xref: /freebsd/sys/contrib/openzfs/module/zfs/dbuf.c (revision bb2d13b686e3ccf6c3ccb36209dfb7dcc108b182)

/*
 * 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 2011 Nexenta Systems, Inc.  All rights reserved.
 * Copyright (c) 2012, 2020 by Delphix. All rights reserved.
 * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
 * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
 * Copyright (c) 2019, Klara Inc.
 * Copyright (c) 2019, Allan Jude
 */

#include <sys/zfs_context.h>
#include <sys/arc.h>
#include <sys/dmu.h>
#include <sys/dmu_send.h>
#include <sys/dmu_impl.h>
#include <sys/dbuf.h>
#include <sys/dmu_objset.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_dir.h>
#include <sys/dmu_tx.h>
#include <sys/spa.h>
#include <sys/zio.h>
#include <sys/dmu_zfetch.h>
#include <sys/sa.h>
#include <sys/sa_impl.h>
#include <sys/zfeature.h>
#include <sys/blkptr.h>
#include <sys/range_tree.h>
#include <sys/trace_zfs.h>
#include <sys/callb.h>
#include <sys/abd.h>
#include <sys/vdev.h>
#include <cityhash.h>
#include <sys/spa_impl.h>
#include <sys/wmsum.h>
#include <sys/vdev_impl.h>

static kstat_t *dbuf_ksp;

typedef struct dbuf_stats {
	/*
	 * Various statistics about the size of the dbuf cache.
	 */
	kstat_named_t cache_count;
	kstat_named_t cache_size_bytes;
	kstat_named_t cache_size_bytes_max;
	/*
	 * Statistics regarding the bounds on the dbuf cache size.
	 */
	kstat_named_t cache_target_bytes;
	kstat_named_t cache_lowater_bytes;
	kstat_named_t cache_hiwater_bytes;
	/*
	 * Total number of dbuf cache evictions that have occurred.
	 */
	kstat_named_t cache_total_evicts;
	/*
	 * The distribution of dbuf levels in the dbuf cache and
	 * the total size of all dbufs at each level.
	 */
	kstat_named_t cache_levels[DN_MAX_LEVELS];
	kstat_named_t cache_levels_bytes[DN_MAX_LEVELS];
	/*
	 * Statistics about the dbuf hash table.
	 */
	kstat_named_t hash_hits;
	kstat_named_t hash_misses;
	kstat_named_t hash_collisions;
	kstat_named_t hash_elements;
	kstat_named_t hash_elements_max;
	/*
	 * Number of sublists containing more than one dbuf in the dbuf
	 * hash table. Keep track of the longest hash chain.
	 */
	kstat_named_t hash_chains;
	kstat_named_t hash_chain_max;
	/*
	 * Number of times a dbuf_create() discovers that a dbuf was
	 * already created and in the dbuf hash table.
	 */
	kstat_named_t hash_insert_race;
	/*
	 * Number of entries in the hash table dbuf and mutex arrays.
	 */
	kstat_named_t hash_table_count;
	kstat_named_t hash_mutex_count;
	/*
	 * Statistics about the size of the metadata dbuf cache.
	 */
	kstat_named_t metadata_cache_count;
	kstat_named_t metadata_cache_size_bytes;
	kstat_named_t metadata_cache_size_bytes_max;
	/*
	 * For diagnostic purposes, this is incremented whenever we can't add
	 * something to the metadata cache because it's full, and instead put
	 * the data in the regular dbuf cache.
	 */
	kstat_named_t metadata_cache_overflow;
} dbuf_stats_t;

dbuf_stats_t dbuf_stats = {
	{ "cache_count",			KSTAT_DATA_UINT64 },
	{ "cache_size_bytes",			KSTAT_DATA_UINT64 },
	{ "cache_size_bytes_max",		KSTAT_DATA_UINT64 },
	{ "cache_target_bytes",			KSTAT_DATA_UINT64 },
	{ "cache_lowater_bytes",		KSTAT_DATA_UINT64 },
	{ "cache_hiwater_bytes",		KSTAT_DATA_UINT64 },
	{ "cache_total_evicts",			KSTAT_DATA_UINT64 },
	{ { "cache_levels_N",			KSTAT_DATA_UINT64 } },
	{ { "cache_levels_bytes_N",		KSTAT_DATA_UINT64 } },
	{ "hash_hits",				KSTAT_DATA_UINT64 },
	{ "hash_misses",			KSTAT_DATA_UINT64 },
	{ "hash_collisions",			KSTAT_DATA_UINT64 },
	{ "hash_elements",			KSTAT_DATA_UINT64 },
	{ "hash_elements_max",			KSTAT_DATA_UINT64 },
	{ "hash_chains",			KSTAT_DATA_UINT64 },
	{ "hash_chain_max",			KSTAT_DATA_UINT64 },
	{ "hash_insert_race",			KSTAT_DATA_UINT64 },
	{ "hash_table_count",			KSTAT_DATA_UINT64 },
	{ "hash_mutex_count",			KSTAT_DATA_UINT64 },
	{ "metadata_cache_count",		KSTAT_DATA_UINT64 },
	{ "metadata_cache_size_bytes",		KSTAT_DATA_UINT64 },
	{ "metadata_cache_size_bytes_max",	KSTAT_DATA_UINT64 },
	{ "metadata_cache_overflow",		KSTAT_DATA_UINT64 }
};

struct {
	wmsum_t cache_count;
	wmsum_t cache_total_evicts;
	wmsum_t cache_levels[DN_MAX_LEVELS];
	wmsum_t cache_levels_bytes[DN_MAX_LEVELS];
	wmsum_t hash_hits;
	wmsum_t hash_misses;
	wmsum_t hash_collisions;
	wmsum_t hash_chains;
	wmsum_t hash_insert_race;
	wmsum_t metadata_cache_count;
	wmsum_t metadata_cache_overflow;
} dbuf_sums;

#define	DBUF_STAT_INCR(stat, val)	\
	wmsum_add(&dbuf_sums.stat, val);
#define	DBUF_STAT_DECR(stat, val)	\
	DBUF_STAT_INCR(stat, -(val));
#define	DBUF_STAT_BUMP(stat)		\
	DBUF_STAT_INCR(stat, 1);
#define	DBUF_STAT_BUMPDOWN(stat)	\
	DBUF_STAT_INCR(stat, -1);
#define	DBUF_STAT_MAX(stat, v) {					\
	uint64_t _m;							\
	while ((v) > (_m = dbuf_stats.stat.value.ui64) &&		\
	    (_m != atomic_cas_64(&dbuf_stats.stat.value.ui64, _m, (v))))\
		continue;						\
}

static boolean_t dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx);
static void dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx);
static void dbuf_sync_leaf_verify_bonus_dnode(dbuf_dirty_record_t *dr);
static int dbuf_read_verify_dnode_crypt(dmu_buf_impl_t *db, uint32_t flags);

/*
 * Global data structures and functions for the dbuf cache.
 */
static kmem_cache_t *dbuf_kmem_cache;
static taskq_t *dbu_evict_taskq;

static kthread_t *dbuf_cache_evict_thread;
static kmutex_t dbuf_evict_lock;
static kcondvar_t dbuf_evict_cv;
static boolean_t dbuf_evict_thread_exit;

/*
 * There are two dbuf caches; each dbuf can only be in one of them at a time.
 *
 * 1. Cache of metadata dbufs, to help make read-heavy administrative commands
 *    from /sbin/zfs run faster. The "metadata cache" specifically stores dbufs
 *    that represent the metadata that describes filesystems/snapshots/
 *    bookmarks/properties/etc. We only evict from this cache when we export a
 *    pool, to short-circuit as much I/O as possible for all administrative
 *    commands that need the metadata. There is no eviction policy for this
 *    cache, because we try to only include types in it which would occupy a
 *    very small amount of space per object but create a large impact on the
 *    performance of these commands. Instead, after it reaches a maximum size
 *    (which should only happen on very small memory systems with a very large
 *    number of filesystem objects), we stop taking new dbufs into the
 *    metadata cache, instead putting them in the normal dbuf cache.
 *
 * 2. LRU cache of dbufs. The dbuf cache maintains a list of dbufs that
 *    are not currently held but have been recently released. These dbufs
 *    are not eligible for arc eviction until they are aged out of the cache.
 *    Dbufs that are aged out of the cache will be immediately destroyed and
 *    become eligible for arc eviction.
 *
 * Dbufs are added to these caches once the last hold is released. If a dbuf is
 * later accessed and still exists in the dbuf cache, then it will be removed
 * from the cache and later re-added to the head of the cache.
 *
 * If a given dbuf meets the requirements for the metadata cache, it will go
 * there, otherwise it will be considered for the generic LRU dbuf cache. The
 * caches and the refcounts tracking their sizes are stored in an array indexed
 * by those caches' matching enum values (from dbuf_cached_state_t).
 */
typedef struct dbuf_cache {
	multilist_t cache;
	zfs_refcount_t size ____cacheline_aligned;
} dbuf_cache_t;
dbuf_cache_t dbuf_caches[DB_CACHE_MAX];

/* Size limits for the caches */
static uint64_t dbuf_cache_max_bytes = UINT64_MAX;
static uint64_t dbuf_metadata_cache_max_bytes = UINT64_MAX;

/* Set the default sizes of the caches to log2 fraction of arc size */
static uint_t dbuf_cache_shift = 5;
static uint_t dbuf_metadata_cache_shift = 6;

/* Set the dbuf hash mutex count as log2 shift (dynamic by default) */
static uint_t dbuf_mutex_cache_shift = 0;

static unsigned long dbuf_cache_target_bytes(void);
static unsigned long dbuf_metadata_cache_target_bytes(void);

/*
 * The LRU dbuf cache uses a three-stage eviction policy:
 *	- A low water marker designates when the dbuf eviction thread
 *	should stop evicting from the dbuf cache.
 *	- When we reach the maximum size (aka mid water mark), we
 *	signal the eviction thread to run.
 *	- The high water mark indicates when the eviction thread
 *	is unable to keep up with the incoming load and eviction must
 *	happen in the context of the calling thread.
 *
 * The dbuf cache:
 *                                                 (max size)
 *                                      low water   mid water   hi water
 * +----------------------------------------+----------+----------+
 * |                                        |          |          |
 * |                                        |          |          |
 * |                                        |          |          |
 * |                                        |          |          |
 * +----------------------------------------+----------+----------+
 *                                        stop        signal     evict
 *                                      evicting     eviction   directly
 *                                                    thread
 *
 * The high and low water marks indicate the operating range for the eviction
 * thread. The low water mark is, by default, 90% of the total size of the
 * cache and the high water mark is at 110% (both of these percentages can be
 * changed by setting dbuf_cache_lowater_pct and dbuf_cache_hiwater_pct,
 * respectively). The eviction thread will try to ensure that the cache remains
 * within this range by waking up every second and checking if the cache is
 * above the low water mark. The thread can also be woken up by callers adding
 * elements into the cache if the cache is larger than the mid water (i.e max
 * cache size). Once the eviction thread is woken up and eviction is required,
 * it will continue evicting buffers until it's able to reduce the cache size
 * to the low water mark. If the cache size continues to grow and hits the high
 * water mark, then callers adding elements to the cache will begin to evict
 * directly from the cache until the cache is no longer above the high water
 * mark.
 */

/*
 * The percentage above and below the maximum cache size.
 */
static uint_t dbuf_cache_hiwater_pct = 10;
static uint_t dbuf_cache_lowater_pct = 10;

static int
dbuf_cons(void *vdb, void *unused, int kmflag)
{
	(void) unused, (void) kmflag;
	dmu_buf_impl_t *db = vdb;
	memset(db, 0, sizeof (dmu_buf_impl_t));

	mutex_init(&db->db_mtx, NULL, MUTEX_DEFAULT, NULL);
	rw_init(&db->db_rwlock, NULL, RW_DEFAULT, NULL);
	cv_init(&db->db_changed, NULL, CV_DEFAULT, NULL);
	multilist_link_init(&db->db_cache_link);
	zfs_refcount_create(&db->db_holds);

	return (0);
}

static void
dbuf_dest(void *vdb, void *unused)
{
	(void) unused;
	dmu_buf_impl_t *db = vdb;
	mutex_destroy(&db->db_mtx);
	rw_destroy(&db->db_rwlock);
	cv_destroy(&db->db_changed);
	ASSERT(!multilist_link_active(&db->db_cache_link));
	zfs_refcount_destroy(&db->db_holds);
}

/*
 * dbuf hash table routines
 */
static dbuf_hash_table_t dbuf_hash_table;

/*
 * We use Cityhash for this. It's fast, and has good hash properties without
 * requiring any large static buffers.
 */
static uint64_t
dbuf_hash(void *os, uint64_t obj, uint8_t lvl, uint64_t blkid)
{
	return (cityhash4((uintptr_t)os, obj, (uint64_t)lvl, blkid));
}

#define	DTRACE_SET_STATE(db, why) \
	DTRACE_PROBE2(dbuf__state_change, dmu_buf_impl_t *, db,	\
	    const char *, why)

#define	DBUF_EQUAL(dbuf, os, obj, level, blkid)		\
	((dbuf)->db.db_object == (obj) &&		\
	(dbuf)->db_objset == (os) &&			\
	(dbuf)->db_level == (level) &&			\
	(dbuf)->db_blkid == (blkid))

dmu_buf_impl_t *
dbuf_find(objset_t *os, uint64_t obj, uint8_t level, uint64_t blkid)
{
	dbuf_hash_table_t *h = &dbuf_hash_table;
	uint64_t hv;
	uint64_t idx;
	dmu_buf_impl_t *db;

	hv = dbuf_hash(os, obj, level, blkid);
	idx = hv & h->hash_table_mask;

	mutex_enter(DBUF_HASH_MUTEX(h, idx));
	for (db = h->hash_table[idx]; db != NULL; db = db->db_hash_next) {
		if (DBUF_EQUAL(db, os, obj, level, blkid)) {
			mutex_enter(&db->db_mtx);
			if (db->db_state != DB_EVICTING) {
				mutex_exit(DBUF_HASH_MUTEX(h, idx));
				return (db);
			}
			mutex_exit(&db->db_mtx);
		}
	}
	mutex_exit(DBUF_HASH_MUTEX(h, idx));
	return (NULL);
}

static dmu_buf_impl_t *
dbuf_find_bonus(objset_t *os, uint64_t object)
{
	dnode_t *dn;
	dmu_buf_impl_t *db = NULL;

	if (dnode_hold(os, object, FTAG, &dn) == 0) {
		rw_enter(&dn->dn_struct_rwlock, RW_READER);
		if (dn->dn_bonus != NULL) {
			db = dn->dn_bonus;
			mutex_enter(&db->db_mtx);
		}
		rw_exit(&dn->dn_struct_rwlock);
		dnode_rele(dn, FTAG);
	}
	return (db);
}

/*
 * Insert an entry into the hash table.  If there is already an element
 * equal to elem in the hash table, then the already existing element
 * will be returned and the new element will not be inserted.
 * Otherwise returns NULL.
 */
static dmu_buf_impl_t *
dbuf_hash_insert(dmu_buf_impl_t *db)
{
	dbuf_hash_table_t *h = &dbuf_hash_table;
	objset_t *os = db->db_objset;
	uint64_t obj = db->db.db_object;
	int level = db->db_level;
	uint64_t blkid, hv, idx;
	dmu_buf_impl_t *dbf;
	uint32_t i;

	blkid = db->db_blkid;
	hv = dbuf_hash(os, obj, level, blkid);
	idx = hv & h->hash_table_mask;

	mutex_enter(DBUF_HASH_MUTEX(h, idx));
	for (dbf = h->hash_table[idx], i = 0; dbf != NULL;
	    dbf = dbf->db_hash_next, i++) {
		if (DBUF_EQUAL(dbf, os, obj, level, blkid)) {
			mutex_enter(&dbf->db_mtx);
			if (dbf->db_state != DB_EVICTING) {
				mutex_exit(DBUF_HASH_MUTEX(h, idx));
				return (dbf);
			}
			mutex_exit(&dbf->db_mtx);
		}
	}

	if (i > 0) {
		DBUF_STAT_BUMP(hash_collisions);
		if (i == 1)
			DBUF_STAT_BUMP(hash_chains);

		DBUF_STAT_MAX(hash_chain_max, i);
	}

	mutex_enter(&db->db_mtx);
	db->db_hash_next = h->hash_table[idx];
	h->hash_table[idx] = db;
	mutex_exit(DBUF_HASH_MUTEX(h, idx));
	uint64_t he = atomic_inc_64_nv(&dbuf_stats.hash_elements.value.ui64);
	DBUF_STAT_MAX(hash_elements_max, he);

	return (NULL);
}

/*
 * This returns whether this dbuf should be stored in the metadata cache, which
 * is based on whether it's from one of the dnode types that store data related
 * to traversing dataset hierarchies.
 */
static boolean_t
dbuf_include_in_metadata_cache(dmu_buf_impl_t *db)
{
	DB_DNODE_ENTER(db);
	dmu_object_type_t type = DB_DNODE(db)->dn_type;
	DB_DNODE_EXIT(db);

	/* Check if this dbuf is one of the types we care about */
	if (DMU_OT_IS_METADATA_CACHED(type)) {
		/* If we hit this, then we set something up wrong in dmu_ot */
		ASSERT(DMU_OT_IS_METADATA(type));

		/*
		 * Sanity check for small-memory systems: don't allocate too
		 * much memory for this purpose.
		 */
		if (zfs_refcount_count(
		    &dbuf_caches[DB_DBUF_METADATA_CACHE].size) >
		    dbuf_metadata_cache_target_bytes()) {
			DBUF_STAT_BUMP(metadata_cache_overflow);
			return (B_FALSE);
		}

		return (B_TRUE);
	}

	return (B_FALSE);
}

/*
 * Remove an entry from the hash table.  It must be in the EVICTING state.
 */
static void
dbuf_hash_remove(dmu_buf_impl_t *db)
{
	dbuf_hash_table_t *h = &dbuf_hash_table;
	uint64_t hv, idx;
	dmu_buf_impl_t *dbf, **dbp;

	hv = dbuf_hash(db->db_objset, db->db.db_object,
	    db->db_level, db->db_blkid);
	idx = hv & h->hash_table_mask;

	/*
	 * We mustn't hold db_mtx to maintain lock ordering:
	 * DBUF_HASH_MUTEX > db_mtx.
	 */
	ASSERT(zfs_refcount_is_zero(&db->db_holds));
	ASSERT(db->db_state == DB_EVICTING);
	ASSERT(!MUTEX_HELD(&db->db_mtx));

	mutex_enter(DBUF_HASH_MUTEX(h, idx));
	dbp = &h->hash_table[idx];
	while ((dbf = *dbp) != db) {
		dbp = &dbf->db_hash_next;
		ASSERT(dbf != NULL);
	}
	*dbp = db->db_hash_next;
	db->db_hash_next = NULL;
	if (h->hash_table[idx] &&
	    h->hash_table[idx]->db_hash_next == NULL)
		DBUF_STAT_BUMPDOWN(hash_chains);
	mutex_exit(DBUF_HASH_MUTEX(h, idx));
	atomic_dec_64(&dbuf_stats.hash_elements.value.ui64);
}

typedef enum {
	DBVU_EVICTING,
	DBVU_NOT_EVICTING
} dbvu_verify_type_t;

static void
dbuf_verify_user(dmu_buf_impl_t *db, dbvu_verify_type_t verify_type)
{
#ifdef ZFS_DEBUG
	int64_t holds;

	if (db->db_user == NULL)
		return;

	/* Only data blocks support the attachment of user data. */
	ASSERT(db->db_level == 0);

	/* Clients must resolve a dbuf before attaching user data. */
	ASSERT(db->db.db_data != NULL);
	ASSERT3U(db->db_state, ==, DB_CACHED);

	holds = zfs_refcount_count(&db->db_holds);
	if (verify_type == DBVU_EVICTING) {
		/*
		 * Immediate eviction occurs when holds == dirtycnt.
		 * For normal eviction buffers, holds is zero on
		 * eviction, except when dbuf_fix_old_data() calls
		 * dbuf_clear_data().  However, the hold count can grow
		 * during eviction even though db_mtx is held (see
		 * dmu_bonus_hold() for an example), so we can only
		 * test the generic invariant that holds >= dirtycnt.
		 */
		ASSERT3U(holds, >=, db->db_dirtycnt);
	} else {
		if (db->db_user_immediate_evict == TRUE)
			ASSERT3U(holds, >=, db->db_dirtycnt);
		else
			ASSERT3U(holds, >, 0);
	}
#endif
}

static void
dbuf_evict_user(dmu_buf_impl_t *db)
{
	dmu_buf_user_t *dbu = db->db_user;

	ASSERT(MUTEX_HELD(&db->db_mtx));

	if (dbu == NULL)
		return;

	dbuf_verify_user(db, DBVU_EVICTING);
	db->db_user = NULL;

#ifdef ZFS_DEBUG
	if (dbu->dbu_clear_on_evict_dbufp != NULL)
		*dbu->dbu_clear_on_evict_dbufp = NULL;
#endif

	/*
	 * There are two eviction callbacks - one that we call synchronously
	 * and one that we invoke via a taskq.  The async one is useful for
	 * avoiding lock order reversals and limiting stack depth.
	 *
	 * Note that if we have a sync callback but no async callback,
	 * it's likely that the sync callback will free the structure
	 * containing the dbu.  In that case we need to take care to not
	 * dereference dbu after calling the sync evict func.
	 */
	boolean_t has_async = (dbu->dbu_evict_func_async != NULL);

	if (dbu->dbu_evict_func_sync != NULL)
		dbu->dbu_evict_func_sync(dbu);

	if (has_async) {
		taskq_dispatch_ent(dbu_evict_taskq, dbu->dbu_evict_func_async,
		    dbu, 0, &dbu->dbu_tqent);
	}
}

boolean_t
dbuf_is_metadata(dmu_buf_impl_t *db)
{
	/*
	 * Consider indirect blocks and spill blocks to be meta data.
	 */
	if (db->db_level > 0 || db->db_blkid == DMU_SPILL_BLKID) {
		return (B_TRUE);
	} else {
		boolean_t is_metadata;

		DB_DNODE_ENTER(db);
		is_metadata = DMU_OT_IS_METADATA(DB_DNODE(db)->dn_type);
		DB_DNODE_EXIT(db);

		return (is_metadata);
	}
}

/*
 * We want to exclude buffers that are on a special allocation class from
 * L2ARC.
 */
boolean_t
dbuf_is_l2cacheable(dmu_buf_impl_t *db)
{
	vdev_t *vd = NULL;
	zfs_cache_type_t cache = db->db_objset->os_secondary_cache;
	blkptr_t *bp = db->db_blkptr;

	if (bp != NULL && !BP_IS_HOLE(bp)) {
		uint64_t vdev = DVA_GET_VDEV(bp->blk_dva);
		vdev_t *rvd = db->db_objset->os_spa->spa_root_vdev;

		if (vdev < rvd->vdev_children)
			vd = rvd->vdev_child[vdev];

		if (cache == ZFS_CACHE_ALL ||
		    (dbuf_is_metadata(db) && cache == ZFS_CACHE_METADATA)) {
			if (vd == NULL)
				return (B_TRUE);

			if ((vd->vdev_alloc_bias != VDEV_BIAS_SPECIAL &&
			    vd->vdev_alloc_bias != VDEV_BIAS_DEDUP) ||
			    l2arc_exclude_special == 0)
				return (B_TRUE);
		}
	}

	return (B_FALSE);
}

static inline boolean_t
dnode_level_is_l2cacheable(blkptr_t *bp, dnode_t *dn, int64_t level)
{
	vdev_t *vd = NULL;
	zfs_cache_type_t cache = dn->dn_objset->os_secondary_cache;

	if (bp != NULL && !BP_IS_HOLE(bp)) {
		uint64_t vdev = DVA_GET_VDEV(bp->blk_dva);
		vdev_t *rvd = dn->dn_objset->os_spa->spa_root_vdev;

		if (vdev < rvd->vdev_children)
			vd = rvd->vdev_child[vdev];

		if (cache == ZFS_CACHE_ALL || ((level > 0 ||
		    DMU_OT_IS_METADATA(dn->dn_handle->dnh_dnode->dn_type)) &&
		    cache == ZFS_CACHE_METADATA)) {
			if (vd == NULL)
				return (B_TRUE);

			if ((vd->vdev_alloc_bias != VDEV_BIAS_SPECIAL &&
			    vd->vdev_alloc_bias != VDEV_BIAS_DEDUP) ||
			    l2arc_exclude_special == 0)
				return (B_TRUE);
		}
	}

	return (B_FALSE);
}


/*
 * This function *must* return indices evenly distributed between all
 * sublists of the multilist. This is needed due to how the dbuf eviction
 * code is laid out; dbuf_evict_thread() assumes dbufs are evenly
 * distributed between all sublists and uses this assumption when
 * deciding which sublist to evict from and how much to evict from it.
 */
static unsigned int
dbuf_cache_multilist_index_func(multilist_t *ml, void *obj)
{
	dmu_buf_impl_t *db = obj;

