anchor.diff:    # Wireless won't work in the VM.
     networking.wireless.enable = mkOverride 50 false;
   
  -  system.requiredKernelConfig = with config.lib.kernelConfig; [
  -    (isEnabled "VIRTIO_BLK")
  -    (isEnabled "VIRTIO_PCI")
  -    (isEnabled "VIRTIO_NET")
  -    (isEnabled "EXT3_FS")
  -    (isEnabled "CIFS")
  -    (isYes "BLK_DEV")
  -    (isYes "PCI")
  -    (isYes "EXPERIMENTAL")
  -    (isYes "NETDEVICES")
  -    (isYes "NET_CORE")
  -    (isYes "INET")
  -    (isYes "NETWORK_FILESYSTEMS")
  -  ] ++ optional (!cfg.graphics) [
  -    (isYes "SERIAL_8250_CONSOLE")
  -    (isYes "SERIAL_8250")
  -  ];
  +  system.requiredKernelConfig = with config.lib.kernelConfig;
  +    [ (isEnabled "VIRTIO_BLK")
  +      (isEnabled "VIRTIO_PCI")
  +      (isEnabled "VIRTIO_NET")
  +      (isEnabled "EXT4_FS")
  +      (isEnabled "CIFS")
  +      (isYes "BLK_DEV")
  +      (isYes "PCI")
  +      (isYes "EXPERIMENTAL")
  +      (isYes "NETDEVICES")
  +      (isYes "NET_CORE")
  +      (isYes "INET")
  +      (isYes "NETWORK_FILESYSTEMS")
  +    ] ++ optional (!cfg.graphics) [
  +      (isYes "SERIAL_8250_CONSOLE")
  +      (isYes "SERIAL_8250")
  +    ];
   }
  
positive.code:     ] ++ optional cfg.useBootLoader
        { mountPoint = "/boot";
          device = "/dev/disk/by-label/boot";
          fsType = "ext3";
          options = "ro";
          noCheck = true; # fsck fails on a r/o filesystem
        });
  
negative.code:       # initialise.
        FSTYPE=$(blkid -o value -s TYPE /dev/vda || true)
        if test -z "$FSTYPE"; then
            mke2fs -t ext4 /dev/vda
        fi
      '';
  
  