2010-11-29 15:30:27 +00:00
|
|
|
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
|
2012-03-09 21:35:11 +00:00
|
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
|
|
|
|
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
|
2010-11-29 15:30:27 +00:00
|
|
|
|
|
|
|
<chapter id='kernel-concepts'>
|
|
|
|
|
|
|
|
<title>Yocto Project Kernel Concepts</title>
|
|
|
|
|
|
|
|
<section id='concepts-org'>
|
|
|
|
<title>Introduction</title>
|
|
|
|
<para>
|
|
|
|
This chapter provides conceptual information about the Yocto Project kernel:
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem><para>Kernel Goals</para></listitem>
|
|
|
|
<listitem><para>Yocto Project Kernel Development and Maintenance Overview</para></listitem>
|
|
|
|
<listitem><para>Kernel Architecture</para></listitem>
|
|
|
|
<listitem><para>Kernel Tools</para></listitem>
|
|
|
|
</itemizedlist>
|
|
|
|
</para>
|
|
|
|
</section>
|
|
|
|
|
|
|
|
<section id='kernel-goals'>
|
|
|
|
<title>Kernel Goals</title>
|
|
|
|
<para>
|
|
|
|
The complexity of embedded kernel design has increased dramatically.
|
|
|
|
Whether it is managing multiple implementations of a particular feature or tuning and
|
|
|
|
optimizing board specific features, flexibility and maintainability are key concerns.
|
|
|
|
The Yocto Project Linux kernel is presented with the embedded
|
|
|
|
developer's needs in mind and has evolved to assist in these key concerns.
|
|
|
|
For example, prior methods such as applying hundreds of patches to an extracted
|
|
|
|
tarball have been replaced with proven techniques that allow easy inspection,
|
|
|
|
bisection and analysis of changes.
|
|
|
|
Application of these techniques also creates a platform for performing integration and
|
|
|
|
collaboration with the thousands of upstream development projects.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
With all these considerations in mind, the Yocto Project kernel and development team
|
|
|
|
strives to attain these goals:
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem><para>Allow the end user to leverage community best practices to seamlessly
|
|
|
|
manage the development, build and debug cycles.</para></listitem>
|
|
|
|
<listitem><para>Create a platform for performing integration and collaboration with the
|
|
|
|
thousands of upstream development projects that exist.</para></listitem>
|
|
|
|
<listitem><para>Provide mechanisms that support many different work flows, front-ends and
|
|
|
|
management techniques.</para></listitem>
|
|
|
|
<listitem><para>Deliver the most up-to-date kernel possible while still ensuring that
|
2010-12-03 15:32:13 +00:00
|
|
|
the baseline kernel is the most stable official release.</para></listitem>
|
2012-01-03 15:47:07 +00:00
|
|
|
<listitem><para>Include major technological features as part of Yocto Project's
|
|
|
|
upward revision strategy.</para></listitem>
|
2011-09-29 17:31:42 +00:00
|
|
|
<listitem><para>Present a kernel Git repository that, similar to the upstream
|
|
|
|
<filename>kernel.org</filename> tree,
|
|
|
|
has a clear and continuous history.</para></listitem>
|
2010-11-29 15:30:27 +00:00
|
|
|
<listitem><para>Deliver a key set of supported kernel types, where each type is tailored
|
2012-01-03 15:47:07 +00:00
|
|
|
to meet a specific use (e.g. networking, consumer, devices, and so forth).</para></listitem>
|
2011-09-29 17:31:42 +00:00
|
|
|
<listitem><para>Employ a Git branching strategy that, from a developer's point of view,
|
|
|
|
results in a linear path from the baseline <filename>kernel.org</filename>,
|
|
|
|
through a select group of features and
|
2010-11-29 15:30:27 +00:00
|
|
|
ends with their BSP-specific commits.</para></listitem>
|
|
|
|
</itemizedlist>
|
|
|
|
</para>
|
|
|
|
</section>
|
|
|
|
|
|
|
|
<section id='kernel-big-picture'>
|
|
|
|
<title>Yocto Project Kernel Development and Maintenance Overview</title>
|
|
|
|
<para>
|
2011-09-29 17:31:42 +00:00
|
|
|
The Yocto Project kernel, like other kernels, is based off the Linux kernel release
|
2010-11-29 15:30:27 +00:00
|
|
|
from <ulink url='http://www.kernel.org'></ulink>.
