mirror of
https://git.yoctoproject.org/poky
synced 2026-05-31 00:39:46 +00:00
getting-started: Created "Some Basic Terms" section.
This section contains some fundamental terms people decided were important enough to have in this getting-started manual. (From yocto-docs rev: 42bfa0d8fc0a61c26f6b2f4b9e285c06255e8b8d) Signed-off-by: Scott Rifenbark <srifenbark@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
committed by
Richard Purdie
Richard Purdie
parent
6f488928cb
commit
3461d890d3
@@ -1147,8 +1147,184 @@
|
||||
<section id='some-basic-terms'>
|
||||
<title>Some Basic Terms</title>
|
||||
|
||||
</section>
|
||||
<para>
|
||||
It helps to understand some basic fundamental terms when
|
||||
learning the Yocto Project.
|
||||
Although a list of terms exists in the
|
||||
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-terms'>Yocto Project Terms</ulink>"
|
||||
section of the Yocto Project Reference Manual, this section
|
||||
provides the definitions of some terms helpful for getting started:
|
||||
<itemizedlist>
|
||||
<listitem><para>
|
||||
<emphasis>Configuration Files:</emphasis>
|
||||
Files that hold global definitions of variables,
|
||||
user-defined variables, and hardware configuration
|
||||
information.
|
||||
These files tell the OpenEmbedded build system what to
|
||||
build and what to put into the image to support a
|
||||
particular platform.
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
<emphasis>Extensible Software Development Kit (eSDK):</emphasis>
|
||||
A custom SDK for application developers.
|
||||
This eSDK allows developers to incorporate their library
|
||||
and programming changes back into the image to make
|
||||
their code available to other application developers.
|
||||
For information on the eSDK, see the
|
||||
<ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and Extensible Software Development Kit (eSDK)</ulink>
|
||||
manual.
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
<emphasis>Layer:</emphasis>
|
||||
A collection of related recipes.
|
||||
Layers allow you to consolidate related metadata to
|
||||
customize your build.
|
||||
Layers also isolate information used when building
|
||||
for multiple architectures.
|
||||
Layers are hierarchical in their ability to override
|
||||
previous specifications.
|
||||
You can include any number of available layers from the
|
||||
Yocto Project and customize the build by adding your
|
||||
layers after them.
|
||||
You can search the Layer Index for layers used within
|
||||
Yocto Project.</para>
|
||||
|
||||
<para>For more detailed information on layers, see the
|
||||
"<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
|
||||
section in the Yocto Project Development Tasks Manual.
|
||||
For a discussion specifically on BSP Layers, see the
|
||||
"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
|
||||
section in the Yocto Project Board Support Packages (BSP)
|
||||
Developer's Guide.
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
<emphasis>Metadata:</emphasis>
|
||||
A key element of the Yocto Project is the Metadata that
|
||||
is used to construct a Linux distribution and is contained
|
||||
in the files that the
|
||||
<link linkend='gs-term-openembedded-build-system'>OpenEmbedded build system</link> parses
|
||||
when building an image.
|
||||
In general, Metadata includes recipes, configuration
|
||||
files, and other information that refers to the build
|
||||
instructions themselves, as well as the data used to
|
||||
control what things get built and the effects of the
|
||||
build.
|
||||
Metadata also includes commands and data used to
|
||||
indicate what versions of software are used, from
|
||||
where they are obtained, and changes or additions to the
|
||||
software itself (patches or auxiliary files) that
|
||||
are used to fix bugs or customize the software for use
|
||||
in a particular situation.
|
||||
OpenEmbedded Core is an important set of validated
|
||||
metadata.
|
||||
</para></listitem>
|
||||
<listitem><para id='gs-term-openembedded-build-system'>
|
||||
<emphasis>OpenEmbedded Build System:</emphasis>
|
||||
The terms "BitBake" and "build system" are sometimes
|
||||
used for the OpenEmbedded Build System.</para>
|
||||
|
||||
<para>BitBake is a task scheduler and execution engine
|
||||
that parses instructions (i.e. recipes) and configuration
|
||||
data.
|
||||
After a parsing phase, BitBake creates a dependency tree
|
||||
to order the compilation, schedules the compilation of
|
||||
the included code, and finally executes the building
|
||||
of the specified custom Linux image (distribution).
|
||||
BitBake is similar to the <filename>make</filename>
|
||||
tool.</para>
|
||||
|
||||
<para>During a build process, the build system tracks
|
||||
dependencies and performs a native or cross-compilation
|
||||
of the package.
|
||||
As a first step in a cross-build setup, the framework
|
||||
attempts to create a cross-compiler toolchain
|
||||
(i.e. Extensible SDK) suited for the target platform.
