linux-kernel - Re: [PATCH v3 4/7] xfs: don't bump the i_version on an atime update in xfs_vn_update

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Date:   Sun, 28 Aug 2022 20:30:07 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Jeff Layton <jlayton@...nel.org>, Theodore Tso <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Dave Chinner <david@...morbit.com>,
        Trond Myklebust <trondmy@...merspace.com>,
        Neil Brown <neilb@...e.de>, Al Viro <viro@...iv.linux.org.uk>,
        Mimi Zohar <zohar@...ux.ibm.com>, xiubli@...hat.com,
        Chuck Lever <chuck.lever@...cle.com>,
        Lukas Czerner <lczerner@...hat.com>, Jan Kara <jack@...e.cz>,
        Christian Brauner <brauner@...nel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Linux Btrfs <linux-btrfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        David Wysochanski <dwysocha@...hat.com>,
        ceph-devel <ceph-devel@...r.kernel.org>
Subject: Re: [PATCH v3 4/7] xfs: don't bump the i_version on an atime update
 in xfs_vn_update_time

> > > >
> > > > Forensics and other applications that care about atime updates can and
> > > > should check atime and don't need i_version to know that it was changed.
> > > > The reliability of atime as an audit tool has dropped considerably since
> > > > the default in relatime.
>
> I've been waiting for Amir to appear in this discussion -- ISTR that a
> few years ago you were wanting the ability to scan a filesystem to look
> for files that have changed since a given point.  If XFS exported its
> di_changecount file attribute (as it currently behaves) via BULKSTAT,
> you'd have the ability to do that, so long as your application could
> persist bulkstat data and compare.
>

It's true that exporting i_version via BULKSTAT could be useful
to some backup/sync applications.

For my case, I was interested in something a bit different -
finding all the changes in a very large fs tree - or IOW finding if
anything has changed inside a large tree since a point in time.
So not sure if i_version would help for that use case.

Thanks,
Amir.