q-dev: simplify parent_device

qubes/devices.py

@@ -291,7 +291,7 @@ def description(self) -> str:
         elif self.serial and self.serial != "unknown":
             prod = self.serial
         elif self.parent_device is not None:
-            return f"partition of {self.parent_device}"
+            return f"sub-device of {self.parent_device}"
         else:
             prod = f"unknown {self.devclass if self.devclass else ''} device"
 
@@ -316,17 +316,14 @@ def interfaces(self) -> List[DeviceInterface]:
         return self._interfaces
 
     @property
-    def parent_device(self) -> Optional['DeviceInfo']:
+    def parent_device(self) -> Optional[Device]:
         """
         The parent device if any.
 
         If the device is part of another device (e.g. it's a single
         partition of an usb stick), the parent device id should be here.
         """
-        if self._parent is None:
-            return None
-        return self.backend_domain.devices.get(
-            self._parent.devclass, {}).get(self._parent.ident, None)
+        return self._parent
 
     @property
     def subdevices(self) -> List['DeviceInfo']:

qubes/ext/block.py

@@ -112,7 +112,7 @@ def device_node(self):
         return '/dev/' + self.ident.replace('_', '/')
 
     @property
-    def parent_device(self) -> Optional[qubes.devices.DeviceInfo]:
+    def parent_device(self) -> Optional[qubes.devices.Device]:
         """
         The parent device if any.
 
@@ -130,13 +130,7 @@ def parent_device(self) -> Optional[qubes.devices.DeviceInfo]:
                 parent_ident = self._sanitize(untrusted_parent)
                 self._parent = qubes.devices.Device(
                     self.backend_domain, parent_ident)
-        return self.backend_domain.devices.get(
-            self._parent.devclass, {}).get(
-            self._parent.ident, qubes.devices.UnknownDevice(
-                backend_domain=self._parent.backend_domain,
-                ident=self._parent.ident
-            )
-        )
+        return self._parent
 
     @staticmethod
     def _sanitize(