xref: /freebsd/lib/libc/stdio/freopen.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
1 /*-
2  * Copyright (c) 1990, 1993
3  *	The Regents of the University of California.  All rights reserved.
4  *
5  * This code is derived from software contributed to Berkeley by
6  * Chris Torek.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 4. Neither the name of the University nor the names of its contributors
17  *    may be used to endorse or promote products derived from this software
18  *    without specific prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30  * SUCH DAMAGE.
31  */
32 
33 #if defined(LIBC_SCCS) && !defined(lint)
34 static char sccsid[] = "@(#)freopen.c	8.1 (Berkeley) 6/4/93";
35 #endif /* LIBC_SCCS and not lint */
36 #include <sys/cdefs.h>
37 __FBSDID("$FreeBSD$");
38 
39 #include "namespace.h"
40 #include <sys/types.h>
41 #include <sys/stat.h>
42 #include <fcntl.h>
43 #include <errno.h>
44 #include <unistd.h>
45 #include <stdio.h>
46 #include <stdlib.h>
47 #include "un-namespace.h"
48 #include "libc_private.h"
49 #include "local.h"
50 
51 /*
52  * Re-direct an existing, open (probably) file to some other file.
53  * ANSI is written such that the original file gets closed if at
54  * all possible, no matter what.
55  */
56 FILE *
57 freopen(file, mode, fp)
58 	const char * __restrict file;
59 	const char * __restrict mode;
60 	FILE *fp;
61 {
62 	int f;
63 	int dflags, flags, isopen, oflags, sverrno, wantfd;
64 
65 	if ((flags = __sflags(mode, &oflags)) == 0) {
66 		sverrno = errno;
67 		(void) fclose(fp);
68 		errno = sverrno;
69 		return (NULL);
70 	}
71 
72 	FLOCKFILE(fp);
73 
74 	if (!__sdidinit)
75 		__sinit();
76 
77 	/*
78 	 * If the filename is a NULL pointer, the caller is asking us to
79 	 * re-open the same file with a different mode. We allow this only
80 	 * if the modes are compatible.
81 	 */
82 	if (file == NULL) {
83 		/* See comment below regarding freopen() of closed files. */
84 		if (fp->_flags == 0) {
85 			FUNLOCKFILE(fp);
86 			errno = EINVAL;
87 			return (NULL);
88 		}
89 		if ((dflags = _fcntl(fp->_file, F_GETFL)) < 0) {
90 			sverrno = errno;
91 			fclose(fp);
92 			FUNLOCKFILE(fp);
93 			errno = sverrno;
94 			return (NULL);
95 		}
96 		if ((dflags & O_ACCMODE) != O_RDWR && (dflags & O_ACCMODE) !=
97 		    (oflags & O_ACCMODE)) {
98 			fclose(fp);
99 			FUNLOCKFILE(fp);
100 			errno = EINVAL;
101 			return (NULL);
102 		}
103 		if (fp->_flags & __SWR)
104 			(void) __sflush(fp);
105 		if ((oflags ^ dflags) & O_APPEND) {
106 			dflags &= ~O_APPEND;
107 			dflags |= oflags & O_APPEND;
108 			if (_fcntl(fp->_file, F_SETFL, dflags) < 0) {
109 				sverrno = errno;
110 				fclose(fp);
111 				FUNLOCKFILE(fp);
112 				errno = sverrno;
113 				return (NULL);
114 			}
115 		}
116 		if (oflags & O_TRUNC)
117 			(void) ftruncate(fp->_file, (off_t)0);
118 		if (!(oflags & O_APPEND))
119 			(void) _sseek(fp, (fpos_t)0, SEEK_SET);
120 		f = fp->_file;
121 		isopen = 0;
122 		wantfd = -1;
123 		goto finish;
124 	}
125 
126 	/*
127 	 * There are actually programs that depend on being able to "freopen"
128 	 * descriptors that weren't originally open.  Keep this from breaking.
