Expose live bcachefs options as Home Assistant MQTT switches

.gitignore

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+.venv/
+__pycache__/
+kent-report-*/

bcachefs_mqtt.py

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+#!/usr/bin/env python3
+"""Expose two live bcachefs options through Home Assistant MQTT discovery."""
+import json
+import logging
+import os
+from pathlib import Path
+import signal
+import socket
+import threading
+import uuid as uuid_module
+
+import paho.mqtt.client as mqtt
+
+OPTIONS = {"reconcile_enabled": "Reconcile", "copygc_enabled": "Copy GC"}
+
+
+class Bridge:
+    def __init__(self, client, uuid, sysfs=Path('/sys/fs/bcachefs'), discovery='homeassistant'):
+        self.client = client
+        self.uuid = str(uuid_module.UUID(uuid))
+        self.options = Path(sysfs) / self.uuid / 'options'
+        self.base = f'bcachefs/{self.uuid}'
+        self.discovery = discovery
+        self.lock = threading.RLock()
+        self.last = {}
+        client.on_connect = self.on_connect
+        client.on_message = self.on_message
+        client.will_set(f'{self.base}/availability', 'offline', qos=1, retain=True)
+
+    def publish(self, topic, payload):
+        return self.client.publish(topic, payload, qos=1, retain=True)
+
+    def announce(self):
+        for option, name in OPTIONS.items():
+            topic = f'{self.base}/{option}'
+            config = {
+                'name': name, 'unique_id': f'bcachefs_{self.uuid}_{option}',
+                'default_entity_id': f'switch.bcachefs_{option}',
+                'command_topic': f'{topic}/set', 'state_topic': f'{topic}/state',
+                'payload_on': '1', 'payload_off': '0', 'optimistic': False,
+                'qos': 1, 'retain': False,
+                'availability_mode': 'all',
+                'availability': [{'topic': f'{self.base}/availability'},
+                                 {'topic': f'{topic}/availability'}],
+                'device': {'identifiers': [f'bcachefs_{self.uuid}'],
+                           'name': f'Bcachefs {socket.gethostname()}',
+                           'manufacturer': 'bcachefs', 'model': 'Filesystem options'},
+            }
+            self.publish(f'{self.discovery}/switch/bcachefs_{self.uuid}/{option}/config', json.dumps(config))
+
+    def sample(self, force=False):
+        with self.lock:
+            for option in OPTIONS:
+                topic = f'{self.base}/{option}'
+                try:
+                    value = (self.options / option).read_text().strip()
+                    if value not in ('0', '1'):
+                        raise ValueError(f'Unexpected option value: {value!r}')
+                except (OSError, ValueError):
+                    value = None
+                if force or option not in self.last or self.last[option] != value:
+                    if value is not None:
+                        self.publish(f'{topic}/state', value)
+                    self.publish(f'{topic}/availability', 'online' if value is not None else 'offline')
+                    self.last[option] = value
+
+    def on_connect(self, client, userdata, flags, reason_code, properties):
+        if reason_code.is_failure:
+            logging.error('MQTT connection refused: %s', reason_code)
+            return
+        with self.lock:
+            self.publish(f'{self.base}/availability', 'offline')
+            self.announce()
+            for option in OPTIONS:
+                client.subscribe(f'{self.base}/{option}/set', qos=1)
+            client.subscribe(f'{self.discovery}/status', qos=1)
+            self.sample(force=True)
+            self.publish(f'{self.base}/availability', 'online')
+        logging.info('Connected; discovery and live states published')
+
+    def on_message(self, client, userdata, message):
+        with self.lock:
+            if message.topic == f'{self.discovery}/status':
+                if message.payload == b'online':
+                    self.announce()
+                    self.sample(force=True)
+                return
+            option = next((name for name in OPTIONS if message.topic == f'{self.base}/{name}/set'), None)
+            if option is None or message.retain or message.payload not in (b'0', b'1'):
+                logging.warning('Ignoring invalid or retained command on %s', message.topic)
+                return
+            try:
+                # Never create a file if the filesystem disappeared between polling and the command.
+                fd = os.open(self.options / option, os.O_WRONLY | os.O_CLOEXEC | os.O_NOFOLLOW)
+                with os.fdopen(fd, 'wb') as target:
+                    target.write(message.payload + b'\n')
+                logging.info('Applied %s=%s', option, message.payload.decode())
+            except OSError as error:
+                logging.error('Could not set %s: %s', option, error)
+            self.sample(force=True)
+
+
+def main():
+    logging.basicConfig(level=logging.INFO, format='%(levelname)s %(message)s')
+    uuid = os.environ['BCACHEFS_UUID']
+    interval = float(os.environ.get('POLL_INTERVAL', '2'))
+    if interval <= 0:
+        raise ValueError('POLL_INTERVAL must be positive')
+    client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2, client_id=f'bcachefs-{uuid}', clean_session=True)
+    bridge = Bridge(client, uuid, discovery=os.environ.get('MQTT_DISCOVERY_PREFIX', 'homeassistant'))
+    if os.environ.get('MQTT_USERNAME'):
+        client.username_pw_set(os.environ['MQTT_USERNAME'], os.environ.get('MQTT_PASSWORD'))
+    if os.environ.get('MQTT_CA_FILE'):
+        client.tls_set(ca_certs=os.environ['MQTT_CA_FILE'])
+    client.reconnect_delay_set(min_delay=1, max_delay=30)
+    stopped = threading.Event()
+    for sig in (signal.SIGINT, signal.SIGTERM):
+        signal.signal(sig, lambda *_: stopped.set())
+    client.connect_async(os.environ['MQTT_HOST'], int(os.environ.get('MQTT_PORT', '1883')), keepalive=15)
+    client.loop_start()
+    try:
+        while not stopped.wait(interval):
+            if client.is_connected():
+                bridge.sample()
+    finally:
+        if client.is_connected():
+            bridge.publish(f'{bridge.base}/availability', 'offline').wait_for_publish(timeout=3)
+        client.disconnect()
+        client.loop_stop()
+
+
+if __name__ == '__main__':
+    main()

