xref: /minix3/lib/libc/stdio/freopen.c (revision f14fb602092e015ff630df58e17c2a9cd57d29b3)
1 /*	$NetBSD: freopen.c,v 1.19 2012/03/27 15:05:42 christos Exp $	*/
2 
3 /*-
4  * Copyright (c) 1990, 1993
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * This code is derived from software contributed to Berkeley by
8  * Chris Torek.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  * 3. Neither the name of the University nor the names of its contributors
19  *    may be used to endorse or promote products derived from this software
20  *    without specific prior written permission.
21  *
22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32  * SUCH DAMAGE.
33  */
34 
35 #include <sys/cdefs.h>
36 #if defined(LIBC_SCCS) && !defined(lint)
37 #if 0
38 static char sccsid[] = "@(#)freopen.c	8.1 (Berkeley) 6/4/93";
39 #else
40 __RCSID("$NetBSD: freopen.c,v 1.19 2012/03/27 15:05:42 christos Exp $");
41 #endif
42 #endif /* LIBC_SCCS and not lint */
43 
44 #include <sys/types.h>
45 #include <sys/stat.h>
46 
47 #include <assert.h>
48 #include <errno.h>
49 #include <fcntl.h>
50 #include <unistd.h>
51 #include <stdio.h>
52 #include <stdlib.h>
53 #include <wchar.h>
54 #include <limits.h>
55 #include "reentrant.h"
56 #include "local.h"
57 
58 /*
59  * Re-direct an existing, open (probably) file to some other file.
60  * ANSI is written such that the original file gets closed if at
61  * all possible, no matter what.
62  */
63 FILE *
freopen(const char * file,const char * mode,FILE * fp)64 freopen(const char *file, const char *mode, FILE *fp)
65 {
66 	int f;
67 	int flags, isopen, oflags, sverrno, wantfd;
68 
69 	_DIAGASSERT(file != NULL);
70 	_DIAGASSERT(mode != NULL);
71 	_DIAGASSERT(fp != NULL);
72 
73 	if ((flags = __sflags(mode, &oflags)) == 0) {
74 		(void) fclose(fp);
75 		return NULL;
76 	}
77 
78 	if (!__sdidinit)
79 		__sinit();
80 
81 	/*
82 	 * There are actually programs that depend on being able to "freopen"
83 	 * descriptors that weren't originally open.  Keep this from breaking.
84 	 * Remember whether the stream was open to begin with, and which file
85 	 * descriptor (if any) was associated with it.  If it was attached to
86 	 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
87 	 * should work.  This is unnecessary if it was not a Unix file.
88 	 */
89 	if (fp->_flags == 0) {
90 		fp->_flags = __SEOF;	/* hold on to it */
91 		isopen = 0;
92 		wantfd = -1;
93 	} else {
94 		/* flush the stream; ANSI doesn't require this. */
95 		if (fp->_flags & __SWR)
96 			(void)__sflush(fp);
97 		/* if close is NULL, closing is a no-op, hence pointless */
98 		isopen = fp->_close != NULL;
99 		if ((wantfd = __sfileno(fp)) == -1 && isopen) {
100 			(void) (*fp->_close)(fp->_cookie);
101 			isopen = 0;
102 		}
103 	}
104 
105 	/* Get a new descriptor to refer to the new file. */
106 	f = open(file, oflags, DEFFILEMODE);
107 	if (f < 0 && isopen) {
108 		/* If out of fd's close the old one and try again. */
109 		if (errno == ENFILE || errno == EMFILE) {
110 			(void) (*fp->_close)(fp->_cookie);
111 			isopen = 0;
112 			f = open(file, oflags, DEFFILEMODE);
113 		}
114 	}
115 	sverrno = errno;
116 
117 	/*
118 	 * Finish closing fp.  Even if the open succeeded above, we cannot
119 	 * keep fp->_base: it may be the wrong size.  This loses the effect
120 	 * of any setbuffer calls, but stdio has always done this before.
121 	 */
122 	if (isopen && f != wantfd)
123 		(void) (*fp->_close)(fp->_cookie);
124 	if (fp->_flags & __SMBF)
125 		free((char *)fp->_bf._base);
126 	fp->_w = 0;
127 	fp->_r = 0;
128 	fp->_p = NULL;
129 	fp->_bf._base = NULL;
130 	fp->_bf._size = 0;
131 	fp->_lbfsize = 0;
132 	if (HASUB(fp))
133 		FREEUB(fp);
134 	WCIO_FREE(fp);
135 	_UB(fp)._size = 0;
136 	FREELB(fp);
137 
138 	if (f < 0) {			/* did not get it after all */
139 		fp->_flags = 0;		/* set it free */
140 		errno = sverrno;	/* restore in case _close clobbered */
141 		return NULL;
142 	}
143 
144 	if (oflags & O_NONBLOCK) {
145 		struct stat st;
146 		if (fstat(f, &st) == -1) {
147 			sverrno = errno;
148 			(void)close(f);
149 			errno = sverrno;
150 			return NULL;
151 		}
152 		if (!S_ISREG(st.st_mode)) {
153 			(void)close(f);
154 			errno = EFTYPE;
155 			return NULL;
156 		}
157 	}
158 
159 	/*
160 	 * If reopening something that was open before on a real file, try
161 	 * to maintain the descriptor.  Various C library routines (perror)
162 	 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
163 	 */
164 	if (wantfd >= 0 && f != wantfd) {
165 		if (dup2(f, wantfd) >= 0) {
166 			(void) close(f);
167 			f = wantfd;
168 		}
169 	}
170 
171 	/*
172 	 * File descriptors are a full int, but _file is only a short.
173 	 * If we get a valid file descriptor that is greater or equal to
174 	 * USHRT_MAX, then the fd will get sign-extended into an
175 	 * invalid file descriptor.  Handle this case by failing the
176 	 * open. (We treat the short as unsigned, and special-case -1).
177 	 */
178 	if (f >= USHRT_MAX) {
179 		(void)close(f);
180 		errno = EMFILE;
181 		return NULL;
182 	}
183 
184 	fp->_flags = flags;
185 	fp->_file = f;
186 	fp->_cookie = fp;
187 	fp->_read = __sread;
188 	fp->_write = __swrite;
189 	fp->_seek = __sseek;
190 	fp->_close = __sclose;
191 
192 	/*
193 	 * When reopening in append mode, even though we use O_APPEND,
194 	 * we need to seek to the end so that ftell() gets the right
195 	 * answer.  If the user then alters the seek pointer, or
196 	 * the file extends, this will fail, but there is not much
197 	 * we can do about this.  (We could set __SAPP and check in
198 	 * fseek and ftell.)
199 	 */
200 	if (oflags & O_APPEND)
201 		(void) __sseek((void *)fp, (off_t)0, SEEK_END);
202 	return fp;
203 }
204