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  Description:  IOCTL: Read Control Data from Block
                Device Driver
 
  Transfers control data from a block device driver directly into an appli-
  cation program's buffer. The length and contents of the data are
  specific to each device driver and do not follow any standard format.
  This function does not necessarily result in any input from the physical
  device.
 
  Input                                     Output
  ══════════════════════════════            ══════════════════════════════
  AH=44H                                    If function successful
  AL=04H                                    Carry flag=clear
  BL=drive code (0 = default,               AX=bytes transferred and buf-
      1=A, 2=B, etc.)                           fer contains control data
  CX=number of bytes to read                    from device driver
  DS:DX=segment:offset of buffer            If function unsuccessful
                                            Carry flag=set
                                            AX=error code
                                    -♦-