|
2011-09-29 17:31:42 +00:00
|
|
|
At the beginning of a major development cycle, the Yocto Project team
|
|
|
|
chooses its Yocto Project kernel
|
|
|
|
based on factors like release timing, the anticipated release timing of final
|
|
|
|
upstream <filename>kernel.org</filename> versions, and Yocto Project feature requirements.
|
|
|
|
Typically, the kernel chosen is in the
|
|
|
|
final stages of development by the community.
|
|
|
|
In other words, the kernel is in the release
|
|
|
|
candidate or "rc" phase and not yet a final release.
|
|
|
|
But, by being in the final stages of external development, the team knows that the
|
|
|
|
<filename>kernel.org</filename> final release will clearly be within the early stages of
|
2010-11-29 15:30:27 +00:00
|
|
|
the Yocto Project development window.
|
|
|
|
</para>
|
|
|
|
<para>
|
2011-09-29 17:31:42 +00:00
|
|
|
This balance allows the team to deliver the most up-to-date kernel
|
2012-01-03 15:47:07 +00:00
|
|
|
as possible, while still ensuring that the team has a stable official release for
|
2011-09-29 17:31:42 +00:00
|
|
|
the baseline kernel version.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
<para>
|
2010-11-29 17:26:22 +00:00
|
|
|
The ultimate source for the Yocto Project kernel is a released kernel
|
2011-09-29 17:31:42 +00:00
|
|
|
from <filename>kernel.org</filename>.
|
|
|
|
In addition to a foundational kernel from <filename>kernel.org</filename>, the released
|
2010-11-29 17:26:22 +00:00
|
|
|
Yocto Project kernel contains a mix of important new mainline
|
2010-12-03 15:32:13 +00:00
|
|
|
developments, non-mainline developments (when there is no alternative),
|
|
|
|
Board Support Package (BSP) developments,
|
2010-11-29 17:26:22 +00:00
|
|
|
and custom features.
|
|
|
|
These additions result in a commercially released Yocto Project kernel that caters
|
|
|
|
to specific embedded designer needs for targeted hardware.
|
|
|
|
</para>
|
2010-11-29 15:30:27 +00:00
|
|
|
<para>
|
2011-09-29 17:31:42 +00:00
|
|
|
Once a Yocto Project kernel is officially released, the Yocto Project team goes into
|
2012-01-03 15:47:07 +00:00
|
|
|
their next development cycle, or upward revision (uprev) cycle, while still
|
|
|
|
continuing maintenance on the released kernel.
|
2010-11-29 15:30:27 +00:00
|
|
|
It is important to note that the most sustainable and stable way
|
|
|
|
to include feature development upstream is through a kernel uprev process.
|
2011-09-29 17:31:42 +00:00
|
|
|
Back-porting hundreds of individual fixes and minor features from various
|
|
|
|
kernel versions is not sustainable and can easily compromise quality.
|
|
|
|
</para>
|
|
|
|
<para>
|
2010-11-29 15:30:27 +00:00
|
|
|
During the uprev cycle, the Yocto Project team uses an ongoing analysis of
|
|
|
|
kernel development, BSP support, and release timing to select the best
|
2011-09-29 17:31:42 +00:00
|
|
|
possible <filename>kernel.org</filename> version.
|
2010-11-29 15:30:27 +00:00
|
|
|
The team continually monitors community kernel
|
|
|
|
development to look for significant features of interest.
|
|
|
|
The team does consider back-porting large features if they have a significant advantage.
