diff --git a/bitbake/doc/user-manual/user-manual-execution.xml b/bitbake/doc/user-manual/user-manual-execution.xml
index aa345de698..e9f19be6de 100644
--- a/bitbake/doc/user-manual/user-manual-execution.xml
+++ b/bitbake/doc/user-manual/user-manual-execution.xml
@@ -5,8 +5,9 @@
Execution
- The primary purpose for running BitBake is to produce an
- image, which can be a kernel or a software development kit (SDK).
+ The primary purpose for running BitBake is to produce some kind
+ of output such as an image, a kernel, or a software development
+ kit.
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
@@ -38,24 +39,56 @@
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 bitbake.conf file resides in the
- conf directory, which must be listed in
- BBPATH.
- This configuratoin file lists and includes other configuration
- files from the conf directory below the
- directories listed in BBPATH.
- In general, the most important of these included
- configuration files from a user's perspective
- is local.conf, which contains the user's
- customized settings for the build environment.
+ The layer.conf files are used to
+ construct key variables such as
+ BBPATH
+ and
+ BBFILES.
+ BBPATH is used to search for
+ configuration and class files under
+ conf/ and class/
+ directories, respectively.
+ BBFILES is used to find recipe 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.
- Other notable configuration files are the distribution configuration
- file and the machine configuration file.
+ Next, the bitbake.conf file is searched
+ using the BBPATH variable that was
+ just constructed.
+ The bitbake.conf file usually indicates
+ all the other key include files to parse.
+ The usual convention is to have machine, distro, site, and local
+ configurations.
+ This means a user provides their own customizations
+ through a local.conf file.
+
+
+
+ As mentioned in the previous paragraph, two of the other notable
+ configuration files are the distro and machine configuration
+ files.
These configuration files are normally identified by
variables unique to the build systems using BitBake.
For example, the Yocto Project uses the
@@ -87,6 +120,9 @@
This file is expected to contain a
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 directly in the environment.
@@ -194,78 +230,210 @@
-
- Locating Recipes
-
-
- The BBFILES variable is how BitBake
- locates files.
- This variable is a space-separated list of files
- that are available, supports wildcards, and is set shortly
- after the parsing phase of BitBake's execution.
-
+
+ Locating and Parsing Recipes
+ During the configuration phase, BitBake will have
+ set
+ 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"
- With regard to dependencies, it expects the
- .bb to define a
- DEPENDS variable, which contains a
- space separated list of “package names”, which themselves
- are the PN variable. The
- PN variable is, in general,
- set to a component of the .bb
- filename by default.
-
-
-
-
- Parsing Recipes
-
-
- After classes are included, the variable
- BBFILES is set, usually in
- local.conf, and defines the list of
- places to search for recipe and append files.
- Adding extra content to BBFILES is best
- achieved through the use of BitBake layers.
+ BitBake parses each recipe and append file located
+ with BBFILES and stores the values of
+ various variables into the datastore.
+ 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
+ BBPATH
+ as the search path.
+ Finally, BitBake parses in order any append files found in
+ BBFILES.
- BitBake parses each recipe and append file located with
- BBFILES and stores the values of various
- variables into the datastore.
- In summary, for each recipe and append file pairing, the configuration
- plus the base class of variables are set, followed by the data in the
- recipe file itself, followed by any inherit commands
- that the recipe file might contain.
+ One common convention is to use the recipe filename to define
+ pieces of metadata.
+ For example, in bitbake.conf the recipe
+ name and version set
+ PN and
+ PV:
+
+ PV = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE'),d)[1] or '1.0'}"
+ PN = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE'),d)[0] or 'defaultpkgname'}"
+
+ In this example, a recipe called "something_1.2.3.bb" sets
+ PN to "something" and
+ PV to "1.2.3".
- Part of parsing a recipe is making sure that all the recipes
- that the recipe being parsed depends on are understood.
