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+.. SPDX-License-Identifier: CC-BY-2.5
+
+=========
+Execution
+=========
+
+|
+
+The primary purpose for running BitBake is to produce some kind of
+output such as a single installable package, a kernel, a software
+development kit, or even a full, board-specific bootable Linux image,
+complete with bootloader, kernel, and root filesystem. Of course, you
+can execute the ``bitbake`` command with options that cause it to
+execute single tasks, compile single recipe files, capture or clear
+data, or simply return information about the execution environment.
+
+This chapter describes BitBake's execution process from start to finish
+when you use it to create an image. The execution process is launched
+using the following command form: ::
+
+  $ bitbake target
+
+For information on
+the BitBake command and its options, see ":ref:`The BitBake Command
+<bitbake-user-manual-command>`" section.
+
+.. note::
+
+   Prior to executing BitBake, you should take advantage of available
+   parallel thread execution on your build host by setting the
+   :term:`BB_NUMBER_THREADS` variable in
+   your project's ``local.conf`` configuration file.
+
+   A common method to determine this value for your build host is to run
+   the following: ::
+
+     $ grep processor /proc/cpuinfo
+
+   This command returns
+   the number of processors, which takes into account hyper-threading.
+   Thus, a quad-core build host with hyper-threading most likely shows
+   eight processors, which is the value you would then assign to
+   ``BB_NUMBER_THREADS``.
+
+   A possibly simpler solution is that some Linux distributions (e.g.
+   Debian and Ubuntu) provide the ``ncpus`` command.
+
+Parsing the Base Configuration Metadata
+=======================================
+
+The first thing BitBake does is parse base configuration metadata. Base
+configuration metadata consists of your project's ``bblayers.conf`` file
+to determine what layers BitBake needs to recognize, all necessary
+``layer.conf`` files (one from each layer), and ``bitbake.conf``. The
+data itself is of various types:
+
+-  **Recipes:** Details about particular pieces of software.
+
+-  **Class Data:** An abstraction of common build information (e.g. how to
+   build a Linux kernel).
+
+-  **Configuration Data:** Machine-specific settings, policy decisions,
+   and so forth. Configuration data acts as the glue to bind everything
+   together.
+
+The ``layer.conf`` files are used to construct key variables such as
+:term:`BBPATH` and :term:`BBFILES`.
+``BBPATH`` is used to search for configuration and class files under the
+``conf`` and ``classes`` directories, respectively. ``BBFILES`` is used
+to locate both recipe and recipe append files (``.bb`` and
+``.bbappend``). If there is no ``bblayers.conf`` file, it is assumed the
+user has set the ``BBPATH`` and ``BBFILES`` directly in the environment.
+
+Next, the ``bitbake.conf`` file is located using the ``BBPATH`` variable
+that was just constructed. The ``bitbake.conf`` file may also include
+other configuration files using the ``include`` or ``require``
+directives.
+
+Prior to parsing configuration files, BitBake looks at certain
+variables, including:
+
+-  :term:`BB_ENV_WHITELIST`
+-  :term:`BB_ENV_EXTRAWHITE`
+-  :term:`BB_PRESERVE_ENV`
+-  :term:`BB_ORIGENV`
+-  :term:`BITBAKE_UI`
+
+The first four variables in this list relate to how BitBake treats shell
+environment variables during task execution. By default, BitBake cleans
+the environment variables and provides tight control over the shell
+execution environment. However, through the use of these first four
+variables, you can apply your control regarding the environment
+variables allowed to be used by BitBake in the shell during execution of
+tasks. See the
+":ref:`bitbake-user-manual/bitbake-user-manual-metadata:Passing Information Into the Build Task Environment`"
+section and the information about these variables in the variable
+glossary for more information on how they work and on how to use them.
+
+The base configuration metadata is global and therefore affects all
+recipes and tasks that are executed.
+
+BitBake first searches the current working directory for an optional
+``conf/bblayers.conf`` configuration file. This file is expected to
+contain a :term:`BBLAYERS` variable that is a
+space-delimited list of 'layer' directories. Recall that if BitBake
+cannot find a ``bblayers.conf`` file, then it is assumed the user has
+set the ``BBPATH`` and ``BBFILES`` variables directly in the
+environment.
+
+For each directory (layer) in this list, a ``conf/layer.conf`` file is
+located and parsed with the :term:`LAYERDIR` variable
+being set to the directory where the layer was found. The idea is these
+files automatically set up :term:`BBPATH` and other
+variables correctly for a given build directory.
+
+BitBake then expects to find the ``conf/bitbake.conf`` file somewhere in
+the user-specified ``BBPATH``. That configuration file generally has
+include directives to pull in any other metadata such as files specific
+to the architecture, the machine, the local environment, and so forth.
+
+Only variable definitions and include directives are allowed in BitBake
+``.conf`` files. Some variables directly influence BitBake's behavior.
+These variables might have been set from the environment depending on
+the environment variables previously mentioned or set in the
+configuration files. The ":ref:`bitbake-user-manual/bitbake-user-manual-ref-variables:Variables Glossary`"
+chapter presents a full list of
+variables.
+
+After parsing configuration files, BitBake uses its rudimentary
+inheritance mechanism, which is through class files, to inherit some
+standard classes. BitBake parses a class when the inherit directive
+responsible for getting that class is encountered.
+
+The ``base.bbclass`` file is always included. Other classes that are
+specified in the configuration using the
+:term:`INHERIT` variable are also included. BitBake
+searches for class files in a ``classes`` subdirectory under the paths
+in ``BBPATH`` in the same way as configuration files.
+
+A good way to get an idea of the configuration files and the class files
+used in your execution environment is to run the following BitBake
+command: ::
+
+  $ bitbake -e > mybb.log
+
+Examining the top of the ``mybb.log``
+shows you the many configuration files and class files used in your
+execution environment.
+
+.. note::
+
+   You need to be aware of how BitBake parses curly braces. If a recipe
+   uses a closing curly brace within the function and the character has
+   no leading spaces, BitBake produces a parsing error. If you use a
+   pair of curly braces in a shell function, the closing curly brace
+   must not be located at the start of the line without leading spaces.
+
+   Here is an example that causes BitBake to produce a parsing error: ::
+
+      fakeroot create_shar() {
+         cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
+      usage()
+      {
+         echo "test"
+         ######  The following "}" at the start of the line causes a parsing error ######
+      }
+      EOF
+      }
+
+      Writing the recipe this way avoids the error:
+      fakeroot create_shar() {
+         cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
+      usage()
+      {
+         echo "test"
+         ###### The following "}" with a leading space at the start of the line avoids the error ######
+       }
+      EOF
+      }
+
+Locating and Parsing Recipes
+============================
+
+During the configuration phase, BitBake will have set
+:term:`BBFILES`. BitBake now uses it to construct a
+list of recipes to parse, along with any append files (``.bbappend``) to
+apply. ``BBFILES`` is a space-separated list of available files and
+supports wildcards. An example would be: ::
+
+  BBFILES = "/path/to/bbfiles/*.bb /path/to/appends/*.bbappend"
+
+BitBake parses each
+recipe and append file located with ``BBFILES`` and stores the values of
+various variables into the datastore.
+
+.. note::
+
+   Append files are applied in the order they are encountered in BBFILES.
+
+For each file, a fresh copy of the base configuration is made, then the
+recipe is parsed line by line. Any inherit statements cause BitBake to
+find and then parse class files (``.bbclass``) using
+:term:`BBPATH` as the search path. Finally, BitBake
+parses in order any append files found in ``BBFILES``.
+
+One common convention is to use the recipe filename to define pieces of
+metadata. For example, in ``bitbake.conf`` the recipe name and version
+are used to set the variables :term:`PN` and
+:term:`PV`: ::
+
+   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'}"
+
+In this example, a recipe called "something_1.2.3.bb" would set
+``PN`` to "something" and ``PV`` to "1.2.3".
+
+By the time parsing is complete for a recipe, BitBake has a list of
+tasks that the recipe defines and a set of data consisting of keys and
+values as well as dependency information about the tasks.
+
+BitBake does not need all of this information. It only needs a small
+subset of the information to make decisions about the recipe.
+Consequently, BitBake caches the values in which it is interested and
+does not store the rest of the information. Experience has shown it is
+faster to re-parse the metadata than to try and write it out to the disk
+and then reload it.
+
+Where possible, subsequent BitBake commands reuse this cache of recipe
+information. The validity of this cache is determined by first computing
+a checksum of the base configuration data (see
+:term:`BB_HASHCONFIG_WHITELIST`) and
+then checking if the checksum matches. If that checksum matches what is
+in the cache and the recipe and class files have not changed, BitBake is
+able to use the cache. BitBake then reloads the cached information about
+the recipe instead of reparsing it from scratch.
+
+Recipe file collections exist to allow the user to have multiple
+repositories of ``.bb`` files that contain the same exact package. For
+example, one could easily use them to make one's own local copy of an
+upstream repository, but with custom modifications that one does not
+want upstream. Here is an example: ::
+
+  BBFILES = "/stuff/openembedded/*/*.bb /stuff/openembedded.modified/*/*.bb"
+  BBFILE_COLLECTIONS = "upstream local"
+  BBFILE_PATTERN_upstream = "^/stuff/openembedded/"
+  BBFILE_PATTERN_local = "^/stuff/openembedded.modified/"
+  BBFILE_PRIORITY_upstream = "5" BBFILE_PRIORITY_local = "10"
+
+.. note::
+
+   The layers mechanism is now the preferred method of collecting code.
+   While the collections code remains, its main use is to set layer
+   priorities and to deal with overlap (conflicts) between layers.
+
+.. _bb-bitbake-providers:
+
+Providers
+=========
+
+Assuming BitBake has been instructed to execute a target and that all
+the recipe files have been parsed, BitBake starts to figure out how to
+build the target. BitBake looks through the ``PROVIDES`` list for each
+of the recipes. A ``PROVIDES`` list is the list of names by which the
+recipe can be known. Each recipe's ``PROVIDES`` list is created
+implicitly through the recipe's :term:`PN` variable and
+explicitly through the recipe's :term:`PROVIDES`
+variable, which is optional.
+
+When a recipe uses ``PROVIDES``, that recipe's functionality can be
+found under an alternative name or names other than the implicit ``PN``
+name. As an example, suppose a recipe named ``keyboard_1.0.bb``
+contained the following: ::
+
+  PROVIDES += "fullkeyboard"
+
+The ``PROVIDES``
+list for this recipe becomes "keyboard", which is implicit, and
+"fullkeyboard", which is explicit. Consequently, the functionality found
+in ``keyboard_1.0.bb`` can be found under two different names.
+
+.. _bb-bitbake-preferences:
+
+Preferences
+===========
+
+The ``PROVIDES`` list is only part of the solution for figuring out a
+target's recipes. Because targets might have multiple providers, BitBake
+needs to prioritize providers by determining provider preferences.
+
+A common example in which a target has multiple providers is
+"virtual/kernel", which is on the ``PROVIDES`` list for each kernel
+recipe. Each machine often selects the best kernel provider by using a
+line similar to the following in the machine configuration file: ::
+
+  PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
+
+The default :term:`PREFERRED_PROVIDER` is the provider
+with the same name as the target. BitBake iterates through each target
+it needs to build and resolves them and their dependencies using this
+process.
+
+Understanding how providers are chosen is made complicated by the fact
+that multiple versions might exist for a given provider. BitBake
+defaults to the highest version of a provider. Version comparisons are
+made using the same method as Debian. You can use the
+:term:`PREFERRED_VERSION` variable to
+specify a particular version. You can influence the order by using the
+:term:`DEFAULT_PREFERENCE` variable.
+
+By default, files have a preference of "0". Setting
+``DEFAULT_PREFERENCE`` to "-1" makes the recipe unlikely to be used
+unless it is explicitly referenced. Setting ``DEFAULT_PREFERENCE`` to
+"1" makes it likely the recipe is used. ``PREFERRED_VERSION`` overrides
+any ``DEFAULT_PREFERENCE`` setting. ``DEFAULT_PREFERENCE`` is often used
+to mark newer and more experimental recipe versions until they have
+undergone sufficient testing to be considered stable.
+
+When there are multiple “versions” of a given recipe, BitBake defaults
+to selecting the most recent version, unless otherwise specified. If the
+recipe in question has a
+:term:`DEFAULT_PREFERENCE` set lower than
+the other recipes (default is 0), then it will not be selected. This
+allows the person or persons maintaining the repository of recipe files
+to specify their preference for the default selected version.
+Additionally, the user can specify their preferred version.
+
+If the first recipe is named ``a_1.1.bb``, then the
+:term:`PN` variable will be set to “a”, and the
+:term:`PV` variable will be set to 1.1.
+
+Thus, if a recipe named ``a_1.2.bb`` exists, BitBake will choose 1.2 by
+default. However, if you define the following variable in a ``.conf``
+file that BitBake parses, you can change that preference: ::
+
+  PREFERRED_VERSION_a = "1.1"
+
+.. note::
+
+   It is common for a recipe to provide two versions -- a stable,
+   numbered (and preferred) version, and a version that is automatically
+   checked out from a source code repository that is considered more
+   "bleeding edge" but can be selected only explicitly.
+
+   For example, in the OpenEmbedded codebase, there is a standard,
+   versioned recipe file for BusyBox, ``busybox_1.22.1.bb``, but there
+   is also a Git-based version, ``busybox_git.bb``, which explicitly
+   contains the line ::
+
+     DEFAULT_PREFERENCE = "-1"
+
+   to ensure that the
+   numbered, stable version is always preferred unless the developer
+   selects otherwise.
+
+.. _bb-bitbake-dependencies:
+
+Dependencies
+============
+
+Each target BitBake builds consists of multiple tasks such as ``fetch``,
+``unpack``, ``patch``, ``configure``, and ``compile``. For best
+performance on multi-core systems, BitBake considers each task as an
+independent entity with its own set of dependencies.
+
+Dependencies are defined through several variables. You can find
+information about variables BitBake uses in the
+:doc:`bitbake-user-manual-ref-variables` near the end of this manual. At a
+basic level, it is sufficient to know that BitBake uses the
+:term:`DEPENDS` and
+:term:`RDEPENDS` variables when calculating
+dependencies.
+
+For more information on how BitBake handles dependencies, see the
+:ref:`bitbake-user-manual/bitbake-user-manual-metadata:Dependencies`
+section.
+
+.. _ref-bitbake-tasklist:
+
+The Task List
+=============
+
+Based on the generated list of providers and the dependency information,
+BitBake can now calculate exactly what tasks it needs to run and in what
+order it needs to run them. The
+:ref:`bitbake-user-manual/bitbake-user-manual-execution:executing tasks`
+section has more information on how BitBake chooses which task to
+execute next.
+
+The build now starts with BitBake forking off threads up to the limit
+set in the :term:`BB_NUMBER_THREADS`
+variable. BitBake continues to fork threads as long as there are tasks
+ready to run, those tasks have all their dependencies met, and the
+thread threshold has not been exceeded.
+
+It is worth noting that you can greatly speed up the build time by
+properly setting the ``BB_NUMBER_THREADS`` variable.
+
+As each task completes, a timestamp is written to the directory
+specified by the :term:`STAMP` variable. On subsequent
+runs, BitBake looks in the build directory within ``tmp/stamps`` and
+does not rerun tasks that are already completed unless a timestamp is
+found to be invalid. Currently, invalid timestamps are only considered
+on a per recipe file basis. So, for example, if the configure stamp has
+a timestamp greater than the compile timestamp for a given target, then
+the compile task would rerun. Running the compile task again, however,
+has no effect on other providers that depend on that target.
+
+The exact format of the stamps is partly configurable. In modern
+versions of BitBake, a hash is appended to the stamp so that if the
+configuration changes, the stamp becomes invalid and the task is
+automatically rerun. This hash, or signature used, is governed by the
+signature policy that is configured (see the
+:ref:`bitbake-user-manual/bitbake-user-manual-execution:checksums (signatures)`
+section for information). It is also
+possible to append extra metadata to the stamp using the
+``[stamp-extra-info]`` task flag. For example, OpenEmbedded uses this
+flag to make some tasks machine-specific.
+
+.. note::
+
+   Some tasks are marked as "nostamp" tasks. No timestamp file is
+   created when these tasks are run. Consequently, "nostamp" tasks are
+   always rerun.
+
+For more information on tasks, see the
+:ref:`bitbake-user-manual/bitbake-user-manual-metadata:tasks` section.
+
+Executing Tasks
+===============
+
+Tasks can be either a shell task or a Python task. For shell tasks,
+BitBake writes a shell script to
+``${``\ :term:`T`\ ``}/run.do_taskname.pid`` and then
+executes the script. The generated shell script contains all the
+exported variables, and the shell functions with all variables expanded.
+Output from the shell script goes to the file
+``${T}/log.do_taskname.pid``. Looking at the expanded shell functions in
+the run file and the output in the log files is a useful debugging
+technique.
+
+For Python tasks, BitBake executes the task internally and logs
+information to the controlling terminal. Future versions of BitBake will
+write the functions to files similar to the way shell tasks are handled.
+Logging will be handled in a way similar to shell tasks as well.
+
+The order in which BitBake runs the tasks is controlled by its task
+scheduler. It is possible to configure the scheduler and define custom
+implementations for specific use cases. For more information, see these
+variables that control the behavior:
+
+-  :term:`BB_SCHEDULER`
+
+-  :term:`BB_SCHEDULERS`
+
+It is possible to have functions run before and after a task's main
+function. This is done using the ``[prefuncs]`` and ``[postfuncs]``
+flags of the task that lists the functions to run.
+
+.. _checksums:
+
+Checksums (Signatures)
+======================
+
+A checksum is a unique signature of a task's inputs. The signature of a
+task can be used to determine if a task needs to be run. Because it is a
+change in a task's inputs that triggers running the task, BitBake needs
+to detect all the inputs to a given task. For shell tasks, this turns
+out to be fairly easy because BitBake generates a "run" shell script for
+each task and it is possible to create a checksum that gives you a good
+idea of when the task's data changes.
+
+To complicate the problem, some things should not be included in the
+checksum. First, there is the actual specific build path of a given task
+- the working directory. It does not matter if the working directory
+changes because it should not affect the output for target packages. The
+simplistic approach for excluding the working directory is to set it to
+some fixed value and create the checksum for the "run" script. BitBake
+goes one step better and uses the
+:term:`BB_HASHBASE_WHITELIST` variable
+to define a list of variables that should never be included when
+generating the signatures.
+
+Another problem results from the "run" scripts containing functions that
+might or might not get called. The incremental build solution contains
+code that figures out dependencies between shell functions. This code is
+used to prune the "run" scripts down to the minimum set, thereby
+alleviating this problem and making the "run" scripts much more readable
+as a bonus.
+
+So far we have solutions for shell scripts. What about Python tasks? The
+same approach applies even though these tasks are more difficult. The
+process needs to figure out what variables a Python function accesses
+and what functions it calls. Again, the incremental build solution
+contains code that first figures out the variable and function
+dependencies, and then creates a checksum for the data used as the input
+to the task.
+
+Like the working directory case, situations exist where dependencies
+should be ignored. For these cases, you can instruct the build process
+to ignore a dependency by using a line like the following: ::
+
+  PACKAGE_ARCHS[vardepsexclude] = "MACHINE"
+
+This example ensures that the
+``PACKAGE_ARCHS`` variable does not depend on the value of ``MACHINE``,
+even if it does reference it.
+
+Equally, there are cases where we need to add dependencies BitBake is
+not able to find. You can accomplish this by using a line like the
+following: ::
+
+  PACKAGE_ARCHS[vardeps] = "MACHINE"
+
+This example explicitly
+adds the ``MACHINE`` variable as a dependency for ``PACKAGE_ARCHS``.
+
+Consider a case with in-line Python, for example, where BitBake is not
+able to figure out dependencies. When running in debug mode (i.e. using
+``-DDD``), BitBake produces output when it discovers something for which
+it cannot figure out dependencies.
+
+Thus far, this section has limited discussion to the direct inputs into
+a task. Information based on direct inputs is referred to as the
+"basehash" in the code. However, there is still the question of a task's
+indirect inputs - the things that were already built and present in the
+build directory. The checksum (or signature) for a particular task needs
+to add the hashes of all the tasks on which the particular task depends.
+Choosing which dependencies to add is a policy decision. However, the
+effect is to generate a master checksum that combines the basehash and
+the hashes of the task's dependencies.
+
+At the code level, there are a variety of ways both the basehash and the
+dependent task hashes can be influenced. Within the BitBake
+configuration file, we can give BitBake some extra information to help
+it construct the basehash. The following statement effectively results
+in a list of global variable dependency excludes - variables never
+included in any checksum. This example uses variables from OpenEmbedded
+to help illustrate the concept: ::
+
+   BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \
+       SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL \
+       USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \
+       PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \
+       CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX"
+
+The previous example excludes the work directory, which is part of
+``TMPDIR``.
+
+The rules for deciding which hashes of dependent tasks to include
+through dependency chains are more complex and are generally
+accomplished with a Python function. The code in
+``meta/lib/oe/sstatesig.py`` shows two examples of this and also
+illustrates how you can insert your own policy into the system if so
+desired. This file defines the two basic signature generators
+OpenEmbedded-Core uses: "OEBasic" and "OEBasicHash". By default, there
+is a dummy "noop" signature handler enabled in BitBake. This means that
+behavior is unchanged from previous versions. ``OE-Core`` uses the
+"OEBasicHash" signature handler by default through this setting in the
+``bitbake.conf`` file: ::
+
+  BB_SIGNATURE_HANDLER ?= "OEBasicHash"
+
+The "OEBasicHash" ``BB_SIGNATURE_HANDLER`` is the same as the "OEBasic"
+version but adds the task hash to the stamp files. This results in any
+metadata change that changes the task hash, automatically causing the
+task to be run again. This removes the need to bump
+:term:`PR` values, and changes to metadata automatically
+ripple across the build.
+
+It is also worth noting that the end result of these signature
+generators is to make some dependency and hash information available to
+the build. This information includes:
+
+-  ``BB_BASEHASH_task-``\ *taskname*: The base hashes for each task in the
+   recipe.
+
+-  ``BB_BASEHASH_``\ *filename:taskname*: The base hashes for each
+   dependent task.
+
+-  ``BBHASHDEPS_``\ *filename:taskname*: The task dependencies for
+   each task.
+
+-  ``BB_TASKHASH``: The hash of the currently running task.
+
+It is worth noting that BitBake's "-S" option lets you debug BitBake's
+processing of signatures. The options passed to -S allow different
+debugging modes to be used, either using BitBake's own debug functions
+or possibly those defined in the metadata/signature handler itself. The
+simplest parameter to pass is "none", which causes a set of signature
+information to be written out into ``STAMPS_DIR`` corresponding to the
+targets specified. The other currently available parameter is
+"printdiff", which causes BitBake to try to establish the closest
+signature match it can (e.g. in the sstate cache) and then run
+``bitbake-diffsigs`` over the matches to determine the stamps and delta
+where these two stamp trees diverge.
+
+.. note::
+
+   It is likely that future versions of BitBake will provide other
+   signature handlers triggered through additional "-S" parameters.
+
+You can find more information on checksum metadata in the
+:ref:`bitbake-user-manual/bitbake-user-manual-metadata:task checksums and setscene`
+section.
+
+Setscene
+========
+
+The setscene process enables BitBake to handle "pre-built" artifacts.
+The ability to handle and reuse these artifacts allows BitBake the
+luxury of not having to build something from scratch every time.
+Instead, BitBake can use, when possible, existing build artifacts.
+
+BitBake needs to have reliable data indicating whether or not an
+artifact is compatible. Signatures, described in the previous section,
+provide an ideal way of representing whether an artifact is compatible.
+If a signature is the same, an object can be reused.
+
+If an object can be reused, the problem then becomes how to replace a
+given task or set of tasks with the pre-built artifact. BitBake solves
+the problem with the "setscene" process.
+
+When BitBake is asked to build a given target, before building anything,
+it first asks whether cached information is available for any of the
+targets it's building, or any of the intermediate targets. If cached
+information is available, BitBake uses this information instead of
+running the main tasks.
+
+BitBake first calls the function defined by the
+:term:`BB_HASHCHECK_FUNCTION` variable
+with a list of tasks and corresponding hashes it wants to build. This
+function is designed to be fast and returns a list of the tasks for
+which it believes in can obtain artifacts.
+
+Next, for each of the tasks that were returned as possibilities, BitBake
+executes a setscene version of the task that the possible artifact
+covers. Setscene versions of a task have the string "_setscene" appended
+to the task name. So, for example, the task with the name ``xxx`` has a
+setscene task named ``xxx_setscene``. The setscene version of the task
+executes and provides the necessary artifacts returning either success
+or failure.
+
+As previously mentioned, an artifact can cover more than one task. For
+example, it is pointless to obtain a compiler if you already have the
+compiled binary. To handle this, BitBake calls the
+:term:`BB_SETSCENE_DEPVALID` function for
+each successful setscene task to know whether or not it needs to obtain
+the dependencies of that task.
+
+Finally, after all the setscene tasks have executed, BitBake calls the
+function listed in
+:term:`BB_SETSCENE_VERIFY_FUNCTION2`
+with the list of tasks BitBake thinks has been "covered". The metadata
+can then ensure that this list is correct and can inform BitBake that it
+wants specific tasks to be run regardless of the setscene result.
+
+You can find more information on setscene metadata in the
+:ref:`bitbake-user-manual/bitbake-user-manual-metadata:task checksums and setscene`
+section.
