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
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
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))
66 /* A hack to get MPASS macro */
69 #include <machine/cpu.h>
72 seq_in_modify(seq_t seqp)
79 seq_write_begin(seq_t *seqp)
82 MPASS(!seq_in_modify(*seqp));
84 atomic_thread_fence_rel();
88 seq_write_end(seq_t *seqp)
91 atomic_store_rel_int(seqp, *seqp + 1);
92 MPASS(!seq_in_modify(*seqp));
96 seq_read(const seq_t *seqp)
101 ret = atomic_load_acq_int(__DECONST(seq_t *, seqp));
102 if (seq_in_modify(ret)) {
112 static __inline seq_t
113 seq_consistent_nomb(const seq_t *seqp, seq_t oldseq)
116 return (*seqp == oldseq);
119 static __inline seq_t
120 seq_consistent(const seq_t *seqp, seq_t oldseq)
123 atomic_thread_fence_acq();
124 return (seq_consistent_nomb(seqp, oldseq));
128 #endif /* _SYS_SEQ_H_ */