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kref.h revision 1.8 
      1 /*	$NetBSD: kref.h,v 1.8 2021/12/19 00:46:50 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2013 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_KREF_H_
     33 #define _LINUX_KREF_H_
     34 
     35 #include <sys/types.h>
     36 #include <sys/atomic.h>
     37 #include <sys/systm.h>
     38 
     39 #include <linux/atomic.h>
     40 #include <linux/mutex.h>
     41 
     42 struct kref {
     43 	unsigned int kr_count;
     44 };
     45 
     46 static inline void
     47 kref_init(struct kref *kref)
     48 {
     49 	kref->kr_count = 1;
     50 }
     51 
     52 static inline void
     53 kref_get(struct kref *kref)
     54 {
     55 	const unsigned int count __unused =
     56 	    atomic_inc_uint_nv(&kref->kr_count);
     57 
     58 	KASSERTMSG((count > 1), "getting released kref");
     59 
     60 #ifndef __HAVE_ATOMIC_AS_MEMBAR
     61 	membar_enter();
     62 #endif
     63 }
     64 
     65 static inline bool
     66 kref_get_unless_zero(struct kref *kref)
     67 {
     68 	unsigned count;
     69 
     70 	do {
     71 		count = kref->kr_count;
     72 		if ((count == 0) || (count == UINT_MAX))
     73 			return false;
     74 	} while (atomic_cas_uint(&kref->kr_count, count, (count + 1)) !=
     75 	    count);
     76 
     77 #ifndef __HAVE_ATOMIC_AS_MEMBAR
     78 	membar_enter();
     79 #endif
     80 
     81 	return true;
     82 }
     83 
     84 static inline int
     85 kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *))
     86 {
     87 	unsigned int old, new;
     88 
     89 #ifndef __HAVE_ATOMIC_AS_MEMBAR
     90 	membar_exit();
     91 #endif
     92 
     93 	do {
     94 		old = kref->kr_count;
     95 		KASSERTMSG((count <= old), "overreleasing kref: %u - %u",
     96 		    old, count);
     97 		new = (old - count);
     98 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
     99 
    100 	if (new == 0) {
    101 		(*release)(kref);
    102 		return 1;
    103 	}
    104 
    105 	return 0;
    106 }
    107 
    108 static inline int
    109 kref_put(struct kref *kref, void (*release)(struct kref *))
    110 {
    111 
    112 	return kref_sub(kref, 1, release);
    113 }
    114 
    115 static inline int
    116 kref_put_mutex(struct kref *kref, void (*release)(struct kref *),
    117     struct mutex *interlock)
    118 {
    119 	unsigned int old, new;
    120 
    121 #ifndef __HAVE_ATOMIC_AS_MEMBAR
    122 	membar_exit();
    123 #endif
    124 
    125 	do {
    126 		old = kref->kr_count;
    127 		KASSERT(old > 0);
    128 		if (old == 1) {
    129 			mutex_lock(interlock);
    130 			if (atomic_add_int_nv(&kref->kr_count, -1) == 0) {
    131 				(*release)(kref);
    132 				return 1;
    133 			}
    134 			mutex_unlock(interlock);
    135 			return 0;
    136 		}
    137 		new = (old - 1);
    138 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
    139 
    140 	return 0;
    141 }
    142 
    143 static inline unsigned
    144 kref_read(const struct kref *kref)
    145 {
    146 	unsigned v;
    147 
    148 	v = kref->kr_count;
    149 	__insn_barrier();
    150 
    151 	return v;
    152 }
    153 
    154 /*
    155  * Not native to Linux.  Mostly used for assertions...
    156  */
    157 
    158 static inline bool
    159 kref_referenced_p(struct kref *kref)
    160 {
    161 
    162 	return (0 < kref->kr_count);
    163 }
    164 
    165 static inline bool
    166 kref_exclusive_p(struct kref *kref)
    167 {
    168 
    169 	KASSERT(0 < kref->kr_count);
    170 	return (kref->kr_count == 1);
    171 }
    172 
    173 #endif  /* _LINUX_KREF_H_ */
    174