Re: Configuration vs. compat hints [was Re: [Qemu-devel] [PATCHv3 03/13] qemu: add routines to manage PCI capabilities]

Michael S. Tsirkin
2009-06-14T09:50:21Z

On Sun, Jun 14, 2009 at 12:37:13PM +0300, Avi Kivity wrote:
> Michael S. Tsirkin wrote:
>>
>> If we want to remove a device from under a running guest, you need
>> hotplug. So we can't just remove several lines from the config and hope
>> that it'll work simply because the PCI address is stable.
>>
>
> Why not?

E.g. configuration cycles address a specific bus/slot.
You need cooperation from guest if you want to move
a device.

>> OTOH, if you reboot the guest, it's ok for addresses to change.
>>
>
> No, it's not. Some guests depend on addressing for their configuration
> (for example older Linux guests will swap eth0/eth1 if you swap their
> slots).

Ah, I misunderstood what's meant by the address. I agree that it's
useful to be able to control device's placement on the bus.

--
MST