1 /* $OpenBSD: freopen.c,v 1.10 2008/04/21 12:28:35 otto 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 * 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 /* 64 * There are actually programs that depend on being able to "freopen" 65 * descriptors that weren't originally open. Keep this from breaking. 66 * Remember whether the stream was open to begin with, and which file 67 * descriptor (if any) was associated with it. If it was attached to 68 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin) 69 * should work. This is unnecessary if it was not a Unix file. 70 */ 71 if (fp->_flags == 0) { 72 fp->_flags = __SEOF; /* hold on to it */ 73 isopen = 0; 74 wantfd = -1; 75 } else { 76 /* flush the stream; ANSI doesn't require this. */ 77 if (fp->_flags & __SWR) 78 (void) __sflush(fp); 79 /* if close is NULL, closing is a no-op, hence pointless */ 80 isopen = fp->_close != NULL; 81 if ((wantfd = fp->_file) < 0 && isopen) { 82 (void) (*fp->_close)(fp->_cookie); 83 isopen = 0; 84 } 85 } 86 87 /* Get a new descriptor to refer to the new file. */ 88 f = open(file, oflags, DEFFILEMODE); 89 if (f < 0 && isopen) { 90 /* If out of fd's close the old one and try again. */ 91 if (errno == ENFILE || errno == EMFILE) { 92 (void) (*fp->_close)(fp->_cookie); 93 isopen = 0; 94 f = open(file, oflags, DEFFILEMODE); 95 } 96 } 97 sverrno = errno; 98 99 /* 100 * Finish closing fp. Even if the open succeeded above, we cannot 101 * keep fp->_base: it may be the wrong size. This loses the effect 102 * of any setbuffer calls, but stdio has always done this before. 103 */ 104 if (isopen && f != wantfd) 105 (void) (*fp->_close)(fp->_cookie); 106 if (fp->_flags & __SMBF) 107 free((char *)fp->_bf._base); 108 fp->_w = 0; 109 fp->_r = 0; 110 fp->_p = NULL; 111 fp->_bf._base = NULL; 112 fp->_bf._size = 0; 113 fp->_lbfsize = 0; 114 if (HASUB(fp)) 115 FREEUB(fp); 116 _UB(fp)._size = 0; 117 WCIO_FREE(fp); 118 if (HASLB(fp)) 119 FREELB(fp); 120 fp->_lb._size = 0; 121 122 if (f < 0) { /* did not get it after all */ 123 fp->_flags = 0; /* set it free */ 124 errno = sverrno; /* restore in case _close clobbered */ 125 return (NULL); 126 } 127 128 /* 129 * If reopening something that was open before on a real file, try 130 * to maintain the descriptor. Various C library routines (perror) 131 * assume stderr is always fd STDERR_FILENO, even if being freopen'd. 132 */ 133 if (wantfd >= 0 && f != wantfd) { 134 if (dup2(f, wantfd) >= 0) { 135 (void) close(f); 136 f = wantfd; 137 } 138 } 139 140 /* _file is only a short */ 141 if (f > SHRT_MAX) { 142 fp->_flags = 0; /* set it free */ 143 errno = EMFILE; 144 return (NULL); 145 } 146 147 fp->_flags = flags; 148 fp->_file = f; 149 fp->_cookie = fp; 150 fp->_read = __sread; 151 fp->_write = __swrite; 152 fp->_seek = __sseek; 153 fp->_close = __sclose; 154 155 /* 156 * When opening in append mode, even though we use O_APPEND, 157 * we need to seek to the end so that ftell() gets the right 158 * answer. If the user then alters the seek pointer, or 159 * the file extends, this will fail, but there is not much 160 * we can do about this. (We could set __SAPP and check in 161 * fseek and ftell.) 162 */ 163 if (oflags & O_APPEND) 164 (void) __sseek((void *)fp, (fpos_t)0, SEEK_END); 165 return (fp); 166 } 167