1/*-
2 * Copyright (c) 2014 Mateusz Guzik <mjg@FreeBSD.org>
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23 * SUCH DAMAGE.
24 */
25
26#ifndef _SYS_SEQC_H_
27#define _SYS_SEQC_H_
28
29#ifdef _KERNEL
30#include <sys/systm.h>
31#endif
32#include <sys/types.h>
33
34/*
35 * seqc_t may be included in structs visible to userspace
36 */
37#include <sys/_seqc.h>
38
39#ifdef _KERNEL
40
41/* A hack to get MPASS macro */
42#include <sys/lock.h>
43
44#include <machine/cpu.h>
45
46#define SEQC_MOD 1
47
48/*
49 * Predicts from inline functions are not honored by clang.
50 */
51#define seqc_in_modify(seqc) ({ \
52 seqc_t __seqc = (seqc); \
53 \
54 __predict_false(__seqc & SEQC_MOD); \
55})
56
57static __inline void
58seqc_write_begin(seqc_t *seqcp)
59{
60
61 critical_enter();
62 MPASS(!seqc_in_modify(*seqcp));
63 *seqcp += SEQC_MOD;
64 atomic_thread_fence_rel();
65}
66
67static __inline void
68seqc_write_end(seqc_t *seqcp)
69{
70
71 atomic_thread_fence_rel();
72 *seqcp += SEQC_MOD;
73 MPASS(!seqc_in_modify(*seqcp));
74 critical_exit();
75}
76
77static __inline seqc_t
78seqc_read_any(const seqc_t *seqcp)
79{
80
81 return (atomic_load_acq_int(seqcp));
82}
83
84static __inline seqc_t
85seqc_read_notmodify(const seqc_t *seqcp)
86{
87
88 return (atomic_load_acq_int(seqcp) & ~SEQC_MOD);
89}
90
91static __inline seqc_t
92seqc_read(const seqc_t *seqcp)
93{
94 seqc_t ret;
95
96 for (;;) {
97 ret = seqc_read_any(seqcp);
98 if (seqc_in_modify(ret)) {
99 cpu_spinwait();
100 continue;
101 }
102 break;
103 }
104
105 return (ret);
106}
107
108#define seqc_consistent_no_fence(seqcp, oldseqc)({ \
109 const seqc_t *__seqcp = (seqcp); \
110 seqc_t __oldseqc = (oldseqc); \
111 \
112 MPASS(!(seqc_in_modify(__oldseqc))); \
113 __predict_true(*__seqcp == __oldseqc); \
114})
115
116#define seqc_consistent(seqcp, oldseqc) ({ \
117 atomic_thread_fence_acq(); \
118 seqc_consistent_no_fence(seqcp, oldseqc); \
119})
120
121/*
122 * Variant which does not critical enter/exit.
123 */
124static __inline void
125seqc_sleepable_write_begin(seqc_t *seqcp)
126{
127
128 MPASS(!seqc_in_modify(*seqcp));
129 *seqcp += SEQC_MOD;
130 atomic_thread_fence_rel();
131}
132
133static __inline void
134seqc_sleepable_write_end(seqc_t *seqcp)
135{
136
137 atomic_thread_fence_rel();
138 *seqcp += SEQC_MOD;
139 MPASS(!seqc_in_modify(*seqcp));
140}
141
142#endif /* _KERNEL */
143#endif /* _SYS_SEQC_H_ */