source: rtems-libbsd/freebsd/sys/sys/seq.h @ c40e45b

5-freebsd-12
Last change on this file since c40e45b was c40e45b, checked in by Sebastian Huber <sebastian.huber@…>, on Oct 7, 2016 at 1:10:20 PM

Update to FreeBSD head 2016-08-23

Git mirror commit 9fe7c416e6abb28b1398fd3e5687099846800cfd.

  • Property mode set to 100644
File size: 2.9 KB
Line 
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_SEQ_H_
29#define _SYS_SEQ_H_
30
31#ifdef _KERNEL
32#include <sys/systm.h>
33#endif
34#include <sys/types.h>
35
36/*
37 * seq_t may be included in structs visible to userspace
38 */
39typedef uint32_t seq_t;
40
41#ifdef _KERNEL
42
43/*
44 * Typical usage:
45 *
46 * writers:
47 *      lock_exclusive(&obj->lock);
48 *      seq_write_begin(&obj->seq);
49 *      .....
50 *      seq_write_end(&obj->seq);
51 *      unlock_exclusive(&obj->unlock);
52 *
53 * readers:
54 *      obj_t lobj;
55 *      seq_t seq;
56 *
57 *      for (;;) {
58 *              seq = seq_read(&gobj->seq);
59 *              lobj = gobj;
60 *              if (seq_consistent(&gobj->seq, seq))
61 *                      break;
62 *              cpu_spinwait();
63 *      }
64 *      foo(lobj);
65 */             
66
67/* A hack to get MPASS macro */
68#include <rtems/bsd/sys/lock.h>
69
70#include <machine/cpu.h>
71
72static __inline bool
73seq_in_modify(seq_t seqp)
74{
75
76        return (seqp & 1);
77}
78
79static __inline void
80seq_write_begin(seq_t *seqp)
81{
82
83        MPASS(!seq_in_modify(*seqp));
84        *seqp += 1;
85        atomic_thread_fence_rel();
86}
87
88static __inline void
89seq_write_end(seq_t *seqp)
90{
91
92        atomic_store_rel_int(seqp, *seqp + 1);
93        MPASS(!seq_in_modify(*seqp));
94}
95
96static __inline seq_t
97seq_read(const seq_t *seqp)
98{
99        seq_t ret;
100
101        for (;;) {
102                ret = atomic_load_acq_int(__DECONST(seq_t *, seqp));
103                if (seq_in_modify(ret)) {
104                        cpu_spinwait();
105                        continue;
106                }
107                break;
108        }
109
110        return (ret);
111}
112
113static __inline seq_t
114seq_consistent_nomb(const seq_t *seqp, seq_t oldseq)
115{
116
117        return (*seqp == oldseq);
118}
119
120static __inline seq_t
121seq_consistent(const seq_t *seqp, seq_t oldseq)
122{
123
124        atomic_thread_fence_acq();
125        return (seq_consistent_nomb(seqp, oldseq));
126}
127
128#endif  /* _KERNEL */
129#endif  /* _SYS_SEQ_H_ */
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