From 4873add6e11c1bd421c83cd08df589f1184aa673 Mon Sep 17 00:00:00 2001 From: Andrew Geissler Date: Mon, 2 Nov 2020 18:44:49 -0600 Subject: Revert "poky: subtree update:b23aa6b753..ad30a6d470" This reverts commit af5e4ef732faedf66c6dc1756432e9de2ac72988. This commit introduced openbmc/openbmc#3720 and no solution has been forthcoming. Revert until we can get to the bottom of this. Change-Id: I2fb0d81eb26cf3dadb2f2abdd1a1bb7a95eaf03c --- poky/documentation/overview-manual/history.rst | 2 +- .../overview-manual/overview-manual-concepts.rst | 2 +- .../overview-manual/overview-manual-concepts.xml | 3235 ++++++++++++++++++++ .../overview-manual-customization.xsl | 29 + .../overview-manual-development-environment.rst | 2 +- .../overview-manual-development-environment.xml | 954 ++++++ .../overview-manual/overview-manual-intro.rst | 2 +- .../overview-manual/overview-manual-intro.xml | 113 + .../overview-manual/overview-manual-style.css | 990 ++++++ .../overview-manual/overview-manual-yp-intro.rst | 2 +- .../overview-manual/overview-manual-yp-intro.xml | 1333 ++++++++ .../overview-manual/overview-manual.rst | 2 +- .../overview-manual/overview-manual.xml | 130 + 13 files changed, 6790 insertions(+), 6 deletions(-) create mode 100644 poky/documentation/overview-manual/overview-manual-concepts.xml create mode 100644 poky/documentation/overview-manual/overview-manual-customization.xsl create mode 100644 poky/documentation/overview-manual/overview-manual-development-environment.xml create mode 100644 poky/documentation/overview-manual/overview-manual-intro.xml create mode 100644 poky/documentation/overview-manual/overview-manual-style.css create mode 100644 poky/documentation/overview-manual/overview-manual-yp-intro.xml create mode 100755 poky/documentation/overview-manual/overview-manual.xml (limited to 'poky/documentation/overview-manual') diff --git a/poky/documentation/overview-manual/history.rst b/poky/documentation/overview-manual/history.rst index 6fc700a01..0273d28b9 100644 --- a/poky/documentation/overview-manual/history.rst +++ b/poky/documentation/overview-manual/history.rst @@ -1,4 +1,4 @@ -.. SPDX-License-Identifier: CC-BY-SA-2.0-UK +.. SPDX-License-Identifier: CC-BY-2.0-UK *********************** Manual Revision History diff --git a/poky/documentation/overview-manual/overview-manual-concepts.rst b/poky/documentation/overview-manual/overview-manual-concepts.rst index d9f50e519..6ce5f80af 100644 --- a/poky/documentation/overview-manual/overview-manual-concepts.rst +++ b/poky/documentation/overview-manual/overview-manual-concepts.rst @@ -1,4 +1,4 @@ -.. SPDX-License-Identifier: CC-BY-SA-2.0-UK +.. SPDX-License-Identifier: CC-BY-2.0-UK ********************** Yocto Project Concepts diff --git a/poky/documentation/overview-manual/overview-manual-concepts.xml b/poky/documentation/overview-manual/overview-manual-concepts.xml new file mode 100644 index 000000000..58b64bd26 --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-concepts.xml @@ -0,0 +1,3235 @@ + %poky; ] > + + + +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 + OpenEmbedded build system + workflow, cross-development toolchains, shared state cache, and so + forth are explained. + + +
+ Yocto Project Components + + + The + BitBake + task executor together with various types of configuration files + form the + OpenEmbedded-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 + "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 + "OpenEmbedded Build System Concepts" + section. + + +
+ BitBake + + + BitBake is the tool at the heart of the + OpenEmbedded build system + and is responsible for parsing the + 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 + BitBake User Manual. + + + + 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 packagename, + where packagename is the name of the + package 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 + "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. + +
+ +
+ 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. + +
+ +
+ Classes + + + Class files (.bbclass) contain information + that is useful to share between recipes files. + An example is the + autotools + class, which contains common settings for any application that + Autotools uses. + The + "Classes" + chapter in the Yocto Project Reference Manual provides + details about classes and how to use them. + +
+ +
+ 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 + Build Directory. + +
+
+ +
+ 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 + 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 + and + OpenEmbedded Layer Index + 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 + "Understanding and Creating Layers" + section of the Yocto Project Development Tasks Manual. + +
+ +
+ OpenEmbedded Build System Concepts + + + This section takes a more detailed look inside the build + process used by the + 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. + + + + + + + + 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 + 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: + + + + + + + + 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 + Source Directory. + For simplicity, this section refers to the Source Directory as + the "Poky Directory." + + + + When you clone the + 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. + + 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 + &OE_INIT_FILE;, + which is the build environment script. + + + + Sourcing the build environment script creates a + 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 &OE_INIT_FILE; script + in the context of separate + OpenEmbedded-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. + + 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 + local.conf.sample + in the meta-poky layer: + + + Target Machine Selection: + Controlled by the + MACHINE + variable. + + + Download Directory: + Controlled by the + DL_DIR + variable. + + + Shared State Directory: + Controlled by the + SSTATE_DIR + variable. + + + Build Output: + Controlled by the + TMPDIR + variable. + + + Distribution Policy: + Controlled by the + DISTRO + variable. + + + Packaging Format: + Controlled by the + PACKAGE_CLASSES + variable. + + + SDK Target Architecture: + Controlled by the + SDKMACHINE + variable. + + + Extra Image Packages: + Controlled by the + EXTRA_IMAGE_FEATURES + variable. + + + + 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 + "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 + PACKAGE_CLASSES + variable. + + One useful scenario for using the + conf/site.conf file is to extend + your + 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 + 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 + "Syntax and Operators" + 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: + + + 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 from the + OpenEmbedded Layer Index. + This layer is for version 5.0 of the popular + 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 + is the + 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 + meta-poky + layer. + Within the distro layer is a + conf/distro directory that + contains distro configuration files (e.g. + 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: + + + + + + + + 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 + "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" and + "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 + also shows layers categorized under "Yocto Metadata Layers." + + 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 + "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 + Yocto Project Board Support Package (BSP) Developer's Guide. + + 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. + + 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 + + + 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 + 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 + 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 + 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 + 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: + + + + + + +
+ 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 + 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. + +
+ +
+ Source Control Managers (Optional) + + + Another place from which the build system can get source + files is with + fetchers + employing various Source Control Managers (SCMs) such as + Git or Subversion. + In such cases, a repository is cloned or checked out. + The + do_fetch + task inside BitBake uses + the SRC_URI + variable and the argument's prefix to determine the correct + fetcher module. + + 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 + BB_GENERATE_MIRROR_TARBALLS + variable in the Yocto Project Reference Manual. + + + + + When fetching a repository, BitBake uses the + 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 + PREMIRRORS + and + 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 + 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 + + + When the OpenEmbedded build system generates an image or an + SDK, it gets the packages from a package feed area located + in the + Build Directory. + The + 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: + + + + + 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 + PACKAGE_CLASSES + variable. + Before placing the packages into package feeds, + the build process validates them with generated output quality + assurance checks through the + 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: + + + 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 + DEPLOY_DIR_RPM, + DEPLOY_DIR_IPK, + DEPLOY_DIR_DEB, + or + DEPLOY_DIR_TAR, + variables are used, respectively. + + + PACKAGE_ARCH: + Defines architecture-specific sub-folders. + For example, packages could exist for the i586 or + qemux86 architectures. + + + + + + BitBake uses the + do_package_write_* + tasks to generate packages and place them into the package + holding area (e.g. do_package_write_ipk + for IPK packages). + See the + "do_package_write_deb", + "do_package_write_ipk", + "do_package_write_rpm", + and + "do_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 + + + The OpenEmbedded build system uses + BitBake + to produce images and Software Development Kits (SDKs). + You can see from the + general workflow figure, + the BitBake area consists of several functional areas. + This section takes a closer look at each of those areas. + + Separate documentation exists for the BitBake tool. + See the + BitBake User Manual + for reference material on BitBake. + + + +
+ Source Fetching + + + The first stages of building a recipe are to fetch and + unpack the source code: + + + + + The + do_fetch + and + do_unpack + tasks fetch the source files and unpack them into the + Build Directory. + + 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 + "build/" + section in the Yocto Project Reference Manual. + + + + Each recipe has an area in the Build Directory where the + unpacked source code resides. + The + 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: + + + TMPDIR: + The base directory where the OpenEmbedded build + system performs all its work during the build. + The default base directory is the + tmp directory. + + + PACKAGE_ARCH: + The architecture of the built package or packages. + Depending on the eventual destination of the + package or packages (i.e. machine architecture, + build host, + SDK, or specific machine), + PACKAGE_ARCH varies. + See the variable's description for details. + + + TARGET_OS: + The operating system of the target device. + A typical value would be "linux" (e.g. + "qemux86-poky-linux"). + + + 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 the name + of the recipe. + + + WORKDIR: + The location where the OpenEmbedded build system + builds a recipe (i.e. does the work to create the + package). + + + PV: + The version of the recipe used to build the + package. + + + PR: + The revision of the recipe used to build the + package. + + + + + S: + Contains the unpacked source files for a given + recipe. + + + 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. + + + PV: + The version of the recipe used to build the + package. + + + + + + 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 + + + Once source code is fetched and unpacked, BitBake locates + patch files and applies them to the source files: + + + + + The + do_patch + task uses a recipe's + SRC_URI + statements and the + 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 + do_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 + S + directory. + + + + For more information on how the source directories are + created, see the + "Source Fetching" + section. + For more information on how to create patches and how the + build system processes patches, see the + "Patching Code" + section in the Yocto Project Development Tasks Manual. + You can also see the + "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 + "Using Traditional Kernel Development to Patch the Kernel" + section in the Yocto Project Linux Kernel Development + Manual. + +
+ +
