lib/libc/stdio/freopen.c

   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  * @(#)freopen.c        8.1 (Berkeley) 6/4/93
  33  * $FreeBSD: src/lib/libc/stdio/freopen.c,v 1.21 2008/04/17 22:17:54 jhb Exp $
  34  */
  35
  36 #include "namespace.h"
  37 #include <sys/types.h>
  38 #include <sys/stat.h>
  39 #include <fcntl.h>
  40 #include <errno.h>
  41 #include <unistd.h>
  42 #include <stdio.h>
  43 #include <stdlib.h>
  44 #include "un-namespace.h"
  45 #include "libc_private.h"
  46 #include "local.h"
  47
  48 /*
  49  * Re-direct an existing, open (probably) file to some other file.
  50  * ANSI is written such that the original file gets closed if at
  51  * all possible, no matter what.
  52  */
  53 FILE *
  54 freopen(const char * __restrict file, const char * __restrict mode, FILE *fp)
  55 {
  56         int f;
  57         int dflags, flags, isopen, oflags, sverrno, wantfd;
  58
  59         if ((flags = __sflags(mode, &oflags)) == 0) {
  60                 sverrno = errno;
  61                 fclose(fp);
  62                 errno = sverrno;
  63                 return (NULL);
  64         }
  65
  66         FLOCKFILE(fp);
  67
  68         if (!__sdidinit)
  69                 __sinit();
  70
  71         /*
  72          * If the filename is a NULL pointer, the caller is asking us to
  73          * re-open the same file with a different mode. We allow this only
  74          * if the modes are compatible.
  75          */
  76         if (file == NULL) {
  77                 /* See comment below regarding freopen() of closed files. */
  78                 if (fp->pub._flags == 0) {
  79                         FUNLOCKFILE(fp);
  80                         errno = EINVAL;
  81                         return (NULL);
  82                 }
  83                 if ((dflags = _fcntl(fp->pub._fileno, F_GETFL)) < 0) {
  84                         sverrno = errno;
  85                         fclose(fp);
  86                         FUNLOCKFILE(fp);
  87                         errno = sverrno;
  88                         return (NULL);
  89                 }
  90                 if ((dflags & O_ACCMODE) != O_RDWR && (dflags & O_ACCMODE) !=
  91                     (oflags & O_ACCMODE)) {
  92                         fclose(fp);
  93                         FUNLOCKFILE(fp);
  94                         errno = EINVAL;
  95                         return (NULL);
  96                 }
  97                 if (fp->pub._flags & __SWR)
  98                         __sflush(fp);
  99                 if ((oflags ^ dflags) & O_APPEND) {
 100                         dflags &= ~O_APPEND;
 101                         dflags |= oflags & O_APPEND;
 102                         if (_fcntl(fp->pub._fileno, F_SETFL, dflags) < 0) {
 103                                 sverrno = errno;
 104                                 fclose(fp);
 105                                 FUNLOCKFILE(fp);
 106                                 errno = sverrno;
 107                                 return (NULL);
 108                         }
 109                 }
 110                 if (oflags & O_TRUNC)
 111                         ftruncate(fp->pub._fileno, (off_t)0);
 112                 if (!(oflags & O_APPEND))
 113                         _sseek(fp, (fpos_t)0, SEEK_SET);
 114                 if (oflags & O_CLOEXEC)
 115                         _fcntl(fileno(fp), F_SETFD, FD_CLOEXEC);
 116
 117                 f = fp->pub._fileno;
 118                 isopen = 0;
 119                 wantfd = -1;
 120                 goto finish;
 121         }
 122
 123         /*
 124          * There are actually programs that depend on being able to "freopen"
 125          * descriptors that weren't originally open.  Keep this from breaking.
 126          * Remember whether the stream was open to begin with, and which file
 127          * descriptor (if any) was associated with it.  If it was attached to
 128          * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
 129          * should work.  This is unnecessary if it was not a Unix file.
