fs/zfs/zap_micro.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2011, 2016 by Delphix. All rights reserved.
 * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
 * Copyright (c) 2014 Integros [integros.com]
 */

#include <sys/zio.h>
#include <sys/spa.h>
#include <sys/dmu.h>
#include <sys/zfs_context.h>
#include <sys/zap.h>
#include <sys/refcount.h>
#include <sys/zap_impl.h>
#include <sys/zap_leaf.h>
#include <sys/avl.h>
#include <sys/arc.h>
#include <sys/dmu_objset.h>

#ifdef _KERNEL
#include <sys/sunddi.h>
#endif

extern inline mzap_phys_t *zap_m_phys(zap_t *zap);

static int mzap_upgrade(zap_t **zapp,
    void *tag, dmu_tx_t *tx, zap_flags_t flags);

uint64_t
zap_getflags(zap_t *zap)
{
    if (zap->zap_ismicro)
        return (0);
    return (zap_f_phys(zap)->zap_flags);
}

int
zap_hashbits(zap_t *zap)
{
    if (zap_getflags(zap) & ZAP_FLAG_HASH64)
        return (48);
    else
        return (28);
}

uint32_t
zap_maxcd(zap_t *zap)
{
    if (zap_getflags(zap) & ZAP_FLAG_HASH64)
        return ((1<<16)-1);
    else
        return (-1U);
}

static uint64_t
zap_hash(zap_name_t *zn)
{
    zap_t *zap = zn->zn_zap;
    uint64_t h = 0;

    if (zap_getflags(zap) & ZAP_FLAG_PRE_HASHED_KEY) {
        ASSERT(zap_getflags(zap) & ZAP_FLAG_UINT64_KEY);
        h = *(uint64_t *)zn->zn_key_orig;
    } else {
        h = zap->zap_salt;
        ASSERT(h != 0);
        ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY);

        if (zap_getflags(zap) & ZAP_FLAG_UINT64_KEY) {
            int i;
            const uint64_t *wp = zn->zn_key_norm;

            ASSERT(zn->zn_key_intlen == 8);
            for (i = 0; i < zn->zn_key_norm_numints; wp++, i++) {
                int j;
                uint64_t word = *wp;

                for (j = 0; j < zn->zn_key_intlen; j++) {
                    h = (h >> 8) ^
                        zfs_crc64_table[(h ^ word) & 0xFF];
                    word >>= NBBY;
                }
            }
        } else {
            int i, len;
            const uint8_t *cp = zn->zn_key_norm;

            /*
             * We previously stored the terminating null on
             * disk, but didn't hash it, so we need to
             * continue to not hash it.  (The
             * zn_key_*_numints includes the terminating
             * null for non-binary keys.)
             */
            len = zn->zn_key_norm_numints - 1;

            ASSERT(zn->zn_key_intlen == 1);
            for (i = 0; i < len; cp++, i++) {
                h = (h >> 8) ^
                    zfs_crc64_table[(h ^ *cp) & 0xFF];
            }
        }
    }
    /*
     * Don't use all 64 bits, since we need some in the cookie for
     * the collision differentiator.  We MUST use the high bits,
     * since those are the ones that we first pay attention to when
     * chosing the bucket.
     */
    h &= ~((1ULL << (64 - zap_hashbits(zap))) - 1);

    return (h);
}

static int
zap_normalize(zap_t *zap, const char *name, char *namenorm)
{
    size_t inlen, outlen;
    int err;

    ASSERT(!(zap_getflags(zap) & ZAP_FLAG_UINT64_KEY));

    inlen = strlen(name) + 1;
    outlen = ZAP_MAXNAMELEN;

    err = 0;
    (void) u8_textprep_str((char *)name, &inlen, namenorm, &outlen,
        zap->zap_normflags | U8_TEXTPREP_IGNORE_NULL |
        U8_TEXTPREP_IGNORE_INVALID, U8_UNICODE_LATEST, &err);

    return (err);
}

boolean_t
zap_match(zap_name_t *zn, const char *matchname)
{
    ASSERT(!(zap_getflags(zn->zn_zap) & ZAP_FLAG_UINT64_KEY));

    if (zn->zn_matchtype == MT_FIRST) {
        char norm[ZAP_MAXNAMELEN];

        if (zap_normalize(zn->zn_zap, matchname, norm) != 0)
            return (B_FALSE);

        return (strcmp(zn->zn_key_norm, norm) == 0);
    } else {
        /* MT_BEST or MT_EXACT */
        return (strcmp(zn->zn_key_orig, matchname) == 0);
    }
}

void
zap_name_free(zap_name_t *zn)
{
    kmem_free(zn, sizeof (zap_name_t));
}

zap_name_t *
zap_name_alloc(zap_t *zap, const char *key, matchtype_t mt)
{
    zap_name_t *zn = kmem_alloc(sizeof (zap_name_t), KM_SLEEP);

    zn->zn_zap = zap;
    zn->zn_key_intlen = sizeof (*key);
    zn->zn_key_orig = key;
    zn->zn_key_orig_numints = strlen(zn->zn_key_orig) + 1;
    zn->zn_matchtype = mt;
    if (zap->zap_normflags) {
        if (zap_normalize(zap, key, zn->zn_normbuf) != 0) {
            zap_name_free(zn);
            return (NULL);
        }
        zn->zn_key_norm = zn->zn_normbuf;
        zn->zn_key_norm_numints = strlen(zn->zn_key_norm) + 1;
    } else {
        if (mt != MT_EXACT) {
            zap_name_free(zn);
            return (NULL);
        }
        zn->zn_key_norm = zn->zn_key_orig;
        zn->zn_key_norm_numints = zn->zn_key_orig_numints;
    }

    zn->zn_hash = zap_hash(zn);
    return (zn);
}

zap_name_t *
zap_name_alloc_uint64(zap_t *zap, const uint64_t *key, int numints)
{
    zap_name_t *zn = kmem_alloc(sizeof (zap_name_t), KM_SLEEP);

