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1<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
2"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
3
4<appendix id='hello-world-example'>
5 <title>Hello World Example</title>
6
7 <section id='bitbake-hello-world'>
8 <title>BitBake Hello World</title>
9
10 <para>
11 The simplest example commonly used to demonstrate any new
12 programming language or tool is the
13 <ulink url="http://en.wikipedia.org/wiki/Hello_world_program">Hello World</ulink>
14 example.
15 This appendix demonstrates, in tutorial form, Hello
16 World within the context of BitBake.
17 The tutorial describes how to create a new Project
18 and the applicable metadata files necessary to allow
19 BitBake to build it.
20 </para>
21 </section>
22
23 <section id='example-obtaining-bitbake'>
24 <title>Obtaining BitBake</title>
25
26 <para>
27 See the
28 "<link linkend='obtaining-bitbake'>Obtaining BitBake</link>"
29 section for information on how to obtain BitBake.
30 Once you have the source code on your machine, the BitBake directory
31 appears as follows:
32 <literallayout class='monospaced'>
33 $ ls -al
34 total 100
35 drwxrwxr-x. 9 wmat wmat 4096 Jan 31 13:44 .
36 drwxrwxr-x. 3 wmat wmat 4096 Feb 4 10:45 ..
37 -rw-rw-r--. 1 wmat wmat 365 Nov 26 04:55 AUTHORS
38 drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 bin
39 drwxrwxr-x. 4 wmat wmat 4096 Jan 31 13:44 build
40 -rw-rw-r--. 1 wmat wmat 16501 Nov 26 04:55 ChangeLog
41 drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 classes
42 drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 conf
43 drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 contrib
44 -rw-rw-r--. 1 wmat wmat 17987 Nov 26 04:55 COPYING
45 drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 doc
46 -rw-rw-r--. 1 wmat wmat 69 Nov 26 04:55 .gitignore
47 -rw-rw-r--. 1 wmat wmat 849 Nov 26 04:55 HEADER
48 drwxrwxr-x. 5 wmat wmat 4096 Jan 31 13:44 lib
49 -rw-rw-r--. 1 wmat wmat 195 Nov 26 04:55 MANIFEST.in
50 -rwxrwxr-x. 1 wmat wmat 3195 Jan 31 11:57 setup.py
51 -rw-rw-r--. 1 wmat wmat 2887 Nov 26 04:55 TODO
52 </literallayout>
53 </para>
54
55 <para>
56 At this point, you should have BitBake cloned to
57 a directory that matches the previous listing except for
58 dates and user names.
59 </para>
60 </section>
61
62 <section id='setting-up-the-bitbake-environment'>
63 <title>Setting Up the BitBake Environment</title>
64
65 <para>
66 The recommended method to run BitBake is from a directory of your
67 choice.
68 The directory can be within your home directory or in
69 <filename>/usr/local</filename>,
70 depending on your preference.
71 </para>
72
73 <para>
74 First, run BitBake to make sure it's working.
75 From the BitBake source code directory, issue the following command:
76 <literallayout class='monospaced'>
77 $ ./bin/bitbake --version
78 BitBake Build Tool Core version 1.19.0, bitbake version
79 1.19.0
80 </literallayout>
81 You are now ready to use BitBake.
82 </para>
83
84 <para>
85 A final step to make development easier is to add the executable
86 binary to your environment <filename>PATH</filename>.
87 First, look at your current <filename>PATH</filename> variable
88 by entering the following:
89 <literallayout class='monospaced'>
90 $ echo $PATH
91 </literallayout>
92 Next, add the directory location for the BitBake binary to the
93 <filename>PATH</filename> using this form:
94 <literallayout class='monospaced'>
95 $ export PATH=&lt;path-to-bitbake-executable&gt;:$PATH
96 </literallayout>
97 This will add the directory to the beginning of your
98 <filename>PATH</filename> environment variable.
99 You should now be able to enter the <filename>bitbake</filename>
100 command at the command line to run BitBake.
101 </para>
102
103 <para>
104 For a more permanent solution assuming you are running the BASH
105 shell, edit <filename>~/.bashrc</filename> and add the following to the end
106 of that file:
107 <literallayout class='monospaced'>
108 PATH=&lt;path-to-bitbake-executable&gt;:$PATH
109 </literallayout>
110 </para>
111
112 <para>
113 If you're a Vim user, you will find useful
114 Vim configuration contributions in the
115 <filename>contrib/vim</filename> directory.
116 Copy the files from that directory to your
117 <filename>/home/yourusername/.vim</filename>
118 directory.
119 If that directory does not exist, create it, and then
120 restart Vim.
