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n class="s">"6in" depth="4in" /> </para></listitem> </itemizedlist> </para> </section> <section id='yocto-project-terms'> <title>Yocto Project Terms</title> <para> Following is a list of terms and definitions users new to the Yocto Project development environment might find helpful. While some of these terms are universal, the list includes them just in case: <itemizedlist> <listitem><para><emphasis>Append Files:</emphasis> Files that append build information to a recipe file. Append files are known as BitBake append files and <filename>.bbappend</filename> files. The OpenEmbedded build system expects every append file to have a corresponding recipe (<filename>.bb</filename>) file. Furthermore, the append file and corresponding recipe file must use the same root filename. The filenames can differ only in the file type suffix used (e.g. <filename>formfactor_0.0.bb</filename> and <filename>formfactor_0.0.bbappend</filename>). </para> <para>Information in append files extends or overrides the information in the similarly-named recipe file. For an example of an append file in use, see the "<link linkend='using-bbappend-files'>Using .bbappend Files</link>" section. <note> Append files can also use wildcard patterns in their version numbers so they can be applied to more than one version of the underlying recipe file. </note> </para></listitem> <listitem><para id='bitbake-term'><emphasis>BitBake:</emphasis> The task executor and scheduler used by the OpenEmbedded build system to build images. For more information on BitBake, see the <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>. </para></listitem> <listitem> <para id='build-directory'><emphasis>Build Directory:</emphasis> This term refers to the area used by the OpenEmbedded build system for builds. The area is created when you <filename>source</filename> the setup environment script that is found in the Source Directory (i.e. <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink> or <ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>). The <ulink url='&YOCTO_DOCS_REF_URL;#var-TOPDIR'><filename>TOPDIR</filename></ulink> variable points to the Build Directory.</para> <para> You have a lot of flexibility when creating the Build Directory. Following are some examples that show how to create the directory. The examples assume your <link linkend='source-directory'>Source Directory</link> is named <filename>poky</filename>: <itemizedlist> <listitem><para>Create the Build Directory inside your Source Directory and let the name of the Build Directory default to <filename>build</filename>: <literallayout class='monospaced'> $ cd $HOME/poky $ source &OE_INIT_FILE; </literallayout></para></listitem> <listitem><para>Create the Build Directory inside your home directory and specifically name it <filename>test-builds</filename>: <literallayout class='monospaced'> $ cd $HOME $ source poky/&OE_INIT_FILE; test-builds </literallayout></para></listitem> <listitem><para> Provide a directory path and specifically name the Build Directory. Any intermediate folders in the pathname must exist. This next example creates a Build Directory named <filename>YP-&POKYVERSION;</filename> in your home directory within the existing directory <filename>mybuilds</filename>: <literallayout class='monospaced'> $cd $HOME $ source $HOME/poky/&OE_INIT_FILE; $HOME/mybuilds/YP-&POKYVERSION; </literallayout></para></listitem> </itemizedlist> <note> By default, the Build Directory contains <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>, which is a temporary directory the build system uses for its work. <filename>TMPDIR</filename> cannot be under NFS. Thus, by default, the Build Directory cannot be under NFS. However, if you need the Build Directory to be under NFS, you can set this up by setting <filename>TMPDIR</filename> in your <filename>local.conf</filename> file to use a local drive. Doing so effectively separates <filename>TMPDIR</filename> from <filename>TOPDIR</filename>, which is the Build Directory. </note> </para></listitem> <listitem><para><emphasis>Classes:</emphasis> Files that provide for logic encapsulation and inheritance so that commonly used patterns can be defined once and then easily used in multiple recipes. For reference information on the Yocto Project classes, see the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes'>Classes</ulink>" chapter of the Yocto Project Reference Manual. Class files end with the <filename>.bbclass</filename> filename extension. </para></listitem> <listitem><para><emphasis>Configuration File:</emphasis> Configuration information in various <filename>.conf</filename> files provides global definitions of variables. The <filename>conf/local.conf</filename> configuration file in the <link linkend='build-directory'>Build Directory</link> contains user-defined variables that affect every build. The <filename>meta-poky/conf/distro/poky.conf</filename> configuration file defines Yocto "distro" configuration variables used only when building with this policy. Machine configuration files, which are located throughout the <link linkend='source-directory'>Source Directory</link>, define variables for specific hardware and are only used when building for that target (e.g. the <filename>machine/beaglebone.conf</filename> configuration file defines variables for the Texas Instruments ARM Cortex-A8 development board). Configuration files end with a <filename>.conf</filename> filename extension. </para></listitem> <listitem><para id='cross-development-toolchain'> <emphasis>Cross-Development Toolchain:</emphasis> In general, a cross-development toolchain is a collection of software development tools and utilities that run on one architecture and allow you to develop software for a different, or targeted, architecture. These toolchains contain cross-compilers, linkers, and debuggers that are specific to the target architecture. </para> <para>The Yocto Project supports two different cross-development toolchains: <itemizedlist> <listitem><para>A toolchain only used by and within BitBake when building an image for a target architecture.