1 /* $OpenBSD: freopen.c,v 1.13 2009/11/09 00:18:27 kurt 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 <limits.h>
39 #include <unistd.h>
40 #include <stdio.h>
41 #include <stdlib.h>
42 #include "local.h"
43
44 /*
45 * Re-direct an existing, open (probably) file to some other file.
46 * ANSI is written such that the original file gets closed if at
47 * all possible, no matter what.
48 */
49 FILE *
freopen(const char * file,const char * mode,FILE * fp)50 freopen(const char *file, const char *mode, FILE *fp)
51 {
52 int f;
53 int flags, isopen, oflags, sverrno, wantfd;
54
55 if ((flags = __sflags(mode, &oflags)) == 0) {
56 (void) fclose(fp);
57 return (NULL);
58 }
59
60 if (!__sdidinit)
61 __sinit();
62
63 FLOCKFILE(fp);
64
65 /*
66 * There are actually programs that depend on being able to "freopen"
67 * descriptors that weren't originally open. Keep this from breaking.
68 * Remember whether the stream was open to begin with, and which file
69 * descriptor (if any) was associated with it. If it was attached to
70 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
71 * should work. This is unnecessary if it was not a Unix file.
72 */
73 if (fp->_flags == 0) {
74 fp->_flags = __SEOF; /* hold on to it */
75 isopen = 0;
76 wantfd = -1;
77 } else {
78 /* flush the stream; ANSI doesn't require this. */
79 if (fp->_flags & __SWR)
80 (void) __sflush(fp);
81 /* if close is NULL, closing is a no-op, hence pointless */
82 isopen = fp->_close != NULL;
83 if ((wantfd = fp->_file) < 0 && isopen) {
84 (void) (*fp->_close)(fp->_cookie);
85 isopen = 0;
86 }
87 }
88
89 /* Get a new descriptor to refer to the new file. */
90 f = open(file, oflags, DEFFILEMODE);
91 if (f < 0 && isopen) {
92 /* If out of fd's close the old one and try again. */
93 if (errno == ENFILE || errno == EMFILE) {
94 (void) (*fp->_close)(fp->_cookie);
95 isopen = 0;
96 f = open(file, oflags, DEFFILEMODE);
97 }
98 }
99 sverrno = errno;
100
101 /*
102 * Finish closing fp. Even if the open succeeded above, we cannot
103 * keep fp->_base: it may be the wrong size. This loses the effect
104 * of any setbuffer calls, but stdio has always done this before.
105 */
106 if (isopen && f != wantfd)
107 (void) (*fp->_close)(fp->_cookie);
108 if (fp->_flags & __SMBF)
109 free((char *)fp->_bf._base);
110 fp->_w = 0;
111 fp->_r = 0;
112 fp->_p = NULL;
113 fp->_bf._base = NULL;
114 fp->_bf._size = 0;
115 fp->_lbfsize = 0;
116 if (HASUB(fp))
117 FREEUB(fp);
118 _UB(fp)._size = 0;
119 WCIO_FREE(fp);
120 if (HASLB(fp))
121 FREELB(fp);
122 fp->_lb._size = 0;
123
124 if (f < 0) { /* did not get it after all */
125 fp->_flags = 0; /* set it free */
126 FUNLOCKFILE(fp);
127 errno = sverrno; /* restore in case _close clobbered */
128 return (NULL);
129 }
130
131 /*
132 * If reopening something that was open before on a real file, try
133 * to maintain the descriptor. Various C library routines (perror)
134 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
135 */
136 if (wantfd >= 0 && f != wantfd) {
137 if (dup2(f, wantfd) >= 0) {
138 (void) close(f);
139 f = wantfd;
140 }
141 }
142
143 /* _file is only a short */
144 if (f > SHRT_MAX) {
145 fp->_flags = 0; /* set it free */
146 FUNLOCKFILE(fp);
147 errno = EMFILE;
148 return (NULL);
149 }
150
151 fp->_flags = flags;
152 fp->_file = f;
153 fp->_cookie = fp;
154 fp->_read = __sread;
155 fp->_write = __swrite;
156 fp->_seek = __sseek;
157 fp->_close = __sclose;
158
159 /*
160 * When opening in append mode, even though we use O_APPEND,
161 * we need to seek to the end so that ftell() gets the right
162 * answer. If the user then alters the seek pointer, or
163 * the file extends, this will fail, but there is not much
164 * we can do about this. (We could set __SAPP and check in
165 * fseek and ftell.)
166 */
167 if (oflags & O_APPEND)
168 (void) __sseek((void *)fp, (fpos_t)0, SEEK_END);
169 FUNLOCKFILE(fp);
170 return (fp);
171 }
172