linux-ext4 - Re: [PATCH v3 1/7] iversion: update comments with info about atime updates

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Date:   Tue, 30 Aug 2022 09:24:43 -0400
From:   bfields@...ldses.org (J. Bruce Fields)
To:     Jeff Layton <jlayton@...nel.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, 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.

--b.