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Date: Fri, 25 Jun 2004 11:04:13 +0200
From: Lars Marowsky-Bree <lmb@suse.de>
To: Andreas Gruenbacher <agruen@suse.de>,
       Andreas Dilger <adilger@clusterfs.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: RFC: Testing for kernel features in external modules
Message-ID: <20040625090413.GM3956@marowsky-bree.de>
References: <20040624203043.GA4557@mars.ravnborg.org> <20040624203516.GV31203@schnapps.adilger.int> <200406251032.22797.agruen@suse.de>
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On 2004-06-25T10:32:22,
   Andreas Gruenbacher <agruen@suse.de> said:

> I disagree. I don't think we want to clutter the code with feature
> definitions that have no known users. That doesn't age/scale very
> well. It's easy enough to test for features in the external module.

True enough, but how do you propose to do that? I do understand the pain
of the external module builds who have to try and support the vanilla
kernel plus several vendor trees.

Yes, of course, we could end up with a autoconf like approach for
building them, but ... you know ... that's sort of ugly.

Having a list of defines to document the version of a specific API in
the kernel, and a set of defines pre-fixed with <vendor>_ to document
vendor tree extensions may not be the worst thing:

- if the vendor backports a given feature + API from mainstream, the
  define can be set to match the mainstream version;
- If vendor introduces a vendor API extension, the vendor extension
  would come into play.
- If the vendor API eventually merges with the mainstream API again, the
  vendor define goes away again and rule 1 applies.

This should age pretty well - as soon as an external code tree drops
support for a given version, they can clean out all the #ifdefs they had
based on this.

Now the granularity of the API versioning is interesting - per .h is too
coarse, and per-call would be too fine. But I'm sure someone could come
up with a sane proposal here.


Sincerely,
    Lars Marowsky-Br?e <lmb@suse.de>

-- 
High Availability & Clustering	    \ ever tried. ever failed. no matter.
SUSE Labs, Research and Development | try again. fail again. fail better.
SUSE LINUX AG - A Novell company    \ 	-- Samuel Beckett

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