010
This definition of the NFS version 4 protocol replaces or obsoletes
the definition present in [12]. While portions of the two documents
have remained the same, there have been substantive changes in
others. The changes made between [12] and this document represent
implementation experience and further review of the protocol. While
some modifications were made for ease of implementation or
clarification, most updates represent errors or situations where the
[12] definition were untenable.
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The following list is not all inclusive of all changes but presents
some of the most notable changes or additions made:
o The state model has added an open_owner4 identifier. This was
done to accommodate Posix based clients and the model they use for
file locking. For Posix clients, an open_owner4 would correspond
to a file descriptor potentially shared amongst a set of processes
and the lock_owner4 identifier would correspond to a process that
is locking a file.
o Clarifications and error conditions were added for the handling of
the owner and group attributes. Since these attributes are string
based (as opposed to the numeric uid/gid of previous versions of
NFS), translations may not be available and hence the changes
made.
o Clarifications for the ACL and mode attributes to address
evaluation and partial support.
o For identifiers that are defined as XDR opaque, limits were set on
their size.
o Added the mounted_on_filed attribute to allow Posix clients to
correctly construct local mounts.
o Modified the SETCLIENTID/SETCLIENTID_CONFIRM operations to deal
correctly with confirmation details along with adding the ability
to specify new client callback information. Also added
clarification of the callback information itself.
o Added a new operation LOCKOWNER_RELEASE to enable notifying the
server that a lock_owner4 will no longer be used by the client.
o RENEW operation changes to identify the client correctly and allow
for additional error returns.
o Verify error return possibilities for all operations.
o Remove use of the pathname4 data type from LOOKUP and OPEN in
favor of having the client construct a sequence of LOOKUP
operations to achieive the same effect.
o Clarification of the internationalization issues and adoption of
the new stringprep profile framework.
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1.3. NFS Version 4 Goals
The NFS version 4 protocol is a further revision of the NFS protocol
defined already by versions 2 [13] and 3 [14]. It retains the
essential characteristics of previous versions: design for easy
recovery, independent of transport protocols, operating systems and
filesystems, simplicity, and good performance. The NFS version 4
revision has the following goals:
o Improved access and good performance on the Internet.
The protocol is designed to transit firewalls easily, perform well
where latency is high and bandwidth is low, and scale to very
large numbers of clients per server.
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 NFS version
4 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 filesystem model that provides a useful,
common set of features that does not unduly favor one filesystem
or operating system over another.
o Designed for protocol extensions.
The protocol is designed to accept standard extensions that do not
compromise backward compatibility.
1.4. Inconsistencies of this Document with the companion document NFS
Version 4 Protocol
[2], NFS Version 4 Protocol, contains the definitions in XDR
description language of the constructs used by the protocol. Inside
this document, several of the constructs are reproduced for purposes
of explanation. The reader is warned of the possibility of errors in
the reproduced constructs outside of [2]. For any part of the
document that is inconsistent with [2], [2] is to be considered
authoritative.
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1.5. Overview of NFS version 4 Features
To provide a reasonable context for the reader, the major features of
NFS version 4 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 fundamental knowledge that is expected. The reader
should be familiar with the XDR and RPC protocols as described in [3]
and [15]. A basic knowledge of filesystems and distributed
filesystems is expected as well.
1.5.1. RPC and Security
As with previous versions of NFS, the External Data Representation
(XDR) and Remote Procedure Call (RPC) mechanisms used for the NFS
version 4 protocol are those defined in [3] and [15]. 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 NFS version 4 protocol. Kerberos V5
will be used as described in [16] to provide one security framework.
The LIPKEY GSS-API mechanism described in [5] will be used to provide
for the use of user password and server public key by the NFS version
4 protocol. With the use of RPCSEC_GSS, other mechanisms may also be
specified and used for NFS version 4 security.
To enable in-band security negotiation, the NFS version 4 protocol
has added a new operation which provides the client a method of
querying the server about its policies regarding which security
mechanisms must be used for access to the server's filesystem
resources. With this, the client can securely match the security
mechanism that meets the policies specified at both the client and
server.
1.5.2. Procedure and Operation Structure
A significant departure from the previous versions of the NFS
protocol is the introduction of the COMPOUND procedure. For the NFS
version 4 protocol, there are two RPC procedures, NULL and COMPOUND.
The COMPOUND procedure is defined in terms of operations and these
operations correspond more closely to the traditional NFS procedures.
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 filesystem
operations. For example, without previous contact with a server a
client will be able to read data from a file in one request by
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combining LOOKUP, OPEN, and READ operations in a single COMPOUND RPC.
With previous versions of the NFS protocol, this type of single
request was not possible.
The model used for COMPOUND is very simple. There is no logical OR
or ANDing of operations. The operations combined within a COMPOUND
request are evaluated in order by the server. Once an operation
returns a failing result, the evaluation ends and the results of all
evaluated operations are returned to the client.
The NFS version 4 protocol continues to have the client refer to a
file or directory at the server by a "filehandle". The COMPOUND
procedure has a method of passing a filehandle from one operation to
another within the sequence of operations. There is a concept of a
"current filehandle" and "saved filehandle". Most operations use the
"current filehandle" as the filesystem object to operate upon. The
"saved filehandle" is used as temporary filehandle storage within a
COMPOUND procedure as well as an additional operand for certain
operations.
1.5.3. Filesystem Model
The general filesystem model used for the NFS version 4 protocol is
the same as previous versions. The server filesystem 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 NFS version 4 protocol does not require a separate protocol to
provide for the initial mapping between path name and filehandle.
Instead of using the older MOUNT protocol for this mapping, the
server provides a ROOT filehandle that represents the logical root or
top of the filesystem tree provided by the server. The server
provides multiple filesystems by gluing them together with pseudo
filesystems. These pseudo filesystems provide for potential gaps in
the path names between real filesystems.
1.5.3.1. Filehandle Types
In previous versions of the NFS protocol, the filehandle provided by
the server was guaranteed to be valid or persistent for the lifetime
of the filesystem object to which it referred. For some server
implementations, this persistence requirement has been difficult to
meet. For the NFS version 4 protocol, this requirement has been
relaxed by introducing another type of filehandle, volatile. With
persistent and volatile filehandle types, the server implementation
can match the abilities of the filesystem at the server along with
the operating environment. The client will have knowledge of the
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type of filehandle being provided by the server and can be prepared
to deal with the semantics of each.
1.5.3.2. Attribute Types
The NFS version 4 protocol introduces three classes of filesystem or
file attributes. Like the additional filehandle type, the
classification of file attributes has been done to ease server
implementations along with extending the overall functionality of the
NFS protocol. This attribute model is structured to be extensible
such that new attributes can be introduced in minor revisions of the
protocol without requiring significant rework.
The three classifications are: mandatory, recommended and named
attributes. This is a significant departure from the previous
attribute model used in the NFS protocol. Previously, the attributes
for the filesystem and file objects were a fixed set of mainly UNIX
attributes. If the server or client did not support a particular
attribute, it would have to simulate the attribute the best it could.
Mandatory attributes are the minimal set of file or filesystem
attributes that must be provided by the server and must be properly
represented by the server. Recommended attributes represent
different filesystem types and operating environments. The
recommended attributes will allow for better interoperability and the
inclusion of more operating environments. The mandatory and
recommended attribute sets are traditional file or filesystem
attributes. The third 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.
One significant addition to the recommended set of file attributes is
the Access Control List (ACL) attribute. This attribute provides for
directory and file access control beyond the model used in previous
versions of the NFS protocol. The ACL definition allows for
specification of user and group level access control.
1.5.3.3. Filesystem Replication and Migration
With the use of a special file attribute, the ability to inform the
client of filesystem locations on another server is enabled. The
filesystem locations attribute provides a method for the client to
probe the server about the location of a filesystem. In the event
that a fileystems is not present on server the client will receive an
error when attempting to operate on the filesystem and it can then
query as to the correct filesystem location. Thus is allowed
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construction of multi-server namespaces..
These features also allow file system replication and migration. In
the event of a migration of a filesystem, the client will receive an
error when operating on the filesystem and it can then query location
attribute to determine the new file system location. Similar steps
are used for replication, the client is able to query the server for
the multiple available locations of a particular filesystem. From
this information, the client can use its own policies to access the
appropriate filesystem location.
1.5.4. OPEN and CLOSE
The NFS version 4 protocol introduces OPEN and CLOSE operations. The
OPEN operation provides a single point where file lookup, creation,
and share semantics can be combined. The CLOSE operation also
provides for the release of state accumulated by OPEN.
1.5.5. File Locking
With the NFS version 4 protocol, the support for byte range file
locking is part of the NFS protocol. The file locking support is
structured so that an RPC callback mechanism is not required. This
is a departure from the previous versions of the NFS file locking
protocol, Network Lock Manager (NLM). The state associated with file
locks is maintained at the server under a lease-based model. The
server defines a single lease period for all state held by a NFS
client. If the client does not renew its lease within the defined
period, all state associated with the client's lease may be released
by the server. The client may renew its lease with use of the RENEW
operation or implicitly by use of other operations (primarily READ).
1.5.6. Client Caching and Delegation
The file, attribute, and directory caching for the NFS version 4
protocol is similar to previous versions. Attributes and directory
information are cached for a duration determined by the client. At
the end of a predefined timeout, the client will query the server to
see if the related filesystem object has been updated.
For file data, the client checks its cache validity when the file is
opened. A query is sent to the server to determine if the file has
been changed. Based on this information, the client determines if
the data cache for the file should kept or released. Also, when the
file is closed, any modified data is written to the server.
If an application wants to serialize access to file data, file
locking of the file data ranges in question should be used.
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The major addition to NFS version 4 in the area of caching is the
ability of the server to delegate certain responsibilities to the
client. When the server grants a delegation for a file to a client,
the client is guaranteed certain semantics with respect to the
sharing of that file with other clients. At OPEN, the server may
provide the client either a read or write delegation for the file.
If the client is granted a read delegation, it is assured that no
other client has the ability to write to the file for the duration of
the delegation. If the client is granted a write delegation, the
client is assured that no other client has read or write access to
the file.
Delegations can be recalled by the server. If another client
requests access to the file in such a way that the access conflicts
with the granted delegation, the server is able to notify the initial
client and recall the delegation. This requires that a callback path
exist between the server and client. If this callback path does not
exist, then delegations can not be granted. The essence of a
delegation is that it allows the client to locally service operations
such as OPEN, CLOSE, LOCK, LOCKU, READ, WRITE without immediate
interaction with the server.
1.6. General Definitions
The following definitions are provided for the purpose of providing
an appropriate context for the reader.
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 remote filesystem services
for a set of applications.
In the case of file locking the client is 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
multiple clients may exist on the same network node.
Clientid A 64-bit quantity used as a unique, short-hand reference to
a client supplied Verifier and ID. The server is responsible for
supplying the Clientid.
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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.
Lock The term "lock" is used to refer to both record (byte-range)
locks as well as share reservations unless specifically stated
otherwise.
Server The "Server" is the entity responsible for coordinating
client access to a set of filesystems.
Stable Storage NFS version 4 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.
Stateids composed of all bits 0 or all bits 1 have special meaning
and are reserved values.
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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.
2. Protocol Data Types
The syntax and semantics to describe the data types of the NFS
version 4 protocol are defined in the XDR [15] and RPC [3] documents.
The next sections build upon the XDR data types to define types and
structures specific to this protocol.
2.1. Basic Data Types
These are the base NFSv4 data types.
+----------------+--------------------------------------------------+
| Data Type | Definition |
+----------------+--------------------------------------------------+
| int32_t | typedef int int32_t; |
| uint32_t | typedef unsigned int uint32_t; |
| int64_t | typedef hyper int64_t; |
| uint64_t | typedef unsigned hyper uint64_t; |
| attrlist4 | typedef opaque attrlist4<>; |
| | Used for file/directory attributes. |
| bitmap4 | typedef uint32_t bitmap4<>; |
| | Used in attribute array encoding. |
| changeid4 | typedef uint64_t changeid4; |
| | Used in the definition of change_info4. |
| 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. |
| mode4 | typedef uint32_t mode4; |
| | Mode attribute data type. |
| nfs_cookie4 | typedef uint64_t nfs_cookie4; |
| | Opaque cookie value for READDIR. |
| nfs_fh4 | typedef opaque nfs_fh4<NFS4_FHSIZE>; |
| | Filehandle definition. |
| nfs_ftype4 | enum nfs_ftype4; |
| | Various defined file types. |
| nfsstat4 | enum nfsstat4; |
| | Return value for operations. |
| offset4 | typedef uint64_t offset4; |
| | Various offset designations (READ, WRITE, LOCK, |
| | COMMIT). |
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| 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 [6] for details. |
| seqid4 | typedef uint32_t seqid4; |
| | Sequence identifier used for file locking. |
| utf8string | typedef opaque utf8string<>; |
| | UTF-8 encoding for strings. |
| utf8_should | typedef utf8string utf8_should; |
| | String expected to be UTF8 but no validation |
| utf8val_should | typedef utf8string utf8val_should; |
| | String SHOULD be sent UTF8 and SHOULD be |
| | validated |
| utf8val_must | typedef utf8string utf8val_must; |
| | String MUST be sent UTF8 and MUST be validated |
| ascii_must | typedef utf8string ascii_must; |
| | String MUST be sent as ASCII and thus is |
| | automatically UTF8 |
| comptag4 | typedef utf8_should comptag4; |
| | Tag should be UTF8 but is not checked |
| component4 | typedef utf8val_should component4; |
| | Represents path name components. |
| linktext4 | typedef utf8val_should linktext4; |
| | Symbolic link contents. |
| pathname4 | typedef component4 pathname4<>; |
| | Represents path name for fs_locations. |
| nfs_lockid4 | typedef uint64_t nfs_lockid4; |
| 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
2.2. Structured Data Types
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2.2.1. 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 filesystem object is less than
defined, loss of precision can occur. An adjunct time maintenance
protocol is recommended to reduce client and server time skew.
2.2.2. time_how4
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
2.2.3. 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.
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2.2.4. 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.
2.2.5. fsid4
struct fsid4 {
uint64_t major;
uint64_t minor;
};
This type is the filesystem identifier that is used as a mandatory
attribute.
2.2.6. fs_location4
struct fs_location4 {
utf8must server<>;
pathname4 rootpath;
};
2.2.7. fs_locations4
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
The fs_location4 and fs_locations4 data types are used for the
fs_locations recommended attribute which is used for migration and
replication support.
2.2.8. fattr4
struct fattr4 {
bitmap4 attrmask;
attrlist4 attr_vals;
};
The fattr4 structure is used to represent file and directory
attributes.
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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 |
+-----------+-----------+-----------+--
2.2.9. 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 filesystem object resides.
2.2.10. clientaddr4
struct clientaddr4 {
/* see struct rpcb in RFC 1833 */
string r_netid<>; /* network id */
string r_addr<>; /* universal address */
};
The clientaddr4 structure is used as part of the SETCLIENTID
operation to either specify the address of the client that is using a
clientid or as part of the callback registration. The r_netid and
r_addr fields are specified in [17], but they are underspecified in
[17] 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:
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
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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 the 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".
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 [18].
Additionally, the two alternative forms specified in Section 2.2 of
[18] 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".
2.2.11. cb_client4
struct cb_client4 {
unsigned int cb_program;
clientaddr4 cb_location;
};
This structure is used by the client to inform the server of its call
back address; includes the program number and client address.
2.2.12. nfs_client_id4
struct nfs_client_id4 {
verifier4 verifier;
opaque id<NFS4_OPAQUE_LIMIT>;
};
This structure is part of the arguments to the SETCLIENTID operation.
NFS4_OPAQUE_LIMIT is defined as 1024.
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2.2.13. open_owner4
struct open_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
This structure is used to identify the owner of open state.
NFS4_OPAQUE_LIMIT is defined as 1024.
2.2.14. lock_owner4
struct lock_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
This structure is used to identify the owner of file locking state.
NFS4_OPAQUE_LIMIT is defined as 1024.
2.2.15. 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.
2.2.16. 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
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will inspect the seqid in OPEN stateids to determine the order of
OPEN processing done by the server.
3. RPC and Security Flavor
The NFS version 4 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 [15]. The RPCSEC_GSS
security flavor as defined in [4] MUST be used as the mechanism to
deliver stronger security for the NFS version 4 protocol.
3.1. Ports and Transports
Historically, NFS version 2 and version 3 servers have resided on
port 2049. The registered port 2049 [19] for the NFS protocol should
be the default configuration. Using the registered port for NFS
services means the NFS client will not need to use the RPC binding
protocols as described in [17]; this will allow NFS to transit
firewalls.
Where an NFS version 4 implementation supports operation over the IP
network protocol, the supported transports between NFS and IP MUST be
among the IETF-approved congestion control transport protocols, which
include TCP and SCTP. To enhance the possibilities for
interoperability, an NFS version 4 implementation MUST support
operation over the TCP transport protocol, at least until such time
as a standards track RFC revises this requirement to use a different
IETF-approved congestion control transport protocol.
If TCP is used as the transport, the client and server SHOULD use
persistent connections. This will prevent the weakening of TCP's
congestion control via short lived connections and will improve
performance for the WAN environment by eliminating the need for SYN
handshakes.
As noted in Section 17, the authentication model for NFS version 4
has moved from machine-based to principal- based. However, this
modification of the authentication model does not imply a technical
requirement to move the TCP connection management model from whole
machine-based to one based on a per user model. In particular, NFS
over TCP client implementations have traditionally multiplexed
traffic for multiple users over a common TCP connection between an
NFS client and server. This has been true, regardless whether the
NFS client is using AUTH_SYS, AUTH_DH, RPCSEC_GSS or any other
flavor. Similarly, NFS over TCP server implementations have assumed
such a model and thus scale the implementation of TCP connection
management in proportion to the number of expected client machines.
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It is intended that NFS version 4 will not modify this connection
management model. NFS version 4 clients that violate this assumption
can expect scaling issues on the server and hence reduced service.
Note that for various timers, the client and server should avoid
inadvertent synchronization of those timers. For further discussion
of the general issue refer to [20].
3.1.1. Client Retransmission Behavior
When processing a request received over a reliable transport such as
TCP, the NFS version 4 server MUST NOT silently drop the request,
except if the transport connection has been broken. Given such a
contract between NFS version 4 clients and servers, clients MUST NOT
retry a request unless one or both of the following are true:
o The transport connection has been broken
o The procedure being retried is the NULL procedure
Since reliable transports, such as TCP, do not always synchronously
inform a peer when the other peer has broken the connection (for
example, when an NFS server reboots), the NFS version 4 client may
want to actively "probe" the connection to see if has been broken.
Use of the NULL procedure is one recommended way to do so. So, when
a client experiences a remote procedure call timeout (of some
arbitrary implementation specific amount), rather than retrying the
remote procedure call, it could instead issue a NULL procedure call
to the server. If the server has died, the transport connection
break will eventually be indicated to the NFS version 4 client. The
client can then reconnect, and then retry the original request. If
the NULL procedure call gets a response, the connection has not
broken. The client can decide to wait longer for the original
request's response, or it can break the transport connection and
reconnect before re-sending the original request.
For callbacks from the server to the client, the same rules apply,
but the server doing the callback becomes the client, and the client
receiving the callback becomes the server.
3.2. Security Flavors
Traditional RPC implementations have included AUTH_NONE, AUTH_SYS,
AUTH_DH, and AUTH_KRB4 as security flavors. With [4] an additional
security flavor of RPCSEC_GSS has been introduced which uses the
functionality of GSS-API [6]. This allows for the use of various
security mechanisms by the RPC layer without the additional
implementation overhead of adding RPC security flavors. For NFS
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version 4, the RPCSEC_GSS security flavor MUST be used to enable the
mandatory security mechanism. Other flavors, such as, AUTH_NONE,
AUTH_SYS, and AUTH_DH MAY be implemented as well.
3.2.1. Security mechanisms for NFS version 4
The use of RPCSEC_GSS requires selection of: mechanism, quality of
protection, and service (authentication, integrity, privacy). The
remainder of this document will refer to these three parameters of
the RPCSEC_GSS security as the security triple.
3.2.1.1. Kerberos V5 as a security triple
The Kerberos V5 GSS-API mechanism as described in [16] MUST be
implemented and provide the following security triples.
column descriptions:
1 == number of pseudo flavor
2 == name of pseudo flavor
3 == mechanism's OID
4 == mechanism's algorithm(s)
5 == RPCSEC_GSS service
1 2 3 4 5
--------------------------------------------------------------------
390003 krb5 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_none
390004 krb5i 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_integrity
390005 krb5p 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_privacy
for integrity,
and 56 bit DES
for privacy.
Note that the pseudo flavor is presented here as a mapping aid to the
implementor. Because this NFS 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 NFS
version 3 since the security negotiation is done via the MOUNT
protocol.
For a discussion of NFS' use of RPCSEC_GSS and Kerberos V5, please
see [21].
Users and implementors are warned that 56 bit DES is no longer
considered state of the art in terms of resistance to brute force
attacks. Once a revision to [16] is available that adds support for
AES, implementors are urged to incorporate AES into their NFSv4 over
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Kerberos V5 protocol stacks, and users are similarly urged to migrate
to the use of AES.
3.2.1.2. LIPKEY as a security triple
The LIPKEY GSS-API mechanism as described in [5] MAY be implemented
and provide the following security triples. The definition of the
columns matches those in Section 3.2.1.1.
1 2 3 4 5
--------------------------------------------------------------------
390006 lipkey 1.3.6.1.5.5.9 negotiated rpc_gss_svc_none
390007 lipkey-i 1.3.6.1.5.5.9 negotiated rpc_gss_svc_integrity
390008 lipkey-p 1.3.6.1.5.5.9 negotiated rpc_gss_svc_privacy
The mechanism algorithm is listed as "negotiated". This is because
LIPKEY is layered on SPKM-3 and in SPKM-3 [5] the confidentiality and
integrity algorithms are negotiated. Since SPKM-3 specifies HMAC-MD5
for integrity as MANDATORY, 128 bit cast5CBC for confidentiality for
privacy as MANDATORY, and further specifies that HMAC-MD5 and
cast5CBC MUST be listed first before weaker algorithms, specifying
"negotiated" in column 4 does not impair interoperability. In the
event an SPKM-3 peer does not support the mandatory algorithms, the
other peer is free to accept or reject the GSS-API context creation.
Because SPKM-3 negotiates the algorithms, subsequent calls to
LIPKEY's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality
of protection value of 0 (zero). See section 5.2 of [22] for an
explanation.
LIPKEY uses SPKM-3 to create a secure channel in which to pass a user
name and password from the client to the server. Once the user name
and password have been accepted by the server, calls to the LIPKEY
context are redirected to the SPKM-3 context. See [5] for more
details.
3.2.1.3. SPKM-3 as a security triple
The SPKM-3 GSS-API mechanism as described in [5] MAY be implemented
and provide the following security triples. The definition of the
columns matches those in Section 3.2.1.1.
1 2 3 4 5
--------------------------------------------------------------------
390009 spkm3 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_none
390010 spkm3i 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_integrity
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390011 spkm3p 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_privacy
For a discussion as to why the mechanism algorithm is listed as
"negotiated", see Section 3.2.1.2.
Because SPKM-3 negotiates the algorithms, subsequent calls to SPKM-
3's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality of
protection value of 0 (zero). See section 5.2 of [22] for an
explanation.
Even though LIPKEY is layered over SPKM-3, SPKM-3 is specified as a
mandatory set of triples to handle the situations where the initiator
(the client) is anonymous or where the initiator has its own
certificate. If the initiator is anonymous, there will not be a user
name and password to send to the target (the server). If the
initiator has its own certificate, then using passwords is
superfluous.
3.3. Security Negotiation
With the NFS version 4 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 filesystem name space
that are available for use by NFS clients. In turn the NFS server
may be configured such that each of these entry points 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 17 for further discussion.
3.3.1. SECINFO
The new SECINFO operation will allow the client to determine, on a
per filehandle basis, what security triple is to be used for server
access. In general, the client will not have to use the SECINFO
operation except during initial communication with the server or when
the client crosses policy boundaries at the server. It is possible
that the server's policies change during the client's interaction
therefore forcing the client to negotiate a new security triple.
3.3.2. Security Error
Based on the assumption that each NFS version 4 client and server
must support a minimum set of security (i.e., LIPKEY, SPKM-3, and
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Kerberos-V5 all under RPCSEC_GSS), the NFS client will start its
communication with the server with one of the minimal security
triples. 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 triple currently being
used is not appropriate for access to the server's filesystem
resources. The client is then responsible for determining what
security triples are available at the server and choose one which is
appropriate for the client. See Section 15.33 for further discussion
of how the client will respond to the NFS4ERR_WRONGSEC error and use
SECINFO.
3.3.3. Callback RPC Authentication
Except as noted elsewhere in this section, the callback RPC
(described later) MUST mutually authenticate the NFS server to the
principal that acquired the clientid (also described later), using
the security flavor the original SETCLIENTID operation used.
For AUTH_NONE, there are no principals, so this is a non-issue.
AUTH_SYS has no notions of mutual authentication or a server
principal, so the callback from the server simply uses the AUTH_SYS
credential that the user used when he set up the delegation.
For AUTH_DH, one commonly used convention is that the server uses the
credential corresponding to this AUTH_DH principal:
unix.host@domain
where host and domain are variables corresponding to the name of
server host and directory services domain in which it lives such as a
Network Information System domain or a DNS domain.
Because LIPKEY is layered over SPKM-3, it is permissible for the
server to use SPKM-3 and not LIPKEY for the callback even if the
client used LIPKEY for SETCLIENTID.
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
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Implementations of security mechanisms will convert nfs@hostname to
various different forms. For Kerberos V5 and LIPKEY, the following
form is RECOMMENDED:
nfs/hostname
For Kerberos V5, nfs/hostname would be a server principal in the
Kerberos Key Distribution Center database. This is the same
principal the client acquired a GSS-API context for when it issued
the SETCLIENTID operation, therefore, the realm name for the server
principal must be the same for the callback as it was for the
SETCLIENTID.
For LIPKEY, this would be the username passed to the target (the NFS
version 4 client that receives the callback).
It should be noted that LIPKEY may not work for callbacks, since the
LIPKEY client uses a user id/password. If the NFS client receiving
the callback can authenticate the NFS server's user name/password
pair, and if the user that the NFS server is authenticating to has a
public key certificate, then it works.
In situations where the NFS client uses LIPKEY and uses a per-host
principal for the SETCLIENTID operation, instead of using LIPKEY for
SETCLIENTID, it is RECOMMENDED that SPKM-3 with mutual authentication
be used. This effectively means that the client will use a
certificate to authenticate and identify the initiator to the target
on the NFS server. Using SPKM-3 and not LIPKEY has the following
advantages:
o When the server does a callback, it must authenticate to the
principal used in the SETCLIENTID. Even if LIPKEY is used,
because LIPKEY is layered over SPKM-3, the NFS client will need to
have a certificate that corresponds to the principal used in the
SETCLIENTID operation. From an administrative perspective, having
a user name, password, and certificate for both the client and
server is redundant.
o LIPKEY was intended to minimize additional infrastructure
requirements beyond a certificate for the target, and the
expectation is that existing password infrastructure can be
leveraged for the initiator. In some environments, a per-host
password does not exist yet. If certificates are used for any
per-host principals, then additional password infrastructure is
not needed.
o In cases when a host is both an NFS client and server, it can
share the same per-host certificate.
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4. Filehandles
The filehandle in the NFS protocol is a per server unique identifier
for a filesystem 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 filesystem
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 NFS version 2
protocol [13] and the NFS version 3 protocol [14], 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 filesystem 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 [23] and [24]. With the use of the
public filehandle in combination with the LOOKUP operation in the NFS
version 2 and 3 protocols, it has been demonstrated that the MOUNT
protocol is unnecessary for viable interaction between NFS client and
server.
Therefore, the NFS version 4 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 filesystem name space
at the NFS server. The client uses or starts with the ROOT
filehandle by employing the PUTROOTFH operation. The PUTROOTFH
operation instructs the server to set the "current" filehandle to the
ROOT of the server's file tree. Once this PUTROOTFH operation is
used, the client can then traverse the entirety of the server's file
tree with the LOOKUP operation. A complete discussion of the server
name space is in Section 8.
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
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arbitrary filesystem 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 filesystem 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 filesystem 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 NFS version 2 and 3 protocols, there was one type of
filehandle with a single set of semantics. This type of filehandle
is termed "persistent" in NFS Version 4. The semantics of a
persistent filehandle remain the same as before. A new type of
filehandle introduced in NFS Version 4 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 filesystem level invariant that can be
used to construct a persistent filehandle. The underlying server
filesystem may not provide the invariant or the server's filesystem
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
filesystem 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.
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
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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
Section 10.3.4.
As an example, in the case that two different path names when
traversed at the server terminate at the same filesystem 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 filesystem object to which it refers. Once the
server creates the filehandle for a filesystem 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 filesystem 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
filesystem 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
filesystem 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 filesystem in whole
has been destroyed or the filesystem has simply been removed from the
server's name space (i.e., unmounted in a UNIX environment).
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 mandatory attribute "fh_expire_type" is used by the client to
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determine what type of filehandle the server is providing for a
particular filesystem. 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 filesystem. 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
migration. If FH4_VOL_ANY is set, FH4_VOL_MIGRATION is redundant.
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
deny all RENAME or REMOVE requests during the grace period upon
server restart.
Note that the bits FH4_VOL_MIGRATION and FH4_VOL_RENAME allow the
client to determine that expiration has occurred whenever a specific
event occurs, without an explicit filehandle expiration error from
the server. FH4_VOL_ANY does not provide this form of information.
In situations where the server will expire many, but not all
filehandles upon migration (e.g., all but those that are open),
FH4_VOLATILE_ANY (in this case with FH4_NOEXPIRE_WITH_OPEN) is a
better choice since the client may not assume that all filehandles
will expire when migration occurs, and it is likely that additional
expirations will occur (as a result of file CLOSE) that are separated
in time from the migration event itself.
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4.2.4. 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.
4.3. Client Recovery from Filehandle Expiration
If possible, the client SHOULD recover from the receipt of an
NFS4ERR_FHEXPIRED error. The client must take on additional
responsibility so that it may prepare itself to recover from the
expiration of a volatile filehandle. If the server returns
persistent filehandles, the client does not need these additional
steps.
For volatile filehandles, most commonly the client will need to store
the component names leading up to and including the filesystem 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 filesystem name space.
If the expired filehandle refers to an object that has been removed
from the filesystem, 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
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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 NFSv4.0 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
supported in the NFSv4.0 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 NFSv4 protocol as part of a new minor version by publishing a
standards-track RFC which allocates a new attribute number value and
defines the encoding for the attribute. See Section 11 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:
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+----------+-----------+---------------------------------+
| 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.
5.1. REQUIRED Attributes
These MUST be supported by every NFSv4.0 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
NFSv4.0 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
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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
returned by OPEN.
Named attributes and the named attribute directory may 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
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attributes, a client which is also able to handle them should be able
to copy a file's data and metadata with complete transparency from
one location to another; this would imply that names allowed for
regular directory entries are valid for named attribute names as
well.
In NFSv4.0, 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 If OPENATTR is done on a named attribute directory or on a named
attribute, the server MUST return NFS4ERR_WRONG_TYPE.
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.
o Creating hard links between named attribute directories or between
named attribute directories and ordinary directories is not
allowed.
Names of attributes will not be controlled by this document or other
IETF standards track documents. See Section 18 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.
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o The per server attribute is:
lease_time
o The per file system attributes are:
supported_attrs, 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,
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
For quota_avail_hard, quota_avail_soft, and quota_used see their
definitions below for the appropriate classification.
