1 /*- 2 * Copyright (c) 2014 Mateusz Guzik <mjg@FreeBSD.org> 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 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. 12 * 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 23 * SUCH DAMAGE. 24 * 25 * $FreeBSD$ 26 */ 27 28 #ifndef _SYS_SEQC_H_ 29 #define _SYS_SEQC_H_ 30 31 #ifdef _KERNEL 32 #include <sys/systm.h> 33 #endif 34 #include <sys/types.h> 35 36 /* 37 * seqc_t may be included in structs visible to userspace 38 */ 39 typedef uint32_t seqc_t; 40 41 #ifdef _KERNEL 42 43 /* A hack to get MPASS macro */ 44 #include <sys/lock.h> 45 46 #include <machine/cpu.h> 47 48 static __inline bool 49 seqc_in_modify(seqc_t seqcp) 50 { 51 52 return (seqcp & 1); 53 } 54 55 static __inline void 56 seqc_write_begin(seqc_t *seqcp) 57 { 58 59 critical_enter(); 60 MPASS(!seqc_in_modify(*seqcp)); 61 *seqcp += 1; 62 atomic_thread_fence_rel(); 63 } 64 65 static __inline void 66 seqc_write_end(seqc_t *seqcp) 67 { 68 69 atomic_store_rel_int(seqcp, *seqcp + 1); 70 MPASS(!seqc_in_modify(*seqcp)); 71 critical_exit(); 72 } 73 74 static __inline seqc_t 75 seqc_read(const seqc_t *seqcp) 76 { 77 seqc_t ret; 78 79 for (;;) { 80 ret = atomic_load_acq_int(__DECONST(seqc_t *, seqcp)); 81 if (__predict_false(seqc_in_modify(ret))) { 82 cpu_spinwait(); 83 continue; 84 } 85 break; 86 } 87 88 return (ret); 89 } 90 91 static __inline bool 92 seqc_consistent_nomb(const seqc_t *seqcp, seqc_t oldseqc) 93 { 94 95 return (*seqcp == oldseqc); 96 } 97 98 static __inline bool 99 seqc_consistent(const seqc_t *seqcp, seqc_t oldseqc) 100 { 101 102 atomic_thread_fence_acq(); 103 return (seqc_consistent_nomb(seqcp, oldseqc)); 104 } 105 106 #endif /* _KERNEL */ 107 #endif /* _SYS_SEQC_H_ */ 108