DoubleSpace IOCTL fn 'F': Flush DoubleSpace Cache

                                                         Compatibility: 6.0+ 
 Expects: AX    4404H (INT 21H IOCTL Read service number)
          BL    any compressed drive number (1=A, 2=B, etc)
          CX    10 (size of an DsIoctlRec; see below)
          DS:DX address of a DsIoctlRec with an 'F' (ASCII 46H) in
                the bCmdCode field)
 Returns: DS:DX bResult contains a DoubleSpace API Error Code (00H=success)
    Info: DoubleSpace maintains internal caches for its cluster data,
          BitFAT and MDFAT data (see CVF Layout).

          This IOCTL fn forces DoubleSpace to update the CVF on disk to
          reflect the currently-cached data.

          The cache is still considered valid.  Use DS IOCTL 'I' to force
          DoubleSpace to invalidate the cache and re-read the disk.

    DS:DX points to a DsIoctlRec as follows:

            Offset Size Contents
            ▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
             +0      2  abSig       must be 444dH ('M','D')
             +2      1  bCmdCode    must be 46H ('F') Flush command
             +3      2  bResult     returns a DoubleSpace API Error Code
             +5      5  res         (reserved; 0)
                    10              size of a DsIoctlRec structure

          To use this fn, set up the packet and the registers, and call
          INT 21H.  See DOS fn 44H (device I/O Control) for related DOS

          On return, check bResult for an error code.  The value 4f4bH
          ('OK') indicates success.

    Note: You can force DoubleSpace and SmartDrive to flush their disk-
          sector caches via DOS fn 0dH (reset disk).

See Also: DoubleSpace Overview
          DoubleSpace API
          INT 2fH: Multiplex Interrupt
          DOS Functions