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| |
| <chapter id='overview-yp'> |
| <title>Introducing the Yocto Project</title> |
| |
| <section id='what-is-the-yocto-project'> |
| <title>What is the Yocto Project?</title> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para id='yp-key-dev-elements'> |
| <imagedata fileref="figures/key-dev-elements.png" format="PNG" align='center' width="8in"/> |
| </para> |
| |
| <para> |
| For further introductory information on the Yocto Project, you |
| might be interested in this |
| <ulink url='https://www.embedded.com/electronics-blogs/say-what-/4458600/Why-the-Yocto-Project-for-my-IoT-Project-'>article</ulink> |
| by Drew Moseley and in this short introductory |
| <ulink url='https://www.youtube.com/watch?v=utZpKM7i5Z4'>video</ulink>. |
| </para> |
| |
| <para> |
| The remainder of this section overviews advantages and challenges |
| tied to the Yocto Project. |
| </para> |
| |
| <section id='gs-features'> |
| <title>Features</title> |
| |
| <para> |
| The following list describes features and advantages of the |
| Yocto Project: |
| <itemizedlist> |
| <listitem><para> |
| <emphasis>Widely Adopted Across the Industry:</emphasis> |
| 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 |
| <ulink url='&YOCTO_HOME_URL;'>Yocto Project</ulink> |
| home page. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Architecture Agnostic:</emphasis> |
| 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.</para> |
| |
| <para>Aside from lots of architecture support, the |
| Yocto Project fully supports a wide range of device |
| emulation through the Quick EMUlator (QEMU). |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Images and Code Transfer Easily:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Flexibility:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Ideal for Constrained Embedded and IoT devices:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Comprehensive Toolchain Capabilities:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Mechanism Rules Over Policy:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Uses a Layer Model:</emphasis> |
| The Yocto Project |
| <link linkend='the-yocto-project-layer-model'>layer infrastructure</link> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Supports Partial Builds:</emphasis> |
| You can build and rebuild individual packages as |
| needed. |
| Yocto Project accomplishes this through its |
| <link linkend='shared-state-cache'>shared-state cache</link> |
| (sstate) scheme. |
| Being able to build and debug components individually |
| eases project development. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Releases According to a Strict Schedule:</emphasis> |
| Major releases occur on a |
| <ulink url='&YOCTO_DOCS_REF_URL;#ref-release-process'>six-month cycle</ulink> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Rich Ecosystem of Individuals and Organizations:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Binary Reproducibility:</emphasis> |
| The Yocto Project allows you to be very specific about |
| dependencies and achieves very high percentages of |
| binary reproducibility (e.g. 99.8% for |
| <filename>core-image-minimal</filename>). |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>License Manifest:</emphasis> |
| The Yocto Project provides a |
| <ulink url='&YOCTO_DOCS_DEV_URL;#maintaining-open-source-license-compliance-during-your-products-lifecycle'>license manifest</ulink> |
| for review by people who need to track the use of open |
| source licenses (e.g.legal teams). |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| |
| <section id='gs-challenges'> |
| <title>Challenges</title> |
| |
| <para> |
| The following list presents challenges you might encounter |
| when developing using the Yocto Project: |
| <itemizedlist> |
| <listitem><para> |
| <emphasis>Steep Learning Curve:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Understanding What Changes You Need to Make |
| For Your Design Requires Some Research:</emphasis> |
| 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 |
| "<ulink url='&YOCTO_HOME_URL;/docs/what-i-wish-id-known/'>What I wish I'd Known</ulink>" |
| and |
| "<ulink url='&YOCTO_HOME_URL;/docs/transitioning-to-a-custom-environment/'>Transitioning to a Custom Environment for Systems Development</ulink>" |
| documents on the Yocto Project website. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Project Workflow Could Be Confusing:</emphasis> |
| The |
| <link linkend='overview-development-environment'>Yocto Project workflow</link> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Working in a Cross-Build Environment Can |
| Feel Unfamiliar:</emphasis> |
| 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.</para> |
| |
