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      1 /*
      2  * CDDL HEADER START
      3  *
      4  * The contents of this file are subject to the terms of the
      5  * Common Development and Distribution License (the "License").
      6  * You may not use this file except in compliance with the License.
      7  *
      8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      9  * or http://www.opensolaris.org/os/licensing.
     10  * See the License for the specific language governing permissions
     11  * and limitations under the License.
     12  *
     13  * When distributing Covered Code, include this CDDL HEADER in each
     14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     15  * If applicable, add the following below this CDDL HEADER, with the
     16  * fields enclosed by brackets "[]" replaced with your own identifying
     17  * information: Portions Copyright [yyyy] [name of copyright owner]
     18  *
     19  * CDDL HEADER END
     20  */
     21 /*
     22  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
     23  * Use is subject to license terms.
     24  */
     25 
     26 /*
     27  * This file contains the top half of the zfs directory structure
     28  * implementation. The bottom half is in zap_leaf.c.
     29  *
     30  * The zdir is an extendable hash data structure. There is a table of
     31  * pointers to buckets (zap_t->zd_data->zd_leafs). The buckets are
     32  * each a constant size and hold a variable number of directory entries.
     33  * The buckets (aka "leaf nodes") are implemented in zap_leaf.c.
     34  *
     35  * The pointer table holds a power of 2 number of pointers.
     36  * (1<<zap_t->zd_data->zd_phys->zd_prefix_len).  The bucket pointed to
     37  * by the pointer at index i in the table holds entries whose hash value
     38  * has a zd_prefix_len - bit prefix
     39  */
     40 
     41 #include <sys/spa.h>
     42 #include <sys/dmu.h>
     43 #include <sys/zfs_context.h>
     44 #include <sys/zfs_znode.h>
     45 #include <sys/fs/zfs.h>
     46 #include <sys/zap.h>
     47 #include <sys/refcount.h>
     48 #include <sys/zap_impl.h>
     49 #include <sys/zap_leaf.h>
     50 
     51 int fzap_default_block_shift = 14; /* 16k blocksize */
     52 
     53 static void zap_leaf_pageout(dmu_buf_t *db, void *vl);
     54 static uint64_t zap_allocate_blocks(zap_t *zap, int nblocks);
     55 
     56 
     57 void
     58 fzap_byteswap(void *vbuf, size_t size)
     59 {
     60 	uint64_t block_type;
     61 
     62 	block_type = *(uint64_t *)vbuf;
     63 
     64 	if (block_type == ZBT_LEAF || block_type == BSWAP_64(ZBT_LEAF))
     65 		zap_leaf_byteswap(vbuf, size);
     66 	else {
     67 		/* it's a ptrtbl block */
     68 		byteswap_uint64_array(vbuf, size);
     69 	}
     70 }
     71 
     72 void
     73 fzap_upgrade(zap_t *zap, dmu_tx_t *tx)
     74 {
     75 	dmu_buf_t *db;
     76 	zap_leaf_t *l;
     77 	int i;
     78 	zap_phys_t *zp;
     79 
     80 	ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
     81 	zap->zap_ismicro = FALSE;
     82 
     83 	(void) dmu_buf_update_user(zap->zap_dbuf, zap, zap,
     84 	    &zap->zap_f.zap_phys, zap_evict);
     85 
     86 	mutex_init(&zap->zap_f.zap_num_entries_mtx, 0, 0, 0);
     87 	zap->zap_f.zap_block_shift = highbit(zap->zap_dbuf->db_size) - 1;
     88 
     89 	zp = zap->zap_f.zap_phys;
     90 	/*
     91 	 * explicitly zero it since it might be coming from an
     92 	 * initialized microzap
     93 	 */
     94 	bzero(zap->zap_dbuf->db_data, zap->zap_dbuf->db_size);
     95 	zp->zap_block_type = ZBT_HEADER;
     96 	zp->zap_magic = ZAP_MAGIC;
     97 
     98 	zp->zap_ptrtbl.zt_shift = ZAP_EMBEDDED_PTRTBL_SHIFT(zap);
     99 
    100 	zp->zap_freeblk = 2;		/* block 1 will be the first leaf */
    101 	zp->zap_num_leafs = 1;
    102 	zp->zap_num_entries = 0;
    103 	zp->zap_salt = zap->zap_salt;
    104 	zp->zap_normflags = zap->zap_normflags;
    105 
    106 	/* block 1 will be the first leaf */
    107 	for (i = 0; i < (1<<zp->zap_ptrtbl.zt_shift); i++)
    108 		ZAP_EMBEDDED_PTRTBL_ENT(zap, i) = 1;
    109 
    110 	/*
    111 	 * set up block 1 - the first leaf
    112 	 */
    113 	VERIFY(0 == dmu_buf_hold(zap->zap_objset, zap->zap_object,
    114 	    1<<FZAP_BLOCK_SHIFT(zap), FTAG, &db));
    115 	dmu_buf_will_dirty(db, tx);
    116 
    117 	l = kmem_zalloc(sizeof (zap_leaf_t), KM_SLEEP);
    118 	l->l_dbuf = db;
    119 	l->l_phys = db->db_data;
    120 
    121 	zap_leaf_init(l, zp->zap_normflags != 0);
    122 
    123 	kmem_free(l, sizeof (zap_leaf_t));
    124 	dmu_buf_rele(db, FTAG);
    125 }
    126 
    127 static int
    128 zap_tryupgradedir(zap_t *zap, dmu_tx_t *tx)
    129 {
    130 	if (RW_WRITE_HELD(&zap->zap_rwlock))
    131 		return (1);
    132 	if (rw_tryupgrade(&zap->zap_rwlock)) {
    133 		dmu_buf_will_dirty(zap->zap_dbuf, tx);
    134 		return (1);
    135 	}
    136 	return (0);
    137 }
    138 
    139 /*
    140  * Generic routines for dealing with the pointer & cookie tables.
