[Subtree] Removing import-layers directory

As part of the move to subtrees, need to bring all the import layers
content to the top level.

Change-Id: I4a163d10898cbc6e11c27f776f60e1a470049d8f
Signed-off-by: Dave Cobbley <david.j.cobbley@linux.intel.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>

1 files changed, 622 insertions, 0 deletions

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+<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
+[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
+
+<appendix id='kernel-dev-concepts-appx'>
+<title>Advanced Kernel Concepts</title>
+
+    <section id='kernel-big-picture'>
+        <title>Yocto Project Kernel Development and Maintenance</title>
+
+        <para>
+            Kernels available through the Yocto Project (Yocto Linux kernels),
+            like other kernels, are based off the Linux kernel releases from
+            <ulink url='http://www.kernel.org'></ulink>.
+            At the beginning of a major Linux kernel development cycle, the
+            Yocto Project team chooses a Linux kernel based on factors such as
+            release timing, the anticipated release timing of final upstream
+            <filename>kernel.org</filename> versions, and Yocto Project
+            feature requirements.
+            Typically, the Linux kernel chosen is in the final stages of
+            development by the Linux community.
+            In other words, the Linux kernel is in the release candidate
+            or "rc" phase and has yet to reach 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 the Yocto Project
+            development window.
+        </para>
+
+        <para>
+            This balance allows the Yocto Project team to deliver the most
+            up-to-date Yocto Linux kernel possible, while still ensuring that
+            the team has a stable official release for the baseline Linux
+            kernel version.
+        </para>
+
+        <para>
+            As implied earlier, the ultimate source for Yocto Linux kernels
+            are released kernels from <filename>kernel.org</filename>.
+            In addition to a foundational kernel from
+            <filename>kernel.org</filename>, the available Yocto Linux kernels
+            contain a mix of important new mainline developments, non-mainline
+            developments (when no alternative exists), Board Support Package
+            (BSP) developments, and custom features.
+            These additions result in a commercially released Yocto
+            Project Linux kernel that caters to specific embedded designer
+            needs for targeted hardware.
+        </para>
+
+        <para>
+            You can find a web interface to the Yocto Linux kernels in the
+            <ulink url='&YOCTO_DOCS_OM_URL;#source-repositories'>Source Repositories</ulink>
+            at
+            <ulink url='&YOCTO_GIT_URL;'></ulink>.
+            If you look at the interface, you will see to the left a
+            grouping of Git repositories titled "Yocto Linux Kernel".
+            Within this group, you will find several Linux Yocto kernels
+            developed and included with Yocto Project releases:
+            <itemizedlist>
+                <listitem><para>
+                    <emphasis><filename>linux-yocto-4.1</filename>:</emphasis>
+                    The stable Yocto Project kernel to use with the Yocto
+                    Project Release 2.0.
+                    This kernel is based on the Linux 4.1 released kernel.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis><filename>linux-yocto-4.4</filename>:</emphasis>
+                    The stable Yocto Project kernel to use with the Yocto
+                    Project Release 2.1.
+                    This kernel is based on the Linux 4.4 released kernel.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis><filename>linux-yocto-4.6</filename>:</emphasis>
+                    A temporary kernel that is not tied to any Yocto Project
+                    release.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis><filename>linux-yocto-4.8</filename>:</emphasis>
+                    The stable yocto Project kernel to use with the Yocto
+                    Project Release 2.2.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis><filename>linux-yocto-4.9</filename>:</emphasis>
+                    The stable Yocto Project kernel to use with the Yocto
+                    Project Release 2.3.
+                    This kernel is based on the Linux 4.9 released kernel.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis><filename>linux-yocto-4.10</filename>:</emphasis>
+                    The default stable Yocto Project kernel to use with the
+                    Yocto Project Release 2.3.
+                    This kernel is based on the Linux 4.10 released kernel.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis><filename>linux-yocto-4.12</filename>:</emphasis>
+                    The default stable Yocto Project kernel to use with the
+                    Yocto Project Release 2.4.
+                    This kernel is based on the Linux 4.12 released kernel.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis><filename>yocto-kernel-cache</filename>:</emphasis>
+                    The <filename>linux-yocto-cache</filename> contains
+                    patches and configurations for the linux-yocto kernel
+                    tree.
+                    This repository is useful when working on the linux-yocto
+                    kernel.