+
+Logging
+=======
+
+In addition to the standard command line option to control how verbose
+builds are when execute, bitbake also supports user defined
+configuration of the `Python
+logging <https://docs.python.org/3/library/logging.html>`__ facilities
+through the :term:`BB_LOGCONFIG` variable. This
+variable defines a json or yaml `logging
+configuration <https://docs.python.org/3/library/logging.config.html>`__
+that will be intelligently merged into the default configuration. The
+logging configuration is merged using the following rules:
+
+-  The user defined configuration will completely replace the default
+   configuration if top level key ``bitbake_merge`` is set to the value
+   ``False``. In this case, all other rules are ignored.
+
+-  The user configuration must have a top level ``version`` which must
+   match the value of the default configuration.
+
+-  Any keys defined in the ``handlers``, ``formatters``, or ``filters``,
+   will be merged into the same section in the default configuration,
+   with the user specified keys taking replacing a default one if there
+   is a conflict. In practice, this means that if both the default
+   configuration and user configuration specify a handler named
+   ``myhandler``, the user defined one will replace the default. To
+   prevent the user from inadvertently replacing a default handler,
+   formatter, or filter, all of the default ones are named with a prefix
+   of "``BitBake.``"
+
+-  If a logger is defined by the user with the key ``bitbake_merge`` set
+   to ``False``, that logger will be completely replaced by user
+   configuration. In this case, no other rules will apply to that
+   logger.
+
+-  All user defined ``filter`` and ``handlers`` properties for a given
+   logger will be merged with corresponding properties from the default
+   logger. For example, if the user configuration adds a filter called
+   ``myFilter`` to the ``BitBake.SigGen``, and the default configuration
+   adds a filter called ``BitBake.defaultFilter``, both filters will be
+   applied to the logger
+
+As an example, consider the following user logging configuration file
+which logs all Hash Equivalence related messages of VERBOSE or higher to
+a file called ``hashequiv.log`` ::
+
+   {
+       "version": 1,
+       "handlers": {
+           "autobuilderlog": {
+               "class": "logging.FileHandler",
+               "formatter": "logfileFormatter",
+               "level": "DEBUG",
+               "filename": "hashequiv.log",
+               "mode": "w"
+           }
+       },
+       "formatters": {
+               "logfileFormatter": {
+                   "format": "%(name)s: %(levelname)s: %(message)s"
+               }
+       },
+       "loggers": {
+           "BitBake.SigGen.HashEquiv": {
+               "level": "VERBOSE",
+               "handlers": ["autobuilderlog"]
+           },
+           "BitBake.RunQueue.HashEquiv": {
+               "level": "VERBOSE",
+               "handlers": ["autobuilderlog"]
+           }
+       }
+   }
diff --git a/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-fetching.rst b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-fetching.rst
new file mode 100644
index 0000000..f62ddff
--- /dev/null
+++ b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-fetching.rst
@@ -0,0 +1,652 @@
+.. SPDX-License-Identifier: CC-BY-2.5
+
+=====================
+File Download Support
+=====================
+
+|
+
+BitBake's fetch module is a standalone piece of library code that deals
+with the intricacies of downloading source code and files from remote
+systems. Fetching source code is one of the cornerstones of building
+software. As such, this module forms an important part of BitBake.
+
+The current fetch module is called "fetch2" and refers to the fact that
+it is the second major version of the API. The original version is
+obsolete and has been removed from the codebase. Thus, in all cases,
+"fetch" refers to "fetch2" in this manual.
+
+The Download (Fetch)
+====================
+
+BitBake takes several steps when fetching source code or files. The
+fetcher codebase deals with two distinct processes in order: obtaining
+the files from somewhere (cached or otherwise) and then unpacking those
+files into a specific location and perhaps in a specific way. Getting
+and unpacking the files is often optionally followed by patching.
+Patching, however, is not covered by this module.
+
+The code to execute the first part of this process, a fetch, looks
+something like the following: ::
+
+   src_uri = (d.getVar('SRC_URI') or "").split()
+   fetcher = bb.fetch2.Fetch(src_uri, d)
+   fetcher.download()
+
+This code sets up an instance of the fetch class. The instance uses a
+space-separated list of URLs from the :term:`SRC_URI`
+variable and then calls the ``download`` method to download the files.
+
+The instantiation of the fetch class is usually followed by: ::
+
+   rootdir = l.getVar('WORKDIR')
+   fetcher.unpack(rootdir)
+
+This code unpacks the downloaded files to the specified by ``WORKDIR``.
+
+.. note::
+
+   For convenience, the naming in these examples matches the variables
+   used by OpenEmbedded. If you want to see the above code in action,
+   examine the OpenEmbedded class file ``base.bbclass``
+   .
+
+The ``SRC_URI`` and ``WORKDIR`` variables are not hardcoded into the
+fetcher, since those fetcher methods can be (and are) called with
+different variable names. In OpenEmbedded for example, the shared state
+(sstate) code uses the fetch module to fetch the sstate files.
+
+When the ``download()`` method is called, BitBake tries to resolve the
+URLs by looking for source files in a specific search order:
+
+-  *Pre-mirror Sites:* BitBake first uses pre-mirrors to try and find
+   source files. These locations are defined using the
+   :term:`PREMIRRORS` variable.
+
+-  *Source URI:* If pre-mirrors fail, BitBake uses the original URL (e.g
+   from ``SRC_URI``).
+
+-  *Mirror Sites:* If fetch failures occur, BitBake next uses mirror
+   locations as defined by the :term:`MIRRORS` variable.
+
+For each URL passed to the fetcher, the fetcher calls the submodule that
+handles that particular URL type. This behavior can be the source of
+some confusion when you are providing URLs for the ``SRC_URI`` variable.
+Consider the following two URLs: ::
+
+   http://git.yoctoproject.org/git/poky;protocol=git
+   git://git.yoctoproject.org/git/poky;protocol=http
+
+In the former case, the URL is passed to the ``wget`` fetcher, which does not
+understand "git". Therefore, the latter case is the correct form since the Git
+fetcher does know how to use HTTP as a transport.
+
+Here are some examples that show commonly used mirror definitions: ::
+
+   PREMIRRORS ?= "\
+      bzr://.*/.\*  http://somemirror.org/sources/ \\n \
+      cvs://.*/.\*  http://somemirror.org/sources/ \\n \
+      git://.*/.\*  http://somemirror.org/sources/ \\n \
+      hg://.*/.\*   http://somemirror.org/sources/ \\n \
+      osc://.*/.\*  http://somemirror.org/sources/ \\n \
+      p4://.*/.\*   http://somemirror.org/sources/ \\n \
+     svn://.*/.\*   http://somemirror.org/sources/ \\n"
+
+   MIRRORS =+ "\
+      ftp://.*/.\*   http://somemirror.org/sources/ \\n \
+      http://.*/.\*  http://somemirror.org/sources/ \\n \
+      https://.*/.\* http://somemirror.org/sources/ \\n"
+
+It is useful to note that BitBake
+supports cross-URLs. It is possible to mirror a Git repository on an
+HTTP server as a tarball. This is what the ``git://`` mapping in the
+previous example does.
+
+Since network accesses are slow, BitBake maintains a cache of files
+downloaded from the network. Any source files that are not local (i.e.
+downloaded from the Internet) are placed into the download directory,
+which is specified by the :term:`DL_DIR` variable.
+
+File integrity is of key importance for reproducing builds. For
+non-local archive downloads, the fetcher code can verify SHA-256 and MD5
+checksums to ensure the archives have been downloaded correctly. You can
+specify these checksums by using the ``SRC_URI`` variable with the
+appropriate varflags as follows: ::
+
+   SRC_URI[md5sum] = "value"
+   SRC_URI[sha256sum] = "value"
+
+You can also specify the checksums as
+parameters on the ``SRC_URI`` as shown below: ::
+
+  SRC_URI = "http://example.com/foobar.tar.bz2;md5sum=4a8e0f237e961fd7785d19d07fdb994d"
+
+If multiple URIs exist, you can specify the checksums either directly as
+in the previous example, or you can name the URLs. The following syntax
+shows how you name the URIs: ::
+
+   SRC_URI = "http://example.com/foobar.tar.bz2;name=foo"
+   SRC_URI[foo.md5sum] = 4a8e0f237e961fd7785d19d07fdb994d
+
+After a file has been downloaded and
+has had its checksum checked, a ".done" stamp is placed in ``DL_DIR``.
+BitBake uses this stamp during subsequent builds to avoid downloading or
+comparing a checksum for the file again.
+
+.. note::
+
+   It is assumed that local storage is safe from data corruption. If
+   this were not the case, there would be bigger issues to worry about.
+
+If :term:`BB_STRICT_CHECKSUM` is set, any
+download without a checksum triggers an error message. The
+:term:`BB_NO_NETWORK` variable can be used to
+make any attempted network access a fatal error, which is useful for
+checking that mirrors are complete as well as other things.
+
+.. _bb-the-unpack:
+
+The Unpack
+==========
+
+The unpack process usually immediately follows the download. For all
+URLs except Git URLs, BitBake uses the common ``unpack`` method.
+
+A number of parameters exist that you can specify within the URL to
+govern the behavior of the unpack stage:
+
+-  *unpack:* Controls whether the URL components are unpacked. If set to
+   "1", which is the default, the components are unpacked. If set to
+   "0", the unpack stage leaves the file alone. This parameter is useful
+   when you want an archive to be copied in and not be unpacked.
+
+-  *dos:* Applies to ``.zip`` and ``.jar`` files and specifies whether
+   to use DOS line ending conversion on text files.
+
+-  *basepath:* Instructs the unpack stage to strip the specified
+   directories from the source path when unpacking.
+
+-  *subdir:* Unpacks the specific URL to the specified subdirectory
+   within the root directory.
+
+The unpack call automatically decompresses and extracts files with ".Z",
+".z", ".gz", ".xz", ".zip", ".jar", ".ipk", ".rpm". ".srpm", ".deb" and
+".bz2" extensions as well as various combinations of tarball extensions.
+
+As mentioned, the Git fetcher has its own unpack method that is
+optimized to work with Git trees. Basically, this method works by
+cloning the tree into the final directory. The process is completed
+using references so that there is only one central copy of the Git
+metadata needed.
+
+.. _bb-fetchers:
+
+Fetchers
+========
+
+As mentioned earlier, the URL prefix determines which fetcher submodule
+BitBake uses. Each submodule can support different URL parameters, which
+are described in the following sections.
+
+.. _local-file-fetcher:
+
+Local file fetcher (``file://``)
+--------------------------------
+
+This submodule handles URLs that begin with ``file://``. The filename
+you specify within the URL can be either an absolute or relative path to
+a file. If the filename is relative, the contents of the
+:term:`FILESPATH` variable is used in the same way
+``PATH`` is used to find executables. If the file cannot be found, it is
+assumed that it is available in :term:`DL_DIR` by the
+time the ``download()`` method is called.
+
+If you specify a directory, the entire directory is unpacked.
+
+Here are a couple of example URLs, the first relative and the second
+absolute: ::
+
+   SRC_URI = "file://relativefile.patch"
+   SRC_URI = "file:///Users/ich/very_important_software"
+
+.. _http-ftp-fetcher:
+
+HTTP/FTP wget fetcher (``http://``, ``ftp://``, ``https://``)
+-------------------------------------------------------------
+
+This fetcher obtains files from web and FTP servers. Internally, the
+fetcher uses the wget utility.
+
+The executable and parameters used are specified by the
+``FETCHCMD_wget`` variable, which defaults to sensible values. The
+fetcher supports a parameter "downloadfilename" that allows the name of
+the downloaded file to be specified. Specifying the name of the
+downloaded file is useful for avoiding collisions in
+:term:`DL_DIR` when dealing with multiple files that
+have the same name.
+
+Some example URLs are as follows: ::
+
+   SRC_URI = "http://oe.handhelds.org/not_there.aac"
+   SRC_URI = "ftp://oe.handhelds.org/not_there_as_well.aac"
+   SRC_URI = "ftp://you@oe.handhelds.org/home/you/secret.plan"
+
+.. note::
+
+   Because URL parameters are delimited by semi-colons, this can
+   introduce ambiguity when parsing URLs that also contain semi-colons,
+   for example:
+   ::
+
+           SRC_URI = "http://abc123.org/git/?p=gcc/gcc.git;a=snapshot;h=a5dd47"
+
+
+   Such URLs should should be modified by replacing semi-colons with '&'
+   characters:
+   ::
+
+           SRC_URI = "http://abc123.org/git/?p=gcc/gcc.git&a=snapshot&h=a5dd47"
+
+
+   In most cases this should work. Treating semi-colons and '&' in
+   queries identically is recommended by the World Wide Web Consortium
+   (W3C). Note that due to the nature of the URL, you may have to
+   specify the name of the downloaded file as well:
+   ::
+
+           SRC_URI = "http://abc123.org/git/?p=gcc/gcc.git&a=snapshot&h=a5dd47;downloadfilename=myfile.bz2"
+
+
+.. _cvs-fetcher:
+
+CVS fetcher (``(cvs://``)
+-------------------------
+
+This submodule handles checking out files from the CVS version control
+system. You can configure it using a number of different variables:
+
+-  :term:`FETCHCMD_cvs <FETCHCMD>`: The name of the executable to use when running
+   the ``cvs`` command. This name is usually "cvs".
+
+-  :term:`SRCDATE`: The date to use when fetching the CVS source code. A
+   special value of "now" causes the checkout to be updated on every
+   build.
+
+-  :term:`CVSDIR`: Specifies where a temporary
+   checkout is saved. The location is often ``DL_DIR/cvs``.
+
+-  CVS_PROXY_HOST: The name to use as a "proxy=" parameter to the
+   ``cvs`` command.
+
+-  CVS_PROXY_PORT: The port number to use as a "proxyport="
+   parameter to the ``cvs`` command.
+
+As well as the standard username and password URL syntax, you can also
+configure the fetcher with various URL parameters:
+
+The supported parameters are as follows:
+
+-  *"method":* The protocol over which to communicate with the CVS
+   server. By default, this protocol is "pserver". If "method" is set to
+   "ext", BitBake examines the "rsh" parameter and sets ``CVS_RSH``. You
+   can use "dir" for local directories.
+
+-  *"module":* Specifies the module to check out. You must supply this
+   parameter.
+
+-  *"tag":* Describes which CVS TAG should be used for the checkout. By
+   default, the TAG is empty.
+
+-  *"date":* Specifies a date. If no "date" is specified, the
+   :term:`SRCDATE` of the configuration is used to
+   checkout a specific date. The special value of "now" causes the
+   checkout to be updated on every build.
+
+-  *"localdir":* Used to rename the module. Effectively, you are
+   renaming the output directory to which the module is unpacked. You
+   are forcing the module into a special directory relative to
+   :term:`CVSDIR`.
+
+-  *"rsh":* Used in conjunction with the "method" parameter.
+
+-  *"scmdata":* Causes the CVS metadata to be maintained in the tarball
+   the fetcher creates when set to "keep". The tarball is expanded into
+   the work directory. By default, the CVS metadata is removed.
+
+-  *"fullpath":* Controls whether the resulting checkout is at the
+   module level, which is the default, or is at deeper paths.
+
+-  *"norecurse":* Causes the fetcher to only checkout the specified
+   directory with no recurse into any subdirectories.
+
+-  *"port":* The port to which the CVS server connects.
+
+Some example URLs are as follows: ::
+
+   SRC_URI = "cvs://CVSROOT;module=mymodule;tag=some-version;method=ext"
+   SRC_URI = "cvs://CVSROOT;module=mymodule;date=20060126;localdir=usethat"
+
+.. _svn-fetcher:
+
+Subversion (SVN) Fetcher (``svn://``)
+-------------------------------------
+
+This fetcher submodule fetches code from the Subversion source control
+system. The executable used is specified by ``FETCHCMD_svn``, which
+defaults to "svn". The fetcher's temporary working directory is set by
+:term:`SVNDIR`, which is usually ``DL_DIR/svn``.
+
+The supported parameters are as follows:
+
+-  *"module":* The name of the svn module to checkout. You must provide
+   this parameter. You can think of this parameter as the top-level
+   directory of the repository data you want.
+
+-  *"path_spec":* A specific directory in which to checkout the
+   specified svn module.
+
+-  *"protocol":* The protocol to use, which defaults to "svn". If
+   "protocol" is set to "svn+ssh", the "ssh" parameter is also used.
+
+-  *"rev":* The revision of the source code to checkout.
+
+-  *"scmdata":* Causes the “.svn” directories to be available during
+   compile-time when set to "keep". By default, these directories are
+   removed.
+
+-  *"ssh":* An optional parameter used when "protocol" is set to
+   "svn+ssh". You can use this parameter to specify the ssh program used
+   by svn.
+
+-  *"transportuser":* When required, sets the username for the
+   transport. By default, this parameter is empty. The transport
+   username is different than the username used in the main URL, which
+   is passed to the subversion command.
+
+Following are three examples using svn: ::
+
+   SRC_URI = "svn://myrepos/proj1;module=vip;protocol=http;rev=667"
+   SRC_URI = "svn://myrepos/proj1;module=opie;protocol=svn+ssh"
+   SRC_URI = "svn://myrepos/proj1;module=trunk;protocol=http;path_spec=${MY_DIR}/proj1"
+
+.. _git-fetcher:
+
+Git Fetcher (``git://``)
+------------------------
+
+This fetcher submodule fetches code from the Git source control system.
+The fetcher works by creating a bare clone of the remote into
+:term:`GITDIR`, which is usually ``DL_DIR/git2``. This
+bare clone is then cloned into the work directory during the unpack
+stage when a specific tree is checked out. This is done using alternates
+and by reference to minimize the amount of duplicate data on the disk
+and make the unpack process fast. The executable used can be set with
+``FETCHCMD_git``.
+
+This fetcher supports the following parameters:
+
+-  *"protocol":* The protocol used to fetch the files. The default is
+   "git" when a hostname is set. If a hostname is not set, the Git
+   protocol is "file". You can also use "http", "https", "ssh" and
+   "rsync".
+
+-  *"nocheckout":* Tells the fetcher to not checkout source code when
+   unpacking when set to "1". Set this option for the URL where there is
+   a custom routine to checkout code. The default is "0".
+
+-  *"rebaseable":* Indicates that the upstream Git repository can be
+   rebased. You should set this parameter to "1" if revisions can become
+   detached from branches. In this case, the source mirror tarball is
+   done per revision, which has a loss of efficiency. Rebasing the
+   upstream Git repository could cause the current revision to disappear
+   from the upstream repository. This option reminds the fetcher to
+   preserve the local cache carefully for future use. The default value
+   for this parameter is "0".
+
+-  *"nobranch":* Tells the fetcher to not check the SHA validation for
+   the branch when set to "1". The default is "0". Set this option for
+   the recipe that refers to the commit that is valid for a tag instead
+   of the branch.
+
+-  *"bareclone":* Tells the fetcher to clone a bare clone into the
+   destination directory without checking out a working tree. Only the
+   raw Git metadata is provided. This parameter implies the "nocheckout"
+   parameter as well.
+
+-  *"branch":* The branch(es) of the Git tree to clone. If unset, this
+   is assumed to be "master". The number of branch parameters much match
+   the number of name parameters.
+
+-  *"rev":* The revision to use for the checkout. The default is
+   "master".
+
+-  *"tag":* Specifies a tag to use for the checkout. To correctly
+   resolve tags, BitBake must access the network. For that reason, tags
+   are often not used. As far as Git is concerned, the "tag" parameter
+   behaves effectively the same as the "rev" parameter.
+
+-  *"subpath":* Limits the checkout to a specific subpath of the tree.
+   By default, the whole tree is checked out.
+
+-  *"destsuffix":* The name of the path in which to place the checkout.
+   By default, the path is ``git/``.
+
+-  *"usehead":* Enables local ``git://`` URLs to use the current branch
+   HEAD as the revision for use with ``AUTOREV``. The "usehead"
+   parameter implies no branch and only works when the transfer protocol
+   is ``file://``.
+
+Here are some example URLs: ::
+
+   SRC_URI = "git://git.oe.handhelds.org/git/vip.git;tag=version-1"
+   SRC_URI = "git://git.oe.handhelds.org/git/vip.git;protocol=http"
+
+.. _gitsm-fetcher:
+
+Git Submodule Fetcher (``gitsm://``)
+------------------------------------
+
+This fetcher submodule inherits from the :ref:`Git
+fetcher<bitbake-user-manual/bitbake-user-manual-fetching:git fetcher
+(\`\`git://\`\`)>` and extends that fetcher's behavior by fetching a
+repository's submodules. :term:`SRC_URI` is passed to the Git fetcher as
+described in the :ref:`bitbake-user-manual/bitbake-user-manual-fetching:git
+fetcher (\`\`git://\`\`)` section.
+
+.. note::
+
+   You must clean a recipe when switching between '``git://``' and
+   '``gitsm://``' URLs.
+
+   The Git Submodules fetcher is not a complete fetcher implementation.
+   The fetcher has known issues where it does not use the normal source
+   mirroring infrastructure properly. Further, the submodule sources it
+   fetches are not visible to the licensing and source archiving
+   infrastructures.
+
+.. _clearcase-fetcher:
+
+ClearCase Fetcher (``ccrc://``)
+-------------------------------
+
+This fetcher submodule fetches code from a
+`ClearCase <http://en.wikipedia.org/wiki/Rational_ClearCase>`__
+repository.
+
+To use this fetcher, make sure your recipe has proper
+:term:`SRC_URI`, :term:`SRCREV`, and
+:term:`PV` settings. Here is an example: ::
+
+   SRC_URI = "ccrc://cc.example.org/ccrc;vob=/example_vob;module=/example_module"
+   SRCREV = "EXAMPLE_CLEARCASE_TAG"
+   PV = "${@d.getVar("SRCREV", False).replace("/", "+")}"
+
+The fetcher uses the ``rcleartool`` or
+``cleartool`` remote client, depending on which one is available.
+
+Following are options for the ``SRC_URI`` statement:
+
+-  *vob*: The name, which must include the prepending "/" character,
+   of the ClearCase VOB. This option is required.
+
+-  *module*: The module, which must include the prepending "/"
+   character, in the selected VOB.
+
+   .. note::
+
+      The module and vob options are combined to create the load rule in the
+      view config spec. As an example, consider the vob and module values from
+      the SRC_URI statement at the start of this section. Combining those values
+      results in the following: ::
+
+         load /example_vob/example_module
+
+-  *proto*: The protocol, which can be either ``http`` or ``https``.
+
+By default, the fetcher creates a configuration specification. If you
+want this specification written to an area other than the default, use
+the ``CCASE_CUSTOM_CONFIG_SPEC`` variable in your recipe to define where
+the specification is written.
+
+.. note::
+
+   the SRCREV loses its functionality if you specify this variable. However,
+   SRCREV is still used to label the archive after a fetch even though it does
+   not define what is fetched.
+
+Here are a couple of other behaviors worth mentioning:
+
+-  When using ``cleartool``, the login of ``cleartool`` is handled by
+   the system. The login require no special steps.
+
+-  In order to use ``rcleartool`` with authenticated users, an
+   "rcleartool login" is necessary before using the fetcher.
+
+.. _perforce-fetcher:
+
+Perforce Fetcher (``p4://``)
+----------------------------
+
+This fetcher submodule fetches code from the
+`Perforce <https://www.perforce.com/>`__ source control system. The
+executable used is specified by ``FETCHCMD_p4``, which defaults to "p4".
+The fetcher's temporary working directory is set by
+:term:`P4DIR`, which defaults to "DL_DIR/p4".
+The fetcher does not make use of a perforce client, instead it
+relies on ``p4 files`` to retrieve a list of
+files and ``p4 print`` to transfer the content
+of those files locally.
+
+To use this fetcher, make sure your recipe has proper
+:term:`SRC_URI`, :term:`SRCREV`, and
+:term:`PV` values. The p4 executable is able to use the
+config file defined by your system's ``P4CONFIG`` environment variable
+in order to define the Perforce server URL and port, username, and
+password if you do not wish to keep those values in a recipe itself. If
+you choose not to use ``P4CONFIG``, or to explicitly set variables that
+``P4CONFIG`` can contain, you can specify the ``P4PORT`` value, which is
+the server's URL and port number, and you can specify a username and
+password directly in your recipe within ``SRC_URI``.
+
+Here is an example that relies on ``P4CONFIG`` to specify the server URL
+and port, username, and password, and fetches the Head Revision: ::
+
+   SRC_URI = "p4://example-depot/main/source/..."
+   SRCREV = "${AUTOREV}"
+   PV = "p4-${SRCPV}"
+   S = "${WORKDIR}/p4"
+
+Here is an example that specifies the server URL and port, username, and
+password, and fetches a Revision based on a Label: ::
+
+   P4PORT = "tcp:p4server.example.net:1666"
+   SRC_URI = "p4://user:passwd@example-depot/main/source/..."
+   SRCREV = "release-1.0"
+   PV = "p4-${SRCPV}"
+   S = "${WORKDIR}/p4"
+
+.. note::
+
+   You should always set S to "${WORKDIR}/p4" in your recipe.
+
+By default, the fetcher strips the depot location from the local file paths. In
+the above example, the content of ``example-depot/main/source/`` will be placed
+in ``${WORKDIR}/p4``.  For situations where preserving parts of the remote depot
+paths locally is desirable, the fetcher supports two parameters:
+
+- *"module":*
+    The top-level depot location or directory to fetch. The value of this
+    parameter can also point to a single file within the depot, in which case
+    the local file path will include the module path.
+- *"remotepath":*
+    When used with the value "``keep``", the fetcher will mirror the full depot
+    paths locally for the specified location, even in combination with the
+    ``module`` parameter.
