diff options
Diffstat (limited to 'import-layers/yocto-poky/documentation/ref-manual/ref-development-environment.xml')
| -rw-r--r-- | import-layers/yocto-poky/documentation/ref-manual/ref-development-environment.xml | 2761 |
1 files changed, 0 insertions, 2761 deletions
diff --git a/import-layers/yocto-poky/documentation/ref-manual/ref-development-environment.xml b/import-layers/yocto-poky/documentation/ref-manual/ref-development-environment.xml deleted file mode 100644 index 52197d16d5..0000000000 --- a/import-layers/yocto-poky/documentation/ref-manual/ref-development-environment.xml +++ /dev/null @@ -1,2761 +0,0 @@ -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" -"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" -[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > - -<chapter id='ref-development-environment'> -<title>The Yocto Project Development Environment</title> - -<para> - This chapter takes a look at the Yocto Project development - environment and also provides a detailed look at what goes on during - development in that environment. - The chapter provides Yocto Project Development environment concepts that - help you understand how work is accomplished in an open source environment, - which is very different as compared to work accomplished in a closed, - proprietary environment. -</para> - -<para> - Specifically, this chapter addresses open source philosophy, workflows, - Git, source repositories, licensing, recipe syntax, and development - syntax. -</para> - -<section id='open-source-philosophy'> - <title>Open Source Philosophy</title> - - <para> - Open source philosophy is characterized by software development - directed by peer production and collaboration through an active - community of developers. - Contrast this to the more standard centralized development models - used by commercial software companies where a finite set of developers - produces a product for sale using a defined set of procedures that - ultimately result in an end product whose architecture and source - material are closed to the public. - </para> - - <para> - Open source projects conceptually have differing concurrent agendas, - approaches, and production. - These facets of the development process can come from anyone in the - public (community) that has a stake in the software project. - The open source environment contains new copyright, licensing, domain, - and consumer issues that differ from the more traditional development - environment. - In an open source environment, the end product, source material, - and documentation are all available to the public at no cost. - </para> - - <para> - A benchmark example of an open source project is the Linux kernel, - which was initially conceived and created by Finnish computer science - student Linus Torvalds in 1991. - Conversely, a good example of a non-open source project is the - <trademark class='registered'>Windows</trademark> family of operating - systems developed by - <trademark class='registered'>Microsoft</trademark> Corporation. - </para> - - <para> - Wikipedia has a good historical description of the Open Source - Philosophy - <ulink url='http://en.wikipedia.org/wiki/Open_source'>here</ulink>. - You can also find helpful information on how to participate in the - Linux Community - <ulink url='http://ldn.linuxfoundation.org/book/how-participate-linux-community'>here</ulink>. - </para> -</section> - -<section id='workflows'> - <title>Workflows</title> - - <para> - This section provides workflow concepts using the Yocto Project and - Git. - In particular, the information covers basic practices that describe - roles and actions in a collaborative development environment. - <note> - If you are familiar with this type of development environment, you - might not want to read this section. - </note> - </para> - - <para> - The Yocto Project files are maintained using Git in "master" - branches whose Git histories track every change and whose structures - provides branches for all diverging functionality. - Although there is no need to use Git, many open source projects do so. - <para> - - </para> - 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 from which final or - most recent 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 - "<ulink url='&YOCTO_DOCS_DEV_URL;#how-to-submit-a-change'>Submitting a Change to the Yocto Project</ulink>" - section of the Yocto Project Development Tasks Manual. - </note> - </para> - - <para> - The Yocto Project <filename>poky</filename> Git repository 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. - The cloned repositories are local to their development platforms and - are used to develop changes. - When a developer is satisfied with a particular feature or change, - they "push" the 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 machine 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 - "<ulink url='&YOCTO_DOCS_DEV_URL;#how-to-submit-a-change'>Submitting a Change to the Yocto Project</ulink>" - section in the Yocto Project Development Tasks Manual. - </para> - - <para> - To summarize the development workflow: 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 - "<ulink url='&YOCTO_DOCS_DEV_URL;#pushing-a-change-upstream'>Using Scripts to Push a Change Upstream and Request a Pull</ulink>" - section in the Yocto Project Development Tasks Manual. - </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 - "<ulink url='&YOCTO_DOCS_DEV_URL;#how-to-submit-a-change'>Submitting a Change to the Yocto Project</ulink>" - section in the Yocto Project Development Tasks Manual. - </para></listitem> - </itemizedlist> - </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. - <note><title>Notes</title> - <itemizedlist> - <listitem><para> - For more information on Git, see - <ulink url='http://git-scm.com/documentation'></ulink>. - </para></listitem> - <listitem><para> - If you need to download Git, it is recommended that you add - Git to your system through your distribution's "software - store" (e.g. for Ubuntu, use the Ubuntu Software feature). - For the Git download page, see - <ulink url='http://git-scm.com/download'></ulink>. - </para></listitem> - <listitem><para> - For examples beyond the limited few in this section on how - to use Git with the Yocto Project, see the - "<ulink url='&YOCTO_DOCS_DEV_URL;#working-with-yocto-project-source-files'>Working With Yocto Project Source Files</ulink>" - section in the Yocto Project Development Tasks Manual. - </para></listitem> - </itemizedlist> - </note> - </para> - - <section id='repositories-tags-and-branches'> - <title>Repositories, Tags, and Branches</title> - - <para> - As mentioned briefly in the previous section and also in the - "<link linkend='workflows'>Workflows</link>" section, - 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 <filename>git 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 - "<ulink url='&YOCTO_DOCS_DEV_URL;#working-with-yocto-project-source-files'>Working With Yocto Project Source Files</ulink>" - section in the Yocto Project Development Tasks Manual. - </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 "&DISTRO_NAME_NO_CAP;" - branch, the "master" branch, and many branches for past - Yocto Project releases. - You can see all the branches by going to - <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 "master" branch represents the current or most recent - development. - All other branches represent offshoots of the "master" 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 upstream source Git repository. - in other words, you can define your local Git environment to - work on any development branch in the repository. - To help illustrate, consider the following example Git commands: - <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 the previous example after moving to the home directory, the - <filename>git clone</filename> command creates a - local copy of the upstream <filename>poky</filename> Git repository. - By default, Git checks out the "master" branch for your work. - After changing the working directory to the new local repository - (i.e. <filename>poky</filename>), the - <filename>git checkout</filename> command creates - and checks out a local branch named "&DISTRO_NAME_NO_CAP;", which - tracks the upstream "origin/&DISTRO_NAME_NO_CAP;" branch. - Changes you make while in this branch would ultimately affect - the upstream "&DISTRO_NAME_NO_CAP;" branch of the - <filename>poky</filename> repository. - </para> - - <para> - It is important to understand that when you create and checkout a - local working branch based on a branch name, - your local environment matches the "tip" of that particular - development branch at the time you created your local branch, - which could be different from the files in the "master" branch - of the upstream repository. - In other words, creating and checking out a local branch based on - the "&DISTRO_NAME_NO_CAP;" branch name is not the same as - cloning and checking out the "master" branch if the repository. - 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 for the <filename>poky</filename> are - <filename>jethro-14.0.3</filename>, - <filename>morty-16.0.1</filename>, - <filename>pyro-17.0.0</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 in the upstream repository. - Similar to branches, you can create and checkout a local working - Git branch based on a tag name. - When you do this, you get a snapshot of the Git repository that - reflects the state of the files when the change was made associated - with that tag. - The most common use is to checkout a working branch that matches - a specific Yocto Project release. - Here is an example: - <literallayout class='monospaced'> - $ cd ~ - $ git clone git://git.yoctoproject.org/poky - $ cd poky - $ git fetch --all --tags --prune - $ git checkout tags/pyro-17.0.0 -b my-pyro-17.0.0 - </literallayout> - In this example, the name of the top-level directory of your - local Yocto Project repository is <filename>poky</filename>. - After moving to the <filename>poky</filename> directory, the - <filename>git fetch</filename> command makes all the upstream - tags available locally in your repository. - Finally, the <filename>git checkout</filename> command - creates and checks out a branch named "my-pyro-17.0.0" that is - based on the specific change upstream in the repository - associated with the "pyro-17.0.0" tag. - The files in your repository now exactly match that particular - Yocto Project release as it is tagged in the upstream Git - repository. - It is important to understand that when you create and - checkout a local working branch based on a tag, your environment - matches a specific point in time and not the entire development - branch (i.e. the "tip" of the 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>. - </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 of Git commands briefly describes some basic - Git operations as a way to get started. - As with any set of commands, this list (in most cases) simply shows - the base command and omits the many arguments 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 id='git-commands-clone'> - <emphasis><filename>git clone</filename>:</emphasis> - Creates a local clone of a Git repository that is on - equal footing with a fellow developer’s Git repository - or an upstream repository. - </para></listitem> - <listitem><para> - <emphasis><filename>git add</filename>:</emphasis> - Locally stages updated file contents to the index that - Git uses to track changes. - You must stage all files that have changed before you - can commit them. - </para></listitem> - <listitem><para> - <emphasis><filename>git commit</filename>:</emphasis> - Creates a local "commit" that documents the changes you - made. - Only changes that have been staged can be committed. - Commits are used for historical purposes, for determining - if a maintainer of a project will allow the change, - and for ultimately pushing the change from your