    141  */
    142 
    143 static int
    144 zap_table_grow(zap_t *zap, zap_table_phys_t *tbl,
    145     void (*transfer_func)(const uint64_t *src, uint64_t *dst, int n),
    146     dmu_tx_t *tx)
    147 {
    148 	uint64_t b, newblk;
    149 	dmu_buf_t *db_old, *db_new;
    150 	int err;
    151 	int bs = FZAP_BLOCK_SHIFT(zap);
    152 	int hepb = 1<<(bs-4);
    153 	/* hepb = half the number of entries in a block */
    154 
    155 	ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
    156 	ASSERT(tbl->zt_blk != 0);
    157 	ASSERT(tbl->zt_numblks > 0);
    158 
    159 	if (tbl->zt_nextblk != 0) {
    160 		newblk = tbl->zt_nextblk;
    161 	} else {
    162 		newblk = zap_allocate_blocks(zap, tbl->zt_numblks * 2);
    163 		tbl->zt_nextblk = newblk;
    164 		ASSERT3U(tbl->zt_blks_copied, ==, 0);
    165 		dmu_prefetch(zap->zap_objset, zap->zap_object,
    166 		    tbl->zt_blk << bs, tbl->zt_numblks << bs);
    167 	}
    168 
    169 	/*
    170 	 * Copy the ptrtbl from the old to new location.
    171 	 */
    172 
    173 	b = tbl->zt_blks_copied;
    174 	err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
    175 	    (tbl->zt_blk + b) << bs, FTAG, &db_old);
    176 	if (err)
    177 		return (err);
    178 
    179 	/* first half of entries in old[b] go to new[2*b+0] */
    180 	VERIFY(0 == dmu_buf_hold(zap->zap_objset, zap->zap_object,
    181 	    (newblk + 2*b+0) << bs, FTAG, &db_new));
    182 	dmu_buf_will_dirty(db_new, tx);
    183 	transfer_func(db_old->db_data, db_new->db_data, hepb);
    184 	dmu_buf_rele(db_new, FTAG);
    185 
    186 	/* second half of entries in old[b] go to new[2*b+1] */
    187 	VERIFY(0 == dmu_buf_hold(zap->zap_objset, zap->zap_object,
    188 	    (newblk + 2*b+1) << bs, FTAG, &db_new));
    189 	dmu_buf_will_dirty(db_new, tx);
    190 	transfer_func((uint64_t *)db_old->db_data + hepb,
    191 	    db_new->db_data, hepb);
    192 	dmu_buf_rele(db_new, FTAG);
    193 
    194 	dmu_buf_rele(db_old, FTAG);
    195 
    196 	tbl->zt_blks_copied++;
    197 
    198 	dprintf("copied block %llu of %llu\n",
    199 	    tbl->zt_blks_copied, tbl->zt_numblks);
    200 
    201 	if (tbl->zt_blks_copied == tbl->zt_numblks) {
    202 		(void) dmu_free_range(zap->zap_objset, zap->zap_object,
    203 		    tbl->zt_blk << bs, tbl->zt_numblks << bs, tx);
    204 
    205 		tbl->zt_blk = newblk;
    206 		tbl->zt_numblks *= 2;
    207 		tbl->zt_shift++;
    208 		tbl->zt_nextblk = 0;
    209 		tbl->zt_blks_copied = 0;
    210 
    211 		dprintf("finished; numblocks now %llu (%lluk entries)\n",
    212 		    tbl->zt_numblks, 1<<(tbl->zt_shift-10));
    213 	}
    214 
    215 	return (0);
    216 }
    217 
    218 static int
    219 zap_table_store(zap_t *zap, zap_table_phys_t *tbl, uint64_t idx, uint64_t val,
    220     dmu_tx_t *tx)
    221 {
    222 	int err;
    223 	uint64_t blk, off;
    224 	int bs = FZAP_BLOCK_SHIFT(zap);
    225 	dmu_buf_t *db;
    226 
    227 	ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    228 	ASSERT(tbl->zt_blk != 0);
    229 
    230 	dprintf("storing %llx at index %llx\n", val, idx);
    231 
    232 	blk = idx >> (bs-3);
    233 	off = idx & ((1<<(bs-3))-1);
    234 
    235 	err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
    236 	    (tbl->zt_blk + blk) << bs, FTAG, &db);
    237 	if (err)
    238 		return (err);
    239 	dmu_buf_will_dirty(db, tx);
    240 
    241 	if (tbl->zt_nextblk != 0) {
    242 		uint64_t idx2 = idx * 2;
    243 		uint64_t blk2 = idx2 >> (bs-3);
    244 		uint64_t off2 = idx2 & ((1<<(bs-3))-1);
    245 		dmu_buf_t *db2;
    246 
    247 		err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
    248 		    (tbl->zt_nextblk + blk2) << bs, FTAG, &db2);
    249 		if (err) {
    250 			dmu_buf_rele(db, FTAG);
    251 			return (err);
    252 		}
    253 		dmu_buf_will_dirty(db2, tx);
    254 		((uint64_t *)db2->db_data)[off2] = val;
    255 		((uint64_t *)db2->db_data)[off2+1] = val;
    256 		dmu_buf_rele(db2, FTAG);
    257 	}
    258 
    259 	((uint64_t *)db->db_data)[off] = val;
    260 	dmu_buf_rele(db, FTAG);
    261 
    262 	return (0);
    263 }
    264 
    265 static int
    266 zap_table_load(zap_t *zap, zap_table_phys_t *tbl, uint64_t idx, uint64_t *valp)
    267 {
    268 	uint64_t blk, off;
    269 	int err;
    270 	dmu_buf_t *db;
    271 	int bs = FZAP_BLOCK_SHIFT(zap);
    272 
    273 	ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    274 
    275 	blk = idx >> (bs-3);
    276 	off = idx & ((1<<(bs-3))-1);
    277 
    278 	err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
    279 	    (tbl->zt_blk + blk) << bs, FTAG, &db);
    280 	if (err)
    281 		return (err);
    282 	*valp = ((uint64_t *)db->db_data)[off];
    283 	dmu_buf_rele(db, FTAG);
    284 
    285 	if (tbl->zt_nextblk != 0) {
    286 		/*
    287 		 * read the nextblk for the sake of i/o error checking,
    288 		 * so that zap_table_load() will catch errors for
    289 		 * zap_table_store.
    290 		 */
    291 		blk = (idx*2) >> (bs-3);
    292 
    293 		err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
    294 		    (tbl->zt_nextblk + blk) << bs, FTAG, &db);
    295 		dmu_buf_rele(db, FTAG);
    296 	}
    297 	return (err);
    298 }
    299 
    300 /*
    301  * Routines for growing the ptrtbl.
