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<!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='dev-manual-newbie'>
<title>The Yocto Project Open Source Development Environment</title>
<para>
This chapter helps you understand the Yocto Project as an open source development project.
In general, working in an open source environment is very different from working in a
closed, proprietary environment.
Additionally, the Yocto Project uses specific tools and constructs as part of its development
environment.
This chapter specifically addresses open source philosophy, licensing issues, code repositories,
the open source distributed version control system Git, and best practices using the Yocto Project.
</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="usingpoky-changes-collaborate">
<title>Using the Yocto Project in a Team Environment</title>
<para>
It might not be immediately clear how you can use the Yocto Project in a team environment,
or scale it for a large team of developers.
The specifics of any situation determine the best solution.
Granted that the Yocto Project offers immense flexibility regarding this, practices do exist
that experience has shown work well.
</para>
<para>
The core component of any development effort with the Yocto Project is often an
automated build and testing framework along with an image generation process.
You can use these core components to check that the metadata can be built,
highlight when commits break the build, and provide up-to-date images that
allow developers to test the end result and use it as a base platform for further
development.
Experience shows that buildbot is a good fit for this role.
What works well is to configure buildbot to make two types of builds:
incremental and full (from scratch).
See <ulink url='http://autobuilder.yoctoproject.org:8010/'>Welcome to the buildbot for the
Yocto Project</ulink> for an example implementation that uses buildbot.
</para>
<para>
You can tie an incremental build to a commit hook that triggers the build
each time a commit is made to the metadata.
This practice results in useful acid tests that determine whether a given commit
breaks the build in some serious way.
Associating a build to a commit can catch a lot of simple errors.
Furthermore, the tests are fast so developers can get quick feedback on changes.
</para>
<para>
Full builds build and test everything from the ground up.
These types of builds usually happen at predetermined times like during the
night when the machine load is low.
</para>
<para>
Most teams have many pieces of software undergoing active development at any given time.
You can derive large benefits by putting these pieces under the control of a source
control system that is compatible (i.e. Git or Subversion (SVN)) with the OpenEmbeded
build system that the Yocto Project uses.
You can then set the autobuilder to pull the latest revisions of the packages
and test the latest commits by the builds.
This practice quickly highlights issues.
The build system easily supports testing configurations that use both a
stable known good revision and a floating revision.
The build system can also take just the changes from specific source control branches.
This capability allows you to track and test specific changes.
</para>
<para>
Perhaps the hardest part of setting this up is defining the software project or
the metadata policies that surround the different source control systems.
Of course circumstances will be different in each case.
However, this situation reveals one of the Yocto Project's advantages -
the system itself does not
force any particular policy on users, unlike a lot of build systems.
The system allows the best policies to be chosen for the given circumstances.
</para>
</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 set up a Git repository for
that particular item.
Having a local Git repository of the Source Directory (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>
Conversely, if you are a developer that is not interested in contributing back to the
Yocto Project, you have the ability to simply download and extract release tarballs
and use them within the Yocto Project environment.
All that is required is a particular release of the Yocto Project and
your application source code.
</para>
<para>
For any supported release of Yocto Project, you can go to the Yocto Project website’s
<ulink url='&YOCTO_HOME_URL;/download'>download page</ulink> and get a
tarball of the release.
You can also go to this site to download any supported BSP tarballs.
Unpacking the tarball gives you a hierarchical Source Directory that lets you develop
using the Yocto Project.
</para>
<para>
Once you are set up through either tarball extraction or creation of Git repositories,
you are ready to develop.
</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" />
</para></listitem>
<listitem><para><anchor id='index-downloads' /><emphasis><ulink url='&YOCTO_DL_URL;/releases/'>Index of /releases:</ulink></emphasis>
This area contains index 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="4in" />
</para></listitem>
<listitem><para><emphasis><ulink url='&YOCTO_HOME_URL;/download'>Yocto Project Download Page</ulink></emphasis>
This page on the Yocto Project website allows you to download any Yocto Project
release or 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" />
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='yocto-project-terms'>
<title>Yocto Project Terms</title>
<para>
Following is a list of terms and definitions users new to the Yocto Project development
environment might find helpful.
While some of these terms are universal, the list includes them just in case:
<itemizedlist>
<listitem><para><emphasis>Append Files:</emphasis> Files that append build information to
a recipe file.
Append files are known as BitBake append files and <filename>.bbappend</filename> files.
The OpenEmbedded build system expects every append file to have a corresponding and
underlying recipe (<filename>.bb</filename>) file.
Furthermore, the append file and the underlying recipe must have the same root filename.
The filenames can differ only in the file type suffix used (e.g.
<filename>formfactor_0.0.bb</filename> and <filename>formfactor_0.0.bbappend</filename>).
</para>
<para>Information in append files overrides the information in the similarly-named recipe file.
For an example of an append file in use, see the
"<link linkend='using-bbappend-files'>Using .bbappend Files</link>" section.
</para></listitem>
<listitem><para id='bitbake-term'><emphasis>BitBake:</emphasis>
The task executor and scheduler used by
the OpenEmbedded build system to build images.
