1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  23  * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
  24  * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
  25  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
  26  * Copyright (c) 2013, Joyent, Inc. All rights reserved.
  27  */
  28 
  29 #include <sys/zfs_context.h>
  30 #include <sys/dmu.h>
  31 #include <sys/dmu_send.h>
  32 #include <sys/dmu_impl.h>
  33 #include <sys/dbuf.h>
  34 #include <sys/dmu_objset.h>
  35 #include <sys/dsl_dataset.h>
  36 #include <sys/dsl_dir.h>
  37 #include <sys/dmu_tx.h>
  38 #include <sys/spa.h>
  39 #include <sys/spa_impl.h>
  40 #include <sys/zio.h>
  41 #include <sys/dmu_zfetch.h>
  42 #include <sys/sa.h>
  43 #include <sys/sa_impl.h>
  44 #include <sys/zfeature.h>
  45 #include <sys/blkptr.h>
  46 #include <sys/range_tree.h>
  47 
  48 /*
  49  * Number of times that zfs_free_range() took the slow path while doing
  50  * a zfs receive.  A nonzero value indicates a potential performance problem.
  51  */
  52 uint64_t zfs_free_range_recv_miss;
  53 
  54 static void dbuf_destroy(dmu_buf_impl_t *db);
  55 static boolean_t dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx);
  56 static void dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx);
  57 
  58 /*
  59  * Global data structures and functions for the dbuf cache.
  60  */
  61 static kmem_cache_t *dbuf_cache;
  62 
  63 /* ARGSUSED */
  64 static int
  65 dbuf_cons(void *vdb, void *unused, int kmflag)
  66 {
  67         dmu_buf_impl_t *db = vdb;
  68         bzero(db, sizeof (dmu_buf_impl_t));
  69 
  70         mutex_init(&db->db_mtx, NULL, MUTEX_DEFAULT, NULL);
  71         cv_init(&db->db_changed, NULL, CV_DEFAULT, NULL);
  72         refcount_create(&db->db_holds);
  73 
  74         return (0);
  75 }
  76 
  77 /* ARGSUSED */
  78 static void
  79 dbuf_dest(void *vdb, void *unused)
  80 {
  81         dmu_buf_impl_t *db = vdb;
  82         mutex_destroy(&db->db_mtx);
  83         cv_destroy(&db->db_changed);
  84         refcount_destroy(&db->db_holds);
  85 }
  86 
  87 /*
  88  * dbuf hash table routines
  89  */
  90 #pragma align 64(dbuf_hash_table)
  91 static dbuf_hash_table_t dbuf_hash_table;
  92 
  93 static uint64_t dbuf_hash_count;
  94 
  95 static uint64_t
  96 dbuf_hash(void *os, uint64_t obj, uint8_t lvl, uint64_t blkid)
  97 {
  98         uintptr_t osv = (uintptr_t)os;
  99         uint64_t crc = -1ULL;
 100 
 101         ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY);
 102         crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (lvl)) & 0xFF];
 103         crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (osv >> 6)) & 0xFF];
 104         crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 0)) & 0xFF];
 105         crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 8)) & 0xFF];
 106         crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (blkid >> 0)) & 0xFF];
 107         crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (blkid >> 8)) & 0xFF];
 108 
 109         crc ^= (osv>>14) ^ (obj>>16) ^ (blkid>>16);
 110 
 111         return (crc);
 112 }
 113 
 114 #define DBUF_HASH(os, obj, level, blkid) dbuf_hash(os, obj, level, blkid);
 115 
 116 #define DBUF_EQUAL(dbuf, os, obj, level, blkid)         \
 117         ((dbuf)->db.db_object == (obj) &&            \
 118         (dbuf)->db_objset == (os) &&                 \
 119         (dbuf)->db_level == (level) &&                       \
 120         (dbuf)->db_blkid == (blkid))
 121 
 122 dmu_buf_impl_t *
 123 dbuf_find(dnode_t *dn, uint8_t level, uint64_t blkid)
 124 {
 125         dbuf_hash_table_t *h = &dbuf_hash_table;
 126         objset_t *os = dn->dn_objset;
 127         uint64_t obj = dn->dn_object;
 128         uint64_t hv = DBUF_HASH(os, obj, level, blkid);
 129         uint64_t idx = hv & h->hash_table_mask;
 130         dmu_buf_impl_t *db;
 131 
 132         mutex_enter(DBUF_HASH_MUTEX(h, idx));
 133         for (db = h->hash_table[idx]; db != NULL; db = db->db_hash_next) {
 134                 if (DBUF_EQUAL(db, os, obj, level, blkid)) {
 135                         mutex_enter(&db->db_mtx);
 136                         if (db->db_state != DB_EVICTING) {
 137                                 mutex_exit(DBUF_HASH_MUTEX(h, idx));
 138                                 return (db);
 139                         }
 140                         mutex_exit(&db->db_mtx);
 141                 }
 142         }
 143         mutex_exit(DBUF_HASH_MUTEX(h, idx));
 144         return (NULL);
 145 }
 146 
 147 /*
 148  * Insert an entry into the hash table.  If there is already an element
 149  * equal to elem in the hash table, then the already existing element
 150  * will be returned and the new element will not be inserted.
 151  * Otherwise returns NULL.
 152  */
 153 static dmu_buf_impl_t *
 154 dbuf_hash_insert(dmu_buf_impl_t *db)
 155 {
 156         dbuf_hash_table_t *h = &dbuf_hash_table;
 157         objset_t *os = db->db_objset;
 158         uint64_t obj = db->db.db_object;
 159         int level = db->db_level;
 160         uint64_t blkid = db->db_blkid;
 161         uint64_t hv = DBUF_HASH(os, obj, level, blkid);
 162         uint64_t idx = hv & h->hash_table_mask;
 163         dmu_buf_impl_t *dbf;
 164 
 165         mutex_enter(DBUF_HASH_MUTEX(h, idx));
 166         for (dbf = h->hash_table[idx]; dbf != NULL; dbf = dbf->db_hash_next) {
 167                 if (DBUF_EQUAL(dbf, os, obj, level, blkid)) {
 168                         mutex_enter(&dbf->db_mtx);
 169                         if (dbf->db_state != DB_EVICTING) {
 170                                 mutex_exit(DBUF_HASH_MUTEX(h, idx));
 171                                 return (dbf);
 172                         }
 173                         mutex_exit(&dbf->db_mtx);
 174                 }
 175         }
 176 
 177         mutex_enter(&db->db_mtx);
 178         db->db_hash_next = h->hash_table[idx];
 179         h->hash_table[idx] = db;
 180         mutex_exit(DBUF_HASH_MUTEX(h, idx));
 181         atomic_inc_64(&dbuf_hash_count);
 182 
 183         return (NULL);
 184 }
 185 
 186 /*
 187  * Remove an entry from the hash table.  It must be in the EVICTING state.
 188  */
 189 static void
 190 dbuf_hash_remove(dmu_buf_impl_t *db)
 191 {
 192         dbuf_hash_table_t *h = &dbuf_hash_table;
 193         uint64_t hv = DBUF_HASH(db->db_objset, db->db.db_object,
 194             db->db_level, db->db_blkid);
 195         uint64_t idx = hv & h->hash_table_mask;
 196         dmu_buf_impl_t *dbf, **dbp;
 197 
 198         /*
 199          * We musn't hold db_mtx to maintain lock ordering:
 200          * DBUF_HASH_MUTEX > db_mtx.
 201          */
 202         ASSERT(refcount_is_zero(&db->db_holds));
 203         ASSERT(db->db_state == DB_EVICTING);
 204         ASSERT(!MUTEX_HELD(&db->db_mtx));
 205 
 206         mutex_enter(DBUF_HASH_MUTEX(h, idx));
 207         dbp = &h->hash_table[idx];
 208         while ((dbf = *dbp) != db) {
 209                 dbp = &dbf->db_hash_next;
 210                 ASSERT(dbf != NULL);
 211         }
 212         *dbp = db->db_hash_next;
 213         db->db_hash_next = NULL;
 214         mutex_exit(DBUF_HASH_MUTEX(h, idx));
 215         atomic_dec_64(&dbuf_hash_count);
 216 }
 217 
 218 static arc_evict_func_t dbuf_do_evict;
 219 
 220 static void
 221 dbuf_evict_user(dmu_buf_impl_t *db)
 222 {
 223         ASSERT(MUTEX_HELD(&db->db_mtx));
 224 
 225         if (db->db_level != 0 || db->db_evict_func == NULL)
 226                 return;
 227 
 228         if (db->db_user_data_ptr_ptr)
 229                 *db->db_user_data_ptr_ptr = db->db.db_data;
 230         db->db_evict_func(&db->db, db->db_user_ptr);
 231         db->db_user_ptr = NULL;
 232         db->db_user_data_ptr_ptr = NULL;
 233         db->db_evict_func = NULL;
 234 }
 235 
 236 boolean_t
 237 dbuf_is_metadata(dmu_buf_impl_t *db)
 238 {
 239         if (db->db_level > 0) {
 240                 return (B_TRUE);
 241         } else {
 242                 boolean_t is_metadata;
 243 
 244                 DB_DNODE_ENTER(db);
 245                 is_metadata = DMU_OT_IS_METADATA(DB_DNODE(db)->dn_type);
 246                 DB_DNODE_EXIT(db);
 247 
 248                 return (is_metadata);
 249         }
 250 }
 251 
 252 void
 253 dbuf_evict(dmu_buf_impl_t *db)
 254 {
 255         ASSERT(MUTEX_HELD(&db->db_mtx));
 256         ASSERT(db->db_buf == NULL);
 257         ASSERT(db->db_data_pending == NULL);
 258 
 259         dbuf_clear(db);
 260         dbuf_destroy(db);
 261 }
 262 
 263 void
 264 dbuf_init(void)
 265 {
 266         uint64_t hsize = 1ULL << 16;
 267         dbuf_hash_table_t *h = &dbuf_hash_table;
 268         int i;
 269 
 270         /*
 271          * The hash table is big enough to fill all of physical memory
 272          * with an average 4K block size.  The table will take up
 273          * totalmem*sizeof(void*)/4K (i.e. 2MB/GB with 8-byte pointers).
 274          */
 275         while (hsize * 4096 < physmem * PAGESIZE)
 276                 hsize <<= 1;
 277 
 278 retry:
 279         h->hash_table_mask = hsize - 1;
 280         h->hash_table = kmem_zalloc(hsize * sizeof (void *), KM_NOSLEEP);
 281         if (h->hash_table == NULL) {
 282                 /* XXX - we should really return an error instead of assert */
 283                 ASSERT(hsize > (1ULL << 10));
 284                 hsize >>= 1;
 285                 goto retry;
 286         }
 287 
 288         dbuf_cache = kmem_cache_create("dmu_buf_impl_t",
 289             sizeof (dmu_buf_impl_t),
 290             0, dbuf_cons, dbuf_dest, NULL, NULL, NULL, 0);
 291 
 292         for (i = 0; i < DBUF_MUTEXES; i++)
 293                 mutex_init(DBUF_HASH_MUTEX(h, i), NULL, MUTEX_DEFAULT, NULL);
 294 }
 295 
 296 void
 297 dbuf_fini(void)
 298 {
 299         dbuf_hash_table_t *h = &dbuf_hash_table;
 300         int i;
 301 
 302         for (i = 0; i < DBUF_MUTEXES; i++)
 303                 mutex_destroy(DBUF_HASH_MUTEX(h, i));
 304         kmem_free(h->hash_table, (h->hash_table_mask + 1) * sizeof (void *));
 305         kmem_cache_destroy(dbuf_cache);
 306 }
 307 
 308 /*
 309  * Other stuff.
 310  */
 311 
 312 #ifdef ZFS_DEBUG
 313 static void
 314 dbuf_verify(dmu_buf_impl_t *db)
 315 {
 316         dnode_t *dn;
 317         dbuf_dirty_record_t *dr;
 318 
 319         ASSERT(MUTEX_HELD(&db->db_mtx));
 320 
 321         if (!(zfs_flags & ZFS_DEBUG_DBUF_VERIFY))
 322                 return;
 323 
 324         ASSERT(db->db_objset != NULL);
 325         DB_DNODE_ENTER(db);
 326         dn = DB_DNODE(db);
 327         if (dn == NULL) {
 328                 ASSERT(db->db_parent == NULL);
 329                 ASSERT(db->db_blkptr == NULL);
 330         } else {
 331                 ASSERT3U(db->db.db_object, ==, dn->dn_object);
 332                 ASSERT3P(db->db_objset, ==, dn->dn_objset);
 333                 ASSERT3U(db->db_level, <, dn->dn_nlevels);
 334                 ASSERT(db->db_blkid == DMU_BONUS_BLKID ||
 335                     db->db_blkid == DMU_SPILL_BLKID ||
 336                     !avl_is_empty(&dn->dn_dbufs));
 337         }
 338         if (db->db_blkid == DMU_BONUS_BLKID) {
 339                 ASSERT(dn != NULL);
 340                 ASSERT3U(db->db.db_size, >=, dn->dn_bonuslen);
 341                 ASSERT3U(db->db.db_offset, ==, DMU_BONUS_BLKID);
 342         } else if (db->db_blkid == DMU_SPILL_BLKID) {
 343                 ASSERT(dn != NULL);
 344                 ASSERT3U(db->db.db_size, >=, dn->dn_bonuslen);
 345                 ASSERT0(db->db.db_offset);
 346         } else {
 347                 ASSERT3U(db->db.db_offset, ==, db->db_blkid * db->db.db_size);
 348         }
 349 
 350         for (dr = db->db_data_pending; dr != NULL; dr = dr->dr_next)
 351                 ASSERT(dr->dr_dbuf == db);
 352 
 353         for (dr = db->db_last_dirty; dr != NULL; dr = dr->dr_next)
 354                 ASSERT(dr->dr_dbuf == db);
 355 
 356         /*
 357          * We can't assert that db_size matches dn_datablksz because it
 358          * can be momentarily different when another thread is doing
 359          * dnode_set_blksz().
 360          */
 361         if (db->db_level == 0 && db->db.db_object == DMU_META_DNODE_OBJECT) {
 362                 dr = db->db_data_pending;
 363                 /*
 364                  * It should only be modified in syncing context, so
 365                  * make sure we only have one copy of the data.
 366                  */
 367                 ASSERT(dr == NULL || dr->dt.dl.dr_data == db->db_buf);
 368         }
 369 
 370         /* verify db->db_blkptr */
 371         if (db->db_blkptr) {
 372                 if (db->db_parent == dn->dn_dbuf) {
 373                         /* db is pointed to by the dnode */
 374                         /* ASSERT3U(db->db_blkid, <, dn->dn_nblkptr); */
 375                         if (DMU_OBJECT_IS_SPECIAL(db->db.db_object))
 376                                 ASSERT(db->db_parent == NULL);
 377                         else
 378                                 ASSERT(db->db_parent != NULL);
 379                         if (db->db_blkid != DMU_SPILL_BLKID)
 380                                 ASSERT3P(db->db_blkptr, ==,
 381                                     &dn->dn_phys->dn_blkptr[db->db_blkid]);
 382                 } else {
 383                         /* db is pointed to by an indirect block */
 384                         int epb = db->db_parent->db.db_size >> SPA_BLKPTRSHIFT;
 385                         ASSERT3U(db->db_parent->db_level, ==, db->db_level+1);
 386                         ASSERT3U(db->db_parent->db.db_object, ==,
 387                             db->db.db_object);
 388                         /*
 389                          * dnode_grow_indblksz() can make this fail if we don't
 390                          * have the struct_rwlock.  XXX indblksz no longer
 391                          * grows.  safe to do this now?
