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Versions: 00 01 02 03 04 05 06 07 08 09 10 11
12 13 14 15 16 17 18 19 20 21 22 23
24 25 26 27 28 29 RFC 5661
NFSv4 S. Shepler
Internet-Draft M. Eisler
Intended status: Standards Track D. Noveck
Expires: April 25, 2007 Editors
October 22, 2006
NFSv4 Minor Version 1
draft-ietf-nfsv4-minorversion1-08.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
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This Internet-Draft will expire on April 25, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This Internet-Draft describes NFSv4 minor version one, including
features retained from the base protocol and protocol extensions made
subsequently. The current draft includes description of the major
extensions, Sessions, Directory Delegations, and parallel NFS (pNFS).
This Internet-Draft is an active work item of the NFSv4 working
group. Active and resolved issues may be found in the issue tracker
at: http://www.nfsv4-editor.org/cgi-bin/roundup/nfsv4. New issues
Shepler, et al. Expires April 25, 2007 [Page 1]
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related to this document should be raised with the NFSv4 Working
Group nfsv4@ietf.org and logged in the issue tracker.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 9
1.1. The NFSv4.1 Protocol . . . . . . . . . . . . . . . . . . 9
1.2. NFS Version 4 Goals . . . . . . . . . . . . . . . . . . 9
1.3. Minor Version 1 Goals . . . . . . . . . . . . . . . . . 10
1.4. Overview of NFS version 4.1 Features . . . . . . . . . . 10
1.4.1. RPC and Security . . . . . . . . . . . . . . . . . . 11
1.4.2. Protocol Structure . . . . . . . . . . . . . . . . . 11
1.4.3. File System Model . . . . . . . . . . . . . . . . . 12
1.4.4. Locking Facilities . . . . . . . . . . . . . . . . . 13
1.5. General Definitions . . . . . . . . . . . . . . . . . . 14
1.6. Differences from NFSv4.0 . . . . . . . . . . . . . . . . 16
2. Core Infrastructure . . . . . . . . . . . . . . . . . . . . . 16
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 16
2.2. RPC and XDR . . . . . . . . . . . . . . . . . . . . . . 16
2.2.1. RPC-based Security . . . . . . . . . . . . . . . . . 16
2.3. COMPOUND and CB_COMPOUND . . . . . . . . . . . . . . . . 20
2.4. Client Identifiers . . . . . . . . . . . . . . . . . . . 20
2.4.1. Server Release of Clientid . . . . . . . . . . . . . 24
2.5. Security Service Negotiation . . . . . . . . . . . . . . 25
2.5.1. NFSv4 Security Tuples . . . . . . . . . . . . . . . 25
2.5.2. SECINFO and SECINFO_NO_NAME . . . . . . . . . . . . 25
2.5.3. Security Error . . . . . . . . . . . . . . . . . . . 26
2.6. Minor Versioning . . . . . . . . . . . . . . . . . . . . 29
2.7. Non-RPC-based Security Services . . . . . . . . . . . . 31
2.7.1. Authorization . . . . . . . . . . . . . . . . . . . 31
2.7.2. Auditing . . . . . . . . . . . . . . . . . . . . . . 32
2.7.3. Intrusion Detection . . . . . . . . . . . . . . . . 32
2.8. Transport Layers . . . . . . . . . . . . . . . . . . . . 32
2.8.1. Required and Recommended Properties of Transports . 32
2.8.2. Client and Server Transport Behavior . . . . . . . . 33
2.8.3. Ports . . . . . . . . . . . . . . . . . . . . . . . 34
2.9. Session . . . . . . . . . . . . . . . . . . . . . . . . 34
2.9.1. Motivation and Overview . . . . . . . . . . . . . . 34
2.9.2. NFSv4 Integration . . . . . . . . . . . . . . . . . 35
2.9.3. Channels . . . . . . . . . . . . . . . . . . . . . . 36
2.9.4. Exactly Once Semantics . . . . . . . . . . . . . . . 39
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2.9.5. RDMA Considerations . . . . . . . . . . . . . . . . 47
2.9.6. Sessions Security . . . . . . . . . . . . . . . . . 50
2.9.7. Session Mechanics - Steady State . . . . . . . . . . 54
2.9.8. Session Mechanics - Recovery . . . . . . . . . . . . 55
3. Protocol Data Types . . . . . . . . . . . . . . . . . . . . . 58
3.1. Basic Data Types . . . . . . . . . . . . . . . . . . . . 59
3.2. Structured Data Types . . . . . . . . . . . . . . . . . 60
4. Filehandles . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.1. Obtaining the First Filehandle . . . . . . . . . . . . . 70
4.1.1. Root Filehandle . . . . . . . . . . . . . . . . . . 70
4.1.2. Public Filehandle . . . . . . . . . . . . . . . . . 70
4.2. Filehandle Types . . . . . . . . . . . . . . . . . . . . 71
4.2.1. General Properties of a Filehandle . . . . . . . . . 71
4.2.2. Persistent Filehandle . . . . . . . . . . . . . . . 72
4.2.3. Volatile Filehandle . . . . . . . . . . . . . . . . 72
4.3. One Method of Constructing a Volatile Filehandle . . . . 73
4.4. Client Recovery from Filehandle Expiration . . . . . . . 74
5. File Attributes . . . . . . . . . . . . . . . . . . . . . . . 75
5.1. Mandatory Attributes . . . . . . . . . . . . . . . . . . 76
5.2. Recommended Attributes . . . . . . . . . . . . . . . . . 76
5.3. Named Attributes . . . . . . . . . . . . . . . . . . . . 77
5.4. Classification of Attributes . . . . . . . . . . . . . . 77
5.5. Mandatory Attributes - Definitions . . . . . . . . . . . 78
5.6. Recommended Attributes - Definitions . . . . . . . . . . 80
5.7. Time Access . . . . . . . . . . . . . . . . . . . . . . 89
5.8. Interpreting owner and owner_group . . . . . . . . . . . 90
5.9. Character Case Attributes . . . . . . . . . . . . . . . 92
5.10. Quota Attributes . . . . . . . . . . . . . . . . . . . . 92
5.11. mounted_on_fileid . . . . . . . . . . . . . . . . . . . 93
5.12. send_impl_id and recv_impl_id . . . . . . . . . . . . . 94
5.13. fs_layout_type . . . . . . . . . . . . . . . . . . . . . 94
5.14. layout_type . . . . . . . . . . . . . . . . . . . . . . 94
5.15. layout_hint . . . . . . . . . . . . . . . . . . . . . . 95
5.16. mdsthreshold . . . . . . . . . . . . . . . . . . . . . . 95
5.17. Retention Attributes . . . . . . . . . . . . . . . . . . 95
6. Access Control Lists . . . . . . . . . . . . . . . . . . . . 97
6.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . 97
6.2. File Attributes Discussion . . . . . . . . . . . . . . . 99
6.2.1. ACL Attribute . . . . . . . . . . . . . . . . . . . 99
6.2.2. mode Attribute . . . . . . . . . . . . . . . . . . . 110
6.3. Common Methods . . . . . . . . . . . . . . . . . . . . . 111
6.3.1. Interpreting an ACL . . . . . . . . . . . . . . . . 111
6.3.2. Computing a Mode Attribute from an ACL . . . . . . . 112
6.4. Requirements . . . . . . . . . . . . . . . . . . . . . . 113
6.4.1. Setting the mode and/or ACL Attributes . . . . . . . 114
6.4.2. Retrieving the mode and/or ACL Attributes . . . . . 115
6.4.3. Creating New Objects . . . . . . . . . . . . . . . . 115
7. Single-server Name Space . . . . . . . . . . . . . . . . . . 117
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7.1. Server Exports . . . . . . . . . . . . . . . . . . . . . 117
7.2. Browsing Exports . . . . . . . . . . . . . . . . . . . . 118
7.3. Server Pseudo File System . . . . . . . . . . . . . . . 118
7.4. Multiple Roots . . . . . . . . . . . . . . . . . . . . . 119
7.5. Filehandle Volatility . . . . . . . . . . . . . . . . . 119
7.6. Exported Root . . . . . . . . . . . . . . . . . . . . . 119
7.7. Mount Point Crossing . . . . . . . . . . . . . . . . . . 119
7.8. Security Policy and Name Space Presentation . . . . . . 120
8. File Locking and Share Reservations . . . . . . . . . . . . . 121
8.1. Locking . . . . . . . . . . . . . . . . . . . . . . . . 121
8.1.1. Client and Session ID . . . . . . . . . . . . . . . 122
8.1.2. State-owner and Stateid Definition . . . . . . . . . 122
8.1.3. Use of the Stateid and Locking . . . . . . . . . . . 124
8.2. Lock Ranges . . . . . . . . . . . . . . . . . . . . . . 127
8.3. Upgrading and Downgrading Locks . . . . . . . . . . . . 127
8.4. Blocking Locks . . . . . . . . . . . . . . . . . . . . . 128
8.5. Lease Renewal . . . . . . . . . . . . . . . . . . . . . 128
8.6. Crash Recovery . . . . . . . . . . . . . . . . . . . . . 129
8.6.1. Client Failure and Recovery . . . . . . . . . . . . 129
8.6.2. Server Failure and Recovery . . . . . . . . . . . . 130
8.6.3. Network Partitions and Recovery . . . . . . . . . . 132
8.7. Server Revocation of Locks . . . . . . . . . . . . . . . 136
8.8. Share Reservations . . . . . . . . . . . . . . . . . . . 137
8.9. OPEN/CLOSE Operations . . . . . . . . . . . . . . . . . 138
8.10. Open Upgrade and Downgrade . . . . . . . . . . . . . . . 139
8.11. Short and Long Leases . . . . . . . . . . . . . . . . . 139
8.12. Clocks, Propagation Delay, and Calculating Lease
Expiration . . . . . . . . . . . . . . . . . . . . . . . 140
8.13. Vestigial Locking Infrastructure From V4.0 . . . . . . . 140
9. Client-Side Caching . . . . . . . . . . . . . . . . . . . . . 141
9.1. Performance Challenges for Client-Side Caching . . . . . 142
9.2. Delegation and Callbacks . . . . . . . . . . . . . . . . 143
9.2.1. Delegation Recovery . . . . . . . . . . . . . . . . 144
9.3. Data Caching . . . . . . . . . . . . . . . . . . . . . . 146
9.3.1. Data Caching and OPENs . . . . . . . . . . . . . . . 146
9.3.2. Data Caching and File Locking . . . . . . . . . . . 147
9.3.3. Data Caching and Mandatory File Locking . . . . . . 149
9.3.4. Data Caching and File Identity . . . . . . . . . . . 149
9.4. Open Delegation . . . . . . . . . . . . . . . . . . . . 150
9.4.1. Open Delegation and Data Caching . . . . . . . . . . 153
9.4.2. Open Delegation and File Locks . . . . . . . . . . . 154
9.4.3. Handling of CB_GETATTR . . . . . . . . . . . . . . . 154
9.4.4. Recall of Open Delegation . . . . . . . . . . . . . 157
9.4.5. Clients that Fail to Honor Delegation Recalls . . . 159
9.4.6. Delegation Revocation . . . . . . . . . . . . . . . 160
9.5. Data Caching and Revocation . . . . . . . . . . . . . . 160
9.5.1. Revocation Recovery for Write Open Delegation . . . 161
9.6. Attribute Caching . . . . . . . . . . . . . . . . . . . 162
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9.7. Data and Metadata Caching and Memory Mapped Files . . . 164
9.8. Name Caching . . . . . . . . . . . . . . . . . . . . . . 166
9.9. Directory Caching . . . . . . . . . . . . . . . . . . . 167
10. Multi-server Name Space . . . . . . . . . . . . . . . . . . . 168
10.1. Location attributes . . . . . . . . . . . . . . . . . . 168
10.2. File System Presence or Absence . . . . . . . . . . . . 168
10.3. Getting Attributes for an Absent File System . . . . . . 170
10.3.1. GETATTR Within an Absent File System . . . . . . . . 170
10.3.2. READDIR and Absent File Systems . . . . . . . . . . 171
10.4. Uses of Location Information . . . . . . . . . . . . . . 172
10.4.1. File System Replication . . . . . . . . . . . . . . 172
10.4.2. File System Migration . . . . . . . . . . . . . . . 174
10.4.3. Referrals . . . . . . . . . . . . . . . . . . . . . 175
10.5. Additional Client-side Considerations . . . . . . . . . 176
10.6. Effecting File System Transitions . . . . . . . . . . . 177
10.6.1. File System Transitions and Simultaneous Access . . 178
10.6.2. Simultaneous Use and Transparent Transitions . . . . 179
10.6.3. Filehandles and File System Transitions . . . . . . 181
10.6.4. Fileid's and File System Transitions . . . . . . . . 181
10.6.5. Fsid's and File System Transitions . . . . . . . . . 182
10.6.6. The Change Attribute and File System Transitions . . 182
10.6.7. Lock State and File System Transitions . . . . . . . 183
10.6.8. Write Verifiers and File System Transitions . . . . 186
10.7. Effecting File System Referrals . . . . . . . . . . . . 186
10.7.1. Referral Example (LOOKUP) . . . . . . . . . . . . . 187
10.7.2. Referral Example (READDIR) . . . . . . . . . . . . . 191
10.8. The Attribute fs_absent . . . . . . . . . . . . . . . . 193
10.9. The Attribute fs_locations . . . . . . . . . . . . . . . 193
10.10. The Attribute fs_locations_info . . . . . . . . . . . . 195
10.10.1. The location4_server Structure . . . . . . . . . . . 198
10.10.2. The location4_info Structure . . . . . . . . . . . . 203
10.10.3. The location4_item Structure . . . . . . . . . . . . 204
10.11. The Attribute fs_status . . . . . . . . . . . . . . . . 205
11. Directory Delegations . . . . . . . . . . . . . . . . . . . . 209
11.1. Introduction to Directory Delegations . . . . . . . . . 209
11.2. Directory Delegation Design (in brief) . . . . . . . . . 210
11.3. Recommended Attributes in support of Directory
Delegations . . . . . . . . . . . . . . . . . . . . . . 211
11.4. Delegation Recall . . . . . . . . . . . . . . . . . . . 212
11.5. Directory Delegation Recovery . . . . . . . . . . . . . 212
12. Parallel NFS (pNFS) . . . . . . . . . . . . . . . . . . . . . 212
12.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 212
12.2. General Definitions . . . . . . . . . . . . . . . . . . 215
12.2.1. Metadata Server . . . . . . . . . . . . . . . . . . 215
12.2.2. Client . . . . . . . . . . . . . . . . . . . . . . . 215
12.2.3. Storage Device . . . . . . . . . . . . . . . . . . . 215
12.2.4. Storage Protocol . . . . . . . . . . . . . . . . . . 215
12.2.5. Control Protocol . . . . . . . . . . . . . . . . . . 216
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12.2.6. Metadata . . . . . . . . . . . . . . . . . . . . . . 216
12.2.7. Layout . . . . . . . . . . . . . . . . . . . . . . . 216
12.3. pNFS protocol semantics . . . . . . . . . . . . . . . . 217
12.3.1. Definitions . . . . . . . . . . . . . . . . . . . . 217
12.3.2. Guarantees Provided by Layouts . . . . . . . . . . . 220
12.3.3. Getting a Layout . . . . . . . . . . . . . . . . . . 221
12.3.4. Committing a Layout . . . . . . . . . . . . . . . . 222
12.3.5. Recalling a Layout . . . . . . . . . . . . . . . . . 224
12.3.6. Metadata Server Write Propagation . . . . . . . . . 230
12.3.7. Crash Recovery . . . . . . . . . . . . . . . . . . . 230
12.3.8. Security Considerations . . . . . . . . . . . . . . 236
12.4. The NFSv4.1 File Layout Type . . . . . . . . . . . . . . 237
12.4.1. Session Considerations . . . . . . . . . . . . . . . 237
12.4.2. File Striping and Data Access . . . . . . . . . . . 237
12.4.3. Global Stateid Requirements . . . . . . . . . . . . 246
12.4.4. The Layout Iomode . . . . . . . . . . . . . . . . . 246
12.4.5. Storage Device State Propagation . . . . . . . . . . 246
12.4.6. Storage Device Component File Size . . . . . . . . . 249
12.4.7. Crash Recovery Considerations . . . . . . . . . . . 249
12.4.8. Security Considerations for the File Layout Type . . 250
12.4.9. Alternate Approaches . . . . . . . . . . . . . . . . 250
13. Internationalization . . . . . . . . . . . . . . . . . . . . 251
13.1. Stringprep profile for the utf8str_cs type . . . . . . . 253
13.2. Stringprep profile for the utf8str_cis type . . . . . . 254
13.3. Stringprep profile for the utf8str_mixed type . . . . . 256
13.4. UTF-8 Related Errors . . . . . . . . . . . . . . . . . . 257
14. Error Values . . . . . . . . . . . . . . . . . . . . . . . . 257
14.1. Error Definitions . . . . . . . . . . . . . . . . . . . 258
14.2. Operations and their valid errors . . . . . . . . . . . 271
14.3. Callback operations and their valid errors . . . . . . . 284
14.4. Errors and the operations that use them . . . . . . . . 285
15. NFS version 4.1 Procedures . . . . . . . . . . . . . . . . . 292
15.1. Procedure 0: NULL - No Operation . . . . . . . . . . . . 292
15.2. Procedure 1: COMPOUND - Compound Operations . . . . . . 293
16. NFS version 4.1 Operations . . . . . . . . . . . . . . . . . 298
16.1. Operation 3: ACCESS - Check Access Rights . . . . . . . 298
16.2. Operation 4: CLOSE - Close File . . . . . . . . . . . . 300
16.3. Operation 5: COMMIT - Commit Cached Data . . . . . . . . 302
16.4. Operation 6: CREATE - Create a Non-Regular File Object . 304
16.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting
Recovery . . . . . . . . . . . . . . . . . . . . . . . . 307
16.6. Operation 8: DELEGRETURN - Return Delegation . . . . . . 308
16.7. Operation 9: GETATTR - Get Attributes . . . . . . . . . 308
16.8. Operation 10: GETFH - Get Current Filehandle . . . . . . 310
16.9. Operation 11: LINK - Create Link to a File . . . . . . . 311
16.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 312
16.11. Operation 13: LOCKT - Test For Lock . . . . . . . . . . 316
16.12. Operation 14: LOCKU - Unlock File . . . . . . . . . . . 317
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16.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 318
16.14. Operation 16: LOOKUPP - Lookup Parent Directory . . . . 320
16.15. Operation 17: NVERIFY - Verify Difference in
Attributes . . . . . . . . . . . . . . . . . . . . . . . 321
16.16. Operation 18: OPEN - Open a Regular File . . . . . . . . 323
16.17. Operation 19: OPENATTR - Open Named Attribute
Directory . . . . . . . . . . . . . . . . . . . . . . . 337
16.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 338
16.19. Operation 22: PUTFH - Set Current Filehandle . . . . . . 339
16.20. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 340
16.21. Operation 24: PUTROOTFH - Set Root Filehandle . . . . . 342
16.22. Operation 25: READ - Read from File . . . . . . . . . . 343
16.23. Operation 26: READDIR - Read Directory . . . . . . . . . 345
16.24. Operation 27: READLINK - Read Symbolic Link . . . . . . 349
16.25. Operation 28: REMOVE - Remove File System Object . . . . 350
16.26. Operation 29: RENAME - Rename Directory Entry . . . . . 352
16.27. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 354
16.28. Operation 32: SAVEFH - Save Current Filehandle . . . . . 355
16.29. Operation 33: SECINFO - Obtain Available Security . . . 355
16.30. Operation 34: SETATTR - Set Attributes . . . . . . . . . 359
16.31. Operation 37: VERIFY - Verify Same Attributes . . . . . 361
16.32. Operation 38: WRITE - Write to File . . . . . . . . . . 362
16.33. Operation 40: BACKCHANNEL_CTL - Backchannel control . . 367
16.34. Operation 41: BIND_CONN_TO_SESSION . . . . . . . . . . . 369
16.35. Operation 42: EXCHANGE_ID - Instantiate Clientid . . . . 373
16.36. Operation 43: CREATE_SESSION - Create New Session and
Confirm Clientid . . . . . . . . . . . . . . . . . . . . 379
16.37. Operation 44: DESTROY_SESSION - Destroy existing
session . . . . . . . . . . . . . . . . . . . . . . . . 389
16.38. Operation 45: FREE_STATEID - Free stateid with no
locks . . . . . . . . . . . . . . . . . . . . . . . . . 390
16.39. Operation 46: GET_DIR_DELEGATION - Get a directory
delegation . . . . . . . . . . . . . . . . . . . . . . . 391
16.40. Operation 47: GETDEVICEINFO - Get Device Information . . 395
16.41. Operation 48: GETDEVICELIST . . . . . . . . . . . . . . 396
16.42. Operation 49: LAYOUTCOMMIT - Commit writes made using
a layout . . . . . . . . . . . . . . . . . . . . . . . . 397
16.43. Operation 50: LAYOUTGET - Get Layout Information . . . . 401
16.44. Operation 51: LAYOUTRETURN - Release Layout
Information . . . . . . . . . . . . . . . . . . . . . . 404
16.45. Operation 52: SECINFO_NO_NAME - Get Security on
Unnamed Object . . . . . . . . . . . . . . . . . . . . . 406
16.46. Operation 53: SEQUENCE - Supply per-procedure
sequencing and control . . . . . . . . . . . . . . . . . 408
16.47. Operation 54: SET_SSV . . . . . . . . . . . . . . . . . 411
16.48. Operation 55: TEST_STATEID - Test stateids for
validity . . . . . . . . . . . . . . . . . . . . . . . . 413
16.49. Operation 56: WANT_DELEGATION . . . . . . . . . . . . . 414
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16.50. Operation 10044: ILLEGAL - Illegal operation . . . . . . 417
17. NFS version 4.1 Callback Procedures . . . . . . . . . . . . . 418
17.1. Procedure 0: CB_NULL - No Operation . . . . . . . . . . 418
17.2. Procedure 1: CB_COMPOUND - Compound Operations . . . . . 418
18. NFS version 4.1 Callback Operations . . . . . . . . . . . . . 420
18.1. Operation 3: CB_GETATTR - Get Attributes . . . . . . . . 420
18.2. Operation 4: CB_RECALL - Recall an Open Delegation . . . 422
18.3. Operation 5: CB_LAYOUTRECALL . . . . . . . . . . . . . . 423
18.4. Operation 6: CB_NOTIFY - Notify directory changes . . . 425
18.5. Operation 7: CB_PUSH_DELEG . . . . . . . . . . . . . . . 428
18.6. Operation 8: CB_RECALL_ANY - Keep any N delegations . . 429
18.7. Operation 9: CB_RECALLABLE_OBJ_AVAIL . . . . . . . . . . 432
18.8. Operation 10: CB_RECALL_SLOT - change flow control
limits . . . . . . . . . . . . . . . . . . . . . . . . . 433
18.9. Operation 11: CB_SEQUENCE - Supply callback channel
sequencing and control . . . . . . . . . . . . . . . . . 434
18.10. Operation 12: CB_WANTS_CANCELLED . . . . . . . . . . . . 436
18.11. Operation 13: CB_NOTIFY_LOCK - Notify of possible
lock availability . . . . . . . . . . . . . . . . . . . 437
18.12. Operation 10044: CB_ILLEGAL - Illegal Callback
Operation . . . . . . . . . . . . . . . . . . . . . . . 438
19. Security Considerations . . . . . . . . . . . . . . . . . . . 439
20. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 439
20.1. Defining new layout types . . . . . . . . . . . . . . . 439
21. References . . . . . . . . . . . . . . . . . . . . . . . . . 440
21.1. Normative References . . . . . . . . . . . . . . . . . . 440
21.2. Informative References . . . . . . . . . . . . . . . . . 441
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 442
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 443
Intellectual Property and Copyright Statements . . . . . . . . . 444
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1. Introduction
1.1. The NFSv4.1 Protocol
The NFSv4.1 protocol is a minor version of the NFSv4 protocol
described in [2]. It generally follows the guidelines for minor
versioning model laid in Section 10 of RFC 3530. However, it
diverges from guidelines 11 ("a client and server that supports minor
version X must support minor versions 0 through X-1"), and 12 ("no
features may be introduced as mandatory in a minor version"). These
divergences are due to the introduction of the sessions model for
managing non-idempotent operations and the RECLAIM_COMPLETE
operation. These two new features are infrastructural in nature and
simplify implementation of existing and other new features. Making
them optional would add undue complexity to protocol definition and
implementation. NFSv4.1 accordingly updates the Minor Versioning
guidelines (Section 2.6).
NFSv4.1, as a minor version, is consistent with the overall goals for
NFS Version 4, but extends the protocol so as to better meet those
goals, based on experiences with NFSv4.0. In addition, NFSv4.1 has
adopted some additional goals, which motivate some of the major
extensions in minor version 1.
1.2. NFS Version 4 Goals
The NFS version 4 protocol is a further revision of the NFS protocol
defined already by versions 2 [17]] and 3 [18]. It retains the
essential characteristics of previous versions: design for easy
recovery, independent of transport protocols, operating systems and
file systems, 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.
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o Good cross-platform interoperability.
The protocol features a file system model that provides a useful,
common set of features that does not unduly favor one file system
or operating system over another.
o Designed for protocol extensions.
The protocol is designed to accept standard extensions within a
framework that enable and encourages backward compatibility.
1.3. Minor Version 1 Goals
Minor version one has the following goals, within the framework
established by the overall version 4 goals.
o To correct significant structural weaknesses and oversights
discovered in the base protocol.
o To add clarity and specificity to areas left unaddressed or not
addressed in sufficient detail in the base protocol.
o To add specific features based on experience with the existing
protocol and recent industry developments.
o To provide protocol support to take advantage of clustered server
deployments including the ability to provide scalable parallel
access to files distributed among multiple servers.
1.4. Overview of NFS version 4.1 Features
To provide a reasonable context for the reader, the major features of
NFS version 4.1 protocol will be reviewed in brief. This will be
done to provide an appropriate context for both the reader who is
familiar with the previous versions of the NFS protocol and the
reader that is new to the NFS protocols. For the reader new to the
NFS protocols, there is still a set of fundamental knowledge that is
expected. The reader should be familiar with the XDR and RPC
protocols as described in [3] and [4]. A basic knowledge of file
systems and distributed file systems is expected as well.
This description of version 4.1 features will not distinguish those
added in minor version one from those present in the base protocol
but will treat minor version 1 as a unified whole. See Section 1.6
for a description of the differences between the two minor versions.
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1.4.1. 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 4.1 protocol are those defined in [3] and [4]. To meet end-
to-end security requirements, the RPCSEC_GSS framework [5] 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 [6] to provide one security framework.
The LIPKEY and SPKM-3 GSS-API mechanisms described in [7] will be
used to provide for the use of user password and client/server public
key certificates by the NFS version 4 protocol. With the use of
RPCSEC_GSS, other mechanisms may also be specified and used for NFS
version 4.1 security.
To enable in-band security negotiation, the NFS version 4.1 protocol
has operations which provide the client a method of querying the
server about its policies regarding which security mechanisms must be
used for access to the server's file system resources. With this,
the client can securely match the security mechanism that meets the
policies specified at both the client and server.
1.4.2. Protocol Structure
1.4.2.1. Core Protocol
Unlike NFS Versions 2 and 3, which used a series of ancillary
protocols (e.g. NLM, NSM, MOUNT), within all minor versions of NFS
version 4 only a single RPC protocol is used to make requests of the
server. Facilities that had been separate protocols, such as
locking, are now integrated within a single unified protocol.
1.4.2.2. Parallel Access
Minor version one supports high-performance data access to a
clustered server implementation by enabling a separation of metadata
access and data access, with the latter done to multiple servers in
parallel.
Such parallel data access is controlled by recallable objects known
as "layouts", which are integrated into the protocol locking model.
Clients direct requests for data access to a set of data servers
specified by the layout via a data storage protocol which may be
NFSv4.1 or may be another protocol.
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1.4.3. File System Model
The general file system model used for the NFS version 4.1 protocol
is the same as previous versions. The server file system is
hierarchical with the regular files contained within being treated as
opaque byte streams. In a slight departure, file and directory names
are encoded with UTF-8 to deal with the basics of
internationalization.
The NFS version 4.1 protocol does not require a separate protocol to
provide for the initial mapping between path name and filehandle.
All file systems exported by a server are presented as a tree so that
all file systems are reachable from a special per-server global root
filehandle. This allows LOOKUP operations to be used to perform
functions previously provided by the MOUNT protocol. The server
provides any necessary pseudo filesystems to bridge any gaps that
arise due unexported gaps between exported file systems.
1.4.3.1. Filehandles
As in previous versions of the NFS protocol, opaque filehandles are
used to identify individual files and directories. Lookup-type and
create operations are used to go from file and directory names to the
filehandle which is then used to identify the object to subsequent
operations.
The NFS version 4.1 protocol provides support for both persistent
filehandles, guaranteed to be valid for the lifetime of the file
system object designated. In addition it provides support to servers
to provide filehandles with more limited validity guarantees, called
volatile filehandles.
1.4.3.2. File Attributes
The NFS version 4.1 protocol has a rich and extensible attribute
structure. Only a small set of the defined attributes are mandatory
and must be provided by all server implementations. The other
attributes are known as "recommended" attributes.
One significant recommended file attribute is the Access Control List
(ACL) attribute. This attribute provides for directory and file
access control beyond the model used in NFS Versions 2 and 3. The
ACL definition allows for specification specific sets of permissions
for individual users and groups. In addition, ACL inheritance allows
propagation of access permissions and restriction down a directory
tree as filesystem objects are created.
One other type of attribute is the named attribute. A named
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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.
1.4.3.3. Multi-server Namespace
NFS Version 4.1 contains a number of features to allow implementation
of namespaces that cross server boundaries and that allow to and
facilitate a non-disruptive transfer of support for individual file
systems between servers. They are all based upon attributes that
allow one file system to specify alternate or new locations for that
file system.
These attributes may be used together with the concept of absent file
system which provide specifications for additional locations but no
actual file system content. This allows a number of important
facilities:
o Location attributes may be used with absent file systems to
implement referrals whereby one server may direct the client to a
file system provided by another server. This allows extensive
multi-server namespaces to be constructed.
o Location attributes may be provided for present file systems to
provide the locations alternate file system instances or replicas
to be used in the event that the current file system instance
becomes unavailable.
o Location attributes may be provided when a previously present file
system becomes absent. This allows non-disruptive migration of
file systems to alternate servers.
1.4.4. Locking Facilities
As mentioned previously, NFS v4.1, is a single protocol which
includes locking facilities. These locking facilities include
support for many types of locks including a number of sorts of
recallable locks. Recallable locks such as delegations allow the
client to be assured that certain events will not occur so long as
that lock is held. When circumstances change, the lock is recalled
via a callback via a callback request. The assurances provided by
delegations allow more extensive caching to be done safely when
circumstances allow it.
o Share reservations as established by OPEN operations.
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o Byte-range locks.
o File delegations which are recallable locks that assure the holder
that inconsistent opens and file changes cannot occur so long as
the delegation is held.
o Directory delegations which are recallable delegations that assure
the holder that inconsistent directory modifications cannot occur
so long as the delegation is held.
o Layouts which are recallable objects that assure the holder that
direct access to the file data may be performed directly by the
client and that no change to the data's location inconsistent with
that access may be made so long as the layout is held.
All locks for a given client are tied together under a single client-
wide lease. All requests made on sessions associated with the client
renew that lease. When leases are not promptly renewed lock are
subject to revocation. In the event of server reinitialization,
clients have the opportunity to safely reclaim their locks within a
special grace period.
1.5. 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 file system
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 any of record (byte- range)
locks, share reservations, delegations or layouts unless
specifically stated otherwise.
Server The "Server" is the entity responsible for coordinating
client access to a set of file systems.
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. 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.
1.6. Differences from NFSv4.0
The following summarizes the differences between minor version one
and the base protocol:
o Implementation of the sessions model.
o Support for parallel access to data.
o Addition of the RECLAIM_COMPLETE operation to better structure the
lock reclamation process.
o Support for delegations on directories and other file types in
addition to regular files.
o Operations to re-obtain a delegation.
o Support for client and server implementation id's.
2. Core Infrastructure
2.1. Introduction
NFS version 4.1 (NFSv4.1) relies on core infrastructure common to
nearly every operation. This core infrastructure is described in the
remainder of this section.
2.2. RPC and XDR
The NFS version 4.1 (NFSv4.1) protocol is a Remote Procedure Call
(RPC) application that uses RPC version 2 and the corresponding
eXternal Data Representation (XDR) as defined in RFC1831 [4] and
RFC4506 [3].
2.2.1. RPC-based Security
Previous NFS versions have been thought of as having a host-based
authentication model, where the NFS server authenticates the NFS
client, and trust the client to authenticate all users. Actually,
NFS has always depended on RPC for authentication. The first form of
RPC authentication which required a host-based authentication
approach. NFSv4 also depends on RPC for basic security services, and
mandates RPC support for a user-based authentication model. The
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user-based authentication model has user principals authenticated by
a server, and in turn the server authenticated by user principals.
RPC provides some basic security services which are used by NFSv4.
2.2.1.1. RPC Security Flavors
As described in section 7.2 "Authentication" of [4], RPC security is
encapsulated in the RPC header, via a security or authentication
flavor, and information specific to the specification of the security
flavor. Every RPC header conveys information used to identify and
authenticate a client and server. As discussed in Section 2.2.1.1.1,
some security flavors provide additional security services.
NFSv4 clients and servers MUST implement RPCSEC_GSS. (This
requirement to implement is not a requirement to use.) Other
flavors, such as AUTH_NONE, and AUTH_SYS, MAY be implemented as well.
2.2.1.1.1. RPCSEC_GSS and Security Services
RPCSEC_GSS ([5]) uses the functionality of GSS-API RFC2743 [8]. This
allows for the use of various security mechanisms by the RPC layer
without the additional implementation overhead of adding RPC security
flavors.
2.2.1.1.1.1. Identification, Authentication, Integrity, Privacy
Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate
users on clients to servers, and servers to users. It can also
perform integrity checking on the entire RPC message, including the
RPC header, and the arguments or results. Finally, privacy, usually
via encryption, is a service available with RPCSEC_GSS. Privacy is
performed on the arguments and results. Note that if privacy is
selected, integrity, authentication, and identification are enabled.
If privacy is not selected, but integrity is selected, authentication
and identification are enabled. If integrity and privacy are not
selected, but authentication is enabled, identification is enabled.
RPCSEC_GSS does not provide identification as a separate service.
Although GSS-API has an authentication service distinct from its
privacy and integrity services, use GSS-API's authentication service
is not used for RPCSEC_GSS's authentication service. Instead, each
RPC request and response header is integrity protected with the GSS-
API integrity service, and this allows RPCSEC_GSS to offer per-RPC
authentication and identity. See [5] for more information.
NFSv4 client and servers MUST support RPCSEC_GSS's integrity and
authentication service. NFSv4.1 servers MUST support RPCSEC_GSS's
privacy service.
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2.2.1.1.1.2. Security mechanisms for NFS version 4
RPCSEC_GSS, via GSS-API, normalizes access to mechanisms that provide
security services. Therefore NFSv4 clients and servers MUST support
three security mechanisms: Kerberos V5, SPKM-3, and LIPKEY.
The use of RPCSEC_GSS requires selection of: mechanism, quality of
protection (QOP), and service (authentication, integrity, privacy).
For the mandated security mechanisms, NFSv4 specifies that a QOP of
zero (0) is used, leaving it up to the mechanism or the mechanism's
configuration to use an appropriate level of protection that QOP zero
maps to. Each mandated mechanism specifies minimum set of
cryptographic algorithms for implementing integrity and privacy.
NFSv4 clients and servers MUST be implemented on operating
environments that comply with the mandatory cryptographic algorithms
of each mandated mechanism.
2.2.1.1.1.2.1. Kerberos V5
The Kerberos V5 GSS-API mechanism as described in RFC1964 [6] (
[[Comment.1: need new Kerberos RFC]] ) MUST be implemented with the
RPCSEC_GSS services as specified in the following table:
column descriptions:
1 == number of pseudo flavor
2 == name of pseudo flavor
3 == mechanism's OID
4 == RPCSEC_GSS service
5 == NFSv4.1 clients MUST support
6 == NFSv4.1 servers MUST support
1 2 3 4 5 6
------------------------------------------------------------------
390003 krb5 1.2.840.113554.1.2.2 rpc_gss_svc_none yes yes
390004 krb5i 1.2.840.113554.1.2.2 rpc_gss_svc_integrity yes yes
390005 krb5p 1.2.840.113554.1.2.2 rpc_gss_svc_privacy no yes
Note that the number and name of the pseudo flavor is presented here
as a mapping aid to the implementor. Because the NFSv4 protocol
includes a method to negotiate security and it understands the GSS-
API mechanism, the pseudo flavor is not needed. The pseudo flavor is
needed for the NFS version 3 since the security negotiation is done
via the MOUNT protocol as described in [19].
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2.2.1.1.1.2.2. LIPKEY
The LIPKEY V5 GSS-API mechanism as described in [7] MUST be
implemented with the RPCSEC_GSS services as specified in the
following table:
1 2 3 4 5 6
------------------------------------------------------------------
390006 lipkey 1.3.6.1.5.5.9 rpc_gss_svc_none yes yes
390007 lipkey-i 1.3.6.1.5.5.9 rpc_gss_svc_integrity yes yes
390008 lipkey-p 1.3.6.1.5.5.9 rpc_gss_svc_privacy no yes
2.2.1.1.1.2.3. SPKM-3 as a security triple
The SPKM-3 GSS-API mechanism as described in [7] MUST be implemented
with the RPCSEC_GSS services as specified in the following table:
1 2 3 4 5 6
------------------------------------------------------------------
390009 spkm3 1.3.6.1.5.5.1.3 rpc_gss_svc_none yes yes
390010 spkm3i 1.3.6.1.5.5.1.3 rpc_gss_svc_integrity yes yes
390011 spkm3p 1.3.6.1.5.5.1.3 rpc_gss_svc_privacy no yes
2.2.1.1.1.3. GSS Server Principal
Regardless of what security mechanism under RPCSEC_GSS is being used,
the NFS server, MUST identify itself in GSS-API via a
GSS_C_NT_HOSTBASED_SERVICE name type. GSS_C_NT_HOSTBASED_SERVICE
names are of the form:
service@hostname
For NFS, the "service" element is
nfs
Implementations of security mechanisms will convert nfs@hostname to
various different forms. For Kerberos V5, LIPKEY, and SPKM-3, the
following form is RECOMMENDED:
nfs/hostname
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2.3. COMPOUND and CB_COMPOUND
A significant departure from the versions of the NFS protocol before
version 4 is the introduction of the COMPOUND procedure. For the
NFSv4 protocol, in all minor versions, there are exactly two RPC
procedures, NULL and COMPOUND. The COMPOUND procedure is defined as
a series of individual operations and these operations perform the
sorts of functions performed by traditional NFS procedures.
The operations combined within a COMPOUND request are evaluated in
order by the server, without any atomicity guarantees. A limited set
of facilities exist to pass results from one operation to another.
Once an operation returns a failing result, the evaluation ends and
the results of all evaluated operations are returned to the client.
With the use of the COMPOUND procedure, the client is able to build
simple or complex requests. These COMPOUND requests allow for a
reduction in the number of RPCs needed for logical file system
operations. For example, multi-component lookup requests can be
constructed by combining multiple LOOKUP operations. Those can be
further combined with operations such as GETATTR, READDIR, or OPEN
plus READ to do more complicated sets of operation without incurring
additional latency.
NFSv4 also contains a considerable set of callback operations in
which the server makes an RPC directed at the client. Callback RPC's
have a similar structure to that of the normal server requests. For
the NFS version 4 protocol callbacks in all minor versions, there are
two RPC procedures, NULL and CB_COMPOUND. The CB_COMPOUND procedure
is defined in analogous fashion to that of COMPOUND with its own set
of callback operations.
Addition of new server and callback operation within the COMPOUND and
CB_COMPOUND request framework provide means of extending the protocol
in subsequent minor versions.
Except for a small number of operations needed for session creation,
server requests and callback requests are performed within the
context of a session. Sessions provide a client context for every
request and support robust replay protection for non-idempotent
requests.
2.4. Client Identifiers
For each operation that obtains or depends on locking state, the
specific client must be determinable by the server. In NFSv4, each
distinct client instance is represented by a clientid, which is a 64-
bit identifier that identifies a specific client at a given time and
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which is changed whenever the client or the server re-initializes.
Clientid's are used to support lock identification and crash
recovery.
In NFSv4.1, the clientid associated with each operation is derived
from the session (see Section 2.9) on which the operation is issued.
Each session is associated with a specific clientid at session
creation and that clientid then becomes the clientid associated with
all requests issued using it. Therefore, unlike NFSv4.0, no NFSv4.1
operation is possible until a clientid is established.
A sequence of an EXCHANGE_ID operation followed by a CREATE_SESSION
operation using that clientid is required to establish the
identification on the server. Establishment of identification by a
new incarnation of the client also has the effect of immediately
releasing any locking state that a previous incarnation of that same
client might have had on the server. Such released state would
include all lock, share reservation, 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 9.2.1.
Releasing such state requires that the server be able to determine
that one client instance is the successor of another. Where this
cannot be done, for any of a number of reasons, the locking state
will remain for a time subject to lease expiration (see Section 8.5)
and the new client will need to wait for such state to be removed, if
it makes conflicting lock requests.
Client identification is encapsulated in the following structure:
struct client_owner4 {
verifier4 co_verifier;
opaque co_ownerid<NFS4_OPAQUE_LIMIT>;
};
The first field, co_verifier, is a client incarnation verifier that
is used to detect client reboots. Only if the co_verifier is
different from that the server had previously recorded for the client
(as identified by the second field of the structure, co_ownerid) does
the server start the process of canceling the client's leased state.
The second field, co_ownerid is a variable length string that
uniquely defines the client so that subsequent instances of the same
client bear the same co_ownerid with a different verifier.
There are several considerations for how the client generates the
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co_ownerid string:
o The string should be unique so that multiple clients do not
present the same string. The consequences of two clients
presenting the same string range from one client getting an error
to one client having its leased state abruptly and unexpectedly
canceled.
o The string should be selected so the subsequent incarnations (e.g.
reboots) of the same client cause the client to present the same
string. The implementor is cautioned from an approach that
requires the string to be recorded in a local file because this
precludes the use of the implementation in an environment where
there is no local disk and all file access is from an NFS version
4 server.
o The string should be the same for each server network address that
the client accesses, rather than common to all server network
addresses (note: the precise opposite was advised in RFC3530).
This way, if a server has multiple interfaces, the client can
trunk traffic over multiple network paths as described in
Section 2.9.3.4.1.
o The algorithm for generating the string should not assume that the
client's network address will not change. This includes changes
between client incarnations and even changes while the client is
still running in its current incarnation. This means that if the
client includes just the client's and server's network address in
the co_ownerid string, there is a real risk, after the client
gives up the network address, that another client, using a similar
algorithm for generating the co_ownerid string, would generate a
conflicting co_ownerid string.
Given the above considerations, an example of a well generated
co_ownerid string is one that includes:
o 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).
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* A MAC address (again, a one way function should be performed).
* 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 co_ownerid
string is not the same as the principal issuing the EXCHANGE_ID.
A server may compare an client_owner4 in a EXCHANGE_ID with an
nfs_client_id4 established using SETCLIENTID using NFSv4 minor
version 0, so that an NFSv4.1 client is not forced to delay until
lease expiration for locking state established by the earlier client
using minor version 0. This requires the client_owner4 be
constructed the same way as the nfs_client_id4. If the latter's
contents included the server's network address, and the NFSv4.1
client does not wish to use a clientid that prevents trunking, it
should issue two EXCHANGE_ID operations. The first EXCHANGE_ID will
have a client_owner4 equal to the nfs_client_id4. This will clear
the state created by the NFSv4.0 client. The second EXCHANGE_ID will
not have the server's network address. The state created for the
second EXCHANGE_ID will not have to wait for lease expiration,
because there will be no state to expire.
Once a EXCHANGE_ID has been done, and the resulting clientid
established as associated with a session, all requests made on that
session implicitly identify that clientid, which in turn designates
the client specified using the long-form client_owner4 structure.
The 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.
In the event of a server restart, a client will find out that its
current clientid is no longer valid when receives a
NFS4ERR_STALE_CLIENTID error. The precise circumstances depend of
the characteristics of the sessions involved, specifically whether
the session is persistent (see Section 2.9.4.5).
When a session is not persistent, the client will need to create a
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new session. When the existing clientid is presented to a server as
part of creating a session 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 EXCHANGE_ID
operation and then use that clientid as the basis of the basis of a
new session and then proceed to any other necessary recovery for the
server reboot case (See Section 8.6.2).
In the case of the session being persistent, the client will re-
establish communication using the existing session after the reboot.
This session will be associated with a stale clientid and the client
will receive an indication of that fact in the sr_status field
returned by the SEQUENCE operation (see Section 2.9.2.1). The client
can then use the existing session to do whatever operations are
necessary to determine the status of requests outstanding at the time
of reboot, while avoiding issuing new requests, particularly any
involving locking on that session. Such requests would fail with
NFS4ERR_STALE_CLIENTID error or an NFS4ERR_STALE_STATEID error, if
attempted. In any case, the client would create a new clientid using
EXCHANGE_ID, create a new session based on that clientid, and proceed
to other necessary recovery for the server reboot case.
See the detailed descriptions of EXCHANGE_ID (Section 16.35 and
CREATE_SESSION (Section 16.36) for a complete specification of these
operations.
2.4.1. 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
EXCHANGE_ID/CREATE_SESSION 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 "associated state" includes sessions. As long as there are
sessions, the server MUST not release the clientid. See
Section 2.9.8.1.4 for discussion on releasing inactive sessions.
Note that if the id string in a EXCHANGE_ID request is properly
constructed, and if the client takes care to use the same principal
for each successive use of EXCHANGE_ID, then, barring an active
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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 EXCHANGE_ID 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 EXCHANGE_ID, and confirm the new clientid if followed by
the appropriate CREATE_SESSION.
2.5. Security Service 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 file system namespace
that are available for use by NFS clients. These points can be
considered security policy boundaries, and in some NFS
implementations are tied to NFS export points. In turn the NFS
server may be configured such that each of these security policy
boundaries may have different or multiple security mechanisms in use.
The security negotiation between client and server must be done with
a secure channel to eliminate the possibility of a third party
intercepting the negotiation sequence and forcing the client and
server to choose a lower level of security than required or desired.
See Section 19 for further discussion.
2.5.1. NFSv4 Security Tuples
An NFS server can assign one or more "security tuples" to each
security policy boundary in its namespace. Each security tuple
consists of a security flavor (see Section 2.2.1.1), and if the
flavor is RPCSEC_GSS, a GSS-API mechanism OID, a GSS-API quality of
protection, and an RPCSEC_GSS service.
2.5.2. SECINFO and SECINFO_NO_NAME
The SECINFO and SECINFO_NO_NAME operations allow the client to
determine, on a per filehandle basis, what security tuple is to be
used for server access. In general, the client will not have to use
either operation except during initial communication with the server
or when the client crosses security policy boundaries at the server.
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It is possible that the server's policies change during the client's
interaction therefore forcing the client to negotiate a new security
tuple.
Where the use of different security tuples would affect the type of
access that would be allowed if a request was issued over the same
connection used for the SECINFO or SECINFO_NO_NAME operation (e.g.
read-only vs. read-write) access, security tuples that allow greater
access should be presented first. Where the general level of access
is the same and different security flavors limit the range of
principals whose privileges are recognized (e.g. allowing or
disallowing root access), flavors supporting the greatest range of
principals should be listed first.
2.5.3. 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
Kerberos-V5 all under RPCSEC_GSS), the NFS client will initiate file
access to the server with one of the minimal security tuples. During
communication with the server, the client may receive an NFS error of
NFS4ERR_WRONGSEC. This error allows the server to notify the client
that the security tuple currently being used is contravenes the
server's security policy. The client is then responsible for
determining (see Section 2.5.3.1) what security tuples are available
at the server and choose one which is appropriate for the client.
2.5.3.1. Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME
This section explains of the mechanics of NFSv4.1 security
negotiation. Unless noted otherwise, for any mention of PUTFH in
this section, the reader should interpret it as applying to PUTROOTFH
and PUTPUBFH in addition to PUTFH.
2.5.3.1.1. PUTFH + LOOKUP (or OPEN by Name)
This situation also applies to a put filehandle operation followed by
an OPEN operation that specifies a component name.
In this situation, the client is potentially crossing a security
policy boundary, and the set of security tuples the parent directory
supports differ from those of the child. The server implementation
may decide whether to impose any restrictions on security policy
administration. There are at least three approaches
(sec_policy_child is the tuple set of the child export,
sec_policy_parent is that of the parent).
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a) sec_policy_child <= sec_policy_parent (<= for subset). This
means that the set of security tuples specified on the security
policy of a child directory is always a subset of that of its
parent directory.
b) sec_policy_child ^ sec_policy_parent != {} (^ for intersection,
{} for the empty set). This means that the security tuples
specified on the security policy of a child directory always has a
non empty intersection with that of the parent.
c) sec_policy_child ^ sec_policy_parent == {}. This means that
the set of tuples specified on the security policy of a child
directory may not intersect with that of the parent. In other
words, there are no restrictions on how the system administrator
may set.
For a server to support approach (b) (when client chooses a flavor
that is not a member of sec_policy_parent) and (c), PUTFH must NOT
return NFS4ERR_WRONGSEC in case of security mismatch. Instead, it
should be returned from the LOOKUP (or OPEN by component name) that
follows.
Since the above guideline does not contradict approach (a), it should
be followed in general. Even if approach (a) is implemented, it is
possible for the security tuple used to be acceptable for the target
of LOOKUP but not for the filehandles used in PUTFH. The PUTFH could
really be a PUTROOTFH or PUTPUBFH, where the client does not know the
security tuples for the root or public filehandle. Or the security
policy for the filehandle used by PUTFH could have changed since the
time the filehandle was obtained.
Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC in
response to PUTFH, PUTROOTFH, or PUTPUBFH if the operation is
immediately followed by a LOOKUP or an OPEN by component name.
2.5.3.1.2. PUTFH + LOOKUPP
Since SECINFO only works its way down, there is no way LOOKUPP can
return NFS4ERR_WRONGSEC without SECINFO_NO_NAME. SECINFO_NO_NAME
solves this issue because via style "parent", it works in the
opposite direction as SECINFO. As with Section 2.5.3.1.1, PUTFH must
not return NFS4ERR_WRONGSEC whenever it is followed by LOOKUPP. If
the server does not support SECINFO_NO_NAME, the client's only
recourse is to issue the PUTFH, LOOKUPP, GETFH sequence of operations
with every security tuple it supports.
Regardless whether SECINFO_NO_NAME is supported, an NFSv4.1 server
MUST NOT return NFS4ERR_WRONGSEC in response to PUTFH, PUTROOTFH, or
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PUTPUBFH if the operation is immediately followed by a LOOKUPP.
2.5.3.1.3. PUTFH + SECINFO or PUTFH + SECINFO_NO_NAME
A security sensitive client is allowed to choose a strong security
tuple when querying a server to determine a file object's permitted
security tuples. The security tuple chosen by the client does not
have to be included in the tuple list of the security policy of the
either parent directory indicated in PUTFH, or the child file object
indicated in SECINFO (or any parent directory indicated in
SECINFO_NO_NAME). Of course the server has to be configured for
whatever security tuple the client selects, otherwise the request
will fail at RPC layer with an appropriate authentication error.
In theory, there is no connection between the security flavor used by
SECINFO or SECINFO_NO_NAME and those supported by the security
policy. But in practice, the client may start looking for strong
flavors from those supported by the security policy, followed by
those in the mandatory set.
The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to PUTFH whenever
it is immediately followed by SECINFO or SECINFO_NO_NAME. The
NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC from SECINFO or
SECINFO_NO_NAME.
2.5.3.1.4. PUTFH + PUTFH
This is a nonsensical situation, because the first put filehandle
operation is wasted. The NFSv4.1 server MAY return NFS4ERR_WRONGSEC
to the first PUTFH, or it MAY NOT. If it does not, it then processes
the subsequent PUTFH and any operation that follows it according to
the rules listed in Section 2.5.3.1.
2.5.3.1.5. PUTFH + Nothing
This too is nonsensical because the PUTFH is wasted. The NFSv4.1
server MAY or MAY NOT return NFS4ERR_WRONGSEC.
2.5.3.1.6. PUTFH + Anything Else
"Anything Else" includes OPEN by filehandle.
The security policy enforcement applies to the filehandle specified
in PUTFH. Therefore PUTFH must return NFS4ERR_WRONGSEC in case of
security tuple on the part of the mismatch. This avoids the
complexity adding NFS4ERR_WRONGSEC as an allowable error to every
other operation.
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PUTFH + SECINFO_NO_NAME (style "current_fh") is an efficient way for
the client to recover from NFS4ERR_WRONGSEC.
The NFSv4.1 server, MUST not return NFS4ERR_WRONGSEC to any operation
other than LOOKUP, LOOKUPP, and OPEN (by component name).
2.6. 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
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 [2], and minor version one is
represented by this document [[Comment.2: change "document" to "RFC"
when we publish]] . The COMPOUND and CB_COMPOUND procedures support
the encoding of the minor version being requested by the client.
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.
* 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.
* 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
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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.
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 may not modify the structure of existing
attributes.
5. Minor versions may not delete operations.
This prevents the potential reuse of a particular operation
"slot" in a future minor version.
6. Minor versions may not delete attributes.
7. Minor versions may not delete flag bits or enumeration values.
8. Minor versions may declare an operation as mandatory to NOT
implement.
Specifying an operation as "mandatory to not implement" is
equivalent to obsoleting an operation. For the client, it means
that the operation should not be sent to the server. For the
server, an NFS error can be returned as opposed to "dropping"
the request as an XDR decode error. This approach allows for
the obsolescence of an operation while maintaining its structure
so that a future minor version can reintroduce the operation.
1. Minor versions may declare attributes mandatory to NOT
implement.
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2. Minor versions may declare flag bits or enumeration values
as mandatory to NOT implement.
9. Minor versions may downgrade features from mandatory to
recommended, or recommended to optional.
10. Minor versions may upgrade features from optional to recommended
or recommended to mandatory.
11. A client and server that supports minor version X should support
minor versions 0 (zero) through X-1 as well.
12. Except for infrastructural changes, no new features may be
introduced as mandatory 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 mandatory. On the other hand, some classes of
features are infrastructural and have broad effects. Allowing
such features to not be mandatory complicates implementation of
the minor version.
13. A client MUST NOT attempt to use a stateid, filehandle, or
similar returned object from the COMPOUND procedure with minor
version X for another COMPOUND procedure with minor version Y,
where X != Y.
2.7. Non-RPC-based Security Services
As described in Section 2.2.1.1.1.1, NFSv4 relies on RPC for
identification, authentication, integrity, and privacy. NFSv4 itself
provides additional security services as described in the next
several subsections.
2.7.1. Authorization
Authorization to access a file object via an NFSv4 operation is
ultimately determined by the NFSv4 server. A client can predetermine
its access to a file object via the OPEN (Section 16.16) and the
ACCESS (Section 16.1) operations.
Principals with appropriate access rights can modify the
authorization on a file object via the SETATTR (Section 16.30)
operation. Four attributes that affect access rights are: mode,
owner, owner_group, and acl. See Section 5.
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2.7.2. Auditing
NFSv4 provides auditing on a per file object basis, via the ACL
attribute as described in Section 6. It is outside the scope of this
specification to specify audit log formats or management policies.
