forked from brl/citadel
496 lines
25 KiB
XML
496 lines
25 KiB
XML
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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<appendix id='hello-world-example'>
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<title>Hello World Example</title>
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<section id='bitbake-hello-world'>
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<title>BitBake Hello World</title>
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<para>
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The simplest example commonly used to demonstrate any new
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programming language or tool is the
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"<ulink url="http://en.wikipedia.org/wiki/Hello_world_program">Hello World</ulink>"
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example.
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This appendix demonstrates, in tutorial form, Hello
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World within the context of BitBake.
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The tutorial describes how to create a new project
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and the applicable metadata files necessary to allow
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BitBake to build it.
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</para>
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</section>
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<section id='example-obtaining-bitbake'>
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<title>Obtaining BitBake</title>
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<para>
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See the
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"<link linkend='obtaining-bitbake'>Obtaining BitBake</link>"
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section for information on how to obtain BitBake.
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Once you have the source code on your machine, the BitBake directory
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appears as follows:
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<literallayout class='monospaced'>
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$ ls -al
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total 100
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drwxrwxr-x. 9 wmat wmat 4096 Jan 31 13:44 .
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drwxrwxr-x. 3 wmat wmat 4096 Feb 4 10:45 ..
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-rw-rw-r--. 1 wmat wmat 365 Nov 26 04:55 AUTHORS
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drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 bin
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drwxrwxr-x. 4 wmat wmat 4096 Jan 31 13:44 build
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-rw-rw-r--. 1 wmat wmat 16501 Nov 26 04:55 ChangeLog
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drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 classes
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drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 conf
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drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 contrib
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-rw-rw-r--. 1 wmat wmat 17987 Nov 26 04:55 COPYING
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drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 doc
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-rw-rw-r--. 1 wmat wmat 69 Nov 26 04:55 .gitignore
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-rw-rw-r--. 1 wmat wmat 849 Nov 26 04:55 HEADER
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drwxrwxr-x. 5 wmat wmat 4096 Jan 31 13:44 lib
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-rw-rw-r--. 1 wmat wmat 195 Nov 26 04:55 MANIFEST.in
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-rw-rw-r--. 1 wmat wmat 2887 Nov 26 04:55 TODO
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</literallayout>
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</para>
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<para>
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At this point, you should have BitBake cloned to
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a directory that matches the previous listing except for
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dates and user names.
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</para>
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</section>
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<section id='setting-up-the-bitbake-environment'>
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<title>Setting Up the BitBake Environment</title>
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<para>
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First, you need to be sure that you can run BitBake.
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Set your working directory to where your local BitBake
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files are and run the following command:
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<literallayout class='monospaced'>
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$ ./bin/bitbake --version
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BitBake Build Tool Core version 1.23.0, bitbake version 1.23.0
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</literallayout>
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The console output tells you what version you are running.
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</para>
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<para>
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The recommended method to run BitBake is from a directory of your
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choice.
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To be able to run BitBake from any directory, you need to add the
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executable binary to your binary to your shell's environment
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<filename>PATH</filename> variable.
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First, look at your current <filename>PATH</filename> variable
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by entering the following:
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<literallayout class='monospaced'>
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$ echo $PATH
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</literallayout>
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Next, add the directory location for the BitBake binary to the
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<filename>PATH</filename>.
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Here is an example that adds the
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<filename>/home/scott-lenovo/bitbake/bin</filename> directory
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to the front of the <filename>PATH</filename> variable:
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<literallayout class='monospaced'>
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$ export PATH=/home/scott-lenovo/bitbake/bin:$PATH
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</literallayout>
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You should now be able to enter the <filename>bitbake</filename>
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command from the command line while working from any directory.
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</para>
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</section>
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<section id='the-hello-world-example'>
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<title>The Hello World Example</title>
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<para>
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The overall goal of this exercise is to build a
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complete "Hello World" example utilizing task and layer
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concepts.
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Because this is how modern projects such as OpenEmbedded and
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the Yocto Project utilize BitBake, the example
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provides an excellent starting point for understanding
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BitBake.
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</para>
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<para>
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To help you understand how to use BitBake to build targets,
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the example starts with nothing but the <filename>bitbake</filename>
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command, which causes BitBake to fail and report problems.
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The example progresses by adding pieces to the build to
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eventually conclude with a working, minimal "Hello World"
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example.
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</para>
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<para>
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While every attempt is made to explain what is happening during
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the example, the descriptions cannot cover everything.