    ASSERT(zap->zap_normflags == 0);
    zn->zn_zap = zap;
    zn->zn_key_intlen = sizeof (*key);
    zn->zn_key_orig = zn->zn_key_norm = key;
    zn->zn_key_orig_numints = zn->zn_key_norm_numints = numints;
    zn->zn_matchtype = MT_EXACT;

    zn->zn_hash = zap_hash(zn);
    return (zn);
}

static void
mzap_byteswap(mzap_phys_t *buf, size_t size)
{
    int i, max;
    buf->mz_block_type = BSWAP_64(buf->mz_block_type);
    buf->mz_salt = BSWAP_64(buf->mz_salt);
    buf->mz_normflags = BSWAP_64(buf->mz_normflags);
    max = (size / MZAP_ENT_LEN) - 1;
    for (i = 0; i < max; i++) {
        buf->mz_chunk[i].mze_value =
            BSWAP_64(buf->mz_chunk[i].mze_value);
        buf->mz_chunk[i].mze_cd =
            BSWAP_32(buf->mz_chunk[i].mze_cd);
    }
}

void
zap_byteswap(void *buf, size_t size)
{
    uint64_t block_type;

    block_type = *(uint64_t *)buf;

    if (block_type == ZBT_MICRO || block_type == BSWAP_64(ZBT_MICRO)) {
        /* ASSERT(magic == ZAP_LEAF_MAGIC); */
        mzap_byteswap(buf, size);
    } else {
        fzap_byteswap(buf, size);
    }
}

static int
mze_compare(const void *arg1, const void *arg2)
{
    const mzap_ent_t *mze1 = arg1;
    const mzap_ent_t *mze2 = arg2;

    if (mze1->mze_hash > mze2->mze_hash)
        return (+1);
    if (mze1->mze_hash < mze2->mze_hash)
        return (-1);
    if (mze1->mze_cd > mze2->mze_cd)
        return (+1);
    if (mze1->mze_cd < mze2->mze_cd)
        return (-1);
    return (0);
}

static void
mze_insert(zap_t *zap, int chunkid, uint64_t hash)
{
    mzap_ent_t *mze;

    ASSERT(zap->zap_ismicro);
    ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));

    mze = kmem_alloc(sizeof (mzap_ent_t), KM_SLEEP);
    mze->mze_chunkid = chunkid;
    mze->mze_hash = hash;
    mze->mze_cd = MZE_PHYS(zap, mze)->mze_cd;
    ASSERT(MZE_PHYS(zap, mze)->mze_name[0] != 0);
    avl_add(&zap->zap_m.zap_avl, mze);
}

static mzap_ent_t *
mze_find(zap_name_t *zn)
{
    mzap_ent_t mze_tofind;
    mzap_ent_t *mze;
    avl_index_t idx;
    avl_tree_t *avl = &zn->zn_zap->zap_m.zap_avl;

    ASSERT(zn->zn_zap->zap_ismicro);
    ASSERT(RW_LOCK_HELD(&zn->zn_zap->zap_rwlock));

    mze_tofind.mze_hash = zn->zn_hash;
    mze_tofind.mze_cd = 0;

again:
    mze = avl_find(avl, &mze_tofind, &idx);
    if (mze == NULL)
        mze = avl_nearest(avl, idx, AVL_AFTER);
    for (; mze && mze->mze_hash == zn->zn_hash; mze = AVL_NEXT(avl, mze)) {
        ASSERT3U(mze->mze_cd, ==, MZE_PHYS(zn->zn_zap, mze)->mze_cd);
        if (zap_match(zn, MZE_PHYS(zn->zn_zap, mze)->mze_name))
            return (mze);
    }
    if (zn->zn_matchtype == MT_BEST) {
        zn->zn_matchtype = MT_FIRST;
        goto again;
    }
    return (NULL);
}

static uint32_t
mze_find_unused_cd(zap_t *zap, uint64_t hash)
{
    mzap_ent_t mze_tofind;
    mzap_ent_t *mze;
    avl_index_t idx;
    avl_tree_t *avl = &zap->zap_m.zap_avl;
    uint32_t cd;

    ASSERT(zap->zap_ismicro);
    ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));

    mze_tofind.mze_hash = hash;
    mze_tofind.mze_cd = 0;

    cd = 0;
    for (mze = avl_find(avl, &mze_tofind, &idx);
        mze && mze->mze_hash == hash; mze = AVL_NEXT(avl, mze)) {
        if (mze->mze_cd != cd)
            break;
        cd++;
    }

    return (cd);
}

static void
mze_remove(zap_t *zap, mzap_ent_t *mze)
{
    ASSERT(zap->zap_ismicro);
    ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));

    avl_remove(&zap->zap_m.zap_avl, mze);
    kmem_free(mze, sizeof (mzap_ent_t));
}

static void
mze_destroy(zap_t *zap)
{
    mzap_ent_t *mze;
    void *avlcookie = NULL;

    while (mze = avl_destroy_nodes(&zap->zap_m.zap_avl, &avlcookie))
        kmem_free(mze, sizeof (mzap_ent_t));
    avl_destroy(&zap->zap_m.zap_avl);
}

static zap_t *
mzap_open(objset_t *os, uint64_t obj, dmu_buf_t *db)
{
    zap_t *winner;
    zap_t *zap;
    int i;
    uint64_t *zap_hdr = (uint64_t *)db->db_data;
    uint64_t zap_block_type = zap_hdr[0];
    uint64_t zap_magic = zap_hdr[1];

