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

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Message-ID: <20110309000753.GA27729@Krystal>
Date:	Tue, 8 Mar 2011 19:07:54 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	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:
> On Tue, 2011-03-08 at 18:22 -0500, Mathieu Desnoyers wrote:
> > * Steven Rostedt (rostedt@...dmis.org) wrote:
> > > A few months ago it was suggested to have a way to enable tracepoints in
> > > a module when it is loaded. I tried various methods, but this one seems
> > > to be the least intrusive. In fact, it requires no modification to the
> > > module code.
> > > 
> > > The trace event now adds its own MODULE_INFO() and kernel_param_ops that
> > > and links the information about a tracepoint into the module's __param
> > > section. A module can be loaded with a tracepoint active by adding
> > > trace_<tracepoint>=1 as one of the parameters.
> > 
> > Hi Steven,
> > 
> > Can you walk me through the expected sequence someone wanting to enable a few
> > specific module tracepoints would have to go through ? I'm thinking here about
> > the context of a distro which has on-demand module loading. The scenario I am
> > thinking about is a distro specifying a basic set of tracepoints to enable in a
> > "standard catch-all tracing configuration", which includes some tracepoints in
> > yet-unloaded modules. I'm trying to figure out what the end user experience will
> > look like if we go for the solution you propose here.
> > 
> 
> You would add it like any other module parameter.
> 
> Just update it in your /etc/modprobe.d/ directory.

So what you are saying here is that modifying /etc/modprobe.d/ is the actual
interface you propose presenting to the end-users to control their tracepoints ?

Maybe I am missing something, but this interface seems to lack the layer of
finish we might want to put into a user-visible API. I don't really see how
distributions can hope to automate any of this for their end-user without making
a mess of the /etc/modprobe.d/ they ship with.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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