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+=============================
+NFSv4.1 Server Implementation
+=============================
+
+Server support for minorversion 1 can be controlled using the
+/proc/fs/nfsd/versions control file. The string output returned
+by reading this file will contain either "+4.1" or "-4.1"
+correspondingly.
+
+Currently, server support for minorversion 1 is enabled by default.
+It can be disabled at run time by writing the string "-4.1" to
+the /proc/fs/nfsd/versions control file. Note that to write this
+control file, the nfsd service must be taken down. You can use rpc.nfsd
+for this; see rpc.nfsd(8).
+
+(Warning: older servers will interpret "+4.1" and "-4.1" as "+4" and
+"-4", respectively. Therefore, code meant to work on both new and old
+kernels must turn 4.1 on or off *before* turning support for version 4
+on or off; rpc.nfsd does this correctly.)
+
+The NFSv4 minorversion 1 (NFSv4.1) implementation in nfsd is based
+on RFC 5661.
+
+From the many new features in NFSv4.1 the current implementation
+focuses on the mandatory-to-implement NFSv4.1 Sessions, providing
+"exactly once" semantics and better control and throttling of the
+resources allocated for each client.
+
+The table below, taken from the NFSv4.1 document, lists
+the operations that are mandatory to implement (REQ), optional
+(OPT), and NFSv4.0 operations that are required not to implement (MNI)
+in minor version 1. The first column indicates the operations that
+are not supported yet by the linux server implementation.
+
+The OPTIONAL features identified and their abbreviations are as follows:
+
+- **pNFS** Parallel NFS
+- **FDELG** File Delegations
+- **DDELG** Directory Delegations
+
+The following abbreviations indicate the linux server implementation status.
+
+- **I** Implemented NFSv4.1 operations.
+- **NS** Not Supported.
+- **NS\*** Unimplemented optional feature.
+
+Operations
+==========
+
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| Implementation status | Operation | REQ,REC, OPT or NMI | Feature (REQ, REC or OPT) | Definition |
++=======================+======================+=====================+===========================+================+
+| | ACCESS | REQ | | Section 18.1 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | BACKCHANNEL_CTL | REQ | | Section 18.33 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | BIND_CONN_TO_SESSION | REQ | | Section 18.34 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | CLOSE | REQ | | Section 18.2 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | COMMIT | REQ | | Section 18.3 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | CREATE | REQ | | Section 18.4 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | CREATE_SESSION | REQ | | Section 18.36 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| NS* | DELEGPURGE | OPT | FDELG (REQ) | Section 18.5 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | DELEGRETURN | OPT | FDELG, | Section 18.6 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | | | DDELG, pNFS | |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | | | (REQ) | |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | DESTROY_CLIENTID | REQ | | Section 18.50 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | DESTROY_SESSION | REQ | | Section 18.37 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | EXCHANGE_ID | REQ | | Section 18.35 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | FREE_STATEID | REQ | | Section 18.38 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | GETATTR | REQ | | Section 18.7 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | GETDEVICEINFO | OPT | pNFS (REQ) | Section 18.40 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| NS* | GETDEVICELIST | OPT | pNFS (OPT) | Section 18.41 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | GETFH | REQ | | Section 18.8 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| NS* | GET_DIR_DELEGATION | OPT | DDELG (REQ) | Section 18.39 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | LAYOUTCOMMIT | OPT | pNFS (REQ) | Section 18.42 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | LAYOUTGET | OPT | pNFS (REQ) | Section 18.43 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | LAYOUTRETURN | OPT | pNFS (REQ) | Section 18.44 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | LINK | OPT | | Section 18.9 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | LOCK | REQ | | Section 18.10 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | LOCKT | REQ | | Section 18.11 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | LOCKU | REQ | | Section 18.12 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | LOOKUP | REQ | | Section 18.13 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | LOOKUPP | REQ | | Section 18.14 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | NVERIFY | REQ | | Section 18.15 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | OPEN | REQ | | Section 18.16 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| NS* | OPENATTR | OPT | | Section 18.17 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | OPEN_CONFIRM | MNI | | N/A |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | OPEN_DOWNGRADE | REQ | | Section 18.18 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | PUTFH | REQ | | Section 18.19 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | PUTPUBFH | REQ | | Section 18.20 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | PUTROOTFH | REQ | | Section 18.21 