perf probe: Show accessible local variables

Add -V (--vars) option for listing accessible local variables at given probe
point. This will help finding which local variables are available for event
arguments.

e.g.)
 # perf probe -V call_timer_fn:23
 Available variables at call_timer_fn:23
         @<run_timer_softirq+345>
                 function_type*  fn
                 int     preempt_count
                 long unsigned int       data
                 struct list_head        work_list
                 struct list_head*       head
                 struct timer_list*      timer
                 struct tvec_base*       base

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20101021101323.3542.40282.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index 5af3924..727a7fe 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -90,6 +90,12 @@
 	struct list_head	line_list;	/* Visible lines */
 };
 
+/* List of variables */
+struct variable_list {
+	struct probe_trace_point	point;	/* Actual probepoint */
+	struct strlist			*vars;	/* Available variables */
+};
+
 /* Command string to events */
 extern int parse_perf_probe_command(const char *cmd,
 				    struct perf_probe_event *pev);
@@ -115,6 +121,8 @@
 extern int del_perf_probe_events(struct strlist *dellist);
 extern int show_perf_probe_events(void);
 extern int show_line_range(struct line_range *lr);
+extern int show_available_vars(struct perf_probe_event *pevs, int npevs,
+			       int max_probe_points);
 
 
 /* Maximum index number of event-name postfix */