+
+Here is an example use of the the ``module`` parameter: ::
+
+   SRC_URI = "p4://user:passwd@example-depot/main;module=source/..."
+
+In this case, the content of the top-level directory ``source/`` will be fetched
+to ``${P4DIR}``, including the directory itself.  The top-level directory will
+be accesible at ``${P4DIR}/source/``.
+
+Here is an example use of the the ``remotepath`` parameter: ::
+
+   SRC_URI = "p4://user:passwd@example-depot/main;module=source/...;remotepath=keep"
+
+In this case, the content of the top-level directory ``source/`` will be fetched
+to ``${P4DIR}``, but the complete depot paths will be mirrored locally. The
+top-level directory will be accessible at
+``${P4DIR}/example-depot/main/source/``.
+
+.. _repo-fetcher:
+
+Repo Fetcher (``repo://``)
+--------------------------
+
+This fetcher submodule fetches code from ``google-repo`` source control
+system. The fetcher works by initiating and syncing sources of the
+repository into :term:`REPODIR`, which is usually
+``${DL_DIR}/repo``.
+
+This fetcher supports the following parameters:
+
+-  *"protocol":* Protocol to fetch the repository manifest (default:
+   git).
+
+-  *"branch":* Branch or tag of repository to get (default: master).
+
+-  *"manifest":* Name of the manifest file (default: ``default.xml``).
+
+Here are some example URLs: ::
+
+   SRC_URI = "repo://REPOROOT;protocol=git;branch=some_branch;manifest=my_manifest.xml"
+   SRC_URI = "repo://REPOROOT;protocol=file;branch=some_branch;manifest=my_manifest.xml"
+
+Other Fetchers
+--------------
+
+Fetch submodules also exist for the following:
+
+-  Bazaar (``bzr://``)
+
+-  Mercurial (``hg://``)
+
+-  npm (``npm://``)
+
+-  OSC (``osc://``)
+
+-  Secure FTP (``sftp://``)
+
+-  Secure Shell (``ssh://``)
+
+-  Trees using Git Annex (``gitannex://``)
+
+No documentation currently exists for these lesser used fetcher
+submodules. However, you might find the code helpful and readable.
+
+Auto Revisions
+==============
+
+We need to document ``AUTOREV`` and ``SRCREV_FORMAT`` here.
diff --git a/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-hello.rst b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-hello.rst
new file mode 100644
index 0000000..e3fd321
--- /dev/null
+++ b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-hello.rst
@@ -0,0 +1,415 @@
+.. SPDX-License-Identifier: CC-BY-2.5
+
+===================
+Hello World Example
+===================
+
+BitBake Hello World
+===================
+
+The simplest example commonly used to demonstrate any new programming
+language or tool is the "`Hello
+World <http://en.wikipedia.org/wiki/Hello_world_program>`__" example.
+This appendix demonstrates, in tutorial form, Hello World within the
+context of BitBake. The tutorial describes how to create a new project
+and the applicable metadata files necessary to allow BitBake to build
+it.
+
+Obtaining BitBake
+=================
+
+See the :ref:`bitbake-user-manual/bitbake-user-manual-hello:obtaining bitbake` section for
+information on how to obtain BitBake. Once you have the source code on
+your machine, the BitBake directory appears as follows: ::
+
+   $ ls -al
+   total 100
+   drwxrwxr-x. 9 wmat wmat  4096 Jan 31 13:44 .
+   drwxrwxr-x. 3 wmat wmat  4096 Feb  4 10:45 ..
+   -rw-rw-r--. 1 wmat wmat   365 Nov 26 04:55 AUTHORS
+   drwxrwxr-x. 2 wmat wmat  4096 Nov 26 04:55 bin
+   drwxrwxr-x. 4 wmat wmat  4096 Jan 31 13:44 build
+   -rw-rw-r--. 1 wmat wmat 16501 Nov 26 04:55 ChangeLog
+   drwxrwxr-x. 2 wmat wmat  4096 Nov 26 04:55 classes
+   drwxrwxr-x. 2 wmat wmat  4096 Nov 26 04:55 conf
+   drwxrwxr-x. 3 wmat wmat  4096 Nov 26 04:55 contrib
+   -rw-rw-r--. 1 wmat wmat 17987 Nov 26 04:55 COPYING
+   drwxrwxr-x. 3 wmat wmat  4096 Nov 26 04:55 doc
+   -rw-rw-r--. 1 wmat wmat    69 Nov 26 04:55 .gitignore
+   -rw-rw-r--. 1 wmat wmat   849 Nov 26 04:55 HEADER
+   drwxrwxr-x. 5 wmat wmat  4096 Jan 31 13:44 lib
+   -rw-rw-r--. 1 wmat wmat   195 Nov 26 04:55 MANIFEST.in
+   -rw-rw-r--. 1 wmat wmat  2887 Nov 26 04:55 TODO
+
+At this point, you should have BitBake cloned to a directory that
+matches the previous listing except for dates and user names.
+
+Setting Up the BitBake Environment
+==================================
+
+First, you need to be sure that you can run BitBake. Set your working
+directory to where your local BitBake files are and run the following
+command: ::
+
+  $ ./bin/bitbake --version
+  BitBake Build Tool Core version 1.23.0, bitbake version 1.23.0
+
+The console output tells you what version
+you are running.
+
+The recommended method to run BitBake is from a directory of your
+choice. To be able to run BitBake from any directory, you need to add
+the executable binary to your binary to your shell's environment
+``PATH`` variable. First, look at your current ``PATH`` variable by
+entering the following: ::
+
+  $ echo $PATH
+
+Next, add the directory location
+for the BitBake binary to the ``PATH``. Here is an example that adds the
+``/home/scott-lenovo/bitbake/bin`` directory to the front of the
+``PATH`` variable: ::
+
+  $ export PATH=/home/scott-lenovo/bitbake/bin:$PATH
+
+You should now be able to enter the ``bitbake`` command from the command
+line while working from any directory.
+
+The Hello World Example
+=======================
+
+The overall goal of this exercise is to build a complete "Hello World"
+example utilizing task and layer concepts. Because this is how modern
+projects such as OpenEmbedded and the Yocto Project utilize BitBake, the
+example provides an excellent starting point for understanding BitBake.
+
+To help you understand how to use BitBake to build targets, the example
+starts with nothing but the ``bitbake`` 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.
+
+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 :oe_lists:`/g/bitbake-devel`
+discussion mailing list about the BitBake build tool.
+
+.. note::
+
+   This example was inspired by and drew heavily from
+   `Mailing List post - The BitBake equivalent of "Hello, World!"
+   <http://www.mail-archive.com/yocto@yoctoproject.org/msg09379.html>`_.
+
+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:
+:ref:`bitbake-user-manual/bitbake-user-manual-intro:configuration files`,
+:ref:`bitbake-user-manual/bitbake-user-manual-intro:classes`, and
+:ref:`bitbake-user-manual/bitbake-user-manual-intro:recipes`.
+But where do they go? How does BitBake find
+them? BitBake's error messaging helps you answer these types of
+questions and helps you better understand exactly what is going on.
+
+Following is the complete "Hello World" example.
+
+#.  **Create a Project Directory:** First, set up a directory for the
+    "Hello World" project. Here is how you can do so in your home
+    directory: ::
+
+      $ mkdir ~/hello
+      $ cd ~/hello
+
+    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.
+
+#.  **Run BitBake:** At this point, you have nothing but a project
+    directory. Run the ``bitbake`` command and see what it does: ::
+
+       $ 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, 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
+
+    The majority of this output is specific to environment variables that
+    are not directly relevant to BitBake. However, the very first
+    message regarding the ``BBPATH`` variable and the
+    ``conf/bblayers.conf`` file is relevant.
+
+    When you run BitBake, it begins looking for metadata files. The
+    :term:`BBPATH` variable is what tells BitBake where
+    to look for those files. ``BBPATH`` is not set and you need to set
+    it. Without ``BBPATH``, BitBake cannot find any configuration files
+    (``.conf``) or recipe files (``.bb``) at all. BitBake also cannot
+    find the ``bitbake.conf`` file.
+
+#.  **Setting BBPATH:** For this example, you can set ``BBPATH`` in
+    the same manner that you set ``PATH`` earlier in the appendix. You
+    should realize, though, that it is much more flexible to set the
+    ``BBPATH`` variable up in a configuration file for each project.
+
+    From your shell, enter the following commands to set and export the
+    ``BBPATH`` variable: ::
+
+      $ BBPATH="projectdirectory"
+      $ export BBPATH
+
+    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.
+
+#.  **Run BitBake:** Now that you have ``BBPATH`` defined, run the
+    ``bitbake`` command again: ::
+
+       $ 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
+
+       ERROR: Unable to parse conf/bitbake.conf: file conf/bitbake.conf not found in /home/scott-lenovo/hello
+
+    This sample output shows that BitBake could not find the
+    ``conf/bitbake.conf`` 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 ``conf/bitbake.conf`` file.
+
+#.  **Creating conf/bitbake.conf:** The ``conf/bitbake.conf`` 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 ``bitbake.conf`` file, see
+    http://git.openembedded.org/bitbake/tree/conf/bitbake.conf.
+
+    Use the following commands to create the ``conf`` directory in the
+    project directory: ::
+
+      $ mkdir conf
+
+    From within the ``conf`` directory,
+    use some editor to create the ``bitbake.conf`` so that it contains
+    the following: ::
+
+       PN  = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}"
+
+       TMPDIR  = "${TOPDIR}/tmp"
+       CACHE   = "${TMPDIR}/cache"
+       STAMP   = "${TMPDIR}/${PN}/stamps"
+       T       = "${TMPDIR}/${PN}/work"
+       B       = "${TMPDIR}/${PN}"
+
+    .. note::
+
+       Without a value for PN , the variables STAMP , T , and B , prevent more
+       than one recipe from working. You can fix this by either setting PN to
+       have a value similar to what OpenEmbedded and BitBake use in the default
+       bitbake.conf file (see previous example). Or, by manually updating each
+       recipe to set PN . You will also need to include PN as part of the STAMP
+       , T , and B variable definitions in the local.conf file.
+
+    The ``TMPDIR`` variable establishes a directory that BitBake uses
+    for build output and intermediate files other than the cached
+    information used by the
+    :ref:`bitbake-user-manual/bitbake-user-manual-execution:setscene`
+    process. Here, the ``TMPDIR`` directory is set to ``hello/tmp``.
+
+    .. tip::
+
+       You can always safely delete the tmp directory in order to rebuild a
+       BitBake target. The build process creates the directory for you when you
+       run BitBake.
+
+    For information about each of the other variables defined in this
+    example, check :term:`PN`, :term:`TOPDIR`, :term:`CACHE`, :term:`STAMP`,
+    :term:`T` or :term:`B` to take you to the definitions in the
+    glossary.
+
+#.  **Run BitBake:** After making sure that the ``conf/bitbake.conf`` file
+    exists, you can run the ``bitbake`` command again: ::
+
+       $ 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 177, in _inherit
+           bb.parse.BBHandler.inherit(bbclass, "configuration INHERITs", 0, data)
+         File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py", line 92, in inherit
+           include(fn, file, lineno, d, "inherit")
+         File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 100, in include
+           raise ParseError("Could not %(error_out)s file %(fn)s" % vars(), oldfn, lineno)
+       ParseError: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
+
+       ERROR: Unable to parse base: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
+
+    In the sample output,
+    BitBake could not find the ``classes/base.bbclass`` file. You need
+    to create that file next.
+
+#.  **Creating classes/base.bbclass:** BitBake uses class files to
+    provide common code and functionality. The minimally required class
+    for BitBake is the ``classes/base.bbclass`` file. The ``base`` class
+    is implicitly inherited by every recipe. BitBake looks for the class
+    in the ``classes`` directory of the project (i.e ``hello/classes``
+    in this example).
+
+    Create the ``classes`` directory as follows: ::
+
+      $ cd $HOME/hello
+      $ mkdir classes
+
+    Move to the ``classes`` directory and then create the
+    ``base.bbclass`` file by inserting this single line: addtask build
+    The minimal task that BitBake runs is the ``do_build`` task. This is
+    all the example needs in order to build the project. Of course, the
+    ``base.bbclass`` can have much more depending on which build
+    environments BitBake is supporting.
+
+#.  **Run BitBake:** After making sure that the ``classes/base.bbclass``
+    file exists, you can run the ``bitbake`` command again: ::
+
+       $ bitbake
+       Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information.
+
+    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.
+
+#.  **Creating a Layer:** 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::
+
+       You can find additional information on layers in the
+       ":ref:`bitbake-user-manual/bitbake-user-manual-intro:Layers`" section.
+
+    Minimally, you need a recipe file and a layer configuration file in
+    your layer. The configuration file needs to be in the ``conf``
+    directory inside the layer. Use these commands to set up the layer
+    and the ``conf`` directory: ::
+
+       $ cd $HOME
+       $ mkdir mylayer
+       $ cd mylayer
+       $ mkdir conf
+
+    Move to the ``conf`` directory and create a ``layer.conf`` file that has the
+    following: ::
+
+      BBPATH .= ":${LAYERDIR}"
+      BBFILES += "${LAYERDIR}/\*.bb"
+      BBFILE_COLLECTIONS += "mylayer"
+     `BBFILE_PATTERN_mylayer := "^${LAYERDIR_RE}/"
+
+    For information on these variables, click on :term:`BBFILES`,
+    :term:`LAYERDIR`, :term:`BBFILE_COLLECTIONS` or :term:`BBFILE_PATTERN_mylayer <BBFILE_PATTERN>`
+    to go to the definitions in the glossary.
+
+    You need to create the recipe file next. Inside your layer at the
+    top-level, use an editor and create a recipe file named
+    ``printhello.bb`` that has the following: ::
+
+       DESCRIPTION = "Prints Hello World"
+       PN = 'printhello'
+       PV = '1'
+
+       python do_build() {
+          bb.plain("********************");
+          bb.plain("*                  *");
+          bb.plain("*  Hello, World!   *");
+          bb.plain("*                  *");
+          bb.plain("********************");
+       }
+
+    The recipe file simply provides
+    a description of the recipe, the name, version, and the ``do_build``
+    task, which prints out "Hello World" to the console. For more
+    information on :term:`DESCRIPTION`, :term:`PN` or :term:`PV`
+    follow the links to the glossary.
+
+#. **Run BitBake With a Target:** Now that a BitBake target exists, run
+    the command and provide that target: ::
+
+      $ 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.
+
+    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 ``conf/bblayers.conf`` that lists
+    the layers for the project. Without this file, BitBake cannot find
+    the recipe.
+
+#. **Creating conf/bblayers.conf:** BitBake uses the
+    ``conf/bblayers.conf`` file to locate layers needed for the project.
+    This file must reside in the ``conf`` directory of the project (i.e.
+    ``hello/conf`` for this example).
+
+    Set your working directory to the ``hello/conf`` directory and then
+    create the ``bblayers.conf`` file so that it contains the following: ::
+
+       BBLAYERS ?= " \
+           /home/<you>/mylayer \
+       "
+
+    You need to provide your own information for ``you`` in the file.
+
+#. **Run BitBake With a Target:** Now that you have supplied the
+    ``bblayers.conf`` file, run the ``bitbake`` command and provide the
+    target: ::
+
+       $ 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.
+
+    .. note::
+
+       After the first execution, re-running bitbake printhello again will not
+       result in a BitBake run that prints the same console output. The reason
+       for this is that the first time the printhello.bb recipe's do_build task
+       executes successfully, BitBake writes a stamp file for the task. Thus,
+       the next time you attempt to run the task using that same bitbake
+       command, BitBake notices the stamp and therefore determines that the task
+       does not need to be re-run. If you delete the tmp directory or run
+       bitbake -c clean printhello and then re-run the build, the "Hello,
+       World!" message will be printed again.
diff --git a/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-intro.rst b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-intro.rst
new file mode 100644
index 0000000..77dc966
--- /dev/null
+++ b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-intro.rst
@@ -0,0 +1,651 @@
+.. SPDX-License-Identifier: CC-BY-2.5
+
+========
+Overview
+========
+
+|
+
+Welcome to the BitBake User Manual. This manual provides information on
+the BitBake tool. The information attempts to be as independent as
+possible regarding systems that use BitBake, such as OpenEmbedded and
+the Yocto Project. In some cases, scenarios or examples within the
+context of a build system are used in the manual to help with
+understanding. For these cases, the manual clearly states the context.
+
+.. _intro:
+
+Introduction
+============
+
+Fundamentally, BitBake is a generic task execution engine that allows
+shell and Python tasks to be run efficiently and in parallel while
+working within complex inter-task dependency constraints. One of
+BitBake's main users, OpenEmbedded, takes this core and builds embedded
+Linux software stacks using a task-oriented approach.
+
+Conceptually, BitBake is similar to GNU Make in some regards but has
+significant differences:
+
+-  BitBake executes tasks according to provided metadata that builds up
+   the tasks. Metadata is stored in recipe (``.bb``) and related recipe
+   "append" (``.bbappend``) files, configuration (``.conf``) and
+   underlying include (``.inc``) files, and in class (``.bbclass``)
+   files. The metadata provides BitBake with instructions on what tasks
+   to run and the dependencies between those tasks.
+
+-  BitBake includes a fetcher library for obtaining source code from
+   various places such as local files, source control systems, or
+   websites.
+
+-  The instructions for each unit to be built (e.g. a piece of software)
+   are known as "recipe" files and contain all the information about the
+   unit (dependencies, source file locations, checksums, description and
+   so on).
+
+-  BitBake includes a client/server abstraction and can be used from a
+   command line or used as a service over XML-RPC and has several
+   different user interfaces.
+
+History and Goals
+=================
+
+BitBake was originally a part of the OpenEmbedded project. It was
+inspired by the Portage package management system used by the Gentoo
+Linux distribution. On December 7, 2004, OpenEmbedded project team
+member Chris Larson split the project into two distinct pieces:
+
+-  BitBake, a generic task executor
+
+-  OpenEmbedded, a metadata set utilized by BitBake
+
+Today, BitBake is the primary basis of the
+`OpenEmbedded <http://www.openembedded.org/>`__ project, which is being
+used to build and maintain Linux distributions such as the `Angstrom
+Distribution <http://www.angstrom-distribution.org/>`__, and which is
+also being used as the build tool for Linux projects such as the `Yocto
+Project <http://www.yoctoproject.org>`__.
+
+Prior to BitBake, no other build tool adequately met the needs of an
+aspiring embedded Linux distribution. All of the build systems used by
+traditional desktop Linux distributions lacked important functionality,
+and none of the ad hoc Buildroot-based systems, prevalent in the
+embedded space, were scalable or maintainable.
+
+Some important original goals for BitBake were:
+
+-  Handle cross-compilation.
+
+-  Handle inter-package dependencies (build time on target architecture,
+   build time on native architecture, and runtime).
+
+-  Support running any number of tasks within a given package,
+   including, but not limited to, fetching upstream sources, unpacking
+   them, patching them, configuring them, and so forth.
+
+-  Be Linux distribution agnostic for both build and target systems.
+
+-  Be architecture agnostic.
+
+-  Support multiple build and target operating systems (e.g. Cygwin, the
+   BSDs, and so forth).
+
+-  Be self-contained, rather than tightly integrated into the build
+   machine's root filesystem.
+
+-  Handle conditional metadata on the target architecture, operating
+   system, distribution, and machine.
+
+-  Be easy to use the tools to supply local metadata and packages
+   against which to operate.
+
+-  Be easy to use BitBake to collaborate between multiple projects for
+   their builds.
+
+-  Provide an inheritance mechanism to share common metadata between
+   many packages.
+
+Over time it became apparent that some further requirements were
+necessary:
+
+-  Handle variants of a base recipe (e.g. native, sdk, and multilib).
+
+-  Split metadata into layers and allow layers to enhance or override
+   other layers.
+
+-  Allow representation of a given set of input variables to a task as a
+   checksum. Based on that checksum, allow acceleration of builds with
+   prebuilt components.
+
+BitBake satisfies all the original requirements and many more with
+extensions being made to the basic functionality to reflect the
+additional requirements. Flexibility and power have always been the
+priorities. BitBake is highly extensible and supports embedded Python
+code and execution of any arbitrary tasks.
+
+.. _Concepts:
+
+Concepts
+========
+
+BitBake is a program written in the Python language. At the highest
+level, BitBake interprets metadata, decides what tasks are required to
+run, and executes those tasks. Similar to GNU Make, BitBake controls how
+software is built. GNU Make achieves its control through "makefiles",
+while BitBake uses "recipes".
+
+BitBake extends the capabilities of a simple tool like GNU Make by
+allowing for the definition of much more complex tasks, such as
+assembling entire embedded Linux distributions.
+
+The remainder of this section introduces several concepts that should be
+understood in order to better leverage the power of BitBake.
+
+Recipes
+-------
+
+BitBake Recipes, which are denoted by the file extension ``.bb``, are
+the most basic metadata files. These recipe files provide BitBake with
+the following:
+
+-  Descriptive information about the package (author, homepage, license,
+   and so on)
+
+-  The version of the recipe
+
+-  Existing dependencies (both build and runtime dependencies)
+
+-  Where the source code resides and how to fetch it
+
+-  Whether the source code requires any patches, where to find them, and
+   how to apply them
+
+-  How to configure and compile the source code
+
+-  How to assemble the generated artifacts into one or more installable
+   packages
+
+-  Where on the target machine to install the package or packages
+   created
+
+Within the context of BitBake, or any project utilizing BitBake as its
+build system, files with the ``.bb`` extension are referred to as
+recipes.
+
+.. note::
+
+   The term "package" is also commonly used to describe recipes.
+   However, since the same word is used to describe packaged output from
+   a project, it is best to maintain a single descriptive term -
+   "recipes". Put another way, a single "recipe" file is quite capable
+   of generating a number of related but separately installable
+   "packages". In fact, that ability is fairly common.
+
+Configuration Files
+-------------------
+
+Configuration files, which are denoted by the ``.conf`` extension,
+define various configuration variables that govern the project's build
+process. These files fall into several areas that define machine
+configuration, distribution configuration, possible compiler tuning,
+general common configuration, and user configuration. The main
+configuration file is the sample ``bitbake.conf`` file, which is located
+within the BitBake source tree ``conf`` directory.
+
+Classes
+-------
+
+Class files, which are denoted by the ``.bbclass`` extension, contain
+information that is useful to share between metadata files. The BitBake
+source tree currently comes with one class metadata file called
+``base.bbclass``. You can find this file in the ``classes`` directory.
+The ``base.bbclass`` class files is special since it is always included
+automatically for all recipes and classes. This class contains
+definitions for standard basic tasks such as fetching, unpacking,
+configuring (empty by default), compiling (runs any Makefile present),
+installing (empty by default) and packaging (empty by default). These
+tasks are often overridden or extended by other classes added during the
+project development process.
+
+Layers
+------
+
+Layers allow you to isolate different types of customizations from each
+other. While you might find it tempting to keep everything in one layer
+when working on a single project, the more modular your metadata, the
+easier it is to cope with future changes.
+
+To illustrate how you can use layers to keep things modular, consider
+customizations you might make to support a specific target machine.
+These types of customizations typically reside in a special layer,
+rather than a general layer, called a Board Support Package (BSP) layer.
+Furthermore, the machine customizations should be isolated from recipes
+and metadata that support a new GUI environment, for example. This
+situation gives you a couple of layers: one for the machine
+configurations and one for the GUI environment. It is important to
+understand, however, that the BSP layer can still make machine-specific
+additions to recipes within the GUI environment layer without polluting
+the GUI layer itself with those machine-specific changes. You can
+accomplish this through a recipe that is a BitBake append
+(``.bbappend``) file.
+
+.. _append-bbappend-files:
+
+Append Files
+------------
+
+Append files, which are files that have the ``.bbappend`` file
+extension, extend or override information in an existing recipe file.
+
+BitBake expects every append file to have a corresponding recipe file.
+Furthermore, the append file and corresponding recipe file must use the
+same root filename. The filenames can differ only in the file type
+suffix used (e.g. ``formfactor_0.0.bb`` and
+``formfactor_0.0.bbappend``).
+
+Information in append files extends or overrides the information in the
+underlying, similarly-named recipe files.
+
+When you name an append file, you can use the "``%``" wildcard character
+to allow for matching recipe names. For example, suppose you have an
+append file named as follows: ::
+
+  busybox_1.21.%.bbappend
+
+That append file
+would match any ``busybox_1.21.``\ x\ ``.bb`` version of the recipe. So,
+the append file would match the following recipe names: ::
+
+  busybox_1.21.1.bb
+  busybox_1.21.2.bb
+  busybox_1.21.3.bb
+
+.. note::
+
+   The use of the " % " character is limited in that it only works directly in
+   front of the .bbappend portion of the append file's name. You cannot use the
+   wildcard character in any other location of the name.
+
+If the ``busybox`` recipe was updated to ``busybox_1.3.0.bb``, the
+append name would not match. However, if you named the append file
+``busybox_1.%.bbappend``, then you would have a match.
+
+In the most general case, you could name the append file something as
+simple as ``busybox_%.bbappend`` to be entirely version independent.
+
+Obtaining BitBake
+=================
+
+You can obtain BitBake several different ways:
+
+-  **Cloning BitBake:** Using Git to clone the BitBake source code
+   repository is the recommended method for obtaining BitBake. Cloning
+   the repository makes it easy to get bug fixes and have access to
+   stable branches and the master branch. Once you have cloned BitBake,
+   you should use the latest stable branch for development since the
+   master branch is for BitBake development and might contain less
+   stable changes.
