linux-kernel - Re: [PATCH] Documentation/trace: Correcting and extending tracepoint documentation

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Date:	Mon, 2 Sep 2013 18:02:47 +0100
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Rob Landley <rob@...dley.net>
CC:	Jiri Kosina <jkosina@...e.cz>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Bolle <pebolle@...cali.nl>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Documentation/trace: Correcting and extending tracepoint
 documentation

Hi,

I'm not very familiar with the tracing framework, but I will try to 
comment on your questions.

On 25/08/13 09:59, Rob Landley wrote:
> On 08/22/2013 04:49:31 PM, Zoltan Kiss wrote:
>> +#if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ)
>> +#define _TRACE_SUBSYS_H
>
> But this makes no sense to me: why is it needed? (I.E. why must it be
> block copied into each _user_ of tracepoints?)
This is to prevent header reinclusion, the second condition makes it 
possible to include it again from trace/define_trace.h

>>  #include <linux/tracepoint.h>
>>
>> @@ -48,10 +54,16 @@ DECLARE_TRACE(subsys_eventname,
>>      TP_PROTO(int firstarg, struct task_struct *p),
>>      TP_ARGS(firstarg, p));
>>
>> +#endif /* _TRACE_SUBSYS_H */
>> +
>> +/* This part must be outside protection */
>> +#include <trace/define_trace.h>
>> +
>
> Why? (Both why do you need to #include a header outside a multiple
> inclusion guard, and why is the additional header needed at all in
> _every_ subsystem trace header?)
I see only one inclusion guard here, the one above. define_trace.h 
should take effect at only one place, where CREATE_TRACE_POINTS is 
defined, to create the tracepoints exactly once. However I don't see as 
well why it should be outside protection. Maybe because the intentional 
header reinclusion in it?

Regards,

Zoli

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