For more information on BitBake, see the BitBake documentation
in the <filename>bitbake/doc/manual</filename> directory of the
<link linkend='source-directory'>Source Directory</link>.</para></listitem>
<listitem>
<para id='build-directory'><emphasis>Build Directory:</emphasis>
This term refers to the area used by the OpenEmbedded build system for builds.
The area is created when you <filename>source</filename> the setup
environment script that is found in the Source Directory
(i.e. <filename>&OE_INIT_FILE;</filename>).
The <ulink url='&YOCTO_DOCS_REF_URL;#var-TOPDIR'><filename>TOPDIR</filename></ulink>
variable points to the Build Directory.</para>
<para>You have a lot of flexibility when creating the Build Directory.
Following are some examples that show how to create the directory:
<itemizedlist>
<listitem><para>Create the Build Directory in your current working directory
and name it <filename>build</filename>.
This is the default behavior.
<literallayout class='monospaced'>
$ source &OE_INIT_PATH;
</literallayout></para></listitem>
<listitem><para>Provide a directory path and specifically name the build
directory.
This next example creates a Build Directory named <filename>YP-&POKYVERSION;</filename>
in your home directory within the directory <filename>mybuilds</filename>.
If <filename>mybuilds</filename> does not exist, the directory is created for you:
<literallayout class='monospaced'>
$ source &OE_INIT_PATH; $HOME/mybuilds/YP-&POKYVERSION;
</literallayout></para></listitem>
<listitem><para>Provide an existing directory to use as the Build Directory.
This example uses the existing <filename>mybuilds</filename> directory
as the Build Directory.
<literallayout class='monospaced'>
$ source &OE_INIT_PATH; $HOME/mybuilds/
</literallayout></para></listitem>
</itemizedlist>
</para></listitem>
<listitem><para><emphasis>Build System:</emphasis> In the context of the Yocto Project
this term refers to the OpenEmbedded build system used by the project.
This build system is based on the project known as "Poky."
For some historical information about Poky, see the
<link linkend='poky'>Poky</link> term further along in this section.
</para></listitem>
<listitem><para><emphasis>Classes:</emphasis> Files that provide for logic encapsulation
and inheritance allowing commonly used patterns to be defined once and easily used
in multiple recipes.
Class files end with the <filename>.bbclass</filename> filename extension.
</para></listitem>
<listitem><para><emphasis>Configuration File:</emphasis> Configuration information in various
<filename>.conf</filename> files provides global definitions of variables.
The <filename>conf/local.conf</filename> configuration file in the
<link linkend='build-directory'>Build Directory</link>
contains user-defined variables that affect each build.
The <filename>meta-yocto/conf/distro/poky.conf</filename> configuration file
defines Yocto ‘distro’ configuration
variables used only when building with this policy.
Machine configuration files, which
are located throughout the
<link linkend='source-directory'>Source Directory</link>, define
variables for specific hardware and are only used when building for that target
(e.g. the <filename>machine/beagleboard.conf</filename> configuration file defines
variables for the Texas Instruments ARM Cortex-A8 development board).
Configuration files end with a <filename>.conf</filename> filename extension.
</para></listitem>
<listitem><para><emphasis>Cross-Development Toolchain:</emphasis>
A collection of software development
tools and utilities that allow you to develop software for targeted architectures.
This toolchain contains cross-compilers, linkers, and debuggers that are specific to
an architecture.
You can use the OpenEmbedded build system to build a cross-development toolchain
installer that when run installs the toolchain that contains the development tools you
need to cross-compile and test your software.
The Yocto Project ships with images that contain installers for
toolchains for supported architectures as well.
Sometimes this toolchain is referred to as the meta-toolchain.</para></listitem>
<listitem><para><emphasis>Image:</emphasis> An image is the result produced when
BitBake processes a given collection of recipes and related metadata.
Images are the binary output that run on specific hardware or QEMU
and for specific use cases.
For a list of the supported image types that the Yocto Project provides, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
chapter in the Yocto Project Reference Manual.</para></listitem>
<listitem><para id='layer'><emphasis>Layer:</emphasis> A collection of recipes representing the core,
a BSP, or an application stack.
For a discussion on BSP Layers, see the
"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
section in the Yocto Project Board Support Packages (BSP) Developer's Guide.</para></listitem>
<listitem><para id='metadata'><emphasis>Metadata:</emphasis> The files that BitBake parses when
building an image.
Metadata includes recipes, classes, and configuration files.</para></listitem>
<listitem><para id='oe-core'><emphasis>OE-Core:</emphasis> A core set of metadata originating
with OpenEmbedded (OE) that is shared between OE and the Yocto Project.
This metadata is found in the <filename>meta</filename> directory of the source
directory.</para></listitem>
<listitem><para><emphasis>Package:</emphasis> In the context of the Yocto Project,
this term refers to the packaged output from a baked recipe.
A package is generally the compiled binaries produced from the recipe's sources.
You ‘bake’ something by running it through BitBake.</para>
<para>It is worth noting that the term "package" can, in general, have subtle
meanings. For example, the packages refered to in the
"<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" section are
compiled binaries that when installed add functionality to your Linux
distribution.</para>
<para>Another point worth noting is that historically within the Yocto Project,
recipes were referred to as packages - thus, the existence of several BitBake
variables that are seemingly mis-named,
(e.g. <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PRINC'><filename>PRINC</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>, and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>).
