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Andrew Geisslerc9f78652020-09-18 14:11:35 -05001.. SPDX-License-Identifier: CC-BY-2.5
2
3===================
4Hello World Example
5===================
6
7BitBake Hello World
8===================
9
10The simplest example commonly used to demonstrate any new programming
11language or tool is the "`Hello
12World <http://en.wikipedia.org/wiki/Hello_world_program>`__" example.
13This appendix demonstrates, in tutorial form, Hello World within the
14context of BitBake. The tutorial describes how to create a new project
15and the applicable metadata files necessary to allow BitBake to build
16it.
17
18Obtaining BitBake
19=================
20
21See the :ref:`bitbake-user-manual/bitbake-user-manual-hello:obtaining bitbake` section for
22information on how to obtain BitBake. Once you have the source code on
23your machine, the BitBake directory appears as follows: ::
24
25 $ ls -al
26 total 100
27 drwxrwxr-x. 9 wmat wmat 4096 Jan 31 13:44 .
28 drwxrwxr-x. 3 wmat wmat 4096 Feb 4 10:45 ..
29 -rw-rw-r--. 1 wmat wmat 365 Nov 26 04:55 AUTHORS
30 drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 bin
31 drwxrwxr-x. 4 wmat wmat 4096 Jan 31 13:44 build
32 -rw-rw-r--. 1 wmat wmat 16501 Nov 26 04:55 ChangeLog
33 drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 classes
34 drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 conf
35 drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 contrib
36 -rw-rw-r--. 1 wmat wmat 17987 Nov 26 04:55 COPYING
37 drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 doc
38 -rw-rw-r--. 1 wmat wmat 69 Nov 26 04:55 .gitignore
39 -rw-rw-r--. 1 wmat wmat 849 Nov 26 04:55 HEADER
40 drwxrwxr-x. 5 wmat wmat 4096 Jan 31 13:44 lib
41 -rw-rw-r--. 1 wmat wmat 195 Nov 26 04:55 MANIFEST.in
42 -rw-rw-r--. 1 wmat wmat 2887 Nov 26 04:55 TODO
43
44At this point, you should have BitBake cloned to a directory that
45matches the previous listing except for dates and user names.
46
47Setting Up the BitBake Environment
48==================================
49
50First, you need to be sure that you can run BitBake. Set your working
51directory to where your local BitBake files are and run the following
52command: ::
53
54 $ ./bin/bitbake --version
55 BitBake Build Tool Core version 1.23.0, bitbake version 1.23.0
56
57The console output tells you what version
58you are running.
59
60The recommended method to run BitBake is from a directory of your
61choice. To be able to run BitBake from any directory, you need to add
62the executable binary to your binary to your shell's environment
63``PATH`` variable. First, look at your current ``PATH`` variable by
64entering the following: ::
65
66 $ echo $PATH
67
68Next, add the directory location
69for the BitBake binary to the ``PATH``. Here is an example that adds the
70``/home/scott-lenovo/bitbake/bin`` directory to the front of the
71``PATH`` variable: ::
72
73 $ export PATH=/home/scott-lenovo/bitbake/bin:$PATH
74
75You should now be able to enter the ``bitbake`` command from the command
76line while working from any directory.
77
78The Hello World Example
79=======================
80
81The overall goal of this exercise is to build a complete "Hello World"
82example utilizing task and layer concepts. Because this is how modern
83projects such as OpenEmbedded and the Yocto Project utilize BitBake, the
84example provides an excellent starting point for understanding BitBake.
85
86To help you understand how to use BitBake to build targets, the example
87starts with nothing but the ``bitbake`` command, which causes BitBake to
88fail and report problems. The example progresses by adding pieces to the
89build to eventually conclude with a working, minimal "Hello World"
90example.
91
92While every attempt is made to explain what is happening during the
93example, the descriptions cannot cover everything. You can find further
94information throughout this manual. Also, you can actively participate
95in the :oe_lists:`/g/bitbake-devel`
96discussion mailing list about the BitBake build tool.
97
98.. note::
99
100 This example was inspired by and drew heavily from
101 `Mailing List post - The BitBake equivalent of "Hello, World!"
102 <http://www.mail-archive.com/yocto@yoctoproject.org/msg09379.html>`_.