|
|
|
|
User or community demand can also trigger a back-port or creation of new
|
|
|
|
functionality in the Yocto Project baseline kernel during the uprev cycle.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
Generally speaking, every new kernel both adds features and introduces new bugs.
|
|
|
|
These consequences are the basic properties of upstream kernel development and are
|
|
|
|
managed by the Yocto Project team's kernel strategy.
|
|
|
|
It is the Yocto Project team's policy to not back-port minor features to the released kernel.
|
|
|
|
They only consider back-porting significant technological jumps - and, that is done
|
|
|
|
after a complete gap analysis.
|
2011-09-29 17:31:42 +00:00
|
|
|
The reason for this policy is that back-porting any small to medium sized change
|
2010-11-29 15:30:27 +00:00
|
|
|
from an evolving kernel can easily create mismatches, incompatibilities and very
|
|
|
|
subtle errors.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
These policies result in both a stable and a cutting
|
|
|
|
edge kernel that mixes forward ports of existing features and significant and critical
|
|
|
|
new functionality.
|
|
|
|
Forward porting functionality in the Yocto Project kernel can be thought of as a
|
|
|
|
"micro uprev."
|
|
|
|
The many “micro uprevs” produce a kernel version with a mix of
|
|
|
|
important new mainline, non-mainline, BSP developments and feature integrations.
|
|
|
|
This kernel gives insight into new features and allows focused
|
|
|
|
amounts of testing to be done on the kernel, which prevents
|
|
|
|
surprises when selecting the next major uprev.
|
2010-12-03 15:32:13 +00:00
|
|
|
The quality of these cutting edge kernels is evolving and the kernels are used in leading edge
|
|
|
|
feature and BSP development.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
</section>
|
|
|
|
|
|
|
|
<section id='kernel-architecture'>
|
|
|
|
<title>Kernel Architecture</title>
|
|
|
|
<para>
|
|
|
|
This section describes the architecture of the Yocto Project kernel and provides information
|
|
|
|
on the mechanisms used to achieve that architecture.
|
|
|
|
</para>
|
|
|
|
|
|
|
|
<section id='architecture-overview'>
|
|
|
|
<title>Overview</title>
|
|
|
|
<para>
|
2012-01-03 15:47:07 +00:00
|
|
|
As mentioned earlier, a key goal of the Yocto Project is to present the
|
|
|
|
developer with
|
2010-11-29 15:30:27 +00:00
|
|
|
a kernel that has a clear and continuous history that is visible to the user.
|
|
|
|
The architecture and mechanisms used achieve that goal in a manner similar to the
|
2011-09-29 17:31:42 +00:00
|
|
|
upstream <filename>kernel.org</filename>.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
You can think of the Yocto Project kernel as consisting of a baseline kernel with
|
|
|
|
added features logically structured on top of the baseline.
|
|
|
|
The features are tagged and organized by way of a branching strategy implemented by the
|
2011-09-29 17:31:42 +00:00
|
|
|
source code manager (SCM) Git.
|
|
|
|
For information on Git as applied to the Yocto Project, see the
|
2012-03-09 21:35:11 +00:00
|
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink>" section in the
|
|
|
|
Yocto Project Development Manual.
|
2011-09-29 17:31:42 +00:00
|
|
|
</para>
|
|
|
|
<para>
|
2010-11-29 15:30:27 +00:00
|
|
|
The result is that the user has the ability to see the added features and
|
|
|
|
the commits that make up those features.
|
|
|
|
In addition to being able to see added features, the user can also view the history of what
|
2011-09-29 17:31:42 +00:00
|
|
|
made up the baseline kernel.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
The following illustration shows the conceptual Yocto Project kernel.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
<imagedata fileref="figures/kernel-architecture-overview.png" width="6in" depth="7in" align="center" scale="100" />
|
|
|
|
</para>
|
|
|
|
<para>
|
2012-01-03 15:47:07 +00:00
|
|
|
In the illustration, the "Kernel.org Branch Point"
|
2011-09-29 17:31:42 +00:00
|
|
|
marks the specific spot (or release) from
|
|
|
|
which the Yocto Project kernel is created.
