864 lines
42 KiB
XML
864 lines
42 KiB
XML
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='kernel-dev-common'>
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<title>Common Tasks</title>
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<para>
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This chapter presents several common tasks you perform when you
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work with the Yocto Project Linux kernel.
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These tasks include preparing a layer, modifying an existing recipe,
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iterative development, working with your own sources, and incorporating
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out-of-tree modules.
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<note>
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The examples presented in this chapter work with the Yocto Project
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1.2.2 Release and forward.
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</note>
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</para>
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<section id='creating-and-preparing-a-layer'>
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<title>Creating and Preparing a Layer</title>
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<para>
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If you are going to be modifying kernel recipes, it is recommended
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that you create and prepare your own layer in which to do your
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work.
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Your layer contains its own BitBake append files
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(<filename>.bbappend</filename>) and provides a convenient
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mechanism to create your own recipe files
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(<filename>.bb</filename>).
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For details on how to create and work with layers, see the following
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sections in the Yocto Project Development Manual:
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<itemizedlist>
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<listitem><para>"<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>" for
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general information on layers and how to create layers.</para></listitem>
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<listitem><para>"<ulink url='&YOCTO_DOCS_DEV_URL;#set-up-your-layer-for-the-build'>Set Up Your Layer for the Build</ulink>" for
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specific instructions on setting up a layer for kernel
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development.</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='modifying-an-existing-recipe'>
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<title>Modifying an Existing Recipe</title>
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<para>
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In many cases, you can customize an existing linux-yocto recipe to
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meet the needs of your project.
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Each release of the Yocto Project provides a few Linux
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kernel recipes from which you can choose.
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These are located in the
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<ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
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in <filename>meta/recipes-kernel/linux</filename>.
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</para>
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<para>
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Modifying an existing recipe can consist of the following:
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<itemizedlist>
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<listitem><para>Creating the append file</para></listitem>
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<listitem><para>Applying patches</para></listitem>
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<listitem><para>Changing the configuration</para></listitem>
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</itemizedlist>
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</para>
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<para>
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Before modifying an existing recipe, be sure that you have created
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a minimal, custom layer from which you can work.
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See the "<link linkend='creating-and-preparing-a-layer'>Creating and Preparing a Layer</link>"
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section for some general resources.
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You can also see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#set-up-your-layer-for-the-build'>Set Up Your Layer for the Build</ulink>" section
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of the Yocto Project Development Manual for a detailed
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example.
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</para>
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<section id='creating-the-append-file'>
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<title>Creating the Append File</title>
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<para>
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You create this file in your custom layer.
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You also name it accordingly based on the linux-yocto recipe
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you are using.
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For example, if you are modifying the
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<filename>meta/recipes-kernel/linux/linux-yocto_3.4.bb</filename>
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recipe, the append file will typical be located as follows
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within your custom layer:
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<literallayout class='monospaced'>
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<your-layer>/recipes-kernel/linux/linux-yocto_3.4.bbappend
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</literallayout>
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The append file should initially extend the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
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search path by prepending the directory that contains your
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files to the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
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variable as follows:
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<literallayout class='monospaced'>
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FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
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</literallayout>
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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>
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expands to "linux-yocto" in the current directory for this
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example.
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If you add any new files that modify the kernel recipe and you
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have extended <filename>FILESPATH</filename> as
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described above, you must place the files in your layer in the
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following area:
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<literallayout class='monospaced'>
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<your-layer>/recipes-kernel/linux/linux-yocto/
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</literallayout>
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<note>If you are working on a new machine Board Support Package
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(BSP), be sure to refer to the
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<ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
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</note>
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</para>
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</section>
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<section id='applying-patches'>
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<title>Applying Patches</title>
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<para>
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If you have a single patch or a small series of patches
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that you want to apply to the Linux kernel source, you
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can do so just as you would with any other recipe.
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You first copy the patches to the path added to
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<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
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in your <filename>.bbappend</filename> file as described in
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the previous section, and then reference them in
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<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
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statements.
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</para>
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<para>
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For example, you can apply a three-patch series by adding the
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following lines to your linux-yocto <filename>.bbappend</filename>
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file in your layer:
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<literallayout class='monospaced'>
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SRC_URI += "file://0001-first-change.patch"
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SRC_URI += "file://0002-first-change.patch"
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SRC_URI += "file://0003-first-change.patch"
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</literallayout>
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The next time you run BitBake to build the Linux kernel, BitBake
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detects the change in the recipe and fetches and applies the patches
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before building the kernel.
