Re: [Qemu-devel] [PATCH v2 10/11] block: add option 'backing' to -drive options

[Fam Zheng <famz@redhat.com>]

On Wed, 07/17 14:36, Paolo Bonzini wrote:
> Il 17/07/2013 11:42, Fam Zheng ha scritto:
> > This option allows overriding backing hd of drive. If the target drive
> > exists, it's referenced as the backing file and refcount incremented.
> > 
> > Example:
> >     qemu-system-x86_64 -drive \
> >         file.filename=foo.qcow2,if=none,id=foo \
> >         -drive file=bar.qcow2,backing=foo
> 
> I guess this is where we need the soft reference.
> 
> This has a _lot_ of potential for misuse, I think Kevin bashed me and
> Federico very heavily when we tried to do something similar.
> 
> block/backup.c is the right place where we can override the backing hd
> of the drive.  Perhaps we can add a way to open a file with
> BDRV_O_NO_BACKING from the command line.

OK. If we get the override in block/backup.c, the only thing we need is
naming the target so we can add it to nbd server. If refcounting,
overriding backing with option and blockdev-backup are still good to
have, I can split them and targeting to future releases.

-- 
Fam