handbook: Move into documentation directory

Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

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+<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<chapter id='extendpoky'>
+
+<title>Extending Poky</title>
+
+    <para>
+        This section gives information about how to extend the functionality
+        already present in Poky, documenting standard tasks such as adding new
+        software packages, extending or customising images or porting poky to
+        new hardware (adding a new machine). It also contains advice about how
+        to manage the process of making changes to Poky to achieve best results.
+    </para>
+
+    <section id='usingpoky-extend-addpkg'>
+        <title>Adding a Package</title>
+
+        <para>
+            To add package into Poky you need to write a recipe for it. 
+            Writing a recipe means creating a .bb file which sets various
+            variables. The variables
+            useful for recipes are detailed in the <link linkend='ref-varlocality-recipe-required'>
+                recipe reference</link> section along with more detailed information 
+            about issues such as recipe naming.
+        </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 hence a wider range of packages.
+            Poky aims to be compatible with OpenEmbedded so 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. There are some examples below of how to add 
+            standard types of packages:
+        </para>
+
+        <section id='usingpoky-extend-addpkg-singlec'>
+            <title>Single .c File Package (Hello World!)</title>
+
+            <para>
+                To build an application from a single file stored locally (e.g. under "files/")
+                requires a recipe which has the file listed in the <glossterm><link
+                linkend='var-SRC_URI'>SRC_URI</link></glossterm> variable. In addition 
+                the <function>do_compile</function> and <function>do_install</function> 
+                tasks need to be manually written. The <glossterm><link linkend='var-S'>
+                S</link></glossterm> variable defines the directory containing the source 
+                code which in this case is set equal to <glossterm><link linkend='var-WORKDIR'>
+                WORKDIR</link></glossterm>, 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>
+                As a result of the build process "helloworld", "helloworld-dbg" and "hellworld-dev"
+                packages will be built by default. It is possible to<link linkend='usingpoky-extend-addpkg-files'>
+                customise the packaging process</link>.
+            </para>
+        </section>
+
+        <section id='usingpoky-extend-addpkg-autotools'>
+            <title>Autotooled Package</title>
+
+            <para>
+                Applications which use autotools (autoconf, automake)
+                require a recipe which has a source archive listed in 
+                <glossterm><link
+                        linkend='var-SRC_URI'>SRC_URI</link></glossterm> and 
+                <command>inherit autotools</command> to instruct BitBake to use the
+                <filename>autotools.bbclass</filename> which has 
+                definitions of all the steps
+                needed to build an autotooled application.
+                The result of the build will be automatically packaged and if
+                the application uses NLS to localise then packages with
+                locale information will be generated (one package per
+                language). Below is one example (hello_2.2.bb)
+            </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>. Autotool based recipe can be quickly
+            created this way like above example.
+            </para>
+
+        </section>
+
+        <section id='usingpoky-extend-addpkg-makefile'>
+            <title>Makefile-Based Package</title>
+
+            <para>
+                Applications which use GNU make require a recipe which has
+                the source archive listed in <glossterm><link
+                        linkend='var-SRC_URI'>SRC_URI</link></glossterm>. 
+                Adding a <function>do_compile</function> step
+                is not needed as by default BitBake will start the "make"
+                command to compile the application. If there is a need for
+                additional options to make then they should be stored in the
+                <glossterm><link
+                        linkend='var-EXTRA_OEMAKE'>EXTRA_OEMAKE</link></glossterm> variable - BitBake 
+                will pass them into the GNU
+                make invocation. A <function>do_install</function> task is required
+                - otherwise BitBake will run an empty <function>do_install</function> 
+                task by default. 
