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

[Anthony Liguori]

On 01/19/2011 11:01 AM, Daniel P. Berrange wrote:
> The reason we specify 'bus' is that we wanted to be flexible wrt
> upgrades of libvirt, without needing restarts of QEMU instances
> it manages. That way we can introduce new functionality into
> libvirt that relies on it having previously set 'bus' on all
> active QEMUs.
>
> If QEMU adds PCI-to-PCI bridges, then I wouldn't expect QEMU to
> be adding the extra bridges. I'd expect that QEMU provided just
> the first bridge and then libvirt would specify how many more
> bridges to create at boot or hotplug them later. So it wouldn't
> ever need to parse topology.
>    

Yeah, but replacing the main chipset will certainly change the PCI 
topology such that if you're specifying bus=X and addr=X and then also 
using -M pc, unless you're parsing the default topology to come up with 
the addressing, it will break in the future.

That's why I think something simpler like a linear index that QEMU maps 
to a static location in the topology is probably the best future proof 
interface.

Regards,

Anthony Liguori

> Regards,
> Daniel
>