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diff --git a/poky/documentation/overview-manual/history.rst b/poky/documentation/overview-manual/history.rst new file mode 100644 index 000000000..0273d28b9 --- /dev/null +++ b/poky/documentation/overview-manual/history.rst @@ -0,0 +1,28 @@ +.. SPDX-License-Identifier: CC-BY-2.0-UK + +*********************** +Manual Revision History +*********************** + +.. list-table:: + :widths: 10 15 40 + :header-rows: 1 + + * - Revision + - Date + - Note + * - 2.5 + - May 2018 + - The initial document released with the Yocto Project 2.5 Release + * - 2.6 + - November 2018 + - Released with the Yocto Project 2.6 Release. + * - 2.7 + - May 2019 + - Released with the Yocto Project 2.7 Release. + * - 3.0 + - October 2019 + - Released with the Yocto Project 3.0 Release. + * - 3.1 + - April 2020 + - Released with the Yocto Project 3.1 Release. diff --git a/poky/documentation/overview-manual/overview-manual-concepts.rst b/poky/documentation/overview-manual/overview-manual-concepts.rst new file mode 100644 index 000000000..6ce5f80af --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-concepts.rst @@ -0,0 +1,2185 @@ +.. SPDX-License-Identifier: CC-BY-2.0-UK + +********************** +Yocto Project Concepts +********************** + +This chapter provides explanations for Yocto Project concepts that go +beyond the surface of "how-to" information and reference (or look-up) +material. Concepts such as components, the :term:`OpenEmbedded Build System` +workflow, +cross-development toolchains, shared state cache, and so forth are +explained. + +Yocto Project Components +======================== + +The :term:`BitBake` task executor +together with various types of configuration files form the +:term:`OpenEmbedded-Core (OE-Core)`. This section +overviews these components by describing their use and how they +interact. + +BitBake handles the parsing and execution of the data files. The data +itself is of various types: + +- *Recipes:* Provides details about particular pieces of software. + +- *Class Data:* Abstracts common build information (e.g. how to build a + Linux kernel). + +- *Configuration Data:* Defines machine-specific settings, policy + decisions, and so forth. Configuration data acts as the glue to bind + everything together. + +BitBake knows how to combine multiple data sources together and refers +to each data source as a layer. For information on layers, see the +":ref:`dev-manual/dev-manual-common-tasks:understanding and creating layers`" +section of the Yocto Project Development Tasks Manual. + +Following are some brief details on these core components. For +additional information on how these components interact during a build, +see the +":ref:`overview-manual/overview-manual-concepts:openembedded build system concepts`" +section. + +.. _usingpoky-components-bitbake: + +BitBake +------- + +BitBake is the tool at the heart of the :term:`OpenEmbedded Build System` +and is responsible +for parsing the :term:`Metadata`, generating +a list of tasks from it, and then executing those tasks. + +This section briefly introduces BitBake. If you want more information on +BitBake, see the :doc:`BitBake User Manual <bitbake:index>`. + +To see a list of the options BitBake supports, use either of the +following commands: +:: + + $ bitbake -h + $ bitbake --help + +The most common usage for BitBake is ``bitbake recipename``, where +``recipename`` is the name of the recipe you want to build (referred +to as the "target"). The target often equates to the first part of a +recipe's filename (e.g. "foo" for a recipe named ``foo_1.3.0-r0.bb``). +So, to process the ``matchbox-desktop_1.2.3.bb`` recipe file, you might +type the following: +:: + + $ bitbake matchbox-desktop + +Several different +versions of ``matchbox-desktop`` might exist. BitBake chooses the one +selected by the distribution configuration. You can get more details +about how BitBake chooses between different target versions and +providers in the +":ref:`Preferences <bitbake:bb-bitbake-preferences>`" section +of the BitBake User Manual. + +BitBake also tries to execute any dependent tasks first. So for example, +before building ``matchbox-desktop``, BitBake would build a cross +compiler and ``glibc`` if they had not already been built. + +A useful BitBake option to consider is the ``-k`` or ``--continue`` +option. This option instructs BitBake to try and continue processing the +job as long as possible even after encountering an error. When an error +occurs, the target that failed and those that depend on it cannot be +remade. However, when you use this option other dependencies can still +be processed. + +.. _overview-components-recipes: + +Recipes +------- + +Files that have the ``.bb`` suffix are "recipes" files. In general, a +recipe contains information about a single piece of software. This +information includes the location from which to download the unaltered +source, any source patches to be applied to that source (if needed), +which special configuration options to apply, how to compile the source +files, and how to package the compiled output. + +The term "package" is sometimes used to refer to recipes. However, since +the word "package" is used for the packaged output from the OpenEmbedded +build system (i.e. ``.ipk`` or ``.deb`` files), this document avoids +using the term "package" when referring to recipes. + +.. _overview-components-classes: + +Classes +------- + +Class files (``.bbclass``) contain information that is useful to share +between recipes files. An example is the +:ref:`autotools <ref-classes-autotools>` class, +which contains common settings for any application that Autotools uses. +The ":ref:`ref-manual/ref-classes:Classes`" chapter in the +Yocto Project Reference Manual provides details about classes and how to +use them. + +.. _overview-components-configurations: + +Configurations +-------------- + +The configuration files (``.conf``) define various configuration +variables that govern the OpenEmbedded build process. These files fall +into several areas that define machine configuration options, +distribution configuration options, compiler tuning options, general +common configuration options, and user configuration options in +``conf/local.conf``, which is found in the :term:`Build Directory`. + + +.. _overview-layers: + +Layers +====== + +Layers are repositories that contain related metadata (i.e. sets of +instructions) that tell the OpenEmbedded build system how to build a +target. Yocto Project's `layer model <#the-yocto-project-layer-model>`__ +facilitates collaboration, sharing, customization, and reuse within the +Yocto Project development environment. Layers logically separate +information for your project. For example, you can use a layer to hold +all the configurations for a particular piece of hardware. Isolating +hardware-specific configurations allows you to share other metadata by +using a different layer where that metadata might be common across +several pieces of hardware. + +Many layers exist that work in the Yocto Project development +environment. The `Yocto Project Curated Layer +Index <https://www.yoctoproject.org/software-overview/layers/>`__ +and `OpenEmbedded Layer +Index <http://layers.openembedded.org/layerindex/branch/master/layers/>`__ +both contain layers from which you can use or leverage. + +By convention, layers in the Yocto Project follow a specific form. +Conforming to a known structure allows BitBake to make assumptions +during builds on where to find types of metadata. You can find +procedures and learn about tools (i.e. ``bitbake-layers``) for creating +layers suitable for the Yocto Project in the +":ref:`dev-manual/dev-manual-common-tasks:understanding and creating layers`" +section of the Yocto Project Development Tasks Manual. + +.. _openembedded-build-system-build-concepts: + +OpenEmbedded Build System Concepts +================================== + +This section takes a more detailed look inside the build process used by +the :term:`OpenEmbedded Build System`, +which is the build +system specific to the Yocto Project. At the heart of the build system +is BitBake, the task executor. + +The following diagram represents the high-level workflow of a build. The +remainder of this section expands on the fundamental input, output, +process, and metadata logical blocks that make up the workflow. + +.. image:: figures/YP-flow-diagram.png + :align: center + +In general, the build's workflow consists of several functional areas: + +- *User Configuration:* metadata you can use to control the build + process. + +- *Metadata Layers:* Various layers that provide software, machine, and + distro metadata. + +- *Source Files:* Upstream releases, local projects, and SCMs. + +- *Build System:* Processes under the control of + :term:`BitBake`. This block expands + on how BitBake fetches source, applies patches, completes + compilation, analyzes output for package generation, creates and + tests packages, generates images, and generates cross-development + tools. + +- *Package Feeds:* Directories containing output packages (RPM, DEB or + IPK), which are subsequently used in the construction of an image or + Software Development Kit (SDK), produced by the build system. These + feeds can also be copied and shared using a web server or other means + to facilitate extending or updating existing images on devices at + runtime if runtime package management is enabled. + +- *Images:* Images produced by the workflow. + +- *Application Development SDK:* Cross-development tools that are + produced along with an image or separately with BitBake. + +User Configuration +------------------ + +User configuration helps define the build. Through user configuration, +you can tell BitBake the target architecture for which you are building +the image, where to store downloaded source, and other build properties. + +The following figure shows an expanded representation of the "User +Configuration" box of the `general workflow +figure <#general-workflow-figure>`__: + +.. image:: figures/user-configuration.png + :align: center + +BitBake needs some basic configuration files in order to complete a +build. These files are ``*.conf`` files. The minimally necessary ones +reside as example files in the ``build/conf`` directory of the +:term:`Source Directory`. For simplicity, +this section refers to the Source Directory as the "Poky Directory." + +When you clone the :term:`Poky` Git repository +or you download and unpack a Yocto Project release, you can set up the +Source Directory to be named anything you want. For this discussion, the +cloned repository uses the default name ``poky``. + +.. note:: + + The Poky repository is primarily an aggregation of existing + repositories. It is not a canonical upstream source. + +The ``meta-poky`` layer inside Poky contains a ``conf`` directory that +has example configuration files. These example files are used as a basis +for creating actual configuration files when you source +:ref:`structure-core-script`, which is the +build environment script. + +Sourcing the build environment script creates a +:term:`Build Directory` if one does not +already exist. BitBake uses the Build Directory for all its work during +builds. The Build Directory has a ``conf`` directory that contains +default versions of your ``local.conf`` and ``bblayers.conf`` +configuration files. These default configuration files are created only +if versions do not already exist in the Build Directory at the time you +source the build environment setup script. + +Because the Poky repository is fundamentally an aggregation of existing +repositories, some users might be familiar with running the +:ref:`structure-core-script` script in the context of separate +:term:`OpenEmbedded-Core (OE-Core)` and BitBake +repositories rather than a single Poky repository. This discussion +assumes the script is executed from within a cloned or unpacked version +of Poky. + +Depending on where the script is sourced, different sub-scripts are +called to set up the Build Directory (Yocto or OpenEmbedded). +Specifically, the script ``scripts/oe-setup-builddir`` inside the poky +directory sets up the Build Directory and seeds the directory (if +necessary) with configuration files appropriate for the Yocto Project +development environment. + +.. note:: + + The + scripts/oe-setup-builddir + script uses the + ``$TEMPLATECONF`` + variable to determine which sample configuration files to locate. + +The ``local.conf`` file provides many basic variables that define a +build environment. Here is a list of a few. To see the default +configurations in a ``local.conf`` file created by the build environment +script, see the +:yocto_git:`local.conf.sample </cgit/cgit.cgi/poky/tree/meta-poky/conf/local.conf.sample>` +in the ``meta-poky`` layer: + +- *Target Machine Selection:* Controlled by the + :term:`MACHINE` variable. + +- *Download Directory:* Controlled by the + :term:`DL_DIR` variable. + +- *Shared State Directory:* Controlled by the + :term:`SSTATE_DIR` variable. + +- *Build Output:* Controlled by the + :term:`TMPDIR` variable. + +- *Distribution Policy:* Controlled by the + :term:`DISTRO` variable. + +- *Packaging Format:* Controlled by the + :term:`PACKAGE_CLASSES` + variable. + +- *SDK Target Architecture:* Controlled by the + :term:`SDKMACHINE` variable. + +- *Extra Image Packages:* Controlled by the + :term:`EXTRA_IMAGE_FEATURES` + variable. + +.. note:: + + Configurations set in the + conf/local.conf + file can also be set in the + conf/site.conf + and + conf/auto.conf + configuration files. + +The ``bblayers.conf`` file tells BitBake what layers you want considered +during the build. By default, the layers listed in this file include +layers minimally needed by the build system. However, you must manually +add any custom layers you have created. You can find more information on +working with the ``bblayers.conf`` file in the +":ref:`dev-manual/dev-manual-common-tasks:enabling your layer`" +section in the Yocto Project Development Tasks Manual. + +The files ``site.conf`` and ``auto.conf`` are not created by the +environment initialization script. If you want the ``site.conf`` file, +you need to create that yourself. The ``auto.conf`` file is typically +created by an autobuilder: + +- *site.conf:* You can use the ``conf/site.conf`` configuration + file to configure multiple build directories. For example, suppose + you had several build environments and they shared some common + features. You can set these default build properties here. A good + example is perhaps the packaging format to use through the + :term:`PACKAGE_CLASSES` + variable. + + One useful scenario for using the ``conf/site.conf`` file is to + extend your :term:`BBPATH` variable + to include the path to a ``conf/site.conf``. Then, when BitBake looks + for Metadata using ``BBPATH``, it finds the ``conf/site.conf`` file + and applies your common configurations found in the file. To override + configurations in a particular build directory, alter the similar + configurations within that build directory's ``conf/local.conf`` + file. + +- *auto.conf:* The file is usually created and written to by an + autobuilder. The settings put into the file are typically the same as + you would find in the ``conf/local.conf`` or the ``conf/site.conf`` + files. + +You can edit all configuration files to further define any particular +build environment. This process is represented by the "User +Configuration Edits" box in the figure. + +When you launch your build with the ``bitbake target`` command, BitBake +sorts out the configurations to ultimately define your build +environment. It is important to understand that the +:term:`OpenEmbedded Build System` reads the +configuration files in a specific order: ``site.conf``, ``auto.conf``, +and ``local.conf``. And, the build system applies the normal assignment +statement rules as described in the +":doc:`bitbake:bitbake-user-manual/bitbake-user-manual-metadata`" chapter +of the BitBake User Manual. Because the files are parsed in a specific +order, variable assignments for the same variable could be affected. For +example, if the ``auto.conf`` file and the ``local.conf`` set variable1 +to different values, because the build system parses ``local.conf`` +after ``auto.conf``, variable1 is assigned the value from the +``local.conf`` file. + +Metadata, Machine Configuration, and Policy Configuration +--------------------------------------------------------- + +The previous section described the user configurations that define +BitBake's global behavior. This section takes a closer look at the +layers the build system uses to further control the build. These layers +provide Metadata for the software, machine, and policies. + +In general, three types of layer input exists. You can see them below +the "User Configuration" box in the `general workflow +figure <#general-workflow-figure>`__: + +- *Metadata (.bb + Patches):* Software layers containing + user-supplied recipe files, patches, and append files. A good example + of a software layer might be the + `meta-qt5 layer <https://github.com/meta-qt5/meta-qt5>`__ from + the `OpenEmbedded Layer + Index <http://layers.openembedded.org/layerindex/branch/master/layers/>`__. + This layer is for version 5.0 of the popular + `Qt <https://wiki.qt.io/About_Qt>`__ cross-platform application + development framework for desktop, embedded and mobile. + +- *Machine BSP Configuration:* Board Support Package (BSP) layers (i.e. + "BSP Layer" in the following figure) providing machine-specific + configurations. This type of information is specific to a particular + target architecture. A good example of a BSP layer from the `Poky + Reference Distribution <#gs-reference-distribution-poky>`__ is the + :yocto_git:`meta-yocto-bsp </cgit/cgit.cgi/poky/tree/meta-yocto-bsp>` + layer. + +- *Policy Configuration:* Distribution Layers (i.e. "Distro Layer" in + the following figure) providing top-level or general policies for the + images or SDKs being built for a particular distribution. For + example, in the Poky Reference Distribution the distro layer is the + :yocto_git:`meta-poky </cgit/cgit.cgi/poky/tree/meta-poky>` + layer. Within the distro layer is a ``conf/distro`` directory that + contains distro configuration files (e.g. + :yocto_git:`poky.conf </cgit/cgit.cgi/poky/tree/meta-poky/conf/distro/poky.conf>` + that contain many policy configurations for the Poky distribution. + +The following figure shows an expanded representation of these three +layers from the `general workflow figure <#general-workflow-figure>`__: + +.. image:: figures/layer-input.png + :align: center + +In general, all layers have a similar structure. They all contain a +licensing file (e.g. ``COPYING.MIT``) if the layer is to be distributed, +a ``README`` file as good practice and especially if the layer is to be +distributed, a configuration directory, and recipe directories. You can +learn about the general structure for layers used with the Yocto Project +in the +":ref:`dev-manual/dev-manual-common-tasks:creating your own layer`" +section in the +Yocto Project Development Tasks Manual. For a general discussion on +layers and the many layers from which you can draw, see the +"`Layers <#overview-layers>`__" and "`The Yocto Project Layer +Model <#the-yocto-project-layer-model>`__" sections both earlier in this +manual. + +If you explored the previous links, you discovered some areas where many +layers that work with the Yocto Project exist. The `Source +Repositories <http://git.yoctoproject.org/>`__ also shows layers +categorized under "Yocto Metadata Layers." + +.. note:: + + Layers exist in the Yocto Project Source Repositories that cannot be + found in the OpenEmbedded Layer Index. These layers are either + deprecated or experimental in nature. + +BitBake uses the ``conf/bblayers.conf`` file, which is part of the user +configuration, to find what layers it should be using as part of the +build. + +Distro Layer +~~~~~~~~~~~~ + +The distribution layer provides policy configurations for your +distribution. Best practices dictate that you isolate these types of +configurations into their own layer. Settings you provide in +``conf/distro/distro.conf`` override similar settings that BitBake finds +in your ``conf/local.conf`` file in the Build Directory. + +The following list provides some explanation and references for what you +typically find in the distribution layer: + +- *classes:* Class files (``.bbclass``) hold common functionality that + can be shared among recipes in the distribution. When your recipes + inherit a class, they take on the settings and functions for that + class. You can read more about class files in the + ":ref:`ref-manual/ref-classes:Classes`" chapter of the Yocto + Reference Manual. + +- *conf:* This area holds configuration files for the layer + (``conf/layer.conf``), the distribution + (``conf/distro/distro.conf``), and any distribution-wide include + files. + +- *recipes-*:* Recipes and append files that affect common + functionality across the distribution. This area could include + recipes and append files to add distribution-specific configuration, + initialization scripts, custom image recipes, and so forth. Examples + of ``recipes-*`` directories are ``recipes-core`` and + ``recipes-extra``. Hierarchy and contents within a ``recipes-*`` + directory can vary. Generally, these directories contain recipe files + (``*.bb``), recipe append files (``*.bbappend``), directories that + are distro-specific for configuration files, and so forth. + +BSP Layer +~~~~~~~~~ + +The BSP Layer provides machine configurations that target specific +hardware. Everything in this layer is specific to the machine for which +you are building the image or the SDK. A common structure or form is +defined for BSP layers. You can learn more about this structure in the +:doc:`../bsp-guide/bsp-guide`. + +.. note:: + + In order for a BSP layer to be considered compliant with the Yocto + Project, it must meet some structural requirements. + +The BSP Layer's configuration directory contains configuration files for +the machine (``conf/machine/machine.conf``) and, of course, the layer +(``conf/layer.conf``). + +The remainder of the layer is dedicated to specific recipes by function: +``recipes-bsp``, ``recipes-core``, ``recipes-graphics``, +``recipes-kernel``, and so forth. Metadata can exist for multiple +formfactors, graphics support systems, and so forth. + +.. note:: + + While the figure shows several + recipes-\* + directories, not all these directories appear in all BSP layers. + +Software Layer +~~~~~~~~~~~~~~ + +The software layer provides the Metadata for additional software +packages used during the build. This layer does not include Metadata +that is specific to the distribution or the machine, which are found in +their respective layers. + +This layer contains any recipes, append files, and patches, that your +project needs. + +.. _sources-dev-environment: + +Sources +------- + +In order for the OpenEmbedded build system to create an image or any +target, it must be able to access source files. The `general workflow +figure <#general-workflow-figure>`__ represents source files using the +"Upstream Project Releases", "Local Projects", and "SCMs (optional)" +boxes. The figure represents mirrors, which also play a role in locating +source files, with the "Source Materials" box. + +The method by which source files are ultimately organized is a function +of the project. For example, for released software, projects tend to use +tarballs or other archived files that can capture the state of a release +guaranteeing that it is statically represented. On the other hand, for a +project that is more dynamic or experimental in nature, a project might +keep source files in a repository controlled by a Source Control Manager +(SCM) such as Git. Pulling source from a repository allows you to +control the point in the repository (the revision) from which you want +to build software. Finally, a combination of the two might exist, which +would give the consumer a choice when deciding where to get source +files. + +BitBake uses the :term:`SRC_URI` +variable to point to source files regardless of their location. Each +recipe must have a ``SRC_URI`` variable that points to the source. + +Another area that plays a significant role in where source files come +from is pointed to by the +:term:`DL_DIR` variable. This area is +a cache that can hold previously downloaded source. You can also +instruct the OpenEmbedded build system to create tarballs from Git +repositories, which is not the default behavior, and store them in the +``DL_DIR`` by using the +:term:`BB_GENERATE_MIRROR_TARBALLS` +variable. + +Judicious use of a ``DL_DIR`` directory can save the build system a trip +across the Internet when looking for files. A good method for using a +download directory is to have ``DL_DIR`` point to an area outside of +your Build Directory. Doing so allows you to safely delete the Build +Directory if needed without fear of removing any downloaded source file. + +The remainder of this section provides a deeper look into the source +files and the mirrors. Here is a more detailed look at the source file +area of the `general workflow figure <#general-workflow-figure>`__: + +.. image:: figures/source-input.png + :align: center + +Upstream Project Releases +~~~~~~~~~~~~~~~~~~~~~~~~~ + +Upstream project releases exist anywhere in the form of an archived file +(e.g. tarball or zip file). These files correspond to individual +recipes. For example, the figure uses specific releases each for +BusyBox, Qt, and Dbus. An archive file can be for any released product +that can be built using a recipe. + +Local Projects +~~~~~~~~~~~~~~ + +Local projects are custom bits of software the user provides. These bits +reside somewhere local to a project - perhaps a directory into which the +user checks in items (e.g. a local directory containing a development +source tree used by the group). + +The canonical method through which to include a local project is to use +the :ref:`externalsrc <ref-classes-externalsrc>` +class to include that local project. You use either the ``local.conf`` +or a recipe's append file to override or set the recipe to point to the +local directory on your disk to pull in the whole source tree. + +.. _scms: + +Source Control Managers (Optional) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Another place from which the build system can get source files is with +:ref:`fetchers <bitbake:bb-fetchers>` employing various Source +Control Managers (SCMs) such as Git or Subversion. In such cases, a +repository is cloned or checked out. The +:ref:`ref-tasks-fetch` task inside +BitBake uses the :term:`SRC_URI` +variable and the argument's prefix to determine the correct fetcher +module. + +.. note:: + + For information on how to have the OpenEmbedded build system generate + tarballs for Git repositories and place them in the + DL_DIR + directory, see the :term:`BB_GENERATE_MIRROR_TARBALLS` + variable in the Yocto Project Reference Manual. + +When fetching a repository, BitBake uses the +:term:`SRCREV` variable to determine +the specific revision from which to build. + +Source Mirror(s) +~~~~~~~~~~~~~~~~ + +Two kinds of mirrors exist: pre-mirrors and regular mirrors. The +:term:`PREMIRRORS` and +:term:`MIRRORS` variables point to +these, respectively. BitBake checks pre-mirrors before looking upstream +for any source files. Pre-mirrors are appropriate when you have a shared +directory that is not a directory defined by the +:term:`DL_DIR` variable. A Pre-mirror +typically points to a shared directory that is local to your +organization. + +Regular mirrors can be any site across the Internet that is used as an +alternative location for source code should the primary site not be +functioning for some reason or another. + +.. _package-feeds-dev-environment: + +Package Feeds +------------- + +When the OpenEmbedded build system generates an image or an SDK, it gets +the packages from a package feed area located in the +:term:`Build Directory`. The `general +workflow figure <#general-workflow-figure>`__ shows this package feeds +area in the upper-right corner. + +This section looks a little closer into the package feeds area used by +the build system. Here is a more detailed look at the area: + +.. image:: figures/package-feeds.png + :align: center + +Package feeds are an intermediary step in the build process. The +OpenEmbedded build system provides classes to generate different package +types, and you specify which classes to enable through the +:term:`PACKAGE_CLASSES` +variable. Before placing the packages into package feeds, the build +process validates them with generated output quality assurance checks +through the :ref:`insane <ref-classes-insane>` +class. + +The package feed area resides in the Build Directory. The directory the +build system uses to temporarily store packages is determined by a +combination of variables and the particular package manager in use. See +the "Package Feeds" box in the illustration and note the information to +the right of that area. In particular, the following defines where +package files are kept: + +- :term:`DEPLOY_DIR`: Defined as + ``tmp/deploy`` in the Build Directory. + +- ``DEPLOY_DIR_*``: Depending on the package manager used, the package + type sub-folder. Given RPM, IPK, or DEB packaging and tarball + creation, the + :term:`DEPLOY_DIR_RPM`, + :term:`DEPLOY_DIR_IPK`, + :term:`DEPLOY_DIR_DEB`, or + :term:`DEPLOY_DIR_TAR`, + variables are used, respectively. + +- :term:`PACKAGE_ARCH`: Defines + architecture-specific sub-folders. For example, packages could exist + for the i586 or qemux86 architectures. + +BitBake uses the +:ref:`do_package_write_* <ref-tasks-package_write_deb>` +tasks to generate packages and place them into the package holding area +(e.g. ``do_package_write_ipk`` for IPK packages). See the +":ref:`ref-tasks-package_write_deb`", +":ref:`ref-tasks-package_write_ipk`", +":ref:`ref-tasks-package_write_rpm`", +and +":ref:`ref-tasks-package_write_tar`" +sections in the Yocto Project Reference Manual for additional +information. As an example, consider a scenario where an IPK packaging +manager is being used and package architecture support for both i586 and +qemux86 exist. Packages for the i586 architecture are placed in +``build/tmp/deploy/ipk/i586``, while packages for the qemux86 +architecture are placed in ``build/tmp/deploy/ipk/qemux86``. + +.. _bitbake-dev-environment: + +BitBake Tool +------------ + +The OpenEmbedded build system uses +:term:`BitBake` to produce images and +Software Development Kits (SDKs). You can see from the `general workflow +figure <#general-workflow-figure>`__, the BitBake area consists of +several functional areas. This section takes a closer look at each of +those areas. + +.. note:: + + Separate documentation exists for the BitBake tool. See the + BitBake User Manual + for reference material on BitBake. + +.. _source-fetching-dev-environment: + +Source Fetching +~~~~~~~~~~~~~~~ + +The first stages of building a recipe are to fetch and unpack the source +code: + +.. image:: figures/source-fetching.png + :align: center + +The :ref:`ref-tasks-fetch` and +:ref:`ref-tasks-unpack` tasks fetch +the source files and unpack them into the +:term:`Build Directory`. + +.. note:: + + For every local file (e.g. + file:// + ) that is part of a recipe's + SRC_URI + statement, the OpenEmbedded build system takes a checksum of the file + for the recipe and inserts the checksum into the signature for the + do_fetch + task. If any local file has been modified, the + do_fetch + task and all tasks that depend on it are re-executed. + +By default, everything is accomplished in the Build Directory, which has +a defined structure. For additional general information on the Build +Directory, see the ":ref:`structure-core-build`" section in +the Yocto Project Reference Manual. + +Each recipe has an area in the Build Directory where the unpacked source +code resides. The :term:`S` variable points +to this area for a recipe's unpacked source code. The name of that +directory for any given recipe is defined from several different +variables. The preceding figure and the following list describe the +Build Directory's hierarchy: + +- :term:`TMPDIR`: The base directory + where the OpenEmbedded build system performs all its work during the + build. The default base directory is the ``tmp`` directory. + +- :term:`PACKAGE_ARCH`: The + architecture of the built package or packages. Depending on the + eventual destination of the package or packages (i.e. machine + architecture, :term:`Build Host`, SDK, or + specific machine), ``PACKAGE_ARCH`` varies. See the variable's + description for details. + +- :term:`TARGET_OS`: The operating + system of the target device. A typical value would be "linux" (e.g. + "qemux86-poky-linux"). + +- :term:`PN`: The name of the recipe used + to build the package. This variable can have multiple meanings. + However, when used in the context of input files, ``PN`` represents + the name of the recipe. + +- :term:`WORKDIR`: The location + where the OpenEmbedded build system builds a recipe (i.e. does the + work to create the package). + + - :term:`PV`: The version of the + recipe used to build the package. + + - :term:`PR`: The revision of the + recipe used to build the package. + +- :term:`S`: Contains the unpacked source + files for a given recipe. + + - :term:`BPN`: The name of the recipe + used to build the package. The ``BPN`` variable is a version of + the ``PN`` variable but with common prefixes and suffixes removed. + + - :term:`PV`: The version of the + recipe used to build the package. + +.. note:: + + In the previous figure, notice that two sample hierarchies exist: one + based on package architecture (i.e. + PACKAGE_ARCH + ) and one based on a machine (i.e. + MACHINE + ). The underlying structures are identical. The differentiator being + what the OpenEmbedded build system is using as a build target (e.g. + general architecture, a build host, an SDK, or a specific machine). + +.. _patching-dev-environment: + +Patching +~~~~~~~~ + +Once source code is fetched and unpacked, BitBake locates patch files +and applies them to the source files: + +.. image:: figures/patching.png + :align: center + +The :ref:`ref-tasks-patch` task uses a +recipe's :term:`SRC_URI` statements +and the :term:`FILESPATH` variable +to locate applicable patch files. + +Default processing for patch files assumes the files have either +``*.patch`` or ``*.diff`` file types. You can use ``SRC_URI`` parameters +to change the way the build system recognizes patch files. See the +:ref:`ref-tasks-patch` task for more +information. + +BitBake finds and applies multiple patches for a single recipe in the +order in which it locates the patches. The ``FILESPATH`` variable +defines the default set of directories that the build system uses to +search for patch files. Once found, patches are applied to the recipe's +source files, which are located in the +:term:`S` directory. + +For more information on how the source directories are created, see the +"`Source Fetching <#source-fetching-dev-environment>`__" section. For +more information on how to create patches and how the build system +processes patches, see the +":ref:`dev-manual/dev-manual-common-tasks:patching code`" +section in the +Yocto Project Development Tasks Manual. You can also see the +":ref:`sdk-manual/sdk-extensible:use \`\`devtool modify\`\` to modify the source of an existing component`" +section in the Yocto Project Application Development and the Extensible +Software Development Kit (SDK) manual and the +":ref:`kernel-dev/kernel-dev-common:using traditional kernel development to patch the kernel`" +section in the Yocto Project Linux Kernel Development Manual. + +.. _configuration-compilation-and-staging-dev-environment: + +Configuration, Compilation, and Staging +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +After source code is patched, BitBake executes tasks that configure and +compile the source code. Once compilation occurs, the files are copied +to a holding area (staged) in preparation for packaging: + +.. image:: figures/configuration-compile-autoreconf.png + :align: center + +This step in the build process consists of the following tasks: + +- :ref:`ref-tasks-prepare_recipe_sysroot`: + This task sets up the two sysroots in + ``${``\ :term:`WORKDIR`\ ``}`` + (i.e. ``recipe-sysroot`` and ``recipe-sysroot-native``) so that + during the packaging phase the sysroots can contain the contents of + the + :ref:`ref-tasks-populate_sysroot` + tasks of the recipes on which the recipe containing the tasks + depends. A sysroot exists for both the target and for the native + binaries, which run on the host system. + +- *do_configure*: This task configures the source by enabling and + disabling any build-time and configuration options for the software + being built. Configurations can come from the recipe itself as well + as from an inherited class. Additionally, the software itself might + configure itself depending on the target for which it is being built. + + The configurations handled by the + :ref:`ref-tasks-configure` task + are specific to configurations for the source code being built by the + recipe. + + If you are using the + :ref:`autotools <ref-classes-autotools>` class, + you can add additional configuration options by using the + :term:`EXTRA_OECONF` or + :term:`PACKAGECONFIG_CONFARGS` + variables. For information on how this variable works within that + class, see the + :ref:`autotools <ref-classes-autotools>` class + :yocto_git:`here </cgit/cgit.cgi/poky/tree/meta/classes/autotools.bbclass>`. + +- *do_compile*: Once a configuration task has been satisfied, + BitBake compiles the source using the + :ref:`ref-tasks-compile` task. + Compilation occurs in the directory pointed to by the + :term:`B` variable. Realize that the + ``B`` directory is, by default, the same as the + :term:`S` directory. + +- *do_install*: After compilation completes, BitBake executes the + :ref:`ref-tasks-install` task. + This task copies files from the ``B`` directory and places them in a + holding area pointed to by the :term:`D` + variable. Packaging occurs later using files from this holding + directory. + +.. _package-splitting-dev-environment: + +Package Splitting +~~~~~~~~~~~~~~~~~ + +After source code is configured, compiled, and staged, the build system +analyzes the results and splits the output into packages: + +.. image:: figures/analysis-for-package-splitting.png + :align: center + +The :ref:`ref-tasks-package` and +:ref:`ref-tasks-packagedata` +tasks combine to analyze the files found in the +:term:`D` directory and split them into +subsets based on available packages and files. Analysis involves the +following as well as other items: splitting out debugging symbols, +looking at shared library dependencies between packages, and looking at +package relationships. + +The ``do_packagedata`` task creates package metadata based on the +analysis such that the build system can generate the final packages. The +:ref:`ref-tasks-populate_sysroot` +task stages (copies) a subset of the files installed by the +:ref:`ref-tasks-install` task into +the appropriate sysroot. Working, staged, and intermediate results of +the analysis and package splitting process use several areas: + +- :term:`PKGD`: The destination + directory (i.e. ``package``) for packages before they are split into + individual packages. + +- :term:`PKGDESTWORK`: A + temporary work area (i.e. ``pkgdata``) used by the ``do_package`` + task to save package metadata. + +- :term:`PKGDEST`: The parent + directory (i.e. ``packages-split``) for packages after they have been + split. + +- :term:`PKGDATA_DIR`: A shared, + global-state directory that holds packaging metadata generated during + the packaging process. The packaging process copies metadata from + ``PKGDESTWORK`` to the ``PKGDATA_DIR`` area where it becomes globally + available. + +- :term:`STAGING_DIR_HOST`: + The path for the sysroot for the system on which a component is built + to run (i.e. ``recipe-sysroot``). + +- :term:`STAGING_DIR_NATIVE`: + The path for the sysroot used when building components for the build + host (i.e. ``recipe-sysroot-native``). + +- :term:`STAGING_DIR_TARGET`: + The path for the sysroot used when a component that is built to + execute on a system and it generates code for yet another machine + (e.g. cross-canadian recipes). + +The :term:`FILES` variable defines the +files that go into each package in +:term:`PACKAGES`. If you want +details on how this is accomplished, you can look at +:yocto_git:`package.bbclass </cgit/cgit.cgi/poky/tree/meta/classes/package.bbclass>`. + +Depending on the type of packages being created (RPM, DEB, or IPK), the +:ref:`do_package_write_* <ref-tasks-package_write_deb>` +task creates the actual packages and places them in the Package Feed +area, which is ``${TMPDIR}/deploy``. You can see the "`Package +Feeds <#package-feeds-dev-environment>`__" section for more detail on +that part of the build process. + +.. note:: + + Support for creating feeds directly from the + deploy/\* + directories does not exist. Creating such feeds usually requires some + kind of feed maintenance mechanism that would upload the new packages + into an official package feed (e.g. the Ångström distribution). This + functionality is highly distribution-specific and thus is not + provided out of the box. + +.. _image-generation-dev-environment: + +Image Generation +~~~~~~~~~~~~~~~~ + +Once packages are split and stored in the Package Feeds area, the build +system uses BitBake to generate the root filesystem image: + +.. image:: figures/image-generation.png + :align: center + +The image generation process consists of several stages and depends on +several tasks and variables. The +:ref:`ref-tasks-rootfs` task creates +the root filesystem (file and directory structure) for an image. This +task uses several key variables to help create the list of packages to +actually install: + +- :term:`IMAGE_INSTALL`: Lists + out the base set of packages from which to install from the Package + Feeds area. + +- :term:`PACKAGE_EXCLUDE`: + Specifies packages that should not be installed into the image. + +- :term:`IMAGE_FEATURES`: + Specifies features to include in the image. Most of these features + map to additional packages for installation. + +- :term:`PACKAGE_CLASSES`: + Specifies the package backend (e.g. RPM, DEB, or IPK) to use and + consequently helps determine where to locate packages within the + Package Feeds area. + +- :term:`IMAGE_LINGUAS`: + Determines the language(s) for which additional language support + packages are installed. + +- :term:`PACKAGE_INSTALL`: + The final list of packages passed to the package manager for + installation into the image. + +With :term:`IMAGE_ROOTFS` +pointing to the location of the filesystem under construction and the +``PACKAGE_INSTALL`` variable providing the final list of packages to +install, the root file system is created. + +Package installation is under control of the package manager (e.g. +dnf/rpm, opkg, or apt/dpkg) regardless of whether or not package +management is enabled for the target. At the end of the process, if +package management is not enabled for the target, the package manager's +data files are deleted from the root filesystem. As part of the final +stage of package installation, post installation scripts that are part +of the packages are run. Any scripts that fail to run on the build host +are run on the target when the target system is first booted. If you are +using a +:ref:`read-only root filesystem <dev-manual/dev-manual-common-tasks:creating a read-only root filesystem>`, +all the post installation scripts must succeed on the build host during +the package installation phase since the root filesystem on the target +is read-only. + +The final stages of the ``do_rootfs`` task handle post processing. Post +processing includes creation of a manifest file and optimizations. + +The manifest file (``.manifest``) resides in the same directory as the +root filesystem image. This file lists out, line-by-line, the installed +packages. The manifest file is useful for the +:ref:`testimage <ref-classes-testimage*>` class, +for example, to determine whether or not to run specific tests. See the +:term:`IMAGE_MANIFEST` +variable for additional information. + +Optimizing processes that are run across the image include ``mklibs``, +``prelink``, and any other post-processing commands as defined by the +:term:`ROOTFS_POSTPROCESS_COMMAND` +variable. The ``mklibs`` process optimizes the size of the libraries, +while the ``prelink`` process optimizes the dynamic linking of shared +libraries to reduce start up time of executables. + +After the root filesystem is built, processing begins on the image +through the :ref:`ref-tasks-image` +task. The build system runs any pre-processing commands as defined by +the +:term:`IMAGE_PREPROCESS_COMMAND` +variable. This variable specifies a list of functions to call before the +build system creates the final image output files. + +The build system dynamically creates ``do_image_*`` tasks as needed, +based on the image types specified in the +:term:`IMAGE_FSTYPES` variable. +The process turns everything into an image file or a set of image files +and can compress the root filesystem image to reduce the overall size of +the image. The formats used for the root filesystem depend on the +``IMAGE_FSTYPES`` variable. Compression depends on whether the formats +support compression. + +As an example, a dynamically created task when creating a particular +image type would take the following form: +:: + + do_image_type + +So, if the type +as specified by the ``IMAGE_FSTYPES`` were ``ext4``, the dynamically +generated task would be as follows: +:: + + do_image_ext4 + +The final task involved in image creation is the +:ref:`do_image_complete <ref-tasks-image-complete>` +task. This task completes the image by applying any image post +processing as defined through the +:term:`IMAGE_POSTPROCESS_COMMAND` +variable. The variable specifies a list of functions to call once the +build system has created the final image output files. + +.. note:: + + The entire image generation process is run under + Pseudo. Running under Pseudo ensures that the files in the root filesystem + have correct ownership. + +.. _sdk-generation-dev-environment: + +SDK Generation +~~~~~~~~~~~~~~ + +The OpenEmbedded build system uses BitBake to generate the Software +Development Kit (SDK) installer scripts for both the standard SDK and +the extensible SDK (eSDK): + +.. image:: figures/sdk-generation.png + :align: center + +.. note:: + + For more information on the cross-development toolchain generation, + see the ":ref:`overview-manual/overview-manual-concepts:cross-development toolchain generation`" + section. For information on advantages gained when building a + cross-development toolchain using the do_populate_sdk task, see the + ":ref:`sdk-manual/sdk-appendix-obtain:building an sdk installer`" section in + the Yocto Project Application Development and the Extensible Software + Development Kit (eSDK) manual. + +Like image generation, the SDK script process consists of several stages +and depends on many variables. The +:ref:`ref-tasks-populate_sdk` +and +:ref:`ref-tasks-populate_sdk_ext` +tasks use these key variables to help create the list of packages to +actually install. For information on the variables listed in the figure, +see the "`Application Development SDK <#sdk-dev-environment>`__" +section. + +The ``do_populate_sdk`` task helps create the standard SDK and handles +two parts: a target part and a host part. The target part is the part +built for the target hardware and includes libraries and headers. The +host part is the part of the SDK that runs on the +:term:`SDKMACHINE`. + +The ``do_populate_sdk_ext`` task helps create the extensible SDK and +handles host and target parts differently than its counter part does for +the standard SDK. For the extensible SDK, the task encapsulates the +build system, which includes everything needed (host and target) for the +SDK. + +Regardless of the type of SDK being constructed, the tasks perform some +cleanup after which a cross-development environment setup script and any +needed configuration files are created. The final output is the +Cross-development toolchain installation script (``.sh`` file), which +includes the environment setup script. + +Stamp Files and the Rerunning of Tasks +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +For each task that completes successfully, BitBake writes a stamp file +into the :term:`STAMPS_DIR` +directory. The beginning of the stamp file's filename is determined by +the :term:`STAMP` variable, and the end +of the name consists of the task's name and current `input +checksum <#overview-checksums>`__. + +.. note:: + + This naming scheme assumes that + BB_SIGNATURE_HANDLER + is "OEBasicHash", which is almost always the case in current + OpenEmbedded. + +To determine if a task needs to be rerun, BitBake checks if a stamp file +with a matching input checksum exists for the task. If such a stamp file +exists, the task's output is assumed to exist and still be valid. If the +file does not exist, the task is rerun. + +.. note:: + + The stamp mechanism is more general than the shared state (sstate) + cache mechanism described in the "`Setscene Tasks and Shared + State <#setscene-tasks-and-shared-state>`__" section. BitBake avoids + rerunning any task that has a valid stamp file, not just tasks that + can be accelerated through the sstate cache. + + However, you should realize that stamp files only serve as a marker + that some work has been done and that these files do not record task + output. The actual task output would usually be somewhere in + :term:`TMPDIR` (e.g. in some + recipe's :term:`WORKDIR`.) What + the sstate cache mechanism adds is a way to cache task output that + can then be shared between build machines. + +Since ``STAMPS_DIR`` is usually a subdirectory of ``TMPDIR``, removing +``TMPDIR`` will also remove ``STAMPS_DIR``, which means tasks will +properly be rerun to repopulate ``TMPDIR``. + +If you want some task to always be considered "out of date", you can +mark it with the :ref:`nostamp <bitbake:bitbake-user-manual/bitbake-user-manual-metadata:variable flags>` +varflag. If some other task depends on such a task, then that task will +also always be considered out of date, which might not be what you want. + +For details on how to view information about a task's signature, see the +":ref:`dev-manual/dev-manual-common-tasks:viewing task variable dependencies`" +section in the Yocto Project Development Tasks Manual. + +Setscene Tasks and Shared State +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The description of tasks so far assumes that BitBake needs to build +everything and no available prebuilt objects exist. BitBake does support +skipping tasks if prebuilt objects are available. These objects are +usually made available in the form of a shared state (sstate) cache. + +.. note:: + + For information on variables affecting sstate, see the + :term:`SSTATE_DIR` + and + :term:`SSTATE_MIRRORS` + variables. + +The idea of a setscene task (i.e ``do_``\ taskname\ ``_setscene``) is a +version of the task where instead of building something, BitBake can +skip to the end result and simply place a set of files into specific +locations as needed. In some cases, it makes sense to have a setscene +task variant (e.g. generating package files in the +:ref:`do_package_write_* <ref-tasks-package_write_deb>` +task). In other cases, it does not make sense (e.g. a +:ref:`ref-tasks-patch` task or a +:ref:`ref-tasks-unpack` task) since +the work involved would be equal to or greater than the underlying task. + +In the build system, the common tasks that have setscene variants are +:ref:`ref-tasks-package`, +``do_package_write_*``, +:ref:`ref-tasks-deploy`, +:ref:`ref-tasks-packagedata`, and +:ref:`ref-tasks-populate_sysroot`. +Notice that these tasks represent most of the tasks whose output is an +end result. + +The build system has knowledge of the relationship between these tasks +and other preceding tasks. For example, if BitBake runs +``do_populate_sysroot_setscene`` for something, it does not make sense +to run any of the ``do_fetch``, ``do_unpack``, ``do_patch``, +``do_configure``, ``do_compile``, and ``do_install`` tasks. However, if +``do_package`` needs to be run, BitBake needs to run those other tasks. + +It becomes more complicated if everything can come from an sstate cache +because some objects are simply not required at all. For example, you do +not need a compiler or native tools, such as quilt, if nothing exists to +compile or patch. If the ``do_package_write_*`` packages are available +from sstate, BitBake does not need the ``do_package`` task data. + +To handle all these complexities, BitBake runs in two phases. The first +is the "setscene" stage. During this stage, BitBake first checks the +sstate cache for any targets it is planning to build. BitBake does a +fast check to see if the object exists rather than a complete download. +If nothing exists, the second phase, which is the setscene stage, +completes and the main build proceeds. + +If objects are found in the sstate cache, the build system works +backwards from the end targets specified by the user. For example, if an +image is being built, the build system first looks for the packages +needed for that image and the tools needed to construct an image. If +those are available, the compiler is not needed. Thus, the compiler is +not even downloaded. If something was found to be unavailable, or the +download or setscene task fails, the build system then tries to install +dependencies, such as the compiler, from the cache. + +The availability of objects in the sstate cache is handled by the +function specified by the +:term:`bitbake:BB_HASHCHECK_FUNCTION` +variable and returns a list of available objects. The function specified +by the +:term:`bitbake:BB_SETSCENE_DEPVALID` +variable is the function that determines whether a given dependency +needs to be followed, and whether for any given relationship the +function needs to be passed. The function returns a True or False value. + +.. _images-dev-environment: + +Images +------ + +The images produced by the build system are compressed forms of the root +filesystem and are ready to boot on a target device. You can see from +the `general workflow figure <#general-workflow-figure>`__ that BitBake +output, in part, consists of images. This section takes a closer look at +this output: + +.. image:: figures/images.png + :align: center + +.. note:: + + For a list of example images that the Yocto Project provides, see the + ":doc:`../ref-manual/ref-images`" chapter in the Yocto Project Reference + Manual. + +The build process writes images out to the :term:`Build Directory` +inside the +``tmp/deploy/images/machine/`` folder as shown in the figure. This +folder contains any files expected to be loaded on the target device. +The :term:`DEPLOY_DIR` variable +points to the ``deploy`` directory, while the +:term:`DEPLOY_DIR_IMAGE` +variable points to the appropriate directory containing images for the +current configuration. + +- kernel-image: A kernel binary file. The + :term:`KERNEL_IMAGETYPE` + variable determines the naming scheme for the kernel image file. + Depending on this variable, the file could begin with a variety of + naming strings. The ``deploy/images/``\ machine directory can contain + multiple image files for the machine. + +- root-filesystem-image: Root filesystems for the target device (e.g. + ``*.ext3`` or ``*.bz2`` files). The + :term:`IMAGE_FSTYPES` + variable determines the root filesystem image type. The + ``deploy/images/``\ machine directory can contain multiple root + filesystems for the machine. + +- kernel-modules: Tarballs that contain all the modules built for the + kernel. Kernel module tarballs exist for legacy purposes and can be + suppressed by setting the + :term:`MODULE_TARBALL_DEPLOY` + variable to "0". The ``deploy/images/``\ machine directory can + contain multiple kernel module tarballs for the machine. + +- bootloaders: If applicable to the target machine, bootloaders + supporting the image. The ``deploy/images/``\ machine directory can + contain multiple bootloaders for the machine. + +- symlinks: The ``deploy/images/``\ machine folder contains a symbolic + link that points to the most recently built file for each machine. + These links might be useful for external scripts that need to obtain + the latest version of each file. + +.. _sdk-dev-environment: + +Application Development SDK +--------------------------- + +In the `general workflow figure <#general-workflow-figure>`__, the +output labeled "Application Development SDK" represents an SDK. The SDK +generation process differs depending on whether you build an extensible +SDK (e.g. ``bitbake -c populate_sdk_ext`` imagename) or a standard SDK +(e.g. ``bitbake -c populate_sdk`` imagename). This section takes a +closer look at this output: + +.. image:: figures/sdk.png + :align: center + +The specific form of this output is a set of files that includes a +self-extracting SDK installer (``*.sh``), host and target manifest +files, and files used for SDK testing. When the SDK installer file is +run, it installs the SDK. The SDK consists of a cross-development +toolchain, a set of libraries and headers, and an SDK environment setup +script. Running this installer essentially sets up your +cross-development environment. You can think of the cross-toolchain as +the "host" part because it runs on the SDK machine. You can think of the +libraries and headers as the "target" part because they are built for +the target hardware. The environment setup script is added so that you +can initialize the environment before using the tools. + +.. note:: + + - The Yocto Project supports several methods by which you can set up + this cross-development environment. These methods include + downloading pre-built SDK installers or building and installing + your own SDK installer. + + - For background information on cross-development toolchains in the + Yocto Project development environment, see the "`Cross-Development + Toolchain Generation <#cross-development-toolchain-generation>`__" + section. + + - For information on setting up a cross-development environment, see + the :doc:`../sdk-manual/sdk-manual` manual. + +All the output files for an SDK are written to the ``deploy/sdk`` folder +inside the :term:`Build Directory` as +shown in the previous figure. Depending on the type of SDK, several +variables exist that help configure these files. The following list +shows the variables associated with an extensible SDK: + +- :term:`DEPLOY_DIR`: Points to + the ``deploy`` directory. + +- :term:`SDK_EXT_TYPE`: + Controls whether or not shared state artifacts are copied into the + extensible SDK. By default, all required shared state artifacts are + copied into the SDK. + +- :term:`SDK_INCLUDE_PKGDATA`: + Specifies whether or not packagedata is included in the extensible + SDK for all recipes in the "world" target. + +- :term:`SDK_INCLUDE_TOOLCHAIN`: + Specifies whether or not the toolchain is included when building the + extensible SDK. + +- :term:`SDK_LOCAL_CONF_WHITELIST`: + A list of variables allowed through from the build system + configuration into the extensible SDK configuration. + +- :term:`SDK_LOCAL_CONF_BLACKLIST`: + A list of variables not allowed through from the build system + configuration into the extensible SDK configuration. + +- :term:`SDK_INHERIT_BLACKLIST`: + A list of classes to remove from the + :term:`INHERIT` value globally + within the extensible SDK configuration. + +This next list, shows the variables associated with a standard SDK: + +- :term:`DEPLOY_DIR`: Points to + the ``deploy`` directory. + +- :term:`SDKMACHINE`: Specifies + the architecture of the machine on which the cross-development tools + are run to create packages for the target hardware. + +- :term:`SDKIMAGE_FEATURES`: + Lists the features to include in the "target" part of the SDK. + +- :term:`TOOLCHAIN_HOST_TASK`: + Lists packages that make up the host part of the SDK (i.e. the part + that runs on the ``SDKMACHINE``). When you use + ``bitbake -c populate_sdk imagename`` to create the SDK, a set of + default packages apply. This variable allows you to add more + packages. + +- :term:`TOOLCHAIN_TARGET_TASK`: + Lists packages that make up the target part of the SDK (i.e. the part + built for the target hardware). + +- :term:`SDKPATH`: Defines the + default SDK installation path offered by the installation script. + +- :term:`SDK_HOST_MANIFEST`: + Lists all the installed packages that make up the host part of the + SDK. This variable also plays a minor role for extensible SDK + development as well. However, it is mainly used for the standard SDK. + +- :term:`SDK_TARGET_MANIFEST`: + Lists all the installed packages that make up the target part of the + SDK. This variable also plays a minor role for extensible SDK + development as well. However, it is mainly used for the standard SDK. + +Cross-Development Toolchain Generation +====================================== + +The Yocto Project does most of the work for you when it comes to +creating :ref:`sdk-manual/sdk-intro:the cross-development toolchain`. This +section provides some technical background on how cross-development +toolchains are created and used. For more information on toolchains, you +can also see the :doc:`../sdk-manual/sdk-manual` manual. + +In the Yocto Project development environment, cross-development +toolchains are used to build images and applications that run on the +target hardware. With just a few commands, the OpenEmbedded build system +creates these necessary toolchains for you. + +The following figure shows a high-level build environment regarding +toolchain construction and use. + +.. image:: figures/cross-development-toolchains.png + :align: center + +Most of the work occurs on the Build Host. This is the machine used to +build images and generally work within the the Yocto Project +environment. When you run +:term:`BitBake` to create an image, the +OpenEmbedded build system uses the host ``gcc`` compiler to bootstrap a +cross-compiler named ``gcc-cross``. The ``gcc-cross`` compiler is what +BitBake uses to compile source files when creating the target image. You +can think of ``gcc-cross`` simply as an automatically generated +cross-compiler that is used internally within BitBake only. + +.. note:: + + The extensible SDK does not use + gcc-cross-canadian + since this SDK ships a copy of the OpenEmbedded build system and the + sysroot within it contains + gcc-cross + . + +The chain of events that occurs when ``gcc-cross`` is bootstrapped is as +follows: +:: + + gcc -> binutils-cross -> gcc-cross-initial -> linux-libc-headers -> glibc-initial -> glibc -> gcc-cross -> gcc-runtime + +- ``gcc``: The build host's GNU Compiler Collection (GCC). + +- ``binutils-cross``: The bare minimum binary utilities needed in order + to run the ``gcc-cross-initial`` phase of the bootstrap operation. + +- ``gcc-cross-initial``: An early stage of the bootstrap process for + creating the cross-compiler. This stage builds enough of the + ``gcc-cross``, the C library, and other pieces needed to finish + building the final cross-compiler in later stages. This tool is a + "native" package (i.e. it is designed to run on the build host). + +- ``linux-libc-headers``: Headers needed for the cross-compiler. + +- ``glibc-initial``: An initial version of the Embedded GNU C Library + (GLIBC) needed to bootstrap ``glibc``. + +- ``glibc``: The GNU C Library. + +- ``gcc-cross``: The final stage of the bootstrap process for the + cross-compiler. This stage results in the actual cross-compiler that + BitBake uses when it builds an image for a targeted device. + + .. note:: + + If you are replacing this cross compiler toolchain with a custom + version, you must replace + gcc-cross + . + + This tool is also a "native" package (i.e. it is designed to run on + the build host). + +- ``gcc-runtime``: Runtime libraries resulting from the toolchain + bootstrapping process. This tool produces a binary that consists of + the runtime libraries need for the targeted device. + +You can use the OpenEmbedded build system to build an installer for the +relocatable SDK used to develop applications. When you run the +installer, it installs the toolchain, which contains the development +tools (e.g., ``gcc-cross-canadian``, ``binutils-cross-canadian``, and +other ``nativesdk-*`` tools), which are tools native to the SDK (i.e. +native to :term:`SDK_ARCH`), you +need to cross-compile and test your software. The figure shows the +commands you use to easily build out this toolchain. This +cross-development toolchain is built to execute on the +:term:`SDKMACHINE`, which might or +might not be the same machine as the Build Host. + +.. note:: + + If your target architecture is supported by the Yocto Project, you + can take advantage of pre-built images that ship with the Yocto + Project and already contain cross-development toolchain installers. + +Here is the bootstrap process for the relocatable toolchain: +:: + + gcc -> binutils-crosssdk -> gcc-crosssdk-initial -> linux-libc-headers -> glibc-initial -> nativesdk-glibc -> gcc-crosssdk -> gcc-cross-canadian + +- ``gcc``: The build host's GNU Compiler Collection (GCC). + +- ``binutils-crosssdk``: The bare minimum binary utilities needed in + order to run the ``gcc-crosssdk-initial`` phase of the bootstrap + operation. + +- ``gcc-crosssdk-initial``: An early stage of the bootstrap process for + creating the cross-compiler. This stage builds enough of the + ``gcc-crosssdk`` and supporting pieces so that the final stage of the + bootstrap process can produce the finished cross-compiler. This tool + is a "native" binary that runs on the build host. + +- ``linux-libc-headers``: Headers needed for the cross-compiler. + +- ``glibc-initial``: An initial version of the Embedded GLIBC needed to + bootstrap ``nativesdk-glibc``. + +- ``nativesdk-glibc``: The Embedded GLIBC needed to bootstrap the + ``gcc-crosssdk``. + +- ``gcc-crosssdk``: The final stage of the bootstrap process for the + relocatable cross-compiler. The ``gcc-crosssdk`` is a transitory + compiler and never leaves the build host. Its purpose is to help in + the bootstrap process to create the eventual ``gcc-cross-canadian`` + compiler, which is relocatable. This tool is also a "native" package + (i.e. it is designed to run on the build host). + +- ``gcc-cross-canadian``: The final relocatable cross-compiler. When + run on the :term:`SDKMACHINE`, + this tool produces executable code that runs on the target device. + Only one cross-canadian compiler is produced per