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bitbake: bitbake-user-manual-hello.xml: First draft of "Hello World" appendix

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Fixes [YOCTO #1973]

Added the complete "Hello World" appendix first draft beyond
what Bill Traynor had supplied.

(Bitbake rev: 176baaf3d0f033091f5ab9d9cfb2cec3d25a5442)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2014-04-15 14:06:21 -07:00
committed by Richard Purdie
parent 4687351d16
commit 61a680fb5d
1 changed files with 334 additions and 327 deletions
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661
bitbake/doc/bitbake-user-manual/bitbake-user-manual-hello.xml
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@@ -120,16 +120,6 @@
<section id='the-hello-world-example'>
<title>The Hello World Example</title>
<para>
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
"<link linkend='bitbake-user-manual-metadata'>Syntax and Operators</link>"
chapter.
</para>
<para>
The overall goal of this exercise is to build a
complete "Hello World" example utilizing task and layer
@@ -141,8 +131,25 @@
</para>
<para>
It should be noted that this chapter was inspired by
and draws heavily from several sources:
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 these sources:
<itemizedlist>
<listitem><para>
<ulink url="http://www.mail-archive.com/yocto@yoctoproject.org/msg09379.html">Mailing List post - The BitBake equivalent of "Hello, World!"</ulink>
@@ -151,114 +158,177 @@
<ulink url="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>
</para></listitem>
</itemizedlist>
</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>
<section id='a-reverse-walk-through'>
<title>A Reverse Walk-Through</title>
<para>
Following is the complete "Hello World" example.
</para>
<para>
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
<filename>-D</filename> or <filename>Debug</filename>
command-line parameter.
</para>
<para>
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:
<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>
<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>
Within this new, empty directory, run BitBake with
debugging output and see what happens:
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 -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?
$ 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,
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
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>
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'>
1. Once you have PATH set up to actually run BB, and then you run it
using:
$ BBPATH="&lt;projectdirectory&gt;"
$ 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
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 &lt;buildir&gt;/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: 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>,
see
<ulink url='http://hambedded.org/blog/2012/11/24/from-bitbake-hello-world-to-an-image/#an-overview-of-bitbakeconf'></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'>
TMPDIR = "${<link linkend='var-TOPDIR'>TOPDIR</link>}/tmp"
<link linkend='var-CACHE'>CACHE</link> = "${TMPDIR}/cache"
<link linkend='var-STAMP'>STAMP</link> = "${TMPDIR}/stamps"
<link linkend='var-T'>T</link> = "${TMPDIR}/work"
<link linkend='var-B'>B</link> = "${TMPDIR}"
</literallayout>
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)
@@ -271,241 +341,178 @@ ERROR: Traceback (most recent call last):
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 #]
</literallayout>
</para>
<para>
You need to set
<link linkend='var-BBPATH'><filename>BBPATH</filename></link>.
</para>
<para>
When you run BitBake, it begins looking for metadata files.
The <filename>BBPATH</filename> variable is what tells
BitBake where to look.
You could set <filename>BBPATH</filename> in the same manner
that you set <filename>PATH</filename> as shown earlier.
However, it is much more flexible to set the
<link linkend='var-BBPATH'><filename>BBPATH</filename></link>
variable for each project.
</para>
<para>
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>
<para>
It is standard practice to organize the project's directory tree
to include both a <filename>conf/</filename> and
<filename>classes/</filename> directory.
You need to add those directories to your project:
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'>
$ mkdir conf classes
$ cd $HOME/hello
$ mkdir classes
</literallayout>
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:
Move to the <filename>classes</filename> directory and then
create the <filename>base.bbclass</filename> file by inserting
this single line:
<literallayout class='monospaced'>
cp conf/bitbake.conf ~/dev/hello/conf/
cp classes/base.bbclass ~/dev/hello/classes/
addtask build
</literallayout>
At this point your project directory structure should look like
the following:
<literallayout class='monospaced'>
~/dev/hello$ tree
.
|-- classes
|   +-- base.bbclass
+-- conf
+-- bitbake.conf
</literallayout>
</para>
<para>
Once you have copied these files into your project, you
can now get back to resolving the <filename>BBPATH</filename>
issue.
</para>
<para>
The first configuration file that BitBake looks for is always
<filename>bblayers.conf</filename>.
With this knowledge, you know that to resolve your
<filename>BBPATH</filename> error you can add a
<filename>conf/bblayers.conf</filename> file to the
project source tree and populate it with the
<filename>BBPATH</filename> variable declaration.
</para>
<para>
From your project source tree:
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.
For more information on the <filename>base.bbclass</filename> file,
you can look at
<ulink url='http://hambedded.org/blog/2012/11/24/from-bitbake-hello-world-to-an-image/#tasks'></ulink>.
</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'>
$ vim conf/bblayers.conf
</literallayout>
Now add the following to the empty
<filename>bblayers.conf</filename> file:
<literallayout class='monospaced'>
BBPATH := "${TOPDIR}"
</literallayout>
</para>
<para>
Now, from the root of your project directory, run BitBake
again and see what happens:
<literallayout class='monospaced'>
$ 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])
$ 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>
From this point forward in the example, the environment
variable removal messages are ignored and omitted.
Examine the relevant DEBUG messages:
You can find additional information on adding a layer at
<ulink url='http://hambedded.org/blog/2012/11/24/from-bitbake-hello-world-to-an-image/#adding-an-example-layer'></ulink>.
</note>
</para>
</section>
</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}/"
</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>
Rerunning the task without removing the <filename>tmp</filename>
directory will not result in a BitBake run that prints the
same console output.
BitBake uses its Setscene process and determines that
nothing needs to be re-run.
If you delete the <filename>tmp</filename> directory and
then re-run the build, the printed output appears
at the console.
</note>
</para></listitem>
</orderedlist>
</section>
</appendix>