/*
 * 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.
 * Copyright (c) 2012, 2019 by Delphix. All rights reserved.
 * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
 * Copyright (c) 2014 Integros [integros.com]
 * Copyright 2017 RackTop Systems.
 */

#include <sys/disp.h>
#include <sys/zfs_context.h>
#include <sys/dbuf.h>
#include <sys/dnode.h>
#include <sys/dmu.h>
#include <sys/dmu_impl.h>
#include <sys/dmu_tx.h>
#include <sys/dmu_objset.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_dataset.h>
#include <sys/spa.h>
#include <sys/zio.h>
#include <sys/dmu_zfetch.h>
#include <sys/range_tree.h>
#include <sys/zfs_project.h>

dnode_stats_t dnode_stats = {
        { "dnode_hold_dbuf_hold",               KSTAT_DATA_UINT64 },
        { "dnode_hold_dbuf_read",               KSTAT_DATA_UINT64 },
        { "dnode_hold_alloc_hits",              KSTAT_DATA_UINT64 },
        { "dnode_hold_alloc_misses",            KSTAT_DATA_UINT64 },
        { "dnode_hold_alloc_interior",          KSTAT_DATA_UINT64 },
        { "dnode_hold_alloc_lock_retry",        KSTAT_DATA_UINT64 },
        { "dnode_hold_alloc_lock_misses",       KSTAT_DATA_UINT64 },
        { "dnode_hold_alloc_type_none",         KSTAT_DATA_UINT64 },
        { "dnode_hold_free_hits",               KSTAT_DATA_UINT64 },
        { "dnode_hold_free_misses",             KSTAT_DATA_UINT64 },
        { "dnode_hold_free_lock_misses",        KSTAT_DATA_UINT64 },
        { "dnode_hold_free_lock_retry",         KSTAT_DATA_UINT64 },
        { "dnode_hold_free_overflow",           KSTAT_DATA_UINT64 },
        { "dnode_hold_free_refcount",           KSTAT_DATA_UINT64 },
        { "dnode_free_interior_lock_retry",     KSTAT_DATA_UINT64 },
        { "dnode_allocate",                     KSTAT_DATA_UINT64 },
        { "dnode_reallocate",                   KSTAT_DATA_UINT64 },
        { "dnode_buf_evict",                    KSTAT_DATA_UINT64 },
        { "dnode_alloc_next_chunk",             KSTAT_DATA_UINT64 },
        { "dnode_alloc_race",                   KSTAT_DATA_UINT64 },
        { "dnode_alloc_next_block",             KSTAT_DATA_UINT64 },
        { "dnode_move_invalid",                 KSTAT_DATA_UINT64 },
        { "dnode_move_recheck1",                KSTAT_DATA_UINT64 },
        { "dnode_move_recheck2",                KSTAT_DATA_UINT64 },
        { "dnode_move_special",                 KSTAT_DATA_UINT64 },
        { "dnode_move_handle",                  KSTAT_DATA_UINT64 },
        { "dnode_move_rwlock",                  KSTAT_DATA_UINT64 },
        { "dnode_move_active",                  KSTAT_DATA_UINT64 },
};

static kstat_t *dnode_ksp;
static kmem_cache_t *dnode_cache;

static dnode_phys_t dnode_phys_zero;

int zfs_default_bs = SPA_MINBLOCKSHIFT;
int zfs_default_ibs = DN_MAX_INDBLKSHIFT;

#ifdef  _KERNEL
static kmem_cbrc_t dnode_move(void *, void *, size_t, void *);
#endif  /* _KERNEL */

static int
dbuf_compare(const void *x1, const void *x2)
{
        const dmu_buf_impl_t *d1 = x1;
        const dmu_buf_impl_t *d2 = x2;

        int cmp = TREE_CMP(d1->db_level, d2->db_level);
        if (likely(cmp))
                return (cmp);

        cmp = TREE_CMP(d1->db_blkid, d2->db_blkid);
        if (likely(cmp))
                return (cmp);

        if (d1->db_state == DB_SEARCH) {
                ASSERT3S(d2->db_state, !=, DB_SEARCH);
                return (-1);
        } else if (d2->db_state == DB_SEARCH) {
                ASSERT3S(d1->db_state, !=, DB_SEARCH);
                return (1);
        }

        return (TREE_PCMP(d1, d2));
}

/* ARGSUSED */
static int
dnode_cons(void *arg, void *unused, int kmflag)
{
        dnode_t *dn = arg;
        int i;

        rw_init(&dn->dn_struct_rwlock, NULL, RW_DEFAULT, NULL);
        mutex_init(&dn->dn_mtx, NULL, MUTEX_DEFAULT, NULL);
        mutex_init(&dn->dn_dbufs_mtx, NULL, MUTEX_DEFAULT, NULL);
        cv_init(&dn->dn_notxholds, NULL, CV_DEFAULT, NULL);
        cv_init(&dn->dn_nodnholds, NULL, CV_DEFAULT, NULL);

        /*
         * Every dbuf has a reference, and dropping a tracked reference is
         * O(number of references), so don't track dn_holds.
         */
        zfs_refcount_create_untracked(&dn->dn_holds);
        zfs_refcount_create(&dn->dn_tx_holds);
        list_link_init(&dn->dn_link);

        bzero(&dn->dn_next_nblkptr[0], sizeof (dn->dn_next_nblkptr));
        bzero(&dn->dn_next_nlevels[0], sizeof (dn->dn_next_nlevels));
        bzero(&dn->dn_next_indblkshift[0], sizeof (dn->dn_next_indblkshift));
        bzero(&dn->dn_next_bonustype[0], sizeof (dn->dn_next_bonustype));
        bzero(&dn->dn_rm_spillblk[0], sizeof (dn->dn_rm_spillblk));
        bzero(&dn->dn_next_bonuslen[0], sizeof (dn->dn_next_bonuslen));
        bzero(&dn->dn_next_blksz[0], sizeof (dn->dn_next_blksz));
        bzero(&dn->dn_next_maxblkid[0], sizeof (dn->dn_next_maxblkid));

        for (i = 0; i < TXG_SIZE; i++) {
                multilist_link_init(&dn->dn_dirty_link[i]);
                dn->dn_free_ranges[i] = NULL;
                list_create(&dn->dn_dirty_records[i],
                    sizeof (dbuf_dirty_record_t),
                    offsetof(dbuf_dirty_record_t, dr_dirty_node));
        }

        dn->dn_allocated_txg = 0;
        dn->dn_free_txg = 0;
        dn->dn_assigned_txg = 0;
        dn->dn_dirty_txg = 0;
        dn->dn_dirtyctx = 0;
        dn->dn_dirtyctx_firstset = NULL;
        dn->dn_bonus = NULL;
        dn->dn_have_spill = B_FALSE;
        dn->dn_zio = NULL;
        dn->dn_oldused = 0;
        dn->dn_oldflags = 0;
        dn->dn_olduid = 0;
        dn->dn_oldgid = 0;
        dn->dn_oldprojid = ZFS_DEFAULT_PROJID;
        dn->dn_newuid = 0;
        dn->dn_newgid = 0;
        dn->dn_newprojid = ZFS_DEFAULT_PROJID;
        dn->dn_id_flags = 0;

        dn->dn_dbufs_count = 0;
        avl_create(&dn->dn_dbufs, dbuf_compare, sizeof (dmu_buf_impl_t),
            offsetof(dmu_buf_impl_t, db_link));

        dn->dn_moved = 0;
        return (0);
}

/* ARGSUSED */
static void
dnode_dest(void *arg, void *unused)
{
        int i;
        dnode_t *dn = arg;

        rw_destroy(&dn->dn_struct_rwlock);
        mutex_destroy(&dn->dn_mtx);
        mutex_destroy(&dn->dn_dbufs_mtx);
        cv_destroy(&dn->dn_notxholds);
        cv_destroy(&dn->dn_nodnholds);
        zfs_refcount_destroy(&dn->dn_holds);
        zfs_refcount_destroy(&dn->dn_tx_holds);
        ASSERT(!list_link_active(&dn->dn_link));

        for (i = 0; i < TXG_SIZE; i++) {
                ASSERT(!multilist_link_active(&dn->dn_dirty_link[i]));
                ASSERT3P(dn->dn_free_ranges[i], ==, NULL);
                list_destroy(&dn->dn_dirty_records[i]);
                ASSERT0(dn->dn_next_nblkptr[i]);
                ASSERT0(dn->dn_next_nlevels[i]);
                ASSERT0(dn->dn_next_indblkshift[i]);
                ASSERT0(dn->dn_next_bonustype[i]);
                ASSERT0(dn->dn_rm_spillblk[i]);
                ASSERT0(dn->dn_next_bonuslen[i]);
                ASSERT0(dn->dn_next_blksz[i]);
                ASSERT0(dn->dn_next_maxblkid[i]);
        }

        ASSERT0(dn->dn_allocated_txg);
        ASSERT0(dn->dn_free_txg);
        ASSERT0(dn->dn_assigned_txg);
        ASSERT0(dn->dn_dirty_txg);
        ASSERT0(dn->dn_dirtyctx);
        ASSERT3P(dn->dn_dirtyctx_firstset, ==, NULL);
        ASSERT3P(dn->dn_bonus, ==, NULL);
        ASSERT(!dn->dn_have_spill);
        ASSERT3P(dn->dn_zio, ==, NULL);
        ASSERT0(dn->dn_oldused);
        ASSERT0(dn->dn_oldflags);
        ASSERT0(dn->dn_olduid);
        ASSERT0(dn->dn_oldgid);
        ASSERT0(dn->dn_oldprojid);
        ASSERT0(dn->dn_newuid);
        ASSERT0(dn->dn_newgid);
        ASSERT0(dn->dn_newprojid);
        ASSERT0(dn->dn_id_flags);

        ASSERT0(dn->dn_dbufs_count);
        avl_destroy(&dn->dn_dbufs);
}

void
dnode_init(void)
{
        ASSERT(dnode_cache == NULL);
        dnode_cache = kmem_cache_create("dnode_t",
            sizeof (dnode_t),
            0, dnode_cons, dnode_dest, NULL, NULL, NULL, 0);
#ifdef  _KERNEL
        kmem_cache_set_move(dnode_cache, dnode_move);

        dnode_ksp = kstat_create("zfs", 0, "dnodestats", "misc",
            KSTAT_TYPE_NAMED, sizeof (dnode_stats) / sizeof (kstat_named_t),
            KSTAT_FLAG_VIRTUAL);
        if (dnode_ksp != NULL) {
                dnode_ksp->ks_data = &dnode_stats;
                kstat_install(dnode_ksp);
        }
#endif  /* _KERNEL */
}

void
dnode_fini(void)
{
        if (dnode_ksp != NULL) {
                kstat_delete(dnode_ksp);
                dnode_ksp = NULL;
        }

        kmem_cache_destroy(dnode_cache);
        dnode_cache = NULL;
}


#ifdef ZFS_DEBUG
void
dnode_verify(dnode_t *dn)
{
        int drop_struct_lock = FALSE;

        ASSERT(dn->dn_phys);
        ASSERT(dn->dn_objset);
        ASSERT(dn->dn_handle->dnh_dnode == dn);