</para></listitem> <listitem><para>A relocatable toolchain used outside of BitBake by developers when developing applications that will run on a targeted device. </para></listitem> </itemizedlist> </para> <para> Creation of these toolchains is simple and automated. For information on toolchain concepts as they apply to the Yocto Project, see the "<ulink url='&YOCTO_DOCS_REF_URL;#cross-development-toolchain-generation'>Cross-Development Toolchain Generation</ulink>" section in the Yocto Project Reference Manual. You can also find more information on using the relocatable toolchain in the <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Software Development Kit (SDK) Developer's Guide</ulink>. </para></listitem> <listitem><para><emphasis>Image:</emphasis> An image is an artifact of the BitBake build process given a collection of recipes and related Metadata. Images are the binary output that run on specific hardware or QEMU and are used for specific use-cases. For a list of the supported image types that the Yocto Project provides, see the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter in the Yocto Project Reference Manual.</para></listitem> <listitem><para id='layer'><emphasis>Layer:</emphasis> A collection of recipes representing the core, a BSP, or an application stack. 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 id='metadata'><emphasis>Metadata:</emphasis> The files that BitBake parses when building an image. In general, Metadata includes recipes, classes, and configuration files. In the context of the kernel ("kernel Metadata"), it refers to Metadata in the <filename>meta</filename> branches of the kernel source Git repositories. </para></listitem> <listitem><para id='oe-core'><emphasis>OE-Core:</emphasis> A core set of Metadata originating with OpenEmbedded (OE) that is shared between OE and the Yocto Project. This Metadata is found in the <filename>meta</filename> directory of the <link linkend='source-directory'>Source Directory</link>.</para></listitem> <listitem><para id='build-system-term'><emphasis>OpenEmbedded Build System:</emphasis> The build system specific to the Yocto Project. The OpenEmbedded build system is based on another project known as "Poky", which uses <link linkend='bitbake-term'>BitBake</link> as the task executor. Throughout the Yocto Project documentation set, the OpenEmbedded build system is sometimes referred to simply as "the build system". If other build systems, such as a host or target build system are referenced, the documentation clearly states the difference. <note> For some historical information about Poky, see the <link linkend='poky'>Poky</link> term. </note> </para></listitem> <listitem><para><emphasis>Package:</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_QS_URL;#packages'>The Build Host Packages</ulink>" section 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>Package Groups:</emphasis> Arbitrary groups of software Recipes. You use package groups to hold recipes that, when built, usually accomplish a single task. For example, a package group could contain the recipes for a company’s proprietary or value-add software. Or, the package group could contain the recipes that enable graphics. A package group is really just another recipe. Because package group files are recipes, they end with the <filename>.bb</filename> filename extension.</para></listitem> <listitem><para id='poky'><emphasis>Poky:</emphasis> The term "poky" can mean several things. In its most general sense, it is an open-source project that was initially developed by OpenedHand. With OpenedHand, poky was developed off of the existing OpenEmbedded build system becoming a commercially supportable build system for embedded Linux. After Intel Corporation acquired OpenedHand, the project poky became the basis for the Yocto Project's build system.</para> <para>Within the Yocto Project source repositories, <filename>poky</filename> exists as a separate Git repository you can clone to yield a local copy on your host system. Thus, "poky" can refer to the local copy of the Source Directory used for development within the Yocto Project.</para> <para>Finally, "poky" can refer to the default <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink> (i.e. distribution) created when you use the Yocto Project in conjunction with the <filename>poky</filename> repository to build an image. </para></listitem> <listitem><para><emphasis>Recipe:</emphasis> A set of instructions for building packages. A recipe describes where you get source code, which patches to apply, how to configure the source, how to compile it and so on. Recipes also describe dependencies for libraries or for other recipes. Recipes represent the logical unit of execution, the software to build, the images to build, and use the <filename>.bb</filename> file extension. </para></listitem> <listitem> <para id='source-directory'><emphasis>Source Directory:</emphasis> This term refers to the directory structure created as a result of creating a local copy of the <filename>poky</filename> Git repository <filename>git://git.yoctoproject.org/poky</filename> or expanding a released <filename>poky</filename> tarball. <note> Creating a local copy of the <filename>poky</filename> Git repository is the recommended method for setting up your Source Directory. </note> Sometimes you might hear the term "poky directory" used to refer to this directory structure. <note> The OpenEmbedded build system does not support file or directory names that contain spaces. Be sure that the Source Directory you use does not contain these types of names. </note></para> <para>The Source Directory contains BitBake, Documentation, Metadata and other files that all support the Yocto Project. Consequently, you must have the Source Directory in place on your development system in order to do any development using the Yocto Project.