|
|
|
|
From this point "up" in the tree, features and differences are organized and tagged.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
The "Yocto Project Baseline Kernel" contains functionality that is common to every kernel
|
2011-09-29 17:31:42 +00:00
|
|
|
type and BSP that is organized further up the tree.
|
|
|
|
Placing these common features in the
|
2010-11-29 15:30:27 +00:00
|
|
|
tree this way means features don't have to be duplicated along individual branches of the
|
|
|
|
structure.
|
|
|
|
</para>
|
|
|
|
<para>
|
2011-09-29 17:31:42 +00:00
|
|
|
From the Yocto Project Baseline Kernel, branch points represent specific functionality
|
2010-11-29 15:30:27 +00:00
|
|
|
for individual BSPs as well as real-time kernels.
|
|
|
|
The illustration represents this through three BSP-specific branches and a real-time
|
|
|
|
kernel branch.
|
|
|
|
Each branch represents some unique functionality for the BSP or a real-time kernel.
|
|
|
|
</para>
|
|
|
|
<para>
|
2010-12-03 15:32:13 +00:00
|
|
|
In this example structure, the real-time kernel branch has common features for all
|
|
|
|
real-time kernels and contains
|
2010-11-29 15:30:27 +00:00
|
|
|
more branches for individual BSP-specific real-time kernels.
|
|
|
|
The illustration shows three branches as an example.
|
|
|
|
Each branch points the way to specific, unique features for a respective real-time
|
|
|
|
kernel as they apply to a given BSP.
|
|
|
|
</para>
|
|
|
|
<para>
|
2011-09-29 17:31:42 +00:00
|
|
|
The resulting tree structure presents a clear path of markers (or branches) to the
|
|
|
|
developer that, for all practical purposes, is the kernel needed for any given set
|
|
|
|
of requirements.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
</section>
|
|
|
|
|
|
|
|
<section id='branching-and-workflow'>
|
|
|
|
<title>Branching Strategy and Workflow</title>
|
|
|
|
<para>
|
|
|
|
The Yocto Project team creates kernel branches at points where functionality is
|
|
|
|
no longer shared and thus, needs to be isolated.
|
|
|
|
For example, board-specific incompatibilities would require different functionality
|
|
|
|
and would require a branch to separate the features.
|
2011-09-29 17:31:42 +00:00
|
|
|
Likewise, for specific kernel features, the same branching strategy is used.
|
|
|
|
</para>
|
|
|
|
<para>
|
2010-11-29 15:30:27 +00:00
|
|
|
This branching strategy results in a tree that has features organized to be specific
|
|
|
|
for particular functionality, single kernel types, or a subset of kernel types.
|
2011-09-29 17:31:42 +00:00
|
|
|
This strategy also results in not having to store the same feature twice
|
|
|
|
internally in the tree.
|
|
|
|
Rather, the kernel team stores the unique differences required to apply the
|
|
|
|
feature onto the kernel type in question.
|
|
|
|
<note>
|
|
|
|
The Yocto Project team strives to place features in the tree such that they can be
|
|
|
|
shared by all boards and kernel types where possible.
|
|
|
|
However, during development cycles or when large features are merged,
|
|
|
|
the team cannot always follow this practice.
|
|
|
|
In those cases, the team uses isolated branches to merge features.
|
|
|
|
</note>
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
BSP-specific code additions are handled in a similar manner to kernel-specific additions.
|
|
|
|
Some BSPs only make sense given certain kernel types.
|
2011-09-29 17:31:42 +00:00
|
|
|
So, for these types, the team creates branches off the end of that kernel type for all
|
2010-11-29 15:30:27 +00:00
|
|
|
of the BSPs that are supported on that kernel type.
