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seqlock.h revision 1.2 
      1 /*	$NetBSD: seqlock.h,v 1.2 2021/12/19 00:47:40 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2018 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 #ifndef	_LINUX_SEQLOCK_H_
     33 #define	_LINUX_SEQLOCK_H_
     34 
     35 #include <sys/types.h>
     36 #include <sys/atomic.h>
     37 #include <sys/lock.h>
     38 
     39 #include <lib/libkern/libkern.h>
     40 
     41 struct seqlock {
     42 	uint64_t	sql_gen;
     43 };
     44 
     45 typedef struct seqlock seqlock_t;
     46 
     47 static inline void
     48 seqlock_init(struct seqlock *seqlock)
     49 {
     50 
     51 	seqlock->sql_gen = 0;
     52 }
     53 
     54 static inline void
     55 write_seqlock(struct seqlock *seqlock)
     56 {
     57 
     58 	KASSERT((seqlock->sql_gen & 1) == 0);
     59 	seqlock->sql_gen |= 1;
     60 	membar_producer();
     61 }
     62 
     63 static inline void
     64 write_sequnlock(struct seqlock *seqlock)
     65 {
     66 
     67 	KASSERT((seqlock->sql_gen & 1) == 1);
     68 	membar_producer();
     69 	seqlock->sql_gen |= 1;	/* paraonia */
     70 	seqlock->sql_gen++;
     71 }
     72 
     73 #define	write_seqlock_irqsave(SEQLOCK, FLAGS)	do {			      \
     74 	(FLAGS) = (unsigned long)splvm();				      \
     75 	write_seqlock(SEQLOCK);						      \
     76 } while (0)
     77 
     78 #define	write_sequnlock_irqrestore(SEQLOCK, FLAGS)	do {		      \
     79 	write_seqlock(SEQLOCK);						      \
     80 	splx((int)(FLAGS));						      \
     81 } while (0)
     82 
     83 static inline uint64_t
     84 read_seqbegin(struct seqlock *seqlock)
     85 {
     86 	uint64_t gen;
     87 
     88 	while ((gen = seqlock->sql_gen) & 1)
     89 		SPINLOCK_BACKOFF_HOOK;
     90 	membar_consumer();
     91 
     92 	return gen;
     93 }
     94 
     95 static inline bool
     96 read_seqretry(struct seqlock *seqlock, uint64_t gen)
     97 {
     98 
     99 	return gen != seqlock->sql_gen;
    100 }
    101 
    102 #endif	/* _LINUX_SEQLOCK_H_ */
    103