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

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [PATCH] qemu-img rebase: Fix for undersized backing files
Date: Wed, 7 Dec 2011 12:06:48 +0000

On Wed, Dec 7, 2011 at 12:02 PM, Kevin Wolf <address@hidden> wrote:
> Am 07.12.2011 12:50, schrieb Stefan Hajnoczi:
>> On Wed, Dec 7, 2011 at 11:45 AM, Kevin Wolf <address@hidden> 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 <address@hidden>
>>> ---
>>>  qemu-img.c |   42 +++++++++++++++++++++++++++++++++---------
>>>  1 files changed, 33 insertions(+), 9 deletions(-)
>> Reviewed-by: Stefan Hajnoczi <address@hidden>
>> 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?

If we can make qemu-img the last user of synchronous interfaces then
it would be nice to convert it.  Right now I'm happy that we're
solidifying coroutines and converting synchronous hardware emulation,
hopefully we'll get to the point where there is no real reason to keep
the synchronous API around anymore.


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