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
kref_init(struct kref * kref)46 kref_init(struct kref *kref)
47 {
48 kref->kr_count = 1;
49 }
50
51 static inline void
kref_get(struct kref * kref)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
kref_get_unless_zero(struct kref * kref)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
kref_sub(struct kref * kref,unsigned int count,void (* release)(struct kref *))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
kref_put(struct kref * kref,void (* release)(struct kref *))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
kref_put_mutex(struct kref * kref,void (* release)(struct kref *),struct mutex * interlock)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
kref_referenced_p(struct kref * kref)131 kref_referenced_p(struct kref *kref)
132 {
133
134 return (0 < kref->kr_count);
135 }
136
137 static inline bool
kref_exclusive_p(struct kref * kref)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