perf report: Support --header-only for pipe mode

The --header-only checks file header and prints the feature data.  But
as pipe mode doesn't have it in the header it prints almost nothing.
Change it to process first few records until it founds HEADER_FEATURE.

Before:
  $ perf record -o- true | perf report -i- --header-only
  # ========
  # captured on    : Thu Dec 10 14:34:59 2020
  # header version : 1
  # data offset    : 0
  # data size      : 0
  # feat offset    : 0
  # ========
  #

After:
  $ perf record -o- true | perf report -i- --header-only
  # ========
  # captured on    : Thu Dec 10 14:49:11 2020
  # header version : 1
  # data offset    : 0
  # data size      : 0
  # feat offset    : 0
  # ========
  #
  # hostname : balhae
  # os release : 5.7.17-1xxx
  # perf version : 5.10.rc6.gdb0ea13c
  # arch : x86_64
  # nrcpus online : 8
  # nrcpus avail : 8
  # cpudesc : Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz
  # cpuid : GenuineIntel,6,142,12
  # total memory : 16158916 kB
  # cmdline : perf record -o- true
  # event : name = cycles, , id = { 81, 82, 83, 84, 85, 86, 87, 88 }, size = 120, ...
  # CPU_TOPOLOGY info available, use -I to display
  # NUMA_TOPOLOGY info available, use -I to display
  # pmu mappings: intel_pt = 9, intel_bts = 8, software = 1, power = 20, uprobe = 7, ...
  # time of first sample : 0.000000
  # time of last sample : 0.000000
  # sample duration :      0.000 ms
  # MEM_TOPOLOGY info available, use -I to display
  # cpu pmu capabilities: branches=32, max_precise=3, pmu_name=skylake
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20201210061302.88213-1-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-report.c

@@ -226,6 +226,8 @@ static int process_feature_event(struct perf_session *session,
 		pr_err("failed: wrong feature ID: %" PRI_lu64 "\n",
 		       event->feat.feat_id);
 		return -1;
+	} else if (rep->header_only) {
+		session_done = 1;
 	}
 
 	/*
@@ -1512,6 +1514,13 @@ int cmd_report(int argc, const char **argv)
 		perf_session__fprintf_info(session, stdout,
 					   report.show_full_info);
 		if (report.header_only) {
+			if (data.is_pipe) {
+				/*
+				 * we need to process first few records
+				 * which contains PERF_RECORD_HEADER_FEATURE.
+				 */
+				perf_session__process_events(session);
+			}
 			ret = 0;
 			goto error;
 		}