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

[Supriya Kannery <supriyak@linux.vnet.ibm.com>]

On 06/12/2012 04:26 PM, Stefan Hajnoczi wrote:
> On Mon, Jun 11, 2012 at 4:37 PM, Jeff Cody<jcody@redhat.com>  wrote:
>> On 06/11/2012 10:24 AM, Stefan Hajnoczi wrote:
>>> On Mon, Jun 11, 2012 at 1:50 PM, Kevin Wolf<kwolf@redhat.com>  wrote:
>>>> Am 11.06.2012 14:09, schrieb Stefan Hajnoczi:
>>>>> On Fri, Jun 8, 2012 at 6:46 PM, Jeff Cody<jcody@redhat.com>  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<jcody@redhat.com>  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.
>>>>
>>>> It's just a bit disappointing that it takes several months between each
>>>> two versions of the patch series. We'd like to have this in qemu 1.2,
>>>> not only in qemu 1.14.
>>>>
>>>> I can understand if someone can't find the time, but then allow at least
>>>> someone else to pick it up.
>>>
>>> Hey, don't shoot the messenger :).  I just wanted add Supriya to CC so
>>> she can join the discussion and see how much overlap there is with
>>> what she's doing.  We all contribute to QEMU from different angles and
>>> with different priorities.  If there is a time critical dependency on
>>> the reopen code then discuss it here and the result will be that
>>> someone officially drives the feature on.
>>>
>>
>> I am more than happy to take the previous reopen() patches, and drive
>> those forward, and also do whatever else is needed for live block
>> commit.
>
> Supriya,
> Can you share with us whether you have enough time to complete the
> reopen() patches you've been working on?  This functionality is a
> dependency for the new block-commit command.  Jeff is willing to take
> on the reopen() work if you do not have time.  Please let us know.
>
> Stefan
>
All,

   Sorry! for not following up these discussions and hence the delay in
responding. After few month's gap, I had resumed working on 
bdrv_reopen() patchset but was not aware of this dependency and urgency. 
Will be posting whatever I have by tomorrow so that Jeff can use that 
code as needed for block-commit.

- Supriya