local - Git repository into the project’s upstream repository. - </para></listitem> - <listitem><para> - <emphasis><filename>git status</filename>:</emphasis> - Reports any modified files that possibly need to be - staged and gives you a status of where you stand regarding - local commits as compared to the upstream repository. - </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 and checks out a working branch on your local - machine that you can use to isolate your work. - It is a good idea to use local branches when adding - specific features or changes. - Using isolated branches facilitates easy removal of - changes if they do not work out. - </para></listitem> - <listitem><para><emphasis><filename>git branch</filename>:</emphasis> - Displays the existing local branches associated with your - local repository. - The branch that you have currently checked out is noted - with an asterisk character. - </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 the upstream Git - repository that your local repository is tracking - (e.g. a contribution repository). - The maintainer of the project draws from these repositories - to merge changes (commits) into the appropriate branch - of project's upstream repository. - </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 that is - based off "master" that you would use for isolated work. - You would make your changes in that isolated branch, - stage and commit them locally, switch to the "master" - branch, and then use the <filename>git merge</filename> - command to apply the changes from your isolated branch - into the currently checked out branch (e.g. "master"). - After the merge is complete and if you are done with - working in that isolated branch, you can safely delete - the isolated branch. - </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. - <note> - You need to install the <filename>gitk</filename> - package on your development system to use this - command. - </note> - </para></listitem> - <listitem><para> - <emphasis><filename>git log</filename>:</emphasis> - Reports a history of your commits to the repository. - This report lists all commits regardless of whether you - have pushed them upstream or not. - </para></listitem> - <listitem><para> - <emphasis><filename>git diff</filename>:</emphasis> - Displays line-by-line differences between a local - working file and the same file as understood by Git. - This command is useful to see what you have changed - in any given file. - </para></listitem> - </itemizedlist> - </para> - </section> -</section> - -<section id='yocto-project-repositories'> - <title>Yocto Project Source Repositories</title> - - <para> - The Yocto Project team maintains complete source repositories for all - Yocto Project files at - <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'></ulink>. - This web-based source code browser is organized into categories by - function such as IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and - so forth. - From the interface, you can click on any particular item in the "Name" - column and see the URL at the bottom of the page that you need to clone - a Git repository for that particular item. - Having a local Git repository of the - <link linkend='source-directory'>Source Directory</link>, which is - usually named "poky", allows - you to make changes, contribute to the history, and ultimately enhance - the Yocto Project's tools, Board Support Packages, and so forth. - </para> - - <para> - For any supported release of Yocto Project, you can also go to the - <ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink> and - select the "Downloads" tab and get a released tarball of the - <filename>poky</filename> repository or any supported BSP tarballs. - Unpacking these tarballs gives you a snapshot of the released - files. - <note><title>Notes</title> - <itemizedlist> - <listitem><para> - The recommended method for setting up the Yocto Project - <link linkend='source-directory'>Source Directory</link> - and the files for supported BSPs - (e.g., <filename>meta-intel</filename>) is to use - <link linkend='git'>Git</link> to create a local copy of - the upstream repositories. - </para></listitem> - <listitem><para> - Be sure to always work in matching branches for both - the selected BSP repository and the - <link linkend='source-directory'>Source Directory</link> - (i.e. <filename>poky</filename>) repository. - For example, if you have checked out the "master" branch - of <filename>poky</filename> and you are going to use - <filename>meta-intel</filename>, be sure to checkout the - "master" branch of <filename>meta-intel</filename>. - </para></listitem> - </itemizedlist> - </note> - </para> - - <para> - In summary, here is where you can get the project files needed for - development: - <itemizedlist> - <listitem><para id='source-repositories'> - <emphasis> - <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'>Source Repositories:</ulink> - </emphasis> - This area contains IDE Plugins, Matchbox, Poky, Poky Support, - Tools, Yocto Linux Kernel, and Yocto Metadata Layers. - You can create local copies of Git repositories for each of - these areas.</para> - - <para> - <imagedata fileref="figures/source-repos.png" align="center" width="6in" depth="4in" /> - For steps on how to view and access these upstream Git - repositories, see the - "<ulink url='&YOCTO_DOCS_DEV_URL;#accessing-source-repositories'>Accessing Source Repositories</ulink>" - Section in the Yocto Project Development Tasks Manual. - </para></listitem> - <listitem><para><anchor id='index-downloads' /> - <emphasis> - <ulink url='&YOCTO_DL_URL;/releases/'>Index of /releases:</ulink> - </emphasis> - This is an index of releases such as - the <trademark class='trade'>Eclipse</trademark> - Yocto Plug-in, miscellaneous support, Poky, Pseudo, installers - for cross-development toolchains, and all released versions of - Yocto Project in the form of images or tarballs. - Downloading and extracting these files does not produce a local - copy of the Git repository but rather a snapshot of a - particular release or image.</para> - - <para> - <imagedata fileref="figures/index-downloads.png" align="center" width="6in" depth="3.5in" /> - For steps on how to view and access these files, see the - "<ulink url='&YOCTO_DOCS_DEV_URL;#accessing-index-of-releases'>Accessing Index of Releases</ulink>" - section in the Yocto Project Development Tasks Manual. - </para></listitem> - <listitem><para id='downloads-page'> - <emphasis>"Downloads" page for the - <ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink>: - </emphasis></para> - - <para role="writernotes">This section will change due to - reworking of the YP Website.</para> - - <para>The Yocto Project website includes a "Downloads" tab - that allows you to download any Yocto Project - release and Board Support Package (BSP) in tarball form. - The tarballs are similar to those found in the - <ulink url='&YOCTO_DL_URL;/releases/'>Index of /releases:</ulink> area.</para> - - <para> - <imagedata fileref="figures/yp-download.png" align="center" width="6in" depth="4in" /> - For steps on how to use the "Downloads" page, see the - "<ulink url='&YOCTO_DOCS_DEV_URL;#using-the-downloads-page'>Using the Downloads Page</ulink>" - section in the Yocto Project Development Tasks Manual. - </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 - "<ulink url='&YOCTO_DOCS_DEV_URL;#maintaining-open-source-license-compliance-during-your-products-lifecycle'>Maintaining Open Source License Compliance During Your Product's Lifecycle</ulink>" - section in the Yocto Project Development Tasks Manual. - </para> -</section> - -<section id='recipe-syntax'> - <title>Recipe Syntax</title> - - <para> - Understanding recipe file syntax is important for - writing recipes. - The following list overviews the basic items that make up a - BitBake recipe file. - For more complete BitBake syntax descriptions, see the - "<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>" - chapter of the BitBake User Manual. - <itemizedlist> - <listitem><para><emphasis>Variable Assignments and Manipulations:</emphasis> - Variable assignments allow a value to be assigned to a - variable. - The assignment can be static text or might include - the contents of other variables. - In addition to the assignment, appending and prepending - operations are also supported.</para> - <para>The following example shows some of the ways - you can use variables in recipes: - <literallayout class='monospaced'> - S = "${WORKDIR}/postfix-${PV}" - CFLAGS += "-DNO_ASM" - SRC_URI_append = " file://fixup.patch" - </literallayout> - </para></listitem> - <listitem><para><emphasis>Functions:</emphasis> - Functions provide a series of actions to be performed. - You usually use functions to override the default - implementation of a task function or to complement - a default function (i.e. append or prepend to an - existing function). - Standard functions use <filename>sh</filename> shell - syntax, although access to OpenEmbedded variables and - internal methods are also available.</para> - <para>The following is an example function from the - <filename>sed</filename> recipe: - <literallayout class='monospaced'> - do_install () { - autotools_do_install - install -d ${D}${base_bindir} - mv ${D}${bindir}/sed ${D}${base_bindir}/sed - rmdir ${D}${bindir}/ - } - </literallayout> - It is also possible to implement new functions that - are called between existing tasks as long as the - new functions are not replacing or complementing the - default functions. - You can implement functions in Python - instead of shell. - Both of these options are not seen in the majority of - recipes.</para></listitem> - <listitem><para><emphasis>Keywords:</emphasis> - BitBake recipes use only a few keywords. - You use keywords to include common - functions (<filename>inherit</filename>), load parts - of a recipe from other files - (<filename>include</filename> and - <filename>require</filename>) and export variables - to the environment (<filename>export</filename>).</para> - <para>The following example shows the use of some of - these keywords: - <literallayout class='monospaced'> - export POSTCONF = "${STAGING_BINDIR}/postconf" - inherit autoconf - require otherfile.inc - </literallayout> - </para></listitem> - <listitem><para><emphasis>Comments:</emphasis> - Any lines that begin with the hash character - (<filename>#</filename>) are treated as comment lines - and are ignored: - <literallayout class='monospaced'> - # This is a comment - </literallayout> - </para></listitem> - </itemizedlist> - </para> - - <para> - This next list summarizes the most important and most commonly - used parts of the recipe syntax. - For more information on these parts of the syntax, you can - reference the - <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink> - chapter in the BitBake User Manual. - <itemizedlist> - <listitem><para><emphasis>Line Continuation: <filename>\</filename></emphasis> - - Use the backward slash (<filename>\</filename>) - character to split a statement over multiple lines. - Place the slash character at the end of the line that - is to be continued on the next line: - <literallayout class='monospaced'> - VAR = "A really long \ - line" - </literallayout> - <note> - You cannot have any characters including spaces - or tabs after the slash character. - </note> - </para></listitem> - <listitem><para> - <emphasis>Using Variables: <filename>${...