Revert "poky: subtree update:b23aa6b753..ad30a6d470"
This reverts commit af5e4ef732faedf66c6dc1756432e9de2ac72988.
This commit introduced openbmc/openbmc#3720 and no solution has been
forthcoming. Revert until we can get to the bottom of this.
Change-Id: I2fb0d81eb26cf3dadb2f2abdd1a1bb7a95eaf03c
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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; ] >
+<!--SPDX-License-Identifier: CC-BY-2.0-UK-->
+
+<chapter id='kernel-dev-common'>
+<title>Common Tasks</title>
+
+ <para>
+ This chapter presents several common tasks you perform when you
+ work with the Yocto Project Linux kernel.
+ These tasks include preparing your host development system for
+ kernel development, preparing a layer, modifying an existing recipe,
+ patching the kernel, configuring the kernel, iterative development,
+ working with your own sources, and incorporating out-of-tree modules.
+ <note>
+ The examples presented in this chapter work with the Yocto Project
+ 2.4 Release and forward.
+ </note>
+ </para>
+
+ <section id='preparing-the-build-host-to-work-on-the-kernel'>
+ <title>Preparing the Build Host to Work on the Kernel</title>
+
+ <para>
+ Before you can do any kernel development, you need to be
+ sure your build host is set up to use the Yocto Project.
+ For information on how to get set up, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#dev-preparing-the-build-host'>Preparing the Build Host</ulink>"
+ section in the Yocto Project Development Tasks Manual.
+ Part of preparing the system is creating a local Git
+ repository of the
+ <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
+ (<filename>poky</filename>) on your system.
+ Follow the steps in the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#cloning-the-poky-repository'>Cloning the <filename>poky</filename> Repository</ulink>"
+ section in the Yocto Project Development Tasks Manual to set up your
+ Source Directory.
+ <note>
+ Be sure you check out the appropriate development branch or
+ you create your local branch by checking out a specific tag
+ to get the desired version of Yocto Project.
+ See the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#checking-out-by-branch-in-poky'>Checking Out by Branch in Poky</ulink>"
+ and
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#checkout-out-by-tag-in-poky'>Checking Out by Tag in Poky</ulink>"
+ sections in the Yocto Project Development Tasks Manual for more
+ information.
+ </note>
+ </para>
+
+ <para>
+ Kernel development is best accomplished using
+ <ulink url='&YOCTO_DOCS_SDK_URL;#using-devtool-in-your-sdk-workflow'><filename>devtool</filename></ulink>
+ and not through traditional kernel workflow methods.
+ The remainder of this section provides information for both
+ scenarios.
+ </para>
+
+ <section id='getting-ready-to-develop-using-devtool'>
+ <title>Getting Ready to Develop Using <filename>devtool</filename></title>
+
+ <para>
+ Follow these steps to prepare to update the kernel image using
+ <filename>devtool</filename>.
+ Completing this procedure leaves you with a clean kernel image
+ and ready to make modifications as described in the
+ "<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
+ section:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Initialize the BitBake Environment:</emphasis>
+ Before building an extensible SDK, you need to
+ initialize the BitBake build environment by sourcing the
+ build environment script
+ (i.e. <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>oe-init-build-env</filename></ulink>):
+ <literallayout class='monospaced'>
+ $ cd ~/poky
+ $ source oe-init-build-env
+ </literallayout>
+ <note>
+ The previous commands assume the
+ <ulink url='&YOCTO_DOCS_OM_URL;#source-repositories'>Source Repositories</ulink>
+ (i.e. <filename>poky</filename>) have been cloned
+ using Git and the local repository is named
+ "poky".
+ </note>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Prepare Your <filename>local.conf</filename> File:</emphasis>
+ By default, the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
+ variable is set to "qemux86-64", which is fine if you are
+ building for the QEMU emulator in 64-bit mode.
+ However, if you are not, you need to set the
+ <filename>MACHINE</filename> variable appropriately in
+ your <filename>conf/local.conf</filename> file found in
+ the
+ <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
+ (i.e. <filename>~/poky/build</filename> in this
+ example).</para>
+
+ <para>Also, since you are preparing to work on the
+ kernel image, you need to set the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS'><filename>MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS</filename></ulink>
+ variable to include kernel modules.</para>
+
+ <para>In this example we wish to build for qemux86 so
+ we must set the <filename>MACHINE</filename> variable
+ to "qemux86" and also add the "kernel-modules". As described
+ we do this by appending to <filename>conf/local.conf</filename>:
+ <literallayout class='monospaced'>
+ MACHINE = "qemux86"
+ MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS += "kernel-modules"
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Create a Layer for Patches:</emphasis>
+ You need to create a layer to hold patches created
+ for the kernel image.
+ You can use the
+ <filename>bitbake-layers create-layer</filename>
+ command as follows:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ bitbake-layers create-layer ../../meta-mylayer
+ NOTE: Starting bitbake server...
+ Add your new layer with 'bitbake-layers add-layer ../../meta-mylayer'
+ $
+ </literallayout>
+ <note>
+ For background information on working with
+ common and BSP layers, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
+ section in the Yocto Project Development Tasks
+ Manual and the
+ "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
+ section in the Yocto Project Board Support (BSP)
+ Developer's Guide, respectively.
+ For information on how to use the
+ <filename>bitbake-layers create-layer</filename>
+ command to quickly set up a layer, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#creating-a-general-layer-using-the-bitbake-layers-script'>Creating a General Layer Using the <filename>bitbake-layers</filename> Script</ulink>"
+ section in the Yocto Project Development Tasks
+ Manual.
+ </note>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Inform the BitBake Build Environment About
+ Your Layer:</emphasis>
+ As directed when you created your layer, you need to
+ add the layer to the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
+ variable in the <filename>bblayers.conf</filename> file
+ as follows:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ bitbake-layers add-layer ../../meta-mylayer
+ NOTE: Starting bitbake server...
+ $
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Build the Extensible SDK:</emphasis>
+ Use BitBake to build the extensible SDK specifically
+ for use with images to be run using QEMU:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ bitbake core-image-minimal -c populate_sdk_ext
+ </literallayout>
+ Once the build finishes, you can find the SDK installer
+ file (i.e. <filename>*.sh</filename> file) in the
+ following directory:
+ <literallayout class='monospaced'>
+ ~/poky/build/tmp/deploy/sdk
+ </literallayout>
+ For this example, the installer file is named
+ <filename>poky-glibc-x86_64-core-image-minimal-i586-toolchain-ext-&DISTRO;.sh</filename>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Install the Extensible SDK:</emphasis>
+ Use the following command to install the SDK.
+ For this example, install the SDK in the default
+ <filename>~/poky_sdk</filename> directory:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build/tmp/deploy/sdk
+ $ ./poky-glibc-x86_64-core-image-minimal-i586-toolchain-ext-&DISTRO;.sh
+ Poky (Yocto Project Reference Distro) Extensible SDK installer version &DISTRO;
+ ============================================================================
+ Enter target directory for SDK (default: ~/poky_sdk):
+ You are about to install the SDK to "/home/scottrif/poky_sdk". Proceed [Y/n]? Y
+ Extracting SDK......................................done
+ Setting it up...
+ Extracting buildtools...
+ Preparing build system...
+ Parsing recipes: 100% |#################################################################| Time: 0:00:52
+ Initializing tasks: 100% |############## ###############################################| Time: 0:00:04
+ Checking sstate mirror object availability: 100% |######################################| Time: 0:00:00
+ Parsing recipes: 100% |#################################################################| Time: 0:00:33
+ Initializing tasks: 100% |##############################################################| Time: 0:00:00
+ done
+ SDK has been successfully set up and is ready to be used.
+ Each time you wish to use the SDK in a new shell session, you need to source the environment setup script e.g.
+ $ . /home/scottrif/poky_sdk/environment-setup-i586-poky-linux
+ </literallayout>
+ </para></listitem>
+ <listitem><para id='setting-up-the-esdk-terminal'>
+ <emphasis>Set Up a New Terminal to Work With the
+ Extensible SDK:</emphasis>
+ You must set up a new terminal to work with the SDK.
+ You cannot use the same BitBake shell used to build the
+ installer.</para>
+
+ <para>After opening a new shell, run the SDK environment
+ setup script as directed by the output from installing
+ the SDK:
+ <literallayout class='monospaced'>
+ $ source ~/poky_sdk/environment-setup-i586-poky-linux
+ "SDK environment now set up; additionally you may now run devtool to perform development tasks.
+ Run devtool --help for further details.
+ </literallayout>
+ <note>
+ If you get a warning about attempting to use the
+ extensible SDK in an environment set up to run
+ BitBake, you did not use a new shell.
+ </note>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Build the Clean Image:</emphasis>
+ The final step in preparing to work on the kernel is to
+ build an initial image using
+ <filename>devtool</filename> in the new terminal you
+ just set up and initialized for SDK work:
+ <literallayout class='monospaced'>
+ $ devtool build-image
+ Parsing recipes: 100% |##########################################| Time: 0:00:05
+ Parsing of 830 .bb files complete (0 cached, 830 parsed). 1299 targets, 47 skipped, 0 masked, 0 errors.
+ WARNING: No packages to add, building image core-image-minimal unmodified
+ Loading cache: 100% |############################################| Time: 0:00:00
+ Loaded 1299 entries from dependency cache.
+ NOTE: Resolving any missing task queue dependencies
+ Initializing tasks: 100% |#######################################| Time: 0:00:07
+ Checking sstate mirror object availability: 100% |###############| Time: 0:00:00
+ NOTE: Executing SetScene Tasks
+ NOTE: Executing RunQueue Tasks
+ NOTE: Tasks Summary: Attempted 2866 tasks of which 2604 didn't need to be rerun and all succeeded.
+ NOTE: Successfully built core-image-minimal. You can find output files in /home/scottrif/poky_sdk/tmp/deploy/images/qemux86
+ </literallayout>
+ If you were building for actual hardware and not for
+ emulation, you could flash the image to a USB stick
+ on <filename>/dev/sdd</filename> and boot your device.
+ For an example that uses a Minnowboard, see the
+ <ulink url='https://wiki.yoctoproject.org/wiki/TipsAndTricks/KernelDevelopmentWithEsdk'>TipsAndTricks/KernelDevelopmentWithEsdk</ulink>
+ Wiki page.
+ </para></listitem>
+ </orderedlist>
+ </para>
+
+ <para>
+ At this point you have set up to start making modifications to
+ the kernel by using the extensible SDK.
+ For a continued example, see the
+ "<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
+ section.
+ </para>
+ </section>
+
+ <section id='getting-ready-for-traditional-kernel-development'>
+ <title>Getting Ready for Traditional Kernel Development</title>
+
+ <para>
+ Getting ready for traditional kernel development using the Yocto
+ Project involves many of the same steps as described in the
+ previous section.
+ However, you need to establish a local copy of the kernel source
+ since you will be editing these files.
+ </para>
+
+ <para>
+ Follow these steps to prepare to update the kernel image using
+ traditional kernel development flow with the Yocto Project.
+ Completing this procedure leaves you ready to make modifications
+ to the kernel source as described in the
+ "<link linkend='using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</link>"
+ section:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Initialize the BitBake Environment:</emphasis>
+ Before you can do anything using BitBake, you need to
+ initialize the BitBake build environment by sourcing the
+ build environment script
+ (i.e. <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>oe-init-build-env</filename></ulink>).