        ASSERT(DMU_OT_IS_VALID(dn->dn_phys->dn_type));

        if (!(zfs_flags & ZFS_DEBUG_DNODE_VERIFY))
                return;

        if (!RW_WRITE_HELD(&dn->dn_struct_rwlock)) {
                rw_enter(&dn->dn_struct_rwlock, RW_READER);
                drop_struct_lock = TRUE;
        }
        if (dn->dn_phys->dn_type != DMU_OT_NONE || dn->dn_allocated_txg != 0) {
                int i;
                int max_bonuslen = DN_SLOTS_TO_BONUSLEN(dn->dn_num_slots);
                ASSERT3U(dn->dn_indblkshift, >=, 0);
                ASSERT3U(dn->dn_indblkshift, <=, SPA_MAXBLOCKSHIFT);
                if (dn->dn_datablkshift) {
                        ASSERT3U(dn->dn_datablkshift, >=, SPA_MINBLOCKSHIFT);
                        ASSERT3U(dn->dn_datablkshift, <=, SPA_MAXBLOCKSHIFT);
                        ASSERT3U(1<<dn->dn_datablkshift, ==, dn->dn_datablksz);
                }
                ASSERT3U(dn->dn_nlevels, <=, 30);
                ASSERT(DMU_OT_IS_VALID(dn->dn_type));
                ASSERT3U(dn->dn_nblkptr, >=, 1);
                ASSERT3U(dn->dn_nblkptr, <=, DN_MAX_NBLKPTR);
                ASSERT3U(dn->dn_bonuslen, <=, max_bonuslen);
                ASSERT3U(dn->dn_datablksz, ==,
                    dn->dn_datablkszsec << SPA_MINBLOCKSHIFT);
                ASSERT3U(ISP2(dn->dn_datablksz), ==, dn->dn_datablkshift != 0);
                ASSERT3U((dn->dn_nblkptr - 1) * sizeof (blkptr_t) +
                    dn->dn_bonuslen, <=, max_bonuslen);
                for (i = 0; i < TXG_SIZE; i++) {
                        ASSERT3U(dn->dn_next_nlevels[i], <=, dn->dn_nlevels);
                }
        }
        if (dn->dn_phys->dn_type != DMU_OT_NONE)
                ASSERT3U(dn->dn_phys->dn_nlevels, <=, dn->dn_nlevels);
        ASSERT(DMU_OBJECT_IS_SPECIAL(dn->dn_object) || dn->dn_dbuf != NULL);
        if (dn->dn_dbuf != NULL) {
                ASSERT3P(dn->dn_phys, ==,
                    (dnode_phys_t *)dn->dn_dbuf->db.db_data +
                    (dn->dn_object % (dn->dn_dbuf->db.db_size >> DNODE_SHIFT)));
        }
        if (drop_struct_lock)
                rw_exit(&dn->dn_struct_rwlock);
}
#endif

void
dnode_byteswap(dnode_phys_t *dnp)
{
        uint64_t *buf64 = (void*)&dnp->dn_blkptr;
        int i;

        if (dnp->dn_type == DMU_OT_NONE) {
                bzero(dnp, sizeof (dnode_phys_t));
                return;
        }

        dnp->dn_datablkszsec = BSWAP_16(dnp->dn_datablkszsec);
        dnp->dn_bonuslen = BSWAP_16(dnp->dn_bonuslen);
        dnp->dn_extra_slots = BSWAP_8(dnp->dn_extra_slots);
        dnp->dn_maxblkid = BSWAP_64(dnp->dn_maxblkid);
        dnp->dn_used = BSWAP_64(dnp->dn_used);

        /*
         * dn_nblkptr is only one byte, so it's OK to read it in either
         * byte order.  We can't read dn_bouslen.
         */
        ASSERT(dnp->dn_indblkshift <= SPA_MAXBLOCKSHIFT);
        ASSERT(dnp->dn_nblkptr <= DN_MAX_NBLKPTR);
        for (i = 0; i < dnp->dn_nblkptr * sizeof (blkptr_t)/8; i++)
                buf64[i] = BSWAP_64(buf64[i]);

        /*
         * OK to check dn_bonuslen for zero, because it won't matter if
         * we have the wrong byte order.  This is necessary because the
         * dnode dnode is smaller than a regular dnode.
         */
        if (dnp->dn_bonuslen != 0) {
                dmu_object_byteswap_t byteswap;
                ASSERT(DMU_OT_IS_VALID(dnp->dn_bonustype));
                byteswap = DMU_OT_BYTESWAP(dnp->dn_bonustype);
                dmu_ot_byteswap[byteswap].ob_func(DN_BONUS(dnp),
                    DN_MAX_BONUS_LEN(dnp));
        }

        /* Swap SPILL block if we have one */
        if (dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR)
                byteswap_uint64_array(DN_SPILL_BLKPTR(dnp), sizeof (blkptr_t));

}

void
dnode_buf_byteswap(void *vbuf, size_t size)
{
        int i = 0;

        ASSERT3U(sizeof (dnode_phys_t), ==, (1<<DNODE_SHIFT));
        ASSERT((size & (sizeof (dnode_phys_t)-1)) == 0);

        while (i < size) {
                dnode_phys_t *dnp = (void *)(((char *)vbuf) + i);
                dnode_byteswap(dnp);

                i += DNODE_MIN_SIZE;
                if (dnp->dn_type != DMU_OT_NONE)
                        i += dnp->dn_extra_slots * DNODE_MIN_SIZE;
        }
}

void
dnode_setbonuslen(dnode_t *dn, int newsize, dmu_tx_t *tx)
{
        ASSERT3U(zfs_refcount_count(&dn->dn_holds), >=, 1);

        dnode_setdirty(dn, tx);
        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
        ASSERT3U(newsize, <=, DN_SLOTS_TO_BONUSLEN(dn->dn_num_slots) -
            (dn->dn_nblkptr-1) * sizeof (blkptr_t));
        dn->dn_bonuslen = newsize;
        if (newsize == 0)
                dn->dn_next_bonuslen[tx->tx_txg & TXG_MASK] = DN_ZERO_BONUSLEN;
        else
                dn->dn_next_bonuslen[tx->tx_txg & TXG_MASK] = dn->dn_bonuslen;
        rw_exit(&dn->dn_struct_rwlock);
}

void
dnode_setbonus_type(dnode_t *dn, dmu_object_type_t newtype, dmu_tx_t *tx)
{
        ASSERT3U(zfs_refcount_count(&dn->dn_holds), >=, 1);
        dnode_setdirty(dn, tx);
        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
        dn->dn_bonustype = newtype;
        dn->dn_next_bonustype[tx->tx_txg & TXG_MASK] = dn->dn_bonustype;
        rw_exit(&dn->dn_struct_rwlock);
}

void
dnode_rm_spill(dnode_t *dn, dmu_tx_t *tx)
{
        ASSERT3U(zfs_refcount_count(&dn->dn_holds), >=, 1);
        ASSERT(RW_WRITE_HELD(&dn->dn_struct_rwlock));
        dnode_setdirty(dn, tx);
        dn->dn_rm_spillblk[tx->tx_txg&TXG_MASK] = DN_KILL_SPILLBLK;
        dn->dn_have_spill = B_FALSE;
}

static void
dnode_setdblksz(dnode_t *dn, int size)
{
        ASSERT0(P2PHASE(size, SPA_MINBLOCKSIZE));
        ASSERT3U(size, <=, SPA_MAXBLOCKSIZE);
        ASSERT3U(size, >=, SPA_MINBLOCKSIZE);
        ASSERT3U(size >> SPA_MINBLOCKSHIFT, <,
            1<<(sizeof (dn->dn_phys->dn_datablkszsec) * 8));
        dn->dn_datablksz = size;
        dn->dn_datablkszsec = size >> SPA_MINBLOCKSHIFT;
        dn->dn_datablkshift = ISP2(size) ? highbit64(size - 1) : 0;
}

static dnode_t *
dnode_create(objset_t *os, dnode_phys_t *dnp, dmu_buf_impl_t *db,
    uint64_t object, dnode_handle_t *dnh)
{
        dnode_t *dn;

        dn = kmem_cache_alloc(dnode_cache, KM_SLEEP);
#ifdef _KERNEL
        ASSERT(!POINTER_IS_VALID(dn->dn_objset));
#endif /* _KERNEL */
        dn->dn_moved = 0;

        /*
         * Defer setting dn_objset until the dnode is ready to be a candidate
         * for the dnode_move() callback.
         */
        dn->dn_object = object;
        dn->dn_dbuf = db;
        dn->dn_handle = dnh;
        dn->dn_phys = dnp;

        if (dnp->dn_datablkszsec) {
                dnode_setdblksz(dn, dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT);
        } else {
                dn->dn_datablksz = 0;
                dn->dn_datablkszsec = 0;
                dn->dn_datablkshift = 0;
        }
        dn->dn_indblkshift = dnp->dn_indblkshift;
        dn->dn_nlevels = dnp->dn_nlevels;
        dn->dn_type = dnp->dn_type;
        dn->dn_nblkptr = dnp->dn_nblkptr;
        dn->dn_checksum = dnp->dn_checksum;
        dn->dn_compress = dnp->dn_compress;
        dn->dn_bonustype = dnp->dn_bonustype;
        dn->dn_bonuslen = dnp->dn_bonuslen;
        dn->dn_num_slots = dnp->dn_extra_slots + 1;
        dn->dn_maxblkid = dnp->dn_maxblkid;
        dn->dn_have_spill = ((dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) != 0);
        dn->dn_id_flags = 0;

        dmu_zfetch_init(&dn->dn_zfetch, dn);

        ASSERT(DMU_OT_IS_VALID(dn->dn_phys->dn_type));
        ASSERT(zrl_is_locked(&dnh->dnh_zrlock));
        ASSERT(!DN_SLOT_IS_PTR(dnh->dnh_dnode));

        mutex_enter(&os->os_lock);

        /*
         * Exclude special dnodes from os_dnodes so an empty os_dnodes
         * signifies that the special dnodes have no references from
         * their children (the entries in os_dnodes).  This allows
         * dnode_destroy() to easily determine if the last child has
         * been removed and then complete eviction of the objset.
         */
        if (!DMU_OBJECT_IS_SPECIAL(object))
                list_insert_head(&os->os_dnodes, dn);
        membar_producer();

        /*
         * Everything else must be valid before assigning dn_objset
         * makes the dnode eligible for dnode_move().
         */
        dn->dn_objset = os;

        dnh->dnh_dnode = dn;
        mutex_exit(&os->os_lock);

        arc_space_consume(sizeof (dnode_t), ARC_SPACE_OTHER);

        return (dn);
}

/*
 * Caller must be holding the dnode handle, which is released upon return.
 */
static void
dnode_destroy(dnode_t *dn)
{
        objset_t *os = dn->dn_objset;
        boolean_t complete_os_eviction = B_FALSE;

        ASSERT((dn->dn_id_flags & DN_ID_NEW_EXIST) == 0);

        mutex_enter(&os->os_lock);
        POINTER_INVALIDATE(&dn->dn_objset);
        if (!DMU_OBJECT_IS_SPECIAL(dn->dn_object)) {
                list_remove(&os->os_dnodes, dn);
                complete_os_eviction =
                    list_is_empty(&os->os_dnodes) &&
                    list_link_active(&os->os_evicting_node);
        }
        mutex_exit(&os->os_lock);

        /* the dnode can no longer move, so we can release the handle */
        if (!zrl_is_locked(&dn->dn_handle->dnh_zrlock))
                zrl_remove(&dn->dn_handle->dnh_zrlock);

        dn->dn_allocated_txg = 0;
        dn->dn_free_txg = 0;
        dn->dn_assigned_txg = 0;
        dn->dn_dirty_txg = 0;

        dn->dn_dirtyctx = 0;
        if (dn->dn_dirtyctx_firstset != NULL) {
                kmem_free(dn->dn_dirtyctx_firstset, 1);
                dn->dn_dirtyctx_firstset = NULL;
        }
        if (dn->dn_bonus != NULL) {
                mutex_enter(&dn->dn_bonus->db_mtx);
                dbuf_destroy(dn->dn_bonus);
                dn->dn_bonus = NULL;
        }
        dn->dn_zio = NULL;

        dn->dn_have_spill = B_FALSE;
        dn->dn_oldused = 0;
        dn->dn_oldflags = 0;
        dn->dn_olduid = 0;
        dn->dn_oldgid = 0;
        dn->dn_oldprojid = ZFS_DEFAULT_PROJID;
        dn->dn_newuid = 0;
        dn->dn_newgid = 0;
        dn->dn_newprojid = ZFS_DEFAULT_PROJID;
        dn->dn_id_flags = 0;

        dmu_zfetch_fini(&dn->dn_zfetch);
        kmem_cache_free(dnode_cache, dn);
        arc_space_return(sizeof (dnode_t), ARC_SPACE_OTHER);

        if (complete_os_eviction)
                dmu_objset_evict_done(os);
}

void
dnode_allocate(dnode_t *dn, dmu_object_type_t ot, int blocksize, int ibs,
    dmu_object_type_t bonustype, int bonuslen, int dn_slots, dmu_tx_t *tx)
{
        int i;

        ASSERT3U(dn_slots, >, 0);
        ASSERT3U(dn_slots << DNODE_SHIFT, <=,
            spa_maxdnodesize(dmu_objset_spa(dn->dn_objset)));
        ASSERT3U(blocksize, <=,
            spa_maxblocksize(dmu_objset_spa(dn->dn_objset)));
        if (blocksize == 0)
                blocksize = 1 << zfs_default_bs;
        else
                blocksize = P2ROUNDUP(blocksize, SPA_MINBLOCKSIZE);

        if (ibs == 0)
                ibs = zfs_default_ibs;

        ibs = MIN(MAX(ibs, DN_MIN_INDBLKSHIFT), DN_MAX_INDBLKSHIFT);

        dprintf_zfs("os=%p obj=%" PRIu64 " txg=%" PRIu64
            " blocksize=%d ibs=%d dn_slots=%d\n",
            dn->dn_objset, dn->dn_object, tx->tx_txg, blocksize, ibs, dn_slots);
        DNODE_STAT_BUMP(dnode_allocate);

