anchor.diff:  
       jobs.swap =
         { task = true;
  -        
  +
           startOn = ["startup" "new-devices"];
   
           script =
             ''
  +            unused="$(sed '1d; s/ .*//' /proc/swaps)"
  +
               ${toString (map (x: x.command) config.swapDevices)}
   
  -            # Remove swap devices not listed in swapDevices.
  -            for used in $(cat /proc/swaps | grep '^/' | sed 's/ .*//'); do
  -                found=
  -                for device in $swapDevices; do
  -                    device=$(readlink -f $device)
  -                    if test "$used" = "$device"; then found=1; fi
  -                done
  -                if test -z "$found"; then
  -                    ${utillinux}/sbin/swapoff "$used" || true
  -                fi
  -            done
  +            # Remove remaining swap devices.
  +            test -n "$unused" && ${utillinux}/sbin/swapoff $unused || true
             '';
         };
   
  
positive.code:     };
  
    };
    
  
    ###### implementation
  
  
negative.code:             example = true;
              type = types.bool;
              description = "
                Cipher the swap device to protect swapped data.  This option
                does not work with labels.
              ";
            };
  
  