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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">
+
+<chapter id="bitbake-user-manual-metadata">
+ <title>Syntax and Operators</title>
+
+ <para>
+ Bitbake files have their own syntax.
+ The syntax has similarities to several
+ other languages but also has some unique features.
+ This section describes the available syntax and operators
+ as well as provides examples.
+ </para>
+
+ <section id='basic-syntax'>
+ <title>Basic Syntax</title>
+
+ <para>
+ This section provides some basic syntax examples.
+ </para>
+
+ <section id='basic-variable-setting'>
+ <title>Basic Variable Setting</title>
+
+ <para>
+ The following example sets <filename>VARIABLE</filename> to
+ "value".
+ This assignment occurs immediately as the statement is parsed.
+ It is a "hard" assignment.
+ <literallayout class='monospaced'>
+ VARIABLE = "value"
+ </literallayout>
+ As expected, if you include leading or trailing spaces as part of
+ an assignment, the spaces are retained:
+ <literallayout class='monospaced'>
+ VARIABLE = " value"
+ VARIABLE = "value "
+ </literallayout>
+ Setting <filename>VARIABLE</filename> to "" sets it to an empty string,
+ while setting the variable to " " sets it to a blank space
+ (i.e. these are not the same values).
+ <literallayout class='monospaced'>
+ VARIABLE = ""
+ VARIABLE = " "
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='variable-expansion'>
+ <title>Variable Expansion</title>
+
+ <para>
+ BitBake supports variables referencing one another's
+ contents using a syntax that is similar to shell scripting.
+ Following is an example that results in <filename>A</filename>
+ containing "aval" and <filename>B</filename> evaluating to
+ "preavalpost" based on that current value of
+ <filename>A</filename>.
+ <literallayout class='monospaced'>
+ A = "aval"
+ B = "pre${A}post"
+ </literallayout>
+ You should realize that whenever <filename>B</filename> is
+ referenced, its evaluation will depend on the state of
+ <filename>A</filename> at that time.
+ Thus, later evaluations of <filename>B</filename> in the
+ previous example could result in different values
+ depending on the value of <filename>A</filename>.
+ </para>
+ </section>
+
+ <section id='setting-a-default-value'>
+ <title>Setting a default value (?=)</title>
+
+ <para>
+ You can use the "?=" operator to achieve a "softer" assignment
+ for a variable.
+ This type of assignment allows you to define a variable if it
+ is undefined when the statement is parsed, but to leave the
+ value alone if the variable has a value.
+ Here is an example:
+ <literallayout class='monospaced'>
+ A ?= "aval"
+ </literallayout>
+ If <filename>A</filename> is set at the time this statement is parsed,
+ the variable retains its value.
+ However, if <filename>A</filename> is not set,
+ the variable is set to "aval".
+ <note>
+ This assignment is immediate.
+ Consequently, if multiple "?=" assignments
+ to a single variable exist, the first of those ends up getting
+ used.
+ </note>
+ </para>
+ </section>
+
+ <section id='setting-a-weak-default-value'>
+ <title>Setting a weak default value (??=)</title>
+
+ <para>
+ It is possible to use a "weaker" assignment than in the
+ previous section by using the "??=" operator.
+ This assignment behaves identical to "?=" except that the
+ assignment is made at the end of the parsing process rather
+ than immediately.
+ Consequently, when multiple "??=" assignments exist, the last
+ one is used.
+ Also, any "=" or "?=" assignment will override the value set with
+ "??=".
+ Here is an example:
+ <literallayout class='monospaced'>
+ A ??= "somevalue"
+ A ??= "someothervalue"
+ </literallayout>
+ If <filename>A</filename> is set before the above statements are parsed,
+ the variable retains its value.
+ If <filename>A</filename> is not set,
+ the variable is set to "someothervalue".
+ </para>
+
+ <para>
+ Again, this assignment is a "lazy" or "weak" assignment
+ because it does not occur until the end
+ of the parsing process.
+ </para>
+ </section>
+
+ <section id='immediate-variable-expansion'>
+ <title>Immediate variable expansion (:=)</title>
+
+ <para>
+ The ":=" operator results in a variable's
+ contents being expanded immediately,
+ rather than when the variable is actually used:
+ <literallayout class='monospaced'>
+ T = "123"
+ A := "${B} ${A} test ${T}"
+ T = "456"
+ B = "${T} bval"
+ C = "cval"
+ C := "${C}append"
+ </literallayout>
+ In this example, <filename>A</filename> contains
+ "test 123" because <filename>${B}</filename> and
+ <filename>${A}</filename> at the time of parsing are undefined,
+ which leaves "test 123".
+ And, the variable <filename>C</filename>
+ contains "cvalappend" since <filename>${C}</filename> immediately
+ expands to "cval".
+ </para>
+ </section>
+
+ <section id='appending-and-prepending'>
+ <title>Appending (+=) and prepending (=+) With Spaces</title>
+
+ <para>
+ Appending and prepending values is common and can be accomplished
+ using the "+=" and "=+" operators.
+ These operators insert a space between the current
+ value and prepended or appended value.
+ </para>
+
+ <para>
+ These operators take immediate effect during parsing.
+ Here are some examples:
+ <literallayout class='monospaced'>
+ B = "bval"
+ B += "additionaldata"
+ C = "cval"
+ C =+ "test"
+ </literallayout>
+ The variable <filename>B</filename> contains
+ "bval additionaldata" and <filename>C</filename>
+ contains "test cval".
+ </para>
+ </section>
+
+ <section id='appending-and-prepending-without-spaces'>
+ <title>Appending (.=) and Prepending (=.) Without Spaces</title>
+
+ <para>
+ If you want to append or prepend values without an
+ inserted space, use the ".=" and "=." operators.
+ </para>
+
+ <para>
+ These operators take immediate effect during parsing.
+ Here are some examples:
+ <literallayout class='monospaced'>
+ B = "bval"
+ B .= "additionaldata"
+ C = "cval"
+ C =. "test"
+ </literallayout>
+ The variable <filename>B</filename> contains
+ "bvaladditionaldata" and
+ <filename>C</filename> contains "testcval".
+ </para>
+ </section>
+
+ <section id='appending-and-prepending-override-style-syntax'>
+ <title>Appending and Prepending (Override Style Syntax)</title>
+
+ <para>
+ You can also append and prepend a variable's value
+ using an override style syntax.
+ When you use this syntax, no spaces are inserted.
+ </para>
+
+ <para>
+ These operators differ from the ":=", ".=", "=.", "+=", and "=+"
+ operators in that their effects are deferred
+ until after parsing completes rather than being immediately
+ applied.
+ Here are some examples:
+ <literallayout class='monospaced'>
+ B = "bval"
+ B_append = " additional data"
+ C = "cval"
+ C_prepend = "additional data "
+ D = "dval"
+ D_append = "additional data"
+ </literallayout>
+ The variable <filename>B</filename> becomes
+ "bval additional data" and <filename>C</filename> becomes
+ "additional data cval".
+ The variable <filename>D</filename> becomes
+ "dvaladditional data".
+ <note>
+ You must control all spacing when you use the
+ override syntax.
+ </note>
+ </para>
+ </section>
+
+ <section id='removing-override-style-syntax'>
+ <title>Removal (Override Style Syntax)</title>
+
+ <para>
+ You can remove values from lists using the removal
+ override style syntax.
+ Specifying a value for removal causes all occurrences of that
+ value to be removed from the variable.
+ </para>
+
+ <para>
+ When you use this syntax, BitBake expects one or more strings.
+ Surrounding spaces are removed as well.
