overlay copy-on-write of overlay copy-on-write out of order

cow_cow_out-of-order.sh

#!/bin/bash

set -o errexit

main() {
        case $1 in
        run)
                prepare_fs

                empty
                cow_cow  # hehe
                cow
                ;;
        clean)
                clean
                ;;
        *)
                echo "Usage: $0 (run|clean)"
                exit 1
                ;;
        esac
}

prepare_fs () {
        mkdir -p empty
        mkdir -p cow/{upper,work,merged}
        mkdir -p cow_cow/{upper,work,merged}
}

empty() {
        echo "empty" > empty/file
}

cow() {
        sudo mount -t overlay \
                cow \
                -o lowerdir=./empty,upperdir=./cow/upper,workdir=./cow/work \
                ./cow/merged
}

cow_cow() {
        sudo mount -t overlay \
                cow_cow \
                -o lowerdir=./cow/merged,upperdir=./cow_cow/upper,workdir=./cow_cow/work \
                ./cow_cow/merged
}

clean() {
        sudo umount ./cow/merged
        sudo umount ./cow_cow/merged
        sudo rm -rf ./{cow,cow_cow,empty}
}

main "$@"