lib/libc/stdio/freopen.c

   1 /*      $NetBSD: freopen.c,v 1.14 2003/08/07 16:43:25 agc Exp $ */
   2
   3 /*-
   4  * Copyright (c) 1990, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * Chris Torek.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include <sys/cdefs.h>
  36 #if defined(LIBC_SCCS) && !defined(lint)
  37 #if 0
  38 static char sccsid[] = "@(#)freopen.c   8.1 (Berkeley) 6/4/93";
  39 #else
  40 __RCSID("$NetBSD: freopen.c,v 1.14 2003/08/07 16:43:25 agc Exp $");
  41 #endif
  42 #endif /* LIBC_SCCS and not lint */
  43
  44 #include <sys/types.h>
  45 #include <sys/stat.h>
  46
  47 #include <assert.h>
  48 #include <errno.h>
  49 #include <fcntl.h>
  50 #include <unistd.h>
  51 #include <stdio.h>
  52 #include <stdlib.h>
  53 #include <wchar.h>
  54 #include <limits.h>
  55 #include "reentrant.h"
  56 #include "local.h"
  57
  58 /*
  59  * Re-direct an existing, open (probably) file to some other file.
  60  * ANSI is written such that the original file gets closed if at
  61  * all possible, no matter what.
  62  */
  63 FILE *
  64 freopen(file, mode, fp)
  65         const char *file, *mode;
  66         FILE *fp;
  67 {
  68         int f;
  69         int flags, isopen, oflags, sverrno, wantfd;
  70
  71         _DIAGASSERT(file != NULL);
  72         _DIAGASSERT(mode != NULL);
  73         _DIAGASSERT(fp != NULL);
  74
  75         if ((flags = __sflags(mode, &oflags)) == 0) {
  76                 (void) fclose(fp);
  77                 return (NULL);
  78         }
  79
  80         if (!__sdidinit)
  81                 __sinit();
  82
  83         /*
  84          * There are actually programs that depend on being able to "freopen"
  85          * descriptors that weren't originally open.  Keep this from breaking.
  86          * Remember whether the stream was open to begin with, and which file
  87          * descriptor (if any) was associated with it.  If it was attached to
  88          * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
  89          * should work.  This is unnecessary if it was not a Unix file.
  90          */
  91         if (fp->_flags == 0) {
  92                 fp->_flags = __SEOF;    /* hold on to it */
  93                 isopen = 0;
  94                 wantfd = -1;
  95         } else {
  96                 /* flush the stream; ANSI doesn't require this. */
  97                 if (fp->_flags & __SWR)
  98                         (void) __sflush(fp);
  99                 /* if close is NULL, closing is a no-op, hence pointless */
 100                 isopen = fp->_close != NULL;
 101                 if ((wantfd = __sfileno(fp)) == -1 && isopen) {
 102                         (void) (*fp->_close)(fp->_cookie);
 103                         isopen = 0;
 104                 }
 105         }
 106
 107         /* Get a new descriptor to refer to the new file. */
 108         f = open(file, oflags, DEFFILEMODE);
 109         if (f < 0 && isopen) {
 110                 /* If out of fd's close the old one and try again. */
 111                 if (errno == ENFILE || errno == EMFILE) {
 112                         (void) (*fp->_close)(fp->_cookie);
 113                         isopen = 0;
 114                         f = open(file, oflags, DEFFILEMODE);
 115                 }
 116         }
 117         sverrno = errno;
 118
 119         /*
 120          * Finish closing fp.  Even if the open succeeded above, we cannot
 121          * keep fp->_base: it may be the wrong size.  This loses the effect
 122          * of any setbuffer calls, but stdio has always done this before.
 123          */
 124         if (isopen && f != wantfd)
 125                 (void) (*fp->_close)(fp->_cookie);
 126         if (fp->_flags & __SMBF)
 127                 free((char *)fp->_bf._base);
 128         fp->_w = 0;
 129         fp->_r = 0;
 130         fp->_p = NULL;
 131         fp->_bf._base = NULL;
 132         fp->_bf._size = 0;
 133         fp->_lbfsize = 0;
 134         if (HASUB(fp))
 135                 FREEUB(fp);
 136         WCIO_FREE(fp);
 137         _UB(fp)._size = 0;
 138         if (HASLB(fp))
 139                 FREELB(fp);
 140         fp->_lb._size = 0;
 141
 142         if (f < 0) {                    /* did not get it after all */
 143                 fp->_flags = 0;         /* set it free */
 144                 errno = sverrno;        /* restore in case _close clobbered */
 145                 return (NULL);
 146         }
 147
 148         if (oflags & O_NONBLOCK) {
 149                 struct stat st;
 150                 if (fstat(f, &st) == -1) {
 151                         sverrno = errno;
 152                         (void)close(f);
 153                         errno = sverrno;
 154                         return (NULL);
 155                 }
 156                 if (!S_ISREG(st.st_mode)) {
 157                         (void)close(f);
 158                         errno = EFTYPE;
 159                         return (NULL);
 160                 }
 161         }
 162
 163         /*
 164          * If reopening something that was open before on a real file, try
 165          * to maintain the descriptor.  Various C library routines (perror)
 166          * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
 167          */
 168         if (wantfd >= 0 && f != wantfd) {
 169                 if (dup2(f, wantfd) >= 0) {
 170                         (void) close(f);
 171                         f = wantfd;
 172                 }
 173         }
 174
 175         /*
 176          * File descriptors are a full int, but _file is only a short.
 177          * If we get a valid file descriptor that is greater or equal to
 178          * USHRT_MAX, then the fd will get sign-extended into an
 179          * invalid file descriptor.  Handle this case by failing the
 180          * open. (We treat the short as unsigned, and special-case -1).
 181          */
 182         if (f >= USHRT_MAX) {
 183                 (void)close(f);
 184                 errno = EMFILE;
 185                 return NULL;
 186         }
 187
 188         fp->_flags = flags;
 189         fp->_file = f;
 190         fp->_cookie = fp;
 191         fp->_read = __sread;
 192         fp->_write = __swrite;
 193         fp->_seek = __sseek;
 194         fp->_close = __sclose;
 195
 196         /*
 197          * When reopening in append mode, even though we use O_APPEND,
 198          * we need to seek to the end so that ftell() gets the right
 199          * answer.  If the user then alters the seek pointer, or
 200          * the file extends, this will fail, but there is not much
 201          * we can do about this.  (We could set __SAPP and check in
 202          * fseek and ftell.)
 203          */
 204         if (oflags & O_APPEND)
 205                 (void) __sseek((void *)fp, (fpos_t)0, SEEK_END);
 206         return (fp);
 207 }