GENERIC DOCKER YOCTO BUILD IMAGE

This is generic docker image that will setup Yocto environment to build custom images and build them inside docker container. It is flexible designed with simple idea in mind: clone this -> setup custom layers -> configure build/conf let docker build. Mostly for personal reference to remember how to setup such flow.

Prerequisites

• docker installed on the host system

Target OS Configuration

The main target OS configuration happen in build/conf/local.conf. This file is Yocto's local config file. There are many options one can set via this file and it is probably the best way to configure the build.

Docker Configuration

To configure the build this setup provides following ARG variables and sets defaults:

• USER=builder - the user doing the build
• POKY_BRANCH=morty - the yocto branch to use. Latest archive will be fetched from Yocto's repos
• OPENEMBEDDED_BRANCH=morty - openembedded branch layers to fetch in container
• BUILD_PATH=/home/$USER/build - path in container for the build
• HOST_CONF_PATH=build/conf - path to conf/ folder on the host that will be copied to container
• HOST_LAYERS_PATH=layers - path to layers/ folder on the host that will be copied to container
• BITBAKE_TARGET - the target for the build

To configure the build this setup provides following ENV variables and sets defaults:

• POKY_PATH=/home/$USER/poky - path to place poky in container
• BBLAYERS_PATH=/home/$USER/bblayers - path to copy custom layers from host $HOST_CONF_PATH to container

Layers included

build/conf/bblayers.conf is used to setup the paths where Yocto layers will be loaded from. Customize the paths here when needed. Note that BBLAYERS is relative to build folder which itself is set via BUILD_PATH(see docker conf bellow).

By default this setup will place poky layers under $POKY_PATH and openembedded repo as sub-folder(meta-openembedded-<$OPENEMBEDDED_BRANCH>) of it. So if one needs to include recipes from meta-openembedded/meta-oe should append ../poky/meta-openembedded-<$OPENEMBEDDED_BRANCH>/meta-oe in bblayers.conf.

Custom layers placed in $HOST_LAYERS_PATH on the host will be copied to container to $BBLAYERS_PATH. This is to make possible loading of custom layers to container easily.

Build the Docker image

In project folder where the Dockerfile is type:

docker build --build-arg BITBAKE_TARGET=<target> -t my/yocto .

This will take long time the first time one executes the command as it is large environment to setup and long time to compile Yocto. It could happen that the build fails due to failed fetching of files. In this case restart the build again until it is completed successfully.

Get the output from the build

Yocto image builds will be placed in container $BUILD_PATH/tmp/deploy/images/<MASHINE>.

Start the container docker run -t my/yocto

In another terminal type docker ps and note the ID of the my/yocto container. Then docker exec -t -i <ID> /bin/bash and navigate to $BUILD_PATH/tmp/deploy/images/<MASHINE> to inspect the build.

Build flow checklist

1. Setup/clone custom layers in layers folder
2. Edit build/conf/bblayers.conf to set correct paths to the layers
3. Edit build/conf/local.conf to configure Yocto build
4. Build

References

Yocto Project Development Manual

Dockerfile reference

Building Raspberry Pi Systems with Yocto