en:docs:dos:api:int21:3d

Note: This API call is for DOS personality only. Use Family API for portability.

2018/09/07 07:04 · prokushev

Int 21H, AH=3DH

Version

2 and higher

Brief

“OPEN” - OPEN EXISTING FILE

Family API

Input

      AH = 3Dh
      AL = access and sharing modes (see #01402)
      DS:DX -> ASCIZ filename
      CL = attribute mask of files to look for (server call only)

Return

 CF clear if successful
          AX = file handle
      CF set on error
          AX = error code (01h,02h,03h,04h,05h,0Ch,56h) (see #01680 at AH=59h)

Notes

file pointer is set to start of file

if SHARE or a network is loaded, the file open may fail if the file is already open, depending on the combination of sharing modes (see #01403,#01404)

file handles which are inherited from a parent also inherit sharing and access restrictions

files may be opened even if given the hidden or system attributes

under the FlashTek X-32 DOS extender, the pointer is in DS:EDX

DR DOS checks the system password or explicitly supplied password at

the end of the filename (following a semicolon) against the reserved

field in the directory entry before allowing access

sharing modes are only effective on local drives if SHARE is loaded

Novell DOS 7 SHARE v1.00 would refuse file access in the cases in #01403 marked with [1] (read-only open of a read-only file which had previously been opened in compatibility mode); this was fixed in SHARE v1.01 of 09/29/94

Bitfields for access and sharing modes:

Bit(s) Description
2-0 access mode
000 read only
001 write only
010 read/write
011 (DOS 5+ internal) passed to redirector on EXEC to allow case-sensitive filenames
3 reserved (0)
6-4 sharing mode (DOS 3.0+) (see #01403)
000 compatibility mode
001 “DENYALL” prohibit both read and write access by others
010 “DENYWRITE” prohibit write access by others
011 “DENYREAD” prohibit read access by others
100 “DENYNONE” allow full access by others
111 network FCB (only available during server call)
7 inheritance
if set, file is private to current process and will not be inherited by child processes

(Table 01403) Values of DOS 2-6.22 file sharing behavior:

First Open Second and subsequent Opens
Compat Deny All Deny Write Deny Read Deny None
R W RW R W RW R W RW R W RW R W RW
Compat R Y Y Y N N N 1 N N N N N 1 N N
W Y Y Y N N N N N N N N N N N N
RW Y Y Y N N N N N N N N N N N N
Deny All R C C C N N N N N N N N N N N N
W C C C N N N N N N N N N N N N
RW C C C N N N N N N N N N N N N
Deny Write R 2 C C N N N Y N N N N N Y N N
W C C C N N N N N N Y N N Y N N
RW C C C N N N N N N N N N Y N N
Deny Read R C C C N N N N Y N N N N N Y N
W C C C N N N N N N N Y N N Y N
RW C C C N N N N N N N N N N Y N
Deny None R 2 C C N N N Y Y Y N N N Y Y Y
W C C C N N N N N N Y Y Y Y Y Y
RW C C C N N N N N N N N N Y Y Y

Legend: Y = open succeeds, N = open fails with error code 05h C = open fails, INT 24 generated 1 = open succeeds if file read-only, else fails with error code 2 = open succeeds if file read-only, else fails with INT 24

(Table 01404) Values for DOS 7.x file sharing behavior:

        |     Second and subsequent Opens

First |Compat Deny Deny Deny Deny Open | All Write Read None

        |R W RW A  R W RW A  R W RW A  R W RW A  R W RW A

- - - - -| - - - - - - - - - - - - - - - - - - - - - - - - Compat R |Y Y Y Y N N N N Y N N Y N N N Y Y N N Y

      W |Y Y Y C   N N N N   N N N N   N N N Y   Y N N Y
      RW|Y Y Y C   N N N N   N N N N   N N N Y   Y N N Y
      NA|Y C C Y   N N N N   Y N N Y   N N N Y   Y N N Y

- - - - -| Deny R |C C C C N N N N N N N N N N N N N N N N All W |C C C C N N N N N N N N N N N N N N N N

      RW|C C C C   N N N N   N N N N   N N N N   N N N N
      NA|C C C C   N N N N   N N N N   N N N N   N N N N

- - - - -| Deny R |Y C C Y N N N N Y N N Y N N N Y Y N N Y Write W |C C C C N N N N N N N N Y N N Y Y N N Y

      RW|C C C C   N N N N   N N N N   N N N Y   Y N N Y
      NA|Y C C Y   N N N N   Y N N Y   N N N Y   Y N N Y

- - - - -| Deny R |C C C C N N N N N Y N N N N N N N Y N N Read W |C C C C N N N N N N N N N Y N N N Y N N

      RW|C C C C   N N N N   N N N N   N N N N   N Y N N
      NA|Y Y Y Y   N N N N   Y Y Y Y   N N N Y   Y Y Y Y

- - - - -| Deny R |Y Y Y Y N N N N Y Y Y Y N N N Y Y Y Y Y None W |C C C C N N N N N N N N Y Y Y Y Y Y Y Y

      RW|C C C C   N N N N   N N N N   N N N Y   Y Y Y Y
      NA|Y Y Y Y   N N N N   Y Y Y Y   N N N Y   Y Y Y Y

Legend: R → reading, W → writing, RW → both reading & writing,

      A/NA -> reading without access time update
      Y = open succeeds, N = open fails with error code 05h
      C = open fails, INT 24 generated
        

See also

AH=0Fh,AH=3Ch,AX=4301h,AX=5D00h,INT 2F/AX=1116h,INT 2F/AX=1226h

Note


en/docs/dos/api/int21/3d.txt · Last modified: 2021/09/29 13:46 by prokushev