Hello World Example
BitBake Hello World The simplest example commonly used to demonstrate any new programming language or tool is the "Hello World" 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.
Obtaining BitBake See the "Obtaining BitBake" section for information on how to obtain BitBake. Once you have the source code on your machine, the BitBake directory appears as follows: $ 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 -rwxrwxr-x. 1 wmat wmat 3195 Jan 31 11:57 setup.py -rw-rw-r--. 1 wmat wmat 2887 Nov 26 04:55 TODO At this point, you should have BitBake cloned to a directory that matches the previous listing except for dates and user names.
Setting Up the BitBake Environment 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: $ ./bin/bitbake --version BitBake Build Tool Core version 1.23.0, bitbake version 1.23.0 The console output tells you what version you are running. 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 PATH variable. First, look at your current PATH variable by entering the following: $ echo $PATH Next, add the directory location for the BitBake binary to the PATH. Here is an example that adds the /home/scott-lenovo/bitbake/bin directory to the front of the PATH variable: $ export PATH=/home/scott-lenovo/bitbake/bin:$PATH You should now be able to enter the bitbake command from the command line while working from any directory. For a more permanent solution, assuming you are running the BASH shell, edit ~/.bashrc and add the following to the end of that file: PATH=<path-to-bitbake-executable>:$PATH If you're a Vim user, you will find useful Vim configuration contributions in the contrib/vim directory. Copy the files from that directory to your /home/yourusername/.vim directory. If that directory does not exist, create it, and then restart Vim.
The Hello World Example The following example leaps directly into how BitBake works. While every attempt is made to explain what is happening, not everything can be covered. You can find further information in the "Syntax and Operators" chapter. 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. It should be noted that this chapter was inspired by and draws heavily from several sources: Mailing List post - The BitBake equivalent of "Hello, World!" Hambedded Linux blog post - From Bitbake Hello World to an Image
A Reverse Walk-Through A good way to understand anything is to walk through the steps that take you to where you want to be and observe first principles. BitBake allows us to do this through the -D or Debug command-line parameter. The goal is to eventually compile a "Hello World" example. However, it is unknown what is needed to achieve that goal. Recall that BitBake utilizes three types of metadata files: Configuration Files, Classes, and Recipes. 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. First, set up a directory for the "Hello World" project. Here is how you can do so in your home directory: $ mkdir ~/hello $ cd ~/hello Within this new, empty directory, run BitBake with debugging output and see what happens: $ bitbake -DDD 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, DEFAULTS_PATH, XDG_SEAT_PATH, XDG_CONFIG_DIRS, LESSOPEN, DBUS_SESSION_BUS_ADDRESS, _, XDG_SESSION_COOKIE, DESKTOP_SESSION, LESSCLOSE, GNOME_KEYRING_PID, UBUNTU_MENUPROXY, OLDPWD, XDG_DATA_DIRS, COLORTERM, LS_COLORS The majority of this output is specific to environment variables that are not directly relevant to BitBake. However, the very first message regarding the BBPATH variable and the conf/bblayers.conf file is relevant. 1. Once you have PATH set up to actually run BB, and then you run it using: bitbake -DDD You get these complaints: 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? 