freopen.c revision 55837 
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 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#if defined(LIBC_SCCS) && !defined(lint)
38#if 0
39static char sccsid[] = "@(#)freopen.c	8.1 (Berkeley) 6/4/93";
40#endif
41static const char rcsid[] =
42    "$FreeBSD: head/lib/libc/stdio/freopen.c 55837 2000-01-12 09:23:48Z jasone $";
43#endif /* LIBC_SCCS and not lint */
44
45#include <sys/types.h>
46#include <sys/stat.h>
47#include <fcntl.h>
48#include <errno.h>
49#include <unistd.h>
50#include <stdio.h>
51#include <stdlib.h>
52#include <libc_private.h>
53#include "local.h"
54
55/*
56 * Re-direct an existing, open (probably) file to some other file.
57 * ANSI is written such that the original file gets closed if at
58 * all possible, no matter what.
59 */
60FILE *
61freopen(file, mode, fp)
62	const char *file, *mode;
63	register FILE *fp;
64{
65	register int f;
66	int flags, isopen, oflags, sverrno, wantfd;
67
68	if ((flags = __sflags(mode, &oflags)) == 0) {
69		(void) fclose(fp);
70		return (NULL);
71	}
72
73	FLOCKFILE(fp);
74
75	if (!__sdidinit)
76		__sinit();
77
78	/*
79	 * There are actually programs that depend on being able to "freopen"
80	 * descriptors that weren't originally open.  Keep this from breaking.
81	 * Remember whether the stream was open to begin with, and which file
82	 * descriptor (if any) was associated with it.  If it was attached to
83	 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
84	 * should work.  This is unnecessary if it was not a Unix file.
85	 */
86	if (fp->_flags == 0) {
87		fp->_flags = __SEOF;	/* hold on to it */
88		isopen = 0;
89		wantfd = -1;
90	} else {
91		/* flush the stream; ANSI doesn't require this. */
92		if (fp->_flags & __SWR)
93			(void) __sflush(fp);
94		/* if close is NULL, closing is a no-op, hence pointless */
95		isopen = fp->_close != NULL;
96		if ((wantfd = fp->_file) < 0 && isopen) {
97			(void) (*fp->_close)(fp->_cookie);
98			isopen = 0;
99		}
100	}
101
102	/* Get a new descriptor to refer to the new file. */
103	f = _libc_open(file, oflags, DEFFILEMODE);
104	if (f < 0 && isopen) {
105		/* If out of fd's close the old one and try again. */
106		if (errno == ENFILE || errno == EMFILE) {
107			(void) (*fp->_close)(fp->_cookie);
108			isopen = 0;
109			f = _libc_open(file, oflags, DEFFILEMODE);
110		}
111	}
112	sverrno = errno;
113
114	/*
115	 * Finish closing fp.  Even if the open succeeded above, we cannot
116	 * keep fp->_base: it may be the wrong size.  This loses the effect
117	 * of any setbuffer calls, but stdio has always done this before.
118	 */
119	if (isopen)
120		(void) (*fp->_close)(fp->_cookie);
121	if (fp->_flags & __SMBF)
122		free((char *)fp->_bf._base);
123	fp->_w = 0;
124	fp->_r = 0;
125	fp->_p = NULL;
126	fp->_bf._base = NULL;
127	fp->_bf._size = 0;
128	fp->_lbfsize = 0;
129	if (HASUB(fp))
130		FREEUB(fp);
131	fp->_ub._size = 0;
132	if (HASLB(fp))
133		FREELB(fp);
134	fp->_lb._size = 0;
135
136	if (f < 0) {			/* did not get it after all */
137		fp->_flags = 0;		/* set it free */
138		errno = sverrno;	/* restore in case _close clobbered */
139		FUNLOCKFILE(fp);
140		return (NULL);
141	}
142
143	/*
144	 * If reopening something that was open before on a real file, try
145	 * to maintain the descriptor.  Various C library routines (perror)
146	 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
147	 */
148	if (wantfd >= 0 && f != wantfd) {
149		if (dup2(f, wantfd) >= 0) {
150			(void)_libc_close(f);
151			f = wantfd;
152		}
153	}
154
155	fp->_flags = flags;
156	fp->_file = f;
157	fp->_cookie = fp;
158	fp->_read = __sread;
159	fp->_write = __swrite;
160	fp->_seek = __sseek;
161	fp->_close = __sclose;
162	FUNLOCKFILE(fp);
163	return (fp);
164}
165