Re: [Qemu-devel] [Qemu-ppc] [PATCH] target-ppc: Add @cpu_dt_id into migration stream

[Alexander Graf <agraf@suse.de>]

On 08.04.14 03:26, Alexey Kardashevskiy wrote:
> On 03/28/2014 12:07 AM, Alexey Kardashevskiy wrote:
>> On 03/27/2014 11:57 PM, Peter Maydell wrote:
>>> On 27 March 2014 12:49, Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>>>> On 03/27/2014 11:37 PM, Andreas Färber wrote:
>>>>> Am 27.03.2014 03:41, schrieb Alexey Kardashevskiy:
>>>>>> This should prevent the destination guest from misbehaving when
>>>>>> the threads number is different in "-smp" command.
>>>>> Sorry, I don't understand. When migrating, surely -smp needs to be the
>>>>> same on source and destination, so how can they differ?
>>>>
>>>> The idea is that "-smp" does not migrate and if we run source and
>>>> destination guests with different numbers in -smp, we end up with weird
>>>> machine
>>> Yes, so don't do that. As I understand it:
>>>   (1) if you don't run QEMU with the exact same command line
>>>       and config at both ends then migration won't work
>>>   (2) we don't guarantee to detect and cleanly fail if you
>>>       don't do (1)
>>>
>>> It would probably be nice if we did detect config mismatches,
>> Yep, we do not send the device tree (as libvirt does). Pure command line
>> matching won't work.
>>
>>> but that seems to me like a problem we should be addressing
>>> more globally than just for one particular config item for
>>> one particular target...
>
> Ok. So. Let's assume I want to implement migration of "-smp" parameters.
> What would be the correct way of doing this in terms of the current QOM
> principles? Thanks.

You don't. The migration protocol doesn't migrate configuration. If you 
want to start to transfer VM configuration (which I'd be all in for), do 
it properly and transfer _all_ configuration.


Alex