Re: [Qemu-devel] [PATCH 0/5] qdev: add driver class support.

[Gerd Hoffmann <kraxel@redhat.com>]

On 07/09/09 15:48, Paul Brook wrote:
> On Thursday 09 July 2009, Gerd Hoffmann wrote:

>> I don't think this will work out in the general case.  Some devices have
>> properties which can be used for that, i.e. network cards have a mac
>> address (no attribute yet but I expect it will come some day).  Not
>> every device class has specific properties you can use to identify them
>> though.  How would you identify a sound card for example?
>
> Ok, put it annother way: Why do you need to identify them? Why would libvirt
> care whether a device is (say) a sound card or a VGA adapter?

Because libvirt-based applications want present that to the user?

The usual GUI workflow for adding devices is a two-step process:  First 
pick the device class, then pick the actual device from a (short) list.

> In principle
> there's no reason why you shouldn't have many or none of both.

Sure.  But when you ask virt-manager to add a sound card to your virtual 
machine you don't want to have a VGA adapter in the list of possible 
devices.

> IMHO the only reason we have the current grouping is because it's forced on us
> by the various commandline options which mix host and machine configuration.

That is actually another reason:  Allow easy support of legacy command 
line options.  Once all sound cards are converted to qdev '-soundhw ?' 
could list all sound cards by just walking the driver list and print the 
ones with class = SOUND.

cheers,
   Gerd