Create missing folder
mkdir -p /etc/hotplug.d/button
Create missing event debug handler /etc/hotplug.d/button/buttons
logger the button was $BUTTON and the action was $ACTION
Create missing button event handler /etc/hotplug.d/button/00-button
#!/bin/sh
. /lib/functions.sh
do_button () {
local button
local action
local handler
local min
local max

config_get button $1 button
config_get action $1 action
config_get handler $1 handler
config_get min $1 min
config_get max $1 max

[ "$ACTION" = "$action" -a "$BUTTON" = "$button" -a -n "$handler" ] && {
[ -z "$min" -o -z "$max" ] && eval $handler
[ -n "$min" -a -n "$max" ] && {
[ $min -le $SEEN -a $max -ge $SEEN ] && eval $handler
}
}
}

config_load system
config_foreach do_button button
Configure buttons, so append at the end of /etc/system/config
config button
option button 'wps'
option action 'pressed'
option handler 'echo 1 > /sys/class/leds/tp-link\:green\:qss/brightness'

config button
option button 'wps'
option action 'released'
option handler 'echo 0 > /sys/class/leds/tp-link\:green\:qss/brightness'