documentation/dev-manual/dev-manual-kernel-appendix.xml: Added kernel reconfigure example.
this example uses the CONFIG_SMP configuration. By default, this configuration is disabled. The example shows how to use menuconfig and explains the .config file role and how you can use it combined with menuconfig to manage multiple configuration changes. Thanks to Darren Hart for identifying this simple change to demonstrate how to change the kernel configuration. (From yocto-docs rev: c571c01b8589ad6f76e66388c3ae24a1de029f65) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark
Richard Purdie
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@ -495,14 +495,176 @@
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<title>Changing the Kernel Configuration</title>
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<para>
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This section presents an example that changes the kernel configuration.
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The example shows how to use <filename>menuconfig</filename> to quickly see
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and set configurations used by the kernel.
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This example changes the default behavior (off) of the Symmetric Multi-processing Support
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(<filename>CONFIG_SMP</filename>) to on.
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It is a simple example that demonstrates how to reconfigure the kernel.
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</para>
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<para>
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[Example to be supplied]
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</para>
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<section id='getting-set-up-to-run-this-example'>
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<title>Getting Set Up to Run this Example</title>
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<para>
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If you took the time to work through the example that modifies the kernel source code
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in <xref linkend='modifying-the-kernel-source-code'>Modifying the Kernel Source
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Code</xref> you are set up to quickly work through this example.
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If not, then work through the following list to prepare:
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<itemizedlist>
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<listitem><para><emphasis>Understand the development environment:</emphasis>
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See <xref linkend='understanding-the-files-you-need'>
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Understanding the Files You Need</xref> for information.</para></listitem>
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<listitem><para><emphasis>Set up the local Yocto Project files Git
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repository:</emphasis>
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See <xref linkend='setting-up-the-local-yocto-project-files-git-repository'>
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Setting Up the Local Yocto Project Files Git Repository</xref> for
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information.</para></listitem>
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<listitem><para><emphasis>Set up the <filename>poky-extras</filename> Git
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repository:</emphasis>
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See <xref linkend='setting-up-the-poky-extras-git-repository'>
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Setting Up <filename>poky-extras</filename> Git repository</xref> for
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information.</para></listitem>
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<listitem><para><emphasis>Set up the the bare clone and its copy:</emphasis>
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See <xref linkend='setting-up-the-bare-clone-and-its-copy'>
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Setting Up the Bare Clone and its Copy</xref> for information.
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</para></listitem>
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<listitem><para><emphasis>Build the default QEMU kernel image:</emphasis>
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See <xref linkend='building-and-booting-the-default-qemu-kernel-image'>
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Building and Booting the Default QEMU Kernel image</xref>
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for information.
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Do not boot the image in the QEMU emulator at this point.</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='examining-the-default-config-smp-behavior'>
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<title>Examining the Default <filename>CONFIG_SMP</filename> Behavior</title>
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<para>
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By default, <filename>CONFIG_SMP</filename> supports single processor machines.
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To see this default setting from within the QEMU emulator boot your image using
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the emulator as follows:
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<literallayout class='monospaced'>
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$ runqemu qemux86
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</literallayout>
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</para>
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<para>
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Login to the machine using <filename>root</filename> with no password.
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After logging in, enter the following command to see how many processors are
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being supported in the emulator.
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The emulator reports support for a single processor:
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<literallayout class='monospaced'>
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# cat /proc/cpuinfo | grep processor
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processor : 0
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#
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</literallayout>
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</para>
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</section>
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<section id='changing-the-config-smp-configuration-using-menuconfig'>
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<title>Changing the <filename>CONFIG_SMP</filename> Configuration Using <filename>menuconfig</filename></title>
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<para>
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The <filename>menuconfig</filename> tool provides an interactive method with which
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to set kernel configurations.
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You need to run <filename>menuconfig</filename> inside the BitBake environment.
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Thus, the environment must be set up using the <filename>oe-init-build-env</filename>
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script found in the Yocto Project files Git repository build directory.
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If you have not sourced this script do so with the following commands:
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<literallayout class='monospaced'>
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$ cd ~/poky
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$ source oe-init-build-env
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</literallayout>
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</para>
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<para>
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After setting up the environment to run <filename>menuconfig</filename>, you are ready
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to use the tool to interactively change the kernel configuration.