+ Here is an example:
+ <literallayout class='monospaced'>
+ FOO = "123 456 789 123456 123 456 123 456"
+ FOO_remove = "123"
+ FOO_remove = "456"
+ FOO2 = "abc def ghi abcdef abc def abc def"
+ FOO2_remove = "abc def"
+ </literallayout>
+ The variable <filename>FOO</filename> becomes
+ "789 123456" and <filename>FOO2</filename> becomes
+ "ghi abcdef".
+ </para>
+ </section>
+
+ <section id='variable-flag-syntax'>
+ <title>Variable Flag Syntax</title>
+
+ <para>
+ Variable flags are BitBake's implementation of variable properties
+ or attributes.
+ It is a way of tagging extra information onto a variable.
+ You can find more out about variable flags in general in the
+ "<link linkend='variable-flags'>Variable Flags</link>"
+ section.
+ </para>
+
+ <para>
+ You can define, append, and prepend values to variable flags.
+ All the standard syntax operations previously mentioned work
+ for variable flags except for override style syntax
+ (i.e. <filename>_prepend</filename>, <filename>_append</filename>,
+ and <filename>_remove</filename>).
+ </para>
+
+ <para>
+ Here are some examples showing how to set variable flags:
+ <literallayout class='monospaced'>
+ FOO[a] = "abc"
+ FOO[b] = "123"
+ FOO[a] += "456"
+ </literallayout>
+ The variable <filename>FOO</filename> has two flags:
+ <filename>a</filename> and <filename>b</filename>.
+ The flags are immediately set to "abc" and "123", respectively.
+ The <filename>a</filename> flag becomes "abc 456".
+ </para>
+
+ <para>
+ No need exists to pre-define variable flags.
+ You can simply start using them.
+ One extremely common application
+ is to attach some brief documentation to a BitBake variable as
+ follows:
+ <literallayout class='monospaced'>
+ CACHE[doc] = "The directory holding the cache of the metadata."
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='inline-python-variable-expansion'>
+ <title>Inline Python Variable Expansion</title>
+
+ <para>
+ You can use inline Python variable expansion to
+ set variables.
+ Here is an example:
+ <literallayout class='monospaced'>
+ DATE = "${@time.strftime('%Y%m%d',time.gmtime())}"
+ </literallayout>
+ This example results in the <filename>DATE</filename>
+ variable being set to the current date.
+ </para>
+
+ <para>
+ Probably the most common use of this feature is to extract
+ the value of variables from BitBake's internal data dictionary,
+ <filename>d</filename>.
+ The following lines select the values of a package name
+ and its version number, respectively:
+ <literallayout class='monospaced'>
+ PN = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}"
+ PV = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE', False),d)[1] or '1.0'}"
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='providing-pathnames'>
+ <title>Providing Pathnames</title>
+
+ <para>
+ When specifying pathnames for use with BitBake,
+ do not use the tilde ("~") character as a shortcut
+ for your home directory.
+ Doing so might cause BitBake to not recognize the
+ path since BitBake does not expand this character in
+ the same way a shell would.
+ </para>
+
+ <para>
+ Instead, provide a fuller path as the following
+ example illustrates:
+ <literallayout class='monospaced'>
+ BBLAYERS ?= " \
+ /home/scott-lenovo/LayerA \
+ "
+ </literallayout>
+ </para>
+ </section>
+ </section>
+
+ <section id='conditional-syntax-overrides'>
+ <title>Conditional Syntax (Overrides)</title>
+
+ <para>
+ BitBake uses
+ <link linkend='var-OVERRIDES'><filename>OVERRIDES</filename></link>
+ to control what variables are overridden after BitBake
+ parses recipes and configuration files.
+ This section describes how you can use
+ <filename>OVERRIDES</filename> as conditional metadata,
+ talks about key expansion in relationship to
+ <filename>OVERRIDES</filename>, and provides some examples
+ to help with understanding.
+ </para>
+
+ <section id='conditional-metadata'>
+ <title>Conditional Metadata</title>
+
+ <para>
+ You can use <filename>OVERRIDES</filename> to conditionally select
+ a specific version of a variable and to conditionally
+ append or prepend the value of a variable.
+ <itemizedlist>
+ <listitem><para><emphasis>Selecting a Variable:</emphasis>
+ The <filename>OVERRIDES</filename> variable is
+ a colon-character-separated list that contains items
+ for which you want to satisfy conditions.
+ Thus, if you have a variable that is conditional on “arm”, and “arm”
+ is in <filename>OVERRIDES</filename>, then the “arm”-specific
+ version of the variable is used rather than the non-conditional
+ version.
+ Here is an example:
+ <literallayout class='monospaced'>
+ OVERRIDES = "architecture:os:machine"
+ TEST = "default"
+ TEST_os = "osspecific"
+ TEST_nooverride = "othercondvalue"
+ </literallayout>
+ In this example, the <filename>OVERRIDES</filename>
+ variable lists three overrides:
+ "architecture", "os", and "machine".
+ The variable <filename>TEST</filename> by itself has a default
+ value of "default".
+ You select the os-specific version of the <filename>TEST</filename>
+ variable by appending the "os" override to the variable
+ (i.e.<filename>TEST_os</filename>).
+ </para>
+
+ <para>
+ To better understand this, consider a practical example
+ that assumes an OpenEmbedded metadata-based Linux
+ kernel recipe file.
+ The following lines from the recipe file first set
+ the kernel branch variable <filename>KBRANCH</filename>
+ to a default value, then conditionally override that
+ value based on the architecture of the build:
+ <literallayout class='monospaced'>
+ KBRANCH = "standard/base"
+ KBRANCH_qemuarm = "standard/arm-versatile-926ejs"
+ KBRANCH_qemumips = "standard/mti-malta32"
+ KBRANCH_qemuppc = "standard/qemuppc"
+ KBRANCH_qemux86 = "standard/common-pc/base"
+ KBRANCH_qemux86-64 = "standard/common-pc-64/base"
+ KBRANCH_qemumips64 = "standard/mti-malta64"
+ </literallayout>
+ </para></listitem>
+ <listitem><para><emphasis>Appending and Prepending:</emphasis>
+ BitBake also supports append and prepend operations to
+ variable values based on whether a specific item is
+ listed in <filename>OVERRIDES</filename>.
+ Here is an example:
+ <literallayout class='monospaced'>
+ DEPENDS = "glibc ncurses"
+ OVERRIDES = "machine:local"
+ DEPENDS_append_machine = "libmad"
+ </literallayout>
+ In this example, <filename>DEPENDS</filename> becomes
+ "glibc ncurses libmad".
+ </para>
+
+ <para>
+ Again, using an OpenEmbedded metadata-based
+ kernel recipe file as an example, the
+ following lines will conditionally append to the
+ <filename>KERNEL_FEATURES</filename> variable based
+ on the architecture:
+ <literallayout class='monospaced'>
+ KERNEL_FEATURES_append = " ${KERNEL_EXTRA_FEATURES}"
+ KERNEL_FEATURES_append_qemux86=" cfg/sound.scc cfg/paravirt_kvm.scc"
+ KERNEL_FEATURES_append_qemux86-64=" cfg/sound.scc cfg/paravirt_kvm.scc"
+ </literallayout>
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='key-expansion'>
+ <title>Key Expansion</title>
+
+ <para>
+ Key expansion happens when the BitBake datastore is finalized
+ just before BitBake expands overrides.
+ To better understand this, consider the following example:
+ <literallayout class='monospaced'>
+ A${B} = "X"
+ B = "2"
+ A2 = "Y"
+ </literallayout>
+ In this case, after all the parsing is complete, and
+ before any overrides are handled, BitBake expands
+ <filename>${B}</filename> into "2".
