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diff --git a/documentation/ref-manual/terms.rst b/documentation/ref-manual/terms.rst new file mode 100644 index 0000000000..c07dd4b128 --- /dev/null +++ b/documentation/ref-manual/terms.rst @@ -0,0 +1,390 @@ +.. SPDX-License-Identifier: CC-BY-SA-2.0-UK + +******************* +Yocto Project Terms +******************* + +Following is a list of terms and definitions users new to the Yocto Project +development environment might find helpful. While some of these terms are +universal, the list includes them just in case: + +.. glossary:: + + :term:`Append Files` + Files that append build information to a recipe file. Append files are + known as BitBake append files and ``.bbappend`` files. The OpenEmbedded + build system expects every append file to have a corresponding recipe + (``.bb``) file. Furthermore, the append file and corresponding recipe file + must use the same root filename. The filenames can differ only in the + file type suffix used (e.g. ``formfactor_0.0.bb`` and + ``formfactor_0.0.bbappend``). + + Information in append files extends or overrides the information in the + similarly-named recipe file. For an example of an append file in use, see + the ":ref:`dev-manual/common-tasks:Using .bbappend Files in + Your Layer`" section in the Yocto Project Development Tasks Manual. + + When you name an append file, you can use the "``%``" wildcard character + to allow for matching recipe names. For example, suppose you have an + append file named as follows: + :: + + busybox_1.21.%.bbappend + + That append file + would match any ``busybox_1.21.``\ x\ ``.bb`` version of the recipe. So, + the append file would match any of the following recipe names: + + .. code-block:: shell + + busybox_1.21.1.bb + busybox_1.21.2.bb + busybox_1.21.3.bb + busybox_1.21.10.bb + busybox_1.21.25.bb + + .. note:: + + The use of the "%" character is limited in that it only works + directly in front of the .bbappend portion of the append file's + name. You cannot use the wildcard character in any other location of + the name. + + :term:`BitBake` + The task executor and scheduler used by the OpenEmbedded build system to + build images. For more information on BitBake, see the :doc:`BitBake User + Manual <bitbake:index>`. + + :term:`Board Support Package (BSP)` + A group of drivers, definitions, and other components that provide support + for a specific hardware configuration. For more information on BSPs, see + the :doc:`/bsp-guide/index`. + + :term:`Build Directory` + This term refers to the area used by the OpenEmbedded build system for + builds. The area is created when you ``source`` the setup environment + script that is found in the Source Directory + (i.e. :ref:`ref-manual/structure:\`\`oe-init-build-env\`\``). The + :term:`TOPDIR` variable points to the Build Directory. + + You have a lot of flexibility when creating the Build Directory. + Following are some examples that show how to create the directory. The + examples assume your :term:`Source Directory` is named ``poky``: + + - Create the Build Directory inside your Source Directory and let + the name of the Build Directory default to ``build``: + + .. code-block:: shell + + $ cd $HOME/poky + $ source oe-init-build-env + + - Create the Build Directory inside your home directory and + specifically name it ``test-builds``: + + .. code-block:: shell + + $ cd $HOME + $ source poky/oe-init-build-env test-builds + + - Provide a directory path and specifically name the Build + Directory. Any intermediate folders in the pathname must exist. + This next example creates a Build Directory named + ``YP-POKYVERSION`` in your home directory within the existing + directory ``mybuilds``: + + .. code-block:: shell + + $ cd $HOME + $ source $HOME/poky/oe-init-build-env $HOME/mybuilds/YP-POKYVERSION + + .. note:: + + By default, the Build Directory contains :term:`TMPDIR`, which is a + temporary directory the build system uses for its work. ``TMPDIR`` cannot + be under NFS. Thus, by default, the Build Directory cannot be under + NFS. However, if you need the Build Directory to be under NFS, you can + set this up by setting ``TMPDIR`` in your ``local.conf`` file to use a local + drive. Doing so effectively separates ``TMPDIR`` from :term:`TOPDIR`, which is the + Build Directory. + + :term:`Build Host` + The system used to build images in a Yocto Project Development + environment. The build system is sometimes referred to as the development + host. + + :term:`Classes` + Files that provide for logic encapsulation and inheritance so that + commonly used patterns can be defined once and then easily used in + multiple recipes. For reference information on the Yocto Project classes, + see the ":ref:`ref-manual/classes:Classes`" chapter. Class files end with the + ``.bbclass`` filename extension. + + :term:`Configuration File` + Files that hold global definitions of variables, user-defined variables, + and hardware configuration information. These files tell the OpenEmbedded + build system what to build and what to put into the image to support a + particular platform. + + Configuration files end with a ``.conf`` filename extension. The + :file:`conf/local.conf` configuration file in the :term:`Build Directory` + contains user-defined variables that affect every build. The + :file:`meta-poky/conf/distro/poky.conf` configuration file defines Yocto + "distro" configuration variables used only when building with this + policy. Machine configuration files, which are located throughout the + :term:`Source Directory`, define variables for specific hardware and are + only used when building for that target (e.g. the + :file:`machine/beaglebone.conf` configuration file defines variables for + the Texas Instruments ARM Cortex-A8 development