+                    For more information on this "Advanced Kernel Metadata",
+                    see the
+                    "<link linkend='kernel-dev-advanced'>Working With Advanced Metadata (<filename>yocto-kernel-cache</filename>)</link>"
+                    Chapter.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis><filename>linux-yocto-dev</filename>:</emphasis>
+                    A development kernel based on the latest upstream release
+                    candidate available.
+                    </para></listitem>
+            </itemizedlist>
+            <note><title>Notes</title>
+                Long Term Support Initiative (LTSI) for Yocto Linux
+                kernels is as follows:
+                <itemizedlist>
+                    <listitem><para>
+                        For Yocto Project releases 1.7, 1.8, and 2.0,
+                        the LTSI kernel is
+                        <filename>linux-yocto-3.14</filename>.
+                        </para></listitem>
+                    <listitem><para>
+                        For Yocto Project releases 2.1, 2.2, and 2.3,
+                        the LTSI kernel is <filename>linux-yocto-4.1</filename>.
+                        </para></listitem>
+                    <listitem><para>
+                        For Yocto Project release 2.4, the LTSI kernel is
+                        <filename>linux-yocto-4.9</filename>
+                        </para></listitem>
+                    <listitem><para>
+                        <filename>linux-yocto-4.4</filename> is an LTS
+                        kernel.
+                        </para></listitem>
+                </itemizedlist>
+            </note>
+        </para>
+
+        <para>
+            Once a Yocto Linux kernel is officially released, the Yocto
+            Project team goes into their next development cycle, or upward
+            revision (uprev) cycle, while still continuing maintenance on the
+            released kernel.
+            It is important to note that the most sustainable and stable way
+            to include feature development upstream is through a kernel uprev
+            process.
+            Back-porting hundreds of individual fixes and minor features from
+            various kernel versions is not sustainable and can easily
+            compromise quality.
+        </para>
+
+        <para>
+            During the uprev cycle, the Yocto Project team uses an ongoing
+            analysis of Linux kernel development, BSP support, and release
+            timing to select the best possible <filename>kernel.org</filename>
+            Linux kernel version on which to base subsequent Yocto Linux
+            kernel development.
+            The team continually monitors Linux 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 Linux kernel both adds features and
+            introduces new bugs.
+            These consequences are the basic properties of upstream
+            Linux kernel development and are managed by the Yocto Project
+            team's Yocto Linux kernel development strategy.
+            It is the Yocto Project team's policy to not back-port minor
+            features to the released Yocto Linux kernel.
+            They only consider back-porting significant technological
+            jumps &dash; and, that is done after a complete gap analysis.
+            The reason for this policy is that back-porting any small to
+            medium sized change from an evolving Linux kernel can easily
+            create mismatches, incompatibilities and very subtle errors.
+        </para>
+
+        <para>
+            The policies described in this section result in both a stable
+            and a cutting edge Yocto Linux kernel that mixes forward ports of
+            existing Linux kernel features and significant and critical new
+            functionality.
+            Forward porting Linux kernel functionality into the Yocto Linux
+            kernels available through the Yocto Project can be thought of as
+            a "micro uprev."
+            The many “micro uprevs” produce a Yocto Linux kernel version with
+            a mix of important new mainline, non-mainline, BSP developments
+            and feature integrations.
+            This Yocto Linux 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.
+            The quality of these cutting edge Yocto Linux kernels is evolving
+            and the kernels are used in leading edge feature and BSP
+            development.
+        </para>
+    </section>
+
+    <section id='yocto-linux-kernel-architecture-and-branching-strategies'>
+        <title>Yocto Linux Kernel Architecture and Branching Strategies</title>
+
+        <para>
+            As mentioned earlier, a key goal of the Yocto Project is
+            to present the developer with a kernel that has a clear and
+            continuous history that is visible to the user.
+            The architecture and mechanisms, in particular the branching
+            strategies, used achieve that goal in a manner similar to
+            upstream Linux kernel development in
+            <filename>kernel.org</filename>.
+        </para>
+
+        <para>
+            You can think of a Yocto Linux kernel as consisting of a
+            baseline Linux 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 Yocto Project team using the
+            Source Code Manager (SCM) Git.
+            <note><title>Notes</title>
+                <itemizedlist>
+                    <listitem><para>
+                        Git is the obvious SCM for meeting the Yocto Linux
+                        kernel organizational and structural goals described
+                        in this section.
