2 * Copyright (c) 2014 Mateusz Guzik <mjg@FreeBSD.org>
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
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.
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
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32 #include <sys/systm.h>
34 #include <sys/types.h>
37 * seq_t may be included in structs visible to userspace
39 typedef uint32_t seq_t;
47 * lock_exclusive(&obj->lock);
48 * seq_write_begin(&obj->seq);
50 * seq_write_end(&obj->seq);
51 * unlock_exclusive(&obj->unlock);
58 * seq = seq_read(&gobj->seq);
60 * if (seq_consistent(&gobj->seq, seq))
67 /* A hack to get MPASS macro */
70 #include <machine/cpu.h>
73 * This is a temporary hack until memory barriers are cleaned up.
75 * atomic_load_acq_int at least on amd64 provides a full memory barrier,
76 * in a way which affects perforance.
78 * Hack below covers all architectures and avoids most of the penalty at least
82 atomic_load_acq_rmb_int(volatile u_int *p)
87 atomic_load_acq_int(&v);
92 seq_in_modify(seq_t seqp)
99 seq_write_begin(seq_t *seqp)
102 MPASS(!seq_in_modify(*seqp));
103 atomic_add_acq_int(seqp, 1);
107 seq_write_end(seq_t *seqp)
110 atomic_add_rel_int(seqp, 1);
111 MPASS(!seq_in_modify(*seqp));
114 static __inline seq_t
115 seq_read(seq_t *seqp)
120 ret = atomic_load_acq_rmb_int(seqp);
121 if (seq_in_modify(ret)) {
131 static __inline seq_t
132 seq_consistent(seq_t *seqp, seq_t oldseq)
135 return (atomic_load_acq_rmb_int(seqp) == oldseq);
138 static __inline seq_t
139 seq_consistent_nomb(seq_t *seqp, seq_t oldseq)
142 return (*seqp == oldseq);
146 #endif /* _SYS_SEQ_H_ */