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dnode.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <sys/zfs_context.h>
#include <sys/dbuf.h>
#include <sys/dnode.h>
#include <sys/dmu.h>
#include <sys/dmu_impl.h>
#include <sys/dmu_tx.h>
#include <sys/dmu_objset.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_dataset.h>
#include <sys/spa.h>
#include <sys/zio.h>
#include <sys/dmu_zfetch.h>

static int free_range_compar(const void *node1, const void *node2);

static kmem_cache_t *dnode_cache;

static dnode_phys_t dnode_phys_zero;

int zfs_default_bs = SPA_MINBLOCKSHIFT;
int zfs_default_ibs = DN_MAX_INDBLKSHIFT;

/* ARGSUSED */
static int
dnode_cons(void *arg, void *unused, int kmflag)
{
      int i;
      dnode_t *dn = arg;
      bzero(dn, sizeof (dnode_t));

      rw_init(&dn->dn_struct_rwlock, NULL, RW_DEFAULT, NULL);
      mutex_init(&dn->dn_mtx, NULL, MUTEX_DEFAULT, NULL);
      mutex_init(&dn->dn_dbufs_mtx, NULL, MUTEX_DEFAULT, NULL);
      cv_init(&dn->dn_notxholds, NULL, CV_DEFAULT, NULL);

      refcount_create(&dn->dn_holds);
      refcount_create(&dn->dn_tx_holds);

      for (i = 0; i < TXG_SIZE; i++) {
            avl_create(&dn->dn_ranges[i], free_range_compar,
                sizeof (free_range_t),
                offsetof(struct free_range, fr_node));
            list_create(&dn->dn_dirty_records[i],
                sizeof (dbuf_dirty_record_t),
                offsetof(dbuf_dirty_record_t, dr_dirty_node));
      }

      list_create(&dn->dn_dbufs, sizeof (dmu_buf_impl_t),
          offsetof(dmu_buf_impl_t, db_link));

      return (0);
}

/* ARGSUSED */
static void
dnode_dest(void *arg, void *unused)
{
      int i;
      dnode_t *dn = arg;

      rw_destroy(&dn->dn_struct_rwlock);
      mutex_destroy(&dn->dn_mtx);
      mutex_destroy(&dn->dn_dbufs_mtx);
      cv_destroy(&dn->dn_notxholds);
      refcount_destroy(&dn->dn_holds);
      refcount_destroy(&dn->dn_tx_holds);

      for (i = 0; i < TXG_SIZE; i++) {
            avl_destroy(&dn->dn_ranges[i]);
            list_destroy(&dn->dn_dirty_records[i]);
      }

      list_destroy(&dn->dn_dbufs);
}

void
dnode_init(void)
{
      dnode_cache = kmem_cache_create("dnode_t",
          sizeof (dnode_t),
          0, dnode_cons, dnode_dest, NULL, NULL, NULL, 0);
}

void
dnode_fini(void)
{
      kmem_cache_destroy(dnode_cache);
}


#ifdef ZFS_DEBUG
void
dnode_verify(dnode_t *dn)
{
      int drop_struct_lock = FALSE;

      ASSERT(dn->dn_phys);
      ASSERT(dn->dn_objset);

      ASSERT(dn->dn_phys->dn_type < DMU_OT_NUMTYPES);

      if (!(zfs_flags & ZFS_DEBUG_DNODE_VERIFY))
            return;

      if (!RW_WRITE_HELD(&dn->dn_struct_rwlock)) {
            rw_enter(&dn->dn_struct_rwlock, RW_READER);
            drop_struct_lock = TRUE;
      }
      if (dn->dn_phys->dn_type != DMU_OT_NONE || dn->dn_allocated_txg != 0) {
            int i;
            ASSERT3U(dn->dn_indblkshift, >=, 0);
            ASSERT3U(dn->dn_indblkshift, <=, SPA_MAXBLOCKSHIFT);
            if (dn->dn_datablkshift) {
                  ASSERT3U(dn->dn_datablkshift, >=, SPA_MINBLOCKSHIFT);
                  ASSERT3U(dn->dn_datablkshift, <=, SPA_MAXBLOCKSHIFT);
                  ASSERT3U(1<<dn->dn_datablkshift, ==, dn->dn_datablksz);
            }
            ASSERT3U(dn->dn_nlevels, <=, 30);
            ASSERT3U(dn->dn_type, <=, DMU_OT_NUMTYPES);
            ASSERT3U(dn->dn_nblkptr, >=, 1);
            ASSERT3U(dn->dn_nblkptr, <=, DN_MAX_NBLKPTR);
            ASSERT3U(dn->dn_bonuslen, <=, DN_MAX_BONUSLEN);
            ASSERT3U(dn->dn_datablksz, ==,
                dn->dn_datablkszsec << SPA_MINBLOCKSHIFT);
            ASSERT3U(ISP2(dn->dn_datablksz), ==, dn->dn_datablkshift != 0);
            ASSERT3U((dn->dn_nblkptr - 1) * sizeof (blkptr_t) +
                dn->dn_bonuslen, <=, DN_MAX_BONUSLEN);
            for (i = 0; i < TXG_SIZE; i++) {
                  ASSERT3U(dn->dn_next_nlevels[i], <=, dn->dn_nlevels);
            }
      }
      if (dn->dn_phys->dn_type != DMU_OT_NONE)
            ASSERT3U(dn->dn_phys->dn_nlevels, <=, dn->dn_nlevels);
      ASSERT(dn->dn_object == DMU_META_DNODE_OBJECT || dn->dn_dbuf != NULL);
      if (dn->dn_dbuf != NULL) {
            ASSERT3P(dn->dn_phys, ==,
                (dnode_phys_t *)dn->dn_dbuf->db.db_data +
                (dn->dn_object % (dn->dn_dbuf->db.db_size >> DNODE_SHIFT)));
      }
      if (drop_struct_lock)
            rw_exit(&dn->dn_struct_rwlock);
}
#endif

void
dnode_byteswap(dnode_phys_t *dnp)
{
      uint64_t *buf64 = (void*)&dnp->dn_blkptr;
      int i;

      if (dnp->dn_type == DMU_OT_NONE) {
            bzero(dnp, sizeof (dnode_phys_t));
            return;
      }

      dnp->dn_datablkszsec = BSWAP_16(dnp->dn_datablkszsec);
      dnp->dn_bonuslen = BSWAP_16(dnp->dn_bonuslen);
      dnp->dn_maxblkid = BSWAP_64(dnp->dn_maxblkid);
      dnp->dn_used = BSWAP_64(dnp->dn_used);

