tracing: add event trace infrastructure

This patch creates the event tracing infrastructure of ftrace.
It will create the files:

 /debug/tracing/available_events
 /debug/tracing/set_event

The available_events will list the trace points that have been
registered with the event tracer.

set_events will allow the user to enable or disable an event hook.

example:

 # echo sched_wakeup > /debug/tracing/set_event

Will enable the sched_wakeup event (if it is registered).

 # echo "!sched_wakeup" >> /debug/tracing/set_event

Will disable the sched_wakeup event (and only that event).

 # echo > /debug/tracing/set_event

Will disable all events (notice the '>')

 # cat /debug/tracing/available_events > /debug/tracing/set_event

Will enable all registered event hooks.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

include/asm-generic/vmlinux.lds.h

@@ -61,6 +61,14 @@
 #define BRANCH_PROFILE()
 #endif
 
+#ifdef CONFIG_EVENT_TRACER
+#define FTRACE_EVENTS()	VMLINUX_SYMBOL(__start_ftrace_events) = .;	\
+			*(_ftrace_events)				\
+			VMLINUX_SYMBOL(__stop_ftrace_events) = .;
+#else
+#define FTRACE_EVENTS()
+#endif
+
 /* .data section */
 #define DATA_DATA							\
 	*(.data)							\
@@ -81,7 +89,8 @@
 	*(__tracepoints)						\
 	VMLINUX_SYMBOL(__stop___tracepoints) = .;			\
 	LIKELY_PROFILE()		       				\
-	BRANCH_PROFILE()
+	BRANCH_PROFILE()						\
+	FTRACE_EVENTS()
 
 #define RO_DATA(align)							\
 	. = ALIGN((align));						\