BitBake Team 2004, 2005 Chris Larson Phil Blundell This work is licensed under the Creative Commons Attribution License. To view a copy of this license, visit http://creativecommons.org/licenses/by/2.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

BitBake is, at its simplest, a tool for executing tasks and managing metadata. As such, its similarities to GNU make and other build tools are readily apparent. It was inspired by Portage, the package management system used by the Gentoo Linux distribution. BitBake is the basis of the OpenEmbedded project, which is being used to build and maintain a number of embedded Linux distributions, including OpenZaurus and Familiar.

Prior to BitBake, no other build tool adequately met the needs of an aspiring embedded Linux distribution. All of the buildsystems used by traditional desktop Linux distributions lacked important functionality, and none of the ad-hoc buildroot systems, prevalent in the embedded space, were scalable or maintainable. Some important goals for BitBake were: Handle crosscompilation. Handle interpackage 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, et cetera. Must be linux distribution agnostic (both build and target). Must be architecture agnostic Must support multiple build and target operating systems (including cygwin, the BSDs, etc). Must be able to be self contained, rather than tightly integrated into the build machine's root filesystem. There must be a way to handle conditional metadata (on target architecture, operating system, distribution, machine). It must be easy for the person using the tools to supply their own local metadata and packages to operate against. Must make it easy to collaborate between multiple projects using BitBake for their builds. Should provide an inheritance mechanism to share common metadata between many packages. Et cetera... BitBake satisfies all these and many more. Flexibility and power have always been the priorities. It is highly extensible, supporting embedded Python code and execution of any arbitrary tasks.

BitBake metadata can be classified into 3 major areas: Configuration Files .bb Files Classes What follows are a large number of examples of BitBake metadata. Any syntax which isn't supported in any of the aforementioned areas will be documented as such.

VARIABLE = "value" In this example, VARIABLE is value.

BitBake supports variables referencing one another's contents using a syntax which is similar to shell scripting A = "aval" B = "pre${A}post" This results in A containing aval and B containing preavalpost.

:= results in a variable's contents being expanded immediately, rather than when the variable is actually used. T = "123" A := "${B} ${A} test ${T}" T = "456" B = "${T} bval" C = "cval" C := "${C}append" In that example, A would contain test 123, B would contain 456 bval, and C would be cvalappend.

B = "bval" B += "additionaldata" C = "cval" C =+ "test" In this example, B is now bval additionaldata and C is test cval.

B = "bval" B += "additionaldata" C = "cval" C =+ "test" In this example, B is now bvaladditionaldata and C is testcval. In contrast to the above Appending and Prepending operators no additional space will be introduced.

OVERRIDES is a : seperated variable containing each item you want to satisfy conditions. So, if you have a variable which 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. Example: OVERRIDES = "architecture:os:machine" TEST = "defaultvalue" TEST_os = "osspecificvalue" TEST_condnotinoverrides = "othercondvalue" In this example, TEST would be osspecificvalue, due to the condition os being in OVERRIDES.

BitBake also supports appending and prepending to variables based on whether something is in OVERRIDES. Example: DEPENDS = "glibc ncurses" OVERRIDES = "machine:local" DEPENDS_append_machine = " libmad" In this example, DEPENDS is set to glibc ncurses libmad.

Next, there is the include directive, which causes BitBake to parse in whatever file you specify, and insert it at that location, which is not unlike make. However, if the path specified on the include line is a relative path, BitBake will locate the first one it can find within BBPATH.

DATE = "${@time.strftime('%Y%m%d',time.gmtime())}" This would result in the DATE variable containing today's date.

NOTE: This is only supported in .bb and .bbclass files. do_mytask () { echo "Hello, world!" } This is essentially identical to setting a variable, except that this variable happens to be executable shell code. python do_printdate () { import time print time.strftime('%Y%m%d', time.gmtime()) } This is the similar to the previous, but flags it as python so that BitBake knows it is python code.

NOTE: This is only supported in .bb and .bbclass files. def get_depends(bb, d): if bb.data.getVar('SOMECONDITION', d, True): return "dependencywithcond" else: return "dependency" SOMECONDITION = "1" DEPENDS = "${@get_depends(bb, d)}" This would result in DEPENDS containing dependencywithcond.

NOTE: This is only supported in .bb and .bbclass files. The inherit directive is a means of specifying what classes of functionality your .bb requires. It is a rudamentary form of inheritence. For example, you can easily abstract out the tasks involved in building a package that uses autoconf and automake, and put that into a bbclass for your packages to make use of. A given bbclass is located by searching for classes/filename.oeclass in BBPATH, where filename is what you inherited.

NOTE: This is only supported in .bb and .bbclass files. In BitBake, each step that needs to be run for a given .bb is known as a task. There is a command addtask to add new tasks (must be a defined python executable metadata and must start with do_) and describe intertask dependencies. python do_printdate () { import time print time.strftime('%Y%m%d', time.gmtime()) } addtask printdate before do_build This defines the necessary python function and adds it as a task which is now a dependency of do_build (the default task). If anyone executes the do_build task, that will result in do_printdate being run first.

NOTE: This is only supported in .bb and .bbclass files. BitBake also implements a means of registering event handlers. Events are triggered at certain points during operation, such as, the beginning of operation against a given .bb, the start of a given task, task failure, task success, et cetera. The intent was to make it easy to do things like email notifications on build failure. addhandler myclass_eventhandler python myclass_eventhandler() { from bb.event import NotHandled, getName from bb import data print "The name of the Event is %s" % getName(e) print "The file we run for is %s" % data.getVar('FILE', e.data, True) return NotHandled This event handler gets called every time an event is triggered. A global variable e is defined. e.data contains an instance of bb.data. With the getName(e) method one can get the name of the triggered event.The above event handler prints the name of the event and the content of the FILE variable.

