VILLASnode/packaging/live-iso/ensure_loop.sh

#!/usr/bin/env bash
#
# Ensure that we have at least two usable loop devices inside our Docker container
#
# Source: https://github.com/jpetazzo/dind/issues/19#issuecomment-48859883
# SPDX-FileCopyrightText: 2014-2023 Institute for Automation of Complex Power Systems, RWTH Aachen University
# SPDX-License-Identifier: Apache-2.0

ensure_loop(){
    num="$1"
    dev="/dev/loop$num"
    if test -b "$dev"; then
        echo "$dev is a usable loop device."
        return 0
    fi

    echo "Attempting to create $dev for docker ..."
    if ! mknod -m660 $dev b 7 $num; then
        echo "Failed to create $dev!" 1>&2
        return 3
    fi

    return 0
}

LOOP_A=$(losetup -f)
LOOP_A=${LOOP_A#/dev/loop}
LOOP_B=$(expr $LOOP_A + 1)
LOOP_C=$(expr $LOOP_A + 2)

ensure_loop $LOOP_A
ensure_loop $LOOP_B
ensure_loop $LOOP_C

losetup -la