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Date: Tue, 30 Aug 2022 09:50:02 -0400 From: Jeff Layton <jlayton@...nel.org> To: "J. Bruce Fields" <bfields@...ldses.org> Cc: NeilBrown <neilb@...e.de>, Dave Chinner <david@...morbit.com>, tytso@....edu, adilger.kernel@...ger.ca, djwong@...nel.org, trondmy@...merspace.com, viro@...iv.linux.org.uk, zohar@...ux.ibm.com, xiubli@...hat.com, chuck.lever@...cle.com, lczerner@...hat.com, jack@...e.cz, brauner@...nel.org, linux-api@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, linux-ceph@...r.kernel.org, linux-ext4@...r.kernel.org, linux-nfs@...r.kernel.org, linux-xfs@...r.kernel.org, Colin Walters <walters@...bum.org> Subject: Re: [PATCH v3 1/7] iversion: update comments with info about atime updates On Tue, 2022-08-30 at 09:24 -0400, J. Bruce Fields wrote: > On Tue, Aug 30, 2022 at 07:40:02AM -0400, Jeff Layton wrote: > > Yes, saying only that it must be different is intentional. What we > > really want is for consumers to treat this as an opaque value for the > > most part [1]. Therefore an implementation based on hashing would > > conform to the spec, I'd think, as long as all of the relevant info is > > part of the hash. > > It'd conform, but it might not be as useful as an increasing value. > > E.g. a client can use that to work out which of a series of reordered > write replies is the most recent, and I seem to recall that can prevent > unnecessary invalidations in some cases. > That's a good point; the linux client does this. That said, NFSv4 has a way for the server to advertise its change attribute behavior [1] (though nfsd hasn't implemented this yet). We don't have a good way to do that in userland for now. This is another place where fsinfo() would have been nice to have. I think until we have something like that, we'd want to keep our promises to userland to a minimum. [1]: https://www.rfc-editor.org/rfc/rfc7862.html#section-12.2.3 . I guess I should look at plumbing this in for IS_I_VERSION inodes... -- Jeff Layton <jlayton@...nel.org>
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