+ This expansion causes <filename>A2</filename>, which was
+ set to "Y" before the expansion, to become "X".
+ </para>
+ </section>
+
+ <section id='variable-interaction-worked-examples'>
+ <title>Examples</title>
+
+ <para>
+ Despite the previous explanations that show the different forms of
+ variable definitions, it can be hard to work
+ out exactly what happens when variable operators, conditional
+ overrides, and unconditional overrides are combined.
+ This section presents some common scenarios along
+ with explanations for variable interactions that
+ typically confuse users.
+ </para>
+
+ <para>
+ There is often confusion concerning the order in which
+ overrides and various "append" operators take effect.
+ Recall that an append or prepend operation using "_append"
+ and "_prepend" does not result in an immediate assignment
+ as would "+=", ".=", "=+", or "=.".
+ Consider the following example:
+ <literallayout class='monospaced'>
+ OVERRIDES = "foo"
+ A = "Z"
+ A_foo_append = "X"
+ </literallayout>
+ For this case, <filename>A</filename> is
+ unconditionally set to "Z" and "X" is
+ unconditionally and immediately appended to the variable
+ <filename>A_foo</filename>.
+ Because overrides have not been applied yet,
+ <filename>A_foo</filename> is set to "X" due to the append
+ and <filename>A</filename> simply equals "Z".
+ </para>
+
+ <para>
+ Applying overrides, however, changes things.
+ Since "foo" is listed in <filename>OVERRIDES</filename>,
+ the conditional variable <filename>A</filename> is replaced
+ with the "foo" version, which is equal to "X".
+ So effectively, <filename>A_foo</filename> replaces <filename>A</filename>.
+ </para>
+
+ <para>
+ This next example changes the order of the override and
+ the append:
+ <literallayout class='monospaced'>
+ OVERRIDES = "foo"
+ A = "Z"
+ A_append_foo = "X"
+ </literallayout>
+ For this case, before overrides are handled,
+ <filename>A</filename> is set to "Z" and <filename>A_append_foo</filename>
+ is set to "X".
+ Once the override for "foo" is applied, however,
+ <filename>A</filename> gets appended with "X".
+ Consequently, <filename>A</filename> becomes "ZX".
+ Notice that spaces are not appended.
+ </para>
+
+ <para>
+ This next example has the order of the appends and overrides reversed
+ back as in the first example:
+ <literallayout class='monospaced'>
+ OVERRIDES = "foo"
+ A = "Y"
+ A_foo_append = "Z"
+ A_foo_append += "X"
+ </literallayout>
+ For this case, before any overrides are resolved,
+ <filename>A</filename> is set to "Y" using an immediate assignment.
+ After this immediate assignment, <filename>A_foo</filename> is set
+ to "Z", and then further appended with
+ "X" leaving the variable set to "Z X".
+ Finally, applying the override for "foo" results in the conditional
+ variable <filename>A</filename> becoming "Z X" (i.e.
+ <filename>A</filename> is replaced with <filename>A_foo</filename>).
+ </para>
+
+ <para>
+ This final example mixes in some varying operators:
+ <literallayout class='monospaced'>
+ A = "1"
+ A_append = "2"
+ A_append = "3"
+ A += "4"
+ A .= "5"
+ </literallayout>
+ For this case, the type of append operators are affecting the
+ order of assignments as BitBake passes through the code
+ multiple times.
+ Initially, <filename>A</filename> is set to "1 45" because
+ of the three statements that use immediate operators.
+ After these assignments are made, BitBake applies the
+ <filename>_append</filename> operations.
+ Those operations result in <filename>A</filename> becoming "1 4523".
+ </para>
+ </section>
+ </section>
+
+ <section id='sharing-functionality'>
+ <title>Sharing Functionality</title>
+
+ <para>
+ BitBake allows for metadata sharing through include files
+ (<filename>.inc</filename>) and class files
+ (<filename>.bbclass</filename>).
+ For example, suppose you have a piece of common functionality
+ such as a task definition that you want to share between
+ more than one recipe.
+ In this case, creating a <filename>.bbclass</filename>
+ file that contains the common functionality and then using
+ the <filename>inherit</filename> directive in your recipes to
+ inherit the class would be a common way to share the task.
+ </para>
+
+ <para>
+ This section presents the mechanisms BitBake provides to
+ allow you to share functionality between recipes.
+ Specifically, the mechanisms include <filename>include</filename>,
+ <filename>inherit</filename>, <filename>INHERIT</filename>, and
+ <filename>require</filename> directives.
+ </para>
+
+ <section id='locating-include-and-class-files'>
+ <title>Locating Include and Class Files</title>
+
+ <para>
+ BitBake uses the
+ <link linkend='var-BBPATH'><filename>BBPATH</filename></link>
+ variable to locate needed include and class files.
+ The <filename>BBPATH</filename> variable is analogous to
+ the environment variable <filename>PATH</filename>.
+ </para>
+
+ <para>
+ In order for include and class files to be found by BitBake,
+ they need to be located in a "classes" subdirectory that can
+ be found in <filename>BBPATH</filename>.
+ </para>
+ </section>
+
+ <section id='inherit-directive'>
+ <title><filename>inherit</filename> Directive</title>
+
+ <para>
+ When writing a recipe or class file, you can use the
+ <filename>inherit</filename> directive to inherit the
+ functionality of a class (<filename>.bbclass</filename>).
+ BitBake only supports this directive when used within recipe
+ and class files (i.e. <filename>.bb</filename> and
+ <filename>.bbclass</filename>).
+ </para>
+
+ <para>
+ The <filename>inherit</filename> directive is a rudimentary
+ means of specifying what classes of functionality your
+ recipes require.
+ For example, you can easily abstract out the tasks involved in
+ building a package that uses Autoconf and Automake and put
+ those tasks into a class file that can be used by your recipe.
+ </para>
+
+ <para>
+ As an example, your recipes could use the following directive
+ to inherit an <filename>autotools.bbclass</filename> file.
+ The class file would contain common functionality for using
+ Autotools that could be shared across recipes:
+ <literallayout class='monospaced'>
+ inherit autotools
+ </literallayout>
+ In this case, BitBake would search for the directory
+ <filename>classes/autotools.bbclass</filename>
+ in <filename>BBPATH</filename>.
+ <note>
+ You can override any values and functions of the
+ inherited class within your recipe by doing so
+ after the "inherit" statement.
+ </note>
+ </para>
+ </section>
+
+ <section id='include-directive'>
+ <title><filename>include</filename> Directive</title>
+
+ <para>
+ BitBake understands the <filename>include</filename>
+ directive.
+ This directive causes BitBake to parse whatever file you specify,
+ and to insert that file at that location.
+ The directive is much like its equivalent in Make except
+ that if the path specified on the include line is a relative
+ path, BitBake locates the first file it can find
+ within <filename>BBPATH</filename>.
+ </para>
+
+ <para>
+ As an example, suppose you needed a recipe to include some
+ self-test definitions:
+ <literallayout class='monospaced'>
+ include test_defs.inc
+ </literallayout>
+ <note>
+ The <filename>include</filename> directive does not
+ produce an error when the file cannot be found.
+ Consequently, it is recommended that if the file you
+ are including is expected to exist, you should use
+ <link linkend='require-inclusion'><filename>require</filename></link>
+ instead of <filename>include</filename>.
+ Doing so makes sure that an error is produced if the
+ file cannot be found.
+ </note>
+ </para>
+ </section>
+
+ <section id='require-inclusion'>
+ <title><filename>require</filename> Directive</title>
+
+ <para>
+ BitBake understands the <filename>require</filename>
+ directive.
