freopen.c revision 331722
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. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33#if defined(LIBC_SCCS) && !defined(lint) 34static char sccsid[] = "@(#)freopen.c 8.1 (Berkeley) 6/4/93"; 35#endif /* LIBC_SCCS and not lint */ 36#include <sys/cdefs.h> 37__FBSDID("$FreeBSD: stable/11/lib/libc/stdio/freopen.c 331722 2018-03-29 02:50:57Z eadler $"); 38 39#include "namespace.h" 40#include <sys/types.h> 41#include <sys/stat.h> 42#include <fcntl.h> 43#include <errno.h> 44#include <limits.h> 45#include <unistd.h> 46#include <stdio.h> 47#include <stdlib.h> 48#include "un-namespace.h" 49#include "libc_private.h" 50#include "local.h" 51 52/* 53 * Re-direct an existing, open (probably) file to some other file. 54 * ANSI is written such that the original file gets closed if at 55 * all possible, no matter what. 56 */ 57FILE * 58freopen(const char * __restrict file, const char * __restrict mode, 59 FILE * __restrict fp) 60{ 61 int f; 62 int dflags, flags, isopen, oflags, sverrno, wantfd; 63 64 if ((flags = __sflags(mode, &oflags)) == 0) { 65 sverrno = errno; 66 (void) fclose(fp); 67 errno = sverrno; 68 return (NULL); 69 } 70 71 FLOCKFILE_CANCELSAFE(fp); 72 73 if (!__sdidinit) 74 __sinit(); 75 76 /* 77 * If the filename is a NULL pointer, the caller is asking us to 78 * re-open the same file with a different mode. We allow this only 79 * if the modes are compatible. 80 */ 81 if (file == NULL) { 82 /* See comment below regarding freopen() of closed files. */ 83 if (fp->_flags == 0) { 84 errno = EINVAL; 85 fp = NULL; 86 goto end; 87 } 88 if ((dflags = _fcntl(fp->_file, F_GETFL)) < 0) { 89 sverrno = errno; 90 fclose(fp); 91 errno = sverrno; 92 fp = NULL; 93 goto end; 94 } 95 /* Work around incorrect O_ACCMODE. */ 96 if ((dflags & O_ACCMODE) != O_RDWR && 97 (dflags & (O_ACCMODE | O_EXEC)) != (oflags & O_ACCMODE)) { 98 fclose(fp); 99 errno = EBADF; 100 fp = NULL; 101 goto end; 102 } 103 if (fp->_flags & __SWR) 104 (void) __sflush(fp); 105 if ((oflags ^ dflags) & O_APPEND) { 106 dflags &= ~O_APPEND; 107 dflags |= oflags & O_APPEND; 108 if (_fcntl(fp->_file, F_SETFL, dflags) < 0) { 109 sverrno = errno; 110 fclose(fp); 111 errno = sverrno; 112 fp = NULL; 113 goto end; 114 } 115 } 116 if (oflags & O_TRUNC) 117 (void) ftruncate(fp->_file, (off_t)0); 118 if (!(oflags & O_APPEND)) 119 (void) _sseek(fp, (fpos_t)0, SEEK_SET); 120 if (oflags & O_CLOEXEC) 121 (void) _fcntl(fp->_file, F_SETFD, FD_CLOEXEC); 122 f = fp->_file; 123 isopen = 0; 124 wantfd = -1; 125 goto finish; 126 } 127 128 /* 129 * There are actually programs that depend on being able to "freopen" 130 * descriptors that weren't originally open. Keep this from breaking. 131 * Remember whether the stream was open to begin with, and which file 132 * descriptor (if any) was associated with it. If it was attached to 133 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin) 134 * should work. This is unnecessary if it was not a Unix file. 135 */ 136 if (fp->_flags == 0) { 137 fp->_flags = __SEOF; /* hold on to it */ 138 isopen = 0; 139 wantfd = -1; 140 } else { 141 /* flush the stream; ANSI doesn't require this. */ 142 if (fp->_flags & __SWR) 143 (void) __sflush(fp); 