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, 43 insertions, 4 deletions

diff --git a/daemon/gdm-session.c b/daemon/gdm-session.c
index 6a116a85..d0e09b53 100644
--- a/daemon/gdm-session.c
+++ b/daemon/gdm-session.c
@@ -2837,6 +2837,7 @@ gdm_session_start_session (GdmSession *self,
         gboolean                allow_remote_connections = FALSE;
         char                   *command;
         char                   *program;
+        gboolean               register_session;
 
         g_return_if_fail (GDM_IS_SESSION (self));
         g_return_if_fail (self->session_conversation == NULL);
@@ -2862,6 +2863,8 @@ gdm_session_start_session (GdmSession *self,
                 run_launcher = TRUE;
         }
 
+        register_session = !gdm_session_session_registers (self);
+
         if (self->selected_program == NULL) {
                 gboolean run_xsession_script;
 
@@ -2879,12 +2882,14 @@ gdm_session_start_session (GdmSession *self,
 
                 if (run_launcher) {
                         if (is_x11) {
-                                program = g_strdup_printf (LIBEXECDIR "/gdm-x-session %s %s\"%s\"",
+                                program = g_strdup_printf (LIBEXECDIR "/gdm-x-session %s%s %s\"%s\"",
+                                                           register_session ? "--register-session " : "",
                                                            run_xsession_script? "--run-script " : "",
                                                            allow_remote_connections? "--allow-remote-connections " : "",
                                                            command);
                         } else {
-                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session \"%s\"",
+                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s\"",
+                                                           register_session ? "--register-session " : "",
                                                            command);
                         }
                 } else if (run_xsession_script) {
@@ -2897,10 +2902,12 @@ gdm_session_start_session (GdmSession *self,
         } else {
                 if (run_launcher) {
                         if (is_x11) {
-                                program = g_strdup_printf (LIBEXECDIR "/gdm-x-session \"%s\"",
+                                program = g_strdup_printf (LIBEXECDIR "/gdm-x-session %s\"%s\"",
+                                                           register_session ? "--register-session " : "",
                                                            self->selected_program);
                         } else {
-                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session \"%s\"",
+                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s\"",
+                                                           register_session ? "--register-session " : "",
                                                            self->selected_program);
                         }
                 } else {
@@ -3178,6 +3185,38 @@ update_session_type (GdmSession *self)
 }
 
 gboolean
+gdm_session_session_registers (GdmSession *self)
+{
+        g_autoptr(GError) error = NULL;
+        g_autoptr(GKeyFile) key_file = NULL;
+        gboolean session_registers = FALSE;
+        g_autofree char *filename = NULL;
+
+        g_return_val_if_fail (self != NULL, FALSE);
+        g_return_val_if_fail (GDM_IS_SESSION (self), FALSE);
+
+        filename = get_session_filename (self);
+
+        key_file = load_key_file_for_file (self, filename, NULL);
+
+        session_registers = g_key_file_get_boolean (key_file,
+                                                    G_KEY_FILE_DESKTOP_GROUP,
+                                                    "X-GDM-SessionRegisters",
+                                                    &error);
+        if (!session_registers &&
+            error != NULL &&
+            !g_error_matches (error, G_KEY_FILE_ERROR, G_KEY_FILE_ERROR_KEY_NOT_FOUND)) {
+                g_warning ("GdmSession: Couldn't read session file '%s'", filename);
+                return FALSE;
+        }
+
+        g_debug ("GdmSession: '%s' %s self", filename,
+                 session_registers ? "registers" : "does not register");
+
+        return session_registers;
+}
+
+gboolean
 gdm_session_bypasses_xsession (GdmSession *self)
 {
         GError     *error;