+
+   You usually need a version of BitBake that matches the metadata you
+   are using. The metadata is generally backwards compatible but not
+   forward compatible.
+
+   Here is an example that clones the BitBake repository: ::
+
+     $ git clone git://git.openembedded.org/bitbake
+
+   This command clones the BitBake
+   Git repository into a directory called ``bitbake``. Alternatively,
+   you can designate a directory after the ``git clone`` command if you
+   want to call the new directory something other than ``bitbake``. Here
+   is an example that names the directory ``bbdev``: ::
+
+     $ git clone git://git.openembedded.org/bitbake bbdev
+
+-  **Installation using your Distribution Package Management System:**
+   This method is not recommended because the BitBake version that is
+   provided by your distribution, in most cases, is several releases
+   behind a snapshot of the BitBake repository.
+
+-  **Taking a snapshot of BitBake:** Downloading a snapshot of BitBake
+   from the source code repository gives you access to a known branch or
+   release of BitBake.
+
+      .. note::
+
+         Cloning the Git repository, as described earlier, is the preferred
+         method for getting BitBake. Cloning the repository makes it easier
+         to update as patches are added to the stable branches.
+
+   The following example downloads a snapshot of BitBake version 1.17.0: ::
+
+     $ wget http://git.openembedded.org/bitbake/snapshot/bitbake-1.17.0.tar.gz
+     $ tar zxpvf bitbake-1.17.0.tar.gz
+
+   After extraction of the tarball using
+   the tar utility, you have a directory entitled ``bitbake-1.17.0``.
+
+-  **Using the BitBake that Comes With Your Build Checkout:** A final
+   possibility for getting a copy of BitBake is that it already comes
+   with your checkout of a larger BitBake-based build system, such as
+   Poky. Rather than manually checking out individual layers and gluing
+   them together yourself, you can check out an entire build system. The
+   checkout will already include a version of BitBake that has been
+   thoroughly tested for compatibility with the other components. For
+   information on how to check out a particular BitBake-based build
+   system, consult that build system's supporting documentation.
+
+.. _bitbake-user-manual-command:
+
+The BitBake Command
+===================
+
+The ``bitbake`` command is the primary interface to the BitBake tool.
+This section presents the BitBake command syntax and provides several
+execution examples.
+
+Usage and syntax
+----------------
+
+Following is the usage and syntax for BitBake: ::
+
+   $ bitbake -h
+   Usage: bitbake [options] [recipename/target recipe:do_task ...]
+
+       Executes the specified task (default is 'build') for a given set of target recipes (.bb files).
+       It is assumed there is a conf/bblayers.conf available in cwd or in BBPATH which
+       will provide the layer, BBFILES and other configuration information.
+
+   Options:
+     --version             show program's version number and exit
+     -h, --help            show this help message and exit
+     -b BUILDFILE, --buildfile=BUILDFILE
+                           Execute tasks from a specific .bb recipe directly.
+                           WARNING: Does not handle any dependencies from other
+                           recipes.
+     -k, --continue        Continue as much as possible after an error. While the
+                           target that failed and anything depending on it cannot
+                           be built, as much as possible will be built before
+                           stopping.
+     -f, --force           Force the specified targets/task to run (invalidating
+                           any existing stamp file).
+     -c CMD, --cmd=CMD     Specify the task to execute. The exact options
+                           available depend on the metadata. Some examples might
+                           be 'compile' or 'populate_sysroot' or 'listtasks' may
+                           give a list of the tasks available.
+     -C INVALIDATE_STAMP, --clear-stamp=INVALIDATE_STAMP
+                           Invalidate the stamp for the specified task such as
+                           'compile' and then run the default task for the
+                           specified target(s).
+     -r PREFILE, --read=PREFILE
+                           Read the specified file before bitbake.conf.
+     -R POSTFILE, --postread=POSTFILE
+                           Read the specified file after bitbake.conf.
+     -v, --verbose         Enable tracing of shell tasks (with 'set -x'). Also
+                           print bb.note(...) messages to stdout (in addition to
+                           writing them to ${T}/log.do_&lt;task&gt;).
+     -D, --debug           Increase the debug level. You can specify this more
+                           than once. -D sets the debug level to 1, where only
+                           bb.debug(1, ...) messages are printed to stdout; -DD
+                           sets the debug level to 2, where both bb.debug(1, ...)
+                           and bb.debug(2, ...) messages are printed; etc.
+                           Without -D, no debug messages are printed. Note that
+                           -D only affects output to stdout. All debug messages
+                           are written to ${T}/log.do_taskname, regardless of the
+                           debug level.
+     -q, --quiet           Output less log message data to the terminal. You can
+                           specify this more than once.
+     -n, --dry-run         Don't execute, just go through the motions.
+     -S SIGNATURE_HANDLER, --dump-signatures=SIGNATURE_HANDLER
+                           Dump out the signature construction information, with
+                           no task execution. The SIGNATURE_HANDLER parameter is
+                           passed to the handler. Two common values are none and
+                           printdiff but the handler may define more/less. none
+                           means only dump the signature, printdiff means compare
+                           the dumped signature with the cached one.
+     -p, --parse-only      Quit after parsing the BB recipes.
+     -s, --show-versions   Show current and preferred versions of all recipes.
+     -e, --environment     Show the global or per-recipe environment complete
+                           with information about where variables were
+                           set/changed.
+     -g, --graphviz        Save dependency tree information for the specified
+                           targets in the dot syntax.
+     -I EXTRA_ASSUME_PROVIDED, --ignore-deps=EXTRA_ASSUME_PROVIDED
+                           Assume these dependencies don't exist and are already
+                           provided (equivalent to ASSUME_PROVIDED). Useful to
+                           make dependency graphs more appealing
+     -l DEBUG_DOMAINS, --log-domains=DEBUG_DOMAINS
+                           Show debug logging for the specified logging domains
+     -P, --profile         Profile the command and save reports.
+     -u UI, --ui=UI        The user interface to use (knotty, ncurses or taskexp
+                           - default knotty).
+     --token=XMLRPCTOKEN   Specify the connection token to be used when
+                           connecting to a remote server.
+     --revisions-changed   Set the exit code depending on whether upstream
+                           floating revisions have changed or not.
+     --server-only         Run bitbake without a UI, only starting a server
+                           (cooker) process.
+     -B BIND, --bind=BIND  The name/address for the bitbake xmlrpc server to bind
+                           to.
+     -T SERVER_TIMEOUT, --idle-timeout=SERVER_TIMEOUT
+                           Set timeout to unload bitbake server due to
+                           inactivity, set to -1 means no unload, default:
+                           Environment variable BB_SERVER_TIMEOUT.
+     --no-setscene         Do not run any setscene tasks. sstate will be ignored
+                           and everything needed, built.
+     --setscene-only       Only run setscene tasks, don't run any real tasks.
+     --remote-server=REMOTE_SERVER
+                           Connect to the specified server.
+     -m, --kill-server     Terminate any running bitbake server.
+     --observe-only        Connect to a server as an observing-only client.
+     --status-only         Check the status of the remote bitbake server.
+     -w WRITEEVENTLOG, --write-log=WRITEEVENTLOG
+                           Writes the event log of the build to a bitbake event
+                           json file. Use '' (empty string) to assign the name
+                           automatically.
+     --runall=RUNALL       Run the specified task for any recipe in the taskgraph
+                           of the specified target (even if it wouldn't otherwise
+                           have run).
+     --runonly=RUNONLY     Run only the specified task within the taskgraph of
+                           the specified targets (and any task dependencies those
+                           tasks may have).
+
+.. _bitbake-examples:
+
+Examples
+--------
+
+This section presents some examples showing how to use BitBake.
+
+.. _example-executing-a-task-against-a-single-recipe:
+
+Executing a Task Against a Single Recipe
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Executing tasks for a single recipe file is relatively simple. You
+specify the file in question, and BitBake parses it and executes the
+specified task. If you do not specify a task, BitBake executes the
+default task, which is "build”. BitBake obeys inter-task dependencies
+when doing so.
+
+The following command runs the build task, which is the default task, on
+the ``foo_1.0.bb`` recipe file: ::
+
+  $ bitbake -b foo_1.0.bb
+
+The following command runs the clean task on the ``foo.bb`` recipe file: ::
+
+  $ bitbake -b foo.bb -c clean
+
+.. note::
+
+   The "-b" option explicitly does not handle recipe dependencies. Other
+   than for debugging purposes, it is instead recommended that you use
+   the syntax presented in the next section.
+
+Executing Tasks Against a Set of Recipe Files
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are a number of additional complexities introduced when one wants
+to manage multiple ``.bb`` files. Clearly there needs to be a way to
+tell BitBake what files are available and, of those, which you want to
+execute. There also needs to be a way for each recipe to express its
+dependencies, both for build-time and runtime. There must be a way for
+you to express recipe preferences when multiple recipes provide the same
+functionality, or when there are multiple versions of a recipe.
+
+The ``bitbake`` command, when not using "--buildfile" or "-b" only
+accepts a "PROVIDES". You cannot provide anything else. By default, a
+recipe file generally "PROVIDES" its "packagename" as shown in the
+following example: ::
+
+  $ bitbake foo
+
+This next example "PROVIDES" the
+package name and also uses the "-c" option to tell BitBake to just
+execute the ``do_clean`` task: ::
+
+  $ bitbake -c clean foo
+
+Executing a List of Task and Recipe Combinations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The BitBake command line supports specifying different tasks for
+individual targets when you specify multiple targets. For example,
+suppose you had two targets (or recipes) ``myfirstrecipe`` and
+``mysecondrecipe`` and you needed BitBake to run ``taskA`` for the first
+recipe and ``taskB`` for the second recipe: ::
+
+  $ bitbake myfirstrecipe:do_taskA mysecondrecipe:do_taskB
+
+Generating Dependency Graphs
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+BitBake is able to generate dependency graphs using the ``dot`` syntax.
+You can convert these graphs into images using the ``dot`` tool from
+`Graphviz <http://www.graphviz.org>`__.
+
+When you generate a dependency graph, BitBake writes two files to the
+current working directory:
+
+-  ``task-depends.dot``: Shows dependencies between tasks. These
+   dependencies match BitBake's internal task execution list.
+
+-  ``pn-buildlist``: Shows a simple list of targets that are to be
+   built.
+
+To stop depending on common depends, use the "-I" depend option and
+BitBake omits them from the graph. Leaving this information out can
+produce more readable graphs. This way, you can remove from the graph
+``DEPENDS`` from inherited classes such as ``base.bbclass``.
+
+Here are two examples that create dependency graphs. The second example
+omits depends common in OpenEmbedded from the graph: ::
+
+  $ bitbake -g foo
+
+  $ bitbake -g -I virtual/kernel -I eglibc foo
+
+Executing a Multiple Configuration Build
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+BitBake is able to build multiple images or packages using a single
+command where the different targets require different configurations
+(multiple configuration builds). Each target, in this scenario, is
+referred to as a "multiconfig".
+
+To accomplish a multiple configuration build, you must define each
+target's configuration separately using a parallel configuration file in
+the build directory. The location for these multiconfig configuration
+files is specific. They must reside in the current build directory in a
+sub-directory of ``conf`` named ``multiconfig``. Following is an example
+for two separate targets:
+
+.. image:: figures/bb_multiconfig_files.png
+   :align: center
+
+The reason for this required file hierarchy is because the ``BBPATH``
+variable is not constructed until the layers are parsed. Consequently,
+using the configuration file as a pre-configuration file is not possible
+unless it is located in the current working directory.
+
+Minimally, each configuration file must define the machine and the
+temporary directory BitBake uses for the build. Suggested practice
+dictates that you do not overlap the temporary directories used during
+the builds.
+
+Aside from separate configuration files for each target, you must also
+enable BitBake to perform multiple configuration builds. Enabling is
+accomplished by setting the
+:term:`BBMULTICONFIG` variable in the
+``local.conf`` configuration file. As an example, suppose you had
+configuration files for ``target1`` and ``target2`` defined in the build
+directory. The following statement in the ``local.conf`` file both
+enables BitBake to perform multiple configuration builds and specifies
+the two extra multiconfigs: ::
+
+  BBMULTICONFIG = "target1 target2"
+
+Once the target configuration files are in place and BitBake has been
+enabled to perform multiple configuration builds, use the following
+command form to start the builds: ::
+
+  $ bitbake [mc:multiconfigname:]target [[[mc:multiconfigname:]target] ... ]
+
+Here is an example for two extra multiconfigs: ``target1`` and ``target2``: ::
+
+  $ bitbake mc::target mc:target1:target mc:target2:target
+
+.. _bb-enabling-multiple-configuration-build-dependencies:
+
+Enabling Multiple Configuration Build Dependencies
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Sometimes dependencies can exist between targets (multiconfigs) in a
+multiple configuration build. For example, suppose that in order to
+build an image for a particular architecture, the root filesystem of
+another build for a different architecture needs to exist. In other
+words, the image for the first multiconfig depends on the root
+filesystem of the second multiconfig. This dependency is essentially
+that the task in the recipe that builds one multiconfig is dependent on
+the completion of the task in the recipe that builds another
+multiconfig.
+
+To enable dependencies in a multiple configuration build, you must
+declare the dependencies in the recipe using the following statement
+form: ::
+
+  task_or_package[mcdepends] = "mc:from_multiconfig:to_multiconfig:recipe_name:task_on_which_to_depend"
+
+To better show how to use this statement, consider an example with two
+multiconfigs: ``target1`` and ``target2``: ::
+
+  image_task[mcdepends] = "mc:target1:target2:image2:rootfs_task"
+
+In this example, the
+``from_multiconfig`` is "target1" and the ``to_multiconfig`` is "target2". The
+task on which the image whose recipe contains image_task depends on the
+completion of the rootfs_task used to build out image2, which is
+associated with the "target2" multiconfig.
+
+Once you set up this dependency, you can build the "target1" multiconfig
+using a BitBake command as follows: ::
+
+  $ bitbake mc:target1:image1
+
+This command executes all the tasks needed to create ``image1`` for the "target1"
+multiconfig. Because of the dependency, BitBake also executes through
+the ``rootfs_task`` for the "target2" multiconfig build.
+
+Having a recipe depend on the root filesystem of another build might not
+seem that useful. Consider this change to the statement in the image1
+recipe: ::
+
+  image_task[mcdepends] = "mc:target1:target2:image2:image_task"
+
+In this case, BitBake must create ``image2`` for the "target2" build since
+the "target1" build depends on it.
+
+Because "target1" and "target2" are enabled for multiple configuration
+builds and have separate configuration files, BitBake places the
+artifacts for each build in the respective temporary build directories.
diff --git a/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
new file mode 100644
index 0000000..ec5d085
--- /dev/null
+++ b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.rst
@@ -0,0 +1,1969 @@
+.. SPDX-License-Identifier: CC-BY-2.5
+
+====================
+Syntax and Operators
+====================
+
+|
+
+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.
+
+Basic Syntax
+============
+
+This section provides some basic syntax examples.
+
+Basic Variable Setting
+----------------------
+
+The following example sets ``VARIABLE`` to "value". This assignment
+occurs immediately as the statement is parsed. It is a "hard"
+assignment. ::
+
+   VARIABLE = "value"
+
+As expected, if you include leading or
+trailing spaces as part of an assignment, the spaces are retained: ::
+
+   VARIABLE = " value"
+   VARIABLE = "value "
+
+Setting ``VARIABLE`` 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). ::
+
+   VARIABLE = ""
+   VARIABLE = " "
+
+You can use single quotes instead of double quotes when setting a
+variable's value. Doing so allows you to use values that contain the
+double quote character: ::
+
+   VARIABLE = 'I have a " in my value'
+
+.. note::
+
+   Unlike in Bourne shells, single quotes work identically to double
+   quotes in all other ways. They do not suppress variable expansions.
+
+Modifying Existing Variables
+----------------------------
+
+Sometimes you need to modify existing variables. Following are some
+cases where you might find you want to modify an existing variable:
+
+-  Customize a recipe that uses the variable.
+
+-  Change a variable's default value used in a ``*.bbclass`` file.
+
+-  Change the variable in a ``*.bbappend`` file to override the variable
+   in the original recipe.
+
+-  Change the variable in a configuration file so that the value
+   overrides an existing configuration.
+
+Changing a variable value can sometimes depend on how the value was
+originally assigned and also on the desired intent of the change. In
+particular, when you append a value to a variable that has a default
+value, the resulting value might not be what you expect. In this case,
+the value you provide might replace the value rather than append to the
+default value.
+
+If after you have changed a variable's value and something unexplained
+occurs, you can use BitBake to check the actual value of the suspect
+variable. You can make these checks for both configuration and recipe
+level changes:
+
+-  For configuration changes, use the following: ::
+
+      $ bitbake -e
+
+   This
+   command displays variable values after the configuration files (i.e.
+   ``local.conf``, ``bblayers.conf``, ``bitbake.conf`` and so forth)
+   have been parsed.
+
+   .. note::
+
+      Variables that are exported to the environment are preceded by the
+      string "export" in the command's output.
+
+-  For recipe changes, use the following: ::
+
+      $ bitbake recipe -e \| grep VARIABLE="
+
+   This command checks to see if the variable actually makes
+   it into a specific recipe.
+
+Line Joining
+------------
+
+Outside of :ref:`functions <bitbake-user-manual/bitbake-user-manual-metadata:functions>`,
+BitBake joins any line ending in
+a backslash character ("\") with the following line before parsing
+statements. The most common use for the "\" character is to split
+variable assignments over multiple lines, as in the following example: ::
+
+   FOO = "bar \
+          baz \
+          qaz"
+
+Both the "\" character and the newline
+character that follow it are removed when joining lines. Thus, no
+newline characters end up in the value of ``FOO``.
+
+Consider this additional example where the two assignments both assign
+"barbaz" to ``FOO``: ::
+
+   FOO = "barbaz"
+   FOO = "bar\
+   baz"
+
+.. note::
+
+   BitBake does not interpret escape sequences like "\n" in variable
+   values. For these to have an effect, the value must be passed to some
+   utility that interprets escape sequences, such as
+   ``printf`` or ``echo -n``.
+
+Variable Expansion
+------------------
+
+Variables can reference the contents of other variables using a syntax
+that is similar to variable expansion in Bourne shells. The following
+assignments result in A containing "aval" and B evaluating to
+"preavalpost". ::
+
+   A = "aval"
+   B = "pre${A}post"
+
+.. note::
+
+   Unlike in Bourne shells, the curly braces are mandatory: Only ``${FOO}`` and not
+   ``$FOO`` is recognized as an expansion of ``FOO``.
+
+The "=" operator does not immediately expand variable references in the
+right-hand side. Instead, expansion is deferred until the variable
+assigned to is actually used. The result depends on the current values
+of the referenced variables. The following example should clarify this
+behavior: ::
+
+   A = "${B} baz"
+   B = "${C} bar"
+   C = "foo"
+   *At this point, ${A} equals "foo bar baz"*
+   C = "qux"
+   *At this point, ${A} equals "qux bar baz"*
+   B = "norf"
+   *At this point, ${A} equals "norf baz"\*
+
+Contrast this behavior with the
+:ref:`bitbake-user-manual/bitbake-user-manual-metadata:immediate variable
+expansion (:=)` operator.
+
+If the variable expansion syntax is used on a variable that does not
+exist, the string is kept as is. For example, given the following
+assignment, ``BAR`` expands to the literal string "${FOO}" as long as
+``FOO`` does not exist. ::
+
+   BAR = "${FOO}"
+
+Setting a default value (?=)
+----------------------------
+
+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: ::
+
+   A ?= "aval"
+
+If ``A`` is
+set at the time this statement is parsed, the variable retains its
+value. However, if ``A`` 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.
+
+Setting a weak default value (??=)
+----------------------------------
+
+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: ::
+
+   A ??= "somevalue"
+   A ??= "someothervalue"
+
+If ``A`` is set before the above statements are
+parsed, the variable retains its value. If ``A`` is not set, the
+variable is set to "someothervalue".
+
+Again, this assignment is a "lazy" or "weak" assignment because it does
+not occur until the end of the parsing process.
+
+Immediate variable expansion (:=)
+---------------------------------
+
+The ":=" operator results in a variable's contents being expanded
+immediately, rather than when the variable is actually used: ::
+
+   T = "123"
+   A := "test ${T}"
+   T = "456"
+   B := "${T} ${C}"
+   C = "cval"
+   C := "${C}append"
+
+In this example, ``A`` contains "test 123", even though the final value
+of ``T`` is "456". The variable ``B`` will end up containing "456
+cvalappend". This is because references to undefined variables are
+preserved as is during (immediate)expansion. This is in contrast to GNU
+Make, where undefined variables expand to nothing. The variable ``C``
+contains "cvalappend" since ``${C}`` immediately expands to "cval".
+
+.. _appending-and-prepending:
+
+Appending (+=) and prepending (=+) With Spaces
+----------------------------------------------
+
+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.
+
+These operators take immediate effect during parsing. Here are some
+examples: ::
+
+   B = "bval"
+   B += "additionaldata"
+   C = "cval"
+   C =+ "test"
+
+The variable ``B`` contains "bval additionaldata" and ``C`` contains "test
+cval".
+
+.. _appending-and-prepending-without-spaces:
+
+Appending (.=) and Prepending (=.) Without Spaces
+-------------------------------------------------
+
+If you want to append or prepend values without an inserted space, use
+the ".=" and "=." operators.
+
+These operators take immediate effect during parsing. Here are some
+examples: ::
+
+   B = "bval"
+   B .= "additionaldata"
+   C = "cval"
+   C =. "test"
+
+The variable ``B`` contains "bvaladditionaldata" and ``C`` contains
+"testcval".
+
+Appending and Prepending (Override Style Syntax)
+------------------------------------------------
+
+You can also append and prepend a variable's value using an override
+style syntax. When you use this syntax, no spaces are inserted.
+
+These operators differ from the ":=", ".=", "=.", "+=", and "=+"
+operators in that their effects are applied at variable expansion time
+rather than being immediately applied. Here are some examples: ::
+
+   B = "bval"
+   B_append = " additional data"
+   C = "cval"
+   C_prepend = "additional data "
+   D = "dval"
+   D_append = "additional data"
+
+The variable ``B``
+becomes "bval additional data" and ``C`` becomes "additional data cval".
+The variable ``D`` becomes "dvaladditional data".
+
+.. note::
+
+   You must control all spacing when you use the override syntax.
+
+It is also possible to append and prepend to shell functions and
+BitBake-style Python functions. See the ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:shell functions`" and ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:bitbake-style python functions`"
+sections for examples.
+
+.. _removing-override-style-syntax:
+
+Removal (Override Style Syntax)
+-------------------------------
+
+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.
+
+When you use this syntax, BitBake expects one or more strings.
+Surrounding spaces and spacing are preserved. Here is an example: ::
+
+   FOO = "123 456 789 123456 123 456 123 456"
+   FOO_remove = "123"
+   FOO_remove = "456"
+   FOO2 = " abc def ghi abcdef abc def abc def def"
+   FOO2_remove = "\
+       def \
+       abc \
+       ghi \
+       "
+
+The variable ``FOO`` becomes
+"  789 123456    " and ``FOO2`` becomes "    abcdef     ".
+
+Like "_append" and "_prepend", "_remove" is applied at variable
+expansion time.
+
+Override Style Operation Advantages
+-----------------------------------
+
+An advantage of the override style operations "_append", "_prepend", and
+"_remove" as compared to the "+=" and "=+" operators is that the
+override style operators provide guaranteed operations. For example,
+consider a class ``foo.bbclass`` that needs to add the value "val" to
+the variable ``FOO``, and a recipe that uses ``foo.bbclass`` as follows: ::
+
+   inherit foo
+   FOO = "initial"
+
+If ``foo.bbclass`` uses the "+=" operator,
+as follows, then the final value of ``FOO`` will be "initial", which is
+not what is desired: ::
+
+   FOO += "val"
+
+If, on the other hand, ``foo.bbclass``
+uses the "_append" operator, then the final value of ``FOO`` will be
+"initial val", as intended: ::
+
+   FOO_append = " val"
+
+.. note::
+
+   It is never necessary to use "+=" together with "_append". The following
+   sequence of assignments appends "barbaz" to FOO: ::
+
+       FOO_append = "bar"
+       FOO_append = "baz"
+
+
+   The only effect of changing the second assignment in the previous
+   example to use "+=" would be to add a space before "baz" in the
+   appended value (due to how the "+=" operator works).
+
+Another advantage of the override style operations is that you can
+combine them with other overrides as described in the
+":ref:`bitbake-user-manual/bitbake-user-manual-metadata:conditional syntax (overrides)`" section.
+
+Variable Flag Syntax
+--------------------
+
+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
+":ref:`bitbake-user-manual/bitbake-user-manual-metadata:variable flags`" section.
+
+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. "_prepend", "_append", and
+"_remove").
+
+Here are some examples showing how to set variable flags: ::
+
+   FOO[a] = "abc"
+   FOO[b] = "123"
+   FOO[a] += "456"
+
+The variable ``FOO`` has two flags:
+``[a]`` and ``[b]``. The flags are immediately set to "abc" and "123",
+respectively. The ``[a]`` flag becomes "abc 456".
+
+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: ::
+
+   CACHE[doc] = "The directory holding the cache of the metadata."
+
+Inline Python Variable Expansion
+--------------------------------
+
+You can use inline Python variable expansion to set variables. Here is
+an example: ::
+
+   DATE = "${@time.strftime('%Y%m%d',time.gmtime())}"
+
+This example results in the ``DATE`` variable being set to the current date.