architecture since + they can be targeted at different processor optimizations using + configurations passed to the compiler through the compile commands. + This circumvents the need for multiple compilers and thus reduces the + size of the toolchains. + +.. note:: + + For information on advantages gained when building a + cross-development toolchain installer, see the + ":ref:`sdk-manual/sdk-appendix-obtain:building an sdk installer`" appendix + in the Yocto Project Application Development and the + Extensible Software Development Kit (eSDK) manual. + +Shared State Cache +================== + +By design, the OpenEmbedded build system builds everything from scratch +unless :term:`BitBake` can determine +that parts do not need to be rebuilt. Fundamentally, building from +scratch is attractive as it means all parts are built fresh and no +possibility of stale data exists that can cause problems. When +developers hit problems, they typically default back to building from +scratch so they have a know state from the start. + +Building an image from scratch is both an advantage and a disadvantage +to the process. As mentioned in the previous paragraph, building from +scratch ensures that everything is current and starts from a known +state. However, building from scratch also takes much longer as it +generally means rebuilding things that do not necessarily need to be +rebuilt. + +The Yocto Project implements shared state code that supports incremental +builds. The implementation of the shared state code answers the +following questions that were fundamental roadblocks within the +OpenEmbedded incremental build support system: + +- What pieces of the system have changed and what pieces have not + changed? + +- How are changed pieces of software removed and replaced? + +- How are pre-built components that do not need to be rebuilt from + scratch used when they are available? + +For the first question, the build system detects changes in the "inputs" +to a given task by creating a checksum (or signature) of the task's +inputs. If the checksum changes, the system assumes the inputs have +changed and the task needs to be rerun. For the second question, the +shared state (sstate) code tracks which tasks add which output to the +build process. This means the output from a given task can be removed, +upgraded or otherwise manipulated. The third question is partly +addressed by the solution for the second question assuming the build +system can fetch the sstate objects from remote locations and install +them if they are deemed to be valid. + +.. note:: + + - The build system does not maintain + :term:`PR` information as part of + the shared state packages. Consequently, considerations exist that + affect maintaining shared state feeds. For information on how the + build system works with packages and can track incrementing ``PR`` + information, see the ":ref:`dev-manual/dev-manual-common-tasks:automatically incrementing a package version number`" + section in the Yocto Project Development Tasks Manual. + + - The code in the build system that supports incremental builds is + not simple code. For techniques that help you work around issues + related to shared state code, see the + ":ref:`dev-manual/dev-manual-common-tasks:viewing metadata used to create the input signature of a shared state task`" + and + ":ref:`dev-manual/dev-manual-common-tasks:invalidating shared state to force a task to run`" + sections both in the Yocto Project Development Tasks Manual. + +The rest of this section goes into detail about the overall incremental +build architecture, the checksums (signatures), and shared state. + +.. _concepts-overall-architecture: + +Overall Architecture +-------------------- + +When determining what parts of the system need to be built, BitBake +works on a per-task basis rather than a per-recipe basis. You might +wonder why using a per-task basis is preferred over a per-recipe basis. +To help explain, consider having the IPK packaging backend enabled and +then switching to DEB. In this case, the +:ref:`ref-tasks-install` and +:ref:`ref-tasks-package` task outputs +are still valid. However, with a per-recipe approach, the build would +not include the ``.deb`` files. Consequently, you would have to +invalidate the whole build and rerun it. Rerunning everything is not the +best solution. Also, in this case, the core must be "taught" much about +specific tasks. This methodology does not scale well and does not allow +users to easily add new tasks in layers or as external recipes without +touching the packaged-staging core. + +.. _overview-checksums: + +Checksums (Signatures) +---------------------- + +The shared state code uses a checksum, which is a unique signature of a +task's inputs, to determine if a task needs to be run again. Because it +is a change in a task's inputs that triggers a rerun, the process needs +to detect all the inputs to a given task. For shell tasks, this turns +out to be fairly easy because the build process generates a "run" shell +script for each task and it is possible to create a checksum that gives +you a good idea of when the task's data changes. + +To complicate the problem, there are things that should not be included +in the checksum. First, there is the actual specific build path of a +given task - the :term:`WORKDIR`. It +does not matter if the work directory changes because it should not +affect the output for target packages. Also, the build process has the +objective of making native or cross packages relocatable. + +.. note:: + + Both native and cross packages run on the + build host. However, cross packages generate output for the target + architecture. + +The checksum therefore needs to exclude ``WORKDIR``. The simplistic +approach for excluding the work directory is to set ``WORKDIR`` to some +fixed value and create the checksum for the "run" script. + +Another problem results from the "run" scripts containing functions that +might or might not get called. The incremental build solution contains +code that figures out dependencies between shell functions. This code is +used to prune the "run" scripts down to the minimum set, thereby +alleviating this problem and making the "run" scripts much more readable +as a bonus. + +So far, solutions for shell scripts exist. What about Python tasks? The +same approach applies even though these tasks are more difficult. The +process needs to figure out what variables a Python function accesses +and what functions it calls. Again, the incremental build solution +contains code that first figures out the variable and function +dependencies, and then creates a checksum for the data used as the input +to the task. + +Like the ``WORKDIR`` case, situations exist where dependencies should be +ignored. For these situations, you can instruct the build process to +ignore a dependency by using a line like the following: +:: + + PACKAGE_ARCHS[vardepsexclude] = "MACHINE" + +This example ensures that the :term:`PACKAGE_ARCHS` variable +does not depend on the value of :term:`MACHINE`, even if it does +reference it. + +Equally, there are cases where you need to add dependencies BitBake is +not able to find. You can accomplish this by using a line like the +following: +:: + + PACKAGE_ARCHS[vardeps] = "MACHINE" + +This example explicitly +adds the ``MACHINE`` variable as a dependency for ``PACKAGE_ARCHS``. + +As an example, consider a case with in-line Python where BitBake is not +able to figure out dependencies. When running in debug mode (i.e. using +``-DDD``), BitBake produces output when it discovers something for which +it cannot figure out dependencies. The Yocto Project team has currently +not managed to cover those dependencies in detail and is aware of the +need to fix this situation. + +Thus far, this section has limited discussion to the direct inputs into +a task. Information based on direct inputs is referred to as the +"basehash" in the code. However, the question of a task's indirect +inputs still exits - items already built and present in the +:term:`Build Directory`. The checksum (or +signature) for a particular task needs to add the hashes of all the +tasks on which the particular task depends. Choosing which dependencies +to add is a policy decision. However, the effect is to generate a master +checksum that combines the basehash and the hashes of the task's +dependencies. + +At the code level, a variety of ways exist by which both the basehash +and the dependent task hashes can be influenced. Within the BitBake +configuration file, you can give BitBake some extra information to help +it construct the basehash. The following statement effectively results +in a list of global variable dependency excludes (i.e. variables never +included in any checksum): +:: + + BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \\ + SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \\ + USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \\ + PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \\ + CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX" + +The +previous example excludes +:term:`WORKDIR` since that variable +is actually constructed as a path within +:term:`TMPDIR`, which is on the +whitelist. + +The rules for deciding which hashes of dependent tasks to include +through dependency chains are more complex and are generally +accomplished with a Python function. The code in +``meta/lib/oe/sstatesig.py`` shows two examples of this and also +illustrates how you can insert your own policy into the system if so +desired. This file defines the two basic signature generators +:term:`OpenEmbedded-Core (OE-Core)` uses: "OEBasic" and +"OEBasicHash". By default, a dummy "noop" signature handler is enabled +in BitBake. This means that behavior is unchanged from previous +versions. OE-Core uses the "OEBasicHash" signature handler by default +through this setting in the ``bitbake.conf`` file: +:: + + BB_SIGNATURE_HANDLER ?= "OEBasicHash" + +The "OEBasicHash" ``BB_SIGNATURE_HANDLER`` is the same +as the "OEBasic" version but adds the task hash to the `stamp +files <#stamp-files-and-the-rerunning-of-tasks>`__. This results in any +metadata change that changes the task hash, automatically causing the +task to be run again. This removes the need to bump +:term:`PR` values, and changes to metadata +automatically ripple across the build. + +It is also worth noting that the end result of these signature +generators is to make some dependency and hash information available to +the build. This information includes: + +- ``BB_BASEHASH_task-``\ taskname: The base hashes for each task in the + recipe. + +- ``BB_BASEHASH_``\ filename\ ``:``\ taskname: The base hashes for each + dependent task. + +- ``BBHASHDEPS_``\ filename\ ``:``\ taskname: The task dependencies for + each task. + +- ``BB_TASKHASH``: The hash of the currently running task. + +Shared State +------------ + +Checksums and dependencies, as discussed in the previous section, solve +half the problem of supporting a shared state. The other half of the +problem is being able to use checksum information during the build and +being able to reuse or rebuild specific components. + +The :ref:`sstate <ref-classes-sstate>` class is a +relatively generic implementation of how to "capture" a snapshot of a +given task. The idea is that the build process does not care about the +source of a task's output. Output could be freshly built or it could be +downloaded and unpacked from somewhere. In other words, the build +process does not need to worry about its origin. + +Two types of output exist. One type is just about creating a directory +in :term:`WORKDIR`. A good example is +the output of either +:ref:`ref-tasks-install` or +:ref:`ref-tasks-package`. The other +type of output occurs when a set of data is merged into a shared +directory tree such as the sysroot. + +The Yocto Project team has tried to keep the details of the +implementation hidden in ``sstate`` class. From a user's perspective, +adding shared state wrapping to a task is as simple as this +:ref:`ref-tasks-deploy` example taken +from the :ref:`deploy <ref-classes-deploy>` class: +:: + + DEPLOYDIR = "${WORKDIR}/deploy-${PN}" + SSTATETASKS += "do_deploy" + do_deploy[sstate-inputdirs] = "${DEPLOYDIR}" + do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}" + + python do_deploy_setscene () { + sstate_setscene(d) + } + addtask do_deploy_setscene + do_deploy[dirs] = "${DEPLOYDIR} ${B}" + do_deploy[stamp-extra-info] = "${MACHINE_ARCH}" + +The following list explains the previous example: + +- Adding "do_deploy" to ``SSTATETASKS`` adds some required + sstate-related processing, which is implemented in the + :ref:`sstate <ref-classes-sstate>` class, to + before and after the + :ref:`ref-tasks-deploy` task. + +- The ``do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"`` declares that + ``do_deploy`` places its output in ``${DEPLOYDIR}`` when run normally + (i.e. when not using the sstate cache). This output becomes the input + to the shared state cache. + +- The ``do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"`` line + causes the contents of the shared state cache to be copied to + ``${DEPLOY_DIR_IMAGE}``. + + .. note:: + + If ``do_deploy`` is not already in the shared state cache or if its input + checksum (signature) has changed from when the output was cached, the task + runs to populate the shared state cache, after which the contents of the + shared state cache is copied to ${:term:`DEPLOY_DIR_IMAGE`}. If + ``do_deploy`` is in the shared state cache and its signature indicates + that the cached output is still valid (i.e. if no relevant task inputs + have changed), then the contents of the shared state cache copies + directly to ${``DEPLOY_DIR_IMAGE``} by the ``do_deploy_setscene`` task + instead, skipping the ``do_deploy`` task. + +- The following task definition is glue logic needed to make the + previous settings effective: + :: + + python do_deploy_setscene () { + sstate_setscene(d) + } + addtask do_deploy_setscene + + ``sstate_setscene()`` takes the flags above as input and accelerates the ``do_deploy`` task + through the shared state cache if possible. If the task was + accelerated, ``sstate_setscene()`` returns True. Otherwise, it + returns False, and the normal ``do_deploy`` task runs. For more + information, see the ":ref:`setscene <bitbake:bitbake-user-manual/bitbake-user-manual-execution:setscene>`" + section in the BitBake User Manual. + +- The ``do_deploy[dirs] = "${DEPLOYDIR} ${B}"`` line creates + ``${DEPLOYDIR}`` and ``${B}`` before the ``do_deploy`` task runs, and + also sets the current working directory of ``do_deploy`` to ``${B}``. + For more information, see the ":ref:`bitbake:bitbake-user-manual/bitbake-user-manual-metadata:variable flags`" + section in the BitBake + User Manual. + + .. note:: + + In cases where ``sstate-inputdirs`` and ``sstate-outputdirs`` would be + the same, you can use ``sstate-plaindirs``. For example, to preserve the + ${:term:`PKGD`} and ${:term:`PKGDEST`} output from the ``do_package`` + task, use the following: + :: + + do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}" + + +- The ``do_deploy[stamp-extra-info] = "${MACHINE_ARCH}"`` line appends + extra metadata to the `stamp + file <#stamp-files-and-the-rerunning-of-tasks>`__. In this case, the + metadata makes the task specific to a machine's architecture. See + ":ref:`bitbake:ref-bitbake-tasklist`" + section in the BitBake User Manual for more information on the + ``stamp-extra-info`` flag. + +- ``sstate-inputdirs`` and ``sstate-outputdirs`` can also be used with + multiple directories. For example, the following declares + ``PKGDESTWORK`` and ``SHLIBWORK`` as shared state input directories, + which populates the shared state cache, and ``PKGDATA_DIR`` and + ``SHLIBSDIR`` as the corresponding shared state output directories: + :: + + do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}" + do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}" + +- These methods also include the ability to take a lockfile when + manipulating shared state directory structures, for cases where file + additions or removals are sensitive: + :: + + do_package[sstate-lockfile] = "${PACKAGELOCK}" + +Behind the scenes, the shared state code works by looking in +:term:`SSTATE_DIR` and +:term:`SSTATE_MIRRORS` for +shared state files. Here is an example: +:: + + SSTATE_MIRRORS ?= "\ + file://.\* http://someserver.tld/share/sstate/PATH;downloadfilename=PATH \n \ + file://.\* file:///some/local/dir/sstate/PATH" + +.. note:: + + The shared state directory (``SSTATE_DIR``) is organized into two-character + subdirectories, where the subdirectory names are based on the first two + characters of the hash. + If the shared state directory structure for a mirror has the same structure + as ``SSTATE_DIR``, you must specify "PATH" as part of the URI to enable the build + system to map to the appropriate subdirectory. + +The shared state package validity can be detected just by looking at the +filename since the filename contains the task checksum (or signature) as +described earlier in this section. If a valid shared state package is +found, the build process downloads it and uses it to accelerate the +task. + +The build processes use the ``*_setscene`` tasks for the task +acceleration phase. BitBake goes through this phase before the main +execution code and tries to accelerate any tasks for which it can find +shared state packages. If a shared state package for a task is +available, the shared state package is used. This means the task and any +tasks on which it is dependent are not executed. + +As a real world example, the aim is when building an IPK-based image, +only the +:ref:`ref-tasks-package_write_ipk` +tasks would have their shared state packages fetched and extracted. +Since the sysroot is not used, it would never get extracted. This is +another reason why a task-based approach is preferred over a +recipe-based approach, which would have to install the output from every +task. + +Automatically Added Runtime Dependencies +======================================== + +The OpenEmbedded build system automatically adds common types of runtime +dependencies between packages, which means that you do not need to +explicitly declare the packages using +:term:`RDEPENDS`. Three automatic +mechanisms exist (``shlibdeps``, ``pcdeps``, and ``depchains``) that +handle shared libraries, package configuration (pkg-config) modules, and +``-dev`` and ``-dbg`` packages, respectively. For other types of runtime +dependencies, you must manually declare the dependencies. + +- ``shlibdeps``: During the + :ref:`ref-tasks-package` task of + each recipe, all shared libraries installed by the recipe are + located. For each shared library, the package that contains the + shared library is registered as providing the shared library. More + specifically, the package is registered as providing the + `soname <https://en.wikipedia.org/wiki/Soname>`__ of the library. The + resulting shared-library-to-package mapping is saved globally in + :term:`PKGDATA_DIR` by the + :ref:`ref-tasks-packagedata` + task. + + Simultaneously, all executables and shared libraries installed by the + recipe are inspected to see what shared libraries they link against. + For each shared library dependency that is found, ``PKGDATA_DIR`` is + queried to see if some package (likely from a different recipe) + contains the shared library. If such a package is found, a runtime + dependency is added from the package that depends on the shared + library to the package that contains the library. + + The automatically added runtime dependency also includes a version + restriction. This version restriction specifies that at least the + current version of the package that provides the shared library must + be used, as if "package (>= version)" had been added to ``RDEPENDS``. + This forces an upgrade of the package containing the shared library + when installing the package that depends on the library, if needed. + + If you want to avoid a package being registered as providing a + particular shared library (e.g. because the library is for internal + use only), then add the library to + :term:`PRIVATE_LIBS` inside + the package's recipe. + +- ``pcdeps``: During the ``do_package`` task of each recipe, all + pkg-config modules (``*.pc`` files) installed by the recipe are + located. For each module, the package that contains the module is + registered as providing the module. The resulting module-to-package + mapping is saved globally in ``PKGDATA_DIR`` by the + ``do_packagedata`` task. + + Simultaneously, all pkg-config modules installed by the recipe are + inspected to see what other pkg-config modules they depend on. A + module is seen as depending on another module if it contains a + "Requires:" line that specifies the other module. For each module + dependency, ``PKGDATA_DIR`` is queried to see if some package + contains the module. If such a package is found, a runtime dependency + is added from the package that depends on the module to the package + that contains the module. + + .. note:: + + The + pcdeps + mechanism most often infers dependencies between + -dev + packages. + +- ``depchains``: If a package ``foo`` depends on a package ``bar``, + then ``foo-dev`` and ``foo-dbg`` are also made to depend on + ``bar-dev`` and ``bar-dbg``, respectively. Taking the ``-dev`` + packages as an example, the ``bar-dev`` package might provide headers + and shared library symlinks needed by ``foo-dev``, which shows the + need for a dependency between the packages. + + The dependencies added by ``depchains`` are in the form of + :term:`RRECOMMENDS`. + + .. note:: + + By default, ``foo-dev`` also has an ``RDEPENDS``-style dependency on + ``foo``, because the default value of ``RDEPENDS_${PN}-dev`` (set in + bitbake.conf) includes "${PN}". + + To ensure that the dependency chain is never broken, ``-dev`` and + ``-dbg`` packages are always generated by default, even if the + packages turn out to be empty. See the + :term:`ALLOW_EMPTY` variable + for more information. + +The ``do_package`` task depends on the ``do_packagedata`` task of each +recipe in :term:`DEPENDS` through use +of a ``[``\ :ref:`deptask <bitbake:bitbake-user-manual/bitbake-user-manual-metadata:variable flags>`\ ``]`` +declaration, which guarantees