	/*
	 * The assumption here, is the hash value for a given
	 * dmu_buf_impl_t will remain constant throughout it's lifetime
	 * (i.e. it's objset, object, level and blkid fields don't change).
	 * Thus, we don't need to store the dbuf's sublist index
	 * on insertion, as this index can be recalculated on removal.
	 *
	 * Also, the low order bits of the hash value are thought to be
	 * distributed evenly. Otherwise, in the case that the multilist
	 * has a power of two number of sublists, each sublists' usage
	 * would not be evenly distributed. In this context full 64bit
	 * division would be a waste of time, so limit it to 32 bits.
	 */
	return ((unsigned int)dbuf_hash(db->db_objset, db->db.db_object,
	    db->db_level, db->db_blkid) %
	    multilist_get_num_sublists(ml));
}

/*
 * The target size of the dbuf cache can grow with the ARC target,
 * unless limited by the tunable dbuf_cache_max_bytes.
 */
static inline unsigned long
dbuf_cache_target_bytes(void)
{
	return (MIN(dbuf_cache_max_bytes,
	    arc_target_bytes() >> dbuf_cache_shift));
}

/*
 * The target size of the dbuf metadata cache can grow with the ARC target,
 * unless limited by the tunable dbuf_metadata_cache_max_bytes.
 */
static inline unsigned long
dbuf_metadata_cache_target_bytes(void)
{
	return (MIN(dbuf_metadata_cache_max_bytes,
	    arc_target_bytes() >> dbuf_metadata_cache_shift));
}

static inline uint64_t
dbuf_cache_hiwater_bytes(void)
{
	uint64_t dbuf_cache_target = dbuf_cache_target_bytes();
	return (dbuf_cache_target +
	    (dbuf_cache_target * dbuf_cache_hiwater_pct) / 100);
}

static inline uint64_t
dbuf_cache_lowater_bytes(void)
{
	uint64_t dbuf_cache_target = dbuf_cache_target_bytes();
	return (dbuf_cache_target -
	    (dbuf_cache_target * dbuf_cache_lowater_pct) / 100);
}

static inline boolean_t
dbuf_cache_above_lowater(void)
{
	return (zfs_refcount_count(&dbuf_caches[DB_DBUF_CACHE].size) >
	    dbuf_cache_lowater_bytes());
}

/*
 * Evict the oldest eligible dbuf from the dbuf cache.
 */
static void
dbuf_evict_one(void)
{
	int idx = multilist_get_random_index(&dbuf_caches[DB_DBUF_CACHE].cache);
	multilist_sublist_t *mls = multilist_sublist_lock(
	    &dbuf_caches[DB_DBUF_CACHE].cache, idx);

	ASSERT(!MUTEX_HELD(&dbuf_evict_lock));

	dmu_buf_impl_t *db = multilist_sublist_tail(mls);
	while (db != NULL && mutex_tryenter(&db->db_mtx) == 0) {
		db = multilist_sublist_prev(mls, db);
	}

	DTRACE_PROBE2(dbuf__evict__one, dmu_buf_impl_t *, db,
	    multilist_sublist_t *, mls);

	if (db != NULL) {
		multilist_sublist_remove(mls, db);
		multilist_sublist_unlock(mls);
		(void) zfs_refcount_remove_many(
		    &dbuf_caches[DB_DBUF_CACHE].size, db->db.db_size, db);
		DBUF_STAT_BUMPDOWN(cache_levels[db->db_level]);
		DBUF_STAT_BUMPDOWN(cache_count);
		DBUF_STAT_DECR(cache_levels_bytes[db->db_level],
		    db->db.db_size);
		ASSERT3U(db->db_caching_status, ==, DB_DBUF_CACHE);
		db->db_caching_status = DB_NO_CACHE;
		dbuf_destroy(db);
		DBUF_STAT_BUMP(cache_total_evicts);
	} else {
		multilist_sublist_unlock(mls);
	}
}

/*
 * The dbuf evict thread is responsible for aging out dbufs from the
 * cache. Once the cache has reached it's maximum size, dbufs are removed
 * and destroyed. The eviction thread will continue running until the size
 * of the dbuf cache is at or below the maximum size. Once the dbuf is aged
 * out of the cache it is destroyed and becomes eligible for arc eviction.
 */
static __attribute__((noreturn)) void
dbuf_evict_thread(void *unused)
{
	(void) unused;
	callb_cpr_t cpr;

	CALLB_CPR_INIT(&cpr, &dbuf_evict_lock, callb_generic_cpr, FTAG);

	mutex_enter(&dbuf_evict_lock);
	while (!dbuf_evict_thread_exit) {
		while (!dbuf_cache_above_lowater() && !dbuf_evict_thread_exit) {
			CALLB_CPR_SAFE_BEGIN(&cpr);
			(void) cv_timedwait_idle_hires(&dbuf_evict_cv,
			    &dbuf_evict_lock, SEC2NSEC(1), MSEC2NSEC(1), 0);
			CALLB_CPR_SAFE_END(&cpr, &dbuf_evict_lock);
		}
		mutex_exit(&dbuf_evict_lock);

		/*
		 * Keep evicting as long as we're above the low water mark
		 * for the cache. We do this without holding the locks to
		 * minimize lock contention.
		 */
		while (dbuf_cache_above_lowater() && !dbuf_evict_thread_exit) {
			dbuf_evict_one();
		}

		mutex_enter(&dbuf_evict_lock);
	}

	dbuf_evict_thread_exit = B_FALSE;
	cv_broadcast(&dbuf_evict_cv);
	CALLB_CPR_EXIT(&cpr);	/* drops dbuf_evict_lock */
	thread_exit();
}

/*
 * Wake up the dbuf eviction thread if the dbuf cache is at its max size.
 * If the dbuf cache is at its high water mark, then evict a dbuf from the
 * dbuf cache using the caller's context.
 */
static void
dbuf_evict_notify(uint64_t size)
{
	/*
	 * We check if we should evict without holding the dbuf_evict_lock,
	 * because it's OK to occasionally make the wrong decision here,
	 * and grabbing the lock results in massive lock contention.
	 */
	if (size > dbuf_cache_target_bytes()) {
		if (size > dbuf_cache_hiwater_bytes())
			dbuf_evict_one();
		cv_signal(&dbuf_evict_cv);
	}
}

static int
dbuf_kstat_update(kstat_t *ksp, int rw)
{
	dbuf_stats_t *ds = ksp->ks_data;
	dbuf_hash_table_t *h = &dbuf_hash_table;

	if (rw == KSTAT_WRITE)
		return (SET_ERROR(EACCES));

	ds->cache_count.value.ui64 =
	    wmsum_value(&dbuf_sums.cache_count);
	ds->cache_size_bytes.value.ui64 =
	    zfs_refcount_count(&dbuf_caches[DB_DBUF_CACHE].size);
	ds->cache_target_bytes.value.ui64 = dbuf_cache_target_bytes();
	ds->cache_hiwater_bytes.value.ui64 = dbuf_cache_hiwater_bytes();
	ds->cache_lowater_bytes.value.ui64 = dbuf_cache_lowater_bytes();
	ds->cache_total_evicts.value.ui64 =
	    wmsum_value(&dbuf_sums.cache_total_evicts);
	for (int i = 0; i < DN_MAX_LEVELS; i++) {
		ds->cache_levels[i].value.ui64 =
		    wmsum_value(&dbuf_sums.cache_levels[i]);
		ds->cache_levels_bytes[i].value.ui64 =
		    wmsum_value(&dbuf_sums.cache_levels_bytes[i]);
	}
	ds->hash_hits.value.ui64 =
	    wmsum_value(&dbuf_sums.hash_hits);
	ds->hash_misses.value.ui64 =
	    wmsum_value(&dbuf_sums.hash_misses);
	ds->hash_collisions.value.ui64 =
	    wmsum_value(&dbuf_sums.hash_collisions);
	ds->hash_chains.value.ui64 =
	    wmsum_value(&dbuf_sums.hash_chains);
	ds->hash_insert_race.value.ui64 =
	    wmsum_value(&dbuf_sums.hash_insert_race);
	ds->hash_table_count.value.ui64 = h->hash_table_mask + 1;
	ds->hash_mutex_count.value.ui64 = h->hash_mutex_mask + 1;
	ds->metadata_cache_count.value.ui64 =
	    wmsum_value(&dbuf_sums.metadata_cache_count);
	ds->metadata_cache_size_bytes.value.ui64 = zfs_refcount_count(
	    &dbuf_caches[DB_DBUF_METADATA_CACHE].size);
	ds->metadata_cache_overflow.value.ui64 =
	    wmsum_value(&dbuf_sums.metadata_cache_overflow);
	return (0);
}

void
dbuf_init(void)
{
	uint64_t hmsize, hsize = 1ULL << 16;
	dbuf_hash_table_t *h = &dbuf_hash_table;

	/*
	 * The hash table is big enough to fill one eighth of physical memory
	 * with an average block size of zfs_arc_average_blocksize (default 8K).
	 * By default, the table will take up
	 * totalmem * sizeof(void*) / 8K (1MB per GB with 8-byte pointers).
	 */
	while (hsize * zfs_arc_average_blocksize < arc_all_memory() / 8)
		hsize <<= 1;

	h->hash_table = NULL;
	while (h->hash_table == NULL) {
		h->hash_table_mask = hsize - 1;

		h->hash_table = vmem_zalloc(hsize * sizeof (void *), KM_SLEEP);
		if (h->hash_table == NULL)
			hsize >>= 1;

		ASSERT3U(hsize, >=, 1ULL << 10);
	}

	/*
	 * The hash table buckets are protected by an array of mutexes where
	 * each mutex is reponsible for protecting 128 buckets.  A minimum
	 * array size of 8192 is targeted to avoid contention.
	 */
	if (dbuf_mutex_cache_shift == 0)
		hmsize = MAX(hsize >> 7, 1ULL << 13);
	else
		hmsize = 1ULL << MIN(dbuf_mutex_cache_shift, 24);

	h->hash_mutexes = NULL;
	while (h->hash_mutexes == NULL) {
		h->hash_mutex_mask = hmsize - 1;

		h->hash_mutexes = vmem_zalloc(hmsize * sizeof (kmutex_t),
		    KM_SLEEP);
		if (h->hash_mutexes == NULL)
			hmsize >>= 1;
	}

	dbuf_kmem_cache = kmem_cache_create("dmu_buf_impl_t",
	    sizeof (dmu_buf_impl_t),
	    0, dbuf_cons, dbuf_dest, NULL, NULL, NULL, 0);

	for (int i = 0; i < hmsize; i++)
		mutex_init(&h->hash_mutexes[i], NULL, MUTEX_DEFAULT, NULL);

	dbuf_stats_init(h);

	/*
	 * All entries are queued via taskq_dispatch_ent(), so min/maxalloc
	 * configuration is not required.
	 */
	dbu_evict_taskq = taskq_create("dbu_evict", 1, defclsyspri, 0, 0, 0);

	for (dbuf_cached_state_t dcs = 0; dcs < DB_CACHE_MAX; dcs++) {
		multilist_create(&dbuf_caches[dcs].cache,
		    sizeof (dmu_buf_impl_t),
		    offsetof(dmu_buf_impl_t, db_cache_link),
		    dbuf_cache_multilist_index_func);
		zfs_refcount_create(&dbuf_caches[dcs].size);
	}

	dbuf_evict_thread_exit = B_FALSE;
	mutex_init(&dbuf_evict_lock, NULL, MUTEX_DEFAULT, NULL);
	cv_init(&dbuf_evict_cv, NULL, CV_DEFAULT, NULL);
	dbuf_cache_evict_thread = thread_create(NULL, 0, dbuf_evict_thread,
	    NULL, 0, &p0, TS_RUN, minclsyspri);

	wmsum_init(&dbuf_sums.cache_count, 0);
	wmsum_init(&dbuf_sums.cache_total_evicts, 0);
	for (int i = 0; i < DN_MAX_LEVELS; i++) {
		wmsum_init(&dbuf_sums.cache_levels[i], 0);
		wmsum_init(&dbuf_sums.cache_levels_bytes[i], 0);
	}
	wmsum_init(&dbuf_sums.hash_hits, 0);
	wmsum_init(&dbuf_sums.hash_misses, 0);
	wmsum_init(&dbuf_sums.hash_collisions, 0);
	wmsum_init(&dbuf_sums.hash_chains, 0);
	wmsum_init(&dbuf_sums.hash_insert_race, 0);
	wmsum_init(&dbuf_sums.metadata_cache_count, 0);
	wmsum_init(&dbuf_sums.metadata_cache_overflow, 0);

	dbuf_ksp = kstat_create("zfs", 0, "dbufstats", "misc",
	    KSTAT_TYPE_NAMED, sizeof (dbuf_stats) / sizeof (kstat_named_t),
	    KSTAT_FLAG_VIRTUAL);
	if (dbuf_ksp != NULL) {
		for (int i = 0; i < DN_MAX_LEVELS; i++) {
			snprintf(dbuf_stats.cache_levels[i].name,
			    KSTAT_STRLEN, "cache_level_%d", i);
			dbuf_stats.cache_levels[i].data_type =
			    KSTAT_DATA_UINT64;
			snprintf(dbuf_stats.cache_levels_bytes[i].name,
			    KSTAT_STRLEN, "cache_level_%d_bytes", i);
			dbuf_stats.cache_levels_bytes[i].data_type =
			    KSTAT_DATA_UINT64;
		}
		dbuf_ksp->ks_data = &dbuf_stats;
		dbuf_ksp->ks_update = dbuf_kstat_update;
		kstat_install(dbuf_ksp);
	}
}

void
dbuf_fini(void)
{
	dbuf_hash_table_t *h = &dbuf_hash_table;

	dbuf_stats_destroy();

	for (int i = 0; i < (h->hash_mutex_mask + 1); i++)
		mutex_destroy(&h->hash_mutexes[i]);

	vmem_free(h->hash_table, (h->hash_table_mask + 1) * sizeof (void *));
	vmem_free(h->hash_mutexes, (h->hash_mutex_mask + 1) *
	    sizeof (kmutex_t));

	kmem_cache_destroy(dbuf_kmem_cache);
	taskq_destroy(dbu_evict_taskq);

	mutex_enter(&dbuf_evict_lock);
	dbuf_evict_thread_exit = B_TRUE;
	while (dbuf_evict_thread_exit) {
		cv_signal(&dbuf_evict_cv);
		cv_wait(&dbuf_evict_cv, &dbuf_evict_lock);
	}
	mutex_exit(&dbuf_evict_lock);

	mutex_destroy(&dbuf_evict_lock);
	cv_destroy(&dbuf_evict_cv);

	for (dbuf_cached_state_t dcs = 0; dcs < DB_CACHE_MAX; dcs++) {
		zfs_refcount_destroy(&dbuf_caches[dcs].size);
		multilist_destroy(&dbuf_caches[dcs].cache);
	}

	if (dbuf_ksp != NULL) {
		kstat_delete(dbuf_ksp);
		dbuf_ksp = NULL;
	}

	wmsum_fini(&dbuf_sums.cache_count);
	wmsum_fini(&dbuf_sums.cache_total_evicts);
	for (int i = 0; i < DN_MAX_LEVELS; i++) {
		wmsum_fini(&dbuf_sums.cache_levels[i]);
		wmsum_fini(&dbuf_sums.cache_levels_bytes[i]);
	}
	wmsum_fini(&dbuf_sums.hash_hits);
	wmsum_fini(&dbuf_sums.hash_misses);
	wmsum_fini(&dbuf_sums.hash_collisions);
	wmsum_fini(&dbuf_sums.hash_chains);
	wmsum_fini(&dbuf_sums.hash_insert_race);
	wmsum_fini(&dbuf_sums.metadata_cache_count);
	wmsum_fini(&dbuf_sums.metadata_cache_overflow);
}

/*
 * Other stuff.
 */

#ifdef ZFS_DEBUG
static void
dbuf_verify(dmu_buf_impl_t *db)
{
	dnode_t *dn;
	dbuf_dirty_record_t *dr;
	uint32_t txg_prev;

	ASSERT(MUTEX_HELD(&db->db_mtx));

	if (!(zfs_flags & ZFS_DEBUG_DBUF_VERIFY))
		return;

	ASSERT(db->db_objset != NULL);
	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);
	if (dn == NULL) {
		ASSERT(db->db_parent == NULL);
		ASSERT(db->db_blkptr == NULL);
	} else {
		ASSERT3U(db->db.db_object, ==, dn->dn_object);
		ASSERT3P(db->db_objset, ==, dn->dn_objset);
		ASSERT3U(db->db_level, <, dn->dn_nlevels);
		ASSERT(db->db_blkid == DMU_BONUS_BLKID ||
		    db->db_blkid == DMU_SPILL_BLKID ||
		    !avl_is_empty(&dn->dn_dbufs));
	}
	if (db->db_blkid == DMU_BONUS_BLKID) {
		ASSERT(dn != NULL);
		ASSERT3U(db->db.db_size, >=, dn->dn_bonuslen);
		ASSERT3U(db->db.db_offset, ==, DMU_BONUS_BLKID);
	} else if (db->db_blkid == DMU_SPILL_BLKID) {
		ASSERT(dn != NULL);
		ASSERT0(db->db.db_offset);
	} else {
		ASSERT3U(db->db.db_offset, ==, db->db_blkid * db->db.db_size);
	}

	if ((dr = list_head(&db->db_dirty_records)) != NULL) {
		ASSERT(dr->dr_dbuf == db);
		txg_prev = dr->dr_txg;
		for (dr = list_next(&db->db_dirty_records, dr); dr != NULL;
		    dr = list_next(&db->db_dirty_records, dr)) {
			ASSERT(dr->dr_dbuf == db);
			ASSERT(txg_prev > dr->dr_txg);
			txg_prev = dr->dr_txg;
		}
	}

	/*
	 * We can't assert that db_size matches dn_datablksz because it
	 * can be momentarily different when another thread is doing
	 * dnode_set_blksz().
	 */
	if (db->db_level == 0 && db->db.db_object == DMU_META_DNODE_OBJECT) {
		dr = db->db_data_pending;
		/*
		 * It should only be modified in syncing context, so
		 * make sure we only have one copy of the data.
		 */
		ASSERT(dr == NULL || dr->dt.dl.dr_data == db->db_buf);
	}

	/* verify db->db_blkptr */
	if (db->db_blkptr) {
		if (db->db_parent == dn->dn_dbuf) {
			/* db is pointed to by the dnode */
			/* ASSERT3U(db->db_blkid, <, dn->dn_nblkptr); */
			if (DMU_OBJECT_IS_SPECIAL(db->db.db_object))
				ASSERT(db->db_parent == NULL);
			else
				ASSERT(db->db_parent != NULL);
			if (db->db_blkid != DMU_SPILL_BLKID)
				ASSERT3P(db->db_blkptr, ==,
				    &dn->dn_phys->dn_blkptr[db->db_blkid]);
		} else {
			/* db is pointed to by an indirect block */
			int epb __maybe_unused = db->db_parent->db.db_size >>
			    SPA_BLKPTRSHIFT;
			ASSERT3U(db->db_parent->db_level, ==, db->db_level+1);
			ASSERT3U(db->db_parent->db.db_object, ==,
			    db->db.db_object);
			/*
			 * dnode_grow_indblksz() can make this fail if we don't
			 * have the parent's rwlock.  XXX indblksz no longer
			 * grows.  safe to do this now?
			 */
			if (RW_LOCK_HELD(&db->db_parent->db_rwlock)) {
				ASSERT3P(db->db_blkptr, ==,
				    ((blkptr_t *)db->db_parent->db.db_data +
				    db->db_blkid % epb));
			}
		}
	}
	if ((db->db_blkptr == NULL || BP_IS_HOLE(db->db_blkptr)) &&
	    (db->db_buf == NULL || db->db_buf->b_data) &&
	    db->db.db_data && db->db_blkid != DMU_BONUS_BLKID &&
	    db->db_state != DB_FILL && !dn->dn_free_txg) {
		/*
		 * If the blkptr isn't set but they have nonzero data,
		 * it had better be dirty, otherwise we'll lose that
		 * data when we evict this buffer.
		 *
		 * There is an exception to this rule for indirect blocks; in
		 * this case, if the indirect block is a hole, we fill in a few
		 * fields on each of the child blocks (importantly, birth time)
		 * to prevent hole birth times from being lost when you
		 * partially fill in a hole.
		 */
		if (db->db_dirtycnt == 0) {
			if (db->db_level == 0) {
				uint64_t *buf = db->db.db_data;
				int i;

				for (i = 0; i < db->db.db_size >> 3; i++) {
					ASSERT(buf[i] == 0);
				}
			} else {
				blkptr_t *bps = db->db.db_data;
				ASSERT3U(1 << DB_DNODE(db)->dn_indblkshift, ==,
				    db->db.db_size);
				/*
				 * We want to verify that all the blkptrs in the
				 * indirect block are holes, but we may have
				 * automatically set up a few fields for them.
				 * We iterate through each blkptr and verify
				 * they only have those fields set.
				 */
				for (int i = 0;
				    i < db->db.db_size / sizeof (blkptr_t);
				    i++) {
					blkptr_t *bp = &bps[i];
					ASSERT(ZIO_CHECKSUM_IS_ZERO(
					    &bp->blk_cksum));
					ASSERT(
					    DVA_IS_EMPTY(&bp->blk_dva[0]) &&
					    DVA_IS_EMPTY(&bp->blk_dva[1]) &&
					    DVA_IS_EMPTY(&bp->blk_dva[2]));
					ASSERT0(bp->blk_fill);
					ASSERT0(bp->blk_pad[0]);
					ASSERT0(bp->blk_pad[1]);
					ASSERT(!BP_IS_EMBEDDED(bp));
					ASSERT(BP_IS_HOLE(bp));
					ASSERT0(bp->blk_phys_birth);
				}
			}
		}
	}
	DB_DNODE_EXIT(db);
}
#endif

static void
dbuf_clear_data(dmu_buf_impl_t *db)
{
	ASSERT(MUTEX_HELD(&db->db_mtx));
	dbuf_evict_user(db);
	ASSERT3P(db->db_buf, ==, NULL);
	db->db.db_data = NULL;
	if (db->db_state != DB_NOFILL) {
		db->db_state = DB_UNCACHED;
		DTRACE_SET_STATE(db, "clear data");
	}
}

static void
dbuf_set_data(dmu_buf_impl_t *db, arc_buf_t *buf)
{
	ASSERT(MUTEX_HELD(&db->db_mtx));
	ASSERT(buf != NULL);

	db->db_buf = buf;
	ASSERT(buf->b_data != NULL);
	db->db.db_data = buf->b_data;
}

static arc_buf_t *
dbuf_alloc_arcbuf(dmu_buf_impl_t *db)
{
	spa_t *spa = db->db_objset->os_spa;

	return (arc_alloc_buf(spa, db, DBUF_GET_BUFC_TYPE(db), db->db.db_size));
}

/*
 * Loan out an arc_buf for read.  Return the loaned arc_buf.
 */
arc_buf_t *
dbuf_loan_arcbuf(dmu_buf_impl_t *db)
{
	arc_buf_t *abuf;

	ASSERT(db->db_blkid != DMU_BONUS_BLKID);
	mutex_enter(&db->db_mtx);
	if (arc_released(db->db_buf) || zfs_refcount_count(&db->db_holds) > 1) {
		int blksz = db->db.db_size;
		spa_t *spa = db->db_objset->os_spa;

		mutex_exit(&db->db_mtx);
		abuf = arc_loan_buf(spa, B_FALSE, blksz);
		memcpy(abuf->b_data, db->db.db_data, blksz);
	} else {
		abuf = db->db_buf;
		arc_loan_inuse_buf(abuf, db);
		db->db_buf = NULL;
		dbuf_clear_data(db);
		mutex_exit(&db->db_mtx);
	}
	return (abuf);
}

/*
 * Calculate which level n block references the data at the level 0 offset
 * provided.
 */
uint64_t
dbuf_whichblock(const dnode_t *dn, const int64_t level, const uint64_t offset)
{
	if (dn->dn_datablkshift != 0 && dn->dn_indblkshift != 0) {
		/*
		 * The level n blkid is equal to the level 0 blkid divided by
		 * the number of level 0s in a level n block.
		 *
		 * The level 0 blkid is offset >> datablkshift =
		 * offset / 2^datablkshift.
		 *
		 * The number of level 0s in a level n is the number of block
		 * pointers in an indirect block, raised to the power of level.
		 * This is 2^(indblkshift - SPA_BLKPTRSHIFT)^level =
		 * 2^(level*(indblkshift - SPA_BLKPTRSHIFT)).
		 *
		 * Thus, the level n blkid is: offset /
		 * ((2^datablkshift)*(2^(level*(indblkshift-SPA_BLKPTRSHIFT))))
		 * = offset / 2^(datablkshift + level *
		 *   (indblkshift - SPA_BLKPTRSHIFT))
		 * = offset >> (datablkshift + level *
		 *   (indblkshift - SPA_BLKPTRSHIFT))
		 */

		const unsigned exp = dn->dn_datablkshift +
		    level * (dn->dn_indblkshift - SPA_BLKPTRSHIFT);

		if (exp >= 8 * sizeof (offset)) {
			/* This only happens on the highest indirection level */
			ASSERT3U(level, ==, dn->dn_nlevels - 1);
			return (0);
		}

