Re: [libvirt] [Qemu-devel] [uq/master PATCH 0/7] x86 CPU subclasses, take 7

On Fri, 31 Jan 2014 13:17:53 -0200 Eduardo Habkost <ehabkost(a)redhat.com&gt; wrote: > On Fri, Jan 31, 2014 at 03:50:23PM +0100, Paolo Bonzini wrote: > > Il 31/01/2014 15:48, Igor Mammedov ha scritto: > > >that's abusing of object-add interface and due to recent changes, object-add > > >won't accept arbitrary objects. > > > > I hope that sooner or later device hotplug will be doable with > > object-add too. But yes, in the meanwhile device_add could work, > > and this patch series is in the right direction anyway. > > In that case, what is holding us from setting > cannot_instantiate_with_device_add_yet on TYPE_X86_CPU? I don't think we > can recommend using "-device" for CPUs just yet, but we would need to > allow it in case object-add doesn't work. > > (But I liked the fact that object-add worked and (it looks like) it > didn't run realize(). All libvirt needs is to be able to create the > object and get instance_init() run, no need for realize() to run.) > > I still need to read the reasoning behind the object-add changes. But is > there some chance we could allow object-add to work for TYPE_X86_CPU > subclasses, to avoid the device_add/cannot_instantiate_with_device_add_yet issues? you can hack around by inheriting from UserCreatable interface, but question is what kind of information libvirt would expect from -object xxx-cpu if it's going to read/interpret feature words then CPU.instance_init() is not sufficient, since properties (read as compat props) and realize() itself are changing feature words and CPU model guest is going to see is very different from what -object would create.

It looks like only -device would be able to create actual CPU models, but for -device to work we need as minimum this series and conversion of CPU features to properties in tree. Then I guess we can override cannot_instantiate_with_device_add_yet for x86 CPUs.