+ 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: + + + + + This step in the build process consists of the following + tasks: + + + do_prepare_recipe_sysroot: + This task sets up the two sysroots in + ${WORKDIR} + (i.e. recipe-sysroot and + recipe-sysroot-native) so that + during the packaging phase the sysroots can contain + the contents of the + do_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 + do_configure + task are specific to configurations for the source + code being built by the recipe. + + If you are using the + autotools + class, you can add additional configuration options + by using the + EXTRA_OECONF + or + PACKAGECONFIG_CONFARGS + variables. + For information on how this variable works within + that class, see the + autotools + class + here. + + + do_compile: + Once a configuration task has been satisfied, + BitBake compiles the source using the + do_compile + task. + Compilation occurs in the directory pointed to by + the + B + variable. + Realize that the B directory + is, by default, the same as the + S + directory. + + + do_install: + After compilation completes, BitBake executes the + do_install + task. + This task copies files from the + B directory and places them + in a holding area pointed to by the + D + variable. + Packaging occurs later using files from this + holding directory. + + + +
+ +
+ Package Splitting + + + After source code is configured, compiled, and staged, the + build system analyzes the results and splits the output + into packages: + + + + + The + do_package + and + do_packagedata + tasks combine to analyze the files found in the + 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 + do_populate_sysroot + task stages (copies) a subset of the files installed by + the + do_install + task into the appropriate sysroot. + Working, staged, and intermediate results of the analysis + and package splitting process use several areas: + + + PKGD: + The destination directory + (i.e. package) for packages + before they are split into individual packages. + + + PKGDESTWORK: + A temporary work area (i.e. + pkgdata) used by the + do_package task to save + package metadata. + + + PKGDEST: + The parent directory (i.e. + packages-split) for packages + after they have been split. + + + 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. + + + STAGING_DIR_HOST: + The path for the sysroot for the system on which + a component is built to run (i.e. + recipe-sysroot). + + + STAGING_DIR_NATIVE: + The path for the sysroot used when building + components for the build host (i.e. + recipe-sysroot-native). + + + 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 + FILES + variable defines the files that go into each package in + PACKAGES. + If you want details on how this is accomplished, you can + look at + package.bbclass. + + + + Depending on the type of packages being created (RPM, DEB, + or IPK), the + do_package_write_* + task creates the actual packages and places them in the + Package Feed area, which is + ${TMPDIR}/deploy. + You can see the + "Package Feeds" + section for more detail on that part of the build process. + + 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 + + + Once packages are split and stored in the Package Feeds + area, the build system uses BitBake to generate the root + filesystem image: + + + + + The image generation process consists of several stages and + depends on several tasks and variables. + The + do_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: + + + IMAGE_INSTALL: + Lists out the base set of packages from which to + install from the Package Feeds area. + + + PACKAGE_EXCLUDE: + Specifies packages that should not be installed + into the image. + + + IMAGE_FEATURES: + Specifies features to include in the image. + Most of these features map to additional packages + for installation. + + + 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. + + + IMAGE_LINGUAS: + Determines the language(s) for which additional + language support packages are installed. + + + PACKAGE_INSTALL: + The final list of packages passed to the package + manager for installation into the image. + + + + + + With + 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 + 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 + testimage + class, for example, to determine whether or not to run + specific tests. + See the + 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 + 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 + do_image + task. + The build system runs any pre-processing commands as + defined by the + 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 + 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 + do_image_complete + task. + This task completes the image by applying any image + post processing as defined through the + IMAGE_POSTPROCESS_COMMAND + variable. + The variable specifies a list of functions to call once the + build system has created the final image output files. + + 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 + + + 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): + + + + + + For more information on the cross-development toolchain + generation, see the + "Cross-Development Toolchain Generation" + section. + For information on advantages gained when building a + cross-development toolchain using the + do_populate_sdk + task, see the + "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 + do_populate_sdk + and + do_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" + 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 + 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 + STAMPS_DIR + directory. + The beginning of the stamp file's filename is determined + by the + STAMP + variable, and the end of the name consists of the task's + name and current + input checksum. + + 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. + + The stamp mechanism is more general than the + shared state (sstate) cache mechanism described in the + "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 + TMPDIR + (e.g. in some recipe's + 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 + nostamp + 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 + "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. + + For information on variables affecting sstate, see the + SSTATE_DIR + and + 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 + do_package_write_* + task). + In other cases, it does not make sense (e.g. a + do_patch + task or a + do_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 + do_package, + do_package_write_*, + do_deploy, + do_packagedata, + and + do_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 + BB_HASHCHECK_FUNCTION + variable and returns a list of available objects. + The function specified by the + 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 + + + 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 + that BitBake output, in part, consists of images. + This section takes a closer look at this output: + + + + + For a list of example images that the Yocto Project provides, + see the + "Images" + chapter in the Yocto Project Reference Manual. + + + + The build process writes images out to the + 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 + DEPLOY_DIR + variable points to the deploy directory, + while the + DEPLOY_DIR_IMAGE + variable points to the appropriate directory containing images + for the current configuration. + + + kernel-image: + A kernel binary file. + The + 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 + 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 + 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. + + + +
