Re: [Qemu-devel] [PATCH v2 3/3] migration: allow to suppress configuration section submission

[Laurent Vivier <lvivier@redhat.com>]

On 18/02/2016 10:24, Greg Kurz wrote:
> On Thu, 18 Feb 2016 12:06:39 +0530
> Amit Shah <amit.shah@redhat.com> wrote:
> 
>> On (Thu) 18 Feb 2016 [13:50:25], David Gibson wrote:
>>> On Wed, Feb 17, 2016 at 05:06:43PM +0100, Greg Kurz wrote:  
>>>> Since the addition of the configuration section in QEMU 2.4, it is impossible
>>>> to migrate a pseries-2.3 machine back to QEMU 2.3.
>>>>
>>>> This patch makes it possible thanks to a new machine property which allows to
>>>> disable configuration section submission.
>>>>
>>>> To disable submission, just add:
>>>>
>>>> -machine suppress-config-section=on
>>>>
>>>> Alternatively, if the target QEMU version isn't known at startup, this can
>>>> be done later from the QEMU monitor with:
>>>>
>>>> qom-set /machine suppress-config-section on
>>>>
>>>> This property won't be automatically set for pseries-2.3 because it would
>>>> then break backward migration to QEMU 2.4. If automatic behaviour is needed,
>>>> it is up to the tooling to handle this.  
>>>
>>> As noted elsewhere, I'd actually be ok with enabling it for
>>> pseries-2.3.  Basically we have to chose whether to work against qemu
>>> 2.3 or 2.4 out of the box, we can't have both, and it sounds like qemu
>>> 2.3 is more widely deployed than qemu 2.4.
>>>   
>>>>
>>>> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>  
>>>
>>> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
>>>
>>> I'm not sure whose tree these need to go in via.  
>>
>> I'd like to see Juan's ack, and I'm fine if you take it via your tree.
>>
>>
>>
>> 		Amit
>>
> 
> Hi,
> 
> I also have another option I'd like to submit. Basically, this would
> be:
> - introduce a enforce-config-section machine property which allows to
>   override the savevm_state.skip_configuration flag
> - update pseries-2.3 to skip configuration section by default (like it
>   should have been done in the beginning)
> 
> It would fix migration from/to QEMU 2.3 of pseries-2.3 without manual
> intervention. Only migration to/from QEMU 2.4/2.5 would require manual
> use of the enforce-config-section.
> 
> Laurent, is this what you had in mind ?

Yes :)

If you post a new series with this idea, I'll test it to be sure we
don't introduce new problems.

Laurent