Book Image

Embedded Linux Development using Yocto Projects - Second Edition

By : Otavio Salvador, Daiane Angolini
Book Image

Embedded Linux Development using Yocto Projects - Second Edition

By: Otavio Salvador, Daiane Angolini

Overview of this book

Yocto Project is turning out to be the best integration framework for creating reliable embedded Linux projects. It has the edge over other frameworks because of its features such as less development time and improved reliability and robustness. Embedded Linux Development using Yocto Project starts with an in-depth explanation of all Yocto Project tools, to help you perform different Linux-based tasks. The book then moves on to in-depth explanations of Poky and BitBake. It also includes some practical use cases for building a Linux subsystem project using Yocto Project tools available for embedded Linux. The book also covers topics such as SDK, recipetool, and others. By the end of the book, you will have learned how to generate and run an image for real hardware boards and will have gained hands-on experience at building efficient Linux systems using Yocto Project.

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Table of Contents (22 chapters)
Title Page
Title Page
Credits
Credits
About the Authors
About the Authors
About the Reviewer
About the Reviewer
www.PacktPub.com
www.PacktPub.com
Customer Feedback
Customer Feedback
Preface
Preface
Free Chapter
1
Meeting the Yocto Project
Meeting the Yocto Project
What is the Yocto Project?
Delineating the Yocto Project
Understanding Poky
Using BitBake
OpenEmbedded-Core
Metadata
The alliance of the OpenEmbedded Project and the Yocto Project
Summary
2
Baking Our Poky-Based System
Baking Our Poky-Based System
Configuring a host system
Downloading the Poky source code
Preparing the build environment
Knowing the local.conf file
Building a target image
Running images in QEMU
Summary
3
Using Toaster to Bake an Image
Using Toaster to Bake an Image
What is Toaster?
Installing Toaster
Starting Toaster
Building an image to QEMU
Summary
4
Grasping the BitBake Tool
Grasping the BitBake Tool
Understanding the BitBake tool
Exploring metadata
Parsing metadata
Dependencies
Preferring and providing recipes
Fetching the source code
Understanding BitBake's tasks
Generating a root filesystem image
Summary
5
Detailing the Temporary Build Directory
Detailing the Temporary Build Directory
Detailing the build directory
Constructing the build directory
Exploring the temporary build directory
Understanding the work directory
Understanding the sysroot directories
Summary
6
Assimilating Packaging Support
Assimilating Packaging Support
Using supported package formats
Understanding shared state cache
Explaining package versioning
Specifying runtime package dependencies
Package feeds
Summary
7
Diving into BitBake Metadata
Diving into BitBake Metadata
Using metadata
Summary
8
Developing with the Yocto Project
Developing with the Yocto Project
Deciphering the software development kit
Working with the Poky SDK
Integrating with Eclipse
Summary
9
Debugging with the Yocto Project
Debugging with the Yocto Project
Differentiating metadata and application debugging
Tracking image, package, and SDK contents
Debugging packaging
Logging information during task execution
Utilizing a development shell
Using the GNU Project Debugger for debugging
Summary
10
Exploring External Layers
Exploring External Layers
Powering flexibility with layers
Detailing the layer's source code
Adding meta layers
The Yocto Project layer ecosystem
Summary
11
Creating Custom Layers
Creating Custom Layers
Making a new layer
Adding metadata to the layer
Creating an image
Adding a package recipe
Adding support to a new machine definition
Using a custom distribution
MACHINE_FEATURES versus DISTRO_FEATURES
Understanding the variables scope
Summary
12
Customizing Existing Recipes
Customizing Existing Recipes
Common use cases
Adding extra options to recipes based on Autoconf
Applying a patch
Adding extra files to the existing packages
Changing recipe feature configuration
Customizing BusyBox
Customizing the linux-yocto framework
Summary
13
Achieving GPL Compliance
Achieving GPL Compliance
Understanding copyleft
Managing software licensing with Poky
Using Poky to achieve copyleft compliance
Summary
14
Booting Our Custom Embedded Linux
Booting Our Custom Embedded Linux
Exploring the boards
Discovering the right BSP layer
Baking for the hardware
Booting our baked image
Next steps
Summary
Index
Index

Fetching the source code

When the Poky source code is downloaded, what is actually copied is the metadata and the BitBake tool. Additional source code is fetched on demand. One of the main features supported by BitBake is source code fetching.

This support has been designed to be as modular and as flexible as possible. Every Linux-based system includes the Linux kernel and several other utilities that form the root filesystem, such as OpenSSH or a Linux kernel.

The OpenSSH source code is available from its upstream website as a tar.gz file hosted on an HTTP server, while the Linux kernel release is usually hosted on a Git repository, and those two different source codes can easily be fetched by BitBake.

BitBake offers support for many different fetcher modules that allow the retrieval of tarball files and a number of other protocols, such as Git, Subversion, Bazaar, OSC, HTTP, HTTPS, FTP, CVS, Mercurial, Perforce, and SSH.

The mechanism used by BitBake to fetch the source code is internally...

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