 130          */
 131         if (fp->pub._flags == 0) {
 132                 fp->pub._flags = __SEOF;        /* hold on to it */
 133                 isopen = 0;
 134                 wantfd = -1;
 135         } else {
 136                 /* flush the stream; ANSI doesn't require this. */
 137                 if (fp->pub._flags & __SWR)
 138                         __sflush(fp);
 139                 /* if close is NULL, closing is a no-op, hence pointless */
 140                 isopen = fp->_close != NULL;
 141                 if ((wantfd = fp->pub._fileno) < 0 && isopen) {
 142                         (*fp->_close)(fp->_cookie);
 143                         isopen = 0;
 144                 }
 145         }
 146
 147         /* Get a new descriptor to refer to the new file. */
 148         f = _open(file, oflags, DEFFILEMODE);
 149         if (f < 0 && isopen) {
 150                 /* If out of fd's close the old one and try again. */
 151                 if (errno == ENFILE || errno == EMFILE) {
 152                         (*fp->_close)(fp->_cookie);
 153                         isopen = 0;
 154                         f = _open(file, oflags, DEFFILEMODE);
 155                 }
 156         }
 157         sverrno = errno;
 158
 159 finish:
 160         /*
 161          * Finish closing fp.  Even if the open succeeded above, we cannot
 162          * keep fp->_base: it may be the wrong size.  This loses the effect
 163          * of any setbuffer calls, but stdio has always done this before.
 164          */
 165         if (isopen)
 166                 (*fp->_close)(fp->_cookie);
 167         if (fp->pub._flags & __SMBF)
 168                 free((char *)fp->_bf._base);
 169         fp->pub._w = 0;
 170         fp->pub._r = 0;
 171         fp->pub._p = NULL;
 172         fp->_bf._base = NULL;
 173         fp->_bf._size = 0;
 174         fp->pub._lbfsize = 0;
 175         if (HASUB(fp))
 176                 FREEUB(fp);
 177         fp->_ub._size = 0;
 178         if (HASLB(fp))
 179                 FREELB(fp);
 180         fp->_lb._size = 0;
 181         memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
 182
 183         if (f < 0) {                    /* did not get it after all */
 184                 fp->pub._flags = 0;             /* set it free */
 185                 FUNLOCKFILE(fp);
 186                 errno = sverrno;        /* restore in case _close clobbered */
 187                 return (NULL);
 188         }
 189
 190         /*
 191          * If reopening something that was open before on a real file, try
 192          * to maintain the descriptor.  Various C library routines (perror)
 193          * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
 194          */
 195         if (wantfd >= 0 && f != wantfd) {
 196                 if (oflags & O_CLOEXEC) {
 197                         if (_fcntl(f, F_DUP2FD_CLOEXEC, wantfd) >= 0) {
 198                                 _close(f);
 199                                 f = wantfd;
 200                         }
 201                 } else {
 202                         if (_dup2(f, wantfd) >= 0) {
 203                                 _close(f);
 204                                 f = wantfd;
 205                         }
 206                 }
 207         }
 208
 209         fp->pub._flags = flags;
 210         fp->pub._fileno = f;
 211         fp->_cookie = fp;
 212         fp->_read = __sread;
 213         fp->_write = __swrite;
 214         fp->_seek = __sseek;
 215         fp->_close = __sclose;
 216         /*
 217          * When opening in append mode, even though we use O_APPEND,
 218          * we need to seek to the end so that ftell() gets the right
 219          * answer.  If the user then alters the seek pointer, or
 220          * the file extends, this will fail, but there is not much
 221          * we can do about this.  (We could set __SAPP and check in
 222          * fseek and ftell.)
 223          */
 224         if (oflags & O_APPEND)
 225                 _sseek(fp, (fpos_t)0, SEEK_END);
 226         FUNLOCKFILE(fp);
 227         return (fp);
 228 }