+ +
+ Application Development SDK + + + In the + 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: + + + + + 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. + + + Notes + + + 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" + section. + + + For information on setting up a cross-development + environment, see the + Yocto Project Application Development and the Extensible Software Development Kit (eSDK) + manual. + + + + + + All the output files for an SDK are written to the + deploy/sdk folder inside the + 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: + + + DEPLOY_DIR: + Points to the deploy directory. + + + 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. + + + SDK_INCLUDE_PKGDATA: + Specifies whether or not packagedata is included in the + extensible SDK for all recipes in the "world" target. + + + SDK_INCLUDE_TOOLCHAIN: + Specifies whether or not the toolchain is included + when building the extensible SDK. + + + SDK_LOCAL_CONF_WHITELIST: + A list of variables allowed through from the build + system configuration into the extensible SDK + configuration. + + + SDK_LOCAL_CONF_BLACKLIST: + A list of variables not allowed through from the build + system configuration into the extensible SDK + configuration. + + + SDK_INHERIT_BLACKLIST: + A list of classes to remove from the + INHERIT + value globally within the extensible SDK configuration. + + + This next list, shows the variables associated with a standard + SDK: + + + DEPLOY_DIR: + Points to the deploy directory. + + + SDKMACHINE: + Specifies the architecture of the machine on which the + cross-development tools are run to create packages for + the target hardware. + + + SDKIMAGE_FEATURES: + Lists the features to include in the "target" part + of the SDK. + + + 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. + + + TOOLCHAIN_TARGET_TASK: + Lists packages that make up the target part of the SDK + (i.e. the part built for the target hardware). + + + SDKPATH: + Defines the default SDK installation path offered by + the installation script. + + + 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. + + + 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 + cross-development toolchains. + 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 + Yocto Project Application Development and the Extensible Software Development Kit (eSDK) + 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. + + + + + + + + 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 + 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. + + 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. + + 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 + 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 + SDKMACHINE, + which might or might not be the same + machine as the Build Host. + + 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 + 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. + + + + + + For information on advantages gained when building a + cross-development toolchain installer, see the + "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 + 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. + Notes + + + The build system does not maintain + 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 + "Automatically Incrementing a Binary Package Revision 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 + "Viewing Metadata Used to Create the Input Signature of a Shared State Task" + and + "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. + + +
+ 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 + do_install + and + do_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. + +
+ +
+ 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 + 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. + + 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 + PACKAGE_ARCHS + variable does not depend on the value of + 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 + 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 + WORKDIR + since that variable is actually constructed as a path within + 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 + 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. + 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 + 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 + 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 + WORKDIR. + A good example is the output of either + do_install + or + do_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 + do_deploy + example taken from the + 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 + sstate + class, to before and after the + do_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}. + + 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 + ${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 + ${DEPLOY_DIR_IMAGE} by the + do_deploy_setscene task + instead, skipping the + do_deploy task. + + + + The following task definition is glue logic needed to + make the previous settings effective: + + python do_deploy_setscene () { + sstate_setscene(d) + } + addtask do_deploy_setscene + + sstate_setscene() takes the flags + above as input and accelerates the + do_deploy task through the + shared state cache if possible. + If the task was accelerated, + sstate_setscene() returns True. + Otherwise, it returns False, and the normal + do_deploy task runs. + For more information, see the + "setscene" + section in the BitBake User Manual. + + + The do_deploy[dirs] = "${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 + "Variable Flags" + section in the BitBake User Manual. + + In cases where + sstate-inputdirs and + sstate-outputdirs would be the + same, you can use + sstate-plaindirs. + For example, to preserve the + ${PKGD} and + ${PKGDEST} output from the + do_package + task, use the following: + + do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}" + + + + + The