121 </para>
122 </section>
123
124 <section id='the-hello-world-example'>
125 <title>The Hello World Example</title>
126
127 <para>
128 The following example leaps directly into how BitBake
129 works.
130 While every attempt is made to explain what is happening,
131 not everything can be covered.
132 You can find further information in the
133 "<link linkend='user-manual-metadata'>Syntax and Operators</link>"
134 chapter.
135 </para>
136
137 <para>
138 The overall goal of this exercise is to build a
139 complete "Hello World" example utilizing task and layer
140 concepts.
141 This is how modern projects such as OpenEmbedded and
142 the Yocto Project utilize BitBake, therefore it
143 provides an excellent starting point for understanding
144 BitBake.
145 </para>
146
147 <para>
148 It should be noted that this chapter was inspired by
149 and draws heavily from several sources:
150 <itemizedlist>
151 <listitem><para>
152 <ulink href="http://www.mail-archive.com/yocto@yoctoproject.org/msg09379.html">Mailing List post - The BitBake equivalent of "Hello, World!"</ulink>
153 </para></listitem>
154 <listitem><para>
155 <ulink href="http://hambedded.org/blog/2012/11/24/from-bitbake-hello-world-to-an-image/">Hambedded Linux blog post - From Bitbake Hello World to an Image</ulink>
156 </para></listitem>
157 </itemizedlist>
158 </para>
159
160 <section id='a-reverse-walk-through'>
161 <title>A Reverse Walk-Through</title>
162
163 <para>
164 A good way to understand anything is to walk through the steps
165 that take you to where you want to be and observe first
166 principles.
167 BitBake allows us to do this through the
168 <filename>-D</filename> or <filename>Debug</filename>
169 command-line parameter.
170 </para>
171
172 <para>
173 The goal is to eventually compile a "Hello World" example.
174 However, it is unknown what is needed to achieve that goal.
175 Recall that BitBake utilizes three types of metadata files:
176 <link linkend='configuration-files'>Configuration Files</link>,
177 <link linkend='classes'>Classes</link>, and
178 <link linkend='recipes'>Recipes</link>.
179 But where do they go?
180 How does BitBake find them?
181 BitBake's error messaging helps you answer these types of questions
182 and helps you better understand exactly what is going on.
183 </para>
184
185 <para>
186 First, set up a directory for the "Hello World" project.
187 Here is how you can do so in your home directory:
188 <literallayout class='monospaced'>
189 $ mkdir ~/dev/hello &amp;&amp; cd ~/dev/hello
190 </literallayout>
191 Within this new, empty directory, run BitBake with
192 debugging output and see what happens:
193 <literallayout class='monospaced'>
194 $ bitbake -DDD
195 The BBPATH variable is not set
196 DEBUG: Removed the following variables from the environment:
197 GNOME_DESKTOP_SESSION_ID, LESSOPEN, WINDOWID,
198 GNOME_KEYRING_CONTROL, DISPLAY, SSH_AGENT_PID, LANG,
199 XDG_SESSION_PATH, XAUTHORITY, LANGUAGE, SESSION_MANAGER,
200 SHLVL, MANDATORY_PATH, COMPIZ_CONFIG_PROFILE, TEXTDOMAIN,
201 GPG_AGENT_INFO, SSH_AUTH_SOCK, XDG_RUNTIME_DIR,
202 COMPIZ_BIN_PATH, GDMSESSION, DEFAULTS_PATH, TEXTDOMAINDIR,
203 XDG_SEAT_PATH, XDG_CONFIG_DIRS, XDG_CURRENT_DESKTOP,
204 DBUS_SESSION_BUS_ADDRESS, _, XDG_SESSION_COOKIE,
205 DESKTOP_SESSION, LESSCLOSE, GNOME_KEYRING_PID,
206 UBUNTU_MENUPROXY, OLDPWD, GTK_MODULES, XDG_DATA_DIRS,
207 COLORTERM, LS_COLORS
208 </literallayout>
209 The majority of this output is specific to environment variables
210 that are not directly relevant to BitBake.
211 However, the very first message
212 "<filename>The BBPATH variable is not set</filename>"
213 is relevant and you need to rectify it by setting
214 <link linkend='var-BBPATH'><filename>BBPATH</filename></link>.
215 </para>
216
217 <para>
218 When you run BitBake, it begins looking for metadata files.
219 The <filename>BBPATH</filename> variable is what tells
220 BitBake where to look.
221 You could set <filename>BBPATH</filename> in the same manner
222 that you set <filename>PATH</filename> as shown earlier.
223 However, it is much more flexible to set the
224 <link linkend='var-BBPATH'><filename>BBPATH</filename></link>
225 variable for each project.
226 </para>
227
228 <para>
229 Without <filename>BBPATH</filename>, Bitbake cannot
230 find any configuration files (<filename>.conf</filename>)
231 or recipe files (<filename>.bb</filename>) at all.
