xref: /freebsd/sys/contrib/openzfs/module/zfs/zap_micro.c (revision 7a7741af)

/*
 * 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 https://opensource.org/licenses/CDDL-1.0.
 * 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, 2018 by Delphix. All rights reserved.
 * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
 * Copyright 2017 Nexenta Systems, Inc.
 * Copyright (c) 2024, Klara, Inc.
 */

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

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

/*
 * The maximum size (in bytes) of a microzap before it is converted to a
 * fatzap. It will be rounded up to next multiple of 512 (SPA_MINBLOCKSIZE).
 *
 * By definition, a microzap must fit into a single block, so this has
 * traditionally been SPA_OLD_MAXBLOCKSIZE, and is set to that by default.
 * Setting this higher requires both the large_blocks feature (to even create
 * blocks that large) and the large_microzap feature (to enable the stream
 * machinery to understand not to try to split a microzap block).
 *
 * If large_microzap is enabled, this value will be clamped to
 * spa_maxblocksize(). If not, it will be clamped to SPA_OLD_MAXBLOCKSIZE.
 */
static int zap_micro_max_size = SPA_OLD_MAXBLOCKSIZE;

uint64_t
zap_get_micro_max_size(spa_t *spa)
{
	uint64_t maxsz = P2ROUNDUP(zap_micro_max_size, SPA_MINBLOCKSIZE);
	if (maxsz <= SPA_OLD_MAXBLOCKSIZE)
		return (maxsz);
	if (spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_MICROZAP))
		return (MIN(maxsz, spa_maxblocksize(spa)));
	return (SPA_OLD_MAXBLOCKSIZE);
}

static int mzap_upgrade(zap_t **zapp,
    const 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) {
			const uint64_t *wp = zn->zn_key_norm;

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

				for (int j = 0; j < 8; j++) {
					h = (h >> 8) ^
					    zfs_crc64_table[(h ^ word) & 0xFF];
					word >>= NBBY;
				}
			}
		} else {
			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.)
			 */
			int len = zn->zn_key_norm_numints - 1;

			ASSERT(zn->zn_key_intlen == 1);
			for (int 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
	 * choosing the bucket.
	 */
	h &= ~((1ULL << (64 - zap_hashbits(zap))) - 1);

	return (h);
}

static int
zap_normalize(zap_t *zap, const char *name, char *namenorm, int normflags,
    size_t outlen)
{
	ASSERT(!(zap_getflags(zap) & ZAP_FLAG_UINT64_KEY));

	size_t inlen = strlen(name) + 1;

	int err = 0;
	(void) u8_textprep_str((char *)name, &inlen, namenorm, &outlen,
	    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)
{
	boolean_t res = B_FALSE;
	ASSERT(!(zap_getflags(zn->zn_zap) & ZAP_FLAG_UINT64_KEY));

	if (zn->zn_matchtype & MT_NORMALIZE) {
		size_t namelen = zn->zn_normbuf_len;
		char normbuf[ZAP_MAXNAMELEN];
		char *norm = normbuf;

		/*
		 * Cannot allocate this on-stack as it exceed the stack-limit of
		 * 1024.
		 */
		if (namelen > ZAP_MAXNAMELEN)
			norm = kmem_alloc(namelen, KM_SLEEP);

		if (zap_normalize(zn->zn_zap, matchname, norm,
		    zn->zn_normflags, namelen) != 0) {
			res = B_FALSE;
		} else {
			res = (strcmp(zn->zn_key_norm, norm) == 0);
		}
		if (norm != normbuf)
			kmem_free(norm, namelen);
	} else {
		res = (strcmp(zn->zn_key_orig, matchname) == 0);
	}
	return (res);
}

static kmem_cache_t *zap_name_cache;
static kmem_cache_t *zap_attr_cache;
static kmem_cache_t *zap_name_long_cache;
static kmem_cache_t *zap_attr_long_cache;

void
zap_init(void)
{
	zap_name_cache = kmem_cache_create("zap_name",
	    sizeof (zap_name_t) + ZAP_MAXNAMELEN, 0, NULL, NULL,
	    NULL, NULL, NULL, 0);

	zap_attr_cache = kmem_cache_create("zap_attr_cache",
	    sizeof (zap_attribute_t) + ZAP_MAXNAMELEN,  0, NULL,
	    NULL, NULL, NULL, NULL, 0);

	zap_name_long_cache = kmem_cache_create("zap_name_long",
	    sizeof (zap_name_t) + ZAP_MAXNAMELEN_NEW, 0, NULL, NULL,
	    NULL, NULL, NULL, 0);

