Hammerspace

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Transport Network File System Version 4 NFSv4 The Network File System v4.2 (NFSv4.2) allows a client to cache directory entries (dirents) for files. By caching dirents, the client avoids querying the server to refresh information. One issue with this caching is that under Access Based Enumeration, the client can not determine if the user has permission to view the dirent's attributes. We introduce a new file attribute called uncacheable which indicates that the client MUST NOT cache the attributes for that dirent. This document extends NFSv4.2 (see RFC7863). 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 version4.2 (NFSv4.2), a client queries for either a file's or directory's attributes via either GETATTR (see Section 18.7 of ) or READDIR (see Section 18.23 of ) 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 object. As such each time the client queries attributes for that file object, the response can be tailored to that user. That decision can be based on either Access Control List (ACL) on a file object (see Section 6 of ) or proprietary policies. 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

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.

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.

Uncacheable Dirents If a file object has the uncacheable attribute set, then the client MUST NOT cache the dirent for that object. I.e., just because it presented the attributes for that object 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.

XDR for Offline Attribute

Extraction of XDR This document contains the external data representation (XDR) 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: 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: uncacheable_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 that XDR.

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.

IANA Considerations There are no IANA considerations.

References Normative References

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