1 /* $OpenBSD: freopen.c,v 1.9 2005/08/08 08:05:36 espie Exp $ */
2 /*-
3 * Copyright (c) 1990, 1993
4 * The Regents of the University of California. All rights reserved.
5 *
6 * This code is derived from software contributed to Berkeley by
7 * Chris Torek.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 #include <sys/types.h>
35 #include <sys/stat.h>
36 #include <fcntl.h>
37 #include <errno.h>
38 #include <unistd.h>
39 #include <stdio.h>
40 #include <stdlib.h>
41 #include "local.h"
42
43 /*
44 * Re-direct an existing, open (probably) file to some other file.
45 * ANSI is written such that the original file gets closed if at
46 * all possible, no matter what.
47 */
48 FILE *
freopen(const char * file,const char * mode,FILE * fp)49 freopen(const char *file, const char *mode, FILE *fp)
50 {
51 int f;
52 int flags, isopen, oflags, sverrno, wantfd;
53
54 if ((flags = __sflags(mode, &oflags)) == 0) {
55 (void) fclose(fp);
56 return (NULL);
57 }
58
59 if (!__sdidinit)
60 __sinit();
61
62 /*
63 * There are actually programs that depend on being able to "freopen"
64 * descriptors that weren't originally open. Keep this from breaking.
65 * Remember whether the stream was open to begin with, and which file
66 * descriptor (if any) was associated with it. If it was attached to
67 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
68 * should work. This is unnecessary if it was not a Unix file.
69 */
70 if (fp->_flags == 0) {
71 fp->_flags = __SEOF; /* hold on to it */
72 isopen = 0;
73 wantfd = -1;
74 } else {
75 /* flush the stream; ANSI doesn't require this. */
76 if (fp->_flags & __SWR)
77 (void) __sflush(fp);
78 /* if close is NULL, closing is a no-op, hence pointless */
79 isopen = fp->_close != NULL;
80 if ((wantfd = fp->_file) < 0 && isopen) {
81 (void) (*fp->_close)(fp->_cookie);
82 isopen = 0;
83 }
84 }
85
86 /* Get a new descriptor to refer to the new file. */
87 f = open(file, oflags, DEFFILEMODE);
88 if (f < 0 && isopen) {
89 /* If out of fd's close the old one and try again. */
90 if (errno == ENFILE || errno == EMFILE) {
91 (void) (*fp->_close)(fp->_cookie);
92 isopen = 0;
93 f = open(file, oflags, DEFFILEMODE);
94 }
95 }
96 sverrno = errno;
97
98 /*
99 * Finish closing fp. Even if the open succeeded above, we cannot
100 * keep fp->_base: it may be the wrong size. This loses the effect
101 * of any setbuffer calls, but stdio has always done this before.
102 */
103 if (isopen && f != wantfd)
104 (void) (*fp->_close)(fp->_cookie);
105 if (fp->_flags & __SMBF)
106 free((char *)fp->_bf._base);
107 fp->_w = 0;
108 fp->_r = 0;
109 fp->_p = NULL;
110 fp->_bf._base = NULL;
111 fp->_bf._size = 0;
112 fp->_lbfsize = 0;
113 if (HASUB(fp))
114 FREEUB(fp);
115 _UB(fp)._size = 0;
116 WCIO_FREE(fp);
117 if (HASLB(fp))
118 FREELB(fp);
119 fp->_lb._size = 0;
120
121 if (f < 0) { /* did not get it after all */
122 fp->_flags = 0; /* set it free */
123 errno = sverrno; /* restore in case _close clobbered */
124 return (NULL);
125 }
126
127 /*
128 * If reopening something that was open before on a real file, try
129 * to maintain the descriptor. Various C library routines (perror)
130 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
131 */
132 if (wantfd >= 0 && f != wantfd) {
133 if (dup2(f, wantfd) >= 0) {
134 (void) close(f);
135 f = wantfd;
136 }
137 }
138
139 fp->_flags = flags;
140 fp->_file = f;
141 fp->_cookie = fp;
142 fp->_read = __sread;
143 fp->_write = __swrite;
144 fp->_seek = __sseek;
145 fp->_close = __sclose;
146
147 /*
148 * When opening in append mode, even though we use O_APPEND,
149 * we need to seek to the end so that ftell() gets the right
150 * answer. If the user then alters the seek pointer, or
151 * the file extends, this will fail, but there is not much
152 * we can do about this. (We could set __SAPP and check in
153 * fseek and ftell.)
154 */
155 if (oflags & O_APPEND)
156 (void) __sseek((void *)fp, (fpos_t)0, SEEK_END);
157 return (fp);
158 }
159