Re: RFC: Testing for kernel features in external modules

[Adrian Bunk <bunk@fs.tum.de>]

On Fri, Jun 25, 2004 at 11:04:13AM +0200, Lars Marowsky-Bree wrote:
> 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:
>...
> 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.

What's an API for modules?
- whether a .h file is present under include/
- every EXPORT_SYMBOL{,_GPL}'ed function
- every inlined function under include/
- every struct defined under include/
- perhaps more things I'm currently forgetting

Every change to something mentioned above during a development kernel 
needs to be cover by an appropriate API versioning.

And then consider as an example cases like a function returning 
irqreturn_t in 2.6:
- in 2.6, this function returns irqreturn_t (typedef'd to int)
- in 2.4, this function might return irqreturn_t (typedef'd to void)
- in 2.4, this function might return void

I'm sure there is a correct solution for such cases - but it's extra
work and easy to get things wrong.

Why do you dislike autoconf? I do not pretend autoconf where perfect -
but it works. Looking at the external ALSA, autoconf seems to be a good 
solution to probe for exact the things a module needs without a big 
overhead in kernel development.

> Sincerely,
>     Lars Marowsky-Brée <lmb@suse.de>

cu
Adrian

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