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
wayland/weston#476 (comment 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>