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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Getting Started With Yocto Project</title><link rel="stylesheet" type="text/css" href="getting-started-style.css" /><meta name="generator" content="DocBook XSL Stylesheets V1.76.1" /></head><body><div xml:lang="en" class="book" title="Getting Started With Yocto Project" id="getting-started-manual" lang="en"><div class="titlepage"><div><div><h1 class="title">
Getting Started With Yocto Project
</h1></div><div><div class="authorgroup">
<div class="author"><h3 class="author"><span class="firstname">Scott</span> <span class="surname">Rifenbark</span></h3><div class="affiliation">
<span class="orgname">Scotty's Documentation Services, INC<br /></span>
</div><code class="email"><<a class="email" href="mailto:srifenbark@gmail.com">srifenbark@gmail.com</a>></code></div>
</div></div><div><p class="copyright">Copyright © 2010-2018 Linux Foundation</p></div><div><div class="legalnotice" title="Legal Notice"><a id="idm45705112624512"></a>
<p>
Permission is granted to copy, distribute and/or modify this document under
the terms of the <a class="ulink" href="http://creativecommons.org/licenses/by-sa/2.0/uk/" target="_top">
Creative Commons Attribution-Share Alike 2.0 UK: England & Wales</a> as published by
Creative Commons.
</p>
<div class="note" title="Manual Notes" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Manual Notes</h3>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
This version of the
<span class="emphasis"><em>Yocto Project Overview Manual</em></span>
is for the 2.5 release of the
Yocto Project.
To be sure you have the latest version of the manual
for this release, use the manual from the
<a class="ulink" href="http://www.yoctoproject.org/documentation" target="_top">Yocto Project documentation page</a>.
</p></li><li class="listitem"><p>
For manuals associated with other releases of the Yocto
Project, go to the
<a class="ulink" href="http://www.yoctoproject.org/documentation" target="_top">Yocto Project documentation page</a>
and use the drop-down "Active Releases" button
and choose the manual associated with the desired
Yocto Project.
</p></li><li class="listitem"><p>
To report any inaccuracies or problems with this
manual, send an email to the Yocto Project
discussion group at
<code class="filename">yocto@yoctoproject.com</code> or log into
the freenode <code class="filename">#yocto</code> channel.
</p></li></ul></div>
</div>
</div></div><div><div class="revhistory"><table border="1" width="100%" summary="Revision history"><tr><th align="left" valign="top" colspan="2"><strong>Revision History</strong></th></tr>
<tr><td align="left">Revision 2.5</td><td align="left">April 2018</td></tr><tr><td align="left" colspan="2">The initial document released with the Yocto Project 2.5 Release.</td></tr>
</table></div></div></div><hr /></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="chapter"><a href="#overview-manual-intro">1. The Yocto Project Overview Manual</a></span></dt><dd><dl><dt><span class="section"><a href="#overview-welcome">1.1. Welcome</a></span></dt><dt><span class="section"><a href="#overview-other-information">1.2. Other Information</a></span></dt></dl></dd><dt><span class="chapter"><a href="#overview-development-environment">2. The Yocto Project Development Environment</a></span></dt><dd><dl><dt><span class="section"><a href="#yp-intro">2.1. Introduction</a></span></dt><dt><span class="section"><a href="#open-source-philosophy">2.2. Open Source Philosophy</a></span></dt><dt><span class="section"><a href="#workflows">2.3. Workflows</a></span></dt><dt><span class="section"><a href="#git">2.4. Git</a></span></dt><dd><dl><dt><span class="section"><a href="#repositories-tags-and-branches">2.4.1. Repositories, Tags, and Branches</a></span></dt><dt><span class="section"><a href="#basic-commands">2.4.2. Basic Commands</a></span></dt></dl></dd><dt><span class="section"><a href="#yocto-project-repositories">2.5. Yocto Project Source Repositories</a></span></dt><dt><span class="section"><a href="#licensing">2.6. Licensing</a></span></dt><dt><span class="section"><a href="#recipe-syntax">2.7. Recipe Syntax</a></span></dt><dt><span class="section"><a href="#development-concepts">2.8. Development Concepts</a></span></dt><dd><dl><dt><span class="section"><a href="#user-configuration">2.8.1. User Configuration</a></span></dt><dt><span class="section"><a href="#metadata-machine-configuration-and-policy-configuration">2.8.2. Metadata, Machine Configuration, and Policy Configuration</a></span></dt><dt><span class="section"><a href="#sources-dev-environment">2.8.3. Sources</a></span></dt><dt><span class="section"><a href="#package-feeds-dev-environment">2.8.4. Package Feeds</a></span></dt><dt><span class="section"><a href="#bitbake-dev-environment">2.8.5. BitBake</a></span></dt><dt><span class="section"><a href="#images-dev-environment">2.8.6. Images</a></span></dt><dt><span class="section"><a href="#sdk-dev-environment">2.8.7. Application Development SDK</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#overview-concepts">3. Yocto Project Concepts</a></span></dt><dd><dl><dt><span class="section"><a href="#yocto-project-components">3.1. Yocto Project Components</a></span></dt><dd><dl><dt><span class="section"><a href="#usingpoky-components-bitbake">3.1.1. BitBake</a></span></dt><dt><span class="section"><a href="#usingpoky-components-metadata">3.1.2. Metadata (Recipes)</a></span></dt><dt><span class="section"><a href="#metadata-virtual-providers">3.1.3. Metadata (Virtual Providers)</a></span></dt><dt><span class="section"><a href="#usingpoky-components-classes">3.1.4. Classes</a></span></dt><dt><span class="section"><a href="#usingpoky-components-configuration">3.1.5. Configuration</a></span></dt></dl></dd><dt><span class="section"><a href="#cross-development-toolchain-generation">3.2. Cross-Development Toolchain Generation</a></span></dt><dt><span class="section"><a href="#shared-state-cache">3.3. Shared State Cache</a></span></dt><dd><dl><dt><span class="section"><a href="#overall-architecture">3.3.1. Overall Architecture</a></span></dt><dt><span class="section"><a href="#overview-checksums">3.3.2. Checksums (Signatures)</a></span></dt><dt><span class="section"><a href="#shared-state">3.3.3. Shared State</a></span></dt><dt><span class="section"><a href="#tips-and-tricks">3.3.4. Tips and Tricks</a></span></dt></dl></dd><dt><span class="section"><a href="#automatically-added-runtime-dependencies">3.4. Automatically Added Runtime Dependencies</a></span></dt><dt><span class="section"><a href="#fakeroot-and-pseudo">3.5. Fakeroot and Pseudo</a></span></dt><dt><span class="section"><a href="#wayland">3.6. Wayland</a></span></dt><dd><dl><dt><span class="section"><a href="#wayland-support">3.6.1. Support</a></span></dt><dt><span class="section"><a href="#enabling-wayland-in-an-image">3.6.2. Enabling Wayland in an Image</a></span></dt><dt><span class="section"><a href="#running-weston">3.6.3. Running Weston</a></span></dt></dl></dd><dt><span class="section"><a href="#overview-licenses">3.7. Licenses</a></span></dt><dd><dl><dt><span class="section"><a href="#usingpoky-configuring-LIC_FILES_CHKSUM">3.7.1. Tracking License Changes</a></span></dt><dt><span class="section"><a href="#enabling-commercially-licensed-recipes">3.7.2. Enabling Commercially Licensed Recipes</a></span></dt></dl></dd><dt><span class="section"><a href="#x32">3.8. x32 psABI</a></span></dt></dl></dd></dl></div>
<div class="chapter" title="Chapter 1. The Yocto Project Overview Manual" id="overview-manual-intro"><div class="titlepage"><div><div><h2 class="title">Chapter 1. The Yocto Project Overview Manual<span class="permalink"><a alt="Permalink" title="Permalink" href="#overview-manual-intro">¶</a></span></h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="section"><a href="#overview-welcome">1.1. Welcome</a></span></dt><dt><span class="section"><a href="#overview-other-information">1.2. Other Information</a></span></dt></dl></div><div class="section" title="1.1. Welcome"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="overview-welcome">1.1. Welcome<span class="permalink"><a alt="Permalink" title="Permalink" href="#overview-welcome">¶</a></span></h2></div></div></div><p>
Welcome to the Yocto Project Overview Manual!
This manual introduces the Yocto Project by providing concepts,
software overviews, best-known-methods (BKMs), and any other
high-level introductory information suitable for a new Yocto
Project user.
</p><p>
The following list describes what you can get from this manual:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<span class="emphasis"><em>Major Topic:</em></span>
Provide a high-level description of this major topic.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Major Topic:</em></span>
Provide a high-level description of this major topic.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Major Topic:</em></span>
Provide a high-level description of this major topic.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Major Topic:</em></span>
Provide a high-level description of this major topic.
</p></li></ul></div><p>
</p><p>
This manual does not give you the following:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<span class="emphasis"><em>Step-by-step Instructions for Development Tasks:</em></span>
Instructional procedures reside in other manuals within
the Yocto Project documentation set.
For example, the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html" target="_top">Yocto Project Development Tasks Manual</a>
provides examples on how to perform various development
tasks.
As another example, the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/sdk-manual/sdk-manual.html" target="_top">Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</a>
manual contains detailed instructions on how to install an
SDK, which is used to develop applications for target
hardware.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Reference Material:</em></span>
This type of material resides in an appropriate reference
manual.
For example, system variables are documented in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html" target="_top">Yocto Project Reference Manual</a>.
As another example, the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bsp-guide/bsp-guide.html" target="_top">Yocto Project Board Support Package (BSP) Developer's Guide</a>
contains reference information on BSPs.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Detailed Public Information Not Specific to the
Yocto Project:</em></span>
For example, exhaustive information on how to use the
Source Control Manager Git is better covered with Internet
searches and official Git Documentation than through the
Yocto Project documentation.
</p></li></ul></div><p>
</p></div><div class="section" title="1.2. Other Information"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="overview-other-information">1.2. Other Information<span class="permalink"><a alt="Permalink" title="Permalink" href="#overview-other-information">¶</a></span></h2></div></div></div><p>
Because this manual presents information for many different
topics, supplemental information is recommended for full
comprehension.
For additional introductory information on the Yocto Project, see
the <a class="ulink" href="http://www.yoctoproject.org" target="_top">Yocto Project Website</a>.
You can find an introductory to using the Yocto Project by working
through the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/yocto-project-qs/yocto-project-qs.html" target="_top">Yocto Project Quick Start</a>.
</p><p>
For a comprehensive list of links and other documentation, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#resources-links-and-related-documentation" target="_top">Links and Related Documentation</a>"
section in the Yocto Project Reference Manual.
</p></div></div>
<div class="chapter" title="Chapter 2. The Yocto Project Development Environment" id="overview-development-environment"><div class="titlepage"><div><div><h2 class="title">Chapter 2. The Yocto Project Development Environment<span class="permalink"><a alt="Permalink" title="Permalink" href="#overview-development-environment">¶</a></span></h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="section"><a href="#yp-intro">2.1. Introduction</a></span></dt><dt><span class="section"><a href="#open-source-philosophy">2.2. Open Source Philosophy</a></span></dt><dt><span class="section"><a href="#workflows">2.3. Workflows</a></span></dt><dt><span class="section"><a href="#git">2.4. Git</a></span></dt><dd><dl><dt><span class="section"><a href="#repositories-tags-and-branches">2.4.1. Repositories, Tags, and Branches</a></span></dt><dt><span class="section"><a href="#basic-commands">2.4.2. Basic Commands</a></span></dt></dl></dd><dt><span class="section"><a href="#yocto-project-repositories">2.5. Yocto Project Source Repositories</a></span></dt><dt><span class="section"><a href="#licensing">2.6. Licensing</a></span></dt><dt><span class="section"><a href="#recipe-syntax">2.7. Recipe Syntax</a></span></dt><dt><span class="section"><a href="#development-concepts">2.8. Development Concepts</a></span></dt><dd><dl><dt><span class="section"><a href="#user-configuration">2.8.1. User Configuration</a></span></dt><dt><span class="section"><a href="#metadata-machine-configuration-and-policy-configuration">2.8.2. Metadata, Machine Configuration, and Policy Configuration</a></span></dt><dt><span class="section"><a href="#sources-dev-environment">2.8.3. Sources</a></span></dt><dt><span class="section"><a href="#package-feeds-dev-environment">2.8.4. Package Feeds</a></span></dt><dt><span class="section"><a href="#bitbake-dev-environment">2.8.5. BitBake</a></span></dt><dt><span class="section"><a href="#images-dev-environment">2.8.6. Images</a></span></dt><dt><span class="section"><a href="#sdk-dev-environment">2.8.7. Application Development SDK</a></span></dt></dl></dd></dl></div><p>
This chapter takes a look at the Yocto Project development
environment and also provides a detailed look at what goes on during
development in that environment.
The chapter provides Yocto Project Development environment concepts that
help you understand how work is accomplished in an open source environment,
which is very different as compared to work accomplished in a closed,
proprietary environment.
</p><p>
Specifically, this chapter addresses open source philosophy, workflows,
Git, source repositories, licensing, recipe syntax, and development
syntax.
</p><div class="section" title="2.1. Introduction"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="yp-intro">2.1. Introduction<span class="permalink"><a alt="Permalink" title="Permalink" href="#yp-intro">¶</a></span></h2></div></div></div><p>
The Yocto Project is an open-source collaboration project whose
focus is for developers of embedded Linux systems.
Among other things, the Yocto Project uses an
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-system-term" target="_top">OpenEmbedded build system</a>.
The build system, which is based on the OpenEmbedded (OE) project and
uses the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#bitbake-term" target="_top">BitBake</a> tool,
constructs complete Linux images for architectures based on ARM, MIPS,
PowerPC, x86 and x86-64.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
Historically, the OpenEmbedded build system, which is the
combination of BitBake and OE components, formed a reference
build host that was known as
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#poky" target="_top">Poky</a>"
(<span class="emphasis"><em>Pah</em></span>-kee).
The term "Poky", as used throughout the Yocto Project Documentation
set, can have different meanings.
</div><p>
The Yocto Project provides various ancillary tools for the embedded
developer and also features the Sato reference User Interface, which
is optimized for stylus-driven, low-resolution screens.
</p><div class="mediaobject" align="center"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="720"><tr><td align="center"><img src="figures/YP-flow-diagram.png" align="middle" width="720" /></td></tr></table></div><p>
Here are some highlights for the Yocto Project:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
Provides a recent Linux kernel along with a set of system
commands and libraries suitable for the embedded
environment.
</p></li><li class="listitem"><p>
Makes available system components such as X11, GTK+, Qt,
Clutter, and SDL (among others) so you can create a rich user
experience on devices that have display hardware.
For devices that do not have a display or where you wish to
use alternative UI frameworks, these components need not be
installed.
</p></li><li class="listitem"><p>
Creates a focused and stable core compatible with the
OpenEmbedded project with which you can easily and reliably
build and develop.
</p></li><li class="listitem"><p>
Fully supports a wide range of hardware and device emulation
through the Quick EMUlator (QEMU).
</p></li><li class="listitem"><p>
Provides a layer mechanism that allows you to easily extend
the system, make customizations, and keep them organized.
</p></li></ul></div><p>
You can use the Yocto Project to generate images for many kinds
of devices.
As mentioned earlier, the Yocto Project supports creation of
reference images that you can boot within and emulate using QEMU.
The standard example machines target QEMU full-system
emulation for 32-bit and 64-bit variants of x86, ARM, MIPS, and
PowerPC architectures.
Beyond emulation, you can use the layer mechanism to extend
support to just about any platform that Linux can run on and that
a toolchain can target.
</p><p>
Another Yocto Project feature is the Sato reference User
Interface.
This optional UI that is based on GTK+ is intended for devices with
restricted screen sizes and is included as part of the
OpenEmbedded Core layer so that developers can test parts of the
software stack.
</p><p>
While the Yocto Project does not provide a strict testing framework,
it does provide or generate for you artifacts that let you perform
target-level and emulated testing and debugging.
Additionally, if you are an
<span class="trademark">Eclipse</span>™ IDE user, you can
install an Eclipse Yocto Plug-in to allow you to develop within that
familiar environment.
</p><p>
By default, using the Yocto Project to build an image creates a Poky
distribution.
However, you can create your own distribution by providing key
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#metadata" target="_top">Metadata</a>.
A good example is Angstrom, which has had a distribution
based on the Yocto Project since its inception.
Other examples include commercial distributions like
<a class="ulink" href="https://www.yoctoproject.org/organization/wind-river-systems" target="_top">Wind River Linux</a>,
<a class="ulink" href="https://www.yoctoproject.org/organization/mentor-graphics" target="_top">Mentor Embedded Linux</a>,
<a class="ulink" href="https://www.yoctoproject.org/organization/enea-ab" target="_top">ENEA Linux</a>
and <a class="ulink" href="https://www.yoctoproject.org/ecosystem/member-organizations" target="_top">others</a>.
See the "<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#creating-your-own-distribution" target="_top">Creating Your Own Distribution</a>"
section in the Yocto Project Development Tasks Manual for more
information.
</p></div><div class="section" title="2.2. Open Source Philosophy"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="open-source-philosophy">2.2. Open Source Philosophy<span class="permalink"><a alt="Permalink" title="Permalink" href="#open-source-philosophy">¶</a></span></h2></div></div></div><p>
Open source philosophy is characterized by software development
directed by peer production and collaboration through an active
community of developers.
Contrast this to the more standard centralized development models
used by commercial software companies where a finite set of developers
produces a product for sale using a defined set of procedures that
ultimately result in an end product whose architecture and source
material are closed to the public.
</p><p>
Open source projects conceptually have differing concurrent agendas,
approaches, and production.
These facets of the development process can come from anyone in the
public (community) that has a stake in the software project.
The open source environment contains new copyright, licensing, domain,
and consumer issues that differ from the more traditional development
environment.
In an open source environment, the end product, source material,
and documentation are all available to the public at no cost.
</p><p>
A benchmark example of an open source project is the Linux kernel,
which was initially conceived and created by Finnish computer science
student Linus Torvalds in 1991.
Conversely, a good example of a non-open source project is the
<span class="trademark">Windows</span>® family of operating
systems developed by
<span class="trademark">Microsoft</span>® Corporation.
</p><p>
Wikipedia has a good historical description of the Open Source
Philosophy
<a class="ulink" href="http://en.wikipedia.org/wiki/Open_source" target="_top">here</a>.
You can also find helpful information on how to participate in the
Linux Community
<a class="ulink" href="http://ldn.linuxfoundation.org/book/how-participate-linux-community" target="_top">here</a>.
</p></div><div class="section" title="2.3. Workflows"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="workflows">2.3. Workflows<span class="permalink"><a alt="Permalink" title="Permalink" href="#workflows">¶</a></span></h2></div></div></div><p>
This section provides workflow concepts using the Yocto Project and
Git.
In particular, the information covers basic practices that describe
roles and actions in a collaborative development environment.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
If you are familiar with this type of development environment, you
might not want to read this section.
</div><p>
</p><p>
The Yocto Project files are maintained using Git in "master"
branches whose Git histories track every change and whose structures
provides branches for all diverging functionality.
Although there is no need to use Git, many open source projects do so.
</p><p>
</p><p>
For the Yocto Project, a key individual called the "maintainer" is
responsible for the "master" branch of a given Git repository.
The "master" branch is the “upstream” repository from which final or
most recent builds of the project occur.
The maintainer is responsible for accepting changes from other
developers and for organizing the underlying branch structure to
reflect release strategies and so forth.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>For information on finding out who is responsible for (maintains)
a particular area of code, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#how-to-submit-a-change" target="_top">Submitting a Change to the Yocto Project</a>"
section of the Yocto Project Development Tasks Manual.
</div><p>
</p><p>
The Yocto Project <code class="filename">poky</code> Git repository also has an
upstream contribution Git repository named
<code class="filename">poky-contrib</code>.
You can see all the branches in this repository using the web interface
of the
<a class="ulink" href="http://git.yoctoproject.org" target="_top">Source Repositories</a> organized
within the "Poky Support" area.
These branches temporarily hold changes to the project that have been
submitted or committed by the Yocto Project development team and by
community members who contribute to the project.
The maintainer determines if the changes are qualified to be moved
from the "contrib" branches into the "master" branch of the Git
repository.
</p><p>
Developers (including contributing community members) create and
maintain cloned repositories of the upstream "master" branch.
The cloned repositories are local to their development platforms and
are used to develop changes.
When a developer is satisfied with a particular feature or change,
they "push" the changes to the appropriate "contrib" repository.
</p><p>
Developers are responsible for keeping their local repository
up-to-date with "master".
They are also responsible for straightening out any conflicts that
might arise within files that are being worked on simultaneously by
more than one person.
All this work is done locally on the developer’s machine before
anything is pushed to a "contrib" area and examined at the maintainer’s
level.
</p><p>
A somewhat formal method exists by which developers commit changes
and push them into the "contrib" area and subsequently request that
the maintainer include them into "master".
This process is called “submitting a patch” or "submitting a change."
For information on submitting patches and changes, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#how-to-submit-a-change" target="_top">Submitting a Change to the Yocto Project</a>"
section in the Yocto Project Development Tasks Manual.
</p><p>
To summarize the development workflow: a single point of entry
exists for changes into the project’s "master" branch of the
Git repository, which is controlled by the project’s maintainer.
And, a set of developers exist who independently develop, test, and
submit changes to "contrib" areas for the maintainer to examine.
The maintainer then chooses which changes are going to become a
permanent part of the project.
</p><p>
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 270px"><td align="left"><img src="figures/git-workflow.png" align="left" height="270" /></td></tr></table><p>
</p><p>
While each development environment is unique, there are some best
practices or methods that help development run smoothly.
The following list describes some of these practices.
For more information about Git workflows, see the workflow topics in
the
<a class="ulink" href="http://book.git-scm.com" target="_top">Git Community Book</a>.
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<span class="emphasis"><em>Make Small Changes:</em></span>
It is best to keep the changes you commit small as compared to
bundling many disparate changes into a single commit.
This practice not only keeps things manageable but also allows
the maintainer to more easily include or refuse changes.</p><p>It is also good practice to leave the repository in a
state that allows you to still successfully build your project.
In other words, do not commit half of a feature,
then add the other half as a separate, later commit.
Each commit should take you from one buildable project state
to another buildable state.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Use Branches Liberally:</em></span>
It is very easy to create, use, and delete local branches in
your working Git repository.
You can name these branches anything you like.
It is helpful to give them names associated with the particular
feature or change on which you are working.
Once you are done with a feature or change and have merged it
into your local master branch, simply discard the temporary
branch.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Merge Changes:</em></span>
The <code class="filename">git merge</code> command allows you to take
the changes from one branch and fold them into another branch.
This process is especially helpful when more than a single
developer might be working on different parts of the same
feature.