- These other recipes could be located in other layers or in
- a specific layer version.
- These two variables in a recipe can help with with these
- cases:
-
-
- LAYERDEPENDS
-
-
- LAYERVERSION
-
-
+ 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.
- Because parsing recipe and append files is a time consuming
- process, a cache, referred to as the "setscene"
- is kept to speed up subsequent parsing.
- The setscene is invalid if the timestamps of a recipe changes,
- any of the include files change, configuration files change,
- or class files on which the recipe file depends change.
+ BitBake does not need all 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.
+
+
+
+ Subsequent BitBake commands then parse the base
+ configuration and compute a checksum of that data.
+ If that checksum matches what is in the cache, the
+ recipe and class files have not changed.
+ In this case, BitBake reloads the cached information
+ about the recipe instead of reparsing it from scratch.
+
+
+
+
+ Preferences and Providers
+
+
+ Assuming BitBake has been instructed to execute a target and
+ that all the recipe files have been parsed, BitBake starts to
+ build the target and look for providers of that target.
+ Once a provider is selected, BitBake resolves all the dependencies for
+ the target.
+ As an example, suppose the target is
+ core-image-sato.
+ In this case, it would lead to
+ packagegroup-core-x11-sato,
+ which in turn leads to recipes like matchbox-terminal,
+ pcmanfm and gthumb.
+ These recipes in turn depend on eglibc and the toolchain.
+
+
+
+ Sometimes a target might have multiple providers.
+ A common example is "virtual/kernel", which is provided by each kernel package.
+ 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
+ PREFERRED_PROVIDER
+ is the provider with the same name as the target.
+
+
+
+ Understanding how providers are chosen is made complicated by the fact
+ that multiple versions might exist.
+ BitBake defaults to the highest version of a provider.
+ Version comparisons are made using the same method as Debian.
+ You can use the
+ PREFERRED_VERSION
+ variable to specify a particular version (usually in the distro configuration).
+ You can influence the order by using the
+ DEFAULT_PREFERENCE
+ variable.
+ By default, files have a preference of "0".
+ Setting the DEFAULT_PREFERENCE to "-1" makes the
+ package unlikely to be used unless it is explicitly referenced.
+ Setting the DEFAULT_PREFERENCE to "1" makes it likely the package is used.
+ PREFERRED_VERSION overrides any DEFAULT_PREFERENCE setting.
+ DEFAULT_PREFERENCE is often used to mark newer and more experimental package
+ versions until they have undergone sufficient testing to be considered stable.
+
+
+
+ In summary, BitBake has created a list of providers, which is prioritized, for each target.
+
+
+
+
+ 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 Variables Glossary
+ near the end of this manual.
+ At a basic level, it is sufficient to know that BitBake uses the
+ DEPENDS and
+ RDEPENDS variables when
+ calculating dependencies.
+
+
+
+ For more information on how BitBake handles dependencies, see the
+ "Dependencies" section.
+
+
+
+
+ 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 build now starts with BitBake forking off threads up to the limit set in the
+ 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
+ STAMP variable.
+ On subsequent runs, BitBake looks in the build directory within
+ tmp/stampsand 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.
+ This behavior could change or become configurable in future versions of BitBake.
+
+
+
+ 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
+ "Tasks" section.
@@ -306,348 +474,182 @@
-
- Source Fetching
+
+ Setscene
- The first stages of building a recipe are to fetch and unpack
- the source code:
-
+ This section needs to get the concept of the setscene across.
+ The reader needs to know what it is and what it is used for during
+ the build process.
- The do_fetch and
- do_unpack tasks fetch the source files
- and unpack them into the work directory.
- By default, everything is accomplished in the
- build directory,
- which has a defined structure.
-
-
-
- Unpacked source files are pointed to by a variable.
- For example, in the Yocto Project and OpenEmbedded build systems,
- the S variable points to these source files.
- Each recipe has an area in the Build Directory where the
- unpacked source code resides.
