mo() {
	local root="${1}"
	if [ -z "${root}" ]; then
		log_error "No root target directory"
		return 1
	fi
	root="$(realpath "${root}")"
	if ! mkdir "overlay"; then
		log_error "Unable to make overlay directory"
		return 2
	fi
	(
		if ! cd "overlay"; then
			log_error "Unable to move into overlay directory"
			return 3
		fi
		local directory
		for directory in "lower" "upper" "work" "mount"; do
			if ! mkdir --parents "${directory}"; then
				log_error "Unable to make directory: ${directory}"
				return 4
			fi
		done
		local file="${root}/filesystem.squashfs"
		if ! mount "${file}" "lower"; then
			log_error "Unable to lower mount: ${file}"
			return 5
		fi
		if ! mount \
			-o "lowerdir=lower,upperdir=upper,workdir=work" \
			-t "overlay" \
			"overlay" "mount"; then
			log_error "Unable to overlay mount"
			return 6
		fi
	)
}

uo() {
	(
		if ! cd "overlay"; then
			log_error "Unable to move into overlay directory"
			return 1
		fi
		if ! umount "mount"; then
			log_error "Unable to unmount mount directory"
			return 2
		fi
		if ! rmdir "mount"; then
			log_error "Unable to remove mount directory"
			return 3
		fi
		local directory
		for directory in "upper" "work"; do
			if ! rm --force --recursive "${directory}"; then
				log_error "Unable to remove directory: ${directory}"
				return 4
			fi
		done
		if ! umount "lower"; then
			log_error "Unable to unmount lower directory"
			return 5
		fi
		if ! rmdir "lower"; then
			log_error "Unable to remove lower directory"
			return 6
		fi
	)
	if ! rmdir "overlay"; then
		log_error "Unable to remove overlay directory"
		return 7
	fi
}

mr() {
	local directory
	for directory in "dev" "dev/pts" "proc" "sys"; do
		if ! mount --bind "/${directory}" "overlay/mount/${directory}"; then
			log_error "Unable to bind mount directory: ${directory}"
			return 1
		fi
	done
}

alias cr="\
chroot \
\"overlay/mount\" \
"

alias cru="\
chroot \
--userspec \"1000:1000\" \
\"overlay/mount\" \
"

ur() {
	local f
	for f in "sys" "proc" "dev/pts" "dev"; do
		umount --lazy "overlay/mount/${f}"
	done
}

mm() {
	mount --make-rslave --rbind "/deb" "overlay/mount/deb"
}

um() {
	umount --recursive "overlay/mount/deb"
}

ms() {
	local directory="${1}"
	local file
	local level="${2}"
	if [ -n "${directory}" ]; then
		if mkdir "${directory}"; then
			[ -n "${level}" ] || level="18"
			for file in "vmlinuz" "initrd.img"; do
				cp "overlay/mount/${file}" "${directory}"
			done
			mksquashfs \
				"overlay/mount" "${directory}/filesystem.squashfs" \
				-noappend \
				-comp "zstd" -Xcompression-level "${level}"
			chown --recursive 1000:1000 "${directory}"
		fi
	fi
}