      /*
       * dn_nblkptr is only one byte, so it's OK to read it in either
       * byte order.  We can't read dn_bouslen.
       */
      ASSERT(dnp->dn_indblkshift <= SPA_MAXBLOCKSHIFT);
      ASSERT(dnp->dn_nblkptr <= DN_MAX_NBLKPTR);
      for (i = 0; i < dnp->dn_nblkptr * sizeof (blkptr_t)/8; i++)
            buf64[i] = BSWAP_64(buf64[i]);

      /*
       * OK to check dn_bonuslen for zero, because it won't matter if
       * we have the wrong byte order.  This is necessary because the
       * dnode dnode is smaller than a regular dnode.
       */
      if (dnp->dn_bonuslen != 0) {
            /*
             * Note that the bonus length calculated here may be
             * longer than the actual bonus buffer.  This is because
             * we always put the bonus buffer after the last block
             * pointer (instead of packing it against the end of the
             * dnode buffer).
             */
            int off = (dnp->dn_nblkptr-1) * sizeof (blkptr_t);
            size_t len = DN_MAX_BONUSLEN - off;
            ASSERT3U(dnp->dn_bonustype, <, DMU_OT_NUMTYPES);
            dmu_ot[dnp->dn_bonustype].ot_byteswap(dnp->dn_bonus + off, len);
      }
}

void
dnode_buf_byteswap(void *vbuf, size_t size)
{
      dnode_phys_t *buf = vbuf;
      int i;

      ASSERT3U(sizeof (dnode_phys_t), ==, (1<<DNODE_SHIFT));
      ASSERT((size & (sizeof (dnode_phys_t)-1)) == 0);

      size >>= DNODE_SHIFT;
      for (i = 0; i < size; i++) {
            dnode_byteswap(buf);
            buf++;
      }
}

static int
free_range_compar(const void *node1, const void *node2)
{
      const free_range_t *rp1 = node1;
      const free_range_t *rp2 = node2;

      if (rp1->fr_blkid < rp2->fr_blkid)
            return (-1);
      else if (rp1->fr_blkid > rp2->fr_blkid)
            return (1);
      else return (0);
}

void
dnode_setbonuslen(dnode_t *dn, int newsize, dmu_tx_t *tx)
{
      ASSERT3U(refcount_count(&dn->dn_holds), >=, 1);

      dnode_setdirty(dn, tx);
      rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
      ASSERT3U(newsize, <=, DN_MAX_BONUSLEN -
          (dn->dn_nblkptr-1) * sizeof (blkptr_t));
      dn->dn_bonuslen = newsize;
      if (newsize == 0)
            dn->dn_next_bonuslen[tx->tx_txg & TXG_MASK] = DN_ZERO_BONUSLEN;
      else
            dn->dn_next_bonuslen[tx->tx_txg & TXG_MASK] = dn->dn_bonuslen;
      rw_exit(&dn->dn_struct_rwlock);
}

static void
dnode_setdblksz(dnode_t *dn, int size)
{
      ASSERT3U(P2PHASE(size, SPA_MINBLOCKSIZE), ==, 0);
      ASSERT3U(size, <=, SPA_MAXBLOCKSIZE);
      ASSERT3U(size, >=, SPA_MINBLOCKSIZE);
      ASSERT3U(size >> SPA_MINBLOCKSHIFT, <,
          1<<(sizeof (dn->dn_phys->dn_datablkszsec) * 8));
      dn->dn_datablksz = size;
      dn->dn_datablkszsec = size >> SPA_MINBLOCKSHIFT;
      dn->dn_datablkshift = ISP2(size) ? highbit(size - 1) : 0;
}

static dnode_t *
dnode_create(objset_impl_t *os, dnode_phys_t *dnp, dmu_buf_impl_t *db,
    uint64_t object)
{
      dnode_t *dn = kmem_cache_alloc(dnode_cache, KM_SLEEP);

      dn->dn_objset = os;
      dn->dn_object = object;
      dn->dn_dbuf = db;
      dn->dn_phys = dnp;

      if (dnp->dn_datablkszsec)
            dnode_setdblksz(dn, dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT);
      dn->dn_indblkshift = dnp->dn_indblkshift;
      dn->dn_nlevels = dnp->dn_nlevels;
      dn->dn_type = dnp->dn_type;
      dn->dn_nblkptr = dnp->dn_nblkptr;
      dn->dn_checksum = dnp->dn_checksum;
      dn->dn_compress = dnp->dn_compress;
      dn->dn_bonustype = dnp->dn_bonustype;
      dn->dn_bonuslen = dnp->dn_bonuslen;
      dn->dn_maxblkid = dnp->dn_maxblkid;

      dmu_zfetch_init(&dn->dn_zfetch, dn);

      ASSERT(dn->dn_phys->dn_type < DMU_OT_NUMTYPES);
      mutex_enter(&os->os_lock);
      list_insert_head(&os->os_dnodes, dn);
      mutex_exit(&os->os_lock);

      arc_space_consume(sizeof (dnode_t), ARC_SPACE_OTHER);
      return (dn);
}

static void
dnode_destroy(dnode_t *dn)
{
      objset_impl_t *os = dn->dn_objset;

#ifdef ZFS_DEBUG
      int i;

      for (i = 0; i < TXG_SIZE; i++) {
            ASSERT(!list_link_active(&dn->dn_dirty_link[i]));
            ASSERT(NULL == list_head(&dn->dn_dirty_records[i]));
            ASSERT(0 == avl_numnodes(&dn->dn_ranges[i]));
      }
      ASSERT(NULL == list_head(&dn->dn_dbufs));
#endif

      mutex_enter(&os->os_lock);
      list_remove(&os->os_dnodes, dn);
      mutex_exit(&os->os_lock);

      if (dn->dn_dirtyctx_firstset) {
            kmem_free(dn->dn_dirtyctx_firstset, 1);
            dn->dn_dirtyctx_firstset = NULL;
      }
      dmu_zfetch_rele(&dn->dn_zfetch);
      if (dn->dn_bonus) {
            mutex_enter(&dn->dn_bonus->db_mtx);
            dbuf_evict(dn->dn_bonus);
            dn->dn_bonus = NULL;
      }
      kmem_cache_free(dnode_cache, dn);
      arc_space_return(sizeof (dnode_t), ARC_SPACE_OTHER);
}

void
dnode_allocate(dnode_t *dn, dmu_object_type_t ot, int blocksize, int ibs,
    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
{
      int i;

      if (blocksize == 0)
            blocksize = 1 << zfs_default_bs;
      else if (blocksize > SPA_MAXBLOCKSIZE)
            blocksize = SPA_MAXBLOCKSIZE;
      else
            blocksize = P2ROUNDUP(blocksize, SPA_MINBLOCKSIZE);

      if (ibs == 0)
            ibs = zfs_default_ibs;

      ibs = MIN(MAX(ibs, DN_MIN_INDBLKSHIFT), DN_MAX_INDBLKSHIFT);

      dprintf("os=%p obj=%llu txg=%llu blocksize=%d ibs=%d\n", dn->dn_objset,
          dn->dn_object, tx->tx_txg, blocksize, ibs);