    302  */
    303 
    304 static void
    305 zap_ptrtbl_transfer(const uint64_t *src, uint64_t *dst, int n)
    306 {
    307 	int i;
    308 	for (i = 0; i < n; i++) {
    309 		uint64_t lb = src[i];
    310 		dst[2*i+0] = lb;
    311 		dst[2*i+1] = lb;
    312 	}
    313 }
    314 
    315 static int
    316 zap_grow_ptrtbl(zap_t *zap, dmu_tx_t *tx)
    317 {
    318 	/* In case things go horribly wrong. */
    319 	if (zap->zap_f.zap_phys->zap_ptrtbl.zt_shift >= ZAP_HASHBITS-2)
    320 		return (ENOSPC);
    321 
    322 	if (zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks == 0) {
    323 		/*
    324 		 * We are outgrowing the "embedded" ptrtbl (the one
    325 		 * stored in the header block).  Give it its own entire
    326 		 * block, which will double the size of the ptrtbl.
    327 		 */
    328 		uint64_t newblk;
    329 		dmu_buf_t *db_new;
    330 		int err;
    331 
    332 		ASSERT3U(zap->zap_f.zap_phys->zap_ptrtbl.zt_shift, ==,
    333 		    ZAP_EMBEDDED_PTRTBL_SHIFT(zap));
    334 		ASSERT3U(zap->zap_f.zap_phys->zap_ptrtbl.zt_blk, ==, 0);
    335 
    336 		newblk = zap_allocate_blocks(zap, 1);
    337 		err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
    338 		    newblk << FZAP_BLOCK_SHIFT(zap), FTAG, &db_new);
    339 		if (err)
    340 			return (err);
    341 		dmu_buf_will_dirty(db_new, tx);
    342 		zap_ptrtbl_transfer(&ZAP_EMBEDDED_PTRTBL_ENT(zap, 0),
    343 		    db_new->db_data, 1 << ZAP_EMBEDDED_PTRTBL_SHIFT(zap));
    344 		dmu_buf_rele(db_new, FTAG);
    345 
    346 		zap->zap_f.zap_phys->zap_ptrtbl.zt_blk = newblk;
    347 		zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks = 1;
    348 		zap->zap_f.zap_phys->zap_ptrtbl.zt_shift++;
    349 
    350 		ASSERT3U(1ULL << zap->zap_f.zap_phys->zap_ptrtbl.zt_shift, ==,
    351 		    zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks <<
    352 		    (FZAP_BLOCK_SHIFT(zap)-3));
    353 
    354 		return (0);
    355 	} else {
    356 		return (zap_table_grow(zap, &zap->zap_f.zap_phys->zap_ptrtbl,
    357 		    zap_ptrtbl_transfer, tx));
    358 	}
    359 }
    360 
    361 static void
    362 zap_increment_num_entries(zap_t *zap, int delta, dmu_tx_t *tx)
    363 {
    364 	dmu_buf_will_dirty(zap->zap_dbuf, tx);
    365 	mutex_enter(&zap->zap_f.zap_num_entries_mtx);
    366 	ASSERT(delta > 0 || zap->zap_f.zap_phys->zap_num_entries >= -delta);
    367 	zap->zap_f.zap_phys->zap_num_entries += delta;
    368 	mutex_exit(&zap->zap_f.zap_num_entries_mtx);
    369 }
    370 
    371 static uint64_t
    372 zap_allocate_blocks(zap_t *zap, int nblocks)
    373 {
    374 	uint64_t newblk;
    375 	ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
    376 	newblk = zap->zap_f.zap_phys->zap_freeblk;
    377 	zap->zap_f.zap_phys->zap_freeblk += nblocks;
    378 	return (newblk);
    379 }
    380 
    381 static zap_leaf_t *
    382 zap_create_leaf(zap_t *zap, dmu_tx_t *tx)
    383 {
    384 	void *winner;
    385 	zap_leaf_t *l = kmem_alloc(sizeof (zap_leaf_t), KM_SLEEP);
    386 
    387 	ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
    388 
    389 	rw_init(&l->l_rwlock, 0, 0, 0);
    390 	rw_enter(&l->l_rwlock, RW_WRITER);
    391 	l->l_blkid = zap_allocate_blocks(zap, 1);
    392 	l->l_dbuf = NULL;
    393 	l->l_phys = NULL;
    394 
    395 	VERIFY(0 == dmu_buf_hold(zap->zap_objset, zap->zap_object,
    396 	    l->l_blkid << FZAP_BLOCK_SHIFT(zap), NULL, &l->l_dbuf));
    397 	winner = dmu_buf_set_user(l->l_dbuf, l, &l->l_phys, zap_leaf_pageout);
    398 	ASSERT(winner == NULL);
    399 	dmu_buf_will_dirty(l->l_dbuf, tx);
    400 
    401 	zap_leaf_init(l, zap->zap_normflags != 0);
    402 
    403 	zap->zap_f.zap_phys->zap_num_leafs++;
    404 
    405 	return (l);
    406 }
    407 
    408 int
    409 fzap_count(zap_t *zap, uint64_t *count)
    410 {
    411 	ASSERT(!zap->zap_ismicro);
    412 	mutex_enter(&zap->zap_f.zap_num_entries_mtx); /* unnecessary */
    413 	*count = zap->zap_f.zap_phys->zap_num_entries;
    414 	mutex_exit(&zap->zap_f.zap_num_entries_mtx);
    415 	return (0);
    416 }
    417 
    418 /*
    419  * Routines for obtaining zap_leaf_t's
    420  */
    421 
    422 void
    423 zap_put_leaf(zap_leaf_t *l)
    424 {
    425 	rw_exit(&l->l_rwlock);
    426 	dmu_buf_rele(l->l_dbuf, NULL);
    427 }
    428 
    429 _NOTE(ARGSUSED(0))
    430 static void
    431 zap_leaf_pageout(dmu_buf_t *db, void *vl)
    432 {
    433 	zap_leaf_t *l = vl;
    434 
    435 	rw_destroy(&l->l_rwlock);
    436 	kmem_free(l, sizeof (zap_leaf_t));
    437 }
    438 
    439 static zap_leaf_t *
    440 zap_open_leaf(uint64_t blkid, dmu_buf_t *db)
    441 {
    442 	zap_leaf_t *l, *winner;
    443 
    444 	ASSERT(blkid != 0);
    445 
    446 	l = kmem_alloc(sizeof (zap_leaf_t), KM_SLEEP);
    447 	rw_init(&l->l_rwlock, 0, 0, 0);
    448 	rw_enter(&l->l_rwlock, RW_WRITER);
    449 	l->l_blkid = blkid;
    450 	l->l_bs = highbit(db->db_size)-1;
    451 	l->l_dbuf = db;
    452 	l->l_phys = NULL;
    453 
    454 	winner = dmu_buf_set_user(db, l, &l->l_phys, zap_leaf_pageout);
    455 
    456 	rw_exit(&l->l_rwlock);
    457 	if (winner != NULL) {
    458 		/* someone else set it first */
    459 		zap_leaf_pageout(NULL, l);
    460 		l = winner;
    461 	}
    462 
    463 	/*
    464 	 * lhr_pad was previously used for the next leaf in the leaf
    465 	 * chain.  There should be no chained leafs (as we have removed
    466 	 * support for them).
