Int 21 Fn 3F  U - Ifshlp.sys - Get Entry Point                             [-]

   AH = 3Fh
   BX = file handle for device "IFS$HLP$"
   CX = 0008h (size of buffer in bytes)
   DS:DX -> buffer for entry point record (see #1102)

Return: CF clear if successful
       AX = number of bytes actually read (0 if at EOF before call)
   CF set on error
       AX = error code (05h,06h) (see #1366 at AH=59h/BX=0000h)
Program: IFSHLP.SYS is a support driver for Microsoft Windows for Workgroups

See Also: AX=4402h"IFSHLP"

Format of IFSHLP.SYS entry point record:
Offset Size    Description (Table 1102)
 00h  4 BYTEs  (call) required signature if called via IOCTL
           70h E9h 34h 37h for Windows 3.11
           70h E9h 35h 37h for Windows 3.11
       (ret) signature 34h 37h 70h EFh (Windows 3.11)
       (ret) signature 35h 37h 70h EFh (Windows95)
 04h   DWORD   (ret) pointer to FAR call entry point (see #1103)

(Table 1103)
Call IFSHLP.SYS entry point with:
   STACK:  WORD    function number (00h-0Ch)
           00h get ??? data
           01h set interrupt intercepts (trap)
           02h remove interrupt intercepts (untrap)
           03h ??? LPT2
           04h ??? LPT1
           05h revector INT 2F to trap and remove trap for others
           06h set ??? flag
           07h clear ??? flag
           08h get ??? flag word
           ---Windows 3.11 only---
           09h ???
           0Ah ???
           0Bh ???
           0Ch get ???
---if function 00h---

Return: DX:AX -> ??? data (see #1104)
   BX destroyed
---if function 01h---
   STACK:  DWORD   new intercept (trap) address

Return: AX = status
       0000h successful
       0001h failed (already set)
       DX = 0000h
   BX destroyed

Note:  the trap handler is called with a function number in BX, and the
     original BX on top of the stack; a null handler must perform a
     POP BX and an IRET
---if function 02h---

Return: AX = status
       0000h successful
       0001h failed (not set)
   DX = 0000h
   BX destroyed
---if function 03h,04h---
   STACK:  WORD    ???

Return: AX = 0000h
   DX = 0000h
   BX destroyed
---if function 05h---
   ???

Return:    BX destroyed
---if function 06h---

Return: AX = 0001h and DX = 0000h if already set
   AX,DX unchanged if successful
   BX destroyed
---if function 07h---

Return: AX = 0001h and DX = 0000h if not set
   AX,DX unchanged if successful
   BX destroyed
---if function 08h---

Return: DX = 0000h
   AX = flags
       bit 0: set/cleared by functions 06h and 07h
       bit 1: trap is currently set (refer to functions 01h/02h)
   BX destroyed
---if function 09h---

Return: AX = status
       0000h successful
       0001h failed (already called)
   BX destroyed
---if function 0Ah---
   STACK:  WORD    ???
   ???

Return:    BX destroyed
---if function 0Bh---

Return: AX = status
       0000h successful
       0001h failed (not set)
   BX destroyed
---if function 0Ch---

Return: AX = 0000h
   ES:BX -> ??? data
---if function > 0Ch---

Return: AX = 0001h
   DX = 0000h
   BX destroyed

Format of IFSHLP ??? data:
Offset Size    Description (Table 1104)
 00h   DWORD   -> DOS Swappable Data Area (see #1373,#1375)
 02h   WORD    ??? offset in DOS data segment?
 04h   WORD    offset in DOS data segment of current-PSP WORD
 06h   WORD    ???
 08h   WORD    ???
 0Ah   WORD    ???
 0Ch   DWORD   -> DOS List of Lists (see #1313)
 10h   ???

See Also: #1103