linux-kernel - Re: [PATCH 1/6] writeback: initial tracing support

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Message-ID: <1275009502.22648.582.camel@gandalf.stny.rr.com>
Date:	Thu, 27 May 2010 21:18:21 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Chinner <david@...morbit.com>, linux-kernel@...r.kernel.org,
	xfs@....sgi.com, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org, tytso@....edu, jens.axboe@...cle.com
Subject: Re: [PATCH 1/6] writeback: initial tracing support

On Thu, 2010-05-27 at 14:32 -0700, Andrew Morton wrote:

> > --- /dev/null
> > +++ b/include/trace/events/writeback.h
> > @@ -0,0 +1,171 @@
> > +#undef TRACE_SYSTEM
> > +#define TRACE_SYSTEM writeback
> > +
> > +#if !defined(_TRACE_WRITEBACK_H) || defined(TRACE_HEADER_MULTI_READ)
> 
> Seems wrong.  If you define TRACE_HEADER_MULTI_READ then include this
> header twice, things explode.  Which negates the purpose of
> _TRACE_WRITEBACK_H.

That's intended. It is documented in
samples/trace_events/trace-events-samples.h

The purpose of the TRACE_HEADER_MULTI_READ is to read the trace header
multi times. ;-)


You can also read about it here:

 http://lwn.net/Articles/379903/

here:

  http://lwn.net/Articles/381064/

and here:

   http://lwn.net/Articles/383362/

-- Steve

> 
> > +#define _TRACE_WRITEBACK_H
> > +
> > +#include <linux/backing-dev.h>
> > +#include <linux/writeback.h>
> > +

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