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Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
 STATX_INO_VERSION field
From:   Jeff Layton <jlayton@kernel.org>
To:     "J. Bruce Fields" <bfields@fieldses.org>
Cc:     Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
        NeilBrown <neilb@suse.de>, adilger.kernel@dilger.ca,
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Date:   Thu, 08 Sep 2022 15:07:58 -0400
In-Reply-To: <20220908182252.GA18939@fieldses.org>
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On Thu, 2022-09-08 at 14:22 -0400, J. Bruce Fields wrote:
> On Thu, Sep 08, 2022 at 01:40:11PM -0400, Jeff Layton wrote:
> > Yeah, ok. That does make some sense. So we would mix this into the
> > i_version instead of the ctime when it was available. Preferably, we'd
> > mix that in when we store the i_version rather than adding it afterward=
.
> >=20
> > Ted, how would we access this? Maybe we could just add a new (generic)
> > super_block field for this that ext4 (and other filesystems) could
> > populate at mount time?
>=20
> Couldn't the filesystem just return an ino_version that already includes
> it?
>=20

Yes. That's simple if we want to just fold it in during getattr. If we
want to fold that into the values stored on disk, then I'm a little less
clear on how that will work.

Maybe I need a concrete example of how that will work:

Suppose we have an i_version value X with the previous crash counter
already factored in that makes it to disk. We hand out a newer version
X+1 to a client, but that value never makes it to disk.

The machine crashes and comes back up, and we get a query for i_version
and it comes back as X. Fine, it's an old version. Now there is a write.
What do we do to ensure that the new value doesn't collide with X+1?=20
--=20
Jeff Layton <jlayton@kernel.org>