[...]
 g_dbus_connection_signal_subscribe (connection,
                                     "org.freedesktop.UDisks",
                                     NULL,
                                     "DeviceAdded",
                                     NULL,
                                     NULL,
                                     G_DBUS_SIGNAL_FLAGS_NONE,
                                     dbus_notification_callback,
                                     NULL,
                                     NULL);
 [...]

 GDBusConnection *connection = NULL;

 connection = g_bus_get_sync (G_BUS_TYPE_SYSTEM, NULL, &error);
 if (connection == NULL)
   {
     printf ("Can't connect to system bus: %s\n", error->message);
     g_error_free (error);
   }
 [...]