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documentation/dev-manual/dev-manual-model.xml: re-write of the kernel dev overview 

After getting the example in kenerl example appendix working I discovered
much that was wrong in this overview.  The overview attempts to generalize
all the situations for kernel modification.  These include code changes,
configuration changes, and the addition of new recipes.  It also includes
the situation where a developer wants to gather all the changes into a
separate layer for distribution and for when they want to push them up
the tree.

(From yocto-docs rev: 5498d7b38d3a2f14befa82b66af9919a449e0f04)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark 2011-08-10 16:27:45 -07:00 committed by Richard Purdie
parent 53a901e92e
commit fe76c380cc
1 changed files with 48 additions and 37 deletions
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@ -299,50 +299,57 @@
<link linkend='local-yp-release'>Yocto Project Release</link> in
<xref linkend='getting-setup'>Getting Setup</xref> earlier in this manual.
</para></listitem>
<listitem><para><emphasis>Establish a local copy of the Linux Yocto kernel files on your
system</emphasis>: In order to make modifications to the kernel you need a base
kernel with which to work.
You can set up a local Git repository of the kernel on which you are basing your
modifications.
<listitem><para><emphasis>Setting up the <filename>poky-extras</filename> Git
repository</emphasis>: This repository is the area for your configuration
fragments, new kernel recipes, and the kernel <filename>.bbappend</filename>
file used during the build.
It is good practice to set this repository up inside the local Yocto
Project files Git repository.
For information on how to get these files, see the bulleted item
<link linkend='poky-extras-repo'>The
<filename>poky-extras</filename> Git Repository</link> in
<xref linkend='getting-setup'>Getting Setup</xref> earlier in this manual.
</para></listitem>
<listitem><para><emphasis>Establish a local copy of the Linux Yocto kernel files on your
system</emphasis>: In order to make modifications to the kernel you need two things:
a bare clone of the Linux Yocto kernel you are modifying and a copy of that
bare clone.
The bare clone is required by the build process and is the area to which you
push your kernel source changes.
The copy of the bare clone is a local Git repository that contains all the kernel's
source files.
You make your changes to the files in this copy of the bare clone.
For information on how to set these two items up, see the bulleted item
<link linkend='local-kernel-files'>Linux Yocto Kernel</link> in
<xref linkend='getting-setup'>Getting Setup</xref> earlier in this manual.
</para></listitem>
<listitem><para><emphasis>Establish a local kernel layer by copying the
<filename>meta-skeleton</filename> layer</emphasis>: When you set up a kernel layer
for your changes you should follow a standard layout.
For kernel layers you can start with <filename>meta-skeleton</filename>, which
is a minimal, base kernel layer in the local Yocto Project files.
You can examine <filename>meta-skeleton</filename>
in the <filename>poky</filename> Git repository.</para>
<para>A layer is really just a location or area in which you place configuration
fragments and recipes that modify your kernel.
The layer, in this case, would be where all the recipes that define those dependencies
are kept.
The key point for a layer is that it is an isolated area that contains
all the relevant information for the project that the Yocto Project build
system knows about.</para>
<para></para></listitem>
<listitem><para><emphasis>Prepare to use the <filename>menuconfig</filename> tool</emphasis>:
The tool <filename>menuconfig</filename> used within Bitbake provides an
interactive method with which you can configure the kernel.
In order to use <filename>menuconfig</filename> you need to first source an environment
setup script found in the local <filename>poky</filename> Git repository.
The script is named <filename>oe-init-build-env</filename>.</para></listitem>
<listitem><para><emphasis>Make changes to the kernel source code if
applicable</emphasis>: Modifying the kernel does not always mean directly
changing source files.
However, if you have to do this then you make the changes in the local
Git repository you set up to hold the source files (i.e. the copy of the
bare clone).
Once the changes are made you need to use Git commands to commit the changes
and then push them to the bare clone.</para></listitem>
<listitem><para><emphasis>Make kernel configuration changes
to your local kernel layer</emphasis>: Use <filename>menuconfig</filename>
to enable and disable the configurations to the Linux Yocto kernel.
to your local kernel layer if applicable</emphasis>:
If your situation calls for changing the kernel's configuration you can
use <filename>menuconfig</filename>
to enable and disable kernel configurations.
Using <filename>menuconfig</filename> allows you to develop and test the
configuration changes you are making to the kernel.</para></listitem>
<listitem><para><emphasis>Make kernel recipe changes to your new kernel
layer</emphasis>: The standard layer structure organizes recipe files you
need to edit in several <filename>recipes-*</filename> directories within the
kernel layer.
Recipe changes include altering recipes (<filename>.bb</filename> files), removing
recipes you don't use, and adding new recipes that you need to support your hardware.
<listitem><para><emphasis>Add new kernel recipes</emphasis>: The standard
layer structure organizes recipe files inside the
<filename>meta-kernel-dev</filename> layer that is within the
<filename>poky-extras</filename> Git repository.
If you need to add new kernel recipes you add them within this layer.
Also within this area you will find the <filename>.bbappend</filename>
file that appends information to the kernel's recipe file used during the
build.
</para></listitem>
<listitem><para><emphasis>Prepare for the build</emphasis>: Once you have made all the
changes to your kernel layer there remains a few things
changes to your kernel (configurations, source code changes, recipe additions,
or recipe changes) there remains a few things
you need to do for the Yocto Project build system in order for it to create your image.
If you have not done so you need to get the build environment ready by sourcing
the environment setup script described earlier.
@ -350,7 +357,9 @@
<para>The entire process for building an image is overviewed in the
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#building-image'>
Building an Image</ulink> section of the Yocto Project Quick Start.
You might want to reference this information.</para></listitem>
You might want to reference this information.
Also, you should look at the detailed examples found in the appendices at
end of this manual.</para></listitem>
<listitem><para><emphasis>Build the image</emphasis>: The Yocto Project uses the BitBake
tool to build images based on the type of image you want to create.
You can find more information on BitBake
@ -366,7 +375,9 @@
in the kernel layer</emphasis>: Up to this point all the configuration changes to the
kernel have been done and tested iteratively.
Once they are tested and ready to go you can move them into the kernel layer,
which allows you to distribute the layer.</para></listitem>
which allows you to distribute the layer.
[WRITER'S NOTE: Not sure if the layer is meta-kernel-dev or if it would be
a new layer copied from the work done there.]</para></listitem>
<listitem><para><emphasis>Push your configuration and recipe changes upstream to the
linux Yocto Git repository (in-tree changes)</emphasis>: If the changes you made
are suited for all Linux Yocto users you might want to push the changes up into