do_deploy[stamp-extra-info] = "${MACHINE_ARCH}" + line appends extra metadata to the + stamp file. + In this case, the metadata makes the task specific + to a machine's architecture. + See + "The Task List" + 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 + SSTATE_DIR + and + 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" + + + 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 + do_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 + 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 + do_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 + of the library. + The resulting shared-library-to-package mapping + is saved globally in + PKGDATA_DIR + by the + do_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 + 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. + + 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 + RRECOMMENDS. + + 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 + ALLOW_EMPTY + variable for more information. + + + + + + The do_package task depends on the + do_packagedata task of each recipe in + DEPENDS + through use of a + [deptask] + 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. + do_install, + do_package_write*, + do_rootfs, + and + do_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 + 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", + which is derived from the BitBake keyword/variable + flag that requests a fake root environment for a task. + + + + In the + OpenEmbedded build system, + the program that implements fakeroot is known as + 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 + ${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. + Caution + 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 + FAKEROOT* + variables in the BitBake User Manual. + You can also reference the + "Why Not Fakeroot?" + article for background information on Fakeroot and Pseudo. + +
+ + diff --git a/poky/documentation/overview-manual/overview-manual-customization.xsl b/poky/documentation/overview-manual/overview-manual-customization.xsl new file mode 100644 index 000000000..1dd91bde8 --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-customization.xsl @@ -0,0 +1,29 @@ + + + + + + + + + + + + + + + + + + + + + + + diff --git a/poky/documentation/overview-manual/overview-manual-development-environment.rst b/poky/documentation/overview-manual/overview-manual-development-environment.rst index 4bedd6df6..bb2c8e72e 100644 --- a/poky/documentation/overview-manual/overview-manual-development-environment.rst +++ b/poky/documentation/overview-manual/overview-manual-development-environment.rst @@ -1,4 +1,4 @@ -.. SPDX-License-Identifier: CC-BY-SA-2.0-UK +.. SPDX-License-Identifier: CC-BY-2.0-UK ***************************************** The Yocto Project Development Environment diff --git a/poky/documentation/overview-manual/overview-manual-development-environment.xml b/poky/documentation/overview-manual/overview-manual-development-environment.xml new file mode 100644 index 000000000..08ad07131 --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-development-environment.xml @@ -0,0 +1,954 @@ + %poky; ] > + + + +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. + You can also find helpful information on how to participate in the + Linux Community + here. + +
+ +
+ The Development Host + + + A development host or + 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, + which leverages + Docker Containers. + 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 + "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 + "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 + 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 + "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 + Yocto Project Board Support Package (BSP) Developer's Guide + provides BSP-related development information. + For specifics on development host preparation, see the + "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 + Yocto Project Linux Kernel Development Manual + provides kernel-related development information. + For specifics on development host preparation, see the + "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 + Toaster User Manual. + + + +
+ +
+ Yocto Project Source Repositories + + + The Yocto Project team maintains complete source repositories for all + Yocto Project files at + . + 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 + 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 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. + Notes + + + The recommended method for setting up the Yocto Project + Source Directory + and the files for supported BSPs + (e.g., meta-intel) is to use + 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: + + + + 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. + + + + For steps on how to view and access these upstream Git + repositories, see the + "Accessing Source Repositories" + Section in the Yocto Project Development Tasks Manual. + + + + Index of /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. + + + + For steps on how to view and access these files, see the + "Accessing Index of Releases" + section in the Yocto Project Development Tasks Manual. + + + "DOWNLOADS" page for the + 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 + Index of /releases: + area. + + + + For steps on how to use the "DOWNLOADS" page, see the + "Using the Downloads Page" + section in the Yocto Project Development Tasks Manual. + + + +
+ +
+ Git Workflows and the Yocto Project + + + Developing using the Yocto Project likely requires the use of + 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. + + 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. + + For information on finding out who is responsible for (maintains) + a particular area of code in the Yocto Project, see the + "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 + 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 + "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. + + + + + + + + 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. + + + 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 + Source Directory. + For information on how to use these scripts, see the + "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 + "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. + Notes + + + For more information on Git, see + . + + + 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 + . + + + For information beyond the introductory nature in this + section, see the + "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" + section, the Yocto Project maintains source