resource/udev: fix intermittent AttributeError in USBSDWireDevice

The control_serial attribute is conditionally declared by assignment
which causes a race where it may not be declared before being
accessed in USBSDWireExport _get_params(). This causes an
AttributeError when starting the exporter.

Remove the unused control_path attribute and explicitly declare
control_serial to fix it.

Signed-off-by: Matt Porter <[email protected]>

Author: ohporter

labgrid/resource/udev.py

@@ -483,7 +483,7 @@ class USBSDWireDevice(USBResource):
     it is identified via USB using udev
     """
 
-    control_path = attr.ib(
+    control_serial = attr.ib(
         default=None,
         validator=attr.validators.optional(str)
     )
@@ -510,7 +510,7 @@ def avail(self, prop):
         pass
 
     # Overwrite the poll function. Only mark the SDWire as available if both
-    # paths are available.
+    # control_serial and disk_path are available.
     def poll(self):
         super().poll()
         if self.device is not None and not self.avail: