perf header: Display missing features

Display missing features in header info, like:

  $ perf report --header-only
  # ========
  # captured on: Mon Oct 10 09:39:47 2016
  ...
  # missing features: HEADER_TRACING_DATA HEADER_CPU_TOPOLOGY ...

To help in diagnosing problems.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-bh5gp84gobdmyl345dcp64se@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.c

@@ -2251,7 +2251,7 @@ int perf_header__fprintf_info(struct perf_session *session, FILE *fp, bool full)
 	struct perf_header *header = &session->header;
 	int fd = perf_data_file__fd(session->file);
 	struct stat st;
-	int ret;
+	int ret, bit;
 
 	hd.fp = fp;
 	hd.full = full;
@@ -2264,6 +2264,14 @@ int perf_header__fprintf_info(struct perf_session *session, FILE *fp, bool full)
 
 	perf_header__process_sections(header, fd, &hd,
 				      perf_file_section__fprintf_info);
+
+	fprintf(fp, "# missing features: ");
+	for_each_clear_bit(bit, header->adds_features, HEADER_LAST_FEATURE) {
+		if (bit)
+			fprintf(fp, "%s ", feat_ops[bit].name);
+	}
+
+	fprintf(fp, "\n");
 	return 0;
 }