#!/bin/bash
# Temperature-aware IPMI fan control for Dell PowerEdge / iDRAC.
#
# Holds the fans at a fixed low duty while the CPUs are cool, and hands control
# back to the BMC's automatic curve once they get hot, so there is still a
# thermal response under load. This is the native equivalent of the
# tigerblue77/dell_idrac_fan_controller container, without needing Docker.
#
# Run under ipmi-fancontrol.service. Configuration lives in
# conf/ipmi-fancontrol.conf (see conf/ipmi-fancontrol.conf.example).

set -uo pipefail

SCRIPT_DIR=$(CDPATH= cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)
CONFIG=${IPMI_FANCONTROL_CONFIG:-$SCRIPT_DIR/conf/ipmi-fancontrol.conf}

if [[ ! -r "$CONFIG" ]]; then
    echo "Error: cannot read $CONFIG" >&2
    echo "Copy conf/ipmi-fancontrol.conf.example there and fill it in." >&2
    exit 1
fi

# shellcheck source=/dev/null
. "$CONFIG"

: "${IPMI_INTERFACE:=open}"
: "${FAN_SPEED:=0x15}"
: "${CPU_TEMP_THRESHOLD:=70}"
: "${CPU_TEMP_HYSTERESIS:=5}"
: "${CHECK_INTERVAL:=60}"
: "${DISABLE_THIRD_PARTY_PCIE_COOLING_RESPONSE:=false}"

RESUME_AT=$((CPU_TEMP_THRESHOLD - CPU_TEMP_HYSTERESIS))

# Build the ipmitool invocation once. The local "open" interface needs no
# credentials and no network, so it is the better choice for a polling loop;
# lanplus stays available for reaching a BMC over the network.
if [[ "$IPMI_INTERFACE" == "lanplus" ]]; then
    : "${IPMI_HOST:?not set in $CONFIG}"
    : "${IPMI_USER:?not set in $CONFIG}"
    : "${IPMI_PASSWORD:?not set in $CONFIG}"
    export IPMI_PASSWORD
    IPMITOOL=(ipmitool -I lanplus -H "$IPMI_HOST" -U "$IPMI_USER" -E)
else
    IPMITOOL=(ipmitool -I open)
fi

# stdout goes to the journal under systemd.
log() { echo "$*"; }

set_manual() {
    "${IPMITOOL[@]}" raw 0x30 0x30 0x01 0x00 >/dev/null &&
        "${IPMITOOL[@]}" raw 0x30 0x30 0x02 0xff "$FAN_SPEED" >/dev/null
}

set_auto() {
    "${IPMITOOL[@]}" raw 0x30 0x30 0x01 0x01 >/dev/null
}

# Highest CPU temperature in degrees C, or empty if none could be read.
# CPU sensors are entity 3.x; 7.x is the system board (inlet/exhaust).
max_cpu_temp() {
    "${IPMITOOL[@]}" sdr type temperature 2>/dev/null | awk -F'|' '
        $4 ~ /^[[:space:]]*3\./ {
            if (match($5, /-?[0-9]+/)) {
                t = substr($5, RSTART, RLENGTH) + 0
                if (!seen || t > max) max = t
                seen = 1
            }
        }
        END { if (seen) print max }
    '
}

MODE=""

cleanup() {
    log "Stopping: returning fan control to the BMC automatic curve."
    set_auto || log "Warning: failed to restore automatic fan control."
    exit 0
}
trap cleanup TERM INT

if [[ "$DISABLE_THIRD_PARTY_PCIE_COOLING_RESPONSE" == "true" ]]; then
    if "${IPMITOOL[@]}" raw 0x30 0xce 0x00 0x16 0x05 0x00 0x00 0x00 0x05 0x00 0x01 0x00 0x00 >/dev/null 2>&1; then
        log "Disabled the third-party PCIe card default cooling response."
    else
        log "Warning: could not disable the third-party PCIe cooling response."
    fi
fi

log "Starting: fans held at $FAN_SPEED below ${CPU_TEMP_THRESHOLD}C, automatic at or above it, re-engaging at ${RESUME_AT}C. Polling every ${CHECK_INTERVAL}s over $IPMI_INTERFACE."

while true; do
    temp=$(max_cpu_temp)

    if [[ -z "$temp" ]]; then
        # Fail safe: if the temperature cannot be read, let the BMC cool the box.
        if [[ "$MODE" != "auto" ]]; then
            log "Cannot read CPU temperature; failing safe to automatic fan control."
            set_auto && MODE="auto"
        fi
    elif (( temp >= CPU_TEMP_THRESHOLD )); then
        if [[ "$MODE" != "auto" ]]; then
            log "CPU at ${temp}C, at or above ${CPU_TEMP_THRESHOLD}C: handing control to the BMC automatic curve."
            set_auto && MODE="auto"
        fi
    elif [[ -z "$MODE" ]] || (( temp <= RESUME_AT )); then
        # The -z test makes the very first pass decide rather than drift, even
        # if we start up inside the hysteresis band.
        if [[ "$MODE" != "manual" ]]; then
            log "CPU at ${temp}C, at or below ${RESUME_AT}C: holding fans at $FAN_SPEED."
            set_manual && MODE="manual"
        fi
    fi
    # Inside the hysteresis band we deliberately keep whatever mode we are in.

    # Backgrounded so that SIGTERM interrupts the wait instead of being deferred
    # until the sleep finishes.
    sleep "$CHECK_INTERVAL" &
    wait $!
done