[lttng-dev] WG: Reading CTF trace using Babeltrace API

[Salman Rafiq]

Hello All,

In continuation to my previous questions related to reading CTF traces from particular timestamp, I can now further summarize few problems/questions I have:


1.       Is it possible to seek CTF file_stream using 'begin' and 'end' iterator position i.e. BT_SEEK_TIME?



a.       We cannot use babel trace API for CTF iterator creation using defined start and end position based on time. Seems this is in progress?

b.      The other possible solution I am using, is to create the iterator using defaults, and then later use API to 'create iterator time position based on Raw Timestamp (only takes raw time)' and then 'set iterator position to that timed position'.



2.       But, since the area of interest for me was only the time when user application which I am tracing using Lttng-kernel tracer, started recording events (application use external trace recording format).

User application contains a definition file which tells me the epoch time (us resolution) when it started and stopped tracing. I wanted to use this information to set iterator positions.



a.       Question is Can I convert this time to raw time which babeltrace API takes as an argument?

b.      Or Is there any way to read Clock struct from CTF metadata file (is there any scope defined for this), so that I can extract offset variable value to convert epoch time from other trace to raw time?


It will be really great if I can get few suggestions/help related to these issues.
Thanking in anticipation!


Best Regards,

Salman Rafiq
Research Engineer
Industrial Communication
Fraunhofer-Einrichtung für Systeme der Kommunikationstechnik ESK

Hansastraße 32 | 80686 München
Telefon, Fax:  +49 89 547088-356 | +49 89 547088-66-356
E-Mail:   salman.rafiq at esk.fraunhofer.de<http://www.esk.fraunhofer.de/>

Internet:
http://www.esk.fraunhofer.de<http://www.esk.fraunhofer.de/>
http://www.facebook.com/FraunhoferESK
http://www.twitter.com/FraunhoferESK

Von: Salman Rafiq [mailto:salman.rafiq at esk.fraunhofer.de]
Gesendet: Mittwoch, 18. Juli 2012 15:28
An: lttng-dev at lists.lttng.org
Betreff: [lttng-dev] Reading CTF trace from time T

Hello All,

I am tracing a user application using lttng kernel tracer, i.e.,

Start lttng kernel trace
./application
Stop lttng kernel trace

Before I was reading kernel CTF trace using babeltrace API's from beginning of trace, e.g.,
struct  bt_iter_pos  begin_pos
struct bt_ctf_iter *iterator

begin_pos.type = BT_SEEK_BEGIN
iterator = create_iterator(context,  &begin_pos, NULL)
.. and then read events start from that iterator postion.

Recently, I have been trying to seek trace using timestamp from when the application started to application end.
I would like to know if I am doing it right. Would the method below enough to achieve this? Or I am missing something here :-S

begin_pos.type = BT_SEEK_TIME
end_pos.type = BT_SEEK_TIME

begin_pos.u.seek_time = timestamp1 (for now manually taken from CTF kernel trace when application started)
end_pos.u.seek_time = timestamp2 (for now manually taken from CTF kernel trace when application ended)

iterator = create_iterator(context,  &begin_pos, &end_pos);
and then with reading events at iterator position until end_pos.


I am using babeltrace package version "1.0.0-pre4".
Any help related to achieving this functionality will be highly appreciated.

Best Regards,
Salman


--
Salman Rafiq
Industrial Communication
Fraunhofer-Einrichtung für Systeme der Kommunikationstechnik ESK

Hansastraße 32 | 80686 München
Telefon, Fax:  +49 89 547088-356 | +49 89 547088-66-356
E-Mail:   salman.rafiq at esk.fraunhofer.de<http://www.esk.fraunhofer.de/>

Internet:
http://www.esk.fraunhofer.de<http://www.esk.fraunhofer.de/>
http://www.facebook.com/FraunhoferESK
http://www.twitter.com/FraunhoferESK

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