[gdm] slave: kill off clients from display when finished

[Ray Strode <halfline src gnome org>]

commit a35135acf75567429d522c9019ee6ceb8f962fc9
Author: Ray Strode <rstrode redhat com>
Date:   Wed Jul 20 17:23:05 2016 -0400

    slave: kill off clients from display when finished
    
    When we're done with the display we need to kill off any clients
    that are lingering and close our own connection to the display.
    
    This is so, for instance, processes from the session don't
    stick around on a -noreset Xvnc server (or something)
    
    https://bugzilla.gnome.org/show_bug.cgi?id=776059

 daemon/gdm-display.c |   29 +++++++++++++++++++++++++++++
 1 files changed, 29 insertions(+), 0 deletions(-)
---
diff --git a/daemon/gdm-display.c b/daemon/gdm-display.c
index 4b035d6..0057e2c 100644
--- a/daemon/gdm-display.c
+++ b/daemon/gdm-display.c
@@ -648,6 +648,35 @@ gdm_display_finish (GdmDisplay *self)
 static void
 gdm_display_disconnect (GdmDisplay *self)
 {
+        /* These 3 bits are reserved/unused by the X protocol */
+        guint32 unused_bits = 0b11100000000000000000000000000000;
+        XID highest_client, client;
+        guint32 client_increment;
+        const xcb_setup_t *setup;
+
+        if (self->priv->xcb_connection == NULL) {
+                return;
+        }
+
+        setup = xcb_get_setup (self->priv->xcb_connection);
+
+        /* resource_id_mask is the bits given to each client for
+         * addressing resources */
+        highest_client = (XID) ~unused_bits & ~setup->resource_id_mask;
+        client_increment = setup->resource_id_mask + 1;
+
+        /* Kill every client but ourselves, then close our own connection
+         */
+        for (client = 0;
+             client <= highest_client;
+             client += client_increment) {
+
+                if (client != setup->resource_id_base)
+                        xcb_kill_client (self->priv->xcb_connection, client);
+        }
+
+        xcb_flush (self->priv->xcb_connection);
+
         g_clear_pointer (&self->priv->xcb_connection, xcb_disconnect);
 }