Int 2F Fn 122A  U - DOS 3.3+ Internal - Set Fastopen Entry Point           [D]

   AX = 122Ah
   BX = entry point to set (0001h or 0002h)
   DS:SI -> FASTOPEN entry point
       (entry point not set if SI = FFFFh for DOS 4+)

Return: CF set if specified entry point already set

Notes: entry point in BX is ignored under DOS 3.30
   both entry points set to same handler by DOS 4.01
   DOS 5.0 and 6.0 only set entry point 1

DOS 3.30+ FASTOPEN is called with:
   AL = 01h  Lookup
       CX = ??? seems to be offset
       DI = ??? seems to be offset
       SI = offset in DOS DS of filename
   AL = 02h  insert file into FASTOPEN cache
   AL = 03h  delete file from FASTOPEN cache
       SI = offset in DOS DS of filename
   AL = 04h  purge FASTOPEN cache
       AH = subfunction (00h,01h,02h)
       ES:DI -> ???
       CX = ??? (subfunctions 01h and 02h only)
Returns: CF set on error or not installed

Note: function 03h calls function 01h first

PC-DOS 4.01 FASTOPEN is additionally called with:
   AL = 04h ???
       AH = 03h
       ???
   AL = 05h ???
   AL = 0Bh ???
   AL = 0Ch ???
   AL = 0Dh ???
   AL = 0Eh ???
   AL = 0Fh ???
   AL = 10h ???

MS-DOS 5.0-6.0 FASTOPEN is additionally called with:
   AL = 04h  purge FASTOPEN cache
       AH = 03h
       ???
   AL = 05h ???
       DL = drive (00h = A:)
       ???
   AL = 06h ???
       ???