kref.h revision 1.6 
1/*	$NetBSD: kref.h,v 1.6 2018/08/27 06:51:52 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
41struct kref {
42	unsigned int kr_count;
43};
44
45static inline void
46kref_init(struct kref *kref)
47{
48	kref->kr_count = 1;
49}
50
51static inline void
52kref_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
60static inline bool
61kref_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
75static inline int
76kref_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
95static inline int
96kref_put(struct kref *kref, void (*release)(struct kref *))
97{
98
99	return kref_sub(kref, 1, release);
100}
101
102static inline int
103kref_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
130static inline bool
131kref_referenced_p(struct kref *kref)
132{
133
134	return (0 < kref->kr_count);
135}
136
137static inline bool
138kref_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