Chapter 7. Diving into BitBake Metadata

At this point, we know how to generate images and packages, as well as how to use package feeds - basically everything we must know for simple usage of Poky. Hereafter, we will learn how to control the behavior of Poky to accomplish our goals and achieve maximum benefit from the Yocto Project as a whole.

In this chapter, we will enhance our understanding of the BitBake metadata syntax. We will learn to use the append, prepend, and remove operators to alter content from variables, variable expansions, and so on. These are the key concepts we can use to make our own recipes and customizations that we will learn about in Chapter 10, Exploring External Layers, Chapter 11, Creating Custom Layers, and Chapter 12, Customizing Existing Recipes.

Using metadata

The amount of metadata used by BitBake is enormous. To get the maximum benefit out of using Poky, we must master it. As we learned in Chapter 4, Grasping the BitBake Tool, metadata can be classified into the following three major areas:

• Configuration (the .conf files): Configuration files define the global content that is used to provide information and configure how the classes and recipes will work
• Classes (the .bbclass files): Classes are available to the whole system and can be inherited by recipes to easily maintain and avoid code duplication
• Recipes (the .bb or .bbappend files): The recipes describe the tasks to be run and provide the required information to allow BitBake to generate the required task chain. They are the most commonly used type of metadata as they are where we put it all at work. The most common types of recipes generate packages and images.

The classes and recipes are written in a mix of Python and shell scripting code. When a recipe is executed by BitBake...

Summary

In this chapter, we learned in detail about the BitBake metadata syntax; its operators to append, prepend, and remove content from variables; variable expansions; and so on, including some usage examples for them.

In the next chapter, we will learn how to use Poky to create external compilation tools and produce a root filesystem suitable for in target development. In addition, the possible use of Eclipse integration will be explained.