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refcount.h revision 1.2 
      1 /*	$NetBSD: refcount.h,v 1.2 2021/12/19 10:48:37 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2020 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     17  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     18  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     19  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     20  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     21  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     22  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     23  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     24  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     25  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     26  * POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #ifndef _LINUX_REFCOUNT_H_
     30 #define _LINUX_REFCOUNT_H_
     31 
     32 #include <linux/atomic.h>
     33 #include <linux/mutex.h>
     34 #include <linux/spinlock.h>
     35 
     36 typedef struct refcount refcount_t;
     37 
     38 struct refcount {
     39 	atomic_t	rc_count;
     40 };
     41 
     42 static inline void
     43 refcount_set(struct refcount *rc, int n)
     44 {
     45 	atomic_set(&rc->rc_count, n);
     46 }
     47 
     48 static inline void
     49 refcount_inc(struct refcount *rc)
     50 {
     51 	atomic_inc(&rc->rc_count);
     52 }
     53 
     54 static inline int __must_check
     55 refcount_inc_not_zero(struct refcount *rc)
     56 {
     57 	unsigned old, new;
     58 
     59 	do {
     60 		old = atomic_read(&rc->rc_count);
     61 		if (old == 0)
     62 			break;
     63 		new = old + 1;
     64 	} while (atomic_cmpxchg(&rc->rc_count, old, new) != old);
     65 
     66 	return old;
     67 }
     68 
     69 static inline bool __must_check
     70 refcount_dec_and_test(struct refcount *rc)
     71 {
     72 	unsigned old, new;
     73 
     74 	do {
     75 		old = atomic_read(&rc->rc_count);
     76 		KASSERT(old);
     77 		new = old - 1;
     78 	} while (atomic_cmpxchg(&rc->rc_count, old, new) != old);
     79 
     80 	return old == 1;
     81 }
     82 
     83 static inline bool __must_check
     84 refcount_dec_and_lock_irqsave(struct refcount *rc, struct spinlock *lock,
     85     unsigned long *flagsp)
     86 {
     87 	unsigned old, new;
     88 
     89 	do {
     90 		old = atomic_read(&rc->rc_count);
     91 		KASSERT(old);
     92 		if (old == 1) {
     93 			spin_lock_irqsave(lock, *flagsp);
     94 			if (atomic_dec_return(&rc->rc_count) == 0)
     95 				return true;
     96 			spin_unlock_irqrestore(lock, *flagsp);
     97 			return false;
     98 		}
     99 		new = old - 1;
    100 	} while (atomic_cmpxchg(&rc->rc_count, old, new) != old);
    101 
    102 	KASSERT(old != 1);
    103 	KASSERT(new != 0);
    104 	return false;
    105 }
    106 
    107 static inline bool __must_check
    108 refcount_dec_and_mutex_lock(struct refcount *rc, struct mutex *lock)
    109 {
    110 	unsigned old, new;
    111 
    112 	do {
    113 		old = atomic_read(&rc->rc_count);
    114 		KASSERT(old);
    115 		if (old == 1) {
    116 			mutex_lock(lock);
    117 			if (atomic_dec_return(&rc->rc_count) == 0)
    118 				return true;
    119 			mutex_unlock(lock);
    120 			return false;
    121 		}
    122 		new = old - 1;
    123 	} while (atomic_cmpxchg(&rc->rc_count, old, new) != old);
    124 
    125 	KASSERT(old != 1);
    126 	KASSERT(new != 0);
    127 	return false;
    128 }
    129 
    130 #endif  /* _LINUX_REFCOUNT_H_ */
    131