Improve udev rule for thinkpad charge threshold

[karypid]

Source: ublue forums thread

The udev rules from package udev-rules-0.8-1.fc39.noarch contain a rule in /usr/lib/udev/rules.d/99-thinkpad-thresholds-udev.rules that attempts to change the permissions of the charge-threshold files. Presumably this is to allow the user to change the charge level without special permissions:

ACTION=="add|change", KERNEL=="BAT[0-1]", GROUP="wheel" , SUBSYSTEM=="power_supply", TEST{0002}!="/sys%p/charge_control_start_threshold", RUN+="/bin/chmod 666 /sys%p/charge_control_start_threshold"
ACTION=="add|change", KERNEL=="BAT[0-1]", GROUP="wheel" , SUBSYSTEM=="power_supply", TEST{0002}!="/sys%p/charge_control_end_threshold", RUN+="/bin/chmod 666 /sys%p/charge_control_end_threshold"
ACTION=="add|change", KERNEL=="BAT[0-1]", GROUP="wheel" , SUBSYSTEM=="power_supply", TEST{0002}!="/sys%p/charge_start_threshold", RUN+="/bin/chmod 666 /sys%p/charge_start_threshold"
ACTION=="add|change", KERNEL=="BAT[0-1]", GROUP="wheel" , SUBSYSTEM=="power_supply", TEST{0002}!="/sys%p/charge_stop_threshold", RUN+="/bin/chmod 666 /sys%p/charge_stop_threshold"

My 2024 Yoga Pro 9i 16IMH9 does not create those charge threshold files. As a result, the udev rule keeps firing and keeps attempting to update the permissions for the 4 files. This fails as they are non-existent. Example output from system log:

Apr 27 12:45:25 myhost (udev-worker)[34230]: BAT0: Process '/bin/chmod 666 /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:16/PNP0C09:00/PNP0C0A:00/power_supply/BAT0/charge_control_start_threshold' failed with exit code 1.
Apr 27 12:45:25 myhost (udev-worker)[34230]: BAT0: Process '/bin/chmod 666 /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:16/PNP0C09:00/PNP0C0A:00/power_supply/BAT0/charge_control_end_threshold' failed with exit code 1.
Apr 27 12:45:25 myhost (udev-worker)[34230]: BAT0: Process '/bin/chmod 666 /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:16/PNP0C09:00/PNP0C0A:00/power_supply/BAT0/charge_start_threshold' failed with exit code 1.
Apr 27 12:45:25 myhost (udev-worker)[34230]: BAT0: Process '/bin/chmod 666 /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:16/PNP0C09:00/PNP0C0A:00/power_supply/BAT0/charge_stop_threshold' failed with exit code 1.

The rule checks if the file with a mask, to fire when the permissions are not set, but it does not check if the file exists in the first place. This results in the above behavior.

The rule should be improved to check if the file exists at all, and then also check the permissions. This way for models without support for this the rule would not attempt running the command and would not spam the logs.