ModemManager: refactoring procd init script

The way the init script is written now, we get a bad output when calling
the ubus service backend.

ubus call service list "{'verbose':true,'name':'modemmanager'}"
>{
>        "modemmanager": {
>                "instances": {
>                        "instance1": {
>                                "running": true,
>                                "pid": 20511,
>                                "command": [
>                                        "sh",
>                                        "-c",
>                                        ".
>/usr/share/ModemManager/modemmanager.common;    \t
>mkdir -m 0755 -p /var/run/modemmanager;          \t
>mm_cleanup_interfaces;                            \t
>( mm_report_events_from_cache ) >/dev/null 2>&1 & \t
>/usr/sbin/ModemManager"
>                                ],
>                                "term_timeout": 5,
>                                "respawn": {
>                                        "threshold": 3600,
>                                        "timeout": 5,
>                                        "retry": 5
>                                },
>                                "pidfile":"/var/run/modemmanager/modemmanager.pid"
>                        }
>                }
>        }
>}"

I also get the output in the log that the PID file cannot be created.

> daemon.err procd: Failed to remove pidfile: :No such file or directory

The changes in this commit fixes this issues, by moving startup into a
wrapper script.

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

net/modemmanager/Makefile

@@ -98,6 +98,7 @@ define Package/modemmanager/install
 
 	$(INSTALL_DIR) $(1)/usr/sbin
 	$(INSTALL_BIN) $(PKG_INSTALL_DIR)/usr/sbin/ModemManager $(1)/usr/sbin
+	$(INSTALL_BIN) ./files/usr/sbin/ModemManager-wrapper $(1)/usr/sbin
 
 	$(INSTALL_DIR) $(1)/usr/bin
 	$(INSTALL_BIN) $(PKG_INSTALL_DIR)/usr/bin/mmcli $(1)/usr/bin

net/modemmanager/files/modemmanager.init

@@ -22,14 +22,12 @@ start_service() {
 	# it starts.
 	#
 	# All these commands need to be executed on every MM start, even after
-	# procd-triggered respawns, which is why they're all included as instance command
+	# procd-triggered respawns, which is why this is wrapped in a startup
+	# wrapper script called '/usr/sbin/ModemManager-wrapper'.
 	#
+	. /usr/share/ModemManager/modemmanager.common
 	procd_open_instance
-	procd_set_param command sh -c ". /usr/share/ModemManager/modemmanager.common;    \
-	                               mkdir -m 0755 -p ${MODEMMANAGER_RUNDIR};          \
-	                               mm_cleanup_interfaces;                            \
-	                               ( mm_report_events_from_cache ) >/dev/null 2>&1 & \
-	                               /usr/sbin/ModemManager"
+	procd_set_param command /usr/sbin/ModemManager-wrapper
 	procd_set_param respawn "${respawn_threshold:-3600}" "${respawn_timeout:-5}" "${respawn_retry:-5}"
 	procd_set_param pidfile "${MODEMMANAGER_PID_FILE}"
 	procd_close_instance

net/modemmanager/files/usr/sbin/ModemManager-wrapper

@@ -0,0 +1,33 @@
+#!/bin/sh
+
+trap_with_arg() {
+	func="$1" ; shift
+	for sig ; do
+		# shellcheck disable=SC2064
+		trap "$func $sig" "$sig"
+	done
+}
+
+func_trap() {
+	logger "ModemManager-wrapper[$$]" "Sending signal ${1}..."
+	kill "-${1}" "$CHILD" 2>/dev/null
+}
+
+main() {
+	. /usr/share/ModemManager/modemmanager.common
+
+	trap_with_arg func_trap INT TERM KILL
+
+	mkdir -p "${MODEMMANAGER_RUNDIR}"
+	chmod 0755 "${MODEMMANAGER_RUNDIR}"
+	mm_cleanup_interfaces
+
+	/usr/sbin/ModemManager "$@" 1>/dev/null 2>/dev/null &
+	CHILD="$!"
+	sleep 2
+	mm_report_events_from_cache
+
+	wait "$CHILD"
+}
+
+main "$@"