5.5. Set-Only and Get-Only Attributes
Some REQUIRED and RECOMMENDED attributes are set-only, i.e., they can
be set via SETATTR but not retrieved via GETATTR. Similarly, some
REQUIRED and RECOMMENDED attributes are get-only, i.e., they can be
retrieved GETATTR but not set via SETATTR. If a client attempts to
set a get-only attribute or get a set-only attributes, the server
MUST return NFS4ERR_INVAL.
5.6. REQUIRED Attributes - List and Definition References
The list of REQUIRED attributes appears in Table 2. The meaning of
the columns of the table are:
o Name: the name of attribute
o Id: the number assigned to the attribute. In the event of
conflicts between the assigned number and [2], the latter is
authoritative.
o Data Type: The XDR data type of the attribute.
o Acc: Access allowed to the attribute. R means read-only (GETATTR
may retrieve, SETATTR may not set). W means write-only (SETATTR
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may set, GETATTR may not retrieve). R W means read/write (GETATTR
may retrieve, SETATTR may set).
o Defined in: the section of this specification that describes the
attribute.
+-----------------+----+------------+-----+------------------+
| Name | Id | Data Type | Acc | Defined in: |
+-----------------+----+------------+-----+------------------+
| supported_attrs | 0 | bitmap4 | R | Section 5.8.1.1 |
| type | 1 | nfs_ftype4 | R | Section 5.8.1.2 |
| fh_expire_type | 2 | uint32_t | R | Section 5.8.1.3 |
| change | 3 | uint64_t | R | Section 5.8.1.4 |
| size | 4 | uint64_t | R W | Section 5.8.1.5 |
| link_support | 5 | bool | R | Section 5.8.1.6 |
| symlink_support | 6 | bool | R | Section 5.8.1.7 |
| named_attr | 7 | bool | R | Section 5.8.1.8 |
| fsid | 8 | fsid4 | R | Section 5.8.1.9 |
| unique_handles | 9 | bool | R | Section 5.8.1.10 |
| lease_time | 10 | nfs_lease4 | R | Section 5.8.1.11 |
| rdattr_error | 11 | enum | R | Section 5.8.1.12 |
| filehandle | 19 | nfs_fh4 | R | Section 5.8.1.13 |
+-----------------+----+------------+-----+------------------+
Table 2
5.7. RECOMMENDED Attributes - List and Definition References
The RECOMMENDED attributes are defined in Table 3. The meanings of
the column headers are the same as Table 2; see Section 5.6 for the
meanings.
+-------------------+----+--------------+-----+------------------+
| Name | Id | Data Type | Acc | Defined in: |
+-------------------+----+--------------+-----+------------------+
| acl | 12 | nfsace4<> | R W | Section 6.2.1 |
| aclsupport | 13 | uint32_t | R | Section 6.2.1.2 |
| archive | 14 | bool | R W | Section 5.8.2.1 |
| cansettime | 15 | bool | R | Section 5.8.2.2 |
| case_insensitive | 16 | bool | R | Section 5.8.2.3 |
| case_preserving | 17 | bool | R | Section 5.8.2.4 |
| chown_restricted | 18 | bool | R | Section 5.8.2.5 |
| fileid | 20 | uint64_t | R | Section 5.8.2.6 |
| files_avail | 21 | uint64_t | R | Section 5.8.2.7 |
| files_free | 22 | uint64_t | R | Section 5.8.2.8 |
| files_total | 23 | uint64_t | R | Section 5.8.2.9 |
| fs_locations | 24 | fs_locations | R | Section 5.8.2.10 |
| hidden | 25 | bool | R W | Section 5.8.2.11 |
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| homogeneous | 26 | bool | R | Section 5.8.2.12 |
| maxfilesize | 27 | uint64_t | R | Section 5.8.2.13 |
| maxlink | 28 | uint32_t | R | Section 5.8.2.14 |
| maxname | 29 | uint32_t | R | Section 5.8.2.15 |
| maxread | 30 | uint64_t | R | Section 5.8.2.16 |
| maxwrite | 31 | uint64_t | R | Section 5.8.2.17 |
| mimetype | 32 | utf8<> | R W | Section 5.8.2.18 |
| mode | 33 | mode4 | R W | Section 6.2.2 |
| mounted_on_fileid | 55 | uint64_t | R | Section 5.8.2.19 |
| no_trunc | 34 | bool | R | Section 5.8.2.20 |
| numlinks | 35 | uint32_t | R | Section 5.8.2.21 |
| owner | 36 | utf8<> | R W | Section 5.8.2.22 |
| owner_group | 37 | utf8<> | R W | Section 5.8.2.23 |
| quota_avail_hard | 38 | uint64_t | R | Section 5.8.2.24 |
| quota_avail_soft | 39 | uint64_t | R | Section 5.8.2.25 |
| quota_used | 40 | uint64_t | R | Section 5.8.2.26 |
| rawdev | 41 | specdata4 | R | Section 5.8.2.27 |
| space_avail | 42 | uint64_t | R | Section 5.8.2.28 |
| space_free | 43 | uint64_t | R | Section 5.8.2.29 |
| space_total | 44 | uint64_t | R | Section 5.8.2.30 |
| space_used | 45 | uint64_t | R | Section 5.8.2.31 |
| system | 46 | bool | R W | Section 5.8.2.32 |
| time_access | 47 | nfstime4 | R | Section 5.8.2.33 |
| time_access_set | 48 | settime4 | W | Section 5.8.2.34 |
| time_backup | 49 | nfstime4 | R W | Section 5.8.2.35 |
| time_create | 50 | nfstime4 | R W | Section 5.8.2.36 |
| time_delta | 51 | nfstime4 | R | Section 5.8.2.37 |
| time_metadata | 52 | nfstime4 | R | Section 5.8.2.38 |
| time_modify | 53 | nfstime4 | R | Section 5.8.2.39 |
| time_modify_set | 54 | settime4 | W | Section 5.8.2.40 |
+-------------------+----+--------------+-----+------------------+
Table 3
5.8. Attribute Definitions
5.8.1. Definitions of REQUIRED Attributes
5.8.1.1. 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.
5.8.1.2. Attribute 1: type
Designates the type of an object in terms of one of a number of
special constants:
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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.
5.8.1.3. Attribute 2: fh_expire_type
Server uses this to specify filehandle expiration behavior to the
client. See Section 4 for additional description.
5.8.1.4. 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.
5.8.1.5. Attribute 4: size
The size of the object in bytes.
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5.8.1.6. Attribute 5: link_support
True, if the object's file system supports hard links.
5.8.1.7. Attribute 6: symlink_support
True, if the object's file system supports symbolic links.
5.8.1.8. Attribute 7: named_attr
True, if this object has named attributes. In other words, object
has a non-empty named attribute directory.
5.8.1.9. 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.
5.8.1.10. Attribute 9: unique_handles
True, if two distinct filehandles guaranteed to refer to two
different file system objects.
5.8.1.11. Attribute 10: lease_time
Duration of leases at server in seconds.
5.8.1.12. Attribute 11: rdattr_error
Error returned from an attempt to retrieve attributes during a
READDIR operation.
5.8.1.13. Attribute 19: filehandle
The filehandle of this object (primarily for READDIR requests).
5.8.2. 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.
5.8.2.1. Attribute 14: archive
True, if this file has been archived since the time of last
modification (deprecated in favor of time_backup).
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5.8.2.2. Attribute 15: cansettime
True, if the server able to change the times for a file system object
as specified in a SETATTR operation.
5.8.2.3. Attribute 16: case_insensitive
True, if file name comparisons on this file system are case
insensitive.
5.8.2.4. Attribute 17: case_preserving
True, if file name case on this file system is preserved.
5.8.2.5. 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).
5.8.2.6. Attribute 20: fileid
A number uniquely identifying the file within the file system.
5.8.2.7. Attribute 21: files_avail
File slots available to this user on the file system containing this
object - this should be the smallest relevant limit.
5.8.2.8. Attribute 22: files_free
Free file slots on the file system containing this object - this
should be the smallest relevant limit.
5.8.2.9. Attribute 23: files_total
Total file slots on the file system containing this object.
5.8.2.10. 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.
5.8.2.11. Attribute 25: hidden
True, if the file is considered hidden with respect to the Windows
API.
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5.8.2.12. 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.
5.8.2.13. Attribute 27: maxfilesize
Maximum supported file size for the file system of this object.
5.8.2.14. Attribute 28: maxlink
Maximum number of links for this object.
5.8.2.15. Attribute 29: maxname
Maximum file name size supported for this object.
5.8.2.16. Attribute 30: maxread
Maximum read size supported for this object.
5.8.2.17. 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.
5.8.2.18. Attribute 32: mimetype
MIME body type/subtype of this object.
5.8.2.19. Attribute 55: mounted_on_fileid
Like fileid, but if the target filehandle is the root of a file
system, this attribute represents the fileid of the underlying
directory.
UNIX-based operating environments connect a file system into the
namespace by connecting (mounting) the file system onto the existing
file object (the mount point, usually a directory) of an existing
file system. When the mount point's parent directory is read via an
API like readdir(), the return results are directory entries, each
with a component name and a fileid. The fileid of the mount point's
directory entry will be different from the fileid that the stat()
system call returns. The stat() system call is returning the fileid
of the root of the mounted file system, whereas readdir() is
returning the fileid stat() would have returned before any file
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systems were mounted on the mount point.
Unlike NFSv3, NFSv4.0 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 NFSv4.0 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.
5.8.2.20. Attribute 34: no_trunc
If this attribute is TRUE, then if the client uses a file name longer
than name_max, an error will be returned instead of the name being
truncated.
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5.8.2.21. Attribute 35: numlinks
Number of hard links to this object.
5.8.2.22. Attribute 36: owner
The string name of the owner of this object.
5.8.2.23. Attribute 37: owner_group
The string name of the group ownership of this object.
5.8.2.24. Attribute 38: quota_avail_hard
The value in bytes which represents the amount of additional disk
space beyond the current allocation that can be allocated to this
file or directory before further allocations will be refused. It is
understood that this space may be consumed by allocations to other
files or directories.
5.8.2.25. 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.
5.8.2.26. 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
in a repeatable way. The rule may be configured per file system or
may be "choose the set with the smallest quota".
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5.8.2.27. Attribute 41: rawdev
Raw device identifier; the UNIX device major/minor node information.
If the value of type is not NF4BLK or NF4CHR, the value returned
SHOULD NOT be considered useful.
5.8.2.28. 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.
5.8.2.29. Attribute 43: space_free
Free disk space in bytes on the file system containing this object -
this should be the smallest relevant limit.
5.8.2.30. Attribute 44: space_total
Total disk space in bytes on the file system containing this object.
5.8.2.31. Attribute 45: space_used
Number of file system bytes allocated to this object.
5.8.2.32. Attribute 46: system
This attribute is TRUE if this file is a "system" file with respect
to the Windows operating environment.
5.8.2.33. 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
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
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time_access updates.
5.8.2.34. Attribute 48: time_access_set
Set the time of last access to the object. SETATTR use only.
5.8.2.35. Attribute 49: time_backup
The time of last backup of the object.
5.8.2.36. 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".
5.8.2.37. Attribute 51: time_delta
Smallest useful server time granularity.
5.8.2.38. Attribute 52: time_metadata
The time of last metadata modification of the object.
5.8.2.39. Attribute 53: time_modify
The time of last modification to the object.
5.8.2.40. Attribute 54: time_modify_set
Set the time of last modification to the object. SETATTR use only.
5.9. 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 [25]
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@
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.
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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 identifier 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 needs to try to return that
same string for which see below) when a corresponding GETATTR is
done. For some internationalization-related exceptions where this is
not possible, see below. Configuration changes (including changes
from the mapping of the string to the local representation) 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.
As mentioned above, it is desirable that a server when accepting a
string of the form user@domain or group@domain in an attribute,
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return this same string when that corresponding attribute is fetched.
Internationalization issues (for a general discussion of which see
Section 12) make this impossible and the client needs to take note of
the following situations:
o The string representing the domain may be converted to equivalent
U-label, if presented using a form other a a U-label. See
Section 12.6 for details.
o The user or group may be returned in a different form, due to
normalization issues, although it will always be a canonically
equivalent string. See See Section 12.7.3 for details.
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 user identifiers and
group identifiers, 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.
5.10. 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
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name" RFC1345 [26] which may or may not include 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, although
there are variations that occur additional characters with a name
including "SMALL" or "CAPITAL" are added in a subsequent version of
Unicode.
For general character handling and internationalization issues, see
Section 12. For details regarding case mapping, see the section
Case-based Mapping Used for Component4 Strings.
6. Access Control Attributes
Access Control Lists (ACLs) are file attributes that specify fine
grained access control. This chapter covers the "acl", "aclsupport",
"mode", file attributes, and their interactions. Note that file
attributes may apply to any file system object.
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.
* 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
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fail, regardless of a previously existing or inherited ACL.
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 NFSv4.0 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;
struct nfsace4 {
acetype4 type;
aceflag4 flag;
acemask4 access_mask;
utf8_must 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.
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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 NFSv4.0 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 NFSv4.0 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
NFSv4.0 access may be different from, but not weaker than, the
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 access to the file more
restrictive 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;
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All four but types 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. |
| 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
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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).
6.2.1.3. ACE Access Mask
The bitmask constants used for the access mask field are as follows:
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_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_FILE, and ACE4_ADD_SUBDIRECTORY are
intended to be used with directory objects, while ACE4_READ_DATA,
ACE4_WRITE_DATA, and ACE4_APPEND_DATA are intended to be used with
non-directory objects.
6.2.1.3.1. Discussion of Mask Attributes
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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.
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
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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.
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.
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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.
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
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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,
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:
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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
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.
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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
NVERIFY
VERIFY
Discussion:
Permission to read the ACL.
ACE4_WRITE_ACL
Operation(s) affected:
SETATTR of acl and mode
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().
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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.
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
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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;
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
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.
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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_SUCCESSFUL_ACCESS_ACE_FLAG
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.
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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.
+---------------+--------------------------------------------------+
| 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 4
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.
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6.2.2. Attribute 33: mode
The NFSv4.0 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.
6.3. 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.
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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.
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
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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.
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.
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6.4.1. Setting the mode and/or ACL Attributes
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 attribute must be modified in accordance with
the updated value of those bits. This must happen 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 are unaffected by changes to the
mode.
In cases in which the permissions bits are subject to change, the acl
attribute 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 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).
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6.4.1.2. Setting ACL and not mode
When setting the acl 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 (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 attribute 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
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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.
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. 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 attributes are implementation defined.
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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. 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.
7. Multi-Server Namespace
NFSv4 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 namespaces 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.
7.1. 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 RECOMMENDED attribute allows specification of the
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file system locations where the data corresponding to a given file
system may be found.
7.2. 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 attribute. There
may also be an actual current file system at that location,
accessible via normal namespace operations (e.g., LOOKUP). In this
case, the file system is said to be "present" at that position in the
namespace, and clients will typically use it, reserving use of
additional locations specified via the location-related attributes to
situations in which the principal location is no longer available.
When there is no actual file system at the namespace location in
question, the file system is said to be "absent". An absent file
system contains no files or directories other than the root. Any
reference to it, except to access a small set of attributes useful in
determining alternate locations, will result in an error,
NFS4ERR_MOVED. Note that if the server ever returns the error
NFS4ERR_MOVED, it MUST support the fs_locations attribute.
While the error name suggests that we have a case of a file system
that once was present, and has only become absent later, this is only
one possibility. A position in the namespace may be permanently
absent with the set of file system(s) designated by the location
attributes being the only realization. The name NFS4ERR_MOVED
reflects an earlier, more limited conception of its function, but
this error will be returned whenever the referenced file system is
absent, whether it has moved or not.
Except in the case of GETATTR-type operations (to be discussed
later), when the current filehandle at the start of an operation is
within an absent file system, that operation is not performed and the
error NFS4ERR_MOVED is returned, to indicate that the file system is
absent on the current server.
Because a GETFH cannot succeed if the current filehandle is within an
absent file system, filehandles within an absent file system cannot
be transferred to the client. When a client does have filehandles
within an absent file system, it is the result of obtaining them when
the file system was present, and having the file system become absent
subsequently.
It should be noted that because the check for the current filehandle
being within an absent file system happens at the start of every
operation, operations that change the current filehandle so that it
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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.
7.3. 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 that which gives
information about the correct current locations for this file system,
fs_locations.
7.3.1. 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 the fs_locations attribute bit, which indicates the client
is interested in a result regarding an absent file system. If it is
not 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 fs_locations attribute, the following
attributes SHOULD be available on absent file systems. In the case
of RECOMMENDED attributes, they should be available at least to the
same degree that they are available on present file systems.
fsid: This attribute should be provided so that the client can
determine file system boundaries, including, in particular, the
boundary between present and absent file systems. This value must
be different from any other fsid on the current server and need
have no particular relationship to fsids on any particular
destination to which the client might be directed.
mounted_on_fileid: For objects at the top of an absent file system,
this attribute needs to be available. Since the fileid is within
the present parent file system, there should be no need to
reference the absent file system to provide this information.
Other attributes SHOULD NOT be made available for absent file
systems, even when it is possible to provide them. The server should
not assume that more information is always better and should avoid
gratuitously providing additional information.
When a GETATTR operation includes a bit mask for the attribute
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fs_locations, but where the bit mask includes attributes that are not
supported, GETATTR will not return an error, but will return the mask
of the actual attributes supported with the results.
Handling of VERIFY/NVERIFY is similar to GETATTR in that if the
attribute mask does not include fs_locations 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.
7.3.2. 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 fs_locations, 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 fs_locations, 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 either of the
attributes fs_locations 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.
7.4. Uses of Location Information
The location-bearing attribute of fs_locations provides, together
with the possibility of absent file systems, a number of important
facilities in providing reliable, manageable, and scalable data
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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
although 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. A
designation of such a location, in place of an absent file system, is
called a "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.
7.4.1. File System Replication
The fs_locations attribute provides 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, the client should obtain
the value of the set of alternate locations by interrogating the
fs_locations attribute.
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 its data. Multiple
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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
attribute 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.
7.4.2. 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 attribute.
Typically, a client will be accessing the file system in question,
get an NFS4ERR_MOVED error, and then use the fs_locations attribute
to determine the new location of the data.
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
used with the choice left to the server implementor. The NFSv4
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 as well as how and whether
data was in fact migrated. These issues will be discussed in detail
below.
When an alternate location is designated as the target for migration,
it must designate the same data. 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
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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.
7.4.3. 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
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 the 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 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.
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. The top-level referral file system or any segment may use
replicated referral file systems for higher availability.
Generally, multi-server namespaces are for the most part uniform, in
that the same data made available to one client at a given location
in the namespace is made available to all clients at that location.
7.5. 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 that may represent multiple IP
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addresses, while multiple location entries may have their own server
address targets that reference the same server.
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. Such
corresponding file system locations can be used as alternate
locations, just as those explicitly specified via the fs_locations
attribute.
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 cases, 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 using 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.
7.6. Additional Client-Side Considerations
When clients make use of servers that implement referrals,
replication, and migration, care should be taken that a user who
mounts a given file system that includes a referral or a relocated
file system continues to see a coherent picture of that user-side
file system despite the fact that it contains a number of server-side
file systems that may be on different servers.
One important issue is upward navigation from the root of a server-
side file system to its parent (specified as ".." in UNIX), in the
case in which it transitions to that file system as a result of
referral, migration, or a transition as a result of replication.
When the client is at such a point, and it needs to ascend to the
parent, it must go back to the parent as seen within the multi-server
namespace rather than sending a LOOKUPP operation to the server,
which would result in the parent within that server's single-server
namespace. In order to do this, the client needs to remember the
filehandles that represent such file system roots and use these
instead of issuing a LOOKUPP operation 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
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are used extensively, they may change as server configurations
change. It is expected that clients will cache information related
to traversing referrals so that future client-side requests are
resolved locally without server communication. This is usually
rooted in client-side name look up caching. Clients should
periodically purge this data for referral points in order to detect
changes in location information.
7.7. Effecting File System Transitions
Transitions between file system instances, whether due to switching
between replicas upon server unavailability or 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
a greater burden on the client to adapt to the transition.
The NFSv4 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 NFSv4.0 protocol does not provide the servers a means
of communicating the transition methods. In the NFSv4.1 protocol
[27], an additional attribute "fs_locations_info" is presented, which
will 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. Again, as the NFSv4.0
protocol does not have an explict means of communicating these issues
to the client, the intent is to document the problems that can be
faced in a multi-server name space and allow the client to use the
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inferred transitions available via fs_locations and other attributes
(see Section 7.9.1).
In the discussion below, references will be made to a file system
having a particular property or to 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 aspects 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 that may cause performance or
other issues in effecting a transition.
While fs_locations is available, default assumptions with regard to
such classifications have to be inferred (see Section 7.9.1 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.
7.7.1. File System Transitions and Simultaneous Access
When a single file system may be accessed at multiple locations,
either because of an indication of file system identity as reported
by the fs_locations attribute, the client will, depending on specific
circumstances as discussed below, either:
o Access multiple instances simultaneously, each of which represents
an alternate path to the same data and metadata.
o Acesses one instance (or set of instances) and then transition to
an alternative instance (or set of instances) as a result of
network issues, server unresponsiveness, or server-directed
migration.
7.7.2. Filehandles and File System Transitions
There are a number of ways in which filehandles can be handled across
a file system transition. These can be divided into two broad
classes depending upon whether the two file systems across which the
transition happens share sufficient state to effect some sort of
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continuity of file system handling.
When there is no such cooperation in filehandle assignment, the two
file systems are reported as being in different handle classes. In
this case, all filehandles are assumed to expire as part of the file
system transition. Note that this behavior does not depend on
fh_expire_type attribute and depends on the specification of the
FH4_VOL_MIGRATION bit.
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 that are only
volatile due to the FH4_VOL_MIGRATION bit) are subject to expiration
on the target server.
7.7.3. Fileids and File System Transitions
The issue of continuity of fileids in the event of a file system
transition needs to be addressed. The general expectation is 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 APIs that depend on fileids.
It is important to note that while clients themselves may have no
trouble with a fileid changing as a result of a file system
transition event, applications do typically have access to the fileid
(e.g., via stat). The result is that an application may work
perfectly well if there is no file system instance transition or if
any such transition is among instances created by a single vendor,
yet be unable to deal with the situation in which a multi-vendor
transition occurs at the wrong time.
Providing the same fileids in a multi-vendor (multiple server
vendors) environment has generally been held to be quite difficult.
While there is work to be done, it needs to be pointed out that this
difficulty is partly self-imposed. Servers have typically identified
fileid with inode number, i.e., with a quantity used to find the file
in question. This identification poses special difficulties for
migration of a file system between vendors where assigning the same
index to a given file may not be possible. Note here that a fileid
is not required to be useful to find the file in question, only that
it is unique within the given file system. Servers prepared to
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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.
7.7.4. 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.
Clients should not make the fsids received from the server visible to
applications since they may not be globally unique, and because they
may change during a file system transition event. Applications are
best served if they are isolated from such transitions to the extent
possible.
7.7.5. The Change Attribute and File System Transitions
Since the change attribute is defined as a server-specific one,
change attributes fetched from one server are normally presumed to be
invalid on another server. Such a presumption is troublesome since
it would invalidate all cached change attributes, requiring
refetching. Even more disruptive, the absence of any assured
continuity for the change attribute means that even if the same value
is retrieved on refetch, no conclusions can be drawn as to whether
the object in question has changed. The identical change attribute
could be merely an artifact of a modified file with a different
change attribute construction algorithm, with that new algorithm just
happening to result in an identical change value.
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When the two file systems have consistent change attribute formats,
and we say that they are 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.
7.7.6. 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.
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.
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.
File systems cooperating in state management may actually share state
or simply divide the identifier space so as to recognize (and reject
as stale) each other's stateids and client IDs. Servers that do
share state may not do so under all conditions or at all times. If
the server cannot be sure when accepting a client ID that it reflects
the locks the client was given, the server must treat all associated
state as stale and report it as such to the client.
The client must establish a new client ID on the destination, if it
does not have one already, and reclaim locks if allowed by the
server. 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.
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,
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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 restart (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 should avoid establishing a grace period. (See
Section 9.14 for further details.)
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
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
its LOCK or OPEN request denied due to a conflicting lock.
The consequences of having no facilities available to reclaim locks
on the new 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 its 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.
7.7.6.1. Transitions and the Lease_time Attribute
In order that the client may appropriately manage its lease in the
case of a file system transition, the destination server must
establish proper values for the lease_time attribute.
When state is transferred transparently, that state should include
the correct value of the lease_time attribute. The lease_time
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attribute on the destination server must never be less than that on
the source, since this would result in premature expiration of a
lease granted by the source server. Upon transitions in which state
is transferred transparently, the client is under no obligation to
refetch the lease_time attribute and may continue to use the value
previously fetched (on the source server).
If state has not been transferred transparently because the client ID
is rejected when presented to the new server, the client should fetch
the value of lease_time on the new (i.e., destination) server, and
use it for subsequent locking requests. However, the server must
respect a grace period of at least as long as the lease_time on the
source server, in order to ensure that clients have ample time to
reclaim their lock before potentially conflicting non-reclaimed locks
are granted.
7.7.7. 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.
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.
7.7.8. 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.
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7.7.9. File System Data and File System Transitions
When multiple replicas exist and are used simultaneously or in
succession by a client, applications using them will normally expect
that they contain either the same data or data that is consistent
with the normal sorts of changes that are made by other clients
updating the data of the file system (with metadata being the same to
the degree inferred by the fs_locations 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 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 four 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, the client may depend on the fact that changes to data,
metadata, or locks made on one file system are immediately
reflected on others.
o When multiple replicas exist and are used simultaneously by a
client, 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 share
reservations or byte-range locks), and delegations obtained on 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 written to stable storage on the original instance are
written to stable storage of the successor (uncommitted writes are
dealt with in Section 7.7.7).
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
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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. Since these file systems are presumed to be unsuitable for
simultaneous use, there is no specification of how locking is
handled; in general, locks obtained on one file system will be
separate from those on others. Since these are going to be read-
only file systems, this is not expected to pose an issue for
clients or applications.
7.8. 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 attribute. 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 file system in question
(so there is nothing to transition). Referrals can only come into
effect when an absent file system is encountered at its root.
The examples given in the sections below are somewhat artificial in
that an actual client will not typically do a multi-component look
up, but will have cached information regarding the upper levels of
the name hierarchy. However, these 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.
7.8.1. 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"
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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.
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 specification
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 it would not be sure where the absent file
system starts. It could be the case, for example, that /this/is/the
is the root of the moved file system and that the reason that the
look up of "path" succeeded is that the file system was not absent on
that operation but was moved between the last LOOKUP and the GETFH
(since COMPOUND is not atomic). Even if we had the fsids for all of
the intermediate directories, we could have no way of knowing that
/this/is/the/path was the root of a new file system, since we don't
yet have its fsid.
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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 at the same time but in most
cases the client will have a good guess as to where file system
boundaries are (because of where NFS4ERR_MOVED was, and was not,
received) making fetching of fs_locations 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
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
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- Current fh is for /this/is/the and is within pseudo-fs.
OP10: GETATTR(fsid) --> NFS_OK
- Get current fsid to see where file system boundaries are. The
fsid will be that for the pseudo-fs in this example, so no
boundary.
OP11: GETFH --> NFS_OK
- Current fh is for /this/is/the and is within pseudo-fs.
OP12: LOOKUP "path" --> NFS_OK
- Current fh is for /this/is/the/path and is within a new, absent
file system, but ...
- The client will never see the value of that fh.
OP13: GETATTR(fsid, fs_locations) --> NFS_OK
- We are getting the fsid to know where the file system boundaries
are. In this operation, the fsid will be different than that of
the parent directory (which in turn was retrieved in OP10). Note
that the fsid we are given will not necessarily be preserved at
the new location. That fsid might be different, and in fact the
fsid we have for this file system might be a valid fsid of a
different file system on that new server.
- In this particular case, we are pretty sure anyway that what has
moved is /this/is/the/path rather than /this/is/the since we have
the fsid of the latter and it is that of the pseudo-fs, which
presumably cannot move. However, in other examples, we might not
have this kind of information to rely on (e.g., /this/is/the might
be a non-pseudo file system separate from /this/is/the/path), so
we need to have other reliable source information on the boundary
of the file system that is moved. If, for example, the file
system /this/is had moved, we would have a case of migration
rather than referral, and once the boundaries of the migrated file
system was clear we could fetch fs_locations.
- We are fetching fs_locations because the fact that we got an
NFS4ERR_MOVED at this point means that it is most likely that this
is a referral and we need the destination. Even if it is the case
that /this/is/the is a file system that has migrated, we will
still need the location information for that file system.
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OP14: GETFH --> NFS4ERR_MOVED
- Fails because current fh is in an absent file system at the start
of the operation, and the specification makes no exception for
GETFH. Note that this means the server will never send the client
a filehandle from within an absent file system.
Given the above, the client knows where the root of the absent file
system is (/this/is/the/path) by noting where the change of fsid
occurred (between "the" and "path"). The fs_locations attribute also
gives the client the actual location of the absent file system, so
that the referral can proceed. The server gives the client the bare
minimum of information about the absent file system so that there
will be very little scope for problems of conflict between
information sent by the referring server and information of the file
system's home. No filehandles and very few attributes are present on
the referring server, and the client can treat those it receives as
transient information with the function of enabling the referral.
7.8.2. Referral Example (READDIR)
Another context in which a client may encounter referrals is when it
does a READDIR on a directory in which some of the sub-directories
are the roots of absent file systems.
Suppose such a directory is read as follows:
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 is
not requested, and some of the attributes cannot be provided, the
result will be an NFS4ERR_MOVED error on the READDIR, with the
detailed results as follows:
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.
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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, but it is returned because the
directory contains the root of an absent file system.
So now suppose that we re-send with rdattr_error:
o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
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 directory entry with the component
named "path" will only contain rdattr_error with the value
NFS4ERR_MOVED, together with an fsid value and a value for
mounted_on_fileid.
So suppose we do another READDIR to get fs_locations (although we
could have used a GETATTR directly, as in Section 7.8.1).
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o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
o LOOKUP "the"
o READDIR (rdattr_error, fs_locations, 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.
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, mounted_on_fileid, fsid,
size, time_modify) --> NFS_OK. The attributes will be as shown
below.
The attributes for the directory entry with the component named
"path" will only contain:
o rdattr_error (value: NFS_OK)
o fs_locations
o mounted_on_fileid (value: unique fileid within referring file
system)
o fsid (value: unique value within referring server)
The attributes for entry "path" will not contain size or time_modify
because these attributes are not available within an absent file
system.
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7.9. The Attribute fs_locations
The fs_locations attribute is structured in the following way:
struct fs_location4 {
utf8must server<>;
pathname4 rootpath;
};
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
The fs_location4 data type is used to represent the location of a
file system by providing a server name and the path to the root of
the file system within that server's namespace. When a set of
servers have corresponding file systems at the same path within their
namespaces, an array of server names may be provided. An entry in
the server array is a UTF-8 string and represents one of a
traditional DNS host name, IPv4 address, IPv6 address, or an zero-
length string. A zero-length string SHOULD be used to indicate the
current address being used for the RPC call. It is not a requirement
that all servers that share the same rootpath be listed in one
fs_location4 instance. The array of server names is provided for
convenience. Servers that share the same rootpath may also be listed
in separate fs_location4 entries in the fs_locations attribute.
