2.8.2. Metadata, Machine Configuration, and Policy Configuration

+2.8.2. Metadata, Machine Configuration, and Policy Configuration

+ 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. +

+ In general, three types of layer input exist: +

Policy Configuration: + 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.
Machine Configuration: + Board Support Package (BSP) layers provide machine + configurations. + This type of information is specific to a particular + target architecture.
Metadata: + Software layers contain user-supplied recipe files, + patches, and append files. +

+ The following figure shows an expanded representation of the + Metadata, Machine Configuration, and Policy Configuration input + (layers) boxes of the + general Yocto Project Development Environment figure: +

+ In general, all layers have a similar structure. + They all contain a licensing file + (e.g. COPYING) if the layer is to be + distributed, a README file as good practice + and especially if the layer is to be distributed, a + configuration directory, and recipe directories. +

+ The Yocto Project has many layers that can be used. + You can see a web-interface listing of them on the + Source Repositories + page. + The layers are shown at the bottom categorized under + "Yocto Metadata Layers." + These layers are fundamentally a subset of the + OpenEmbedded Metadata Index, + 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. +

+ BitBake uses the conf/bblayers.conf file, + which is part of the user configuration, to find what layers it + should be using as part of the build. +

+ For more information on layers, see the + "Understanding and Creating Layers" + section in the Yocto Project Development Tasks Manual. +