[ltt-dev] [UST PATCH] Tracepoints: add noargs support

[mathieu.desnoyers@efficios.com (Mathieu Desnoyers)]

Add support for tracepoints receiving no argument as parameters. Copied
from Linux kernel:

commit 38516ab59fbc5b3bb278cf5e1fe2867c70cff32e
Author: Steven Rostedt <srostedt at redhat.com>
Date:   Tue Apr 20 17:04:50 2010 -0400

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
CC: Nils Carlson <nils.carlson at ericsson.com>
CC: Steven Rostedt <srostedt at redhat.com>
---
 include/ust/tracepoint.h |   25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

Index: ust/include/ust/tracepoint.h
===================================================================
--- ust.orig/include/ust/tracepoint.h
+++ ust/include/ust/tracepoint.h
@@ -175,10 +175,27 @@ static inline void tracepoint_update_pro
 { }
 #endif /* CONFIG_TRACEPOINTS */
 
-#define DECLARE_TRACE(name, proto, args)			\
-	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),	\
-			PARAMS(void *__data, proto),		\
-			PARAMS(__data, args))
+/*
+ * The need for the DECLARE_TRACE_NOARGS() is to handle the prototype
+ * (void). "void" is a special value in a function prototype and can
+ * not be combined with other arguments. Since the DECLARE_TRACE()
+ * macro adds a data element at the beginning of the prototype,
+ * we need a way to differentiate "(void *data, proto)" from
+ * "(void *data, void)". The second prototype is invalid.
+ *
+ * DECLARE_TRACE_NOARGS() passes "void" as the tracepoint prototype
+ * and "void *__data" as the callback prototype.
+ *
+ * DECLARE_TRACE() passes "proto" as the tracepoint protoype and
+ * "void *__data, proto" as the callback prototype.
+ */
+#define DECLARE_TRACE_NOARGS(name)					\
+		__DECLARE_TRACE(name, void, , void *__data, __data)
+
+#define DECLARE_TRACE(name, proto, args)				\
+		__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),	\
+				PARAMS(void *__data, proto),		\
+				PARAMS(__data, args))
 
 /*
  * Connect a probe to a tracepoint.

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com