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<?xml version="1.0" encoding="UTF-8"?>
<chapter id="chapter_metadata">
<title>Metadata</title>
<section id="metadata_file_layout">
<title>File Layout</title>
<para>OpenEmbedded has six directories three of them hold
<application>BitBake</application> metadata.</para>
<para>The <emphasis>conf</emphasis> directory is holding the bitbake.conf,
machine and distribution configuration. bitbake.conf is read when
<application>BitBake</application> is started and this will include among
others a local.conf the machine and distribution configuration files.
These files will be searched in the <command>BBPATH</command> environment
variable.</para>
<para><emphasis>classes</emphasis> is the directory holding
<application>BitBake</application> bbclass. These classes can be inherited
by the <application>BitBake</application> files. BitBake automatically
inherits the base.bbclass on every parsed file. <command>BBPATH</command>
is used to find the class.</para>
<para>In <emphasis>packages</emphasis> the
<application>BitBake</application> files are stored. For each task or
application we have a directory. These directories store the real
<application>BitBake</application> files. They are the ones ending with
<emphasis>.bb</emphasis>. And for each application and version we have
one.</para>
</section>
<section id="metadata_syntax">
<title>Syntax</title>
<para>OpenEmbedded has files ending with <emphasis>.conf</emphasis>,
<emphasis>.inc</emphasis>, <emphasis>.bb</emphasis>
and<emphasis>.bbclass</emphasis>. The syntax and semantic of these files
are best described in the <ulink
url="http://bitbake.berlios.de/manual"><application>BitBake</application>
manual</ulink>.</para>
</section>
<section id="metadata_classes">
<title>Classes</title>
<para>OpenEmbedded provides special <application>BitBake</application>
classes to ease compiling, packaging and other things. FIXME.</para>
</section>
<section id="metadata_writing_data">
<title>Writing Meta Data (Adding packages)</title>
<para>This page will guide you trough the effort of writing a .bb file or
<emphasis>recipe</emphasis> in BitBake speak.</para>
<para>Let's start with the easy stuff, like the package description,
license, etc: <screen>
DESCRIPTION = "My first application, a really cool app containing lots of foo and bar"
LICENSE = "GPLv2"
HOMEPAGE = "http://www.host.com/foo/"
</screen> The description and license fields are mandatory, so
better check them twice.</para>
<para>The next step is to specify what the package needs to build and run,
the so called <emphasis>dependencies</emphasis>: <screen>
DEPENDS = "gtk+"
RDEPENDS = "cool-ttf-fonts"
</screen> The package needs gtk+ to build ('DEPENDS') and
requires the 'cool-ttf-fonts' package to run ('RDEPENDS'). OE will add
run-time dependencies on libraries on its own via the so called
<emphasis>shlibs</emphasis>-code, but you need to specify everything other
by yourself, which in this case is the 'cool-ttf-fonts' package.</para>
<para>After entering all this OE will know what to build before trying to
build your application, but it doesn't know where to get it yet. So let's
add the source location: <screen>
SRC_URI = "http://www.host.com/foo/files/${P}.tar.bz2;md5sum=yoursum"
</screen> This will tell the fetcher to where to download the
sources from and it will check the integrity using md5sum if you provided
the appropriate <emphasis>yoursum</emphasis>. You can make one by doing
<screen>md5sum foo-1.9.tar.bz2</screen> and replacing
<emphasis>yoursum</emphasis> with the md5sum on your screen. A typical
md5sum will look like this: <screen>a6434b0fc8a54c3dec3d6875bf3be8mtn </screen>Notice
the <emphasis>${P}</emphasis> variable, that one holds the package name,
<emphasis>${PN}</emphasis> in BitBake speak and the package version,
<emphasis>${PV}</emphasis> in BitBake speak. It's a short way of writing
<emphasis>${PN}-${PV}</emphasis>. Using this notation means you can copy
the recipe when a new version is released without having to alter the
contents. You do need to check if everything is still correct, because new
versions mean new bugs.</para>
<para>Before we can move to the actual building we need to find out which
build system the package is using. If we're lucky, we see a
<emphasis>configure</emphasis> file in the build tree this is an indicator
that we can <emphasis>inherit autotools</emphasis> if we see a
<emphasis>.pro</emphasis> file, it might be qmake, which needs
<emphasis>inherit qmake</emphasis>. Virtually all gtk apps use autotools:
<screen>
inherit autotools pkgconfig
</screen> We are in luck! The package is a well-behaved
application using autotools and pkgconfig to configure and build it
self.</para>
<para>Lets start the build: <screen>
<command>bitbake</command> foo
</screen> Depending on what you have built before and the
speed of your computer this can take a few seconds to a few hours, so be
prepared.</para>
<para>.... some time goes by .....</para>
<para>Your screen should now have something like this on it: <screen>
NOTE: package foo-1.9-r0: task do_build: completed
NOTE: package foo-1.9: completed
NOTE: build 200605052219: completed
</screen></para>
<para>All looks well, but wait, let's scroll up: <screen>
NOTE: the following files where installed but not shipped:
/usr/weirdpath/importantfile.foo
</screen> OE has a standard list of paths which need to be
included, but it can't know everything, so we have to tell OE to include
that file as well: <screen>
FILES_${PN} += "/usr/weirdpath/importantfile.foo"
</screen> It's important to use <emphasis>+=</emphasis> so it
will get appended to the standard file-list, not replace the standard
one.</para>
</section>
</chapter>
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