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</para>
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<para>
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For a detailed example showing how to patch the kernel, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#patching-the-kernel'>Patching the Kernel</ulink>"
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section in the Yocto Project Development Manual.
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</para>
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</section>
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<section id='changing-the-configuration'>
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<title>Changing the Configuration</title>
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<para>
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You can make wholesale or incremental changes to the Linux
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kernel <filename>.config</filename> file by including a
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<filename>defconfig</filename> and by specifying
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configuration fragments in the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
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</para>
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<para>
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If you have a final Linux kernel <filename>.config</filename>
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file you want to use, copy it to a directory named
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<filename>files</filename>, which must be in
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your layer's <filename>recipes-kernel/linux</filename>
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directory, and name the file "defconfig".
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Then, add the following lines to your linux-yocto
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<filename>.bbappend</filename> file in your layer:
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<literallayout class='monospaced'>
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FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
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SRC_URI += "file://defconfig"
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</literallayout>
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The <filename>SRC_URI</filename> tells the build system how to
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search for the file, while the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
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extends the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
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variable (search directories) to include the
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<filename>files</filename> directory you created for the
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configuration changes.
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</para>
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<note>
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The build system applies the configurations from the
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<filename>.config</filename> file before applying any
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subsequent configuration fragments.
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The final kernel configuration is a combination of the
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configurations in the <filename>.config</filename> file and
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any configuration fragments you provide.
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You need to realize that if you have any configuration
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fragments, the build system applies these on top of and
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after applying the existing <filename>.config</filename>
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file configurations.
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</note>
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<para>
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Generally speaking, the preferred approach is to determine the
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incremental change you want to make and add that as a
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configuration fragment.
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For example, if you want to add support for a basic serial
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console, create a file named <filename>8250.cfg</filename> in
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the <filename>files</filename> directory with the following
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content (without indentation):
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<literallayout class='monospaced'>
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CONFIG_SERIAL_8250=y
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CONFIG_SERIAL_8250_CONSOLE=y
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CONFIG_SERIAL_8250_PCI=y
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CONFIG_SERIAL_8250_NR_UARTS=4
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CONFIG_SERIAL_8250_RUNTIME_UARTS=4
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CONFIG_SERIAL_CORE=y
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CONFIG_SERIAL_CORE_CONSOLE=y
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</literallayout>
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Next, include this configuration fragment and extend the
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<filename>FILESPATH</filename> variable in your
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<filename>.bbappend</filename> file:
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<literallayout class='monospaced'>
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FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
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SRC_URI += "file://8250.cfg"
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</literallayout>
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The next time you run BitBake to build the Linux kernel, BitBake
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detects the change in the recipe and fetches and applies the
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new configuration before building the kernel.
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</para>
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<para>
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For a detailed example showing how to configure the kernel,
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see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#configuring-the-kernel'>Configuring the Kernel</ulink>"
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section in the Yocto Project Development Manual.
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</para>
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</section>
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</section>
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<section id='using-an-iterative-development-process'>
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<title>Using an Iterative Development Process</title>
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<para>
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If you do not have existing patches or configuration files,
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you can iteratively generate them from within the BitBake build
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environment as described within this section.
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During an iterative workflow, running a previously completed BitBake
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task causes BitBake to invalidate the tasks that follow the
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completed task in the build sequence.
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Invalidated tasks rebuild the next time you run the build using
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BitBake.
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</para>
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<para>
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As you read this section, be sure to substitute the name
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of your Linux kernel recipe for the term
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"linux-yocto".
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</para>
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<section id='tip-dirty-string'>
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<title>"-dirty" String</title>
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<!--
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<para>
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<emphasis>AR - Darrren Hart:</emphasis> This section
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originated from the old Yocto Project Kernel Architecture
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and Use Manual.
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It was decided we need to put it in this section here.
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Darren needs to figure out where we want it and what part
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of it we want (all, revision???)
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</para>
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-->
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<para>
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If kernel images are being built with "-dirty" on the
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end of the version string, this simply means that
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modifications in the source directory have not been committed.
