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      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