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

Steven Rostedt
2010-05-28T01:16:03Z

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>
> > +