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You can find further information throughout this manual.
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Also, you can actively participate in the
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<ulink url='http://lists.openembedded.org/mailman/listinfo/bitbake-devel'></ulink>
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discussion mailing list about the BitBake build tool.
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</para>
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<note>
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This example was inspired by and drew heavily from
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<ulink url="http://www.mail-archive.com/yocto@yoctoproject.org/msg09379.html">Mailing List post - The BitBake equivalent of "Hello, World!"</ulink>.
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</note>
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<para>
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As stated earlier, the goal of this example
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is to eventually compile "Hello World".
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However, it is unknown what BitBake needs and what you have
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to provide in order to achieve that goal.
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Recall that BitBake utilizes three types of metadata files:
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<link linkend='configuration-files'>Configuration Files</link>,
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<link linkend='classes'>Classes</link>, and
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<link linkend='recipes'>Recipes</link>.
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But where do they go?
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How does BitBake find them?
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BitBake's error messaging helps you answer these types of questions
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and helps you better understand exactly what is going on.
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</para>
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<para>
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Following is the complete "Hello World" example.
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</para>
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<orderedlist>
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<listitem><para><emphasis>Create a Project Directory:</emphasis>
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First, set up a directory for the "Hello World" project.
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Here is how you can do so in your home directory:
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<literallayout class='monospaced'>
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$ mkdir ~/hello
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$ cd ~/hello
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</literallayout>
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This is the directory that BitBake will use to do all of
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its work.
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You can use this directory to keep all the metafiles needed
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by BitBake.
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Having a project directory is a good way to isolate your
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project.
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</para></listitem>
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<listitem><para><emphasis>Run Bitbake:</emphasis>
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At this point, you have nothing but a project directory.
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Run the <filename>bitbake</filename> command and see what
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it does:
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<literallayout class='monospaced'>
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$ bitbake
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The BBPATH variable is not set and bitbake did not
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find a conf/bblayers.conf file in the expected location.
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Maybe you accidentally invoked bitbake from the wrong directory?
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DEBUG: Removed the following variables from the environment:
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GNOME_DESKTOP_SESSION_ID, XDG_CURRENT_DESKTOP,
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GNOME_KEYRING_CONTROL, DISPLAY, SSH_AGENT_PID, LANG, no_proxy,
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XDG_SESSION_PATH, XAUTHORITY, SESSION_MANAGER, SHLVL,
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MANDATORY_PATH, COMPIZ_CONFIG_PROFILE, WINDOWID, EDITOR,
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GPG_AGENT_INFO, SSH_AUTH_SOCK, GDMSESSION, GNOME_KEYRING_PID,
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XDG_SEAT_PATH, XDG_CONFIG_DIRS, LESSOPEN, DBUS_SESSION_BUS_ADDRESS,
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_, XDG_SESSION_COOKIE, DESKTOP_SESSION, LESSCLOSE, DEFAULTS_PATH,
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UBUNTU_MENUPROXY, OLDPWD, XDG_DATA_DIRS, COLORTERM, LS_COLORS
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</literallayout>
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The majority of this output is specific to environment variables
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that are not directly relevant to BitBake.
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However, the very first message regarding the
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<filename>BBPATH</filename> variable and the
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<filename>conf/bblayers.conf</filename> file
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is relevant.</para>
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<para>
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When you run BitBake, it begins looking for metadata files.
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The
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<link linkend='var-BBPATH'><filename>BBPATH</filename></link>
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variable is what tells BitBake where to look for those files.
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<filename>BBPATH</filename> is not set and you need to set it.
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Without <filename>BBPATH</filename>, Bitbake cannot
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find any configuration files (<filename>.conf</filename>)
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or recipe files (<filename>.bb</filename>) at all.
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BitBake also cannot find the <filename>bitbake.conf</filename>
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file.
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</para></listitem>
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<listitem><para><emphasis>Setting <filename>BBPATH</filename>:</emphasis>
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For this example, you can set <filename>BBPATH</filename>
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in the same manner that you set <filename>PATH</filename>
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earlier in the appendix.
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You should realize, though, that it is much more flexible to set the
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<filename>BBPATH</filename> variable up in a configuration
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file for each project.</para>
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<para>From your shell, enter the following commands to set and
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export the <filename>BBPATH</filename> variable:
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<literallayout class='monospaced'>
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$ BBPATH="<replaceable>projectdirectory</replaceable>"
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$ export BBPATH
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</literallayout>
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Use your actual project directory in the command.