144 /* if close is NULL, closing is a no-op, hence pointless */ 145 isopen = fp->_close != NULL; 146 if ((wantfd = fp->_file) < 0 && isopen) { 147 (void) (*fp->_close)(fp->_cookie); 148 isopen = 0; 149 } 150 } 151 152 /* Get a new descriptor to refer to the new file. */ 153 f = _open(file, oflags, DEFFILEMODE); 154 /* If out of fd's close the old one and try again. */ 155 if (f < 0 && isopen && wantfd > STDERR_FILENO && 156 (errno == ENFILE || errno == EMFILE)) { 157 (void) (*fp->_close)(fp->_cookie); 158 isopen = 0; 159 wantfd = -1; 160 f = _open(file, oflags, DEFFILEMODE); 161 } 162 sverrno = errno; 163 164finish: 165 /* 166 * Finish closing fp. Even if the open succeeded above, we cannot 167 * keep fp->_base: it may be the wrong size. This loses the effect 168 * of any setbuffer calls, but stdio has always done this before. 169 * 170 * Leave the existing file descriptor open until dup2() is called 171 * below to avoid races where a concurrent open() in another thread 172 * could claim the existing descriptor. 173 */ 174 if (fp->_flags & __SMBF) 175 free((char *)fp->_bf._base); 176 fp->_w = 0; 177 fp->_r = 0; 178 fp->_p = NULL; 179 fp->_bf._base = NULL; 180 fp->_bf._size = 0; 181 fp->_lbfsize = 0; 182 if (HASUB(fp)) 183 FREEUB(fp); 184 fp->_ub._size = 0; 185 if (HASLB(fp)) 186 FREELB(fp); 187 fp->_lb._size = 0; 188 fp->_orientation = 0; 189 memset(&fp->_mbstate, 0, sizeof(mbstate_t)); 190 fp->_flags2 = 0; 191 192 if (f < 0) { /* did not get it after all */ 193 if (isopen) 194 (void) (*fp->_close)(fp->_cookie); 195 fp->_flags = 0; /* set it free */ 196 errno = sverrno; /* restore in case _close clobbered */ 197 fp = NULL; 198 goto end; 199 } 200 201 /* 202 * If reopening something that was open before on a real file, try 203 * to maintain the descriptor. Various C library routines (perror) 204 * assume stderr is always fd STDERR_FILENO, even if being freopen'd. 205 */ 206 if (wantfd >= 0) { 207 if ((oflags & O_CLOEXEC ? _fcntl(f, F_DUP2FD_CLOEXEC, wantfd) : 208 _dup2(f, wantfd)) >= 0) { 209 (void)_close(f); 210 f = wantfd; 211 } else 212 (void)_close(fp->_file); 213 } 214 215 /* 216 * File descriptors are a full int, but _file is only a short. 217 * If we get a valid file descriptor that is greater than 218 * SHRT_MAX, then the fd will get sign-extended into an 219 * invalid file descriptor. Handle this case by failing the 220 * open. 221 */ 222 if (f > SHRT_MAX) { 223 fp->_flags = 0; /* set it free */ 224 errno = EMFILE; 225 fp = NULL; 226 goto end; 227 } 228 229 fp->_flags = flags; 230 fp->_file = f; 231 fp->_cookie = fp; 232 fp->_read = __sread; 233 fp->_write = __swrite; 234 fp->_seek = __sseek; 235 fp->_close = __sclose; 236 /* 237 * When opening in append mode, even though we use O_APPEND, 238 * we need to seek to the end so that ftell() gets the right 239 * answer. If the user then alters the seek pointer, or 240 * the file extends, this will fail, but there is not much 241 * we can do about this. (We could set __SAPP and check in 242 * fseek and ftell.) 243 */ 244 if (oflags & O_APPEND) { 245 fp->_flags2 |= __S2OAP; 246 (void) _sseek(fp, (fpos_t)0, SEEK_END); 247 } 248end: 249 FUNLOCKFILE_CANCELSAFE(); 250 return (fp); 251} 252