Merging changes also automatically identifies any collisions
or "conflicts" that might happen as a result of the same lines
of code being altered by two different developers.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Manage Branches:</em></span>
Because branches are easy to use, you should use a system
where branches indicate varying levels of code readiness.
For example, you can have a "work" branch to develop in, a
"test" branch where the code or change is tested, a "stage"
branch where changes are ready to be committed, and so forth.
As your project develops, you can merge code across the
branches to reflect ever-increasing stable states of the
development.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Use Push and Pull:</em></span>
The push-pull workflow is based on the concept of developers
"pushing" local commits to a remote repository, which is
usually a contribution repository.
This workflow is also based on developers "pulling" known
states of the project down into their local development
repositories.
The workflow easily allows you to pull changes submitted by
other developers from the upstream repository into your
work area ensuring that you have the most recent software
on which to develop.
The Yocto Project has two scripts named
<code class="filename">create-pull-request</code> and
<code class="filename">send-pull-request</code> that ship with the
release to facilitate this workflow.
You can find these scripts in the <code class="filename">scripts</code>
folder of the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#source-directory" target="_top">Source Directory</a>.
For information on how to use these scripts, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#pushing-a-change-upstream" target="_top">Using Scripts to Push a Change Upstream and Request a Pull</a>"
section in the Yocto Project Development Tasks Manual.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Patch Workflow:</em></span>
This workflow allows you to notify the maintainer through an
email that you have a change (or patch) you would like
considered for the "master" branch of the Git repository.
To send this type of change, you format the patch and then
send the email using the Git commands
<code class="filename">git format-patch</code> and
<code class="filename">git send-email</code>.
For information on how to use these scripts, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#how-to-submit-a-change" target="_top">Submitting a Change to the Yocto Project</a>"
section in the Yocto Project Development Tasks Manual.
</p></li></ul></div><p>
</p></div><div class="section" title="2.4. Git"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="git">2.4. Git<span class="permalink"><a alt="Permalink" title="Permalink" href="#git">¶</a></span></h2></div></div></div><p>
The Yocto Project makes extensive use of Git, which is a
free, open source distributed version control system.
Git supports distributed development, non-linear development,
and can handle large projects.
It is best that you have some fundamental understanding
of how Git tracks projects and how to work with Git if
you are going to use the Yocto Project for development.
This section provides a quick overview of how Git works and
provides you with a summary of some essential Git commands.
</p><div class="note" title="Notes" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Notes</h3><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
For more information on Git, see
<a class="ulink" href="http://git-scm.com/documentation" target="_top">http://git-scm.com/documentation</a>.
</p></li><li class="listitem"><p>
If you need to download Git, it is recommended that you add
Git to your system through your distribution's "software
store" (e.g. for Ubuntu, use the Ubuntu Software feature).
For the Git download page, see
<a class="ulink" href="http://git-scm.com/download" target="_top">http://git-scm.com/download</a>.
</p></li><li class="listitem"><p>
For examples beyond the limited few in this section on how
to use Git with the Yocto Project, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#working-with-yocto-project-source-files" target="_top">Working With Yocto Project Source Files</a>"
section in the Yocto Project Development Tasks Manual.
</p></li></ul></div></div><p>
</p><div class="section" title="2.4.1. Repositories, Tags, and Branches"><div class="titlepage"><div><div><h3 class="title" id="repositories-tags-and-branches">2.4.1. Repositories, Tags, and Branches<span class="permalink"><a alt="Permalink" title="Permalink" href="#repositories-tags-and-branches">¶</a></span></h3></div></div></div><p>
As mentioned briefly in the previous section and also in the
"<a class="link" href="#workflows" title="2.3. Workflows">Workflows</a>" section,
the Yocto Project maintains source repositories at
<a class="ulink" href="http://git.yoctoproject.org/cgit.cgi" target="_top">http://git.yoctoproject.org/cgit.cgi</a>.
If you look at this web-interface of the repositories, each item
is a separate Git repository.
</p><p>
Git repositories use branching techniques that track content
change (not files) within a project (e.g. a new feature or updated
documentation).
Creating a tree-like structure based on project divergence allows
for excellent historical information over the life of a project.
This methodology also allows for an environment from which you can
do lots of local experimentation on projects as you develop
changes or new features.
</p><p>
A Git repository represents all development efforts for a given
project.
For example, the Git repository <code class="filename">poky</code> contains
all changes and developments for Poky over the course of its
entire life.
That means that all changes that make up all releases are captured.
The repository maintains a complete history of changes.
</p><p>
You can create a local copy of any repository by "cloning" it
with the <code class="filename">git clone</code> command.
When you clone a Git repository, you end up with an identical
copy of the repository on your development system.
Once you have a local copy of a repository, you can take steps to
develop locally.
For examples on how to clone Git repositories, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#working-with-yocto-project-source-files" target="_top">Working With Yocto Project Source Files</a>"
section in the Yocto Project Development Tasks Manual.
</p><p>
It is important to understand that Git tracks content change and
not files.
Git uses "branches" to organize different development efforts.
For example, the <code class="filename">poky</code> repository has
several branches that include the current "sumo"
branch, the "master" branch, and many branches for past
Yocto Project releases.
You can see all the branches by going to
<a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/" target="_top">http://git.yoctoproject.org/cgit.cgi/poky/</a> and
clicking on the
<code class="filename"><a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/refs/heads" target="_top">[...]</a></code>
link beneath the "Branch" heading.
</p><p>
Each of these branches represents a specific area of development.
The "master" branch represents the current or most recent
development.
All other branches represent offshoots of the "master" branch.
</p><p>
When you create a local copy of a Git repository, the copy has
the same set of branches as the original.
This means you can use Git to create a local working area
(also called a branch) that tracks a specific development branch
from the upstream source Git repository.
in other words, you can define your local Git environment to
work on any development branch in the repository.
To help illustrate, consider the following example Git commands:
</p><pre class="literallayout">
$ cd ~
$ git clone git://git.yoctoproject.org/poky
$ cd poky
$ git checkout -b sumo origin/sumo
</pre><p>
In the previous example after moving to the home directory, the
<code class="filename">git clone</code> command creates a
local copy of the upstream <code class="filename">poky</code> Git repository.
By default, Git checks out the "master" branch for your work.
After changing the working directory to the new local repository
(i.e. <code class="filename">poky</code>), the
<code class="filename">git checkout</code> command creates
and checks out a local branch named "sumo", which
tracks the upstream "origin/sumo" branch.
Changes you make while in this branch would ultimately affect
the upstream "sumo" branch of the
<code class="filename">poky</code> repository.
</p><p>
It is important to understand that when you create and checkout a
local working branch based on a branch name,
your local environment matches the "tip" of that particular
development branch at the time you created your local branch,
which could be different from the files in the "master" branch
of the upstream repository.
In other words, creating and checking out a local branch based on
the "sumo" branch name is not the same as
cloning and checking out the "master" branch if the repository.
Keep reading to see how you create a local snapshot of a Yocto
Project Release.
</p><p>
Git uses "tags" to mark specific changes in a repository.
Typically, a tag is used to mark a special point such as the final
change before a project is released.
You can see the tags used with the <code class="filename">poky</code> Git
repository by going to
<a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/" target="_top">http://git.yoctoproject.org/cgit.cgi/poky/</a> and
clicking on the
<code class="filename"><a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/refs/tags" target="_top">[...]</a></code>
link beneath the "Tag" heading.
</p><p>
Some key tags for the <code class="filename">poky</code> are
<code class="filename">jethro-14.0.3</code>,
<code class="filename">morty-16.0.1</code>,
<code class="filename">pyro-17.0.0</code>, and
<code class="filename">sumo-20.0.0</code>.
These tags represent Yocto Project releases.
</p><p>
When you create a local copy of the Git repository, you also
have access to all the tags in the upstream repository.
Similar to branches, you can create and checkout a local working
Git branch based on a tag name.
When you do this, you get a snapshot of the Git repository that
reflects the state of the files when the change was made associated
with that tag.
The most common use is to checkout a working branch that matches
a specific Yocto Project release.
Here is an example:
</p><pre class="literallayout">
$ cd ~
$ git clone git://git.yoctoproject.org/poky
$ cd poky
$ git fetch --all --tags --prune
$ git checkout tags/pyro-17.0.0 -b my-pyro-17.0.0
</pre><p>
In this example, the name of the top-level directory of your
local Yocto Project repository is <code class="filename">poky</code>.
After moving to the <code class="filename">poky</code> directory, the
<code class="filename">git fetch</code> command makes all the upstream
tags available locally in your repository.
Finally, the <code class="filename">git checkout</code> command
creates and checks out a branch named "my-pyro-17.0.0" that is
based on the specific change upstream in the repository
associated with the "pyro-17.0.0" tag.
The files in your repository now exactly match that particular
Yocto Project release as it is tagged in the upstream Git
repository.
It is important to understand that when you create and
checkout a local working branch based on a tag, your environment
matches a specific point in time and not the entire development
branch (i.e. the "tip" of the branch).
</p></div><div class="section" title="2.4.2. Basic Commands"><div class="titlepage"><div><div><h3 class="title" id="basic-commands">2.4.2. Basic Commands<span class="permalink"><a alt="Permalink" title="Permalink" href="#basic-commands">¶</a></span></h3></div></div></div><p>
Git has an extensive set of commands that lets you manage changes
and perform collaboration over the life of a project.
Conveniently though, you can manage with a small set of basic
operations and workflows once you understand the basic
philosophy behind Git.
You do not have to be an expert in Git to be functional.
A good place to look for instruction on a minimal set of Git
commands is
<a class="ulink" href="http://git-scm.com/documentation" target="_top">here</a>.
</p><p>
If you do not know much about Git, you should educate
yourself by visiting the links previously mentioned.
</p><p>
The following list of Git commands briefly describes some basic
Git operations as a way to get started.
As with any set of commands, this list (in most cases) simply shows
the base command and omits the many arguments they support.
See the Git documentation for complete descriptions and strategies
on how to use these commands:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git init</code>:</em></span>
Initializes an empty Git repository.
You cannot use Git commands unless you have a
<code class="filename">.git</code> repository.
</p></li><li class="listitem"><p><a id="git-commands-clone"></a>
<span class="emphasis"><em><code class="filename">git clone</code>:</em></span>
Creates a local clone of a Git repository that is on
equal footing with a fellow developer’s Git repository
or an upstream repository.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git add</code>:</em></span>
Locally stages updated file contents to the index that
Git uses to track changes.
You must stage all files that have changed before you
can commit them.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git commit</code>:</em></span>
Creates a local "commit" that documents the changes you
made.
Only changes that have been staged can be committed.
Commits are used for historical purposes, for determining
if a maintainer of a project will allow the change,
and for ultimately pushing the change from your local
Git repository into the project’s upstream repository.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git status</code>:</em></span>
Reports any modified files that possibly need to be
staged and gives you a status of where you stand regarding
local commits as compared to the upstream repository.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git checkout</code> <em class="replaceable"><code>branch-name</code></em>:</em></span>
Changes your working branch.
This command is analogous to "cd".
</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git checkout –b</code> <em class="replaceable"><code>working-branch</code></em>:</em></span>
Creates and checks out a working branch on your local
machine that you can use to isolate your work.
It is a good idea to use local branches when adding
specific features or changes.
Using isolated branches facilitates easy removal of
changes if they do not work out.
</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git branch</code>:</em></span>
Displays the existing local branches associated with your
local repository.
The branch that you have currently checked out is noted
with an asterisk character.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git branch -D</code> <em class="replaceable"><code>branch-name</code></em>:</em></span>
Deletes an existing local branch.
You need to be in a local branch other than the one you
are deleting in order to delete
<em class="replaceable"><code>branch-name</code></em>.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git pull</code>:</em></span>
Retrieves information from an upstream Git repository
and places it in your local Git repository.
You use this command to make sure you are synchronized with
the repository from which you are basing changes
(.e.g. the "master" branch).
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git push</code>:</em></span>
Sends all your committed local changes to the upstream Git
repository that your local repository is tracking
(e.g. a contribution repository).
The maintainer of the project draws from these repositories
to merge changes (commits) into the appropriate branch
of project's upstream repository.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git merge</code>:</em></span>
Combines or adds changes from one
local branch of your repository with another branch.
When you create a local Git repository, the default branch
is named "master".
A typical workflow is to create a temporary branch that is
based off "master" that you would use for isolated work.
You would make your changes in that isolated branch,
stage and commit them locally, switch to the "master"
branch, and then use the <code class="filename">git merge</code>
command to apply the changes from your isolated branch
into the currently checked out branch (e.g. "master").
After the merge is complete and if you are done with
working in that isolated branch, you can safely delete
the isolated branch.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git cherry-pick</code>:</em></span>
Choose and apply specific commits from one branch
into another branch.
There are times when you might not be able to merge
all the changes in one branch with
another but need to pick out certain ones.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">gitk</code>:</em></span>
Provides a GUI view of the branches and changes in your
local Git repository.
This command is a good way to graphically see where things
have diverged in your local repository.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
You need to install the <code class="filename">gitk</code>
package on your development system to use this
command.
</div><p>
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git log</code>:</em></span>
Reports a history of your commits to the repository.
This report lists all commits regardless of whether you
have pushed them upstream or not.
</p></li><li class="listitem"><p>
<span class="emphasis"><em><code class="filename">git diff</code>:</em></span>
Displays line-by-line differences between a local
working file and the same file as understood by Git.
This command is useful to see what you have changed
in any given file.
</p></li></ul></div><p>
</p></div></div><div class="section" title="2.5. Yocto Project Source Repositories"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="yocto-project-repositories">2.5. Yocto Project Source Repositories<span class="permalink"><a alt="Permalink" title="Permalink" href="#yocto-project-repositories">¶</a></span></h2></div></div></div><p>
The Yocto Project team maintains complete source repositories for all
Yocto Project files at
<a class="ulink" href="http://git.yoctoproject.org/cgit/cgit.cgi" target="_top">http://git.yoctoproject.org/cgit/cgit.cgi</a>.
This web-based source code browser is organized into categories by
function such as IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and
so forth.
From the interface, you can click on any particular item in the "Name"
column and see the URL at the bottom of the page that you need to clone
a Git repository for that particular item.
Having a local Git repository of the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#source-directory" target="_top">Source Directory</a>,
which is usually named "poky", allows
you to make changes, contribute to the history, and ultimately enhance
the Yocto Project's tools, Board Support Packages, and so forth.
</p><p>
For any supported release of Yocto Project, you can also go to the
<a class="ulink" href="http://www.yoctoproject.org" target="_top">Yocto Project Website</a> and
select the "Downloads" tab and get a released tarball of the
<code class="filename">poky</code> repository or any supported BSP tarballs.
Unpacking these tarballs gives you a snapshot of the released
files.
</p><div class="note" title="Notes" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Notes</h3><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
The recommended method for setting up the Yocto Project
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#source-directory" target="_top">Source Directory</a>
and the files for supported BSPs
(e.g., <code class="filename">meta-intel</code>) is to use
<a class="link" href="#git" title="2.4. Git">Git</a> to create a local copy of
the upstream repositories.
</p></li><li class="listitem"><p>
Be sure to always work in matching branches for both
the selected BSP repository and the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#source-directory" target="_top">Source Directory</a>
(i.e. <code class="filename">poky</code>) repository.
For example, if you have checked out the "master" branch
of <code class="filename">poky</code> and you are going to use
<code class="filename">meta-intel</code>, be sure to checkout the
"master" branch of <code class="filename">meta-intel</code>.
</p></li></ul></div></div><p>
</p><p>
In summary, here is where you can get the project files needed for
development:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a id="source-repositories"></a>
<span class="emphasis"><em>
<a class="ulink" href="http://git.yoctoproject.org/cgit/cgit.cgi" target="_top">Source Repositories:</a>
</em></span>
This area contains IDE Plugins, Matchbox, Poky, Poky Support,
Tools, Yocto Linux Kernel, and Yocto Metadata Layers.
You can create local copies of Git repositories for each of
these areas.</p><p>
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 360px"><td align="center"><img src="figures/source-repos.png" align="middle" width="540" /></td></tr></table><p>
For steps on how to view and access these upstream Git
repositories, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#accessing-source-repositories" target="_top">Accessing Source Repositories</a>"
Section in the Yocto Project Development Tasks Manual.
</p></li><li class="listitem"><p><a id="index-downloads"></a>
<span class="emphasis"><em>
<a class="ulink" href="http://downloads.yoctoproject.org/releases/" target="_top">Index of /releases:</a>
</em></span>
This is an index of releases such as
the <span class="trademark">Eclipse</span>™
Yocto Plug-in, miscellaneous support, Poky, Pseudo, installers
for cross-development toolchains, and all released versions of
Yocto Project in the form of images or tarballs.
Downloading and extracting these files does not produce a local
copy of the Git repository but rather a snapshot of a
particular release or image.</p><p>
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 315px"><td align="center"><img src="figures/index-downloads.png" align="middle" height="315" /></td></tr></table><p>
For steps on how to view and access these files, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#accessing-index-of-releases" target="_top">Accessing Index of Releases</a>"
section in the Yocto Project Development Tasks Manual.
</p></li><li class="listitem"><p><a id="downloads-page"></a>
<span class="emphasis"><em>"Downloads" page for the
<a class="ulink" href="http://www.yoctoproject.org" target="_top">Yocto Project Website</a>:
</em></span></p><p class="writernotes">This section will change due to
reworking of the YP Website.</p><p>The Yocto Project website includes a "Downloads" tab
that allows you to download any Yocto Project
release and Board Support Package (BSP) in tarball form.
The tarballs are similar to those found in the
<a class="ulink" href="http://downloads.yoctoproject.org/releases/" target="_top">Index of /releases:</a> area.</p><p>
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 360px"><td align="center"><img src="figures/yp-download.png" align="middle" width="540" /></td></tr></table><p>
For steps on how to use the "Downloads" page, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#using-the-downloads-page" target="_top">Using the Downloads Page</a>"
section in the Yocto Project Development Tasks Manual.
</p></li></ul></div><p>
</p></div><div class="section" title="2.6. Licensing"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="licensing">2.6. Licensing<span class="permalink"><a alt="Permalink" title="Permalink" href="#licensing">¶</a></span></h2></div></div></div><p>
Because open source projects are open to the public, they have
different licensing structures in place.
License evolution for both Open Source and Free Software has an
interesting history.
If you are interested in this history, you can find basic information
here:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<a class="ulink" href="http://en.wikipedia.org/wiki/Open-source_license" target="_top">Open source license history</a>
</p></li><li class="listitem"><p>
<a class="ulink" href="http://en.wikipedia.org/wiki/Free_software_license" target="_top">Free software license history</a>
</p></li></ul></div><p>
</p><p>
In general, the Yocto Project is broadly licensed under the
Massachusetts Institute of Technology (MIT) License.
MIT licensing permits the reuse of software within proprietary
software as long as the license is distributed with that software.
MIT is also compatible with the GNU General Public License (GPL).
Patches to the Yocto Project follow the upstream licensing scheme.
You can find information on the MIT license
<a class="ulink" href="http://www.opensource.org/licenses/mit-license.php" target="_top">here</a>.
You can find information on the GNU GPL
<a class="ulink" href="http://www.opensource.org/licenses/LGPL-3.0" target="_top">here</a>.
</p><p>
When you build an image using the Yocto Project, the build process
uses a known list of licenses to ensure compliance.
You can find this list in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#source-directory" target="_top">Source Directory</a>
at <code class="filename">meta/files/common-licenses</code>.
Once the build completes, the list of all licenses found and used
during that build are kept in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-directory" target="_top">Build Directory</a>
at <code class="filename">tmp/deploy/licenses</code>.
</p><p>
If a module requires a license that is not in the base list, the
build process generates a warning during the build.
These tools make it easier for a developer to be certain of the
licenses with which their shipped products must comply.
However, even with these tools it is still up to the developer to
resolve potential licensing issues.
</p><p>
The base list of licenses used by the build process is a combination
of the Software Package Data Exchange (SPDX) list and the Open
Source Initiative (OSI) projects.
<a class="ulink" href="http://spdx.org" target="_top">SPDX Group</a> is a working group of
the Linux Foundation that maintains a specification for a standard
format for communicating the components, licenses, and copyrights
associated with a software package.
<a class="ulink" href="http://opensource.org" target="_top">OSI</a> is a corporation
dedicated to the Open Source Definition and the effort for reviewing
and approving licenses that conform to the Open Source Definition
(OSD).
</p><p>
You can find a list of the combined SPDX and OSI licenses that the
Yocto Project uses in the
<code class="filename">meta/files/common-licenses</code> directory in your
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#source-directory" target="_top">Source Directory</a>.
</p><p>
For information that can help you maintain compliance with various
open source licensing during the lifecycle of a product created using
the Yocto Project, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#maintaining-open-source-license-compliance-during-your-products-lifecycle" target="_top">Maintaining Open Source License Compliance During Your Product's Lifecycle</a>"
section in the Yocto Project Development Tasks Manual.
</p></div><div class="section" title="2.7. Recipe Syntax"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="recipe-syntax">2.7. Recipe Syntax<span class="permalink"><a alt="Permalink" title="Permalink" href="#recipe-syntax">¶</a></span></h2></div></div></div><p>
Understanding recipe file syntax is important for
writing recipes.
The following list overviews the basic items that make up a
BitBake recipe file.
For more complete BitBake syntax descriptions, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#bitbake-user-manual-metadata" target="_top">Syntax and Operators</a>"
chapter of the BitBake User Manual.
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Variable Assignments and Manipulations:</em></span>
Variable assignments allow a value to be assigned to a
variable.
The assignment can be static text or might include
the contents of other variables.
In addition to the assignment, appending and prepending
operations are also supported.</p><p>The following example shows some of the ways
you can use variables in recipes:
</p><pre class="literallayout">
S = "${WORKDIR}/postfix-${PV}"
CFLAGS += "-DNO_ASM"
SRC_URI_append = " file://fixup.patch"
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Functions:</em></span>
Functions provide a series of actions to be performed.
You usually use functions to override the default
implementation of a task function or to complement
a default function (i.e. append or prepend to an
existing function).
Standard functions use <code class="filename">sh</code> shell
syntax, although access to OpenEmbedded variables and
internal methods are also available.</p><p>The following is an example function from the
<code class="filename">sed</code> recipe:
</p><pre class="literallayout">
do_install () {
autotools_do_install
install -d ${D}${base_bindir}
mv ${D}${bindir}/sed ${D}${base_bindir}/sed
rmdir ${D}${bindir}/
}
</pre><p>
It is also possible to implement new functions that
are called between existing tasks as long as the
new functions are not replacing or complementing the
default functions.
You can implement functions in Python
instead of shell.
Both of these options are not seen in the majority of
recipes.</p></li><li class="listitem"><p><span class="emphasis"><em>Keywords:</em></span>
BitBake recipes use only a few keywords.
