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

[Lucian Buga]

Yann, All,

To be more precise, the patch fixes the host depmod utility from kmod package. 

Host depmod runs in target-finalize and in will create emty modules.dep if not buit with compression support.

So the issue is not insmod/modprobe on target. 

Regards,
Lucian

> On 3 May 2020, at 10:54, Yann E. MORIN <yann.morin.1998 at free.fr> wrote:
> 
> 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 at 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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> 
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