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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  * Copyright (c) 2012 by Delphix. All rights reserved.
     27  */
     28 
     29 #ifndef	_SYS_RR_RW_LOCK_H
     30 #define	_SYS_RR_RW_LOCK_H
     31 
     32 #ifdef	__cplusplus
     33 extern "C" {
     34 #endif
     35 
     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 	boolean_t	rr_track_all;
     61 } rrwlock_t;
     62 
     63 /*
     64  * 'tag' is used in reference counting tracking.  The
     65  * 'tag' must be the same in a rrw_enter() as in its
     66  * corresponding rrw_exit().
     67  */
     68 void rrw_init(rrwlock_t *rrl, boolean_t track_all);
     69 void rrw_destroy(rrwlock_t *rrl);
     70 void rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag);
     71 void rrw_enter_read(rrwlock_t *rrl, void *tag);
     72 void rrw_enter_read_prio(rrwlock_t *rrl, void *tag);
     73 void rrw_enter_write(rrwlock_t *rrl);
     74 void rrw_exit(rrwlock_t *rrl, void *tag);
     75 boolean_t rrw_held(rrwlock_t *rrl, krw_t rw);
     76 void rrw_tsd_destroy(void *arg);
     77 
     78 #define	RRW_READ_HELD(x)	rrw_held(x, RW_READER)
     79 #define	RRW_WRITE_HELD(x)	rrw_held(x, RW_WRITER)
     80 #define	RRW_LOCK_HELD(x) \
     81 	(rrw_held(x, RW_WRITER) || rrw_held(x, RW_READER))
     82 
     83 /*
     84  * A reader-mostly lock implementation, tuning above reader-writer locks
     85  * for hightly parallel read acquisitions, pessimizing write acquisitions.
     86  *
     87  * This should be a prime number.  See comment in rrwlock.c near
     88  * RRM_TD_LOCK() for details.
     89  */
     90 #define	RRM_NUM_LOCKS		17
     91 typedef struct rrmlock {
     92 	rrwlock_t	locks[RRM_NUM_LOCKS];
     93 } rrmlock_t;
     94 
     95 void rrm_init(rrmlock_t *rrl, boolean_t track_all);
     96 void rrm_destroy(rrmlock_t *rrl);
     97 void rrm_enter(rrmlock_t *rrl, krw_t rw, void *tag);
     98 void rrm_enter_read(rrmlock_t *rrl, void *tag);
     99 void rrm_enter_write(rrmlock_t *rrl);
    100 void rrm_exit(rrmlock_t *rrl, void *tag);
    101 boolean_t rrm_held(rrmlock_t *rrl, krw_t rw);
    102 
    103 #define	RRM_READ_HELD(x)	rrm_held(x, RW_READER)
    104 #define	RRM_WRITE_HELD(x)	rrm_held(x, RW_WRITER)
    105 #define	RRM_LOCK_HELD(x) \
    106 	(rrm_held(x, RW_WRITER) || rrm_held(x, RW_READER))
    107 
    108 #ifdef	__cplusplus
    109 }
    110 #endif
    111 
    112 #endif	/* _SYS_RR_RW_LOCK_H */
    113