}</filename></emphasis> - - Use the <filename>${<replaceable>VARNAME</replaceable>}</filename> syntax to - access the contents of a variable: - <literallayout class='monospaced'> - SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz" - </literallayout> - <note> - It is important to understand that the value of a - variable expressed in this form does not get - substituted automatically. - The expansion of these expressions happens - on-demand later (e.g. usually when a function that - makes reference to the variable executes). - This behavior ensures that the values are most - appropriate for the context in which they are - finally used. - On the rare occasion that you do need the variable - expression to be expanded immediately, you can use - the <filename>:=</filename> operator instead of - <filename>=</filename> when you make the - assignment, but this is not generally needed. - </note> - </para></listitem> - <listitem><para><emphasis>Quote All Assignments: <filename>"<replaceable>value</replaceable>"</filename></emphasis> - - Use double quotes around the value in all variable - assignments. - <literallayout class='monospaced'> - VAR1 = "${OTHERVAR}" - VAR2 = "The version is ${PV}" - </literallayout> - </para></listitem> - <listitem><para><emphasis>Conditional Assignment: <filename>?=</filename></emphasis> - - Conditional assignment is used to assign a value to - a variable, but only when the variable is currently - unset. - Use the question mark followed by the equal sign - (<filename>?=</filename>) to make a "soft" assignment - used for conditional assignment. - Typically, "soft" assignments are used in the - <filename>local.conf</filename> file for variables - that are allowed to come through from the external - environment. - </para> - <para>Here is an example where - <filename>VAR1</filename> is set to "New value" if - it is currently empty. - However, if <filename>VAR1</filename> has already been - set, it remains unchanged: - <literallayout class='monospaced'> - VAR1 ?= "New value" - </literallayout> - In this next example, <filename>VAR1</filename> - is left with the value "Original value": - <literallayout class='monospaced'> - VAR1 = "Original value" - VAR1 ?= "New value" - </literallayout> - </para></listitem> - <listitem><para><emphasis>Appending: <filename>+=</filename></emphasis> - - Use the plus character followed by the equals sign - (<filename>+=</filename>) to append values to existing - variables. - <note> - This operator adds a space between the existing - content of the variable and the new content. - </note></para> - <para>Here is an example: - <literallayout class='monospaced'> - SRC_URI += "file://fix-makefile.patch" - </literallayout> - </para></listitem> - <listitem><para><emphasis>Prepending: <filename>=+</filename></emphasis> - - Use the equals sign followed by the plus character - (<filename>=+</filename>) to prepend values to existing - variables. - <note> - This operator adds a space between the new content - and the existing content of the variable. - </note></para> - <para>Here is an example: - <literallayout class='monospaced'> - VAR =+ "Starts" - </literallayout> - </para></listitem> - <listitem><para><emphasis>Appending: <filename>_append</filename></emphasis> - - Use the <filename>_append</filename> operator to - append values to existing variables. - This operator does not add any additional space. - Also, the operator is applied after all the - <filename>+=</filename>, and - <filename>=+</filename> operators have been applied and - after all <filename>=</filename> assignments have - occurred. - </para> - <para>The following example shows the space being - explicitly added to the start to ensure the appended - value is not merged with the existing value: - <literallayout class='monospaced'> - SRC_URI_append = " file://fix-makefile.patch" - </literallayout> - You can also use the <filename>_append</filename> - operator with overrides, which results in the actions - only being performed for the specified target or - machine: - <literallayout class='monospaced'> - SRC_URI_append_sh4 = " file://fix-makefile.patch" - </literallayout> - </para></listitem> - <listitem><para><emphasis>Prepending: <filename>_prepend</filename></emphasis> - - Use the <filename>_prepend</filename> operator to - prepend values to existing variables. - This operator does not add any additional space. - Also, the operator is applied after all the - <filename>+=</filename>, and - <filename>=+</filename> operators have been applied and - after all <filename>=</filename> assignments have - occurred. - </para> - <para>The following example shows the space being - explicitly added to the end to ensure the prepended - value is not merged with the existing value: - <literallayout class='monospaced'> - CFLAGS_prepend = "-I${S}/myincludes " - </literallayout> - You can also use the <filename>_prepend</filename> - operator with overrides, which results in the actions - only being performed for the specified target or - machine: - <literallayout class='monospaced'> - CFLAGS_prepend_sh4 = "-I${S}/myincludes " - </literallayout> - </para></listitem> - <listitem><para><emphasis>Overrides:</emphasis> - - You can use overrides to set a value conditionally, - typically based on how the recipe is being built. - For example, to set the - <link linkend='var-KBRANCH'><filename>KBRANCH</filename></link> - variable's value to "standard/base" for any target - <link linkend='var-MACHINE'><filename>MACHINE</filename></link>, - except for qemuarm where it should be set to - "standard/arm-versatile-926ejs", you would do the - following: - <literallayout class='monospaced'> - KBRANCH = "standard/base" - KBRANCH_qemuarm = "standard/arm-versatile-926ejs" - </literallayout> - Overrides are also used to separate alternate values - of a variable in other situations. - For example, when setting variables such as - <link linkend='var-FILES'><filename>FILES</filename></link> - and - <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link> - that are specific to individual packages produced by - a recipe, you should always use an override that - specifies the name of the package. - </para></listitem> - <listitem><para><emphasis>Indentation:</emphasis> - Use spaces for indentation rather than than tabs. - For shell functions, both currently work. - However, it is a policy decision of the Yocto Project - to use tabs in shell functions. - Realize that some layers have a policy to use spaces - for all indentation. - </para></listitem> - <listitem><para><emphasis>Using Python for Complex Operations: <filename>${@<replaceable>python_code</replaceable>}</filename></emphasis> - - For more advanced processing, it is possible to use - Python code during variable assignments (e.g. - search and replacement on a variable).</para> - <para>You indicate Python code using the - <filename>${@<replaceable>python_code</replaceable>}</filename> - syntax for the variable assignment: - <literallayout class='monospaced'> - SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz - </literallayout> - </para></listitem> - <listitem><para><emphasis>Shell Function Syntax:</emphasis> - Write shell functions as if you were writing a shell - script when you describe a list of actions to take. - You should ensure that your script works with a generic - <filename>sh</filename> and that it does not require - any <filename>bash</filename> or other shell-specific - functionality. - The same considerations apply to various system - utilities (e.g. <filename>sed</filename>, - <filename>grep</filename>, <filename>awk</filename>, - and so forth) that you might wish to use. - If in doubt, you should check with multiple - implementations - including those from BusyBox. - </para></listitem> - </itemizedlist> - </para> -</section> - -<section id="development-concepts"> - <title>Development Concepts</title> - - <para> - This section takes a more detailed look inside the development - process. - The following diagram represents development at a high level. - The remainder of this chapter expands on the fundamental input, output, - process, and - <link linkend='metadata'>Metadata</link>) blocks - that make up development in the Yocto Project environment. - </para> - - <para id='general-yocto-environment-figure'> - <imagedata fileref="figures/yocto-environment-ref.png" align="center" width="8in" depth="4.25in" /> - </para> - - <para> - In general, development consists of several functional areas: - <itemizedlist> - <listitem><para><emphasis>User Configuration:</emphasis> - Metadata you can use to control the build process. - </para></listitem> - <listitem><para><emphasis>Metadata Layers:</emphasis> - Various layers that provide software, machine, and - distro Metadata.</para></listitem> - <listitem><para><emphasis>Source Files:</emphasis> - Upstream releases, local projects, and SCMs.</para></listitem> - <listitem><para><emphasis>Build System:</emphasis> - Processes under the control of - <link linkend='bitbake-term'>BitBake</link>. - This block expands on how BitBake fetches source, applies - patches, completes compilation, analyzes output for package - generation, creates and tests packages, generates images, and - generates cross-development tools.</para></listitem> - <listitem><para><emphasis>Package Feeds:</emphasis> - Directories containing output packages (RPM, DEB or IPK), - which are subsequently used in the construction of an image or - SDK, produced by the build system. - These feeds can also be copied and shared using a web server or - other means to facilitate extending or updating existing - images on devices at runtime if runtime package management is - enabled.</para></listitem> - <listitem><para><emphasis>Images:</emphasis> - Images produced by the development process. - </para></listitem> - <listitem><para><emphasis>Application Development SDK:</emphasis> - Cross-development tools that are produced along with an image - or separately with BitBake.</para></listitem> - </itemizedlist> - </para> - - <section id="user-configuration"> - <title>User Configuration</title> - - <para> - User configuration helps define the build. - Through user configuration, you can tell BitBake the - target architecture for which you are building the image, - where to store downloaded source, and other build properties. - </para> - - <para> - The following figure shows an expanded representation of the - "User Configuration" box of the - <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>: - </para> - - <para> - <imagedata fileref="figures/user-configuration.png" align="center" /> - </para> - - <para> - BitBake needs some basic configuration files in order to complete - a build. - These files are <filename>*.conf</filename> files. - The minimally necessary ones reside as example files in the - <link linkend='source-directory'>Source Directory</link>. - For simplicity, this section refers to the Source Directory as - the "Poky Directory." - </para> - - <para> - When you clone the <filename>poky</filename> Git repository or you - download and unpack a Yocto Project release, you can set up the - Source Directory to be named anything you want. - For this discussion, the cloned repository uses the default - name <filename>poky</filename>. - <note> - The Poky repository is primarily an aggregation of existing - repositories. - It is not a canonical upstream source. - </note> - </para> - - <para> - The <filename>meta-poky</filename> layer inside Poky contains - a <filename>conf</filename> directory that has example - configuration files. - These example files are used as a basis for creating actual - configuration files when you source the build environment - script - (i.e. - <link linkend='structure-core-script'><filename>&OE_INIT_FILE;</filename></link>). - </para> - - <para> - Sourcing the build environment script creates a - <link linkend='build-directory'>Build Directory</link> - if one does not already exist. - BitBake uses the Build Directory for all its work during builds. - The Build Directory has a <filename>conf</filename> directory that - contains default versions of your <filename>local.conf</filename> - and <filename>bblayers.conf</filename> configuration files. - These default configuration files are created only if versions - do not already exist in the Build Directory at the time you - source the build environment setup script. - </para> - - <para> - Because the Poky repository is fundamentally an aggregation of - existing repositories, some users might be familiar with running - the <filename>&OE_INIT_FILE;</filename> script in the context - of separate OpenEmbedded-Core and BitBake repositories rather than a - single Poky repository. - This discussion assumes the script is executed from within a cloned - or unpacked version of Poky. - </para> - - <para> - Depending on where the script is sourced, different sub-scripts - are called to set up the Build Directory (Yocto or OpenEmbedded). - Specifically, the script - <filename>scripts/oe-setup-builddir</filename> inside the - poky directory sets up the Build Directory and seeds the directory - (if necessary) with configuration files appropriate for the - Yocto Project development environment. - <note> - The <filename>scripts/oe-setup-builddir</filename> script - uses the <filename>$TEMPLATECONF</filename> variable to - determine which sample configuration files to locate. - </note> - </para> - - <para> - The <filename>local.conf</filename> file provides many - basic variables that define a build environment. - Here is a list of a few. - To see the default configurations in a <filename>local.conf</filename> - file created by the build environment script, see the - <filename>local.conf.sample</filename> in the - <filename>meta-poky</filename> layer: - <itemizedlist> - <listitem><para><emphasis>Parallelism Options:</emphasis> - Controlled by the - <link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename></link>, - <link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></link>, - and - <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_NUMBER_PARSE_THREADS'><filename>BB_NUMBER_PARSE_THREADS</filename></ulink> - variables.