[tip:perf/core] perf tools: Describe pipe mode in perf.data-file-fomat.txt

[tip-bot for David Carrillo-Cisneros]

Commit-ID:  6d13491e2d4944180c9b4fb6ddca4e34b1537836
Gitweb:     http://git.kernel.org/tip/6d13491e2d4944180c9b4fb6ddca4e34b1537836
Author:     David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
AuthorDate: Mon, 10 Apr 2017 13:14:28 -0700
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Tue, 11 Apr 2017 15:23:41 -0300

perf tools: Describe pipe mode in perf.data-file-fomat.txt

Add a minimal description of pipe's data format.

Signed-off-by: David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: He Kuang <hekuang@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Simon Que <sque@xxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170410201432.24807-4-davidcc@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/Documentation/perf.data-file-format.txt | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
index b664b18..fa2a913 100644
--- a/tools/perf/Documentation/perf.data-file-format.txt
+++ b/tools/perf/Documentation/perf.data-file-format.txt
@@ -11,8 +11,8 @@ All fields are in native-endian of the machine that generated the perf.data.
 
 When perf is writing to a pipe it uses a special version of the file
 format that does not rely on seeking to adjust data offsets.  This
-format is not described here. The pipe version can be converted to
-normal perf.data with perf inject.
+format is described in "Pipe-mode data" section. The pipe data version can be
+augmented with additional events using perf inject.
 
 The file starts with a perf_header:
 
@@ -411,6 +411,21 @@ An array bound by the perf_file_section size.
 
 ids points to a array of uint64_t defining the ids for event attr attr.
 
+Pipe-mode data
+
+Pipe-mode avoid seeks in the file by removing the perf_file_section and flags
+from the struct perf_header. The trimmed header is:
+
+struct perf_pipe_file_header {
+	u64				magic;
+	u64				size;
+};
+
+The information about attrs, data, and event_types is instead in the
+synthesized events PERF_RECORD_ATTR, PERF_RECORD_HEADER_TRACING_DATA and
+PERF_RECORD_HEADER_EVENT_TYPE that are generated by perf record in pipe-mode.
+
+
 References:
 
 include/uapi/linux/perf_event.h