+
+Probably the most common use of this feature is to extract the value of
+variables from BitBake's internal data dictionary, ``d``. The following
+lines select the values of a package name and its version number,
+respectively: ::
+
+   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'}"
+
+.. note::
+
+   Inline Python expressions work just like variable expansions insofar as the
+   "=" and ":=" operators are concerned. Given the following assignment, foo()
+   is called each time FOO is expanded: ::
+
+      FOO = "${@foo()}"
+
+   Contrast this with the following immediate assignment, where foo() is only
+   called once, while the assignment is parsed: ::
+
+      FOO := "${@foo()}"
+
+For a different way to set variables with Python code during parsing,
+see the
+":ref:`bitbake-user-manual/bitbake-user-manual-metadata:anonymous python functions`" section.
+
+Unsetting variables
+-------------------
+
+It is possible to completely remove a variable or a variable flag from
+BitBake's internal data dictionary by using the "unset" keyword. Here is
+an example: ::
+
+   unset DATE
+   unset do_fetch[noexec]
+
+These two statements remove the ``DATE`` and the ``do_fetch[noexec]`` flag.
+
+Providing Pathnames
+-------------------
+
+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.
+
+Instead, provide a fuller path as the following example illustrates: ::
+
+   BBLAYERS ?= " \
+       /home/scott-lenovo/LayerA \
+   "
+
+Exporting Variables to the Environment
+======================================
+
+You can export variables to the environment of running tasks by using
+the ``export`` keyword. For example, in the following example, the
+``do_foo`` task prints "value from the environment" when run: ::
+
+   export ENV_VARIABLE
+   ENV_VARIABLE = "value from the environment"
+
+   do_foo() {
+       bbplain "$ENV_VARIABLE"
+   }
+
+.. note::
+
+   BitBake does not expand ``$ENV_VARIABLE`` in this case because it lacks the
+   obligatory ``{}`` . Rather, ``$ENV_VARIABLE`` is expanded by the shell.
+
+It does not matter whether ``export ENV_VARIABLE`` appears before or
+after assignments to ``ENV_VARIABLE``.
+
+It is also possible to combine ``export`` with setting a value for the
+variable. Here is an example: ::
+
+   export ENV_VARIABLE = "variable-value"
+
+In the output of ``bitbake -e``, variables that are exported to the
+environment are preceded by "export".
+
+Among the variables commonly exported to the environment are ``CC`` and
+``CFLAGS``, which are picked up by many build systems.
+
+Conditional Syntax (Overrides)
+==============================
+
+BitBake uses :term:`OVERRIDES` to control what
+variables are overridden after BitBake parses recipes and configuration
+files. This section describes how you can use ``OVERRIDES`` as
+conditional metadata, talks about key expansion in relationship to
+``OVERRIDES``, and provides some examples to help with understanding.
+
+Conditional Metadata
+--------------------
+
+You can use ``OVERRIDES`` to conditionally select a specific version of
+a variable and to conditionally append or prepend the value of a
+variable.
+
+.. note::
+
+   Overrides can only use lower-case characters. Additionally,
+   underscores are not permitted in override names as they are used to
+   separate overrides from each other and from the variable name.
+
+-  *Selecting a Variable:* The ``OVERRIDES`` 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 ``OVERRIDES``, then the
+   “arm”-specific version of the variable is used rather than the
+   non-conditional version. Here is an example: ::
+
+      OVERRIDES = "architecture:os:machine"
+      TEST = "default"
+      TEST_os = "osspecific"
+      TEST_nooverride = "othercondvalue"
+
+   In this example, the ``OVERRIDES``
+   variable lists three overrides: "architecture", "os", and "machine".
+   The variable ``TEST`` by itself has a default value of "default". You
+   select the os-specific version of the ``TEST`` variable by appending
+   the "os" override to the variable (i.e. ``TEST_os``).
+
+   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 ``KBRANCH`` to a default value, then conditionally override
+   that value based on the architecture of the build: ::
+
+      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"
+
+-  *Appending and Prepending:* BitBake also supports append and prepend
+   operations to variable values based on whether a specific item is
+   listed in ``OVERRIDES``. Here is an example: ::
+
+      DEPENDS = "glibc ncurses"
+      OVERRIDES = "machine:local"
+      DEPENDS_append_machine = "libmad"
+
+   In this example, ``DEPENDS`` becomes "glibc ncurses libmad".
+
+   Again, using an OpenEmbedded metadata-based kernel recipe file as an
+   example, the following lines will conditionally append to the
+   ``KERNEL_FEATURES`` variable based on the architecture: ::
+
+      KERNEL_FEATURES_append = " ${KERNEL_EXTRA_FEATURES}"
+      KERNEL_FEATURES_append_qemux86=" cfg/sound.scc cfg/paravirt_kvm.scc"
+      KERNEL_FEATURES_append_qemux86-64=" cfg/sound.scc cfg/paravirt_kvm.scc"
+
+-  *Setting a Variable for a Single Task:* BitBake supports setting a
+   variable just for the duration of a single task. Here is an example: ::
+
+      FOO_task-configure = "val 1"
+      FOO_task-compile = "val 2"
+
+   In the
+   previous example, ``FOO`` has the value "val 1" while the
+   ``do_configure`` task is executed, and the value "val 2" while the
+   ``do_compile`` task is executed.
+
+   Internally, this is implemented by prepending the task (e.g.
+   "task-compile:") to the value of
+   :term:`OVERRIDES` for the local datastore of the
+   ``do_compile`` task.
+
+   You can also use this syntax with other combinations (e.g.
+   "``_prepend``") as shown in the following example: ::
+
+      EXTRA_OEMAKE_prepend_task-compile = "${PARALLEL_MAKE} "
+
+Key Expansion
+-------------
+
+Key expansion happens when the BitBake datastore is finalized. To better
+understand this, consider the following example: ::
+
+   A${B} = "X"
+   B = "2"
+   A2 = "Y"
+
+In this case, after all the parsing is complete, BitBake expands
+``${B}`` into "2". This expansion causes ``A2``, which was set to "Y"
+before the expansion, to become "X".
+
+.. _variable-interaction-worked-examples:
+
+Examples
+--------
+
+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.
+
+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: ::
+
+   OVERRIDES = "foo"
+   A = "Z"
+   A_foo_append = "X"
+
+For this case,
+``A`` is unconditionally set to "Z" and "X" is unconditionally and
+immediately appended to the variable ``A_foo``. Because overrides have
+not been applied yet, ``A_foo`` is set to "X" due to the append and
+``A`` simply equals "Z".
+
+Applying overrides, however, changes things. Since "foo" is listed in
+``OVERRIDES``, the conditional variable ``A`` is replaced with the "foo"
+version, which is equal to "X". So effectively, ``A_foo`` replaces
+``A``.
+
+This next example changes the order of the override and the append: ::
+
+   OVERRIDES = "foo"
+   A = "Z"
+   A_append_foo = "X"
+
+For this case, before
+overrides are handled, ``A`` is set to "Z" and ``A_append_foo`` is set
+to "X". Once the override for "foo" is applied, however, ``A`` gets
+appended with "X". Consequently, ``A`` becomes "ZX". Notice that spaces
+are not appended.
+
+This next example has the order of the appends and overrides reversed
+back as in the first example: ::
+
+   OVERRIDES = "foo"
+   A = "Y"
+   A_foo_append = "Z"
+   A_foo_append = "X"
+
+For this case, before any overrides are resolved,
+``A`` is set to "Y" using an immediate assignment. After this immediate
+assignment, ``A_foo`` is set to "Z", and then further appended with "X"
+leaving the variable set to "ZX". Finally, applying the override for
+"foo" results in the conditional variable ``A`` becoming "ZX" (i.e.
+``A`` is replaced with ``A_foo``).
+
+This final example mixes in some varying operators: ::
+
+   A = "1"
+   A_append = "2"
+   A_append = "3"
+   A += "4"
+   A .= "5"
+
+For this case, the type of append
+operators are affecting the order of assignments as BitBake passes
+through the code multiple times. Initially, ``A`` is set to "1 45"
+because of the three statements that use immediate operators. After
+these assignments are made, BitBake applies the "_append" operations.
+Those operations result in ``A`` becoming "1 4523".
+
+Sharing Functionality
+=====================
+
+BitBake allows for metadata sharing through include files (``.inc``) and
+class files (``.bbclass``). 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 ``.bbclass`` file
+that contains the common functionality and then using the ``inherit``
+directive in your recipes to inherit the class would be a common way to
+share the task.
+
+This section presents the mechanisms BitBake provides to allow you to
+share functionality between recipes. Specifically, the mechanisms
+include ``include``, ``inherit``, ``INHERIT``, and ``require``
+directives.
+
+Locating Include and Class Files
+--------------------------------
+
+BitBake uses the :term:`BBPATH` variable to locate
+needed include and class files. Additionally, BitBake searches the
+current directory for ``include`` and ``require`` directives.
+
+.. note::
+
+   The BBPATH variable is analogous to the environment variable PATH .
+
+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
+``BBPATH``.
+
+``inherit`` Directive
+---------------------
+
+When writing a recipe or class file, you can use the ``inherit``
+directive to inherit the functionality of a class (``.bbclass``).
+BitBake only supports this directive when used within recipe and class
+files (i.e. ``.bb`` and ``.bbclass``).
+
+The ``inherit`` directive is a rudimentary means of specifying
+functionality contained in class files that 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 and then have your recipe inherit that class file.
+
+As an example, your recipes could use the following directive to inherit
+an ``autotools.bbclass`` file. The class file would contain common
+functionality for using Autotools that could be shared across recipes: ::
+
+   inherit autotools
+
+In this case, BitBake would search for the directory
+``classes/autotools.bbclass`` in ``BBPATH``.
+
+.. note::
+
+   You can override any values and functions of the inherited class
+   within your recipe by doing so after the "inherit" statement.
+
+If you want to use the directive to inherit multiple classes, separate
+them with spaces. The following example shows how to inherit both the
+``buildhistory`` and ``rm_work`` classes: ::
+
+   inherit buildhistory rm_work
+
+An advantage with the inherit directive as compared to both the
+:ref:`include <bitbake-user-manual/bitbake-user-manual-metadata:\`\`include\`\` directive>` and :ref:`require <bitbake-user-manual/bitbake-user-manual-metadata:\`\`require\`\` directive>`
+directives is that you can inherit class files conditionally. You can
+accomplish this by using a variable expression after the ``inherit``
+statement. Here is an example: ::
+
+   inherit ${VARNAME}
+
+If ``VARNAME`` is
+going to be set, it needs to be set before the ``inherit`` statement is
+parsed. One way to achieve a conditional inherit in this case is to use
+overrides: ::
+
+   VARIABLE = ""
+   VARIABLE_someoverride = "myclass"
+
+Another method is by using anonymous Python. Here is an example: ::
+
+   python () {
+       if condition == value:
+           d.setVar('VARIABLE', 'myclass')
+       else:
+           d.setVar('VARIABLE', '')
+   }
+
+Alternatively, you could use an in-line Python expression in the
+following form: ::
+
+   inherit ${@'classname' if condition else ''}
+   inherit ${@functionname(params)}
+
+In all cases, if the expression evaluates to an
+empty string, the statement does not trigger a syntax error because it
+becomes a no-op.
+
+``include`` Directive
+---------------------
+
+BitBake understands the ``include`` 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 ``BBPATH``.
+
+The include directive is a more generic method of including
+functionality as compared to the :ref:`inherit <bitbake-user-manual/bitbake-user-manual-metadata:\`\`inherit\`\` directive>`
+directive, which is restricted to class (i.e. ``.bbclass``) files. The
+include directive is applicable for any other kind of shared or
+encapsulated functionality or configuration that does not suit a
+``.bbclass`` file.
+
+As an example, suppose you needed a recipe to include some self-test
+definitions: ::
+
+   include test_defs.inc
+
+.. note::
+
+   The include 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 :ref:`require <require-inclusion>` instead
+   of include . Doing so makes sure that an error is produced if the file cannot
+   be found.
+
+.. _require-inclusion:
+
+``require`` Directive
+---------------------
+
+BitBake understands the ``require`` directive. This directive behaves
+just like the ``include`` 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.
+
+The require directive, like the include directive previously described,
+is a more generic method of including functionality as compared to the
+:ref:`inherit <bitbake-user-manual/bitbake-user-manual-metadata:\`\`inherit\`\` directive>` directive, which is restricted to class
+(i.e. ``.bbclass``) files. The require directive is applicable for any
+other kind of shared or encapsulated functionality or configuration that
+does not suit a ``.bbclass`` file.
+
+Similar to how BitBake handles :ref:`include <bitbake-user-manual/bitbake-user-manual-metadata:\`\`include\`\` directive>`, if
+the path specified on the require line is a relative path, BitBake
+locates the first file it can find within ``BBPATH``.
+
+As an example, suppose you have two versions of a recipe (e.g.
+``foo_1.2.2.bb`` and ``foo_2.0.0.bb``) where each version contains some
+identical functionality that could be shared. You could create an
+include file named ``foo.inc`` that contains the common definitions
+needed to build "foo". You need to be sure ``foo.inc`` 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 ``require``
+directive from within each recipe: ::
+
+   require foo.inc
+
+``INHERIT`` Configuration Directive
+-----------------------------------
+
+When creating a configuration file (``.conf``), you can use the
+:term:`INHERIT` configuration directive to inherit a
+class. BitBake only supports this directive when used within a
+configuration file.
+
+As an example, suppose you needed to inherit a class file called
+``abc.bbclass`` from a configuration file as follows: ::
+
+   INHERIT += "abc"
+
+This configuration directive causes the named class to be inherited at
+the point of the directive during parsing. As with the ``inherit``
+directive, the ``.bbclass`` file must be located in a "classes"
+subdirectory in one of the directories specified in ``BBPATH``.
+
+.. note::
+
+   Because .conf files are parsed first during BitBake's execution, using
+   INHERIT to inherit a class effectively inherits the class globally (i.e. for
+   all recipes).
+
+If you want to use the directive to inherit multiple classes, you can
+provide them on the same line in the ``local.conf`` file. Use spaces to
+separate the classes. The following example shows how to inherit both
+the ``autotools`` and ``pkgconfig`` classes: ::
+
+   INHERIT += "autotools pkgconfig"
+
+Functions
+=========
+
+As with most languages, functions are the building blocks that are used
+to build up operations into tasks. BitBake supports these types of
+functions:
+
+-  *Shell Functions:* Functions written in shell script and executed
+   either directly as functions, tasks, or both. They can also be called
+   by other shell functions.
+
+-  *BitBake-Style Python Functions:* Functions written in Python and
+   executed by BitBake or other Python functions using
+   ``bb.build.exec_func()``.
+
+-  *Python Functions:* Functions written in Python and executed by
+   Python.
+
+-  *Anonymous Python Functions:* Python functions executed automatically
+   during parsing.
+
+Regardless of the type of function, you can only define them in class
+(``.bbclass``) and recipe (``.bb`` or ``.inc``) files.
+
+Shell Functions
+---------------
+
+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: ::
+
+   some_function () {
+       echo "Hello World"
+   }
+
+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 ``/bin/sh``, which may not be a bash
+shell but might be something such as ``dash``. You should not use
+Bash-specific script (bashisms).
+
+Overrides and override-style operators like ``_append`` and ``_prepend``
+can also be applied to shell functions. Most commonly, this application
+would be used in a ``.bbappend`` file to modify functions in the main
+recipe. It can also be used to modify functions inherited from classes.
+
+As an example, consider the following: ::
+
+   do_foo() {
+       bbplain first
+       fn
+   }
+
+   fn_prepend() {
+       bbplain second
+   }
+
+   fn() {
+       bbplain third
+   }
+
+   do_foo_append() {
+       bbplain fourth
+   }
+
+Running ``do_foo`` prints the following: ::
+
+   recipename do_foo: first
+   recipename do_foo: second
+   recipename do_foo: third
+   recipename do_foo: fourth
+
+.. note::
+
+   Overrides and override-style operators can be applied to any shell
+   function, not just :ref:`tasks <bitbake-user-manual/bitbake-user-manual-metadata:tasks>`.
+
+You can use the ``bitbake -e`` recipename command to view the final
+assembled function after all overrides have been applied.
+
+BitBake-Style Python Functions
+------------------------------
+
+These functions are written in Python and executed by BitBake or other
+Python functions using ``bb.build.exec_func()``.
+
+An example BitBake function is: ::
+
+   python some_python_function () {
+       d.setVar("TEXT", "Hello World")
+       print d.getVar("TEXT")
+   }
+
+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.
+
+.. note::
+
+   Variable expressions (e.g.  ``${X}`` ) are no longer expanded within Python
+   functions. This behavior is intentional in order to allow you to freely set
+   variable values to expandable expressions without having them expanded
+   prematurely. If you do wish to expand a variable within a Python function,
+   use ``d.getVar("X")`` . Or, for more complicated expressions, use ``d.expand()``.
+
+Similar to shell functions, you can also apply overrides and
+override-style operators to BitBake-style Python functions.
+
+As an example, consider the following: ::
+
+   python do_foo_prepend() {
+       bb.plain("first")
+   }
+
+   python do_foo() {
+       bb.plain("second")
+   }
+
+   python do_foo_append() {
+       bb.plain("third")
+   }
+
+Running ``do_foo`` prints the following: ::
+
+   recipename do_foo: first
+   recipename do_foo: second
+   recipename do_foo: third
+
+You can use the ``bitbake -e`` recipename command to view
+the final assembled function after all overrides have been applied.
+
+Python Functions
+----------------
+
+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: ::
+
+   def get_depends(d):
+       if d.getVar('SOMECONDITION'):
+           return "dependencywithcond"
+       else:
+           return "dependency"
+
+   SOMECONDITION = "1"
+   DEPENDS = "${@get_depends(d)}"
+
+This would result in ``DEPENDS`` containing ``dependencywithcond``.
+
+Here are some things to know about Python functions:
+
+-  Python functions can take parameters.
+
+-  The BitBake datastore is not automatically available. Consequently,
+   you must pass it in as a parameter to the function.
+
+-  The "bb" and "os" Python modules are automatically available. You do
+   not need to import them.
+
+BitBake-Style Python Functions Versus Python Functions
+------------------------------------------------------
+
+Following are some important differences between BitBake-style Python
+functions and regular Python functions defined with "def":
+
+-  Only BitBake-style Python functions can be :ref:`tasks <bitbake-user-manual/bitbake-user-manual-metadata:tasks>`.
+
+-  Overrides and override-style operators can only be applied to
+   BitBake-style Python functions.
+
+-  Only regular Python functions can take arguments and return values.
+
+-  :ref:`Variable flags <bitbake-user-manual/bitbake-user-manual-metadata:variable flags>` such as
+   ``[dirs]``, ``[cleandirs]``, and ``[lockfiles]`` can be used on BitBake-style
+   Python functions, but not on regular Python functions.
+
+-  BitBake-style Python functions generate a separate
+   ``${``\ :term:`T`\ ``}/run.``\ function-name\ ``.``\ pid
+   script that is executed to run the function, and also generate a log
+   file in ``${T}/log.``\ function-name\ ``.``\ pid if they are executed
+   as tasks.
+
+   Regular Python functions execute "inline" and do not generate any
+   files in ``${T}``.
+
+-  Regular Python functions are called with the usual Python syntax.
+   BitBake-style Python functions are usually tasks and are called
+   directly by BitBake, but can also be called manually from Python code
+   by using the ``bb.build.exec_func()`` function. Here is an example: ::
+
+      bb.build.exec_func("my_bitbake_style_function", d)
+
+   .. note::
+
+      ``bb.build.exec_func()`` can also be used to run shell functions from Python
+      code. If you want to run a shell function before a Python function within
+      the same task, then you can use a parent helper Python function that
+      starts by running the shell function with ``bb.build.exec_func()`` and then
+      runs the Python code.
+
+   To detect errors from functions executed with
+   ``bb.build.exec_func()``, you can catch the ``bb.build.FuncFailed``
+   exception.
+
+   .. note::
+
+      Functions in metadata (recipes and classes) should not themselves raise
+      ``bb.build.FuncFailed``. Rather, ``bb.build.FuncFailed`` should be viewed as a
+      general indicator that the called function failed by raising an
+      exception. For example, an exception raised by ``bb.fatal()`` will be caught
+      inside ``bb.build.exec_func()``, and a ``bb.build.FuncFailed`` will be raised in
+      response.
+
+Due to their simplicity, you should prefer regular Python functions over
+BitBake-style Python functions unless you need a feature specific to
+BitBake-style Python functions. Regular Python functions in metadata are
+a more recent invention than BitBake-style Python functions, and older
+code tends to use ``bb.build.exec_func()`` more often.
+
+Anonymous Python Functions
+--------------------------
+
+Sometimes it is useful to set variables or perform other operations
+programmatically during parsing. To do this, you can define special
+Python functions, called anonymous Python functions, that run at the end
+of parsing. For example, the following conditionally sets a variable
+based on the value of another variable: ::
+
+   python () {
+       if d.getVar('SOMEVAR') == 'value':
+           d.setVar('ANOTHERVAR', 'value2')
+   }
+
+An equivalent way to mark a function as an anonymous function is to give it
+the name "__anonymous", rather than no name.
+
+Anonymous Python functions always run at the end of parsing, regardless
+of where they are defined. If a recipe contains many anonymous
+functions, they run in the same order as they are defined within the
+recipe. As an example, consider the following snippet: ::
+
+   python () {
+       d.setVar('FOO', 'foo 2')
+   }
+
+   FOO = "foo 1"
+
+   python () {
+       d.appendVar('BAR',' bar 2')
+   }
+
+   BAR = "bar 1"
+
+The previous example is conceptually
+equivalent to the following snippet: ::
+
+   FOO = "foo 1"
+   BAR = "bar 1"
+   FOO = "foo 2"
+   BAR += "bar 2"
+
+``FOO`` ends up with the value "foo 2", and
+``BAR`` with the value "bar 1 bar 2". Just as in the second snippet, the
+values set for the variables within the anonymous functions become
+available to tasks, which always run after parsing.
+
+Overrides and override-style operators such as "``_append``" are applied
+before anonymous functions run. In the following example, ``FOO`` ends
+up with the value "foo from anonymous": ::
+
+   FOO = "foo"
+   FOO_append = " from outside"
+
+   python () {
+       d.setVar("FOO", "foo from anonymous")
+   }
+
+For methods
+you can use with anonymous Python functions, see the
+":ref:`bitbake-user-manual/bitbake-user-manual-metadata:functions you can call from within python`"
+section. For a different method to run Python code during parsing, see
+the ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:inline python variable expansion`" section.
+
+Flexible Inheritance for Class Functions
+----------------------------------------
+
+Through coding techniques and the use of ``EXPORT_FUNCTIONS``, 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.
+
+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. ``EXPORT_FUNCTIONS`` provides a mechanism that
+enables the recipe's version of the function to call the original
+version of the function.
+
+To make use of this technique, you need the following things in place:
+
+-  The class needs to define the function as follows: ::
+
+      classname_functionname
+
+   For example, if you have a class file
+   ``bar.bbclass`` and a function named ``do_foo``, the class must
+   define the function as follows: ::
+
+      bar_do_foo
+
+-  The class needs to contain the ``EXPORT_FUNCTIONS`` statement as
+   follows: ::
+
+      EXPORT_FUNCTIONS functionname
+
+   For example, continuing with
+   the same example, the statement in the ``bar.bbclass`` would be as
+   follows: ::
+
+      EXPORT_FUNCTIONS do_foo
+
+-  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 ``bar_do_foo``.
+   Assuming ``do_foo`` was a shell function and ``EXPORT_FUNCTIONS`` was
+   used as above, the recipe's function could conditionally call the
+   class version of the function as follows: ::
+
+      do_foo() {
+          if [ somecondition ] ; then
+              bar_do_foo
+          else
+              # Do something else
+          fi
+      }
+
+   To call your modified version of the function as defined in your recipe,
+   call it as ``do_foo``.
+
+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.
+
+Tasks
+=====
+
+Tasks are BitBake execution units that make up the steps that BitBake
+can run for a given recipe. Tasks are only supported in recipes and
+classes (i.e. in ``.bb`` files and files included or inherited from
+``.bb`` files). By convention, tasks have names that start with "do\_".
+
+Promoting a Function to a Task
+------------------------------
+
+Tasks are either :ref:`shell functions <bitbake-user-manual/bitbake-user-manual-metadata:shell functions>` or
+:ref:`BitBake-style Python functions <bitbake-user-manual/bitbake-user-manual-metadata:bitbake-style python functions>`
+that have been promoted to tasks by using the ``addtask`` command. The
+``addtask`` command can also optionally describe dependencies between
+the task and other tasks. Here is an example that shows how to define a
+task and declare some dependencies: ::
+
+   python do_printdate () {
+       import time
+       print time.strftime('%Y%m%d', time.gmtime())
+   }
+   addtask printdate after do_fetch before do_build
+
+The first argument to ``addtask`` is the name
+of the function to promote to a task. If the name does not start with
+"do\_", "do\_" is implicitly added, which enforces the convention that all
+task names start with "do\_".
+
+In the previous example, the ``do_printdate`` task becomes a dependency
+of the ``do_build`` task, which is the default task (i.e. the task run
+by the ``bitbake`` command unless another task is specified explicitly).
+Additionally, the ``do_printdate`` task becomes dependent upon the
+``do_fetch`` task. Running the ``do_build`` task results in the
+``do_printdate`` task running first.
