net/mwan3: registrate SIGUSR1 trap on interface down event

If interface is getting down by netifd (unplug ethernet cable)
mwan3track will not recognize this change. It will also generate an
additional down event when he notice does his tracking interface is offline.

Mwan3track will now be informed by a signal (trap) USR1 during down event
that the interface is already down. An additional down event will not be
generated.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

net/mwan3/files/usr/sbin/mwan3track

@@ -4,6 +4,9 @@
 
 LOG="/usr/bin/logger -t $(basename "$0")[$$] -p"
 INTERFACE=""
+DEVICE=""
+
+IFDOWN_EVENT=0
 
 clean_up() {
 	$LOG notice "Stopping mwan3track for interface \"${INTERFACE}\""
@@ -15,6 +18,11 @@ clean_up() {
 	exit 0
 }
 
+if_down() {
+	$LOG info "Detect ifdown event on interface ${INTERFACE} (${DEVICE})"
+	IFDOWN_EVENT=1
+}
+
 main() {
 	local reliability count timeout interval failure_interval
 	local recovery_interval down up size
@@ -22,9 +30,11 @@ main() {
 	[ -z "$3" ] && echo "Error: should not be started manually" && exit 0
 
 	INTERFACE=$1
+	DEVICE=$2
 	echo "$$" > /var/run/mwan3track-$1.pid
 	mkdir -p /var/run/mwan3track/$1
 	trap clean_up SIGINT SIGTERM
+	trap if_down SIGUSR1
 
 	config_load mwan3
 	config_get reliability $1 reliability 1
@@ -106,6 +116,12 @@ main() {
 
 		host_up_count=0
 		sleep $sleep_time
+
+		if [ "${IFDOWN_EVENT}" -eq 1 ]; then
+			score=0
+			echo "offline" > /var/run/mwan3track/$1/STATUS
+			IFDOWN_EVENT=0
+		fi
 	done
 }