| <para>The Yocto Project |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> |
| 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 <filename>rpm</filename> or |
| <filename>ipk</filename>. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Initial Build Times Can be Significant:</emphasis> |
| 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. |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| </section> |
| |
| <section id='the-yocto-project-layer-model'> |
| <title>The Yocto Project Layer Model</title> |
| |
| <para> |
| 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 |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> |
| what to do. |
| You can collaborate, share, and reuse layers. |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| You use different layers to logically separate information in your |
| build. |
| As an example, you could have BSP, GUI, distro configuration, |
| middleware, or application layers. |
| Putting your entire build into one layer limits and complicates |
| future customization and reuse. |
| Isolating information into layers, on the other hand, helps |
| simplify future customizations and reuse. |
| You might find it tempting to keep everything in one layer when |
| working on a single project. |
| However, the more modular your Metadata, the easier |
| it is to cope with future changes. |
| <note><title>Notes</title> |
| <itemizedlist> |
| <listitem><para> |
| Use Board Support Package (BSP) layers from silicon |
| vendors when possible. |
| </para></listitem> |
| <listitem><para> |
| Familiarize yourself with the |
| <ulink url='https://caffelli-staging.yoctoproject.org/software-overview/layers/'>Yocto Project curated layer index</ulink> |
| or the |
| <ulink url='http://layers.openembedded.org/layerindex/branch/master/layers/'>OpenEmbedded layer index</ulink>. |
| The latter contains more layers but they are less |
| universally validated. |
| </para></listitem> |
| <listitem><para> |
| Layers support the inclusion of technologies, hardware |
| components, and software components. |
| The |
| <ulink url='&YOCTO_DOCS_DEV_URL;#making-sure-your-layer-is-compatible-with-yocto-project'>Yocto Project Compatible</ulink> |
| 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. |
| </para></listitem> |
| </itemizedlist> |
| </note> |
| </para> |
| |
| <para> |
| 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 |
| (<filename>.bbappend</filename>) file, which is described later |
| in this section. |
| <note> |
| For general information on BSP layer structure, see the |
| <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Packages (BSP) Developer's Guide</ulink>. |
| </note> |
| </para> |
| |
| <para> |
| The |
| <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink> |
| 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 |
| <filename>meta-</filename>. |
| <note> |
| It is not a requirement that a layer name begin with the |
| prefix <filename>meta-</filename>, but it is a commonly |
| accepted standard in the Yocto Project community. |
| </note> |
| For example, if you were to examine the |
| <ulink url='https://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/'>tree view</ulink> |
| of the <filename>poky</filename> repository, you will see several |
| layers: <filename>meta</filename>, |
| <filename>meta-skeleton</filename>, |
| <filename>meta-selftest</filename>, |
| <filename>meta-poky</filename>, and |
| <filename>meta-yocto-bsp</filename>. |
| Each of these repositories represents a distinct layer. |
| </para> |
| |
| <para> |
| For procedures on how to create layers, see the |
| "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>" |
| section in the Yocto Project Development Tasks Manual. |
| </para> |
| </section> |
| |
| <section id='components-and-tools'> |
| <title>Components and Tools</title> |
| |
| <para> |
| 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 |
| (<ulink url='&YOCTO_DOCS_REF_URL;#poky'>Poky</ulink>) |
| and the |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink>. |
| Most of the components and tools are downloaded separately. |
| </para> |
| |
| <para> |
| This section provides brief overviews of the components and |
| tools associated with the Yocto Project. |
| </para> |
| |
| <section id='gs-development-tools'> |
| <title>Development Tools</title> |
| |
| <para> |
| The following list consists of tools that help you develop |
| images and applications using the Yocto Project: |
| <itemizedlist> |
| <listitem><para id='gs-crops-overview'> |
| <emphasis>CROPS:</emphasis> |
| <ulink url='https://git.yoctoproject.org/cgit/cgit.cgi/crops/about/'>CROPS</ulink> |
| is an open source, cross-platform development framework |
| that leverages |
| <ulink url='https://www.docker.com/'>Docker Containers</ulink>. |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis><filename>devtool</filename>:</emphasis> |
