Avoid use of startwith in a large loop

qubesusbproxy/core3ext.py

@@ -426,27 +426,32 @@ def _load_usb_known_devices(cls) -> Dict[str, Dict[str, Tuple[str, str]]]:
             vendor_name: Optional[str] = None
             for line in usb_ids.readlines():
                 line = line.rstrip()
-                if line.startswith("#"):
-                    # skip comments
-                    continue
                 if not line:
                     # skip empty lines
                     continue
-                if line.startswith("\t\t"):
-                    # skip interfaces
+                first_char = line[0]
+                if first_char == "#":
+                    # skip comments
                     continue
-                if line.startswith("C "):
+                if first_char == "C" and len(line) >= 2 and line[1] == " ":
                     # description of classes starts here, we can finish
                     break
-                if line.startswith("\t"):
+                if first_char == "\t":
+                    if len(line) >= 2 and line[1] == "\t":
+                        # skip interfaces
+                        continue
+                    # device line
+                    parts = line[1:].split(" ", 2)
+                    if len(parts) < 3:
+                        continue
                     # save vendor, device pair
-                    device_id, _, device_name = line[1:].split(" ", 2)
+                    device_id, _, device_name = parts
                     if vendor_id is None or vendor_name is None:
                         continue
-                    result[vendor_id][device_id] = vendor_name, device_name
+                    result[vendor_id][device_id] = (vendor_name, device_name)
                 else:
-                    # new vendor
-                    vendor_id, _, vendor_name = line[:].split(" ", 2)
+                    parts = line.split(" ", 2)
+                    vendor_id, _, vendor_name = parts
                     result[vendor_id] = {}
 
         cls._usb_known_devices = result
@@ -648,26 +653,17 @@ def on_device_get_usb(self, vm, event, port_id):
         ):
             yield USBDevice(Port(vm, port_id, "usb"))
 
-    @staticmethod
-    def get_all_devices(app):
-        for vm in app.domains:
-            if not vm.is_running() or not hasattr(vm, "devices"):
-                continue
-
-            for dev in vm.devices["usb"]:
-                # there may be more than one USB-passthrough implementation
-                if isinstance(dev, USBDevice):
-                    yield dev
-
     @qubes.ext.handler("device-list-attached:usb")
     def on_device_list_attached(self, vm, event, **kwargs):
         # pylint: disable=unused-argument
         if not vm.is_running():
             return
 
-        for dev in self.get_all_devices(vm.app):
-            if dev.attachment == vm:
-                yield (dev, {})
+        for ports in self.devices_cache.values():
+            for port_id, attachment in ports.items():
+                if attachment == vm:
+                    dev = USBDevice(Port(vm, port_id, "usb"))
+                    yield (dev, {})
 
     @qubes.ext.handler("device-pre-attach:usb")
     async def on_device_attach_usb(self, vm, event, device, options):