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BitBake uses that directory to find the metadata it needs for
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your project.
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<note>
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When specifying your project directory, do not use the
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tilde ("~") character as BitBake does not expand that character
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as the shell would.
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</note>
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</para></listitem>
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<listitem><para><emphasis>Run Bitbake:</emphasis>
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Now that you have <filename>BBPATH</filename> defined, run
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the <filename>bitbake</filename> command again:
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<literallayout class='monospaced'>
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$ bitbake
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ERROR: Traceback (most recent call last):
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File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 163, in wrapped
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return func(fn, *args)
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File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 173, in parse_config_file
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return bb.parse.handle(fn, data, include)
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File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 99, in handle
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return h['handle'](fn, data, include)
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File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 120, in handle
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abs_fn = resolve_file(fn, data)
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File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 117, in resolve_file
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raise IOError("file %s not found in %s" % (fn, bbpath))
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IOError: file conf/bitbake.conf not found in /home/scott-lenovo/hello
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ERROR: Unable to parse conf/bitbake.conf: file conf/bitbake.conf not found in /home/scott-lenovo/hello
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</literallayout>
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This sample output shows that BitBake could not find the
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<filename>conf/bitbake.conf</filename> file in the project
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directory.
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This file is the first thing BitBake must find in order
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to build a target.
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And, since the project directory for this example is
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empty, you need to provide a <filename>conf/bitbake.conf</filename>
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file.
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</para></listitem>
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<listitem><para><emphasis>Creating <filename>conf/bitbake.conf</filename>:</emphasis>
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The <filename>conf/bitbake.conf</filename> includes a number of
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configuration variables BitBake uses for metadata and recipe
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files.
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For this example, you need to create the file in your project directory
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and define some key BitBake variables.
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For more information on the <filename>bitbake.conf</filename>,
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see
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<ulink url='http://git.openembedded.org/bitbake/tree/conf/bitbake.conf'></ulink>.
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</para>
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<para>Use the following commands to create the <filename>conf</filename>
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directory in the project directory:
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<literallayout class='monospaced'>
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$ mkdir conf
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</literallayout>
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From within the <filename>conf</filename> directory, use
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some editor to create the <filename>bitbake.conf</filename>
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so that it contains the following:
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<literallayout class='monospaced'>
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TMPDIR = "${<link linkend='var-TOPDIR'>TOPDIR</link>}/tmp"
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<link linkend='var-CACHE'>CACHE</link> = "${TMPDIR}/cache"
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<link linkend='var-STAMP'>STAMP</link> = "${TMPDIR}/stamps"
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<link linkend='var-T'>T</link> = "${TMPDIR}/work"
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<link linkend='var-B'>B</link> = "${TMPDIR}"
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</literallayout>
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The <filename>TMPDIR</filename> variable establishes a directory
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that BitBake uses for build output and intermediate files (other
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than the cached information used by the
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<link linkend='setscene'>Setscene</link> process.
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Here, the <filename>TMPDIR</filename> directory is set to
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<filename>hello/tmp</filename>.
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<note><title>Tip</title>
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You can always safely delete the <filename>tmp</filename>
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directory in order to rebuild a BitBake target.
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The build process creates the directory for you
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when you run BitBake.
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</note></para>
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<para>For information about each of the other variables defined in this
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example, click on the links to take you to the definitions in
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the glossary.
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</para></listitem>
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<listitem><para><emphasis>Run Bitbake:</emphasis>
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After making sure that the <filename>conf/bitbake.conf</filename>
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file exists, you can run the <filename>bitbake</filename>
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command again:
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<literallayout class='monospaced'>
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$ bitbake
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ERROR: Traceback (most recent call last):
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File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 163, in wrapped
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return func(fn, *args)
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File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 177, in _inherit
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bb.parse.BBHandler.inherit(bbclass, "configuration INHERITs", 0, data)
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File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py", line 92, in inherit
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include(fn, file, lineno, d, "inherit")
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File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 100, in include
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raise ParseError("Could not %(error_out)s file %(fn)s" % vars(), oldfn, lineno)
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ParseError: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
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ERROR: Unable to parse base: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
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</literallayout>
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In the sample output, BitBake could not find the
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<filename>classes/base.bbclass</filename> file.
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You need to create that file next.