</para> <para>When you create a local copy of the Git repository, you can name the repository anything you like. Throughout much of the documentation, "poky" is used as the name of the top-level folder of the local copy of the poky Git repository. So, for example, cloning the <filename>poky</filename> Git repository results in a local Git repository whose top-level folder is also named "poky".</para> <para>While it is not recommended that you use tarball expansion to set up the Source Directory, if you do, the top-level directory name of the Source Directory is derived from the Yocto Project release tarball. For example, downloading and unpacking <filename>&YOCTO_POKY_TARBALL;</filename> results in a Source Directory whose root folder is named <filename>&YOCTO_POKY;</filename>.</para> <para>It is important to understand the differences between the Source Directory created by unpacking a released tarball as compared to cloning <filename>git://git.yoctoproject.org/poky</filename>. When you unpack a tarball, you have an exact copy of the files based on the time of release - a fixed release point. Any changes you make to your local files in the Source Directory are on top of the release and will remain local only. On the other hand, when you clone the <filename>poky</filename> Git repository, you have an active development repository with access to the upstream repository's branches and tags. In this case, any local changes you make to the local Source Directory can be later applied to active development branches of the upstream <filename>poky</filename> Git repository.</para> <para>For more information on concepts related to Git repositories, branches, and tags, see the "<link linkend='repositories-tags-and-branches'>Repositories, Tags, and Branches</link>" section.</para></listitem> <listitem><para><emphasis>Task:</emphasis> A unit of execution for BitBake (e.g. <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>, <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>, <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>, and so forth). </para></listitem> <listitem><para><emphasis>Upstream:</emphasis> A reference to source code or repositories that are not local to the development system but located in a master area that is controlled by the maintainer of the source code. For example, in order for a developer to work on a particular piece of code, they need to first get a copy of it from an "upstream" source.</para></listitem> </itemizedlist> </para> </section> <section id='licensing'> <title>Licensing</title> <para> 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: <itemizedlist> <listitem><para><ulink url='http://en.wikipedia.org/wiki/Open-source_license'>Open source license history</ulink> </para></listitem> <listitem><para><ulink url='http://en.wikipedia.org/wiki/Free_software_license'>Free software license history</ulink></para></listitem> </itemizedlist> </para> <para> 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 <ulink url='http://www.opensource.org/licenses/mit-license.php'>here</ulink>. You can find information on the GNU GPL <ulink url='http://www.opensource.org/licenses/LGPL-3.0'> here</ulink>. </para> <para> 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 <link linkend='source-directory'>Source Directory</link> at <filename>meta/files/common-licenses</filename>. Once the build completes, the list of all licenses found and used during that build are kept in the <link linkend='build-directory'>Build Directory</link> at <filename>tmp/deploy/licenses</filename>. </para> <para> 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. </para> <para> 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. <ulink url='http://spdx.org'>SPDX Group</ulink> 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. <ulink url='http://opensource.org'>OSI</ulink> 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). </para> <para> You can find a list of the combined SPDX and OSI licenses that the Yocto Project uses in the <filename>meta/files/common-licenses</filename> directory in your <link linkend='source-directory'>Source Directory</link>. </para> <para> 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 "<link linkend='maintaining-open-source-license-compliance-during-your-products-lifecycle'>Maintaining Open Source License Compliance During Your Product's Lifecycle</link>" section. </para> </section> <section id='git'> <title>Git</title> <para> 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. </para> <para> For more information on Git, see <ulink url='http://git-scm.com/documentation'></ulink>. If you need to download Git, go to <ulink url='http://git-scm.com/download'></ulink>. </para> <section id='repositories-tags-and-branches'> <title>Repositories, Tags, and Branches</title> <para> As mentioned earlier in the section "<link linkend='yocto-project-repositories'>Yocto Project Source Repositories</link>", the Yocto Project maintains source repositories at <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>. If you look at this web-interface of the repositories, each item is a separate Git repository. </para> <para> 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. </para> <para> A Git repository represents all development efforts for a given project. For example, the Git repository <filename>poky</filename> contains all changes and developments for Poky 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. </para> <para> You can create a local copy of any repository by "cloning" it with the Git <filename>clone</filename> 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 "<link linkend='getting-setup'>Getting Set Up</link>" section. </para> <para> It is important to understand that Git tracks content change and not files. Git uses "branches" to organize different development efforts. For example, the <filename>poky</filename> repository has several branches that include the current <filename>&DISTRO_NAME_NO_CAP;</filename> branch, the <filename>master</filename> branch, and many branches for past Yocto Project releases. You can see all the branches by going to <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/'></ulink> and clicking on the <filename><ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/refs/heads'>[...]