virtchnl: Add a macro to check the size of a union

This patch adds a macro to check if the size of a union is correct.
It throws a divide by zero error if the union is not of the correct
size.
Signed-off-by: NHarshitha Ramamurthy <harshitha.ramamurthy@intel.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

include/linux/avf/virtchnl.h

@@ -140,13 +140,15 @@ enum virtchnl_ops {
 	VIRTCHNL_OP_DISABLE_CHANNELS = 31,
 };
 
-/* This macro is used to generate a compilation error if a structure
+/* These macros are used to generate compilation errors if a structure/union
  * is not exactly the correct length. It gives a divide by zero error if the
- * structure is not of the correct size, otherwise it creates an enum that is
- * never used.
+ * structure/union is not of the correct size, otherwise it creates an enum
+ * that is never used.
  */
 #define VIRTCHNL_CHECK_STRUCT_LEN(n, X) enum virtchnl_static_assert_enum_##X \
 	{ virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
+#define VIRTCHNL_CHECK_UNION_LEN(n, X) enum virtchnl_static_asset_enum_##X \
+	{ virtchnl_static_assert_##X = (n)/((sizeof(union X) == (n)) ? 1 : 0) }
 
 /* Virtual channel message descriptor. This overlays the admin queue
  * descriptor. All other data is passed in external buffers.