    ASSERT3U(MZAP_ENT_LEN, ==, sizeof (mzap_ent_phys_t));

    zap = kmem_zalloc(sizeof (zap_t), KM_SLEEP);
    rw_init(&zap->zap_rwlock, 0, 0, 0);
    rw_enter(&zap->zap_rwlock, RW_WRITER);
    zap->zap_objset = os;
    zap->zap_object = obj;
    zap->zap_dbuf = db;

    if (zap_block_type != ZBT_MICRO) {
        mutex_init(&zap->zap_f.zap_num_entries_mtx, 0, 0, 0);
        zap->zap_f.zap_block_shift = highbit64(db->db_size) - 1;
        if (zap_block_type != ZBT_HEADER || zap_magic != ZAP_MAGIC) {
            winner = NULL;  /* No actual winner here... */
            goto handle_winner;
        }
    } else {
        zap->zap_ismicro = TRUE;
    }

    /*
     * Make sure that zap_ismicro is set before we let others see
     * it, because zap_lockdir() checks zap_ismicro without the lock
     * held.
     */
    dmu_buf_init_user(&zap->zap_dbu, zap_evict_sync, NULL, &zap->zap_dbuf);
    winner = dmu_buf_set_user(db, &zap->zap_dbu);

    if (winner != NULL)
        goto handle_winner;

    if (zap->zap_ismicro) {
        zap->zap_salt = zap_m_phys(zap)->mz_salt;
        zap->zap_normflags = zap_m_phys(zap)->mz_normflags;
        zap->zap_m.zap_num_chunks = db->db_size / MZAP_ENT_LEN - 1;
        avl_create(&zap->zap_m.zap_avl, mze_compare,
            sizeof (mzap_ent_t), offsetof(mzap_ent_t, mze_node));

        for (i = 0; i < zap->zap_m.zap_num_chunks; i++) {
            mzap_ent_phys_t *mze =
                &zap_m_phys(zap)->mz_chunk[i];
            if (mze->mze_name[0]) {
                zap_name_t *zn;

                zap->zap_m.zap_num_entries++;
                zn = zap_name_alloc(zap, mze->mze_name,
                    MT_EXACT);
                mze_insert(zap, i, zn->zn_hash);
                zap_name_free(zn);
            }
        }
    } else {
        zap->zap_salt = zap_f_phys(zap)->zap_salt;
        zap->zap_normflags = zap_f_phys(zap)->zap_normflags;

        ASSERT3U(sizeof (struct zap_leaf_header), ==,
            2*ZAP_LEAF_CHUNKSIZE);

        /*
         * The embedded pointer table should not overlap the
         * other members.
         */
        ASSERT3P(&ZAP_EMBEDDED_PTRTBL_ENT(zap, 0), >,
            &zap_f_phys(zap)->zap_salt);

        /*
         * The embedded pointer table should end at the end of
         * the block
         */
        ASSERT3U((uintptr_t)&ZAP_EMBEDDED_PTRTBL_ENT(zap,
            1<<ZAP_EMBEDDED_PTRTBL_SHIFT(zap)) -
            (uintptr_t)zap_f_phys(zap), ==,
            zap->zap_dbuf->db_size);
    }
    rw_exit(&zap->zap_rwlock);
    return (zap);

handle_winner:
    rw_exit(&zap->zap_rwlock);
    rw_destroy(&zap->zap_rwlock);
    if (!zap->zap_ismicro)
        mutex_destroy(&zap->zap_f.zap_num_entries_mtx);
    kmem_free(zap, sizeof (zap_t));
    return (winner);
}

static int
zap_lockdir_impl(dmu_buf_t *db, void *tag, dmu_tx_t *tx,
    krw_t lti, boolean_t fatreader, boolean_t adding, zap_t **zapp)
{
    zap_t *zap;
    krw_t lt;

    ASSERT0(db->db_offset);
    objset_t *os = dmu_buf_get_objset(db);
    uint64_t obj = db->db_object;

    *zapp = NULL;

#ifdef ZFS_DEBUG
    {
        dmu_object_info_t doi;
        dmu_object_info_from_db(db, &doi);
        ASSERT3U(DMU_OT_BYTESWAP(doi.doi_type), ==, DMU_BSWAP_ZAP);
    }
#endif

    zap = dmu_buf_get_user(db);
    if (zap == NULL) {
        zap = mzap_open(os, obj, db);
        if (zap == NULL) {
            /*
             * mzap_open() didn't like what it saw on-disk.
             * Check for corruption!
             */
            return (SET_ERROR(EIO));
        }
    }

    /*
     * We're checking zap_ismicro without the lock held, in order to
     * tell what type of lock we want.  Once we have some sort of
     * lock, see if it really is the right type.  In practice this
     * can only be different if it was upgraded from micro to fat,
     * and micro wanted WRITER but fat only needs READER.
     */
    lt = (!zap->zap_ismicro && fatreader) ? RW_READER : lti;
    rw_enter(&zap->zap_rwlock, lt);
    if (lt != ((!zap->zap_ismicro && fatreader) ? RW_READER : lti)) {
        /* it was upgraded, now we only need reader */
        ASSERT(lt == RW_WRITER);
        ASSERT(RW_READER ==
            (!zap->zap_ismicro && fatreader) ? RW_READER : lti);
        rw_downgrade(&zap->zap_rwlock);
        lt = RW_READER;
    }

    zap->zap_objset = os;

    if (lt == RW_WRITER)
        dmu_buf_will_dirty(db, tx);

    ASSERT3P(zap->zap_dbuf, ==, db);

    ASSERT(!zap->zap_ismicro ||
        zap->zap_m.zap_num_entries <= zap->zap_m.zap_num_chunks);
    if (zap->zap_ismicro && tx && adding &&
        zap->zap_m.zap_num_entries == zap->zap_m.zap_num_chunks) {
        uint64_t newsz = db->db_size + SPA_MINBLOCKSIZE;
        if (newsz > MZAP_MAX_BLKSZ) {
            dprintf("upgrading obj %llu: num_entries=%u\n",
                obj, zap->zap_m.zap_num_entries);
            *zapp = zap;
            int err = mzap_upgrade(zapp, tag, tx, 0);
            if (err != 0)
                rw_exit(&zap->zap_rwlock);
            return (err);
        }
        VERIFY0(dmu_object_set_blocksize(os, obj, newsz, 0, tx));
        zap->zap_m.zap_num_chunks =
            db->db_size / MZAP_ENT_LEN - 1;
    }

