supervisor: systemd support

Running supervisord under systemd sounds wrong, but it is possible
and probably makes sense in some cases.

[Thomas: use relative symbolic link instead of an absolute symbolic
link.]

Signed-off-by: Alex Suykov <alex.suykov@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/supervisor/supervisor.mk

@@ -22,4 +22,12 @@ define SUPERVISOR_INSTALL_INIT_SYSV
 		$(TARGET_DIR)/etc/init.d/S99supervisord
 endef
 
+define SUPERVISOR_INSTALL_INIT_SYSTEMD
+	$(INSTALL) -D -m 644 package/supervisor/supervisord.service \
+		$(TARGET_DIR)/usr/lib/systemd/system/supervisord.service
+	mkdir -p $(TARGET_DIR)/etc/systemd/system/multi-user.target.wants
+	ln -sf ../../../../usr/lib/systemd/system/supervisord.service \
+		$(TARGET_DIR)/etc/systemd/system/multi-user.target.wants/supervisord.service
+endef
+
 $(eval $(python-package))

package/supervisor/supervisord.service

@@ -0,0 +1,10 @@
+[Unit]
+Description=Process Control System
+After=syslog.target
+
+[Service]
+ExecStart=/usr/bin/supervisord -n
+Restart=always
+
+[Install]
+WantedBy=multi-user.target