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Date: Fri, 26 Oct 2012 10:34:27 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH V14 1/6] docs: document for add-cow file
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To: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

Am 26.10.2012 04:54, schrieb Dong Xu Wang:
> On Thu, Oct 25, 2012 at 10:56 PM, Eric Blake <eblake@redhat.com> wrote:
>> On 10/25/2012 07:36 AM, Dong Xu Wang wrote:
>>> +
>>> +            64 - 79:    image file format
>>> +                        Format of image file. It must be non-empty. It is coded
>>> +                        in free-form ASCII, and is not NUL-terminated. Zero
>>> +                        padded on the right.
>>
>> [1]...here you claim that backing and image file format are mandatory
>> (must not be empty).  Shouldn't you allow the file format to be empty,
>> in which case qemu will probe?  And why do you even need image file
>> format - isn't the whole point of add-cow to wrap a raw image file, or
>> are you planning on also being able to wrap non-raw files?  Are there
>> other non-raw file formats that lack backing file support, where add-cow
>> can be used to give it a backing file?
>>
> 
> Kevin or Stefan, can you give me some opinion? Thanks.

Yes, there are plenty of other block drivers that don't support backing
files, either because their image format/protocol can't provide such
information or just because it's not implemented in qemu today.

Kevin