freebsd-src/lib/libc/stdio/fflush.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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. 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.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)fflush.c	8.1 (Berkeley) 6/4/93";
#endif /* LIBC_SCCS and not lint */
#include <sys/cdefs.h>
#include "namespace.h"
#include <errno.h>
#include <stdio.h>
#include "un-namespace.h"
#include "libc_private.h"
#include "local.h"

static int	sflush_locked(FILE *);

/*
 * Flush a single file, or (if fp is NULL) all files.
 * MT-safe version
 */
int
fflush(FILE *fp)
{
	int retval;

	if (fp == NULL)
		return (_fwalk(sflush_locked));
	FLOCKFILE_CANCELSAFE(fp);

	/*
	 * There is disagreement about the correct behaviour of fflush()
	 * when passed a file which is not open for writing.  According to
	 * the ISO C standard, the behaviour is undefined.
	 * Under linux, such an fflush returns success and has no effect;
	 * under Windows, such an fflush is documented as behaving instead
	 * as fpurge().
	 * Given that applications may be written with the expectation of
	 * either of these two behaviours, the only safe (non-astonishing)
	 * option is to return EBADF and ask that applications be fixed.
	 * SUSv3 now requires that fflush() returns success on a read-only
	 * stream.
	 *
	 */
	if ((fp->_flags & (__SWR | __SRW)) == 0)
		retval = 0;
	else
		retval = __sflush(fp);
	FUNLOCKFILE_CANCELSAFE();
	return (retval);
}

/*
 * Flush a single file, or (if fp is NULL) all files.
 * Non-MT-safe version
 */
int
__fflush(FILE *fp)
{
	int retval;

	if (fp == NULL)
		return (_fwalk(sflush_locked));
	if ((fp->_flags & (__SWR | __SRW)) == 0)
		retval = 0;
	else
		retval = __sflush(fp);
	return (retval);
}

__weak_reference(__fflush, fflush_unlocked);

int
__sflush(FILE *fp)
{
	unsigned char *p;
	int n, f, t;

	f = fp->_flags;
	if ((f & __SWR) == 0)
		return (0);

	if ((p = fp->_bf._base) == NULL)
		return (0);

	n = fp->_p - p;		/* write this much */

	/*
	 * Set these immediately to avoid problems with longjmp and to allow
	 * exchange buffering (via setvbuf) in user write function.
	 */
	fp->_p = p;
	fp->_w = f & (__SLBF|__SNBF) ? 0 : fp->_bf._size;

	for (; n > 0; n -= t, p += t) {
		t = _swrite(fp, (char *)p, n);
		if (t <= 0) {
			if (p > fp->_p)
				/* Some was written. */
				memmove(fp->_p, p, n);
			/* Reset _p and _w. */
			fp->_p += n;
			if ((fp->_flags & __SNBF) == 0)
				fp->_w -= n;
			fp->_flags |= __SERR;
			return (EOF);
		}
	}
	return (0);
}

static int
sflush_locked(FILE *fp)
{
	int	ret;

	FLOCKFILE_CANCELSAFE(fp);
	ret = __sflush(fp);
	FUNLOCKFILE_CANCELSAFE();
	return (ret);
}