		ASSERT3U(exp, <, 8 * sizeof (offset));

		return (offset >> exp);
	} else {
		ASSERT3U(offset, <, dn->dn_datablksz);
		return (0);
	}
}

/*
 * This function is used to lock the parent of the provided dbuf. This should be
 * used when modifying or reading db_blkptr.
 */
db_lock_type_t
dmu_buf_lock_parent(dmu_buf_impl_t *db, krw_t rw, const void *tag)
{
	enum db_lock_type ret = DLT_NONE;
	if (db->db_parent != NULL) {
		rw_enter(&db->db_parent->db_rwlock, rw);
		ret = DLT_PARENT;
	} else if (dmu_objset_ds(db->db_objset) != NULL) {
		rrw_enter(&dmu_objset_ds(db->db_objset)->ds_bp_rwlock, rw,
		    tag);
		ret = DLT_OBJSET;
	}
	/*
	 * We only return a DLT_NONE lock when it's the top-most indirect block
	 * of the meta-dnode of the MOS.
	 */
	return (ret);
}

/*
 * We need to pass the lock type in because it's possible that the block will
 * move from being the topmost indirect block in a dnode (and thus, have no
 * parent) to not the top-most via an indirection increase. This would cause a
 * panic if we didn't pass the lock type in.
 */
void
dmu_buf_unlock_parent(dmu_buf_impl_t *db, db_lock_type_t type, const void *tag)
{
	if (type == DLT_PARENT)
		rw_exit(&db->db_parent->db_rwlock);
	else if (type == DLT_OBJSET)
		rrw_exit(&dmu_objset_ds(db->db_objset)->ds_bp_rwlock, tag);
}

static void
dbuf_read_done(zio_t *zio, const zbookmark_phys_t *zb, const blkptr_t *bp,
    arc_buf_t *buf, void *vdb)
{
	(void) zb, (void) bp;
	dmu_buf_impl_t *db = vdb;

	mutex_enter(&db->db_mtx);
	ASSERT3U(db->db_state, ==, DB_READ);
	/*
	 * All reads are synchronous, so we must have a hold on the dbuf
	 */
	ASSERT(zfs_refcount_count(&db->db_holds) > 0);
	ASSERT(db->db_buf == NULL);
	ASSERT(db->db.db_data == NULL);
	if (buf == NULL) {
		/* i/o error */
		ASSERT(zio == NULL || zio->io_error != 0);
		ASSERT(db->db_blkid != DMU_BONUS_BLKID);
		ASSERT3P(db->db_buf, ==, NULL);
		db->db_state = DB_UNCACHED;
		DTRACE_SET_STATE(db, "i/o error");
	} else if (db->db_level == 0 && db->db_freed_in_flight) {
		/* freed in flight */
		ASSERT(zio == NULL || zio->io_error == 0);
		arc_release(buf, db);
		memset(buf->b_data, 0, db->db.db_size);
		arc_buf_freeze(buf);
		db->db_freed_in_flight = FALSE;
		dbuf_set_data(db, buf);
		db->db_state = DB_CACHED;
		DTRACE_SET_STATE(db, "freed in flight");
	} else {
		/* success */
		ASSERT(zio == NULL || zio->io_error == 0);
		dbuf_set_data(db, buf);
		db->db_state = DB_CACHED;
		DTRACE_SET_STATE(db, "successful read");
	}
	cv_broadcast(&db->db_changed);
	dbuf_rele_and_unlock(db, NULL, B_FALSE);
}

/*
 * Shortcut for performing reads on bonus dbufs.  Returns
 * an error if we fail to verify the dnode associated with
 * a decrypted block. Otherwise success.
 */
static int
dbuf_read_bonus(dmu_buf_impl_t *db, dnode_t *dn, uint32_t flags)
{
	int bonuslen, max_bonuslen, err;

	err = dbuf_read_verify_dnode_crypt(db, flags);
	if (err)
		return (err);

	bonuslen = MIN(dn->dn_bonuslen, dn->dn_phys->dn_bonuslen);
	max_bonuslen = DN_SLOTS_TO_BONUSLEN(dn->dn_num_slots);
	ASSERT(MUTEX_HELD(&db->db_mtx));
	ASSERT(DB_DNODE_HELD(db));
	ASSERT3U(bonuslen, <=, db->db.db_size);
	db->db.db_data = kmem_alloc(max_bonuslen, KM_SLEEP);
	arc_space_consume(max_bonuslen, ARC_SPACE_BONUS);
	if (bonuslen < max_bonuslen)
		memset(db->db.db_data, 0, max_bonuslen);
	if (bonuslen)
		memcpy(db->db.db_data, DN_BONUS(dn->dn_phys), bonuslen);
	db->db_state = DB_CACHED;
	DTRACE_SET_STATE(db, "bonus buffer filled");
	return (0);
}

static void
dbuf_handle_indirect_hole(dmu_buf_impl_t *db, dnode_t *dn)
{
	blkptr_t *bps = db->db.db_data;
	uint32_t indbs = 1ULL << dn->dn_indblkshift;
	int n_bps = indbs >> SPA_BLKPTRSHIFT;

	for (int i = 0; i < n_bps; i++) {
		blkptr_t *bp = &bps[i];

		ASSERT3U(BP_GET_LSIZE(db->db_blkptr), ==, indbs);
		BP_SET_LSIZE(bp, BP_GET_LEVEL(db->db_blkptr) == 1 ?
		    dn->dn_datablksz : BP_GET_LSIZE(db->db_blkptr));
		BP_SET_TYPE(bp, BP_GET_TYPE(db->db_blkptr));
		BP_SET_LEVEL(bp, BP_GET_LEVEL(db->db_blkptr) - 1);
		BP_SET_BIRTH(bp, db->db_blkptr->blk_birth, 0);
	}
}

/*
 * Handle reads on dbufs that are holes, if necessary.  This function
 * requires that the dbuf's mutex is held. Returns success (0) if action
 * was taken, ENOENT if no action was taken.
 */
static int
dbuf_read_hole(dmu_buf_impl_t *db, dnode_t *dn)
{
	ASSERT(MUTEX_HELD(&db->db_mtx));

	int is_hole = db->db_blkptr == NULL || BP_IS_HOLE(db->db_blkptr);
	/*
	 * For level 0 blocks only, if the above check fails:
	 * Recheck BP_IS_HOLE() after dnode_block_freed() in case dnode_sync()
	 * processes the delete record and clears the bp while we are waiting
	 * for the dn_mtx (resulting in a "no" from block_freed).
	 */
	if (!is_hole && db->db_level == 0) {
		is_hole = dnode_block_freed(dn, db->db_blkid) ||
		    BP_IS_HOLE(db->db_blkptr);
	}

	if (is_hole) {
		dbuf_set_data(db, dbuf_alloc_arcbuf(db));
		memset(db->db.db_data, 0, db->db.db_size);

		if (db->db_blkptr != NULL && db->db_level > 0 &&
		    BP_IS_HOLE(db->db_blkptr) &&
		    db->db_blkptr->blk_birth != 0) {
			dbuf_handle_indirect_hole(db, dn);
		}
		db->db_state = DB_CACHED;
		DTRACE_SET_STATE(db, "hole read satisfied");
		return (0);
	}
	return (ENOENT);
}

/*
 * This function ensures that, when doing a decrypting read of a block,
 * we make sure we have decrypted the dnode associated with it. We must do
 * this so that we ensure we are fully authenticating the checksum-of-MACs
 * tree from the root of the objset down to this block. Indirect blocks are
 * always verified against their secure checksum-of-MACs assuming that the
 * dnode containing them is correct. Now that we are doing a decrypting read,
 * we can be sure that the key is loaded and verify that assumption. This is
 * especially important considering that we always read encrypted dnode
 * blocks as raw data (without verifying their MACs) to start, and
 * decrypt / authenticate them when we need to read an encrypted bonus buffer.
 */
static int
dbuf_read_verify_dnode_crypt(dmu_buf_impl_t *db, uint32_t flags)
{
	int err = 0;
	objset_t *os = db->db_objset;
	arc_buf_t *dnode_abuf;
	dnode_t *dn;
	zbookmark_phys_t zb;

	ASSERT(MUTEX_HELD(&db->db_mtx));

	if ((flags & DB_RF_NO_DECRYPT) != 0 ||
	    !os->os_encrypted || os->os_raw_receive)
		return (0);

	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);
	dnode_abuf = (dn->dn_dbuf != NULL) ? dn->dn_dbuf->db_buf : NULL;

	if (dnode_abuf == NULL || !arc_is_encrypted(dnode_abuf)) {
		DB_DNODE_EXIT(db);
		return (0);
	}

	SET_BOOKMARK(&zb, dmu_objset_id(os),
	    DMU_META_DNODE_OBJECT, 0, dn->dn_dbuf->db_blkid);
	err = arc_untransform(dnode_abuf, os->os_spa, &zb, B_TRUE);

	/*
	 * An error code of EACCES tells us that the key is still not
	 * available. This is ok if we are only reading authenticated
	 * (and therefore non-encrypted) blocks.
	 */
	if (err == EACCES && ((db->db_blkid != DMU_BONUS_BLKID &&
	    !DMU_OT_IS_ENCRYPTED(dn->dn_type)) ||
	    (db->db_blkid == DMU_BONUS_BLKID &&
	    !DMU_OT_IS_ENCRYPTED(dn->dn_bonustype))))
		err = 0;

	DB_DNODE_EXIT(db);

	return (err);
}

/*
 * Drops db_mtx and the parent lock specified by dblt and tag before
 * returning.
 */
static int
dbuf_read_impl(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags,
    db_lock_type_t dblt, const void *tag)
{
	dnode_t *dn;
	zbookmark_phys_t zb;
	uint32_t aflags = ARC_FLAG_NOWAIT;
	int err, zio_flags;

	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));
	ASSERT(MUTEX_HELD(&db->db_mtx));
	ASSERT(db->db_state == DB_UNCACHED);
	ASSERT(db->db_buf == NULL);
	ASSERT(db->db_parent == NULL ||
	    RW_LOCK_HELD(&db->db_parent->db_rwlock));

	if (db->db_blkid == DMU_BONUS_BLKID) {
		err = dbuf_read_bonus(db, dn, flags);
		goto early_unlock;
	}

	err = dbuf_read_hole(db, dn);
	if (err == 0)
		goto early_unlock;

	/*
	 * Any attempt to read a redacted block should result in an error. This
	 * will never happen under normal conditions, but can be useful for
	 * debugging purposes.
	 */
	if (BP_IS_REDACTED(db->db_blkptr)) {
		ASSERT(dsl_dataset_feature_is_active(
		    db->db_objset->os_dsl_dataset,
		    SPA_FEATURE_REDACTED_DATASETS));
		err = SET_ERROR(EIO);
		goto early_unlock;
	}

	SET_BOOKMARK(&zb, dmu_objset_id(db->db_objset),
	    db->db.db_object, db->db_level, db->db_blkid);

	/*
	 * All bps of an encrypted os should have the encryption bit set.
	 * If this is not true it indicates tampering and we report an error.
	 */
	if (db->db_objset->os_encrypted && !BP_USES_CRYPT(db->db_blkptr)) {
		spa_log_error(db->db_objset->os_spa, &zb);
		zfs_panic_recover("unencrypted block in encrypted "
		    "object set %llu", dmu_objset_id(db->db_objset));
		err = SET_ERROR(EIO);
		goto early_unlock;
	}

	err = dbuf_read_verify_dnode_crypt(db, flags);
	if (err != 0)
		goto early_unlock;

	DB_DNODE_EXIT(db);

	db->db_state = DB_READ;
	DTRACE_SET_STATE(db, "read issued");
	mutex_exit(&db->db_mtx);

	if (dbuf_is_l2cacheable(db))
		aflags |= ARC_FLAG_L2CACHE;

	dbuf_add_ref(db, NULL);

	zio_flags = (flags & DB_RF_CANFAIL) ?
	    ZIO_FLAG_CANFAIL : ZIO_FLAG_MUSTSUCCEED;

	if ((flags & DB_RF_NO_DECRYPT) && BP_IS_PROTECTED(db->db_blkptr))
		zio_flags |= ZIO_FLAG_RAW;
	/*
	 * The zio layer will copy the provided blkptr later, but we need to
	 * do this now so that we can release the parent's rwlock. We have to
	 * do that now so that if dbuf_read_done is called synchronously (on
	 * an l1 cache hit) we don't acquire the db_mtx while holding the
	 * parent's rwlock, which would be a lock ordering violation.
	 */
	blkptr_t bp = *db->db_blkptr;
	dmu_buf_unlock_parent(db, dblt, tag);
	(void) arc_read(zio, db->db_objset->os_spa, &bp,
	    dbuf_read_done, db, ZIO_PRIORITY_SYNC_READ, zio_flags,
	    &aflags, &zb);
	return (err);
early_unlock:
	DB_DNODE_EXIT(db);
	mutex_exit(&db->db_mtx);
	dmu_buf_unlock_parent(db, dblt, tag);
	return (err);
}

/*
 * This is our just-in-time copy function.  It makes a copy of buffers that
 * have been modified in a previous transaction group before we access them in
 * the current active group.
 *
 * This function is used in three places: when we are dirtying a buffer for the
 * first time in a txg, when we are freeing a range in a dnode that includes
 * this buffer, and when we are accessing a buffer which was received compressed
 * and later referenced in a WRITE_BYREF record.
 *
 * Note that when we are called from dbuf_free_range() we do not put a hold on
 * the buffer, we just traverse the active dbuf list for the dnode.
 */
static void
dbuf_fix_old_data(dmu_buf_impl_t *db, uint64_t txg)
{
	dbuf_dirty_record_t *dr = list_head(&db->db_dirty_records);

	ASSERT(MUTEX_HELD(&db->db_mtx));
	ASSERT(db->db.db_data != NULL);
	ASSERT(db->db_level == 0);
	ASSERT(db->db.db_object != DMU_META_DNODE_OBJECT);

	if (dr == NULL ||
	    (dr->dt.dl.dr_data !=
	    ((db->db_blkid  == DMU_BONUS_BLKID) ? db->db.db_data : db->db_buf)))
		return;

	/*
	 * If the last dirty record for this dbuf has not yet synced
	 * and its referencing the dbuf data, either:
	 *	reset the reference to point to a new copy,
	 * or (if there a no active holders)
	 *	just null out the current db_data pointer.
	 */
	ASSERT3U(dr->dr_txg, >=, txg - 2);
	if (db->db_blkid == DMU_BONUS_BLKID) {
		dnode_t *dn = DB_DNODE(db);
		int bonuslen = DN_SLOTS_TO_BONUSLEN(dn->dn_num_slots);
		dr->dt.dl.dr_data = kmem_alloc(bonuslen, KM_SLEEP);
		arc_space_consume(bonuslen, ARC_SPACE_BONUS);
		memcpy(dr->dt.dl.dr_data, db->db.db_data, bonuslen);
	} else if (zfs_refcount_count(&db->db_holds) > db->db_dirtycnt) {
		dnode_t *dn = DB_DNODE(db);
		int size = arc_buf_size(db->db_buf);
		arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
		spa_t *spa = db->db_objset->os_spa;
		enum zio_compress compress_type =
		    arc_get_compression(db->db_buf);
		uint8_t complevel = arc_get_complevel(db->db_buf);

		if (arc_is_encrypted(db->db_buf)) {
			boolean_t byteorder;
			uint8_t salt[ZIO_DATA_SALT_LEN];
			uint8_t iv[ZIO_DATA_IV_LEN];
			uint8_t mac[ZIO_DATA_MAC_LEN];

			arc_get_raw_params(db->db_buf, &byteorder, salt,
			    iv, mac);
			dr->dt.dl.dr_data = arc_alloc_raw_buf(spa, db,
			    dmu_objset_id(dn->dn_objset), byteorder, salt, iv,
			    mac, dn->dn_type, size, arc_buf_lsize(db->db_buf),
			    compress_type, complevel);
		} else if (compress_type != ZIO_COMPRESS_OFF) {
			ASSERT3U(type, ==, ARC_BUFC_DATA);
			dr->dt.dl.dr_data = arc_alloc_compressed_buf(spa, db,
			    size, arc_buf_lsize(db->db_buf), compress_type,
			    complevel);
		} else {
			dr->dt.dl.dr_data = arc_alloc_buf(spa, db, type, size);
		}
		memcpy(dr->dt.dl.dr_data->b_data, db->db.db_data, size);
	} else {
		db->db_buf = NULL;
		dbuf_clear_data(db);
	}
}

int
dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
{
	int err = 0;
	boolean_t prefetch;
	dnode_t *dn;

	/*
	 * We don't have to hold the mutex to check db_state because it
	 * can't be freed while we have a hold on the buffer.
	 */
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));

	if (db->db_state == DB_NOFILL)
		return (SET_ERROR(EIO));

	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);

	prefetch = db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID &&
	    (flags & DB_RF_NOPREFETCH) == 0 && dn != NULL &&
	    DBUF_IS_CACHEABLE(db);

	mutex_enter(&db->db_mtx);
	if (db->db_state == DB_CACHED) {
		/*
		 * Ensure that this block's dnode has been decrypted if
		 * the caller has requested decrypted data.
		 */
		err = dbuf_read_verify_dnode_crypt(db, flags);

		/*
		 * If the arc buf is compressed or encrypted and the caller
		 * requested uncompressed data, we need to untransform it
		 * before returning. We also call arc_untransform() on any
		 * unauthenticated blocks, which will verify their MAC if
		 * the key is now available.
		 */
		if (err == 0 && db->db_buf != NULL &&
		    (flags & DB_RF_NO_DECRYPT) == 0 &&
		    (arc_is_encrypted(db->db_buf) ||
		    arc_is_unauthenticated(db->db_buf) ||
		    arc_get_compression(db->db_buf) != ZIO_COMPRESS_OFF)) {
			spa_t *spa = dn->dn_objset->os_spa;
			zbookmark_phys_t zb;

			SET_BOOKMARK(&zb, dmu_objset_id(db->db_objset),
			    db->db.db_object, db->db_level, db->db_blkid);
			dbuf_fix_old_data(db, spa_syncing_txg(spa));
			err = arc_untransform(db->db_buf, spa, &zb, B_FALSE);
			dbuf_set_data(db, db->db_buf);
		}
		mutex_exit(&db->db_mtx);
		if (err == 0 && prefetch) {
			dmu_zfetch(&dn->dn_zfetch, db->db_blkid, 1, B_TRUE,
			    B_FALSE, flags & DB_RF_HAVESTRUCT);
		}
		DB_DNODE_EXIT(db);
		DBUF_STAT_BUMP(hash_hits);
	} else if (db->db_state == DB_UNCACHED) {
		boolean_t need_wait = B_FALSE;

		db_lock_type_t dblt = dmu_buf_lock_parent(db, RW_READER, FTAG);

		if (zio == NULL &&
		    db->db_blkptr != NULL && !BP_IS_HOLE(db->db_blkptr)) {
			spa_t *spa = dn->dn_objset->os_spa;
			zio = zio_root(spa, NULL, NULL, ZIO_FLAG_CANFAIL);
			need_wait = B_TRUE;
		}
		err = dbuf_read_impl(db, zio, flags, dblt, FTAG);
		/*
		 * dbuf_read_impl has dropped db_mtx and our parent's rwlock
		 * for us
		 */
		if (!err && prefetch) {
			dmu_zfetch(&dn->dn_zfetch, db->db_blkid, 1, B_TRUE,
			    db->db_state != DB_CACHED,
			    flags & DB_RF_HAVESTRUCT);
		}

		DB_DNODE_EXIT(db);
		DBUF_STAT_BUMP(hash_misses);

		/*
		 * If we created a zio_root we must execute it to avoid
		 * leaking it, even if it isn't attached to any work due
		 * to an error in dbuf_read_impl().
		 */
		if (need_wait) {
			if (err == 0)
				err = zio_wait(zio);
			else
				VERIFY0(zio_wait(zio));
		}
	} else {
		/*
		 * Another reader came in while the dbuf was in flight
		 * between UNCACHED and CACHED.  Either a writer will finish
		 * writing the buffer (sending the dbuf to CACHED) or the
		 * first reader's request will reach the read_done callback
		 * and send the dbuf to CACHED.  Otherwise, a failure
		 * occurred and the dbuf went to UNCACHED.
		 */
		mutex_exit(&db->db_mtx);
		if (prefetch) {
			dmu_zfetch(&dn->dn_zfetch, db->db_blkid, 1, B_TRUE,
			    B_TRUE, flags & DB_RF_HAVESTRUCT);
		}
		DB_DNODE_EXIT(db);
		DBUF_STAT_BUMP(hash_misses);

		/* Skip the wait per the caller's request. */
		if ((flags & DB_RF_NEVERWAIT) == 0) {
			mutex_enter(&db->db_mtx);
			while (db->db_state == DB_READ ||
			    db->db_state == DB_FILL) {
				ASSERT(db->db_state == DB_READ ||
				    (flags & DB_RF_HAVESTRUCT) == 0);
				DTRACE_PROBE2(blocked__read, dmu_buf_impl_t *,
				    db, zio_t *, zio);
				cv_wait(&db->db_changed, &db->db_mtx);
			}
			if (db->db_state == DB_UNCACHED)
				err = SET_ERROR(EIO);
			mutex_exit(&db->db_mtx);
		}
	}

	return (err);
}

static void
dbuf_noread(dmu_buf_impl_t *db)
{
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));
	ASSERT(db->db_blkid != DMU_BONUS_BLKID);
	mutex_enter(&db->db_mtx);
	while (db->db_state == DB_READ || db->db_state == DB_FILL)
		cv_wait(&db->db_changed, &db->db_mtx);
	if (db->db_state == DB_UNCACHED) {
		ASSERT(db->db_buf == NULL);
		ASSERT(db->db.db_data == NULL);
		dbuf_set_data(db, dbuf_alloc_arcbuf(db));
		db->db_state = DB_FILL;
		DTRACE_SET_STATE(db, "assigning filled buffer");
	} else if (db->db_state == DB_NOFILL) {
		dbuf_clear_data(db);
	} else {
		ASSERT3U(db->db_state, ==, DB_CACHED);
	}
	mutex_exit(&db->db_mtx);
}

void
dbuf_unoverride(dbuf_dirty_record_t *dr)
{
	dmu_buf_impl_t *db = dr->dr_dbuf;
	blkptr_t *bp = &dr->dt.dl.dr_overridden_by;
	uint64_t txg = dr->dr_txg;

	ASSERT(MUTEX_HELD(&db->db_mtx));
	/*
	 * This assert is valid because dmu_sync() expects to be called by
	 * a zilog's get_data while holding a range lock.  This call only
	 * comes from dbuf_dirty() callers who must also hold a range lock.
	 */
	ASSERT(dr->dt.dl.dr_override_state != DR_IN_DMU_SYNC);
	ASSERT(db->db_level == 0);

	if (db->db_blkid == DMU_BONUS_BLKID ||
	    dr->dt.dl.dr_override_state == DR_NOT_OVERRIDDEN)
		return;

	ASSERT(db->db_data_pending != dr);

	/* free this block */
	if (!BP_IS_HOLE(bp) && !dr->dt.dl.dr_nopwrite)
		zio_free(db->db_objset->os_spa, txg, bp);

	dr->dt.dl.dr_override_state = DR_NOT_OVERRIDDEN;
	dr->dt.dl.dr_nopwrite = B_FALSE;
	dr->dt.dl.dr_has_raw_params = B_FALSE;

	/*
	 * Release the already-written buffer, so we leave it in
	 * a consistent dirty state.  Note that all callers are
	 * modifying the buffer, so they will immediately do
	 * another (redundant) arc_release().  Therefore, leave
	 * the buf thawed to save the effort of freezing &
	 * immediately re-thawing it.
	 */
	arc_release(dr->dt.dl.dr_data, db);
}

/*
 * Evict (if its unreferenced) or clear (if its referenced) any level-0
 * data blocks in the free range, so that any future readers will find
 * empty blocks.
 */
void
dbuf_free_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
    dmu_tx_t *tx)
{
	dmu_buf_impl_t *db_search;
	dmu_buf_impl_t *db, *db_next;
	uint64_t txg = tx->tx_txg;
	avl_index_t where;
	dbuf_dirty_record_t *dr;

	if (end_blkid > dn->dn_maxblkid &&
	    !(start_blkid == DMU_SPILL_BLKID || end_blkid == DMU_SPILL_BLKID))
		end_blkid = dn->dn_maxblkid;
	dprintf_dnode(dn, "start=%llu end=%llu\n", (u_longlong_t)start_blkid,
	    (u_longlong_t)end_blkid);

	db_search = kmem_alloc(sizeof (dmu_buf_impl_t), KM_SLEEP);
	db_search->db_level = 0;
	db_search->db_blkid = start_blkid;
	db_search->db_state = DB_SEARCH;

	mutex_enter(&dn->dn_dbufs_mtx);
	db = avl_find(&dn->dn_dbufs, db_search, &where);
	ASSERT3P(db, ==, NULL);

	db = avl_nearest(&dn->dn_dbufs, where, AVL_AFTER);

	for (; db != NULL; db = db_next) {
		db_next = AVL_NEXT(&dn->dn_dbufs, db);
		ASSERT(db->db_blkid != DMU_BONUS_BLKID);

		if (db->db_level != 0 || db->db_blkid > end_blkid) {
			break;
		}
		ASSERT3U(db->db_blkid, >=, start_blkid);