+                        Not only is Git the SCM for Linux kernel development in
+                        <filename>kernel.org</filename> but, Git continues to
+                         grow in popularity and supports many different work
+                         flows, front-ends and management techniques.
+                        </para></listitem>
+                    <listitem><para>
+                        You can find documentation on Git at
+                        <ulink url='http://git-scm.com/documentation'></ulink>.
+                        You can also get an introduction to Git as it
+                        applies to the Yocto Project in the
+                        "<ulink url='&YOCTO_DOCS_OM_URL;#git'>Git</ulink>"
+                        section in the Yocto Project Overview and Concepts
+                        Manual.
+                        The latter reference provides an overview of
+                        Git and presents a minimal set of Git commands
+                        that allows you to be functional using Git.
+                        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 Expert" in order to
+                        use it with the Yocto Project.
+                        </para></listitem>
+                </itemizedlist>
+            </note>
+        </para>
+
+        <para>
+            Using Git's tagging and branching features, 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.
+            Likewise, for specific kernel features, the same branching
+            strategy is used.
+        </para>
+
+        <para>
+            This "tree-like" architecture results in a structure that has
+            features organized to be specific for particular functionality,
+            single kernel types, or a subset of kernel types.
+            Thus, 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 made up the baseline
+            Linux kernel.
+        </para>
+
+        <para>
+            Another consequence of this strategy 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 features 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>
+        </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.
+            So, for these types, the team creates branches off the end
+            of that kernel type for all 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 kernel features.
+            So again, rather than store the BSP twice, the team only
+            stores the unique differences for the BSP across the supported
+            multiple kernels.
+        </para>
+
+        <para>
+            While this strategy can result in a tree with a significant number
+            of branches, it is 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.
+            In other words, the divisions of the kernel are transparent and
+            are not relevant to the developer on a day-to-day basis.
+            From the developer's perspective, this path is the "master" branch
+            in Git terms.
+            The developer does not need to be aware of the existence of any
+            other branches at all.
+            Of course, value exists in the having these branches 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 code <filename>diff</filename> level
+            is now a trivial operation.
+        </para>
+
+        <para>
+            The following illustration shows the conceptual Yocto
+            Linux kernel.
+            <imagedata fileref="figures/kernel-architecture-overview.png" width="6in" depth="7in" align="center" scale="100" />
+        </para>
+
+        <para>
+            In the illustration, the "Kernel.org Branch Point" marks the
+            specific spot (or Linux kernel release) from which the
+            Yocto Linux kernel is created.
+            From this point forward in the tree, features and differences
+            are organized and tagged.
+        </para>
+
+        <para>
+            The "Yocto Project Baseline Kernel" contains functionality that
+            is common to every kernel type and BSP that is organized
+            further along in the tree.
+            Placing these common features in the tree this way means
+            features do not have to be duplicated along individual
+            branches of the tree structure.
+        </para>
+
+        <para>
+            From the "Yocto Project Baseline Kernel", branch points represent
+            specific functionality for individual Board Support Packages
+            (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 for a real-time Yocto Linux kernel.
+        </para>
+
+        <para>
+            In this example structure, the "Real-time (rt) Kernel" branch has
+            common features for all real-time Yocto Linux kernels and
+            contains 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>
+            The resulting tree structure presents a clear path of markers
+            (or branches) to the developer that, for all practical
+            purposes, is the Yocto Linux kernel needed for any given set of
+            requirements.
+            <note>
+                Keep in mind the figure does not take into account all the
+                supported Yocto Linux kernels, but rather shows a single
+                generic kernel just for conceptual purposes.
+                Also keep in mind that this structure represents the Yocto
+                Project
+                <ulink url='&YOCTO_DOCS_OM_URL;#source-repositories'>Source Repositories</ulink>
+                that are either pulled from during the build or established
+                on the host development system prior to the build by either
+                cloning a particular kernel's Git repository or by
+                downloading and unpacking a tarball.
+            </note>
+        </para>
+
+        <para>
+            Working with the kernel as a structured tree follows recognized
+            community best practices.
+            In particular, the kernel as shipped with the product, should be
+            considered an "upstream source" and viewed as a series of
+            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 Linux
+            kernel.
+            As mentioned previously, the structure is transparent to the
+            developer because the kernel tree is left in this state after
+            cloning and building the kernel.
