Re: [Qemu-discuss] Enabling multiple guest monitors

[Michael Thayer]

Answering my own question.

03.12.2016 20:59, Michael Thayer wrote:
> I was wondering if anyone could give me a hand getting Qemu working with
> multiple monitors, preferably virtio-gpu, otherwise qxl.  I am trying to
> get Fedora 25 to work better under VirtualBox, and want to compare with
> how it works under Qemu.  Currently known problems on our side are that
> Mutter is not sending dirty rectangle information when using software
> rendering and that absolute input from the tablet emulation is not
> translated to the right co-ordinates inside the guest (I think Mutter
> expects one tablet per monitor, which we currently do not do, and that
> any other Wayland compositor might potentially do this differently).  I
> am particularly interested in the second issue.
>
> I am currently using Qemu from git, with all default configuration
> parameters except SDL ABI 2.0.  I am starting it with max_outputs=2.
> sysfs in the guest says that the second output is present but not
> connected.  So far I have not found a way to enable it; I am sure that I
> will eventually do so between reading the Qemu source and looking at
> code paths in gdb, but if someone has a hint for me it would be very
> helpful.

I was able to achieve this by commenting out the line
  dpy_gfx_replace_surface(g->scanout[i].con, NULL);
in hw/display/virtio-gpu.c and by resizing the second monitor once 
gnome-shell had started to make it notice it.  Probably not quite the 
way it is supposed to work, but good enough for my needs.

If anyone is interested, Qemu is using VMMouse emulation by default, and 
GNOME Shell is clearly mapping the absolute positions sent to the entire 
virtual desktop, while with our device it is mapping all input to the 
first screen.  And Qemu is getting screen updates.

Regards
Michael
--
Michael Thayer | VirtualBox engineer
ORACLE Deutschland B.V. & Co. KG | Werkstr. 24 | D-71384 Weinstadt

ORACLE Deutschland B.V. & Co. KG
Hauptverwaltung: Riesstraße 25, D-80992 München
Registergericht: Amtsgericht München, HRA 95603

Komplementärin: ORACLE Deutschland Verwaltung B.V.
Hertogswetering 163/167, 3543 AS Utrecht, Niederlande Handelsregister 
der Handelskammer Midden-Nederland, Nr. 30143697
Geschäftsführer: Alexander van der Ven, Jan Schultheiss, Val Maher