perf evlist: Add --group option

Add '-g/--group' option for showing event groups.  For simplicity it is
currently not compatible with other options.

  $ perf evlist --group
  {ref-cycles,cycles}

  $ perf evlist
  ref-cycles
  cycles

Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1358845787-1350-20-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-evlist.c b/tools/perf/builtin-evlist.c
index 1312a5e..85a5e35 100644
--- a/tools/perf/builtin-evlist.c
+++ b/tools/perf/builtin-evlist.c
@@ -39,6 +39,8 @@
 	OPT_BOOLEAN('F', "freq", &details.freq, "Show the sample frequency"),
 	OPT_BOOLEAN('v', "verbose", &details.verbose,
 		    "Show all event attr details"),
+	OPT_BOOLEAN('g', "group", &symbol_conf.event_group,
+		    "Show event group information"),
 	OPT_END()
 	};
 	const char * const evlist_usage[] = {
@@ -50,5 +52,10 @@
 	if (argc)
 		usage_with_options(evlist_usage, options);
 
+	if (symbol_conf.event_group && (details.verbose || details.freq)) {
+		pr_err("--group option is not compatible with other options\n");
+		usage_with_options(evlist_usage, options);
+	}
+
 	return __cmd_evlist(input_name, &details);
 }