On Mon, Jul 22, 2013 at 02:07:15PM +0800, Fam Zheng wrote: > 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.
In my latest patchset I have attempted to override the backing hd of the target. It is a little over my head however so any input there would be appreciated. It seems to me like applying that patch would get us a working baseline and then you can add the more fancy stuff on top of that? That sound reasonable? Ian