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Re: [nfsv4] follow-up of xattr discussion

"J. Bruce Fields" <bfields@fieldses.org> Thu, 23 July 2015 18:45 UTC

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Date: Thu, 23 Jul 2015 14:45:47 -0400
From: "J. Bruce Fields" <bfields@fieldses.org>
To: David Noveck <davenoveck@gmail.com>
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Cc: Christoph Hellwig <hch@lst.de>, "nfsv4@ietf.org" <nfsv4@ietf.org>
Subject: Re: [nfsv4] follow-up of xattr discussion
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On Thu, Jul 23, 2015 at 01:15:22PM -0400, David Noveck wrote:
> which sound to me like such uses for not allowed.  I'll be reviewing
> this document in a bit and will propose some toughening up of the
> language.

One of the practical difference is the caching.  A lot of the
filesystem-specific attributes look incompatible with client caching.

Looking at the "caching" section: it does say clients may cache reads,
and that the change attribute can be depended on to validate that cache,
but:

	https://tools.ietf.org/html/draft-naik-nfsv4-xattrs-02#section-6.2.2

	Such caching is write through in that modification to xattrs is
	always done by means of requests to the server and should not be
	only done locally. Due to the relative infrequency of xattr
	updates, it is suggested that all changes be propagated
	synchronously. The client MUST NOT maintain a cache of modified
	xattrs.

What's the rationale for that MUST NOT?

--b.

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