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This is inspired by the same section in the yocto-docs. It aims to provide information in what contexts(recipes, .conf, bbclass,...) a variable is usually used. For that I tried to group similar variables, so that a short overview is given. This was inspired by [YOCTO #14072], but of course does not implement a warning if a variable is used in an unintended context. (Bitbake rev: 5ced476685376b1a32b7fdd9546f9b61c5962aa0) Signed-off-by: Simone Weiß <simone.p.weiss@posteo.com> Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
92 lines
3.2 KiB
ReStructuredText
92 lines
3.2 KiB
ReStructuredText
.. SPDX-License-Identifier: CC-BY-2.5
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================
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Variable Context
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================
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Variables might only have an impact or can be used in certain contexts. Some
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should only be used in global files like ``.conf``, while others are intended only
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for local files like ``.bb``. This chapter aims to describe some important variable
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contexts.
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.. _ref-varcontext-configuration:
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BitBake's own configuration
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===========================
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Variables starting with ``BB_`` usually configure the behaviour of BitBake itself.
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For example, one could configure:
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- System resources, like disk space to be used (:term:`BB_DISKMON_DIRS`),
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or the number of tasks to be run in parallel by BitBake (:term:`BB_NUMBER_THREADS`).
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- How the fetchers shall behave, e.g., :term:`BB_FETCH_PREMIRRORONLY` is used
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by BitBake to determine if BitBake's fetcher shall search only
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:term:`PREMIRRORS` for files.
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Those variables are usually configured globally.
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BitBake configuration
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=====================
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There are variables:
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- Like :term:`B` or :term:`T`, that are used to specify directories used by
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BitBake during the build of a particular recipe. Those variables are
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specified in ``bitbake.conf``. Some, like :term:`B`, are quite often
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overwritten in recipes.
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- Starting with ``FAKEROOT``, to configure how the ``fakeroot`` command is
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handled. Those are usually set by ``bitbake.conf`` and might get adapted in a
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``bbclass``.
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- Detailing where BitBake will store and fetch information from, for
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data reuse between build runs like :term:`CACHE`, :term:`DL_DIR` or
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:term:`PERSISTENT_DIR`. Those are usually global.
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Layers and files
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================
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Variables starting with ``LAYER`` configure how BitBake handles layers.
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Additionally, variables starting with ``BB`` configure how layers and files are
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handled. For example:
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- :term:`LAYERDEPENDS` is used to configure on which layers a given layer
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depends.
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- The configured layers are contained in :term:`BBLAYERS` and files in
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:term:`BBFILES`.
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Those variables are often used in the files ``layer.conf`` and ``bblayers.conf``.
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Recipes and packages
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====================
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Variables handling recipes and packages can be split into:
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- :term:`PN`, :term:`PV` or :term:`PF` for example, contain information about
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the name or revision of a recipe or package. Usually, the default set in
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``bitbake.conf`` is used, but those are from time to time overwritten in
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recipes.
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- :term:`SUMMARY`, :term:`DESCRIPTION`, :term:`LICENSE` or :term:`HOMEPAGE`
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contain the expected information and should be set specifically for every
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recipe.
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- In recipes, variables are also used to control build and runtime
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dependencies between recipes/packages with other recipes/packages. The
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most common should be: :term:`PROVIDES`, :term:`RPROVIDES`, :term:`DEPENDS`,
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and :term:`RDEPENDS`.
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- There are further variables starting with ``SRC`` that specify the sources in
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a recipe like :term:`SRC_URI` or :term:`SRCDATE`. Those are also usually set
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in recipes.
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- Which version or provider of a recipe should be given preference when
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multiple recipes would provide the same item, is controlled by variables
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starting with ``PREFERRED_``. Those are normally set in the configuration
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files of a ``MACHINE`` or ``DISTRO``.
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