+ This directive behaves just like the
+ <filename>include</filename> directive with the exception that
+ BitBake raises a parsing error if the file to be included cannot
+ be found.
+ Thus, any file you require is inserted into the file that is
+ being parsed at the location of the directive.
+ </para>
+
+ <para>
+ Similar to how BitBake handles
+ <link linkend='include-directive'><filename>include</filename></link>,
+ if the path specified
+ on the require line is a relative path, BitBake locates
+ the first file it can find within <filename>BBPATH</filename>.
+ </para>
+
+ <para>
+ As an example, suppose you have two versions of a recipe
+ (e.g. <filename>foo_1.2.2.bb</filename> and
+ <filename>foo_2.0.0.bb</filename>) where
+ each version contains some identical functionality that could be
+ shared.
+ You could create an include file named <filename>foo.inc</filename>
+ that contains the common definitions needed to build "foo".
+ You need to be sure <filename>foo.inc</filename> is located in the
+ same directory as your two recipe files as well.
+ Once these conditions are set up, you can share the functionality
+ using a <filename>require</filename> directive from within each
+ recipe:
+ <literallayout class='monospaced'>
+ require foo.inc
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='inherit-configuration-directive'>
+ <title><filename>INHERIT</filename> Configuration Directive</title>
+
+ <para>
+ When creating a configuration file (<filename>.conf</filename>),
+ you can use the <filename>INHERIT</filename> directive to
+ inherit a class.
+ BitBake only supports this directive when used within
+ a configuration file.
+ </para>
+
+ <para>
+ As an example, suppose you needed to inherit a class
+ file called <filename>abc.bbclass</filename> from a
+ configuration file as follows:
+ <literallayout class='monospaced'>
+ INHERIT += "abc"
+ </literallayout>
+ This configuration directive causes the named
+ class to be inherited at the point of the directive
+ during parsing.
+ As with the <filename>inherit</filename> directive, the
+ <filename>.bbclass</filename> file must be located in a
+ "classes" subdirectory in one of the directories specified
+ in <filename>BBPATH</filename>.
+ <note>
+ Because <filename>.conf</filename> files are parsed
+ first during BitBake's execution, using
+ <filename>INHERIT</filename> to inherit a class effectively
+ inherits the class globally (i.e. for all recipes).
+ </note>
+ </para>
+ </section>
+ </section>
+
+ <section id='functions'>
+ <title>Functions</title>
+
+ <para>
+ As with most languages, functions are the building blocks that
+ are used to build up operations into tasks.
+ BitBake supports these types of functions:
+ <itemizedlist>
+ <listitem><para><emphasis>Shell Functions:</emphasis>
+ Functions written in shell script and executed either
+ directly as functions, tasks, or both.
+ They can also be called by other shell functions.
+ </para></listitem>
+ <listitem><para><emphasis>BitBake Style Python Functions:</emphasis>
+ Functions written in Python and executed by BitBake or other
+ Python functions using <filename>bb.build.exec_func()</filename>.
+ </para></listitem>
+ <listitem><para><emphasis>Python Functions:</emphasis>
+ Functions written in Python and executed by Python.
+ </para></listitem>
+ <listitem><para><emphasis>Anonymous Python Functions:</emphasis>
+ Python functions executed automatically during
+ parsing.
+ </para></listitem>
+ </itemizedlist>
+ Regardless of the type of function, you can only
+ define them in class (<filename>.bbclass</filename>)
+ and recipe (<filename>.bb</filename> or <filename>.inc</filename>)
+ files.
+ </para>
+
+ <section id='shell-functions'>
+ <title>Shell Functions</title>
+
+ <para>
+ Functions written in shell script and executed either
+ directly as functions, tasks, or both.
+ They can also be called by other shell functions.
+ Here is an example shell function definition:
+ <literallayout class='monospaced'>
+ some_function () {
+ echo "Hello World"
+ }
+ </literallayout>
+ When you create these types of functions in your recipe
+ or class files, you need to follow the shell programming
+ rules.
+ The scripts are executed by <filename>/bin/sh</filename>,
+ which may not be a bash shell but might be something
+ such as <filename>dash</filename>.
+ You should not use Bash-specific script (bashisms).
+ </para>
+ </section>
+
+ <section id='bitbake-style-python-functions'>
+ <title>BitBake Style Python Functions</title>
+
+ <para>
+ These functions are written in Python and executed by
+ BitBake or other Python functions using
+ <filename>bb.build.exec_func()</filename>.
+ </para>
+
+ <para>
+ An example BitBake function is:
+ <literallayout class='monospaced'>
+ python some_python_function () {
+ d.setVar("TEXT", "Hello World")
+ print d.getVar("TEXT", True)
+ }
+ </literallayout>
+ Because the Python "bb" and "os" modules are already
+ imported, you do not need to import these modules.
+ Also in these types of functions, the datastore ("d")
+ is a global variable and is always automatically
+ available.
+ </para>
+ </section>
+
+ <section id='python-functions'>
+ <title>Python Functions</title>
+
+ <para>
+ These functions are written in Python and are executed by
+ other Python code.
+ Examples of Python functions are utility functions
+ that you intend to call from in-line Python or
+ from within other Python functions.
+ Here is an example:
+ <literallayout class='monospaced'>
+ def get_depends(d):
+ if d.getVar('SOMECONDITION', True):
+ return "dependencywithcond"
+ else:
+ return "dependency"
+ SOMECONDITION = "1"
+ DEPENDS = "${@get_depends(d)}"
+ </literallayout>
+ This would result in <filename>DEPENDS</filename>
+ containing <filename>dependencywithcond</filename>.
+ </para>
+
+ <para>
+ Here are some things to know about Python functions:
+ <itemizedlist>
+ <listitem><para>Python functions can take parameters.
+ </para></listitem>
+ <listitem><para>The BitBake datastore is not
+ automatically available.
+ Consequently, you must pass it in as a
+ parameter to the function.
+ </para></listitem>
+ <listitem><para>The "bb" and "os" Python modules are
+ automatically available.
+ You do not need to import them.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='anonymous-python-functions'>
+ <title>Anonymous Python Functions</title>
+
+ <para>
+ Sometimes it is useful to run some code during
+ parsing to set variables or to perform other operations
+ programmatically.
+ To do this, you can define an anonymous Python function.
+ Here is an example that conditionally sets a
+ variable based on the value of another variable:
+ <literallayout class='monospaced'>
+ python __anonymous () {
+ if d.getVar('SOMEVAR', True) == 'value':
+ d.setVar('ANOTHERVAR', 'value2')
+ }
+ </literallayout>
+ The "__anonymous" function name is optional, so the
+ following example is functionally equivalent to the above:
+ <literallayout class='monospaced'>
+ python () {
+ if d.getVar('SOMEVAR', True) == 'value':
+ d.setVar('ANOTHERVAR', 'value2')
+ }
+ </literallayout>
+ Because unlike other Python functions anonymous
+ Python functions are executed during parsing, the
+ "d" variable within an anonymous Python function represents
+ the datastore for the entire recipe.
+ Consequently, you can set variable values here and
+ those values can be picked up by other functions.
+ </para>
+ </section>
+
+ <section id='flexible-inheritance-for-class-functions'>
+ <title>Flexible Inheritance for Class Functions</title>
+
+ <para>
+ Through coding techniques and the use of
+ <filename>EXPORT_FUNCTIONS</filename>, BitBake supports
+ exporting a function from a class such that the
+ class function appears as the default implementation
+ of the function, but can still be called if a recipe
+ inheriting the class needs to define its own version of
+ the function.