that the required +shared-library/module-to-package mapping information will be available +when needed as long as ``DEPENDS`` has been correctly set. + +Fakeroot and Pseudo +=================== + +Some tasks are easier to implement when allowed to perform certain +operations that are normally reserved for the root user (e.g. +:ref:`ref-tasks-install`, +:ref:`do_package_write* <ref-tasks-package_write_deb>`, +:ref:`ref-tasks-rootfs`, and +:ref:`do_image* <ref-tasks-image>`). For example, +the ``do_install`` task benefits from being able to set the UID and GID +of installed files to arbitrary values. + +One approach to allowing tasks to perform root-only operations would be +to require :term:`BitBake` to run as +root. However, this method is cumbersome and has security issues. The +approach that is actually used is to run tasks that benefit from root +privileges in a "fake" root environment. Within this environment, the +task and its child processes believe that they are running as the root +user, and see an internally consistent view of the filesystem. As long +as generating the final output (e.g. a package or an image) does not +require root privileges, the fact that some earlier steps ran in a fake +root environment does not cause problems. + +The capability to run tasks in a fake root environment is known as +"`fakeroot <http://man.he.net/man1/fakeroot>`__", which is derived from +the BitBake keyword/variable flag that requests a fake root environment +for a task. + +In the :term:`OpenEmbedded Build System`, +the program that +implements fakeroot is known as +`Pseudo <https://www.yoctoproject.org/software-item/pseudo/>`__. Pseudo +overrides system calls by using the environment variable ``LD_PRELOAD``, +which results in the illusion of running as root. To keep track of +"fake" file ownership and permissions resulting from operations that +require root permissions, Pseudo uses an SQLite 3 database. This +database is stored in +``${``\ :term:`WORKDIR`\ ``}/pseudo/files.db`` +for individual recipes. Storing the database in a file as opposed to in +memory gives persistence between tasks and builds, which is not +accomplished using fakeroot. + +.. note:: + + If you add your own task that manipulates the same files or + directories as a fakeroot task, then that task also needs to run + under fakeroot. Otherwise, the task cannot run root-only operations, + and cannot see the fake file ownership and permissions set by the + other task. You need to also add a dependency on + virtual/fakeroot-native:do_populate_sysroot + , giving the following: + :: + + fakeroot do_mytask () { + ... + } + do_mytask[depends] += "virtual/fakeroot-native:do_populate_sysroot" + + +For more information, see the +:term:`FAKEROOT* <bitbake:FAKEROOT>` variables in the +BitBake User Manual. You can also reference the "`Why Not +Fakeroot? <https://github.com/wrpseudo/pseudo/wiki/WhyNotFakeroot>`__" +article for background information on Fakeroot and Pseudo. diff --git a/poky/documentation/overview-manual/overview-manual-concepts.xml b/poky/documentation/overview-manual/overview-manual-concepts.xml index f085dd710..58b64bd26 100644 --- a/poky/documentation/overview-manual/overview-manual-concepts.xml +++ b/poky/documentation/overview-manual/overview-manual-concepts.xml @@ -1,6 +1,7 @@ <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > +<!--SPDX-License-Identifier: CC-BY-2.0-UK--> <chapter id=' overview-manual-concepts'> <title>Yocto Project Concepts</title> diff --git a/poky/documentation/overview-manual/overview-manual-customization.xsl b/poky/documentation/overview-manual/overview-manual-customization.xsl index 22360e7ba..1dd91bde8 100644 --- a/poky/documentation/overview-manual/overview-manual-customization.xsl +++ b/poky/documentation/overview-manual/overview-manual-customization.xsl @@ -1,4 +1,6 @@ <?xml version='1.0'?> +<!--SPDX-License-Identifier: CC-BY-2.0-UK--> + <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns="http://www.w3.org/1999/xhtml" xmlns:fo="http://www.w3.org/1999/XSL/Format" version="1.0"> <xsl:import href="http://downloads.yoctoproject.org/mirror/docbook-mirror/docbook-xsl-1.76.1/xhtml/docbook.xsl" /> diff --git a/poky/documentation/overview-manual/overview-manual-development-environment.rst b/poky/documentation/overview-manual/overview-manual-development-environment.rst new file mode 100644 index 000000000..bb2c8e72e --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-development-environment.rst @@ -0,0 +1,672 @@ +.. SPDX-License-Identifier: CC-BY-2.0-UK + +***************************************** +The Yocto Project Development Environment +***************************************** + +This chapter takes a look at the Yocto Project development environment. +The chapter provides Yocto Project Development environment concepts that +help you understand how work is accomplished in an open source +environment, which is very different as compared to work accomplished in +a closed, proprietary environment. + +Specifically, this chapter addresses open source philosophy, source +repositories, workflows, Git, and licensing. + +Open Source Philosophy +====================== + +Open source philosophy is characterized by software development directed +by peer production and collaboration through an active community of +developers. Contrast this to the more standard centralized development +models used by commercial software companies where a finite set of +developers produces a product for sale using a defined set of procedures +that ultimately result in an end product whose architecture and source +material are closed to the public. + +Open source projects conceptually have differing concurrent agendas, +approaches, and production. These facets of the development process can +come from anyone in the public (community) who has a stake in the +software project. The open source environment contains new copyright, +licensing, domain, and consumer issues that differ from the more +traditional development environment. In an open source environment, the +end product, source material, and documentation are all available to the +public at no cost. + +A benchmark example of an open source project is the Linux kernel, which +was initially conceived and created by Finnish computer science student +Linus Torvalds in 1991. Conversely, a good example of a non-open source +project is the Windows family of operating systems developed by +Microsoft Corporation. + +Wikipedia has a good historical description of the Open Source +Philosophy `here <http://en.wikipedia.org/wiki/Open_source>`__. You can +also find helpful information on how to participate in the Linux +Community +`here <https://www.kernel.org/doc/html/latest/process/index.html>`__. + +.. _gs-the-development-host: + +The Development Host +==================== + +A development host or :term:`Build Host` is key to +using the Yocto Project. Because the goal of the Yocto Project is to +develop images or applications that run on embedded hardware, +development of those images and applications generally takes place on a +system not intended to run the software - the development host. + +You need to set up a development host in order to use it with the Yocto +Project. Most find that it is best to have a native Linux machine +function as the development host. However, it is possible to use a +system that does not run Linux as its operating system as your +development host. When you have a Mac or Windows-based system, you can +set it up as the development host by using +`CROPS <https://github.com/crops/poky-container>`__, which leverages +`Docker Containers <https://www.docker.com/>`__. Once you take the steps +to set up a CROPS machine, you effectively have access to a shell +environment that is similar to what you see when using a Linux-based +development host. For the steps needed to set up a system using CROPS, +see the +":ref:`dev-manual/dev-manual-start:setting up to use cross platforms (crops)`" +section in +the Yocto Project Development Tasks Manual. + +If your development host is going to be a system that runs a Linux +distribution, steps still exist that you must take to prepare the system +for use with the Yocto Project. You need to be sure that the Linux +distribution on the system is one that supports the Yocto Project. You +also need to be sure that the correct set of host packages are installed +that allow development using the Yocto Project. For the steps needed to +set up a development host that runs Linux, see the +":ref:`dev-manual/dev-manual-start:setting up a native linux host`" +section in the Yocto Project Development Tasks Manual. + +Once your development host is set up to use the Yocto Project, several +methods exist for you to do work in the Yocto Project environment: + +- *Command Lines, BitBake, and Shells:* Traditional development in the + Yocto Project involves using the :term:`OpenEmbedded Build System`, + which uses + BitBake, in a command-line environment from a shell on your + development host. You can accomplish this from a host that is a + native Linux machine or from a host that has been set up with CROPS. + Either way, you create, modify, and build images and applications all + within a shell-based environment using components and tools available + through your Linux distribution and the Yocto Project. + + For a general flow of the build procedures, see the + ":ref:`dev-manual/dev-manual-common-tasks:building a simple image`" + section in the Yocto Project Development Tasks Manual. + +- *Board Support Package (BSP) Development:* Development of BSPs + involves using the Yocto Project to create and test layers that allow + easy development of images and applications targeted for specific + hardware. To development BSPs, you need to take some additional steps + beyond what was described in setting up a development host. + + The :doc:`../bsp-guide/bsp-guide` provides BSP-related development + information. For specifics on development host preparation, see the + ":ref:`bsp-guide/bsp:preparing your build host to work with bsp layers`" + section in the Yocto Project Board Support Package (BSP) Developer's + Guide. + +- *Kernel Development:* If you are going to be developing kernels using + the Yocto Project you likely will be using ``devtool``. A workflow + using ``devtool`` makes kernel development quicker by reducing + iteration cycle times. + + The :doc:`../kernel-dev/kernel-dev` provides kernel-related + development information. For specifics on development host + preparation, see the + ":ref:`kernel-dev/kernel-dev-common:preparing the build host to work on the kernel`" + section in the Yocto Project Linux Kernel Development Manual. + +- *Using Toaster:* The other Yocto Project development method that + involves an interface that effectively puts the Yocto Project into + the background is Toaster. Toaster provides an interface to the + OpenEmbedded build system. The interface enables you to configure and + run your builds. Information about builds is collected and stored in + a database. You can use Toaster to configure and start builds on + multiple remote build servers. + + For steps that show you how to set up your development host to use + Toaster and on how to use Toaster in general, see the + :doc:`../toaster-manual/toaster-manual`. + +.. _yocto-project-repositories: + +Yocto Project Source Repositories +================================= + +The Yocto Project team maintains complete source repositories for all +Yocto Project files at :yocto_git:`/`. This web-based source +code browser is organized into categories by function such as IDE +Plugins, Matchbox, Poky, Yocto Linux Kernel, and so forth. From the +interface, you can click on any particular item in the "Name" column and +see the URL at the bottom of the page that you need to clone a Git +repository for that particular item. Having a local Git repository of +the :term:`Source Directory`, which +is usually named "poky", allows you to make changes, contribute to the +history, and ultimately enhance the Yocto Project's tools, Board Support +Packages, and so forth. + +For any supported release of Yocto Project, you can also go to the +:yocto_home:`Yocto Project Website <>` and select the "DOWNLOADS" +item from the "SOFTWARE" menu and get a released tarball of the ``poky`` +repository, any supported BSP tarball, or Yocto Project tools. Unpacking +these tarballs gives you a snapshot of the released files. + +.. note:: + + - The recommended method for setting up the Yocto Project + :term:`Source Directory` and the files + for supported BSPs (e.g., ``meta-intel``) is to use `Git <#git>`__ + to create a local copy of the upstream repositories. + + - Be sure to always work in matching branches for both the selected + BSP repository and the Source Directory (i.e. ``poky``) + repository. For example, if you have checked out the "master" + branch of ``poky`` and you are going to use ``meta-intel``, be + sure to checkout the "master" branch of ``meta-intel``. + +In summary, here is where you can get the project files needed for +development: + +- :yocto_git:`Source Repositories: <>` This area contains IDE + Plugins, Matchbox, Poky, Poky Support, Tools, Yocto Linux Kernel, and + Yocto Metadata Layers. You can create local copies of Git + repositories for each of these areas. + + .. image:: figures/source-repos.png + :align: center + + For steps on how to view and access these upstream Git repositories, + see the ":ref:`dev-manual/dev-manual-start:accessing source repositories`" + Section in the Yocto Project Development Tasks Manual. + +- :yocto_dl:`Index of /releases: </releases>` This is an index + of releases such as Poky, Pseudo, installers for cross-development + toolchains, miscellaneous support and all released versions of Yocto + Project in the form of images or tarballs. Downloading and extracting + these files does not produce a local copy of the Git repository but + rather a snapshot of a particular release or image. + + .. image:: figures/index-downloads.png + :align: center + + For steps on how to view and access these files, see the + ":ref:`dev-manual/dev-manual-start:accessing index of releases`" + section in the Yocto Project Development Tasks Manual. + +- *"DOWNLOADS" page for the* :yocto_home:`Yocto Project Website <>` *:* + + The Yocto Project website includes a "DOWNLOADS" page accessible + through the "SOFTWARE" menu that allows you to download any Yocto + Project release, tool, and Board Support Package (BSP) in tarball + form. The tarballs are similar to those found in the + :yocto_dl:`Index of /releases: </releases>` area. + + .. image:: figures/yp-download.png + :align: center + + For steps on how to use the "DOWNLOADS" page, see the + ":ref:`dev-manual/dev-manual-start:using the downloads page`" + section in the Yocto Project Development Tasks Manual. + +.. _gs-git-workflows-and-the-yocto-project: + +Git Workflows and the Yocto Project +=================================== + +Developing using the Yocto Project likely requires the use of +`Git <#git>`__. Git is a free, open source distributed version control +system used as part of many collaborative design environments. This +section provides workflow concepts using the Yocto Project and Git. In +particular, the information covers basic practices that describe roles +and actions in a collaborative development environment. + +.. note:: + + If you are familiar with this type of development environment, you + might not want to read this section. + +The Yocto Project files are maintained using Git in "branches" whose Git +histories track every change and whose structures provide branches for +all diverging functionality. Although there is no need to use Git, many +open source projects do so. + +For the Yocto Project, a key individual called the "maintainer" is +responsible for the integrity of the "master" branch of a given Git +repository. The "master" branch is the "upstream" repository from which +final or most recent builds of a project occur. The maintainer is +responsible for accepting changes from other developers and for +organizing the underlying branch structure to reflect release strategies +and so forth. + +.. note:: + + For information on finding out who is responsible for (maintains) a + particular area of code in the Yocto Project, see the + ":ref:`dev-manual/dev-manual-common-tasks:submitting a change to the yocto project`" + section of the Yocto Project Development Tasks Manual. + +The Yocto Project ``poky`` Git repository also has an upstream +contribution Git repository named ``poky-contrib``. You can see all the +branches in this repository using the web interface of the +:yocto_git:`Source Repositories <>` organized within the "Poky Support" +area. These branches hold changes (commits) to the project that have +been submitted or committed by the Yocto Project development team and by +community members who contribute to the project. The maintainer +determines if the changes are qualified to be moved from the "contrib" +branches into the "master" branch of the Git repository. + +Developers (including contributing community members) create and +maintain cloned repositories of upstream branches. The cloned +repositories are local to their development platforms and are used to +develop changes. When a developer is satisfied with a particular feature +or change, they "push" the change to the appropriate "contrib" +repository. + +Developers are responsible for keeping their local repository up-to-date +with whatever upstream branch they are working against. They are also +responsible for straightening out any conflicts that might arise within +files that are being worked on simultaneously by more than one person. +All this work is done locally on the development host before anything is +pushed to a "contrib" area and examined at the maintainer's level. + +A somewhat formal method exists by which developers commit changes and +push them into the "contrib" area and subsequently request that the +maintainer include them into an upstream branch. This process is called +"submitting a patch" or "submitting a change." For information on +submitting patches and changes, see the +":ref:`dev-manual/dev-manual-common-tasks:submitting a change to the yocto project`" +section in the Yocto Project Development Tasks Manual. + +In summary, a single point of entry exists for changes into a "master" +or development branch of the Git repository, which is controlled by the +project's maintainer. And, a set of developers exist who independently +develop, test, and submit changes to "contrib" areas for the maintainer +to examine. The maintainer then chooses which changes are going to +become a permanent part of the project. + +.. image:: figures/git-workflow.png + :align: center + +While each development environment is unique, there are some best +practices or methods that help development run smoothly. The following +list describes some of these practices. For more information about Git +workflows, see the workflow topics in the `Git Community +Book <http://book.git-scm.com>`__. + +- *Make Small Changes:* It is best to keep the changes you commit small + as compared to bundling many disparate changes into a single commit. + This practice not only keeps things manageable but also allows the + maintainer to more easily include or refuse changes. + +- *Make Complete Changes:* It is also good practice to leave the + repository in a state that allows you to still successfully build + your project. In other words, do not commit half of a feature, then + add the other half as a separate, later commit. Each commit should + take you from one buildable project state to another buildable state. + +- *Use Branches Liberally:* It is very easy to create, use, and delete + local branches in your working Git repository on the development + host. You can name these branches anything you like. It is helpful to + give them names associated with the particular feature or change on + which you are working. Once you are done with a feature or change and + have merged it into your local master branch, simply discard the + temporary branch. + +- *Merge Changes:* The ``git merge`` command allows you to take the + changes from one branch and fold them into another branch. This + process is especially helpful when more than a single developer might + be working on different parts of the same feature. Merging changes + also automatically identifies any collisions or "conflicts" that + might happen as a result of the same lines of code being altered by + two different developers. + +- *Manage Branches:* Because branches are easy to use, you should use a + system where branches indicate varying levels of code readiness. For + example, you can have a "work" branch to develop in, a "test" branch + where the code or change is tested, a "stage" branch where changes + are ready to be committed, and so forth. As your project develops, + you can merge code across the branches to reflect ever-increasing + stable states of the development. + +- *Use Push and Pull:* The push-pull workflow is based on the concept + of developers "pushing" local commits to a remote repository, which + is usually a contribution repository. This workflow is also based on + developers "pulling" known states of the project down into their + local development repositories. The workflow easily allows you to + pull changes submitted by other developers from the upstream + repository into your work area ensuring that you have the most recent + software on which to develop. The Yocto Project has two scripts named + ``create-pull-request`` and ``send-pull-request`` that ship with the + release to facilitate this workflow. You can find these scripts in + the ``scripts`` folder of the + :term:`Source Directory`. For information + on how to use these scripts, see the + ":ref:`dev-manual/dev-manual-common-tasks:using scripts to push a change upstream and request a pull`" + section in the Yocto Project Development Tasks Manual. + +- *Patch Workflow:* This workflow allows you to notify the maintainer + through an email that you have a change (or patch) you would like + considered for the "master" branch of the Git repository. To send + this type of change, you format the patch and then send the email + using the Git commands ``git format-patch`` and ``git send-email``. + For information on how to use these scripts, see the + ":ref:`dev-manual/dev-manual-common-tasks:submitting a change to the yocto project`" + section in the Yocto Project Development Tasks Manual. + +Git +=== + +The Yocto Project makes extensive use of Git, which is a free, open +source distributed version control system. Git supports distributed +development, non-linear development, and can handle large projects. It +is best that you have some fundamental understanding of how Git tracks +projects and how to work with Git if you are going to use the Yocto +Project for development. This section provides a quick overview of how +Git works and provides you with a summary of some essential Git +commands. + +.. note:: + + - For more information on Git, see + http://git-scm.com/documentation. + + - If you need to download Git, it is recommended that you add Git to + your system through your distribution's "software store" (e.g. for + Ubuntu, use the Ubuntu Software feature). For the Git download + page, see http://git-scm.com/download. + + - For information beyond the introductory nature in this section, + see the ":ref:`dev-manual/dev-manual-start:locating yocto project source files`" + section in the Yocto Project Development Tasks Manual. + +Repositories, Tags, and Branches +-------------------------------- + +As mentioned briefly in the previous section and also in the "`Git +Workflows and the Yocto +Project <#gs-git-workflows-and-the-yocto-project>`__" section, the Yocto +Project maintains source repositories at :yocto_git:`/`. If you +look at this web-interface of the repositories, each item is a separate +Git repository. + +Git repositories use branching techniques that track content change (not +files) within a project (e.g. a new feature or updated documentation). +Creating a tree-like structure based on project divergence allows for +excellent historical information over the life of a project. This +methodology also allows for an environment from which you can do lots of +local experimentation on projects as you develop changes or new +features. + +A Git repository represents all development efforts for a given project. +For example, the Git repository ``poky`` contains all changes and +developments for that repository over the course of its entire life. +That means that all changes that make up all releases are captured. The +repository maintains a complete history of changes. + +You can create a local copy of any repository by "cloning" it with the +``git clone`` command. When you clone a Git repository, you end up with +an identical copy of the repository on your development system. Once you +have a local copy of a repository, you can take steps to develop +locally. For examples on how to clone Git repositories, see the +":ref:`dev-manual/dev-manual-start:locating yocto project source files`" +section in the Yocto Project Development Tasks Manual. + +It is important to understand that Git tracks content change and not +files. Git uses "branches" to organize different development efforts. +For example, the ``poky`` repository has several branches that include +the current "&DISTRO_NAME_NO_CAP;" branch, the "master" branch, and many +branches for past Yocto Project releases. You can see all the branches +by going to https://git.yoctoproject.org/cgit.cgi/poky/ and clicking on the +``[...]