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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 04/10/2014 10:10 PM, Alexander Graf wrote:
> 
> 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.


Then what is the purpose of many, many VMSTATE_.*_EQUAL?

And I do not want to send configuration by the proposed patch, I want to
make sure that the new guest is able to continue. Why exactly is this bad?


-- 
Alexey