      ASSERT(dn->dn_type == DMU_OT_NONE);
      ASSERT(bcmp(dn->dn_phys, &dnode_phys_zero, sizeof (dnode_phys_t)) == 0);
      ASSERT(dn->dn_phys->dn_type == DMU_OT_NONE);
      ASSERT(ot != DMU_OT_NONE);
      ASSERT3U(ot, <, DMU_OT_NUMTYPES);
      ASSERT((bonustype == DMU_OT_NONE && bonuslen == 0) ||
          (bonustype != DMU_OT_NONE && bonuslen != 0));
      ASSERT3U(bonustype, <, DMU_OT_NUMTYPES);
      ASSERT3U(bonuslen, <=, DN_MAX_BONUSLEN);
      ASSERT(dn->dn_type == DMU_OT_NONE);
      ASSERT3U(dn->dn_maxblkid, ==, 0);
      ASSERT3U(dn->dn_allocated_txg, ==, 0);
      ASSERT3U(dn->dn_assigned_txg, ==, 0);
      ASSERT(refcount_is_zero(&dn->dn_tx_holds));
      ASSERT3U(refcount_count(&dn->dn_holds), <=, 1);
      ASSERT3P(list_head(&dn->dn_dbufs), ==, NULL);

      for (i = 0; i < TXG_SIZE; i++) {
            ASSERT3U(dn->dn_next_nlevels[i], ==, 0);
            ASSERT3U(dn->dn_next_indblkshift[i], ==, 0);
            ASSERT3U(dn->dn_next_bonuslen[i], ==, 0);
            ASSERT3U(dn->dn_next_blksz[i], ==, 0);
            ASSERT(!list_link_active(&dn->dn_dirty_link[i]));
            ASSERT3P(list_head(&dn->dn_dirty_records[i]), ==, NULL);
            ASSERT3U(avl_numnodes(&dn->dn_ranges[i]), ==, 0);
      }

      dn->dn_type = ot;
      dnode_setdblksz(dn, blocksize);
      dn->dn_indblkshift = ibs;
      dn->dn_nlevels = 1;
      dn->dn_nblkptr = 1 + ((DN_MAX_BONUSLEN - bonuslen) >> SPA_BLKPTRSHIFT);
      dn->dn_bonustype = bonustype;
      dn->dn_bonuslen = bonuslen;
      dn->dn_checksum = ZIO_CHECKSUM_INHERIT;
      dn->dn_compress = ZIO_COMPRESS_INHERIT;
      dn->dn_dirtyctx = 0;

      dn->dn_free_txg = 0;
      if (dn->dn_dirtyctx_firstset) {
            kmem_free(dn->dn_dirtyctx_firstset, 1);
            dn->dn_dirtyctx_firstset = NULL;
      }

      dn->dn_allocated_txg = tx->tx_txg;

      dnode_setdirty(dn, tx);
      dn->dn_next_indblkshift[tx->tx_txg & TXG_MASK] = ibs;
      dn->dn_next_bonuslen[tx->tx_txg & TXG_MASK] = dn->dn_bonuslen;
      dn->dn_next_blksz[tx->tx_txg & TXG_MASK] = dn->dn_datablksz;
}

void
dnode_reallocate(dnode_t *dn, dmu_object_type_t ot, int blocksize,
    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
{
      int nblkptr;

      ASSERT3U(blocksize, >=, SPA_MINBLOCKSIZE);
      ASSERT3U(blocksize, <=, SPA_MAXBLOCKSIZE);
      ASSERT3U(blocksize % SPA_MINBLOCKSIZE, ==, 0);
      ASSERT(dn->dn_object != DMU_META_DNODE_OBJECT || dmu_tx_private_ok(tx));
      ASSERT(tx->tx_txg != 0);
      ASSERT((bonustype == DMU_OT_NONE && bonuslen == 0) ||
          (bonustype != DMU_OT_NONE && bonuslen != 0));
      ASSERT3U(bonustype, <, DMU_OT_NUMTYPES);
      ASSERT3U(bonuslen, <=, DN_MAX_BONUSLEN);

      /* clean up any unreferenced dbufs */
      dnode_evict_dbufs(dn);

      rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
      dnode_setdirty(dn, tx);
      if (dn->dn_datablksz != blocksize) {
            /* change blocksize */
            ASSERT(dn->dn_maxblkid == 0 &&
                (BP_IS_HOLE(&dn->dn_phys->dn_blkptr[0]) ||
                dnode_block_freed(dn, 0)));
            dnode_setdblksz(dn, blocksize);
            dn->dn_next_blksz[tx->tx_txg&TXG_MASK] = blocksize;
      }
      if (dn->dn_bonuslen != bonuslen)
            dn->dn_next_bonuslen[tx->tx_txg&TXG_MASK] = bonuslen;
      nblkptr = 1 + ((DN_MAX_BONUSLEN - bonuslen) >> SPA_BLKPTRSHIFT);
      if (dn->dn_nblkptr != nblkptr)
            dn->dn_next_nblkptr[tx->tx_txg&TXG_MASK] = nblkptr;
      rw_exit(&dn->dn_struct_rwlock);

      /* change type */
      dn->dn_type = ot;

      /* change bonus size and type */
      mutex_enter(&dn->dn_mtx);
      dn->dn_bonustype = bonustype;
      dn->dn_bonuslen = bonuslen;
      dn->dn_nblkptr = nblkptr;
      dn->dn_checksum = ZIO_CHECKSUM_INHERIT;
      dn->dn_compress = ZIO_COMPRESS_INHERIT;
      ASSERT3U(dn->dn_nblkptr, <=, DN_MAX_NBLKPTR);

      /* fix up the bonus db_size */
      if (dn->dn_bonus) {
            dn->dn_bonus->db.db_size =
                DN_MAX_BONUSLEN - (dn->dn_nblkptr-1) * sizeof (blkptr_t);
            ASSERT(dn->dn_bonuslen <= dn->dn_bonus->db.db_size);
      }

      dn->dn_allocated_txg = tx->tx_txg;
      mutex_exit(&dn->dn_mtx);
}

void
dnode_special_close(dnode_t *dn)
{
      /*
       * Wait for final references to the dnode to clear.  This can
       * only happen if the arc is asyncronously evicting state that
       * has a hold on this dnode while we are trying to evict this
       * dnode.
       */
      while (refcount_count(&dn->dn_holds) > 0)
            delay(1);
      dnode_destroy(dn);
}

dnode_t *
dnode_special_open(objset_impl_t *os, dnode_phys_t *dnp, uint64_t object)
{
      dnode_t *dn = dnode_create(os, dnp, NULL, object);
      DNODE_VERIFY(dn);
      return (dn);
}