+ Also, for this example, be sure that the local branch
+ you have checked out for <filename>poky</filename> is
+ the Yocto Project &DISTRO_NAME; branch.
+ If you need to checkout out the &DISTRO_NAME; branch,
+ see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#checking-out-by-branch-in-poky'>Checking out by Branch in Poky</ulink>"
+ section in the Yocto Project Development Tasks Manual.
+ <literallayout class='monospaced'>
+ $ cd ~/poky
+ $ git branch
+ master
+ * &DISTRO_NAME;
+ $ source oe-init-build-env
+ </literallayout>
+ <note>
+ The previous commands assume the
+ <ulink url='&YOCTO_DOCS_OM_URL;#source-repositories'>Source Repositories</ulink>
+ (i.e. <filename>poky</filename>) have been cloned
+ using Git and the local repository is named
+ "poky".
+ </note>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Prepare Your <filename>local.conf</filename>
+ File:</emphasis>
+ By default, the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
+ variable is set to "qemux86-64", which is fine if you are
+ building for the QEMU emulator in 64-bit mode.
+ However, if you are not, you need to set the
+ <filename>MACHINE</filename> variable appropriately in
+ your <filename>conf/local.conf</filename> file found
+ in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
+ (i.e. <filename>~/poky/build</filename> in this
+ example).</para>
+
+ <para>Also, since you are preparing to work on the
+ kernel image, you need to set the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS'><filename>MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS</filename></ulink>
+ variable to include kernel modules.</para>
+
+ <para>In this example we wish to build for qemux86 so
+ we must set the <filename>MACHINE</filename> variable
+ to "qemux86" and also add the "kernel-modules". As described
+ we do this by appending to <filename>conf/local.conf</filename>:
+ <literallayout class='monospaced'>
+ MACHINE = "qemux86"
+ MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS += "kernel-modules"
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Create a Layer for Patches:</emphasis>
+ You need to create a layer to hold patches created
+ for the kernel image.
+ You can use the
+ <filename>bitbake-layers create-layer</filename>
+ command as follows:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ bitbake-layers create-layer ../../meta-mylayer
+ NOTE: Starting bitbake server...
+ Add your new layer with 'bitbake-layers add-layer ../../meta-mylayer'
+ </literallayout>
+ <note>
+ For background information on working with
+ common and BSP layers, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
+ section in the Yocto Project Development Tasks
+ Manual and the
+ "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
+ section in the Yocto Project Board Support (BSP)
+ Developer's Guide, respectively.
+ For information on how to use the
+ <filename>bitbake-layers create-layer</filename>
+ command to quickly set up a layer, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#creating-a-general-layer-using-the-bitbake-layers-script'>Creating a General Layer Using the <filename>bitbake-layers</filename> Script</ulink>"
+ section in the Yocto Project Development Tasks
+ Manual.
+ </note>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Inform the BitBake Build Environment About
+ Your Layer:</emphasis>
+ As directed when you created your layer, you need to add
+ the layer to the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
+ variable in the <filename>bblayers.conf</filename> file
+ as follows:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ bitbake-layers add-layer ../../meta-mylayer
+ NOTE: Starting bitbake server ...
+ $
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Create a Local Copy of the Kernel Git
+ Repository:</emphasis>
+ You can find Git repositories of supported Yocto Project
+ kernels organized under "Yocto Linux Kernel" in the
+ Yocto Project Source Repositories at
+ <ulink url='&YOCTO_GIT_URL;'></ulink>.
+ </para>
+
+ <para>
+ For simplicity, it is recommended that you create your
+ copy of the kernel Git repository outside of the
+ <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>,
+ which is usually named <filename>poky</filename>.
+ Also, be sure you are in the
+ <filename>standard/base</filename> branch.
+ </para>
+
+ <para>
+ The following commands show how to create a local copy
+ of the <filename>linux-yocto-4.12</filename> kernel and
+ be in the <filename>standard/base</filename> branch.
+ <note>
+ The <filename>linux-yocto-4.12</filename> kernel
+ can be used with the Yocto Project 2.4 release
+ and forward.
+ You cannot use the
+ <filename>linux-yocto-4.12</filename> kernel with
+ releases prior to Yocto Project 2.4:
+ </note>
+ <literallayout class='monospaced'>
+ $ cd ~
+ $ git clone git://git.yoctoproject.org/linux-yocto-4.12 --branch standard/base
+ Cloning into 'linux-yocto-4.12'...
+ remote: Counting objects: 6097195, done.
+ remote: Compressing objects: 100% (901026/901026), done.
+ remote: Total 6097195 (delta 5152604), reused 6096847 (delta 5152256)
+ Receiving objects: 100% (6097195/6097195), 1.24 GiB | 7.81 MiB/s, done.
+ Resolving deltas: 100% (5152604/5152604), done.
+ Checking connectivity... done.
+ Checking out files: 100% (59846/59846), done.
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Create a Local Copy of the Kernel Cache Git
+ Repository:</emphasis>
+ For simplicity, it is recommended that you create your
+ copy of the kernel cache Git repository outside of the
+ <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>,
+ which is usually named <filename>poky</filename>.
+ Also, for this example, be sure you are in the
+ <filename>yocto-4.12</filename> branch.
+ </para>
+
+ <para>
+ The following commands show how to create a local copy
+ of the <filename>yocto-kernel-cache</filename> and
+ be in the <filename>yocto-4.12</filename> branch:
+ <literallayout class='monospaced'>
+ $ cd ~
+ $ git clone git://git.yoctoproject.org/yocto-kernel-cache --branch yocto-4.12
+ Cloning into 'yocto-kernel-cache'...
+ remote: Counting objects: 22639, done.
+ remote: Compressing objects: 100% (9761/9761), done.
+ remote: Total 22639 (delta 12400), reused 22586 (delta 12347)
+ Receiving objects: 100% (22639/22639), 22.34 MiB | 6.27 MiB/s, done.
+ Resolving deltas: 100% (12400/12400), done.
+ Checking connectivity... done.
+ </literallayout>
+ </para></listitem>
+ </orderedlist>
+ </para>
+
+ <para>
+ At this point, you are ready to start making modifications to
+ the kernel using traditional kernel development steps.
+ For a continued example, see the
+ "<link linkend='using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</link>"
+ section.
+ </para>
+ </section>
+ </section>
+
+ <section id='creating-and-preparing-a-layer'>
+ <title>Creating and Preparing a Layer</title>
+
+ <para>
+ If you are going to be modifying kernel recipes, it is recommended
+ that you create and prepare your own layer in which to do your
+ work.
+ Your layer contains its own
+ <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink>
+ append files (<filename>.bbappend</filename>) and provides a
+ convenient mechanism to create your own recipe files
+ (<filename>.bb</filename>) as well as store and use kernel
+ patch files.
+ For background information on working with layers, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
+ section in the Yocto Project Development Tasks Manual.
+ <note><title>Tip</title>
+ The Yocto Project comes with many tools that simplify
+ tasks you need to perform.
+ One such tool is the
+ <filename>bitbake-layers create-layer</filename>
+ command, which simplifies creating a new layer.
+ See the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#creating-a-general-layer-using-the-bitbake-layers-script'>Creating a General Layer Using the <filename>bitbake-layers</filename> Script</ulink>"
+ section in the Yocto Project Development Tasks Manual for
+ information on how to use this script to quick set up a
+ new layer.
+ </note>
+ </para>
+
+ <para>
+ To better understand the layer you create for kernel development,
+ the following section describes how to create a layer
+ without the aid of tools.
+ These steps assume creation of a layer named
+ <filename>mylayer</filename> in your home directory:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Create Structure</emphasis>:
+ Create the layer's structure:
+ <literallayout class='monospaced'>
+ $ cd $HOME
+ $ mkdir meta-mylayer
+ $ mkdir meta-mylayer/conf
+ $ mkdir meta-mylayer/recipes-kernel
+ $ mkdir meta-mylayer/recipes-kernel/linux
+ $ mkdir meta-mylayer/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 eventual patch files.
+ </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 kernel's append file.
+ This example uses the
+ <filename>linux-yocto-4.12</filename> kernel.
+ Thus, the name of the append file is
+ <filename>linux-yocto_4.12.bbappend</filename>:
+ <literallayout class='monospaced'>
+ FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+
+ SRC_URI_append = " file://<replaceable>patch-file-one</replaceable>"
+ SRC_URI_append = " file://<replaceable>patch-file-two</replaceable>"
+ SRC_URI_append = " file://<replaceable>patch-file-three</replaceable>"
+ </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
+ patch files.
+ 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 Tasks Manual.
+ </para></listitem>
+ </orderedlist>
+ </para>
+ </section>
+
+ <section id='modifying-an-existing-recipe'>
+ <title>Modifying an Existing Recipe</title>
+
+ <para>
+ In many cases, you can customize an existing linux-yocto recipe to
+ meet the needs of your project.
+ Each release of the Yocto Project provides a few Linux
+ kernel recipes from which you can choose.
+ These are located in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
+ in <filename>meta/recipes-kernel/linux</filename>.
+ </para>
+
+ <para>
+ Modifying an existing recipe can consist of the following:
+ <itemizedlist>
+ <listitem><para>Creating the append file</para></listitem>
+ <listitem><para>Applying patches</para></listitem>
+ <listitem><para>Changing the configuration</para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ Before modifying an existing recipe, be sure that you have created
+ a minimal, custom layer from which you can work.
+ See the
+ "<link linkend='creating-and-preparing-a-layer'>Creating and Preparing a Layer</link>"
+ section for information.
+ </para>
+
+ <section id='creating-the-append-file'>
+ <title>Creating the Append File</title>
+
+ <para>
+ You create this file in your custom layer.
+ You also name it accordingly based on the linux-yocto recipe
+ you are using.
+ For example, if you are modifying the
+ <filename>meta/recipes-kernel/linux/linux-yocto_4.12.bb</filename>
+ recipe, the append file will typically be located as follows
+ within your custom layer:
+ <literallayout class='monospaced'>
+ <replaceable>your-layer</replaceable>/recipes-kernel/linux/linux-yocto_4.12.bbappend
+ </literallayout>
+ The append file should initially extend the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
+ search path by prepending the directory that contains your
+ files to the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
+ variable as follows:
+ <literallayout class='monospaced'>
+ FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+ </literallayout>
+ The path <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-THISDIR'><filename>THISDIR</filename></ulink><filename>}/${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
+ expands to "linux-yocto" in the current directory for this
+ example.
+ If you add any new files that modify the kernel recipe and you
+ have extended <filename>FILESPATH</filename> as
+ described above, you must place the files in your layer in the
+ following area:
+ <literallayout class='monospaced'>
+ <replaceable>your-layer</replaceable>/recipes-kernel/linux/linux-yocto/
+ </literallayout>
+ <note>If you are working on a new machine Board Support Package
+ (BSP), be sure to refer to the
+ <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
+ </note>
+ </para>
+
+ <para>
+ As an example, consider the following append file
+ used by the BSPs in <filename>meta-yocto-bsp</filename>:
+ <literallayout class='monospaced'>
+ meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.12.bbappend
+ </literallayout>
+ The following listing shows the file.
+ Be aware that the actual commit ID strings in this
+ example listing might be different than the actual strings
+ in the file from the <filename>meta-yocto-bsp</filename>
+ layer upstream.