103
104As stated earlier, the goal of this example is to eventually compile
105"Hello World". However, it is unknown what BitBake needs and what you
106have to provide in order to achieve that goal. Recall that BitBake
107utilizes three types of metadata files:
108:ref:`bitbake-user-manual/bitbake-user-manual-intro:configuration files`,
109:ref:`bitbake-user-manual/bitbake-user-manual-intro:classes`, and
110:ref:`bitbake-user-manual/bitbake-user-manual-intro:recipes`.
111But where do they go? How does BitBake find
112them? BitBake's error messaging helps you answer these types of
113questions and helps you better understand exactly what is going on.
114
115Following is the complete "Hello World" example.
116
117#. **Create a Project Directory:** First, set up a directory for the
118 "Hello World" project. Here is how you can do so in your home
119 directory: ::
120
121 $ mkdir ~/hello
122 $ cd ~/hello
123
124 This is the directory that
125 BitBake will use to do all of its work. You can use this directory
126 to keep all the metafiles needed by BitBake. Having a project
127 directory is a good way to isolate your project.
128
129#. **Run BitBake:** At this point, you have nothing but a project
130 directory. Run the ``bitbake`` command and see what it does: ::
131
132 $ bitbake
133 The BBPATH variable is not set and bitbake did not
134 find a conf/bblayers.conf file in the expected location.
135 Maybe you accidentally invoked bitbake from the wrong directory?
136 DEBUG: Removed the following variables from the environment:
137 GNOME_DESKTOP_SESSION_ID, XDG_CURRENT_DESKTOP,
138 GNOME_KEYRING_CONTROL, DISPLAY, SSH_AGENT_PID, LANG, no_proxy,
139 XDG_SESSION_PATH, XAUTHORITY, SESSION_MANAGER, SHLVL,
140 MANDATORY_PATH, COMPIZ_CONFIG_PROFILE, WINDOWID, EDITOR,
141 GPG_AGENT_INFO, SSH_AUTH_SOCK, GDMSESSION, GNOME_KEYRING_PID,
142 XDG_SEAT_PATH, XDG_CONFIG_DIRS, LESSOPEN, DBUS_SESSION_BUS_ADDRESS,
143 _, XDG_SESSION_COOKIE, DESKTOP_SESSION, LESSCLOSE, DEFAULTS_PATH,
144 UBUNTU_MENUPROXY, OLDPWD, XDG_DATA_DIRS, COLORTERM, LS_COLORS
145
146 The majority of this output is specific to environment variables that
147 are not directly relevant to BitBake. However, the very first
148 message regarding the ``BBPATH`` variable and the
149 ``conf/bblayers.conf`` file is relevant.
150
151 When you run BitBake, it begins looking for metadata files. The
152 :term:`BBPATH` variable is what tells BitBake where
153 to look for those files. ``BBPATH`` is not set and you need to set
154 it. Without ``BBPATH``, BitBake cannot find any configuration files
155 (``.conf``) or recipe files (``.bb``) at all. BitBake also cannot
156 find the ``bitbake.conf`` file.
157
158#. **Setting BBPATH:** For this example, you can set ``BBPATH`` in
159 the same manner that you set ``PATH`` earlier in the appendix. You
160 should realize, though, that it is much more flexible to set the
161 ``BBPATH`` variable up in a configuration file for each project.
162
163 From your shell, enter the following commands to set and export the
164 ``BBPATH`` variable: ::
165
166 $ BBPATH="projectdirectory"
167 $ export BBPATH
168
169 Use your actual project directory in the command. BitBake uses that
170 directory to find the metadata it needs for your project.
171
172 .. note::
173
174 When specifying your project directory, do not use the tilde
175 ("~") character as BitBake does not expand that character as the
176 shell would.
177
178#. **Run BitBake:** Now that you have ``BBPATH`` defined, run the
179 ``bitbake`` command again: ::
180
181 $ bitbake
182 ERROR: Traceback (most recent call last):
183 File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 163, in wrapped
184 return func(fn, *args)
185 File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 173, in parse_config_file
186 return bb.parse.handle(fn, data, include)
187 File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 99, in handle
188 return h['handle'](fn, data, include)
189 File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 120, in handle
190 abs_fn = resolve_file(fn, data)
191 File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 117, in resolve_file
192 raise IOError("file %s not found in %s" % (fn, bbpath))
193 IOError: file conf/bitbake.conf not found in /home/scott-lenovo/hello
194
195 ERROR: Unable to parse conf/bitbake.conf: file conf/bitbake.conf not found in /home/scott-lenovo/hello
196
197 This sample output shows that BitBake could not find the
198 ``conf/bitbake.conf`` file in the project directory. This file is
199 the first thing BitBake must find in order to build a target. And,
200 since the project directory for this example is empty, you need to
201 provide a ``conf/bitbake.conf`` file.
