dev-manual, kernel-dev, sdk-manual: Moved patching kernel section

Moved the "Patching the Kernel" section, which was in the
dev-manual to the kernel-dev manual.  During the move,
renamed the section to "Using devtool to Patch the Kernel".

This move bothered a lot of links so I had to fix them in
various manuals.

(From yocto-docs rev: a000be1eddf33e4d7de8f350e076d48e27ca4b98)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 356 insertions, 8 deletions

diff --git a/documentation/kernel-dev/kernel-dev-common.xml b/documentation/kernel-dev/kernel-dev-common.xml
index bb50a7def6..c55f68bc24 100644
--- a/documentation/kernel-dev/kernel-dev-common.xml
+++ b/documentation/kernel-dev/kernel-dev-common.xml
@@ -75,9 +75,8 @@
             See the "<link linkend='creating-and-preparing-a-layer'>Creating and Preparing a Layer</link>"
             section for some general resources.
             You can also see the
-            "<ulink url='&YOCTO_DOCS_DEV_URL;#set-up-your-layer-for-the-build'>Set Up Your Layer for the Build</ulink>" section
-            of the Yocto Project Development Manual for a detailed
-            example.
+            "<link linkend='set-up-your-layer-for-the-build'>Set Up Your Layer for the Build</link>"
+            section for a detailed example.
         </para>
 
         <section id='creating-the-append-file'>
@@ -295,9 +294,10 @@
             </para>
 
             <para>
-                For a detailed example showing how to patch the kernel, see the
-                "<ulink url='&YOCTO_DOCS_DEV_URL;#patching-the-kernel'>Patching the Kernel</ulink>"
-                section in the Yocto Project Development Manual.
+                For a detailed example showing how to patch the kernel using
+                <filename>devtool</filename>, see the
+                "<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
+                section.
             </para>
         </section>
 