2.7.3. Intrusion Detection
NFSv4 provides alarm control on a per file object basis, via the ACL
attribute as described in Section 6. Alarms may serve as the basis
for instrusion detection. It is outside the scope of this
specification to specify heuristics for detecting intrusion via
alarms.
2.8. Transport Layers
2.8.1. Required and Recommended Properties of Transports
NFSv4 works over RDMA and non-RDMA_based transports with the
following attributes:
o The transport supports reliable delivery of data, which NFSv4
requires but neither NFSv4 nor RPC has facilities for ensuring.
[20]
o The transport delivers data in the order it was sent. Ordered
delivery simplifies detection of transmit errors, and simplifies
the sending of arbitrary sized requests and responses, via the
record marking protocol [4].
Where an NFS version 4 implementation supports operation over the IP
network protocol, any transport used between NFS and IP MUST be among
the IETF-approved congestion control transport protocols. At the
time this document was written, the only two transports that had the
above attributes were TCP and SCTP. To enhance the possibilities for
interoperability, an NFS version 4 implementation MUST support
operation over the TCP transport protocol.
Even if NFS version 4 is used over a non-IP network protocol, it is
RECOMMENDED that the transport support congestion control.
Note that it is permissible for connectionless transports to be used
under NFSv4.1, however reliable and in-order delivery of data is
still required. NFSv4.1 assumes that a client transport address and
server transport address used to send data over a transport together
constitute a connection, even if the underlying transport eschews the
concept of a connection.
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2.8.2. Client and Server Transport Behavior
If a connection-oriented transport (e.g. TCP) is used the client and
server SHOULD use long lived connections for at least three reasons:
1. This will prevent the weakening of the transport's congestion
control mechanisms via short lived connections.
2. This will improve performance for the WAN environment by
eliminating the need for connection setup handshakes.
3. The NFSv4.1 callback model differs from NFSv4.0, and requires the
client and server to maintain a client-created channel (see
Section 2.9.3.4for the server to use.
In order to reduce congestion, if a connection-oriented transport is
used, and the request is not the NULL procedure,
o A client (or the server, if issuing a callback), MUST NOT retry a
request unless the connection the request was issued over was
disconnected before the reply was received.
o A server (or the client, if receiving a callback), MUST NOT
silently drop a request, even if the request is a retry. (The
silent drop behavior of RPCSEC_GSS [5] does not apply because this
behavior happens at the RPCSEC_GSS layer, a lower layer in the
request processing). Instead, the server SHOULD return an
appropriate error (see Section 2.9.4.1) or it MAY disconnect the
connection.
When using RDMA transports there are other reasons not tolerating
retries over the same connection:
o RDMA transports use "credits" to enforce flow control, where a
credit is a right to a peer to transmit a message. If one peer
were to retransmit a request (or reply), it would consume an
additional credit. If the server retransmitted a reply, it would
certainly result in an RDMA connection loss, since the client
would typically only post a single receive buffer for each
request. If the client retransmitted a request, the additional
credit consumed on the server might lead to RDMA connection
failure unless the client accounted for it and decreased its
available credit, leading to wasted resources.
o RDMA credits present a new issue to the reply cache in NFSv4.1.
The reply cache may be used when a connection within a session is
lost, such as after the client reconnects. Credit information is
a dynamic property of the RDMA connection, and stale values must
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not be replayed from the cache. This implies that the reply cache
contents must not be blindly used when replies are issued from it,
and credit information appropriate to the channel must be
refreshed by the RPC layer.
In addition, the sender of an NFSv4.1 request is not allowed to stop
waiting for a reply, as described in Section 2.9.4.2.
2.8.3. Ports
Historically, NFS version 2 and version 3 servers have resided on
port 2049. The registered port 2049 RFC3232 [21] for the NFS
protocol should be the default configuration. NFSv4 clients SHOULD
NOT use the RPC binding protocols as described in RFC1833 [22].
2.9. Session
2.9.1. Motivation and Overview
Previous versions and minor versions of NFS have suffered from the
following:
o Lack of support for exactly once semantics (EOS). This includes
lack of support for EOS through server failure and recovery.
o Limited callback support, including no support for sending
callbacks through firewalls, and races between responses from
normal requests, and callbacks.
o Limited trunking over multiple network paths.
o Requiring machine credentials for fully secure operation.
Through the introduction of a session, NFSv4.1 addresses the above
shortfalls with practical solutions:
o EOS is enabled by a reply cache with a bounded size, making it
feasible to keep on persistent storage and enable EOS through
server failure and recovery. One reason that previous revisions
of NFS did not support EOS was because some EOS approaches often
limited parallelism. As will be explained in Section 2.9.4),
NFSv4.1 supports both EOS and unlimited parallelism.
o The NFSv4.1 client provides creates transport connections and
gives them to the server for sending callbacks, thus solving the
firewall issue (Section 16.34). Races between responses from
client requests, and callbacks caused by the requests are detected
via the session's sequencing properties which are a byproduct of
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EOS (Section 2.9.4.3).
o The NFSv4.1 client can add an arbitrary number of connections to
the session, and thus provide trunking (Section 2.9.3.4.1).
o The NFSv4.1 session produces a session key independent of client
and server machine credentials which can be used to compute a
digest for protecting key session management operations
Section 2.9.6.3).
o The NFSv4.1 client can also create secure RPCSEC_GSS contexts for
use by the session's callback channel that do not require the
server to authenticate to a client machine principal
(Section 2.9.6.2).
A session is a dynamically created, long-lived server object created
by a client, used over time from one or more transport connections.
Its function is to maintain the server's state relative to the
connection(s) belonging to a client instance. This state is entirely
independent of the connection itself, and indeed the state exists
whether the connection exists or not (though locks, delegations, etc.
and generally expire in the extended absence of an open connection).
The session in effect becomes the object representing an active
client on a set of zero or more connections.
2.9.2. NFSv4 Integration
Sessions are part of NFSv4.1 and not NFSv4.0. Normally, a major
infrastructure change like sessions would require a new major version
number to an RPC program like NFS. However, because NFSv4
encapsulates its functionality in a single procedure, COMPOUND, and
because COMPOUND can support an arbitrary number of operations,
sessions are almost trivially added. COMPOUND includes a minor
version number field, and for NFSv4.1 this minor version is set to 1.
When the NFSv4 server processes a COMPOUND with the minor version set
to 1, it expects a different set of operations than it does for
NFSv4.0. One operation it expects is the SEQUENCE operation, which
is required for every COMPOUND that operates over an established
session.
2.9.2.1. SEQUENCE and CB_SEQUENCE
In NFSv4.1, when the SEQUENCE operation is present, it is always the
first operation in the COMPOUND procedure. The primary purpose of
SEQUENCE is to carry the session identifier. The session identifier
associates all other operations in the COMPOUND procedure with a
particular session. SEQUENCE also contains required information for
maintaining EOS (see Section 2.9.4). Session-enabled NFSv4.1
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COMPOUND requests thus have the form:
+-----+--------------+-----------+------------+-----------+----
| tag | minorversion | numops |SEQUENCE op | op + args | ...
| | (== 1) | (limited) | + args | |
+-----+--------------+-----------+------------+-----------+----
and the reply's structure is:
+------------+-----+--------+-------------------------------+--//
|last status | tag | numres |status + SEQUENCE op + results | //
+------------+-----+--------+-------------------------------+--//
//-----------------------+----
// status + op + results | ...
//-----------------------+----
A CB_COMPOUND procedure request and reply has a similar form, but
instead of a SEQUENCE operation, there is a CB_SEQUENCE operation,
and there is an additional field called "callback_ident", which is
superfluous in NFSv4.1. CB_SEQUENCE has the same information as
SEQUENCE, but includes other information needed to solve callback
races (Section 2.9.4.3).
2.9.2.2. Clientid and Session Association
Sessions are subordinate to the clientid (Section 2.4). Each
clientid can have zero or more active sessions. A clientid, and a
session bound to it are required to do anything useful in NFSv4.1.
Each time a session is used, the state leased to it associated
clientid is automatically renewed.
State such as share reservations, locks, delegations, and layouts
(Section 1.4.4) is tied to the clientid, not the sessions of the
clientid. Successive state changing operations from a given state
owner can go over different sessions, as long each session is
associated with the same clientid. Callbacks can arrive over a
different session than the session that sent the operation the
acquired the state that the callback is for. For example, if session
A is used to acquire a delegation, a request to recall the delegation
can arrive over session B.
2.9.3. Channels
Each session has one or two channels: the "operation" or "fore"
channel used for ordinary requests from client to server, and the
"back" channel, used for callback requests from server to client.
The session allocates resources for each channel, including separate
reply caches (see Section 2.9.4.1 These resources are for the most
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part specified at time the session is created.
2.9.3.1. Operation Channel
The operation channel carries COMPOUND requests and responses. A
session always has an operation channel.
2.9.3.2. Backchannel
The backchannel carries CB_COMPOUND requests and responses. Whether
there is a backchannel or not is a decision of the client; NFSv4.1
servers MUST support backchannels.
2.9.3.3. Session and Channel Association
Because there are at most two channels per session, and because each
channel has a distinct purpose, channels are not assigned
identifiers. The operation and backchannel are implicitly created
and associated when the session is created.
2.9.3.4. Connection and Channel Association
Each channel is associated with zero or more transport connections.
A connection can be bound to one channel or both channels of a
session; the client and server negotiate whether a connection will
carry traffic for one channel or both channels via the CREATE_SESSION
(Section 16.36) and the BIND_CONN_TO_SESSION (Section 16.34)
operations. When a session is created via CREATE_SESSION, it is
automatically bound to the operation channel, and optionally the
backchannel. If the client does not specify connecting binding
enforcement when the session is created, then additional connections
are automatically bound to the operation channel when the are used
with a SEQUENCE operation that has the session's sessionid.
A connection MAY be bound to the channels of other sessions. The
client decides, and the NFSv4.1 server MUST allow it. A connection
MAY be bound to the channels of other sessions of other clientids.
Again, the client decides, and the server MUST allow it.
It is permissible for connections of multiple types to be bound to
the same channel. For example a TCP and RDMA connection can be bound
to the operation channel. In the event an RDMA and non-RDMA
connection are bound to the same channel, the maximum number of slots
must be at least one more than the total number of credits. This way
if all RDMA credits are use, the non-RDMA connection can have at
least one outstanding request.
It is permissible for a connection of one type to be bound to the
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operation channel, and another type bound to the backchannel.
2.9.3.4.1. Trunking
The eir_server_owner results from EXCHANGE_ID give a client a hint
that the server it is connected to may be the same as the server it
is connected to via another connection. When two connections have
the same eir_server_owner.so_major_id, the client treats the
connections as connected to the same server (even if the destination
network addresses are different) and uses a common clientid to
identify itself. The eir_server_owner.so_minor_id field allows the
server to control binding of connections to sessions. When two
connections have a matching so_major_id and so_minor_id, the client
may bind both connections to a common session; this is session
trunking. When two connections have a matching so_major_id, but
different so_minor_id, the client will need to create a new session
for the clientid in order to use the connection; this is clientid
trunking. In either session or clientid trunking, the bandwidth
capacity can scale with the number of connections.
Just because two servers over two connections claim matching or
partially matching server_owner4 values does not the client should or
must trust the servers' claims. The client may verify these claims
before trunking traffic.
For session trunking, clients and servers can reliably verify if
connections between different network paths are in fact bound to the
same NFSv4.1 server and usable on the same session. The SET_SSV
(Section 16.47) operation allows a client and server to establish a
unique, shared key value (the SSV). When a new connection is bound
to the session (via the BIND_CONN_TO_SESSION operation, see
Section 16.34), the client offers a digest that based on the SSV. If
the client mistakenly tries to bind a connection to a session of a
wrong server, the server will either reject the attempt because it is
not aware of the session identifier of the BIND_CONN_TO_SESSION
arguments, or it will reject the attempt because the digest for the
SSV does not match what the server expects. Even if the server
mistakenly or maliciously accepts the connection bind attempt, the
digest it computes in the response will not be verified by the
client, the client will know it cannot use the connection for
trunking the specified channel.
In the case of clientid trunking, the client can use RPCSEC_GSS to
verify that each connection is aimed at the same server. When the
client invokes EXCHANGE_ID, it should use RPCSEC_GSS. If each
RPCSEC_GSS context over each connection has the same server
principal, then the servers at the end of each connection are the
same.
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2.9.4. Exactly Once Semantics
Via the session, NFSv4.1 offers exactly once semantics (EOS) for
requests sent over a channel. EOS is supported on both the operation
and back channels.
Each COMPOUND or CB_COMPOUND request that is issued with a leading
SEQUENCE or CB_SEQUENCE operation MUST be executed by the receiver
exactly once. This requirement is regardless whether the request is
issued with reply caching specified (see Section 2.9.4.1.2). The
requirement holds even if the requester is issuing the request over a
session created between a pNFS data client and pNFS data server. The
rationale for this requirement is understood by categorizing requests
into three classifications:
o Nonidempotent requests.
o Idempotent modifying requests.
o Idempotent non-modifying requests.
An example of a non-idempotent request is RENAME. If is obvious that
if a replier executes the same RENAME request twice, and the first
execution succeeds, the re-execution will fail. If the replier
returns the result from the re-execution, this result is incorrect.
Therefore, EOS is required for nonidempotent requests.
An example of an idempotent modifying request is a COMPOUND request
containing a WRITE operation. Repeated execution of the same WRITE
has the same effect as execution of that write once. Nevertheless,
putting enforcing EOS for WRITEs and other idempotent modifying
requests is necessary to avoid data corruption.
Suppose a client issues WRITEs A, B, C to a noncompliant server that
does not enforce EOS, and receives no response, perhaps due to a
network partition. The client reconnects to the server and re-issues
all three WRITEs. Now, the server has outstanding two instances of
each of A, B, and C. The server can be in a situation in which it
executes and replies to the retries of A, B, and C while the first A,
B, and C are still waiting around in the server's I/O system for some
resource. Upon receiving the replies to the second attempts of
WRITEs A, B, and C, the client believes its writes are done so it is
free to do issue WRITE D which overlaps the range of one or more of
A, B, C. If any of A, B, or C are subsequently are executed for the
second time, then what has been written by D can be overwritten and
thus corrupted.
Note that it is not required the server cache the reply to the
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modifying operation to avoid data corruption (but if the client
specified the reply to be cached, the server must cache it).
An example of an idempotent non-modifying request is a COMPOUND
containing SEQUENCE, PUTFH, READLINK and nothing else. The re-
execution of a such a request will not cause data corruption, or
produce an incorrect result. Nonetheless, for simplicity, the
replier MUST enforce EOS for such requests.
2.9.4.1. Slot Identifiers and Reply Cache
The RPC layer provides a transaction ID (xid), which, while required
to be unique, is not especially convenient for tracking requests.
The xid is only meaningful to the requester it cannot be interpreted
at the replier except to test for equality with previously issued
requests. Because RPC operations may be completed by the replier in
any order, many transaction IDs may be outstanding at any time. The
requester may therefore perform a computationally expensive lookup
operation in the process of demultiplexing each reply.
In the NFSv4.1, there is a limit to the number of active requests.
This immediately enables a computationally efficient index for each
request which is designated as a Slot Identifier, or slotid.
When the requester issues a new request, it selects a slotid in the
range 0..N-1, where N is the replier's current "totalrequests" limit
granted to the requester on the session over which the request is to
be issued. The slotid must be unused by any of the requests which
the requester has already active on the session. "Unused" here means
the requester has no outstanding request for that slotid. Because
the slot id is always an integer in the range 0..N-1, requester
implementations can use the slotid from a replier response to
efficiently match responses with outstanding requests, such as, for
example, by using the slotid to index into a outstanding request
array. This can be used to avoid expensive hashing and lookup
functions in the performance-critical receive path.
The sequenceid, which accompanies the slotid in each request, is
important for an important check at the server: it must be able to be
determined efficiently whether a request using a certain slotid is a
retransmit or a new, never-before-seen request. It is not feasible
for the client to assert that it is retransmitting to implement this,
because for any given request the client cannot know the server has
seen it unless the server actually replies. Of course, if the client
has seen the server's reply, the client would not retransmit.
The sequenceid MUST increase monotonically for each new transmit of a
given slotid, and MUST remain unchanged for any retransmission. The
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server must in turn compare each newly received request's sequenceid
with the last one previously received for that slotid, to see if the
new request is:
o A new request, in which the sequenceid is one greater than that
previously seen in the slot (accounting for sequence wraparound).
The replier proceeds to execute the new request.
o A retransmitted request, in which the sequenceid is equal to that
last seen in the slot. Note that this request may be either
complete, or in progress. The replier performs replay processing
in these cases.
o A misordered replay, in which the sequenceid is less than
(accounting for sequence wraparound) than that previously seen in
the slot. The replier MUST return NFS4ERR_SEQ_MISORDERED (as the
result from SEQUENCE or CB_SEQUENCE).
o A misordered new request, in which the sequenceid is two or more
than (accounting for sequence wraparound) than that previously
seen in the slot. Note that because the sequenceid must
wraparound one it reaches 0xFFFFFFFF, a misordered new request and
a misordered replay cannot be distinguished. Thus, the replier
MUST return NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
CB_SEQUENCE).
Unlike the XID, the slotid is always within a specific range; this
has two implications. The first implication is that for a given
session, the replier need only cache the results of a limited number
of COMPOUND requests. The second implication derives from the first,
which is unlike XID-indexed reply caches (also know as duplicate
request caches - DRCs), the slotid-based reply cache cannot be
overflowed. Through use of the sequenceid to identify retransmitted
requests, the replier does not need to actually cache the request
itself, reducing the storage requirements of the reply cache further.
These new facilities makes it practical to maintain all the required
entries for an effective reply cache.
The slotid and sequenceid therefore take over the traditional role of
the XID and port number in the replier reply cache implementation,
and the session replaces the IP address. This approach is
considerably more portable and completely robust - it is not subject
to the frequent reassignment of ports as clients reconnect over IP
networks. In addition, the RPC XID is not used in the reply cache,
enhancing robustness of the cache in the face of any rapid reuse of
XIDs by the client. [[Comment.3: We need to discuss the requirements
of the client for changing the XID.]] .
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It is required to encode the slotid information into each request in
a way that does not violate the minor versioning rules of the NFSv4.0
specification. This is accomplished here by encoding it in the
SEQUENCE operation within each NFSv4.1 COMPOUND and CB_COMPOUND
procedure. The operation easily piggybacks within existing messages.
[[Comment.4: Need a better term than piggyback]]
In general, the receipt of a new sequenced request arriving on any
valid slot is an indication that the previous reply cache contents of
that slot may be discarded. In order to further assist the replier
in slot management, the requester is required to use the lowest
available slot when issuing a new request. In this way, the replier
may be able to retire additional entries.
However, in the case where the replier is actively adjusting its
granted maximum request count to the requester, it may not be able to
use receipt of the slotid to retire cache entries. The slotid used
in an incoming request may not reflect the server's current idea of
the requester's session limit, because the request may have been sent
from the requester before the update was received. Therefore, in the
downward adjustment case, the replier may have to retain a number of
reply cache entries at least as large as the old value, until
operation sequencing rules allow it to infer that the requester has
seen its reply.
The SEQUENCE (and CB_SEQUENCE) operation also carries a "maxslot"
value which carries additional client slot usage information. The
requester must always provide its highest-numbered outstanding slot
value in the maxslot argument, and the replier may reply with a new
recognized value. The requester should in all cases provide the most
conservative value possible, although it can be increased somewhat
above the actual instantaneous usage to maintain some minimum or
optimal level. This provides a way for the requester to yield unused
request slots back to the replier, which in turn can use the
information to reallocate resources. Obviously, maxslot can never be
zero, or the session would deadlock.
The replier also provides a target maxslot value to the requester,
which is an indication to the requester of the maxslot the replier
wishes the requester to be using. This permits the server to
withdraw (or add) resources from a requester that has been found to
not be using them, in order to more fairly share resources among a
varying level of demand from other requesters. The requester must
always comply with the replier's value updates, since they indicate
newly established hard limits on the requester's access to session
resources. However, because of request pipelining, the requester may
have active requests in flight reflecting prior values, therefore the
replier must not immediately require the requester to comply.
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2.9.4.1.1. Errors from SEQUENCE and CB_SEQUENCE
Any time SEQUENCE or CB_SEQUENCE return an error, the sequenceid of
the slot MUST NOT change. The replier MUST NOT modify the reply
cache entry for the slot whenever an error is returned from SEQUENCE
or CB_SEQUENCE.
2.9.4.1.2. Optional Reply Caching
On a per-request basis the requester can choose to direct the replier
to cache the reply to all operations after the first operation
(SEQUENCE or CB_SEQUENCE) via the sa_cachethis or csa_cachethis
fields of the arguments to SEQUENCE or CB_SEQUENCE. The reason it
would not direct the replier to cache the entire reply is that the
request is composed of all idempotent operations [20]. Caching the
reply may offer little benefit, and if the reply is too large (see
Section 2.9.4.4, it may not be cacheable anyway.
Whether the requester requests the reply to be cached or not has no
effect on the slot processing. If the results of SEQUENCE or
CB_SEQUENCE are NFS4_OK, then the slot's sequenceid MUST be
incremented by one. If a requester does not direct the replier to
cache, the reply, the replier MUST do one of following:
o The replier can cache the entire original reply. Even though
sa_cachethis or csa_cachethis are FALSE, the replier is always
free to cache. It may choose this approach in order to simplify
implementation.
o The replier enters into its reply cache a reply consisting of the
original results to the SEQUENCE or CB_SEQUENCE operation,
followed by the error NFS4ERR_RETRY_UNCACHED_REP. Thus when the
requester later retries the request, it will get
NFS4ERR_RETRY_UNCACHE_REP.
2.9.4.1.3. Multiple Connections and Sharing the Reply Cache
Multiple connections can be bound to a session's channel, hence the
connections share the same table of slotids. For connections over
non-RDMA transports like TCP, there are no particular considerations.
Considerations for multiple RDMA connections sharing a slot table are
discussed in Section 2.9.5.1. [[Comment.5: Also need to discuss when
RDMA and non-RDMA share a slot table.]]
2.9.4.2. Retry and Replay
A client MUST NOT retry a request, unless the connection it used to
send the request disconnects. The client can then reconnect and
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resend the request, or it can resend the request over a different
connection. In the case of the server resending over the
backchannel, it cannot reconnect, and either resends the request over
another connection that the client has bound to the backchannel, or
if there is no other backchannel connection, waits for the client to
bind a connection to the backchannel.
A client MUST wait for a reply to a request before using the slot for
another request. If it does not wait for a reply, then the client
does not know what sequenceid to use for the slot on its next
request. For example, suppose a client sends a request with
sequenceid 1, and does not wait for the response. The next time it
uses the slot, it sends the new request with sequenceid 2. If the
server has not seen the request with sequenceid 1, then the server is
expecting sequenceid 2, and rejects the client's new request with
NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or CB_SEQUENCE).
RDMA fabrics do not guarantee that the memory handles (Steering Tags)
within each RDMA three-tuple are valid on a scope [[Comment.6: What
is a three-tuple?]] outside that of a single connection. Therefore,
handles used by the direct operations become invalid after connection
loss. The server must ensure that any RDMA operations which must be
replayed from the reply cache use the newly provided handle(s) from
the most recent request.
2.9.4.3. Resolving server callback races with sessions
It is possible for server callbacks to arrive at the client before
the reply from related forward channel operations. For example, a
client may have been granted a delegation to a file it has opened,
but the reply to the OPEN (informing the client of the granting of
the delegation) may be delayed in the network. If a conflicting
operation arrives at the server, it will recall the delegation using
the callback channel, which may be on a different transport
connection, perhaps even a different network. In NFSv4.0, if the
callback request arrives before the related reply, the client may
reply to the server with an error.
The presence of a session between client and server alleviates this
issue. When a session is in place, each client request is uniquely
identified by its { slotid, sequenceid } pair. By the rules under
which slot entries (reply cache entries) are retired, the server has
knowledge whether the client has "seen" each of the server's replies.
The server can therefore provide sufficient information to the client
to allow it to disambiguate between an erroneous or conflicting
callback and a race condition.
For each client operation which might result in some sort of server
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callback, the server should "remember" the { slotid, sequenceid }
pair of the client request until the slotid retirement rules allow
the server to determine that the client has, in fact, seen the
server's reply. Until the time the { slotid, sequenceid } request
pair can be retired, any recalls of the associated object MUST carry
an array of these referring identifiers (in the CB_SEQUENCE
operation's arguments), for the benefit of the client. After this
time, it is not necessary for the server to provide this information
in related callbacks, since it is certain that a race condition can
no longer occur.
The CB_SEQUENCE operation which begins each server callback carries a
list of "referring" { slotid, sequenceid } tuples. If the client
finds the request corresponding to the referring slotid and sequenced
id be currently outstanding (i.e. the server's reply has not been
seen by the client), it can determine that the callback has raced the
reply, and act accordingly.
The client must not simply wait forever for the expected server reply
to arrive on any of the session's operations channels, because it is
possible that they will be delayed indefinitely. However, it should
wait for a period of time, and if the time expires it can provide a
more meaningful error such as NFS4ERR_DELAY.
[[Comment.7: We need to consider the clients' options here, and
describe them... NFS4ERR_DELAY has been discussed as a legal reply
to CB_RECALL?]]
There are other scenarios under which callbacks may race replies,
among them pnfs layout recalls, described in Section 12.3.5.3
[[Comment.8: fill in the blanks w/others, etc...]]
2.9.4.4. COMPOUND and CB_COMPOUND Construction Issues
Very large requests and replies may pose both buffer management
issues (especially with RDMA) and reply cache issues. When the
session is created, (Section 16.36) the client and server negotiate
the maximum sized request they will send or process
(ca_maxrequestsize), the maximum sized reply they will return or
process (ca_maxresponsesize), and the maximum sized reply they will
store in the reply cache (ca_maxresponsesize_cached).
If a request exceeds ca_maxrequestsize, the reply will have the
status NFS4ERR_REQ_TOO_BIG. A replier may return NFS4ERR_REQ_TOO_BIG
as the status for first operation (SEQUENCE or CB_SEQUENCE) in the
request, or it may chose to return it on a subsequent operation.
If a reply exceeds ca_maxresponsesize, the reply will have the status
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NFS4ERR_REP_TOO_BIG. A replier may return NFS4ERR_REP_TOO_BIG as the
status for first operation (SEQUENCE or CB_SEQUENCE) in the request,
or it may chose to return it on a subsequent operation.
If sa_cachethis or csa_cachethis are TRUE, then the replier MUST
cache a reply except if an error is returned by the SEQUENCE or
CB_SEQUENCE operation (see Section 2.9.4.1.1). If the reply exceeds
ca_maxresponsesize_cached, (and sa_cachethis or csa_cachethis are
TRUE) then the server MUST return NFS4ERR_REP_TOO_BIG_TO_CACHE. Even
if NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for that matter)
is returned on a operation other than first operation (SEQUENCE or
CB_SEQUENCE), then the reply MUST be cached if sa_cachethis or
csa_cachethis are TRUE. For example, if a COMPOUND has eleven
operations, including SEQUENCE, the fifth operation is a RENAME, and
the tenth operation is a READ for one million bytes, server may
return NFS4ERR_REP_TOO_BIG_TO_CACHE on the tenth operation. Since
the server executed several operations, especially the non-idempotent
RENAME, the client's request to cache the reply needs to be honored
in order for correct operation of exactly once semantics. If the
client retries the request, the server will have cached a reply that
contains results for ten of the eleven requested operations, with the
tenth operation having a status of NFS4ERR_REP_TOO_BIG_TO_CACHE.
A client needs to take care that when sending operations that change
the current filehandle (except for PUTFH, PUTPUBFH, and PUTROOFFH)
that it not exceed the maximum reply buffer before the GETFH
operation. Otherwise the client will have to retry the operation
that changed the current filehandle, in order obtain the desired
filehandle. For the OPEN operation (see Section 16.16), retry is not
always available as an option. The following guidelines for the
handling of filehandle changing operations are advised:
o A client SHOULD issue GETFH immediately after a current filehandle
changing operation. This is especially important after any
current filehandle changing non-idempotent operation. It is
critical to issue GETFH immediately after OPEN.
o A server MAY return NFS4ERR_REP_TOO_BIG or
NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
filehandle changing operation if the reply would be too large on
the next operation.
o A server SHOULD return NFS4ERR_REP_TOO_BIG or
NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
filehandle changing non-idempotent operation if the reply would be
too large on the next operation, especially if the operation is
OPEN.
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o A server MAY return NFS4ERR_UNSAFE_COMPOUND if it looks at the
next operation after a non-idempotent current filehandle changing
operation, and finds it is not GETFH. The server would do this if
it is unable to determine in advance whether the total response
size would exceed ca_maxresponsesize_cached or ca_maxresponsesize.
2.9.4.5. Persistence
Since the reply cache is bounded, it is practical for the server
reply cache to persist across server reboots, and to be kept in
stable storage (a client's reply cache for callbacks need not persist
across client reboots unless the client intends for its session and
other state to persist across reboots).
o The slot table including the sequenceid and cached reply for each
slot.
o The sessionid.
o The clientid.
o The SSV (see Section 2.9.6.3).
The CREATE_SESSION (see Section 16.36 operation determines the
persistence of the reply cache.
2.9.5. RDMA Considerations
A complete discussion of the operation of RPC-based protocols atop
RDMA transports is in [RPCRDMA]. A discussion of the operation of
NFSv4, including NFSv4.1 over RDMA is in [NFSDDP]. Where RDMA is
considered, this specification assumes the use of such a layering; it
addresses only the upper layer issues relevant to making best use of
RPC/RDMA.
2.9.5.1. RDMA Connection Resources
RDMA requires its consumers to register memory and post buffers of a
specific size and number for receive operations.
Registration of memory can be a relatively high-overhead operation,
since it requires pinning of buffers, assignment of attributes (e.g.
readable/writable), and initialization of hardware translation.
Preregistration is desirable to reduce overhead. These registrations
are specific to hardware interfaces and even to RDMA connection
endpoints, therefore negotiation of their limits is desirable to
manage resources effectively.
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Following the basic registration, these buffers must be posted by the
RPC layer to handle receives. These buffers remain in use by the
RPC/NFSv4 implementation; the size and number of them must be known
to the remote peer in order to avoid RDMA errors which would cause a
fatal error on the RDMA connection.
NFSv4.1 manages slots as resources on a per session basis (see
Section 2.9), while RDMA connections manage credits on a per
connection basis. This means that in order for a peer to send data
over RDMA to a remote buffer, it has to have both an NFSv4.1 slot,
and an RDMA credit.
2.9.5.2. Flow Control
NFSv4.0 and all previous versions do not provide for any form of flow
control; instead they rely on the windowing provided by transports
like TCP to throttle requests. This does not work with RDMA, which
provides no operation flow control and will terminate a connection in
error when limits are exceeded. Limits such as maximum number of
requests outstanding are therefore negotiated when a session is
created (see the ca_maxrequests field in Section 16.36). These
limits then provide the maxima each session's channels' connections
must operate within. RDMA connections are managed within these
limits as described in section 3.3 of [RPCRDMA]; if there are
multiple RDMA connections, then the maximum requests for a channel
will be divided among the RDMA connections. The limits may also be
modified dynamically at the server's choosing by manipulating certain
parameters present in each NFSv4.1 request. In addition, the
CB_RECALL_SLOT callback operation (see Section 18.8 can be issued by
a server to a client to return RDMA credits to the server, thereby
lowering the maximum number of requests a client can have outstanding
to the server.
2.9.5.3. Padding
Header padding is requested by each peer at session initiation (see
the csa_headerpadsize argument to CREATE_SESSION in Section 16.36),
and subsequently used by the RPC RDMA layer, as described in
[RPCRDMA]. Zero padding is permitted.
Padding leverages the useful property that RDMA receives preserve
alignment of data, even when they are placed into anonymous
(untagged) buffers. If requested, client inline writes will insert
appropriate pad bytes within the request header to align the data
payload on the specified boundary. The client is encouraged to add
sufficient padding (up to the negotiated size) so that the "data"
field of the NFSv4.1 WRITE operation is aligned. Most servers can
make good use of such padding, which allows them to chain receive
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buffers in such a way that any data carried by client requests will
be placed into appropriate buffers at the server, ready for file
system processing. The receiver's RPC layer encounters no overhead
from skipping over pad bytes, and the RDMA layer's high performance
makes the insertion and transmission of padding on the sender a
significant optimization. In this way, the need for servers to
perform RDMA Read to satisfy all but the largest client writes is
obviated. An added benefit is the reduction of message round trips
on the network - a potentially good trade, where latency is present.
The value to choose for padding is subject to a number of criteria.
A primary source of variable-length data in the RPC header is the
authentication information, the form of which is client-determined,
possibly in response to server specification. The contents of
COMPOUNDs, sizes of strings such as those passed to RENAME, etc. all
go into the determination of a maximal NFSv4 request size and
therefore minimal buffer size. The client must select its offered
value carefully, so as not to overburden the server, and vice- versa.
The payoff of an appropriate padding value is higher performance.
Sender gather:
|RPC Request|Pad bytes|Length| -> |User data...|
\------+---------------------/ \
\ \
\ Receiver scatter: \-----------+- ...
/-----+----------------\ \ \
|RPC Request|Pad|Length| -> |FS buffer|->|FS buffer|->...
In the above case, the server may recycle unused buffers to the next
posted receive if unused by the actual received request, or may pass
the now-complete buffers by reference for normal write processing.
For a server which can make use of it, this removes any need for data
copies of incoming data, without resorting to complicated end-to-end
buffer advertisement and management. This includes most kernel-based
and integrated server designs, among many others. The client may
perform similar optimizations, if desired.
2.9.5.4. Dual RDMA and Non-RDMA Transports
Some RDMA transports (for example see [RDDP]), [[Comment.9: need
xref]] require a "streaming" (non-RDMA) phase, where ordinary traffic
might flow before "stepping" up to RDMA mode, commencing RDMA
traffic. Some RDMA transports start connections always in RDMA mode.
NFSv4.1 allows, but does not assume, a streaming phase before RDMA
mode. When a connection is bound to a session, the client and server
negotiate whether the connection is used in RDMA or non-RDMA mode
(see Section 16.36 and Section 16.34).
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2.9.6. Sessions Security
2.9.6.1. Session Callback Security
The session connection binding improves security over that provided
by NFSv4.0 for the callback channel. The connection is client-
initiated (see Section 16.34), and subject to the same firewall and
routing checks as the operations channel. The connection cannot be
hijacked by an attacker who connects to the client port prior to the
intended server. At the client's option (see Section 16.36 binding
is fully authenticated before being activated (see Section 16.34).
Traffic from the server over the callback channel is authenticated
exactly as the client specifies (see Section 2.9.6.2).
2.9.6.2. Backchannel RPC Security
When the NFSv4.1 client establishes the backchannel, it informs the
server what security flavors and principals it must use when sending
requests over the backchannel. If the security flavor is RPCSEC_GSS,
the client expresses the principal in the form of an established
RPCSEC_GSS context. The server is free to use any flavor/principal
combination the server offers, but MUST NOT use unoffered
combinations.
This way, the client does not have to provide a target GSS principal
as it did with NFSv4.0, and the server does not have to implement an
RPCSEC_GSS initiator as it did with NFSv4.0. [[Comment.10: xrefs]]
The CREATE_SESSION (Section 16.36) and BACKCHANNEL_CTL
(Section 16.33) operations allow the client to specify flavor/
principal combinations.
2.9.6.3. Protection from Unauthorized State Changes
Under some conditions, NFSv4.0 is vulnerable to a denial of service
issue with respect to its state management.
The attack works via an unauthorized client faking an open_owner4, an
open_owner/lock_owner pair, or stateid, combined with a seqid. The
operation is sent to the NFSv4 server. The NFSv4 server accepts the
state information, and as long as any status code from the result of
this operation is not NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
NFS4ERR_RESOURCE, or NFS4ERR_NOFILEHANDLE, the sequence number is
incremented. When the authorized client issues an operation, it gets
back NFS4ERR_BAD_SEQID, because its idea of the current sequence
number is off by one. The authorized client's recovery options are
pretty limited, with SETCLIENTID, followed by complete reclaim of
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state, which may or may not succeed completely. That qualifies as a
denial of service attack.
If the client uses RPCSEC_GSS authentication and integrity, and every
client maps each open_owner and lock_owner one and only one
principal, and the server enforces this binding, then the conditions
leading to vulnerability to the denial of service do not exist. One
should keep in mind that if AUTH_SYS is being used, far simpler
easier denial of service and other attacks are possible.
With NFSv4.1 sessions, the per-operation sequence number is ignored
(see Section 8.13) therefore the NFSv4.0 denial of service
vulnerability described above does not apply. However as described
to this point in the specification, an attacker could forge the
sessionid and issue a SEQUENCE with a slot id that he expects the
legitimate client to use next. The legitimate client could then use
the slotid with the same sequence number, and the server returns the
attacker's result from the replay cache, thereby disrupting the
legitimate client.
If we give each NFSv4.1 user their own session, and each user uses
RPCSEC_GSS authentication and integrity, then the denial of service
issue is solved, at the cost of additional per session state. The
alternative NFSv4.1 specifies is described as follows.
Transport connections MUST be bound to a session by the client. The
server MUST return an error to an operation (other than the operation
that binds the connection to the session) that uses an unbound
connection. As a simplification, the transport connection used by
CREATE_SESSION (see Section 16.36) is automatically bound to the
session. Additional connections are bound to a session via
BIND_CONN_TO_SESSION (see Section 16.34).
To prevent attackers from issuing BIND_CONN_TO_SESSION operations,
the arguments to BIND_CONN_TO_SESSION include a digest of a shared
secret called the secret session verifier (SSV) that only the client
and server know. The digest is created via a one way, collision
resistant hash function, making it intractable for the attacker to
forge.
The SSV is sent to the server via SET_SSV (see Section 16.47). To
prevent eavesdropping, a SET_SSV for the SSV SHOULD be protected via
RPCSEC_GSS with the privacy service. The SSV can be changed by the
client at any time, by any principal. However several aspects of SSV
changing prevent an attacker from engaging in a successful denial of
service attack:
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o A SET_SSV on the SSV does not replace the SSV with the argument to
SET_SSV. Instead, the current SSV on the server is logically
exclusive ORed (XORed) with the argument to SET_SSV. SET_SSV MUST
NOT be called with an SSV value that is zero.
o The arguments to and results of SET_SSV include digests of the old
and new SSV, respectively.
o Because the initial value of the SSV is zero, therefore known, the
client that opts for connecting binding enforcement, MUST issue at
least one SET_SSV operation before the first BIND_CONN_TO_SESSION
operation. A client SHOULD issue SET_SSV as soon as a session is
created.
If a connection is disconnected, BIND_CONN_TO_SESSION is required to
bind a connection to the session, even if the connection that was
disconnected was the one CREATE_SESSION was created with.
If a client is assigned a machine principal then the client SHOULD
use the machine principal's RPCSEC_GSS context to privacy protect the
SSV from eavesdropping during the SET_SSV operation. If a machine
principal is not being used, then the client MAY use the non-machine
principal's RPCSEC_GSS context to privacy protect the SSV. The
server MUST accept either type of principal. A client SHOULD change
the SSV each time a new principal uses the session.
Here are the types of attacks that can be attempted by an attacker
named Eve, and how the connection to session binding approach
addresses each attack:
o If the Eve creates a connection after the legitimate client
establishes an SSV via privacy protection from a machine
principal's RPCSEC_GSS session, she does not know the SSV and so
cannot compute a digest that BIND_CONN_TO_SESSION will accept.
Users on the legitimate client cannot be disrupted by Eve.
o If Eve is the first one log into the legitimate client, and the
client does not use machine principals, then Eve can cause an SSV
to be created via the legitimate client's NFSv4.1 implementation,
protected by the RPCSEC_GSS context created by the legitimate
client (which uses Eve's GSS principal and credentials). Eve can
then eavesdrop on the network, and because she knows her
credentials, she can decrypt the SSV. Eve can compute a digest
BIND_CONN_TO_SESSION will accept, and so bind a new connection to
the session. Eve can change the slotid, sequence state, and/or
the SSV state in such a way that when Bob accesses the server via
the legitimate client, the legitimate client will be unable to use
the session.
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The client's only recourse is to create a new session, which will
cause any state Eve created on the legitimate client over the old
(but hijacked) session to be lost. This disrupts Eve, but because
she is the attacker, this is acceptable.
Once the legitimate client establishes an SSV over the new session
using Bob's RPCSEC_GSS context, Eve can use the new session via
the legitimate client, but she cannot disrupt Bob. Moreover,
because the client SHOULD have modified the SSV due to Eve using
the new session, Bob cannot get revenge on Eve by binding a rogue
connection to the session.
The question is how does the legitimate client detect that Eve has
hijacked the old session? When the client detects that a new
principal, Bob, wants to use the session, it SHOULD have issued a
SET_SSV.
* Let us suppose that from the rogue connection, Eve issued a
SET_SSV with the same slotid and sequence that the legitimate
client later uses. The server will assume this is a replay,
and return to the legitimate client the reply it sent Eve.
However, unless Eve can correctly guess the SSV the legitimate
client will use, the digest verification checks in the SET_SSV
response will fail. That is the clue to the client that the
session has been hijacked.
* Alternatively, Eve issued a SET_SSV with a different slotid
than the legitimate client uses for its SET_SSV. Then the
digest verification on the server fails, and the client is
again clued that the session has been hijacked.
* Alternatively, Eve issued an operation other than SET_SSV, but
with the same slotid and sequence that the legitimate client
uses for its SET_SSV. The server returns to the legitimate
client the response it sent Eve. The client sees that the
response is not at all what it expects. The client assumes
either session hijacking or server bug, and either way destroys
the old session.
o Eve binds a rogue connection to the session as above, and then
destroys the session. Again, Bob goes to use the server from the
legitimate client. The client has a very clear indication that
its session was hijacked, and does not even have to destroy the
old session before creating a new session, which Eve will be
unable to hijack because it will be protected with an SSV created
via Bob's RPCSEC_GSS protection.
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o If Eve creates a connection before the legitimate client
establishes an SSV, because the initial value of the SSV is zero
and therefore known, Eve can issue a SET_SSV that will pass the
digest verification check. However because the new connection has
not been bound to the session, the SET_SSV is rejected for that
reason.
o The connection to session binding model does not prevent
connection hijacking. However, if an attacker can perform
connection hijacking, it can issue denial of service attacks that
are less difficult than attacks based on forging sessions.
2.9.7. Session Mechanics - Steady State
2.9.7.1. Obligations of the Server
The server has the primary obligation to monitor the state of
backchannel resources that the client has created for the server
(RPCSEC_GSS contexts and back channel connections). When these
resources go away, the server takes action as specified in
Section 2.9.8.2.
2.9.7.2. Obligations of the Client
The client has the following obligations in order to utilize the
session:
o Keep a necessary session from going idle on the server. A client
that requires a session, but nonetheless is not sending operations
risks having the session be destroyed by the server. This is
because sessions consume resources, and resource limitations may
force the server to cull the least recently used session.
o Destroy the session when idle. When a session has no state other
than the session, and no outstanding requests, the client should
consider destroying the session.
o Maintain GSS contexts for callback. If the client requires the
server to use the RPCSEC_GSS security flavor for callbacks, then
it needs to be sure the contexts handed to the server via
BACKCHANNEL_CTL are unexpired. A good practice is to keep at
least two contexts outstanding, where the expiration time of the
newest context at the time it was created, is N times that of the
oldest context, where N is the number of contexts available for
callbacks.
o Maintain an active connection. The server requires a callback
path in order to gracefully recall recallable state, or notify the
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client of certain events.
2.9.7.3. Steps the Client Takes To Establish a Session
The client issues EXCHANGE_ID to establish a clientid.
The client uses the clientid to issue a CREATE_SESSION on a
connection to the server. The results of CREATE_SESSION indicate
whether the server will persist the session replay cache through a
server reboot or not, and the client notes this for future reference.
The client SHOULD have specified connecting binding enforcement when
the session was created. If so, the client SHOULD issue SET_SSV in
the first COMPOUND after the session is created. If it is not using
machine credentials, then each time a new principal goes to use the
session, it SHOULD issue a SET_SSV again.
If the client wants to use delegations, layouts, directory
notifications, or any other state that requires a callback channel,
then it MUST add a connection to the backchannel if CREATE_SESSION
did not already do so. The client creates a connection, and calls
BIND_CONN_TO_SESSION to bind the connection to the session and the
session's backchannel. If CREATE_SESSION did not already do so, the
client MUST tell the server what security is required in order for
the client to accept callbacks. The client does this via
BACKCHANNEL_CTL.
If the client wants to use additional connections for the
backchannel, then it MUST call BIND_CONN_TO_SESSION on each
connection it wants to use with the session. If the client wants to
use additional connections for the operation channel, then it MUST
call BIND_CONN_TO_SESSION if it specified connection binding
enforcement before using the connection.
At this point the client has reached a steady state as far as session
use.
2.9.8. Session Mechanics - Recovery
2.9.8.1. Events Requiring Client Action
The following events require client action to recover.
2.9.8.1.1. RPCSEC_GSS Context Loss by Callback Path
If all RPCSEC_GSS contexts granted to by the client to the server for
callback use have expired, the client MUST establish a new context
via BACKCHANNEL_CTL. The sr_status field of SEQUENCE results
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indicates when callback contexts are nearly expired, or fully expired
(see Section 16.46.4).
2.9.8.1.2. Connection Disconnect
If the client loses the last connection of the session, then it MUST
create a new connection, and if connecting binding enforcement was
specified when the session was created, bind it to the session via
BIND_CONN_TO_SESSION.
If there were requests outstanding at the time the of connection
disconnect, then the client MUST retry the request, as described in
Section 2.9.4.2. Note that it is not necessary to retry requests
over a connection with the same source network address or the same
destination network address as the disconnected connection. As long
as the sessionid, slotid, and sequenceid in the retry match that of
the original request, the server will recognize the request as a
retry if it did see the request prior to disconnect.
If the connection that was bound to the backchannel is lost, the
client may need to reconnect, and use BIND_CONN_TO_SESSION, to give
the connection to the backchannel. If the connection that was lost
was the last one bound to the backchannel, the client MUST reconnect,
and bind the connection to the session and backchannel. The server
should indicate when it has no callback connection via the sr_status
result from SEQUENCE.
2.9.8.1.3. Backchannel GSS Context Loss
Via the sr_status result of the SEQUENCE operation or other means,
the client will learn if some or all of the RPCSEC_GSS contexts it
assigned to the backchannel have been lost. The client may need to
use BACKCHANNEL_CTL to assign new contexts. It MUST assign new
contexts if there are no more contexts.
2.9.8.1.4. Loss of Session
The server may lose a record of the session. Causes include:
o Server crash and reboot
o A catastrophe that causes the cache to be corrupted or lost on the
media it was stored on. This applies even if the server indicated
in the CREATE_SESSION results that it would persist the cache.
o The server purges the session of a client that has been inactive
for a very extended period of time. [[Comment.11: XXX - Should we
add a value to the CREATE_SESSION results that tells a client how
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long he can let a session stay idle before losing it?]]
Loss of replay cache is equivalent to loss of session. The server
indicates loss of session to the client by returning
NFS4ERR_BADSESSION on the next operation that uses the sessionid
associated with the lost session.
After an event like a server reboot, the client may have lost its
connections. The client assumes for the moment that the session has
not been lost. It reconnects, and if it specified connecting binding
enforcement when the session was created, it invokes
BIND_CONN_TO_SESSION using the sessionid. Otherwise, it invokes
SEQUENCE. If BIND_CONN_TO_SESSION or SEQUENCE returns
NFS4ERR_BADSESSION, the client knows the session was lost. If the
connection survives session loss, then the next SEQUENCE operation
the client issues over the connection will get back
NFS4ERR_BADSESSION. The client again knows the session was lost.
When the client detects session loss, it must call CREATE_SESSION to
recover. Any non-idempotent operations that were in progress may
have been performed on the server at the time of session loss. The
client has no general way to recover from this.
Note that loss of session does not imply loss of lock, open,
delegation, or layout state. Nor does loss of lock, open,
delegation, or layout state imply loss of session state.
[[Comment.12: Add reference to lock recovery section]] . A session
can survive a server reboot, but lock recovery may still be needed.
The converse is also true.
It is possible CREATE_SESSION will fail with NFS4ERR_STALE_CLIENTID
(for example the server reboots and does not preserve clientid
state). If so, the client needs to call EXCHANGE_ID, followed by
CREATE_SESSION.
2.9.8.1.5. Failover
[[Comment.13: Dave Noveck requested this section; not sure what is
needed here if this refers to failover to a replica. What are the
session ramifications?]]
2.9.8.2. Events Requiring Server Action
The following events require server action to recover.
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2.9.8.2.1. Client Crash and Reboot
As described in Section 16.35, a rebooted client causes the server to
delete any sessions it had.
2.9.8.2.2. Client Crash with No Reboot
If a client crashes and never comes back, it will never issue
EXCHANGE_ID with its old clientid. Thus the server has session state
that will never be used again. After an extended period of time and
if the server has resource constraints, it MAY destroy the old
session.
2.9.8.2.3. Extended Network Partition
To the server, the extended network partition may be no different
than a client crash with no reboot (see Section 2.9.8.2.2). Unless
the server can discern that there is a network partition, it is free
to treat the situation as if the client has crashed for good.
2.9.8.2.4. Backchannel Connection Loss
If there were callback requests outstanding at the time the of a
connection disconnect, then the server MUST retry the request, as
described in Section 2.9.4.2. Note that it is not necessary to retry
requests over a connection with the same source network address or
the same destination network address as the disconnected connection.
As long as the sessionid, slotid, and sequenceid in the retry match
that of the original request, the callback target will recognize the
request as a retry if it did see the request prior to disconnect.
If the connection lost is the last one bound to the backchannel, then
the server MUST indicate that in the sr_status field of the next
SEQUENCE reply.
2.9.8.2.5. GSS Context Loss
The server SHOULD monitor when the last RPCSEC_GSS context assigned
to the backchannel is near expiry (i.e. between one and two periods
of lease time), and indicate so in the sr_status field of the next
SEQUENCE reply. The server MUST indicate when the backchannel's last
RPCSEC_GSS context has expired in the sr_status field of the next
SEQUENCE reply.
3. Protocol Data Types
The syntax and semantics to describe the data types of the NFS
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version 4 protocol are defined in the XDR RFC4506 [3] and RPC RFC1831
[4] documents. The next sections build upon the XDR data types to
define types and structures specific to this protocol.
3.1. 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 definition of change_info |
| clientid4 | typedef uint64_t clientid4; |
| | Shorthand reference to client identification |
| component4 | typedef utf8str_cs component4; |
| | Represents path name components |
| count4 | typedef uint32_t count4; |
| | Various count parameters (READ, WRITE, COMMIT) |
| length4 | typedef uint64_t length4; |
| | Describes LOCK lengths |
| linktext4 | typedef utf8str_cs linktext4; |
| | Symbolic link contents |
| 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; NFS4_FHSIZE is defined as |
| | 128 |
| 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) |
| pathname4 | typedef component4 pathname4<>; |
| | Represents path name for fs_locations |
| qop4 | typedef uint32_t qop4; |
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| | 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 contains an ASN.1 |
| | OBJECT IDENTIFIER as used by GSS-API in the |
| | mech_type argument to GSS_Init_sec_context. See |
| | RFC2743 [8] for details. |
| seqid4 | typedef uint32_t seqid4; |
| | Sequence identifier used for file locking |
| utf8string | typedef opaque utf8string<>; |
| | UTF-8 encoding for strings |
| utf8str_cis | typedef opaque utf8str_cis; |
| | Case-insensitive UTF-8 string |
| utf8str_cs | typedef opaque utf8str_cs; |
| | Case-sensitive UTF-8 string |
| utf8str_mixed | typedef opaque utf8str_mixed; |
| | UTF-8 strings with a case sensitive prefix and a |
| | case insensitive suffix. |
| verifier4 | typedef opaque verifier4[NFS4_VERIFIER_SIZE]; |
| | Verifier used for various operations (COMMIT, |
| | CREATE, OPEN, READDIR, SETCLIENTID, |
| | SETCLIENTID_CONFIRM, WRITE) NFS4_VERIFIER_SIZE is |
| | defined as 8. |
+---------------+---------------------------------------------------+
End of Base Data Types
Table 1
3.2. Structured Data Types
3.2.1. 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).
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Values greater than 999,999,999 for nseconds are considered invalid.
This data type is used to pass time and date information. A server
converts to and from its local representation of time when processing
time values, preserving as much accuracy as possible. If the
precision of timestamps stored for a file system object is less than
defined, loss of precision can occur. An adjunct time maintenance
protocol is recommended to reduce client and server time skew.
3.2.2. time_how4
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
3.2.3. 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.
3.2.4. 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.
3.2.5. fsid4
struct fsid4 {
uint64_t major;
uint64_t minor;
};
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3.2.6. fs_location4
struct fs_location4 {
utf8str_cis server<>;
pathname4 rootpath;
};
3.2.7. 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.
3.2.8. fattr4
struct fattr4 {
bitmap4 attrmask;
attrlist4 attr_vals;
};
The fattr4 structure is used to represent file and directory
attributes.
The bitmap is a counted array of 32 bit integers used to contain bit
values. The position of the integer in the array that contains bit n
can be computed from the expression (n / 32) and its bit within that
integer is (n mod 32).
0 1
+-----------+-----------+-----------+--
| count | 31 .. 0 | 63 .. 32 |
+-----------+-----------+-----------+--
3.2.9. change_info4
struct change_info4 {
bool atomic;
changeid4 before;
changeid4 after;
};
This structure is used with the CREATE, LINK, REMOVE, RENAME
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operations to let the client know the value of the change attribute
for the directory in which the target file system object resides.
3.2.10. netaddr4
struct netaddr4 {
/* see struct rpcb in RFC1833 */
string r_netid<>; /* network id */
string r_addr<>; /* universal address */
};
The netaddr4 structure is used to identify TCP/IP based endpoints.
The r_netid and r_addr fields are specified in RFC1833 [22], but they
are underspecified in RFC1833 [22] 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
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 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 RFC1884
[9]. Additionally, the two alternative forms specified in Section
2.2 of RFC1884 [9] 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".
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3.2.11. clientaddr4
typedef netaddr4 clientaddr4;
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.
3.2.12. cb_client4
struct cb_client4 {
unsigned int cb_program;
netaddr4 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.
3.2.13. 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.
3.2.14. 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.
3.2.15. 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.
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3.2.16. open_to_lock_owner4
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
This structure is used for the first LOCK operation done for an
open_owner4. It provides both the open_stateid and lock_owner such
that the transition is made from a valid open_stateid sequence to
that of the new lock_stateid sequence. Using this mechanism avoids
the confirmation of the lock_owner/lock_seqid pair since it is tied
to established state in the form of the open_stateid/open_seqid.
3.2.17. stateid4
struct stateid4 {
uint32_t seqid;
opaque other[12];
};
This structure is used for the various state sharing mechanisms
between the client and server. For the client, this data structure
is read-only. The starting value of the seqid field is undefined.
The server is required to increment the seqid field monotonically at
each transition of the stateid. This is important since the client
will inspect the seqid in OPEN stateids to determine the order of
OPEN processing done by the server.
