[Buildroot] [PATCH] package/kmod - fix host build dependecies

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

Lucian, All,

+Thomas +Peter: question for you.

On 2020-05-03 09:51 +0300, Lucian Buga spake thusly:
> When kernel is configured with CONFIG_MODULE_COMPRESS, host-kmod must
> be built with zlib / xz support to be able to properly generate
> dependency files for target.
> 
> Signed-off-by: Lucian Buga <lucianbuga@gmail.com>
> ---
>  package/kmod/kmod.mk | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/package/kmod/kmod.mk b/package/kmod/kmod.mk
> index e2dfea5c7b..7149658ac7 100644
> --- a/package/kmod/kmod.mk
> +++ b/package/kmod/kmod.mk
> @@ -35,11 +35,15 @@ endif
>  ifeq ($(BR2_PACKAGE_ZLIB),y)
>  KMOD_DEPENDENCIES += zlib
>  KMOD_CONF_OPTS += --with-zlib
> +HOST_KMOD_DEPENDENCIES += host-zlib
> +HOST_KMOD_CONF_OPTS += --with-zlib

At first, I was going to say that this was incorrect, because support
for gz/xz on the target should not mandate whether the host variant has
such support of not.

However, it is my understanding that the uncompressing of modules is
done by the modprobe/insmod, and the uncompressed blurb is handled to
the kernel.

If that is true, then indeed, this patch makes sense:

  - if the target variant does not have compression support, then it
    will not be able to load compresed modules, so it would be useless
    or the host variant to have compression support,

  - if the target variant has compression support, then it may have to
    handle compressed modules, and thus the host variant must have
    ompression support.

So this patch kinda makes sense in the end.

However, there is still a gotcha: the kernel can be configured to
compress modules on installation, and that is (in Buildroot) orthogonal
with the selection of BR2_PACKAGE_ZLIB or BR2_PACKAGE_XZ.

So, it would be invaliud, but possible to have a Buildroot configuration
that contains:

    # BR2_PACKAGE_ZLIB is not set
    # BR2_PACKAGE_XZ is not set

while at the same time having a kernel configuration that contains:

    CONFIG_MODULE_COMPRESS=y
    CONFIG_MODULE_COMPRESS_GZIP=y  (or XZ, you get the point)

To address this problem, I did a 6-patch series two years ago:
    https://git.buildroot.org/~ymorin/git/buildroot/log?h=yem/host-kmod

I just rebased it, but I did not pursue this endeavour much further than
just posting it once...

I think your patch is good, but I'd like some feedback from Thomas or
Peter. Or any other that can confirm who is responsible for
uncompressing kernel modules on load...

Regards,
Yann E. MORIN.

>  endif
>  
>  ifeq ($(BR2_PACKAGE_XZ),y)
>  KMOD_DEPENDENCIES += xz
>  KMOD_CONF_OPTS += --with-xz
> +HOST_KMOD_DEPENDENCIES += host-xz
> +HOST_KMOD_CONF_OPTS += --with-xz
>  endif
>  
>  ifeq ($(BR2_PACKAGE_PYTHON)$(BR2_PACKAGE_PYTHON3),y)
> -- 
> 2.17.1
> 
> _______________________________________________
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> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot

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