Variant concept in Yocto

A Yocto project often has to support several variations in software and hardware composition, such as supporting a graphical software stack as well as a non-graphical software stack on several different CPU architectures.

A variation in either hardware of software is in the Software Factory referred to as a variant.

Each variant potentially needs its own set of Yocto configuration files (most notably, its own bblayers.conf and local.conf). Yocto has a built-in way to handle deployment of configuration files with its TEMPLATECONF variable which can be supplied to the oe-init-build-env script 1, and this scheme is also used in the Software Factory.

Recommended variant management

The recommended way to handle variants is to keep one directory per variant in your layer. The variant directories should go into <meta-yourlayer>/conf/variant/<variant name>. Each variant should supply a README, bblayers.conf.sample and local.conf.sample.

• README contains a short description of the variant, such as the hardware it supports and the software variation it supports. For instance, if this variant only supports a non-graphical system on a Raspberry Pi 3, this is where this should be noted.

• bblayers.conf.sample contains the sample bblayers.conf which will be copied into the users' build/conf directory when initializing a new build. This bblayers.sonf.sample is specific to the current variant, and should be written to include the layers needed to build the current variant.

• local.conf.sample is also specific to the current variant in the same way as bblayers.conf.sample, but should contain the local.conf needed for the current variant.

If many variants are using the same directives, it is recommended to have a common directory with these directives in. The files that contain those common directives can then be included by the more specific variants that add the specific settings.

Note

BitBake searches paths that are listed in the BBPATH variable, so before including any files in bblayers.conf or local.conf, one has to make sure that those files can be found by setting BBPATH to include the layer in which they are located.

Recommended usage of variants

A variant is selected using the TEMPLATECONF variable when issuing the oe-init-build-env script from the poky project. The scheme described in Recommended variant management is fully compatible with the oe-init-build-env script, all the user needs to do is to specify the full path to the desired variant directory when running the script. More information on the TEMPLATECONF variable is available in 1.

1(1,2)

http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#creating-a-custom-template-configuration-directory