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</para></listitem>
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<listitem><para><emphasis>Creating <filename>classes/base.bbclass</filename>:</emphasis>
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BitBake uses class files to provide common code and functionality.
|
||
|
|
The minimally required class for BitBake is the
|
||
|
|
<filename>classes/base.bbclass</filename> file.
|
||
|
|
The <filename>base</filename> class is implicitly inherited by
|
||
|
|
every recipe.
|
||
|
|
BitBake looks for the class in the <filename>classes</filename>
|
||
|
|
directory of the project (i.e <filename>hello/classes</filename>
|
||
|
|
in this example).
|
||
|
|
</para>
|
||
|
|
<para>Create the <filename>classes</filename> directory as follows:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
$ cd $HOME/hello
|
||
|
|
$ mkdir classes
|
||
|
|
</literallayout>
|
||
|
|
Move to the <filename>classes</filename> directory and then
|
||
|
|
create the <filename>base.bbclass</filename> file by inserting
|
||
|
|
this single line:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
addtask build
|
||
|
|
</literallayout>
|
||
|
|
The minimal task that BitBake runs is the
|
||
|
|
<filename>do_build</filename> task.
|
||
|
|
This is all the example needs in order to build the project.
|
||
|
|
Of course, the <filename>base.bbclass</filename> can have much
|
||
|
|
more depending on which build environments BitBake is
|
||
|
|
supporting.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><emphasis>Run Bitbake:</emphasis>
|
||
|
|
After making sure that the <filename>classes/base.bbclass</filename>
|
||
|
|
file exists, you can run the <filename>bitbake</filename>
|
||
|
|
command again:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
$ bitbake
|
||
|
|
Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information.
|
||
|
|
</literallayout>
|
||
|
|
BitBake is finally reporting no errors.
|
||
|
|
However, you can see that it really does not have anything
|
||
|
|
to do.
|
||
|
|
You need to create a recipe that gives BitBake something to do.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><emphasis>Creating a Layer:</emphasis>
|
||
|
|
While it is not really necessary for such a small example,
|
||
|
|
it is good practice to create a layer in which to keep your
|
||
|
|
code separate from the general metadata used by BitBake.
|
||
|
|
Thus, this example creates and uses a layer called "mylayer".
|
||
|
|
<note>
|
||
|
|
You can find additional information on layers at
|
||
|
|
<ulink url='http://www.yoctoproject.org/docs/2.3/bitbake-user-manual/bitbake-user-manual.html#layers'></ulink>.
|
||
|
|
</note>
|
||
|
|
</para>
|
||
|
|
<para>Minimally, you need a recipe file and a layer configuration
|
||
|
|
file in your layer.
|
||
|
|
The configuration file needs to be in the <filename>conf</filename>
|
||
|
|
directory inside the layer.
|
||
|
|
Use these commands to set up the layer and the <filename>conf</filename>
|
||
|
|
directory:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
$ cd $HOME
|
||
|
|
$ mkdir mylayer
|
||
|
|
$ cd mylayer
|
||
|
|
$ mkdir conf
|
||
|
|
</literallayout>
|
||
|
|
Move to the <filename>conf</filename> directory and create a
|
||
|
|
<filename>layer.conf</filename> file that has the following:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
BBPATH .= ":${<link linkend='var-LAYERDIR'>LAYERDIR</link>}"
|
||
|
|
|
||
|
|
<link linkend='var-BBFILES'>BBFILES</link> += "${LAYERDIR}/*.bb"
|
||
|
|
|
||
|
|
<link linkend='var-BBFILE_COLLECTIONS'>BBFILE_COLLECTIONS</link> += "mylayer"
|
||
|
|
<link linkend='var-BBFILE_PATTERN'>BBFILE_PATTERN_mylayer</link> := "^${LAYERDIR_RE}/"
|
||
|
|
</literallayout>
|
||
|
|
For information on these variables, click the links
|
||
|
|
to go to the definitions in the glossary.</para>
|
||
|
|
<para>You need to create the recipe file next.
|
||
|
|
Inside your layer at the top-level, use an editor and create
|
||
|
|
a recipe file named <filename>printhello.bb</filename> that
|
||
|
|
has the following:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
<link linkend='var-DESCRIPTION'>DESCRIPTION</link> = "Prints Hello World"
|
||
|
|
<link linkend='var-PN'>PN</link> = 'printhello'
|
||
|
|
<link linkend='var-PV'>PV</link> = '1'
|
||
|
|
|
||
|
|
python do_build() {
|
||
|
|
bb.plain("********************");
|
||
|
|
bb.plain("* *");
|
||
|
|
bb.plain("* Hello, World! *");
|
||
|
|
bb.plain("* *");
|
||
|
|
bb.plain("********************");
|
||
|
|
}
|
||
|
|
</literallayout>
|
||
|
|
The recipe file simply provides a description of the
|
||
|
|
recipe, the name, version, and the <filename>do_build</filename>
|
||
|
|
task, which prints out "Hello World" to the console.
