linux-kernel - Re: ftrace and debugfs weird interaction

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Message-ID: <20080428203411.GC27154@Krystal>
Date:	Mon, 28 Apr 2008 16:34:11 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Pekka Paalanen <pq@....fi>
Cc:	Ingo Molnar <mingo@...e.hu>, Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: ftrace and debugfs weird interaction

* Pekka Paalanen (pq@....fi) wrote:
> > * Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> > 
> > > Hi,
> > > 
> > > When trying to figure out what was going on with the sched tracer
> > > "tracing_enabled" file (sched-devel.git tree), I fell on this strange
> > > behavior :
> > > 
> > > echo 1>tracing_enabled seems _not_ to send 1 to the tracing_ctrl_write
> 
> Wait a minute, are you literally running the command:
> echo 1>tracing_enabled
> 
> If you are, you just echoed only a newline and directed stdout, stream 1,
> to the file. No? :-)
> 
> Could you try with a space:
> echo 1 > tracing_enabled
> 
> > > callback. However, sending garbage, e.g. echo s> tracing_enabled,
> > > correctly sends the 's' character down the chain. echo 0>tracing_enabled
> > > sometimes results in the callback not even being called.
> 
> Stream 0 is stdin, so... not sure what this would do. Probably nothing,
> just like you experienced.
> 

*duh*. Ok. That wasn't smart. You spotted the problem. Thanks a lot :)

Mathieu

> 
> Thanks.
> 
> -- 
> Pekka Paalanen
> http://www.iki.fi/pq/

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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