[Bug 772936] New: Allow outputting logs (in particualr tracer logs) in Common Trace Format (ctf)

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=772936

            Bug ID: 772936
           Summary: Allow outputting logs (in particualr tracer logs) in
                    Common Trace Format (ctf)
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: Normal
         Component: gstreamer (core)
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: tsaunier at gnome.org
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

Currently we are going through the standard GStreamer logging subsystem to
output the tracer logs, but it has several issues:

  * it has not been designed to output structured data
  * it is a plain text format which is not optimal at all in term of speed to
write as well as size of the output
  * it is not a standardized format and we need to write our own tools to
analyze the traces
  * we currently use a lock around each call to the debug function which is
suboptimal


Starting from that I think many of us agree (from conversations we had during
the hackfest) that a nice way to solve those issues would be to allow
outputting our traces as Common Trace Format[0]. This format is used by the
lttng[1] project and is the main tracing format outputted by the Linux kernel.
Many tools are available from the LTTNG project and we can use the
babeltrace[2] library to simplify CTF trace generation (the important part of
the library is licenced under MIT[3] so we should not have any problem using it
in GStreamer core ifaiu).

Also during the hackfest we talked about the possibility to use that same
format to ouput our debug logs, but that work will be part of another bug.

This feature can currently be activated through the
GST_DEBUG_FORMAT=ctf,directory=/some/dir environment variable, and this same
variable should be used for any format (still supporting the GST_DEBUG_FILE var
too).


I am attaching here the first iteration of the implementation.


[0] http://diamon.org/ctf/
[1] http://lttng.org/
[2] http://diamon.org/babeltrace/
[3] https://github.com/efficios/babeltrace/blob/master/LICENSE

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