In this chapter, we will initially explore the metadata (the basic concept) and recipes that are used by Poky (the dependencies among them). We will then look at the different ways in which BitBake downloads source code. We will end this chapter by presenting the tasks used by BitBake to get to the creation of the root filesystem image.
As presented in Chapter 1, Meeting the Yocto Project, BitBake is a task scheduler (like GNU Make) that parses shell and Python scripts. The code parsed generates and runs tasks (configure, compile, and so on), which are basically sets of steps ordered according to the code's dependencies.
Here are some points taken directly from the BitBake user manual:
- BitBake executes tasks according to the provided metadata, which builds up the tasks. Metadata is stored in recipe (
.bb), configuration (.conf), and class (.bbclass) files and provides BitBake with instructions on what tasks to run and the dependencies between those tasks. - BitBake includes a fetcher library for obtaining source code from various places, such as source control systems or websites.
- The instructions for each unit to be built (such as a piece of software) are known as recipe files and contain all the information about the unit (dependencies, source file locations, checksums, description, and so on).
- BitBake includes a client/server abstraction, can be used from a command line or as a service over XMLRPC, and has several different user interfaces.
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