Creating Friendly Layers - Yocto Project 2022 Edition

Overview

Explore the intricacies of creating compatible and well-designed Yocto Project layers in this 30-minute conference talk by Paul Barker. Learn essential design principles to maximize layer compatibility and ensure useful error messages when layers are used incorrectly. Gain a comprehensive understanding of variables, tasks, distro features, and overrides within the Yocto Project ecosystem. Discover proper techniques for using bbappends, conditionals, distro & machine features, and sanity checks. Examine examples of well-behaved layers and update your knowledge to target the Langdale (4.1) and Kirkstone (4.0, LTS) releases. Delve into topics such as layer documentation, simplifying layer.conf, adding new content, modifying existing recipes, using overrides and features, implementing conditional syntax, adding build-time checks, and utilizing anonymous Python functions and classes. Gain insights into the bblayers.conf parsing details and learn how to effectively use the yocto-check-layer script to improve your layer development process.

Syllabus

Intro
What is a Friendly Layer?
But Can't You Just Dynamically Set BBLAYERS?
Build a Friendly Community
Documenting Your Layer
Keep layer.conf Simple
Adding New Content in Layers
Modifying Existing Recipes
Avoid Network Access Outside do_fetch
Using Overrides
Example: Toolchain Override in meta-clang
Using Features
Conditional Syntax
Include vs Require Statements
Example: Distro Features in meta-virtualization
Example: Conditional Inheritance in meta-integrity
Adding Build-time Checks
Example: Checks in meta-virtualization
Using Anonymous Python Functions
Using Classes to Modify Recipes
Modifying BBCLASSEXTEND
yocto-check-layer Script
In Summary: Think About Downstream Developers
Appendix: bblayers.conf Parsing Details