perf evlist: Support pipe mode display

Likewise, perf evlist command should print event attributes by reading
PERF_RECORD_HEADER_ATTR records.

Before:
  $ perf record -o- true | ./perf evlist -i-
  (prints nothing)

After:
  $ perf record -o- true | ./perf evlist -i-
  cycles:pppH

Committer testing:

Verbose mode also works as expected:

  $ perf record -o- true | perf evlist -i-
  cycles:uhH
  $ perf record -o- true | perf evlist -vi-
  cycles:uhH: size: 120, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|ID|PERIOD, read_format: ID, disabled: 1, inherit: 1, exclude_kernel: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
  $

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@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/20201210061302.88213-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-evlist.c

@@ -17,6 +17,14 @@
 #include "util/data.h"
 #include "util/debug.h"
 #include <linux/err.h>
+#include "util/tool.h"
+
+static int process_header_feature(struct perf_session *session __maybe_unused,
+				  union perf_event *event __maybe_unused)
+{
+	session_done = 1;
+	return 0;
+}
 
 static int __cmd_evlist(const char *file_name, struct perf_attr_details *details)
 {
@@ -27,12 +35,20 @@ static int __cmd_evlist(const char *file_name, struct perf_attr_details *details
 		.mode      = PERF_DATA_MODE_READ,
 		.force     = details->force,
 	};
+	struct perf_tool tool = {
+		/* only needed for pipe mode */
+		.attr = perf_event__process_attr,
+		.feature = process_header_feature,
+	};
 	bool has_tracepoint = false;
 
-	session = perf_session__new(&data, 0, NULL);
+	session = perf_session__new(&data, 0, &tool);
 	if (IS_ERR(session))
 		return PTR_ERR(session);
 
+	if (data.is_pipe)
+		perf_session__process_events(session);
+
 	evlist__for_each_entry(session->evlist, pos) {
 		evsel__fprintf(pos, details, stdout);