Re: [PATCH 0/2] kbuild updates

[Andreas Gruenbacher <agruen@suse.de>]

On Sunday 20 June 2004 23:52, Martin Schlemmer wrote:
> On Sun, 2004-06-20 at 23:42, Arjan van de Ven wrote:
> > > Given, but to 'use' the kbuild infrastructure, you must still call it
> > > via:
> > >
> > >   make -C _path_to_sources M=`pwd`
> >
> > I see no problem with requiring this though; requiring a correct
> > makefile is perfectly fine with me, and this is the only and documented
> > way for 2.6 already.
> > (And it's also the only way to build modules against Fedora Core 2
> > kernels by the way)
>
> I did not mean I have a problem with that.  Say you take svgalib, and
> you want the build system to automatically compile the kernel module,
> you might do something like:
>
> ---
> build_2_6_module:
> 	@make -C /lib/modules/`uname -r`/build M=`PWD`
> ---
>
> will break with proposed patch ...

No it won't.

You always need to figure out $(objtree) to build external modules, with or 
without a separate output directory. Many modules don't need to know 
$(srctree) explicitly at all.

In case you want to do something depending on the sources/confguration, there 
are two ways:
  - follow the new source symlink,
  - let kbuild take you to $(srctree): When the makefile in the M directory
    is included, the current working directory is $(srctree). besides, all the
    usual variables like $(srctree), $(objtree), CONFIG_* variables, etc. are
    all available. That's a good time to check for features, etc.

> And the point I wanted to make was that AFIAK
> '/lib/modules/`uname -r`/build' is an interface to figure
> out where the _sources_ for the current running kernel are
> located.

That's a misconception. At the minimum, you want to be able to build the 
module. Directly messing with the sources is usually wrong. I know external 
module authors like to do that nevertheless; in a few cases it's actually 
useful. Most of the time it really is not. Most external modules have totally 
braindead/broken makefiles.

Regards,
-- 
Andreas Gruenbacher <agruen@suse.de>
SUSE Labs, SUSE LINUX AG