linux-kernel - Re: [ltt-dev] [PATCH] Simple LTTng userspace events through debugfs

Open Source and information security mailing list archives

Message-ID: <20081217041628.GA5409@Krystal>
Date:	Tue, 16 Dec 2008 23:16:28 -0500
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	ltt-dev@...ts.casi.polymtl.ca, Linus Torvalds <torvalds@...l.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [ltt-dev] [PATCH] Simple LTTng userspace events through debugfs

* Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > Hi,
> > 
> > I looked at kmemtrace and noticed that the presence of a debugfs 
> > "marker" file, which lets userspace write events into the trace buffers.
> > 
> > So I just did the same with a
> > 
> > /debugfs/ltt/write_event
> 
> you mean similar to ftrace's /debug/tracing/trace_marker ? ;-)
> 

Quite similar, yes :)

Looking at tracing_mark_write(), I am wondering if the fact that it
returns a count including the added \n is an expected side effect ? A
write() returning a count larger than the number of bytes written seems
to be a bit unexpected... But if we remove the \n from the count, then
the case where one write \0 into the event content would end up doing an
endless loop.

Mathieu

> 	Ingo
> 
> _______________________________________________
> ltt-dev mailing list
> ltt-dev@...ts.casi.polymtl.ca
> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
> 

-- 
Mathieu Desnoyers
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