3.2.18. layouttype4
enum layouttype4 {
LAYOUT_NFSV4_FILES = 1,
LAYOUT_OSD2_OBJECTS = 2,
LAYOUT_BLOCK_VOLUME = 3
};
A layout type specifies the layout being used. The implication is
that clients have "layout drivers" that support one or more layout
types. The file server advertises the layout types it supports
through the LAYOUT_TYPES file system attribute. A client asks for
layouts of a particular type in LAYOUTGET, and passes those layouts
to its layout driver.
The layouttype4 structure is 32 bits in length. The range
represented by the layout type is split into two parts. Types within
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the range 0x00000000-0x7FFFFFFF are globally unique and are assigned
according to the description in Section 20.1; they are maintained by
IANA. Types within the range 0x80000000-0xFFFFFFFF are site specific
and for "private use" only.
The LAYOUT_NFSV4_FILES enumeration specifies that the NFSv4 file
layout type is to be used. The LAYOUT_OSD2_OBJECTS enumeration
specifies that the object layout, as defined in [23], is to be used.
Similarly, the LAYOUT_BLOCK_VOLUME enumeration that the block/volume
layout, as defined in [24], is to be used.
3.2.19. deviceid4
typedef uint32_t deviceid4; /* 32-bit device ID */
Layout information includes device IDs that specify a storage device
through a compact handle. Addressing and type information is
obtained with the GETDEVICEINFO operation. A client must not assume
that device IDs are valid across metadata server reboots. The device
ID is qualified by the layout type and are unique per file system
(FSID). This allows different layout drivers to generate device IDs
without the need for co-ordination. See Section 12.3.1.4 for more
details.
3.2.20. devlist_item4
struct devlist_item4 {
deviceid4 dli_id;
opaque dli_device_addr<>;
};
An array of these values is returned by the GETDEVICELIST operation.
They define the set of devices associated with a file system for the
layout type specified in the GETDEVICELIST4args.
The device address is used to set up a communication channel with the
storage device. Different layout types will require different types
of structures to define how they communicate with storage devices.
The opaque device_addr field must be interpreted based on the
specified layout type.
This document defines the device address for the NFSv4 file layout
(struct netaddr4 (Section 3.2.10)), which identifies a storage device
by network IP address and port number. This is sufficient for the
clients to communicate with the NFSv4 storage devices, and may be
sufficient for other layout types as well. Device types for object
storage devices and block storage devices (e.g., SCSI volume labels)
will be defined by their respective layout specifications.
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3.2.21. layout4
struct layout4 {
offset4 lo_offset;
length4 lo_length;
layoutiomode4 lo_iomode;
layouttype4 lo_type;
opaque lo_layout<>;
};
The layout4 structure defines a layout for a file. The layout type
specific data is opaque within this structure and must be
interepreted based on the layout type. Currently, only the NFSv4
file layout type is defined; see Section 12.4.2 for its definition.
Since layouts are sub-dividable, the offset and length together with
the file's filehandle, the clientid, iomode, and layout type,
identifies the layout.
3.2.22. layoutupdate4
struct layoutupdate4 {
layouttype4 lou_type;
opaque lou_data<>;
};
The layoutupdate4 structure is used by the client to return 'updated'
layout information to the metadata server at LAYOUTCOMMIT time. This
structure provides a channel to pass layout type specific information
back to the metadata server. E.g., for block/volume layout types
this could include the list of reserved blocks that were written.
The contents of the opaque lou_data argument are determined by the
layout type and are defined in their context. The NFSv4 file-based
layout does not use this structure, thus the update_data field should
have a zero length.
3.2.23. layouthint4
struct layouthint4 {
layouttype4 loh_type;
opaque loh_data<>;
};
The layouthint4 structure is used by the client to pass in a hint
about the type of layout it would like created for a particular file.
It is the structure specified by the FILE_LAYOUT_HINT attribute
described below. The metadata server may ignore the hint, or may
selectively ignore fields within the hint. This hint should be
provided at create time as part of the initial attributes within
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OPEN. The NFSv4 file-based layout uses the "nfsv4_file_layouthint"
structure as defined in Section 12.4.2.
3.2.24. layoutiomode4
enum layoutiomode4 {
LAYOUTIOMODE_READ = 1,
LAYOUTIOMODE_RW = 2,
LAYOUTIOMODE_ANY = 3
};
The iomode specifies whether the client intends to read or write
(with the possibility of reading) the data represented by the layout.
The ANY iomode MUST NOT be used for LAYOUTGET, however, it can be
used for LAYOUTRETURN and LAYOUTRECALL. The ANY iomode specifies
that layouts pertaining to both READ and RW iomodes are being
returned or recalled, respectively. The metadata server's use of the
iomode may depend on the layout type being used. The storage devices
may validate I/O accesses against the iomode and reject invalid
accesses.
3.2.25. nfs_impl_id4
struct nfs_impl_id4 {
utf8str_cis nii_domain;
utf8str_cs nii_name;
nfstime4 nii_date;
};
This structure is used to identify client and server implementation
detail. The nii_domain field is the DNS domain name that the
implementer is associated with. The nii_name field is the product
name of the implementation and is completely free form. It is
encouraged that the nii_name be used to distinguish machine
architecture, machine platforms, revisions, versions, and patch
levels. The nii_date field is the timestamp of when the software
instance was published or built.
3.2.26. threshold_item4
struct threshold_item4 {
layouttype4 thi_layout_type;
bitmap4 thi_hintset;
opaque thi_hintlist<>;
};
This structure contains a list of hints specific to a layout type for
helping the client determine when it should issue I/O directly
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through the metadata server vs. the data servers. The hint structure
consists of the layout type, a bitmap describing the set of hints
supported by the server, they may differ based on the layout type,
and a list of hints, whose structure is determined by the hintset
bitmap. See the mdsthreshold attribute for more details.
The hintset is a bitmap of the following values:
+-------------------------+---+---------+---------------------------+
| name | # | Data | Description |
| | | Type | |
+-------------------------+---+---------+---------------------------+
| threshold4_read_size | 0 | length4 | The file size below which |
| | | | it is recommended to read |
| | | | data through the MDS. |
| threshold4_write_size | 1 | length4 | The file size below which |
| | | | it is recommended to |
| | | | write data through the |
| | | | MDS. |
| threshold4_read_iosize | 2 | length4 | For read I/O sizes below |
| | | | this threshold it is |
| | | | recommended to read data |
| | | | through the MDS |
| threshold4_write_iosize | 3 | length4 | For write I/O sizes below |
| | | | this threshold it is |
| | | | recommended to write data |
| | | | through the MDS |
+-------------------------+---+---------+---------------------------+
3.2.27. mdsthreshold4
struct mdsthreshold4 {
threshold_item4 mth_hints<>;
};
This structure holds an array of threshold_item4 structures each of
which is valid for a particular layout type. An array is necessary
since a server can support multiple layout types for a single file.
4. Filehandles
The filehandle in the NFS protocol is a per server unique identifier
for a file system object. The contents of the filehandle are opaque
to the client. Therefore, the server is responsible for translating
the filehandle to an internal representation of the file system
object.
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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 RFC1094 [17] and the NFS version 3 protocol RFC1813 [18],
there exists an ancillary protocol to obtain this first filehandle.
The MOUNT protocol, RPC program number 100005, provides the mechanism
of translating a string based file system path name to a filehandle
which can then be used by the NFS protocols.
The MOUNT protocol has deficiencies in the area of security and use
via firewalls. This is one reason that the use of the public
filehandle was introduced in RFC2054 [25] and RFC2055 [26]. 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 file system 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 the section "NFS Server Name Space".
4.1.2. Public Filehandle
The second special filehandle is the PUBLIC filehandle. Unlike the
ROOT filehandle, the PUBLIC filehandle may be bound or represent an
arbitrary file system object at the server. The server is
responsible for this binding. It may be that the PUBLIC filehandle
and the ROOT filehandle refer to the same file system object.
However, it is up to the administrative software at the server and
the policies of the server administrator to define the binding of the
PUBLIC filehandle and server file system object. The client may not
make any assumptions about this binding. The client uses the PUBLIC
filehandle via the PUTPUBFH operation.
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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 file system level invariant that can be
used to construct a persistent filehandle. The underlying server
file system may not provide the invariant or the server's file system
programming interfaces may not provide access to the needed
invariant. Volatile filehandles may ease the implementation of
server functionality such as hierarchical storage management or file
system reorganization or migration. However, the volatile filehandle
increases the implementation burden for the client.
Since the client will need to handle persistent and volatile
filehandles differently, a file attribute is defined which may be
used by the client to determine the filehandle types being returned
by the server.
4.2.1. General Properties of a Filehandle
The filehandle contains all the information the server needs to
distinguish an individual file. To the client, the filehandle is
opaque. The client stores filehandles for use in a later request and
can compare two filehandles from the same server for equality by
doing a byte-by-byte comparison. However, the client MUST NOT
otherwise interpret the contents of filehandles. If two filehandles
from the same server are equal, they MUST refer to the same file.
Servers SHOULD try to maintain a one-to-one correspondence between
filehandles and files but this is not required. Clients MUST use
filehandle comparisons only to improve performance, not for correct
behavior. All clients need to be prepared for situations in which it
cannot be determined whether two filehandles denote the same object
and in such cases, avoid making invalid assumptions which might cause
incorrect behavior. Further discussion of filehandle and attribute
comparison in the context of data caching is presented in the section
"Data Caching and File Identity".
As an example, in the case that two different path names when
traversed at the server terminate at the same file system object, the
server SHOULD return the same filehandle for each path. This can
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occur if a hard link is used to create two file names which refer to
the same underlying file object and associated data. For example, if
paths /a/b/c and /a/d/c refer to the same file, the server SHOULD
return the same filehandle for both path names traversals.
4.2.2. Persistent Filehandle
A persistent filehandle is defined as having a fixed value for the
lifetime of the file system object to which it refers. Once the
server creates the filehandle for a file system object, the server
MUST accept the same filehandle for the object for the lifetime of
the object. If the server restarts or reboots the NFS server must
honor the same filehandle value as it did in the server's previous
instantiation. Similarly, if the file system is migrated, the new
NFS server must honor the same filehandle as the old NFS server.
The persistent filehandle will be become stale or invalid when the
file system object is removed. When the server is presented with a
persistent filehandle that refers to a deleted object, it MUST return
an error of NFS4ERR_STALE. A filehandle may become stale when the
file system containing the object is no longer available. The file
system may become unavailable if it exists on removable media and the
media is no longer available at the server or the file system in
whole has been destroyed or the file system has simply been removed
from the server's name space (i.e. unmounted in a UNIX environment).
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
determine what type of filehandle the server is providing for a
particular file system. This attribute is a bitmask with the
following values:
FH4_PERSISTENT The value of FH4_PERSISTENT is used to indicate a
persistent filehandle, which is valid until the object is removed
from the file system. The server will not return
NFS4ERR_FHEXPIRED for this filehandle. FH4_PERSISTENT is defined
as a value in which none of the bits specified below are set.
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FH4_VOLATILE_ANY The filehandle may expire at any time, except as
specifically excluded (i.e. FH4_NO_EXPIRE_WITH_OPEN).
FH4_NOEXPIRE_WITH_OPEN May only be set when FH4_VOLATILE_ANY is set.
If this bit is set, then the meaning of FH4_VOLATILE_ANY is
qualified to exclude any expiration of the filehandle when it is
open.
FH4_VOL_MIGRATION The filehandle will expire as a result of a file
system transition (migration or replication), in those case in
which the continuity of filehandle use is not specified by
_handle_ class information within the fs_locations_info attribute.
When this bit is set, clients without access to fs_locations_info
information should assume filehandles will expire on file system
transitions.
FH4_VOL_RENAME The filehandle will expire during rename. This
includes a rename by the requesting client or a rename by any
other client. If FH4_VOL_ANY is set, FH4_VOL_RENAME is redundant.
Servers which provide volatile filehandles that may expire while open
(i.e. if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if
FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), should
deny a RENAME or REMOVE that would affect an OPEN file of any of the
components leading to the OPEN file. In addition, the server should
deny all RENAME or REMOVE requests during the grace period upon
server restart.
Servers which provide volatile filehandles that may expire while open
require special care as regards handling of RENAMESs and REMOVEs.
This situation can arise if FH4_VOL_MIGRATION or FH4_VOL_RENAME is
set, if FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set,
or if a non-readonly file system has a transition target in a
different _handle _ class. In these cases, the server should deny a
RENAME or REMOVE that would affect an OPEN file of any of the
components leading to the OPEN file. In addition, the server should
deny all RENAME or REMOVE requests during the grace period, in order
to make sure that reclaims of files where filehandles may have
expired do not do a reclaim for the wrong file.
4.3. One Method of Constructing a Volatile Filehandle
A volatile filehandle, while opaque to the client could contain:
[volatile bit = 1 | server boot time | slot | generation number]
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o slot is an index in the server volatile filehandle table
o generation number is the generation number for the table entry/
slot
When the client presents a volatile filehandle, the server makes the
following checks, which assume that the check for the volatile bit
has passed. If the server boot time is less than the current server
boot time, return NFS4ERR_FHEXPIRED. If slot is out of range, return
NFS4ERR_BADHANDLE. If the generation number does not match, return
NFS4ERR_FHEXPIRED.
When the server reboots, the table is gone (it is volatile).
If volatile bit is 0, then it is a persistent filehandle with a
different structure following it.
4.4. Client Recovery from Filehandle Expiration
If possible, the client SHOULD recover from the receipt of an
NFS4ERR_FHEXPIRED error. The client must take on additional
responsibility so that it may prepare itself to recover from the
expiration of a volatile filehandle. If the server returns
persistent filehandles, the client does not need these additional
steps.
For volatile filehandles, most commonly the client will need to store
the component names leading up to and including the file system
object in question. With these names, the client should be able to
recover by finding a filehandle in the name space that is still
available or by starting at the root of the server's file system name
space.
If the expired filehandle refers to an object that has been removed
from the file system, obviously the client will not be able to
recover from the expired filehandle.
It is also possible that the expired filehandle refers to a file that
has been renamed. If the file was renamed by another client, again
it is possible that the original client will not be able to recover.
However, in the case that the client itself is renaming the file and
the file is open, it is possible that the client may be able to
recover. The client can determine the new path name based on the
processing of the rename request. The client can then regenerate the
new filehandle based on the new path name. The client could also use
the compound operation mechanism to construct a set of operations
like:
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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 NFS version 3 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 NFS version 4 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: mandatory,
recommended, and named. Both mandatory and recommended attributes
are supported in the NFS version 4 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 mandatory or recommended attributes
may be added to the NFS protocol between major revisions by
publishing a standards-track RFC which allocates a new attribute
number value and defines the encoding for the attribute. See the
section "Minor Versioning" 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 mandatory 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 mandatory 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. Mandatory Attributes
These MUST be supported by every NFS version 4 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 mandatory 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
NFS version 4 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 NFS
Version 4 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 "attribute
directory" and further perusal of the name space may be done using
READDIR and LOOKUP operations on this filehandle. Named attributes
may then be examined or changed by normal READ and WRITE and CREATE
operations on the filehandles returned from READDIR and LOOKUP.
Named attributes may have attributes.
It is recommended that servers support arbitrary named attributes. A
client should not depend on the ability to store any named attributes
in the server's file system. If a server does support named
attributes, a client which is also able to handle them should be able
to copy a file's data and meta-data with complete transparency from
one location to another; this would imply that names allowed for
regular directory entries are valid for named attribute names as
well.
Names of attributes will not be controlled by this document or other
IETF standards track documents. See the section "IANA
Considerations" for further discussion.
5.4. Classification of Attributes
Each of the Mandatory 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
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because they are write-only attributes corresponding to time_access
and time_modify, and are used in a special instance of SETATTR.
o The per server attributes are:
lease_time, send_impl_id, recv_impl_id
o The per file system attributes are:
supp_attr, 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, fs_layout_type
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, layout_type, layout_hint,
layout_blksize, layout_alignment
For quota_avail_hard, quota_avail_soft, and quota_used see their
definitions below for the appropriate classification.
5.5. Mandatory Attributes - Definitions
+-----------------+----+------------+--------+----------------------+
| name | # | Data Type | Access | Description |
+-----------------+----+------------+--------+----------------------+
| supp_attr | 0 | bitmap | READ | The bit vector which |
| | | | | would retrieve all |
| | | | | mandatory and |
| | | | | recommended |
| | | | | attributes that are |
| | | | | supported for this |
| | | | | object. The scope of |
| | | | | this attribute |
| | | | | applies to all |
| | | | | objects with a |
| | | | | matching fsid. |
| type | 1 | nfs4_ftype | READ | The type of the |
| | | | | object (file, |
| | | | | directory, symlink, |
| | | | | etc.) |
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| fh_expire_type | 2 | uint32 | READ | Server uses this to |
| | | | | specify filehandle |
| | | | | expiration behavior |
| | | | | to the client. See |
| | | | | the section |
| | | | | "Filehandles" for |
| | | | | additional |
| | | | | description. |
| change | 3 | uint64 | READ | 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. |
| size | 4 | uint64 | R/W | The size of the |
| | | | | object in bytes. |
| link_support | 5 | bool | READ | True, if the |
| | | | | object's file system |
| | | | | supports hard links. |
| symlink_support | 6 | bool | READ | True, if the |
| | | | | object's file system |
| | | | | supports symbolic |
| | | | | links. |
| named_attr | 7 | bool | READ | True, if this object |
| | | | | has named |
| | | | | attributes. In other |
| | | | | words, object has a |
| | | | | non-empty named |
| | | | | attribute directory. |
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| fsid | 8 | fsid4 | READ | Unique file system |
| | | | | identifier for the |
| | | | | file system holding |
| | | | | this object. fsid |
| | | | | contains major and |
| | | | | minor components |
| | | | | each of which are |
| | | | | uint64. |
| unique_handles | 9 | bool | READ | True, if two |
| | | | | distinct filehandles |
| | | | | guaranteed to refer |
| | | | | to two different |
| | | | | file system objects. |
| lease_time | 10 | nfs_lease4 | READ | Duration of leases |
| | | | | at server in |
| | | | | seconds. |
| rdattr_error | 11 | enum | READ | Error returned from |
| | | | | getattr during |
| | | | | readdir. |
| filehandle | 19 | nfs_fh4 | READ | The filehandle of |
| | | | | this object |
| | | | | (primarily for |
| | | | | readdir requests). |
+-----------------+----+------------+--------+----------------------+
5.6. Recommended Attributes - Definitions
+-------------------+----+----------------+--------+----------------+
| name | # | Data Type | Access | Description |
+-------------------+----+----------------+--------+----------------+
| ACL | 12 | nfsace4<> | R/W | The access |
| | | | | control list |
| | | | | for the |
| | | | | object. |
| aclsupport | 13 | uint32 | READ | Indicates what |
| | | | | types of ACLs |
| | | | | are supported |
| | | | | on the current |
| | | | | file system. |
| archive | 14 | bool | R/W | True, if this |
| | | | | file has been |
| | | | | archived since |
| | | | | the time of |
| | | | | last |
| | | | | modification |
| | | | | (deprecated in |
| | | | | favor of |
| | | | | time_backup). |
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| cansettime | 15 | bool | READ | True, if the |
| | | | | server able to |
| | | | | change the |
| | | | | times for a |
| | | | | file system |
| | | | | object as |
| | | | | specified in a |
| | | | | SETATTR |
| | | | | operation. |
| case_insensitive | 16 | bool | READ | True, if |
| | | | | filename |
| | | | | comparisons on |
| | | | | this file |
| | | | | system are |
| | | | | case |
| | | | | insensitive. |
| case_preserving | 17 | bool | READ | True, if |
| | | | | filename case |
| | | | | on this file |
| | | | | system are |
| | | | | preserved. |
| chown_restricted | 18 | bool | READ | 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). |
| dir_notif_delay | 56 | nfstime4 | READ | notification |
| | | | | delays on |
| | | | | directory |
| | | | | attributes |
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| dirent_ | 57 | nfstime4 | READ | notification |
| notif_delay | | | | delays on |
| | | | | child |
| | | | | attributes |
| fileid | 20 | uint64 | READ | A number |
| | | | | uniquely |
| | | | | identifying |
| | | | | the file |
| | | | | within the |
| | | | | file system. |
| files_avail | 21 | uint64 | READ | File slots |
| | | | | available to |
| | | | | this user on |
| | | | | the file |
| | | | | system |
| | | | | containing |
| | | | | this object - |
| | | | | this should be |
| | | | | the smallest |
| | | | | relevant |
| | | | | limit. |
| files_free | 22 | uint64 | READ | Free file |
| | | | | slots on the |
| | | | | file system |
| | | | | containing |
| | | | | this object - |
| | | | | this should be |
| | | | | the smallest |
| | | | | relevant |
| | | | | limit. |
| files_total | 23 | uint64 | READ | Total file |
| | | | | slots on the |
| | | | | file system |
| | | | | containing |
| | | | | this object. |
| fs_absent | 60 | bool | READ | Is current |
| | | | | file system |
| | | | | present or |
| | | | | absent. |
| fs_layout_type | 62 | layouttype4<> | READ | Layout types |
| | | | | available for |
| | | | | the file |
| | | | | system. |
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| fs_locations | 24 | fs_locations | READ | Locations |
| | | | | where this |
| | | | | file system |
| | | | | may be found. |
| | | | | If the server |
| | | | | returns |
| | | | | NFS4ERR_MOVED |
| | | | | as an error, |
| | | | | this attribute |
| | | | | MUST be |
| | | | | supported. |
| fs_locations_info | 67 | | READ | Full function |
| | | | | file system |
| | | | | location. |
| fs_status | 61 | fs4_status | READ | Generic file |
| | | | | system type |
| | | | | information. |
| hidden | 25 | bool | R/W | True, if the |
| | | | | file is |
| | | | | considered |
| | | | | hidden with |
| | | | | respect to the |
| | | | | Windows API? |
| homogeneous | 26 | bool | READ | True, if this |
| | | | | object's file |
| | | | | system is |
| | | | | homogeneous, |
| | | | | i.e. are per |
| | | | | file system |
| | | | | attributes the |
| | | | | same for all |
| | | | | file system's |
| | | | | objects. |
| layout_alignment | 66 | uint32_t | READ | Preferred |
| | | | | alignment for |
| | | | | layout related |
| | | | | I/O. |
| layout_blksize | 65 | uint32_t | READ | Preferred |
| | | | | block size for |
| | | | | layout related |
| | | | | I/O. |
| layout_hint | 63 | layouthint4 | WRITE | Client |
| | | | | specified hint |
| | | | | for file |
| | | | | layout. |
| layout_type | 64 | layouttype4<> | READ | Layout types |
| | | | | available for |
| | | | | the file. |
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| maxfilesize | 27 | uint64 | READ | Maximum |
| | | | | supported file |
| | | | | size for the |
| | | | | file system of |
| | | | | this object. |
| maxlink | 28 | uint32 | READ | Maximum number |
| | | | | of links for |
| | | | | this object. |
| maxname | 29 | uint32 | READ | Maximum |
| | | | | filename size |
| | | | | supported for |
| | | | | this object. |
| maxread | 30 | uint64 | READ | Maximum read |
| | | | | size supported |
| | | | | for this |
| | | | | object. |
| maxwrite | 31 | uint64 | READ | 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. |
| mdsthreshold | 68 | mdsthreshold4 | READ | Hint to client |
| | | | | as to when to |
| | | | | write through |
| | | | | the pnfs |
| | | | | metadata |
| | | | | server. |
| mimetype | 32 | utf8<> | R/W | MIME body |
| | | | | type/subtype |
| | | | | of this |
| | | | | object. |
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| mode | 33 | mode4 | R/W | UNIX-style |
| | | | | mode and |
| | | | | permission |
| | | | | bits for this |
| | | | | object. |
| mounted_on_fileid | 55 | uint64 | READ | Like fileid, |
| | | | | but if the |
| | | | | target |
| | | | | filehandle is |
| | | | | the root of a |
| | | | | file system |
| | | | | return the |
| | | | | fileid of the |
| | | | | underlying |
| | | | | directory. |
| no_trunc | 34 | bool | READ | True, if a |
| | | | | name longer |
| | | | | than name_max |
| | | | | is used, an |
| | | | | error be |
| | | | | returned and |
| | | | | name is not |
| | | | | truncated. |
| numlinks | 35 | uint32 | READ | Number of hard |
| | | | | links to this |
| | | | | object. |
| owner | 36 | utf8<> | R/W | The string |
| | | | | name of the |
| | | | | owner of this |
| | | | | object. |
| owner_group | 37 | utf8<> | R/W | The string |
| | | | | name of the |
| | | | | group |
| | | | | ownership of |
| | | | | this object. |
| quota_avail_hard | 38 | uint64 | READ | For definition |
| | | | | see "Quota |
| | | | | Attributes" |
| | | | | section below. |
| quota_avail_soft | 39 | uint64 | READ | For definition |
| | | | | see "Quota |
| | | | | Attributes" |
| | | | | section below. |
| quota_used | 40 | uint64 | READ | For definition |
| | | | | see "Quota |
| | | | | Attributes" |
| | | | | section below. |
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| rawdev | 41 | specdata4 | READ | Raw device |
| | | | | identifier. |
| | | | | UNIX device |
| | | | | major/minor |
| | | | | node |
| | | | | information. |
| | | | | If the value |
| | | | | of type is not |
| | | | | NF4BLK or |
| | | | | NF4CHR, the |
| | | | | value return |
| | | | | SHOULD NOT be |
| | | | | considered |
| | | | | useful. |
| recv_impl_id | 59 | impl_ident4 | READ | Client obtains |
| | | | | the server's |
| | | | | implementation |
| | | | | identity via |
| | | | | GETATTR. |
| retentevt_get | 71 | retention_get4 | READ | Get the |
| | | | | event-based |
| | | | | retention |
| | | | | duration, and |
| | | | | if enabled, |
| | | | | the |
| | | | | event-based |
| | | | | retention |
| | | | | begin time of |
| | | | | the file |
| | | | | object. |
| | | | | GETATTR use |
| | | | | only. |
| retentevt_set | 72 | retention_set4 | WRITE | Set the |
| | | | | event-based |
| | | | | retention |
| | | | | duration, and |
| | | | | optionally |
| | | | | enable |
| | | | | event-based |
| | | | | retention on |
| | | | | the file |
| | | | | object. |
| | | | | SETATTR use |
| | | | | only. |
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| retention_get | 69 | retention_get4 | READ | Get the |
| | | | | retention |
| | | | | duration, and |
| | | | | if enabled, |
| | | | | the retention |
| | | | | begin time of |
| | | | | the file |
| | | | | object. |
| | | | | GETATTR use |
| | | | | only. |
| retention_hold | 69 | uint64_t | R/W | Get or set |
| | | | | administrative |
| | | | | retention |
| | | | | holds, one |
| | | | | hold per bit |
| | | | | position. |
| retention_set | 70 | retention_set4 | WRITE | Set the |
| | | | | retention |
| | | | | duration, and |
| | | | | optionally |
| | | | | enable |
| | | | | retention on |
| | | | | the file |
| | | | | object. |
| | | | | SETATTR use |
| | | | | only. |
| send_impl_id | 58 | impl_ident4 | WRITE | Client |
| | | | | provides |
| | | | | server with |
| | | | | its |
| | | | | implementation |
| | | | | identity via |
| | | | | SETATTR. |
| space_avail | 42 | uint64 | READ | Disk space in |
| | | | | bytes |
| | | | | available to |
| | | | | this user on |
| | | | | the file |
| | | | | system |
| | | | | containing |
| | | | | this object - |
| | | | | this should be |
| | | | | the smallest |
| | | | | relevant |
| | | | | limit. |
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| space_free | 43 | uint64 | READ | Free disk |
| | | | | space in bytes |
| | | | | on the file |
| | | | | system |
| | | | | containing |
| | | | | this object - |
| | | | | this should be |
| | | | | the smallest |
| | | | | relevant |
| | | | | limit. |
| space_total | 44 | uint64 | READ | Total disk |
| | | | | space in bytes |
| | | | | on the file |
| | | | | system |
| | | | | containing |
| | | | | this object. |
| space_used | 45 | uint64 | READ | Number of file |
| | | | | system bytes |
| | | | | allocated to |
| | | | | this object. |
| system | 46 | bool | R/W | True, if this |
| | | | | file is a |
| | | | | "system" file |
| | | | | with respect |
| | | | | to the Windows |
| | | | | API? |
| time_access | 47 | nfstime4 | READ | The time of |
| | | | | last access to |
| | | | | the object by |
| | | | | a read that |
| | | | | was satisfied |
| | | | | by the server. |
| time_access_set | 48 | settime4 | WRITE | Set the time |
| | | | | of last access |
| | | | | to the object. |
| | | | | SETATTR use |
| | | | | only. |
| time_backup | 49 | nfstime4 | R/W | The time of |
| | | | | last backup of |
| | | | | the object. |
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| time_create | 50 | nfstime4 | R/W | The time of |
| | | | | creation of |
| | | | | the object. |
| | | | | This attribute |
| | | | | does not have |
| | | | | any relation |
| | | | | to the |
| | | | | traditional |
| | | | | UNIX file |
| | | | | attribute |
| | | | | "ctime" or |
| | | | | "change time". |
| time_delta | 51 | nfstime4 | READ | Smallest |
| | | | | useful server |
| | | | | time |
| | | | | granularity. |
| time_metadata | 52 | nfstime4 | READ | The time of |
| | | | | last meta-data |
| | | | | modification |
| | | | | of the object. |
| time_modify | 53 | nfstime4 | READ | The time of |
| | | | | last |
| | | | | modification |
| | | | | to the object. |
| time_modify_set | 54 | settime4 | WRITE | Set the time |
| | | | | of last |
| | | | | modification |
| | | | | to the object. |
| | | | | SETATTR use |
| | | | | only. |
+-------------------+----+----------------+--------+----------------+
5.7. Time Access
As defined above, the time_access attribute represents the time of
last access to the object by a read that was satisfied by the server.
The notion of what is an "access" depends on server's operating
environment and/or the server's file system semantics. For example,
for servers obeying POSIX semantics, time_access would be updated
only by the READLINK, READ, and READDIR operations and not any of the
operations that modify the content of the object. Of course, setting
the corresponding time_access_set attribute is another way to modify
the time_access attribute.
Whenever the file object resides on a writable file system, the
server should make best efforts to record time_access into stable
storage. However, to mitigate the performance effects of doing so,
and most especially whenever the server is satisfying the read of the
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object's content from its cache, the server MAY cache access time
updates and lazily write them to stable storage. It is also
acceptable to give administrators of the server the option to disable
time_access updates.
5.8. Interpreting owner and owner_group
The recommended attributes "owner" and "owner_group" (and also users
and groups within the "acl" attribute) are represented in terms of a
UTF-8 string. To avoid a representation that is tied to a particular
underlying implementation at the client or server, the use of the
UTF-8 string has been chosen. Note that section 6.1 of RFC2624 [27]
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.
Similarly, security principals may be represented in different ways
by different security mechanisms. Servers normally translate these
representations into a common format, generally that used by local
storage, to serve as a means of identifying the users corresponding
to these security principals. When these local identifiers are
translated to the form of the owner attribute, associated with files
created by such principals they identify, in a common format, the
users associated with each corresponding set of security principals.
The translation used to interpret owner and group strings is not
specified as part of the protocol. This allows various solutions to
be employed. For example, a local translation table may be consulted
that maps between a numeric id to the user@dns_domain syntax. A name
service may also be used to accomplish the translation. A server may
provide a more general service, not limited by any particular
translation (which would only translate a limited set of possible
strings) by storing the owner and owner_group attributes in local
storage without any translation or it may augment a translation
method by storing the entire string for attributes for which no
translation is available while using the local representation for
those cases in which a translation is available.
Servers that do not provide support for all possible values of the
owner and owner_group attributes, should return an error
(NFS4ERR_BADOWNER) when a string is presented that has no
translation, as the value to be set for a SETATTR of the owner,
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owner_group, or acl attributes. When a server does accept an owner
or owner_group value as valid on a SETATTR (and similarly for the
owner and group strings in an acl), it is promising to return that
same string when a corresponding GETATTR is done. Configuration
changes and ill-constructed name translations (those that contain
aliasing) may make that promise impossible to honor. Servers should
make appropriate efforts to avoid a situation in which these
attributes have their values changed when no real change to ownership
has occurred.
The "dns_domain" portion of the owner string is meant to be a DNS
domain name. For example, user@ietf.org. Servers should accept as
valid a set of users for at least one domain. A server may treat
other domains as having no valid translations. A more general
service is provided when a server is capable of accepting users for
multiple domains, or for all domains, subject to security
constraints.
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 previous versions
of NFS (i.e. v2 and v3), which identified users and groups by 32-bit
unsigned uid's and gid's, owner and group strings that consist of
decimal numeric values with no leading zeros can be given a special
interpretation by clients and servers which choose to provide such
support. The receiver may treat such a user or group string as
representing the same user as would be represented by a v2/v3 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.
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5.9. Character Case Attributes
With respect to the case_insensitive and case_preserving attributes,
each UCS-4 character (which UTF-8 encodes) has a "long descriptive
name" RFC1345 [28] which may or may not included the word "CAPITAL"
or "SMALL". The presence of SMALL or CAPITAL allows an NFS server to
implement unambiguous and efficient table driven mappings for case
insensitive comparisons, and non-case-preserving storage. For
general character handling and internationalization issues, see the
section "Internationalization".
5.10. Quota Attributes
For the attributes related to file system quotas, the following
definitions apply:
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.
quota_avail_hard The value in bytes which represent the amount of
additional disk space beyond the current allocation that can be
allocated to this file or directory before further allocations
will be refused. It is understood that this space may be consumed
by allocations to other files or directories.
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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5.11. mounted_on_fileid
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
systems were mounted on the mount point.
Unlike NFS version 3, NFS version 4 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 NFS version 4 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
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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.
5.12. send_impl_id and recv_impl_id
These recommended attributes are used to identify the client and
server. In the case of the send_impl_id attribute, the client sends
its nfs_impl_id4. In the case of the recv_impl_id attribute, the
client receives the server's nfs_impl_id4 value.
Access to this identification information can be most useful at both
client and server. Being able to identify specific implementations
can help in planning by administrators or implementors. For example,
diagnostic software may extract this information in an attempt to
identify interoperability problems, performance workload behaviors or
general usage statistics. Since the intent of having access to this
information is for planning or general diagnosis only, the client and
server MUST NOT interpret this implementation identity information in
a way that affects interoperational behavior of the implementation.
The reason is the if clients and servers did such a thing, they might
use fewer capabilities of the protocol than the peer can support, or
the client and server might refuse to interoperate.
Because it is likely some implementations will violate the protocol
specification and interpret the identity information, implementations
MUST allow the users of the NFSv4 client and server to set the
contents of the sent nfs_impl_id structure to any value.
Even though these attributes are RECOMMENDED, if the server supports
one of them it MUST support the other.
5.13. fs_layout_type
This attribute applies to a file system and indicates what layout
types are supported by the file system. We expect this attribute to
be queried when a client encounters a new fsid. This attribute is
used by the client to determine if it has applicable layout drivers.
5.14. layout_type
This attribute indicates the particular layout type(s) used for a
file. This is for informational purposes only. The client needs to
use the LAYOUTGET operation in order to get enough information (e.g.,
specific device information) in order to perform I/O.
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5.15. layout_hint
This attribute may be set on newly created files to influence the
metadata server's choice for the file's layout. It is suggested that
this attribute is set as one of the initial attributes within the
OPEN call. The metadata server may ignore this attribute. This
attribute is a sub-set of the layout structure returned by LAYOUTGET.
For example, instead of specifying particular devices, this would be
used to suggest the stripe width of a file. It is up to the server
implementation to determine which fields within the layout it uses.
5.16. mdsthreshold
This attribute acts as a hint to the client to help it determine when
it is more efficient to issue read and write requests to the metadata
server vs. the data server. Two types of thresholds are described:
file size thresholds and I/O size thresholds. If a file's size is
smaller than the file size threshold, data accesses should be issued
to the metadata server. If an I/O is below the I/O size threshold,
the I/O should be issued to the metadata server. Each threshold can
be specified independently for read and write requests. For either
threshold type, a value of 0 indicates no read or write should be
issued to the metadata server, while a value of all 1s indicates all
reads or writes should be issued to the metadata server.
The attribute is available on a per filehandle basis. If the current
filehandle refers to a non-pNFS file or directory, the metadata
server should return an attribute that is representative of the
filehandle's file system. It is suggested that this attribute is
queried as part of the OPEN operation. Due to dynamic system
changes, the client should not assume that the attribute will remain
constant for any specific time period, thus it should be periodically
refreshed.
5.17. Retention Attributes
Retention is a concept whereby a file object can be placed in an
immutable, undeletable, unrenamable state for a fixed or infinite
duration of time. Once in this "retained" state, the file cannot be
moved out of the state until the duration of retention has been
reached.
When retention is enabled, retention MUST extend to the data of the
file, and the name of file. The server MAY extend retention any
other property of the file, including any subset of mandatory,
recommended, and named attributes, with the exceptions noted in this
section.
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Servers MAY support or not support retention on any file object type.
There are five retention attributes:
o retention_get. This attribute is only readable via GETATTR and
not setable via SETATTR. The value of the attribute consists of:
const RET4_DURATION_INFINITE = 0xffffffffffffffff;
struct retention_get4 {
uint64_t rg_duration;
nfstime4 rg_begin_time<1>;
};
The field rg_duration is duration in seconds indicating how long
the file will be retained once retention is enabled. The field
rg_begin_time is an array of up to one absolute time value. If
the array is zero length, no beginning retention time has been
established, and retention is not enabled. If rg_duration is
equal to RET4_DURATION_INFINITE, the file, once retention is
enabled, will be retained for an infinite duration.
o retention_set. This attribute corresponds to retention_get. This
attribute is only setable via SETATTR and not readable via
GETATTR. The value of the attribute consists of:
struct retention_set4 {
bool rs_enable;
uint64_t rs_duration<1>;
};
If the client sets rs_enable to TRUE, then it is enabling
retention on the file object with the begin time of retention
commencing from the server's current time and date. The duration
of the retention can also be provided if the rs_duration array is
of length one. The duration is time is seconds from the begin
time of retention, and if set to RET4_DURATION_INFINITE, the file
is to be retained forever. If retention is enabled, with no
duration specified in either this SETATTR or a previous SETATTR,
the duration defaults to zero seconds. The server MAY restrict
the enabling of retention or the duration of retention on the
basis of the ACE4_WRITE_RETENTION ACL permission. The enabling of
retention does not prevent the enabling of event-based retention
nor the modification of the retention_hold attribute.
o retentevt_get. This attribute is like retention_get, but refers
to event-based retention. The event that triggers event-based
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retention is not defined by the NFSv4.1 specification.
o retentevt_set. This attribute corresponds to retentevt_get, is
like retention_set, but refers to event-based retention. When
event based retention is set, the file MUST be retained even if
non-event-based retention has been set, and the duration of non-
event-based retention has been reached. Conversely, when non-
event-based retention has been set, the file MUST be retained even
the event-based retention has been set, and the duration of event-
based retention has been reached. The server MAY restrict the
enabling of event-based retention or the duration of event-based
retention on the basis of the ACE4_WRITE_RETENTION ACL permission.
The enabling of event-based retention does not prevent the
enabling of non-event-based retention nor the modification of the
retention_hold attribute.
o retention_hold. This attribute allows one to 64 administrative
holds, one hold per bit on the attribute. If retention_hold is
not zero, then the file MUST NOT be deleted, renamed, or modified,
even if the duration on enabled event or non-event-based retention
has been reached. The server MAY restrict the modification of
retention_hold on the basis of the ACE4_WRITE_RETENTION_HOLD ACL
permission. The enabling of administration retention holds does
not prevent the enabling of event-based or non-event-based
retention.
6. Access Control Lists
Access Control Lists (ACLs) are a file attribute that specify fine
grained access control. This chapter covers the "acl", "aclsupport",
and "mode" file attributes, and their interactions.
6.1. Goals
ACLs and modes represent two well established but different 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 the ACL attribute, it should provide
reasonable semantics to clients that only set and retrieve the ACL
attribute.
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o On servers that support the mode attribute, if the ACL attribute
has 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 attribute
has 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
should fail, regardless of a previously existing or inherited
ACL.
o It must be possible to implement a server such that its clients
can have POSIX compliant semantics.
o This minor version of NFSv4 should not introduce significantly
different semantics relating to the mode and ACL attributes, nor
should it render invalid any existing implementations. Rather,
this chapter provides clarifications based on previous
implementations and discussions around them.
o If a server supports the ACL attribute, then at any time, the
server can provide an ACL attribute when requested. The ACL
attribute will describe all permissions on the file object, except
for the three high-order bits of the mode attribute (described in
Section 6.2.2). The ACL attribute will not conflict with the mode
attribute, on servers that support the mode attribute.
o If a server supports the mode attribute, then at any time, the
server can provide a mode attribute when requested. The mode
attribute will not conflict with the ACL attribute, on servers
that support the ACL attribute.
o When a mode attribute is set on an object, the ACL attribute 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.
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6.2. File Attributes Discussion
6.2.1. ACL Attribute
The NFS version 4 ACL attribute is an array of access control entries
(ACEs). 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 attribute 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;
utf8str_mixed who;
};
To determine if a request succeeds, the server processes each nfsace4
entry in order. Only ACEs which have a "who" that matches the
requester are considered. Each ACE is processed until all of the
bits of the requester's access have been ALLOWED. Once a bit (see
below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
considered in the processing of later ACEs. If an ACCESS_DENIED_ACE
is encountered where the requester's access still has unALLOWED bits
in common with the "access_mask" of the ACE, the request is denied.
When the ACL is fully processed, if there are bits in the requester's
mask that have not been ALLOWED or DENIED, access is denied.
Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE types do
not affect a requester's access, and instead are for triggering
events as a result of a requester's access attempt. Therefore, all
AUDIT and ALARM ACEs are processed until end of the ACL.
The NFS version 4 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 indicate that it supports ACLs as long as it follows the
guidelines for mapping between its ACL model and the NFS version 4
ACL model.
The situation is complicated by the fact that a server may have
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multiple modules that enforce ACLs. For example, the enforcement for
NFS version 4 access may be different from 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 in all cases is that the server must not accept
ACLs that appear to make the file more secure than it really is.
6.2.1.1. ACE Type
The constants used for the type field (acetype4) are as follows:
const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
const ACE4_ACCESS_DENIED_ACE_TYPE = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE = 0x00000003;
+------------------------------+--------------+---------------------+
| 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 (system |
| | | dependent) 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. |
+------------------------------+--------------+---------------------+
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The "Abbreviation" column denotes how the types will be referred to
throughout the rest of this document.
6.2.1.2. The aclsupport Attribute
A server need not support all of the above ACE types. 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;
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.
Example: suppose a server can enforce NFS ACLs for NFS access but
cannot enforce ACLs for local access. If arbitrary processes can run
on the server, then the server SHOULD NOT indicate ACL support. On
the other hand, if only trusted administrative programs run locally,
then the server may indicate ACL support.
6.2.1.3. ACE Access Mask
The bitmask constants used for the access mask field are as follows:
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const ACE4_READ_DATA = 0x00000001;
const ACE4_LIST_DIRECTORY = 0x00000001;
const ACE4_WRITE_DATA = 0x00000002;
const ACE4_ADD_FILE = 0x00000002;
const ACE4_APPEND_DATA = 0x00000004;
const ACE4_ADD_SUBDIRECTORY = 0x00000004;
const ACE4_READ_NAMED_ATTRS = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS = 0x00000010;
const ACE4_EXECUTE = 0x00000020;
const ACE4_DELETE_CHILD = 0x00000040;
const ACE4_READ_ATTRIBUTES = 0x00000080;
const ACE4_WRITE_ATTRIBUTES = 0x00000100;
const ACE4_WRITE_RETENTION = 0x00000200;
const ACE4_WRITE_RETENTION_HOLD = 0x00000400;
const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
6.2.1.3.1. Discussion of Mask Attributes
ACE4_READ_DATA
Operation(s) affected:
READ
OPEN
Discussion:
Permission to read the data of the file.
Servers SHOULD allow a user the ability to read the data
of the file when only the ACE4_EXECUTE access mask bit is
allowed.
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 anywhere in the file's
offset range. This includes the ability to write to any
arbitrary offset and as a result to grow the file.
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ACE4_ADD_FILE
Operation(s) affected:
CREATE
OPEN
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.
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
Discussion:
Permission to create a subdirectory in a directory. The
CREATE operation is affected when nfs_ftype4 is NF4DIR.
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
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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:
LOOKUP
READ
OPEN
Discussion:
Permission to execute a file or traverse/search a
directory.
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_DELETE_CHILD
Operation(s) affected:
REMOVE
Discussion:
Permission to delete a file or directory within a
directory. See section "ACE4_DELETE vs. ACE4_DELETE_CHILD"
for information on how these two access mask bits interact.
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ACE4_READ_ATTRIBUTES
Operation(s) affected:
GETATTR of file system object attributes
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.
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 permission, but lacking
ACE4_WRITE_ATTRIBUTES must be allowed to implicitly set
the times associated with a file.
ACE4_WRITE_RETENTION
Operation(s) affected:
SETATTR of retention_set, retentevt_set.
Discussion:
Permission to modify the durations of event and non-event-based
retention. Also permission to enable event and non-event-based
retention. A server MAY map ACE4_WRITE_ATTRIBUTES to
ACE_WRITE_RETENTION.
ACE4_WRITE_RETENTION_HOLD
Operation(s) affected:
SETATTR of retention_hold.
Discussion:
Permission to modify the administration retention holds.
A server MAY map ACE4_WRITE_ATTRIBUTES to
ACE_WRITE_RETENTION_HOLD.
ACE4_DELETE
Operation(s) affected:
REMOVE
Discussion:
Permission to delete the file or directory. See section
"ACE4_DELETE vs. ACE4_DELETE_CHILD" for information on how
these two access mask bits interact.
ACE4_READ_ACL
Operation(s) affected:
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GETATTR of acl
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
Discussions:
Permission to write the owner and owner_group attributes.
On UNIX systems, this is the ability to execute chown().
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 error in the direction of more restricted
access. For example, suppose a server cannot distinguish overwriting
data from appending new data, as described in the previous paragraph.
If a client submits an ACE where ACE4_APPEND_DATA is set but
ACE4_WRITE_DATA is not (or vice versa), the server should reject the
request with NFS4ERR_ATTRNOTSUPP. Nonetheless, if the ACE has type
DENY, the server may silently turn on the other bit, so that both
ACE4_APPEND_DATA and ACE4_WRITE_DATA are denied.
6.2.1.3.2. ACE4_DELETE vs. ACE4_DELETE_CHILD
Two access mask bits govern the ability to delete a file or directory
object: ACE4_DELETE on the object itself, and ACE4_DELETE_CHILD on
the object's parent directory.
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Many systems also consult the "sticky bit" (MODE4_SVTX) and write
mode bit on the parent directory when determining whether to allow a
file to be deleted. The mode bit for write corresponds to
ACE4_WRITE_DATA, which is the same physical bit as ACE4_ADD_FILE.
Therefore, ACE4_ADD_FILE can come into play when determining
permission to delete.
In the algorithm below, the strategy is that ACE4_DELETE and
ACE4_DELETE_CHILD take precedence over the sticky bit, and the sticky
bit takes precedence over the "write" mode bits (reflected in
ACE4_ADD_FILE).
Server implementations SHOULD grant or deny permission to delete
based on the following algorithm.
if ACE4_EXECUTE is denied by the parent directory ACL:
deny delete
else if ACE4_DELETE is allowed by the target object ACL:
allow delete
else if ACE4_DELETE_CHILD is allowed by the parent
directory ACL:
allow delete
else if ACE4_DELETE_CHILD is denied by the
parent directory ACL:
deny delete
else if ACE4_ADD_FILE is allowed by the parent directory ACL:
if MODE4_SVTX is set for the parent directory:
if the principal owns the parent directory OR
the principal owns the target object OR
ACE4_WRITE_DATA is allowed by the target
object ACL:
allow delete
else:
deny delete
else:
allow delete
else:
deny delete
6.2.1.4. ACE flag
The bitmask constants used for the flag field are as follows:
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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. Again, the guiding
principle is that the file not appear to be more secure than it
really is.
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
Can be placed on a directory and indicates that this ACE should be
added to each new non-directory file created.
ACE4_DIRECTORY_INHERIT_ACE
Can be placed on a directory and indicates that this ACE should be
added to each new directory created.
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.
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.
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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 relate only to
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 that of the ACCESS
operation as well, the difference being that "success" or
"failure" does not mean whether ACCESS returns NFS4_OK or not.
Success means whether ACCESS returns all requested and supported
bits. Failure means whether ACCESS failed to return a bit that
was requested and supported.
ACE4_IDENTIFIER_GROUP
Indicates that the "who" refers to a GROUP as defined under UNIX
or a GROUP ACCOUNT as defined under Windows. Clients and servers
must ignore the ACE4_IDENTIFIER_GROUP flag on ACEs with a who
value equal to one of the special identifiers outlined in
Section 6.2.1.5.
6.2.1.5. ACE Who
The "who" field of an ACE is an identifier that specifies the
principal or principals to whom the ACE applies. It may refer to a
user or a group, with the flag bit ACE4_IDENTIFIER_GROUP specifying
which.
There are several special identifiers which need to be understood
universally, rather than in the context of a particular DNS domain.
Some of these identifiers cannot be understood when an NFS client
accesses the server, but have meaning when a local process accesses
the file. The ability to display and modify these permissions is
permitted over NFS, even if none of the access methods on the server
understands the identifiers.
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+---------------+--------------------------------------------------+
| Who | Description |
+---------------+--------------------------------------------------+
| OWNER | The owner of the file |
| GROUP | The group associated with the file. |
| EVERYONE | The world, including the owner and owning group. |
| INTERACTIVE | Accessed from an interactive terminal. |
| NETWORK | Accessed via the network. |
| DIALUP | Accessed as a dialup user to the server. |
| BATCH | Accessed from a batch job. |
| ANONYMOUS | Accessed without any authentication. |
| AUTHENTICATED | Any authenticated user (opposite of ANONYMOUS) |
| SERVICE | Access from a system service. |
+---------------+--------------------------------------------------+
Table 7
To avoid conflict, these special identifiers are distinguish by an
appended "@" and should appear in the form "xxxx@" (note: no domain
name after the "@"). For example: ANONYMOUS@.
6.2.1.5.1. Discussion of EVERYONE@
It is important to note that "EVERYONE@" is not equivalent to the
UNIX "other" entity. This is because, by definition, UNIX "other"
does not include the owner or owning group of a file. "EVERYONE@"
means literally everyone, including the owner or owning group.
6.2.2. mode Attribute
The NFS version 4 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
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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.
The remaining bits 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, or OPEN
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.
o Server implementations MAY grant ACE4_WRITE_ACL and ACE4_READ_ACL
permissions in order to prevent the owner from getting into the
situation where they can't ever modify the ACL.
o All servers will allow a user the ability to read the data of the
file when only the execute permission is granted (i.e. If the ACL
denies the user the ACE4_READ_DATA access and allows the user
ACE4_EXECUTE, the server will allow the user to read the data of
the file).
o Many servers have the notion of owner-override in which the owner
of the object is allowed to override accesses that are denied by
the ACL. This may be helpful, for example, to allow users
continued access to open files on which the permissions have
changed.
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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 issue 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.
1. To determine MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH:
1. If the special identifier EVERYONE@ is granted
ACE4_READ_DATA, then the bit MODE4_ROTH SHOULD be set.
Otherwise, MODE4_ROTH SHOULD NOT be set.
2. If the special identifier EVERYONE@ is granted
ACE4_WRITE_DATA or ACE4_APPEND_DATA, then the bit MODE4_WOTH
SHOULD be set. Otherwise, MODE4_WOTH SHOULD NOT be set.
3. If the special identifier EVERYONE@ is granted ACE4_EXECUTE,
then the bit MODE4_XOTH SHOULD be set. Otherwise, MODE4_XOTH
SHOULD NOT be set.
2. To determine MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP, note that
the EVERYONE@ special identifier SHOULD be taken into account.
In other words, when determining if the GROUP@ special identifier
is granted a permission, ACEs with the identifier EVERYONE@
should take effect just as ACEs with the special identifier
GROUP@ would.
1. If the special identifier GROUP@ is granted ACE4_READ_DATA,
then the bit MODE4_RGRP SHOULD be set. Otherwise, MODE4_RGRP
SHOULD NOT be set.
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2. If the special identifier GROUP@ is granted ACE4_WRITE_DATA
or ACE4_APPEND_DATA, then the bit MODE4_WGRP SHOULD be set.
Otherwise, MODE4_WGRP SHOULD NOT be set.
3. If the special identifier GROUP@ is granted ACE4_EXECUTE,
then the bit MODE4_XGRP SHOULD be set. Otherwise, MODE4_XGRP
SHOULD NOT be set.
3. To determine MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR, note that
the EVERYONE@ special identifier SHOULD be taken into account.
In other words, when determining if the OWNER@ special identifier
is granted a permission, ACEs with the identifier EVERYONE@
should take effect just as ACEs with the special identifer OWNER@
would.
1. If the special identifier OWNER@ is granted ACE4_READ_DATA,
then the bit MODE4_RUSR SHOULD be set. Otherwise, MODE4_RUSR
SHOULD NOT be set.
2. If the special identifier OWNER@ is granted ACE4_WRITE_DATA
or ACE4_APPEND_DATA, then the bit MODE4_WUSR SHOULD be set.
Otherwise, MODE4_WUSR SHOULD NOT be set.
3. If the special identifier OWNER@ is granted ACE4_EXECUTE,
then the bit MODE4_XUSR SHOULD be set. Otherwise, MODE4_XUSR
SHOULD NOT be set.
6.3.2.1. Discussion
The nine low-order mode bits (MODE4_R*, MODE4_W*, MODE4_X*)
correspond to ACE4_READ_DATA, ACE4_WRITE_DATA/ACE4_APPEND_DATA, and
ACE4_EXECUTE for OWNER@, GROUP@, and EVERYONE@. On some
implementations, mode bits may represent a superset of these
permissions, e.g. if a specific user is granted ACE4_WRITE_DATA, then
MODE4_WGRP will be set, even though the file's owner_group is not
granted ACE4_WRITE_DATA.
Server implementations are discouraged from doing this, as experience
has shown that this is confusing and annoying to end users. The
specifications above also discourage this practice to enforce the
semantic that setting the mode attribute effectively specifies read,
write, and execute for owner, group, and other.
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
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"EVERYONE@" so that the client can see semantically equivalent access
permissions exist whether the client asks for owner, owner_group and
mode attributes, or for just the ACL.
In this section, much is made of the methods in Section 6.3.2. Many
requirements refer to this section. But note that the methods have
behaviors specified with "SHOULD". This is intentional, to avoid
invalidating existing implementations that compute the mode according
to the withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
actual permissions on owner, group, and other.
6.4.1. Setting the mode and/or ACL Attributes
6.4.1.1. Setting mode and not ACL
When setting a mode attribute and not an ACL attribute, the mode
attribute MUST be set as given. 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 newly
set mode attribute. The ACL 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 attribute.
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 an ACL attribute and not a mode attribute, 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 and the ACL attribute in the same
operation, the attributes MUST be applied in this order: mode, then
ACL. The mode 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
the ACL attribute.
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 the ACL attribute, it may use the ACL attribute
on the parent directory to compute an initial ACL attribute for a
newly created object. This will be referred to as the inherited ACL
within this section. The act of adding one or more ACEs to the
inherited ACL that are based upon ACEs in the parent directory's ACL
will be referred to as inheriting an ACE within this section.
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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 mode is given:
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 ACL is given:
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 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 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. It is worth
noting that if no inheritable ACEs exist on the parent directory,
the file will be created with an empty ACL, thus granting no
access.