static void
dnode_buf_pageout(dmu_buf_t *db, void *arg)
{
      dnode_t **children_dnodes = arg;
      int i;
      int epb = db->db_size >> DNODE_SHIFT;

      for (i = 0; i < epb; i++) {
            dnode_t *dn = children_dnodes[i];
            int n;

            if (dn == NULL)
                  continue;
#ifdef ZFS_DEBUG
            /*
             * If there are holds on this dnode, then there should
             * be holds on the dnode's containing dbuf as well; thus
             * it wouldn't be eligable for eviction and this function
             * would not have been called.
             */
            ASSERT(refcount_is_zero(&dn->dn_holds));
            ASSERT(list_head(&dn->dn_dbufs) == NULL);
            ASSERT(refcount_is_zero(&dn->dn_tx_holds));

            for (n = 0; n < TXG_SIZE; n++)
                  ASSERT(!list_link_active(&dn->dn_dirty_link[n]));
#endif
            children_dnodes[i] = NULL;
            dnode_destroy(dn);
      }
      kmem_free(children_dnodes, epb * sizeof (dnode_t *));
}

/*
 * errors:
 * EINVAL - invalid object number.
 * EIO - i/o error.
 * succeeds even for free dnodes.
 */
int
dnode_hold_impl(objset_impl_t *os, uint64_t object, int flag,
    void *tag, dnode_t **dnp)
{
      int epb, idx, err;
      int drop_struct_lock = FALSE;
      int type;
      uint64_t blk;
      dnode_t *mdn, *dn;
      dmu_buf_impl_t *db;
      dnode_t **children_dnodes;

      /*
       * If you are holding the spa config lock as writer, you shouldn't
       * be asking the DMU to do *anything*.
       */
      ASSERT(spa_config_held(os->os_spa, SCL_ALL, RW_WRITER) == 0);

      if (object == 0 || object >= DN_MAX_OBJECT)
            return (EINVAL);

      mdn = os->os_meta_dnode;

      DNODE_VERIFY(mdn);

      if (!RW_WRITE_HELD(&mdn->dn_struct_rwlock)) {
            rw_enter(&mdn->dn_struct_rwlock, RW_READER);
            drop_struct_lock = TRUE;
      }

      blk = dbuf_whichblock(mdn, object * sizeof (dnode_phys_t));

      db = dbuf_hold(mdn, blk, FTAG);
      if (drop_struct_lock)
            rw_exit(&mdn->dn_struct_rwlock);
      if (db == NULL)
            return (EIO);
      err = dbuf_read(db, NULL, DB_RF_CANFAIL);
      if (err) {
            dbuf_rele(db, FTAG);
            return (err);
      }

      ASSERT3U(db->db.db_size, >=, 1<<DNODE_SHIFT);
      epb = db->db.db_size >> DNODE_SHIFT;

      idx = object & (epb-1);

      children_dnodes = dmu_buf_get_user(&db->db);
      if (children_dnodes == NULL) {
            dnode_t **winner;
            children_dnodes = kmem_zalloc(epb * sizeof (dnode_t *),
                KM_SLEEP);
            if (winner = dmu_buf_set_user(&db->db, children_dnodes, NULL,
                dnode_buf_pageout)) {
                  kmem_free(children_dnodes, epb * sizeof (dnode_t *));
                  children_dnodes = winner;
            }
      }

      if ((dn = children_dnodes[idx]) == NULL) {
            dnode_phys_t *dnp = (dnode_phys_t *)db->db.db_data+idx;
            dnode_t *winner;

            dn = dnode_create(os, dnp, db, object);
            winner = atomic_cas_ptr(&children_dnodes[idx], NULL, dn);
            if (winner != NULL) {
                  dnode_destroy(dn);
                  dn = winner;
            }
      }

      mutex_enter(&dn->dn_mtx);
      type = dn->dn_type;
      if (dn->dn_free_txg ||
          ((flag & DNODE_MUST_BE_ALLOCATED) && type == DMU_OT_NONE) ||
          ((flag & DNODE_MUST_BE_FREE) && type != DMU_OT_NONE)) {
            mutex_exit(&dn->dn_mtx);
            dbuf_rele(db, FTAG);
            return (type == DMU_OT_NONE ? ENOENT : EEXIST);
      }
      mutex_exit(&dn->dn_mtx);

      if (refcount_add(&dn->dn_holds, tag) == 1)
            dbuf_add_ref(db, dn);

      DNODE_VERIFY(dn);
      ASSERT3P(dn->dn_dbuf, ==, db);
      ASSERT3U(dn->dn_object, ==, object);
      dbuf_rele(db, FTAG);

      *dnp = dn;
      return (0);
}

/*
 * Return held dnode if the object is allocated, NULL if not.
 */
int
dnode_hold(objset_impl_t *os, uint64_t object, void *tag, dnode_t **dnp)
{
      return (dnode_hold_impl(os, object, DNODE_MUST_BE_ALLOCATED, tag, dnp));
}

/*
 * Can only add a reference if there is already at least one
 * reference on the dnode.  Returns FALSE if unable to add a
 * new reference.
 */
boolean_t
dnode_add_ref(dnode_t *dn, void *tag)
{
      mutex_enter(&dn->dn_mtx);
      if (refcount_is_zero(&dn->dn_holds)) {
            mutex_exit(&dn->dn_mtx);
            return (FALSE);
      }
      VERIFY(1 < refcount_add(&dn->dn_holds, tag));
      mutex_exit(&dn->dn_mtx);
      return (TRUE);
}

void
dnode_rele(dnode_t *dn, void *tag)
{
      uint64_t refs;

      mutex_enter(&dn->dn_mtx);
      refs = refcount_remove(&dn->dn_holds, tag);
      mutex_exit(&dn->dn_mtx);
      /* NOTE: the DNODE_DNODE does not have a dn_dbuf */
      if (refs == 0 && dn->dn_dbuf)
            dbuf_rele(dn->dn_dbuf, dn);
}

void
dnode_setdirty(dnode_t *dn, dmu_tx_t *tx)
{
      objset_impl_t *os = dn->dn_objset;
      uint64_t txg = tx->tx_txg;

      if (dn->dn_object == DMU_META_DNODE_OBJECT)
            return;

      DNODE_VERIFY(dn);

#ifdef ZFS_DEBUG
      mutex_enter(&dn->dn_mtx);
      ASSERT(dn->dn_phys->dn_type || dn->dn_allocated_txg);
      /* ASSERT(dn->dn_free_txg == 0 || dn->dn_free_txg >= txg); */
      mutex_exit(&dn->dn_mtx);
#endif

      mutex_enter(&os->os_lock);

      /*
       * If we are already marked dirty, we're done.
       */
      if (list_link_active(&dn->dn_dirty_link[txg & TXG_MASK])) {
            mutex_exit(&os->os_lock);
            return;
      }

