feat(dbus): Add D-Bus interface for managing software services

Introduce `InterfaceSoftwareServices` to handle service enable/disable
actions, status, and availability via D-Bus. Consolidate `avahi` service
configuration into the new interface by removing redundant logic from
`revpi_config.py`.

Signed-off-by: Sven Sager <s.sager@kunbus.com>

src/revpi_middleware/dbus_middleware1/system_config/__init__.py

@@ -3,3 +3,4 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 """D-Bus interfaces for system configuration."""
 from .interface_config import InterfaceRevpiConfig
+from .interface_services import InterfaceSoftwareServices

src/revpi_middleware/dbus_middleware1/system_config/interface_config.py

@@ -9,7 +9,6 @@ from pydbus.generic import signal
 
 from .revpi_config import (
     ConfigActions,
-    configure_avahi_daemon,
     configure_bluetooth,
     configure_con_can,
     configure_dphys_swapfile,
@@ -96,17 +95,7 @@ AVAILABLE_FEATURES = {
     "gui": FeatureFunction(configure_gui, []),
     "revpi-con-can": FeatureFunction(configure_con_can, []),
     "dphys-swapfile": FeatureFunction(configure_dphys_swapfile, []),
-    "pimodbus-master": FeatureFunction(simple_systemd, ["pimodbus-master.service"]),
-    "pimodbus-slave": FeatureFunction(simple_systemd, ["pimodbus-slave.service"]),
-    "systemd-timesyncd": FeatureFunction(simple_systemd, ["systemd-timesyncd.service"]),
-    "ssh": FeatureFunction(simple_systemd, ["ssh.service"]),
-    "nodered": FeatureFunction(simple_systemd, ["nodered.service"]),
-    "noderedrevpinodes-server": FeatureFunction(
-        simple_systemd, ["noderedrevpinodes-server.service"]
-    ),
-    "revpipyload": FeatureFunction(simple_systemd, ["revpipyload.service"]),
     "bluetooth": FeatureFunction(configure_bluetooth, []),
     "wlan": FeatureFunction(configure_wlan, []),
-    "avahi": FeatureFunction(configure_avahi_daemon, []),
     "external-antenna": FeatureFunction(configure_external_antenna, []),
 }

