linux-kernel - Re: [PATCH][RFC] tracing: Enable tracepoints via module parameters

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Message-ID: <20130813223453.GB15394@Krystal>
Date:	Tue, 13 Aug 2013 18:34:53 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Yuanhan Liu <yuanhan.liu@...ux.intel.com>,
	chris <chris@...is-wilson.co.uk>
Subject: Re: [PATCH][RFC] tracing: Enable tracepoints via module parameters

* Steven Rostedt (rostedt@...dmis.org) wrote:
[...]
> But the thing about this that bothers me is that there's no way to say,
> "Enable all tracepoints in this module on load". I would like a way to
> do that, but I don't know of a way to do that without modifying the
> module code. Have any ideas? Basically, I would love to have:
> 
> insmod foo tracepoints=all
> 
> or something and have all tracepoints enabled.

If it can help, here is a very similar scenario: tracepoints in
lttng-ust (user land) deal with dynamically loaded libraries that are
loaded at any point during program execution, which is very much similar
to the kernel module use-case discussed here.

The way a user interacts with lttng to enable, e.g. all tracepoints
within "app_component" would be:

lttng enable-event -u 'app_component:*'

Then, whenever a library containing tracepoints is loaded, the
tracepoints contained within the library are registered to lttng-ust,
and it enables all tracepoint matching the user-specified wildcard.

What I like about this approach, if applied to kernel modules, is that
it does not require users to interact with module load parameters to
specify which tracepoints should be enabled: this is all done through
the regular tracer UI, thus greatly improving user experience.

Thoughts ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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