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ref-manual: Start of new section on deeper look into dev env. 

Start of the new section on the closer look into the development
environment.

(From yocto-docs rev: e1f1cee951433144d1adedcb4f0bbc8d8296c444)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark 2013-07-08 21:42:32 +03:00 committed by Richard Purdie
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@ -153,6 +153,216 @@
</section>
</section>
<section id="a-closer-look-at-the-yocto-project-development-environment">
<title>A Closer Look at the Yocto Project Development Environment</title>
<para>
This section is a work-in-progress for an expanded discussion of the
Yocto Project Development Environment.
The section is rooted in the figure found in the
"<ulink url='&YOCTO_DOCS_QS_URL;#yp-intro'>Introducing the Yocto Project Development Environment</ulink>"
section of the Yocto Project Quick Start.
This expanded discussion presents a deeper level of detail regarding
sources of input, generated output, and controlling
<ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>.
</para>
<para>
I will either replicate the exact figure from the YP Quick Start here
or I will create a more simplified version that can be used as the
top-level diagram from which to base subsequent sections and expanded
illustrations.
</para>
<para>
[NEED REPEATED FIGURE HERE OR A NEW FIGURE]
</para>
<para>
This paragraph will introduce the main blocks of the preceding figure
to overview and organize the remainder of the section:
<itemizedlist>
<listitem><para><emphasis>User Configuration:</emphasis>
Methods by with the user can directly control the build
process.</para></listitem>
<listitem><para><emphasis>Metadata Layers:</emphasis>
Various layers that provide software, machine, and
distro Metadata.</para></listitem>
<listitem><para><emphasis>Soure Files:</emphasis>
Upstream releases, local projects, and SCMs.</para></listitem>
<listitem><para><emphasis>Build System:</emphasis>
Processes inside the BitBake "box".
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.</para></listitem>
<listitem><para><emphasis>Package Feeds</emphasis>
Package feeds into the BitBake process.</para></listitem>
<listitem><para><emphasis>Images</emphasis>
Images produced by the development process.
Where do they go?
Can you mess with them (i.e. freely delete them or move them?).
</para></listitem>
<listitem><para><emphasis>Application Development SDK</emphasis>
Cross-development tools that are produced along with an image
or separately with BitBake.</para></listitem>
</itemizedlist>
</para>
<section id="user-configuration">
<title>User Configuration</title>
<para>
User configuration affects how you define the build.
The following figure shows an expanded representation of the
user configuration in the Yocto Project development environment:
</para>
<mediaobject>
<imageobject>
<imagedata fileref="figures/user-configuration.png"
format="PNG" align='center' scalefit='1' width="100%"/>
</imageobject>
</mediaobject>
<para>
BitBake needs some basic configuration files in order to complete
a build.
These files are <filename>*.conf</filename> files and the
minimally necessary ones reside as example files in the
<ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
For simplicity, this section refers to the Source Directory as
the "Poky Directory."
<note>
Poky is primarily an aggregation of existing repositories and
is not actual canonical upstream source for anything.
</note>
When you clone the <filename>poky</filename> Git repository or you
download and unpack a Yocto Project release, you can set up the
Source Directory to be named anything you want.
Here, though, we will assume that you have a cloned repository that
has the default name <filename>poky</filename>.
</para>
<para>
The <filename>meta-yocto</filename> layer inside Poky contains
a <filename>conf</filename> 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 <filename>oe-init-build-env</filename>.
<note>
The <filename>oe-init-build-env</filename> script also exists
in the <filename>meta</filename> directory of the OE-Core
root directory.
Both scripts look for sample configuration files through
a <filename>$TEMPLATECONF</filename> variable.
When using the Yocto Project Development Environment,
that location resolves to the samples found in the
<filename>poky/meta-yocto/conf</filename> directory.
</note>
</para>
<para>
When you source the build environment script, it creates a
<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>
that BitBake uses as the area in which it does all its work
during builds.
The Build Directory has a <filename>conf</filename> directory that
contains default versions of your <filename>local.conf</filename>
and <filename>bblayers.conf</filename> configuration files.
These default configuration files are created by
<filename>oe-init-build-env</filename> only if versions of these
files do not already exist in the Build Directory you specify
when you run the script.
</para>
<para>
The <filename>local.conf</filename> file provides many
basic variables that define your build.
Here is a list of a few.
To see the default configurations in a <filename>local.conf</filename>
file created by the build environment script, see the
<filename>local.conf.sample</filename> in the
<filename>meta-yocto</filename> layer:
<itemizedlist>
<listitem><para><emphasis>Parallelism Options:</emphasis>
Controlled by the
<link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename></link>
and
<link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></link>
variables.</para></listitem>
<listitem><para><emphasis>Target Machine Selection:</emphasis>
Controlled by the
<link linkend='var-MACHINE'><filename>MACHINE</filename></link>
variable.</para></listitem>
<listitem><para><emphasis>Download Directory:</emphasis>
Controlled by the
<link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
variable.</para></listitem>
<listitem><para><emphasis>Shared State Directory:</emphasis>
Controlled by the
<link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link>
variable.</para></listitem>
<listitem><para><emphasis>Build Output:</emphasis>
Controlled by the
<link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>
variable.</para></listitem>
</itemizedlist>
</para>
<para>
The <filename>bblayers.conf</filename> file tells BitBake what
layers you want it to consider during the build.
The list of layers includes default layers needed by the build
system.
You have to manually add any custom layers that you have created.
You can find more information on working with the
<filename>bblayers.conf</filename> file in the
"<ulink url='&YOCTO_DOCS_DEV_URL;#enabling-your-layer'>Enabling Your Layer</ulink>"
section in the Yocto Project Development Manual.
</para>
<para>
The files <filename>site.conf</filename> and
<filename>auto.conf</filename> are not created by the environment
initialization script.
If you want these configuration files, you must create them
yourself.
Here a bit about what these files do:
<itemizedlist>
<listitem><para><emphasis><filename>site.conf</filename>:</emphasis>
I don't really know what this does.
All I know is that if you want it, you need to hand-create
it.
I need some information on it.</para></listitem>
<listitem><para><emphasis><filename>auto.conf</filename>:</emphasis>
This file is not hand-created.
Rather, 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 <filename>local.conf</filename>
or <filename>site.conf</filename> files.
</para></listitem>
</itemizedlist>
</para>
<para>
All configuration files can undergo edits to further define
the build.
This process is represented by the "User Configuration Edits"
box in the figure.
</para>
<para>
When you launch your build with the
<filename>bitbake &lt;target&gt;</filename> command, BitBake
draws on the user configurations you have provided in your
Build Directory.
</para>
</section>
</section>
<section id="cross-development-toolchain-generation">
<title>Cross-Development Toolchain Generation</title>