[lttng-dev] Using LTTng for existing Qt-based tracepoints?

[Arnaud Clère]

Hi all,
I am evaluating the feasibility of using LTTng as a backend for existing Qt tracepoints following the discussions at Qt Contributors Summit : https://wiki.qt.io/QtCS2017_Discuss_Qt_Logging_enhancements .
The idea would be to get less performance impact when tracing and more structured data to analyse without changing Qt users' code.

I see that instead of describing all tracepoints, we could use a generic LTT tracepoint like in Python:
http://git.lttng.org/?p=lttng-ust.git;a=blob;f=liblttng-ust-python-agent/lttng_ust_python.h

Except, I would like to structure the tracepoint data at run-time following a JSON-based data model.
I think I could encode that part of CTF dynamically by appending binary user data, CTF variants, dynamically-sized CTF structures and sequences in a local buffer.

But I am wondering how to pass this buffer along with its size to LTTng.
I am afraid a TP_ARGS(void*, buffer) and TP_FIELDS(buffer) would not work since it would require LTTng to read the CTF in "buffer" to discover where it stops...

Or should I use some other API?

Thanks for any advice on how to do that.
Arnaud

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.lttng.org/pipermail/lttng-dev/attachments/20171019/753065a0/attachment.html>