Re: [Qemu-devel] [PATCH 28/35] kvm: x86: Introduce kvmclock device to save/restore its state

[Daniel P. Berrange]

On Thu, Jan 20, 2011 at 09:44:05AM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> >For (2), you cannot use bus=X,addr=Y because it makes assumptions about
> >the PCI topology which may change in newer -M pc's.
> 
> Why should the PCI topology for 'pc' ever change?
> 
> We'll probably get q35 support some day, but when this lands I
> expect we'll see a new machine type 'q35', so '-m q35' will pick the
> ich9 chipset (which will have a different pci topology of course)
> and '-m pc' will pick the existing piix chipset (which will continue
> to look like it looks today).

If the topology does ever change (eg in the kind of way anthony
suggests, first bus only has the graphics card), I think libvirt
is going to need a little work to adapt to the new topology,
regardless of whether we currently specify a bus= arg to -device
or not. I'm not sure there's anything we could do to future proof
us to that kind of change.

Regards,
Daniel