 392                          */
 393                         if (RW_WRITE_HELD(&dn->dn_struct_rwlock)) {
 394                                 ASSERT3P(db->db_blkptr, ==,
 395                                     ((blkptr_t *)db->db_parent->db.db_data +
 396                                     db->db_blkid % epb));
 397                         }
 398                 }
 399         }
 400         if ((db->db_blkptr == NULL || BP_IS_HOLE(db->db_blkptr)) &&
 401             (db->db_buf == NULL || db->db_buf->b_data) &&
 402             db->db.db_data && db->db_blkid != DMU_BONUS_BLKID &&
 403             db->db_state != DB_FILL && !dn->dn_free_txg) {
 404                 /*
 405                  * If the blkptr isn't set but they have nonzero data,
 406                  * it had better be dirty, otherwise we'll lose that
 407                  * data when we evict this buffer.
 408                  */
 409                 if (db->db_dirtycnt == 0) {
 410                         uint64_t *buf = db->db.db_data;
 411                         int i;
 412 
 413                         for (i = 0; i < db->db.db_size >> 3; i++) {
 414                                 ASSERT(buf[i] == 0);
 415                         }
 416                 }
 417         }
 418         DB_DNODE_EXIT(db);
 419 }
 420 #endif
 421 
 422 static void
 423 dbuf_update_data(dmu_buf_impl_t *db)
 424 {
 425         ASSERT(MUTEX_HELD(&db->db_mtx));
 426         if (db->db_level == 0 && db->db_user_data_ptr_ptr) {
 427                 ASSERT(!refcount_is_zero(&db->db_holds));
 428                 *db->db_user_data_ptr_ptr = db->db.db_data;
 429         }
 430 }
 431 
 432 static void
 433 dbuf_set_data(dmu_buf_impl_t *db, arc_buf_t *buf)
 434 {
 435         ASSERT(MUTEX_HELD(&db->db_mtx));
 436         db->db_buf = buf;
 437         if (buf != NULL) {
 438                 ASSERT(buf->b_data != NULL);
 439                 db->db.db_data = buf->b_data;
 440                 if (!arc_released(buf))
 441                         arc_set_callback(buf, dbuf_do_evict, db);
 442                 dbuf_update_data(db);
 443         } else {
 444                 dbuf_evict_user(db);
 445                 db->db.db_data = NULL;
 446                 if (db->db_state != DB_NOFILL)
 447                         db->db_state = DB_UNCACHED;
 448         }
 449 }
 450 
 451 /*
 452  * Loan out an arc_buf for read.  Return the loaned arc_buf.
 453  */
 454 arc_buf_t *
 455 dbuf_loan_arcbuf(dmu_buf_impl_t *db)
 456 {
 457         arc_buf_t *abuf;
 458 
 459         mutex_enter(&db->db_mtx);
 460         if (arc_released(db->db_buf) || refcount_count(&db->db_holds) > 1) {
 461                 int blksz = db->db.db_size;
 462                 spa_t *spa = db->db_objset->os_spa;
 463 
 464                 mutex_exit(&db->db_mtx);
 465                 abuf = arc_loan_buf(spa, blksz);
 466                 bcopy(db->db.db_data, abuf->b_data, blksz);
 467         } else {
 468                 abuf = db->db_buf;
 469                 arc_loan_inuse_buf(abuf, db);
 470                 dbuf_set_data(db, NULL);
 471                 mutex_exit(&db->db_mtx);
 472         }
 473         return (abuf);
 474 }
 475 
 476 uint64_t
 477 dbuf_whichblock(dnode_t *dn, uint64_t offset)
 478 {
 479         if (dn->dn_datablkshift) {
 480                 return (offset >> dn->dn_datablkshift);
 481         } else {
 482                 ASSERT3U(offset, <, dn->dn_datablksz);
 483                 return (0);
 484         }
 485 }
 486 
 487 static void
 488 dbuf_read_done(zio_t *zio, arc_buf_t *buf, void *vdb)
 489 {
 490         dmu_buf_impl_t *db = vdb;
 491 
 492         mutex_enter(&db->db_mtx);
 493         ASSERT3U(db->db_state, ==, DB_READ);
 494         /*
 495          * All reads are synchronous, so we must have a hold on the dbuf
 496          */
 497         ASSERT(refcount_count(&db->db_holds) > 0);
 498         ASSERT(db->db_buf == NULL);
 499         ASSERT(db->db.db_data == NULL);
 500         if (db->db_level == 0 && db->db_freed_in_flight) {
 501                 /* we were freed in flight; disregard any error */
 502                 arc_release(buf, db);
 503                 bzero(buf->b_data, db->db.db_size);
 504                 arc_buf_freeze(buf);
 505                 db->db_freed_in_flight = FALSE;
 506                 dbuf_set_data(db, buf);
 507                 db->db_state = DB_CACHED;
 508         } else if (zio == NULL || zio->io_error == 0) {
 509                 dbuf_set_data(db, buf);
 510                 db->db_state = DB_CACHED;
 511         } else {
 512                 ASSERT(db->db_blkid != DMU_BONUS_BLKID);
 513                 ASSERT3P(db->db_buf, ==, NULL);
 514                 VERIFY(arc_buf_remove_ref(buf, db));
 515                 db->db_state = DB_UNCACHED;
 516         }
 517         cv_broadcast(&db->db_changed);
 518         dbuf_rele_and_unlock(db, NULL);
 519 }
 520 
 521 static void
 522 dbuf_read_impl(dmu_buf_impl_t *db, zio_t *zio, uint32_t *flags)
 523 {
 524         dnode_t *dn;
 525         zbookmark_phys_t zb;
 526         uint32_t aflags = ARC_NOWAIT;
 527 
 528         DB_DNODE_ENTER(db);
 529         dn = DB_DNODE(db);
 530         ASSERT(!refcount_is_zero(&db->db_holds));
 531         /* We need the struct_rwlock to prevent db_blkptr from changing. */
 532         ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
 533         ASSERT(MUTEX_HELD(&db->db_mtx));
 534         ASSERT(db->db_state == DB_UNCACHED);
 535         ASSERT(db->db_buf == NULL);
 536 
 537         if (db->db_blkid == DMU_BONUS_BLKID) {
 538                 int bonuslen = MIN(dn->dn_bonuslen, dn->dn_phys->dn_bonuslen);
 539 
 540                 ASSERT3U(bonuslen, <=, db->db.db_size);
 541                 db->db.db_data = zio_buf_alloc(DN_MAX_BONUSLEN);
 542                 arc_space_consume(DN_MAX_BONUSLEN, ARC_SPACE_OTHER);
 543                 if (bonuslen < DN_MAX_BONUSLEN)
 544                         bzero(db->db.db_data, DN_MAX_BONUSLEN);
 545                 if (bonuslen)
 546                         bcopy(DN_BONUS(dn->dn_phys), db->db.db_data, bonuslen);
 547                 DB_DNODE_EXIT(db);
 548                 dbuf_update_data(db);
 549                 db->db_state = DB_CACHED;
 550                 mutex_exit(&db->db_mtx);
 551                 return;
 552         }
 553 
 554         /*
 555          * Recheck BP_IS_HOLE() after dnode_block_freed() in case dnode_sync()
 556          * processes the delete record and clears the bp while we are waiting
 557          * for the dn_mtx (resulting in a "no" from block_freed).
 558          */
 559         if (db->db_blkptr == NULL || BP_IS_HOLE(db->db_blkptr) ||
 560             (db->db_level == 0 && (dnode_block_freed(dn, db->db_blkid) ||
 561             BP_IS_HOLE(db->db_blkptr)))) {
 562                 arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
 563 
 564                 DB_DNODE_EXIT(db);
 565                 dbuf_set_data(db, arc_buf_alloc(db->db_objset->os_spa,
 566                     db->db.db_size, db, type));
 567                 bzero(db->db.db_data, db->db.db_size);
 568                 db->db_state = DB_CACHED;
 569                 *flags |= DB_RF_CACHED;
 570                 mutex_exit(&db->db_mtx);
 571                 return;
 572         }
 573 
 574         DB_DNODE_EXIT(db);
 575 
 576         db->db_state = DB_READ;
 577         mutex_exit(&db->db_mtx);
 578 
 579         if (DBUF_IS_L2CACHEABLE(db))
 580                 aflags |= ARC_L2CACHE;
 581         if (DBUF_IS_L2COMPRESSIBLE(db))
 582                 aflags |= ARC_L2COMPRESS;
 583 
 584         SET_BOOKMARK(&zb, db->db_objset->os_dsl_dataset ?
 585             db->db_objset->os_dsl_dataset->ds_object : DMU_META_OBJSET,
 586             db->db.db_object, db->db_level, db->db_blkid);
 587 
 588         dbuf_add_ref(db, NULL);
 589 
 590         (void) arc_read(zio, db->db_objset->os_spa, db->db_blkptr,
 591             dbuf_read_done, db, ZIO_PRIORITY_SYNC_READ,
 592             (*flags & DB_RF_CANFAIL) ? ZIO_FLAG_CANFAIL : ZIO_FLAG_MUSTSUCCEED,
 593             &aflags, &zb);
 594         if (aflags & ARC_CACHED)
 595                 *flags |= DB_RF_CACHED;
 596 }
 597 
 598 int
 599 dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
 600 {
 601         int err = 0;
 602         boolean_t havepzio = (zio != NULL);
 603         boolean_t prefetch;
 604         dnode_t *dn;
 605 
 606         /*
 607          * We don't have to hold the mutex to check db_state because it
 608          * can't be freed while we have a hold on the buffer.
 609          */
 610         ASSERT(!refcount_is_zero(&db->db_holds));
 611 
 612         if (db->db_state == DB_NOFILL)
 613                 return (SET_ERROR(EIO));
 614 
 615         DB_DNODE_ENTER(db);
 616         dn = DB_DNODE(db);
 617         if ((flags & DB_RF_HAVESTRUCT) == 0)
 618                 rw_enter(&dn->dn_struct_rwlock, RW_READER);
 619 
 620         prefetch = db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID &&
 621             (flags & DB_RF_NOPREFETCH) == 0 && dn != NULL &&
 622             DBUF_IS_CACHEABLE(db);
 623 
 624         mutex_enter(&db->db_mtx);
 625         if (db->db_state == DB_CACHED) {
 626                 mutex_exit(&db->db_mtx);
 627                 if (prefetch)
 628                         dmu_zfetch(&dn->dn_zfetch, db->db.db_offset,
 629                             db->db.db_size, TRUE);
 630                 if ((flags & DB_RF_HAVESTRUCT) == 0)
 631                         rw_exit(&dn->dn_struct_rwlock);
 632                 DB_DNODE_EXIT(db);
 633         } else if (db->db_state == DB_UNCACHED) {
 634                 spa_t *spa = dn->dn_objset->os_spa;
 635 
 636                 if (zio == NULL)
 637                         zio = zio_root(spa, NULL, NULL, ZIO_FLAG_CANFAIL);
 638                 dbuf_read_impl(db, zio, &flags);
 639 
 640                 /* dbuf_read_impl has dropped db_mtx for us */
 641 
 642                 if (prefetch)
 643                         dmu_zfetch(&dn->dn_zfetch, db->db.db_offset,
 644                             db->db.db_size, flags & DB_RF_CACHED);
 645 
 646                 if ((flags & DB_RF_HAVESTRUCT) == 0)
 647                         rw_exit(&dn->dn_struct_rwlock);
 648                 DB_DNODE_EXIT(db);
 649 
 650                 if (!havepzio)
 651                         err = zio_wait(zio);
 652         } else {
 653                 /*
 654                  * Another reader came in while the dbuf was in flight
 655                  * between UNCACHED and CACHED.  Either a writer will finish
 656                  * writing the buffer (sending the dbuf to CACHED) or the
 657                  * first reader's request will reach the read_done callback
 658                  * and send the dbuf to CACHED.  Otherwise, a failure
 659                  * occurred and the dbuf went to UNCACHED.
 660                  */
 661                 mutex_exit(&db->db_mtx);
 662                 if (prefetch)
 663                         dmu_zfetch(&dn->dn_zfetch, db->db.db_offset,
 664                             db->db.db_size, TRUE);
 665                 if ((flags & DB_RF_HAVESTRUCT) == 0)
 666                         rw_exit(&dn->dn_struct_rwlock);
 667                 DB_DNODE_EXIT(db);
 668 
 669                 /* Skip the wait per the caller's request. */
 670                 mutex_enter(&db->db_mtx);
 671                 if ((flags & DB_RF_NEVERWAIT) == 0) {
 672                         while (db->db_state == DB_READ ||
 673                             db->db_state == DB_FILL) {
 674                                 ASSERT(db->db_state == DB_READ ||
 675                                     (flags & DB_RF_HAVESTRUCT) == 0);
 676                                 cv_wait(&db->db_changed, &db->db_mtx);
 677                         }
 678                         if (db->db_state == DB_UNCACHED)
 679                                 err = SET_ERROR(EIO);
 680                 }
 681                 mutex_exit(&db->db_mtx);
 682         }
 683 
 684         ASSERT(err || havepzio || db->db_state == DB_CACHED);
 685         return (err);
 686 }
 687 
 688 static void
 689 dbuf_noread(dmu_buf_impl_t *db)
 690 {
 691         ASSERT(!refcount_is_zero(&db->db_holds));
 692         ASSERT(db->db_blkid != DMU_BONUS_BLKID);
 693         mutex_enter(&db->db_mtx);
 694         while (db->db_state == DB_READ || db->db_state == DB_FILL)
 695                 cv_wait(&db->db_changed, &db->db_mtx);
 696         if (db->db_state == DB_UNCACHED) {
 697                 arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
 698                 spa_t *spa = db->db_objset->os_spa;
 699 
 700                 ASSERT(db->db_buf == NULL);
 701                 ASSERT(db->db.db_data == NULL);
 702                 dbuf_set_data(db, arc_buf_alloc(spa, db->db.db_size, db, type));
 703                 db->db_state = DB_FILL;
 704         } else if (db->db_state == DB_NOFILL) {
 705                 dbuf_set_data(db, NULL);
 706         } else {
 707                 ASSERT3U(db->db_state, ==, DB_CACHED);
 708         }
 709         mutex_exit(&db->db_mtx);
 710 }
 711 
 712 /*
 713  * This is our just-in-time copy function.  It makes a copy of
 714  * buffers, that have been modified in a previous transaction
 715  * group, before we modify them in the current active group.
 716  *
 717  * This function is used in two places: when we are dirtying a
 718  * buffer for the first time in a txg, and when we are freeing
 719  * a range in a dnode that includes this buffer.
 720  *
 721  * Note that when we are called from dbuf_free_range() we do
 722  * not put a hold on the buffer, we just traverse the active
 723  * dbuf list for the dnode.
 724  */
 725 static void
 726 dbuf_fix_old_data(dmu_buf_impl_t *db, uint64_t txg)
 727 {
 728         dbuf_dirty_record_t *dr = db->db_last_dirty;
 729 
 730         ASSERT(MUTEX_HELD(&db->db_mtx));
 731         ASSERT(db->db.db_data != NULL);
 732         ASSERT(db->db_level == 0);
 733         ASSERT(db->db.db_object != DMU_META_DNODE_OBJECT);
 734 
 735         if (dr == NULL ||
 736             (dr->dt.dl.dr_data !=
 737             ((db->db_blkid  == DMU_BONUS_BLKID) ? db->db.db_data : db->db_buf)))
 738                 return;
 739 
 740         /*
 741          * If the last dirty record for this dbuf has not yet synced
 742          * and its referencing the dbuf data, either:
 743          *      reset the reference to point to a new copy,
 744          * or (if there a no active holders)
 745          *      just null out the current db_data pointer.