    467 	 */
    468 	ASSERT3U(l->l_phys->l_hdr.lh_pad1, ==, 0);
    469 
    470 	/*
    471 	 * There should be more hash entries than there can be
    472 	 * chunks to put in the hash table
    473 	 */
    474 	ASSERT3U(ZAP_LEAF_HASH_NUMENTRIES(l), >, ZAP_LEAF_NUMCHUNKS(l) / 3);
    475 
    476 	/* The chunks should begin at the end of the hash table */
    477 	ASSERT3P(&ZAP_LEAF_CHUNK(l, 0), ==,
    478 	    &l->l_phys->l_hash[ZAP_LEAF_HASH_NUMENTRIES(l)]);
    479 
    480 	/* The chunks should end at the end of the block */
    481 	ASSERT3U((uintptr_t)&ZAP_LEAF_CHUNK(l, ZAP_LEAF_NUMCHUNKS(l)) -
    482 	    (uintptr_t)l->l_phys, ==, l->l_dbuf->db_size);
    483 
    484 	return (l);
    485 }
    486 
    487 static int
    488 zap_get_leaf_byblk(zap_t *zap, uint64_t blkid, dmu_tx_t *tx, krw_t lt,
    489     zap_leaf_t **lp)
    490 {
    491 	dmu_buf_t *db;
    492 	zap_leaf_t *l;
    493 	int bs = FZAP_BLOCK_SHIFT(zap);
    494 	int err;
    495 
    496 	ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    497 
    498 	err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
    499 	    blkid << bs, NULL, &db);
    500 	if (err)
    501 		return (err);
    502 
    503 	ASSERT3U(db->db_object, ==, zap->zap_object);
    504 	ASSERT3U(db->db_offset, ==, blkid << bs);
    505 	ASSERT3U(db->db_size, ==, 1 << bs);
    506 	ASSERT(blkid != 0);
    507 
    508 	l = dmu_buf_get_user(db);
    509 
    510 	if (l == NULL)
    511 		l = zap_open_leaf(blkid, db);
    512 
    513 	rw_enter(&l->l_rwlock, lt);
    514 	/*
    515 	 * Must lock before dirtying, otherwise l->l_phys could change,
    516 	 * causing ASSERT below to fail.
    517 	 */
    518 	if (lt == RW_WRITER)
    519 		dmu_buf_will_dirty(db, tx);
    520 	ASSERT3U(l->l_blkid, ==, blkid);
    521 	ASSERT3P(l->l_dbuf, ==, db);
    522 	ASSERT3P(l->l_phys, ==, l->l_dbuf->db_data);
    523 	ASSERT3U(l->l_phys->l_hdr.lh_block_type, ==, ZBT_LEAF);
    524 	ASSERT3U(l->l_phys->l_hdr.lh_magic, ==, ZAP_LEAF_MAGIC);
    525 
    526 	*lp = l;
    527 	return (0);
    528 }
    529 
    530 static int
    531 zap_idx_to_blk(zap_t *zap, uint64_t idx, uint64_t *valp)
    532 {
    533 	ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    534 
    535 	if (zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks == 0) {
    536 		ASSERT3U(idx, <,
    537 		    (1ULL << zap->zap_f.zap_phys->zap_ptrtbl.zt_shift));
    538 		*valp = ZAP_EMBEDDED_PTRTBL_ENT(zap, idx);
    539 		return (0);
    540 	} else {
    541 		return (zap_table_load(zap, &zap->zap_f.zap_phys->zap_ptrtbl,
    542 		    idx, valp));
    543 	}
    544 }
    545 
    546 static int
    547 zap_set_idx_to_blk(zap_t *zap, uint64_t idx, uint64_t blk, dmu_tx_t *tx)
    548 {
    549 	ASSERT(tx != NULL);
    550 	ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
    551 
    552 	if (zap->zap_f.zap_phys->zap_ptrtbl.zt_blk == 0) {
    553 		ZAP_EMBEDDED_PTRTBL_ENT(zap, idx) = blk;
    554 		return (0);
    555 	} else {
    556 		return (zap_table_store(zap, &zap->zap_f.zap_phys->zap_ptrtbl,
    557 		    idx, blk, tx));
    558 	}
    559 }
    560 
    561 static int
    562 zap_deref_leaf(zap_t *zap, uint64_t h, dmu_tx_t *tx, krw_t lt, zap_leaf_t **lp)
    563 {
    564 	uint64_t idx, blk;
    565 	int err;
    566 
    567 	ASSERT(zap->zap_dbuf == NULL ||
    568 	    zap->zap_f.zap_phys == zap->zap_dbuf->db_data);
    569 	ASSERT3U(zap->zap_f.zap_phys->zap_magic, ==, ZAP_MAGIC);
    570 	idx = ZAP_HASH_IDX(h, zap->zap_f.zap_phys->zap_ptrtbl.zt_shift);
    571 	err = zap_idx_to_blk(zap, idx, &blk);
    572 	if (err != 0)
    573 		return (err);
    574 	err = zap_get_leaf_byblk(zap, blk, tx, lt, lp);
    575 
    576 	ASSERT(err || ZAP_HASH_IDX(h, (*lp)->l_phys->l_hdr.lh_prefix_len) ==
    577 	    (*lp)->l_phys->l_hdr.lh_prefix);
    578 	return (err);
    579 }
    580 
    581 static int
    582 zap_expand_leaf(zap_name_t *zn, zap_leaf_t *l, dmu_tx_t *tx, zap_leaf_t **lp)
    583 {
    584 	zap_t *zap = zn->zn_zap;
    585 	uint64_t hash = zn->zn_hash;
    586 	zap_leaf_t *nl;
    587 	int prefix_diff, i, err;
    588 	uint64_t sibling;
    589 	int old_prefix_len = l->l_phys->l_hdr.lh_prefix_len;
    590 
    591 	ASSERT3U(old_prefix_len, <=, zap->zap_f.zap_phys->zap_ptrtbl.zt_shift);
    592 	ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    593 
