This is an example Celun system implementing a USB Mass Storage system.
This is WIP.
$ nix-build --arg device ./devices/... -A ...
This will depend on the exact device.
For many systems, burning the build.disk-image output to a bootable will be
sufficient.
On EFI-based systems, using build.efiKernel is an alternative option. The
output is a self-contained EFI "program" consisting of the kernel and the
required userspace.