The fs_locations4 data type and fs_locations 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. The fs_root
is simply the pathname the client used to reach the object on the
current server (i.e., the object to which the fs_locations attribute
applies).
When the fs_locations attribute is interrogated and there are no
alternate file system locations, the server SHOULD return a zero-
length array of fs_location4 structures, together with a valid
fs_root.
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As an example, suppose there is a replicated file system located at
two servers (servA and servB). At servA, the file system is located
at path /a/b/c. At, servB the file system is located at path /x/y/z.
If the client were to obtain the fs_locations value for the directory
at /a/b/c/d, it might not necessarily know that the file system's
root is located in servA's namespace at /a/b/c. When the client
switches to servB, it will need to determine that the directory it
first referenced at servA is now represented by the path /x/y/z/d on
servB. To facilitate this, the fs_locations attribute provided by
servA would have an fs_root value of /a/b/c and two entries in
fs_locations. One entry in fs_locations will be for itself (servA)
and the other will be for servB with a path of /x/y/z. With this
information, the client is able to substitute /x/y/z for the /a/b/c
at the beginning of its access path and construct /x/y/z/d to use for
the new server.
Note that: there is no requirement that the number of components in
each rootpath be the same; there is no relation between the number of
components in rootpath or fs_root, and none of the components in each
rootpath and fs_root have to be the same. In the above example, we
could have had a third element in the locations array, with server
equal to "servC", and rootpath equal to "/I/II", and a fourth element
in locations with server equal to "servD" and rootpath equal to
"/aleph/beth/gimel/daleth/he".
The relationship between fs_root to a rootpath is that the client
replaces the pathname indicated in fs_root for the current server for
the substitute indicated in rootpath for the new server.
For an example of a referred or migrated file system, suppose there
is a file system located at serv1. At serv1, the file system is
located at /az/buky/vedi/glagoli. The client finds that object at
glagoli has migrated (or is a referral). The client gets the
fs_locations attribute, which contains an fs_root of /az/buky/vedi/
glagoli, and one element in the locations array, with server equal to
serv2, and rootpath equal to /izhitsa/fita. The client replaces /az/
buky/vedi/glagoli with /izhitsa/fita, and uses the latter pathname on
serv2.
Thus, the server MUST return an fs_root that is equal to the path the
client used to reach the object to which the fs_locations attribute
applies. Otherwise, the client cannot determine the new path to use
on the new server.
7.9.1. Inferring Transition Modes
When fs_locations is used, information about the specific locations
should be assumed based on the following rules.
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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.
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.
o All file system instances servers should be considered as of
different readdir 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 a new file system after receiving an NFS4ERR_MOVED
error, the target should be treated as being of the same write-
verifier class as the source.
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.
See Section 17 for a discussion on the recommendations for the
security flavor to be used by any GETATTR operation that requests the
"fs_locations" attribute.
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8. NFS Server Name Space
8.1. Server Exports
On a UNIX server the name space describes all the files reachable by
pathnames under the root directory or "/". On a Windows NT server
the name space constitutes all the files on disks named by mapped
disk letters. NFS server administrators rarely make the entire
server's filesystem name space available to NFS clients. More often
portions of the name space are made available via an "export"
feature. In previous versions of the NFS protocol, the root
filehandle for each export is obtained through the MOUNT protocol;
the client sends a string that identifies the export of name space
and the server returns the root filehandle for it. The MOUNT
protocol supports an EXPORTS procedure that will enumerate the
server's exports.
8.2. Browsing Exports
The NFS version 4 protocol provides a root filehandle that clients
can use to obtain filehandles for these exports via a multi-component
LOOKUP. 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 NFS version 2 and
3 protocols. The client expects all LOOKUP operations to remain
within a single server filesystem. For example, the device attribute
will not change. This prevents a client from taking name space paths
that span exports.
An automounter on the client can obtain a snapshot of the server's
name space 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 name space on the client. The parts of the name space
that are not exported by the server are filled in with a "pseudo
filesystem" that allows the user to browse from one mounted
filesystem to another. There is a drawback to this representation of
the server's name space on the client: it is static. If the server
administrator adds a new export the client will be unaware of it.
8.3. Server Pseudo Filesystem
NFS version 4 servers avoid this name space inconsistency by
presenting all the exports within the framework of a single server
name space. An NFS version 4 client uses LOOKUP and READDIR
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operations to browse seamlessly from one export to another. Portions
of the server name space that are not exported are bridged via a
"pseudo filesystem" that provides a view of exported directories
only. A pseudo filesystem has a unique fsid and behaves like a
normal, read only filesystem.
Based on the construction of the server's name space, it is possible
that multiple pseudo filesystems may exist. For example,
/a pseudo filesystem
/a/b real filesystem
/a/b/c pseudo filesystem
/a/b/c/d real filesystem
Each of the pseudo filesystems are considered separate entities and
therefore will have a unique fsid.
8.4. Multiple Roots
The DOS and Windows operating environments are sometimes described as
having "multiple roots". Filesystems are commonly represented as
disk letters. MacOS represents filesystems as top level names. NFS
version 4 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.
8.5. Filehandle Volatility
The nature of the server's pseudo filesystem is that it is a logical
representation of filesystem(s) available from the server.
Therefore, the pseudo filesystem is most likely constructed
dynamically when the server is first instantiated. It is expected
that the pseudo filesystem 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 filesystem, 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 multi-component
LOOKUP) when receiving an error of NFS4ERR_FHEXPIRED.
8.6. Exported Root
If the server's root filesystem is exported, one might conclude that
a pseudo-filesystem is not needed. This would be wrong. Assume the
following filesystems on a server:
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/ disk1 (exported)
/a disk2 (not exported)
/a/b disk3 (exported)
Because disk2 is not exported, disk3 cannot be reached with simple
LOOKUPs. The server must bridge the gap with a pseudo-filesystem.
8.7. Mount Point Crossing
The server filesystem environment may be constructed in such a way
that one filesystem contains a directory which is 'covered' or
mounted upon by a second filesystem. For example:
/a/b (filesystem 1)
/a/b/c/d (filesystem 2)
The pseudo filesystem for this server may be constructed to look
like:
/ (place holder/not exported)
/a/b (filesystem 1)
/a/b/c/d (filesystem 2)
It is the server's responsibility to present the pseudo filesystem
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 filesystem "/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 filesystem "/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.
8.8. Security Policy and Name Space Presentation
The application of the server's security policy needs to be carefully
considered by the implementor. One may choose to limit the
viewability of portions of the pseudo filesystem based on the
server's perception of the client's ability to authenticate itself
properly. However, with the support of multiple security mechanisms
and the ability to negotiate the appropriate use of these mechanisms,
the server is unable to properly determine if a client will be able
to authenticate itself. If, based on its policies, the server
chooses to limit the contents of the pseudo filesystem, the server
may effectively hide filesystems from a client that may otherwise
have legitimate access.
As suggested practice, the server should apply the security policy of
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a shared resource in the server's namespace to the components of the
resource's ancestors. For example:
/
/a/b
/a/b/c
The /a/b/c directory is a real filesystem and is the shared resource.
The security policy for /a/b/c is Kerberos with integrity. The
server should apply the same security policy to /, /a, and /a/b.
This allows for the extension of the protection of the server's
namespace to the ancestors of the real shared resource.
For the case of the use of multiple, disjoint security mechanisms in
the server's resources, the security for a particular object in the
server's namespace should be the union of all security mechanisms of
all direct descendants.
9. File Locking and Share Reservations
Integrating locking into the NFS protocol necessarily causes it to be
stateful. With the inclusion of share reservations the protocol
becomes substantially more dependent on state than the traditional
combination of NFS and NLM [28]. There are 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
communicates its view of this state to the server as needed. The
client is also able to detect inconsistent state before modifying a
file.
To support Win32 share reservations it is necessary to 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 NFS version 4 protocol has
an OPEN operation that subsumes the NFS version 3 methodology of
LOOKUP, CREATE, and ACCESS. However, because many operations require
a filehandle, the traditional LOOKUP is preserved to map a file name
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to filehandle without establishing state on the server. The policy
of granting access or modifying files is managed by the server based
on the client's state. These mechanisms can implement policy ranging
from advisory only locking to full mandatory locking.
9.1. Locking
It is assumed that manipulating a 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 lock request contains the heavyweight
information required to establish a lock and uniquely define the lock
owner.
The following sections describe the transition from the heavy weight
information to the eventual stateid used for most client and server
locking and lease interactions.
9.1.1. Client ID
For each LOCK request, the client must identify itself to the server.
This is done in such a way as to allow for correct lock
identification and crash recovery. A sequence of a SETCLIENTID
operation followed by a SETCLIENTID_CONFIRM operation is required to
establish the identification onto the server. Establishment of
identification by a new incarnation of the client also has the effect
of immediately breaking any leased state that a previous incarnation
of the client might have had on the server, as opposed to forcing the
new client incarnation to wait for the leases to expire. Breaking
the lease state amounts to the server removing all lock, share
reservation, and, where the server is not supporting the
CLAIM_DELEGATE_PREV claim type, all delegation state associated with
same client with the same identity. For discussion of delegation
state recovery, see Section 10.2.1.
Client identification is encapsulated in the following structure:
struct nfs_client_id4 {
verifier4 verifier;
opaque id<NFS4_OPAQUE_LIMIT>;
};
The first field, verifier is a client incarnation verifier that is
used to detect client reboots. Only if the verifier is different
from that which the server has previously recorded the client (as
identified by the second field of the structure, id) does the server
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start the process of canceling the client's leased state.
The second field, id is a variable length string that uniquely
defines the client.
There are several considerations for how the client generates the id
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 the subsequent incarnations
(e.g., reboots) of the same client cause the client to present the
same string. The implementor is cautioned against 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 NFS
version 4 server.
o The string should be different for each server network address
that the client accesses, rather than common to all server network
addresses. The reason is that it may not be possible for the
client to tell if the same server is listening on multiple network
addresses. If the client issues SETCLIENTID with the same id
string to each network address of such a server, the server will
think it is the same client, and each successive SETCLIENTID will
cause the server to begin the process of removing the client's
previous leased state.
o The algorithm for generating the string should not assume that the
client's network address won't change. This includes changes
between client incarnations and even changes while the client is
stilling running in its current incarnation. This means that if
the client includes just the client's and server's network address
in the id string, there is a real risk, after the client gives up
the network address, that another client, using a similar
algorithm for generating the id string, will generate a
conflicting id string.
Given the above considerations, an example of a well generated id
string is one that includes:
o The server's network address.
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o The client's network address.
o For a user level NFS version 4 client, it should contain
additional information to distinguish the client from other user
level clients running on the same host, such as a process id or
other unique sequence.
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.
* The timestamp of when the NFS version 4 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 NFS version 4).
* 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.
As a security measure, the server MUST NOT cancel a client's leased
state if the principal established the state for a given id string is
not the same as the principal issuing the SETCLIENTID.
Note that SETCLIENTID and SETCLIENTID_CONFIRM has a secondary purpose
of establishing the information the server needs to make callbacks to
the client for purpose of supporting delegations. It is permitted to
change this information via SETCLIENTID and SETCLIENTID_CONFIRM
within the same incarnation of the client without removing the
client's leased state.
Once a SETCLIENTID and SETCLIENTID_CONFIRM sequence has successfully
completed, the client uses the shorthand client identifier, of type
clientid4, instead of the longer and less compact nfs_client_id4
structure. This shorthand client identifier (a clientid) is assigned
by the server and should be chosen so that it will not conflict with
a clientid previously assigned by the server. This applies across
server restarts or reboots. When a clientid is presented to a server
and that clientid is not recognized, as would happen after a server
reboot, the server will reject the request with the error
NFS4ERR_STALE_CLIENTID. When this happens, the client must obtain a
new clientid by use of the SETCLIENTID operation and then proceed to
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any other necessary recovery for the server reboot case (See
Section 9.6.2).
The client must also employ the SETCLIENTID operation when it
receives a NFS4ERR_STALE_STATEID error using a stateid derived from
its current clientid, since this also indicates a server reboot which
has invalidated the existing clientid (see Section 9.1.3 for
details).
See the detailed descriptions of SETCLIENTID and SETCLIENTID_CONFIRM
for a complete specification of the operations.
9.1.2. Server Release of Clientid
If the server determines that the client holds no associated state
for its clientid, the server may choose to release the clientid. 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
SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new identity.
It should be clear that the server must be very hesitant to release a
clientid 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 clientid unless
there had been no activity from that client for many minutes.
Note that if the id string in a SETCLIENTID request is properly
constructed, and if the client takes care to use the same principal
for each successive use of SETCLIENTID, then, barring an active
denial of service attack, NFS4ERR_CLID_INUSE should never be
returned.
However, client bugs, server bugs, or perhaps a deliberate change of
the principal owner of the id string (such as the case of a client
that changes security flavors, and under the new flavor, there is no
mapping to the previous owner) will in rare cases result in
NFS4ERR_CLID_INUSE.
In that event, when the server gets a SETCLIENTID for a client id
that currently has no state, or it has state, but the lease has
expired, rather than returning NFS4ERR_CLID_INUSE, the server MUST
allow the SETCLIENTID, and confirm the new clientid if followed by
the appropriate SETCLIENTID_CONFIRM.
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9.1.3. lock_owner and stateid Definition
When requesting a lock, the client must present to the server the
clientid and an identifier for the owner of the requested lock.
These two fields are referred to as the lock_owner and the definition
of those fields are:
o A clientid returned by the server as part of the client's use of
the SETCLIENTID operation.
o A variable length opaque array used to uniquely define the owner
of a lock managed by the client.
This may be a thread id, process id, or other unique value.
When the server grants the lock, it responds with a unique stateid.
The stateid is used as a shorthand reference to the lock_owner, since
the server will be maintaining the correspondence between them.
The server is free to form the stateid in any manner that it chooses
as long as it is able to recognize invalid and out-of-date stateids.
This requirement includes those stateids generated by earlier
instances of the server. From this, the client can be properly
notified of a server restart. This notification will occur when the
client presents a stateid to the server from a previous
instantiation.
The server must be able to distinguish the following situations and
return the error as specified:
o The stateid was generated by an earlier server instance (i.e.,
before a server reboot). The error NFS4ERR_STALE_STATEID should
be returned.
o The stateid was generated by the current server instance but the
stateid no longer designates the current locking state for the
lockowner-file pair in question (i.e., one or more locking
operations has occurred). The error NFS4ERR_OLD_STATEID should be
returned.
This error condition will only occur when the client issues a
locking request which changes a stateid while an I/O request that
uses that stateid is outstanding.
o The stateid was generated by the current server instance but the
stateid does not designate a locking state for any active
lockowner-file pair. The error NFS4ERR_BAD_STATEID should be
returned.
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This error condition will occur when there has been a logic error
on the part of the client or server. This should not happen.
One mechanism that may be used to satisfy these requirements is for
the server to,
o divide the "other" field of each stateid into two fields:
* A server verifier which uniquely designates a particular server
instantiation.
* An index into a table of locking-state structures.
o utilize the "seqid" field of each stateid, such that seqid is
monotonically incremented for each stateid that is associated with
the same index into the locking-state table.
By matching the incoming stateid and its field values with the state
held at the server, the server is able to easily determine if a
stateid is valid for its current instantiation and state. If the
stateid is not valid, the appropriate error can be supplied to the
client.
9.1.4. 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.
If the lock_owner performs a READ or WRITE in a situation in which it
has established a 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 lockowner. If
no state is established by the client, either record lock or share
reservation, a stateid of all bits 0 is used. Regardless whether a
stateid of all bits 0, 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
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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
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 issue 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).
With NFS version 3, there was no notion of a stateid so there was no
way to tell if the application process of the client sending the READ
or WRITE operation had also acquired the appropriate record lock on
the file. Thus there was no way to implement mandatory locking.
With the stateid construct, this barrier has been removed.
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
lockowner 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
the behalf of the lockowner, 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 NFS version 4 LOCK operation does not need to distinguish
between advisory and mandatory record locks. It is the NFS version 4
server's processing of the READ and WRITE operations that introduces
the distinction.
Every stateid other than the special stateid values noted in this
section, whether returned by an OPEN-type operation (i.e., OPEN,
OPEN_DOWNGRADE), or by a LOCK-type operation (i.e., LOCK or LOCKU),
defines an access mode for the file (i.e., READ, WRITE, or READ-
WRITE) as established by the original OPEN which began the stateid
sequence, and as modified by subsequent OPENs and OPEN_DOWNGRADEs
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within that stateid sequence. 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 OPEN with which the operation is associated.
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.
A stateid of all bits 1 (one) MAY allow READ operations to bypass
locking checks at the server. However, WRITE operations with a
stateid with bits all 1 (one) MUST NOT bypass locking checks and are
treated exactly the same as if a stateid of all bits 0 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 range of the lock
request 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. A SETATTR that sets size is treated similarly to a
WRITE as discussed above.
9.1.5. Sequencing of Lock Requests
Locking is different than most NFS operations as it requires "at-
most-one" semantics that are not provided by ONCRPC. ONCRPC over a
reliable transport is not sufficient because a sequence of locking
requests may span multiple TCP connections. In the face of
retransmission or reordering, lock or unlock requests must have a
well defined and consistent behavior. To accomplish this, each lock
request contains a sequence number that is a consecutively increasing
integer. Different lock_owners have different sequences. The server
maintains the last sequence number (L) received and the response that
was returned. The first request issued for any given lock_owner is
issued with a sequence number of zero.
Note that for requests that contain a sequence number, for each
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lock_owner, there should be no more than one outstanding request.
If a request (r) with a previous sequence number (r < L) is received,
it is rejected with the return of error NFS4ERR_BAD_SEQID. Given a
properly-functioning client, the response to (r) must have been
received before the last request (L) was sent. If a duplicate of
last request (r == L) is received, the stored response is returned.
If a request beyond the next sequence (r == L + 2) is received, it is
rejected with the return of error NFS4ERR_BAD_SEQID. Sequence
history is reinitialized whenever the SETCLIENTID/SETCLIENTID_CONFIRM
sequence changes the client verifier.
Since the sequence number is represented with an unsigned 32-bit
integer, the arithmetic involved with the sequence number is mod
2^32. For an example of modulo arithmetic involving sequence numbers
see [29].
It is critical the server maintain the last response sent to the
client to provide a more reliable cache of duplicate non-idempotent
requests than that of the traditional cache described in [30]. The
traditional duplicate request cache uses a least recently used
algorithm for removing unneeded requests. However, the last lock
request and response on a given lock_owner must be cached as long as
the lock state exists on the server.
The client MUST monotonically increment the sequence number for the
CLOSE, LOCK, LOCKU, OPEN, OPEN_CONFIRM, and OPEN_DOWNGRADE
operations. This is true even in the event that the previous
operation that used the sequence number received an error. The only
exception to this rule is if the previous operation received one of
the following errors: NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE, NFS4ERR_LEASE_MOVED, or
NFS4ERR_MOVED.
9.1.6. Recovery from Replayed Requests
As described above, the sequence number is per lock_owner. As long
as the server maintains the last sequence number received and follows
the methods described above, there are no risks of a Byzantine router
re-sending old requests. The server need only maintain the
(lock_owner, sequence number) state as long as there are open files
or closed files with locks outstanding.
LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and CLOSE each contain a sequence
number and therefore the risk of the replay of these operations
resulting in undesired effects is non-existent while the server
maintains the lock_owner state.
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9.1.7. Releasing lock_owner State
When a particular lock_owner no longer holds open or file locking
state at the server, the server may choose to release the sequence
number state associated with the lock_owner. The server may make
this choice based on lease expiration, for the reclamation of server
memory, or other implementation specific details. In any event, the
server is able to do this safely only when the lock_owner no longer
is being utilized by the client. The server may choose to hold the
lock_owner state in the event that retransmitted requests are
received. However, the period to hold this state is implementation
specific.
In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
retransmitted after the server has previously released the lock_owner
state, the server will find that the lock_owner has no files open and
an error will be returned to the client. If the lock_owner does have
a file open, the stateid will not match and again an error is
returned to the client.
9.1.8. Use of Open Confirmation
In the case that an OPEN is retransmitted and the lock_owner is being
used for the first time or the lock_owner state has been previously
released by the server, the use of the OPEN_CONFIRM operation will
prevent incorrect behavior. When the server observes the use of the
lock_owner for the first time, it will direct the client to perform
the OPEN_CONFIRM for the corresponding OPEN. This sequence
establishes the use of a lock_owner and associated sequence number.
Since the OPEN_CONFIRM sequence connects a new open_owner on the
server with an existing open_owner on a client, the sequence number
may have any value. The OPEN_CONFIRM step assures the server that
the value received is the correct one. (see Section 15.20 for further
details.)
There are a number of situations in which the requirement to confirm
an OPEN would pose difficulties for the client and server, in that
they would be prevented from acting in a timely fashion on
information received, because that information would be provisional,
subject to deletion upon non-confirmation. Fortunately, these are
situations in which the server can avoid the need for confirmation
when responding to open requests. The two constraints are:
o The server must not bestow a delegation for any open which would
require confirmation.
o The server MUST NOT require confirmation on a reclaim-type open
(i.e., one specifying claim type CLAIM_PREVIOUS or
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CLAIM_DELEGATE_PREV).
These constraints are related in that reclaim-type opens are the only
ones in which the server may be required to send a delegation. For
CLAIM_NULL, sending the delegation is optional while for
CLAIM_DELEGATE_CUR, no delegation is sent.
Delegations being sent with an open requiring confirmation are
troublesome because recovering from non-confirmation adds undue
complexity to the protocol while requiring confirmation on reclaim-
type opens poses difficulties in that the inability to resolve the
status of the reclaim until lease expiration may make it difficult to
have timely determination of the set of locks being reclaimed (since
the grace period may expire).
Requiring open confirmation on reclaim-type opens is avoidable
because of the nature of the environments in which such opens are
done. For CLAIM_PREVIOUS opens, this is immediately after server
reboot, so there should be no time for lockowners to be created,
found to be unused, and recycled. For CLAIM_DELEGATE_PREV opens, we
are dealing with a client reboot situation. A server which supports
delegation can be sure that no lockowners for that client have been
recycled since client initialization and thus can ensure that
confirmation will not be required.
9.2. Lock Ranges
The protocol allows a lock owner to request a lock with a byte range
and then either upgrade 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 filesystems 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 the Section 9.6.2 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.
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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 issued 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
requesting application.
9.4. Blocking Locks
Some clients require the support of blocking locks. The NFS version
4 protocol must not rely on a callback mechanism and therefore is
unable to notify a client when a previously denied lock has been
granted. Clients have no choice but 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. 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.
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9.5. Lease Renewal
The purpose of a lease is to allow a server to remove stale locks
that are held by a client that has crashed or is otherwise
unreachable. It is not a mechanism for cache consistency and lease
renewals may not be denied if the lease interval has not expired.
The following events cause implicit renewal of all of the leases for
a given client (i.e., all those sharing a given clientid). Each of
these is a positive indication that the client is still active and
that the associated state held at the server, for the client, is
still valid.
o An OPEN with a valid clientid.
o Any operation made with a valid stateid (CLOSE, DELEGPURGE,
DELEGRETURN, LOCK, LOCKU, OPEN, OPEN_CONFIRM, OPEN_DOWNGRADE,
READ, RENEW, SETATTR, WRITE). This does not include the special
stateids of all bits 0 or all bits 1.
Note that if the client had restarted or rebooted, the client
would not be making these requests without issuing the
SETCLIENTID/SETCLIENTID_CONFIRM sequence. The use of the
SETCLIENTID/SETCLIENTID_CONFIRM sequence (one that changes the
client verifier) notifies the server to drop the locking state
associated with the client. SETCLIENTID/SETCLIENTID_CONFIRM never
renews a lease.
If the server has rebooted, the stateids (NFS4ERR_STALE_STATEID
error) or the clientid (NFS4ERR_STALE_CLIENTID error) will not be
valid hence preventing spurious renewals.
This approach allows for low overhead lease renewal which scales
well. In the typical case no extra RPC calls are required for lease
renewal and in the worst case one RPC is required every lease period
(i.e., a RENEW operation). The number of locks held by the client is
not a factor since all state for the client is involved with the
lease renewal action.
Since all operations that create a new lease also renew existing
leases, the server must maintain a common lease expiration time for
all valid leases for a given client. This lease time can then be
easily updated upon implicit lease renewal actions.
9.6. Crash Recovery
The important requirement in crash recovery is that both the client
and the server know when the other has failed. Additionally, it is
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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.
9.6.1. Client Failure and Recovery
In the event that a client fails, the server may recover the client's
locks when the associated leases have expired. Conflicting locks
from another client may only be granted after this lease expiration.
If the client is able to restart or reinitialize within the lease
period the client may be forced to wait the remainder of the lease
period before obtaining new locks.
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 initial SETCLIENTID call made by the client.
The server returns a clientid as a result of the SETCLIENTID
operation. The client then confirms the use of the clientid with
SETCLIENTID_CONFIRM. The clientid in combination with an opaque
owner field is then used by the client to identify the lock owner for
OPEN. This chain of associations is then used to identify all locks
for a particular client.
Since the verifier will be changed by the client upon each
initialization, the server can compare a new verifier to the verifier
associated with currently held locks and determine that they do not
match. This signifies the client's new instantiation and subsequent
loss of locking state. As a result, the server is free to release
all locks held which are associated with the old clientid which was
derived from the old verifier.
Note that the verifier must have the same uniqueness properties of
the verifier for the COMMIT operation.
9.6.2. 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 the possibility that clients have not
yet re-established their locking state for a file, the server must
disallow READ and WRITE operations for that file. The duration of
this recovery period is equal to the duration of the lease period.
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A client can determine that server failure (and thus loss of locking
state) has occurred, when it receives one of two errors. The
NFS4ERR_STALE_STATEID error indicates a stateid invalidated by a
reboot or restart. The NFS4ERR_STALE_CLIENTID error indicates a
clientid invalidated by reboot or restart. When either of these are
received, the client must establish a new clientid (see
Section 9.1.1) and re-establish the locking state as discussed below.
The period of special handling of locking and READs and WRITEs, equal
in duration to the lease period, is referred to as the "grace
period". During the grace period, clients recover locks and the
associated state by reclaim-type locking requests (i.e., LOCK
requests with reclaim set to true and OPEN operations with a claim
type of CLAIM_PREVIOUS). During the grace period, the server must
reject READ and WRITE operations and non-reclaim locking requests
(i.e., other LOCK and OPEN operations) with an error of
NFS4ERR_GRACE.
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 and the non-
reclaim client request can be serviced. 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 an impending 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 a count of locks on a given file is available in
stable storage, the server can track reclaimed locks for the file and
when all reclaims have been processed, non-reclaim locking requests
may be processed. This way the server can ensure that non-reclaim
locking requests will not conflict with potential reclaim requests.
With respect to I/O requests, if the server is able to determine that
there are no outstanding reclaim requests for a file by information
from stable storage or another similar mechanism, the processing of
I/O requests could proceed normally for the file.
To reiterate, for a server that allows non-reclaim lock and I/O
requests to be processed during the grace period, it MUST determine
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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
[20]. 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 clientid 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.
9.6.3. 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. As a result, all stateids held by the
client will become invalid or stale. Once the client is able to
reach the server after such a network partition, all I/O submitted by
the client with the now invalid stateids will fail with the server
returning the error NFS4ERR_EXPIRED. Once this error is received,
the client will suitably notify the application that held the lock.
As a courtesy to the client or as an optimization, the server may
continue to hold locks on behalf of a client for which recent
communication has extended beyond the lease period. If the server
receives a lock or I/O request that conflicts with one of these
courtesy locks, the server must free the courtesy lock and grant the
new request.
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
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these edge conditions are known, and are discussed below.
The first edge condition has the following scenario:
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, so server releases lock.
4. Client B acquires a lock that would have conflicted with that of
Client A.
5. Client B releases the lock
6. Server reboots
7. Network partition between client A and server heals.
8. Client A issues a RENEW operation, and gets back a
NFS4ERR_STALE_CLIENTID.
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 follows:
1. Client A acquires a lock.
2. Server reboots.
3. Client A and server experience mutual network partition, such
that client A is unable to reclaim its lock within the grace
period.
4. Server's reclaim grace period ends. Client A has no locks
recorded on server.
5. Client B acquires a lock that would have conflicted with that of
Client A.
6. Client B releases the lock.
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7. Server reboots a second time.
8. Network partition between client A and server heals.
9. Client A issues a RENEW operation, and gets back a
NFS4ERR_STALE_CLIENTID.
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 assume after it reboots that edge condition occurs, and thus
return NFS4ERR_NO_GRACE for all reclaim attempts, or that the server
record some information stable storage. The amount of information
the server records in stable storage is in inverse proportion to how
harsh the server wants to be whenever the edge conditions occur. 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 unlocked by the
client and the lock's lockowner advances the sequence number such
that the lock release is not the last stateful event for the
lockowner's sequence. For the two aforementioned edge conditions,
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 client's id string
o a boolean that indicates if the client's lease expired or if there
was administrative intervention (see Section 9.8) to revoke a
record lock, share reservation, or delegation
o a timestamp that is updated the first time after a server boot or
reboot the client acquires record locking, share reservation, or
delegation state on the server. The timestamp need not be updated
on subsequent lock requests until the server reboots.
The server implementation would also record in the stable storage the
timestamps from the two most recent server reboots.
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
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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 record that the client had an unexpired record lock, share
reservation, or delegation established before the server's previous
incarnation means that the server must reject a reclaim from client A
with the error NFS4ERR_NO_GRACE.
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 superharsh,
but necessary if the server does not want to 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. False positives are acceptable.
Note that at this time, it is not known if there are other edge
conditions. In the event, after a server reboot, the server
determines that there is unrecoverable damage or corruption to
the the stable storage, then for all clients and/or locks
affected, the server MUST return NFS4ERR_NO_GRACE.
A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
outside the scope of this specification, since the strategies for
such handling are very dependent on the client's operating
environment. However, one potential approach is described below.
When the client receives NFS4ERR_NO_GRACE, it could examine the
change attribute of the objects 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 otherwords, 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 9.8.
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9.7. Recovery from a Lock Request Timeout or Abort
In the event a lock request times out, a client may decide to not
retry the request. The client may also abort the request when the
process for which it was issued is terminated (e.g., in UNIX due to a
signal). It is possible though that the server received the request
and acted upon it. This would change the state on the server without
the client being aware of the change. It is paramount that the
client re-synchronize state with server before it attempts any other
operation that takes a seqid and/or a stateid with the same
lock_owner. This is straightforward to do without a special re-
synchronize operation.
Since the server maintains the last lock request and response
received on the lock_owner, for each lock_owner, the client should
cache the last lock request it sent such that the lock request did
not receive a response. From this, the next time the client does a
lock operation for the lock_owner, it can send the cached request, if
there is one, and if the request was one that established state
(e.g., a LOCK or OPEN operation), the server will return the cached
result or if never saw the request, perform it. The client can
follow up with a request to remove the state (e.g., a LOCKU or CLOSE
operation). With this approach, the sequencing and stateid
information on the client and server for the given lock_owner will
re-synchronize and in turn the lock state will re-synchronize.
9.8. 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 instance of lock revocation is upon server reboot or re-
initialization. In this instance the client will receive an error
(NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and the client will
proceed with normal crash recovery as described in the previous
section.
The second lock revocation event is the inability to renew the lease
before expiration. While this is considered a rare or unusual event,
the client must be prepared to recover. Both the server and client
will be able to detect the failure to renew the lease and are capable
of recovering without data corruption. For the server, it tracks the
last renewal event serviced for the client and knows when the lease
will expire. Similarly, the client must track operations which will
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renew the lease period. Using the time that each such request was
sent and the time that the corresponding reply was received, the
client should bound the time that the corresponding renewal could
have occurred on the server and thus determine if it is possible that
a lease period expiration could have occurred.
