Re: Storing command line options in qcow2 images

Anthony Liguori
2007-08-08T00:36:41Z

Avi Kivity wrote:
> Daniel P. Berrange wrote:
>> On Tue, Aug 07, 2007 at 07:10:17AM +0300, Avi Kivity wrote:
>>
>>> Anthony Liguori wrote:
>>>
>>>> I don't think adding annotations as snapshots is the right
>>>> approach. I think proper support should be added in the header. I
>>>> wouldn't be too concerned with breaking compatibility in qcow2.
>>>> That's why it's qcow2 and not just an updated version of qcow,
>>>> qcow2 is still, AFAIK, open for breakage.
>>>>
>>> Are all the users' images open for breakage too?
>>>
>>
>> I'd say not. QCow2 has been around for a long time now so breaking
>> compat
>> with existing images would be a very bad idea. Ideally though some
>> extension
>> would be both backwards & forwards compatible - eg existing qcow2
>> impls would just ignore any new extension, while new impls would work
>> any image with or without extension. If this isn't possible then at
>> least call any
>> new format qcow3 to make it obvious to users that it is not compatible.
>>
>
> It was, of course, a rhetorical question. I initially suggested using
> a special snapshot as a means of preserving compatibility with qcow2,
> which I think is better than introducing yet a new format.

There are still more features I'd like to see added to qcow2 so I'm
hoping that it's not frozen. For instance, copy-on-read would be very
useful.

Regards,

Anthony Liguori