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | READ | REQ | | Section 18.22 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | READDIR | REQ | | Section 18.23 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | READLINK | OPT | | Section 18.24 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | RECLAIM_COMPLETE | REQ | | Section 18.51 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | RELEASE_LOCKOWNER | MNI | | N/A |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | REMOVE | REQ | | Section 18.25 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | RENAME | REQ | | Section 18.26 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | RENEW | MNI | | N/A |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | RESTOREFH | REQ | | Section 18.27 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | SAVEFH | REQ | | Section 18.28 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | SECINFO | REQ | | Section 18.29 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | SECINFO_NO_NAME | REC | pNFS files | Section 18.45, |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | | | layout (REQ) | Section 13.12 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | SEQUENCE | REQ | | Section 18.46 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | SETATTR | REQ | | Section 18.30 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | SETCLIENTID | MNI | | N/A |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | SETCLIENTID_CONFIRM | MNI | | N/A |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| NS | SET_SSV | REQ | | Section 18.47 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| I | TEST_STATEID | REQ | | Section 18.48 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | VERIFY | REQ | | Section 18.31 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| NS* | WANT_DELEGATION | OPT | FDELG (OPT) | Section 18.49 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+| | WRITE | REQ | | Section 18.32 |
++-----------------------+----------------------+---------------------+---------------------------+----------------+
+
+
+Callback Operations
+===================
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| Implementation status | Operation | REQ,REC, OPT or NMI | Feature (REQ, REC or OPT) | Definition |
++=======================+=========================+=====================+===========================+===============+
+| | CB_GETATTR | OPT | FDELG (REQ) | Section 20.1 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| I | CB_LAYOUTRECALL | OPT | pNFS (REQ) | Section 20.3 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| NS* | CB_NOTIFY | OPT | DDELG (REQ) | Section 20.4 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| NS* | CB_NOTIFY_DEVICEID | OPT | pNFS (OPT) | Section 20.12 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| NS* | CB_NOTIFY_LOCK | OPT | | Section 20.11 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| NS* | CB_PUSH_DELEG | OPT | FDELG (OPT) | Section 20.5 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | CB_RECALL | OPT | FDELG, | Section 20.2 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | DDELG, pNFS | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | (REQ) | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| NS* | CB_RECALL_ANY | OPT | FDELG, | Section 20.6 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | DDELG, pNFS | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | (REQ) | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| NS | CB_RECALL_SLOT | REQ | | Section 20.8 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| NS* | CB_RECALLABLE_OBJ_AVAIL | OPT | DDELG, pNFS | Section 20.7 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | (REQ) | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| I | CB_SEQUENCE | OPT | FDELG, | Section 20.9 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | DDELG, pNFS | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | (REQ) | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| NS* | CB_WANTS_CANCELLED | OPT | FDELG, | Section 20.10 |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | DDELG, pNFS | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+| | | | (REQ) | |
++-----------------------+-------------------------+---------------------+---------------------------+---------------+
+
+
+Implementation notes:
+=====================
+
+SSV:
+ The spec claims this is mandatory, but we don't actually know of any
+ implementations, so we're ignoring it for now. The server returns
+ NFS4ERR_ENCR_ALG_UNSUPP on EXCHANGE_ID, which should be future-proof.
+
+GSS on the backchannel:
+ Again, theoretically required but not widely implemented (in
+ particular, the current Linux client doesn't request it). We return
+ NFS4ERR_ENCR_ALG_UNSUPP on CREATE_SESSION.
+
+DELEGPURGE:
+ mandatory only for servers that support CLAIM_DELEGATE_PREV and/or
+ CLAIM_DELEG_PREV_FH (which allows clients to keep delegations that
+ persist across client reboots). Thus we need not implement this for
+ now.
+
+EXCHANGE_ID:
+ implementation ids are ignored
+
+CREATE_SESSION:
+ backchannel attributes are ignored
+
+SEQUENCE:
+ no support for dynamic slot table renegotiation (optional)
+
+Nonstandard compound limitations:
+ No support for a sessions fore channel RPC compound that requires both a
+ ca_maxrequestsize request and a ca_maxresponsesize reply, so we may
+ fail to live up to the promise we made in CREATE_SESSION fore channel
+ negotiation.
+
+See also http://wiki.linux-nfs.org/wiki/index.php/Server_4.0_and_4.1_issues.