</para></listitem> - <listitem><para><emphasis>Target Machine Selection:</emphasis> - Controlled by the - <link linkend='var-MACHINE'><filename>MACHINE</filename></link> - variable.</para></listitem> - <listitem><para><emphasis>Download Directory:</emphasis> - Controlled by the - <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link> - variable.</para></listitem> - <listitem><para><emphasis>Shared State Directory:</emphasis> - Controlled by the - <link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link> - variable.</para></listitem> - <listitem><para><emphasis>Build Output:</emphasis> - Controlled by the - <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link> - variable.</para></listitem> - </itemizedlist> - <note> - Configurations set in the <filename>conf/local.conf</filename> - file can also be set in the - <filename>conf/site.conf</filename> and - <filename>conf/auto.conf</filename> configuration files. - </note> - </para> - - <para> - The <filename>bblayers.conf</filename> file tells BitBake what - layers you want considered during the build. - By default, the layers listed in this file include layers - minimally needed by the build system. - However, you must manually add any custom layers you have created. - You can find more information on working with the - <filename>bblayers.conf</filename> file in the - "<ulink url='&YOCTO_DOCS_DEV_URL;#enabling-your-layer'>Enabling Your Layer</ulink>" - section in the Yocto Project Development Tasks Manual. - </para> - - <para> - The files <filename>site.conf</filename> and - <filename>auto.conf</filename> are not created by the environment - initialization script. - If you want the <filename>site.conf</filename> file, you need to - create that yourself. - The <filename>auto.conf</filename> file is typically created by - an autobuilder: - <itemizedlist> - <listitem><para><emphasis><filename>site.conf</filename>:</emphasis> - You can use the <filename>conf/site.conf</filename> - configuration file to configure multiple build directories. - For example, suppose you had several build environments and - they shared some common features. - You can set these default build properties here. - A good example is perhaps the packaging format to use - through the - <link linkend='var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></link> - variable.</para> - <para>One useful scenario for using the - <filename>conf/site.conf</filename> file is to extend your - <link linkend='var-BBPATH'><filename>BBPATH</filename></link> - variable to include the path to a - <filename>conf/site.conf</filename>. - Then, when BitBake looks for Metadata using - <filename>BBPATH</filename>, it finds the - <filename>conf/site.conf</filename> file and applies your - common configurations found in the file. - To override configurations in a particular build directory, - alter the similar configurations within that build - directory's <filename>conf/local.conf</filename> file. - </para></listitem> - <listitem><para><emphasis><filename>auto.conf</filename>:</emphasis> - The file is usually created and written to by - an autobuilder. - The settings put into the file are typically the same as - you would find in the <filename>conf/local.conf</filename> - or the <filename>conf/site.conf</filename> files. - </para></listitem> - </itemizedlist> - </para> - - <para> - You can edit all configuration files to further define - any particular build environment. - This process is represented by the "User Configuration Edits" - box in the figure. - </para> - - <para> - When you launch your build with the - <filename>bitbake <replaceable>target</replaceable></filename> - command, BitBake sorts out the configurations to ultimately - define your build environment. - It is important to understand that the OpenEmbedded build system - reads the configuration files in a specific order: - <filename>site.conf</filename>, <filename>auto.conf</filename>, - and <filename>local.conf</filename>. - And, the build system applies the normal assignment statement - rules. - Because the files are parsed in a specific order, variable - assignments for the same variable could be affected. - For example, if the <filename>auto.conf</filename> file and - the <filename>local.conf</filename> set - <replaceable>variable1</replaceable> to different values, because - the build system parses <filename>local.conf</filename> after - <filename>auto.conf</filename>, - <replaceable>variable1</replaceable> is assigned the value from - the <filename>local.conf</filename> file. - </para> - </section> - - <section id="metadata-machine-configuration-and-policy-configuration"> - <title>Metadata, Machine Configuration, and Policy Configuration</title> - - <para> - The previous section described the user configurations that - define BitBake's global behavior. - This section takes a closer look at the layers the build system - uses to further control the build. - These layers provide Metadata for the software, machine, and - policy. - </para> - - <para> - In general, three types of layer input exist: - <itemizedlist> - <listitem><para><emphasis>Policy Configuration:</emphasis> - Distribution Layers provide top-level or general - policies for the image or SDK being built. - For example, this layer would dictate whether BitBake - produces RPM or IPK packages.</para></listitem> - <listitem><para><emphasis>Machine Configuration:</emphasis> - Board Support Package (BSP) layers provide machine - configurations. - This type of information is specific to a particular - target architecture.</para></listitem> - <listitem><para><emphasis>Metadata:</emphasis> - Software layers contain user-supplied recipe files, - patches, and append files. - </para></listitem> - </itemizedlist> - </para> - - <para> - The following figure shows an expanded representation of the - Metadata, Machine Configuration, and Policy Configuration input - (layers) boxes of the - <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>: - </para> - - <para> - <imagedata fileref="figures/layer-input.png" align="center" width="8in" depth="7.5in" /> - </para> - - <para> - In general, all layers have a similar structure. - They all contain a licensing file - (e.g. <filename>COPYING</filename>) if the layer is to be - distributed, a <filename>README</filename> file as good practice - and especially if the layer is to be distributed, a - configuration directory, and recipe directories. - </para> - - <para> - The Yocto Project has many layers that can be used. - You can see a web-interface listing of them on the - <ulink url="http://git.yoctoproject.org/">Source Repositories</ulink> - page. - The layers are shown at the bottom categorized under - "Yocto Metadata Layers." - These layers are fundamentally a subset of the - <ulink url="http://layers.openembedded.org/layerindex/layers/">OpenEmbedded Metadata Index</ulink>, - which lists all layers provided by the OpenEmbedded community. - <note> - Layers exist in the Yocto Project Source Repositories that - cannot be found in the OpenEmbedded Metadata Index. - These layers are either deprecated or experimental in nature. - </note> - </para> - - <para> - BitBake uses the <filename>conf/bblayers.conf</filename> file, - which is part of the user configuration, to find what layers it - should be using as part of the build. - </para> - - <para> - For more 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. - </para> - - <section id="distro-layer"> - <title>Distro Layer</title> - - <para> - The distribution layer provides policy configurations for your - distribution. - Best practices dictate that you isolate these types of - configurations into their own layer. - Settings you provide in - <filename>conf/distro/<replaceable>distro</replaceable>.conf</filename> override - similar - settings that BitBake finds in your - <filename>conf/local.conf</filename> file in the Build - Directory. - </para> - - <para> - The following list provides some explanation and references - for what you typically find in the distribution layer: - <itemizedlist> - <listitem><para><emphasis>classes:</emphasis> - Class files (<filename>.bbclass</filename>) hold - common functionality that can be shared among - recipes in the distribution. - When your recipes inherit a class, they take on the - settings and functions for that class. - You can read more about class files in the - "<link linkend='ref-classes'>Classes</link>" section. - </para></listitem> - <listitem><para><emphasis>conf:</emphasis> - This area holds configuration files for the - layer (<filename>conf/layer.conf</filename>), - the distribution - (<filename>conf/distro/<replaceable>distro</replaceable>.conf</filename>), - and any distribution-wide include files. - </para></listitem> - <listitem><para><emphasis>recipes-*:</emphasis> - Recipes and append files that affect common - functionality across the distribution. - This area could include recipes and append files - to add distribution-specific configuration, - initialization scripts, custom image recipes, - and so forth.