Re: [docs] [PATCH v2] ref-manual: document KERNEL_SPLIT_MODULES variable

["Antonin Godard" <antonin.godard@bootlin.com>]

On Tue Jun 10, 2025 at 10:55 AM CEST, Antonin Godard wrote:
> On Sun Jun 8, 2025 at 12:44 PM CEST, Dixit Parmar via lists.yoctoproject.org wrote:
>> This variable controls the kernel module spliting.
>>
>> Signed-off-by: Dixit Parmar <dixitparmar19@gmail.com>
>> ---
>>  documentation/ref-manual/variables.rst | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
>> index 9768d8f5b..b7dde2604 100644
>> --- a/documentation/ref-manual/variables.rst
>> +++ b/documentation/ref-manual/variables.rst
>> @@ -5359,6 +5359,20 @@ system and gives an overview of their function and contents.
>>        the :term:`KERNEL_PATH` variable. Both variables are common variables
>>        used by external Makefiles to point to the kernel source directory.
>>  
>> +   :term:`KERNEL_SPLIT_MODULES`
>> +      When inheriting the :ref:`ref-classes-kernel-module-split` class, this
>> +      variable controls whether kernel modules are split into separate packages
>> +      or bundled into a single package.
>> +
>> +      For some use cases, a monolithic kernel module package
>> +      :ref:`KERNEL_PACKAGE_NAME` (by default named ``kernel``) that contains
>
> This should be :term:`KERNEL_PACKAGE_NAME` (not :ref:). Otherwise fails to
> build.
>
>> +      all modules built from the kernel sources may be preferred. Because a
>> +      monolithic package can reduce download time and speed up installation.
>
> I think this can be simplified by "...may be preferred to speed up
> installation". "Download time" is too context specific, probably related to
> package management on the target.
>
>> +
>> +      By default, this variable is set to ``1``, resulting in one package per
>> +      module. Setting it to any other value will generate a single monolithic
>> +      package containing all kernel modules.
>> +
>>     :term:`KERNEL_SRC`
>>        The location of the kernel sources. This variable is set to the value
>>        of the :term:`STAGING_KERNEL_DIR` within the :ref:`ref-classes-module`

Not sure about the "kernel" package name. After building with
KERNEL_SPLIT_MODULES to 0:

$ bitbake-getvar KERNEL_PACKAGE_NAME -r virtual/kernel
#
# $KERNEL_PACKAGE_NAME [2 operations]
#   set /build/../work/openembedded-core/meta/conf/documentation.conf:253
#     [doc] "Name prefix for kernel packages. Defaults to 'kernel'."
#   set /build/../work/openembedded-core/meta/classes-recipe/kernel.bbclass:11
#     [_defaultval] "kernel"
# pre-expansion value:
#   "kernel"
KERNEL_PACKAGE_NAME="kernel"

$ oe-pkgdata-util list-pkgs | grep kernel
kernel
kernel-base
kernel-dbg
kernel-dev
kernel-image
kernel-image-image
kernel-modules
kernel-vmlinux

$ oe-pkgdata-util list-pkg-files kernel-modules | head -7
kernel-modules:
        /lib/modules/6.12.30-yocto-standard/kernel/crypto/af_alg.ko
        /lib/modules/6.12.30-yocto-standard/kernel/crypto/algif_aead.ko
        /lib/modules/6.12.30-yocto-standard/kernel/crypto/algif_hash.ko
        /lib/modules/6.12.30-yocto-standard/kernel/crypto/algif_rng.ko
        /lib/modules/6.12.30-yocto-standard/kernel/crypto/algif_skcipher.ko
        /lib/modules/6.12.30-yocto-standard/kernel/crypto/blowfish_common.ko
        ...

So it seems to me that the name of the package is "kernel-modules", not
"kernel"?

Another side question: in my experience I never had to set KERNEL_SPLIT_MODULES
to be able to install *all* kernel modules. Whatever the value of
KERNEL_SPLIT_MODULES, installing the package "kernel-modules" would just install
the modules. So what is the difference after setting this variable?

Antonin

-- 
Antonin Godard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com