+ <literallayout class='monospaced'>
+ KBRANCH_genericx86 = "standard/base"
+ KBRANCH_genericx86-64 = "standard/base"
+
+ KMACHINE_genericx86 ?= "common-pc"
+ KMACHINE_genericx86-64 ?= "common-pc-64"
+ KBRANCH_edgerouter = "standard/edgerouter"
+ KBRANCH_beaglebone = "standard/beaglebone"
+
+ SRCREV_machine_genericx86 ?= "d09f2ce584d60ecb7890550c22a80c48b83c2e19"
+ SRCREV_machine_genericx86-64 ?= "d09f2ce584d60ecb7890550c22a80c48b83c2e19"
+ SRCREV_machine_edgerouter ?= "b5c8cfda2dfe296410d51e131289fb09c69e1e7d"
+ SRCREV_machine_beaglebone ?= "b5c8cfda2dfe296410d51e131289fb09c69e1e7d"
+
+
+ COMPATIBLE_MACHINE_genericx86 = "genericx86"
+ COMPATIBLE_MACHINE_genericx86-64 = "genericx86-64"
+ COMPATIBLE_MACHINE_edgerouter = "edgerouter"
+ COMPATIBLE_MACHINE_beaglebone = "beaglebone"
+
+ LINUX_VERSION_genericx86 = "4.12.7"
+ LINUX_VERSION_genericx86-64 = "4.12.7"
+ LINUX_VERSION_edgerouter = "4.12.10"
+ LINUX_VERSION_beaglebone = "4.12.10"
+ </literallayout>
+ This append file contains statements used to support
+ several BSPs that ship with the Yocto Project.
+ The file defines machines using the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'><filename>COMPATIBLE_MACHINE</filename></ulink>
+ variable and uses the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>
+ variable to ensure the machine name used by the OpenEmbedded
+ build system maps to the machine name used by the Linux Yocto
+ kernel.
+ The file also uses the optional
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
+ variable to ensure the build process uses the
+ appropriate kernel branch.
+ </para>
+
+ <para>
+ Although this particular example does not use it, the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
+ variable could be used to enable features specific to
+ the kernel.
+ The append file points to specific commits in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
+ Git repository and the <filename>meta</filename> Git repository
+ branches to identify the exact kernel needed to build the
+ BSP.
+ </para>
+
+ <para>
+ One thing missing in this particular BSP, which you will
+ typically need when developing a BSP, is the kernel
+ configuration file (<filename>.config</filename>) for your BSP.
+ When developing a BSP, you probably have a kernel configuration
+ file or a set of kernel configuration files that, when taken
+ together, define the kernel configuration for your BSP.
+ You can accomplish this definition by putting the configurations
+ in a file or a set of files inside a directory located at the
+ same level as your kernel's append file and having the same
+ name as the kernel's main recipe file.
+ With all these conditions met, simply reference those files in
+ the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ statement in the append file.
+ </para>
+
+ <para>
+ For example, suppose you had some configuration options
+ in a file called <filename>network_configs.cfg</filename>.
+ You can place that file inside a directory named
+ <filename>linux-yocto</filename> and then add
+ a <filename>SRC_URI</filename> statement such as the
+ following to the append file.
+ When the OpenEmbedded build system builds the kernel, the
+ configuration options are picked up and applied.
+ <literallayout class='monospaced'>
+ SRC_URI += "file://network_configs.cfg"
+ </literallayout>
+ </para>
+
+ <para>
+ To group related configurations into multiple files, you
+ perform a similar procedure.
+ Here is an example that groups separate configurations
+ specifically for Ethernet and graphics into their own
+ files and adds the configurations by using a
+ <filename>SRC_URI</filename> statement like the following
+ in your append file:
+ <literallayout class='monospaced'>
+ SRC_URI += "file://myconfig.cfg \
+ file://eth.cfg \
+ file://gfx.cfg"
+ </literallayout>
+ </para>
+
+ <para>
+ Another variable you can use in your kernel recipe append
+ file is the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
+ variable.
+ When you use this statement, you are extending the locations
+ used by the OpenEmbedded system to look for files and
+ patches as the recipe is processed.
+ </para>
+
+ <note>
+ <para>
+ Other methods exist to accomplish grouping and defining
+ configuration options.
+ For example, if you are working with a local clone of the
+ kernel repository, you could checkout the kernel's
+ <filename>meta</filename> branch, make your changes, and
+ then push the changes to the local bare clone of the
+ kernel.
+ The result is that you directly add configuration options
+ to the <filename>meta</filename> branch for your BSP.
+ The configuration options will likely end up in that
+ location anyway if the BSP gets added to the Yocto Project.
+ </para>
+
+ <para>
+ In general, however, the Yocto Project maintainers take
+ care of moving the <filename>SRC_URI</filename>-specified
+ configuration options to the kernel's
+ <filename>meta</filename> branch.
+ Not only is it easier for BSP developers to not have to
+ worry about putting those configurations in the branch,
+ but having the maintainers do it allows them to apply
+ 'global' knowledge about the kinds of common configuration
+ options multiple BSPs in the tree are typically using.
+ This allows for promotion of common configurations into
+ common features.
+ </para>
+ </note>
+ </section>
+
+ <section id='applying-patches'>
+ <title>Applying Patches</title>
+
+ <para>
+ If you have a single patch or a small series of patches
+ that you want to apply to the Linux kernel source, you
+ can do so just as you would with any other recipe.
+ You first copy the patches to the path added to
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
+ in your <filename>.bbappend</filename> file as described in
+ the previous section, and then reference them in
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ statements.
+ </para>
+
+ <para>
+ For example, you can apply a three-patch series by adding the
+ following lines to your linux-yocto
+ <filename>.bbappend</filename> file in your layer:
+ <literallayout class='monospaced'>
+ SRC_URI += "file://0001-first-change.patch"
+ SRC_URI += "file://0002-second-change.patch"
+ SRC_URI += "file://0003-third-change.patch"
+ </literallayout>
+ The next time you run BitBake to build the Linux kernel,
+ BitBake detects the change in the recipe and fetches and
+ applies the patches before building the kernel.
+ </para>
+
+ <para>
+ 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>"
+ and
+ "<link linkend='using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</link>"
+ sections.
+ </para>
+ </section>
+
+ <section id='changing-the-configuration'>
+ <title>Changing the Configuration</title>
+
+ <para>
+ You can make wholesale or incremental changes to the final
+ <filename>.config</filename> file used for the eventual
+ Linux kernel configuration by including a
+ <filename>defconfig</filename> file and by specifying
+ configuration fragments in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ to be applied to that file.
+ </para>
+
+ <para>
+ If you have a complete, working Linux kernel
+ <filename>.config</filename>
+ file you want to use for the configuration, as before, copy
+ that file to the appropriate <filename>${PN}</filename>
+ directory in your layer's
+ <filename>recipes-kernel/linux</filename> directory,
+ and rename the copied file to "defconfig".
+ Then, add the following lines to the linux-yocto
+ <filename>.bbappend</filename> file in your layer:
+ <literallayout class='monospaced'>
+ FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+ SRC_URI += "file://defconfig"
+ </literallayout>
+ The <filename>SRC_URI</filename> tells the build system how to
+ search for the file, while the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
+ extends the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
+ variable (search directories) to include the
+ <filename>${PN}</filename> directory you created to hold the
+ configuration changes.
+ </para>
+
+ <note>
+ The build system applies the configurations from the
+ <filename>defconfig</filename> file before applying any
+ subsequent configuration fragments.
+ The final kernel configuration is a combination of the
+ configurations in the <filename>defconfig</filename> file and
+ any configuration fragments you provide.
+ You need to realize that if you have any configuration
+ fragments, the build system applies these on top of and
+ after applying the existing <filename>defconfig</filename>
+ file configurations.
+ </note>
+
+ <para>
+ Generally speaking, the preferred approach is to determine the
+ incremental change you want to make and add that as a
+ configuration fragment.
+ For example, if you want to add support for a basic serial
+ console, create a file named <filename>8250.cfg</filename> in
+ the <filename>${PN}</filename> directory with the following
+ content (without indentation):
+ <literallayout class='monospaced'>
+ CONFIG_SERIAL_8250=y
+ CONFIG_SERIAL_8250_CONSOLE=y
+ CONFIG_SERIAL_8250_PCI=y
+ CONFIG_SERIAL_8250_NR_UARTS=4
+ CONFIG_SERIAL_8250_RUNTIME_UARTS=4
+ CONFIG_SERIAL_CORE=y
+ CONFIG_SERIAL_CORE_CONSOLE=y
+ </literallayout>
+ Next, include this configuration fragment and extend the
+ <filename>FILESPATH</filename> variable in your
+ <filename>.bbappend</filename> file:
+ <literallayout class='monospaced'>
+ FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+ SRC_URI += "file://8250.cfg"
+ </literallayout>
+ The next time you run BitBake to build the Linux kernel, BitBake
+ detects the change in the recipe and fetches and applies the
+ new configuration before building the kernel.
+ </para>
+
+ <para>
+ For a detailed example showing how to configure the kernel,
+ see the
+ "<link linkend='configuring-the-kernel'>Configuring the Kernel</link>"
+ section.
+ </para>
+ </section>
+
+ <section id='using-an-in-tree-defconfig-file'>
+ <title>Using an "In-Tree" <filename>defconfig</filename> File</title>
+
+ <para>
+ It might be desirable to have kernel configuration fragment
+ support through a <filename>defconfig</filename> file that
+ is pulled from the kernel source tree for the configured
+ machine.
+ By default, the OpenEmbedded build system looks for
+ <filename>defconfig</filename> files in the layer used for
+ Metadata, which is "out-of-tree", and then configures them
+ using the following:
+ <literallayout class='monospaced'>
+ SRC_URI += "file://defconfig"
+ </literallayout>
+ If you do not want to maintain copies of
+ <filename>defconfig</filename> files in your layer but would
+ rather allow users to use the default configuration from the
+ kernel tree and still be able to add configuration fragments
+ to the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ through, for example, append files, you can direct the
+ OpenEmbedded build system to use a
+ <filename>defconfig</filename> file that is "in-tree".
+ </para>
+
+ <para>
+ To specify an "in-tree" <filename>defconfig</filename> file,
+ use the following statement form:
+ <literallayout class='monospaced'>
+ KBUILD_DEFCONFIG_<replaceable>KMACHINE</replaceable> ?= <replaceable>defconfig_file</replaceable>
+ </literallayout>
+ Here is an example that assigns the
+ <filename>KBUILD_DEFCONFIG</filename> variable based on
+ "raspberrypi2" and provides the path to the "in-tree"
+ <filename>defconfig</filename> file
+ to be used for a Raspberry Pi 2,
+ which is based on the Broadcom 2708/2709 chipset:
+ <literallayout class='monospaced'>
+ KBUILD_DEFCONFIG_raspberrypi2 ?= "bcm2709_defconfig"
+ </literallayout>
+ </para>
+
+ <para>
+ Aside from modifying your kernel recipe and providing your own
+ <filename>defconfig</filename> file, you need to be sure no
+ files or statements set <filename>SRC_URI</filename> to use a
+ <filename>defconfig</filename> other than your "in-tree"
+ file (e.g. a kernel's
+ <filename>linux-</filename><replaceable>machine</replaceable><filename>.inc</filename>
+ file).
