A bash script to quickly unmount my layered external block device

ext1_handler.sh

#!/bin/bash
# A script to quickly unmount an external USB drive I have that I am using
# multiple block device layers with, like bcache, lvm, luks, etc.
# Assumptions here are that the aforementioned relevant crypttab and fstab
# entries are present. If they are, systemd should take care of the rest.
# If it works correctly, the last thing the mounting command should do is
# ask you for the unlocking password.
#
#  Author: Michael Goodwin
#  Date: 2017-10-10
#
BTRFS_LUKS=/dev/mapper/luks-btrfs_backup
BCACHE_DEV=bcache0
LVM_VG=ext1
SCRIPT_NAME=$0

__usage() {
        cat <<-EOF

                Usage:
                  - Unmount: $SCRIPT_NAME -u
                  - Mount:   $SCRIPT_NAME -m

EOF
}

__umount() {
        sudo -s \
        LVM_VG="${LVM_VG}" \
        BTRFS_LUKS="${BTRFS_LUKS}" \
        BCACHE_DEV="${BCACHE_DEV}" \
        <<-'EOF'
        mountpoint -qx "${BTRFS_LUKS}" >/dev/null 2>&1 || { echo "Not mounted!"; exit 1; }
        umount -l "${BTRFS_LUKS}" \
        && cryptsetup close "${BTRFS_LUKS}" \
        && vgchange -an "${LVM_VG}" \
        && echo 1 > "/sys/block/${BCACHE_DEV}/bcache/stop"
EOF
}

__mount() {
        # In this instance, simply activating the bcache devices
        # triggers systemd/udev to do everything else, we just
        # need to supply the password to cryptsetup through tty-ask-password
        sudo BCACHE_DEV="${BCACHE_DEV}" -s <<-'EOF'
        readarray -t devs < <(find /dev -type b -name "sd*")
        for ((i=0;i<${#devs[@]};i++)); do
                echo "${devs[i]}" > "/sys/fs/bcache/register_quiet"
        done
        sleep 2
        systemd-tty-ask-password-agent --query
EOF
}

while getopts "hum" opt; do
        case $opt in
                m) __mount ;;
                u) __umount ;;
                *) __usage ;;
        esac
done