repositories at + . + 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 + "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 + 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 + 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. + + + + 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. + + 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 + + + Free software license history + + + + + + 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. + You can find information on the GNU GPL + here. + + + + 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 + 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 + 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 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 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 + 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 + "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-intro.rst b/poky/documentation/overview-manual/overview-manual-intro.rst index 8885eb89f..3f206fd54 100644 --- a/poky/documentation/overview-manual/overview-manual-intro.rst +++ b/poky/documentation/overview-manual/overview-manual-intro.rst @@ -1,4 +1,4 @@ -.. SPDX-License-Identifier: CC-BY-SA-2.0-UK +.. SPDX-License-Identifier: CC-BY-2.0-UK ********************************************** The Yocto Project Overview and Concepts Manual diff --git a/poky/documentation/overview-manual/overview-manual-intro.xml b/poky/documentation/overview-manual/overview-manual-intro.xml new file mode 100644 index 000000000..0e0bfed6e --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-intro.xml @@ -0,0 +1,113 @@ + %poky; ] > + + + + +The Yocto Project Overview and Concepts Manual +
+ 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: + 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 + Poky + reference distribution, the OpenEmbedded build system + workflow, and some basic Yocto terms. + + + The Yocto Project 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. + + + Yocto Project 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 + Yocto Project Development Tasks Manual + provides examples on how to perform various development + tasks. + As another example, the + Yocto Project Application Development and the Extensible Software Development Kit (eSDK) + 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 + Yocto Project Reference Manual. + As another example, the + Yocto Project Board Support Package (BSP) Developer's 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. + + + +
+ +
+ 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 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 + Yocto Project Quick Build + document. + For a comprehensive list of links and other documentation, see the + "Links and Related Documentation" + section in the Yocto Project Reference Manual. + +
+ + diff --git a/poky/documentation/overview-manual/overview-manual-style.css b/poky/documentation/overview-manual/overview-manual-style.css new file mode 100644 index 000000000..eec934161 --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-style.css @@ -0,0 +1,990 @@ +/* + SPDX-License-Identifier: CC-BY-2.0-UK + + Generic XHTML / DocBook XHTML CSS Stylesheet. + + Browser wrangling and typographic design by + Oyvind Kolas / pippin@gimp.org + + Customised for Poky by + Matthew Allum / mallum@o-hand.com + + Thanks to: + Liam R. E. Quin + William Skaggs + Jakub Steiner + + Structure + --------- + + The stylesheet is divided into the following sections: + + Positioning + Margins, paddings, width, font-size, clearing. + Decorations + Borders, style + Colors + Colors + Graphics + Graphical backgrounds + Nasty IE tweaks + Workarounds needed to make it work in internet explorer, + currently makes the stylesheet non validating, but up until + this point it is validating. + Mozilla extensions + Transparency for footer + Rounded corners on boxes + +*/ + + + /*************** / + / Positioning / +/ ***************/ + +body { + font-family: Verdana, Sans, sans-serif; + + min-width: 640px; + width: 80%; + margin: 0em auto; + padding: 2em 5em 5em 5em; + color: #333; +} + +h1,h2,h3,h4,h5,h6,h7 { + font-family: Arial, Sans; + color: #00557D; + clear: both; +} + +h1 { + font-size: 2em; + text-align: left; + padding: 0em 0em 0em 0em; + margin: 2em 0em 0em 0em; +} + +h2.subtitle { + margin: 0.10em 0em 3.0em 0em; + padding: 0em 0em 0em 0em; 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+ background-attachment: fixed; +} + +.navheader, +.note, +.tip { + background-image: url("images/note_bg.jpg"); + background-attachment: fixed; +} + +.warning, +.caution { + background-image: url("images/warning_bg.jpg"); + background-attachment: fixed; +} + +.figure, +.informalfigure, +.example, +.informalexample, +.table, +.informaltable { + background-image: url("images/figure_bg.jpg"); + background-attachment: fixed; +} + +*/ +h1, +h2, +h3, +h4, +h5, +h6, +h7{ +} + +/* +Example of how to stick an image as part of the title. + +div.article .titlepage .title +{ + background-image: url("figures/white-on-black.png"); + background-position: center; + background-repeat: repeat-x; +} +*/ + +div.preface .titlepage .title, +div.colophon .title, +div.chapter .titlepage .title, +div.article .titlepage .title +{ +} + +div.section div.section .titlepage .title, +div.sect2 .titlepage .title { + background: none; +} + + +h1.title { + background-color: transparent; + background-repeat: no-repeat; + height: 256px; + text-indent: -9000px; + overflow:hidden; +} + +h2.subtitle { + background-color: transparent; + text-indent: -9000px; + overflow:hidden; + width: 0px; + display: none; +} + + /*************************************** / + / pippin.gimp.org specific alterations / +/ ***************************************/ + +/* +div.heading, div.navheader { + color: #777; + font-size: 80%; + padding: 0; + margin: 0; + text-align: left; + position: absolute; + top: 0px; + left: 0px; + width: 100%; + height: 50px; + background: url('/gfx/heading_bg.png') transparent; + background-repeat: repeat-x; + background-attachment: fixed; + border: none; +} + +div.heading a { + color: #444; +} + +div.footing, div.navfooter { + border: none; + color: #ddd; + font-size: 80%; + text-align:right; + + width: 100%; + padding-top: 10px; + position: absolute; + bottom: 0px; + left: 0px; + + background: url('/gfx/footing_bg.png') transparent; +} +*/ + + + + /****************** / + / nasty ie tweaks / +/ ******************/ + +/* +div.heading, div.navheader { + width:expression(document.body.clientWidth + "px"); +} + +div.footing, div.navfooter { + width:expression(document.body.clientWidth + "px"); + margin-left:expression("-5em"); +} +body { + padding:expression("4em 5em 0em 5em"); +} +*/ + + /**************************************** / + / mozilla vendor specific css extensions / +/ ****************************************/ +/* +div.navfooter, div.footing{ + -moz-opacity: 0.8em; +} + +div.figure, +div.table, +div.informalfigure, +div.informaltable, +div.informalexample, +div.example, +.tip, +.warning, +.caution, +.note { + -moz-border-radius: 0.5em; +} + +b.keycap, +.keycap { + -moz-border-radius: 0.3em; +} +*/ + +table tr td table tr td { + display: none; +} + + +hr { + display: none; +} + +table { + border: 0em; +} + + .photo { + float: right; + margin-left: 1.5em; + margin-bottom: 1.5em; + margin-top: 0em; + max-width: 17em; + border: 1px solid gray; + padding: 3px; + background: white; +} + .seperator { + padding-top: 2em; + clear: both; + } + + #validators { + margin-top: 5em; + text-align: right; + color: #777; + } + @media print { + body { + font-size: 8pt; + } + .noprint { + display: none; + } + } + + +.tip, +.note { + background: #f0f0f2; + color: #333; + padding: 20px; + margin: 20px; +} + +.tip h3, +.note h3 { + padding: 0em; + margin: 0em; + font-size: 2em; + font-weight: bold; + color: #333; +} + +.tip a, +.note a { + color: #333; + text-decoration: underline; +} + +.footnote { + font-size: small; + color: #333; +} + +/* Changes the announcement text */ +.tip h3, +.warning h3, +.caution h3, +.note h3 { + font-size:large; + color: #00557D; +} diff --git a/poky/documentation/overview-manual/overview-manual-yp-intro.rst b/poky/documentation/overview-manual/overview-manual-yp-intro.rst index 9073582ac..5cdab7ca4 100644 --- a/poky/documentation/overview-manual/overview-manual-yp-intro.rst +++ b/poky/documentation/overview-manual/overview-manual-yp-intro.rst @@ -1,4 +1,4 @@ -.. SPDX-License-Identifier: CC-BY-SA-2.0-UK +.. SPDX-License-Identifier: CC-BY-2.0-UK ***************************** Introducing the Yocto Project diff --git a/poky/documentation/overview-manual/overview-manual-yp-intro.xml b/poky/documentation/overview-manual/overview-manual-yp-intro.xml new file mode 100644 index 000000000..a2a1f494b --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual-yp-intro.xml @@ -0,0 +1,1333 @@ + %poky; ] > + + + + 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. + + + + + + + + For further introductory information on the Yocto Project, you + might be interested in this + article + by Drew Moseley and in this short introductory + video. + + + + The remainder of this section overviews advantages and challenges + tied to the Yocto Project. + + +
+ 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 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 + 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 + (sstate) scheme. + Being able to build and debug components individually + eases project development. + + + Releases According to a Strict Schedule: + Major releases occur on a + six-month cycle + 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 + license manifest + for review by people who need to track the use of open + source licenses (e.g.legal teams). + + + +
+ +
+ 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 + "What I wish I'd Known" + and + "Transitioning to a Custom Environment for Systems Development" + documents on the Yocto Project website. + + + Project Workflow Could Be Confusing: + The + Yocto Project workflow + 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 + 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 + 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. + Notes + + + Use Board Support Package (BSP) layers from silicon + vendors when possible. + + + Familiarize yourself with the + Yocto Project curated layer index + or the + OpenEmbedded layer index. + The latter contains more layers but they are less + universally validated. + + + Layers support the inclusion of technologies, hardware + components, and software components. + The + Yocto Project Compatible + 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. + + For general information on BSP layer structure, see the + Yocto Project Board Support Packages (BSP) Developer's Guide. + + + + + The + 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-. + + 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 + 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 + "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 + (Poky) + and the + 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. + + +
+ Development Tools + + + The following list consists of tools that help you develop + images and applications using the Yocto Project: + + + CROPS: + CROPS + is an open source, cross-platform development framework + that leverages + Docker Containers. + 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 + "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 + Yocto Project Application Development and the Extensible Software Development Kit (eSDK) + 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 + Toaster User Manual. + + + +
+ +
+ 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 + OpenEmbedded build system + (BitBake and OE-Core) automatically generates upgrades + for recipes that are based on new versions of the + recipes published upstream. + + + 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, + which is a website that indexes OpenEmbedded-Core + layers. + + + Patchwork: + Patchwork + is a fork of a project originally started by + OzLabs. + 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. + + 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 + here. + + + 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 + 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, + 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" + section. + + + +
+ +
+ Open-Embedded Build System Components + + + The following list consists of components associated with the + 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 + BitBake User Manual. + + + 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 + Source Repositories. + + + 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. + The Yocto Project combines various components such as + BitBake, OE-Core, script "glue", and documentation + for its build system. + + + +
+ +
+ Reference Distribution (Poky) + + + Poky is the Yocto Project reference distribution. + It contains the + Open-Embedded build system + (BitBake and OE-Core) as well as a set of metadata to get you + started building your own distribution. + See the + figure 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. + + 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)" + section. + +