+            </para>
+
+            <para>
+                Some applications may require extra parameters to be passed to
+                the compiler, for example an additional header path. This can
+                be done buy adding to the <glossterm><link
+                        linkend='var-CFLAGS'>CFLAGS</link></glossterm> variable, as in the example below:
+            </para>
+
+            <programlisting>
+CFLAGS_prepend = "-I ${S}/include "
+            </programlisting>
+
+            <para>
+            mtd-utils is an example as Makefile-based:
+            </para>
+
+            <programlisting>
+DESCRIPTION = "Tools for managing memory technology devices."
+SECTION = "base"
+DEPENDS = "zlib lzo e2fsprogs util-linux"
+HOMEPAGE = "http://www.linux-mtd.infradead.org/"
+LICENSE = "GPLv2"
+
+SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=v${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 packages content</title>
+
+            <para>                        
+                The variables <glossterm><link
+                        linkend='var-PACKAGES'>PACKAGES</link></glossterm> and 
+                <glossterm><link linkend='var-FILES'>FILES</link></glossterm> are used to split an
+                application into multiple packages.
+            </para>
+
+            <para>
+                Below the "libXpm" recipe (libxpm_3.5.7.bb) is used as an example. By
+                default the "libXpm" recipe generates one package 
+                which contains the library
+                and also a few binaries. The recipe can be adapted 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 this 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 as standard we prepend the <glossterm><link
+                linkend='var-PACKAGES'>PACKAGES</link></glossterm> variable so
+                additional package names are added to the start of list. The 
+                extra <glossterm><link linkend='var-FILES'>FILES</link></glossterm>_*
+                variables then contain information to specify which files and
+                directories goes into which package. Files included by earlier
+                package are skipped by latter packages, and thus main <glossterm>
+                <link linkend='var-PN'>PN</link></glossterm> will not include 
+                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 .bb file
+                where PACKAGENAME is the name of the package to attach
+                the postinst script to. Normally <glossterm><link
+                linkend='var-PN'>PN</link></glossterm> can be used which expands
+                to PACKAGENAME automatically. 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
+                gets 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 will be
+                executed again on the first boot of the image.
+            </para>
+
+            <para>
+                Sometimes it is necessary that the execution of a post-installation
+                script is delayed until the first boot, because the script 
+                needs to be executed on the device itself.  To delay script execution
+                until boot time, the post-installation function should have the
+                following structure:
+            </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 structure above delays execution until first boot 
+                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>
+        Poky images can be customised to satisfy 
+        particular requirements. Several methods are detailed below 
+        along with guidelines of when to use them.
+        </para>
+
+        <section id='usingpoky-extend-customimage-custombb'>
+            <title>Customising Images through a custom image .bb files</title>
+
+            <para>
+                One way to get additional software into an image is by creating a
+                custom image. The recipe will contain two lines:
+            </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. 
+                The names must be in 
+                the OpenEmbedded notation instead of Debian notation, for example
+                "glibc-dev" instead of "libc6-dev" etc.
+            </para>
+
+            <para>
+                The other method of creating a new image is by modifying
+                an existing image. For example if a developer wants to add
+                "strace" into "poky-image-sato" the following recipe can
+                be used:
+            </para>
+
+            <programlisting>
+require poky-image-sato.bb
+
+IMAGE_INSTALL += "strace"
+            </programlisting>
+
+        </section>
+
+        <section id='usingpoky-extend-customimage-customtasks'>
+            <title>Customising Images through custom tasks</title>
+
+            <para>
+                For complex custom images, the best approach is to create a custom 
+                task package which is then used to build the image (or images). A good
+                example of a tasks package is <filename>meta/packages/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,
+                <glossterm><link linkend='var-PACKAGES'>RDEPENDS</link></glossterm> and
+                <glossterm><link linkend='var-PACKAGES'>RRECOMMENDS</link></glossterm> 
+                entries can then be added each containing a list of packages the parent 
+                task package should contain. An example would be:
+            </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 this example, two task packages are created, task-custom-apps and 
+                task-custom-tools with the dependencies and recommended package dependencies 
+                listed. To build an image using these task packages, you would then 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 through custom <glossterm><link linkend='var-IMAGE_FEATURES'>IMAGE_FEATURES</link></glossterm></title>
+
+            <para>
+                Ultimately users may 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, the best reference is <filename>meta/classes/poky-image.bbclass</filename>
+                which illustrates 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 this into a set of tasks or packages. Based on this then the 
+                <glossterm><link linkend='var-IMAGE_INSTALL'> IMAGE_INSTALL</link></glossterm> 
+                variable is generated automatically. Extra features can be added by 
+                extending the class or creating a custom class for use with specialised image .bb files.