+ In other words, if the build system detects a statement
+ that identifies an "out-of-tree"
+ <filename>defconfig</filename> file, that statement
+ will override your
+ <filename>KBUILD_DEFCONFIG</filename> variable.
+ </para>
+
+ <para>
+ See the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KBUILD_DEFCONFIG'><filename>KBUILD_DEFCONFIG</filename></ulink>
+ variable description for more information.
+ </para>
+ </section>
+ </section>
+
+ <section id="using-devtool-to-patch-the-kernel">
+ <title>Using <filename>devtool</filename> to Patch the Kernel</title>
+
+ <para>
+ The steps in this procedure show you how you can patch the
+ kernel using the extensible SDK and <filename>devtool</filename>.
+ <note>
+ Before attempting this procedure, be sure you have performed
+ the steps to get ready for updating the kernel as described
+ in the
+ "<link linkend='getting-ready-to-develop-using-devtool'>Getting Ready to Develop Using <filename>devtool</filename></link>"
+ section.
+ </note>
+ </para>
+
+ <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.
+ </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.
+ The example is a continuation of the setup procedure found in
+ the
+ "<link linkend='getting-ready-to-develop-using-devtool'>Getting Ready to Develop Using <filename>devtool</filename></link>"
+ Section.
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Check Out the Kernel Source Files:</emphasis>
+ First you must use <filename>devtool</filename> to checkout
+ the kernel source code in its workspace.
+ Be sure you are in the terminal set up to do work
+ with the extensible SDK.
+ <note>
+ See this
+ <link linkend='setting-up-the-esdk-terminal'>step</link>
+ in the
+ "<link linkend='getting-ready-to-develop-using-devtool'>Getting Ready to Develop Using <filename>devtool</filename></link>"
+ section for more information.
+ </note>
+ Use the following <filename>devtool</filename> command
+ to check out the code:
+ <literallayout class='monospaced'>
+ $ devtool modify linux-yocto
+ </literallayout>
+ <note>
+ During the checkout operation, a bug exists that could
+ cause errors such as the following to appear:
+ <literallayout class='monospaced'>
+ ERROR: Taskhash mismatch 2c793438c2d9f8c3681fd5f7bc819efa versus
+ be3a89ce7c47178880ba7bf6293d7404 for
+ /path/to/esdk/layers/poky/meta/recipes-kernel/linux/linux-yocto_4.10.bb.do_unpack
+ </literallayout>
+ You can safely ignore these messages.
+ The source code is correctly checked out.
+ </note>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Edit the Source Files</emphasis>
+ Follow these steps to make some simple changes to the source
+ files:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Change the working directory</emphasis>:
+ In the previous step, the output noted where you can find
+ the source files (e.g.
+ <filename>~/poky_sdk/workspace/sources/linux-yocto</filename>).
+ Change to where the kernel source code is before making
+ your edits to the <filename>calibrate.c</filename> file:
+ <literallayout class='monospaced'>
+ $ cd ~/poky_sdk/workspace/sources/linux-yocto
+ </literallayout>
+ </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>
+ </orderedlist>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Build the Updated Kernel Source:</emphasis>
+ To build the updated kernel source, use
+ <filename>devtool</filename>:
+ <literallayout class='monospaced'>
+ $ devtool build linux-yocto
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Create the Image With the New Kernel:</emphasis>
+ Use the <filename>devtool build-image</filename> command
+ to create a new image that has the new kernel.
+ <note>
+ If the image you originally created resulted in a Wic
+ file, you can use an alternate method to create the new
+ image with the updated kernel.
+ For an example, see the steps in the
+ <ulink url='https://wiki.yoctoproject.org/wiki/TipsAndTricks/KernelDevelopmentWithEsdk'>TipsAndTricks/KernelDevelopmentWithEsdk</ulink>
+ Wiki Page.
+ </note>
+ <literallayout class='monospaced'>
+ $ cd ~
+ $ devtool build-image core-image-minimal
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Test the New Image:</emphasis>
+ For this example, you can run the new image using QEMU
+ to verify your 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 when you scroll down the
+ console window.
+ </para></listitem>
+ </orderedlist>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Stage and commit your changes</emphasis>:
+ Within your eSDK terminal, change your working directory to
+ where you modified the <filename>calibrate.c</filename>
+ file and use these Git commands to stage and commit your
+ changes:
+ <literallayout class='monospaced'>
+ $ cd ~/poky_sdk/workspace/sources/linux-yocto
+ $ git status
+ $ git add init/calibrate.c
+ $ git commit -m "calibrate: Add printk example"
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Export the Patches and Create an Append File:</emphasis>
+ To export your commits as patches and create a
+ <filename>.bbappend</filename> file, use the following
+ command in the terminal used to work with the extensible
+ SDK.
+ This example uses the previously established layer named
+ <filename>meta-mylayer</filename>.
+ <note>
+ See Step 3 of the
+ "<link linkend='getting-ready-to-develop-using-devtool'>Getting Ready to Develop Using devtool</link>"
+ section for information on setting up this layer.
+ </note>
+ <literallayout class='monospaced'>
+ $ devtool finish linux-yocto ~/meta-mylayer
+ </literallayout>
+ Once the command finishes, the patches and the
+ <filename>.bbappend</filename> file are located in the
+ <filename>~/meta-mylayer/recipes-kernel/linux</filename>
+ directory.
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Build the Image With Your Modified Kernel:</emphasis>
+ You can now build an image that includes your kernel
+ patches.
+ Execute the following command from your
+ <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
+ in the terminal set up to run BitBake:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ bitbake core-image-minimal
+ </literallayout>
+ </para></listitem>
+ </orderedlist>
+ </para>
+ </section>
+
+ <section id="using-traditional-kernel-development-to-patch-the-kernel">
+ <title>Using Traditional Kernel Development to Patch the Kernel</title>
+
+ <para>
+ The steps in this procedure show you how you can patch the
+ kernel using traditional kernel development (i.e. not using
+ <filename>devtool</filename> and the extensible SDK as
+ described in the
+ "<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
+ section).
+ <note>
+ Before attempting this procedure, be sure you have performed
+ the steps to get ready for updating the kernel as described
+ in the
+ "<link linkend='getting-ready-for-traditional-kernel-development'>Getting Ready for Traditional Kernel Development</link>"
+ section.
+ </note>
+ </para>
+
+ <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.
+ </para>
+
+ <para>
+ The example in this section 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.
+ The example is a continuation of the setup procedure found in
+ the
+ "<link linkend='getting-ready-for-traditional-kernel-development'>Getting Ready for Traditional Kernel Development</link>"
+ Section.
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Edit the Source Files</emphasis>
+ Prior to this step, you should have used Git to create a
+ local copy of the repository for your kernel.
+ Assuming you created the repository as directed in the
+ "<link linkend='getting-ready-for-traditional-kernel-development'>Getting Ready for Traditional Kernel Development</link>"
+ section, use the following commands to edit the
+ <filename>calibrate.c</filename> file:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Change the working directory</emphasis>:
+ You need to locate the source files in the
+ local copy of the kernel Git repository:
+ Change to where the kernel source code is before making
+ your edits to the <filename>calibrate.c</filename> file:
+ <literallayout class='monospaced'>
+ $ cd ~/linux-yocto-4.12/init
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Edit the source file</emphasis>:
+ Edit the <filename>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>
+ </orderedlist>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Stage and Commit Your Changes:</emphasis>
+ Use standard Git commands to stage and commit the changes
+ you just made:
+ <literallayout class='monospaced'>
+ $ git add calibrate.c
+ $ git commit -m "calibrate.c - Added some printk statements"
+ </literallayout>
+ If you do not stage and commit your changes, the OpenEmbedded
+ Build System will not pick up the changes.
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Update Your <filename>local.conf</filename> File
+ to Point to Your Source Files:</emphasis>
+ In addition to your <filename>local.conf</filename> file
+ specifying to use "kernel-modules" and the "qemux86"
+ machine, it must also point to the updated kernel source
+ files.
+ Add
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ and
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
+ statements similar to the following to your
+ <filename>local.conf</filename>:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build/conf
+ </literallayout>
+ Add the following to the <filename>local.conf</filename>:
+ <literallayout class='monospaced'>
+ SRC_URI_pn-linux-yocto = "git:///<replaceable>path-to</replaceable>/linux-yocto-4.12;protocol=file;name=machine;branch=standard/base; \
+ git:///<replaceable>path-to</replaceable>/yocto-kernel-cache;protocol=file;type=kmeta;name=meta;branch=yocto-4.12;destsuffix=${KMETA}"
+ SRCREV_meta_qemux86 = "${AUTOREV}"
+ SRCREV_machine_qemux86 = "${AUTOREV}"
+ </literallayout>
+ <note>
+ Be sure to replace
+ <replaceable>path-to</replaceable> with the pathname
+ to your local Git repositories.
+ Also, you must be sure to specify the correct branch
+ and machine types.
+ For this example, the branch is
+ <filename>standard/base</filename> and the machine is
+ "qemux86".
+ </note>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Build the Image:</emphasis>
+ With the source modified, your changes staged and
+ committed, and the <filename>local.conf</filename> file
+ pointing to the kernel files, you can now use BitBake to
+ build the image:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ bitbake core-image-minimal
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Boot the image</emphasis>:
+ Boot the modified image in the QEMU emulator
+ using this command.
+ When prompted to login to the QEMU console, use "root"
+ with no password:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ runqemu qemux86
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Look for Your Changes:</emphasis>
+ As QEMU booted, you might have seen your changes rapidly
+ scroll by.
+ If not, use these commands to see your changes:
+ <literallayout class='monospaced'>
+ # dmesg | less
+ </literallayout>
+ You should see the results of your
+ <filename>printk</filename> statements
+ as part of the output when you scroll down the
+ console window.
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Generate the Patch File:</emphasis>
+ Once you are sure that your patch works correctly, you
+ can generate a <filename>*.patch</filename> file in the
+ kernel source repository:
+ <literallayout class='monospaced'>
+ $ cd ~/linux-yocto-4.12/init
+ $ git format-patch -1
+ 0001-calibrate.c-Added-some-printk-statements.patch
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Move the Patch File to Your Layer:</emphasis>
+ In order for subsequent builds to pick up patches, you
+ need to move the patch file you created in the previous
+ step to your layer <filename>meta-mylayer</filename>.
+ For this example, the layer created earlier is located
+ in your home directory as <filename>meta-mylayer</filename>.
+ When the layer was created using the
+ <filename>yocto-create</filename> script, no additional
+ hierarchy was created to support patches.
+ Before moving the patch file, you need to add additional
+ structure to your layer using the following commands:
+ <literallayout class='monospaced'>
+ $ cd ~/meta-mylayer
+ $ mkdir recipes-kernel
+ $ mkdir recipes-kernel/linux
+ $ mkdir recipes-kernel/linux/linux-yocto
+ </literallayout>
+ Once you have created this hierarchy in your layer, you can
+ move the patch file using the following command:
+ <literallayout class='monospaced'>
+ $ mv ~/linux-yocto-4.12/init/0001-calibrate.c-Added-some-printk-statements.patch ~/meta-mylayer/recipes-kernel/linux/linux-yocto
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Create the Append File:</emphasis>
+ Finally, you need to create the
+ <filename>linux-yocto_4.12.bbappend</filename> file and
+ insert statements that allow the OpenEmbedded build
+ system to find the patch.
