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diff --git a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-ref-variables-context.rst b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-ref-variables-context.rst new file mode 100644 index 0000000000..e9c454ba11 --- /dev/null +++ b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-ref-variables-context.rst @@ -0,0 +1,91 @@ +.. SPDX-License-Identifier: CC-BY-2.5 + +================ +Variable Context +================ + +| + +Variables might only have an impact or can be used in certain contexts. Some +should only be used in global files like ``.conf``, while others are intended only +for local files like ``.bb``. This chapter aims to describe some important variable +contexts. + +.. _ref-varcontext-configuration: + +BitBake's own configuration +=========================== + +Variables starting with ``BB_`` usually configure the behaviour of BitBake itself. +For example, one could configure: + +- System resources, like disk space to be used (:term:`BB_DISKMON_DIRS`), + or the number of tasks to be run in parallel by BitBake (:term:`BB_NUMBER_THREADS`). + +- How the fetchers shall behave, e.g., :term:`BB_FETCH_PREMIRRORONLY` is used + by BitBake to determine if BitBake's fetcher shall search only + :term:`PREMIRRORS` for files. + +Those variables are usually configured globally. + +BitBake configuration +===================== + +There are variables: + +- Like :term:`B` or :term:`T`, that are used to specify directories used by + BitBake during the build of a particular recipe. Those variables are + specified in ``bitbake.conf``. Some, like :term:`B`, are quite often + overwritten in recipes. + +- Starting with ``FAKEROOT``, to configure how the ``fakeroot`` command is + handled. Those are usually set by ``bitbake.conf`` and might get adapted in a + ``bbclass``. + +- Detailing where BitBake will store and fetch information from, for + data reuse between build runs like :term:`CACHE`, :term:`DL_DIR` or + :term:`PERSISTENT_DIR`. Those are usually global. + + +Layers and files +================ + +Variables starting with ``LAYER`` configure how BitBake handles layers. +Additionally, variables starting with ``BB`` configure how layers and files are +handled. For example: + +- :term:`LAYERDEPENDS` is used to configure on which layers a given layer + depends. + +- The configured layers are contained in :term:`BBLAYERS` and files in + :term:`BBFILES`. + +Those variables are often used in the files ``layer.conf`` and ``bblayers.conf``. + +Recipes and packages +==================== + +Variables handling recipes and packages can be split into: + +- :term:`PN`, :term:`PV` or :term:`PF` for example, contain information about + the name or revision of a recipe or package. Usually, the default set in + ``bitbake.conf`` is used, but those are from time to time overwritten in + recipes. + +- :term:`SUMMARY`, :term:`DESCRIPTION`, :term:`LICENSE` or :term:`HOMEPAGE` + contain the expected information and should be set specifically for every + recipe. + +- In recipes, variables are also used to control build and runtime + dependencies between recipes/packages with other recipes/packages. The + most common should be: :term:`PROVIDES`, :term:`RPROVIDES`, :term:`DEPENDS`, + and :term:`RDEPENDS`. + +- There are further variables starting with ``SRC`` that specify the sources in + a recipe like :term:`SRC_URI` or :term:`SRCDATE`. Those are also usually set + in recipes. + +- Which version or provider of a recipe should be given preference when + multiple recipes would provide the same item, is controlled by variables + starting with ``PREFERRED_``. Those are normally set in the configuration + files of a ``MACHINE`` or ``DISTRO``. |