| This command-line tool is available as part of the |
| extensible SDK (eSDK) and is its cornerstone. |
| You can use <filename>devtool</filename> 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.</para> |
| |
| <para>The <filename>devtool</filename> command employs |
| a number of sub-commands that allow you to add, modify, |
| and upgrade recipes. |
| As with the OpenEmbedded build system, “recipes” |
| represent software packages within |
| <filename>devtool</filename>. |
| When you use <filename>devtool add</filename>, a recipe |
| is automatically created. |
| When you use <filename>devtool modify</filename>, 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 <filename>devtool upgrade</filename> command |
| updates an existing recipe so that you can build it |
| for an updated set of source files.</para> |
| |
| <para>You can read about the |
| <filename>devtool</filename> workflow in the Yocto |
| Project Application Development and Extensible |
| Software Development Kit (eSDK) Manual in the |
| "<ulink url='&YOCTO_DOCS_SDK_URL;#using-devtool-in-your-sdk-workflow'>Using <filename>devtool</filename> in Your SDK Workflow'</ulink>" |
| section. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Extensible Software Development Kit (eSDK):</emphasis> |
| 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 <filename>devtool</filename> |
| commands tailored for the Yocto Project environment. |
| </para> |
| |
| <para>For information on the eSDK, see the |
| <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink> |
| Manual. |
| </para></listitem> |
| <listitem><para> |
| <emphasis><trademark class='trade'>Eclipse</trademark> IDE Plug-in:</emphasis> |
| This plug-in enables you to use the popular Eclipse |
| Integrated Development Environment (IDE), which allows |
| for development using the Yocto Project all within the |
| Eclipse IDE. |
| You can work within Eclipse to cross-compile, deploy, |
| and execute your output into a QEMU emulation session |
| as well as onto actual target hardware.</para> |
| |
| <para>The environment also supports performance |
| enhancing tools that allow you to perform remote |
| profiling, tracing, collection of power data, |
| collection of latency data, and collection of |
| performance data.</para> |
| |
| <para>Once you enable the plug-in, standard Eclipse |
| functions automatically use the cross-toolchain |
| and target system libraries. |
| You can build applications using any of these |
| libraries.</para> |
| |
| <para>For more information on the Eclipse plug-in, |
| see the |
| "<ulink url='&YOCTO_DOCS_SDK_URL;#adt-eclipse'>Working Within Eclipse</ulink>" |
| section in the Yocto Project Application Development |
| and the Extensible Software Development Kit (eSDK) |
| manual. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Toaster:</emphasis> |
| 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 |
| <ulink url='&YOCTO_DOCS_TOAST_URL;'>Toaster User Manual</ulink>. |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| |
| <section id='gs-production-tools'> |
| <title>Production Tools</title> |
| |
| <para> |
| The following list consists of tools that help production |
| related activities using the Yocto Project: |
| <itemizedlist> |
| <listitem><para> |
| <emphasis>Auto Upgrade Helper:</emphasis> |
| This utility when used in conjunction with the |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> |
| (BitBake and OE-Core) automatically generates upgrades |
| for recipes that are based on new versions of the |
| recipes published upstream. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Recipe Reporting System:</emphasis> |
| 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 |
| <ulink url="http://layers.openembedded.org/layerindex/layers/">OpenEmbedded Layer Index</ulink>, |
| which is a website that indexes OpenEmbedded-Core |
| layers. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Patchwork:</emphasis> |
| <ulink url='http://jk.ozlabs.org/projects/patchwork/'>Patchwork</ulink> |
| is a fork of a project originally started by |
| <ulink url='http://ozlabs.org/'>OzLabs</ulink>. |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>AutoBuilder:</emphasis> |
| AutoBuilder is a project that automates build tests |
| and quality assurance (QA). |
| By using the public AutoBuilder, anyone can determine |
| the status of the current "master" branch of Poky. |
| <note> |
| AutoBuilder is based on |
| <ulink url='https://buildbot.net/'>buildbot</ulink>. |
| </note></para> |
| |
| <para>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.</para> |
| |
| <para>You can learn more about the AutoBuilder used |
| by the Yocto Project |
| <ulink url='&YOCTO_AB_URL;'>here</ulink>. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Cross-Prelink:</emphasis> |
