plugins/dbus: adapt to other operating systems

Not all Linux systems are based on Debian, and even if they are inspired
by Debian (Buildroot), they do not necessarily use the same defaults.

This patch probes the current system for:

 - dbus user and group
 - dbus PID file

If the user/group cannot be found we fall back to "root", if the PID
file cannot be determined we ignore PID file readiness.

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

plugins/dbus.c

@@ -47,13 +47,58 @@
 #define DBUS_DAEMONGROUP "messagebus"
 #endif
 
-#ifndef DBUS_DAEMONPIDFILE
+/*
-#define DBUS_DAEMONPIDFILE "/var/run/dbus/pid"
+ * Dumnpster diving for the D-Bus main configuration file
-#endif
+ * where <pidfile> is defined.
+ */
+static char *dbus_pidfn(void)
+{
+	char *alt[] = {
+		"/usr/share/dbus-1/system.conf",
+		"/etc/dbus-1/system.conf",
+		NULL
+	};
+	int i;
+
+	for (i = 0; alt[i]; i++) {
+		char *fn = alt[i];
+		char buf[256];
+		FILE *fp;
+
+		fp = fopen(fn, "r");
+		if (!fp)
+			continue;
+
+		fn = NULL;
+		while (fgets(buf, sizeof(buf), fp)) {
+			char *pos;
+
+			pos = strstr(buf, "<pidfile>");
+			if (!pos)
+				continue;
+			fn = pos + strlen("<pidfile>");
+			pos = strstr(fn, "</pidfile>");
+			if (!pos) {
+				fn = NULL;
+				break;
+			}
+			*pos = 0;
+		}
+
+		fclose(fp);
+		if (fn)
+			return strdup(fn);
+	}
+
+	return NULL;
+}
 
 static void setup(void *arg)
 {
+	char *group = DBUS_DAEMONGROUP;
+	char *user = DBUS_DAEMONUSER;
 	char line[256];
+	char *pidfn;
 	mode_t prev;
 	char *cmd;
 
@@ -68,29 +113,53 @@ static void setup(void *arg)
 		return;
 	}
 
-	prev =umask(0);
+	if (getuser(user, NULL) == -1) {
+		if (getuser("dbus", NULL) == -1)
+			user = "root"; /* fallback */
+		else
+			user = "dbus"; /* e.g., Buildroot */
+	}
+
+	if (getgroup(group) == -1) {
+		if (getgroup("dbus") == -1)
+			group = "root"; /* fallback */
+		else
+			group = "dbus"; /* e.g., Buildroot */
+	}
+
+	/* Clean up from any previous pre-bootstrap run */
+	pidfn = dbus_pidfn();
+	if (pidfn)
+		remove(pidfn);
 
 	dbg("Creating D-Bus Required Directories ...");
-	mksubsys("/var/run/dbus", 0755, DBUS_DAEMONUSER, DBUS_DAEMONGROUP);
+	prev = umask(0);
-	mksubsys("/var/run/lock/subsys", 0755, DBUS_DAEMONUSER, DBUS_DAEMONGROUP);
+	mksubsys("/var/run/dbus", 0755, user, group);
-	mksubsys("/var/lib/dbus", 0755, DBUS_DAEMONUSER, DBUS_DAEMONGROUP);
+	mksubsys("/var/run/lock/subsys", 0755, user, group);
-	mksubsys("/tmp/dbus", 0755, DBUS_DAEMONUSER, DBUS_DAEMONGROUP);
+	mksubsys("/var/lib/dbus", 0755, user, group);
+	mksubsys("/tmp/dbus", 0755, user, group);
+	umask(prev);
 
 	/* Generate machine id for dbus */
 	if (whichp("dbus-uuidgen"))
 		run_interactive("dbus-uuidgen --ensure", "Creating machine UUID for D-Bus");
 
-	/* Clean up from any previous pre-bootstrap run */
+	/*
-	remove(DBUS_DAEMONPIDFILE);
+	 * Register service with Finit
+	 * Note: dbus drops privs after starting up.
+	 */
+	if (pidfn) {
+		snprintf(line, sizeof(line), "[123456789] cgroup.system name:dbus pid:!%s %s %s -- %s",
+			 pidfn, cmd, DBUS_ARGS, DBUS_DESC);
+		free(pidfn);
+	} else
+		snprintf(line, sizeof(line), "[123456789] cgroup.system name:dbus %s %s -- %s",
+			 cmd, DBUS_ARGS, DBUS_DESC);
 
-	/* Register service with Finit */
-	snprintf(line, sizeof(line), "[S12345789] cgroup.system pid:!%s @%s:%s %s %s -- %s",
-		 DBUS_DAEMONPIDFILE, DBUS_DAEMONUSER, DBUS_DAEMONGROUP, cmd, DBUS_ARGS, DBUS_DESC);
 	if (service_register(SVC_TYPE_SERVICE, line, global_rlimit, NULL))
 		err(1, "Failed registering %s", DBUS_DAEMON);
-	free(cmd);
 
-	umask(prev);
+	free(cmd);
 }
 
 static plugin_t plugin = {