        ASSERT(dn->dn_type == DMU_OT_NONE);
        ASSERT(bcmp(dn->dn_phys, &dnode_phys_zero, sizeof (dnode_phys_t)) == 0);
        ASSERT(dn->dn_phys->dn_type == DMU_OT_NONE);
        ASSERT(ot != DMU_OT_NONE);
        ASSERT(DMU_OT_IS_VALID(ot));
        ASSERT((bonustype == DMU_OT_NONE && bonuslen == 0) ||
            (bonustype == DMU_OT_SA && bonuslen == 0) ||
            (bonustype != DMU_OT_NONE && bonuslen != 0));
        ASSERT(DMU_OT_IS_VALID(bonustype));
        ASSERT3U(bonuslen, <=, DN_SLOTS_TO_BONUSLEN(dn_slots));
        ASSERT(dn->dn_type == DMU_OT_NONE);
        ASSERT0(dn->dn_maxblkid);
        ASSERT0(dn->dn_allocated_txg);
        ASSERT0(dn->dn_dirty_txg);
        ASSERT0(dn->dn_assigned_txg);
        ASSERT(zfs_refcount_is_zero(&dn->dn_tx_holds));
        ASSERT3U(zfs_refcount_count(&dn->dn_holds), <=, 1);
        ASSERT(avl_is_empty(&dn->dn_dbufs));

        for (i = 0; i < TXG_SIZE; i++) {
                ASSERT0(dn->dn_next_nblkptr[i]);
                ASSERT0(dn->dn_next_nlevels[i]);
                ASSERT0(dn->dn_next_indblkshift[i]);
                ASSERT0(dn->dn_next_bonuslen[i]);
                ASSERT0(dn->dn_next_bonustype[i]);
                ASSERT0(dn->dn_rm_spillblk[i]);
                ASSERT0(dn->dn_next_blksz[i]);
                ASSERT0(dn->dn_next_maxblkid[i]);
                ASSERT(!multilist_link_active(&dn->dn_dirty_link[i]));
                ASSERT3P(list_head(&dn->dn_dirty_records[i]), ==, NULL);
                ASSERT3P(dn->dn_free_ranges[i], ==, NULL);
        }

        dn->dn_type = ot;
        dnode_setdblksz(dn, blocksize);
        dn->dn_indblkshift = ibs;
        dn->dn_nlevels = 1;
        dn->dn_num_slots = dn_slots;
        if (bonustype == DMU_OT_SA) /* Maximize bonus space for SA */
                dn->dn_nblkptr = 1;
        else {
                dn->dn_nblkptr = MIN(DN_MAX_NBLKPTR,
                    1 + ((DN_SLOTS_TO_BONUSLEN(dn_slots) - bonuslen) >>
                    SPA_BLKPTRSHIFT));
        }

        dn->dn_bonustype = bonustype;
        dn->dn_bonuslen = bonuslen;
        dn->dn_checksum = ZIO_CHECKSUM_INHERIT;
        dn->dn_compress = ZIO_COMPRESS_INHERIT;
        dn->dn_dirtyctx = 0;

        dn->dn_free_txg = 0;
        if (dn->dn_dirtyctx_firstset) {
                kmem_free(dn->dn_dirtyctx_firstset, 1);
                dn->dn_dirtyctx_firstset = NULL;
        }

        dn->dn_allocated_txg = tx->tx_txg;
        dn->dn_id_flags = 0;

        dnode_setdirty(dn, tx);
        dn->dn_next_indblkshift[tx->tx_txg & TXG_MASK] = ibs;
        dn->dn_next_bonuslen[tx->tx_txg & TXG_MASK] = dn->dn_bonuslen;
        dn->dn_next_bonustype[tx->tx_txg & TXG_MASK] = dn->dn_bonustype;
        dn->dn_next_blksz[tx->tx_txg & TXG_MASK] = dn->dn_datablksz;
}

void
dnode_reallocate(dnode_t *dn, dmu_object_type_t ot, int blocksize,
    dmu_object_type_t bonustype, int bonuslen, int dn_slots,
    boolean_t keep_spill, dmu_tx_t *tx)
{
        int nblkptr;

        ASSERT3U(blocksize, >=, SPA_MINBLOCKSIZE);
        ASSERT3U(blocksize, <=,
            spa_maxblocksize(dmu_objset_spa(dn->dn_objset)));
        ASSERT0(blocksize % SPA_MINBLOCKSIZE);
        ASSERT(dn->dn_object != DMU_META_DNODE_OBJECT || dmu_tx_private_ok(tx));
        ASSERT(tx->tx_txg != 0);
        ASSERT((bonustype == DMU_OT_NONE && bonuslen == 0) ||
            (bonustype != DMU_OT_NONE && bonuslen != 0) ||
            (bonustype == DMU_OT_SA && bonuslen == 0));
        ASSERT(DMU_OT_IS_VALID(bonustype));
        ASSERT3U(bonuslen, <=,
            DN_BONUS_SIZE(spa_maxdnodesize(dmu_objset_spa(dn->dn_objset))));
        ASSERT3U(bonuslen, <=, DN_BONUS_SIZE(dn_slots << DNODE_SHIFT));

        dnode_free_interior_slots(dn);
        DNODE_STAT_BUMP(dnode_reallocate);

        /* clean up any unreferenced dbufs */
        dnode_evict_dbufs(dn);

        dn->dn_id_flags = 0;

        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
        dnode_setdirty(dn, tx);
        if (dn->dn_datablksz != blocksize) {
                /* change blocksize */
                ASSERT(dn->dn_maxblkid == 0 &&
                    (BP_IS_HOLE(&dn->dn_phys->dn_blkptr[0]) ||
                    dnode_block_freed(dn, 0)));
                dnode_setdblksz(dn, blocksize);
                dn->dn_next_blksz[tx->tx_txg&TXG_MASK] = blocksize;
        }
        if (dn->dn_bonuslen != bonuslen)
                dn->dn_next_bonuslen[tx->tx_txg&TXG_MASK] = bonuslen;

        if (bonustype == DMU_OT_SA) /* Maximize bonus space for SA */
                nblkptr = 1;
        else
                nblkptr = MIN(DN_MAX_NBLKPTR,
                    1 + ((DN_SLOTS_TO_BONUSLEN(dn_slots) - bonuslen) >>
                    SPA_BLKPTRSHIFT));
        if (dn->dn_bonustype != bonustype)
                dn->dn_next_bonustype[tx->tx_txg&TXG_MASK] = bonustype;
        if (dn->dn_nblkptr != nblkptr)
                dn->dn_next_nblkptr[tx->tx_txg&TXG_MASK] = nblkptr;
        if (dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR && !keep_spill) {
                dbuf_rm_spill(dn, tx);
                dnode_rm_spill(dn, tx);
        }
        rw_exit(&dn->dn_struct_rwlock);

        /* change type */
        dn->dn_type = ot;

        /* change bonus size and type */
        mutex_enter(&dn->dn_mtx);
        dn->dn_bonustype = bonustype;
        dn->dn_bonuslen = bonuslen;
        dn->dn_num_slots = dn_slots;
        dn->dn_nblkptr = nblkptr;
        dn->dn_checksum = ZIO_CHECKSUM_INHERIT;
        dn->dn_compress = ZIO_COMPRESS_INHERIT;
        ASSERT3U(dn->dn_nblkptr, <=, DN_MAX_NBLKPTR);

        /* fix up the bonus db_size */
        if (dn->dn_bonus) {
                dn->dn_bonus->db.db_size =
                    DN_SLOTS_TO_BONUSLEN(dn->dn_num_slots) -
                    (dn->dn_nblkptr - 1) * sizeof (blkptr_t);
                ASSERT(dn->dn_bonuslen <= dn->dn_bonus->db.db_size);
        }

        dn->dn_allocated_txg = tx->tx_txg;
        mutex_exit(&dn->dn_mtx);
}

#ifdef  _KERNEL
static void
dnode_move_impl(dnode_t *odn, dnode_t *ndn)
{
        int i;

        ASSERT(!RW_LOCK_HELD(&odn->dn_struct_rwlock));
        ASSERT(MUTEX_NOT_HELD(&odn->dn_mtx));
        ASSERT(MUTEX_NOT_HELD(&odn->dn_dbufs_mtx));
        ASSERT(!RW_LOCK_HELD(&odn->dn_zfetch.zf_rwlock));

        /* Copy fields. */
        ndn->dn_objset = odn->dn_objset;
        ndn->dn_object = odn->dn_object;
        ndn->dn_dbuf = odn->dn_dbuf;
        ndn->dn_handle = odn->dn_handle;
        ndn->dn_phys = odn->dn_phys;
        ndn->dn_type = odn->dn_type;
        ndn->dn_bonuslen = odn->dn_bonuslen;
        ndn->dn_bonustype = odn->dn_bonustype;
        ndn->dn_nblkptr = odn->dn_nblkptr;
        ndn->dn_checksum = odn->dn_checksum;
        ndn->dn_compress = odn->dn_compress;
        ndn->dn_nlevels = odn->dn_nlevels;
        ndn->dn_indblkshift = odn->dn_indblkshift;
        ndn->dn_datablkshift = odn->dn_datablkshift;
        ndn->dn_datablkszsec = odn->dn_datablkszsec;
        ndn->dn_datablksz = odn->dn_datablksz;
        ndn->dn_maxblkid = odn->dn_maxblkid;
        ndn->dn_num_slots = odn->dn_num_slots;
        bcopy(&odn->dn_next_type[0], &ndn->dn_next_type[0],
            sizeof (odn->dn_next_type));
        bcopy(&odn->dn_next_nblkptr[0], &ndn->dn_next_nblkptr[0],
            sizeof (odn->dn_next_nblkptr));
        bcopy(&odn->dn_next_nlevels[0], &ndn->dn_next_nlevels[0],
            sizeof (odn->dn_next_nlevels));
        bcopy(&odn->dn_next_indblkshift[0], &ndn->dn_next_indblkshift[0],
            sizeof (odn->dn_next_indblkshift));
        bcopy(&odn->dn_next_bonustype[0], &ndn->dn_next_bonustype[0],
            sizeof (odn->dn_next_bonustype));
        bcopy(&odn->dn_rm_spillblk[0], &ndn->dn_rm_spillblk[0],
            sizeof (odn->dn_rm_spillblk));
        bcopy(&odn->dn_next_bonuslen[0], &ndn->dn_next_bonuslen[0],
            sizeof (odn->dn_next_bonuslen));
        bcopy(&odn->dn_next_blksz[0], &ndn->dn_next_blksz[0],
            sizeof (odn->dn_next_blksz));
        bcopy(&odn->dn_next_maxblkid[0], &ndn->dn_next_maxblkid[0],
            sizeof (odn->dn_next_maxblkid));
        for (i = 0; i < TXG_SIZE; i++) {
                list_move_tail(&ndn->dn_dirty_records[i],
                    &odn->dn_dirty_records[i]);
        }
        bcopy(&odn->dn_free_ranges[0], &ndn->dn_free_ranges[0],
            sizeof (odn->dn_free_ranges));
        ndn->dn_allocated_txg = odn->dn_allocated_txg;
        ndn->dn_free_txg = odn->dn_free_txg;
        ndn->dn_assigned_txg = odn->dn_assigned_txg;
        ndn->dn_dirty_txg = odn->dn_dirty_txg;
        ndn->dn_dirtyctx = odn->dn_dirtyctx;
        ndn->dn_dirtyctx_firstset = odn->dn_dirtyctx_firstset;
        ASSERT(zfs_refcount_count(&odn->dn_tx_holds) == 0);
        zfs_refcount_transfer(&ndn->dn_holds, &odn->dn_holds);
        ASSERT(avl_is_empty(&ndn->dn_dbufs));
        avl_swap(&ndn->dn_dbufs, &odn->dn_dbufs);
        ndn->dn_dbufs_count = odn->dn_dbufs_count;
        ndn->dn_bonus = odn->dn_bonus;
        ndn->dn_have_spill = odn->dn_have_spill;
        ndn->dn_zio = odn->dn_zio;
        ndn->dn_oldused = odn->dn_oldused;
        ndn->dn_oldflags = odn->dn_oldflags;
        ndn->dn_olduid = odn->dn_olduid;
        ndn->dn_oldgid = odn->dn_oldgid;
        ndn->dn_oldprojid = odn->dn_oldprojid;
        ndn->dn_newuid = odn->dn_newuid;
        ndn->dn_newgid = odn->dn_newgid;
        ndn->dn_newprojid = odn->dn_newprojid;
        ndn->dn_id_flags = odn->dn_id_flags;
        dmu_zfetch_init(&ndn->dn_zfetch, NULL);
        list_move_tail(&ndn->dn_zfetch.zf_stream, &odn->dn_zfetch.zf_stream);
        ndn->dn_zfetch.zf_dnode = odn->dn_zfetch.zf_dnode;

