generic-poky/documentation/poky-ref-manual/extendpoky.xml

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<chapter id='extendpoky'>

<title>Extending Poky</title>
    <para>
        This section provides information about how to extend the functionality
        already present in Poky.
        The section also documents standard tasks such as adding new
        software packages, extending or customizing images or porting Poky to
        new hardware (adding a new machine). 
        Finally, the section contains advice about how
        to make changes to Poky to achieve the best results.
    </para>

    <section id='usingpoky-extend-addpkg'>
        <title>Adding a Package</title>
        <para>
            To add a package into Poky you need to write a recipe for it. 
            Writing a recipe means creating a <filename>.bb</filename> file that sets some
            variables.
            For information on variables that are useful for recipes and for information about recipe naming
            issues, see <link linkend='ref-varlocality-recipe-required'>Recipe Variables - Required</link>
            appendix.
        </para>
        <para>
            Before writing a recipe from scratch it is often useful to check
            whether someone else has written one already. 
            OpenEmbedded is a good place to look as it has a wider scope and range of packages.
            Because Poky aims to be compatible with OpenEmbedded, most recipes should
            just work in Poky.
        </para>
        <para>
            For new packages, the simplest way to add a recipe is to base it on a similar
            pre-existing recipe. 
            Following are some examples showing how to add standard types of packages:
        </para>

        <section id='usingpoky-extend-addpkg-singlec'>
            <title>Single .c File Package (Hello World!)</title>
            <para>
                Building an application from a single file that is stored locally (e.g. under 
                <filename>files/</filename>) requires a recipe that has the file listed in 
                the <glossterm><link linkend='var-SRC_URI'>SRC_URI</link></glossterm> variable. 
                Additionally, you need to manually write the <function>do_compile</function> and
                <function>do_install</function> tasks.
                The <glossterm><link linkend='var-S'>S</link></glossterm> variable defines the 
                directory containing the source code, which is set to <glossterm><link linkend='var-WORKDIR'>
                WORKDIR</link></glossterm> in this case - the directory BitBake uses for the build.
            </para>
            <programlisting>
DESCRIPTION = "Simple helloworld application"
SECTION = "examples"
LICENSE = "MIT"
PR = "r0"

SRC_URI = "file://helloworld.c"

S = "${WORKDIR}"

do_compile() {
	${CC} helloworld.c -o helloworld
}

do_install() {
	install -d ${D}${bindir}
	install -m 0755 helloworld ${D}${bindir}
}
            </programlisting>
            <para>
                By default, the "helloworld", "helloworld-dbg" and "hellworld-dev"
                packages are built. 
                For information on how to customize the packaging process, see
                <link linkend='usingpoky-extend-addpkg-files'>Controlling Package Content</link>.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-autotools'>
            <title>Autotooled Package</title>
            <para>
                Applications that use autotools such as <filename>autoconf</filename> and 
                <filename>automake</filename> require a recipe that has a source archive listed in 
                <glossterm><link linkend='var-SRC_URI'>SRC_URI</link></glossterm> and 
                <filename>also inherits autotools</filename>, which instructs BitBake to use the
                <filename>autotools.bbclass</filename> containing the definitions of all the steps
                needed to build an autotooled application.
                The result of the build is automatically packaged. 
                And, if the application uses NLS for localization, packages with local information are 
                generated (one package per language). 
                Following is one example (<filename>hello_2.2.bb</filename>)
            </para>
            <programlisting>
DESCRIPTION = "GNU Helloworld application"
SECTION = "examples"
LICENSE = "GPLv2+"
LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
PR = "r0"

SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

inherit autotools gettext
            </programlisting>
            <para>
                <glossterm><link linkend='var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</link>
                </glossterm> is used to <link linkend='usingpoky-configuring-LIC_FILES_CHKSUM'>
                track source license change</link>. 
                You can quickly create autotool-based recipes in a manner similar to the previous example.
            </para>

        </section>
        <section id='usingpoky-extend-addpkg-makefile'>
            <title>Makefile-Based Package</title>
            <para>
                Applications that use GNU <filename>make</filename> also require a recipe that has
                the source archive listed in <glossterm><link linkend='var-SRC_URI'>SRC_URI</link></glossterm>. 
                You do not need to add a <function>do_compile</function> step since by default BitBake 
                starts the <filename>make</filename> command to compile the application. 
                If you need additional <filename>make</filename> options you should store them in the 
                <glossterm><link linkend='var-EXTRA_OEMAKE'>EXTRA_OEMAKE</link></glossterm> variable.
                Bitbake passes these options into the <filename>make</filename> GNU invocation. 
                Note that a <function>do_install</function> task is still required.
                Otherwise BitBake runs an empty <function>do_install</function> task by default. 
            </para>
            <para>
                Some applications might require extra parameters to be passed to the compiler.
                For example the application might need an additional header path. 
                You can accomplish this by adding to the <glossterm><link linkend='var-CFLAGS'>CFLAGS</link>
                </glossterm> variable.
                The following example shows this:
            </para>
            <programlisting>
CFLAGS_prepend = "-I ${S}/include "
            </programlisting>
            <para>
            In the following example <filename>mtd-utils</filename> is a Makefile-based package:
            </para>
            <programlisting>
DESCRIPTION = "Tools for managing memory technology devices."
SECTION = "base"
DEPENDS = "zlib lzo e2fsprogs util-linux"
HOMEPAGE = "http://www.linux-mtd.infradead.org/"
LICENSE = "GPLv2"

SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=v${PV}"

S = "${WORKDIR}/git/"

EXTRA_OEMAKE = "'CC=${CC}' 'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' \
                'BUILDDIR=${S}'"

do_install () {
        oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} \
                           INCLUDEDIR=${includedir}
        install -d ${D}${includedir}/mtd/
        for f in ${S}/include/mtd/*.h; do
                install -m 0644 $f ${D}${includedir}/mtd/
        done
}
            </programlisting>

        </section>
        <section id='usingpoky-extend-addpkg-files'>
            <title>Controlling Package Content</title>
            <para>                        
                You can use the variables <glossterm><link linkend='var-PACKAGES'>PACKAGES</link></glossterm> and 
                <glossterm><link linkend='var-FILES'>FILES</link></glossterm> to split an application into 
                multiple packages.
            </para>
            <para>
                Following is an example that uses the "libXpm" recipe (<filename>libxpm_3.5.7.bb</filename>).
                By default, the "libXpm" recipe generates a single package containing the library, along 
                with a few binaries.  
                You can modify the recipe to split the binaries into separate packages:
            </para>
            <programlisting>
require xorg-lib-common.inc

DESCRIPTION = "X11 Pixmap library"
LICENSE = "X-BSD"
DEPENDS += "libxext libsm libxt"
PR = "r3"
PE = "1"

XORG_PN = "libXpm"

PACKAGES =+ "sxpm cxpm"
FILES_cxpm = "${bindir}/cxpm"
FILES_sxpm = "${bindir}/sxpm"
            </programlisting>
            <para>
                In the previous example we want to ship the "sxpm" and "cxpm" binaries 
                in separate packages. 
                Since "bindir" would be packaged into the main 
                <glossterm><link linkend='var-PN'>PN</link></glossterm> 
                package by default, we prepend the <glossterm><link linkend='var-PACKAGES'>PACKAGES</link>
                </glossterm> variable so additional package names are added to the start of list. 
                This results in the extra <glossterm><link linkend='var-FILES'>FILES</link></glossterm>_*
                variables then containing information defining which files and
                directories go into which package. 
                Files included by earlier packages are skipped by latter packages.
                Thus, the main <glossterm><link linkend='var-PN'>PN</link></glossterm> package does not include 
                the above listed files.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-postinstalls'>
            <title>Post Install Scripts</title>

            <para>
                To add a post-installation script to a package, add a <function>pkg_postinst_PACKAGENAME()
                </function> function to the <filename>.bb</filename> file and use 
                <filename>PACKAGENAME</filename> as the name of the package you want to attach to the 
                <filename>postinst</filename> script.
                Normally <glossterm><link linkend='var-PN'>PN</link></glossterm> can be used, which 
                automatically expands to PACKAGENAME.
                A post-installation function has the following structure:
            </para>
            <programlisting>
pkg_postinst_PACKAGENAME () {
#!/bin/sh -e
# Commands to carry out
}
            </programlisting>
            <para>
                The script defined in the post-installation function is called when the rootfs is made. 
                If the script succeeds, the package is marked as installed. 
                If the script fails, the package is marked as unpacked and the script is
                executed when the image boots again.
            </para>
            <para>
                Sometimes it is necessary for the execution of a post-installation
                script to be delayed until the first boot.  
                For example, the script might need to be executed on the device itself. 
                To delay script execution until boot time, use the following structure for the 
                post-installation script:
            </para>
            <programlisting>
pkg_postinst_PACKAGENAME () {
#!/bin/sh -e
if [ x"$D" = "x" ]; then
	# Actions to carry out on the device go here
else
	exit 1
fi
}
            </programlisting>
            <para>
                The previous example delays execution until the image boots again because the 
                <glossterm><link linkend='var-D'>D</link></glossterm> variable points
                to the 'image' directory when the rootfs is being made at build time but
                is unset when executed on the first boot. 
            </para>
        </section>
    </section>

    <section id='usingpoky-extend-customimage'>
        <title>Customising Images</title>
        <para>
        You can customize Poky images to satisfy particular requirements. 
        This section describes several methods and provides guidelines for each.
        </para>