+
+.. note::
+
+   If you try out the previous example, you might see that the
+   ``do_printdate``
+   task is only run the first time you build the recipe with the
+   ``bitbake``
+   command. This is because BitBake considers the task "up-to-date"
+   after that initial run. If you want to force the task to always be
+   rerun for experimentation purposes, you can make BitBake always
+   consider the task "out-of-date" by using the
+   :ref:`[nostamp] <bitbake-user-manual/bitbake-user-manual-metadata:Variable Flags>`
+   variable flag, as follows: ::
+
+      do_printdate[nostamp] = "1"
+
+   You can also explicitly run the task and provide the
+   -f option as follows: ::
+
+      $ bitbake recipe -c printdate -f
+
+   When manually selecting a task to run with the bitbake ``recipe
+   -c task`` command, you can omit the "do\_" prefix as part of the task
+   name.
+
+You might wonder about the practical effects of using ``addtask``
+without specifying any dependencies as is done in the following example: ::
+
+   addtask printdate
+
+In this example, assuming dependencies have not been
+added through some other means, the only way to run the task is by
+explicitly selecting it with ``bitbake`` recipe ``-c printdate``. You
+can use the ``do_listtasks`` task to list all tasks defined in a recipe
+as shown in the following example: ::
+
+   $ bitbake recipe -c listtasks
+
+For more information on task dependencies, see the
+":ref:`bitbake-user-manual/bitbake-user-manual-execution:dependencies`" section.
+
+See the ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:variable flags`" section for information
+on variable flags you can use with tasks.
+
+Deleting a Task
+---------------
+
+As well as being able to add tasks, you can delete them. Simply use the
+``deltask`` command to delete a task. For example, to delete the example
+task used in the previous sections, you would use: ::
+
+   deltask printdate
+
+If you delete a task using the ``deltask`` command and the task has
+dependencies, the dependencies are not reconnected. For example, suppose
+you have three tasks named ``do_a``, ``do_b``, and ``do_c``.
+Furthermore, ``do_c`` is dependent on ``do_b``, which in turn is
+dependent on ``do_a``. Given this scenario, if you use ``deltask`` to
+delete ``do_b``, the implicit dependency relationship between ``do_c``
+and ``do_a`` through ``do_b`` no longer exists, and ``do_c``
+dependencies are not updated to include ``do_a``. Thus, ``do_c`` is free
+to run before ``do_a``.
+
+If you want dependencies such as these to remain intact, use the
+``[noexec]`` varflag to disable the task instead of using the
+``deltask`` command to delete it: ::
+
+   do_b[noexec] = "1"
+
+Passing Information Into the Build Task Environment
+---------------------------------------------------
+
+When running a task, BitBake tightly controls the shell execution
+environment of the build tasks to make sure unwanted contamination from
+the build machine cannot influence the build.
+
+.. note::
+
+   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. You can prevent this
+   "cleaning" by setting the :term:`BB_PRESERVE_ENV` variable.
+
+Consequently, if you do want something to get passed into the build task
+environment, you must take these two steps:
+
+#. Tell BitBake to load what you want from the environment into the
+   datastore. You can do so through the
+   :term:`BB_ENV_WHITELIST` and
+   :term:`BB_ENV_EXTRAWHITE` variables. For
+   example, assume you want to prevent the build system from accessing
+   your ``$HOME/.ccache`` directory. The following command "whitelists"
+   the environment variable ``CCACHE_DIR`` causing BitBake to allow that
+   variable into the datastore: ::
+
+      export BB_ENV_EXTRAWHITE="$BB_ENV_EXTRAWHITE CCACHE_DIR"
+
+#. 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 ``local.conf`` or your distribution
+   configuration file: ::
+
+      export CCACHE_DIR
+
+   .. 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.
+
+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 :term:`BB_ORIGENV`.
+
+The ``BB_ORIGENV`` variable returns a datastore object that can be
+queried using the standard datastore operators such as
+``getVar(, False)``. The datastore object is useful, for example, to
+find the original ``DISPLAY`` variable. Here is an example: ::
+
+   origenv = d.getVar("BB_ORIGENV", False)
+   bar = origenv.getVar("BAR", False)
+
+The previous example returns ``BAR`` from the original execution
+environment.
+
+Variable Flags
+==============
+
+Variable flags (varflags) help control a task's functionality and
+dependencies. BitBake reads and writes varflags to the datastore using
+the following command forms: ::
+
+   variable = d.getVarFlags("variable")
+   self.d.setVarFlags("FOO", {"func": True})
+
+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
+":ref:`bitbake-user-manual/bitbake-user-manual-metadata:variable flag syntax`" section for details.
+
+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:
+
+-  ``[cleandirs]``: Empty directories that should be created before
+   the task runs. Directories that already exist are removed and
+   recreated to empty them.
+
+-  ``[depends]``: Controls inter-task dependencies. See the
+   :term:`DEPENDS` variable and the
+   ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:inter-task
+   dependencies`" section for more information.
+
+-  ``[deptask]``: Controls task build-time dependencies. See the
+   :term:`DEPENDS` variable and the ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:build dependencies`" section for more information.
+
+-  ``[dirs]``: Directories that should be created before the task
+   runs. Directories that already exist are left as is. The last
+   directory listed is used as the current working directory for the
+   task.
+
+-  ``[lockfiles]``: 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.
+
+-  ``[noexec]``: When set to "1", marks the task as being empty, with
+   no execution required. You can use the ``[noexec]`` flag to set up
+   tasks as dependency placeholders, or to disable tasks defined
+   elsewhere that are not needed in a particular recipe.
+
+-  ``[nostamp]``: When set to "1", tells BitBake to not generate a
+   stamp file for a task, which implies the task should always be
+   executed.
+
+   .. caution::
+
+      Any task that depends (possibly indirectly) on a ``[nostamp]`` task will
+      always be executed as well. This can cause unnecessary rebuilding if you
+      are not careful.
+
+-  ``[number_threads]``: Limits tasks to a specific number of
+   simultaneous threads during execution. This varflag is useful when
+   your build host has a large number of cores but certain tasks need to
+   be rate-limited due to various kinds of resource constraints (e.g. to
+   avoid network throttling). ``number_threads`` works similarly to the
+   :term:`BB_NUMBER_THREADS` variable but is task-specific.
+
+   Set the value globally. For example, the following makes sure the
+   ``do_fetch`` task uses no more than two simultaneous execution
+   threads: do_fetch[number_threads] = "2"
+
+   .. warning::
+
+      -  Setting the varflag in individual recipes rather than globally
+         can result in unpredictable behavior.
+
+      -  Setting the varflag to a value greater than the value used in
+         the ``BB_NUMBER_THREADS`` variable causes ``number_threads`` to
+         have no effect.
+
+-  ``[postfuncs]``: List of functions to call after the completion of
+   the task.
+
+-  ``[prefuncs]``: List of functions to call before the task executes.
+
+-  ``[rdepends]``: Controls inter-task runtime dependencies. See the
+   :term:`RDEPENDS` variable, the
+   :term:`RRECOMMENDS` variable, and the
+   ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:inter-task dependencies`" section for
+   more information.
+
+-  ``[rdeptask]``: Controls task runtime dependencies. See the
+   :term:`RDEPENDS` variable, the
+   :term:`RRECOMMENDS` variable, and the
+   ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:runtime dependencies`" section for more
+   information.
+
+-  ``[recideptask]``: When set in conjunction with ``recrdeptask``,
+   specifies a task that should be inspected for additional
+   dependencies.
+
+-  ``[recrdeptask]``: Controls task recursive runtime dependencies.
+   See the :term:`RDEPENDS` variable, the
+   :term:`RRECOMMENDS` variable, and the
+   ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:recursive dependencies`" section for
+   more information.
+
+-  ``[stamp-extra-info]``: Extra stamp information to append to the
+   task's stamp. As an example, OpenEmbedded uses this flag to allow
+   machine-specific tasks.
+
+-  ``[umask]``: The umask to run the task under.
+
+Several varflags are useful for controlling how signatures are
+calculated for variables. For more information on this process, see the
+":ref:`bitbake-user-manual/bitbake-user-manual-execution:checksums (signatures)`" section.
+
+-  ``[vardeps]``: 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.
+
+-  ``[vardepsexclude]``: Specifies a space-separated list of variables
+   that should be excluded from a variable's dependencies for the
+   purposes of calculating its signature.
+
+-  ``[vardepvalue]``: If set, instructs BitBake to ignore the actual
+   value of the variable and instead use the specified value when
+   calculating the variable's signature.
+
+-  ``[vardepvalueexclude]``: Specifies a pipe-separated list of
+   strings to exclude from the variable's value when calculating the
+   variable's signature.
+
+Events
+======
+
+BitBake allows installation of event handlers within recipe and class
+files. Events are triggered at certain points during operation, such as
+the beginning of operation against a given recipe (i.e. ``*.bb``), the
+start of a given task, a task failure, a task success, and so forth. The
+intent is to make it easy to do things like email notification on build
+failures.
+
+Following is an example event handler that prints the name of the event
+and the content of the ``FILE`` variable: ::
+
+   addhandler myclass_eventhandler
+   python myclass_eventhandler() {
+       from bb.event import getName
+       print("The name of the Event is %s" % getName(e))
+       print("The file we run for is %s" % d.getVar('FILE'))
+   }
+   myclass_eventhandler[eventmask] = "bb.event.BuildStarted
+   bb.event.BuildCompleted"
+
+In the previous example, an eventmask has been
+set so that the handler only sees the "BuildStarted" and
+"BuildCompleted" events. This event handler gets called every time an
+event matching the eventmask is triggered. A global variable "e" is
+defined, which represents the current event. With the ``getName(e)``
+method, you can get the name of the triggered event. The global
+datastore is available as "d". In legacy code, you might see "e.data"
+used to get the datastore. However, realize that "e.data" is deprecated
+and you should use "d" going forward.
+
+The context of the datastore is appropriate to the event in question.
+For example, "BuildStarted" and "BuildCompleted" events run before any
+tasks are executed so would be in the global configuration datastore
+namespace. No recipe-specific metadata exists in that namespace. The
+"BuildStarted" and "BuildCompleted" events also run in the main
+cooker/server process rather than any worker context. Thus, any changes
+made to the datastore would be seen by other cooker/server events within
+the current build but not seen outside of that build or in any worker
+context. Task events run in the actual tasks in question consequently
+have recipe-specific and task-specific contents. These events run in the
+worker context and are discarded at the end of task execution.
+
+During a standard build, the following common events might occur. The
+following events are the most common kinds of events that most metadata
+might have an interest in viewing:
+
+-  ``bb.event.ConfigParsed()``: Fired when the base configuration; which
+   consists of ``bitbake.conf``, ``base.bbclass`` and any global
+   ``INHERIT`` statements; has been parsed. You can see multiple such
+   events when each of the workers parse the base configuration or if
+   the server changes configuration and reparses. Any given datastore
+   only has one such event executed against it, however. If
+   ```BB_INVALIDCONF`` <#>`__ is set in the datastore by the event
+   handler, the configuration is reparsed and a new event triggered,
+   allowing the metadata to update configuration.
+
+-  ``bb.event.HeartbeatEvent()``: Fires at regular time intervals of one
+   second. You can configure the interval time using the
+   ``BB_HEARTBEAT_EVENT`` variable. The event's "time" attribute is the
+   ``time.time()`` value when the event is triggered. This event is
+   useful for activities such as system state monitoring.
+
+-  ``bb.event.ParseStarted()``: Fired when BitBake is about to start
+   parsing recipes. This event's "total" attribute represents the number
+   of recipes BitBake plans to parse.
+
+-  ``bb.event.ParseProgress()``: Fired as parsing progresses. This
+   event's "current" attribute is the number of recipes parsed as well
+   as the "total" attribute.
+
+-  ``bb.event.ParseCompleted()``: Fired when parsing is complete. This
+   event's "cached", "parsed", "skipped", "virtuals", "masked", and
+   "errors" attributes provide statistics for the parsing results.
+
+-  ``bb.event.BuildStarted()``: Fired when a new build starts. BitBake
+   fires multiple "BuildStarted" events (one per configuration) when
+   multiple configuration (multiconfig) is enabled.
+
+-  ``bb.build.TaskStarted()``: Fired when a task starts. This event's
+   "taskfile" attribute points to the recipe from which the task
+   originates. The "taskname" attribute, which is the task's name,
+   includes the ``do_`` prefix, and the "logfile" attribute point to
+   where the task's output is stored. Finally, the "time" attribute is
+   the task's execution start time.
+
+-  ``bb.build.TaskInvalid()``: Fired if BitBake tries to execute a task
+   that does not exist.
+
+-  ``bb.build.TaskFailedSilent()``: Fired for setscene tasks that fail
+   and should not be presented to the user verbosely.
+
+-  ``bb.build.TaskFailed()``: Fired for normal tasks that fail.
+
+-  ``bb.build.TaskSucceeded()``: Fired when a task successfully
+   completes.
+
+-  ``bb.event.BuildCompleted()``: Fired when a build finishes.
+
+-  ``bb.cooker.CookerExit()``: Fired when the BitBake server/cooker
+   shuts down. This event is usually only seen by the UIs as a sign they
+   should also shutdown.
+
+This next list of example events occur based on specific requests to the
+server. These events are often used to communicate larger pieces of
+information from the BitBake server to other parts of BitBake such as
+user interfaces:
+
+-  ``bb.event.TreeDataPreparationStarted()``
+-  ``bb.event.TreeDataPreparationProgress()``
+-  ``bb.event.TreeDataPreparationCompleted()``
+-  ``bb.event.DepTreeGenerated()``
+-  ``bb.event.CoreBaseFilesFound()``
+-  ``bb.event.ConfigFilePathFound()``
+-  ``bb.event.FilesMatchingFound()``
+-  ``bb.event.ConfigFilesFound()``
+-  ``bb.event.TargetsTreeGenerated()``
+
+.. _variants-class-extension-mechanism:
+
+Variants - Class Extension Mechanism
+====================================
+
+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
+:term:`BBCLASSEXTEND` and :term:`BBVERSIONS` variables.
+
+.. note::
+
+   The mechanism for this class extension is extremely specific to the
+   implementation. Usually, the recipe's :term:`PROVIDES` , :term:`PN` , and
+   :term:`DEPENDS` variables would need to be modified by the extension
+   class. For specific examples, see the OE-Core native , nativesdk , and
+   multilib classes.
+
+-  ``BBCLASSEXTEND``: 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. ::
+
+      BBCLASSEXTEND = "native"
+
+-  ``BBVERSIONS``: 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
+   :term:`OVERRIDES` mechanism) for a single
+   version, or an optionally named range of versions. Here is an
+   example: ::
+
+      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"
+
+   The name of the range defaults to the original version of the recipe. For
+   example, in OpenEmbedded, the recipe file ``foo_1.0.0+.bb`` creates a default
+   name range of ``1.0.0+``. 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 ``file://``
+   search paths (:term:`FILESPATH`).
+
+Dependencies
+============
+
+To allow for efficient parallel processing, BitBake handles dependencies
+at the task level. Dependencies can exist both between tasks within a
+single recipe and between tasks in different recipes. Following are
+examples of each:
+
+-  For tasks within a single recipe, a recipe's ``do_configure`` task
+   might need to complete before its ``do_compile`` task can run.
+
+-  For tasks in different recipes, one recipe's ``do_configure`` task
+   might require another recipe's ``do_populate_sysroot`` task to finish
+   first such that the libraries and headers provided by the other
+   recipe are available.
+
+This section describes several ways to declare dependencies. Remember,
+even though dependencies are declared in different ways, they are all
+simply dependencies between tasks.
+
+.. _dependencies-internal-to-the-bb-file:
+
+Dependencies Internal to the ``.bb`` File
+-----------------------------------------
+
+BitBake uses the ``addtask`` directive to manage dependencies that are
+internal to a given recipe file. You can use the ``addtask`` directive
+to indicate when a task is dependent on other tasks or when other tasks
+depend on that recipe. Here is an example: ::
+
+   addtask printdate after do_fetch before do_build
+
+In this example, the ``do_printdate`` task
+depends on the completion of the ``do_fetch`` task, and the ``do_build``
+task depends on the completion of the ``do_printdate`` task.
+
+.. note::
+
+   For a task to run, it must be a direct or indirect dependency of some
+   other task that is scheduled to run.
+
+   For illustration, here are some examples:
+
+   -  The directive ``addtask mytask before do_configure`` causes
+      ``do_mytask`` to run before ``do_configure`` runs. Be aware that
+      ``do_mytask`` still only runs if its :ref:`input
+      checksum <bitbake-user-manual/bitbake-user-manual-execution:checksums (signatures)>` has changed since the last time it was
+      run. Changes to the input checksum of ``do_mytask`` also
+      indirectly cause ``do_configure`` to run.
+
+   -  The directive ``addtask mytask after do_configure`` by itself
+      never causes ``do_mytask`` to run. ``do_mytask`` can still be run
+      manually as follows: ::
+
+         $ bitbake recipe -c mytask
+
+      Declaring ``do_mytask`` as a dependency of some other task that is
+      scheduled to run also causes it to run. Regardless, the task runs after
+      ``do_configure``.
+
+Build Dependencies
+------------------
+
+BitBake uses the :term:`DEPENDS` variable to manage
+build time dependencies. The ``[deptask]`` varflag for tasks signifies
+the task of each item listed in ``DEPENDS`` that must complete before
+that task can be executed. Here is an example: ::
+
+   do_configure[deptask] = "do_populate_sysroot"
+
+In this example, the ``do_populate_sysroot`` task
+of each item in ``DEPENDS`` must complete before ``do_configure`` can
+execute.
+
+Runtime Dependencies
+--------------------
+
+BitBake uses the :term:`PACKAGES`, :term:`RDEPENDS`, and :term:`RRECOMMENDS`
+variables to manage runtime dependencies.
+
+The ``PACKAGES`` variable lists runtime packages. Each of those packages
+can have ``RDEPENDS`` and ``RRECOMMENDS`` 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. ::
+
+   do_package_qa[rdeptask] = "do_packagedata"
+
+In the previous
+example, the ``do_packagedata`` task of each item in ``RDEPENDS`` must
+have completed before ``do_package_qa`` can execute.
+Although ``RDEPENDS`` contains entries from the
+runtime dependency namespace, BitBake knows how to map them back
+to the build-time dependency namespace, in which the tasks are defined.
+
+Recursive Dependencies
+----------------------
+
+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.
+
+The ``[recrdeptask]`` flag is most commonly used in high-level recipes
+that need to wait for some task to finish "globally". For example,
+``image.bbclass`` has the following: ::
+
+   do_rootfs[recrdeptask] += "do_packagedata"
+
+This statement says that the ``do_packagedata`` task of
+the current recipe and all recipes reachable (by way of dependencies)
+from the image recipe must run before the ``do_rootfs`` task can run.
+
+BitBake allows a task to recursively depend on itself by
+referencing itself in the task list: ::
+
+   do_a[recrdeptask] = "do_a do_b"
+
+In the same way as before, this means that the ``do_a``
+and ``do_b`` tasks of the current recipe and all
+recipes reachable (by way of dependencies) from the recipe
+must run before the ``do_a`` task can run. In this
+case BitBake will ignore the current recipe's ``do_a``
+task circular dependency on itself.
+
+Inter-Task Dependencies
+-----------------------
+
+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 ``DEPENDS``. Here is an example: ::
+
+   do_patch[depends] = "quilt-native:do_populate_sysroot"
+
+In this example, the ``do_populate_sysroot`` task of the target ``quilt-native``
+must have completed before the ``do_patch`` task can execute.
+
+The ``[rdepends]`` flag works in a similar way but takes targets in the
+runtime namespace instead of the build-time dependency namespace.
+
+Functions You Can Call From Within Python
+=========================================
+
+BitBake provides many functions you can call from within Python
+functions. This section lists the most commonly used functions, and
+mentions where to find others.
+
+Functions for Accessing Datastore Variables
+-------------------------------------------
+
+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:
+
+.. list-table::
+   :widths: auto
+   :header-rows: 1
+
+   * - *Operation*
+     - *Description*
+   * - ``d.getVar("X", expand)``
+     - Returns the value of variable "X". Using "expand=True" expands the
+       value. Returns "None" if the variable "X" does not exist.
+   * - ``d.setVar("X", "value")``
+     - Sets the variable "X" to "value"
+   * - ``d.appendVar("X", "value")``
+     - Adds "value" to the end of the variable "X". Acts like ``d.setVar("X",
+       "value")`` if the variable "X" does not exist.
+   * - ``d.prependVar("X", "value")``
+     - Adds "value" to the start of the variable "X". Acts like
+       ``d.setVar("X","value")`` if the variable "X" does not exist.
+   * - ``d.delVar("X")``
+     - Deletes the variable "X" from the datastore. Does nothing if the variable
+       "X" does not exist.
+   * - ``d.renameVar("X", "Y")``
+     - Renames the variable "X" to "Y". Does nothing if the variable "X" does
+       not exist.
+   * - ``d.getVarFlag("X", flag, expand)``
+     - Returns the value of variable "X". Using "expand=True" expands the
+       value. Returns "None" if either the variable "X" or the named flag does
+       not exist.
+   * - ``d.setVarFlag("X", flag, "value")``
+     - Sets the named flag for variable "X" to "value".
+   * - ``d.appendVarFlag("X", flag, "value")``
+     - Appends "value" to the named flag on the variable "X". Acts like
+       ``d.setVarFlag("X", flag, "value")`` if the named flag does not exist.
+   * - ``d.prependVarFlag("X", flag, "value")``
+     - Prepends "value" to the named flag on the variable "X". Acts like
+       ``d.setVarFlag("X", flag, "value")`` if the named flag does not exist.
+   * - ``d.delVarFlag("X", flag)``
+     - Deletes the named flag on the variable "X" from the datastore.
+   * - ``d.setVarFlags("X", flagsdict)``
+     - Sets the flags specified in the ``flagsdict()``
+       parameter. ``setVarFlags`` does not clear previous flags. Think of this
+       operation as ``addVarFlags``.
+   * - ``d.getVarFlags("X")``
+     - Returns a ``flagsdict`` of the flags for the variable "X". Returns "None"
+       if the variable "X" does not exist.
+   * - ``d.delVarFlags("X")``
+     - Deletes all the flags for the variable "X". Does nothing if the variable
+       "X" does not exist.
+   * - ``d.expand(expression)``
+     - Expands variable references in the specified string
+       expression. References to variables that do not exist are left as is. For
+       example, ``d.expand("foo ${X}")`` expands to the literal string "foo
+       ${X}" if the variable "X" does not exist.
+
+Other Functions
+---------------
+
+You can find many other functions that can be called from Python by
+looking at the source code of the ``bb`` module, which is in
+``bitbake/lib/bb``. For example, ``bitbake/lib/bb/utils.py`` includes
+the commonly used functions ``bb.utils.contains()`` and
+``bb.utils.mkdirhier()``, which come with docstrings.
+
+Task Checksums and Setscene
+===========================
+
+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.
+
+These checksums are stored in :term:`STAMP`. You can
+examine the checksums using the following BitBake command: ::
+
+   $ bitbake-dumpsigs
+
+This command returns the signature data in a readable
+format that allows you to examine the inputs used when the OpenEmbedded
+build system generates signatures. For example, using
+``bitbake-dumpsigs`` allows you to examine the ``do_compile`` task's
+“sigdata” for a C application (e.g. ``bash``). Running the command also
+reveals that the “CC” variable is part of the inputs that are hashed.
+Any changes to this variable would invalidate the stamp and cause the
+``do_compile`` task to run.
+
+The following list describes related variables:
+
+-  :term:`BB_HASHCHECK_FUNCTION`:
+   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.
+
+-  :term:`BB_SETSCENE_DEPVALID`:
+   Specifies a function BitBake calls that determines whether BitBake
+   requires a setscene dependency to be met.
+
+-  :term:`BB_SETSCENE_VERIFY_FUNCTION2`:
+   Specifies a function to call that verifies the list of planned task
+   execution before the main task execution happens.
+
+-  :term:`BB_STAMP_POLICY`: Defines the mode
+   for comparing timestamps of stamp files.
+
+-  :term:`BB_STAMP_WHITELIST`: Lists stamp
+   files that are looked at when the stamp policy is "whitelist".
+
+-  :term:`BB_TASKHASH`: Within an executing task,
+   this variable holds the hash of the task as returned by the currently
+   enabled signature generator.
+
+-  :term:`STAMP`: The base path to create stamp files.
+
+-  :term:`STAMPCLEAN`: Again, the base path to
+   create stamp files but can use wildcards for matching a range of
+   files for clean operations.
+
+Wildcard Support in Variables
+=============================
+
+Support for wildcard use in variables varies depending on the context in
+which it is used. For example, some variables and file names allow
+limited use of wildcards through the "``%``" and "``*``" characters.
+Other variables or names support Python's
+`glob <https://docs.python.org/3/library/glob.html>`_ syntax,
+`fnmatch <https://docs.python.org/3/library/fnmatch.html#module-fnmatch>`_
+syntax, or
+`Regular Expression (re) <https://docs.python.org/3/library/re.html>`_
+syntax.
+
+For variables that have wildcard suport, the documentation describes
+which form of wildcard, its use, and its limitations.
diff --git a/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst
new file mode 100644
index 0000000..fb1b353
--- /dev/null
+++ b/poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst
@@ -0,0 +1,1372 @@
+.. SPDX-License-Identifier: CC-BY-2.5
+
+==================
+Variables Glossary
+==================
+
+|
+
+This chapter lists common variables used by BitBake and gives an
+overview of their function and contents.
+
+.. note::
+
+   Following are some points regarding the variables listed in this
+   glossary:
+
+   -  The variables listed in this glossary are specific to BitBake.
+      Consequently, the descriptions are limited to that context.
