bitbake: user-manual-metadata: Add section about layers

(Bitbake rev: 0a99fe01dc273c548f7f83f9a7695c21184e7331) Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
2026-06-01 00:59:48 +00:00 · 2014-01-18 14:30:45 +00:00
parent 76072eaa8e
commit d6b8f746d4
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@@ -615,6 +615,46 @@
                Only variable definitions and include directives are allowed
                in <filename>.conf</filename> files.
            </para>
            <section id='layers'>
                <title>Layers</title>
                <para>
                    Layers allow you to isolate different types of
                    customizations from each other.
                    You might find it tempting to keep everything in one layer
                    when working on a single project.
                    However, the more modular you organize your Metadata, the
                    easier it is to cope with future changes.
                </para>
                <para>
                    To illustrate how layers are used to keep things modular,
                    consider machine customizations.
                    These types of customizations typically reside in a special layer,
                    rather than a general layer, called a Board Specific Package (BSP) Layer.
                    Furthermore, the machine customizations should be isolated from
                    recipes and Metadata that support a new GUI environment, for
                    example.
                    This situation gives you a couple of layers: one for the machine
                    configurations, and one for the GUI environment.
                    It is important to understand, however, that the BSP layer can still
                    make machine-specific additions to recipes within
                    the GUI environment layer without polluting the GUI layer itself
                    with those machine-specific changes.
                    You can accomplish this through a recipe that is a BitBake append
                    (<filename>.bbappend</filename>) file, which is described
                    later in this section.
                </para>
                <para>
                    There are certain variable specific to layers, including:
                    <itemizedlist>
                        <listitem><para><filename>LAYERDEPENDS</filename></para></listitem>
                        <listitem><para><filename>LAYERVERSION</filename></para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>
        <section id='classes'>