linux-kernel - Re: [patch 3/3] kmsg: convert xpram messages to kmsg api.

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Message-ID: <20080806201118.GB30086@suse.de>
Date:	Wed, 6 Aug 2008 13:11:19 -0700
From:	Greg KH <gregkh@...e.de>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
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>,
	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 3/3] kmsg: convert xpram messages to kmsg api.

On Wed, Aug 06, 2008 at 10:46:13AM +0200, Martin Schwidefsky wrote:
> On Tue, 2008-08-05 at 15:34 -0700, Greg KH wrote:
> > On Thu, Jul 31, 2008 at 10:33:42AM +0200, Martin Schwidefsky wrote:
> > > On Wed, 2008-07-30 at 12:43 -0700, Greg KH wrote:
> > > > On Wed, Jul 30, 2008 at 06:56:59PM +0200, Martin Schwidefsky wrote:
> > > > > Index: linux-2.6/Documentation/kmsg/s390/xpram
> > > > > ===================================================================
> > > > > --- /dev/null
> > > > > +++ linux-2.6/Documentation/kmsg/s390/xpram
> > > > > @@ -0,0 +1,54 @@
> > > > > +/*?
> > > > > + * Tag: xpram.1
> > > > 
> > > > Ick, so you are going to have to define a message number per file?
> > > > How is that going to work, it looks like you use ids 0-2 below in the .c
> > > > file, yet in this documentation file they are 1-3.  Off by one
> > > > somewhere?  :)
> > > 
> > > The kmsg number 0 is special, the message tag will not include the
> > > message number for id 0. And the script won't complain that the message
> > > description is missing.
> > 
> > Was "0 is special" defined anywhere that I missed?
> 
> >From the patch description of the kernel message catalog script:
> 
> The kmsg check is invoked with "make D=1" and reads the source files for
> all objects that are built by the current configuration and searches for
> matching kmsg descriptions for the kmsg messages in the source which
> have a messages id > 0. If a message description can not be found the
> script prints a blueprint and causes a make error.

Ok, but you don't describe messages with "0" in them :)

> > > > > +#define KMSG_COMPONENT "xpram"
> > > > 
> > > > Can't you just use KBUILD_MODULE_NAME instead?  That makes it one less
> > > > thing you have to define in the code (and forget about when moving files
> > > > around or cut-and-pasting).
> > > 
> > > Two reason why we don't want to use KBUILD_MODULE_NAME:
> > > 1) the message tag (message component + message id) should never change,
> > > if you change the code structure the module name might change as well.
> > 
> > Um, isn't that the point?  If the code structure changes, then perhaps
> > the message also should change?  If not, it's trival to adjust.
> 
> NO! The message nor the message tag should change if the message
> semantically still reports the same thing. If the meaning of the message
> changes then change the message AND the message tag.

Why can't the message reporting change?  What's the reluctance for
change here for something that did happen to move to a different file?
It shouldn't matter _at all_ as you are only looking at the
tags/messages for a specific kernel version to ensure they match up.
Any future kernel version might have different ones.

It's not like once you write a message/tag it will stay that way fixed
for all time, that's just not going to fly with the way the Linux kernel
is developed.

> > > 2) we want to be able to use the same kmsg component in multiple .c
> > > files. 
> > 
> > Why would this matter?  It's just a "tag", who cares about the actual
> > name?
> 
> The actual name is not really important, but if the name is choosen
> wisely it does convey information. Guess what "dasd.17" tells you
> something about the dasd driver, "zfcp.42" about the zfcp driver and so
> on. The code structure should not dictate how the message tag is
> created.

The message tag should not dictate anything except how to look it up
somehow.  So it doesn't matter if the name changes, as long as the
ability to get the real information is still there.

So the kernel could change the tags every other release and there would
be no problem.

thanks,

greg k-h
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