        <section id='usingpoky-extend-customimage-custombb'>
            <title>Customising Images Using Custom .bb Files</title>
            <para>
                One way to get additional software into an image is to create a custom image. 
                The following example shows the form for the two lines you need:
            </para>
            <programlisting>
IMAGE_INSTALL = "task-poky-x11-base package1 package2"

inherit poky-image
            </programlisting>
            <para>
                By creating a custom image, a developer has total control
                over the contents of the image. 
                It is important to use the correct names of packages in the 
                <glossterm><link linkend='var-IMAGE_INSTALL'>IMAGE_INSTALL</link></glossterm> variable. 
                You must use the OpenEmbedded notation and not the Debian notation for the names 
                (e.g. "glibc-dev" instead of "libc6-dev").
            </para>
            <para>
                The other method for creating a custom image is to modify an existing image. 
                For example, if a developer wants to add "strace" into "poky-image-sato", they can use 
                the following recipe:
            </para>
            <programlisting>
require poky-image-sato.bb

IMAGE_INSTALL += "strace"
            </programlisting>
        </section>

        <section id='usingpoky-extend-customimage-customtasks'>
            <title>Customising Images Using Custom Tasks</title>
            <para>
                For complex custom images, the best approach is to create a custom task package
                that is used to build the image or images. 
                A good example of a tasks package is <filename>meta/recipes-sato/tasks/task-poky.bb
                </filename>. 
                The <glossterm><link linkend='var-PACKAGES'>PACKAGES</link></glossterm> 
                variable lists the task packages to build along with the complementary
                -dbg and -dev packages. 
                For each package added, you can use 
                <glossterm><link linkend='var-PACKAGES'>RDEPENDS</link></glossterm>
                and <glossterm><link linkend='var-PACKAGES'>RRECOMMENDS</link></glossterm> 
                entries to provide a list of packages the parent task package should contain. 
                Following is an example:
            </para>
            <para>
            <programlisting>
DESCRIPTION = "My Custom Tasks"

PACKAGES = "\
    task-custom-apps \
    task-custom-apps-dbg \
    task-custom-apps-dev \
    task-custom-tools \
    task-custom-tools-dbg \
    task-custom-tools-dev \
    "

RDEPENDS_task-custom-apps = "\
    dropbear \
    portmap \
    psplash"

RDEPENDS_task-custom-tools = "\
    oprofile \
    oprofileui-server \
    lttng-control \
    lttng-viewer"

RRECOMMENDS_task-custom-tools = "\
    kernel-module-oprofile"
</programlisting>
            </para>
            <para>
                In the previous example, two task packages are created with their dependencies and their
                recommended package dependencies listed: <filename>task-custom-apps</filename>, and 
                <filename>task-custom-tools</filename>. 
                To build an image using these task packages, you need to add 
                "task-custom-apps" and/or "task-custom-tools" to <glossterm><link 
                linkend='var-IMAGE_INSTALL'>IMAGE_INSTALL</link></glossterm> or other forms 
                of image dependencies as described in other areas of this section.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-imagefeatures'>
            <title>Customising Images Using Custom <glossterm>
                <link linkend='var-IMAGE_FEATURES'>IMAGE_FEATURES</link></glossterm></title>
            <para>
                Ultimately users might want to add extra image "features" as used by Poky with the 
                <glossterm><link linkend='var-IMAGE_FEATURES'>IMAGE_FEATURES</link></glossterm>
                variable. 
                To create these features, the best reference is 
                <filename>meta/classes/poky-image.bbclass</filename>, which shows how poky achieves this. 
                In summary, the file looks at the contents of the 
                <glossterm><link linkend='var-IMAGE_FEATURES'>IMAGE_FEATURES</link></glossterm>
                variable and then maps them into a set of tasks or packages. 
                Based on this information the <glossterm><link linkend='var-IMAGE_INSTALL'> IMAGE_INSTALL</link>
                </glossterm> variable is generated automatically. 
                Users can add extra features by extending the class or creating a custom class for use 
                with specialized image <filename>.bb</filename> files.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-localconf'>
            <title>Customising Images Using local.conf</title>
            <para>
                It is possible to customise image contents by abusing variables used by distribution 
                maintainers in local.conf.
                This method only allows the addition of packages and is not recommended.
            </para>
            <para>
                For example, to add the "strace" package into the image the you would add this to the 
                <filename>local.conf</filename> file:
            </para>
            <programlisting>
DISTRO_EXTRA_RDEPENDS += "strace"
            </programlisting>
            <para>
                However, since the <glossterm><link linkend='var-DISTRO_EXTRA_RDEPENDS'>
                DISTRO_EXTRA_RDEPENDS</link></glossterm> variable is for
                distribution maintainers, adding packages using this method is not as simple as adding 
                them using a custom <filename>.bb</filename> file. 
                Using the <filename>local.conf</filename> file method could result in some packages 
                requiring recreation.
                For example, if packages were previously created and the image was rebuilt then the packages
                would need to be recreated.
            </para>
            <para>
                Cleaning task-* packages is required because they use the
                <glossterm><link linkend='var-DISTRO_EXTRA_RDEPENDS'>
                DISTRO_EXTRA_RDEPENDS</link></glossterm> variable. 
                You do not have to build them by hand because Poky images depend on the packages they contain.
                This means dependencies are automatically built when the image builds. 
                For this reason we don't use the "rebuild" task.
                In this case the "rebuild" task does does not care about
                dependencies - it only rebuilds the specified package.
            </para>
            <programlisting>
bitbake -c clean task-boot task-base task-poky
bitbake poky-image-sato
            </programlisting>
        </section>