      ASSERT(!refcount_is_zero(&dn->dn_holds) || list_head(&dn->dn_dbufs));
      ASSERT(dn->dn_datablksz != 0);
      ASSERT3U(dn->dn_next_bonuslen[txg&TXG_MASK], ==, 0);
      ASSERT3U(dn->dn_next_blksz[txg&TXG_MASK], ==, 0);

      dprintf_ds(os->os_dsl_dataset, "obj=%llu txg=%llu\n",
          dn->dn_object, txg);

      if (dn->dn_free_txg > 0 && dn->dn_free_txg <= txg) {
            list_insert_tail(&os->os_free_dnodes[txg&TXG_MASK], dn);
      } else {
            list_insert_tail(&os->os_dirty_dnodes[txg&TXG_MASK], dn);
      }

      mutex_exit(&os->os_lock);

      /*
       * The dnode maintains a hold on its containing dbuf as
       * long as there are holds on it.  Each instantiated child
       * dbuf maintaines a hold on the dnode.  When the last child
       * drops its hold, the dnode will drop its hold on the
       * containing dbuf. We add a "dirty hold" here so that the
       * dnode will hang around after we finish processing its
       * children.
       */
      VERIFY(dnode_add_ref(dn, (void *)(uintptr_t)tx->tx_txg));

      (void) dbuf_dirty(dn->dn_dbuf, tx);

      dsl_dataset_dirty(os->os_dsl_dataset, tx);
}

void
dnode_free(dnode_t *dn, dmu_tx_t *tx)
{
      int txgoff = tx->tx_txg & TXG_MASK;

      dprintf("dn=%p txg=%llu\n", dn, tx->tx_txg);

      /* we should be the only holder... hopefully */
      /* ASSERT3U(refcount_count(&dn->dn_holds), ==, 1); */

      mutex_enter(&dn->dn_mtx);
      if (dn->dn_type == DMU_OT_NONE || dn->dn_free_txg) {
            mutex_exit(&dn->dn_mtx);
            return;
      }
      dn->dn_free_txg = tx->tx_txg;
      mutex_exit(&dn->dn_mtx);

      /*
       * If the dnode is already dirty, it needs to be moved from
       * the dirty list to the free list.
       */
      mutex_enter(&dn->dn_objset->os_lock);
      if (list_link_active(&dn->dn_dirty_link[txgoff])) {
            list_remove(&dn->dn_objset->os_dirty_dnodes[txgoff], dn);
            list_insert_tail(&dn->dn_objset->os_free_dnodes[txgoff], dn);
            mutex_exit(&dn->dn_objset->os_lock);
      } else {
            mutex_exit(&dn->dn_objset->os_lock);
            dnode_setdirty(dn, tx);
      }
}

/*
 * Try to change the block size for the indicated dnode.  This can only
 * succeed if there are no blocks allocated or dirty beyond first block
 */
int
dnode_set_blksz(dnode_t *dn, uint64_t size, int ibs, dmu_tx_t *tx)
{
      dmu_buf_impl_t *db, *db_next;
      int err;

      if (size == 0)
            size = SPA_MINBLOCKSIZE;
      if (size > SPA_MAXBLOCKSIZE)
            size = SPA_MAXBLOCKSIZE;
      else
            size = P2ROUNDUP(size, SPA_MINBLOCKSIZE);

      if (ibs == dn->dn_indblkshift)
            ibs = 0;

      if (size >> SPA_MINBLOCKSHIFT == dn->dn_datablkszsec && ibs == 0)
            return (0);

      rw_enter(&dn->dn_struct_rwlock, RW_WRITER);

      /* Check for any allocated blocks beyond the first */
      if (dn->dn_phys->dn_maxblkid != 0)
            goto fail;

      mutex_enter(&dn->dn_dbufs_mtx);
      for (db = list_head(&dn->dn_dbufs); db; db = db_next) {
            db_next = list_next(&dn->dn_dbufs, db);

            if (db->db_blkid != 0 && db->db_blkid != DB_BONUS_BLKID) {
                  mutex_exit(&dn->dn_dbufs_mtx);
                  goto fail;
            }
      }
      mutex_exit(&dn->dn_dbufs_mtx);

      if (ibs && dn->dn_nlevels != 1)
            goto fail;

      /* resize the old block */
      err = dbuf_hold_impl(dn, 0, 0, TRUE, FTAG, &db);
      if (err == 0)
            dbuf_new_size(db, size, tx);
      else if (err != ENOENT)
            goto fail;

      dnode_setdblksz(dn, size);
      dnode_setdirty(dn, tx);
      dn->dn_next_blksz[tx->tx_txg&TXG_MASK] = size;
      if (ibs) {
            dn->dn_indblkshift = ibs;
            dn->dn_next_indblkshift[tx->tx_txg&TXG_MASK] = ibs;
      }
      /* rele after we have fixed the blocksize in the dnode */
      if (db)
            dbuf_rele(db, FTAG);

      rw_exit(&dn->dn_struct_rwlock);
      return (0);

fail:
      rw_exit(&dn->dn_struct_rwlock);
      return (ENOTSUP);
}

/* read-holding callers must not rely on the lock being continuously held */
void
dnode_new_blkid(dnode_t *dn, uint64_t blkid, dmu_tx_t *tx, boolean_t have_read)
{
      uint64_t txgoff = tx->tx_txg & TXG_MASK;
      int epbs, new_nlevels;
      uint64_t sz;

      ASSERT(blkid != DB_BONUS_BLKID);

      ASSERT(have_read ?
          RW_READ_HELD(&dn->dn_struct_rwlock) :
          RW_WRITE_HELD(&dn->dn_struct_rwlock));

      /*
       * if we have a read-lock, check to see if we need to do any work
       * before upgrading to a write-lock.
       */
      if (have_read) {
            if (blkid <= dn->dn_maxblkid)
                  return;

            if (!rw_tryupgrade(&dn->dn_struct_rwlock)) {
                  rw_exit(&dn->dn_struct_rwlock);
                  rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
            }
      }

      if (blkid <= dn->dn_maxblkid)
            goto out;

      dn->dn_maxblkid = blkid;

      /*
       * Compute the number of levels necessary to support the new maxblkid.
       */
      new_nlevels = 1;
      epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
      for (sz = dn->dn_nblkptr;
          sz <= blkid && sz >= dn->dn_nblkptr; sz <<= epbs)
            new_nlevels++;

      if (new_nlevels > dn->dn_nlevels) {
            int old_nlevels = dn->dn_nlevels;
            dmu_buf_impl_t *db;
            list_t *list;
            dbuf_dirty_record_t *new, *dr, *dr_next;

            dn->dn_nlevels = new_nlevels;

            ASSERT3U(new_nlevels, >, dn->dn_next_nlevels[txgoff]);
            dn->dn_next_nlevels[txgoff] = new_nlevels;