    594 	ASSERT3U(ZAP_HASH_IDX(hash, old_prefix_len), ==,
    595 	    l->l_phys->l_hdr.lh_prefix);
    596 
    597 	if (zap_tryupgradedir(zap, tx) == 0 ||
    598 	    old_prefix_len == zap->zap_f.zap_phys->zap_ptrtbl.zt_shift) {
    599 		/* We failed to upgrade, or need to grow the pointer table */
    600 		objset_t *os = zap->zap_objset;
    601 		uint64_t object = zap->zap_object;
    602 
    603 		zap_put_leaf(l);
    604 		zap_unlockdir(zap);
    605 		err = zap_lockdir(os, object, tx, RW_WRITER,
    606 		    FALSE, FALSE, &zn->zn_zap);
    607 		zap = zn->zn_zap;
    608 		if (err)
    609 			return (err);
    610 		ASSERT(!zap->zap_ismicro);
    611 
    612 		while (old_prefix_len ==
    613 		    zap->zap_f.zap_phys->zap_ptrtbl.zt_shift) {
    614 			err = zap_grow_ptrtbl(zap, tx);
    615 			if (err)
    616 				return (err);
    617 		}
    618 
    619 		err = zap_deref_leaf(zap, hash, tx, RW_WRITER, &l);
    620 		if (err)
    621 			return (err);
    622 
    623 		if (l->l_phys->l_hdr.lh_prefix_len != old_prefix_len) {
    624 			/* it split while our locks were down */
    625 			*lp = l;
    626 			return (0);
    627 		}
    628 	}
    629 	ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
    630 	ASSERT3U(old_prefix_len, <, zap->zap_f.zap_phys->zap_ptrtbl.zt_shift);
    631 	ASSERT3U(ZAP_HASH_IDX(hash, old_prefix_len), ==,
    632 	    l->l_phys->l_hdr.lh_prefix);
    633 
    634 	prefix_diff = zap->zap_f.zap_phys->zap_ptrtbl.zt_shift -
    635 	    (old_prefix_len + 1);
    636 	sibling = (ZAP_HASH_IDX(hash, old_prefix_len + 1) | 1) << prefix_diff;
    637 
    638 	/* check for i/o errors before doing zap_leaf_split */
    639 	for (i = 0; i < (1ULL<<prefix_diff); i++) {
    640 		uint64_t blk;
    641 		err = zap_idx_to_blk(zap, sibling+i, &blk);
    642 		if (err)
    643 			return (err);
    644 		ASSERT3U(blk, ==, l->l_blkid);
    645 	}
    646 
    647 	nl = zap_create_leaf(zap, tx);
    648 	zap_leaf_split(l, nl, zap->zap_normflags != 0);
    649 
    650 	/* set sibling pointers */
    651 	for (i = 0; i < (1ULL<<prefix_diff); i++) {
    652 		err = zap_set_idx_to_blk(zap, sibling+i, nl->l_blkid, tx);
    653 		ASSERT3U(err, ==, 0); /* we checked for i/o errors above */
    654 	}
    655 
    656 	if (hash & (1ULL << (64 - l->l_phys->l_hdr.lh_prefix_len))) {
    657 		/* we want the sibling */
    658 		zap_put_leaf(l);
    659 		*lp = nl;
    660 	} else {
    661 		zap_put_leaf(nl);
    662 		*lp = l;
    663 	}
    664 
    665 	return (0);
    666 }
    667 
    668 static void
    669 zap_put_leaf_maybe_grow_ptrtbl(zap_name_t *zn, zap_leaf_t *l, dmu_tx_t *tx)
    670 {
    671 	zap_t *zap = zn->zn_zap;
    672 	int shift = zap->zap_f.zap_phys->zap_ptrtbl.zt_shift;
    673 	int leaffull = (l->l_phys->l_hdr.lh_prefix_len == shift &&
    674 	    l->l_phys->l_hdr.lh_nfree < ZAP_LEAF_LOW_WATER);
    675 
    676 	zap_put_leaf(l);
    677 
    678 	if (leaffull || zap->zap_f.zap_phys->zap_ptrtbl.zt_nextblk) {
    679 		int err;
    680 
    681 		/*
    682 		 * We are in the middle of growing the pointer table, or
    683 		 * this leaf will soon make us grow it.
    684 		 */
    685 		if (zap_tryupgradedir(zap, tx) == 0) {
    686 			objset_t *os = zap->zap_objset;
    687 			uint64_t zapobj = zap->zap_object;
    688 
    689 			zap_unlockdir(zap);
    690 			err = zap_lockdir(os, zapobj, tx,
    691 			    RW_WRITER, FALSE, FALSE, &zn->zn_zap);
    692 			zap = zn->zn_zap;
    693 			if (err)
    694 				return;
    695 		}
    696 
    697 		/* could have finished growing while our locks were down */
    698 		if (zap->zap_f.zap_phys->zap_ptrtbl.zt_shift == shift)
    699 			(void) zap_grow_ptrtbl(zap, tx);
    700 	}
    701 }
    702 
    703 
    704 static int
    705 fzap_checksize(const char *name, uint64_t integer_size, uint64_t num_integers)
    706 {
    707 	if (name && strlen(name) > ZAP_MAXNAMELEN)
    708 		return (E2BIG);
    709 
    710 	/* Only integer sizes supported by C */
    711 	switch (integer_size) {
    712 	case 1:
    713 	case 2:
    714 	case 4:
    715 	case 8:
    716 		break;
    717 	default:
    718 		return (EINVAL);
    719 	}
    720 
    721 	if (integer_size * num_integers > ZAP_MAXVALUELEN)
    722 		return (E2BIG);
    723 
    724 	return (0);
    725 }
    726 
    727 /*
    728  * Routines for manipulating attributes.