</ulink></filename> link beneath the "Branch" heading. </para> <para> Each of these branches represents a specific area of development. The <filename>master</filename> branch represents the current or most recent development. All other branches represent offshoots of the <filename>master</filename> branch. </para> <para> 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 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, here is a set of commands that creates a local copy of the <filename>poky</filename> Git repository and then creates and checks out a local Git branch that tracks the Yocto Project &DISTRO; Release (&DISTRO_NAME;) development: <literallayout class='monospaced'> $ cd ~ $ git clone git://git.yoctoproject.org/poky $ cd poky $ git checkout -b &DISTRO_NAME_NO_CAP; origin/&DISTRO_NAME_NO_CAP; </literallayout> In this example, the name of the top-level directory of your local <link linkend='source-directory'>Source Directory</link> is "poky" and the name of that local working area (local branch) you just created and checked out is "&DISTRO_NAME_NO_CAP;". The files in your local repository now reflect the same files that are in the "&DISTRO_NAME_NO_CAP;" development branch of the Yocto Project's "poky" upstream 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 development branch at the time you created your local branch, which could be different from the files at the time of a similarly named release. In other words, creating and checking out a local branch based on the "&DISTRO_NAME_NO_CAP;" branch name is not the same as cloning and checking out the "master" branch. Keep reading to see how you create a local snapshot of a Yocto Project Release. </para> <para> Git uses "tags" to mark specific changes in a repository. Typically, a tag is used to mark a special point such as the final change before a project is released. You can see the tags used with the <filename>poky</filename> Git repository by going to <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/'></ulink> and clicking on the <filename><ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/refs/tags'>[...]</ulink></filename> link beneath the "Tag" heading. </para> <para> Some key tags are <filename>dizzy-12.0.0</filename>, <filename>fido-13.0.0</filename>, <filename>jethro-14.0.0</filename>, and <filename>&DISTRO_NAME_NO_CAP;-&POKYVERSION;</filename>. These tags represent Yocto Project releases. </para> <para> When you create a local copy of the Git repository, you also have access to all the tags. 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: <literallayout class='monospaced'> $ cd ~ $ git clone git://git.yoctoproject.org/poky $ cd poky $ git checkout -b my-&DISTRO_NAME_NO_CAP;-&POKYVERSION; &DISTRO_NAME_NO_CAP;-&POKYVERSION; </literallayout> In this example, the name of the top-level directory of your local Yocto Project Files Git repository is <filename>poky</filename>. And, the name of the local branch you have created and checked out is <filename>my-&DISTRO_NAME_NO_CAP;-&POKYVERSION;</filename>. The files in your repository now exactly match the Yocto Project &DISTRO; Release tag (<filename>&DISTRO_NAME_NO_CAP;-&POKYVERSION;</filename>). 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. </para> </section> <section id='basic-commands'> <title>Basic Commands</title> <para> 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 <ulink url='http://git-scm.com/documentation'>here</ulink>. If you need to download Git, you can do so <ulink url='http://git-scm.com/download'>here</ulink>, although any reasonably current Linux distribution should already have an installable package for Git. </para> <para> If you do not know much about Git, you should educate yourself by visiting the links previously mentioned. </para> <para> The following list 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 they support. See the Git documentation for complete descriptions and strategies on how to use these commands: <itemizedlist> <listitem><para><emphasis><filename>git init</filename>:</emphasis> Initializes an empty Git repository. You cannot use Git commands unless you have a <filename>.git</filename> repository.</para></listitem> <listitem><para><emphasis><filename>git clone</filename>:</emphasis> Creates a local clone of a Git repository. During collaboration, this command allows you to create a local Git repository that is on equal footing with a fellow developer’s Git repository. </para></listitem> <listitem><para><emphasis><filename>git add</filename>:</emphasis> 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.</para></listitem> <listitem><para><emphasis><filename>git commit</filename>:</emphasis> Creates a "commit" that documents the changes you made. 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 (or master) repository.</para></listitem> <listitem><para><emphasis><filename>git status</filename>:</emphasis> Reports any modified files that possibly need to be staged and committed.</para></listitem> <listitem><para><emphasis><filename>git checkout</filename> <replaceable>branch-name</replaceable>:</emphasis> Changes your working branch. This command is analogous to "cd".