    *zapp = zap;
    return (0);
}

static int
zap_lockdir_by_dnode(dnode_t *dn, dmu_tx_t *tx,
    krw_t lti, boolean_t fatreader, boolean_t adding, void *tag, zap_t **zapp)
{
    dmu_buf_t *db;
    int err;

    err = dmu_buf_hold_by_dnode(dn, 0, tag, &db, DMU_READ_NO_PREFETCH);
    if (err != 0) {
        return (err);
    }
    err = zap_lockdir_impl(db, tag, tx, lti, fatreader, adding, zapp);
    if (err != 0) {
        dmu_buf_rele(db, tag);
    }
    return (err);
}

int
zap_lockdir(objset_t *os, uint64_t obj, dmu_tx_t *tx,
    krw_t lti, boolean_t fatreader, boolean_t adding, void *tag, zap_t **zapp)
{
    dmu_buf_t *db;
    int err;

    err = dmu_buf_hold(os, obj, 0, tag, &db, DMU_READ_NO_PREFETCH);
    if (err != 0)
        return (err);
    err = zap_lockdir_impl(db, tag, tx, lti, fatreader, adding, zapp);
    if (err != 0)
        dmu_buf_rele(db, tag);
    return (err);
}

void
zap_unlockdir(zap_t *zap, void *tag)
{
    rw_exit(&zap->zap_rwlock);
    dmu_buf_rele(zap->zap_dbuf, tag);
}

static int
mzap_upgrade(zap_t **zapp, void *tag, dmu_tx_t *tx, zap_flags_t flags)
{
    mzap_phys_t *mzp;
    int i, sz, nchunks;
    int err = 0;
    zap_t *zap = *zapp;

    ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));

    sz = zap->zap_dbuf->db_size;
    mzp = zio_buf_alloc(sz);
    bcopy(zap->zap_dbuf->db_data, mzp, sz);
    nchunks = zap->zap_m.zap_num_chunks;

    if (!flags) {
        err = dmu_object_set_blocksize(zap->zap_objset, zap->zap_object,
            1ULL << fzap_default_block_shift, 0, tx);
        if (err) {
            zio_buf_free(mzp, sz);
            return (err);
        }
    }

    dprintf("upgrading obj=%llu with %u chunks\n",
        zap->zap_object, nchunks);
    /* XXX destroy the avl later, so we can use the stored hash value */
    mze_destroy(zap);

    fzap_upgrade(zap, tx, flags);

    for (i = 0; i < nchunks; i++) {
        mzap_ent_phys_t *mze = &mzp->mz_chunk[i];
        zap_name_t *zn;
        if (mze->mze_name[0] == 0)
            continue;
        dprintf("adding %s=%llu\n",
            mze->mze_name, mze->mze_value);
        zn = zap_name_alloc(zap, mze->mze_name, MT_EXACT);
        err = fzap_add_cd(zn, 8, 1, &mze->mze_value, mze->mze_cd,
            tag, tx);
        zap = zn->zn_zap;   /* fzap_add_cd() may change zap */
        zap_name_free(zn);
        if (err)
            break;
    }
    zio_buf_free(mzp, sz);
    *zapp = zap;
    return (err);
}

void
mzap_create_impl(objset_t *os, uint64_t obj, int normflags, zap_flags_t flags,
    dmu_tx_t *tx)
{
    dmu_buf_t *db;
    mzap_phys_t *zp;

    VERIFY(0 == dmu_buf_hold(os, obj, 0, FTAG, &db, DMU_READ_NO_PREFETCH));

#ifdef ZFS_DEBUG
    {
        dmu_object_info_t doi;
        dmu_object_info_from_db(db, &doi);
        ASSERT3U(DMU_OT_BYTESWAP(doi.doi_type), ==, DMU_BSWAP_ZAP);
    }
#endif

    dmu_buf_will_dirty(db, tx);
    zp = db->db_data;
    zp->mz_block_type = ZBT_MICRO;
    zp->mz_salt = ((uintptr_t)db ^ (uintptr_t)tx ^ (obj << 1)) | 1ULL;
    zp->mz_normflags = normflags;
    dmu_buf_rele(db, FTAG);

    if (flags != 0) {
        zap_t *zap;
        /* Only fat zap supports flags; upgrade immediately. */
        VERIFY(0 == zap_lockdir(os, obj, tx, RW_WRITER,
            B_FALSE, B_FALSE, FTAG, &zap));
        VERIFY3U(0, ==, mzap_upgrade(&zap, FTAG, tx, flags));
        zap_unlockdir(zap, FTAG);
    }
}

int
zap_create_claim(objset_t *os, uint64_t obj, dmu_object_type_t ot,
    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
{
    return (zap_create_claim_norm(os, obj,
        0, ot, bonustype, bonuslen, tx));
}

int
zap_create_claim_norm(objset_t *os, uint64_t obj, int normflags,
    dmu_object_type_t ot,
    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
{
    int err;

    err = dmu_object_claim(os, obj, ot, 0, bonustype, bonuslen, tx);
    if (err != 0)
        return (err);
    mzap_create_impl(os, obj, normflags, 0, tx);
    return (0);
}

uint64_t
zap_create(objset_t *os, dmu_object_type_t ot,
    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
{
    return (zap_create_norm(os, 0, ot, bonustype, bonuslen, tx));
}

uint64_t
zap_create_norm(objset_t *os, int normflags, dmu_object_type_t ot,
    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
{
    uint64_t obj = dmu_object_alloc(os, ot, 0, bonustype, bonuslen, tx);

    mzap_create_impl(os, obj, normflags, 0, tx);
    return (obj);
}

uint64_t
zap_create_flags(objset_t *os, int normflags, zap_flags_t flags,
    dmu_object_type_t ot, int leaf_blockshift, int indirect_blockshift,
    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
{
    uint64_t obj = dmu_object_alloc(os, ot, 0, bonustype, bonuslen, tx);