| 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.</para> |
| |
| <para>Historically, cross-prelink is a variant of |
| prelink, which was conceived by |
| <ulink url='http://people.redhat.com/jakub/prelink.pdf'>Jakub Jelínek</ulink> |
| 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. <filename>glibc</filename>-derived |
| <filename>ld.so</filename> 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.</para> |
| |
| <para>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. |
| </para> |
| |
| <para>The original upstream prelink project only |
| supports running prelink on the end target device |
| due to the reliance on the target device’s dynamic |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Pseudo:</emphasis> |
| Pseudo is the Yocto Project implementation of |
| <ulink url='http://man.he.net/man1/fakeroot'>fakeroot</ulink>, |
| which is used to run commands in an environment |
| that seemingly has root privileges.</para> |
| |
| <para>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 |
| <filename>LD_PRELOAD</filename>. |
| Either method allows these operations to succeed as |
| if system administrator privileges exist even |
| when they do not.</para> |
| |
| <para>You can read more about Pseudo in the |
| "<link linkend='fakeroot-and-pseudo'>Fakeroot and Pseudo</link>" |
| section. |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| |
| <section id='gs-openembedded-build-system'> |
| <title>Open-Embedded Build System Components</title> |
| |
| <para> |
| The following list consists of components associated with the |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink>: |
| <itemizedlist> |
| <listitem><para> |
| <emphasis>BitBake:</emphasis> |
| 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.</para> |
| |
| <para>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.</para> |
| |
| <para>You can learn more about BitBake in the |
| <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>OpenEmbedded-Core:</emphasis> |
| 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 |
| <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta'>Source Repositories</ulink>. |
| </para> |
| |
| <para>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. |
| </para> |
| |
| <para>Sharing a core set of metadata results in Poky |
| as an integration layer on top of OE-Core. |
| You can see that in this |
| <link linkend='yp-key-dev-elements'>figure</link>. |
| The Yocto Project combines various components such as |
| BitBake, OE-Core, script “glue”, and documentation |
| for its build system. |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| |
| <section id='gs-reference-distribution-poky'> |
| <title>Reference Distribution (Poky)</title> |
| |
| <para> |
| Poky is the Yocto Project reference distribution. |
| It contains the |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>Open-Embedded build system</ulink> |
| (BitBake and OE-Core) as well as a set of metadata to get you |
| started building your own distribution. |
| See the |
| <link linkend='what-is-the-yocto-project'>figure</link> in |
| "What is the Yocto Project?" section for an illustration |
| that shows Poky and its relationship with other parts of the |
| Yocto Project.</para> |
| |
| <para>To use the Yocto Project tools and components, you |
| can download (<filename>clone</filename>) Poky and use it |
| to bootstrap your own distribution. |
| <note> |
| Poky does not contain binary files. |
| It is a working example of how to build your own custom |
| Linux distribution from source. |
| </note> |
| You can read more about Poky in the |
| "<link linkend='reference-embedded-distribution'>Reference Embedded Distribution (Poky)</link>" |
| section. |
| </para> |
| </section> |
| |
| <section id='gs-packages-for-finished-targets'> |
| <title>Packages for Finished Targets</title> |
| |
| <para> |
| The following lists components associated with packages |
| for finished targets: |
| <itemizedlist> |
| <listitem><para> |
| <emphasis>Matchbox:</emphasis> |
| 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.</para> |
| |
| <para>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.</para> |
| |
| <para>You can find the Matchbox source in the Yocto |
| Project |
| <ulink url='&YOCTO_GIT_URL;'>Source Repositories</ulink>. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Opkg</emphasis> |
| 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. |
| </para> |
| |
| <para>Opkg is intended for use on embedded Linux |
| devices and is used in this capacity in the |
| <ulink url='http://www.openembedded.org/wiki/Main_Page'>OpenEmbedded</ulink> |
| and |
| <ulink url='https://openwrt.org/'>OpenWrt</ulink> |
| projects, as well as the Yocto Project. |
| <note> |
| As best it can, opkg maintains backwards |
