Re: [Qemu-devel] [PATCH 1/8] spec: add qcow2-dirty-bitmaps specification

[John Snow]

On 06/12/2015 06:28 AM, Stefan Hajnoczi wrote:
> On Thu, Jun 11, 2015 at 12:21:31PM -0400, John Snow wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA256
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>>
>>
>> On 06/11/2015 09:03 AM, Stefan Hajnoczi wrote:
>>> On Thu, Jun 11, 2015 at 01:19:24PM +0300, Vladimir
>>> Sementsov-Ogievskiy wrote:
>>>> On 10.06.2015 16:24, Stefan Hajnoczi wrote:
>>>>> On Wed, Jun 10, 2015 at 11:19:30AM +0300, Vladimir
>>>>> Sementsov-Ogievskiy wrote:
>>>>>> On 09.06.2015 20:03, Stefan Hajnoczi wrote:
>>>>>>> On Mon, Jun 08, 2015 at 06:21:19PM +0300, Vladimir
>>>>>>> Sementsov-Ogievskiy wrote:
>>>>>>>> @@ -166,6 +167,19 @@ the header extension data. Each
>>>>>>>> entry look like this: terminated if it has full length) 
>>>>>>>> +== Dirty bitmaps == + +Dirty bitmaps is an optional
>>>>>>>> header extension. It provides a possibility of +storing
>>>>>>>> dirty bitmaps in qcow2 image. The fields are: + +
>>>>>>>> 0 -  3:  nb_dirty_bitmaps +                   Number of
>>>>>>>> dirty bitmaps contained in the image
>>>>>>> Is there a maximum?
>>>>>> hmm. any proposals for this?
>>>>> 65535 seems practical.
>>>>
>>>> So, you suggest to reduce this field width to 2b? And additional
>>>> 2 bytes reserved field, to achieve 8b-alignment?
>>>
>>> No, I would leave it 32-bit but impose a little (which can be
> 
> s/little/limit/
> 
>>> increased later if necessary).  That's how nb_snapshots works too.
>>>
>>
>> Doesn't the code already limit the number of bitmaps via +#define
>> QCOW_MAX_DIRTY_BITMAPS 65536, from patch 2?
> 
> It needs to be in the specification.
> 

Yes, but the way the replies read made it sound like we hadn't decided
on what the limit *was*, so I was just trying to clarify for myself, here.