linux-kernel - Re: [patch 1/3] kmsg: Kernel message catalog macros.

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Date:	Sat, 16 Aug 2008 19:49:45 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	lf_kernel_messages@...ts.linux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Holzheu <holzheu@...ibm.com>,
	Gerrit Huizenga <gh@...ibm.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Jan Kara <jack@...e.cz>, Pavel Machek <pavel@....cz>,
	Sam Ravnborg <sam@...nborg.org>, Joe Perches <joe@...ches.com>,
	Jochen Voß <jochen.voss@...glemail.com>,
	Kunai Takashi <kunai@...ux-foundation.jp>,
	Tim Bird <tim.bird@...sony.com>
Subject: Re: [patch 1/3] kmsg: Kernel message catalog macros.

On Fri, 2008-08-15 at 09:22 +1000, Rusty Russell wrote:
> On Friday 15 August 2008 03:07:03 Martin Schwidefsky wrote:
> > On Wed, 2008-08-13 at 14:33 +1000, Rusty Russell wrote:
> > > On Thursday 31 July 2008 02:56:57 Martin Schwidefsky wrote:
> > > > From: Michael Holzheu <holzheu@...ibm.com>
> > > > From: Martin Schwidefsky <schwidefsky@...ibm.com>
> > > >
> > > > Introduce a new family of printk macros which prefixes each kmsg
> > > > message with a component name and allows to tag the printk with a
> > > > message id.
> > >
> > > Can you hash the format string to generate the id?  6 hex digits should
> > > be enough, and your tool can check for clashes.  As it's bad form to have
> > > identical strings for different semantics anyway, this seems to make
> > > sense.
> >
> > First, how do you do that with the C preprocessor? Second the kmsg-doc
> > script will check that the message format strings match if a kmsg with a
> > specific id is used in multiple locations.
> 
> Well, why would you do it with the preprocessor?  It's simplest to spit it out 
> at runtime.

Ok, so  a specialized version of printk will do the work to calculate
the hash. Only, what will we do if there ever is a conflict? The message
tag has to be unique. The shorter the hash is, the more likely a
collision gets. Don't know if 6 hash digits is enough to just ignore the
problem. 

> The (offline) catalogger will need to generate them, of course.
> Rusty.

Sounds doable to me.

-- 
blue skies,
  Martin.

"Reality continues to ruin my life." - Calvin.


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