`` link beneath the "Branch" heading. + +Each of these branches represents a specific area of development. The +"master" branch represents the current or most recent development. All +other branches represent offshoots of the "master" branch. + +When you create a local copy of a Git repository, the copy has the same +set of branches as the original. This means you can use Git to create a +local working area (also called a branch) that tracks a specific +development branch from the upstream source Git repository. in other +words, you can define your local Git environment to work on any +development branch in the repository. To help illustrate, consider the +following example Git commands: +:: + + $ cd ~ + $ git clone git://git.yoctoproject.org/poky + $ cd poky + $ git checkout -b &DISTRO_NAME_NO_CAP; origin/&DISTRO_NAME_NO_CAP; + +In the previous example +after moving to the home directory, the ``git clone`` command creates a +local copy of the upstream ``poky`` Git repository. By default, Git +checks out the "master" branch for your work. After changing the working +directory to the new local repository (i.e. ``poky``), the +``git checkout`` command creates and checks out a local branch named +"&DISTRO_NAME_NO_CAP;", which tracks the upstream +"origin/&DISTRO_NAME_NO_CAP;" branch. Changes you make while in this +branch would ultimately affect the upstream "&DISTRO_NAME_NO_CAP;" branch +of the ``poky`` repository. + +It is important to understand that when you create and checkout a local +working branch based on a branch name, your local environment matches +the "tip" of that particular development branch at the time you created +your local branch, which could be different from the files in the +"master" branch of the upstream repository. In other words, creating and +checking out a local branch based on the "&DISTRO_NAME_NO_CAP;" branch +name is not the same as checking out the "master" branch in the +repository. Keep reading to see how you create a local snapshot of a +Yocto Project Release. + +Git uses "tags" to mark specific changes in a repository branch +structure. Typically, a tag is used to mark a special point such as the +final change (or commit) before a project is released. You can see the +tags used with the ``poky`` Git repository by going to +https://git.yoctoproject.org/cgit.cgi/poky/ and clicking on the ``[...]`` link +beneath the "Tag" heading. + +Some key tags for the ``poky`` repository are ``jethro-14.0.3``, +``morty-16.0.1``, ``pyro-17.0.0``, and +``&DISTRO_NAME_NO_CAP;-&POKYVERSION;``. These tags represent Yocto Project +releases. + +When you create a local copy of the Git repository, you also have access +to all the tags in the upstream repository. Similar to branches, you can +create and checkout a local working Git branch based on a tag name. When +you do this, you get a snapshot of the Git repository that reflects the +state of the files when the change was made associated with that tag. +The most common use is to checkout a working branch that matches a +specific Yocto Project release. Here is an example: +:: + + $ cd ~ + $ git clone git://git.yoctoproject.org/poky + $ cd poky + $ git fetch --tags + $ git checkout tags/rocko-18.0.0 -b my_rocko-18.0.0 + +In this example, the name +of the top-level directory of your local Yocto Project repository is +``poky``. After moving to the ``poky`` directory, the ``git fetch`` +command makes all the upstream tags available locally in your +repository. Finally, the ``git checkout`` command creates and checks out +a branch named "my-rocko-18.0.0" that is based on the upstream branch +whose "HEAD" matches the commit in the repository associated with the +"rocko-18.0.0" tag. The files in your repository now exactly match that +particular Yocto Project release as it is tagged in the upstream Git +repository. It is important to understand that when you create and +checkout a local working branch based on a tag, your environment matches +a specific point in time and not the entire development branch (i.e. +from the "tip" of the branch backwards). + +Basic Commands +-------------- + +Git has an extensive set of commands that lets you manage changes and +perform collaboration over the life of a project. Conveniently though, +you can manage with a small set of basic operations and workflows once +you understand the basic philosophy behind Git. You do not have to be an +expert in Git to be functional. A good place to look for instruction on +a minimal set of Git commands is +`here <http://git-scm.com/documentation>`__. + +The following list of Git commands briefly describes some basic Git +operations as a way to get started. As with any set of commands, this +list (in most cases) simply shows the base command and omits the many +arguments it supports. See the Git documentation for complete +descriptions and strategies on how to use these commands: + +- *git init:* Initializes an empty Git repository. You cannot use + Git commands unless you have a ``.git`` repository. + +- *git clone:* Creates a local clone of a Git repository that is on + equal footing with a fellow developer's Git repository or an upstream + repository. + +- *git add:* Locally stages updated file contents to the index that + Git uses to track changes. You must stage all files that have changed + before you can commit them. + +- *git commit:* Creates a local "commit" that documents the changes + you made. Only changes that have been staged can be committed. + Commits are used for historical purposes, for determining if a + maintainer of a project will allow the change, and for ultimately + pushing the change from your local Git repository into the project's + upstream repository. + +- *git status:* Reports any modified files that possibly need to be + staged and gives you a status of where you stand regarding local + commits as compared to the upstream repository. + +- *git checkout branch-name:* Changes your local working branch and + in this form assumes the local branch already exists. This command is + analogous to "cd". + +- *git checkout –b working-branch upstream-branch:* Creates and + checks out a working branch on your local machine. The local branch + tracks the upstream branch. You can use your local branch to isolate + your work. It is a good idea to use local branches when adding + specific features or changes. Using isolated branches facilitates + easy removal of changes if they do not work out. + +- *git branch:* Displays the existing local branches associated + with your local repository. The branch that you have currently + checked out is noted with an asterisk character. + +- *git branch -D branch-name:* Deletes an existing local branch. + You need to be in a local branch other than the one you are deleting + in order to delete branch-name. + +- *git pull --rebase:* Retrieves information from an upstream Git + repository and places it in your local Git repository. You use this + command to make sure you are synchronized with the repository from + which you are basing changes (.e.g. the "master" branch). The + "--rebase" option ensures that any local commits you have in your + branch are preserved at the top of your local branch. + +- *git push repo-name local-branch:upstream-branch:* Sends + all your committed local changes to the upstream Git repository that + your local repository is tracking (e.g. a contribution repository). + The maintainer of the project draws from these repositories to merge + changes (commits) into the appropriate branch of project's upstream + repository. + +- *git merge:* Combines or adds changes from one local branch of + your repository with another branch. When you create a local Git + repository, the default branch is named "master". A typical workflow + is to create a temporary branch that is based off "master" that you + would use for isolated work. You would make your changes in that + isolated branch, stage and commit them locally, switch to the + "master" branch, and then use the ``git merge`` command to apply the + changes from your isolated branch into the currently checked out + branch (e.g. "master"). After the merge is complete and if you are + done with working in that isolated branch, you can safely delete the + isolated branch. + +- *git cherry-pick commits:* Choose and apply specific commits from + one branch into another branch. There are times when you might not be + able to merge all the changes in one branch with another but need to + pick out certain ones. + +- *gitk:* Provides a GUI view of the branches and changes in your + local Git repository. This command is a good way to graphically see + where things have diverged in your local repository. + + .. note:: + + You need to install the + gitk + package on your development system to use this command. + +- *git log:* Reports a history of your commits to the repository. + This report lists all commits regardless of whether you have pushed + them upstream or not. + +- *git diff:* Displays line-by-line differences between a local + working file and the same file as understood by Git. This command is + useful to see what you have changed in any given file. + +Licensing +========= + +Because open source projects are open to the public, they have different +licensing structures in place. License evolution for both Open Source +and Free Software has an interesting history. If you are interested in +this history, you can find basic information here: + +- `Open source license + history <http://en.wikipedia.org/wiki/Open-source_license>`__ + +- `Free software license + history <http://en.wikipedia.org/wiki/Free_software_license>`__ + +In general, the Yocto Project is broadly licensed under the +Massachusetts Institute of Technology (MIT) License. MIT licensing +permits the reuse of software within proprietary software as long as the +license is distributed with that software. MIT is also compatible with +the GNU General Public License (GPL). Patches to the Yocto Project +follow the upstream licensing scheme. You can find information on the +MIT license +`here <http://www.opensource.org/licenses/mit-license.php>`__. You can +find information on the GNU GPL +`here <http://www.opensource.org/licenses/LGPL-3.0>`__. + +When you build an image using the Yocto Project, the build process uses +a known list of licenses to ensure compliance. You can find this list in +the :term:`Source Directory` at +``meta/files/common-licenses``. Once the build completes, the list of +all licenses found and used during that build are kept in the +:term:`Build Directory` at +``tmp/deploy/licenses``. + +If a module requires a license that is not in the base list, the build +process generates a warning during the build. These tools make it easier +for a developer to be certain of the licenses with which their shipped +products must comply. However, even with these tools it is still up to +the developer to resolve potential licensing issues. + +The base list of licenses used by the build process is a combination of +the Software Package Data Exchange (SPDX) list and the Open Source +Initiative (OSI) projects. `SPDX Group <http://spdx.org>`__ is a working +group of the Linux Foundation that maintains a specification for a +standard format for communicating the components, licenses, and +copyrights associated with a software package. +`OSI <http://opensource.org>`__ is a corporation dedicated to the Open +Source Definition and the effort for reviewing and approving licenses +that conform to the Open Source Definition (OSD). + +You can find a list of the combined SPDX and OSI licenses that the Yocto +Project uses in the ``meta/files/common-licenses`` directory in your +:term:`Source Directory`. + +For information that can help you maintain compliance with various open +source licensing during the lifecycle of a product created using the +Yocto Project, see the +":ref:`dev-manual/dev-manual-common-tasks:maintaining open source license compliance during your product's lifecycle`" +section in the Yocto Project Development Tasks Manual. diff --git a/poky/documentation/overview-manual/overview-manual-development-environment.xml b/poky/documentation/overview-manual/overview-manual-development-environment.xml index 36ebf8a32..08ad07131 100644 --- a/poky/documentation/overview-manual/overview-manual-development-environment.xml +++ b/poky/documentation/overview-manual/overview-manual-development-environment.xml @@ -1,6 +1,7 @@ <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > +<!--SPDX-License-Identifier: CC-BY-2.0-UK--> <chapter id='overview-development-environment'> <title>The Yocto Project Development Environment</title> @@ -326,7 +327,7 @@ For the Yocto Project, a key individual called the "maintainer" is responsible for the integrity of the "master" branch of a given Git repository. - The "master" branch is the “upstream” repository from which final or + The "master" branch is the "upstream" repository from which final or most recent builds of a project occur. The maintainer is responsible for accepting changes from other developers and for organizing the underlying branch structure to @@ -371,7 +372,7 @@ might arise within files that are being worked on simultaneously by more than one person. All this work is done locally on the development host before - anything is pushed to a "contrib" area and examined at the maintainer’s + anything is pushed to a "contrib" area and examined at the maintainer's level. </para> @@ -379,7 +380,7 @@ A somewhat formal method exists by which developers commit changes and push them into the "contrib" area and subsequently request that the maintainer include them into an upstream branch. - This process is called “submitting a patch” or "submitting a change." + This process is called "submitting a patch" or "submitting a change." For information on submitting patches and changes, see the "<ulink url='&YOCTO_DOCS_DEV_URL;#how-to-submit-a-change'>Submitting a Change to the Yocto Project</ulink>" section in the Yocto Project Development Tasks Manual. @@ -388,7 +389,7 @@ <para> In summary, a single point of entry exists for changes into a "master" or development branch of the - Git repository, which is controlled by the project’s maintainer. + Git repository, which is controlled by the project's maintainer. And, a set of developers exist who independently develop, test, and submit changes to "contrib" areas for the maintainer to examine. The maintainer then chooses which changes are going to become a @@ -733,7 +734,7 @@ <listitem><para id='git-commands-clone'> <emphasis><filename>git clone</filename>:</emphasis> Creates a local clone of a Git repository that is on - equal footing with a fellow developer’s Git repository + equal footing with a fellow developer's Git repository or an upstream repository. </para></listitem> <listitem><para> @@ -751,7 +752,7 @@ Commits are used for historical purposes, for determining if a maintainer of a project will allow the change, and for ultimately pushing the change from your local - Git repository into the project’s upstream repository. + Git repository into the project's upstream repository. </para></listitem> <listitem><para> <emphasis><filename>git status</filename>:</emphasis> diff --git a/poky/documentation/overview-manual/overview-manual-intro.rst b/poky/documentation/overview-manual/overview-manual-intro.rst new file mode 100644 index 000000000..3f206fd54 --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-intro.rst @@ -0,0 +1,74 @@ +.. SPDX-License-Identifier: CC-BY-2.0-UK + +********************************************** +The Yocto Project Overview and Concepts Manual +********************************************** + +.. _overview-manual-welcome: + +Welcome +======= + +Welcome to the Yocto Project Overview and Concepts Manual! This manual +introduces the Yocto Project by providing concepts, software overviews, +best-known-methods (BKMs), and any other high-level introductory +information suitable for a new Yocto Project user. + +The following list describes what you can get from this manual: + +- `Introducing the Yocto Project <#overview-yp>`__\ *:* This chapter + provides an introduction to the Yocto Project. You will learn about + features and challenges of the Yocto Project, the layer model, + components and tools, development methods, the + :term:`Poky` reference distribution, the + OpenEmbedded build system workflow, and some basic Yocto terms. + +- `The Yocto Project Development + Environment <#overview-development-environment>`__\ *:* This chapter + helps you get started understanding the Yocto Project development + environment. You will learn about open source, development hosts, + Yocto Project source repositories, workflows using Git and the Yocto + Project, a Git primer, and information about licensing. + +- :doc:`overview-manual-concepts` *:* This + chapter presents various concepts regarding the Yocto Project. You + can find conceptual information about components, development, + cross-toolchains, and so forth. + +This manual does not give you the following: + +- *Step-by-step Instructions for Development Tasks:* Instructional + procedures reside in other manuals within the Yocto Project + documentation set. For example, the :doc:`../dev-manual/dev-manual` + provides examples on how to perform + various development tasks. As another example, the + :doc:`../sdk-manual/sdk-manual` manual contains detailed + instructions on how to install an SDK, which is used to develop + applications for target hardware. + +- *Reference Material:* This type of material resides in an appropriate + reference manual. For example, system variables are documented in the + :doc:`../ref-manual/ref-manual`. As another + example, the :doc:`../bsp-guide/bsp-guide` contains reference information on + BSPs. + +- *Detailed Public Information Not Specific to the Yocto Project:* For + example, exhaustive information on how to use the Source Control + Manager Git is better covered with Internet searches and official Git + Documentation than through the Yocto Project documentation. + +.. _overview-manual-other-information: + +Other Information +================= + +Because this manual presents information for many different topics, +supplemental information is recommended for full comprehension. For +additional introductory information on the Yocto Project, see the +:yocto_home:`Yocto Project Website <>`. If you want to build an image +with no knowledge of Yocto Project as a way of quickly testing it out, +see the :doc:`../brief-yoctoprojectqs/brief-yoctoprojectqs` document. +For a comprehensive list of links and other documentation, see the +":ref:`Links and Related +Documentation <resources-links-and-related-documentation>`" +section in the Yocto Project Reference Manual. diff --git a/poky/documentation/overview-manual/overview-manual-intro.xml b/poky/documentation/overview-manual/overview-manual-intro.xml index 39433aa41..0e0bfed6e 100644 --- a/poky/documentation/overview-manual/overview-manual-intro.xml +++ b/poky/documentation/overview-manual/overview-manual-intro.xml @@ -1,6 +1,7 @@ <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > +<!