|
|
|
|
From the perspective of the tools that create the BSP branch, the BSP is really no
|
|
|
|
different than a feature.
|
|
|
|
Consequently, the same branching strategy applies to BSPs as it does to features.
|
2011-09-29 17:31:42 +00:00
|
|
|
So again, rather than store the BSP twice, the team only stores the unique
|
|
|
|
differences for the BSP across the supported multiple kernels.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
<para>
|
2010-12-03 15:32:13 +00:00
|
|
|
While this strategy can result in a tree with a significant number of branches, it is
|
2011-09-29 17:31:42 +00:00
|
|
|
important to realize that from the developer's point of view, there is a linear
|
|
|
|
path that travels from the baseline <filename>kernel.org</filename>, through a select
|
|
|
|
group of features and ends with their BSP-specific commits.
|
2010-11-29 15:30:27 +00:00
|
|
|
In other words, the divisions of the kernel are transparent and are not relevant
|
|
|
|
to the developer on a day-to-day basis.
|
2011-09-29 17:31:42 +00:00
|
|
|
From the developer's perspective, this path is the "master" branch.
|
|
|
|
The developer does not need not be aware of the existence of any other branches at all.
|
|
|
|
Of course, there is value in the existence of these branches
|
2010-11-29 15:30:27 +00:00
|
|
|
in the tree, should a person decide to explore them.
|
|
|
|
For example, a comparison between two BSPs at either the commit level or at the line-by-line
|
2011-09-29 17:31:42 +00:00
|
|
|
code <filename>diff</filename> level is now a trivial operation.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
Working with the kernel as a structured tree follows recognized community best practices.
|
2011-09-29 17:31:42 +00:00
|
|
|
In particular, the kernel as shipped with the product, should be
|
|
|
|
considered an "upstream source" and viewed as a series of
|
2010-11-29 15:30:27 +00:00
|
|
|
historical and documented modifications (commits).
|
|
|
|
These modifications represent the development and stabilization done
|
|
|
|
by the Yocto Project kernel development team.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
Because commits only change at significant release points in the product life cycle,
|
|
|
|
developers can work on a branch created
|
|
|
|
from the last relevant commit in the shipped Yocto Project kernel.
|
2011-09-29 17:31:42 +00:00
|
|
|
As mentioned previously, the structure is transparent to the developer
|
2010-11-29 15:30:27 +00:00
|
|
|
because the kernel tree is left in this state after cloning and building the kernel.
|
|
|
|
</para>
|
|
|
|
</section>
|
|
|
|
|
|
|
|
<section id='source-code-manager-git'>
|
2011-07-14 14:46:18 +00:00
|
|
|
<title>Source Code Manager - Git</title>
|
2010-11-29 15:30:27 +00:00
|
|
|
<para>
|
2011-09-29 17:31:42 +00:00
|
|
|
The Source Code Manager (SCM) is Git.
|
|
|
|
This SCM is the obvious mechanism for meeting the previously mentioned goals.
|
|
|
|
Not only is it the SCM for <filename>kernel.org</filename> but,
|
|
|
|
Git continues to grow in popularity and supports many different work flows,
|
|
|
|
front-ends and management techniques.
|
2010-11-29 15:30:27 +00:00
|
|
|
</para>
|
2011-07-14 18:14:54 +00:00
|
|
|
<para>
|
|
|
|
You can find documentation on Git at <ulink url='http://git-scm.com/documentation'></ulink>.
|
2011-09-29 17:31:42 +00:00
|
|
|
You can also get an introduction to Git as it applies to the Yocto Project in the
|
2012-03-09 21:35:11 +00:00
|
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink>"
|
|
|
|
section in the Yocto Project Development Manual.
|
2012-01-03 15:47:07 +00:00
|
|
|
These referenced sections overview Git and describe a minimal set of
|
|
|
|
commands that allow you to be functional using Git.