    729  */
    730 int
    731 fzap_lookup(zap_name_t *zn,
    732     uint64_t integer_size, uint64_t num_integers, void *buf,
    733     char *realname, int rn_len, boolean_t *ncp)
    734 {
    735 	zap_leaf_t *l;
    736 	int err;
    737 	zap_entry_handle_t zeh;
    738 
    739 	err = fzap_checksize(zn->zn_name_orij, integer_size, num_integers);
    740 	if (err != 0)
    741 		return (err);
    742 
    743 	err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, NULL, RW_READER, &l);
    744 	if (err != 0)
    745 		return (err);
    746 	err = zap_leaf_lookup(l, zn, &zeh);
    747 	if (err == 0) {
    748 		err = zap_entry_read(&zeh, integer_size, num_integers, buf);
    749 		(void) zap_entry_read_name(&zeh, rn_len, realname);
    750 		if (ncp) {
    751 			*ncp = zap_entry_normalization_conflict(&zeh,
    752 			    zn, NULL, zn->zn_zap);
    753 		}
    754 	}
    755 
    756 	zap_put_leaf(l);
    757 	return (err);
    758 }
    759 
    760 int
    761 fzap_add_cd(zap_name_t *zn,
    762     uint64_t integer_size, uint64_t num_integers,
    763     const void *val, uint32_t cd, dmu_tx_t *tx)
    764 {
    765 	zap_leaf_t *l;
    766 	int err;
    767 	zap_entry_handle_t zeh;
    768 	zap_t *zap = zn->zn_zap;
    769 
    770 	ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    771 	ASSERT(!zap->zap_ismicro);
    772 	ASSERT(fzap_checksize(zn->zn_name_orij,
    773 	    integer_size, num_integers) == 0);
    774 
    775 	err = zap_deref_leaf(zap, zn->zn_hash, tx, RW_WRITER, &l);
    776 	if (err != 0)
    777 		return (err);
    778 retry:
    779 	err = zap_leaf_lookup(l, zn, &zeh);
    780 	if (err == 0) {
    781 		err = EEXIST;
    782 		goto out;
    783 	}
    784 	if (err != ENOENT)
    785 		goto out;
    786 
    787 	err = zap_entry_create(l, zn->zn_name_orij, zn->zn_hash, cd,
    788 	    integer_size, num_integers, val, &zeh);
    789 
    790 	if (err == 0) {
    791 		zap_increment_num_entries(zap, 1, tx);
    792 	} else if (err == EAGAIN) {
    793 		err = zap_expand_leaf(zn, l, tx, &l);
    794 		zap = zn->zn_zap;	/* zap_expand_leaf() may change zap */
    795 		if (err == 0)
    796 			goto retry;
    797 	}
    798 
    799 out:
    800 	if (zap != NULL)
    801 		zap_put_leaf_maybe_grow_ptrtbl(zn, l, tx);
    802 	return (err);
    803 }
    804 
    805 int
    806 fzap_add(zap_name_t *zn,
    807     uint64_t integer_size, uint64_t num_integers,
    808     const void *val, dmu_tx_t *tx)
    809 {
    810 	int err = fzap_checksize(zn->zn_name_orij, integer_size, num_integers);
    811 	if (err != 0)
    812 		return (err);
    813 
    814 	return (fzap_add_cd(zn, integer_size, num_integers,
    815 	    val, ZAP_MAXCD, tx));
    816 }
    817 
    818 int
    819 fzap_update(zap_name_t *zn,
    820     int integer_size, uint64_t num_integers, const void *val, dmu_tx_t *tx)
    821 {
    822 	zap_leaf_t *l;
    823 	int err, create;
    824 	zap_entry_handle_t zeh;
    825 	zap_t *zap = zn->zn_zap;
    826 
    827 	ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    828 	err = fzap_checksize(zn->zn_name_orij, integer_size, num_integers);
    829 	if (err != 0)
    830 		return (err);
    831 
    832 	err = zap_deref_leaf(zap, zn->zn_hash, tx, RW_WRITER, &l);
    833 	if (err != 0)
    834 		return (err);
    835 retry:
    836 	err = zap_leaf_lookup(l, zn, &zeh);
    837 	create = (err == ENOENT);
    838 	ASSERT(err == 0 || err == ENOENT);
    839 
    840 	if (create) {
    841 		err = zap_entry_create(l, zn->zn_name_orij, zn->zn_hash,
    842 		    ZAP_MAXCD, integer_size, num_integers, val, &zeh);
    843 		if (err == 0)
    844 			zap_increment_num_entries(zap, 1, tx);
    845 	} else {
    846 		err = zap_entry_update(&zeh, integer_size, num_integers, val);
    847 	}
    848 
    849 	if (err == EAGAIN) {
    850 		err = zap_expand_leaf(zn, l, tx, &l);
    851 		zap = zn->zn_zap;	/* zap_expand_leaf() may change zap */
    852 		if (err == 0)
    853 			goto retry;
    854 	}
    855 
    856 	if (zap != NULL)
    857 		zap_put_leaf_maybe_grow_ptrtbl(zn, l, tx);
    858 	return (err);
    859 }
    860 
    861 int
    862 fzap_length(zap_name_t *zn,
    863     uint64_t *integer_size, uint64_t *num_integers)
    864 {
    865 	zap_leaf_t *l;
    866 	int err;
    867 	zap_entry_handle_t zeh;
    868 
    869 	err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, NULL, RW_READER, &l);
    870 	if (err != 0)
    871 		return (err);
    872 	err = zap_leaf_lookup(l, zn, &zeh);
    873 	if (err != 0)
    874 		goto out;
    875 
    876 	if (integer_size)
    877 		*integer_size = zeh.zeh_integer_size;
    878 	if (num_integers)
    879 		*num_integers = zeh.zeh_num_integers;
    880 out:
    881 	zap_put_leaf(l);
    882 	return (err);
    883 }
    884 
    885 int
    886 fzap_remove(zap_name_t *zn, dmu_tx_t *tx)
    887 {
    888 	zap_leaf_t *l;
    889 	int err;
    890 	zap_entry_handle_t zeh;
    891 
    892 	err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, tx, RW_WRITER, &l);
    893 	if (err != 0)
    894 		return (err);
    895 	err = zap_leaf_lookup(l, zn, &zeh);
    896 	if (err == 0) {
    897 		zap_entry_remove(&zeh);
    898 		zap_increment_num_entries(zn->zn_zap, -1, tx);
    899 	}
    900 	zap_put_leaf(l);
    901 	return (err);
    902 }
    903 
    904 /*
    905  * Helper functions for consumers.
