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

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

On 06/14/2012 07:59 PM, Jeff Cody wrote:
> On 06/14/2012 10:23 AM, Zhi Hui Li wrote:
>> On 2012年06月11日 23:37, Jeff Cody 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.
>>>
>>> It sounds like Zhi Hui is working on live block commit patches, and
>>> Supriya is working on the bdrv_reopen() portion - I don't want to
>>> duplicate any effort, but if there is anything I can do to help with
>>> either of those areas, just let me know.
>>>
>>> Thanks,
>>> Jeff
>>>
>>>
>>>
>> Jeff please go ahead with block-commit, I
>> am finishing up my fdc async conversion patch series first.  I will
>> reply when I'm ready to work on block-commit.
>>
>> Thank you very much!
>>
>
> Hi Zhi,
>
> I will do that.  Thanks!
>
> Jeff
>
Jeff,
    Need another day's time for posting bdrv_reopen() patchset. Getting 
few hmp related build errors in hostcache toggling code when built on 
latest git. Will correct those and post the patchset soon.
- Supriya