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Date:   Mon, 2 Aug 2021 16:41:25 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Patrick Goetz <pgoetz@math.utexas.edu>
Cc:     NeilBrown <neilb@suse.de>, Miklos Szeredi <miklos@szeredi.hu>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Josef Bacik <josef@toxicpanda.com>,
        Chuck Lever <chuck.lever@oracle.com>, Chris Mason <clm@fb.com>,
        David Sterba <dsterba@suse.com>, linux-fsdevel@vger.kernel.org,
        Linux NFS list <linux-nfs@vger.kernel.org>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: A Third perspective on BTRFS nfsd subvol dev/inode number issues.
Message-ID: <20210802204125.GE6890@fieldses.org>
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On Mon, Aug 02, 2021 at 03:32:45PM -0500, Patrick Goetz wrote:
> On 8/2/21 7:39 AM, J. Bruce Fields wrote:
> >On Mon, Aug 02, 2021 at 02:18:29PM +1000, NeilBrown wrote:
> >>For btrfs, the "location" is root.objectid ++ file.objectid.  I think
> >>the inode should become (file.objectid ^ swab64(root.objectid)).  This
> >>will provide numbers that are unique until you get very large subvols,
> >>and very many subvols.
> >
> >If you snapshot a filesystem, I'd expect, at least by default, that
> >inodes in the snapshot to stay the same as in the snapshotted
> >filesystem.
> 
> For copy on right systems like ZFS, how could it be otherwise?

I'm reacting to Neil's suggesting above, which (as I understand it)
would result in different inode numbers.

--b.