+            </para>
+        </section>
+
+        <section id='usingpoky-extend-customimage-localconf'>
+            <title>Customising Images through 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>
+                To add an "strace" package into the image the following is 
+                added to local.conf:
+            </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 this method does not make
+                adding packages as simple as a custom .bb file. Using
+                this method, a few packages will need to be recreated if they have been
+                created before and then the image is rebuilt.
+            </para>
+            <programlisting>
+bitbake -c clean task-boot task-base task-poky
+bitbake poky-image-sato
+            </programlisting>
+
+            <para>
+                Cleaning task-* packages is required because they use the
+                <glossterm><link linkend='var-DISTRO_EXTRA_RDEPENDS'>
+                DISTRO_EXTRA_RDEPENDS</link></glossterm> variable. There is no need to
+                build them by hand as Poky images depend on the packages they contain so
+                dependencies will be built automatically when building the image. For this reason we don't use the
+                "rebuild" task in this case since "rebuild" does not care about
+                dependencies - it only rebuilds the specified package.
+            </para>
+
+        </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 and
+        this section gives an idea of the changes that are needed. This guide is
+        meant to cover adding machines similar to those Poky already supports. 
+        Adding a totally new architecture might require gcc/glibc changes as 
+        well as updates to the site information and, whilst well within Poky's 
+        capabilities, is outside the scope of this section.
+    </para>
+
+    <section id="platdev-newmachine-conffile">
+        <title>Adding the machine configuration file</title>
+        <para>
+            A .conf file needs to be added to conf/machine/ with details of the
+            device being added. The name of the file determines the name Poky will
+            use to reference this 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"). 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") might also be 
+            needed. Full details on what these variables do and the meaning of
+            their contents is available through the links. There're lots of existing
+            machine .conf files which can be easily leveraged from meta/conf/machine/.
+        </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. There are plenty of kernel examples in the 
+             meta/recipes-kernel/linux directory which can be used as references.
+        </para>
+        <para>
+             If creating a new recipe the "normal" recipe writing rules apply 
+             for setting up a <glossterm><link linkend='var-SRC_URI'>SRC_URI
+             </link></glossterm> including any patches and setting <glossterm>
+             <link linkend='var-S'>S</link></glossterm> to point at the source 
+             code. You will need to create a configure task which configures the 
+             unpacked kernel with a defconfig be that through a "make defconfig" 
+             command or more usually though copying in a suitable defconfig and 
+             running "make oldconfig". By making use of "inherit kernel" and also 
+             maybe some of the linux-*.inc files, most other functionality is 
+             centralised and the the defaults of the class normally work well.
+        </para>
+        <para>
+            If extending an existing kernel it is usually a case of adding a 
+            suitable defconfig file in a location similar to that used by other 
+            machine's defconfig files in a given kernel, possibly listing it in
+            the SRC_URI 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-moblin \
+  /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 layers packages, classes and configuration 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}:${LAYERDIR}"
+
+# We have a packages directory, add to BBFILES
+BBFILES := "${BBFILES} ${LAYERDIR}/packages/*/*.bb \
+        ${LAYERDIR}/packages/*/*.bbappend"
+
+BBFILE_COLLECTIONS += "emenlow"
+BBFILE_PATTERN_emenlow := "^${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>
+
+<!-- 
+vim: expandtab tw=80 ts=4 
+-->