[PATCH] perf session: Try to read pipe data from file

[Jiri Olsa <jolsa@kernel.org>]

From: Jiri Olsa <jolsa@redhat.com>

Ian came with the idea of having support to read the pipe
data also from file [1]. Currently pipe mode files fails
like:

  $ perf record -o - sleep 1 > /tmp/perf.pipe.data
  $ perf report -i /tmp/perf.pipe.data
  incompatible file format (rerun with -v to learn more)

This patch adds the support to do that by trying the pipe
header first, and if its successfully detected, switching
the perf data to pipe mode.

[1] https://lore.kernel.org/lkml/20200409185744.255881-1-irogers@google.com/
Original-patch-by: Ian Rogers <irogers@google.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/perf/util/header.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 0ce47283a8a1..8ca709f938b8 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -3574,7 +3574,7 @@ static int perf_header__read_pipe(struct perf_session *session)
 		return -EINVAL;
 	}
 
-	return 0;
+	return f_header.size == sizeof(f_header) ? 0 : -1;
 }
 
 static int read_attr(int fd, struct perf_header *ph,
@@ -3676,7 +3676,7 @@ int perf_session__read_header(struct perf_session *session)
 	struct perf_file_header	f_header;
 	struct perf_file_attr	f_attr;
 	u64			f_id;
-	int nr_attrs, nr_ids, i, j;
+	int nr_attrs, nr_ids, i, j, err;
 	int fd = perf_data__fd(data);
 
 	session->evlist = evlist__new();
@@ -3685,8 +3685,16 @@ int perf_session__read_header(struct perf_session *session)
 
 	session->evlist->env = &header->env;
 	session->machines.host.env = &header->env;
-	if (perf_data__is_pipe(data))
-		return perf_header__read_pipe(session);
+
+	/*
+	 * We can read 'pipe' data event from regular file,
+	 * check for the pipe header regardless of source.
+	 */
+	err = perf_header__read_pipe(session);
+	if (!err || (err && perf_data__is_pipe(data))) {
+		data->is_pipe = true;
+		return err;
+	}
 
 	if (perf_file_header__read(&f_header, header, fd) < 0)
 		return -EINVAL;
-- 
2.25.4