+
+   -  Also, variables exist in other systems that use BitBake (e.g. The
+      Yocto Project and OpenEmbedded) that have names identical to those
+      found in this glossary. For such cases, the variables in those
+      systems extend the functionality of the variable as it is
+      described here in this glossary.
+
+   -  Finally, there are variables mentioned in this glossary that do
+      not appear in the BitBake glossary. These other variables are
+      variables used in systems that use BitBake.
+
+.. glossary::
+
+   ASSUME_PROVIDED
+      Lists recipe names (:term:`PN` values) BitBake does not
+      attempt to build. Instead, BitBake assumes these recipes have already
+      been built.
+
+      In OpenEmbedded-Core, ``ASSUME_PROVIDED`` mostly specifies native
+      tools that should not be built. An example is ``git-native``, which
+      when specified allows for the Git binary from the host to be used
+      rather than building ``git-native``.
+
+   B
+      The directory in which BitBake executes functions during a recipe's
+      build process.
+
+   BB_ALLOWED_NETWORKS
+      Specifies a space-delimited list of hosts that the fetcher is allowed
+      to use to obtain the required source code. Following are
+      considerations surrounding this variable:
+
+      -  This host list is only used if
+         :term:`BB_NO_NETWORK` is either not set or
+         set to "0".
+
+      -  Limited support for the "``*``" wildcard character for matching
+         against the beginning of host names exists. For example, the
+         following setting matches ``git.gnu.org``, ``ftp.gnu.org``, and
+         ``foo.git.gnu.org``. ::
+
+            BB_ALLOWED_NETWORKS = "\*.gnu.org"
+
+         .. important::
+
+            The use of the "``*``" character only works at the beginning of
+            a host name and it must be isolated from the remainder of the
+            host name. You cannot use the wildcard character in any other
+            location of the name or combined with the front part of the
+            name.
+
+            For example, ``*.foo.bar`` is supported, while ``*aa.foo.bar``
+            is not.
+
+      -  Mirrors not in the host list are skipped and logged in debug.
+
+      -  Attempts to access networks not in the host list cause a failure.
+
+      Using ``BB_ALLOWED_NETWORKS`` in conjunction with
+      :term:`PREMIRRORS` is very useful. Adding the
+      host you want to use to ``PREMIRRORS`` results in the source code
+      being fetched from an allowed location and avoids raising an error
+      when a host that is not allowed is in a
+      :term:`SRC_URI` statement. This is because the
+      fetcher does not attempt to use the host listed in ``SRC_URI`` after
+      a successful fetch from the ``PREMIRRORS`` occurs.
+
+   BB_CONSOLELOG
+      Specifies the path to a log file into which BitBake's user interface
+      writes output during the build.
+
+   BB_CURRENTTASK
+      Contains the name of the currently running task. The name does not
+      include the ``do_`` prefix.
+
+   BB_DANGLINGAPPENDS_WARNONLY
+      Defines how BitBake handles situations where an append file
+      (``.bbappend``) has no corresponding recipe file (``.bb``). This
+      condition often occurs when layers get out of sync (e.g. ``oe-core``
+      bumps a recipe version and the old recipe no longer exists and the
+      other layer has not been updated to the new version of the recipe
+      yet).
+
+      The default fatal behavior is safest because it is the sane reaction
+      given something is out of sync. It is important to realize when your
+      changes are no longer being applied.
+
+   BB_DEFAULT_TASK
+      The default task to use when none is specified (e.g. with the ``-c``
+      command line option). The task name specified should not include the
+      ``do_`` prefix.
+
+   BB_DISKMON_DIRS
+      Monitors disk space and available inodes during the build and allows
+      you to control the build based on these parameters.
+
+      Disk space monitoring is disabled by default. When setting this
+      variable, use the following form: ::
+
+         BB_DISKMON_DIRS = "<action>,<dir>,<threshold> [...]"
+
+         where:
+
+            <action> is:
+               ABORT:     Immediately abort the build when
+                          a threshold is broken.
+               STOPTASKS: Stop the build after the currently
+                          executing tasks have finished when
+                          a threshold is broken.
+               WARN:      Issue a warning but continue the
+                          build when a threshold is broken.
+                          Subsequent warnings are issued as
+                          defined by the
+                          BB_DISKMON_WARNINTERVAL variable,
+                          which must be defined.
+
+            <dir> is:
+               Any directory you choose. You can specify one or
+               more directories to monitor by separating the
+               groupings with a space.  If two directories are
+               on the same device, only the first directory
+               is monitored.
+
+            <threshold> is:
+               Either the minimum available disk space,
+               the minimum number of free inodes, or
+               both.  You must specify at least one.  To
+               omit one or the other, simply omit the value.
+               Specify the threshold using G, M, K for Gbytes,
+               Mbytes, and Kbytes, respectively. If you do
+               not specify G, M, or K, Kbytes is assumed by
+               default.  Do not use GB, MB, or KB.
+
+      Here are some examples: ::
+
+         BB_DISKMON_DIRS = "ABORT,${TMPDIR},1G,100K WARN,${SSTATE_DIR},1G,100K"
+         BB_DISKMON_DIRS = "STOPTASKS,${TMPDIR},1G"
+         BB_DISKMON_DIRS = "ABORT,${TMPDIR},,100K"
+
+      The first example works only if you also set the
+      :term:`BB_DISKMON_WARNINTERVAL`
+      variable. This example causes the build system to immediately abort
+      when either the disk space in ``${TMPDIR}`` drops below 1 Gbyte or
+      the available free inodes drops below 100 Kbytes. Because two
+      directories are provided with the variable, the build system also
+      issues a warning when the disk space in the ``${SSTATE_DIR}``
+      directory drops below 1 Gbyte or the number of free inodes drops
+      below 100 Kbytes. Subsequent warnings are issued during intervals as
+      defined by the ``BB_DISKMON_WARNINTERVAL`` variable.
+
+      The second example stops the build after all currently executing
+      tasks complete when the minimum disk space in the ``${TMPDIR}``
+      directory drops below 1 Gbyte. No disk monitoring occurs for the free
+      inodes in this case.
+
+      The final example immediately aborts the build when the number of
+      free inodes in the ``${TMPDIR}`` directory drops below 100 Kbytes. No
+      disk space monitoring for the directory itself occurs in this case.
+
+   BB_DISKMON_WARNINTERVAL
+      Defines the disk space and free inode warning intervals.
+
+      If you are going to use the ``BB_DISKMON_WARNINTERVAL`` variable, you
+      must also use the :term:`BB_DISKMON_DIRS`
+      variable and define its action as "WARN". During the build,
+      subsequent warnings are issued each time disk space or number of free
+      inodes further reduces by the respective interval.
+
+      If you do not provide a ``BB_DISKMON_WARNINTERVAL`` variable and you
+      do use ``BB_DISKMON_DIRS`` with the "WARN" action, the disk
+      monitoring interval defaults to the following:
+      BB_DISKMON_WARNINTERVAL = "50M,5K"
+
+      When specifying the variable in your configuration file, use the
+      following form: ::
+
+         BB_DISKMON_WARNINTERVAL = "<disk_space_interval>,<disk_inode_interval>"
+
+         where:
+
+            <disk_space_interval> is:
+               An interval of memory expressed in either
+               G, M, or K for Gbytes, Mbytes, or Kbytes,
+               respectively. You cannot use GB, MB, or KB.
+
+            <disk_inode_interval> is:
+               An interval of free inodes expressed in either
+               G, M, or K for Gbytes, Mbytes, or Kbytes,
+               respectively. You cannot use GB, MB, or KB.
+
+      Here is an example: ::
+
+         BB_DISKMON_DIRS = "WARN,${SSTATE_DIR},1G,100K"
+         BB_DISKMON_WARNINTERVAL = "50M,5K"
+
+      These variables cause BitBake to
+      issue subsequent warnings each time the available disk space further
+      reduces by 50 Mbytes or the number of free inodes further reduces by
+      5 Kbytes in the ``${SSTATE_DIR}`` directory. Subsequent warnings
+      based on the interval occur each time a respective interval is
+      reached beyond the initial warning (i.e. 1 Gbytes and 100 Kbytes).
+
+   BB_ENV_WHITELIST
+      Specifies the internal whitelist of variables to allow through from
+      the external environment into BitBake's datastore. If the value of
+      this variable is not specified (which is the default), the following
+      list is used: :term:`BBPATH`, :term:`BB_PRESERVE_ENV`,
+      :term:`BB_ENV_WHITELIST`, and :term:`BB_ENV_EXTRAWHITE`.
+
+      .. note::
+
+         You must set this variable in the external environment in order
+         for it to work.
+
+   BB_ENV_EXTRAWHITE
+      Specifies an additional set of variables to allow through (whitelist)
+      from the external environment into BitBake's datastore. This list of
+      variables are on top of the internal list set in
+      :term:`BB_ENV_WHITELIST`.
+
+      .. note::
+
+         You must set this variable in the external environment in order
+         for it to work.
+
+   BB_FETCH_PREMIRRORONLY
+      When set to "1", causes BitBake's fetcher module to only search
+      :term:`PREMIRRORS` for files. BitBake will not
+      search the main :term:`SRC_URI` or
+      :term:`MIRRORS`.
+
+   BB_FILENAME
+      Contains the filename of the recipe that owns the currently running
+      task. For example, if the ``do_fetch`` task that resides in the
+      ``my-recipe.bb`` is executing, the ``BB_FILENAME`` variable contains
+      "/foo/path/my-recipe.bb".
+
+   BBFILES_DYNAMIC
+      Activates content depending on presence of identified layers.  You
+      identify the layers by the collections that the layers define.
+
+      Use the ``BBFILES_DYNAMIC`` variable to avoid ``.bbappend`` files whose
+      corresponding ``.bb`` file is in a layer that attempts to modify other
+      layers through ``.bbappend`` but does not want to introduce a hard
+      dependency on those other layers.
+
+      Additionally you can prefix the rule with "!" to add ``.bbappend`` and
+      ``.bb`` files in case a layer is not present.  Use this avoid hard
+      dependency on those other layers.
+
+      Use the following form for ``BBFILES_DYNAMIC``: ::
+
+         collection_name:filename_pattern
+
+      The following example identifies two collection names and two filename
+      patterns: ::
+
+         BBFILES_DYNAMIC += "\
+             clang-layer:${LAYERDIR}/bbappends/meta-clang/*/*/*.bbappend \
+             core:${LAYERDIR}/bbappends/openembedded-core/meta/*/*/*.bbappend \
+         "
+
+      When the collection name is prefixed with "!" it will add the file pattern in case
+      the layer is absent: ::
+
+         BBFILES_DYNAMIC += "\
+             !clang-layer:${LAYERDIR}/backfill/meta-clang/*/*/*.bb \
+         "
+
+      This next example shows an error message that occurs because invalid
+      entries are found, which cause parsing to abort: ::
+
+         ERROR: BBFILES_DYNAMIC entries must be of the form {!}<collection name>:<filename pattern>, not:
+         /work/my-layer/bbappends/meta-security-isafw/*/*/*.bbappend
+         /work/my-layer/bbappends/openembedded-core/meta/*/*/*.bbappend
+
+   BB_GENERATE_MIRROR_TARBALLS
+      Causes tarballs of the Git repositories, including the Git metadata,
+      to be placed in the :term:`DL_DIR` directory. Anyone
+      wishing to create a source mirror would want to enable this variable.
+
+      For performance reasons, creating and placing tarballs of the Git
+      repositories is not the default action by BitBake. ::
+
+         BB_GENERATE_MIRROR_TARBALLS = "1"
+
+   BB_HASHCONFIG_WHITELIST
+      Lists variables that are excluded from base configuration checksum,
+      which is used to determine if the cache can be reused.
+
+      One of the ways BitBake determines whether to re-parse the main
+      metadata is through checksums of the variables in the datastore of
+      the base configuration data. There are variables that you typically
+      want to exclude when checking whether or not to re-parse and thus
+      rebuild the cache. As an example, you would usually exclude ``TIME``
+      and ``DATE`` because these variables are always changing. If you did
+      not exclude them, BitBake would never reuse the cache.
+
+   BB_HASHBASE_WHITELIST
+      Lists variables that are excluded from checksum and dependency data.
+      Variables that are excluded can therefore change without affecting
+      the checksum mechanism. A common example would be the variable for
+      the path of the build. BitBake's output should not (and usually does
+      not) depend on the directory in which it was built.
+
+   BB_HASHCHECK_FUNCTION
+      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.
+      The function returns the list of setscene tasks that should be
+      executed.
+
+      At this point in the execution of the code, the objective is to
+      quickly verify if a given setscene function is likely to work or not.
+      It's easier to check the list of setscene functions in one pass than
+      to call many individual tasks. The returned list need not be
+      completely accurate. A given setscene task can still later fail.
+      However, the more accurate the data returned, the more efficient the
+      build will be.
+
+   BB_INVALIDCONF
+      Used in combination with the ``ConfigParsed`` event to trigger
+      re-parsing the base metadata (i.e. all the recipes). The
+      ``ConfigParsed`` event can set the variable to trigger the re-parse.
+      You must be careful to avoid recursive loops with this functionality.
+
+   BB_LOGCONFIG
+      Specifies the name of a config file that contains the user logging
+      configuration. See
+      :ref:`bitbake-user-manual/bitbake-user-manual-execution:logging`
+      for additional information
+
+   BB_LOGFMT
+      Specifies the name of the log files saved into
+      ``${``\ :term:`T`\ ``}``. By default, the ``BB_LOGFMT``
+      variable is undefined and the log file names get created using the
+      following form: ::
+
+         log.{task}.{pid}
+
+      If you want to force log files to take a specific name, you can set this
+      variable in a configuration file.
+
+   BB_NICE_LEVEL
+      Allows BitBake to run at a specific priority (i.e. nice level).
+      System permissions usually mean that BitBake can reduce its priority
+      but not raise it again. See :term:`BB_TASK_NICE_LEVEL` for
+      additional information.
+
+   BB_NO_NETWORK
+      Disables network access in the BitBake fetcher modules. With this
+      access disabled, any command that attempts to access the network
+      becomes an error.
+
+      Disabling network access is useful for testing source mirrors,
+      running builds when not connected to the Internet, and when operating
+      in certain kinds of firewall environments.
+
+   BB_NUMBER_THREADS
+      The maximum number of tasks BitBake should run in parallel at any one
+      time. If your host development system supports multiple cores, a good
+      rule of thumb is to set this variable to twice the number of cores.
+
+   BB_NUMBER_PARSE_THREADS
+      Sets the number of threads BitBake uses when parsing. By default, the
+      number of threads is equal to the number of cores on the system.
+
+   BB_ORIGENV
+      Contains a copy of the original external environment in which BitBake
+      was run. The copy is taken before any whitelisted variable values are
+      filtered into BitBake's datastore.
+
+      .. note::
+
+         The contents of this variable is a datastore object that can be
+         queried using the normal datastore operations.
+
+   BB_PRESERVE_ENV
+      Disables whitelisting and instead allows all variables through from
+      the external environment into BitBake's datastore.
+
+      .. note::
+
+         You must set this variable in the external environment in order
+         for it to work.
+
+   BB_RUNFMT
+      Specifies the name of the executable script files (i.e. run files)
+      saved into ``${``\ :term:`T`\ ``}``. By default, the
+      ``BB_RUNFMT`` variable is undefined and the run file names get
+      created using the following form: ::
+
+         run.{task}.{pid}
+
+      If you want to force run files to take a specific name, you can set this
+      variable in a configuration file.
+
+   BB_RUNTASK
+      Contains the name of the currently executing task. The value includes
+      the "do\_" prefix. For example, if the currently executing task is
+      ``do_config``, the value is "do_config".
+
+   BB_SCHEDULER
+      Selects the name of the scheduler to use for the scheduling of
+      BitBake tasks. Three options exist:
+
+      -  *basic* - The basic framework from which everything derives. Using
+         this option causes tasks to be ordered numerically as they are
+         parsed.
+
+      -  *speed* - Executes tasks first that have more tasks depending on
+         them. The "speed" option is the default.
+
+      -  *completion* - Causes the scheduler to try to complete a given
+         recipe once its build has started.
+
+   BB_SCHEDULERS
+      Defines custom schedulers to import. Custom schedulers need to be
+      derived from the ``RunQueueScheduler`` class.
+
+      For information how to select a scheduler, see the
+      :term:`BB_SCHEDULER` variable.
+
+   BB_SETSCENE_DEPVALID
+      Specifies a function BitBake calls that determines whether BitBake
+      requires a setscene dependency to be met.
+
+      When running a setscene task, BitBake needs to know which
+      dependencies of that setscene task also need to be run. Whether
+      dependencies also need to be run is highly dependent on the metadata.
+      The function specified by this variable returns a "True" or "False"
+      depending on whether the dependency needs to be met.
+
+   BB_SETSCENE_VERIFY_FUNCTION2
+      Specifies a function to call that verifies the list of planned task
+      execution before the main task execution happens. The function is
+      called once BitBake has a list of setscene tasks that have run and
+      either succeeded or failed.
+
+      The function allows for a task list check to see if they make sense.
+      Even if BitBake was planning to skip a task, the returned value of
+      the function can force BitBake to run the task, which is necessary
+      under certain metadata defined circumstances.
+
+   BB_SIGNATURE_EXCLUDE_FLAGS
+      Lists variable flags (varflags) that can be safely excluded from
+      checksum and dependency data for keys in the datastore. When
+      generating checksum or dependency data for keys in the datastore, the
+      flags set against that key are normally included in the checksum.
+
+      For more information on varflags, see the
+      ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:variable flags`"
+      section.
+
+   BB_SIGNATURE_HANDLER
+      Defines the name of the signature handler BitBake uses. The signature
+      handler defines the way stamp files are created and handled, if and
+      how the signature is incorporated into the stamps, and how the
+      signature itself is generated.
+
+      A new signature handler can be added by injecting a class derived
+      from the ``SignatureGenerator`` class into the global namespace.
+
+   BB_SRCREV_POLICY
+      Defines the behavior of the fetcher when it interacts with source
+      control systems and dynamic source revisions. The
+      ``BB_SRCREV_POLICY`` variable is useful when working without a
+      network.
+
+      The variable can be set using one of two policies:
+
+      -  *cache* - Retains the value the system obtained previously rather
+         than querying the source control system each time.
+
+      -  *clear* - Queries the source controls system every time. With this
+         policy, there is no cache. The "clear" policy is the default.
+
+   BB_STAMP_POLICY
+      Defines the mode used for how timestamps of stamp files are compared.
+      You can set the variable to one of the following modes:
+
+      -  *perfile* - Timestamp comparisons are only made between timestamps
+         of a specific recipe. This is the default mode.
+
+      -  *full* - Timestamp comparisons are made for all dependencies.
+
+      -  *whitelist* - Identical to "full" mode except timestamp
+         comparisons are made for recipes listed in the
+         :term:`BB_STAMP_WHITELIST` variable.
+
+      .. note::
+
+         Stamp policies are largely obsolete with the introduction of
+         setscene tasks.
+
+   BB_STAMP_WHITELIST
+      Lists files whose stamp file timestamps are compared when the stamp
+      policy mode is set to "whitelist". For information on stamp policies,
+      see the :term:`BB_STAMP_POLICY` variable.
+
+   BB_STRICT_CHECKSUM
+      Sets a more strict checksum mechanism for non-local URLs. Setting
+      this variable to a value causes BitBake to report an error if it
+      encounters a non-local URL that does not have at least one checksum
+      specified.
+
+   BB_TASK_IONICE_LEVEL
+      Allows adjustment of a task's Input/Output priority. During
+      Autobuilder testing, random failures can occur for tasks due to I/O
+      starvation. These failures occur during various QEMU runtime
+      timeouts. You can use the ``BB_TASK_IONICE_LEVEL`` variable to adjust
+      the I/O priority of these tasks.
+
+      .. note::
+
+         This variable works similarly to the :term:`BB_TASK_NICE_LEVEL`
+         variable except with a task's I/O priorities.
+
+      Set the variable as follows: ::
+
+         BB_TASK_IONICE_LEVEL = "class.prio"
+
+      For *class*, the default value is "2", which is a best effort. You can use
+      "1" for realtime and "3" for idle. If you want to use realtime, you
+      must have superuser privileges.
+
+      For *prio*, you can use any value from "0", which is the highest
+      priority, to "7", which is the lowest. The default value is "4". You
+      do not need any special privileges to use this range of priority
+      values.
+
+      .. note::
+
+         In order for your I/O priority settings to take effect, you need the
+         Completely Fair Queuing (CFQ) Scheduler selected for the backing block
+         device. To select the scheduler, use the following command form where
+         device is the device (e.g. sda, sdb, and so forth): ::
+
+            $ sudo sh -c “echo cfq > /sys/block/device/queu/scheduler
+
+   BB_TASK_NICE_LEVEL
+      Allows specific tasks to change their priority (i.e. nice level).
+
+      You can use this variable in combination with task overrides to raise
+      or lower priorities of specific tasks. For example, on the `Yocto
+      Project <http://www.yoctoproject.org>`__ autobuilder, QEMU emulation
+      in images is given a higher priority as compared to build tasks to
+      ensure that images do not suffer timeouts on loaded systems.
+
+   BB_TASKHASH
+      Within an executing task, this variable holds the hash of the task as
+      returned by the currently enabled signature generator.
+
+   BB_VERBOSE_LOGS
+      Controls how verbose BitBake is during builds. If set, shell scripts
+      echo commands and shell script output appears on standard out
+      (stdout).
+
+   BB_WORKERCONTEXT
+      Specifies if the current context is executing a task. BitBake sets
+      this variable to "1" when a task is being executed. The value is not
+      set when the task is in server context during parsing or event
+      handling.
+
+   BBCLASSEXTEND
+      Allows you to extend a recipe so that it builds variants of the
+      software. Some examples of these variants for recipes from the
+      OpenEmbedded-Core metadata are "natives" such as ``quilt-native``,
+      which is a copy of Quilt built to run on the build system; "crosses"
+      such as ``gcc-cross``, which is a compiler built to run on the build
+      machine but produces binaries that run on the target ``MACHINE``;
+      "nativesdk", which targets the SDK machine instead of ``MACHINE``;
+      and "mulitlibs" in the form "``multilib:``\ multilib_name".
+
+      To build a different variant of the recipe with a minimal amount of
+      code, it usually is as simple as adding the variable to your recipe.
+      Here are two examples. The "native" variants are from the
+      OpenEmbedded-Core metadata: ::
+
+         BBCLASSEXTEND =+ "native nativesdk"
+         BBCLASSEXTEND =+ "multilib:multilib_name"
+
+      .. note::
+
+         Internally, the ``BBCLASSEXTEND`` mechanism generates recipe
+         variants by rewriting variable values and applying overrides such
+         as ``_class-native``. For example, to generate a native version of
+         a recipe, a :term:`DEPENDS` on "foo" is
+         rewritten to a ``DEPENDS`` on "foo-native".
+
+         Even when using ``BBCLASSEXTEND``, the recipe is only parsed once.
+         Parsing once adds some limitations. For example, it is not
+         possible to include a different file depending on the variant,
+         since ``include`` statements are processed when the recipe is
+         parsed.
+
+   BBDEBUG
+      Sets the BitBake debug output level to a specific value as
+      incremented by the ``-D`` command line option.
+
+      .. note::
+
+         You must set this variable in the external environment in order
+         for it to work.
+
+   BBFILE_COLLECTIONS
+      Lists the names of configured layers. These names are used to find
+      the other ``BBFILE_*`` variables. Typically, each layer appends its
+      name to this variable in its ``conf/layer.conf`` file.
+
+   BBFILE_PATTERN
+      Variable that expands to match files from
+      :term:`BBFILES` in a particular layer. This
+      variable is used in the ``conf/layer.conf`` file and must be suffixed
+      with the name of the specific layer (e.g.
+      ``BBFILE_PATTERN_emenlow``).
+
+   BBFILE_PRIORITY
+      Assigns the priority for recipe files in each layer.
+
+      This variable is useful in situations where the same recipe appears
+      in more than one layer. Setting this variable allows you to
+      prioritize a layer against other layers that contain the same recipe
+      - effectively letting you control the precedence for the multiple
+      layers. The precedence established through this variable stands
+      regardless of a recipe's version (:term:`PV` variable).
+      For example, a layer that has a recipe with a higher ``PV`` value but
+      for which the ``BBFILE_PRIORITY`` is set to have a lower precedence
+      still has a lower precedence.
+
+      A larger value for the ``BBFILE_PRIORITY`` variable results in a
+      higher precedence. For example, the value 6 has a higher precedence
+      than the value 5. If not specified, the ``BBFILE_PRIORITY`` variable
+      is set based on layer dependencies (see the ``LAYERDEPENDS`` variable
+      for more information. The default priority, if unspecified for a
+      layer with no dependencies, is the lowest defined priority + 1 (or 1
+      if no priorities are defined).
+
+      .. tip::
+
+         You can use the command bitbake-layers show-layers to list all
+         configured layers along with their priorities.
+
+   BBFILES
+      A space-separated list of recipe files BitBake uses to build
+      software.
+
+      When specifying recipe files, you can pattern match using Python's
+      `glob <https://docs.python.org/3/library/glob.html>`_ syntax.
+      For details on the syntax, see the documentation by following the
+      previous link.
+
+   BBINCLUDED
+      Contains a space-separated list of all of all files that BitBake's
+      parser included during parsing of the current file.
+
+   BBINCLUDELOGS
+      If set to a value, enables printing the task log when reporting a
+      failed task.
