daemon: clean up greeter when unused

When user switching GDM needs to show a transient greeter for
the user to pick a name from the list and jump to that session.

After the user has been jumped to the selected session we don't
really have a use for the greeter session.  Historically, we've
kept it around anyway, though, because X by default jumps back
to the VT it started on when it exits, and we don't want the
user to get thrown to an empty VT after they log out.

This commit changes X to get started with the "-novtswitch"
option, so that it doesn't do the undesirable switch-on-exit
thing.

This allows us to clean up the useless greeter following user
switches.

Based on work by Josselin Mouette <joss@debian.org>

https://bugzilla.gnome.org/show_bug.cgi?id=618047

2 files changed, 17 insertions, 6 deletions

diff --git a/daemon/gdm-server.c b/daemon/gdm-server.c
index 7135ffaf..8dacdb51 100644
--- a/daemon/gdm-server.c
+++ b/daemon/gdm-server.c
@@ -52,6 +52,12 @@
 
 extern char **environ;
 
+#ifdef WITH_VT_SWITCH_WORKAROUND
+#define X_SERVER_COMMAND_LINE X_SERVER " -br -verbose -logverbose 7"
+#else
+#define X_SERVER_COMMAND_LINE X_SERVER " -br -verbose -logverbose 7 -novtswitch"
+#endif
+
 #define GDM_SERVER_GET_PRIVATE(o) (G_TYPE_INSTANCE_GET_PRIVATE ((o), GDM_TYPE_SERVER, GdmServerPrivate))
 
 /* These are the servstat values, also used as server
@@ -941,7 +947,7 @@ gdm_server_init (GdmServer *server)
         server->priv = GDM_SERVER_GET_PRIVATE (server);
 
         server->priv->pid = -1;
-        server->priv->command = g_strdup (X_SERVER " -br -verbose -logverbose 7");
+        server->priv->command = g_strdup (X_SERVER_COMMAND_LINE);
         server->priv->log_dir = g_strdup (LOGDIR);
 
         add_ready_handler (server);
diff --git a/daemon/gdm-simple-slave.c b/daemon/gdm-simple-slave.c
index 7b9d7d8b..55c0f19a 100644
--- a/daemon/gdm-simple-slave.c
+++ b/daemon/gdm-simple-slave.c
@@ -463,12 +463,17 @@ start_session_timeout (GdmSimpleSlave *slave)
         if (migrated) {
                 destroy_session (slave);
 
-                /* We don't stop the slave here because
-                   when Xorg exits it switches to the VT it was
-                   started from.  That interferes with fast
-                   user switching. */
+#ifdef WITH_VT_SWITCH_WORKAROUND
+                /* If the X server doesn't support -novtswitch, then when the
+                 * user logs out from their session later, they're going to get thrown
+                 * back to the VT the greeter is currently running on. We keep the
+                 * greeter alive here, so when that happens the user doesn't see
+                 * a blank VT or some confusing thing.
+                 */
                 queue_greeter_reset (slave);
-
+#else
+                gdm_slave_stopped (GDM_SLAVE (slave));
+#endif
                 goto out;
         }