	zap_attr_long_cache = kmem_cache_create("zap_attr_long_cache",
	    sizeof (zap_attribute_t) + ZAP_MAXNAMELEN_NEW,  0, NULL,
	    NULL, NULL, NULL, NULL, 0);
}

void
zap_fini(void)
{
	kmem_cache_destroy(zap_name_cache);
	kmem_cache_destroy(zap_attr_cache);
	kmem_cache_destroy(zap_name_long_cache);
	kmem_cache_destroy(zap_attr_long_cache);
}

static zap_name_t *
zap_name_alloc(zap_t *zap, boolean_t longname)
{
	kmem_cache_t *cache = longname ? zap_name_long_cache : zap_name_cache;
	zap_name_t *zn = kmem_cache_alloc(cache, KM_SLEEP);

	zn->zn_zap = zap;
	zn->zn_normbuf_len = longname ? ZAP_MAXNAMELEN_NEW : ZAP_MAXNAMELEN;
	return (zn);
}

void
zap_name_free(zap_name_t *zn)
{
	if (zn->zn_normbuf_len == ZAP_MAXNAMELEN) {
		kmem_cache_free(zap_name_cache, zn);
	} else {
		ASSERT3U(zn->zn_normbuf_len, ==, ZAP_MAXNAMELEN_NEW);
		kmem_cache_free(zap_name_long_cache, zn);
	}
}

static int
zap_name_init_str(zap_name_t *zn, const char *key, matchtype_t mt)
{
	zap_t *zap = zn->zn_zap;
	size_t key_len = strlen(key) + 1;

	/* Make sure zn is allocated for longname if key is long */
	IMPLY(key_len > ZAP_MAXNAMELEN,
	    zn->zn_normbuf_len == ZAP_MAXNAMELEN_NEW);

	zn->zn_key_intlen = sizeof (*key);
	zn->zn_key_orig = key;
	zn->zn_key_orig_numints = key_len;
	zn->zn_matchtype = mt;
	zn->zn_normflags = zap->zap_normflags;

	/*
	 * If we're dealing with a case sensitive lookup on a mixed or
	 * insensitive fs, remove U8_TEXTPREP_TOUPPER or the lookup
	 * will fold case to all caps overriding the lookup request.
	 */
	if (mt & MT_MATCH_CASE)
		zn->zn_normflags &= ~U8_TEXTPREP_TOUPPER;

	if (zap->zap_normflags) {
		/*
		 * We *must* use zap_normflags because this normalization is
		 * what the hash is computed from.
		 */
		if (zap_normalize(zap, key, zn->zn_normbuf,
		    zap->zap_normflags, zn->zn_normbuf_len) != 0)
			return (SET_ERROR(ENOTSUP));
		zn->zn_key_norm = zn->zn_normbuf;
		zn->zn_key_norm_numints = strlen(zn->zn_key_norm) + 1;
	} else {
		if (mt != 0)
			return (SET_ERROR(ENOTSUP));
		zn->zn_key_norm = zn->zn_key_orig;
		zn->zn_key_norm_numints = zn->zn_key_orig_numints;
	}

	zn->zn_hash = zap_hash(zn);

	if (zap->zap_normflags != zn->zn_normflags) {
		/*
		 * We *must* use zn_normflags because this normalization is
		 * what the matching is based on.  (Not the hash!)
		 */
		if (zap_normalize(zap, key, zn->zn_normbuf,
		    zn->zn_normflags, zn->zn_normbuf_len) != 0)
			return (SET_ERROR(ENOTSUP));
		zn->zn_key_norm_numints = strlen(zn->zn_key_norm) + 1;
	}

	return (0);
}

zap_name_t *
zap_name_alloc_str(zap_t *zap, const char *key, matchtype_t mt)
{
	size_t key_len = strlen(key) + 1;
	zap_name_t *zn = zap_name_alloc(zap, (key_len > ZAP_MAXNAMELEN));
	if (zap_name_init_str(zn, key, mt) != 0) {
		zap_name_free(zn);
		return (NULL);
	}
	return (zn);
}

static zap_name_t *
zap_name_alloc_uint64(zap_t *zap, const uint64_t *key, int numints)
{
	zap_name_t *zn = kmem_cache_alloc(zap_name_cache, 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 = 0;
	zn->zn_normbuf_len = ZAP_MAXNAMELEN;

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

static void
mzap_byteswap(mzap_phys_t *buf, size_t size)
{
	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);
	int max = (size / MZAP_ENT_LEN) - 1;
	for (int 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 = *(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);
	}
}

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

	return (TREE_CMP((uint64_t)(mze1->mze_hash) << 32 | mze1->mze_cd,
	    (uint64_t)(mze2->mze_hash) << 32 | mze2->mze_cd));
}