+        </para>
+    </section>
+
+    <section id='kernel-build-file-hierarchy'>
+        <title>Kernel Build File Hierarchy</title>
+
+        <para>
+            Upstream storage of all the available kernel source code is
+            one thing, while representing and using the code on your host
+            development system is another.
+            Conceptually, you can think of the kernel source repositories
+            as all the source files necessary for all the supported
+            Yocto Linux kernels.
+            As a developer, you are just interested in the source files
+            for the kernel on which you are working.
+            And, furthermore, you need them available on your host system.
+        </para>
+
+        <para>
+            Kernel source code is available on your host system several
+            different ways:
+            <itemizedlist>
+                <listitem><para>
+                    <emphasis>Files Accessed While using <filename>devtool</filename>:</emphasis>
+                    <filename>devtool</filename>, which is available with the
+                    Yocto Project, is the preferred method by which to
+                    modify the kernel.
+                    See the
+                    "<link linkend='kernel-modification-workflow'>Kernel Modification Workflow</link>"
+                    section.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis>Cloned Repository:</emphasis>
+                    If you are working in the kernel all the time, you probably
+                    would want to set up your own local Git repository of the
+                    Yocto Linux kernel tree.
+                    For information on how to clone a Yocto Linux kernel
+                    Git repository, see the
+                    "<link linkend='preparing-the-build-host-to-work-on-the-kernel'>Preparing the Build Host to Work on the Kernel</link>"
+                    section.
+                    </para></listitem>
+                <listitem><para>
+                    <emphasis>Temporary Source Files from a Build:</emphasis>
+                    If you just need to make some patches to the kernel using
+                    a traditional BitBake workflow (i.e. not using the
+                    <filename>devtool</filename>), you can access temporary
+                    kernel source files that were extracted and used during
+                    a kernel build.
+                    </para></listitem>
+            </itemizedlist>
+        </para>
+
+        <para>
+            The temporary kernel source files resulting from a build using
+            BitBake have a particular hierarchy.
+            When you build the kernel on your development system, all files
+            needed for the build are taken from the source repositories
+            pointed to by the
+            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+            variable and gathered in a temporary work area where they are
+            subsequently used to create the unique kernel.
+            Thus, in a sense, the process constructs a local source tree
+            specific to your kernel from which to generate the new kernel
+            image.
+        </para>
+
+        <para>
+            The following figure shows the temporary file structure
+            created on your host system when you build the kernel using
+            Bitbake.
+            This
+            <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
+            contains all the source files used during the build.
+            <imagedata fileref="figures/kernel-overview-2-generic.png"
+                width="6in" depth="5in" align="center" scale="100" />
+        </para>
+
+        <para>
+            Again, for additional information on the Yocto Project kernel's
+            architecture and its branching strategy, see the
+            "<link linkend='yocto-linux-kernel-architecture-and-branching-strategies'>Yocto Linux Kernel Architecture and Branching Strategies</link>"
+            section.
+            You can also reference the
+            "<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
+            and
+            "<link linkend='using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</link>"
+            sections for detailed example that modifies the kernel.
+        </para>
+    </section>
+
+    <section id='determining-hardware-and-non-hardware-features-for-the-kernel-configuration-audit-phase'>
+        <title>Determining Hardware and Non-Hardware Features for the Kernel Configuration Audit Phase</title>
+
+        <para>
+            This section describes part of the kernel configuration audit
+            phase that most developers can ignore.
+            For general information on kernel configuration including
+            <filename>menuconfig</filename>, <filename>defconfig</filename>
+            files, and configuration fragments, see the
+            "<link linkend='configuring-the-kernel'>Configuring the Kernel</link>"
+            section.
+        </para>
+
+        <para>
+            During this part of the audit phase, the contents of the final
+            <filename>.config</filename> file are compared against the
+            fragments specified by the system.
+            These fragments can be system fragments, distro fragments,
+            or user-specified configuration elements.
+            Regardless of their origin, the OpenEmbedded build system
+            warns the user if a specific option is not included in the
+            final kernel configuration.
+        </para>
+
+        <para>
+            By default, in order to not overwhelm the user with
+            configuration warnings, the system only reports missing
+            "hardware" options as they could result in a boot
+            failure or indicate that important hardware is not available.
