linux-kernel - Re: [PATCH v7 0/9] fs: clean up handling of i

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Date:   Wed, 19 Oct 2022 16:36:47 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Christian Brauner <brauner@...nel.org>, tytso@....edu,
        adilger.kernel@...ger.ca, david@...morbit.com,
        trondmy@...merspace.com, neilb@...e.de, viro@...iv.linux.org.uk,
        zohar@...ux.ibm.com, xiubli@...hat.com, chuck.lever@...cle.com,
        lczerner@...hat.com, jack@...e.cz, bfields@...ldses.org,
        fweimer@...hat.com, 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: [PATCH v7 0/9] fs: clean up handling of i_version counter

On Wed, 2022-10-19 at 08:45 -0700, Darrick J. Wong wrote:
> On Wed, Oct 19, 2022 at 08:18:15AM -0400, Jeff Layton wrote:
> > On Wed, 2022-10-19 at 13:13 +0200, Christian Brauner wrote:
> > > On Mon, Oct 17, 2022 at 06:57:00AM -0400, Jeff Layton wrote:
> > > > This patchset is intended to clean up the handling of the i_version
> > > > counter by nfsd. Most of the changes are to internal interfaces.
> > > > 
> > > > This set is not intended to address crash resilience, or the fact that
> > > > the counter is bumped before a change and not after. I intend to tackle
> > > > those in follow-on patchsets.
> > > > 
> > > > My intention is to get this series included into linux-next soon, with
> > > > an eye toward merging most of it during the v6.2 merge window. The last
> > > > patch in the series is probably not suitable for merge as-is, at least
> > > > until we sort out the semantics we want to present to userland for it.
> > > 
> > > Over the course of the series I struggled a bit - and sorry for losing
> > > focus - with what i_version is supposed to represent for userspace. So I
> > > would support not exposing it to userspace before that. But that
> > > shouldn't affect your other changes iiuc.
> > 
> > Thanks Christian,
> > 
> > It has been a real struggle to nail this down, and yeah I too am not
> > planning to expose this to userland until we have this much better
> > defined. Patch #9 is just to give you an idea of what this would
> > ultimately look like. I intend to re-post the first 8 patches with an
> > eye toward merge in v6.2, once we've settled on the naming. On that
> > note...
> > 
> > I believe you had mentioned that you didn't like STATX_CHANGE_ATTR for
> > the name, and suggested STATX_I_VERSION (or something similar), which I
> > later shortened to STATX_VERSION.
> > 
> > Dave C. objected to STATX_VERSION, as "version" fields in a struct
> > usually refer to the version of the struct itself rather than the
> > version of the thing it describes. It also sort of implies a monotonic
> > counter, and I'm not ready to require that just yet.
> > 
> > What about STATX_CHANGE for the name (with corresponding names for the
> > field and other flags)? That drops the redundant "_ATTR" postfix, while
> > being sufficiently vague to allow for alternative implementations in the
> > future.
> > 
> > Do you (or anyone else) have other suggestions for a name?
> 
> Welllll it's really a u32 whose value doesn't have any intrinsic meaning
> other than "if (value_now != value_before) flush_cache();" right?
> I think it really only tracks changes to file data, right?
> 

It's a u64, but yeah, you're not supposed to assign any intrinsic
meaning to the value itself.

> STATX_CHANGE_COOKIE	(wait, does this cookie augment i_ctime?)
> 
> STATX_MOD_COOKIE	(...or just file modifications/i_mtime?)
> 
> STATX_MONITOR_COOKIE	(...what are we monitoring??)
> 
> STATX_MON_COOKIE
> 
> STATX_COOKIE_MON
> 
> STATX_COOKIE_MONSTER
> 
> There we go. ;)
> 
> In seriousness, I'd probably go with one of the first two.  I wouldn't
> be opposed to the last one, either, but others may disagree. ;)
> 
> --D
> 
> 

STATX_CHANGE_COOKIE is probably the best one. I'll plan to go with that
unless someone has a better idea. Thanks for the suggestions!

Cheers,
-- 
Jeff Layton <jlayton@...nel.org>