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
<emphasis>OpenEmbedded-Core (OE-Core):</emphasis>
|
||||
OE-Core is metadata comprised of foundation recipes,
|
||||
classes, and associated files that are meant to be
|
||||
common among many different OpenEmbedded-derived systems,
|
||||
including the Yocto Project.
|
||||
OE-Core is a curated subset of an original repository
|
||||
developed by the OpenEmbedded community that has been
|
||||
pared down into a smaller, core set of continuously
|
||||
validated recipes.
|
||||
The result is a tightly controlled and an quality-assured
|
||||
core set of recipes.</para>
|
||||
|
||||
<para>You can see the Metadata in the
|
||||
<filename>meta</filename> directory of the Yocto Project
|
||||
<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi'>Source Repositories</ulink>.
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
<emphasis>Packages:</emphasis>
|
||||
In the context of the Yocto Project, this term refers to a
|
||||
recipe's packaged output produced by BitBake (i.e. a
|
||||
"baked recipe").
|
||||
A package is generally the compiled binaries produced from the
|
||||
recipe's sources.
|
||||
You "bake" something by running it through BitBake.</para>
|
||||
|
||||
<para>It is worth noting that the term "package" can,
|
||||
in general, have subtle meanings.
|
||||
For example, the packages referred to in the
|
||||
"<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Build Host Packages</ulink>"
|
||||
section in the Yocto Project Quick Start are compiled binaries
|
||||
that, when installed, add functionality to your Linux
|
||||
distribution.</para>
|
||||
|
||||
<para>Another point worth noting is that historically within
|
||||
the Yocto Project, recipes were referred to as packages - thus,
|
||||
the existence of several BitBake variables that are seemingly
|
||||
mis-named,
|
||||
(e.g. <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>,
|
||||
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>,
|
||||
and
|
||||
<ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>).
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
<emphasis>Poky:</emphasis>
|
||||
Poky, which is pronounced <emphasis>Pock</emphasis>-ee,
|
||||
is a reference embedded distribution and a reference
|
||||
test configuration.
|
||||
Poky provides the following:
|
||||
<itemizedlist>
|
||||
<listitem><para>
|
||||
A base-level functional distro used to illustrate
|
||||
how to customize a distribution.
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
A means by which to test the Yocto Project
|
||||
components (i.e. Poky is used to validate
|
||||
the Yocto Project).
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
A vehicle through which you can download
|
||||
the Yocto Project.
|
||||
</para></listitem>
|
||||
</itemizedlist>
|
||||
Poky is not a product level distro.
|
||||
Rather, it is a good starting point for customization.
|
||||
<note>
|
||||
Poky is an integration layer on top of OE-Core.
|
||||
</note>
|
||||
</para></listitem>
|
||||
<listitem><para>
|
||||
<emphasis>Recipe:</emphasis>
|
||||
The most common form of metadata.
|
||||
A recipe contains a list of settings and tasks
|
||||
(i.e. instructions) for building packages that are then
|
||||
used to build the binary image.
|
||||
A recipe describes where you get source code and which
|
||||
patches to apply.
|
||||
Recipes describe dependencies for libraries or for other
|
||||
recipes as well as configuration and compilation options.
|
||||
Related recipes are consolidated into a layer.
|
||||
</para></listitem>
|
||||
</itemizedlist>
|
||||
</para>
|
||||
</section>
|
||||
</chapter>
|
||||
<!--
|
||||
vim: expandtab tw=80 ts=4
|
||||
|
||||
Reference in New Issue
Block a user