</para></listitem> - </itemizedlist> - </para> - </section> - - <section id="bsp-layer"> - <title>BSP Layer</title> - - <para> - The BSP Layer provides machine configurations. - Everything in this layer is specific to the machine for which - you are building the image or the SDK. - A common structure or form is defined for BSP layers. - You can learn more about this structure in the - <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>. - <note> - In order for a BSP layer to be considered compliant with the - Yocto Project, it must meet some structural requirements. - </note> - </para> - - <para> - The BSP Layer's configuration directory contains - configuration files for the machine - (<filename>conf/machine/<replaceable>machine</replaceable>.conf</filename>) and, - of course, the layer (<filename>conf/layer.conf</filename>). - </para> - - <para> - The remainder of the layer is dedicated to specific recipes - by function: <filename>recipes-bsp</filename>, - <filename>recipes-core</filename>, - <filename>recipes-graphics</filename>, and - <filename>recipes-kernel</filename>. - Metadata can exist for multiple formfactors, graphics - support systems, and so forth. - <note> - While the figure shows several <filename>recipes-*</filename> - directories, not all these directories appear in all - BSP layers. - </note> - </para> - </section> - - <section id="software-layer"> - <title>Software Layer</title> - - <para> - The software layer provides the Metadata for additional - software packages used during the build. - This layer does not include Metadata that is specific to the - distribution or the machine, which are found in their - respective layers. - </para> - - <para> - This layer contains any new recipes that your project needs - in the form of recipe files. - </para> - </section> - </section> - - <section id="sources-dev-environment"> - <title>Sources</title> - - <para> - In order for the OpenEmbedded build system to create an image or - any target, it must be able to access source files. - The - <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link> - represents source files using the "Upstream Project Releases", - "Local Projects", and "SCMs (optional)" boxes. - The figure represents mirrors, which also play a role in locating - source files, with the "Source Mirror(s)" box. - </para> - - <para> - The method by which source files are ultimately organized is - a function of the project. - For example, for released software, projects tend to use tarballs - or other archived files that can capture the state of a release - guaranteeing that it is statically represented. - On the other hand, for a project that is more dynamic or - experimental in nature, a project might keep source files in a - repository controlled by a Source Control Manager (SCM) such as - Git. - Pulling source from a repository allows you to control - the point in the repository (the revision) from which you want to - build software. - Finally, a combination of the two might exist, which would give the - consumer a choice when deciding where to get source files. - </para> - - <para> - BitBake uses the - <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link> - variable to point to source files regardless of their location. - Each recipe must have a <filename>SRC_URI</filename> variable - that points to the source. - </para> - - <para> - Another area that plays a significant role in where source files - come from is pointed to by the - <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link> - variable. - This area is a cache that can hold previously downloaded source. - You can also instruct the OpenEmbedded build system to create - tarballs from Git repositories, which is not the default behavior, - and store them in the <filename>DL_DIR</filename> by using the - <link linkend='var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></link> - variable. - </para> - - <para> - Judicious use of a <filename>DL_DIR</filename> directory can - save the build system a trip across the Internet when looking - for files. - A good method for using a download directory is to have - <filename>DL_DIR</filename> point to an area outside of your - Build Directory. - Doing so allows you to safely delete the Build Directory - if needed without fear of removing any downloaded source file. - </para> - - <para> - The remainder of this section provides a deeper look into the - source files and the mirrors. - Here is a more detailed look at the source file area of the - base figure: - <imagedata fileref="figures/source-input.png" align="center" width="7in" depth="7.5in" /> - </para> - - <section id='upstream-project-releases'> - <title>Upstream Project Releases</title> - - <para> - Upstream project releases exist anywhere in the form of an - archived file (e.g. tarball or zip file). - These files correspond to individual recipes. - For example, the figure uses specific releases each for - BusyBox, Qt, and Dbus. - An archive file can be for any released product that can be - built using a recipe. - </para> - </section> - - <section id='local-projects'> - <title>Local Projects</title> - - <para> - Local projects are custom bits of software the user provides. - These bits reside somewhere local to a project - perhaps - a directory into which the user checks in items (e.g. - a local directory containing a development source tree - used by the group). - </para> - - <para> - The canonical method through which to include a local project - is to use the - <link linkend='ref-classes-externalsrc'><filename>externalsrc</filename></link> - class to include that local project. - You use either the <filename>local.conf</filename> or a - recipe's append file to override or set the - recipe to point to the local directory on your disk to pull - in the whole source tree. - </para> - - <para> - For information on how to use the - <filename>externalsrc</filename> class, see the - "<link linkend='ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></link>" - section. - </para> - </section> - - <section id='scms'> - <title>Source Control Managers (Optional)</title> - - <para> - Another place the build system can get source files from is - through an SCM such as Git or Subversion. - In this case, a repository is cloned or checked out. - The - <link linkend='ref-tasks-fetch'><filename>do_fetch</filename></link> - task inside BitBake uses - the <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link> - variable and the argument's prefix to determine the correct - fetcher module. - </para> - - <note> - For information on how to have the OpenEmbedded build system - generate tarballs for Git repositories and place them in the - <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link> - directory, see the - <link linkend='var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></link> - variable. - </note> - - <para> - When fetching a repository, BitBake uses the - <link linkend='var-SRCREV'><filename>SRCREV</filename></link> - variable to determine the specific revision from which to - build. - </para> - </section> - - <section id='source-mirrors'> - <title>Source Mirror(s)</title> - - <para> - Two kinds of mirrors exist: pre-mirrors and regular mirrors. - The <link linkend='var-PREMIRRORS'><filename>PREMIRRORS</filename></link> - and - <link linkend='var-MIRRORS'><filename>MIRRORS</filename></link> - variables point to these, respectively. - BitBake checks pre-mirrors before looking upstream for any - source files. - Pre-mirrors are appropriate when you have a shared directory - that is not a directory defined by the - <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link> - variable. - A Pre-mirror typically points to a shared directory that is - local to your organization. - </para> - - <para> - Regular mirrors can be any site across the Internet that is - used as an alternative location for source code should the - primary site not be functioning for some reason or another. - </para> - </section> - </section> - - <section id="package-feeds-dev-environment"> - <title>Package Feeds</title> - - <para> - When the OpenEmbedded build system generates an image or an SDK, - it gets the packages from a package feed area located in the - <link linkend='build-directory'>Build Directory</link>. - The - <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link> - shows this package feeds area in the upper-right corner. - </para> - - <para> - This section looks a little closer into the package feeds area used - by the build system. - Here is a more detailed look at the area: - <imagedata fileref="figures/package-feeds.png" align="center" width="7in" depth="6in" /> - </para> - - <para> - Package feeds are an intermediary step in the build process. - The OpenEmbedded build system provides classes to generate - different package types, and you specify which classes to enable - through the - <link linkend='var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></link> - variable. - Before placing the packages into package feeds, - the build process validates them with generated output quality - assurance checks through the - <link linkend='ref-classes-insane'><filename>insane</filename></link> - class. - </para> - - <para> - The package feed area resides in the Build Directory. - The directory the build system uses to temporarily store packages - is determined by a combination of variables and the particular - package manager in use. - See the "Package Feeds" box in the illustration and note the - information to the right of that area. - In particular, the following defines where package files are - kept: - <itemizedlist> - <listitem><para><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link>: - Defined as <filename>tmp/deploy</filename> in the Build - Directory. - </para></listitem> - <listitem><para><filename>DEPLOY_DIR_*</filename>: - Depending on the package manager used, the package type - sub-folder. - Given RPM, IPK, or DEB packaging and tarball creation, the - <link linkend='var-DEPLOY_DIR_RPM'><filename>DEPLOY_DIR_RPM</filename></link>, - <link linkend='var-DEPLOY_DIR_IPK'><filename>DEPLOY_DIR_IPK</filename></link>, - <link linkend='var-DEPLOY_DIR_DEB'><filename>DEPLOY_DIR_DEB</filename></link>, - or - <link linkend='var-DEPLOY_DIR_TAR'><filename>DEPLOY_DIR_TAR</filename></link>, - variables are used, respectively. - </para></listitem> - <listitem><para><link linkend='var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></link>: - Defines architecture-specific sub-folders. - For example, packages could exist for the i586 or qemux86 - architectures. - </para></listitem> - </itemizedlist> - </para> - - <para> - BitBake uses the <filename>do_package_write_*</filename> tasks to - generate packages and place them into the package holding area (e.g. - <filename>do_package_write_ipk</filename> for IPK packages). - See the - "<link linkend='ref-tasks-package_write_deb'><filename>do_package_write_deb</filename></link>", - "<link linkend='ref-tasks-package_write_ipk'><filename>do_package_write_ipk</filename></link>", - "<link linkend='ref-tasks-package_write_rpm'><filename>do_package_write_rpm</filename></link>", - and - "<link linkend='ref-tasks-package_write_tar'><filename>do_package_write_tar</filename></link>" - sections for additional information. - As an example, consider a scenario where an IPK packaging manager - is being used and package architecture support for both i586 - and qemux86 exist. - Packages for the i586 architecture are placed in - <filename>build/tmp/deploy/ipk/i586</filename>, while packages for - the qemux86 architecture are placed in - <filename>build/tmp/deploy/ipk/qemux86</filename>. - </para> - </section> - - <section id='bitbake-dev-environment'> - <title>BitBake</title> - - <para> - The OpenEmbedded build system uses - <link linkend='bitbake-term'>BitBake</link> - to produce images. - You can see from the - <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>, - the BitBake area consists of several functional areas. - This section takes a closer look at each of those areas. - </para> - - <para> - Separate documentation exists for the BitBake tool. - See the - <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual'>BitBake User Manual</ulink> - for reference material on BitBake. - </para> - - <section id='source-fetching-dev-environment'> - <title>Source Fetching</title> - - <para> - The first stages of building a recipe are to fetch and unpack - the source code: - <imagedata fileref="figures/source-fetching.png" align="center" width="6.5in" depth="5in" /> - </para> - - <para> - The - <link linkend='ref-tasks-fetch'><filename>do_fetch</filename></link> - and - <link linkend='ref-tasks-unpack'><filename>do_unpack</filename></link> - tasks fetch the source files and unpack them into the work - directory. - <note> - For every local file (e.g. <filename>file://</filename>) - that is part of a recipe's - <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link> - statement, the OpenEmbedded build system takes a checksum - of the file for the recipe and inserts the checksum into - the signature for the <filename>do_fetch</filename>. - If any local file has been modified, the - <filename>do_fetch</filename> task and all tasks that - depend on it are