INT 2F U - DOS 3.3+ internal - SET FASTOPEN ENTRY POINT
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 3.30+ FASTOPEN is called with:
AL = 01h  ???
CX = ??? seems to be offset
DI = ??? seems to be offset
SI = offset in DOS DS of filename
AL = 02h  ???
AL = 03h  open file???
SI = offset in DOS DS of filename
AL = 04h  ???
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

PCDOS 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 ???

MSDOS 5.0 FASTOPEN is additionally called with:
AL = 04h ???
AH = 03h
???
AL = 05h ???
DL = drive (00h = A:)
???
AL = 06h ???


2F122A - DOS 3.3+ internal - SET FASTOPEN ENTRY POINT