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wiki/gofurther/display.md
lukas fb251ea7ef Various clean-ups, additions 
Refactoring of the home page. Adding a page for virtual machine monitors.
2024-01-28 17:21:40 +01:00

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title description published date tags editor dateCreated
Display How to access a virtual machine's display true 2023-10-15T15:11:00.161Z markdown 2022-07-31T09:22:05.854Z

Display

A virtual display can be attached to a virtual machine. It is a must-have for non-headless scenarios.

Display types

SDL display

The Simple DirectMedia Layer (SDL)-powered display is a local-only low-latency display.

The SDL display is only avalable with virtual machines created using the QEMU/KVM User Session {.is-info}

Mouse grab does not currently work with the SDL display {.is-warning}

The display resolution of your guest display should not exceed that of your physical screen {.is-info}

SELinux-related configuration

By default, SELinux will block access to X Windows Server for the virtualization stack. An exception has to be set.

  • Set new rule
sudo setsebool -P virt_use_xserver 1
  • Do some magic trick
sudo ausearch -c 'qemu-system-x86' --raw | audit2allow -M my-qemusystemx86
k
  • And another one
sudo semodule -X 300 -i my-qemusystemx86.pp

SDL XML configuration

  • The default display can be identified using echo $DISPLAY.
$ echo $DISPLAY
:0

The same applies to xauth. On Wayland, it would look like that.

$ echo $XAUTHORITY
/run/user/1000/.mutter-Xwaylandauth.ARIY51
  • Example of an XML SDL configuration, with OpenGL enabled. This example requires a 3D-capable graphic card to be attached to the guest computer, such as virtio-gpu.
<graphics type="sdl" display=":0" xauth="/run/user/1000/.mutter-Xwaylandauth.ARIY51" fullscreen="yes">
  <gl enable="yes"/>
</graphics>

The fullscreen attribute is not honored at the moment {.is-warning}

D-Bus display

D-Bus is a desktop-oriented middleware that can be used to create a display for a virtual machine.

Libvirt

  • Add a D-Bus video backend and add enable for OpenGL:
<graphics type="dbus">
  <gl enable="yes"/>
</graphics>

This equates to -display dbus,gl=on in QEMU

{.is-info}

When the virtual machine is launched, a specific D-Bus address will be choosen, as well as a rendering device:

<graphics type="dbus" address="unix:path=/run/user/1000/libvirt/qemu/run/dbus/8-user-d-bus-dbus.sock">
  <gl enable="yes" rendernode="/dev/dri/renderD128"/>
</graphics>
  • Add a D-Bus audio backend:
<graphics type="dbus">
  <audio id="1">
</graphics>

Connect to the D-Bus display

A third-party tool is required to interact to the D-Bus display.

Libmks, which is under development, is such a tool.

Due to a bug, it is currenlty only possible to connect a D-Bus display with plain QEMU {.is-warning}

Libmks has to be built from source.

  • Clone the repository
git clone https://gitlab.gnome.org/GNOME/libmks
  • Change directory
cd libmks
  • Build it
meson setup build
cd build
ninja
  • Launch a diskless virtual machine
qemu-system-x86_64 \
  -enable-kvm \
  -machine q35 \
  -drive if=pflash,format=raw,readonly=on,file=/usr/share/edk2-ovmf/x64/OVMF_CODE.fd \
  -cpu host \
  -device virtio-vga-gl \
  -m 4G \
  -smp 2,sockets=1,dies=1,cores=2,threads=1 \
  -display dbus,gl=on \
  -device virtio-tablet-pci \
  -device virtio-keyboard-pci \
  • From another terminal tab or window, launch the previously built MKS using the following command
./build/tools/mks

As there is no Live ISO or disk attached to the virtual machine, you will eventually land in the UEFI shell.

Resources

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