Blame - Documentation/filesystems/nfs/nfs41-server.txt - kernel/msm-5.4

2009-04-03 08:29:20 +0300

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NFSv4.1 Server Implementation

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Server support for minorversion 1 can be controlled using the

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/proc/fs/nfsd/versions control file. The string output returned

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by reading this file will contain either "+4.1" or "-4.1"

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correspondingly.

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Currently, server support for minorversion 1 is disabled by default.

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It can be enabled at run time by writing the string "+4.1" to

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the /proc/fs/nfsd/versions control file. Note that to write this

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control file, the nfsd service must be taken down. Use your user-mode

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nfs-utils to set this up; see rpc.nfsd(8)

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(Warning: older servers will interpret "+4.1" and "-4.1" as "+4" and

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"-4", respectively. Therefore, code meant to work on both new and old

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kernels must turn 4.1 on or off *before* turning support for version 4

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on or off; rpc.nfsd does this correctly.)

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The NFSv4 minorversion 1 (NFSv4.1) implementation in nfsd is based

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on RFC 5661.

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From the many new features in NFSv4.1 the current implementation

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focuses on the mandatory-to-implement NFSv4.1 Sessions, providing

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"exactly once" semantics and better control and throttling of the

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resources allocated for each client.

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Other NFSv4.1 features, Parallel NFS operations in particular,

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are still under development out of tree.

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See http://wiki.linux-nfs.org/wiki/index.php/PNFS_prototype_design

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for more information.

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The current implementation is intended for developers only: while it

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does support ordinary file operations on clients we have tested against

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(including the linux client), it is incomplete in ways which may limit

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features unexpectedly, cause known bugs in rare cases, or cause

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interoperability problems with future clients. Known issues:

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- gss support is questionable: currently mounts with kerberos

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from a linux client are possible, but we aren't really

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conformant with the spec (for example, we don't use kerberos

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on the backchannel correctly).

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- We do not support SSV, which provides security for shared

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client-server state (thus preventing unauthorized tampering

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with locks and opens, for example). It is mandatory for

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servers to support this, though no clients use it yet.

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- Mandatory operations which we do not support, such as

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DESTROY_CLIENTID, are not currently used by clients, but will be

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(and the spec recommends their uses in common cases), and

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clients should not be expected to know how to recover from the

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case where they are not supported. This will eventually cause

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interoperability failures.

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In addition, some limitations are inherited from the current NFSv4

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implementation:

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- Incomplete delegation enforcement: if a file is renamed or

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unlinked by a local process, a client holding a delegation may

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continue to indefinitely allow opens of the file under the old

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name.

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The table below, taken from the NFSv4.1 document, lists

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the operations that are mandatory to implement (REQ), optional

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(OPT), and NFSv4.0 operations that are required not to implement (MNI)

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in minor version 1. The first column indicates the operations that

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are not supported yet by the linux server implementation.

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The OPTIONAL features identified and their abbreviations are as follows:

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pNFS Parallel NFS

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FDELG File Delegations

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DDELG Directory Delegations

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The following abbreviations indicate the linux server implementation status.

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I Implemented NFSv4.1 operations.

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NS Not Supported.

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NS* unimplemented optional feature.

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P pNFS features implemented out of tree.

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PNS pNFS features that are not supported yet (out of tree).

Operations

+----------------------+------------+--------------+----------------+

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| | MNI | or OPT) | |

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+----------------------+------------+--------------+----------------+

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I | BACKCHANNEL_CTL | REQ | | Section 18.33 |

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I | BIND_CONN_TO_SESSION | REQ | | Section 18.34 |

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I | CREATE_SESSION | REQ | | Section 18.36 |

| | | (REQ) | |

NS | DESTROY_CLIENTID | REQ | | Section 18.50 |

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I | DESTROY_SESSION | REQ | | Section 18.37 |

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I | EXCHANGE_ID | REQ | | Section 18.35 |

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I | FREE_STATEID | REQ | | Section 18.38 |

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NS*| OPENATTR | OPT | | Section 18.17 |

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| OPEN_CONFIRM | MNI | | N/A |

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| RELEASE_LOCKOWNER | MNI | | N/A |

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| RENEW | MNI | | N/A |

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I | SEQUENCE | REQ | | Section 18.46 |

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| SETCLIENTID | MNI | | N/A |

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| SETCLIENTID_CONFIRM | MNI | | N/A |

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NS | SET_SSV | REQ | | Section 18.47 |

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I | TEST_STATEID | REQ | | Section 18.48 |

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Callback Operations

+-------------------------+-----------+-------------+---------------+

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| | MNI | or OPT) | |

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+-------------------------+-----------+-------------+---------------+

NS*| CB_NOTIFY_LOCK | OPT | | Section 20.11 |

| | | (REQ) | |

| | | (REQ) | |

NS | CB_RECALL_SLOT | REQ | | Section 20.8 |

| | | (REQ) | |

| | | (REQ) | |

| | | (REQ) | |

+-------------------------+-----------+-------------+---------------+

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Implementation notes:

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DELEGPURGE:

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* mandatory only for servers that support CLAIM_DELEGATE_PREV and/or

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CLAIM_DELEG_PREV_FH (which allows clients to keep delegations that

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persist across client reboots). Thus we need not implement this for

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now.

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EXCHANGE_ID:

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* only SP4_NONE state protection supported

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* implementation ids are ignored

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CREATE_SESSION:

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* backchannel attributes are ignored

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* backchannel security parameters are ignored

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SEQUENCE:

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* no support for dynamic slot table renegotiation (optional)

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Nonstandard compound limitations:

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* No support for a sessions fore channel RPC compound that requires both a

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ca_maxrequestsize request and a ca_maxresponsesize reply, so we may

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fail to live up to the promise we made in CREATE_SESSION fore channel

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negotiation.

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* No more than one IO operation (read, write, readdir) allowed per

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compound.

J. Bruce Fields