    </section>

<section id="platdev-newmachine">
    <title>Porting Poky to a New Machine</title>
    <para>
        Adding a new machine to Poky is a straightforward process. 
        This section provides information that gives you an idea of the changes you must make.
        The information covers adding machines similar to those Poky already supports. 
        Although well within the capabilities of Poky, adding a totally new architecture might require 
        changes to <filename>gcc/glibc</filename> and to the site information.
        Consequently, the information is beyond the scope of this manual.
    </para>

    <section id="platdev-newmachine-conffile">
        <title>Adding the Machine Configuration File</title>
        <para>
            To add a machine configuration you need to add a <filename>.conf</filename> file
            with details of the device being added to <filename>conf/machine/</filename>.
            The name of the file determines the name Poky uses to reference the new machine.
        </para>
        <para>
            The most important variables to set in this file are <glossterm>
            <link linkend='var-TARGET_ARCH'>TARGET_ARCH</link></glossterm> 
            (e.g. "arm"), <glossterm><link linkend='var-PREFERRED_PROVIDER'>
            PREFERRED_PROVIDER</link></glossterm>_virtual/kernel (see below) and 
            <glossterm><link linkend='var-MACHINE_FEATURES'>MACHINE_FEATURES
            </link></glossterm> (e.g. "kernel26 apm screen wifi"). 
            You might also need other variables like <glossterm><link linkend='var-SERIAL_CONSOLE'>SERIAL_CONSOLE
            </link></glossterm> (e.g. "115200 ttyS0"), <glossterm> 
            <link linkend='var-KERNEL_IMAGETYPE'>KERNEL_IMAGETYPE</link>
            </glossterm> (e.g. "zImage") and <glossterm><link linkend='var-IMAGE_FSTYPES'>
            IMAGE_FSTYPES</link></glossterm> (e.g. "tar.gz jffs2"). 
            You can find full details on these variables in the reference section. 
            You can leverage many existing machine <filename>.conf</filename> files from 
            <filename>meta/conf/machine/</filename>.
        </para>
    </section>

    <section id="platdev-newmachine-kernel">
        <title>Adding a Kernel for the Machine</title>
        <para>
            Poky needs to be able to build a kernel for the machine. 
            You need to either create a new kernel recipe for this machine, or extend an 
            existing recipe. 
            You can find several kernel examples in the <filename>meta/recipes-kernel/linux</filename>
            directory that can be used as references.
        </para>
        <para>
            If you are creating a new recipe, the "normal" recipe-writing rules apply for setting 
            up a <glossterm><link linkend='var-SRC_URI'>SRC_URI</link></glossterm>. 
            This means specifying any necessary patches and setting <glossterm>
            <link linkend='var-S'>S</link></glossterm> to point at the source code. 
            You need to create a "configure" task that configures the unpacked kernel with a defconfig.
            You can do this by using a <filename>make defconfig</filename> command or
            more commonly by copying in a suitable defconfig and and then running 
            <filename>make oldconfig</filename>. 
            By making use of "inherit kernel" and potentially some of the 
            <filename>linux-*.inc</filename> files, most other functionality is 
            centralized and the the defaults of the class normally work well.
        </para>
        <para>
            If you are extending an existing kernel, it is usually a matter of adding a 
            suitable <filename>defconfig</filename> file.
            The file needs to be added into a location similar to <filename>defconfig</filename> files
            used for other machines in a given kernel. 
            A possible way to do this is by listing the file in the 
            <glossterm><link linkend='var-SRC_URI'>SRC_URI</link></glossterm>
            and adding the machine to the expression in 
            <glossterm><link linkend='var-COMPATIBLE_MACHINE'>COMPATIBLE_MACHINE</link></glossterm>:
        </para>
        <programlisting>
COMPATIBLE_MACHINE = '(qemux86|qemumips)'
        </programlisting>
    </section>