</para></listitem>
<listitem><para id='poky'><emphasis>Poky:</emphasis> The term "poky" can mean several things.
In its most general sense, it is an open-source project that was initially developed
by OpenedHand. With OpenedHand, poky was developed off of the existing OpenEmbedded
build system becoming a build system for embedded images.
After Intel Corporation aquired OpenedHand, the project poky became the basis for
the Yocto Project's build system.
Within the Yocto Project source repositories, poky exists as a separate Git repository
that can be cloned to yield a local copy on the host system.
Thus, "poky" can refer to the local copy of the Source Directory used to develop within
the Yocto Project.</para></listitem>
<listitem><para><emphasis>Recipe:</emphasis> A set of instructions for building packages.
A recipe describes where you get source code and which patches to apply.
Recipes describe dependencies for libraries or for other recipes, and they
also contain configuration and compilation options.
Recipes contain the logical unit of execution, the software/images to build, and
use the <filename>.bb</filename> file extension.</para></listitem>
<listitem>
<para id='source-directory'><emphasis>Source Directory:</emphasis>
This term refers to the directory structure created as a result of either downloading
and unpacking a Yocto Project release tarball or creating a local copy of
the <filename>poky</filename> Git repository
<filename>git://git.yoctoproject.org/poky</filename>.
Sometimes you might here the term "poky directory" used to refer to this
directory structure.
<note>
The OpenEmbedded build system does not support file or directory names that
contain spaces.
Be sure that the Source Directory you use does not contain these types
of names.
</note></para>
<para>The Source Directory contains BitBake, Documentation, metadata and
other files that all support the Yocto Project.
Consequently, you must have the Source Directory in place on your development
system in order to do any development using the Yocto Project.</para>
<para>For tarball expansion, the name of the top-level directory of the Source Directory
is derived from the Yocto Project release tarball.
For example, downloading and unpacking <filename>&YOCTO_POKY_TARBALL;</filename>
results in a Source Directory whose top-level folder is named
<filename>&YOCTO_POKY;</filename>.
If you create a local copy of the Git repository, then you can name the repository
anything you like.
Throughout much of the documentation, <filename>poky</filename> is used as the name of
the top-level folder of the local copy of the poky Git repository.
So, for example, cloning the <filename>poky</filename> Git repository results in a
local Git repository whose top-level folder is also named <filename>poky</filename>.</para>
<para>It is important to understand the differences between the Source Directory created
by unpacking a released tarball as compared to cloning
<filename>git://git.yoctoproject.org/poky</filename>.
When you unpack a tarball, you have an exact copy of the files based on the time of
release - a fixed release point.
Any changes you make to your local files in the Source Directory are on top of the release.
On the other hand, when you clone the <filename>poky</filename> Git repository, you have an
active development repository.
In this case, any local changes you make to the Source Directory can be later applied
to active development branches of the upstream <filename>poky</filename> Git
repository.</para>
<para>Finally, if you want to track a set of local changes while starting from the same point
as a release tarball, you can create a local Git branch that
reflects the exact copy of the files at the time of their release.
You do this by using Git tags that are part of the repository.</para>
<para>For more information on concepts around Git repositories, branches, and tags,
see the
"<link linkend='repositories-tags-and-branches'>Repositories, Tags, and Branches</link>"
section.</para></listitem>
<listitem><para><emphasis>Tasks:</emphasis> Arbitrary groups of software Recipes.
You simply use Tasks to hold recipes that, when built, usually accomplish a single task.
For example, a task could contain the recipes for a company’s proprietary or value-add software.
Or, the task could contain the recipes that enable graphics.
A task is really just another recipe.
Because task files are recipes, they end with the <filename>.bb</filename> filename
extension.</para></listitem>
<listitem><para><emphasis>Upstream:</emphasis> A reference to source code or repositories
that are not local to the development system but located in a master area that is controlled
by the maintainer of the source code.
For example, in order for a developer to work on a particular piece of code, they need to
first get a copy of it from an "upstream" source.</para></listitem>
</itemizedlist>
</para>
</section>
<section id='licensing'>
<title>Licensing</title>
<para>
Because open source projects are open to the public, they have different licensing structures in place.
License evolution for both Open Source and Free Software has an interesting history.
If you are interested in this history, you can find basic information here:
<itemizedlist>
<listitem><para><ulink url='http://en.wikipedia.org/wiki/Open-source_license'>Open source license history</ulink>
</para></listitem>
<listitem><para><ulink url='http://en.wikipedia.org/wiki/Free_software_license'>Free software license
history</ulink></para></listitem>
</itemizedlist>
</para>
<para>
In general, the Yocto Project is broadly licensed under the Massachusetts Institute of Technology
(MIT) License.
MIT licensing permits the reuse of software within proprietary software as long as the
license is distributed with that software.
MIT is also compatible with the GNU General Public License (GPL).
Patches to the Yocto Project follow the upstream licensing scheme.
You can find information on the MIT license at
<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 Yocto Project files directory 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/images/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 are OSD-conformant.