ZFS_BTREE_FIND_IN_BUF_FUNC(mze_find_in_buf, mzap_ent_t,
    mze_compare)

static void
mze_insert(zap_t *zap, uint16_t chunkid, uint64_t hash)
{
	mzap_ent_t mze;

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

	mze.mze_chunkid = chunkid;
	ASSERT0(hash & 0xffffffff);
	mze.mze_hash = hash >> 32;
	ASSERT3U(MZE_PHYS(zap, &mze)->mze_cd, <=, 0xffff);
	mze.mze_cd = (uint16_t)MZE_PHYS(zap, &mze)->mze_cd;
	ASSERT(MZE_PHYS(zap, &mze)->mze_name[0] != 0);
	zfs_btree_add(&zap->zap_m.zap_tree, &mze);
}

static mzap_ent_t *
mze_find(zap_name_t *zn, zfs_btree_index_t *idx)
{
	mzap_ent_t mze_tofind;
	mzap_ent_t *mze;
	zfs_btree_t *tree = &zn->zn_zap->zap_m.zap_tree;

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

	ASSERT0(zn->zn_hash & 0xffffffff);
	mze_tofind.mze_hash = zn->zn_hash >> 32;
	mze_tofind.mze_cd = 0;

	mze = zfs_btree_find(tree, &mze_tofind, idx);
	if (mze == NULL)
		mze = zfs_btree_next(tree, idx, idx);
	for (; mze && mze->mze_hash == mze_tofind.mze_hash;
	    mze = zfs_btree_next(tree, idx, idx)) {
		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);
	}

	return (NULL);
}

static uint32_t
mze_find_unused_cd(zap_t *zap, uint64_t hash)
{
	mzap_ent_t mze_tofind;
	zfs_btree_index_t idx;
	zfs_btree_t *tree = &zap->zap_m.zap_tree;

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

	ASSERT0(hash & 0xffffffff);
	hash >>= 32;
	mze_tofind.mze_hash = hash;
	mze_tofind.mze_cd = 0;

	uint32_t cd = 0;
	for (mzap_ent_t *mze = zfs_btree_find(tree, &mze_tofind, &idx);
	    mze && mze->mze_hash == hash;
	    mze = zfs_btree_next(tree, &idx, &idx)) {
		if (mze->mze_cd != cd)
			break;
		cd++;
	}

	return (cd);
}

/*
 * Each mzap entry requires at max : 4 chunks
 * 3 chunks for names + 1 chunk for value.
 */
#define	MZAP_ENT_CHUNKS	(1 + ZAP_LEAF_ARRAY_NCHUNKS(MZAP_NAME_LEN) + \
	ZAP_LEAF_ARRAY_NCHUNKS(sizeof (uint64_t)))

/*
 * Check if the current entry keeps the colliding entries under the fatzap leaf
 * size.
 */
static boolean_t
mze_canfit_fzap_leaf(zap_name_t *zn, uint64_t hash)
{
	zap_t *zap = zn->zn_zap;
	mzap_ent_t mze_tofind;
	zfs_btree_index_t idx;
	zfs_btree_t *tree = &zap->zap_m.zap_tree;
	uint32_t mzap_ents = 0;

	ASSERT0(hash & 0xffffffff);
	hash >>= 32;
	mze_tofind.mze_hash = hash;
	mze_tofind.mze_cd = 0;

	for (mzap_ent_t *mze = zfs_btree_find(tree, &mze_tofind, &idx);
	    mze && mze->mze_hash == hash;
	    mze = zfs_btree_next(tree, &idx, &idx)) {
		mzap_ents++;
	}

	/* Include the new entry being added */
	mzap_ents++;

	return (ZAP_LEAF_NUMCHUNKS_DEF > (mzap_ents * MZAP_ENT_CHUNKS));
}

static void
mze_destroy(zap_t *zap)
{
	zfs_btree_clear(&zap->zap_m.zap_tree);
	zfs_btree_destroy(&zap->zap_m.zap_tree);
}

static zap_t *
mzap_open(dmu_buf_t *db)
{
	zap_t *winner;
	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_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 = dmu_buf_get_objset(db);
	zap->zap_object = db->db_object;
	zap->zap_dbuf = db;

	if (zap_block_type != ZBT_MICRO) {
		mutex_init(&zap->zap_f.zap_num_entries_mtx, 0, MUTEX_DEFAULT,
		    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;

