Re: [Qemu-devel] [Qemu-ppc] [PATCH v2 2/2] Fix return value of vga initlization on ppc

[Paolo Bonzini]

Il 10/03/2014 13:45, Alexey Kardashevskiy ha scritto:
> > > As I was told in this list before, even with -nodefaults, QEMU should not
> > > create a machine which is known for not working or not being supported.
> > > Having VGA and not having any input device is kind of such a config, no?
> >
> > -nodefaults is exactly the opposite of that: no magic whatsoever.  No VGA,
> > no serial, nothing.
>
> qemu-system-x86_64 -enable-kvm -nographic -nodefaults -monitor stdio
>
> "info qtree" shows a whole bunch of devices like "i440FX-pcihost",
> "isa-fdc", "piix3-ide", "vmmouse", "vmport" (what are the last two?). I was
> told here that 8042 is to emulate A20, ok, but others - I do not really
> understand. "q35" is bit different than "pc" but not smaller. The point was
> made that there is no point in emulating a machine which does not exist in
> the real world. Has it changed recently?

-nodefaults should be the bare minimum that is necessary for the VM 
firmware to work.  On x86, isa-fdc/vmmouse/vmport are there only for 
backwards compatibility reasons.

> > And especially, with -nodefaults adding a VGA means just that: adding a VGA.
>
> Usual issue - libvirt expects keyboard with VGA and x86 provides this as it
> always has keyboard. PPC does not have such default.

I don't think it's even a libvirt bug.  Then in the libvirt XML you 
should have:

   <devices>
     <input type='keyboard' bus='usb'/>
   </devices>

explicitly.  If libvirt uses -nodefaults, it's up to virt-manager or 
oVirt or whatever management layer you're using to add all the necessary 
controllers (USB in this case) and devices (keyboard) for the machine to 
be usable.

Paolo