</para>
<para>
You can find a list of the combined SPDX and OSI licenses that the Yocto Project uses
<ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta/files/common-licenses'>here</ulink>.
This wiki page discusses the license infrastructure used by the Yocto Project.
</para>
<para>
For information that can help you to maintain compliance with various open source licensing
during the lifecycle of a product created using the Yocto Project, see the
"<link linkend='maintaining-open-source-license-compliance-during-your-products-lifecycle'>Maintaining Open Source License Compliance During Your Product's Lifecycle</link>" section.
</para>
</section>
<section id='git'>
<title>Git</title>
<para>
The Yocto Project uses 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 Yocto Project for development.
This section provides a quick overview of how Git works and provides you with a summary
of some essential Git commands.
</para>
<para>
For more information on Git, see
<ulink url='http://git-scm.com/documentation'></ulink>.
If you need to download Git, go to <ulink url='http://git-scm.com/download'></ulink>.
</para>
<section id='repositories-tags-and-branches'>
<title>Repositories, Tags, and Branches</title>
<para>
As mentioned earlier in section
"<link linkend='yocto-project-repositories'>Yocto Project Source Repositories</link>",
the Yocto Project maintains source repositories at
<ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.
If you look at this web-interface of the repositories, each item is a separate
Git repository.
</para>
<para>
Git repositories use branching techniques that track content change (not files)
within a project (e.g. a new feature or updated documentation).
Creating a tree-like structure based on project divergence allows for excellent historical
information over the life of a project.
This methodology also allows for an environment in which you can do lots of
local experimentation on a project as you develop changes or new features.
</para>
<para>
A Git repository represents all development efforts for a given project.
For example, the Git repository <filename>poky</filename> contains all changes
and developments for Poky over the course of its entire life.
That means that all changes that make up all releases are captured.
The repository maintains a complete history of changes.
</para>
<para>
You can create a local copy of any repository by "cloning" it with the Git
<filename>clone</filename> command.
When you clone a Git repository, you end up with an identical copy of the
repository on your development system.
Once you have a local copy of a repository, you can take steps to develop locally.
For examples on how to clone Git repositories, see the section
"<link linkend='getting-setup'>Getting Set Up</link>" earlier in this 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
<filename>bernard</filename>,
<filename>edison</filename>, <filename>denzil</filename>, <filename>danny</filename>
and <filename>master</filename> branches among others.
You can see all the branches by going to
<ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/'></ulink> and
clicking on the
<filename><ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/refs/heads'>[...]</ulink></filename>
link beneath the "Branch" heading.
</para>
<para>
Each of these branches represents a specific area of development.
The <filename>master</filename> branch represents the current or most recent
development.
All other branches represent off-shoots of the <filename>master</filename>
branch.
</para>
<para>
When you create a local copy of a Git repository, the copy has the same set
of branches as the original.
This means you can use Git to create a local working area (also called a branch)
that tracks a specific development branch from the source Git repository.
in other words, you can define your local Git environment to work on any development
branch in the repository.
To help illustrate, here is a set of commands that creates a local copy of the
<filename>poky</filename> Git repository and then creates and checks out a local
Git branch that tracks the Yocto Project &DISTRO; Release (&DISTRO_NAME;) development:
<literallayout class='monospaced'>
$ cd ~
$ git clone git://git.yoctoproject.org/poky
$ cd poky
$ git checkout -b &DISTRO_NAME; origin/&DISTRO_NAME;
</literallayout>
In this example, the name of the top-level directory of your local Yocto Project
Files Git repository is <filename>poky</filename>,
and the name of the local working area (or local branch) you have created and checked
out is <filename>&DISTRO_NAME;</filename>.
The files in your repository now reflect the same files that are in the
<filename>&DISTRO_NAME;</filename> development branch of the Yocto Project's
<filename>poky</filename> repository.
It is important to understand that when you create and checkout a
local working branch based on a branch name,
your local environment matches the "tip" of that development branch
at the time you created your local branch, which could be
different than the files at the time of a similarly named release.
In other words, creating and checking out a local branch based on the
<filename>&DISTRO_NAME;</filename> branch name is not the same as
cloning and checking out the <filename>master</filename> branch.
Keep reading to see how you create a local snapshot of a Yocto Project Release.
</para>
<para>
Git uses "tags" to mark specific changes in a repository.
Typically, a tag is used to mark a special point such as the final change
before a project is released.
You can see the tags used with the <filename>poky</filename> Git repository
by going to <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/'></ulink> and
clicking on the
<filename><ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/refs/tags'>[...]</ulink></filename>
link beneath the "Tag" heading.
</para>
<para>
Some key tags are <filename>bernard-5.0</filename>, <filename>denzil-7.0</filename>,
and <filename>&DISTRO_NAME;-&POKYVERSION;</filename>.
These tags represent Yocto Project releases.
</para>
<para>
When you create a local copy of the Git repository, you also have access to all the
tags.
Similar to branches, you can create and checkout a local working Git branch based
on a tag name.
When you do this, you get a snapshot of the Git repository that reflects
the state of the files when the change was made associated with that tag.
