anchor.diff:  
     fileSystems."/".device = "/dev/disk/by-label/nixos";
   
  -  boot.initrd.kernelModules = [ "xen-blkfront" "aufs" ];
  +  boot.initrd.kernelModules = [ "xen-blkfront" ];
     boot.kernelModules = [ "xen-netfront" ];
  -
  -  boot.extraModulePackages = [ config.boot.kernelPackages.aufs ];
   
     # Generate a GRUB menu.  Amazon's pv-grub uses this to boot our kernel/initrd.
     boot.loader.grub.device = "nodev";
  
positive.code:               diskNr=$((diskNr + 1))
                echo "mounting $device on $mp..."
                if mountFS "$device" "$mp" "" ext3; then
                    if [ -z "$diskForAufs" ]; then diskForAufs="$mp"; fi
                fi
            else
                echo "skipping unknown device type $device"
            fi
        done
  
        if [ -n "$diskForAufs" ]; then
            mkdir -m 755 -p $targetRoot/$diskForAufs/root
  
            mkdir -m 1777 -p $targetRoot/$diskForAufs/root/tmp $targetRoot/tmp
            mount --bind $targetRoot/$diskForAufs/root/tmp $targetRoot/tmp
  
            if [ ! -e $targetRoot/.ebs ]; then
                mkdir -m 755 -p $targetRoot/$diskForAufs/root/var $targetRoot/var
                mount --bind $targetRoot/$diskForAufs/root/var $targetRoot/var
  
                mkdir -m 755 -p $targetRoot/$diskForAufs/root/nix
                mount -t aufs -o dirs=$targetRoot/$diskForAufs/root/nix=rw:$targetRoot/nix=rr none $targetRoot/nix
            fi
        fi
      '';
  
negative.code:   # while "m1.large" has two ephemeral filesystems and no swap
    # devices).  Also, put /tmp and /var on /disk0, since it has a lot
    # more space than the root device.  Similarly, "move" /nix to /disk0
    # by layering a unionfs-fuse mount on top of it so we have a lot more space for
    # Nix operations.
    boot.initrd.postMountCommands =
      ''
        diskNr=0
        diskForUnionfs=
        for device in /dev/xvd[abcde]*; do
            if [ "$device" = /dev/xvda -o "$device" = /dev/xvda1 ]; then continue; fi
            fsType=$(blkid -o value -s TYPE "$device" || true)
  