129 	 * Remember whether the stream was open to begin with, and which file
130 	 * descriptor (if any) was associated with it.  If it was attached to
131 	 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
132 	 * should work.  This is unnecessary if it was not a Unix file.
133 	 */
134 	if (fp->_flags == 0) {
135 		fp->_flags = __SEOF;	/* hold on to it */
136 		isopen = 0;
137 		wantfd = -1;
138 	} else {
139 		/* flush the stream; ANSI doesn't require this. */
140 		if (fp->_flags & __SWR)
141 			(void) __sflush(fp);
142 		/* if close is NULL, closing is a no-op, hence pointless */
143 		isopen = fp->_close != NULL;
144 		if ((wantfd = fp->_file) < 0 && isopen) {
145 			(void) (*fp->_close)(fp->_cookie);
146 			isopen = 0;
147 		}
148 	}
149 
150 	/* Get a new descriptor to refer to the new file. */
151 	f = _open(file, oflags, DEFFILEMODE);
152 	if (f < 0 && isopen) {
153 		/* If out of fd's close the old one and try again. */
154 		if (errno == ENFILE || errno == EMFILE) {
155 			(void) (*fp->_close)(fp->_cookie);
156 			isopen = 0;
157 			f = _open(file, oflags, DEFFILEMODE);
158 		}
159 	}
160 	sverrno = errno;
161 
162 finish:
163 	/*
164 	 * Finish closing fp.  Even if the open succeeded above, we cannot
165 	 * keep fp->_base: it may be the wrong size.  This loses the effect
166 	 * of any setbuffer calls, but stdio has always done this before.
167 	 */
168 	if (isopen)
169 		(void) (*fp->_close)(fp->_cookie);
170 	if (fp->_flags & __SMBF)
171 		free((char *)fp->_bf._base);
172 	fp->_w = 0;
173 	fp->_r = 0;
174 	fp->_p = NULL;
175 	fp->_bf._base = NULL;
176 	fp->_bf._size = 0;
177 	fp->_lbfsize = 0;
178 	if (HASUB(fp))
179 		FREEUB(fp);
180 	fp->_ub._size = 0;
181 	if (HASLB(fp))
182 		FREELB(fp);
183 	fp->_lb._size = 0;
184 	fp->_extra->orientation = 0;
185 	memset(&fp->_extra->mbstate, 0, sizeof(mbstate_t));
186 
187 	if (f < 0) {			/* did not get it after all */
188 		fp->_flags = 0;		/* set it free */
189 		FUNLOCKFILE(fp);
190 		errno = sverrno;	/* restore in case _close clobbered */
191 		return (NULL);
192 	}
193 
194 	/*
195 	 * If reopening something that was open before on a real file, try
196 	 * to maintain the descriptor.  Various C library routines (perror)
197 	 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
198 	 */
199 	if (wantfd >= 0 && f != wantfd) {
200 		if (_dup2(f, wantfd) >= 0) {
201 			(void)_close(f);
202 			f = wantfd;
203 		}
204 	}
205 
206 	fp->_flags = flags;
207 	fp->_file = f;
208 	fp->_cookie = fp;
209 	fp->_read = __sread;
210 	fp->_write = __swrite;
211 	fp->_seek = __sseek;
212 	fp->_close = __sclose;
213 	/*
214 	 * When opening in append mode, even though we use O_APPEND,
215 	 * we need to seek to the end so that ftell() gets the right
216 	 * answer.  If the user then alters the seek pointer, or
217 	 * the file extends, this will fail, but there is not much
218 	 * we can do about this.  (We could set __SAPP and check in
219 	 * fseek and ftell.)
220 	 */
221 	if (oflags & O_APPEND)
222 		(void) _sseek(fp, (fpos_t)0, SEEK_END);
223 	FUNLOCKFILE(fp);
224 	return (fp);
225 }
226