		/*
		 * Reduce B-tree leaf from 4KB to 512 bytes to reduce memmove()
		 * overhead on massive inserts below.  It still allows to store
		 * 62 entries before we have to add 2KB B-tree core node.
		 */
		zfs_btree_create_custom(&zap->zap_m.zap_tree, mze_compare,
		    mze_find_in_buf, sizeof (mzap_ent_t), 512);

		zap_name_t *zn = zap_name_alloc(zap, B_FALSE);
		for (uint16_t 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->zap_m.zap_num_entries++;
				zap_name_init_str(zn, mze->mze_name, 0);
				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);
}

/*
 * This routine "consumes" the caller's hold on the dbuf, which must
 * have the specified tag.
 */
static int
zap_lockdir_impl(dnode_t *dn, dmu_buf_t *db, const void *tag, dmu_tx_t *tx,
    krw_t lti, boolean_t fatreader, boolean_t adding, zap_t **zapp)
{
	ASSERT0(db->db_offset);
	objset_t *os = dmu_buf_get_objset(db);
	uint64_t obj = db->db_object;
	dmu_object_info_t doi;

	*zapp = NULL;

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

	zap_t *zap = dmu_buf_get_user(db);
	if (zap == NULL) {
		zap = mzap_open(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.
	 */
	krw_t 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;
	zap->zap_dnode = dn;

	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 > zap_get_micro_max_size(dmu_objset_spa(os))) {
			dprintf("upgrading obj %llu: num_entries=%u\n",
			    (u_longlong_t)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;

		if (newsz > SPA_OLD_MAXBLOCKSIZE) {
			dsl_dataset_t *ds = dmu_objset_ds(os);
			if (!dsl_dataset_feature_is_active(ds,
			    SPA_FEATURE_LARGE_MICROZAP)) {
				/*
				 * A microzap just grew beyond the old limit
				 * for the first time, so we have to ensure the
				 * feature flag is activated.
				 * zap_get_micro_max_size() won't let us get
				 * here if the feature is not enabled, so we
				 * don't need any other checks beforehand.
				 *
				 * Since we're in open context, we can't
				 * activate the feature directly, so we instead
				 * flag it on the dataset for next sync.
				 */
				dsl_dataset_dirty(ds, tx);
				mutex_enter(&ds->ds_lock);
				ds->ds_feature_activation
				    [SPA_FEATURE_LARGE_MICROZAP] =
				    (void *)B_TRUE;
				mutex_exit(&ds->ds_lock);
			}
		}
	}

	*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, const 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(dn, db, tag, tx, lti, fatreader, adding, zapp);
	if (err != 0)
		dmu_buf_rele(db, tag);
	else
		VERIFY(dnode_add_ref(dn, 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, const void *tag,
    zap_t **zapp)
{
	dnode_t *dn;
	dmu_buf_t *db;
	int err;

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

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

static int
mzap_upgrade(zap_t **zapp, const void *tag, dmu_tx_t *tx, zap_flags_t flags)
{
	int err = 0;
	zap_t *zap = *zapp;

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

	int sz = zap->zap_dbuf->db_size;
	mzap_phys_t *mzp = vmem_alloc(sz, KM_SLEEP);
	memcpy(mzp, zap->zap_dbuf->db_data, sz);
	int 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 != 0) {
			vmem_free(mzp, sz);
			return (err);
		}
	}

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

	fzap_upgrade(zap, tx, flags);

	zap_name_t *zn = zap_name_alloc(zap, B_FALSE);
	for (int i = 0; i < nchunks; i++) {
		mzap_ent_phys_t *mze = &mzp->mz_chunk[i];
		if (mze->mze_name[0] == 0)
			continue;
		dprintf("adding %s=%llu\n",
		    mze->mze_name, (u_longlong_t)mze->mze_value);
		zap_name_init_str(zn, mze->mze_name, 0);
		/* If we fail here, we would end up losing entries */
		VERIFY0(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);
	vmem_free(mzp, sz);
	*zapp = zap;
	return (0);
}

/*
 * The "normflags" determine the behavior of the matchtype_t which is
 * passed to zap_lookup_norm().  Names which have the same normalized
 * version will be stored with the same hash value, and therefore we can
 * perform normalization-insensitive lookups.  We can be Unicode form-
 * insensitive and/or case-insensitive.  The following flags are valid for
 * "normflags":
 *
 * U8_TEXTPREP_NFC
 * U8_TEXTPREP_NFD
 * U8_TEXTPREP_NFKC
 * U8_TEXTPREP_NFKD
 * U8_TEXTPREP_TOUPPER
 *
 * The *_NF* (Normalization Form) flags are mutually exclusive; at most one
 * of them may be supplied.
 */
void
mzap_create_impl(dnode_t *dn, int normflags, zap_flags_t flags, dmu_tx_t *tx)
{
	dmu_buf_t *db;