+ </para>
+
+ <para>
+ To understand the benefits of this feature, consider
+ the basic scenario where a class defines a task function
+ and your recipe inherits the class.
+ In this basic scenario, your recipe inherits the task
+ function as defined in the class.
+ If desired, your recipe can add to the start and end of the
+ function by using the "_prepend" or "_append" operations
+ respectively, or it can redefine the function completely.
+ However, if it redefines the function, there is
+ no means for it to call the class version of the function.
+ <filename>EXPORT_FUNCTIONS</filename> provides a mechanism
+ that enables the recipe's version of the function to call
+ the original version of the function.
+ </para>
+
+ <para>
+ To make use of this technique, you need the following
+ things in place:
+ <itemizedlist>
+ <listitem><para>
+ The class needs to define the function as follows:
+ <literallayout class='monospaced'>
+ <replaceable>classname</replaceable><filename>_</filename><replaceable>functionname</replaceable>
+ </literallayout>
+ For example, if you have a class file
+ <filename>bar.bbclass</filename> and a function named
+ <filename>do_foo</filename>, the class must define the function
+ as follows:
+ <literallayout class='monospaced'>
+ bar_do_foo
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ The class needs to contain the <filename>EXPORT_FUNCTIONS</filename>
+ statement as follows:
+ <literallayout class='monospaced'>
+ EXPORT_FUNCTIONS <replaceable>functionname</replaceable>
+ </literallayout>
+ For example, continuing with the same example, the
+ statement in the <filename>bar.bbclass</filename> would be
+ as follows:
+ <literallayout class='monospaced'>
+ EXPORT_FUNCTIONS do_foo
+ </literallayout>
+ </para></listitem>
+ <listitem><para>
+ You need to call the function appropriately from within your
+ recipe.
+ Continuing with the same example, if your recipe
+ needs to call the class version of the function,
+ it should call <filename>bar_do_foo</filename>.
+ Assuming <filename>do_foo</filename> was a shell function
+ and <filename>EXPORT_FUNCTIONS</filename> was used as above,
+ the recipe's function could conditionally call the
+ class version of the function as follows:
+ <literallayout class='monospaced'>
+ do_foo() {
+ if [ somecondition ] ; then
+ bar_do_foo
+ else
+ # Do something else
+ fi
+ }
+ </literallayout>
+ To call your modified version of the function as defined
+ in your recipe, call it as <filename>do_foo</filename>.
+ </para></listitem>
+ </itemizedlist>
+ With these conditions met, your single recipe
+ can freely choose between the original function
+ as defined in the class file and the modified function in your recipe.
+ If you do not set up these conditions, you are limited to using one function
+ or the other.
+ </para>
+ </section>
+ </section>
+
+ <section id='tasks'>
+ <title>Tasks</title>
+
+ <para>
+ Tasks are BitBake execution units that originate as
+ functions and make up the steps that BitBake needs to run
+ for given recipe.
+ Tasks are only supported in recipe (<filename>.bb</filename>
+ or <filename>.inc</filename>) and class
+ (<filename>.bbclass</filename>) files.
+ By convention, task names begin with the string "do_".
+ </para>
+
+ <para>
+ Here is an example of a task that prints out the date:
+ <literallayout class='monospaced'>
+ python do_printdate () {
+ import time
+ print time.strftime('%Y%m%d', time.gmtime())
+ }
+ addtask printdate after do_fetch before do_build
+ </literallayout>
+ </para>
+
+ <section id='promoting-a-function-to-a-task'>
+ <title>Promoting a Function to a Task</title>
+
+ <para>
+ Any function can be promoted to a task by applying the
+ <filename>addtask</filename> command.
+ The <filename>addtask</filename> command also describes
+ inter-task dependencies.
+ Here is the function from the previous section but with the
+ <filename>addtask</filename> command promoting it to a task
+ and defining some dependencies:
+ <literallayout class='monospaced'>
+ python do_printdate () {
+ import time
+ print time.strftime('%Y%m%d', time.gmtime())
+ }
+ addtask printdate after do_fetch before do_build
+ </literallayout>
+ In the example, the function is defined and then promoted
+ as a task.
+ The <filename>do_printdate</filename> task becomes a dependency of
+ the <filename>do_build</filename> task, which is the default
+ task.
+ And, the <filename>do_printdate</filename> task is dependent upon
+ the <filename>do_fetch</filename> task.
+ Execution of the <filename>do_build</filename> task results
+ in the <filename>do_printdate</filename> task running first.
+ </para>
+ </section>
+
+ <section id='deleting-a-task'>
+ <title>Deleting a Task</title>
+
+ <para>
+ As well as being able to add tasks, you can delete them.
+ Simply use the <filename>deltask</filename> command to
+ delete a task.
+ For example, to delete the example task used in the previous
+ sections, you would use:
+ <literallayout class='monospaced'>
+ deltask printdate
+ </literallayout>
+ If you delete a task using the <filename>deltask</filename>
+ command and the task has dependencies, the dependencies are
+ not reconnected.
+ For example, suppose you have three tasks named
+ <filename>do_a</filename>, <filename>do_b</filename>, and
+ <filename>do_c</filename>.
+ Furthermore, <filename>do_c</filename> is dependent on
+ <filename>do_b</filename>, which in turn is dependent on
+ <filename>do_a</filename>.
+ Given this scenario, if you use <filename>deltask</filename>
+ to delete <filename>do_b</filename>, the implicit dependency
+ relationship between <filename>do_c</filename> and
+ <filename>do_a</filename> through <filename>do_b</filename>
+ no longer exists, and <filename>do_c</filename> dependencies
+ are not updated to include <filename>do_a</filename>.
+ Thus, <filename>do_c</filename> is free to run before
+ <filename>do_a</filename>.
+ </para>
+
+ <para>
+ If you want dependencies such as these to remain intact, use
+ the <filename>noexec</filename> varflag to disable the task
+ instead of using the <filename>deltask</filename> command to
+ delete it:
+ <literallayout class='monospaced'>
+ do_b[noexec] = "1"
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='passing-information-into-the-build-task-environment'>
+ <title>Passing Information Into the Build Task Environment</title>
+
+ <para>
+ When running a task, BitBake tightly controls the execution
+ environment of the build tasks to make
+ sure unwanted contamination from the build machine cannot
+ influence the build.
+ Consequently, if you do want something to get passed into the
+ build task environment, you must take these two steps:
+ <orderedlist>
+ <listitem><para>
+ Tell BitBake to load what you want from the environment
+ into the datastore.
+ You can do so through the
+ <link linkend='var-BB_ENV_EXTRAWHITE'><filename>BB_ENV_EXTRAWHITE</filename></link>
+ variable.
+ For example, assume you want to prevent the build system from
+ accessing your <filename>$HOME/.ccache</filename>
+ directory.
+ The following command tells BitBake to load
+ <filename>CCACHE_DIR</filename> from the environment into
+ the datastore:
+ <literallayout class='monospaced'>
+ export BB_ENV_EXTRAWHITE="$BB_ENV_EXTRAWHITE CCACHE_DIR"
+ </literallayout></para></listitem>
+ <listitem><para>
+ Tell BitBake to export what you have loaded into the
+ datastore to the task environment of every running task.
+ Loading something from the environment into the datastore
+ (previous step) only makes it available in the datastore.
+ To export it to the task environment of every running task,
+ use a command similar to the following in your local configuration
+ file <filename>local.conf</filename> or your
+ distribution configuration file:
+ <literallayout class='monospaced'>
+ export CCACHE_DIR
+ </literallayout>
+ <note>
+ A side effect of the previous steps is that BitBake
+ records the variable as a dependency of the build process
+ in things like the setscene checksums.
