1/* $NetBSD: rwlock.h,v 1.19 2023/09/07 20:05:41 ad Exp $ */
2
3/*-
4 * Copyright (c) 2002, 2006, 2007, 2008, 2019, 2020 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Jason R. Thorpe and Andrew Doran.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32#ifndef _SYS_RWLOCK_H_
33#define _SYS_RWLOCK_H_
34
35/*
36 * The rwlock provides exclusive access when held as a "writer",
37 * and shared access when held as a "reader".
38 *
39 * Architectures may optionally provide stubs for the following functions to
40 * implement the easy (unlocked, no waiters) cases. If these stubs are
41 * provided, __HAVE_RW_STUBS should be defined.
42 *
43 * rw_enter()
44 * rw_exit()
45 * rw_tryenter()
46 */
47
48#if !defined(_KERNEL)
49#include <sys/types.h>
50#include <sys/inttypes.h>
51#endif
52
53typedef enum krw_t {
54 RW_READER = 0,
55 RW_WRITER = 1
56} krw_t;
57
58typedef struct krwlock krwlock_t;
59
60#ifdef __RWLOCK_PRIVATE
61#include <sys/stdbool.h>
62/*
63 * Bits in the owner field of the lock that indicate lock state. If the
64 * WRITE_LOCKED bit is clear, then the owner field is actually a count of
65 * the number of readers. The rw_owner field is laid out like so:
66 *
67 * N 5 4 3 2 1 0
68 * +------------------------------------------------------------------+
69 * | owner or read count | nodbug | <free> | wrlock | wrwant | wait |
70 * +------------------------------------------------------------------+
71 */
72#define RW_HAS_WAITERS 0x01UL /* lock has waiters */
73#define RW_WRITE_WANTED 0x02UL /* >= 1 waiter is a writer */
74#define RW_WRITE_LOCKED 0x04UL /* lock is currently write locked */
75#define RW_NODEBUG 0x10UL /* LOCKDEBUG disabled */
76
77#define RW_READ_COUNT_SHIFT 5
78#define RW_READ_INCR (1UL << RW_READ_COUNT_SHIFT)
79#define RW_THREAD ((uintptr_t)-RW_READ_INCR)
80#define RW_OWNER(rw) ((rw)->rw_owner & RW_THREAD)
81#define RW_COUNT(rw) ((rw)->rw_owner & RW_THREAD)
82#define RW_FLAGS(rw) ((rw)->rw_owner & ~RW_THREAD)
83
84void rw_vector_enter(krwlock_t *, const krw_t);
85void rw_vector_exit(krwlock_t *);
86int rw_vector_tryenter(krwlock_t *, const krw_t);
87#endif /* __RWLOCK_PRIVATE */
88
89struct krwlock {
90 volatile uintptr_t rw_owner;
91};
92
93#ifdef _KERNEL
94
95void _rw_init(krwlock_t *, uintptr_t);
96void rw_init(krwlock_t *);
97void rw_destroy(krwlock_t *);
98
99int rw_tryenter(krwlock_t *, const krw_t);
100int rw_tryupgrade(krwlock_t *);
101void rw_downgrade(krwlock_t *);
102
103int rw_read_held(krwlock_t *);
104int rw_write_held(krwlock_t *);
105int rw_lock_held(krwlock_t *);
106krw_t rw_lock_op(krwlock_t *);
107
108void rw_enter(krwlock_t *, const krw_t);
109void rw_exit(krwlock_t *);
110
111void rw_obj_init(void);
112krwlock_t *rw_obj_alloc(void);
113void rw_obj_hold(krwlock_t *);
114bool rw_obj_free(krwlock_t *);
115u_int rw_obj_refcnt(krwlock_t *);
116krwlock_t *rw_obj_tryalloc(void);
117
118#endif /* _KERNEL */
119
120#endif /* _SYS_RWLOCK_H_ */