The most common use is to checkout a working branch that matches a specific
Yocto Project release.
Here is an example:
<literallayout class='monospaced'>
$ cd ~
$ git clone git://git.yoctoproject.org/poky
$ cd poky
$ git checkout -b my-&DISTRO_NAME;-&POKYVERSION; &DISTRO_NAME;-&POKYVERSION;
</literallayout>
In this example, the name of the top-level directory of your local Yocto Project
Files Git repository is <filename>poky</filename>.
And, the name of the local branch you have created and checked out is
<filename>my-&DISTRO_NAME;-&POKYVERSION;</filename>.
The files in your repository now exactly match the Yocto Project &DISTRO;
Release tag (<filename>&DISTRO_NAME;-&POKYVERSION;</filename>).
It is important to understand that when you create and checkout a local
working branch based on a tag, your environment matches a specific point
in time and not a development branch.
</para>
</section>
<section id='basic-commands'>
<title>Basic Commands</title>
<para>
Git has an extensive set of commands that lets you manage changes and perform
collaboration over the life of a project.
Conveniently though, you can manage with a small set of basic operations and workflows
once you understand the basic philosophy behind Git.
You do not have to be an expert in Git to be functional.
A good place to look for instruction on a minimal set of Git commands is
<ulink url='http://git-scm.com/documentation'>here</ulink>.
If you need to download Git, you can do so
<ulink url='http://git-scm.com/download'>here</ulink>.
</para>
<para>
If you don’t know much about Git, we suggest you educate
yourself by visiting the links previously mentioned.
</para>
<para>
The following list briefly describes some basic Git operations as a way to get started.
As with any set of commands, this list (in most cases) simply shows the base command and
omits the many arguments they support.
See the Git documentation for complete descriptions and strategies on how to use these commands:
<itemizedlist>
<listitem><para><emphasis><filename>git init</filename>:</emphasis> Initializes an empty Git repository.
You cannot use Git commands unless you have a <filename>.git</filename> repository.</para></listitem>
<listitem><para><emphasis><filename>git clone</filename>:</emphasis> Creates a clone of a repository.
During collaboration, this command allows you to create a local repository that is on
equal footing with a fellow developer’s repository.</para></listitem>
<listitem><para><emphasis><filename>git add</filename>:</emphasis> Adds updated file contents
to the index that
Git uses to track changes.
You must add all files that have changed before you can commit them.</para></listitem>
<listitem><para><emphasis><filename>git commit</filename>:</emphasis> Creates a “commit” that documents
the changes you made.
Commits are used for historical purposes, for determining if a maintainer of a project
will allow the change, and for ultimately pushing the change from your local Git repository
into the project’s upstream (or master) repository.</para></listitem>
<listitem><para><emphasis><filename>git status</filename>:</emphasis> Reports any modified files that
possibly need to be added and committed.</para></listitem>
<listitem><para><emphasis><filename>git checkout &lt;branch-name&gt;</filename>:</emphasis> Changes
your working branch.
This command is analogous to “cd”.</para></listitem>
<listitem><para><emphasis><filename>git checkout –b &lt;working-branch&gt;</filename>:</emphasis> Creates
a working branch on your local machine where you can isolate work.
It is a good idea to use local branches when adding specific features or changes.
This way if you don’t like what you have done you can easily get rid of the work.</para></listitem>
<listitem><para><emphasis><filename>git branch</filename>:</emphasis> Reports
existing local branches and
tells you the branch in which you are currently working.</para></listitem>
<listitem><para><emphasis><filename>git branch -D &lt;branch-name&gt;</filename>:</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 <filename>&lt;branch-name&gt;</filename>.</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 local changes you
have committed to an upstream Git repository (e.g. a contribution repository).
The maintainer of the project draws from these repositories when adding your changes to the
project’s master 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 for isolated work, make and commit your
changes, switch to your local master branch, merge the changes from the temporary branch into the
local master branch, and then delete the temporary branch.</para></listitem>
<listitem><para><emphasis><filename>git cherry-pick</filename>:</emphasis> Choose and apply specific
commits from one branch into another branch.
There are times when you might not be able to merge all the changes in one branch with
another but need to pick out certain ones.</para></listitem>
<listitem><para><emphasis><filename>gitk</filename>:</emphasis> Provides a GUI view of the branches
and changes in your local Git repository.
This command is a good way to graphically see where things have diverged in your
local repository.</para></listitem>
<listitem><para><emphasis><filename>git log</filename>:</emphasis> Reports a history of your changes to the
repository.</para></listitem>
<listitem><para><emphasis><filename>git diff</filename>:</emphasis> Displays line-by-line differences
between your local working files and the same files in the upstream Git repository that your
branch currently tracks.</para></listitem>
</itemizedlist>
</para>
</section>
</section>
<section id='workflows'>
<title>Workflows</title>
<para>
This section provides some overview on workflows using Git.
In particular, the information covers basic practices that describe roles and actions in a
collaborative development environment.
Again, if you are familiar with this type of development environment, you might want to just
skip this section.
</para>
<para>
The Yocto Project files are maintained using Git in a "master" branch whose Git history
tracks every change and whose structure provides branches for all diverging functionality.