 746          */
 747         ASSERT(dr->dr_txg >= txg - 2);
 748         if (db->db_blkid == DMU_BONUS_BLKID) {
 749                 /* Note that the data bufs here are zio_bufs */
 750                 dr->dt.dl.dr_data = zio_buf_alloc(DN_MAX_BONUSLEN);
 751                 arc_space_consume(DN_MAX_BONUSLEN, ARC_SPACE_OTHER);
 752                 bcopy(db->db.db_data, dr->dt.dl.dr_data, DN_MAX_BONUSLEN);
 753         } else if (refcount_count(&db->db_holds) > db->db_dirtycnt) {
 754                 int size = db->db.db_size;
 755                 arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
 756                 spa_t *spa = db->db_objset->os_spa;
 757 
 758                 dr->dt.dl.dr_data = arc_buf_alloc(spa, size, db, type);
 759                 bcopy(db->db.db_data, dr->dt.dl.dr_data->b_data, size);
 760         } else {
 761                 dbuf_set_data(db, NULL);
 762         }
 763 }
 764 
 765 void
 766 dbuf_unoverride(dbuf_dirty_record_t *dr)
 767 {
 768         dmu_buf_impl_t *db = dr->dr_dbuf;
 769         blkptr_t *bp = &dr->dt.dl.dr_overridden_by;
 770         uint64_t txg = dr->dr_txg;
 771 
 772         ASSERT(MUTEX_HELD(&db->db_mtx));
 773         ASSERT(dr->dt.dl.dr_override_state != DR_IN_DMU_SYNC);
 774         ASSERT(db->db_level == 0);
 775 
 776         if (db->db_blkid == DMU_BONUS_BLKID ||
 777             dr->dt.dl.dr_override_state == DR_NOT_OVERRIDDEN)
 778                 return;
 779 
 780         ASSERT(db->db_data_pending != dr);
 781 
 782         /* free this block */
 783         if (!BP_IS_HOLE(bp) && !dr->dt.dl.dr_nopwrite)
 784                 zio_free(db->db_objset->os_spa, txg, bp);
 785 
 786         dr->dt.dl.dr_override_state = DR_NOT_OVERRIDDEN;
 787         dr->dt.dl.dr_nopwrite = B_FALSE;
 788 
 789         /*
 790          * Release the already-written buffer, so we leave it in
 791          * a consistent dirty state.  Note that all callers are
 792          * modifying the buffer, so they will immediately do
 793          * another (redundant) arc_release().  Therefore, leave
 794          * the buf thawed to save the effort of freezing &
 795          * immediately re-thawing it.
 796          */
 797         arc_release(dr->dt.dl.dr_data, db);
 798 }
 799 
 800 /*
 801  * Evict (if its unreferenced) or clear (if its referenced) any level-0
 802  * data blocks in the free range, so that any future readers will find
 803  * empty blocks.
 804  *
 805  * This is a no-op if the dataset is in the middle of an incremental
 806  * receive; see comment below for details.
 807  */
 808 void
 809 dbuf_free_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
 810     dmu_tx_t *tx)
 811 {
 812         dmu_buf_impl_t *db, *db_next, db_search;
 813         uint64_t txg = tx->tx_txg;
 814         avl_index_t where;
 815 
 816         if (end_blkid > dn->dn_maxblkid && (end_blkid != DMU_SPILL_BLKID))
 817                 end_blkid = dn->dn_maxblkid;
 818         dprintf_dnode(dn, "start=%llu end=%llu\n", start_blkid, end_blkid);
 819 
 820         db_search.db_level = 0;
 821         db_search.db_blkid = start_blkid;
 822         db_search.db_state = DB_SEARCH;
 823 
 824         mutex_enter(&dn->dn_dbufs_mtx);
 825         if (start_blkid >= dn->dn_unlisted_l0_blkid) {
 826                 /* There can't be any dbufs in this range; no need to search. */
 827 #ifdef DEBUG
 828                 db = avl_find(&dn->dn_dbufs, &db_search, &where);
 829                 ASSERT3P(db, ==, NULL);
 830                 db = avl_nearest(&dn->dn_dbufs, where, AVL_AFTER);
 831                 ASSERT(db == NULL || db->db_level > 0);
 832 #endif
 833                 mutex_exit(&dn->dn_dbufs_mtx);
 834                 return;
 835         } else if (dmu_objset_is_receiving(dn->dn_objset)) {
 836                 /*
 837                  * If we are receiving, we expect there to be no dbufs in
 838                  * the range to be freed, because receive modifies each
 839                  * block at most once, and in offset order.  If this is
 840                  * not the case, it can lead to performance problems,
 841                  * so note that we unexpectedly took the slow path.
 842                  */
 843                 atomic_inc_64(&zfs_free_range_recv_miss);
 844         }
 845 
 846         db = avl_find(&dn->dn_dbufs, &db_search, &where);
 847         ASSERT3P(db, ==, NULL);
 848         db = avl_nearest(&dn->dn_dbufs, where, AVL_AFTER);
 849 
 850         for (; db != NULL; db = db_next) {
 851                 db_next = AVL_NEXT(&dn->dn_dbufs, db);
 852                 ASSERT(db->db_blkid != DMU_BONUS_BLKID);
 853 
 854                 if (db->db_level != 0 || db->db_blkid > end_blkid) {
 855                         break;
 856                 }
 857                 ASSERT3U(db->db_blkid, >=, start_blkid);
 858 
 859                 /* found a level 0 buffer in the range */
 860                 mutex_enter(&db->db_mtx);
 861                 if (dbuf_undirty(db, tx)) {
 862                         /* mutex has been dropped and dbuf destroyed */
 863                         continue;
 864                 }
 865 
 866                 if (db->db_state == DB_UNCACHED ||
 867                     db->db_state == DB_NOFILL ||
 868                     db->db_state == DB_EVICTING) {
 869                         ASSERT(db->db.db_data == NULL);
 870                         mutex_exit(&db->db_mtx);
 871                         continue;
 872                 }
 873                 if (db->db_state == DB_READ || db->db_state == DB_FILL) {
 874                         /* will be handled in dbuf_read_done or dbuf_rele */
 875                         db->db_freed_in_flight = TRUE;
 876                         mutex_exit(&db->db_mtx);
 877                         continue;
 878                 }
 879                 if (refcount_count(&db->db_holds) == 0) {
 880                         ASSERT(db->db_buf);
 881                         dbuf_clear(db);
 882                         continue;
 883                 }
 884                 /* The dbuf is referenced */
 885 
 886                 if (db->db_last_dirty != NULL) {
 887                         dbuf_dirty_record_t *dr = db->db_last_dirty;
 888 
 889                         if (dr->dr_txg == txg) {
 890                                 /*
 891                                  * This buffer is "in-use", re-adjust the file
 892                                  * size to reflect that this buffer may
 893                                  * contain new data when we sync.
 894                                  */
 895                                 if (db->db_blkid != DMU_SPILL_BLKID &&
 896                                     db->db_blkid > dn->dn_maxblkid)
 897                                         dn->dn_maxblkid = db->db_blkid;
 898                                 dbuf_unoverride(dr);
 899                         } else {
 900                                 /*
 901                                  * This dbuf is not dirty in the open context.
 902                                  * Either uncache it (if its not referenced in
 903                                  * the open context) or reset its contents to
 904                                  * empty.
 905                                  */
 906                                 dbuf_fix_old_data(db, txg);
 907                         }
 908                 }
 909                 /* clear the contents if its cached */
 910                 if (db->db_state == DB_CACHED) {
 911                         ASSERT(db->db.db_data != NULL);
 912                         arc_release(db->db_buf, db);
 913                         bzero(db->db.db_data, db->db.db_size);
 914                         arc_buf_freeze(db->db_buf);
 915                 }
 916 
 917                 mutex_exit(&db->db_mtx);
 918         }
 919         mutex_exit(&dn->dn_dbufs_mtx);
 920 }
 921 
 922 static int
 923 dbuf_block_freeable(dmu_buf_impl_t *db)
 924 {
 925         dsl_dataset_t *ds = db->db_objset->os_dsl_dataset;
 926         uint64_t birth_txg = 0;
 927 
 928         /*
 929          * We don't need any locking to protect db_blkptr:
 930          * If it's syncing, then db_last_dirty will be set
 931          * so we'll ignore db_blkptr.
 932          *
 933          * This logic ensures that only block births for
 934          * filled blocks are considered.
 935          */
 936         ASSERT(MUTEX_HELD(&db->db_mtx));
 937         if (db->db_last_dirty && (db->db_blkptr == NULL ||
 938             !BP_IS_HOLE(db->db_blkptr))) {
 939                 birth_txg = db->db_last_dirty->dr_txg;
 940         } else if (db->db_blkptr != NULL && !BP_IS_HOLE(db->db_blkptr)) {
 941                 birth_txg = db->db_blkptr->blk_birth;
 942         }
 943 
 944         /*
 945          * If this block don't exist or is in a snapshot, it can't be freed.
 946          * Don't pass the bp to dsl_dataset_block_freeable() since we
 947          * are holding the db_mtx lock and might deadlock if we are
 948          * prefetching a dedup-ed block.
 949          */
 950         if (birth_txg != 0)
 951                 return (ds == NULL ||
 952                     dsl_dataset_block_freeable(ds, NULL, birth_txg));
 953         else
 954                 return (B_FALSE);
 955 }
 956 
 957 void
 958 dbuf_new_size(dmu_buf_impl_t *db, int size, dmu_tx_t *tx)
 959 {
 960         arc_buf_t *buf, *obuf;
 961         int osize = db->db.db_size;
 962         arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
 963         dnode_t *dn;
 964 
 965         ASSERT(db->db_blkid != DMU_BONUS_BLKID);
 966 
 967         DB_DNODE_ENTER(db);
 968         dn = DB_DNODE(db);
 969 
 970         /* XXX does *this* func really need the lock? */
 971         ASSERT(RW_WRITE_HELD(&dn->dn_struct_rwlock));
 972 
 973         /*
 974          * This call to dmu_buf_will_dirty() with the dn_struct_rwlock held
 975          * is OK, because there can be no other references to the db
 976          * when we are changing its size, so no concurrent DB_FILL can
 977          * be happening.
 978          */
 979         /*
 980          * XXX we should be doing a dbuf_read, checking the return
 981          * value and returning that up to our callers
 982          */
 983         dmu_buf_will_dirty(&db->db, tx);
 984 
 985         /* create the data buffer for the new block */
 986         buf = arc_buf_alloc(dn->dn_objset->os_spa, size, db, type);
 987 
 988         /* copy old block data to the new block */
 989         obuf = db->db_buf;
 990         bcopy(obuf->b_data, buf->b_data, MIN(osize, size));
 991         /* zero the remainder */
 992         if (size > osize)
 993                 bzero((uint8_t *)buf->b_data + osize, size - osize);
 994 
 995         mutex_enter(&db->db_mtx);
 996         dbuf_set_data(db, buf);
 997         VERIFY(arc_buf_remove_ref(obuf, db));
 998         db->db.db_size = size;
 999 
1000         if (db->db_level == 0) {
1001                 ASSERT3U(db->db_last_dirty->dr_txg, ==, tx->tx_txg);
1002                 db->db_last_dirty->dt.dl.dr_data = buf;
1003         }
1004         mutex_exit(&db->db_mtx);
1005 
1006         dnode_willuse_space(dn, size-osize, tx);
1007         DB_DNODE_EXIT(db);
1008 }
1009 
1010 void
1011 dbuf_release_bp(dmu_buf_impl_t *db)
1012 {
1013         objset_t *os = db->db_objset;
1014 
1015         ASSERT(dsl_pool_sync_context(dmu_objset_pool(os)));
1016         ASSERT(arc_released(os->os_phys_buf) ||
1017             list_link_active(&os->os_dsl_dataset->ds_synced_link));
1018         ASSERT(db->db_parent == NULL || arc_released(db->db_parent->db_buf));
1019 
1020         (void) arc_release(db->db_buf, db);
1021 }
1022 
1023 dbuf_dirty_record_t *
1024 dbuf_dirty_sc(dmu_buf_impl_t *db, dmu_tx_t *tx, boolean_t usesc)
1025 {
1026         dnode_t *dn;
1027         objset_t *os;
1028         dbuf_dirty_record_t **drp, *dr;
1029         int drop_struct_lock = FALSE;
1030         boolean_t do_free_accounting = B_FALSE;
1031         int txgoff = tx->tx_txg & TXG_MASK;
1032 
1033         ASSERT(tx->tx_txg != 0);
1034         ASSERT(!refcount_is_zero(&db->db_holds));
1035         DMU_TX_DIRTY_BUF(tx, db);
1036 
1037         DB_DNODE_ENTER(db);
1038         dn = DB_DNODE(db);
1039         /*
1040          * Shouldn't dirty a regular buffer in syncing context.  Private
1041          * objects may be dirtied in syncing context, but only if they
1042          * were already pre-dirtied in open context.
1043          */
1044         ASSERT(!dmu_tx_is_syncing(tx) ||
1045             BP_IS_HOLE(dn->dn_objset->os_rootbp) ||
1046             DMU_OBJECT_IS_SPECIAL(dn->dn_object) ||
1047             dn->dn_objset->os_dsl_dataset == NULL);
1048         /*
1049          * We make this assert for private objects as well, but after we
1050          * check if we're already dirty.  They are allowed to re-dirty
1051          * in syncing context.
1052          */
1053         ASSERT(dn->dn_object == DMU_META_DNODE_OBJECT ||
1054             dn->dn_dirtyctx == DN_UNDIRTIED || dn->dn_dirtyctx ==
1055             (dmu_tx_is_syncing(tx) ? DN_DIRTY_SYNC : DN_DIRTY_OPEN));
1056 
1057         mutex_enter(&db->db_mtx);
1058         /*
1059          * XXX make this true for indirects too?  The problem is that
1060          * transactions created with dmu_tx_create_assigned() from
1061          * syncing context don't bother holding ahead.
1062          */
1063         ASSERT(db->db_level != 0 ||
1064             db->db_state == DB_CACHED || db->db_state == DB_FILL ||
1065             db->db_state == DB_NOFILL);
1066 
1067         mutex_enter(&dn->dn_mtx);
1068         /*
1069          * Don't set dirtyctx to SYNC if we're just modifying this as we
1070          * initialize the objset.
1071          */
1072         if (dn->dn_dirtyctx == DN_UNDIRTIED &&
1073             !BP_IS_HOLE(dn->dn_objset->os_rootbp)) {
1074                 dn->dn_dirtyctx =
1075                     (dmu_tx_is_syncing(tx) ? DN_DIRTY_SYNC : DN_DIRTY_OPEN);
1076                 ASSERT(dn->dn_dirtyctx_firstset == NULL);
1077                 dn->dn_dirtyctx_firstset = kmem_alloc(1, KM_SLEEP);
1078         }
1079         mutex_exit(&dn->dn_mtx);
1080 
1081         if (db->db_blkid == DMU_SPILL_BLKID)
1082                 dn->dn_have_spill = B_TRUE;
1083 
1084         /*
1085          * If this buffer is already dirty, we're done.
1086          */
1087         drp = &db->db_last_dirty;
1088         ASSERT(*drp == NULL || (*drp)->dr_txg <= tx->tx_txg ||
1089             db->db.db_object == DMU_META_DNODE_OBJECT);
1090         while ((dr = *drp) != NULL && dr->dr_txg > tx->tx_txg)
1091                 drp = &dr->dr_next;
1092         if (dr && dr->dr_txg == tx->tx_txg) {
1093                 DB_DNODE_EXIT(db);
1094 
1095                 if (db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID) {
1096                         /*
1097                          * If this buffer has already been written out,
1098                          * we now need to reset its state.