	VERIFY0(dmu_buf_hold_by_dnode(dn, 0, FTAG, &db, DMU_READ_NO_PREFETCH));

	dmu_buf_will_dirty(db, tx);
	mzap_phys_t *zp = db->db_data;
	zp->mz_block_type = ZBT_MICRO;
	zp->mz_salt =
	    ((uintptr_t)db ^ (uintptr_t)tx ^ (dn->dn_object << 1)) | 1ULL;
	zp->mz_normflags = normflags;

	if (flags != 0) {
		zap_t *zap;
		/* Only fat zap supports flags; upgrade immediately. */
		VERIFY(dnode_add_ref(dn, FTAG));
		VERIFY0(zap_lockdir_impl(dn, db, FTAG, tx, RW_WRITER,
		    B_FALSE, B_FALSE, &zap));
		VERIFY0(mzap_upgrade(&zap, FTAG, tx, flags));
		zap_unlockdir(zap, FTAG);
	} else {
		dmu_buf_rele(db, FTAG);
	}
}

static uint64_t
zap_create_impl(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,
    dnode_t **allocated_dnode, const void *tag, dmu_tx_t *tx)
{
	uint64_t obj;

	ASSERT3U(DMU_OT_BYTESWAP(ot), ==, DMU_BSWAP_ZAP);

	if (allocated_dnode == NULL) {
		dnode_t *dn;
		obj = dmu_object_alloc_hold(os, ot, 1ULL << leaf_blockshift,
		    indirect_blockshift, bonustype, bonuslen, dnodesize,
		    &dn, FTAG, tx);
		mzap_create_impl(dn, normflags, flags, tx);
		dnode_rele(dn, FTAG);
	} else {
		obj = dmu_object_alloc_hold(os, ot, 1ULL << leaf_blockshift,
		    indirect_blockshift, bonustype, bonuslen, dnodesize,
		    allocated_dnode, tag, tx);
		mzap_create_impl(*allocated_dnode, normflags, flags, tx);
	}

	return (obj);
}

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)
{
	dnode_t *dn;
	int error;

	ASSERT3U(DMU_OT_BYTESWAP(ot), ==, DMU_BSWAP_ZAP);
	error = dmu_object_claim_dnsize(os, obj, ot, 0, bonustype, bonuslen,
	    dnodesize, tx);
	if (error != 0)
		return (error);

	error = dnode_hold(os, obj, FTAG, &dn);
	if (error != 0)
		return (error);

	mzap_create_impl(dn, normflags, 0, tx);

	dnode_rele(dn, FTAG);

	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)
{
	return (zap_create_impl(os, normflags, 0, ot, 0, 0,
	    bonustype, bonuslen, dnodesize, NULL, NULL, tx));
}

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)
{
	return (zap_create_impl(os, normflags, flags, ot, leaf_blockshift,
	    indirect_blockshift, bonustype, bonuslen, dnodesize, NULL, NULL,
	    tx));
}

/*
 * Create a zap object and return a pointer to the newly allocated dnode via
 * the allocated_dnode argument.  The returned dnode will be held and the
 * caller is responsible for releasing the hold by calling dnode_rele().
 */
uint64_t
zap_create_hold(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,
    dnode_t **allocated_dnode, const void *tag, dmu_tx_t *tx)
{
	return (zap_create_impl(os, normflags, flags, ot, leaf_blockshift,
	    indirect_blockshift, bonustype, bonuslen, dnodesize,
	    allocated_dnode, tag, tx));
}

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 =
	    zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
	if (err != 0)
		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,
    zfs_btree_index_t *idx)
{
	boolean_t allocdzn = B_FALSE;
	mzap_ent_t *other;
	zfs_btree_index_t oidx;

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

	for (other = zfs_btree_prev(&zap->zap_m.zap_tree, idx, &oidx);
	    other && other->mze_hash == mze->mze_hash;
	    other = zfs_btree_prev(&zap->zap_m.zap_tree, &oidx, &oidx)) {

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

	for (other = zfs_btree_next(&zap->zap_m.zap_tree, idx, &oidx);
	    other && other->mze_hash == mze->mze_hash;
	    other = zfs_btree_next(&zap->zap_m.zap_tree, &oidx, &oidx)) {

