Allow sessions to register with GDM

Recording when sessions start, for Wayland → Xorg fallback or
transitioning to the user session, is currently done with timeouts.

This isn't ideal, because on some very slow machines the timeout can be
hit before the session has had a chance to fail: if gnome-session takes
more than 3 seconds to fail then the session will be considered to have
exited rather than failed, and so we don't do Xorg fallback.

We can do this more reliably if we allow sessions to optionally register
themselves with GDM. Then we will know when they've started, so can shut
down the greeter or fall back to Xorg as appropriate. The mechanism is
that they specify X-GDM-SessionRegisters=true in their file, and then
call RegsterSession on the DisplayManager interface on the bus (added in
the previous commit) to say that they've started up.

If X-GDM-SessionRegisters is missing or false, GDM will call the same
method for them after 10 seconds.

Closes: #483

1 files changed, 27 insertions, 23 deletions

diff --git a/daemon/gdm-local-display-factory.c b/daemon/gdm-local-display-factory.c
index 7dd74a62..ee41308b 100644
--- a/daemon/gdm-local-display-factory.c
+++ b/daemon/gdm-local-display-factory.c
@@ -66,7 +66,6 @@ struct _GdmLocalDisplayFactory
 #if defined(ENABLE_WAYLAND_SUPPORT) && defined(ENABLE_USER_DISPLAY_SERVER)
         unsigned int     active_vt;
         guint            active_vt_watch_id;
-        guint            wait_to_finish_timeout_id;
 #endif
 };
 
@@ -299,6 +298,25 @@ finish_waiting_displays_on_seat (GdmLocalDisplayFactory *factory,
 }
 
 static void
+on_session_registered_cb (GObject *gobject,
+                          GParamSpec *pspec,
+                          gpointer user_data)
+{
+        GdmDisplay *display = GDM_DISPLAY (gobject);
+        GdmLocalDisplayFactory *factory = GDM_LOCAL_DISPLAY_FACTORY (user_data);
+        gboolean registered;
+
+        g_object_get (display, "session-registered", &registered, NULL);
+
+        if (!registered)
+                return;
+
+        g_debug ("GdmLocalDisplayFactory: session registered on display, looking for any background displays to kill");
+
+        finish_waiting_displays_on_seat (factory, "seat0");
+}
+
+static void
 on_display_status_changed (GdmDisplay             *display,
                            GParamSpec             *arg1,
                            GdmLocalDisplayFactory *factory)
@@ -376,6 +394,13 @@ on_display_status_changed (GdmDisplay             *display,
         case GDM_DISPLAY_PREPARED:
                 break;
         case GDM_DISPLAY_MANAGED:
+#if defined(ENABLE_WAYLAND_SUPPORT) && defined(ENABLE_USER_DISPLAY_SERVER)
+                g_signal_connect_object (display,
+                                         "notify::session-registered",
+                                         G_CALLBACK (on_session_registered_cb),
+                                         factory,
+                                         0);
+#endif
                 break;
         case GDM_DISPLAY_WAITING_TO_FINISH:
                 break;
@@ -604,14 +629,6 @@ lookup_by_session_id (const char *id,
 }
 
 #if defined(ENABLE_WAYLAND_SUPPORT) && defined(ENABLE_USER_DISPLAY_SERVER)
-static gboolean
-wait_to_finish_timeout (GdmLocalDisplayFactory *factory)
-{
-        finish_waiting_displays_on_seat (factory, "seat0");
-        factory->wait_to_finish_timeout_id = 0;
-        return G_SOURCE_REMOVE;
-}
-
 static void
 maybe_stop_greeter_in_background (GdmLocalDisplayFactory *factory,
                                   GdmDisplay             *display)
@@ -643,16 +660,8 @@ maybe_stop_greeter_in_background (GdmLocalDisplayFactory *factory,
         }
 
         g_debug ("GdmLocalDisplayFactory: killing login window once its unused");
-        g_object_set (G_OBJECT (display), "status", GDM_DISPLAY_WAITING_TO_FINISH, NULL);
-
-        /* We stop the greeter after a timeout to avoid flicker */
-        if (factory->wait_to_finish_timeout_id != 0)
-                g_source_remove (factory->wait_to_finish_timeout_id);
 
-        factory->wait_to_finish_timeout_id =
-                g_timeout_add_seconds (WAIT_TO_FINISH_TIMEOUT,
-                                       (GSourceFunc)wait_to_finish_timeout,
-                                       factory);
+        g_object_set (G_OBJECT (display), "status", GDM_DISPLAY_WAITING_TO_FINISH, NULL);
 }
 
 static gboolean
@@ -748,7 +757,6 @@ on_vt_changed (GIOChannel    *source,
                                 display = gdm_display_store_find (store,
                                                                   lookup_by_session_id,
                                                                   (gpointer) login_session_id);
-
                                 if (display != NULL)
                                         maybe_stop_greeter_in_background (factory, display);
                         } else {
@@ -831,10 +839,6 @@ gdm_local_display_factory_stop_monitor (GdmLocalDisplayFactory *factory)
                 factory->seat_removed_id = 0;
         }
 #if defined(ENABLE_WAYLAND_SUPPORT) && defined(ENABLE_USER_DISPLAY_SERVER)
-        if (factory->wait_to_finish_timeout_id != 0) {
-                g_source_remove (factory->wait_to_finish_timeout_id);
-                factory->wait_to_finish_timeout_id = 0;
-        }
         if (factory->active_vt_watch_id) {
                 g_source_remove (factory->active_vt_watch_id);
                 factory->active_vt_watch_id = 0;