board). + + :term:`Container Layer` + Layers that hold other layers. An example of a container layer is + OpenEmbedded's `meta-openembedded + <https://github.com/openembedded/meta-openembedded>`_ layer. The + ``meta-openembedded`` layer contains many ``meta-*`` layers. + + :term:`Cross-Development Toolchain` + In general, a cross-development toolchain is a collection of software + development tools and utilities that run on one architecture and allow you + to develop software for a different, or targeted, architecture. These + toolchains contain cross-compilers, linkers, and debuggers that are + specific to the target architecture. + + The Yocto Project supports two different cross-development toolchains: + + - A toolchain only used by and within BitBake when building an image for a + target architecture. + + - A relocatable toolchain used outside of BitBake by developers when + developing applications that will run on a targeted device. + + Creation of these toolchains is simple and automated. For information on + toolchain concepts as they apply to the Yocto Project, see the + ":ref:`overview-manual/concepts:Cross-Development + Toolchain Generation`" section in the Yocto Project Overview and Concepts + Manual. You can also find more information on using the relocatable + toolchain in the :doc:`/sdk-manual/index` manual. + + :term:`Extensible Software Development Kit (eSDK)` + A custom SDK for application developers. This eSDK allows developers to + incorporate their library and programming changes back into the image to + make their code available to other application developers. + + For information on the eSDK, see the :doc:`/sdk-manual/index` manual. + + :term:`Image` + An image is an artifact of the BitBake build process given a collection of + recipes and related Metadata. Images are the binary output that run on + specific hardware or QEMU and are used for specific use-cases. For a list + of the supported image types that the Yocto Project provides, see the + ":ref:`ref-manual/images:Images`" chapter. + + :term:`Layer` + A collection of related recipes. Layers allow you to consolidate related + metadata to customize your build. Layers also isolate information used + when building for multiple architectures. Layers are hierarchical in + their ability to override previous specifications. You can include any + number of available layers from the Yocto Project and customize the build + by adding your layers after them. You can search the Layer Index for + layers used within Yocto Project. + + For introductory information on layers, see the + ":ref:`overview-manual/yp-intro:The Yocto Project Layer + Model`" section in the Yocto Project Overview and Concepts Manual. For + more detailed information on layers, see the + ":ref:`dev-manual/common-tasks:Understanding and Creating + Layers`" section in the Yocto Project Development Tasks Manual. For a + discussion specifically on BSP Layers, see the ":ref:`bsp-guide/bsp:BSP + Layers`" section in the Yocto Project Board Support Packages (BSP) + Developer's Guide. + + :term:`Metadata` + A key element of the Yocto Project is the Metadata that + is used to construct a Linux distribution and is contained in the + files that the :term:`OpenEmbedded Build System` + parses when building an image. In general, Metadata includes recipes, + configuration files, and other information that refers to the build + instructions themselves, as well as the data used to control what + things get built and the effects of the build. Metadata also includes + commands and data used to indicate what versions of software are + used, from where they are obtained, and changes or additions to the + software itself (patches or auxiliary files) that are used to fix + bugs or customize the software for use in a particular situation. + OpenEmbedded-Core is an important set of validated metadata. + + In the context of the kernel ("kernel Metadata"), the term refers to + the kernel config fragments and features contained in the + :yocto_git:`yocto-kernel-cache </yocto-kernel-cache>` + Git repository. + + :term:`OpenEmbedded-Core (OE-Core)` + OE-Core is metadata comprised of + foundational recipes, classes, and associated files that are meant to + be common among many different OpenEmbedded-derived systems, + including the Yocto Project. OE-Core is a curated subset of an + original repository developed by the OpenEmbedded community that has + been pared down into a smaller, core set of continuously validated + recipes. The result is a tightly controlled and an quality-assured + core set of recipes. + + You can see the Metadata in the ``meta`` directory of the Yocto + Project :yocto_git:`Source Repositories </poky>`. + + :term:`OpenEmbedded Build System` + The build system specific to the Yocto + Project. The OpenEmbedded build system is based on another project + known as "Poky", which uses :term:`BitBake` as the task + executor. Throughout the Yocto Project documentation set, the + OpenEmbedded build system is sometimes referred to simply as "the + build system". If other build systems, such as a host or target build + system are referenced, the documentation clearly states the + difference. + + .. note:: + + For some historical information about Poky, see the :term:`Poky` term. + + :term:`Package` + In the context of the Yocto Project, this term refers to a + recipe's packaged output produced by BitBake (i.e. a "baked recipe"). + A package is generally the compiled binaries produced from the + recipe's sources. You "bake" something by running it through BitBake. + + It is worth noting that the term "package" can, in general, have + subtle meanings. For example, the packages referred to in the + ":ref:`ref-manual/system-requirements:required packages for the build host`" + section are compiled binaries that, when