- The name of that directory for any given recipe is defined from
- several different variables.
- You can see the variables that define these directories
- by looking at the figure that shows the structure and variables
- used in the Yocto Project:
-
- TMPDIR
-
- PACKAGE_ARCH
-
- TARGET_OS
-
- PN
-
- PV
-
- PR
-
- WORKDIR
-
- S
-
-
-
-
-
- Briefly, the S directory contains the
- unpacked source files for a recipe.
- The WORKDIR directory is where all the
- building goes on for a given recipe.
-
-
-
-
- Patching
-
-
- Once source code is fetched and unpacked, BitBake locates
- patch files and applies them to the source files:
-
-
-
-
- The do_patch task processes recipes by
- using the
- SRC_URI
- variable to locate applicable patch files, which by default
- are *.patch or
- *.diff files, or any file if
- "apply=yes" is specified for the file in
- SRC_URI.
-
-
-
- BitBake finds and applies multiple patches for a single recipe
- in the order in which it finds the patches.
- Patches are applied to the recipe's source files located in the
- S directory.
-
-
-
- For more information on how the source directories are
- created, see the
- "Source Fetching"
+ You can find more information on setscene metadata in the
+ "Task Checksums and Setscene"
section.
-
- Configuration and Compilation
+
+ Checksums (Signatures)
- After source code is patched, BitBake executes tasks that
- configure and compile the source code:
-
+ A checksum is a unique signature of a task's inputs.
+ The setscene code uses a checksum to determine if a task needs
+ to be run.
+ Because it is a change in a task's inputs that triggers running
+ the task, the process 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.
- This step in the build process consists of three tasks:
+ 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.
+
+
+
+ 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 TERM \
+ 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
+ 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:
- do_configure:
- This task configures the source by enabling and
- disabling any build-time and configuration options for
- the software being built.
- Configurations can come from the recipe itself as well
- as from an inherited class.
- Additionally, the software itself might configure itself
- depending on the target for which it is being built.
-
-
- The configurations handled by the
- do_configure task are specific
- to source code configuration for the source code
- being built by the recipe.
-
- If you are using the Autotools class
- (autotools.bbclass),
- you can add additional configuration options by using
- the EXTRA_OECONF
- variable.
- For information on how this variable works within
- that class, see the
- meta/classes/autotools.bbclass file.
+ BB_BASEHASH_task-<taskname>:
+ The base hashes for each task in the recipe.
- do_compile:
- Once a configuration task has been satisfied, BitBake
- compiles the source using the
- do_compile task.
- Compilation occurs in the directory pointed to by the
- B
- variable.
- Realize that the B directory is, by
- default, the same as the
- S
- directory.
- do_install:
- Once compilation is done, BitBake executes the
- do_install task.
- This task copies files from the B
- directory and places them in a holding area pointed to
- by the D variable.
-
-
-
-
-
- Package Splitting
-
-
- After source code is configured and compiled, the
- OpenEmbedded build system analyzes
- the results and splits the output into packages:
-
-
-
-
- The do_package and
- do_packagedata tasks combine to analyze
- the files found in the D directory
- and split them into subsets based on available packages and
- files.
- The analyzing process involves the following as well as other
- items: splitting out debugging symbols,
- looking at shared library dependencies between packages,
- and looking at package relationships.
- The do_packagedata task creates package
- metadata based on the analysis such that the
- OpenEmbedded build system can generate the final packages.
- Working, staged, and intermediate results of the analysis
- and package splitting process use these areas:
-
- PKGD
+ BB_BASEHASH_<filename:taskname>:
+ The base hashes for each dependent task.
- PKGDATA_DIR
+ BBHASHDEPS_<filename:taskname>:
+ The task dependencies for each task.
- PKGDESTWORK
-
- PKGDEST
-
-
- The FILES
- variable defines the files that go into each package in
- PACKAGES.