    ASSERT(leaf_blockshift >= SPA_MINBLOCKSHIFT &&
        leaf_blockshift <= SPA_OLD_MAXBLOCKSHIFT &&
        indirect_blockshift >= SPA_MINBLOCKSHIFT &&
        indirect_blockshift <= SPA_OLD_MAXBLOCKSHIFT);

    VERIFY(dmu_object_set_blocksize(os, obj,
        1ULL << leaf_blockshift, indirect_blockshift, tx) == 0);

    mzap_create_impl(os, obj, normflags, flags, tx);
    return (obj);
}

int
zap_destroy(objset_t *os, uint64_t zapobj, dmu_tx_t *tx)
{
    /*
     * dmu_object_free will free the object number and free the
     * data.  Freeing the data will cause our pageout function to be
     * called, which will destroy our data (zap_leaf_t's and zap_t).
     */

    return (dmu_object_free(os, zapobj, tx));
}

void
zap_evict_sync(void *dbu)
{
    zap_t *zap = dbu;

    rw_destroy(&zap->zap_rwlock);

    if (zap->zap_ismicro)
        mze_destroy(zap);
    else
        mutex_destroy(&zap->zap_f.zap_num_entries_mtx);

    kmem_free(zap, sizeof (zap_t));
}

int
zap_count(objset_t *os, uint64_t zapobj, uint64_t *count)
{
    zap_t *zap;
    int err;

    err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
    if (err)
        return (err);
    if (!zap->zap_ismicro) {
        err = fzap_count(zap, count);
    } else {
        *count = zap->zap_m.zap_num_entries;
    }
    zap_unlockdir(zap, FTAG);
    return (err);
}

/*
 * zn may be NULL; if not specified, it will be computed if needed.
 * See also the comment above zap_entry_normalization_conflict().
 */
static boolean_t
mzap_normalization_conflict(zap_t *zap, zap_name_t *zn, mzap_ent_t *mze)
{
    mzap_ent_t *other;
    int direction = AVL_BEFORE;
    boolean_t allocdzn = B_FALSE;

    if (zap->zap_normflags == 0)
        return (B_FALSE);

again:
    for (other = avl_walk(&zap->zap_m.zap_avl, mze, direction);
        other && other->mze_hash == mze->mze_hash;
        other = avl_walk(&zap->zap_m.zap_avl, other, direction)) {

        if (zn == NULL) {
            zn = zap_name_alloc(zap, MZE_PHYS(zap, mze)->mze_name,
                MT_FIRST);
            allocdzn = B_TRUE;
        }
        if (zap_match(zn, MZE_PHYS(zap, other)->mze_name)) {
            if (allocdzn)
                zap_name_free(zn);
            return (B_TRUE);
        }
    }

    if (direction == AVL_BEFORE) {
        direction = AVL_AFTER;
        goto again;
    }

    if (allocdzn)
        zap_name_free(zn);
    return (B_FALSE);
}

/*
 * Routines for manipulating attributes.
 */

int
zap_lookup(objset_t *os, uint64_t zapobj, const char *name,
    uint64_t integer_size, uint64_t num_integers, void *buf)
{
    return (zap_lookup_norm(os, zapobj, name, integer_size,
        num_integers, buf, MT_EXACT, NULL, 0, NULL));
}

static int
zap_lookup_impl(zap_t *zap, const char *name,
    uint64_t integer_size, uint64_t num_integers, void *buf,
    matchtype_t mt, char *realname, int rn_len,
    boolean_t *ncp)
{
    int err = 0;
    mzap_ent_t *mze;
    zap_name_t *zn;

    zn = zap_name_alloc(zap, name, mt);
    if (zn == NULL)
        return (SET_ERROR(ENOTSUP));

    if (!zap->zap_ismicro) {
        err = fzap_lookup(zn, integer_size, num_integers, buf,
            realname, rn_len, ncp);
    } else {
        mze = mze_find(zn);
        if (mze == NULL) {
            err = SET_ERROR(ENOENT);
        } else {
            if (num_integers < 1) {
                err = SET_ERROR(EOVERFLOW);
            } else if (integer_size != 8) {
                err = SET_ERROR(EINVAL);
            } else {
                *(uint64_t *)buf =
                    MZE_PHYS(zap, mze)->mze_value;
                (void) strlcpy(realname,
                    MZE_PHYS(zap, mze)->mze_name, rn_len);
                if (ncp) {
                    *ncp = mzap_normalization_conflict(zap,
                        zn, mze);
                }
            }
        }
    }
    zap_name_free(zn);
    return (err);
}

int
zap_lookup_norm(objset_t *os, uint64_t zapobj, const char *name,
    uint64_t integer_size, uint64_t num_integers, void *buf,
    matchtype_t mt, char *realname, int rn_len,
    boolean_t *ncp)
{
    zap_t *zap;
    int err;

    err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
    if (err != 0)
        return (err);
    err = zap_lookup_impl(zap, name, integer_size,
        num_integers, buf, mt, realname, rn_len, ncp);
    zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_lookup_by_dnode(dnode_t *dn, const char *name,
    uint64_t integer_size, uint64_t num_integers, void *buf)
{
    return (zap_lookup_norm_by_dnode(dn, name, integer_size,
        num_integers, buf, MT_EXACT, NULL, 0, NULL));
}

int
zap_lookup_norm_by_dnode(dnode_t *dn, const char *name,
    uint64_t integer_size, uint64_t num_integers, void *buf,
    matchtype_t mt, char *realname, int rn_len,
    boolean_t *ncp)
{
    zap_t *zap;
    int err;