You use keywords to include common
functions (<code class="filename">inherit</code>), load parts
of a recipe from other files
(<code class="filename">include</code> and
<code class="filename">require</code>) and export variables
to the environment (<code class="filename">export</code>).</p><p>The following example shows the use of some of
these keywords:
</p><pre class="literallayout">
export POSTCONF = "${STAGING_BINDIR}/postconf"
inherit autoconf
require otherfile.inc
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Comments:</em></span>
Any lines that begin with the hash character
(<code class="filename">#</code>) are treated as comment lines
and are ignored:
</p><pre class="literallayout">
# This is a comment
</pre><p>
</p></li></ul></div><p>
</p><p>
This next list summarizes the most important and most commonly
used parts of the recipe syntax.
For more information on these parts of the syntax, you can
reference the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#bitbake-user-manual-metadata" target="_top">Syntax and Operators</a>
chapter in the BitBake User Manual.
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Line Continuation: <code class="filename">\</code></em></span> -
Use the backward slash (<code class="filename">\</code>)
character to split a statement over multiple lines.
Place the slash character at the end of the line that
is to be continued on the next line:
</p><pre class="literallayout">
VAR = "A really long \
line"
</pre><p>
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
You cannot have any characters including spaces
or tabs after the slash character.
</div><p>
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Using Variables: <code class="filename">${...}</code></em></span> -
Use the <code class="filename">${<em class="replaceable"><code>VARNAME</code></em>}</code> syntax to
access the contents of a variable:
</p><pre class="literallayout">
SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz"
</pre><p>
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
It is important to understand that the value of a
variable expressed in this form does not get
substituted automatically.
The expansion of these expressions happens
on-demand later (e.g. usually when a function that
makes reference to the variable executes).
This behavior ensures that the values are most
appropriate for the context in which they are
finally used.
On the rare occasion that you do need the variable
expression to be expanded immediately, you can use
the <code class="filename">:=</code> operator instead of
<code class="filename">=</code> when you make the
assignment, but this is not generally needed.
</div><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Quote All Assignments: <code class="filename">"<em class="replaceable"><code>value</code></em>"</code></em></span> -
Use double quotes around the value in all variable
assignments.
</p><pre class="literallayout">
VAR1 = "${OTHERVAR}"
VAR2 = "The version is ${PV}"
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Conditional Assignment: <code class="filename">?=</code></em></span> -
Conditional assignment is used to assign a value to
a variable, but only when the variable is currently
unset.
Use the question mark followed by the equal sign
(<code class="filename">?=</code>) to make a "soft" assignment
used for conditional assignment.
Typically, "soft" assignments are used in the
<code class="filename">local.conf</code> file for variables
that are allowed to come through from the external
environment.
</p><p>Here is an example where
<code class="filename">VAR1</code> is set to "New value" if
it is currently empty.
However, if <code class="filename">VAR1</code> has already been
set, it remains unchanged:
</p><pre class="literallayout">
VAR1 ?= "New value"
</pre><p>
In this next example, <code class="filename">VAR1</code>
is left with the value "Original value":
</p><pre class="literallayout">
VAR1 = "Original value"
VAR1 ?= "New value"
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Appending: <code class="filename">+=</code></em></span> -
Use the plus character followed by the equals sign
(<code class="filename">+=</code>) to append values to existing
variables.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
This operator adds a space between the existing
content of the variable and the new content.
</div><p>Here is an example:
</p><pre class="literallayout">
SRC_URI += "file://fix-makefile.patch"
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Prepending: <code class="filename">=+</code></em></span> -
Use the equals sign followed by the plus character
(<code class="filename">=+</code>) to prepend values to existing
variables.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
This operator adds a space between the new content
and the existing content of the variable.
</div><p>Here is an example:
</p><pre class="literallayout">
VAR =+ "Starts"
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Appending: <code class="filename">_append</code></em></span> -
Use the <code class="filename">_append</code> operator to
append values to existing variables.
This operator does not add any additional space.
Also, the operator is applied after all the
<code class="filename">+=</code>, and
<code class="filename">=+</code> operators have been applied and
after all <code class="filename">=</code> assignments have
occurred.
</p><p>The following example shows the space being
explicitly added to the start to ensure the appended
value is not merged with the existing value:
</p><pre class="literallayout">
SRC_URI_append = " file://fix-makefile.patch"
</pre><p>
You can also use the <code class="filename">_append</code>
operator with overrides, which results in the actions
only being performed for the specified target or
machine:
</p><pre class="literallayout">
SRC_URI_append_sh4 = " file://fix-makefile.patch"
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Prepending: <code class="filename">_prepend</code></em></span> -
Use the <code class="filename">_prepend</code> operator to
prepend values to existing variables.
This operator does not add any additional space.
Also, the operator is applied after all the
<code class="filename">+=</code>, and
<code class="filename">=+</code> operators have been applied and
after all <code class="filename">=</code> assignments have
occurred.
</p><p>The following example shows the space being
explicitly added to the end to ensure the prepended
value is not merged with the existing value:
</p><pre class="literallayout">
CFLAGS_prepend = "-I${S}/myincludes "
</pre><p>
You can also use the <code class="filename">_prepend</code>
operator with overrides, which results in the actions
only being performed for the specified target or
machine:
</p><pre class="literallayout">
CFLAGS_prepend_sh4 = "-I${S}/myincludes "
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Overrides:</em></span> -
You can use overrides to set a value conditionally,
typically based on how the recipe is being built.
For example, to set the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-KBRANCH" target="_top"><code class="filename">KBRANCH</code></a>
variable's value to "standard/base" for any target
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-MACHINE" target="_top"><code class="filename">MACHINE</code></a>,
except for qemuarm where it should be set to
"standard/arm-versatile-926ejs", you would do the
following:
</p><pre class="literallayout">
KBRANCH = "standard/base"
KBRANCH_qemuarm = "standard/arm-versatile-926ejs"
</pre><p>
Overrides are also used to separate alternate values
of a variable in other situations.
For example, when setting variables such as
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-FILES" target="_top"><code class="filename">FILES</code></a>
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-RDEPENDS" target="_top"><code class="filename">RDEPENDS</code></a>
that are specific to individual packages produced by
a recipe, you should always use an override that
specifies the name of the package.
</p></li><li class="listitem"><p><span class="emphasis"><em>Indentation:</em></span>
Use spaces for indentation rather than than tabs.
For shell functions, both currently work.
However, it is a policy decision of the Yocto Project
to use tabs in shell functions.
Realize that some layers have a policy to use spaces
for all indentation.
</p></li><li class="listitem"><p><span class="emphasis"><em>Using Python for Complex Operations: <code class="filename">${@<em class="replaceable"><code>python_code</code></em>}</code></em></span> -
For more advanced processing, it is possible to use
Python code during variable assignments (e.g.
search and replacement on a variable).</p><p>You indicate Python code using the
<code class="filename">${@<em class="replaceable"><code>python_code</code></em>}</code>
syntax for the variable assignment:
</p><pre class="literallayout">
SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
</pre><p>
</p></li><li class="listitem"><p><span class="emphasis"><em>Shell Function Syntax:</em></span>
Write shell functions as if you were writing a shell
script when you describe a list of actions to take.
You should ensure that your script works with a generic
<code class="filename">sh</code> and that it does not require
any <code class="filename">bash</code> or other shell-specific
functionality.
The same considerations apply to various system
utilities (e.g. <code class="filename">sed</code>,
<code class="filename">grep</code>, <code class="filename">awk</code>,
and so forth) that you might wish to use.
If in doubt, you should check with multiple
implementations - including those from BusyBox.
</p></li></ul></div><p>
</p></div><div class="section" title="2.8. Development Concepts"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="development-concepts">2.8. Development Concepts<span class="permalink"><a alt="Permalink" title="Permalink" href="#development-concepts">¶</a></span></h2></div></div></div><p>
This section takes a more detailed look inside the development
process.
The following diagram represents development at a high level.
The remainder of this chapter expands on the fundamental input, output,
process, and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#metadata" target="_top">Metadata</a>) blocks
that make up development in the Yocto Project environment.
</p><p><a id="general-yocto-environment-figure"></a>
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="720"><tr style="height: 383px"><td align="center"><img src="figures/yocto-environment-ref.png" align="middle" height="383" /></td></tr></table><p>
</p><p>
In general, development consists of several functional areas:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>User Configuration:</em></span>
Metadata you can use to control the build process.
</p></li><li class="listitem"><p><span class="emphasis"><em>Metadata Layers:</em></span>
Various layers that provide software, machine, and
distro Metadata.</p></li><li class="listitem"><p><span class="emphasis"><em>Source Files:</em></span>
Upstream releases, local projects, and SCMs.</p></li><li class="listitem"><p><span class="emphasis"><em>Build System:</em></span>
Processes under the control of
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#bitbake-term" target="_top">BitBake</a>.
This block expands on how BitBake fetches source, applies
patches, completes compilation, analyzes output for package
generation, creates and tests packages, generates images, and
generates cross-development tools.</p></li><li class="listitem"><p><span class="emphasis"><em>Package Feeds:</em></span>
Directories containing output packages (RPM, DEB or IPK),
which are subsequently used in the construction of an image or
SDK, produced by the build system.
These feeds can also be copied and shared using a web server or
other means to facilitate extending or updating existing
images on devices at runtime if runtime package management is
enabled.</p></li><li class="listitem"><p><span class="emphasis"><em>Images:</em></span>
Images produced by the development process.
</p></li><li class="listitem"><p><span class="emphasis"><em>Application Development SDK:</em></span>
Cross-development tools that are produced along with an image
or separately with BitBake.</p></li></ul></div><p>
</p><div class="section" title="2.8.1. User Configuration"><div class="titlepage"><div><div><h3 class="title" id="user-configuration">2.8.1. User Configuration<span class="permalink"><a alt="Permalink" title="Permalink" href="#user-configuration">¶</a></span></h3></div></div></div><p>
User configuration helps define the build.
Through user configuration, you can tell BitBake the
target architecture for which you are building the image,
where to store downloaded source, and other build properties.
</p><p>
The following figure shows an expanded representation of the
"User Configuration" box of the
<a class="link" href="#general-yocto-environment-figure">general Yocto Project Development Environment figure</a>:
</p><p>
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="720"><tr style="height: 405px"><td align="center"><img src="figures/user-configuration.png" align="middle" height="405" /></td></tr></table><p>
</p><p>
BitBake needs some basic configuration files in order to complete
a build.
These files are <code class="filename">*.conf</code> files.
The minimally necessary ones reside as example files in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#source-directory" target="_top">Source Directory</a>.
For simplicity, this section refers to the Source Directory as
the "Poky Directory."
</p><p>
When you clone the <code class="filename">poky</code> Git repository or you
download and unpack a Yocto Project release, you can set up the
Source Directory to be named anything you want.
For this discussion, the cloned repository uses the default
name <code class="filename">poky</code>.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
The Poky repository is primarily an aggregation of existing
repositories.
It is not a canonical upstream source.
</div><p>
</p><p>
The <code class="filename">meta-poky</code> layer inside Poky contains
a <code class="filename">conf</code> directory that has example
configuration files.
These example files are used as a basis for creating actual
configuration files when you source the build environment
script
(i.e.
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#structure-core-script" target="_top"><code class="filename">oe-init-build-env</code></a>).
</p><p>
Sourcing the build environment script creates a
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-directory" target="_top">Build Directory</a>
if one does not already exist.
BitBake uses the Build Directory for all its work during builds.
The Build Directory has a <code class="filename">conf</code> directory that
contains default versions of your <code class="filename">local.conf</code>
and <code class="filename">bblayers.conf</code> configuration files.
These default configuration files are created only if versions
do not already exist in the Build Directory at the time you
source the build environment setup script.
</p><p>
Because the Poky repository is fundamentally an aggregation of
existing repositories, some users might be familiar with running
the <code class="filename">oe-init-build-env</code> script in the context
of separate OpenEmbedded-Core and BitBake repositories rather than a
single Poky repository.
This discussion assumes the script is executed from within a cloned
or unpacked version of Poky.
</p><p>
Depending on where the script is sourced, different sub-scripts
are called to set up the Build Directory (Yocto or OpenEmbedded).
Specifically, the script
<code class="filename">scripts/oe-setup-builddir</code> inside the
poky directory sets up the Build Directory and seeds the directory
(if necessary) with configuration files appropriate for the
Yocto Project development environment.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
The <code class="filename">scripts/oe-setup-builddir</code> script
uses the <code class="filename">$TEMPLATECONF</code> variable to
determine which sample configuration files to locate.
</div><p>
</p><p>
The <code class="filename">local.conf</code> file provides many
basic variables that define a build environment.
Here is a list of a few.
To see the default configurations in a <code class="filename">local.conf</code>
file created by the build environment script, see the
<code class="filename">local.conf.sample</code> in the
<code class="filename">meta-poky</code> layer:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Parallelism Options:</em></span>
Controlled by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-BB_NUMBER_THREADS" target="_top"><code class="filename">BB_NUMBER_THREADS</code></a>,
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PARALLEL_MAKE" target="_top"><code class="filename">PARALLEL_MAKE</code></a>,
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#var-BB_NUMBER_PARSE_THREADS" target="_top"><code class="filename">BB_NUMBER_PARSE_THREADS</code></a>
variables.</p></li><li class="listitem"><p><span class="emphasis"><em>Target Machine Selection:</em></span>
Controlled by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-MACHINE" target="_top"><code class="filename">MACHINE</code></a>
variable.</p></li><li class="listitem"><p><span class="emphasis"><em>Download Directory:</em></span>
Controlled by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DL_DIR" target="_top"><code class="filename">DL_DIR</code></a>
variable.</p></li><li class="listitem"><p><span class="emphasis"><em>Shared State Directory:</em></span>
Controlled by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SSTATE_DIR" target="_top"><code class="filename">SSTATE_DIR</code></a>
variable.</p></li><li class="listitem"><p><span class="emphasis"><em>Build Output:</em></span>
Controlled by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-TMPDIR" target="_top"><code class="filename">TMPDIR</code></a>
variable.</p></li></ul></div><p>
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
Configurations set in the <code class="filename">conf/local.conf</code>
file can also be set in the
<code class="filename">conf/site.conf</code> and
<code class="filename">conf/auto.conf</code> configuration files.
</div><p>
</p><p>
The <code class="filename">bblayers.conf</code> file tells BitBake what
layers you want considered during the build.
By default, the layers listed in this file include layers
minimally needed by the build system.
However, you must manually add any custom layers you have created.
You can find more information on working with the
<code class="filename">bblayers.conf</code> file in the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#enabling-your-layer" target="_top">Enabling Your Layer</a>"
section in the Yocto Project Development Tasks Manual.
</p><p>
The files <code class="filename">site.conf</code> and
<code class="filename">auto.conf</code> are not created by the environment
initialization script.
If you want the <code class="filename">site.conf</code> file, you need to
create that yourself.
The <code class="filename">auto.conf</code> file is typically created by
an autobuilder:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em><code class="filename">site.conf</code>:</em></span>
You can use the <code class="filename">conf/site.conf</code>
configuration file to configure multiple build directories.
For example, suppose you had several build environments and
they shared some common features.
You can set these default build properties here.
A good example is perhaps the packaging format to use
through the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGE_CLASSES" target="_top"><code class="filename">PACKAGE_CLASSES</code></a>
variable.</p><p>One useful scenario for using the
<code class="filename">conf/site.conf</code> file is to extend your
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-BBPATH" target="_top"><code class="filename">BBPATH</code></a>
variable to include the path to a
<code class="filename">conf/site.conf</code>.
Then, when BitBake looks for Metadata using
<code class="filename">BBPATH</code>, it finds the
<code class="filename">conf/site.conf</code> file and applies your
common configurations found in the file.
To override configurations in a particular build directory,
alter the similar configurations within that build
directory's <code class="filename">conf/local.conf</code> file.
</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">auto.conf</code>:</em></span>
The file is usually created and written to by
an autobuilder.
The settings put into the file are typically the same as
you would find in the <code class="filename">conf/local.conf</code>
or the <code class="filename">conf/site.conf</code> files.
</p></li></ul></div><p>
</p><p>
You can edit all configuration files to further define
any particular build environment.
This process is represented by the "User Configuration Edits"
box in the figure.
</p><p>
When you launch your build with the
<code class="filename">bitbake <em class="replaceable"><code>target</code></em></code>
command, BitBake sorts out the configurations to ultimately
define your build environment.
It is important to understand that the OpenEmbedded build system
reads the configuration files in a specific order:
<code class="filename">site.conf</code>, <code class="filename">auto.conf</code>,
and <code class="filename">local.conf</code>.
And, the build system applies the normal assignment statement
rules.
Because the files are parsed in a specific order, variable
assignments for the same variable could be affected.
For example, if the <code class="filename">auto.conf</code> file and
the <code class="filename">local.conf</code> set
<em class="replaceable"><code>variable1</code></em> to different values, because
the build system parses <code class="filename">local.conf</code> after
<code class="filename">auto.conf</code>,
<em class="replaceable"><code>variable1</code></em> is assigned the value from
the <code class="filename">local.conf</code> file.
</p></div><div class="section" title="2.8.2. Metadata, Machine Configuration, and Policy Configuration"><div class="titlepage"><div><div><h3 class="title" id="metadata-machine-configuration-and-policy-configuration">2.8.2. Metadata, Machine Configuration, and Policy Configuration<span class="permalink"><a alt="Permalink" title="Permalink" href="#metadata-machine-configuration-and-policy-configuration">¶</a></span></h3></div></div></div><p>
The previous section described the user configurations that
define BitBake's global behavior.
This section takes a closer look at the layers the build system
uses to further control the build.
These layers provide Metadata for the software, machine, and
policy.
</p><p>
In general, three types of layer input exist:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Policy Configuration:</em></span>
Distribution Layers provide top-level or general
policies for the image or SDK being built.
For example, this layer would dictate whether BitBake
produces RPM or IPK packages.</p></li><li class="listitem"><p><span class="emphasis"><em>Machine Configuration:</em></span>
Board Support Package (BSP) layers provide machine
configurations.
This type of information is specific to a particular
target architecture.</p></li><li class="listitem"><p><span class="emphasis"><em>Metadata:</em></span>
Software layers contain user-supplied recipe files,
patches, and append files.
</p></li></ul></div><p>
</p><p>
The following figure shows an expanded representation of the
Metadata, Machine Configuration, and Policy Configuration input
(layers) boxes of the
<a class="link" href="#general-yocto-environment-figure">general Yocto Project Development Environment figure</a>:
</p><p>
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="720"><tr style="height: 675px"><td align="center"><img src="figures/layer-input.png" align="middle" width="720" /></td></tr></table><p>
</p><p>
In general, all layers have a similar structure.
They all contain a licensing file
(e.g. <code class="filename">COPYING</code>) if the layer is to be
distributed, a <code class="filename">README</code> file as good practice
and especially if the layer is to be distributed, a
configuration directory, and recipe directories.
</p><p>
The Yocto Project has many layers that can be used.
You can see a web-interface listing of them on the
<a class="ulink" href="http://git.yoctoproject.org/" target="_top">Source Repositories</a>
page.
The layers are shown at the bottom categorized under
"Yocto Metadata Layers."
These layers are fundamentally a subset of the
<a class="ulink" href="http://layers.openembedded.org/layerindex/layers/" target="_top">OpenEmbedded Metadata Index</a>,
which lists all layers provided by the OpenEmbedded community.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
Layers exist in the Yocto Project Source Repositories that
cannot be found in the OpenEmbedded Metadata Index.
These layers are either deprecated or experimental in nature.
</div><p>
</p><p>
BitBake uses the <code class="filename">conf/bblayers.conf</code> file,
which is part of the user configuration, to find what layers it
should be using as part of the build.
</p><p>
For more information on layers, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#understanding-and-creating-layers" target="_top">Understanding and Creating Layers</a>"
section in the Yocto Project Development Tasks Manual.
</p><div class="section" title="2.8.2.1. Distro Layer"><div class="titlepage"><div><div><h4 class="title" id="distro-layer">2.8.2.1. Distro Layer<span class="permalink"><a alt="Permalink" title="Permalink" href="#distro-layer">¶</a></span></h4></div></div></div><p>
The distribution layer provides policy configurations for your
distribution.
Best practices dictate that you isolate these types of
configurations into their own layer.
Settings you provide in
<code class="filename">conf/distro/<em class="replaceable"><code>distro</code></em>.conf</code> override
similar
settings that BitBake finds in your
<code class="filename">conf/local.conf</code> file in the Build
Directory.
</p><p>
The following list provides some explanation and references
for what you typically find in the distribution layer:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>classes:</em></span>
Class files (<code class="filename">.bbclass</code>) hold
common functionality that can be shared among
recipes in the distribution.
When your recipes inherit a class, they take on the
settings and functions for that class.
You can read more about class files in the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes" target="_top">Classes</a>"
section of the Yocto Reference Manual.
</p></li><li class="listitem"><p><span class="emphasis"><em>conf:</em></span>
This area holds configuration files for the
layer (<code class="filename">conf/layer.conf</code>),
the distribution
(<code class="filename">conf/distro/<em class="replaceable"><code>distro</code></em>.conf</code>),
and any distribution-wide include files.
</p></li><li class="listitem"><p><span class="emphasis"><em>recipes-*:</em></span>
Recipes and append files that affect common
functionality across the distribution.
This area could include recipes and append files
to add distribution-specific configuration,
initialization scripts, custom image recipes,
and so forth.</p></li></ul></div><p>
</p></div><div class="section" title="2.8.2.2. BSP Layer"><div class="titlepage"><div><div><h4 class="title" id="bsp-layer">2.8.2.2. BSP Layer<span class="permalink"><a alt="Permalink" title="Permalink" href="#bsp-layer">¶</a></span></h4></div></div></div><p>
The BSP Layer provides machine configurations.
Everything in this layer is specific to the machine for which
you are building the image or the SDK.
A common structure or form is defined for BSP layers.
You can learn more about this structure in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bsp-guide/bsp-guide.html" target="_top">Yocto Project Board Support Package (BSP) Developer's Guide</a>.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
In order for a BSP layer to be considered compliant with the
Yocto Project, it must meet some structural requirements.
</div><p>
</p><p>
The BSP Layer's configuration directory contains
configuration files for the machine
(<code class="filename">conf/machine/<em class="replaceable"><code>machine</code></em>.conf</code>) and,
of course, the layer (<code class="filename">conf/layer.conf</code>).
</p><p>
The remainder of the layer is dedicated to specific recipes
by function: <code class="filename">recipes-bsp</code>,
<code class="filename">recipes-core</code>,
<code class="filename">recipes-graphics</code>, and
<code class="filename">recipes-kernel</code>.
Metadata can exist for multiple formfactors, graphics
support systems, and so forth.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
While the figure shows several <code class="filename">recipes-*</code>
directories, not all these directories appear in all
BSP layers.
