Complete Yocto mirror with license table for TQMa6UL (2038-compliance)
- 264 license table entries with exact download URLs (224/264 resolved) - Complete sources/ directory with all BitBake recipes - Build configuration: tqma6ul-multi-mba6ulx, spaetzle (musl) - Full traceability for Softwarefreigabeantrag - GCC 13.4.0, Linux 6.6.102, U-Boot 2023.04, musl 1.2.4 - License distribution: GPL-2.0 (24), MIT (23), GPL-2.0+ (18), BSD-3 (16)
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sources/poky/documentation/kernel-dev/intro.rst
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sources/poky/documentation/kernel-dev/intro.rst
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.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
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************
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Introduction
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************
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Overview
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========
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Regardless of how you intend to make use of the Yocto Project, chances
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are you will work with the Linux kernel. This manual describes how to
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set up your build host to support kernel development, introduces the
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kernel development process, provides background information on the Yocto
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Linux kernel :term:`Metadata`, describes
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common tasks you can perform using the kernel tools, shows you how to
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use the kernel Metadata needed to work with the kernel inside the Yocto
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Project, and provides insight into how the Yocto Project team develops
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and maintains Yocto Linux kernel Git repositories and Metadata.
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Each Yocto Project release has a set of Yocto Linux kernel recipes,
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whose Git repositories you can view in the Yocto
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:yocto_git:`Source Repositories <>` under the "Yocto Linux Kernel"
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heading. New recipes for the release track the latest Linux kernel
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upstream developments from https://www.kernel.org and introduce
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newly-supported platforms. Previous recipes in the release are refreshed
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and supported for at least one additional Yocto Project release. As they
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align, these previous releases are updated to include the latest from
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the Long Term Support Initiative (LTSI) project. You can learn more
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about Yocto Linux kernels and LTSI in the
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":ref:`kernel-dev/concepts-appx:yocto project kernel development and maintenance`" section.
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Also included is a Yocto Linux kernel development recipe
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(``linux-yocto-dev.bb``) should you want to work with the very latest in
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upstream Yocto Linux kernel development and kernel Metadata development.
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.. note::
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For more on Yocto Linux kernels, see the
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":ref:`kernel-dev/concepts-appx:yocto project kernel development and maintenance`"
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section.
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The Yocto Project also provides a powerful set of kernel tools for
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managing Yocto Linux kernel sources and configuration data. You can use
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these tools to make a single configuration change, apply multiple
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patches, or work with your own kernel sources.
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In particular, the kernel tools allow you to generate configuration
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fragments that specify only what you must, and nothing more.
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Configuration fragments only need to contain the highest level visible
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``CONFIG`` options as presented by the Yocto Linux kernel ``menuconfig``
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system. Contrast this against a complete Yocto Linux kernel ``.config``
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file, which includes all the automatically selected ``CONFIG`` options.
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This efficiency reduces your maintenance effort and allows you to
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further separate your configuration in ways that make sense for your
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project. A common split separates policy and hardware. For example, all
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your kernels might support the ``proc`` and ``sys`` filesystems, but
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only specific boards require sound, USB, or specific drivers. Specifying
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these configurations individually allows you to aggregate them together
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as needed, but maintains them in only one place. Similar logic applies
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to separating source changes.
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If you do not maintain your own kernel sources and need to make only
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minimal changes to the sources, the released recipes provide a vetted
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base upon which to layer your changes. Doing so allows you to benefit
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from the continual kernel integration and testing performed during
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development of the Yocto Project.
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If, instead, you have a very specific Linux kernel source tree and are
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unable to align with one of the official Yocto Linux kernel recipes,
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you have a way to use the Yocto Project Linux kernel tools with your
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own kernel sources.
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The remainder of this manual provides instructions for completing
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specific Linux kernel development tasks. These instructions assume you
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are comfortable working with :oe_wiki:`BitBake </Bitbake>` recipes and basic
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open-source development tools. Understanding these concepts will
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facilitate the process of working with the kernel recipes. If you find
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you need some additional background, please be sure to review and
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understand the following documentation:
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- :doc:`/brief-yoctoprojectqs/index` document.
