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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>
This commit is contained in:
Scott Rifenbark
committed by
Richard Purdie
Richard Purdie
parent
2c0c962dd9
commit
a99c2c5581
@@ -75,9 +75,8 @@
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See the "<link linkend='creating-and-preparing-a-layer'>Creating and Preparing a Layer</link>"
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section for some general resources.
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You can also see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#set-up-your-layer-for-the-build'>Set Up Your Layer for the Build</ulink>" section
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of the Yocto Project Development Manual for a detailed
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example.
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"<link linkend='set-up-your-layer-for-the-build'>Set Up Your Layer for the Build</link>"
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section for a detailed example.
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</para>
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<section id='creating-the-append-file'>
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@@ -295,9 +294,10 @@
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</para>
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<para>
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For a detailed example showing how to patch the kernel, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#patching-the-kernel'>Patching the Kernel</ulink>"
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section in the Yocto Project Development Manual.
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For a detailed example showing how to patch the kernel using
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<filename>devtool</filename>, see the
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"<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
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section.
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</para>
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</section>
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@@ -449,6 +449,354 @@
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</section>
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</section>
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<section id="using-devtool-to-patch-the-kernel">
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<title>Using <filename>devtool</filename> to Patch the Kernel</title>
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<para>
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Patching the kernel involves changing or adding configurations to an existing kernel,
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changing or adding recipes to the kernel that are needed to support specific hardware features,
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or even altering the source code itself.
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<note>
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You can use the <filename>yocto-kernel</filename> script
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found in the <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
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under <filename>scripts</filename> to manage kernel patches and configuration.
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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>"
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section in the Yocto Project Board Support Packages (BSP) Developer's Guide for
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more information.</note>
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</para>
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<para>
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This example creates a simple patch by adding some QEMU emulator console
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output at boot time through <filename>printk</filename> statements in the kernel's
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<filename>calibrate.c</filename> source code file.
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Applying the patch and booting the modified image causes the added
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messages to appear on the emulator's console.
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</para>
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<para>
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The example assumes a clean build exists for the <filename>qemux86</filename>
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machine in a
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<ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
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named <filename>poky</filename>.
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Furthermore, the
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<ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
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is <filename>build</filename> and is located in
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<filename>poky</filename> and the kernel is based on the
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Linux 3.4 kernel.
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</para>
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<para>
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Also, for more information on patching the kernel, see the
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"<link linkend='applying-patches'>Applying Patches</link>"
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section.
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</para>
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<section id='create-a-layer-for-your-changes'>
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<title>Create a Layer for your Changes</title>
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<para>
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The first step is to create a layer so you can isolate your
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changes.
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Rather than use the <filename>yocto-layer</filename> script
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to create the layer, this example steps through the process
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by hand.
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If you want information on the script that creates a general
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layer, see the
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"<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>"
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section in the Yocto Project Development Manual.
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</para>
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<para>
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These two commands create a directory you can use for your
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layer:
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<literallayout class='monospaced'>
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$ cd ~/poky
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$ mkdir meta-mylayer
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</literallayout>
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Creating a directory that follows the Yocto Project layer naming
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conventions sets up the layer for your changes.
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The layer is where you place your configuration files, append
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files, and patch files.
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To learn more about creating a layer and filling it with the
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files you need, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
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section in the Yocto Project Development Manual.
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</para>
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</section>
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<section id='finding-the-kernel-source-code'>
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<title>Finding the Kernel Source Code</title>
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<para>
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Each time you build a kernel image, the kernel source code
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is fetched and unpacked into the following directory:
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<literallayout class='monospaced'>
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${S}/linux
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</literallayout>
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See the "<ulink url='&YOCTO_DOCS_DEV_URL;#finding-the-temporary-source-code'>Finding Temporary Source Code</ulink>"
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section in the Yocto Project Development Manual and the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
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variable for more information about where source is kept
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during a build.
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</para>
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<para>
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For this example, we are going to patch the
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<filename>init/calibrate.c</filename> file
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by adding some simple console <filename>printk</filename> statements that we can
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see when we boot the image using QEMU.
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</para>
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</section>
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<section id='creating-the-patch'>
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<title>Creating the Patch</title>
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<para>
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Two methods exist by which you can create the patch:
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<ulink url='&YOCTO_DOCS_SDK_URL;#using-devtool-in-your-sdk-workflow'><filename>devtool</filename></ulink>
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and
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<ulink url='&YOCTO_DOCS_DEV_URL;#using-a-quilt-workflow'>Quilt</ulink>.
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For kernel patches, the Git workflow is more appropriate.