installed, add functionality to + your Linux distribution. + + Another point worth noting is that historically within the Yocto + Project, recipes were referred to as packages - thus, the existence + of several BitBake variables that are seemingly mis-named, (e.g. + :term:`PR`, :term:`PV`, and + :term:`PE`). + + :term:`Package Groups` + Arbitrary groups of software Recipes. You use + package groups to hold recipes that, when built, usually accomplish a + single task. For example, a package group could contain the recipes + for a company's proprietary or value-add software. Or, the package + group could contain the recipes that enable graphics. A package group + is really just another recipe. Because package group files are + recipes, they end with the ``.bb`` filename extension. + + :term:`Poky` + Poky, which is pronounced *Pock*-ee, is a reference embedded + distribution and a reference test configuration. Poky provides the + following: + + - A base-level functional distro used to illustrate how to customize + a distribution. + + - A means by which to test the Yocto Project components (i.e. Poky + is used to validate the Yocto Project). + + - A vehicle through which you can download the Yocto Project. + + Poky is not a product level distro. Rather, it is a good starting + point for customization. + + .. note:: + + Poky began as an open-source project initially developed by + OpenedHand. OpenedHand developed Poky from the existing + OpenEmbedded build system to create a commercially supportable + build system for embedded Linux. After Intel Corporation acquired + OpenedHand, the poky project became the basis for the Yocto + Project's build system. + + :term:`Recipe` + A set of instructions for building packages. A recipe + describes where you get source code, which patches to apply, how to + configure the source, how to compile it and so on. Recipes also + describe dependencies for libraries or for other recipes. Recipes + represent the logical unit of execution, the software to build, the + images to build, and use the ``.bb`` file extension. + + :term:`Reference Kit` + A working example of a system, which includes a + :term:`BSP<Board Support Package (BSP)>` as well as a + :term:`build host<Build Host>` and other components, that can + work on specific hardware. + + :term:`Source Directory` + This term refers to the directory structure + created as a result of creating a local copy of the ``poky`` Git + repository ``git://git.yoctoproject.org/poky`` or expanding a + released ``poky`` tarball. + + .. note:: + + Creating a local copy of the + poky + Git repository is the recommended method for setting up your + Source Directory. + + Sometimes you might hear the term "poky directory" used to refer to + this directory structure. + + .. note:: + + The OpenEmbedded build system does not support file or directory + names that contain spaces. Be sure that the Source Directory you + use does not contain these types of names. + + The Source Directory contains BitBake, Documentation, Metadata and + other files that all support the Yocto Project. Consequently, you + must have the Source Directory in place on your development system in + order to do any development using the Yocto Project. + + When you create a local copy of the Git repository, you can name the + repository anything you like. Throughout much of the documentation, + "poky" is used as the name of the top-level folder of the local copy + of the poky Git repository. So, for example, cloning the ``poky`` Git + repository results in a local Git repository whose top-level folder + is also named "poky". + + While it is not recommended that you use tarball expansion to set up + the Source Directory, if you do, the top-level directory name of the + Source Directory is derived from the Yocto Project release tarball. + For example, downloading and unpacking + :yocto_dl:`/releases/yocto/&DISTRO_REL_TAG;/&YOCTO_POKY;.tar.bz2` + results in a Source Directory whose root folder is named ``poky``. + + It is important to understand the differences between the Source + Directory created by unpacking a released tarball as compared to + cloning ``git://git.yoctoproject.org/poky``. When you unpack a + tarball, you have an exact copy of the files based on the time of + release - a fixed release point. Any changes you make to your local + files in the Source Directory are on top of the release and will + remain local only. On the other hand, when you clone the ``poky`` Git + repository, you have an active development repository with access to + the upstream repository's branches and tags. In this case, any local + changes you make to the local Source Directory can be later applied + to active development branches of the upstream ``poky`` Git + repository. + + For more information on concepts related to Git repositories, + branches, and tags, see the + ":ref:`overview-manual/development-environment:repositories, tags, and branches`" + section in the Yocto Project Overview and Concepts Manual. + + :term:`Task` + A unit of execution for BitBake (e.g. + :ref:`ref-tasks-compile`, + :ref:`ref-tasks-fetch`, + :ref:`ref-tasks-patch`, and so forth). + + :term:`Toaster` + A web interface to the Yocto Project's :term:`OpenEmbedded Build System`. + The interface enables you to + configure and run your builds. Information about builds is collected + and stored in a database. For information on Toaster, see the + :doc:`/toaster-manual/index`. + + :term:`Upstream` + A reference to source code or repositories that are not + local to the development system but located in a master area that is + controlled by the maintainer of the source code. For example, in + order for a developer to work on a particular piece of code, they + need to first get a copy of it from an "upstream" source. |