+``nfds``
+ The highest-numbered file descriptor in any of the three sets, plus 1.
+
+``readfds``
+ File descriptions to be watched if a read() call won't block.
+
+``writefds``
+ File descriptions to be watched if a write() won't block.
+
+``exceptfds``
+ File descriptions to be watched for V4L2 events.
+
+``timeout``
+ Maximum time to wait.