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

	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, 0, 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;

	zap_name_t *zn = zap_name_alloc_str(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 {
		zfs_btree_index_t idx;
		mzap_ent_t *mze = mze_find(zn, &idx);
		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;
				if (realname != NULL)
					(void) strlcpy(realname,
					    MZE_PHYS(zap, mze)->mze_name,
					    rn_len);
				if (ncp) {
					*ncp = mzap_normalization_conflict(zap,
					    zn, mze, &idx);
				}
			}
		}
	}
	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 =
	    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_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, FTAG, &zap);
	if (err)
		return (err);
	zn = zap_name_alloc_str(zap, name, 0);
	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_prefetch_object(objset_t *os, uint64_t zapobj)
{
	int error;
	dmu_object_info_t doi;

	error = dmu_object_info(os, zapobj, &doi);
	if (error == 0 && DMU_OT_BYTESWAP(doi.doi_type) != DMU_BSWAP_ZAP)
		error = SET_ERROR(EINVAL);
	if (error == 0)
		dmu_prefetch_wait(os, zapobj, 0, doi.doi_max_offset);

	return (error);
}

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, 0, 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 = 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_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
	if (err != 0)
		return (err);
	zap_name_t *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_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
	if (err != 0)
		return (err);
	zap_name_t *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, 0, 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 =
	    zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
	if (err != 0)
		return (err);
	zap_name_t *zn = zap_name_alloc_str(zap, name, 0);
	if (zn == NULL) {
		zap_unlockdir(zap, FTAG);
		return (SET_ERROR(ENOTSUP));
	}
	if (!zap->zap_ismicro) {
		err = fzap_length(zn, integer_size, num_integers);
	} else {
		zfs_btree_index_t idx;
		mzap_ent_t *mze = mze_find(zn, &idx);
		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_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
	if (err != 0)
		return (err);
	zap_name_t *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)
{
	zap_t *zap = zn->zn_zap;
	uint16_t start = zap->zap_m.zap_alloc_next;

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

#ifdef ZFS_DEBUG
	for (int 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

	uint32_t 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 (uint16_t 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) strlcpy(mze->mze_name, zn->zn_key_orig,
			    sizeof (mze->mze_name));
			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!");
}

static int
zap_add_impl(zap_t *zap, const char *key,
    int integer_size, uint64_t num_integers,
    const void *val, dmu_tx_t *tx, const void *tag)
{
	const uint64_t *intval = val;
	int err = 0;

	zap_name_t *zn = zap_name_alloc_str(zap, key, 0);
	if (zn == NULL) {
		zap_unlockdir(zap, tag);
		return (SET_ERROR(ENOTSUP));
	}
	if (!zap->zap_ismicro) {
		err = fzap_add(zn, integer_size, num_integers, val, tag, tx);
		zap = zn->zn_zap;	/* fzap_add() may change zap */
	} else if (integer_size != 8 || num_integers != 1 ||
	    strlen(key) >= MZAP_NAME_LEN ||
	    !mze_canfit_fzap_leaf(zn, zn->zn_hash)) {
		err = mzap_upgrade(&zn->zn_zap, tag, tx, 0);
		if (err == 0) {
			err = fzap_add(zn, integer_size, num_integers, val,
			    tag, tx);
		}
		zap = zn->zn_zap;	/* fzap_add() may change zap */
	} else {
		zfs_btree_index_t idx;
		if (mze_find(zn, &idx) != 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, tag);
	return (err);
}

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;

	err = zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
	if (err != 0)
		return (err);
	err = zap_add_impl(zap, key, integer_size, num_integers, val, tx, FTAG);
	/* zap_add_impl() calls zap_unlockdir() */
	return (err);
}

int
zap_add_by_dnode(dnode_t *dn, const char *key,
    int integer_size, uint64_t num_integers,
    const void *val, dmu_tx_t *tx)
{
	zap_t *zap;
	int err;

	err = zap_lockdir_by_dnode(dn, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
	if (err != 0)
		return (err);
	err = zap_add_impl(zap, key, integer_size, num_integers, val, tx, FTAG);
	/* zap_add_impl() calls zap_unlockdir() */
	return (err);
}

static int
zap_add_uint64_impl(zap_t *zap, const uint64_t *key,
    int key_numints, int integer_size, uint64_t num_integers,
    const void *val, dmu_tx_t *tx, const void *tag)
{
	int err;

	zap_name_t *zn = zap_name_alloc_uint64(zap, key, key_numints);
	if (zn == NULL) {
		zap_unlockdir(zap, tag);
		return (SET_ERROR(ENOTSUP));
	}
	err = fzap_add(zn, integer_size, num_integers, val, tag, 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, tag);
	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_lockdir(os, zapobj, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
	if (err != 0)
		return (err);
	err = zap_add_uint64_impl(zap, key, key_numints,
	    integer_size, num_integers, val, tx, FTAG);
	/* zap_add_uint64_impl() calls zap_unlockdir() */
	return (err);
}

int
zap_add_uint64_by_dnode(dnode_t *dn, 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_lockdir_by_dnode(dn, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
	if (err != 0)
		return (err);
	err = zap_add_uint64_impl(zap, key, key_numints,
	    integer_size, num_integers, val, tx, FTAG);
	/* zap_add_uint64_impl() calls zap_unlockdir() */
	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;
	const uint64_t *intval = val;

