xace: Add XaceHookIsSet helper function

Signed-off-by: Andrew Eikum <aeikum@codeweavers.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit 5dc2a9aae4)

Xext/xace.c

@@ -213,6 +213,21 @@ XaceHook(int hook, ...)
     return prv ? *prv : Success;
 }
 
+/* XaceHookIsSet
+ *
+ * Utility function to determine whether there are any callbacks listening on a
+ * particular XACE hook.
+ *
+ * Returns non-zero if there is a callback, zero otherwise.
+ */
+int
+XaceHookIsSet(int hook)
+{
+    if (hook < 0 || hook >= XACE_NUM_HOOKS)
+        return 0;
+    return XaceHooks[hook] != NULL;
+}
+
 /* XaceCensorImage
  *
  * Called after pScreen->GetImage to prevent pieces or trusted windows from

Xext/xace.h

@@ -65,6 +65,9 @@ extern _X_EXPORT int XaceHook(int /*hook */ ,
                               ...       /*appropriate args for hook */
     );
 
+/* determine whether any callbacks are present for the XACE hook */
+extern _X_EXPORT int XaceHookIsSet(int hook);
+
 /* Special-cased hook functions
  */
 extern _X_EXPORT int XaceHookDispatch(ClientPtr ptr, int major);