</para></listitem> <listitem><para><emphasis><filename>git checkout –b</filename> <replaceable>working-branch</replaceable>:</emphasis> Creates a working branch on your local machine where you can isolate work. It is a good idea to use local branches when adding specific features or changes. This way if you do not like what you have done you can easily get rid of the work.</para></listitem> <listitem><para><emphasis><filename>git branch</filename>:</emphasis> Reports existing local branches and tells you the branch in which you are currently working.</para></listitem> <listitem><para><emphasis><filename>git branch -D</filename> <replaceable>branch-name</replaceable>:</emphasis> Deletes an existing local branch. You need to be in a local branch other than the one you are deleting in order to delete <replaceable>branch-name</replaceable>.</para></listitem> <listitem><para><emphasis><filename>git pull</filename>:</emphasis> 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).</para></listitem> <listitem><para><emphasis><filename>git push</filename>:</emphasis> Sends all your committed local changes to an upstream Git repository (e.g. a contribution repository). The maintainer of the project draws from these repositories when adding changes to the project’s master repository or other development branch. </para></listitem> <listitem><para><emphasis><filename>git merge</filename>:</emphasis> 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 for isolated work, make and commit your changes, switch to your local master branch, merge the changes from the temporary branch into the local master branch, and then delete the temporary branch.</para></listitem> <listitem><para><emphasis><filename>git cherry-pick</filename>:</emphasis> 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.</para></listitem> <listitem><para><emphasis><filename>gitk</filename>:</emphasis> 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.</para></listitem> <listitem><para><emphasis><filename>git log</filename>:</emphasis> Reports a history of your changes to the repository.</para></listitem> <listitem><para><emphasis><filename>git diff</filename>:</emphasis> Displays line-by-line differences between your local working files and the same files in the upstream Git repository that your branch currently tracks.</para></listitem> </itemizedlist> </para> </section> </section> <section id='workflows'> <title>Workflows</title> <para> This section provides some overview on workflows using Git. In particular, the information covers basic practices that describe roles and actions in a collaborative development environment. Again, if you are familiar with this type of development environment, you might want to just skip this section. </para> <para> The Yocto Project files are maintained using Git in a "master" branch whose Git history tracks every change and whose structure provides 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 "master" branch of a given Git repository. The "master" branch is the “upstream” repository where the final builds of the project occur. The maintainer is responsible for accepting changes from other developers and for organizing the underlying branch structure to reflect release strategies and so forth. <note>For information on finding out who is responsible for (maintains) a particular area of code, see the "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section. </note> </para> <para> The project also has an upstream contribution Git repository named <filename>poky-contrib</filename>. You can see all the branches in this repository using the web interface of the <ulink url='&YOCTO_GIT_URL;'>Source Repositories</ulink> organized within the "Poky Support" area. These branches temporarily hold changes 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. </para> <para> Developers (including contributing community members) create and maintain cloned repositories of the upstream "master" branch. These 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 changes to the appropriate "contrib" repository. </para> <para> Developers are responsible for keeping their local repository up-to-date with "master". 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 developer’s machines before anything is pushed to a "contrib" area and examined at the maintainer’s level. </para> <para> 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 "master" This process is called “submitting a patch” or "submitting a change." For information on submitting patches and changes, see the "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section. </para> <para> To summarize the environment: a single point of entry exists for changes into the project’s "master" 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. </para> <para> <imagedata fileref="figures/git-workflow.png" width="6in" depth="3in" align="left" scalefit="1" /> </para> <para> 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 <ulink url='http://book.git-scm.com'>Git Community Book</ulink>. <itemizedlist> <listitem><para><emphasis>Make Small Changes:</emphasis> 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.</para> <para>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.</para></listitem> <listitem><para><emphasis>Use Branches Liberally:</emphasis> It is very easy to create, use, and delete local branches in your working Git repository. 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.</para></listitem> <listitem><para><emphasis>Merge Changes:</emphasis> The <filename>git merge</filename> 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.</para></listitem> <listitem><para><emphasis>Manage Branches:</emphasis> 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.