        /*
         * Update back pointers. Updating the handle fixes the back pointer of
         * every descendant dbuf as well as the bonus dbuf.
         */
        ASSERT(ndn->dn_handle->dnh_dnode == odn);
        ndn->dn_handle->dnh_dnode = ndn;
        if (ndn->dn_zfetch.zf_dnode == odn) {
                ndn->dn_zfetch.zf_dnode = ndn;
        }

        /*
         * Invalidate the original dnode by clearing all of its back pointers.
         */
        odn->dn_dbuf = NULL;
        odn->dn_handle = NULL;
        avl_create(&odn->dn_dbufs, dbuf_compare, sizeof (dmu_buf_impl_t),
            offsetof(dmu_buf_impl_t, db_link));
        odn->dn_dbufs_count = 0;
        odn->dn_bonus = NULL;
        odn->dn_zfetch.zf_dnode = NULL;

        /*
         * Set the low bit of the objset pointer to ensure that dnode_move()
         * recognizes the dnode as invalid in any subsequent callback.
         */
        POINTER_INVALIDATE(&odn->dn_objset);

        /*
         * Satisfy the destructor.
         */
        for (i = 0; i < TXG_SIZE; i++) {
                list_create(&odn->dn_dirty_records[i],
                    sizeof (dbuf_dirty_record_t),
                    offsetof(dbuf_dirty_record_t, dr_dirty_node));
                odn->dn_free_ranges[i] = NULL;
                odn->dn_next_nlevels[i] = 0;
                odn->dn_next_indblkshift[i] = 0;
                odn->dn_next_bonustype[i] = 0;
                odn->dn_rm_spillblk[i] = 0;
                odn->dn_next_bonuslen[i] = 0;
                odn->dn_next_blksz[i] = 0;
        }
        odn->dn_allocated_txg = 0;
        odn->dn_free_txg = 0;
        odn->dn_assigned_txg = 0;
        odn->dn_dirty_txg = 0;
        odn->dn_dirtyctx = 0;
        odn->dn_dirtyctx_firstset = NULL;
        odn->dn_have_spill = B_FALSE;
        odn->dn_zio = NULL;
        odn->dn_oldused = 0;
        odn->dn_oldflags = 0;
        odn->dn_olduid = 0;
        odn->dn_oldgid = 0;
        odn->dn_oldprojid = ZFS_DEFAULT_PROJID;
        odn->dn_newuid = 0;
        odn->dn_newgid = 0;
        odn->dn_newprojid = ZFS_DEFAULT_PROJID;
        odn->dn_id_flags = 0;

        /*
         * Mark the dnode.
         */
        ndn->dn_moved = 1;
        odn->dn_moved = (uint8_t)-1;
}

/*ARGSUSED*/
static kmem_cbrc_t
dnode_move(void *buf, void *newbuf, size_t size, void *arg)
{
        dnode_t *odn = buf, *ndn = newbuf;
        objset_t *os;
        int64_t refcount;
        uint32_t dbufs;

        /*
         * The dnode is on the objset's list of known dnodes if the objset
         * pointer is valid. We set the low bit of the objset pointer when
         * freeing the dnode to invalidate it, and the memory patterns written
         * by kmem (baddcafe and deadbeef) set at least one of the two low bits.
         * A newly created dnode sets the objset pointer last of all to indicate
         * that the dnode is known and in a valid state to be moved by this
         * function.
         */
        os = odn->dn_objset;
        if (!POINTER_IS_VALID(os)) {
                DNODE_STAT_BUMP(dnode_move_invalid);
                return (KMEM_CBRC_DONT_KNOW);
        }

        /*
         * Ensure that the objset does not go away during the move.
         */
        rw_enter(&os_lock, RW_WRITER);
        if (os != odn->dn_objset) {
                rw_exit(&os_lock);
                DNODE_STAT_BUMP(dnode_move_recheck1);
                return (KMEM_CBRC_DONT_KNOW);
        }

        /*
         * If the dnode is still valid, then so is the objset. We know that no
         * valid objset can be freed while we hold os_lock, so we can safely
         * ensure that the objset remains in use.
         */
        mutex_enter(&os->os_lock);

        /*
         * Recheck the objset pointer in case the dnode was removed just before
         * acquiring the lock.
         */
        if (os != odn->dn_objset) {
                mutex_exit(&os->os_lock);
                rw_exit(&os_lock);
                DNODE_STAT_BUMP(dnode_move_recheck2);
                return (KMEM_CBRC_DONT_KNOW);
        }

        /*
         * At this point we know that as long as we hold os->os_lock, the dnode
         * cannot be freed and fields within the dnode can be safely accessed.
         * The objset listing this dnode cannot go away as long as this dnode is
         * on its list.
         */
        rw_exit(&os_lock);
        if (DMU_OBJECT_IS_SPECIAL(odn->dn_object)) {
                mutex_exit(&os->os_lock);
                DNODE_STAT_BUMP(dnode_move_special);
                return (KMEM_CBRC_NO);
        }
        ASSERT(odn->dn_dbuf != NULL); /* only "special" dnodes have no parent */

        /*
         * Lock the dnode handle to prevent the dnode from obtaining any new
         * holds. This also prevents the descendant dbufs and the bonus dbuf
         * from accessing the dnode, so that we can discount their holds. The
         * handle is safe to access because we know that while the dnode cannot
         * go away, neither can its handle. Once we hold dnh_zrlock, we can
         * safely move any dnode referenced only by dbufs.
         */
        if (!zrl_tryenter(&odn->dn_handle->dnh_zrlock)) {
                mutex_exit(&os->os_lock);
                DNODE_STAT_BUMP(dnode_move_handle);
                return (KMEM_CBRC_LATER);
        }

        /*
         * Ensure a consistent view of the dnode's holds and the dnode's dbufs.
         * We need to guarantee that there is a hold for every dbuf in order to
         * determine whether the dnode is actively referenced. Falsely matching
         * a dbuf to an active hold would lead to an unsafe move. It's possible
         * that a thread already having an active dnode hold is about to add a
         * dbuf, and we can't compare hold and dbuf counts while the add is in
         * progress.
         */
        if (!rw_tryenter(&odn->dn_struct_rwlock, RW_WRITER)) {
                zrl_exit(&odn->dn_handle->dnh_zrlock);
                mutex_exit(&os->os_lock);
                DNODE_STAT_BUMP(dnode_move_rwlock);
                return (KMEM_CBRC_LATER);
        }

        /*
         * A dbuf may be removed (evicted) without an active dnode hold. In that
         * case, the dbuf count is decremented under the handle lock before the
         * dbuf's hold is released. This order ensures that if we count the hold
         * after the dbuf is removed but before its hold is released, we will
         * treat the unmatched hold as active and exit safely. If we count the
         * hold before the dbuf is removed, the hold is discounted, and the
         * removal is blocked until the move completes.
         */
        refcount = zfs_refcount_count(&odn->dn_holds);
        ASSERT(refcount >= 0);
        dbufs = odn->dn_dbufs_count;

        /* We can't have more dbufs than dnode holds. */
        ASSERT3U(dbufs, <=, refcount);
        DTRACE_PROBE3(dnode__move, dnode_t *, odn, int64_t, refcount,
            uint32_t, dbufs);

        if (refcount > dbufs) {
                rw_exit(&odn->dn_struct_rwlock);
                zrl_exit(&odn->dn_handle->dnh_zrlock);
                mutex_exit(&os->os_lock);
                DNODE_STAT_BUMP(dnode_move_active);
                return (KMEM_CBRC_LATER);
        }

        rw_exit(&odn->dn_struct_rwlock);

        /*
         * At this point we know that anyone with a hold on the dnode is not
         * actively referencing it. The dnode is known and in a valid state to
         * move. We're holding the locks needed to execute the critical section.
         */
        dnode_move_impl(odn, ndn);

        list_link_replace(&odn->dn_link, &ndn->dn_link);
        /* If the dnode was safe to move, the refcount cannot have changed. */
        ASSERT(refcount == zfs_refcount_count(&ndn->dn_holds));
        ASSERT(dbufs == ndn->dn_dbufs_count);
        zrl_exit(&ndn->dn_handle->dnh_zrlock); /* handle has moved */
        mutex_exit(&os->os_lock);

        return (KMEM_CBRC_YES);
}
#endif  /* _KERNEL */

static void
dnode_slots_hold(dnode_children_t *children, int idx, int slots)
{
        ASSERT3S(idx + slots, <=, DNODES_PER_BLOCK);

        for (int i = idx; i < idx + slots; i++) {
                dnode_handle_t *dnh = &children->dnc_children[i];
                zrl_add(&dnh->dnh_zrlock);
        }
}

static void
dnode_slots_rele(dnode_children_t *children, int idx, int slots)
{
        ASSERT3S(idx + slots, <=, DNODES_PER_BLOCK);

        for (int i = idx; i < idx + slots; i++) {
                dnode_handle_t *dnh = &children->dnc_children[i];

                if (zrl_is_locked(&dnh->dnh_zrlock))
                        zrl_exit(&dnh->dnh_zrlock);
                else
                        zrl_remove(&dnh->dnh_zrlock);
        }
}

static void
dnode_slots_enter(dnode_children_t *children, int idx, int slots,
    kstat_named_t *statp)
{
        ASSERT3S(idx + slots, <=, DNODES_PER_BLOCK);

retry:
        for (int i = idx; i < idx + slots; i++) {
                dnode_handle_t *dnh = &children->dnc_children[i];

                if (!zrl_tryenter(&dnh->dnh_zrlock)) {
                        for (int j = idx; j < i; j++) {
                                dnh = &children->dnc_children[j];
                                zrl_exit(&dnh->dnh_zrlock);
                        }

                        atomic_add_64(&statp->value.ui64, 1);
                        kpreempt(KPREEMPT_SYNC);
                        goto retry;
                }
        }
}

static void
dnode_set_slots(dnode_children_t *children, int idx, int slots, void *ptr)
{
        ASSERT3S(idx + slots, <=, DNODES_PER_BLOCK);

        for (int i = idx; i < idx + slots; i++) {
                dnode_handle_t *dnh = &children->dnc_children[i];
                dnh->dnh_dnode = ptr;
        }
}

static boolean_t
dnode_check_slots_free(dnode_children_t *children, int idx, int slots)
{
        ASSERT3S(idx + slots, <=, DNODES_PER_BLOCK);

        /*
         * If all dnode slots are either already free or
         * evictable return B_TRUE.
         */
        for (int i = idx; i < idx + slots; i++) {
                dnode_handle_t *dnh = &children->dnc_children[i];
                dnode_t *dn = dnh->dnh_dnode;

                if (dn == DN_SLOT_FREE) {
                        continue;
                } else if (DN_SLOT_IS_PTR(dn)) {
                        mutex_enter(&dn->dn_mtx);
                        boolean_t can_free = (dn->dn_type == DMU_OT_NONE &&
                            zfs_refcount_is_zero(&dn->dn_holds) &&
                            !DNODE_IS_DIRTY(dn));
                        mutex_exit(&dn->dn_mtx);

                        if (!can_free)
                                return (B_FALSE);
                        else
                                continue;
                } else {
                        return (B_FALSE);
                }
        }

        return (B_TRUE);
}

static void
dnode_reclaim_slots(dnode_children_t *children, int idx, int slots)
{
        ASSERT3S(idx + slots, <=, DNODES_PER_BLOCK);

        for (int i = idx; i < idx + slots; i++) {
                dnode_handle_t *dnh = &children->dnc_children[i];

                ASSERT(zrl_is_locked(&dnh->dnh_zrlock));

                if (DN_SLOT_IS_PTR(dnh->dnh_dnode)) {
                        ASSERT3S(dnh->dnh_dnode->dn_type, ==, DMU_OT_NONE);
                        dnode_destroy(dnh->dnh_dnode);
                        dnh->dnh_dnode = DN_SLOT_FREE;
                }
        }
}

void
dnode_free_interior_slots(dnode_t *dn)
{
        dnode_children_t *children = dmu_buf_get_user(&dn->dn_dbuf->db);
        int epb = dn->dn_dbuf->db.db_size >> DNODE_SHIFT;
        int idx = (dn->dn_object & (epb - 1)) + 1;
        int slots = dn->dn_num_slots - 1;

        if (slots == 0)
                return;

