* as the OVS_USERSPACE_ATTR_PID attribute's value, for use in flows whose
* packets arrived on port 'port_no'.
*
+ * A 'port_no' of UINT16_MAX is a special case: it returns a reserved PID, not
+ * allocated to any port, that the client may use for special purposes.
+ *
* The return value is only meaningful when DPIF_UC_ACTION has been enabled in
* the 'dpif''s listen mask. It is allowed to change when DPIF_UC_ACTION is
* disabled and then re-enabled, so a client that does that must be prepared to