|
2011-09-29 17:31:42 +00:00
|
|
|
<note>
|
|
|
|
You can use as much, or as little, of what Git has to offer to accomplish what
|
|
|
|
you need for your project.
|
|
|
|
You do not have to be a "Git Master" in order to use it with the Yocto Project.
|
|
|
|
</note>
|
2011-07-14 18:14:54 +00:00
|
|
|
</para>
|
2010-11-29 15:30:27 +00:00
|
|
|
</section>
|
|
|
|
</section>
|
|
|
|
|
2012-01-26 23:08:17 +00:00
|
|
|
<section id='kernel-configuration'>
|
|
|
|
<title>Kernel Configuration</title>
|
|
|
|
<para>
|
2012-02-07 21:47:22 +00:00
|
|
|
Kernel configuration, along with kernel features, defines how a Linux Yocto
|
|
|
|
kernel image is built.
|
2012-01-26 23:08:17 +00:00
|
|
|
Through configuration settings, you can customize a Linux Yocto kernel to be
|
|
|
|
specific to particular hardware.
|
|
|
|
For example, you can specify sound support or networking support.
|
|
|
|
This section describes basic concepts behind Kernel configuration within the
|
2012-02-07 21:47:22 +00:00
|
|
|
Yocto Project and references you to other areas for specific configuration
|
|
|
|
applications.
|
2012-01-26 23:08:17 +00:00
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
2012-02-07 21:47:22 +00:00
|
|
|
Conceptually, Linux Yocto kernel configuration occurs similarly to that needed for any
|
|
|
|
Linux kernel.
|
2012-03-13 18:34:30 +00:00
|
|
|
The Linux Yocto kernel build process uses a <filename>.config</filename> file, which
|
2012-02-07 21:47:22 +00:00
|
|
|
is created through the Linux Kernel Coinfiguration (LKC) tool.
|
|
|
|
You can directly set various configurations in the
|
|
|
|
<filename>.config</filename> file by using the <filename>menuconfig</filename>
|
|
|
|
tool as built by BitBake.
|
2012-03-13 18:34:30 +00:00
|
|
|
You can also define configurations in the file by using configuration fragments.
|
2012-02-07 21:47:22 +00:00
|
|
|
<note>
|
|
|
|
It is not recommended that you edit the <filename>.config</filename> file directly.
|
|
|
|
</note>
|
2012-03-13 18:34:30 +00:00
|
|
|
Here are some brief descriptions of the ways you can affect the
|
2012-02-07 21:47:22 +00:00
|
|
|
<filename>.config</filename> file:
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem><para><emphasis>The <filename>menuconfig</filename> Tool:</emphasis>
|
|
|
|
One of many front-ends that allows you to define kernel configurations.
|
|
|
|
Some others are <filename>make config</filename>,
|
|
|
|
<filename>make nconfig</filename>, and <filename>make gconfig</filename>.
|
|
|
|
In the Yocto Project environment, you must use BitBake to build the
|
|
|
|
<filename>menuconfig</filename> tool before you can use it to define
|
|
|
|
configurations:
|
|
|
|
<literallayout class='monospaced'>
|
2012-01-26 23:08:17 +00:00
|
|
|
$ bitbake linux-yocto -c menuconfig
|
2012-02-07 21:47:22 +00:00
|
|
|
</literallayout>
|
|
|
|
After the tool is built, you can interact with it normally.
|
|
|
|
You can see how <filename>menuconfig</filename> is used to change a simple
|
|
|
|
kernel configuration in the
|
2012-03-09 21:35:11 +00:00
|
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#changing-the-config-smp-configuration-using-menuconfig'>Changing the <filename>CONFIG_SMP</filename> Configuration Using <filename>menuconfig</filename></ulink>"
|
2012-02-07 21:47:22 +00:00
|
|
|
section of The Yocto Project Development Manual.
