plugin: start a system bus by default

Finit speaks D-Bus itself now and claims org.finit on the system bus
when it finds one, but nothing in a default build ever brings that bus
up.  The plugin that does was opt-in, so the built-in support sat idle
unless the integrator knew to ask for both halves.

Defaulting it on is only reasonable if the result stays the admin's to
change, and a service registered from C through conf_save_service() is
not: it lands in the run path where it cannot be overridden or emptied
out.  So the daemon moves to 20-dbus.conf and its directories to
tmpfiles.d/dbus.conf, the same way hotplug and every other daemon we
ship them for.  The plugin keeps only what has to look at the running
system, the stale pidfile and the machine UUID.

Those directories are no longer chowned to messagebus.  tmpfiles.d
skips a line whose user does not exist rather than falling back, so
the plugin's messagebus/dbus/root ladder has no equivalent there, and
dbus-daemon binds its socket before dropping privileges anyway.

The plugin already bows out where there is no dbus-daemon installed,
so systems that never wanted a bus are unaffected, and
--disable-dbus-plugin is there for those that have one and would still
rather init left it alone.

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

plugins/dbus.c

@@ -32,22 +32,11 @@
 #include "config.h"
 #include "helpers.h"
 #include "plugin.h"
-#include "service.h"
-#include "util.h"
 #include "conf.h"
+#include "util.h"
 #include "log.h"
 
 #define DBUS_DAEMON "dbus-daemon"
-#define DBUS_ARGS   "--nofork --system --syslog-only"
-#define DBUS_DESC   "D-Bus message bus daemon"
-
-#ifndef DBUS_DAEMONUSER
-#define DBUS_DAEMONUSER "messagebus"
-#endif
-
-#ifndef DBUS_DAEMONGROUP
-#define DBUS_DAEMONGROUP "messagebus"
-#endif
 
 /*
  * Dumnpster diving for the D-Bus main configuration file
@@ -96,79 +85,35 @@ static char *dbus_pidfn(void)
 	return NULL;
 }
 
+/*
+ * The directories live in tmpfiles.d/dbus.conf and the service in
+ * system/20-dbus.conf, both of which an administrator can override.
+ * What is left needs to look at the running system, so it stays here.
+ */
 static void setup(void *arg)
 {
-	char *group = DBUS_DAEMONGROUP;
-	char *user = DBUS_DAEMONUSER;
-	char esccmd[256];
-	char pid[300];
 	char *pidfn;
-	mode_t prev;
-	char *cmd;
 
 	if (rescue) {
 		dbg("Skipping %s plugin in rescue mode.", "dbus");
 		return;
 	}
 
-	cmd = which(DBUS_DAEMON);
-	if (!cmd) {
+	if (!whichp(DBUS_DAEMON)) {
 		dbg("Skipping plugin, %s is not installed.", DBUS_DAEMON);
 		return;
 	}
 
-	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)
+	if (pidfn) {
 		remove(pidfn);
-
-	dbg("Creating D-Bus Required Directories ...");
-	prev = umask(0);
-	mksubsys("/var/run/dbus", 0755, user, group);
-	mksubsys("/var/run/lock/subsys", 0755, user, group);
-	mksubsys("/var/lib/dbus", 0755, user, group);
-	mksubsys("/tmp/dbus", 0755, user, group);
-	umask(prev);
+		free(pidfn);
+	}
 
 	/* Generate machine id for dbus */
 	if (whichp("dbus-uuidgen"))
 		run_interactive("dbus-uuidgen --ensure", "Verifying D-Bus machine UUID");
-
-	/*
-	 * Register service with Finit
-	 * Note: dbus drops privs after starting up.
-	 */
-	pid[0] = 0;
-	if (pidfn) {
-		char esc[280];
-
-		snprintf(pid, sizeof(pid), "\tpidfile     = \"%s\"\n",
-			 conf_escape(pidfn, esc, sizeof(esc)));
-		free(pidfn);
-	}
-	conf_save_service(SVC_TYPE_SERVICE, "dbus", "dbus.conf",
-			  "\tdescription = \"" DBUS_DESC "\"\n"
-			  "\trunlevel    = \"S123456789\"\n"
-			  "\tnotify      = \"none\"\n"
-			  "\tcgroup system {}\n"
-			  "%s"
-			  "\tcommand     = \"%s " DBUS_ARGS "\"\n",
-			  pid, conf_escape(cmd, esccmd, sizeof(esccmd)));
-	free(cmd);
 }
 
 static plugin_t plugin = {