From 9e93251397788b73728afcf44372127de7b26332 Mon Sep 17 00:00:00 2001
From: Martin Willi <martin@revosec.ch>
Date: Wed, 22 Jan 2014 16:55:27 +0100
Subject: [PATCH] utils: Provide a CALLBACK macro, similar to METHOD, but for
 void* callbacks

Using the same mechanism as the METHOD macro, the CALLBACK macro defines
a hybrid function signature. It strictly uses a weak void* for the first
function parameter, in contrast to the dynamic METHOD object "this" type.
---
 src/libstrongswan/utils/utils.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/libstrongswan/utils/utils.h b/src/libstrongswan/utils/utils.h
index 75b31ec1b..53bfceda6 100644
--- a/src/libstrongswan/utils/utils.h
+++ b/src/libstrongswan/utils/utils.h
@@ -203,6 +203,19 @@ static inline bool memeq(const void *x, const void *y, size_t len)
 	static typeof(name) *_##name = (typeof(name)*)name; \
 	static ret name(this, ##__VA_ARGS__)
 
+/**
+ * Callback declaration/definition macro, allowing casted first parameter.
+ *
+ * This is very similar to METHOD, but instead of casting the first parameter
+ * to a public interface, it uses a void*. This allows type safe definition
+ * of a callback function, while using the real type for the first parameter.
+ */
+#define CALLBACK(name, ret, param1, ...) \
+	static ret _cb_##name(union {void *_generic; param1;} \
+	__attribute__((transparent_union)), ##__VA_ARGS__); \
+	static typeof(_cb_##name) *name = (typeof(_cb_##name)*)_cb_##name; \
+	static ret _cb_##name(param1, ##__VA_ARGS__)
+
 /**
  * Architecture independent bitfield definition helpers (at least with GCC).
  *