|
||
|
|
For more information on these variables, follow the links
|
||
|
|
to the glossary.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><emphasis>Run Bitbake With a Target:</emphasis>
|
||
|
|
Now that a BitBake target exists, run the command and provide
|
||
|
|
that target:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
$ cd $HOME/hello
|
||
|
|
$ bitbake printhello
|
||
|
|
ERROR: no recipe files to build, check your BBPATH and BBFILES?
|
||
|
|
|
||
|
|
Summary: There was 1 ERROR message shown, returning a non-zero exit code.
|
||
|
|
</literallayout>
|
||
|
|
We have created the layer with the recipe and the layer
|
||
|
|
configuration file but it still seems that BitBake cannot
|
||
|
|
find the recipe.
|
||
|
|
BitBake needs a <filename>conf/bblayers.conf</filename> that
|
||
|
|
lists the layers for the project.
|
||
|
|
Without this file, BitBake cannot find the recipe.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><emphasis>Creating <filename>conf/bblayers.conf</filename>:</emphasis>
|
||
|
|
BitBake uses the <filename>conf/bblayers.conf</filename> file
|
||
|
|
to locate layers needed for the project.
|
||
|
|
This file must reside in the <filename>conf</filename> directory
|
||
|
|
of the project (i.e. <filename>hello/conf</filename> for this
|
||
|
|
example).</para>
|
||
|
|
<para>Set your working directory to the <filename>hello/conf</filename>
|
||
|
|
directory and then create the <filename>bblayers.conf</filename>
|
||
|
|
file so that it contains the following:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
BBLAYERS ?= " \
|
||
|
|
/home/<you>/mylayer \
|
||
|
|
"
|
||
|
|
</literallayout>
|
||
|
|
You need to provide your own information for
|
||
|
|
<filename>you</filename> in the file.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><emphasis>Run Bitbake With a Target:</emphasis>
|
||
|
|
Now that you have supplied the <filename>bblayers.conf</filename>
|
||
|
|
file, run the <filename>bitbake</filename> command and provide
|
||
|
|
the target:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
$ bitbake printhello
|
||
|
|
Parsing recipes: 100% |##################################################################################|
|
||
|
|
Time: 00:00:00
|
||
|
|
Parsing of 1 .bb files complete (0 cached, 1 parsed). 1 targets, 0 skipped, 0 masked, 0 errors.
|
||
|
|
NOTE: Resolving any missing task queue dependencies
|
||
|
|
NOTE: Preparing RunQueue
|
||
|
|
NOTE: Executing RunQueue Tasks
|
||
|
|
********************
|
||
|
|
* *
|
||
|
|
* Hello, World! *
|
||
|
|
* *
|
||
|
|
********************
|
||
|
|
NOTE: Tasks Summary: Attempted 1 tasks of which 0 didn't need to be rerun and all succeeded.
|
||
|
|
</literallayout>
|
||
|
|
BitBake finds the <filename>printhello</filename> recipe and
|
||
|
|
successfully runs the task.
|
||
|
|
<note>
|
||
|
|
After the first execution, re-running
|
||
|
|
<filename>bitbake printhello</filename> again will not
|
||
|
|
result in a BitBake run that prints the same console
|
||
|
|
output.
|
||
|
|
The reason for this is that the first time the
|
||
|
|
<filename>printhello.bb</filename> recipe's
|
||
|
|
<filename>do_build</filename> task executes
|
||
|
|
successfully, BitBake writes a stamp file for the task.
|
||
|
|
Thus, the next time you attempt to run the task
|
||
|
|
using that same <filename>bitbake</filename> command,
|
||
|
|
BitBake notices the stamp and therefore determines
|
||
|
|
that the task does not need to be re-run.
|
||
|
|
If you delete the <filename>tmp</filename> directory
|
||
|
|
or run <filename>bitbake -c clean printhello</filename>
|
||
|
|
and then re-run the build, the "Hello, World!" message will
|
||
|
|
be printed again.
|
||
|
|
</note>
|
||
|
|
</para></listitem>
|
||
|
|
</orderedlist>
|
||
|
|
</section>
|
||
|
|
</appendix>
|