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.