linux-kernel - Re: [PATCH] tracing: add trace console

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Date:	Wed, 16 Nov 2011 09:48:48 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] tracing: add trace console

On Wed, 2011-11-16 at 15:30 +0100, Johannes Berg wrote:
> On Wed, 2011-11-16 at 15:25 +0100, Peter Zijlstra wrote:
> 
> > > >  kernel/trace/Kconfig         |   13 ++++++++++
> > > >  kernel/trace/Makefile        |    2 +
> > > >  kernel/trace/trace-console.c |   55 +++++++++++++++++++++++++++++++++++++++++++
> > > >  3 files changed, 70 insertions(+)
> > > > 
> > > > --- a/kernel/trace/Kconfig    2011-11-16 11:11:27.000000000 +0100
> > > > +++ b/kernel/trace/Kconfig    2011-11-16 11:11:35.000000000 +0100
> > > > @@ -368,6 +368,19 @@ config BLK_DEV_IO_TRACE
> > > >  
> > > >         If unsure, say N.
> > > >  
> > > > +config TRACE_CONSOLE
> > > > +     tristate "Support for a tracing console"
> > > > +     help
> > > > +       Say M (or Y if you must, but this is not recommended) 
> > 
> > Why not?
> 
> It'll always be registered and you have no way to turn it off then, so
> you can't trace without getting every printk. I didn't want to add extra
> API to toggle it, but building it in might be a bit odd that way.

Actually, that's not quite true. You could just do:

echo 0 > /debug/tracing/options/trace_printk

-- Steve


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