src/revpi_middleware/dbus_middleware1/system_config/interface_services.py

@@ -0,0 +1,205 @@
+# -*- coding: utf-8 -*-
+# SPDX-FileCopyrightText: 2025 KUNBUS GmbH
+# SPDX-License-Identifier: GPL-2.0-or-later
+"""D-Bus interfaces for software services."""
+from logging import getLogger
+from typing import List
+
+from pydbus.generic import signal
+
+from ..dbus_helper import DbusInterface
+from ..systemd_helper import simple_systemd, ServiceActions
+
+log = getLogger(__name__)
+
+
+class InterfaceSoftwareServices(DbusInterface):
+    """
+    <node>
+        <interface name="com.revolutionpi.middleware1.SoftwareServices">
+            <method name="Disable">
+                <arg name="feature" type="s" direction="in"/>
+            </method>
+            <method name="Enable">
+                <arg name="feature" type="s" direction="in"/>
+            </method>
+            <method name="GetStatus">
+                <arg name="feature" type="s" direction="in"/>
+                <arg name="status" type="b" direction="out"/>
+            </method>
+            <method name="GetAvailability">
+                <arg name="feature" type="s" direction="in"/>
+                <arg name="available" type="b" direction="out"/>
+            </method>
+            <property name="available_features" type="as" access="read"/>
+            <signal name="StatusChanged">
+                <arg name="feature" type="s"/>
+                <arg name="status" type="b"/>
+            </signal>
+            <signal name="AvailabilityChanged">
+                <arg name="feature" type="s"/>
+                <arg name="available" type="b"/>
+            </signal>
+        </interface>
+    </node>
+    """
+
+    AvailabilityChanged = signal()
+    StatusChanged = signal()
+
+    def __init__(self, bus):
+        super().__init__(bus)
+
+        self.mrk_available = {}
+        self.mrk_status = {}
+
+        self.services = {
+            "pimodbus-master": ["pimodbus-master.service"],
+            "pimodbus-slave": ["pimodbus-slave.service"],
+            "systemd-timesyncd": ["systemd-timesyncd.service"],
+            "ssh": ["ssh.service"],
+            "nodered": ["nodered.service"],
+            "noderedrevpinodes-server": ["noderedrevpinodes-server.service"],
+            "revpipyload": ["revpipyload.service"],
+            "avahi": ["avahi-daemon.service", "avahi-daemon.socket"],
+        }
+
+        # Create a systemd manager interface object
+        systemd = self.bus.get(
+            "org.freedesktop.systemd1",
+            "/org/freedesktop/systemd1",
+        )
+        systemd_manager = systemd["org.freedesktop.systemd1.Manager"]
+
+        # Load all unit paths and subscribe to properties changed signal
+        self.object_paths = {}
+        for feature in self.services:
+
+            # Get the status and availability of the feature
+            self.mrk_available[feature] = self.GetAvailability(feature)
+            self.mrk_status[feature] = self.GetStatus(feature)
+
+            # Subscribe to properties changed signal for each unit
+            for unit_name in self.services[feature]:
+                unit_path = systemd_manager.LoadUnit(unit_name)
+                self.object_paths[unit_path] = feature
+
+                self.bus.subscribe(
+                    iface="org.freedesktop.DBus.Properties",
+                    signal="PropertiesChanged",
+                    object=unit_path,
+                    signal_fired=self._callback_properties_changed,
+                )
+
+        # Subscribe to the reloading signal to update the availability of the feature
+        self.bus.subscribe(
+            iface="org.freedesktop.systemd1.Manager",
+            signal="Reloading",
+            object="/org/freedesktop/systemd1",
+            signal_fired=self._callback_reloading_signal,
+        )
+
+    def _callback_reloading_signal(self, sender, object_path, interface, signal, parameters):
+        """
+        Handles the signal emitted for reloading and checks for changes in availability
+        and status for a set of services. If changes are identified, corresponding
+        update methods are triggered to reflect the new states.
+
+        Args:
+            sender: The entity sending the signal.
+            object_path: Path to the object emitting the signal.
+            interface: Interface through which the signal is sent.
+            signal: The signal being received.
+            parameters: A list of parameters associated with the signal.
+
+        Raises:
+            None
+        """
+        if parameters[0]:
+            return
+
+        for feature in self.services:
+            availability = self.GetAvailability(feature)
+            if self.mrk_available[feature] != availability:
+                self.mrk_available[feature] = availability
+                self.AvailabilityChanged(feature, availability)
+
+            status = self.GetStatus(feature)
+            if self.mrk_status[feature] != status:
+                self.mrk_status[feature] = status
+                self.StatusChanged(feature, status)
+
+    def _callback_properties_changed(self, sender, object_path, interface, signal, parameters):
+        """
+        Handles the 'PropertiesChanged' signal callback by updating internal status tracking for given
+        features and invoking status change notifications if necessary.
+
+        Args:
+            sender (Any): Information about the signal sender.
+            object_path (str): The path of the object emitting the signal.
+            interface (str): The interface where the signal was emitted.
+            signal (str): The name of the emitted signal.
+            parameters (tuple): Signal parameters containing interface name, changed properties, and
+                invalidated properties.
+
+        Raises:
+            TypeError: If the 'parameters' argument does not unpack to three expected values.
+        """
+        interface, changed_properties, invalidated_properties = parameters
+        if "ActiveState" not in changed_properties:
+            return
+
+        feature = self.object_paths[object_path]
+        status = self.GetStatus(feature)
+        if self.mrk_status[feature] != status:
+            self.mrk_status[feature] = status
+            self.StatusChanged(feature, status)
+
+    def _get_unit_names(self, feature: str) -> List[str]:
+        if feature not in self.services:
+            raise ValueError(f"feature {feature} does not exist")
+        return self.services[feature]
+
+    def Disable(self, feature: str) -> None:
+        """Disable the feature."""
+        action = ServiceActions.DISABLE
+        unit_names = self._get_unit_names(feature)
+
+        for unit_name in unit_names:
+            simple_systemd(action, unit_name)
+
+    def Enable(self, feature: str) -> None:
+        """Enable the feature."""
+        action = ServiceActions.ENABLE
+        unit_names = self._get_unit_names(feature)
+
+        for unit_name in unit_names:
+            simple_systemd(action, unit_name)
+
+    def GetStatus(self, feature: str) -> bool:
+        """Get feature status."""
+        unit_names = self._get_unit_names(feature)
+        rc_status = True
+
+        for unit_name in unit_names:
+            if not simple_systemd(ServiceActions.STATUS, unit_name):
+                rc_status = False
+                break
+
+        return rc_status
+
+    def GetAvailability(self, feature: str) -> bool:
+        """Get feature availability on the RevPi."""
+        unit_names = self._get_unit_names(feature)
+        rc_available = True
+
+        for unit_name in unit_names:
+            if not simple_systemd(ServiceActions.AVAILABLE, unit_name):
+                rc_available = False
+                break
+
+        return rc_available
+
+    @property
+    def available_features(self) -> list[str]:
+        return list(self.services.keys())

src/revpi_middleware/dbus_middleware1/system_config/revpi_config.py

@@ -435,18 +435,6 @@ class ConfigTxt:
         return self._config_txt_path
 
 
-def configure_avahi_daemon(action: ConfigActions):
-    return_value = simple_systemd(action, "avahi-daemon.service")
-
-    # Post actions for avahi-daemon
-    if action in (ConfigActions.ENABLE, ConfigActions.DISABLE):
-        # Apply the enable/disable action to the avahi socket AFTER the service
-        # unit, because a connected socket could interrupt stop
-        simple_systemd(action, "avahi-daemon.socket")
-
-    return return_value
-
-
 def configure_bluetooth(action: ConfigActions):
     hci_device = join(LINUX_BT_CLASS_PATH, "hci0")
     bt_rfkill_index = get_rfkill_index(hci_device)