    <section id="platdev-newmachine-formfactor">
        <title>Adding a Formfactor Configuration File</title>
        <para>
            A formfactor configuration file provides information about the 
            target hardware on which Poky is running, and that Poky cannot 
            obtain from other sources such as the kernel.  Some examples of 
            information contained in a formfactor configuration file include 
            framebuffer orientation, whether or not the system has a keyboard, 
            the positioning of the keyboard in relation to the screen, and 
            screen resolution.
        </para>
        <para>
            Sane defaults should be used in most cases, but if customisation is 
            necessary you need to create a <filename>machconfig</filename> file 
            under <filename>meta/packages/formfactor/files/MACHINENAME/</filename>
            where <literal>MACHINENAME</literal> is the name for which this infomation
            applies. For information about the settings available and the defaults, please see 
            <filename>meta/packages/formfactor/files/config</filename>. Below is one
            example for qemuarm:
        </para>
        <programlisting>
HAVE_TOUCHSCREEN=1
HAVE_KEYBOARD=1

DISPLAY_CAN_ROTATE=0
DISPLAY_ORIENTATION=0
#DISPLAY_WIDTH_PIXELS=640
#DISPLAY_HEIGHT_PIXELS=480
#DISPLAY_BPP=16
DISPLAY_DPI=150
DISPLAY_SUBPIXEL_ORDER=vrgb
        </programlisting>
    </section>
</section>

<section id='usingpoky-changes'>
        <title>Making and Maintaining Changes</title>

        <para>
            We recognise that people will want to extend/configure/optimise Poky for
            their specific uses, especially due to the extreme configurability and 
            flexibility Poky offers. To ensure ease of keeping pace with future 
            changes in Poky we recommend making changes to Poky in a controlled way.
        </para>
        <para>
            Poky supports the idea of <link
                linkend='usingpoky-changes-layers'>"layers"</link> which when used
            properly can massively ease future upgrades and allow segregation
            between the Poky core and a given developer's changes. Some other advice on 
            managing changes to Poky is also given in the following section.
        </para>

        <section id="usingpoky-changes-layers">
          <title>Bitbake Layers</title>

          <para>
                Often, people want to extend Poky either through adding packages
                or overriding files contained within Poky to add their own
                functionality. Bitbake has a powerful mechanism called
                layers which provides a way to handle this extension in a fully
                supported and non-invasive fashion.
           </para>

           <para>
               The Poky tree includes several additional layers which demonstrate
               this functionality, such as meta-emenlow and meta-extras.
               The meta-emenlow layer is an example layer enabled by default. The meta-extras 
               repostory is not enabled by default but enabling any layer is as easy as adding
               the layers path to the BBLAYERS variable in your bblayers.conf. this is how 
               meta-extras are enabled in Poky builds:
          </para>
          <para>
               <literallayout class='monospaced'>LCONF_VERSION = "1"

BBFILES ?= ""
BBLAYERS = " \
  /path/to/poky/meta \
  /path/to/poky/meta-emenlow \
  /path/to/poky/meta-extras \
  "
</literallayout>
           </para>

          <para>
               Bitbake parses the conf/layer.conf of each of the layers in BBLAYERS
               to add the recipes, classes and configuration contained within the layer to Poky.
               To create your own layer, independent of the main Poky repository,
               you need only create a directory with a conf/layer.conf file and
               add the directory to your bblayers.conf.
          </para>

          <para>
               The meta-emenlow/conf/layer.conf demonstrates the required syntax:
               <literallayout class='monospaced'># We have a conf and classes directory, add to BBPATH
BBPATH := "${BBPATH}:${LAYERDIR}"

# We have a recipes directory containing both .bb and .bbappend files, add to BBFILES
BBFILES := "${BBFILES} ${LAYERDIR}/recipes/*/*.bb \
        ${LAYERDIR}/recipes/*/*.bbappend"

BBFILE_COLLECTIONS += "emenlow"
BBFILE_PATTERN_emenlow := "^${LAYERDIR}/"
BBFILE_PRIORITY_emenlow = "6"
               </literallayout>
          </para>

          <para>
                As can be seen, the layers recipes are added to 
                <glossterm> <link linkend='var-BBFILES'>BBFILES</link></glossterm>. The
                BBFILE_COLLECTIONS variable is then appended to with the
                layer name. The BBFILE_PATTERN variable is immediately expanded
                with a regular expression used to match files from BBFILES into
                a particular layer, in this case by using the base pathname.
                The BBFILE_PRIORITY variable then assigns different
                priorities to the files in different layers. This is useful
                in situations where the same package might appear in multiple
                layers and allows you to choose which layer should 'win'.
                Note the use of <glossterm><link linkend='var-LAYERDIR'>
                LAYERDIR</link></glossterm> with the immediate expansion operator.
                <glossterm><link linkend='var-LAYERDIR'>LAYERDIR</link></glossterm>
                expands to the directory of the current layer and
                requires use of the immediate expansion operator so that Bitbake
                does not lazily expand the variable when it's parsing a
                different directory.
            </para>

            <para>
                Additional bbclass and configuration files can be locationed by 
                bitbake through the addition to the BBPATH
                environment variable. In this case, the first file with the
                matching name found in BBPATH is the one that is used, just
                like the PATH variable for binaries. It is therefore recommended
                that you use unique bbclass and configuration file names in your
                custom layer.
            </para>

