This is needed for generic DRM devices like the VirtualBox vboxvideo
driver, which exposes itself as a generic, ID-less DRM device at
/dev/dri/card0 (after applying this commit):
$ udevadm info --query=all --path \
/sys/devices/pci0000:00/0000:00:02.0/drm/card0
P: /devices/pci0000:00/0000:00:02.0/drm/card0
N: dri/card0
E: DEVNAME=/dev/dri/card0
E: DEVPATH=/devices/pci0000:00/0000:00:02.0/drm/card0
E: DEVTYPE=drm_minor
E: ID_FOR_SEAT=drm-pci-0000_00_02_0
E: ID_PATH=pci-0000:00:02.0
E: ID_PATH_TAG=pci-0000_00_02_0
E: MAJOR=226
E: MINOR=0
E: SUBSYSTEM=drm
E: TAGS=:master-of-seat:seat:uaccess:
E: USEC_INITIALIZED=59893
Without this patch, the capabilities for a seat on a VirtualBox
installation of systemd v219 incorrectly show it as non-graphical, even
though I can type these commands from an xterm:
$ loginctl show-seat seat0
Id=seat0
CanMultiSession=yes
CanTTY=yes
CanGraphical=no
…
https://bugs.freedesktop.org/show_bug.cgi?id=90822