</para></listitem> <listitem><para><emphasis>Use Push and Pull:</emphasis> 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 <filename>create-pull-request</filename> and <filename>send-pull-request</filename> that ship with the release to facilitate this workflow. You can find these scripts in the <filename>scripts</filename> folder of the <link linkend='source-directory'>Source Directory</link>. For information on how to use these scripts, see the "<link linkend='pushing-a-change-upstream'>Using Scripts to Push a Change Upstream and Request a Pull</link>" section. </para></listitem> <listitem><para><emphasis>Patch Workflow:</emphasis> 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 <filename>git format-patch</filename> and <filename>git send-email</filename>. For information on how to use these scripts, see the "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section. </para></listitem> </itemizedlist> </para> </section> <section id='tracking-bugs'> <title>Tracking Bugs</title> <para> The Yocto Project uses its own implementation of <ulink url='http://www.bugzilla.org/about/'>Bugzilla</ulink> to track bugs. Implementations of Bugzilla work well for group development because they track bugs and code changes, can be used to communicate changes and problems with developers, can be used to submit and review patches, and can be used to manage quality assurance. The home page for the Yocto Project implementation of Bugzilla is <ulink url='&YOCTO_BUGZILLA_URL;'>&YOCTO_BUGZILLA_URL;</ulink>. </para> <para> Sometimes it is helpful to submit, investigate, or track a bug against the Yocto Project itself such as when discovering an issue with some component of the build system that acts contrary to the documentation or your expectations. Following is the general procedure for submitting a new bug using the Yocto Project Bugzilla. You can find more information on defect management, bug tracking, and feature request processes all accomplished through the Yocto Project Bugzilla on the <ulink url='&YOCTO_WIKI_URL;/wiki/Bugzilla_Configuration_and_Bug_Tracking'>wiki page</ulink>. <orderedlist> <listitem><para>Always use the Yocto Project implementation of Bugzilla to submit a bug.</para></listitem> <listitem><para>When submitting a new bug, be sure to choose the appropriate Classification, Product, and Component for which the issue was found. Defects for the Yocto Project fall into one of seven classifications: Yocto Project Components, Infrastructure, Build System &amp; Metadata, Documentation, QA/Testing, Runtime and Hardware. Each of these Classifications break down into multiple Products and, in some cases, multiple Components.</para></listitem> <listitem><para>Use the bug form to choose the correct Hardware and Architecture for which the bug applies.</para></listitem> <listitem><para>Indicate the Yocto Project version you were using when the issue occurred.</para></listitem> <listitem><para>Be sure to indicate the Severity of the bug. Severity communicates how the bug impacted your work.</para></listitem> <listitem><para>Select the appropriate "Documentation change" item for the bug. Fixing a bug may or may not affect the Yocto Project documentation.</para></listitem> <listitem><para>Provide a brief summary of the issue. Try to limit your summary to just a line or two and be sure to capture the essence of the issue.</para></listitem> <listitem><para>Provide a detailed description of the issue. You should provide as much detail as you can about the context, behavior, output, and so forth that surrounds the issue. You can even attach supporting files for output from logs by using the "Add an attachment" button.</para></listitem> <listitem><para>Be sure to copy the appropriate people in the "CC List" for the bug. See the "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section for information about finding out who is responsible for code.</para></listitem> <listitem><para>Submit the bug by clicking the "Submit Bug" button.</para></listitem> </orderedlist> </para> </section> <section id='how-to-submit-a-change'> <title>How to Submit a Change</title> <para> Contributions to the Yocto Project and OpenEmbedded are very welcome. Because the system is extremely configurable and flexible, we recognize that developers will want to extend, configure or optimize it for their specific uses. You should send patches to the appropriate mailing list so that they can be reviewed and merged by the appropriate maintainer. </para> <para> Before submitting any change, be sure to find out who you should be notifying. Several methods exist through which you find out who you should be copying or notifying: <itemizedlist> <listitem><para><emphasis>Maintenance File:</emphasis> Examine the <filename>maintainers.inc</filename> file, which is located in the <link linkend='source-directory'>Source Directory</link> at <filename>meta-poky/conf/distro/include</filename>, to see who is responsible for code. </para></listitem> <listitem><para><emphasis>Board Support Package (BSP) README Files:</emphasis> For BSP maintainers of supported BSPs, you can examine individual BSP <filename>README</filename> files. In addition, some layers (such as the <filename>meta-intel</filename> layer), include a <filename>MAINTAINERS</filename> file which contains a list of all supported BSP maintainers for that layer. </para></listitem> <listitem><para><emphasis>Search by File:</emphasis> Using <link linkend='git'>Git</link>, you can enter the following command to bring up a short list of all commits against a specific file: <literallayout class='monospaced'> git shortlog -- <replaceable>filename</replaceable> </literallayout> Just provide the name of the file for which you are interested. The information returned is not ordered by history but does include a list of all committers grouped by name. From the list, you can see who is responsible for the bulk of the changes against the file. </para></listitem> </itemizedlist> </para> <para> For a list of the Yocto Project and related mailing lists, see the "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing lists</ulink>" section in the Yocto Project Reference Manual. </para> <para> Here is some guidance on which mailing list to use for what type of change: <itemizedlist> <listitem><para>For changes to the core <link linkend='metadata'>Metadata</link>, send your patch to the <ulink url='&OE_LISTS_URL;/listinfo/openembedded-core'>openembedded-core</ulink> mailing list. For example, a change to anything under the <filename>meta</filename> or <filename>scripts</filename> directories should be sent to this mailing list.