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<literallayout class='monospaced'>
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$ git status
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</literallayout>
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</para>
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<para>
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You can use the above Git command to report modified,
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removed, or added files.
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You should commit those changes to the tree regardless of
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whether they will be saved, exported, or used.
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Once you commit the changes, you need to rebuild the kernel.
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</para>
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<para>
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To force a pickup and commit of all such pending changes,
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enter the following:
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<literallayout class='monospaced'>
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$ git add .
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$ git commit -s -a -m "getting rid of -dirty"
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</literallayout>
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</para>
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<para>
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Next, rebuild the kernel.
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</para>
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</section>
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<section id='generating-configuration-files'>
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<title>Generating Configuration Files</title>
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<para>
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You can manipulate the <filename>.config</filename> file
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used to build a linux-yocto recipe with the
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<filename>menuconfig</filename> command as follows:
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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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This command starts the Linux kernel configuration tool,
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which allows you to prepare a new
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<filename>.config</filename> file for the build.
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When you exit the tool, be sure to save your changes
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at the prompt.
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</para>
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<para>
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The resulting <filename>.config</filename> file is
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located in
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<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename> under the
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<filename>linux-${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink><filename>}-${<ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'><filename>KTYPE</filename></ulink>}-build</filename> directory.
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You can use the entire <filename>.config</filename> file as the
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<filename>defconfig</filename> file as described in the
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"<link linkend='changing-the-configuration'>Changing the Configuration</link>" section.
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</para>
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<para>
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A better method is to create a configuration fragment using the
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differences between two configuration files: one previously
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created and saved, and one freshly created using the
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<filename>menuconfig</filename> tool.
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</para>
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<para>
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To create a configuration fragment using this method, follow
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these steps:
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<orderedlist>
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<listitem><para>Complete a build at least through the kernel
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configuration task as follows:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c kernel_configme -f
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</literallayout></para></listitem>
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<listitem><para>Copy and rename the resulting
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<filename>.config</filename> file (e.g.
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<filename>config.orig</filename>).
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</para></listitem>
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<listitem><para>Run the <filename>menuconfig</filename>
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command:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c menuconfig
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</literallayout></para></listitem>
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<listitem><para>Prepare a configuration fragment based on
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the differences between the two files.
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</para></listitem>
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</orderedlist>
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</para>
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<para>
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Ultimately, the configuration fragment file needs to be a
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list of Linux kernel <filename>CONFIG_</filename> assignments.
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It cannot be in <filename>diff</filename> format.
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Here is an example of a command that creates your
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configuration fragment file.
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Regardless of the exact command you use, plan on reviewing
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the output as you can usually remove some of the defaults:
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<literallayout class='monospaced'>
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$ diff -Nurp config.orig .config | sed -n "s/^\+//p" > frag.cfg
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</literallayout>
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See the "<link linkend='changing-the-configuration'>Changing the Configuration</link>"
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section for information on how to use the output as a
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configuration fragment.
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<note>
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You can also use this method to create configuration
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fragments for a BSP.
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See the "<link linkend='bsp-descriptions'>BSP Descriptions</link>"
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section for more information.
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</note>
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</para>
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<para>
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The kernel tools also provide configuration validation.
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You can use these tools to produce warnings for when a
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requested configuration does not appear in the final
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<filename>.config</filename> file or when you override a
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policy configuration in a hardware configuration fragment.
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Here is an example with some sample output of the command
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that runs these tools:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c kernel_configcheck -f
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...
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NOTE: validating kernel configuration
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This BSP sets 3 invalid/obsolete kernel options.
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These config options are not offered anywhere within this kernel.
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The full list can be found in your kernel src dir at:
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meta/cfg/standard/mybsp/invalid.cfg
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This BSP sets 21 kernel options that are possibly non-hardware related.
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The full list can be found in your kernel src dir at:
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meta/cfg/standard/mybsp/specified_non_hdw.cfg
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WARNING: There were 2 hardware options requested that do not
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have a corresponding value present in the final ".config" file.
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This probably means you are not't getting the config you wanted.
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The full list can be found in your kernel src dir at:
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meta/cfg/standard/mybsp/mismatch.cfg
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</literallayout>
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</para>
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<para>
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The output describes the various problems that you can
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encounter along with where to find the offending configuration
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items.
