On Thu, Oct 28, 2010 at 10:35:02AM +0100, Daniel P. Berrange wrote:
> On Thu, Oct 28, 2010 at 09:30:09AM +0100, Stefan Hajnoczi wrote:
> > On Wed, Oct 27, 2010 at 7:19 PM, Anthony Liguori <aligu...@us.ibm.com>
> > wrote:
> > > Signed-off-by: Anthony Liguori <aligu...@us.ibm.com>
> > >
> > > diff --git a/block.c b/block.c
> > > index 1a965b2..00b6f21 100644
> > > --- a/block.c
> > > +++ b/block.c
> > > @@ -603,10 +603,16 @@ int bdrv_open(BlockDriverState *bs, const char
> > > *filename, int flags,
> > > BlockDriver *back_drv = NULL;
> > >
> > > bs->backing_hd = bdrv_new("");
> > > - path_combine(backing_filename, sizeof(backing_filename),
> > > - filename, bs->backing_file);
> > > - if (bs->backing_format[0] != '\0')
> > > - back_drv = bdrv_find_format(bs->backing_format);
> > > + back_drv = bdrv_find_protocol(bs->backing_file);
> > > + if (!back_drv) {
> > > + path_combine(backing_filename, sizeof(backing_filename),
> > > + filename, bs->backing_file);
> > > + if (bs->backing_format[0] != '\0')
> > > + back_drv = bdrv_find_format(bs->backing_format);
> > > + } else {
> > > + pstrcpy(backing_filename, sizeof(backing_filename),
> > > + bs->backing_file);
> > > + }
> > >
> > > /* backing files always opened read-only */
> > > back_flags =
> > > --
> > > 1.7.0.4
> >
> > I think this makes sense.
> >
> > Now it is possible to specify backing files that are relative to
> > QEMU's current working directory using file:filename. I don't see
> > harm in this.
>
> Shouldn't a backing file be treated as relative to the image file pointing
> to it, rather than the QEMU working directory. eg so you can do
>
> # qemu-img create backing.img
> # qemu-img create -o backing_file=file:backing.img main.img
>
> And have main.img be able to resolve backing.img in its same directory,
> no matter what directory QEMU itself is executing from
This works relative to main.img:
# qemu-img create -o backing_file=backing.img main.img
but this works relative to QEMU's cwd:
# qemu-img create -o backing_file=file:backing.img main.img
As Kevin mentioned, special-casing the file: protocol isn't ideal. We
shouldn't make assumptions about specific protocols.
Stefan