</para></listitem> <listitem><para>For changes to BitBake (anything under the <filename>bitbake</filename> directory), send your patch to the <ulink url='&OE_LISTS_URL;/listinfo/bitbake-devel'>bitbake-devel</ulink> mailing list.</para></listitem> <listitem><para>For changes to <filename>meta-poky</filename>, send your patch to the <ulink url='&YOCTO_LISTS_URL;/listinfo/poky'>poky</ulink> mailing list.</para></listitem> <listitem><para>For changes to other layers hosted on <filename>yoctoproject.org</filename> (unless the layer's documentation specifies otherwise), tools, and Yocto Project documentation, use the <ulink url='&YOCTO_LISTS_URL;/listinfo/yocto'>yocto</ulink> mailing list.</para></listitem> <listitem><para>For additional recipes that do not fit into the core Metadata, you should determine which layer the recipe should go into and submit the change in the manner recommended by the documentation (e.g. README) supplied with the layer. If in doubt, please ask on the <ulink url='&YOCTO_LISTS_URL;/listinfo/yocto'>yocto</ulink> or <ulink url='&OE_LISTS_URL;/listinfo/openembedded-devel'>openembedded-devel</ulink> mailing lists.</para></listitem> </itemizedlist> </para> <para> When you send a patch, be sure to include a "Signed-off-by:" line in the same style as required by the Linux kernel. Adding this line signifies that you, the submitter, have agreed to the Developer's Certificate of Origin 1.1 as follows: <literallayout class='monospaced'> Developer's Certificate of Origin 1.1 By making a contribution to this project, I certify that: (a) The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or (b) The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or (c) The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it. (d) I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved. </literallayout> </para> <para> In a collaborative environment, it is necessary to have some sort of standard or method through which you submit changes. Otherwise, things could get quite chaotic. One general practice to follow is to make small, controlled changes. Keeping changes small and isolated aids review, makes merging/rebasing easier and keeps the change history clean when anyone needs to refer to it in future. </para> <para> When you make a commit, you must follow certain standards established by the OpenEmbedded and Yocto Project development teams. For each commit, you must provide a single-line summary of the change and you should almost always provide a more detailed description of what you did (i.e. the body of the commit message). The only exceptions for not providing a detailed description would be if your change is a simple, self-explanatory change that needs no further description beyond the summary. Here are the guidelines for composing a commit message: <itemizedlist> <listitem><para>Provide a single-line, short summary of the change. This summary is typically viewable in the "shortlist" of changes. Thus, providing something short and descriptive that gives the reader a summary of the change is useful when viewing a list of many commits. This short description should be prefixed by the recipe name (if changing a recipe), or else the short form path to the file being changed. </para></listitem> <listitem><para>For the body of the commit message, provide detailed information that describes what you changed, why you made the change, and the approach you used. It may also be helpful if you mention how you tested the change. Provide as much detail as you can in the body of the commit message. </para></listitem> <listitem><para> If the change addresses a specific bug or issue that is associated with a bug-tracking ID, include a reference to that ID in your detailed description. For example, the Yocto Project uses a specific convention for bug references - any commit that addresses a specific bug should use the following form for the detailed description: <literallayout class='monospaced'> Fixes [YOCTO #<replaceable>bug-id</replaceable>] <replaceable>detailed description of change</replaceable> </literallayout></para></listitem> Where <replaceable>bug-id</replaceable> is replaced with the specific bug ID from the Yocto Project Bugzilla instance. </itemizedlist> </para> <para> You can find more guidance on creating well-formed commit messages at this OpenEmbedded wiki page: <ulink url='&OE_HOME_URL;/wiki/Commit_Patch_Message_Guidelines'></ulink>. </para> <para> The next two sections describe general instructions for both pushing changes upstream and for submitting changes as patches. </para> <section id='pushing-a-change-upstream'> <title>Using Scripts to Push a Change Upstream and Request a Pull</title> <para> The basic flow for pushing a change to an upstream "contrib" Git repository is as follows: <itemizedlist> <listitem><para>Make your changes in your local Git repository.</para></listitem> <listitem><para>Stage your changes by using the <filename>git add</filename> command on each file you changed.</para></listitem> <listitem><para> Commit the change by using the <filename>git commit</filename> command. Be sure to provide a commit message that follows the project’s commit message standards as described earlier. </para></listitem> <listitem><para> Push the change to the upstream "contrib" repository by using the <filename>git push</filename> command. </para></listitem> <listitem><para>Notify the maintainer that you have pushed a change by making a pull request. The Yocto Project provides two scripts that conveniently let you generate and send pull requests to the Yocto Project. These scripts are <filename>create-pull-request</filename> and <filename>send-pull-request</filename>. You can find these scripts in the <filename>scripts</filename> directory within the <link linkend='source-directory'>Source Directory</link>.