+/* PROCESSES
+ *
+ * If you are in a shell and run "dbus-launch myapp", here is what happens:
+ *
+ * shell [*]
+ * \- main() --exec--> myapp[*]
+ * \- "intermediate parent"
+ * \- bus-runner --exec--> dbus-daemon --fork
+ * \- babysitter[*] \- final dbus-daemon[*]
+ *
+ * Processes marked [*] survive the initial flurry of activity.
+ *
+ * If you run "dbus-launch --sh-syntax" then the diagram is the same, except
+ * that main() prints variables and exits 0 instead of exec'ing myapp.
+ *
+ * PIPES
+ *
+ * dbus-daemon --print-pid -> bus_pid_to_launcher_pipe -> main
+ * dbus-daemon --print-address -> bus_address_to_launcher_pipe -> main
+ * main -> bus_pid_to_babysitter_pipe -> babysitter
+ *
+ * The intermediate parent looks pretty useless at first glance. Its purpose
+ * is to avoid the bus-runner becoming a zombie: when the intermediate parent
+ * terminates, the bus-runner and babysitter are reparented to init, which
+ * reaps them if they have finished. We can't rely on main() to reap arbitrary
+ * children because it might exec myapp, after which it can't be relied on to
+ * reap its children. We *can* rely on main() to reap the intermediate parent,
+ * because that happens before it execs myapp.
+ *
+ * It's unclear why dbus-daemon needs to fork, but we explicitly tell it to
+ * for some reason, then wait for it. If we left it undefined, a forking
+ * dbus-daemon would get the parent process reparented to init and reaped
+ * when the intermediate parent terminated, and a non-forking dbus-daemon
+ * would get reparented to init and carry on there.
+ *
+ * myapp is exec'd by the process that initially ran main() so that it's
+ * the shell's child, so the shell knows how to do job control and stuff.
+ * This is desirable for the "dbus-launch an application" use-case, less so
+ * for the "dbus-launch a test suite in an isolated session" use-case.
+ */
+
+static char* machine_uuid = NULL;
+
+const char*
+get_machine_uuid (void)
+{
+ return machine_uuid;
+}
+
+static void
+save_machine_uuid (const char *uuid_arg)
+{
+ if (strlen (uuid_arg) != 32)
+ {
+ fprintf (stderr, "machine ID '%s' looks like it's the wrong length, should be 32 hex digits",
+ uuid_arg);
+ exit (1);
+ }
+
+ machine_uuid = xstrdup (uuid_arg);
+}
+
+#ifdef DBUS_BUILD_X11
+#define UUID_MAXLEN 40
+/* Read the machine uuid from file if needed. Returns TRUE if machine_uuid is
+ * set after this function */
+static int
+read_machine_uuid_if_needed (void)
+{
+ FILE *f;
+ char uuid[UUID_MAXLEN];
+ size_t len;
+ int ret = FALSE;
+
+ if (machine_uuid != NULL)
+ return TRUE;
+
+ f = fopen (DBUS_MACHINE_UUID_FILE, "r");
+ if (f == NULL)
+ return FALSE;
+
+ if (fgets (uuid, UUID_MAXLEN, f) == NULL)
+ goto out;
+
+ len = strlen (uuid);
+ if (len < 32)
+ goto out;
+
+ /* rstrip the read uuid */
+ while (len > 31 && isspace(uuid[len - 1]))
+ len--;
+
+ if (len != 32)
+ goto out;
+
+ uuid[len] = '\0';
+ machine_uuid = xstrdup (uuid);
+ verbose ("UID: %s\n", machine_uuid);
+ ret = TRUE;
+
+out:
+ fclose(f);
+ return ret;
+}
+#endif /* DBUS_BUILD_X11 */
+