hdparm_is_on_battery() {
    on_ac_power 2>/dev/null
    [ $? -eq 1 ]
}

hdparm_set_option()
{
  local NEW_OPT= NEW_DEF=
  if test -n "$DISC"; then
    for i in $OPTIONS; do
      if test x${i%${i#??}} != x${1%${1#??}}; then
        NEW_OPT="$NEW_OPT $i"
      else
        NEW_OPT=${NEW_OPT%-q}
      fi
    done
    OPTIONS="$NEW_OPT $OPT_QUIET $1"
  else
    for i in $DEFAULT; do
      if test x${i%${i#??}} != x${1%${1#??}}; then
        NEW_DEF="$NEW_DEF $i"
      else
        NEW_DEF=${NEW_DEF%-q}
      fi
    done
    DEFAULT="$NEW_DEF $DEF_QUIET $1"
  fi
}

hdparm_eval_value()
{
  case $1 in
    off|0)
      hdparm_set_option "$2"0
       ;;
    on|1)
      hdparm_set_option "$2"1
      ;;
    *)
      log_failure_msg "Unknown Value for $2: $1"
      exit 1
      ;;
  esac
}

# It isn't safe to set an APM policy by default on Firewire or USB devices.
# See https://bugs.launchpad.net/bugs/515023.
hdparm_try_apm()
{
    # set our default global apm policy here.
    if [ -z "$ID_PATH" ]; then
        local ID_PATH="$(udevadm info -n "$1" -q property 2>/dev/null | sed -n 's/^ID_PATH=//p')" || true
    fi
    case $ID_PATH in
        pci-*-ieee1394-*|pci-*-usb-*)
            return 1
            ;;
    esac

    # Only activate APM on disks that support it.
    if [ -z "$ID_ATA_FEATURE_SET_APM" ]; then
        local ID_ATA_FEATURE_SET_APM="$(udevadm info -n "$1" -q property 2>/dev/null | sed -n 's/^ID_ATA_FEATURE_SET_APM=//p')" || true
    fi
    if [ "$ID_ATA_FEATURE_SET_APM" = "1" ]; then
        return 0
    fi
    return 1
}

# parse /etc/hdparm.conf and spit out a list of options for the specified
# disk, taking into account global settings in /etc/hdparm.conf, current AC
# power status, and (as a fallback) the default apm settings on Ubuntu.
# arguments: device_name
# returns 0 on success, 1 on failure.
# options to be passed to hdparm are returned on stdout.
hdparm_options()
{
    local WANTED_DISK="$1"

    local DISC= DEFAULT= DEF_QUIET= COMMAND_LINE=
    # if the below is guaranteed to spawn a subshell, then this next line is
    # unnecessary
    local OPTIONS OPT_QUIET KEY SEP VALUE

    egrep -v '^[[:space:]]*(#|$)' /etc/hdparm.conf |
    {
        # set our default global apm policy here.
        if hdparm_try_apm "$WANTED_DISK"; then
            if hdparm_is_on_battery; then
                hdparm_set_option -B128
        # set a spindown time of 3 minutes by default so the disk isn't
        # constantly power cycling on a busy machine if spindown is
        # enabled
        hdparm_set_option -S36
            else
                hdparm_set_option -B254
            fi
        fi

