add docker build

First passing build with a container. The `Dockerfile` contains
a current set of build dependencies to install on Unbuntu Server 22.04
as of the time of this commit

Dockerfile

@@ -0,0 +1,28 @@
+FROM ubuntu:22.04
+
+ARG UNAME=build
+ARG UID=1000
+ARG GID=1000
+
+RUN apt-get update && \
+    DEBIAN_FRONTEND=noninteractive TZ=Etc/UTC \
+    apt-get install -y \
+        sudo time git make curl wget subversion build-essential gcc file bc cpio gawk flex gettext unzip grep rsync pkg-config \
+        openssl libssl-dev libncurses5-dev zlib1g-dev libwayland-dev libkf5config-dev-bin libkf5coreaddons-dev-bin \
+        python3 python3-distutils \
+        qttools5-dev qttools5-dev-tools qtdeclarative5-dev && \
+    apt-get clean
+
+VOLUME ["/ccache"]
+VOLUME ["/downloads"]
+VOLUME ["/src"]
+
+ENV BR2_DL_DIR="/downloads"
+ENV BR2_CCACHE_DIR="/ccache"
+
+RUN groupadd -g $GID -o $UNAME && useradd -m -u $UID -g $GID -o -s /bin/bash $UNAME
+USER $UNAME
+
+WORKDIR /src
+
+CMD ["/bin/bash"]

README.md

@@ -51,6 +51,24 @@ The following system packages are required to build the image:
 - wget
 - qtdeclarative5-dev
 
+#### Docker Build Environment
+To build the build environment run the following from the root folder of the project:
+```sh
+docker build --build-arg UID=$(id -u) --build-arg GID=$(id -g) -t buildroot-agent .
+```
+
+To execute a build, run the following, replacing <MAKE_ARG> with an argument to be passed in to `make`, such as `clean` or `rpi4_64-gui`
+```sh
+docker run -v ./:/src -v ./ccache/:/ccache -v ../downloads/:/downloads  --entrypoint /usr/bin/make -e BR2_JLEVEL=$(nproc) buildroot <MAKE_ARG>
+```
+Adjust paths to the `/ccache` and `/downloads` volumes accordingly. If these are not passed in, the caches will reside inside the container file system.
+
+On `podman`, the Dockerfile has been configured to run as a user with the same uid/gid as the current user (passed in as a build-arg). 
+This will require passing the --userns=keep-id argument, e.g.:
+```sh
+podman run --userns=keep-id -v ./:/src -v ./ccache/:/ccache -v ../downloads/:/downloads  --entrypoint /usr/bin/make -e BR2_JLEVEL=$(nproc) buildroot clean
+```
+
 #### The following firewall ports need to be allowed to the internet.
 In addition to the usual http/https ports (tcp 80, tcp 443) a couple of other ports need to be allowed to the internet :
 - tcp 9418 (git).