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    Subject[tip:perf/core] perf tools: Describe pipe mode in perf.data-file-fomat.txt
    Commit-ID:  6d13491e2d4944180c9b4fb6ddca4e34b1537836
    Gitweb: http://git.kernel.org/tip/6d13491e2d4944180c9b4fb6ddca4e34b1537836
    Author: David Carrillo-Cisneros <davidcc@google.com>
    AuthorDate: Mon, 10 Apr 2017 13:14:28 -0700
    Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
    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@google.com>
    Acked-by: Jiri Olsa <jolsa@kernel.org>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: He Kuang <hekuang@huawei.com>
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Paul Turner <pjt@google.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Simon Que <sque@chromium.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Wang Nan <wangnan0@huawei.com>
    Link: http://lkml.kernel.org/r/20170410201432.24807-4-davidcc@google.com
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.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 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
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