</para> <para>Using these scripts correctly formats the requests without introducing any whitespace or HTML formatting. The maintainer that receives your patches needs to be able to save and apply them directly from your emails. Using these scripts is the preferred method for sending patches.</para> <para>For help on using these scripts, simply provide the <filename>-h</filename> argument as follows: <literallayout class='monospaced'> $ poky/scripts/create-pull-request -h $ poky/scripts/send-pull-request -h </literallayout></para></listitem> </itemizedlist> </para> <para> You can find general Git information on how to push a change upstream in the <ulink url='http://git-scm.com/book/en/v2/Distributed-Git-Distributed-Workflows'>Git Community Book</ulink>. </para> </section> <section id='submitting-a-patch'> <title>Using Email to Submit a Patch</title> <para> You can submit patches without using the <filename>create-pull-request</filename> and <filename>send-pull-request</filename> scripts described in the previous section. However, keep in mind, the preferred method is to use the scripts. </para> <para> Depending on the components changed, you need to submit the email to a specific mailing list. For some guidance on which mailing list to use, see the list in the "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section. For a description of the available mailing lists, see the "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing Lists</ulink>" section in the Yocto Project Reference Manual. </para> <para> Here is the general procedure on how to submit a patch through email without using the scripts: <itemizedlist> <listitem><para>Make your changes in your local Git repository.</para></listitem> <listitem><para>Stage your changes by using the <filename>git add</filename> command on each file you changed.</para></listitem> <listitem><para>Commit the change by using the <filename>git commit --signoff</filename> command. Using the <filename>--signoff</filename> option identifies you as the person making the change and also satisfies the Developer's Certificate of Origin (DCO) shown earlier.</para> <para>When you form a commit, you must follow certain standards established by the Yocto Project development team. See the earlier section "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" for Yocto Project commit message standards.</para></listitem> <listitem><para>Format the commit into an email message. To format commits, use the <filename>git format-patch</filename> command. When you provide the command, you must include a revision list or a number of patches as part of the command. For example, either of these two commands takes your most recent single commit and formats it as an email message in the current directory: <literallayout class='monospaced'> $ git format-patch -1 </literallayout> or <literallayout class='monospaced'> $ git format-patch HEAD~ </literallayout></para> <para>After the command is run, the current directory contains a numbered <filename>.patch</filename> file for the commit.</para> <para>If you provide several commits as part of the command, the <filename>git format-patch</filename> command produces a series of numbered files in the current directory – one for each commit. If you have more than one patch, you should also use the <filename>--cover</filename> option with the command, which generates a cover letter as the first "patch" in the series. You can then edit the cover letter to provide a description for the series of patches. For information on the <filename>git format-patch</filename> command, see <filename>GIT_FORMAT_PATCH(1)</filename> displayed using the <filename>man git-format-patch</filename> command.</para> <note>If you are or will be a frequent contributor to the Yocto Project or to OpenEmbedded, you might consider requesting a contrib area and the necessary associated rights.</note></listitem> <listitem><para>Import the files into your mail client by using the <filename>git send-email</filename> command. <note>In order to use <filename>git send-email</filename>, you must have the the proper Git packages installed. For Ubuntu, Debian, and Fedora the package is <filename>git-email</filename>.</note></para> <para>The <filename>git send-email</filename> command sends email by using a local or remote Mail Transport Agent (MTA) such as <filename>msmtp</filename>, <filename>sendmail</filename>, or through a direct <filename>smtp</filename> configuration in your Git <filename>config</filename> file. If you are submitting patches through email only, it is very important that you submit them without any whitespace or HTML formatting that either you or your mailer introduces. The maintainer that receives your patches needs to be able to save and apply them directly from your emails. A good way to verify that what you are sending will be applicable by the maintainer is to do a dry run and send them to yourself and then save and apply them as the maintainer would.</para> <para>The <filename>git send-email</filename> command is the preferred method for sending your patches since there is no risk of compromising whitespace in the body of the message, which can occur when you use your own mail client. The command also has several options that let you specify recipients and perform further editing of the email message. For information on how to use the <filename>git send-email</filename> command, see <filename>GIT-SEND-EMAIL(1)</filename> displayed using the <filename>man git-send-email</filename> command. </para></listitem> </itemizedlist> </para> </section> </section> </chapter> <!-- vim: expandtab tw=80 ts=4 -->