            <para>
                The recommended approach for custom layers is to store them in a
                git repository of the format meta-prvt-XXXX and have this repository
                cloned alongside the other meta directories in the Poky tree.
                This way you can keep your Poky tree and it's configuration entirely
                inside POKYBASE.
            </para>
        </section>

        <section id='usingpoky-changes-commits'>
            <title>Committing Changes</title>

            <para>
                Modifications to Poky are often managed under some kind of source
                revision control system. The policy for committing to such systems
                is important as some simple policy can significantly improve 
                usability. The tips below are based on the policy followed for the 
                Poky core.
            </para>

            <para>
                It helps to use a consistent style for commit messages when committing 
                changes. We've found a style where the first line of a commit message 
                summarises the change and starts with the name of any package affected
                work well. Not all changes are to specific packages so the prefix could 
                also be a machine name or class name instead. If a change needs a longer 
                description this should follow the summary:
            </para>

            <literallayout class='monospaced'>
    bitbake/data.py: Add emit_func() and generate_dependencies() functions
    
    These functions allow generation of dependency data between funcitons and
    variables allowing moves to be made towards generating checksums and allowing
    use of the dependency information in other parts of bitbake.
    
    Signed-off-by: Richard Purdie rpurdie@linux.intel.com
            </literallayout>

            <para>
                Any commit should be self contained in that it should leave the 
                metadata in a consistent state, buildable before and after the 
                commit. This helps ensure the autobuilder test results are valid 
                but is good practice regardless.
            </para>
        </section>

        <section id='usingpoky-changes-prbump'>
            <title>Package Revision Incrementing</title>

            <para>
                If a committed change will result in changing the package output
                then the value of the <glossterm><link linkend='var-PR'>PR</link>
                </glossterm> variable needs to be increased (commonly referred to 
                as 'bumped') as part of that commit. Only integer values are used
                and <glossterm><link linkend='var-PR'>PR</link></glossterm> = 
                "r0" should be added into new recipes as, while this is the
                default value, not having the variable defined in a recipe makes
                it easy to miss incrementing it when updating the recipe.
                When upgrading the version of a package (<glossterm><link 
                linkend='var-PV'>PV</link></glossterm>), the <glossterm><link 
                linkend='var-PR'>PR</link></glossterm> variable should be reset to "r0".
            </para>

            <para>
                The aim is that the package version will only ever increase. If 
                for some reason <glossterm><link linkend='var-PV'>PV</link></glossterm> 
                will change and but not increase, the <glossterm><link 
                linkend='var-PE'>PE</link></glossterm> (Package Epoch) can 
                be increased (it defaults to '0'). The version numbers aim to 
                follow the <ulink url='http://www.debian.org/doc/debian-policy/ch-controlfields.html'>
                Debian Version Field Policy Guidelines</ulink> which define how 
                versions are compared and hence what "increasing" means.
            </para>

            <para>
                There are two reasons for doing this, the first is to ensure that 
                when a developer updates and rebuilds, they get all the changes to
                the repository and don't have to remember to rebuild any sections.
                The second is to ensure that target users are able to upgrade their
                devices via their package manager such as with the <command>
                opkg upgrade</command> commands (or similar for 
                dpkg/apt or rpm based systems). The aim is to ensure Poky has 
                upgradable packages in all cases.
            </para>
        </section>
        <section id='usingpoky-changes-collaborate'>
            <title>Using Poky in a Team Environment</title>

            <para>
                It may not be immediately clear how Poky can work in a team environment, 
                or scale to a large team of developers. The specifics of any situation
                will determine the best solution and poky offers immense flexibility in 
                that aspect but there are some practises that experience has shown to work
                well.
            </para>

            <para>
                The core component of any development effort with Poky is often an 
                automated build testing framework and image generation process. This 
                can be used to check that the metadata is buildable, highlight when 
                commits break the builds and provide up to date images allowing people 
                to test the end result and use them as a base platform for further 
                development. Experience shows that buildbot is a good fit for this role 
                and that it works well to configure it to make two types of build - 
                incremental builds and 'from scratch'/full builds. The incremental builds 
                can be tied to a commit hook which triggers them each time a commit is 
                made to the metadata and are a useful acid test of whether a given commit 
                breaks the build in some serious way. They catch lots of simple errors 
                and whilst they won't catch 100% of failures, the tests are fast so 
                developers can get feedback on their changes quickly. The full builds
                are builds that build everything from the ground up and test everything. 
                They usually happen at preset times such as at night when the machine 
                load isn't high from the incremental builds.
                <ulink url='http://autobuilder.pokylinux.org:8010'>poky autobuilder</ulink>
                is an example implementation with buildbot.
            </para>