        ASSERT3S(idx + slots, <=, DNODES_PER_BLOCK);

        dnode_slots_enter(children, idx, slots,
            &dnode_stats.dnode_free_interior_lock_retry);

        dnode_set_slots(children, idx, slots, DN_SLOT_FREE);
        dnode_slots_rele(children, idx, slots);
}

void
dnode_special_close(dnode_handle_t *dnh)
{
        dnode_t *dn = dnh->dnh_dnode;

        /*
         * Ensure dnode_rele_and_unlock() has released dn_mtx, after final
         * zfs_refcount_remove()
         */
        mutex_enter(&dn->dn_mtx);
        if (zfs_refcount_count(&dn->dn_holds) > 0)
                cv_wait(&dn->dn_nodnholds, &dn->dn_mtx);
        mutex_exit(&dn->dn_mtx);
        ASSERT3U(zfs_refcount_count(&dn->dn_holds), ==, 0);

        ASSERT(dn->dn_dbuf == NULL ||
            dmu_buf_get_user(&dn->dn_dbuf->db) == NULL);
        zrl_add(&dnh->dnh_zrlock);
        dnode_destroy(dn); /* implicit zrl_remove() */
        zrl_destroy(&dnh->dnh_zrlock);
        dnh->dnh_dnode = NULL;
}

void
dnode_special_open(objset_t *os, dnode_phys_t *dnp, uint64_t object,
    dnode_handle_t *dnh)
{
        dnode_t *dn;

        zrl_init(&dnh->dnh_zrlock);
        VERIFY3U(1, ==, zrl_tryenter(&dnh->dnh_zrlock));

        dn = dnode_create(os, dnp, NULL, object, dnh);
        DNODE_VERIFY(dn);

        zrl_exit(&dnh->dnh_zrlock);
}

static void
dnode_buf_evict_async(void *dbu)
{
        dnode_children_t *dnc = dbu;

        DNODE_STAT_BUMP(dnode_buf_evict);

        for (int i = 0; i < dnc->dnc_count; i++) {
                dnode_handle_t *dnh = &dnc->dnc_children[i];
                dnode_t *dn;

                /*
                 * The dnode handle lock guards against the dnode moving to
                 * another valid address, so there is no need here to guard
                 * against changes to or from NULL.
                 */
                if (!DN_SLOT_IS_PTR(dnh->dnh_dnode)) {
                        zrl_destroy(&dnh->dnh_zrlock);
                        dnh->dnh_dnode = DN_SLOT_UNINIT;
                        continue;
                }

                zrl_add(&dnh->dnh_zrlock);
                dn = dnh->dnh_dnode;
                /*
                 * If there are holds on this dnode, then there should
                 * be holds on the dnode's containing dbuf as well; thus
                 * it wouldn't be eligible for eviction and this function
                 * would not have been called.
                 */
                ASSERT(zfs_refcount_is_zero(&dn->dn_holds));
                ASSERT(zfs_refcount_is_zero(&dn->dn_tx_holds));

                dnode_destroy(dn); /* implicit zrl_remove() for first slot */
                zrl_destroy(&dnh->dnh_zrlock);
                dnh->dnh_dnode = DN_SLOT_UNINIT;
        }
        kmem_free(dnc, sizeof (dnode_children_t) +
            dnc->dnc_count * sizeof (dnode_handle_t));
}

/*
 * When the DNODE_MUST_BE_FREE flag is set, the "slots" parameter is used
 * to ensure the hole at the specified object offset is large enough to
 * hold the dnode being created. The slots parameter is also used to ensure
 * a dnode does not span multiple dnode blocks. In both of these cases, if
 * a failure occurs, ENOSPC is returned. Keep in mind, these failure cases
 * are only possible when using DNODE_MUST_BE_FREE.
 *
 * If the DNODE_MUST_BE_ALLOCATED flag is set, "slots" must be 0.
 * dnode_hold_impl() will check if the requested dnode is already consumed
 * as an extra dnode slot by an large dnode, in which case it returns
 * ENOENT.
 *
 * If the DNODE_DRY_RUN flag is set, we don't actually hold the dnode, just
 * return whether the hold would succeed or not. tag and dnp should set to
 * NULL in this case.
 *
 * errors:
 * EINVAL - invalid object number or flags.
 * ENOSPC - hole too small to fulfill "slots" request (DNODE_MUST_BE_FREE)
 * EEXIST - Refers to an allocated dnode (DNODE_MUST_BE_FREE)
 *        - Refers to a freeing dnode (DNODE_MUST_BE_FREE)
 *        - Refers to an interior dnode slot (DNODE_MUST_BE_ALLOCATED)
 * ENOENT - The requested dnode is not allocated (DNODE_MUST_BE_ALLOCATED)
 *        - The requested dnode is being freed (DNODE_MUST_BE_ALLOCATED)
 * EIO    - i/o error error when reading the meta dnode dbuf.
 * succeeds even for free dnodes.
 */
int
dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
    void *tag, dnode_t **dnp)
{
        int epb, idx, err;
        int drop_struct_lock = FALSE;
        int type;
        uint64_t blk;
        dnode_t *mdn, *dn;
        dmu_buf_impl_t *db;
        dnode_children_t *dnc;
        dnode_phys_t *dn_block;
        dnode_handle_t *dnh;

        ASSERT(!(flag & DNODE_MUST_BE_ALLOCATED) || (slots == 0));
        ASSERT(!(flag & DNODE_MUST_BE_FREE) || (slots > 0));
        IMPLY(flag & DNODE_DRY_RUN, (tag == NULL) && (dnp == NULL));

        /*
         * If you are holding the spa config lock as writer, you shouldn't
         * be asking the DMU to do *anything* unless it's the root pool
         * which may require us to read from the root filesystem while
         * holding some (not all) of the locks as writer.
         */
        ASSERT(spa_config_held(os->os_spa, SCL_ALL, RW_WRITER) == 0 ||
            (spa_is_root(os->os_spa) &&
            spa_config_held(os->os_spa, SCL_STATE, RW_WRITER)));

        ASSERT((flag & DNODE_MUST_BE_ALLOCATED) || (flag & DNODE_MUST_BE_FREE));

        if (object == DMU_USERUSED_OBJECT || object == DMU_GROUPUSED_OBJECT ||
            object == DMU_PROJECTUSED_OBJECT) {
                if (object == DMU_USERUSED_OBJECT)
                        dn = DMU_USERUSED_DNODE(os);
                else if (object == DMU_GROUPUSED_OBJECT)
                        dn = DMU_GROUPUSED_DNODE(os);
                else
                        dn = DMU_PROJECTUSED_DNODE(os);
                if (dn == NULL)
                        return (SET_ERROR(ENOENT));
                type = dn->dn_type;
                if ((flag & DNODE_MUST_BE_ALLOCATED) && type == DMU_OT_NONE)
                        return (SET_ERROR(ENOENT));
                if ((flag & DNODE_MUST_BE_FREE) && type != DMU_OT_NONE)
                        return (SET_ERROR(EEXIST));
                DNODE_VERIFY(dn);
                /* Don't actually hold if dry run, just return 0 */
                if (!(flag & DNODE_DRY_RUN)) {
                        (void) zfs_refcount_add(&dn->dn_holds, tag);
                        *dnp = dn;
                }
                return (0);
        }

        if (object == 0 || object >= DN_MAX_OBJECT)
                return (SET_ERROR(EINVAL));

        mdn = DMU_META_DNODE(os);
        ASSERT(mdn->dn_object == DMU_META_DNODE_OBJECT);

        DNODE_VERIFY(mdn);

        if (!RW_WRITE_HELD(&mdn->dn_struct_rwlock)) {
                rw_enter(&mdn->dn_struct_rwlock, RW_READER);
                drop_struct_lock = TRUE;
        }

        blk = dbuf_whichblock(mdn, 0, object * sizeof (dnode_phys_t));
        db = dbuf_hold(mdn, blk, FTAG);
        if (drop_struct_lock)
                rw_exit(&mdn->dn_struct_rwlock);
        if (db == NULL) {
                DNODE_STAT_BUMP(dnode_hold_dbuf_hold);
                return (SET_ERROR(EIO));
        }
        /*
         * We do not need to decrypt to read the dnode so it doesn't matter
         * if we get the encrypted or decrypted version.
         */
        err = dbuf_read(db, NULL, DB_RF_CANFAIL | DB_RF_NO_DECRYPT);
        if (err) {
                DNODE_STAT_BUMP(dnode_hold_dbuf_read);
                dbuf_rele(db, FTAG);
                return (err);
        }

        ASSERT3U(db->db.db_size, >=, 1<<DNODE_SHIFT);
        epb = db->db.db_size >> DNODE_SHIFT;

        idx = object & (epb - 1);
        dn_block = (dnode_phys_t *)db->db.db_data;

        ASSERT(DB_DNODE(db)->dn_type == DMU_OT_DNODE);
        dnc = dmu_buf_get_user(&db->db);
        dnh = NULL;
        if (dnc == NULL) {
                dnode_children_t *winner;
                int skip = 0;

                dnc = kmem_zalloc(sizeof (dnode_children_t) +
                    epb * sizeof (dnode_handle_t), KM_SLEEP);
                dnc->dnc_count = epb;
                dnh = &dnc->dnc_children[0];

                /* Initialize dnode slot status from dnode_phys_t */
                for (int i = 0; i < epb; i++) {
                        zrl_init(&dnh[i].dnh_zrlock);

                        if (skip) {
                                skip--;
                                continue;
                        }

                        if (dn_block[i].dn_type != DMU_OT_NONE) {
                                int interior = dn_block[i].dn_extra_slots;

                                dnode_set_slots(dnc, i, 1, DN_SLOT_ALLOCATED);
                                dnode_set_slots(dnc, i + 1, interior,
                                    DN_SLOT_INTERIOR);
                                skip = interior;
                        } else {
                                dnh[i].dnh_dnode = DN_SLOT_FREE;
                                skip = 0;
                        }
                }

                dmu_buf_init_user(&dnc->dnc_dbu, NULL,
                    dnode_buf_evict_async, NULL);
                winner = dmu_buf_set_user(&db->db, &dnc->dnc_dbu);
                if (winner != NULL) {

                        for (int i = 0; i < epb; i++)
                                zrl_destroy(&dnh[i].dnh_zrlock);

                        kmem_free(dnc, sizeof (dnode_children_t) +
                            epb * sizeof (dnode_handle_t));
                        dnc = winner;
                }
        }

        ASSERT(dnc->dnc_count == epb);

        if (flag & DNODE_MUST_BE_ALLOCATED) {
                slots = 1;

                dnode_slots_hold(dnc, idx, slots);
                dnh = &dnc->dnc_children[idx];

                if (DN_SLOT_IS_PTR(dnh->dnh_dnode)) {
                        dn = dnh->dnh_dnode;
                } else if (dnh->dnh_dnode == DN_SLOT_INTERIOR) {
                        DNODE_STAT_BUMP(dnode_hold_alloc_interior);
                        dnode_slots_rele(dnc, idx, slots);
                        dbuf_rele(db, FTAG);
                        return (SET_ERROR(EEXIST));
                } else if (dnh->dnh_dnode != DN_SLOT_ALLOCATED) {
                        DNODE_STAT_BUMP(dnode_hold_alloc_misses);
                        dnode_slots_rele(dnc, idx, slots);
                        dbuf_rele(db, FTAG);
                        return (SET_ERROR(ENOENT));
                } else {
                        dnode_slots_rele(dnc, idx, slots);
                        dnode_slots_enter(dnc, idx, slots,
                            &dnode_stats.dnode_hold_alloc_lock_retry);

                        /*
                         * Someone else won the race and called dnode_create()
                         * after we checked DN_SLOT_IS_PTR() above but before
                         * we acquired the lock.
                         */
                        if (DN_SLOT_IS_PTR(dnh->dnh_dnode)) {
                                DNODE_STAT_BUMP(dnode_hold_alloc_lock_misses);
                                dn = dnh->dnh_dnode;
                        } else {
                                dn = dnode_create(os, dn_block + idx, db,
                                    object, dnh);
                        }
                }

                mutex_enter(&dn->dn_mtx);
                if (dn->dn_type == DMU_OT_NONE || dn->dn_free_txg != 0) {
                        DNODE_STAT_BUMP(dnode_hold_alloc_type_none);
                        mutex_exit(&dn->dn_mtx);
                        dnode_slots_rele(dnc, idx, slots);
                        dbuf_rele(db, FTAG);
                        return (SET_ERROR(ENOENT));
                }

