INT 2F U - NETWORK REDIRECTOR (DOS 4+) - LOCK/UNLOCK REGION OF FILE
        AX = 110Ah
        BL = function
            00h lock
            01h unlock
        DS:DX -> parameter block (see below)
        ES:DI -> SFT
            SFT DPB field -> DPB of drive containing file
        SS = DOS DS
Return: CF set on error
           AL = DOS error code (see INT 21/AH=59h)
Notes:  called by DOS 4.0+ kernel
        the redirector is expected to resolve lock conflicts
SeeAlso: INT 21/AH=5Ch

Format of parameter block:
Offset  Size    Description
 00h    DWORD   start offset
 04h    DWORD   size of region