Re: [Qemu-devel] [PATCH v5 00/16] uq/master: Introduce basic irqchip support

[Anthony Liguori <anthony@codemonkey.ws>]

On 12/19/2011 06:37 PM, Jan Kiszka wrote:
> On 2011-12-20 01:32, Anthony Liguori wrote:
>> On 12/19/2011 05:49 PM, Jan Kiszka wrote:
>>> On 2011-12-19 23:24, Anthony Liguori wrote:
>>>> On 12/19/2011 03:17 PM, Marcelo Tosatti wrote:
>>>>>
>>>>> Anthony,
>>>>>
>>>>> Can you please review&    ACK?
>>>>>
>>>>> You could even apply directly but well do a kvm-autotest run through
>>>>> uq/master. Still, your review is needed.
>>>>
>>>> Overall, it looks good except for the backend/frontend split.  This
>>>> should be done in terms of qdev inheritance.
>>>
>>> I cannot follow your idea here yet. There is no inheritance as we end up
>>> with only a single class that permutes (selects a different backend) on
>>> creation. I'm not sure how to model two classes that will still only
>>> mean a single qdev registration.
>>
>> See other reply in thread.
>>
>> We should model this as two separate qdev devices.  We can avoid
>> regressing migration in qemu-kvm by just having a common vmstate name.
>>
>> apic is a no-user device so there's no way that changing the name of it
>> in qemu-kvm can affect users.
>
> Look down http://thread.gmane.org/gmane.comp.emulators.kvm.devel/82598
> for the discussion of that model.

I have.  I don't understand the rationale for jumping through hoops here.

There seems to be an assertion that migrating from in-kernel APIC to userspace 
APIC is an important use case.  I don't really see how that's true.

But nonetheless, the direction migration is heading is not just to migrate the 
QOM path names to identify devices, but to provide a way to introspect the 
device model, transfer the current device model description to the other end, 
and create the device model on the destination.

This is the only way to reliably support things like hot-plug during live 
migration which is something we punt to management tools (which really can't 
implement it properly).

So we'll already be migrating the apic backend property which means that you are 
not going to have migration to and from in-kernel APIC and userspace APIC 
without some sort of in-between translation layer (which could just as easily 
change the device names).

Regards,

Anthony Liguori

>
> Jan
>