diff --git a/documentation/dev-manual/common-tasks.rst b/documentation/dev-manual/common-tasks.rst index 1856d4c3ad..fd394c3ae2 100644 --- a/documentation/dev-manual/common-tasks.rst +++ b/documentation/dev-manual/common-tasks.rst @@ -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/${MACHINE}" + + The variables :term:`INITRAMFS_MULTICONFIG` and :term:`INITRAMFS_DEPLOY_DIR_IMAGE` + are used to create a multiconfig dependency from the kernel to the :term:`INITRAMFS_IMAGE` + to be built coming from the ``initramfscfg`` multiconfig, and to let the + buildsystem know where the :term:`INITRAMFS_IMAGE` will be located. + + Building a system with such configuration will build the kernel using the + main configuration but the ``do_bundle_initramfs`` task will grab the + selected :term:`INITRAMFS_IMAGE` from :term:`INITRAMFS_DEPLOY_DIR_IMAGE` + instead, resulting in a musl based initramfs image bundled in the kernel + but a glibc based main image. + + The same is applicable to avoid inheriting :term:`DISTRO_FEATURES` on :term:`INITRAMFS_IMAGE` + or to build a different :term:`DISTRO` for it such as ``poky-tiny``. + + Building a Tiny System ---------------------- diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst index d4f40b6929..caa9713935 100644 --- a/documentation/ref-manual/variables.rst +++ b/documentation/ref-manual/variables.rst @@ -3554,6 +3554,13 @@ system and gives an overview of their function and contents. even if the toolchain's binaries are strippable, there are other files needed for the build that are not strippable. + :term:`INITRAMFS_DEPLOY_DIR_IMAGE` + Indicates the deploy directory used by ``do_bundle_initramfs`` where the + :term:`INITRAMFS_IMAGE` will be fetched from. + This variable is set by default to ``${DEPLOY_DIR_IMAGE}`` in the + :ref:`kernel ` class and it's only meant to be changed + when building an initramfs image from a separate multiconfig via :term:`INITRAMFS_MULTICONFIG`. + :term:`INITRAMFS_FSTYPES` Defines the format for the output image of an initial RAM filesystem (initramfs), which is used during boot. Supported formats are the @@ -3673,6 +3680,16 @@ system and gives an overview of their function and contents. See the :term:`MACHINE` variable for additional information. + :term:`INITRAMFS_MULTICONFIG` + Defines the multiconfig to create a multiconfig dependency to be used by the :ref:`kernel ` class. + + This allows the kernel to bundle an :term:`INITRAMFS_IMAGE` coming from + a separate multiconfig, this is meant to be used in addition to :term:`INITRAMFS_DEPLOY_DIR_IMAGE`. + + For more information on how to bundle an initramfs image from a separate + multiconfig see the ":ref:`dev-manual/common-tasks:Bundling an Initramfs Image From a Separate Multiconfig`" + section in the Yocto Project Development Tasks Manual. + :term:`INITRAMFS_NAME` The base name of the initial RAM filesystem image. This variable is set in the ``meta/classes/kernel-artifact-names.bbclass`` file as