    906  */
    907 
    908 int
    909 zap_value_search(objset_t *os, uint64_t zapobj, uint64_t value, uint64_t mask,
    910     char *name)
    911 {
    912 	zap_cursor_t zc;
    913 	zap_attribute_t *za;
    914 	int err;
    915 
    916 	if (mask == 0)
    917 		mask = -1ULL;
    918 
    919 	za = kmem_alloc(sizeof (zap_attribute_t), KM_SLEEP);
    920 	for (zap_cursor_init(&zc, os, zapobj);
    921 	    (err = zap_cursor_retrieve(&zc, za)) == 0;
    922 	    zap_cursor_advance(&zc)) {
    923 		if ((za->za_first_integer & mask) == (value & mask)) {
    924 			(void) strcpy(name, za->za_name);
    925 			break;
    926 		}
    927 	}
    928 	zap_cursor_fini(&zc);
    929 	kmem_free(za, sizeof (zap_attribute_t));
    930 	return (err);
    931 }
    932 
    933 int
    934 zap_join(objset_t *os, uint64_t fromobj, uint64_t intoobj, dmu_tx_t *tx)
    935 {
    936 	zap_cursor_t zc;
    937 	zap_attribute_t za;
    938 	int err;
    939 
    940 	for (zap_cursor_init(&zc, os, fromobj);
    941 	    zap_cursor_retrieve(&zc, &za) == 0;
    942 	    (void) zap_cursor_advance(&zc)) {
    943 		if (za.za_integer_length != 8 || za.za_num_integers != 1)
    944 			return (EINVAL);
    945 		err = zap_add(os, intoobj, za.za_name,
    946 		    8, 1, &za.za_first_integer, tx);
    947 		if (err)
    948 			return (err);
    949 	}
    950 	zap_cursor_fini(&zc);
    951 	return (0);
    952 }
    953 
    954 int
    955 zap_add_int(objset_t *os, uint64_t obj, uint64_t value, dmu_tx_t *tx)
    956 {
    957 	char name[20];
    958 
    959 	(void) snprintf(name, sizeof (name), "%llx", (longlong_t)value);
    960 	return (zap_add(os, obj, name, 8, 1, &value, tx));
    961 }
    962 
    963 int
    964 zap_remove_int(objset_t *os, uint64_t obj, uint64_t value, dmu_tx_t *tx)
    965 {
    966 	char name[20];
    967 
    968 	(void) snprintf(name, sizeof (name), "%llx", (longlong_t)value);
    969 	return (zap_remove(os, obj, name, tx));
    970 }
    971 
    972 int
    973 zap_lookup_int(objset_t *os, uint64_t obj, uint64_t value)
    974 {
    975 	char name[20];
    976 
    977 	(void) snprintf(name, sizeof (name), "%llx", (longlong_t)value);
    978 	return (zap_lookup(os, obj, name, 8, 1, &value));
    979 }
    980 
    981 /*
    982  * Routines for iterating over the attributes.
    983  */
    984 
    985 int
    986 fzap_cursor_retrieve(zap_t *zap, zap_cursor_t *zc, zap_attribute_t *za)
    987 {
    988 	int err = ENOENT;
    989 	zap_entry_handle_t zeh;
    990 	zap_leaf_t *l;
    991 
    992 	/* retrieve the next entry at or after zc_hash/zc_cd */
    993 	/* if no entry, return ENOENT */
    994 
    995 	if (zc->zc_leaf &&
    996 	    (ZAP_HASH_IDX(zc->zc_hash,
    997 	    zc->zc_leaf->l_phys->l_hdr.lh_prefix_len) !=
    998 	    zc->zc_leaf->l_phys->l_hdr.lh_prefix)) {
    999 		rw_enter(&zc->zc_leaf->l_rwlock, RW_READER);
   1000 		zap_put_leaf(zc->zc_leaf);
   1001 		zc->zc_leaf = NULL;
   1002 	}
   1003 
   1004 again:
   1005 	if (zc->zc_leaf == NULL) {
   1006 		err = zap_deref_leaf(zap, zc->zc_hash, NULL, RW_READER,
   1007 		    &zc->zc_leaf);
   1008 		if (err != 0)
   1009 			return (err);
   1010 	} else {
   1011 		rw_enter(&zc->zc_leaf->l_rwlock, RW_READER);
   1012 	}
   1013 	l = zc->zc_leaf;
   1014 
   1015 	err = zap_leaf_lookup_closest(l, zc->zc_hash, zc->zc_cd, &zeh);
   1016 
   1017 	if (err == ENOENT) {
   1018 		uint64_t nocare =
   1019 		    (1ULL << (64 - l->l_phys->l_hdr.lh_prefix_len)) - 1;
   1020 		zc->zc_hash = (zc->zc_hash & ~nocare) + nocare + 1;
   1021 		zc->zc_cd = 0;
   1022 		if (l->l_phys->l_hdr.lh_prefix_len == 0 || zc->zc_hash == 0) {
   1023 			zc->zc_hash = -1ULL;
   1024 		} else {
   1025 			zap_put_leaf(zc->zc_leaf);
   1026 			zc->zc_leaf = NULL;
   1027 			goto again;
   1028 		}
   1029 	}
   1030 
   1031 	if (err == 0) {
   1032 		zc->zc_hash = zeh.zeh_hash;
   1033 		zc->zc_cd = zeh.zeh_cd;
   1034 		za->za_integer_length = zeh.zeh_integer_size;
   1035 		za->za_num_integers = zeh.zeh_num_integers;
   1036 		if (zeh.zeh_num_integers == 0) {
   1037 			za->za_first_integer = 0;
   1038 		} else {
   1039 			err = zap_entry_read(&zeh, 8, 1, &za->za_first_integer);
   1040 			ASSERT(err == 0 || err == EOVERFLOW);
   1041 		}
   1042 		err = zap_entry_read_name(&zeh,
   1043 		    sizeof (za->za_name), za->za_name);
   1044 		ASSERT(err == 0);
   1045 
   1046 		za->za_normalization_conflict =
   1047 		    zap_entry_normalization_conflict(&zeh,
   1048 		    NULL, za->za_name, zap);
   1049 	}
   1050 	rw_exit(&zc->zc_leaf->l_rwlock);
   1051 	return (err);
   1052 }
   1053 
   1054 
   1055 static void
   1056 zap_stats_ptrtbl(zap_t *zap, uint64_t *tbl, int len, zap_stats_t *zs)
   1057 {
   1058 	int i, err;
   1059 	uint64_t lastblk = 0;
   1060 
   1061 	/*
   1062 	 * NB: if a leaf has more pointers than an entire ptrtbl block
   1063 	 * can hold, then it'll be accounted for more than once, since
   1064 	 * we won't have lastblk.
