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      1 /*	$NetBSD: rwsem.h,v 1.5 2021/12/19 11:22:00 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2014 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Taylor R. Campbell.
      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  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 /*
     33  * These are not really semaphores; they are just reader/writer sleep
     34  * locks, whereas what Linux calls an rwlock is a reader/writer spin
     35  * lock.
     36  *
     37  * Notes on porting:
     38  *
     39  * - Linux does not have destroy_rwsem.  You must add it yourself in
     40  *   the appropriate place.
     41  */
     42 
     43 #ifndef _LINUX_RWSEM_H_
     44 #define _LINUX_RWSEM_H_
     45 
     46 #include <sys/mutex.h>
     47 
     48 #define	destroy_rwsem		linux_destroy_rwsem
     49 #define	down_read		linux_down_read
     50 #define	down_read_trylock	linux_down_read_trylock
     51 #define	down_write		linux_down_write
     52 #define	downgrade_write		linux_downgrade_write
     53 #define	init_rwsem		linux_init_rwsem
     54 #define	up_read			linux_up_read
     55 #define	up_write		linux_up_write
     56 
     57 struct rw_semaphore {
     58 	/*
     59 	 * Note: rws_lock and rws_cv must not be first; doing so
     60 	 * confuses lockdebug.
     61 	 */
     62 	struct lwp	*rws_writer;
     63 	unsigned	rws_readers;
     64 	bool		rws_writewanted;
     65 	bool		rws_debug;
     66 	kmutex_t	rws_lock;
     67 	kcondvar_t	rws_cv;
     68 };
     69 
     70 void init_rwsem(struct rw_semaphore *);
     71 void destroy_rwsem(struct rw_semaphore *);
     72 void down_read(struct rw_semaphore *);
     73 bool down_read_trylock(struct rw_semaphore *);
     74 void down_write(struct rw_semaphore *);
     75 void up_read(struct rw_semaphore *);
     76 void up_write(struct rw_semaphore *);
     77 void downgrade_write(struct rw_semaphore *);
     78 
     79 #endif  /* _LINUX_RWSEM_H_ */
     80