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 #define __USE_BSD
35
36 #include <sys/types.h>
37 #include <sys/stat.h>
38 #include <fcntl.h>
39 #include <errno.h>
40 #include <unistd.h>
41 #include <stdio.h>
42 #include <stdlib.h>
43 #include "local.h"
44
45 /*
46 * Re-direct an existing, open (probably) file to some other file.
47 * ANSI is written such that the original file gets closed if at
48 * all possible, no matter what.
49 */
50 FILE *
freopen(const char * file,const char * mode,FILE * fp)51 freopen(const char *file, const char *mode, FILE *fp)
52 {
53 int f;
54 int flags, isopen, oflags, sverrno, wantfd;
55
56 if ((flags = __sflags(mode, &oflags)) == 0) {
57 (void) fclose(fp);
58 return (NULL);
59 }
60
61 if (!__sdidinit)
62 __sinit();
63
64 FLOCKFILE(fp);
65
66 /*
67 * There are actually programs that depend on being able to "freopen"
68 * descriptors that weren't originally open. Keep this from breaking.
69 * Remember whether the stream was open to begin with, and which file
70 * descriptor (if any) was associated with it. If it was attached to
71 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
72 * should work. This is unnecessary if it was not a Unix file.
73 */
74 if (fp->_flags == 0) {
75 fp->_flags = __SEOF; /* hold on to it */
76 isopen = 0;
77 wantfd = -1;
78 } else {
79 /* flush the stream; ANSI doesn't require this. */
80 if (fp->_flags & __SWR)
81 (void) __sflush(fp);
82 /* if close is NULL, closing is a no-op, hence pointless */
83 isopen = fp->_close != NULL;
84 if ((wantfd = fp->_file) < 0 && isopen) {
85 (void) (*fp->_close)(fp->_cookie);
86 isopen = 0;
87 }
88 }
89
90 /* Get a new descriptor to refer to the new file. */
91 f = open(file, oflags, DEFFILEMODE);
92 if (f < 0 && isopen) {
93 /* If out of fd's close the old one and try again. */
94 if (errno == ENFILE || errno == EMFILE) {
95 (void) (*fp->_close)(fp->_cookie);
96 isopen = 0;
97 f = open(file, oflags, DEFFILEMODE);
98 }
99 }
100 sverrno = errno;
101
102 /*
103 * Finish closing fp. Even if the open succeeded above, we cannot
104 * keep fp->_base: it may be the wrong size. This loses the effect
105 * of any setbuffer calls, but stdio has always done this before.
106 */
107 if (isopen && f != wantfd)
108 (void) (*fp->_close)(fp->_cookie);
109 if (fp->_flags & __SMBF)
110 free((char *)fp->_bf._base);
111 fp->_w = 0;
112 fp->_r = 0;
113 fp->_p = NULL;
114 fp->_bf._base = NULL;
115 fp->_bf._size = 0;
116 fp->_lbfsize = 0;
117 if (HASUB(fp))
118 FREEUB(fp);
119 _UB(fp)._size = 0;
120 WCIO_FREE(fp);
121 if (HASLB(fp))
122 FREELB(fp);
123 fp->_lb._size = 0;
124
125 if (f < 0) { /* did not get it after all */
126 fp->_flags = 0; /* set it free */
127 FUNLOCKFILE(fp);
128 errno = sverrno; /* restore in case _close clobbered */
129 return (NULL);
130 }
131
132 /*
133 * If reopening something that was open before on a real file, try
134 * to maintain the descriptor. Various C library routines (perror)
135 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
136 */
137 if (wantfd >= 0 && f != wantfd) {
138 if (dup2(f, wantfd) >= 0) {
139 (void) close(f);
140 f = wantfd;
141 }
142 }
143
144 fp->_flags = flags;
145 fp->_file = f;
146 fp->_cookie = fp;
147 fp->_read = __sread;
148 fp->_write = __swrite;
149 fp->_seek = __sseek;
150 fp->_close = __sclose;
151
152 /*
153 * When opening in append mode, even though we use O_APPEND,
154 * we need to seek to the end so that ftell() gets the right
155 * answer. If the user then alters the seek pointer, or
156 * the file extends, this will fail, but there is not much
157 * we can do about this. (We could set __SAPP and check in
158 * fseek and ftell.)
159 */
160 if (oflags & O_APPEND)
161 (void) __sseek((void *)fp, (fpos_t)0, SEEK_END);
162 FUNLOCKFILE(fp);
163 return (fp);
164 }
165