   1065 	 */
   1066 	for (i = 0; i < len; i++) {
   1067 		zap_leaf_t *l;
   1068 
   1069 		if (tbl[i] == lastblk)
   1070 			continue;
   1071 		lastblk = tbl[i];
   1072 
   1073 		err = zap_get_leaf_byblk(zap, tbl[i], NULL, RW_READER, &l);
   1074 		if (err == 0) {
   1075 			zap_leaf_stats(zap, l, zs);
   1076 			zap_put_leaf(l);
   1077 		}
   1078 	}
   1079 }
   1080 
   1081 void
   1082 fzap_get_stats(zap_t *zap, zap_stats_t *zs)
   1083 {
   1084 	int bs = FZAP_BLOCK_SHIFT(zap);
   1085 	zs->zs_blocksize = 1ULL << bs;
   1086 
   1087 	/*
   1088 	 * Set zap_phys_t fields
   1089 	 */
   1090 	zs->zs_num_leafs = zap->zap_f.zap_phys->zap_num_leafs;
   1091 	zs->zs_num_entries = zap->zap_f.zap_phys->zap_num_entries;
   1092 	zs->zs_num_blocks = zap->zap_f.zap_phys->zap_freeblk;
   1093 	zs->zs_block_type = zap->zap_f.zap_phys->zap_block_type;
   1094 	zs->zs_magic = zap->zap_f.zap_phys->zap_magic;
   1095 	zs->zs_salt = zap->zap_f.zap_phys->zap_salt;
   1096 
   1097 	/*
   1098 	 * Set zap_ptrtbl fields
   1099 	 */
   1100 	zs->zs_ptrtbl_len = 1ULL << zap->zap_f.zap_phys->zap_ptrtbl.zt_shift;
   1101 	zs->zs_ptrtbl_nextblk = zap->zap_f.zap_phys->zap_ptrtbl.zt_nextblk;
   1102 	zs->zs_ptrtbl_blks_copied =
   1103 	    zap->zap_f.zap_phys->zap_ptrtbl.zt_blks_copied;
   1104 	zs->zs_ptrtbl_zt_blk = zap->zap_f.zap_phys->zap_ptrtbl.zt_blk;
   1105 	zs->zs_ptrtbl_zt_numblks = zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks;
   1106 	zs->zs_ptrtbl_zt_shift = zap->zap_f.zap_phys->zap_ptrtbl.zt_shift;
   1107 
   1108 	if (zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks == 0) {
   1109 		/* the ptrtbl is entirely in the header block. */
   1110 		zap_stats_ptrtbl(zap, &ZAP_EMBEDDED_PTRTBL_ENT(zap, 0),
   1111 		    1 << ZAP_EMBEDDED_PTRTBL_SHIFT(zap), zs);
   1112 	} else {
   1113 		int b;
   1114 
   1115 		dmu_prefetch(zap->zap_objset, zap->zap_object,
   1116 		    zap->zap_f.zap_phys->zap_ptrtbl.zt_blk << bs,
   1117 		    zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks << bs);
   1118 
   1119 		for (b = 0; b < zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks;
   1120 		    b++) {
   1121 			dmu_buf_t *db;
   1122 			int err;
   1123 
   1124 			err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
   1125 			    (zap->zap_f.zap_phys->zap_ptrtbl.zt_blk + b) << bs,
   1126 			    FTAG, &db);
   1127 			if (err == 0) {
   1128 				zap_stats_ptrtbl(zap, db->db_data,
   1129 				    1<<(bs-3), zs);
   1130 				dmu_buf_rele(db, FTAG);
   1131 			}
   1132 		}
   1133 	}
   1134 }
   1135 
   1136 int
   1137 fzap_count_write(zap_name_t *zn, int add, uint64_t *towrite,
   1138     uint64_t *tooverwrite)
   1139 {
   1140 	zap_t *zap = zn->zn_zap;
   1141 	zap_leaf_t *l;
   1142 	int err;
   1143 
   1144 	/*
   1145 	 * Account for the header block of the fatzap.
   1146 	 */
   1147 	if (!add && dmu_buf_freeable(zap->zap_dbuf)) {
   1148 		tooverwrite += zap->zap_dbuf->db_size;
   1149 	} else {
   1150 		towrite += zap->zap_dbuf->db_size;
   1151 	}
   1152 
   1153 	/*
   1154 	 * Account for the pointer table blocks.
   1155 	 * If we are adding we need to account for the following cases :
   1156 	 * - If the pointer table is embedded, this operation could force an
   1157 	 *   external pointer table.
   1158 	 * - If this already has an external pointer table this operation
   1159 	 *   could extend the table.
   1160 	 */
   1161 	if (add) {
   1162 		if (zap->zap_f.zap_phys->zap_ptrtbl.zt_blk == 0)
   1163 			towrite += zap->zap_dbuf->db_size;
   1164 		else
   1165 			towrite += (zap->zap_dbuf->db_size * 3);
   1166 	}
   1167 
   1168 	/*
   1169 	 * Now, check if the block containing leaf is freeable
   1170 	 * and account accordingly.
   1171 	 */
   1172 	err = zap_deref_leaf(zap, zn->zn_hash, NULL, RW_READER, &l);
   1173 	if (err != 0) {
   1174 		return (err);
   1175 	}
   1176 
   1177 	if (!add && dmu_buf_freeable(l->l_dbuf)) {
   1178 		tooverwrite += l->l_dbuf->db_size;
   1179 	} else {
   1180 		/*
   1181 		 * If this an add operation, the leaf block could split.
   1182 		 * Hence, we need to account for an additional leaf block.
   1183 		 */
   1184 		towrite += (add ? 2 : 1) * l->l_dbuf->db_size;
   1185 	}
   1186 
   1187 	zap_put_leaf(l);
   1188 	return (0);
   1189 }
   1190