[lttng-dev] instrumenting "tutorial" and RTAI

Philippe Proulx eeppeliteloop at gmail.com
Wed Nov 26 13:35:36 EST 2014

On Wed, Nov 26, 2014 at 11:59 AM,  <fmahn at technik-emden.de> wrote:
> Hello, right now I am reading the LTTng documentation and I am at the point
> with the "tutorial" for adding a tracepoint to the usb_probe_device(). I
> updated the files as instructed, rebuilt the kernel and bootet it, but the
> "/sys/kernel/debug/tracing/events/hello" directory wasnt created. It exists
> up to the debug directory, but the directory itself is empty. What could
> have gone wrong? Is this directory necessary? I still followed the other
> instructions and I was able to trace the USB event but I am curios about the
> directory.

No, this directory is not needed for LTTng to work, as you noticed yourself.
It's only a simple way to confirm your kernel TRACE_EVENT() tracepoints
exist using Ftrace. My guess is that debugfs is not mounted (usually mounted
at /sys/kernel/debug) on your system. But do not waste your time fixing
this, as you're able to record USB events with LTTng.

> Furthermore, I am planning to instrument an RTAI kernel (for my
> Bachelorthesis), so I can trace it with LTTng. Is it even possible with
> these methods?

I'll let others answer this as I never had the chance to have fun with RTAI ;-)

> Thank you for your time!
> PS:
> I am using an RTAI patched linux kernel with debian
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