Re: [Qemu-devel] [PATCH 2/2] block: resize backing image during active layer commit, if needed

[Jeff Cody]

On Wed, Jan 15, 2014 at 01:58:29PM +0800, Fam Zheng wrote:
> On Mon, 01/13 15:18, Jeff Cody wrote:
> > If the top image to commit is the active layer, and also larger than
> > the base image, then an I/O error will likely be returned during
> > block-commit.
> > 
> > For instance, if we have a base image with a virtual size 10G, and a
> > active layer image of size 20G, then committing the snapshot via
> > 'block-commit' will likely fail.
> > 
> > This will automatically attempt to resize the base image, if the
> > active layer image to be committed is larger.
> > 
> > Signed-off-by: Jeff Cody <address@hidden>
> > ---
> >  block/mirror.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/block/mirror.c b/block/mirror.c
> > index 2932bab..c4e42fa 100644
> > --- a/block/mirror.c
> > +++ b/block/mirror.c
> > @@ -630,9 +630,22 @@ void commit_active_start(BlockDriverState *bs, 
> > BlockDriverState *base,
> >                           BlockDriverCompletionFunc *cb,
> >                           void *opaque, Error **errp)
> >  {
> > +    int64_t length;
> >      if (bdrv_reopen(base, bs->open_flags, errp)) {
> >          return;
> >      }
> 
> "base" is already reopened here.
> 
> > +
> > +    length = bdrv_getlength(bs);
> > +
> > +    if (length > bdrv_getlength(base)) {
> > +        if (bdrv_truncate(base, length) < 0) {
> > +            error_setg(errp, "Top image %s is larger than base image %s, 
> > and "
> > +                             "resize of base image failed.",
> > +                             bs->filename, base->filename);
> > +            return;
> 
> Should we restore open flags for base?
>

Good catch.  Yes, I think we should; and I think we should also do it
after the call to mirror_start_job, if errp is set.  I'll add that in
for v2.

> > +        }
> > +    }
> > +
> >      bdrv_ref(base);
> >      mirror_start_job(bs, base, speed, 0, 0,
> >                       on_error, on_error, cb, opaque, errp,
> > -- 
> > 1.8.3.1
> >