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In this example we are basing our changes on the <filename>linux-yocto-3.0</filename>
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kernel.
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The Yocto Project build environment recognizes this kernel as
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<filename>linux-yocto</filename>.
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Thus, the following command from the shell in which you previously sourced the
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environment initialization script launches <filename>menuconfig</filename>:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c menuconfig
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</literallayout>
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</para>
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<para>
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Once <filename>menuconfig</filename> launches, navigate through the user interface
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to find the <filename>CONFIG_SMP</filename> configuration setting.
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You can find it at <filename>Processor Type and Features</filename>.
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The configuration selection is
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<filename>Symmetric Multi-processing Support</filename>.
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</para>
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<para>
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Once you save the selection the <filename>.config</filename> configuration file
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is updated.
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This is the file that the build system uses to configure the Linux Yocto kernel
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when it is built.
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You can find and examine this file in the Yocto Project files Git repository in
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the build directory.
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This example uses the following:
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<literallayout class='monospaced'>
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~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-2.6.37+git1+84f...r20/linux-qemux86-standard-build
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</literallayout>
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</para>
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<para>
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Within the <filename>.config</filename> you can see the following setting:
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<literallayout class='monospaced'>
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CONFIG_SMP=y
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</literallayout>
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</para>
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<para>
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A good method to isolate changed configurations is to use a combination of the
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<filename>menuconfig</filename> tool and simple shell commands.
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Before changing configurations with <filename>menuconfig</filename> simply rename
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the default <filename>.config</filename>, use <filename>menuconfig</filename> to make
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as many changes an you want and save them, then compare the renamed configuration
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file against the newly created file.
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You can use the resulting differences as your base to create configuration fragments
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to permanently save in your kernel layer.
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For an example of this procedure, see [WRITER'S NOTE: need forwarding link to section].
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</para>
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</section>
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<section id='recompiling-the-kernel-and-testing-the-new-configuration'>
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<title>Recompiling the Kernel and Testing the New Configuration</title>
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<para>
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At this point you are ready to recompile your kernel image with
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the new setting in effect using the BitBake commands below:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c compile -f
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$ bitbake linux-yocto
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</literallayout>
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</para>
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<para>
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Now run the QEMU emulator:
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<literallayout class='monospaced'>
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$ runqemu qemux86
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</literallayout>
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</para>
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<para>
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Login to the machine using <filename>root</filename> with no password
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and test for the number of processors the kernel supports:
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<literallayout class='monospaced'>
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# cat /proc/cpuinfo | grep processor
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processor : 0
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processor : 1
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#
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</literallayout>
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</para>
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<para>
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From the output you can see that you have successfully reconfigured the kernel.
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</para>
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</section>
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</section>
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<section id='adding-kernel-recipes'>
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@ -516,7 +678,7 @@
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<para>
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[Example to be supplied]
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</para>
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</section>
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</section>
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@ -584,40 +746,6 @@ It should just build whatever is necessary and not go through an entire build ag
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<section id='prepare-to-use-menuconfig'>
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<title>Prepare to use <filename>menuconfig</filename></title>
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<para>
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The <filename>menuconfig</filename> tool provides an interactive method with which
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to set kernel configurations.
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In order to use <filename>menuconfig</filename> from within the BitBake environment
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you need to source an environment setup script.
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This script is located in the local Yocto Project file structure and is called
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<filename>oe-init-build-env</filename>.
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</para>
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<para>
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The following command sets up the environment:
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<literallayout class='monospaced'>
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$ cd ~/poky
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$ source oe-init-build-env
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</literallayout>
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</para>
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</section>
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<section id='make-configuration-changes-to-the-kernel'>
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<title>Make Configuration Changes to the Kernel</title>
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<para>
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After setting up the environment to run <filename>menuconfig</filename> you are ready
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to use the tool to interactively change the kernel configuration.
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In this example we are basing our changes on the <filename>linux-yocto-2.6.37</filename>
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kernel.
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The Yocto Project build environment recognizes this kernel as
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<filename>linux-yocto</filename>.
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Thus, the following command from the shell in which you previously sourced the
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environment initialization script launches <filename>menuconfig</filename>:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c menuconfig
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</literallayout>
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</para>
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<para>
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[WRITER'S NOTE: Stuff from here down are crib notes]
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