1099                          */
1100                         dbuf_unoverride(dr);
1101                         if (db->db.db_object != DMU_META_DNODE_OBJECT &&
1102                             db->db_state != DB_NOFILL)
1103                                 arc_buf_thaw(db->db_buf);
1104                 }
1105 
1106                 /*
1107                  * Special class usage of dirty dbuf could be changed,
1108                  * update the dirty entry.
1109                  */
1110                 dr->dr_usesc = usesc;
1111                 mutex_exit(&db->db_mtx);
1112                 return (dr);
1113         }
1114 
1115         /*
1116          * Only valid if not already dirty.
1117          */
1118         ASSERT(dn->dn_object == 0 ||
1119             dn->dn_dirtyctx == DN_UNDIRTIED || dn->dn_dirtyctx ==
1120             (dmu_tx_is_syncing(tx) ? DN_DIRTY_SYNC : DN_DIRTY_OPEN));
1121 
1122         ASSERT3U(dn->dn_nlevels, >, db->db_level);
1123         ASSERT((dn->dn_phys->dn_nlevels == 0 && db->db_level == 0) ||
1124             dn->dn_phys->dn_nlevels > db->db_level ||
1125             dn->dn_next_nlevels[txgoff] > db->db_level ||
1126             dn->dn_next_nlevels[(tx->tx_txg-1) & TXG_MASK] > db->db_level ||
1127             dn->dn_next_nlevels[(tx->tx_txg-2) & TXG_MASK] > db->db_level);
1128 
1129         /*
1130          * We should only be dirtying in syncing context if it's the
1131          * mos or we're initializing the os or it's a special object.
1132          * However, we are allowed to dirty in syncing context provided
1133          * we already dirtied it in open context.  Hence we must make
1134          * this assertion only if we're not already dirty.
1135          */
1136         os = dn->dn_objset;
1137         ASSERT(!dmu_tx_is_syncing(tx) || DMU_OBJECT_IS_SPECIAL(dn->dn_object) ||
1138             os->os_dsl_dataset == NULL || BP_IS_HOLE(os->os_rootbp));
1139         ASSERT(db->db.db_size != 0);
1140 
1141         dprintf_dbuf(db, "size=%llx\n", (u_longlong_t)db->db.db_size);
1142 
1143         if (db->db_blkid != DMU_BONUS_BLKID) {
1144                 /*
1145                  * Update the accounting.
1146                  * Note: we delay "free accounting" until after we drop
1147                  * the db_mtx.  This keeps us from grabbing other locks
1148                  * (and possibly deadlocking) in bp_get_dsize() while
1149                  * also holding the db_mtx.
1150                  */
1151                 dnode_willuse_space(dn, db->db.db_size, tx);
1152                 do_free_accounting = dbuf_block_freeable(db);
1153         }
1154 
1155         /*
1156          * If this buffer is dirty in an old transaction group we need
1157          * to make a copy of it so that the changes we make in this
1158          * transaction group won't leak out when we sync the older txg.
1159          */
1160         dr = kmem_zalloc(sizeof (dbuf_dirty_record_t), KM_SLEEP);
1161         if (db->db_level == 0) {
1162                 void *data_old = db->db_buf;
1163 
1164                 if (db->db_state != DB_NOFILL) {
1165                         if (db->db_blkid == DMU_BONUS_BLKID) {
1166                                 dbuf_fix_old_data(db, tx->tx_txg);
1167                                 data_old = db->db.db_data;
1168                         } else if (db->db.db_object != DMU_META_DNODE_OBJECT) {
1169                                 /*
1170                                  * Release the data buffer from the cache so
1171                                  * that we can modify it without impacting
1172                                  * possible other users of this cached data
1173                                  * block.  Note that indirect blocks and
1174                                  * private objects are not released until the
1175                                  * syncing state (since they are only modified
1176                                  * then).
1177                                  */
1178                                 arc_release(db->db_buf, db);
1179                                 dbuf_fix_old_data(db, tx->tx_txg);
1180                                 data_old = db->db_buf;
1181                         }
1182                         ASSERT(data_old != NULL);
1183                 }
1184                 dr->dt.dl.dr_data = data_old;
1185         } else {
1186                 mutex_init(&dr->dt.di.dr_mtx, NULL, MUTEX_DEFAULT, NULL);
1187                 list_create(&dr->dt.di.dr_children,
1188                     sizeof (dbuf_dirty_record_t),
1189                     offsetof(dbuf_dirty_record_t, dr_dirty_node));
1190         }
1191         if (db->db_blkid != DMU_BONUS_BLKID && os->os_dsl_dataset != NULL)
1192                 dr->dr_accounted = db->db.db_size;
1193         dr->dr_dbuf = db;
1194         dr->dr_txg = tx->tx_txg;
1195         dr->dr_next = *drp;
1196         dr->dr_usesc = usesc;
1197         *drp = dr;
1198 
1199         /*
1200          * We could have been freed_in_flight between the dbuf_noread
1201          * and dbuf_dirty.  We win, as though the dbuf_noread() had
1202          * happened after the free.
1203          */
1204         if (db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID &&
1205             db->db_blkid != DMU_SPILL_BLKID) {
1206                 mutex_enter(&dn->dn_mtx);
1207                 if (dn->dn_free_ranges[txgoff] != NULL) {
1208                         range_tree_clear(dn->dn_free_ranges[txgoff],
1209                             db->db_blkid, 1);
1210                 }
1211                 mutex_exit(&dn->dn_mtx);
1212                 db->db_freed_in_flight = FALSE;
1213         }
1214 
1215         /*
1216          * This buffer is now part of this txg
1217          */
1218         dbuf_add_ref(db, (void *)(uintptr_t)tx->tx_txg);
1219         db->db_dirtycnt += 1;
1220         ASSERT3U(db->db_dirtycnt, <=, 3);
1221 
1222         mutex_exit(&db->db_mtx);
1223 
1224         if (db->db_blkid == DMU_BONUS_BLKID ||
1225             db->db_blkid == DMU_SPILL_BLKID) {
1226                 mutex_enter(&dn->dn_mtx);
1227                 ASSERT(!list_link_active(&dr->dr_dirty_node));
1228                 list_insert_tail(&dn->dn_dirty_records[txgoff], dr);
1229                 mutex_exit(&dn->dn_mtx);
1230                 dnode_setdirty_sc(dn, tx, usesc);
1231                 DB_DNODE_EXIT(db);
1232                 return (dr);
1233         } else if (do_free_accounting) {
1234                 blkptr_t *bp = db->db_blkptr;
1235                 int64_t willfree = (bp && !BP_IS_HOLE(bp)) ?
1236                     bp_get_dsize(os->os_spa, bp) : db->db.db_size;
1237                 /*
1238                  * This is only a guess -- if the dbuf is dirty
1239                  * in a previous txg, we don't know how much
1240                  * space it will use on disk yet.  We should
1241                  * really have the struct_rwlock to access
1242                  * db_blkptr, but since this is just a guess,
1243                  * it's OK if we get an odd answer.
1244                  */
1245                 ddt_prefetch(os->os_spa, bp);
1246                 dnode_willuse_space(dn, -willfree, tx);
1247         }
1248 
1249         if (!RW_WRITE_HELD(&dn->dn_struct_rwlock)) {
1250                 rw_enter(&dn->dn_struct_rwlock, RW_READER);
1251                 drop_struct_lock = TRUE;
1252         }
1253 
1254         if (db->db_level == 0) {
1255                 dnode_new_blkid(dn, db->db_blkid, tx, usesc, drop_struct_lock);
1256                 ASSERT(dn->dn_maxblkid >= db->db_blkid);
1257         }
1258 
1259         if (db->db_level+1 < dn->dn_nlevels) {
1260                 dmu_buf_impl_t *parent = db->db_parent;
1261                 dbuf_dirty_record_t *di;
1262                 int parent_held = FALSE;
1263 
1264                 if (db->db_parent == NULL || db->db_parent == dn->dn_dbuf) {
1265                         int epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
1266 
1267                         parent = dbuf_hold_level(dn, db->db_level+1,
1268                             db->db_blkid >> epbs, FTAG);
1269                         ASSERT(parent != NULL);
1270                         parent_held = TRUE;
1271                 }
1272                 if (drop_struct_lock)
1273                         rw_exit(&dn->dn_struct_rwlock);
1274                 ASSERT3U(db->db_level+1, ==, parent->db_level);
1275                 di = dbuf_dirty_sc(parent, tx, usesc);
1276                 if (parent_held)
1277                         dbuf_rele(parent, FTAG);
1278 
1279                 mutex_enter(&db->db_mtx);
1280                 /*
1281                  * Since we've dropped the mutex, it's possible that
1282                  * dbuf_undirty() might have changed this out from under us.
1283                  */
1284                 if (db->db_last_dirty == dr ||
1285                     dn->dn_object == DMU_META_DNODE_OBJECT) {
1286                         mutex_enter(&di->dt.di.dr_mtx);
1287                         ASSERT3U(di->dr_txg, ==, tx->tx_txg);
1288                         ASSERT(!list_link_active(&dr->dr_dirty_node));
1289                         list_insert_tail(&di->dt.di.dr_children, dr);
1290                         mutex_exit(&di->dt.di.dr_mtx);
1291                         dr->dr_parent = di;
1292                 }
1293 
1294                 /*
1295                  * Special class usage of dirty dbuf could be changed,
1296                  * update the dirty entry.
1297                  */
1298                 dr->dr_usesc = usesc;
1299                 mutex_exit(&db->db_mtx);
1300         } else {
1301                 ASSERT(db->db_level+1 == dn->dn_nlevels);
1302                 ASSERT(db->db_blkid < dn->dn_nblkptr);
1303                 ASSERT(db->db_parent == NULL || db->db_parent == dn->dn_dbuf);
1304                 mutex_enter(&dn->dn_mtx);
1305                 ASSERT(!list_link_active(&dr->dr_dirty_node));
1306                 list_insert_tail(&dn->dn_dirty_records[txgoff], dr);
1307                 mutex_exit(&dn->dn_mtx);
1308                 if (drop_struct_lock)
1309                         rw_exit(&dn->dn_struct_rwlock);
1310         }
1311 
1312         dnode_setdirty_sc(dn, tx, usesc);
1313         DB_DNODE_EXIT(db);
1314         return (dr);
1315 }
1316 
1317 dbuf_dirty_record_t *
1318 dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
1319 {
1320         spa_t *spa;
1321 
1322         ASSERT(db->db_objset != NULL);
1323         spa = db->db_objset->os_spa;
1324 
1325         return (dbuf_dirty_sc(db, tx, spa->spa_usesc));
1326 }
1327 
1328 /*
1329  * Undirty a buffer in the transaction group referenced by the given
1330  * transaction.  Return whether this evicted the dbuf.
1331  */
1332 static boolean_t
1333 dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
1334 {
1335         dnode_t *dn;
1336         uint64_t txg = tx->tx_txg;
1337         dbuf_dirty_record_t *dr, **drp;
1338 
1339         ASSERT(txg != 0);
1340         ASSERT(db->db_blkid != DMU_BONUS_BLKID);
1341         ASSERT0(db->db_level);
1342         ASSERT(MUTEX_HELD(&db->db_mtx));
1343 
1344         /*
1345          * If this buffer is not dirty, we're done.
1346          */
1347         for (drp = &db->db_last_dirty; (dr = *drp) != NULL; drp = &dr->dr_next)
1348                 if (dr->dr_txg <= txg)
1349                         break;
1350         if (dr == NULL || dr->dr_txg < txg)
1351                 return (B_FALSE);
1352         ASSERT(dr->dr_txg == txg);
1353         ASSERT(dr->dr_dbuf == db);
1354 
1355         DB_DNODE_ENTER(db);
1356         dn = DB_DNODE(db);
1357 
1358         dprintf_dbuf(db, "size=%llx\n", (u_longlong_t)db->db.db_size);
1359 
1360         ASSERT(db->db.db_size != 0);
1361 
1362         /*
1363          * Any space we accounted for in dp_dirty_* will be cleaned up by
1364          * dsl_pool_sync().  This is relatively rare so the discrepancy
1365          * is not a big deal.
1366          */
1367 
1368         *drp = dr->dr_next;
1369 
1370         /*
1371          * Note that there are three places in dbuf_dirty()
1372          * where this dirty record may be put on a list.
1373          * Make sure to do a list_remove corresponding to
1374          * every one of those list_insert calls.
