kernel-dev: Added new appendix for kernel concepts.

(From yocto-docs rev: e25465c6d177a27d3dee742ebc958ae30f968ffa)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 89 insertions, 0 deletions

diff --git a/documentation/kernel-dev/kernel-dev-concepts-appx.xml b/documentation/kernel-dev/kernel-dev-concepts-appx.xml
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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, like other kernels, are based off the Linux
+            kernel releases from <ulink url='http://www.kernel.org'></ulink>.
+            At the beginning of a major development cycle, the Yocto Project team
+            chooses its 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 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
+            the Yocto Project development window.
+        </para>
+        <para>
+            This balance allows the team to deliver the most up-to-date kernel
+            possible, while still ensuring that the team has a stable official release for
+            the baseline Linux kernel version.
+        </para>
+        <para>
+            The ultimate source for kernels available through the Yocto Project are released kernels
+            from <filename>kernel.org</filename>.
+            In addition to a foundational kernel from <filename>kernel.org</filename>, the
+            kernels available contain a mix of important new mainline
+            developments, non-mainline developments (when there is no alternative),
+            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>
+            Once a 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
+            kernel development, BSP support, and release timing to select the best
+            possible <filename>kernel.org</filename> version.
+            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.
+            The reason for this policy is that back-porting any small to medium sized change
+            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 kernels available through 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.
+            The quality of these cutting edge kernels is evolving and the kernels are used in leading edge
+            feature and BSP development.
+        </para>
+    </section>
+</appendix>
+<!--
+vim: expandtab tw=80 ts=4
+-->