The first of the classifications of metadata in BitBake is configuration metadata. This metadata is global, and therefore affects all packages and tasks which are executed. Currently, BitBake has hardcoded knowledge of a single configuration file. It expects to find 'conf/bitbake.conf' somewhere in the user specified BBPATH. That configuration file generally has include directives to pull in any other metadata (generally files specific to architecture, machine, local and so on. Only variable definitions and include directives are allowed in .conf files.

BitBake classes are our rudamentary inheritence mechanism. As briefly mentioned in the metadata introduction, they're parsed when an inherit directive is encountered, and they are located in classes/ relative to the dirs in BBPATH.

A BitBake (.bb) file is a logical unit of tasks to be executed. Normally this is a package to be built. Inter-.bb dependencies are obeyed. The files themselves are located via the BBFILES variable, which is set to a space seperated list of .bb files, and does handle wildcards.

bbread is a command for displaying BitBake metadata. When run with no arguments, it has the core parse 'conf/bitbake.conf', as located in BBPATH, and displays that. If you supply a file on the commandline, such as a .bb, then it parses that afterwards, using the aforementioned configuration metadata. NOTE: the stand a lone bbread command was removed. Instead of bbread use bitbake -e.

bitbake is the primary command in the system. It facilitates executing tasks in a single .bb file, or executing a given task on a set of multiple .bb files, accounting for interdependencies amongst them.

$ bitbake --help usage: bitbake [options] [package ...] Executes the specified task (default is 'build') for a given set of BitBake files. It expects that BBFILES is defined, which is a space seperated list of files to be executed. BBFILES does support wildcards. Default BBFILES are the .bb files in the current directory. options: --version show program's version number and exit -h, --help show this help message and exit -b BUILDFILE, --buildfile=BUILDFILE execute the task against this .bb file, rather than a package from BBFILES. -k, --continue continue as much as possible after an error. While the target that failed, and those that depend on it, cannot be remade, the other dependencies of these targets can be processed all the same. -f, --force force run of specified cmd, regardless of stamp status -i, --interactive drop into the interactive mode. -c CMD, --cmd=CMD Specify task to execute. Note that this only executes the specified task for the providee and the packages it depends on, i.e. 'compile' does not implicitly call stage for the dependencies (IOW: use only if you know what you are doing) -r FILE, --read=FILE read the specified file before bitbake.conf -v, --verbose output more chit-chat to the terminal -D, --debug Increase the debug level -n, --dry-run don't execute, just go through the motions -p, --parse-only quit after parsing the BB files (developers only) -d, --disable-psyco disable using the psyco just-in-time compiler (not recommended) -s, --show-versions show current and preferred versions of all packages -e, --environment show the global or per-package environment (this is what used to be bbread) Executing tasks for a single file is relatively simple. You specify the file in question, and bitbake parses it and executes the specified task (or build by default). It obeys intertask dependencies when doing so. clean task: $ bitbake -b blah_1.0.bb -c clean build task: $ bitbake -b blah_1.0.bb 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 we want to execute at this time. There also needs to be a way for each .bb to express its dependencies, both for build time and runtime. There must be a way for the user to express their preferences when multiple .bb's provide the same functionality, or when there are multiple versions of a .bb. The next section, Metadata, outlines how one goes about specifying such things. Note that the bitbake command, when not using --buildfile, accepts a PROVIDER, not a filename or anything else. By default, a .bb generally PROVIDES its packagename, packagename-version, and packagename-version-revision. $ bitbake blah $ bitbake blah-1.0 $ bitbake blah-1.0-r0 $ bitbake -c clean blah $ bitbake virtual/whatever $ bitbake -c clean virtual/whatever

As you may have seen in the usage information, or in the information about .bb files, the BBFILES variable is how the bitbake tool locates its files. This variable is a space seperated list of files that are available, and supports wildcards. BBFILES = "/path/to/bbfiles/*.bb" With regard to dependencies, it expects the .bb to define a DEPENDS variable, which contains a space seperated list of package names, which themselves are the PN variable. The PN variable is, in general, by default, set to a component of the .bb filename. a.bb: PN = "package-a" DEPENDS += "package-b" b.bb: PN = "package-b" This example shows the usage of the PROVIDES variable, which allows a given .bb to specify what functionality it provides. package1.bb: PROVIDES += "virtual/package" package2.bb: DEPENDS += "virtual/package" package3.bb: PROVIDES += "virtual/package" As you can see, here there are two different .bb's that provide the same functionality (virtual/package). Clearly, there needs to be a way for the person running bitbake to control which of those providers gets used. There is, indeed, such a way. The following would go into a .conf file, to select package1: PREFERRED_PROVIDER_virtual/package = "package1" When there are multiple versions of a given package, bitbake defaults to selecting the most recent version, unless otherwise specified. If the .bb in question has a DEFAULT_PREFERENCE set lower than the other .bb's (default is 0), then it will not be selected. This allows the person or persons maintaining the repository of .bb files to specify their preferences for the default selected version. In addition, the user can specify their preferences with regard to version. If the first .bb is named a_1.1.bb, then the PN variable will be set to a, and the PV variable will be set to 1.1. If we then have an a_1.2.bb, bitbake will choose 1.2 by default. However, if we define the following variable in a .conf that bitbake parses, we can change that. PREFERRED_VERSION_a = "1.1" bbfile collections exist to allow the user to have multiple repositories of bbfiles 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. Usage: 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"