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kref.h revision 1.4 
      1 /*	$NetBSD: kref.h,v 1.4 2014/07/16 20:59:58 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/mutex.h>
     40 
     41 struct kref {
     42 	unsigned int kr_count;
     43 };
     44 
     45 static inline void
     46 kref_init(struct kref *kref)
     47 {
     48 	kref->kr_count = 1;
     49 }
     50 
     51 static inline void
     52 kref_get(struct kref *kref)
     53 {
     54 	const unsigned int count __unused =
     55 	    atomic_inc_uint_nv(&kref->kr_count);
     56 
     57 	KASSERTMSG((count > 1), "getting released kref");
     58 }
     59 
     60 static inline bool
     61 kref_get_unless_zero(struct kref *kref)
     62 {
     63 	unsigned count;
     64 
     65 	do {
     66 		count = kref->kr_count;
     67 		if ((count == 0) || (count == UINT_MAX))
     68 			return false;
     69 	} while (atomic_cas_uint(&kref->kr_count, count, (count + 1)) !=
     70 	    count);
     71 
     72 	return true;
     73 }
     74 
     75 static inline int
     76 kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *))
     77 {
     78 	unsigned int old, new;
     79 
     80 	do {
     81 		old = kref->kr_count;
     82 		KASSERTMSG((count <= old), "overreleasing kref: %u - %u",
     83 		    old, count);
     84 		new = (old - count);
     85 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
     86 
     87 	if (new == 0) {
     88 		(*release)(kref);
     89 		return 1;
     90 	}
     91 
     92 	return 0;
     93 }
     94 
     95 static inline int
     96 kref_put(struct kref *kref, void (*release)(struct kref *))
     97 {
     98 
     99 	return kref_sub(kref, 1, release);
    100 }
    101 
    102 static inline int
    103 kref_put_mutex(struct kref *kref, void (*release)(struct kref *),
    104     struct mutex *interlock)
    105 {
    106 	unsigned int old, new;
    107 
    108 	do {
    109 		old = kref->kr_count;
    110 		KASSERT(old > 0);
    111 		if (old == 1) {
    112 			mutex_lock(interlock);
    113 			if (atomic_add_int_nv(&kref->kr_count, -1) == 0) {
    114 				(*release)(kref);
    115 				return 1;
    116 			}
    117 			mutex_unlock(interlock);
    118 			return 0;
    119 		}
    120 		new = (old - 1);
    121 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
    122 
    123 	return 0;
    124 }
    125 
    126 /*
    127  * Not native to Linux.  Mostly used for assertions...
    128  */
    129 
    130 static inline bool
    131 kref_referenced_p(struct kref *kref)
    132 {
    133 
    134 	return (0 < kref->kr_count);
    135 }
    136 
    137 static inline bool
    138 kref_exclusive_p(struct kref *kref)
    139 {
    140 
    141 	KASSERT(0 < kref->kr_count);
    142 	return (kref->kr_count == 1);
    143 }
    144 
    145 #endif  /* _LINUX_KREF_H_ */
    146