+ The append file needs to be in your layer's
+ <filename>recipes-kernel/linux</filename>
+ directory and it must be named
+ <filename>linux-yocto_4.12.bbappend</filename> and have
+ the following contents:
+ <literallayout class='monospaced'>
+ FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+
+ SRC_URI_append = " file://0001-calibrate.c-Added-some-printk-statements.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.</para>
+
+ <para>For more information on append files and patches,
+ see the
+ "<link linkend='creating-the-append-file'>Creating the Append File</link>"
+ and
+ "<link linkend='applying-patches'>Applying Patches</link>"
+ sections.
+ You can also see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#using-bbappend-files'>Using .bbappend Files in Your Layer"</ulink>"
+ section in the Yocto Project Development Tasks Manual.
+ <note>
+ To build <filename>core-image-minimal</filename>
+ again and see the effects of your patch, you can
+ essentially eliminate the temporary source files
+ saved in <filename>poky/build/tmp/work/...</filename>
+ and residual effects of the build by entering the
+ following sequence of commands:
+ <literallayout class='monospaced'>
+ $ cd ~/poky/build
+ $ bitbake -c cleanall yocto-linux
+ $ bitbake core-image-minimal -c cleanall
+ $ bitbake core-image-minimal
+ $ runqemu qemux86
+ </literallayout>
+ </note>
+ </para></listitem>
+ </orderedlist>
+ </para>
+ </section>
+
+ <section id='configuring-the-kernel'>
+ <title>Configuring the Kernel</title>
+
+ <para>
+ Configuring the Yocto Project kernel consists of making sure the
+ <filename>.config</filename> file has all the right information
+ in it for the image you are building.
+ You can use the <filename>menuconfig</filename> tool and
+ configuration fragments to make sure your
+ <filename>.config</filename> file is just how you need it.
+ You can also save known configurations in a
+ <filename>defconfig</filename> file that the build system can use
+ for kernel configuration.
+ </para>
+
+ <para>
+ This section describes how to use <filename>menuconfig</filename>,
+ create and use configuration fragments, and how to interactively
+ modify your <filename>.config</filename> file to create the
+ leanest kernel configuration file possible.
+ </para>
+
+ <para>
+ For more information on kernel configuration, see the
+ "<link linkend='changing-the-configuration'>Changing the Configuration</link>"
+ section.
+ </para>
+
+ <section id='using-menuconfig'>
+ <title>Using <filename>menuconfig</filename></title>
+
+ <para>
+ The easiest way to define kernel configurations is to set
+ them through the <filename>menuconfig</filename> tool.
+ This tool provides an interactive method with which
+ to set kernel configurations.
+ For general information on <filename>menuconfig</filename>, see
+ <ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
+ </para>
+
+ <para>
+ To use the <filename>menuconfig</filename> tool in the Yocto
+ Project development environment, you must do the following:
+ <itemizedlist>
+ <listitem><para>
+ Because you launch <filename>menuconfig</filename>
+ using BitBake, you must be sure to set up your
+ environment by running the
+ <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
+ script found in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
+ </para></listitem>
+ <listitem><para>
+ You must be sure of the state of your build's
+ configuration in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
+ </para></listitem>
+ <listitem><para>
+ Your build host must have the following two packages
+ installed:
+ <literallayout class='monospaced'>
+ libncurses5-dev
+ libtinfo-dev
+ </literallayout>
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ The following commands initialize the BitBake environment,
+ run the
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-kernel_configme'><filename>do_kernel_configme</filename></ulink>
+ task, and launch <filename>menuconfig</filename>.
+ These commands assume the Source Directory's top-level folder
+ is <filename>~/poky</filename>:
+ <literallayout class='monospaced'>
+ $ cd poky
+ $ source oe-init-build-env
+ $ bitbake linux-yocto -c kernel_configme -f
+ $ bitbake linux-yocto -c menuconfig
+ </literallayout>
+ Once <filename>menuconfig</filename> comes up, its standard
+ interface allows you to interactively examine and configure
+ all the kernel configuration parameters.
+ After making your changes, simply exit the tool and save your
+ changes to create an updated version of the
+ <filename>.config</filename> configuration file.
+ <note>
+ You can use the entire <filename>.config</filename> file
+ as the <filename>defconfig</filename> file.
+ For information on <filename>defconfig</filename> files,
+ see the
+ "<link linkend='changing-the-configuration'>Changing the Configuration</link>",
+ "<link linkend='using-an-in-tree-defconfig-file'>Using an In-Tree <filename>defconfig</filename> File</link>,
+ and
+ "<link linkend='creating-a-defconfig-file'>Creating a <filename>defconfig</filename> File</link>"
+ sections.
+ </note>
+ </para>
+
+ <para>
+ Consider an example that configures the "CONFIG_SMP" setting
+ for the <filename>linux-yocto-4.12</filename> kernel.
+ <note>
+ The OpenEmbedded build system recognizes this kernel as
+ <filename>linux-yocto</filename> through Metadata (e.g.
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_VERSION'><filename>PREFERRED_VERSION</filename></ulink><filename>_linux-yocto ?= "12.4%"</filename>).
+ </note>
+ Once <filename>menuconfig</filename> launches, use the
+ interface to navigate through the selections to find the
+ configuration settings in which you are interested.
+ For this example, you deselect "CONFIG_SMP" by clearing the
+ "Symmetric Multi-Processing Support" option.
+ Using the interface, you can find the option under
+ "Processor Type and Features".
+ To deselect "CONFIG_SMP", use the arrow keys to
+ highlight "Symmetric Multi-Processing Support" and enter "N"
+ to clear the asterisk.
+ When you are finished, exit out and save the change.
+ </para>
+
+ <para>
+ Saving the selections updates the <filename>.config</filename>
+ configuration file.
+ This is the file that the OpenEmbedded build system uses to
+ configure the kernel during the build.
+ You can find and examine this file in the Build Directory in
+ <filename>tmp/work/</filename>.
+ The actual <filename>.config</filename> is located in the
+ area where the specific kernel is built.
+ For example, if you were building a Linux Yocto kernel based
+ on the <filename>linux-yocto-4.12</filename> kernel and you
+ were building a QEMU image targeted for
+ <filename>x86</filename> architecture, the
+ <filename>.config</filename> file would be:
+ <literallayout class='monospaced'>
+ poky/build/tmp/work/qemux86-poky-linux/linux-yocto/4.12.12+gitAUTOINC+eda4d18...
+ ...967-r0/linux-qemux86-standard-build/.config
+ </literallayout>
+ <note>
+ The previous example directory is artificially split and
+ many of the characters in the actual filename are omitted
+ in order to make it more readable.
+ Also, depending on the kernel you are using, the exact
+ pathname might differ.
+ </note>
+ </para>
+
+ <para>
+ Within the <filename>.config</filename> file, you can see the
+ kernel settings.
+ For example, the following entry shows that symmetric
+ multi-processor support is not set:
+ <literallayout class='monospaced'>
+ # CONFIG_SMP is not set
+ </literallayout>
+ </para>
+
+ <para>
+ A good method to isolate changed configurations is to use a
+ combination of the <filename>menuconfig</filename> tool and
+ simple shell commands.
+ Before changing configurations with
+ <filename>menuconfig</filename>, copy the existing
+ <filename>.config</filename> and rename it to something else,
+ use <filename>menuconfig</filename> to make as many changes as
+ you want and save them, then compare the renamed configuration
+ file against the newly created file.
+ You can use the resulting differences as your base to create
+ configuration fragments to permanently save in your kernel
+ layer.
+ <note>
+ Be sure to make a copy of the <filename>.config</filename>
+ file and do not just rename it.
+ The build system needs an existing
+ <filename>.config</filename> file from which to work.
+ </note>
+ </para>
+ </section>
+
+ <section id='creating-a-defconfig-file'>
+ <title>Creating a <filename>defconfig</filename> File</title>
+
+ <para>
+ A <filename>defconfig</filename> file in the context of
+ the Yocto Project is often a <filename>.config</filename>
+ file that is copied from a build or a
+ <filename>defconfig</filename> taken from the kernel tree
+ and moved into recipe space.
+ You can use a <filename>defconfig</filename> file
+ to retain a known set of kernel configurations from which the
+ OpenEmbedded build system can draw to create the final
+ <filename>.config</filename> file.
+ <note>
+ Out-of-the-box, the Yocto Project never ships a
+ <filename>defconfig</filename> or
+ <filename>.config</filename> file.
+ The OpenEmbedded build system creates the final
+ <filename>.config</filename> file used to configure the
+ kernel.
+ </note>
+ </para>
+
+ <para>
+ To create a <filename>defconfig</filename>, start with a
+ complete, working Linux kernel <filename>.config</filename>
+ file.
+ Copy that file to the appropriate
+ <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
+ directory in your layer's
+ <filename>recipes-kernel/linux</filename> directory, and rename
+ the copied file to "defconfig" (e.g.
+ <filename>~/meta-mylayer/recipes-kernel/linux/linux-yocto/defconfig</filename>).
+ Then, add the following lines to the linux-yocto
+ <filename>.bbappend</filename> file in your layer:
+ <literallayout class='monospaced'>
+ FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+ SRC_URI += "file://defconfig"
+ </literallayout>
+ The
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ tells the build system how to search for the file, while the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
+ extends the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
+ variable (search directories) to include the
+ <filename>${PN}</filename> directory you created to hold the
+ configuration changes.
+ <note>
+ The build system applies the configurations from the
+ <filename>defconfig</filename> file before applying any
+ subsequent configuration fragments.
+ The final kernel configuration is a combination of the
+ configurations in the <filename>defconfig</filename>
+ file and any configuration fragments you provide.
+ You need to realize that if you have any configuration
+ fragments, the build system applies these on top of and
+ after applying the existing defconfig file configurations.
+ </note>
+ For more information on configuring the kernel, see the
+ "<link linkend='changing-the-configuration'>Changing the Configuration</link>"
+ section.
+ </para>
+ </section>
+
+ <section id='creating-config-fragments'>
+ <title>Creating Configuration Fragments</title>
+
+ <para>
+ Configuration fragments are simply kernel options that
+ appear in a file placed where the OpenEmbedded build system
+ can find and apply them.
+ The build system applies configuration fragments after
+ applying configurations from a <filename>defconfig</filename>
+ file.
+ Thus, the final kernel configuration is a combination of the
+ configurations in the <filename>defconfig</filename>
+ file and then any configuration fragments you provide.
+ The build system applies fragments on top of and
+ after applying the existing defconfig file configurations.
+ </para>
+
+ <para>
+ Syntactically, the configuration statement is identical to
+ what would appear in the <filename>.config</filename> file,
+ which is in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
+ <note>
+ For more information about where the
+ <filename>.config</filename> file is located, see the
+ example in the
+ "<link linkend='using-menuconfig'>Using <filename>menuconfig</filename></link>"
+ section.
+ </note>
+ </para>
+
+ <para>
+ It is simple to create a configuration fragment.
+ One method is to use shell commands.
+ For example, issuing the following from the shell creates a
+ configuration fragment file named
+ <filename>my_smp.cfg</filename> that enables multi-processor
+ support within the kernel:
+ <literallayout class='monospaced'>
+ $ echo "CONFIG_SMP=y" >> my_smp.cfg
+ </literallayout>
+ <note>
+ All configuration fragment files must use the
+ <filename>.cfg</filename> extension in order for the
+ OpenEmbedded build system to recognize them as a
+ configuration fragment.
