[mutter] wayland: don't let the login screen steal :0

[Ray Strode <halfline src gnome org>]

commit 8c16ac47c1b88fc48ad8ea621a75a86e028a2764
Author: Ray Strode <rstrode redhat com>
Date:   Mon Mar 16 10:57:44 2015 -0400

    wayland: don't let the login screen steal :0
    
    In 3.16, GDM keeps a login screen running on vt1.
    This login screen starts an Xwayland instance.
    Since it's the first X server to start, it gets
    the prized :0 display number.
    
    This commit works around that problem, for now,
    by having GDM's display number start at 1024.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=746295

 src/wayland/meta-xwayland.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/src/wayland/meta-xwayland.c b/src/wayland/meta-xwayland.c
index 6ea4371..468b31b 100644
--- a/src/wayland/meta-xwayland.c
+++ b/src/wayland/meta-xwayland.c
@@ -352,6 +352,13 @@ choose_xdisplay (MetaXWaylandManager *manager)
   int display = 0;
   char *lockfile = NULL;
 
+  /* Hack to keep the unused Xwayland instance on
+   * the login screen from taking the prime :0 display
+   * number.
+   */
+  if (g_getenv ("RUNNING_UNDER_GDM") != NULL)
+    display = 1024;
+
   do
     {
       lockfile = create_lockfile (display, &display);