freopen.c revision a910abcd194830d2d113b3e183eb7df4d36cd92e 
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#include <sys/types.h>
35#include <sys/stat.h>
36#include <fcntl.h>
37#include <errno.h>
38#include <unistd.h>
39#include <stdio.h>
40#include <stdlib.h>
41#include "local.h"
42
43/*
44 * Re-direct an existing, open (probably) file to some other file.
45 * ANSI is written such that the original file gets closed if at
46 * all possible, no matter what.
47 */
48FILE *
49freopen(const char *file, const char *mode, FILE *fp)
50{
51	int f;
52	int flags, isopen, oflags, sverrno, wantfd;
53
54	if ((flags = __sflags(mode, &oflags)) == 0) {
55		(void) fclose(fp);
56		return (NULL);
57	}
58
59	if (!__sdidinit)
60		__sinit();
61
62	/*
63	 * There are actually programs that depend on being able to "freopen"
64	 * descriptors that weren't originally open.  Keep this from breaking.
65	 * Remember whether the stream was open to begin with, and which file
66	 * descriptor (if any) was associated with it.  If it was attached to
67	 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
68	 * should work.  This is unnecessary if it was not a Unix file.
69	 */
70	if (fp->_flags == 0) {
71		fp->_flags = __SEOF;	/* hold on to it */
72		isopen = 0;
73		wantfd = -1;
74	} else {
75		/* flush the stream; ANSI doesn't require this. */
76		if (fp->_flags & __SWR)
77			(void) __sflush(fp);
78		/* if close is NULL, closing is a no-op, hence pointless */
79		isopen = fp->_close != NULL;
80		if ((wantfd = fp->_file) < 0 && isopen) {
81			(void) (*fp->_close)(fp->_cookie);
82			isopen = 0;
83		}
84	}
85
86	/* Get a new descriptor to refer to the new file. */
87	f = open(file, oflags, DEFFILEMODE);
88	if (f < 0 && isopen) {
89		/* If out of fd's close the old one and try again. */
90		if (errno == ENFILE || errno == EMFILE) {
91			(void) (*fp->_close)(fp->_cookie);
92			isopen = 0;
93			f = open(file, oflags, DEFFILEMODE);
94		}
95	}
96	sverrno = errno;
97
98	/*
99	 * Finish closing fp.  Even if the open succeeded above, we cannot
100	 * keep fp->_base: it may be the wrong size.  This loses the effect
101	 * of any setbuffer calls, but stdio has always done this before.
102	 */
103	if (isopen && f != wantfd)
104		(void) (*fp->_close)(fp->_cookie);
105	if (fp->_flags & __SMBF)
106		free((char *)fp->_bf._base);
107	fp->_w = 0;
108	fp->_r = 0;
109	fp->_p = NULL;
110	fp->_bf._base = NULL;
111	fp->_bf._size = 0;
112	fp->_lbfsize = 0;
113	if (HASUB(fp))
114		FREEUB(fp);
115	_UB(fp)._size = 0;
116	WCIO_FREE(fp);
117	if (HASLB(fp))
118		FREELB(fp);
119	fp->_lb._size = 0;
120
121	if (f < 0) {			/* did not get it after all */
122		fp->_flags = 0;		/* set it free */
123		errno = sverrno;	/* restore in case _close clobbered */
124		return (NULL);
125	}
126
127	/*
128	 * If reopening something that was open before on a real file, try
129	 * to maintain the descriptor.  Various C library routines (perror)
130	 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
131	 */
132	if (wantfd >= 0 && f != wantfd) {
133		if (dup2(f, wantfd) >= 0) {
134			(void) close(f);
135			f = wantfd;
136		}
137	}
138
139	fp->_flags = flags;
140	fp->_file = f;
141	fp->_cookie = fp;
142	fp->_read = __sread;
143	fp->_write = __swrite;
144	fp->_seek = __sseek;
145	fp->_close = __sclose;
146
147	/*
148	 * When opening in append mode, even though we use O_APPEND,
149	 * we need to seek to the end so that ftell() gets the right
150	 * answer.  If the user then alters the seek pointer, or
151	 * the file extends, this will fail, but there is not much
152	 * we can do about this.  (We could set __SAPP and check in
153	 * fseek and ftell.)
154	 */
155	if (oflags & O_APPEND)
156		(void) __sseek((void *)fp, (fpos_t)0, SEEK_END);
157	return (fp);
158}
159