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.
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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.
If when a new directory is created and it inherits ACEs from its
parent, for each inheritable ACE which affects the directory's
permissions, a server MAY create two ACEs on the directory being
created; one effective and one which is only inheritable (i.e. has
ACE4_INHERIT_ONLY_ACE flag set). This gives the user and the server,
in the cases which it must mask certain permissions upon creation,
the ability to modify the effective permissions without modifying the
ACE which is to be inherited to the new directory's children.
When a newly created object is created with attributes, and those
attributes contain an ACL attribute and/or a mode attribute, the
server MUST apply those attributes to the newly created object, as
described in Section 6.4.1.
7. Single-server Name Space
This chapter describes the NFSv4 single-server name space. Single-
server namespaces may be presented directly to clients, or they may
be used as a basis to form larger multi-server namespaces (e.g. site-
wide or organization-wide) to be presented to clients, as described
in Section 10.
7.1. 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 file system 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.
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7.2. Browsing Exports
The NFS version 4 protocol provides a root filehandle that clients
can use to obtain filehandles for the exports of a particular server,
via a series of LOOKUP operations within a COMPOUND, to traverse a
path. A common user experience is to use a graphical user interface
(perhaps a file "Open" dialog window) to find a file via progressive
browsing through a directory tree. The client must be able to move
from one export to another export via single-component, progressive
LOOKUP operations.
This style of browsing is not well supported by the NFS version 2 and
3 protocols. The client expects all LOOKUP operations to remain
within a single server file system. For example, the device
attribute will not change. This prevents a client from taking 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 file
system" that allows the user to browse from one mounted file system
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.
7.3. Server Pseudo File System
NFS version 4 servers avoid this name space inconsistency by
presenting all the exports for a given server within the framework of
a single namespace, for that server. An NFS version 4 client uses
LOOKUP and READDIR operations to browse seamlessly from one export to
another. Portions of the server name space that are not exported are
bridged via a "pseudo file system" that provides a view of exported
directories only. A pseudo file system has a unique fsid and behaves
like a normal, read only file system.
Based on the construction of the server's name space, it is possible
that multiple pseudo file systems may exist. For example,
/a pseudo file system
/a/b real file system
/a/b/c pseudo file system
/a/b/c/d real file system
Each of the pseudo file systems are considered separate entities and
therefore will have its own unique fsid.
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7.4. Multiple Roots
The DOS and Windows operating environments are sometimes described as
having "multiple roots". File Systems are commonly represented as
disk letters. MacOS represents file systems 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.
7.5. Filehandle Volatility
The nature of the server's pseudo file system is that it is a logical
representation of file system(s) available from the server.
Therefore, the pseudo file system is most likely constructed
dynamically when the server is first instantiated. It is expected
that the pseudo file system may not have an on disk counterpart from
which persistent filehandles could be constructed. Even though it is
preferable that the server provide persistent filehandles for the
pseudo file system, the NFS client should expect that pseudo file
system filehandles are volatile. This can be confirmed by checking
the associated "fh_expire_type" attribute for those filehandles in
question. If the filehandles are volatile, the NFS client must be
prepared to recover a filehandle value (e.g. with a series of LOOKUP
operations) when receiving an error of NFS4ERR_FHEXPIRED.
7.6. Exported Root
If the server's root file system is exported, one might conclude that
a pseudo-file system is unneeded. This not necessarily so. Assume
the following file systems on a server:
/ 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-file system.
7.7. Mount Point Crossing
The server file system environment may be constructed in such a way
that one file system contains a directory which is 'covered' or
mounted upon by a second file system. For example:
/a/b (file system 1)
/a/b/c/d (file system 2)
The pseudo file system for this server may be constructed to look
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like:
/ (place holder/not exported)
/a/b (file system 1)
/a/b/c/d (file system 2)
It is the server's responsibility to present the pseudo file system
that is complete to the client. If the client sends a lookup request
for the path "/a/b/c/d", the server's response is the filehandle of
the file system "/a/b/c/d". In previous versions of the NFS
protocol, the server would respond with the filehandle of directory
"/a/b/c/d" within the file system "/a/b".
The NFS client will be able to determine if it crosses a server mount
point by a change in the value of the "fsid" attribute.
7.8. Security Policy and 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 file system 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 file system, the server
may effectively hide file systems from a client that may otherwise
have legitimate access.
As suggested practice, the server should apply the security policy of
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 file system 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.
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8. File Locking and Share Reservations
Integrating locking into the NFS protocol necessarily causes it to be
stateful. With the inclusion of such features as share reservations,
file and directory delegations, recallable layouts, and support for
mandatory byte-range locking the protocol becomes substantially more
dependent on state than the traditional combination of NFS and NLM
[XNFS]. 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
requests changes in locks and the server responds with the changes
made. Non-client-initiated changes in locking state are infrequent
and the client receives prompt notification of them and can adjust
his view of the locking state to reflect the server's changes.
To support Win32 share reservations it is necessary to provide
operations which atomically OPEN or CREATE files. Having a separate
share/unshare operation would not allow correct implementation of the
Win32 OpenFile API. In order to correctly implement share semantics,
the previous NFS protocol mechanisms used when a file is opened or
created (LOOKUP, CREATE, ACCESS) need to be replaced. The NFS
version 4.1 protocol defines OPEN operation which looks up or creates
a file and establishes locking state on the server.
8.1. 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 heavyweight
information to the eventual lightweight stateid used for most client
and server locking interactions.
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8.1.1. Client and Session ID
A client must establish a clientid (see Section 2.4) and then one or
more sessionids (see Section 2.9) before performing any operations to
open, lock, or delegate a file object. The sessionid services as a
shorthand referral to an NFSv4.1 client.
8.1.2. State-owner and Stateid Definition
When opening a file or requesting a byte-range lock, the client must
specify an identifier which represents the owner of the requested
lock. This identifier is in the form of a state-owner, represented
in the protocol by a state_owner4, a variable-length opaque array
which, when concatenated with the current clientid uniquely defines
the owner of lock managed by the client. This may be a thread id,
process id, or other unique value.
Owners of opens and owners of byte-range locks are separate entities
and remain separate even if the same opaque arrays are used to
designate owners of each. The protocol distinguishes between open-
owners (represented by open_owner4 structures) and lock-owners
(represented by lock_owner4 structures).
Each open is associated with a specific open-owner while each byte-
range lock is associated with a lock-owner and an open-owner, the
latter being the open-owner associated with the open file under which
the LOCK operation was done. Delegations and layouts, on the other
hand, are not associated with a specific owner but are associated the
client as a whole.
When the server grants a lock of any type (including opens, byte-
range locks, delegations, and layouts) it responds with a unique
stateid, that represents a set of locks (often a single lock) for the
same file, of the same type, and sharing the same ownership
characteristics. Thus opens of the same file by different open-
owners each have an identifying stateid. Similarly, each set of
byte-range locks on a file owned by a specific lock-owner and gotten
via an open for a specific open-owner, has its own identifying
stateid. Delegations and layouts also have associated stateid's by
which they may be referenced. The stateid is used as a shorthand
reference to a lock or set of locks and given a stateid the client
can determine the associated state-owner or state-owners (in the case
of an open-owner/lock-owner pair) and the associated. Clients,
however, must not assume any such mapping and must not use a stateid
returned for a given filehandle and state-owner in the context of a
different filehandle or a different state-owner.
The server is free to form the stateid in any manner that it chooses
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as long as it is able to recognize invalid and out-of-date stateids.
Although the protocol XDR definition divides the stateid into 'seqid'
and 'other' fields, for the purposes of minor version one, this
distinction is not important and the server may use the available
space as it chooses, with one exception.
The exception is that stateids whose 'other' field is either all
zeros or all ones are reserved and may not be generated by the
server. Clients may use the protocol-defined special stateid values
for their defined purposes, but any use of stateid's in this reserved
class that are not specially defined by the protocol MUST result in
an NFS4ERR_BAD_STATED being returned.
Clients may not compare stateids associated with different
filehandles, so that a server might use stateids with the same bit
pattern for all opens with a given open-owner or for all sets of
byte-range locks associated with a given lock-owner/open-owner pair.
However, if it does so, it must recognize and reject any use of
stateid when the current filehandle is such that no lock for that
filehandle by that open owner (or lock-owner/open-owner pair) exists.
Stateid's must remain valid until either a client reboot or a sever
reboot or until the client returns all of the locks associated with
the stateid by means of an operation such as CLOSE or DELEGRETURN.
If the locks are lost due to revocation the stateid remains usable
until the client frees it by using FREE_STATEID. Stateid's
associated with byte-range locks are an exception. They remain valid
even if a LOCKU free all remaining locks, so long as the open file
with which they are associated remains open, unless the client does a
FREE_STATEID to caused the stateid to be freed.
Because each operation using a stateid occurs as part of a session,
each stateid is implicitly associated with the clientid assigned to
that session. Use of a stateid in the context of a session where the
clientid is invalid should result in the error NFS4ERR_STALE_STATEID.
Servers MUST NOT do any validation or return other errors in this
case, even if they have sufficient information available to validate
stateids associated with an out-of-date client.
One mechanism that may be used to satisfy the requirement that the
server recognize invalid and out-of-date stateids is for the server
to divide the stateid into two fields. This division may coincide
with the documented division into 'seqid' and 'other' fields or it
may divide the stateid field up in any other ay it chooses.
o An index into a table of locking-state structures.
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o A generation number which is incremented on each allocation of a
table entry a particular allocation of a stateid.
And then store in each table entry,
o The current generation number.
o The clientid with which the stateid is associated.
o The filehandle of the file on which the locks are taken.
o An indication of the type of stateid (open, byte-range lock, file
delegation, directory delegation, layout).
With this information, the following procedure would be used to
validate an incoming stateid and return an appropriate error, when
necessary:
o If the current session is associated with an invalid clientid,
return NFS4ERR_STALE_STATEID.
o If the table index field is outside the range of the associated
table, return NFS4ERR_BAD_STATEID.
o If the selected table entry is of a different generation than that
specified in the incoming stateid, return NFS4ERR_BAD_STATEID.
o If the selected table entry does not match the current file
handle, return NFS4ERR_BAD_STATEID.
o If the clientid in the table entry does not match the clientid
associated with the current session, return NFS4ERR_BAD_STATEID.
o If the stateid type is not valid for the context in which the
stateid appears, return NFS4ERR_BAD_STATEID.
o Otherwise, the stateid is valid and the table entry should contain
any additional information about the associated set of locks, such
as open-owner and lock-owner information, as well as information
on the specific locks, such as open modes and byte ranges.
8.1.3. 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
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explicitly mentioned in the text.
If the state-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
state-owner. If no state is established by the client, either record
lock or share reservation, a special stateid of all bits 0 (including
all fields of the stateid) 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
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).
Note that for UNIX environments that support mandatory file locking,
the distinction between advisory and mandatory locking is subtle. In
fact, advisory and mandatory record locks are exactly the same in so
far as the APIs and requirements on implementation. If the mandatory
lock attribute is set on the file, the server checks to see if the
lock-owner has an appropriate shared (read) or exclusive (write)
record lock on the region it wishes to read or write to. If there is
no appropriate lock, the server checks if there is a conflicting lock
(which can be done by attempting to acquire the conflicting lock on
the behalf of the lock-owner, and if successful, release the lock
after the READ or WRITE is done), and if there is, the server returns
NFS4ERR_LOCKED.
For Windows environments, there are no advisory record locks, so the
server always checks for record locks during I/O requests.
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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 caused the
allocation of the open stateid and as modified by subsequent OPENs
and OPEN_DOWNGRADEs for the same open-owner/file pair. Stateids
returned by byte-range lock operations imply the access mode for the
open stateid associated with the lock set represented by the stateid.
Delegation stateids have an access mode based on the type of
delegation. When a READ, WRITE, or SETATTR which specifies the size
attribute, is done, the operation is subject to checking against the
access mode to verify that the operation is appropriate given the
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 special stateid of all bits 1 (one), including all fields in the
stateid indicates a desire to bypass locking checks. The server MAY
allow READ operations to bypass locking checks at the server, when
this special stateid is used. However, WRITE operations with this
special stateid value MUST NOT bypass locking checks and are treated
exactly the same as if a 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
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WRITE as discussed above.
8.2. Lock Ranges
The protocol allows a lock owner to request a lock with a byte range
and then either upgrade, downgrade, or unlock a sub-range of the
initial lock. It is expected that this will be an uncommon type of
request. In any case, servers or server 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 "Server Failure and Recovery" 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.
8.3. 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.
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8.4. Blocking Locks
Some clients require the support of blocking locks. NFSv4.1 does not
provide a callback when a previously unavailable lock becomes
available. Clients thus 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.
If a server receives a blocking lock request, denies it, and then
later receives a nonblocking request for the same lock, which is also
denied, then it should remove the lock in question from its list of
pending blocking locks. Clients should use such a nonblocking
request to indicate to the server that this is the last time they
intend to poll for the lock, as may happen when the process
requesting the lock is interrupted. This is a courtesy to the
server, to prevent it from unnecessarily waiting a lease period
before granting other lock requests. However, clients are not
required to perform this courtesy, and servers must not depend on
them doing so. Also, clients must be prepared for the possibility
that this final locking request will be accepted.
8.5. 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.
Since each session is associated with a specific client, any
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operation issued on that session is an indication that the associated
client is reachable. When a request is issued for a given session,
execution of a SEQUENCE operation will result in all leases for the
associated client to be implicitly renewed. 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, via a COMPOUND that consists
solely of a single SEQUENCE 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.
8.6. 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
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.
8.6.1. Client Failure and Recovery
In the event that a client fails, the server may release the client's
locks when the associated leases have expired. Conflicting locks
from another client may only be granted after this lease expiration.
When a client has not failed and re-establishes his lease before
expiration occurs, requests for conflicting locks will not be
granted.
To minimize client delay upon restart, lock requests are associated
with an instance of the client by a client supplied verifier. This
verifier is part of the initial EXCHANGE_ID call made by the client.
The server returns a clientid as a result of the EXCHANGE_ID
operation. The client then confirms the use of the clientid by
establishing a session associated with that clientid. All locks,
including opens, byte-range locks, delegations, and layout obtained
by sessions using that clientid are associated with that clientid.
Since the verifier will be changed by the client upon each
initialization, the server can compare a new verifier to the verifier
associated with currently held locks and determine that they do not
match. This signifies the client's new instantiation and subsequent
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loss of locking state. As a result, the server is free to release
all locks held which are associated with the old clientid which was
derived from the old verifier. At this point conflicting locks from
other clients, kept waiting while the leaser had not yet expired, can
be granted.
Note that the verifier must have the same uniqueness properties of
the verifier for the COMMIT operation.
8.6.2. 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 a 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.
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 8.1.1) and re-establish its locking state.
Once a session is established using the new clientid, the client will
use reclaim-type locking requests (i.e. LOCK requests with reclaim
set to true and OPEN operations with a claim type of CLAIM_PREVIOUS)
to re-establish its locking state. Once this is done, or if there is
no such locking state to reclaim, the client does a RECLAIM_COMPLETE
operation to indicate that it has reclaimed all of the locking state
that it will reclaim. Once a client does a RECLAIM_COMPLETE
operation, it may attempt non-reclaim locking operations, although it
may get NFS4ERR_GRACE errors on these until the period of special
handling is over.
The period of special handling of locking and READs and WRITEs, is
referred to as the "grace period". During the grace period, clients
recover locks and the associated state using reclaim-type locking
requests. During this 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, unless it is able to
guarantee that these may be done safely, as described below.
The grace period may last until all clients who are known to possibly
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have had locks have done a RECLAIM_COMPLETE operation, indicating
that they have finished reclaiming the locks they held before the
server reboot. The server is assumed to maintain in stable storage a
list of clients who may have such locks. The server may also
terminate the grace period before all clients have done
RECLAIM_COMPLETE. The server SHOULD NOT terminate the grace period
before a time equal to the lease period in order to give clients an
opportunity to find out about the server reboot. Some additional
time in order to allow time to establish a new clientid and session
and to effect lock reclaims may be added.
If the server can reliably determine that granting a non-reclaim
request will not conflict with reclamation of locks by other clients,
the NFS4ERR_GRACE error does not have to be returned even within the
grace period, although NFS4ERR_GRACE must always be returned to
clients attempting a non-reclaim lock request before doing their own
RECLAIM_COMPLETE. For the server to be able to service READ and
WRITE operations during the grace period, it must again be able to
guarantee that no possible conflict could arise between a potential
reclaim locking request and the READ or WRITE operation. If the
server is unable to offer that guarantee, the NFS4ERR_GRACE error
must be returned to the client.
For a server to provide simple, valid handling during the grace
period, the easiest method is to simply reject all non-reclaim
locking requests and READ and WRITE operations by returning the
NFS4ERR_GRACE error. However, a server may keep information about
granted locks in stable storage. With this information, the server
could determine if a regular lock or READ or WRITE operation can be
safely processed.
For example, if the server maintained on stable storage summary
information on whether mandatory locks exist, either mandatory byte-
range locks, or share reservations specifying deny modes, many
requests could be allowed during the grace period. If it is known
that no such share reservations exist, OPEN request that do not
specify deny modes may be safely granted. If, in addition, it is
known that no mandatory byte-range locks exist, either through
information stored on stable storage or simply because the server
does not support such locks, READ and WRITE requests may be safely
processed during the grace period.
To reiterate, for a server that allows non-reclaim lock and I/O
requests to be processed during the grace period, it MUST determine
that no lock subsequently reclaimed will be rejected and that no lock
subsequently reclaimed would have prevented any I/O operation
processed during the grace period.
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Clients should be prepared for the return of NFS4ERR_GRACE errors for
non-reclaim lock and I/O requests. In this case the client should
employ a retry mechanism for the request. A delay (on the order of
several seconds) between retries should be used to avoid overwhelming
the server. Further discussion of the general issue is included in
[Floyd]. The client must account for the server that is able to
perform I/O and non-reclaim locking requests within the grace period
as well as those that can not do so.
A reclaim-type locking request outside the server's grace period can
only succeed if the server can guarantee that no conflicting lock or
I/O request has been granted since reboot or restart.
A server may, upon restart, establish a new value for the lease
period. Therefore, clients should, once a new 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.
8.6.3. 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, or it may allow the lock state to
remain for a considerable period, subject to the constraint that if a
request for a conflicting lock is made, locks associated with expired
leases do not prevent such a conflicting lock from being granted but
are revoked as necessary so as not to interfere with such conflicting
requests.
If the server chooses to delay freeing of lock state until there is a
conflict, it may either free all of the clients locks once there is a
conflict, or it may only revoke the minimum set of locks necessary to
allow conflicting requests. When it adopts the finer-grained
approach, it must revoke all locks associated with a given stateid,
as long as it revokes a single such lock.
When the server chooses to free all of a client's lock state, either
immediately upon lease expiration, or a result of the first attempt
to get a lock, 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, the status returned by the SEQUENCE operation will
indicate a loss of locking state. In addition all I/O submitted by
the client with the now invalid stateids will fail with the server
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returning the error NFS4ERR_EXPIRED. Once the client learns of the
loss of locking state, it will suitably notify the applications that
held the invalidated locks. The client should then take action to
free invalidated stateid's, either by establishing a new client id
using a new verifier or by doing a FREE_STATEID operation to release
each of the invalidated stateid's.
When the server adopts a finer-grained approach to revocation of
locks when lease have expired, only a subset of stateids will
normally become invalid during a network partition. When the client
is able to communicate with the server after such a network
partition, the status returned by the SEQUENCE operation will
indicate a partial loss of locking state. In addition, operations,
including I/O submitted by the client with the now invalid stateids
will fail with the server returning the error NFS4ERR_EXPIRED. Once
the client learns of the loss of locking state, it will use the
TEST_STATEID operation on all of its stateid's to determine which
locks have been lost and them suitably notify the applications that
held the invalidated locks. The client can then release the
invalidated locking state and acknowledge the revocation of the
associated locks by doing a FREE_STATEID operation on each of the
invalidated stateid's.
When a network partition is combined with a server reboot, there are
edge conditions that place requirements on the server in order to
avoid silent data corruption following the server reboot. Two of
these edge conditions are known, and are discussed below.
The first edge condition arises as a result of the scenarios such as
the following:
1. Client A acquires a lock.
2. Client A and server experience mutual network partition, such
that client A is unable to renew its lease.
3. Client A's lease expires, and the server releases lock.
4. Client B acquires a lock that would have conflicted with that of
Client A.
5. Client B releases its lock.
6. Server reboots.
7. Network partition between client A and server heals.
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8. Client A connects to new server instance and finds out about
server reboot.
9. Client A reclaims its lock within the server's grace period.
Thus, at the final step, the server has erroneously granted client
A's lock reclaim. If client B modified the object the lock was
protecting, client A will experience object corruption.
The second known edge condition arises in situations such as the
following:
1. Client A acquires one or more locks.
2. Server reboots.
3. Client A and server experience mutual network partition, such
that client A is unable to reclaim all of its locks within the
grace period.
4. Server's reclaim grace period ends. Client A has either no
locks or an incomplete set of locks known to the server.
5. Client B acquires a lock that would have conflicted with a lock
of client A that was not reclaimed.
6. Client B releases the lock.
7. Server reboots a second time.
8. Network partition between client A and server heals.
9. Client A connects to new server instance and finds out about
server reboot.
10. Client A reclaims its lock within the server's grace period.
As with the first edge condition, the final step of the scenario of
the second edge condition has the server erroneously granting client
A's lock reclaim.
Solving the first and second edge conditions requires that the server
either always assumes after it reboots that some edge condition
occurs, and thus return NFS4ERR_NO_GRACE for all reclaim attempts, or
that the server record some information in stable storage. The
amount of information the server records in stable storage is in
inverse proportion to how harsh the server intends to be whenever
edge conditions arise. The server that is completely tolerant of all
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edge conditions will record in stable storage every lock that is
acquired, removing the lock record from stable storage only when the
lock is released. For the two edge conditions discussed above, the
harshest a server can be, and still support a grace period for
reclaims, requires that the server record in stable storage
information some minimal information. For example, a server
implementation could, for each client, save in stable storage a
record containing:
o the client's id string
o a boolean that indicates if the client's lease expired or if there
was administrative intervention (see Section 8.7) to revoke a
record lock, share reservation, or delegation and there has been
no acknowledgement (via FREE_STATEID) of such revocation.
o a boolean that indicates whether the client may have locks that it
believes to be reclaimable in situations which the grace period
was terminated, making the server's view of lock reclaimability
suspect. The server will set this for any client record in stable
storage where the client has not done a RECLAIM_COMPLETE, before
it grants any new (i.e. not reclaimed) lock to any client.
Assuming the above record keeping, for the first edge condition,
after the server reboots, the record that client A's lease expired
means that another client could have acquired a conflicting record
lock, share reservation, or delegation. Hence the server must reject
a reclaim from client A with the error NFS4ERR_NO_GRACE.
For the second edge condition, after the server reboots for a second
time, the indication that the client had not completed its reclaims
at the time at which the grace period ended means that the server
must reject a reclaim from client A with the error NFS4ERR_NO_GRACE.
When either edge condition occurs, the client's attempt to reclaim
locks will result in the error NFS4ERR_NO_GRACE. When this is
received, or after the client reboots with no lock state, the client
will issue a RECLAIM_COMPLETE. When the RECLAIM_COMPLETE is
received, the server and client are again in agreement regarding
reclaimable locks and both booleans in persistent storage can be
reset, to be set again only when there is a subsequent event that
causes lock reclaim operations to be questionable.
Regardless of the level and approach to record keeping, the server
MUST implement one of the following strategies (which apply to
reclaims of share reservations, record locks, and delegations):
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1. Reject all reclaims with NFS4ERR_NO_GRACE. This is extremely
unforgiving, but necessary if the server does not record lock
state in stable storage.
2. Record sufficient state in stable storage such that all known
edge conditions involving server reboot, including the two noted
in this section, are detected. False positives are acceptable.
Note that at this time, it is not known if there are other edge
conditions.
In the event that, after a server reboot, the server determines
that there is unrecoverable damage or corruption to the
information in stable storage, then for all clients and/or locks
which may be affected, the server MUST return NFS4ERR_NO_GRACE.
A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
outside the scope of this specification, since the strategies for
such handling are very dependent on the client's operating
environment. However, one potential approach is described below.
When the client receives NFS4ERR_NO_GRACE, it could examine the
change attribute of the objects the client is trying to reclaim state
for, and use that to determine whether to re-establish the state via
normal OPEN or LOCK requests. This is acceptable provided the
client's operating environment allows it. In other words, the client
implementor is advised to document for his users the behavior. The
client could also inform the application that its record lock or
share reservations (whether they were delegated or not) have been
lost, such as via a UNIX signal, a GUI pop-up window, etc. See the
section, "Data Caching and Revocation" for a discussion of what the
client should do for dealing with unreclaimed delegations on client
state.
For further discussion of revocation of locks see Section 8.7.
8.7. Server Revocation of Locks
At any point, the server can revoke locks held by a client and the
client must be prepared for this event. When the client detects that
its locks have been or may have been revoked, the client is
responsible for validating the state information between itself and
the server. Validating locking state for the client means that it
must verify or reclaim state for each lock currently held.
The first occasion of lock revocation is upon server reboot or 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
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section.
The second occasion of lock revocation is the inability to renew the
lease before expiration, as discussed above. While this is
considered a rare or unusual event, the client must be prepared to
recover. The server is responsible for determining lease expiration,
and deciding exactly how to deal with it, informing the client of the
scope of the lock revocation. The client then uses the status
information provided by the server to synchronize his locking state
with that of the server, in order to recover.
The third occasion of lock revocation can occur as a result of
revocation of locks within the lease period, either because of
administrative intervention, or because a recallable lock (a
delegation or layout) was not returned within the lease period after
having been recalled. While these are considered rare events, they
are possible and the client must be prepared to deal with them. When
either of these events occur, the client finds out about the
situation through the status returned by the SEQUENCE operation. Any
use of stateids associated with revoked locks will receive the error
NFS4ERR_ADMIN_REVOKED or NFS4ERR_DELEG_REVOKED, as appropriate.
In all situations in which a subset of locking state may have been
revoked, which include all cases in which locking state is revoked
within the lease period, it is up to the client to determine which
locks have been revoked and which have not. It does this by using
the TEST_STATEID operation on the appropriate set of stateid's. Once
the set of revoked locks has been determined, the applications can be
notified, and the invalidated stateid's can be freed and lock
revocation acknowledged by using FREE_STATEID.
8.8. 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:
if (request.access == 0)
return (NFS4ERR_INVAL)
else
if ((request.access & file_state.deny)) ||
(request.deny & file_state.access))
return (NFS4ERR_DENIED)
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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;
8.9. 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 open-
owner on that file. If record locks are held, the client SHOULD
release all locks before issuing a CLOSE. The server MAY free all
outstanding locks on CLOSE but some servers may not support the CLOSE
of a file that still has record locks held. The server MUST return
failure, NFS4ERR_LOCKS_HELD, if any locks would exist after the
CLOSE.
The LOOKUP operation will return a filehandle without establishing
any lock state on the server. Without a valid stateid, the server
will assume the client has the least access. For example, a file
opened with deny READ/WRITE cannot be accessed using a filehandle
obtained through LOOKUP because it would not have a valid stateid
(i.e. using a stateid of all bits 0 or all bits 1).
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8.10. Open Upgrade and Downgrade
When an OPEN is done for a file and the open-owner for which the open
is being done already has the file open, the result is to upgrade the
open file status maintained on the server to include the access and
deny bits specified by the new OPEN as well as those for the existing
OPEN. The result is that there is one open file, as far as the
protocol is concerned, and it includes the union of the access and
deny bits for all of the OPEN requests completed. Only a single
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.
8.11. Short and Long Leases
When determining the time period for the server lease, the usual
lease tradeoffs apply. Short leases are good for fast server
recovery at a cost of increased operations to effect lease renewal
(when there are no other operations during the period to effect lease
renewal as a side-effect). Long leases are certainly kinder and
gentler to servers trying to handle very large numbers of clients.
The number of extra requests to effect lock renewal drop in inverse
proportion to the lease time. The disadvantages of long leases
include the possibility of slower recovery after certain failures.
After server failure, a longer grace period may be required when some
clients do not promptly reclaim their locks and do a
RECLAIM_COMPLETE. In the event of client failure, it can longer
period for leases to expire thus forcing conflicting requests to
wait.
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Long leases are usable if the server is able to store lease state in
non-volatile memory. Upon recovery, the server can reconstruct the
lease state from its non-volatile memory and continue operation with
its clients and therefore long leases would not be an issue.
8.12. 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
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.
8.13. Vestigial Locking Infrastructure From V4.0
There are a number of operations and fields within existing
operations that no longer have a function in minor version one. In
one way or another, these changes are all due to the implementation
of sessions which provides client context and replay protection as a
base feature of the protocol, separate from locking itself.
The following operations have become mandatory-to-not-implement. The
server should return NFS4ERR_NOTSUPP if these operations are found in
an NFSv4.1 COMPOUND.
o SETCLIENTID since its function has been replaced by EXCHANGE_ID.
o SETCLIENTID_CONFIRM since clientid confirmation now happens by
means of CREATE_SESSION.
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o OPEN_CONFIRM because OPEN's no longer require confirmation to
establish an owner-based sequence value.
o RELEASE_LOCKOWNER because lock-owners with no associated locks
have any sequence-related state and so can be deleted by the
server at will.
o RENEW because every SEQUENCE operation for a session causes lease
renewal, making a separate operation useless.
Also, there are a number of fields, present in existing operations
related to locking that have no use in minor version one. They were
used in minor version zero to perform functions now provided in a
different fashion.
o Sequence id's used to sequence requests for a given state-owner
and to provide replay protection, now provided via sessions.
o Clientid's used to identify the client associated with a given
request. Client identification is now available using the
clientid associated with the current session, without needing an
explicit clientid field.
Such vestigial fields in existing operations should be set by the
client to zero. When they are not, the server MUST return an
NFS4ERR_INVAL error.
9. 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
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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.
9.1. Performance Challenges for Client-Side Caching
Caching techniques used in previous versions of the NFS protocol have
been successful in providing good performance. However, several
scalability challenges can arise when those techniques are used with
very large numbers of clients. This is particularly true when
clients are geographically distributed which classically increases
the latency for cache revalidation requests.
The previous versions of the NFS protocol repeat their file data
cache validation requests at the time the file is opened. This
behavior can have serious performance drawbacks. A common case is
one in which a file is only accessed by a single client. Therefore,
sharing is infrequent.
In this case, repeated reference to the server to find that no
conflicts exist is expensive. A better option with regards to
performance is to allow a client that repeatedly opens a file to do
so without reference to the server. This is done until potentially
conflicting operations from another client actually occur.
A similar situation arises in connection with file locking. Sending
file lock and unlock requests to the server as well as the read and
write requests necessary to make data caching consistent with the
locking semantics (see the section "Data Caching and File Locking")
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:
.IP o Compatibility with a large range of server semantics. .IP o
Provide the same caching benefits as previous versions of the NFS
protocol when unable to provide the more aggressive model. .IP 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. .LP The appropriate requirements for the
server are discussed in later sections in which specific forms of
caching are covered. (see the section "Open Delegation").
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9.2. Delegation and Callbacks
Recallable delegation of server responsibilities for a file to a
client improves performance by avoiding repeated requests to the
server in the absence of inter-client conflict. With the use of a
"callback" RPC from server to client, a server recalls delegated
responsibilities when another client engages in sharing of a
delegated file.
A delegation is passed from the server to the client, specifying the
object of the delegation and the type of delegation. There are
different types of delegations but each type contains a stateid to be
used to represent the delegation when performing operations that
depend on the delegation. This stateid is similar to those
associated with locks and share reservations but differs in that the
stateid for a delegation is associated with a 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.
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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 the section "Open Delegation").
The server will not know what opens are in effect on the client.
Without this knowledge the server will be unable to determine if the
access and deny state for the file allows any particular open until
the delegation for the file has been returned.
A client failure or a network partition can result in failure to
respond to a recall callback. In this case, the server will revoke
the delegation which in turn will render useless any modified state
still on the client.
9.2.1. 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
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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 the sections on "Data Caching and
Revocation" and "Operation 18: OPEN" 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
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.
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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 the section "Revocation Recovery for Write Open
Delegation" 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 the
section "Crash Recovery"). This is done to deal with the case in
which a server reboots after revoking a delegation but before the
client holding the revoked delegation is notified about the
revocation.
9.3. 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.
9.3.1. 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 the section "Open
Delegation") 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
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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 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.
9.3.2. 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 file system. However, they may not work with
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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 cache data
exists) must be revalidated. If the change attribute indicates
that the file may have been updated since the cached data was
obtained, the client must flush or invalidate the cached data for
the newly locked region. A client might choose to invalidate all
of non-modified cached data that it has for the file but the only
requirement for correct operation is to invalidate all of the data
in the newly locked region.
o Second, before releasing a write lock for a region, all modified
data for that region must be flushed to the server. The modified
data must also be written to stable storage.
Note that flushing data to the server and the invalidation of cached
data must reflect the actual byte ranges locked or unlocked.
Rounding these up or down to reflect client cache block boundaries
will cause problems if not carefully done. For example, writing a
modified block when only half of that block is within an area being
unlocked may cause invalid modification to the region outside the
unlocked area. This, in turn, may be part of a region locked by
another client. Clients can avoid this situation by synchronously
performing portions of write operations that overlap that portion
(initial or final) that is not a full block. Similarly, invalidating
a locked area which is not an integral number of full buffer blocks
would require the client to read one or two partial blocks from the
server if the revalidation procedure shows that the data which the
client possesses may not be valid.
The data that is written to the server as a prerequisite to the
unlocking of a region must be written, at the server, to stable
storage. The client may accomplish this either with synchronous
writes or by following asynchronous writes with a COMMIT operation.
This is required because retransmission of the modified data after a
server reboot might conflict with a lock held by another client.
A client implementation may choose to accommodate applications which
use record locking in non-standard ways (e.g. using a record lock as
a global semaphore) by flushing to the server more data upon an LOCKU
than is covered by the locked range. This may include modified data
within files other than the one for which the unlocks are being done.
In such cases, the client must not interfere with applications whose
READs and WRITEs are being done only within the bounds of record
locks which the application holds. For example, an application locks
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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.
9.3.3. 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.
9.3.4. Data Caching and File Identity
When clients cache data, the file data needs to be organized
according to the file system object to which the data belongs. For
NFS version 3 clients, the typical practice has been to assume for
the purpose of caching that distinct filehandles represent distinct
file system objects. The client then has the choice to organize and
maintain the data cache on this basis.
In the 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 file system object. If clients
were simply to assume that all distinct filehandles denote distinct
objects and proceed to do data caching on this basis, caching
inconsistencies would arise between the distinct client side objects
which mapped to the same server side object.
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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:
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.
9.4. 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.
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o The client must have responded properly to previous recalls.
o There must be no current open conflicting with the requested
delegation.
o There should be no current delegation that conflicts with the
delegation being requested.
o The probability of future conflicting open requests should be low
based on the recent history of the file.
o The existence of any server-specific semantics of OPEN/CLOSE that
would make the required handling incompatible with the prescribed
handling that the delegated client would apply (see below).
There are two types of open delegations, read and write. A read open
delegation allows a client to handle, on its own, requests to open a
file for reading that do not deny read access to others. Multiple
read open delegations may be outstanding simultaneously and do not
conflict. A write open delegation allows the client to handle, on
its own, all opens. Only one write open delegation may exist for a
given file at a given time and it is inconsistent with any read open
delegations.
When a client has a read open delegation, it 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 the section "Open Delegation and
Data Caching")
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o an nfsace4 specifying read and write permissions
o a stateid to represent the delegation for READ and WRITE
The delegation stateid is separate and distinct from the stateid for
the OPEN proper. The standard stateid, unlike the delegation
stateid, is associated with a particular lock_owner and will continue
to be valid after the delegation is recalled and the file remains
open.
When a request internal to the client is made to open a file and open
delegation is in effect, it will be accepted or rejected solely on
the basis of the following conditions. Any requirement for other
checks to be made by the delegate should result in open delegation
being denied so that the checks can be made by the server itself.
o The access and deny bits for the request and the file as described
in the section "Share Reservations".
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.
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9.4.1. Open Delegation and Data Caching
OPEN delegation allows much of the message overhead associated with
the opening and closing files to be eliminated. An open when an open
delegation is in effect does not require that a validation message be
sent to the server. The continued endurance of the "read open
delegation" provides a guarantee that no OPEN for write and thus no
write has occurred. Similarly, when closing a file opened for write
and if write open delegation is in effect, the data written does not
have to be flushed to the server until the open delegation is
recalled. The continued endurance of the open delegation provides a
guarantee that no open and thus no read or write has been done by
another client.
For the purposes of open delegation, READs and WRITEs done without an
OPEN are treated as the functional equivalents of a corresponding
type of OPEN. 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 file system 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 file system space and any applicable quotas.
The server can recall delegations as a result of managing the
available file system space. The client should abide by the server's
state space limits for delegations. If the client exceeds the stated
limits for the delegation, the server's behavior is undefined.
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Based on server conditions, quotas or available file system space,
the server may grant write open delegations with very restrictive
space limitations. The limitations may be defined in a way that will
always force modified data to be flushed to the server on close.
With respect to authentication, flushing modified data to the server
after a CLOSE has occurred may be problematic. For example, the user
of the application may have logged off the client and unexpired
authentication credentials may not be present. In this case, the
client may need to take special care to ensure that local unexpired
credentials will in fact be available. This may be accomplished by
tracking the expiration time of credentials and flushing data well in
advance of their expiration or by making private copies of
credentials to assure their availability when needed.
9.4.2. Open Delegation and File Locks
When a client holds a write open delegation, lock operations are
performed locally. This includes those required for mandatory file
locking. This can be done since the delegation implies that there
can be no conflicting locks. Similarly, all of the revalidations
that would normally be associated with obtaining locks and the
flushing of data associated with the releasing of locks need not be
done.
When a client holds a read open delegation, lock operations are not
performed locally. All lock operations, including those requesting
non-exclusive locks, are sent to the server for resolution.
9.4.3. 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
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the second client's GETATTR as if the file had been modified locally
at the server.
Since the form of the change attribute is determined by the server
and is opaque to the client, the client and server need to agree on a
method of communicating the modified state of the file. For the size
attribute, the client will report its current view of the file size.
For the change attribute, the handling is more involved.
For the client, the following steps will be taken when receiving a
write delegation:
o The value of the change attribute will be obtained from the server
and cached. Let this value be represented by c.
o The client will create a value greater than c that will be used
for communicating modified data is held at the client. Let this
value be represented by d.
o When the client is queried via CB_GETATTR for the change
attribute, it checks to see if it holds modified data. If the
file is modified, the value d is returned for the change attribute
value. If this file is not currently modified, the client returns
the value c for the change attribute.
For simplicity of implementation, the client MAY for each CB_GETATTR
return the same value d. This is true even if, between successive
CB_GETATTR operations, the client again modifies in the file's data
or metadata in its cache. The client can return the same value
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:
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o Upon providing a write delegation, the server will cache a copy of
the change attribute in the data structure it uses to record the
delegation. Let this value be represented by sc.
o When a second client sends a GETATTR operation on the same file to
the server, the server obtains the change attribute from the first
client. Let this value be cc.
o If the value cc is equal to sc, the file is not modified and the
server returns the current values for change, time_metadata, and
time_modify (for example) to the second client.
o If the value cc is NOT equal to sc, the file is currently modified
at the first client and most likely will be modified at the server
at a future time. The server then uses its current time to
construct attribute values for time_metadata and time_modify. A
new value of sc, which we will call nsc, is computed by the
server, such that nsc >= sc + 1. The server then returns the
constructed time_metadata, time_modify, and nsc values to the
requester. The server replaces sc in the delegation record with
nsc. To prevent the possibility of time_modify, time_metadata,
and change from appearing to go backward (which would happen if
the client holding the delegation fails to write its modified data
to the server before the delegation is revoked or returned), the
server SHOULD update the file's metadata record with the
constructed attribute values. For reasons of reasonable
performance, committing the constructed attribute values to stable
storage is OPTIONAL.
As discussed earlier in this section, the client MAY return the same
cc value on subsequent CB_GETATTR calls, even if the file was
modified in the client's cache yet again between successive
CB_GETATTR calls. Therefore, the server must assume that the file
has been modified yet again, and MUST take care to ensure that the
new nsc it constructs and returns is greater than the previous nsc it
returned. An example implementation's delegation record would
satisfy this mandate by including a boolean field (let us call it
"modified") that is set to false when the delegation is granted, and
an sc value set at the time of grant to the change attribute value.
The modified field would be set to true the first time cc != sc, and
would stay true until the delegation is returned or revoked. The
processing for constructing nsc, time_modify, and time_metadata would
use this pseudo code:
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if (!modified) {
do CB_GETATTR for change and size;
if (cc != sc)
modified = TRUE;
} else {
do CB_GETATTR for size;
}
if (modified) {
sc = sc + 1;
time_modify = time_metadata = current_time;
update sc, time_modify, time_metadata into file's metadata;
}
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
with the client's modified size.
In the case that the file attribute size is different than the
server's current value, the server treats this as a modification
regardless of the value of the change attribute retrieved via
CB_GETATTR and responds to the second client as in the last step.
This methodology resolves issues of clock differences between client
and server and other scenarios where the use of CB_GETATTR break
down.
It should be noted that the server is under no obligation to use
CB_GETATTR and therefore the server MAY simply recall the delegation
to avoid its use.
9.4.4. 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
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results in recall of an open delegation depends on the semantics of
the server file system. If that file system denies such RENAMEs when
a file is open, the recall must be performed to determine whether the
file in question is, in fact, open.
In addition to the situations above, the server may choose to recall
open delegations at any time if resource constraints make it
advisable to do so. Clients should always be prepared for the
possibility of recall.
When a client receives a recall for an open delegation, it needs to
update state on the server before returning the delegation. These
same updates must be done whenever a client chooses to return a
delegation voluntarily. The following items of state need to be
dealt with:
o If the file associated with the delegation is no longer open and
no previous CLOSE operation has been sent to the server, a CLOSE
operation must be sent to the server.
o If a file has other open references at the client, then OPEN
operations must be sent to the server. The appropriate stateids
will be provided by the server for subsequent use by the client
since the delegation stateid will 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 the section "Operation 18: OPEN" 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
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any modified data is written to the server.
In the case of write open delegation, file locking imposes some
additional requirements. To precisely maintain the associated
invariant, it is required to flush any modified data in any region
for which a write lock was released while the write delegation was in
effect. However, because the write open delegation implies no other
locking by other clients, a simpler implementation is to flush all
modified data for the file (as described just above) if any write
lock has been released while the write open delegation was in effect.
An implementation need not wait until delegation recall (or deciding
to voluntarily return a delegation) to perform any of the above
actions, if implementation considerations (e.g. resource availability
constraints) make that desirable. Generally, however, the fact that
the actual open state of the file may continue to change makes it not
worthwhile to send information about opens and closes to the server,
except as part of delegation return. Only in the case of closing the
open that resulted in obtaining the delegation would clients be
likely to do this early, since, in that case, the close once done
will not be undone. Regardless of the client's choices on scheduling
these actions, all must be performed before the delegation is
returned, including (when applicable) the close that corresponds to
the open that resulted in the delegation. These actions can be
performed either in previous requests or in previous operations in
the same COMPOUND request.
9.4.5. 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:
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* 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.
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.
9.4.6. 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 the section "Revocation
Recovery for Write Open Delegation" for additional details.
9.5. 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.
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For example, another client may have been granted a conflicting lock
after the revocation of the lock at the first client. Therefore, the
data within the lock range may have been modified by the other
client. Obviously, the first client is unable to guarantee to the
application what has occurred to the file in the case of revocation.
Notification to a lock owner will in many cases consist of simply
returning an error on the next and all subsequent READs/WRITEs to the
open file or on the close. Where the methods available to a client
make such notification impossible because errors for certain
operations may not be returned, more drastic action such as signals
or process termination may be appropriate. The justification for
this is that an invariant for which an application depends on may be
violated. Depending on how errors are typically treated for the
client operating environment, further levels of notification
including logging, console messages, and GUI pop-ups may be
appropriate.
9.5.1. Revocation Recovery for Write Open Delegation
Revocation recovery for a write open delegation poses the special
issue of modified data in the client cache while the file is not
open. In this situation, any client which does not flush modified
data to the server on each close must ensure that the user receives
appropriate notification of the failure as a result of the
revocation. Since such situations may require human action to
correct problems, notification schemes in which the appropriate user
or administrator is notified may be necessary. Logging and console
messages are typical examples.
If there is modified data on the client, it must not be flushed
normally to the server. A client may attempt to provide a copy of
the file data as modified during the delegation under a different
name in the file system name space to ease recovery. Note that when
the client can determine that the file has not been modified by any
other client, or when the client has a complete cached copy of file
in question, such a saved copy of the client's view of the file may
be of particular value for recovery. In other case, recovery using a
copy of the file based partially on the client's cached data and
partially on the server copy as modified by other clients, will be
anything but straightforward, so clients may avoid saving file
contents in these situations or mark the results specially to warn
users of possible problems.
Saving of such modified data in delegation revocation situations may
be limited to files of a certain size or might be used only when
sufficient disk space is available within the target file system.
Such saving may also be restricted to situations when the client has
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sufficient buffering resources to keep the cached copy available
until it is properly stored to the target file system.
9.6. Attribute Caching
The attributes discussed in this section do not include named
attributes. Individual named attributes are analogous to files and
caching of the data for these needs to be handled just as data
caching is for ordinary files. Similarly, LOOKUP results from an
OPENATTR directory are to be cached on the same basis as any other
pathnames and similarly for directory contents.
Clients may cache file attributes obtained from the server and use
them to avoid subsequent GETATTR requests. Such caching is write
through in that modification to file attributes is always done by
means of requests to the server and should not be done locally and
cached. The exception to this are modifications to attributes that
are intimately connected with data caching. Therefore, extending a
file by writing data to the local data cache is reflected immediately
in the size as seen on the client without this change being
immediately reflected on the server. Normally such changes are not
propagated directly to the server but when the modified data is
flushed to the server, analogous attribute changes are made on the
server. When open delegation is in effect, the modified attributes
may be returned to the server in the response to a CB_RECALL call.
The result of local caching of attributes is that the attribute
caches maintained on individual clients will not be coherent.
Changes made in one order on the server may be seen in a different
order on one client and in a third order on a different client.
The typical file system application programming interfaces do not
provide means to atomically modify or interrogate attributes for
multiple files at the same time. The following rules provide an
environment where the potential incoherences mentioned above can be
reasonably managed. These rules are derived from the practice of
previous NFS protocols.
o All attributes for a given file (per-fsid attributes excepted) are
cached as a unit at the client so that no non-serializability can
arise within the context of a single file.
o An upper time boundary is maintained on how long a client cache
entry can be kept without being refreshed from the server.
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
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attributes indirectly. This is accomplished by following the
modifying operation with a GETATTR operation and then using the
results of the GETATTR to update the client's cached attributes.
Note that if the full set of attributes to be cached is requested by
READDIR, the results can be cached by the client on the same basis as
attributes obtained via GETATTR.
A client may validate its cached version of attributes for a file by
fetching just both the change and time_access attributes and assuming
that if the change attribute has the same value as it did when the
attributes were cached, then no attributes other than time_access
have changed. The reason why time_access is also fetched is because
many servers operate in environments where the operation that updates
change does not update time_access. For example, POSIX file
semantics do not update access time when a file is modified by the
write system call. Therefore, the client that wants a current
time_access value should fetch it with change during the attribute
cache validation processing and update its cached time_access.
The client may maintain a cache of modified attributes for those
attributes intimately connected with data of modified regular files
(size, time_modify, and change). Other than those three attributes,
the client MUST NOT maintain a cache of modified attributes.
Instead, attribute changes are immediately sent to the server.
In some operating environments, the equivalent to time_access is
expected to be implicitly updated by each read of the content of the
file object. If an NFS client is caching the content of a file
object, whether it is a regular file, directory, or symbolic link,
the client SHOULD NOT update the time_access attribute (via SETATTR
or a small READ or READDIR request) on the server with each read that
is satisfied from cache. The reason is that this can defeat the
performance benefits of caching content, especially since an explicit
SETATTR of time_access may alter the change attribute on the server.
If the change attribute changes, clients that are caching the content
will think the content has changed, and will re-read unmodified data
from the server. Nor is the client encouraged to maintain a modified
version of time_access in its cache, since this would mean that the
client will either eventually have to write the access time to the
server with bad performance effects, or it would never update the
server's time_access, thereby resulting in a situation where an
application that caches access time between a close and open of the
same file observes the access time oscillating between the past and
present. The time_access attribute always means the time of last
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.
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9.7. Data and Metadata Caching and Memory Mapped Files
Some operating environments include the capability for an application
to map a file's content into the application's address space. Each
time the application accesses a memory location that corresponds to a
block that has not been loaded into the address space, a page fault
occurs and the file is read (or if the block does not exist in the
file, the block is allocated and then instantiated in the
application's address space).
As long as each memory mapped access to the file requires a page
fault, the relevant attributes of the file that are used to detect
access and modification (time_access, time_metadata, time_modify, and
change) will be updated. However, in many operating environments,
when page faults are not required these attributes will not be
updated on reads or updates to the file via memory access (regardless
whether the file is local file or is being access remotely). A
client or server MAY fail to update attributes of a file that is
being accessed via memory mapped I/O. This has several implications:
o If there is an application on the server that has memory mapped a
file that a client is also accessing, the client may not be able
to get a consistent value of the change attribute to determine
whether its cache is stale or not. A server that knows that the
file is memory mapped could always pessimistically return updated
values for change so as to force the application to always get the
most up to date data and metadata for the file. However, due to
the negative performance implications of this, such behavior is
OPTIONAL.
o If the memory mapped file is not being modified on the server, and
instead is just being read by an application via the memory mapped
interface, the client will not see an updated time_access
attribute. However, in many operating environments, neither will
any process running on the server. Thus NFS clients are at no
disadvantage with respect to local processes.
o If there is another client that is memory mapping the file, and if
that client is holding a write delegation, the same set of issues
as discussed in the previous two bullet items apply. So, when a
server does a CB_GETATTR to a file that the client has modified in
its cache, the response from CB_GETATTR will not necessarily be
accurate. As discussed earlier, the client's obligation is to
report that the file has been modified since the delegation was
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
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client's memory management system, this weak obligation may not be
possible. A client MAY return stale information in CB_GETATTR
whenever the file is memory mapped.
o The mixture of memory mapping and file locking on the same file is
problematic. Consider the following scenario, where a page size
on each client is 8192 bytes.
* Client A memory maps first page (8192 bytes) of file X
* Client B memory maps first page (8192 bytes) of file X
* Client A write locks first 4096 bytes
* Client B write locks second 4096 bytes
* Client A, via a STORE instruction modifies part of its locked
region.
* Simultaneous to client A, client B 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.
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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.
9.8. 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 file system APIs, an upper time boundary is
maintained on how long a client name cache entry can be kept without
verifying that the entry has not been made invalid by a directory
change operation performed by another client. .LP 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
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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.
9.9. 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 file system APIs, the following rules should be
followed:
o Cached READDIR information for a directory which is not obtained
in a single READDIR operation must always be a consistent snapshot
of directory contents. This is determined by using a GETATTR
before the first READDIR and after the last of READDIR that
contributes to the cache.
o An upper time boundary is maintained to indicate the length of
time a directory cache entry is considered valid before the client
must revalidate the cached information.
The revalidation technique parallels that discussed in the case of
name caching. When the client is not changing the directory in
question, checking the change attribute of the directory with GETATTR
is adequate. The lifetime of the cache entry can be extended at
these checkpoints. When a client is modifying the directory, the
client needs to use the change_info4 data to determine whether there
are other clients modifying the directory. If it is determined that
no other client modifications are occurring, the client may update
its directory cache to reflect its own changes.
As demonstrated previously, directory caching requires that the
client revalidate directory cache data by inspecting the change
attribute of a directory at the point when the directory was cached.
This requires that the server update the change attribute for
directories when the contents of the corresponding directory is
modified. For a client to use the change_info4 information
appropriately and correctly, the server must report the pre and post
operation change attribute values atomically. When the server is
unable to report the before and after values atomically with respect
to the directory operation, the server must indicate that fact in the
change_info4 return value. When the information is not atomically
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reported, the client should not assume that other clients have not
changed the directory.
10. Multi-server Name Space
NFSv4.1 supports attributes that allow a namespace to extend beyond
the boundaries of a single server. Use of such multi-server
namespaces is optional, and for many purposes, single-server
namespace are perfectly acceptable. Use of multi-server namespaces
can provide many advantages, however, by separating a file system's
logical position in a name space from the (possibly changing)
logistical and administrative considerations that result in
particular file systems being located on particular servers.
10.1. 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 systems
by specifying a server name (either a DNS name or an IP address)
together with the path of that file system within that server's
single-server name space.
The fs_locations_info recommended attribute allows specification of
one more file systems instance locations where the data corresponding
to a given file system may be found. This attribute provides to the
client, in addition to information about file system instance
locations, extensive information about the various file system
instance choices (e.g. priority for use, writability, currency, etc.)
as well as information to help the client efficiently effect as
seamless a transition as possible among multiple file system
instances, when and if that should be necessary.
The fs_locations recommended attribute is inherited from NFSv4.0 and
only allows specification of the file system locations where the data
corresponding to a given file system may be found. Servers should
make this attribute available whenever fs_locations_info is
supported, but client use of fs_locations_info is to be preferred.
10.2. File System Presence or Absence
A given location in an NFSv4 namespace (typically but not necessarily
a multi-server namespace) can have a number of file system instance
locations associated with it (via the fs_locations or
fs_locations_info attribute). There may also be an actual current
file system at that location, accessible via normal namespace
operations (e.g. LOOKUP). In this case, the file system is said to
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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 and 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 NFS4ERR_MOVED
(i.e. file systems may be absent), it MUST support the fs_locations
attribute and SHOULD support the fs_locations_info and fs_absent
attributes.
While the error name suggests that we have a case of a file system
which once was present, and has only become absent later, this is
only one possibility. A position in the namespace may be permanently
absent with the file system(s) designated by the location attributes
the only realization. The name NFS4ERR_MOVED reflects an earlier,
more limited conception of its function, but this error will be
returned whenever the referenced file system is absent, whether it
has moved or not.
Except in the case of GETATTR-type operations (to be discussed
later), when the current filehandle at the start of an operation is
within an absent file system, that operation is not performed and the
error NFS4ERR_MOVED returned, to indicate that the file system is
absent on the current server.
Because a GETFH cannot succeed if the current filehandle is within an
absent file system, filehandles within an absent file system cannot
be transferred to the client. When a client does have filehandles
within an absent file system, it is the result of obtaining them when
the file system was present, and having the file system become absent
subsequently.
It should be noted that because the check for the current filehandle
being within an absent file system happens at the start of every
operation, operations which change the current filehandle so that it
is within an absent file system will not result in an error. This
allows such combinations as PUTFH-GETATTR and LOOKUP-GETATTR to be
used to get attribute information, particularly location attribute
information, as discussed below.
The recommended file system attribute fs_absent can used to
interrogate the present/absent status of a given file system.
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10.3. Getting Attributes for an Absent File System
When a file system is absent, most attributes are not available, but
it is necessary to allow the client access to the small set of
attributes that are available, and most particularly those that give
information about the correct current locations for this file system,
fs_locations and fs_locations_info.