--SPDX-License-Identifier: CC-BY-2.0-UK--> <chapter id='overview-manual-intro'> diff --git a/poky/documentation/overview-manual/overview-manual-style.css b/poky/documentation/overview-manual/overview-manual-style.css index 97a364b12..eec934161 100644 --- a/poky/documentation/overview-manual/overview-manual-style.css +++ b/poky/documentation/overview-manual/overview-manual-style.css @@ -1,4 +1,6 @@ /* + SPDX-License-Identifier: CC-BY-2.0-UK + Generic XHTML / DocBook XHTML CSS Stylesheet. Browser wrangling and typographic design by diff --git a/poky/documentation/overview-manual/overview-manual-yp-intro.rst b/poky/documentation/overview-manual/overview-manual-yp-intro.rst new file mode 100644 index 000000000..5cdab7ca4 --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-yp-intro.rst @@ -0,0 +1,941 @@ +.. SPDX-License-Identifier: CC-BY-2.0-UK + +***************************** +Introducing the Yocto Project +***************************** + +What is the Yocto Project? +========================== + +The Yocto Project is an open source collaboration project that helps +developers create custom Linux-based systems that are designed for +embedded products regardless of the product's hardware architecture. +Yocto Project provides a flexible toolset and a development environment +that allows embedded device developers across the world to collaborate +through shared technologies, software stacks, configurations, and best +practices used to create these tailored Linux images. + +Thousands of developers worldwide have discovered that Yocto Project +provides advantages in both systems and applications development, +archival and management benefits, and customizations used for speed, +footprint, and memory utilization. The project is a standard when it +comes to delivering embedded software stacks. The project allows +software customizations and build interchange for multiple hardware +platforms as well as software stacks that can be maintained and scaled. + +.. image:: figures/key-dev-elements.png + :align: center + +For further introductory information on the Yocto Project, you might be +interested in this +`article <https://www.embedded.com/electronics-blogs/say-what-/4458600/Why-the-Yocto-Project-for-my-IoT-Project->`__ +by Drew Moseley and in this short introductory +`video <https://www.youtube.com/watch?v=utZpKM7i5Z4>`__. + +The remainder of this section overviews advantages and challenges tied +to the Yocto Project. + +.. _gs-features: + +Features +-------- + +The following list describes features and advantages of the Yocto +Project: + +- *Widely Adopted Across the Industry:* Semiconductor, operating + system, software, and service vendors exist whose products and + services adopt and support the Yocto Project. For a look at the Yocto + Project community and the companies involved with the Yocto Project, + see the "COMMUNITY" and "ECOSYSTEM" tabs on the + :yocto_home:`Yocto Project <>` home page. + +- *Architecture Agnostic:* Yocto Project supports Intel, ARM, MIPS, + AMD, PPC and other architectures. Most ODMs, OSVs, and chip vendors + create and supply BSPs that support their hardware. If you have + custom silicon, you can create a BSP that supports that architecture. + + Aside from lots of architecture support, the Yocto Project fully + supports a wide range of device emulation through the Quick EMUlator + (QEMU). + +- *Images and Code Transfer Easily:* Yocto Project output can easily + move between architectures without moving to new development + environments. Additionally, if you have used the Yocto Project to + create an image or application and you find yourself not able to + support it, commercial Linux vendors such as Wind River, Mentor + Graphics, Timesys, and ENEA could take it and provide ongoing + support. These vendors have offerings that are built using the Yocto + Project. + +- *Flexibility:* Corporations use the Yocto Project many different + ways. One example is to create an internal Linux distribution as a + code base the corporation can use across multiple product groups. + Through customization and layering, a project group can leverage the + base Linux distribution to create a distribution that works for their + product needs. + +- *Ideal for Constrained Embedded and IoT devices:* Unlike a full Linux + distribution, you can use the Yocto Project to create exactly what + you need for embedded devices. You only add the feature support or + packages that you absolutely need for the device. For devices that + have display hardware, you can use available system components such + as X11, GTK+, Qt, Clutter, and SDL (among others) to create a rich + user experience. For devices that do not have a display or where you + want to use alternative UI frameworks, you can choose to not install + these components. + +- *Comprehensive Toolchain Capabilities:* Toolchains for supported + architectures satisfy most use cases. However, if your hardware + supports features that are not part of a standard toolchain, you can + easily customize that toolchain through specification of + platform-specific tuning parameters. And, should you need to use a + third-party toolchain, mechanisms built into the Yocto Project allow + for that. + +- *Mechanism Rules Over Policy:* Focusing on mechanism rather than + policy ensures that you are free to set policies based on the needs + of your design instead of adopting decisions enforced by some system + software provider. + +- *Uses a Layer Model:* The Yocto Project `layer + infrastructure <#the-yocto-project-layer-model>`__ groups related + functionality into separate bundles. You can incrementally add these + grouped functionalities to your project as needed. Using layers to + isolate and group functionality reduces project complexity and + redundancy, allows you to easily extend the system, make + customizations, and keep functionality organized. + +- *Supports Partial Builds:* You can build and rebuild individual + packages as needed. Yocto Project accomplishes this through its + `shared-state cache <#shared-state-cache>`__ (sstate) scheme. Being + able to build and debug components individually eases project + development. + +- *Releases According to a Strict Schedule:* Major releases occur on a + :doc:`six-month cycle <../ref-manual/ref-release-process>` + predictably in October and April. The most recent two releases + support point releases to address common vulnerabilities and + exposures. This predictability is crucial for projects based on the + Yocto Project and allows development teams to plan activities. + +- *Rich Ecosystem of Individuals and Organizations:* For open source + projects, the value of community is very important. Support forums, + expertise, and active developers who continue to push the Yocto + Project forward are readily available. + +- *Binary Reproducibility:* The Yocto Project allows you to be very + specific about dependencies and achieves very high percentages of + binary reproducibility (e.g. 99.8% for ``core-image-minimal``). When + distributions are not specific about which packages are pulled in and + in what order to support dependencies, other build systems can + arbitrarily include packages. + +- *License Manifest:* The Yocto Project provides a :ref:`license + manifest <dev-manual/dev-manual-common-tasks:maintaining open source license compliance during your product's lifecycle>` + for review by people who need to track the use of open source + licenses (e.g. legal teams). + +.. _gs-challenges: + +Challenges +---------- + +The following list presents challenges you might encounter when +developing using the Yocto Project: + +- *Steep Learning Curve:* The Yocto Project has a steep learning curve + and has many different ways to accomplish similar tasks. It can be + difficult to choose how to proceed when varying methods exist by + which to accomplish a given task. + +- *Understanding What Changes You Need to Make For Your Design Requires + Some Research:* Beyond the simple tutorial stage, understanding what + changes need to be made for your particular design can require a + significant amount of research and investigation. For information + that helps you transition from trying out the Yocto Project to using + it for your project, see the ":ref:`what-i-wish-id-known:what i wish i'd known about yocto project`" and + ":ref:`transitioning-to-a-custom-environment:transitioning to a custom environment for systems development`" + documents on the Yocto Project website. + +- *Project Workflow Could Be Confusing:* The `Yocto Project + workflow <#overview-development-environment>`__ could be confusing if + you are used to traditional desktop and server software development. + In a desktop development environment, mechanisms exist to easily pull + and install new packages, which are typically pre-compiled binaries + from servers accessible over the Internet. Using the Yocto Project, + you must modify your configuration and rebuild to add additional + packages. + +- *Working in a Cross-Build Environment Can Feel Unfamiliar:* When + developing code to run on a target, compilation, execution, and + testing done on the actual target can be faster than running a + BitBake build on a development host and then deploying binaries to + the target for test. While the Yocto Project does support development + tools on the target, the additional step of integrating your changes + back into the Yocto Project build environment would be required. + Yocto Project supports an intermediate approach that involves making + changes on the development system within the BitBake environment and + then deploying only the updated packages to the target. + + The Yocto Project :term:`OpenEmbedded Build System` + produces packages + in standard formats (i.e. RPM, DEB, IPK, and TAR). You can deploy + these packages into the running system on the target by using + utilities on the target such as ``rpm`` or ``ipk``. + +- *Initial Build Times Can be Significant:* Long initial build times + are unfortunately unavoidable due to the large number of packages + initially built from scratch for a fully functioning Linux system. + Once that initial build is completed, however, the shared-state + (sstate) cache mechanism Yocto Project uses keeps the system from + rebuilding packages that have not been "touched" since the last + build. The sstate mechanism significantly reduces times for + successive builds. + +The Yocto Project Layer Model +============================= + +The Yocto Project's "Layer Model" is a development model for embedded +and IoT Linux creation that distinguishes the Yocto Project from other +simple build systems. The Layer Model simultaneously supports +collaboration and customization. Layers are repositories that contain +related sets of instructions that tell the :term:`OpenEmbedded Build System` +what to do. You can +collaborate, share, and reuse layers. + +Layers can contain changes to previous instructions or settings at any +time. This powerful override capability is what allows you to customize +previously supplied collaborative or community layers to suit your +product requirements. + +You use different layers to logically separate information in your +build. As an example, you could have BSP, GUI, distro configuration, +middleware, or application layers. Putting your entire build into one +layer limits and complicates future customization and reuse. Isolating +information into layers, on the other hand, helps simplify future +customizations and reuse. You might find it tempting to keep everything +in one layer when working on a single project. However, the more modular +your Metadata, the easier it is to cope with future changes. + +.. note:: + + - Use Board Support Package (BSP) layers from silicon vendors when + possible. + + - Familiarize yourself with the `Yocto Project curated layer + index <https://www.yoctoproject.org/software-overview/layers/>`__ + or the `OpenEmbedded layer + index <http://layers.openembedded.org/layerindex/branch/master/layers/>`__. + The latter contains more layers but they are less universally + validated. + + - Layers support the inclusion of technologies, hardware components, + and software components. The :ref:`Yocto Project + Compatible <dev-manual/dev-manual-common-tasks:making sure your layer is compatible with yocto project>` + designation provides a minimum level of standardization that + contributes to a strong ecosystem. "YP Compatible" is applied to + appropriate products and software components such as BSPs, other + OE-compatible layers, and related open-source projects, allowing + the producer to use Yocto Project badges and branding assets. + +To illustrate how layers are used to keep things modular, consider +machine customizations. These types of customizations typically reside +in a special layer, rather than a general layer, called a BSP Layer. +Furthermore, the machine customizations should be isolated from recipes +and Metadata that support a new GUI environment, for example. This +situation gives you a couple of layers: one for the machine +configurations, and one for the GUI environment. It is important to +understand, however, that the BSP layer can still make machine-specific +additions to recipes within the GUI environment layer without polluting +the GUI layer itself with those machine-specific changes. You can +accomplish this through a recipe that is a BitBake append +(``.bbappend``) file, which is described later in this section. + +.. note:: + + For general information on BSP layer structure, see the + :doc:`../bsp-guide/bsp-guide` + . + +The :term:`Source Directory` +contains both general layers and BSP layers right out of the box. You +can easily identify layers that ship with a Yocto Project release in the +Source Directory by their names. Layers typically have names that begin +with the string ``meta-``. + +.. note:: + + It is not a requirement that a layer name begin with the prefix + meta- + , but it is a commonly accepted standard in the Yocto Project + community. + +For example, if you were to examine the `tree +view <https://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/>`__ of the +``poky`` repository, you will see several layers: ``meta``, +``meta-skeleton``, ``meta-selftest``, ``meta-poky``, and +``meta-yocto-bsp``. Each of these repositories represents a distinct +layer. + +For procedures on how to create layers, see the +":ref:`dev-manual/dev-manual-common-tasks:understanding and creating layers`" +section in the Yocto Project Development Tasks Manual. + +Components and Tools +==================== + +The Yocto Project employs a collection of components and tools used by +the project itself, by project developers, and by those using the Yocto +Project. These components and tools are open source projects and +metadata that are separate from the reference distribution +(:term:`Poky`) and the +:term:`OpenEmbedded Build System`. Most of the +components and tools are downloaded separately. + +This section provides brief overviews of the components and tools +associated with the Yocto Project. + +.. _gs-development-tools: + +Development Tools +----------------- + +The following list consists of tools that help you develop images and +applications using the Yocto Project: + +- *CROPS:* `CROPS <https://github.com/crops/poky-container/>`__ is an + open source, cross-platform development framework that leverages + `Docker Containers <https://www.docker.com/>`__. CROPS provides an + easily managed, extensible environment that allows you to build + binaries for a variety of architectures on Windows, Linux and Mac OS + X hosts. + +- *devtool:* This command-line tool is available as part of the + extensible SDK (eSDK) and is its cornerstone. You can use ``devtool`` + to help build, test, and package software within the eSDK. You can + use the tool to optionally integrate what you build into an image + built by the OpenEmbedded build system. + + The ``devtool`` command employs a number of sub-commands that allow + you to add, modify, and upgrade recipes. As with the OpenEmbedded + build system, "recipes" represent software packages within + ``devtool``. When you use ``devtool add``, a recipe is automatically + created. When you use ``devtool modify``, the specified existing + recipe is used in order to determine where to get the source code and + how to patch it. In both cases, an environment is set up so that when + you build the recipe a source tree that is under your control is used + in order to allow you to make changes to the source as desired. By + default, both new recipes and the source go into a "workspace" + directory under the eSDK. The ``devtool upgrade`` command updates an + existing recipe so that you can build it for an updated set of source + files. + + You can read about the ``devtool`` workflow in the Yocto Project + Application Development and Extensible Software Development Kit + (eSDK) Manual in the + ":ref:`sdk-manual/sdk-extensible:using \`\`devtool\`\` in your sdk workflow`" + section. + +- *Extensible Software Development Kit (eSDK):* The eSDK provides a + cross-development toolchain and libraries tailored to the contents of + a specific image. The eSDK makes it easy to add new applications and + libraries to an image, modify the source for an existing component, + test changes on the target hardware, and integrate into the rest of + the OpenEmbedded build system. The eSDK gives you a toolchain + experience supplemented with the powerful set of ``devtool`` commands + tailored for the Yocto Project environment. + + For information on the eSDK, see the :doc:`../sdk-manual/sdk-manual` Manual. + +- *Toaster:* Toaster is a web interface to the Yocto Project + OpenEmbedded build system. Toaster allows you to configure, run, and + view information about builds. For information on Toaster, see the + :doc:`../toaster-manual/toaster-manual`. + +.. _gs-production-tools: + +Production Tools +---------------- + +The following list consists of tools that help production related +activities using the Yocto Project: + +- *Auto Upgrade Helper:* This utility when used in conjunction with the + :term:`OpenEmbedded Build System` + (BitBake and + OE-Core) automatically generates upgrades for recipes that are based + on new versions of the recipes published upstream. See + :ref:`dev-manual/dev-manual-common-tasks:using the auto upgrade helper (auh)` + for how to set it up. + +- *Recipe Reporting System:* The Recipe Reporting System tracks recipe + versions available for Yocto Project. The main purpose of the system + is to help you manage the recipes you maintain and to offer a dynamic + overview of the project. The Recipe Reporting System is built on top + of the `OpenEmbedded Layer + Index <http://layers.openembedded.org/layerindex/layers/>`__, which + is a website that indexes OpenEmbedded-Core layers. + +- *Patchwork:* `Patchwork <http://jk.ozlabs.org/projects/patchwork/>`__ + is a fork of a project originally started by + `OzLabs <http://ozlabs.org/>`__. The project is a web-based tracking + system designed to streamline the process of bringing contributions + into a project. The Yocto Project uses Patchwork as an organizational + tool to handle patches, which number in the thousands for every + release. + +- *AutoBuilder:* AutoBuilder is a project that automates build tests + and quality assurance (QA). By using the public AutoBuilder, anyone + can determine the status of the current "master" branch of Poky. + + .. note:: + + AutoBuilder is based on buildbot. + + A goal of the Yocto Project is to lead the open source industry with + a project that automates testing and QA procedures. In doing so, the + project encourages a development community that publishes QA and test + plans, publicly demonstrates QA and test plans, and encourages + development of tools that automate and test and QA procedures for the + benefit of the development community. + + You can learn more about the AutoBuilder used by the Yocto Project + Autobuilder :doc:`here <../test-manual/test-manual-understand-autobuilder>`. + +- *Cross-Prelink:* Prelinking is the process of pre-computing the load + addresses and link tables generated by the dynamic linker as compared + to doing this at runtime. Doing this ahead of time results in + performance improvements when the application is launched and reduced + memory usage for libraries shared by many applications. + + Historically, cross-prelink is a variant of prelink, which was + conceived by `Jakub + Jelínek <http://people.redhat.com/jakub/prelink.pdf>`__ a number of + years ago. Both prelink and cross-prelink are maintained in the same + repository albeit on separate branches. By providing an emulated + runtime dynamic linker (i.e. ``glibc``-derived ``ld.so`` emulation), + the cross-prelink project extends the prelink software's ability to + prelink a sysroot environment. Additionally, the cross-prelink + software enables the ability to work in sysroot style environments. + + The dynamic linker determines standard load address calculations + based on a variety of factors such as mapping addresses, library + usage, and library function conflicts. The prelink tool uses this + information, from the dynamic linker, to determine unique load + addresses for executable and linkable format (ELF) binaries that are + shared libraries and dynamically linked. The prelink tool modifies + these ELF binaries with the pre-computed information. The result is + faster loading and often lower memory consumption because more of the + library code can be re-used from shared Copy-On-Write (COW) pages. + + The original upstream prelink project only supports running prelink + on the end target device due to the reliance on the target device's + dynamic linker. This restriction causes issues when developing a + cross-compiled system. The cross-prelink adds a synthesized dynamic + loader that runs on the host, thus permitting cross-prelinking + without ever having to run on a read-write target filesystem. + +- *Pseudo:* Pseudo is the Yocto Project implementation of + `fakeroot <http://man.he.net/man1/fakeroot>`__, which is used to run + commands in an environment that seemingly has root privileges. + + During a build, it can be necessary to perform operations that + require system administrator