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Dogcows Code - chaz/tar/blob - src/open3.c
1 /* Defines for Sys V style 3-argument open call.
2 Copyright (C) 1988, 1994, 1995, 1996 Free Software Foundation, Inc.
4 This program is free software; you can redistribute it and/or modify it
5 under the terms of the GNU General Public License as published by the
6 Free Software Foundation; either version 2, or (at your option) any later
9 This program is distributed in the hope that it will be useful, but
10 WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
12 Public License for more details.
14 You should have received a copy of the GNU General Public License along
15 with this program; if not, write to the Free Software Foundation, Inc.,
16 59 Place - Suite 330, Boston, MA 02111-1307, USA. */
22 /* open3.h -- #defines for the various flags for the Sys V style 3-argument
23 open() call. On BSD or System 5, the system already has this in an
24 include file. This file is needed for V7 and MINIX systems for the
25 benefit of open3() in port.c, a routine that emulates the 3-argument call
26 using system calls available on V7/MINIX.
28 Written 1987-06-10 by Richard Todd.
30 The names have been changed by John Gilmore, 1987-07-31, since Richard
31 called it "bsdopen", and really this change was introduced in AT&T Unix
32 systems before BSD picked it up. */
34 /*-----------------------------------------------------------------------.
35 | open3 -- routine to emulate the 3-argument open system. |
37 | open3 (path, flag, mode); |
39 | Attempts to open the file specified by the given pathname. The |
40 | following flag bits specify options to the routine. Needless to say, |
41 | you should only specify one of the first three. Function returns file |
42 | descriptor if successful, -1 and errno if not. |
43 `-----------------------------------------------------------------------*/
45 /* The routine obeys the following mode arguments:
47 O_RDONLY file open for read only
48 O_WRONLY file open for write only
49 O_RDWR file open for both read & write
51 O_CREAT file is created with specified mode if it needs to be
52 O_TRUNC if file exists, it is truncated to 0 bytes
53 O_EXCL used with O_CREAT--routine returns error if file exists */
55 /* Call that if present in most modern Unix systems. This version attempts
56 to support all the flag bits except for O_NDELAY and O_APPEND, which are
57 silently ignored. The emulation is not as efficient as the real thing
58 (at worst, 4 system calls instead of one), but there's not much I can do
61 /* Array to give arguments to access for various modes FIXME, this table
62 depends on the specific integer values of O_*, and also contains
63 integers (args to 'access') that should be #define's. */
70 06, /* invalid, just cope: O_WRONLY+O_RDWR */
73 /* Shut off the automatic emulation of open(), we'll need it. */
77 open3 (char *path
, int flags
, int mode
)
82 /* We actually do the work by calling the open() or creat() system
83 call, depending on the flags. Call_creat is true if we will use
84 creat(), false if we will use open(). */
86 /* See if the file exists and is accessible in the requested mode.
88 Strictly speaking we shouldn't be using access, since access checks
89 against real uid, and the open call should check against euid. Most
90 cases real uid == euid, so it won't matter. FIXME. FIXME, the
91 construction "flags & 3" and the modes table depends on the specific
92 integer values of the O_* #define's. Foo! */
94 if (access (path
, modes
[flags
& 3]) < 0)
98 /* The file does not exist. */
104 /* Probably permission violation. */
108 /* Oops, the file exists, we didn't want it. No matter
109 what the error, claim EEXIST. */
111 errno
= EEXIST
; /* FIXME: errno should be read-only */
117 /* If we have the O_CREAT bit set, check for O_EXCL. */
121 if ((flags
& O_EXCL
) && exists
)
123 /* Oops, the file exists and we didn't want it to. */
125 errno
= EEXIST
; /* FIXME: errno should be read-only */
129 /* If the file doesn't exist, be sure to call creat() so that it
130 will be created with the proper mode. */
137 /* If O_CREAT isn't set and the file doesn't exist, error. */
141 errno
= ENOENT
; /* FIXME: errno should be read-only */
146 /* If the O_TRUNC flag is set and the file exists, we want to call
147 creat() anyway, since creat() guarantees that the file will be
148 truncated and open()-for-writing doesn't. (If the file doesn't
149 exist, we're calling creat() anyway and the file will be created
150 with zero length.) */
152 if ((flags
& O_TRUNC
) && exists
)
155 /* Actually do the call. */
159 /* Call creat. May have to close and reopen the file if we want
160 O_RDONLY or O_RDWR access -- creat() only gives O_WRONLY. */
163 int fd
= creat (path
, mode
);
165 if (fd
< 0 || (flags
& O_WRONLY
))
170 /* Fall out to reopen the file we've created. */
173 /* Calling old open, we strip most of the new flags just in case. */
175 return open (path
, flags
& (O_RDONLY
| O_WRONLY
| O_RDWR
| O_BINARY
));
178 #endif /* EMUL_OPEN3 */
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