+ </note>
+ </para>
+
+ <para>
+ Another method is to create a configuration fragment using the
+ differences between two configuration files: one previously
+ created and saved, and one freshly created using the
+ <filename>menuconfig</filename> tool.
+ </para>
+
+ <para>
+ To create a configuration fragment using this method, follow
+ these steps:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Complete a Build Through Kernel Configuration:</emphasis>
+ Complete a build at least through the kernel
+ configuration task as follows:
+ <literallayout class='monospaced'>
+ $ bitbake linux-yocto -c kernel_configme -f
+ </literallayout>
+ This step ensures that you create a
+ <filename>.config</filename> file from a known state.
+ Because situations exist where your build state might
+ become unknown, it is best to run this task prior
+ to starting <filename>menuconfig</filename>.
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Launch <filename>menuconfig</filename>:</emphasis>
+ Run the <filename>menuconfig</filename> command:
+ <literallayout class='monospaced'>
+ $ bitbake linux-yocto -c menuconfig
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Create the Configuration Fragment:</emphasis>
+ Run the <filename>diffconfig</filename>
+ command to prepare a configuration fragment.
+ The resulting file <filename>fragment.cfg</filename>
+ is placed in the
+ <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename> directory:
+ <literallayout class='monospaced'>
+ $ bitbake linux-yocto -c diffconfig
+ </literallayout>
+ </para></listitem>
+ </orderedlist>
+ </para>
+
+ <para>
+ The <filename>diffconfig</filename> command creates a file
+ that is a list of Linux kernel <filename>CONFIG_</filename>
+ assignments.
+ See the "<link linkend='changing-the-configuration'>Changing the Configuration</link>"
+ section for additional information on how to use the output
+ as a configuration fragment.
+ <note>
+ You can also use this method to create configuration
+ fragments for a BSP.
+ See the "<link linkend='bsp-descriptions'>BSP Descriptions</link>"
+ section for more information.
+ </note>
+ </para>
+
+ <para>
+ Where do you put your configuration fragment files?
+ You can place these files in an area pointed to by
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ as directed by your <filename>bblayers.conf</filename> file,
+ which is located in your layer.
+ The OpenEmbedded build system picks up the configuration and
+ adds it to the kernel's configuration.
+ For example, suppose you had a set of configuration options
+ in a file called <filename>myconfig.cfg</filename>.
+ If you put that file inside a directory named
+ <filename>linux-yocto</filename> that resides in the same
+ directory as the kernel's append file within your layer
+ and then add the following statements to the kernel's append
+ file, those configuration options will be picked up and applied
+ when the kernel is built:
+ <literallayout class='monospaced'>
+ FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
+ SRC_URI += "file://myconfig.cfg"
+ </literallayout>
+ </para>
+
+ <para>
+ As mentioned earlier, you can group related configurations
+ into multiple files and name them all in the
+ <filename>SRC_URI</filename> statement as well.
+ For example, you could group separate configurations
+ specifically for Ethernet and graphics into their own files
+ and add those by using a <filename>SRC_URI</filename> statement
+ like the following in your append file:
+ <literallayout class='monospaced'>
+ SRC_URI += "file://myconfig.cfg \
+ file://eth.cfg \
+ file://gfx.cfg"
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='validating-configuration'>
+ <title>Validating Configuration</title>
+
+ <para>
+ You can use the
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-kernel_configcheck'><filename>do_kernel_configcheck</filename></ulink>
+ task to provide configuration validation:
+ <literallayout class='monospaced'>
+ $ bitbake linux-yocto -c kernel_configcheck -f
+ </literallayout>
+ Running this task produces warnings for when a
+ requested configuration does not appear in the final
+ <filename>.config</filename> file or when you override a
+ policy configuration in a hardware configuration fragment.
+ </para>
+
+ <para>
+ In order to run this task, you must have an existing
+ <filename>.config</filename> file.
+ See the
+ "<link linkend='using-menuconfig'>Using <filename>menuconfig</filename></link>"
+ section for information on how to create a configuration file.
+ </para>
+
+ <para>
+ Following is sample output from the
+ <filename>do_kernel_configcheck</filename> task:
+ <literallayout class='monospaced'>
+ Loading cache: 100% |########################################################| Time: 0:00:00
+ Loaded 1275 entries from dependency cache.
+ NOTE: Resolving any missing task queue dependencies
+
+ Build Configuration:
+ .
+ .
+ .
+
+ NOTE: Executing SetScene Tasks
+ NOTE: Executing RunQueue Tasks
+ WARNING: linux-yocto-4.12.12+gitAUTOINC+eda4d18ce4_16de014967-r0 do_kernel_configcheck:
+ [kernel config]: specified values did not make it into the kernel's final configuration:
+
+ ---------- CONFIG_X86_TSC -----------------
+ Config: CONFIG_X86_TSC
+ From: /home/scottrif/poky/build/tmp/work-shared/qemux86/kernel-source/.kernel-meta/configs/standard/bsp/common-pc/common-pc-cpu.cfg
+ Requested value: CONFIG_X86_TSC=y
+ Actual value:
+
+
+ ---------- CONFIG_X86_BIGSMP -----------------
+ Config: CONFIG_X86_BIGSMP
+ From: /home/scottrif/poky/build/tmp/work-shared/qemux86/kernel-source/.kernel-meta/configs/standard/cfg/smp.cfg
+ /home/scottrif/poky/build/tmp/work-shared/qemux86/kernel-source/.kernel-meta/configs/standard/defconfig
+ Requested value: # CONFIG_X86_BIGSMP is not set
+ Actual value:
+
+
+ ---------- CONFIG_NR_CPUS -----------------
+ Config: CONFIG_NR_CPUS
+ From: /home/scottrif/poky/build/tmp/work-shared/qemux86/kernel-source/.kernel-meta/configs/standard/cfg/smp.cfg
+ /home/scottrif/poky/build/tmp/work-shared/qemux86/kernel-source/.kernel-meta/configs/standard/bsp/common-pc/common-pc.cfg
+ /home/scottrif/poky/build/tmp/work-shared/qemux86/kernel-source/.kernel-meta/configs/standard/defconfig
+ Requested value: CONFIG_NR_CPUS=8
+ Actual value: CONFIG_NR_CPUS=1
+
+
+ ---------- CONFIG_SCHED_SMT -----------------
+ Config: CONFIG_SCHED_SMT
+ From: /home/scottrif/poky/build/tmp/work-shared/qemux86/kernel-source/.kernel-meta/configs/standard/cfg/smp.cfg
+ /home/scottrif/poky/build/tmp/work-shared/qemux86/kernel-source/.kernel-meta/configs/standard/defconfig
+ Requested value: CONFIG_SCHED_SMT=y
+ Actual value:
+
+
+
+ NOTE: Tasks Summary: Attempted 288 tasks of which 285 didn't need to be rerun and all succeeded.
+
+ Summary: There were 3 WARNING messages shown.
+ </literallayout>
+ <note>
+ The previous output example has artificial line breaks
+ to make it more readable.
+ </note>
+ </para>
+
+ <para>
+ The output describes the various problems that you can
+ encounter along with where to find the offending configuration
+ items.
+ You can use the information in the logs to adjust your
+ configuration files and then repeat the
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-kernel_configme'><filename>do_kernel_configme</filename></ulink>
+ and
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-kernel_configcheck'><filename>do_kernel_configcheck</filename></ulink>
+ tasks until they produce no warnings.
+ </para>
+
+ <para>
+ For more information on how to use the
+ <filename>menuconfig</filename> tool, see the
+ "<link linkend='using-menuconfig'>Using <filename>menuconfig</filename></link>"
+ section.
+ </para>
+ </section>
+
+ <section id='fine-tuning-the-kernel-configuration-file'>
+ <title>Fine-Tuning the Kernel Configuration File</title>
+
+ <para>
+ You can make sure the <filename>.config</filename> file is as
+ lean or efficient as possible by reading the output of the
+ kernel configuration fragment audit, noting any issues, making
+ changes to correct the issues, and then repeating.
+ </para>
+
+ <para>
+ As part of the kernel build process, the
+ <filename>do_kernel_configcheck</filename> task runs.
+ This task validates the kernel configuration by checking the
+ final <filename>.config</filename> file against the input
+ files.
+ During the check, the task produces warning messages for the
+ following issues:
+ <itemizedlist>
+ <listitem><para>
+ Requested options that did not make the final
+ <filename>.config</filename> file.
+ </para></listitem>
+ <listitem><para>
+ Configuration items that appear twice in the same
+ configuration fragment.
+ </para></listitem>
+ <listitem><para>
+ Configuration items tagged as "required" that were
+ overridden.
+ </para></listitem>
+ <listitem><para>
+ A board overrides a non-board specific option.
+ </para></listitem>
+ <listitem><para>
+ Listed options not valid for the kernel being
+ processed.
+ In other words, the option does not appear anywhere.
+ </para></listitem>
+ </itemizedlist>
+ <note>
+ The <filename>do_kernel_configcheck</filename> task can
+ also optionally report if an option is overridden during
+ processing.
+ </note>
+ </para>
+
+ <para>
+ For each output warning, a message points to the file
+ that contains a list of the options and a pointer to the
+ configuration fragment that defines them.
+ Collectively, the files are the key to streamlining the
+ configuration.
+ </para>
+
+ <para>
+ To streamline the configuration, do the following:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Use a Working Configuration:</emphasis>
+ Start with a full configuration that you
+ know works.
+ Be sure the configuration builds and boots
+ successfully.
+ Use this configuration file as your baseline.
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Run Configure and Check Tasks:</emphasis>
+ Separately run the
+ <filename>do_kernel_configme</filename> and
+ <filename>do_kernel_configcheck</filename> tasks:
+ <literallayout class='monospaced'>
+ $ bitbake linux-yocto -c kernel_configme -f
+ $ bitbake linux-yocto -c kernel_configcheck -f
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Process the Results:</emphasis>
+ Take the resulting list of files from the
+ <filename>do_kernel_configcheck</filename> task
+ warnings and do the following:
+ <itemizedlist>
+ <listitem><para>
+ Drop values that are redefined in the fragment
+ but do not change the final
+ <filename>.config</filename> file.
+ </para></listitem>
+ <listitem><para>
+ Analyze and potentially drop values from the
+ <filename>.config</filename> file that override
+ required configurations.
+ </para></listitem>
+ <listitem><para>
+ Analyze and potentially remove non-board
+ specific options.
+ </para></listitem>
+ <listitem><para>
+ Remove repeated and invalid options.
+ </para></listitem>
+ </itemizedlist>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Re-Run Configure and Check Tasks:</emphasis>
+ After you have worked through the output of the kernel
+ configuration audit, you can re-run the
+ <filename>do_kernel_configme</filename> and
+ <filename>do_kernel_configcheck</filename> tasks to
+ see the results of your changes.
+ If you have more issues, you can deal with them as
+ described in the previous step.
+ </para></listitem>
+ </orderedlist>
+ </para>
+
+ <para>
+ Iteratively working through steps two through four eventually
+ yields a minimal, streamlined configuration file.
+ Once you have the best <filename>.config</filename>, you can
+ build the Linux Yocto kernel.
