Add support for starting/stopping services on Netlink events

This commit adds support for event based services to Finit.  Along with
the previously added support for multiple instances of the same process,
the feature scope for Finit v2.0 has been reached!

As of now a service can be declared in /etc/finit.conf or /etc/finit.d/
like this:

    service :1 [2345] <!IFUP:eth0,GW> /sbin/dropbear -R -F -p 22 -- SSH daemon

Here the first instance `:1` of dropbear is declared to run in runlevels
2-5, but only if eth0 `IFUP:eth0` is up and a gateway `GW` is set.  When
the configuration changes, a new gateway is set, or somehow a new `IFUP`
event for eth0 is received, then dropbear is not SIGHUP'ed, but instead
stop-started `<!>`.  The latter trick applies to all services, even
those that do not define any events.

Currently inetd services are not supported for event based starting, but
it could easily be added.  Likely scenario is to deny incoming requests
on, e.g., eth0 if there is no gateway.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

service.c

@@ -31,6 +31,7 @@
 
 #include "finit.h"
 #include "conf.h"
+#include "event.h"
 #include "helpers.h"
 #include "private.h"
 #include "sig.h"
@@ -94,6 +95,12 @@ svc_cmd_t service_enabled(svc_t *svc, int event, void *arg)
 	if (!svc_in_runlevel(svc, runlevel))
 		return SVC_STOP;
 
+	/*
+	 * Event conditions for services are ignored during bootstrap.
+	 */
+	if (runlevel && !event_service_cond(svc->events))
+		return SVC_STOP;
+
 	/* Is there a service plugin registered? */
 	if (svc->cb) {
 		int   status;
@@ -373,7 +380,11 @@ void service_stop_dynamic(void)
 	plugin_run_hooks(HOOK_SVC_RECONF); /* Reconfigure HW/VLANs/etc here */
 }
 
-/* stop + start */
+/* stop + start
+ *
+ * XXX: This should be refactored into a background job AND marked such
+ *      so that the service monitor doesn't attempt to restart it!
+ */
 int service_restart(svc_t *svc)
 {
 	int result = 0;
@@ -537,7 +548,7 @@ void service_runlevel(int newlevel)
  * The @line can optionally start with a username, denoted by an @
  * character. Like this:
  *
- *     service @username [!0-6,S] /path/to/daemon arg       -- Description
+ *     service @username [!0-6,S] <!EV> /path/to/daemon arg -- Description
  *     task @username [!0-6,S] /path/to/task arg            -- Description
  *     run  @username [!0-6,S] /path/to/cmd arg             -- Description
  *     inetd tcp/ssh nowait [2345] @root:root /sbin/sshd -i -- Description
@@ -550,6 +561,18 @@ void service_runlevel(int newlevel)
  * command is listed in more than the [S] runlevel they will be called
  * when changing runlevel.
  *
+ * Services (daemons, not inetd services) also support an optional <!EV>
+ * argument.  This is for services that, e.g., require a system gateway
+ * or interface to be up before they are started.  Or restarted, or even
+ * SIGHUP'ed, when the gateway changes or interfaces come and go.  The
+ * special case when a service is declared with <!> means it does not
+ * support SIGHUP but must be STOP/START'ed at system reconfiguration.
+ *
+ * Supported service events are: GW, IFUP[:ifname], IFDN[:ifname], where
+ * the interface name (:ifname) is optional.  Actully, the check with a
+ * service event declaration is string based, so 'IFUP:ppp' will match
+ * any of "IFUP:ppp0" or "IFUP:pppoe1" sent by the netlink.so plugin.
+ *
  * For multiple instances of the same command, e.g. multiple DHCP
  * clients, the user must enter an ID, using the :ID syntax.
  *
@@ -570,7 +593,7 @@ int service_register(int type, char *line, time_t mtime, char *username)
 	int forking = 0;
 #endif
 	char *service = NULL, *proto = NULL, *ifaces = NULL;
-	char *cmd, *desc, *runlevels = NULL;
+	char *cmd, *desc, *runlevels = NULL, *events = NULL;
 	svc_t *svc;
 	plugin_t *plugin = NULL;
 
@@ -603,6 +626,8 @@ int service_register(int type, char *line, time_t mtime, char *username)
 			username = &cmd[1];
 		else if (cmd[0] == '[')	/* [runlevels] */
 			runlevels = &cmd[0];
+		else if (cmd[0] == '<')	/* [!ev] */
+			events = &cmd[1];
 		else if (cmd[0] == ':')	/* :ID */
 			id = atoi(&cmd[1]);
 		else
@@ -701,6 +726,9 @@ int service_register(int type, char *line, time_t mtime, char *username)
 	svc->runlevels = conf_parse_runlevels(runlevels);
 	_d("Service %s runlevel 0x%2x", svc->cmd, svc->runlevels);
 
+	if (type == SVC_TYPE_SERVICE)
+		conf_parse_events(svc, events);
+
 #ifndef INETD_DISABLED
 	if (svc_is_inetd(svc)) {
 		char *iface, *name = service;