The third lock revocation event can occur as a result of
administrative intervention within the lease period. While this is
considered a rare event, it is possible that the server's
administrator has decided to release or revoke a particular lock held
by the client. As a result of revocation, the client will receive an
error of NFS4ERR_ADMIN_REVOKED. In this instance the client may
assume that only the lock_owner's locks have been lost. The client
notifies the lock holder appropriately. The client may not assume
the lease period has been renewed as a result of a failed operation.
When the client determines the lease period may have expired, the
client must mark all locks held for the associated lease as
"unvalidated". This means the client has been unable to re-establish
or confirm the appropriate lock state with the server. As described
in Section 9.6, there are scenarios in which the server may grant
conflicting locks after the lease period has expired for a client.
When it is possible that the lease period has expired, the client
must validate each lock currently held to ensure that a conflicting
lock has not been granted. The client may accomplish this task by
issuing an I/O request, either a pending I/O or a zero-length read,
specifying the stateid associated with the lock in question. If the
response to the request is success, the client has validated all of
the locks governed by that stateid and re-established the appropriate
state between itself and the server.
If the I/O request is not successful, then one or more of the locks
associated with the stateid was revoked by the server and the client
must notify the owner.
9.9. 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 issues 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:
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if (request.access == 0)
return (NFS4ERR_INVAL)
else if ((request.access & file_state.deny)) ||
(request.deny & file_state.access))
return (NFS4ERR_DENIED)
This checking of share reservations on OPEN is done with no exception
for an existing OPEN for the same open_owner.
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;
9.10. 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 if any access to deny. Even if the client intends to
use a stateid of all 0's or all 1's, 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
lock_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 cannot be accessed using a filehandle
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obtained through LOOKUP because it would not have a valid stateid
(i.e., using a stateid of all bits 0 or all bits 1).
9.10.1. Close and Retention of State Information
Since a CLOSE operation requests deallocation of a stateid, dealing
with retransmission of the CLOSE, may pose special difficulties,
since the state information, which normally would be used to
determine the state of the open file being designated, might be
deallocated, resulting in an NFS4ERR_BAD_STATEID error.
Servers may deal with this problem in a number of ways. To provide
the greatest degree assurance that the protocol is being used
properly, a server should, rather than deallocate the stateid, mark
it as close-pending, and retain the stateid with this status, until
later deallocation. In this way, a retransmitted CLOSE can be
recognized since the stateid points to state information with this
distinctive status, so that it can be handled without error.
When adopting this strategy, a server should retain the state
information until the earliest of:
o Another validly sequenced request for the same lockowner, that is
not a retransmission.
o The time that a lockowner is freed by the server due to period
with no activity.
o All locks for the client are freed as a result of a SETCLIENTID.
Servers may avoid this complexity, at the cost of less complete
protocol error checking, by simply responding NFS4_OK in the event of
a CLOSE for a deallocated stateid, on the assumption that this case
must be caused by a retransmitted close. When adopting this
approach, it is desirable to at least log an error when returning a
no-error indication in this situation. If the server maintains a
reply-cache mechanism, it can verify the CLOSE is indeed a
retransmission and avoid error logging in most cases.
9.11. Open Upgrade and Downgrade
When an OPEN is done for a file and the lockowner 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. Only a single
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CLOSE will be done to reset the effects of both OPENs. 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
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.
9.12. 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 RENEW or READ (with zero length)
requests. Longer leases are certainly kinder and gentler to servers
trying to handle very large numbers of clients. The number of RENEW
requests drop in proportion to the lease time. The disadvantages of
long leases are slower recovery after server failure (the server must
wait for the leases to expire and the grace period to elapse before
granting new lock requests) and increased file contention (if client
fails to transmit an unlock request then server must wait for lease
expiration before granting new locks).
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.
9.13. 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 lock. There is also the issue of propagation delay across the
network which could easily be several hundred milliseconds as well as
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the possibility that requests will be lost and need to be
retransmitted.
To take propagation delay into account, the client should subtract it
from lease times (e.g., if the client estimates the one-way
propagation delay as 200 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 lock 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.
9.14. Migration, Replication and State
When responsibility for handling a given file system is transferred
to a new server (migration) or the client chooses to use an alternate
server (e.g., in response to server unresponsiveness) in the context
of file system replication, the appropriate handling of state shared
between the client and server (i.e., locks, leases, stateids, and
clientids) is as described below. The handling differs between
migration and replication. For related discussion of file server
state and recover of such see the sections under Section 9.6.
If a server replica or a server immigrating a filesystem agrees to,
or is expected to, accept opaque values from the client that
originated from another server, then it is a wise implementation
practice for the servers to encode the "opaque" values in network
byte order. This way, servers acting as replicas or immigrating
filesystems will be able to parse values like stateids, directory
cookies, filehandles, etc. even if their native byte order is
different from other servers cooperating in the replication and
migration of the filesystem.
9.14.1. Migration and State
In the case of migration, the servers involved in the migration of a
filesystem SHOULD transfer all server state from the original to the
new server. This must be done in a way that is transparent to the
client. This state transfer will ease the client's transition when a
filesystem migration occurs. If the servers are successful in
transferring all state, the client will continue to use stateids
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assigned by the original server. Therefore the new server must
recognize these stateids as valid. This holds true for the clientid
as well. Since responsibility for an entire filesystem is
transferred with a migration event, there is no possibility that
conflicts will arise on the new server as a result of the transfer of
locks.
As part of the transfer of information between servers, leases would
be transferred as well. The leases being transferred to the new
server will typically have a different expiration time from those for
the same client, previously on the old server. To maintain the
property that all leases on a given server for a given client expire
at the same time, the server should advance the expiration time to
the later of the leases being transferred or the leases already
present. This allows the client to maintain lease renewal of both
classes without special effort.
The servers may choose not to transfer the state information upon
migration. However, this choice is discouraged. In this case, when
the client presents state information from the original server (e.g.,
in a RENEW op or a READ op of zero length), the client must be
prepared to receive either NFS4ERR_STALE_CLIENTID or
NFS4ERR_STALE_STATEID from the new server. The client should then
recover its state information as it normally would in response to a
server failure. The new server must take care to allow for the
recovery of state information as it would in the event of server
restart.
A client SHOULD re-establish new callback information with the new
server as soon as possible, according to sequences described in
Section 15.35 and Section 15.36. This ensures that server operations
are not blocked by the inability to recall delegations.
9.14.2. Replication and State
Since client switch-over in the case of replication is not under
server control, the handling of state is different. In this case,
leases, stateids and clientids do not have validity across a
transition from one server to another. The client must re-establish
its locks on the new server. This can be compared to the re-
establishment of locks by means of reclaim-type requests after a
server reboot. The difference is that the server has no provision to
distinguish requests reclaiming locks from those obtaining new locks
or to defer the latter. Thus, a client re-establishing a lock on the
new server (by means of a LOCK or OPEN request), may have the
requests denied due to a conflicting lock. Since replication is
intended for read-only use of filesystems, such denial of locks
should not pose large difficulties in practice. When an attempt to
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re-establish a lock on a new server is denied, the client should
treat the situation as if his original lock had been revoked.
9.14.3. Notification of Migrated Lease
In the case of lease renewal, the client may not be submitting
requests for a filesystem that has been migrated to another server.
This can occur because of the implicit lease renewal mechanism. The
client renews leases for all filesystems when submitting a request to
any one filesystem at the server.
In order for the client to schedule renewal of leases that may have
been relocated to the new server, the client must find out about
lease relocation before those leases expire. To accomplish this, all
operations which implicitly renew leases for a client (such as OPEN,
CLOSE, READ, WRITE, RENEW, LOCK, and others), will return the error
NFS4ERR_LEASE_MOVED if responsibility for any of the leases to be
renewed has been transferred to a new server. This condition will
continue until the client receives an NFS4ERR_MOVED error and the
server receives the subsequent GETATTR(fs_locations) for an access to
each filesystem for which a lease has been moved to a new server. By
convention, the compound including the GETATTR(fs_locations) SHOULD
append a RENEW operation to permit the server to identify the client
doing the access.
When a client receives an NFS4ERR_LEASE_MOVED error, it should
perform an operation on each filesystem associated with the server in
question. When the client receives an NFS4ERR_MOVED error, the
client can follow the normal process to obtain the new server
information (through the fs_locations attribute) and perform renewal
of those leases on the new server. If the server has not had state
transferred to it transparently, the client will receive either
NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new server,
as described above, and the client can then recover state information
as it does in the event of server failure.
9.14.4. Migration and the Lease_time Attribute
In order that the client may appropriately manage its leases in the
case of migration, 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 migration in which state is
transferred transparently, the client is under no obligation to re-
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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 (i.e., the client
sees a real or simulated server reboot), 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
locks before potentially conflicting non-reclaimed locks are granted.
The means by which the new server obtains the value of lease_time on
the old server is left to the server implementations. It is not
specified by the NFS version 4 protocol.
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 NFS version 4 protocol uses many techniques similar to those that
have been used in previous protocol versions. The NFS version 4
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 NFS version 4 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.
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.
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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 NFS version 4 protocol provides more aggressive caching
strategies with the following design goals:
o Compatibility with a large range of server semantics.
o Provide the same caching benefits as previous versions of the NFS
protocol when unable to provide 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).
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
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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 clientid 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.
Because callback RPCs may not work in all environments (due to
firewalls, for example), correct protocol operation does not depend
on them. Preliminary testing of callback functionality by means of a
CB_NULL procedure determines whether callbacks can be supported. The
CB_NULL procedure checks the continuity of the callback path. A
server makes a preliminary assessment of callback availability to a
given client and avoids delegating responsibilities until it has
determined that callbacks are supported. 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 to be processed without any
delegations being granted.
Once granted, a delegation behaves in most 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.
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 receive a response
until the recall is complete. The recall is considered complete when
the client returns the delegation or the server times out on the
recall and revokes the delegation as a result of the timeout.
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
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
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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 callback-only)
In the event the client reboots or restarts, the failure to renew
leases 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
delegations, such delegations are reclaimed using OPEN with a claim
type of CLAIM_DELEGATE_PREV. (See Section 10.5 and Section 15.18 for
discussion of open delegation and the details of OPEN respectively).
A server MAY support a claim type of CLAIM_DELEGATE_PREV, but if it
does, it MUST NOT remove delegations upon SETCLIENTID_CONFIRM, 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
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time for the client to issue 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 NFS version 4 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 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 callback path (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 the error
NFS4ERR_EXPIRED. 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 9.6). This is done to deal with the case in
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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 NFS
version 4 protocol provides to allow applications to coordinate
access by providing mutual exclusion facilities. The NFS version 4
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, NFS version 4 clients should not provide cached
data to applications or modify it on behalf of an application when it
would not be valid to obtain or modify that same data via a READ or
WRITE operation.
Furthermore, in the absence of open delegation (see Section 10.4) two
additional rules apply. Note that these rules are obeyed in practice
by many NFS version 2 and version 3 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 NFS version 3 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
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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
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 filesystem. However, they may not work with the
NFS version 4 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 cached 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.
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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.
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 a LOCKU
than is covered by the locked range. This may include modified data
within files other than the one for which the unlocks are being done.
In such cases, the client must not interfere with applications whose
READs and WRITEs are being done only within the bounds of 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.
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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 filesystem object to which the data belongs. For
NFS version 3 clients, the typical practice has been to assume for
the purpose of caching that distinct filehandles represent distinct
filesystem objects. The client then has the choice to organize and
maintain the data cache on this basis.
In the NFS version 4 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 filesystem 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 NFS version 4
protocol alleviates a potential functional regression in comparison
with the NFS version 3 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 NFS
version 4 client to determine whether two distinct filehandles denote
the same server side object:
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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.
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.
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.
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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 may not make any changes
to the contents or attributes of the file but it is assured that no
other client may do so. When a client has a write open delegation,
it may modify the file data since no other client will be accessing
the file's data. The client holding a write delegation may only
affect file attributes which are intimately connected with the file
data: size, time_modify, change.
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
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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 9.9.
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.
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.
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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. This refers to the READs and WRITEs that use the
special stateids consisting of all zero bits or all one bits.
Therefore, READs or WRITEs with a special stateid done by another
client will force the server to recall a write open delegation. A
WRITE with a special stateid done by another client will force a
recall of read open delegations.
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 filesystem space for the data has been exceeded (i.e.,
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 filesystem space and any applicable quotas.
The server can recall delegations as a result of managing the
available filesystem 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 filesystem 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.
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10.4.2. Open Delegation and File Locks
When a client holds a write open delegation, lock operations may be
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.
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.
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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
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 octets.
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
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new value of sc, which we will call nsc, is computed by the
server, such that nsc >= sc + 1. The server then returns the
constructed time_metadata, time_modify, and nsc values to the
requester. The server replaces sc in the delegation record with
nsc. To prevent the possibility of time_modify, time_metadata,
and change from appearing to go backward (which would happen if
the client holding the delegation fails to write its modified data
to the server before the delegation is revoked or returned), the
server SHOULD update the file's metadata record with the
constructed attribute values. For reasons of reasonable
performance, committing the constructed attribute values to stable
storage is OPTIONAL.
As discussed earlier in this section, the client MAY return the
same cc value on subsequent CB_GETATTR calls, even if the file was
modified in the client's cache yet again between successive
CB_GETATTR calls. Therefore, the server must assume that the file
has been modified yet again, and MUST take care to ensure that the
new nsc it constructs and returns is greater than the previous nsc
it returned. An example implementation's delegation record would
satisfy this mandate by including a boolean field (let us call it
"modified") that is set to false when the delegation is granted,
and an sc value set at the time of grant to the change attribute
value. The modified field would be set to true the first time cc
!= sc, and would stay true until the delegation is returned or
revoked. The processing for constructing nsc, time_modify, and
time_metadata would use this pseudo code:
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;
}
return to client (that sent GETATTR) the attributes
it requested, but make sure size comes from what
CB_GETATTR returned. Do not update the file's metadata
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with the client's modified size.
o 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.
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 issued 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 filesystem. If that filesystem 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
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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 not longer be valid. These OPEN
requests are done with the claim type of CLAIM_DELEGATE_CUR. This
will allow the presentation of the delegation stateid so that the
client can establish the appropriate rights to perform the OPEN.
(see Section 15.18 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.
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
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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 callback path from server to the client. The client
may be unaware of a failure in the callback path. This lack of
awareness could result in the client finding out long after the
failure that its delegation has been revoked, and another client has
modified the data for which the client had a delegation. This is
especially a problem for the client that held a write delegation.
The server also has a dilemma in that the client that fails to
respond to the recall might also be sending other NFS requests,
including those that renew the lease before the lease expires.
Without returning an error for those lease renewing operations, the
server leads the client to believe that the delegation it has is in
force.
This difficulty is solved by the following rules:
o When the callback path is down, the server MUST NOT revoke the
delegation if one of the following occurs:
* The client has issued a RENEW operation and the server has
returned an NFS4ERR_CB_PATH_DOWN error. The server MUST renew
the lease for any record locks and share reservations the
client has that the server has known about (as opposed to those
locks and share reservations the client has established but not
yet sent to the server, due to the delegation). The server
SHOULD give the client a reasonable time to return its
delegations to the server before revoking the client's
delegations.
* The client has not issued a RENEW operation for some period of
time after the server attempted to recall the delegation. This
period of time MUST NOT be less than the value of the
lease_time attribute.
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o When the client holds a delegation, it can not rely on operations,
except for RENEW, that take a stateid, to renew delegation leases
across callback path failures. The client that wants to keep
delegations in force across callback path failures must use RENEW
to do so.
10.4.6. Delegation Revocation
At the point a delegation is revoked, if there are associated opens
on the client, the applications holding these opens 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
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.
10.5. 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,
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
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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 filesystem 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
be limited to files of a certain size or might be used only when
sufficient disk space is available within the target filesystem.
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 filesystem.
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
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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 filesystem 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.
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
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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
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,
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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
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 the 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
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* 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 issues 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 issue 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:
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.
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10.8. 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 filesystem 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 is then able to compare
the pre-operation change value with the change value in the client's
name cache. 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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10.9. 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 filesystem 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.
11. Minor Versioning
To address the requirement of an NFS protocol that can evolve as the
need arises, the NFS version 4 protocol contains the rules and
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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 NFS
version 4 protocol is represented by this RFC. The COMPOUND
procedure will support the encoding of the minor version being
requested by the client.
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, NFS version 4 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.
1. Minor versions may append attributes to GETATTR4args,
bitmap4, and GETATTR4res.
This allows for the expansion of the attribute model to
allow for future growth or adaptation.
2. 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 will
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.
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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
* adding bits to existing attributes like ACLs that have flag
words
* extending enumerated types (including NFS4ERR_*) with new
values
4. Minor versions must not modify the structure of existing
attributes.
5. Minor versions must not delete operations.
This prevents the potential reuse of a particular operation
"slot" in a future minor version.
6. Minor versions must not delete attributes.
7. Minor versions must not delete flag bits or enumeration values.
8. Minor versions may declare an operation MUST NOT be implement.
Specifying that an operation MUST NOT be implemented is
equivalent to obsoleting an operation. For the client, it means
that the operation MUST 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 that an attribute MUST NOT be
implemented.
2. Minor versions may declare that 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 support minor version X SHOULD support
minor versions 0 (zero) through X-1 as well.
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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
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.
12. Internationalization
This chapter describes the string-handling aspects of the NFS version
4 protocol, and how they address issues related to
internationalization, including issues related to UTF-8,
normalization, string preparation, case folding, and handling of
internationalization issues related to domains.
The NFS version 4 protocol needs to deal with internationalization,
or I18N, with respect to file names and other strings as used within
the protocol. The choice of string representation must allow for
reasonable name/string access to clients, applications, and users
which use various languages. The UTF-8 encoding of the UCS as
defined by [7] allows for this type of access and follows the policy
described in "IETF Policy on Character Sets and Languages", [8].
In implementing such policies, it is important to understand and
respect the nature of NFS version 4 as a means by which client
implementations may invoke operations on remote file systems. Server
implementations act as a conduit to a range of file system
implementations that the NFS version 4 server typically invokes
through a virtual-file-system interface.
Keeping this context in mind, one needs to understand that the file
systems with which clients will be interacting will generally not be
devoted solely to access using NFS version 4. Local access and its
requirements will generally be important and often access over other
remote file access protocols will be as well. It is generally a
functional requirement in practice for the users of the NFS version 4
protocol (although it may be formally out of scope for this document)
for the implementation to allow files created by other protocols and
by local operations on the file system to be accessed using NFS
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version 4 as well.
It also needs to be understood that a considerable portion of file
name processing will occur within the implementation of the file
system rather than within the limits of the NFS version 4 server
implementation per se. As a result, cetain aspects of name
processing may change as the locus of processing moves from file
system to file system. As a result of these factors, the protocol
cannot enforce uniformity of name-related processing upon NFS version
4 server requests on the server as a whole. Because the server
interacts with existing file system implementations, the same server
handling will produce different behavior when interacting with
different file system implementations. To attempt to require uniform
behavior, and treat the the protocol server and the file system as a
unified application, would considerably limit the usefulness of the
protocol.
12.1. Use of UTF-8
As mentioned above, UTF-8 is used as a convenient way to encode
Unicode which allows clients that have no internationalization
requirements to avoid these issues since the mapping of ASCII names
to UTF-8 is the identity.
12.1.1. Relation to Stringprep
RFC 3454 [9], otherwise known as "stringprep", documents a framework
for using Unicode/UTF-8 in networking protocols, intended "to
increase the likelihood that string input and string comparison work
in ways that make sense for typical users throughout the world." A
protocol conforming to this framework must define a profile of
stringprep "in order to fully specify the processing options." NFS
version 4, while it does make normative references to stringprep and
uses elements of that framework, it does not, for reasons that are
explained below, conform to that framework, for all of the strings
that are used within it.
In addition to some specific issues which have caused stringprep to
add confusion in handling certain characters for certain languages,
there are a number of general reasons why stringprep profiles are not
suitable for describing NFS version 4.
o Restricting the character repertoire to Unicode 3.2, as required
by stringprep is unduly constricting.
o Many of the character tables in stringprep are inappropriate
because of this limited character repertoire, so that normative
reference to stringprep is not desirable in many case and instead,
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we allow more flexibility in the definition of case mapping
tables.
o Because of the presence of different file systems, the specifics
of processing are not fully defined and some aspects that are are
RECOMMENDED, rather than REQUIRED.
Despite these issues, in many cases the general structure of
stringprep profiles, consisting of sections which deal with the
applicability of the description, the character repertoire, charcter
mapping, normalization, prohibited characters, and issues of the
handling (i.e., possible prohibition) of bidirectional strings, is a
convenient way to describe the string handling which is needed and
will be used where appropriate.
12.1.2. Normalization, Equivalence, and Confusability
Unicode has defined several equivalence relationships among the set
of possible strings. Understanding the nature and purpose of these
equivalence relations is important to understand the handling of
Unicode strings within NFS version 4.
Some string pairs are thought as only differing in the way accents
and other diacritics are encoded, as illustrated in the examples
below. Such string pairs are called "canonically equivalent".
Such equivalence can occur when there are precomposed characters,
as an alternative to encoding a base character in addition to a
combining accent. For example, the character LATIN SMALL LETTER E
WITH ACUTE (U+00E9) is defined as canonically equivalent to the
string consisting of LATIN SMALL LETTER E followed by COMBINING
ACUTE ACCENT (U+0065, U+0301).
When multiple combining diacritics are present, differences in the
ordering are not reflected in resulting display and the strings
are defined as canonically equivalent. For example, the string
consisting of LATIN SMALL LETTER Q, COMBINING ACUTE ACCENT,
COMBINING GRAVE ACCENT (U+0071, U+0301, U+0300) is canonically
quivalent to the string consisting of LATIN SMALL LETTER Q,
COMBINING GRAVE ACCENT, COMBINING ACUTE ACCENT (U+0071, U+0300,
U+0301)
When both situations are present, the number of canonically
equivalent strings can be greater. Thus, the following strings
are all canonically equivalent:
LATIN SMALL LETTER E, COMBINING MACRON, ACCENT, COMBINING ACUTE
ACCENT (U+0xxx, U+0304, U+0301)
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LATIN SMALL LETTER E, COMBINING ACUTE ACCENT, COMBINING MACRON
(U+0xxx, U+0301, U+0304)
LATIN SMALL LETTER E WITH MACRON, COMBINING ACUTE ACCENT
(U+011E, U+0301)
LATIN SMALL LETTER E WITH ACUTE, COMBINING MACRON (U+00E9,
U+0304)
LATIN SMALL LETTER E WITH MACRON AND ACUTE (U+1E16)
Additionally there is an equivalence relation of "compatibility
equivalence". Two canonically equivalent strings are necessarily
compatibility equivalent, although not the converse. An example of
compatibility equivalent strings which are not canonically equivalent
are GREEK CAPITAL LETTER OMEGA (U+03A9) and OHM SIGN (U+2129). These
are identical in appearance while other compatibility equivalent
strings are not. Another example would be "x2" and the two character
string denoting x-squared which are clearly differnt in appearance
although compatibility equivalent and not canonically equivalent.
These have Unicode encodings LATIN SMALL LETTER X, DIGIT TWO (U+0078,
U+0032) and LATIN SMALL LETTER X, SUPERSCRIPT TWO (U+0078, U+00B2),
One way to deal with these equivalence relations is via
normalization. A normalization form maps all strings to a
correspondig normalized string in such a fashion that all strings
that are equivalent (canonically or compatibly, depending on the
form) are mapped to the same value. Thus the image of the mapping is
a subset of Unicode strings conceived as the representives of the
equivalence classes defined by the chosen equivalence relation.
In the NFS version 4 protocol, handling of issues related to
internationalization with regard to normalization follows one of two
basic patterns:
o For strings whose function is related to other internet standards,
such as server and domain naming, the normalization form defined
by the appropriate internet standards is used. For server and
domain naming, this involves normalization form NFKC as specified
in [10]
o For other strings, particular those passed by the server to file
system implementations, normalization requirements are the
province of the file system and the job of this specification is
not to specify a particular form but to make sure that
interoperability is maximmized, even when clients and server-based
file systems have different preferences.
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A related but distinct issue concerns string confusability. This can
occur when two strings (including single-charcter strings) having a
similar appearance. There have been attempts to define uniform
processing in an attempt to avoid such confusion (see stringprep [9])
but the results have often added confusion.
Some examples of possible confusions and proposed processing intended
to reduce/avoid confusions:
o Deletion of characters believed to be invisible and appropriately
ignored, justifying their deletion, including, WORD JOINER
(U+2060), and the ZERO WIDTH SPACE (U+200B).
o Deletion of characters supposed to not bear semantics and only
affect glyph choice, including the ZERO WIDTH NON-JOINER (U+200C)
and the ZERO WIDTH JOINER (U+200D), where the deletion turns out
to be a problem for Farsi speakers.
o Prohibition of space characters such as the EM SPACE (U+2003), the
EN SPACE (U+2002), and the THIN SPACE (U+2009).
In addition, character pairs which apprear very similar and could and
often do result in confusion. In addition to what Unicode defines as
"compatibility equivalence", there are a considerable number of
additional character pairs that could cause confusion. This includes
characters such as LATIN CAPITAL LETTER O (U+004F) and DIGIT ZERO
(U+0030), and CYRILLIC SMALL LETTER ER (U+0440) LATIN SMALL LETTER P
(U+0070) (also with MATHEMATICAL BOLD SMALL P (U+1D429) and GREEK
SMALL LETTER RHO (U+1D56, for good measure).
NFS version 4, as it does with normalization, takes a two-part
approach to this issue:
o For strings whose function is related to other internet standards,
such as server and domain naming, any string processing to address
the confusability issue is defined by the appropriate internet
standards is used. For server and domain naming, this is the
responsibility of IDNA as described in [10].
o For other strings, particularly those passed by the server to file
system implementations, any such preparation requirements
including the choice of how, or whether to address the
confusability issue, are the responsibility of the file system to
define, and for this specification to try to add its own set would
add unacceptably to complexity, and make many files accessible
locally and by other remote file access protocols, inaccessible by
NFS version 4. This specification defines how the protocol
maximizes interoperability in the face of different file system
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implementations . NFS version 4 does allow file systems to map
and to reject characters, including those likely to result in
confusion, since file systems may choose to do such things. It
defines what the client will see in such cases, in order to limit
problems that can arise when a file name is created and it appears
to have a different name from the one it is assigned when the name
is created.
12.2. String Type Overview
12.2.1. Overall String Class Divisions
NFS version 4 has to deal with a large set of diffreent types of
strings and because of the different role of each,
internationalization issues will be different for each:
o For some types of strings, the fundamental internationalization-
related decisions are the province of the file system or the
security-handling functions of the server and the protocol's job
is to establish the rules under which file systems and servers are
allowed to exercise this freedom, to avoid adding to confusion.
o In other cases, the fundamental internationalization issues are
the responsibility of other IETF groups and our jobis simply to
reference those and perhaps make a few choices as to how they are
to be used (e.g., U-labels vs. A-labels).
o There are also cases in which a string has a small amount of NFS
version 4 processing which results in one or more strings being
referred to one of the other categories.
We will divide strings to be dealt with into the following classes:
MIX indicating that there is small amount of preparatory processing
that either picks an internationalization hadling mode or divides
the string into a set of (two) strings with a different mode
internationalization handling for each. The details are discussed
in the section "Types with Pre-processing to Resolve Mixture
Issues".
NIP indicating that, for various reasons, there is no need for
internationalization-specific processing to be performed. The
specifics of the various string types handled in this way are
described in the section "String Types without
Internationalization Processing".
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INET indicating that the string needs to be processed in a fashion
goverened by non-NFS-specific internet specifications. The
details are discussed in the section "Types with Processing
Defined by Other Internet Areas".
NFS indicating that the string needs to be processed in a fashion
governed by NFSv4-specific considerations. The primary focus is
on enabling flexibility for the various file systems to be
accessed and is described in the section "String Types with NFS-
specific Processing".
12.2.2. Divisions by Typedef Parent types
There are a number of different string types within NFS version 4 and
internationalization handling will be different for different types
of strings. Each the types will be in one of four groups based on
the parent type that specifies the nature of its relationship to utf8
and ascii.
utf8_should/USHOULD: indicating that strings of this type SHOULD be
UTF-8 but clients and servers will not check for valid UTF-8
encoding.
utf8val_should/UVSHOULD: indicating that strings of this type SHOULD
be and generally will be in the form of the UTF-8 encoding of
Unicode. Strings in most cases will be checked by the server for
valid UTF-8 but for certain file systems, such checking may be
inhibited.
utf8val_must/UVMUST: indicating that strings of this type MUST be in
the form of the UTF-8 encoding of Unicode. Strings will be
checked by the server for valid UTF-8 and the server SHOULD ensure
that when sent to the client, they are valid UTF-8.
ascii_must/ASCII: indicating that strings of this type MUST be pure
ASCII, and thus automatically UTF-8. The processing of these
string must ensure that they are only have ASCII characters but
this need not be a separate step if any normally required check
for validity inherently assures that only ASCII characters are
present.
In those cases where UTF-8 is not required, USHOULD and UVSHOULD, and
strings that are not valid UTF-8 are received and accepted, the
receiver MUST NOT modify the strings. For example, setting
particular bits such as the high-order bit to zero MUST NOT be done.
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12.2.3. Individual Types and Their Handling
The first table outlines the handling for the primary string types,
i.e., those not derived as a prefix or a suffix from a mixture type.
+-----------------+----------+-------+------------------------------+
| Type | Parent | Class | Explanation |
+-----------------+----------+-------+------------------------------+
| comptag4 | USHOULD | NIP | Should be utf8 but no |
| | | | validation by server or |
| | | | client is to be done. |
| component4 | UVSHOULD | NFS | Should be utf8 but clients |
| | | | may need to access file |
| | | | systems with a different |
| | | | name structure, such as file |
| | | | systems that have non-utf8 |
| | | | names. |
| linktext4 | UVSHOULD | NFS | Should be utf8 since text |
| | | | may include name components. |
| | | | Because of the need to |
| | | | access existing file |
| | | | systems, this check may be |
| | | | inhibited. |
| fattr4_mimetype | ASCII | NIP | All mime types are ascii so |
| | | | no specific utf8 processing |
| | | | is required, given that you |
| | | | are comparing to that list. |
+-----------------+----------+-------+------------------------------+
Table 5
There are a number of string types that are subject to preliminary
processing. This processing may take the form either of selecting
one of two possible forms based on the string contents or it in may
consist of dividing the string into multiple conjoined strings each
with different utf8-related processing.
+---------+--------+-------+----------------------------------------+
| Type | Parent | Class | Explanation |
+---------+--------+-------+----------------------------------------+
| prin4 | UVMUST | MIX | Consists of two parts separated by an |
| | | | at-sign, a prinpfx4 and a prinsfx4. |
| | | | These are described in the next table. |
| server4 | UVMUST | MIX | Is either an IP address (serveraddr4) |
| | | | which has to be pure ascii or a server |
| | | | name svrname4, which is described |
| | | | immediately below. |
+---------+--------+-------+----------------------------------------+
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Table 6
The last table describes the components of the compound types
described above.
