[Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts

[Michael S. Tsirkin]

On Tue, Nov 24, 2009 at 12:39:50PM +0200, Dor Laor wrote:
> On 11/23/2009 02:15 PM, Juan Quintela wrote:
>> Dor Laor<address@hidden>  wrote:
>>> >  In the last couple of days we discovered some issues regarding stable
>>> >  ABI and the robustness of the live migration protocol. Let's just jump
>>> >  right into it, ordered by complexity:
>>> >
>>> >  1. Control*every*  feature exposed to the guest by qemu cmdline:
>>> >
>>> >      While thinking on cross version migration, and reviewing some
>>> >      patches, I noticed that there are many times that we use feature bits
>>> >      in order to expose functionality for the guest driver - example:
>>> >      VIRTIO_BLK_F_BARRIER, but we do not control it from qemu cmdline.
>> In my opinion this is madness, qemu command line is already too
>> complicated.  I agree with anthony to put it in the command line.
>
> Qemu's cmdline is currently our config file.. Actually there is nothing  
> wrong with it. Human users shouldn't be interested with these changes  
> and management software should not have problem manipulating it.
> We do need flexibility of controlling our features like any other  
> software component.
>
>> I will go further, and think that this kind of issues should be put into
>> the machine type.
>>
>> If you start qemu with -M pc-0.10, it should save the state in a 0.10
>> compatible way (that don't happens at the moment, but it should work
>> that way).
>
> That's the idea - to keep it part of qdev and by default use it with -M.

I think we want to keep these things separate:
machine description should be for things that
are both guest visible and not changeable by guest,
so it absolutely must stay constant as long as guest
it alive.



-- 
MST