Re: [Qemu-devel] CoW image commit+shrink(= make_empty) support

[Stefan Hajnoczi]

On Fri, Jun 8, 2012 at 6:46 PM, Jeff Cody <address@hidden> wrote:
> On 06/08/2012 12:11 PM, Kevin Wolf wrote:
>> Am 08.06.2012 16:32, schrieb Jeff Cody:
>>> On 06/08/2012 09:53 AM, Stefan Hajnoczi wrote:
>>>> On Fri, Jun 8, 2012 at 2:19 PM, Jeff Cody <address@hidden> wrote:
>>>>> On 06/08/2012 08:42 AM, Stefan Hajnoczi wrote:
>>>>>> Let's figure out how to specify block-commit so we're all happy, that
>>>>>> way we can avoid duplicating work.  Any comments on my notes above?
>>>>>>
>>>>>
>>>>> I think we are almost completely on the same page - devil is in the
>>>>> details, of course (for instance, on how to convert the destination base
>>>>> from r/o to r/w).
>>>>
>>>> Great.  The atomic r/o -> r/w transition and the commit coroutine can
>>>> be implemented on in parallel.  Are you happy to implement the atomic
>>>> r/o -> r/w transition since you wrote bdrv_append()?  Then Zhi Hui can
>>>> assume that part already works and focus on implementing the commit
>>>> coroutine in the meantime.  I'm just suggesting a way to split up the
>>>> work, please let me know if you think this is good.
>>>
>>> I am happy to do it that way.  I'll shift my focus to the atomic image
>>> reopen in r/w mode.  I'll go ahead and post my diagrams and other info
>>> for block-commit on the wiki, because I don't think it conflicts with we
>>> discussed above (although I will modify my diagrams to not show commit
>>> from the top-level image).  Of course, feel free to change it as
>>> necessary.
>>
>> I may have mentioned it before, but just in case: I think Supriya's
>> bdrv_reopen() patches are a good starting point. I don't know why they
>> were never completed, but I think we all agreed on the general design,
>> so it should be possible to pick that up.
>>
>> Though if you have already started with your own work on it, Jeff, I
>> expect that it won't be much different because it's basically the same
>> transactional approach that you know and that we already used for group
>> snapshots.
>>
>
> I will definitely use parts of Supriya's as it makes sense - what I
> started work on is similar to bdrv_append() and the current transaction
> approach, so there will be plenty in common to reuse, even with some
> differences.

I have CCed Supriya who has been working on the reopen patch series.
She is close to posting a new version.

Stefan