Int 2C Fn 002D  P - Cloaking - Set Port-trapping Passalong                 [m]

   AX = 002Dh
   DX:EBX = new I/O trapping passalong address (see #2254)

Return: CF clear

Notes: RM386 calls the passalong address whenever an access to a monitored
     I/O port is attempted; the handler should check whether it is a port
     that it is interested in, and if not call the previous passalong
     address (which was retrieved with AX=002Ch before installing the
     new handler)
   this function was first introduced with RM386 (RAM-MAN/386) v6.00

See Also: AX=0009h,AX=002Ch,INT 67/AX=5DEAh

(Table 2254)
Values Cloaking port-trapping passalong address is called with:
   EAX = CS:IP of faulting instruction (unless executing in protected-mode
       ring 3)
   SS:EBX -> caller register structure (see #2247)
       check EFLAGS V86-mode bit for type
   CX = first two bytes of I/O instruction which was trapped
   DX = port to which I/O is being performed
   CF clear

Return: CF clear if RM386 should perform I/O operation
   CF set if I/O should be skipped

Note:  RM386 skips the trapped I/O instruction, so the passalong handler
     should not modify the client CS:EIP