Re: [Qemu-devel] [PATCH] qemu-img rebase: Fix for undersized backing files

[Kevin Wolf <kwolf@redhat.com>]

Am 07.12.2011 12:50, schrieb Stefan Hajnoczi:
> On Wed, Dec 7, 2011 at 11:45 AM, Kevin Wolf <kwolf@redhat.com> wrote:
>> Backing files may be smaller than the corresponding COW file. When
>> reading directly from the backing file, qemu-img rebase must consider
>> this and assume zero sectors after the end of backing files.
>>
>> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>> ---
>>  qemu-img.c |   42 +++++++++++++++++++++++++++++++++---------
>>  1 files changed, 33 insertions(+), 9 deletions(-)
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> 
> It almost feels like we want a bdrv_read() variation that does the
> zeroing beyond end of image instead of duplicating this.

Almost. If we have a third user, it's probably worth it.

Actually, if we make a bdrv_co_readv_backing() instead of a synchronous
one, qcow2 would be the third user (and maybe VMDK could use it, too).
That would require moving qemu-img into a coroutine first, which I think
you wanted to do anyway?

Kevin