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

To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 1/6] writeback: initial tracing support
From: Steven Rostedt <rostedt@xxxxxxxxxxx>
Date: Thu, 27 May 2010 21:18:21 -0400
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, tytso@xxxxxxx, jens.axboe@xxxxxxxxxx
In-reply-to: <20100527143233.836b2c47.akpm@xxxxxxxxxxxxxxxxxxxx>
Organization: Kihon Technologies Inc.
References: <1274784852-30502-1-git-send-email-david@xxxxxxxxxxxxx> <1274784852-30502-2-git-send-email-david@xxxxxxxxxxxxx> <20100527143233.836b2c47.akpm@xxxxxxxxxxxxxxxxxxxx>
Reply-to: rostedt@xxxxxxxxxxx
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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