Network File System Version 4 T. Haynes
Internet-Draft Hammerspace
Intended status: Standards Track 18 March 2025
Expires: 19 September 2025
Adding an Uncacheable Attribute to NFSv4.2
draft-haynes-nfsv4-uncacheable-02
Abstract
The Network File System version 4.2 (NFSv4.2) allows a client to
cache both metadata and data for file objects, as well as metadata
for directory objects. While caching directory entries (dirents) can
improve performance, it can also prevent the server from enforcing
access control on individual dirents. Similarly, caching file data
can lead to performance issues if the cache hit rate is low. This
document introduces a new uncacheable attribute for NFSv4. Files and
dirents marked as uncacheable MUST NOT be stored in client-side
caches. This ensures data consistency and integrity by requiring
clients to always retrieve the most recent data directly from the
server. This document extends NFSv4.2 (see RFC7862).
Note to Readers
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/search/?email_list=nfsv4. Source
code and issues list for this draft can be found at
https://github.com/ietf-wg-nfsv4/uncacheable.
Working Group information can be found at https://github.com/ietf-wg-
nfsv4.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 19 September 2025.
Copyright Notice
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document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Uncacheable Dirents . . . . . . . . . . . . . . . . . . . . . 4
3. Uncacheable Files . . . . . . . . . . . . . . . . . . . . . . 4
4. XDR for Offline Attribute . . . . . . . . . . . . . . . . . . 4
5. Extraction of XDR . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
In the Network File System version 4.2 (NFSv4.2) [RFC7863], a client
queries for either a file's or directory's attributes via either
GETATTR Section 18.7 of [RFC8881] or READDIR Section 18.23 of
[RFC8881] to the server. These directory entries (dirents) can be
cached locally by the client.
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Since cached dirents are shared by all users on a client, and the
client cannot determine access permissions for individual dirents,
all users are presented with the same set of attributes. To address
this, this document introduces the new uncacheable attribute. This
attribute instructs the client not to cache the dirent for a file or
directory object. Consequently, each time a client queries for these
attributes, the server's response can be tailored to the specific
user making the request, based on factors such as Access Control
Lists (ACLs) on the file or directory object Section 6 of [RFC8881]
or proprietary policies.
In addition to caching metadata, clients can also cache file data.
The uncacheable attribute also instructs the client to bypass its
page cache for the file. This behavior is similar to using the
O_DIRECT flag with the open call. This can be beneficial for files
that are not shared or for files that do not exhibit access patterns
suitable for caching.
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 a READDIR or GETATTR
operation, the server provides results based on the access
permissions of the user making the request.
dirent A directory entry, representing either a file or a
subdirectory. In the context of NFSv4, a dirent marked as
uncacheable MUST NOT be cached by clients.
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.
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2. Uncacheable Dirents
If a file object or directory has the uncacheable attribute set, then
the client MUST NOT cache its dirent attributes. This means that
even if the client has previously retrieved the attributes for a
user, it MUST query the server again for those attributes on
subsequent requests. Additionally, the client MUST NOT share
attributes between different users.
3. Uncacheable Files
If a file object is marked as uncacheable, all modifications to the
file MUST be immediately sent from the client to the server. In
other words, the file data is also not cacheable.
4. XDR for Offline Attribute
///
/// typedef bool fattr4_uncacheable;
///
/// const FATTR4_UNCACHEABLE = 87;
///
5. Extraction of XDR
This document contains the external data representation (XDR)
[RFC4506] description of the uncacheable attribute. The XDR
description is presented in a manner that facilitates easy extraction
into a ready-to-compile format. To extract the machine-readable XDR
description, use the following shell script:
#!/bin/sh
grep '^ *///' $* | sed 's?^ */// ??' | sed 's?^ *///$??'
For example, if the script is named 'extract.sh' and this document is
named 'spec.txt', execute the following command:
sh extract.sh < spec.txt > uncacheable_prot.x
This script removes leading blank spaces and the sentinel sequence
'///' from each line. 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.
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While the XDR can be appended to that from [RFC7863], the code
snippets should be placed in their appropriate sections within the
existing XDR.
6. Security Considerations
Clients MUST NOT make access decisions for uncacheable dirents.
These decisions MUST be made by the server. The uncacheable
attribute allows dirents to be annotated such that attributes are
presented to the user based on the server's access control decisions.
7. IANA Considerations
This document has no IANA actions.
8. 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/rfc/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/rfc/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/rfc/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/rfc/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/rfc/rfc8174>.
[RFC8178] Noveck, D., "Rules for NFSv4 Extensions and Minor
Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
<https://www.rfc-editor.org/rfc/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/rfc/rfc8881>.
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Acknowledgments
Trond Myklebust and Thomas Haynes all worked on the prototype at
Hammerspace.
Author's Address
Thomas Haynes
Hammerspace
Email: loghyr@gmail.com
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