	int err =
	    zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
	if (err != 0)
		return (err);
	zap_name_t *zn = zap_name_alloc_str(zap, name, 0);
	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",
		    (u_longlong_t)zapobj, integer_size,
		    (u_longlong_t)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 {
		zfs_btree_index_t idx;
		mzap_ent_t *mze = mze_find(zn, &idx);
		if (mze != NULL) {
			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);
}

static int
zap_update_uint64_impl(zap_t *zap, const uint64_t *key, int key_numints,
    int integer_size, uint64_t num_integers, const void *val, dmu_tx_t *tx,
    const void *tag)
{
	int err;

	zap_name_t *zn = zap_name_alloc_uint64(zap, key, key_numints);
	if (zn == NULL) {
		zap_unlockdir(zap, tag);
		return (SET_ERROR(ENOTSUP));
	}
	err = fzap_update(zn, integer_size, num_integers, val, tag, 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, tag);
	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;

	int err =
	    zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
	if (err != 0)
		return (err);
	err = zap_update_uint64_impl(zap, key, key_numints,
	    integer_size, num_integers, val, tx, FTAG);
	/* zap_update_uint64_impl() calls zap_unlockdir() */
	return (err);
}

int
zap_update_uint64_by_dnode(dnode_t *dn, 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_lockdir_by_dnode(dn, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
	if (err != 0)
		return (err);
	err = zap_update_uint64_impl(zap, key, key_numints,
	    integer_size, num_integers, val, tx, FTAG);
	/* zap_update_uint64_impl() calls zap_unlockdir() */
	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, 0, tx));
}

static int
zap_remove_impl(zap_t *zap, const char *name,
    matchtype_t mt, dmu_tx_t *tx)
{
	int err = 0;

	zap_name_t *zn = zap_name_alloc_str(zap, name, mt);
	if (zn == NULL)
		return (SET_ERROR(ENOTSUP));
	if (!zap->zap_ismicro) {
		err = fzap_remove(zn, tx);
	} else {
		zfs_btree_index_t idx;
		mzap_ent_t *mze = mze_find(zn, &idx);
		if (mze == NULL) {
			err = SET_ERROR(ENOENT);
		} else {
			zap->zap_m.zap_num_entries--;
			memset(MZE_PHYS(zap, mze), 0, sizeof (mzap_ent_phys_t));
			zfs_btree_remove_idx(&zap->zap_m.zap_tree, &idx);
		}
	}
	zap_name_free(zn);
	return (err);
}

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;

	err = zap_lockdir(os, zapobj, tx, RW_WRITER, TRUE, FALSE, FTAG, &zap);
	if (err)
		return (err);
	err = zap_remove_impl(zap, name, mt, tx);
	zap_unlockdir(zap, FTAG);
	return (err);
}

int
zap_remove_by_dnode(dnode_t *dn, const char *name, dmu_tx_t *tx)
{
	zap_t *zap;
	int err;

	err = zap_lockdir_by_dnode(dn, tx, RW_WRITER, TRUE, FALSE, FTAG, &zap);
	if (err)
		return (err);
	err = zap_remove_impl(zap, name, 0, tx);
	zap_unlockdir(zap, FTAG);
	return (err);
}

static int
zap_remove_uint64_impl(zap_t *zap, const uint64_t *key, int key_numints,
    dmu_tx_t *tx, const void *tag)
{
	int err;

	zap_name_t *zn = zap_name_alloc_uint64(zap, key, key_numints);
	if (zn == NULL) {
		zap_unlockdir(zap, tag);
		return (SET_ERROR(ENOTSUP));
	}
	err = fzap_remove(zn, tx);
	zap_name_free(zn);
	zap_unlockdir(zap, tag);
	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_lockdir(os, zapobj, tx, RW_WRITER, TRUE, FALSE, FTAG, &zap);
	if (err != 0)
		return (err);
	err = zap_remove_uint64_impl(zap, key, key_numints, tx, FTAG);
	/* zap_remove_uint64_impl() calls zap_unlockdir() */
	return (err);
}

int
zap_remove_uint64_by_dnode(dnode_t *dn, const uint64_t *key, int key_numints,
    dmu_tx_t *tx)
{
	zap_t *zap;

	int err =
	    zap_lockdir_by_dnode(dn, tx, RW_WRITER, TRUE, FALSE, FTAG, &zap);
	if (err != 0)
		return (err);
	err = zap_remove_uint64_impl(zap, key, key_numints, tx, FTAG);
	/* zap_remove_uint64_impl() calls zap_unlockdir() */
	return (err);
}


