Re: [Qemu-devel] [PATCH 1/1] block: check full backing filename when searching protocol filenames

[Jeff Cody <jcody@redhat.com>]

On Wed, Jan 25, 2017 at 07:27:07PM +0100, Max Reitz wrote:
> On 25.01.2017 18:22, Jeff Cody wrote:
> > In bdrv_find_backing_image(), if we are searching an image for a backing
> > file that contains a protocol, we currently only compare unmodified
> > paths.
> > 
> > However, some management software will change the backing filename to be
> > a relative filename in a path.  QEMU is able to handle this fine,
> > because internally it will use path_combine to put together the full
> > protocol URI.
> > 
> > However, this can lead to an inability to match an image during a QAPI
> > command that needs to use bdrv_find_backing_image() to find the image,
> > when it is searched by the full URI.
> > 
> > When searching for a protocol filename, if the straight comparison
> > fails, this patch will also compare against the full backing filename to
> > see if that is a match.
> > 
> > Signed-off-by: Jeff Cody <jcody@redhat.com>
> > ---
> >  block.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/block.c b/block.c
> > index 39ddea3..a173afc 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -3145,6 +3145,7 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
> >      int is_protocol = 0;
> >      BlockDriverState *curr_bs = NULL;
> >      BlockDriverState *retval = NULL;
> > +    Error *local_error = NULL;
> >  
> >      if (!bs || !bs->drv || !backing_file) {
> >          return NULL;
> > @@ -3165,6 +3166,17 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
> >                  retval = curr_bs->backing->bs;
> >                  break;
> >              }
> > +            /* Also check against the full backing filename for the image */
> > +            bdrv_get_full_backing_filename(curr_bs, backing_file_full, PATH_MAX,
> > +                                           &local_error);
> > +            if (local_error == NULL) {
> > +                if (strcmp(backing_file, backing_file_full) == 0) {
> > +                    retval = curr_bs->backing->bs;
> > +                    break;
> > +                }
> > +            } else {
> > +                error_free(local_error);
> 
> Oops, I was a bit too quick there. You should either follow Eric's
> remark about the scope, or you have to reset local_error to NULL here.
>

OK. I'll submit a v2, and add an iotest to that as well.

> 
> > +            }
> >          } else {
> >              /* If not an absolute filename path, make it relative to the current
> >               * image's filename path */
> > 
> 
>