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This section assumes the Git workflow and shows the steps
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specific to this example.
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<orderedlist>
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<listitem><para>
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<emphasis>Change the working directory</emphasis>:
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Change to where the kernel source code is before making
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your edits to the <filename>calibrate.c</filename> file:
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<literallayout class='monospaced'>
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$ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux
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</literallayout>
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Because you are working in an established Git repository,
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you must be in this directory in order to commit your changes
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and create the patch file.
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<note>The <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink> and
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<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> variables
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represent the version and revision for the
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<filename>linux-yocto</filename> recipe.
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The <filename>PV</filename> variable includes the Git meta and machine
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hashes, which make the directory name longer than you might
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expect.
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</note></para></listitem>
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<listitem><para>
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<emphasis>Edit the source file</emphasis>:
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Edit the <filename>init/calibrate.c</filename> file to have the
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following changes:
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<literallayout class='monospaced'>
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void calibrate_delay(void)
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{
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unsigned long lpj;
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static bool printed;
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int this_cpu = smp_processor_id();
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printk("*************************************\n");
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printk("* *\n");
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printk("* HELLO YOCTO KERNEL *\n");
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printk("* *\n");
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printk("*************************************\n");
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if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
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.
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.
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.
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</literallayout></para></listitem>
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<listitem><para><emphasis>Stage and commit your changes</emphasis>:
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These Git commands display the modified file, stage it, and then
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commit the file:
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<literallayout class='monospaced'>
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$ git status
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$ git add init/calibrate.c
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$ git commit -m "calibrate: Add printk example"
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</literallayout></para></listitem>
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<listitem><para><emphasis>Generate the patch file</emphasis>:
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This Git command creates the a patch file named
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<filename>0001-calibrate-Add-printk-example.patch</filename>
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in the current directory.
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<literallayout class='monospaced'>
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$ git format-patch -1
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</literallayout>
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</para></listitem>
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</orderedlist>
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</para>
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</section>
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<section id='set-up-your-layer-for-the-build'>
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<title>Set Up Your Layer for the Build</title>
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<para>These steps get your layer set up for the build:
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<orderedlist>
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<listitem><para><emphasis>Create additional structure</emphasis>:
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Create the additional layer structure:
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<literallayout class='monospaced'>
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$ cd ~/poky/meta-mylayer
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$ mkdir conf
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$ mkdir recipes-kernel
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$ mkdir recipes-kernel/linux
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$ mkdir recipes-kernel/linux/linux-yocto
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</literallayout>
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The <filename>conf</filename> directory holds your configuration files, while the
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<filename>recipes-kernel</filename> directory holds your append file and
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your patch file.</para></listitem>
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<listitem><para><emphasis>Create the layer configuration file</emphasis>:
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Move to the <filename>meta-mylayer/conf</filename> directory and create
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the <filename>layer.conf</filename> file as follows:
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<literallayout class='monospaced'>
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# We have a conf and classes directory, add to BBPATH
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BBPATH .= ":${LAYERDIR}"
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# We have recipes-* directories, add to BBFILES
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BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
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${LAYERDIR}/recipes-*/*/*.bbappend"
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BBFILE_COLLECTIONS += "mylayer"
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BBFILE_PATTERN_mylayer = "^${LAYERDIR}/"
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BBFILE_PRIORITY_mylayer = "5"
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</literallayout>
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Notice <filename>mylayer</filename> as part of the last three
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statements.</para></listitem>
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<listitem><para><emphasis>Create the kernel recipe append file</emphasis>:
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Move to the <filename>meta-mylayer/recipes-kernel/linux</filename> directory and create
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the <filename>linux-yocto_3.4.bbappend</filename> file as follows:
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<literallayout class='monospaced'>
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FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
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SRC_URI += "file://0001-calibrate-Add-printk-example.patch"
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</literallayout>
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The <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
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and <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
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statements enable the OpenEmbedded build system to find the patch file.
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For more information on using append files, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#using-bbappend-files'>Using .bbappend Files in Your Layer</ulink>"
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section in the Yocto Project Development Manual.
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</para></listitem>
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<listitem><para>
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<emphasis>Put the patch file in your layer</emphasis>:
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Move the <filename>0001-calibrate-Add-printk-example.patch</filename> file to
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the <filename>meta-mylayer/recipes-kernel/linux/linux-yocto</filename>
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directory.</para></listitem>
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</orderedlist>
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</para>
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</section>
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<section id='set-up-for-the-build'>
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<title>Set Up for the Build</title>
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<para>
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Do the following to make sure the build parameters are set up for the example.