            <para>
                Most teams have pieces of software undergoing active development. It is of
                significant benefit to put these under control of a source control system 
                compatible with Poky such as git or svn. The autobuilder can then be set to 
                pull the latest revisions of these packages so the latest commits get tested 
                by the builds allowing any issues to be highlighted quickly. Poky easily
                supports configurations where there is both a stable known good revision 
                and a floating revision to test. Poky can also only take changes from specific
                source control branches giving another way it can be used to track/test only
                specified changes.
            </para>
            <para>
                Perhaps the hardest part of setting this up is the policy that surrounds 
                the different source control systems, be them software projects or the Poky 
                metadata itself. The circumstances will be different in each case but this is
                one of Poky's advantages - the system itself doesn't force any particular policy
                unlike a lot of build systems, allowing the best policy to be chosen for the 
                circumstances.
            </para>
        </section>

        <section id='usingpoky-changes-updatingimages'>
            <title>Updating Existing Images</title>

            <para>
                Often, rather than reflashing a new image you might wish to install updated 
                packages into an existing running system. This can be done by sharing the <filename class="directory">tmp/deploy/ipk/</filename> directory through a web server and then on the device, changing <filename>/etc/opkg/base-feeds.conf</filename> to point at this server, for example by adding:
            </para>
            <literallayout class='monospaced'>
src/gz all http://www.mysite.com/somedir/deploy/ipk/all
src/gz armv7a http://www.mysite.com/somedir/deploy/ipk/armv7a
src/gz beagleboard http://www.mysite.com/somedir/deploy/ipk/beagleboard</literallayout>
        </section>
    </section>

    <section id='usingpoky-modifing-packages'>
        <title>Modifying Package Source Code</title>

        <para>
            Poky is usually used to build software rather than modifying
            it. However, there are ways Poky can be used to modify software. 
        </para>

        <para>
            During building, the sources are available in <glossterm><link
                    linkend='var-WORKDIR'>WORKDIR</link></glossterm> directory.
            Where exactly this is depends on the type of package and the
            architecture of target device. For a standard recipe not
            related to <glossterm><link
                    linkend='var-MACHINE'>MACHINE</link></glossterm> it will be
            <filename>tmp/work/PACKAGE_ARCH-poky-TARGET_OS/PN-PV-PR/</filename>.
            Target device dependent packages use <glossterm><link
                    linkend='var-MACHINE'>MACHINE
            </link></glossterm> 
            instead of <glossterm><link linkend='var-PACKAGE_ARCH'>PACKAGE_ARCH
            </link></glossterm> 
            in the directory name.
        </para>

        <tip>
            <para>
                Check the package recipe sets the <glossterm><link
                        linkend='var-S'>S</link></glossterm> variable to something
            other than standard <filename>WORKDIR/PN-PV/</filename> value.
            </para>
        </tip>
        <para>
            After building a package, a user can modify the package source code
            without problem. The easiest way to test changes is by calling the
            "compile" task:
        </para>

        <programlisting>
bitbake -c compile -f NAME_OF_PACKAGE
        </programlisting>

        <para>
            "-f" or "--force" is used to force re-execution of the specified task.
            Other tasks may also be called this way. But note that all the modifications
            in <glossterm><link linkend='var-WORKDIR'>WORKDIR</link></glossterm>
            are gone once you executes "-c clean" for a package.
        </para>

        <section id='usingpoky-modifying-packages-quilt'>
            <title>Modifying Package Source Code with quilt</title>

            <para>
                By default Poky uses <ulink
                    url='http://savannah.nongnu.org/projects/quilt'>quilt</ulink>
                to manage patches in <function>do_patch</function> task. 
                It is a powerful tool which can be used to track all
                modifications done to package sources.
            </para>

            <para>
                Before modifying source code it is important to
                notify quilt so it will track changes into new patch
                file:
                <programlisting>
quilt new NAME-OF-PATCH.patch
                </programlisting>

                Then add all files which will be modified into that
                patch:
                <programlisting>
quilt add file1 file2 file3
                </programlisting>

                Now start editing. At the end quilt needs to be used
                to generate final patch which will contain all
                modifications:
                <programlisting>
quilt refresh
                </programlisting>

                The resulting patch file can be found in the
                <filename class="directory">patches/</filename> subdirectory of the source 
                (<glossterm><link linkend='var-S'>S</link></glossterm>) directory. For future builds it
                should be copied into
                Poky metadata and added into <glossterm><link
                        linkend='var-SRC_URI'>SRC_URI</link></glossterm> of a recipe:
                <programlisting>
SRC_URI += "file://NAME-OF-PATCH.patch"
                </programlisting>

                This also requires a bump of <glossterm><link
                        linkend='var-PR'>PR</link></glossterm> value in the same recipe as we changed resulting packages.
            </para>