</div><p>
</p></div><div class="section" title="2.8.2.3. Software Layer"><div class="titlepage"><div><div><h4 class="title" id="software-layer">2.8.2.3. Software Layer<span class="permalink"><a alt="Permalink" title="Permalink" href="#software-layer">¶</a></span></h4></div></div></div><p>
The software layer provides the Metadata for additional
software packages used during the build.
This layer does not include Metadata that is specific to the
distribution or the machine, which are found in their
respective layers.
</p><p>
This layer contains any new recipes that your project needs
in the form of recipe files.
</p></div></div><div class="section" title="2.8.3. Sources"><div class="titlepage"><div><div><h3 class="title" id="sources-dev-environment">2.8.3. Sources<span class="permalink"><a alt="Permalink" title="Permalink" href="#sources-dev-environment">¶</a></span></h3></div></div></div><p>
In order for the OpenEmbedded build system to create an image or
any target, it must be able to access source files.
The
<a class="link" href="#general-yocto-environment-figure">general Yocto Project Development Environment figure</a>
represents source files using the "Upstream Project Releases",
"Local Projects", and "SCMs (optional)" boxes.
The figure represents mirrors, which also play a role in locating
source files, with the "Source Mirror(s)" box.
</p><p>
The method by which source files are ultimately organized is
a function of the project.
For example, for released software, projects tend to use tarballs
or other archived files that can capture the state of a release
guaranteeing that it is statically represented.
On the other hand, for a project that is more dynamic or
experimental in nature, a project might keep source files in a
repository controlled by a Source Control Manager (SCM) such as
Git.
Pulling source from a repository allows you to control
the point in the repository (the revision) from which you want to
build software.
Finally, a combination of the two might exist, which would give the
consumer a choice when deciding where to get source files.
</p><p>
BitBake uses the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SRC_URI" target="_top"><code class="filename">SRC_URI</code></a>
variable to point to source files regardless of their location.
Each recipe must have a <code class="filename">SRC_URI</code> variable
that points to the source.
</p><p>
Another area that plays a significant role in where source files
come from is pointed to by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DL_DIR" target="_top"><code class="filename">DL_DIR</code></a>
variable.
This area is a cache that can hold previously downloaded source.
You can also instruct the OpenEmbedded build system to create
tarballs from Git repositories, which is not the default behavior,
and store them in the <code class="filename">DL_DIR</code> by using the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-BB_GENERATE_MIRROR_TARBALLS" target="_top"><code class="filename">BB_GENERATE_MIRROR_TARBALLS</code></a>
variable.
</p><p>
Judicious use of a <code class="filename">DL_DIR</code> directory can
save the build system a trip across the Internet when looking
for files.
A good method for using a download directory is to have
<code class="filename">DL_DIR</code> point to an area outside of your
Build Directory.
Doing so allows you to safely delete the Build Directory
if needed without fear of removing any downloaded source file.
</p><p>
The remainder of this section provides a deeper look into the
source files and the mirrors.
Here is a more detailed look at the source file area of the
base figure:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="630"><tr style="height: 675px"><td align="center"><img src="figures/source-input.png" align="middle" width="630" /></td></tr></table><p>
</p><div class="section" title="2.8.3.1. Upstream Project Releases"><div class="titlepage"><div><div><h4 class="title" id="upstream-project-releases">2.8.3.1. Upstream Project Releases<span class="permalink"><a alt="Permalink" title="Permalink" href="#upstream-project-releases">¶</a></span></h4></div></div></div><p>
Upstream project releases exist anywhere in the form of an
archived file (e.g. tarball or zip file).
These files correspond to individual recipes.
For example, the figure uses specific releases each for
BusyBox, Qt, and Dbus.
An archive file can be for any released product that can be
built using a recipe.
</p></div><div class="section" title="2.8.3.2. Local Projects"><div class="titlepage"><div><div><h4 class="title" id="local-projects">2.8.3.2. Local Projects<span class="permalink"><a alt="Permalink" title="Permalink" href="#local-projects">¶</a></span></h4></div></div></div><p>
Local projects are custom bits of software the user provides.
These bits reside somewhere local to a project - perhaps
a directory into which the user checks in items (e.g.
a local directory containing a development source tree
used by the group).
</p><p>
The canonical method through which to include a local project
is to use the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-externalsrc" target="_top"><code class="filename">externalsrc</code></a>
class to include that local project.
You use either the <code class="filename">local.conf</code> or a
recipe's append file to override or set the
recipe to point to the local directory on your disk to pull
in the whole source tree.
</p><p>
For information on how to use the
<code class="filename">externalsrc</code> class, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-externalsrc" target="_top"><code class="filename">externalsrc.bbclass</code></a>"
section.
</p></div><div class="section" title="2.8.3.3. Source Control Managers (Optional)"><div class="titlepage"><div><div><h4 class="title" id="scms">2.8.3.3. Source Control Managers (Optional)<span class="permalink"><a alt="Permalink" title="Permalink" href="#scms">¶</a></span></h4></div></div></div><p>
Another place the build system can get source files from is
through an SCM such as Git or Subversion.
In this case, a repository is cloned or checked out.
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-fetch" target="_top"><code class="filename">do_fetch</code></a>
task inside BitBake uses
the <a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SRC_URI" target="_top"><code class="filename">SRC_URI</code></a>
variable and the argument's prefix to determine the correct
fetcher module.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
For information on how to have the OpenEmbedded build system
generate tarballs for Git repositories and place them in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DL_DIR" target="_top"><code class="filename">DL_DIR</code></a>
directory, see the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-BB_GENERATE_MIRROR_TARBALLS" target="_top"><code class="filename">BB_GENERATE_MIRROR_TARBALLS</code></a>
variable.
</div><p>
When fetching a repository, BitBake uses the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SRCREV" target="_top"><code class="filename">SRCREV</code></a>
variable to determine the specific revision from which to
build.
</p></div><div class="section" title="2.8.3.4. Source Mirror(s)"><div class="titlepage"><div><div><h4 class="title" id="source-mirrors">2.8.3.4. Source Mirror(s)<span class="permalink"><a alt="Permalink" title="Permalink" href="#source-mirrors">¶</a></span></h4></div></div></div><p>
Two kinds of mirrors exist: pre-mirrors and regular mirrors.
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PREMIRRORS" target="_top"><code class="filename">PREMIRRORS</code></a>
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-MIRRORS" target="_top"><code class="filename">MIRRORS</code></a>
variables point to these, respectively.
BitBake checks pre-mirrors before looking upstream for any
source files.
Pre-mirrors are appropriate when you have a shared directory
that is not a directory defined by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DL_DIR" target="_top"><code class="filename">DL_DIR</code></a>
variable.
A Pre-mirror typically points to a shared directory that is
local to your organization.
</p><p>
Regular mirrors can be any site across the Internet that is
used as an alternative location for source code should the
primary site not be functioning for some reason or another.
</p></div></div><div class="section" title="2.8.4. Package Feeds"><div class="titlepage"><div><div><h3 class="title" id="package-feeds-dev-environment">2.8.4. Package Feeds<span class="permalink"><a alt="Permalink" title="Permalink" href="#package-feeds-dev-environment">¶</a></span></h3></div></div></div><p>
When the OpenEmbedded build system generates an image or an SDK,
it gets the packages from a package feed area located in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-directory" target="_top">Build Directory</a>.
The
<a class="link" href="#general-yocto-environment-figure">general Yocto Project Development Environment figure</a>
shows this package feeds area in the upper-right corner.
</p><p>
This section looks a little closer into the package feeds area used
by the build system.
Here is a more detailed look at the area:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="630"><tr style="height: 540px"><td align="center"><img src="figures/package-feeds.png" align="middle" width="630" /></td></tr></table><p>
</p><p>
Package feeds are an intermediary step in the build process.
The OpenEmbedded build system provides classes to generate
different package types, and you specify which classes to enable
through the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGE_CLASSES" target="_top"><code class="filename">PACKAGE_CLASSES</code></a>
variable.
Before placing the packages into package feeds,
the build process validates them with generated output quality
assurance checks through the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-insane" target="_top"><code class="filename">insane</code></a>
class.
</p><p>
The package feed area resides in the Build Directory.
The directory the build system uses to temporarily store packages
is determined by a combination of variables and the particular
package manager in use.
See the "Package Feeds" box in the illustration and note the
information to the right of that area.
In particular, the following defines where package files are
kept:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR" target="_top"><code class="filename">DEPLOY_DIR</code></a>:
Defined as <code class="filename">tmp/deploy</code> in the Build
Directory.
</p></li><li class="listitem"><p><code class="filename">DEPLOY_DIR_*</code>:
Depending on the package manager used, the package type
sub-folder.
Given RPM, IPK, or DEB packaging and tarball creation, the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR_RPM" target="_top"><code class="filename">DEPLOY_DIR_RPM</code></a>,
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR_IPK" target="_top"><code class="filename">DEPLOY_DIR_IPK</code></a>,
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR_DEB" target="_top"><code class="filename">DEPLOY_DIR_DEB</code></a>,
or
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR_TAR" target="_top"><code class="filename">DEPLOY_DIR_TAR</code></a>,
variables are used, respectively.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGE_ARCH" target="_top"><code class="filename">PACKAGE_ARCH</code></a>:
Defines architecture-specific sub-folders.
For example, packages could exist for the i586 or qemux86
architectures.
</p></li></ul></div><p>
</p><p>
BitBake uses the <code class="filename">do_package_write_*</code> tasks to
generate packages and place them into the package holding area (e.g.
<code class="filename">do_package_write_ipk</code> for IPK packages).
See the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package_write_deb" target="_top"><code class="filename">do_package_write_deb</code></a>",
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package_write_ipk" target="_top"><code class="filename">do_package_write_ipk</code></a>",
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package_write_rpm" target="_top"><code class="filename">do_package_write_rpm</code></a>",
and
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package_write_tar" target="_top"><code class="filename">do_package_write_tar</code></a>"
sections for additional information.
As an example, consider a scenario where an IPK packaging manager
is being used and package architecture support for both i586
and qemux86 exist.
Packages for the i586 architecture are placed in
<code class="filename">build/tmp/deploy/ipk/i586</code>, while packages for
the qemux86 architecture are placed in
<code class="filename">build/tmp/deploy/ipk/qemux86</code>.
</p></div><div class="section" title="2.8.5. BitBake"><div class="titlepage"><div><div><h3 class="title" id="bitbake-dev-environment">2.8.5. BitBake<span class="permalink"><a alt="Permalink" title="Permalink" href="#bitbake-dev-environment">¶</a></span></h3></div></div></div><p>
The OpenEmbedded build system uses
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#bitbake-term" target="_top">BitBake</a>
to produce images.
You can see from the
<a class="link" href="#general-yocto-environment-figure">general Yocto Project Development Environment figure</a>,
the BitBake area consists of several functional areas.
This section takes a closer look at each of those areas.
</p><p>
Separate documentation exists for the BitBake tool.
See the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#bitbake-user-manual" target="_top">BitBake User Manual</a>
for reference material on BitBake.
</p><div class="section" title="2.8.5.1. Source Fetching"><div class="titlepage"><div><div><h4 class="title" id="source-fetching-dev-environment">2.8.5.1. Source Fetching<span class="permalink"><a alt="Permalink" title="Permalink" href="#source-fetching-dev-environment">¶</a></span></h4></div></div></div><p>
The first stages of building a recipe are to fetch and unpack
the source code:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="585"><tr style="height: 450px"><td align="center"><img src="figures/source-fetching.png" align="middle" width="585" /></td></tr></table><p>
</p><p>
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-fetch" target="_top"><code class="filename">do_fetch</code></a>
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-unpack" target="_top"><code class="filename">do_unpack</code></a>
tasks fetch the source files and unpack them into the work
directory.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
For every local file (e.g. <code class="filename">file://</code>)
that is part of a recipe's
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SRC_URI" target="_top"><code class="filename">SRC_URI</code></a>
statement, the OpenEmbedded build system takes a checksum
of the file for the recipe and inserts the checksum into
the signature for the <code class="filename">do_fetch</code>.
If any local file has been modified, the
<code class="filename">do_fetch</code> task and all tasks that
depend on it are re-executed.
</div><p>
By default, everything is accomplished in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-directory" target="_top">Build Directory</a>,
which has a defined structure.
For additional general information on the Build Directory,
see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#structure-core-build" target="_top"><code class="filename">build/</code></a>"
section in the Yocto Project Reference Manual.
</p><p>
Unpacked source files are pointed to by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-S" target="_top"><code class="filename">S</code></a>
variable.
Each recipe has an area in the Build Directory where the
unpacked source code resides.
The name of that directory for any given recipe is defined from
several different variables.
You can see the variables that define these directories
by looking at the figure:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-TMPDIR" target="_top"><code class="filename">TMPDIR</code></a> -
The base directory where the OpenEmbedded build system
performs all its work during the build.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGE_ARCH" target="_top"><code class="filename">PACKAGE_ARCH</code></a> -
The architecture of the built package or packages.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-TARGET_OS" target="_top"><code class="filename">TARGET_OS</code></a> -
The operating system of the target device.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PN" target="_top"><code class="filename">PN</code></a> -
The name of the built package.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PV" target="_top"><code class="filename">PV</code></a> -
The version of the recipe used to build the package.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PR" target="_top"><code class="filename">PR</code></a> -
The revision of the recipe used to build the package.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-WORKDIR" target="_top"><code class="filename">WORKDIR</code></a> -
The location within <code class="filename">TMPDIR</code> where
a specific package is built.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-S" target="_top"><code class="filename">S</code></a> -
Contains the unpacked source files for a given recipe.
</p></li></ul></div><p>
</p></div><div class="section" title="2.8.5.2. Patching"><div class="titlepage"><div><div><h4 class="title" id="patching-dev-environment">2.8.5.2. Patching<span class="permalink"><a alt="Permalink" title="Permalink" href="#patching-dev-environment">¶</a></span></h4></div></div></div><p>
Once source code is fetched and unpacked, BitBake locates
patch files and applies them to the source files:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 450px"><td align="center"><img src="figures/patching.png" align="middle" width="540" /></td></tr></table><p>
</p><p>
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-patch" target="_top"><code class="filename">do_patch</code></a>
task processes recipes by
using the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SRC_URI" target="_top"><code class="filename">SRC_URI</code></a>
variable to locate applicable patch files, which by default
are <code class="filename">*.patch</code> or
<code class="filename">*.diff</code> files, or any file if
"apply=yes" is specified for the file in
<code class="filename">SRC_URI</code>.
</p><p>
BitBake finds and applies multiple patches for a single recipe
in the order in which it finds the patches.
Patches are applied to the recipe's source files located in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-S" target="_top"><code class="filename">S</code></a>
directory.
</p><p>
For more information on how the source directories are
created, see the
"<a class="link" href="#source-fetching-dev-environment" title="2.8.5.1. Source Fetching">Source Fetching</a>"
section.
</p></div><div class="section" title="2.8.5.3. Configuration and Compilation"><div class="titlepage"><div><div><h4 class="title" id="configuration-and-compilation-dev-environment">2.8.5.3. Configuration and Compilation<span class="permalink"><a alt="Permalink" title="Permalink" href="#configuration-and-compilation-dev-environment">¶</a></span></h4></div></div></div><p>
After source code is patched, BitBake executes tasks that
configure and compile the source code:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="630"><tr style="height: 450px"><td align="center"><img src="figures/configuration-compile-autoreconf.png" align="middle" width="630" /></td></tr></table><p>
</p><p>
This step in the build process consists of three tasks:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<span class="emphasis"><em><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-prepare_recipe_sysroot" target="_top"><code class="filename">do_prepare_recipe_sysroot</code></a>:</em></span>
This task sets up the two sysroots in
<code class="filename">${</code><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-WORKDIR" target="_top"><code class="filename">WORKDIR</code></a><code class="filename">}</code>
(i.e. <code class="filename">recipe-sysroot</code> and
<code class="filename">recipe-sysroot-native</code>) so that
the sysroots contain the contents of the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-populate_sysroot" target="_top"><code class="filename">do_populate_sysroot</code></a>
tasks of the recipes on which the recipe
containing the tasks depends.
A sysroot exists for both the target and for the native
binaries, which run on the host system.
</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">do_configure</code>:</em></span>
This task configures the source by enabling and
disabling any build-time and configuration options for
the software being built.
Configurations can come from the recipe itself as well
as from an inherited class.
Additionally, the software itself might configure itself
depending on the target for which it is being built.
</p><p>The configurations handled by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-configure" target="_top"><code class="filename">do_configure</code></a>
task are specific
to source code configuration for the source code
being built by the recipe.</p><p>If you are using the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-autotools" target="_top"><code class="filename">autotools</code></a>
class,
you can add additional configuration options by using
the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-EXTRA_OECONF" target="_top"><code class="filename">EXTRA_OECONF</code></a>
or
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGECONFIG_CONFARGS" target="_top"><code class="filename">PACKAGECONFIG_CONFARGS</code></a>
variables.
For information on how this variable works within
that class, see the
<code class="filename">meta/classes/autotools.bbclass</code> file.
</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">do_compile</code>:</em></span>
Once a configuration task has been satisfied, BitBake
compiles the source using the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-compile" target="_top"><code class="filename">do_compile</code></a>
task.
Compilation occurs in the directory pointed to by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-B" target="_top"><code class="filename">B</code></a>
variable.
Realize that the <code class="filename">B</code> directory is, by
default, the same as the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-S" target="_top"><code class="filename">S</code></a>
directory.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">do_install</code>:</em></span>
Once compilation is done, BitBake executes the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-install" target="_top"><code class="filename">do_install</code></a>
task.
This task copies files from the <code class="filename">B</code>
directory and places them in a holding area pointed to
by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-D" target="_top"><code class="filename">D</code></a>
variable.</p></li></ul></div><p>
</p></div><div class="section" title="2.8.5.4. Package Splitting"><div class="titlepage"><div><div><h4 class="title" id="package-splitting-dev-environment">2.8.5.4. Package Splitting<span class="permalink"><a alt="Permalink" title="Permalink" href="#package-splitting-dev-environment">¶</a></span></h4></div></div></div><p>
After source code is configured and compiled, the
OpenEmbedded build system analyzes
the results and splits the output into packages:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="630"><tr style="height: 630px"><td align="center"><img src="figures/analysis-for-package-splitting.png" align="middle" width="630" /></td></tr></table><p>
</p><p>
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package" target="_top"><code class="filename">do_package</code></a>
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-packagedata" target="_top"><code class="filename">do_packagedata</code></a>
tasks combine to analyze
the files found in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-D" target="_top"><code class="filename">D</code></a> directory
and split them into subsets based on available packages and
files.
The analyzing process involves the following as well as other
items: splitting out debugging symbols,
looking at shared library dependencies between packages,
and looking at package relationships.
The <code class="filename">do_packagedata</code> task creates package
metadata based on the analysis such that the
OpenEmbedded build system can generate the final packages.
Working, staged, and intermediate results of the analysis
and package splitting process use these areas:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PKGD" target="_top"><code class="filename">PKGD</code></a> -
The destination directory for packages before they are
split.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PKGDATA_DIR" target="_top"><code class="filename">PKGDATA_DIR</code></a> -
A shared, global-state directory that holds data
generated during the packaging process.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PKGDESTWORK" target="_top"><code class="filename">PKGDESTWORK</code></a> -
A temporary work area used by the
<code class="filename">do_package</code> task.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PKGDEST" target="_top"><code class="filename">PKGDEST</code></a> -
The parent directory for packages after they have
been split.
</p></li></ul></div><p>
The <a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-FILES" target="_top"><code class="filename">FILES</code></a>
variable defines the files that go into each package in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGES" target="_top"><code class="filename">PACKAGES</code></a>.
If you want details on how this is accomplished, you can
look at the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-package" target="_top"><code class="filename">package</code></a>
class.
</p><p>
Depending on the type of packages being created (RPM, DEB, or
IPK), the <code class="filename">do_package_write_*</code> task
creates the actual packages and places them in the
Package Feed area, which is
<code class="filename">${TMPDIR}/deploy</code>.
You can see the
"<a class="link" href="#package-feeds-dev-environment" title="2.8.4. Package Feeds">Package Feeds</a>"
section for more detail on that part of the build process.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
Support for creating feeds directly from the
<code class="filename">deploy/*</code> directories does not exist.
Creating such feeds usually requires some kind of feed
maintenance mechanism that would upload the new packages
into an official package feed (e.g. the
Ångström distribution).
This functionality is highly distribution-specific
and thus is not provided out of the box.
</div><p>
</p></div><div class="section" title="2.8.5.5. Image Generation"><div class="titlepage"><div><div><h4 class="title" id="image-generation-dev-environment">2.8.5.5. Image Generation<span class="permalink"><a alt="Permalink" title="Permalink" href="#image-generation-dev-environment">¶</a></span></h4></div></div></div><p>
Once packages are split and stored in the Package Feeds area,
the OpenEmbedded build system uses BitBake to generate the
root filesystem image:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 630px"><td align="center"><img src="figures/image-generation.png" align="middle" width="540" /></td></tr></table><p>
</p><p>
The image generation process consists of several stages and
depends on several tasks and variables.
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-rootfs" target="_top"><code class="filename">do_rootfs</code></a>
task creates the root filesystem (file and directory structure)
for an image.
This task uses several key variables to help create the list
of packages to actually install:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_INSTALL" target="_top"><code class="filename">IMAGE_INSTALL</code></a>:
Lists out the base set of packages to install from
the Package Feeds area.</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGE_EXCLUDE" target="_top"><code class="filename">PACKAGE_EXCLUDE</code></a>:
Specifies packages that should not be installed.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_FEATURES" target="_top"><code class="filename">IMAGE_FEATURES</code></a>:
Specifies features to include in the image.
Most of these features map to additional packages for
installation.</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGE_CLASSES" target="_top"><code class="filename">PACKAGE_CLASSES</code></a>:
Specifies the package backend to use and consequently
helps determine where to locate packages within the
Package Feeds area.</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_LINGUAS" target="_top"><code class="filename">IMAGE_LINGUAS</code></a>:
Determines the language(s) for which additional
language support packages are installed.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGE_INSTALL" target="_top"><code class="filename">PACKAGE_INSTALL</code></a>:
The final list of packages passed to the package manager
for installation into the image.
</p></li></ul></div><p>
</p><p>
With
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_ROOTFS" target="_top"><code class="filename">IMAGE_ROOTFS</code></a>
pointing to the location of the filesystem under construction and
the <code class="filename">PACKAGE_INSTALL</code> variable providing the
final list of packages to install, the root file system is
created.
</p><p>
Package installation is under control of the package manager
(e.g. dnf/rpm, opkg, or apt/dpkg) regardless of whether or
not package management is enabled for the target.
At the end of the process, if package management is not
enabled for the target, the package manager's data files
are deleted from the root filesystem.
As part of the final stage of package installation, postinstall
scripts that are part of the packages are run.