		/* found a level 0 buffer in the range */
		mutex_enter(&db->db_mtx);
		if (dbuf_undirty(db, tx)) {
			/* mutex has been dropped and dbuf destroyed */
			continue;
		}

		if (db->db_state == DB_UNCACHED ||
		    db->db_state == DB_NOFILL ||
		    db->db_state == DB_EVICTING) {
			ASSERT(db->db.db_data == NULL);
			mutex_exit(&db->db_mtx);
			continue;
		}
		if (db->db_state == DB_READ || db->db_state == DB_FILL) {
			/* will be handled in dbuf_read_done or dbuf_rele */
			db->db_freed_in_flight = TRUE;
			mutex_exit(&db->db_mtx);
			continue;
		}
		if (zfs_refcount_count(&db->db_holds) == 0) {
			ASSERT(db->db_buf);
			dbuf_destroy(db);
			continue;
		}
		/* The dbuf is referenced */

		dr = list_head(&db->db_dirty_records);
		if (dr != NULL) {
			if (dr->dr_txg == txg) {
				/*
				 * This buffer is "in-use", re-adjust the file
				 * size to reflect that this buffer may
				 * contain new data when we sync.
				 */
				if (db->db_blkid != DMU_SPILL_BLKID &&
				    db->db_blkid > dn->dn_maxblkid)
					dn->dn_maxblkid = db->db_blkid;
				dbuf_unoverride(dr);
			} else {
				/*
				 * This dbuf is not dirty in the open context.
				 * Either uncache it (if its not referenced in
				 * the open context) or reset its contents to
				 * empty.
				 */
				dbuf_fix_old_data(db, txg);
			}
		}
		/* clear the contents if its cached */
		if (db->db_state == DB_CACHED) {
			ASSERT(db->db.db_data != NULL);
			arc_release(db->db_buf, db);
			rw_enter(&db->db_rwlock, RW_WRITER);
			memset(db->db.db_data, 0, db->db.db_size);
			rw_exit(&db->db_rwlock);
			arc_buf_freeze(db->db_buf);
		}

		mutex_exit(&db->db_mtx);
	}

	mutex_exit(&dn->dn_dbufs_mtx);
	kmem_free(db_search, sizeof (dmu_buf_impl_t));
}

void
dbuf_new_size(dmu_buf_impl_t *db, int size, dmu_tx_t *tx)
{
	arc_buf_t *buf, *old_buf;
	dbuf_dirty_record_t *dr;
	int osize = db->db.db_size;
	arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
	dnode_t *dn;

	ASSERT(db->db_blkid != DMU_BONUS_BLKID);

	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);

	/*
	 * XXX we should be doing a dbuf_read, checking the return
	 * value and returning that up to our callers
	 */
	dmu_buf_will_dirty(&db->db, tx);

	/* create the data buffer for the new block */
	buf = arc_alloc_buf(dn->dn_objset->os_spa, db, type, size);

	/* copy old block data to the new block */
	old_buf = db->db_buf;
	memcpy(buf->b_data, old_buf->b_data, MIN(osize, size));
	/* zero the remainder */
	if (size > osize)
		memset((uint8_t *)buf->b_data + osize, 0, size - osize);

	mutex_enter(&db->db_mtx);
	dbuf_set_data(db, buf);
	arc_buf_destroy(old_buf, db);
	db->db.db_size = size;

	dr = list_head(&db->db_dirty_records);
	/* dirty record added by dmu_buf_will_dirty() */
	VERIFY(dr != NULL);
	if (db->db_level == 0)
		dr->dt.dl.dr_data = buf;
	ASSERT3U(dr->dr_txg, ==, tx->tx_txg);
	ASSERT3U(dr->dr_accounted, ==, osize);
	dr->dr_accounted = size;
	mutex_exit(&db->db_mtx);

	dmu_objset_willuse_space(dn->dn_objset, size - osize, tx);
	DB_DNODE_EXIT(db);
}

void
dbuf_release_bp(dmu_buf_impl_t *db)
{
	objset_t *os __maybe_unused = db->db_objset;

	ASSERT(dsl_pool_sync_context(dmu_objset_pool(os)));
	ASSERT(arc_released(os->os_phys_buf) ||
	    list_link_active(&os->os_dsl_dataset->ds_synced_link));
	ASSERT(db->db_parent == NULL || arc_released(db->db_parent->db_buf));

	(void) arc_release(db->db_buf, db);
}

/*
 * We already have a dirty record for this TXG, and we are being
 * dirtied again.
 */
static void
dbuf_redirty(dbuf_dirty_record_t *dr)
{
	dmu_buf_impl_t *db = dr->dr_dbuf;

	ASSERT(MUTEX_HELD(&db->db_mtx));

	if (db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID) {
		/*
		 * If this buffer has already been written out,
		 * we now need to reset its state.
		 */
		dbuf_unoverride(dr);
		if (db->db.db_object != DMU_META_DNODE_OBJECT &&
		    db->db_state != DB_NOFILL) {
			/* Already released on initial dirty, so just thaw. */
			ASSERT(arc_released(db->db_buf));
			arc_buf_thaw(db->db_buf);
		}
	}
}

dbuf_dirty_record_t *
dbuf_dirty_lightweight(dnode_t *dn, uint64_t blkid, dmu_tx_t *tx)
{
	rw_enter(&dn->dn_struct_rwlock, RW_READER);
	IMPLY(dn->dn_objset->os_raw_receive, dn->dn_maxblkid >= blkid);
	dnode_new_blkid(dn, blkid, tx, B_TRUE, B_FALSE);
	ASSERT(dn->dn_maxblkid >= blkid);

	dbuf_dirty_record_t *dr = kmem_zalloc(sizeof (*dr), KM_SLEEP);
	list_link_init(&dr->dr_dirty_node);
	list_link_init(&dr->dr_dbuf_node);
	dr->dr_dnode = dn;
	dr->dr_txg = tx->tx_txg;
	dr->dt.dll.dr_blkid = blkid;
	dr->dr_accounted = dn->dn_datablksz;

	/*
	 * There should not be any dbuf for the block that we're dirtying.
	 * Otherwise the buffer contents could be inconsistent between the
	 * dbuf and the lightweight dirty record.
	 */
	ASSERT3P(NULL, ==, dbuf_find(dn->dn_objset, dn->dn_object, 0, blkid));

	mutex_enter(&dn->dn_mtx);
	int txgoff = tx->tx_txg & TXG_MASK;
	if (dn->dn_free_ranges[txgoff] != NULL) {
		range_tree_clear(dn->dn_free_ranges[txgoff], blkid, 1);
	}

	if (dn->dn_nlevels == 1) {
		ASSERT3U(blkid, <, dn->dn_nblkptr);
		list_insert_tail(&dn->dn_dirty_records[txgoff], dr);
		mutex_exit(&dn->dn_mtx);
		rw_exit(&dn->dn_struct_rwlock);
		dnode_setdirty(dn, tx);
	} else {
		mutex_exit(&dn->dn_mtx);

		int epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
		dmu_buf_impl_t *parent_db = dbuf_hold_level(dn,
		    1, blkid >> epbs, FTAG);
		rw_exit(&dn->dn_struct_rwlock);
		if (parent_db == NULL) {
			kmem_free(dr, sizeof (*dr));
			return (NULL);
		}
		int err = dbuf_read(parent_db, NULL,
		    (DB_RF_NOPREFETCH | DB_RF_CANFAIL));
		if (err != 0) {
			dbuf_rele(parent_db, FTAG);
			kmem_free(dr, sizeof (*dr));
			return (NULL);
		}

		dbuf_dirty_record_t *parent_dr = dbuf_dirty(parent_db, tx);
		dbuf_rele(parent_db, FTAG);
		mutex_enter(&parent_dr->dt.di.dr_mtx);
		ASSERT3U(parent_dr->dr_txg, ==, tx->tx_txg);
		list_insert_tail(&parent_dr->dt.di.dr_children, dr);
		mutex_exit(&parent_dr->dt.di.dr_mtx);
		dr->dr_parent = parent_dr;
	}

	dmu_objset_willuse_space(dn->dn_objset, dr->dr_accounted, tx);

	return (dr);
}

dbuf_dirty_record_t *
dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
{
	dnode_t *dn;
	objset_t *os;
	dbuf_dirty_record_t *dr, *dr_next, *dr_head;
	int txgoff = tx->tx_txg & TXG_MASK;
	boolean_t drop_struct_rwlock = B_FALSE;

	ASSERT(tx->tx_txg != 0);
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));
	DMU_TX_DIRTY_BUF(tx, db);

	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);
	/*
	 * Shouldn't dirty a regular buffer in syncing context.  Private
	 * objects may be dirtied in syncing context, but only if they
	 * were already pre-dirtied in open context.
	 */
#ifdef ZFS_DEBUG
	if (dn->dn_objset->os_dsl_dataset != NULL) {
		rrw_enter(&dn->dn_objset->os_dsl_dataset->ds_bp_rwlock,
		    RW_READER, FTAG);
	}
	ASSERT(!dmu_tx_is_syncing(tx) ||
	    BP_IS_HOLE(dn->dn_objset->os_rootbp) ||
	    DMU_OBJECT_IS_SPECIAL(dn->dn_object) ||
	    dn->dn_objset->os_dsl_dataset == NULL);
	if (dn->dn_objset->os_dsl_dataset != NULL)
		rrw_exit(&dn->dn_objset->os_dsl_dataset->ds_bp_rwlock, FTAG);
#endif
	/*
	 * We make this assert for private objects as well, but after we
	 * check if we're already dirty.  They are allowed to re-dirty
	 * in syncing context.
	 */
	ASSERT(dn->dn_object == DMU_META_DNODE_OBJECT ||
	    dn->dn_dirtyctx == DN_UNDIRTIED || dn->dn_dirtyctx ==
	    (dmu_tx_is_syncing(tx) ? DN_DIRTY_SYNC : DN_DIRTY_OPEN));

	mutex_enter(&db->db_mtx);
	/*
	 * XXX make this true for indirects too?  The problem is that
	 * transactions created with dmu_tx_create_assigned() from
	 * syncing context don't bother holding ahead.
	 */
	ASSERT(db->db_level != 0 ||
	    db->db_state == DB_CACHED || db->db_state == DB_FILL ||
	    db->db_state == DB_NOFILL);

	mutex_enter(&dn->dn_mtx);
	dnode_set_dirtyctx(dn, tx, db);
	if (tx->tx_txg > dn->dn_dirty_txg)
		dn->dn_dirty_txg = tx->tx_txg;
	mutex_exit(&dn->dn_mtx);

	if (db->db_blkid == DMU_SPILL_BLKID)
		dn->dn_have_spill = B_TRUE;

	/*
	 * If this buffer is already dirty, we're done.
	 */
	dr_head = list_head(&db->db_dirty_records);
	ASSERT(dr_head == NULL || dr_head->dr_txg <= tx->tx_txg ||
	    db->db.db_object == DMU_META_DNODE_OBJECT);
	dr_next = dbuf_find_dirty_lte(db, tx->tx_txg);
	if (dr_next && dr_next->dr_txg == tx->tx_txg) {
		DB_DNODE_EXIT(db);

		dbuf_redirty(dr_next);
		mutex_exit(&db->db_mtx);
		return (dr_next);
	}

	/*
	 * Only valid if not already dirty.
	 */
	ASSERT(dn->dn_object == 0 ||
	    dn->dn_dirtyctx == DN_UNDIRTIED || dn->dn_dirtyctx ==
	    (dmu_tx_is_syncing(tx) ? DN_DIRTY_SYNC : DN_DIRTY_OPEN));

	ASSERT3U(dn->dn_nlevels, >, db->db_level);

	/*
	 * We should only be dirtying in syncing context if it's the
	 * mos or we're initializing the os or it's a special object.
	 * However, we are allowed to dirty in syncing context provided
	 * we already dirtied it in open context.  Hence we must make
	 * this assertion only if we're not already dirty.
	 */
	os = dn->dn_objset;
	VERIFY3U(tx->tx_txg, <=, spa_final_dirty_txg(os->os_spa));
#ifdef ZFS_DEBUG
	if (dn->dn_objset->os_dsl_dataset != NULL)
		rrw_enter(&os->os_dsl_dataset->ds_bp_rwlock, RW_READER, FTAG);
	ASSERT(!dmu_tx_is_syncing(tx) || DMU_OBJECT_IS_SPECIAL(dn->dn_object) ||
	    os->os_dsl_dataset == NULL || BP_IS_HOLE(os->os_rootbp));
	if (dn->dn_objset->os_dsl_dataset != NULL)
		rrw_exit(&os->os_dsl_dataset->ds_bp_rwlock, FTAG);
#endif
	ASSERT(db->db.db_size != 0);

	dprintf_dbuf(db, "size=%llx\n", (u_longlong_t)db->db.db_size);

	if (db->db_blkid != DMU_BONUS_BLKID) {
		dmu_objset_willuse_space(os, db->db.db_size, tx);
	}

	/*
	 * If this buffer is dirty in an old transaction group we need
	 * to make a copy of it so that the changes we make in this
	 * transaction group won't leak out when we sync the older txg.
	 */
	dr = kmem_zalloc(sizeof (dbuf_dirty_record_t), KM_SLEEP);
	list_link_init(&dr->dr_dirty_node);
	list_link_init(&dr->dr_dbuf_node);
	dr->dr_dnode = dn;
	if (db->db_level == 0) {
		void *data_old = db->db_buf;

		if (db->db_state != DB_NOFILL) {
			if (db->db_blkid == DMU_BONUS_BLKID) {
				dbuf_fix_old_data(db, tx->tx_txg);
				data_old = db->db.db_data;
			} else if (db->db.db_object != DMU_META_DNODE_OBJECT) {
				/*
				 * Release the data buffer from the cache so
				 * that we can modify it without impacting
				 * possible other users of this cached data
				 * block.  Note that indirect blocks and
				 * private objects are not released until the
				 * syncing state (since they are only modified
				 * then).
				 */
				arc_release(db->db_buf, db);
				dbuf_fix_old_data(db, tx->tx_txg);
				data_old = db->db_buf;
			}
			ASSERT(data_old != NULL);
		}
		dr->dt.dl.dr_data = data_old;
	} else {
		mutex_init(&dr->dt.di.dr_mtx, NULL, MUTEX_NOLOCKDEP, NULL);
		list_create(&dr->dt.di.dr_children,
		    sizeof (dbuf_dirty_record_t),
		    offsetof(dbuf_dirty_record_t, dr_dirty_node));
	}
	if (db->db_blkid != DMU_BONUS_BLKID)
		dr->dr_accounted = db->db.db_size;
	dr->dr_dbuf = db;
	dr->dr_txg = tx->tx_txg;
	list_insert_before(&db->db_dirty_records, dr_next, dr);

	/*
	 * We could have been freed_in_flight between the dbuf_noread
	 * and dbuf_dirty.  We win, as though the dbuf_noread() had
	 * happened after the free.
	 */
	if (db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID &&
	    db->db_blkid != DMU_SPILL_BLKID) {
		mutex_enter(&dn->dn_mtx);
		if (dn->dn_free_ranges[txgoff] != NULL) {
			range_tree_clear(dn->dn_free_ranges[txgoff],
			    db->db_blkid, 1);
		}
		mutex_exit(&dn->dn_mtx);
		db->db_freed_in_flight = FALSE;
	}

	/*
	 * This buffer is now part of this txg
	 */
	dbuf_add_ref(db, (void *)(uintptr_t)tx->tx_txg);
	db->db_dirtycnt += 1;
	ASSERT3U(db->db_dirtycnt, <=, 3);

	mutex_exit(&db->db_mtx);

	if (db->db_blkid == DMU_BONUS_BLKID ||
	    db->db_blkid == DMU_SPILL_BLKID) {
		mutex_enter(&dn->dn_mtx);
		ASSERT(!list_link_active(&dr->dr_dirty_node));
		list_insert_tail(&dn->dn_dirty_records[txgoff], dr);
		mutex_exit(&dn->dn_mtx);
		dnode_setdirty(dn, tx);
		DB_DNODE_EXIT(db);
		return (dr);
	}

	if (!RW_WRITE_HELD(&dn->dn_struct_rwlock)) {
		rw_enter(&dn->dn_struct_rwlock, RW_READER);
		drop_struct_rwlock = B_TRUE;
	}

	/*
	 * If we are overwriting a dedup BP, then unless it is snapshotted,
	 * when we get to syncing context we will need to decrement its
	 * refcount in the DDT.  Prefetch the relevant DDT block so that
	 * syncing context won't have to wait for the i/o.
	 */
	if (db->db_blkptr != NULL) {
		db_lock_type_t dblt = dmu_buf_lock_parent(db, RW_READER, FTAG);
		ddt_prefetch(os->os_spa, db->db_blkptr);
		dmu_buf_unlock_parent(db, dblt, FTAG);
	}

	/*
	 * We need to hold the dn_struct_rwlock to make this assertion,
	 * because it protects dn_phys / dn_next_nlevels from changing.
	 */
	ASSERT((dn->dn_phys->dn_nlevels == 0 && db->db_level == 0) ||
	    dn->dn_phys->dn_nlevels > db->db_level ||
	    dn->dn_next_nlevels[txgoff] > db->db_level ||
	    dn->dn_next_nlevels[(tx->tx_txg-1) & TXG_MASK] > db->db_level ||
	    dn->dn_next_nlevels[(tx->tx_txg-2) & TXG_MASK] > db->db_level);


	if (db->db_level == 0) {
		ASSERT(!db->db_objset->os_raw_receive ||
		    dn->dn_maxblkid >= db->db_blkid);
		dnode_new_blkid(dn, db->db_blkid, tx,
		    drop_struct_rwlock, B_FALSE);
		ASSERT(dn->dn_maxblkid >= db->db_blkid);
	}

	if (db->db_level+1 < dn->dn_nlevels) {
		dmu_buf_impl_t *parent = db->db_parent;
		dbuf_dirty_record_t *di;
		int parent_held = FALSE;

		if (db->db_parent == NULL || db->db_parent == dn->dn_dbuf) {
			int epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
			parent = dbuf_hold_level(dn, db->db_level + 1,
			    db->db_blkid >> epbs, FTAG);
			ASSERT(parent != NULL);
			parent_held = TRUE;
		}
		if (drop_struct_rwlock)
			rw_exit(&dn->dn_struct_rwlock);
		ASSERT3U(db->db_level + 1, ==, parent->db_level);
		di = dbuf_dirty(parent, tx);
		if (parent_held)
			dbuf_rele(parent, FTAG);

		mutex_enter(&db->db_mtx);
		/*
		 * Since we've dropped the mutex, it's possible that
		 * dbuf_undirty() might have changed this out from under us.
		 */
		if (list_head(&db->db_dirty_records) == dr ||
		    dn->dn_object == DMU_META_DNODE_OBJECT) {
			mutex_enter(&di->dt.di.dr_mtx);
			ASSERT3U(di->dr_txg, ==, tx->tx_txg);
			ASSERT(!list_link_active(&dr->dr_dirty_node));
			list_insert_tail(&di->dt.di.dr_children, dr);
			mutex_exit(&di->dt.di.dr_mtx);
			dr->dr_parent = di;
		}
		mutex_exit(&db->db_mtx);
	} else {
		ASSERT(db->db_level + 1 == dn->dn_nlevels);
		ASSERT(db->db_blkid < dn->dn_nblkptr);
		ASSERT(db->db_parent == NULL || db->db_parent == dn->dn_dbuf);
		mutex_enter(&dn->dn_mtx);
		ASSERT(!list_link_active(&dr->dr_dirty_node));
		list_insert_tail(&dn->dn_dirty_records[txgoff], dr);
		mutex_exit(&dn->dn_mtx);
		if (drop_struct_rwlock)
			rw_exit(&dn->dn_struct_rwlock);
	}

	dnode_setdirty(dn, tx);
	DB_DNODE_EXIT(db);
	return (dr);
}

static void
dbuf_undirty_bonus(dbuf_dirty_record_t *dr)
{
	dmu_buf_impl_t *db = dr->dr_dbuf;

	if (dr->dt.dl.dr_data != db->db.db_data) {
		struct dnode *dn = dr->dr_dnode;
		int max_bonuslen = DN_SLOTS_TO_BONUSLEN(dn->dn_num_slots);

		kmem_free(dr->dt.dl.dr_data, max_bonuslen);
		arc_space_return(max_bonuslen, ARC_SPACE_BONUS);
	}
	db->db_data_pending = NULL;
	ASSERT(list_next(&db->db_dirty_records, dr) == NULL);
	list_remove(&db->db_dirty_records, dr);
	if (dr->dr_dbuf->db_level != 0) {
		mutex_destroy(&dr->dt.di.dr_mtx);
		list_destroy(&dr->dt.di.dr_children);
	}
	kmem_free(dr, sizeof (dbuf_dirty_record_t));
	ASSERT3U(db->db_dirtycnt, >, 0);
	db->db_dirtycnt -= 1;
}

/*
 * Undirty a buffer in the transaction group referenced by the given
 * transaction.  Return whether this evicted the dbuf.
 */
static boolean_t
dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
{
	uint64_t txg = tx->tx_txg;

	ASSERT(txg != 0);

	/*
	 * Due to our use of dn_nlevels below, this can only be called
	 * in open context, unless we are operating on the MOS.
	 * From syncing context, dn_nlevels may be different from the
	 * dn_nlevels used when dbuf was dirtied.
	 */
	ASSERT(db->db_objset ==
	    dmu_objset_pool(db->db_objset)->dp_meta_objset ||
	    txg != spa_syncing_txg(dmu_objset_spa(db->db_objset)));
	ASSERT(db->db_blkid != DMU_BONUS_BLKID);
	ASSERT0(db->db_level);
	ASSERT(MUTEX_HELD(&db->db_mtx));

	/*
	 * If this buffer is not dirty, we're done.
	 */
	dbuf_dirty_record_t *dr = dbuf_find_dirty_eq(db, txg);
	if (dr == NULL)
		return (B_FALSE);
	ASSERT(dr->dr_dbuf == db);

	dnode_t *dn = dr->dr_dnode;

	dprintf_dbuf(db, "size=%llx\n", (u_longlong_t)db->db.db_size);

	ASSERT(db->db.db_size != 0);

	dsl_pool_undirty_space(dmu_objset_pool(dn->dn_objset),
	    dr->dr_accounted, txg);

	list_remove(&db->db_dirty_records, dr);

	/*
	 * Note that there are three places in dbuf_dirty()
	 * where this dirty record may be put on a list.
	 * Make sure to do a list_remove corresponding to
	 * every one of those list_insert calls.
	 */
	if (dr->dr_parent) {
		mutex_enter(&dr->dr_parent->dt.di.dr_mtx);
		list_remove(&dr->dr_parent->dt.di.dr_children, dr);
		mutex_exit(&dr->dr_parent->dt.di.dr_mtx);
	} else if (db->db_blkid == DMU_SPILL_BLKID ||
	    db->db_level + 1 == dn->dn_nlevels) {
		ASSERT(db->db_blkptr == NULL || db->db_parent == dn->dn_dbuf);
		mutex_enter(&dn->dn_mtx);
		list_remove(&dn->dn_dirty_records[txg & TXG_MASK], dr);
		mutex_exit(&dn->dn_mtx);
	}

	if (db->db_state != DB_NOFILL) {
		dbuf_unoverride(dr);

		ASSERT(db->db_buf != NULL);
		ASSERT(dr->dt.dl.dr_data != NULL);
		if (dr->dt.dl.dr_data != db->db_buf)
			arc_buf_destroy(dr->dt.dl.dr_data, db);
	}

	kmem_free(dr, sizeof (dbuf_dirty_record_t));

	ASSERT(db->db_dirtycnt > 0);
	db->db_dirtycnt -= 1;

	if (zfs_refcount_remove(&db->db_holds, (void *)(uintptr_t)txg) == 0) {
		ASSERT(db->db_state == DB_NOFILL || arc_released(db->db_buf));
		dbuf_destroy(db);
		return (B_TRUE);
	}

	return (B_FALSE);
}

static void
dmu_buf_will_dirty_impl(dmu_buf_t *db_fake, int flags, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

	ASSERT(tx->tx_txg != 0);
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));

	/*
	 * Quick check for dirtiness.  For already dirty blocks, this
	 * reduces runtime of this function by >90%, and overall performance
	 * by 50% for some workloads (e.g. file deletion with indirect blocks
	 * cached).
	 */
	mutex_enter(&db->db_mtx);

	if (db->db_state == DB_CACHED) {
		dbuf_dirty_record_t *dr = dbuf_find_dirty_eq(db, tx->tx_txg);
		/*
		 * It's possible that it is already dirty but not cached,
		 * because there are some calls to dbuf_dirty() that don't
		 * go through dmu_buf_will_dirty().
		 */
		if (dr != NULL) {
			/* This dbuf is already dirty and cached. */
			dbuf_redirty(dr);
			mutex_exit(&db->db_mtx);
			return;
		}
	}
	mutex_exit(&db->db_mtx);