202
203#. **Creating conf/bitbake.conf:** The ``conf/bitbake.conf`` includes
204 a number of configuration variables BitBake uses for metadata and
205 recipe files. For this example, you need to create the file in your
206 project directory and define some key BitBake variables. For more
207 information on the ``bitbake.conf`` file, see
208 http://git.openembedded.org/bitbake/tree/conf/bitbake.conf.
209
210 Use the following commands to create the ``conf`` directory in the
211 project directory: ::
212
213 $ mkdir conf
214
215 From within the ``conf`` directory,
216 use some editor to create the ``bitbake.conf`` so that it contains
217 the following: ::
218
219 PN = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}"
220
221 TMPDIR = "${TOPDIR}/tmp"
222 CACHE = "${TMPDIR}/cache"
223 STAMP = "${TMPDIR}/${PN}/stamps"
224 T = "${TMPDIR}/${PN}/work"
225 B = "${TMPDIR}/${PN}"
226
227 .. note::
228
229 Without a value for PN , the variables STAMP , T , and B , prevent more
230 than one recipe from working. You can fix this by either setting PN to
231 have a value similar to what OpenEmbedded and BitBake use in the default
232 bitbake.conf file (see previous example). Or, by manually updating each
233 recipe to set PN . You will also need to include PN as part of the STAMP
234 , T , and B variable definitions in the local.conf file.
235
236 The ``TMPDIR`` variable establishes a directory that BitBake uses
237 for build output and intermediate files other than the cached
238 information used by the
239 :ref:`bitbake-user-manual/bitbake-user-manual-execution:setscene`
240 process. Here, the ``TMPDIR`` directory is set to ``hello/tmp``.
241
242 .. tip::
243
244 You can always safely delete the tmp directory in order to rebuild a
245 BitBake target. The build process creates the directory for you when you
246 run BitBake.
247
248 For information about each of the other variables defined in this
249 example, check :term:`PN`, :term:`TOPDIR`, :term:`CACHE`, :term:`STAMP`,
250 :term:`T` or :term:`B` to take you to the definitions in the
251 glossary.
252
253#. **Run BitBake:** After making sure that the ``conf/bitbake.conf`` file
254 exists, you can run the ``bitbake`` command again: ::
255
256 $ bitbake
257 ERROR: Traceback (most recent call last):
258 File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 163, in wrapped
259 return func(fn, *args)
260 File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 177, in _inherit
261 bb.parse.BBHandler.inherit(bbclass, "configuration INHERITs", 0, data)
262 File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py", line 92, in inherit
263 include(fn, file, lineno, d, "inherit")
264 File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 100, in include
265 raise ParseError("Could not %(error_out)s file %(fn)s" % vars(), oldfn, lineno)
266 ParseError: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
267
268 ERROR: Unable to parse base: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
269
270 In the sample output,
271 BitBake could not find the ``classes/base.bbclass`` file. You need
272 to create that file next.
273
274#. **Creating classes/base.bbclass:** BitBake uses class files to
275 provide common code and functionality. The minimally required class
276 for BitBake is the ``classes/base.bbclass`` file. The ``base`` class
277 is implicitly inherited by every recipe. BitBake looks for the class
278 in the ``classes`` directory of the project (i.e ``hello/classes``
279 in this example).
280
281 Create the ``classes`` directory as follows: ::
282
283 $ cd $HOME/hello
284 $ mkdir classes
285
286 Move to the ``classes`` directory and then create the
287 ``base.bbclass`` file by inserting this single line: addtask build
288 The minimal task that BitBake runs is the ``do_build`` task. This is
289 all the example needs in order to build the project. Of course, the
290 ``base.bbclass`` can have much more depending on which build
291 environments BitBake is supporting.
292
293#. **Run BitBake:** After making sure that the ``classes/base.bbclass``
294 file exists, you can run the ``bitbake`` command again: ::
295
296 $ bitbake
297 Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information.
298
299 BitBake is finally reporting
300 no errors. However, you can see that it really does not have
301 anything to do. You need to create a recipe that gives BitBake
302 something to do.
303
304#. **Creating a Layer:** While it is not really necessary for such a
305 small example, it is good practice to create a layer in which to
306 keep your code separate from the general metadata used by BitBake.