    err = zap_lockdir_by_dnode(dn, NULL, RW_READER, TRUE, FALSE,
        FTAG, &zap);
    if (err != 0)
        return (err);
    err = zap_lookup_impl(zap, name, integer_size,
        num_integers, buf, mt, realname, rn_len, ncp);
    zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_prefetch_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
    int key_numints)
{
    zap_t *zap;
    int err;
    zap_name_t *zn;

    err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc_uint64(zap, key, key_numints);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }

    fzap_prefetch(zn);
    zap_name_free(zn);
    zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_lookup_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
    int key_numints, uint64_t integer_size, uint64_t num_integers, void *buf)
{
    zap_t *zap;
    int err;
    zap_name_t *zn;

    err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc_uint64(zap, key, key_numints);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }

    err = fzap_lookup(zn, integer_size, num_integers, buf,
        NULL, 0, NULL);
    zap_name_free(zn);
    zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_contains(objset_t *os, uint64_t zapobj, const char *name)
{
    int err = zap_lookup_norm(os, zapobj, name, 0,
        0, NULL, MT_EXACT, NULL, 0, NULL);
    if (err == EOVERFLOW || err == EINVAL)
        err = 0; /* found, but skipped reading the value */
    return (err);
}

int
zap_length(objset_t *os, uint64_t zapobj, const char *name,
    uint64_t *integer_size, uint64_t *num_integers)
{
    zap_t *zap;
    int err;
    mzap_ent_t *mze;
    zap_name_t *zn;

    err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc(zap, name, MT_EXACT);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }
    if (!zap->zap_ismicro) {
        err = fzap_length(zn, integer_size, num_integers);
    } else {
        mze = mze_find(zn);
        if (mze == NULL) {
            err = SET_ERROR(ENOENT);
        } else {
            if (integer_size)
                *integer_size = 8;
            if (num_integers)
                *num_integers = 1;
        }
    }
    zap_name_free(zn);
    zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_length_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
    int key_numints, uint64_t *integer_size, uint64_t *num_integers)
{
    zap_t *zap;
    int err;
    zap_name_t *zn;

    err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc_uint64(zap, key, key_numints);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }
    err = fzap_length(zn, integer_size, num_integers);
    zap_name_free(zn);
    zap_unlockdir(zap, FTAG);
    return (err);
}

static void
mzap_addent(zap_name_t *zn, uint64_t value)
{
    int i;
    zap_t *zap = zn->zn_zap;
    int start = zap->zap_m.zap_alloc_next;
    uint32_t cd;

    ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));

#ifdef ZFS_DEBUG
    for (i = 0; i < zap->zap_m.zap_num_chunks; i++) {
        mzap_ent_phys_t *mze = &zap_m_phys(zap)->mz_chunk[i];
        ASSERT(strcmp(zn->zn_key_orig, mze->mze_name) != 0);
    }
#endif

    cd = mze_find_unused_cd(zap, zn->zn_hash);
    /* given the limited size of the microzap, this can't happen */
    ASSERT(cd < zap_maxcd(zap));

again:
    for (i = start; i < zap->zap_m.zap_num_chunks; i++) {
        mzap_ent_phys_t *mze = &zap_m_phys(zap)->mz_chunk[i];
        if (mze->mze_name[0] == 0) {
            mze->mze_value = value;
            mze->mze_cd = cd;
            (void) strcpy(mze->mze_name, zn->zn_key_orig);
            zap->zap_m.zap_num_entries++;
            zap->zap_m.zap_alloc_next = i+1;
            if (zap->zap_m.zap_alloc_next ==
                zap->zap_m.zap_num_chunks)
                zap->zap_m.zap_alloc_next = 0;
            mze_insert(zap, i, zn->zn_hash);
            return;
        }
    }
    if (start != 0) {
        start = 0;
        goto again;
    }
    ASSERT(!"out of entries!");
}

int
zap_add(objset_t *os, uint64_t zapobj, const char *key,
    int integer_size, uint64_t num_integers,
    const void *val, dmu_tx_t *tx)
{
    zap_t *zap;
    int err;
    mzap_ent_t *mze;
    const uint64_t *intval = val;
    zap_name_t *zn;

    err = zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc(zap, key, MT_EXACT);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }
    if (!zap->zap_ismicro) {
        err = fzap_add(zn, integer_size, num_integers, val, FTAG, tx);
        zap = zn->zn_zap;   /* fzap_add() may change zap */
    } else if (integer_size != 8 || num_integers != 1 ||
        strlen(key) >= MZAP_NAME_LEN) {
        err = mzap_upgrade(&zn->zn_zap, FTAG, tx, 0);
        if (err == 0) {
            err = fzap_add(zn, integer_size, num_integers, val,
                FTAG, tx);
        }
        zap = zn->zn_zap;   /* fzap_add() may change zap */
    } else {
        mze = mze_find(zn);
        if (mze != NULL) {
            err = SET_ERROR(EEXIST);
        } else {
            mzap_addent(zn, *intval);
        }
    }
    ASSERT(zap == zn->zn_zap);
    zap_name_free(zn);
    if (zap != NULL)    /* may be NULL if fzap_add() failed */
        zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_add_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
    int key_numints, int integer_size, uint64_t num_integers,
    const void *val, dmu_tx_t *tx)
{
    zap_t *zap;
    int err;
    zap_name_t *zn;

    err = zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc_uint64(zap, key, key_numints);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }
    err = fzap_add(zn, integer_size, num_integers, val, FTAG, tx);
    zap = zn->zn_zap;   /* fzap_add() may change zap */
    zap_name_free(zn);
    if (zap != NULL)    /* may be NULL if fzap_add() failed */
        zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_update(objset_t *os, uint64_t zapobj, const char *name,
    int integer_size, uint64_t num_integers, const void *val, dmu_tx_t *tx)
{
    zap_t *zap;
    mzap_ent_t *mze;
    uint64_t oldval;
    const uint64_t *intval = val;
    zap_name_t *zn;
    int err;