            /* dirty the left indirects */
            db = dbuf_hold_level(dn, old_nlevels, 0, FTAG);
            new = dbuf_dirty(db, tx);
            dbuf_rele(db, FTAG);

            /* transfer the dirty records to the new indirect */
            mutex_enter(&dn->dn_mtx);
            mutex_enter(&new->dt.di.dr_mtx);
            list = &dn->dn_dirty_records[txgoff];
            for (dr = list_head(list); dr; dr = dr_next) {
                  dr_next = list_next(&dn->dn_dirty_records[txgoff], dr);
                  if (dr->dr_dbuf->db_level != new_nlevels-1 &&
                      dr->dr_dbuf->db_blkid != DB_BONUS_BLKID) {
                        ASSERT(dr->dr_dbuf->db_level == old_nlevels-1);
                        list_remove(&dn->dn_dirty_records[txgoff], dr);
                        list_insert_tail(&new->dt.di.dr_children, dr);
                        dr->dr_parent = new;
                  }
            }
            mutex_exit(&new->dt.di.dr_mtx);
            mutex_exit(&dn->dn_mtx);
      }

out:
      if (have_read)
            rw_downgrade(&dn->dn_struct_rwlock);
}

void
dnode_clear_range(dnode_t *dn, uint64_t blkid, uint64_t nblks, dmu_tx_t *tx)
{
      avl_tree_t *tree = &dn->dn_ranges[tx->tx_txg&TXG_MASK];
      avl_index_t where;
      free_range_t *rp;
      free_range_t rp_tofind;
      uint64_t endblk = blkid + nblks;

      ASSERT(MUTEX_HELD(&dn->dn_mtx));
      ASSERT(nblks <= UINT64_MAX - blkid); /* no overflow */

      dprintf_dnode(dn, "blkid=%llu nblks=%llu txg=%llu\n",
          blkid, nblks, tx->tx_txg);
      rp_tofind.fr_blkid = blkid;
      rp = avl_find(tree, &rp_tofind, &where);
      if (rp == NULL)
            rp = avl_nearest(tree, where, AVL_BEFORE);
      if (rp == NULL)
            rp = avl_nearest(tree, where, AVL_AFTER);

      while (rp && (rp->fr_blkid <= blkid + nblks)) {
            uint64_t fr_endblk = rp->fr_blkid + rp->fr_nblks;
            free_range_t *nrp = AVL_NEXT(tree, rp);

            if (blkid <= rp->fr_blkid && endblk >= fr_endblk) {
                  /* clear this entire range */
                  avl_remove(tree, rp);
                  kmem_free(rp, sizeof (free_range_t));
            } else if (blkid <= rp->fr_blkid &&
                endblk > rp->fr_blkid && endblk < fr_endblk) {
                  /* clear the beginning of this range */
                  rp->fr_blkid = endblk;
                  rp->fr_nblks = fr_endblk - endblk;
            } else if (blkid > rp->fr_blkid && blkid < fr_endblk &&
                endblk >= fr_endblk) {
                  /* clear the end of this range */
                  rp->fr_nblks = blkid - rp->fr_blkid;
            } else if (blkid > rp->fr_blkid && endblk < fr_endblk) {
                  /* clear a chunk out of this range */
                  free_range_t *new_rp =
                      kmem_alloc(sizeof (free_range_t), KM_SLEEP);

                  new_rp->fr_blkid = endblk;
                  new_rp->fr_nblks = fr_endblk - endblk;
                  avl_insert_here(tree, new_rp, rp, AVL_AFTER);
                  rp->fr_nblks = blkid - rp->fr_blkid;
            }
            /* there may be no overlap */
            rp = nrp;
      }
}

void
dnode_free_range(dnode_t *dn, uint64_t off, uint64_t len, dmu_tx_t *tx)
{
      dmu_buf_impl_t *db;
      uint64_t blkoff, blkid, nblks;
      int blksz, blkshift, head, tail;
      int trunc = FALSE;
      int epbs;

      rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
      blksz = dn->dn_datablksz;
      blkshift = dn->dn_datablkshift;
      epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;

      if (len == -1ULL) {
            len = UINT64_MAX - off;
            trunc = TRUE;
      }

      /*
       * First, block align the region to free:
       */
      if (ISP2(blksz)) {
            head = P2NPHASE(off, blksz);
            blkoff = P2PHASE(off, blksz);
            if ((off >> blkshift) > dn->dn_maxblkid)
                  goto out;
      } else {
            ASSERT(dn->dn_maxblkid == 0);
            if (off == 0 && len >= blksz) {
                  /* Freeing the whole block; fast-track this request */
                  blkid = 0;
                  nblks = 1;
                  goto done;
            } else if (off >= blksz) {
                  /* Freeing past end-of-data */
                  goto out;
            } else {
                  /* Freeing part of the block. */
                  head = blksz - off;
                  ASSERT3U(head, >, 0);
            }
            blkoff = off;
      }
      /* zero out any partial block data at the start of the range */
      if (head) {
            ASSERT3U(blkoff + head, ==, blksz);
            if (len < head)
                  head = len;
            if (dbuf_hold_impl(dn, 0, dbuf_whichblock(dn, off), TRUE,
                FTAG, &db) == 0) {
                  caddr_t data;

                  /* don't dirty if it isn't on disk and isn't dirty */
                  if (db->db_last_dirty ||
                      (db->db_blkptr && !BP_IS_HOLE(db->db_blkptr))) {
                        rw_exit(&dn->dn_struct_rwlock);
                        dbuf_will_dirty(db, tx);
                        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
                        data = db->db.db_data;
                        bzero(data + blkoff, head);
                  }
                  dbuf_rele(db, FTAG);
            }
            off += head;
            len -= head;
      }

      /* If the range was less than one block, we're done */
      if (len == 0)
            goto out;

      /* If the remaining range is past end of file, we're done */
      if ((off >> blkshift) > dn->dn_maxblkid)
            goto out;

      ASSERT(ISP2(blksz));
      if (trunc)
            tail = 0;
      else
            tail = P2PHASE(len, blksz);

      ASSERT3U(P2PHASE(off, blksz), ==, 0);
      /* zero out any partial block data at the end of the range */
      if (tail) {
            if (len < tail)
                  tail = len;
            if (dbuf_hold_impl(dn, 0, dbuf_whichblock(dn, off+len),
                TRUE, FTAG, &db) == 0) {
                  /* don't dirty if not on disk and not dirty */
                  if (db->db_last_dirty ||
                      (db->db_blkptr && !BP_IS_HOLE(db->db_blkptr))) {
                        rw_exit(&dn->dn_struct_rwlock);
                        dbuf_will_dirty(db, tx);
                        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
                        bzero(db->db.db_data, tail);
                  }
                  dbuf_rele(db, FTAG);
            }
            len -= tail;
      }

