mirror of
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8615d47a3a
Fixes [YOCTO #12399] The bug was to get the BitBake User Manual into the YP Mega-manual. All the changes here create unique tags used with variables in the BitBake Manual. Prior to the fix, tags were identical between like variables in the YP reference manual and the BitBake User Manual. The reason for this is because when I created the BitBake manual's glossary, it was a cut-and-paste operation to get the bulk of the work started. At the time, the BitBake User Manual was not a part of the Mega-manual. Once we decided to include the BitBake User Manual as part of the Mega-Manual, building the mega-manual produced warnings for all these duplicate links. To fix, I have updated the variable tags in the BitBake User Manual to use the following form: 'var-bb-<variable_name>' The tags used in the YP ref-manual follow this form (original): 'var-<variable_name>' (Bitbake rev: fb6de2057aae3fbdf37f007d2e47794b332020e1) Signed-off-by: Scott Rifenbark <srifenbark@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
514 lines
26 KiB
XML
514 lines
26 KiB
XML
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<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-bb-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> file,
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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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<link linkend='var-bb-PN'>PN</link> = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}"
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</literallayout>
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<literallayout class='monospaced'>
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TMPDIR = "${<link linkend='var-bb-TOPDIR'>TOPDIR</link>}/tmp"
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<link linkend='var-bb-CACHE'>CACHE</link> = "${TMPDIR}/cache"
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<link linkend='var-bb-STAMP'>STAMP</link> = "${TMPDIR}/${PN}/stamps"
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<link linkend='var-bb-T'>T</link> = "${TMPDIR}/${PN}/work"
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<link linkend='var-bb-B'>B</link> = "${TMPDIR}/${PN}"
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</literallayout>
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<note>
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Without a value for <filename>PN</filename>, the
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variables <filename>STAMP</filename>,
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<filename>T</filename>, and <filename>B</filename>,
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prevent more than one recipe from working. You can fix
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this by either setting <filename>PN</filename> to have
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a value similar to what OpenEmbedded and BitBake use
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in the default <filename>bitbake.conf</filename> file
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(see previous example). Or, by manually updating each
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recipe to set <filename>PN</filename>. You will also
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need to include <filename>PN</filename> as part of the
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<filename>STAMP</filename>, <filename>T</filename>, and
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<filename>B</filename> variable definitions in the
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<filename>local.conf</filename> file.
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</note>
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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.
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The minimally required class for BitBake is the
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<filename>classes/base.bbclass</filename> file.
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The <filename>base</filename> class is implicitly inherited by
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every recipe.
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BitBake looks for the class in the <filename>classes</filename>
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directory of the project (i.e <filename>hello/classes</filename>
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in this example).
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</para>
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<para>Create the <filename>classes</filename> directory as follows:
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<literallayout class='monospaced'>
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$ cd $HOME/hello
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$ mkdir classes
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</literallayout>
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Move to the <filename>classes</filename> directory and then
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create the <filename>base.bbclass</filename> file by inserting
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this single line:
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<literallayout class='monospaced'>
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addtask build
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</literallayout>
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The minimal task that BitBake runs is the
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<filename>do_build</filename> task.
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This is all the example needs in order to build the project.
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Of course, the <filename>base.bbclass</filename> can have much
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more depending on which build environments BitBake is
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supporting.
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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>classes/base.bbclass</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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Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information.
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</literallayout>
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BitBake is finally reporting no errors.
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However, you can see that it really does not have anything
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to do.
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You need to create a recipe that gives BitBake something to do.
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</para></listitem>
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<listitem><para><emphasis>Creating a Layer:</emphasis>
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While it is not really necessary for such a small example,
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it is good practice to create a layer in which to keep your
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code separate from the general metadata used by BitBake.
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Thus, this example creates and uses a layer called "mylayer".
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<note>
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You can find additional information on layers in the
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"<link linkend='layers'>Layers</link>" section.
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</note></para>
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<para>Minimally, you need a recipe file and a layer configuration
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file in your layer.
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The configuration file needs to be in the <filename>conf</filename>
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directory inside the layer.
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Use these commands to set up the layer and the <filename>conf</filename>
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directory:
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<literallayout class='monospaced'>
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$ cd $HOME
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$ mkdir mylayer
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$ cd mylayer
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$ mkdir conf
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</literallayout>
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Move to the <filename>conf</filename> directory and create a
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<filename>layer.conf</filename> file that has the following:
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<literallayout class='monospaced'>
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BBPATH .= ":${<link linkend='var-bb-LAYERDIR'>LAYERDIR</link>}"
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<link linkend='var-bb-BBFILES'>BBFILES</link> += "${LAYERDIR}/*.bb"
|
|
|
|
<link linkend='var-bb-BBFILE_COLLECTIONS'>BBFILE_COLLECTIONS</link> += "mylayer"
|
|
<link linkend='var-bb-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-bb-DESCRIPTION'>DESCRIPTION</link> = "Prints Hello World"
|
|
<link linkend='var-bb-PN'>PN</link> = 'printhello'
|
|
<link linkend='var-bb-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>
|