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, 63 insertions, 18 deletions

diff --git a/daemon/gdm-wayland-session.c b/daemon/gdm-wayland-session.c
index 94f49e19..35679b19 100644
--- a/daemon/gdm-wayland-session.c
+++ b/daemon/gdm-wayland-session.c
@@ -45,6 +45,7 @@ typedef struct
 
         GSubprocess     *bus_subprocess;
         GDBusConnection *bus_connection;
+        GdmDBusManager  *display_manager_proxy;
         char            *bus_address;
 
         char           **environment;
@@ -53,6 +54,8 @@ typedef struct
         char         *session_command;
         int           session_exit_status;
 
+        guint         register_session_id;
+
         GMainLoop    *main_loop;
 
         guint32       debug_enabled : 1;
@@ -385,29 +388,14 @@ static gboolean
 register_display (State        *state,
                   GCancellable *cancellable)
 {
-        GdmDBusManager  *manager = NULL;
         GError          *error = NULL;
         gboolean         registered = FALSE;
         GVariantBuilder  details;
 
-        manager = gdm_dbus_manager_proxy_new_for_bus_sync (G_BUS_TYPE_SYSTEM,
-                                                           G_DBUS_PROXY_FLAGS_DO_NOT_LOAD_PROPERTIES |
-                                                           G_DBUS_PROXY_FLAGS_DO_NOT_CONNECT_SIGNALS,
-                                                           "org.gnome.DisplayManager",
-                                                           "/org/gnome/DisplayManager/Manager",
-                                                           cancellable,
-                                                           &error);
-
-        if (!manager) {
-                g_debug ("could not contact display manager: %s", error->message);
-                g_error_free (error);
-                goto out;
-        }
-
         g_variant_builder_init (&details, G_VARIANT_TYPE ("a{ss}"));
         g_variant_builder_add (&details, "{ss}", "session-type", "wayland");
 
-        registered = gdm_dbus_manager_call_register_display_sync (manager,
+        registered = gdm_dbus_manager_call_register_display_sync (state->display_manager_proxy,
                                                                   g_variant_builder_end (&details),
                                                                   cancellable,
                                                                   &error);
@@ -416,8 +404,6 @@ register_display (State        *state,
                 g_error_free (error);
         }
 
-out:
-        g_clear_object (&manager);
         return registered;
 }
 
@@ -439,6 +425,7 @@ clear_state (State **out_state)
         g_clear_object (&state->session_subprocess);
         g_clear_pointer (&state->environment, g_strfreev);
         g_clear_pointer (&state->main_loop, g_main_loop_unref);
+        g_clear_handle_id (&state->register_session_id, g_source_remove);
         *out_state = NULL;
 }
 
@@ -454,6 +441,49 @@ on_sigterm (State *state)
         return G_SOURCE_CONTINUE;
 }
 
+static gboolean
+register_session_timeout_cb (gpointer user_data)
+{
+        State *state;
+        GError *error = NULL;
+
+        state = (State *) user_data;
+
+        gdm_dbus_manager_call_register_session_sync (state->display_manager_proxy,
+                                                     g_variant_new ("a{sv}", NULL),
+                                                     state->cancellable,
+                                                     &error);
+
+        if (error != NULL) {
+                g_warning ("Could not register session: %s", error->message);
+                g_error_free (error);
+        }
+
+        return G_SOURCE_REMOVE;
+}
+
+static gboolean
+connect_to_display_manager (State *state)
+{
+        g_autoptr (GError) error = NULL;
+
+        state->display_manager_proxy = gdm_dbus_manager_proxy_new_for_bus_sync (
+                G_BUS_TYPE_SYSTEM,
+                G_DBUS_PROXY_FLAGS_DO_NOT_LOAD_PROPERTIES | G_DBUS_PROXY_FLAGS_DO_NOT_CONNECT_SIGNALS,
+                "org.gnome.DisplayManager",
+                "/org/gnome/DisplayManager/Manager",
+                state->cancellable,
+                &error);
+
+        if (state->display_manager_proxy == NULL) {
+                g_printerr ("gdm-wayland-session: could not contact display manager: %s\n",
+                            error->message);
+                return FALSE;
+        }
+
+        return TRUE;
+}
+
 int
 main (int    argc,
       char **argv)
@@ -464,7 +494,10 @@ main (int    argc,
         gboolean         debug = FALSE;
         gboolean         ret;
         int              exit_status = EX_OK;
+        static gboolean  register_session = FALSE;
+
         static GOptionEntry entries []   = {
+                { "register-session", 0, 0, G_OPTION_ARG_NONE, &register_session, "Register session after a delay", NULL },
                 { G_OPTION_REMAINING, 0, 0, G_OPTION_ARG_STRING_ARRAY, &args, "", "" },
                 { NULL }
         };
@@ -528,6 +561,9 @@ main (int    argc,
                 goto out;
         }
 
+        if (!connect_to_display_manager (state))
+                goto out;
+
         ret = register_display (state, state->cancellable);
 
         if (!ret) {
@@ -536,6 +572,15 @@ main (int    argc,
                 goto out;
         }
 
+        if (register_session) {
+                g_debug ("gdm-wayland-session: Will register session in %d seconds", REGISTER_SESSION_TIMEOUT);
+                state->register_session_id = g_timeout_add_seconds (REGISTER_SESSION_TIMEOUT,
+                                                                    register_session_timeout_cb,
+                                                                    state);
+        } else {
+                g_debug ("gdm-wayland-session: Session will register itself");
+        }
+
         g_main_loop_run (state->main_loop);
 
         /* Only use exit status of session if we're here because it exit */