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freopen.c revision 1.4 
      1 /*	$NetBSD: freopen.c,v 1.4 1995/02/02 02:09:36 jtc 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. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *	This product includes software developed by the University of
     21  *	California, Berkeley and its contributors.
     22  * 4. Neither the name of the University nor the names of its contributors
     23  *    may be used to endorse or promote products derived from this software
     24  *    without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     36  * SUCH DAMAGE.
     37  */
     38 
     39 #if defined(LIBC_SCCS) && !defined(lint)
     40 #if 0
     41 static char sccsid[] = "@(#)freopen.c	8.1 (Berkeley) 6/4/93";
     42 #endif
     43 static char rcsid[] = "$NetBSD: freopen.c,v 1.4 1995/02/02 02:09:36 jtc Exp $";
     44 #endif /* LIBC_SCCS and not lint */
     45 
     46 #include <sys/types.h>
     47 #include <sys/stat.h>
     48 #include <fcntl.h>
     49 #include <errno.h>
     50 #include <unistd.h>
     51 #include <stdio.h>
     52 #include <stdlib.h>
     53 #include "local.h"
     54 
     55 /*
     56  * Re-direct an existing, open (probably) file to some other file.
     57  * ANSI is written such that the original file gets closed if at
     58  * all possible, no matter what.
     59  */
     60 FILE *
     61 freopen(file, mode, fp)
     62 	const char *file, *mode;
     63 	register FILE *fp;
     64 {
     65 	register int f;
     66 	int flags, isopen, oflags, sverrno, wantfd;
     67 
     68 	if ((flags = __sflags(mode, &oflags)) == 0) {
     69 		(void) fclose(fp);
     70 		return (NULL);
     71 	}
     72 
     73 	if (!__sdidinit)
     74 		__sinit();
     75 
     76 	/*
     77 	 * There are actually programs that depend on being able to "freopen"
     78 	 * descriptors that weren't originally open.  Keep this from breaking.
     79 	 * Remember whether the stream was open to begin with, and which file
     80 	 * descriptor (if any) was associated with it.  If it was attached to
     81 	 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
     82 	 * should work.  This is unnecessary if it was not a Unix file.
     83 	 */
     84 	if (fp->_flags == 0) {
     85 		fp->_flags = __SEOF;	/* hold on to it */
     86 		isopen = 0;
     87 		wantfd = -1;
     88 	} else {
     89 		/* flush the stream; ANSI doesn't require this. */
     90 		if (fp->_flags & __SWR)
     91 			(void) __sflush(fp);
     92 		/* if close is NULL, closing is a no-op, hence pointless */
     93 		isopen = fp->_close != NULL;
     94 		if ((wantfd = fp->_file) < 0 && isopen) {
     95 			(void) (*fp->_close)(fp->_cookie);
     96 			isopen = 0;
     97 		}
     98 	}
     99 
    100 	/* Get a new descriptor to refer to the new file. */
    101 	f = open(file, oflags, DEFFILEMODE);
    102 	if (f < 0 && isopen) {
    103 		/* If out of fd's close the old one and try again. */
    104 		if (errno == ENFILE || errno == EMFILE) {
    105 			(void) (*fp->_close)(fp->_cookie);
    106 			isopen = 0;
    107 			f = open(file, oflags, DEFFILEMODE);
    108 		}
    109 	}
    110 	sverrno = errno;
    111 
    112 	/*
    113 	 * Finish closing fp.  Even if the open succeeded above, we cannot
    114 	 * keep fp->_base: it may be the wrong size.  This loses the effect
    115 	 * of any setbuffer calls, but stdio has always done this before.
    116 	 */
    117 	if (isopen)
    118 		(void) (*fp->_close)(fp->_cookie);
    119 	if (fp->_flags & __SMBF)
    120 		free((char *)fp->_bf._base);
    121 	fp->_w = 0;
    122 	fp->_r = 0;
    123 	fp->_p = NULL;
    124 	fp->_bf._base = NULL;
    125 	fp->_bf._size = 0;
    126 	fp->_lbfsize = 0;
    127 	if (HASUB(fp))
    128 		FREEUB(fp);
    129 	fp->_ub._size = 0;
    130 	if (HASLB(fp))
    131 		FREELB(fp);
    132 	fp->_lb._size = 0;
    133 
    134 	if (f < 0) {			/* did not get it after all */
    135 		fp->_flags = 0;		/* set it free */
    136 		errno = sverrno;	/* restore in case _close clobbered */
    137 		return (NULL);
    138 	}
    139 
    140 	/*
    141 	 * If reopening something that was open before on a real file, try
    142 	 * to maintain the descriptor.  Various C library routines (perror)
    143 	 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
    144 	 */
    145 	if (wantfd >= 0 && f != wantfd) {
    146 		if (dup2(f, wantfd) >= 0) {
    147 			(void) close(f);
    148 			f = wantfd;
    149 		}
    150 	}
    151 
    152 	fp->_flags = flags;
    153 	fp->_file = f;
    154 	fp->_cookie = fp;
    155 	fp->_read = __sread;
    156 	fp->_write = __swrite;
    157 	fp->_seek = __sseek;
    158 	fp->_close = __sclose;
    159 	return (fp);
    160 }
    161