Any scripts that fail to run
on the build host are run on the target when the target system
is first booted.
If you are using a
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#creating-a-read-only-root-filesystem" target="_top">read-only root filesystem</a>,
all the post installation scripts must succeed during the
package installation phase since the root filesystem is
read-only.
</p><p>
The final stages of the <code class="filename">do_rootfs</code> task
handle post processing.
Post processing includes creation of a manifest file and
optimizations.
</p><p>
The manifest file (<code class="filename">.manifest</code>) resides
in the same directory as the root filesystem image.
This file lists out, line-by-line, the installed packages.
The manifest file is useful for the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-testimage*" target="_top"><code class="filename">testimage</code></a>
class, for example, to determine whether or not to run
specific tests.
See the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_MANIFEST" target="_top"><code class="filename">IMAGE_MANIFEST</code></a>
variable for additional information.
</p><p>
Optimizing processes run across the image include
<code class="filename">mklibs</code>, <code class="filename">prelink</code>,
and any other post-processing commands as defined by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-ROOTFS_POSTPROCESS_COMMAND" target="_top"><code class="filename">ROOTFS_POSTPROCESS_COMMAND</code></a>
variable.
The <code class="filename">mklibs</code> process optimizes the size
of the libraries, while the
<code class="filename">prelink</code> process optimizes the dynamic
linking of shared libraries to reduce start up time of
executables.
</p><p>
After the root filesystem is built, processing begins on
the image through the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-image" target="_top"><code class="filename">do_image</code></a>
task.
The build system runs any pre-processing commands as defined
by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_PREPROCESS_COMMAND" target="_top"><code class="filename">IMAGE_PREPROCESS_COMMAND</code></a>
variable.
This variable specifies a list of functions to call before
the OpenEmbedded build system creates the final image output
files.
</p><p>
The OpenEmbedded build system dynamically creates
<code class="filename">do_image_*</code> tasks as needed, based
on the image types specified in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_FSTYPES" target="_top"><code class="filename">IMAGE_FSTYPES</code></a>
variable.
The process turns everything into an image file or a set of
image files and compresses the root filesystem image to reduce
the overall size of the image.
The formats used for the root filesystem depend on the
<code class="filename">IMAGE_FSTYPES</code> variable.
</p><p>
As an example, a dynamically created task when creating a
particular image <em class="replaceable"><code>type</code></em> would take the
following form:
</p><pre class="literallayout">
do_image_<em class="replaceable"><code>type</code></em>[depends]
</pre><p>
So, if the <em class="replaceable"><code>type</code></em> as specified by the
<code class="filename">IMAGE_FSTYPES</code> were
<code class="filename">ext4</code>, the dynamically generated task
would be as follows:
</p><pre class="literallayout">
do_image_ext4[depends]
</pre><p>
</p><p>
The final task involved in image creation is the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-image-complete" target="_top"><code class="filename">do_image_complete</code></a>
task.
This task completes the image by applying any image
post processing as defined through the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_POSTPROCESS_COMMAND" target="_top"><code class="filename">IMAGE_POSTPROCESS_COMMAND</code></a>
variable.
The variable specifies a list of functions to call once the
OpenEmbedded build system has created the final image output
files.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
The entire image generation process is run under Pseudo.
Running under Pseudo ensures that the files in the root
filesystem have correct ownership.
</div></div><div class="section" title="2.8.5.6. SDK Generation"><div class="titlepage"><div><div><h4 class="title" id="sdk-generation-dev-environment">2.8.5.6. SDK Generation<span class="permalink"><a alt="Permalink" title="Permalink" href="#sdk-generation-dev-environment">¶</a></span></h4></div></div></div><p>
The OpenEmbedded build system uses BitBake to generate the
Software Development Kit (SDK) installer script for both the
standard and extensible SDKs:
<img src="figures/sdk-generation.png" align="middle" />
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
For more information on the cross-development toolchain
generation, see the
"<a class="link" href="#cross-development-toolchain-generation" title="3.2. Cross-Development Toolchain Generation">Cross-Development Toolchain Generation</a>"
section.
For information on advantages gained when building a
cross-development toolchain using the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-populate_sdk" target="_top"><code class="filename">do_populate_sdk</code></a>
task, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/sdk-manual/sdk-manual.html#sdk-building-an-sdk-installer" target="_top">Building an SDK Installer</a>"
section in the Yocto Project Application Development and the
Extensible Software Development Kit (SDK) manual.
</div><p>
Like image generation, the SDK script process consists of
several stages and depends on many variables.
The <code class="filename">do_populate_sdk</code> and
<code class="filename">do_populate_sdk_ext</code> tasks use these
key variables to help create the list of packages to actually
install.
For information on the variables listed in the figure, see the
"<a class="link" href="#sdk-dev-environment" title="2.8.7. Application Development SDK">Application Development SDK</a>"
section.
</p><p>
The <code class="filename">do_populate_sdk</code> task helps create
the standard SDK and handles two parts: a target part and a
host part.
The target part is the part built for the target hardware and
includes libraries and headers.
The host part is the part of the SDK that runs on the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDKMACHINE" target="_top"><code class="filename">SDKMACHINE</code></a>.
</p><p>
The <code class="filename">do_populate_sdk_ext</code> task helps create
the extensible SDK and handles host and target parts
differently than its counter part does for the standard SDK.
For the extensible SDK, the task encapsulates the build system,
which includes everything needed (host and target) for the SDK.
</p><p>
Regardless of the type of SDK being constructed, the
tasks perform some cleanup after which a cross-development
environment setup script and any needed configuration files
are created.
The final output is the Cross-development
toolchain installation script (<code class="filename">.sh</code> file),
which includes the environment setup script.
</p></div><div class="section" title="2.8.5.7. Stamp Files and the Rerunning of Tasks"><div class="titlepage"><div><div><h4 class="title" id="stamp-files-and-the-rerunning-of-tasks">2.8.5.7. Stamp Files and the Rerunning of Tasks<span class="permalink"><a alt="Permalink" title="Permalink" href="#stamp-files-and-the-rerunning-of-tasks">¶</a></span></h4></div></div></div><p>
For each task that completes successfully, BitBake writes a
stamp file into the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-STAMPS_DIR" target="_top"><code class="filename">STAMPS_DIR</code></a>
directory.
The beginning of the stamp file's filename is determined by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-STAMP" target="_top"><code class="filename">STAMP</code></a>
variable, and the end of the name consists of the task's name
and current
<a class="link" href="#overview-checksums" title="3.3.2. Checksums (Signatures)">input checksum</a>.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
This naming scheme assumes that
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#var-BB_SIGNATURE_HANDLER" target="_top"><code class="filename">BB_SIGNATURE_HANDLER</code></a>
is "OEBasicHash", which is almost always the case in
current OpenEmbedded.
</div><p>
To determine if a task needs to be rerun, BitBake checks if a
stamp file with a matching input checksum exists for the task.
If such a stamp file exists, the task's output is assumed to
exist and still be valid.
If the file does not exist, the task is rerun.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The stamp mechanism is more general than the shared
state (sstate) cache mechanism described in the
"<a class="link" href="#setscene-tasks-and-shared-state" title="2.8.5.8. Setscene Tasks and Shared State">Setscene Tasks and Shared State</a>"
section.
BitBake avoids rerunning any task that has a valid
stamp file, not just tasks that can be accelerated through
the sstate cache.</p><p>However, you should realize that stamp files only
serve as a marker that some work has been done and that
these files do not record task output.
The actual task output would usually be somewhere in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-TMPDIR" target="_top"><code class="filename">TMPDIR</code></a>
(e.g. in some recipe's
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-WORKDIR" target="_top"><code class="filename">WORKDIR</code></a>.)
What the sstate cache mechanism adds is a way to cache task
output that can then be shared between build machines.
</p></div><p>
Since <code class="filename">STAMPS_DIR</code> is usually a subdirectory
of <code class="filename">TMPDIR</code>, removing
<code class="filename">TMPDIR</code> will also remove
<code class="filename">STAMPS_DIR</code>, which means tasks will
properly be rerun to repopulate <code class="filename">TMPDIR</code>.
</p><p>
If you want some task to always be considered "out of date",
you can mark it with the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#variable-flags" target="_top"><code class="filename">nostamp</code></a>
varflag.
If some other task depends on such a task, then that task will
also always be considered out of date, which might not be what
you want.
</p><p>
For details on how to view information about a task's
signature, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#dev-viewing-task-variable-dependencies" target="_top">Viewing Task Variable Dependencies</a>"
section in the Yocto Project Development Tasks Manual.
</p></div><div class="section" title="2.8.5.8. Setscene Tasks and Shared State"><div class="titlepage"><div><div><h4 class="title" id="setscene-tasks-and-shared-state">2.8.5.8. Setscene Tasks and Shared State<span class="permalink"><a alt="Permalink" title="Permalink" href="#setscene-tasks-and-shared-state">¶</a></span></h4></div></div></div><p>
The description of tasks so far assumes that BitBake needs to
build everything and there are no prebuilt objects available.
BitBake does support skipping tasks if prebuilt objects are
available.
These objects are usually made available in the form of a
shared state (sstate) cache.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
For information on variables affecting sstate, see the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SSTATE_DIR" target="_top"><code class="filename">SSTATE_DIR</code></a>
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SSTATE_MIRRORS" target="_top"><code class="filename">SSTATE_MIRRORS</code></a>
variables.
</div><p>
</p><p>
The idea of a setscene task (i.e
<code class="filename">do_</code><em class="replaceable"><code>taskname</code></em><code class="filename">_setscene</code>)
is a version of the task where
instead of building something, BitBake can skip to the end
result and simply place a set of files into specific locations
as needed.
In some cases, it makes sense to have a setscene task variant
(e.g. generating package files in the
<code class="filename">do_package_write_*</code> task).
In other cases, it does not make sense, (e.g. a
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-patch" target="_top"><code class="filename">do_patch</code></a>
task or
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-unpack" target="_top"><code class="filename">do_unpack</code></a>
task) since the work involved would be equal to or greater than
the underlying task.
</p><p>
In the OpenEmbedded build system, the common tasks that have
setscene variants are
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package" target="_top"><code class="filename">do_package</code></a>,
<code class="filename">do_package_write_*</code>,
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-deploy" target="_top"><code class="filename">do_deploy</code></a>,
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-packagedata" target="_top"><code class="filename">do_packagedata</code></a>,
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-populate_sysroot" target="_top"><code class="filename">do_populate_sysroot</code></a>.
Notice that these are most of the tasks whose output is an
end result.
</p><p>
The OpenEmbedded build system has knowledge of the relationship
between these tasks and other tasks that precede them.
For example, if BitBake runs
<code class="filename">do_populate_sysroot_setscene</code> for
something, there is little point in running any of the
<code class="filename">do_fetch</code>, <code class="filename">do_unpack</code>,
<code class="filename">do_patch</code>,
<code class="filename">do_configure</code>,
<code class="filename">do_compile</code>, and
<code class="filename">do_install</code> tasks.
However, if <code class="filename">do_package</code> needs to be run,
BitBake would need to run those other tasks.
</p><p>
It becomes more complicated if everything can come from an
sstate cache because some objects are simply not required at
all.
For example, you do not need a compiler or native tools, such
as quilt, if there is nothing to compile or patch.
If the <code class="filename">do_package_write_*</code> packages are
available from sstate, BitBake does not need the
<code class="filename">do_package</code> task data.
</p><p>
To handle all these complexities, BitBake runs in two phases.
The first is the "setscene" stage.
During this stage, BitBake first checks the sstate cache for
any targets it is planning to build.
BitBake does a fast check to see if the object exists rather
than a complete download.
If nothing exists, the second phase, which is the setscene
stage, completes and the main build proceeds.
</p><p>
If objects are found in the sstate cache, the OpenEmbedded
build system works backwards from the end targets specified
by the user.
For example, if an image is being built, the OpenEmbedded build
system first looks for the packages needed for that image and
the tools needed to construct an image.
If those are available, the compiler is not needed.
Thus, the compiler is not even downloaded.
If something was found to be unavailable, or the download or
setscene task fails, the OpenEmbedded build system then tries
to install dependencies, such as the compiler, from the cache.
</p><p>
The availability of objects in the sstate cache is handled by
the function specified by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#var-BB_HASHCHECK_FUNCTION" target="_top"><code class="filename">BB_HASHCHECK_FUNCTION</code></a>
variable and returns a list of the objects that are available.
The function specified by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#var-BB_SETSCENE_DEPVALID" target="_top"><code class="filename">BB_SETSCENE_DEPVALID</code></a>
variable is the function that determines whether a given
dependency needs to be followed, and whether for any given
relationship the function needs to be passed.
The function returns a True or False value.
</p></div></div><div class="section" title="2.8.6. Images"><div class="titlepage"><div><div><h3 class="title" id="images-dev-environment">2.8.6. Images<span class="permalink"><a alt="Permalink" title="Permalink" href="#images-dev-environment">¶</a></span></h3></div></div></div><p>
The images produced by the OpenEmbedded build system
are compressed forms of the
root filesystem that are ready to boot on a target device.
You can see from the
<a class="link" href="#general-yocto-environment-figure">general Yocto Project Development Environment figure</a>
that BitBake output, in part, consists of images.
This section is going to look more closely at this output:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="495"><tr style="height: 495px"><td align="center"><img src="figures/images.png" align="middle" width="495" /></td></tr></table><p>
</p><p>
For a list of example images that the Yocto Project provides,
see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-images" target="_top">Images</a>"
chapter in the Yocto Project Reference Manual.
</p><p>
Images are written out to the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-directory" target="_top">Build Directory</a>
inside the
<code class="filename">tmp/deploy/images/<em class="replaceable"><code>machine</code></em>/</code>
folder as shown in the figure.
This folder contains any files expected to be loaded on the
target device.
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR" target="_top"><code class="filename">DEPLOY_DIR</code></a>
variable points to the <code class="filename">deploy</code> directory,
while the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR_IMAGE" target="_top"><code class="filename">DEPLOY_DIR_IMAGE</code></a>
variable points to the appropriate directory containing images for
the current configuration.
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><code class="filename"><em class="replaceable"><code>kernel-image</code></em></code>:
A kernel binary file.
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-KERNEL_IMAGETYPE" target="_top"><code class="filename">KERNEL_IMAGETYPE</code></a>
variable setting determines the naming scheme for the
kernel image file.
Depending on that variable, the file could begin with
a variety of naming strings.
The <code class="filename">deploy/images/<em class="replaceable"><code>machine</code></em></code>
directory can contain multiple image files for the
machine.</p></li><li class="listitem"><p><code class="filename"><em class="replaceable"><code>root-filesystem-image</code></em></code>:
Root filesystems for the target device (e.g.
<code class="filename">*.ext3</code> or <code class="filename">*.bz2</code>
files).
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-IMAGE_FSTYPES" target="_top"><code class="filename">IMAGE_FSTYPES</code></a>
variable setting determines the root filesystem image
type.
The <code class="filename">deploy/images/<em class="replaceable"><code>machine</code></em></code>
directory can contain multiple root filesystems for the
machine.</p></li><li class="listitem"><p><code class="filename"><em class="replaceable"><code>kernel-modules</code></em></code>:
Tarballs that contain all the modules built for the kernel.
Kernel module tarballs exist for legacy purposes and
can be suppressed by setting the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-MODULE_TARBALL_DEPLOY" target="_top"><code class="filename">MODULE_TARBALL_DEPLOY</code></a>
variable to "0".
The <code class="filename">deploy/images/<em class="replaceable"><code>machine</code></em></code>
directory can contain multiple kernel module tarballs
for the machine.</p></li><li class="listitem"><p><code class="filename"><em class="replaceable"><code>bootloaders</code></em></code>:
Bootloaders supporting the image, if applicable to the
target machine.
The <code class="filename">deploy/images/<em class="replaceable"><code>machine</code></em></code>
directory can contain multiple bootloaders for the
machine.</p></li><li class="listitem"><p><code class="filename"><em class="replaceable"><code>symlinks</code></em></code>:
The <code class="filename">deploy/images/<em class="replaceable"><code>machine</code></em></code>
folder contains
a symbolic link that points to the most recently built file
for each machine.
These links might be useful for external scripts that
need to obtain the latest version of each file.
</p></li></ul></div><p>
</p></div><div class="section" title="2.8.7. Application Development SDK"><div class="titlepage"><div><div><h3 class="title" id="sdk-dev-environment">2.8.7. Application Development SDK<span class="permalink"><a alt="Permalink" title="Permalink" href="#sdk-dev-environment">¶</a></span></h3></div></div></div><p>
In the
<a class="link" href="#general-yocto-environment-figure">general Yocto Project Development Environment figure</a>,
the output labeled "Application Development SDK" represents an
SDK.
The SDK generation process differs depending on whether you build
a standard SDK
(e.g. <code class="filename">bitbake -c populate_sdk</code> <em class="replaceable"><code>imagename</code></em>)
or an extensible SDK
(e.g. <code class="filename">bitbake -c populate_sdk_ext</code> <em class="replaceable"><code>imagename</code></em>).
This section is going to take a closer look at this output:
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="810"><tr style="height: 653px"><td align="center"><img src="figures/sdk.png" align="middle" width="810" /></td></tr></table><p>
</p><p>
The specific form of this output is a self-extracting
SDK installer (<code class="filename">*.sh</code>) that, when run,
installs the SDK, which consists of a cross-development
toolchain, a set of libraries and headers, and an SDK
environment setup script.
Running this installer essentially sets up your
cross-development environment.
You can think of the cross-toolchain as the "host"
part because it runs on the SDK machine.
You can think of the libraries and headers as the "target"
part because they are built for the target hardware.
The environment setup script is added so that you can initialize
the environment before using the tools.
</p><div class="note" title="Notes" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Notes</h3><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
The Yocto Project supports several methods by which you can
set up this cross-development environment.
These methods include downloading pre-built SDK installers
or building and installing your own SDK installer.
</p></li><li class="listitem"><p>
For background information on cross-development toolchains
in the Yocto Project development environment, see the
"<a class="link" href="#cross-development-toolchain-generation" title="3.2. Cross-Development Toolchain Generation">Cross-Development Toolchain Generation</a>"
section.
</p></li><li class="listitem"><p>
For information on setting up a cross-development
environment, see the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/sdk-manual/sdk-manual.html" target="_top">Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</a>
manual.
</p></li></ul></div></div><p>
Once built, the SDK installers are written out to the
<code class="filename">deploy/sdk</code> folder inside the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-directory" target="_top">Build Directory</a>
as shown in the figure at the beginning of this section.
Depending on the type of SDK, several variables exist that help
configure these files.
The following list shows the variables associated with a standard
SDK:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR" target="_top"><code class="filename">DEPLOY_DIR</code></a>:
Points to the <code class="filename">deploy</code>
directory.</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDKMACHINE" target="_top"><code class="filename">SDKMACHINE</code></a>:
Specifies the architecture of the machine
on which the cross-development tools are run to
create packages for the target hardware.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDKIMAGE_FEATURES" target="_top"><code class="filename">SDKIMAGE_FEATURES</code></a>:
Lists the features to include in the "target" part
of the SDK.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-TOOLCHAIN_HOST_TASK" target="_top"><code class="filename">TOOLCHAIN_HOST_TASK</code></a>:
Lists packages that make up the host
part of the SDK (i.e. the part that runs on
the <code class="filename">SDKMACHINE</code>).
When you use
<code class="filename">bitbake -c populate_sdk <em class="replaceable"><code>imagename</code></em></code>
to create the SDK, a set of default packages
apply.
This variable allows you to add more packages.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-TOOLCHAIN_TARGET_TASK" target="_top"><code class="filename">TOOLCHAIN_TARGET_TASK</code></a>:
Lists packages that make up the target part
of the SDK (i.e. the part built for the
target hardware).
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDKPATH" target="_top"><code class="filename">SDKPATH</code></a>:
Defines the default SDK installation path offered by the
installation script.
</p></li></ul></div><p>
This next list, shows the variables associated with an extensible
SDK:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPLOY_DIR" target="_top"><code class="filename">DEPLOY_DIR</code></a>:
Points to the <code class="filename">deploy</code> directory.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDK_EXT_TYPE" target="_top"><code class="filename">SDK_EXT_TYPE</code></a>:
Controls whether or not shared state artifacts are copied
into the extensible SDK.
By default, all required shared state artifacts are copied
into the SDK.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDK_INCLUDE_PKGDATA" target="_top"><code class="filename">SDK_INCLUDE_PKGDATA</code></a>:
Specifies whether or not packagedata will be included in
the extensible SDK for all recipes in the "world" target.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDK_INCLUDE_TOOLCHAIN" target="_top"><code class="filename">SDK_INCLUDE_TOOLCHAIN</code></a>:
Specifies whether or not the toolchain will be included
when building the extensible SDK.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDK_LOCAL_CONF_WHITELIST" target="_top"><code class="filename">SDK_LOCAL_CONF_WHITELIST</code></a>:
A list of variables allowed through from the build system
configuration into the extensible SDK configuration.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDK_LOCAL_CONF_BLACKLIST" target="_top"><code class="filename">SDK_LOCAL_CONF_BLACKLIST</code></a>:
A list of variables not allowed through from the build
system configuration into the extensible SDK configuration.
</p></li><li class="listitem"><p><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDK_INHERIT_BLACKLIST" target="_top"><code class="filename">SDK_INHERIT_BLACKLIST</code></a>:
A list of classes to remove from the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-INHERIT" target="_top"><code class="filename">INHERIT</code></a>
value globally within the extensible SDK configuration.