#ifdef ZFS_DEBUG
    /*
     * If there is an old value, it shouldn't change across the
     * lockdir (eg, due to bprewrite's xlation).
     */
    if (integer_size == 8 && num_integers == 1)
        (void) zap_lookup(os, zapobj, name, 8, 1, &oldval);
#endif

    err = zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc(zap, name, MT_EXACT);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }
    if (!zap->zap_ismicro) {
        err = fzap_update(zn, integer_size, num_integers, val,
            FTAG, tx);
        zap = zn->zn_zap;   /* fzap_update() may change zap */
    } else if (integer_size != 8 || num_integers != 1 ||
        strlen(name) >= MZAP_NAME_LEN) {
        dprintf("upgrading obj %llu: intsz=%u numint=%llu name=%s\n",
            zapobj, integer_size, num_integers, name);
        err = mzap_upgrade(&zn->zn_zap, FTAG, tx, 0);
        if (err == 0) {
            err = fzap_update(zn, integer_size, num_integers,
                val, FTAG, tx);
        }
        zap = zn->zn_zap;   /* fzap_update() may change zap */
    } else {
        mze = mze_find(zn);
        if (mze != NULL) {
            ASSERT3U(MZE_PHYS(zap, mze)->mze_value, ==, oldval);
            MZE_PHYS(zap, mze)->mze_value = *intval;
        } else {
            mzap_addent(zn, *intval);
        }
    }
    ASSERT(zap == zn->zn_zap);
    zap_name_free(zn);
    if (zap != NULL)    /* may be NULL if fzap_upgrade() failed */
        zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_update_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
    int key_numints,
    int integer_size, uint64_t num_integers, const void *val, dmu_tx_t *tx)
{
    zap_t *zap;
    zap_name_t *zn;
    int err;

    err = zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc_uint64(zap, key, key_numints);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }
    err = fzap_update(zn, integer_size, num_integers, val, FTAG, tx);
    zap = zn->zn_zap;   /* fzap_update() may change zap */
    zap_name_free(zn);
    if (zap != NULL)    /* may be NULL if fzap_upgrade() failed */
        zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_remove(objset_t *os, uint64_t zapobj, const char *name, dmu_tx_t *tx)
{
    return (zap_remove_norm(os, zapobj, name, MT_EXACT, tx));
}

int
zap_remove_norm(objset_t *os, uint64_t zapobj, const char *name,
    matchtype_t mt, dmu_tx_t *tx)
{
    zap_t *zap;
    int err;
    mzap_ent_t *mze;
    zap_name_t *zn;

    err = zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, FALSE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc(zap, name, mt);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }
    if (!zap->zap_ismicro) {
        err = fzap_remove(zn, tx);
    } else {
        mze = mze_find(zn);
        if (mze == NULL) {
            err = SET_ERROR(ENOENT);
        } else {
            zap->zap_m.zap_num_entries--;
            bzero(&zap_m_phys(zap)->mz_chunk[mze->mze_chunkid],
                sizeof (mzap_ent_phys_t));
            mze_remove(zap, mze);
        }
    }
    zap_name_free(zn);
    zap_unlockdir(zap, FTAG);
    return (err);
}

int
zap_remove_uint64(objset_t *os, uint64_t zapobj, const uint64_t *key,
    int key_numints, dmu_tx_t *tx)
{
    zap_t *zap;
    int err;
    zap_name_t *zn;

    err = zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, FALSE, FTAG, &zap);
    if (err)
        return (err);
    zn = zap_name_alloc_uint64(zap, key, key_numints);
    if (zn == NULL) {
        zap_unlockdir(zap, FTAG);
        return (SET_ERROR(ENOTSUP));
    }
    err = fzap_remove(zn, tx);
    zap_name_free(zn);
    zap_unlockdir(zap, FTAG);
    return (err);
}

/*
 * Routines for iterating over the attributes.
 */

void
zap_cursor_init_serialized(zap_cursor_t *zc, objset_t *os, uint64_t zapobj,
    uint64_t serialized)
{
    zc->zc_objset = os;
    zc->zc_zap = NULL;
    zc->zc_leaf = NULL;
    zc->zc_zapobj = zapobj;
    zc->zc_serialized = serialized;
    zc->zc_hash = 0;
    zc->zc_cd = 0;
}

void
zap_cursor_init(zap_cursor_t *zc, objset_t *os, uint64_t zapobj)
{
    zap_cursor_init_serialized(zc, os, zapobj, 0);
}

void
zap_cursor_fini(zap_cursor_t *zc)
{
    if (zc->zc_zap) {
        rw_enter(&zc->zc_zap->zap_rwlock, RW_READER);
        zap_unlockdir(zc->zc_zap, NULL);
        zc->zc_zap = NULL;
    }
    if (zc->zc_leaf) {
        rw_enter(&zc->zc_leaf->l_rwlock, RW_READER);
        zap_put_leaf(zc->zc_leaf);
        zc->zc_leaf = NULL;
    }
    zc->zc_objset = NULL;
}

uint64_t
zap_cursor_serialize(zap_cursor_t *zc)
{
    if (zc->zc_hash == -1ULL)
        return (-1ULL);
    if (zc->zc_zap == NULL)
        return (zc->zc_serialized);
    ASSERT((zc->zc_hash & zap_maxcd(zc->zc_zap)) == 0);
    ASSERT(zc->zc_cd < zap_maxcd(zc->zc_zap));

    /*
     * We want to keep the high 32 bits of the cursor zero if we can, so
     * that 32-bit programs can access this.  So usually use a small
     * (28-bit) hash value so we can fit 4 bits of cd into the low 32-bits
     * of the cursor.
     *
     * [ collision differentiator | zap_hashbits()-bit hash value ]
     */
    return ((zc->zc_hash >> (64 - zap_hashbits(zc->zc_zap))) |
        ((uint64_t)zc->zc_cd << zap_hashbits(zc->zc_zap)));
}

int
zap_cursor_retrieve(zap_cursor_t *zc, zap_attribute_t *za)
{
    int err;
    avl_index_t idx;
    mzap_ent_t mze_tofind;
    mzap_ent_t *mze;

    if (zc->zc_hash == -1ULL)
        return (SET_ERROR(ENOENT));

    if (zc->zc_zap == NULL) {
        int hb;
        err = zap_lockdir(zc->zc_objset, zc->zc_zapobj, NULL,
            RW_READER, TRUE, FALSE, NULL, &zc->zc_zap);
        if (err)
            return (err);

