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Add O_REGULAR to enforce opening of only regular files
(like we have O_DIRECTORY for directories).
This is better than open(, O_NONBLOCK), fstat()+S_ISREG() because opening
devices can have side effects.

/*	$NetBSD: flags.c,v 1.19 2017/11/09 20:30:02 christos Exp $	*/

/*-
 * 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.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)flags.c	8.1 (Berkeley) 6/4/93";
#else
__RCSID("$NetBSD: flags.c,v 1.19 2017/11/09 20:30:02 christos Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>
#include <assert.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include "reentrant.h"
#include "local.h"

/*
 * Return the (stdio) flags for a given mode.  Store the flags
 * to be passed to an open() syscall through *optr.
 * Return 0 on error.
 */
int
__sflags(const char *mode, int *optr)
{
	int ret, m, o;

	_DIAGASSERT(mode != NULL);

	switch (*mode++) {

	case 'r':	/* open for reading */
		ret = __SRD;
		m = O_RDONLY;
		o = 0;
		break;

	case 'w':	/* open for writing */
		ret = __SWR;
		m = O_WRONLY;
		o = O_CREAT | O_TRUNC;
		break;

	case 'a':	/* open for appending */
		ret = __SWR;
		m = O_WRONLY;
		o = O_CREAT | O_APPEND;
		break;

	default:	/* illegal mode */
		errno = EINVAL;
		return 0;
	}

	/*
	 * [rwa]\+ or [rwa]b\+ means read and write 
	 * e means set close on exec.
	 * f means open only plain files.
	 * l means don't follow symlinks.
	 * x means exclusive open.
	 */
	for (; *mode; mode++)
		switch (*mode) {
		case '+':
			ret = __SRW;
			m = O_RDWR;
			break;
		case 'b':
			break;
		case 'e':
			o |= O_CLOEXEC;
			break;
		case 'f':
			o |= O_REGULAR;
			break;
		case 'l':
			o |= O_NOFOLLOW;
			break;
		case 'x':
			o |= O_EXCL;
			break;
		default:	/* We could produce a warning here */
			break;
		}

	*optr = m | o;
	return ret;
}