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Date:   Sat, 27 Aug 2022 09:38:18 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Colin Walters <walters@verbum.org>
Cc:     Dave Chinner <david@fromorbit.com>,
        Jeff Layton <jlayton@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>, linux-api@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
        Jeff Layton <jlayton@redhat.com>,
        David Howells <dhowells@redhat.com>,
        Frank Filz <ffilzlnx@mindspring.com>
Subject: Re: [PATCH] vfs: report an inode version in statx for IS_I_VERSION
 inodes
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References: <20220819115641.14744-1-jlayton@kernel.org>
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On Thu, Aug 25, 2022 at 02:48:02PM -0400, Colin Walters wrote:
> 
> 
> On Tue, Aug 23, 2022, at 5:53 PM, Dave Chinner wrote:
> > 
> > THere's no definition of what consitutes an "inode change" and this
> > exposes internal filesystem implementation details (i.e. on disk
> > format behaviour) directly to userspace. That means when the
> > internal filesystem behaviour changes, userspace applications will
> > see changes in stat->ino_version changes and potentially break them.
> 
> As a userspace developer (ostree, etc. who is definitely interested in this functionality) I do agree with this concern; but a random drive by comment: would it be helpful to expose iversion (or other bits like this from the vfs) via e.g. debugfs to start?  I think that'd unblock writing fstests in the short term right?
> 
> 

This would not work at all for "virtual" filesystems like debugfs and
sysfs which only create the data when the file is read, and there's no
way to know if the data is going to be different than the last time it
was read, sorry.

greg k-h