fix-qemu-guest-resolution

fix-qemu-guest-resolution

#!/bin/bash

# SPICE clipboard sharing is not safe to use:
# https://bugzilla.redhat.com/show_bug.cgi?id=1320263
# but guests that have <clipboard copypaste='no'/> can't fix their screen
# resolution with `xrandr --output Virtual-0 --auto`, so use this program
# to fix the screen resolution for a qemu guest over ssh.  This should be
# run on the host machine, not the guest.

set -eu -o pipefail

set-qemu-guest-resolution() {
	width=$1
	height=$2
	# 2> /dev/null to ignore cryptic complaint about mode already existing
	xrandr --newmode ${width}x${height} $(gtf ${width} ${height} 60 | grep -o 'Modeline .*' | cut -f 3- -d ' ')  2> /dev/null
	xrandr --addmode Virtual-0        ${width}x${height}
	xrandr --output  Virtual-0 --mode ${width}x${height}
}

get-spice-window-resolution() {
	host=$1
	window=$(wmctrl -l | grep -- "$host on QEMU/KVM$" | cut -f 1 -d ' ')
	width=$(xwininfo  -id "$window" | grep -P -o 'Width: \d+$'  | cut -f 2 -d ' ')
	height=$(xwininfo -id "$window" | grep -P -o 'Height: \d+$' | cut -f 2 -d ' ')
	echo "$width $height"
}

# Adjust these numbers for your machine
spice_ui_height=91
spice_ui_width=2

host=$1
res=($(get-spice-window-resolution "$host"))
guest_width=$((${res[0]} - $spice_ui_width))
guest_height=$((${res[1]} - $spice_ui_height))
typeset -f set-qemu-guest-resolution | ssh -- "$host" "$(cat); DISPLAY=:0.0 set-qemu-guest-resolution $guest_width $guest_height"

Usage:

sudo apt-get install --no-install-recommends wmctrl x11-utils

fix-qemu-guest-resolution HOSTNAME

HOSTNAME should be both the name of the virtual machine and the hostname by which ssh can reach it.

You may need to adjust the DISPLAY= and spice_ui_ variables.

If you have a 4K display, you will also need to increase the amount of VRAM allocated to the machine.

If you get tired of running fix-qemu-guest-resolution and mostly work with maximized SPICE windows anyway, copy set-display-resolution to the guest and create a ~/.config/autostart/ task with e.g.:

[Desktop Entry]
Encoding=UTF-8
Version=0.9.4
Type=Application
Name=fix-resolution
Comment=
Exec=set-display-resolution Virtual-0 3840 1966 60
OnlyShowIn=XFCE;
StartupNotify=false
Terminal=false
Hidden=false

Linked from https://unix.stackexchange.com/questions/341881/virt-manager-copy-and-paste-is-possible-to-disable-it