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- :doc:`/overview-manual/index`.
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- :ref:`devtool
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workflow <sdk-manual/extensible:using \`\`devtool\`\` in your sdk workflow>`
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as described in the Yocto Project Application Development and the
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Extensible Software Development Kit (eSDK) manual.
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- The ":ref:`dev-manual/layers:understanding and creating layers`"
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section in the Yocto Project Development Tasks Manual.
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- The ":ref:`kernel-dev/intro:kernel modification workflow`" section.
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Kernel Modification Workflow
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============================
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Kernel modification involves changing the Yocto Project kernel, which
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could involve changing configuration options as well as adding new
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kernel recipes. Configuration changes can be added in the form of
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configuration fragments, while recipe modification comes through the
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kernel's ``recipes-kernel`` area in a kernel layer you create.
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This section presents a high-level overview of the Yocto Project kernel
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modification workflow. The illustration and accompanying list provide
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general information and references for further information.
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.. image:: figures/kernel-dev-flow.png
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:width: 100%
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#. *Set up Your Host Development System to Support Development Using the
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Yocto Project*: See the ":doc:`/dev-manual/start`" section in
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the Yocto Project Development Tasks Manual for options on how to get
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a build host ready to use the Yocto Project.
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#. *Set Up Your Host Development System for Kernel Development:* It is
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recommended that you use ``devtool`` for kernel
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development. Alternatively, you can use traditional kernel
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development methods with the Yocto Project. Either way, there are
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steps you need to take to get the development environment ready.
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Using ``devtool`` requires that you have a clean build
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of the image. For
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more information, see the
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":ref:`kernel-dev/common:getting ready to develop using ``devtool```"
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section.
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Using traditional kernel development requires that you have the
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kernel source available in an isolated local Git repository. For more
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information, see the
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":ref:`kernel-dev/common:getting ready for traditional kernel development`"
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section.
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#. *Make Changes to the Kernel Source Code if applicable:* Modifying the
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kernel does not always mean directly changing source files. However,
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if you have to do this, you make the changes to the files in the
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Yocto's :term:`Build Directory` if you are using ``devtool``. For more
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information, see the
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":ref:`kernel-dev/common:using \`\`devtool\`\` to patch the kernel`"
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section.
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If you are using traditional kernel development, you edit the source
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files in the kernel's local Git repository. For more information, see the
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":ref:`kernel-dev/common:using traditional kernel development to patch the kernel`"
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section.
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#. *Make Kernel Configuration Changes if Applicable:* If your situation
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calls for changing the kernel's configuration, you can use
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:ref:`menuconfig <kernel-dev/common:using \`\`menuconfig\`\`>`,
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which allows you to
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interactively develop and test the configuration changes you are
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making to the kernel. Saving changes you make with ``menuconfig``
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updates the kernel's ``.config`` file.
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.. note::
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Try to resist the temptation to directly edit an existing ``.config``
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file, which is found in the :term:`Build Directory` among the source code
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used for the build. Doing so, can produce unexpected results when
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the OpenEmbedded build system regenerates the configuration file.
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Once you are satisfied with the configuration changes made using
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``menuconfig`` and you have saved them, you can directly compare the
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resulting ``.config`` file against an existing original and gather
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those changes into a
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:ref:`configuration fragment file <kernel-dev/common:creating configuration fragments>` to be
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referenced from within the kernel's ``.bbappend`` file.
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Additionally, if you are working in a BSP layer and need to modify
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the BSP's kernel's configuration, you can use ``menuconfig``.
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#. *Rebuild the Kernel Image With Your Changes:* Rebuilding the kernel
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image applies your changes. Depending on your target hardware, you
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can verify your changes on actual hardware or perhaps QEMU.
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The remainder of this developer's guide covers common tasks typically
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used during kernel development, advanced Metadata usage, and Yocto Linux
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kernel maintenance concepts.
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