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

From: Jiri Olsa
Date: Fri May 01 2020 - 07:35:01 EST


From: Jiri Olsa <jolsa@xxxxxxxxxx>

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@xxxxxxxxxx/
Original-patch-by: Ian Rogers <irogers@xxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
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