      /* If the range did not include a full block, we are done */
      if (len == 0)
            goto out;

      ASSERT(IS_P2ALIGNED(off, blksz));
      ASSERT(trunc || IS_P2ALIGNED(len, blksz));
      blkid = off >> blkshift;
      nblks = len >> blkshift;
      if (trunc)
            nblks += 1;

      /*
       * Read in and mark all the level-1 indirects dirty,
       * so that they will stay in memory until syncing phase.
       * Always dirty the first and last indirect to make sure
       * we dirty all the partial indirects.
       */
      if (dn->dn_nlevels > 1) {
            uint64_t i, first, last;
            int shift = epbs + dn->dn_datablkshift;

            first = blkid >> epbs;
            if (db = dbuf_hold_level(dn, 1, first, FTAG)) {
                  dbuf_will_dirty(db, tx);
                  dbuf_rele(db, FTAG);
            }
            if (trunc)
                  last = dn->dn_maxblkid >> epbs;
            else
                  last = (blkid + nblks - 1) >> epbs;
            if (last > first && (db = dbuf_hold_level(dn, 1, last, FTAG))) {
                  dbuf_will_dirty(db, tx);
                  dbuf_rele(db, FTAG);
            }
            for (i = first + 1; i < last; i++) {
                  uint64_t ibyte = i << shift;
                  int err;

                  err = dnode_next_offset(dn,
                      DNODE_FIND_HAVELOCK, &ibyte, 1, 1, 0);
                  i = ibyte >> shift;
                  if (err == ESRCH || i >= last)
                        break;
                  ASSERT(err == 0);
                  db = dbuf_hold_level(dn, 1, i, FTAG);
                  if (db) {
                        dbuf_will_dirty(db, tx);
                        dbuf_rele(db, FTAG);
                  }
            }
      }
done:
      /*
       * Add this range to the dnode range list.
       * We will finish up this free operation in the syncing phase.
       */
      mutex_enter(&dn->dn_mtx);
      dnode_clear_range(dn, blkid, nblks, tx);
      {
            free_range_t *rp, *found;
            avl_index_t where;
            avl_tree_t *tree = &dn->dn_ranges[tx->tx_txg&TXG_MASK];

            /* Add new range to dn_ranges */
            rp = kmem_alloc(sizeof (free_range_t), KM_SLEEP);
            rp->fr_blkid = blkid;
            rp->fr_nblks = nblks;
            found = avl_find(tree, rp, &where);
            ASSERT(found == NULL);
            avl_insert(tree, rp, where);
            dprintf_dnode(dn, "blkid=%llu nblks=%llu txg=%llu\n",
                blkid, nblks, tx->tx_txg);
      }
      mutex_exit(&dn->dn_mtx);

      dbuf_free_range(dn, blkid, blkid + nblks - 1, tx);
      dnode_setdirty(dn, tx);
out:
      if (trunc && dn->dn_maxblkid >= (off >> blkshift))
            dn->dn_maxblkid = (off >> blkshift ? (off >> blkshift) - 1 : 0);

      rw_exit(&dn->dn_struct_rwlock);
}

/* return TRUE if this blkid was freed in a recent txg, or FALSE if it wasn't */
uint64_t
dnode_block_freed(dnode_t *dn, uint64_t blkid)
{
      free_range_t range_tofind;
      void *dp = spa_get_dsl(dn->dn_objset->os_spa);
      int i;

      if (blkid == DB_BONUS_BLKID)
            return (FALSE);

      /*
       * If we're in the process of opening the pool, dp will not be
       * set yet, but there shouldn't be anything dirty.
       */
      if (dp == NULL)
            return (FALSE);

      if (dn->dn_free_txg)
            return (TRUE);

      range_tofind.fr_blkid = blkid;
      mutex_enter(&dn->dn_mtx);
      for (i = 0; i < TXG_SIZE; i++) {
            free_range_t *range_found;
            avl_index_t idx;

            range_found = avl_find(&dn->dn_ranges[i], &range_tofind, &idx);
            if (range_found) {
                  ASSERT(range_found->fr_nblks > 0);
                  break;
            }
            range_found = avl_nearest(&dn->dn_ranges[i], idx, AVL_BEFORE);
            if (range_found &&
                range_found->fr_blkid + range_found->fr_nblks > blkid)
                  break;
      }
      mutex_exit(&dn->dn_mtx);
      return (i < TXG_SIZE);
}

/* call from syncing context when we actually write/free space for this dnode */
void
dnode_diduse_space(dnode_t *dn, int64_t delta)
{
      uint64_t space;
      dprintf_dnode(dn, "dn=%p dnp=%p used=%llu delta=%lld\n",
          dn, dn->dn_phys,
          (u_longlong_t)dn->dn_phys->dn_used,
          (longlong_t)delta);

      mutex_enter(&dn->dn_mtx);
      space = DN_USED_BYTES(dn->dn_phys);
      if (delta > 0) {
            ASSERT3U(space + delta, >=, space); /* no overflow */
      } else {
            ASSERT3U(space, >=, -delta); /* no underflow */
      }
      space += delta;
      if (spa_version(dn->dn_objset->os_spa) < SPA_VERSION_DNODE_BYTES) {
            ASSERT((dn->dn_phys->dn_flags & DNODE_FLAG_USED_BYTES) == 0);
            ASSERT3U(P2PHASE(space, 1<<DEV_BSHIFT), ==, 0);
            dn->dn_phys->dn_used = space >> DEV_BSHIFT;
      } else {
            dn->dn_phys->dn_used = space;
            dn->dn_phys->dn_flags |= DNODE_FLAG_USED_BYTES;
      }
      mutex_exit(&dn->dn_mtx);
}

/*
 * Call when we think we're going to write/free space in open context.
 * Be conservative (ie. OK to write less than this or free more than
 * this, but don't write more or free less).
 */
void
dnode_willuse_space(dnode_t *dn, int64_t space, dmu_tx_t *tx)
{
      objset_impl_t *os = dn->dn_objset;
      dsl_dataset_t *ds = os->os_dsl_dataset;

      if (space > 0)
            space = spa_get_asize(os->os_spa, space);

      if (ds)
            dsl_dir_willuse_space(ds->ds_dir, space, tx);

      dmu_tx_willuse_space(tx, space);
}

/*
 * This function scans a block at the indicated "level" looking for
 * a hole or data (depending on 'flags').  If level > 0, then we are
 * scanning an indirect block looking at its pointers.  If level == 0,
 * then we are looking at a block of dnodes.  If we don't find what we
 * are looking for in the block, we return ESRCH.  Otherwise, return
 * with *offset pointing to the beginning (if searching forwards) or
 * end (if searching backwards) of the range covered by the block
 * pointer we matched on (or dnode).
 *
 * The basic search algorithm used below by dnode_next_offset() is to
 * use this function to search up the block tree (widen the search) until
 * we find something (i.e., we don't return ESRCH) and then search back
 * down the tree (narrow the search) until we reach our original search
 * level.
 */
static int
dnode_next_offset_level(dnode_t *dn, int flags, uint64_t *offset,
      int lvl, uint64_t blkfill, uint64_t txg)
{
      dmu_buf_impl_t *db = NULL;
      void *data = NULL;
      uint64_t epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
      uint64_t epb = 1ULL << epbs;
      uint64_t minfill, maxfill;
      boolean_t hole;
      int i, inc, error, span;

