anchor.diff:          type = types.bool;
           example = "true";
           description = ''
  -          Run smartd from the smartmontools package.
  +          Run smartd from the smartmontools package. Note that e-mail
  +          notifications will not be enabled unless you configure the list of
  +          devices with <varname>services.smartd.devices</varname> as well.
           '';
         };
   
  +      devices = mkOption {
  +        default = [];
  +        example = ["/dev/sda" "/dev/sdb"];
  +        description = ''
  +          List of devices to monitor. By default -- if this list is empty --,
  +          smartd will monitor all devices connected to the machine at the time
  +          it's being run. Configuring this option has the added benefit of
  +          enabling e-mail notifications to "root" every time smartd detects an
  +          error.
  +        '';
  +       };
       };
   
     };
  
positive.code: 
          daemonType = "daemon";
  
          exec = "${pkgs.smartmontools}/sbin/smartd";
        };
  
    };
  
negative.code: let
  
    cfg = config.services.smartd;
  
    smartdMail = pkgs.writeScript "smartdmail.sh" ''
      #! /bin/sh
      TMPNAM=/tmp/smartd-message.$$.tmp
      if test -n "$SMARTD_ADDRESS"; then
        echo  >"$TMPNAM" "From: smartd <root>"
        echo >>"$TMPNAM" 'To: undisclosed-recipients:;'
        echo >>"$TMPNAM" "Subject: $SMARTD_SUBJECT"
        echo >>"$TMPNAM"
        echo >>"$TMPNAM" "Failure on $SMARTD_DEVICESTRING: $SMARTD_FAILTYPE"
        echo >>"$TMPNAM"
        cat  >>"$TMPNAM"
        ${pkgs.smartmontools}/sbin/smartctl >>"$TMPNAM" -a -d "$SMARTD_DEVICETYPE" "$SMARTD_DEVICE"
        /var/setuid-wrappers/sendmail  <"$TMPNAM" -f "$SENDER" -i "$SMARTD_ADDRESS"
      fi
    '';
  
    smartdConf = pkgs.writeText "smartd.conf" (concatMapStrings (device:
      ''
        ${device} -m root -M exec ${smartdMail}
      ''
      ) cfg.devices);
  
    smartdFlags = if (cfg.devices == []) then "" else "--configfile=${smartdConf}";
  
  in
  
  