+----------+--------+------+----------------------------------------+
| Type | Class | Def | Explanation |
+----------+--------+------+----------------------------------------+
| svraddr4 | ASCII | NIP | Server as IP address, whether IPv4 or |
| | | | IPv6. |
| svrname4 | UVMUST | INET | Server name as returned by server. |
| | | | Not sent by client, except in |
| | | | VERIFY/NVERIFY. |
| prinsfx4 | UVMUST | INET | Suffix part of principal, in the form |
| | | | of a domain name. |
| prinpfx4 | UVMUST | NFS | Must match one of a list of valid |
| | | | users or groups for that particular |
| | | | domain. |
+----------+--------+------+----------------------------------------+
Table 7
12.3. Errors Related to Strings
When the client sends an invalid UTF-8 string in a context in which
UTF-8 is REQUIRED, the server MUST return an NFS4ERR_INVAL error.
Within the framework of the previous section, this applies to strings
whose type is defined as utf8val_must or ascii_must. When the client
sends an invalid UTF-8 string in a context in which UTF-8 is
RECOMMENDED and the server should test for UTF-8, the server SHOULD
return an NFS4ERR_INVAL error. Within the framework of the previous
section, this applies to strings whose type is defined as
utf8val_should. These situations apply to 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
characters that are not supported by the server file system as a
value for that string (e.g., names containing characters that have
more than two octets on a file system that supports UCS-2 characters
only, file name components containing slashes on file systems that do
not allow them in file name components), the server MUST return an
NFS4ERR_BADCHAR error.
Where a UTF-8 string is used as a file name component, 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. This includes file system prohibitions of
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"." and ".." as file names for certain operations, and other such
similar constraints. It does not include use of strings with non-
preferred normalization modes.
Where a UTF-8 string is used as a file name component, the file
system implementation MUST NOT return NFS4ERR_BADNAME, simply due to
a normalization mismatch. In such cases the implementation SHOULD
convert the string to its own preferred normalization mode before
performing the operation. As a result, a client cannot assume that a
file created with a name it specifies will have that name when the
directory is read. It may have instead, the name converted to the
file system's preferred normalization form.
Where a UTF-8 string is used as other than as file name component (or
as symbolic link text) and the string does not meet the normalization
requirements specified for it, the error NFS4ERR_INVAL is returned.
12.4. Types with Pre-processing to Resolve Mixture Issues
12.4.1. Processing of Principal Strings
Strings denoting principals (users or groups) MUST be UTF-8 but since
they consist of a principal prefix, an at-sign, and a domain, all
three of which either are checked for being UTF-8, or inherently are
UTF-8, checking the string as a whole for being UTF-8 is not
required. Although a server implementation may choose to make this
check on the string as whole, for example in converting it to
Unicode, the description within this document, will reflect a
processing model in which such checking happens after the division
into a principal prefix and suffix, the latter being in the form of a
domain name.
The string should be scanned for at-signs. If there is more that one
at-sign, the string is considered invalid. For cases in which there
are no at-signs or the at-sign appears at the start or end of the
string see Interpreting owner and owner_group. Otherwise, the
portion before the at-sign is dealt with as a prinpfx4 and the
portion after is dealt with as a prinsfx4.
12.4.2. Processing of Server Id Strings
Server id strings typically appear in responses (as attribute values)
and only appear in requests as an attribute value presented to VERIFY
and NVERIFY. With that exception, they are not subject to server
validation and posible rejection. It is not expected that clients
will typically do such validation on receipt of responses but they
may as a way to check for proper server behavior. The responsibility
for sending correct UTF-8 strings is with the server.
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Servers are identified by either server names or IP addresses. Once
an id has been identified as an IP address, then there is no
processing specific to internationalization to be done, since such an
address must be ASCII to be valid.
12.5. String Types without Internationalization Processing
There are a number of types of strings which, for a number of
different reasons, do not require any internationalization-specific
handling, such as validation of UTF-8, normalization, or character
mapping or checking. This does not necessarily mean that the strings
need not be UTF-8. In some case, other checking on the string
ensures that they are valid UTF-8, without doing any checking
specific to internationalization.
The following are the specific types:
comptag4 strings are an aid to debugging and the sender should avoid
confusion by not using anything but valid UTF-8. But any work
validating the string or modifying it would only add complication
to a mechanism whose basic function is best supported by making it
not subject to any checking and having data maximally available to
be looked at in a network trace.
fattr4_mimetype strings need to be validated by matching against a
list of valid mime types. Since these are all ASCII, no
processing specific to internationaliztion is required since
anything that does not match is invalid and anything which does
not obey the rules of UTF-8 will not be ASCII and consequently
will not match, and will be invalid.
svraddr4 strings, in order to be valid, need to be ASCII, but if you
check them for validity, you have inherently checked that that
they are ASCII and thus UTF-8.
12.6. Types with Processing Defined by Other Internet Areas
There are two types of strings which NFS version 4 deals with whose
processing is defined by other Internet standards, and where issues
related to different handling choices by server operating systems or
server file systems do not apply.
These are as follows:
o Server names as they appear in the fs_locations attribute. Note
that for most purposes, such server names will only be sent by the
server to the client. The exception is use of the fs_locations
attribute in a VERIFY or NVERIFY operation.
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o Principal suffixes which are used to denote sets of users and
groups, and are in the form of domain names.
The general rules for handling all of these domain-related strings
are similar and independent of role the of the sender or receiver as
client or server although the consequences of failure to obey these
rules may be different for client or server. The server can report
errors when it is sent invalid strings, whereas the client will
simply ignore invalid string or use a default value in their place.
The string sent SHOULD be in the form of a U-label although it MAY be
in the form of an A-label or a UTF-8 string that would not map to
itself when canonicalized by applying ToUnicode(ToASCII(...)). The
receiver needs to be able to accept domain and server names in any of
the formats allowed. The server MUST reject, using the the error
NFS4ERR_INVAL, a string which is not valid UTF-8 or which begins with
"xn--" and violates the rules for a valid A-label.
When a domain string is part of id@domain or group@domain, the server
SHOULD map domain strings which are A-labels or are UTF-8 domain
names which are not U-labels, to the corresponding U-label, using
ToUnicode(domain) or ToUnicode(ToASCII(domain)). As a result, the
domain name returned within a userid on a GETATTR may not match that
sent when the userid is set using SETATTR, although when this
happens, the domain will be in the form of a U-label. When the
server does not map domain strings which are not U-labels into a
U-label, which it MAY do, it MUST NOT modify the domain and the
domain returned on a GETATTR of the userid MUST be the same as that
used when setting the userid by the SETATTTR.
The server MAY implement VERIFY and NVERIFY without translating
internal state to a string form, so that, for example, a user
principal which represents a specific numeric user id, will match a
different principal string which represents the same numeric user id.
12.7. String Types with NFS-specific Processing
For a number of data types within NFSv4, the primary responsbibility
for internationalization-related handling is that of some entity
other than the server itself (see below for details). In these
situations, the primary responsibility of NFS version 4 is to provide
a framework in which that other entity (file system and server
operating system principal naming framework) implements its own
decisions while establishing rules to limit interoperability issues.
This pattern applies to the following data types:
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o In the case of name components (strings of type component4), the
server-side file system implementation (of which there may be more
than one for a particular server) deals with internationalization
issues, in a fashion that is appropriate to NFS version 4, other
remote file access protocols, and local file access methods. See
"Handling of File Name Components" for the detailed treatment.
o In the case of link text strings (strings of type lintext4), the
issues are similar, but file systems are restricted in the set of
acceptable internationalization-related processing that they may
do, principally because symbolic links may contain name componetns
that, when used, are presented to other file systems and/or other
servers. See "Processing of Link Text" for the detailed
treatment.
o In the case of principal prefix strings, any decisions regarding
internationalization are the responsibility of the server
operating systems which may make its own rules regarding user and
group name encoding. See "Processing of Principal Prefixes" for
the detailed treatment.
12.7.1. Handling of File Name Components
There are a number of places within client and server where file name
components are processed:
o On the client, file names may be processed as part of forming NFS
version 4 requests. Any such processing will reflect specific
needs of the client's environment and will be treated as out-of-
scope from the viewpoint of this specification.
o On the server, file names are processed as part of processing NFS
version 4 requests. In practice, parts of the processing will be
implemented within the NFS version 4 server while other parts will
be implemented within the file system. This processing is
described in the sections below. These sections are organized in
a fashion parallel to a stringprep profile. The same sorts of
topics are dealt with but they differ in that there is a wider
range of possible processing choices.
o On the server, file name components might potentially be subject
to processing as part of generating NFS version 4 responses. This
specification assumes that this processing will be empty and that
file name components will be copied verbatim at this point. The
file name components may be modified as they appear in responses,
relative to the values used in the request but this is only
treated as reflecting changes made as part of request processing.
For example, a change to a file name component made in processing
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a CREATE operation will be reflected in the READDIR since the
files created will have names that reflect CREATE-time processing.
o On the client, responses will need to be properly dealt with and
the relevant issues will be discussed in the sections below.
Primarily, this will involve dealing with the fact that file name
components received in responses may need to be processed to meet
the requirements of the client's internal environment. This will
mainly involve dealing with changes in name components possibly
made by server processing. It also addresses other sorts of
expected behavior that do not involve a returned component4, such
as whether a LOOKUP finds a given component4 or whether a CREATE
or OPEN finds that a specified name already exists.
12.7.1.1. Nature of Server Processing of Name Components in Request
The component4 type defines a potentially case sensitive string,
typically of UTF-8 characters. Its use in NFS version 4 is for
representing file name components. Since file systems can implement
case insensitive file name handling, it can be used for both case
sensitive and case insensitive file name handling, based on the
attributes of the file system.
It may be the case that two valid distinct UTF-8 strings will be the
same after the processing described below. In such a case, a server
may either,
o disallow the creation of a second name if its 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.
12.7.1.2. Character Repertoire for the Component4 Type
The RECOMMENDED character repertoire for file name components is a
recent/current version of Unicode, as encoded via UTF-8. There are a
number of alternate character repertoires which may be chosen by the
server based on implementation constraints including the requirements
of the file system being accessed.
Two important alternative repertoires are:
o One alternate character repertoire is to represent file name
components as strings of bytes with no protocol-defined encoding
of multi-byte characters. Most typically, implementations that
support this single-byte alternative will make it available as an
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option set by an administrator for all file systems within a
server or for some particular file systems. If a server accepts
non-UTF-8 strings anywhere within a specific file system, then it
MUST do so throughout the entire file system.
o Another alternate character repertoire is the set of codepoints,
representable by the file system, most typically UCS-4.
Individual file system implementations may have more restricted
character repertoires, as for example file system that only are
capable of storing names consisting of UCS-2 characters. When this
is the case, and the character repertoire is not restricted to
single-byte characters, characters not within that repertoire are
treated as prohibited and the error NFS4ERR_BADCHAR is returned by
the server when that character is encountered.
Strings are intended to be in UTF-8 format and servers SHOULD return
NFS4ERR_INVAL, as discussed above, when the characters sent are not
valid UTF-8. When the character repertoire consists of single-byte
characters, UTF-8 is not enforced. Such situations should be
restricted to those where use is within a restricted environment
where a single character mapping locale can be administratively
enforced, allowing a file name to be treated as a string of bytes,
rather than as a string of characters. Such an arrangement might be
necessary when NFS version 4 access to a file system containing names
which are not valid UTF-8 needs to be provided.
However, in any of the following situations, file names have to be
treated as strings of Unicode characters and servers MUST return
NFS4ERR_INVAL when file names that are not in UTF-8 format:
o Case-insensitive comparisons are specified by the file system and
any characters sent contain non-ASCII byte codes.
o Any normalization constraints are enforced by the server or file
system implementation.
o The server accepts a given name when creating a file and reports a
different one when the directory is being examined.
Much of the discussion below regarding normalization and silent
deletion of characters within component4 strings is not applicable
when the server does not enforce UTF-8 component4 strings and treats
them as strings of bytes. A client may determine that a given
filesystem is operating in this mode by performing a LOOKUP using a
non-UTF-8 string, if NFS4ERR_INVAL is not returned, then name
components will be treated as opaque and those sorts of modifications
will not be seen.
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12.7.1.3. Case-based Mapping Used for Component4 Strings
Case-based mapping is not always a required part of server processing
of name components. However, if the NFS version 4 file server
supports the case_insensitive file system attribute, and if the
case_insensitive attribute is true for a given file system, the NFS
version 4 server MUST use the Unicode case mapping tables for the
version of Unicode corresponding to the character repertoire. In the
case where the character repertoire is UCS-2 or UCS-4, the case
mapping tables from the latest available version of Unicode SHOULD be
used.
If the case_preserving attribute is present and set to false, then
the NFS version 4 server MUST use the corresponding Unicode case
mapping table to map case when processing component4 strings.
Whether the server maps from lower to upper case or the upper to
lower case is a matter for implementation choice.
Stringprep Table B.2 should not be used for these purpose since it is
limited to Unicode version 3.2 and also because it erroneously maps
the German ligature eszett to the string "ss", whereas later versions
of Unicode contain both lower-case and upper-case versions of Eszett
(SMALL LETTER SHARP S and CAPITAL LETTER SHARP S).
Clients should be aware that servers may have mapped SMALL LETTER
SHARP S to the string "ss" when case-insensitive mapping is in
effect, with result that file whose name contains SMALL LETTER SHARP
S may have that character replaced by "ss" or "SS".
12.7.1.4. Other Mapping Used for Component4 Strings
Other than for issues of case mapping, an NFS version 4 server SHOULD
limit visible (i.e., those that change the name of file to reflect
those mappings to those from from a subset of the stringprep table
B.1. Note particularly, the mapings from U+200C and U+200D to the
empty string should be avoided, due to their undesirable effect on
some strings in Farsi.
Table B.1 may be used but it should be used only if required by the
local file system implementation. For example, if the file system in
question accepts file names containing the MONGOLIAN TODO SOFT HYPHEN
character (U+1806) and they are distinct from the corresponding file
names with this character removed, then using Table B.1 will cause
functional problems when clients attempt to interact with that file
system. The NFS version 4 server implementation including the
filesystem MUST NOT silently remove characters not within Table B.1.
If an implementation wishes to eliminate other characters because it
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is believed that allowing component name versions that both include
the character and do not have while otherwise the same, will
contribute to confusion, it has two options:
o Treat the characters as prohibited and return NFS4ERR_BADCHAR.
o Eliminate the character as part of the name matching processing,
while retaining it when a file is created. This would be
analogous to file systems that are both case-insensitive and case-
preserving,as dicussed above, or those which are both
normalization-insensitive and normalization-preserving, as
discussed below. The handling will be insensitive to the presence
of the chosen characters while preserving the presence or absence
of such characters within names.
Note that the second of these choices is a desirable way to handle
characters within table B.1, again with the exception of U+200C and
U+200D, which can cause issues for Farsi.
In addition to modification due to normalization, discussed below,
clients have to be able to deal with name modifications and other
consequences of character mapping on the server, as discussed above.
12.7.1.5. Normalization Issues for Component Strings
The issues are best discussed separately for the server and the
client. It is important to note that the server and client may have
different approaches to this area, and that the server choice may not
match the client operating environment. The issue of mismatches and
how they may be best dealt with by the client is discussed in a later
section.
12.7.1.5.1. Server Normalization Issues for Component Strings
The NFS version 4 does not specify required use of a particular
normalization form for component4 strings. Therefore, the server may
receive unnormalized strings or strings that reflect either
normalization form within protocol requests and responses. If the
file system requires normalization, then the server implementation
must normalize component4 strings within the protocol server before
presenting the information to the local file system.
With regard to normalization, servers have the following choices,
with the possibility that different choices may be selected for
different file systems.
o Implement a particular normalization form, either NFC, or NFD, in
which case file names received from a client are converted to that
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normalization form and as a consequence, the client will always
receive names in that normalization form. If this option is
chosen, then it is impossible to create two files in the same
directory that have different names which map to the same name
when normalized.
o Implement handling which is both normalization-insensitive and
normalization-preserving. This makes it impossible to create two
files in the same directory that have two different canonically
equivalent names, i.e., names which map to the same name when
normalized. However, unlike the previous option, clients will not
have the names that they present modified to meet the server's
normalization constraints.
o Implement normalization-sensitive handling without enforcing a
normalization form constraint on file names. This exposes the
client to the possibility that two files can be created in the
same directory which have different names which map to the same
name when normalized. This may be a significant issue when
clients which use different normalization forms are used on the
same file system, but this issue needs to be set against the
difficulty of providing other sorts of normalization handling for
some existing file systems.
12.7.1.5.2. Client Normalization Issues for Component Strings
The client, in processing name components, needs to deal with the
fact that the server may impose normalization on file name components
presented to it. As a result, a file can be created within a
directory and that name be different from that sent by the client due
to normalization at the server.
Client operating environments differ in their handling of canonically
equivalent names. Some environments treat canonically equivalent
strings as essentially equal and we will call these environments
normalization-aware. Others, because of the pattern of their
development with regard to these issues treat different strings as
different, even if they are canonically equivalent. We call these
normalization-unaware.
We discuss below issues that may arise when each of these types of
environments interact with the various types of file systems, with
regard to normalization handling. Note that complexity for the
client is increased given that there are no file system attributes to
determine the normalization handling present for that file system.
Where the client has the ability to create files (file system not
read-only and security allows it), attempting to create multiple
files with canonically equivalent names and looking at success
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paaaters and the names assigned by the server to these files can
serve as a way to determine the relevant information.
Normalization-aware environments interoperate most normally with
servers that either impose a given normalization form or those that
implement name handling which is both normalization-insensitive and
normalization-preserving name handling. However, clients need to be
prepared to interoperate with servers that have normalization-
sensitive file naming. In this situation, the client needs to be
prepared for the fact that a directory may contain multiple names
that it considers equivalent.
The following suggestions may be helpful in handling interoperability
issues for normalization-aware client environments, when they
interact with normalization-sensitive file systems.
When READDIR is done, the names returned may include names that do
not match the client's normalization form, but instead are other
names canonically equivalent to the normalized name.
When it can be determined that a normalization-insensitive server
file system is not involved, the client can simply normalize
filename components strings to its preferred normalization form.
When it cannot be determined that a normalization-insensitive
server file system is not involved, the client is generally best
advised to process incoming name components so as to allow all
name components in a canonical equivalence class to be together.
When only a single member of class exists, it should generally
mapped directly to the preferred normalization form, whether the
name was of that form or not.
When the client sees multiple names that are canonically
equivalent, it is clear you have a file systen which is
normalization sensitive. Clients should generally replace each
canonically equivalent name with one that appends some
distinguishing suffix, usually including a number. The numbers
should be assigned so that each distinct possible name with the
set of canonically equivalent names has an assigned numeric value.
Note that for some cases in which there are multiple instances of
strings that might be composed or decomposed and/or situations
with multiple diacritics to be applied to the same character, the
class might be large.
When interacting with a normalization-sensitive filesystem, it may
be that the environment contains clients or implementations local
to the OS in which the file system is embedded, which use a
different normalization form. In such situations, a LOOKUP may
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well fail, even though the directory contains a name canonically
equivalent to the name sought. One solution to this problem is to
re-do the LOOKUP in that situation with name converted to the
alternate normalization form.
In the case in which normalization-unaware clients are involved in
the mix, LOOKUP can fail and then the second lOOKUP, described
above can also fail, even though there may well be a oanonically
equivalent name in the directory. One possible approach in that
case is to use a READDIR to find the equivalent name and lookup
that, although this can greatly add to client implementation
complexity.
When interacting with a normalization-sensitive filesystem, the
situation where the environment contains clients or
implementations local to the OS in which the file system is
embedded, which use a different normalization form can also cause
issues when a file (or symlink or directory, etc.) is being
created. In such cases, you may be able to create an object of
the specified name even though, the directory contains a
canonically equivalent name. Similar issues can occur with LINK
and RENAME. The client can't really do much about such
sitautions, except be aware that they may occur. That's one of
the reasons normalization-sensitive server file system
implementations can be problematic to use when
internationalization issues are important.
Normalization-unaware environments interoperate most normally with
servers that implement normalization-sensitive file naming. However,
clients need to be prepared to interoperate with servers that impose
a given normalization form or that implement name handling which is
both normalization-insensitive and normalization-preserving. In the
former case, a file created with a given name may find it changed to
a different (although related name). In both cases, the client will
have to deal with the fact that it is unable to create two names
within a directory that are canonically equivalent.
Note that although the client implementation itself and the kernel
implementation may be normalization-unware, treating name components
as strings not subject to normalization, the environment as a whole
may be normalization-aware if commonly used libraries result in an
application environment where a single normalization form is used
throughout. Because of this, normalization-unaware environments may
be relatively rare.
The following suggestions may be helpful in handling interoperability
issues for truely normalization-unaware client environments, when
they interact with file systems other than those which are
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normalization-sensitive. The issues tend to be the inverse of those
for normalization-aware environments. The implementer should be
careful not to erroneously treat the environment as normalization-
unaware, based solely on the details of the kernel implementation.
Unless the file system is normalization-preserving, when files (or
other objects) are created, the object name as reported by a
READDIR of the associated directory may show a name different than
the one used to create the object. This behavior is something
that the client has to accept. Since it has no preferred
normalization form, it has no way of converting the name to a
preferred form.
In situations where there is an attempt to create multiple objects
in the same directory which have canonically-equivalent names.
these file systems will either report that an object of name
already exists or simply open a file of that other name.
If it desired to have those two obects in the same directory, the
names must be made not canonically equivalent. It is possible to
append some distinguishing character to the name of the second
object but in clients having a typical file API (such as POSIX),
the fact that the name change occurred cannot be propagated back
to the requester.
In cases where a client is application-specific, it may be
possible for it to deal with such a collision by modifying the
name and taking note of the changed name.
12.7.1.6. Prohibited Characters for Component Names
The NFS version 4 protocol does not specify particular characters
that may not appear in component names. File systems may have their
own set of prohibited characters for which the error NFS4ERR_BADCHAR
should be returned by the server. Clients need to be prepared for
this error to occur whenever file name components are presented to
the server.
Clients whose character repertoire for acceptable characters in file
name components is smaller than the entire scope of UCS-4 may need to
deal with names returned by the server that contain characters
outside that repertoire. It is up to the client whether it simply
ignores these files or modifies the name to meet its own rules for
acceptable names.
Clients may encounter names that do not consist of valid UTF-8, if
they interact with servers configured to allow this option. They are
not required to deal with this case and may treat the server as not
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functioning correctly, or they may handle this as normal. Clients
will normally make this a configuration option. As discussed above,
a client can determine whether a particular file system is being
supported by the server in this mode by issuing a LOOKUP specifying a
name which is not valid UTF-8 and seeing if NFS4ERR_INVAL is
returned.
12.7.1.7. Bidirectional String Checking for Component Names
The NFS version 4 protocol does not require processing of component
names to check for and reject bidirectional strings. Such processing
may be a part of the file system implementation but if so, its
particular form will be defined by the file system implementation.
When strings are rejected on this basis, the error NFS4ERR_BADNAME
would be returned.
Clients need to be prepared for the fact that the server may reject a
file name component if it consists of a bidirectional string,
returning NFS4ERR_BADNAME.
Clients may encounter names with bidirectional strings returned in
responses from the server. If clients treat such strings as not
valid file name components, it is up to the client whether it simply
ignores these files or modifies the name component to meet its own
rules for acceptable name component strings.
12.7.2. Processing of Link Text
Symbolic link text is defined as utf8val_should and therefore the
server SHOULD validate link text on a CREATE and return NFS4ERR_INVAL
if it is is not valid UTF-8. Note that file systems which treat
names as strings of byte are an exception for which such validation
need not be done. One other situation in which an NFS version 4
might choose (or be configured) not to make such a check is when
links within file system reference names in another which is
configured to treat names as strings of bytes.
On the other hand, UTF-8 validation of symbolic link text need not be
done on the data resulting from a READLINK. Such data might have
been stored by an NFS Version 4 server configured to allow non-UTF-8
link text or it might have resulted from symbolic link text stored
via local file system access or access via another remote file access
protocol.
Note that because of the role of the symbolic link, as data stored
and read by the user, other sorts of validations or modifications
should not be done. Note that when component names with the symbolic
link text are used, such checks and modifications will be done at
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that time. In particular,
o Limitation of the character repertoire MUST NOT be done. This
includes limitations to reflect a particular version of unicode,
or the inability of any particualr file system to store characters
beyond UCS-2.
o Name mapping, whether for case folding or otherwise MUST NOT be
done.
o Checks for a type of normalization or normalization to a
particular form MUST NOT be done.
o Checks for specific characters excluded by the server or file
system MUST NOT be done.
o Checks for bidrectional strings MUST NOT be done.
12.7.3. Processing of Principal Prefixes
As mentioned above, users and groups are designated as a particular
string at a specified domain. Servers will recognize a set of valid
principals for one or more domains. With regard to the handling of
these strings, the following rules MUST be followed
o The string MUST be checked by the server for valid UTF-8 and the
error NFS4ERR_INVAL returned if it is not valid.
o The character repertoire for the principal prefix string should be
limited to a current version of Unicode when the server is
implemented. However, the client cannot be assured that all
characters it receives as part of a user or group attribute are
those that are defined in the Unicode version it expects to work
with.
o No character mapping is to be done, as for example table B.1 in
stringprep, and no case mapping is to be done. The user and group
names are to be treated as case-sensitive.
o Strings must not be rejected based on their normalization.
Servers should do normalization insensitive matching in converting
a user to group to an internal id. The client cannot assume that
the server preserves normalization so a user set to one string
value may be returned as a string which differs in nomralization
and the client must be prepared to deal with that, by, for
example, normalizing the string to the client's prferred form.
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o There are no checks for specific invalid characters but servers
may limit the characters, with the result that any principal
presented by the client which has such a characters is treated as
invalid.
o Specific checks for bidrectional strings are not done but servers
may limit the principal prefix strings to those which are
unidirectional or are of a certain direction, with the result that
any principal presented by the client which done not meet that
criterion will be treated as invaid.
13. 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.
13.1. Error Definitions
Protocol Error Definitions
+-----------------------------+--------+-------------------+
| Error | Number | Description |
+-----------------------------+--------+-------------------+
| NFS4_OK | 0 | Section 13.1.3.1 |
| NFS4ERR_ACCESS | 13 | Section 13.1.6.1 |
| NFS4ERR_ATTRNOTSUPP | 10032 | Section 13.1.11.1 |
| NFS4ERR_ADMIN_REVOKED | 10047 | Section 13.1.5.1 |
| NFS4ERR_BADCHAR | 10040 | Section 13.1.7.1 |
| NFS4ERR_BADHANDLE | 10001 | Section 13.1.2.1 |
| NFS4ERR_BADNAME | 10041 | Section 13.1.7.2 |
| NFS4ERR_BADOWNER | 10039 | Section 13.1.11.2 |
| NFS4ERR_BADTYPE | 10007 | Section 13.1.4.1 |
| NFS4ERR_BADXDR | 10036 | Section 13.1.1.1 |
| NFS4ERR_BAD_COOKIE | 10003 | Section 13.1.1.2 |
| NFS4ERR_BAD_RANGE | 10042 | Section 13.1.8.1 |
| NFS4ERR_BAD_SEQID | 10026 | Section 13.1.8.2 |
| NFS4ERR_BAD_STATEID | 10025 | Section 13.1.5.2 |
| NFS4ERR_CLID_INUSE | 10017 | Section 13.1.10.1 |
| NFS4ERR_DEADLOCK | 10045 | Section 13.1.8.3 |
| NFS4ERR_DELAY | 10008 | Section 13.1.1.3 |
| NFS4ERR_DENIED | 10010 | Section 13.1.8.4 |
| NFS4ERR_DQUOT | 69 | Section 13.1.4.2 |
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| NFS4ERR_EXIST | 17 | Section 13.1.4.3 |
| NFS4ERR_EXPIRED | 10011 | Section 13.1.5.3 |
| NFS4ERR_FBIG | 27 | Section 13.1.4.4 |
| NFS4ERR_FHEXPIRED | 10014 | Section 13.1.2.2 |
| NFS4ERR_FILE_OPEN | 10046 | Section 13.1.4.5 |
| NFS4ERR_GRACE | 10013 | Section 13.1.9.1 |
| NFS4ERR_INVAL | 22 | Section 13.1.1.4 |
| NFS4ERR_IO | 5 | Section 13.1.4.6 |
| NFS4ERR_ISDIR | 21 | Section 13.1.2.3 |
| NFS4ERR_LEASE_MOVED | 10031 | Section 13.1.5.4 |
| NFS4ERR_LOCKED | 10012 | Section 13.1.8.5 |
| NFS4ERR_LOCKS_HELD | 10037 | Section 13.1.8.6 |
| NFS4ERR_LOCK_NOTSUPP | 10043 | Section 13.1.8.7 |
| NFS4ERR_LOCK_RANGE | 10028 | Section 13.1.8.8 |
| NFS4ERR_MINOR_VERS_MISMATCH | 10021 | Section 13.1.3.2 |
| NFS4ERR_MLINK | 31 | Section 13.1.4.7 |
| NFS4ERR_MOVED | 10019 | Section 13.1.2.4 |
| NFS4ERR_NAMETOOLONG | 63 | Section 13.1.7.3 |
| NFS4ERR_NOENT | 2 | Section 13.1.4.8 |
| NFS4ERR_NOFILEHANDLE | 10020 | Section 13.1.2.5 |
| NFS4ERR_NOSPC | 28 | Section 13.1.4.9 |
| NFS4ERR_NOTDIR | 20 | Section 13.1.2.6 |
| NFS4ERR_NOTEMPTY | 66 | Section 13.1.4.10 |
| NFS4ERR_NOTSUPP | 10004 | Section 13.1.1.5 |
| NFS4ERR_NOT_SAME | 10027 | Section 13.1.11.3 |
| NFS4ERR_NO_GRACE | 10033 | Section 13.1.9.2 |
| NFS4ERR_NXIO | 6 | Section 13.1.4.11 |
| NFS4ERR_OLD_STATEID | 10024 | Section 13.1.5.5 |
| NFS4ERR_OPENMODE | 10038 | Section 13.1.8.9 |
| NFS4ERR_OP_ILLEGAL | 10044 | Section 13.1.3.3 |
| NFS4ERR_PERM | 1 | Section 13.1.6.2 |
| NFS4ERR_RECLAIM_BAD | 10034 | Section 13.1.9.3 |
| NFS4ERR_RECLAIM_CONFLICT | 10035 | Section 13.1.9.4 |
| NFS4ERR_RESOURCE | 10018 | Section 13.1.3.4 |
| NFS4ERR_RESTOREFH | 10030 | Section 13.1.4.12 |
| NFS4ERR_ROFS | 30 | Section 13.1.4.13 |
| NFS4ERR_SAME | 10009 | Section 13.1.11.4 |
| NFS4ERR_SERVERFAULT | 10006 | Section 13.1.1.6 |
| NFS4ERR_STALE | 70 | Section 13.1.2.7 |
| NFS4ERR_STALE_CLIENTID | 10022 | Section 13.1.10.2 |
| NFS4ERR_STALE_STATEID | 10023 | Section 13.1.5.6 |
| NFS4ERR_SYMLINK | 10029 | Section 13.1.2.8 |
| NFS4ERR_TOOSMALL | 10005 | Section 13.1.1.7 |
| NFS4ERR_WRONGSEC | 10016 | Section 13.1.6.3 |
| NFS4ERR_XDEV | 18 | Section 13.1.4.14 |
+-----------------------------+--------+-------------------+
Table 8
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13.1.1. General Errors
This section deals with errors that are applicable to a broad set of
different purposes.
13.1.1.1. NFS4ERR_BADXDR (Error Code 10036)
The arguments for this operation do not match those specified in the
XDR definition. This includes situations in which the request ends
before all the arguments have been seen. Note that this error
applies when fixed enumerations (these include booleans) have a value
within the input stream which is not valid for the enum. A replier
may pre-parse all operations for a Compound procedure before doing
any operation execution and return RPC-level XDR errors in that case.