                /* Don't actually hold if dry run, just return 0 */
                if (flag & DNODE_DRY_RUN) {
                        mutex_exit(&dn->dn_mtx);
                        dnode_slots_rele(dnc, idx, slots);
                        dbuf_rele(db, FTAG);
                        return (0);
                }

                DNODE_STAT_BUMP(dnode_hold_alloc_hits);
        } else if (flag & DNODE_MUST_BE_FREE) {

                if (idx + slots - 1 >= DNODES_PER_BLOCK) {
                        DNODE_STAT_BUMP(dnode_hold_free_overflow);
                        dbuf_rele(db, FTAG);
                        return (SET_ERROR(ENOSPC));
                }

                dnode_slots_hold(dnc, idx, slots);

                if (!dnode_check_slots_free(dnc, idx, slots)) {
                        DNODE_STAT_BUMP(dnode_hold_free_misses);
                        dnode_slots_rele(dnc, idx, slots);
                        dbuf_rele(db, FTAG);
                        return (SET_ERROR(ENOSPC));
                }

                dnode_slots_rele(dnc, idx, slots);
                dnode_slots_enter(dnc, idx, slots,
                    &dnode_stats.dnode_hold_free_lock_retry);

                if (!dnode_check_slots_free(dnc, idx, slots)) {
                        DNODE_STAT_BUMP(dnode_hold_free_lock_misses);
                        dnode_slots_rele(dnc, idx, slots);
                        dbuf_rele(db, FTAG);
                        return (SET_ERROR(ENOSPC));
                }

                /*
                 * Allocated but otherwise free dnodes which would
                 * be in the interior of a multi-slot dnodes need
                 * to be freed.  Single slot dnodes can be safely
                 * re-purposed as a performance optimization.
                 */
                if (slots > 1)
                        dnode_reclaim_slots(dnc, idx + 1, slots - 1);

                dnh = &dnc->dnc_children[idx];
                if (DN_SLOT_IS_PTR(dnh->dnh_dnode)) {
                        dn = dnh->dnh_dnode;
                } else {
                        dn = dnode_create(os, dn_block + idx, db,
                            object, dnh);
                }

                mutex_enter(&dn->dn_mtx);
                if (!zfs_refcount_is_zero(&dn->dn_holds) || dn->dn_free_txg) {
                        DNODE_STAT_BUMP(dnode_hold_free_refcount);
                        mutex_exit(&dn->dn_mtx);
                        dnode_slots_rele(dnc, idx, slots);
                        dbuf_rele(db, FTAG);
                        return (SET_ERROR(EEXIST));
                }

                /* Don't actually hold if dry run, just return 0 */
                if (flag & DNODE_DRY_RUN) {
                        mutex_exit(&dn->dn_mtx);
                        dnode_slots_rele(dnc, idx, slots);
                        dbuf_rele(db, FTAG);
                        return (0);
                }

                dnode_set_slots(dnc, idx + 1, slots - 1, DN_SLOT_INTERIOR);
                DNODE_STAT_BUMP(dnode_hold_free_hits);
        } else {
                dbuf_rele(db, FTAG);
                return (SET_ERROR(EINVAL));
        }

        ASSERT0(dn->dn_free_txg);

        if (zfs_refcount_add(&dn->dn_holds, tag) == 1)
                dbuf_add_ref(db, dnh);

        mutex_exit(&dn->dn_mtx);

        /* Now we can rely on the hold to prevent the dnode from moving. */
        dnode_slots_rele(dnc, idx, slots);

        DNODE_VERIFY(dn);
        ASSERT3P(dn->dn_dbuf, ==, db);
        ASSERT3U(dn->dn_object, ==, object);
        dbuf_rele(db, FTAG);

        *dnp = dn;
        return (0);
}

/*
 * Return held dnode if the object is allocated, NULL if not.
 */
int
dnode_hold(objset_t *os, uint64_t object, void *tag, dnode_t **dnp)
{
        return (dnode_hold_impl(os, object, DNODE_MUST_BE_ALLOCATED, 0, tag,
            dnp));
}

/*
 * Can only add a reference if there is already at least one
 * reference on the dnode.  Returns FALSE if unable to add a
 * new reference.
 */
boolean_t
dnode_add_ref(dnode_t *dn, void *tag)
{
        mutex_enter(&dn->dn_mtx);
        if (zfs_refcount_is_zero(&dn->dn_holds)) {
                mutex_exit(&dn->dn_mtx);
                return (FALSE);
        }
        VERIFY(1 < zfs_refcount_add(&dn->dn_holds, tag));
        mutex_exit(&dn->dn_mtx);
        return (TRUE);
}

void
dnode_rele(dnode_t *dn, void *tag)
{
        mutex_enter(&dn->dn_mtx);
        dnode_rele_and_unlock(dn, tag, B_FALSE);
}

void
dnode_rele_and_unlock(dnode_t *dn, void *tag, boolean_t evicting)
{
        uint64_t refs;
        /* Get while the hold prevents the dnode from moving. */
        dmu_buf_impl_t *db = dn->dn_dbuf;
        dnode_handle_t *dnh = dn->dn_handle;

        refs = zfs_refcount_remove(&dn->dn_holds, tag);
        if (refs == 0)
                cv_broadcast(&dn->dn_nodnholds);
        mutex_exit(&dn->dn_mtx);
        /* dnode could get destroyed at this point, so don't use it anymore */

        /*
         * It's unsafe to release the last hold on a dnode by dnode_rele() or
         * indirectly by dbuf_rele() while relying on the dnode handle to
         * prevent the dnode from moving, since releasing the last hold could
         * result in the dnode's parent dbuf evicting its dnode handles. For
         * that reason anyone calling dnode_rele() or dbuf_rele() without some
         * other direct or indirect hold on the dnode must first drop the dnode
         * handle.
         */
        ASSERT(refs > 0 || dnh->dnh_zrlock.zr_owner != curthread);

        /* NOTE: the DNODE_DNODE does not have a dn_dbuf */
        if (refs == 0 && db != NULL) {
                /*
                 * Another thread could add a hold to the dnode handle in
                 * dnode_hold_impl() while holding the parent dbuf. Since the
                 * hold on the parent dbuf prevents the handle from being
                 * destroyed, the hold on the handle is OK. We can't yet assert
                 * that the handle has zero references, but that will be
                 * asserted anyway when the handle gets destroyed.
                 */
                mutex_enter(&db->db_mtx);
                dbuf_rele_and_unlock(db, dnh, evicting);
        }
}

/*
 * Test whether we can create a dnode at the specified location.
 */
int
dnode_try_claim(objset_t *os, uint64_t object, int slots)
{
        return (dnode_hold_impl(os, object, DNODE_MUST_BE_FREE | DNODE_DRY_RUN,
            slots, NULL, NULL));
}

void
dnode_setdirty(dnode_t *dn, dmu_tx_t *tx)
{
        objset_t *os = dn->dn_objset;
        uint64_t txg = tx->tx_txg;

        if (DMU_OBJECT_IS_SPECIAL(dn->dn_object)) {
                dsl_dataset_dirty(os->os_dsl_dataset, tx);
                return;
        }

        DNODE_VERIFY(dn);

#ifdef ZFS_DEBUG
        mutex_enter(&dn->dn_mtx);
        ASSERT(dn->dn_phys->dn_type || dn->dn_allocated_txg);
        ASSERT(dn->dn_free_txg == 0 || dn->dn_free_txg >= txg);
        mutex_exit(&dn->dn_mtx);
#endif

        /*
         * Determine old uid/gid when necessary
         */
        dmu_objset_userquota_get_ids(dn, B_TRUE, tx);

        multilist_t *dirtylist = os->os_dirty_dnodes[txg & TXG_MASK];
        multilist_sublist_t *mls = multilist_sublist_lock_obj(dirtylist, dn);

        /*
         * If we are already marked dirty, we're done.
         */
        if (multilist_link_active(&dn->dn_dirty_link[txg & TXG_MASK])) {
                multilist_sublist_unlock(mls);
                return;
        }

        ASSERT(!zfs_refcount_is_zero(&dn->dn_holds) ||
            !avl_is_empty(&dn->dn_dbufs));
        ASSERT(dn->dn_datablksz != 0);
        ASSERT0(dn->dn_next_bonuslen[txg&TXG_MASK]);
        ASSERT0(dn->dn_next_blksz[txg&TXG_MASK]);
        ASSERT0(dn->dn_next_bonustype[txg&TXG_MASK]);

        dprintf_ds(os->os_dsl_dataset, "obj=%llu txg=%llu\n",
            dn->dn_object, txg);

        multilist_sublist_insert_head(mls, dn);

        multilist_sublist_unlock(mls);

        /*
         * The dnode maintains a hold on its containing dbuf as
         * long as there are holds on it.  Each instantiated child
         * dbuf maintains a hold on the dnode.  When the last child
         * drops its hold, the dnode will drop its hold on the
         * containing dbuf. We add a "dirty hold" here so that the
         * dnode will hang around after we finish processing its
         * children.
         */
        VERIFY(dnode_add_ref(dn, (void *)(uintptr_t)tx->tx_txg));

        (void) dbuf_dirty(dn->dn_dbuf, tx);

        dsl_dataset_dirty(os->os_dsl_dataset, tx);
}

void
dnode_free(dnode_t *dn, dmu_tx_t *tx)
{
        mutex_enter(&dn->dn_mtx);
        if (dn->dn_type == DMU_OT_NONE || dn->dn_free_txg) {
                mutex_exit(&dn->dn_mtx);
                return;
        }
        dn->dn_free_txg = tx->tx_txg;
        mutex_exit(&dn->dn_mtx);

        dnode_setdirty(dn, tx);
}

/*
 * Try to change the block size for the indicated dnode.  This can only
 * succeed if there are no blocks allocated or dirty beyond first block
 */
int
dnode_set_blksz(dnode_t *dn, uint64_t size, int ibs, dmu_tx_t *tx)
{
        dmu_buf_impl_t *db;
        int err;

        ASSERT3U(size, <=, spa_maxblocksize(dmu_objset_spa(dn->dn_objset)));
        if (size == 0)
                size = SPA_MINBLOCKSIZE;
        else
                size = P2ROUNDUP(size, SPA_MINBLOCKSIZE);

        if (ibs == dn->dn_indblkshift)
                ibs = 0;

        if (size >> SPA_MINBLOCKSHIFT == dn->dn_datablkszsec && ibs == 0)
                return (0);

        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);

        /* Check for any allocated blocks beyond the first */
        if (dn->dn_maxblkid != 0)
                goto fail;

        mutex_enter(&dn->dn_dbufs_mtx);
        for (db = avl_first(&dn->dn_dbufs); db != NULL;
            db = AVL_NEXT(&dn->dn_dbufs, db)) {
                if (db->db_blkid != 0 && db->db_blkid != DMU_BONUS_BLKID &&
                    db->db_blkid != DMU_SPILL_BLKID) {
                        mutex_exit(&dn->dn_dbufs_mtx);
                        goto fail;
                }
        }
        mutex_exit(&dn->dn_dbufs_mtx);

        if (ibs && dn->dn_nlevels != 1)
                goto fail;

        /* resize the old block */
        err = dbuf_hold_impl(dn, 0, 0, TRUE, FALSE, FTAG, &db);
        if (err == 0) {
                dbuf_new_size(db, size, tx);
        } else if (err != ENOENT) {
                goto fail;
        }

        dnode_setdblksz(dn, size);
        dnode_setdirty(dn, tx);
        dn->dn_next_blksz[tx->tx_txg&TXG_MASK] = size;
        if (ibs) {
                dn->dn_indblkshift = ibs;
                dn->dn_next_indblkshift[tx->tx_txg&TXG_MASK] = ibs;
        }
        /* rele after we have fixed the blocksize in the dnode */
        if (db)
                dbuf_rele(db, FTAG);

        rw_exit(&dn->dn_struct_rwlock);
        return (0);

fail:
        rw_exit(&dn->dn_struct_rwlock);
        return (SET_ERROR(ENOTSUP));
}

static void
dnode_set_nlevels_impl(dnode_t *dn, int new_nlevels, dmu_tx_t *tx)
{
        uint64_t txgoff = tx->tx_txg & TXG_MASK;
        int old_nlevels = dn->dn_nlevels;
        dmu_buf_impl_t *db;
        list_t *list;
        dbuf_dirty_record_t *new, *dr, *dr_next;