|
|
|
|
For general information on <filename>menuconfig</filename>, see
|
|
|
|
<ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
|
|
|
|
</para></listitem>
|
|
|
|
<listitem><para><emphasis>Configuration Fragments:</emphasis> A file with a
|
|
|
|
list of kernel options just as they would appear syntactically in the
|
|
|
|
<filename>.config</filename> file.
|
|
|
|
Configuration fragments are typically logical groupings and are assembled
|
|
|
|
by the Yocto Project build system to produce input used by the LKC
|
|
|
|
that ultimately generates the <filename>.config</filename> file.</para>
|
|
|
|
<para>The
|
2012-03-09 21:35:11 +00:00
|
|
|
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'>KERNEL_FEATURES</ulink></filename>
|
2012-02-07 21:47:22 +00:00
|
|
|
variable can be used to list configuration fragments.
|
|
|
|
For further discussion on applying configuration fragments, see the
|
2012-03-09 21:35:11 +00:00
|
|
|
"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout-kernel'>Linux Kernel Configuration</ulink>"
|
2012-02-07 21:47:22 +00:00
|
|
|
section in the Yocto Project Board Support Package (BSP) Guide.
|
|
|
|
</para></listitem>
|
|
|
|
</itemizedlist>
|
2012-01-26 23:08:17 +00:00
|
|
|
</para>
|
|
|
|
</section>
|
|
|
|
|
2010-11-29 15:30:27 +00:00
|
|
|
<section id='kernel-tools'>
|
|
|
|
<title>Kernel Tools</title>
|
|
|
|
<para>
|
2011-07-14 18:20:41 +00:00
|
|
|
Since most standard workflows involve moving forward with an existing tree by
|
|
|
|
continuing to add and alter the underlying baseline, the tools that manage
|
|
|
|
the Yocto Project's kernel construction are largely hidden from the developer to
|
|
|
|
present a simplified view of the kernel for ease of use.
|
|
|
|
</para>
|
|
|
|
<para>
|
2011-09-29 17:31:42 +00:00
|
|
|
Fundamentally, the kernel tools that manage and construct the
|
|
|
|
Yocto Project kernel accomplish the following:
|
2011-07-14 18:20:41 +00:00
|
|
|
<itemizedlist>
|
|
|
|
<listitem><para>Group patches into named, reusable features.</para></listitem>
|
2011-09-29 17:31:42 +00:00
|
|
|
<listitem><para>Allow top-down control of included features.</para></listitem>
|
|
|
|
<listitem><para>Bind kernel configurations to kernel patches and features.</para></listitem>
|
2011-07-14 18:20:41 +00:00
|
|
|
<listitem><para>Present a seamless Git repository that blends Yocto Project value
|
2011-09-29 17:31:42 +00:00
|
|
|
with the <filename>kernel.org</filename> history and development.</para></listitem>
|
2011-07-14 18:20:41 +00:00
|
|
|
</itemizedlist>
|
|
|
|
</para>
|
2010-11-29 15:30:27 +00:00
|
|
|
<!--<para>
|
2011-09-29 17:31:42 +00:00
|
|
|
WRITER NOTE: Put this in for post 1.1 if possible:
|
|
|
|
|
2010-11-29 15:30:27 +00:00
|
|
|
The tools that construct a kernel tree will be discussed later in this
|
|
|
|
document. The following tools form the foundation of the Yocto Project
|
|
|
|
kernel toolkit:
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem><para>git : distributed revision control system created by Linus Torvalds</para></listitem>
|
|
|
|
<listitem><para>guilt: quilt on top of git</para></listitem>
|
|
|
|
<listitem><para>*cfg : kernel configuration management and classification</para></listitem>
|
|
|
|
<listitem><para>kgit*: Yocto Project kernel tree creation and management tools</para></listitem>
|
|
|
|
<listitem><para>scc : series & configuration compiler</para></listitem>
|
|
|
|
</itemizedlist>
|
|
|
|
</para> -->
|
|
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
<!--
|
|
|
|
vim: expandtab tw=80 ts=4
|
|
|
|
-->
|