linux-kernel - Re: [PATCH] dynamic_debug: allow to set dynamic debug flags right at module load time

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Message-ID: <20100526183559.GA5094@redhat.com>
Date:	Wed, 26 May 2010 14:35:59 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Roman Fietze <roman.fietze@...emotive.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dynamic_debug: allow to set dynamic debug flags right
	at module load time

On Wed, May 26, 2010 at 02:25:38PM +0200, Roman Fietze wrote:
> Hello Jason, hello list,
> 
> If I'm not wrong one could only enable any dynamic debugging flag
> after a module had been completely loaded, using debugfs. This makes
> it impossible to use dev_dbg or pr_debug e.g. inside the module init
> function or any function called by it.
> 

yes, that's correct.

> My patch works by replacing _DPRINTK_FLAGS_DEFAULT after including all
> kernel headers in my module source file and some small patch inside
> dynamic_debug.c setting up the internal variables already when loading
> a module with flags unequal to zero. This patch can of course be
> optimized somewhat by reusing existing variables.
> 
> Subject: [PATCH] dynamic_debug: allow to set dynamic debug flags right at module load time
> 
> This allows to use e.g. pr_debug right from the beginning, e.g. in the
> module init function.
> 
> - the module must redefine _DPRINTK_FLAGS_DEFAULT, e.g.
> 
>   #undef _DPRINTK_FLAGS_DEFAULT
>   #define _DPRINTK_FLAGS_DEFAULT _DPRINTK_FLAGS_PRINT
> 
> - when a module is loaded and the flags are not zero, the enabled
>   count and hash masks are enabled right away
> 

it's a good idea, but i think we want this to be runtime configurable.
That is, we probably want this implemented as a module parameter, not as
a compile time thing. something like: modprobe module verbose=1

thanks,

-Jason
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