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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">
+
+<appendix id='hello-world-example'>
+ <title>Hello World Example</title>
+
+ <section id='bitbake-hello-world'>
+ <title>BitBake Hello World</title>
+
+ <para>
+ The simplest example commonly used to demonstrate any new
+ programming language or tool is the
+ "<ulink url="http://en.wikipedia.org/wiki/Hello_world_program">Hello World</ulink>"
+ example.
+ This appendix demonstrates, in tutorial form, Hello
+ World within the context of BitBake.
+ The tutorial describes how to create a new project
+ and the applicable metadata files necessary to allow
+ BitBake to build it.
+ </para>
+ </section>
+
+ <section id='example-obtaining-bitbake'>
+ <title>Obtaining BitBake</title>
+
+ <para>
+ See the
+ "<link linkend='obtaining-bitbake'>Obtaining BitBake</link>"
+ section for information on how to obtain BitBake.
+ Once you have the source code on your machine, the BitBake directory
+ appears as follows:
+ <literallayout class='monospaced'>
+ $ ls -al
+ total 100
+ drwxrwxr-x. 9 wmat wmat 4096 Jan 31 13:44 .
+ drwxrwxr-x. 3 wmat wmat 4096 Feb 4 10:45 ..
+ -rw-rw-r--. 1 wmat wmat 365 Nov 26 04:55 AUTHORS
+ drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 bin
+ drwxrwxr-x. 4 wmat wmat 4096 Jan 31 13:44 build
+ -rw-rw-r--. 1 wmat wmat 16501 Nov 26 04:55 ChangeLog
+ drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 classes
+ drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 conf
+ drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 contrib
+ -rw-rw-r--. 1 wmat wmat 17987 Nov 26 04:55 COPYING
+ drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 doc
+ -rw-rw-r--. 1 wmat wmat 69 Nov 26 04:55 .gitignore
+ -rw-rw-r--. 1 wmat wmat 849 Nov 26 04:55 HEADER
+ drwxrwxr-x. 5 wmat wmat 4096 Jan 31 13:44 lib
+ -rw-rw-r--. 1 wmat wmat 195 Nov 26 04:55 MANIFEST.in
+ -rw-rw-r--. 1 wmat wmat 2887 Nov 26 04:55 TODO
+ </literallayout>
+ </para>
+
+ <para>
+ At this point, you should have BitBake cloned to
+ a directory that matches the previous listing except for
+ dates and user names.
+ </para>
+ </section>
+
+ <section id='setting-up-the-bitbake-environment'>
+ <title>Setting Up the BitBake Environment</title>
+
+ <para>
+ First, you need to be sure that you can run BitBake.
+ Set your working directory to where your local BitBake
+ files are and run the following command:
+ <literallayout class='monospaced'>
+ $ ./bin/bitbake --version
+ BitBake Build Tool Core version 1.23.0, bitbake version 1.23.0
+ </literallayout>
+ The console output tells you what version you are running.
+ </para>
+
+ <para>
+ The recommended method to run BitBake is from a directory of your
+ choice.
+ To be able to run BitBake from any directory, you need to add the
+ executable binary to your binary to your shell's environment
+ <filename>PATH</filename> variable.
+ First, look at your current <filename>PATH</filename> variable
+ by entering the following:
+ <literallayout class='monospaced'>
+ $ echo $PATH
+ </literallayout>
+ Next, add the directory location for the BitBake binary to the
+ <filename>PATH</filename>.
+ Here is an example that adds the
+ <filename>/home/scott-lenovo/bitbake/bin</filename> directory
+ to the front of the <filename>PATH</filename> variable:
+ <literallayout class='monospaced'>
+ $ export PATH=/home/scott-lenovo/bitbake/bin:$PATH
+ </literallayout>
+ You should now be able to enter the <filename>bitbake</filename>
+ command from the command line while working from any directory.
+ </para>
+ </section>
+
+ <section id='the-hello-world-example'>
+ <title>The Hello World Example</title>
+
+ <para>
+ The overall goal of this exercise is to build a
+ complete "Hello World" example utilizing task and layer
+ concepts.
+ Because this is how modern projects such as OpenEmbedded and
+ the Yocto Project utilize BitBake, the example
+ provides an excellent starting point for understanding
+ BitBake.
+ </para>
+
+ <para>
+ To help you understand how to use BitBake to build targets,
+ the example starts with nothing but the <filename>bitbake</filename>
+ command, which causes BitBake to fail and report problems.
+ The example progresses by adding pieces to the build to
+ eventually conclude with a working, minimal "Hello World"
+ example.
+ </para>
+
+ <para>
+ While every attempt is made to explain what is happening during
+ the example, the descriptions cannot cover everything.
+ You can find further information throughout this manual.
+ Also, you can actively participate in the
+ <ulink url='http://lists.openembedded.org/mailman/listinfo/bitbake-devel'></ulink>
+ discussion mailing list about the BitBake build tool.
