dix: macro for checking X protocol types

The X protocol types from xorgproto all have corresponding sz_<typename>
defines with their actual network payload size (this can be checked via
SIZEOF() macro).

In theory, this should always be the same as sizeof(), but just to be sure,
adding a macro for a static assert on that.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

dix/dix_priv.h

@@ -38,6 +38,13 @@
         }                                       \
     } while (0)
 
+/* static assert for protocol structure sizes */
+#ifndef __size_assert
+#define __size_assert(what, howmuch) \
+  typedef char what##_size_wrong_[( !!(sizeof(what) == howmuch) )*2-1 ]
+#endif
+#define XTYPE_SIZE_ASSERT(typename) __size_assert(typename,SIZEOF(typename))
+
 /* server setting: maximum size for big requests */
 #define MAX_BIG_REQUEST_SIZE 4194303
 extern long maxBigRequestSize;