install-mqtt.sh

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+#!/bin/bash
+set -euo pipefail
+repo=$(dirname -- "$(readlink -f -- "${BASH_SOURCE[0]}")")
+[[ $EUID == 0 ]] || { echo 'Run with sudo after preparing .venv (see README).' >&2; exit 1; }
+[[ $repo != *[[:space:]]* ]] || { echo 'Checkout path must not contain whitespace.' >&2; exit 1; }
+"$repo/.venv/bin/python" -c 'import paho.mqtt.client'
+if [[ ! -e /etc/default/bcachefs-mqtt ]]; then
+    install -m 600 "$repo/systemd/bcachefs-mqtt.env.example" /etc/default/bcachefs-mqtt
+fi
+sed "s|@REPO@|$repo|g" "$repo/systemd/bcachefs-mqtt.service.in" > /etc/systemd/system/bcachefs-mqtt.service
+systemctl daemon-reload
+systemctl enable bcachefs-mqtt.service
+systemctl restart bcachefs-mqtt.service

requirements-mqtt.txt

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+paho-mqtt==2.1.0

systemd/bcachefs-mqtt.env.example

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+MQTT_HOST=192.168.0.11
+MQTT_PORT=1883
+BCACHEFS_UUID=3d3a0763-4dfe-41e6-93c1-8c791ec98176
+POLL_INTERVAL=2
+# MQTT_USERNAME=
+# MQTT_PASSWORD=
+# MQTT_CA_FILE=/path/to/ca.pem
+# MQTT_DISCOVERY_PREFIX=homeassistant

systemd/bcachefs-mqtt.service.in

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+[Unit]
+Description=Bcachefs Home Assistant MQTT switches
+Wants=network-online.target
+After=network-online.target
+
+[Service]
+Type=simple
+User=root
+EnvironmentFile=/etc/default/bcachefs-mqtt
+Environment=PYTHONDONTWRITEBYTECODE=1
+ExecStart=@REPO@/.venv/bin/python @REPO@/bcachefs_mqtt.py
+Restart=always
+RestartSec=5
+TimeoutStopSec=10
+NoNewPrivileges=yes
+ProtectSystem=strict
+ProtectHome=read-only
+ReadWritePaths=-/sys/fs/bcachefs
+PrivateTmp=yes
+UMask=0077
+
+[Install]
+WantedBy=multi-user.target