vendor/opensolaris/20100818vendor/opensolaris

1 files changed, 1455 insertions, 0 deletions

diff --git a/uts/common/fs/zfs/zap_micro.c b/uts/common/fs/zfs/zap_micro.c
new file mode 100644
index 000000000000..2d89c20c47d7
--- /dev/null
+++ b/uts/common/fs/zfs/zap_micro.c
@@ -0,0 +1,1455 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
+ */
+
+#include <sys/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>
+
+#ifdef _KERNEL
+#include <sys/sunddi.h>
+#endif
+
+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->zap_u.zap_fat.zap_phys->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;
+
+	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 (*(uint64_t *)db->db_data != ZBT_MICRO) {
+		mutex_init(&zap->zap_f.zap_num_entries_mtx, 0, 0, 0);
+		zap->zap_f.zap_block_shift = highbit(db->db_size) - 1;
+	} 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.
+	 */
+	winner = dmu_buf_set_user(db, zap, &zap->zap_m.zap_phys, zap_evict);
+
+	if (winner != NULL) {
+		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);
+	}
+
+	if (zap->zap_ismicro) {
+		zap->zap_salt = zap->zap_m.zap_phys->mz_salt;
+		zap->zap_normflags = zap->zap_m.zap_phys->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->zap_m.zap_phys->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->zap_f.zap_phys->zap_salt;
+		zap->zap_normflags = zap->zap_f.zap_phys->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->zap_f.zap_phys->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->zap_f.zap_phys, ==,
+		    zap->zap_dbuf->db_size);
+	}
+	rw_exit(&zap->zap_rwlock);
+	return (zap);
+}
+
+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)
+{
+	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);
+
+#ifdef ZFS_DEBUG
+	{
+		dmu_object_info_t doi;
+		dmu_object_info_from_db(db, &doi);
+		ASSERT(dmu_ot[doi.doi_type].ot_byteswap == zap_byteswap);
+	}
+#endif
+
+	zap = dmu_buf_get_user(db);
+	if (zap == NULL)
+		zap = mzap_open(os, obj, db);
+
+	/*
+	 * 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);
+		ASSERT3U(err, ==, 0);
+		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 = kmem_alloc(sz, KM_SLEEP);
+	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) {
+			kmem_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;
+	}
+	kmem_free(mzp, sz);
+	*zapp = zap;
+	return (err);
+}
+
+static 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);
+		ASSERT(dmu_ot[doi.doi_type].ot_byteswap == zap_byteswap);
+	}
+#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_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_MAXBLOCKSHIFT &&
+	    indirect_blockshift >= SPA_MINBLOCKSHIFT &&
+	    indirect_blockshift <= SPA_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));
+}
+
+_NOTE(ARGSUSED(0))
+void
+zap_evict(dmu_buf_t *db, void *vzap)
+{
+	zap_t *zap = vzap;
+
+	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 (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 = ENOENT;
+		} else {
+			if (num_integers < 1) {
+				err = EOVERFLOW;
+			} else if (integer_size != 8) {
+				err = 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_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 (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 (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 (ENOTSUP);
+	}
+	if (!zap->zap_ismicro) {
+		err = fzap_length(zn, integer_size, num_integers);
+	} else {
+		mze = mze_find(zn);
+		if (mze == NULL) {
+			err = 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 (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++) {
+		mzap_ent_phys_t *mze = &zap->zap_m.zap_phys->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->zap_m.zap_phys->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, &zap);
+	if (err)
+		return (err);
+	zn = zap_name_alloc(zap, key, MT_EXACT);
+	if (zn == NULL) {
+		zap_unlockdir(zap);
+		return (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 = 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 (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;
+	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, &zap);
+	if (err)
+		return (err);
+	zn = zap_name_alloc(zap, name, MT_EXACT);
+	if (zn == NULL) {
+		zap_unlockdir(zap);
+		return (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 (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 (ENOTSUP);
+	}
+	if (!zap->zap_ismicro) {
+		err = fzap_remove(zn, tx);
+	} else {
+		mze = mze_find(zn);
+		if (mze == NULL) {
+			err = ENOENT;
+		} else {
+			zap->zap_m.zap_num_entries--;
+			bzero(&zap->zap_m.zap_phys->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 (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 (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 {
+		err = ENOENT;
+
+		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;
+		}
+	}
+	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_cursor_move_to_key(zap_cursor_t *zc, const char *name, matchtype_t mt)
+{
+	int err = 0;
+	mzap_ent_t *mze;
+	zap_name_t *zn;
+
+	if (zc->zc_zap == NULL) {
+		err = zap_lockdir(zc->zc_objset, zc->zc_zapobj, NULL,
+		    RW_READER, TRUE, FALSE, &zc->zc_zap);
+		if (err)
+			return (err);
+	} else {
+		rw_enter(&zc->zc_zap->zap_rwlock, RW_READER);
+	}
+
+	zn = zap_name_alloc(zc->zc_zap, name, mt);
+	if (zn == NULL) {
+		rw_exit(&zc->zc_zap->zap_rwlock);
+		return (ENOTSUP);
+	}
+
+	if (!zc->zc_zap->zap_ismicro) {
+		err = fzap_cursor_move_to_key(zc, zn);
+	} else {
+		mze = mze_find(zn);
+		if (mze == NULL) {
+			err = ENOENT;
+			goto out;
+		}
+		zc->zc_hash = mze->mze_hash;
+		zc->zc_cd = mze->mze_cd;
+	}
+
+out:
+	zap_name_free(zn);
+	rw_exit(&zc->zc_zap->zap_rwlock);
+	return (err);
+}
+
+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_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_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 += SPA_MAXBLOCKSIZE;
+		else
+			*towrite += SPA_MAXBLOCKSIZE;
+
+		if (add) {
+			*towrite += 4 * SPA_MAXBLOCKSIZE;
+		}
+	}
+
+	zap_unlockdir(zap);
+	return (err);
+}