| compatibility with ipkg and conforms to a subset |
| of Debian’s policy manual regarding control files. |
| </note> |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| |
| <section id='gs-archived-components'> |
| <title>Archived Components</title> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| 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. |
| <orderedlist> |
| <listitem><para> |
| <emphasis>Hob:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Build Appliance:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>CROPS:</emphasis> |
| The final and best solution available now for |
| developing using the Yocto Project on a system |
| not native to Linux is with |
| <link linkend='gs-crops-overview'>CROPS</link>. |
| </para></listitem> |
| </orderedlist> |
| </para> |
| </section> |
| </section> |
| |
| <section id='gs-development-methods'> |
| <title>Development Methods</title> |
| |
| <para> |
| The Yocto Project development environment usually involves a |
| <ulink url='&YOCTO_DOCS_REF_URL;#hardware-build-system-term'>Build Host</ulink> |
| and target hardware. |
| You use the Build Host to build images and develop applications, |
| while you use the target hardware to test deployed software. |
| </para> |
| |
| <para> |
| This section provides an introduction to the choices or |
| development methods you have when setting up your Build Host. |
| Depending on the your particular workflow preference and the |
| type of operating system your Build Host runs, several choices |
| exist that allow you to use the Yocto Project. |
| <note> |
| For additional detail about the Yocto Project development |
| environment, see the |
| "<link linkend='overview-development-environment'>The Yocto Project Development Environment</link>" |
| chapter. |
| </note> |
| <itemizedlist> |
| <listitem><para> |
| <emphasis>Native Linux Host:</emphasis> |
| 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 |
| <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink> |
| tool. |
| You can accomplish all aspects of development from a |
| familiar shell of a supported Linux distribution.</para> |
| |
| <para>For information on how to set up a Build Host on |
| a system running Linux as its native operating system, |
| see the |
| "<ulink url='&YOCTO_DOCS_DEV_URL;#setting-up-a-native-linux-host'>Setting Up a Native Linux Host</ulink>" |
| section in the Yocto Project Development Tasks Manual. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>CROss PlatformS (CROPS):</emphasis> |
| Typically, you use |
| <ulink url='https://git.yoctoproject.org/cgit/cgit.cgi/crops/about/'>CROPS</ulink>, |
| which leverages |
| <ulink url='https://www.docker.com/'>Docker Containers</ulink>, |
| to set up a Build Host that is not running Linux (e.g. |
| <trademark class='registered'>Microsoft</trademark> |
| <trademark class='trademark'>Windows</trademark> |
| or |
| <trademark class='registered'>macOS</trademark>). |
| <note> |
| You can, however, use CROPS on a Linux-based system. |
| </note> |
| 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.</para> |
| |
| <para>For information on how to set up a Build Host with |
| CROPS, see the |
| "<ulink url='&YOCTO_DOCS_DEV_URL;#setting-up-to-use-crops'>Setting Up to Use CROss PlatformS (CROPS)</ulink>" |
| section in the Yocto Project Development Tasks Manual. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Toaster:</emphasis> |
| 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 |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>Open-Embedded build system</ulink>. |
| 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.</para> |
| |
| <para>For information about and how to use Toaster, |
| see the |
| <ulink url='&YOCTO_DOCS_TOAST_URL;'>Toaster User Manual</ulink>. |
| </para></listitem> |
| <listitem><para> |
| <emphasis><trademark class='trade'>Eclipse</trademark> IDE:</emphasis> |
| If your Build Host supports and runs the popular |
| Eclipse IDE, you can install the Yocto Project Eclipse |
| plug-in and use the Yocto Project to develop software. |
| The plug-in integrates the Yocto Project functionality |
| into Eclipse development practices.</para> |
| |
| <para>For information about how to install and use the |
| Yocto Project Eclipse plug-in, see the |
| "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-eclipse-project'>Developing Applications Using Eclipse</ulink>" |
| chapter in the Yocto Project Application Development and |
| the Extensible Software Development Kit (eSDK) Manual. |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| |
| <section id='reference-embedded-distribution'> |
| <title>Reference Embedded Distribution (Poky)</title> |
| |
| <para> |
| "Poky", which is pronounced <emphasis>Pock</emphasis>-ee, is the |
| name of the Yocto Project's reference distribution or Reference OS |