10.3.1. GETATTR Within an Absent File System
As mentioned above, an exception is made for GETATTR in that
attributes may be obtained for a filehandle within an absent file
system. This exception only applies if the attribute mask contains
at least one attribute bit that indicates the client is interested in
a result regarding an absent file system: fs_locations,
fs_locations_info, or fs_absent. If none of these attributes is
requested, GETATTR will result in an NFS4ERR_MOVED error.
When a GETATTR is done on an absent file system, the set of supported
attributes is very limited. Many attributes, including those that
are normally mandatory will not be available on an absent file
system. In addition to the attributes mentioned above (fs_locations,
fs_locations_info, fs_absent), the following attributes SHOULD be
available on absent file systems, in the case of recommended
attributes at least to the same degree that they are available on
present file systems.
change: This attribute is useful for absent file systems and can be
helpful in summarizing to the client when any of the location-
related attributes changes.
fsid: This attribute should be provided so that the client can
determine file system boundaries, including, in particular, the
boundary between present and absent file systems.
mounted_on_fileid: For objects at the top of an absent file system
this attribute needs to be available. Since the fileid is one
which is within the present parent file system, there should be no
need to reference the absent file system to provide this
information.
Other attributes SHOULD NOT be made available for absent file
systems, even when it is possible to provide them. The server should
not assume that more information is always better and should avoid
gratuitously providing additional information.
When a GETATTR operation includes a bit mask for one of the
attributes fs_locations, fs_locations_info, or absent, but where the
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bit mask includes attributes which are not supported, GETATTR will
not return an error, but will return the mask of the actual
attributes supported with the results.
Handling of VERIFY/NVERIFY is similar to GETATTR in that if the
attribute mask does not include fs_locations, fs_locations_info, or
fs_absent, 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 mandatory attributes), will also cause an NFS4ERR_MOVED
result.
10.3.2. READDIR and Absent File Systems
A READDIR performed when the current filehandle is within an absent
file system will result in an NFS4ERR_MOVED error, since, unlike the
case of GETATTR, no such exception is made for READDIR.
Attributes for an absent file system may be fetched via a READDIR for
a directory in a present file system, when that directory contains
the root directories of one or more absent file systems. In this
case, the handling is as follows:
o If the attribute set requested includes one of the attributes
fs_locations, fs_locations_info, or fs_absent, then fetching of
attributes proceeds normally and no NFS4ERR_MOVED indication is
returned, even when the rdattr_error attribute is requested.
o If the attribute set requested does not include one of the
attributes fs_locations, fs_locations_info, or fs_absent, then if
the rdattr_error attribute is requested, each directory entry for
the root of an absent file system, will report NFS4ERR_MOVED as
the value of the rdattr_error attribute.
o If the attribute set requested does not include any of the
attributes fs_locations, fs_locations_info, fs_absent, 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 NFSERR_MOVED error.
o The unavailability of an attribute because of a file system's
absence, even one that is ordinarily mandatory, does not result in
any error indication. The set of attributes returned for the root
directory of the absent file system in that case is simply
restricted to those actually available.
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10.4. Uses of Location Information
The location-bearing attributes (fs_locations and fs_locations_info),
provide, together with the possibility of absent file systems, a
number of important facilities in providing reliable, manageable, and
scalable data access.
When a file system is present, these attribute can provide
alternative locations, to be used to access the same data, in the
event that server failures, communications problems, or other
difficulties, 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 NFSERR_MOVED
error and at that point the successor locations (typically only one
but multiple choices are possible) can be fetched and used to
continue access. Transfer of the file system contents to the new
location is referred to as "migration", but it should be kept in mind
that there are cases in which this term can be used, like
"replication", when there is no actual data migration per se.
Where a file system was not previously present, specification of file
system location provides a means by which file systems located on one
server can be associated with a name space defined by another server,
thus allowing a general multi-server namespace facility. Designation
of such a location, in place of an absent file system, is called
"referral".
10.4.1. File System Replication
The fs_locations and fs_locations_info attributes provide alternative
locations, to be used to access data in place of or in a addition to
the current file system instance. On first access to a file system,
the client should obtain the value of the set alternate locations by
interrogating the fs_locations or fs_locations_info attribute, with
the latter being preferred.
In the event that server failures, communications problems, or other
difficulties, make continued access to the current file system
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impossible or otherwise impractical, the client can use the alternate
locations as a way to get continued access to his data. Depending on
specific attributes of these alternate locations, as indicated within
the fs_locations_info attribute, multiple locations may be used
simultaneously, to provide higher performance through the
exploitation of multiple paths between client and target filesystem.
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 form of server
clustering in which multiple servers provide alternate ways of
accessing the same physical file system. How these different modes
of file system transition are represented within the fs_locations and
fs_locations_info attributes and how the client deals with file
system transition issues will be discussed in detail below.
When multiple server addresses correspond to the same actual server,
as shown by a common so_major_id field within the server_owner4 field
returned by EXCHANGE_ID, the client may assume that for each
filesystem in the namespace of a given server IP, there exist
filesystems at corresponding namespace locations for each of the
other server IP's, even in the absence of explicit listing in
fs_locations and fs_locations_info. Such corresponding file system
locations can be used as alternate locations, just as those
explicitly specified via the fs_locations and fs_locations_info
attributes. Where these specific locations are designated in the
fs_locations_info attribute, the conditions of use specified in this
attribute (e.g. priorities, specification of simultaneous use) may
limit the clients use of these alternate locations.
When multiple replicas exist and are used simultaneously or in
succession by a client, they must designate the same data (with
metadata being the same to the degree indicated by the
fs_locations_info attribute). Where filesystems are writable, a
change made on one instance must be visible on all instances,
immediately upon the earlier of the return of the modifying request
or the visibility of that change on any of the associated replicas.
Where a filesystem is not writable but represents a read-only copy
(possibly periodically updated) of a writable filesystem, similar
requirements apply to the propagation of updates. It must be
guaranteed 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, to avoid any possibility, that a
client in effecting a transition to a replica, will see any reversion
in filesystem state. The specific means by which this will be
prevented varies based on fs4_status_type reported as part of the
fs_status attribute. (See Section 10.11).
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10.4.2. File System Migration
When a file system is present and becomes absent, clients can be
given the opportunity to have continued access to their data, at an
alternate location, as specified by the fs_locations or
fs_locations_info attribute. Typically, a client will be accessing
the file system in question, get an NFS4ERR_MOVED error, and then use
the fs_locations or fs_locations_info attribute to determine the new
location of the data. When fs_locations_info is used, additional
information will be available which will define the nature of the
client's handling of the transition to a new server.
Such migration can be helpful in providing load balancing or general
resource reallocation. The protocol does not specify how the file
system will be moved between servers. It is anticipated that a
number of different server-to-server transfer mechanisms might be
used with the choice left to the server implementer. The NFSv4.1
protocol specifies the method used to communicate the migration event
between client and server.
The new location may be an alternate communication path to the same
server, or, in the case of various forms of server clustering,
another server providing access to the same physical file system.
The client's responsibilities in dealing with this transition depend
on the specific nature of the new access path and how and whether
data was in fact migrated. These issues will be discussed in detail
below.
When multiple server addresses correspond to the same actual server,
as shown by a common value for so_major_id field of the server_owner4
value returned by EXCHANGE_ID, the location or locations may
designate alternate server addresses in the form of specific server
IP addresses, when the filesystem in question is available at those
addresses, and no longer accessible at the original address.
Although a single successor location is typical, multiple locations
may be provided, together with information that allows priority among
the choices to be indicated, via information in the fs_locations_info
attribute. Where suitable clustering mechanisms make it possible to
provide multiple identical file systems or paths to them, this allows
the client the opportunity to deal with any resource or
communications issues that might limit data availability.
When an alternate location is designated as the target for migration,
it must designate the same data (with metadata being the same to the
degree indicated by the fs_locations_info attribute). Where
filesystems are writable, a change made on the original filesystem
must be visible on all migration targets. Where a filesystem is not
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writable but represents a read-only copy (possibly periodically
updated) of a writable filesystem, similar requirements apply to the
propagation of updates. Any change visible in the original
filesystem 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 filesystem state.
10.4.3. Referrals
Referrals provide a way of placing a file system in a location
essentially without respect to its physical location on a given
server. This allows a single server of 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 that file system is absent. When this occurs,
typically by receiving the error NFS4ERR_MOVED, the actual location
or locations of the file system can be determined by fetching the
fs_locations or fs_locations_info attribute.
The locations-related attribute may designate a single file system
location or multiple file system locations, to be selected based on
the needs of the client. The server, in the locations_info attribute
may specify priorities to be associated with various file system
location choices. The server may assign different priorities to
different locations as reported to individual clients, in order to
adapt to client physical location or to effect load balancing. When
both read-only and read-write filesystems are present, some of the
read-only locations may not absolutely up-to-date (as they would have
to be in the case of replication and migration). Servers may also
specify filesystem locations that include client-substituted variable
so that different clients are referred to different file systems
(with different data contents) based on client attributes such as cpu
architecture.
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
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separate servers) for each separately-administered section of the
name space. Any segment or the top-level referral file system 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 availably to all clients at that location.
There are however facilities provided which allow different client to
be directed to different sets of data, so as to adapt to such client
characteristics as cpu architecture.
10.5. Additional Client-side Considerations
When clients make use of servers that implement referrals,
replication, and migration, care should be taken so that a user who
mounts a given file system that includes a referral or a relocated
file system continue to see a coherent picture of that user-side file
system despite the fact that it contains a number of server-side file
systems which may be on different servers.
One important issue is upward navigation from the root of a server-
side file system to its parent (specified as ".." in UNIX). The
client needs to determine when it hits an fsid root going up the file
tree. When at such a point, and needs to ascend to the parent, it
must do so locally instead of sending a LOOKUPP call to the server.
The LOOKUPP would normally return the ancestor of the target file
system on the target server, which may not be part of the space that
the client mounted.
A related issue is upward navigation from named attribute
directories. The named attribute directories are essentially
detached from the namespace and this property should be safely
represented in the client operating environment. LOOKUPP on a named
attribute directory may return the filehandle of the associated file
and conveying this to applications might be unsafe as many
applications expect the parent of a directory to be a directory by
itself. Therefore the client may want to hide the parent of named
attribute directories (represented as ".." in UNIX) or represent the
named attribute directory as its own parent (as typically done for
the filesystem root directory in UNIX)
Another issue concerns refresh of referral locations. When referrals
are used extensively, they may change as server configurations
change. It is expected that clients will cache information related
to traversing referrals so that future client side requests are
resolved locally without server communication. This is usually
rooted in client-side name lookup caching. Clients should
periodically purge this data for referral points in order to detect
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changes in location information. When the change attribute changes
for directories that hold referral entries or for the referral
entries themselves, clients should consider any associated cached
referral information to be out of date.
10.6. Effecting File System Transitions
Transitions between file system instances, whether due to switching
between replicas upon server unavailability, or in response to a
server-initiated migration events are best dealt with together. Even
though the prototypical use cases of replication and migration
contain distinctive sets of features, when all possibilities for
these operations are considered, the underlying unity of these
operations, from the client's point of view is clear, even though for
the server pragmatic considerations will normally force different
implementation strategies for planned and unplanned transitions.
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 NFSv4.1 protocol does not impose choices on clients and servers
with regard to that spectrum of transition methods. In fact, there
are many valid choices, depending on client and application
requirements and their interaction with server implementation
choices. The NFSv4.1 protocol does define the specific choices that
can be made, how these choices are communicated to the client and how
the client is to deal with any discontinuities.
In the sections below, references will be made to various possible
server implementation choices as a way of illustrating the transition
scenarios that clients may deal with. The intent here is not to
define or limit server implementations but rather to illustrate the
range of issues that clients may face.
In the discussion below, references will be made to a file system
having a particular property or of two file systems (typically the
source and destination) belonging to a common class of any of several
types. Two file systems that belong to such a class share some
important aspect of file system behavior that clients may depend upon
when present, to easily effect a seamless transition between file
system instances. Conversely, where the file systems do not belong
to such a common class, the client has to deal with various sorts of
implementation discontinuities which may cause performance or other
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issues in effecting a transition.
Where the fs_locations_info attribute is available, such file system
classification data will be made directly available to the client.
See Section 10.10 for details. When only fs_locations is available,
default assumptions with regard to such classifications have to be
inferred. See Section 10.9 for details.
In cases in which one server is expected to accept opaque values from
the client that originated from another server, it is a wise
implementation practice for the servers to encode the "opaque" values
in network 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.
10.6.1. File System Transitions and Simultaneous Access
When a single filesystem may be accessed at multiple locations,
whether this is because of an indication of file system identity as
reported by the fs_locations or fs_locations_info attributes or
because two file systems instances have corresponding locations on
server addresses which connect to the same server as indicated by a
common so_major_id field in the server_owner4 field returned by
EXCHANGE_ID, the client will, depending on specific circumstances as
discussed below, either:
o Access multiple instances simultaneously, as representing
alternate paths to the same data and metadata.
o The client accesses one instance (or set of instances) and then
transitions to an alternative instance (or set of instances) as a
result of network issues, server unresponsiveness, or server-
directed migration. The transition may involve changes in
filehandles, fileids, the change attribute, and or locking state,
depending on the attributes of the source and destination file
system instances, as specified in the fs_locations_info attribute.
Which of these choices is possible, and how a transition is effected
is governed by equivalence classes of file system instances as
reported by the fs_locations_info attribute, and, for file systems
instances in the same location within multiple single-server
namespace, by the so_major_id field in the server_owner4 returned by
EXCHANGE_ID.
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10.6.2. Simultaneous Use and Transparent Transitions
When two file system instances have the same location within their
respective single-server namespaces and those two server IP addresses
return the so_major_id value in the server_owner4 value returned in
response to EXCHANGE_ID, those file systems instances can be treated
as the same, and either used together simultaneously or serially with
no transition activity required on the part of the client.
Whether simultaneous use of the two file system instances is valid is
controlled by whether the fs_locations_info attribute shows the two
instances as having the same _simultaneous-use_ class.
Note that for two such file systems, any information within the
fs_locations_info attribute that indicates the need for special
transition activity, i.e. the appearance of the two file system
instances with different _handle_, _fileid_, _verifier_, _change_
classes, MUST be ignored by the client. The server SHOULD not
indicate that these instances belong to different _handle_, _fileid_,
_verifier_, _change_ classes, whether the two instances are shown
belonging to the same _simultaneous-use_ class or not.
Where these conditions do not apply, a non-transparent file system
instance transition is required with the details depending on the
respective _handle_, _fileid_, _verifier_, _change_ classes of the
two file system instances and whether the two servers in question
have the same eir_server_scope value as reported by EXCHANGE_ID.
10.6.2.1. Simultaneous Use of File System Instances
When the conditions above hold, in either of the following two cases,
the client may use the two file system instances simultaneously.
o The fs_locations_info attribute does not contain separate per-IP
address entries for file systems instances at the distinct IP
addresses. This includes the case in which the fs_locations_info
attribute is unavailable.
o The fs_locations_info attribute indicates that two file system
instances belong to the same _simultaneous-use_ class.
In this case, the client may use both file system instances
simultaneously, as representations of the same file system, whether
that happens because the two IP addresses connect to the same
physical server or because different servers connect to clustered
file systems and export their data in common. When simultaneous use
is in effect, any change made to one file system instance must be
immediately reflected in the other file system instance(s). Locks
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are treated as part of a common lease, associated with a common
clientid. Depending on the details of the serverver_owner4 returned
by EXCHANGE_ID, the two server instances may be accessed by different
sessions or a single session in common.
10.6.2.2. Transparent File System Transitions
When the conditions above hold and the fs_locations_info attribute
explicitly shows the file system instances for these distinct IP
addresses as belonging to different _simultaneous-use_ classes, the
file system instances should not be used by the client
simultaneously, but rather serially with one being used unless and
until communication difficulties, lack of responsiveness, or an
explicit migration event causes another file system instance (or set
of file system instances sharing a common _simultaneous-use_ class to
be used.
When a change in file system instance is to be done, the client will
use the same clientid already in effect. If it already has
connections to the new server address, these will be used. Otherwise
new connections to existing sessions or new sessions associated with
the existing clientid are established as indicated by the
server_owner4 returned by EXCHANGE_ID.
In all such transparent transition cases, the following apply:
o File handles stay the same if persistent and if volatile are only
subject to expiration, if they would be in the absence of file
system transition.
o Fileid values do not change across the transition.
o The file system will have the same fsid in both the old and new
locations.
o Change attribute values are consistent across the transition and
do not have to be refetched. When change attributes indicate that
a cached object is still valid, it can remain cached.
o Client, and state identifier retain their validity across the
transition, except where their staleness is recognized and
reported by the new server. Except where such staleness requires
it, no lock reclamation is needed.
o Write verifiers are presumed to retain their validity and can be
presented to COMMIT, with the expectation that if COMMIT on the
new server accept them as valid, then that server has all of the
data unstably written to the original server and has committed it
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to stable storage as requested.
10.6.3. Filehandles and File System Transitions
There are a number of ways in which filehandles can be handled across
a file system transition. These can be divided into two broad
classes depending upon whether the two file systems across which the
transition happens share sufficient state to effect some sort of
continuity of file system handling.
When there is no such co-operation in filehandle assignment, the two
file systems are reported as being in different _handle_ classes. In
this case, all filehandles are assumed to expire as part of the file
system transition. Note that this behavior does not depend on
fh_expire_type attribute and supersedes the specification of
FH4_VOL_MIGRATION bit, which only affects behavior when
fs_locations_info is not available.
When there is co-operation in filehandle assignment, the two file
systems are reported as being in the same _handle_ classes. In this
case, persistent filehandle remain valid after the file system
transition, while volatile filehandles (excluding those while are
only volatile due to the FH4_VOL_MIGRATION bit) are subject to
expiration on the target server.
10.6.4. Fileid's and File System Transitions
In NFSv4.0, the issue of continuity of fileid's in the event of a
file system transition was not addressed. The general expectation
had been that in situations in which the two file system instances
are created by a single vendor using some sort of file system image
copy, fileid's 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 of the transition mechanisms adopted by the server.
It is important to note that while clients themselves may have no
trouble with a fileid changing as a result of a file system
transition event, applications do typically have access to the fileid
(e.g. via stat), and the result of this is that an application may
work perfectly well if there is no file system instance transition or
if any such transition is among instances created by a single vendor,
yet be unable to deal with the situation in which a multi-vendor
transition occurs, at the wrong time.
Providing the same fileid's 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
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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 an fs between vendors where assigning the same index to
a given file may not be possible. Note here that a fileid does not
require that it be useful to find the file in question, only that it
is unique within the given fs. Servers prepared to accept a fileid
as a single piece of metadata and store it apart from the value used
to index the file information can relatively easily maintain a fileid
value across a migration event, allowing a truly transparent
migration event.
In any case, where servers can provide continuity of fileids, they
should and the client should be able to find out that such continuity
is available, and take appropriate action. Information about the
continuity (or lack thereof) of fileid's across a file system is
represented by specifying whether the file systems in question are of
the same _fileid_ class.
10.6.5. Fsid's and File System Transitions
Since fsid's are only unique within a per-server basis, it is to be
expected that they will change during a file system transition.
Clients should not make the fsid's received from the server visible
to application 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.
When a file system transition is made and the fs_locations_info
indicates that file system in question may be split into multiple
file systems (via the LIF_MULTI_FS flag), client should do GETATTR's
on all known objects within the file system undergoing transition, to
determine the new file system boundaries. Clients may maintain the
fsid's passed to existing applications by mapping all of the fsid for
the descendent file systems to a the common fsid used for the
original file system.
10.6.6. The Change Attribute and File System Transitions
Since the change attribute is defined as a server-specific one,
change attributes fetched from one server are normally presumed to be
invalid on another server. Such a presumption is troublesome since
it would invalidate all cached change attributes, requiring
refetching. Even more disruptive, the absence of any assured
continuity for the change attribute means that even if the same value
is gotten on refetch no conclusions can drawn as to whether the
object in question has changed. The identical change attribute could
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be merely an artifact, of a modified file with a different change
attribute construction algorithm, with that new algorithm just
happening to result in an identical change value.
When the two file systems have consistent change attribute formats,
and this fact is communicated to the client by reporting as in the
same _change_ class, the client may assume a continuity of change
attribute construction and handle this situation just as it would be
handled without any file system transition.
10.6.7. Lock State and File System Transitions
In a file system transition, the client needs to handle cases in
which the two servers have cooperated in state management and in
which they have not. Cooperation by two servers in state management
requires coordination of clientids. Before the client attempts to
use a clientid 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 clientid by accident.
The client needs to compare the eir_server_scope values returned by
each server. If the scope values do not match, then the servers have
not cooperated in state management. If the scope values match, then
this indicates the servers have cooperated in assigning clientids to
the point that they will reject clientids that refer to state they do
not know about.
In the case of migration, the servers involved in the migration of a
file system SHOULD transfer all server state from the original to the
new server. When this done, it must be done in a way that is
transparent to the client. With replication, such a degree of common
state is typically not the case. Clients, however should use the
information provided by the eir_server_scope returned by EXCHANGE_ID
to determine whether such sharing may be in effect, rather than
making assumptions based on the reason for the transition.
This state transfer will reduce disruption to the client when a file
system transition 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 clientid, then the client may used the
existing stateid's associated with that clientid for the old file
system instance in connection with the that same clientid in
connection with the file system instance.
When the two servers belong to the same server scope, it does
necessarily mean that when dealing with the transition, the client
will not have to reclaim state. However it does mean that the client
may proceed using his current clientid when establishing
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communication with the new server and that that new server will
either recognize that clientid as valid, or reject it, in which case
locks must be reclaimed by the client.
File systems co-operating in state management may actually share
state or simply divide the id space so as to recognize (and reject as
stale) each others state and clients id's. Servers which do share
state may not do so under all conditions or at all times. The
requirement for the server is that if it cannot be sure in accepting
a clientid that it reflects the locks the client was given, it must
treat all associated state as stale and report it as such to the
client.
When the two file systems instances are on servers that do not share
a server scope value the client must establish a new clientid on the
destination, if it does not have one already and reclaim if possible.
In this case, old stateids and clientid's should not be presented to
the new server since there is no assurance that they will not
conflict with id's valid on that server.
In either case, when actual locks are not known to be maintained, the
destination server may establish a grace period specific to the given
file system, with non-reclaim locks being rejected for that file
system, even though normal locks are being granted for other file
systems. Clients should not infer the absence of a grace period for
file systems being transitioned to a server from responses to
requests for other file systems.
In the case of lock reclamation for a given file system after a file
system transition, edge conditions can arise similar to those for
reclaim after server reboot (although in the case of the planned
state transfer associated with migration, these can be avoided by
securely recording lock state as part of state migration. Where the
destination server cannot guarantee that locks will not be
incorrectly granted, the destination server should not establish a
file-system-specific grace period.
In place of a file-system-specific version of RECLAIM_COMPLETE,
servers may assume that an attempt to obtain a new lock, other than
be reclaim, indicate the end of the client's attempt to reclaim locks
for that file system. [NOTE: The alternative would be to adapt
RECLAIM_COMPLETE to this task].
Information about client identity that 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.
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Servers are encouraged to provide facilities to allow locks to be
reclaimed on the new server after a file system transition. Often,
however, in cases in which the two servers do not share a server
scope value, such facilities may not be available and client should
be prepared to re-obtain locks, even though it is possible that the
client may have his LOCK or OPEN request denied due to a conflicting
lock. In some environments, such as the transition between read-only
file systems, such denial of locks should not pose large difficulties
in practice. When an attempt to re-establish a lock on a new server
is denied, the client should treat the situation as if his original
lock had been revoked. In all cases in which the lock is granted,
the client cannot assume that no conflicting 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.
10.6.7.1. Leases and File System Transitions
In the case of lease renewal, the client may not be submitting
requests for a file system that has been transferred to another
server. This can occur because of the lease renewal mechanism. The
client renews leases for all file systems when submitting a request
on an associated session, regardless of the specific file system
being referenced.
In order for the client to schedule renewal of leases that may have
been relocated to the new server, the client must find out about
lease relocation before those leases expire. To accomplish this, the
SEQUENCE operation will return the status bit
SEQ4_STATUS_LEASE_MOVED, if responsibility for any of the 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 for the fs_locations or
fs_locations_info attribute for an access to each file system for
which a lease has been moved to a new server.
When a client receives an SEQ4_STATUS_LEASE_MOVED indication, it
should perform an operation on each file system 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 and fs_locations_info
attributes) and perform renewal of those leases on the new server,
unless information in fs_locations_info attribute shows that no state
could have been transferred. If the server has not had state
transferred to it transparently, the client will receive either
NFS4ERR_STALE_CLIENTID from the new server, as described above, and
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the client can then reclaim locks as is done in the event of server
failure.
10.6.7.2. Transitions and the Lease_time Attribute
In order that the client may appropriately manage its leases in the
case of a file system transition, the destination server must
establish proper values for the lease_time attribute.
When state is transferred transparently, that state should include
the correct value of the lease_time attribute. The lease_time
attribute on the destination server must never be less than that on
the source since this would result in premature expiration of leases
granted by the source server. Upon transitions in which state is
transferred transparently, the client is under no obligation to re-
fetch the lease_time attribute and may continue to use the value
previously fetched (on the source server).
If state has not been transferred transparently, either because the
associated servers are show as have different eir_server_scope
strings or because the clientid is rejected when presented to the new
server, the client should fetch the value of lease_time on the new
(i.e. destination) server, and use it for subsequent locking
requests. However the server must respect a grace period at least as
long as the lease_time on the source server, in order to ensure that
clients have ample time to reclaim their lock before potentially
conflicting non-reclaimed locks are granted.
10.6.8. Write Verifiers and File System Transitions
In a file system transition, the two file systems may be clustered in
the handling of unstably written data. When this is the case, and
the two file systems belong to the same _verifier_ class, valid
verifiers from one system may be recognized by the other and
superfluous writes avoided. There is no requirement that all valid
verifiers be recognized, but it cannot be the case that a verifier is
recognized as valid when it is not. [NOTE: We need to resolve the
issue of proper verifier scope].
When two file systems belong to different _verifier_ classes, the
client must assume that all unstable writes in existence at the time
file system transition, have been lost since there is no way the old
verifier can recognized as valid (or not) on the target server.
10.7. 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
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fs_locations or fs_locations_info attributes. The client will
typically get an NFS4ERR_MOVED error, fetch the appropriate location
information and proceed to access the file system on different
server, even though it retains its logical position within the
original namespace.
The examples given in the sections below are somewhat artificial in
that an actual client will not typically do a multi-component lookup,
but will have cached information regarding the upper levels of the
name hierarchy. However, these example are chosen to make the
required behavior clear and easy to put within the scope of a small
number of requests, without getting unduly into details of how
specific clients might choose to cache things.
10.7.1. Referral Example (LOOKUP)
Let us suppose that the following COMPOUND is issued in an
environment in which /this/is/the/path is absent from the target
server. This may be for a number of reasons. It may be the case
that the file system has moved, or, it may be the case that the
target server is functioning mainly, or solely, to refer clients to
the servers on which various file systems are located.
o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
o LOOKUP "the"
o LOOKUP "path"
o GETFH
o GETATTR fsid,fileid,size,ctime
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.
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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 fs, but ... the client will never see
the value of that fh.
o GETFH --> NFS4ERR_MOVED. Fails because current fh is in an absent
fs at the start of the operation and the spec makes no exception
for GETFH.
o GETATTR fsid,fileid,size,ctime. Not executed because the failure
of the GETFH stops processing of the COMPOUND.
Given the failure of the GETFH, the client has the job of determining
the root of the absent file system and where to find that file
system, i.e. the server and path relative to that server's root fh.
Note here that in this example, the client did not obtain filehandles
and attribute information (e.g. fsid) for the intermediate
directories, so that he would not be sure where the absent file
system starts. It could be the case, for example, that /this/is/the
is the root of the moved file system and that the reason that the
lookup of "path" succeeded is that the file system was not absent on
that op but was moved between the last LOOKUP and the GETFH (since
COMPOUND is not atomic). Even if we had the fsid's for all of the
intermediate directories, we could have no way of knowing that /this/
is/the/path was the root of a new fs, since we don't yet have its
fsid.
In order to get the necessary information, let us re-issue the chain
of lookup's with GETFH's and GETATTR's to at least get the fsid's so
we can be sure where the appropriate fs boundaries are. The client
could choose to get fs_locations_info at the same time but in most
cases the client will have a good guess as to where fs boundaries are
(because of where NFS4ERR_MOVED was gotten and where not) making
fetching of fs_locations_info unnecessary.
OP01: PUTROOTFH --> NFS_OK
- Current fh is root of pseudo-fs.
OP02: GETATTR(fsid) --> NFS_OK
- Just for completeness. Normally, clients will know the fsid of
the pseudo-fs as soon as they establish communication with a
server.
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OP03: LOOKUP "this" --> NFS_OK
OP04: GETATTR(fsid) --> NFS_OK
- Get current fsid to see where fs 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 fs boundaries are. The fsid will be
that for the pseudo-fs in this example, so no boundary.
OP08: GETFH --> NFS_OK
- Current fh is for /this/is and is within pseudo-fs.
OP09: LOOKUP "the" --> NFS_OK
- Current fh is for /this/is/the and is within pseudo-fs.
OP10: GETATTR(fsid) --> NFS_OK
- Get current fsid to see where fs 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
fs, but ...
- The client will never see the value of that fh
OP13: GETATTR(fsid, fs_locations_info) --> NFS_OK
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- We are getting the fsid to know where the fs boundaries are. Note
that the fsid we are given will not necessarily be preserved at
the new location. That fsid might be different and in fact the
fsid we have for this fs might a valid fsid of a different fs on
that new server.
- In this particular case, we are pretty sure anyway that what has
moved is /this/is/the/path rather than /this/is/the since we have
the fsid of the latter and it is that of the pseudo-fs, which
presumably cannot move. However, in other examples, we might not
have this kind of information to rely on (e.g. /this/is/the might
be a non-pseudo file system separate from /this/is/the/path), so
we need to have another reliable source information on the
boundary of the fs which is moved. If, for example, the file
system "/this/is" had moved we would have a case of migration
rather than referral and once the boundaries of the migrated file
system was clear we could fetch fs_locations_info.
- We are fetching fs_locations_info because the fact that we got an
NFS4ERR_MOVED at this point means that it most likely that this is
a referral and we need the destination. Even if it is the case
that "/this/is/the" is a file system which has migrated, we will
still need the location information for that file system.
OP14: GETFH --> NFS4ERR_MOVED
- Fails because current fh is in an absent fs at the start of the
operation and the spec makes no exception for GETFH. Note that
this has the happy consequence that we don't have to worry about
the volatility or lack thereof of the fh. If the root of the fs
on the new location is a persistent fh, then we can assume that
this fh, which we never saw is a persistent fh, which, if we could
see it, would exactly match the new fh. At least, there is no
evidence to disprove that. On the other hand, if we find a
volatile root at the new location, then the filehandle which we
never saw must have been volatile or at least nobody can prove
otherwise.
Given the above, the client knows where the root of the absent file
system is, by noting where the change of fsid occurred. The
fs_locations_info attribute also gives the client the actual location
of the absent file system, so that the referral can proceed. The
server gives the client the bare minimum of information about the
absent file system so that there will be very little scope for
problems of conflict between information sent by the referring server
and information of the file system's home. No filehandles and very
few attributes are present on the referring server and the client can
treat those it receives as basically transient information with the
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function of enabling the referral.
10.7.2. Referral Example (READDIR)
Another context in which a client may encounter referrals is when it
does a READDIR on directory in which some of the sub-directories are
the roots of absent file systems.
Suppose such a directory is read as follows:
o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
o LOOKUP "the"
o READDIR (fsid, size, ctime, mounted_on_fileid)
In this case, because rdattr_error is not requested,
fs_locations_info is not requested, and some of attributes cannot be
provided the result will be an NFS4ERR_MOVED error on the READDIR,
with the detailed results as follows:
o PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
o LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
o LOOKUP "is" --> NFS_OK. The current fh is for /this/is and is
within the pseudo-fs.
o LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the and
is within the pseudo-fs.
o READDIR (fsid, size, ctime, mounted_on_fileid) --> NFS4ERR_MOVED.
Note that the same error would have been returned if /this/is/the
had migrated, when in fact it is because the directory contains
the root of an absent fs.
So now suppose that we reissue with rdattr_error:
o PUTROOTFH
o LOOKUP "this"
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o LOOKUP "is"
o LOOKUP "the"
o READDIR (rdattr_error, fsid, size, ctime, 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, ctime, mounted_on_fileid) -->
NFS_OK. The attributes for "path" will only contain rdattr_error
with the value will be NFS4ERR_MOVED, together with an fsid value
and an a value for mounted_on_fileid.
So suppose we do another READDIR to get fs_locations_info, although
we could have used a GETATTR directly, as in the previous section.
o PUTROOTFH
o LOOKUP "this"
o LOOKUP "is"
o LOOKUP "the"
o READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
size, ctime)
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.
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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 (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
size, ctime) --> NFS_OK. The attributes will be as shown below.
The attributes for "path" will only contain
o rdattr_error (value: NFS4ERR_MOVED)
o fs_locations_info )
o mounted_on_fileid (value: unique fileid within referring fs)
o fsid (value: unique value within referring server)
The attribute entry for "latest" will not contain size or ctime.
10.8. The Attribute fs_absent
In order to provide the client information about whether the current
file system is present or absent, the fs_absent attribute may be
interrogated.
As noted above, this attribute, when supported, may be requested of
absent file systems without causing NFS4ERR_MOVED to be returned and
it should always be available. Servers are strongly urged to support
this attribute on all file systems if they support it on any file
system.
10.9. The Attribute fs_locations
The fs_locations attribute is structured in the following way:
struct fs_location {
utf8str_cis server<>;
pathname4 rootpath;
};
struct fs_locations {
pathname4 fs_root;
fs_location locations<>;
};
The fs_location struct is used to represent the location of a file
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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 an UTF8 string and represents one of a
traditional DNS host name, IPv4 address, or IPv6 address. It is not
a requirement that all servers that share the same rootpath be listed
in one fs_location struct. The array of server names is provided for
convenience. Servers that share the same rootpath may also be listed
in separate fs_location entries in the fs_locations attribute.
The fs_locations struct and attribute contains an array of such
locations. Since the name space 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 name space, 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.
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 name space at "/a/b/c".
When the client switches to servB, it will need to determine that the
directory it first referenced at servA is now represented by the path
"/x/y/z/d" on servB. To facilitate this, the fs_locations attribute
provided by servA would have a fs_root value of "/a/b/c" and two
entries in fs_locations. One entry in fs_locations will be for
itself (servA) and the other will be for servB with a path of
"/x/y/z". With this information, the client is able to substitute
"/x/y/z" for the "/a/b/c" at the beginning of its access path and
construct "/x/y/z/d" to use for the new server.
Since fs_locations attribute lacks information defining various
attributes of the various file system choices presented, it should
only be interrogated and used when fs_locations_info is not
available. When fs_locations is used, information about the specific
locations should be assumed based on the following rules.
The following rules are general and apply irrespective of the
context.
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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.
For other class assignments, handling depends of file system
transitions depends on the reasons for the transition:
o When the transition is due to migration, the target should be
treated as being of the same _verifier_ class as the source.
o When the transition is due to failover to another replica, the
target should be treated as being of a different _verifier_ class
from the source.
The specific choices reflect typical implementation patterns for
failover and controlled migration respectively. Since other choices
are possible and useful, this information is better obtained by using
fs_locations_info.
See the section "Security Considerations" for a discussion on the
recommendations for the security flavor to be used by any GETATTR
operation that requests the "fs_locations" attribute.
10.10. The Attribute fs_locations_info
The fs_locations_info attribute is intended as a more functional
replacement for fs_locations which will continue to exist and be
supported. Clients can use it get a more complete set of information
about alternative file system locations. When the server does not
support fs_locations_info, fs_locations can be used to get a subset
of the information. A server which supports fs_locations_info MUST
support fs_locations as well.
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There are several sorts of additional information present in
fs_locations_info, that aren't available in fs_locations:
o Attribute continuity information to allow a client to select a
location which meets the transparency requirements of the
applications accessing the data and to take advantage of
optimizations that server guarantees as to attribute continuity
may provide (e.g. change attribute).
o File System identity information which indicates when multiple
replicas, from the clients point of view, correspond to the same
target file system, allowing them to be used interchangeably,
without disruption, as multiple paths to the same thing.
o Information which will bear on the suitability of various
replicas, depending on the use that the client intends. For
example, many applications need an absolutely up-to-date copy
(e.g. those that write), while others may only need access to the
most up-to-date copy reasonably available.
o Server-derived preference information for replicas, which can be
used to implement load-balancing while giving the client the
entire fs list to be used in case the primary fails.
The fs_locations_info attribute consists of a root pathname (just
like fs_locations), together with an array of location4_item
structures.
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struct locations4_server {
int32_t currency;
opaque info<>;
utf8str_cis server;
};
const LIBX_GFLAGS = 0;
const LIBX_TFLAGS = 1;
const LIBX_CLSIMUL = 2;
const LIBX_CLHANDLE = 3;
const LIBX_CLFILEID = 4;
const LIBX_CLVERIFIER = 5;
const LIBX_CHANGE = 6;
const LIBX_READRANK = 7;
const LIBX_WRITERANK = 8;
const LIBX_READORDER = 9;
const LIBX_WRITEORDER = 10;
const LIGF_WRITABLE = 0x01;
const LIGF_CUR_REQ = 0x02;
const LIGF_ABSENT = 0x04;
const LIGF_GOING = 0x08;
const LIGF_SPLIT = 0x10;
const LITF_RDMA = 0x01;
struct locations4_item {
locations4_server entries<>;
pathname4 rootpath;
};
struct locations4_info {
uint32_t info_flags;
pathname4 fs_root;
locations4_item items<>;
};
const LIIF_VAR_SUB = 0x00000001;
The fs_locations_info attribute is structured similarly to the
fs_locations attribute. A top-level structure (fs_locations4 or
locations4_info) contains the entire attribute including the root
pathname of the fs and an array of lower-level structures that define
replicas that share a common root path on their respective servers.
Those lower-level structures in turn (fs_locations4 or
location4_item) contain a specific pathname and information on one or
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more individual server replicas. For that last lowest-level
information, fs_locations has a server name in the form of
utf8str_cis, while fs_locations_info has a location4_server structure
that contains per-server-replica information in addition to the
server name.
As noted above, the fs_locations_info attribute, when supported, may
be requested of absent file systems without causing NFS4ERR_MOVED to
be returned and it is generally expected that it will be available
for both present and absent file systems even if only a single
location_server entry is present, designating the current (present)
file system, or two location_server entries designating the current
(and now previous) location of an absent file system and its
successor location. Servers are strongly urged to support this
attribute on all file systems if they support it on any file system.
10.10.1. The location4_server Structure
The location4_server structure consists of the following items:
o An indication of file system up-to-date-ness (currency) in terms
of approximate seconds before the present. A negative value
indicates that the server is unable to give any reasonably useful
value here. A zero indicates that file system is the actual
writable data or a reliably coherent and fully up-to-date copy.
Positive values indicate how out- of-date this copy can normally
be before it is considered for update. Such a value is not a
guarantee that such updates will always be performed on the
required schedule but instead serve as a hint about how far behind
the most up-to-date copy of the data, this copy would normally be
expected to be.
o A counted array of one-byte values containing various sorts of
data, about the particular file system instance. This data
includes general flags, transport capability flags, file system
equivalence class information, and selection priority information.
The encoding will be discussed below.
o The server string. For the case of the replica currently being
accessed (via GETATTR), a null string may be used to indicate the
current address being used for the RPC call.
Data within the info array, is in the form of 8-bit data items with
constants giving the offsets within the array of various values
describing this particular file system instance. This style of
definition was chosen, in preference to explicit XDR structure
definitions for these values for a number of reasons.
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o The kinds of data in the info array, representing, flags, file
system classes and priorities among set of file systems
representing the same data are such that eight bits provides a
quite acceptable range of values. Even where there might be more
than 256 such file system instances, having more than 256 distinct
classes or priorities is unlikely.
o Explicit definition of the various specific data items within XDR
would limit expandability in that any extension within a
subsequent minor version would require yet another attribute,
leading to specification and implementation clumsiness.
o Such explicit definitions would also make it impossible to propose
standards-track extensions apart from a full minor version.
This encoding scheme can be adapted to the specification of multi-
byte numeric values, even though none are currently defined. If
extensions are made via standards-track RFC's, multi-byte quantities
will be encoded as a range of bytes with a range of indices with the
bytes interpreted in network byte order.
The set of info data is subject to expansion in a future minor
version, or in a standard-track RFC, within the context of a single
minor version. The server SHOULD NOT send and the client MUST not
use indices within the info array that are not defined in standards-
track RFC's.
The info array contains within it:
o Two 8-bit flag fields, one devoted to general file-system
characteristics and a second reserved for transport-related
capabilities.
o Four 8-bit class values which define various file system
equivalence classes as explained below.
o Four 8-bit priority values which govern file system selection as
explained below.
The general file system characteristics flag (at byte index
LIBX_GFLAGS) has the following bits defined within it:
o LIGF_WRITABLE indicates that this fs target is writable, allowing
it to be selected by clients which may need to write on this file
system. When the current file system instance is writable, then
any other file system to which the client might switch must
incorporate within its data any committed write made on the
current file system instance. See the section on verifier class,
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for issues related to uncommitted writes. While there is no harm
in not setting this flag for a file system that turns out to be
writable, turning the flag on for read-only file system can cause
problems for clients who select a migration or replication target
based on it and then find themselves unable to write.
o LIGF_CUR_REQ indicates that this replica is the one on which the
request is being made. Only a single server entry may have this
flag set and in the case of a referral, no entry will have it.
o LIGF_ABSENT indicates that this entry corresponds an absent file
system replica. It can only be set if LIGF_CUR_REQ is set. When
both such bits are set it indicates that a file system instance is
not usable but that the information in the entry can be used to
determine the sorts of continuity available when switching from
this replica to other possible replicas. Since this bit can only
be true if LIGF_CUR_REQ is true, the value could be determined
using the fs_absent attribute but the information is also made
available here for the convenience of the client. An entry with
this bit, since it represents a true file system (albeit absent)
does not appear in the event of a referral, but only where a file
system has been accessed at this location and subsequently been
migrated.
o LIGF_GOING indicates that a replica, while still available, should
not be used further. The client, if using it, should make an
orderly transfer to another file system instance as expeditiously
as possible. It is expected that file systems going out of
service will be announced as LIGF_GOING some time before the
actual loss of service and that the valid_for value will be
sufficiently small to allow clients to detect and act on scheduled
events while large enough that the cost of the requests to fetch
the fs_locations_info values will not be excessive. Values on the
order of ten minutes seem reasonable.
o LIGF_SPLIT indicates that when a transition occurs from the
current filesystem instance to this one, the replacement may
consist of multiple filesystems. In this case, the client has to
be prepared for the possibility that objects on the same fs before
migration will be on different ones after. Note that LIGF_SPLIT
is not incompatible with the filesystems belong to the same
_fileid_ class since, if one has a set of fileid's that are unique
within an fs, each subset assigned to a smaller fs after migration
would not have any conflicts internal to that fs.
A client, in the case of a split filesystem will interrogate
existing files with which it has continuing connection (it is free
simply forget cached filehandles). If the client remembers the
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directory filehandle associated with each open file, it may
proceed upward using LOOKUPP to find the new fs boundaries.
Once the client recognizes that one filesystem has been split into
two, it could maintain applications running without disruption by
presenting the two filesystems as a single one until a convenient
point to recognize the transition, such as a reboot. This would
require a mapping of fsid's from the server's fsid's to fsid's as
seen by the client but this already necessary for other reasons
anyway. As noted above, existing fileids within the two
descendant fs's will not conflict. Creation of new files in the
two descendent fs's may require some amount of fileid mapping
which can be performed very simply in many important cases.
The transport-flag field (at byte index LIBX_TFLAGS) contains the
following bits related to the transport capabilities of the specific
file system.
o LITF_RDMA indicates that this file system provides NFSv4.1 file
system access using an RDMA-capable transport.
Attribute continuity and file system identity information are
expressed by defining equivalence relations on the sets of file
systems presented to the client. Each such relation is expressed as
a set of file system equivalence classes. For each relation, a file
system has an 8-bit class number. Two file systems belong to the
same class if both have identical non-zero class numbers. Zero is
treated as non-matching. Most often, the relevant question for the
client will be whether a given replica is identical-to/
continuous-with the current one in a given respect but the
information should be available also as to whether two other replicas
match in that respect as well.
The following fields specify the file system's class numbers for the
equivalence relations used in determining the nature of file system
transitions. See Section 10.6 for details about how this information
is to be used.
o The field with byte-index LIBX_CLSIMUL defines the simultaneous-
use class for the file system.
o The field with byte-index LIBX_CLHANDLE defines the handle class
for the file system.
o The field with byte-index LIBX_CLFILEID defines the fileid class
for the file system.
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o The field with byte-index LIBX_CLVERIFIER defines the verifier
class for the file system.
o The field with byte-index LIBX_CLCHANGE defines the change class
for the file system.
Server-specified preference information is also provided via 8-bit
values within the info array. The values provide a rank and an order
(see below) to be used with separate values specifiable for the cases
of read-only and writable file systems. These values are compared
for different file systems to establish the server-specified
preference, with lower values indicating "more preferred".
Rank is used to express a strict server-imposed ordering on clients,
with lower values indicating "more preferred." Clients should
attempt to use all replicas with a given rank before they use one
with a higher rank. Only if all of those file systems are
unavailable should the client proceed to those of a higher rank.
Within a rank, the order value is used to specify the server's
preference to guide the client's selection when the client's own
preferences are not controlling, with lower values of order
indicating "more preferred." If replicas are approximately equal in
all respects, clients should defer to the order specified by the
server. When clients look at server latency as part of their
selection, they are free to use this criterion but it is suggested
that when latency differences are not significant, the server-
specified order should guide selection.
o The field at byte index LIBX_READRANK gives the rank value to be
used for read-only access.
o The field at byte index LIBX_READOREDER gives the order value to
be used for read-only access.
o The field at byte index LIBX_WRITERANK gives the rank value to be
used for writable access.
o The field at byte index LIBX_WRITEOREDER gives the order value to
be used for writable access.
Depending on the potential need for write access by a given client,
one of the pairs of rank and order values is used. The read rank and
order should only be used if the client knows that only reading will
ever be done or if it is prepared to switch to a different replica in
the event that any write access capability is required in the future.
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10.10.2. The location4_info Structure
The locations4_info structure, encoding the fs_locations_info
attribute contains the following:
o The info_flags field which contains general flags that affect the
interpretation of this location4_info structures and all
location4_item structures within it. The only flag currently
defined is LIIF_VAR_SUB. All bits in flag field which are not
defined should always be returned as zero.
o The fs_root field which contains the pathname of the root of the
current file system on the current server, just as it does the
fs_locations4 structure.
o An array of locations4_item structures, which contain information
about replicas of the current file system. Where the current file
system is actually present, or has been present, i.e. this is not
a referral situation, one of the locations4_item structure will
contain a locations4_server for the current server. This
structure will have LIGF_ABSENT set if the current file system is
absent, i.e. normal access to it will return NFS4ERR_MOVED.
o The valid_for field specifies a time for which it is reasonable
for a client to use the fs_locations_info attribute without
refetch. The valid_for value does not provide a guarantee of
validity since servers can unexpectedly go out of service or
become inaccessible for any number of reasons. Clients are well-
advised to refetch this information for actively accessed file
system at every valid_for seconds. This is particularly important
when file system replicas may go out of service in a controlled
way using the LIGF_GOING flag to communicate an ongoing change.
The server should set valid_for to a value which allows well-
behaved clients to notice the LIGF_GOING flag and make an orderly
switch before the loss of service becomes effective. If this
value is zero, then no refetch interval is appropriate and the
client need not refetch this data on any particular schedule. In
the event of a transition to a new file system instance, a new
value of the fs_locations_info attribute will be fetched at the
destination and it is to be expected that this may have a
different valid_for value, which the client should then use, in
the same fashion as the previous value.
The LIIF_VAR_SUB flag within info_flags controls whether variable
substitution is to be enabled
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10.10.3. The location4_item Structure
The location4_item structure contains a pathname (in the variable
"rootpath") which encodes the path of the target filesystem replicas
on the set of server designated by the included location4_server
entries. The precise manner in which this target location is
specified depends on the value of the LIIF_VAR_SUB flag within the
associated location4_info structure.
If this flag is not set, then rootpath simply designates the location
of the target filesystem within each server's single-server namespace
just as it does for the rootpath within the fs_location structure.
When this bit is set, however, component entries of a certain form
are subject to client-specific variable substitution so as to allow a
degree of namespace non-uniformity in order to accommodate the
selection of client-specific filesystem targets to adapt to different
client architectures or other characteristics.
When such substitution is in effect a variable beginning with the
string "${" and ending with the string "}" and containing a colon is
to be replaced by the client-specific value associated with that
variable. The string "unknown" should be used by the client when it
has no value for such a variable. The pathname resulting from such
substitutions is used to designate the target filesystem, so that
different clients may have different filesystems, corresponding to
that location in the multi-sever namespace.
As mentioned above, such substituted pathname variables contain a
colon. The part before the colon is to be a DNS domain name with the
part after being a case-insensitive alphanumeric string.
Where the domain is "ietf.org", only variable names defined in this
document or subsequent standards-track RFC's are subject to such
substitution. Organizations are free to use their domain names to
create their own sets of client-specific variables, to be subject to
such substitution. In case where such variables are intended to be
used more broadly than a single organization, publication of an
informational RFC defining such variables is recommended.
The variable ${ietf.org:CPU_ARCH} is used to denote the CPU
architecture object files are compiled. This specification does not
limit the acceptable values (except that they must be valid UTF-8
strings) but such values as "x86", "x86_64" and "sparc" would be
expected to be used in line with industry practice.
The variable ${ietf.org:OS_TYPE} is used to denote the operating
system and thus the kernel and library API's for which code might be
compiled. This specification does not limit the acceptable values
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(except that they must be valid UTF-8 strings) but such values as
"linux" and "freebsd" would be expected to be used in line with
industry practice.
The variable ${ietf.org:OS_VERSION} is used to denote the operating
system version and the thus the specific details of versioned
interfaces for which code might be compiled. This specification does
not limit the acceptable values (except that they must be valid UTF-8
strings) but combinations of numbers and letters with interspersed
dots would be expected to be used in line with industry practice,
with the details of the version format depending on the specific
value of the value of the variable ${ietf.org:OS_TYPE} with which it
is used.
Use of these variable could result in direction of different clients
to different file systems on the same server, as appropriate to
particular clients. In cases in which the target filesystems are
located on different servers, a single server could serve as a
referral point so that each valid combination of variable values
would designate a referral hosted on a single server, with the
targets of those referrals on a number of different servers.
Although variable substitution is most suitable for use in the
context of referrals, if may be used in the context of replication
and migration. If it is used in these contexts, the server must
ensure that no matter what values the client presents for the
substituted variables, the result is always a valid successor file
system instance to that from which a transition is occurring, i.e.
that the data is identical or represents a later image of a writable
file system.
Note that when "rootpath" is a null pathname (that is, one with zero
components), the file system designated is at the root of the
specified server, whether the LIIF_VAR_SUB flag within the associated
location4_info structure is set or not.
10.11. The Attribute fs_status
In an environment in which multiple copies of the same basic set of
data are available, information regarding the particular source of
such data and the relationships among different copies, can be very
helpful in providing consistent data to applications.
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enum fs4_status_type {
STATUS4_FIXED = 1,
STATUS4_VERSIONED = 2,
STATUS4_UPDATED = 3,
STATUS4_WRITABLE = 4,
STATUS4_ABSENT = 5
};
struct fs4_status {
fs4_status_type fsstat_type;
utf8str_cs fsstat_source;
utf8str_cs fsstat_current;
int32_t fsstat_age;
nfstime4 fsstat_version;
};
The type value indicates the kind of file system image represented.
This is of particular importance when using the version values to
determine appropriate succession of file system images. Five types
are distinguished:
o STATUS4_FIXED which indicates a read-only image in the sense that
it will never change. The possibility is allowed that as a result
of migration or switch to a different image, changed data can be
accessed but within the confines of this instance, no change is
allowed. The client can use this fact to aggressively cache.
o STATUS4_VERSIONED which indicates that the image, like the
STATUS4_UPDATED case, is updated exogenously, but it provides a
guarantee that the server will carefully update an associated
version value so that the client can protect itself from a
situation in which it reads data from one version of the file
system, and then later reads data from an earlier version of the
same file system. See below for a discussion of how this can be
done.
o STATUS4_UPDATED which indicates an image that cannot be updated by
the user writing to it but may be changed exogenously, typically
because it is a periodically updated copy of another writable file
system somewhere else. In this case, version information is not
provided and the client does not have the responsibility of making
sure that this version only advances upon a file system instance
transition. In this case, it is the responsibility of the server
to make sure that the data presented after a file system instance
transition is a proper successor image and includes all changes
seen by the client and any change made before all such changes.
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o STATUS4_WRITABLE which indicates that the file system is an actual
writable one. The client need not of course actually write to the
file system, but once it does, it should not accept a transition
to anything other than a writable instance of that same file
system.
o STATUS4_ABSENT which indicates that the information is the last
valid for a file system which is no longer present.
The opaque strings source and current provide a way of presenting
information about the source of the file system image being present.
It is not intended that client do anything with this information
other than make it available to administrative tools. It is intended
that this information be helpful when researching possible problems
with a file system image that might arise when it is unclear if the
correct image is being accessed and if not, how that image came to be
made. This kind of debugging information will be helpful, if, as
seems likely, copies of file systems are made in many different ways
(e.g. simple user-level copies, file system- level point-in-time
copies, cloning of the underlying storage), under a variety of
administrative arrangements. In such environments, determining how a
given set of data was constructed can be very helpful in resolving
problems.
The opaque string 'source' is used to indicate the source of a given
file system with the expectation that tools capable of creating a
file system image propagate this information, when that is possible.
It is understood that this may not always be possible since a user-
level copy may be thought of as creating a new data set and the tools
used may have no mechanism to propagate this data. When a file
system is initially created associating with it data regarding how
the file system was created, where it was created, by whom, etc. can
be put in this attribute in a human- readable string form so that it
will be available when propagated to subsequent copies of this data.
The opaque string 'current' should provide whatever information is
available about the source of the current copy. Such information as
the tool creating it, any relevant parameters to that tool, the time
at which the copy was done, the user making the change, the server on
which the change was made etc. All information should be in a human-
readable string form.
The age provides an indication of how out-of-date the file system
currently is with respect to its ultimate data source (in case of
cascading data updates). This complements the currency field of
locations4_server (See Section 10.10) in the following way: the
information in locations4_server.currency gives a bound for how out
of date the data in a file system might typically get, while the age
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gives a bound on how out of date that data actually is. Negative
values imply no information is available. A zero means that this
data is known to be current. A positive value means that this data
is known to be no older than that number of seconds with respect to
the ultimate data source.
The version field provides a version identification, in the form of a
time value, such that successive versions always have later time
values. When the file system type is anything other than
STATUS4_VERSIONED, the server may provide such a value but there is
no guarantee as to its validity and clients will not use it except to
provide additional information to add to 'source' and 'current'.
When the type is STATUS4_VERSIONED, servers should provide a value of
version which progresses monotonically whenever any new version of
the data is established. This allows the client, if reliable image
progression is important to it, to fetch this attribute as part of
each COMPOUND where data or metadata from the file system is used.
