installing and removing snaps triggers display failures

[Chris Patterson]

Hardware: Thinkpad 490s with Thinkpad USB-C Gen 2 Dock with connected displays

Upon installing/removing snaps, snapd will execute udevadm trigger --subsystem-nomatch=input.

Indirectly, I believe this causes the `drm` subsystem to be triggered which, in my case, results in my USB-C dock connected displays to be reset, and often not restored. Unplugging and replugging the dock doesn't always work (probably outside of the scope of snapd).

I assume the the trigger of drm subsystem shouldn't break like this, and the bug(s) may lie elsewhere. However, it may be useful to either:
(a) only trigger necessary subsystems (does DRM need to be triggered in the case of installing Firefox?) or
(b) support some sort of blacklist to prevent specific subsystems from being triggered when there are known issues.

I'll be back to attach some logs...

Thank you!

[Chris Patterson (cjp256)]

FWIW, either there was a fix for this or updating to 20.04 resolved this issue for me. :)