Hammerspace

loghyr@hammerspace.com

Hammerspace

trondmy@hammerspace.com

Transport Network File System Version 4 NFSv4 The Network File System v4 (NFSv4) allows a client to both open a file and be granted a delegation of that file. This provides the client the right to cache metadata on the file locally. This document presents several refinements to RFC8881 for both the opening and delegating of the file to the client. Discussion of this draft takes place on the NFSv4 working group mailing list (nfsv4@ietf.org), which is archived at . Working Group information can be found at .

Introduction In the Network File System version4 (NFSv4) a client may be granted a delegation for a file. This allows the client to act as the authority of the file's metadata and data. In this document, we introduce some new semantics to both the open and the delegation process which allows the client to:

• detect an offline file, which may be located off premise.
• determine the extension of OPEN (see Section 18.16 of ) flags.
• during the OPEN procedure, get either the open or delegation stateids, but not both.
• cache both the access and modify times, reducing the number of times the client needs to go to the server to get that information.

Using the process detailed in , the revisions in this document become an extension of NFSv4.2 . They are built on top of the external data representation (XDR) generated from .

Definitions

delegation:

A file delegation, which is a recall-able lock that assures the holder that inconsistent opens and file changes cannot occur so long as the delegation is held.

proxy:

A proxy of attributes occurs when the client has the authority to represent the server's attributes.

stateid:

A stateid is a 128-bit quantity returned by a server that uniquely defines state held by the server for the client. (See Section 8 of )

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Offline Files If a file is offline, then the server has immediate high-performance access to the file's attributes, but not to the file's content. The cost of retrieving the data content is expensive, to the extent that the content should only be retrieved if it is going to be used. For example, a graphical file manager (such as OSX's Finder) may want to access the beginning of the file to preview it for an user who is hovering their pointer over the file name. If the file is retrieved, it will most likely either be immediately thrown away or returned. A compound with a GETATTR or READDIR can report the file's attributes without bringing the file online. However, either an OPEN or a LAYOUTGET might cause the file server to retrieve the archived data contents, bringing the file online. For non-pNFS systems, the OPEN operation requires a filehandle to the data content. For pNFS systems, the filehandle retrieved from an OPEN need not cause the data content to be retrieved. But when the LAYOUTGET operation is processed, a layout type specific mapping will cause the data content to be retrieved from offline storage. If an operating system is not aware that the file is offline, it might inadvertently open the file to determine what type of file it is accessing. By adding the new attribute FATTR4_OFFLINE, a client can predetermine the availability of the file, avoiding the need to open it at all. Being offline might also involve situations in which the file is archived in the cloud, i.e., there can be an expense in both retrieving the file to bring online and in sending the file back to offline status.

OPEN grants only one of Open or Delegation Stateid The OPEN (See Section 18.16 of ) procedure returns an open stateid to the client to reference the state of the file. The client could also request a delegation stateid in the OPEN arguments. The file is said to be "open" to the client as long as the count of open and delegated stateids is greater than 0. Either type of stateid is sufficient to enable the server to treat the file as if it were open, which allows READ (See Section 18.25 of ), WRITE (See Section 18.38 of ), LOCK (See Section 18.12 of ), and LAYOUTGET (see Section 18.50 of ) operations to proceed. If the client gets both a open and a delegation stateid as part of the OPEN, then it has to return them both. And during each operation, the client can send a costly GETATTR (See Section 18.9 of ). If the client knows that the server supports the OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION flag (as determined by an earlier GETATTR operation which queried for the FATTR4_OPEN_ARGUMENTS attribute), then the client can supply that flag during the OPEN and only get either an open or delegation stateid. The client is already prepared to not get a delegation stateid even if requested. In order to not send an open stateid, the server can indicate that fact with the result flag of OPEN4_RESULT_NO_OPEN_STATEID. The open stateid field, OPEN4resok.stateid (see Section 18.16.2 of ), will also be set to the special all zero stateid.