        ASSERT(RW_WRITE_HELD(&dn->dn_struct_rwlock));

        dn->dn_nlevels = new_nlevels;

        ASSERT3U(new_nlevels, >, dn->dn_next_nlevels[txgoff]);
        dn->dn_next_nlevels[txgoff] = new_nlevels;

        /* dirty the left indirects */
        db = dbuf_hold_level(dn, old_nlevels, 0, FTAG);
        ASSERT(db != NULL);
        new = dbuf_dirty(db, tx);
        dbuf_rele(db, FTAG);

        /* transfer the dirty records to the new indirect */
        mutex_enter(&dn->dn_mtx);
        mutex_enter(&new->dt.di.dr_mtx);
        list = &dn->dn_dirty_records[txgoff];
        for (dr = list_head(list); dr; dr = dr_next) {
                dr_next = list_next(&dn->dn_dirty_records[txgoff], dr);
                if (dr->dr_dbuf->db_level != new_nlevels-1 &&
                    dr->dr_dbuf->db_blkid != DMU_BONUS_BLKID &&
                    dr->dr_dbuf->db_blkid != DMU_SPILL_BLKID) {
                        ASSERT(dr->dr_dbuf->db_level == old_nlevels-1);
                        list_remove(&dn->dn_dirty_records[txgoff], dr);
                        list_insert_tail(&new->dt.di.dr_children, dr);
                        dr->dr_parent = new;
                }
        }
        mutex_exit(&new->dt.di.dr_mtx);
        mutex_exit(&dn->dn_mtx);
}

int
dnode_set_nlevels(dnode_t *dn, int nlevels, dmu_tx_t *tx)
{
        int ret = 0;

        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);

        if (dn->dn_nlevels == nlevels) {
                ret = 0;
                goto out;
        } else if (nlevels < dn->dn_nlevels) {
                ret = SET_ERROR(EINVAL);
                goto out;
        }

        dnode_set_nlevels_impl(dn, nlevels, tx);

out:
        rw_exit(&dn->dn_struct_rwlock);
        return (ret);
}

/* read-holding callers must not rely on the lock being continuously held */
void
dnode_new_blkid(dnode_t *dn, uint64_t blkid, dmu_tx_t *tx, boolean_t have_read,
    boolean_t force)
{
        int epbs, new_nlevels;
        uint64_t sz;

        ASSERT(blkid != DMU_BONUS_BLKID);

        ASSERT(have_read ?
            RW_READ_HELD(&dn->dn_struct_rwlock) :
            RW_WRITE_HELD(&dn->dn_struct_rwlock));

        /*
         * if we have a read-lock, check to see if we need to do any work
         * before upgrading to a write-lock.
         */
        if (have_read) {
                if (blkid <= dn->dn_maxblkid)
                        return;

                if (!rw_tryupgrade(&dn->dn_struct_rwlock)) {
                        rw_exit(&dn->dn_struct_rwlock);
                        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
                }
        }

        /*
         * Raw sends (indicated by the force flag) require that we take the
         * given blkid even if the value is lower than the current value.
         */
        if (!force && blkid <= dn->dn_maxblkid)
                goto out;

        /*
         * We use the (otherwise unused) top bit of dn_next_maxblkid[txgoff]
         * to indicate that this field is set. This allows us to set the
         * maxblkid to 0 on an existing object in dnode_sync().
         */
        dn->dn_maxblkid = blkid;
        dn->dn_next_maxblkid[tx->tx_txg & TXG_MASK] =
            blkid | DMU_NEXT_MAXBLKID_SET;

        /*
         * Compute the number of levels necessary to support the new maxblkid.
         * Raw sends will ensure nlevels is set correctly for us.
         */
        new_nlevels = 1;
        epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
        for (sz = dn->dn_nblkptr;
            sz <= blkid && sz >= dn->dn_nblkptr; sz <<= epbs)
                new_nlevels++;

        if (!force) {
                if (new_nlevels > dn->dn_nlevels)
                        dnode_set_nlevels_impl(dn, new_nlevels, tx);
        } else {
                ASSERT3U(dn->dn_nlevels, >=, new_nlevels);
        }

out:
        if (have_read)
                rw_downgrade(&dn->dn_struct_rwlock);
}

static void
dnode_dirty_l1(dnode_t *dn, uint64_t l1blkid, dmu_tx_t *tx)
{
        dmu_buf_impl_t *db = dbuf_hold_level(dn, 1, l1blkid, FTAG);
        if (db != NULL) {
                dmu_buf_will_dirty(&db->db, tx);
                dbuf_rele(db, FTAG);
        }
}

/*
 * Dirty all the in-core level-1 dbufs in the range specified by start_blkid
 * and end_blkid.
 */
static void
dnode_dirty_l1range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
    dmu_tx_t *tx)
{
        dmu_buf_impl_t db_search;
        dmu_buf_impl_t *db;
        avl_index_t where;

        mutex_enter(&dn->dn_dbufs_mtx);

        db_search.db_level = 1;
        db_search.db_blkid = start_blkid + 1;
        db_search.db_state = DB_SEARCH;
        for (;;) {

                db = avl_find(&dn->dn_dbufs, &db_search, &where);
                if (db == NULL)
                        db = avl_nearest(&dn->dn_dbufs, where, AVL_AFTER);

                if (db == NULL || db->db_level != 1 ||
                    db->db_blkid >= end_blkid) {
                        break;
                }

                /*
                 * Setup the next blkid we want to search for.
                 */
                db_search.db_blkid = db->db_blkid + 1;
                ASSERT3U(db->db_blkid, >=, start_blkid);

                /*
                 * If the dbuf transitions to DB_EVICTING while we're trying
                 * to dirty it, then we will be unable to discover it in
                 * the dbuf hash table. This will result in a call to
                 * dbuf_create() which needs to acquire the dn_dbufs_mtx
                 * lock. To avoid a deadlock, we drop the lock before
                 * dirtying the level-1 dbuf.
                 */
                mutex_exit(&dn->dn_dbufs_mtx);
                dnode_dirty_l1(dn, db->db_blkid, tx);
                mutex_enter(&dn->dn_dbufs_mtx);
        }

#ifdef ZFS_DEBUG
        /*
         * Walk all the in-core level-1 dbufs and verify they have been dirtied.
         */
        db_search.db_level = 1;
        db_search.db_blkid = start_blkid + 1;
        db_search.db_state = DB_SEARCH;
        db = avl_find(&dn->dn_dbufs, &db_search, &where);
        if (db == NULL)
                db = avl_nearest(&dn->dn_dbufs, where, AVL_AFTER);
        for (; db != NULL; db = AVL_NEXT(&dn->dn_dbufs, db)) {
                if (db->db_level != 1 || db->db_blkid >= end_blkid)
                        break;
                ASSERT(db->db_dirtycnt > 0);
        }
#endif
        mutex_exit(&dn->dn_dbufs_mtx);
}

void
dnode_free_range(dnode_t *dn, uint64_t off, uint64_t len, dmu_tx_t *tx)
{
        dmu_buf_impl_t *db;
        uint64_t blkoff, blkid, nblks;
        int blksz, blkshift, head, tail;
        int trunc = FALSE;
        int epbs;

        blksz = dn->dn_datablksz;
        blkshift = dn->dn_datablkshift;
        epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;

        if (len == DMU_OBJECT_END) {
                len = UINT64_MAX - off;
                trunc = TRUE;
        }

        /*
         * First, block align the region to free:
         */
        if (ISP2(blksz)) {
                head = P2NPHASE(off, blksz);
                blkoff = P2PHASE(off, blksz);
                if ((off >> blkshift) > dn->dn_maxblkid)
                        return;
        } else {
                ASSERT(dn->dn_maxblkid == 0);
                if (off == 0 && len >= blksz) {
                        /*
                         * Freeing the whole block; fast-track this request.
                         */
                        blkid = 0;
                        nblks = 1;
                        if (dn->dn_nlevels > 1) {
                                rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
                                dnode_dirty_l1(dn, 0, tx);
                                rw_exit(&dn->dn_struct_rwlock);
                        }
                        goto done;
                } else if (off >= blksz) {
                        /* Freeing past end-of-data */
                        return;
                } else {
                        /* Freeing part of the block. */
                        head = blksz - off;
                        ASSERT3U(head, >, 0);
                }
                blkoff = off;
        }
        /* zero out any partial block data at the start of the range */
        if (head) {
                int res;
                ASSERT3U(blkoff + head, ==, blksz);
                if (len < head)
                        head = len;
                rw_enter(&dn->dn_struct_rwlock, RW_READER);
                res = dbuf_hold_impl(dn, 0, dbuf_whichblock(dn, 0, off),
                    TRUE, FALSE, FTAG, &db);
                rw_exit(&dn->dn_struct_rwlock);
                if (res == 0) {
                        caddr_t data;
                        boolean_t dirty;

                        db_lock_type_t dblt = dmu_buf_lock_parent(db, RW_READER,
                            FTAG);
                        /* don't dirty if it isn't on disk and isn't dirty */
                        dirty = db->db_last_dirty ||
                            (db->db_blkptr && !BP_IS_HOLE(db->db_blkptr));
                        dmu_buf_unlock_parent(db, dblt, FTAG);
                        if (dirty) {
                                dmu_buf_will_dirty(&db->db, tx);
                                data = db->db.db_data;
                                bzero(data + blkoff, head);
                        }
                        dbuf_rele(db, FTAG);
                }
                off += head;
                len -= head;
        }

        /* If the range was less than one block, we're done */
        if (len == 0)
                return;

        /* If the remaining range is past end of file, we're done */
        if ((off >> blkshift) > dn->dn_maxblkid)
                return;

        ASSERT(ISP2(blksz));
        if (trunc)
                tail = 0;
        else
                tail = P2PHASE(len, blksz);

        ASSERT0(P2PHASE(off, blksz));
        /* zero out any partial block data at the end of the range */
        if (tail) {
                int res;
                if (len < tail)
                        tail = len;
                rw_enter(&dn->dn_struct_rwlock, RW_READER);
                res = dbuf_hold_impl(dn, 0, dbuf_whichblock(dn, 0, off+len),
                    TRUE, FALSE, FTAG, &db);
                rw_exit(&dn->dn_struct_rwlock);
                if (res == 0) {
                        boolean_t dirty;
                        /* don't dirty if not on disk and not dirty */
                        db_lock_type_t type = dmu_buf_lock_parent(db, RW_READER,
                            FTAG);
                        dirty = db->db_last_dirty ||
                            (db->db_blkptr && !BP_IS_HOLE(db->db_blkptr));
                        dmu_buf_unlock_parent(db, type, FTAG);
                        if (dirty) {
                                dmu_buf_will_dirty(&db->db, tx);
                                bzero(db->db.db_data, tail);
                        }
                        dbuf_rele(db, FTAG);
                }
                len -= tail;
        }

        /* If the range did not include a full block, we are done */
        if (len == 0)
                return;

        ASSERT(IS_P2ALIGNED(off, blksz));
        ASSERT(trunc || IS_P2ALIGNED(len, blksz));
        blkid = off >> blkshift;
        nblks = len >> blkshift;
        if (trunc)
                nblks += 1;

        /*
         * Dirty all the indirect blocks in this range.  Note that only
         * the first and last indirect blocks can actually be written
         * (if they were partially freed) -- they must be dirtied, even if
         * they do not exist on disk yet.  The interior blocks will
         * be freed by free_children(), so they will not actually be written.
         * Even though these interior blocks will not be written, we
         * dirty them for two reasons:
         *
         *  - It ensures that the indirect blocks remain in memory until
         *    syncing context.  (They have already been prefetched by
         *    dmu_tx_hold_free(), so we don't have to worry about reading
         *    them serially here.)
         *
         *  - The dirty space accounting will put pressure on the txg sync
         *    mechanism to begin syncing, and to delay transactions if there
         *    is a large amount of freeing.  Even though these indirect
         *    blocks will not be written, we could need to write the same
         *    amount of space if we copy the freed BPs into deadlists.
         */
        if (dn->dn_nlevels > 1) {
                rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
                uint64_t first, last;

                first = blkid >> epbs;
                dnode_dirty_l1(dn, first, tx);
                if (trunc)
                        last = dn->dn_maxblkid >> epbs;
                else
                        last = (blkid + nblks - 1) >> epbs;
                if (last != first)
                        dnode_dirty_l1(dn, last, tx);

                dnode_dirty_l1range(dn, first, last, tx);

                int shift = dn->dn_datablkshift + dn->dn_indblkshift -
                    SPA_BLKPTRSHIFT;
                for (uint64_t i = first + 1; i < last; i++) {
                        /*
                         * Set i to the blockid of the next non-hole
                         * level-1 indirect block at or after i.  Note
                         * that dnode_next_offset() operates in terms of
                         * level-0-equivalent bytes.
                         */
                        uint64_t ibyte = i << shift;
                        int err = dnode_next_offset(dn, DNODE_FIND_HAVELOCK,
                            &ibyte, 2, 1, 0);
                        i = ibyte >> shift;
                        if (i >= last)
                                break;

