barebox/defaultenv-2/base/bin/bootargs-root-ext

#!/bin/sh

while getopt "m:r:" opt; do
	if [ ${opt} = m ]; then
		part=${OPTARG}
	fi
	if [ ${opt} = r ]; then
		type=${OPTARG}
	fi
done

global.linux.bootargs.dyn.root="root=/dev/$part rootfstype=ext$type rootwait"