re-executed. - </note> - By default, everything is accomplished in the - <link linkend='build-directory'>Build Directory</link>, - which has a defined structure. - For additional general information on the Build Directory, - see the - "<link linkend='structure-core-build'><filename>build/</filename></link>" - section. - </para> - - <para> - Unpacked source files are pointed to by the - <link linkend='var-S'><filename>S</filename></link> variable. - Each recipe has an area in the Build Directory where the - unpacked source code resides. - The name of that directory for any given recipe is defined from - several different variables. - You can see the variables that define these directories - by looking at the figure: - <itemizedlist> - <listitem><para><link linkend='var-TMPDIR'><filename>TMPDIR</filename></link> - - The base directory where the OpenEmbedded build system - performs all its work during the build. - </para></listitem> - <listitem><para><link linkend='var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></link> - - The architecture of the built package or packages. - </para></listitem> - <listitem><para><link linkend='var-TARGET_OS'><filename>TARGET_OS</filename></link> - - The operating system of the target device. - </para></listitem> - <listitem><para><link linkend='var-PN'><filename>PN</filename></link> - - The name of the built package. - </para></listitem> - <listitem><para><link linkend='var-PV'><filename>PV</filename></link> - - The version of the recipe used to build the package. - </para></listitem> - <listitem><para><link linkend='var-PR'><filename>PR</filename></link> - - The revision of the recipe used to build the package. - </para></listitem> - <listitem><para><link linkend='var-WORKDIR'><filename>WORKDIR</filename></link> - - The location within <filename>TMPDIR</filename> where - a specific package is built. - </para></listitem> - <listitem><para><link linkend='var-S'><filename>S</filename></link> - - Contains the unpacked source files for a given recipe. - </para></listitem> - </itemizedlist> - </para> - </section> - - <section id='patching-dev-environment'> - <title>Patching</title> - - <para> - Once source code is fetched and unpacked, BitBake locates - patch files and applies them to the source files: - <imagedata fileref="figures/patching.png" align="center" width="6in" depth="5in" /> - </para> - - <para> - The - <link linkend='ref-tasks-patch'><filename>do_patch</filename></link> - task processes recipes by - using the - <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link> - variable to locate applicable patch files, which by default - are <filename>*.patch</filename> or - <filename>*.diff</filename> files, or any file if - "apply=yes" is specified for the file in - <filename>SRC_URI</filename>. - </para> - - <para> - BitBake finds and applies multiple patches for a single recipe - in the order in which it finds the patches. - Patches are applied to the recipe's source files located in the - <link linkend='var-S'><filename>S</filename></link> directory. - </para> - - <para> - For more information on how the source directories are - created, see the - "<link linkend='source-fetching-dev-environment'>Source Fetching</link>" - section. - </para> - </section> - - <section id='configuration-and-compilation-dev-environment'> - <title>Configuration and Compilation</title> - - <para> - After source code is patched, BitBake executes tasks that - configure and compile the source code: - <imagedata fileref="figures/configuration-compile-autoreconf.png" align="center" width="7in" depth="5in" /> - </para> - - <para> - This step in the build process consists of three tasks: - <itemizedlist> - <listitem><para> - <emphasis><link linkend='ref-tasks-prepare_recipe_sysroot'><filename>do_prepare_recipe_sysroot</filename></link>:</emphasis> - This task sets up the two sysroots in - <filename>${</filename><link linkend='var-WORKDIR'><filename>WORKDIR</filename></link><filename>}</filename> - (i.e. <filename>recipe-sysroot</filename> and - <filename>recipe-sysroot-native</filename>) so that - the sysroots contain the contents of the - <link linkend='ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></link> - tasks of the recipes on which the recipe - containing the tasks depends. - A sysroot exists for both the target and for the native - binaries, which run on the host system. - </para></listitem> - <listitem><para><emphasis><filename>do_configure</filename>:</emphasis> - This task configures the source by enabling and - disabling any build-time and configuration options for - the software being built. - Configurations can come from the recipe itself as well - as from an inherited class. - Additionally, the software itself might configure itself - depending on the target for which it is being built. - </para> - - <para>The configurations handled by the - <link linkend='ref-tasks-configure'><filename>do_configure</filename></link> - task are specific - to source code configuration for the source code - being built by the recipe.</para> - - <para>If you are using the - <link linkend='ref-classes-autotools'><filename>autotools</filename></link> - class, - you can add additional configuration options by using - the <link linkend='var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></link> - or - <link linkend='var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></link> - variables. - For information on how this variable works within - that class, see the - <filename>meta/classes/autotools.bbclass</filename> file. - </para></listitem> - <listitem><para><emphasis><filename>do_compile</filename>:</emphasis> - Once a configuration task has been satisfied, BitBake - compiles the source using the - <link linkend='ref-tasks-compile'><filename>do_compile</filename></link> - task. - Compilation occurs in the directory pointed to by the - <link linkend='var-B'><filename>B</filename></link> - variable. - Realize that the <filename>B</filename> directory is, by - default, the same as the - <link linkend='var-S'><filename>S</filename></link> - directory.</para></listitem> - <listitem><para><emphasis><filename>do_install</filename>:</emphasis> - Once compilation is done, BitBake executes the - <link linkend='ref-tasks-install'><filename>do_install</filename></link> - task. - This task copies files from the <filename>B</filename> - directory and places them in a holding area pointed to - by the - <link linkend='var-D'><filename>D</filename></link> - variable.</para></listitem> - </itemizedlist> - </para> - </section> - - <section id='package-splitting-dev-environment'> - <title>Package Splitting</title> - - <para> - After source code is configured and compiled, the - OpenEmbedded build system analyzes - the results and splits the output into packages: - <imagedata fileref="figures/analysis-for-package-splitting.png" align="center" width="7in" depth="7in" /> - </para> - - <para> - The - <link linkend='ref-tasks-package'><filename>do_package</filename></link> - and - <link linkend='ref-tasks-packagedata'><filename>do_packagedata</filename></link> - tasks combine to analyze - the files found in the - <link linkend='var-D'><filename>D</filename></link> directory - and split them into subsets based on available packages and - files. - The analyzing process involves the following as well as other - items: splitting out debugging symbols, - looking at shared library dependencies between packages, - and looking at package relationships. - The <filename>do_packagedata</filename> task creates package - metadata based on the analysis such that the - OpenEmbedded build system can generate the final packages. - Working, staged, and intermediate results of the analysis - and package splitting process use these areas: - <itemizedlist> - <listitem><para><link linkend='var-PKGD'><filename>PKGD</filename></link> - - The destination directory for packages before they are - split. - </para></listitem> - <listitem><para><link linkend='var-PKGDATA_DIR'><filename>PKGDATA_DIR</filename></link> - - A shared, global-state directory that holds data - generated during the packaging process. - </para></listitem> - <listitem><para><link linkend='var-PKGDESTWORK'><filename>PKGDESTWORK</filename></link> - - A temporary work area used by the - <filename>do_package</filename> task. - </para></listitem> - <listitem><para><link linkend='var-PKGDEST'><filename>PKGDEST</filename></link> - - The parent directory for packages after they have - been split. - </para></listitem> - </itemizedlist> - The <link linkend='var-FILES'><filename>FILES</filename></link> - variable defines the files that go into each package in - <link linkend='var-PACKAGES'><filename>PACKAGES</filename></link>. - If you want details on how this is accomplished, you can - look at the - <link linkend='ref-classes-package'><filename>package</filename></link> - class. - </para> - - <para> - Depending on the type of packages being created (RPM, DEB, or - IPK), the <filename>do_package_write_*</filename> task - creates the actual packages and places them in the - Package Feed area, which is - <filename>${TMPDIR}/deploy</filename>. - You can see the - "<link linkend='package-feeds-dev-environment'>Package Feeds</link>" - section for more detail on that part of the build process. - <note> - Support for creating feeds directly from the - <filename>deploy/*</filename> directories does not exist. - Creating such feeds usually requires some kind of feed - maintenance mechanism that would upload the new packages - into an official package feed (e.g. the - Ångström distribution). - This functionality is highly distribution-specific - and thus is not provided out of the box. - </note> - </para> - </section> - - <section id='image-generation-dev-environment'> - <title>Image Generation</title> - - <para> - Once packages are split and stored in the Package Feeds area, - the OpenEmbedded build system uses BitBake to generate the - root filesystem image: - <imagedata fileref="figures/image-generation.png" align="center" width="6in" depth="7in" /> - </para> - - <para> - The image generation process consists of several stages and - depends on several tasks and variables. - The - <link linkend='ref-tasks-rootfs'><filename>do_rootfs</filename></link> - task creates the root filesystem (file and directory structure) - for an image. - This task uses several key variables to help create the list - of packages to actually install: - <itemizedlist> - <listitem><para><link linkend='var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></link>: - Lists out the base set of packages to install from - the Package Feeds area.</para></listitem> - <listitem><para><link linkend='var-PACKAGE_EXCLUDE'><filename>PACKAGE_EXCLUDE</filename></link>: - Specifies packages that should not be installed. - </para></listitem> - <listitem><para><link linkend='var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></link>: - Specifies features to include in the image. - Most of these features map to additional packages for - installation.</para></listitem> - <listitem><para><link linkend='var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></link>: - Specifies the package backend to use and consequently - helps determine where to locate packages within the - Package Feeds area.