                        /*
                         * Normally we should not see an error, either
                         * from dnode_next_offset() or dbuf_hold_level()
                         * (except for ESRCH from dnode_next_offset).
                         * If there is an i/o error, then when we read
                         * this block in syncing context, it will use
                         * ZIO_FLAG_MUSTSUCCEED, and thus hang/panic according
                         * to the "failmode" property.  dnode_next_offset()
                         * doesn't have a flag to indicate MUSTSUCCEED.
                         */
                        if (err != 0)
                                break;

                        dnode_dirty_l1(dn, i, tx);
                }
                rw_exit(&dn->dn_struct_rwlock);
        }

done:
        /*
         * Add this range to the dnode range list.
         * We will finish up this free operation in the syncing phase.
         */
        mutex_enter(&dn->dn_mtx);
        int txgoff = tx->tx_txg & TXG_MASK;
        if (dn->dn_free_ranges[txgoff] == NULL) {
                dn->dn_free_ranges[txgoff] = range_tree_create(NULL,
                    RANGE_SEG64, NULL, 0, 0);
        }
        range_tree_clear(dn->dn_free_ranges[txgoff], blkid, nblks);
        range_tree_add(dn->dn_free_ranges[txgoff], blkid, nblks);
        dprintf_dnode(dn, "blkid=%llu nblks=%llu txg=%llu\n",
            blkid, nblks, tx->tx_txg);
        mutex_exit(&dn->dn_mtx);

        dbuf_free_range(dn, blkid, blkid + nblks - 1, tx);
        dnode_setdirty(dn, tx);
}

static boolean_t
dnode_spill_freed(dnode_t *dn)
{
        int i;

        mutex_enter(&dn->dn_mtx);
        for (i = 0; i < TXG_SIZE; i++) {
                if (dn->dn_rm_spillblk[i] == DN_KILL_SPILLBLK)
                        break;
        }
        mutex_exit(&dn->dn_mtx);
        return (i < TXG_SIZE);
}

/* return TRUE if this blkid was freed in a recent txg, or FALSE if it wasn't */
uint64_t
dnode_block_freed(dnode_t *dn, uint64_t blkid)
{
        void *dp = spa_get_dsl(dn->dn_objset->os_spa);
        int i;

        if (blkid == DMU_BONUS_BLKID)
                return (FALSE);

        /*
         * If we're in the process of opening the pool, dp will not be
         * set yet, but there shouldn't be anything dirty.
         */
        if (dp == NULL)
                return (FALSE);

        if (dn->dn_free_txg)
                return (TRUE);

        if (blkid == DMU_SPILL_BLKID)
                return (dnode_spill_freed(dn));

        mutex_enter(&dn->dn_mtx);
        for (i = 0; i < TXG_SIZE; i++) {
                if (dn->dn_free_ranges[i] != NULL &&
                    range_tree_contains(dn->dn_free_ranges[i], blkid, 1))
                        break;
        }
        mutex_exit(&dn->dn_mtx);
        return (i < TXG_SIZE);
}

/* call from syncing context when we actually write/free space for this dnode */
void
dnode_diduse_space(dnode_t *dn, int64_t delta)
{
        uint64_t space;
        dprintf_dnode(dn, "dn=%p dnp=%p used=%llu delta=%lld\n",
            dn, dn->dn_phys,
            (u_longlong_t)dn->dn_phys->dn_used,
            (longlong_t)delta);

        mutex_enter(&dn->dn_mtx);
        space = DN_USED_BYTES(dn->dn_phys);
        if (delta > 0) {
                ASSERT3U(space + delta, >=, space); /* no overflow */
        } else {
                ASSERT3U(space, >=, -delta); /* no underflow */
        }
        space += delta;
        if (spa_version(dn->dn_objset->os_spa) < SPA_VERSION_DNODE_BYTES) {
                ASSERT((dn->dn_phys->dn_flags & DNODE_FLAG_USED_BYTES) == 0);
                ASSERT0(P2PHASE(space, 1<<DEV_BSHIFT));
                dn->dn_phys->dn_used = space >> DEV_BSHIFT;
        } else {
                dn->dn_phys->dn_used = space;
                dn->dn_phys->dn_flags |= DNODE_FLAG_USED_BYTES;
        }
        mutex_exit(&dn->dn_mtx);
}

/*
 * Scans a block at the indicated "level" looking for a hole or data,
 * depending on 'flags'.
 *
 * If level > 0, then we are scanning an indirect block looking at its
 * pointers.  If level == 0, then we are looking at a block of dnodes.
 *
 * If we don't find what we are looking for in the block, we return ESRCH.
 * Otherwise, return with *offset pointing to the beginning (if searching
 * forwards) or end (if searching backwards) of the range covered by the
 * block pointer we matched on (or dnode).
 *
 * The basic search algorithm used below by dnode_next_offset() is to
 * use this function to search up the block tree (widen the search) until
 * we find something (i.e., we don't return ESRCH) and then search back
 * down the tree (narrow the search) until we reach our original search
 * level.
 */
static int
dnode_next_offset_level(dnode_t *dn, int flags, uint64_t *offset,
    int lvl, uint64_t blkfill, uint64_t txg)
{
        dmu_buf_impl_t *db = NULL;
        void *data = NULL;
        uint64_t epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
        uint64_t epb = 1ULL << epbs;
        uint64_t minfill, maxfill;
        boolean_t hole;
        int i, inc, error, span;

        dprintf_zfs("probing object %llu offset %llx level %d of %u\n",
            dn->dn_object, *offset, lvl, dn->dn_phys->dn_nlevels);

        ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));

        hole = ((flags & DNODE_FIND_HOLE) != 0);
        inc = (flags & DNODE_FIND_BACKWARDS) ? -1 : 1;
        ASSERT(txg == 0 || !hole);

        if (lvl == dn->dn_phys->dn_nlevels) {
                error = 0;
                epb = dn->dn_phys->dn_nblkptr;
                data = dn->dn_phys->dn_blkptr;
        } else {
                uint64_t blkid = dbuf_whichblock(dn, lvl, *offset);
                error = dbuf_hold_impl(dn, lvl, blkid, TRUE, FALSE, FTAG, &db);
                if (error) {
                        if (error != ENOENT)
                                return (error);
                        if (hole)
                                return (0);
                        /*
                         * This can only happen when we are searching up
                         * the block tree for data.  We don't really need to
                         * adjust the offset, as we will just end up looking
                         * at the pointer to this block in its parent, and its
                         * going to be unallocated, so we will skip over it.
                         */
                        return (SET_ERROR(ESRCH));
                }
                error = dbuf_read(db, NULL,
                    DB_RF_CANFAIL | DB_RF_HAVESTRUCT | DB_RF_NO_DECRYPT);
                if (error) {
                        dbuf_rele(db, FTAG);
                        return (error);
                }
                data = db->db.db_data;
                rw_enter(&db->db_rwlock, RW_READER);
        }

        if (db != NULL && txg != 0 && (db->db_blkptr == NULL ||
            db->db_blkptr->blk_birth <= txg ||
            BP_IS_HOLE(db->db_blkptr))) {
                /*
                 * This can only happen when we are searching up the tree
                 * and these conditions mean that we need to keep climbing.
                 */
                error = SET_ERROR(ESRCH);
        } else if (lvl == 0) {
                dnode_phys_t *dnp = data;

                ASSERT(dn->dn_type == DMU_OT_DNODE);
                ASSERT(!(flags & DNODE_FIND_BACKWARDS));

                for (i = (*offset >> DNODE_SHIFT) & (blkfill - 1);
                    i < blkfill; i += dnp[i].dn_extra_slots + 1) {
                        if ((dnp[i].dn_type == DMU_OT_NONE) == hole)
                                break;
                }

                if (i == blkfill)
                        error = SET_ERROR(ESRCH);

                *offset = (*offset & ~(DNODE_BLOCK_SIZE - 1)) +
                    (i << DNODE_SHIFT);
        } else {
                blkptr_t *bp = data;
                uint64_t start = *offset;
                span = (lvl - 1) * epbs + dn->dn_datablkshift;
                minfill = 0;
                maxfill = blkfill << ((lvl - 1) * epbs);

                if (hole)
                        maxfill--;
                else
                        minfill++;

                *offset = *offset >> span;
                for (i = BF64_GET(*offset, 0, epbs);
                    i >= 0 && i < epb; i += inc) {
                        if (BP_GET_FILL(&bp[i]) >= minfill &&
                            BP_GET_FILL(&bp[i]) <= maxfill &&
                            (hole || bp[i].blk_birth > txg))
                                break;
                        if (inc > 0 || *offset > 0)
                                *offset += inc;
                }
                *offset = *offset << span;
                if (inc < 0) {
                        /* traversing backwards; position offset at the end */
                        ASSERT3U(*offset, <=, start);
                        *offset = MIN(*offset + (1ULL << span) - 1, start);
                } else if (*offset < start) {
                        *offset = start;
                }
                if (i < 0 || i >= epb)
                        error = SET_ERROR(ESRCH);
        }

        if (db != NULL) {
                rw_exit(&db->db_rwlock);
                dbuf_rele(db, FTAG);
        }

        return (error);
}

/*
 * Find the next hole, data, or sparse region at or after *offset.
 * The value 'blkfill' tells us how many items we expect to find
 * in an L0 data block; this value is 1 for normal objects,
 * DNODES_PER_BLOCK for the meta dnode, and some fraction of
 * DNODES_PER_BLOCK when searching for sparse regions thereof.
 *
 * Examples:
 *
 * dnode_next_offset(dn, flags, offset, 1, 1, 0);
 *      Finds the next/previous hole/data in a file.
 *      Used in dmu_offset_next().
 *
 * dnode_next_offset(mdn, flags, offset, 0, DNODES_PER_BLOCK, txg);
 *      Finds the next free/allocated dnode an objset's meta-dnode.
 *      Only finds objects that have new contents since txg (ie.
 *      bonus buffer changes and content removal are ignored).
 *      Used in dmu_object_next().
 *
 * dnode_next_offset(mdn, DNODE_FIND_HOLE, offset, 2, DNODES_PER_BLOCK >> 2, 0);
 *      Finds the next L2 meta-dnode bp that's at most 1/4 full.
 *      Used in dmu_object_alloc().
 */
int
dnode_next_offset(dnode_t *dn, int flags, uint64_t *offset,
    int minlvl, uint64_t blkfill, uint64_t txg)
{
        uint64_t initial_offset = *offset;
        int lvl, maxlvl;
        int error = 0;

        if (!(flags & DNODE_FIND_HAVELOCK))
                rw_enter(&dn->dn_struct_rwlock, RW_READER);

        if (dn->dn_phys->dn_nlevels == 0) {
                error = SET_ERROR(ESRCH);
                goto out;
        }

        if (dn->dn_datablkshift == 0) {
                if (*offset < dn->dn_datablksz) {
                        if (flags & DNODE_FIND_HOLE)
                                *offset = dn->dn_datablksz;
                } else {
                        error = SET_ERROR(ESRCH);
                }
                goto out;
        }

        maxlvl = dn->dn_phys->dn_nlevels;

        for (lvl = minlvl; lvl <= maxlvl; lvl++) {
                error = dnode_next_offset_level(dn,
                    flags, offset, lvl, blkfill, txg);
                if (error != ESRCH)
                        break;
        }

        while (error == 0 && --lvl >= minlvl) {
                error = dnode_next_offset_level(dn,
                    flags, offset, lvl, blkfill, txg);
        }

        /*
         * There's always a "virtual hole" at the end of the object, even
         * if all BP's which physically exist are non-holes.
         */
        if ((flags & DNODE_FIND_HOLE) && error == ESRCH && txg == 0 &&
            minlvl == 1 && blkfill == 1 && !(flags & DNODE_FIND_BACKWARDS)) {
                error = 0;
        }

        if (error == 0 && (flags & DNODE_FIND_BACKWARDS ?
            initial_offset < *offset : initial_offset > *offset))
                error = SET_ERROR(ESRCH);
out:
        if (!(flags & DNODE_FIND_HAVELOCK))
                rw_exit(&dn->dn_struct_rwlock);

        return (error);
}