Re: [Qemu-devel] [PATCH v13 00/14] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD

[Ian Main <imain@redhat.com>]

On Sat, Feb 01, 2014 at 11:21:17PM +0800, Fam Zheng wrote:
> On Fri, 01/31 19:00, Ian Main wrote:
> > On Wed, Jan 29, 2014 at 01:07:27PM +0800, Fam Zheng wrote:
> > > This series adds for point-in-time snapshot NBD exporting based on
> > > blockdev-backup (variant of drive-backup with existing device as target).
> > > 
> > > We get a thin point-in-time snapshot by COW mechanism of drive-backup, and
> > > export it through built in NBD server. The steps are as below:
> > > 
> > >  1. (SHELL) qemu-img create -f qcow2 BACKUP.qcow2 <source size here>
> > > 
> > >     (Alternatively we can use -o backing_file=RUNNING-VM.img to omit explicitly
> > >     providing the size by ourselves, but it's risky because RUNNING-VM.qcow2 is
> > >     used r/w by guest. Whether or not setting backing file in the image file
> > >     doesn't matter, as we are going to override the backing hd in the next
> > >     step)
> > > 
> > >  2. (QMP) blockdev-add backing=source-drive file.driver=file file.filename=BACKUP.qcow2 id=target0 if=none driver=qcow2
> > 
> > It seems like we have a regression here.  I sent you a private email
> > earlier and after some more testing I am finding that the setup that I
> > had to test this before is no longer working.  Now when I try to use
> > blockdev-add I get:
> > 
> > rsp = srv.cmd(command, {'options': {
> >                         'backing': 'ide0-hd0',
> >                         'driver': 'qcow2',
> >                         'id': 'target0',
> >                         'file': {
> >                             'driver': 'file',
> >                             'filename': '/home/imain/tmp/BACKUP.qcow2'
> >                             }
> >                         } 
> >                    })
> > 
> > rsp is {u'error': {u'class': u'GenericError', u'desc': u"could not open
> > disk image target0: Block format 'qcow2' used by device 'target0'
> > doesn't support the option 'backing'"}}
> > 
> > It's possible I'm messing something up but I'm pretty sure something has
> > changed with the options handling in bdrv_open() to make this not work
> > anymore.
> > 
> 
> My local test script is very similar to this, so as the case added in this
> series. They both work here. Have you found what is wrong there yet?

Hrrm, so I cleaned up my tree, pulled to latest and applied these and it
worked.  Not sure what happened there but it all seems good now.  I
should have tried that before I posted.

	Ian