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documentation: Add multiconfig initramfs configuration:

Browse Source 
dev-manual/common-tasks.rst: Add section to create an initramfs
image from a separate multiconfig.

ref-manual/variables.rst: Add new variable definitions for
INITRAMFS_DEPLOY_DIR_IMAGE and INITRAMFS_MULTICONFIG

(From yocto-docs rev: 7853ab3df82c27ba309879a66a084b2e597dc1e5)

Signed-off-by: Alejandro Enedino Hernandez Samaniego <alhe@linux.microsoft.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Alejandro Hernandez Samaniego
2022-02-16 13:17:31 -07:00
committed by Richard Purdie
parent b6c1329501
commit 552ff6e3d5
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@@ -3919,6 +3919,48 @@ Follow these steps to create an initramfs image:
:term:`INITRAMFS_IMAGE_BUNDLE`
variable described earlier.
Bundling an Initramfs Image From a Separate Multiconfig
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There may be a case where we want to build an initramfs image which does not
inherit the same distro policy as our main image, for example, we may want
our main image to use ``TCLIBC="glibc"``, but to use ``TCLIBC="musl"`` in our initramfs
image to keep a smaller footprint. However, by performing the steps mentioned
above the initramfs image will inherit ``TCLIBC="glibc"`` without allowing us
to override it.
To achieve this, you need to perform some additional steps:
1. *Create a multiconfig for your initramfs image:* You can perform the steps
on ":ref:`dev-manual/common-tasks:building images for multiple targets using multiple configurations`" to create a separate multiconfig.
For the sake of simplicity let's assume such multiconfig is called: ``initramfscfg.conf`` and
contains the variables::
TMPDIR="${TOPDIR}/tmp-initramfscfg"
TCLIBC="musl"
2. *Set additional initramfs variables on your main configuration:*
Additionally, on your main configuration (``local.conf``) you need to set the
variables::
INITRAMFS_MULTICONFIG = "initramfscfg"
INITRAMFS_DEPLOY_DIR_IMAGE = "${TOPDIR}/tmp-initramfscfg/deploy/images/${MACHINE}"
The variables :term:`INITRAMFS_MULTICONFIG` and :term:`INITRAMFS_DEPLOY_DIR_IMAGE`
are used to create a multiconfig dependency from the kernel to the :term:`INITRAMFS_IMAGE`
to be built coming from the ``initramfscfg`` multiconfig, and to let the
buildsystem know where the :term:`INITRAMFS_IMAGE` will be located.
Building a system with such configuration will build the kernel using the
main configuration but the ``do_bundle_initramfs`` task will grab the
selected :term:`INITRAMFS_IMAGE` from :term:`INITRAMFS_DEPLOY_DIR_IMAGE`
instead, resulting in a musl based initramfs image bundled in the kernel
but a glibc based main image.
The same is applicable to avoid inheriting :term:`DISTRO_FEATURES` on :term:`INITRAMFS_IMAGE`
or to build a different :term:`DISTRO` for it such as ``poky-tiny``.
Building a Tiny System
----------------------