@@ -449,6 +449,354 @@
         </section>
     </section>
 
+    <section id="using-devtool-to-patch-the-kernel">
+        <title>Using <filename>devtool</filename> to Patch the Kernel</title>
+
+        <para>
+            Patching the kernel involves changing or adding configurations to an existing kernel,
+            changing or adding recipes to the kernel that are needed to support specific hardware features,
+            or even altering the source code itself.
+            <note>
+                You can use the <filename>yocto-kernel</filename> script
+                found in the <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
+                under <filename>scripts</filename> to manage kernel patches and configuration.
+                See the "<ulink url='&YOCTO_DOCS_BSP_URL;#managing-kernel-patches-and-config-items-with-yocto-kernel'>Managing kernel Patches and Config Items with yocto-kernel</ulink>"
+                section in the Yocto Project Board Support Packages (BSP) Developer's Guide for
+                more information.</note>
+        </para>
+
+        <para>
+            This example creates a simple patch by adding some QEMU emulator console
+            output at boot time through <filename>printk</filename> statements in the kernel's
+            <filename>calibrate.c</filename> source code file.
+            Applying the patch and booting the modified image causes the added
+            messages to appear on the emulator's console.
+        </para>
+
+        <para>
+            The example assumes a clean build exists for the <filename>qemux86</filename>
+            machine in a
+            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
+            named <filename>poky</filename>.
+            Furthermore, the
+            <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
+            is <filename>build</filename> and is located in
+            <filename>poky</filename> and the kernel is based on the
+            Linux 3.4 kernel.
+        </para>
+
+        <para>
+            Also, for more information on patching the kernel, see the
+            "<link linkend='applying-patches'>Applying Patches</link>"
+            section.
+        </para>
+
+        <section id='create-a-layer-for-your-changes'>
+            <title>Create a Layer for your Changes</title>
+
+            <para>
+                The first step is to create a layer so you can isolate your
+                changes.
+                Rather than use the <filename>yocto-layer</filename> script
+                to create the layer, this example steps through the process
+                by hand.
+                If you want information on the script that creates a general
+                layer, see the
+                "<ulink url='&YOCTO_DOCS_DEV_URL;#creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</ulink>"
+                section in the Yocto Project Development Manual.
+            </para>
+
+            <para>
+                These two commands create a directory you can use for your
+                layer:
+                <literallayout class='monospaced'>
+     $ cd ~/poky
+     $ mkdir meta-mylayer
+                </literallayout>
+                Creating a directory that follows the Yocto Project layer naming
+                conventions sets up the layer for your changes.
+                The layer is where you place your configuration files, append
+                files, and patch files.
+                To learn more about creating a layer and filling it with the
+                files you need, see the
+                "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
+                section in the Yocto Project Development Manual.
+            </para>
+        </section>
+
+        <section id='finding-the-kernel-source-code'>
+            <title>Finding the Kernel Source Code</title>
+
+            <para>
+                Each time you build a kernel image, the kernel source code
+                is fetched and unpacked into the following directory:
+                <literallayout class='monospaced'>
+     ${S}/linux
+                </literallayout>
+                See the "<ulink url='&YOCTO_DOCS_DEV_URL;#finding-the-temporary-source-code'>Finding Temporary Source Code</ulink>"
+                section in the Yocto Project Development Manual and the
+                <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
+                variable for more information about where source is kept
+                during a build.
+            </para>
+
+            <para>
+                For this example, we are going to patch the
+                <filename>init/calibrate.c</filename> file
+                by adding some simple console <filename>printk</filename> statements that we can
+                see when we boot the image using QEMU.
+            </para>
+        </section>
+
+        <section id='creating-the-patch'>
+            <title>Creating the Patch</title>
+
+            <para>
+                Two methods exist by which you can create the patch:
+                <ulink url='&YOCTO_DOCS_SDK_URL;#using-devtool-in-your-sdk-workflow'><filename>devtool</filename></ulink>
+                and
+                <ulink url='&YOCTO_DOCS_DEV_URL;#using-a-quilt-workflow'>Quilt</ulink>.
+                For kernel patches, the Git workflow is more appropriate.
+                This section assumes the Git workflow and shows the steps
+                specific to this example.
+                <orderedlist>
+                    <listitem><para>
+                        <emphasis>Change the working directory</emphasis>:
+                        Change to where the kernel source code is before making
+                        your edits to the <filename>calibrate.c</filename> file:
+                        <literallayout class='monospaced'>
+     $ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux
+                        </literallayout>
+                        Because you are working in an established Git repository,
+                        you must be in this directory in order to commit your changes
+                        and create the patch file.
+                        <note>The <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink> and
+                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> variables
+                            represent the version and revision for the
+                            <filename>linux-yocto</filename> recipe.
