ptpd: systemd support

[Thomas:
   - use relative symbolic link instead of absolute one
   - remove the -S option, since redirecting stdout is not needed,
     it's already taken care of by systemd. Suggested by Maxime
     Hadjinlian.]

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

package/ptpd/ptpd.mk

@@ -22,4 +22,12 @@ define PTPD_INSTALL_INIT_SYSV
 		$(TARGET_DIR)/etc/init.d/S65ptpd
 endef
 
+define PTPD_INSTALL_INIT_SYSTEMD
+	$(INSTALL) -D -m 644 package/ptpd/ptpd.service \
+		$(TARGET_DIR)/usr/lib/systemd/system/ptpd.service
+	mkdir -p $(TARGET_DIR)/etc/systemd/system/multi-user.target.wants
+	ln -sf ../../../../usr/lib/systemd/system/ptpd.service \
+		$(TARGET_DIR)/etc/systemd/system/multi-user.target.wants/ptpd.service
+endef
+
 $(eval $(generic-package))

package/ptpd/ptpd.service

@@ -0,0 +1,10 @@
+[Unit]
+Description=Precision Time Protocol daemon
+After=syslog.target network.target
+
+[Service]
+ExecStart=/usr/sbin/ptpd -c
+Restart=always
+
+[Install]
+WantedBy=multi-user.target