+ </para>
+ </section>
+ </section>
+
+ <section id='expanding-variables'>
+ <title>Expanding Variables</title>
+
+ <para>
+ Sometimes it is helpful to determine what a variable expands
+ to during a build.
+ You can do examine the values of variables by examining the
+ output of the <filename>bitbake -e</filename> command.
+ The output is long and is more easily managed in a text file,
+ which allows for easy searches:
+ <literallayout class='monospaced'>
+ $ bitbake -e virtual/kernel > <replaceable>some_text_file</replaceable>
+ </literallayout>
+ Within the text file, you can see exactly how each variable is
+ expanded and used by the OpenEmbedded build system.
+ </para>
+ </section>
+
+ <section id='working-with-a-dirty-kernel-version-string'>
+ <title>Working with a "Dirty" Kernel Version String</title>
+
+ <para>
+ If you build a kernel image and the version string has a
+ "+" or a "-dirty" at the end, uncommitted modifications exist
+ in the kernel's source directory.
+ Follow these steps to clean up the version string:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Discover the Uncommitted Changes:</emphasis>
+ Go to the kernel's locally cloned Git repository
+ (source directory) and use the following Git command
+ to list the files that have been changed, added, or
+ removed:
+ <literallayout class='monospaced'>
+ $ git status
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Commit the Changes:</emphasis>
+ You should commit those changes to the kernel source
+ tree regardless of whether or not you will save,
+ export, or use the changes:
+ <literallayout class='monospaced'>
+ $ git add
+ $ git commit -s -a -m "getting rid of -dirty"
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Rebuild the Kernel Image:</emphasis>
+ Once you commit the changes, rebuild the kernel.</para>
+
+ <para>Depending on your particular kernel development
+ workflow, the commands you use to rebuild the
+ kernel might differ.
+ For information on building the kernel image when
+ using <filename>devtool</filename>, see the
+ "<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
+ section.
+ For information on building the kernel image when
+ using Bitbake, see the
+ "<link linkend='using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</link>"
+ section.
+ </para></listitem>
+ </orderedlist>
+ </para>
+ </section>
+
+ <section id='working-with-your-own-sources'>
+ <title>Working With Your Own Sources</title>
+
+ <para>
+ If you cannot work with one of the Linux kernel
+ versions supported by existing linux-yocto recipes, you can
+ still make use of the Yocto Project Linux kernel tooling by
+ working with your own sources.
+ When you use your own sources, you will not be able to
+ leverage the existing kernel
+ <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink> and
+ stabilization work of the linux-yocto sources.
+ However, you will be able to manage your own Metadata in the same
+ format as the linux-yocto sources.
+ Maintaining format compatibility facilitates converging with
+ linux-yocto on a future, mutually-supported kernel version.
+ </para>
+
+ <para>
+ To help you use your own sources, the Yocto Project provides a
+ linux-yocto custom recipe
+ (<filename>linux-yocto-custom.bb</filename>) that uses
+ <filename>kernel.org</filename> sources
+ and the Yocto Project Linux kernel tools for managing
+ kernel Metadata.
+ You can find this recipe in the
+ <filename>poky</filename> Git repository of the
+ Yocto Project <ulink url='&YOCTO_GIT_URL;'>Source Repository</ulink>
+ at:
+ <literallayout class="monospaced">
+ poky/meta-skeleton/recipes-kernel/linux/linux-yocto-custom.bb
+ </literallayout>
+ </para>
+
+ <para>
+ Here are some basic steps you can use to work with your own
+ sources:
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Create a Copy of the Kernel Recipe:</emphasis>
+ Copy the <filename>linux-yocto-custom.bb</filename>
+ recipe to your layer and give it a meaningful name.
+ The name should include the version of the Yocto Linux
+ kernel you are using (e.g.
+ <filename>linux-yocto-myproject_4.12.bb</filename>,
+ where "4.12" is the base version of the Linux kernel
+ with which you would be working).
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Create a Directory for Your Patches:</emphasis>
+ In the same directory inside your layer, create a matching
+ directory to store your patches and configuration files
+ (e.g. <filename>linux-yocto-myproject</filename>).
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Ensure You Have Configurations:</emphasis>
+ Make sure you have either a <filename>defconfig</filename>
+ file or configuration fragment files in your layer.
+ When you use the <filename>linux-yocto-custom.bb</filename>
+ recipe, you must specify a configuration.
+ If you do not have a <filename>defconfig</filename> file,
+ you can run the following:
+ <literallayout class='monospaced'>
+ $ make defconfig
+ </literallayout>
+ After running the command, copy the resulting
+ <filename>.config</filename> file to the
+ <filename>files</filename> directory in your layer
+ as "defconfig" and then add it to the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ variable in the recipe.</para>
+
+ <para>Running the <filename>make defconfig</filename>
+ command results in the default configuration for your
+ architecture as defined by your kernel.
+ However, no guarantee exists that this configuration is
+ valid for your use case, or that your board will even boot.
+ This is particularly true for non-x86 architectures.</para>
+
+ <para>To use non-x86 <filename>defconfig</filename> files,
+ you need to be more specific and find one that matches your
+ board (i.e. for arm, you look in
+ <filename>arch/arm/configs</filename> and use the one that
+ is the best starting point for your board).
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Edit the Recipe:</emphasis>
+ Edit the following variables in your recipe as appropriate
+ for your project:
+ <itemizedlist>
+ <listitem><para>
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>:
+ The <filename>SRC_URI</filename> should specify
+ a Git repository that uses one of the supported Git
+ fetcher protocols (i.e. <filename>file</filename>,
+ <filename>git</filename>, <filename>http</filename>,
+ and so forth).
+ The <filename>SRC_URI</filename> variable should
+ also specify either a <filename>defconfig</filename>
+ file or some configuration fragment files.
+ The skeleton recipe provides an example
+ <filename>SRC_URI</filename> as a syntax reference.
+ </para></listitem>
+ <listitem><para>
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_VERSION'><filename>LINUX_VERSION</filename></ulink>:
+ The Linux kernel version you are using (e.g.
+ "4.12").
+ </para></listitem>
+ <listitem><para>
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_VERSION_EXTENSION'><filename>LINUX_VERSION_EXTENSION</filename></ulink>:
+ The Linux kernel
+ <filename>CONFIG_LOCALVERSION</filename> that is
+ compiled into the resulting kernel and visible
+ through the <filename>uname</filename> command.
+ </para></listitem>
+ <listitem><para>
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>:
+ The commit ID from which you want to build.
+ </para></listitem>
+ <listitem><para>
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>:
+ Treat this variable the same as you would in any
+ other recipe.
+ Increment the variable to indicate to the
+ OpenEmbedded build system that the recipe has
+ changed.
+ </para></listitem>
+ <listitem><para>
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>:
+ The default <filename>PV</filename> assignment is
+ typically adequate.
+ It combines the <filename>LINUX_VERSION</filename>
+ with the Source Control Manager (SCM) revision
+ as derived from the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>
+ variable.
+ The combined results are a string with the
+ following form:
+ <literallayout class='monospaced'>
+ 3.19.11+git1+68a635bf8dfb64b02263c1ac80c948647cc76d5f_1+218bd8d2022b9852c60d32f0d770931e3cf343e2
+ </literallayout>
+ While lengthy, the extra verbosity in
+ <filename>PV</filename> helps ensure you are using
+ the exact sources from which you intend to build.
+ </para></listitem>
+ <listitem><para>
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'><filename>COMPATIBLE_MACHINE</filename></ulink>:
+ A list of the machines supported by your new recipe.
+ This variable in the example recipe is set
+ by default to a regular expression that matches
+ only the empty string, "(^$)".
+ This default setting triggers an explicit build
+ failure.
+ You must change it to match a list of the machines
+ that your new recipe supports.
+ For example, to support the
+ <filename>qemux86</filename> and
+ <filename>qemux86-64</filename> machines, use
+ the following form:
+ <literallayout class='monospaced'>
+ COMPATIBLE_MACHINE = "qemux86|qemux86-64"
+ </literallayout>
+ </para></listitem>
+ </itemizedlist>
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Customize Your Recipe as Needed:</emphasis>
+ Provide further customizations to your recipe
+ as needed just as you would customize an existing
+ linux-yocto recipe.
+ See the
+ "<link linkend='modifying-an-existing-recipe'>Modifying an Existing Recipe</link>"
+ section for information.
+ </para></listitem>
+ </orderedlist>
+ </para>
+ </section>
+
+ <section id='working-with-out-of-tree-modules'>
+ <title>Working with Out-of-Tree Modules</title>
+
+ <para>
+ This section describes steps to build out-of-tree modules on
+ your target and describes how to incorporate out-of-tree modules
+ in the build.
+ </para>
+
+ <section id='building-out-of-tree-modules-on-the-target'>
+ <title>Building Out-of-Tree Modules on the Target</title>
+
+ <para>
+ While the traditional Yocto Project development model would be
+ to include kernel modules as part of the normal build
+ process, you might find it useful to build modules on the
+ target.
+ This could be the case if your target system is capable
+ and powerful enough to handle the necessary compilation.
+ Before deciding to build on your target, however, you should
+ consider the benefits of using a proper cross-development
+ environment from your build host.
+ </para>
+
+ <para>
+ If you want to be able to build out-of-tree modules on
+ the target, there are some steps you need to take
+ on the target that is running your SDK image.
+ Briefly, the <filename>kernel-dev</filename> package
+ is installed by default on all
+ <filename>*.sdk</filename> images and the
+ <filename>kernel-devsrc</filename> package is installed
+ on many of the <filename>*.sdk</filename> images.
+ However, you need to create some scripts prior to
+ attempting to build the out-of-tree modules on the target
+ that is running that image.
+ </para>
+
+ <para>
+ Prior to attempting to build the out-of-tree modules,
+ you need to be on the target as root and you need to
+ change to the <filename>/usr/src/kernel</filename> directory.
+ Next, <filename>make</filename> the scripts:
+ <literallayout class='monospaced'>
+ # cd /usr/src/kernel
+ # make scripts
+ </literallayout>
+ Because all SDK image recipes include
+ <filename>dev-pkgs</filename>, the
+ <filename>kernel-dev</filename> packages will be installed
+ as part of the SDK image and the
+ <filename>kernel-devsrc</filename> packages will be installed
+ as part of applicable SDK images.
+ The SDK uses the scripts when building out-of-tree
+ modules.
+ Once you have switched to that directory and created the
+ scripts, you should be able to build your out-of-tree modules
+ on the target.
+ </para>
+ </section>
+
+ <section id='incorporating-out-of-tree-modules'>
+ <title>Incorporating Out-of-Tree Modules</title>
+
+ <para>
+ While it is always preferable to work with sources integrated
+ into the Linux kernel sources, if you need an external kernel
+ module, the <filename>hello-mod.bb</filename> recipe is
+ available as a template from which you can create your
+ own out-of-tree Linux kernel module recipe.
+ </para>
+
+ <para>
+ This template recipe is located in the
+ <filename>poky</filename> Git repository of the
+ Yocto Project <ulink url='&YOCTO_GIT_URL;'>Source Repository</ulink>
+ at:
+ <literallayout class="monospaced">
+ poky/meta-skeleton/recipes-kernel/hello-mod/hello-mod_0.1.bb
+ </literallayout>
+ </para>
+
+ <para>
+ To get started, copy this recipe to your layer and give it a
+ meaningful name (e.g. <filename>mymodule_1.0.bb</filename>).
