Compatibility: 6.0+
Expects: AX    4a11H (mux number)
BX    0008H (DoubleSpace fn code)
DL    any compressed drive number (0=A, 1=B, etc.)
                                                                  
Returns: AX    DoubleSpace API Error Code (0000H=success)
BX    maximum entries in file fragment heap
CX    available entries in file fragment heap
                                                                  
Info: DoubleSpace maintains an internal list of information that
describes the fragmentation of CVFs .  This fn obtains
information about that list.

DL on entry, is any valid compressed drive number.  A single
fragment heap is used for all CVFs.

CX on return, is the total size of the fragment heap.  It is the
value of the MaxFileFragments setting in DBLSPACE.INI.

BX on return, is the number of unused fragment entries in the file
fragment heap.

Notes:   By tracking CVF fragments internally, DoubleSpace avoids
needing to reread the FAT of the host drive.

  A CVF will be very fragmented if, during initial compression,
there was very little free space on the disk.  By default,
MaxFileFragments is initially set to a whopping 2600.  But
DBLSPACE.EXE adjusts it downward (to the actual needs plus a
fudge factor of 110) to avoid forcing DBLSPACE.BIN to allocate
a lot of memory each time DOS boots.

  You can save some memory by defragmenting your CVFs with the
DOS 6 Defrag command; however, Defrag won't modify a mounted
CVF.  Before defragmenting a CVF, you must unmount it (which is
awkward for your boot drive) and change its file attributes to
clear the hidden, system, and read-only bits.

- -

INT 2fH 4a11H BX=0008H: Get CVF Fragmentation Info