Create a big raw file that can be treated as a disk

fs.sh

fs=ext4

function create {
  fallocate -L $1 "$fs"
  mount
  dev=$(cat "$fs.lock")
  mkfs -t ext4 $dev
  fsck -t ext4 $dev
  umount
}

function grow {
  dd if=/dev/zero of="$fs" iflag=count_bytes oflag=append conv=notrunc bs=4K count=$1
  e2fsck -f "$fs"
  resize2fs "$fs"
  e2fsck -f "$fs"
}

function mount {
  if [ ! -f "$fs.lock" ]; then
    sudo losetup -f --show "$fs" > "$fs.lock";
  else
    echo "Already mounted or $fs.lock exists.";
  fi
}

function umount {
  if [ -f "$fs.lock" ]; then
    sudo losetup -d $(cat "$fs.lock");
    sudo rm "$fs.lock";
  else
    echo "$fs doesn't seem to be mounted.";
  fi
}