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 disabled by default. It can be enabled 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. Use your user-mode nfs-utils to set this up; 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. Other NFSv4.1 features, Parallel NFS operations in particular, are still under development out of tree. See http://wiki.linux-nfs.org/wiki/index.php/PNFS_prototype_design for more information. The current implementation is intended for developers only: while it does support ordinary file operations on clients we have tested against (including the linux client), it is incomplete in ways which may limit features unexpectedly, cause known bugs in rare cases, or cause interoperability problems with future clients. Known issues: - gss support is questionable: currently mounts with kerberos from a linux client are possible, but we aren't really conformant with the spec (for example, we don't use kerberos on the backchannel correctly). - Incomplete backchannel support: incomplete backchannel gss support and no support for BACKCHANNEL_CTL mean that callbacks (hence delegations and layouts) may not be available and clients confused by the incomplete implementation may fail. - We do not support SSV, which provides security for shared client-server state (thus preventing unauthorized tampering with locks and opens, for example). It is mandatory for servers to support this, though no clients use it yet. - Mandatory operations which we do not support, such as DESTROY_CLIENTID, are not currently used by clients, but will be (and the spec recommends their uses in common cases), and clients should not be expected to know how to recover from the case where they are not supported. This will eventually cause interoperability failures. In addition, some limitations are inherited from the current NFSv4 implementation: - Incomplete delegation enforcement: if a file is renamed or unlinked by a local process, a client holding a delegation may continue to indefinitely allow opens of the file under the old name. 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. P pNFS features implemented out of tree. PNS pNFS features that are not supported yet (out of tree). Operations +----------------------+------------+--------------+----------------+ | Operation | REQ, REC, | Feature | Definition | | | OPT, or | (REQ, REC, | | | | MNI | or OPT) | | +----------------------+------------+--------------+----------------+ | ACCESS | REQ | | Section 18.1 | NS | 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) | | NS | 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 | P | GETDEVICEINFO | OPT | pNFS (REQ) | Section 18.40 | P | GETDEVICELIST | OPT | pNFS (OPT) | Section 18.41 | | GETFH | REQ | | Section 18.8 | NS*| GET_DIR_DELEGATION | OPT | DDELG (REQ) | Section 18.39 | P | LAYOUTCOMMIT | OPT | pNFS (REQ) | Section 18.42 | P | LAYOUTGET | OPT | pNFS (REQ) | Section 18.43 | P | 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 +-------------------------+-----------+-------------+---------------+ | Operation | REQ, REC, | Feature | Definition | | | OPT, or | (REQ, REC, | | | | MNI | or OPT) | | +-------------------------+-----------+-------------+---------------+ | CB_GETATTR | OPT | FDELG (REQ) | Section 20.1 | P | CB_LAYOUTRECALL | OPT | pNFS (REQ) | Section 20.3 | NS*| CB_NOTIFY | OPT | DDELG (REQ) | Section 20.4 | P | 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: 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: * only SP4_NONE state protection supported * implementation ids are ignored CREATE_SESSION: * backchannel attributes are ignored * backchannel security parameters 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. * No more than one IO operation (read, write, readdir) allowed per compound. See also http://wiki.linux-nfs.org/wiki/index.php/Server_4.0_and_4.1_issues.