2. If you export BBPATH to point to your build directory and do nothing else, BB will look for the <buildir>/conf/bitbake.conf file. It will throw and error with a bunch of traceback stuff and say: scott-lenovo@scott-lenovo:~ [master #] $ mkdir junk scott-lenovo@scott-lenovo:~ [master #] $ BBPATH="/home/scott-lenovo/junk" scott-lenovo@scott-lenovo:~ [master #] $ export BBPATH scott-lenovo@scott-lenovo:~ [master #] $ bitbake -DDD 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/junk ERROR: Unable to parse conf/bitbake.conf: file conf/bitbake.conf not found in /home/scott-lenovo/junk scott-lenovo@scott-lenovo:~ [master #] 3. Now I am going to create the conf/bitbake.conf file I need for the hello world example. Then run it again. Time it complains about not finding classes/base.bbclass. scott-lenovo@scott-lenovo:~/junk [master #] $ bitbake -DDD 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 scott-lenovo@scott-lenovo:~/junk [master #] 4. So now we add that classes/base.bbclass file and put in one line that says "addtask build", which is the minimum task you need. We run it again and things work but there is nothing to do. That stands to reason since I gave it no target. scott-lenovo@scott-lenovo:~/junk [master #] $ bitbake -DDD Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information. 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 DEBUG: LOAD /home/scott-lenovo/junk/conf/bitbake.conf DEBUG: BB configuration INHERITs:0: inheriting /home/scott-lenovo/junk/classes/base.bbclass DEBUG: BB /home/scott-lenovo/junk/classes/base.bbclass: handle(data, include) DEBUG: LOAD /home/scott-lenovo/junk/classes/base.bbclass DEBUG: Clearing SRCREV cache due to cache policy of: clear DEBUG: Using cache in '/home/scott-lenovo/junk/tmp/cache/local_file_checksum_cache.dat' DEBUG: Using cache in '/home/scott-lenovo/junk/tmp/cache/bb_codeparser.dat' DEBUG: Features set [3] (was [3]) scott-lenovo@scott-lenovo:~/junk [master #] 5. Here is what happens when you do provide a target but the target doesn't exist yet. scott-lenovo@scott-lenovo:~/junk [master #] $ bitbake a ERROR: no recipe files to build, check your BBPATH and BBFILES? Summary: There was 1 ERROR message shown, returning a non-zero exit code. scott-lenovo@scott-lenovo:~/junk [master #] 6. Create a layer that has your metadata in it. You need your recipe file and your layer.conf file. That is all good but you still need to tell BB where your layers are. You do that through a bblayers.conf file. We will use this one: BBLAYERS ?=" \ /home/scott-lenovo/LayerA \ " Now when you run it, you get this: $ bitbake -DDD a 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 DEBUG: Found bblayers.conf (/home/scott-lenovo/junk/conf/bblayers.conf) DEBUG: LOAD /home/scott-lenovo/junk/conf/bblayers.conf DEBUG: Adding layer /home/scott-lenovo/LayerA DEBUG: LOAD /home/scott-lenovo/LayerA/conf/layer.conf DEBUG: LOAD /home/scott-lenovo/junk/conf/bitbake.conf DEBUG: BB configuration INHERITs:0: inheriting /home/scott-lenovo/junk/classes/base.bbclass DEBUG: BB /home/scott-lenovo/junk/classes/base.bbclass: handle(data, include) DEBUG: LOAD /home/scott-lenovo/junk/classes/base.bbclass DEBUG: Clearing SRCREV cache due to cache policy of: clear DEBUG: Using cache in '/home/scott-lenovo/junk/tmp/cache/local_file_checksum_cache.dat' DEBUG: Using cache in '/home/scott-lenovo/junk/tmp/cache/bb_codeparser.dat' DEBUG: Features set [3] (was [3]) DEBUG: Calculated priority of layer A as 1 DEBUG: collecting .bb files DEBUG: Using cache in '/home/scott-lenovo/junk/tmp/cache' DEBUG: Cache: /home/scott-lenovo/LayerA/a.bb is not cached DEBUG: BB /home/scott-lenovo/LayerA/a.bb: handle(data) | ETA: --:--:-- DEBUG: LOAD /home/scott-lenovo/LayerA/a.bb 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. DEBUG: parsing complete DEBUG: providers for a are: ['a'] DEBUG: sorted providers for a are: ['/home/scott-lenovo/LayerA/a.bb'] DEBUG: adding /home/scott-lenovo/LayerA/a.bb to satisfy a DEBUG: Added dependencies [] for /home/scott-lenovo/LayerA/a.bb NOTE: Resolving any missing task queue dependencies DEBUG: Resolved 0 extra dependencies NOTE: Preparing runqueue NOTE: Marking Active Tasks NOTE: Pruned 0 inactive tasks, 1 left NOTE: Assign Weightings NOTE: Compute totals (have 1 endpoint(s)) DEBUG: Starting bitbake-worker NOTE: Executing RunQueue Tasks DEBUG: Considering 0 (/home/scott-lenovo/LayerA/a.bb, do_build): set([]) DEBUG: Skip list (pre