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documentation/kernel-manual/kernel-how-to.xml: Tree Construction section further explained 

Added text to help put tree construction into context with the developer.
The section felt as if the developer needed to be taking action on the steps
when in reality the steps are describing a lot of "behind-the-scenes" stuff
that happens when the YP tree is constructed.

(From yocto-docs rev: 1aafca94f3f3d5e07a0b2244ff5dbfe4a2c1ba8f)

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 2011-07-14 14:17:49 -07:00 committed by Richard Purdie
parent 0a7b3f8fdd
commit 51b3a231b0
1 changed files with 54 additions and 32 deletions
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@ -40,12 +40,24 @@
in the product.
Those feature descriptions list all necessary patches,
configuration, branching, tagging and feature divisions found in the kernel.
Thus, the Yocto Project kernel repository (or tree) is built.
The existence of this tree allows you to build images based on your configurations
and features.
</para>
<para>
You can find the files used to describe all the valid features and BSPs in the Yocto Project
kernel in any clone of the kernel Git tree.
The directory <filename>meta/cfg/kernel-cache/</filename> is a snapshot of all the kernel
configuration and feature descriptions (.scc) used to build the kernel repository.
kernel in any clone of the kernel Git tree.
For example, the following command clones the Yocto Project baseline kernel that
branched off of linux.org version 2.6.37:
<literallayout class='monospaced'>
$ git clone http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-2.6.37
</literallayout>
After you switch to the <filename>meta</filename> branch within the repository
you can see a snapshot of all the kernel configuration and feature descriptions that are
used to build the kernel repository.
These descriptions are in the form of <filename>.scc</filename> files.
</para>
<para>
You should realize, however, that browsing the snapshot of feature
descriptions and patches is not an effective way to determine what is in a
particular kernel branch.
@ -62,46 +74,56 @@
and development.
</para></note>
<para>
The general flow for constructing a project-specific kernel tree is as follows:
<orderedlist>
<listitem><para>A top-level kernel feature is passed to the kernel build subsystem.
Normally, this is a BSP for a particular kernel type.</para></listitem>
The following steps describe what happens during tree construction given the introduction
of a new top-level kernel feature or BSP.
These are the actions that effectively create the tree that includes the new feature, patch,
or BSP:
<orderedlist>
<listitem><para>A top-level kernel feature is passed to the kernel build subsystem.
Normally, this is a BSP for a particular kernel type.</para></listitem>
<listitem><para>The file that describes the top-level feature is located by searching
these system directories:</para>
<listitem><para>The file that describes the top-level feature is located by searching
these system directories:
<itemizedlist>
<listitem><para>The in-tree kernel-cache directories</para></listitem>
<itemizedlist>
<listitem><para>The in-tree kernel-cache directories, which are located
in <filename>meta/cfg/kernel-cache</filename></para></listitem>
<!-- <listitem><para>kernel-*-cache directories in layers</para></listitem> -->
<listitem><para>Recipe SRC_URIs</para></listitem>
<listitem><para>Areas pointed to by <filename>SRC_URI</filename> statements
found in recipes</para></listitem>
<!-- <listitem><para>configured and default templates</para></listitem> -->
</itemizedlist>
</itemizedlist>
<para>For a typical build a feature description of the format:
&lt;bsp name&gt;-&lt;kernel type&gt;.scc is the target of the search.
</para></listitem>
For a typical build, the target of the search is a
feature description in an <filename>.scc</filename> file
whose name follows this format:
<literallayout class='monospaced'>
&lt;bsp_name&gt;-&lt;kernel_type&gt;.scc
</literallayout>
</para></listitem>
<listitem><para>Once located, the feature description is either compiled into a simple script
of actions, or an existing equivalent script that was part of the
shipped kernel is located.</para></listitem>
<listitem><para>Once located, the feature description is either compiled into a simple script
of actions, or into an existing equivalent script that is already part of the
shipped kernel.</para></listitem>
<listitem><para>Extra features are appended to the top-level feature description.
These features can come from the KERNEL_FEATURES variable in recipes.</para></listitem>
<listitem><para>Extra features are appended to the top-level feature description.
These features can come from the <filename>KERNEL_FEATURES</filename> variable in
recipes.</para></listitem>
<listitem><para>Each extra feature is located, compiled and appended to the script from
step #3</para></listitem>
<listitem><para>Each extra feature is located, compiled and appended to the script
as described in step three.</para></listitem>
<listitem><para>The script is executed, and a meta-series is produced.
The meta-series is a description of all the branches, tags, patches and configurations that
need to be applied to the base Git repository to completely create the
BSP source (build) branch.</para></listitem>
<listitem><para>The script is executed to produce a meta-series.
The meta-series is a description of all the branches, tags, patches and configurations that
need to be applied to the base Git repository to completely create the
source (build) branch for the new BSP or feature.</para></listitem>
<listitem><para>The base repository is cloned, and the actions
listed in the meta-series are applied to the tree.</para></listitem>
<listitem><para>The base repository is cloned, and the actions
listed in the meta-series are applied to the tree.</para></listitem>
<listitem><para>The Git repository is left with the desired branch checked out and any
required branching, patching and tagging has been performed.</para></listitem>
</orderedlist>
<listitem><para>The Git repository is left with the desired branch checked out and any
required branching, patching and tagging has been performed.</para></listitem>
</orderedlist>
</para>
<para>