+                            The <filename>PV</filename> variable includes the Git meta and machine
+                            hashes, which make the directory name longer than you might
+                            expect.
+                        </note></para></listitem>
+                    <listitem><para>
+                        <emphasis>Edit the source file</emphasis>:
+                        Edit the <filename>init/calibrate.c</filename> file to have the
+                        following changes:
+                        <literallayout class='monospaced'>
+     void calibrate_delay(void)
+     {
+         unsigned long lpj;
+         static bool printed;
+         int this_cpu = smp_processor_id();
+
+         printk("*************************************\n");
+         printk("*                                   *\n");
+         printk("*        HELLO YOCTO KERNEL         *\n");
+         printk("*                                   *\n");
+         printk("*************************************\n");
+
+        if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
+               .
+               .
+               .
+                        </literallayout></para></listitem>
+                    <listitem><para><emphasis>Stage and commit your changes</emphasis>:
+                        These Git commands display the modified file, stage it, and then
+                        commit the file:
+                        <literallayout class='monospaced'>
+     $ git status
+     $ git add init/calibrate.c
+     $ git commit -m "calibrate: Add printk example"
+                        </literallayout></para></listitem>
+                    <listitem><para><emphasis>Generate the patch file</emphasis>:
+                        This Git command creates the a patch file named
+                        <filename>0001-calibrate-Add-printk-example.patch</filename>
+                        in the current directory.
+                        <literallayout class='monospaced'>
+     $ git format-patch -1
+                        </literallayout>
+                        </para></listitem>
+                </orderedlist>
+            </para>
+        </section>
+
+        <section id='set-up-your-layer-for-the-build'>
+            <title>Set Up Your Layer for the Build</title>
+
+            <para>These steps get your layer set up for the build:
+                <orderedlist>
+                    <listitem><para><emphasis>Create additional structure</emphasis>:
+                        Create the additional layer structure:
+                        <literallayout class='monospaced'>
+     $ cd ~/poky/meta-mylayer
+     $ mkdir conf
+     $ mkdir recipes-kernel
+     $ mkdir recipes-kernel/linux
+     $ mkdir recipes-kernel/linux/linux-yocto
+                         </literallayout>
+                         The <filename>conf</filename> directory holds your configuration files, while the
+                         <filename>recipes-kernel</filename> directory holds your append file and
+                         your patch file.</para></listitem>
+                    <listitem><para><emphasis>Create the layer configuration file</emphasis>:
+                        Move to the <filename>meta-mylayer/conf</filename> directory and create
+                        the <filename>layer.conf</filename> file as follows:
+                        <literallayout class='monospaced'>
+     # We have a conf and classes directory, add to BBPATH
+     BBPATH .= ":${LAYERDIR}"
+
+     # We have recipes-* directories, add to BBFILES
+     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
+                 ${LAYERDIR}/recipes-*/*/*.bbappend"
+
+     BBFILE_COLLECTIONS += "mylayer"
+     BBFILE_PATTERN_mylayer = "^${LAYERDIR}/"
+     BBFILE_PRIORITY_mylayer = "5"
+                         </literallayout>
+                         Notice <filename>mylayer</filename> as part of the last three
+                         statements.</para></listitem>
+                    <listitem><para><emphasis>Create the kernel recipe append file</emphasis>:
+                        Move to the <filename>meta-mylayer/recipes-kernel/linux</filename> directory and create
+                        the <filename>linux-yocto_3.4.bbappend</filename> file as follows:
+                        <literallayout class='monospaced'>
+     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+
+     SRC_URI += "file://0001-calibrate-Add-printk-example.patch"
+                        </literallayout>
+                        The <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
+                        and <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+                        statements enable the OpenEmbedded build system to find the patch file.
+                        For more information on using append files, see the
+                        "<ulink url='&YOCTO_DOCS_DEV_URL;#using-bbappend-files'>Using .bbappend Files in Your Layer</ulink>"
+                        section in the Yocto Project Development Manual.
+                        </para></listitem>
+                    <listitem><para>
+                        <emphasis>Put the patch file in your layer</emphasis>:
+                        Move the <filename>0001-calibrate-Add-printk-example.patch</filename> file to
+                        the <filename>meta-mylayer/recipes-kernel/linux/linux-yocto</filename>
+                        directory.</para></listitem>
+                </orderedlist>
+            </para>
+        </section>
+
+        <section id='set-up-for-the-build'>
+            <title>Set Up for the Build</title>
+
+            <para>
+                Do the following to make sure the build parameters are set up for the example.
+                Once you set up these build parameters, they do not have to change unless you
+                change the target architecture of the machine you are building:
+                <itemizedlist>
+                    <listitem><para><emphasis>Build for the correct target architecture:</emphasis> Your
+                        selected <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
+                        definition within the <filename>local.conf</filename> file in the
+                        <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
+                        specifies the target architecture used when building the Linux kernel.
+                        By default, <filename>MACHINE</filename> is set to