</p></li></ul></div><p>
</p></div></div></div>
<div class="chapter" title="Chapter 3. Yocto Project Concepts" id="overview-concepts"><div class="titlepage"><div><div><h2 class="title">Chapter 3. Yocto Project Concepts<span class="permalink"><a alt="Permalink" title="Permalink" href="#overview-concepts">¶</a></span></h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="section"><a href="#yocto-project-components">3.1. Yocto Project Components</a></span></dt><dd><dl><dt><span class="section"><a href="#usingpoky-components-bitbake">3.1.1. BitBake</a></span></dt><dt><span class="section"><a href="#usingpoky-components-metadata">3.1.2. Metadata (Recipes)</a></span></dt><dt><span class="section"><a href="#metadata-virtual-providers">3.1.3. Metadata (Virtual Providers)</a></span></dt><dt><span class="section"><a href="#usingpoky-components-classes">3.1.4. Classes</a></span></dt><dt><span class="section"><a href="#usingpoky-components-configuration">3.1.5. Configuration</a></span></dt></dl></dd><dt><span class="section"><a href="#cross-development-toolchain-generation">3.2. Cross-Development Toolchain Generation</a></span></dt><dt><span class="section"><a href="#shared-state-cache">3.3. Shared State Cache</a></span></dt><dd><dl><dt><span class="section"><a href="#overall-architecture">3.3.1. Overall Architecture</a></span></dt><dt><span class="section"><a href="#overview-checksums">3.3.2. Checksums (Signatures)</a></span></dt><dt><span class="section"><a href="#shared-state">3.3.3. Shared State</a></span></dt><dt><span class="section"><a href="#tips-and-tricks">3.3.4. Tips and Tricks</a></span></dt></dl></dd><dt><span class="section"><a href="#automatically-added-runtime-dependencies">3.4. Automatically Added Runtime Dependencies</a></span></dt><dt><span class="section"><a href="#fakeroot-and-pseudo">3.5. Fakeroot and Pseudo</a></span></dt><dt><span class="section"><a href="#wayland">3.6. Wayland</a></span></dt><dd><dl><dt><span class="section"><a href="#wayland-support">3.6.1. Support</a></span></dt><dt><span class="section"><a href="#enabling-wayland-in-an-image">3.6.2. Enabling Wayland in an Image</a></span></dt><dt><span class="section"><a href="#running-weston">3.6.3. Running Weston</a></span></dt></dl></dd><dt><span class="section"><a href="#overview-licenses">3.7. Licenses</a></span></dt><dd><dl><dt><span class="section"><a href="#usingpoky-configuring-LIC_FILES_CHKSUM">3.7.1. Tracking License Changes</a></span></dt><dt><span class="section"><a href="#enabling-commercially-licensed-recipes">3.7.2. Enabling Commercially Licensed Recipes</a></span></dt></dl></dd><dt><span class="section"><a href="#x32">3.8. x32 psABI</a></span></dt></dl></div><p>
This chapter describes concepts for various areas of the Yocto Project.
Currently, topics include Yocto Project components, cross-development
generation, shared state (sstate) cache, runtime dependencies,
Pseudo and Fakeroot, x32 psABI, Wayland support, and Licenses.
</p><div class="section" title="3.1. Yocto Project Components"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="yocto-project-components">3.1. Yocto Project Components<span class="permalink"><a alt="Permalink" title="Permalink" href="#yocto-project-components">¶</a></span></h2></div></div></div><p>
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#bitbake-term" target="_top">BitBake</a>
task executor together with various types of configuration files
form the OpenEmbedded Core.
This section overviews these components by describing their use and
how they interact.
</p><p>
BitBake handles the parsing and execution of the data files.
The data itself is of various types:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<span class="emphasis"><em>Recipes:</em></span>
Provides details about particular pieces of software.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Class Data:</em></span>
Abstracts common build information (e.g. how to build a
Linux kernel).
</p></li><li class="listitem"><p>
<span class="emphasis"><em>Configuration Data:</em></span>
Defines machine-specific settings, policy decisions, and
so forth.
Configuration data acts as the glue to bind everything
together.
</p></li></ul></div><p>
</p><p>
BitBake knows how to combine multiple data sources together and
refers to each data source as a layer.
For information on layers, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#understanding-and-creating-layers" target="_top">Understanding and Creating Layers</a>"
section of the Yocto Project Development Tasks Manual.
</p><p>
Following are some brief details on these core components.
For additional information on how these components interact during
a build, see the
"<a class="link" href="#development-concepts" title="2.8. Development Concepts">Development Concepts</a>"
section.
</p><div class="section" title="3.1.1. BitBake"><div class="titlepage"><div><div><h3 class="title" id="usingpoky-components-bitbake">3.1.1. BitBake<span class="permalink"><a alt="Permalink" title="Permalink" href="#usingpoky-components-bitbake">¶</a></span></h3></div></div></div><p>
BitBake is the tool at the heart of the OpenEmbedded build
system and is responsible for parsing the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#metadata" target="_top">Metadata</a>,
generating a list of tasks from it, and then executing those
tasks.
</p><p>
This section briefly introduces BitBake.
If you want more information on BitBake, see the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#bitbake-user-manual" target="_top">BitBake User Manual</a>.
</p><p>
To see a list of the options BitBake supports, use either of
the following commands:
</p><pre class="literallayout">
$ bitbake -h
$ bitbake --help
</pre><p>
</p><p>
The most common usage for BitBake is
<code class="filename">bitbake <em class="replaceable"><code>packagename</code></em></code>,
where <code class="filename">packagename</code> is the name of the
package you want to build (referred to as the "target" in this
manual).
The target often equates to the first part of a recipe's
filename (e.g. "foo" for a recipe named
<code class="filename">foo_1.3.0-r0.bb</code>).
So, to process the
<code class="filename">matchbox-desktop_1.2.3.bb</code> recipe file, you
might type the following:
</p><pre class="literallayout">
$ bitbake matchbox-desktop
</pre><p>
Several different versions of
<code class="filename">matchbox-desktop</code> might exist.
BitBake chooses the one selected by the distribution
configuration.
You can get more details about how BitBake chooses between
different target versions and providers in the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#bb-bitbake-preferences" target="_top">Preferences</a>"
section of the BitBake User Manual.
</p><p>
BitBake also tries to execute any dependent tasks first.
So for example, before building
<code class="filename">matchbox-desktop</code>, BitBake would build a
cross compiler and <code class="filename">glibc</code> if they had not
already been built.
</p><p>
A useful BitBake option to consider is the
<code class="filename">-k</code> or <code class="filename">--continue</code>
option.
This option instructs BitBake to try and continue processing
the job as long as possible even after encountering an error.
When an error occurs, the target that failed and those that
depend on it cannot be remade.
However, when you use this option other dependencies can
still be processed.
</p></div><div class="section" title="3.1.2. Metadata (Recipes)"><div class="titlepage"><div><div><h3 class="title" id="usingpoky-components-metadata">3.1.2. Metadata (Recipes)<span class="permalink"><a alt="Permalink" title="Permalink" href="#usingpoky-components-metadata">¶</a></span></h3></div></div></div><p>
Files that have the <code class="filename">.bb</code> suffix are
"recipes" files.
In general, a recipe contains information about a single piece
of software.
This information includes the location from which to download
the unaltered source, any source patches to be applied to that
source (if needed), which special configuration options to
apply, how to compile the source files, and how to package the
compiled output.
</p><p>
The term "package" is sometimes used to refer to recipes.
However, since the word "package" is used for the packaged
output from the OpenEmbedded build system (i.e.
<code class="filename">.ipk</code> or <code class="filename">.deb</code> files),
this document avoids using the term "package" when referring
to recipes.
</p></div><div class="section" title="3.1.3. Metadata (Virtual Providers)"><div class="titlepage"><div><div><h3 class="title" id="metadata-virtual-providers">3.1.3. Metadata (Virtual Providers)<span class="permalink"><a alt="Permalink" title="Permalink" href="#metadata-virtual-providers">¶</a></span></h3></div></div></div><p>
Prior to the build, if you know that several different recipes
provide the same functionality, you can use a virtual provider
(i.e. <code class="filename">virtual/*</code>) as a placeholder for the
actual provider.
The actual provider would be determined at build time.
In this case, you should add <code class="filename">virtual/*</code>
to
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPENDS" target="_top"><code class="filename">DEPENDS</code></a>,
rather than listing the specified provider.
You would select the actual provider by setting the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PREFERRED_PROVIDER" target="_top"><code class="filename">PREFERRED_PROVIDER</code></a>
variable (i.e.
<code class="filename">PREFERRED_PROVIDER_virtual/*</code>)
in the build's configuration file (e.g.
<code class="filename">poky/build/conf/local.conf</code>).
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
Any recipe that PROVIDES a <code class="filename">virtual/*</code>
item that is ultimately not selected through
<code class="filename">PREFERRED_PROVIDER</code> does not get built.
Preventing these recipes from building is usually the
desired behavior since this mechanism's purpose is to
select between mutually exclusive alternative providers.
</div><p>
</p><p>
The following lists specific examples of virtual providers:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<code class="filename">virtual/mesa</code>:
Provides <code class="filename">gbm.pc</code>.
</p></li><li class="listitem"><p>
<code class="filename">virtual/egl</code>:
Provides <code class="filename">egl.pc</code> and possibly
<code class="filename">wayland-egl.pc</code>.
</p></li><li class="listitem"><p>
<code class="filename">virtual/libgl</code>:
Provides <code class="filename">gl.pc</code> (i.e. libGL).
</p></li><li class="listitem"><p>
<code class="filename">virtual/libgles1</code>:
Provides <code class="filename">glesv1_cm.pc</code>
(i.e. libGLESv1_CM).
</p></li><li class="listitem"><p>
<code class="filename">virtual/libgles2</code>:
Provides <code class="filename">glesv2.pc</code>
(i.e. libGLESv2).
</p></li></ul></div><p>
</p></div><div class="section" title="3.1.4. Classes"><div class="titlepage"><div><div><h3 class="title" id="usingpoky-components-classes">3.1.4. Classes<span class="permalink"><a alt="Permalink" title="Permalink" href="#usingpoky-components-classes">¶</a></span></h3></div></div></div><p>
Class files (<code class="filename">.bbclass</code>) contain information
that is useful to share between
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#metadata" target="_top">Metadata</a>
files.
An example is the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-autotools" target="_top"><code class="filename">autotools</code></a>
class, which contains common settings for any application that
Autotools uses.
The
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes" target="_top">Classes</a>"
chapter in the Yocto Project Reference Manual provides
details about classes and how to use them.
</p></div><div class="section" title="3.1.5. Configuration"><div class="titlepage"><div><div><h3 class="title" id="usingpoky-components-configuration">3.1.5. Configuration<span class="permalink"><a alt="Permalink" title="Permalink" href="#usingpoky-components-configuration">¶</a></span></h3></div></div></div><p>
The configuration files (<code class="filename">.conf</code>) define
various configuration variables that govern the OpenEmbedded
build process.
These files fall into several areas that define machine
configuration options, distribution configuration options,
compiler tuning options, general common configuration options,
and user configuration options in
<code class="filename">local.conf</code>, which is found in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-directory" target="_top">Build Directory</a>.
</p></div></div><div class="section" title="3.2. Cross-Development Toolchain Generation"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="cross-development-toolchain-generation">3.2. Cross-Development Toolchain Generation<span class="permalink"><a alt="Permalink" title="Permalink" href="#cross-development-toolchain-generation">¶</a></span></h2></div></div></div><p>
The Yocto Project does most of the work for you when it comes to
creating
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#cross-development-toolchain" target="_top">cross-development toolchains</a>.
This section provides some technical background on how
cross-development toolchains are created and used.
For more information on toolchains, you can also see the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/sdk-manual/sdk-manual.html" target="_top">Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</a>
manual.
</p><p>
In the Yocto Project development environment, cross-development
toolchains are used to build the image and applications that run
on the target hardware.
With just a few commands, the OpenEmbedded build system creates
these necessary toolchains for you.
</p><p>
The following figure shows a high-level build environment regarding
toolchain construction and use.
</p><p>
</p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="720"><tr style="height: 540px"><td align="center"><img src="figures/cross-development-toolchains.png" align="middle" width="720" /></td></tr></table><p>
</p><p>
Most of the work occurs on the Build Host.
This is the machine used to build images and generally work within the
the Yocto Project environment.
When you run BitBake to create an image, the OpenEmbedded build system
uses the host <code class="filename">gcc</code> compiler to bootstrap a
cross-compiler named <code class="filename">gcc-cross</code>.
The <code class="filename">gcc-cross</code> compiler is what BitBake uses to
compile source files when creating the target image.
You can think of <code class="filename">gcc-cross</code> simply as an
automatically generated cross-compiler that is used internally within
BitBake only.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
The extensible SDK does not use
<code class="filename">gcc-cross-canadian</code> since this SDK
ships a copy of the OpenEmbedded build system and the sysroot
within it contains <code class="filename">gcc-cross</code>.
</div><p>
</p><p>
The chain of events that occurs when <code class="filename">gcc-cross</code> is
bootstrapped is as follows:
</p><pre class="literallayout">
gcc -> binutils-cross -> gcc-cross-initial -> linux-libc-headers -> glibc-initial -> glibc -> gcc-cross -> gcc-runtime
</pre><p>
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<code class="filename">gcc</code>:
The build host's GNU Compiler Collection (GCC).
</p></li><li class="listitem"><p>
<code class="filename">binutils-cross</code>:
The bare minimum binary utilities needed in order to run
the <code class="filename">gcc-cross-initial</code> phase of the
bootstrap operation.
</p></li><li class="listitem"><p>
<code class="filename">gcc-cross-initial</code>:
An early stage of the bootstrap process for creating
the cross-compiler.
This stage builds enough of the <code class="filename">gcc-cross</code>,
the C library, and other pieces needed to finish building the
final cross-compiler in later stages.
This tool is a "native" package (i.e. it is designed to run on
the build host).
</p></li><li class="listitem"><p>
<code class="filename">linux-libc-headers</code>:
Headers needed for the cross-compiler.
</p></li><li class="listitem"><p>
<code class="filename">glibc-initial</code>:
An initial version of the Embedded GLIBC needed to bootstrap
<code class="filename">glibc</code>.
</p></li><li class="listitem"><p>
<code class="filename">gcc-cross</code>:
The final stage of the bootstrap process for the
cross-compiler.
This stage results in the actual cross-compiler that
BitBake uses when it builds an image for a targeted
device.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
If you are replacing this cross compiler toolchain
with a custom version, you must replace
<code class="filename">gcc-cross</code>.
</div><p>
This tool is also a "native" package (i.e. it is
designed to run on the build host).
</p></li><li class="listitem"><p>
<code class="filename">gcc-runtime</code>:
Runtime libraries resulting from the toolchain bootstrapping
process.
This tool produces a binary that consists of the
runtime libraries need for the targeted device.
</p></li></ul></div><p>
</p><p>
You can use the OpenEmbedded build system to build an installer for
the relocatable SDK used to develop applications.
When you run the installer, it installs the toolchain, which contains
the development tools (e.g., the
<code class="filename">gcc-cross-canadian</code>),
<code class="filename">binutils-cross-canadian</code>, and other
<code class="filename">nativesdk-*</code> tools,
which are tools native to the SDK (i.e. native to
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDK_ARCH" target="_top"><code class="filename">SDK_ARCH</code></a>),
you need to cross-compile and test your software.
The figure shows the commands you use to easily build out this
toolchain.
This cross-development toolchain is built to execute on the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDKMACHINE" target="_top"><code class="filename">SDKMACHINE</code></a>,
which might or might not be the same
machine as the Build Host.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
If your target architecture is supported by the Yocto Project,
you can take advantage of pre-built images that ship with the
Yocto Project and already contain cross-development toolchain
installers.
</div><p>
</p><p>
Here is the bootstrap process for the relocatable toolchain:
</p><pre class="literallayout">
gcc -> binutils-crosssdk -> gcc-crosssdk-initial -> linux-libc-headers ->
glibc-initial -> nativesdk-glibc -> gcc-crosssdk -> gcc-cross-canadian
</pre><p>
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<code class="filename">gcc</code>:
The build host's GNU Compiler Collection (GCC).
</p></li><li class="listitem"><p>
<code class="filename">binutils-crosssdk</code>:
The bare minimum binary utilities needed in order to run
the <code class="filename">gcc-crosssdk-initial</code> phase of the
bootstrap operation.
</p></li><li class="listitem"><p>
<code class="filename">gcc-crosssdk-initial</code>:
An early stage of the bootstrap process for creating
the cross-compiler.
This stage builds enough of the
<code class="filename">gcc-crosssdk</code> and supporting pieces so that
the final stage of the bootstrap process can produce the
finished cross-compiler.
This tool is a "native" binary that runs on the build host.
</p></li><li class="listitem"><p>
<code class="filename">linux-libc-headers</code>:
Headers needed for the cross-compiler.
</p></li><li class="listitem"><p>
<code class="filename">glibc-initial</code>:
An initial version of the Embedded GLIBC needed to bootstrap
<code class="filename">nativesdk-glibc</code>.
</p></li><li class="listitem"><p>
<code class="filename">nativesdk-glibc</code>:
The Embedded GLIBC needed to bootstrap the
<code class="filename">gcc-crosssdk</code>.
</p></li><li class="listitem"><p>
<code class="filename">gcc-crosssdk</code>:
The final stage of the bootstrap process for the
relocatable cross-compiler.
The <code class="filename">gcc-crosssdk</code> is a transitory compiler
and never leaves the build host.
Its purpose is to help in the bootstrap process to create the
eventual relocatable <code class="filename">gcc-cross-canadian</code>
compiler, which is relocatable.
This tool is also a "native" package (i.e. it is
designed to run on the build host).
</p></li><li class="listitem"><p>
<code class="filename">gcc-cross-canadian</code>:
The final relocatable cross-compiler.
When run on the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SDKMACHINE" target="_top"><code class="filename">SDKMACHINE</code></a>,
this tool
produces executable code that runs on the target device.
Only one cross-canadian compiler is produced per architecture
since they can be targeted at different processor optimizations
using configurations passed to the compiler through the
compile commands.
This circumvents the need for multiple compilers and thus
reduces the size of the toolchains.
</p></li></ul></div><p>
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
For information on advantages gained when building a
cross-development toolchain installer, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/sdk-manual/sdk-manual.html#sdk-building-an-sdk-installer" target="_top">Building an SDK Installer</a>"
section in the Yocto Project Application Development and the
Extensible Software Development Kit (eSDK) manual.
</div></div><div class="section" title="3.3. Shared State Cache"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="shared-state-cache">3.3. Shared State Cache<span class="permalink"><a alt="Permalink" title="Permalink" href="#shared-state-cache">¶</a></span></h2></div></div></div><p>
By design, the OpenEmbedded build system builds everything from
scratch unless BitBake can determine that parts do not need to be
rebuilt.
Fundamentally, building from scratch is attractive as it means all
parts are built fresh and there is no possibility of stale data
causing problems.
When developers hit problems, they typically default back to
building from scratch so they know the state of things from the
start.
</p><p>
Building an image from scratch is both an advantage and a
disadvantage to the process.
As mentioned in the previous paragraph, building from scratch
ensures that everything is current and starts from a known state.
However, building from scratch also takes much longer as it
generally means rebuilding things that do not necessarily need
to be rebuilt.
</p><p>
The Yocto Project implements shared state code that supports
incremental builds.
The implementation of the shared state code answers the following
questions that were fundamental roadblocks within the OpenEmbedded
incremental build support system:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
What pieces of the system have changed and what pieces have
not changed?
</p></li><li class="listitem"><p>
How are changed pieces of software removed and replaced?
</p></li><li class="listitem"><p>
How are pre-built components that do not need to be rebuilt
from scratch used when they are available?
</p></li></ul></div><p>
</p><p>
For the first question, the build system detects changes in the
"inputs" to a given task by creating a checksum (or signature) of
the task's inputs.
If the checksum changes, the system assumes the inputs have changed
and the task needs to be rerun.
For the second question, the shared state (sstate) code tracks
which tasks add which output to the build process.
This means the output from a given task can be removed, upgraded
or otherwise manipulated.
The third question is partly addressed by the solution for the
second question assuming the build system can fetch the sstate
objects from remote locations and install them if they are deemed
to be valid.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
The OpenEmbedded build system does not maintain
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PR" target="_top"><code class="filename">PR</code></a>
information as part of the shared state packages.
Consequently, considerations exist that affect maintaining
shared state feeds.
For information on how the OpenEmbedded build system
works with packages and can track incrementing
<code class="filename">PR</code> information, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#automatically-incrementing-a-binary-package-revision-number" target="_top">Automatically Incrementing a Binary Package Revision Number</a>"
section in the Yocto Project Development Tasks Manual.
</div><p>
</p><p>
The rest of this section goes into detail about the overall
incremental build architecture, the checksums (signatures), shared
state, and some tips and tricks.
</p><div class="section" title="3.3.1. Overall Architecture"><div class="titlepage"><div><div><h3 class="title" id="overall-architecture">3.3.1. Overall Architecture<span class="permalink"><a alt="Permalink" title="Permalink" href="#overall-architecture">¶</a></span></h3></div></div></div><p>
When determining what parts of the system need to be built,
BitBake works on a per-task basis rather than a per-recipe
basis.
You might wonder why using a per-task basis is preferred over
a per-recipe basis.
To help explain, consider having the IPK packaging backend
enabled and then switching to DEB.
In this case, the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-install" target="_top"><code class="filename">do_install</code></a>
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package" target="_top"><code class="filename">do_package</code></a>
task outputs are still valid.
However, with a per-recipe approach, the build would not
include the <code class="filename">.deb</code> files.
Consequently, you would have to invalidate the whole build and
rerun it.
Rerunning everything is not the best solution.
Also, in this case, the core must be "taught" much about
specific tasks.
This methodology does not scale well and does not allow users
to easily add new tasks in layers or as external recipes
without touching the packaged-staging core.
</p></div><div class="section" title="3.3.2. Checksums (Signatures)"><div class="titlepage"><div><div><h3 class="title" id="overview-checksums">3.3.2. Checksums (Signatures)<span class="permalink"><a alt="Permalink" title="Permalink" href="#overview-checksums">¶</a></span></h3></div></div></div><p>
The shared state code uses a checksum, which is a unique
signature of a task's inputs, to determine if a task needs to
be run again.
Because it is a change in a task's inputs that triggers a
rerun, the process needs to detect all the inputs to a given
task.
For shell tasks, this turns out to be fairly easy because
the build process generates a "run" shell script for each task
and it is possible to create a checksum that gives you a good
idea of when the task's data changes.
</p><p>
To complicate the problem, there are things that should not be
included in the checksum.
First, there is the actual specific build path of a given
task - the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-WORKDIR" target="_top"><code class="filename">WORKDIR</code></a>.
It does not matter if the work directory changes because it
should not affect the output for target packages.
Also, the build process has the objective of making native
or cross packages relocatable.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
Both native and cross packages run on the build host.
However, cross packages generate output for the target
architecture.
</div><p>
The checksum therefore needs to exclude
<code class="filename">WORKDIR</code>.
The simplistic approach for excluding the work directory is to
set <code class="filename">WORKDIR</code> to some fixed value and
create the checksum for the "run" script.
</p><p>
Another problem results from the "run" scripts containing
functions that might or might not get called.
The incremental build solution contains code that figures out
dependencies between shell functions.
This code is used to prune the "run" scripts down to the
minimum set, thereby alleviating this problem and making the
"run" scripts much more readable as a bonus.
</p><p>
So far we have solutions for shell scripts.
What about Python tasks?
The same approach applies even though these tasks are more
difficult.
The process needs to figure out what variables a Python
function accesses and what functions it calls.
Again, the incremental build solution contains code that first
figures out the variable and function dependencies, and then
creates a checksum for the data used as the input to the task.
</p><p>
Like the <code class="filename">WORKDIR</code> case, situations exist
where dependencies should be ignored.
