/*	$NetBSD: rwsem.h,v 1.5 2021/12/19 11:22:00 riastradh Exp $	*/

/*-
 * Copyright (c) 2014 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Taylor R. Campbell.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

/*
 * These are not really semaphores; they are just reader/writer sleep
 * locks, whereas what Linux calls an rwlock is a reader/writer spin
 * lock.
 *
 * Notes on porting:
 *
 * - Linux does not have destroy_rwsem.  You must add it yourself in
 *   the appropriate place.
 */

#ifndef _LINUX_RWSEM_H_
#define _LINUX_RWSEM_H_

#include <sys/mutex.h>

#define	destroy_rwsem		linux_destroy_rwsem
#define	down_read		linux_down_read
#define	down_read_trylock	linux_down_read_trylock
#define	down_write		linux_down_write
#define	downgrade_write		linux_downgrade_write
#define	init_rwsem		linux_init_rwsem
#define	up_read			linux_up_read
#define	up_write		linux_up_write

struct rw_semaphore {
	/*
	 * Note: rws_lock and rws_cv must not be first; doing so
	 * confuses lockdebug.
	 */
	struct lwp	*rws_writer;
	unsigned	rws_readers;
	bool		rws_writewanted;
	bool		rws_debug;
	kmutex_t	rws_lock;
	kcondvar_t	rws_cv;
};

void init_rwsem(struct rw_semaphore *);
void destroy_rwsem(struct rw_semaphore *);
void down_read(struct rw_semaphore *);
bool down_read_trylock(struct rw_semaphore *);
void down_write(struct rw_semaphore *);
void up_read(struct rw_semaphore *);
void up_write(struct rw_semaphore *);
void downgrade_write(struct rw_semaphore *);

#endif  /* _LINUX_RWSEM_H_ */