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+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright 2007 Sun Microsystems, Inc. All rights reserved.
+ * Use is subject to license terms.
+ */
+
+#ifndef _SYS_RR_RW_LOCK_H
+#define _SYS_RR_RW_LOCK_H
+
+#pragma ident "%Z%%M% %I% %E% SMI"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <sys/inttypes.h>
+#include <sys/zfs_context.h>
+#include <sys/refcount.h>
+
+/*
+ * A reader-writer lock implementation that allows re-entrant reads, but
+ * still gives writers priority on "new" reads.
+ *
+ * See rrwlock.c for more details about the implementation.
+ *
+ * Fields of the rrwlock_t structure:
+ * - rr_lock: protects modification and reading of rrwlock_t fields
+ * - rr_cv: cv for waking up readers or waiting writers
+ * - rr_writer: thread id of the current writer
+ * - rr_anon_rount: number of active anonymous readers
+ * - rr_linked_rcount: total number of non-anonymous active readers
+ * - rr_writer_wanted: a writer wants the lock
+ */
+typedef struct rrwlock {
+ kmutex_t rr_lock;
+ kcondvar_t rr_cv;
+ kthread_t *rr_writer;
+ refcount_t rr_anon_rcount;
+ refcount_t rr_linked_rcount;
+ boolean_t rr_writer_wanted;
+} rrwlock_t;
+
+/*
+ * 'tag' is used in reference counting tracking. The
+ * 'tag' must be the same in a rrw_enter() as in its
+ * corresponding rrw_exit().
+ */
+void rrw_init(rrwlock_t *rrl);
+void rrw_destroy(rrwlock_t *rrl);
+void rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag);
+void rrw_exit(rrwlock_t *rrl, void *tag);
+boolean_t rrw_held(rrwlock_t *rrl, krw_t rw);
+
+#define RRW_READ_HELD(x) rrw_held(x, RW_READER)
+#define RRW_WRITE_HELD(x) rrw_held(x, RW_WRITER)
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _SYS_RR_RW_LOCK_H */