static zap_attribute_t *
zap_attribute_alloc_impl(boolean_t longname)
{
	zap_attribute_t *za;

	za = kmem_cache_alloc((longname)? zap_attr_long_cache : zap_attr_cache,
	    KM_SLEEP);
	za->za_name_len = (longname)? ZAP_MAXNAMELEN_NEW : ZAP_MAXNAMELEN;
	return (za);
}

zap_attribute_t *
zap_attribute_alloc(void)
{
	return (zap_attribute_alloc_impl(B_FALSE));
}

zap_attribute_t *
zap_attribute_long_alloc(void)
{
	return (zap_attribute_alloc_impl(B_TRUE));
}

void
zap_attribute_free(zap_attribute_t *za)
{
	if (za->za_name_len == ZAP_MAXNAMELEN) {
		kmem_cache_free(zap_attr_cache, za);
	} else {
		ASSERT3U(za->za_name_len, ==, ZAP_MAXNAMELEN_NEW);
		kmem_cache_free(zap_attr_long_cache, za);
	}
}

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

static void
zap_cursor_init_impl(zap_cursor_t *zc, objset_t *os, uint64_t zapobj,
    uint64_t serialized, boolean_t prefetch)
{
	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;
	zc->zc_prefetch = prefetch;
}
void
zap_cursor_init_serialized(zap_cursor_t *zc, objset_t *os, uint64_t zapobj,
    uint64_t serialized)
{
	zap_cursor_init_impl(zc, os, zapobj, serialized, B_TRUE);
}

/*
 * Initialize a cursor at the beginning of the ZAP object.  The entire
 * ZAP object will be prefetched.
 */
void
zap_cursor_init(zap_cursor_t *zc, objset_t *os, uint64_t zapobj)
{
	zap_cursor_init_impl(zc, os, zapobj, 0, B_TRUE);
}

/*
 * Initialize a cursor at the beginning, but request that we not prefetch
 * the entire ZAP object.
 */
void
zap_cursor_init_noprefetch(zap_cursor_t *zc, objset_t *os, uint64_t zapobj)
{
	zap_cursor_init_impl(zc, os, zapobj, 0, B_FALSE);
}

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;

	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 != 0)
			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 {
		zfs_btree_index_t idx;
		mzap_ent_t mze_tofind;

		mze_tofind.mze_hash = zc->zc_hash >> 32;
		mze_tofind.mze_cd = zc->zc_cd;

		mzap_ent_t *mze = zfs_btree_find(&zc->zc_zap->zap_m.zap_tree,
		    &mze_tofind, &idx);
		if (mze == NULL) {
			mze = zfs_btree_next(&zc->zc_zap->zap_m.zap_tree,
			    &idx, &idx);
		}
		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, &idx);
			za->za_integer_length = 8;
			za->za_num_integers = 1;
			za->za_first_integer = mzep->mze_value;
			(void) strlcpy(za->za_name, mzep->mze_name,
			    za->za_name_len);
			zc->zc_hash = (uint64_t)mze->mze_hash << 32;
			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)
{
	zap_t *zap;

	int err =
	    zap_lockdir(os, zapobj, NULL, RW_READER, TRUE, FALSE, FTAG, &zap);
	if (err != 0)
		return (err);

	memset(zs, 0, 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);
}

#if defined(_KERNEL)
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_create_hold);
EXPORT_SYMBOL(zap_destroy);
EXPORT_SYMBOL(zap_lookup);
EXPORT_SYMBOL(zap_lookup_by_dnode);
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_prefetch_object);
EXPORT_SYMBOL(zap_add);
EXPORT_SYMBOL(zap_add_by_dnode);
EXPORT_SYMBOL(zap_add_uint64);
EXPORT_SYMBOL(zap_add_uint64_by_dnode);
EXPORT_SYMBOL(zap_update);
EXPORT_SYMBOL(zap_update_uint64);
EXPORT_SYMBOL(zap_update_uint64_by_dnode);
EXPORT_SYMBOL(zap_length);
EXPORT_SYMBOL(zap_length_uint64);
EXPORT_SYMBOL(zap_remove);
EXPORT_SYMBOL(zap_remove_by_dnode);
EXPORT_SYMBOL(zap_remove_norm);
EXPORT_SYMBOL(zap_remove_uint64);
EXPORT_SYMBOL(zap_remove_uint64_by_dnode);
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);

/* CSTYLED */
ZFS_MODULE_PARAM(zfs, , zap_micro_max_size, INT, ZMOD_RW,
	"Maximum micro ZAP size, before converting to a fat ZAP, in bytes");
#endif