For these cases, you can instruct the build process to
ignore a dependency by using a line like the following:
</p><pre class="literallayout">
PACKAGE_ARCHS[vardepsexclude] = "MACHINE"
</pre><p>
This example ensures that the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PACKAGE_ARCHS" target="_top"><code class="filename">PACKAGE_ARCHS</code></a>
variable does not depend on the value of
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-MACHINE" target="_top"><code class="filename">MACHINE</code></a>,
even if it does reference it.
</p><p>
Equally, there are cases where we need to add dependencies
BitBake is not able to find.
You can accomplish this by using a line like the following:
</p><pre class="literallayout">
PACKAGE_ARCHS[vardeps] = "MACHINE"
</pre><p>
This example explicitly adds the <code class="filename">MACHINE</code>
variable as a dependency for
<code class="filename">PACKAGE_ARCHS</code>.
</p><p>
Consider a case with in-line Python, for example, where
BitBake is not able to figure out dependencies.
When running in debug mode (i.e. using
<code class="filename">-DDD</code>), BitBake produces output when it
discovers something for which it cannot figure out dependencies.
The Yocto Project team has currently not managed to cover
those dependencies in detail and is aware of the need to fix
this situation.
</p><p>
Thus far, this section has limited discussion to the direct
inputs into a task.
Information based on direct inputs is referred to as the
"basehash" in the code.
However, there is still the question of a task's indirect
inputs - the things that were already built and present in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#build-directory" target="_top">Build Directory</a>.
The checksum (or signature) for a particular task needs to add
the hashes of all the tasks on which the particular task
depends.
Choosing which dependencies to add is a policy decision.
However, the effect is to generate a master checksum that
combines the basehash and the hashes of the task's
dependencies.
</p><p>
At the code level, there are a variety of ways both the
basehash and the dependent task hashes can be influenced.
Within the BitBake configuration file, we can give BitBake
some extra information to help it construct the basehash.
The following statement effectively results in a list of
global variable dependency excludes - variables never
included in any checksum:
</p><pre class="literallayout">
BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \
SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \
USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \
PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \
CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX"
</pre><p>
The previous example excludes
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-WORKDIR" target="_top"><code class="filename">WORKDIR</code></a>
since that variable is actually constructed as a path within
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-TMPDIR" target="_top"><code class="filename">TMPDIR</code></a>,
which is on the whitelist.
</p><p>
The rules for deciding which hashes of dependent tasks to
include through dependency chains are more complex and are
generally accomplished with a Python function.
The code in <code class="filename">meta/lib/oe/sstatesig.py</code> shows
two examples of this and also illustrates how you can insert
your own policy into the system if so desired.
This file defines the two basic signature generators
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#oe-core" target="_top">OE-Core</a>
uses: "OEBasic" and "OEBasicHash".
By default, there is a dummy "noop" signature handler enabled
in BitBake.
This means that behavior is unchanged from previous versions.
OE-Core uses the "OEBasicHash" signature handler by default
through this setting in the <code class="filename">bitbake.conf</code>
file:
</p><pre class="literallayout">
BB_SIGNATURE_HANDLER ?= "OEBasicHash"
</pre><p>
The "OEBasicHash" <code class="filename">BB_SIGNATURE_HANDLER</code>
is the same as the "OEBasic" version but adds the task hash to
the stamp files.
This results in any
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#metadata" target="_top">Metadata</a>
change that changes the task hash, automatically
causing the task to be run again.
This removes the need to bump
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PR" target="_top"><code class="filename">PR</code></a>
values, and changes to Metadata automatically ripple across
the build.
</p><p>
It is also worth noting that the end result of these
signature generators is to make some dependency and hash
information available to the build.
This information includes:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<code class="filename">BB_BASEHASH_task-</code><em class="replaceable"><code>taskname</code></em>:
The base hashes for each task in the recipe.
</p></li><li class="listitem"><p>
<code class="filename">BB_BASEHASH_</code><em class="replaceable"><code>filename</code></em><code class="filename">:</code><em class="replaceable"><code>taskname</code></em>:
The base hashes for each dependent task.
</p></li><li class="listitem"><p>
<code class="filename">BBHASHDEPS_</code><em class="replaceable"><code>filename</code></em><code class="filename">:</code><em class="replaceable"><code>taskname</code></em>:
The task dependencies for each task.
</p></li><li class="listitem"><p>
<code class="filename">BB_TASKHASH</code>:
The hash of the currently running task.
</p></li></ul></div><p>
</p></div><div class="section" title="3.3.3. Shared State"><div class="titlepage"><div><div><h3 class="title" id="shared-state">3.3.3. Shared State<span class="permalink"><a alt="Permalink" title="Permalink" href="#shared-state">¶</a></span></h3></div></div></div><p>
Checksums and dependencies, as discussed in the previous
section, solve half the problem of supporting a shared state.
The other part of the problem is being able to use checksum
information during the build and being able to reuse or rebuild
specific components.
</p><p>
The
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-sstate" target="_top"><code class="filename">sstate</code></a>
class is a relatively generic implementation of how to
"capture" a snapshot of a given task.
The idea is that the build process does not care about the
source of a task's output.
Output could be freshly built or it could be downloaded and
unpacked from somewhere - the build process does not need to
worry about its origin.
</p><p>
There are two types of output, one is just about creating a
directory in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-WORKDIR" target="_top"><code class="filename">WORKDIR</code></a>.
A good example is the output of either
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-install" target="_top"><code class="filename">do_install</code></a>
or
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package" target="_top"><code class="filename">do_package</code></a>.
The other type of output occurs when a set of data is merged
into a shared directory tree such as the sysroot.
</p><p>
The Yocto Project team has tried to keep the details of the
implementation hidden in <code class="filename">sstate</code> class.
From a user's perspective, adding shared state wrapping to a task
is as simple as this
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-deploy" target="_top"><code class="filename">do_deploy</code></a>
example taken from the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-deploy" target="_top"><code class="filename">deploy</code></a>
class:
</p><pre class="literallayout">
DEPLOYDIR = "${WORKDIR}/deploy-${PN}"
SSTATETASKS += "do_deploy"
do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"
do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"
python do_deploy_setscene () {
sstate_setscene(d)
}
addtask do_deploy_setscene
do_deploy[dirs] = "${DEPLOYDIR} ${B}"
</pre><p>
The following list explains the previous example:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
Adding "do_deploy" to <code class="filename">SSTATETASKS</code>
adds some required sstate-related processing, which is
implemented in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-classes-sstate" target="_top"><code class="filename">sstate</code></a>
class, to before and after the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-deploy" target="_top"><code class="filename">do_deploy</code></a>
task.
</p></li><li class="listitem"><p>
The
<code class="filename">do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"</code>
declares that <code class="filename">do_deploy</code> places its
output in <code class="filename">${DEPLOYDIR}</code> when run
normally (i.e. when not using the sstate cache).
This output becomes the input to the shared state cache.
</p></li><li class="listitem"><p>
The
<code class="filename">do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"</code>
line causes the contents of the shared state cache to be
copied to <code class="filename">${DEPLOY_DIR_IMAGE}</code>.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
If <code class="filename">do_deploy</code> is not already in
the shared state cache or if its input checksum
(signature) has changed from when the output was
cached, the task will be run to populate the shared
state cache, after which the contents of the shared
state cache is copied to
<code class="filename">${DEPLOY_DIR_IMAGE}</code>.
If <code class="filename">do_deploy</code> is in the shared
state cache and its signature indicates that the
cached output is still valid (i.e. if no
relevant task inputs have changed), then the
contents of the shared state cache will be copied
directly to
<code class="filename">${DEPLOY_DIR_IMAGE}</code> by the
<code class="filename">do_deploy_setscene</code> task
instead, skipping the
<code class="filename">do_deploy</code> task.
</div><p>
</p></li><li class="listitem"><p>
The following task definition is glue logic needed to
make the previous settings effective:
</p><pre class="literallayout">
python do_deploy_setscene () {
sstate_setscene(d)
}
addtask do_deploy_setscene
</pre><p>
<code class="filename">sstate_setscene()</code> takes the flags
above as input and accelerates the
<code class="filename">do_deploy</code> task through the
shared state cache if possible.
If the task was accelerated,
<code class="filename">sstate_setscene()</code> returns True.
Otherwise, it returns False, and the normal
<code class="filename">do_deploy</code> task runs.
For more information, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#setscene" target="_top">setscene</a>"
section in the BitBake User Manual.
</p></li><li class="listitem"><p>
The <code class="filename">do_deploy[dirs] = "${DEPLOYDIR} ${B}"</code>
line creates <code class="filename">${DEPLOYDIR}</code> and
<code class="filename">${B}</code> before the
<code class="filename">do_deploy</code> task runs, and also sets
the current working directory of
<code class="filename">do_deploy</code> to
<code class="filename">${B}</code>.
For more information, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#variable-flags" target="_top">Variable Flags</a>"
section in the BitBake User Manual.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
In cases where
<code class="filename">sstate-inputdirs</code> and
<code class="filename">sstate-outputdirs</code> would be the
same, you can use
<code class="filename">sstate-plaindirs</code>.
For example, to preserve the
<code class="filename">${PKGD}</code> and
<code class="filename">${PKGDEST}</code> output from the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package" target="_top"><code class="filename">do_package</code></a>
task, use the following:
<pre class="literallayout">
do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}"
</pre></div><p>
</p></li><li class="listitem"><p>
<code class="filename">sstate-inputdirs</code> and
<code class="filename">sstate-outputdirs</code> can also be used
with multiple directories.
For example, the following declares
<code class="filename">PKGDESTWORK</code> and
<code class="filename">SHLIBWORK</code> as shared state
input directories, which populates the shared state
cache, and <code class="filename">PKGDATA_DIR</code> and
<code class="filename">SHLIBSDIR</code> as the corresponding
shared state output directories:
</p><pre class="literallayout">
do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}"
do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}"
</pre><p>
</p></li><li class="listitem"><p>
These methods also include the ability to take a
lockfile when manipulating shared state directory
structures, for cases where file additions or removals
are sensitive:
</p><pre class="literallayout">
do_package[sstate-lockfile] = "${PACKAGELOCK}"
</pre><p>
</p></li></ul></div><p>
</p><p>
Behind the scenes, the shared state code works by looking in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SSTATE_DIR" target="_top"><code class="filename">SSTATE_DIR</code></a>
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SSTATE_MIRRORS" target="_top"><code class="filename">SSTATE_MIRRORS</code></a>
for shared state files.
Here is an example:
</p><pre class="literallayout">
SSTATE_MIRRORS ?= "\
file://.* http://someserver.tld/share/sstate/PATH;downloadfilename=PATH \n \
file://.* file:///some/local/dir/sstate/PATH"
</pre><p>
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
The shared state directory
(<code class="filename">SSTATE_DIR</code>) is organized into
two-character subdirectories, where the subdirectory
names are based on the first two characters of the hash.
If the shared state directory structure for a mirror has the
same structure as <code class="filename">SSTATE_DIR</code>, you must
specify "PATH" as part of the URI to enable the build system
to map to the appropriate subdirectory.
</div><p>
</p><p>
The shared state package validity can be detected just by
looking at the filename since the filename contains the task
checksum (or signature) as described earlier in this section.
If a valid shared state package is found, the build process
downloads it and uses it to accelerate the task.
</p><p>
The build processes use the <code class="filename">*_setscene</code>
tasks for the task acceleration phase.
BitBake goes through this phase before the main execution
code and tries to accelerate any tasks for which it can find
shared state packages.
If a shared state package for a task is available, the
shared state package is used.
This means the task and any tasks on which it is dependent
are not executed.
</p><p>
As a real world example, the aim is when building an IPK-based
image, only the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package_write_ipk" target="_top"><code class="filename">do_package_write_ipk</code></a>
tasks would have their shared state packages fetched and
extracted.
Since the sysroot is not used, it would never get extracted.
This is another reason why a task-based approach is preferred
over a recipe-based approach, which would have to install the
output from every task.
</p></div><div class="section" title="3.3.4. Tips and Tricks"><div class="titlepage"><div><div><h3 class="title" id="tips-and-tricks">3.3.4. Tips and Tricks<span class="permalink"><a alt="Permalink" title="Permalink" href="#tips-and-tricks">¶</a></span></h3></div></div></div><p>
The code in the build system that supports incremental builds
is not simple code.
This section presents some tips and tricks that help you work
around issues related to shared state code.
</p><div class="section" title="3.3.4.1. Debugging"><div class="titlepage"><div><div><h4 class="title" id="overview-debugging">3.3.4.1. Debugging<span class="permalink"><a alt="Permalink" title="Permalink" href="#overview-debugging">¶</a></span></h4></div></div></div><p>
Seeing what metadata went into creating the input signature
of a shared state (sstate) task can be a useful debugging
aid.
This information is available in signature information
(<code class="filename">siginfo</code>) files in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-SSTATE_DIR" target="_top"><code class="filename">SSTATE_DIR</code></a>.
For information on how to view and interpret information in
<code class="filename">siginfo</code> files, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#dev-viewing-task-variable-dependencies" target="_top">Viewing Task Variable Dependencies</a>"
section in the Yocto Project Development Tasks Manual.
</p></div><div class="section" title="3.3.4.2. Invalidating Shared State"><div class="titlepage"><div><div><h4 class="title" id="invalidating-shared-state">3.3.4.2. Invalidating Shared State<span class="permalink"><a alt="Permalink" title="Permalink" href="#invalidating-shared-state">¶</a></span></h4></div></div></div><p>
The OpenEmbedded build system uses checksums and shared
state cache to avoid unnecessarily rebuilding tasks.
Collectively, this scheme is known as "shared state code."
</p><p>
As with all schemes, this one has some drawbacks.
It is possible that you could make implicit changes to your
code that the checksum calculations do not take into
account.
These implicit changes affect a task's output but do not
trigger the shared state code into rebuilding a recipe.
Consider an example during which a tool changes its output.
Assume that the output of <code class="filename">rpmdeps</code>
changes.
The result of the change should be that all the
<code class="filename">package</code> and
<code class="filename">package_write_rpm</code> shared state cache
items become invalid.
However, because the change to the output is
external to the code and therefore implicit,
the associated shared state cache items do not become
invalidated.
In this case, the build process uses the cached items
rather than running the task again.
Obviously, these types of implicit changes can cause
problems.
</p><p>
To avoid these problems during the build, you need to
understand the effects of any changes you make.
Realize that changes you make directly to a function
are automatically factored into the checksum calculation.
Thus, these explicit changes invalidate the associated
area of shared state cache.
However, you need to be aware of any implicit changes that
are not obvious changes to the code and could affect
the output of a given task.
</p><p>
When you identify an implicit change, you can easily
take steps to invalidate the cache and force the tasks
to run.
The steps you can take are as simple as changing a
function's comments in the source code.
For example, to invalidate package shared state files,
change the comment statements of
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package" target="_top"><code class="filename">do_package</code></a>
or the comments of one of the functions it calls.
Even though the change is purely cosmetic, it causes the
checksum to be recalculated and forces the OpenEmbedded
build system to run the task again.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
For an example of a commit that makes a cosmetic
change to invalidate shared state, see this
<a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/commit/meta/classes/package.bbclass?id=737f8bbb4f27b4837047cb9b4fbfe01dfde36d54" target="_top">commit</a>.
</div><p>
</p></div></div></div><div class="section" title="3.4. Automatically Added Runtime Dependencies"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="automatically-added-runtime-dependencies">3.4. Automatically Added Runtime Dependencies<span class="permalink"><a alt="Permalink" title="Permalink" href="#automatically-added-runtime-dependencies">¶</a></span></h2></div></div></div><p>
The OpenEmbedded build system automatically adds common types of
runtime dependencies between packages, which means that you do not
need to explicitly declare the packages using
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-RDEPENDS" target="_top"><code class="filename">RDEPENDS</code></a>.
Three automatic mechanisms exist (<code class="filename">shlibdeps</code>,
<code class="filename">pcdeps</code>, and <code class="filename">depchains</code>)
that handle shared libraries, package configuration (pkg-config)
modules, and <code class="filename">-dev</code> and
<code class="filename">-dbg</code> packages, respectively.
For other types of runtime dependencies, you must manually declare
the dependencies.
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
<code class="filename">shlibdeps</code>:
During the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package" target="_top"><code class="filename">do_package</code></a>
task of each recipe, all shared libraries installed by the
recipe are located.
For each shared library, the package that contains the
shared library is registered as providing the shared
library.
More specifically, the package is registered as providing
the
<a class="ulink" href="https://en.wikipedia.org/wiki/Soname" target="_top">soname</a>
of the library.
The resulting shared-library-to-package mapping
is saved globally in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PKGDATA_DIR" target="_top"><code class="filename">PKGDATA_DIR</code></a>
by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-packagedata" target="_top"><code class="filename">do_packagedata</code></a>
task.</p><p>Simultaneously, all executables and shared libraries
installed by the recipe are inspected to see what shared
libraries they link against.
For each shared library dependency that is found,
<code class="filename">PKGDATA_DIR</code> is queried to
see if some package (likely from a different recipe)
contains the shared library.
If such a package is found, a runtime dependency is added
from the package that depends on the shared library to the
package that contains the library.</p><p>The automatically added runtime dependency also
includes a version restriction.
This version restriction specifies that at least the
current version of the package that provides the shared
library must be used, as if
"<em class="replaceable"><code>package</code></em> (>= <em class="replaceable"><code>version</code></em>)"
had been added to
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-RDEPENDS" target="_top"><code class="filename">RDEPENDS</code></a>.
This forces an upgrade of the package containing the shared
library when installing the package that depends on the
library, if needed.</p><p>If you want to avoid a package being registered as
providing a particular shared library (e.g. because the library
is for internal use only), then add the library to
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PRIVATE_LIBS" target="_top"><code class="filename">PRIVATE_LIBS</code></a>
inside the package's recipe.
</p></li><li class="listitem"><p>
<code class="filename">pcdeps</code>:
During the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package" target="_top"><code class="filename">do_package</code></a>
task of each recipe, all pkg-config modules
(<code class="filename">*.pc</code> files) installed by the recipe
are located.
For each module, the package that contains the module is
registered as providing the module.
The resulting module-to-package mapping is saved globally in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-PKGDATA_DIR" target="_top"><code class="filename">PKGDATA_DIR</code></a>
by the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-packagedata" target="_top"><code class="filename">do_packagedata</code></a>
task.</p><p>Simultaneously, all pkg-config modules installed by
the recipe are inspected to see what other pkg-config
modules they depend on.
A module is seen as depending on another module if it
contains a "Requires:" line that specifies the other module.
For each module dependency,
<code class="filename">PKGDATA_DIR</code> is queried to see if some
package contains the module.
If such a package is found, a runtime dependency is added
from the package that depends on the module to the package
that contains the module.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
The <code class="filename">pcdeps</code> mechanism most often
infers dependencies between <code class="filename">-dev</code>
packages.
</div><p>
</p></li><li class="listitem"><p>
<code class="filename">depchains</code>:
If a package <code class="filename">foo</code> depends on a package
<code class="filename">bar</code>, then <code class="filename">foo-dev</code>
and <code class="filename">foo-dbg</code> are also made to depend on
<code class="filename">bar-dev</code> and
<code class="filename">bar-dbg</code>, respectively.
Taking the <code class="filename">-dev</code> packages as an
example, the <code class="filename">bar-dev</code> package might
provide headers and shared library symlinks needed by
<code class="filename">foo-dev</code>, which shows the need
for a dependency between the packages.</p><p>The dependencies added by
<code class="filename">depchains</code> are in the form of
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-RRECOMMENDS" target="_top"><code class="filename">RRECOMMENDS</code></a>.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
By default, <code class="filename">foo-dev</code> also has an
<code class="filename">RDEPENDS</code>-style dependency on
<code class="filename">foo</code>, because the default value of
<code class="filename">RDEPENDS_${PN}-dev</code> (set in
<code class="filename">bitbake.conf</code>) includes
"${PN}".
</div><p>To ensure that the dependency chain is never broken,
<code class="filename">-dev</code> and <code class="filename">-dbg</code>
packages are always generated by default, even if the
packages turn out to be empty.
See the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-ALLOW_EMPTY" target="_top"><code class="filename">ALLOW_EMPTY</code></a>
variable for more information.
</p></li></ul></div><p>
</p><p>
The <code class="filename">do_package</code> task depends on the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-packagedata" target="_top"><code class="filename">do_packagedata</code></a>
task of each recipe in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DEPENDS" target="_top"><code class="filename">DEPENDS</code></a>
through use of a
<code class="filename">[</code><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#variable-flags" target="_top"><code class="filename">deptask</code></a><code class="filename">]</code>
declaration, which guarantees that the required
shared-library/module-to-package mapping information will be available
when needed as long as <code class="filename">DEPENDS</code> has been
correctly set.
</p></div><div class="section" title="3.5. Fakeroot and Pseudo"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="fakeroot-and-pseudo">3.5. Fakeroot and Pseudo<span class="permalink"><a alt="Permalink" title="Permalink" href="#fakeroot-and-pseudo">¶</a></span></h2></div></div></div><p>
Some tasks are easier to implement when allowed to perform certain
operations that are normally reserved for the root user (e.g.
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-install" target="_top"><code class="filename">do_install</code></a>,
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-package_write_deb" target="_top"><code class="filename">do_package_write*</code></a>,
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-rootfs" target="_top"><code class="filename">do_rootfs</code></a>,
and
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#ref-tasks-image" target="_top"><code class="filename">do_image*</code></a>).
For example, the <code class="filename">do_install</code> task benefits
from being able to set the UID and GID of installed files to
arbitrary values.
</p><p>
One approach to allowing tasks to perform root-only operations
would be to require BitBake to run as root.
However, this method is cumbersome and has security issues.
The approach that is actually used is to run tasks that benefit
from root privileges in a "fake" root environment.
Within this environment, the task and its child processes believe
that they are running as the root user, and see an internally
consistent view of the filesystem.
As long as generating the final output (e.g. a package or an image)
does not require root privileges, the fact that some earlier
steps ran in a fake root environment does not cause problems.
</p><p>
The capability to run tasks in a fake root environment is known as
"<a class="ulink" href="http://man.he.net/man1/fakeroot" target="_top">fakeroot</a>",
which is derived from the BitBake keyword/variable
flag that requests a fake root environment for a task.
</p><p>
In the OpenEmbedded build system, the program that implements
fakeroot is known as Pseudo.
Pseudo overrides system calls by using the environment variable
<code class="filename">LD_PRELOAD</code>, which results in the illusion
of running as root.
To keep track of "fake" file ownership and permissions resulting
from operations that require root permissions, Pseudo uses
an SQLite 3 database.
This database is stored in
<code class="filename">${</code><a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-WORKDIR" target="_top"><code class="filename">WORKDIR</code></a><code class="filename">}/pseudo/files.db</code>
for individual recipes.
Storing the database in a file as opposed to in memory
gives persistence between tasks and builds, which is not
accomplished using fakeroot.
