linux-kernel - Re: [RFC] New kernel-message logging API (take 2)

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Message-Id: <DC4D133C-42B3-4CE3-A7A9-C507AE8A0B92@mac.com>
Date:	Fri, 28 Sep 2007 03:44:24 -0400
From:	Kyle Moffett <mrmacman_g4@....com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Vegard Nossum <vegard.nossum@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Joe Perches <joe@...ches.com>, Rob Landley <rob@...dley.net>,
	Dick Streefland <dick.streefland@...ium.nl>,
	Jesse Barnes <jesse.barnes@...el.com>,
	Arnd Bergmann <arnd@...db.de>,
	Jan Engelhardt <jengelh@...putergmbh.de>,
	Emil Medve <Emilian.Medve@...escale.com>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	"linux@...izon.com" <linux@...izon.com>
Subject: Re: [RFC] New kernel-message logging API (take 2)

On Sep 28, 2007, at 03:31:11, Geert Uytterhoeven wrote:
> Can't you store the loglevel in the kprint_block and check it in  
> all successive kprint_*() macros? If gcc knows it's constant, it  
> can optimize the non-wanted code away. As other fields in struct  
> kprint_block cannot be constant (they store internal state), you  
> have to split it like:
>
>     struct kprint_block {
> 	    int loglevel;
> 	    struct real_kprint_block real;  /* internal state */
>     }
>
> and pass &block.real() instead of &block to all successive internal  
> functions.  I haven't tried this, so let's hope gcc is actually  
> smart enough...

Well actually, I believe you could just do:

struct kprint_block {
	const int loglevel;
	[...];
};

Then cast away the constness to actually set it initially:
*((int *)&block.loglevel) = LOGLEVEL;

Cheers,
Kyle Moffett

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