* actions 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 should be treated as a special case. The
+ * implementation should return a reserved PID, not allocated to any port,
+ * that the client may use for special purposes.
+ *
* The return value only needs to be meaningful when DPIF_UC_ACTION has
* been enabled in the 'dpif''s listen mask, and it is allowed to change
* when DPIF_UC_ACTION is disabled and then re-enabled.