1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21/*
22 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
23 * Use is subject to license terms.
24 */
25
26#ifndef	_SYS_RR_RW_LOCK_H
27#define	_SYS_RR_RW_LOCK_H
28
29#pragma ident	"%Z%%M%	%I%	%E% SMI"
30
31#ifdef	__cplusplus
32extern "C" {
33#endif
34
35#include <sys/inttypes.h>
36#include <sys/zfs_context.h>
37#include <sys/refcount.h>
38
39/*
40 * A reader-writer lock implementation that allows re-entrant reads, but
41 * still gives writers priority on "new" reads.
42 *
43 * See rrwlock.c for more details about the implementation.
44 *
45 * Fields of the rrwlock_t structure:
46 * - rr_lock: protects modification and reading of rrwlock_t fields
47 * - rr_cv: cv for waking up readers or waiting writers
48 * - rr_writer: thread id of the current writer
49 * - rr_anon_rount: number of active anonymous readers
50 * - rr_linked_rcount: total number of non-anonymous active readers
51 * - rr_writer_wanted: a writer wants the lock
52 */
53typedef struct rrwlock {
54	kmutex_t	rr_lock;
55	kcondvar_t	rr_cv;
56	kthread_t	*rr_writer;
57	refcount_t	rr_anon_rcount;
58	refcount_t	rr_linked_rcount;
59	boolean_t	rr_writer_wanted;
60} rrwlock_t;
61
62/*
63 * 'tag' is used in reference counting tracking.  The
64 * 'tag' must be the same in a rrw_enter() as in its
65 * corresponding rrw_exit().
66 */
67void rrw_init(rrwlock_t *rrl);
68void rrw_destroy(rrwlock_t *rrl);
69void rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag);
70void rrw_exit(rrwlock_t *rrl, void *tag);
71boolean_t rrw_held(rrwlock_t *rrl, krw_t rw);
72
73#define	RRW_READ_HELD(x)	rrw_held(x, RW_READER)
74#define	RRW_WRITE_HELD(x)	rrw_held(x, RW_WRITER)
75
76#ifdef	__cplusplus
77}
78#endif
79
80#endif	/* _SYS_RR_RW_LOCK_H */
81