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

[Anthony Liguori <aliguori@linux.vnet.ibm.com>]

On 01/19/2011 07:11 AM, Markus Armbruster wrote:
> Gerd Hoffmann<kraxel@redhat.com>  writes:
>
>    
>> On 01/18/11 18:09, Anthony Liguori wrote:
>>      
>>> On 01/18/2011 10:56 AM, Jan Kiszka wrote:
>>>        
>>>>          
>>>>> The device model topology is 100% a hidden architectural detail.
>>>>>            
>>>> This is true for the sysbus, it is obviously not the case for PCI and
>>>> similarly discoverable buses. There we have a guest-explorable topology
>>>> that is currently equivalent to the the qdev layout.
>>>>          
>>> But we also don't do PCI passthrough so we really haven't even explored
>>> how that maps in qdev. I don't know if qemu-kvm has attempted to
>>> qdev-ify it.
>>>        
>> It is qdev-ified.  It is a normal pci device from qdev's point of view.
>>
>> BTW: is there any reason why (vfio-based) pci passthrough couldn't
>> work with tcg?
>>
>>      
>>> The -device interface is a stable interface. Right now, you don't
>>> specify any type of identifier of the pci bus when you create a PCI
>>> device. It's implied in the interface.
>>>        
>> Wrong.  You can specify the bus you want attach the device to via
>> bus=<name>.  This is true for *every* device, including all pci
>> devices. If unspecified qdev uses the first bus it finds.
>>
>> As long as there is a single pci bus only there is simply no need to
>> specify it, thats why nobody does that today.  Once q35 finally
>> arrives this will change of course.
>>      
> As far as I know, libvirt does it already.
>    

I think that's a bad idea from a forward compatibility perspective.

Regards,

Anthony Liguori