Although there is no need to use Git, many open source projects do so.
For the Yocto Project, a key individual called the "maintainer" is responsible for the "master"
branch of the Git repository.
The "master" branch is the “upstream” repository where the final builds of the project occur.
The maintainer is responsible for allowing changes in from other developers and for
organizing the underlying branch structure to reflect release strategies and so forth.
<note>You can see who is the maintainer for Yocto Project files by examining the
<filename>distro_tracking_fields.inc</filename> file in the Yocto Project
<filename>meta/conf/distro/include</filename> directory.</note>
</para>
<para>
The project also has contribution repositories known as “contrib” areas.
These areas temporarily hold changes to the project that have been submitted or committed
by the Yocto Project development team and by community members that contribute to the project.
The maintainer determines if the changes are qualified to be moved from the "contrib" areas
into the "master" branch of the Git repository.
</para>
<para>
Developers (including contributing community members) create and maintain cloned repositories
of the upstream "master" branch.
These repositories are local to their development platforms and are used to develop changes.
When a developer is satisfied with a particular feature or change, they “push” the changes
to the appropriate "contrib" repository.
</para>
<para>
Developers are responsible for keeping their local repository up-to-date with "master".
They are also responsible for straightening out any conflicts that might arise within files
that are being worked on simultaneously by more than one person.
All this work is done locally on the developer’s 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
"<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section.
</para>
<para>
To summarize the environment: we have a single point of entry for changes into the project’s
"master" branch of the Git repository, which is controlled by the project’s maintainer.
And, we have a set of developers 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 in 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, simply discard the 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 local Yocto Project files Git repository in
the <filename>scripts</filename> directory.</para>
<para>You can find more information on these scripts in the
"<link linkend='pushing-a-change-upstream'>Using
Scripts to Push a Change Upstream and Request a Pull</link>" section.
</para></listitem>
<listitem><para><emphasis>Patch Workflow:</emphasis> This workflow allows you to notify the
maintainer through an email that you have a change (or patch) you would like considered
for the "master" branch of the Git repository.
To send this type of change you format the patch and then send the email using the Git commands
<filename>git format-patch</filename> and <filename>git send-email</filename>.
You can find information on how to submit changes
later in this chapter.</para></listitem>
</itemizedlist>
</para>
</section>
<section id='tracking-bugs'>
<title>Tracking Bugs</title>
<para>
The Yocto Project uses its own implementation of
<ulink url='http://www.bugzilla.org/about/'>Bugzilla</ulink> to track bugs.
Implementations of Bugzilla work well for group development because they track bugs and code
changes, can be used to communicate changes and problems with developers, can be used to
submit and review patches, and can be used to manage quality assurance.
The home page for the Yocto Project implementation of Bugzilla is
<ulink url='&YOCTO_BUGZILLA_URL;'>&YOCTO_BUGZILLA_URL;</ulink>.
</para>
<para>
Sometimes it is helpful to submit, investigate, or track a bug against the Yocto Project itself
such as when discovering an issue with some component of the build system that acts contrary
to the documentation or your expectations.
Following is the general procedure for submitting a new bug using the Yocto Project
Bugzilla.
You can find more information on defect management, bug tracking, and feature request
processes all accomplished through the Yocto Project Bugzilla on the wiki page
<ulink url='&YOCTO_WIKI_URL;/wiki/Bugzilla_Configuration_and_Bug_Tracking'>here</ulink>.
<orderedlist>
<listitem><para>Always use the Yocto Project implementation of Bugzilla to submit
a bug.</para></listitem>
<listitem><para>When submitting a new bug, be sure to choose the appropriate
Classification, Product, and Component for which the issue was found.
Defects for Yocto Project fall into one of six classifications: Yocto Project
Components, Infrastructure, Build System &amp; Metadata, Documentation,
QA/Testing, and Runtime.
Each of these Classifications break down into multiple Products and, in some
cases, multiple Components.</para></listitem>
<listitem><para>Use the bug form to choose the correct Hardware and Architecture
for which the bug applies.</para></listitem>
<listitem><para>Indicate the Yocto Project version you were using when the issue
occurred.</para></listitem>
<listitem><para>Be sure to indicate the Severity of the bug.
Severity communicates how the bug impacted your work.</para></listitem>
<listitem><para>Provide a brief summary of the issue.
Try to limit your summary to just a line or two and be sure to capture the
essence of the issue.</para></listitem>
<listitem><para>Provide a detailed description of the issue.
You should provide as much detail as you can about the context, behavior, output,
and so forth that surround the issue.
You can even attach supporting files for output or log by using the "Add an attachment"
button.</para></listitem>
<listitem><para>Submit the bug by clicking the "Submit Bug" button.</para></listitem>
</orderedlist>
</para>
</section>
<section id='how-to-submit-a-change'>
<title>How to Submit a Change</title>
<para>
Contributions to the Yocto Project and OpenEmbedded are very welcome.
Because the system is extremely configurable and flexible, we recognize that developers
will want to extend, configure or optimize it for their specific uses.
You should send patches to the appropriate mailing list so that they
can be reviewed and merged by the appropriate maintainer.
