Re: linux-module-builder leads to huge store items

[Ludovic Courtès]

Hello,

Danny Milosavljevic <dannym@scratchpost.org> skribis:

> On Thu, 10 Sep 2020 10:09:11 +0200
> Ludovic Courtès <ludovic.courtes@inria.fr> wrote:
>
>> Surely we don’t need that much just to build a kernel module.  :-)
>
> Since Linux is a monolithic kernel and since C has no modules: Yes, yes we
> do--in the general case.
>
> Linux kernel developers have no interest in supporting out-of-tree modules for
> free (and no interesting in having the Linux kernel API frozen) so there's no
> incentive to support a use case where you can compile a Linux kernel module
> without having the full source of the Linux kernel (that would be just asking
> for license abuse, too).

Understood.

> That would mean that we would have to both design and then support out-of-tree
> build infrastructure ourselves in Guix.  And for what?  It's only used when
> building the module--it will be thrown away afterwards anyway.
>
> Or is it not garbage-collected afterwards?  That would be a serious bug.

It *is* thrown-away afterwards.  But until then, it must be deduplicated
(upon build completion, reception, etc.), and that’s a lot of work I/O
wise given the large number of files.

>>   ;; TODO: Only preserve the minimum, i.e. [Kbuild], Kconfig,
>>   ;; scripts, include, ".config".
>> 
>> Which files exactly are needed?  Can we go ahead and implement this TODO?
>
> Who knows?

[...]

> Even if we did, there are much worse build-time storage space wastes
> (*cough* llvm *cough*).

But it’s build-time.

> That said, I did a quick size comparison and found those big items:
>
> 150 MB 
> a2fs24bgghjvlzq5lzr6zki7mqxx8mpi-linux-libre-module-builder-5.8.7/lib/modules/build/drivers/gpu/drm/amd/include/asic_reg
> 30 MB 
> a2fs24bgghjvlzq5lzr6zki7mqxx8mpi-linux-libre-module-builder-5.8.7/lib/modules/build/drivers/staging
>
> I don't think we need these in any potential Linux kernel module--but who
> knows?  Maybe somebody does need those.

So, I can think of the following ways to address that:

  1. Remove for example *.c, assuming the out-of-tree modules we package
     only care about *.h + build machinery.

  2. Don’t add all of the Linux source to the store, or at least not
     under a new name each time.  One way to do that would be to unpack
     the Linux-libre tree within the build tree of the out-of-tree
     module.  We’d be reducing GC stress at the expense of a
     (reasonable?) increase in module build time.

Thoughts?

Ludo’.