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You can use the information in the logs to adjust your
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configuration files and then repeat the
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<filename>kernel_configme</filename> and
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<filename>kernel_configcheck</filename> commands until
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they produce no warnings.
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</para>
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<para>
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For more information on how to use the
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<filename>menuconfig</filename> tool, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#using-menuconfig'>Using <filename>menuconfig</filename></ulink>"
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section in the Yocto Project Development Manual.
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</para>
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</section>
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<section id='modifying-source-code'>
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<title>Modifying Source Code</title>
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<para>
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You can experiment with source code changes and create a
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simple patch without leaving the BitBake environment.
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To get started, be sure to complete a build at
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least through the kernel configuration task:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c kernel_configme -f
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</literallayout>
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Taking this step ensures you have the sources prepared
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and the configuration completed.
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You can find the sources in the
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<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/linux</filename> directory.
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</para>
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<para>
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You can edit the sources as you would any other Linux source
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tree.
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However, keep in mind that you will lose changes if you
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trigger the <filename>fetch</filename> task for the recipe.
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You can avoid triggering this task by not issuing BitBake's
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<filename>cleanall</filename>, <filename>cleansstate</filename>,
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or forced <filename>fetch</filename> commands.
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Also, do not modify the recipe itself while working
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with temporary changes or BitBake might run the
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<filename>fetch</filename> command depending on the
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changes to the recipe.
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</para>
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<para>
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To test your temporary changes, instruct BitBake to run the
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<filename>compile</filename> again.
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The <filename>-f</filename> option forces the command to run
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even though BitBake might think it has already done so:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c compile -f
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</literallayout>
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If the compile fails, you can update the sources and repeat
|
|
the <filename>compile</filename>.
|
|
Once compilation is successful, you can inspect and test
|
|
the resulting build (i.e. kernel, modules, and so forth) from
|
|
the <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
|
|
<literallayout class='monospaced'>
|
|
${WORKDIR}/linux-${MACHINE}-${KTYPE}-build
|
|
</literallayout>
|
|
Alternatively, you can run the <filename>deploy</filename>
|
|
command to place the kernel image in the
|
|
<filename>tmp/deploy/images</filename> directory:
|
|
<literallayout class='monospaced'>
|
|
$ bitbake linux-yocto -c deploy
|
|
</literallayout>
|
|
And, of course, you can perform the remaining installation and
|
|
packaging steps by issuing:
|
|
<literallayout class='monospaced'>
|
|
$ bitbake linux-yocto
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
For rapid iterative development, the edit-compile-repeat loop
|
|
described in this section is preferable to rebuilding the
|
|
entire recipe because the installation and packaging tasks
|
|
are very time consuming.
|
|
</para>
|
|
|
|
<para>
|
|
Once you are satisfied with your source code modifications,
|
|
you can make them permanent by generating patches and
|
|
applying them to the
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
|
|
statement as described in section
|
|
"<link linkend='applying-patches'>Applying Patches</link>" section.
|
|
If you are not familiar with generating patches, refer to the
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#creating-the-patch'>Creating the Patch</ulink>"
|
|
section in the Yocto Project Development Manual.
|
|
</para>
|
|
</section>
|
|
</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_DEV_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>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 Linux kernel you
|
|
are using (e.g. <filename>linux-yocto-myproject_3.5.bb</filename>,
|
|
where "3.5" is the base version of the Linux kernel
|
|
with which you would be working).</para></listitem>
|
|
<listitem><para>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>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 be 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 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.
|
|
"3.4").</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'>
|
|
3.4.11+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>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='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 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 appropriate 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 class <filename>module.bbclass</filename> sets this variable,
|
|
as well as 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
|
|
<filename>do_compile()</filename> 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 as
|
|
appropriate in 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>
|
|
Where 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 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='http://git.yoctoproject.org/cgit.cgi'></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
|
|
(<filename><commit>..<commit></filename>).
|
|
</para>
|
|
|
|
<para>
|
|
Here is an example that looks at what has changed in the
|
|
<filename>emenlow</filename> branch of the
|
|
<filename>linux-yocto-3.4</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 <tag></filename> 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 <tag></filename> 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>
|
|
</chapter>
|
|
<!--
|
|
vim: expandtab tw=80 ts=4
|
|
-->
|