</p><div class="note" title="Caution" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Caution</h3>
If you add your own task that manipulates the same files or
directories as a fakeroot task, then that task also needs to
run under fakeroot.
Otherwise, the task cannot run root-only operations, and
cannot see the fake file ownership and permissions set by the
other task.
You need to also add a dependency on
<code class="filename">virtual/fakeroot-native:do_populate_sysroot</code>,
giving the following:
<pre class="literallayout">
fakeroot do_mytask () {
...
}
do_mytask[depends] += "virtual/fakeroot-native:do_populate_sysroot"
</pre></div><p>
For more information, see the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html#var-FAKEROOT" target="_top"><code class="filename">FAKEROOT*</code></a>
variables in the BitBake User Manual.
You can also reference the
"<a class="ulink" href="http://www.ibm.com/developerworks/opensource/library/os-aapseudo1/index.html" target="_top">Pseudo</a>"
and
"<a class="ulink" href="https://github.com/wrpseudo/pseudo/wiki/WhyNotFakeroot" target="_top">Why Not Fakeroot?</a>"
articles for background information on Pseudo.
</p></div><div class="section" title="3.6. Wayland"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="wayland">3.6. Wayland<span class="permalink"><a alt="Permalink" title="Permalink" href="#wayland">¶</a></span></h2></div></div></div><p>
<a class="ulink" href="http://en.wikipedia.org/wiki/Wayland_(display_server_protocol)" target="_top">Wayland</a>
is a computer display server protocol that
provides a method for compositing window managers to communicate
directly with applications and video hardware and expects them to
communicate with input hardware using other libraries.
Using Wayland with supporting targets can result in better control
over graphics frame rendering than an application might otherwise
achieve.
</p><p>
The Yocto Project provides the Wayland protocol libraries and the
reference
<a class="ulink" href="http://en.wikipedia.org/wiki/Wayland_(display_server_protocol)#Weston" target="_top">Weston</a>
compositor as part of its release.
This section describes what you need to do to implement Wayland and
use the compositor when building an image for a supporting target.
</p><div class="section" title="3.6.1. Support"><div class="titlepage"><div><div><h3 class="title" id="wayland-support">3.6.1. Support<span class="permalink"><a alt="Permalink" title="Permalink" href="#wayland-support">¶</a></span></h3></div></div></div><p>
The Wayland protocol libraries and the reference Weston
compositor ship as integrated packages in the
<code class="filename">meta</code> layer of the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#source-directory" target="_top">Source Directory</a>.
Specifically, you can find the recipes that build both Wayland
and Weston at
<code class="filename">meta/recipes-graphics/wayland</code>.
</p><p>
You can build both the Wayland and Weston packages for use only
with targets that accept the
<a class="ulink" href="https://en.wikipedia.org/wiki/Mesa_(computer_graphics)" target="_top">Mesa 3D and Direct Rendering Infrastructure</a>,
which is also known as Mesa DRI.
This implies that you cannot build and use the packages if your
target uses, for example, the
<span class="trademark">Intel</span>® Embedded Media
and Graphics Driver
(<span class="trademark">Intel</span>® EMGD) that
overrides Mesa DRI.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
Due to lack of EGL support, Weston 1.0.3 will not run
directly on the emulated QEMU hardware.
However, this version of Weston will run under X emulation
without issues.
</div><p>
</p></div><div class="section" title="3.6.2. Enabling Wayland in an Image"><div class="titlepage"><div><div><h3 class="title" id="enabling-wayland-in-an-image">3.6.2. Enabling Wayland in an Image<span class="permalink"><a alt="Permalink" title="Permalink" href="#enabling-wayland-in-an-image">¶</a></span></h3></div></div></div><p>
To enable Wayland, you need to enable it to be built and enable
it to be included in the image.
</p><div class="section" title="3.6.2.1. Building"><div class="titlepage"><div><div><h4 class="title" id="enable-building">3.6.2.1. Building<span class="permalink"><a alt="Permalink" title="Permalink" href="#enable-building">¶</a></span></h4></div></div></div><p>
To cause Mesa to build the <code class="filename">wayland-egl</code>
platform and Weston to build Wayland with Kernel Mode
Setting
(<a class="ulink" href="https://wiki.archlinux.org/index.php/Kernel_Mode_Setting" target="_top">KMS</a>)
support, include the "wayland" flag in the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-DISTRO_FEATURES" target="_top"><code class="filename">DISTRO_FEATURES</code></a>
statement in your <code class="filename">local.conf</code> file:
</p><pre class="literallayout">
DISTRO_FEATURES_append = " wayland"
</pre><p>
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
If X11 has been enabled elsewhere, Weston will build
Wayland with X11 support
</div><p>
</p></div><div class="section" title="3.6.2.2. Installing"><div class="titlepage"><div><div><h4 class="title" id="enable-installation-in-an-image">3.6.2.2. Installing<span class="permalink"><a alt="Permalink" title="Permalink" href="#enable-installation-in-an-image">¶</a></span></h4></div></div></div><p>
To install the Wayland feature into an image, you must
include the following
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-CORE_IMAGE_EXTRA_INSTALL" target="_top"><code class="filename">CORE_IMAGE_EXTRA_INSTALL</code></a>
statement in your <code class="filename">local.conf</code> file:
</p><pre class="literallayout">
CORE_IMAGE_EXTRA_INSTALL += "wayland weston"
</pre><p>
</p></div></div><div class="section" title="3.6.3. Running Weston"><div class="titlepage"><div><div><h3 class="title" id="running-weston">3.6.3. Running Weston<span class="permalink"><a alt="Permalink" title="Permalink" href="#running-weston">¶</a></span></h3></div></div></div><p>
To run Weston inside X11, enabling it as described earlier and
building a Sato image is sufficient.
If you are running your image under Sato, a Weston Launcher
appears in the "Utility" category.
</p><p>
Alternatively, you can run Weston through the command-line
interpretor (CLI), which is better suited for development work.
To run Weston under the CLI, you need to do the following after
your image is built:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Run these commands to export
<code class="filename">XDG_RUNTIME_DIR</code>:
</p><pre class="literallayout">
mkdir -p /tmp/$USER-weston
chmod 0700 /tmp/$USER-weston
export XDG_RUNTIME_DIR=/tmp/$USER-weston
</pre><p>
</p></li><li class="listitem"><p>
Launch Weston in the shell:
</p><pre class="literallayout">
weston
</pre></li></ol></div><p>
</p></div></div><div class="section" title="3.7. Licenses"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="overview-licenses">3.7. Licenses<span class="permalink"><a alt="Permalink" title="Permalink" href="#overview-licenses">¶</a></span></h2></div></div></div><p>
This section describes the mechanism by which the OpenEmbedded
build system tracks changes to licensing text.
The section also describes how to enable commercially licensed
recipes, which by default are disabled.
</p><p>
For information that can help you maintain compliance with
various open source licensing during the lifecycle of the product,
see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#maintaining-open-source-license-compliance-during-your-products-lifecycle" target="_top">Maintaining Open Source License Compliance During Your Project's Lifecycle</a>"
section in the Yocto Project Development Tasks Manual.
</p><div class="section" title="3.7.1. Tracking License Changes"><div class="titlepage"><div><div><h3 class="title" id="usingpoky-configuring-LIC_FILES_CHKSUM">3.7.1. Tracking License Changes<span class="permalink"><a alt="Permalink" title="Permalink" href="#usingpoky-configuring-LIC_FILES_CHKSUM">¶</a></span></h3></div></div></div><p>
The license of an upstream project might change in the future.
In order to prevent these changes going unnoticed, the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-LIC_FILES_CHKSUM" target="_top"><code class="filename">LIC_FILES_CHKSUM</code></a>
variable tracks changes to the license text. The checksums are
validated at the end of the configure step, and if the
checksums do not match, the build will fail.
</p><div class="section" title="3.7.1.1. Specifying the LIC_FILES_CHKSUM Variable"><div class="titlepage"><div><div><h4 class="title" id="usingpoky-specifying-LIC_FILES_CHKSUM">3.7.1.1. Specifying the <code class="filename">LIC_FILES_CHKSUM</code> Variable<span class="permalink"><a alt="Permalink" title="Permalink" href="#usingpoky-specifying-LIC_FILES_CHKSUM">¶</a></span></h4></div></div></div><p>
The <code class="filename">LIC_FILES_CHKSUM</code>
variable contains checksums of the license text in the
source code for the recipe.
Following is an example of how to specify
<code class="filename">LIC_FILES_CHKSUM</code>:
</p><pre class="literallayout">
LIC_FILES_CHKSUM = "file://COPYING;md5=xxxx \
file://licfile1.txt;beginline=5;endline=29;md5=yyyy \
file://licfile2.txt;endline=50;md5=zzzz \
..."
</pre><p>
</p><div class="note" title="Notes" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Notes</h3><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
When using "beginline" and "endline", realize
that line numbering begins with one and not
zero.
Also, the included lines are inclusive (i.e.
lines five through and including 29 in the
previous example for
<code class="filename">licfile1.txt</code>).
</p></li><li class="listitem"><p>
When a license check fails, the selected license
text is included as part of the QA message.
Using this output, you can determine the exact
start and finish for the needed license text.
</p></li></ul></div></div><p>
</p><p>
The build system uses the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-S" target="_top"><code class="filename">S</code></a>
variable as the default directory when searching files
listed in <code class="filename">LIC_FILES_CHKSUM</code>.
The previous example employs the default directory.
</p><p>
Consider this next example:
</p><pre class="literallayout">
LIC_FILES_CHKSUM = "file://src/ls.c;beginline=5;endline=16;\
md5=bb14ed3c4cda583abc85401304b5cd4e"
LIC_FILES_CHKSUM = "file://${WORKDIR}/license.html;md5=5c94767cedb5d6987c902ac850ded2c6"
</pre><p>
</p><p>
The first line locates a file in
<code class="filename">${S}/src/ls.c</code> and isolates lines five
through 16 as license text.
The second line refers to a file in
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-WORKDIR" target="_top"><code class="filename">WORKDIR</code></a>.
</p><p>
Note that <code class="filename">LIC_FILES_CHKSUM</code> variable is
mandatory for all recipes, unless the
<code class="filename">LICENSE</code> variable is set to "CLOSED".
</p></div><div class="section" title="3.7.1.2. Explanation of Syntax"><div class="titlepage"><div><div><h4 class="title" id="usingpoky-LIC_FILES_CHKSUM-explanation-of-syntax">3.7.1.2. Explanation of Syntax<span class="permalink"><a alt="Permalink" title="Permalink" href="#usingpoky-LIC_FILES_CHKSUM-explanation-of-syntax">¶</a></span></h4></div></div></div><p>
As mentioned in the previous section, the
<code class="filename">LIC_FILES_CHKSUM</code> variable lists all
the important files that contain the license text for the
source code.
It is possible to specify a checksum for an entire file,
or a specific section of a file (specified by beginning and
ending line numbers with the "beginline" and "endline"
parameters, respectively).
The latter is useful for source files with a license
notice header, README documents, and so forth.
If you do not use the "beginline" parameter, then it is
assumed that the text begins on the first line of the file.
Similarly, if you do not use the "endline" parameter,
it is assumed that the license text ends with the last
line of the file.
</p><p>
The "md5" parameter stores the md5 checksum of the license
text.
If the license text changes in any way as compared to
this parameter then a mismatch occurs.
This mismatch triggers a build failure and notifies
the developer.
Notification allows the developer to review and address
the license text changes.
Also note that if a mismatch occurs during the build,
the correct md5 checksum is placed in the build log and
can be easily copied to the recipe.
</p><p>
There is no limit to how many files you can specify using
the <code class="filename">LIC_FILES_CHKSUM</code> variable.
Generally, however, every project requires a few
specifications for license tracking.
Many projects have a "COPYING" file that stores the
license information for all the source code files.
This practice allows you to just track the "COPYING"
file as long as it is kept up to date.
</p><div class="note" title="Tips" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Tips</h3><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
If you specify an empty or invalid "md5"
parameter, BitBake returns an md5 mis-match
error and displays the correct "md5" parameter
value during the build.
The correct parameter is also captured in
the build log.
</p></li><li class="listitem"><p>
If the whole file contains only license text,
you do not need to use the "beginline" and
"endline" parameters.
</p></li></ul></div></div><p>
</p></div></div><div class="section" title="3.7.2. Enabling Commercially Licensed Recipes"><div class="titlepage"><div><div><h3 class="title" id="enabling-commercially-licensed-recipes">3.7.2. Enabling Commercially Licensed Recipes<span class="permalink"><a alt="Permalink" title="Permalink" href="#enabling-commercially-licensed-recipes">¶</a></span></h3></div></div></div><p>
By default, the OpenEmbedded build system disables
components that have commercial or other special licensing
requirements.
Such requirements are defined on a
recipe-by-recipe basis through the
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-LICENSE_FLAGS" target="_top"><code class="filename">LICENSE_FLAGS</code></a>
variable definition in the affected recipe.
For instance, the
<code class="filename">poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly</code>
recipe contains the following statement:
</p><pre class="literallayout">
LICENSE_FLAGS = "commercial"
</pre><p>
Here is a slightly more complicated example that contains both
an explicit recipe name and version (after variable expansion):
</p><pre class="literallayout">
LICENSE_FLAGS = "license_${PN}_${PV}"
</pre><p>
In order for a component restricted by a
<code class="filename">LICENSE_FLAGS</code> definition to be enabled and
included in an image, it needs to have a matching entry in the
global
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-LICENSE_FLAGS_WHITELIST" target="_top"><code class="filename">LICENSE_FLAGS_WHITELIST</code></a>
variable, which is a variable typically defined in your
<code class="filename">local.conf</code> file.
For example, to enable the
<code class="filename">poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly</code>
package, you could add either the string
"commercial_gst-plugins-ugly" or the more general string
"commercial" to <code class="filename">LICENSE_FLAGS_WHITELIST</code>.
See the
"<a class="link" href="#license-flag-matching" title="3.7.2.1. License Flag Matching">License Flag Matching</a>"
section for a full
explanation of how <code class="filename">LICENSE_FLAGS</code> matching
works.
Here is the example:
</p><pre class="literallayout">
LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly"
</pre><p>
Likewise, to additionally enable the package built from the
recipe containing
<code class="filename">LICENSE_FLAGS = "license_${PN}_${PV}"</code>,
and assuming that the actual recipe name was
<code class="filename">emgd_1.10.bb</code>, the following string would
enable that package as well as the original
<code class="filename">gst-plugins-ugly</code> package:
</p><pre class="literallayout">
LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly license_emgd_1.10"
</pre><p>
As a convenience, you do not need to specify the complete
license string in the whitelist for every package.
You can use an abbreviated form, which consists
of just the first portion or portions of the license
string before the initial underscore character or characters.
A partial string will match any license that contains the
given string as the first portion of its license.
For example, the following whitelist string will also match
both of the packages previously mentioned as well as any other
packages that have licenses starting with "commercial" or
"license".
</p><pre class="literallayout">
LICENSE_FLAGS_WHITELIST = "commercial license"
</pre><p>
</p><div class="section" title="3.7.2.1. License Flag Matching"><div class="titlepage"><div><div><h4 class="title" id="license-flag-matching">3.7.2.1. License Flag Matching<span class="permalink"><a alt="Permalink" title="Permalink" href="#license-flag-matching">¶</a></span></h4></div></div></div><p>
License flag matching allows you to control what recipes
the OpenEmbedded build system includes in the build.
Fundamentally, the build system attempts to match
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-LICENSE_FLAGS" target="_top"><code class="filename">LICENSE_FLAGS</code></a>
strings found in recipes against
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-LICENSE_FLAGS_WHITELIST" target="_top"><code class="filename">LICENSE_FLAGS_WHITELIST</code></a>
strings found in the whitelist.
A match causes the build system to include a recipe in the
build, while failure to find a match causes the build
system to exclude a recipe.
</p><p>
In general, license flag matching is simple.
However, understanding some concepts will help you
correctly and effectively use matching.
</p><p>
Before a flag
defined by a particular recipe is tested against the
contents of the whitelist, the expanded string
<code class="filename">_${PN}</code> is appended to the flag.
This expansion makes each
<code class="filename">LICENSE_FLAGS</code> value recipe-specific.
After expansion, the string is then matched against the
whitelist.
Thus, specifying
<code class="filename">LICENSE_FLAGS = "commercial"</code>
in recipe "foo", for example, results in the string
<code class="filename">"commercial_foo"</code>.
And, to create a match, that string must appear in the
whitelist.
</p><p>
Judicious use of the <code class="filename">LICENSE_FLAGS</code>
strings and the contents of the
<code class="filename">LICENSE_FLAGS_WHITELIST</code> variable
allows you a lot of flexibility for including or excluding
recipes based on licensing.
For example, you can broaden the matching capabilities by
using license flags string subsets in the whitelist.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
When using a string subset, be sure to use the part of
the expanded string that precedes the appended
underscore character (e.g.
<code class="filename">usethispart_1.3</code>,
<code class="filename">usethispart_1.4</code>, and so forth).
</div><p>
For example, simply specifying the string "commercial" in
the whitelist matches any expanded
<code class="filename">LICENSE_FLAGS</code> definition that starts
with the string "commercial" such as "commercial_foo" and
"commercial_bar", which are the strings the build system
automatically generates for hypothetical recipes named
"foo" and "bar" assuming those recipes simply specify the
following:
</p><pre class="literallayout">
LICENSE_FLAGS = "commercial"
</pre><p>
Thus, you can choose to exhaustively
enumerate each license flag in the whitelist and
allow only specific recipes into the image, or
you can use a string subset that causes a broader range of
matches to allow a range of recipes into the image.
</p><p>
This scheme works even if the
<code class="filename">LICENSE_FLAGS</code> string already
has <code class="filename">_${PN}</code> appended.
For example, the build system turns the license flag
"commercial_1.2_foo" into "commercial_1.2_foo_foo" and
would match both the general "commercial" and the specific
"commercial_1.2_foo" strings found in the whitelist, as
expected.
</p><p>
Here are some other scenarios:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
You can specify a versioned string in the recipe
such as "commercial_foo_1.2" in a "foo" recipe.
The build system expands this string to
"commercial_foo_1.2_foo".
Combine this license flag with a whitelist that has
the string "commercial" and you match the flag
along with any other flag that starts with the
string "commercial".
</p></li><li class="listitem"><p>
Under the same circumstances, you can use
"commercial_foo" in the whitelist and the build
system not only matches "commercial_foo_1.2" but
also matches any license flag with the string
"commercial_foo", regardless of the version.
</p></li><li class="listitem"><p>
You can be very specific and use both the
package and version parts in the whitelist (e.g.
"commercial_foo_1.2") to specifically match a
versioned recipe.
</p></li></ul></div><p>
</p></div><div class="section" title="3.7.2.2. Other Variables Related to Commercial Licenses"><div class="titlepage"><div><div><h4 class="title" id="other-variables-related-to-commercial-licenses">3.7.2.2. Other Variables Related to Commercial Licenses<span class="permalink"><a alt="Permalink" title="Permalink" href="#other-variables-related-to-commercial-licenses">¶</a></span></h4></div></div></div><p>
Other helpful variables related to commercial
license handling exist and are defined in the
<code class="filename">poky/meta/conf/distro/include/default-distrovars.inc</code> file:
</p><pre class="literallayout">
COMMERCIAL_AUDIO_PLUGINS ?= ""
COMMERCIAL_VIDEO_PLUGINS ?= ""
</pre><p>
If you want to enable these components, you can do so by
making sure you have statements similar to the following
in your <code class="filename">local.conf</code> configuration file:
</p><pre class="literallayout">
COMMERCIAL_AUDIO_PLUGINS = "gst-plugins-ugly-mad \
gst-plugins-ugly-mpegaudioparse"
COMMERCIAL_VIDEO_PLUGINS = "gst-plugins-ugly-mpeg2dec \
gst-plugins-ugly-mpegstream gst-plugins-bad-mpegvideoparse"
LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly commercial_gst-plugins-bad commercial_qmmp"
</pre><p>
Of course, you could also create a matching whitelist
for those components using the more general "commercial"
in the whitelist, but that would also enable all the
other packages with
<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#var-LICENSE_FLAGS" target="_top"><code class="filename">LICENSE_FLAGS</code></a>
containing "commercial", which you may or may not want:
</p><pre class="literallayout">
LICENSE_FLAGS_WHITELIST = "commercial"
</pre><p>
</p><p>
Specifying audio and video plug-ins as part of the
<code class="filename">COMMERCIAL_AUDIO_PLUGINS</code> and
<code class="filename">COMMERCIAL_VIDEO_PLUGINS</code> statements
(along with the enabling
<code class="filename">LICENSE_FLAGS_WHITELIST</code>) includes the
plug-ins or components into built images, thus adding
support for media formats or components.
</p></div></div></div><div class="section" title="3.8. x32 psABI"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="x32">3.8. x32 psABI<span class="permalink"><a alt="Permalink" title="Permalink" href="#x32">¶</a></span></h2></div></div></div><p>
x32 processor-specific Application Binary Interface
(<a class="ulink" href="https://software.intel.com/en-us/node/628948" target="_top">x32 psABI</a>)
is a native 32-bit processor-specific ABI for
<span class="trademark">Intel</span>® 64 (x86-64)
architectures.
An ABI defines the calling conventions between functions in a
processing environment.
The interface determines what registers are used and what the sizes are
for various C data types.
</p><p>
Some processing environments prefer using 32-bit applications even
when running on Intel 64-bit platforms.
Consider the i386 psABI, which is a very old 32-bit ABI for Intel
64-bit platforms.
The i386 psABI does not provide efficient use and access of the
Intel 64-bit processor resources, leaving the system underutilized.
Now consider the x86_64 psABI.
This ABI is newer and uses 64-bits for data sizes and program
pointers.
The extra bits increase the footprint size of the programs,
libraries, and also increases the memory and file system size
requirements.
Executing under the x32 psABI enables user programs to utilize CPU
and system resources more efficiently while keeping the memory
footprint of the applications low.
Extra bits are used for registers but not for addressing mechanisms.
</p><p>
The Yocto Project supports the final specifications of x32 psABI
as follows:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
You can create packages and images in x32 psABI format on
x86_64 architecture targets.
</p></li><li class="listitem"><p>
You can successfully build recipes with the x32 toolchain.
</p></li><li class="listitem"><p>
You can create and boot
<code class="filename">core-image-minimal</code> and
<code class="filename">core-image-sato</code> images.
</p></li><li class="listitem"><p>
RPM Package Manager (RPM) support exists for x32 binaries.
</p></li><li class="listitem"><p>
Support for large images exists.
</p></li></ul></div><p>
</p><p>
For steps on how to use x32 psABI, see the
"<a class="ulink" href="http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#using-x32-psabi" target="_top">Using x32 psABI</a>"
section in the Yocto Project Development Tasks Manual.
</p></div></div>
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