linux-kernel - Re: [PATCH] markers: let marker

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Date:	Tue, 30 Sep 2008 09:15:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] markers: let marker_debug as module parameter


* Lai Jiangshan <laijs@...fujitsu.com> wrote:

> if we want to enable marker debug output, we have to modify
> the code and remake/reinstall the kernel in current code.
> 
> this patch enable marker_debug to be set when kernel start.
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> diff --git a/kernel/marker.c b/kernel/marker.c
> index 9f76c4a..5d8404f 100644
> --- a/kernel/marker.c
> +++ b/kernel/marker.c
> @@ -28,8 +28,9 @@
>  extern struct marker __start___markers[];
>  extern struct marker __stop___markers[];
>  
> -/* Set to 1 to enable marker debug output */
> -static const int marker_debug;
> +static int marker_debug;
> +module_param(marker_debug, bool, 0);
> +MODULE_PARM_DESC(marker_debug, "Set to 1 to enable marker debug output");

hm, in tip/master we already have ftrace_printk(), which allows such 
debug output to any of the active tracers. That is a far more useful way 
of debugging such things. See:

  http://people.redhat.com/mingo/tip.git/README

and:

  http://redhat.com/~mingo/sched-devel.git/readme-tracer.txt

note how much cleaner and more usable it will also become: no silly 
module flags or recompilation to activate this debug output, and no 
debug clutter in the syslog.

if you enable tracing in the 'nop' tracer then only the 
ftrace_printk()'s will be printed, no other trace entries.

	Ingo
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