Re: [Qemu-devel] [PATCH v5 07/16] apic: Open-code timer save/restore

[Anthony Liguori <anthony@codemonkey.ws>]

On 12/19/2011 05:45 PM, Jan Kiszka wrote:
> On 2011-12-19 23:21, Anthony Liguori wrote:
>> On 12/15/2011 06:33 AM, Jan Kiszka wrote:
>>> To enable migration between accelerated and non-accelerated APIC models,
>>> we will need to handle the timer saving and restoring specially and can
>>> no longer rely on the automatics of VMSTATE_TIMER. Specifically,
>>> accelerated model will not start any QEMUTimer.
>>>
>>> This patch therefore factors out the generic bits into apic_next_timer
>>> and introduces a post-load callback that can be implemented differently
>>> by both models.
>>>
>>> Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
>>
>> So you basically want the timer to be a dummy field for the in-kernel apic?
>>
>> Can you fix this up in a pre-save routine (put QEMUTimer into a state
>> where there isn't an event pending)?
>
> It is not a dummy field, it contains the proper state in both cases. We
> just need to convert it to an open-coded state to avoid the QEMUTimer
> restoration magic in the in-kernel case (where there must be no QEMUTimer).

So the state gets fed into the kernel instead of userspace?

This seems a bit much to me, can't we just have two VMStateDescriptions that 
happen to look the same and break migration between userspace and in-kernel?

Are we trying to solve a problem no one cares about?

If you want to avoid regressing migration compat in qemu-kvm, have the vmstate 
name both be the same, it can be two separate devices as the vmstate name is not 
tied to the qdev name right now.

Regards,

Anthony Liguori

>
> Jan
>