1375          */
1376         if (dr->dr_parent) {
1377                 mutex_enter(&dr->dr_parent->dt.di.dr_mtx);
1378                 list_remove(&dr->dr_parent->dt.di.dr_children, dr);
1379                 mutex_exit(&dr->dr_parent->dt.di.dr_mtx);
1380         } else if (db->db_blkid == DMU_SPILL_BLKID ||
1381             db->db_level+1 == dn->dn_nlevels) {
1382                 ASSERT(db->db_blkptr == NULL || db->db_parent == dn->dn_dbuf);
1383                 mutex_enter(&dn->dn_mtx);
1384                 list_remove(&dn->dn_dirty_records[txg & TXG_MASK], dr);
1385                 mutex_exit(&dn->dn_mtx);
1386         }
1387         DB_DNODE_EXIT(db);
1388 
1389         if (db->db_state != DB_NOFILL) {
1390                 dbuf_unoverride(dr);
1391 
1392                 ASSERT(db->db_buf != NULL);
1393                 ASSERT(dr->dt.dl.dr_data != NULL);
1394                 if (dr->dt.dl.dr_data != db->db_buf)
1395                         VERIFY(arc_buf_remove_ref(dr->dt.dl.dr_data, db));
1396         }
1397 
1398         if (db->db_level != 0) {
1399                 mutex_destroy(&dr->dt.di.dr_mtx);
1400                 list_destroy(&dr->dt.di.dr_children);
1401         }
1402 
1403         kmem_free(dr, sizeof (dbuf_dirty_record_t));
1404 
1405         ASSERT(db->db_dirtycnt > 0);
1406         db->db_dirtycnt -= 1;
1407 
1408         if (refcount_remove(&db->db_holds, (void *)(uintptr_t)txg) == 0) {
1409                 arc_buf_t *buf = db->db_buf;
1410 
1411                 ASSERT(db->db_state == DB_NOFILL || arc_released(buf));
1412                 dbuf_set_data(db, NULL);
1413                 VERIFY(arc_buf_remove_ref(buf, db));
1414                 dbuf_evict(db);
1415                 return (B_TRUE);
1416         }
1417 
1418         return (B_FALSE);
1419 }
1420 
1421 void
1422 dmu_buf_will_dirty(dmu_buf_t *db_fake, dmu_tx_t *tx)
1423 {
1424         dmu_buf_will_dirty_sc(db_fake, tx, B_TRUE);
1425 }
1426 
1427 void
1428 dmu_buf_will_dirty_sc(dmu_buf_t *db_fake, dmu_tx_t *tx, boolean_t usesc)
1429 {
1430         dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
1431         int rf = DB_RF_MUST_SUCCEED | DB_RF_NOPREFETCH;
1432 
1433         ASSERT(tx->tx_txg != 0);
1434         ASSERT(!refcount_is_zero(&db->db_holds));
1435 
1436         DB_DNODE_ENTER(db);
1437         if (RW_WRITE_HELD(&DB_DNODE(db)->dn_struct_rwlock))
1438                 rf |= DB_RF_HAVESTRUCT;
1439         DB_DNODE_EXIT(db);
1440         (void) dbuf_read(db, NULL, rf);
1441         (void) dbuf_dirty_sc(db, tx, usesc);
1442 }
1443 
1444 
1445 void
1446 dmu_buf_will_not_fill(dmu_buf_t *db_fake, dmu_tx_t *tx)
1447 {
1448         dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
1449 
1450         db->db_state = DB_NOFILL;
1451 
1452         dmu_buf_will_fill(db_fake, tx);
1453 }
1454 
1455 void
1456 dmu_buf_will_fill(dmu_buf_t *db_fake, dmu_tx_t *tx)
1457 {
1458         dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
1459 
1460         ASSERT(db->db_blkid != DMU_BONUS_BLKID);
1461         ASSERT(tx->tx_txg != 0);
1462         ASSERT(db->db_level == 0);
1463         ASSERT(!refcount_is_zero(&db->db_holds));
1464 
1465         ASSERT(db->db.db_object != DMU_META_DNODE_OBJECT ||
1466             dmu_tx_private_ok(tx));
1467 
1468         dbuf_noread(db);
1469         (void) dbuf_dirty(db, tx);
1470 }
1471 
1472 #pragma weak dmu_buf_fill_done = dbuf_fill_done
1473 /* ARGSUSED */
1474 void
1475 dbuf_fill_done(dmu_buf_impl_t *db, dmu_tx_t *tx)
1476 {
1477         mutex_enter(&db->db_mtx);
1478         DBUF_VERIFY(db);
1479 
1480         if (db->db_state == DB_FILL) {
1481                 if (db->db_level == 0 && db->db_freed_in_flight) {
1482                         ASSERT(db->db_blkid != DMU_BONUS_BLKID);
1483                         /* we were freed while filling */
1484                         /* XXX dbuf_undirty? */
1485                         bzero(db->db.db_data, db->db.db_size);
1486                         db->db_freed_in_flight = FALSE;
1487                 }
1488                 db->db_state = DB_CACHED;
1489                 cv_broadcast(&db->db_changed);
1490         }
1491         mutex_exit(&db->db_mtx);
1492 }
1493 
1494 void
1495 dmu_buf_write_embedded(dmu_buf_t *dbuf, void *data,
1496     bp_embedded_type_t etype, enum zio_compress comp,
1497     int uncompressed_size, int compressed_size, int byteorder,
1498     dmu_tx_t *tx)
1499 {
1500         dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbuf;
1501         struct dirty_leaf *dl;
1502         dmu_object_type_t type;
1503 
1504         DB_DNODE_ENTER(db);
1505         type = DB_DNODE(db)->dn_type;
1506         DB_DNODE_EXIT(db);
1507 
1508         ASSERT0(db->db_level);
1509         ASSERT(db->db_blkid != DMU_BONUS_BLKID);
1510 
1511         dmu_buf_will_not_fill(dbuf, tx);
1512 
1513         ASSERT3U(db->db_last_dirty->dr_txg, ==, tx->tx_txg);
1514         dl = &db->db_last_dirty->dt.dl;
1515         encode_embedded_bp_compressed(&dl->dr_overridden_by,
1516             data, comp, uncompressed_size, compressed_size);
1517         BPE_SET_ETYPE(&dl->dr_overridden_by, etype);
1518         BP_SET_TYPE(&dl->dr_overridden_by, type);
1519         BP_SET_LEVEL(&dl->dr_overridden_by, 0);
1520         BP_SET_BYTEORDER(&dl->dr_overridden_by, byteorder);
1521 
1522         dl->dr_override_state = DR_OVERRIDDEN;
1523         dl->dr_overridden_by.blk_birth = db->db_last_dirty->dr_txg;
1524 }
1525 
1526 /*
1527  * Directly assign a provided arc buf to a given dbuf if it's not referenced
1528  * by anybody except our caller. Otherwise copy arcbuf's contents to dbuf.
1529  */
1530 void
1531 dbuf_assign_arcbuf(dmu_buf_impl_t *db, arc_buf_t *buf, dmu_tx_t *tx)
1532 {
1533         ASSERT(!refcount_is_zero(&db->db_holds));
1534         ASSERT(db->db_blkid != DMU_BONUS_BLKID);
1535         ASSERT(db->db_level == 0);
1536         ASSERT(DBUF_GET_BUFC_TYPE(db) == ARC_BUFC_DATA);
1537         ASSERT(buf != NULL);
1538         ASSERT(arc_buf_size(buf) == db->db.db_size);
1539         ASSERT(tx->tx_txg != 0);
1540 
1541         arc_return_buf(buf, db);
1542         ASSERT(arc_released(buf));
1543 
1544         mutex_enter(&db->db_mtx);
1545 
1546         while (db->db_state == DB_READ || db->db_state == DB_FILL)
1547                 cv_wait(&db->db_changed, &db->db_mtx);
1548 
1549         ASSERT(db->db_state == DB_CACHED || db->db_state == DB_UNCACHED);
1550 
1551         if (db->db_state == DB_CACHED &&
1552             refcount_count(&db->db_holds) - 1 > db->db_dirtycnt) {
1553                 mutex_exit(&db->db_mtx);
1554                 (void) dbuf_dirty(db, tx);
1555                 bcopy(buf->b_data, db->db.db_data, db->db.db_size);
1556                 VERIFY(arc_buf_remove_ref(buf, db));
1557                 xuio_stat_wbuf_copied();
1558                 return;
1559         }
1560 
1561         xuio_stat_wbuf_nocopy();
1562         if (db->db_state == DB_CACHED) {
1563                 dbuf_dirty_record_t *dr = db->db_last_dirty;
1564 
1565                 ASSERT(db->db_buf != NULL);
1566                 if (dr != NULL && dr->dr_txg == tx->tx_txg) {
1567                         ASSERT(dr->dt.dl.dr_data == db->db_buf);
1568                         if (!arc_released(db->db_buf)) {
1569                                 ASSERT(dr->dt.dl.dr_override_state ==
1570                                     DR_OVERRIDDEN);
1571                                 arc_release(db->db_buf, db);
1572                         }
1573                         dr->dt.dl.dr_data = buf;
1574                         VERIFY(arc_buf_remove_ref(db->db_buf, db));
1575                 } else if (dr == NULL || dr->dt.dl.dr_data != db->db_buf) {
1576                         arc_release(db->db_buf, db);
1577                         VERIFY(arc_buf_remove_ref(db->db_buf, db));
1578                 }
1579                 db->db_buf = NULL;
1580         }
1581         ASSERT(db->db_buf == NULL);
1582         dbuf_set_data(db, buf);
1583         db->db_state = DB_FILL;
1584         mutex_exit(&db->db_mtx);
1585         (void) dbuf_dirty(db, tx);
1586         dmu_buf_fill_done(&db->db, tx);
1587 }
1588 
1589 /*
1590  * "Clear" the contents of this dbuf.  This will mark the dbuf
1591  * EVICTING and clear *most* of its references.  Unfortunately,
1592  * when we are not holding the dn_dbufs_mtx, we can't clear the
1593  * entry in the dn_dbufs list.  We have to wait until dbuf_destroy()
1594  * in this case.  For callers from the DMU we will usually see:
1595  *      dbuf_clear()->arc_clear_callback()->dbuf_do_evict()->dbuf_destroy()
1596  * For the arc callback, we will usually see:
1597  *      dbuf_do_evict()->dbuf_clear();dbuf_destroy()
1598  * Sometimes, though, we will get a mix of these two:
1599  *      DMU: dbuf_clear()->arc_clear_callback()
1600  *      ARC: dbuf_do_evict()->dbuf_destroy()
1601  *
1602  * This routine will dissociate the dbuf from the arc, by calling
1603  * arc_clear_callback(), but will not evict the data from the ARC.
1604  */
1605 void
1606 dbuf_clear(dmu_buf_impl_t *db)
1607 {
1608         dnode_t *dn;
1609         dmu_buf_impl_t *parent = db->db_parent;
1610         dmu_buf_impl_t *dndb;
1611         boolean_t dbuf_gone = B_FALSE;
1612 
1613         ASSERT(MUTEX_HELD(&db->db_mtx));
1614         ASSERT(refcount_is_zero(&db->db_holds));
1615 
1616         dbuf_evict_user(db);
1617 
1618         if (db->db_state == DB_CACHED) {
1619                 ASSERT(db->db.db_data != NULL);
1620                 if (db->db_blkid == DMU_BONUS_BLKID) {
1621                         zio_buf_free(db->db.db_data, DN_MAX_BONUSLEN);
1622                         arc_space_return(DN_MAX_BONUSLEN, ARC_SPACE_OTHER);
1623                 }
1624                 db->db.db_data = NULL;
1625                 db->db_state = DB_UNCACHED;
1626         }
1627 
1628         ASSERT(db->db_state == DB_UNCACHED || db->db_state == DB_NOFILL);
1629         ASSERT(db->db_data_pending == NULL);
1630 
1631         db->db_state = DB_EVICTING;
1632         db->db_blkptr = NULL;
1633 
1634         DB_DNODE_ENTER(db);
1635         dn = DB_DNODE(db);
1636         dndb = dn->dn_dbuf;
1637         if (db->db_blkid != DMU_BONUS_BLKID && MUTEX_HELD(&dn->dn_dbufs_mtx)) {
1638                 avl_remove(&dn->dn_dbufs, db);
1639                 atomic_dec_32(&dn->dn_dbufs_count);
1640                 membar_producer();
1641                 DB_DNODE_EXIT(db);
1642                 /*
1643                  * Decrementing the dbuf count means that the hold corresponding
1644                  * to the removed dbuf is no longer discounted in dnode_move(),
1645                  * so the dnode cannot be moved until after we release the hold.
1646                  * The membar_producer() ensures visibility of the decremented
1647                  * value in dnode_move(), since DB_DNODE_EXIT doesn't actually
1648                  * release any lock.
1649                  */
1650                 dnode_rele(dn, db);
1651                 db->db_dnode_handle = NULL;
1652         } else {
1653                 DB_DNODE_EXIT(db);
1654         }
1655 
1656         if (db->db_buf)
1657                 dbuf_gone = arc_clear_callback(db->db_buf);
1658 
1659         if (!dbuf_gone)
1660                 mutex_exit(&db->db_mtx);
1661 
1662         /*
1663          * If this dbuf is referenced from an indirect dbuf,
1664          * decrement the ref count on the indirect dbuf.
1665          */
1666         if (parent && parent != dndb)
1667                 dbuf_rele(parent, db);
1668 }
1669 
1670 static int
1671 dbuf_findbp(dnode_t *dn, int level, uint64_t blkid, int fail_sparse,
1672     dmu_buf_impl_t **parentp, blkptr_t **bpp)
1673 {
1674         int nlevels, epbs;
1675 
1676         *parentp = NULL;
1677         *bpp = NULL;
1678 
1679         ASSERT(blkid != DMU_BONUS_BLKID);
1680 
1681         if (blkid == DMU_SPILL_BLKID) {
1682                 mutex_enter(&dn->dn_mtx);
1683                 if (dn->dn_have_spill &&
1684                     (dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR))
1685                         *bpp = &dn->dn_phys->dn_spill;
1686                 else
1687                         *bpp = NULL;
1688                 dbuf_add_ref(dn->dn_dbuf, NULL);
1689                 *parentp = dn->dn_dbuf;
1690                 mutex_exit(&dn->dn_mtx);
1691                 return (0);
1692         }
1693 
1694         if (dn->dn_phys->dn_nlevels == 0)
1695                 nlevels = 1;
1696         else
1697                 nlevels = dn->dn_phys->dn_nlevels;
1698 
1699         epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
1700 
1701         ASSERT3U(level * epbs, <, 64);
1702         ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
1703         if (level >= nlevels ||
1704             (blkid > (dn->dn_phys->dn_maxblkid >> (level * epbs)))) {
1705                 /* the buffer has no parent yet */
1706                 return (SET_ERROR(ENOENT));
1707         } else if (level < nlevels-1) {
1708                 /* this block is referenced from an indirect block */
1709                 int err = dbuf_hold_impl(dn, level+1,
1710                     blkid >> epbs, fail_sparse, NULL, parentp);
1711                 if (err)
1712                         return (err);
1713                 err = dbuf_read(*parentp, NULL,
1714                     (DB_RF_HAVESTRUCT | DB_RF_NOPREFETCH | DB_RF_CANFAIL));
1715                 if (err) {
1716                         dbuf_rele(*parentp, NULL);
1717                         *parentp = NULL;
1718                         return (err);
1719                 }
1720                 *bpp = ((blkptr_t *)(*parentp)->db.db_data) +
1721                     (blkid & ((1ULL << epbs) - 1));
1722                 return (0);
1723         } else {
1724                 /* the block is referenced from the dnode */
1725                 ASSERT3U(level, ==, nlevels-1);
1726                 ASSERT(dn->dn_phys->dn_nblkptr == 0 ||
1727                     blkid < dn->dn_phys->dn_nblkptr);
1728                 if (dn->dn_dbuf) {
1729                         dbuf_add_ref(dn->dn_dbuf, NULL);
1730                         *parentp = dn->dn_dbuf;
1731                 }
1732                 *bpp = &dn->dn_phys->dn_blkptr[blkid];
1733                 return (0);
1734         }
1735 }
1736 
1737 static dmu_buf_impl_t *
1738 dbuf_create(dnode_t *dn, uint8_t level, uint64_t blkid,
1739     dmu_buf_impl_t *parent, blkptr_t *blkptr)
1740 {
1741         objset_t *os = dn->dn_objset;
1742         dmu_buf_impl_t *db, *odb;
1743 
1744         ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
1745         ASSERT(dn->dn_type != DMU_OT_NONE);
1746 
1747         db = kmem_cache_alloc(dbuf_cache, KM_SLEEP);
1748 
1749         db->db_objset = os;
1750         db->db.db_object = dn->dn_object;
1751         db->db_level = level;
1752         db->db_blkid = blkid;
1753         db->db_last_dirty = NULL;
1754         db->db_dirtycnt = 0;
1755         db->db_dnode_handle = dn->dn_handle;
1756         db->db_parent = parent;
1757         db->db_blkptr = blkptr;
1758 
1759         db->db_user_ptr = NULL;
1760         db->db_user_data_ptr_ptr = NULL;
1761         db->db_evict_func = NULL;
1762         db->db_immediate_evict = 0;
1763         db->db_freed_in_flight = 0;
1764 
1765         if (blkid == DMU_BONUS_BLKID) {
1766                 ASSERT3P(parent, ==, dn->dn_dbuf);
1767                 db->db.db_size = DN_MAX_BONUSLEN -
1768                     (dn->dn_nblkptr-1) * sizeof (blkptr_t);
1769                 ASSERT3U(db->db.db_size, >=, dn->dn_bonuslen);
1770                 db->db.db_offset = DMU_BONUS_BLKID;
1771                 db->db_state = DB_UNCACHED;
1772                 /* the bonus dbuf is not placed in the hash table */
1773                 arc_space_consume(sizeof (dmu_buf_impl_t), ARC_SPACE_OTHER);
1774                 return (db);
1775         } else if (blkid == DMU_SPILL_BLKID) {
1776                 db->db.db_size = (blkptr != NULL) ?
1777                     BP_GET_LSIZE(blkptr) : SPA_MINBLOCKSIZE;
1778                 db->db.db_offset = 0;
1779         } else {
1780                 int blocksize =
1781                     db->db_level ? 1 << dn->dn_indblkshift : dn->dn_datablksz;
1782                 db->db.db_size = blocksize;
1783                 db->db.db_offset = db->db_blkid * blocksize;
1784         }
1785 
1786         /*
1787          * Hold the dn_dbufs_mtx while we get the new dbuf
1788          * in the hash table *and* added to the dbufs list.
1789          * This prevents a possible deadlock with someone
1790          * trying to look up this dbuf before its added to the
1791          * dn_dbufs list.
