Re: [PATCH] Symlinks for building external modules

["Måns Rullgård" <mru@kth.se>]

Sam Ravnborg <sam@ravnborg.org> writes:

> On Fri, Jun 04, 2004 at 08:15:02PM +0300, Jari Ruusu wrote:
>> 
>> How long have you recommended building external modules like this:
>> 
>>  make -C /lib/modules/`uname -r`/build modules SUBDIRS=`pwd`
>>   or
>>  make -C /lib/modules/`uname -r`/build modules M=`pwd`
>> 
>> Now they all have to be changed to:
>> 
>>  make -C /lib/modules/`uname -r`/source modules SUBDIRS=`pwd`
>>   or
>>  make -C /lib/modules/`uname -r`/source modules M=`pwd`
>
> That would not work either.
> You need to tell kbuild both where to find the source and the output files.
> So you have to specify both -C ... and O=...
> KERNEL=/lib/modules/`uname -r`
> make -C $KERNEL/source O=$KERNEL/build M=`pwd`
>
> There is no way to do the proposed chang and be backward compatible
> when the kernel is build using seperate output directories.

There are many external module packages that assume
/lib/modules/`uname -r`/build to contain the kernel sources.  These
can be built with

  make O=/some/path

If the content of /lib/modules/`uname -r`/build changes this will no
longer work.

> Think of the following situation
> /usr/src/linux-2.6.6-xx/  <= kernel src
>
> /lib/modules/linux-2.6.6-xx-smp/build/ <= output files (or a symlink to them)
> /lib/modules/linux-2.6.6-xx-smp/source/ <= symlink to kernel src
>
> /lib/modules/linux-2.6.6-xx-up/build/ <= output files (or symlink)
> /lib/modules/linux-2.6.6-xx-up/source/ <= symlink to kernel src
>
> /lib/modules/linux-2.6.6-xx-4g/build/ <= output files (or symlink)
> /lib/modules/linux-2.6.6-xx-4g/source/ <= symlink to kernel src
>
> Notice they all share the _same_ kernel src.
> We just have three different .config files.
>
> If there is a way to be backward compatible with
> this feature please demonstrate it.
>
> Plese note that the patch Andreas made did not break existing setups
> if a seperate output directory was not used. The only effect
> would be an additional symlink to the same dir. (build and source would
> be links to the same dir).
>
> Andreas - please expalin why you want build to be a symlink, and not
> the directory used when actually building the kernel.

I can't speak for Andreas, but I prefer to keep my root filesystem as
clean as possible.  Often it's mounted read-only.

-- 
Måns Rullgård
mru@kth.se