For a list of the Yocto Project and related mailing lists, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing lists</ulink>" section in
the Yocto Project Reference Manual.
</para>
<para>
The following is some guidance on which mailing list to use for what type of change:
<itemizedlist>
<listitem><para>For changes to the core metadata, send your patch to the
<ulink url='&OE_LISTS_URL;/listinfo/openembedded-core'>openembedded-core</ulink> mailing list.
For example, a change to anything under the <filename>meta</filename> or
<filename>scripts</filename> directories
should be sent to this mailing list.</para></listitem>
<listitem><para>For changes to BitBake (anything under the <filename>bitbake</filename>
directory), send your patch to the
<ulink url='&OE_LISTS_URL;/listinfo/bitbake-devel'>bitbake-devel</ulink> mailing list.</para></listitem>
<listitem><para>For changes to <filename>meta-yocto</filename>, send your patch to the
<ulink url='&YOCTO_LISTS_URL;/listinfo/poky'>poky</ulink> mailing list.</para></listitem>
<listitem><para>For changes to other layers hosted on
<filename>yoctoproject.org</filename> (unless the
layer's documentation specifies otherwise), tools, and Yocto Project
documentation, use the
<ulink url='&YOCTO_LISTS_URL;/listinfo/yocto'>yocto</ulink> mailing list.</para></listitem>
<listitem><para>For additional recipes that do not fit into the core metadata,
you should determine which layer the recipe should go into and submit the
change in the manner recommended by the documentation (e.g. README) supplied
with the layer. If in doubt, please ask on the
<ulink url='&YOCTO_LISTS_URL;/listinfo/yocto'>yocto</ulink> or
<ulink url='&OE_LISTS_URL;/listinfo/openembedded-devel'>openembedded-devel</ulink>
mailing lists.</para></listitem>
</itemizedlist>
</para>
<para>
When you send a patch, be sure to include a "Signed-off-by:"
line in the same style as required by the Linux kernel.
Adding this line signifies that you, the submitter, have agreed to the Developer's Certificate of Origin 1.1
as follows:
<literallayout class='monospaced'>
Developer's Certificate of Origin 1.1
By making a contribution to this project, I certify that:
(a) The contribution was created in whole or in part by me and I
have the right to submit it under the open source license
indicated in the file; or
(b) The contribution is based upon previous work that, to the best
of my knowledge, is covered under an appropriate open source
license and I have the right under that license to submit that
work with modifications, whether created in whole or in part
by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated
in the file; or
(c) The contribution was provided directly to me by some other
person who certified (a), (b) or (c) and I have not modified
it.
(d) I understand and agree that this project and the contribution
are public and that a record of the contribution (including all
personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with
this project or the open source license(s) involved.
</literallayout>
</para>
<para>
In a collaborative environment, it is necessary to have some sort of standard
or method through which you submit changes.
Otherwise, things could get quite chaotic.
One general practice to follow is to make small, controlled changes.
Keeping changes small and isolated aids review, makes merging/rebasing easier
and keeps the change history clean when anyone needs to refer to it in future.
</para>
<para>
When you make a commit, you must follow certain standards established by the
OpenEmbedded and Yocto Project development teams.
For each commit, you must provide a single-line summary of the change and you
should almost always provide a more detailed description of what you did (i.e.
the body of the commit message).
The only exceptions for not providing a detailed description would be if your
change is a simple, self-explanatory change that needs no further description
beyond the summary.
Here are the guidelines for composing a commit message:
<itemizedlist>
<listitem><para>Provide a single-line, short summary of the change.
This summary is typically viewable in the "shortlist" of changes.
Thus, providing something short and descriptive that gives the reader
a summary of the change is useful when viewing a list of many commits.
This should be prefixed by the recipe name (if changing a recipe), or
else the short form path to the file being changed.
</para></listitem>
<listitem><para>For the body of the commit message, provide detailed information
that describes what you changed, why you made the change, and the approach
you used. It may also be helpful if you mention how you tested the change.
Provide as much detail as you can in the body of the commit message.
</para></listitem>
<listitem><para>If the change addresses a specific bug or issue that is
associated with a bug-tracking ID, include a reference to that ID in
your detailed description.
For example, the Yocto Project uses a specific convention for bug
references - any commit that addresses a specific bug should include the
bug ID in the description (typically at the beginning) as follows:
<literallayout class='monospaced'>
[YOCTO #&lt;bug-id&gt;]
&lt;detailed description of change&gt;
</literallayout></para></listitem>
Where &lt;bug-id&gt; is replaced with the specific bug ID from the
Yocto Project Bugzilla instance.
</itemizedlist>
</para>
<para>
You can find more guidance on creating well-formed commit messages at this OpenEmbedded
wiki page:
<ulink url='&OE_HOME_URL;/wiki/Commit_Patch_Message_Guidelines'></ulink>.
</para>
<para>
Following are general instructions for both pushing changes upstream and for submitting
changes as patches.
</para>
<section id='pushing-a-change-upstream'>
<title>Using Scripts to Push a Change Upstream and Request a Pull</title>
<para>
The basic flow for pushing a change to an upstream "contrib" Git repository is as follows:
<itemizedlist>
<listitem><para>Make your changes in your local Git repository.</para></listitem>
<listitem><para>Stage your changes by using the <filename>git add</filename>
command on each file you changed.</para></listitem>
<listitem><para>Commit the change by using the <filename>git commit</filename>
command and push it to the "contrib" repository.
