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Date:   Wed, 7 Sep 2022 08:20:33 -0400
To:     NeilBrown <neilb@suse.de>
Cc:     Jeff Layton <jlayton@kernel.org>, tytso@mit.edu,
        adilger.kernel@dilger.ca, djwong@kernel.org, david@fromorbit.com,
        trondmy@hammerspace.com, viro@zeniv.linux.org.uk,
        zohar@linux.ibm.com, xiubli@redhat.com, chuck.lever@oracle.com,
        lczerner@redhat.com, jack@suse.cz, brauner@kernel.org,
        fweimer@redhat.com, linux-man@vger.kernel.org,
        linux-api@vger.kernel.org, linux-btrfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        ceph-devel@vger.kernel.org, linux-ext4@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
 STATX_INO_VERSION field
Message-ID: <20220907122033.GA17729@fieldses.org>
References: <20220907111606.18831-1-jlayton@kernel.org>
 <166255065346.30452.6121947305075322036@noble.neil.brown.name>
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From:   bfields@fieldses.org (J. Bruce Fields)
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On Wed, Sep 07, 2022 at 09:37:33PM +1000, NeilBrown wrote:
> On Wed, 07 Sep 2022, Jeff Layton wrote:
> > +The change to \fIstatx.stx_ino_version\fP is not atomic with respect to the
> > +other changes in the inode. On a write, for instance, the i_version it usually
> > +incremented before the data is copied into the pagecache. Therefore it is
> > +possible to see a new i_version value while a read still shows the old data.
> 
> Doesn't that make the value useless?  Surely the change number must
> change no sooner than the change itself is visible, otherwise stale data
> could be cached indefinitely.

For the purposes of NFS close-to-open, I guess all we need is for the
change attribute increment to happen sometime between the open and the
close.

But, yes, it'd seem a lot more useful if it was guaranteed to happen
after.  (Or before and after both--extraneous increments aren't a big
problem here.)

--b.

> 
> If currently implementations behave this way, surely they are broken.
> 
> NeilBrown