+ If doing so results in unnecessary rebuilds of tasks, you can
+ whitelist the variable so that the setscene code
+ ignores the dependency when it creates checksums.
+ </note></para></listitem>
+ </orderedlist>
+ </para>
+
+ <para>
+ Sometimes, it is useful to be able to obtain information
+ from the original execution environment.
+ Bitbake saves a copy of the original environment into
+ a special variable named
+ <link linkend='var-BB_ORIGENV'><filename>BB_ORIGENV</filename></link>.
+ </para>
+
+ <para>
+ The <filename>BB_ORIGENV</filename> variable returns a datastore
+ object that can be queried using the standard datastore operators
+ such as <filename>getVar(, False)</filename>.
+ The datastore object is useful, for example, to find the original
+ <filename>DISPLAY</filename> variable.
+ Here is an example:
+ <literallayout class='monospaced'>
+ origenv = d.getVar("BB_ORIGENV", False)
+ bar = origenv.getVar("BAR", False)
+ </literallayout>
+ The previous example returns <filename>BAR</filename> from the original
+ execution environment.
+ </para>
+
+ <para>
+ By default, BitBake cleans the environment to include only those
+ things exported or listed in its whitelist to ensure that the build
+ environment is reproducible and consistent.
+ </para>
+ </section>
+ </section>
+
+ <section id='variable-flags'>
+ <title>Variable Flags</title>
+
+ <para>
+ Variable flags (varflags) help control a task's functionality
+ and dependencies.
+ BitBake reads and writes varflags to the datastore using the following
+ command forms:
+ <literallayout class='monospaced'>
+ <replaceable>variable</replaceable> = d.getVarFlags("<replaceable>variable</replaceable>")
+ self.d.setVarFlags("FOO", {"func": True})
+ </literallayout>
+ </para>
+
+ <para>
+ When working with varflags, the same syntax, with the exception of
+ overrides, applies.
+ In other words, you can set, append, and prepend varflags just like
+ variables.
+ See the
+ "<link linkend='variable-flag-syntax'>Variable Flag Syntax</link>"
+ section for details.
+ </para>
+
+ <para>
+ BitBake has a defined set of varflags available for recipes and
+ classes.
+ Tasks support a number of these flags which control various
+ functionality of the task:
+ <itemizedlist>
+ <listitem><para><emphasis>cleandirs:</emphasis>
+ Empty directories that should created before the task runs.
+ </para></listitem>
+ <listitem><para><emphasis>depends:</emphasis>
+ Controls inter-task dependencies.
+ See the
+ <link linkend='var-DEPENDS'><filename>DEPENDS</filename></link>
+ variable and the
+ "<link linkend='inter-task-dependencies'>Inter-Task Dependencies</link>"
+ section for more information.
+ </para></listitem>
+ <listitem><para><emphasis>deptask:</emphasis>
+ Controls task build-time dependencies.
+ See the
+ <link linkend='var-DEPENDS'><filename>DEPENDS</filename></link>
+ variable and the
+ "<link linkend='build-dependencies'>Build Dependencies</link>"
+ section for more information.
+ </para></listitem>
+ <listitem><para><emphasis>dirs:</emphasis>
+ Directories that should be created before the task runs.
+ </para></listitem>
+ <listitem><para><emphasis>lockfiles:</emphasis>
+ Specifies one or more lockfiles to lock while the task
+ executes.
+ Only one task may hold a lockfile, and any task that
+ attempts to lock an already locked file will block until
+ the lock is released.
+ You can use this variable flag to accomplish mutual
+ exclusion.
+ </para></listitem>
+ <listitem><para><emphasis>noexec:</emphasis>
+ Marks the tasks as being empty and no execution required.
+ The <filename>noexec</filename> flag can be used to set up
+ tasks as dependency placeholders, or to disable tasks defined
+ elsewhere that are not needed in a particular recipe.
+ </para></listitem>
+ <listitem><para><emphasis>nostamp:</emphasis>
+ Tells BitBake to not generate a stamp file for a task,
+ which implies the task should always be executed.
+ </para></listitem>
+ <listitem><para><emphasis>postfuncs:</emphasis>
+ List of functions to call after the completion of the task.
+ </para></listitem>
+ <listitem><para><emphasis>prefuncs:</emphasis>
+ List of functions to call before the task executes.
+ </para></listitem>
+ <listitem><para><emphasis>rdepends:</emphasis>
+ Controls inter-task runtime dependencies.
+ See the
+ <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link>
+ variable, the
+ <link linkend='var-RRECOMMENDS'><filename>RRECOMMENDS</filename></link>
+ variable, and the
+ "<link linkend='inter-task-dependencies'>Inter-Task Dependencies</link>"
+ section for more information.
+ </para></listitem>
+ <listitem><para><emphasis>rdeptask:</emphasis>
+ Controls task runtime dependencies.
+ See the
+ <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link>
+ variable, the
+ <link linkend='var-RRECOMMENDS'><filename>RRECOMMENDS</filename></link>
+ variable, and the
+ "<link linkend='runtime-dependencies'>Runtime Dependencies</link>"
+ section for more information.
+ </para></listitem>
+ <listitem><para><emphasis>recideptask:</emphasis>
+ When set in conjunction with
+ <filename>recrdeptask</filename>, specifies a task that
+ should be inspected for additional dependencies.
+ </para></listitem>
+ <listitem><para><emphasis>recrdeptask:</emphasis>
+ Controls task recursive runtime dependencies.
+ See the
+ <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link>
+ variable, the
+ <link linkend='var-RRECOMMENDS'><filename>RRECOMMENDS</filename></link>
+ variable, and the
+ "<link linkend='recursive-dependencies'>Recursive Dependencies</link>"
+ section for more information.
+ </para></listitem>
+ <listitem><para><emphasis>stamp-extra-info:</emphasis>
+ Extra stamp information to append to the task's stamp.
+ As an example, OpenEmbedded uses this flag to allow
+ machine-specific tasks.
+ </para></listitem>
+ <listitem><para><emphasis>umask:</emphasis>
+ The umask to run the task under.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ Several varflags are useful for controlling how signatures are
+ calculated for variables.
+ For more information on this process, see the
+ "<link linkend='checksums'>Checksums (Signatures)</link>"
+ section.
+ <itemizedlist>
+ <listitem><para><emphasis>vardeps:</emphasis>
+ Specifies a space-separated list of additional
+ variables to add to a variable's dependencies
+ for the purposes of calculating its signature.
+ Adding variables to this list is useful, for example, when
+ a function refers to a variable in a manner that
+ does not allow BitBake to automatically determine
+ that the variable is referred to.
+ </para></listitem>
+ <listitem><para><emphasis>vardepsexclude:</emphasis>
+ Specifies a space-separated list of variables
+ that should be excluded from a variable's dependencies
+ for the purposes of calculating its signature.
+ </para></listitem>
+ <listitem><para><emphasis>vardepvalue:</emphasis>
+ If set, instructs BitBake to ignore the actual
+ value of the variable and instead use the specified
+ value when calculating the variable's signature.
+ </para></listitem>
+ <listitem><para><emphasis>vardepvalueexclude:</emphasis>
+ Specifies a pipe-separated list of strings to exclude
+ from the variable's value when calculating the
+ variable's signature.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='events'>
+ <title>Events</title>
+
+ <para>
+ BitBake allows installation of event handlers within
+ recipe and class files.
+ Events are triggered at certain points during operation,
+ such as the beginning of an operation against a given recipe
+ (<filename>*.bb</filename> file), the start of a given task,
+ task failure, task success, and so forth.
