Int 15 Fn 81  C - Os Hook - Device Close                                   [B]

   AH = 81h
   BX = device ID
   CX = process ID
   CF clear

Return: CF clear if successful
       AH = 00h
   CF set on error
       AH = status (see #0422)

Note:  this function should be hooked by a multitasker which wishes to keep
     track of device ownership; the default BIOS handler merely returns
     successfully

See Also: AH=80h,AH=82h