base-files: maintain LED config state

Record the state of any hardware LED configured through UCI and use that
information to revert the state when applying updated settings while
maintaining default behaviour of system LEDs.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/base-files/files/etc/init.d/led

@@ -37,6 +37,12 @@ load_led() {
 	[ -e /sys/class/leds/${sysfs}/brightness ] && {
 		echo "setting up led ${name}"
 
+		printf "%s %s %d\n" \
+			"$sysfs" \
+			"$(sed -ne 's/^.*\[\(.*\)\].*$/\1/p' /sys/class/leds/${sysfs}/trigger)" \
+			"$(cat /sys/class/leds/${sysfs}/brightness)" \
+				>> /var/run/led.state
+
 		[ "$default" = 0 ] &&
 			echo 0 >/sys/class/leds/${sysfs}/brightness
 
@@ -103,11 +109,17 @@ load_led() {
 
 start() {
 	[ -e /sys/class/leds/ ] && {
-		local led
-		for led in /sys/class/leds/*; do
-			[ -e "$led/trigger" ] && echo "none" > "$led/trigger"
-			[ -e "$led/brightness" ] && echo "0" > "$led/brightness"
-		done
+		[ -s /var/run/led.state ] && {
+			local led trigger brightness
+			while read led trigger brightness; do
+				[ -e "/sys/class/leds/$led/trigger" ] && \
+					echo "$trigger" > "/sys/class/leds/$led/trigger"
+
+				[ -e "/sys/class/leds/$led/brightness" ] && \
+					echo "$brightness" > "/sys/class/leds/$led/brightness"
+			done < /var/run/led.state
+			rm /var/run/led.state
+		}
 
 		config_load system
 		config_foreach load_led led