	DB_DNODE_ENTER(db);
	if (RW_WRITE_HELD(&DB_DNODE(db)->dn_struct_rwlock))
		flags |= DB_RF_HAVESTRUCT;
	DB_DNODE_EXIT(db);
	(void) dbuf_read(db, NULL, flags);
	(void) dbuf_dirty(db, tx);
}

void
dmu_buf_will_dirty(dmu_buf_t *db_fake, dmu_tx_t *tx)
{
	dmu_buf_will_dirty_impl(db_fake,
	    DB_RF_MUST_SUCCEED | DB_RF_NOPREFETCH, tx);
}

boolean_t
dmu_buf_is_dirty(dmu_buf_t *db_fake, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
	dbuf_dirty_record_t *dr;

	mutex_enter(&db->db_mtx);
	dr = dbuf_find_dirty_eq(db, tx->tx_txg);
	mutex_exit(&db->db_mtx);
	return (dr != NULL);
}

void
dmu_buf_will_not_fill(dmu_buf_t *db_fake, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

	db->db_state = DB_NOFILL;
	DTRACE_SET_STATE(db, "allocating NOFILL buffer");
	dmu_buf_will_fill(db_fake, tx);
}

void
dmu_buf_will_fill(dmu_buf_t *db_fake, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

	ASSERT(db->db_blkid != DMU_BONUS_BLKID);
	ASSERT(tx->tx_txg != 0);
	ASSERT(db->db_level == 0);
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));

	ASSERT(db->db.db_object != DMU_META_DNODE_OBJECT ||
	    dmu_tx_private_ok(tx));

	dbuf_noread(db);
	(void) dbuf_dirty(db, tx);
}

/*
 * This function is effectively the same as dmu_buf_will_dirty(), but
 * indicates the caller expects raw encrypted data in the db, and provides
 * the crypt params (byteorder, salt, iv, mac) which should be stored in the
 * blkptr_t when this dbuf is written.  This is only used for blocks of
 * dnodes, during raw receive.
 */
void
dmu_buf_set_crypt_params(dmu_buf_t *db_fake, boolean_t byteorder,
    const uint8_t *salt, const uint8_t *iv, const uint8_t *mac, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
	dbuf_dirty_record_t *dr;

	/*
	 * dr_has_raw_params is only processed for blocks of dnodes
	 * (see dbuf_sync_dnode_leaf_crypt()).
	 */
	ASSERT3U(db->db.db_object, ==, DMU_META_DNODE_OBJECT);
	ASSERT3U(db->db_level, ==, 0);
	ASSERT(db->db_objset->os_raw_receive);

	dmu_buf_will_dirty_impl(db_fake,
	    DB_RF_MUST_SUCCEED | DB_RF_NOPREFETCH | DB_RF_NO_DECRYPT, tx);

	dr = dbuf_find_dirty_eq(db, tx->tx_txg);

	ASSERT3P(dr, !=, NULL);

	dr->dt.dl.dr_has_raw_params = B_TRUE;
	dr->dt.dl.dr_byteorder = byteorder;
	memcpy(dr->dt.dl.dr_salt, salt, ZIO_DATA_SALT_LEN);
	memcpy(dr->dt.dl.dr_iv, iv, ZIO_DATA_IV_LEN);
	memcpy(dr->dt.dl.dr_mac, mac, ZIO_DATA_MAC_LEN);
}

static void
dbuf_override_impl(dmu_buf_impl_t *db, const blkptr_t *bp, dmu_tx_t *tx)
{
	struct dirty_leaf *dl;
	dbuf_dirty_record_t *dr;

	dr = list_head(&db->db_dirty_records);
	ASSERT3P(dr, !=, NULL);
	ASSERT3U(dr->dr_txg, ==, tx->tx_txg);
	dl = &dr->dt.dl;
	dl->dr_overridden_by = *bp;
	dl->dr_override_state = DR_OVERRIDDEN;
	dl->dr_overridden_by.blk_birth = dr->dr_txg;
}

void
dmu_buf_fill_done(dmu_buf_t *dbuf, dmu_tx_t *tx)
{
	(void) tx;
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbuf;
	dbuf_states_t old_state;
	mutex_enter(&db->db_mtx);
	DBUF_VERIFY(db);

	old_state = db->db_state;
	db->db_state = DB_CACHED;
	if (old_state == DB_FILL) {
		if (db->db_level == 0 && db->db_freed_in_flight) {
			ASSERT(db->db_blkid != DMU_BONUS_BLKID);
			/* we were freed while filling */
			/* XXX dbuf_undirty? */
			memset(db->db.db_data, 0, db->db.db_size);
			db->db_freed_in_flight = FALSE;
			DTRACE_SET_STATE(db,
			    "fill done handling freed in flight");
		} else {
			DTRACE_SET_STATE(db, "fill done");
		}
		cv_broadcast(&db->db_changed);
	}
	mutex_exit(&db->db_mtx);
}

void
dmu_buf_write_embedded(dmu_buf_t *dbuf, void *data,
    bp_embedded_type_t etype, enum zio_compress comp,
    int uncompressed_size, int compressed_size, int byteorder,
    dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbuf;
	struct dirty_leaf *dl;
	dmu_object_type_t type;
	dbuf_dirty_record_t *dr;

	if (etype == BP_EMBEDDED_TYPE_DATA) {
		ASSERT(spa_feature_is_active(dmu_objset_spa(db->db_objset),
		    SPA_FEATURE_EMBEDDED_DATA));
	}

	DB_DNODE_ENTER(db);
	type = DB_DNODE(db)->dn_type;
	DB_DNODE_EXIT(db);

	ASSERT0(db->db_level);
	ASSERT(db->db_blkid != DMU_BONUS_BLKID);

	dmu_buf_will_not_fill(dbuf, tx);

	dr = list_head(&db->db_dirty_records);
	ASSERT3P(dr, !=, NULL);
	ASSERT3U(dr->dr_txg, ==, tx->tx_txg);
	dl = &dr->dt.dl;
	encode_embedded_bp_compressed(&dl->dr_overridden_by,
	    data, comp, uncompressed_size, compressed_size);
	BPE_SET_ETYPE(&dl->dr_overridden_by, etype);
	BP_SET_TYPE(&dl->dr_overridden_by, type);
	BP_SET_LEVEL(&dl->dr_overridden_by, 0);
	BP_SET_BYTEORDER(&dl->dr_overridden_by, byteorder);

	dl->dr_override_state = DR_OVERRIDDEN;
	dl->dr_overridden_by.blk_birth = dr->dr_txg;
}

void
dmu_buf_redact(dmu_buf_t *dbuf, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbuf;
	dmu_object_type_t type;
	ASSERT(dsl_dataset_feature_is_active(db->db_objset->os_dsl_dataset,
	    SPA_FEATURE_REDACTED_DATASETS));

	DB_DNODE_ENTER(db);
	type = DB_DNODE(db)->dn_type;
	DB_DNODE_EXIT(db);

	ASSERT0(db->db_level);
	dmu_buf_will_not_fill(dbuf, tx);

	blkptr_t bp = { { { {0} } } };
	BP_SET_TYPE(&bp, type);
	BP_SET_LEVEL(&bp, 0);
	BP_SET_BIRTH(&bp, tx->tx_txg, 0);
	BP_SET_REDACTED(&bp);
	BPE_SET_LSIZE(&bp, dbuf->db_size);

	dbuf_override_impl(db, &bp, tx);
}

/*
 * Directly assign a provided arc buf to a given dbuf if it's not referenced
 * by anybody except our caller. Otherwise copy arcbuf's contents to dbuf.
 */
void
dbuf_assign_arcbuf(dmu_buf_impl_t *db, arc_buf_t *buf, dmu_tx_t *tx)
{
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));
	ASSERT(db->db_blkid != DMU_BONUS_BLKID);
	ASSERT(db->db_level == 0);
	ASSERT3U(dbuf_is_metadata(db), ==, arc_is_metadata(buf));
	ASSERT(buf != NULL);
	ASSERT3U(arc_buf_lsize(buf), ==, db->db.db_size);
	ASSERT(tx->tx_txg != 0);

	arc_return_buf(buf, db);
	ASSERT(arc_released(buf));

	mutex_enter(&db->db_mtx);

	while (db->db_state == DB_READ || db->db_state == DB_FILL)
		cv_wait(&db->db_changed, &db->db_mtx);

	ASSERT(db->db_state == DB_CACHED || db->db_state == DB_UNCACHED);

	if (db->db_state == DB_CACHED &&
	    zfs_refcount_count(&db->db_holds) - 1 > db->db_dirtycnt) {
		/*
		 * In practice, we will never have a case where we have an
		 * encrypted arc buffer while additional holds exist on the
		 * dbuf. We don't handle this here so we simply assert that
		 * fact instead.
		 */
		ASSERT(!arc_is_encrypted(buf));
		mutex_exit(&db->db_mtx);
		(void) dbuf_dirty(db, tx);
		memcpy(db->db.db_data, buf->b_data, db->db.db_size);
		arc_buf_destroy(buf, db);
		return;
	}

	if (db->db_state == DB_CACHED) {
		dbuf_dirty_record_t *dr = list_head(&db->db_dirty_records);

		ASSERT(db->db_buf != NULL);
		if (dr != NULL && dr->dr_txg == tx->tx_txg) {
			ASSERT(dr->dt.dl.dr_data == db->db_buf);

			if (!arc_released(db->db_buf)) {
				ASSERT(dr->dt.dl.dr_override_state ==
				    DR_OVERRIDDEN);
				arc_release(db->db_buf, db);
			}
			dr->dt.dl.dr_data = buf;
			arc_buf_destroy(db->db_buf, db);
		} else if (dr == NULL || dr->dt.dl.dr_data != db->db_buf) {
			arc_release(db->db_buf, db);
			arc_buf_destroy(db->db_buf, db);
		}
		db->db_buf = NULL;
	}
	ASSERT(db->db_buf == NULL);
	dbuf_set_data(db, buf);
	db->db_state = DB_FILL;
	DTRACE_SET_STATE(db, "filling assigned arcbuf");
	mutex_exit(&db->db_mtx);
	(void) dbuf_dirty(db, tx);
	dmu_buf_fill_done(&db->db, tx);
}

void
dbuf_destroy(dmu_buf_impl_t *db)
{
	dnode_t *dn;
	dmu_buf_impl_t *parent = db->db_parent;
	dmu_buf_impl_t *dndb;

	ASSERT(MUTEX_HELD(&db->db_mtx));
	ASSERT(zfs_refcount_is_zero(&db->db_holds));

	if (db->db_buf != NULL) {
		arc_buf_destroy(db->db_buf, db);
		db->db_buf = NULL;
	}

	if (db->db_blkid == DMU_BONUS_BLKID) {
		int slots = DB_DNODE(db)->dn_num_slots;
		int bonuslen = DN_SLOTS_TO_BONUSLEN(slots);
		if (db->db.db_data != NULL) {
			kmem_free(db->db.db_data, bonuslen);
			arc_space_return(bonuslen, ARC_SPACE_BONUS);
			db->db_state = DB_UNCACHED;
			DTRACE_SET_STATE(db, "buffer cleared");
		}
	}

	dbuf_clear_data(db);

	if (multilist_link_active(&db->db_cache_link)) {
		ASSERT(db->db_caching_status == DB_DBUF_CACHE ||
		    db->db_caching_status == DB_DBUF_METADATA_CACHE);

		multilist_remove(&dbuf_caches[db->db_caching_status].cache, db);
		(void) zfs_refcount_remove_many(
		    &dbuf_caches[db->db_caching_status].size,
		    db->db.db_size, db);

		if (db->db_caching_status == DB_DBUF_METADATA_CACHE) {
			DBUF_STAT_BUMPDOWN(metadata_cache_count);
		} else {
			DBUF_STAT_BUMPDOWN(cache_levels[db->db_level]);
			DBUF_STAT_BUMPDOWN(cache_count);
			DBUF_STAT_DECR(cache_levels_bytes[db->db_level],
			    db->db.db_size);
		}
		db->db_caching_status = DB_NO_CACHE;
	}

	ASSERT(db->db_state == DB_UNCACHED || db->db_state == DB_NOFILL);
	ASSERT(db->db_data_pending == NULL);
	ASSERT(list_is_empty(&db->db_dirty_records));

	db->db_state = DB_EVICTING;
	DTRACE_SET_STATE(db, "buffer eviction started");
	db->db_blkptr = NULL;

	/*
	 * Now that db_state is DB_EVICTING, nobody else can find this via
	 * the hash table.  We can now drop db_mtx, which allows us to
	 * acquire the dn_dbufs_mtx.
	 */
	mutex_exit(&db->db_mtx);

	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);
	dndb = dn->dn_dbuf;
	if (db->db_blkid != DMU_BONUS_BLKID) {
		boolean_t needlock = !MUTEX_HELD(&dn->dn_dbufs_mtx);
		if (needlock)
			mutex_enter_nested(&dn->dn_dbufs_mtx,
			    NESTED_SINGLE);
		avl_remove(&dn->dn_dbufs, db);
		membar_producer();
		DB_DNODE_EXIT(db);
		if (needlock)
			mutex_exit(&dn->dn_dbufs_mtx);
		/*
		 * Decrementing the dbuf count means that the hold corresponding
		 * to the removed dbuf is no longer discounted in dnode_move(),
		 * so the dnode cannot be moved until after we release the hold.
		 * The membar_producer() ensures visibility of the decremented
		 * value in dnode_move(), since DB_DNODE_EXIT doesn't actually
		 * release any lock.
		 */
		mutex_enter(&dn->dn_mtx);
		dnode_rele_and_unlock(dn, db, B_TRUE);
		db->db_dnode_handle = NULL;

		dbuf_hash_remove(db);
	} else {
		DB_DNODE_EXIT(db);
	}

	ASSERT(zfs_refcount_is_zero(&db->db_holds));

	db->db_parent = NULL;

	ASSERT(db->db_buf == NULL);
	ASSERT(db->db.db_data == NULL);
	ASSERT(db->db_hash_next == NULL);
	ASSERT(db->db_blkptr == NULL);
	ASSERT(db->db_data_pending == NULL);
	ASSERT3U(db->db_caching_status, ==, DB_NO_CACHE);
	ASSERT(!multilist_link_active(&db->db_cache_link));

	/*
	 * If this dbuf is referenced from an indirect dbuf,
	 * decrement the ref count on the indirect dbuf.
	 */
	if (parent && parent != dndb) {
		mutex_enter(&parent->db_mtx);
		dbuf_rele_and_unlock(parent, db, B_TRUE);
	}

	kmem_cache_free(dbuf_kmem_cache, db);
	arc_space_return(sizeof (dmu_buf_impl_t), ARC_SPACE_DBUF);
}

/*
 * Note: While bpp will always be updated if the function returns success,
 * parentp will not be updated if the dnode does not have dn_dbuf filled in;
 * this happens when the dnode is the meta-dnode, or {user|group|project}used
 * object.
 */
__attribute__((always_inline))
static inline int
dbuf_findbp(dnode_t *dn, int level, uint64_t blkid, int fail_sparse,
    dmu_buf_impl_t **parentp, blkptr_t **bpp)
{
	*parentp = NULL;
	*bpp = NULL;

	ASSERT(blkid != DMU_BONUS_BLKID);

	if (blkid == DMU_SPILL_BLKID) {
		mutex_enter(&dn->dn_mtx);
		if (dn->dn_have_spill &&
		    (dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR))
			*bpp = DN_SPILL_BLKPTR(dn->dn_phys);
		else
			*bpp = NULL;
		dbuf_add_ref(dn->dn_dbuf, NULL);
		*parentp = dn->dn_dbuf;
		mutex_exit(&dn->dn_mtx);
		return (0);
	}

	int nlevels =
	    (dn->dn_phys->dn_nlevels == 0) ? 1 : dn->dn_phys->dn_nlevels;
	int epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;

	ASSERT3U(level * epbs, <, 64);
	ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
	/*
	 * This assertion shouldn't trip as long as the max indirect block size
	 * is less than 1M.  The reason for this is that up to that point,
	 * the number of levels required to address an entire object with blocks
	 * of size SPA_MINBLOCKSIZE satisfies nlevels * epbs + 1 <= 64.	 In
	 * other words, if N * epbs + 1 > 64, then if (N-1) * epbs + 1 > 55
	 * (i.e. we can address the entire object), objects will all use at most
	 * N-1 levels and the assertion won't overflow.	 However, once epbs is
	 * 13, 4 * 13 + 1 = 53, but 5 * 13 + 1 = 66.  Then, 4 levels will not be
	 * enough to address an entire object, so objects will have 5 levels,
	 * but then this assertion will overflow.
	 *
	 * All this is to say that if we ever increase DN_MAX_INDBLKSHIFT, we
	 * need to redo this logic to handle overflows.
	 */
	ASSERT(level >= nlevels ||
	    ((nlevels - level - 1) * epbs) +
	    highbit64(dn->dn_phys->dn_nblkptr) <= 64);
	if (level >= nlevels ||
	    blkid >= ((uint64_t)dn->dn_phys->dn_nblkptr <<
	    ((nlevels - level - 1) * epbs)) ||
	    (fail_sparse &&
	    blkid > (dn->dn_phys->dn_maxblkid >> (level * epbs)))) {
		/* the buffer has no parent yet */
		return (SET_ERROR(ENOENT));
	} else if (level < nlevels-1) {
		/* this block is referenced from an indirect block */
		int err;

		err = dbuf_hold_impl(dn, level + 1,
		    blkid >> epbs, fail_sparse, FALSE, NULL, parentp);

		if (err)
			return (err);
		err = dbuf_read(*parentp, NULL,
		    (DB_RF_HAVESTRUCT | DB_RF_NOPREFETCH | DB_RF_CANFAIL));
		if (err) {
			dbuf_rele(*parentp, NULL);
			*parentp = NULL;
			return (err);
		}
		rw_enter(&(*parentp)->db_rwlock, RW_READER);
		*bpp = ((blkptr_t *)(*parentp)->db.db_data) +
		    (blkid & ((1ULL << epbs) - 1));
		if (blkid > (dn->dn_phys->dn_maxblkid >> (level * epbs)))
			ASSERT(BP_IS_HOLE(*bpp));
		rw_exit(&(*parentp)->db_rwlock);
		return (0);
	} else {
		/* the block is referenced from the dnode */
		ASSERT3U(level, ==, nlevels-1);
		ASSERT(dn->dn_phys->dn_nblkptr == 0 ||
		    blkid < dn->dn_phys->dn_nblkptr);
		if (dn->dn_dbuf) {
			dbuf_add_ref(dn->dn_dbuf, NULL);
			*parentp = dn->dn_dbuf;
		}
		*bpp = &dn->dn_phys->dn_blkptr[blkid];
		return (0);
	}
}

static dmu_buf_impl_t *
dbuf_create(dnode_t *dn, uint8_t level, uint64_t blkid,
    dmu_buf_impl_t *parent, blkptr_t *blkptr)
{
	objset_t *os = dn->dn_objset;
	dmu_buf_impl_t *db, *odb;

	ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
	ASSERT(dn->dn_type != DMU_OT_NONE);

	db = kmem_cache_alloc(dbuf_kmem_cache, KM_SLEEP);

	list_create(&db->db_dirty_records, sizeof (dbuf_dirty_record_t),
	    offsetof(dbuf_dirty_record_t, dr_dbuf_node));

	db->db_objset = os;
	db->db.db_object = dn->dn_object;
	db->db_level = level;
	db->db_blkid = blkid;
	db->db_dirtycnt = 0;
	db->db_dnode_handle = dn->dn_handle;
	db->db_parent = parent;
	db->db_blkptr = blkptr;

	db->db_user = NULL;
	db->db_user_immediate_evict = FALSE;
	db->db_freed_in_flight = FALSE;
	db->db_pending_evict = FALSE;

	if (blkid == DMU_BONUS_BLKID) {
		ASSERT3P(parent, ==, dn->dn_dbuf);
		db->db.db_size = DN_SLOTS_TO_BONUSLEN(dn->dn_num_slots) -
		    (dn->dn_nblkptr-1) * sizeof (blkptr_t);
		ASSERT3U(db->db.db_size, >=, dn->dn_bonuslen);
		db->db.db_offset = DMU_BONUS_BLKID;
		db->db_state = DB_UNCACHED;
		DTRACE_SET_STATE(db, "bonus buffer created");
		db->db_caching_status = DB_NO_CACHE;
		/* the bonus dbuf is not placed in the hash table */
		arc_space_consume(sizeof (dmu_buf_impl_t), ARC_SPACE_DBUF);
		return (db);
	} else if (blkid == DMU_SPILL_BLKID) {
		db->db.db_size = (blkptr != NULL) ?
		    BP_GET_LSIZE(blkptr) : SPA_MINBLOCKSIZE;
		db->db.db_offset = 0;
	} else {
		int blocksize =
		    db->db_level ? 1 << dn->dn_indblkshift : dn->dn_datablksz;
		db->db.db_size = blocksize;
		db->db.db_offset = db->db_blkid * blocksize;
	}

	/*
	 * Hold the dn_dbufs_mtx while we get the new dbuf
	 * in the hash table *and* added to the dbufs list.
	 * This prevents a possible deadlock with someone
	 * trying to look up this dbuf before it's added to the
	 * dn_dbufs list.
	 */
	mutex_enter(&dn->dn_dbufs_mtx);
	db->db_state = DB_EVICTING; /* not worth logging this state change */
	if ((odb = dbuf_hash_insert(db)) != NULL) {
		/* someone else inserted it first */
		mutex_exit(&dn->dn_dbufs_mtx);
		kmem_cache_free(dbuf_kmem_cache, db);
		DBUF_STAT_BUMP(hash_insert_race);
		return (odb);
	}
	avl_add(&dn->dn_dbufs, db);

	db->db_state = DB_UNCACHED;
	DTRACE_SET_STATE(db, "regular buffer created");
	db->db_caching_status = DB_NO_CACHE;
	mutex_exit(&dn->dn_dbufs_mtx);
	arc_space_consume(sizeof (dmu_buf_impl_t), ARC_SPACE_DBUF);

	if (parent && parent != dn->dn_dbuf)
		dbuf_add_ref(parent, db);

	ASSERT(dn->dn_object == DMU_META_DNODE_OBJECT ||
	    zfs_refcount_count(&dn->dn_holds) > 0);
	(void) zfs_refcount_add(&dn->dn_holds, db);

	dprintf_dbuf(db, "db=%p\n", db);

	return (db);
}

/*
 * This function returns a block pointer and information about the object,
 * given a dnode and a block.  This is a publicly accessible version of
 * dbuf_findbp that only returns some information, rather than the
 * dbuf.  Note that the dnode passed in must be held, and the dn_struct_rwlock
 * should be locked as (at least) a reader.
 */
int
dbuf_dnode_findbp(dnode_t *dn, uint64_t level, uint64_t blkid,
    blkptr_t *bp, uint16_t *datablkszsec, uint8_t *indblkshift)
{
	dmu_buf_impl_t *dbp = NULL;
	blkptr_t *bp2;
	int err = 0;
	ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));

	err = dbuf_findbp(dn, level, blkid, B_FALSE, &dbp, &bp2);
	if (err == 0) {
		*bp = *bp2;
		if (dbp != NULL)
			dbuf_rele(dbp, NULL);
		if (datablkszsec != NULL)
			*datablkszsec = dn->dn_phys->dn_datablkszsec;
		if (indblkshift != NULL)
			*indblkshift = dn->dn_phys->dn_indblkshift;
	}

	return (err);
}

typedef struct dbuf_prefetch_arg {
	spa_t *dpa_spa;	/* The spa to issue the prefetch in. */
	zbookmark_phys_t dpa_zb; /* The target block to prefetch. */
	int dpa_epbs; /* Entries (blkptr_t's) Per Block Shift. */
	int dpa_curlevel; /* The current level that we're reading */
	dnode_t *dpa_dnode; /* The dnode associated with the prefetch */
	zio_priority_t dpa_prio; /* The priority I/Os should be issued at. */
	zio_t *dpa_zio; /* The parent zio_t for all prefetches. */
	arc_flags_t dpa_aflags; /* Flags to pass to the final prefetch. */
	dbuf_prefetch_fn dpa_cb; /* prefetch completion callback */
	void *dpa_arg; /* prefetch completion arg */
} dbuf_prefetch_arg_t;

static void
dbuf_prefetch_fini(dbuf_prefetch_arg_t *dpa, boolean_t io_done)
{
	if (dpa->dpa_cb != NULL) {
		dpa->dpa_cb(dpa->dpa_arg, dpa->dpa_zb.zb_level,
		    dpa->dpa_zb.zb_blkid, io_done);
	}
	kmem_free(dpa, sizeof (*dpa));
}

static void
dbuf_issue_final_prefetch_done(zio_t *zio, const zbookmark_phys_t *zb,
    const blkptr_t *iobp, arc_buf_t *abuf, void *private)
{
	(void) zio, (void) zb, (void) iobp;
	dbuf_prefetch_arg_t *dpa = private;

	if (abuf != NULL)
		arc_buf_destroy(abuf, private);

	dbuf_prefetch_fini(dpa, B_TRUE);
}

/*
 * Actually issue the prefetch read for the block given.
 */
static void
dbuf_issue_final_prefetch(dbuf_prefetch_arg_t *dpa, blkptr_t *bp)
{
	ASSERT(!BP_IS_REDACTED(bp) ||
	    dsl_dataset_feature_is_active(
	    dpa->dpa_dnode->dn_objset->os_dsl_dataset,
	    SPA_FEATURE_REDACTED_DATASETS));

	if (BP_IS_HOLE(bp) || BP_IS_EMBEDDED(bp) || BP_IS_REDACTED(bp))
		return (dbuf_prefetch_fini(dpa, B_FALSE));

	int zio_flags = ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE;
	arc_flags_t aflags =
	    dpa->dpa_aflags | ARC_FLAG_NOWAIT | ARC_FLAG_PREFETCH |
	    ARC_FLAG_NO_BUF;

