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

[Michael S. Tsirkin]

On Mon, Jun 15, 2009 at 12:27:08PM +0300, Avi Kivity wrote:
> On 06/15/2009 12:08 PM, Mark McLoughlin wrote:
>>> This last option makes sense to me: in a real world the user has
>>> control over where he places the device on the bus, so why
>>> not with qemu?
>>>      
>>
>> Yep, most people seem to agree that it makes sense to allow this, but
>> some believe it should only be via a machine description file, not the
>> command line.
>>    
>
> I don't understand this opposition.  It's clear a machine config file is  
> a long way in our future.  It's also clear lack of stable PCI addresses  
> hurts us now.
>
>> However, the first problem is that it isn't a solution to the guest ABI
>> problem more generally.
>>    
>
> pci_addr was never meant to bring world peace, just stable PCI  
> addresses.  The other issues should be addressed separately.
>
>> And the second problem is that for e.g. libvirt to use it, it would have
>> to be possible to query qemu for what PCI slots were assigned to the
>> devices - libvirt would need to be able to parse 'info pci' and match
>> the devices listed with the devices specified on the command line.
>>    
>
> If all devices (including vga, ide) are set up with pci_addr, then this  
> is unneeded.

Right. I think it could be an all or nothing at all approach.

> You do need to export available slot numbers from qemu.

Why would a slot be unavailable?