+                        <filename>qemux86</filename>, which specifies a 32-bit
+                        <trademark class='registered'>Intel</trademark> Architecture
+                        target machine suitable for the QEMU emulator.</para></listitem>
+                    <listitem><para><emphasis>Identify your <filename>meta-mylayer</filename>
+                        layer:</emphasis> The
+                        <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
+                        variable in the
+                        <filename>bblayers.conf</filename> file found in the
+                        <filename>poky/build/conf</filename> directory needs to have the path to your local
+                        <filename>meta-mylayer</filename> layer.
+                        By default, the <filename>BBLAYERS</filename> variable contains paths to
+                        <filename>meta</filename>, <filename>meta-poky</filename>, and
+                        <filename>meta-yocto-bsp</filename> in the
+                        <filename>poky</filename> Git repository.
+                        Add the path to your <filename>meta-mylayer</filename> location:
+                        <literallayout class='monospaced'>
+     BBLAYERS ?= " \
+       $HOME/poky/meta \
+       $HOME/poky/meta-poky \
+       $HOME/poky/meta-yocto-bsp \
+       $HOME/poky/meta-mylayer \
+       "
+                        </literallayout></para></listitem>
+                </itemizedlist>
+            </para>
+        </section>
+
+        <section id='build-the-modified-qemu-kernel-image'>
+            <title>Build the Modified QEMU Kernel Image</title>
+
+            <para>
+                The following steps build your modified kernel image:
+                <orderedlist>
+                    <listitem><para><emphasis>Be sure your build environment is initialized</emphasis>:
+                        Your environment should be set up since you previously sourced
+                        the
+                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
+                        script.
+                        If it is not, source the script again from <filename>poky</filename>.
+                        <literallayout class='monospaced'>
+     $ cd ~/poky
+     $ source &OE_INIT_FILE;
+                        </literallayout>
+                        </para></listitem>
+                    <listitem><para>
+                        <emphasis>Clean up</emphasis>:
+                        Be sure to clean the shared state out by using BitBake
+                        to run from within the Build Directory the
+                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleansstate'><filename>do_cleansstate</filename></ulink>
+                        task as follows:
+                        <literallayout class='monospaced'>
+     $ bitbake -c cleansstate linux-yocto
+                        </literallayout></para>
+                        <para>
+                           <note>
+                               Never remove any files by hand from the
+                               <filename>tmp/deploy</filename>
+                               directory inside the
+                               <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
+                               Always use the various BitBake clean tasks to
+                               clear out previous build artifacts.
+                               For information on the clean tasks, see the
+                               "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-clean'><filename>do_clean</filename></ulink>",
+                               "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleanall'><filename>do_cleanall</filename></ulink>",
+                               and
+                               "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleansstate'><filename>do_cleansstate</filename></ulink>"
+                               sections all in the Yocto Project Reference
+                               Manual.
+                           </note>
+                        </para></listitem>
+                    <listitem><para>
+                        <emphasis>Build the image</emphasis>:
+                        Next, build the kernel image using this command:
+                        <literallayout class='monospaced'>
+     $ bitbake -k linux-yocto
+                        </literallayout></para></listitem>
+                </orderedlist>
+            </para>
+        </section>
+
+        <section id='boot-the-image-and-verify-your-changes'>
+            <title>Boot the Image and Verify Your Changes</title>
+
+            <para>
+                These steps boot the image and allow you to see the changes
+                <orderedlist>
+                    <listitem><para><emphasis>Boot the image</emphasis>:
+                        Boot the modified image in the QEMU emulator
+                        using this command:
+                        <literallayout class='monospaced'>
+     $ runqemu qemux86
+                        </literallayout></para></listitem>
+                    <listitem><para><emphasis>Verify the changes</emphasis>:
+                        Log into the machine using <filename>root</filename> with no password and then
+                        use the following shell command to scroll through the console's boot output.
+                        <literallayout class='monospaced'>
+     # dmesg | less
+                        </literallayout>
+                        You should see the results of your <filename>printk</filename> statements
+                        as part of the output.</para></listitem>
+                </orderedlist>
+            </para>
+        </section>
+    </section>
+
     <section id='using-an-iterative-development-process'>
         <title>Using an Iterative Development Process</title>
 
@@ -747,8 +1095,8 @@
                 "<link linkend='applying-patches'>Applying Patches</link>"
                 section.
                 If you are not familiar with generating patches, refer to the
-                "<ulink url='&YOCTO_DOCS_DEV_URL;#creating-the-patch'>Creating the Patch</ulink>"
-                section in the Yocto Project Development Manual.
+                "<link linkend='creating-the-patch'>Creating the Patch</link>"
+                section.
             </para>
         </section>
     </section>