Support for monitoring forking services/sysv daemons

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

ChangeLog.md

@@ -12,6 +12,8 @@ Bug fix release, but also cgroups and a new progress!
   https://twitter.com/b0rk/status/1214341831049252870?s=20
 
 ### Changes
+* Support for `sysv` start/stop scripts as well as monitoring forking
+  services, stared using `sysv` or `service` stanza
 * Add support for `--disable-docs` and `--disable-contrib` to speed up
   builds and work around issue with massively parallel builds
 * Add `-b`, batch mode, for non-interactive use to `initctl`

docs/config.md

@@ -160,17 +160,28 @@ Syntax
   When entering an allowed runlevel, Finit calls `init-script start`,
   when entering a disallowed runlevel, Finit calls `init-script stop`,
   and if the Finit .conf, where `sysv` stanza is declared, is modified,
-  Finit calls `init-script restart` on `initctl restart`.  Similar
+  Finit calls `init-script restart` on `initctl reload`.  Similar to
-  to how a `service` stanza works.
+  how `service` stanzas work.
-  
-  > **Note:** there is currently now supervision of daemons started as
-  > sysv services.  I.e., the `pid:!...` support is still missing.
 
+  Forking services started with `sysv` scripts can be monitored by Finit
+  by declaring the PID file to look for: `pid:!/path/to/pidfile.pid`.
+  
 * `service [LVLS] <COND> /path/to/daemon ARGS -- Optional description`  
   Service, or daemon, to be monitored and automatically restarted if it
-  exits prematurely.  Please note that you often need to provide a
+  exits prematurely.
-  `--foreground` or `--no-background` argument to most daemons to
+  
-  prevent them from forking off a sub-process in the background.
+  For daemons that support it, we recommend appending `--foreground`, or
+  `--no-background`, argument to prevent them from forking off a
+  sub-process in the background.  This is the most reliable way to
+  monitor a service.
+
+  However, not all daemons support running in the foreground, or they
+  may start logging to the foreground as well, these are called forking
+  services and are supported using the same syntax as forking `sysv`
+  services, using the `pid:!/path/to/pidfile.pid` syntax.
+  
+  In the case of `ospfd` (below), we omit the `-d` flag to prevent it
+  from forking (daemonizing):
 
 ```shell
         service [2345] <svc/sbin/zebra> /sbin/ospfd -- OSPF daemon
@@ -198,7 +209,7 @@ Syntax
   can depend on `<svc/foo>`.
 
   If a service `bar` *does* maintain a PID file, but using `foo.pid`, we
-  can inform Finit of this by simplly prepending an `!` to the argument.
+  can inform Finit of this by prepending an `!` to the argument.
 
         pid:!/run/foo.pid
 

plugins/pidfile.c

@@ -29,6 +29,7 @@
 #include "finit.h"
 #include "cond.h"
 #include "helpers.h"
+#include "pid.h"
 #include "plugin.h"
 #include "service.h"
 
@@ -66,6 +67,15 @@ static void pidfile_callback(void *arg, int fd, int events)
 		mkcond(cond, sizeof(cond), svc->cmd);
 		if (ev->mask & (IN_CREATE | IN_ATTRIB | IN_MODIFY | IN_MOVED_TO)) {
 			svc_started(svc);
+			if (svc_is_forking(svc)) {
+				pid_t pid;
+
+				pid = pid_file_read(pid_file(svc));
+				_d("Forking service %s changed PID from %d to %d",
+				   svc->cmd, svc->pid, pid);
+				svc->pid = pid;
+			}
+
 			cond_set(cond);
 		} else if (ev->mask & IN_DELETE)
 			cond_clear(cond);

src/service.c

@@ -485,7 +485,25 @@ static int service_stop(svc_t *svc)
 		print_desc("Stopping ", svc->desc);
 
 	if (!svc_is_sysv(svc)) {
+		if (svc->pid <= 1)
+			goto cleanup;
+
 		res = kill(svc->pid, SIGTERM);
+
+		/* PID lost or forking process never really started */
+		if (res == -1 && ESRCH == errno) {
+			char *fn;
+
+			/* XXX: Same clenup as done by service_monitor(), refactor */
+		cleanup:
+			fn = pid_file(svc);
+			if (remove(fn) && errno != ENOENT)
+				logit(LOG_CRIT, "Failed removing service %s pidfile %s",
+				      basename(svc->cmd), fn);
+
+			/* No longer running, update books. */
+			svc->start_time = svc->pid = 0;
+		}
 	} else {
 		char *args[] = { svc->cmd, "stop", NULL };
 		pid_t pid;
@@ -1042,6 +1060,10 @@ void service_monitor(pid_t lost, int status)
 	   svc->cmd, lost, WIFEXITED(status), WIFSIGNALED(status), WEXITSTATUS(status));
 	svc->status = status;
 
+	/* Forking sysv/services declare themselves with pid:!/path/to/pid.file  */
+	if (svc_is_starting(svc) && svc_is_forking(svc))
+		return;
+
 	/* Try removing PID file (in case service does not clean up after itself) */
 	if (svc_is_daemon(svc)) {
 		char *fn;

src/svc.h

@@ -187,6 +187,7 @@ static inline int svc_is_inetd_conn(svc_t *svc) { return svc && SVC_TYPE_INETD_C
 static inline int svc_is_daemon    (svc_t *svc) { return svc && SVC_TYPE_SERVICE    == svc->type; }
 static inline int svc_is_sysv      (svc_t *svc) { return svc && SVC_TYPE_SYSV       == svc->type; }
 static inline int svc_is_runtask   (svc_t *svc) { return svc && (SVC_TYPE_RUNTASK & svc->type);   }
+static inline int svc_is_forking   (svc_t *svc) { return (svc_is_daemon(svc) || svc_is_sysv(svc)) && svc->pidfile[0] == '!'; }
 
 static inline int svc_in_runlevel  (svc_t *svc, int runlevel) { return svc && ISSET(svc->runlevels, runlevel); }
 static inline int svc_has_sighup   (svc_t *svc) { return svc &&  0 != svc->sighup; }