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

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Message-ID: <19f34abd0709280449s34042f9cxfeaa7364a3659f0@mail.gmail.com>
Date:	Fri, 28 Sep 2007 13:49:43 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Kyle Moffett" <mrmacman_g4@....com>
Cc:	"Geert Uytterhoeven" <geert@...ux-m68k.org>,
	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 9/28/07, Kyle Moffett <mrmacman_g4@....com> wrote:
> 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;

This doesn't seem to work either (i.e. it is not optimized out). I
tried initializing the struct statically too, to no avail. But thanks
for the tip.

Vegard
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