nixpkgs/nixos/tests/overlayfs.nix

import ./make-test-python.nix ({ pkgs, ... }: {
  name = "overlayfs";
  meta.maintainers = with pkgs.stdenv.lib.maintainers; [ bachp ];

  machine = { pkgs, ... }: {
    virtualisation.emptyDiskImages = [ 512 ];
    networking.hostId = "deadbeef";
    environment.systemPackages = with pkgs; [ parted ];
  };

  testScript = ''
    machine.succeed("ls /dev")

    machine.succeed("mkdir -p /tmp/mnt")

    # Test ext4 + overlayfs
    machine.succeed(
        """
          mkfs.ext4 -F -L overlay-ext4 /dev/vdb
          mount -t ext4 /dev/vdb /tmp/mnt
          mkdir -p /tmp/mnt/upper /tmp/mnt/lower /tmp/mnt/work /tmp/mnt/merged
          # Setup some existing files
          echo 'Replace' > /tmp/mnt/lower/replace.txt
          echo 'Append' > /tmp/mnt/lower/append.txt
          echo 'Overwrite' > /tmp/mnt/lower/overwrite.txt
          mount -t overlay overlay -o lowerdir=/tmp/mnt/lower,upperdir=/tmp/mnt/upper,workdir=/tmp/mnt/work /tmp/mnt/merged
          # Test new
          echo 'New' > /tmp/mnt/merged/new.txt
          [[ "\$(cat /tmp/mnt/merged/new.txt)" == "New" ]]
          # Test replace
          [[ "\$(cat /tmp/mnt/merged/replace.txt)" == "Replace" ]]
          echo 'Replaced' > /tmp/mnt/merged/replace-tmp.txt
          mv /tmp/mnt/merged/replace-tmp.txt /tmp/mnt/merged/replace.txt
          [[ "\$(cat /tmp/mnt/merged/replace.txt)" == "Replaced" ]]
          # Overwrite
          [[ "\$(cat /tmp/mnt/merged/overwrite.txt)" == "Overwrite" ]]
          echo 'Overwritten' > /tmp/mnt/merged/overwrite.txt
          [[ "\$(cat /tmp/mnt/merged/overwrite.txt)" == "Overwritten" ]]
          # Test append
          [[ "\$(cat /tmp/mnt/merged/append.txt)" == "Append" ]]
          echo 'ed' >> /tmp/mnt/merged/append.txt
          #"cat /tmp/mnt/merged/append.txt && exit 1
          [[ "\$(cat /tmp/mnt/merged/append.txt)" == "Append\ned" ]]
          umount /tmp/mnt/merged
          umount /tmp/mnt
          udevadm settle
      """
    )
  '';
})