13.1.1.2. NFS4ERR_BAD_COOKIE (Error Code 10003)
Used for operations that provide a set of information indexed by some
quantity provided by the client or cookie sent by the server for an
earlier invocation. Where the value cannot be used for its intended
purpose, this error results.
13.1.1.3. 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 RPC transaction ID.
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. After delaying for period of time, the client can then
re-send the operation in question.
13.1.1.4. NFS4ERR_INVAL (Error Code 22)
The arguments for this operation are not valid for some reason, even
though they do match those specified in the XDR definition for the
request.
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13.1.1.5. 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 MUST
NOT be implemented in the current minor version.
13.1.1.6. 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.
13.1.1.7. 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.
13.1.2. 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.
13.1.2.1. 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.
13.1.2.2. 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.
13.1.2.3. 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.
13.1.2.4. 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
attribute for the current filehandle. For further discussion, refer
to Section 7
13.1.2.5. 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).
13.1.2.6. 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.
13.1.2.7. 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.
13.1.2.8. 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.
13.1.3. 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.
There are a number of basic constraints on the operations that may
appear in a Compound request.
13.1.3.1. NFS_OK (Error code 0)
Indicates the operation completed successfully, in that all of the
constituent operations completed without error.
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13.1.3.2. 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.
13.1.3.3. NFS4ERR_OP_ILLEGAL (Error Code 10044)
The operation code is not a valid one for the current Compound
procedure. The opcode in the result stream matched with this error
is the ILLEGAL value, although the value that appears in the request
stream may be different. Where an illegal value appears and the
replier pre-parses all operations for a Compound procedure before
doing any operation execution, an RPC-level XDR error may be returned
in this case.
13.1.3.4. NFS4ERR_RESOURCE (Error Code 10018)
For the processing of the Compound procedure, the server may exhaust
available resources and can not continue processing operations within
the Compound procedure. This error will be returned from the server
in those instances of resource exhaustion related to the processing
of the Compound procedure.
13.1.4. 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.
13.1.4.1. 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.
13.1.4.2. NFS4ERR_DQUOT (Error Code 19)
Resource (quota) hard limit exceeded. The user's resource limit on
the server has been exceeded.
13.1.4.3. NFS4ERR_EXIST (Error Code 17)
A file of the specified target name (when creating, renaming or
linking) already exists.
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13.1.4.4. NFS4ERR_FBIG (Error Code 27)
File too large. The operation would have caused a file to grow
beyond the server's limit.
13.1.4.5. 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.
13.1.4.6. NFS4ERR_IO (Error Code 5)
Indicates that an I/O error occurred for which the file system was
unable to provide recovery.
13.1.4.7. 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.
13.1.4.8. NFS4ERR_NOENT (Error Code 2)
Indicates no such file or directory. The file or directory name
specified does not exist.
13.1.4.9. 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.
13.1.4.10. NFS4ERR_NOTEMPTY (Error Code 66)
An attempt was made to remove a directory that was not empty.
13.1.4.11. NFS4ERR_NXIO (Error Code 5)
I/O error. No such device or address.
13.1.4.12. NFS4ERR_RESTOREFH (Error Code 10030)
The RESTOREFH operation does not have a saved filehandle (identified
by SAVEFH) to operate upon.
13.1.4.13. NFS4ERR_ROFS (Error Code 30)
Indicates a read-only file system. A modifying operation was
attempted on a read-only file system.
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13.1.4.14. 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 file systems (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.
13.1.5. 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.
13.1.5.1. 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.
13.1.5.2. NFS4ERR_BAD_STATEID (Error Code 10026)
A stateid generated by the current server instance, but which does
not designate any locking state (either current or superseded) for a
current lockowner-file pair, was used.
13.1.5.3. 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.
13.1.5.4. NFS4ERR_LEASE_MOVED (Error Code 10031)
A lease being renewed is associated with a file system that has been
migrated to a new server.
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13.1.5.5. 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.
13.1.5.6. NFS4ERR_STALE_STATEID (Error Code 10023)
A stateid generated by an earlier server instance was used.
13.1.6. Security Errors
These are the various permission-related errors in NFSv4.1.
13.1.6.1. 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 13.1.6.2), which restricts itself to owner or
privileged user permission failures.
13.1.6.2. 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.
13.1.6.3. NFS4ERR_WRONGSEC (Error Code 10016)
Indicates that the security mechanism being used by the client for
the operation does not match the server's security policy. The
client should change the security mechanism being used and re-send
the operation. SECINFO can be used to determine the appropriate
mechanism.
13.1.7. Name Errors
Names in NFSv4 are UTF-8 strings. When the strings are not are of
length zero, the error NFS4ERR_INVAL results. When they are not
valid UTF-8 the error NFS4ERR_INVAL also results, but servers may
accommodate file systems with different character formats and not
return this error. Besides this, there are a number of other errors
to indicate specific problems with names.
13.1.7.1. 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.
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13.1.7.2. 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.
This error should not be returned due a normalization issue in a
string. When a file system keeps names in a particular normalization
form, it is the server's responsiblity to do the approproriate
normalization, rather than rejecting the name.
13.1.7.3. NFS4ERR_NAMETOOLONG (Error Code 63)
Returned when the filename in an operation exceeds the server's
implementation limit.
13.1.8. 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.
13.1.8.1. 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. E.g., this error
results when a server which only supports 32-bit ranges receives a
range that cannot be handled by that server. (See Section 15.12.4).
13.1.8.2. NFS4ERR_BAD_SEQID (Error Code 10026)
The sequence number (seqid) in a locking request is neither the next
expected number or the last number processed.
13.1.8.3. NFS4ERR_DEADLOCK (Error Code 10045)
The server has been able to determine a file locking deadlock
condition for a blocking lock request.
13.1.8.4. NFS4ERR_DENIED (Error Code 10010)
An attempt to lock a file is denied. Since this may be a temporary
condition, the client is encouraged to re-send the lock request until
the lock is accepted. See Section 9.4 for a discussion of the re-
send.
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13.1.8.5. 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.
13.1.8.6. NFS4ERR_LOCKS_HELD (Error Code 10037)
An operation was prevented by the unexpected presence of locks.
13.1.8.7. 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.
13.1.8.8. 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 15.12.5, Section 15.13.5, and Section 15.14.5 for a
discussion of how this applies to LOCK, LOCKT, and LOCKU
respectively.
13.1.8.9. 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).
13.1.9. Reclaim Errors
These errors relate to the process of reclaiming locks after a server
restart.
13.1.9.1. 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.
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13.1.9.2. 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. As a result, the server can not guarantee that
conflicting state has not been provided to another client.
13.1.9.3. 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.
13.1.9.4. 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.
13.1.10. Client Management Errors
This sections deals with errors associated with requests used to
create and manage client IDs.
13.1.10.1. NFS4ERR_CLID_INUSE (Error Code 10017)
The SETCLIENTID operation has found that a client id is already in
use by another client.
13.1.10.2. NFS4ERR_STALE_CLIENTID (Error Code 10022)
A clientid not recognized by the server was used in a locking or
SETCLIENTID_CONFIRM request.
13.1.11. Attribute Handling Errors
This section deals with errors specific to attribute handling within
NFSv4.
13.1.11.1. NFS4ERR_ATTRNOTSUPP (Error Code 10032)
An attribute specified is not supported by the server. This error
MUST NOT be returned by the GETATTR operation.
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13.1.11.2. 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.
13.1.11.3. 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.
13.1.11.4. 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.
13.2. 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 except ILLEGAL.
Valid error returns for each protocol operation
+---------------------+---------------------------------------------+
| Operation | Errors |
+---------------------+---------------------------------------------+
| ACCESS | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| CLOSE | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_ISDIR, |
| | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCKS_HELD, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
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| COMMIT | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_RESOURCE, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK |
| CREATE | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADNAME, NFS4ERR_BADOWNER, |
| | NFS4ERR_BADTYPE, NFS4ERR_BADXDR, |
| | NFS4ERR_DELAY, NFS4ERR_DQUOT, |
| | NFS4ERR_EXIST, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_NOTDIR, |
| | NFS4ERR_PERM, NFS4ERR_RESOURCE, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE |
| DELEGPURGE | NFS4ERR_BADXDR, NFS4ERR_NOTSUPP, |
| | NFS4ERR_LEASE_MOVED, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE_CLIENTID |
| DELEGRETURN | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_BADXDR, NFS4ERR_EXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOTSUPP, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_STALE_STATEID |
| GETATTR | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| GETFH | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE |
| ILLEGAL | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL |
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| LINK | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_DQUOT, NFS4ERR_EXIST, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, |
| | NFS4ERR_MLINK, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_NOTDIR, NFS4ERR_NOTSUPP, |
| | NFS4ERR_RESOURCE, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_WRONGSEC, NFS4ERR_XDEV |
| LOCK | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BAD_RANGE, |
| | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_BADXDR, NFS4ERR_DEADLOCK, |
| | NFS4ERR_DELAY, NFS4ERR_DENIED, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, |
| | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_LOCK_NOTSUPP, NFS4ERR_LOCK_RANGE, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OPENMODE, NFS4ERR_RECLAIM_BAD, |
| | NFS4ERR_RECLAIM_CONFLICT, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_CLIENTID, |
| | NFS4ERR_STALE_STATEID |
| LOCKT | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BAD_RANGE, NFS4ERR_BADXDR, |
| | NFS4ERR_DELAY, NFS4ERR_DENIED, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_ISDIR, |
| | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCK_RANGE, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_STALE_CLIENTID |
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| LOCKU | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BAD_RANGE, |
| | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_BADXDR, NFS4ERR_EXPIRED, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_ISDIR, |
| | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCK_RANGE, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
| LOOKUP | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_SYMLINK, |
| | NFS4ERR_WRONGSEC |
| LOOKUPP | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_SYMLINK, |
| | NFS4ERR_WRONGSEC |
| NVERIFY | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_SAME, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
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| OPEN | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADOWNER, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DELAY, NFS4ERR_DQUOT, |
| | NFS4ERR_EXIST, NFS4ERR_EXPIRED, |
| | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_ISDIR, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_NOTDIR, NFS4ERR_NOTSUP, |
| | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_PERM, NFS4ERR_RECLAIM_BAD, |
| | NFS4ERR_RECLAIM_CONFLICT, NFS4ERR_RESOURCE, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_SHARE_DENIED, NFS4ERR_STALE, |
| | NFS4ERR_STALE_CLIENTID, NFS4ERR_SYMLINK, |
| | NFS4ERR_WRONGSEC |
| OPENATTR | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_DQUOT, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_NOTSUPP, NFS4ERR_RESOURCE, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE |
| OPEN_CONFIRM | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_BADXDR, NFS4ERR_EXPIRED, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
| OPEN_DOWNGRADE | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_SEQID, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, NFS4ERR_RESOURCE, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_STALE_STATEID |
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| PUTFH | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_MOVED, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_WRONGSEC |
| PUTPUBFH | NFS4ERR_DELAY, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_WRONGSEC |
| PUTROOTFH | NFS4ERR_DELAY, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_WRONGSEC |
| READ | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OPENMODE, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID, NFS4ERR_SYMLINK |
| READDIR | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_COOKIE, |
| | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_NOT_SAME, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOOSMALL |
| READLINK | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, |
| | NFS4ERR_MOVED, NFS4ERR_NOTSUP, |
| | NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| RELEASE_LOCKOWNER | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR, |
| | NFS4ERR_EXPIRED, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_LOCKS_HELD, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE_CLIENTID |
| REMOVE | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADXDR, 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_RESOURCE, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
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| RENAME | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADXDR, 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_RESOURCE, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_WRONGSEC, |
| | NFS4ERR_XDEV |
| RENEW | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADXDR, NFS4ERR_CB_PATH_DOWN, |
| | NFS4ERR_EXPIRED, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE_CLIENTID |
| RESTOREFH | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_MOVED, NFS4ERR_RESOURCE, |
| | NFS4ERR_RESTOREFH, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_WRONGSEC |
| SAVEFH | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE |
| SECINFO | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG, |
| | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOTDIR, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
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| SETATTR | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADOWNER, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_DELAY, NFS4ERR_DQUOT, |
| | NFS4ERR_EXPIRED, NFS4ERR_FBIG, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, |
| | NFS4ERR_LEASE_MOVED, NFS4ERR_LOCKED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OPENMODE, NFS4ERR_PERM, |
| | NFS4ERR_RESOURCE, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
| SETCLIENTID | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE, |
| | NFS4ERR_DELAY, NFS4ERR_INVAL, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT |
| SETCLIENTID_CONFIRM | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE, |
| | NFS4ERR_DELAY, NFS4ERR_RESOURCE, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE_CLIENTID |
| VERIFY | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOT_SAME, |
| | NFS4ERR_RESOURCE, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE |
| WRITE | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADXDR, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY, |
| | NFS4ERR_DQUOT, NFS4ERR_EXPIRED, |
| | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_NXIO, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OPENMODE, NFS4ERR_RESOURCE, |
| | NFS4ERR_ROFS, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_STALE_STATEID, |
| | NFS4ERR_SYMLINK |
+---------------------+---------------------------------------------+
Table 9
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13.3. 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 | Errors |
| Operation | |
+-------------+-----------------------------------------------------+
| CB_GETATTR | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_INVAL, NFS4ERR_SERVERFAULT |
| CB_ILLEGAL | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL |
| CB_RECALL | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY, |
| | NFS4ERR_SERVERFAULT |
+-------------+-----------------------------------------------------+
Table 10
13.4. Errors and the operations that use them
+--------------------------+----------------------------------------+
| Error | Operations |
+--------------------------+----------------------------------------+
| NFS4ERR_ACCESS | ACCESS, COMMIT, CREATE, GETATTR, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, LOOKUPP, |
| | NVERIFY, OPEN, OPENATTR, READ, |
| | READDIR, READLINK, REMOVE, RENAME, |
| | RENEW, SECINFO, SETATTR, VERIFY, WRITE |
| NFS4ERR_ADMIN_REVOKED | CLOSE, DELEGRETURN, LOCK, LOCKU, OPEN, |
| | OPEN_CONFIRM, OPEN_DOWNGRADE, READ, |
| | RELEASE_LOCKOWNER, RENEW, SETATTR, |
| | WRITE |
| NFS4ERR_ATTRNOTSUPP | CREATE, NVERIFY, OPEN, SETATTR, VERIFY |
| NFS4ERR_BADCHAR | CREATE, LINK, LOOKUP, NVERIFY, OPEN, |
| | REMOVE, RENAME, SECINFO, SETATTR, |
| | VERIFY |
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| NFS4ERR_BADHANDLE | ACCESS, CB_GETATTR, CB_RECALL, CLOSE, |
| | COMMIT, CREATE, GETATTR, GETFH, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, LOOKUPP, |
| | NVERIFY, OPEN, OPENATTR, OPEN_CONFIRM, |
| | OPEN_DOWNGRADE, PUTFH, READ, READDIR, |
| | READLINK, REMOVE, RENAME, RESTOREFH, |
| | SAVEFH, SECINFO, SETATTR, VERIFY, |
| | WRITE |
| NFS4ERR_BADNAME | CREATE, LINK, LOOKUP, OPEN, REMOVE, |
| | RENAME, SECINFO |
| NFS4ERR_BADOWNER | CREATE, OPEN, SETATTR |
| NFS4ERR_BADTYPE | CREATE |
| NFS4ERR_BADXDR | ACCESS, CB_GETATTR, CB_ILLEGAL, |
| | CB_RECALL, CLOSE, COMMIT, CREATE, |
| | DELEGPURGE, DELEGRETURN, GETATTR, |
| | ILLEGAL, LINK, LOCK, LOCKT, LOCKU, |
| | LOOKUP, NVERIFY, OPEN, OPENATTR, |
| | OPEN_CONFIRM, OPEN_DOWNGRADE, PUTFH, |
| | READ, READDIR, RELEASE_LOCKOWNER, |
| | REMOVE, RENAME, RENEW, SECINFO, |
| | SETATTR, SETCLIENTID, |
| | SETCLIENTID_CONFIRM, VERIFY, WRITE |
| NFS4ERR_BAD_COOKIE | READDIR |
| NFS4ERR_BAD_RANGE | LOCK, LOCKT, LOCKU |
| NFS4ERR_BAD_SEQID | CLOSE, LOCK, LOCKU, OPEN, |
| | OPEN_CONFIRM, OPEN_DOWNGRADE |
| NFS4ERR_BAD_STATEID | CB_RECALL, CLOSE, DELEGRETURN, LOCK, |
| | LOCKU, OPEN, OPEN_CONFIRM, |
| | OPEN_DOWNGRADE, READ, SETATTR, WRITE |
| NFS4ERR_CB_PATH_DOWN | RENEW |
| NFS4ERR_CLID_INUSE | SETCLIENTID, SETCLIENTID_CONFIRM |
| NFS4ERR_DEADLOCK | LOCK |
| NFS4ERR_DELAY | ACCESS, CB_GETATTR, CB_RECALL, CLOSE, |
| | CREATE, GETATTR, LINK, LOCK, LOCKT, |
| | LOOKUPP, NVERIFY, OPEN, OPENATTR, |
| | OPEN_DOWNGRADE, PUTFH, PUTPUBFH, |
| | PUTROOTFH, READ, READDIR, READLINK, |
| | REMOVE, RENAME, SECINFO, SETATTR, |
| | SETCLIENTID, SETCLIENTID_CONFIRM, |
| | VERIFY, WRITE |
| NFS4ERR_DENIED | LOCK, LOCKT |
| NFS4ERR_DQUOT | CREATE, LINK, OPEN, OPENATTR, RENAME, |
| | SETATTR, WRITE |
| NFS4ERR_EXIST | CREATE, LINK, OPEN, RENAME |
| NFS4ERR_EXPIRED | CLOSE, DELEGRETURN, LOCK, LOCKU, OPEN, |
| | OPEN_CONFIRM, OPEN_DOWNGRADE, READ, |
| | RELEASE_LOCKOWNER, RENEW, SETATTR, |
| | WRITE |
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| NFS4ERR_FBIG | OPEN, SETATTR, WRITE |
| NFS4ERR_FHEXPIRED | ACCESS, CLOSE, COMMIT, CREATE, |
| | GETATTR, GETFH, LINK, LOCK, LOCKT, |
| | LOCKU, LOOKUP, LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_CONFIRM, |
| | OPEN_DOWNGRADE, PUTFH, READ, READDIR, |
| | READLINK, REMOVE, RENAME, RESTOREFH, |
| | SAVEFH, SECINFO, SETATTR, VERIFY, |
| | WRITE |
| NFS4ERR_FILE_OPEN | LINK, REMOVE, RENAME |
| NFS4ERR_GRACE | GETATTR, LOCK, LOCKT, LOCKU, NVERIFY, |
| | OPEN, READ, REMOVE, RENAME, SETATTR, |
| | VERIFY, WRITE |
| NFS4ERR_INVAL | ACCESS, CB_GETATTR, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, GETATTR, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, NVERIFY, |
| | OPEN, OPEN_CONFIRM, OPEN_DOWNGRADE, |
| | READ, READDIR, READLINK, REMOVE, |
| | RENAME, SECINFO, SETATTR, SETCLIENTID, |
| | VERIFY, WRITE |
| NFS4ERR_IO | ACCESS, COMMIT, CREATE, GETATTR, LINK, |
| | LOOKUP, LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, READ, READDIR, READLINK, |
| | REMOVE, RENAME, SETATTR, VERIFY, WRITE |
| NFS4ERR_ISDIR | CLOSE, COMMIT, LINK, LOCK, LOCKT, |
| | LOCKU, OPEN, OPEN_CONFIRM, READ, |
| | READLINK, SETATTR, WRITE |
| NFS4ERR_LEASE_MOVED | CLOSE, DELEGPURGE, DELEGRETURN, LOCK, |
| | LOCKT, LOCKU, OPEN_CONFIRM, |
| | OPEN_DOWNGRADE, READ, |
| | RELEASE_LOCKOWNER, RENEW, SETATTR, |
| | WRITE |
| NFS4ERR_LOCKED | READ, SETATTR, WRITE |
| NFS4ERR_LOCKS_HELD | CLOSE, RELEASE_LOCKOWNER |
| NFS4ERR_LOCK_NOTSUPP | LOCK |
| NFS4ERR_LOCK_RANGE | LOCK, LOCKT, LOCKU |
| NFS4ERR_MLINK | LINK |
| NFS4ERR_MOVED | ACCESS, CLOSE, COMMIT, CREATE, |
| | DELEGRETURN, GETATTR, GETFH, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, LOOKUPP, |
| | NVERIFY, OPEN, OPENATTR, OPEN_CONFIRM, |
| | OPEN_DOWNGRADE, PUTFH, READ, READDIR, |
| | READLINK, REMOVE, RENAME, RESTOREFH, |
| | SAVEFH, SECINFO, SETATTR, VERIFY, |
| | WRITE |
| NFS4ERR_NAMETOOLONG | CREATE, LINK, LOOKUP, OPEN, REMOVE, |
| | RENAME, SECINFO |
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| NFS4ERR_NOENT | LINK, LOOKUP, LOOKUPP, OPEN, OPENATTR, |
| | REMOVE, RENAME, SECINFO |
| NFS4ERR_NOFILEHANDLE | ACCESS, CLOSE, COMMIT, CREATE, |
| | DELEGRETURN, GETATTR, GETFH, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, LOOKUPP, |
| | NVERIFY, OPEN, OPENATTR, OPEN_CONFIRM, |
| | OPEN_DOWNGRADE, READ, READDIR, |
| | READLINK, REMOVE, RENAME, SAVEFH, |
| | SECINFO, SETATTR, VERIFY, WRITE |
| NFS4ERR_NOSPC | CREATE, LINK, OPEN, OPENATTR, RENAME, |
| | SETATTR, WRITE |
| NFS4ERR_NOTDIR | CREATE, LINK, LOOKUP, LOOKUPP, OPEN, |
| | READDIR, REMOVE, RENAME, SECINFO |
| NFS4ERR_NOTEMPTY | REMOVE, RENAME |
| NFS4ERR_NOTSUP | OPEN, READLINK |
| NFS4ERR_NOTSUPP | DELEGPURGE, DELEGRETURN, LINK, |
| | OPENATTR |
| NFS4ERR_NOT_SAME | READDIR, VERIFY |
| NFS4ERR_NO_GRACE | LOCK, OPEN |
| NFS4ERR_NXIO | WRITE |
| NFS4ERR_OLD_STATEID | CLOSE, DELEGRETURN, LOCK, LOCKU, OPEN, |
| | OPEN_CONFIRM, OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
| NFS4ERR_OPENMODE | LOCK, READ, SETATTR, WRITE |
| NFS4ERR_OP_ILLEGAL | CB_ILLEGAL, ILLEGAL |
| NFS4ERR_PERM | CREATE, OPEN, SETATTR |
| NFS4ERR_RECLAIM_BAD | LOCK, OPEN |
| NFS4ERR_RECLAIM_CONFLICT | LOCK, OPEN |
| NFS4ERR_RESOURCE | ACCESS, CLOSE, COMMIT, CREATE, |
| | DELEGPURGE, DELEGRETURN, GETATTR, |
| | GETFH, LINK, LOCK, LOCKT, LOCKU, |
| | LOOKUP, LOOKUPP, OPEN, OPENATTR, |
| | OPEN_CONFIRM, OPEN_DOWNGRADE, READ, |
| | READDIR, READLINK, RELEASE_LOCKOWNER, |
| | REMOVE, RENAME, RENEW, RESTOREFH, |
| | SAVEFH, SECINFO, SETATTR, SETCLIENTID, |
| | SETCLIENTID_CONFIRM, VERIFY, WRITE |
| NFS4ERR_RESTOREFH | RESTOREFH |
| NFS4ERR_ROFS | COMMIT, CREATE, LINK, OPEN, OPENATTR, |
| | OPEN_DOWNGRADE, REMOVE, RENAME, |
| | SETATTR, WRITE |
| NFS4ERR_SAME | NVERIFY |
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| NFS4ERR_SERVERFAULT | ACCESS, CB_GETATTR, CB_RECALL, CLOSE, |
| | COMMIT, CREATE, DELEGPURGE, |
| | DELEGRETURN, GETATTR, GETFH, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, LOOKUPP, |
| | NVERIFY, OPEN, OPENATTR, OPEN_CONFIRM, |
| | OPEN_DOWNGRADE, PUTFH, PUTPUBFH, |
| | PUTROOTFH, READ, READDIR, READLINK, |
| | RELEASE_LOCKOWNER, REMOVE, RENAME, |
| | RENEW, RESTOREFH, SAVEFH, SECINFO, |
| | SETATTR, SETCLIENTID, |
| | SETCLIENTID_CONFIRM, VERIFY, WRITE |
| NFS4ERR_SHARE_DENIED | OPEN |
| NFS4ERR_STALE | ACCESS, CLOSE, COMMIT, CREATE, |
| | DELEGRETURN, GETATTR, GETFH, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, LOOKUPP, |
| | NVERIFY, OPEN, OPENATTR, OPEN_CONFIRM, |
| | OPEN_DOWNGRADE, PUTFH, READ, READDIR, |
| | READLINK, REMOVE, RENAME, RESTOREFH, |
| | SAVEFH, SECINFO, SETATTR, VERIFY, |
| | WRITE |
| NFS4ERR_STALE_CLIENTID | DELEGPURGE, LOCK, LOCKT, OPEN, |
| | RELEASE_LOCKOWNER, RENEW, |
| | SETCLIENTID_CONFIRM |
| NFS4ERR_STALE_STATEID | CLOSE, DELEGRETURN, LOCK, LOCKU, |
| | OPEN_CONFIRM, OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
| NFS4ERR_SYMLINK | COMMIT, LOOKUP, LOOKUPP, OPEN, READ, |
| | WRITE |
| NFS4ERR_TOOSMALL | READDIR |
| NFS4ERR_WRONGSEC | LINK, LOOKUP, LOOKUPP, OPEN, PUTFH, |
| | PUTPUBFH, PUTROOTFH, RENAME, RESTOREFH |
| NFS4ERR_XDEV | LINK, RENAME |
+--------------------------+----------------------------------------+
Table 11
14. NFS version 4 Requests
For the NFS version 4 RPC program, there are two traditional RPC
procedures: NULL and COMPOUND. All other functionality is defined as
a set of operations and these operations are defined in normal XDR/
RPC syntax and semantics. However, these operations are encapsulated
within the COMPOUND procedure. This requires that the client combine
one or more of the NFS version 4 operations into a single request.
The NFS4_CALLBACK program is used to provide server to client
signaling and is constructed in a similar fashion as the NFS version
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4 program. The procedures CB_NULL and CB_COMPOUND are defined in the
same way as NULL and COMPOUND are within the NFS program. The
CB_COMPOUND request also encapsulates the remaining operations of the
NFS4_CALLBACK program. There is no predefined RPC program number for
the NFS4_CALLBACK program. It is up to the client to specify a
program number in the "transient" program range. The program and
port number of the NFS4_CALLBACK program are provided by the client
as part of the SETCLIENTID/SETCLIENTID_CONFIRM sequence. The program
and port can be changed by another SETCLIENTID/SETCLIENTID_CONFIRM
sequence, and it is possible to use the sequence to change them
within a client incarnation without removing relevant leased client
state.
14.1. Compound Procedure
The COMPOUND procedure provides the opportunity for better
performance within high latency networks. The client can avoid
cumulative latency of multiple RPCs by combining multiple dependent
operations into a single COMPOUND procedure. A compound operation
may provide for protocol simplification by allowing the client to
combine basic procedures into a single request that is customized for
the client's environment.
The CB_COMPOUND procedure precisely parallels the features of
COMPOUND as described above.
The basic structure of the COMPOUND procedure is:
+-----+--------------+--------+-----------+-----------+-----------+--
| tag | minorversion | numops | op + args | op + args | op + args |
+-----+--------------+--------+-----------+-----------+-----------+--
and the reply's structure is:
+------------+-----+--------+-----------------------+--
|last status | tag | numres | status + op + results |
+------------+-----+--------+-----------------------+--
The numops and numres fields, used in the depiction above, represent
the count for the counted array encoding use to signify the number of
arguments or results encoded in the request and response. As per the
XDR encoding, these counts must match exactly the number of operation
arguments or results encoded.
14.2. Evaluation of a Compound Request
The server will process the COMPOUND procedure by evaluating each of
the operations within the COMPOUND procedure in order. Each
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component operation consists of a 32 bit operation code, followed by
the argument of length determined by the type of operation. The
results of each operation are encoded in sequence into a reply
buffer. The results of each operation are preceded by the opcode and
a status code (normally zero). If an operation results in a non-zero
status code, the status will be encoded and evaluation of the
compound sequence will halt and the reply will be returned. Note
that evaluation stops even in the event of "non error" conditions
such as NFS4ERR_SAME.
There are no atomicity requirements for the operations contained
within the COMPOUND procedure. The operations being evaluated as
part of a COMPOUND request may be evaluated simultaneously with other
COMPOUND requests that the server receives.
It is the client's responsibility for recovering from any partially
completed COMPOUND procedure. Partially completed COMPOUND
procedures may occur at any point due to errors such as
NFS4ERR_RESOURCE and NFS4ERR_DELAY. This may occur even given an
otherwise valid operation string. Further, a server reboot which
occurs in the middle of processing a COMPOUND procedure may leave the
client with the difficult task of determining how far COMPOUND
processing has proceeded. Therefore, the client should avoid overly
complex COMPOUND procedures in the event of the failure of an
operation within the procedure.
Each operation assumes a "current" and "saved" filehandle that is
available as part of the execution context of the compound request.
Operations may set, change, or return the current filehandle. The
"saved" filehandle is used for temporary storage of a filehandle
value and as operands for the RENAME and LINK operations.
14.3. Synchronous Modifying Operations
NFS version 4 operations that modify the filesystem are synchronous.
When an operation is successfully completed at the server, the client
can depend that any data associated with the request is now on stable
storage (the one exception is in the case of the file data in a WRITE
operation with the UNSTABLE option specified).
This implies that any previous operations within the same compound
request are also reflected in stable storage. This behavior enables
the client's ability to recover from a partially executed compound
request which may resulted from the failure of the server. For
example, if a compound request contains operations A and B and the
server is unable to send a response to the client, depending on the
progress the server made in servicing the request the result of both
operations may be reflected in stable storage or just operation A may
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be reflected. The server must not have just the results of operation
B in stable storage.
14.4. Operation Values
The operations encoded in the COMPOUND procedure are identified by
operation values. To avoid overlap with the RPC procedure numbers,
operations 0 (zero) and 1 are not defined. Operation 2 is not
defined but reserved for future use with minor versioning.
15. NFS version 4 Procedures
15.1. Procedure 0: NULL - No Operation
15.1.1. SYNOPSIS
<null>
15.1.2. ARGUMENT
void;
15.1.3. RESULT
void;
15.1.4. 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.
15.2. Procedure 1: COMPOUND - Compound Operations
15.2.1. SYNOPSIS
compoundargs -> compoundres
15.2.2. ARGUMENT
union nfs_argop4 switch (nfs_opnum4 argop) {
case <OPCODE>: <argument>;
...
};
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struct COMPOUND4args {
comptag4 tag;
uint32_t minorversion;
nfs_argop4 argarray<>;
};
15.2.3. RESULT
union nfs_resop4 switch (nfs_opnum4 resop) {
case <OPCODE>: <argument>;
...
