[Buildroot] Package can create LINUX_FINAL_RECURSIVE_DEPENDENCIES

[Yann E. MORIN <yann.morin.1998@free.fr>]

Heiko, All,

On 2020-01-24 08:37 +0100, Heiko Thiery spake thusly:
> I have a custom package (MYPACKAGE) in my BR2_EXTERNAL. This package
> uses the "$(eval $(kernel-module))". In addition this package also
> adds a kernel patch hook via BR2_EXTERNAL/linux-ext-MYPACKAGE.mk.
> 
> As far as I see MYPACKAGE depends on linux (due to kernel-module) and
> LINUX depends on MYPACKAGE due to the dependency created to
> LINUX_PATCH_DEPENDENCIES.
> 
> ----
> # make linux-legal-info
> linux/linux.mk:578: *** Recursive variable
> 'LINUX_FINAL_RECURSIVE_DEPENDENCIES' references itself (eventually).
> Stop.
> make: *** [Makefile:23: _all] Error 2
> ----
> 
> Is having a package that does both (linux kernel module and kernel
> patching) allowed?

The linux-extensions are only _PATCH_DEPENDENCIES, that is the packages
providing the extensions shall be extracted and patched before linux is
patched.

So, as far as a build is concerned, this does not cause a circular
dependency.

However, as you noticed later, this does generate a circular dependency,
like gathering the elgal-info.

> Can this be fixed?

No, that 'can't be, I'm afraid... :-/

> I think linux only need the
> dependency to the MYPACKAGE_EXTRACT because the patch is not a result
> of the build of this package.

This is already the case, see above.

> What do you think?

As a short-term solution, just provide towo packages: one that provides
the extension, one that provides the kernel module.

However, if your package provides a kernel patch, why does it not patch
the kernel with your new module to begin with, and have the module built
as part of the kernel build? After all, that's the whole point of linux
extensions: inject new code in the kernel build process.

Regards,
Yann E. MORIN.

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