This used a cargo-culted form of the ACTION check. Kernel is allowed to
invent new ACTIONs and IIRC there are already actions like bind and
unbind.
Udev events before rule processing always start with a clean property
list. This means that if you only match ACTION==add to add some value to
the event, then that value will not be present for ACTION==bind. Udev
event consumers do not accumulate values, so inconsistent value setting
may confuse them.
Therefore one needs to match ACTION!=remove, not ACTION==add|change, to
keep the device properties consistent for every event. It doesn't hurt
to set them on remove either, but it's a habit to try to avoid
processing when not strictly needed.
This issue came up in
https://gitlab.freedesktop.org/wayland/weston/-/issues/476#note_841430
For more information, see
https://lists.freedesktop.org/archives/systemd-devel/2020-November/045570.html
the part "KERNEL API INCOMPATIBILITY" near the beginning.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This is not to be installed, except maybe as a doc. It is just an
example of what one might do. It also has not been tested, it's just
for giving an idea of what it should do.
It also contains untested speculation.
v2:
- use syspath instead of devpath
- add license blurb
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Pekka Paalanen
Marius Vlad
Pekka Paalanen