        while read KEY SEP VALUE; do
            case $SEP in
                '{')
                    case $KEY in
                        command_line)
                            unset DISC
                            unset OPTIONS
                            unset OPT_QUIET
                            COMMAND_LINE=1
                            ;;
                        *)
                            if [ -h "$KEY" ]
                            then
                                DISC=$(readlink -m "$KEY")
                                DISC=${DISC%%[[:digit:]]*}
                            else
                                DISC=$KEY
                            fi
                            OPTIONS=$DEFAULT
                            OPT_QUIET=$DEF_QUIET
                            ;;
                    esac
                    ;;
                =)
                    case $KEY in
                         read_ahead_sect)
                             hdparm_set_option -a$VALUE
                            ;;
                        lookahead)
                            hdparm_eval_value $VALUE -A
                            ;;
                        bus)
                            hdparm_eval_value $VALUE -b
                            ;;
                        apm)
                            if ! hdparm_is_on_battery; then
                                hdparm_set_option -B$VALUE
                            fi
                            ;;
                        apm_battery)
                            if hdparm_is_on_battery; then
                                hdparm_set_option -B$VALUE
                            fi
                            ;;
                        io32_support)
                            hdparm_set_option -c$VALUE
                            ;;
                        dma)
                            hdparm_eval_value $VALUE -d
                            ;;
                        defect_mana)
                            hdparm_eval_value $VALUE -D
                            ;;
                        cd_speed)
                            hdparm_set_option -E$VALUE
                            ;;
                        mult_sect_io)
                            hdparm_set_option -m$VALUE
                            ;;
                        prefetch_sect)
                            hdparm_set_option -P$VALUE
                            ;;
                        read_only)
                            hdparm_eval_value $VALUE -r
                            ;;
                        write_read_verify)
                            hdparm_eval_value $VALUE -R
                            ;;
                        spindown_time)
                            hdparm_set_option -S$VALUE
                            ;;
                        force_spindown_time)
                            hdparm_set_option force_spindown_time$VALUE
                            ;;
                        poweron_standby)
                            hdparm_eval_value $VALUE -s
                            ;;
                        interrupt_unmask)
                            hdparm_eval_value $VALUE -u
                            ;;
                        write_cache)
                            hdparm_eval_value $VALUE -W
                            ;;
                        transfer_mode)
                            hdparm_set_option -X$VALUE
                            ;;
                        acoustic_management)
                            hdparm_set_option -M$VALUE
                            ;;
                        keep_settings_over_reset)
                            hdparm_eval_value $VALUE -k
                            ;;
                        keep_features_over_reset)
                            hdparm_eval_value $VALUE -K
                            ;;
                        chipset_pio_mode)
                            hdparm_set_option -p$VALUE
                            ;;
                        security_unlock)
                            hdparm_set_option --security-unlock $VALUE
                            ;;
                        security_pass)
                            hdparm_set_option --security-set-pass $VALUE
                            ;;
                        security_disable)
                            hdparm_set_option --security-disable $VALUE
                            ;;
                        user-master)
                            hdparm_set_option --user-master $VALUE
                            ;;
                        security_mode)
                            hdparm_set_option --security-mode $VALUE
                            ;;
                        ROOTFS)
                            ;;
                        *)
                            echo "Unknown option $KEY"
                            exit 1
                            ;;
                    esac
                    ;;
                "")
                    case $KEY in
                        '}')
                            if [ -z "$DISC" ] && [ -z "$COMMAND_LINE" ]; then
                                echo "No disk enabled. Exiting" >&2
                                return 1
                            fi
                            if [ -n "$OPTIONS" ] && [ "$DISC" = "$WANTED_DISK" ]
                            then
                                echo $OPTIONS
                                return 0
                            fi
                            COMMAND_LINE=
                            ;;
                        quiet)
                            if [ -n "$DISC" ]; then
                                OPT_QUIET=-q
                            else
                                DEF_QUIET=-q
                            fi
                            ;;
                        standby)
                            hdparm_set_option -y
                            ;;
                        sleep)
                            hdparm_set_option -Y
                            ;;
                        disable_seagate)
                            hdparm_set_option -Z
                            ;;
                        security_freeze)
                            hdparm_set_option --security-freeze
                            ;;
                        *)
                            if [ -z "$COMMAND_LINE" ]; then
                                echo "unknown option $KEY" >&2
                                return 1
                            fi
                            ;;
                    esac
                    ;;
                *)
                    if [ -z "$COMMAND_LINE" ]; then
                        echo "unknown separator $SEP" >&2
                        return 1
                    fi
                    ;;
            esac
        done
        # parsed the whole file and didn't find the disk,
        # so try the default instead.
        if [ -n "$DEFAULT" ]; then
            echo $DEFAULT
            return 0
        fi
    }
}