</para></listitem> - <listitem><para><link linkend='var-IMAGE_LINGUAS'><filename>IMAGE_LINGUAS</filename></link>: - Determines the language(s) for which additional - language support packages are installed. - </para></listitem> - <listitem><para><link linkend='var-PACKAGE_INSTALL'><filename>PACKAGE_INSTALL</filename></link>: - The final list of packages passed to the package manager - for installation into the image. - </para></listitem> - </itemizedlist> - </para> - - <para> - With - <link linkend='var-IMAGE_ROOTFS'><filename>IMAGE_ROOTFS</filename></link> - pointing to the location of the filesystem under construction and - the <filename>PACKAGE_INSTALL</filename> variable providing the - final list of packages to install, the root file system is - created. - </para> - - <para> - Package installation is under control of the package manager - (e.g. dnf/rpm, opkg, or apt/dpkg) regardless of whether or - not package management is enabled for the target. - At the end of the process, if package management is not - enabled for the target, the package manager's data files - are deleted from the root filesystem. - As part of the final stage of package installation, postinstall - scripts that are part of the packages are run. - Any scripts that fail to run - on the build host are run on the target when the target system - is first booted. - If you are using a - <ulink url='&YOCTO_DOCS_DEV_URL;#creating-a-read-only-root-filesystem'>read-only root filesystem</ulink>, - all the post installation scripts must succeed during the - package installation phase since the root filesystem is - read-only. - </para> - - <para> - The final stages of the <filename>do_rootfs</filename> task - handle post processing. - Post processing includes creation of a manifest file and - optimizations. - </para> - - <para> - The manifest file (<filename>.manifest</filename>) resides - in the same directory as the root filesystem image. - This file lists out, line-by-line, the installed packages. - The manifest file is useful for the - <link linkend='ref-classes-testimage*'><filename>testimage</filename></link> - class, for example, to determine whether or not to run - specific tests. - See the - <link linkend='var-IMAGE_MANIFEST'><filename>IMAGE_MANIFEST</filename></link> - variable for additional information. - </para> - - <para> - Optimizing processes run across the image include - <filename>mklibs</filename>, <filename>prelink</filename>, - and any other post-processing commands as defined by the - <link linkend='var-ROOTFS_POSTPROCESS_COMMAND'><filename>ROOTFS_POSTPROCESS_COMMAND</filename></link> - variable. - The <filename>mklibs</filename> process optimizes the size - of the libraries, while the - <filename>prelink</filename> process optimizes the dynamic - linking of shared libraries to reduce start up time of - executables. - </para> - - <para> - After the root filesystem is built, processing begins on - the image through the - <link linkend='ref-tasks-image'><filename>do_image</filename></link> - task. - The build system runs any pre-processing commands as defined - by the - <link linkend='var-IMAGE_PREPROCESS_COMMAND'><filename>IMAGE_PREPROCESS_COMMAND</filename></link> - variable. - This variable specifies a list of functions to call before - the OpenEmbedded build system creates the final image output - files. - </para> - - <para> - The OpenEmbedded build system dynamically creates - <filename>do_image_*</filename> tasks as needed, based - on the image types specified in the - <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link> - variable. - The process turns everything into an image file or a set of - image files and compresses the root filesystem image to reduce - the overall size of the image. - The formats used for the root filesystem depend on the - <filename>IMAGE_FSTYPES</filename> variable. - </para> - - <para> - As an example, a dynamically created task when creating a - particular image <replaceable>type</replaceable> would take the - following form: - <literallayout class='monospaced'> - do_image_<replaceable>type</replaceable>[depends] - </literallayout> - So, if the <replaceable>type</replaceable> as specified by the - <filename>IMAGE_FSTYPES</filename> were - <filename>ext4</filename>, the dynamically generated task - would be as follows: - <literallayout class='monospaced'> - do_image_ext4[depends] - </literallayout> - </para> - - <para> - The final task involved in image creation is the - <link linkend='ref-tasks-image-complete'><filename>do_image_complete</filename></link> - task. - This task completes the image by applying any image - post processing as defined through the - <link linkend='var-IMAGE_POSTPROCESS_COMMAND'><filename>IMAGE_POSTPROCESS_COMMAND</filename></link> - variable. - The variable specifies a list of functions to call once the - OpenEmbedded build system has created the final image output - files. - </para> - - <note> - The entire image generation process is run under Pseudo. - Running under Pseudo ensures that the files in the root - filesystem have correct ownership. - </note> - </section> - - <section id='sdk-generation-dev-environment'> - <title>SDK Generation</title> - - <para> - The OpenEmbedded build system uses BitBake to generate the - Software Development Kit (SDK) installer script for both the - standard and extensible SDKs: - <imagedata fileref="figures/sdk-generation.png" align="center" /> - </para> - - <note> - For more information on the cross-development toolchain - generation, see the - "<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>" - section. - For information on advantages gained when building a - cross-development toolchain using the - <link linkend='ref-tasks-populate_sdk'><filename>do_populate_sdk</filename></link> - task, see the - "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-building-an-sdk-installer'>Building an SDK Installer</ulink>" - section in the Yocto Project Application Development and the - Extensible Software Development Kit (SDK) manual. - </note> - - <para> - Like image generation, the SDK script process consists of - several stages and depends on many variables. - The <filename>do_populate_sdk</filename> and - <filename>do_populate_sdk_ext</filename> tasks use these - key variables to help create the list of packages to actually - install. - For information on the variables listed in the figure, see the - "<link linkend='sdk-dev-environment'>Application Development SDK</link>" - section. - </para> - - <para> - The <filename>do_populate_sdk</filename> task helps create - the standard SDK and handles two parts: a target part and a - host part. - The target part is the part built for the target hardware and - includes libraries and headers. - The host part is the part of the SDK that runs on the - <link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>. - </para> - - <para> - The <filename>do_populate_sdk_ext</filename> task helps create - the extensible SDK and handles host and target parts - differently than its counter part does for the standard SDK. - For the extensible SDK, the task encapsulates the build system, - which includes everything needed (host and target) for the SDK. - </para> - - <para> - Regardless of the type of SDK being constructed, the - tasks perform some cleanup after which a cross-development - environment setup script and any needed configuration files - are created. - The final output is the Cross-development - toolchain installation script (<filename>.sh</filename> file), - which includes the environment setup script. - </para> - </section> - - <section id='stamp-files-and-the-rerunning-of-tasks'> - <title>Stamp Files and the Rerunning of Tasks</title> - - <para> - For each task that completes successfully, BitBake writes a - stamp file into the - <link linkend='var-STAMPS_DIR'><filename>STAMPS_DIR</filename></link> - directory. - The beginning of the stamp file's filename is determined by the - <link linkend='var-STAMP'><filename>STAMP</filename></link> - variable, and the end of the name consists of the task's name - and current - <ulink url='&YOCTO_DOCS_BB_URL;#checksums'>input checksum</ulink>. - <note> - This naming scheme assumes that - <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_SIGNATURE_HANDLER'><filename>BB_SIGNATURE_HANDLER</filename></ulink> - is "OEBasicHash", which is almost always the case in - current OpenEmbedded. - </note> - To determine if a task needs to be rerun, BitBake checks if a - stamp file with a matching input checksum exists for the task. - If such a stamp file exists, the task's output is assumed to - exist and still be valid. - If the file does not exist, the task is rerun. - <note> - <para>The stamp mechanism is more general than the shared - state (sstate) cache mechanism described in the - "<link linkend='setscene-tasks-and-shared-state'>Setscene Tasks and Shared State</link>" - section. - BitBake avoids rerunning any task that has a valid - stamp file, not just tasks that can be accelerated through - the sstate cache.</para> - <para>However, you should realize that stamp files only - serve as a marker that some work has been done and that - these files do not record task output. - The actual task output would usually be somewhere in - <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link> - (e.g. in some recipe's - <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>.) - What the sstate cache mechanism adds is a way to cache task - output that can then be shared between build machines. - </para> - </note> - Since <filename>STAMPS_DIR</filename> is usually a subdirectory - of <filename>TMPDIR</filename>, removing - <filename>TMPDIR</filename> will also remove - <filename>STAMPS_DIR</filename>, which means tasks will - properly be rerun to repopulate <filename>TMPDIR</filename>. - </para> - - <para> - If you want some task to always be considered "out of date", - you can mark it with the - <ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'><filename>nostamp</filename></ulink> - varflag. - If some other task depends on such a task, then that task will - also always be considered out of date, which might not be what - you want. - </para> - - <para> - For details on how to view information about a task's - signature, see the - "<link linkend='usingpoky-viewing-task-variable-dependencies'>Viewing Task Variable Dependencies</link>" - section. - </para> - </section> - - <section id='setscene-tasks-and-shared-state'> - <title>Setscene Tasks and Shared State</title> - - <para> - The description of tasks so far assumes that BitBake needs to - build everything and there are no prebuilt objects available. - BitBake does support skipping tasks if prebuilt objects are - available. - These objects are usually made available in the form of a - shared state (sstate) cache. - <note> - For information on variables affecting sstate, see the - <link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link> - and - <link linkend='var-SSTATE_MIRRORS'><filename>SSTATE_MIRRORS</filename></link> - variables. - </note> - </para> - - <para> - The idea of a setscene task (i.e - <filename>do_</filename><replaceable>taskname</replaceable><filename>_setscene</filename>) - is a version of the task where - instead of building something, BitBake can skip to the end - result and simply place a set of files into specific locations - as needed. - In some cases, it makes sense to have a setscene task variant - (e.g. generating package files in the - <filename>do_package_write_*</filename> task). - In other cases, it does not make sense, (e.g. a - <link linkend='ref-tasks-patch'><filename>do_patch</filename></link> - task or - <link linkend='ref-tasks-unpack'><filename>do_unpack</filename></link> - task) since the work involved would be equal to or greater than - the underlying task. - </para> - - <para> - In the OpenEmbedded build system, the common tasks that have - setscene variants are <link linkend='ref-tasks-package'><filename>do_package</filename></link>, - <filename>do_package_write_*</filename>, - <link linkend='ref-tasks-deploy'><filename>do_deploy</filename></link>, - <link linkend='ref-tasks-packagedata'><filename>do_packagedata</filename></link>, - and - <link linkend='ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></link>. - Notice that these are most of the tasks whose output is an - end result. - </para> - - <para> - The OpenEmbedded build system has knowledge of the relationship - between these tasks and other tasks that precede them. - For example, if BitBake runs - <filename>do_populate_sysroot_setscene</filename> for - something, there is little point in running any of the - <filename>do_fetch</filename>, <filename>do_unpack</filename>, - <filename>do_patch</filename>, - <filename>do_configure</filename>, - <filename>do_compile</filename>, and - <filename>do_install</filename> tasks. - However, if <filename>do_package</filename> needs to be run, - BitBake would need to run those other tasks. - </para> - - <para> - It becomes more complicated if everything can come from an - sstate cache because some objects are simply not required at - all. - For example, you do not need a compiler or native tools, such - as quilt, if there is nothing to compile or patch. - If the <filename>do_package_write_*</filename> packages are - available from sstate, BitBake does not need the - <filename>do_package</filename> task data. - </para> - - <para> - To handle all these complexities, BitBake runs in two phases. - The first is the "setscene" stage. - During this stage, BitBake first checks the sstate cache for - any targets it is planning to build. - BitBake does a fast check to see if the object exists rather - than a complete download. - If nothing exists, the second phase, which is the setscene - stage, completes and the main build proceeds. - </para> - - <para> - If objects are found in the sstate cache, the OpenEmbedded - build system works backwards from the end targets specified - by the user. - For example, if an image is being built, the OpenEmbedded build - system first looks for the packages needed for that image and - the tools needed to construct an image. - If those are available, the compiler is not needed. - Thus, the compiler is not even downloaded. - If something was found to be unavailable, or the download or - setscene task fails, the OpenEmbedded build system then tries - to install dependencies, such as the compiler, from the cache. - </para> - - <para> - The availability of objects in the sstate cache is handled by - the function specified by the - <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_HASHCHECK_FUNCTION'><filename>BB_HASHCHECK_FUNCTION</filename></ulink> - variable and returns a list of the objects that are available. - The function specified by the - <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_SETSCENE_DEPVALID'><filename>BB_SETSCENE_DEPVALID</filename></ulink> - variable is the function that determines whether a given - dependency needs to be followed, and whether for any given - relationship the function needs to be passed. - The function returns a True or False value. - </para> - </section> - </section> - - <section id='images-dev-environment'> - <title>Images</title> - - <para> - The images produced by the OpenEmbedded build system - are compressed forms of the - root filesystem that are ready to boot on a target device. - You can see from the - <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link> - that BitBake output, in part, consists of images. - This section is going to look more closely at this output: - <imagedata fileref="figures/images.png" align="center" width="5.5in" depth="5.5in" /> - </para> - - <para> - For a list of example images that the Yocto Project provides, - see the - "<link linkend='ref-images'>Images</link>" chapter. - </para> - - <para> - Images are written out to the - <link linkend='build-directory'>Build Directory</link> - inside the <filename>tmp/deploy/images/<replaceable>machine</replaceable>/</filename> - folder as shown in the figure. - This folder contains any files expected to be loaded on the - target device. - The - <link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link> - variable points to the <filename>deploy</filename> directory, - while the - <link linkend='var-DEPLOY_DIR_IMAGE'><filename>DEPLOY_DIR_IMAGE</filename></link> - variable points to the appropriate directory containing images for - the current configuration. - <itemizedlist> - <listitem><para><filename><replaceable>kernel-image</replaceable></filename>: - A kernel binary file. - The <link linkend='var-KERNEL_IMAGETYPE'><filename>KERNEL_IMAGETYPE</filename></link> - variable setting determines the naming scheme for the - kernel image file. - Depending on that variable, the file could begin with - a variety of naming strings. - The <filename>deploy/images/<replaceable>machine</replaceable></filename> - directory can contain multiple image files for the - machine.</para></listitem> - <listitem><para><filename><replaceable>root-filesystem-image</replaceable></filename>: - Root filesystems for the target device (e.g. - <filename>*.ext3</filename> or <filename>*.bz2</filename> - files). - The <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link> - variable setting determines the root filesystem image - type. - The <filename>deploy/images/<replaceable>machine</replaceable></filename> - directory can contain multiple root filesystems for the - machine.</para></listitem> - <listitem><para><filename><replaceable>kernel-modules</replaceable></filename>: - Tarballs that contain all the modules built for the kernel. - Kernel module tarballs exist for legacy purposes and - can be suppressed by setting the - <link linkend='var-MODULE_TARBALL_DEPLOY'><filename>MODULE_TARBALL_DEPLOY</filename></link> - variable to "0". - The <filename>deploy/images/<replaceable>machine</replaceable></filename> - directory can contain multiple kernel module tarballs - for the machine.</para></listitem> - <listitem><para><filename><replaceable>bootloaders</replaceable></filename>: - Bootloaders supporting the image, if applicable to the - target machine. - The <filename>deploy/images/<replaceable>machine</replaceable></filename> - directory can contain multiple bootloaders for the - machine.</para></listitem> - <listitem><para><filename><replaceable>symlinks</replaceable></filename>: - The <filename>deploy/images/<replaceable>machine</replaceable></filename> - folder contains - a symbolic link that points to the most recently built file - for each machine. - These links might be useful for external scripts that - need to obtain the latest version of each file. - </para></listitem> - </itemizedlist> - </para> - </section> - - <section id='sdk-dev-environment'> - <title>Application Development SDK</title> - - <para> - In the - <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>, - the output labeled "Application Development SDK" represents an - SDK. - The SDK generation process differs depending on whether you build - a standard SDK - (e.g. <filename>bitbake -c populate_sdk</filename> <replaceable>imagename</replaceable>) - or an extensible SDK - (e.g. <filename>bitbake -c populate_sdk_ext</filename> <replaceable>imagename</replaceable>). - This section is going to take a closer look at this output: - <imagedata fileref="figures/sdk.png" align="center" width="9in" depth="7.25in" /> - </para> - - <para> - The specific form of this output is a self-extracting - SDK installer (<filename>*.sh</filename>) that, when run, - installs the SDK, which consists of a cross-development - toolchain, a set of libraries and headers, and an SDK - environment setup script. - Running this installer essentially sets up your - cross-development environment. - You can think of the cross-toolchain as the "host" - part because it runs on the SDK machine. - You can think of the libraries and headers as the "target" - part because they are built for the target hardware. - The environment setup script is added so that you can initialize - the environment before using the tools. - </para> - - <note><title>Notes</title> - <itemizedlist> - <listitem><para> - The Yocto Project supports several methods by which you can - set up this cross-development environment. - These methods include downloading pre-built SDK installers - or building and installing your own SDK installer. - </para></listitem> - <listitem><para> - For background information on cross-development toolchains - in the Yocto Project development environment, see the - "<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>" - section. - </para></listitem> - <listitem><para> - For information on setting up a cross-development - environment, see the - <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Software Development Kit (SDK) Developer's Guide</ulink>. - </para></listitem> - </itemizedlist> - </note> - <para> - Once built, the SDK installers are written out to the - <filename>deploy/sdk</filename> folder inside the - <link linkend='build-directory'>Build Directory</link> - as shown in the figure at the beginning of this section. - Depending on the type of SDK, several variables exist that help - configure these files. - The following list shows the variables associated with a standard - SDK: - <itemizedlist> - <listitem><para><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link>: - Points to the <filename>deploy</filename> - directory.</para></listitem> - <listitem><para><link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>: - Specifies the architecture of the machine - on which the cross-development tools are run to - create packages for the target hardware. - </para></listitem> - <listitem><para><link linkend='var-SDKIMAGE_FEATURES'><filename>SDKIMAGE_FEATURES</filename></link>: - Lists the features to include in the "target" part - of the SDK. - </para></listitem> - <listitem><para><link linkend='var-TOOLCHAIN_HOST_TASK'><filename>TOOLCHAIN_HOST_TASK</filename></link>: - Lists packages that make up the host - part of the SDK (i.e. the part that runs on - the <filename>SDKMACHINE</filename>). - When you use - <filename>bitbake -c populate_sdk <replaceable>imagename</replaceable></filename> - to create the SDK, a set of default packages - apply. - This variable allows you to add more packages. - </para></listitem> - <listitem><para><link linkend='var-TOOLCHAIN_TARGET_TASK'><filename>TOOLCHAIN_TARGET_TASK</filename></link>: - Lists packages that make up the target part - of the SDK (i.e. the part built for the - target hardware). - </para></listitem> - <listitem><para><link linkend='var-SDKPATH'><filename>SDKPATH</filename></link>: - Defines the default SDK installation path offered by the - installation script. - </para></listitem> - </itemizedlist> - This next list, shows the variables associated with an extensible - SDK: - <itemizedlist> - <listitem><para><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link>: - Points to the <filename>deploy</filename> directory. - </para></listitem> - <listitem><para><link linkend='var-SDK_EXT_TYPE'><filename>SDK_EXT_TYPE</filename></link>: - Controls whether or not shared state artifacts are copied - into the extensible SDK. - By default, all required shared state artifacts are copied - into the SDK. - </para></listitem> - <listitem><para><link linkend='var-SDK_INCLUDE_PKGDATA'><filename>SDK_INCLUDE_PKGDATA</filename></link>: - Specifies whether or not packagedata will be included in - the extensible SDK for all recipes in the "world" target. - </para></listitem> - <listitem><para><link linkend='var-SDK_INCLUDE_TOOLCHAIN'><filename>SDK_INCLUDE_TOOLCHAIN</filename></link>: - Specifies whether or not the toolchain will be included - when building the extensible SDK. - </para></listitem> - <listitem><para><link linkend='var-SDK_LOCAL_CONF_WHITELIST'><filename>SDK_LOCAL_CONF_WHITELIST</filename></link>: - A list of variables allowed through from the build system - configuration into the extensible SDK configuration. - </para></listitem> - <listitem><para><link linkend='var-SDK_LOCAL_CONF_BLACKLIST'><filename>SDK_LOCAL_CONF_BLACKLIST</filename></link>: - A list of variables not allowed through from the build - system configuration into the extensible SDK configuration. - </para></listitem> - <listitem><para><link linkend='var-SDK_INHERIT_BLACKLIST'><filename>SDK_INHERIT_BLACKLIST</filename></link>: - A list of classes to remove from the - <link linkend='var-INHERIT'><filename>INHERIT</filename></link> - value globally within the extensible SDK configuration. - </para></listitem> - </itemizedlist> - </para> - </section> -</section> - -</chapter> -<!-- -vim: expandtab tw=80 ts=4 ---> |