File:  [DragonFly] / src / lib / libc / stdio / freopen.c
Revision 1.4: download - view: text, annotated - select for diffs
Tue Jun 8 00:45:00 2004 UTC (9 years, 10 months ago) by hmp
Branches: MAIN
CVS tags: HEAD, DragonFly_Snap29Sep2004, DragonFly_Snap13Sep2004, DragonFly_1_0_REL, DragonFly_1_0_RC1, DragonFly_1_0A_REL
C99 update: freopen(3) with NULL 'path' argument so that it opens the
same file with a different mode.

At the moment, we just recycle the old file descriptor instead of storing
it somewhere and using that to reopen the file, as the standard seems to
require.  Strictly conforming C99 applications would probably not be able
to tell the difference but POSIX ones can.

While I am there, update the manual page about the new functionality and
correct nearby mdoc(7) markup errors.

Original-work-by:    	Tim J. Robbins <tjr@freebsd.org>
Additional-work-by: 	Hiten Pandya <hmp@backplane.com>

/*-
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * @(#)freopen.c	8.1 (Berkeley) 6/4/93
 * $FreeBSD: src/lib/libc/stdio/freopen.c,v 1.5.2.1 2001/03/05 10:54:53 obrien Exp $
 * $DragonFly: src/lib/libc/stdio/freopen.c,v 1.4 2004/06/08 00:45:00 hmp Exp $
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include "libc_private.h"
#include "local.h"

/*
 * Re-direct an existing, open (probably) file to some other file.
 * ANSI is written such that the original file gets closed if at
 * all possible, no matter what.
 */
FILE *
freopen(const char *file, const char *mode, FILE *fp)
{
	int f;
	int dflags, flags, isopen, oflags, sverrno, wantfd;

	if ((flags = __sflags(mode, &oflags)) == 0) {
		(void) fclose(fp);
		return (NULL);
	}

	FLOCKFILE(fp);

	if (!__sdidinit)
		__sinit();

	sverrno = 0;

	/*
	 * If the filename is a NULL pointer, the caller is asking us to
	 * re-open the same file with a different mode. We allow this only
	 * if the modes are compatible.
	 */
	if (file == NULL) {
		/* See comment below regarding freopen() of closed files. */
		if (fp->_flags == 0) {
			FUNLOCKFILE(fp);
			errno = EINVAL;
			return (NULL);
		}
		if ((dflags = fcntl(fp->_file, F_GETFL)) < 0) {
			sverrno = errno;
			fclose(fp);
			FUNLOCKFILE(fp);
			errno = sverrno;
			return (NULL);
		}
		if ((dflags & O_ACCMODE) != O_RDWR && (dflags & O_ACCMODE) !=
		    (oflags & O_ACCMODE)) {
			fclose(fp);
			FUNLOCKFILE(fp);
			errno = EINVAL;
			return (NULL);
		}
		if ((oflags ^ dflags) & O_APPEND) {
			dflags &= ~O_APPEND;
			dflags |= oflags & O_APPEND;
			if (fcntl(fp->_file, F_SETFL, dflags) < 0) {
				sverrno = errno;
				fclose(fp);
				FUNLOCKFILE(fp);
				errno = sverrno;
				return (NULL);
			}
		}
		if (oflags & O_TRUNC)
			ftruncate(fp->_file, 0);
		if (fseeko(fp, 0, oflags & O_APPEND ? SEEK_END : SEEK_SET) < 0 &&
		    errno != ESPIPE) {
			sverrno = errno;
			fclose(fp);
			FUNLOCKFILE(fp);
			errno = sverrno;
			return (NULL);
		}
		f = fp->_file;
		isopen = 0;
		wantfd = -1;
		goto finish;
	}

	/*
	 * There are actually programs that depend on being able to "freopen"
	 * descriptors that weren't originally open.  Keep this from breaking.
	 * Remember whether the stream was open to begin with, and which file
	 * descriptor (if any) was associated with it.  If it was attached to
	 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
	 * should work.  This is unnecessary if it was not a Unix file.
	 */
	if (fp->_flags == 0) {
		fp->_flags = __SEOF;	/* hold on to it */
		isopen = 0;
		wantfd = -1;
	} else {
		/* flush the stream; ANSI doesn't require this. */
		if (fp->_flags & __SWR)
			(void) __sflush(fp);
		/* if close is NULL, closing is a no-op, hence pointless */
		isopen = fp->_close != NULL;
		if ((wantfd = fp->_file) < 0 && isopen) {
			(void) (*fp->_close)(fp->_cookie);
			isopen = 0;
		}
	}

	/* Get a new descriptor to refer to the new file. */
	f = _open(file, oflags, DEFFILEMODE);
	if (f < 0 && isopen) {
		/* If out of fd's close the old one and try again. */
		if (errno == ENFILE || errno == EMFILE) {
			(void) (*fp->_close)(fp->_cookie);
			isopen = 0;
			f = _open(file, oflags, DEFFILEMODE);
		}
	}
	sverrno = errno;

finish:
	/*
	 * Finish closing fp.  Even if the open succeeded above, we cannot
	 * keep fp->_base: it may be the wrong size.  This loses the effect
	 * of any setbuffer calls, but stdio has always done this before.
	 */
	if (isopen)
		(void) (*fp->_close)(fp->_cookie);
	if (fp->_flags & __SMBF)
		free((char *)fp->_bf._base);
	fp->_w = 0;
	fp->_r = 0;
	fp->_p = NULL;
	fp->_bf._base = NULL;
	fp->_bf._size = 0;
	fp->_lbfsize = 0;
	if (HASUB(fp))
		FREEUB(fp);
	fp->_ub._size = 0;
	if (HASLB(fp))
		FREELB(fp);
	fp->_lb._size = 0;

	if (f < 0) {			/* did not get it after all */
		fp->_flags = 0;		/* set it free */
		errno = sverrno;	/* restore in case _close clobbered */
		FUNLOCKFILE(fp);
		return (NULL);
	}

	/*
	 * If reopening something that was open before on a real file, try
	 * to maintain the descriptor.  Various C library routines (perror)
	 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
	 */
	if (wantfd >= 0 && f != wantfd) {
		if (dup2(f, wantfd) >= 0) {
			(void)_close(f);
			f = wantfd;
		}
	}

	fp->_flags = flags;
	fp->_file = f;
	fp->_cookie = fp;
	fp->_read = __sread;
	fp->_write = __swrite;
	fp->_seek = __sseek;
	fp->_close = __sclose;
	FUNLOCKFILE(fp);
	return (fp);
}