q-dev: development of auto-attach and required flags

mic cannot be auto-attached since we have to wait to pulseaudio client to start first
make auto-attach and required as immutable properties
unassign non-required device from running vm

qubes/devices.py

@@ -738,10 +738,6 @@ def required(self) -> bool:
         """
         return self.__required
 
-    @required.setter
-    def required(self, required: bool):
-        self.__required = required
-
     @property
     def attach_automatically(self) -> bool:
         """
@@ -750,10 +746,6 @@ def attach_automatically(self) -> bool:
         """
         return self.__attach_automatically
 
-    @attach_automatically.setter
-    def attach_automatically(self, attach_automatically: bool):
-        self.__attach_automatically = attach_automatically
-
     @property
     def options(self) -> Dict[str, Any]:
         """ Device options (same as in the legacy API). """
@@ -1009,11 +1001,12 @@ async def assign(self, assignment: DeviceAssignment):
         if (assignment.devclass not in ('pci', 'testclass')
                 and assignment.required):
             raise qubes.exc.QubesValueError(
-                "Only pci devices can be set as required.")
-        if (assignment.devclass not in ('pci', 'testclass', 'mic', 'usb')
+                "Only pci devices can be assigned as required.")
+        if (assignment.devclass not in ('pci', 'testclass', 'usb')
                 and assignment.attach_automatically):
             raise qubes.exc.QubesValueError(
-                "Only pci, mic and usb devices can be automatically attached.")
+                "Only pci and usb devices can be assigned "
+                "to be automatically attached.")
 
         await self._vm.fire_event_async(
             'device-pre-assign:' + self._bus,
@@ -1113,10 +1106,11 @@ async def unassign(self, device_assignment: DeviceAssignment):
                 f'device {device_assignment.ident!s} of class {self._bus} not '
                 f'assigned to {self._vm!s}')
 
-        if not self._vm.is_halted():
+        if not self._vm.is_halted() and assignment.required:
             raise qubes.exc.QubesVMNotHaltedError(
                 self._vm,
-                "Can not remove an assignment from a non halted qube.")
+                "Can not remove an required assignment from "
+                "a non halted qube.")
 
         device = device_assignment.device
         await self._vm.fire_event_async(