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Once you set up these build parameters, they do not have to change unless you
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change the target architecture of the machine you are building:
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<itemizedlist>
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<listitem><para><emphasis>Build for the correct target architecture:</emphasis> Your
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selected <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
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definition within the <filename>local.conf</filename> file in the
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<ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
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specifies the target architecture used when building the Linux kernel.
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By default, <filename>MACHINE</filename> is set to
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<filename>qemux86</filename>, which specifies a 32-bit
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<trademark class='registered'>Intel</trademark> Architecture
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target machine suitable for the QEMU emulator.</para></listitem>
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<listitem><para><emphasis>Identify your <filename>meta-mylayer</filename>
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layer:</emphasis> The
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<ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
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variable in the
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<filename>bblayers.conf</filename> file found in the
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<filename>poky/build/conf</filename> directory needs to have the path to your local
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<filename>meta-mylayer</filename> layer.
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By default, the <filename>BBLAYERS</filename> variable contains paths to
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<filename>meta</filename>, <filename>meta-poky</filename>, and
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<filename>meta-yocto-bsp</filename> in the
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<filename>poky</filename> Git repository.
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Add the path to your <filename>meta-mylayer</filename> location:
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<literallayout class='monospaced'>
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BBLAYERS ?= " \
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$HOME/poky/meta \
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$HOME/poky/meta-poky \
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$HOME/poky/meta-yocto-bsp \
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$HOME/poky/meta-mylayer \
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"
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</literallayout></para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='build-the-modified-qemu-kernel-image'>
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<title>Build the Modified QEMU Kernel Image</title>
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<para>
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The following steps build your modified kernel image:
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<orderedlist>
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<listitem><para><emphasis>Be sure your build environment is initialized</emphasis>:
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Your environment should be set up since you previously sourced
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the
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<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
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script.
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If it is not, source the script again from <filename>poky</filename>.
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<literallayout class='monospaced'>
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$ cd ~/poky
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$ source &OE_INIT_FILE;
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</literallayout>
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</para></listitem>
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<listitem><para>
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<emphasis>Clean up</emphasis>:
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Be sure to clean the shared state out by using BitBake
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to run from within the Build Directory the
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<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleansstate'><filename>do_cleansstate</filename></ulink>
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task as follows:
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<literallayout class='monospaced'>
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$ bitbake -c cleansstate linux-yocto
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</literallayout></para>
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<para>
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<note>
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Never remove any files by hand from the
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<filename>tmp/deploy</filename>
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directory inside the
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<ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
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Always use the various BitBake clean tasks to
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clear out previous build artifacts.
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For information on the clean tasks, see the
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"<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-clean'><filename>do_clean</filename></ulink>",
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"<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleanall'><filename>do_cleanall</filename></ulink>",
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and
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"<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleansstate'><filename>do_cleansstate</filename></ulink>"
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sections all in the Yocto Project Reference
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Manual.
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</note>
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</para></listitem>
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<listitem><para>
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<emphasis>Build the image</emphasis>:
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Next, build the kernel image using this command:
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<literallayout class='monospaced'>
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$ bitbake -k linux-yocto
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</literallayout></para></listitem>
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</orderedlist>
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</para>
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</section>
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<section id='boot-the-image-and-verify-your-changes'>
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<title>Boot the Image and Verify Your Changes</title>
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<para>
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These steps boot the image and allow you to see the changes
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<orderedlist>
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<listitem><para><emphasis>Boot the image</emphasis>:
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Boot the modified image in the QEMU emulator
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using this command:
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<literallayout class='monospaced'>
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$ runqemu qemux86
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</literallayout></para></listitem>
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<listitem><para><emphasis>Verify the changes</emphasis>:
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Log into the machine using <filename>root</filename> with no password and then
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use the following shell command to scroll through the console's boot output.
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<literallayout class='monospaced'>
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# dmesg | less
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</literallayout>
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You should see the results of your <filename>printk</filename> statements
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as part of the output.</para></listitem>
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</orderedlist>
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</para>
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</section>
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</section>
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|
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<section id='using-an-iterative-development-process'>
|
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<title>Using an Iterative Development Process</title>
|
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|
||||
@@ -747,8 +1095,8 @@
|
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"<link linkend='applying-patches'>Applying Patches</link>"
|
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section.
|
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If you are not familiar with generating patches, refer to the
|
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"<ulink url='&YOCTO_DOCS_DEV_URL;#creating-the-patch'>Creating the Patch</ulink>"
|
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section in the Yocto Project Development Manual.
|
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"<link linkend='creating-the-patch'>Creating the Patch</link>"
|
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section.
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</para>
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</section>
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</section>
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Reference in New Issue
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