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Date: Thu, 20 Jan 2011 10:33:41 +0000
From: "Daniel P. Berrange" <berrange@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 28/35] kvm: x86: Introduce kvmclock device
	to save/restore its state
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>, Jan Kiszka <jan.kiszka@siemens.com>, Glauber Costa <glommer@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, Markus Armbruster <armbru@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Anthony Liguori <aliguori@linux.vnet.ibm.com>, Avi Kivity <avi@redhat.com>

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