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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." Haynes Expires 19 September 2025 [Page 1] Internet-Draft Uncacheable Attribute March 2025 This Internet-Draft will expire on 19 September 2025. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. 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. Haynes Expires 19 September 2025 [Page 2] Internet-Draft Uncacheable Attribute March 2025 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. Haynes Expires 19 September 2025 [Page 3] Internet-Draft Uncacheable Attribute March 2025 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. Haynes Expires 19 September 2025 [Page 4] Internet-Draft Uncacheable Attribute March 2025 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, . [RFC4506] Eisler, M., Ed., "XDR: External Data Representation Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May 2006, . [RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862, November 2016, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8178] Noveck, D., "Rules for NFSv4 Extensions and Minor Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017, . [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, . Haynes Expires 19 September 2025 [Page 5] Internet-Draft Uncacheable Attribute March 2025 Acknowledgments Trond Myklebust and Thomas Haynes all worked on the prototype at Hammerspace. Author's Address Thomas Haynes Hammerspace Email: loghyr@gmail.com Haynes Expires 19 September 2025 [Page 6]