+ In the same directory, create a new directory named
+ <filename>files</filename> where you can store any source files,
+ patches, or other files necessary for building
+ the module that do not come with the sources.
+ Finally, update the recipe as needed for the module.
+ Typically, you will need to set the following variables:
+ <itemizedlist>
+ <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-DESCRIPTION'><filename>DESCRIPTION</filename></ulink>
+ </para></listitem>
+ <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE*</filename></ulink>
+ </para></listitem>
+ <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ </para></listitem>
+ <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ Depending on the build system used by the module sources,
+ you might need to make some adjustments.
+ For example, a typical module <filename>Makefile</filename>
+ looks much like the one provided with the
+ <filename>hello-mod</filename> template:
+ <literallayout class='monospaced'>
+ obj-m := hello.o
+
+ SRC := $(shell pwd)
+
+ all:
+ $(MAKE) -C $(KERNEL_SRC) M=$(SRC)
+
+ modules_install:
+ $(MAKE) -C $(KERNEL_SRC) M=$(SRC) modules_install
+ ...
+ </literallayout>
+ </para>
+
+ <para>
+ The important point to note here is the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_SRC'><filename>KERNEL_SRC</filename></ulink>
+ variable.
+ The
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-module'><filename>module</filename></ulink>
+ class sets this variable and the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_PATH'><filename>KERNEL_PATH</filename></ulink>
+ variable to
+ <filename>${<ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_KERNEL_DIR'><filename>STAGING_KERNEL_DIR</filename></ulink>}</filename>
+ with the necessary Linux kernel build information to build
+ modules.
+ If your module <filename>Makefile</filename> uses a different
+ variable, you might want to override the
+ <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
+ step, or create a patch to
+ the <filename>Makefile</filename> to work with the more typical
+ <filename>KERNEL_SRC</filename> or
+ <filename>KERNEL_PATH</filename> variables.
+ </para>
+
+ <para>
+ After you have prepared your recipe, you will likely want to
+ include the module in your images.
+ To do this, see the documentation for the following variables in
+ the Yocto Project Reference Manual and set one of them
+ appropriately for your machine configuration file:
+ <itemizedlist>
+ <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ESSENTIAL_EXTRA_RDEPENDS'><filename>MACHINE_ESSENTIAL_EXTRA_RDEPENDS</filename></ulink>
+ </para></listitem>
+ <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS'><filename>MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS</filename></ulink>
+ </para></listitem>
+ <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_EXTRA_RDEPENDS'><filename>MACHINE_EXTRA_RDEPENDS</filename></ulink>
+ </para></listitem>
+ <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_EXTRA_RRECOMMENDS'><filename>MACHINE_EXTRA_RRECOMMENDS</filename></ulink>
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ Modules are often not required for boot and can be excluded from
+ certain build configurations.
+ The following allows for the most flexibility:
+ <literallayout class='monospaced'>
+ MACHINE_EXTRA_RRECOMMENDS += "kernel-module-mymodule"
+ </literallayout>
+ The value is derived by appending the module filename without
+ the <filename>.ko</filename> extension to the string
+ "kernel-module-".
+ </para>
+
+ <para>
+ Because the variable is
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>
+ and not a
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
+ variable, the build will not fail if this module is not
+ available to include in the image.
+ </para>
+ </section>
+ </section>
+
+
+ <section id='inspecting-changes-and-commits'>
+ <title>Inspecting Changes and Commits</title>
+
+ <para>
+ A common question when working with a kernel is:
+ "What changes have been applied to this tree?"
+ Rather than using "grep" across directories to see what has
+ changed, you can use Git to inspect or search the kernel tree.
+ Using Git is an efficient way to see what has changed in the tree.
+ </para>
+
+ <section id='what-changed-in-a-kernel'>
+ <title>What Changed in a Kernel?</title>
+
+ <para>
+ Following are a few examples that show how to use Git
+ commands to examine changes.
+ These examples are by no means the only way to see changes.
+ <note>
+ In the following examples, unless you provide a commit
+ range, <filename>kernel.org</filename> history is blended
+ with Yocto Project kernel changes.
+ You can form ranges by using branch names from the
+ kernel tree as the upper and lower commit markers with
+ the Git commands.
+ You can see the branch names through the web interface
+ to the Yocto Project source repositories at
+ <ulink url='&YOCTO_GIT_URL;'></ulink>.
+ </note>
+ To see a full range of the changes, use the
+ <filename>git whatchanged</filename> command and specify a
+ commit range for the branch
+ (<replaceable>commit</replaceable><filename>..</filename><replaceable>commit</replaceable>).
+ </para>
+
+ <para>
+ Here is an example that looks at what has changed in the
+ <filename>emenlow</filename> branch of the
+ <filename>linux-yocto-3.19</filename> kernel.
+ The lower commit range is the commit associated with the
+ <filename>standard/base</filename> branch, while
+ the upper commit range is the commit associated with the
+ <filename>standard/emenlow</filename> branch.
+ <literallayout class='monospaced'>
+ $ git whatchanged origin/standard/base..origin/standard/emenlow
+ </literallayout>
+ </para>
+
+ <para>
+ To see short, one line summaries of changes use the
+ <filename>git log</filename> command:
+ <literallayout class='monospaced'>
+ $ git log --oneline origin/standard/base..origin/standard/emenlow
+ </literallayout>
+ </para>
+
+ <para>
+ Use this command to see code differences for the changes:
+ <literallayout class='monospaced'>
+ $ git diff origin/standard/base..origin/standard/emenlow
+ </literallayout>
+ </para>
+
+ <para>
+ Use this command to see the commit log messages and the
+ text differences:
+ <literallayout class='monospaced'>
+ $ git show origin/standard/base..origin/standard/emenlow
+ </literallayout>
+ </para>
+
+ <para>
+ Use this command to create individual patches for
+ each change.
+ Here is an example that that creates patch files for each
+ commit and places them in your <filename>Documents</filename>
+ directory:
+ <literallayout class='monospaced'>
+ $ git format-patch -o $HOME/Documents origin/standard/base..origin/standard/emenlow
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='showing-a-particular-feature-or-branch-change'>
+ <title>Showing a Particular Feature or Branch Change</title>
+
+ <para>
+ Tags in the Yocto Project kernel tree divide changes for
+ significant features or branches.
+ The <filename>git show</filename> <replaceable>tag</replaceable>
+ command shows changes based on a tag.
+ Here is an example that shows <filename>systemtap</filename>
+ changes:
+ <literallayout class='monospaced'>
+ $ git show systemtap
+ </literallayout>
+ You can use the
+ <filename>git branch --contains</filename> <replaceable>tag</replaceable>
+ command to show the branches that contain a particular feature.
+ This command shows the branches that contain the
+ <filename>systemtap</filename> feature:
+ <literallayout class='monospaced'>
+ $ git branch --contains systemtap
+ </literallayout>
+ </para>
+ </section>
+ </section>
+
+ <section id='adding-recipe-space-kernel-features'>
+ <title>Adding Recipe-Space Kernel Features</title>
+
+ <para>
+ You can add kernel features in the
+ <link linkend='recipe-space-metadata'>recipe-space</link> by
+ using the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
+ variable and by specifying the feature's <filename>.scc</filename>
+ file path in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
+ statement.
+ When you add features using this method, the OpenEmbedded build
+ system checks to be sure the features are present.
+ If the features are not present, the build stops.
+ Kernel features are the last elements processed for configuring
+ and patching the kernel.
+ Therefore, adding features in this manner is a way
+ to enforce specific features are present and enabled
+ without needing to do a full audit of any other layer's additions
+ to the <filename>SRC_URI</filename> statement.
+ </para>
+
+ <para>
+ You add a kernel feature by providing the feature as part of the
+ <filename>KERNEL_FEATURES</filename> variable and by providing the
+ path to the feature's <filename>.scc</filename> file, which is
+ relative to the root of the kernel Metadata.
+ The OpenEmbedded build system searches all forms of kernel
+ Metadata on the <filename>SRC_URI</filename> statement regardless
+ of whether the Metadata is in the "kernel-cache", system kernel
+ Metadata, or a recipe-space Metadata (i.e. part of the kernel
+ recipe).
+ See the
+ "<link linkend='kernel-metadata-location'>Kernel Metadata Location</link>"
+ section for additional information.
+ </para>
+
+ <para>
+ When you specify the feature's <filename>.scc</filename> file
+ on the <filename>SRC_URI</filename> statement, the OpenEmbedded
+ build system adds the directory of that
+ <filename>.scc</filename> file along with all its subdirectories
+ to the kernel feature search path.
+ Because subdirectories are searched, you can reference a single
+ <filename>.scc</filename> file in the
+ <filename>SRC_URI</filename> statement to reference multiple kernel
+ features.
+ </para>
+
+ <para>
+ Consider the following example that adds the "test.scc" feature
+ to the build.
+ <orderedlist>
+ <listitem><para>
+ <emphasis>Create the Feature File:</emphasis>
+ Create a <filename>.scc</filename> file and locate it
+ just as you would any other patch file,
+ <filename>.cfg</filename> file, or fetcher item
+ you specify in the <filename>SRC_URI</filename>
+ statement.
+ <note><title>Notes</title>
+ <itemizedlist>
+ <listitem><para>
+ You must add the directory of the
+ <filename>.scc</filename> file to the fetcher's
+ search path in the same manner as you would
+ add a <filename>.patch</filename> file.
+ </para></listitem>
+ <listitem><para>
+ You can create additional
+ <filename>.scc</filename> files beneath the
+ directory that contains the file you are
+ adding.
+ All subdirectories are searched during the
+ build as potential feature directories.
+ </para></listitem>
+ </itemizedlist>
+ </note>
+ Continuing with the example, suppose the "test.scc"
+ feature you are adding has a
+ <filename>test.scc</filename> file in the following
+ directory:
+ <literallayout class='monospaced'>
+ <replaceable>my_recipe</replaceable>
+ |
+ +-linux-yocto
+ |
+ +-test.cfg
+ +-test.scc
+ </literallayout>
+ In this example, the <filename>linux-yocto</filename>
+ directory has both the feature
+ <filename>test.scc</filename> file and a similarly
+ named configuration fragment file
+ <filename>test.cfg</filename>.
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Add the Feature File to <filename>SRC_URI</filename>:</emphasis>
+ Add the <filename>.scc</filename> file to the
+ recipe's <filename>SRC_URI</filename> statement:
+ <literallayout class='monospaced'>
+ SRC_URI_append = " file://test.scc"
+ </literallayout>
+ The leading space before the path is important as the
+ path is appended to the existing path.
+ </para></listitem>
+ <listitem><para>
+ <emphasis>Specify the Feature as a Kernel Feature:</emphasis>
+ Use the <filename>KERNEL_FEATURES</filename> statement
+ to specify the feature as a kernel feature:
+ <literallayout class='monospaced'>
+ KERNEL_FEATURES_append = " test.scc"
+ </literallayout>
+ The OpenEmbedded build system processes the kernel feature
+ when it builds the kernel.
+ <note>
+ If other features are contained below "test.scc",
+ then their directories are relative to the directory
+ containing the <filename>test.scc</filename> file.
+ </note>
+ </para></listitem>
+ </orderedlist>
+ </para>
+ </section>
+</chapter>
+<!--
+vim: expandtab tw=80 ts=4
+-->