Be sure to provide a commit message that follows the project’s commit message standards
as described earlier.</para></listitem>
<listitem><para>Notify the maintainer that you have pushed a change by making a pull
request.
The Yocto Project provides two scripts that conveniently let you generate and send
pull requests to the Yocto Project.
These scripts are <filename>create-pull-request</filename> and
<filename>send-pull-request</filename>.
You can find these scripts in the <filename>scripts</filename> directory
within the <link linkend='source-directory'>Source Directory</link>.</para>
<para>Using these scripts correctly formats the requests without introducing any
whitespace or HTML formatting.
The maintainer that receives your patches needs to be able to save and apply them
directly from your emails.
Using these scripts is the preferred method for sending patches.</para>
<para>For help on using these scripts, simply provide the
<filename>-h</filename> argument as follows:
<literallayout class='monospaced'>
$ ~/poky/scripts/create-pull-request -h
$ ~/poky/scripts/send-pull-request -h
</literallayout></para></listitem>
</itemizedlist>
</para>
<para>
You can find general Git information on how to push a change upstream in the
<ulink url='http://book.git-scm.com/3_distributed_workflows.html'>Git Community Book</ulink>.
</para>
</section>
<section id='submitting-a-patch'>
<title>Using Email to Submit a Patch</title>
<para>
You can submit patches without using the <filename>create-pull-request</filename> and
<filename>send-pull-request</filename> scripts described in the previous section.
Keep in mind, the preferred method is to use the scripts, however.
</para>
<para>
Depending on the components changed, you need to submit the email to a specific
mailing list.
For some guidance on which mailing list to use, see the list in the
"<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section
earlier in this manual.
For a description of the available mailing lists, see
"<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing Lists</ulink>"
section in the Yocto Project Reference Manual.
</para>
<para>
Here is the general procedure on how to submit a patch through email without using the
scripts:
<itemizedlist>
<listitem><para>Make your changes in your local Git repository.</para></listitem>
<listitem><para>Stage your changes by using the <filename>git add</filename>
command on each file you changed.</para></listitem>
<listitem><para>Commit the change by using the
<filename>git commit --signoff</filename> command.
Using the <filename>--signoff</filename> option identifies you as the person
making the change and also satisfies the Developer's Certificate of
Origin (DCO) shown earlier.</para>
<para>When you form a commit you must follow certain standards established by the
Yocto Project development team.
See the earlier section
"<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
for Yocto Project commit message standards.</para></listitem>
<listitem><para>Format the commit into an email message.
To format commits, use the <filename>git format-patch</filename> command.
When you provide the command, you must include a revision list or a number of patches
as part of the command.
For example, these two commands each take the most recent single commit and
format it as an email message in the current directory:
<literallayout class='monospaced'>
$ git format-patch -1
$ git format-patch HEAD~
</literallayout></para>
<para>After the command is run, the current directory contains a
numbered <filename>.patch</filename> file for the commit.</para>
<para>If you provide several commits as part of the command,
the <filename>git format-patch</filename> command produces a numbered
series of files in the current directory – one for each commit.
If you have more than one patch, you should also use the
<filename>--cover</filename> option with the command, which generates a
cover letter as the first "patch" in the series.
You can then edit the cover letter to provide a description for
the series of patches.
For information on the <filename>git format-patch</filename> command,
see <filename>GIT_FORMAT_PATCH(1)</filename> displayed using the
<filename>man git-format-patch</filename> command.</para>
<note>If you are or will be a frequent contributor to the Yocto Project
or to OpenEmbedded, you might consider requesting a contrib area and the
necessary associated rights.</note></listitem>
<listitem><para>Import the files into your mail client by using the
<filename>git send-email</filename> command.
<note>In order to use <filename>git send-email</filename>, you must have the
the proper Git packages installed.
For Ubuntu and Fedora the package is <filename>git-email</filename>.</note></para>
<para>The <filename>git send-email</filename> command sends email by using a local
or remote Mail Transport Agent (MTA) such as
<filename>msmtp</filename>, <filename>sendmail</filename>, or through a direct
<filename>smtp</filename> configuration in your Git <filename>config</filename>
file.
If you are submitting patches through email only, it is very important
that you submit them without any whitespace or HTML formatting that
either you or your mailer introduces.
The maintainer that receives your patches needs to be able to save and
apply them directly from your emails.
A good way to verify that what you are sending will be applicable by the
maintainer is to do a dry run and send them to yourself and then
save and apply them as the maintainer would.</para>
<para>The <filename>git send-email</filename> command is the preferred method
for sending your patches since there is no risk of compromising whitespace
in the body of the message, which can occur when you use your own mail client.
The command also has several options that let you
specify recipients and perform further editing of the email message.
For information on how to use the <filename>git send-email</filename> command,
use the <filename>man git-send-email</filename> command.</para></listitem>
</itemizedlist>
</para>
</section>
</section>
</chapter>
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