+ </para>
+
+ <note>
+ This example was inspired by and drew heavily from
+ <ulink url="http://www.mail-archive.com/yocto@yoctoproject.org/msg09379.html">Mailing List post - The BitBake equivalent of "Hello, World!"</ulink>.
+ </note>
+
+ <para>
+ As stated earlier, the goal of this example
+ is to eventually compile "Hello World".
+ However, it is unknown what BitBake needs and what you have
+ to provide in order to achieve that goal.
+ Recall that BitBake utilizes three types of metadata files:
+ <link linkend='configuration-files'>Configuration Files</link>,
+ <link linkend='classes'>Classes</link>, and
+ <link linkend='recipes'>Recipes</link>.
+ But where do they go?
+ How does BitBake find them?
+ BitBake's error messaging helps you answer these types of questions
+ and helps you better understand exactly what is going on.
+ </para>
+
+ <para>
+ Following is the complete "Hello World" example.
+ </para>
+
+ <orderedlist>
+ <listitem><para><emphasis>Create a Project Directory:</emphasis>
+ First, set up a directory for the "Hello World" project.
+ Here is how you can do so in your home directory:
+ <literallayout class='monospaced'>
+ $ mkdir ~/hello
+ $ cd ~/hello
+ </literallayout>
+ This is the directory that BitBake will use to do all of
+ its work.
+ You can use this directory to keep all the metafiles needed
+ by BitBake.
+ Having a project directory is a good way to isolate your
+ project.
+ </para></listitem>
+ <listitem><para><emphasis>Run Bitbake:</emphasis>
+ At this point, you have nothing but a project directory.
+ Run the <filename>bitbake</filename> command and see what
+ it does:
+ <literallayout class='monospaced'>
+ $ bitbake
+ The BBPATH variable is not set and bitbake did not
+ find a conf/bblayers.conf file in the expected location.
+ Maybe you accidentally invoked bitbake from the wrong directory?
+ DEBUG: Removed the following variables from the environment:
+ GNOME_DESKTOP_SESSION_ID, XDG_CURRENT_DESKTOP,
+ GNOME_KEYRING_CONTROL, DISPLAY, SSH_AGENT_PID, LANG, no_proxy,
+ XDG_SESSION_PATH, XAUTHORITY, SESSION_MANAGER, SHLVL,
+ MANDATORY_PATH, COMPIZ_CONFIG_PROFILE, WINDOWID, EDITOR,
+ GPG_AGENT_INFO, SSH_AUTH_SOCK, GDMSESSION, GNOME_KEYRING_PID,
+ XDG_SEAT_PATH, XDG_CONFIG_DIRS, LESSOPEN, DBUS_SESSION_BUS_ADDRESS,
+ _, XDG_SESSION_COOKIE, DESKTOP_SESSION, LESSCLOSE, DEFAULTS_PATH,
+ UBUNTU_MENUPROXY, OLDPWD, XDG_DATA_DIRS, COLORTERM, LS_COLORS
+ </literallayout>
+ The majority of this output is specific to environment variables
+ that are not directly relevant to BitBake.
+ However, the very first message regarding the
+ <filename>BBPATH</filename> variable and the
+ <filename>conf/bblayers.conf</filename> file
+ is relevant.</para>
+ <para>
+ When you run BitBake, it begins looking for metadata files.
+ The
+ <link linkend='var-BBPATH'><filename>BBPATH</filename></link>
+ variable is what tells BitBake where to look for those files.
+ <filename>BBPATH</filename> is not set and you need to set it.
+ Without <filename>BBPATH</filename>, Bitbake cannot
+ find any configuration files (<filename>.conf</filename>)
+ or recipe files (<filename>.bb</filename>) at all.
+ BitBake also cannot find the <filename>bitbake.conf</filename>
+ file.
+ </para></listitem>
+ <listitem><para><emphasis>Setting <filename>BBPATH</filename>:</emphasis>
+ For this example, you can set <filename>BBPATH</filename>
+ in the same manner that you set <filename>PATH</filename>
+ earlier in the appendix.
+ You should realize, though, that it is much more flexible to set the
+ <filename>BBPATH</filename> variable up in a configuration
+ file for each project.</para>
+ <para>From your shell, enter the following commands to set and
+ export the <filename>BBPATH</filename> variable:
+ <literallayout class='monospaced'>
+ $ BBPATH="<replaceable>projectdirectory</replaceable>"
+ $ export BBPATH
+ </literallayout>
+ Use your actual project directory in the command.
+ BitBake uses that directory to find the metadata it needs for
+ your project.
+ <note>
+ When specifying your project directory, do not use the
+ tilde ("~") character as BitBake does not expand that character
+ as the shell would.