	/* dnodes are always read as raw and then converted later */
	if (BP_GET_TYPE(bp) == DMU_OT_DNODE && BP_IS_PROTECTED(bp) &&
	    dpa->dpa_curlevel == 0)
		zio_flags |= ZIO_FLAG_RAW;

	ASSERT3U(dpa->dpa_curlevel, ==, BP_GET_LEVEL(bp));
	ASSERT3U(dpa->dpa_curlevel, ==, dpa->dpa_zb.zb_level);
	ASSERT(dpa->dpa_zio != NULL);
	(void) arc_read(dpa->dpa_zio, dpa->dpa_spa, bp,
	    dbuf_issue_final_prefetch_done, dpa,
	    dpa->dpa_prio, zio_flags, &aflags, &dpa->dpa_zb);
}

/*
 * Called when an indirect block above our prefetch target is read in.  This
 * will either read in the next indirect block down the tree or issue the actual
 * prefetch if the next block down is our target.
 */
static void
dbuf_prefetch_indirect_done(zio_t *zio, const zbookmark_phys_t *zb,
    const blkptr_t *iobp, arc_buf_t *abuf, void *private)
{
	(void) zb, (void) iobp;
	dbuf_prefetch_arg_t *dpa = private;

	ASSERT3S(dpa->dpa_zb.zb_level, <, dpa->dpa_curlevel);
	ASSERT3S(dpa->dpa_curlevel, >, 0);

	if (abuf == NULL) {
		ASSERT(zio == NULL || zio->io_error != 0);
		dbuf_prefetch_fini(dpa, B_TRUE);
		return;
	}
	ASSERT(zio == NULL || zio->io_error == 0);

	/*
	 * The dpa_dnode is only valid if we are called with a NULL
	 * zio. This indicates that the arc_read() returned without
	 * first calling zio_read() to issue a physical read. Once
	 * a physical read is made the dpa_dnode must be invalidated
	 * as the locks guarding it may have been dropped. If the
	 * dpa_dnode is still valid, then we want to add it to the dbuf
	 * cache. To do so, we must hold the dbuf associated with the block
	 * we just prefetched, read its contents so that we associate it
	 * with an arc_buf_t, and then release it.
	 */
	if (zio != NULL) {
		ASSERT3S(BP_GET_LEVEL(zio->io_bp), ==, dpa->dpa_curlevel);
		if (zio->io_flags & ZIO_FLAG_RAW_COMPRESS) {
			ASSERT3U(BP_GET_PSIZE(zio->io_bp), ==, zio->io_size);
		} else {
			ASSERT3U(BP_GET_LSIZE(zio->io_bp), ==, zio->io_size);
		}
		ASSERT3P(zio->io_spa, ==, dpa->dpa_spa);

		dpa->dpa_dnode = NULL;
	} else if (dpa->dpa_dnode != NULL) {
		uint64_t curblkid = dpa->dpa_zb.zb_blkid >>
		    (dpa->dpa_epbs * (dpa->dpa_curlevel -
		    dpa->dpa_zb.zb_level));
		dmu_buf_impl_t *db = dbuf_hold_level(dpa->dpa_dnode,
		    dpa->dpa_curlevel, curblkid, FTAG);
		if (db == NULL) {
			arc_buf_destroy(abuf, private);
			dbuf_prefetch_fini(dpa, B_TRUE);
			return;
		}
		(void) dbuf_read(db, NULL,
		    DB_RF_MUST_SUCCEED | DB_RF_NOPREFETCH | DB_RF_HAVESTRUCT);
		dbuf_rele(db, FTAG);
	}

	dpa->dpa_curlevel--;
	uint64_t nextblkid = dpa->dpa_zb.zb_blkid >>
	    (dpa->dpa_epbs * (dpa->dpa_curlevel - dpa->dpa_zb.zb_level));
	blkptr_t *bp = ((blkptr_t *)abuf->b_data) +
	    P2PHASE(nextblkid, 1ULL << dpa->dpa_epbs);

	ASSERT(!BP_IS_REDACTED(bp) || (dpa->dpa_dnode &&
	    dsl_dataset_feature_is_active(
	    dpa->dpa_dnode->dn_objset->os_dsl_dataset,
	    SPA_FEATURE_REDACTED_DATASETS)));
	if (BP_IS_HOLE(bp) || BP_IS_REDACTED(bp)) {
		arc_buf_destroy(abuf, private);
		dbuf_prefetch_fini(dpa, B_TRUE);
		return;
	} else if (dpa->dpa_curlevel == dpa->dpa_zb.zb_level) {
		ASSERT3U(nextblkid, ==, dpa->dpa_zb.zb_blkid);
		dbuf_issue_final_prefetch(dpa, bp);
	} else {
		arc_flags_t iter_aflags = ARC_FLAG_NOWAIT;
		zbookmark_phys_t zb;

		/* flag if L2ARC eligible, l2arc_noprefetch then decides */
		if (dpa->dpa_aflags & ARC_FLAG_L2CACHE)
			iter_aflags |= ARC_FLAG_L2CACHE;

		ASSERT3U(dpa->dpa_curlevel, ==, BP_GET_LEVEL(bp));

		SET_BOOKMARK(&zb, dpa->dpa_zb.zb_objset,
		    dpa->dpa_zb.zb_object, dpa->dpa_curlevel, nextblkid);

		(void) arc_read(dpa->dpa_zio, dpa->dpa_spa,
		    bp, dbuf_prefetch_indirect_done, dpa,
		    ZIO_PRIORITY_SYNC_READ,
		    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE,
		    &iter_aflags, &zb);
	}

	arc_buf_destroy(abuf, private);
}

/*
 * Issue prefetch reads for the given block on the given level.  If the indirect
 * blocks above that block are not in memory, we will read them in
 * asynchronously.  As a result, this call never blocks waiting for a read to
 * complete. Note that the prefetch might fail if the dataset is encrypted and
 * the encryption key is unmapped before the IO completes.
 */
int
dbuf_prefetch_impl(dnode_t *dn, int64_t level, uint64_t blkid,
    zio_priority_t prio, arc_flags_t aflags, dbuf_prefetch_fn cb,
    void *arg)
{
	blkptr_t bp;
	int epbs, nlevels, curlevel;
	uint64_t curblkid;

	ASSERT(blkid != DMU_BONUS_BLKID);
	ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));

	if (blkid > dn->dn_maxblkid)
		goto no_issue;

	if (level == 0 && dnode_block_freed(dn, blkid))
		goto no_issue;

	/*
	 * This dnode hasn't been written to disk yet, so there's nothing to
	 * prefetch.
	 */
	nlevels = dn->dn_phys->dn_nlevels;
	if (level >= nlevels || dn->dn_phys->dn_nblkptr == 0)
		goto no_issue;

	epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
	if (dn->dn_phys->dn_maxblkid < blkid << (epbs * level))
		goto no_issue;

	dmu_buf_impl_t *db = dbuf_find(dn->dn_objset, dn->dn_object,
	    level, blkid);
	if (db != NULL) {
		mutex_exit(&db->db_mtx);
		/*
		 * This dbuf already exists.  It is either CACHED, or
		 * (we assume) about to be read or filled.
		 */
		goto no_issue;
	}

	/*
	 * Find the closest ancestor (indirect block) of the target block
	 * that is present in the cache.  In this indirect block, we will
	 * find the bp that is at curlevel, curblkid.
	 */
	curlevel = level;
	curblkid = blkid;
	while (curlevel < nlevels - 1) {
		int parent_level = curlevel + 1;
		uint64_t parent_blkid = curblkid >> epbs;
		dmu_buf_impl_t *db;

		if (dbuf_hold_impl(dn, parent_level, parent_blkid,
		    FALSE, TRUE, FTAG, &db) == 0) {
			blkptr_t *bpp = db->db_buf->b_data;
			bp = bpp[P2PHASE(curblkid, 1 << epbs)];
			dbuf_rele(db, FTAG);
			break;
		}

		curlevel = parent_level;
		curblkid = parent_blkid;
	}

	if (curlevel == nlevels - 1) {
		/* No cached indirect blocks found. */
		ASSERT3U(curblkid, <, dn->dn_phys->dn_nblkptr);
		bp = dn->dn_phys->dn_blkptr[curblkid];
	}
	ASSERT(!BP_IS_REDACTED(&bp) ||
	    dsl_dataset_feature_is_active(dn->dn_objset->os_dsl_dataset,
	    SPA_FEATURE_REDACTED_DATASETS));
	if (BP_IS_HOLE(&bp) || BP_IS_REDACTED(&bp))
		goto no_issue;

	ASSERT3U(curlevel, ==, BP_GET_LEVEL(&bp));

	zio_t *pio = zio_root(dmu_objset_spa(dn->dn_objset), NULL, NULL,
	    ZIO_FLAG_CANFAIL);

	dbuf_prefetch_arg_t *dpa = kmem_zalloc(sizeof (*dpa), KM_SLEEP);
	dsl_dataset_t *ds = dn->dn_objset->os_dsl_dataset;
	SET_BOOKMARK(&dpa->dpa_zb, ds != NULL ? ds->ds_object : DMU_META_OBJSET,
	    dn->dn_object, level, blkid);
	dpa->dpa_curlevel = curlevel;
	dpa->dpa_prio = prio;
	dpa->dpa_aflags = aflags;
	dpa->dpa_spa = dn->dn_objset->os_spa;
	dpa->dpa_dnode = dn;
	dpa->dpa_epbs = epbs;
	dpa->dpa_zio = pio;
	dpa->dpa_cb = cb;
	dpa->dpa_arg = arg;

	/* flag if L2ARC eligible, l2arc_noprefetch then decides */
	if (dnode_level_is_l2cacheable(&bp, dn, level))
		dpa->dpa_aflags |= ARC_FLAG_L2CACHE;

	/*
	 * If we have the indirect just above us, no need to do the asynchronous
	 * prefetch chain; we'll just run the last step ourselves.  If we're at
	 * a higher level, though, we want to issue the prefetches for all the
	 * indirect blocks asynchronously, so we can go on with whatever we were
	 * doing.
	 */
	if (curlevel == level) {
		ASSERT3U(curblkid, ==, blkid);
		dbuf_issue_final_prefetch(dpa, &bp);
	} else {
		arc_flags_t iter_aflags = ARC_FLAG_NOWAIT;
		zbookmark_phys_t zb;

		/* flag if L2ARC eligible, l2arc_noprefetch then decides */
		if (dnode_level_is_l2cacheable(&bp, dn, level))
			iter_aflags |= ARC_FLAG_L2CACHE;

		SET_BOOKMARK(&zb, ds != NULL ? ds->ds_object : DMU_META_OBJSET,
		    dn->dn_object, curlevel, curblkid);
		(void) arc_read(dpa->dpa_zio, dpa->dpa_spa,
		    &bp, dbuf_prefetch_indirect_done, dpa,
		    ZIO_PRIORITY_SYNC_READ,
		    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE,
		    &iter_aflags, &zb);
	}
	/*
	 * We use pio here instead of dpa_zio since it's possible that
	 * dpa may have already been freed.
	 */
	zio_nowait(pio);
	return (1);
no_issue:
	if (cb != NULL)
		cb(arg, level, blkid, B_FALSE);
	return (0);
}

int
dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
    arc_flags_t aflags)
{

	return (dbuf_prefetch_impl(dn, level, blkid, prio, aflags, NULL, NULL));
}

/*
 * Helper function for dbuf_hold_impl() to copy a buffer. Handles
 * the case of encrypted, compressed and uncompressed buffers by
 * allocating the new buffer, respectively, with arc_alloc_raw_buf(),
 * arc_alloc_compressed_buf() or arc_alloc_buf().*
 *
 * NOTE: Declared noinline to avoid stack bloat in dbuf_hold_impl().
 */
noinline static void
dbuf_hold_copy(dnode_t *dn, dmu_buf_impl_t *db)
{
	dbuf_dirty_record_t *dr = db->db_data_pending;
	arc_buf_t *data = dr->dt.dl.dr_data;
	enum zio_compress compress_type = arc_get_compression(data);
	uint8_t complevel = arc_get_complevel(data);

	if (arc_is_encrypted(data)) {
		boolean_t byteorder;
		uint8_t salt[ZIO_DATA_SALT_LEN];
		uint8_t iv[ZIO_DATA_IV_LEN];
		uint8_t mac[ZIO_DATA_MAC_LEN];

		arc_get_raw_params(data, &byteorder, salt, iv, mac);
		dbuf_set_data(db, arc_alloc_raw_buf(dn->dn_objset->os_spa, db,
		    dmu_objset_id(dn->dn_objset), byteorder, salt, iv, mac,
		    dn->dn_type, arc_buf_size(data), arc_buf_lsize(data),
		    compress_type, complevel));
	} else if (compress_type != ZIO_COMPRESS_OFF) {
		dbuf_set_data(db, arc_alloc_compressed_buf(
		    dn->dn_objset->os_spa, db, arc_buf_size(data),
		    arc_buf_lsize(data), compress_type, complevel));
	} else {
		dbuf_set_data(db, arc_alloc_buf(dn->dn_objset->os_spa, db,
		    DBUF_GET_BUFC_TYPE(db), db->db.db_size));
	}

	rw_enter(&db->db_rwlock, RW_WRITER);
	memcpy(db->db.db_data, data->b_data, arc_buf_size(data));
	rw_exit(&db->db_rwlock);
}

/*
 * Returns with db_holds incremented, and db_mtx not held.
 * Note: dn_struct_rwlock must be held.
 */
int
dbuf_hold_impl(dnode_t *dn, uint8_t level, uint64_t blkid,
    boolean_t fail_sparse, boolean_t fail_uncached,
    const void *tag, dmu_buf_impl_t **dbp)
{
	dmu_buf_impl_t *db, *parent = NULL;

	/* If the pool has been created, verify the tx_sync_lock is not held */
	spa_t *spa = dn->dn_objset->os_spa;
	dsl_pool_t *dp = spa->spa_dsl_pool;
	if (dp != NULL) {
		ASSERT(!MUTEX_HELD(&dp->dp_tx.tx_sync_lock));
	}

	ASSERT(blkid != DMU_BONUS_BLKID);
	ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
	ASSERT3U(dn->dn_nlevels, >, level);

	*dbp = NULL;

	/* dbuf_find() returns with db_mtx held */
	db = dbuf_find(dn->dn_objset, dn->dn_object, level, blkid);

	if (db == NULL) {
		blkptr_t *bp = NULL;
		int err;

		if (fail_uncached)
			return (SET_ERROR(ENOENT));

		ASSERT3P(parent, ==, NULL);
		err = dbuf_findbp(dn, level, blkid, fail_sparse, &parent, &bp);
		if (fail_sparse) {
			if (err == 0 && bp && BP_IS_HOLE(bp))
				err = SET_ERROR(ENOENT);
			if (err) {
				if (parent)
					dbuf_rele(parent, NULL);
				return (err);
			}
		}
		if (err && err != ENOENT)
			return (err);
		db = dbuf_create(dn, level, blkid, parent, bp);
	}

	if (fail_uncached && db->db_state != DB_CACHED) {
		mutex_exit(&db->db_mtx);
		return (SET_ERROR(ENOENT));
	}

	if (db->db_buf != NULL) {
		arc_buf_access(db->db_buf);
		ASSERT3P(db->db.db_data, ==, db->db_buf->b_data);
	}

	ASSERT(db->db_buf == NULL || arc_referenced(db->db_buf));

	/*
	 * If this buffer is currently syncing out, and we are
	 * still referencing it from db_data, we need to make a copy
	 * of it in case we decide we want to dirty it again in this txg.
	 */
	if (db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID &&
	    dn->dn_object != DMU_META_DNODE_OBJECT &&
	    db->db_state == DB_CACHED && db->db_data_pending) {
		dbuf_dirty_record_t *dr = db->db_data_pending;
		if (dr->dt.dl.dr_data == db->db_buf)
			dbuf_hold_copy(dn, db);
	}

	if (multilist_link_active(&db->db_cache_link)) {
		ASSERT(zfs_refcount_is_zero(&db->db_holds));
		ASSERT(db->db_caching_status == DB_DBUF_CACHE ||
		    db->db_caching_status == DB_DBUF_METADATA_CACHE);

		multilist_remove(&dbuf_caches[db->db_caching_status].cache, db);
		(void) zfs_refcount_remove_many(
		    &dbuf_caches[db->db_caching_status].size,
		    db->db.db_size, db);

		if (db->db_caching_status == DB_DBUF_METADATA_CACHE) {
			DBUF_STAT_BUMPDOWN(metadata_cache_count);
		} else {
			DBUF_STAT_BUMPDOWN(cache_levels[db->db_level]);
			DBUF_STAT_BUMPDOWN(cache_count);
			DBUF_STAT_DECR(cache_levels_bytes[db->db_level],
			    db->db.db_size);
		}
		db->db_caching_status = DB_NO_CACHE;
	}
	(void) zfs_refcount_add(&db->db_holds, tag);
	DBUF_VERIFY(db);
	mutex_exit(&db->db_mtx);

	/* NOTE: we can't rele the parent until after we drop the db_mtx */
	if (parent)
		dbuf_rele(parent, NULL);

	ASSERT3P(DB_DNODE(db), ==, dn);
	ASSERT3U(db->db_blkid, ==, blkid);
	ASSERT3U(db->db_level, ==, level);
	*dbp = db;

	return (0);
}

dmu_buf_impl_t *
dbuf_hold(dnode_t *dn, uint64_t blkid, const void *tag)
{
	return (dbuf_hold_level(dn, 0, blkid, tag));
}

dmu_buf_impl_t *
dbuf_hold_level(dnode_t *dn, int level, uint64_t blkid, const void *tag)
{
	dmu_buf_impl_t *db;
	int err = dbuf_hold_impl(dn, level, blkid, FALSE, FALSE, tag, &db);
	return (err ? NULL : db);
}

void
dbuf_create_bonus(dnode_t *dn)
{
	ASSERT(RW_WRITE_HELD(&dn->dn_struct_rwlock));

	ASSERT(dn->dn_bonus == NULL);
	dn->dn_bonus = dbuf_create(dn, 0, DMU_BONUS_BLKID, dn->dn_dbuf, NULL);
}

int
dbuf_spill_set_blksz(dmu_buf_t *db_fake, uint64_t blksz, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

	if (db->db_blkid != DMU_SPILL_BLKID)
		return (SET_ERROR(ENOTSUP));
	if (blksz == 0)
		blksz = SPA_MINBLOCKSIZE;
	ASSERT3U(blksz, <=, spa_maxblocksize(dmu_objset_spa(db->db_objset)));
	blksz = P2ROUNDUP(blksz, SPA_MINBLOCKSIZE);

	dbuf_new_size(db, blksz, tx);

	return (0);
}

void
dbuf_rm_spill(dnode_t *dn, dmu_tx_t *tx)
{
	dbuf_free_range(dn, DMU_SPILL_BLKID, DMU_SPILL_BLKID, tx);
}

#pragma weak dmu_buf_add_ref = dbuf_add_ref
void
dbuf_add_ref(dmu_buf_impl_t *db, const void *tag)
{
	int64_t holds = zfs_refcount_add(&db->db_holds, tag);
	VERIFY3S(holds, >, 1);
}

#pragma weak dmu_buf_try_add_ref = dbuf_try_add_ref
boolean_t
dbuf_try_add_ref(dmu_buf_t *db_fake, objset_t *os, uint64_t obj, uint64_t blkid,
    const void *tag)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
	dmu_buf_impl_t *found_db;
	boolean_t result = B_FALSE;

	if (blkid == DMU_BONUS_BLKID)
		found_db = dbuf_find_bonus(os, obj);
	else
		found_db = dbuf_find(os, obj, 0, blkid);

	if (found_db != NULL) {
		if (db == found_db && dbuf_refcount(db) > db->db_dirtycnt) {
			(void) zfs_refcount_add(&db->db_holds, tag);
			result = B_TRUE;
		}
		mutex_exit(&found_db->db_mtx);
	}
	return (result);
}

/*
 * If you call dbuf_rele() you had better not be referencing the dnode handle
 * unless you have some other direct or indirect hold on the dnode. (An indirect
 * hold is a hold on one of the dnode's dbufs, including the bonus buffer.)
 * Without that, the dbuf_rele() could lead to a dnode_rele() followed by the
 * dnode's parent dbuf evicting its dnode handles.
 */
void
dbuf_rele(dmu_buf_impl_t *db, const void *tag)
{
	mutex_enter(&db->db_mtx);
	dbuf_rele_and_unlock(db, tag, B_FALSE);
}

void
dmu_buf_rele(dmu_buf_t *db, const void *tag)
{
	dbuf_rele((dmu_buf_impl_t *)db, tag);
}

/*
 * dbuf_rele() for an already-locked dbuf.  This is necessary to allow
 * db_dirtycnt and db_holds to be updated atomically.  The 'evicting'
 * argument should be set if we are already in the dbuf-evicting code
 * path, in which case we don't want to recursively evict.  This allows us to
 * avoid deeply nested stacks that would have a call flow similar to this:
 *
 * dbuf_rele()-->dbuf_rele_and_unlock()-->dbuf_evict_notify()
 *	^						|
 *	|						|
 *	+-----dbuf_destroy()<--dbuf_evict_one()<--------+
 *
 */
void
dbuf_rele_and_unlock(dmu_buf_impl_t *db, const void *tag, boolean_t evicting)
{
	int64_t holds;
	uint64_t size;

	ASSERT(MUTEX_HELD(&db->db_mtx));
	DBUF_VERIFY(db);

	/*
	 * Remove the reference to the dbuf before removing its hold on the
	 * dnode so we can guarantee in dnode_move() that a referenced bonus
	 * buffer has a corresponding dnode hold.
	 */
	holds = zfs_refcount_remove(&db->db_holds, tag);
	ASSERT(holds >= 0);

	/*
	 * We can't freeze indirects if there is a possibility that they
	 * may be modified in the current syncing context.
	 */
	if (db->db_buf != NULL &&
	    holds == (db->db_level == 0 ? db->db_dirtycnt : 0)) {
		arc_buf_freeze(db->db_buf);
	}

	if (holds == db->db_dirtycnt &&
	    db->db_level == 0 && db->db_user_immediate_evict)
		dbuf_evict_user(db);

	if (holds == 0) {
		if (db->db_blkid == DMU_BONUS_BLKID) {
			dnode_t *dn;
			boolean_t evict_dbuf = db->db_pending_evict;

			/*
			 * If the dnode moves here, we cannot cross this
			 * barrier until the move completes.
			 */
			DB_DNODE_ENTER(db);

			dn = DB_DNODE(db);
			atomic_dec_32(&dn->dn_dbufs_count);

			/*
			 * Decrementing the dbuf count means that the bonus
			 * buffer's dnode hold is no longer discounted in
			 * dnode_move(). The dnode cannot move until after
			 * the dnode_rele() below.
			 */
			DB_DNODE_EXIT(db);