| Kit. |
| Poky contains the |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded Build System</ulink> |
| (<ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink> and |
| <ulink url='&YOCTO_DOCS_REF_URL;#oe-core'>OpenEmbedded-Core</ulink>) |
| as well as a set of |
| <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>metadata</ulink> 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. |
| </para> |
| |
| <para> |
| Poky is a combined repository of BitBake, OpenEmbedded-Core |
| (which is found in <filename>meta</filename>), |
| <filename>meta-poky</filename>, |
| <filename>meta-yocto-bsp</filename>, and documentation provided |
| all together and known to work well together. |
| You can view these items that make up the Poky repository in the |
| <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/'>Source Repositories</ulink>. |
| <note> |
| If you are interested in all the contents of the |
| <filename>poky</filename> Git repository, see the |
| "<ulink url='&YOCTO_DOCS_REF_URL;#structure-core'>Top-Level Core Components</ulink>" |
| section in the Yocto Project Reference Manual. |
| </note> |
| </para> |
| |
| <para id='gs-poky-reference-distribution'> |
| The following figure illustrates what generally comprises Poky: |
| <imagedata fileref="figures/poky-reference-distribution.png" format="PNG" align='center' width="8in"/> |
| <itemizedlist> |
| <listitem><para> |
| BitBake is a task executor and scheduler that is the heart of |
| the OpenEmbedded build system. |
| </para></listitem> |
| <listitem><para> |
| <filename>meta-poky</filename>, which is Poky-specific |
| metadata. |
| </para></listitem> |
| <listitem><para> |
| <filename>meta-yocto-bsp</filename>, which are Yocto |
| Project-specific Board Support Packages (BSPs). |
| </para></listitem> |
| <listitem><para> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| Documentation, which contains the Yocto Project source |
| files used to make the set of user manuals. |
| </para></listitem> |
| </itemizedlist> |
| <note> |
| While Poky is a "complete" distribution specification and is |
| tested and put through QA, you cannot use it as a product |
| "out of the box" in its current form. |
| </note> |
| </para> |
| |
| <para> |
| To use the Yocto Project tools, you can use Git to clone (download) |
| the Poky repository then use your local copy of the reference |
| distribution to bootstrap your own distribution. |
| <note> |
| Poky does not contain binary files. |
| It is a working example of how to build your own custom Linux distribution |
| from source. |
| </note> |
| </para> |
| |
| <para> |
| 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 |
| "<ulink url='&YOCTO_DOCS_REF_URL;#ref-release-process'>Yocto Project Releases and the Stable Release Process</ulink>" |
| chapter in the Yocto Project Reference Manual. |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| 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 |
| <link linkend='the-yocto-project-layer-model'>layers</link> |
| 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. |
| </para> |
| |
| <para> |
| 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 |
| <filename>./meta/classes</filename>. |
| Within a recipe you can also define additional tasks as well as |
| task prerequisites. |
| Recipe syntax through BitBake also supports both |
| <filename>_prepend</filename> and <filename>_append</filename> |
| 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 |
| "<ulink url='&YOCTO_DOCS_BB_URL;#appending-and-prepending-override-style-syntax'>Appending and Prepending (Override Style Syntax)</ulink>" |
| section in the BitBake User's Manual. |
| </para> |
| </section> |
| |
| <section id='openembedded-build-system-workflow'> |
| <title>The OpenEmbedded Build System Workflow</title> |
| |
| <para> |
| The |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> |
| uses a "workflow" to accomplish image and SDK generation. |
| The following figure overviews that workflow: |
| <imagedata fileref="figures/YP-flow-diagram.png" |
| format="PNG" align='center' width="8in"/> |
| Following is a brief summary of the "workflow": |
| <orderedlist> |
| <listitem><para> |
| Developers specify architecture, policies, patches and |
| configuration details. |
| </para></listitem> |
| <listitem><para> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| 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. |
| </para></listitem> |
| <listitem><para> |
| Different QA and sanity checks run throughout entire |
| build process. |
| </para></listitem> |
| <listitem><para> |
| After the binaries are created, the build system |
| generates a binary package feed that is used to create |
| the final root file image. |
| </para></listitem> |
| <listitem><para> |
