perf tools: Introduce stat perf.data header feature

Introducing the 'stat' feature to mark a perf.data as created by  the
'perf stat record' command. It contains no data.

It's needed so that the report tools (report/script) can differentiate
sampling data from counting data, because they need to be treated in a
different way.

In the future it might be used to store the version of the stat storage
system used.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Kan Liang <kan.liang@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1445784728-21732-28-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -452,6 +452,8 @@ static void record__init_features(struct record *rec)
 
 	if (!rec->opts.full_auxtrace)
 		perf_header__clear_feat(&session->header, HEADER_AUXTRACE);
+
+	perf_header__clear_feat(&session->header, HEADER_STAT);
 }
 
 static volatile int workload_exec_errno;

tools/perf/util/header.c

@@ -868,6 +868,13 @@ static int write_auxtrace(int fd, struct perf_header *h,
 	return err;
 }
 
+static int write_stat(int fd __maybe_unused,
+		      struct perf_header *h __maybe_unused,
+		      struct perf_evlist *evlist __maybe_unused)
+{
+	return 0;
+}
+
 static void print_hostname(struct perf_header *ph, int fd __maybe_unused,
 			   FILE *fp)
 {
@@ -1159,6 +1166,12 @@ static void print_auxtrace(struct perf_header *ph __maybe_unused,
 	fprintf(fp, "# contains AUX area data (e.g. instruction trace)\n");
 }
 
+static void print_stat(struct perf_header *ph __maybe_unused,
+		       int fd __maybe_unused, FILE *fp)
+{
+	fprintf(fp, "# contains stat data\n");
+}
+
 static void print_pmu_mappings(struct perf_header *ph, int fd __maybe_unused,
 			       FILE *fp)
 {
@@ -1948,6 +1961,7 @@ static const struct feature_ops feat_ops[HEADER_LAST_FEATURE] = {
 	FEAT_OPP(HEADER_PMU_MAPPINGS,	pmu_mappings),
 	FEAT_OPP(HEADER_GROUP_DESC,	group_desc),
 	FEAT_OPP(HEADER_AUXTRACE,	auxtrace),
+	FEAT_OPA(HEADER_STAT,		stat),
 };
 
 struct header_print_data {

tools/perf/util/header.h

@@ -31,6 +31,7 @@ enum {
 	HEADER_PMU_MAPPINGS,
 	HEADER_GROUP_DESC,
 	HEADER_AUXTRACE,
+	HEADER_STAT,
 	HEADER_LAST_FEATURE,
 	HEADER_FEAT_BITS	= 256,
 };