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

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH] qemu-img rebase: Fix for undersized backing files
Date: Wed, 07 Dec 2011 13:02:30 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0

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?


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