Re: [Qemu-devel] Re: [PATCH v2 9/9] Add -kvm option

[Anthony Liguori <aliguori@us.ibm.com>]

Gerd Hoffmann wrote:
> On 10/08/09 01:28, Anthony Liguori wrote:
>> Glauber Costa wrote:
>>> even if we have qdev on the irq controllers, one could still come up 
>>> with
>>> situations in which we'd like to force the use of one device over
>>> another.
>>
>> Right, my assumption is that the devices will have different qdev names
>> and therefore a user can select which one gets used.
>>
>> Right now, -device is just additive. I'm not sure the best way to
>> express something like, replace this existing device with this new
>> device. Maybe some trickery with id=. Gerd, any thoughts?
>
> -M $machine gives you a barebone machine with all core devices which 
> belong to it. You can't easily remove and/or replace devices. 
> Especially not something central as the IRQ controller.  But also no 
> other core components, i.e. you wouldn't stick a piix4 ide controller 
> into a Q35 machine.  Just say 'no'.

This seems fundamentally flawed to me.  If you cannot remove a device 
from a machine using command line options, then how do we support 
something like -net none?  Do we make the default machine not contain a nic?

The value of a machine type to a user is that it presents a useful 
machine--not a barebones machine.  A user should not have to think about 
which type of nic they need or whether they want to enable usb.

>
> That leaves two options:
>
>   (1) create two devices, create new machines which use the kvm
>       versions (aka -M pc-kvm).
>   (2) make using the in-kernel kvm code a device property.

(3) Add the ability to remove device from a machine type.

-- 
Regards,

Anthony Liguori