+ </note>
+ </para></listitem>
+ <listitem><para><emphasis>Run Bitbake:</emphasis>
+ Now that you have <filename>BBPATH</filename> defined, run
+ the <filename>bitbake</filename> command again:
+ <literallayout class='monospaced'>
+ $ bitbake
+ ERROR: Traceback (most recent call last):
+ File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 163, in wrapped
+ return func(fn, *args)
+ File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 173, in parse_config_file
+ return bb.parse.handle(fn, data, include)
+ File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 99, in handle
+ return h['handle'](fn, data, include)
+ File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 120, in handle
+ abs_fn = resolve_file(fn, data)
+ File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 117, in resolve_file
+ raise IOError("file %s not found in %s" % (fn, bbpath))
+ IOError: file conf/bitbake.conf not found in /home/scott-lenovo/hello
+
+ ERROR: Unable to parse conf/bitbake.conf: file conf/bitbake.conf not found in /home/scott-lenovo/hello
+ </literallayout>
+ This sample output shows that BitBake could not find the
+ <filename>conf/bitbake.conf</filename> file in the project
+ directory.
+ This file is the first thing BitBake must find in order
+ to build a target.
+ And, since the project directory for this example is
+ empty, you need to provide a <filename>conf/bitbake.conf</filename>
+ file.
+ </para></listitem>
+ <listitem><para><emphasis>Creating <filename>conf/bitbake.conf</filename>:</emphasis>
+ The <filename>conf/bitbake.conf</filename> includes a number of
+ configuration variables BitBake uses for metadata and recipe
+ files.
+ For this example, you need to create the file in your project directory
+ and define some key BitBake variables.
+ For more information on the <filename>bitbake.conf</filename> file,
+ see
+ <ulink url='http://git.openembedded.org/bitbake/tree/conf/bitbake.conf'></ulink>.
+ </para>
+ <para>Use the following commands to create the <filename>conf</filename>
+ directory in the project directory:
+ <literallayout class='monospaced'>
+ $ mkdir conf
+ </literallayout>
+ From within the <filename>conf</filename> directory, use
+ some editor to create the <filename>bitbake.conf</filename>
+ so that it contains the following:
+ <literallayout class='monospaced'>
+ <link linkend='var-PN'>PN</link> = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}"
+ </literallayout>
+ <literallayout class='monospaced'>
+ TMPDIR = "${<link linkend='var-TOPDIR'>TOPDIR</link>}/tmp"
+ <link linkend='var-CACHE'>CACHE</link> = "${TMPDIR}/cache"
+ <link linkend='var-STAMP'>STAMP</link> = "${TMPDIR}/${PN}/stamps"
+ <link linkend='var-T'>T</link> = "${TMPDIR}/${PN}/work"
+ <link linkend='var-B'>B</link> = "${TMPDIR}/${PN}"
+ </literallayout>
+ <note>
+ Without a value for <filename>PN</filename>, the
+ variables <filename>STAMP</filename>,
+ <filename>T</filename>, and <filename>B</filename>,
+ prevent more than one recipe from working. You can fix
+ this by either setting <filename>PN</filename> to have
+ a value similar to what OpenEmbedded and BitBake use
+ in the default <filename>bitbake.conf</filename> file
+ (see previous example). Or, by manually updating each
+ recipe to set <filename>PN</filename>. You will also
+ need to include <filename>PN</filename> as part of the
+ <filename>STAMP</filename>, <filename>T</filename>, and
+ <filename>B</filename> variable definitions in the
+ <filename>local.conf</filename> file.
+ </note>
+ The <filename>TMPDIR</filename> variable establishes a directory
+ that BitBake uses for build output and intermediate files other
+ than the cached information used by the
+ <link linkend='setscene'>Setscene</link> process.
+ Here, the <filename>TMPDIR</filename> directory is set to
+ <filename>hello/tmp</filename>.
+ <note><title>Tip</title>
+ You can always safely delete the <filename>tmp</filename>
+ directory in order to rebuild a BitBake target.
+ The build process creates the directory for you
+ when you run BitBake.
+ </note></para>
+ <para>For information about each of the other variables defined in this
+ example, click on the links to take you to the definitions in
+ the glossary.
+ </para></listitem>
+ <listitem><para><emphasis>Run Bitbake:</emphasis>
+ After making sure that the <filename>conf/bitbake.conf</filename>
+ file exists, you can run the <filename>bitbake</filename>
+ command again:
+ <literallayout class='monospaced'>
+ $ bitbake
+ ERROR: Traceback (most recent call last):
+ File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 163, in wrapped
+ return func(fn, *args)
+ File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 177, in _inherit
+ bb.parse.BBHandler.inherit(bbclass, "configuration INHERITs", 0, data)
+ File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py", line 92, in inherit
+ include(fn, file, lineno, d, "inherit")
+ File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 100, in include
+ raise ParseError("Could not %(error_out)s file %(fn)s" % vars(), oldfn, lineno)
+ ParseError: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
+
+ ERROR: Unable to parse base: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
+ </literallayout>
+ In the sample output, BitBake could not find the
+ <filename>classes/base.bbclass</filename> file.
+ You need to create that file next.
+ </para></listitem>
+ <listitem><para><emphasis>Creating <filename>classes/base.bbclass</filename>:</emphasis>
+ 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 in the
+ "<link linkend='layers'>Layers</link>" section.
+ </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/&lt;you&gt;/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>