When it is important to the client to make sure that only valid
successor images are accepted, it must make sure that it does not
read data or metadata from the file system without updating its sense
of the current state of the image, to avoid the possibility that the
fs_status which the client holds will be one for an earlier image,
and so accept a new file system instance which is later than that but
still earlier than updated data read by the client.
In order to do this reliably, it must do a GETATTR of fs_status that
follows any interrogation of data or metadata within the file system
in question. Often this is most conveniently done by appending such
a GETATTR after all other operations that reference a given file
system. When errors occur between reading file system data and
performing such a GETATTR, care must be exercised to make sure that
the data in question is not used before obtaining the proper
fs_status value. In this connection, when an OPEN is done within
such a versioned file system and the associated GETATTR of fs_status
is not successfully completed, the open file in question must not be
accessed until that fs_status is fetched.
The procedure above will ensure that before using any data from the
file system the client has in hand a newly-fetched current version of
the file system image. Multiple values for multiple requests in
flight can be resolved by assembling them into the required partial
order (and the elements should form a total order within it) and
using the last. The client may then, when switching among file
system instances, decline to use an instance which is not of type
STATUS4_VERSIONED or whose version field is earlier than the last one
obtained from the predecessor file system instance.
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11. Directory Delegations
11.1. Introduction to Directory Delegations
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 receives 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. This
reduces network traffic and server load by allowing the client to
perform certain operations on local file data and can also provide
stronger consistency for the local data.
Directory caching for the NFS version 4 protocol is similar to
previous versions. Clients typically cache directory information for
a duration determined by the client. At the end of a predefined
timeout, the client will query the server to see if the directory has
been updated. By caching attributes, clients reduce the number of
GETATTR calls made to the server to validate attributes.
Furthermore, frequently accessed files and directories, such as the
current working directory, have their attributes cached on the client
so that some NFS operations can be performed without having to make
an RPC call. By caching name and inode information about most
recently looked up entries in DNLC (Directory Name Lookup Cache),
clients do not need to send LOOKUP calls to the server every time
these files are accessed.
This caching approach works reasonably well at reducing network
traffic in many environments. However, it does not address
environments where there are numerous queries for files that do not
exist. In these cases of "misses", the client must make RPC calls to
the server in order to provide reasonable application semantics and
promptly detect the creation of new directory entries. Examples of
high miss activity are compilation in software development
environments. The current behavior of NFS limits its potential
scalability and wide-area sharing effectiveness in these types of
environments. Other distributed stateful filesystem architectures
such as AFS and DFS have proven that adding state around directory
contents can greatly reduce network traffic in high miss
environments.
Delegation of directory contents is proposed as an extension for
NFSv4. Such an extension would provide similar traffic reduction
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benefits as with file delegations. By allowing clients to cache
directory contents (in a read-only fashion) while being notified of
changes, the client can avoid making frequent requests to interrogate
the contents of slowly-changing directories, reducing network traffic
and improving client performance.
These extensions allow improved namespace cache consistency to be
achieved through delegations and synchronous recalls alone without
asking for notifications. In addition, if time-based consistency is
sufficient, asynchronous notifications can provide performance
benefits for the client, and possibly the server, under some common
operating conditions such as slowly-changing and/or very large
directories.
11.2. Directory Delegation Design (in brief)
A new operation GET_DIR_DELEGATION is used by the client to ask for a
directory delegation. The delegation covers directory attributes and
all entries in the directory. If either of these change the
delegation will be recalled synchronously. The operation causing the
recall will have to wait before the recall is complete. Any changes
to directory entry attributes will not cause the delegation to be
recalled.
In addition to asking for delegations, a client can also ask for
notifications for certain events. These events include changes to
directory attributes and/or its contents. If a client asks for
notification for a certain event, the server will notify the client
when that event occurs. This will not result in the delegation being
recalled for that client. The notifications are asynchronous and
provide a way of avoiding recalls in situations where a directory is
changing enough that the pure recall model may not be effective while
trying to allow the client to get substantial benefit. In the
absence of notifications, once the delegation is recalled the client
has to refresh its directory cache which might not be very efficient
for very large directories.
The delegation is read only and the client may not make changes to
the directory other than by performing NFSv4 operations that modify
the directory or the associated file attributes so that the server
has knowledge of these changes. In order to keep the client
namespace in sync with the server, the server will notify the client
holding the delegation of the changes made as a result. This is to
avoid any subsequent GETATTR or READDIR calls to the server. If a
client holding the delegation makes any changes to the directory, the
delegation will not be recalled.
Delegations can be recalled by the server at any time. Normally, the
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server will recall the delegation when the directory changes in a way
that is not covered by the notification, or when the directory
changes and notifications have not been requested.
Also if the server notices that handing out a delegation for a
directory is causing too many notifications to be sent out, it may
decide not to hand out a delegation for that directory or recall
existing delegations. If another client removes the directory for
which a delegation has been granted, the server will recall the
delegation.
Both the notification and recall operations need a callback path to
exist between the client and server. If the callback path does not
exist, then delegation can not be granted. Note that with the
session extensions [talpey] that should not be an issue. In the
absence of sessions, the server will have to establish a callback
path to the client to send callbacks.
11.3. Recommended Attributes in support of Directory Delegations
dir_notif_delay - notification delays on directory attributes
dir_entry_notif_delay - notification delays on child attributes
These attributes allow the client and server to negotiate the
frequency of notifications sent due to changes in attributes. These
attributes are returned as part of a GETATTR call on the directory.
The dir_notif_delay value covers all attribute changes to the
directory and the dir_entry_notif_delay covers all attribute changes
to any child in the directory.
These attributes are per directory. The client needs to get these
values by doing a GETATTR on the directory for which it wants
notifications. However these attributes are only required when the
client is interested in getting attribute notifications. For all
other types of notifications and delegation requests without
notifications, these attributes are not required.
When the client calls the GET_DIR_DELEGATION operation and asks for
attribute change notifications, it should request notification delays
that are no less than the values in the server-provided attributes.
If the client requests smaller delays, the server should not commit
to sending notifications for that change event.
A value of zero for these attributes means the server will send the
notification as soon as the change occurs. It is not recommended to
set this value to zero since that can put a lot of burden on the
server.nfstime4 values that compute to negative values are illegal.
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By granting a request for notifications, the server commits to
delaying notifications to that client by no more than the
notification delay which the client requested.
11.4. Delegation Recall
The server will recall the directory delegation by sending a callback
to the client. It will use the same callback procedure as used for
recalling file delegations. The server will recall the delegation
when the directory changes in a way that is not covered by the
notification. However the server will not recall the delegation if
attributes of an entry within the directory change. Also if the
server notices that handing out a delegation for a directory is
causing too many notifications to be sent out, it may decide not to
hand out a delegation for that directory. If another client tries to
remove the directory for which a delegation has been granted, the
server will recall the delegation.
The server will recall the delegation by sending a CB_RECALL callback
to the client. If the recall is done because of a directory changing
event, the request making that change will need to wait while the
client returns the delegation.
11.5. Directory Delegation Recovery
Crash recovery has two main goals, avoiding the necessity of breaking
application guarantees with respect to locked files and delivery of
updates cached at the client. Neither of these applies to
directories protected by read delegations and notifications. Thus,
the client is required to establish a new delegation on a server or
client reboot. [[Comment.14: we have special reclaim types allow
clients to recovery delegations through client reboot. Do we really
want EXCHANGE_ID/CREATE_SESSION to destroy directory delegation
state?]]
12. Parallel NFS (pNFS)
12.1. Introduction
The NFSv4.0 protocol [2] specifies the interaction between a client
that accesses files and a server that provides access to files and is
responsible for coordinating access by multiple clients. As
described in the pNFS problem statement, this requires that all
access to a set of files exported by a single NFSv4 server be
performed by that server; at high data rates the server may become a
bottleneck.
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The parallel NFS (pNFS) extensions to NFSv4 allow data accesses to
bypass this bottleneck by permitting direct client access to the
storage devices containing the file data. When file data for a
single NFSv4 server is stored on multiple and/or higher throughput
storage devices (by comparison to the server's throughput
capability), the result can be significantly better file access
performance. The relationship among multiple clients, a single
server, and multiple storage devices for pNFS (server and clients
have access to all storage devices) is shown in this diagram:
+-----------+
|+-----------+ +-----------+
||+-----------+ | |
||| | NFSv4 + pNFS | |
+|| Clients |<------------------------------>| Server |
+| | | |
+-----------+ | |
||| +-----------+
||| |
||| |
||| Storage +-----------+ |
||| Protocol |+-----------+ |
||+----------------||+-----------+ Control|
|+-----------------||| | Protocol|
+------------------+|| Storage |------------+
+| Devices |
+-----------+
Figure 61
In this structure, the responsibility for coordination of file access
by multiple clients is shared among the server, clients, and storage
devices. This is in contrast to NFSv4 without pNFS extensions, in
which this is primarily the server's responsibility, some of which
can be delegated to clients under strictly specified conditions.
The pNFS extension to NFSv4 takes the form of new operations that
manage data location information called a "layout". The layout is
managed in a similar fashion as NFSv4 data delegations (e.g., they
are recallable and revocable). However, they are distinct
abstractions and are manipulated with new operations. When a client
holds a layout, it has rights to access the data directly using the
location information in the layout.
There are new attributes that describe general layout
characteristics. However, much of the required information cannot be
managed solely within the attribute framework, because it will need
to have a strictly limited term of validity, subject to invalidation
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by the server. This requires the use of new operations to obtain,
return, recall, and modify layouts, in addition to new attributes.
This document specifies both the NFSv4 extensions required to
distribute file access coordination between the server and its
clients and a NFSv4 file storage protocol that may be used to access
data stored on NFSv4 storage devices.
Storage protocols used to access a variety of other storage devices
are deliberately not specified here. These might include:
o Block/volume protocols such as iSCSI ([29]), and FCP ([30]). The
block/volume protocol support can be independent of the addressing
structure of the block/volume protocol used, allowing more than
one protocol to access the same file data and enabling
extensibility to other block/volume protocols.
o Object protocols such as OSD over iSCSI or Fibre Channel [31].
o Other storage protocols, including PVFS and other file systems
that are in use in HPC environments.
pNFS is designed to accommodate these protocols and be extensible to
new classes of storage protocols that may be of interest.
The distribution of file access coordination between the server and
its clients increases the level of responsibility placed on clients.
Clients are already responsible for ensuring that suitable access
checks are made to cached data and that attributes are suitably
propagated to the server. Generally, a misbehaving client that hosts
only a single-user can only impact files accessible to that single
user. Misbehavior by a client hosting multiple users may impact
files accessible to all of its users. NFSv4 delegations increase the
level of client responsibility as a client that carries out actions
requiring a delegation without obtaining that delegation will cause
its user(s) to see unexpected and/or incorrect behavior.
Some uses of pNFS extend the responsibility of clients beyond
delegations. In some configurations, the storage devices cannot
perform fine-grained access checks to ensure that clients are only
performing accesses within the bounds permitted to them by the pNFS
operations with the server (e.g., the checks may only be possible at
file system granularity rather than file granularity). In situations
where this added responsibility placed on clients creates
unacceptable security risks, pNFS configurations in which storage
devices cannot perform fine-grained access checks SHOULD NOT be used.
All pNFS server implementations MUST support NFSv4 access to any file
accessible via pNFS in order to provide an interoperable means of
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file access in such situations. See Section 12.3.8 on Security for
further discussion.
Finally, there are issues about how layouts interact with the
existing NFSv4 abstractions of data delegations and byte range
locking. These issues, and others, are also discussed here.
12.2. General Definitions
This protocol extension partitions the NFSv4 file system protocol
into two parts, the control path and the data path. The control path
is implemented by the extended (p)NFSv4 server. When the file system
being exported by (p)NFSv4 uses storage devices that are visible to
clients over the network, the data path may be implemented by direct
communication between the extended (p)NFSv4 file system client and
the storage devices. This leads to a few new terms used to describe
the protocol extension and some clarifications of existing terms.
12.2.1. Metadata Server
A pNFS "server" or "metadata server" is a server as defined by
RFC3530 [2], which additionally provides support of the pNFS minor
extension. When using the pNFS NFSv4 minor extension, the metadata
server may hold only the metadata associated with a file, while the
data can be stored on the storage devices. However, similar to
NFSv4, data may also be written through the metadata server. Note:
directory data is always accessed through the metadata server.
12.2.2. Client
A pNFS "client" is a client as defined by RFC3530 [2], with the
addition of supporting the pNFS minor extension server protocol and
with the addition of supporting at least one storage protocol for
performing I/O directly to storage devices.
12.2.3. Storage Device
This is a device, or server, that controls the file's data, but
leaves other metadata management up to the metadata server. A
storage device could be another NFS server, or an Object Storage
Device (OSD) or a block device accessed over a SAN (e.g., either
FiberChannel or iSCSI SAN). The goal of this extension is to allow
direct communication between clients and storage devices.
12.2.4. Storage Protocol
This is the protocol between the pNFS client and the storage device
used to access the file data. Three following types have been
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described: file protocols (e.g., NFSv4), object protocols (e.g.,
OSD), and block/volume protocols (e.g., based on SCSI-block
commands). These protocols are in turn realizable over a variety of
transport stacks. We anticipate there will be variations on these
storage protocols, including new protocols that are unknown at this
time or experimental in nature. The details of the storage protocols
will be described in other documents so that pNFS clients can be
written to use these storage protocols. Use of NFSv4 itself as a
file-based storage protocol is described in Section 12.4.
12.2.5. Control Protocol
This is a protocol used by the exported file system between the
server and storage devices. Specification of such protocols is
outside the scope of this draft. Such control protocols would be
used to control such activities as the allocation and deallocation of
storage and the management of state required by the storage devices
to perform client access control. The control protocol should not be
confused with protocols used to manage LUNs in a SAN and other
sysadmin kinds of tasks.
While the pNFS protocol allows for any control protocol, in practice
the control protocol is closely related to the storage protocol. For
example, if the storage devices are NFS servers, then the protocol
between the pNFS metadata server and the storage devices is likely to
involve NFS operations. Similarly, when object storage devices are
used, the pNFS metadata server will likely use iSCSI/OSD commands to
manipulate storage.
However, this document does not mandate any particular control
protocol. Instead, it just describes the requirements on the control
protocol for maintaining attributes like modify time, the change
attribute, and the end-of-file position.
12.2.6. Metadata
This is information about a file, like its name, owner, where it
stored, and so forth. The information is managed by the exported
file system server (metadata server). Metadata also includes lower-
level information like block addresses and indirect block pointers.
Depending the storage protocol, block-level metadata may or may not
be managed by the metadata server, but is instead managed by Object
Storage Devices or other servers acting as a storage device.
12.2.7. Layout
A layout defines how a file's data is organized on one or more
storage devices. There are many possible layout types. They vary in
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the storage protocol used to access the data, and in the aggregation
scheme that lays out the file data on the underlying storage devices.
Layouts are described in more detail below.
12.3. pNFS protocol semantics
This section describes the semantics of the pNFS protocol extension
to NFSv4; this is the protocol between the client and the metadata
server.
12.3.1. Definitions
This sub-section defines a number of terms necessary for describing
layouts and their semantics. In addition, it more precisely defines
how layouts are identified and how they can be composed of smaller
granularity layout segments.
12.3.1.1. Layout Types
A layout describes the mapping of a file's data to the storage
devices that hold the data. A layout is said to belong to a specific
"layout type" (see Section 3.2.18 for its RPC definition). The
layout type allows for variants to handle different storage protocols
(e.g., block/volume [24], object [23], and file [Section 12.4] layout
types). A metadata server, along with its control protocol, must
support at least one layout type. A private sub-range of the layout
type name space is also defined. Values from the private layout type
range can be used for internal testing or experimentation.
As an example, a file layout type could be an array of tuples (e.g.,
deviceID, file_handle), along with a definition of how the data is
stored across the devices (e.g., striping). A block/volume layout
might be an array of tuples that store <deviceID, block_number, block
count> along with information about block size and the file offset of
the first block. An object layout might be an array of tuples
<deviceID, objectID> and an additional structure (i.e., the
aggregation map) that defines how the logical byte sequence of the
file data is serialized into the different objects. Note, the actual
layouts are more complex than these simple expository examples.
This document defines a NFSv4 file layout type using a stripe-based
aggregation scheme (see Section 12.4). Adjunct specifications are
being drafted that precisely define other layout formats (e.g.,
block/volume [24], and object [23] layouts) to allow interoperability
among clients and metadata servers.
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12.3.1.2. Layout Iomode
The iomode indicates to the metadata server the client's intent to
perform either READs (only) or a mixture of I/O possibly containing
WRITEs as well as READs (i.e., READ/WRITE). For certain layout
types, it is useful for a client to specify this intent at LAYOUTGET
time. E.g., for block/volume based protocols, block allocation could
occur when a READ/WRITE iomode is specified. A special
LAYOUTIOMODE_ANY iomode is defined and can only be used for
LAYOUTRETURN and LAYOUTRECALL, not for LAYOUTGET. It specifies that
layouts pertaining to both READ and RW iomodes are being returned or
recalled, respectively.
A storage device may validate I/O with regards to the iomode; this is
dependent upon storage device implementation. Thus, if the client's
layout iomode differs from the I/O being performed the storage device
may reject the client's I/O with an error indicating a new layout
with the correct I/O mode should be fetched. E.g., if a client gets
a layout with a READ iomode and performs a WRITE to a storage device,
the storage device is allowed to reject that WRITE.
The iomode does not conflict with OPEN share modes or lock requests;
open mode checks and lock enforcement are always enforced, and are
logically separate from the pNFS layout level. As well, open modes
and locks are the preferred method for restricting user access to
data files. E.g., an OPEN of read, deny-write does not conflict with
a LAYOUTGET containing an iomode of READ/WRITE performed by another
client. Applications that depend on writing into the same file
concurrently may use byte range locking to serialize their accesses.
12.3.1.3. Layout Segments
Until this point, layouts have been defined in a fairly vague manner.
A layout is more precisely identified by the following tuple:
<ClientID, FH, layout type>; the FH refers to the FH of the file on
the metadata server. Note, layouts describe a file, not a byte-range
of a file.
Since a layout that describes an entire file may be very large, there
is a desire to manage layouts in smaller chunks that correspond to
byte-ranges of the file. For example, the entire layout need not be
returned, recalled, or committed. These chunks are called "layout
segments" and are further identified by the byte-range they
represent. Layout operations require the identification of the
layout segment (i.e., clientID, FH, layout type, and byte-range), as
well as the iomode. This structure allows clients and metadata
servers to aggregate the results of layout operations into a singly
maintained layout.
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It is important to define when layout segments overlap and/or
conflict with each other. For a layout segment to overlap another
layout segment both segments must be of the same layout type,
correspond to the same filehandle, and have the same iomode; in
addition, the byte-ranges of the segments must overlap. Layout
segments conflict, when they overlap and differ in the content of the
layout (i.e., the storage device/file mapping parameters differ).
Note, differing iomodes do not lead to conflicting layouts. It is
permissible for layout segments with different iomodes, pertaining to
the same byte range, to be held by the same client.
12.3.1.4. Device IDs
The "deviceID" is a short name for a storage device. In practice, a
significant amount of information may be required to fully identify a
storage device. Instead of embedding all that information in a
layout, a level of indirection is used. Layouts embed device IDs,
and a new operation (GETDEVICEINFO) is used to retrieve the complete
identity information about the storage device according to its layout
type. For example, the identity of a file server or object server
could be an IP address and port. The identity of a block device
could be a volume label. Due to multipath connectivity in a SAN
environment, agreement on a volume label is considered the reliable
way to locate a particular storage device.
The device ID is qualified by the layout type and unique per file
system (FSID). This allows different layout drivers to generate
device IDs without the need for co-ordination. In addition to
GETDEVICEINFO, another operation, GETDEVICELIST, has been added to
allow clients to fetch the mappings of multiple storage devices
attached to a metadata server.
Clients cannot expect the mapping between device ID and storage
device address to persist across server reboots, hence a client MUST
fetch new mappings on startup or upon detection of a metadata server
reboot unless it can revalidate its existing mappings. Not all
layout types support such revalidation, and the means of doing so is
layout specific. If data are reorganized from a storage device with
a given device ID to a different storage device (i.e., if the mapping
between storage device and data changes), the layout describing the
data MUST be recalled rather than assigning the new storage device to
the old device ID.
12.3.1.5. Aggregation Schemes
Aggregation schemes can describe layouts like simple one-to-one
mapping, concatenation, and striping. A general aggregation scheme
allows nested maps so that more complex layouts can be compactly
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described. The canonical aggregation type for this extension is
striping, which allows a client to access storage devices in
parallel. Even a one-to-one mapping is useful for a file server that
wishes to distribute its load among a set of other file servers.
12.3.2. Guarantees Provided by Layouts
Layouts delegate to the client the ability to access data out of
band. The layout guarantees the holder that the layout will be
recalled when the state encapsulated by the layout becomes invalid
(e.g., through some operation that directly or indirectly modifies
the layout) or, possibly, when a conflicting layout is requested, as
determined by the layout's iomode. When a layout is recalled, and
then returned by the client, the client retains the ability to access
file data with normal NFSv4 I/O operations through the metadata
server. Only the right to do I/O out-of-band is affected.
Holding a layout does not guarantee that a user of the layout has the
rights to access the data represented by the layout. All user access
rights MUST be obtained through the appropriate open, lock, and
access operations (i.e., those that would be used in the absence of
pNFS). However, if a valid layout for a file is not held by the
client, the storage device should reject all I/Os to that file's byte
range that originate from that client. In summary, layouts and
ordinary file access controls are independent. The act of modifying
a file for which a layout is held, does not necessarily conflict with
the holding of the layout that describes the file being modified.
However, with certain layout types (e.g., block/volume layouts), the
layout's iomode must agree with the type of I/O being performed.
Depending upon the layout type and storage protocol in use, storage
device access permissions may be granted by LAYOUTGET and may be
encoded within the type specific layout. If access permissions are
encoded within the layout, the metadata server must recall the layout
when those permissions become invalid for any reason; for example
when a file becomes unwritable or inaccessible to a client. Note,
clients are still required to perform the appropriate access
operations as described above (e.g., open and lock ops). The degree
to which it is possible for the client to circumvent these access
operations must be clearly addressed by the individual layout type
documents, as well as the consequences of doing so. In addition,
these documents must be clear about the requirements and non-
requirements for the checking performed by the server.
If the pNFS metadata server supports mandatory byte range locks then
byte range locks must behave as specified by the NFSv4 protocol, as
observed by users of files. If a storage device is unable to
restrict access by a pNFS client who does not hold a required
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mandatory byte range lock then the metadata server must not grant
layouts to a client, for that storage device, that permits any access
that conflicts with a mandatory byte range lock held by another
client. In this scenario, it is also necessary for the metadata
server to ensure that byte range locks are not granted to a client if
any other client holds a conflicting layout; in this case all
conflicting layouts must be recalled and returned before the lock
request can be granted. This requires the pNFS server to understand
the capabilities of its storage devices.
12.3.3. Getting a Layout
A client obtains a layout through a new operation, LAYOUTGET. The
metadata server will give out layouts of a particular type (e.g.,
block/volume, object, or file) and aggregation as requested by the
client. The client selects an appropriate layout type which the
server supports and the client is prepared to use. The layout
returned to the client may not line up exactly with the requested
byte range. A field within the LAYOUTGET request, "minlength",
specifies the minimum overlap that MUST exist between the requested
layout and the layout returned by the metadata server. The
"minlength" field should specify a size of at least one. A metadata
server may give-out multiple overlapping, non-conflicting layout
segments to the same client in response to a LAYOUTGET.
There is no implied ordering between getting a layout and performing
a file OPEN. For example, a layout may first be retrieved by placing
a LAYOUTGET operation in the same compound as the initial file OPEN.
Once the layout has been retrieved, it can be held across multiple
OPEN and CLOSE sequences.
The storage protocol used by the client to access the data on the
storage device is determined by the layout's type. The client needs
to select a "layout driver" that understands how to interpret and use
that layout. The API used by the client to talk to its drivers is
outside the scope of the pNFS extension. The storage protocol
between the client's layout driver and the actual storage is covered
by other protocols specifications such as iSCSI (block storage), OSD
(object storage) or NFS (file storage).
Although, the metadata server is in control of the layout for a file,
the pNFS client can provide hints to the server when a file is opened
or created about preferred layout type and aggregation scheme. The
pNFS extension introduces a LAYOUT_HINT attribute that the client can
set at creation time to provide a hint to the server for new files.
It is suggested that this attribute be set as one of the initial
attributes to OPEN when creating a new file. Setting this attribute
separately, after the file has been created could make it difficult,
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or impossible, for the server implementation to comply.
12.3.4. Committing a Layout
Due to the nature of the protocol, the file attributes, and data
location mapping (e.g., which offsets store data vs. store holes)
that exist on the metadata storage device may become inconsistent in
relation to the data stored on the storage devices; e.g., when WRITEs
occur before a layout has been committed (e.g., between a LAYOUTGET
and a LAYOUTCOMMIT). Thus, it is necessary to occasionally re-sync
this state and make it visible to other clients through the metadata
server.
The LAYOUTCOMMIT operation is responsible for committing a modified
layout segment to the metadata server. Note: the data should be
written and committed to the appropriate storage devices before the
LAYOUTCOMMIT occurs. Note, if the data is being written
asynchronously through the metadata server a COMMIT to the metadata
server is required to sync the data and make it visible on the
storage devices (see Section 12.3.6 for more details). The scope of
this operation depends on the storage protocol in use. For block/
volume-based layouts, it may require updating the block list that
comprises the file and committing this layout to stable storage.
While, for file-layouts it requires some synchronization of
attributes between the metadata and storage devices (i.e., mainly the
size attribute; EOF). It is important to note that the level of
synchronization is from the point of view of the client who issued
the LAYOUTCOMMIT. The updated state on the metadata server need only
reflect the state as of the client's last operation previous to the
LAYOUTCOMMIT, it need not reflect a globally synchronized state
(e.g., other clients may be performing, or may have performed I/O
since the client's last operation and the LAYOUTCOMMIT).
The control protocol is free to synchronize the attributes before it
receives a LAYOUTCOMMIT, however upon successful completion of a
LAYOUTCOMMIT, state that exists on the metadata server that describes
the file MUST be in sync with the state existing on the storage
devices that comprise that file as of the issuing client's last
operation. Thus, a client that queries the size of a file between a
WRITE to a storage device and the LAYOUTCOMMIT may observe a size
that does not reflects the actual data written.
12.3.4.1. LAYOUTCOMMIT and mtime/atime/change
The change attribute and the modify/access times may be updated, by
the server, at LAYOUTCOMMIT time; since for some layout types, the
change attribute and atime/mtime can not be updated by the
appropriate I/O operation performed at a storage device. The
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arguments to LAYOUTCOMMIT allow the client to provide suggested
access and modify time values to the server. Again, depending upon
the layout type, these client provided values may or may not be used.
The server should sanity check the client provided values before they
are used. For example, the server should ensure that time does not
flow backwards. According to the NFSv4 specification, The client
always has the option to set these attributes through an explicit
SETATTR operation.
As mentioned, for some layout protocols the change attribute and
mtime/atime may be updated at or after the time the I/O occurred
(e.g., if the storage device is able to communicate these attributes
to the metadata server). If, upon receiving a LAYOUTCOMMIT, the
server implementation is able to determine that the file did not
change since the last time the change attribute was updated (e.g., no
WRITEs or over-writes occurred), the implementation need not update
the change attribute; file-based protocols may have enough state to
make this determination or may update the change attribute upon each
file modification. This also applies for mtime and atime; if the
server implementation is able to determine that the file has not been
modified since the last mtime update, the server need not update
mtime at LAYOUTCOMMIT time. Once LAYOUTCOMMIT completes, the new
change attribute and mtime/atime should be visible if that file was
modified since the latest previous LAYOUTCOMMIT or LAYOUTGET.
12.3.4.2. LAYOUTCOMMIT and size
The file's size may be updated at LAYOUTCOMMIT time as well. The
LAYOUTCOMMIT operation contains an argument ("last_write_offset")
that indicates the highest byte offset written but not yet committed
via LAYOUTCOMMIT. Note: this argument is switched on a boolean value
indicating whether or not a previous write occurred. If the switch
is false, no "last_write_offset" is given; a "last_write_offset"
specifying an offset of 0 means byte 0 was the highest last byte
written.
The metadata server may do one of the following:
1. It may update the file's size based on the last write offset.
However, to the extent possible, the metadata server should
sanity check any value to which the file's size is going to be
set. E.g., it must not truncate the file based on the client
presenting a smaller last write offset than the file's current
size.
2. If it has sufficient other knowledge of file size (e.g., by
querying the storage devices through the control protocol), it
may ignore the client provided argument and use the query-derived
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value.
3. It may use the last write offset as a hint, subject to correction
when other information is available as above.
The method chosen to update the file's size will depend on the
storage device's and/or the control protocol's implementation. For
example, if the storage devices are block devices with no knowledge
of file size, the metadata server must rely on the client to set the
size appropriately. A new size flag and length are also returned in
the results of a LAYOUTCOMMIT. This union indicates whether a new
size was set, and to what length it was set. If a new size is set as
a result of LAYOUTCOMMIT, then the metadata server must reply with
the new size. As well, if the size is updated, the metadata server
in conjunction with the control protocol SHOULD ensure that the new
size is reflected by the storage devices immediately upon return of
the LAYOUTCOMMIT operation; e.g., a READ up to the new file size
should succeed on the storage devices (assuming no intervening
truncations). Again, if the client wants to explicitly zero-extend
or truncate a file, SETATTR must be used; it need not be used when
simply writing past EOF.
12.3.4.3. LAYOUTCOMMIT and layoutupdate
The LAYOUTCOMMIT operation contains a "layoutupdate" argument. This
argument is a layout type specific structure. The structure can be
used to pass arbitrary layout type specific information from the
client to the metadata server at LAYOUTCOMMIT time. For example, if
using a block/volume layout, the client can indicate to the metadata
server which reserved or allocated blocks it used and which it did
not. The "layoutupdate" structure need not be the same structure as
the layout returned by LAYOUTGET. The structure is defined by the
layout type and is opaque to LAYOUTCOMMIT.
12.3.5. Recalling a Layout
12.3.5.1. Basic Operation
Since a layout protects a client's access to a file via a direct
client-storage-device path, a layout need only be recalled when it is
semantically unable to serve this function. Typically, this occurs
when the layout no longer encapsulates the true location of the file
over the byte range it represents. Any operation or action (e.g.,
server driven restriping or load balancing) that changes the layout
will result in a recall of the layout. A layout is recalled by the
CB_LAYOUTRECALL callback operation (see Section 18.3). This callback
can either recall a layout segment identified by a byte range, all
the layouts associated with a filesystem (FSID), or all layouts.
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Recalling all layouts or all the layouts associated with a filesystem
also invalidates the client's device cache for the affected
filesystems. Multiple layout segments may be returned in a single
compound operation. Section 12.3.5.3 discusses sequencing issues
surrounding the getting, returning, and recalling of layouts.
The iomode is also specified when recalling a layout or layout
segment. Generally, the iomode in the recall request must match the
layout, or segment, being returned; e.g., a recall with an iomode of
RW should cause the client to only return RW layout segments (not R
segments). However, a special LAYOUTIOMODE_ANY enumeration is
defined to enable recalling a layout of any type (i.e., the client
must return both read-only and read/write layouts).
A REMOVE operation may cause the metadata server to recall the layout
to prevent the client from accessing a non-existent file and to
reclaim state stored on the client. Since a REMOVE may be delayed
until the last close of the file has occurred, the recall may also be
delayed until this time. As well, once the file has been removed,
after the last reference, the client SHOULD no longer be able to
perform I/O using the layout (e.g., with file-based layouts an error
such as ESTALE could be returned).
Although, the pNFS extension does not alter the caching capabilities
of clients, or their semantics, it recognizes that some clients may
perform more aggressive write-behind caching to optimize the benefits
provided by pNFS. However, write-behind caching may impact the
latency in returning a layout in response to a CB_LAYOUTRECALL; just
as caching impacts DELEGRETURN with regards to data delegations.
Client implementations should limit the amount of dirty data they
have outstanding at any one time. Server implementations may fence
clients from performing direct I/O to the storage devices if they
perceive that the client is taking too long to return a layout once
recalled. A server may be able to monitor client progress by
watching client I/Os or by observing LAYOUTRETURNs of sub-portions of
the recalled layout. The server can also limit the amount of dirty
data to be flushed to storage devices by limiting the byte ranges
covered in the layouts it gives out.
Once a layout has been returned, the client MUST NOT issue I/Os to
the storage devices for the file, byte range, and iomode represented
by the returned layout. If a client does issue an I/O to a storage
device for which it does not hold a layout, the storage device SHOULD
reject the I/O.
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12.3.5.2. Recall Callback Robustness
It has been assumed thus far that pNFS client state for a file
exactly matches the pNFS server state for that file and client
regarding layout ranges and permissions. This assumption leads to
the implicit assumption that any callback results in a LAYOUTRETURN
or set of LAYOUTRETURNs that exactly match the range in the callback,
since both client and server agree about the state being maintained.
However, it can be useful if this assumption does not always hold.
For example:
o It may be useful for clients to be able to discard layout
information without calling LAYOUTRETURN. If conflicts that
require callbacks are very rare, and a server can use a multi-file
callback to recover per-client resources (e.g., via a FSID recall,
or a multi-file recall within a single compound), the result may
be significantly less client-server pNFS traffic.
o It may be similarly useful for servers to maintain information
about what ranges are held by a client on a coarse-grained basis,
leading to the server's layout ranges being beyond those actually
held by the client. In the extreme, a server could manage
conflicts on a per-file basis, only issuing whole-file callbacks
even though clients may request and be granted sub-file ranges.
o In order to avoid errors, it is vital that a client not assign
itself layout permissions beyond what the server has granted and
that the server not forget layout permissions that have been
granted. On the other hand, if a server believes that a client
holds a layout segment that the client does not know about, it's
useful for the client to cleanly indicate completion of the
requested recall either by issuing a LAYOUTRETURN for the entire
requested range or by returning an NFS4ERR_NOMATCHING_LAYOUT error
to the layout recall callback.
Thus, in light of the above, it is useful for a server to be able to
issue callbacks for layout ranges it has not granted to a client, and
for a client to return ranges it does not hold. A pNFS client must
always return layout segments that comprise the full range specified
by the recall. Note, the full recalled layout range need not be
returned as part of a single operation, but may be returned in
segments. This allows the client to stage the flushing of dirty
data, layout commits, and returns. Also, it indicates to the
metadata server that the client is making progress.
It is possible that write requests may be presented to a data server
no longer allowed to perform them. This behavior is limited by
requiring that a client MUST wait for completion of all writes
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covered by a layout range before returning a layout that covers that
range. Since, the server has no control as to when the client will
return the layout, the server may, at some time, decide to
unilaterally revoke the client's access provided by the layout in
question. Upon doing so the server must deal with the possibility of
lingering writes, outstanding writes still in flight to data servers
identified by the revoked layout. Each layout-specification MUST
define whether unilateral layout revocation by the metadata server is
supported, and if so, the specification must also outline how
lingering writes are to be dealt with; e.g., data servers identified
by the revoked layout in question could be fenced off from the
appropriate client. If unilateral revocation is not supported, there
MUST be no possibility that the client has outstanding write requests
when a layout is returned.
In order to ensure client/server convergence on the layout state, the
final LAYOUTRETURN operation in a sequence of returns for a
particular recall, MUST specify the entire range being recalled,
echoing the recalled layout type, iomode, recall/return type (FILE,
FSID, or ALL), and byte range; even if layout segments pertaining to
partial ranges were previously returned. In addition, if the client
holds no layout segment that overlaps the range being recalled, the
client should return the NFS4ERR_NOMATCHING_LAYOUT error code. This
allows the server to update its view of the client's layout state.
12.3.5.3. Serialization of Layout Operations
As with other stateful operations, pNFS requires the correct
sequencing of layout operations. pNFS relies on the sessions feature
of NFSv4.1 to provide the correct sequencing between regular
operations and callbacks. It is the server's responsibility to avoid
inconsistencies regarding the layouts it hands out and the client's
responsibility to properly serialize its layout requests and layout
returns.
12.3.5.3.1. Get/Return Serialization
The protocol allows the client to send concurrent LAYOUTGET and
LAYOUTRETURN operations to the server. However, the protocol does
not provide any means for the server to process the requests in the
same order in which they were created, nor it provides a way for the
client to determine the order in which parallel outstanding
operations were processed by the server. Thus, when a layout segment
retrieved by an outstanding LAYOUTGET operation intersects with a
layout segment returned by an outstanding LAYOUTRETURN the order in
which the two conflicting operations are processed determines the
final state of the overlapping segment. To disambiguate between the
two cases the client MUST serialize LAYOUTGET operations and
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voluntary LAYOUTRETURN operations for the same file.
It is permissible for the client to send in parallel multiple
LAYOUTGET operations for the same file or multiple LAYOUTRETURN
operations for the same file; but never a mix of both. It is also
permissible for the client to combine LAYOUTRETURN and LAYOUTGET
operations for the same file in the same COMPOUND request as the
server must process these in order. If a client does issue such
requests, it must not have more than one outstanding for the same
file at the same time and must not have other LAYOUTGET or
LAYOUTRETURN operations outstanding at the same time for that same
file.
12.3.5.3.2. Recall/Return Sequencing
One critical issue with operation sequencing concerns callbacks. The
protocol must defend against races between the reply to a LAYOUTGET
operation and a subsequent CB_LAYOUTRECALL. A client MUST NOT
process a CB_LAYOUTRECALL that identifies an outstanding LAYOUTGET
operation to which the client has not yet received a reply.
Conflicting LAYOUTGET operations are identified in the CB_SEQUENCE
preceding the CB_LAYOUTRECALL.
The callback races section (Section 2.9.4.3) describes the sessions
mechanism for allowing the client to detect such situations in order
to not process such a CB_LAYOUTRECALL. The server MUST reference all
conflicting LAYOUTGET operations in the CB_SEQUENCE that precedes the
CB_LAYOUTRECALL. A zero length array of referenced operations is
used by the server to tell the client that the server does not know
of any LAYOUTGET operations that conflict with the recall.
12.3.5.3.2.1. Client Side Considerations
Consider a pNFS client that has issued a LAYOUTGET and then receives
an overlapping recall callback for the same file. There are two
possibilities, which the client would be unable to distinguish
without additional information provided by the sessions
implementation.
1. The server processed the LAYOUTGET before issuing the recall, so
the LAYOUTGET response is in flight, and must be waited for
because it may be carrying layout info that will need to be
returned to deal with the recall callback.
2. The server issued the callback before receiving the LAYOUTGET.
The server will not respond to the LAYOUTGET until the recall
callback is processed.
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This could cause deadlock, as the client must wait for the LAYOUTGET
response before processing the recall in the first case, but that
response will not arrive until after the recall is processed in the
second case. Via the CB_SEQUENCE operation, the server provides the
client with the { slotid , sequenceid } of any earlier LAYOUTGET
operations which remain unconfirmed at the server by the session slot
usage rules. This allows the client to disambiguate between the two
cases, in case 1, the server will provide the operation reference(s),
whereas in case 2 it will not (because there are no dependent client
operations). Therefore, the action at the client will only require
waiting in the case that the client has not yet seen the server's
earlier responses to the LAYOUTGET operation(s).
The following requirements apply to avoid this deadlock: by adhering
to the following requirements:
o A LAYOUTGET MUST be rejected with an error (i.e.,
NFS4ERR_RECALLCONFLICT) if there's an overlapping outstanding
recall callback to the same client.
o When processing a recall, the client MUST wait for a response to
all conflicting outstanding LAYOUTGETs that are referenced in the
CB_SEQUENCE for the recall before performing any RETURN that could
be affected by any such response.
o The client SHOULD wait for responses to all operations required to
complete a recall before sending any LAYOUTGETs that would
conflict with the recall because the server is likely to return
errors for them.
o Before sending a new LAYOUTGET for a range covered by a layout
recall, the client SHOULD wait for responses to any outstanding
LAYOUTGET that overlaps any portion of the new LAYOUTGET's range .
This is because it is possible (although unlikely) that the prior
operation may have arrived at the server after the recall
completed and hence will succeed.
o The recall process can be considered as done by the client when
the final LAYOUTRETURN operation for the recalled range is issued.
12.3.5.3.2.2. Server Side Considerations
Consider a related situation from the pNFS server's point of view.
The server has issued a recall callback and receives an overlapping
LAYOUTGET for the same file before the LAYOUTRETURN(s) that respond
to the recall callback. Again, there are two cases:
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1. The client issued the LAYOUTGET before processing the recall
callback.
2. The client issued the LAYOUTGET after processing the recall
callback, but it arrived before the LAYOUTRETURN that completed
that processing.
The simplest approach is to always reject the overlapping LAYOUTGET;
the pNFS server MUST do this. The client has two ways to avoid this
result - it can issue the LAYOUTGET as a subsequent element of a
COMPOUND containing the LAYOUTRETURN that completes the recall
callback, or it can wait for the response to that LAYOUTRETURN.
There is little the session sequence logic can do to disambiguate
between these two cases, because both operations are independent of
one another. They are simply asynchronous events which crossed. The
situation can even occur if the session is configured to use a single
connection for both operations and callbacks.
12.3.6. Metadata Server Write Propagation
Asynchronous writes written through the metadata server may be
propagated lazily to the storage devices. For data written
asynchronously through the metadata server, a client performing a
read at the appropriate storage device is not guaranteed to see the
newly written data until a COMMIT occurs at the metadata server.
While the write is pending, reads to the storage device can give out
either the old data, the new data, or a mixture thereof. After
either a synchronous write completes, or a COMMIT is received (for
asynchronously written data), the metadata server must ensure that
storage devices give out the new data and that the data has been
written to stable storage. If the server implements its storage in
any way such that it cannot obey these constraints, then it must
recall the layouts to prevent reads being done that cannot be handled
correctly.
12.3.7. Crash Recovery
Crash recovery is complicated due to the distributed nature of the
pNFS protocol. In general, crash recovery for layouts is similar to
crash recovery for delegations in the base NFSv4 protocol. However,
the client's ability to perform I/O without contacting the metadata
server introduces subtleties that must be handled correctly if file
system corruption is to be avoided.
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12.3.7.1. Leases
The layout lease period plays a critical role in crash recovery.
Depending on the capabilities of the storage protocol, it is crucial
that the client is able to maintain an accurate layout lease timer to
ensure that I/Os are not issued to storage devices after expiration
of the layout lease period. In order for the client to do so, it
must know which operations renew a lease.
12.3.7.1.1. Lease Renewal
The current NFSv4 specification allows for implicit lease renewals to
occur upon receiving an I/O. However, due to the distributed pNFS
architecture, implicit lease renewals are limited to operations
performed at the metadata server; this includes I/O performed through
the metadata server. So, a client must not assume that READ and
WRITE I/O to storage devices implicitly renew lease state.
If sessions are required for pNFS, as has been suggested, then the
SEQUENCE operation is to be used to explicitly renew leases. It is
proposed that the SEQUENCE operation be extended to return all the
specific information that RENEW does, but not as an error as RENEW
returns it. Since, when using session, beginning each compound with
the SEQUENCE op allows renews to be performed without an additional
operation and without an additional request. Again, the client must
not rely on any operation to the storage devices to renew a lease.
Using the SEQUENCE operation for renewals, simplifies the client's
perception of lease renewal.
12.3.7.1.2. Client Lease Timer
Depending on the storage protocol and layout type in use, it may be
crucial that the client not issue I/Os to storage devices if the
corresponding layout's lease has expired. Doing so may lead to file
system corruption if the layout has been given out and used by
another client. In order to prevent this, the client must maintain
an accurate lease timer for all layouts held. RFC3530 [2] has the
following to say regarding the maintenance of a client lease timer:
...the client must track operations which will 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.
To be conservative, the client should start its lease timer based on
the time that the it issued the operation to the metadata server,
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rather than based on the time of the response.
It is also necessary to take propagation delay into account when
requesting a renewal of the lease:
...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.
Thus, the client must be aware of the one-way propagation delay and
should issue renewals well in advance of lease expiration. Clients,
to the extent possible, should try not to issue I/Os that may extend
past the lease expiration time period. However, since this is not
always possible, the storage protocol must be able to protect against
the effects of in-flight I/Os, as is discussed later.
12.3.7.2. Client Recovery
Client recovery for layouts works in much the same way as NFSv4
client recovery works for other lock/delegation state. When an NFSv4
client reboots, it will lose all information about the layouts that
it previously owned. There are two methods by which the server can
reclaim these resources and allow otherwise conflicting layouts to be
provided to other clients.
The first is through the expiry of the client's lease. If the client
recovery time is longer than the lease period, the client's lease
will expire and the server will know that state may be released. for
layouts the server may release the state immediately upon lease
expiry or it may allow the layout to persist awaiting possible lease
revival, as long as there are no conflicting requests.
On the other hand, the client may recover in less time than it takes
for the lease period to expire. In such a case, the client will
contact the server through the standard SETCLIENTID protocol. The
server will find that the client's id matches the id of the previous
client invocation, but that the verifier is different. The server
uses this as a signal to release all the state associated with the
client's previous invocation.
12.3.7.3. Metadata Server Recovery
The server recovery case is slightly more complex. In general, the
recovery process again follows the standard NFSv4 recovery model: the
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client will discover that the metadata server has rebooted when it
receives an unexpected STALE_STATEID or STALE_CLIENTID reply from the
server; it will then proceed to try to reclaim its previous
delegations during the server's recovery grace period. However,
layouts have a slightly different mechanism for reclaim. The problem
is that a client which uses LAYOUTGET to reclaim a layout might not
get the same layout it had previously. The range might be different
or it might get the same range but the content of the layout might be
different. For example, if using a block/volume-based layout, the
blocks provisionally assigned by the layout might be different, in
which case the client will have to write the corresponding blocks
again.
Instead of reclaiming a layout with LAYOUTGET, a client can attempt
to commit data written before the file server crash by setting a
reclaim bit on the LAYOUTCOMMIT operation. This should only be done
for data that the client has already written using a layout obtained
before the server restart. For data still dirty in the client
memory, the client should get a new layout segment after the server's
grace period has elapsed. Alternatively, the client can write that
data through the metadata server using the standard NFSv4 WRITE. In
the case that the client has written dirty data to a provisionally
allocated region of the layout, but was unable to commit the layout
changes for this data before the server rebooted, the client may be
unable to reliably re-read the data from the data storage devices in
order to write it again via the metadata server. In this case the
client needs to inform the metadata server that the layout has
changed, before the server has completed its recovery grace period
and starts allowing updates to the file-system. For this purpose,
the LAYOUTCOMMIT operation contains a "reclaim" field. During the
metadata server's recovery grace period (and only during the recovery
grace period) the client may send a LAYOUTCOMMIT request with the
"reclaim" field set to "true". This indicates that the client is
attempting to commit changes to the file layout that occurred prior
to the reboot of the metadata server. The "layout update" field of
the request must contain the portion of the layout that the client
held prior to the metadata server reboot which covers the outstanding
writes. The metadata server is free to apply consistency checks on
the layout update provided by the client, and reject the request if
the checks fail. If the checks do not fail, then the server MUST
commit the changes to the file layout contained in the "layoutupdate"
field of the LAYOUTCOMMIT request, ensuring that the clients
outstanding writes are not lost.
During the recovery grace period the metadata server should apply the
standard approach to handling WRITE and LAYOUTGET requests. That is,
if the server can reliably determine that servicing such a request
will not conflict with an impending LAYOUTCOMMIT reclaim request, it
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may choose to service the request. If the server is unable to offer
this guarantee, it MUST reject the request with status NFS4ERR_GRACE.
For a metadata server to provide simple, valid handling during the
grace period with respect to pNFS layouts, the easiest method is to
simply reject all non-reclaim pNFS requests and WRITE operations by
returning the NFS4ERR_GRACE error. However, depending on the storage
protocol and server implementation, the server may be able to
determine that a particular request is safe. For example, a server
may save provisional allocation mappings for each file to stable
storage, and use this information during the recovery grace period to
determine that a WRITE request is safe. Under such circumstances,
the WRITE request MAY be serviced. To re-iterate, for a server to
allow non-reclaim pNFS requests and WRITE operations to be serviced
during the recovery grace period, it MUST determine that the request
will not conflict with any subsequent LAYOUTCOMMIT with reclaim
request.
There is an important safety concern associated with layouts that
does not come into play in the standard NFSv4 case. If a standard
NFSv4 client makes use of a stale delegation, while reading, the
consequence could be to deliver stale data to an application. If
writing, using a stale delegation or a stale state stateid for an
open or lock would result in the rejection of the client's write with
the appropriate stale stateid error.
However, the pNFS layout enables the client to directly access the
file system storage; if this access is not properly managed by the
NFSv4 server the client can potentially corrupt the file system data
or metadata. Thus, it is vitally important that the client discover
that the metadata server has rebooted, and that the client stops
using stale layouts before the metadata server gives them away to
other clients. To ensure this, the client must be implemented so
that layouts are never used to access the storage after the client's
lease timer has expired. It is crucial that clients have precise
knowledge of the lease periods of their layouts. For specific
details on lease renewal and client lease timers, see
Section 12.3.7.1.
The prohibition on using stale layouts applies to all layout related
accesses, especially the flushing of dirty data to the storage
devices. If the client's lease timer expires because the client
could not contact the server for any reason, the client MUST
immediately stop using the layout until the server can be contacted
and the layout can be officially recovered or reclaimed. However,
this is only part of the solution. It is also necessary to deal with
the consequences of I/Os already in flight.
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The issue of the effects of I/Os started before lease expiration and
possibly continuing through lease expiration is the responsibility of
the data storage protocol and as such is layout type specific. There
are two approaches the data storage protocol can take. The protocol
may adopt a global solution which prevents all I/Os from being
executed after the lease expiration and thus is safe against a client
who issues I/Os after lease expiration. This is the preferred
solution and the solution used by NFSv4 file based layouts (see
Section 12.4.7); as well, the object storage device protocol allows
storage to fence clients after lease expiration. Alternatively, the
storage protocol may rely on proper client operation and only deal
with the effects of lingering I/Os. These solutions may impact the
client layout-driver, the metadata server layout-driver, and the
control protocol.
12.3.7.4. Storage Device Recovery
Storage device crash recovery is mostly dependent upon the layout
type in use. However, there are a few general techniques a client
can use if it discovers a storage device has crashed while holding
asynchronously written, non-committed, data. First and foremost, it
is important to realize that the client is the only one who has the
information necessary to recover asynchronously written data; since,
it holds the dirty data and most probably nobody else does. Second,
the best solution is for the client to err on the side or caution and
attempt to re-write the dirty data through another path.
The client, rather than hold the asynchronously written data
indefinitely, is encouraged to, and can make sure that the data is
written by using other paths to that data. The client may write the
data to the metadata server, either synchronously or asynchronously
with a subsequent COMMIT. Once it does this, there is no need to
wait for the original storage device. In the event that the data
range to be committed is transferred to a different storage device,
as indicated in a new layout, the client may write to that storage
device. Once the data has been committed at that storage device,
either through a synchronous write or through a commit to that
storage device (e.g., through the NFSv4 COMMIT operation for the
NFSv4 file layout), the client should consider the transfer of
responsibility for the data to the new server as strong evidence that
this is the intended and most effective method for the client to get
the data written. In either case, once the write is on stable
storage (through either the storage device or metadata server), there
is no need to continue either attempting to commit or attempting to
synchronously write the data to the original storage device or wait
for that storage device to become available. That storage device may
never be visible to the client again.
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This approach does have a "lingering write" problem, similar to
regular NFSv4. Suppose a WRITE is issued to a storage device for
which no response is received. The client breaks the connection,
trying to re-establish a new one, and gets a recall of the layout.
The client issues the I/O for the dirty data through an alternative
path, for example, through the metadata server and it succeeds. The
client then goes on to perform additional writes that all succeed.
If at some time later, the original write to the storage device
succeeds, data inconsistency could result. The same problem can
occur in regular NFSv4. For example, a WRITE is held in a switch for
some period of time while other writes are issued and replied to, if
the original WRITE finally succeeds, the same issues can occur.
However, this is solved by sessions in NFSv4.x.
12.3.8. Security Considerations
The pNFS extension partitions the NFSv4 file system protocol into two
parts, the control path and the data path (i.e., storage protocol).
The control path contains all the new operations described by this
extension; all existing NFSv4 security mechanisms and features apply
to the control path. The combination of components in a pNFS system
(see Figure 61) is required to preserve the security properties of
NFSv4 with respect to an entity accessing data via a client,
including security countermeasures to defend against threats that
NFSv4 provides defenses for in environments where these threats are
considered significant.
In some cases, the security countermeasures for connections to
storage devices may take the form of physical isolation or a
recommendation not to use pNFS in an environment. For example, it is
currently infeasible to provide confidentiality protection for some
storage device access protocols to protect against eavesdropping; in
environments where eavesdropping on such protocols is of sufficient
concern to require countermeasures, physical isolation of the
communication channel (e.g., via direct connection from client(s) to
storage device(s)) and/or a decision to forego use of pNFS (e.g., and
fall back to NFSv4) may be appropriate courses of action.
In full generality where communication with storage devices is
subject to the same threats as client-server communication, the
protocols used for that communication need to provide security
mechanisms comparable to those available via RPSEC_GSS for NFSv4.
Many situations in which pNFS is likely to be used will not be
subject to the overall threat profile for which NFSv4 is required to
provide countermeasures.
pNFS implementations MUST NOT remove NFSv4's access controls. The
combination of clients, storage devices, and the server are
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responsible for ensuring that all client to storage device file data
access respects NFSv4 ACLs and file open modes. This entails
performing both of these checks on every access in the client, the
storage device, or both. If a pNFS configuration performs these
checks only in the client, the risk of a misbehaving client obtaining
unauthorized access is an important consideration in determining when
it is appropriate to use such a pNFS configuration. Such
configurations SHOULD NOT be used when client- only access checks do
not provide sufficient assurance that NFSv4 access control is being
applied correctly.
12.4. The NFSv4.1 File Layout Type
This section describes the semantics and format of NFSv4.1 file-based
layouts.
12.4.1. Session Considerations
Sessions are a mandatory feature of NFSv4.1, and this extends to both
the metadata server and file-based data servers. If data is served
by both the metadata server and a data server, the metadata and data
server:
o MUST share the same clientid.
o MUST have separate sessions (unless the metadata server and data
server are the same entity). Both sessions MUST be associated
with the same clientid.
It is legal for a data server to also act as a metadata server. A
server serving both roles will provide service for one set of file
systems in one role, and a another possibly intersecting, possibly
disjoint set of filesystems in the other role. A client using a
server serving both roles is free to use the same clientid and
sessionid when interacting with either of the server's roles.
12.4.2. File Striping and Data Access
The file layout type describes a method for striping data across
multiple devices. The data for each stripe unit is stored within an
NFSv4.1 file located on a particular storage device.
