perf report: Display perf.data header info

Display more header info from perf.data file, following values:

  $ perf report -i perf.data --header-only
  ...
  # header version : 1
  # data offset    : 424
  # data size      : 3364280
  # feat offset    : 3364704

It's handy for debuging.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180307155020.32613-3-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.c

@@ -2318,7 +2318,12 @@ int perf_header__fprintf_info(struct perf_session *session, FILE *fp, bool full)
 	if (ret == -1)
 		return -1;
 
-	fprintf(fp, "# captured on: %s", ctime(&st.st_ctime));
+	fprintf(fp, "# captured on    : %s", ctime(&st.st_ctime));
+
+	fprintf(fp, "# header version : %u\n", header->version);
+	fprintf(fp, "# data offset    : %" PRIu64 "\n", header->data_offset);
+	fprintf(fp, "# data size      : %" PRIu64 "\n", header->data_size);
+	fprintf(fp, "# feat offset    : %" PRIu64 "\n", header->feat_offset);
 
 	perf_header__process_sections(header, fd, &hd,
 				      perf_file_section__fprintf_info);