1 /* $OpenBSD: freopen.c,v 1.18 2024/08/12 20:53:09 guenther 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 FLOCKFILE(fp); 64 65 /* 66 * There are actually programs that depend on being able to "freopen" 67 * descriptors that weren't originally open. Keep this from breaking. 68 * Remember whether the stream was open to begin with, and which file 69 * descriptor (if any) was associated with it. If it was attached to 70 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin) 71 * should work. This is unnecessary if it was not a Unix file. 72 */ 73 if (fp->_flags == 0) { 74 fp->_flags = __SEOF; /* hold on to it */ 75 isopen = 0; 76 wantfd = -1; 77 } else { 78 /* flush the stream; POSIX, not ANSI, requires this. */ 79 (void) __sflush(fp); 80 /* if close is NULL, closing is a no-op, hence pointless */ 81 isopen = fp->_close != NULL; 82 if ((wantfd = fp->_file) < 0 && isopen) { 83 (void) (*fp->_close)(fp->_cookie); 84 isopen = 0; 85 } 86 } 87 88 /* Get a new descriptor to refer to the new file. */ 89 f = open(file, oflags, DEFFILEMODE); 90 if (f == -1 && isopen) { 91 /* If out of fd's close the old one and try again. */ 92 if (errno == ENFILE || errno == EMFILE) { 93 (void) (*fp->_close)(fp->_cookie); 94 isopen = 0; 95 f = open(file, oflags, DEFFILEMODE); 96 } 97 } 98 sverrno = errno; 99 100 /* 101 * Finish closing fp. Even if the open succeeded above, we cannot 102 * keep fp->_base: it may be the wrong size. This loses the effect 103 * of any setbuffer calls, but stdio has always done this before. 104 */ 105 if (isopen && f != wantfd) 106 (void) (*fp->_close)(fp->_cookie); 107 if (fp->_flags & __SMBF) 108 free((char *)fp->_bf._base); 109 fp->_w = 0; 110 fp->_r = 0; 111 fp->_p = NULL; 112 fp->_bf._base = NULL; 113 fp->_bf._size = 0; 114 fp->_lbfsize = 0; 115 if (HASUB(fp)) 116 FREEUB(fp); 117 _UB(fp)._size = 0; 118 WCIO_FREE(fp); 119 if (HASLB(fp)) 120 FREELB(fp); 121 fp->_lb._size = 0; 122 123 if (f == -1) { /* did not get it after all */ 124 fp->_flags = 0; /* set it free */ 125 FUNLOCKFILE(fp); 126 errno = sverrno; /* restore in case _close clobbered */ 127 return (NULL); 128 } 129 130 /* 131 * If reopening something that was open before on a real file, try 132 * to maintain the descriptor. Various C library routines (perror) 133 * assume stderr is always fd STDERR_FILENO, even if being freopen'd. 134 */ 135 if (wantfd >= 0 && f != wantfd) { 136 if (dup3(f, wantfd, oflags & O_CLOEXEC) >= 0) { 137 (void) close(f); 138 f = wantfd; 139 } 140 } 141 142 /* _file is only a short */ 143 if (f > SHRT_MAX) { 144 fp->_flags = 0; /* set it free */ 145 FUNLOCKFILE(fp); 146 errno = EMFILE; 147 return (NULL); 148 } 149 150 fp->_flags = flags; 151 fp->_file = f; 152 fp->_cookie = fp; 153 fp->_read = __sread; 154 fp->_write = __swrite; 155 fp->_seek = __sseek; 156 fp->_close = __sclose; 157 158 /* 159 * When opening in append mode, even though we use O_APPEND, 160 * we need to seek to the end so that ftell() gets the right 161 * answer. If the user then alters the seek pointer, or 162 * the file extends, this will fail, but there is not much 163 * we can do about this. (We could set __SAPP and check in 164 * fseek and ftell.) 165 */ 166 if (oflags & O_APPEND) 167 (void) __sseek(fp, 0, SEEK_END); 168 FUNLOCKFILE(fp); 169 return (fp); 170 } 171 DEF_STRONG(freopen); 172