[PATCH 3/7] perf tool: describe pipe mode in perf.data-file-fomat.txt

[David Carrillo-Cisneros <davidcc@google.com>]

Add a minimal description of pipe's data format.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
 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 b664b18d3991..fa2a9132f0a9 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
-- 
2.12.2.715.g7642488e1d-goog