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Date:   Mon, 12 Sep 2022 09:51:31 -0400
To:     Jeff Layton <jlayton@kernel.org>
Cc:     Florian Weimer <fweimer@redhat.com>, Theodore Ts'o <tytso@mit.edu>,
        Jan Kara <jack@suse.cz>, NeilBrown <neilb@suse.de>,
        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,
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        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
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From:   bfields@fieldses.org (J. Bruce Fields)
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On Mon, Sep 12, 2022 at 08:55:04AM -0400, Jeff Layton wrote:
> Because of the "seen" flag, we have a 63 bit counter to play with. Could
> we use a similar scheme to the one we use to handle when "jiffies"
> wraps? Assume that we'd never compare two values that were more than
> 2^62 apart? We could add i_version_before/i_version_after macros to make
> it simple to handle this.

As far as I recall the protocol just assumes it can never wrap.  I guess
you could add a new change_attr_type that works the way you describe.
But without some new protocol clients aren't going to know what to do
with a change attribute that wraps.

I think this just needs to be designed so that wrapping is impossible in
any realistic scenario.  I feel like that's doable?

If we feel we have to catch that case, the only 100% correct behavior
would probably be to make the filesystem readonly.

--b.