};
struct COMPOUND4res {
nfsstat4 status;
comptag4 tag;
nfs_resop4 resarray<>;
};
15.2.4. 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. In this case, the error
NFS4ERR_RESOURCE will be returned for the particular operation within
the COMPOUND procedure where the resource exhaustion occurred. This
assumes that all previous operations within the COMPOUND sequence
have been evaluated successfully. The results for all of the
evaluated operations must be returned to the client.
The server will generally choose between two methods of decoding the
client's request. The first would be the traditional one-pass XDR
decode, in which decoding of the entire COMPOUND precedes execution
of any operation within it. If there is an XDR decoding error in
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this case, an 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 each of the individual operations, as
the server is ready to execute it. In this case, the server may
encounter an XDR decode error during such an operation decode, after
previous operations within the COMPOUND have been executed. In this
case, the server would return the error NFS4ERR_BADXDR to signify the
decode error.
The COMPOUND arguments contain a "minorversion" field. The initial
and default value for this field is 0 (zero). This field will be
used by future minor versions such that the client can communicate to
the server what minor version is being requested. If the server
receives a COMPOUND procedure with a minorversion field value that it
does not support, the server MUST return an error of
NFS4ERR_MINOR_VERS_MISMATCH and a zero length resultdata array.
Contained within the COMPOUND results is a "status" field. If the
results array length is non-zero, this status must be equivalent to
the status of the last operation that was executed within the
COMPOUND procedure. Therefore, if an operation incurred an error
then the "status" value will be the same error value as is being
returned for the operation that failed.
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
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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.
15.2.5. IMPLEMENTATION
Since an error of any type may occur after only a portion of the
operations have been evaluated, the client must be prepared to
recover from any failure. If the source of an NFS4ERR_RESOURCE error
was a complex or lengthy set of operations, it is likely that if the
number of operations were reduced the server would be able to
evaluate them successfully. Therefore, the client is responsible for
dealing with this type of complexity in recovery.
15.3. Operation 3: ACCESS - Check Access Rights
15.3.1. SYNOPSIS
(cfh), accessreq -> supported, accessrights
15.3.2. ARGUMENT
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;
};
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15.3.3. RESULT
struct ACCESS4resok {
uint32_t supported;
uint32_t access;
};
union ACCESS4res switch (nfsstat4 status) {
case NFS4_OK:
ACCESS4resok resok4;
default:
void;
};
15.3.4. 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
were 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 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).
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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.
15.3.5. 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 NFS version 2 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 NFS version 4
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.
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
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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.
15.4. Operation 4: CLOSE - Close File
15.4.1. SYNOPSIS
(cfh), seqid, open_stateid -> open_stateid
15.4.2. ARGUMENT
struct CLOSE4args {
/* CURRENT_FH: object */
seqid4 seqid;
stateid4 open_stateid;
};
15.4.3. RESULT
union CLOSE4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 open_stateid;
default:
void;
};
15.4.4. DESCRIPTION
The CLOSE operation releases share reservations for the regular or
named attribute file as specified by the current filehandle. The
share reservations and other state information released at the server
as a result of this CLOSE is only associated with the supplied
stateid. The sequence id provides for the correct ordering. 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.
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On success, the current filehandle retains its value.
15.4.5. 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.
15.5. Operation 5: COMMIT - Commit Cached Data
15.5.1. SYNOPSIS
(cfh), offset, count -> verifier
15.5.2. ARGUMENT
struct COMMIT4args {
/* CURRENT_FH: file */
offset4 offset;
count4 count;
};
15.5.3. RESULT
struct COMMIT4resok {
verifier4 writeverf;
};
union COMMIT4res switch (nfsstat4 status) {
case NFS4_OK:
COMMIT4resok resok4;
default:
void;
};
15.5.4. 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
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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.
15.5.5. 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
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
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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
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.
15.6. Operation 6: CREATE - Create a Non-Regular File Object
15.6.1. SYNOPSIS
(cfh), name, type, attrs -> (cfh), change_info, attrs_set
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15.6.2. ARGUMENT
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;
};
15.6.3. RESULT
struct CREATE4resok {
change_info4 cinfo;
bitmap4 attrset; /* attributes set */
};
union CREATE4res switch (nfsstat4 status) {
case NFS4_OK:
CREATE4resok resok4;
default:
void;
};
15.6.4. DESCRIPTION
The CREATE operation creates a non-regular file object in a directory
with a given name. The OPEN operation MUST be used to create a
regular file.
The objname specifies the name for the new object. The objtype
determines the type of object to be created: directory, symlink, etc.
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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 struct, the server will indicate if the before and
after change attributes were obtained atomically with respect to the
file object creation.
If the objname is of zero length, NFS4ERR_INVAL will be returned.
The objname is also subject to the normal UTF-8, character support,
and name checks. See Section 12.3 for further discussion.
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
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 filesystem 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 filesystem semantics may
dictate other methods of derivation. Similarly, if createattrs
includes neither the group attribute nor a group ACE, and if the
server's filesystem 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 filesystem 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
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NFS4ERR_PERM. This applies to the OPEN operation too.
15.6.5. 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.
15.7. Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery
15.7.1. SYNOPSIS
clientid ->
15.7.2. ARGUMENT
struct DELEGPURGE4args {
clientid4 clientid;
};
15.7.3. RESULT
struct DELEGPURGE4res {
nfsstat4 status;
};
15.7.4. 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 issued 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.
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The server MAY support DELEGPURGE, but if it does not, it MUST NOT
support CLAIM_DELEGATE_PREV.
15.8. Operation 8: DELEGRETURN - Return Delegation
15.8.1. SYNOPSIS
(cfh), stateid ->
15.8.2. ARGUMENT
struct DELEGRETURN4args {
/* CURRENT_FH: delegated file */
stateid4 deleg_stateid;
};
15.8.3. RESULT
struct DELEGRETURN4res {
nfsstat4 status;
};
15.8.4. 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.
15.9. Operation 9: GETATTR - Get Attributes
15.9.1. SYNOPSIS
(cfh), attrbits -> attrbits, attrvals
15.9.2. ARGUMENT
struct GETATTR4args {
/* CURRENT_FH: directory or file */
bitmap4 attr_request;
};
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15.9.3. RESULT
struct GETATTR4resok {
fattr4 obj_attributes;
};
union GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
GETATTR4resok resok4;
default:
void;
};
15.9.4. DESCRIPTION
The GETATTR operation will obtain attributes for the filesystem
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 for which it was able to return,
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. If the server
does not support an attribute or cannot approximate a useful value
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 but cannot obtain its value. In that
case no attribute values will be returned.
All servers must support the mandatory attributes as specified in the
section "File Attributes".
On success, the current filehandle retains its value.
15.9.5. IMPLEMENTATION
15.10. Operation 10: GETFH - Get Current Filehandle
15.10.1. SYNOPSIS
(cfh) -> filehandle
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15.10.2. ARGUMENT
/* CURRENT_FH: */
void;
15.10.3. RESULT
struct GETFH4resok {
nfs_fh4 object;
};
union GETFH4res switch (nfsstat4 status) {
case NFS4_OK:
GETFH4resok resok4;
default:
void;
};
15.10.4. DESCRIPTION
This operation returns the current filehandle value.
On success, the current filehandle retains its value.
15.10.5. 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
15.11. Operation 11: LINK - Create Link to a File
15.11.1. SYNOPSIS
(sfh), (cfh), newname -> (cfh), change_info
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15.11.2. ARGUMENT
struct LINK4args {
/* SAVED_FH: source object */
/* CURRENT_FH: target directory */
component4 newname;
};
15.11.3. RESULT
struct LINK4resok {
change_info4 cinfo;
};
union LINK4res switch (nfsstat4 status) {
case NFS4_OK:
LINK4resok resok4;
default:
void;
};
15.11.4. 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 filesystem
on the server. On success, the current filehandle will continue to
be the target directory. If an object exists in the target directory
with the same name as newname, the server must return NFS4ERR_EXIST.
For the target directory, the server returns change_info4 information
in cinfo. With the atomic field of the change_info4 struct, 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.
15.11.5. IMPLEMENTATION
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.
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The statement "file and the target directory must reside within the
same filesystem on the server" means that the fsid fields in the
attributes for the objects are the same. If they reside on different
filesystems, the error, NFS4ERR_XDEV, is returned. On some servers,
the filenames, "." and "..", are illegal as newname.
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.
15.12. Operation 12: LOCK - Create Lock
15.12.1. SYNOPSIS
(cfh) locktype, reclaim, offset, length, locker -> stateid
15.12.2. ARGUMENT
enum nfs_lock_type4 {
READ_LT = 1,
WRITE_LT = 2,
READW_LT = 3, /* blocking read */
WRITEW_LT = 4 /* blocking write */
};
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/*
* For LOCK, transition from open_owner to new lock_owner
*/
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
/*
* For LOCK, existing lock_owner continues to request file locks
*/
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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15.12.3. RESULT
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;
};
15.12.4. 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.
Some servers may only support locking for byte offsets that fit
within 32 bits. If the client specifies a range that includes a byte
beyond the last byte offset of the 32-bit range, but does not include
the last byte offset of the 32-bit and all of the byte offsets beyond
it, up to the end of the valid 64-bit range, such a 32-bit server
MUST return the error NFS4ERR_BAD_RANGE.
In the case that the lock is denied, the owner, offset, and length of
a conflicting lock are returned.
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On success, the current filehandle retains its value.
15.12.5. 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. Section 9
contains a full description of this and the other file locking
operations.
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 filesystem, 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
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.
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 lock_owner is known to the server or if the
lock_owner is new to the server. In the case that the lock_owner is
known to the server and has an established lock_seqid, the argument
is just the lock_owner and lock_seqid. In the case that the
lock_owner is not known to the server, the argument contains not only
the lock_owner and lock_seqid but also the open_stateid and
open_seqid. The new lock_owner case covers the very first lock done
by the lock_owner and offers a method to use the established state of
the open_stateid to transition to the use of the lock_owner.
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15.13. Operation 13: LOCKT - Test For Lock
15.13.1. SYNOPSIS
(cfh) locktype, offset, length owner -> {void, NFS4ERR_DENIED ->
owner}
15.13.2. ARGUMENT
struct LOCKT4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
offset4 offset;
length4 length;
lock_owner4 owner;
};
15.13.3. RESULT
union LOCKT4res switch (nfsstat4 status) {
case NFS4ERR_DENIED:
LOCK4denied denied;
case NFS4_OK:
void;
default:
void;
};
15.13.4. 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; 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.
On success, the current filehandle retains its value.
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15.13.5. 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. Section 9
contains further discussion of the file locking mechanisms.
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.
15.14. Operation 14: LOCKU - Unlock File
15.14.1. SYNOPSIS
(cfh) type, seqid, stateid, offset, length -> stateid
15.14.2. ARGUMENT
struct LOCKU4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
stateid4 lock_stateid;
offset4 offset;
length4 length;
};
15.14.3. RESULT
union LOCKU4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 lock_stateid;
default:
void;
};
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15.14.4. 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
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.
On success, the current filehandle retains its value.
15.14.5. 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.
15.15. Operation 15: LOOKUP - Lookup Filename
15.15.1. SYNOPSIS
(cfh), component -> (cfh)
15.15.2. ARGUMENT
struct LOOKUP4args {
/* CURRENT_FH: directory */
component4 objname;
};
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15.15.3. RESULT
struct LOOKUP4res {
/* CURRENT_FH: object */
nfsstat4 status;
};
15.15.4. DESCRIPTION
This operation LOOKUPs or finds a filesystem 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 of zero length, NFS4ERR_INVAL will be returned.
The component is also subject to the normal UTF-8, character support,
and name checks. See Section 12.3 for further discussion.
15.15.5. 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
NFS version 4 servers depart from the semantics of previous NFS
versions in allowing LOOKUP requests to cross mountpoints on the
server. The client can detect a mountpoint crossing by comparing the
fsid attribute of the directory with the fsid attribute of the
directory looked up. If the fsids are different then the new
directory is a server mountpoint. UNIX clients that detect a
mountpoint crossing will need to mount the server's filesystem. This
needs to be done to maintain the file object identity checking
mechanisms common to UNIX clients.
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Servers that limit NFS access to "shares" or "exported" filesystems
should provide a pseudo-filesystem into which the exported
filesystems can be integrated, so that clients can browse the
server's name space. The clients' view of a pseudo filesystem will
be limited to paths that lead to exported filesystems.
Note: previous versions of the protocol assigned special semantics to
the names "." and "..". NFS version 4 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.
15.16. Operation 16: LOOKUPP - Lookup Parent Directory
15.16.1. SYNOPSIS
(cfh) -> (cfh)
15.16.2. ARGUMENT
/* CURRENT_FH: object */
void;
15.16.3. RESULT
struct LOOKUPP4res {
/* CURRENT_FH: directory */
nfsstat4 status;
};
15.16.4. 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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15.16.5. IMPLEMENTATION
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.
15.17. Operation 17: NVERIFY - Verify Difference in Attributes
15.17.1. SYNOPSIS
(cfh), fattr -> -
15.17.2. ARGUMENT
struct NVERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
15.17.3. RESULT
struct NVERIFY4res {
nfsstat4 status;
};
15.17.4. DESCRIPTION
This operation is used to prefix a sequence of operations to be
performed if one or more attributes have changed on some filesystem
object. If all the attributes match then the error NFS4ERR_SAME must
be returned.
On success, the current filehandle retains its value.
15.17.5. 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
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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
filesystem 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.
15.18. Operation 18: OPEN - Open a Regular File
15.18.1. SYNOPSIS
(cfh), seqid, share_access, share_deny, owner, openhow, claim ->
(cfh), stateid, cinfo, rflags, open_confirm, attrset delegation
15.18.2. ARGUMENT
/*
* Various definitions for OPEN
*/
enum createmode4 {
UNCHECKED4 = 0,
GUARDED4 = 1,
EXCLUSIVE4 = 2
};
union createhow4 switch (createmode4 mode) {
case UNCHECKED4:
case GUARDED4:
fattr4 createattrs;
case EXCLUSIVE4:
verifier4 createverf;
};
enum opentype4 {
OPEN4_NOCREATE = 0,
OPEN4_CREATE = 1
};
union openflag4 switch (opentype4 opentype) {
case OPEN4_CREATE:
createhow4 how;
default:
void;
};
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/* Next definitions used for OPEN delegation */
enum limit_by4 {
NFS_LIMIT_SIZE = 1,
NFS_LIMIT_BLOCKS = 2
/* others as needed */
};
struct nfs_modified_limit4 {
uint32_t num_blocks;
uint32_t bytes_per_block;
};
union nfs_space_limit4 switch (limit_by4 limitby) {
/* limit specified as file size */
case NFS_LIMIT_SIZE:
uint64_t filesize;
/* limit specified by number of blocks */
case NFS_LIMIT_BLOCKS:
nfs_modified_limit4 mod_blocks;
} ;
enum open_delegation_type4 {
OPEN_DELEGATE_NONE = 0,
OPEN_DELEGATE_READ = 1,
OPEN_DELEGATE_WRITE = 2
};
enum open_claim_type4 {
CLAIM_NULL = 0,
CLAIM_PREVIOUS = 1,
CLAIM_DELEGATE_CUR = 2,
CLAIM_DELEGATE_PREV = 3
};
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;
/*
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* Right to the file established by an
* open previous to server reboot. File
* identified by filehandle obtained at
* that time rather than by name.
*/
case CLAIM_PREVIOUS:
/* CURRENT_FH: file being reclaimed */
open_delegation_type4 delegate_type;
/*
* Right to file based on a delegation
* granted by the server. File is
* specified by name.
*/
case CLAIM_DELEGATE_CUR:
/* CURRENT_FH: directory */
open_claim_delegate_cur4 delegate_cur_info;
/*
* Right to file based on a delegation
* granted to a previous boot instance
* of the client. File is specified by name.
*/
case CLAIM_DELEGATE_PREV:
/* CURRENT_FH: directory */
component4 file_delegate_prev;
};
/*
* OPEN: Open a file, potentially receiving an open delegation
*/
struct OPEN4args {
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
open_owner4 owner;
openflag4 openhow;
open_claim4 claim;
};
15.18.3. RESULT
struct open_read_delegation4 {
stateid4 stateid; /* Stateid for delegation*/
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim (CLAIM_PREVIOUS) */
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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. */
};
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;
};
/*
* 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;
struct OPEN4resok {
stateid4 stateid; /* Stateid for open */
change_info4 cinfo; /* Directory Change Info */
uint32_t rflags; /* Result flags */
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bitmap4 attrset; /* attribute set for create*/
open_delegation4 delegation; /* Info on any open
delegation */
};
union OPEN4res switch (nfsstat4 status) {
case NFS4_OK:
/* CURRENT_FH: opened file */
OPEN4resok resok4;
default:
void;
};
15.18.4. 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
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.
15.18.5. DESCRIPTION
The OPEN operation creates and/or opens a regular file in a directory
with the provided name. If the file does not exist at the server and
creation is desired, specification of the method of creation is
provided by the openhow parameter. The client has the choice of
three creation methods: UNCHECKED, GUARDED, or EXCLUSIVE.
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 and the current filehandle is a named attribute directory,
the server will return EINVAL.
UNCHECKED 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
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may include any writable attribute valid for regular files. When an
UNCHECKED create encounters an existing file, the attributes
specified by createattrs are not used, except that when an size of
zero is specified, the existing file is truncated. If GUARDED 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 UNCHECKED. For
each of these cases (UNCHECKED and GUARDED) where the operation is
successful, the server will return to the client an attribute mask
signifying which attributes were successfully set for the object.
EXCLUSIVE specifies 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. No attributes may be provided in this case, since the
server may use an attribute of the target object to store the
verifier. If the server uses an attribute to store the exclusive
create verifier, it will signify which attribute by setting the
appropriate bit in the attribute mask that is returned in the
results.
For the target directory, the server returns change_info4 information
in cinfo. With the atomic field of the change_info4 struct, 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 a complete SHARE request, the client must provide values for the
owner and seqid fields for the OPEN argument. For additional
discussion of SHARE semantics see Section 9.9.
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
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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 four basic claim types which cover the various
situations for an OPEN. They are as follows:
CLAIM_NULL For the client, this is a new OPEN request and there is
no previous state associate with the file for the client.
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 OPEN as
granted by the server. Generally this is done as part of
recalling a delegation.
CLAIM_DELEGATE_PREV The client is claiming a delegation granted to a
previous client instance; used after the client reboots. The
server MAY support CLAIM_DELEGATE_PREV. If it does support
CLAIM_DELEGATE_PREV, SETCLIENTID_CONFIRM 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.
OPEN4_RESULT_CONFIRM indicates that the client MUST execute an
OPEN_CONFIRM operation before using the open file.
OPEN4_RESULT_LOCKTYPE_POSIX indicates the server's file locking
behavior supports the complete set of Posix locking techniques. From
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this the client can choose to manage file locking state in a way to
handle a mis-match of file locking management.
If the component is of zero length, NFS4ERR_INVAL will be returned.
The component is also subject to the normal UTF-8, character support,
and name checks. See Section 12.3 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.
If the underlying filesystem 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 filesystem.
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 filesystem. 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 is specified, and includes owner or group (or
corresponding ACEs) 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.
15.18.6. IMPLEMENTATION
The OPEN operation contains support for EXCLUSIVE create. The
mechanism is similar to the support in NFS version 3 [14]. As in NFS
version 3, this mechanism provides reliable exclusive creation.
Exclusive create is invoked when the how parameter is EXCLUSIVE. In
this case, 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 filesystems that do not
provide a mechanism for the storage of arbitrary file attributes, the
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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
semantics are critical to the application. Because of the expected
usage, exclusive CREATE does not rely solely on the normally volatile
duplicate request cache for storage of the verifier. The duplicate
request cache in volatile storage does not survive a crash and may
actually flush on a long network partition, opening failure windows.
In the UNIX local filesystem environment, the expected storage
location for the verifier on creation is the meta-data (time stamps)
of the object. For this reason, an exclusive object create may not
include initial attributes because the server would have nowhere to
store the verifier.
If the server can not support these 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.
Once the client has performed a successful exclusive create, it must
issue a SETATTR to set the correct object attributes. Until it does
so, it should not rely upon any of the object attributes, since the
server implementation may need to overload object meta-data to store
the verifier. The subsequent SETATTR must not occur in the same
COMPOUND request as the OPEN. This separation will guarantee that
the exclusive create mechanism will continue to function properly in
the face of retransmission of the request.
Use of the GUARDED 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 GUARDED
to prevent against a sequence like: create, write, create
(retransmitted) from occurring.
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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 NFS
version 4 protocol does not impose any requirement that READs and
WRITEs issued 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. If the current
filehandle is not a directory, the error NFS4ERR_NOTDIR will be
returned.
15.19. Operation 19: OPENATTR - Open Named Attribute Directory
15.19.1. SYNOPSIS
(cfh) createdir -> (cfh)
15.19.2. ARGUMENT
struct OPENATTR4args {
/* CURRENT_FH: object */
bool createdir;
};
15.19.3. RESULT
struct OPENATTR4res {
/* CURRENT_FH: named attr directory */
nfsstat4 status;
};
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15.19.4. 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 filesystem object. Filehandles returned
within the named attribute directory will have a type of
NF4NAMEDATTR.
The createdir argument allows the client to signify if a named
attribute directory should be created as a result of the OPENATTR
operation. Some clients may use the OPENATTR operation with a value
of FALSE for createdir to determine if any named attributes exist for
the object. If none exist, then NFS4ERR_NOENT will be returned. If
createdir has a value of TRUE and no named attribute directory
exists, one is created. 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.
15.19.5. IMPLEMENTATION
If the server does not support named attributes for the current
filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
client.
15.20. Operation 20: OPEN_CONFIRM - Confirm Open
15.20.1. SYNOPSIS
(cfh), seqid, stateid-> stateid
15.20.2. ARGUMENT
struct OPEN_CONFIRM4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
};
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15.20.3. RESULT
struct OPEN_CONFIRM4resok {
stateid4 open_stateid;
};
union OPEN_CONFIRM4res switch (nfsstat4 status) {
case NFS4_OK:
OPEN_CONFIRM4resok resok4;
default:
void;
};
15.20.4. DESCRIPTION
This operation is used to confirm the sequence id usage for the first
time that a open_owner is used by a client. The stateid returned
from the OPEN operation is used as the argument for this operation
along with the next sequence id for the open_owner. The sequence id
passed to the OPEN_CONFIRM must be 1 (one) greater than the seqid
passed to the OPEN operation from which the open_confirm value was
obtained. If the server receives an unexpected sequence id with
respect to the original open, then the server assumes that the client
will not confirm the original OPEN and all state associated with the
original OPEN is released by the server.
On success, the current filehandle retains its value.
15.20.5. IMPLEMENTATION
A given client might generate many open_owner4 data structures for a
given clientid. The client will periodically either dispose of its
open_owner4s or stop using them for indefinite periods of time. The
latter situation is why the NFS version 4 protocol does not have an
explicit operation to exit an open_owner4: such an operation is of no
use in that situation. Instead, to avoid unbounded memory use, the
server needs to implement a strategy for disposing of open_owner4s
that have no current lock, open, or delegation state for any files
and have not been used recently. The time period used to determine
when to dispose of open_owner4s is an implementation choice. The
time period should certainly be no less than the lease time plus any
grace period the server wishes to implement beyond a lease time. The
OPEN_CONFIRM operation allows the server to safely dispose of unused
open_owner4 data structures.
In the case that a client issues an OPEN operation and the server no
longer has a record of the open_owner4, the server needs to ensure
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that this is a new OPEN and not a replay or retransmission.
Servers must not require confirmation on OPENs that grant delegations
or are doing reclaim operations. See Section 9.1.8 for details. The
server can easily avoid this by noting whether it has disposed of one
open_owner4 for the given clientid. If the server does not support
delegation, it might simply maintain a single bit that notes whether
any open_owner4 (for any client) has been disposed of.
The server must hold unconfirmed OPEN state until one of three events
occur. First, the client sends an OPEN_CONFIRM request with the
appropriate sequence id and stateid within the lease period. In this
case, the OPEN state on the server goes to confirmed, and the
open_owner4 on the server is fully established.
Second, the client sends another OPEN request with a sequence id that
is incorrect for the open_owner4 (out of sequence). In this case,
the server assumes the second OPEN request is valid and the first one
is a replay. The server cancels the OPEN state of the first OPEN
request, establishes an unconfirmed OPEN state for the second OPEN
request, and responds to the second OPEN request with an indication
that an OPEN_CONFIRM is needed. The process then repeats itself.
While there is a potential for a denial of service attack on the
client, it is mitigated if the client and server require the use of a
security flavor based on Kerberos V5, LIPKEY, or some other flavor
that uses cryptography.
What if the server is in the unconfirmed OPEN state for a given
open_owner4, and it receives an operation on the open_owner4 that has
a stateid but the operation is not OPEN, or it is OPEN_CONFIRM but
with the wrong stateid? Then, even if the seqid is correct, the
server returns NFS4ERR_BAD_STATEID, because the server assumes the
operation is a replay: if the server has no established OPEN state,
then there is no way, for example, a LOCK operation could be valid.
Third, neither of the two aforementioned events occur for the
open_owner4 within the lease period. In this case, the OPEN state is
canceled and disposal of the open_owner4 can occur.
15.21. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access
15.21.1. SYNOPSIS
(cfh), stateid, seqid, access, deny -> stateid
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15.21.2. ARGUMENT
struct OPEN_DOWNGRADE4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
15.21.3. RESULT
struct OPEN_DOWNGRADE4resok {
stateid4 open_stateid;
};
union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
case NFS4_OK:
OPEN_DOWNGRADE4resok resok4;
default:
void;
};
15.21.4. DESCRIPTION
This operation is used to adjust the share_access and share_deny bits
for a given open. This is necessary when a given openowner 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 error NFS4ERR_INVAL
should be returned. 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.
On success, the current filehandle retains its value.
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15.22. Operation 22: PUTFH - Set Current Filehandle
15.22.1. SYNOPSIS
filehandle -> (cfh)
15.22.2. ARGUMENT
struct PUTFH4args {
nfs_fh4 object;
};
15.22.3. RESULT
struct PUTFH4res {
/* CURRENT_FH: */
nfsstat4 status;
};
15.22.4. 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.
15.22.5. IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
15.23. Operation 23: PUTPUBFH - Set Public Filehandle
15.23.1. SYNOPSIS
- -> (cfh)
15.23.2. ARGUMENT
void;
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15.23.3. RESULT
struct PUTPUBFH4res {
/* CURRENT_FH: public fh */
nfsstat4 status;
};
15.23.4. 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.
The public filehandle represents the concepts embodied in [23], [24],
[31]. The intent for NFS version 4 is that the public filehandle
(represented by the PUTPUBFH operation) be used as a method of
providing WebNFS server compatibility with NFS versions 2 and 3.
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.
15.23.5. IMPLEMENTATION
Used as the first operator in an NFS request to set the context for
following operations.
With the NFS version 2 and 3 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. [31] contains further discussion
of the functionality. With NFS version 4, 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 NFS version 4. 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 [31] 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 NFS version 4. It is
likely, therefore that because of server implementation details, an
NFS version 3 absolute public filehandle lookup may behave
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differently than an NFS version 4 absolute resolution.
There is a form of security negotiation as described in [32] that
uses the public filehandle a method of employing SNEGO. This method
is not available with NFS version 4 as filehandles are not overloaded
with special meaning and therefore do not provide the same framework
as NFS versions 2 and 3. Clients should therefore use the security
negotiation mechanisms described in this RFC.
15.24. Operation 24: PUTROOTFH - Set Root Filehandle
15.24.1. SYNOPSIS
- -> (cfh)
15.24.2. ARGUMENT
void;
15.24.3. RESULT
struct PUTROOTFH4res {
/* CURRENT_FH: root fh */
nfsstat4 status;
};
15.24.4. 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.
15.24.5. IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
15.25. Operation 25: READ - Read from File
15.25.1. SYNOPSIS
(cfh), stateid, offset, count -> eof, data
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15.25.2. ARGUMENT
struct READ4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
count4 count;
};
15.25.3. RESULT
struct READ4resok {
bool eof;
opaque data<>;
};
union READ4res switch (nfsstat4 status) {
case NFS4_OK:
READ4resok resok4;
default:
void;
};
15.25.4. 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.
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 is used by the server to
verify that the associated share reservation and any record locks are
still valid and to update lease timeouts for the client.
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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 a regular file, an error will be
returned to the client. In the case the current filehandle
represents a directory, NFS4ERR_ISDIR is return; otherwise,
NFS4ERR_INVAL 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.
15.25.5. 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 issue 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 on 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.
15.26. Operation 26: READDIR - Read Directory
15.26.1. SYNOPSIS
(cfh), cookie, cookieverf, dircount, maxcount, attr_request ->
cookieverf { cookie, name, attrs }
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15.26.2. ARGUMENT
struct READDIR4args {
/* CURRENT_FH: directory */
nfs_cookie4 cookie;
verifier4 cookieverf;
count4 dircount;
count4 maxcount;
bitmap4 attr_request;
};
15.26.3. RESULT
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;
};
15.26.4. DESCRIPTION
The READDIR operation retrieves a variable number of entries from a
filesystem directory and returns client requested attributes for each
entry along with information to allow the client to request
additional directory entries in a subsequent READDIR.
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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
attributes for a directory entry. Instead of returning an error for
the entire READDIR operation, the server can instead return the
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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 filesystem 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 MUST NOT be
returned.
On success, the current filehandle retains its value.
15.26.5. IMPLEMENTATION
The server's filesystem 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.
The use of the cookieverf will also protect the client from using
READDIR cookie values that may be stale. For example, if the file
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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.
15.27. Operation 27: READLINK - Read Symbolic Link
15.27.1. SYNOPSIS
(cfh) -> linktext
15.27.2. ARGUMENT
/* CURRENT_FH: symlink */
void;
15.27.3. RESULT
struct READLINK4resok {
linktext4 link;
};
union READLINK4res switch (nfsstat4 status) {
case NFS4_OK:
READLINK4resok resok4;
default:
void;
};
15.27.4. 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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15.27.5. 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_INVAL, if the object is
not of type, NF4LNK.
15.28. Operation 28: REMOVE - Remove Filesystem Object
15.28.1. SYNOPSIS
(cfh), filename -> change_info
15.28.2. ARGUMENT
struct REMOVE4args {
/* CURRENT_FH: directory */
component4 target;
};
15.28.3. RESULT
struct REMOVE4resok {
change_info4 cinfo;
};
union REMOVE4res switch (nfsstat4 status) {
case NFS4_OK:
REMOVE4resok resok4;
default:
void;
};
15.28.4. DESCRIPTION
The REMOVE operation removes (deletes) a directory entry M named by
filename from the directory corresponding to the current filehandle.
If the entry in the directory was the last reference to the
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corresponding filesystem object, the object may be destroyed.
For the directory where the filename was removed, the server returns
change_info4 information in cinfo. With the atomic field of the
change_info4 struct, the server will indicate if the before and after
change attributes were obtained atomically with respect to the
removal.
If the target is of zero length, NFS4ERR_INVAL will be returned. The
target is also subject to the normal UTF-8, character support, and
name checks. See Section 12.3 for further discussion.
On success, the current filehandle retains its value.
15.28.5. IMPLEMENTATION
NFS versions 2 and 3 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.
NFS version 4 REMOVE can be used to delete any directory entry
independent of its file type. The implementor of an NFS version 4
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.
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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
filehandle.
