Add HOOK_SVC_START to detect started processes

This patch adds support for the runtime `HOOK_SVC_START`.

Customer request.

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

README.md

@@ -538,6 +538,11 @@ state, etc.  Available hook points are:
 
   **NOTE:** This hook callback gets the lost PID as argument.
 
+* `HOOK_SVC_START`: Like `HOOK_SVC_LOST`, but called when a process is
+  started.  Same caveats apply.
+
+  **NOTE:** This hook callback gets the new PID as argument.
+
 * `HOOK_RUNLEVEL_CHANGE`: Called when the user has issued a runlevel
   change.  The hook is called when services not matching the new
   runlevel have been been stopped.  When the hook has completed, Finit

plugin.h

@@ -52,6 +52,7 @@ typedef enum {
 	/* Runtime hooks */
 	HOOK_SVC_RECONF,
 	HOOK_SVC_LOST,
+	HOOK_SVC_START,
 	HOOK_RUNLEVEL_CHANGE,
 
 	/* Shutdown hooks */

service.c

@@ -248,6 +248,8 @@ static int service_start(svc_t *svc)
 			close(svc->stdin);
 #endif
 
+	plugin_run_hook(HOOK_SVC_START, (void *)(uintptr_t)pid);
+
 	if (SVC_TYPE_RUN == svc->type) {
 		result = WEXITSTATUS(complete(svc->cmd, pid));
 		svc->pid = 0;