linux-kernel - Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO

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Message-ID: <20220912134208.GB9304@fieldses.org>
Date:   Mon, 12 Sep 2022 09:42:08 -0400
From:   bfields@...ldses.org (J. Bruce Fields)
To:     NeilBrown <neilb@...e.de>
Cc:     Jeff Layton <jlayton@...nel.org>, Theodore Ts'o <tytso@....edu>,
        Jan Kara <jack@...e.cz>, adilger.kernel@...ger.ca,
        djwong@...nel.org, david@...morbit.com, trondmy@...merspace.com,
        viro@...iv.linux.org.uk, zohar@...ux.ibm.com, xiubli@...hat.com,
        chuck.lever@...cle.com, lczerner@...hat.com, brauner@...nel.org,
        fweimer@...hat.com, linux-man@...r.kernel.org,
        linux-api@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        ceph-devel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
 STATX_INO_VERSION field

On Sun, Sep 11, 2022 at 08:13:11AM +1000, NeilBrown wrote:
> On Fri, 09 Sep 2022, Jeff Layton wrote:
> > 
> > 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? 
> 
> (I missed this bit in my earlier reply..)
> 
> How is it "Fine" to see an old version?
> The file could have changed without the version changing.
> And I thought one of the goals of the crash-count was to be able to
> provide a monotonic change id.

I was still mainly thinking about how to provide reliable close-to-open
semantics between NFS clients.  In the case the writer was an NFS
client, it wasn't done writing (or it would have COMMITted), so those
writes will come in and bump the change attribute soon, and as long as
we avoid the small chance of reusing an old change attribute, we're OK,
and I think it'd even still be OK to advertise
CHANGE_TYPE_IS_MONOTONIC_INCR.

If we're trying to do better than that, I'm just not sure what's right.

--b.