15.29. Operation 29: RENAME - Rename Directory Entry
15.29.1. SYNOPSIS
(sfh), oldname, (cfh), newname -> source_change_info,
target_change_info
15.29.2. ARGUMENT
struct RENAME4args {
/* SAVED_FH: source directory */
component4 oldname;
/* CURRENT_FH: target directory */
component4 newname;
};
15.29.3. RESULT
struct RENAME4resok {
change_info4 source_cinfo;
change_info4 target_cinfo;
};
union RENAME4res switch (nfsstat4 status) {
case NFS4_OK:
RENAME4resok resok4;
default:
void;
};
15.29.4. 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
filesystem on the server. On success, the current filehandle will
continue to be the target directory.
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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 (See Section 15.28 for client and server actions
whenever a target is removed). If they 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 (they might be
hard links of each other), then RENAME should perform no action and
return success.
For both directories involved in the RENAME, the server returns
change_info4 information. With the atomic field of the change_info4
struct, 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 filesystem objects, the server will
return NFS4ERR_XDEV just as if the saved and current filehandles
represented directories on different filesystems.
If the oldname or newname is of zero length, NFS4ERR_INVAL will be
returned. The oldname and newname are also subject to the normal
UTF-8, character support, and name checks. See Section 12.3 for
further discussion.
15.29.5. IMPLEMENTATION
The RENAME operation must be atomic to the client. The statement
"source and target directories must reside on the same filesystem on
the server" means that the fsid fields in the attributes for the
directories are the same. If they reside on different filesystems,
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,
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the server will return NFS4ERR_NOTDIR.
15.30. Operation 30: RENEW - Renew a Lease
15.30.1. SYNOPSIS
clientid -> ()
15.30.2. ARGUMENT
struct RENEW4args {
clientid4 clientid;
};
15.30.3. RESULT
struct RENEW4res {
nfsstat4 status;
};
15.30.4. DESCRIPTION
The RENEW operation is used by the client to renew leases which it
currently holds at a server. In processing the RENEW request, the
server renews all leases associated with the client. The associated
leases are determined by the clientid provided via the SETCLIENTID
operation.
15.30.5. IMPLEMENTATION
When the client holds delegations, it needs to use RENEW to detect
when the server has determined that the callback path is down. When
the server has made such a determination, only the RENEW operation
will renew the lease on delegations. If the server determines the
callback path is down, it returns NFS4ERR_CB_PATH_DOWN. Even though
it returns NFS4ERR_CB_PATH_DOWN, the server MUST renew the lease on
the record locks and share reservations that the client has
established on the server. If for some reason the lock and share
reservation lease cannot be renewed, then the server MUST return an
error other than NFS4ERR_CB_PATH_DOWN, even if the callback path is
also down. In the event that the server has conditions such that is
could return either NFS4ERR_CB_PATH_DOWN or NFS4ERR_LEASE_MOVED,
NFS4ERR_LEASE_MOVED MUST be handled first.
The client that issues RENEW MUST choose the principal, RPC security
flavor, and if applicable, GSS-API mechanism and service via one of
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the following algorithms:
o The client uses the same principal, RPC security flavor -- and if
the flavor was RPCSEC_GSS -- the same mechanism and service that
was used when the client id was established via
SETCLIENTID_CONFIRM.
o The client uses any principal, RPC security flavor mechanism and
service combination that currently has an OPEN file on the server.
I.e., the same principal had a successful OPEN operation, the file
is still open by that principal, and the flavor, mechanism, and
service of RENEW match that of the previous OPEN.
The server MUST reject a RENEW that does not use one the
aforementioned algorithms, with the error NFS4ERR_ACCESS.
15.31. Operation 31: RESTOREFH - Restore Saved Filehandle
15.31.1. SYNOPSIS
(sfh) -> (cfh)
15.31.2. ARGUMENT
/* SAVED_FH: */
void;
15.31.3. RESULT
struct RESTOREFH4res {
/* CURRENT_FH: value of saved fh */
nfsstat4 status;
};
15.31.4. DESCRIPTION
Set the current filehandle to the value in the saved filehandle. If
there is no saved filehandle then return the error NFS4ERR_RESTOREFH.
15.31.5. 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.,
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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)
15.32. Operation 32: SAVEFH - Save Current Filehandle
15.32.1. SYNOPSIS
(cfh) -> (sfh)
15.32.2. ARGUMENT
/* CURRENT_FH: */
void;
15.32.3. RESULT
struct SAVEFH4res {
/* SAVED_FH: value of current fh */
nfsstat4 status;
};
15.32.4. 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.
On success, the current filehandle retains its value.
15.32.5. IMPLEMENTATION
15.33. Operation 33: SECINFO - Obtain Available Security
15.33.1. SYNOPSIS
(cfh), name -> { secinfo }
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15.33.2. ARGUMENT
struct SECINFO4args {
/* CURRENT_FH: directory */
component4 name;
};
15.33.3. RESULT
/*
* 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:
SECINFO4resok resok4;
default:
void;
};
15.33.4. 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
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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 server's
preferences, the most preferred being first in the array. The client
is free to pick whatever security mechanism it both desires and
supports, or to pick in the server's preference order the first one
it supports. The array entries are represented by the secinfo4
structure. The field 'flavor' will contain a value of AUTH_NONE,
AUTH_SYS (as defined in [3]), or RPCSEC_GSS (as defined in [4]).
For the flavors AUTH_NONE and AUTH_SYS, no additional security
information is returned. For a return value of RPCSEC_GSS, a
security triple is returned that contains the mechanism object id (as
defined in [6]), the quality of protection (as defined in [6]) and
the service type (as defined in [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 retains its value.
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.
15.33.5. 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, 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
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inspection for a security match, the server will check it again on
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, RENAME, and RESTOREFH, the client will use
SECINFO and provide the parent directory filehandle and object
name which corresponds to the filehandle originally provided by
the PUTFH RESTOREFH, or for LINK and RENAME, the SAVEFH.
o For PUTROOTFH and PUTPUBFH, the client will be unable to use the
SECINFO operation since SECINFO requires a current filehandle and
none exist for these two operations. Therefore, the client must
iterate through the security triples available at the client and
reattempt the PUTROOTFH or PUTPUBFH operation. In the unfortunate
event none of the MANDATORY 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 AUTH_NONE, but
because such forms lack integrity checks, this puts the client at
risk. Nonetheless, the server SHOULD allow the client to use
whatever security form the client requests and the server
supports, since the risks of doing so are on the client.
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
does 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 17 for a discussion on the recommendations for security
flavor used by SECINFO.
15.34. Operation 34: SETATTR - Set Attributes
15.34.1. SYNOPSIS
(cfh), stateid, attrmask, attr_vals -> attrsset
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15.34.2. ARGUMENT
struct SETATTR4args {
/* CURRENT_FH: target object */
stateid4 stateid;
fattr4 obj_attributes;
};
15.34.3. RESULT
struct SETATTR4res {
nfsstat4 status;
bitmap4 attrsset;
};
15.34.4. DESCRIPTION
The SETATTR operation changes one or more of the attributes of a
filesystem 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.
15.34.5. 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
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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
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.
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
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 NFS version 3. 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
NFS version 4 emulation. Therefore, NFS version 4 servers should
take care to avoid such delays, to the degree possible, when
executing such a request.
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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.
15.35. Operation 35: SETCLIENTID - Negotiate Clientid
15.35.1. SYNOPSIS
client, callback, callback_ident -> clientid, setclientid_confirm
15.35.2. ARGUMENT
struct SETCLIENTID4args {
nfs_client_id4 client;
cb_client4 callback;
uint32_t callback_ident;
};
15.35.3. RESULT
struct SETCLIENTID4resok {
clientid4 clientid;
verifier4 setclientid_confirm;
};
union SETCLIENTID4res switch (nfsstat4 status) {
case NFS4_OK:
SETCLIENTID4resok resok4;
case NFS4ERR_CLID_INUSE:
clientaddr4 client_using;
default:
void;
};
15.35.4. DESCRIPTION
The client uses the SETCLIENTID operation to notify the server of its
intention to use a particular client identifier, callback, and
callback_ident for subsequent requests that entail creating lock,
share reservation, and delegation state on the server. Upon
successful completion the server will return a shorthand clientid
which, if confirmed via a separate step, will be used in subsequent
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file locking and file open requests. Confirmation of the clientid
must be done via the SETCLIENTID_CONFIRM operation to return the
clientid and setclientid_confirm values, as verifiers, to the server.
The reason why two verifiers are necessary is that it is possible to
use SETCLIENTID and SETCLIENTID_CONFIRM to modify the callback and
callback_ident information but not the shorthand clientid. In that
event, the setclientid_confirm value is effectively the only
verifier.
The callback information provided in this operation will be used if
the client is provided an open delegation at a future point.
Therefore, the client must correctly reflect the program and port
numbers for the callback program at the time SETCLIENTID is used.
The callback_ident value is used by the server on the callback. The
client can leverage the callback_ident to eliminate the need for more
than one callback RPC program number, while still being able to
determine which server is initiating the callback.
15.35.5. IMPLEMENTATION
To understand how to implement SETCLIENTID, make the following
notations. Let:
x be the value of the client.id subfield of the SETCLIENTID4args
structure.
v be the value of the client.verifier subfield of the
SETCLIENTID4args structure.
c be the value of the clientid field returned in the
SETCLIENTID4resok structure.
k represent the value combination of the fields callback and
callback_ident fields of the SETCLIENTID4args structure.
s be the setclientid_confirm value returned in the SETCLIENTID4resok
structure.
{ v, x, c, k, s } be a quintuple for a client record. A client
record is confirmed if there has been a SETCLIENTID_CONFIRM
operation to confirm it. Otherwise it is unconfirmed. An
unconfirmed record is established by a SETCLIENTID call.
Since SETCLIENTID is a non-idempotent operation, let us assume that
the server is implementing the duplicate request cache (DRC).
When the server gets a SETCLIENTID { v, x, k } request, it processes
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it in the following manner.
o It first looks up the request in the DRC. If there is a hit, it
returns the result cached in the DRC. The server does NOT remove
client state (locks, shares, delegations) nor does it modify any
recorded callback and callback_ident information for client { x }.
For any DRC miss, the server takes the client id string x, and
searches for client records for x that the server may have
recorded from previous SETCLIENTID calls. For any confirmed
record with the same id string x, if the recorded principal does
not match that of SETCLIENTID call, then the server returns a
NFS4ERR_CLID_INUSE error.
For brevity of discussion, the remaining description of the
processing assumes that there was a DRC miss, and that where the
server has previously recorded a confirmed record for client x,
the aforementioned principal check has successfully passed.
o The server checks if it has recorded a confirmed record for { v,
x, c, l, s }, where l may or may not equal k. If so, and since
the id verifier v of the request matches that which is confirmed
and recorded, the server treats this as a probable callback
information update and records an unconfirmed { v, x, c, k, t }
and leaves the confirmed { v, x, c, l, s } in place, such that t
!= s. It does not matter if k equals l or not. Any pre-existing
unconfirmed { v, x, c, *, * } is removed.
The server returns { c, t }. It is indeed returning the old
clientid4 value c, because the client apparently only wants to
update callback value k to value l. It's possible this request is
one from the Byzantine router that has stale callback information,
but this is not a problem. The callback information update is
only confirmed if followed up by a SETCLIENTID_CONFIRM { c, t }.
The server awaits confirmation of k via SETCLIENTID_CONFIRM { c, t
}.
The server does NOT remove client (lock/share/delegation) state
for x.
o The server has previously recorded a confirmed { u, x, c, l, s }
record such that v != u, l may or may not equal k, and has not
recorded any unconfirmed { *, x, *, *, * } record for x. The
server records an unconfirmed { v, x, d, k, t } (d != c, t != s).
The server returns { d, t }.
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The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
{ d, t }.
The server does NOT remove client (lock/share/delegation) state
for x.
o The server has previously recorded a confirmed { u, x, c, l, s }
record such that v != u, l may or may not equal k, and recorded an
unconfirmed { w, x, d, m, t } record such that c != d, t != s, m
may or may not equal k, m may or may not equal l, and k may or may
not equal l. Whether w == v or w != v makes no difference. The
server simply removes the unconfirmed { w, x, d, m, t } record and
replaces it with an unconfirmed { v, x, e, k, r } record, such
that e != d, e != c, r != t, r != s.
The server returns { e, r }.
The server awaits confirmation of { e, k } via SETCLIENTID_CONFIRM
{ e, r }.
The server does NOT remove client (lock/share/delegation) state
for x.
o The server has no confirmed { *, x, *, *, * } for x. It may or
may not have recorded an unconfirmed { u, x, c, l, s }, where l
may or may not equal k, and u may or may not equal v. Any
unconfirmed record { u, x, c, l, * }, regardless whether u == v or
l == k, is replaced with an unconfirmed record { v, x, d, k, t }
where d != c, t != s.
The server returns { d, t }.
The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
{ d, t }. The server does NOT remove client (lock/share/
delegation) state for x.
The server generates the clientid and setclientid_confirm values and
must take care to ensure that these values are extremely unlikely to
ever be regenerated.
15.36. Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid
15.36.1. SYNOPSIS
clientid, verifier -> -
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15.36.2. ARGUMENT
struct SETCLIENTID_CONFIRM4args {
clientid4 clientid;
verifier4 setclientid_confirm;
};
15.36.3. RESULT
struct SETCLIENTID_CONFIRM4res {
nfsstat4 status;
};
15.36.4. DESCRIPTION
This operation is used by the client to confirm the results from a
previous call to SETCLIENTID. The client provides the server
supplied (from a SETCLIENTID response) clientid. The server responds
with a simple status of success or failure.
15.36.5. IMPLEMENTATION
The client must use the SETCLIENTID_CONFIRM operation to confirm the
following two distinct cases:
o The client's use of a new shorthand client identifier (as returned
from the server in the response to SETCLIENTID), a new callback
value (as specified in the arguments to SETCLIENTID) and a new
callback_ident (as specified in the arguments to SETCLIENTID)
value. The client's use of SETCLIENTID_CONFIRM in this case also
confirms the removal of any of the client's previous relevant
leased state. Relevant leased client state includes record locks,
share reservations, and where the server does not support the
CLAIM_DELEGATE_PREV claim type, delegations. If the server
supports CLAIM_DELEGATE_PREV, then SETCLIENTID_CONFIRM MUST NOT
remove delegations for this client; relevant leased client state
would then just include record locks and share reservations.
o The client's re-use of an old, previously confirmed, shorthand
client identifier, a new callback value, and a new callback_ident
value. The client's use of SETCLIENTID_CONFIRM in this case MUST
NOT result in the removal of any previous leased state (locks,
share reservations, and delegations)
We use the same notation and definitions for v, x, c, k, s, and
unconfirmed and confirmed client records as introduced in the
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description of the SETCLIENTID operation. The arguments to
SETCLIENTID_CONFIRM are indicated by the notation { c, s }, where c
is a value of type clientid4, and s is a value of type verifier4
corresponding to the setclientid_confirm field.
As with SETCLIENTID, SETCLIENTID_CONFIRM is a non-idempotent
operation, and we assume that the server is implementing the
duplicate request cache (DRC).
When the server gets a SETCLIENTID_CONFIRM { c, s } request, it
processes it in the following manner.
o It first looks up the request in the DRC. If there is a hit, it
returns the result cached in the DRC. The server does not remove
any relevant leased client state nor does it modify any recorded
callback and callback_ident information for client { x } as
represented by the shorthand value c.
For a DRC miss, the server checks for client records that match the
shorthand value c. The processing cases are as follows:
o The server has recorded an unconfirmed { v, x, c, k, s } record
and a confirmed { v, x, c, l, t } record, such that s != t. If
the principals of the records do not match that of the
SETCLIENTID_CONFIRM, the server returns NFS4ERR_CLID_INUSE, and no
relevant leased client state is removed and no recorded callback
and callback_ident information for client { x } is changed.
Otherwise, the confirmed { v, x, c, l, t } record is removed and
the unconfirmed { v, x, c, k, s } is marked as confirmed, thereby
modifying recorded and confirmed callback and callback_ident
information for client { x }.
The server does not remove any relevant leased client state.
The server returns NFS4_OK.
o The server has not recorded an unconfirmed { v, x, c, *, * } and
has recorded a confirmed { v, x, c, *, s }. If the principals of
the record and of SETCLIENTID_CONFIRM do not match, the server
returns NFS4ERR_CLID_INUSE without removing any relevant leased
client state and without changing recorded callback and
callback_ident values for client { x }.
If the principals match, then what has likely happened is that the
client never got the response from the SETCLIENTID_CONFIRM, and
the DRC entry has been purged. Whatever the scenario, since the
principals match, as well as { c, s } matching a confirmed record,
the server leaves client x's relevant leased client state intact,
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leaves its callback and callback_ident values unmodified, and
returns NFS4_OK.
o The server has not recorded a confirmed { *, *, c, *, * }, and has
recorded an unconfirmed { *, x, c, k, s }. Even if this is a
retry from client, nonetheless the client's first
SETCLIENTID_CONFIRM attempt was not received by the server. Retry
or not, the server doesn't know, but it processes it as if were a
first try. If the principal of the unconfirmed { *, x, c, k, s }
record mismatches that of the SETCLIENTID_CONFIRM request the
server returns NFS4ERR_CLID_INUSE without removing any relevant
leased client state.
Otherwise, the server records a confirmed { *, x, c, k, s }. If
there is also a confirmed { *, x, d, *, t }, the server MUST
remove the client x's relevant leased client state, and overwrite
the callback state with k. The confirmed record { *, x, d, *, t }
is removed.
Server returns NFS4_OK.
o The server has no record of a confirmed or unconfirmed { *, *, c,
*, s }. The server returns NFS4ERR_STALE_CLIENTID. The server
does not remove any relevant leased client state, nor does it
modify any recorded callback and callback_ident information for
any client.
The server needs to cache unconfirmed { v, x, c, k, s } client
records and await for some time their confirmation. As should be
clear from the record processing discussions for SETCLIENTID and
SETCLIENTID_CONFIRM, there are cases where the server does not
deterministically remove unconfirmed client records. To avoid
running out of resources, the server is not required to hold
unconfirmed records indefinitely. One strategy the server might use
is to set a limit on how many unconfirmed client records it will
maintain, and then when the limit would be exceeded, remove the
oldest record. Another strategy might be to remove an unconfirmed
record when some amount of time has elapsed. The choice of the
amount of time is fairly arbitrary but it is surely no higher than
the server's lease time period. Consider that leases need to be
renewed before the lease time expires via an operation from the
client. If the client cannot issue a SETCLIENTID_CONFIRM after a
SETCLIENTID before a period of time equal to that of a lease expires,
then the client is unlikely to be able maintain state on the server
during steady state operation.
If the client does send a SETCLIENTID_CONFIRM for an unconfirmed
record that the server has already deleted, the client will get
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NFS4ERR_STALE_CLIENTID back. If so, the client should then start
over, and send SETCLIENTID to reestablish an unconfirmed client
record and get back an unconfirmed clientid and setclientid_confirm
verifier. The client should then send the SETCLIENTID_CONFIRM to
confirm the clientid.
SETCLIENTID_CONFIRM does not establish or renew a lease. However, if
SETCLIENTID_CONFIRM removes relevant leased client state, and that
state does not include existing delegations, the server MUST allow
the client a period of time no less than the value of lease_time
attribute, to reclaim, (via the CLAIM_DELEGATE_PREV claim type of the
OPEN operation) its delegations before removing unreclaimed
delegations.
15.37. Operation 37: VERIFY - Verify Same Attributes
15.37.1. SYNOPSIS
(cfh), fattr -> -
15.37.2. ARGUMENT
struct VERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
15.37.3. RESULT
struct VERIFY4res {
nfsstat4 status;
};
15.37.4. 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.
15.37.5. 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
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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
filesystem 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.
15.38. Operation 38: WRITE - Write to File
15.38.1. SYNOPSIS
(cfh), stateid, offset, stable, data -> count, committed, writeverf
15.38.2. ARGUMENT
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<>;
};
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15.38.3. RESULT
struct WRITE4resok {
count4 count;
stable_how4 committed;
verifier4 writeverf;
};
union WRITE4res switch (nfsstat4 status) {
case NFS4_OK:
WRITE4resok resok4;
default:
void;
};
15.38.4. 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
is FILE_SYNC4, the server must commit the data written plus all
filesystem metadata to stable storage before returning results. This
corresponds to the NFS version 2 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.
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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 is used by the
server to verify that the associated share reservation and any record
locks are still valid and to update lease timeouts for the client.
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 NFS version 4 protocol
service and must be unique between instances of the NFS version 4
protocol server, where uncommitted data may be lost.
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.
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15.38.5. 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 issue
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 issues 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 NFS version 4 protocol server over which cached,
uncommitted data may be lost. In the most likely case, the verifier
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
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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 a directory, the server will return
NFS4ERR_ISDIR. If the current filehandle is not a regular file or a
directory, the server will return NFS4ERR_INVAL.
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
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.
15.39. Operation 39: RELEASE_LOCKOWNER - Release Lockowner State
15.39.1. SYNOPSIS
lockowner -> ()
15.39.2. ARGUMENT
struct RELEASE_LOCKOWNER4args {
lock_owner4 lock_owner;
};
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15.39.3. RESULT
struct RELEASE_LOCKOWNER4res {
nfsstat4 status;
};
15.39.4. DESCRIPTION
This operation is used to notify the server that the lock_owner is no
longer in use by the client. This allows the server to release
cached state related to the specified lock_owner. If file locks,
associated with the lock_owner, are held at the server, the error
NFS4ERR_LOCKS_HELD will be returned and no further action will be
taken.
15.39.5. IMPLEMENTATION
The client may choose to use this operation to ease the amount of
server state that is held. Depending on behavior of applications at
the client, it may be important for the client to use this operation
since the server has certain obligations with respect to holding a
reference to a lock_owner as long as the associated file is open.
Therefore, if the client knows for certain that the lock_owner will
no longer be used under the context of the associated open_owner4, it
should use RELEASE_LOCKOWNER.
15.40. Operation 10044: ILLEGAL - Illegal operation
15.40.1. SYNOPSIS
<null> -> ()
15.40.2. ARGUMENT
void;
15.40.3. RESULT
struct ILLEGAL4res {
nfsstat4 status;
};
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15.40.4. 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 Section 15.2.4 for more details.
The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
15.40.5. 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.
16. NFS version 4 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.
16.1. Procedure 0: CB_NULL - No Operation
16.1.1. SYNOPSIS
<null>
16.1.2. ARGUMENT
void;
16.1.3. RESULT
void;
16.1.4. 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.
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16.2. Procedure 1: CB_COMPOUND - Compound Operations
16.2.1. SYNOPSIS
compoundargs -> compoundres
16.2.2. ARGUMENT
enum nfs_cb_opnum4 {
OP_CB_GETATTR = 3,
OP_CB_RECALL = 4,
OP_CB_ILLEGAL = 10044
};
union nfs_cb_argop4 switch (unsigned argop) {
case OP_CB_GETATTR:
CB_GETATTR4args opcbgetattr;
case OP_CB_RECALL:
CB_RECALL4args opcbrecall;
case OP_CB_ILLEGAL: void;
};
struct CB_COMPOUND4args {
comptag4 tag;
uint32_t minorversion;
uint32_t callback_ident;
nfs_cb_argop4 argarray<>;
};
16.2.3. RESULT
union nfs_cb_resop4 switch (unsigned resop) {
case OP_CB_GETATTR: CB_GETATTR4res opcbgetattr;
case OP_CB_RECALL: CB_RECALL4res opcbrecall;
case OP_CB_ILLEGAL: CB_ILLEGAL4res opcbillegal;
};
struct CB_COMPOUND4res {
nfsstat4 status;
comptag4 tag;
nfs_cb_resop4 resarray<>;
};
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16.2.4. 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. In this case, the
error NFS4ERR_RESOURCE will be returned for the particular operation
within the CB_COMPOUND procedure where the resource exhaustion
occurred. This assumes that all previous operations within the
CB_COMPOUND sequence have been evaluated successfully.
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 the definition of the "tag" field, see Section 15.2.
The value of callback_ident is supplied by the client during
SETCLIENTID. The server must use the client supplied callback_ident
during the CB_COMPOUND to allow the client to properly identify the
server.
Illegal operation codes are handled in the same way as they are
handled for the COMPOUND procedure.
16.2.5. 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.
16.2.6. Operation 3: CB_GETATTR - Get Attributes
16.2.6.1. SYNOPSIS
fh, attr_request -> attrmask, attr_vals
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16.2.6.2. ARGUMENT
struct CB_GETATTR4args {
nfs_fh4 fh;
bitmap4 attr_request;
};
16.2.6.3. RESULT
struct CB_GETATTR4resok {
fattr4 obj_attributes;
};
union CB_GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
CB_GETATTR4resok resok4;
default:
void;
};
16.2.6.4. 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.
16.2.6.5. 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).
16.2.7. Operation 4: CB_RECALL - Recall an Open Delegation
16.2.7.1. SYNOPSIS
stateid, truncate, fh -> ()
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16.2.7.2. ARGUMENT
struct CB_RECALL4args {
stateid4 stateid;
bool truncate;
nfs_fh4 fh;
};
16.2.7.3. RESULT
struct CB_RECALL4res {
nfsstat4 status;
};
16.2.7.4. 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.
16.2.7.5. 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.
16.2.8. Operation 10044: CB_ILLEGAL - Illegal Callback Operation
16.2.8.1. SYNOPSIS
<null> -> ()
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16.2.8.2. ARGUMENT
void;
16.2.8.3. RESULT
/*
* CB_ILLEGAL: Response for illegal operation numbers
*/
struct CB_ILLEGAL4res {
nfsstat4 status;
};
16.2.8.4. 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 Section 15.2.4 for more details.
The status field of CB_ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
16.2.8.5. 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.
17. Security Considerations
NFS has historically used a model where, from an authentication
perspective, the client was the entire machine, or at least the
source IP 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 IP 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 IP 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 safe
model. Thus, NFSv4 mandates that implementations 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
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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 as part of Section 3.
Note that while NFSv4 mandates an end to end mutual authentication
model, the "classic" model of machine authentication via IP address
checking and AUTH_SYS identification can still be supported with the
caveat that the AUTH_SYS flavor is neither MANDATORY 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 NFS version 4
implementations may choose to not use security mechanisms that enable
integrity protection on each remote procedure call and response. The
use of mechanisms without integrity leaves the customer vulnerable to
an attacker in between 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 two
operations in particular that warrant the implementation overriding
user choices.
The first such operation is SECINFO. It is recommended that the
client issue the SECINFO call such that it is protected with a
security flavor that has integrity protection, such as RPCSEC_GSS
with a security triple that uses either rpc_gss_svc_integrity or
rpc_gss_svc_privacy (rpc_gss_svc_privacy includes integrity
protection) service. Without integrity protection encapsulating
SECINFO and therefore its 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.
Because the operations SETCLIENTID/SETCLIENTID_CONFIRM are
responsible for the release of client state, it is imperative that
the principal used for these operations is checked against and match
the previous use of these operations. See Section 9.1.1 for further
discussion.
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18. IANA Considerations
18.1. Named Attribute Definition
The NFS version 4 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
NFS version 4 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.
18.2. ONC RPC Network Identifiers (netids)
Section 2.2 discussed the r_netid field and the corresponding r_addr
field of a clientaddr4 structure. The NFS version 4 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 2.2 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:
"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.
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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 [18]. Additionally, the
two alternative forms specified in Section 2.2 of [18] are also
acceptable.
As mentioned, the registration of new Network Identifiers will
require the publication of an Information RFC with similar detail as
listed above for the Network Identifier itself and corresponding
Universal Address.
19. References
19.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", March 1997.
[2] Haynes, T. and D. Noveck, "NFSv4 Version 0 XDR Description",
draft-ietf-nfsv4-rfc3530bis-dot-x-02 (work in progress),
Jul 2010.
[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
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Internet-Draft NFSv4 October 2010
Specification", RFC 2203, September 1997.
[5] Eisler, M., "LIPKEY - A Low Infrastructure Public Key Mechanism
Using SPKM", RFC 2847, June 2000.
[6] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[7] 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.
[8] Alvestrand, H., "IETF Policy on Character Sets and Languages",
BCP 18, RFC 2277, January 1998.
[9] Hoffman, P. and M. Blanchet, "Preparation of Internationalized
Strings ("stringprep")", RFC 3454, December 2002.
[10] Klensin, J., "Internationalized Domain Names in Applications
(IDNA): Protocol", draft-ietf-idnabis-protocol-18 (work in
progress), January 2010.
19.2. Informative References
[11] 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.
[12] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame,
C., Eisler, M., and D. Noveck, "Network File System (NFS)
version 4 Protocol", RFC 3010, December 2000.
[13] Nowicki, B., "NFS: Network File System Protocol specification",
RFC 1094, March 1989.
[14] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS Version 3
Protocol Specification", RFC 1813, June 1995.
[15] Srinivasan, R., "XDR: External Data Representation Standard",
RFC 1832, August 1995.
[16] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1964,
June 1996.
[17] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, August 1995.
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[18] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[19] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
line Database", RFC 3232, January 2002.
[20] Floyd, S. and V. Jacobson, "The Synchronization of Periodic
Routing Messages", IEEE/ACM Transactions on Networking 2(2),
pp. 122-136, April 1994.
[21] 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.
[22] Adams, C., "The Simple Public-Key GSS-API Mechanism (SPKM)",
RFC 2025, October 1996.
[23] Callaghan, B., "WebNFS Client Specification", RFC 2054,
October 1996.
[24] Callaghan, B., "WebNFS Server Specification", RFC 2055,
October 1996.
[25] Shepler, S., "NFS Version 4 Design Considerations", RFC 2624,
June 1999.
[26] Simonsen, K., "Character Mnemonics and Character Sets",
RFC 1345, June 1992.
[27] Shepler, S., Eisler, M., and D. Noveck, "Network File System
(NFS) Version 4 Minor Version 1 Protocol", RFC 5661,
January 2010.
[28] The Open Group, "Protocols for Interworking: XNFS, Version 3W,
ISBN 1-85912-184-5", February 1998.
[29] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981.
[30] Juszczak, C., "Improving the Performance and Correctness of an
NFS Server", USENIX Conference Proceedings , June 1990.
[31] Callaghan, B., "NFS URL Scheme", RFC 2224, October 1997.
[32] Chiu, A., Eisler, M., and B. Callaghan, "Security Negotiation
for WebNFS", RFC 2755, January 2000.
[33] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
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Internet-Draft NFSv4 October 2010
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
Appendix A. Acknowledgments
Rob Thurlow clarified how a client should contact a new server if a
migration has occured.
David Black, Nico Williams, Mike Eisler, Trond Myklebust, and James
Lentini read many drafts of Section 12 and contributed numerous
useful suggestions, without which the necessary revision of that
section for this document would not have been possible.
Peter Staubach read almost all of the drafts of Section 12 leading to
the published result and his numerous comments were always useful and
contributed substantially to improving the quality of the final
result.
James Lentini graciously read the rewrite of Section 7 and his
comments were vital in improving the quality of that effort.
Rob Thurlow, Sorin Faibish, James Lentini, Bruce Fields, and Trond
Myklebust were faithful attendants of the biweekly triage meeting and
accepted many an action item.
Appendix B. RFC Editor Notes
[RFC Editor: please remove this section prior to publishing this
document as an RFC]
[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the
RFC number of this document]
Authors' Addresses
Thomas Haynes
NetApp
9110 E 66th St
Tulsa, OK 74133
USA
Phone: +1 918 307 1415
Email: thomas@netapp.com
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David Noveck
EMC
32 Coslin Drive
Southborough, MA 01772
US
Phone: +1 508 305 8404
Email: novecd@emc.com
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