tracing: Add DECLARE_TRACE_WITH_CALLBACK() macro

Introduce a new 'DECLARE_TRACE_WITH_CALLBACK()' macro, so that
tracepoints can associate an external register/unregister function.

This prepares for the syscalls tracer conversion to trace events. We
will need to perform arch level operations once a syscall event is
turned on/off, such as TIF flags setting, hence the need of such
specific callbacks.
Signed-off-by: Jason Baron <jbaron@redhat.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Jiaying Zhang <jiayingz@google.com>
Cc: Martin Bligh <mbligh@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

include/linux/tracepoint.h

@@ -60,8 +60,10 @@ struct tracepoint {
  * Make sure the alignment of the structure in the __tracepoints section will
  * not add unwanted padding between the beginning of the section and the
  * structure. Force alignment to the same alignment as the section start.
+ * An optional set of (un)registration functions can be passed to perform any
+ * additional (un)registration work.
  */
-#define DECLARE_TRACE(name, proto, args)				\
+#define DECLARE_TRACE_WITH_CALLBACK(name, proto, args, reg, unreg)	\
 	extern struct tracepoint __tracepoint_##name;			\
 	static inline void trace_##name(proto)				\
 	{								\
@@ -71,13 +73,30 @@ struct tracepoint {
 	}								\
 	static inline int register_trace_##name(void (*probe)(proto))	\
 	{								\
-		return tracepoint_probe_register(#name, (void *)probe);	\
+		int ret;						\
+		void (*func)(void) = reg;				\
+									\
+		ret = tracepoint_probe_register(#name, (void *)probe);	\
+		if (func && !ret)					\
+			func();						\
+		return ret;						\
 	}								\
 	static inline int unregister_trace_##name(void (*probe)(proto))	\
 	{								\
-		return tracepoint_probe_unregister(#name, (void *)probe);\
+		int ret;						\
+		void (*func)(void) = unreg;				\
+									\
+		ret = tracepoint_probe_unregister(#name, (void *)probe);\
+		if (func && !ret)					\
+			func();						\
+		return ret;						\
 	}
 
+
+#define DECLARE_TRACE(name, proto, args)				 \
+	DECLARE_TRACE_WITH_CALLBACK(name, TP_PROTO(proto), TP_ARGS(args),\
+					NULL, NULL);
+
 #define DEFINE_TRACE(name)						\
 	static const char __tpstrtab_##name[]				\
 	__attribute__((section("__tracepoints_strings"))) = #name;	\
@@ -94,7 +113,7 @@ extern void tracepoint_update_probe_range(struct tracepoint *begin,
 	struct tracepoint *end);
 
 #else /* !CONFIG_TRACEPOINTS */
-#define DECLARE_TRACE(name, proto, args)				\
+#define DECLARE_TRACE_WITH_CALLBACK(name, proto, args, reg, unreg)	\
 	static inline void _do_trace_##name(struct tracepoint *tp, proto) \
 	{ }								\
 	static inline void trace_##name(proto)				\
@@ -108,6 +127,10 @@ extern void tracepoint_update_probe_range(struct tracepoint *begin,
 		return -ENOSYS;						\
 	}
 
+#define DECLARE_TRACE(name, proto, args)				 \
+	DECLARE_TRACE_WITH_CALLBACK(name, TP_PROTO(proto), TP_ARGS(args),\
+					NULL, NULL);
+
 #define DEFINE_TRACE(name)
 #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
 #define EXPORT_TRACEPOINT_SYMBOL(name)