Implement large_dnode pool feature

[mirror_zfs.git] / module / 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, 2014 by Delphix. All rights reserved.
 * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
 */

#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, 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, NULL, RW_DEFAULT, NULL);
        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, &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);
}

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

        *zapp = NULL;

        err = dmu_buf_hold(os, obj, 0, NULL, &db, DMU_READ_NO_PREFETCH);
        if (err)
                return (err);

        dmu_object_info_from_db(db, &doi);
        if (DMU_OT_BYTESWAP(doi.doi_type) != DMU_BSWAP_ZAP)
                return (SET_ERROR(EINVAL));

        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!
                         */
                        dmu_buf_rele(db, NULL);
                        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;
                        return (mzap_upgrade(zapp, tx, 0));
                }
                err = dmu_object_set_blocksize(os, obj, newsz, 0, tx);
                ASSERT0(err);
                zap->zap_m.zap_num_chunks =
                    db->db_size / MZAP_ENT_LEN - 1;
        }

        *zapp = zap;
        return (0);
}

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

static int
mzap_upgrade(zap_t **zapp, 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, 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, &zap));
                VERIFY3U(0, ==, mzap_upgrade(&zap, tx, flags));
                zap_unlockdir(zap);
        }
}

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_dnsize(os, obj, ot, bonustype, bonuslen,
            0, tx));
}

int
zap_create_claim_dnsize(objset_t *os, uint64_t obj, dmu_object_type_t ot,
    dmu_object_type_t bonustype, int bonuslen, int dnodesize, dmu_tx_t *tx)
{
        return (zap_create_claim_norm_dnsize(os, obj,
            0, ot, bonustype, bonuslen, dnodesize, 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)
{
        return (zap_create_claim_norm_dnsize(os, obj, normflags, ot, bonustype,
            bonuslen, 0, tx));
}

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

        err = dmu_object_claim_dnsize(os, obj, ot, 0, bonustype, bonuslen,
            dnodesize, 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_dnsize(objset_t *os, dmu_object_type_t ot,
    dmu_object_type_t bonustype, int bonuslen, int dnodesize, dmu_tx_t *tx)
{
        return (zap_create_norm_dnsize(os, 0, ot, bonustype, bonuslen,
            dnodesize, 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)
{
        return (zap_create_norm_dnsize(os, normflags, ot, bonustype, bonuslen,
            0, tx));
}

uint64_t
zap_create_norm_dnsize(objset_t *os, int normflags, dmu_object_type_t ot,
    dmu_object_type_t bonustype, int bonuslen, int dnodesize, dmu_tx_t *tx)
{
        uint64_t obj = dmu_object_alloc_dnsize(os, ot, 0, bonustype, bonuslen,
            dnodesize, 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)
{
        return (zap_create_flags_dnsize(os, normflags, flags, ot,
            leaf_blockshift, indirect_blockshift, bonustype, bonuslen, 0, tx));
}

uint64_t
zap_create_flags_dnsize(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, int dnodesize, dmu_tx_t *tx)
{
        uint64_t obj = dmu_object_alloc_dnsize(os, ot, 0, bonustype, bonuslen,
            dnodesize, 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(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, &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);
        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));
}

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;
        mzap_ent_t *mze;
        zap_name_t *zn;

        err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc(zap, name, mt);
        if (zn == NULL) {
                zap_unlockdir(zap);
                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);
        zap_unlockdir(zap);
        return (err);
}

int
zap_prefetch(objset_t *os, uint64_t zapobj, const char *name)
{
        zap_t *zap;
        int err;
        zap_name_t *zn;

        err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc(zap, name, MT_EXACT);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }

        fzap_prefetch(zn);
        zap_name_free(zn);
        zap_unlockdir(zap);
        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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc_uint64(zap, key, key_numints);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }

        fzap_prefetch(zn);
        zap_name_free(zn);
        zap_unlockdir(zap);
        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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc_uint64(zap, key, key_numints);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }

        err = fzap_lookup(zn, integer_size, num_integers, buf,
            NULL, 0, NULL);
        zap_name_free(zn);
        zap_unlockdir(zap);
        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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc(zap, name, MT_EXACT);
        if (zn == NULL) {
                zap_unlockdir(zap);
                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);
        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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc_uint64(zap, key, key_numints);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }
        err = fzap_length(zn, integer_size, num_integers);
        zap_name_free(zn);
        zap_unlockdir(zap);
        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++) {
                ASSERTV(mzap_ent_phys_t *mze);
                ASSERT(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;
        }
        cmn_err(CE_PANIC, "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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc(zap, key, MT_EXACT);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }
        if (!zap->zap_ismicro) {
                err = fzap_add(zn, integer_size, num_integers, val, 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, tx, 0);
                if (err == 0)
                        err = fzap_add(zn, integer_size, num_integers, val, 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);
        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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc_uint64(zap, key, key_numints);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }
        err = fzap_add(zn, integer_size, num_integers, val, 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);
        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;
        const uint64_t *intval = val;
        zap_name_t *zn;
        int err;