Proxying of Times When a client is granted a write delegation on a file, it is the authority for the file. If the server queries the client as to the state of the file via a CB_GETATTR (see Section 20.1 of ), then it can only determine the size of the file. Likewise, if the client holding the delegation wants to know either of the access, modify, or change times, it has to send a GETATTR to the server. While it is the authority for these values, it has no way to transfer these values to the server when the delegation is being returned and the server reclaims its authority with regard to these values. And as such, it can not pass these times up to an application expecting posix compliance. With the addition of the new flag: OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS, the client and server can negotiate that the client will be the authority for these values and upon return of the delegation stateid via a DELEGRETURN (see section 18.6 of ), the times will be passed back to the server. If the server is queried by another client for either the size or the times, it will need to use a CB_GETATTR to query the client which holds the delegation (see Section 20.1 of ). If a server informs the client via the FATTR4_OPEN_ARGUMENTS attribute that it supports OPEN_ARGS_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS and it returns a valid delegation stateid for an OPEN operation which sets the OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS flag, then it MUST query the client via a CB_GETATTR for the FATTR4_TIME_DELEG_ACCESS attribute and FATTR4_TIME_DELEG_MODIFY attribute. (The change time can be derived from the modify time.) Further, when it gets a SETATTR (see Section 18.34 of ) in the same compound as the DELEGRETURN, then it MUST accept those FATTR4_TIME_DELEG_ACCESS attribute and FATTR4_TIME_DELEG_MODIFY attribute changes and derive the change time or reject the changes with NFS4ERR_DELAY. Note that the SETATTR SHOULD either be in a separate compound before the one containing the DELEGRETURN or if in the same compound, as an operation before the DELEGRETURN. Failure to properly sequence the operations may lead to race cases. A key prerequisite of this approach is that the server and client are in time synchronization with each other. Note that while the base NFSv4.2 does not require such synchronization, the use of RPCSEC_GSS typically makes such a requirement. When the client presents either FATTR4_TIME_DELEG_ACCESS or FATTR4_TIME_DELEG_MODIFY attributes to the server, the server MUST decide whether the times presented are before the old times or past the current time. If the time presented is before the original time, then the update is ignored. If the time presented is in the future, the server can either clamp the new time to the current time, or it may return NFS4ERR_DELAY to the client, allowing it to retry. Note that if the clock skew is large, this policy will result in access to the file being denied until such time that the clock skew is exceeded. A change in the access time MUST NOT advance the change time, also known as the time_metadata attribute (see Section 5.8.2.42 of ), but a change in the modify time might advance the change time (and in turn the change attribute (See Section 5.8.1.4 of ). If the modify time is greater than the change time and before the current time, then the change time is adjusted to the modify time and not the current time (as is most likely done on most SETATTR calls that change the metadata). If the modify time is in the future, it will be clamped to the current time. Note that each of the possible times, access, modify, and change, are compared to the current time. They should all be compared against the same time value for the current time. I.e., do not retrieve a different value of the current time for each calculation. If the client sets the OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS flag in an OPEN operation, then it MUST support the FATTR4_TIME_DELEG_ACCESS and FATTR4_TIME_DELEG_MODIFY attributes both in the CB_GETATTR and SETATTR operations.

Use case When a server is a proxy for a NFSv4 server, it is a client to the NFSv4 server and during file I/O, it may get a delegation on a file. The client of the proxy would be querying the proxy for attributes and not the NFSv4 server. Each GETATTR from that client would result in at least one additional GETATTR being sent across the wire.

XDR for Proxying of Times

Determining OPEN Feature Support (see Section 4.4.2) allows for extending a particular minor version of the NFSv4 protocol without requiring the definition of a new minor version. The client can probe the capabilities of the server and based on the result, determine if both it and the server support optional features not previously specified as part of the minor version. The XDR extensions presented in this section provide helpful support when the OPEN procedure is extended in such a fashion. It models all of the parameters via bitmap4 data structures, which allows for the addition of a new flag to any of the OPEN arguments (see Section 18.16.1 of ). Two new flags are provided:

• OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION (see )
• OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS (see )

Subsequent extensions can use this framework when introducing new OPTIONAL functionality to OPEN, by creating a new flags for each OPTIONAL parameter.

Extraction of XDR This document contains the external data representation (XDR) description of the new open flags for delegating the file to the client. The XDR description is embedded in this document in a way that makes it simple for the reader to extract into a ready-to-compile form. The reader can feed this document into the following shell script to produce the machine readable XDR description of the new flags: That is, if the above script is stored in a file called "extract.sh", and this document is in a file called "spec.txt", then the reader can do: delstid_prot.x ]]> The effect of the script is to remove leading white space from each line, plus a sentinel sequence of "///". XDR descriptions with the sentinel sequence are embedded throughout the document. Note that the XDR code contained in this document depends on types from the NFSv4.2 nfs4_prot.x file (generated from ). This includes both nfs types that end with a 4, such as offset4, length4, etc., as well as more generic types such as uint32_t and uint64_t. While the XDR can be appended to that from , the various code snippets belong in their respective areas of the that XDR.

Code Components Licensing Notice Both the XDR description and the scripts used for extracting the XDR description are Code Components as described in Section 4 of "Legal Provisions Relating to IETF Documents". These Code Components are licensed according to the terms of that document.

Security Considerations There are no new security considerations beyond those in .

IANA Considerations IANA should use the current document (RFC-TBD) as the reference for the new entries.

References Normative References Informative References IETF Trust

Acknowledgments Trond Myklebust and David Flynn all worked on the prototype at Hammerspace. Dave Noveck provided reviews of the document.