        /*
         * To support zap_cursor_init_serialized, advance, retrieve,
         * we must add to the existing zc_cd, which may already
         * be 1 due to the zap_cursor_advance.
         */
        ASSERT(zc->zc_hash == 0);
        hb = zap_hashbits(zc->zc_zap);
        zc->zc_hash = zc->zc_serialized << (64 - hb);
        zc->zc_cd += zc->zc_serialized >> hb;
        if (zc->zc_cd >= zap_maxcd(zc->zc_zap)) /* corrupt serialized */
            zc->zc_cd = 0;
    } else {
        rw_enter(&zc->zc_zap->zap_rwlock, RW_READER);
    }
    if (!zc->zc_zap->zap_ismicro) {
        err = fzap_cursor_retrieve(zc->zc_zap, zc, za);
    } else {
        mze_tofind.mze_hash = zc->zc_hash;
        mze_tofind.mze_cd = zc->zc_cd;

        mze = avl_find(&zc->zc_zap->zap_m.zap_avl, &mze_tofind, &idx);
        if (mze == NULL) {
            mze = avl_nearest(&zc->zc_zap->zap_m.zap_avl,
                idx, AVL_AFTER);
        }
        if (mze) {
            mzap_ent_phys_t *mzep = MZE_PHYS(zc->zc_zap, mze);
            ASSERT3U(mze->mze_cd, ==, mzep->mze_cd);
            za->za_normalization_conflict =
                mzap_normalization_conflict(zc->zc_zap, NULL, mze);
            za->za_integer_length = 8;
            za->za_num_integers = 1;
            za->za_first_integer = mzep->mze_value;
            (void) strcpy(za->za_name, mzep->mze_name);
            zc->zc_hash = mze->mze_hash;
            zc->zc_cd = mze->mze_cd;
            err = 0;
        } else {
            zc->zc_hash = -1ULL;
            err = SET_ERROR(ENOENT);
        }
    }
    rw_exit(&zc->zc_zap->zap_rwlock);
    return (err);
}

void
zap_cursor_advance(zap_cursor_t *zc)
{
    if (zc->zc_hash == -1ULL)
        return;
    zc->zc_cd++;
}

int
zap_get_stats(objset_t *os, uint64_t zapobj, zap_stats_t *zs)
{
    int err;
    zap_t *zap;

    err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
    if (err)
        return (err);

    bzero(zs, sizeof (zap_stats_t));

    if (zap->zap_ismicro) {
        zs->zs_blocksize = zap->zap_dbuf->db_size;
        zs->zs_num_entries = zap->zap_m.zap_num_entries;
        zs->zs_num_blocks = 1;
    } else {
        fzap_get_stats(zap, zs);
    }
    zap_unlockdir(zap, FTAG);
    return (0);
}

int
zap_count_write_by_dnode(dnode_t *dn, const char *name, int add,
    refcount_t *towrite, refcount_t *tooverwrite)
{
    zap_t *zap;
    int err = 0;

    /*
     * Since, we don't have a name, we cannot figure out which blocks will
     * be affected in this operation. So, account for the worst case :
     * - 3 blocks overwritten: target leaf, ptrtbl block, header block
     * - 4 new blocks written if adding:
     *    - 2 blocks for possibly split leaves,
     *    - 2 grown ptrtbl blocks
     *
     * This also accommodates the case where an add operation to a fairly
     * large microzap results in a promotion to fatzap.
     */
    if (name == NULL) {
        (void) refcount_add_many(towrite,
            (3 + (add ? 4 : 0)) * SPA_OLD_MAXBLOCKSIZE, FTAG);
        return (err);
    }

    /*
     * We lock the zap with adding == FALSE. Because, if we pass
     * the actual value of add, it could trigger a mzap_upgrade().
     * At present we are just evaluating the possibility of this operation
     * and hence we do not want to trigger an upgrade.
     */
    err = zap_lockdir_by_dnode(dn, NULL, RW_READER, TRUE, FALSE,
        FTAG, &zap);
    if (err != 0)
        return (err);

    if (!zap->zap_ismicro) {
        zap_name_t *zn = zap_name_alloc(zap, name, MT_EXACT);
        if (zn) {
            err = fzap_count_write(zn, add, towrite,
                tooverwrite);
            zap_name_free(zn);
        } else {
            /*
             * We treat this case as similar to (name == NULL)
             */
            (void) refcount_add_many(towrite,
                (3 + (add ? 4 : 0)) * SPA_OLD_MAXBLOCKSIZE, FTAG);
        }
    } else {
        /*
         * We are here if (name != NULL) and this is a micro-zap.
         * We account for the header block depending on whether it
         * is freeable.
         *
         * Incase of an add-operation it is hard to find out
         * if this add will promote this microzap to fatzap.
         * Hence, we consider the worst case and account for the
         * blocks assuming this microzap would be promoted to a
         * fatzap.
         *
         * 1 block overwritten  : header block
         * 4 new blocks written : 2 new split leaf, 2 grown
         *          ptrtbl blocks
         */
        if (dmu_buf_freeable(zap->zap_dbuf)) {
            (void) refcount_add_many(tooverwrite,
                MZAP_MAX_BLKSZ, FTAG);
        } else {
            (void) refcount_add_many(towrite,
                MZAP_MAX_BLKSZ, FTAG);
        }

        if (add) {
            (void) refcount_add_many(towrite,
                4 * MZAP_MAX_BLKSZ, FTAG);
        }
    }

    zap_unlockdir(zap, FTAG);
    return (err);
}