Re: [Qemu-devel] [PATCH v2] qapi: converted commit

[Jeff Cody <jcody@redhat.com>]

On 06/15/2012 10:44 AM, Luiz Capitulino wrote:
> On Fri, 15 Jun 2012 10:11:46 -0400
> Jeff Cody <jcody@redhat.com> wrote:
> 
>> On 06/15/2012 10:02 AM, Luiz Capitulino wrote:
>>> On Thu, 14 Jun 2012 17:21:44 +0200
>>> Pavel Hrdina <phrdina@redhat.com> wrote:
>>>
>>>> On 06/14/2012 05:04 PM, Eric Blake wrote:
>>>>> On 06/14/2012 08:56 AM, Pavel Hrdina wrote:
>>>>>> On 06/14/2012 02:18 PM, Eric Blake wrote:
>>>>>>> On 06/14/2012 01:35 AM, Pavel Hrdina wrote:
>>>>>>>> Signed-off-by: Pavel Hrdina<phrdina@redhat.com>
>>>>>>>> ---
>>>>>>>> +++ b/qapi-schema.json
>>>>>>>> @@ -1169,6 +1169,21 @@
>>>>>>>>    { 'command': 'block_resize', 'data': { 'device': 'str', 'size':
>>>>>>>> 'int' }}
>>>>>>>>
>>>>>>>>    ##
>>>>>>>> +# @commit
>>>>>>>> +#
>>>>>>>> +# Commit changes to the disk images (if -snapshot is used) or
>>>>>>>> backing files.
>>>>>>>> +#
>>>>>>>> +# @device: the name of the device or the "all" to commit all devices
>>>>>>>> +#
>>>>>>>> +# Returns: nothing on success
>>>>>>>> +#          If @device is not a valid block device, DeviceNotFound
>>>>>>>> +#          If a long-running operation is using the device, DeviceInUse
>>>>>>>> +#
>>>>>>>> +# Since: 1.2
>>>>>>>> +##
>>>>>>>> +{ 'command': 'commit', 'data': { 'device': 'str' }}
>>>>>>> Should we use this as an opportunity to make the command more powerful?
>>>>>>>    For example, integrating this with the 'transaction' command or a block
>>>>>>> job queried by 'query-block-jobs' to track its progress would be useful.
>>>>>>>    Also, suppose I have A<- B<- C.  Does 'commit' only do one layer (C
>>>>>>> into B), or all layers (B and C into A)?  That argues that we need an
>>>>>>> optional parameter that says how deep to commit (committing C into B
>>>>>>> only to repeat and commit B into A is more time-consuming than directly
>>>>>>> committing both B and C into A to start with).  When a commit is
>>>>>>> complete, which file is backing the device - is it still C (which
>>>>>>> continues to diverge, but now from the point of the commit) or does qemu
>>>>>>> pivot things to have the device now backed by B (and C can be discarded,
>>>>>>> particularly true if changes are now going into B which invalidate C).
>>>>>> What i find out is that 'commit' will commit changes only from C to B
>>>>>> and qemu continues with C from the new commit point. I couldn't find a
>>>>>> way to commit changes and go back to backing file. This should be
>>>>>> supported by parameter and also as you mention that commit all changes
>>>>>> through all snapshots should be supported by another parameter.
>>>>>> The 'transaction' feature would be nice to have too.
>>>>> Which makes it sound like we're starting to overlap with Jeff's work on
>>>>> 'block-commit'.
>>>>>
>>>>> If 'block-commit' proves to be better all around at doing what we want,
>>>>> do we even need to keep 'commit' in QMP, or would it be okay for HMP only?
>>>> If the 'block-commit' will be better I think that we could drop the 
>>>> 'commit' completely. And have only 'block-commit' for both QMP and HMP.
>>>
>>> I completely agree about the QMP part, but for HMP it's a good idea to
>>> maintain the commit command. To achieve this, we can implement hmp_commit()
>>> in terms of block-commit.
>>>
>>> Jeff, can you answer us here? Does block-commit supersedes the commit command
>>> we have today?
>>
>> The block-commit will supercede in functionality the commit command in
>> place today, but it is a live operation - as such, it will take longer
>> to complete, but it won't pause the guest.
> 
> This is very nice, is this being targeted for 1.2?

Yes, I'd like to see this in 1.2, so that is my goal.