Before discussing the file layout, it is necessary to describe the
file layout device type; the structures are as follows:
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typedef netaddr4 nfsv4_file_layout_simple_device4;
enum file_layout_device_type {
FILE_SIMPLE = 1,
FILE_COMPLEX = 2
};
union nfsv4_file_layout_device4
switch (file_layout_device_type fld_type) {
case FILE_SIMPLE:
nfsv4_file_layout_simple_device4 nfld_dev_list<>;
case FILE_COMPLEX:
deviceid4 dev_list<>;
default:
void;
};
The "nfsv4_file_layout_device4" structure is a union composed of a
SIMPLE or a COMPLEX device type. A Simple device is composed of an
array of nfsv4_file_layout_simple_device4 structures. All devices
identified by a Simple device must be 'equivalent' and are used for
device multipathing; see Section 12.4.2.3 for more details on
equivalent devices. Simple devices always refer to actual physical
devices. On the other hand, a Complex device is a virtual device
that is constructed of multiple Simple devices. Each device within
the Complex device list is identified by its device ID. A Complex
device MUST NOT reference other Complex devices; only Simple devices
are to be referenced. This enables multiple physical devices to be
identified through a single device ID and provides a space efficient
mechanism by which to identify multiple devices within a layout.
Complex devices can be thought of as a table of devices. Complex and
Simple devices share the same device ID space and should be cached
similarly by the client.
The structures used to describe the stripe layout are as follows:
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enum stripetype4 {
STRIPE_SPARSE = 1,
STRIPE_DENSE = 2
};
struct nfsv4_file_layouthint4 {
stripetype4 nflh_stripe_type;
length4 nflh_stripe_unit;
uint32_t nflh_stripe_width;
};
struct nfsv4_file_layout4 {
deviceid4 nfl_dev_id;
uint32_t nfl_dev_index;
nfs_fh4 nfl_fh;
};
struct nfsv4_file_layouttype4 {
stripetype4 nflt_stripe_type;
bool nflt_commit_through_mds;
length4 nflt_stripe_unit;
length4 nflt_file_size;
uint32_t nflt_stripe_devs<>;
nfsv4_file_layout4 nflt_dev_list<>;
};
At a high level, the file layout specifies an ordered array of
<deviceID, filehandle> tuples, as well as the stripe size, type of
stripe layout (discussed later), and the file's current size as of
LAYOUTGET time.
The "dev_list" array within the nfsv4_file_layouttype4 contains a
list of nfsv4_file_layout structures ("dev_list"). Each of these
structures describes one or more physical devices that contribute to
a stripe of the file. The "stripe_devs" array contains a list of
indices into the "dev_list" array; an index of zero specifies the
first "dev_list" entry. Each successive index selects a "dev_list"
entry whose filehandle and device id are to be used next in sequence
for that stripe. This allows an arbitrary sequencing through the
possible devices to be encoded compactly. When the "stripe_devs"
array is of zero length, the elements of the "dev_list" array are
simply used in order, so that the portion of the stripe held by the
corresponding entry is determined by its position within the device
list.
Each "dev_list" entry (the nfsv4_file_layout structure) contains a
filehandle, device ID, and device index. The filehandle, "fh",
identifies the file on the storage device identified. The device ID
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("dev_id") may refer to either a Simple or a Complex device; see the
description of the nfsv4_file_layout_device4 for details. When a
Complex device is referenced by the "dev_id", the "dev_index" field
specifies the starting index within the device's "dev_list". If the
"dev_id" references a Simple device, the "dev_index" has no meaning
and should be zero. The "dev_index" plays a critical role in the
flattening of a Complex device.
The client is expected to construct a 'flat' list of devices over
which the file is striped. A flat device list can be constructed by
concatenating each device encountered while traversing "stripe_devs"
(or "dev_list" in the case of a zero sized "stripe_devs" array),
while expanding out each Complex device. The flat device list must
contain only Simple devices. The client must expand the Complex
device's device list by starting at the device indexed by
"dev_index", ending with the device prior to "dev_index". All
devices in the device list must be consumed; this may require
wrapping around the end of the array if "dev_index" is non-zero. The
stripe width is determined by the stripe unit size multiplied by the
number of device entries within the flattened stripe.
Consider the following example:
Given a set of devices as follows:
1->{simple}; 2->{complex, dev_list=<3,4>}; 3->{simple}; 4->{simple}
Device ID 1,3,4 and 5 are Simple devices. Device ID 2 is a Complex
device constructed of Simple devices 3 and 4.
Within the nfsv4_file_layouttype4, imagine a "dev_list" constructed
of <device ID, device index, FH> tuples:
dev_list = [<1, 0, 0x12>, <2, 0, 0x13>, <3, 0, 0x14>, <4, 0, 0x15>]
And a "stripe_devs" array containing the following indices:
stripe_devs = [2, 3, 0, 1]
Using the stripe_devs as indices into the dev_list, we get the
following ordered list of nfsv4_file_layouts:
[<3, 0, 0x14>, <4, 0, 0x15>, <1, 0, 0x12>, <2, 0, 0x13>]
Continuing to flatten the Complex devices gives us the following list
of 5 simple <device ID, FH> tuples. Note device 2 is a Complex
device that gets replaced with devices 3 and 4:
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[<3, 0x14>, <4, 0x15>, <1, 0x12>, <3, 0x13>, <4, 0x13>]
The flattened device list specifies the order over which the devices
must be striped. It also specifies the filehandle to be used for
each stripe unit. Data must be written in increments of the stripe
unit size. Devices may be repeated multiple times within the
flattened device list. However, if a dense stripe type is used
(described later), the same filehandle MUST NOT be used on the same
device for different stripe units of the same file.
A data file stored on a storage device MUST map to a single file as
defined by the metadata server; i.e., data from two files as viewed
by the metadata server MUST NOT be stored within the same data file
on any storage device.
The "stripe_type" field specifies how the data is laid out within the
data file on a storage device. It allows for two different data
layouts: sparse and dense or packed. The stripe type determines the
calculation that must be made to map the client visible file offset
to the offset within the data file located on the storage device.
The layout hint structure is described in more detail in Section
4.15. It is used, by the client, as by the FILE_LAYOUT_HINT
attribute to specify the type of layout to be used for a newly
created file.
12.4.2.1. Sparse and Dense Storage Device Data Layouts
The stripe_type field allows for two storage device data file
representations. Example sparse and dense storage device data
layouts are illustrated below:
Sparse file-layout (stripe_unit = 4KB)
------------------
Is represented by the following file layout on the storage devices:
Offset ID:0 ID:1 ID:2
0 +--+ +--+ +--+ +--+ indicates a
|//| | | | | |//| stripe that
4KB +--+ +--+ +--+ +--+ contains data
| | |//| | |
8KB +--+ +--+ +--+
| | | | |//|
12KB +--+ +--+ +--+
|//| | | | |
16KB +--+ +--+ +--+
| | |//| | |
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+--+ +--+ +--+
The sparse file-layout has holes for the byte ranges not exported by
that storage device. This allows clients to access data using the
real offset into the file, regardless of the storage device's
position within the stripe. However, if a client writes to one of
the holes (e.g., offset 4-12KB on device 1), then an error MUST be
returned by the storage device. This requires that the storage
device have knowledge of the layout for each file.
When using a sparse layout, the offset into the storage device data
file is the same as the offset into the main file.
Dense/packed file-layout (stripe_unit = 4KB)
------------------------
Is represented by the following file layout on the storage devices:
Offset ID:0 ID:1 ID:2
0 +--+ +--+ +--+
|//| |//| |//|
4KB +--+ +--+ +--+
|//| |//| |//|
8KB +--+ +--+ +--+
|//| |//| |//|
12KB +--+ +--+ +--+
|//| |//| |//|
16KB +--+ +--+ +--+
|//| |//| |//|
+--+ +--+ +--+
The dense or packed file-layout does not leave holes on the storage
devices. Each stripe unit is spread across the storage devices. As
such, the storage devices need not know the file's layout since the
client is allowed to write to any offset.
The calculation to determine the byte offset within the data file for
dense storage device layouts is:
stripe_width = stripe_unit * N; where N = |dev_list|
dev_offset = floor(file_offset / stripe_width) * stripe_unit +
file_offset % stripe_unit
Regardless of the storage device data file layout, the calculation to
determine the index into the device array is the same:
dev_idx = floor(file_offset / stripe_unit) mod N
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Section 12.4.6 describe the semantics for dealing with reads to holes
within the striped file. This is of particular concern, since each
individual component stripe file (i.e., the component of the striped
file that lives on a particular storage device) may be of different
length. Thus, clients may experience 'short' reads when reading off
the end of one of these component files.
12.4.2.2. Metadata and Storage Device Roles
In many cases, the metadata server and the storage device will be
separate pieces of physical hardware. The specification text is
written as if that were always case. However, it can be the case
that the same physical hardware is used to implement both a metadata
and storage device and in this case, the specification text's
references to these two entities are to be understood as referring to
the same physical hardware implementing two distinct roles and it is
important that it be clearly understood on behalf of which role the
hardware is executing at any given time.
Two sub-cases can be distinguished. In the first sub-case, the same
physical hardware is used to implement both a metadata and data
server in which each role is addressed through a distinct network
interface (e.g., IP addresses for the metadata server and storage
device are distinct). As long as the storage device address is
obtained from the layout and is distinct from the metadata server's
address, using the device ID therein to obtain the appropriate
storage device address, it is always clear, for any given request, to
what role it is directed, based on the destination IP address.
However, it may also be the case that even though the metadata server
and storage device are distinct from one client's point of view, the
roles may be reversed according to another client's point of view.
For example, in the cluster file system model a metadata server to
one client, may be a storage device to another client. Thus, it is
safer to always mark the filehandle so that operations addressed to
storage devices can be distinguished.
The second sub-case is where both the metadata and storage device
have the same network address. This requires us to make the
distinction as to which role each request is directed, on a another
basis. Since the network address is the same, the request is
understood as being directed at one or the other, based on the
filehandle of the first current filehandle value for the request. If
the first current filehandle is one derived from a layout (i.e., it
is specified within the layout) (and it is recommended that these be
distinguishable), then the request is to be considered as executed by
a storage device. Otherwise, the operation is to be understood as
executed by the metadata server.
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If a current filehandle is set that is inconsistent with the role to
which it is directed, then the error NFS4ERR_BADHANDLE should result.
For example, if a request is directed at the storage device, because
the first current handle is from a layout, any attempt to set the
current filehandle to be a value not from a layout should be
rejected. Similarly, if the first current file handle was for a
value not from a layout, a subsequent attempt to set the current
filehandle to a value obtained from a layout should be rejected.
12.4.2.3. Device Multipathing
The NFSv4.1 file layout supports multipathing to 'equivalent'
devices. Device-level multipathing is primarily of use in the case
of a data server failure --- it allows the client to switch to
another storage device that is exporting the same data stripe,
without having to contact the metadata server for a new layout.
To support device multipathing, an array of device IDs is encoded
within the SIMPLE case of the nfsv4_file_layout_device4 union. This
array represents an ordered list of devices where the first element
has the highest priority. Each device in the list MUST be
'equivalent' to every other device in the list and each device must
be attempted in the order specified.
Equivalent devices MUST export the same system image (e.g., the
stateids and filehandles that they use are the same) and must provide
the same consistency guarantees. Two equivalent storage devices must
also have sufficient connections to the storage, such that writing to
one storage device is equivalent to writing to another, this also
applies to reading. Also, if multiple copies of the same data exist,
reading from one must provide access to all existing copies. As
such, it is unlikely that multipathing will provide additional
benefit in the case of an I/O error.
[NOTE: the error cases in which a client is expected to attempt an
equivalent storage device should be specified.]
12.4.2.4. Operations Issued to Storage Devices
Clients MUST use the filehandle described within the layout when
accessing data on the storage devices. When using the layout's
filehandle, the client MUST only issue the NULL procedure and the
BACKCHANNEL_CTL, BIND_CONN_TO_SESSION, CREATE_SESSION, COMMIT,
DESTROY_SESSION, READ, WRITE, PUTFH, SECINFO_NO_NAME, SET_SSV, and
SEQUENCE operations to the storage device associated with that
filehandle. If a client issues an operation other than those
specified above, using the filehandle and storage device listed in
the client's layout, that storage device SHOULD return an error to
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the client. The client MUST follow the instruction implied by the
layout (i.e., which filehandles to use on which devices). As
described in Section 12.3.2, a client MUST NOT issue I/Os to storage
devices for which it does not hold a valid layout. The storage
devices may reject such requests.
GETATTR and SETATTR MUST be directed to the metadata server. In the
case of a SETATTR of the size attribute, the control protocol is
responsible for propagating size updates/truncations to the storage
devices. In the case of extending WRITEs to the storage devices, the
new size must be visible on the metadata server once a LAYOUTCOMMIT
has completed (see Section 12.3.4.2). Section 12.4.6, describes the
mechanism by which the client is to handle storage device file's that
do not reflect the metadata server's size.
12.4.2.5. COMMIT through metadata server
commit_through_mds in the file layout gives the metadata server a
preferred way of performing COMMIT. If this flag is true, the client
SHOULD send COMMIT to the metadata server instead of sending it to
the same data server to which the associated WRITEs were sent. In
order to maintain the current NFSv4.1 commit and recovery model, all
the data servers MUST return a common verifier for all WRITEs in a
given file layout. The value of the write verifier MUST be changed
at the metadata server or any data server that is referenced in the
layout, whenever there is a server event that can possibly lead to
loss of uncommitted data. The scope of the verifier can be for a
file or for the entire pNFS server. It might be more difficult for
the server to maintain the verifier at the file level but the benefit
is that only events that impact a given file will require recovery
action.
The single COMMIT to the metadata server will return a verifier and
the client should compare it to all the verifiers from the WRITEs and
fail the COMMIT if there is any mismatched verifiers. If COMMIT to
the MDS fails, the client should reissue WRITEs for all the dirty
data in the file. The client should treat dirty data with mismatched
verifier as WRITE failure and try to recover by reissuing the WRITEs
to the original DS or using other path to that data if the layout has
not been recalled. Other option the client has is getting a new
layout or just rewrite the data through the metadata server. If the
flag commit_through_mds is false the client should not send COMMIT to
the metadata server. Although it is valid to send COMMIT to the
metadata server it should be used only to commit data that was
written through the metadata server. See also section 14.7.4
"Storage Device Recover" for recovery options.
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12.4.3. Global Stateid Requirements
Note, there are no stateids returned embedded within the layout. The
client MUST use the stateid representing open or lock state as
returned by an earlier metadata operation (e.g., OPEN, LOCK), or a
special stateid to perform I/O on the storage devices, as in regular
NFSv4. Special stateid usage for I/O is subject to the NFSv4
protocol specification. The stateid used for I/O MUST have the same
effect and be subject to the same validation on storage device as it
would if the I/O was being performed on the metadata server itself in
the absence of pNFS. This has the implication that stateids are
globally valid on both the metadata and storage devices. This
requires the metadata server to propagate changes in lock and open
state to the storage devices, so that the storage devices can
validate I/O accesses. This is discussed further in Section 12.4.5.
Depending on when stateids are propagated, the existence of a valid
stateid on the storage device may act as proof of a valid layout.
[NOTE: a number of proposals have been made that have the possibility
of limiting the amount of validation performed by the storage device,
if any of these proposals are accepted or obtain consensus, the
global stateid requirement can be revisited.]
12.4.4. The Layout Iomode
The layout iomode need not used by the metadata server when servicing
NFSv4.1 file-based layouts, although in some circumstances it may be
useful to use. For example, if the server implementation supports
reading from read-only replicas or mirrors, it would be useful for
the server to return a layout enabling the client to do so. As such,
the client should set the iomode based on its intent to read or write
the data. The client may default to an iomode of READ/WRITE
(LAYOUTIOMODE_RW). The iomode need not be checked by the storage
devices when clients perform I/O. However, the storage devices SHOULD
still validate that the client holds a valid layout and return an
error if the client does not.
12.4.5. Storage Device State Propagation
Since the metadata server, which handles lock and open-mode state
changes, as well as ACLs, may not be co-located with the storage
devices where I/O access are validated, as such, the server
implementation MUST take care of propagating changes of this state to
the storage devices. Once the propagation to the storage devices is
complete, the full effect of those changes must be in effect at the
storage devices. However, some state changes need not be propagated
immediately, although all changes SHOULD be propagated promptly.
These state propagations have an impact on the design of the control
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protocol, even though the control protocol is outside of the scope of
this specification. Immediate propagation refers to the synchronous
propagation of state from the metadata server to the storage
device(s); the propagation must be complete before returning to the
client.
12.4.5.1. Lock State Propagation
Mandatory locks MUST be made effective at the storage devices before
the request that establishes them returns to the caller. Thus,
mandatory lock state MUST be synchronously propagated to the storage
devices. On the other hand, since advisory lock state is not used
for checking I/O accesses at the storage devices, there is no
semantic reason for propagating advisory lock state to the storage
devices. However, since all lock, unlock, open downgrades and
upgrades affect the sequence ID stored within the stateid, the
stateid changes which may cause difficulty if this state is not
propagated. Thus, when a client uses a stateid on a storage device
for I/O with a newer sequence number than the one the storage device
has, the storage device should query the metadata server and get any
pending updates to that stateid. This allows stateid sequence number
changes to be propagated lazily, on-demand.
[NOTE: With the reliance on the sessions protocol, there is no real
need for sequence ID portion of the stateid to be validated on I/O
accesses. It is proposed that the seq. ID checking is obsoleted.]
Since updates to advisory locks neither confer nor remove privileges,
these changes need not be propagated immediately, and may not need to
be propagated promptly. The updates to advisory locks need only be
propagated when the storage device needs to resolve a question about
a stateid. In fact, if byte-range locking is not mandatory (i.e., is
advisory) the clients are advised not to use the lock-based stateids
for I/O at all. The stateids returned by open are sufficient and
eliminate overhead for this kind of state propagation.
12.4.5.2. Open-mode Validation
Open-mode validation MUST be performed against the open mode(s) held
by the storage devices. However, the server implementation may not
always require the immediate propagation of changes. Reduction in
access because of CLOSEs or DOWNGRADEs do not have to be propagated
immediately, but SHOULD be propagated promptly; whereas changes due
to revocation MUST be propagated immediately. On the other hand,
changes that expand access (e.g., new OPEN's and upgrades) don't have
to be propagated immediately but the storage device SHOULD NOT reject
a request because of mode issues without making sure that the upgrade
is not in flight.
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12.4.5.3. File Attributes
Since the SETATTR operation has the ability to modify state that is
visible on both the metadata and storage devices (e.g., the size),
care must be taken to ensure that the resultant state across the set
of storage devices is consistent; especially when truncating or
growing the file.
As described earlier, the LAYOUTCOMMIT operation is used to ensure
that the metadata is synced with changes made to the storage devices.
For the file-based protocol, it is necessary to re-sync state such as
the size attribute, and the setting of mtime/atime. See
Section 12.3.4 for a full description of the semantics regarding
LAYOUTCOMMIT and attribute synchronization. It should be noted, that
by using a file-based layout type, it is possible to synchronize this
state before LAYOUTCOMMIT occurs. For example, the control protocol
can be used to query the attributes present on the storage devices.
Any changes to file attributes that control authorization or access
as reflected by ACCESS calls or READs and WRITEs on the metadata
server, MUST be propagated to the storage devices for enforcement on
READ and WRITE I/O calls. If the changes made on the metadata server
result in more restrictive access permissions for any user, those
changes MUST be propagated to the storage devices synchronously.
Recall that the NFSv4 protocol RFC3530 [2] specifies 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.
This also includes changes to ACLs. The propagation of access right
changes due to changes in ACLs may be asynchronous only if the server
implementation is able to determine that the updated ACL is not more
restrictive for any user specified in the old ACL. Due to the
relative infrequency of ACL updates, it is suggested that all changes
be propagated synchronously.
[NOTE: it has been suggested that the NFSv4 specification is in error
with regard to allowing principals other than those used for OPEN to
be used for file I/O. If changes within a minor version alter the
behavior of NFSv4 with regard to OPEN principals and stateids some
access control checking at the storage device can be made less
expensive. pNFS should be altered to take full advantage of these
changes.]
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12.4.6. Storage Device Component File Size
A potential problem exists when a component data file on a particular
storage device is grown past EOF; the problem exists for both dense
and sparse layouts. Imagine the following scenario: a client creates
a new file (size == 0) and writes to byte 128KB; the client then
seeks to the beginning of the file and reads byte 100. The client
should receive 0s back as a result of the read. However, if the read
falls on a different storage device to the client's original write,
the storage device servicing the READ may still believe that the
file's size is at 0 and return no data with the EOF flag set. The
storage device can only return 0s if it knows that the file's size
has been extended. This would require the immediate propagation of
the file's size to all storage devices, which is potentially very
costly. Therefore, the client that has initiated the extension of
the file's size MUST be prepared to deal with these EOF conditions;
the EOF'd or short reads will be treated as a hole in the file and
the NFS client will substitute 0s for the data when the offset is
less than the client's view of the file size.
The NFS protocol only provides close to open file data cache
semantics; meaning that when the file is closed all modified data is
written to the NFS server. When a subsequent open of the file is
done, the change time is inspected for a difference from a cached
value for the change time. For the case above, this means that a
LAYOUTCOMMIT will be done at close (along with the data writes) and
will update the file's size and change time. Access from another
client after that point will result in the appropriate size being
returned.
12.4.7. Crash Recovery Considerations
As described in Section 12.3.7, the layout type specific storage
protocol is responsible for handling the effects of I/Os started
before lease expiration, extending through lease expiration. The
NFSv4.1 file layout type prevents all I/Os from being executed after
lease expiration, without relying on a precise client lease timer and
without requiring storage devices to maintain lease timers.
It works as follows. In the presence of sessions, each compound
begins with a SEQUENCE operation that contains the "clientID". On
the storage device, the clientID can be used to validate that the
client has a valid layout for the I/O being performed, if it does
not, the I/O is rejected. Before the metadata server takes any
action to invalidate a layout given out by a previous instance, it
must make sure that all layouts from that previous instance are
invalidated at the storage devices. Note: it is sufficient to
invalidate the stateids associated with the layout only if special
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stateids are not being used for I/O at the storage devices, otherwise
the layout itself must be invalidated.
This means that a metadata server may not restripe a file until it
has contacted all of the storage devices to invalidate the layouts
from the previous instance nor may it give out locks that conflict
with locks embodied by the stateids associated with any layout from
the previous instance without either doing a specific invalidation
(as it would have to do anyway) or doing a global storage device
invalidation.
12.4.8. Security Considerations for the File Layout Type
The NFSv4.1 file layout type MUST adhere to the security
considerations outlined in Section 12.3.8. More specifically,
storage devices must make all of the required access checks on each
READ or WRITE I/O as determined by the [[Comment.15: get rid of
references tro RFC3530]]NFSv4 protocol RFC3530 [2]. If the metadata
server would deny an operation on a given file due its ACL, mode
attribute, open mode, open deny mode, mandatory lock state, or any
other attributes and state, the data server MUST also deny the
operation. This impacts the control protocol and the propagation of
state from the metadata server to the storage devices; see
Section 12.4.5 for more details.
The methods for authentication, integrity, and privacy for file
layout-based data servers are the same as that used for metadata
servers. Metadata and data servers use ONC RPC security flavors to
authenticate, and SECINFO and SECINFO_NO_NAME to negotiate the
security mechanism and services to be used.
For a given file object, a metadata server MAY require different
security parameters (secinfo4 value) than the data server. For a
given file object with multiple data servers, the secinfo4 value
SHOULD be the same across all data servers.
If an NFSv4.1 implementation supports parallel NFS and supports file
layouts, then the implementation MUST support the SECINFO_NO_NAME
operation, on both the metadata and data servers.
12.4.9. Alternate Approaches
Two alternate approaches exist for file-based layouts and the method
used by clients to obtain stateids used for I/O. Both approaches
embed stateids within the layout.
However, before examining these approaches it is important to
understand the distinction between clients and owners. Delegations
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belong to clients, while locks (e.g., record and share reservations)
are held by owners which in turn belong to a specific client. As
such, delegations can only protect against inter-client conflicts,
not intra-client conflicts. Layouts are held by clients and SHOULD
NOT be associated with state held by owners. Therefore, if stateids
used for data access are embedded within a layout, these stateids can
only act as delegation stateids, protecting against inter-client
conflicts; stateids pertaining to an owner can not be embedded within
the layout. This has the implication that the client MUST arbitrate
among all intra-client conflicts (e.g., arbitrating among lock
requests by different processes) before issuing pNFS operations.
Using the stateids stored within the layout, storage devices can only
arbitrate between clients (not owners).
The first alternate approach is to do away with global stateids,
stateids returned by OPEN/LOCK that are valid on the metadata server
and storage devices, and use only stateids embedded within the
layout. This approach has the drawback that the stateids used for
I/O access can not be validated against per owner state, since they
are only associated with the client holding the layout. It breaks
the semantics of tying a stateid used for I/O to an open instance.
This has the implication that clients must delegate per owner lock
and open requests internally, rather than push the work onto the
storage devices. The storage devices can still arbitrate and enforce
inter-client lock and open state.
The second approach is a hybrid approach. This approach allows for
stateids to be embedded with the layout, but also allows for the
possibility of global stateids. If the stateid embedded within the
layout is a special stateid of all zeros, then the stateid referring
to the last successful OPEN/LOCK should be used. This approach is
recommended if it is decided that using NFSv4 as a control protocol
is required.
This proposal suggests the global stateid approach due to the cleaner
semantics it provides regarding the relationship between stateids
used for I/O and their corresponding open instance or lock state.
However, it does have a profound impact on the control protocol's
implementation and the state propagation that is required (as
described in Section 12.4.5).
13. Internationalization
The primary issue in which NFS version 4 needs to deal with
internationalization, or I18N, is with respect to file names and
other strings as used within the protocol. The choice of string
representation must allow reasonable name/string access to clients
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which use various languages. The UTF-8 encoding of the UCS as
defined by ISO10646 [10] allows for this type of access and follows
the policy described in "IETF Policy on Character Sets and
Languages", RFC2277 [11].
RFC3454 [12], otherwise know as "stringprep", documents a framework
for using Unicode/UTF-8 in networking protocols, so as "to increase
the likelihood that string input and string comparison work in ways
that make sense for typical users throughout the world." A protocol
must define a profile of stringprep "in order to fully specify the
processing options." The remainder of this Internationalization
section defines the NFS version 4 stringprep profiles. Much of
terminology used for the remainder of this section comes from
stringprep.
There are three UTF-8 string types defined for NFS version 4:
utf8str_cs, utf8str_cis, and utf8str_mixed. Separate profiles are
defined for each. Each profile defines the following, as required by
stringprep:
o The intended applicability of the profile
o The character repertoire that is the input and output to
stringprep (which is Unicode 3.2 for referenced version of
stringprep)
o The mapping tables from stringprep used (as described in section 3
of stringprep)
o Any additional mapping tables specific to the profile
o The Unicode normalization used, if any (as described in section 4
of stringprep)
o The tables from stringprep listing of characters that are
prohibited as output (as described in section 5 of stringprep)
o The bidirectional string testing used, if any (as described in
section 6 of stringprep)
o Any additional characters that are prohibited as output specific
to the profile
Stringprep discusses Unicode characters, whereas NFS version 4
renders UTF-8 characters. Since there is a one-to-one mapping from
UTF-8 to Unicode, when the remainder of this document refers to
Unicode, the reader should assume UTF-8.
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Much of the text for the profiles comes from RFC3491 [13].
13.1. Stringprep profile for the utf8str_cs type
Every use of the utf8str_cs type definition in the NFS version 4
protocol specification follows the profile named nfs4_cs_prep.
13.1.1. Intended applicability of the nfs4_cs_prep profile
The utf8str_cs type is a case sensitive string of UTF-8 characters.
Its primary use in NFS Version 4 is for naming components and
pathnames. Components and pathnames are stored on the server's file
system. Two valid distinct UTF-8 strings might be the same after
processing via the utf8str_cs profile. If the strings are two names
inside a directory, the NFS version 4 server will need to either:
o disallow the creation of a second name if it's post processed form
collides with that of an existing name, or
o allow the creation of the second name, but arrange so that after
post processing, the second name is different than the post
processed form of the first name.
13.1.2. Character repertoire of nfs4_cs_prep
The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
Appendix A.1
13.1.3. Mapping used by nfs4_cs_prep
The nfs4_cs_prep profile specifies mapping using the following tables
from stringprep:
Table B.1
Table B.2 is normally not part of the nfs4_cs_prep profile as it is
primarily for dealing with case-insensitive comparisons. However, if
the NFS version 4 file server supports the case_insensitive file
system attribute, and if case_insensitive is true, the NFS version 4
server MUST use Table B.2 (in addition to Table B1) when processing
utf8str_cs strings, and the NFS version 4 client MUST assume Table
B.2 (in addition to Table B.1) are being used.
If the case_preserving attribute is present and set to false, then
the NFS version 4 server MUST use table B.2 to map case when
processing utf8str_cs strings. Whether the server maps from lower to
upper case or the upper to lower case is an implementation
dependency.
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13.1.4. Normalization used by nfs4_cs_prep
The nfs4_cs_prep profile does not specify a normalization form. A
later revision of this specification may specify a particular
normalization form. Therefore, the server and client can expect that
they may receive unnormalized characters within protocol requests and
responses. If the operating environment requires normalization, then
the implementation must normalize utf8str_cs strings within the
protocol before presenting the information to an application (at the
client) or local file system (at the server).
13.1.5. Prohibited output for nfs4_cs_prep
The nfs4_cs_prep profile specifies prohibiting using the following
tables from stringprep:
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
13.1.6. Bidirectional output for nfs4_cs_prep
The nfs4_cs_prep profile does not specify any checking of
bidirectional strings.
13.2. Stringprep profile for the utf8str_cis type
Every use of the utf8str_cis type definition in the NFS version 4
protocol specification follows the profile named nfs4_cis_prep.
13.2.1. Intended applicability of the nfs4_cis_prep profile
The utf8str_cis type is a case insensitive string of UTF-8
characters. Its primary use in NFS Version 4 is for naming NFS
servers.
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13.2.2. Character repertoire of nfs4_cis_prep
The nfs4_cis_prep profile uses Unicode 3.2, as defined in
stringprep's Appendix A.1
13.2.3. Mapping used by nfs4_cis_prep
The nfs4_cis_prep profile specifies mapping using the following
tables from stringprep:
Table B.1
Table B.2
13.2.4. Normalization used by nfs4_cis_prep
The nfs4_cis_prep profile specifies using Unicode normalization form
KC, as described in stringprep.
13.2.5. Prohibited output for nfs4_cis_prep
The nfs4_cis_prep profile specifies prohibiting using the following
tables from stringprep:
Table C.1.2
Table C.2.2
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
13.2.6. Bidirectional output for nfs4_cis_prep
The nfs4_cis_prep profile specifies checking bidirectional strings as
described in stringprep's section 6.
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13.3. Stringprep profile for the utf8str_mixed type
Every use of the utf8str_mixed type definition in the NFS version 4
protocol specification follows the profile named nfs4_mixed_prep.
13.3.1. Intended applicability of the nfs4_mixed_prep profile
The utf8str_mixed type is a string of UTF-8 characters, with a prefix
that is case sensitive, a separator equal to '@', and a suffix that
is fully qualified domain name. Its primary use in NFS Version 4 is
for naming principals identified in an Access Control Entry.
13.3.2. Character repertoire of nfs4_mixed_prep
The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
stringprep's Appendix A.1
13.3.3. Mapping used by nfs4_cis_prep
For the prefix and the separator of a utf8str_mixed string, the
nfs4_mixed_prep profile specifies mapping using the following table
from stringprep:
Table B.1
For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
specifies mapping using the following tables from stringprep:
Table B.1
Table B.2
13.3.4. Normalization used by nfs4_mixed_prep
The nfs4_mixed_prep profile specifies using Unicode normalization
form KC, as described in stringprep.
13.3.5. Prohibited output for nfs4_mixed_prep
The nfs4_mixed_prep profile specifies prohibiting using the following
tables from stringprep:
Table C.1.2
Table C.2.2
Table C.3
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Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
13.3.6. Bidirectional output for nfs4_mixed_prep
The nfs4_mixed_prep profile specifies checking bidirectional strings
as described in stringprep's section 6.
13.4. UTF-8 Related Errors
Where the client sends an invalid UTF-8 string, the server should
return an NFS4ERR_INVAL (Table 8) error. This includes cases in
which inappropriate prefixes are detected and where the count
includes trailing bytes that do not constitute a full UCS character.
Where the client supplied string is valid UTF-8 but contains
characters that are not supported by the server as a value for that
string (e.g. names containing characters that have more than two
octets on a file system that supports Unicode characters only), the
server should return an NFS4ERR_BADCHAR (Table 8) error.
Where a UTF-8 string is used as a file name, and the file system,
while supporting all of the characters within the name, does not
allow that particular name to be used, the server should return the
error NFS4ERR_BADNAME (Table 8). This includes situations in which
the server file system imposes a normalization constraint on name
strings, but will also include such situations as file system
prohibitions of "." and ".." as file names for certain operations,
and other such constraints.
14. Error Values
NFS error numbers are assigned to failed operations within a 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
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compound request will be terminated.
14.1. Error Definitions
Protocol Error Definitions
+-----------------------------------+--------+----------------------+
| Error | Number | Description |
+-----------------------------------+--------+----------------------+
| NFS4_OK | 0 | Indicates the |
| | | operation completed |
| | | successfully. |
| NFS4ERR_ACCESS | 13 | Permission denied. |
| | | The caller does not |
| | | have the correct |
| | | permission to |
| | | perform the |
| | | requested operation. |
| | | Contrast this with |
| | | NFS4ERR_PERM, which |
| | | restricts itself to |
| | | owner or privileged |
| | | user permission |
| | | failures. |
| NFS4ERR_ATTRNOTSUPP | 10032 | An attribute |
| | | specified is not |
| | | supported by the |
| | | server. Does not |
| | | apply to the GETATTR |
| | | operation. |
| NFS4ERR_ADMIN_REVOKED | 10047 | Due to administrator |
| | | intervention, the |
| | | lockowner's record |
| | | locks, share |
| | | reservations, and |
| | | delegations have |
| | | been revoked by the |
| | | server. |
| NFS4ERR_BADCHAR | 10040 | A UTF-8 string |
| | | contains a character |
| | | which is not |
| | | supported by the |
| | | server in the |
| | | context in which it |
| | | being used. |
| NFS4ERR_BAD_COOKIE | 10003 | READDIR cookie is |
| | | stale. |
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| NFS4ERR_BADHANDLE | 10001 | Illegal NFS |
| | | filehandle. The |
| | | filehandle failed |
| | | internal consistency |
| | | checks. |
| NFS4ERR_BADIOMODE | 10049 | Layout iomode is |
| | | invalid. |
| NFS4ERR_BADLAYOUT | 10050 | Layout specified is |
| | | invalid. |
| NFS4ERR_BADNAME | 10041 | A name string in a |
| | | request consists 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. |
| NFS4ERR_BADOWNER | 10039 | An owner, |
| | | owner_group, or ACL |
| | | attribute value can |
| | | not be translated to |
| | | local |
| | | representation. |
| NFS4ERR_BAD_SESSION_DIGEST | 10051 | The digest used in a |
| | | SET_SSV or |
| | | BIND_CONN_TO_SESSION |
| | | request is not |
| | | valid. |
| NFS4ERR_BADTYPE | 10007 | An attempt was made |
| | | to create an object |
| | | of a type not |
| | | supported by the |
| | | server. |
| NFS4ERR_BAD_RANGE | 10042 | The range for a |
| | | LOCK, LOCKT, or |
| | | LOCKU operation is |
| | | not appropriate to |
| | | the allowable range |
| | | of offsets for the |
| | | server. |
| NFS4ERR_BAD_SEQID | 10026 | The sequence number |
| | | in a locking request |
| | | is neither the next |
| | | expected number or |
| | | the last number |
| | | processed. |
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| NFS4ERR_BADSESSION | 10052 | TDB |
| NFS4ERR_BADSLOT | 10053 | TDB |
| NFS4ERR_BAD_STATEID | 10025 | 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. |
| NFS4ERR_BADXDR | 10036 | The server |
| | | encountered an XDR |
| | | decoding error while |
| | | processing an |
| | | operation. |
| NFS4ERR_CLID_INUSE | 10017 | The EXCHANGE_ID |
| | | operation has found |
| | | that a client id is |
| | | already in use by |
| | | another client. |
| NFS4ERR_COMPLETE_ALREADY | 10054 | A RECLAIM_COMPLETE |
| | | operation was done |
| | | by a client which |
| | | had already |
| | | performed one. |
| NFS4ERR_CONN_NOT_BOUND_TO_SESSION | 10055 | The connection is |
| | | not bound to the |
| | | specified session. |
| NFS4ERR_CONN_BINDING_NOT_ENFORCED | 10073 | Client is trying use |
| | | enforced connection |
| | | binding, but it |
| | | disabled enforcement |
| | | when the session was |
| | | created. |
| NFS4ERR_DEADLOCK | 10045 | The server has been |
| | | able to determine a |
| | | file locking |
| | | deadlock condition |
| | | for a blocking lock |
| | | request. |
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| NFS4ERR_DELAY | 10008 | The server initiated |
| | | the request, but was |
| | | not able to complete |
| | | it in a timely |
| | | fashion. The client |
| | | should wait and then |
| | | try the request with |
| | | a new RPC |
| | | transaction ID. For |
| | | example, this error |
| | | should be returned |
| | | from a server that |
| | | supports |
| | | hierarchical storage |
| | | and receives a |
| | | request to process a |
| | | file that has been |
| | | migrated. In this |
| | | case, the server |
| | | should start the |
| | | immigration process |
| | | and respond to |
| | | client with this |
| | | error. This error |
| | | may also occur when |
| | | a necessary |
| | | delegation recall |
| | | makes processing a |
| | | request in a timely |
| | | fashion impossible. |
| NFS4ERR_DELEG_ALREADY_WANTED | 10056 | The client has |
| | | already registered |
| | | that it wants a |
| | | delegation. |
| NFS4ERR_DENIED | 10010 | An attempt to lock a |
| | | file is denied. |
| | | Since this may be a |
| | | temporary condition, |
| | | the client is |
| | | encouraged to retry |
| | | the lock request |
| | | until the lock is |
| | | accepted. |
| NFS4ERR_DIRDELEG_UNAVAIL | 10057 | TBD |
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| NFS4ERR_DQUOT | 69 | Resource (quota) |
| | | hard limit exceeded. |
| | | The user's resource |
| | | limit on the server |
| | | has been exceeded. |
| NFS4ERR_EXIST | 17 | File exists. The |
| | | file specified |
| | | already exists. |
| NFS4ERR_EXPIRED | 10011 | A lease has expired |
| | | that is being used |
| | | in the current |
| | | operation. |
| NFS4ERR_FBIG | 27 | File too large. The |
| | | operation would have |
| | | caused a file to |
| | | grow beyond the |
| | | server's limit. |
| NFS4ERR_FHEXPIRED | 10014 | The filehandle |
| | | provided is volatile |
| | | and has expired at |
| | | the server. |
| NFS4ERR_FILE_OPEN | 10046 | The operation can |
| | | not be successfully |
| | | processed because a |
| | | file involved in the |
| | | operation is |
| | | currently open. |
| NFS4ERR_GRACE | 10013 | The server is in its |
| | | recovery or grace |
| | | period which should |
| | | match the lease |
| | | period of the |
| | | server. |
| NFS4ERR_INVAL | 22 | Invalid argument or |
| | | unsupported argument |
| | | for an operation. |
| | | Two examples are |
| | | attempting a |
| | | READLINK on an |
| | | object other than a |
| | | symbolic link or |
| | | specifying a value |
| | | for an enum field |
| | | that is not defined |
| | | in the protocol |
| | | (e.g. nfs_ftype4). |
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| NFS4ERR_IO | 5 | I/O error. A hard |
| | | error (for example, |
| | | a disk error) |
| | | occurred while |
| | | processing the |
| | | requested operation. |
| NFS4ERR_ISDIR | 21 | Is a directory. The |
| | | caller specified a |
| | | directory in a |
| | | non-directory |
| | | operation. |
| NFS4ERR_LAYOUTTRYLATER | 10058 | Layouts are |
| | | temporarily |
| | | unavailable for the |
| | | file, client should |
| | | retry later. |
| NFS4ERR_LAYOUTUNAVAILABLE | 10059 | Layouts are not |
| | | available for the |
| | | file or its |
| | | containing file |
| | | system. |
| NFS4ERR_LEASE_MOVED | 10031 | A lease being |
| | | renewed is |
| | | associated with a |
| | | file system that has |
| | | been migrated to a |
| | | new server. |
| NFS4ERR_LOCKED | 10012 | A read or write |
| | | operation was |
| | | attempted on a |
| | | locked file. |
| NFS4ERR_LOCK_NOTSUPP | 10043 | Server does not |
| | | support atomic |
| | | upgrade or downgrade |
| | | of locks. |
| NFS4ERR_LOCK_RANGE | 10028 | A lock request is |
| | | operating on a |
| | | sub-range of a |
| | | current lock for the |
| | | lock owner and the |
| | | server does not |
| | | support this type of |
| | | request. |
| NFS4ERR_LOCKS_HELD | 10037 | A CLOSE was |
| | | attempted and file |
| | | locks would exist |
| | | after the CLOSE. |
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| NFS4ERR_MINOR_VERS_MISMATCH | 10021 | The server has |
| | | received a request |
| | | that specifies an |
| | | unsupported minor |
| | | version. The server |
| | | must return a |
| | | COMPOUND4res with a |
| | | zero length |
| | | operations result |
| | | array. |
| NFS4ERR_SEQ_MISORDERED | 10063 | The requester sent a |
| | | SEQUENCE or |
| | | CB_SEQUENCE |
| | | operation with an |
| | | invalid sequenceid. |
| NFS4ERR_SEQUENCE_POS | 10064 | The requester sent a |
| | | COMPOUND or |
| | | CB_COMPOUND with a |
| | | SEQUENCE or |
| | | CB_SEQUENCE |
| | | operation that was |
| | | not the first |
| | | operation. |
| NFS4ERR_MLINK | 31 | Too many hard links. |
| NFS4ERR_MOVED | 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" |
| | | attribute for the |
| | | current filehandle. |
| | | For further |
| | | discussion, refer to |
| | | the section |
| | | "Multi-server Name |
| | | Space". |
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| NFS4ERR_NAMETOOLONG | 63 | The filename in an |
| | | operation was too |
| | | long. |
| NFS4ERR_NOENT | 2 | No such file or |
| | | directory. The file |
| | | or directory name |
| | | specified does not |
| | | exist. |
| NFS4ERR_NOFILEHANDLE | 10020 | The logical current |
| | | filehandle value |
| | | (or, in the case of |
| | | RESTOREFH, the saved |
| | | filehandle value) |
| | | has not been set |
| | | properly. 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). |
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| NFS4ERR_NO_GRACE | 10033 | A reclaim of client |
| | | state was attempted |
| | | in circumstances in |
| | | which the server |
| | | cannot guarantee |
| | | that conflicting |
| | | state has not been |
| | | provided to another |
| | | client. This can |
| | | occur because the |
| | | reclaim has been |
| | | done outside of the |
| | | grace period of the |
| | | server, after the |
| | | client has done a |
| | | RECLAIM_COMPLETE |
| | | operation, or |
| | | because previous |
| | | operations have |
| | | created a situation |
| | | in which the server |
| | | is not able to |
| | | determine that a |
| | | reclaim-interfering |
| | | edge condition does |
| | | not exist. |
| NFS4ERR_NOMATCHING_LAYOUT | 10060 | Client has no |
| | | matching layout |
| | | (segment) to return. |
| NFS4ERR_NOSPC | 28 | No space left on |
| | | device. The |
| | | operation would have |
| | | caused the server's |
| | | file system to |
| | | exceed its limit. |
| NFS4ERR_NOTDIR | 20 | Not a directory. The |
| | | caller specified a |
| | | non-directory in a |
| | | directory operation. |
| NFS4ERR_NOTEMPTY | 66 | An attempt was made |
| | | to remove a |
| | | directory that was |
| | | not empty. |
| NFS4ERR_NOTSUPP | 10004 | Operation is not |
| | | supported. |
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| NFS4ERR_NOT_SAME | 10027 | This error is |
| | | returned by the |
| | | VERIFY operation to |
| | | signify that the |
| | | attributes compared |
| | | were not the same as |
| | | provided in the |
| | | client's request. |
| NFS4ERR_NXIO | 6 | I/O error. No such |
| | | device or address. |
| NFS4ERR_OLD_STATEID | 10024 | A stateid which |
| | | designates the |
| | | locking state for a |
| | | lockowner-file at an |
| | | earlier time was |
| | | used. |
| NFS4ERR_OPENMODE | 10038 | The client attempted |
| | | a READ, WRITE, LOCK |
| | | or SETATTR operation |
| | | not sanctioned by |
| | | the stateid passed |
| | | (e.g. writing to a |
| | | file opened only for |
| | | read). |
| NFS4ERR_OP_ILLEGAL | 10044 | An illegal operation |
| | | value has been |
| | | specified in the |
| | | argop field of a |
| | | COMPOUND or |
| | | CB_COMPOUND |
| | | procedure. |
| NFS4ERR_OP_NOT_IN_SESSION | 10070 | The COMPOUND or |
| | | CB_COMPOUND contains |
| | | an operation that |
| | | requires a SEQUENCE |
| | | or CB_SEQUENCE |
| | | operation to precede |
| | | it in order to |
| | | establish a session. |
| NFS4ERR_PERM | 1 | Not owner. The |
| | | operation was not |
| | | allowed because the |
| | | caller is either not |
| | | a privileged user |
| | | (root) or not the |
| | | owner of the target |
| | | of the operation. |
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| NFS4ERR_RECALLCONFLICT | 10061 | Layout is |
| | | unavailable due to a |
| | | conflicting |
| | | LAYOUTRECALL that is |
| | | in progress. |
| NFS4ERR_RECLAIM_BAD | 10034 | The reclaim provided |
| | | by the client does |
| | | not match any of the |
| | | server's state |
| | | consistency checks |
| | | and is bad. |
| NFS4ERR_RECLAIM_CONFLICT | 10035 | The reclaim provided |
| | | by the client has |
| | | encountered a |
| | | conflict and can not |
| | | be provided. |
| | | Potentially |
| | | indicates a |
| | | misbehaving client. |
| NFS4ERR_REP_TOO_BIG | 10066 | The reply to a |
| | | COMPOUND or |
| | | CB_COMPOUND would |
| | | exceed the channel's |
| | | negotiated maximum |
| | | response size. |
| NFS4ERR_REP_TOO_BIG_TO_CACHE | 10067 | The reply to a |
| | | COMPOUND or |
| | | CB_COMPOUND would |
| | | exceed the channel's |
| | | negotiated maximum |
| | | size for replies |
| | | cached in the reply |
| | | cache. |
| NFS4ERR_REQ_TOO_BIG | 10065 | The COMPOUND or |
| | | CB_COMPOUND request |
| | | exceeds the |
| | | channel's negotiated |
| | | maximum size for |
| | | requests. |
| NFS4ERR_RESTOREFH | 10030 | The RESTOREFH |
| | | operation does not |
| | | have a saved |
| | | filehandle |
| | | (identified by |
| | | SAVEFH) to operate |
| | | upon. |
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| NFS4ERR_RETRY_UNCACHED_REP | 10068 | The requester has |
| | | attempted a retry of |
| | | COMPOUND or |
| | | CB_COMPOUND which it |
| | | previously requested |
| | | not be placed in the |
| | | reply cache. |
| NFS4ERR_ROFS | 30 | Read-only file |
| | | system. A modifying |
| | | operation was |
| | | attempted on a |
| | | read-only file |
| | | system. |
| NFS4ERR_SAME | 10009 | This error is |
| | | returned by the |
| | | NVERIFY operation to |
| | | signify that the |
| | | attributes compared |
| | | were the same as |
| | | provided in the |
| | | client's request. |
| NFS4ERR_SERVERFAULT | 10006 | An error occurred on |
| | | the server which |
| | | does not map to any |
| | | of the legal NFS |
| | | version 4 protocol |
| | | error values. The |
| | | client should |
| | | translate this into |
| | | an appropriate |
| | | error. UNIX clients |
| | | may choose to |
| | | translate this to |
| | | EIO. |
| NFS4ERR_SHARE_DENIED | 10015 | An attempt to OPEN a |
| | | file with a share |
| | | reservation has |
| | | failed because of a |
| | | share conflict. |
| NFS4ERR_STALE | 70 | Invalid filehandle. |
| | | The filehandle given |
| | | in the arguments was |
| | | invalid. The file |
| | | referred to by that |
| | | filehandle no longer |
| | | exists or access to |
| | | it has been revoked. |
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| NFS4ERR_STALE_CLIENTID | 10022 | A clientid not |
| | | recognized by the |
| | | server was used in a |
| | | locking or |
| | | CREATE_SESSION |
| | | request. |
| NFS4ERR_STALE_STATEID | 10023 | A stateid generated |
| | | by an earlier server |
| | | instance was used. |
| NFS4ERR_SYMLINK | 10029 | The current |
| | | filehandle provided |
| | | for a LOOKUP is not |
| | | a directory but a |
| | | symbolic link. Also |
| | | used if the final |
| | | component of the |
| | | OPEN path is a |
| | | symbolic link. |
| NFS4ERR_TOOSMALL | 10005 | The encoded response |
| | | to a READDIR request |
| | | exceeds the size |
| | | limit set by the |
| | | initial request. |
| NFS4ERR_TOO_MANY_OPS | 10070 | The COMPOUND or |
| | | CB_COMPOUND request |
| | | has too many |
| | | operations. |
| NFS4ERR_UNKNOWN_LAYOUTTYPE | 10062 | Layout type is |
| | | unknown. |
| NFS4ERR_UNSAFE_COMPOUND | 10069 | The client has sent |
| | | a COMPOUND request |
| | | with an unsafe mix |
| | | of operations. |
| NFS4ERR_WRONGSEC | 10016 | The security |
| | | mechanism being used |
| | | by the client for |
| | | the operation does |
| | | not match the |
| | | server's security |
| | | policy. The client |
| | | should change the |
| | | security mechanism |
| | | being used and retry |
| | | the operation. |
| NFS4ERR_XDEV | 18 | Attempt to do an |
| | | operation between |
| | | different fsids. |
+-----------------------------------+--------+----------------------+
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Table 8
14.2. Operations and their valid errors
Mappings of 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| BIND_CONN_TO_SESSION | NFS4ERR_BAD_SESSION_DIGEST, |
| | NFS4ERR_CONN_BINDING_NOT_ENFORCED |
| 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
| COMMIT | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
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| 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_OP_NOT_IN_SESSION, NFS4ERR_PERM, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| EXCHANGE_ID | |
| CREATE_SESSION | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE_CLIENTID |
| DELEGPURGE | NFS4ERR_BADXDR, NFS4ERR_NOTSUPP, |
| | NFS4ERR_LEASE_MOVED, NFS4ERR_MOVED, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
| DESTROY_SESSION | |
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| GET_DIR_DELEGATION | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_DIRDELEG_UNAVAIL, |
| | NFS4ERR_WRONGSEC, NFS4ERR_EIO, |
| | NFS4ERR_NOTSUPP |
| GETATTR | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| GETDEVICEINFO | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_TOOSMALL, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE |
| GETDEVICELIST | NFS4ERR_BAD_COOKIE, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_TOOSMALL, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE |
| GETFH | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| ILLEGAL | NFS4ERR_OP_ILLEGAL |
| LAYOUTCOMMIT | NFS4ERR_BADLAYOUT, NFS4ERR_BADIOMODE, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NO_GRACE, |
| | NFS4ERR_RECLAIM_BAD, NFS4ERR_STALE, |
| | NFS4ERR_STALE_CLIENTID, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE |
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| LAYOUTGET | NFS4ERR_BADLAYOUT, NFS4ERR_BADIOMODE, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_LAYOUTUNAVAILABLE, |
| | NFS4ERR_LAYOUTTRYLATER, NFS4ERR_LOCKED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP, |
| | NFS4ERR_RECALLCONFLICT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_CLIENTID, NFS4ERR_TOOSMALL, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE |
| LAYOUTRETURN | NFS4ERR_BADLAYOUT, NFS4ERR_BADIOMODE, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NO_GRACE, |
| | NFS4ERR_STALE, NFS4ERR_STALE_CLIENTID, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE |
| 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_WRONGSEC, NFS4ERR_XDEV |
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| 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_RECLAIM_BAD, |
| | NFS4ERR_RECLAIM_CONFLICT, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_SYMLINK, NFS4ERR_WRONGSEC |
| LOOKUPP | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_IO, |
| | NFS4ERR_MOVED, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_WRONGSEC |
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| NVERIFY | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_SAME, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| OPEN | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADOWNER, NFS4ERR_BAD_SEQID, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_DQUOT, NFS4ERR_EXIST, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_IO, NFS4ERR_INVAL, |
| | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG, |
| | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_NOTDIR, |
| | NFS4ERR_NO_GRACE, NFS4ERR_PERM, |
| | NFS4ERR_RECLAIM_BAD, |
| | NFS4ERR_RECLAIM_CONFLICT, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_SHARE_DENIED, |
| | NFS4ERR_STALE, NFS4ERR_STALE_CLIENTID, |
| | NFS4ERR_SYMLINK, NFS4ERR_WRONGSEC |
| OPEN_DOWNGRADE | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BAD_SEQID, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_BADXDR, NFS4ERR_EXPIRED, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
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| 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| PUTFH | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_MOVED, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_WRONGSEC |
| PUTPUBFH | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_WRONGSEC |
| PUTROOTFH | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_WRONGSEC |
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| READ | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_IO, NFS4ERR_INVAL, |
| | NFS4ERR_ISDIR, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NXIO, |
| | NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_OPENMODE, NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
| READDIR | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BAD_COOKIE, NFS4ERR_BADXDR, |
| | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_NOT_SAME, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOOSMALL |
| READLINK | NFS4ERR_ACCESS, NFS4ERR_BADHANDLE, |
| | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| RECLAIM_COMPLETE | NFS4ERR_COMPLETE_ALREADY |
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| RELEASE_LOCKOWNER | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR, |
| | NFS4ERR_EXPIRED, NFS4ERR_LEASE_MOVED, |
| | NFS4ERR_LOCKS_HELD, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE_CLIENTID |
| REMOVE | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_NOTEMPTY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| RENAME | 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_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_NOTDIR, NFS4ERR_NOTEMPTY, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_WRONGSEC, NFS4ERR_XDEV |
| RESTOREFH | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_MOVED, NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_RESTOREFH, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE, NFS4ERR_WRONGSEC |
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| SAVEFH | NFS4ERR_BADHANDLE, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| SECINFO | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| SECINFO_NO_NAME | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADNAME, |
| | NFS4ERR_BADXDR, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_INVAL, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| SEQUENCE | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT, |
| | NFS4ERR_CONN_NOT_BOUND_TO_SESSION, |
| | NFS4ERR_SEQ_MISORDERED, |
| | NFS4ERR_SEQUENCE_POS, NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE |
| SET_SSV | NFS4ERR_BAD_SESSION_DIGEST, |
| | NFS4ERR_CONN_BINDING_NOT_ENFORCED |
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| SETATTR | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BADOWNER, |
| | NFS4ERR_BAD_STATEID, NFS4ERR_BADXDR, |
| | NFS4ERR_DELAY, NFS4ERR_DQUOT, |
| | NFS4ERR_EXPIRED, NFS4ERR_FBIG, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC, |
| | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE, |
| | NFS4ERR_PERM, NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
| EXCHANGE_ID | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE, |
| | NFS4ERR_INVAL, NFS4ERR_SERVERFAULT |
| CREATE_SESSION | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE, |
| | NFS4ERR_DELAY, NFS4ERR_SERVERFAULT, |
| | NFS4ERR_STALE_CLIENTID |
| VERIFY | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP, |
| | NFS4ERR_BADCHAR, NFS4ERR_BADHANDLE, |
| | NFS4ERR_BADXDR, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOT_SAME, |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE |
| WANT_DELEGATION | |
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| WRITE | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_BADHANDLE, NFS4ERR_BAD_STATEID, |
| | NFS4ERR_BADXDR, 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_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_STALE_STATEID |
+----------------------+--------------------------------------------+
Table 9
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14.3. Callback operations and their valid errors
Mappings of valid error returns for each protocol callback operation
+-------------------------+-----------------------------------------+
| Callback Operation | Errors |
+-------------------------+-----------------------------------------+
| CB_GETATTR | NFS4ERR_BADHANDLE NFS4ERR_BADXDR |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_UNSAFE_COMPOUND, |
| | NFS4ERR_SERVERFAULT |
| CB_ILLEGAL | NFS4ERR_OP_ILLEGAL |
| CB_LAYOUTRECALL | NFS4ERR_NOMATCHING_LAYOUT |
| CB_NOTIFY | NFS4ERR_BAD_STATEID NFS4ERR_INVAL |
| | NFS4ERR_BADXDR NFS4ERR_SERVERFAULT |
| CB_PUSH_DELEG | |
| CB_RECALL | NFS4ERR_BADHANDLE NFS4ERR_BAD_STATEID |
| | NFS4ERR_BADXDR |
| | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_SERVERFAULT |
| CB_RECALL_ANY | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_INVAL |
| CB_RECALLABLE_OBJ_AVAIL | |
| CB_RECALL_CREDIT | |
| CB_SEQUENCE | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT, |
| | NFS4ERR_CONN_NOT_BOUND_TO_SESSION, |
| | NFS4ERR_SEQ_MISORDERED, |
| | NFS4ERR_SEQUENCE_POS, |
| | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE |
+-------------------------+-----------------------------------------+
Table 10
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14.4. Errors and the operations that use them
+-----------------------------------+-------------------------------+
| Error | Operations |
+-----------------------------------+-------------------------------+
| NFS4ERR_ACCESS | ACCESS, COMMIT, CREATE, |
| | GETATTR, GET_DIR_DELEGATION, |
| | LINK, LOCK, LOCKT, LOCKU, |
| | LOOKUP, LOOKUPP, NVERIFY, |
| | OPEN, OPENATTR, READ, |
| | READDIR, READLINK, REMOVE, |
| | RENAME, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WRITE |
| NFS4ERR_ADMIN_REVOKED | CLOSE, DELEGRETURN, LOCK, |
| | LOCKU, OPEN, OPEN_DOWNGRADE, |
| | READ, RELEASE_LOCKOWNER, |
| | SETATTR, WRITE |
| NFS4ERR_ATTRNOTSUPP | CREATE, NVERIFY, OPEN, |
| | SETATTR, VERIFY |
| NFS4ERR_BADCHAR | CREATE, LINK, LOOKUP, |
| | NVERIFY, OPEN, REMOVE, |
| | RENAME, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY |
| NFS4ERR_BADHANDLE | ACCESS, CB_GETATTR, |
| | CB_RECALL, CLOSE, COMMIT, |
| | CREATE, GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, READ, READDIR, |
| | READLINK, REMOVE, RENAME, |
| | RESTOREFH, SAVEFH, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WRITE |
| NFS4ERR_BADIOMODE | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN |
| NFS4ERR_BADLAYOUT | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN |
| NFS4ERR_BADNAME | CREATE, LINK, LOOKUP, OPEN, |
| | REMOVE, RENAME, SECINFO, |
| | SECINFO_NO_NAME |
| NFS4ERR_BADOWNER | CREATE, OPEN, SETATTR |
| NFS4ERR_BADSESSION | CB_SEQUENCE, SEQUENCE |
| NFS4ERR_BADSLOT | CB_SEQUENCE, SEQUENCE |
| NFS4ERR_BADTYPE | CREATE |
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| NFS4ERR_BADXDR | ACCESS, CB_GETATTR, |
| | CB_NOTIFY, CB_RECALL, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, EXCHANGE_ID, |
| | GETATTR, GET_DIR_DELEGATION, |
| | LINK, LOCK, LOCKT, LOCKU, |
| | LOOKUP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, READ, READDIR, |
| | RELEASE_LOCKOWNER, REMOVE, |
| | RENAME, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WRITE |
| NFS4ERR_BAD_COOKIE | GETDEVICELIST, READDIR |
| NFS4ERR_BAD_RANGE | LOCK, LOCKT, LOCKU |
| NFS4ERR_BAD_SEQID | CLOSE, LOCK, LOCKU, OPEN, |
| | OPEN_DOWNGRADE |
| NFS4ERR_BAD_SESSION_DIGEST | BIND_CONN_TO_SESSION, SET_SSV |
| NFS4ERR_BAD_STATEID | CB_NOTIFY, CB_RECALL, CLOSE, |
| | DELEGRETURN, LOCK, LOCKU, |
| | OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
| NFS4ERR_CLID_INUSE | CREATE_SESSION, EXCHANGE_ID |
| NFS4ERR_COMPLETE_ALREADY | RECLAIM_COMPLETE |
| NFS4ERR_CONN_BINDING_NOT_ENFORCED | BIND_CONN_TO_SESSION, SET_SSV |
| NFS4ERR_CONN_NOT_BOUND_TO_SESSION | CB_SEQUENCE, SEQUENCE |
| NFS4ERR_DEADLOCK | LOCK |
| NFS4ERR_DELAY | ACCESS, CLOSE, CREATE, |
| | CREATE_SESSION, GETATTR, |
| | LINK, LOCK, LOCKT, NVERIFY, |
| | OPEN, OPENATTR, READ, |
| | READDIR, READLINK, REMOVE, |
| | RENAME, SETATTR, VERIFY, |
| | WRITE |
| NFS4ERR_DENIED | LOCK, LOCKT |
| NFS4ERR_DIRDELEG_UNAVAIL | GET_DIR_DELEGATION |
| NFS4ERR_DQUOT | CREATE, LINK, OPEN, OPENATTR, |
| | RENAME, SETATTR, WRITE |
| NFS4ERR_EIO | GET_DIR_DELEGATION |
| NFS4ERR_EXIST | CREATE, LINK, OPEN, RENAME |
| NFS4ERR_EXPIRED | CLOSE, DELEGRETURN, LOCK, |
| | LOCKU, OPEN, OPEN_DOWNGRADE, |
| | READ, RELEASE_LOCKOWNER, |
| | SETATTR, WRITE |
| NFS4ERR_FBIG | SETATTR, WRITE |
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| NFS4ERR_FHEXPIRED | ACCESS, CLOSE, COMMIT, |
| | CREATE, GETATTR, |
| | GETDEVICEINFO, GETDEVICELIST, |
| | GETFH, GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, READ, READDIR, |
| | READLINK, REMOVE, RENAME, |
| | RESTOREFH, SAVEFH, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WRITE |
| NFS4ERR_FILE_OPEN | LINK, REMOVE, RENAME |
| NFS4ERR_GRACE | LOCK, LOCKT, LOCKU, OPEN, |
| | READ, SETATTR, WRITE |
| NFS4ERR_INVAL | ACCESS, CB_NOTIFY, |
| | CB_RECALL_ANY, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, |
| | EXCHANGE_ID, GETATTR, |
| | GETDEVICEINFO, GETDEVICELIST, |
| | GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | NVERIFY, OPEN, |
| | OPEN_DOWNGRADE, READ, |
| | READDIR, READLINK, REMOVE, |
| | RENAME, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WRITE |
| NFS4ERR_IO | ACCESS, COMMIT, CREATE, |
| | GETATTR, LINK, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, READ, READDIR, |
| | READLINK, REMOVE, RENAME, |
| | SETATTR, WRITE |
| NFS4ERR_ISDIR | CLOSE, COMMIT, LINK, LOCK, |
| | LOCKT, LOCKU, OPEN, READ, |
| | READLINK, SETATTR, WRITE |
| NFS4ERR_LAYOUTTRYLATER | LAYOUTGET |
| NFS4ERR_LAYOUTUNAVAILABLE | LAYOUTGET |
| NFS4ERR_LEASE_MOVED | CLOSE, DELEGPURGE, |
| | DELEGRETURN, LOCK, LOCKT, |
| | LOCKU, OPEN, READ, |
| | RELEASE_LOCKOWNER, WRITE |
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| NFS4ERR_LOCKED | LAYOUTGET, 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, DELEGPURGE, |
| | DELEGRETURN, GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, READ, READDIR, |
| | READLINK, REMOVE, RENAME, |
| | RESTOREFH, SAVEFH, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WRITE |
| NFS4ERR_NAMETOOLONG | CREATE, LINK, LOOKUP, OPEN, |
| | REMOVE, RENAME, SECINFO, |
| | SECINFO_NO_NAME |
| NFS4ERR_NOENT | LINK, LOOKUP, LOOKUPP, OPEN, |
| | OPENATTR, REMOVE, RENAME, |
| | SECINFO, SECINFO_NO_NAME |
| NFS4ERR_NOFILEHANDLE | ACCESS, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, GETATTR, |
| | GETFH, GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | READ, READDIR, READLINK, |
| | REMOVE, RENAME, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SETATTR, VERIFY, WRITE |
| NFS4ERR_NOMATCHING_LAYOUT | CB_LAYOUTRECALL |
| NFS4ERR_NOSPC | CREATE, LINK, OPEN, OPENATTR, |
| | RENAME, SETATTR, WRITE |
| NFS4ERR_NOTDIR | CREATE, GET_DIR_DELEGATION, |
| | LINK, LOOKUP, LOOKUPP, OPEN, |
| | READDIR, REMOVE, RENAME, |
| | SECINFO, SECINFO_NO_NAME |
| NFS4ERR_NOTEMPTY | REMOVE, RENAME |
| NFS4ERR_NOTSUPP | DELEGPURGE, DELEGRETURN, |
| | GET_DIR_DELEGATION, |
| | LAYOUTGET, LINK, OPENATTR, |
| | READLINK |
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| NFS4ERR_NOT_SAME | READDIR, VERIFY |
| NFS4ERR_NO_GRACE | LAYOUTCOMMIT, LAYOUTRETURN, |
| | LOCK, OPEN |
| NFS4ERR_NXIO | READ, WRITE |
| NFS4ERR_OLD_STATEID | CLOSE, DELEGRETURN, LOCK, |
| | LOCKU, OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
| NFS4ERR_OPENMODE | LOCK, READ, SETATTR, WRITE |
| NFS4ERR_OP_ILLEGAL | CB_ILLEGAL, ILLEGAL |
| NFS4ERR_OP_NOT_IN_SESSION | ACCESS, CB_GETATTR, |
| | CB_RECALL, CB_RECALL_ANY, |
| | CLOSE, COMMIT, CREATE, |
| | DELEGPURGE, DELEGRETURN, |
| | GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RELEASE_LOCKOWNER, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SETATTR, VERIFY, WRITE |
| NFS4ERR_PERM | CREATE, OPEN, SETATTR |
| NFS4ERR_RECALLCONFLICT | LAYOUTGET |
| NFS4ERR_RECLAIM_BAD | LAYOUTCOMMIT, LOCK, OPEN |
| NFS4ERR_RECLAIM_CONFLICT | LOCK, OPEN |
| NFS4ERR_REP_TOO_BIG | ACCESS, CB_GETATTR, |
| | CB_RECALL, CB_RECALL_ANY, |
| | CB_SEQUENCE, CLOSE, COMMIT, |
| | CREATE, DELEGPURGE, |
| | DELEGRETURN, GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RELEASE_LOCKOWNER, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, VERIFY, |
| | WRITE |
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| NFS4ERR_REP_TOO_BIG_TO_CACHE | ACCESS, CB_GETATTR, |
| | CB_RECALL, CB_RECALL_ANY, |
| | CB_SEQUENCE, CLOSE, COMMIT, |
| | CREATE, DELEGPURGE, |
| | DELEGRETURN, GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RELEASE_LOCKOWNER, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, VERIFY, |
| | WRITE |
| NFS4ERR_REQ_TOO_BIG | ACCESS, CB_GETATTR, |
| | CB_RECALL, CB_RECALL_ANY, |
| | CB_SEQUENCE, CLOSE, COMMIT, |
| | CREATE, DELEGPURGE, |
| | DELEGRETURN, GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RELEASE_LOCKOWNER, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, VERIFY, |
| | WRITE |
| NFS4ERR_RESTOREFH | RESTOREFH |
| NFS4ERR_ROFS | COMMIT, CREATE, LINK, OPEN, |
| | OPENATTR, REMOVE, RENAME, |
| | SETATTR, WRITE |
| NFS4ERR_SAME | NVERIFY |
| NFS4ERR_SEQUENCE_POS | CB_SEQUENCE, SEQUENCE |
| NFS4ERR_SEQ_MISORDERED | CB_SEQUENCE, SEQUENCE |
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| NFS4ERR_SERVERFAULT | ACCESS, CB_GETATTR, |
| | CB_NOTIFY, CB_RECALL, CLOSE, |
| | COMMIT, CREATE, |
| | CREATE_SESSION, DELEGPURGE, |
| | DELEGRETURN, EXCHANGE_ID, |
| | GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RELEASE_LOCKOWNER, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SETATTR, VERIFY, WRITE |
| NFS4ERR_SHARE_DENIED | OPEN |
| NFS4ERR_STALE | ACCESS, CLOSE, COMMIT, |
| | CREATE, DELEGRETURN, GETATTR, |
| | GETFH, GET_DIR_DELEGATION, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LINK, LOCK, |
| | LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, READ, READDIR, |
| | READLINK, REMOVE, RENAME, |
| | RESTOREFH, SAVEFH, SECINFO, |
| | SECINFO_NO_NAME, SETATTR, |
| | VERIFY, WRITE |
| NFS4ERR_STALE_CLIENTID | CREATE_SESSION, DELEGPURGE, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN, LOCK, LOCKT, |
| | OPEN, RELEASE_LOCKOWNER |
| NFS4ERR_STALE_STATEID | CLOSE, DELEGRETURN, LOCK, |
| | LOCKU, OPEN_DOWNGRADE, READ, |
| | SETATTR, WRITE |
| NFS4ERR_SYMLINK | LOOKUP, OPEN |
| NFS4ERR_TOOSMALL | GETDEVICEINFO, GETDEVICELIST, |
| | LAYOUTGET, READDIR |
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| NFS4ERR_TOO_MANY_OPS | ACCESS, CB_GETATTR, |
| | CB_RECALL, CB_RECALL_ANY, |
| | CB_SEQUENCE, CLOSE, COMMIT, |
| | CREATE, DELEGPURGE, |
| | DELEGRETURN, GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RELEASE_LOCKOWNER, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SEQUENCE, SETATTR, VERIFY, |
| | WRITE |
| NFS4ERR_UNKNOWN_LAYOUTTYPE | GETDEVICEINFO, GETDEVICELIST, |
| | LAYOUTCOMMIT, LAYOUTGET, |
| | LAYOUTRETURN |
| NFS4ERR_UNSAFE_COMPOUND | ACCESS, CB_GETATTR, CLOSE, |
| | COMMIT, CREATE, DELEGPURGE, |
| | DELEGRETURN, GETATTR, GETFH, |
| | GET_DIR_DELEGATION, LINK, |
| | LOCK, LOCKT, LOCKU, LOOKUP, |
| | LOOKUPP, NVERIFY, OPEN, |
| | OPENATTR, OPEN_DOWNGRADE, |
| | PUTFH, PUTPUBFH, PUTROOTFH, |
| | READ, READDIR, READLINK, |
| | RELEASE_LOCKOWNER, REMOVE, |
| | RENAME, RESTOREFH, SAVEFH, |
| | SECINFO, SECINFO_NO_NAME, |
| | SETATTR, VERIFY, WRITE |
| NFS4ERR_WRONGSEC | GET_DIR_DELEGATION, LINK, |
| | LOOKUP, LOOKUPP, OPEN, PUTFH, |
| | PUTPUBFH, PUTROOTFH, RENAME, |
| | RESTOREFH |
| NFS4ERR_XDEV | LINK, RENAME |
+-----------------------------------+-------------------------------+
Table 11
15. NFS version 4.1 Procedures
15.1. Procedure 0: NULL - No Operation
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15.1.1. SYNOPSIS
15.1.2. ARGUMENTS
void;
15.1.3. RESULTS
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.
