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<p class="MsoNormal"><span lang="EN-GB">Hi all,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I am evaluating the feasibility of using LTTng as a backend for existing Qt tracepoints following the discussions at Qt Contributors Summit :
<a href="https://wiki.qt.io/QtCS2017_Discuss_Qt_Logging_enhancements">https://wiki.qt.io/QtCS2017_Discuss_Qt_Logging_enhancements</a> .<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">The idea would be to get less performance impact when tracing and more structured data to analyse without changing Qt users’ code.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I see that instead of describing all tracepoints, we could use a generic LTT tracepoint like in Python:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><a href="http://git.lttng.org/?p=lttng-ust.git;a=blob;f=liblttng-ust-python-agent/lttng_ust_python.h">http://git.lttng.org/?p=lttng-ust.git;a=blob;f=liblttng-ust-python-agent/lttng_ust_python.h</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Except, I would like to structure the tracepoint data at run-time following a JSON-based data model.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">But I am wondering how to pass this buffer along with its size to LTTng.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">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…<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Or should I use some other API?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Thanks for any advice on how to do that.<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-GB" style="mso-fareast-language:FR">Arnaud<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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