linux-ext4 - Re: should we make "-o iversion" the default on ext4 ?

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Message-ID: <e84b9caf376a9b958a95ca4e0d088808c482f109.camel@kernel.org>
Date:   Wed, 20 Jul 2022 12:15:05 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Benjamin Coddington <bcodding@...hat.com>
Cc:     Lukas Czerner <lczerner@...hat.com>, tytso@....edu,
        adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: should we make "-o iversion" the default on ext4 ?

On Wed, 2022-07-20 at 11:56 -0400, Benjamin Coddington wrote:
> On 20 Jul 2022, at 10:38, Jeff Layton wrote:
> > On Wed, 2022-07-20 at 16:15 +0200, Lukas Czerner wrote:
> > > 
> > > Is there a different way I am not seeing?
> > > 
> > 
> > Right, implementing this is the difficult bit actually since this uses a
> > MS_* flag. If we do make this the default, we'd definitely want to
> > continue allowing "-o noiversion" to disable it.
> > 
> > Could we just reverse the default in libmount? It might cause this to
> > suddenly be enabled in some deployments, but in most cases, people
> > wouldn't even notice and they could still specify -o noiversion to turn
> > it off.
> > 
> > Another idea would be to introduce new mount options for this, but
> > that's kind of nasty from a UI standpoint.
> 
> Is it safe to set SB_I_VERSION at export time?  If so, export_operations
> could grow an ->enable_iversion().
> 

That sounds like it might be problematic.

Consider the case where a NFSv4 client has cached file data and the
change attribute for the file. Server then reboots, but before the
export happens a local user makes a change to the file and it doesn't
update the i_version.
-- 
Jeff Layton <jlayton@...nel.org>