1792          */
1793         mutex_enter(&dn->dn_dbufs_mtx);
1794         db->db_state = DB_EVICTING;
1795         if ((odb = dbuf_hash_insert(db)) != NULL) {
1796                 /* someone else inserted it first */
1797                 kmem_cache_free(dbuf_cache, db);
1798                 mutex_exit(&dn->dn_dbufs_mtx);
1799                 return (odb);
1800         }
1801         avl_add(&dn->dn_dbufs, db);
1802         if (db->db_level == 0 && db->db_blkid >=
1803             dn->dn_unlisted_l0_blkid)
1804                 dn->dn_unlisted_l0_blkid = db->db_blkid + 1;
1805         db->db_state = DB_UNCACHED;
1806         mutex_exit(&dn->dn_dbufs_mtx);
1807         arc_space_consume(sizeof (dmu_buf_impl_t), ARC_SPACE_OTHER);
1808 
1809         if (parent && parent != dn->dn_dbuf)
1810                 dbuf_add_ref(parent, db);
1811 
1812         ASSERT(dn->dn_object == DMU_META_DNODE_OBJECT ||
1813             refcount_count(&dn->dn_holds) > 0);
1814         (void) refcount_add(&dn->dn_holds, db);
1815         atomic_inc_32(&dn->dn_dbufs_count);
1816 
1817         dprintf_dbuf(db, "db=%p\n", db);
1818 
1819         return (db);
1820 }
1821 
1822 static int
1823 dbuf_do_evict(void *private)
1824 {
1825         dmu_buf_impl_t *db = private;
1826 
1827         if (!MUTEX_HELD(&db->db_mtx))
1828                 mutex_enter(&db->db_mtx);
1829 
1830         ASSERT(refcount_is_zero(&db->db_holds));
1831 
1832         if (db->db_state != DB_EVICTING) {
1833                 ASSERT(db->db_state == DB_CACHED);
1834                 DBUF_VERIFY(db);
1835                 db->db_buf = NULL;
1836                 dbuf_evict(db);
1837         } else {
1838                 mutex_exit(&db->db_mtx);
1839                 dbuf_destroy(db);
1840         }
1841         return (0);
1842 }
1843 
1844 static void
1845 dbuf_destroy(dmu_buf_impl_t *db)
1846 {
1847         ASSERT(refcount_is_zero(&db->db_holds));
1848 
1849         if (db->db_blkid != DMU_BONUS_BLKID) {
1850                 /*
1851                  * If this dbuf is still on the dn_dbufs list,
1852                  * remove it from that list.
1853                  */
1854                 if (db->db_dnode_handle != NULL) {
1855                         dnode_t *dn;
1856 
1857                         DB_DNODE_ENTER(db);
1858                         dn = DB_DNODE(db);
1859                         mutex_enter(&dn->dn_dbufs_mtx);
1860                         avl_remove(&dn->dn_dbufs, db);
1861                         atomic_dec_32(&dn->dn_dbufs_count);
1862                         mutex_exit(&dn->dn_dbufs_mtx);
1863                         DB_DNODE_EXIT(db);
1864                         /*
1865                          * Decrementing the dbuf count means that the hold
1866                          * corresponding to the removed dbuf is no longer
1867                          * discounted in dnode_move(), so the dnode cannot be
1868                          * moved until after we release the hold.
1869                          */
1870                         dnode_rele(dn, db);
1871                         db->db_dnode_handle = NULL;
1872                 }
1873                 dbuf_hash_remove(db);
1874         }
1875         db->db_parent = NULL;
1876         db->db_buf = NULL;
1877 
1878         ASSERT(db->db.db_data == NULL);
1879         ASSERT(db->db_hash_next == NULL);
1880         ASSERT(db->db_blkptr == NULL);
1881         ASSERT(db->db_data_pending == NULL);
1882 
1883         kmem_cache_free(dbuf_cache, db);
1884         arc_space_return(sizeof (dmu_buf_impl_t), ARC_SPACE_OTHER);
1885 }
1886 
1887 void
1888 dbuf_prefetch(dnode_t *dn, uint64_t blkid, zio_priority_t prio)
1889 {
1890         dmu_buf_impl_t *db = NULL;
1891         blkptr_t *bp = NULL;
1892 
1893         ASSERT(blkid != DMU_BONUS_BLKID);
1894         ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
1895 
1896         if (dnode_block_freed(dn, blkid))
1897                 return;
1898 
1899         /* dbuf_find() returns with db_mtx held */
1900         if (db = dbuf_find(dn, 0, blkid)) {
1901                 /*
1902                  * This dbuf is already in the cache.  We assume that
1903                  * it is already CACHED, or else about to be either
1904                  * read or filled.
1905                  */
1906                 mutex_exit(&db->db_mtx);
1907                 return;
1908         }
1909 
1910         if (dbuf_findbp(dn, 0, blkid, TRUE, &db, &bp) == 0) {
1911                 if (bp && !BP_IS_HOLE(bp) && !BP_IS_EMBEDDED(bp)) {
1912                         dsl_dataset_t *ds = dn->dn_objset->os_dsl_dataset;
1913                         uint32_t aflags = ARC_NOWAIT | ARC_PREFETCH;
1914                         zbookmark_phys_t zb;
1915 
1916                         SET_BOOKMARK(&zb, ds ? ds->ds_object : DMU_META_OBJSET,
1917                             dn->dn_object, 0, blkid);
1918 
1919                         (void) arc_read(NULL, dn->dn_objset->os_spa,
1920                             bp, NULL, NULL, prio,
1921                             ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE,
1922                             &aflags, &zb);
1923                 }
1924                 if (db)
1925                         dbuf_rele(db, NULL);
1926         }
1927 }
1928 
1929 /*
1930  * Returns with db_holds incremented, and db_mtx not held.
1931  * Note: dn_struct_rwlock must be held.
1932  */
1933 int
1934 dbuf_hold_impl(dnode_t *dn, uint8_t level, uint64_t blkid, int fail_sparse,
1935     void *tag, dmu_buf_impl_t **dbp)
1936 {
1937         dmu_buf_impl_t *db, *parent = NULL;
1938 
1939         ASSERT(blkid != DMU_BONUS_BLKID);
1940         ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
1941         ASSERT3U(dn->dn_nlevels, >, level);
1942 
1943         *dbp = NULL;
1944 top:
1945         /* dbuf_find() returns with db_mtx held */
1946         db = dbuf_find(dn, level, blkid);
1947 
1948         if (db == NULL) {
1949                 blkptr_t *bp = NULL;
1950                 int err;
1951 
1952                 ASSERT3P(parent, ==, NULL);
1953                 err = dbuf_findbp(dn, level, blkid, fail_sparse, &parent, &bp);
1954                 if (fail_sparse) {
1955                         if (err == 0 && bp && BP_IS_HOLE(bp))
1956                                 err = SET_ERROR(ENOENT);
1957                         if (err) {
1958                                 if (parent)
1959                                         dbuf_rele(parent, NULL);
1960                                 return (err);
1961                         }
1962                 }
1963                 if (err && err != ENOENT)
1964                         return (err);
1965                 db = dbuf_create(dn, level, blkid, parent, bp);
1966         }
1967 
1968         if (db->db_buf && refcount_is_zero(&db->db_holds)) {
1969                 arc_buf_add_ref(db->db_buf, db);
1970                 if (db->db_buf->b_data == NULL) {
1971                         dbuf_clear(db);
1972                         if (parent) {
1973                                 dbuf_rele(parent, NULL);
1974                                 parent = NULL;
1975                         }
1976                         goto top;
1977                 }
1978                 ASSERT3P(db->db.db_data, ==, db->db_buf->b_data);
1979         }
1980 
1981         ASSERT(db->db_buf == NULL || arc_referenced(db->db_buf));
1982 
1983         /*
1984          * If this buffer is currently syncing out, and we are are
1985          * still referencing it from db_data, we need to make a copy
1986          * of it in case we decide we want to dirty it again in this txg.
1987          */
1988         if (db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID &&
1989             dn->dn_object != DMU_META_DNODE_OBJECT &&
1990             db->db_state == DB_CACHED && db->db_data_pending) {
1991                 dbuf_dirty_record_t *dr = db->db_data_pending;
1992 
1993                 if (dr->dt.dl.dr_data == db->db_buf) {
1994                         arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
1995 
1996                         dbuf_set_data(db,
1997                             arc_buf_alloc(dn->dn_objset->os_spa,
1998                             db->db.db_size, db, type));
1999                         bcopy(dr->dt.dl.dr_data->b_data, db->db.db_data,
2000                             db->db.db_size);
2001                 }
2002         }
2003 
2004         (void) refcount_add(&db->db_holds, tag);
2005         dbuf_update_data(db);
2006         DBUF_VERIFY(db);
2007         mutex_exit(&db->db_mtx);
2008 
2009         /* NOTE: we can't rele the parent until after we drop the db_mtx */
2010         if (parent)
2011                 dbuf_rele(parent, NULL);
2012 
2013         ASSERT3P(DB_DNODE(db), ==, dn);
2014         ASSERT3U(db->db_blkid, ==, blkid);
2015         ASSERT3U(db->db_level, ==, level);
2016         *dbp = db;
2017 
2018         return (0);
2019 }
2020 
2021 dmu_buf_impl_t *
2022 dbuf_hold(dnode_t *dn, uint64_t blkid, void *tag)
2023 {
2024         dmu_buf_impl_t *db;
2025         int err = dbuf_hold_impl(dn, 0, blkid, FALSE, tag, &db);
2026         return (err ? NULL : db);
2027 }
2028 
2029 dmu_buf_impl_t *
2030 dbuf_hold_level(dnode_t *dn, int level, uint64_t blkid, void *tag)
2031 {
2032         dmu_buf_impl_t *db;
2033         int err = dbuf_hold_impl(dn, level, blkid, FALSE, tag, &db);
2034         return (err ? NULL : db);
2035 }
2036 
2037 void
2038 dbuf_create_bonus(dnode_t *dn)
2039 {
2040         ASSERT(RW_WRITE_HELD(&dn->dn_struct_rwlock));
2041 
2042         ASSERT(dn->dn_bonus == NULL);
2043         dn->dn_bonus = dbuf_create(dn, 0, DMU_BONUS_BLKID, dn->dn_dbuf, NULL);
2044 }
2045 
2046 int
2047 dbuf_spill_set_blksz(dmu_buf_t *db_fake, uint64_t blksz, dmu_tx_t *tx)
2048 {
2049         dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
2050         dnode_t *dn;
2051 
2052         if (db->db_blkid != DMU_SPILL_BLKID)
2053                 return (SET_ERROR(ENOTSUP));
2054         if (blksz == 0)
2055                 blksz = SPA_MINBLOCKSIZE;
2056         if (blksz > SPA_MAXBLOCKSIZE)
2057                 blksz = SPA_MAXBLOCKSIZE;
2058         else
2059                 blksz = P2ROUNDUP(blksz, SPA_MINBLOCKSIZE);
2060 
2061         DB_DNODE_ENTER(db);
2062         dn = DB_DNODE(db);
2063         rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
2064         dbuf_new_size(db, blksz, tx);
2065         rw_exit(&dn->dn_struct_rwlock);
2066         DB_DNODE_EXIT(db);
2067 
2068         return (0);
2069 }
2070 
2071 void
2072 dbuf_rm_spill(dnode_t *dn, dmu_tx_t *tx)
2073 {
2074         dbuf_free_range(dn, DMU_SPILL_BLKID, DMU_SPILL_BLKID, tx);
2075 }
2076 
2077 #pragma weak dmu_buf_add_ref = dbuf_add_ref
2078 void
2079 dbuf_add_ref(dmu_buf_impl_t *db, void *tag)
2080 {
2081         int64_t holds = refcount_add(&db->db_holds, tag);
2082         ASSERT(holds > 1);
2083 }
2084 
2085 /*
2086  * If you call dbuf_rele() you had better not be referencing the dnode handle
2087  * unless you have some other direct or indirect hold on the dnode. (An indirect
2088  * hold is a hold on one of the dnode's dbufs, including the bonus buffer.)
2089  * Without that, the dbuf_rele() could lead to a dnode_rele() followed by the
2090  * dnode's parent dbuf evicting its dnode handles.
2091  */
2092 void
2093 dbuf_rele(dmu_buf_impl_t *db, void *tag)
2094 {
2095         mutex_enter(&db->db_mtx);
2096         dbuf_rele_and_unlock(db, tag);
2097 }
2098 
2099 void
2100 dmu_buf_rele(dmu_buf_t *db, void *tag)
2101 {
2102         dbuf_rele((dmu_buf_impl_t *)db, tag);
2103 }
2104 
2105 /*
2106  * dbuf_rele() for an already-locked dbuf.  This is necessary to allow
2107  * db_dirtycnt and db_holds to be updated atomically.
2108  */
2109 void
2110 dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
2111 {
2112         int64_t holds;
2113 
2114         ASSERT(MUTEX_HELD(&db->db_mtx));
2115         DBUF_VERIFY(db);
2116 
2117         /*
2118          * Remove the reference to the dbuf before removing its hold on the
2119          * dnode so we can guarantee in dnode_move() that a referenced bonus
2120          * buffer has a corresponding dnode hold.
2121          */
2122         holds = refcount_remove(&db->db_holds, tag);
2123         ASSERT(holds >= 0);
2124 
2125         /*
2126          * We can't freeze indirects if there is a possibility that they
2127          * may be modified in the current syncing context.
2128          */
2129         if (db->db_buf && holds == (db->db_level == 0 ? db->db_dirtycnt : 0))
2130                 arc_buf_freeze(db->db_buf);
2131 
2132         if (holds == db->db_dirtycnt &&
2133             db->db_level == 0 && db->db_immediate_evict)
2134                 dbuf_evict_user(db);
2135 
2136         if (holds == 0) {
2137                 if (db->db_blkid == DMU_BONUS_BLKID) {
2138                         mutex_exit(&db->db_mtx);
2139 
2140                         /*
2141                          * If the dnode moves here, we cannot cross this barrier
2142                          * until the move completes.
2143                          */
2144                         DB_DNODE_ENTER(db);
2145                         atomic_dec_32(&DB_DNODE(db)->dn_dbufs_count);
2146                         DB_DNODE_EXIT(db);
2147                         /*
2148                          * The bonus buffer's dnode hold is no longer discounted
2149                          * in dnode_move(). The dnode cannot move until after
2150                          * the dnode_rele().
2151                          */
2152                         dnode_rele(DB_DNODE(db), db);
2153                 } else if (db->db_buf == NULL) {
2154                         /*
2155                          * This is a special case: we never associated this
2156                          * dbuf with any data allocated from the ARC.
2157                          */
2158                         ASSERT(db->db_state == DB_UNCACHED ||
2159                             db->db_state == DB_NOFILL);
2160                         dbuf_evict(db);
2161                 } else if (arc_released(db->db_buf)) {
2162                         arc_buf_t *buf = db->db_buf;
2163                         /*
2164                          * This dbuf has anonymous data associated with it.
2165                          */
2166                         dbuf_set_data(db, NULL);
2167                         VERIFY(arc_buf_remove_ref(buf, db));
2168                         dbuf_evict(db);
2169                 } else {
2170                         VERIFY(!arc_buf_remove_ref(db->db_buf, db));
2171 
2172                         /*
2173                          * A dbuf will be eligible for eviction if either the
2174                          * 'primarycache' property is set or a duplicate
2175                          * copy of this buffer is already cached in the arc.
2176                          *
2177                          * In the case of the 'primarycache' a buffer
2178                          * is considered for eviction if it matches the
2179                          * criteria set in the property.