307 Thus, this example creates and uses a layer called "mylayer".
308
309 .. note::
310
311 You can find additional information on layers in the
312 ":ref:`bitbake-user-manual/bitbake-user-manual-intro:Layers`" section.
313
314 Minimally, you need a recipe file and a layer configuration file in
315 your layer. The configuration file needs to be in the ``conf``
316 directory inside the layer. Use these commands to set up the layer
317 and the ``conf`` directory: ::
318
319 $ cd $HOME
320 $ mkdir mylayer
321 $ cd mylayer
322 $ mkdir conf
323
324 Move to the ``conf`` directory and create a ``layer.conf`` file that has the
325 following: ::
326
327 BBPATH .= ":${LAYERDIR}"
328 BBFILES += "${LAYERDIR}/\*.bb"
329 BBFILE_COLLECTIONS += "mylayer"
330 `BBFILE_PATTERN_mylayer := "^${LAYERDIR_RE}/"
331
332 For information on these variables, click on :term:`BBFILES`,
333 :term:`LAYERDIR`, :term:`BBFILE_COLLECTIONS` or :term:`BBFILE_PATTERN_mylayer <BBFILE_PATTERN>`
334 to go to the definitions in the glossary.
335
336 You need to create the recipe file next. Inside your layer at the
337 top-level, use an editor and create a recipe file named
338 ``printhello.bb`` that has the following: ::
339
340 DESCRIPTION = "Prints Hello World"
341 PN = 'printhello'
342 PV = '1'
343
344 python do_build() {
345 bb.plain("********************");
346 bb.plain("* *");
347 bb.plain("* Hello, World! *");
348 bb.plain("* *");
349 bb.plain("********************");
350 }
351
352 The recipe file simply provides
353 a description of the recipe, the name, version, and the ``do_build``
354 task, which prints out "Hello World" to the console. For more
355 information on :term:`DESCRIPTION`, :term:`PN` or :term:`PV`
356 follow the links to the glossary.
357
358#. **Run BitBake With a Target:** Now that a BitBake target exists, run
359 the command and provide that target: ::
360
361 $ cd $HOME/hello
362 $ bitbake printhello
363 ERROR: no recipe files to build, check your BBPATH and BBFILES?
364
365 Summary: There was 1 ERROR message shown, returning a non-zero exit code.
366
367 We have created the layer with the recipe and
368 the layer configuration file but it still seems that BitBake cannot
369 find the recipe. BitBake needs a ``conf/bblayers.conf`` that lists
370 the layers for the project. Without this file, BitBake cannot find
371 the recipe.
372
373#. **Creating conf/bblayers.conf:** BitBake uses the
374 ``conf/bblayers.conf`` file to locate layers needed for the project.
375 This file must reside in the ``conf`` directory of the project (i.e.
376 ``hello/conf`` for this example).
377
378 Set your working directory to the ``hello/conf`` directory and then
379 create the ``bblayers.conf`` file so that it contains the following: ::
380
381 BBLAYERS ?= " \
382 /home/<you>/mylayer \
383 "
384
385 You need to provide your own information for ``you`` in the file.
386
387#. **Run BitBake With a Target:** Now that you have supplied the
388 ``bblayers.conf`` file, run the ``bitbake`` command and provide the
389 target: ::
390
391 $ bitbake printhello
392 Parsing recipes: 100% |##################################################################################|
393 Time: 00:00:00
394 Parsing of 1 .bb files complete (0 cached, 1 parsed). 1 targets, 0 skipped, 0 masked, 0 errors.
395 NOTE: Resolving any missing task queue dependencies
396 NOTE: Preparing RunQueue
397 NOTE: Executing RunQueue Tasks
398 ********************
399 * *
400 * Hello, World! *
401 * *
402 ********************
403 NOTE: Tasks Summary: Attempted 1 tasks of which 0 didn't need to be rerun and all succeeded.
404
405 .. note::
406
407 After the first execution, re-running bitbake printhello again will not
408 result in a BitBake run that prints the same console output. The reason
409 for this is that the first time the printhello.bb recipe's do_build task
410 executes successfully, BitBake writes a stamp file for the task. Thus,
411 the next time you attempt to run the task using that same bitbake
412 command, BitBake notices the stamp and therefore determines that the task
413 does not need to be re-run. If you delete the tmp directory or run
414 bitbake -c clean printhello and then re-run the build, the "Hello,
415 World!" message will be printed again.