diff options
Diffstat (limited to 'freebsd/sys/sys/seq.h')
-rw-r--r-- | freebsd/sys/sys/seq.h | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/freebsd/sys/sys/seq.h b/freebsd/sys/sys/seq.h new file mode 100644 index 00000000..82efbdf1 --- /dev/null +++ b/freebsd/sys/sys/seq.h @@ -0,0 +1,129 @@ +/*- + * 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_SEQ_H_ +#define _SYS_SEQ_H_ + +#ifdef _KERNEL +#include <sys/systm.h> +#endif +#include <sys/types.h> + +/* + * seq_t may be included in structs visible to userspace + */ +typedef uint32_t seq_t; + +#ifdef _KERNEL + +/* + * Typical usage: + * + * writers: + * lock_exclusive(&obj->lock); + * seq_write_begin(&obj->seq); + * ..... + * seq_write_end(&obj->seq); + * unlock_exclusive(&obj->unlock); + * + * readers: + * obj_t lobj; + * seq_t seq; + * + * for (;;) { + * seq = seq_read(&gobj->seq); + * lobj = gobj; + * if (seq_consistent(&gobj->seq, seq)) + * break; + * cpu_spinwait(); + * } + * foo(lobj); + */ + +/* A hack to get MPASS macro */ +#include <rtems/bsd/sys/lock.h> + +#include <machine/cpu.h> + +static __inline bool +seq_in_modify(seq_t seqp) +{ + + return (seqp & 1); +} + +static __inline void +seq_write_begin(seq_t *seqp) +{ + + MPASS(!seq_in_modify(*seqp)); + *seqp += 1; + atomic_thread_fence_rel(); +} + +static __inline void +seq_write_end(seq_t *seqp) +{ + + atomic_store_rel_int(seqp, *seqp + 1); + MPASS(!seq_in_modify(*seqp)); +} + +static __inline seq_t +seq_read(const seq_t *seqp) +{ + seq_t ret; + + for (;;) { + ret = atomic_load_acq_int(__DECONST(seq_t *, seqp)); + if (seq_in_modify(ret)) { + cpu_spinwait(); + continue; + } + break; + } + + return (ret); +} + +static __inline seq_t +seq_consistent_nomb(const seq_t *seqp, seq_t oldseq) +{ + + return (*seqp == oldseq); +} + +static __inline seq_t +seq_consistent(const seq_t *seqp, seq_t oldseq) +{ + + atomic_thread_fence_acq(); + return (seq_consistent_nomb(seqp, oldseq)); +} + +#endif /* _KERNEL */ +#endif /* _SYS_SEQ_H_ */ |