+ The intent is to make it easy to do things like email
+ notification on build failure.
+ </para>
+
+ <para>
+ Following is an example event handler that
+ prints the name of the event and the content of
+ the <filename>FILE</filename> variable:
+ <literallayout class='monospaced'>
+ addhandler myclass_eventhandler
+ python myclass_eventhandler() {
+ from bb.event import getName
+ from bb import data
+ print("The name of the Event is %s" % getName(e))
+ print("The file we run for is %s" % data.getVar('FILE', e.data, True))
+ }
+ </literallayout>
+ This event handler gets called every time an event is
+ triggered.
+ A global variable "<filename>e</filename>" is defined and
+ "<filename>e.data</filename>" contains an instance of
+ "<filename>bb.data</filename>".
+ With the <filename>getName(e)</filename> method, one can get
+ the name of the triggered event.
+ </para>
+
+ <para>
+ Because you probably are only interested in a subset of events,
+ you would likely use the <filename>[eventmask]</filename> flag
+ for your event handler to be sure that only certain events
+ trigger the handler.
+ Given the previous example, suppose you only wanted the
+ <filename>bb.build.TaskFailed</filename> event to trigger that
+ event handler.
+ Use the flag as follows:
+ <literallayout class='monospaced'>
+ addhandler myclass_eventhandler
+ myclass_eventhandler[eventmask] = "bb.build.TaskFailed"
+ python myclass_eventhandler() {
+ from bb.event import getName
+ from bb import data
+ print("The name of the Event is %s" % getName(e))
+ print("The file we run for is %s" % data.getVar('FILE', e.data, True))
+ }
+ </literallayout>
+ </para>
+
+ <para>
+ During a standard build, the following common events might occur:
+ <itemizedlist>
+ <listitem><para>
+ <filename>bb.event.ConfigParsed()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.ParseStarted()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.ParseProgress()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.ParseCompleted()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.BuildStarted()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.build.TaskStarted()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.build.TaskInvalid()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.build.TaskFailedSilent()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.build.TaskFailed()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.build.TaskSucceeded()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.BuildCompleted()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.cooker.CookerExit()</filename>
+ </para></listitem>
+ </itemizedlist>
+ Here is a list of other events that occur based on specific requests
+ to the server:
+ <itemizedlist>
+ <listitem><para>
+ <filename>bb.event.TreeDataPreparationStarted()</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.TreeDataPreparationProgress</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.TreeDataPreparationCompleted</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.DepTreeGenerated</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.CoreBaseFilesFound</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.ConfigFilePathFound</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.FilesMatchingFound</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.ConfigFilesFound</filename>
+ </para></listitem>
+ <listitem><para>
+ <filename>bb.event.TargetsTreeGenerated</filename>
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='variants-class-extension-mechanism'>
+ <title>Variants - Class Extension Mechanism</title>
+
+ <para>
+ BitBake supports two features that facilitate creating
+ from a single recipe file multiple incarnations of that
+ recipe file where all incarnations are buildable.
+ These features are enabled through the
+ <link linkend='var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></link>
+ and
+ <link linkend='var-BBVERSIONS'><filename>BBVERSIONS</filename></link>
+ variables.
+ <note>
+ The mechanism for this class extension is extremely
+ specific to the implementation.
+ Usually, the recipe's
+ <link linkend='var-PROVIDES'><filename>PROVIDES</filename></link>,
+ <link linkend='var-PN'><filename>PN</filename></link>, and
+ <link linkend='var-DEPENDS'><filename>DEPENDS</filename></link>
+ variables would need to be modified by the extension class.
+ For specific examples, see the OE-Core
+ <filename>native</filename>, <filename>nativesdk</filename>,
+ and <filename>multilib</filename> classes.
+ </note>
+ <itemizedlist>
+ <listitem><para><emphasis><filename>BBCLASSEXTEND</filename>:</emphasis>
+ This variable is a space separated list of classes used to "extend" the
+ recipe for each variant.
+ Here is an example that results in a second incarnation of the current
+ recipe being available.
+ This second incarnation will have the "native" class inherited.
+ <literallayout class='monospaced'>
+ BBCLASSEXTEND = "native"
+ </literallayout></para></listitem>
+ <listitem><para><emphasis><filename>BBVERSIONS</filename>:</emphasis>
+ This variable allows a single recipe to build multiple versions of a
+ project from a single recipe file.
+ You can also specify conditional metadata
+ (using the
+ <link linkend='var-OVERRIDES'><filename>OVERRIDES</filename></link>
+ mechanism) for a single version, or an optionally named range of versions.
+ Here is an example:
+ <literallayout class='monospaced'>
+ BBVERSIONS = "1.0 2.0 git"
+ SRC_URI_git = "git://someurl/somepath.git"
+
+ BBVERSIONS = "1.0.[0-6]:1.0.0+ \ 1.0.[7-9]:1.0.7+"
+ SRC_URI_append_1.0.7+ = "file://some_patch_which_the_new_versions_need.patch;patch=1"
+ </literallayout>
+ The name of the range defaults to the original version of the
+ recipe.
+ For example, in OpenEmbedded, the recipe file
+ <filename>foo_1.0.0+.bb</filename> creates a default name range
+ of <filename>1.0.0+</filename>.
+ This is useful because the range name is not only placed
+ into overrides, but it is also made available for the metadata to use
+ in the variable that defines the base recipe versions for use in
+ <filename>file://</filename> search paths
+ (<link linkend='var-FILESPATH'><filename>FILESPATH</filename></link>).
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='dependencies'>
+ <title>Dependencies</title>
+
+ <para>
+ To allow for efficient operation given multiple processes
+ executing in parallel, BitBake handles dependencies at
+ the task level.
+ BitBake supports a robust method to handle these dependencies.
+ </para>
+
+ <para>
+ This section describes several types of dependency mechanisms.
+ </para>
+
+ <section id='dependencies-internal-to-the-bb-file'>
+ <title>Dependencies Internal to the <filename>.bb</filename> File</title>
+
+ <para>
+ BitBake uses the <filename>addtask</filename> directive
+ to manage dependencies that are internal to a given recipe
+ file.
+ You can use the <filename>addtask</filename> directive to
+ indicate when a task is dependent on other tasks or when
+ other tasks depend on that recipe.
+ Here is an example:
+ <literallayout class='monospaced'>
+ addtask printdate after do_fetch before do_build
+ </literallayout>
+ In this example, the <filename>printdate</filename> task is
+ depends on the completion of the <filename>do_fetch</filename>
+ task.
+ And, the <filename>do_build</filename> depends on the completion
+ of the <filename>printdate</filename> task.
+ </para>
+ </section>
+
+ <section id='build-dependencies'>
+ <title>Build Dependencies</title>
+
+ <para>
+ BitBake uses the
+ <link linkend='var-DEPENDS'><filename>DEPENDS</filename></link>
+ variable to manage build time dependencies.
+ The "deptask" varflag for tasks signifies the task of each
+ item listed in <filename>DEPENDS</filename> that must
+ complete before that task can be executed.
+ Here is an example:
+ <literallayout class='monospaced'>
+ do_configure[deptask] = "do_populate_sysroot"
+ </literallayout>
+ In this example, the <filename>do_populate_sysroot</filename>
+ task of each item in <filename>DEPENDS</filename> must complete before
+ <filename>do_configure</filename> can execute.
+ </para>
+ </section>
+
+ <section id='runtime-dependencies'>
+ <title>Runtime Dependencies</title>
+
+ <para>
+ BitBake uses the
+ <link linkend='var-PACKAGES'><filename>PACKAGES</filename></link>,
+ <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link>, and
+ <link linkend='var-RRECOMMENDS'><filename>RRECOMMENDS</filename></link>
+ variables to manage runtime dependencies.
