xlib/shm: Note the bug is an interaction between libXext and xorg

Søren thought it was bit harsh to lay the blame solely on xorg for it
crashing due to an unexpected input value, and that we should mention
libXext was also partly to blame for incorrectly setting the SEND_EVENT
bit in the ShmCompletionEvent.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 6 insertions, 3 deletions

diff --git a/src/cairo-xlib-surface-shm.c b/src/cairo-xlib-surface-shm.c
index 3e6eaf276..ec8a6e1dd 100644
--- a/src/cairo-xlib-surface-shm.c
+++ b/src/cairo-xlib-surface-shm.c
@@ -1125,9 +1125,12 @@ _cairo_xlib_shm_surface_is_idle (cairo_surface_t *surface)
     (((major) * 10000000) + ((minor) * 100000) + ((patch) * 1000) + snap)
 
 static cairo_bool_t
-xorg_has_buggy_send_event(Display *dpy)
+xorg_has_buggy_send_shm_completion_event(Display *dpy)
 {
-    /* Avoid incurring the wrath fixed by:
+    /* As libXext sets the SEND_EVENT bit in the ShmCompletionEvent,
+     * the Xserver may crash if it does not take care when processing
+     * the event type. For instance versions of Xorg prior to 1.11.1
+     * exhibited this bug, and was fixed by:
      *
      * commit 2d2dce558d24eeea0eb011ec9ebaa6c5c2273c39
      * Author: Sam Spilsbury <sam.spilsbury@canonical.com>
@@ -1171,7 +1174,7 @@ _cairo_xlib_display_init_shm (cairo_xlib_display_t *display)
 				 DefaultVisual (display->display, scr),
 				 CWOverrideRedirect, &attr);
 
-    if (xorg_has_buggy_send_event(display->display))
+    if (xorg_has_buggy_send_shm_completion_event(display->display))
 	has_pixmap = 0;
 
     shm->has_pixmaps = has_pixmap ? MIN_PIXMAP_SIZE : 0;