Re: [Qemu-devel] [PATCH v4 3/8] block: don't make snapshots for filters

["Pavel Dovgalyuk" <dovgaluk@ispras.ru>]

> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> Sent: Wednesday, September 21, 2016 6:37 PM
> To: Pavel Dovgalyuk; qemu-devel@nongnu.org
> Cc: peter.maydell@linaro.org; jasowang@redhat.com; quintela@redhat.com; mst@redhat.com
> Subject: Re: [PATCH v4 3/8] block: don't make snapshots for filters
> 
> 
> 
> On 21/09/2016 13:33, Pavel Dovgalyuk wrote:
> > This patch disables snapshotting for block driver filters.
> > It is needed, because snapshots should be created
> > in underlying disk images, not in filters itself.
> 
> I don't understand this patch.  Who would take care of doing the
> bdrv_snapshot_goto on the underlying image?

loadvm needs to make bdrv_snapshot_goto. It discovers top-level replay driver and
tries to perform bdrv_snapshot_goto for it.

Patches 3 and 4 fix that. They allow passing through the replay driver and
make saving/restoring of the actual image.

Pavel Dovgalyuk

> 
> > Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
> > ---
> >  block/snapshot.c |    3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/block/snapshot.c b/block/snapshot.c
> > index bf5c2ca..8998b8b 100644
> > --- a/block/snapshot.c
> > +++ b/block/snapshot.c
> > @@ -184,6 +184,9 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
> >      if (!drv) {
> >          return -ENOMEDIUM;
> >      }
> > +    if (drv->is_filter) {
> > +        return 0;
> > +    }
> >      if (drv->bdrv_snapshot_goto) {
> >          return drv->bdrv_snapshot_goto(bs, snapshot_id);
> >      }
> >