Adding an Uncacheable Attribute to NFSv4.2
draft-haynes-nfsv4-uncacheable-01

Network File System Version 4                                  T. Haynes
Internet-Draft                                               Hammerspace
Intended status: Standards Track                         13 October 2024
Expires: 16 April 2025

               Adding an Uncacheable Attribute to NFSv4.2
                   draft-haynes-nfsv4-uncacheable-01

Abstract

   The Network File System v4.2 (NFSv4.2) allows a client to cache both
   the metadata and the data for a file object.  It can also cache the
   metadata for a directory object.  Caching the dirents (i.e., the
   metadata) allows the client to avoid querying the server to refresh
   information.  But this defeats the server checking to see if the user
   has permission to view the dirent's attributes.  Caching the data can
   cause performance impacts if the page cache hit rate is low..  This
   document introduces a new file attribute called uncacheable which
   indicates that the client MUST NOT cache the metadata or data for
   that dirent.  This document extends NFSv4.2 (see RFC7863).

Note

   This note is to be removed before publishing as an RFC.

   Discussion of this draft takes place on the NFSv4 working group
   mailing list (nfsv4@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/nfsv4/.  Working Group
   information can be found at https://datatracker.ietf.org/wg/nfsv4/
   about/.

Status of This Memo

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   This Internet-Draft will expire on 16 April 2025.

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Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Uncacheable Dirents . . . . . . . . . . . . . . . . . . . . .   3
   3.  Uncacheable Files . . . . . . . . . . . . . . . . . . . . . .   3
   4.  XDR for Offline Attribute . . . . . . . . . . . . . . . . . .   3
   5.  Extraction of XDR . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In the Network File System version 4.2 (NFSv4.2) (see [RFC7863]) , a
   client queries for either a file's or directory's attributes via
   either GETATTR (see Section 18.7 of [RFC8881]) or READDIR (see
   Section 18.23 of [RFC8881]) to the server.  These directory entries
   (dirents) can be cached locally by the client.

   As these cached dirents are shared by all users on the clients and
   the client can not determine access to these dirents, all users are
   presented with the same set of attributes.  We introduce the new
   uncacheable attribute, which informs the client not to cache a dirent
   for that file or directory object.  As such each time the client
   queries for those attributes, the response can be tailored to that
   user.  That decision can be based on either Access Control List (ACL)
   on a file or directory object (see Section 6 of [RFC8881]) or
   proprietary policies.

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   Besides the caching of metadata for both files and directories, the
   client can also cache data for files.  The uncacheable attribute also
   informs the client to avoid its page cache.  It is very similar to
   passing the O_DIRECT to the open call.  This can be useful for files
   that are not shared and also for ones which do not meet the
   expectations of the caching patterns of the page cache.

   Using the process detailed in [RFC8178], the revisions in this
   document become an extension of NFSv4.2 [RFC7862].  They are built on
   top of the external data representation (XDR) [RFC4506] generated
   from [RFC7863].

1.1.  Definitions

   Access Based Enumeration:  When servicing either a READDIR or a
      GETATTR, base the result on the access permitted to the user
      making the request.

   dirent:  A directory entry, describing either a directory or a file.

1.2.  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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Uncacheable Dirents

   If a file object or directory has the uncacheable attribute set, then
   the client MUST NOT cache their dirent attributes.  I.e., just
   because it presented the attributes to user A on the first request,
   then on a subsequent request, it MUST query for those attributes
   again.  Also, the client MUST NOT share attributes between different
   users.

3.  Uncacheable Files

   If a file object is marked as uncacheable, that also means all
   modifications to the file MUST immediately be sent from the client to
   the server.  I.e., the data is also not cacheable.

4.  XDR for Offline Attribute

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   <CODE BEGINS>
   ///
   /// typedef bool            fattr4_uncacheable;
   ///
   /// const FATTR4_UNCACHEABLE            = 87;
   ///
   <CODE ENDS>

5.  Extraction of XDR

   This document contains the external data representation (XDR)
   [RFC4506] description of the uncacheable attribute.  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:

   <CODE BEGINS>
   #!/bin/sh
   grep '^ *///' $* | sed 's?^ */// ??' | sed 's?^ *///$??'
   <CODE ENDS>

   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:

   <CODE BEGINS>
   sh extract.sh < spec.txt > uncacheable_prot.x
   <CODE ENDS>

   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 [RFC7863]).  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 [RFC7863], the various
   code snippets belong in their respective areas of that XDR.

6.  Security Considerations

   Clients MUST NOT make access decisions to uncacheable dirents, these
   decisions MUST be made by the server.  With the uncacheable
   attribute, dirents can be annotated such that attributes can be
   presented to the user based on the server's decision.

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7.  IANA Considerations

   There are no IANA considerations.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4506]  Eisler, M., Ed., "XDR: External Data Representation
              Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
              2006, <https://www.rfc-editor.org/info/rfc4506>.

   [RFC7862]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
              November 2016, <https://www.rfc-editor.org/info/rfc7862>.

   [RFC7863]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 External Data Representation Standard (XDR)
              Description", RFC 7863, DOI 10.17487/RFC7863, November
              2016, <https://www.rfc-editor.org/info/rfc7863>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8178]  Noveck, D., "Rules for NFSv4 Extensions and Minor
              Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
              <https://www.rfc-editor.org/info/rfc8178>.

   [RFC8881]  Noveck, D., Ed. and C. Lever, "Network File System (NFS)
              Version 4 Minor Version 1 Protocol", RFC 8881,
              DOI 10.17487/RFC8881, August 2020,
              <https://www.rfc-editor.org/info/rfc8881>.

Appendix A.  Acknowledgments

   Trond Myklebust and Thomas Haynes all worked on the prototype at
   Hammerspace.

Author's Address

   Thomas Haynes
   Hammerspace

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   Email: loghyr@gmail.com

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