			/*
			 * Do not reference db after its lock is dropped.
			 * Another thread may evict it.
			 */
			mutex_exit(&db->db_mtx);

			if (evict_dbuf)
				dnode_evict_bonus(dn);

			dnode_rele(dn, db);
		} else if (db->db_buf == NULL) {
			/*
			 * This is a special case: we never associated this
			 * dbuf with any data allocated from the ARC.
			 */
			ASSERT(db->db_state == DB_UNCACHED ||
			    db->db_state == DB_NOFILL);
			dbuf_destroy(db);
		} else if (arc_released(db->db_buf)) {
			/*
			 * This dbuf has anonymous data associated with it.
			 */
			dbuf_destroy(db);
		} else {
			boolean_t do_arc_evict = B_FALSE;
			blkptr_t bp;
			spa_t *spa = dmu_objset_spa(db->db_objset);

			if (!DBUF_IS_CACHEABLE(db) &&
			    db->db_blkptr != NULL &&
			    !BP_IS_HOLE(db->db_blkptr) &&
			    !BP_IS_EMBEDDED(db->db_blkptr)) {
				do_arc_evict = B_TRUE;
				bp = *db->db_blkptr;
			}

			if (!DBUF_IS_CACHEABLE(db) ||
			    db->db_pending_evict) {
				dbuf_destroy(db);
			} else if (!multilist_link_active(&db->db_cache_link)) {
				ASSERT3U(db->db_caching_status, ==,
				    DB_NO_CACHE);

				dbuf_cached_state_t dcs =
				    dbuf_include_in_metadata_cache(db) ?
				    DB_DBUF_METADATA_CACHE : DB_DBUF_CACHE;
				db->db_caching_status = dcs;

				multilist_insert(&dbuf_caches[dcs].cache, db);
				uint64_t db_size = db->db.db_size;
				size = zfs_refcount_add_many(
				    &dbuf_caches[dcs].size, db_size, db);
				uint8_t db_level = db->db_level;
				mutex_exit(&db->db_mtx);

				if (dcs == DB_DBUF_METADATA_CACHE) {
					DBUF_STAT_BUMP(metadata_cache_count);
					DBUF_STAT_MAX(
					    metadata_cache_size_bytes_max,
					    size);
				} else {
					DBUF_STAT_BUMP(cache_count);
					DBUF_STAT_MAX(cache_size_bytes_max,
					    size);
					DBUF_STAT_BUMP(cache_levels[db_level]);
					DBUF_STAT_INCR(
					    cache_levels_bytes[db_level],
					    db_size);
				}

				if (dcs == DB_DBUF_CACHE && !evicting)
					dbuf_evict_notify(size);
			}

			if (do_arc_evict)
				arc_freed(spa, &bp);
		}
	} else {
		mutex_exit(&db->db_mtx);
	}

}

#pragma weak dmu_buf_refcount = dbuf_refcount
uint64_t
dbuf_refcount(dmu_buf_impl_t *db)
{
	return (zfs_refcount_count(&db->db_holds));
}

uint64_t
dmu_buf_user_refcount(dmu_buf_t *db_fake)
{
	uint64_t holds;
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

	mutex_enter(&db->db_mtx);
	ASSERT3U(zfs_refcount_count(&db->db_holds), >=, db->db_dirtycnt);
	holds = zfs_refcount_count(&db->db_holds) - db->db_dirtycnt;
	mutex_exit(&db->db_mtx);

	return (holds);
}

void *
dmu_buf_replace_user(dmu_buf_t *db_fake, dmu_buf_user_t *old_user,
    dmu_buf_user_t *new_user)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

	mutex_enter(&db->db_mtx);
	dbuf_verify_user(db, DBVU_NOT_EVICTING);
	if (db->db_user == old_user)
		db->db_user = new_user;
	else
		old_user = db->db_user;
	dbuf_verify_user(db, DBVU_NOT_EVICTING);
	mutex_exit(&db->db_mtx);

	return (old_user);
}

void *
dmu_buf_set_user(dmu_buf_t *db_fake, dmu_buf_user_t *user)
{
	return (dmu_buf_replace_user(db_fake, NULL, user));
}

void *
dmu_buf_set_user_ie(dmu_buf_t *db_fake, dmu_buf_user_t *user)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

	db->db_user_immediate_evict = TRUE;
	return (dmu_buf_set_user(db_fake, user));
}

void *
dmu_buf_remove_user(dmu_buf_t *db_fake, dmu_buf_user_t *user)
{
	return (dmu_buf_replace_user(db_fake, user, NULL));
}

void *
dmu_buf_get_user(dmu_buf_t *db_fake)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

	dbuf_verify_user(db, DBVU_NOT_EVICTING);
	return (db->db_user);
}

void
dmu_buf_user_evict_wait(void)
{
	taskq_wait(dbu_evict_taskq);
}

blkptr_t *
dmu_buf_get_blkptr(dmu_buf_t *db)
{
	dmu_buf_impl_t *dbi = (dmu_buf_impl_t *)db;
	return (dbi->db_blkptr);
}

objset_t *
dmu_buf_get_objset(dmu_buf_t *db)
{
	dmu_buf_impl_t *dbi = (dmu_buf_impl_t *)db;
	return (dbi->db_objset);
}

dnode_t *
dmu_buf_dnode_enter(dmu_buf_t *db)
{
	dmu_buf_impl_t *dbi = (dmu_buf_impl_t *)db;
	DB_DNODE_ENTER(dbi);
	return (DB_DNODE(dbi));
}

void
dmu_buf_dnode_exit(dmu_buf_t *db)
{
	dmu_buf_impl_t *dbi = (dmu_buf_impl_t *)db;
	DB_DNODE_EXIT(dbi);
}

static void
dbuf_check_blkptr(dnode_t *dn, dmu_buf_impl_t *db)
{
	/* ASSERT(dmu_tx_is_syncing(tx) */
	ASSERT(MUTEX_HELD(&db->db_mtx));

	if (db->db_blkptr != NULL)
		return;

	if (db->db_blkid == DMU_SPILL_BLKID) {
		db->db_blkptr = DN_SPILL_BLKPTR(dn->dn_phys);
		BP_ZERO(db->db_blkptr);
		return;
	}
	if (db->db_level == dn->dn_phys->dn_nlevels-1) {
		/*
		 * This buffer was allocated at a time when there was
		 * no available blkptrs from the dnode, or it was
		 * inappropriate to hook it in (i.e., nlevels mismatch).
		 */
		ASSERT(db->db_blkid < dn->dn_phys->dn_nblkptr);
		ASSERT(db->db_parent == NULL);
		db->db_parent = dn->dn_dbuf;
		db->db_blkptr = &dn->dn_phys->dn_blkptr[db->db_blkid];
		DBUF_VERIFY(db);
	} else {
		dmu_buf_impl_t *parent = db->db_parent;
		int epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;

		ASSERT(dn->dn_phys->dn_nlevels > 1);
		if (parent == NULL) {
			mutex_exit(&db->db_mtx);
			rw_enter(&dn->dn_struct_rwlock, RW_READER);
			parent = dbuf_hold_level(dn, db->db_level + 1,
			    db->db_blkid >> epbs, db);
			rw_exit(&dn->dn_struct_rwlock);
			mutex_enter(&db->db_mtx);
			db->db_parent = parent;
		}
		db->db_blkptr = (blkptr_t *)parent->db.db_data +
		    (db->db_blkid & ((1ULL << epbs) - 1));
		DBUF_VERIFY(db);
	}
}

static void
dbuf_sync_bonus(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = dr->dr_dbuf;
	void *data = dr->dt.dl.dr_data;

	ASSERT0(db->db_level);
	ASSERT(MUTEX_HELD(&db->db_mtx));
	ASSERT(db->db_blkid == DMU_BONUS_BLKID);
	ASSERT(data != NULL);

	dnode_t *dn = dr->dr_dnode;
	ASSERT3U(DN_MAX_BONUS_LEN(dn->dn_phys), <=,
	    DN_SLOTS_TO_BONUSLEN(dn->dn_phys->dn_extra_slots + 1));
	memcpy(DN_BONUS(dn->dn_phys), data, DN_MAX_BONUS_LEN(dn->dn_phys));

	dbuf_sync_leaf_verify_bonus_dnode(dr);

	dbuf_undirty_bonus(dr);
	dbuf_rele_and_unlock(db, (void *)(uintptr_t)tx->tx_txg, B_FALSE);
}

/*
 * When syncing out a blocks of dnodes, adjust the block to deal with
 * encryption.  Normally, we make sure the block is decrypted before writing
 * it.  If we have crypt params, then we are writing a raw (encrypted) block,
 * from a raw receive.  In this case, set the ARC buf's crypt params so
 * that the BP will be filled with the correct byteorder, salt, iv, and mac.
 */
static void
dbuf_prepare_encrypted_dnode_leaf(dbuf_dirty_record_t *dr)
{
	int err;
	dmu_buf_impl_t *db = dr->dr_dbuf;

	ASSERT(MUTEX_HELD(&db->db_mtx));
	ASSERT3U(db->db.db_object, ==, DMU_META_DNODE_OBJECT);
	ASSERT3U(db->db_level, ==, 0);

	if (!db->db_objset->os_raw_receive && arc_is_encrypted(db->db_buf)) {
		zbookmark_phys_t zb;

		/*
		 * Unfortunately, there is currently no mechanism for
		 * syncing context to handle decryption errors. An error
		 * here is only possible if an attacker maliciously
		 * changed a dnode block and updated the associated
		 * checksums going up the block tree.
		 */
		SET_BOOKMARK(&zb, dmu_objset_id(db->db_objset),
		    db->db.db_object, db->db_level, db->db_blkid);
		err = arc_untransform(db->db_buf, db->db_objset->os_spa,
		    &zb, B_TRUE);
		if (err)
			panic("Invalid dnode block MAC");
	} else if (dr->dt.dl.dr_has_raw_params) {
		(void) arc_release(dr->dt.dl.dr_data, db);
		arc_convert_to_raw(dr->dt.dl.dr_data,
		    dmu_objset_id(db->db_objset),
		    dr->dt.dl.dr_byteorder, DMU_OT_DNODE,
		    dr->dt.dl.dr_salt, dr->dt.dl.dr_iv, dr->dt.dl.dr_mac);
	}
}

/*
 * dbuf_sync_indirect() is called recursively from dbuf_sync_list() so it
 * is critical the we not allow the compiler to inline this function in to
 * dbuf_sync_list() thereby drastically bloating the stack usage.
 */
noinline static void
dbuf_sync_indirect(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = dr->dr_dbuf;
	dnode_t *dn = dr->dr_dnode;

	ASSERT(dmu_tx_is_syncing(tx));

	dprintf_dbuf_bp(db, db->db_blkptr, "blkptr=%p", db->db_blkptr);

	mutex_enter(&db->db_mtx);

	ASSERT(db->db_level > 0);
	DBUF_VERIFY(db);

	/* Read the block if it hasn't been read yet. */
	if (db->db_buf == NULL) {
		mutex_exit(&db->db_mtx);
		(void) dbuf_read(db, NULL, DB_RF_MUST_SUCCEED);
		mutex_enter(&db->db_mtx);
	}
	ASSERT3U(db->db_state, ==, DB_CACHED);
	ASSERT(db->db_buf != NULL);

	/* Indirect block size must match what the dnode thinks it is. */
	ASSERT3U(db->db.db_size, ==, 1<<dn->dn_phys->dn_indblkshift);
	dbuf_check_blkptr(dn, db);

	/* Provide the pending dirty record to child dbufs */
	db->db_data_pending = dr;

	mutex_exit(&db->db_mtx);

	dbuf_write(dr, db->db_buf, tx);

	zio_t *zio = dr->dr_zio;
	mutex_enter(&dr->dt.di.dr_mtx);
	dbuf_sync_list(&dr->dt.di.dr_children, db->db_level - 1, tx);
	ASSERT(list_head(&dr->dt.di.dr_children) == NULL);
	mutex_exit(&dr->dt.di.dr_mtx);
	zio_nowait(zio);
}

/*
 * Verify that the size of the data in our bonus buffer does not exceed
 * its recorded size.
 *
 * The purpose of this verification is to catch any cases in development
 * where the size of a phys structure (i.e space_map_phys_t) grows and,
 * due to incorrect feature management, older pools expect to read more
 * data even though they didn't actually write it to begin with.
 *
 * For a example, this would catch an error in the feature logic where we
 * open an older pool and we expect to write the space map histogram of
 * a space map with size SPACE_MAP_SIZE_V0.
 */
static void
dbuf_sync_leaf_verify_bonus_dnode(dbuf_dirty_record_t *dr)
{
#ifdef ZFS_DEBUG
	dnode_t *dn = dr->dr_dnode;

	/*
	 * Encrypted bonus buffers can have data past their bonuslen.
	 * Skip the verification of these blocks.
	 */
	if (DMU_OT_IS_ENCRYPTED(dn->dn_bonustype))
		return;

	uint16_t bonuslen = dn->dn_phys->dn_bonuslen;
	uint16_t maxbonuslen = DN_SLOTS_TO_BONUSLEN(dn->dn_num_slots);
	ASSERT3U(bonuslen, <=, maxbonuslen);

	arc_buf_t *datap = dr->dt.dl.dr_data;
	char *datap_end = ((char *)datap) + bonuslen;
	char *datap_max = ((char *)datap) + maxbonuslen;

	/* ensure that everything is zero after our data */
	for (; datap_end < datap_max; datap_end++)
		ASSERT(*datap_end == 0);
#endif
}

static blkptr_t *
dbuf_lightweight_bp(dbuf_dirty_record_t *dr)
{
	/* This must be a lightweight dirty record. */
	ASSERT3P(dr->dr_dbuf, ==, NULL);
	dnode_t *dn = dr->dr_dnode;

	if (dn->dn_phys->dn_nlevels == 1) {
		VERIFY3U(dr->dt.dll.dr_blkid, <, dn->dn_phys->dn_nblkptr);
		return (&dn->dn_phys->dn_blkptr[dr->dt.dll.dr_blkid]);
	} else {
		dmu_buf_impl_t *parent_db = dr->dr_parent->dr_dbuf;
		int epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
		VERIFY3U(parent_db->db_level, ==, 1);
		VERIFY3P(parent_db->db_dnode_handle->dnh_dnode, ==, dn);
		VERIFY3U(dr->dt.dll.dr_blkid >> epbs, ==, parent_db->db_blkid);
		blkptr_t *bp = parent_db->db.db_data;
		return (&bp[dr->dt.dll.dr_blkid & ((1 << epbs) - 1)]);
	}
}

static void
dbuf_lightweight_ready(zio_t *zio)
{
	dbuf_dirty_record_t *dr = zio->io_private;
	blkptr_t *bp = zio->io_bp;

	if (zio->io_error != 0)
		return;

	dnode_t *dn = dr->dr_dnode;

	blkptr_t *bp_orig = dbuf_lightweight_bp(dr);
	spa_t *spa = dmu_objset_spa(dn->dn_objset);
	int64_t delta = bp_get_dsize_sync(spa, bp) -
	    bp_get_dsize_sync(spa, bp_orig);
	dnode_diduse_space(dn, delta);

	uint64_t blkid = dr->dt.dll.dr_blkid;
	mutex_enter(&dn->dn_mtx);
	if (blkid > dn->dn_phys->dn_maxblkid) {
		ASSERT0(dn->dn_objset->os_raw_receive);
		dn->dn_phys->dn_maxblkid = blkid;
	}
	mutex_exit(&dn->dn_mtx);

	if (!BP_IS_EMBEDDED(bp)) {
		uint64_t fill = BP_IS_HOLE(bp) ? 0 : 1;
		BP_SET_FILL(bp, fill);
	}

	dmu_buf_impl_t *parent_db;
	EQUIV(dr->dr_parent == NULL, dn->dn_phys->dn_nlevels == 1);
	if (dr->dr_parent == NULL) {
		parent_db = dn->dn_dbuf;
	} else {
		parent_db = dr->dr_parent->dr_dbuf;
	}
	rw_enter(&parent_db->db_rwlock, RW_WRITER);
	*bp_orig = *bp;
	rw_exit(&parent_db->db_rwlock);
}

static void
dbuf_lightweight_physdone(zio_t *zio)
{
	dbuf_dirty_record_t *dr = zio->io_private;
	dsl_pool_t *dp = spa_get_dsl(zio->io_spa);
	ASSERT3U(dr->dr_txg, ==, zio->io_txg);

	/*
	 * The callback will be called io_phys_children times.  Retire one
	 * portion of our dirty space each time we are called.  Any rounding
	 * error will be cleaned up by dbuf_lightweight_done().
	 */
	int delta = dr->dr_accounted / zio->io_phys_children;
	dsl_pool_undirty_space(dp, delta, zio->io_txg);
}

static void
dbuf_lightweight_done(zio_t *zio)
{
	dbuf_dirty_record_t *dr = zio->io_private;

	VERIFY0(zio->io_error);

	objset_t *os = dr->dr_dnode->dn_objset;
	dmu_tx_t *tx = os->os_synctx;

	if (zio->io_flags & (ZIO_FLAG_IO_REWRITE | ZIO_FLAG_NOPWRITE)) {
		ASSERT(BP_EQUAL(zio->io_bp, &zio->io_bp_orig));
	} else {
		dsl_dataset_t *ds = os->os_dsl_dataset;
		(void) dsl_dataset_block_kill(ds, &zio->io_bp_orig, tx, B_TRUE);
		dsl_dataset_block_born(ds, zio->io_bp, tx);
	}

	/*
	 * See comment in dbuf_write_done().
	 */
	if (zio->io_phys_children == 0) {
		dsl_pool_undirty_space(dmu_objset_pool(os),
		    dr->dr_accounted, zio->io_txg);
	} else {
		dsl_pool_undirty_space(dmu_objset_pool(os),
		    dr->dr_accounted % zio->io_phys_children, zio->io_txg);
	}

	abd_free(dr->dt.dll.dr_abd);
	kmem_free(dr, sizeof (*dr));
}

noinline static void
dbuf_sync_lightweight(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
{
	dnode_t *dn = dr->dr_dnode;
	zio_t *pio;
	if (dn->dn_phys->dn_nlevels == 1) {
		pio = dn->dn_zio;
	} else {
		pio = dr->dr_parent->dr_zio;
	}

	zbookmark_phys_t zb = {
		.zb_objset = dmu_objset_id(dn->dn_objset),
		.zb_object = dn->dn_object,
		.zb_level = 0,
		.zb_blkid = dr->dt.dll.dr_blkid,
	};

	/*
	 * See comment in dbuf_write().  This is so that zio->io_bp_orig
	 * will have the old BP in dbuf_lightweight_done().
	 */
	dr->dr_bp_copy = *dbuf_lightweight_bp(dr);

	dr->dr_zio = zio_write(pio, dmu_objset_spa(dn->dn_objset),
	    dmu_tx_get_txg(tx), &dr->dr_bp_copy, dr->dt.dll.dr_abd,
	    dn->dn_datablksz, abd_get_size(dr->dt.dll.dr_abd),
	    &dr->dt.dll.dr_props, dbuf_lightweight_ready, NULL,
	    dbuf_lightweight_physdone, dbuf_lightweight_done, dr,
	    ZIO_PRIORITY_ASYNC_WRITE,
	    ZIO_FLAG_MUSTSUCCEED | dr->dt.dll.dr_flags, &zb);

	zio_nowait(dr->dr_zio);
}

/*
 * dbuf_sync_leaf() is called recursively from dbuf_sync_list() so it is
 * critical the we not allow the compiler to inline this function in to
 * dbuf_sync_list() thereby drastically bloating the stack usage.
 */
noinline static void
dbuf_sync_leaf(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
{
	arc_buf_t **datap = &dr->dt.dl.dr_data;
	dmu_buf_impl_t *db = dr->dr_dbuf;
	dnode_t *dn = dr->dr_dnode;
	objset_t *os;
	uint64_t txg = tx->tx_txg;

	ASSERT(dmu_tx_is_syncing(tx));

	dprintf_dbuf_bp(db, db->db_blkptr, "blkptr=%p", db->db_blkptr);

	mutex_enter(&db->db_mtx);
	/*
	 * To be synced, we must be dirtied.  But we
	 * might have been freed after the dirty.
	 */
	if (db->db_state == DB_UNCACHED) {
		/* This buffer has been freed since it was dirtied */
		ASSERT(db->db.db_data == NULL);
	} else if (db->db_state == DB_FILL) {
		/* This buffer was freed and is now being re-filled */
		ASSERT(db->db.db_data != dr->dt.dl.dr_data);
	} else {
		ASSERT(db->db_state == DB_CACHED || db->db_state == DB_NOFILL);
	}
	DBUF_VERIFY(db);

	if (db->db_blkid == DMU_SPILL_BLKID) {
		mutex_enter(&dn->dn_mtx);
		if (!(dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR)) {
			/*
			 * In the previous transaction group, the bonus buffer
			 * was entirely used to store the attributes for the
			 * dnode which overrode the dn_spill field.  However,
			 * when adding more attributes to the file a spill
			 * block was required to hold the extra attributes.
			 *
			 * Make sure to clear the garbage left in the dn_spill
			 * field from the previous attributes in the bonus
			 * buffer.  Otherwise, after writing out the spill
			 * block to the new allocated dva, it will free
			 * the old block pointed to by the invalid dn_spill.
			 */
			db->db_blkptr = NULL;
		}
		dn->dn_phys->dn_flags |= DNODE_FLAG_SPILL_BLKPTR;
		mutex_exit(&dn->dn_mtx);
	}

	/*
	 * If this is a bonus buffer, simply copy the bonus data into the
	 * dnode.  It will be written out when the dnode is synced (and it
	 * will be synced, since it must have been dirty for dbuf_sync to
	 * be called).
	 */
	if (db->db_blkid == DMU_BONUS_BLKID) {
		ASSERT(dr->dr_dbuf == db);
		dbuf_sync_bonus(dr, tx);
		return;
	}

	os = dn->dn_objset;

	/*
	 * This function may have dropped the db_mtx lock allowing a dmu_sync
	 * operation to sneak in. As a result, we need to ensure that we
	 * don't check the dr_override_state until we have returned from
	 * dbuf_check_blkptr.
	 */
	dbuf_check_blkptr(dn, db);

	/*
	 * If this buffer is in the middle of an immediate write,
	 * wait for the synchronous IO to complete.
	 */
	while (dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC) {
		ASSERT(dn->dn_object != DMU_META_DNODE_OBJECT);
		cv_wait(&db->db_changed, &db->db_mtx);
		ASSERT(dr->dt.dl.dr_override_state != DR_NOT_OVERRIDDEN);
	}

	/*
	 * If this is a dnode block, ensure it is appropriately encrypted
	 * or decrypted, depending on what we are writing to it this txg.
	 */
	if (os->os_encrypted && dn->dn_object == DMU_META_DNODE_OBJECT)
		dbuf_prepare_encrypted_dnode_leaf(dr);

	if (db->db_state != DB_NOFILL &&
	    dn->dn_object != DMU_META_DNODE_OBJECT &&
	    zfs_refcount_count(&db->db_holds) > 1 &&
	    dr->dt.dl.dr_override_state != DR_OVERRIDDEN &&
	    *datap == db->db_buf) {
		/*
		 * If this buffer is currently "in use" (i.e., there
		 * are active holds and db_data still references it),
		 * then make a copy before we start the write so that
		 * any modifications from the open txg will not leak
		 * into this write.
		 *
		 * NOTE: this copy does not need to be made for
		 * objects only modified in the syncing context (e.g.
		 * DNONE_DNODE blocks).
		 */
		int psize = arc_buf_size(*datap);
		int lsize = arc_buf_lsize(*datap);
		arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
		enum zio_compress compress_type = arc_get_compression(*datap);
		uint8_t complevel = arc_get_complevel(*datap);

		if (arc_is_encrypted(*datap)) {
			boolean_t byteorder;
			uint8_t salt[ZIO_DATA_SALT_LEN];
			uint8_t iv[ZIO_DATA_IV_LEN];
			uint8_t mac[ZIO_DATA_MAC_LEN];

			arc_get_raw_params(*datap, &byteorder, salt, iv, mac);
			*datap = arc_alloc_raw_buf(os->os_spa, db,
			    dmu_objset_id(os), byteorder, salt, iv, mac,
			    dn->dn_type, psize, lsize, compress_type,
			    complevel);
		} else if (compress_type != ZIO_COMPRESS_OFF) {
			ASSERT3U(type, ==, ARC_BUFC_DATA);
			*datap = arc_alloc_compressed_buf(os->os_spa, db,
			    psize, lsize, compress_type, complevel);
		} else {
			*datap = arc_alloc_buf(os->os_spa, db, type, psize);
		}
		memcpy((*datap)->b_data, db->db.db_data, psize);
	}
	db->db_data_pending = dr;

	mutex_exit(&db->db_mtx);

	dbuf_write(dr, *datap, tx);

	ASSERT(!list_link_active(&dr->dr_dirty_node));
	if (dn->dn_object == DMU_META_DNODE_OBJECT) {
		list_insert_tail(&dn->dn_dirty_records[txg & TXG_MASK], dr);
	} else {
		zio_nowait(dr->dr_zio);
	}
}

void
dbuf_sync_list(list_t *list, int level, dmu_tx_t *tx)
{
	dbuf_dirty_record_t *dr;

	while ((dr = list_head(list))) {
		if (dr->dr_zio != NULL) {
			/*
			 * If we find an already initialized zio then we
			 * are processing the meta-dnode, and we have finished.
			 * The dbufs for all dnodes are put back on the list
			 * during processing, so that we can zio_wait()
			 * these IOs after initiating all child IOs.
			 */
			ASSERT3U(dr->dr_dbuf->db.db_object, ==,
			    DMU_META_DNODE_OBJECT);
			break;
		}
		list_remove(list, dr);
		if (dr->dr_dbuf == NULL) {
			dbuf_sync_lightweight(dr, tx);
		} else {
			if (dr->dr_dbuf->db_blkid != DMU_BONUS_BLKID &&
			    dr->dr_dbuf->db_blkid != DMU_SPILL_BLKID) {
				VERIFY3U(dr->dr_dbuf->db_level, ==, level);
			}
			if (dr->dr_dbuf->db_level > 0)
				dbuf_sync_indirect(dr, tx);
			else
				dbuf_sync_leaf(dr, tx);
		}
	}
}

static void
dbuf_write_ready(zio_t *zio, arc_buf_t *buf, void *vdb)
{
	(void) buf;
	dmu_buf_impl_t *db = vdb;
	dnode_t *dn;
	blkptr_t *bp = zio->io_bp;
	blkptr_t *bp_orig = &zio->io_bp_orig;
	spa_t *spa = zio->io_spa;
	int64_t delta;
	uint64_t fill = 0;
	int i;

