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

[Gerd Hoffmann]

On 10/12/09 16:04, Anthony Liguori wrote:
> Gerd Hoffmann wrote:
> > -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?

'-net none' does not remove a nic.  It makes qemu not add the default nic.

> 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.

There are a bunch of places where qemu does something like

   if (user-did-not-specify-a-$foo-device) {
       add_$foo_device_with_defaults()
   }

That applies (for pc) to:

  * nic.
  * vga.
  * serial port.
  * parallel port.
  * cdrom drive.

For all of these (except cdrom) you can disable the creation of the 
default device via "-$dev none".  I don't consider them core devices.
Core devices are the ones which a machine can't live without, i.e. rtc, 
pic, ...

You can't add/remove core stuff like rtc, interrupt controller.  The 
virtual machine will simply not work then ...

> > (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.

-rtc none ?  Have fun booting your machine.

cheers,
  Gerd