Yocto Project Linux Kernel Development Manual

The Yocto Project

Copyright © 2010-2020, The Linux Foundation

<docs@lists.yoctoproject.org>

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Note

• This version of this manual is for the 3.1 release of the Yocto Project. To be sure you have the latest version of the manual for this release, go to the Yocto Project documentation page and select the manual from that site. Manuals from the site are more up-to-date than manuals derived from the Yocto Project released TAR files.

• If you located this manual through a web search, the version of the manual might not be the one you want (e.g. the search might have returned a manual much older than the Yocto Project version with which you are working). You can see all Yocto Project major releases by visiting the Releases page. If you need a version of this manual for a different Yocto Project release, visit the Yocto Project documentation page and select the manual set by using the “ACTIVE RELEASES DOCUMENTATION” or “DOCUMENTS ARCHIVE” pull-down menus.

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Revision	Date	Note
1.4	April 2013	The initial document released with the Yocto Project 1.4 Release
1.5	October 2013	Released with the Yocto Project 1.5 Release.
1.6	April 2014	Released with the Yocto Project 1.6 Release.
1.7	October 2014	Released with the Yocto Project 1.7 Release.
1.8	April 2015	Released with the Yocto Project 1.8 Release.
2.0	October 2015	Released with the Yocto Project 2.0 Release.
2.1	April 2016	Released with the Yocto Project 2.1 Release.
2.2	October 2016	Released with the Yocto Project 2.2 Release.
2.3	May 2017	Released with the Yocto Project 2.3 Release.
2.4	October 2017	Released with the Yocto Project 2.4 Release.
2.5	May 2018	Released with the Yocto Project 2.5 Release.
2.6	November 2018	Released with the Yocto Project 2.6 Release.
2.7	May 2019	Released with the Yocto Project 2.7 Release.
3.0	October 2019	Released with the Yocto Project 3.0 Release.
3.1	April 2020	Released with the Yocto Project 3.1 Release.

Table of Contents

• 1. Introduction
  • 1.1. Overview
  • 1.2. Kernel Modification Workflow
• 2. Common Tasks
  • 2.1. Preparing the Build Host to Work on the Kernel
    • 2.1.1. Getting Ready to Develop Using devtool
    • 2.1.2. Getting Ready for Traditional Kernel Development
  • 2.2. Creating and Preparing a Layer
  • 2.3. Modifying an Existing Recipe
    • 2.3.1. Creating the Append File
    • 2.3.2. Applying Patches
    • 2.3.3. Changing the Configuration
    • 2.3.4. Using an “In-Tree”  defconfig File
  • 2.4. Using devtool to Patch the Kernel
  • 2.5. Using Traditional Kernel Development to Patch the Kernel
  • 2.6. Configuring the Kernel
    • 2.6.1. Using  menuconfig
    • 2.6.2. Creating a  defconfig File
    • 2.6.3. Creating Configuration Fragments
    • 2.6.4. Validating Configuration
    • 2.6.5. Fine-Tuning the Kernel Configuration File
  • 2.7. Expanding Variables
  • 2.8. Working with a “Dirty” Kernel Version String
  • 2.9. Working With Your Own Sources
  • 2.10. Working with Out-of-Tree Modules
    • 2.10.1. Building Out-of-Tree Modules on the Target
    • 2.10.2. Incorporating Out-of-Tree Modules
  • 2.11. Inspecting Changes and Commits
    • 2.11.1. What Changed in a Kernel?
    • 2.11.2. Showing a Particular Feature or Branch Change
  • 2.12. Adding Recipe-Space Kernel Features
• 3. Working with Advanced Metadata (yocto-kernel-cache)
  • 3.1. Overview
  • 3.2. Using Kernel Metadata in a Recipe
  • 3.3. Kernel Metadata Syntax
    • 3.3.1. Configuration
    • 3.3.2. Patches
    • 3.3.3. Features
    • 3.3.4. Kernel Types
    • 3.3.5. BSP Descriptions
      • 3.3.5.1. Overview
      • 3.3.5.2. Example
  • 3.4. Kernel Metadata Location
    • 3.4.1. Recipe-Space Metadata
    • 3.4.2. Metadata Outside the Recipe-Space
  • 3.5. Organizing Your Source
    • 3.5.1. Encapsulating Patches
    • 3.5.2. Machine Branches
    • 3.5.3. Feature Branches
  • 3.6. SCC Description File Reference
• 4. Advanced Kernel Concepts
  • 4.1. Yocto Project Kernel Development and Maintenance
  • 4.2. Yocto Linux Kernel Architecture and Branching Strategies
  • 4.3. Kernel Build File Hierarchy
  • 4.4. Determining Hardware and Non-Hardware Features for the Kernel Configuration Audit Phase
• 5. Kernel Maintenance
  • 5.1. Tree Construction
  • 5.2. Build Strategy
• 6. Kernel Development FAQ
  • 6.1. Common Questions and Solutions