feat(dbus): Add D-Bus interface for system configuration in middleware

Introduced `InterfaceRevpiConfig` to manage feature actions like
enable/disable, status, and availability using D-Bus. Includes support
for predefined features with systemd integration and exception handling
for unsupported features.

src/revpi_middleware/dbus_middleware1/system_config/__init__.py

@@ -0,0 +1,5 @@
+# -*- coding: utf-8 -*-
+# SPDX-FileCopyrightText: 2025 KUNBUS GmbH
+# SPDX-License-Identifier: GPL-2.0-or-later
+"""D-Bus interfaces for system configuration."""
+from .interface_config import InterfaceRevpiConfig

src/revpi_middleware/dbus_middleware1/system_config/interface_config.py

@@ -0,0 +1,137 @@
+# -*- coding: utf-8 -*-
+# SPDX-FileCopyrightText: 2025 KUNBUS GmbH
+# SPDX-License-Identifier: GPL-2.0-or-later
+"""D-Bus interfaces for hardware configuration."""
+from collections import namedtuple
+from enum import Enum
+from logging import getLogger
+
+from pydbus import SystemBus
+
+from ..dbus_helper import DbusInterface
+
+log = getLogger(__name__)
+
+FeatureFunction = namedtuple("FeatureFunction", ["function", "args"])
+
+
+class ConfigActions(Enum):
+    ENABLE = "enable"
+    DISABLE = "disable"
+    STATUS = "status"
+    AVAILABLE = "available"
+
+
+class InterfaceRevpiConfig(DbusInterface):
+    """
+    <node>
+        <interface name="com.revolutionpi.middleware1.RevpiConfig">
+            <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"/>
+        </interface>
+    </node>
+    """
+
+    def Disable(self, feature: str) -> None:
+        """Disable the feature."""
+        feature_function = get_feature(feature)
+        feature_function.function(ConfigActions.DISABLE, *feature_function.args)
+
+    def Enable(self, feature: str) -> None:
+        """Enable the feature."""
+        feature_function = get_feature(feature)
+        feature_function.function(ConfigActions.ENABLE, *feature_function.args)
+
+    def GetStatus(self, feature: str) -> bool:
+        """Get feature status."""
+        feature_function = get_feature(feature)
+        return feature_function.function(ConfigActions.STATUS, *feature_function.args)
+
+    def GetAvailability(self, feature: str) -> bool:
+        """Get feature availability on the RevPi."""
+        feature_function = get_feature(feature)
+        return feature_function.function(ConfigActions.AVAILABLE, *feature_function.args)
+
+    @property
+    def available_features(self) -> list[str]:
+        return list(AVAILABLE_FEATURES.keys())
+
+
+def get_feature(feature: str) -> FeatureFunction:
+    if feature not in AVAILABLE_FEATURES:
+        raise ValueError(f"feature {feature} does not exist")
+    feature_function = AVAILABLE_FEATURES[feature]
+    if not feature_function:
+        raise NotImplementedError(f"feature {feature} is not implemented")
+    return feature_function
+
+
+def simple_systemd(action: ConfigActions, unit: str):
+    bus = SystemBus()
+    systemd_manager = bus.get(".systemd1")
+
+    if action is ConfigActions.ENABLE:
+        systemd_manager.UnmaskUnitFiles([unit], False)
+        systemd_manager.EnableUnitFiles([unit], False, False)
+        systemd_manager.StartUnit(unit, "replace")
+
+    elif action is ConfigActions.DISABLE:
+        systemd_manager.StopUnit(unit, "replace")
+        systemd_manager.DisableUnitFiles([unit], False)
+
+    elif action is ConfigActions.STATUS:
+        try:
+            unit_path = systemd_manager.LoadUnit(unit)
+            properties = bus.get(".systemd1", unit_path)
+        except Exception:
+            log.warning(f"could not get systemd unit {unit}")
+            return False
+
+        return properties.UnitFileState == "enabled" and properties.ActiveState == "active"
+
+    elif action is ConfigActions.AVAILABLE:
+        try:
+            unit_path = systemd_manager.LoadUnit(unit)
+            properties = bus.get(".systemd1", unit_path)
+        except Exception:
+            log.warning(f"could not get systemd unit {unit}")
+            return False
+
+        return properties.LoadState != "not-found"
+
+    else:
+        raise ValueError(f"action {action} not supported")
+
+
+AVAILABLE_FEATURES = {
+    "gui": False,
+    "revpi-con-can": False,
+    "var-log.mount": False,
+    "dphys-swapfile": False,
+    "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": False,
+    "ieee80211": False,
+    "avahi": False,
+    "external-antenna": False,
+}