From: Rusty Russell <rusty@rustcorp.com.au>
To: "Tim Hockin" <thockin@hockin.org>
Subject: Re: [patch 1/3] kmsg: Kernel message catalog macros.
Date: Sun, 17 Aug 2008 15:11:08 +1000
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Cc: schwidefsky@de.ibm.com, linux-kernel@vger.kernel.org,
       linux-s390@vger.kernel.org,
       lf_kernel_messages@lists.linux-foundation.org,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "Michael Holzheu" <holzheu@de.ibm.com>,
       "Gerrit Huizenga" <gh@us.ibm.com>,
       "Greg Kroah-Hartman" <gregkh@suse.de>,
       "Randy Dunlap" <randy.dunlap@oracle.com>, "Jan Kara" <jack@suse.cz>,
       "Pavel Machek" <pavel@ucw.cz>, "Sam Ravnborg" <sam@ravnborg.org>,
       "Joe Perches" <joe@perches.com>,
       "Jochen =?utf-8?q?Vo=C3=9F?=" <jochen.voss@googlemail.com>,
       "Kunai Takashi" <kunai@linux-foundation.jp>,
       "Tim Bird" <tim.bird@am.sony.com>
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On Sunday 17 August 2008 06:40:50 Tim Hockin wrote:
> On Sat, Aug 16, 2008 at 10:49 AM, Martin Schwidefsky
>
> <schwidefsky@de.ibm.com> wrote:
> >> > > 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.
> >
> > 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.
>
> And if you ever need to change the text that is in the format string?
> The hash changes.  That seems exactly counter to your goal...

You need to catalogue them all anyway, so you can detect clashes at build 
time.  Yes, you have to change the new string in that case, but that's easy.

And the number changing as the message changes is arguably a feature.  You 
shouldn't (and we generally don't) idly change kernel messages.

Rusty.


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