Table of Contents
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.
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
:= "${C}append"
In that example, A
would contain test 123
, B
would contain 456 bval
, and C
would be cvalappend
.
B
= "bval"B
+= "additionaldata"C
= "cval"C
=+ "test"
In this example, B
is now bval additionaldata
and C
is test cval
.
B
= "bval"B
.= "additionaldata"C
= "cval"C
=. "test"
In this example, B
is now bvaladditionaldata
and C
is testcval
. In contrast to the above Appending and Prepending operators no additional space
will be introduced.
OVERRIDES is a “:” seperated variable containing each item you want to satisfy conditions. So, if you have a variable which is conditional on “arm”, and “arm” is in OVERRIDES, then the “arm” specific version of the variable is used rather than the non-conditional version. Example:
OVERRIDES
= "architecture:os:machine"TEST
= "defaultvalue"TEST_os
= "osspecificvalue"TEST_condnotinoverrides
= "othercondvalue"
In this example, TEST
would be osspecificvalue
, due to the condition “os” being in OVERRIDES
.
BitBake also supports appending and prepending to variables based on whether something is in OVERRIDES. Example:
DEPENDS
= "glibc ncurses"OVERRIDES
= "machine:local"DEPENDS_append_machine
= " libmad"
In this example, DEPENDS
is set to glibc ncurses libmad
.
Next, there is the include
directive, which causes BitBake to parse in whatever file you specify, and insert it at that location, which is not unlike make. However, if the path specified on the include
line is a relative path, BitBake will locate the first one it can find within BBPATH
.
In contrast to the include
directive, require
will
raise an ParseError if the to be included file can not be found. Otherwise it will behave just like the
include
directive.
DATE
= "${@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 allows to install 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.