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))
67 /* A hack to get MPASS macro */
70 #include <machine/cpu.h>
73 seq_in_modify(seq_t seqp)
80 seq_write_begin(seq_t *seqp)
83 MPASS(!seq_in_modify(*seqp));
85 atomic_thread_fence_rel();
89 seq_write_end(seq_t *seqp)
92 atomic_store_rel_int(seqp, *seqp + 1);
93 MPASS(!seq_in_modify(*seqp));
97 seq_read(const seq_t *seqp)
102 ret = atomic_load_acq_int(__DECONST(seq_t *, seqp));
103 if (seq_in_modify(ret)) {
113 static __inline seq_t
114 seq_consistent_nomb(const seq_t *seqp, seq_t oldseq)
117 return (*seqp == oldseq);
120 static __inline seq_t
121 seq_consistent(const seq_t *seqp, seq_t oldseq)
124 atomic_thread_fence_acq();
125 return (seq_consistent_nomb(seqp, oldseq));
129 #endif /* _SYS_SEQ_H_ */