refcount.c

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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 (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/refcount.h>

#ifdef  ZFS_DEBUG

#ifdef _KERNEL
int reference_tracking_enable = FALSE; /* runs out of memory too easily */
#else
int reference_tracking_enable = TRUE;
#endif
int reference_history = 4; /* tunable */

static kmem_cache_t *reference_cache;
static kmem_cache_t *reference_history_cache;

void
refcount_sysinit(void)
{
        reference_cache = kmem_cache_create("reference_cache",
            sizeof (reference_t), 0, NULL, NULL, NULL, NULL, NULL, 0);

        reference_history_cache = kmem_cache_create("reference_history_cache",
            sizeof (uint64_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
}

void
refcount_fini(void)
{
        kmem_cache_destroy(reference_cache);
        kmem_cache_destroy(reference_history_cache);
}

void
refcount_create(refcount_t *rc)
{
        mutex_init(&rc->rc_mtx, NULL, MUTEX_DEFAULT, NULL);
        list_create(&rc->rc_list, sizeof (reference_t),
            offsetof(reference_t, ref_link));
        list_create(&rc->rc_removed, sizeof (reference_t),
            offsetof(reference_t, ref_link));
        rc->rc_count = 0;
        rc->rc_removed_count = 0;
}

void
refcount_destroy_many(refcount_t *rc, uint64_t number)
{
        reference_t *ref;

        ASSERT(rc->rc_count == number);
        while (ref = list_head(&rc->rc_list)) {
                list_remove(&rc->rc_list, ref);
                kmem_cache_free(reference_cache, ref);
        }
        list_destroy(&rc->rc_list);

        while (ref = list_head(&rc->rc_removed)) {
                list_remove(&rc->rc_removed, ref);
                kmem_cache_free(reference_history_cache, ref->ref_removed);
                kmem_cache_free(reference_cache, ref);
        }
        list_destroy(&rc->rc_removed);
        mutex_destroy(&rc->rc_mtx);
}

void
refcount_destroy(refcount_t *rc)
{
        refcount_destroy_many(rc, 0);
}

int
refcount_is_zero(refcount_t *rc)
{
        ASSERT(rc->rc_count >= 0);
        return (rc->rc_count == 0);
}

int64_t
refcount_count(refcount_t *rc)
{
        ASSERT(rc->rc_count >= 0);
        return (rc->rc_count);
}

int64_t
refcount_add_many(refcount_t *rc, uint64_t number, void *holder)
{
        reference_t *ref;
        int64_t count;

        if (reference_tracking_enable) {
                ref = kmem_cache_alloc(reference_cache, KM_SLEEP);
                ref->ref_holder = holder;
                ref->ref_number = number;
        }
        mutex_enter(&rc->rc_mtx);
        ASSERT(rc->rc_count >= 0);
        if (reference_tracking_enable)
                list_insert_head(&rc->rc_list, ref);
        rc->rc_count += number;
        count = rc->rc_count;
        mutex_exit(&rc->rc_mtx);

        return (count);
}

int64_t
refcount_add(refcount_t *rc, void *holder)
{
        return (refcount_add_many(rc, 1, holder));
}

int64_t
refcount_remove_many(refcount_t *rc, uint64_t number, void *holder)
{
        reference_t *ref;
        int64_t count;

        mutex_enter(&rc->rc_mtx);
        ASSERT(rc->rc_count >= number);

        if (!reference_tracking_enable) {
                rc->rc_count -= number;
                count = rc->rc_count;
                mutex_exit(&rc->rc_mtx);
                return (count);
        }

        for (ref = list_head(&rc->rc_list); ref;
            ref = list_next(&rc->rc_list, ref)) {
                if (ref->ref_holder == holder && ref->ref_number == number) {
                        list_remove(&rc->rc_list, ref);
                        if (reference_history > 0) {
                                ref->ref_removed =
                                    kmem_cache_alloc(reference_history_cache,
                                    KM_SLEEP);
                                list_insert_head(&rc->rc_removed, ref);
                                rc->rc_removed_count++;
                                if (rc->rc_removed_count >= reference_history) {
                                        ref = list_tail(&rc->rc_removed);
                                        list_remove(&rc->rc_removed, ref);
                                        kmem_cache_free(reference_history_cache,
                                            ref->ref_removed);
                                        kmem_cache_free(reference_cache, ref);
                                        rc->rc_removed_count--;
                                }
                        } else {
                                kmem_cache_free(reference_cache, ref);
                        }
                        rc->rc_count -= number;
                        count = rc->rc_count;
                        mutex_exit(&rc->rc_mtx);
                        return (count);
                }
        }
        panic("No such hold %p on refcount %llx", holder,
            (u_longlong_t)(uintptr_t)rc);
        return (-1);
}

int64_t
refcount_remove(refcount_t *rc, void *holder)
{
        return (refcount_remove_many(rc, 1, holder));
}

void
refcount_transfer(refcount_t *dst, refcount_t *src)
{
        int64_t count, removed_count;
        list_t list, removed;

        list_create(&list, sizeof (reference_t),
            offsetof(reference_t, ref_link));
        list_create(&removed, sizeof (reference_t),
            offsetof(reference_t, ref_link));

        mutex_enter(&src->rc_mtx);
        count = src->rc_count;
        removed_count = src->rc_removed_count;
        src->rc_count = 0;
        src->rc_removed_count = 0;
        list_move_tail(&list, &src->rc_list);
        list_move_tail(&removed, &src->rc_removed);
        mutex_exit(&src->rc_mtx);

        mutex_enter(&dst->rc_mtx);
        dst->rc_count += count;
        dst->rc_removed_count += removed_count;
        list_move_tail(&dst->rc_list, &list);
        list_move_tail(&dst->rc_removed, &removed);
        mutex_exit(&dst->rc_mtx);

        list_destroy(&list);
        list_destroy(&removed);
}

#endif  /* ZFS_DEBUG */