        </section>

    </section>
    <section id='usingpoky-configuring-LIC_FILES_CHKSUM'>
        <title>Track license change</title>
        <para>
        The license of one upstream project may change in the future, and Poky provides
        one mechanism to track such license change - <glossterm>
        <link linkend='var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</link></glossterm> variable.
        </para>

        <section id='usingpoky-specifying-LIC_FILES_CHKSUM'>
            <title>Specifying the LIC_FILES_CHKSUM variable </title>

            <programlisting>
LIC_FILES_CHKSUM = "file://COPYING; md5=xxxx \
                    file://licfile1.txt; beginline=5; endline=29;md5=yyyy \
                    file://licfile2.txt; endline=50;md5=zzzz \
                    ..."
            </programlisting>

            <para>
            <glossterm><link linkend='var-S'>S</link></glossterm> is the default directory
            for searching files listed in <glossterm><link linkend='var-LIC_FILES_CHKSUM'>
            LIC_FILES_CHKSUM</link></glossterm>. Relative path could be used too:
            </para>

            <programlisting>
LIC_FILES_CHKSUM = "file://src/ls.c;startline=5;endline=16;\
                                    md5=bb14ed3c4cda583abc85401304b5cd4e"
LIC_FILES_CHKSUM = "file://../license.html;md5=5c94767cedb5d6987c902ac850ded2c6"
            </programlisting>

            <para>
            The first line locates a file in <glossterm><link linkend='var-S'>
            S</link></glossterm>/src/ls.c, and the second line refers to a file in 
            <glossterm><link linkend='var-WORKDIR'>WORKDIR</link></glossterm>, which is the parent
            of <glossterm><link linkend='var-S'>S</link></glossterm>
            </para>

        </section>

        <section id='usingpoky-LIC_FILES_CHKSUM-explanation-of-syntax'>
            <title>Explanation of syntax</title>

            <para>
            This parameter lists all the important files containing the text 
of licenses for the
source code. It is also possible to specify on which line the license text
starts and on which line it ends within that file using the "beginline" and
"endline" parameters. If the "beginline" parameter is not specified then license
text begins from the 1st line is assumed. Similarly if "endline" parameter is
not specified then the license text ends at the last line in the file is
assumed. So if a file contains only licensing information, then there is no need
to specify "beginline" and "endline" parameters.
            </para>
            <para>
The "md5" parameter stores the md5 checksum of the license text. So if
the license text changes in any way from a file, then its md5 sum will differ and will not
match with the previously stored md5 checksum. This mismatch will trigger build
failure, notifying developer about the license text md5 mismatch, and allowing
the developer to review the license text changes. Also note that if md5 checksum
is not matched while building, the correct md5 checksum is printed in the build
log which can be easily copied to .bb file.
            </para>
            <para>
There is no limit on how many files can be specified on this parameter. But generally every
project would need specifying of just one or two files for license tracking.
Many projects would have a "COPYING" file which will store all the
license information for all the source code files. If the "COPYING" file
is valid then tracking only that file would be enough.
            </para>
            <tip>
                <para>
1. If you specify empty or invalid "md5" parameter; then while building
the package, bitbake will give md5 not matched error, and also show the correct
"md5" parameter value both on the screen and in the build log 
                </para>
                <para>
2. If the whole file contains only license text, then there is no need to
specify "beginline" and "endline" parameters. 
                </para>
            </tip>
        </section>
    </section>
    <section id='usingpoky-configuring-DISTRO_PN_ALIAS'>
        <title>Handle package name alias</title>
        <para>
Poky implements a distro_check task which automatically connects to major distributions
and checks whether they contains same package. Sometimes the same package has different 
names in different distributions, which results in a mismatch from distro_check task
This can be solved by defining per distro recipe name alias - 
<glossterm><link linkend='var-DISTRO_PN_ALIAS'>DISTRO_PN_ALIAS</link></glossterm>
        </para>

        <section id='usingpoky-specifying-DISTRO_PN_ALIAS'>
            <title>Specifying the DISTRO_PN_ALIAS variable </title>

            <programlisting>
DISTRO_PN_ALIAS_pn-PACKAGENAME = "distro1=package_name_alias1 \
                                  distro2=package_name_alias2 \
                                  distro3=package_name_alias3 \
                                  ..."
            </programlisting>
            <para>
Use space as the delimiter if there're multiple distro aliases
            </para>
            <tip>
                <para>
The current code can check if the src package for a recipe exists in the latest
releases of these distributions automatically.
                </para>
                <programlisting>
Fedora, OpenSuSE, Debian, Ubuntu, Mandriva
                </programlisting>
                <para>
For example, this command will generate a report, listing which linux distros include the
sources for each of the poky recipe.
                </para>
                <programlisting>
bitbake world -f -c distro_check
                </programlisting>
                <para>
The results will be stored in the build/tmp/log/distro_check-${DATETIME}.results file.
                </para>
            </tip>
        </section>
    </section>
</chapter>

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