On Mon, Mar 19, 2018 at 02:02:23PM +0100, David Sterba wrote:
> On Mon, Mar 19, 2018 at 08:20:10AM +0000, Hugo Mills wrote:
> > On Mon, Mar 19, 2018 at 05:16:42PM +0900, Misono, Tomohiro wrote:
> > > Currently, the top-level subvolume lacks the UUID. As a result, both
> > > non-snapshot subvolume and snapshot of top-level subvolume do not have
> > > Parent UUID and cannot be distinguisued. Therefore "fi show" of
> > > top-level lists all the subvolumes which lacks the UUID in
> > > "Snapshot(s)" filed.  Also, it lacks the otime information.
> > > 
> > > Fix this by adding the UUID and otime at the mkfs time.  As a
> > > consequence, snapshots of top-level subvolume now have a Parent UUID and
> > > UUID tree will create an entry for top-level subvolume at mount time.
> > > This should not cause the problem for current kernel, but user program
> > > which relies on the empty Parent UUID may be affected by this change.
> > 
> >    Is there any way of adding a UUID to the top level subvol on an
> > existing filesystem? It would be helpful not to have to rebuild every
> > filesystem in the world to fix this.
> 
> We can do that by a special purpose tool. The easiest way is to set the
> uuid on an unmouted filesystem, but as this is a one-time action I hope
> this is acceptable. Added to todo, thanks for the suggestion.

   Sounds good to me.

   Hugo.

-- 
Hugo Mills             | Talking about music is like dancing about
hugo@... carfax.org.uk | architecture
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                           Frank Zappa