generic-poky/bitbake/doc/user-manual/user-manual-intro.xml

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
    "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<chapter id="user-manual-intro">
    <title>BitBake User Manual</title>

    <section id="intro">
        <title>Introduction</title>

        <para>
            BitBake is a tool for executing tasks commonly performed by software
            developers when building systems on a daily basis.
            BitBake can build Systems consisting of numerous individual pieces
            of software, or can be used to build a single application.
            Example tasks that BitBake can execute are fetching source code,
            applying patches to source code, configuring, compiling, and
            packaging applications into a complete system, and managing metadata.
            BitBake abstracts the information for completing individual tasks
            into files known as recipes.
            Recipes contain all of the relevant information required by BitBake
            to complete a given task including dependencies, source file
            locations, etc.
            BitBake is similar to
            <ulink url='http://www.gnu.org/software/make/'>GNU Make</ulink>
            and other build tools.
        </para>
    </section>

    <section id="history-and-goals">
        <title>History and Goals</title>

        <para>
            BitBake was originally a part of the OpenEmbedded project.
            It was inspired by the Portage package management system
            used by the Gentoo Linux distribution.
            On December 7, 2004, OpenEmbedded project team member,
            Chris Larson split the project into two distinct pieces:
            <itemizedlist>
                <listitem><para>BitBake, a generic task executor</para></listitem>
                <listitem><para>OpenEmbedded, a metadata set utilized by
                    BitBake.</para></listitem>
            </itemizedlist>
            Today, BitBake is the primary basis of the
            <ulink url="http://www.openembedded.org/">OpenEmbedded</ulink>
            project, which is being used to build and maintain a
            number of projects and embedded Linux distributions
            such as the Angstrom Distribution and the Yocto
            Project.
        </para>

        <para>
            Prior to BitBake, no other build tool adequately met the needs of
            an aspiring embedded Linux distribution.
            All of the build systems used by traditional desktop Linux
            distributions lacked important functionality, and none of the
            ad-hoc <emphasis>buildroot</emphasis> systems, prevalent in the
            embedded space, were scalable or maintainable.
        </para>

        <para>
            Some important original goals for BitBake were:
            <itemizedlist>
                <listitem><para>
                    Handle cross-compilation.
                    </para></listitem>
                <listitem><para>
                    Handle inter-package dependencies (build time on
                    target architecture, build time on native
                    architecture, and runtime).
                    </para></listitem>
                <listitem><para>
                    Support running any number of tasks within a given
                    package, including, but not limited to, fetching
                    upstream sources, unpacking them, patching them,
                    configuring them, etc.
                    </para></listitem>
                <listitem><para>
                    Must be Linux distribution agnostic (both build and
                    target).
                    </para></listitem>
                <listitem><para>
                    Must be architecture agnostic
                    </para></listitem>
                <listitem><para>
                    Must support multiple build and target operating systems
                    (including Cygwin, the BSDs, etc).
                    </para></listitem>
                <listitem><para>
                    Must be able to be self contained, rather than tightly
                    integrated into the build machine's root
                    filesystem.
                    </para></listitem>
                <listitem><para>
                    There must be a way to handle conditional metadata
                    (on target architecture, operating system,
                    distribution, machine).
                    </para></listitem>
                <listitem><para>
                    It must be easy for the person using the tools to
                    supply their own local metadata and packages
                    to operate against.
                    </para></listitem>
                <listitem><para>
                    Must make it easy to collaborate between multiple
                    projects using BitBake for their builds.
                    </para></listitem>
                <listitem><para>
                    Should provide an inheritance mechanism to share
                    common metadata between many packages.
                    </para></listitem>
            </itemizedlist>
        </para>

        <para>
            Over time it has become apparent that some further requirements
            were necessary:
            <itemizedlist>
                <listitem><para>
                    Handle variants of a base recipe (native, sdk, multilib).
                    </para></listitem>
                <listitem><para>
                    Able to split metadata into layers and allow layers
                    to override each other.
                    </para></listitem>
                <listitem><para>
                    Allow representation of a given set of input variables
                    to a task as a checksum.
                    Based on that checksum, allow acceleration of builds
                    with prebuilt components.
                    </para></listitem>
            </itemizedlist>
        </para>

        <para>
            BitBake satisfies all the original requirements and many more
            with extensions being made to the basic functionality to
            reflect the additional requirements.
            Flexibility and power have always been the priorities.
            It is highly extensible, supporting embedded Python code and
            execution of any arbitrary tasks.
        </para>
   </section>
</chapter>