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Re: [Qemu-devel] [PATCH v2 1/2] qapi: Introduce blockdev-group-snapshot-


From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [PATCH v2 1/2] qapi: Introduce blockdev-group-snapshot-sync command
Date: Mon, 27 Feb 2012 15:31:53 +0000

On Mon, Feb 27, 2012 at 3:23 PM, Jeff Cody <address@hidden> wrote:
> On 02/27/2012 09:40 AM, Stefan Hajnoczi wrote:
>> On Mon, Feb 27, 2012 at 2:26 PM, Jeff Cody <address@hidden> wrote:
>>> On 02/27/2012 06:13 AM, Stefan Hajnoczi wrote:
>>>> On Sun, Feb 26, 2012 at 7:31 PM, Jeff Cody <address@hidden> wrote:
>>>>> + * It is assumed that bs_new already points to an existing image,
>>>>> + * with the correct backing filename of top->backing_file
>>>>
>>>> Not sure what this means.  Isn't bs_new going to use bs_top as its
>>>> backing file?  Why "top->backing_file"?
>>>
>>> Sorry, that should have been 'bs_top->backing_file'. The image file is
>>> not created by this function.  I added some more explanation, and
>>> corrected that typo, in the above comment block.  Let me know if you
>>> think it still needs more clarification.
>>
>> I still don't follow.  Old bs_top's image file itself becomes the
>> backing file, not bs_top->backing_file.  Perhaps I'm misinterpreting
>> because of how swap changes bs_top and bs_new, but I'm reading it from
>> the perspective of the caller when they pass in bs_top.
>>
>
> Maybe it would be better to just replace that part of the comment with
> something that says "This function does not create the image file".
>
> The function bdrv_append() will neither create the image file, or set
> (in the case of qcow2) the extended headers of the file to have the
> backing filename.  It is only concerned with the bs contents.

Makes sense.

Stefan



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