      dprintf("probing object %llu offset %llx level %d of %u\n",
          dn->dn_object, *offset, lvl, dn->dn_phys->dn_nlevels);

      hole = flags & DNODE_FIND_HOLE;
      inc = (flags & DNODE_FIND_BACKWARDS) ? -1 : 1;
      ASSERT(txg == 0 || !hole);

      if (lvl == dn->dn_phys->dn_nlevels) {
            error = 0;
            epb = dn->dn_phys->dn_nblkptr;
            data = dn->dn_phys->dn_blkptr;
      } else {
            uint64_t blkid = dbuf_whichblock(dn, *offset) >> (epbs * lvl);
            error = dbuf_hold_impl(dn, lvl, blkid, TRUE, FTAG, &db);
            if (error) {
                  if (error != ENOENT)
                        return (error);
                  if (hole)
                        return (0);
                  /*
                   * This can only happen when we are searching up
                   * the block tree for data.  We don't really need to
                   * adjust the offset, as we will just end up looking
                   * at the pointer to this block in its parent, and its
                   * going to be unallocated, so we will skip over it.
                   */
                  return (ESRCH);
            }
            error = dbuf_read(db, NULL, DB_RF_CANFAIL | DB_RF_HAVESTRUCT);
            if (error) {
                  dbuf_rele(db, FTAG);
                  return (error);
            }
            data = db->db.db_data;
      }

      if (db && txg &&
          (db->db_blkptr == NULL || db->db_blkptr->blk_birth <= txg)) {
            /*
             * This can only happen when we are searching up the tree
             * and these conditions mean that we need to keep climbing.
             */
            error = ESRCH;
      } else if (lvl == 0) {
            dnode_phys_t *dnp = data;
            span = DNODE_SHIFT;
            ASSERT(dn->dn_type == DMU_OT_DNODE);

            for (i = (*offset >> span) & (blkfill - 1);
                i >= 0 && i < blkfill; i += inc) {
                  boolean_t newcontents = B_TRUE;
                  if (txg) {
                        int j;
                        newcontents = B_FALSE;
                        for (j = 0; j < dnp[i].dn_nblkptr; j++) {
                              if (dnp[i].dn_blkptr[j].blk_birth > txg)
                                    newcontents = B_TRUE;
                        }
                  }
                  if (!dnp[i].dn_type == hole && newcontents)
                        break;
                  *offset += (1ULL << span) * inc;
            }
            if (i < 0 || i == blkfill)
                  error = ESRCH;
      } else {
            blkptr_t *bp = data;
            uint64_t start = *offset;
            span = (lvl - 1) * epbs + dn->dn_datablkshift;
            minfill = 0;
            maxfill = blkfill << ((lvl - 1) * epbs);

            if (hole)
                  maxfill--;
            else
                  minfill++;

            *offset = *offset >> span;
            for (i = BF64_GET(*offset, 0, epbs);
                i >= 0 && i < epb; i += inc) {
                  if (bp[i].blk_fill >= minfill &&
                      bp[i].blk_fill <= maxfill &&
                      (hole || bp[i].blk_birth > txg))
                        break;
                  if (inc > 0 || *offset > 0)
                        *offset += inc;
            }
            *offset = *offset << span;
            if (inc < 0) {
                  /* traversing backwards; position offset at the end */
                  ASSERT3U(*offset, <=, start);
                  *offset = MIN(*offset + (1ULL << span) - 1, start);
            } else if (*offset < start) {
                  *offset = start;
            }
            if (i < 0 || i >= epb)
                  error = ESRCH;
      }

      if (db)
            dbuf_rele(db, FTAG);

      return (error);
}

/*
 * Find the next hole, data, or sparse region at or after *offset.
 * The value 'blkfill' tells us how many items we expect to find
 * in an L0 data block; this value is 1 for normal objects,
 * DNODES_PER_BLOCK for the meta dnode, and some fraction of
 * DNODES_PER_BLOCK when searching for sparse regions thereof.
 *
 * Examples:
 *
 * dnode_next_offset(dn, flags, offset, 1, 1, 0);
 *    Finds the next/previous hole/data in a file.
 *    Used in dmu_offset_next().
 *
 * dnode_next_offset(mdn, flags, offset, 0, DNODES_PER_BLOCK, txg);
 *    Finds the next free/allocated dnode an objset's meta-dnode.
 *    Only finds objects that have new contents since txg (ie.
 *    bonus buffer changes and content removal are ignored).
 *    Used in dmu_object_next().
 *
 * dnode_next_offset(mdn, DNODE_FIND_HOLE, offset, 2, DNODES_PER_BLOCK >> 2, 0);
 *    Finds the next L2 meta-dnode bp that's at most 1/4 full.
 *    Used in dmu_object_alloc().
 */
int
dnode_next_offset(dnode_t *dn, int flags, uint64_t *offset,
    int minlvl, uint64_t blkfill, uint64_t txg)
{
      uint64_t initial_offset = *offset;
      int lvl, maxlvl;
      int error = 0;

      if (!(flags & DNODE_FIND_HAVELOCK))
            rw_enter(&dn->dn_struct_rwlock, RW_READER);

      if (dn->dn_phys->dn_nlevels == 0) {
            error = ESRCH;
            goto out;
      }

      if (dn->dn_datablkshift == 0) {
            if (*offset < dn->dn_datablksz) {
                  if (flags & DNODE_FIND_HOLE)
                        *offset = dn->dn_datablksz;
            } else {
                  error = ESRCH;
            }
            goto out;
      }

      maxlvl = dn->dn_phys->dn_nlevels;

      for (lvl = minlvl; lvl <= maxlvl; lvl++) {
            error = dnode_next_offset_level(dn,
                flags, offset, lvl, blkfill, txg);
            if (error != ESRCH)
                  break;
      }

      while (error == 0 && --lvl >= minlvl) {
            error = dnode_next_offset_level(dn,
                flags, offset, lvl, blkfill, txg);
      }

      if (error == 0 && (flags & DNODE_FIND_BACKWARDS ?
          initial_offset < *offset : initial_offset > *offset))
            error = ESRCH;
out:
      if (!(flags & DNODE_FIND_HAVELOCK))
            rw_exit(&dn->dn_struct_rwlock);

      return (error);
}

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