232 BitBake also cannot find the <filename>bitbake.conf</filename>
233 file.
234 </para>
235
236 <para>
237 It is standard practice to organize the project's directory tree
238 to include both a <filename>conf/</filename> and
239 <filename>classes/</filename> directory.
240 You need to add those directories to your project:
241 <literallayout class='monospaced'>
242 $ mkdir conf classes
243 </literallayout>
244 Once those directories are in place, you can copy the
245 sample configuration files provided in the
246 BitBake source tree to their appropriate directories.
247 First, change to the BitBake source tree directory and
248 then copy the directories:
249 <literallayout class='monospaced'>
250 cp conf/bitbake.conf ~/dev/hello/conf/
251 cp classes/base.bbclass ~/dev/hello/classes/
252 </literallayout>
253 At this point your project directory structure should look like
254 the following:
255 <literallayout class='monospaced'>
256 ~/dev/hello$ tree
257 .
258 |-- classes
259 |   +-- base.bbclass
260 +-- conf
261 +-- bitbake.conf
262 </literallayout>
263 </para>
264
265 <para>
266 Once you have copied these files into your project, you
267 can now get back to resolving the <filename>BBPATH</filename>
268 issue.
269 </para>
270
271 <para>
272 The first configuration file that BitBake looks for is always
273 <filename>bblayers.conf</filename>.
274 With this knowledge, you know that to resolve your
275 <filename>BBPATH</filename> error you can add a
276 <filename>conf/bblayers.conf</filename> file to the
277 project source tree and populate it with the
278 <filename>BBPATH</filename> variable declaration.
279 </para>
280
281 <para>
282 From your project source tree:
283 <literallayout class='monospaced'>
284 $ vim conf/bblayers.conf
285 </literallayout>
286 Now add the following to the empty
287 <filename>bblayers.conf</filename> file:
288 <literallayout class='monospaced'>
289 BBPATH := "${TOPDIR}"
290 </literallayout>
291 </para>
292
293 <para>
294 Now, from the root of your project directory, run BitBake
295 again and see what happens:
296 <literallayout class='monospaced'>
297 $ bitbake -DDD
298 Nothing to do. Use 'bitbake world' to build everything, or run
299 'bitbake --help' for usage information.
300 DEBUG: Removed the following variables from the environment:
301 GNOME_DESKTOP_SESSION_ID, LESSOPEN, WINDOWID,
302 GNOME_KEYRING_CONTROL, DISPLAY, SSH_AGENT_PID, LANG,
303 XDG_SESSION_PATH, XAUTHORITY, LANGUAGE, SESSION_MANAGER,
304 SHLVL, MANDATORY_PATH, COMPIZ_CONFIG_PROFILE, TEXTDOMAIN,
305 GPG_AGENT_INFO, SSH_AUTH_SOCK, XDG_RUNTIME_DIR,
306 COMPIZ_BIN_PATH, GDMSESSION, DEFAULTS_PATH, TEXTDOMAINDIR,
307 XDG_SEAT_PATH, XDG_CONFIG_DIRS, XDG_CURRENT_DESKTOP,
308 DBUS_SESSION_BUS_ADDRESS, _, XDG_SESSION_COOKIE,
309 DESKTOP_SESSION, LESSCLOSE, GNOME_KEYRING_PID, UBUNTU_MENUPROXY,
310 OLDPWD, GTK_MODULES, XDG_DATA_DIRS, COLORTERM, LS_COLORS
311 DEBUG: Found bblayers.conf (/home/wmat/dev/hello/conf/
312 bblayers.conf)
313 DEBUG: LOAD /home/wmat/dev/hello/conf/bblayers.conf
314 DEBUG: LOAD /home/wmat/dev/hello/conf/bitbake.conf
315 DEBUG: BB configuration INHERITs:0: inheriting /home/wmat/dev/
316 hello/classes/base.bbclass
317 DEBUG: BB /home/wmat/dev/hello/classes/base.bbclass: handle
318 (data, include)
319 DEBUG: LOAD /home/wmat/dev/hello/classes/base.bbclass
320 DEBUG: Clearing SRCREV cache due to cache policy of: clear
321 DEBUG: Using cache in '/home/wmat/dev/hello/tmp/cache/
322 local_file_checksum_cache.dat'
323 DEBUG: Using cache in '/home/wmat/dev/hello/tmp/cache/
324 bb_codeparser.dat'
325 </literallayout>
326 <note>
327 From this point forward in the example, the environment
328 variable removal messages are ignored and omitted.
329 Examine the relevant DEBUG messages:
330 </note>
331 </para>
332 </section>
333 </section>
334</appendix>
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