| The build system generates the file system image and a |
| customized Extensible SDK (eSDK) for application |
| development in parallel. |
| </para></listitem> |
| </orderedlist> |
| </para> |
| |
| <para> |
| For a very detailed look at this workflow, see the |
| "<link linkend='openembedded-build-system-build-concepts'>OpenEmbedded Build System Concepts</link>" |
| section. |
| </para> |
| </section> |
| |
| |
| <section id='some-basic-terms'> |
| <title>Some Basic Terms</title> |
| |
| <para> |
| It helps to understand some basic fundamental terms when |
| learning the Yocto Project. |
| Although a list of terms exists in the |
| "<ulink url='&YOCTO_DOCS_REF_URL;#ref-terms'>Yocto Project Terms</ulink>" |
| section of the Yocto Project Reference Manual, this section |
| provides the definitions of some terms helpful for getting started: |
| <itemizedlist> |
| <listitem><para> |
| <emphasis>Configuration Files:</emphasis> |
| Files that hold global definitions of variables, |
| user-defined variables, and hardware configuration |
| information. |
| These files tell the |
| <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>Open-Embedded build system</ulink> |
| what to build and what to put into the image to support a |
| particular platform. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Extensible Software Development Kit (eSDK):</emphasis> |
| 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 |
| <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink> |
| manual. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Layer:</emphasis> |
| 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.</para> |
| |
| <para>For more detailed information on layers, see the |
| "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>" |
| section in the Yocto Project Development Tasks Manual. |
| For a discussion specifically on BSP Layers, see the |
| "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>" |
| section in the Yocto Project Board Support Packages (BSP) |
| Developer's Guide. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Metadata:</emphasis> |
| 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. |
| </para></listitem> |
| <listitem><para id='gs-term-openembedded-build-system'> |
| <emphasis>OpenEmbedded Build System:</emphasis> |
| The terms "BitBake" and "build system" are sometimes |
| used for the OpenEmbedded Build System.</para> |
| |
| <para>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 <filename>make</filename> |
| tool.</para> |
| |
| <para>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. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>OpenEmbedded-Core (OE-Core):</emphasis> |
| 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.</para> |
| |
| <para>You can see the Metadata in the |
| <filename>meta</filename> directory of the Yocto Project |
| <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi'>Source Repositories</ulink>. |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Packages:</emphasis> |
| 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.</para> |
| |
| <para>It is worth noting that the term "package" can, |
| in general, have subtle meanings. |
| For example, the packages referred to in the |
| "<ulink url='&YOCTO_DOCS_REF_URL;#required-packages-for-the-build-host'>Required Packages for the Build Host</ulink>" |
| section in the Yocto Project Reference Manual are compiled |
| binaries that, when installed, add functionality to your |
| Linux distribution.</para> |
| |
| <para>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. <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>, |
| <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>, |
| and |
| <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>). |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Poky:</emphasis> |
| Poky is a reference embedded distribution and a reference |
| test configuration. |
| Poky provides the following: |
| <itemizedlist> |
| <listitem><para> |
| A base-level functional distro used to illustrate |
| how to customize a distribution. |
| </para></listitem> |
| <listitem><para> |
| A means by which to test the Yocto Project |
| components (i.e. Poky is used to validate |
| the Yocto Project). |
| </para></listitem> |
| <listitem><para> |
| A vehicle through which you can download |
| the Yocto Project. |
| </para></listitem> |
| </itemizedlist> |
| Poky is not a product level distro. |
| Rather, it is a good starting point for customization. |
| <note> |
| Poky is an integration layer on top of OE-Core. |
| </note> |
| </para></listitem> |
| <listitem><para> |
| <emphasis>Recipe:</emphasis> |
| 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. |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </section> |
| </chapter> |
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