setsceneverify) [] DEBUG: Full skip list set([]) DEBUG: Using runqueue scheduler 'speed' DEBUG: Stampfile /home/scott-lenovo/junk/tmp/stamps.do_build not available DEBUG: Found bblayers.conf (/home/scott-lenovo/junk/conf/bblayers.conf) DEBUG: LOAD /home/scott-lenovo/junk/conf/bblayers.conf DEBUG: Adding layer /home/scott-lenovo/LayerA DEBUG: LOAD /home/scott-lenovo/LayerA/conf/layer.conf DEBUG: LOAD /home/scott-lenovo/junk/conf/bitbake.conf DEBUG: BB configuration INHERITs:0: inheriting /home/scott-lenovo/junk/classes/base.bbclass DEBUG: BB /home/scott-lenovo/junk/classes/base.bbclass: handle(data, include) DEBUG: LOAD /home/scott-lenovo/junk/classes/base.bbclass DEBUG: Using cache in '/home/scott-lenovo/junk/tmp/cache/bb_codeparser.dat' ************************ * * * Hello, World! * * * ************************ DEBUG: Teardown for bitbake-worker NOTE: Tasks Summary: Attempted 1 tasks of which 0 didn't need to be rerun and all succeeded. scott-lenovo@scott-lenovo:~/junk/conf [master #] 7. If you run it without the "-DDD" option, the output is cleaner. scott-lenovo@scott-lenovo:~/junk [master #] $ bitbake a 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. scott-lenovo@scott-lenovo:~/junk [master #] You need to set BBPATH. When you run BitBake, it begins looking for metadata files. The BBPATH variable is what tells BitBake where to look. You could set BBPATH in the same manner that you set PATH as shown earlier. However, it is much more flexible to set the BBPATH variable for each project. Without BBPATH, Bitbake cannot find any configuration files (.conf) or recipe files (.bb) at all. BitBake also cannot find the bitbake.conf file. It is standard practice to organize the project's directory tree to include both a conf/ and classes/ directory. You need to add those directories to your project: $ mkdir conf classes Once those directories are in place, you can copy the sample configuration files provided in the BitBake source tree to their appropriate directories. First, change to the BitBake source tree directory and then copy the directories: cp conf/bitbake.conf ~/dev/hello/conf/ cp classes/base.bbclass ~/dev/hello/classes/ At this point your project directory structure should look like the following: ~/dev/hello$ tree . |-- classes |   +-- base.bbclass +-- conf +-- bitbake.conf Once you have copied these files into your project, you can now get back to resolving the BBPATH issue. The first configuration file that BitBake looks for is always bblayers.conf. With this knowledge, you know that to resolve your BBPATH error you can add a conf/bblayers.conf file to the project source tree and populate it with the BBPATH variable declaration. From your project source tree: $ vim conf/bblayers.conf Now add the following to the empty bblayers.conf file: BBPATH := "${TOPDIR}" Now, from the root of your project directory, run BitBake again and see what happens: $ bitbake -DDD Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information. 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, DEFAULTS_PATH, XDG_SEAT_PATH, XDG_CONFIG_DIRS, LESSOPEN, DBUS_SESSION_BUS_ADDRESS, _, XDG_SESSION_COOKIE, DESKTOP_SESSION, LESSCLOSE, GNOME_KEYRING_PID, UBUNTU_MENUPROXY, OLDPWD, XDG_DATA_DIRS, COLORTERM, LS_COLORS DEBUG: Found bblayers.conf (/home/scott-lenovo/dev/hello/conf/bblayers.conf) DEBUG: LOAD /home/scott-lenovo/dev/hello/conf/bblayers.conf DEBUG: LOAD /home/scott-lenovo/dev/hello/conf/bitbake.conf DEBUG: BB configuration INHERITs:0: inheriting /home/scott-lenovo/dev/hello/classes/base.bbclass DEBUG: BB /home/scott-lenovo/dev/hello/classes/base.bbclass: handle(data, include) DEBUG: LOAD /home/scott-lenovo/dev/hello/classes/base.bbclass DEBUG: Clearing SRCREV cache due to cache policy of: clear DEBUG: Using cache in '/home/scott-lenovo/dev/hello/tmp/cache/local_file_checksum_cache.dat' DEBUG: Using cache in '/home/scott-lenovo/dev/hello/tmp/cache/bb_codeparser.dat' DEBUG: Features set [3] (was [3]) From this point forward in the example, the environment variable removal messages are ignored and omitted. Examine the relevant DEBUG messages: