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 * seqc_t may be included in structs visible to userspace
39 typedef uint32_t seqc_t;
43 /* A hack to get MPASS macro */
46 #include <machine/cpu.h>
49 seqc_in_modify(seqc_t seqcp)
56 seqc_write_begin(seqc_t *seqcp)
60 MPASS(!seqc_in_modify(*seqcp));
62 atomic_thread_fence_rel();
66 seqc_write_end(seqc_t *seqcp)
69 atomic_store_rel_int(seqcp, *seqcp + 1);
70 MPASS(!seqc_in_modify(*seqcp));
74 static __inline seqc_t
75 seqc_read(const seqc_t *seqcp)
80 ret = atomic_load_acq_int(__DECONST(seqc_t *, seqcp));
81 if (seqc_in_modify(ret)) {
91 static __inline seqc_t
92 seqc_consistent_nomb(const seqc_t *seqcp, seqc_t oldseqc)
95 return (*seqcp == oldseqc);
98 static __inline seqc_t
99 seqc_consistent(const seqc_t *seqcp, seqc_t oldseqc)
102 atomic_thread_fence_acq();
103 return (seqc_consistent_nomb(seqcp, oldseqc));
107 #endif /* _SYS_SEQC_H_ */