+
+   BBINCLUDELOGS_LINES
+      If :term:`BBINCLUDELOGS` is set, specifies
+      the maximum number of lines from the task log file to print when
+      reporting a failed task. If you do not set ``BBINCLUDELOGS_LINES``,
+      the entire log is printed.
+
+   BBLAYERS
+      Lists the layers to enable during the build. This variable is defined
+      in the ``bblayers.conf`` configuration file in the build directory.
+      Here is an example: ::
+
+         BBLAYERS = " \
+             /home/scottrif/poky/meta \
+             /home/scottrif/poky/meta-yocto \
+             /home/scottrif/poky/meta-yocto-bsp \
+             /home/scottrif/poky/meta-mykernel \
+         "
+
+      This example enables four layers, one of which is a custom, user-defined
+      layer named ``meta-mykernel``.
+
+   BBLAYERS_FETCH_DIR
+      Sets the base location where layers are stored. This setting is used
+      in conjunction with ``bitbake-layers layerindex-fetch`` and tells
+      ``bitbake-layers`` where to place the fetched layers.
+
+   BBMASK
+      Prevents BitBake from processing recipes and recipe append files.
+
+      You can use the ``BBMASK`` variable to "hide" these ``.bb`` and
+      ``.bbappend`` files. BitBake ignores any recipe or recipe append
+      files that match any of the expressions. It is as if BitBake does not
+      see them at all. Consequently, matching files are not parsed or
+      otherwise used by BitBake.
+
+      The values you provide are passed to Python's regular expression
+      compiler. Consequently, the syntax follows Python's Regular
+      Expression (re) syntax. The expressions are compared against the full
+      paths to the files. For complete syntax information, see Python's
+      documentation at http://docs.python.org/3/library/re.html.
+
+      The following example uses a complete regular expression to tell
+      BitBake to ignore all recipe and recipe append files in the
+      ``meta-ti/recipes-misc/`` directory: ::
+
+         BBMASK = "meta-ti/recipes-misc/"
+
+      If you want to mask out multiple directories or recipes, you can
+      specify multiple regular expression fragments. This next example
+      masks out multiple directories and individual recipes: ::
+
+         BBMASK += "/meta-ti/recipes-misc/ meta-ti/recipes-ti/packagegroup/"
+         BBMASK += "/meta-oe/recipes-support/"
+         BBMASK += "/meta-foo/.*/openldap"
+         BBMASK += "opencv.*\.bbappend"
+         BBMASK += "lzma"
+
+      .. note::
+
+         When specifying a directory name, use the trailing slash character
+         to ensure you match just that directory name.
+
+   BBMULTICONFIG
+      Enables BitBake to perform multiple configuration builds and lists
+      each separate configuration (multiconfig). You can use this variable
+      to cause BitBake to build multiple targets where each target has a
+      separate configuration. Define ``BBMULTICONFIG`` in your
+      ``conf/local.conf`` configuration file.
+
+      As an example, the following line specifies three multiconfigs, each
+      having a separate configuration file: ::
+
+         BBMULTIFONFIG = "configA configB configC"
+
+      Each configuration file you use must reside in the
+      build directory within a directory named ``conf/multiconfig`` (e.g.
+      build_directory\ ``/conf/multiconfig/configA.conf``).
+
+      For information on how to use ``BBMULTICONFIG`` in an environment
+      that supports building targets with multiple configurations, see the
+      ":ref:`bitbake-user-manual/bitbake-user-manual-intro:executing a multiple configuration build`"
+      section.
+
+   BBPATH
+      Used by BitBake to locate class (``.bbclass``) and configuration
+      (``.conf``) files. This variable is analogous to the ``PATH``
+      variable.
+
+      If you run BitBake from a directory outside of the build directory,
+      you must be sure to set ``BBPATH`` to point to the build directory.
+      Set the variable as you would any environment variable and then run
+      BitBake: ::
+
+         $ BBPATH="build_directory"
+         $ export BBPATH
+         $ bitbake target
+
+   BBSERVER
+      Points to the server that runs memory-resident BitBake. The variable
+      is only used when you employ memory-resident BitBake.
+
+   BBTARGETS
+      Allows you to use a configuration file to add to the list of
+      command-line target recipes you want to build.
+
+   BBVERSIONS
+      Allows a single recipe to build multiple versions of a project from a
+      single recipe file. You also able to specify conditional metadata
+      using the :term:`OVERRIDES` mechanism for a
+      single version or for an optionally named range of versions.
+
+      For more information on ``BBVERSIONS``, see the
+      ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:variants - class extension mechanism`"
+      section.
+
+   BITBAKE_UI
+      Used to specify the UI module to use when running BitBake. Using this
+      variable is equivalent to using the ``-u`` command-line option.
+
+      .. note::
+
+         You must set this variable in the external environment in order
+         for it to work.
+
+   BUILDNAME
+      A name assigned to the build. The name defaults to a datetime stamp
+      of when the build was started but can be defined by the metadata.
+
+   BZRDIR
+      The directory in which files checked out of a Bazaar system are
+      stored.
+
+   CACHE
+      Specifies the directory BitBake uses to store a cache of the metadata
+      so it does not need to be parsed every time BitBake is started.
+
+   CVSDIR
+      The directory in which files checked out under the CVS system are
+      stored.
+
+   DEFAULT_PREFERENCE
+      Specifies a weak bias for recipe selection priority.
+
+      The most common usage of this is variable is to set it to "-1" within
+      a recipe for a development version of a piece of software. Using the
+      variable in this way causes the stable version of the recipe to build
+      by default in the absence of ``PREFERRED_VERSION`` being used to
+      build the development version.
+
+      .. note::
+
+         The bias provided by DEFAULT_PREFERENCE is weak and is overridden by
+         :term:`BBFILE_PRIORITY` if that variable is different between two
+         layers that contain different versions of the same recipe.
+
+   DEPENDS
+      Lists a recipe's build-time dependencies (i.e. other recipe files).
+
+      Consider this simple example for two recipes named "a" and "b" that
+      produce similarly named packages. In this example, the ``DEPENDS``
+      statement appears in the "a" recipe: ::
+
+         DEPENDS = "b"
+
+      Here, the dependency is such that the ``do_configure`` task for recipe "a"
+      depends on the ``do_populate_sysroot`` task of recipe "b". This means
+      anything that recipe "b" puts into sysroot is available when recipe "a" is
+      configuring itself.
+
+      For information on runtime dependencies, see the :term:`RDEPENDS`
+      variable.
+
+   DESCRIPTION
+      A long description for the recipe.
+
+   DL_DIR
+      The central download directory used by the build process to store
+      downloads. By default, ``DL_DIR`` gets files suitable for mirroring for
+      everything except Git repositories. If you want tarballs of Git
+      repositories, use the :term:`BB_GENERATE_MIRROR_TARBALLS` variable.
+
+   EXCLUDE_FROM_WORLD
+      Directs BitBake to exclude a recipe from world builds (i.e.
+      ``bitbake world``). During world builds, BitBake locates, parses and
+      builds all recipes found in every layer exposed in the
+      ``bblayers.conf`` configuration file.
+
+      To exclude a recipe from a world build using this variable, set the
+      variable to "1" in the recipe.
+
+      .. note::
+
+         Recipes added to ``EXCLUDE_FROM_WORLD`` may still be built during a world
+         build in order to satisfy dependencies of other recipes. Adding a
+         recipe to ``EXCLUDE_FROM_WORLD`` only ensures that the recipe is not
+         explicitly added to the list of build targets in a world build.
+
+   FAKEROOT
+      Contains the command to use when running a shell script in a fakeroot
+      environment. The ``FAKEROOT`` variable is obsolete and has been
+      replaced by the other ``FAKEROOT*`` variables. See these entries in
+      the glossary for more information.
+
+   FAKEROOTBASEENV
+      Lists environment variables to set when executing the command defined
+      by :term:`FAKEROOTCMD` that starts the
+      bitbake-worker process in the fakeroot environment.
+
+   FAKEROOTCMD
+      Contains the command that starts the bitbake-worker process in the
+      fakeroot environment.
+
+   FAKEROOTDIRS
+      Lists directories to create before running a task in the fakeroot
+      environment.
+
+   FAKEROOTENV
+      Lists environment variables to set when running a task in the
+      fakeroot environment. For additional information on environment
+      variables and the fakeroot environment, see the
+      :term:`FAKEROOTBASEENV` variable.
+
+   FAKEROOTNOENV
+      Lists environment variables to set when running a task that is not in
+      the fakeroot environment. For additional information on environment
+      variables and the fakeroot environment, see the
+      :term:`FAKEROOTENV` variable.
+
+   FETCHCMD
+      Defines the command the BitBake fetcher module executes when running
+      fetch operations. You need to use an override suffix when you use the
+      variable (e.g. ``FETCHCMD_git`` or ``FETCHCMD_svn``).
+
+   FILE
+      Points at the current file. BitBake sets this variable during the
+      parsing process to identify the file being parsed. BitBake also sets
+      this variable when a recipe is being executed to identify the recipe
+      file.
+
+   FILESPATH
+      Specifies directories BitBake uses when searching for patches and
+      files. The "local" fetcher module uses these directories when
+      handling ``file://`` URLs. The variable behaves like a shell ``PATH``
+      environment variable. The value is a colon-separated list of
+      directories that are searched left-to-right in order.
+
+   GITDIR
+      The directory in which a local copy of a Git repository is stored
+      when it is cloned.
+
+   HGDIR
+      The directory in which files checked out of a Mercurial system are
+      stored.
+
+   HOMEPAGE
+      Website where more information about the software the recipe is
+      building can be found.
+
+   INHERIT
+      Causes the named class or classes to be inherited globally. Anonymous
+      functions in the class or classes are not executed for the base
+      configuration and in each individual recipe. The OpenEmbedded build
+      system ignores changes to ``INHERIT`` in individual recipes.
+
+      For more information on ``INHERIT``, see the
+      ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:\`\`inherit\`\` configuration directive`"
+      section.
+
+   LAYERDEPENDS
+      Lists the layers, separated by spaces, upon which this recipe
+      depends. Optionally, you can specify a specific layer version for a
+      dependency by adding it to the end of the layer name with a colon,
+      (e.g. "anotherlayer:3" to be compared against
+      :term:`LAYERVERSION`\ ``_anotherlayer`` in
+      this case). BitBake produces an error if any dependency is missing or
+      the version numbers do not match exactly (if specified).
+
+      You use this variable in the ``conf/layer.conf`` file. You must also
+      use the specific layer name as a suffix to the variable (e.g.
+      ``LAYERDEPENDS_mylayer``).
+
+   LAYERDIR
+      When used inside the ``layer.conf`` configuration file, this variable
+      provides the path of the current layer. This variable is not
+      available outside of ``layer.conf`` and references are expanded
+      immediately when parsing of the file completes.
+
+   LAYERDIR_RE
+      When used inside the ``layer.conf`` configuration file, this variable
+      provides the path of the current layer, escaped for use in a regular
+      expression (:term:`BBFILE_PATTERN`). This
+      variable is not available outside of ``layer.conf`` and references
+      are expanded immediately when parsing of the file completes.
+
+   LAYERVERSION
+      Optionally specifies the version of a layer as a single number. You
+      can use this variable within
+      :term:`LAYERDEPENDS` for another layer in
+      order to depend on a specific version of the layer.
+
+      You use this variable in the ``conf/layer.conf`` file. You must also
+      use the specific layer name as a suffix to the variable (e.g.
+      ``LAYERDEPENDS_mylayer``).
+
+   LICENSE
+      The list of source licenses for the recipe.
+
+   MIRRORS
+      Specifies additional paths from which BitBake gets source code. When
+      the build system searches for source code, it first tries the local
+      download directory. If that location fails, the build system tries
+      locations defined by :term:`PREMIRRORS`, the
+      upstream source, and then locations specified by ``MIRRORS`` in that
+      order.
+
+   MULTI_PROVIDER_WHITELIST
+      Allows you to suppress BitBake warnings caused when building two
+      separate recipes that provide the same output.
+
+      BitBake normally issues a warning when building two different recipes
+      where each provides the same output. This scenario is usually
+      something the user does not want. However, cases do exist where it
+      makes sense, particularly in the ``virtual/*`` namespace. You can use
+      this variable to suppress BitBake's warnings.
+
+      To use the variable, list provider names (e.g. recipe names,
+      ``virtual/kernel``, and so forth).
+
+   OVERRIDES
+      BitBake uses ``OVERRIDES`` to control what variables are overridden
+      after BitBake parses recipes and configuration files.
+
+      Following is a simple example that uses an overrides list based on
+      machine architectures: OVERRIDES = "arm:x86:mips:powerpc" You can
+      find information on how to use ``OVERRIDES`` in the
+      ":ref:`bitbake-user-manual/bitbake-user-manual-metadata:conditional syntax
+      (overrides)`" section.
+
+   P4DIR
+      The directory in which a local copy of a Perforce depot is stored
+      when it is fetched.
+
+   PACKAGES
+      The list of packages the recipe creates.
+
+   PACKAGES_DYNAMIC
+      A promise that your recipe satisfies runtime dependencies for
+      optional modules that are found in other recipes.
+      ``PACKAGES_DYNAMIC`` does not actually satisfy the dependencies, it
+      only states that they should be satisfied. For example, if a hard,
+      runtime dependency (:term:`RDEPENDS`) of another
+      package is satisfied during the build through the
+      ``PACKAGES_DYNAMIC`` variable, but a package with the module name is
+      never actually produced, then the other package will be broken.
+
+   PE
+      The epoch of the recipe. By default, this variable is unset. The
+      variable is used to make upgrades possible when the versioning scheme
+      changes in some backwards incompatible way.
+
+   PERSISTENT_DIR
+      Specifies the directory BitBake uses to store data that should be
+      preserved between builds. In particular, the data stored is the data
+      that uses BitBake's persistent data API and the data used by the PR
+      Server and PR Service.
+
+   PF
+      Specifies the recipe or package name and includes all version and
+      revision numbers (i.e. ``eglibc-2.13-r20+svnr15508/`` and
+      ``bash-4.2-r1/``).
+
+   PN
+      The recipe name.
+
+   PR
+      The revision of the recipe.
+
+   PREFERRED_PROVIDER
+      Determines which recipe should be given preference when multiple
+      recipes provide the same item. You should always suffix the variable
+      with the name of the provided item, and you should set it to the
+      :term:`PN` of the recipe to which you want to give
+      precedence. Some examples: ::
+
+         PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
+         PREFERRED_PROVIDER_virtual/xserver = "xserver-xf86"
+         PREFERRED_PROVIDER_virtual/libgl ?= "mesa"
+
+   PREFERRED_PROVIDERS
+      Determines which recipe should be given preference for cases where
+      multiple recipes provide the same item. Functionally,
+      ``PREFERRED_PROVIDERS`` is identical to
+      :term:`PREFERRED_PROVIDER`. However, the ``PREFERRED_PROVIDERS`` variable
+      lets you define preferences for multiple situations using the following
+      form: ::
+
+         PREFERRED_PROVIDERS = "xxx:yyy aaa:bbb ..."
+
+      This form is a convenient replacement for the following: ::
+
+         PREFERRED_PROVIDER_xxx = "yyy"
+         PREFERRED_PROVIDER_aaa = "bbb"
+
+   PREFERRED_VERSION
+      If there are multiple versions of recipes available, this variable
+      determines which recipe should be given preference. You must always
+      suffix the variable with the :term:`PN` you want to
+      select, and you should set :term:`PV` accordingly for
+      precedence.
+
+      The ``PREFERRED_VERSION`` variable supports limited wildcard use
+      through the "``%``" character. You can use the character to match any
+      number of characters, which can be useful when specifying versions
+      that contain long revision numbers that potentially change. Here are
+      two examples: ::
+
+         PREFERRED_VERSION_python = "2.7.3"
+         PREFERRED_VERSION_linux-yocto = "4.12%"
+
+      .. important::
+
+         The use of the " % " character is limited in that it only works at the
+         end of the string. You cannot use the wildcard character in any other
+         location of the string.
+
+   PREMIRRORS
+      Specifies additional paths from which BitBake gets source code. When
+      the build system searches for source code, it first tries the local
+      download directory. If that location fails, the build system tries
+      locations defined by ``PREMIRRORS``, the upstream source, and then
+      locations specified by :term:`MIRRORS` in that order.
+
+      Typically, you would add a specific server for the build system to
+      attempt before any others by adding something like the following to
+      your configuration: ::
+
+         PREMIRRORS_prepend = "\
+         git://.*/.* http://www.yoctoproject.org/sources/ \n \
+         ftp://.*/.* http://www.yoctoproject.org/sources/ \n \
+         http://.*/.* http://www.yoctoproject.org/sources/ \n \
+         https://.*/.* http://www.yoctoproject.org/sources/ \n"
+
+      These changes cause the build system to intercept Git, FTP, HTTP, and
+      HTTPS requests and direct them to the ``http://`` sources mirror. You can
+      use ``file://`` URLs to point to local directories or network shares as
+      well.
+
+   PROVIDES
+      A list of aliases by which a particular recipe can be known. By
+      default, a recipe's own ``PN`` is implicitly already in its
+      ``PROVIDES`` list. If a recipe uses ``PROVIDES``, the additional
+      aliases are synonyms for the recipe and can be useful satisfying
+      dependencies of other recipes during the build as specified by
+      ``DEPENDS``.
+
+      Consider the following example ``PROVIDES`` statement from a recipe
+      file ``libav_0.8.11.bb``: ::
+
+         PROVIDES += "libpostproc"
+
+      The ``PROVIDES`` statement results in the "libav" recipe also being known
+      as "libpostproc".
+
+      In addition to providing recipes under alternate names, the
+      ``PROVIDES`` mechanism is also used to implement virtual targets. A
+      virtual target is a name that corresponds to some particular
+      functionality (e.g. a Linux kernel). Recipes that provide the
+      functionality in question list the virtual target in ``PROVIDES``.
+      Recipes that depend on the functionality in question can include the
+      virtual target in :term:`DEPENDS` to leave the
+      choice of provider open.
+
+      Conventionally, virtual targets have names on the form
+      "virtual/function" (e.g. "virtual/kernel"). The slash is simply part
+      of the name and has no syntactical significance.
+
+   PRSERV_HOST
+      The network based :term:`PR` service host and port.
+
+      Following is an example of how the ``PRSERV_HOST`` variable is set: ::
+
+         PRSERV_HOST = "localhost:0"
+
+      You must set the variable if you want to automatically start a local PR
+      service. You can set ``PRSERV_HOST`` to other values to use a remote PR
+      service.
+
+   PV
+      The version of the recipe.
+
+   RDEPENDS
+      Lists a package's runtime dependencies (i.e. other packages) that
+      must be installed in order for the built package to run correctly. If
+      a package in this list cannot be found during the build, you will get
+      a build error.
+
+      Because the ``RDEPENDS`` variable applies to packages being built,
+      you should always use the variable in a form with an attached package
+      name. For example, suppose you are building a development package
+      that depends on the ``perl`` package. In this case, you would use the
+      following ``RDEPENDS`` statement: ::
+
+         RDEPENDS_${PN}-dev += "perl"
+
+      In the example, the development package depends on the ``perl`` package.
+      Thus, the ``RDEPENDS`` variable has the ``${PN}-dev`` package name as part
+      of the variable.
+
+      BitBake supports specifying versioned dependencies. Although the
+      syntax varies depending on the packaging format, BitBake hides these
+      differences from you. Here is the general syntax to specify versions
+      with the ``RDEPENDS`` variable: ::
+
+         RDEPENDS_${PN} = "package (operator version)"
+
+      For ``operator``, you can specify the following: ::
+
+         =
+         <
+         >
+         <=
+         >=
+
+      For example, the following sets up a dependency on version 1.2 or
+      greater of the package ``foo``: ::
+
+         RDEPENDS_${PN} = "foo (>= 1.2)"
+
+      For information on build-time dependencies, see the :term:`DEPENDS`
+      variable.
+
+   REPODIR
+      The directory in which a local copy of a ``google-repo`` directory is
+      stored when it is synced.
+
+   RPROVIDES
+      A list of package name aliases that a package also provides. These
+      aliases are useful for satisfying runtime dependencies of other
+      packages both during the build and on the target (as specified by
+      ``RDEPENDS``).
+
+      As with all package-controlling variables, you must always use the
+      variable in conjunction with a package name override. Here is an
+      example: ::
+
+         RPROVIDES_${PN} = "widget-abi-2"
+
+   RRECOMMENDS
+      A list of packages that extends the usability of a package being
+      built. The package being built does not depend on this list of
+      packages in order to successfully build, but needs them for the
+      extended usability. To specify runtime dependencies for packages, see
+      the ``RDEPENDS`` variable.
+
+      BitBake supports specifying versioned recommends. Although the syntax
+      varies depending on the packaging format, BitBake hides these
+      differences from you. Here is the general syntax to specify versions
+      with the ``RRECOMMENDS`` variable: ::
+
+         RRECOMMENDS_${PN} = "package (operator version)"
+
+      For ``operator``, you can specify the following: ::
+
+         =
+         <
+         >
+         <=
+         >=
+
+      For example, the following sets up a recommend on version
+      1.2 or greater of the package ``foo``: ::
+
+         RRECOMMENDS_${PN} = "foo (>= 1.2)"
+
+   SECTION
+      The section in which packages should be categorized.
+
+   SRC_URI
+      The list of source files - local or remote. This variable tells
+      BitBake which bits to pull for the build and how to pull them. For
+      example, if the recipe or append file needs to fetch a single tarball
+      from the Internet, the recipe or append file uses a ``SRC_URI`` entry
+      that specifies that tarball. On the other hand, if the recipe or
+      append file needs to fetch a tarball and include a custom file, the
+      recipe or append file needs an ``SRC_URI`` variable that specifies
+      all those sources.
+
+      The following list explains the available URI protocols:
+
+      -  ``file://`` : Fetches files, which are usually files shipped
+         with the metadata, from the local machine. The path is relative to
+         the :term:`FILESPATH` variable.
+
+      -  ``bzr://`` : Fetches files from a Bazaar revision control
+         repository.
+
+      -  ``git://`` : Fetches files from a Git revision control
+         repository.
+
+      -  ``osc://`` : Fetches files from an OSC (OpenSUSE Build service)
+         revision control repository.
+
+      -  ``repo://`` : Fetches files from a repo (Git) repository.
+
+      -  ``http://`` : Fetches files from the Internet using HTTP.
+
+      -  ``https://`` : Fetches files from the Internet using HTTPS.
+
+      -  ``ftp://`` : Fetches files from the Internet using FTP.
+
+      -  ``cvs://`` : Fetches files from a CVS revision control
+         repository.
+
+      -  ``hg://`` : Fetches files from a Mercurial (``hg``) revision
+         control repository.
+
+      -  ``p4://`` : Fetches files from a Perforce (``p4``) revision
+         control repository.
+
+      -  ``ssh://`` : Fetches files from a secure shell.
+
+      -  ``svn://`` : Fetches files from a Subversion (``svn``) revision
+         control repository.
+
+      Here are some additional options worth mentioning:
+
+      -  ``unpack`` : Controls whether or not to unpack the file if it is
+         an archive. The default action is to unpack the file.
+
+      -  ``subdir`` : Places the file (or extracts its contents) into the
+         specified subdirectory. This option is useful for unusual tarballs
+         or other archives that do not have their files already in a
+         subdirectory within the archive.
+
+      -  ``name`` : Specifies a name to be used for association with
+         ``SRC_URI`` checksums when you have more than one file specified
+         in ``SRC_URI``.
+
+      -  ``downloadfilename`` : Specifies the filename used when storing
+         the downloaded file.
+
+   SRCDATE
+      The date of the source code used to build the package. This variable
+      applies only if the source was fetched from a Source Code Manager
+      (SCM).
+
+   SRCREV
+      The revision of the source code used to build the package. This
+      variable applies only when using Subversion, Git, Mercurial and
+      Bazaar. If you want to build a fixed revision and you want to avoid
+      performing a query on the remote repository every time BitBake parses
+      your recipe, you should specify a ``SRCREV`` that is a full revision
+      identifier and not just a tag.
+
+   SRCREV_FORMAT
+      Helps construct valid :term:`SRCREV` values when
+      multiple source controlled URLs are used in
+      :term:`SRC_URI`.
+
+      The system needs help constructing these values under these
+      circumstances. Each component in the ``SRC_URI`` is assigned a name
+      and these are referenced in the ``SRCREV_FORMAT`` variable. Consider
+      an example with URLs named "machine" and "meta". In this case,
+      ``SRCREV_FORMAT`` could look like "machine_meta" and those names
+      would have the SCM versions substituted into each position. Only one
+      ``AUTOINC`` placeholder is added and if needed. And, this placeholder
+      is placed at the start of the returned string.
+
+   STAMP
+      Specifies the base path used to create recipe stamp files. The path
+      to an actual stamp file is constructed by evaluating this string and
+      then appending additional information.
+
+   STAMPCLEAN
+      Specifies the base path used to create recipe stamp files. Unlike the
+      :term:`STAMP` variable, ``STAMPCLEAN`` can contain
+      wildcards to match the range of files a clean operation should
+      remove. BitBake uses a clean operation to remove any other stamps it
+      should be removing when creating a new stamp.
+
+   SUMMARY
+      A short summary for the recipe, which is 72 characters or less.
+
+   SVNDIR
+      The directory in which files checked out of a Subversion system are
+      stored.
+
+   T
+      Points to a directory were BitBake places temporary files, which
+      consist mostly of task logs and scripts, when building a particular
+      recipe.
+
+   TOPDIR
+      Points to the build directory. BitBake automatically sets this
+      variable.