FreeBSD/Linux Kernel Cross Reference
sys/sys/seqc.h
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 * $FreeBSD$
26 */
27
28 #ifndef _SYS_SEQC_H_
29 #define _SYS_SEQC_H_
30
31 #ifdef _KERNEL
32 #include <sys/systm.h>
33 #endif
34 #include <sys/types.h>
35
36 /*
37 * seqc_t may be included in structs visible to userspace
38 */
39 #include <sys/_seqc.h>
40
41 #ifdef _KERNEL
42
43 /* A hack to get MPASS macro */
44 #include <sys/lock.h>
45
46 #include <machine/cpu.h>
47
48 #define SEQC_MOD 1
49
50 /*
51 * Predicts from inline functions are not honored by clang.
52 */
53 #define seqc_in_modify(seqc) ({ \
54 seqc_t __seqc = (seqc); \
55 \
56 __predict_false(__seqc & SEQC_MOD); \
57 })
58
59 static __inline void
60 seqc_write_begin(seqc_t *seqcp)
61 {
62
63 critical_enter();
64 MPASS(!seqc_in_modify(*seqcp));
65 *seqcp += SEQC_MOD;
66 atomic_thread_fence_rel();
67 }
68
69 static __inline void
70 seqc_write_end(seqc_t *seqcp)
71 {
72
73 atomic_thread_fence_rel();
74 *seqcp += SEQC_MOD;
75 MPASS(!seqc_in_modify(*seqcp));
76 critical_exit();
77 }
78
79 static __inline seqc_t
80 seqc_read_any(const seqc_t *seqcp)
81 {
82
83 return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp)));
84 }
85
86 static __inline seqc_t
87 seqc_read_notmodify(const seqc_t *seqcp)
88 {
89
90 return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp)) & ~SEQC_MOD);
91 }
92
93 static __inline seqc_t
94 seqc_read(const seqc_t *seqcp)
95 {
96 seqc_t ret;
97
98 for (;;) {
99 ret = seqc_read_any(seqcp);
100 if (seqc_in_modify(ret)) {
101 cpu_spinwait();
102 continue;
103 }
104 break;
105 }
106
107 return (ret);
108 }
109
110 #define seqc_consistent_no_fence(seqcp, oldseqc)({ \
111 const seqc_t *__seqcp = (seqcp); \
112 seqc_t __oldseqc = (oldseqc); \
113 \
114 MPASS(!(seqc_in_modify(__oldseqc))); \
115 __predict_true(*__seqcp == __oldseqc); \
116 })
117
118 #define seqc_consistent(seqcp, oldseqc) ({ \
119 atomic_thread_fence_acq(); \
120 seqc_consistent_no_fence(seqcp, oldseqc); \
121 })
122
123 /*
124 * Variant which does not critical enter/exit.
125 */
126 static __inline void
127 seqc_sleepable_write_begin(seqc_t *seqcp)
128 {
129
130 MPASS(!seqc_in_modify(*seqcp));
131 *seqcp += SEQC_MOD;
132 atomic_thread_fence_rel();
133 }
134
135 static __inline void
136 seqc_sleepable_write_end(seqc_t *seqcp)
137 {
138
139 atomic_thread_fence_rel();
140 *seqcp += SEQC_MOD;
141 MPASS(!seqc_in_modify(*seqcp));
142 }
143
144 #endif /* _KERNEL */
145 #endif /* _SYS_SEQC_H_ */
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