fs/zfs/unique.c

/*
 * 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.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#include <sys/zfs_context.h>
#include <sys/avl.h>
#include <sys/unique.h>

static avl_tree_t unique_avl;
static kmutex_t unique_mtx;

typedef struct unique {
    avl_node_t un_link;
    uint64_t un_value;
} unique_t;

#define UNIQUE_MASK ((1ULL << UNIQUE_BITS) - 1)

static int
unique_compare(const void *a, const void *b)
{
    const unique_t *una = a;
    const unique_t *unb = b;

    if (una->un_value < unb->un_value)
        return (-1);
    if (una->un_value > unb->un_value)
        return (+1);
    return (0);
}

void
unique_init(void)
{
    avl_create(&unique_avl, unique_compare,
        sizeof (unique_t), offsetof(unique_t, un_link));
    mutex_init(&unique_mtx, NULL, MUTEX_DEFAULT, NULL);
}

void
unique_fini(void)
{
    avl_destroy(&unique_avl);
    mutex_destroy(&unique_mtx);
}

uint64_t
unique_create(void)
{
    uint64_t value = unique_insert(0);
    unique_remove(value);
    return (value);
}

uint64_t
unique_insert(uint64_t value)
{
    avl_index_t idx;
    unique_t *un = kmem_alloc(sizeof (unique_t), KM_SLEEP);

    un->un_value = value;

    mutex_enter(&unique_mtx);
    while (un->un_value == 0 || un->un_value & ~UNIQUE_MASK ||
        avl_find(&unique_avl, un, &idx)) {
        mutex_exit(&unique_mtx);
        (void) random_get_pseudo_bytes((void*)&un->un_value,
            sizeof (un->un_value));
        un->un_value &= UNIQUE_MASK;
        mutex_enter(&unique_mtx);
    }

    avl_insert(&unique_avl, un, idx);
    mutex_exit(&unique_mtx);

    return (un->un_value);
}

void
unique_remove(uint64_t value)
{
    unique_t un_tofind;
    unique_t *un;

    un_tofind.un_value = value;
    mutex_enter(&unique_mtx);
    un = avl_find(&unique_avl, &un_tofind, NULL);
    if (un != NULL) {
        avl_remove(&unique_avl, un);
        kmem_free(un, sizeof (unique_t));
    }
    mutex_exit(&unique_mtx);
}