+ </para>
+
+ <para>
+ The <filename>PACKAGES</filename> variable lists runtime
+ packages.
+ Each of those packages can have <filename>RDEPENDS</filename> and
+ <filename>RRECOMMENDS</filename> runtime dependencies.
+ The "rdeptask" flag for tasks is used to signify the task of each
+ item runtime dependency which must have completed before that
+ task can be executed.
+ <literallayout class='monospaced'>
+ do_package_qa[rdeptask] = "do_packagedata"
+ </literallayout>
+ In the previous example, the <filename>do_packagedata</filename>
+ task of each item in <filename>RDEPENDS</filename> must have
+ completed before <filename>do_package_qa</filename> can execute.
+ </para>
+ </section>
+
+ <section id='recursive-dependencies'>
+ <title>Recursive Dependencies</title>
+
+ <para>
+ BitBake uses the "recrdeptask" flag to manage
+ recursive task dependencies.
+ BitBake looks through the build-time and runtime
+ dependencies of the current recipe, looks through
+ the task's inter-task
+ dependencies, and then adds dependencies for the
+ listed task.
+ Once BitBake has accomplished this, it recursively works through
+ the dependencies of those tasks.
+ Iterative passes continue until all dependencies are discovered
+ and added.
+ </para>
+
+ <para>
+ You might want to not only have BitBake look for
+ dependencies of those tasks, but also have BitBake look
+ for build-time and runtime dependencies of the dependent
+ tasks as well.
+ If that is the case, you need to reference the task name
+ itself in the task list:
+ <literallayout class='monospaced'>
+ do_a[recrdeptask] = "do_a do_b"
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='inter-task-dependencies'>
+ <title>Inter-Task Dependencies</title>
+
+ <para>
+ BitBake uses the "depends" flag in a more generic form
+ to manage inter-task dependencies.
+ This more generic form allows for inter-dependency
+ checks for specific tasks rather than checks for
+ the data in <filename>DEPENDS</filename>.
+ Here is an example:
+ <literallayout class='monospaced'>
+ do_patch[depends] = "quilt-native:do_populate_sysroot"
+ </literallayout>
+ In this example, the <filename>do_populate_sysroot</filename>
+ task of the target <filename>quilt-native</filename>
+ must have completed before the
+ <filename>do_patch</filename> task can execute.
+ </para>
+
+ <para>
+ The "rdepends" flag works in a similar way but takes targets
+ in the runtime namespace instead of the build-time dependency
+ namespace.
+ </para>
+ </section>
+ </section>
+
+ <section id='accessing-datastore-variables-using-python'>
+ <title>Accessing Datastore Variables Using Python</title>
+
+ <para>
+ It is often necessary to access variables in the
+ BitBake datastore using Python functions.
+ The Bitbake datastore has an API that allows you this
+ access.
+ Here is a list of available operations:
+ </para>
+
+ <para>
+ <informaltable frame='none'>
+ <tgroup cols='2' align='left' colsep='1' rowsep='1'>
+ <colspec colname='c1' colwidth='1*'/>
+ <colspec colname='c2' colwidth='1*'/>
+ <thead>
+ <row>
+ <entry align="left"><emphasis>Operation</emphasis></entry>
+ <entry align="left"><emphasis>Description</emphasis></entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry align="left"><filename>d.getVar("X", expand=False)</filename></entry>
+ <entry align="left">Returns the value of variable "X".
+ Using "expand=True" expands the value.</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.setVar("X", "value")</filename></entry>
+ <entry align="left">Sets the variable "X" to "value".</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.appendVar("X", "value")</filename></entry>
+ <entry align="left">Adds "value" to the end of the variable "X".</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.prependVar("X", "value")</filename></entry>
+ <entry align="left">Adds "value" to the start of the variable "X".</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.delVar("X")</filename></entry>
+ <entry align="left">Deletes the variable "X" from the datastore.</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.renameVar("X", "Y")</filename></entry>
+ <entry align="left">Renames the variable "X" to "Y".</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.getVarFlag("X", flag, expand=False)</filename></entry>
+ <entry align="left">Gets then named flag from the variable "X".
+ Using "expand=True" expands the named flag.</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.setVarFlag("X", flag, "value")</filename></entry>
+ <entry align="left">Sets the named flag for variable "X" to "value".</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.appendVarFlag("X", flag, "value")</filename></entry>
+ <entry align="left">Appends "value" to the named flag on the
+ variable "X".</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.prependVarFlag("X", flag, "value")</filename></entry>
+ <entry align="left">Prepends "value" to the named flag on
+ the variable "X".</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.delVarFlag("X", flag)</filename></entry>
+ <entry align="left">Deletes the named flag on the variable
+ "X" from the datastore.</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.setVarFlags("X", flagsdict)</filename></entry>
+ <entry align="left">Sets the flags specified in
+ the <filename>flagsdict()</filename> parameter.
+ <filename>setVarFlags</filename> does not clear previous flags.
+ Think of this operation as <filename>addVarFlags</filename>.</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.getVarFlags("X")</filename></entry>
+ <entry align="left">Returns a <filename>flagsdict</filename> of the flags for
+ the variable "X".</entry>
+ </row>
+ <row>
+ <entry align="left"><filename>d.delVarFlags("X")</filename></entry>
+ <entry align="left">Deletes all the flags for the variable "X".</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </para>
+ </section>
+
+ <section id='task-checksums-and-setscene'>
+ <title>Task Checksums and Setscene</title>
+
+ <para>
+ BitBake uses checksums (or signatures) along with the setscene
+ to determine if a task needs to be run.
+ This section describes the process.
+ To help understand how BitBake does this, the section assumes an
+ OpenEmbedded metadata-based example.
+ </para>
+
+ <para>
+ This list is a place holder of content existed from previous work
+ on the manual.
+ Some or all of it probably needs integrated into the subsections
+ that make up this section.
+ For now, I have just provided a short glossary-like description
+ for each variable.
+ Ultimately, this list goes away.
+ <itemizedlist>
+ <listitem><para><filename>STAMP</filename>:
+ The base path to create stamp files.</para></listitem>
+ <listitem><para><filename>STAMPCLEAN</filename>
+ Again, the base path to create stamp files but can use wildcards
+ for matching a range of files for clean operations.
+ </para></listitem>
+ <listitem><para><filename>BB_STAMP_WHITELIST</filename>
+ Lists stamp files that are looked at when the stamp policy
+ is "whitelist".
+ </para></listitem>
+ <listitem><para><filename>BB_STAMP_POLICY</filename>
+ Defines the mode for comparing timestamps of stamp files.
+ </para></listitem>
+ <listitem><para><filename>BB_HASHCHECK_FUNCTION</filename>
+ Specifies the name of the function to call during
+ the "setscene" part of the task's execution in order
+ to validate the list of task hashes.
+ </para></listitem>
+ <listitem><para><filename>BB_SETSCENE_VERIFY_FUNCTION</filename>
+ Specifies a function to call that verifies the list of
+ planned task execution before the main task execution
+ happens.
+ </para></listitem>
+ <listitem><para><filename>BB_SETSCENE_DEPVALID</filename>
+ Specifies a function BitBake calls that determines
+ whether BitBake requires a setscene dependency to
+ be met.
+ </para></listitem>
+ <listitem><para><filename>BB_TASKHASH</filename>
+ Within an executing task, this variable holds the hash
+ of the task as returned by the currently enabled
+ signature generator.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+</chapter>