privileges. For example, file ownership + or permissions might need definition. Pseudo is a tool that you can + either use directly or through the environment variable + ``LD_PRELOAD``. Either method allows these operations to succeed as + if system administrator privileges exist even when they do not. + + You can read more about Pseudo in the "`Fakeroot and + Pseudo <#fakeroot-and-pseudo>`__" section. + +.. _gs-openembedded-build-system: + +Open-Embedded Build System Components +------------------------------------- + +The following list consists of components associated with the +:term:`OpenEmbedded Build System`: + +- *BitBake:* BitBake is a core component of the Yocto Project and is + used by the OpenEmbedded build system to build images. While BitBake + is key to the build system, BitBake is maintained separately from the + Yocto Project. + + BitBake is a generic task execution engine that allows shell and + Python tasks to be run efficiently and in parallel while working + within complex inter-task dependency constraints. In short, BitBake + is a build engine that works through recipes written in a specific + format in order to perform sets of tasks. + + You can learn more about BitBake in the :doc:`BitBake User + Manual <bitbake:index>`. + +- *OpenEmbedded-Core:* OpenEmbedded-Core (OE-Core) is a common layer of + metadata (i.e. recipes, classes, and associated files) used by + OpenEmbedded-derived systems, which includes the Yocto Project. The + Yocto Project and the OpenEmbedded Project both maintain the + OpenEmbedded-Core. You can find the OE-Core metadata in the Yocto + Project :yocto_git:`Source Repositories </cgit/cgit.cgi/poky/tree/meta>`. + + Historically, the Yocto Project integrated the OE-Core metadata + throughout the Yocto Project source repository reference system + (Poky). After Yocto Project Version 1.0, the Yocto Project and + OpenEmbedded agreed to work together and share a common core set of + metadata (OE-Core), which contained much of the functionality + previously found in Poky. This collaboration achieved a long-standing + OpenEmbedded objective for having a more tightly controlled and + quality-assured core. The results also fit well with the Yocto + Project objective of achieving a smaller number of fully featured + tools as compared to many different ones. + + Sharing a core set of metadata results in Poky as an integration + layer on top of OE-Core. You can see that in this + `figure <#yp-key-dev-elements>`__. The Yocto Project combines various + components such as BitBake, OE-Core, script "glue", and documentation + for its build system. + +.. _gs-reference-distribution-poky: + +Reference Distribution (Poky) +----------------------------- + +Poky is the Yocto Project reference distribution. It contains the +:term:`OpenEmbedded Build System` +(BitBake and OE-Core) as well as a set of metadata to get you started +building your own distribution. See the +`figure <#what-is-the-yocto-project>`__ in "What is the Yocto Project?" +section for an illustration that shows Poky and its relationship with +other parts of the Yocto Project. + +To use the Yocto Project tools and components, you can download +(``clone``) Poky and use it to bootstrap your own distribution. + +.. note:: + + Poky does not contain binary files. It is a working example of how to + build your own custom Linux distribution from source. + +You can read more about Poky in the "`Reference Embedded Distribution +(Poky) <#reference-embedded-distribution>`__" section. + +.. _gs-packages-for-finished-targets: + +Packages for Finished Targets +----------------------------- + +The following lists components associated with packages for finished +targets: + +- *Matchbox:* Matchbox is an Open Source, base environment for the X + Window System running on non-desktop, embedded platforms such as + handhelds, set-top boxes, kiosks, and anything else for which screen + space, input mechanisms, or system resources are limited. + + Matchbox consists of a number of interchangeable and optional + applications that you can tailor to a specific, non-desktop platform + to enhance usability in constrained environments. + + You can find the Matchbox source in the Yocto Project + :yocto_git:`Source Repositories <>`. + +- *Opkg:* Open PacKaGe management (opkg) is a lightweight package + management system based on the itsy package (ipkg) management system. + Opkg is written in C and resembles Advanced Package Tool (APT) and + Debian Package (dpkg) in operation. + + Opkg is intended for use on embedded Linux devices and is used in + this capacity in the + `OpenEmbedded <http://www.openembedded.org/wiki/Main_Page>`__ and + `OpenWrt <https://openwrt.org/>`__ projects, as well as the Yocto + Project. + + .. note:: + + As best it can, opkg maintains backwards compatibility with ipkg + and conforms to a subset of Debian's policy manual regarding + control files. + + You can find the opkg source in the Yocto Project + :yocto_git:`Source Repositories <>`. + +.. _gs-archived-components: + +Archived Components +------------------- + +The Build Appliance is a virtual machine image that enables you to build +and boot a custom embedded Linux image with the Yocto Project using a +non-Linux development system. + +Historically, the Build Appliance was the second of three methods by +which you could use the Yocto Project on a system that was not native to +Linux. + +1. *Hob:* Hob, which is now deprecated and is no longer available since + the 2.1 release of the Yocto Project provided a rudimentary, + GUI-based interface to the Yocto Project. Toaster has fully replaced + Hob. + +2. *Build Appliance:* Post Hob, the Build Appliance became available. It + was never recommended that you use the Build Appliance as a + day-to-day production development environment with the Yocto Project. + Build Appliance was useful as a way to try out development in the + Yocto Project environment. + +3. *CROPS:* The final and best solution available now for developing + using the Yocto Project on a system not native to Linux is with + `CROPS <#gs-crops-overview>`__. + +.. _gs-development-methods: + +Development Methods +=================== + +The Yocto Project development environment usually involves a +:term:`Build Host` and target +hardware. You use the Build Host to build images and develop +applications, while you use the target hardware to test deployed +software. + +This section provides an introduction to the choices or development +methods you have when setting up your Build Host. Depending on the your +particular workflow preference and the type of operating system your +Build Host runs, several choices exist that allow you to use the Yocto +Project. + +.. note:: + + For additional detail about the Yocto Project development + environment, see the ":doc:`overview-manual-development-environment`" + chapter. + +- *Native Linux Host:* By far the best option for a Build Host. A + system running Linux as its native operating system allows you to + develop software by directly using the + :term:`BitBake` tool. You can + accomplish all aspects of development from a familiar shell of a + supported Linux distribution. + + For information on how to set up a Build Host on a system running + Linux as its native operating system, see the + ":ref:`dev-manual/dev-manual-start:setting up a native linux host`" + section in the Yocto Project Development Tasks Manual. + +- *CROss PlatformS (CROPS):* Typically, you use + `CROPS <https://github.com/crops/poky-container/>`__, which leverages + `Docker Containers <https://www.docker.com/>`__, to set up a Build + Host that is not running Linux (e.g. Microsoft Windows or macOS). + + .. note:: + + You can, however, use CROPS on a Linux-based system. + + CROPS is an open source, cross-platform development framework that + provides an easily managed, extensible environment for building + binaries targeted for a variety of architectures on Windows, macOS, + or Linux hosts. Once the Build Host is set up using CROPS, you can + prepare a shell environment to mimic that of a shell being used on a + system natively running Linux. + + For information on how to set up a Build Host with CROPS, see the + ":ref:`dev-manual/dev-manual-start:setting up to use cross platforms (crops)`" + section in the Yocto Project Development Tasks Manual. + +- *Windows Subsystem For Linux (WSLv2):* You may use Windows Subsystem + For Linux v2 to set up a build host using Windows 10. + + .. note:: + + The Yocto Project is not compatible with WSLv1, it is compatible + but not officially supported nor validated with WSLv2, if you + still decide to use WSL please upgrade to WSLv2. + + The Windows Subsystem For Linux allows Windows 10 to run a real Linux + kernel inside of a lightweight utility virtual machine (VM) using + virtualization technology. + + For information on how to set up a Build Host with WSLv2, see the + ":ref:`dev-manual/dev-manual-start:setting up to use windows subsystem for linux (wslv2)`" + section in the Yocto Project Development Tasks Manual. + +- *Toaster:* Regardless of what your Build Host is running, you can use + Toaster to develop software using the Yocto Project. Toaster is 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. You can use Toaster to + configure and start builds on multiple remote build servers. + + For information about and how to use Toaster, see the + :doc:`../toaster-manual/toaster-manual`. + +.. _reference-embedded-distribution: + +Reference Embedded Distribution (Poky) +====================================== + +"Poky", which is pronounced *Pock*-ee, is the name of the Yocto +Project's reference distribution or Reference OS Kit. Poky contains the +:term:`OpenEmbedded Build System` +(:term:`BitBake` and +:term:`OpenEmbedded-Core (OE-Core)`) as well as a set +of :term:`Metadata` to get you started +building your own distro. In other words, Poky is a base specification +of the functionality needed for a typical embedded system as well as the +components from the Yocto Project that allow you to build a distribution +into a usable binary image. + +Poky is a combined repository of BitBake, OpenEmbedded-Core (which is +found in ``meta``), ``meta-poky``, ``meta-yocto-bsp``, and documentation +provided all together and known to work well together. You can view +these items that make up the Poky repository in the +:yocto_git:`Source Repositories </cgit/cgit.cgi/poky/tree/>`. + +.. note:: + + If you are interested in all the contents of the + poky + Git repository, see the ":ref:`ref-manual/ref-structure:top-level core components`" + section in the Yocto Project Reference Manual. + +The following figure illustrates what generally comprises Poky: + +.. image:: figures/poky-reference-distribution.png + :align: center + +- BitBake is a task executor and scheduler that is the heart of the + OpenEmbedded build system. + +- ``meta-poky``, which is Poky-specific metadata. + +- ``meta-yocto-bsp``, which are Yocto Project-specific Board Support + Packages (BSPs). + +- OpenEmbedded-Core (OE-Core) metadata, which includes shared + configurations, global variable definitions, shared classes, + packaging, and recipes. Classes define the encapsulation and + inheritance of build logic. Recipes are the logical units of software + and images to be built. + +- Documentation, which contains the Yocto Project source files used to + make the set of user manuals. + +.. note:: + + While Poky is a "complete" distribution specification and is tested + and put through QA, you cannot use it as a product "out of the box" + in its current form. + +To use the Yocto Project tools, you can use Git to clone (download) the +Poky repository then use your local copy of the reference distribution +to bootstrap your own distribution. + +.. note:: + + Poky does not contain binary files. It is a working example of how to + build your own custom Linux distribution from source. + +Poky has a regular, well established, six-month release cycle under its +own version. Major releases occur at the same time major releases (point +releases) occur for the Yocto Project, which are typically in the Spring +and Fall. For more information on the Yocto Project release schedule and +cadence, see the ":doc:`../ref-manual/ref-release-process`" chapter in the +Yocto Project Reference Manual. + +Much has been said about Poky being a "default configuration". A default +configuration provides a starting image footprint. You can use Poky out +of the box to create an image ranging from a shell-accessible minimal +image all the way up to a Linux Standard Base-compliant image that uses +a GNOME Mobile and Embedded (GMAE) based reference user interface called +Sato. + +One of the most powerful properties of Poky is that every aspect of a +build is controlled by the metadata. You can use metadata to augment +these base image types by adding metadata +`layers <#the-yocto-project-layer-model>`__ that extend functionality. +These layers can provide, for example, an additional software stack for +an image type, add a board support package (BSP) for additional +hardware, or even create a new image type. + +Metadata is loosely grouped into configuration files or package recipes. +A recipe is a collection of non-executable metadata used by BitBake to +set variables or define additional build-time tasks. A recipe contains +fields such as the recipe description, the recipe version, the license +of the package and the upstream source repository. A recipe might also +indicate that the build process uses autotools, make, distutils or any +other build process, in which case the basic functionality can be +defined by the classes it inherits from the OE-Core layer's class +definitions in ``./meta/classes``. Within a recipe you can also define +additional tasks as well as task prerequisites. Recipe syntax through +BitBake also supports both ``_prepend`` and ``_append`` operators as a +method of extending task functionality. These operators inject code into +the beginning or end of a task. For information on these BitBake +operators, see the +":ref:`bitbake:bitbake-user-manual/bitbake-user-manual-metadata:appending and prepending (override style syntax)`" +section in the BitBake User's Manual. + +.. _openembedded-build-system-workflow: + +The OpenEmbedded Build System Workflow +====================================== + +The :term:`OpenEmbedded Build System` uses a "workflow" to +accomplish image and SDK generation. The following figure overviews that +workflow: + +.. image:: figures/YP-flow-diagram.png + :align: center + +Following is a brief summary of the "workflow": + +1. Developers specify architecture, policies, patches and configuration + details. + +2. The build system fetches and downloads the source code from the + specified location. The build system supports standard methods such + as tarballs or source code repositories systems such as Git. + +3. Once source code is downloaded, the build system extracts the sources + into a local work area where patches are applied and common steps for + configuring and compiling the software are run. + +4. The build system then installs the software into a temporary staging + area where the binary package format you select (DEB, RPM, or IPK) is + used to roll up the software. + +5. Different QA and sanity checks run throughout entire build process. + +6. After the binaries are created, the build system generates a binary + package feed that is used to create the final root file image. + +7. The build system generates the file system image and a customized + Extensible SDK (eSDK) for application development in parallel. + +For a very detailed look at this workflow, see the "`OpenEmbedded Build +System Concepts <#openembedded-build-system-build-concepts>`__" section. + +Some Basic Terms +================ + +It helps to understand some basic fundamental terms when learning the +Yocto Project. Although a list of terms exists in the ":doc:`Yocto Project +Terms <../ref-manual/ref-terms>`" section of the Yocto Project +Reference Manual, this section provides the definitions of some terms +helpful for getting started: + +- *Configuration Files:* Files that hold global definitions of + variables, user-defined variables, and hardware configuration + information. These files tell the :term:`OpenEmbedded Build System` + what to build and + what to put into the image to support a particular platform. + +- *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/sdk-manual` manual. + +- *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 more detailed information on layers, see the + ":ref:`dev-manual/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. + +- *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 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. + +- *OpenEmbedded Build System:* The terms "BitBake" and "build system" + are sometimes used for the OpenEmbedded Build System. + + BitBake is a task scheduler and execution engine that parses + instructions (i.e. recipes) and configuration data. After a parsing + phase, BitBake creates a dependency tree to order the compilation, + schedules the compilation of the included code, and finally executes + the building of the specified custom Linux image (distribution). + BitBake is similar to the ``make`` tool. + + During a build process, the build system tracks dependencies and + performs a native or cross-compilation of the package. As a first + step in a cross-build setup, the framework attempts to create a + cross-compiler toolchain (i.e. Extensible SDK) suited for the target + platform. + +- *OpenEmbedded-Core (OE-Core):* OE-Core is metadata comprised of + foundation 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 quality-assured core + set of recipes. + + You can see the Metadata in the ``meta`` directory of the Yocto + Project `Source + Repositories <http://git.yoctoproject.org/cgit/cgit.cgi>`__. + +- *Packages:* 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/ref-system-requirements:required packages for the build host`" + section in the Yocto Project Reference Manual 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`). + +- *Poky:* Poky 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 is an integration layer on top of OE-Core. + +- *Recipe:* The most common form of metadata. A recipe contains a list + of settings and tasks (i.e. instructions) for building packages that + are then used to build the binary image. A recipe describes where you + get source code and which patches to apply. Recipes describe + dependencies for libraries or for other recipes as well as + configuration and compilation options. Related recipes are + consolidated into a layer. diff --git a/poky/documentation/overview-manual/overview-manual-yp-intro.xml b/poky/documentation/overview-manual/overview-manual-yp-intro.xml index 1b60a3030..a2a1f494b 100644 --- a/poky/documentation/overview-manual/overview-manual-yp-intro.xml +++ b/poky/documentation/overview-manual/overview-manual-yp-intro.xml @@ -1,6 +1,7 @@ <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > +<!--SPDX-License-Identifier: CC-BY-2.0-UK--> <chapter id='overview-yp'> <title>Introducing the Yocto Project</title> @@ -458,7 +459,7 @@ <para>The <filename>devtool</filename> command employs a number of sub-commands that allow you to add, modify, and upgrade recipes. - As with the OpenEmbedded build system, “recipes” + As with the OpenEmbedded build system, "recipes" represent software packages within <filename>devtool</filename>. When you use <filename>devtool add</filename>, a recipe @@ -471,7 +472,7 @@ control is used in order to allow you to make changes to the source as desired. By default, both new recipes and the source go into - a “workspace” directory under the eSDK. + a "workspace" directory under the eSDK. The <filename>devtool upgrade</filename> command updates an existing recipe so that you can build it for an updated set of source files.</para> @@ -597,7 +598,7 @@ By providing an emulated runtime dynamic linker (i.e. <filename>glibc</filename>-derived <filename>ld.so</filename> emulation), the - cross-prelink project extends the prelink software’s + cross-prelink project extends the prelink software's ability to prelink a sysroot environment. Additionally, the cross-prelink software enables the ability to work in sysroot style environments.</para> @@ -619,7 +620,7 @@ <para>The original upstream prelink project only supports running prelink on the end target device - due to the reliance on the target device’s dynamic + due to the reliance on the target device's dynamic linker. This restriction causes issues when developing a cross-compiled system. @@ -712,7 +713,7 @@ You can see that in this <link linkend='yp-key-dev-elements'>figure</link>. The Yocto Project combines various components such as - BitBake, OE-Core, script “glue”, and documentation + BitBake, OE-Core, script "glue", and documentation for its build system. </para></listitem> </itemizedlist> @@ -790,7 +791,7 @@ <note> As best it can, opkg maintains backwards compatibility with ipkg and conforms to a subset - of Debian’s policy manual regarding control files. + of Debian's policy manual regarding control files. </note> </para></listitem> </itemizedlist> diff --git a/poky/documentation/overview-manual/overview-manual.rst b/poky/documentation/overview-manual/overview-manual.rst new file mode 100644 index 000000000..80ce9aae7 --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual.rst @@ -0,0 +1,19 @@ +.. SPDX-License-Identifier: CC-BY-2.0-UK + +========================================== +Yocto Project Overview and Concepts Manual +========================================== + +| + +.. toctree:: + :caption: Table of Contents + :numbered: + + overview-manual-intro + overview-manual-yp-intro + overview-manual-development-environment + overview-manual-concepts + history + +.. include:: /boilerplate.rst diff --git a/poky/documentation/overview-manual/overview-manual.xml b/poky/documentation/overview-manual/overview-manual.xml index 210d644b3..8021a2e95 100755 --- a/poky/documentation/overview-manual/overview-manual.xml +++ b/poky/documentation/overview-manual/overview-manual.xml @@ -1,6 +1,7 @@ <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > +<!--SPDX-License-Identifier: CC-BY-2.0-UK--> <book id='overview-manual' lang='en' xmlns:xi="http://www.w3.org/2003/XInclude" |