+ +
+ 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 + 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 + and + OpenWrt + projects, as well as the Yocto Project. + + As best it can, opkg maintains backwards + compatibility with ipkg and conforms to a subset + of Debian's policy manual regarding control files. + + + + +
+ +
+ 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. + + + 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. + + + 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. + + + CROPS: + The final and best solution available now for + developing using the Yocto Project on a system + not native to Linux is with + CROPS. + + + +
+
+ +
+ Development Methods + + + The Yocto Project development environment usually involves a + 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. + + For additional detail about the Yocto Project development + environment, see the + "The Yocto Project 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 + 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 + "Setting Up a Native Linux Host" + section in the Yocto Project Development Tasks Manual. + + + CROss PlatformS (CROPS): + Typically, you use + CROPS, + which leverages + Docker Containers, + to set up a Build Host that is not running Linux (e.g. + Microsoft + Windows + or + macOS). + + 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 + "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. + + 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 + "Setting Up to Use Windows Subsystem For Linux" + 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 + Open-Embedded 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 + Toaster User Manual. + + + +
+ +
+ 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 + OpenEmbedded Build System + (BitBake and + OpenEmbedded-Core) + as well as a set of + 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 + Source Repositories. + + If you are interested in all the contents of the + poky Git repository, see the + "Top-Level Core Components" + section in the Yocto Project Reference Manual. + + + + + The following figure illustrates what generally comprises Poky: + + + + 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. + + + + 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. + + 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 + "Yocto Project Releases and the Stable 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 + 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 + "Appending and Prepending (Override Style Syntax)" + section in the BitBake User's Manual. + +
+ +
+ The OpenEmbedded Build System Workflow + + + The + OpenEmbedded build system + uses a "workflow" to accomplish image and SDK generation. + The following figure overviews that workflow: + + Following is a brief summary of the "workflow": + + + Developers specify architecture, policies, patches and + configuration details. + + + 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. + + + 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. + + + 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. + + + Different QA and sanity checks run throughout entire + build process. + + + After the binaries are created, the build system + generates a binary package feed that is used to create + the final root file image. + + + 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" + 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 + "Yocto Project 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 + Open-Embedded 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 + Yocto Project Application Development and the Extensible Software Development Kit (eSDK) + 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 + "Understanding and Creating Layers" + section in the Yocto Project Development Tasks Manual. + For a discussion specifically on BSP Layers, see the + "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. + + + 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 + "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. PR, + PV, + and + 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. + + 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.rst b/poky/documentation/overview-manual/overview-manual.rst index f20b20e32..80ce9aae7 100644 --- a/poky/documentation/overview-manual/overview-manual.rst +++ b/poky/documentation/overview-manual/overview-manual.rst @@ -1,4 +1,4 @@ -.. SPDX-License-Identifier: CC-BY-SA-2.0-UK +.. SPDX-License-Identifier: CC-BY-2.0-UK ========================================== Yocto Project Overview and Concepts Manual diff --git a/poky/documentation/overview-manual/overview-manual.xml b/poky/documentation/overview-manual/overview-manual.xml new file mode 100755 index 000000000..8021a2e95 --- /dev/null +++ b/poky/documentation/overview-manual/overview-manual.xml @@ -0,0 +1,130 @@ + %poky; ] > + + + + + + + + + + + + + Yocto Project Overview and Concepts Manual + + + + + + &ORGNAME; + + &ORGEMAIL; + + + + + + 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 + &REL_MONTH_YEAR; + Released with the Yocto Project 3.1 Release. + + + + + ©RIGHT_YEAR; + Linux Foundation + + + + + Permission is granted to copy, distribute and/or modify this document under + the terms of the + Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by + Creative Commons. + + Manual Notes + + + This version of the + Yocto Project Overview and Concepts Manual + is for the &YOCTO_DOC_VERSION; release of the + Yocto Project. + To be sure you have the latest version of the manual + for this release, go to the + Yocto Project documentation page + and select the manual from that site. + Manuals from the site are more up-to-date than manuals + derived from the Yocto Project released TAR files. + + + If you located this manual through a web search, the + version of the manual might not be the one you want + (e.g. the search might have returned a manual much + older than the Yocto Project version with which you + are working). + You can see all Yocto Project major releases by + visiting the + Releases + page. + If you need a version of this manual for a different + Yocto Project release, visit the + Yocto Project documentation page + and select the manual set by using the + "ACTIVE RELEASES DOCUMENTATION" or "DOCUMENTS ARCHIVE" + pull-down menus. + + + + To report any inaccuracies or problems with this + (or any other Yocto Project) manual, send an email to + the Yocto Project documentation mailing list at + docs@lists.yoctoproject.org or + log into the freenode #yocto channel. + + + + + + + + + + + + + + + + + + -- cgit v1.2.3