	ASSERT3P(db->db_blkptr, !=, NULL);
	ASSERT3P(&db->db_data_pending->dr_bp_copy, ==, bp);

	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);
	delta = bp_get_dsize_sync(spa, bp) - bp_get_dsize_sync(spa, bp_orig);
	dnode_diduse_space(dn, delta - zio->io_prev_space_delta);
	zio->io_prev_space_delta = delta;

	if (bp->blk_birth != 0) {
		ASSERT((db->db_blkid != DMU_SPILL_BLKID &&
		    BP_GET_TYPE(bp) == dn->dn_type) ||
		    (db->db_blkid == DMU_SPILL_BLKID &&
		    BP_GET_TYPE(bp) == dn->dn_bonustype) ||
		    BP_IS_EMBEDDED(bp));
		ASSERT(BP_GET_LEVEL(bp) == db->db_level);
	}

	mutex_enter(&db->db_mtx);

#ifdef ZFS_DEBUG
	if (db->db_blkid == DMU_SPILL_BLKID) {
		ASSERT(dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR);
		ASSERT(!(BP_IS_HOLE(bp)) &&
		    db->db_blkptr == DN_SPILL_BLKPTR(dn->dn_phys));
	}
#endif

	if (db->db_level == 0) {
		mutex_enter(&dn->dn_mtx);
		if (db->db_blkid > dn->dn_phys->dn_maxblkid &&
		    db->db_blkid != DMU_SPILL_BLKID) {
			ASSERT0(db->db_objset->os_raw_receive);
			dn->dn_phys->dn_maxblkid = db->db_blkid;
		}
		mutex_exit(&dn->dn_mtx);

		if (dn->dn_type == DMU_OT_DNODE) {
			i = 0;
			while (i < db->db.db_size) {
				dnode_phys_t *dnp =
				    (void *)(((char *)db->db.db_data) + i);

				i += DNODE_MIN_SIZE;
				if (dnp->dn_type != DMU_OT_NONE) {
					fill++;
					i += dnp->dn_extra_slots *
					    DNODE_MIN_SIZE;
				}
			}
		} else {
			if (BP_IS_HOLE(bp)) {
				fill = 0;
			} else {
				fill = 1;
			}
		}
	} else {
		blkptr_t *ibp = db->db.db_data;
		ASSERT3U(db->db.db_size, ==, 1<<dn->dn_phys->dn_indblkshift);
		for (i = db->db.db_size >> SPA_BLKPTRSHIFT; i > 0; i--, ibp++) {
			if (BP_IS_HOLE(ibp))
				continue;
			fill += BP_GET_FILL(ibp);
		}
	}
	DB_DNODE_EXIT(db);

	if (!BP_IS_EMBEDDED(bp))
		BP_SET_FILL(bp, fill);

	mutex_exit(&db->db_mtx);

	db_lock_type_t dblt = dmu_buf_lock_parent(db, RW_WRITER, FTAG);
	*db->db_blkptr = *bp;
	dmu_buf_unlock_parent(db, dblt, FTAG);
}

/*
 * This function gets called just prior to running through the compression
 * stage of the zio pipeline. If we're an indirect block comprised of only
 * holes, then we want this indirect to be compressed away to a hole. In
 * order to do that we must zero out any information about the holes that
 * this indirect points to prior to before we try to compress it.
 */
static void
dbuf_write_children_ready(zio_t *zio, arc_buf_t *buf, void *vdb)
{
	(void) zio, (void) buf;
	dmu_buf_impl_t *db = vdb;
	dnode_t *dn;
	blkptr_t *bp;
	unsigned int epbs, i;

	ASSERT3U(db->db_level, >, 0);
	DB_DNODE_ENTER(db);
	dn = DB_DNODE(db);
	epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
	ASSERT3U(epbs, <, 31);

	/* Determine if all our children are holes */
	for (i = 0, bp = db->db.db_data; i < 1ULL << epbs; i++, bp++) {
		if (!BP_IS_HOLE(bp))
			break;
	}

	/*
	 * If all the children are holes, then zero them all out so that
	 * we may get compressed away.
	 */
	if (i == 1ULL << epbs) {
		/*
		 * We only found holes. Grab the rwlock to prevent
		 * anybody from reading the blocks we're about to
		 * zero out.
		 */
		rw_enter(&db->db_rwlock, RW_WRITER);
		memset(db->db.db_data, 0, db->db.db_size);
		rw_exit(&db->db_rwlock);
	}
	DB_DNODE_EXIT(db);
}

/*
 * The SPA will call this callback several times for each zio - once
 * for every physical child i/o (zio->io_phys_children times).  This
 * allows the DMU to monitor the progress of each logical i/o.  For example,
 * there may be 2 copies of an indirect block, or many fragments of a RAID-Z
 * block.  There may be a long delay before all copies/fragments are completed,
 * so this callback allows us to retire dirty space gradually, as the physical
 * i/os complete.
 */
static void
dbuf_write_physdone(zio_t *zio, arc_buf_t *buf, void *arg)
{
	(void) buf;
	dmu_buf_impl_t *db = arg;
	objset_t *os = db->db_objset;
	dsl_pool_t *dp = dmu_objset_pool(os);
	dbuf_dirty_record_t *dr;
	int delta = 0;

	dr = db->db_data_pending;
	ASSERT3U(dr->dr_txg, ==, zio->io_txg);

	/*
	 * The callback will be called io_phys_children times.  Retire one
	 * portion of our dirty space each time we are called.  Any rounding
	 * error will be cleaned up by dbuf_write_done().
	 */
	delta = dr->dr_accounted / zio->io_phys_children;
	dsl_pool_undirty_space(dp, delta, zio->io_txg);
}

static void
dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
{
	(void) buf;
	dmu_buf_impl_t *db = vdb;
	blkptr_t *bp_orig = &zio->io_bp_orig;
	blkptr_t *bp = db->db_blkptr;
	objset_t *os = db->db_objset;
	dmu_tx_t *tx = os->os_synctx;

	ASSERT0(zio->io_error);
	ASSERT(db->db_blkptr == bp);

	/*
	 * For nopwrites and rewrites we ensure that the bp matches our
	 * original and bypass all the accounting.
	 */
	if (zio->io_flags & (ZIO_FLAG_IO_REWRITE | ZIO_FLAG_NOPWRITE)) {
		ASSERT(BP_EQUAL(bp, bp_orig));
	} else {
		dsl_dataset_t *ds = os->os_dsl_dataset;
		(void) dsl_dataset_block_kill(ds, bp_orig, tx, B_TRUE);
		dsl_dataset_block_born(ds, bp, tx);
	}

	mutex_enter(&db->db_mtx);

	DBUF_VERIFY(db);

	dbuf_dirty_record_t *dr = db->db_data_pending;
	dnode_t *dn = dr->dr_dnode;
	ASSERT(!list_link_active(&dr->dr_dirty_node));
	ASSERT(dr->dr_dbuf == db);
	ASSERT(list_next(&db->db_dirty_records, dr) == NULL);
	list_remove(&db->db_dirty_records, dr);

#ifdef ZFS_DEBUG
	if (db->db_blkid == DMU_SPILL_BLKID) {
		ASSERT(dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR);
		ASSERT(!(BP_IS_HOLE(db->db_blkptr)) &&
		    db->db_blkptr == DN_SPILL_BLKPTR(dn->dn_phys));
	}
#endif

	if (db->db_level == 0) {
		ASSERT(db->db_blkid != DMU_BONUS_BLKID);
		ASSERT(dr->dt.dl.dr_override_state == DR_NOT_OVERRIDDEN);
		if (db->db_state != DB_NOFILL) {
			if (dr->dt.dl.dr_data != db->db_buf)
				arc_buf_destroy(dr->dt.dl.dr_data, db);
		}
	} else {
		ASSERT(list_head(&dr->dt.di.dr_children) == NULL);
		ASSERT3U(db->db.db_size, ==, 1 << dn->dn_phys->dn_indblkshift);
		if (!BP_IS_HOLE(db->db_blkptr)) {
			int epbs __maybe_unused = dn->dn_phys->dn_indblkshift -
			    SPA_BLKPTRSHIFT;
			ASSERT3U(db->db_blkid, <=,
			    dn->dn_phys->dn_maxblkid >> (db->db_level * epbs));
			ASSERT3U(BP_GET_LSIZE(db->db_blkptr), ==,
			    db->db.db_size);
		}
		mutex_destroy(&dr->dt.di.dr_mtx);
		list_destroy(&dr->dt.di.dr_children);
	}

	cv_broadcast(&db->db_changed);
	ASSERT(db->db_dirtycnt > 0);
	db->db_dirtycnt -= 1;
	db->db_data_pending = NULL;
	dbuf_rele_and_unlock(db, (void *)(uintptr_t)tx->tx_txg, B_FALSE);

	/*
	 * If we didn't do a physical write in this ZIO and we
	 * still ended up here, it means that the space of the
	 * dbuf that we just released (and undirtied) above hasn't
	 * been marked as undirtied in the pool's accounting.
	 *
	 * Thus, we undirty that space in the pool's view of the
	 * world here. For physical writes this type of update
	 * happens in dbuf_write_physdone().
	 *
	 * If we did a physical write, cleanup any rounding errors
	 * that came up due to writing multiple copies of a block
	 * on disk [see dbuf_write_physdone()].
	 */
	if (zio->io_phys_children == 0) {
		dsl_pool_undirty_space(dmu_objset_pool(os),
		    dr->dr_accounted, zio->io_txg);
	} else {
		dsl_pool_undirty_space(dmu_objset_pool(os),
		    dr->dr_accounted % zio->io_phys_children, zio->io_txg);
	}

	kmem_free(dr, sizeof (dbuf_dirty_record_t));
}

static void
dbuf_write_nofill_ready(zio_t *zio)
{
	dbuf_write_ready(zio, NULL, zio->io_private);
}

static void
dbuf_write_nofill_done(zio_t *zio)
{
	dbuf_write_done(zio, NULL, zio->io_private);
}

static void
dbuf_write_override_ready(zio_t *zio)
{
	dbuf_dirty_record_t *dr = zio->io_private;
	dmu_buf_impl_t *db = dr->dr_dbuf;

	dbuf_write_ready(zio, NULL, db);
}

static void
dbuf_write_override_done(zio_t *zio)
{
	dbuf_dirty_record_t *dr = zio->io_private;
	dmu_buf_impl_t *db = dr->dr_dbuf;
	blkptr_t *obp = &dr->dt.dl.dr_overridden_by;

	mutex_enter(&db->db_mtx);
	if (!BP_EQUAL(zio->io_bp, obp)) {
		if (!BP_IS_HOLE(obp))
			dsl_free(spa_get_dsl(zio->io_spa), zio->io_txg, obp);
		arc_release(dr->dt.dl.dr_data, db);
	}
	mutex_exit(&db->db_mtx);

	dbuf_write_done(zio, NULL, db);

	if (zio->io_abd != NULL)
		abd_free(zio->io_abd);
}

typedef struct dbuf_remap_impl_callback_arg {
	objset_t	*drica_os;
	uint64_t	drica_blk_birth;
	dmu_tx_t	*drica_tx;
} dbuf_remap_impl_callback_arg_t;

static void
dbuf_remap_impl_callback(uint64_t vdev, uint64_t offset, uint64_t size,
    void *arg)
{
	dbuf_remap_impl_callback_arg_t *drica = arg;
	objset_t *os = drica->drica_os;
	spa_t *spa = dmu_objset_spa(os);
	dmu_tx_t *tx = drica->drica_tx;

	ASSERT(dsl_pool_sync_context(spa_get_dsl(spa)));

	if (os == spa_meta_objset(spa)) {
		spa_vdev_indirect_mark_obsolete(spa, vdev, offset, size, tx);
	} else {
		dsl_dataset_block_remapped(dmu_objset_ds(os), vdev, offset,
		    size, drica->drica_blk_birth, tx);
	}
}

static void
dbuf_remap_impl(dnode_t *dn, blkptr_t *bp, krwlock_t *rw, dmu_tx_t *tx)
{
	blkptr_t bp_copy = *bp;
	spa_t *spa = dmu_objset_spa(dn->dn_objset);
	dbuf_remap_impl_callback_arg_t drica;

	ASSERT(dsl_pool_sync_context(spa_get_dsl(spa)));

	drica.drica_os = dn->dn_objset;
	drica.drica_blk_birth = bp->blk_birth;
	drica.drica_tx = tx;
	if (spa_remap_blkptr(spa, &bp_copy, dbuf_remap_impl_callback,
	    &drica)) {
		/*
		 * If the blkptr being remapped is tracked by a livelist,
		 * then we need to make sure the livelist reflects the update.
		 * First, cancel out the old blkptr by appending a 'FREE'
		 * entry. Next, add an 'ALLOC' to track the new version. This
		 * way we avoid trying to free an inaccurate blkptr at delete.
		 * Note that embedded blkptrs are not tracked in livelists.
		 */
		if (dn->dn_objset != spa_meta_objset(spa)) {
			dsl_dataset_t *ds = dmu_objset_ds(dn->dn_objset);
			if (dsl_deadlist_is_open(&ds->ds_dir->dd_livelist) &&
			    bp->blk_birth > ds->ds_dir->dd_origin_txg) {
				ASSERT(!BP_IS_EMBEDDED(bp));
				ASSERT(dsl_dir_is_clone(ds->ds_dir));
				ASSERT(spa_feature_is_enabled(spa,
				    SPA_FEATURE_LIVELIST));
				bplist_append(&ds->ds_dir->dd_pending_frees,
				    bp);
				bplist_append(&ds->ds_dir->dd_pending_allocs,
				    &bp_copy);
			}
		}

		/*
		 * The db_rwlock prevents dbuf_read_impl() from
		 * dereferencing the BP while we are changing it.  To
		 * avoid lock contention, only grab it when we are actually
		 * changing the BP.
		 */
		if (rw != NULL)
			rw_enter(rw, RW_WRITER);
		*bp = bp_copy;
		if (rw != NULL)
			rw_exit(rw);
	}
}

/*
 * Remap any existing BP's to concrete vdevs, if possible.
 */
static void
dbuf_remap(dnode_t *dn, dmu_buf_impl_t *db, dmu_tx_t *tx)
{
	spa_t *spa = dmu_objset_spa(db->db_objset);
	ASSERT(dsl_pool_sync_context(spa_get_dsl(spa)));

	if (!spa_feature_is_active(spa, SPA_FEATURE_DEVICE_REMOVAL))
		return;

	if (db->db_level > 0) {
		blkptr_t *bp = db->db.db_data;
		for (int i = 0; i < db->db.db_size >> SPA_BLKPTRSHIFT; i++) {
			dbuf_remap_impl(dn, &bp[i], &db->db_rwlock, tx);
		}
	} else if (db->db.db_object == DMU_META_DNODE_OBJECT) {
		dnode_phys_t *dnp = db->db.db_data;
		ASSERT3U(db->db_dnode_handle->dnh_dnode->dn_type, ==,
		    DMU_OT_DNODE);
		for (int i = 0; i < db->db.db_size >> DNODE_SHIFT;
		    i += dnp[i].dn_extra_slots + 1) {
			for (int j = 0; j < dnp[i].dn_nblkptr; j++) {
				krwlock_t *lock = (dn->dn_dbuf == NULL ? NULL :
				    &dn->dn_dbuf->db_rwlock);
				dbuf_remap_impl(dn, &dnp[i].dn_blkptr[j], lock,
				    tx);
			}
		}
	}
}


/* Issue I/O to commit a dirty buffer to disk. */
static void
dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx)
{
	dmu_buf_impl_t *db = dr->dr_dbuf;
	dnode_t *dn = dr->dr_dnode;
	objset_t *os;
	dmu_buf_impl_t *parent = db->db_parent;
	uint64_t txg = tx->tx_txg;
	zbookmark_phys_t zb;
	zio_prop_t zp;
	zio_t *pio; /* parent I/O */
	int wp_flag = 0;

	ASSERT(dmu_tx_is_syncing(tx));

	os = dn->dn_objset;

	if (db->db_state != DB_NOFILL) {
		if (db->db_level > 0 || dn->dn_type == DMU_OT_DNODE) {
			/*
			 * Private object buffers are released here rather
			 * than in dbuf_dirty() since they are only modified
			 * in the syncing context and we don't want the
			 * overhead of making multiple copies of the data.
			 */
			if (BP_IS_HOLE(db->db_blkptr)) {
				arc_buf_thaw(data);
			} else {
				dbuf_release_bp(db);
			}
			dbuf_remap(dn, db, tx);
		}
	}

	if (parent != dn->dn_dbuf) {
		/* Our parent is an indirect block. */
		/* We have a dirty parent that has been scheduled for write. */
		ASSERT(parent && parent->db_data_pending);
		/* Our parent's buffer is one level closer to the dnode. */
		ASSERT(db->db_level == parent->db_level-1);
		/*
		 * We're about to modify our parent's db_data by modifying
		 * our block pointer, so the parent must be released.
		 */
		ASSERT(arc_released(parent->db_buf));
		pio = parent->db_data_pending->dr_zio;
	} else {
		/* Our parent is the dnode itself. */
		ASSERT((db->db_level == dn->dn_phys->dn_nlevels-1 &&
		    db->db_blkid != DMU_SPILL_BLKID) ||
		    (db->db_blkid == DMU_SPILL_BLKID && db->db_level == 0));
		if (db->db_blkid != DMU_SPILL_BLKID)
			ASSERT3P(db->db_blkptr, ==,
			    &dn->dn_phys->dn_blkptr[db->db_blkid]);
		pio = dn->dn_zio;
	}

	ASSERT(db->db_level == 0 || data == db->db_buf);
	ASSERT3U(db->db_blkptr->blk_birth, <=, txg);
	ASSERT(pio);

	SET_BOOKMARK(&zb, os->os_dsl_dataset ?
	    os->os_dsl_dataset->ds_object : DMU_META_OBJSET,
	    db->db.db_object, db->db_level, db->db_blkid);

	if (db->db_blkid == DMU_SPILL_BLKID)
		wp_flag = WP_SPILL;
	wp_flag |= (db->db_state == DB_NOFILL) ? WP_NOFILL : 0;

	dmu_write_policy(os, dn, db->db_level, wp_flag, &zp);

	/*
	 * We copy the blkptr now (rather than when we instantiate the dirty
	 * record), because its value can change between open context and
	 * syncing context. We do not need to hold dn_struct_rwlock to read
	 * db_blkptr because we are in syncing context.
	 */
	dr->dr_bp_copy = *db->db_blkptr;

	if (db->db_level == 0 &&
	    dr->dt.dl.dr_override_state == DR_OVERRIDDEN) {
		/*
		 * The BP for this block has been provided by open context
		 * (by dmu_sync() or dmu_buf_write_embedded()).
		 */
		abd_t *contents = (data != NULL) ?
		    abd_get_from_buf(data->b_data, arc_buf_size(data)) : NULL;

		dr->dr_zio = zio_write(pio, os->os_spa, txg, &dr->dr_bp_copy,
		    contents, db->db.db_size, db->db.db_size, &zp,
		    dbuf_write_override_ready, NULL, NULL,
		    dbuf_write_override_done,
		    dr, ZIO_PRIORITY_ASYNC_WRITE, ZIO_FLAG_MUSTSUCCEED, &zb);
		mutex_enter(&db->db_mtx);
		dr->dt.dl.dr_override_state = DR_NOT_OVERRIDDEN;
		zio_write_override(dr->dr_zio, &dr->dt.dl.dr_overridden_by,
		    dr->dt.dl.dr_copies, dr->dt.dl.dr_nopwrite);
		mutex_exit(&db->db_mtx);
	} else if (db->db_state == DB_NOFILL) {
		ASSERT(zp.zp_checksum == ZIO_CHECKSUM_OFF ||
		    zp.zp_checksum == ZIO_CHECKSUM_NOPARITY);
		dr->dr_zio = zio_write(pio, os->os_spa, txg,
		    &dr->dr_bp_copy, NULL, db->db.db_size, db->db.db_size, &zp,
		    dbuf_write_nofill_ready, NULL, NULL,
		    dbuf_write_nofill_done, db,
		    ZIO_PRIORITY_ASYNC_WRITE,
		    ZIO_FLAG_MUSTSUCCEED | ZIO_FLAG_NODATA, &zb);
	} else {
		ASSERT(arc_released(data));

		/*
		 * For indirect blocks, we want to setup the children
		 * ready callback so that we can properly handle an indirect
		 * block that only contains holes.
		 */
		arc_write_done_func_t *children_ready_cb = NULL;
		if (db->db_level != 0)
			children_ready_cb = dbuf_write_children_ready;

		dr->dr_zio = arc_write(pio, os->os_spa, txg,
		    &dr->dr_bp_copy, data, dbuf_is_l2cacheable(db),
		    &zp, dbuf_write_ready,
		    children_ready_cb, dbuf_write_physdone,
		    dbuf_write_done, db, ZIO_PRIORITY_ASYNC_WRITE,
		    ZIO_FLAG_MUSTSUCCEED, &zb);
	}
}

EXPORT_SYMBOL(dbuf_find);
EXPORT_SYMBOL(dbuf_is_metadata);
EXPORT_SYMBOL(dbuf_destroy);
EXPORT_SYMBOL(dbuf_loan_arcbuf);
EXPORT_SYMBOL(dbuf_whichblock);
EXPORT_SYMBOL(dbuf_read);
EXPORT_SYMBOL(dbuf_unoverride);
EXPORT_SYMBOL(dbuf_free_range);
EXPORT_SYMBOL(dbuf_new_size);
EXPORT_SYMBOL(dbuf_release_bp);
EXPORT_SYMBOL(dbuf_dirty);
EXPORT_SYMBOL(dmu_buf_set_crypt_params);
EXPORT_SYMBOL(dmu_buf_will_dirty);
EXPORT_SYMBOL(dmu_buf_is_dirty);
EXPORT_SYMBOL(dmu_buf_will_not_fill);
EXPORT_SYMBOL(dmu_buf_will_fill);
EXPORT_SYMBOL(dmu_buf_fill_done);
EXPORT_SYMBOL(dmu_buf_rele);
EXPORT_SYMBOL(dbuf_assign_arcbuf);
EXPORT_SYMBOL(dbuf_prefetch);
EXPORT_SYMBOL(dbuf_hold_impl);
EXPORT_SYMBOL(dbuf_hold);
EXPORT_SYMBOL(dbuf_hold_level);
EXPORT_SYMBOL(dbuf_create_bonus);
EXPORT_SYMBOL(dbuf_spill_set_blksz);
EXPORT_SYMBOL(dbuf_rm_spill);
EXPORT_SYMBOL(dbuf_add_ref);
EXPORT_SYMBOL(dbuf_rele);
EXPORT_SYMBOL(dbuf_rele_and_unlock);
EXPORT_SYMBOL(dbuf_refcount);
EXPORT_SYMBOL(dbuf_sync_list);
EXPORT_SYMBOL(dmu_buf_set_user);
EXPORT_SYMBOL(dmu_buf_set_user_ie);
EXPORT_SYMBOL(dmu_buf_get_user);
EXPORT_SYMBOL(dmu_buf_get_blkptr);

ZFS_MODULE_PARAM(zfs_dbuf_cache, dbuf_cache_, max_bytes, U64, ZMOD_RW,
	"Maximum size in bytes of the dbuf cache.");

ZFS_MODULE_PARAM(zfs_dbuf_cache, dbuf_cache_, hiwater_pct, UINT, ZMOD_RW,
	"Percentage over dbuf_cache_max_bytes for direct dbuf eviction.");

ZFS_MODULE_PARAM(zfs_dbuf_cache, dbuf_cache_, lowater_pct, UINT, ZMOD_RW,
	"Percentage below dbuf_cache_max_bytes when dbuf eviction stops.");

ZFS_MODULE_PARAM(zfs_dbuf, dbuf_, metadata_cache_max_bytes, U64, ZMOD_RW,
	"Maximum size in bytes of dbuf metadata cache.");

ZFS_MODULE_PARAM(zfs_dbuf, dbuf_, cache_shift, UINT, ZMOD_RW,
	"Set size of dbuf cache to log2 fraction of arc size.");

ZFS_MODULE_PARAM(zfs_dbuf, dbuf_, metadata_cache_shift, UINT, ZMOD_RW,
	"Set size of dbuf metadata cache to log2 fraction of arc size.");

ZFS_MODULE_PARAM(zfs_dbuf, dbuf_, mutex_cache_shift, UINT, ZMOD_RD,
	"Set size of dbuf cache mutex array as log2 shift.");