#ifdef ZFS_DEBUG
        uint64_t oldval;

        /*
         * 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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc(zap, name, MT_EXACT);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }
        if (!zap->zap_ismicro) {
                err = fzap_update(zn, integer_size, num_integers, val, 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, tx, 0);
                if (err == 0)
                        err = fzap_update(zn, integer_size, num_integers,
                            val, 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);
        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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc_uint64(zap, key, key_numints);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }
        err = fzap_update(zn, integer_size, num_integers, val, 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);
        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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc(zap, name, mt);
        if (zn == NULL) {
                zap_unlockdir(zap);
                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);
        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, &zap);
        if (err)
                return (err);
        zn = zap_name_alloc_uint64(zap, key, key_numints);
        if (zn == NULL) {
                zap_unlockdir(zap);
                return (SET_ERROR(ENOTSUP));
        }
        err = fzap_remove(zn, tx);
        zap_name_free(zn);
        zap_unlockdir(zap);
        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);
                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, &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, &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);
        return (0);
}

int
zap_count_write(objset_t *os, uint64_t zapobj, const char *name, int add,
    uint64_t *towrite, uint64_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 accomodates the case where an add operation to a fairly
         * large microzap results in a promotion to fatzap.
         */
        if (name == NULL) {
                *towrite += (3 + (add ? 4 : 0)) * SPA_OLD_MAXBLOCKSIZE;
                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 donot want to trigger an upgrade.
         */
        err = zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, &zap);
        if (err)
                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)
                         */
                        *towrite += (3 + (add ? 4 : 0)) * SPA_OLD_MAXBLOCKSIZE;
                }
        } 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))
                        *tooverwrite += MZAP_MAX_BLKSZ;
                else
                        *towrite += MZAP_MAX_BLKSZ;

                if (add) {
                        *towrite += 4 * MZAP_MAX_BLKSZ;
                }
        }

        zap_unlockdir(zap);
        return (err);
}

#if defined(_KERNEL) && defined(HAVE_SPL)
EXPORT_SYMBOL(zap_create);
EXPORT_SYMBOL(zap_create_dnsize);
EXPORT_SYMBOL(zap_create_norm);
EXPORT_SYMBOL(zap_create_norm_dnsize);
EXPORT_SYMBOL(zap_create_flags);
EXPORT_SYMBOL(zap_create_flags_dnsize);
EXPORT_SYMBOL(zap_create_claim);
EXPORT_SYMBOL(zap_create_claim_norm);
EXPORT_SYMBOL(zap_create_claim_norm_dnsize);
EXPORT_SYMBOL(zap_destroy);
EXPORT_SYMBOL(zap_lookup);
EXPORT_SYMBOL(zap_lookup_norm);
EXPORT_SYMBOL(zap_lookup_uint64);
EXPORT_SYMBOL(zap_contains);
EXPORT_SYMBOL(zap_prefetch);
EXPORT_SYMBOL(zap_prefetch_uint64);
EXPORT_SYMBOL(zap_count_write);
EXPORT_SYMBOL(zap_add);
EXPORT_SYMBOL(zap_add_uint64);
EXPORT_SYMBOL(zap_update);
EXPORT_SYMBOL(zap_update_uint64);
EXPORT_SYMBOL(zap_length);
EXPORT_SYMBOL(zap_length_uint64);
EXPORT_SYMBOL(zap_remove);
EXPORT_SYMBOL(zap_remove_norm);
EXPORT_SYMBOL(zap_remove_uint64);
EXPORT_SYMBOL(zap_count);
EXPORT_SYMBOL(zap_value_search);
EXPORT_SYMBOL(zap_join);
EXPORT_SYMBOL(zap_join_increment);
EXPORT_SYMBOL(zap_add_int);
EXPORT_SYMBOL(zap_remove_int);
EXPORT_SYMBOL(zap_lookup_int);
EXPORT_SYMBOL(zap_increment_int);
EXPORT_SYMBOL(zap_add_int_key);
EXPORT_SYMBOL(zap_lookup_int_key);
EXPORT_SYMBOL(zap_increment);
EXPORT_SYMBOL(zap_cursor_init);
EXPORT_SYMBOL(zap_cursor_fini);
EXPORT_SYMBOL(zap_cursor_retrieve);
EXPORT_SYMBOL(zap_cursor_advance);
EXPORT_SYMBOL(zap_cursor_serialize);
EXPORT_SYMBOL(zap_cursor_init_serialized);
EXPORT_SYMBOL(zap_get_stats);
#endif