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/*-
* Copyright (c) 2014 Mateusz Guzik <mjg@FreeBSD.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#ifndef _SYS_SEQC_H_
#define _SYS_SEQC_H_
#ifdef _KERNEL
#include <sys/systm.h>
#endif
#include <sys/types.h>
/*
* seqc_t may be included in structs visible to userspace
*/
typedef uint32_t seqc_t;
#ifdef _KERNEL
/* A hack to get MPASS macro */
#include <sys/lock.h>
#include <machine/cpu.h>
static __inline bool
seqc_in_modify(seqc_t seqcp)
{
return (seqcp & 1);
}
static __inline void
seqc_write_begin(seqc_t *seqcp)
{
critical_enter();
MPASS(!seqc_in_modify(*seqcp));
*seqcp += 1;
atomic_thread_fence_rel();
}
static __inline void
seqc_write_end(seqc_t *seqcp)
{
atomic_store_rel_int(seqcp, *seqcp + 1);
MPASS(!seqc_in_modify(*seqcp));
critical_exit();
}
static __inline seqc_t
seqc_read(const seqc_t *seqcp)
{
seqc_t ret;
for (;;) {
ret = atomic_load_acq_int(__DECONST(seqc_t *, seqcp));
if (__predict_false(seqc_in_modify(ret))) {
cpu_spinwait();
continue;
}
break;
}
return (ret);
}
static __inline bool
seqc_consistent_nomb(const seqc_t *seqcp, seqc_t oldseqc)
{
return (*seqcp == oldseqc);
}
static __inline bool
seqc_consistent(const seqc_t *seqcp, seqc_t oldseqc)
{
atomic_thread_fence_acq();
return (seqc_consistent_nomb(seqcp, oldseqc));
}
#endif /* _KERNEL */
#endif /* _SYS_SEQC_H_ */
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