- If you want details on how this is accomplished in the Yocto Project
- for example, you can look at the package.bbclass
- file in a Yocto tree.
-
-
-
- Depending on the type of packages being created (RPM, DEB, or
- IPK), the do_package_write_* task
- creates the actual packages and places them in the
- Package Feed area, which is
- ${TMPDIR}/deploy.
-
- Support for creating feeds directly from the
- deploy/* directories does not exist.
- Creating such feeds usually requires some kind of feed
- maintenance mechanism that would upload the new packages
- into an official package feed (e.g. the
- Ångström distribution).
- This functionality is highly distribution-specific
- and thus is not provided out of the box.
-
-
-
-
-
- Image Generation
-
-
- Once packages are split and stored in the Package Feeds area,
- the OpenEmbedded build system uses BitBake to generate the
- root filesystem image:
-
-
-
-
- The image generation process consists of several stages and
- depends on many variables.
- The do_rootfs task uses these key variables
- to help create the list of packages to actually install:
-
- IMAGE_INSTALL:
- Lists out the base set of packages to install from
- the Package Feeds area.
- PACKAGE_EXCLUDE:
- Specifies packages that should not be installed.
-
- IMAGE_FEATURES:
- Specifies features to include in the image.
- Most of these features map to additional packages for
- installation.
- PACKAGE_CLASSES:
- Specifies the package backend to use and consequently
- helps determine where to locate packages within the
- Package Feeds area.
- IMAGE_LINGUAS:
- Determines the language(s) for which additional
- language support packages are installed.
+ BB_TASKHASH:
+ The hash of the currently running task.
- Package installation is under control of the package manager
- (e.g. smart/rpm, opkg, or apt/dpkg) regardless of whether or
- not package management is enabled for the target.
- At the end of the process, if package management is not
- enabled for the target, the package manager's data files
- are deleted from the root filesystem.
-
-
-
- During image generation, the build system attempts to run
- all post-installation scripts.
- Any that fail to run on the build host are run on the
- target when the target system is first booted.
- If you are using a
- read-only root filesystem,
- all the post installation scripts must succeed during the
- package installation phase since the root filesystem cannot be
- written into.
-
-
-
- During Optimization, optimizing processes are run across
- the image.
- These processes include mklibs and
- prelink.
- The mklibs process optimizes the size
- of the libraries.
- A prelink process optimizes the dynamic
- linking of shared libraries to reduce start up time of
- executables.
-
-
-
- Part of the image generation process includes compressing the
- root filesystem image.
- Compression is accomplished through several optimization
- routines designed to reduce the overall size of the image.
-
-
-
- After the root filesystem has been constructed, the image
- generation process turns everything into an image file or
- a set of image files.
- The formats used for the root filesystem depend on the
- IMAGE_FSTYPES variable.
-
-
-
- The entire image generation process is run under Pseudo.
- Running under Pseudo ensures that the files in the root
- filesystem have correct ownership.
-
-
-
-
- SDK Generation
-
-
- The OpenEmbedded build system uses BitBake to generate the
- Software Development Kit (SDK) installer script:
-
-
-
-
- Like image generation, the SDK script process consists of
- several stages and depends on many variables.
- The do_populate_sdk task uses these
- key variables to help create the list of packages to actually
- install.
-
-
-
- The do_populate_sdk task handles two
- parts: a target part and a host part.
- The target part is the part built for the target hardware and
- includes libraries and headers.
- The host part is the part of the SDK that runs on the
- SDKMACHINE.
-
-
-
- Once both parts are constructed, the
- do_populate_sdk task performs some cleanup
- on both parts.
- After the cleanup, the task creates a cross-development
- environment setup script and any configuration files that
- might be needed.
-
-
-
- The final output of the task is the Cross-development
- toolchain installation script (.sh file),
- which includes the environment setup script.
+ You can find more information on checksum metadata in the
+ "Task Checksums and Setscene"
+ section.