2180                          *
2181                          * To decide if our buffer is considered a
2182                          * duplicate, we must call into the arc to determine
2183                          * if multiple buffers are referencing the same
2184                          * block on-disk. If so, then we simply evict
2185                          * ourselves.
2186                          */
2187                         if (!DBUF_IS_CACHEABLE(db)) {
2188                                 if (db->db_blkptr != NULL &&
2189                                     !BP_IS_HOLE(db->db_blkptr) &&
2190                                     !BP_IS_EMBEDDED(db->db_blkptr)) {
2191                                         spa_t *spa =
2192                                             dmu_objset_spa(db->db_objset);
2193                                         blkptr_t bp = *db->db_blkptr;
2194                                         dbuf_clear(db);
2195                                         arc_freed(spa, &bp);
2196                                 } else {
2197                                         dbuf_clear(db);
2198                                 }
2199                         } else if (arc_buf_eviction_needed(db->db_buf)) {
2200                                 dbuf_clear(db);
2201                         } else {
2202                                 mutex_exit(&db->db_mtx);
2203                         }
2204                 }
2205         } else {
2206                 mutex_exit(&db->db_mtx);
2207         }
2208 }
2209 
2210 #pragma weak dmu_buf_refcount = dbuf_refcount
2211 uint64_t
2212 dbuf_refcount(dmu_buf_impl_t *db)
2213 {
2214         return (refcount_count(&db->db_holds));
2215 }
2216 
2217 void *
2218 dmu_buf_set_user(dmu_buf_t *db_fake, void *user_ptr, void *user_data_ptr_ptr,
2219     dmu_buf_evict_func_t *evict_func)
2220 {
2221         return (dmu_buf_update_user(db_fake, NULL, user_ptr,
2222             user_data_ptr_ptr, evict_func));
2223 }
2224 
2225 void *
2226 dmu_buf_set_user_ie(dmu_buf_t *db_fake, void *user_ptr, void *user_data_ptr_ptr,
2227     dmu_buf_evict_func_t *evict_func)
2228 {
2229         dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
2230 
2231         db->db_immediate_evict = TRUE;
2232         return (dmu_buf_update_user(db_fake, NULL, user_ptr,
2233             user_data_ptr_ptr, evict_func));
2234 }
2235 
2236 void *
2237 dmu_buf_update_user(dmu_buf_t *db_fake, void *old_user_ptr, void *user_ptr,
2238     void *user_data_ptr_ptr, dmu_buf_evict_func_t *evict_func)
2239 {
2240         dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
2241         ASSERT(db->db_level == 0);
2242 
2243         ASSERT((user_ptr == NULL) == (evict_func == NULL));
2244 
2245         mutex_enter(&db->db_mtx);
2246 
2247         if (db->db_user_ptr == old_user_ptr) {
2248                 db->db_user_ptr = user_ptr;
2249                 db->db_user_data_ptr_ptr = user_data_ptr_ptr;
2250                 db->db_evict_func = evict_func;
2251 
2252                 dbuf_update_data(db);
2253         } else {
2254                 old_user_ptr = db->db_user_ptr;
2255         }
2256 
2257         mutex_exit(&db->db_mtx);
2258         return (old_user_ptr);
2259 }
2260 
2261 void *
2262 dmu_buf_get_user(dmu_buf_t *db_fake)
2263 {
2264         dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
2265         ASSERT(!refcount_is_zero(&db->db_holds));
2266 
2267         return (db->db_user_ptr);
2268 }
2269 
2270 boolean_t
2271 dmu_buf_freeable(dmu_buf_t *dbuf)
2272 {
2273         boolean_t res = B_FALSE;
2274         dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbuf;
2275 
2276         if (db->db_blkptr)
2277                 res = dsl_dataset_block_freeable(db->db_objset->os_dsl_dataset,
2278                     db->db_blkptr, db->db_blkptr->blk_birth);
2279 
2280         return (res);
2281 }
2282 
2283 blkptr_t *
2284 dmu_buf_get_blkptr(dmu_buf_t *db)
2285 {
2286         dmu_buf_impl_t *dbi = (dmu_buf_impl_t *)db;
2287         return (dbi->db_blkptr);
2288 }
2289 
2290 static void
2291 dbuf_check_blkptr(dnode_t *dn, dmu_buf_impl_t *db)
2292 {
2293         /* ASSERT(dmu_tx_is_syncing(tx) */
2294         ASSERT(MUTEX_HELD(&db->db_mtx));
2295 
2296         if (db->db_blkptr != NULL)
2297                 return;
2298 
2299         if (db->db_blkid == DMU_SPILL_BLKID) {
2300                 db->db_blkptr = &dn->dn_phys->dn_spill;
2301                 BP_ZERO(db->db_blkptr);
2302                 return;
2303         }
2304         if (db->db_level == dn->dn_phys->dn_nlevels-1) {
2305                 /*
2306                  * This buffer was allocated at a time when there was
2307                  * no available blkptrs from the dnode, or it was
2308                  * inappropriate to hook it in (i.e., nlevels mis-match).
2309                  */
2310                 ASSERT(db->db_blkid < dn->dn_phys->dn_nblkptr);
2311                 ASSERT(db->db_parent == NULL);
2312                 db->db_parent = dn->dn_dbuf;
2313                 db->db_blkptr = &dn->dn_phys->dn_blkptr[db->db_blkid];
2314                 DBUF_VERIFY(db);
2315         } else {
2316                 dmu_buf_impl_t *parent = db->db_parent;
2317                 int epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
2318 
2319                 ASSERT(dn->dn_phys->dn_nlevels > 1);
2320                 if (parent == NULL) {
2321                         mutex_exit(&db->db_mtx);
2322                         rw_enter(&dn->dn_struct_rwlock, RW_READER);
2323                         (void) dbuf_hold_impl(dn, db->db_level+1,
2324                             db->db_blkid >> epbs, FALSE, db, &parent);
2325                         rw_exit(&dn->dn_struct_rwlock);
2326                         mutex_enter(&db->db_mtx);
2327                         db->db_parent = parent;
2328                 }
2329                 db->db_blkptr = (blkptr_t *)parent->db.db_data +
2330                     (db->db_blkid & ((1ULL << epbs) - 1));
2331                 DBUF_VERIFY(db);
2332         }
2333 }
2334 
2335 static void
2336 dbuf_sync_indirect(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
2337 {
2338         dmu_buf_impl_t *db = dr->dr_dbuf;
2339         dnode_t *dn;
2340         zio_t *zio;
2341 
2342         ASSERT(dmu_tx_is_syncing(tx));
2343 
2344         dprintf_dbuf_bp(db, db->db_blkptr, "blkptr=%p", db->db_blkptr);
2345 
2346         mutex_enter(&db->db_mtx);
2347 
2348         ASSERT(db->db_level > 0);
2349         DBUF_VERIFY(db);
2350 
2351         /* Read the block if it hasn't been read yet. */
2352         if (db->db_buf == NULL) {
2353                 mutex_exit(&db->db_mtx);
2354                 (void) dbuf_read(db, NULL, DB_RF_MUST_SUCCEED);
2355                 mutex_enter(&db->db_mtx);
2356         }
2357         ASSERT3U(db->db_state, ==, DB_CACHED);
2358         ASSERT(db->db_buf != NULL);
2359 
2360         DB_DNODE_ENTER(db);
2361         dn = DB_DNODE(db);
2362         /* Indirect block size must match what the dnode thinks it is. */
2363         ASSERT3U(db->db.db_size, ==, 1<<dn->dn_phys->dn_indblkshift);
2364         dbuf_check_blkptr(dn, db);
2365         DB_DNODE_EXIT(db);
2366 
2367         /* Provide the pending dirty record to child dbufs */
2368         db->db_data_pending = dr;
2369 
2370         mutex_exit(&db->db_mtx);
2371         dbuf_write(dr, db->db_buf, tx);
2372 
2373         zio = dr->dr_zio;
2374         mutex_enter(&dr->dt.di.dr_mtx);
2375         dbuf_sync_list(&dr->dt.di.dr_children, tx);
2376         ASSERT(list_head(&dr->dt.di.dr_children) == NULL);
2377         mutex_exit(&dr->dt.di.dr_mtx);
2378         zio_nowait(zio);
2379 }
2380 
2381 static void
2382 dbuf_sync_leaf(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
2383 {
2384         arc_buf_t **datap = &dr->dt.dl.dr_data;
2385         dmu_buf_impl_t *db = dr->dr_dbuf;
2386         dnode_t *dn;
2387         objset_t *os;
2388         uint64_t txg = tx->tx_txg;
2389 
2390         ASSERT(dmu_tx_is_syncing(tx));
2391 
2392         dprintf_dbuf_bp(db, db->db_blkptr, "blkptr=%p", db->db_blkptr);
2393 
2394         mutex_enter(&db->db_mtx);
2395         /*
2396          * To be synced, we must be dirtied.  But we
2397          * might have been freed after the dirty.
2398          */
2399         if (db->db_state == DB_UNCACHED) {
2400                 /* This buffer has been freed since it was dirtied */
2401                 ASSERT(db->db.db_data == NULL);
2402         } else if (db->db_state == DB_FILL) {
2403                 /* This buffer was freed and is now being re-filled */
2404                 ASSERT(db->db.db_data != dr->dt.dl.dr_data);
2405         } else {
2406                 ASSERT(db->db_state == DB_CACHED || db->db_state == DB_NOFILL);
2407         }
2408         DBUF_VERIFY(db);
2409 
2410         DB_DNODE_ENTER(db);
2411         dn = DB_DNODE(db);
2412 
2413         if (db->db_blkid == DMU_SPILL_BLKID) {
2414                 mutex_enter(&dn->dn_mtx);
2415                 dn->dn_phys->dn_flags |= DNODE_FLAG_SPILL_BLKPTR;
2416                 mutex_exit(&dn->dn_mtx);
2417         }
2418 
2419         /*
2420          * If this is a bonus buffer, simply copy the bonus data into the
2421          * dnode.  It will be written out when the dnode is synced (and it
2422          * will be synced, since it must have been dirty for dbuf_sync to
2423          * be called).
2424          */
2425         if (db->db_blkid == DMU_BONUS_BLKID) {
2426                 dbuf_dirty_record_t **drp;
2427 
2428                 ASSERT(*datap != NULL);
2429                 ASSERT0(db->db_level);
2430                 ASSERT3U(dn->dn_phys->dn_bonuslen, <=, DN_MAX_BONUSLEN);
2431                 bcopy(*datap, DN_BONUS(dn->dn_phys), dn->dn_phys->dn_bonuslen);
2432                 DB_DNODE_EXIT(db);
2433 
2434                 if (*datap != db->db.db_data) {
2435                         zio_buf_free(*datap, DN_MAX_BONUSLEN);
2436                         arc_space_return(DN_MAX_BONUSLEN, ARC_SPACE_OTHER);
2437                 }
2438                 db->db_data_pending = NULL;
2439                 drp = &db->db_last_dirty;
2440                 while (*drp != dr)
2441                         drp = &(*drp)->dr_next;
2442                 ASSERT(dr->dr_next == NULL);
2443                 ASSERT(dr->dr_dbuf == db);
2444                 *drp = dr->dr_next;
2445                 kmem_free(dr, sizeof (dbuf_dirty_record_t));
2446                 ASSERT(db->db_dirtycnt > 0);
2447                 db->db_dirtycnt -= 1;
2448                 dbuf_rele_and_unlock(db, (void *)(uintptr_t)txg);
2449                 return;
2450         }
2451 
2452         os = dn->dn_objset;
2453 
2454         /*
2455          * This function may have dropped the db_mtx lock allowing a dmu_sync
2456          * operation to sneak in. As a result, we need to ensure that we
2457          * don't check the dr_override_state until we have returned from
2458          * dbuf_check_blkptr.
2459          */
2460         dbuf_check_blkptr(dn, db);
2461 
2462         /*
2463          * If this buffer is in the middle of an immediate write,
2464          * wait for the synchronous IO to complete.
2465          */
2466         while (dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC) {
2467                 ASSERT(dn->dn_object != DMU_META_DNODE_OBJECT);
2468                 cv_wait(&db->db_changed, &db->db_mtx);
2469                 ASSERT(dr->dt.dl.dr_override_state != DR_NOT_OVERRIDDEN);
2470         }
2471 
2472         if (db->db_state != DB_NOFILL &&
2473             dn->dn_object != DMU_META_DNODE_OBJECT &&
2474             refcount_count(&db->db_holds) > 1 &&
2475             dr->dt.dl.dr_override_state != DR_OVERRIDDEN &&
2476             *datap == db->db_buf) {
2477                 /*
2478                  * If this buffer is currently "in use" (i.e., there
2479                  * are active holds and db_data still references it),
2480                  * then make a copy before we start the write so that
2481                  * any modifications from the open txg will not leak
2482                  * into this write.
2483                  *
2484                  * NOTE: this copy does not need to be made for
2485                  * objects only modified in the syncing context (e.g.
2486                  * DNONE_DNODE blocks).
2487                  */
2488                 int blksz = arc_buf_size(*datap);
2489                 arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
2490                 *datap = arc_buf_alloc(os->os_spa, blksz, db, type);
2491                 bcopy(db->db.db_data, (*datap)->b_data, blksz);
2492         }
2493         db->db_data_pending = dr;
2494 
2495         mutex_exit(&db->db_mtx);
2496 
2497         dbuf_write(dr, *datap, tx);
2498 
2499         ASSERT(!list_link_active(&dr->dr_dirty_node));
2500         if (dn->dn_object == DMU_META_DNODE_OBJECT) {
2501                 list_insert_tail(&dn->dn_dirty_records[txg&TXG_MASK], dr);
2502                 DB_DNODE_EXIT(db);
2503         } else {
2504                 /*
2505                  * Although zio_nowait() does not "wait for an IO", it does
2506                  * initiate the IO. If this is an empty write it seems plausible
2507                  * that the IO could actually be completed before the nowait
2508                  * returns. We need to DB_DNODE_EXIT() first in case
2509                  * zio_nowait() invalidates the dbuf.
2510                  */
2511                 DB_DNODE_EXIT(db);
2512                 zio_nowait(dr->dr_zio);
2513         }
2514 }
2515 
2516 void
2517 dbuf_sync_list(list_t *list, dmu_tx_t *tx)
2518 {
2519         dbuf_dirty_record_t *dr;
2520 
2521         while (dr = list_head(list)) {
2522                 if (dr->dr_zio != NULL) {
2523                         /*
2524                          * If we find an already initialized zio then we
2525                          * are processing the meta-dnode, and we have finished.
2526                          * The dbufs for all dnodes are put back on the list
2527                          * during processing, so that we can zio_wait()
2528                          * these IOs after initiating all child IOs.