+        </para>
+
+        <para>
+            To determine whether or not a given option is "hardware" or
+            "non-hardware", the kernel Metadata in
+            <filename>yocto-kernel-cache</filename> contains files that
+            classify individual or groups of options as either hardware
+            or non-hardware.
+            To better show this, consider a situation where the
+            <filename>yocto-kernel-cache</filename> contains the following
+            files:
+            <literallayout class='monospaced'>
+     yocto-kernel-cache/features/drm-psb/hardware.cfg
+     yocto-kernel-cache/features/kgdb/hardware.cfg
+     yocto-kernel-cache/ktypes/base/hardware.cfg
+     yocto-kernel-cache/bsp/mti-malta32/hardware.cfg
+     yocto-kernel-cache/bsp/fsl-mpc8315e-rdb/hardware.cfg
+     yocto-kernel-cache/bsp/qemu-ppc32/hardware.cfg
+     yocto-kernel-cache/bsp/qemuarma9/hardware.cfg
+     yocto-kernel-cache/bsp/mti-malta64/hardware.cfg
+     yocto-kernel-cache/bsp/arm-versatile-926ejs/hardware.cfg
+     yocto-kernel-cache/bsp/common-pc/hardware.cfg
+     yocto-kernel-cache/bsp/common-pc-64/hardware.cfg
+     yocto-kernel-cache/features/rfkill/non-hardware.cfg
+     yocto-kernel-cache/ktypes/base/non-hardware.cfg
+     yocto-kernel-cache/features/aufs/non-hardware.kcf
+     yocto-kernel-cache/features/ocf/non-hardware.kcf
+     yocto-kernel-cache/ktypes/base/non-hardware.kcf
+     yocto-kernel-cache/ktypes/base/hardware.kcf
+     yocto-kernel-cache/bsp/qemu-ppc32/hardware.kcf
+            </literallayout>
+            The following list provides explanations for the various
+            files:
+            <itemizedlist>
+                <listitem><para>
+                    <filename>hardware.kcf</filename>:
+                    Specifies a list of kernel Kconfig files that contain
+                    hardware options only.
+                    </para></listitem>
+                <listitem><para>
+                    <filename>non-hardware.kcf</filename>:
+                    Specifies a list of kernel Kconfig files that contain
+                    non-hardware options only.
+                    </para></listitem>
+                <listitem><para>
+                    <filename>hardware.cfg</filename>:
+                    Specifies a list of kernel <filename>CONFIG_</filename>
+                    options that are hardware, regardless of whether or not
+                    they are within a Kconfig file specified by a hardware
+                    or non-hardware Kconfig file (i.e.
+                    <filename>hardware.kcf</filename> or
+                    <filename>non-hardware.kcf</filename>).
+                    </para></listitem>
+                <listitem><para>
+                    <filename>non-hardware.cfg</filename>:
+                    Specifies a list of kernel <filename>CONFIG_</filename>
+                    options that are not hardware, regardless of whether or
+                    not they are within a Kconfig file specified by a
+                    hardware or non-hardware Kconfig file (i.e.
+                    <filename>hardware.kcf</filename> or
+                    <filename>non-hardware.kcf</filename>).
+                    </para></listitem>
+            </itemizedlist>
+            Here is a specific example using the
+            <filename>kernel-cache/bsp/mti-malta32/hardware.cfg</filename>:
+            <literallayout class='monospaced'>
+     CONFIG_SERIAL_8250
+     CONFIG_SERIAL_8250_CONSOLE
+     CONFIG_SERIAL_8250_NR_UARTS
+     CONFIG_SERIAL_8250_PCI
+     CONFIG_SERIAL_CORE
+     CONFIG_SERIAL_CORE_CONSOLE
+     CONFIG_VGA_ARB
+            </literallayout>
+            The kernel configuration audit automatically detects these
+            files (hence the names must be exactly the ones discussed here),
+            and uses them as inputs when generating warnings about the
+            final <filename>.config</filename> file.
+        </para>
+
+        <para>
+            A user-specified kernel Metadata repository, or recipe space
+            feature, can use these same files to classify options that are
+            found within its <filename>.cfg</filename> files as hardware
+            or non-hardware, to prevent the OpenEmbedded build system from
+            producing an error or warning when an option is not in the
+            final <filename>.config</filename> file.
+        </para>
+    </section>
+</appendix>
+<!--
+vim: expandtab tw=80 ts=4
+-->