15.1.5. ERRORS
None.
15.2. Procedure 1: COMPOUND - Compound Operations
15.2.1. SYNOPSIS
compoundargs -> compoundres
15.2.2. ARGUMENTS
union nfs_argop4 switch (nfs_opnum4 argop) {
case <OPCODE>: <argument>;
...
};
struct COMPOUND4args {
utf8str_cs tag;
uint32_t minorversion;
nfs_argop4 argarray<>;
};
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15.2.3. RESULTS
union nfs_resop4 switch (nfs_opnum4 resop){
case <OPCODE>: <result>;
...
};
struct COMPOUND4res {
nfsstat4 status;
utf8str_cs 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. See Section 2.9.4.4 for a
more detailed discussion.
The server will generally choose between two methods of decoding the
client's request. The first would be the traditional one pass XDR
decode. If there is an XDR decoding error in this case, the RPC XDR
decode error would be returned. The second method would be to make
an initial pass to decode the basic COMPOUND request and then to XDR
decode the individual operations; the most interesting is the decode
of attributes. In this case, the server may encounter an XDR decode
error during the second pass. In this case, the server would return
the error NFS4ERR_BADXDR to signify the decode error.
The COMPOUND arguments contain a "minorversion" field. For NFSv4.1,
the value for this field is 1. If the server receives a COMPOUND
procedure with a minorversion field value that it does not support,
the server MUST return an error of NFS4ERR_MINOR_VERS_MISMATCH and a
zero length resultdata array.
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Contained within the COMPOUND results is a "status" field. If the
results array length is non-zero, this status must be equivalent to
the status of the last operation that was executed within the
COMPOUND procedure. Therefore, if an operation incurred an error
then the "status" value will be the same error value as is being
returned for the operation that failed.
Note that operations, 0 (zero) and 1 (one) are not defined for the
COMPOUND procedure. Operation 2 is not defined but reserved for
future definition and use with minor versioning. If the server
receives a operation array that contains operation 2 and the
minorversion field has a value of 0 (zero), an error of
NFS4ERR_OP_ILLEGAL, as described in the next paragraph, is returned
to the client. If an operation array contains an operation 2 and the
minorversion field is non-zero and the server does not support the
minor version, the server returns an error of
NFS4ERR_MINOR_VERS_MISMATCH. Therefore, the
NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
errors.
It is possible that the server receives a request that contains an
operation that is less than the first legal operation (OP_ACCESS) or
greater than the last legal operation (OP_RELEASE_LOCKOWNER). In
this case, the server's response will encode the opcode OP_ILLEGAL
rather than the illegal opcode of the request. The status field in
the ILLEGAL return results will set to NFS4ERR_OP_ILLEGAL. The
COMPOUND procedure's return results will also be NFS4ERR_OP_ILLEGAL.
The definition of the "tag" in the request is left to the
implementor. It may be used to summarize the content of the compound
request for the benefit of packet sniffers and engineers debugging
implementations. However, the value of "tag" in the response SHOULD
be the same value as provided in the request. This applies to the
tag field of the CB_COMPOUND procedure as well.
15.2.4.1. Current File Handle and Stateid
The COMPOUND procedure offers a simple environment for the execution
of the operations specified by the client. The first two relate to
the file handle while the second two relate to the current stateid.
15.2.4.1.1. Current File Handle
The current and saved file handle are used throughout the protocol.
Most operations implicitly use the current file handle as a argument
and many set the current file handle as part of the results. The
combination of client specified sequences of operations and current
and saved file handle arguments and results allows for greater
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protocol flexibility. The best or easiest example of current file
handle usage is a sequence like the following:
PUTFH fh1 {fh1}
LOOKUP "compA" {fh2}
GETATTR {fh2}
LOOKUP "compB" {fh3}
GETATTR {fh3}
LOOKUP "compC" {fh4}
GETATTR {fh4}
GETFH
Figure 72
In this example, the PUTFH operation explicitly sets the current file
handle value while the result of each LOOKUP operation sets the
current file handle value to the resultant file system object. Also,
the client is able to insert GETATTR operations using the current
file handle as an argument.
Along with the current file handle, there is a saved file handle.
While the current file handle is set as the result of operations like
LOOKUP, the saved file handle must be set directly with the use of
the SAVEFH operation. The SAVEFH operations copies the current file
handle value to the saved value. The saved file handle value is used
in combination with the current file handle value for the LINK and
RENAME operations. The RESTOREFH operation will copy the saved file
handle value to the current file handle value; as a result, the saved
file handle value may be used a sort of "scratch" area for the
client's series of operations.
15.2.4.1.2. Current Stateid
With NFSv4.1, additions of a current stateid and a saved stateid have
been made to the COMPOUND processing environment; this allows for the
passing of stateids between operations. There are no changes to the
syntax of the protocol, only changes to the semantics of a few
operations.
A "current stateid" is the stateid that is associated with the
current file handle. The current stateid may only be changed by an
operation that modifies the current file handle or returns a stateid.
If an operation returns a stateid it MUST set the current stateid to
the returned value. If an operation sets the current file handle but
does not return a stateid, the current stateid MUST be set to the
all-zeros special stateid. As an example, PUTFH will change the
current server state from {ocfh, osid} to {cfh, 0} while LOCK will
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change the current state from {cfh, osid} to {cfh, nsid}. The SAVEFH
and RESTOREFH operations will save and restore both the file handle
and the stateid as a set.
Any operation which takes as an argument a stateid that is not the
special all-zeros stateid MUST set the current stateid to the all-
zeros value before evaluating the operation. If the argument is the
special all-zeros stateid, the operation is evaluated using the
current stateid.
The following example is the common case of a simple READ operation
with a supplied stateid showing that the PUTFH initializes the
current stateid to zero. The subsequent READ with stateid sid1
replaces the current stateid before evaluating the operation.
PUTFH fh1 - -> {fh1, 0}
READ sid1,0,1024 {fh1, sid1} -> {fh1, sid1}
Figure 73
This next example performs an OPEN with the client provided stateid
sid1 and as a result generates stateid sid2. The next operation
specifies the READ with the special all-zero stateid but the current
stateid set by the previous operation is actually used when the
operation is evaluated, allowing correct interaction with any
existing, potentially conflicting, locks.
PUTFH fh1 - -> {fh1, 0}
OPEN R,sid1,"compA" {fh1, sid1} -> {fh2, sid2}
READ 0,0,1024 {fh2, sid2} -> {fh2, sid2}
CLOSE 0 {fh2, sid2} -> {fh2, sid3}
Figure 74
The final example is similar to the second in how it passes the
stateid sid2 generated by the LOCK operation to the next READ
operation. This allows the client to explicitly surround a single
I/O operation with a lock and its appropriate stateid to guarantee
correctness with other client locks.
PUTFH fh1 - -> {fh1, 0}
LOCK W,0,1024,sid1 {fh1, sid1} -> {fh1, sid2}
READ 0,0,1024 {fh1, sid2} -> {fh1, sid2}
LOCKU W,0,1024,0 {fh1, sid2} -> {fh1, sid3}
Figure 75
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15.2.5. IMPLEMENTATION
15.2.6. ERRORS
All errors defined in the protocol
16. NFS version 4.1 Operations
16.1. Operation 3: ACCESS - Check Access Rights
16.1.1. SYNOPSIS
(cfh), accessreq -> supported, accessrights
16.1.2. ARGUMENTS
/*
* ACCESS: Check access permission
*/
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;
};
16.1.3. RESULTS
struct ACCESS4resok {
uint32_t supported;
uint32_t access;
};
union ACCESS4res switch (nfsstat4 status) {
case NFS4_OK:
ACCESS4resok resok4;
default:
void;
};
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16.1.4. 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 was
originally sent in the arguments. For example, if the client sends
an ACCESS operation with only the ACCESS4_READ value set and the
server supports this value, the server will return only ACCESS4_READ
even if it could have reliably checked other values.
The results of this operation are necessarily advisory in nature. A
return status of NFS4_OK and the appropriate bit set in the bit mask
does not imply that such access will be allowed to the file system
object in the future. This is because access rights can be revoked
by the server at any time.
The following access permissions may be requested:
ACCESS4_READ Read data from file or read a directory.
ACCESS4_LOOKUP Look up a name in a directory (no meaning for non-
directory objects).
ACCESS4_MODIFY Rewrite existing file data or modify existing
directory entries.
ACCESS4_EXTEND Write new data or add directory entries.
ACCESS4_DELETE Delete an existing directory entry.
ACCESS4_EXECUTE Execute file (no meaning for a directory).
On success, the current filehandle retains its value.
16.1.5. 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
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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
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.
16.2. Operation 4: CLOSE - Close File
16.2.1. SYNOPSIS
(cfh), seqid, open_stateid -> open_stateid
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16.2.2. ARGUMENTS
/*
* CLOSE: Close a file and release share reservations
*/
struct CLOSE4args {
/* CURRENT_FH: object */
seqid4 seqid;
stateid4 open_stateid;
};
16.2.3. RESULTS
union CLOSE4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 open_stateid;
default:
void;
};
16.2.4. 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.
On success, the current filehandle retains its value.
16.2.5. 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.
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16.3. Operation 5: COMMIT - Commit Cached Data
16.3.1. SYNOPSIS
(cfh), offset, count -> verifier
16.3.2. ARGUMENTS
/*
* COMMIT: Commit cached data on server to stable storage
*/
struct COMMIT4args {
/* CURRENT_FH: file */
offset4 offset;
count4 count;
};
16.3.3. RESULTS
struct COMMIT4resok {
verifier4 writeverf;
};
union COMMIT4res switch (nfsstat4 status) {
case NFS4_OK:
COMMIT4resok resok4;
default:
void;
};
16.3.4. 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
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
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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.
16.3.5. 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
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
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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.
16.4. Operation 6: CREATE - Create a Non-Regular File Object
16.4.1. SYNOPSIS
(cfh), name, type, attrs -> (cfh), change_info, attrs_set
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16.4.2. ARGUMENTS
/*
* CREATE: Create a non-regular file
*/
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;
};
16.4.3. RESULTS
struct CREATE4resok {
change_info4 cinfo;
bitmap4 attrset; /* attributes set */
};
union CREATE4res switch (nfsstat4 status) {
case NFS4_OK:
CREATE4resok resok4;
default:
void;
};
16.4.4. 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.
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The objname specifies the name for the new object. The objtype
determines the type of object to be created: directory, symlink, etc.
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 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 file system both supports
and requires an owner attribute (or an owner ACE) then the server
MUST derive the owner (or the owner ACE). This would typically be
from the principal indicated in the RPC credentials of the call, but
the server's operating environment or file system semantics may
dictate other methods of derivation. Similarly, if createattrs
includes neither the group attribute nor a group ACE, and if the
server's file system both supports and requires the notion of a group
attribute (or group ACE), the server MUST derive the group attribute
(or the corresponding owner ACE) for the file. This could be from
the RPC call's credentials, such as the group principal if the
credentials include it (such as with AUTH_SYS), from the group
identifier associated with the principal in the credentials (for
e.g., POSIX systems have a passwd database that has the group
identifier for every user identifier), inherited from directory the
object is created in, or whatever else the server's operating
environment or file system semantics dictate. This applies to the
OPEN operation too.
Conversely, it is possible the client will specify in createattrs an
owner attribute or group attribute or ACL that the principal
indicated the RPC call's credentials does not have permissions to
create files for. The error to be returned in this instance is
NFS4ERR_PERM. This applies to the OPEN operation too.
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16.4.5. 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.
16.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery
16.5.1. SYNOPSIS
clientid ->
16.5.2. ARGUMENTS
/*
* DELEGPURGE: Purge Delegations Awaiting Recovery
*/
struct DELEGPURGE4args {
clientid4 clientid;
};
16.5.3. RESULTS
struct DELEGPURGE4res {
nfsstat4 status;
};
16.5.4. 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.
16.6. Operation 8: DELEGRETURN - Return Delegation
16.6.1. SYNOPSIS
(cfh), stateid ->
16.6.2. ARGUMENTS
/*
* DELEGRETURN: Return a delegation
*/
struct DELEGRETURN4args {
/* CURRENT_FH: delegated file */
stateid4 deleg_stateid;
};
16.6.3. RESULTS
struct DELEGRETURN4res {
nfsstat4 status;
};
16.6.4. 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.
16.7. Operation 9: GETATTR - Get Attributes
16.7.1. SYNOPSIS
(cfh), attrbits -> attrbits, attrvals
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16.7.2. ARGUMENTS
/*
* GETATTR: Get file attributes
*/
struct GETATTR4args {
/* CURRENT_FH: directory or file */
bitmap4 attr_request;
};
16.7.3. RESULTS
struct GETATTR4resok {
fattr4 obj_attributes;
};
union GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
GETATTR4resok resok4;
default:
void;
};
16.7.4. DESCRIPTION
The GETATTR operation will obtain attributes for the file system
object specified by the current filehandle. The client sets a bit in
the bitmap argument for each attribute value that it would like the
server to return. The server returns an attribute bitmap that
indicates the attribute values 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
File Attributes (Section 5).
On success, the current filehandle retains its value.
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16.7.5. IMPLEMENTATION
16.8. Operation 10: GETFH - Get Current Filehandle
16.8.1. SYNOPSIS
(cfh) -> filehandle
16.8.2. ARGUMENTS
/* CURRENT_FH: */
void;
16.8.3. RESULTS
/*
* GETFH: Get current filehandle
*/
struct GETFH4resok {
nfs_fh4 object;
};
union GETFH4res switch (nfsstat4 status) {
case NFS4_OK:
GETFH4resok resok4;
default:
void;
};
16.8.4. DESCRIPTION
This operation returns the current filehandle value.
On success, the current filehandle retains its value.
16.8.5. 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)
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GETFH
16.9. Operation 11: LINK - Create Link to a File
16.9.1. SYNOPSIS
(sfh), (cfh), newname -> (cfh), change_info
16.9.2. ARGUMENTS
/*
* LINK: Create link to an object
*/
struct LINK4args {
/* SAVED_FH: source object */
/* CURRENT_FH: target directory */
component4 newname;
};
16.9.3. RESULTS
struct LINK4resok {
change_info4 cinfo;
};
union LINK4res switch (nfsstat4 status) {
case NFS4_OK:
LINK4resok resok4;
default:
void;
};
16.9.4. 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 file system
on the server. On success, the current filehandle will continue to
be the target directory. If an object exists in the target directory
with the same name as newname, the server must return NFS4ERR_EXIST.
For the target directory, the server returns change_info4 information
in cinfo. With the atomic field of the change_info4 struct, the
server will indicate if the before and after change attributes were
obtained atomically with respect to the link creation.
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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.
16.9.5. 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.
The statement "file and the target directory must reside within the
same file system on the server" means that the fsid fields in the
attributes for the objects are the same. If they reside on different
file systems, the error, NFS4ERR_XDEV, is returned. 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.
16.10. Operation 12: LOCK - Create Lock
16.10.1. SYNOPSIS
(cfh) locktype, reclaim, offset, length, locker -> stateid
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16.10.2. ARGUMENTS
/*
* 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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16.10.3. RESULTS
struct LOCK4denied {
offset4 offset;
length4 length;
nfs_lock_type4 locktype;
lock_owner4 owner;
};
struct LOCK4resok {
stateid4 lock_stateid;
};
union LOCK4res switch (nfsstat4 status) {
case NFS4_OK:
LOCK4resok resok4;
case NFS4ERR_DENIED:
LOCK4denied denied;
default:
void;
};
16.10.4. 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.
16.10.5. 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. The File
Locking section 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 file system, and are not
specified by the protocol. For example, Windows 2000 allows a write
lock of a file open for READ, while a POSIX-compliant system does
not.
When the client makes a lock request that corresponds to a range that
the lockowner has locked already (with the same or different lock
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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16.11. Operation 13: LOCKT - Test For Lock
16.11.1. SYNOPSIS
(cfh) locktype, offset, length owner -> {void, NFS4ERR_DENIED ->
owner}
16.11.2. ARGUMENTS
struct LOCKT4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
offset4 offset;
length4 length;
lock_owner4 owner;
};
16.11.3. RESULTS
union LOCKT4res switch (nfsstat4 status) {
case NFS4ERR_DENIED:
LOCK4denied denied;
case NFS4_OK:
void;
default:
void;
};
16.11.4. 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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16.11.5. 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. The File
Locking section 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.
16.12. Operation 14: LOCKU - Unlock File
16.12.1. SYNOPSIS
(cfh) type, seqid, stateid, offset, length -> stateid
16.12.2. ARGUMENTS
struct LOCKU4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
stateid4 lock_stateid;
offset4 offset;
length4 length;
};
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16.12.3. RESULTS
union LOCKU4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 lock_stateid;
default:
void;
};
16.12.4. 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.
16.12.5. 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.
16.13. Operation 15: LOOKUP - Lookup Filename
16.13.1. SYNOPSIS
(cfh), component -> (cfh)
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16.13.2. ARGUMENTS
/*
* LOOKUP: Lookup filename
*/
struct LOOKUP4args {
/* CURRENT_FH: directory */
component4 objname;
};
16.13.3. RESULTS
struct LOOKUP4res {
/* CURRENT_FH: object */
nfsstat4 status;
};
16.13.4. DESCRIPTION
This operation LOOKUPs or finds a file system object using the
directory specified by the current filehandle. LOOKUP evaluates the
component and if the object exists the current filehandle is replaced
with the component's filehandle.
If the component cannot be evaluated either because it does not exist
or because the client does not have permission to evaluate the
component, then an error will be returned and the current filehandle
will be unchanged.
If the component is a zero length string or if any component does not
obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
16.13.5. 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
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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 file system.
This needs to be done to maintain the file object identity checking
mechanisms common to UNIX clients.
Servers that limit NFS access to "shares" or "exported" file systems
should provide a pseudo file system into which the exported file
systems can be integrated, so that clients can browse the server's
name space. The clients view of a pseudo file system will be limited
to paths that lead to exported file systems.
Note: previous versions of the protocol assigned special semantics to
the names "." and "..". 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.
16.14. Operation 16: LOOKUPP - Lookup Parent Directory
16.14.1. SYNOPSIS
(cfh) -> (cfh)
16.14.2. ARGUMENTS
/* CURRENT_FH: object */
void;
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16.14.3. RESULTS
/*
* LOOKUPP: Lookup parent directory
*/
struct LOOKUPP4res {
/* CURRENT_FH: directory */
nfsstat4 status;
};
16.14.4. 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.
As for LOOKUP, LOOKUPP will also cross mountpoints.
If the current filehandle is not a directory or named attribute
directory, the error NFS4ERR_NOTDIR is returned.
If the requester's security flavor does not match that configured for
the parent directory, then the server SHOULD return NFS4ERR_WRONGSEC
(a future minor revision of NFSv4 may upgrade this to MUST) in the
LOOKUPP response. However, if the server does so, it MUST support
the new SECINFO_NO_NAME operation, so that the client can gracefully
determine the correct security flavor. See the discussion of the
SECINFO_NO_NAME operation for a description.
If the current filehandle is a named attribute directory that is
associated with a filesystem object via OPENATTR (i.e. not a sub-
directory of a named attribute directory) LOOKUPP SHOULD return the
filehandle of the associated filesystem object.
16.14.5. IMPLEMENTATION
16.15. Operation 17: NVERIFY - Verify Difference in Attributes
16.15.1. SYNOPSIS
(cfh), fattr -> -
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16.15.2. ARGUMENTS
/*
* NVERIFY: Verify attributes different
*/
struct NVERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
16.15.3. RESULTS
struct NVERIFY4res {
nfsstat4 status;
};
16.15.4. DESCRIPTION
This operation is used to prefix a sequence of operations to be
performed if one or more attributes have changed on some file system
object. If all the attributes match then the error NFS4ERR_SAME must
be returned.
On success, the current filehandle retains its value.
16.15.5. 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
READ 0 32767
In the case that a recommended attribute is specified in the NVERIFY
operation and the server does not support that attribute for the file
system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
client.
When the attribute rdattr_error or any write-only attribute (e.g.
time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
the client.
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16.16. Operation 18: OPEN - Open a Regular File
16.16.1. SYNOPSIS
(cfh), seqid, share_access, share_deny, owner, openhow, claim ->
(cfh), stateid, cinfo, rflags, open_confirm, attrset delegation
16.16.2. ARGUMENTS
/*
* 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;
};
/* 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;
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};
union nfs_space_limit4 switch (limit_by4 limitby) {
/* limit specified as file size */
case NFS_LIMIT_SIZE:
uint64_t filesize;
/* limit specified by number of blocks */
case NFS_LIMIT_BLOCKS:
nfs_modified_limit4 mod_blocks;
} ;
/*
* Share Access and Deny constants for open argument
*/
const OPEN4_SHARE_ACCESS_READ = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH = 0x00000003;
const OPEN4_SHARE_DENY_NONE = 0x00000000;
const OPEN4_SHARE_DENY_READ = 0x00000001;
const OPEN4_SHARE_DENY_WRITE = 0x00000002;
const OPEN4_SHARE_DENY_BOTH = 0x00000003;
/* new flags for share_access field of OPEN4args */
const OPEN4_SHARE_ACCESS_WANT_DELEG_MASK = 0xFF00;
const OPEN4_SHARE_ACCESS_WANT_NO_PREFERENCE = 0x0000;
const OPEN4_SHARE_ACCESS_WANT_READ_DELEG = 0x0100;
const OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG = 0x0200;
const OPEN4_SHARE_ACCESS_WANT_ANY_DELEG = 0x0300;
const OPEN4_SHARE_ACCESS_WANT_NO_DELEG = 0x0400;
const OPEN4_SHARE_ACCESS_WANT_CANCEL = 0x0500;
const OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL = 0x10000;
const OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED = 0x20000;
enum open_delegation_type4 {
OPEN_DELEGATE_NONE = 0,
OPEN_DELEGATE_READ = 1,
OPEN_DELEGATE_WRITE = 2,
OPEN_DELEGATE_NONE_EXT = 3 /* new to v4.1 */
};
enum open_claim_type4 {
CLAIM_NULL = 0,
CLAIM_PREVIOUS = 1,
CLAIM_DELEGATE_CUR = 2,
CLAIM_DELEGATE_PREV = 3,
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/*
* Like CLAIM_NULL, but object identified
* by the current filehandle.
*/
CLAIM_FH = 4, /* new to v4.1 */
/*
* Like CLAIM_DELEGATE_CUR, but object identified
* by current filehandle.
*/
CLAIM_DELEG_CUR_FH = 5, /* new to v4.1 */
/*
* Like CLAIM_DELEGATE_PREV, but object identified
* by current filehandle.
*/
CLAIM_DELEG_PREV_FH = 6 /* new to v4.1 */
};
struct open_claim_delegate_cur4 {
stateid4 delegate_stateid;
component4 file;
};
union open_claim4 switch (open_claim_type4 claim) {
/*
* No special rights to file. Ordinary OPEN of the specified file.
*/
case CLAIM_NULL:
/* CURRENT_FH: directory */
component4 file;
/*
* Right to the file established by an open previous to server
* reboot. File identified by filehandle obtained at that time
* rather than by name.
*/
case CLAIM_PREVIOUS:
/* CURRENT_FH: file being reclaimed */
open_delegation_type4 delegate_type;
/*
* Right to file based on a delegation granted by the server.
* File is specified by name.
*/
case CLAIM_DELEGATE_CUR:
/* CURRENT_FH: directory */
open_claim_delegate_cur4 delegate_cur_info;
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/* 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;
};
16.16.3. RESULTS
struct open_read_delegation4 {
stateid4 stateid; /* Stateid for delegation*/
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfsace4 permissions; /* Defines users who don't
need an ACCESS call to
open for read */
};
struct open_write_delegation4 {
stateid4 stateid; /* Stateid for delegation */
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfs_space_limit4 space_limit; /* Defines condition that
the client must check to
determine whether the
file needs to be flushed
to the server on close.
*/
nfsace4 permissions; /* Defines users who don't
need an ACCESS call as
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part of a delegated
open. */
};
enum why_no_delegation4 { /* new to v4.1 */
WND_NOT_WANTED = 0,
WND_CONTENTION = 1,
WND_RESOURCE = 2,
WND_NOT_SUPP_FTYPE = 3,
WND_WRITE_DELEG_NOT_SUPP_FTYPE = 4,
WND_NOT_SUPP_UPGRADE = 5,
WND_NOT_SUPP_DOWNGRADE = 6,
WND_CANCELED = 7,
WND_IS_DIR = 8
};
union open_none_delegation4 /* new to v4.1 */
switch (why_no_delegation4 ond_why) {
case WND_CONTENTION:
bool ond_server_will_push_deleg;
case WND_RESOURCE:
bool ond_server_will_signal_avail;
default:
void;
};
union open_delegation4
switch (open_delegation_type4 delegation_type) {
case OPEN_DELEGATE_NONE:
void;
case OPEN_DELEGATE_READ:
open_read_delegation4 read;
case OPEN_DELEGATE_WRITE:
open_write_delegation4 write;
case OPEN_DELEGATE_NONE_EXT: /* new to v4.1 */
open_none_delegation4 od_whynone;
};
/*
* Result flags
*/
/* Client must confirm open */
const OPEN4_RESULT_CONFIRM = 0x00000002;
/* Type of file locking behavior at the server */
const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
/* Server will preserve file if removed while open */
const OPEN4_RESULT_PRESERVE_UNLINKED = 0x00000008;
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/* Server may use CB_NOTIFY_LOCK on locks derived from this open */
const OPEN4_RESULT_MAY_NOTIFY_LOCK = 0x00000020;
struct OPEN4resok {
stateid4 stateid; /* Stateid for open */
change_info4 cinfo; /* Directory Change Info */
uint32_t rflags; /* Result flags */
bitmap4 attrset; /* attribute set for create*/
open_delegation4 delegation; /* Info on any open
delegation */
};
union OPEN4res switch (nfsstat4 status) {
case NFS4_OK:
/* CURRENT_FH: opened file */
OPEN4resok resok4;
default:
void;
};
16.16.4. 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
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
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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 the section on 'Share
Reservations'. [[Comment.16: Add an xref to the Share Reservations
section]]
In the case that the client is recovering state from a server
failure, the claim field of the OPEN argument is used to signify that
the request is meant to reclaim state previously held.
The "claim" field of the OPEN argument is used to specify the file to
be opened and the state information which the client claims to
possess. There are seven claim types as follows:
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+---------------------+---------------------------------------------+
| open type | description |
+---------------------+---------------------------------------------+
| CLAIM_NULL CLAIM_FH | For the client, this is a new OPEN request |
| | and there is no previous state associate |
| | with the file for the client. With |
| | CLAIM_NULL the file is identified by the |
| | current filehandle and the specified |
| | component name. With CLAIM_FH (new to v4.1) |
| | the file is identified by just the current |
| | filehandle. |
| CLAIM_PREVIOUS | The client is claiming basic OPEN state for |
| | a file that was held previous to a server |
| | reboot. Generally used when a server is |
| | returning persistent filehandles; the |
| | client may not have the file name to |
| | reclaim the OPEN. |
| CLAIM_DELEGATE_CUR | The client is claiming a delegation for |
| CLAIM_DELEG_PREV_FH | OPEN as granted by the server. Generally |
| | this is done as part of recalling a |
| | delegation. With CLAIM_DELEGATE_CUR, the |
| | file is identified by the current |
| | filehandle and the specified component |
| | name. With CLAIM_DELEG_PREV_FH (new to |
| | v4.1), the file is identified by just the |
| | current filehandle. |
| CLAIM_DELEGATE_PREV | The client is claiming a delegation granted |
| CLAIM_DELEG_PREV_FH | to a previous client instance; used after |
| | the client reboots. The server MAY support |
| | CLAIM_DELEGATE_PREV or CLAIM_DELEG_PREV_FH. |
| | If it does support either open type, |
| | 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 the section Open Delegation. 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
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claimed. In this case, delegation will always be granted, although
the server may specify an immediate recall in the delegation
structure.
The rflags returned by a successful OPEN allow the server to return
information governing how the open file is to be handled.
o OPEN4_RESULT_CONFIRM is deprecated and MUST not be returned by an
NFSv4.1 server.
o OPEN4_RESULT_LOCKTYPE_POSIX indicates the server's file locking
behavior supports the complete set of Posix locking techniques.
From this the client can choose to manage file locking state in a
way to handle a mis-match of file locking management.
o OPEN4_RESULT_PRESERVE_UNLINKED indicates the server will preserve
the open file if the client (or any other client) removes the file
as long as it is open. Furthermore, the server promises to
preserve the file through the grace period after server reboot,
thereby giving the client the opportunity to reclaim his open.
o OPEN4_RESULT_MAY_NOTIFY_LOCK indicates that the server may attempt
CB_NOTIFY_LOCK callbacks for locks on this file. This flag is a
hint only, and may be safely ignored by the client.
If the component is of zero length, NFS4ERR_INVAL will be returned.
The component is also subject to the normal UTF-8, character support,
and name checks. See the section "UTF-8 Related Errors" for further
[[Comment.17: add an xref to the UTD-8 section]]. 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 file system at the server is only accessible in a
read-only mode and the OPEN request has specified ACCESS_WRITE or
ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a read-
only file system.
As with the CREATE operation, the server MUST derive the owner, owner
ACE, group, or group ACE if any of the four attributes are required
and supported by the server's file system. For an OPEN with the
EXCLUSIVE4 createmode, the server has no choice, since such OPEN
calls do not include the createattrs field. Conversely, if
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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.
NFSv4.1 gives more precise control to clients over acquisition of
delegations via the following new flags for the share_access field of
OPEN4args:
OPEN4_SHARE_ACCESS_WANT_READ_DELEG
OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
OPEN4_SHARE_ACCESS_WANT_NO_DELEG
OPEN4_SHARE_ACCESS_WANT_CANCEL
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
If (share_access & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) is not zero,
then the client will have specified one and only one of:
OPEN4_SHARE_ACCESS_WANT_READ_DELEG
OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
OPEN4_SHARE_ACCESS_WANT_NO_DELEG
OPEN4_SHARE_ACCESS_WANT_CANCEL
Otherwise the client is indicating no desire for a delegation and the
server MAY or MAY not return a delegation in the OPEN response.
If the server supports the new _WANT_ flags and the client issues one
or more of the new flags, then in the event the server does not
return a delegation, it MUST return a delegation type of
OPEN_DELEGATE_NONE_EXT. od_whynone indicates why no delegation was
returned and will be one of:
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WND_NOT_WANTED The client specified
OPEN4_SHARE_ACCESS_WANT_NO_DELEG.
WND_CONTENTION There is a conflicting delegation or open on the
file.
WND_RESOURCE Resource limitations prevent the server from granting a
delegation.
WND_NOT_SUPP_FTYPE The server does not support delegations on this
file type.
WND_WRITE_DELEG_NOT_SUPP_FTYPE The server does not support write
delegations on this file type.
WND_NOT_SUPP_UPGRADE The server does not support atomic upgrade of a
read delegation to a write delegation.
WND_NOT_SUPP_DOWNGRADE The server does not support atomic downgrade
of a write delegation to a read delegation.
WND_CANCELED The client specified OPEN4_SHARE_ACCESS_WANT_CANCEL and
now any "want" for this file object is cancelled.
WND_IS_DIR The specified file object is a directory, and the
operation is OPEN or WANT_DELEGATION which do not support
delegations on directories.
OPEN4_SHARE_ACCESS_WANT_READ_DELEG,
OPEN_SHARE_ACCESS_WANT_WRITE_DELEG, or
OPEN_SHARE_ACCESS_WANT_ANY_DELEG mean, respectively, the client wants
a read, write, or any delegation regardless which of
OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
OPEN4_SHARE_ACCESS_BOTH is set. If the client has a read delegation
on a file, and requests a write delegation, then the client is
requesting atomic upgrade of its read delegation to a write
delegation. If the client has a write delegation on a file, and
requests a read delegation, then the client is requesting atomic
downgrade to a read delegation. A server MAY support atomic upgrade
or downgrade. If it does, then the returned delegation_type of
OPEN_DELEGATE_READ or OPEN_DELEGATE_WRITE that is different than the
delegation type the client currently has, indicates successful
upgrade or downgrade. If it does not support atomic delegation
upgrade or downgrade, then od_whynone will be WND_NOT_SUPP_UPGRADE or
WND_NOT_SUPP_DOWNGRADE.
OPEN4_SHARE_ACCESS_WANT_NO_DELEG means the client wants no
delegation.
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OPEN4_SHARE_ACCESS_WANT_CANCEL means the client wants no delegation
and wants to cancel any previously registered "want" for a
delegation.
The client may set one or both of
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL and
OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED. However, they
will have no effect unless one of following are set:
o OPEN4_SHARE_ACCESS_WANT_READ_DELEG
o OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
o OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
If the client specifies
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it wishes
to register a "want" for a delegation, in the event the OPEN results
do not include a delegation. If so and the server denies the
delegation due to insufficient resources, the server MAY later inform
the client, via the CB_RECALLABLE_OBJ_AVAIL operation, that the
resource limitation condition has eased. The server will tell the
client that it intends to send a future CB_RECALLABLE_OBJ_AVAIL
operation by setting delegation_type in the results to
OPEN_DELEGATE_NONE_EXT, ond_why to WND_RESOURCE, and
ond_server_will_signal_avail set to TRUE. If
ond_server_will_signal_avail is set to TRUE, the server MUST later
send a CB_RECALLABLE_OBJ_AVAIL operation.
If the client specifies
OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_UNCONTENDED, then it wishes
to register a "want" for a delegation, in the event the OPEN results
do not include a delegation. If so and the server denies the
delegation due to insufficient resources, the server MAY later inform
the client, via the CB_PUSH_DELEG operation, that the resource
limitation condition has eased. The server will tell the client that
it intends to send a future CB_PUSH_DELEG operation by setting
delegation_type in the results to OPEN_DELEGATE_NONE_EXT, ond_why to
WND_CONTENTION, and ond_server_will_push_deleg to TRUE. If
ond_server_will_push_deleg is TRUE, the server MUST later send a
CB_RECALLABLE_OBJ_AVAIL operation.
If the client has previously registered a want for a delegation on a
file, and then sends a request to register a want for a delegation on
the same file, the server MUST return a new error:
NFS4ERR_DELEG_ALREADY_WANTED. If the client wishes to register a
different type of delegation want for the same file, it MUST cancel
the existing delegation WANT.
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16.16.5. IMPLEMENTATION
The OPEN operation contains support for EXCLUSIVE create. The
mechanism is similar to the support in NFS version 3 [18]. 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.
[[Comment.18: Isn't this mechanism redundant if the server supports a
stable session replay cache?]]
If the object does not exist, the server creates the object and
stores the verifier in stable storage. For file systems that do not
provide a mechanism for the storage of arbitrary file attributes, the
server may use one or more elements of the object meta-data to store
the verifier. The verifier must be stored in stable storage to
prevent erroneous failure on retransmission of the request. It is
assumed that an exclusive create is being performed because exclusive
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 file system 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
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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.
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.
The use of the OPEN4_RESULT_PRESERVE_UNLINKED result flag allows a
client avoid the common implementation practice of renaming an open
file to ".nfs<unique value>" after it removes the file. After the
server returns OPEN4_RESULT_PRESERVE_UNLINKED, if a client issues a
REMOVE operation that would reduce the file's link count to zero, the
server SHOULD report a value of zero for the FATTR4_NUMLINKS
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attribute on the file.
16.16.5.1. WARNING TO CLIENT IMPLEMENTORS
OPEN resembles LOOKUP in that it generates a filehandle for the
client to use. Unlike LOOKUP though, OPEN creates server state on
the filehandle. In normal circumstances, the client can only release
this state with a CLOSE operation. CLOSE uses the current filehandle
to determine which file to close. Therefore the client MUST follow
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.
16.17. Operation 19: OPENATTR - Open Named Attribute Directory
16.17.1. SYNOPSIS
(cfh) createdir -> (cfh)
16.17.2. ARGUMENTS
/*
* OPENATTR: open named attributes directory
*/
struct OPENATTR4args {
/* CURRENT_FH: object */
bool createdir;
};
16.17.3. RESULTS
struct OPENATTR4res {
/* CURRENT_FH: named attr directory */
nfsstat4 status;
};
16.17.4. 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
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NF4ATTRDIR. From this filehandle, READDIR and LOOKUP operations can
be used to obtain filehandles for the various named attributes
associated with the original file system object. Filehandles
returned within the named attribute directory will 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.
16.17.5. IMPLEMENTATION
If the server does not support named attributes for the current
filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
client.
16.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access
16.18.1. SYNOPSIS
(cfh), stateid, seqid, access, deny -> stateid
16.18.2. ARGUMENTS
/*
* OPEN_DOWNGRADE: downgrade the access/deny for a file
*/
struct OPEN_DOWNGRADE4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
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16.18.3. RESULTS
struct OPEN_DOWNGRADE4resok {
stateid4 open_stateid;
};
union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
case NFS4_OK:
OPEN_DOWNGRADE4resok resok4;
default:
void;
};
16.18.4. DESCRIPTION
This operation is used to adjust the share_access and share_deny bits
for a given open. This is necessary when a given lockowner opens the
same file multiple times with different share_access and share_deny
flags. In this situation, a close of one of the opens may change the
appropriate share_access and share_deny flags to remove bits
associated with opens no longer in effect.
The share_access and share_deny bits specified in this operation
replace the current ones for the specified open file. The
share_access and share_deny bits specified must be exactly equal to
the union of the share_access and share_deny bits specified for some
subset of the OPENs in effect for current openowner on the current
file. If that constraint is not respected, the 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.
16.19. Operation 22: PUTFH - Set Current Filehandle
16.19.1. SYNOPSIS
filehandle -> (cfh)
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16.19.2. ARGUMENTS
/*
* PUTFH: Set current filehandle
*/
struct PUTFH4args {
nfs_fh4 object;
};
16.19.3. RESULTS
struct PUTFH4res {
/* CURRENT_FH: */
nfsstat4 status;
};
16.19.4. 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.
16.19.5. IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
16.20. Operation 23: PUTPUBFH - Set Public Filehandle
16.20.1. SYNOPSIS
- -> (cfh)
16.20.2. ARGUMENT
void;
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16.20.3. RESULT
/*
* PUTPUBFH: Set public filehandle
*/
struct PUTPUBFH4res {
/* CURRENT_FH: public fh */
nfsstat4 status;
};
16.20.4. 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 RFC2054
[25], RFC2055 [26], RFC2224 [32]. 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.
16.20.5. 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. RFC2224 [32] 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 RFC2224 [32] with respect
to the use of absolute evaluation and the restrictions the server may
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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 differently than an NFS version 4 absolute resolution.
There is a form of security negotiation as described in RFC2755 [33]
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.
16.20.6. ERRORS
16.21. Operation 24: PUTROOTFH - Set Root Filehandle
16.21.1. SYNOPSIS
- -> (cfh)
16.21.2. ARGUMENTS
void;
16.21.3. RESULTS
/*
* PUTROOTFH: Set root filehandle
*/
struct PUTROOTFH4res {
/* CURRENT_FH: root fh */
nfsstat4 status;
};
16.21.4. 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.
16.21.5. IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
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16.22. Operation 25: READ - Read from File
16.22.1. SYNOPSIS
(cfh), stateid, offset, count -> eof, data
16.22.2. ARGUMENTS
/*
* READ: Read from file
*/
struct READ4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
count4 count;
};
16.22.3. RESULTS
struct READ4resok {
bool eof;
opaque data<>;
};
union READ4res switch (nfsstat4 status) {
case NFS4_OK:
READ4resok resok4;
default:
void;
};
16.22.4. 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
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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. 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.
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.
16.22.5. 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
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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.
16.23. Operatio