2529                          */
2530                         ASSERT3U(dr->dr_dbuf->db.db_object, ==,
2531                             DMU_META_DNODE_OBJECT);
2532                         break;
2533                 }
2534                 list_remove(list, dr);
2535                 if (dr->dr_dbuf->db_level > 0)
2536                         dbuf_sync_indirect(dr, tx);
2537                 else
2538                         dbuf_sync_leaf(dr, tx);
2539         }
2540 }
2541 
2542 /* ARGSUSED */
2543 static void
2544 dbuf_write_ready(zio_t *zio, arc_buf_t *buf, void *vdb)
2545 {
2546         dmu_buf_impl_t *db = vdb;
2547         dnode_t *dn;
2548         blkptr_t *bp = zio->io_bp;
2549         blkptr_t *bp_orig = &zio->io_bp_orig;
2550         spa_t *spa = zio->io_spa;
2551         int64_t delta;
2552         uint64_t fill = 0;
2553         int i;
2554 
2555         ASSERT3P(db->db_blkptr, ==, bp);
2556 
2557         DB_DNODE_ENTER(db);
2558         dn = DB_DNODE(db);
2559         delta = bp_get_dsize_sync(spa, bp) - bp_get_dsize_sync(spa, bp_orig);
2560         dnode_diduse_space(dn, delta - zio->io_prev_space_delta);
2561         zio->io_prev_space_delta = delta;
2562 
2563         if (bp->blk_birth != 0) {
2564                 ASSERT((db->db_blkid != DMU_SPILL_BLKID &&
2565                     BP_GET_TYPE(bp) == dn->dn_type) ||
2566                     (db->db_blkid == DMU_SPILL_BLKID &&
2567                     BP_GET_TYPE(bp) == dn->dn_bonustype) ||
2568                     BP_IS_EMBEDDED(bp));
2569                 ASSERT(BP_GET_LEVEL(bp) == db->db_level);
2570         }
2571 
2572         mutex_enter(&db->db_mtx);
2573 
2574 #ifdef ZFS_DEBUG
2575         if (db->db_blkid == DMU_SPILL_BLKID) {
2576                 ASSERT(dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR);
2577                 ASSERT(!(BP_IS_HOLE(db->db_blkptr)) &&
2578                     db->db_blkptr == &dn->dn_phys->dn_spill);
2579         }
2580 #endif
2581 
2582         if (db->db_level == 0) {
2583                 mutex_enter(&dn->dn_mtx);
2584                 if (db->db_blkid > dn->dn_phys->dn_maxblkid &&
2585                     db->db_blkid != DMU_SPILL_BLKID)
2586                         dn->dn_phys->dn_maxblkid = db->db_blkid;
2587                 mutex_exit(&dn->dn_mtx);
2588 
2589                 if (dn->dn_type == DMU_OT_DNODE) {
2590                         dnode_phys_t *dnp = db->db.db_data;
2591                         for (i = db->db.db_size >> DNODE_SHIFT; i > 0;
2592                             i--, dnp++) {
2593                                 if (dnp->dn_type != DMU_OT_NONE)
2594                                         fill++;
2595                         }
2596                 } else {
2597                         if (BP_IS_HOLE(bp)) {
2598                                 fill = 0;
2599                         } else {
2600                                 fill = 1;
2601                         }
2602                 }
2603         } else {
2604                 blkptr_t *ibp = db->db.db_data;
2605                 ASSERT3U(db->db.db_size, ==, 1<<dn->dn_phys->dn_indblkshift);
2606                 for (i = db->db.db_size >> SPA_BLKPTRSHIFT; i > 0; i--, ibp++) {
2607                         if (BP_IS_HOLE(ibp))
2608                                 continue;
2609                         fill += BP_GET_FILL(ibp);
2610                 }
2611         }
2612         DB_DNODE_EXIT(db);
2613 
2614         if (!BP_IS_EMBEDDED(bp))
2615                 bp->blk_fill = fill;
2616 
2617         mutex_exit(&db->db_mtx);
2618 }
2619 
2620 /*
2621  * The SPA will call this callback several times for each zio - once
2622  * for every physical child i/o (zio->io_phys_children times).  This
2623  * allows the DMU to monitor the progress of each logical i/o.  For example,
2624  * there may be 2 copies of an indirect block, or many fragments of a RAID-Z
2625  * block.  There may be a long delay before all copies/fragments are completed,
2626  * so this callback allows us to retire dirty space gradually, as the physical
2627  * i/os complete.
2628  */
2629 /* ARGSUSED */
2630 static void
2631 dbuf_write_physdone(zio_t *zio, arc_buf_t *buf, void *arg)
2632 {
2633         dmu_buf_impl_t *db = arg;
2634         objset_t *os = db->db_objset;
2635         dsl_pool_t *dp = dmu_objset_pool(os);
2636         dbuf_dirty_record_t *dr;
2637         int delta = 0;
2638 
2639         dr = db->db_data_pending;
2640         ASSERT3U(dr->dr_txg, ==, zio->io_txg);
2641 
2642         /*
2643          * The callback will be called io_phys_children times.  Retire one
2644          * portion of our dirty space each time we are called.  Any rounding
2645          * error will be cleaned up by dsl_pool_sync()'s call to
2646          * dsl_pool_undirty_space().
2647          */
2648         delta = dr->dr_accounted / zio->io_phys_children;
2649         dsl_pool_undirty_space(dp, delta, zio->io_txg);
2650 }
2651 
2652 /* ARGSUSED */
2653 static void
2654 dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
2655 {
2656         dmu_buf_impl_t *db = vdb;
2657         blkptr_t *bp_orig = &zio->io_bp_orig;
2658         blkptr_t *bp = db->db_blkptr;
2659         objset_t *os = db->db_objset;
2660         dmu_tx_t *tx = os->os_synctx;
2661         dbuf_dirty_record_t **drp, *dr;
2662 
2663         ASSERT0(zio->io_error);
2664         ASSERT(db->db_blkptr == bp);
2665 
2666         /*
2667          * For nopwrites and rewrites we ensure that the bp matches our
2668          * original and bypass all the accounting.
2669          */
2670         if (zio->io_flags & (ZIO_FLAG_IO_REWRITE | ZIO_FLAG_NOPWRITE)) {
2671                 ASSERT(BP_EQUAL(bp, bp_orig));
2672         } else {
2673                 dsl_dataset_t *ds = os->os_dsl_dataset;
2674                 (void) dsl_dataset_block_kill(ds, bp_orig, tx, B_TRUE);
2675                 dsl_dataset_block_born(ds, bp, tx);
2676         }
2677 
2678         mutex_enter(&db->db_mtx);
2679 
2680         DBUF_VERIFY(db);
2681 
2682         drp = &db->db_last_dirty;
2683         while ((dr = *drp) != db->db_data_pending)
2684                 drp = &dr->dr_next;
2685         ASSERT(!list_link_active(&dr->dr_dirty_node));
2686         ASSERT(dr->dr_dbuf == db);
2687         ASSERT(dr->dr_next == NULL);
2688         *drp = dr->dr_next;
2689 
2690 #ifdef ZFS_DEBUG
2691         if (db->db_blkid == DMU_SPILL_BLKID) {
2692                 dnode_t *dn;
2693 
2694                 DB_DNODE_ENTER(db);
2695                 dn = DB_DNODE(db);
2696                 ASSERT(dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR);
2697                 ASSERT(!(BP_IS_HOLE(db->db_blkptr)) &&
2698                     db->db_blkptr == &dn->dn_phys->dn_spill);
2699                 DB_DNODE_EXIT(db);
2700         }
2701 #endif
2702 
2703         if (db->db_level == 0) {
2704                 ASSERT(db->db_blkid != DMU_BONUS_BLKID);
2705                 ASSERT(dr->dt.dl.dr_override_state == DR_NOT_OVERRIDDEN);
2706                 if (db->db_state != DB_NOFILL) {
2707                         if (dr->dt.dl.dr_data != db->db_buf)
2708                                 VERIFY(arc_buf_remove_ref(dr->dt.dl.dr_data,
2709                                     db));
2710                         else if (!arc_released(db->db_buf))
2711                                 arc_set_callback(db->db_buf, dbuf_do_evict, db);
2712                 }
2713         } else {
2714                 dnode_t *dn;
2715 
2716                 DB_DNODE_ENTER(db);
2717                 dn = DB_DNODE(db);
2718                 ASSERT(list_head(&dr->dt.di.dr_children) == NULL);
2719                 ASSERT3U(db->db.db_size, ==, 1 << dn->dn_phys->dn_indblkshift);
2720                 if (!BP_IS_HOLE(db->db_blkptr)) {
2721                         int epbs =
2722                             dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
2723                         ASSERT3U(db->db_blkid, <=,
2724                             dn->dn_phys->dn_maxblkid >> (db->db_level * epbs));
2725                         ASSERT3U(BP_GET_LSIZE(db->db_blkptr), ==,
2726                             db->db.db_size);
2727                         if (!arc_released(db->db_buf))
2728                                 arc_set_callback(db->db_buf, dbuf_do_evict, db);
2729                 }
2730                 DB_DNODE_EXIT(db);
2731                 mutex_destroy(&dr->dt.di.dr_mtx);
2732                 list_destroy(&dr->dt.di.dr_children);
2733         }
2734         kmem_free(dr, sizeof (dbuf_dirty_record_t));
2735 
2736         cv_broadcast(&db->db_changed);
2737         ASSERT(db->db_dirtycnt > 0);
2738         db->db_dirtycnt -= 1;
2739         db->db_data_pending = NULL;
2740         dbuf_rele_and_unlock(db, (void *)(uintptr_t)tx->tx_txg);
2741 }
2742 
2743 static void
2744 dbuf_write_nofill_ready(zio_t *zio)
2745 {
2746         dbuf_write_ready(zio, NULL, zio->io_private);
2747 }
2748 
2749 static void
2750 dbuf_write_nofill_done(zio_t *zio)
2751 {
2752         dbuf_write_done(zio, NULL, zio->io_private);
2753 }
2754 
2755 static void
2756 dbuf_write_override_ready(zio_t *zio)
2757 {
2758         dbuf_dirty_record_t *dr = zio->io_private;
2759         dmu_buf_impl_t *db = dr->dr_dbuf;
2760 
2761         dbuf_write_ready(zio, NULL, db);
2762 }
2763 
2764 static void
2765 dbuf_write_override_done(zio_t *zio)
2766 {
2767         dbuf_dirty_record_t *dr = zio->io_private;
2768         dmu_buf_impl_t *db = dr->dr_dbuf;
2769         blkptr_t *obp = &dr->dt.dl.dr_overridden_by;
2770 
2771         mutex_enter(&db->db_mtx);
2772         if (!BP_EQUAL(zio->io_bp, obp)) {
2773                 if (!BP_IS_HOLE(obp))
2774                         dsl_free(spa_get_dsl(zio->io_spa), zio->io_txg, obp);
2775                 arc_release(dr->dt.dl.dr_data, db);
2776         }
2777         mutex_exit(&db->db_mtx);
2778 
2779         dbuf_write_done(zio, NULL, db);
2780 }
2781 
2782 /* Issue I/O to commit a dirty buffer to disk. */
2783 static void
2784 dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx)
2785 {
2786         dmu_buf_impl_t *db = dr->dr_dbuf;
2787         dnode_t *dn;
2788         objset_t *os;
2789         dmu_buf_impl_t *parent = db->db_parent;
2790         uint64_t txg = tx->tx_txg;
2791         zbookmark_phys_t zb;
2792         zio_prop_t zp;
2793         zio_t *zio;
2794         int wp_flag = 0;
2795 
2796         DB_DNODE_ENTER(db);
2797         dn = DB_DNODE(db);
2798         os = dn->dn_objset;
2799 
2800         if (db->db_state != DB_NOFILL) {
2801                 if (db->db_level > 0 || dn->dn_type == DMU_OT_DNODE) {
2802                         /*
2803                          * Private object buffers are released here rather
2804                          * than in dbuf_dirty() since they are only modified
2805                          * in the syncing context and we don't want the
2806                          * overhead of making multiple copies of the data.
2807                          */
2808                         if (BP_IS_HOLE(db->db_blkptr)) {
2809                                 arc_buf_thaw(data);
2810                         } else {
2811                                 dbuf_release_bp(db);
2812                         }
2813                 }
2814         }
2815 
2816         if (parent != dn->dn_dbuf) {
2817                 /* Our parent is an indirect block. */
2818                 /* We have a dirty parent that has been scheduled for write. */
2819                 ASSERT(parent && parent->db_data_pending);
2820                 /* Our parent's buffer is one level closer to the dnode. */
2821                 ASSERT(db->db_level == parent->db_level-1);
2822                 /*
2823                  * We're about to modify our parent's db_data by modifying
2824                  * our block pointer, so the parent must be released.
2825                  */
2826                 ASSERT(arc_released(parent->db_buf));
2827                 zio = parent->db_data_pending->dr_zio;
2828         } else {
2829                 /* Our parent is the dnode itself. */
2830                 ASSERT((db->db_level == dn->dn_phys->dn_nlevels-1 &&
2831                     db->db_blkid != DMU_SPILL_BLKID) ||
2832                     (db->db_blkid == DMU_SPILL_BLKID && db->db_level == 0));
2833                 if (db->db_blkid != DMU_SPILL_BLKID)
2834                         ASSERT3P(db->db_blkptr, ==,
2835                             &dn->dn_phys->dn_blkptr[db->db_blkid]);
2836                 zio = dn->dn_zio;
2837         }
2838 
2839         ASSERT(db->db_level == 0 || data == db->db_buf);
2840         ASSERT3U(db->db_blkptr->blk_birth, <=, txg);
2841         ASSERT(zio);
2842 
2843         SET_BOOKMARK(&zb, os->os_dsl_dataset ?
2844             os->os_dsl_dataset->ds_object : DMU_META_OBJSET,
2845             db->db.db_object, db->db_level, db->db_blkid);
2846 
2847         if (db->db_blkid == DMU_SPILL_BLKID)
2848                 wp_flag = WP_SPILL;
2849         wp_flag |= (db->db_state == DB_NOFILL) ? WP_NOFILL : 0;
2850         WP_SET_SPECIALCLASS(wp_flag, dr->dr_usesc);
2851 
2852         dmu_write_policy(os, dn, db->db_level, wp_flag, &zp);
2853         DB_DNODE_EXIT(db);
2854 
2855         if (db->db_level == 0 &&
2856             dr->dt.dl.dr_override_state == DR_OVERRIDDEN) {
2857                 /*
2858                  * The BP for this block has been provided by open context
2859                  * (by dmu_sync() or dmu_buf_write_embedded()).
2860                  */
2861                 void *contents = (data != NULL) ? data->b_data : NULL;
2862 
2863                 dr->dr_zio = zio_write(zio, os->os_spa, txg,
2864                     db->db_blkptr, contents, db->db.db_size, &zp,
2865                     dbuf_write_override_ready, NULL, dbuf_write_override_done,
2866                     dr, ZIO_PRIORITY_ASYNC_WRITE, ZIO_FLAG_MUSTSUCCEED, &zb);
2867                 mutex_enter(&db->db_mtx);
2868                 dr->dt.dl.dr_override_state = DR_NOT_OVERRIDDEN;
2869                 zio_write_override(dr->dr_zio, &dr->dt.dl.dr_overridden_by,
2870                     dr->dt.dl.dr_copies, dr->dt.dl.dr_nopwrite);
2871                 mutex_exit(&db->db_mtx);
2872         } else if (db->db_state == DB_NOFILL) {
2873                 ASSERT(zp.zp_checksum == ZIO_CHECKSUM_OFF ||
2874                     zp.zp_checksum == ZIO_CHECKSUM_NOPARITY);
2875                 dr->dr_zio = zio_write(zio, os->os_spa, txg,
2876                     db->db_blkptr, NULL, db->db.db_size, &zp,
2877                     dbuf_write_nofill_ready, NULL, dbuf_write_nofill_done, db,
2878                     ZIO_PRIORITY_ASYNC_WRITE,
2879                     ZIO_FLAG_MUSTSUCCEED | ZIO_FLAG_NODATA, &zb);
2880         } else {
2881                 ASSERT(arc_released(data));
2882                 dr->dr_zio = arc_write(zio, os->os_spa, txg,
2883                     db->db_blkptr, data, DBUF_IS_L2CACHEABLE(db),
2884                     DBUF_IS_L2COMPRESSIBLE(db), &zp, dbuf_write_ready,
2885                     dbuf_write_physdone, dbuf_write_done, db,
2886                     ZIO_PRIORITY_ASYNC_WRITE, ZIO_FLAG_MUSTSUCCEED, &zb);
2887         }
2888 }