xref: /illumos-gate/usr/src/uts/common/fs/zfs/sys/rrwlock.h (revision e4d060fb4c00d44cd578713eb9a921f594b733b8)
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
32 extern "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  */
53 typedef 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  */
67 void rrw_init(rrwlock_t *rrl);
68 void rrw_destroy(rrwlock_t *rrl);
69 void rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag);
70 void rrw_exit(rrwlock_t *rrl, void *tag);
71 boolean_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