FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/dmu_tx.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 https://opensource.org/licenses/CDDL-1.0.
     * See the License for the specific language governing permissions
     * and limitations under the License.
     *
     * When distributing Covered Code, include this CDDL HEADER in each
     * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     * If applicable, add the following below this CDDL HEADER, with the
     * fields enclosed by brackets "[]" replaced with your own identifying
     * information: Portions Copyright [yyyy] [name of copyright owner]
     *
     * CDDL HEADER END
     */
    /*
     * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
     * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
     * Copyright (c) 2012, 2017 by Delphix. All rights reserved.
     */
    
    #include <sys/dmu.h>
    #include <sys/dmu_impl.h>
    #include <sys/dbuf.h>
    #include <sys/dmu_tx.h>
    #include <sys/dmu_objset.h>
    #include <sys/dsl_dataset.h>
    #include <sys/dsl_dir.h>
    #include <sys/dsl_pool.h>
    #include <sys/zap_impl.h>
    #include <sys/spa.h>
    #include <sys/sa.h>
    #include <sys/sa_impl.h>
    #include <sys/zfs_context.h>
    #include <sys/trace_zfs.h>
    
    typedef void (*dmu_tx_hold_func_t)(dmu_tx_t *tx, struct dnode *dn,
        uint64_t arg1, uint64_t arg2);
    
    dmu_tx_stats_t dmu_tx_stats = {
            { "dmu_tx_assigned",            KSTAT_DATA_UINT64 },
            { "dmu_tx_delay",               KSTAT_DATA_UINT64 },
            { "dmu_tx_error",               KSTAT_DATA_UINT64 },
            { "dmu_tx_suspended",           KSTAT_DATA_UINT64 },
            { "dmu_tx_group",               KSTAT_DATA_UINT64 },
            { "dmu_tx_memory_reserve",      KSTAT_DATA_UINT64 },
            { "dmu_tx_memory_reclaim",      KSTAT_DATA_UINT64 },
            { "dmu_tx_dirty_throttle",      KSTAT_DATA_UINT64 },
            { "dmu_tx_dirty_delay",         KSTAT_DATA_UINT64 },
            { "dmu_tx_dirty_over_max",      KSTAT_DATA_UINT64 },
            { "dmu_tx_dirty_frees_delay",   KSTAT_DATA_UINT64 },
            { "dmu_tx_wrlog_delay",         KSTAT_DATA_UINT64 },
            { "dmu_tx_quota",               KSTAT_DATA_UINT64 },
    };
    
    static kstat_t *dmu_tx_ksp;
    
    dmu_tx_t *
    dmu_tx_create_dd(dsl_dir_t *dd)
    {
            dmu_tx_t *tx = kmem_zalloc(sizeof (dmu_tx_t), KM_SLEEP);
            tx->tx_dir = dd;
            if (dd != NULL)
                    tx->tx_pool = dd->dd_pool;
            list_create(&tx->tx_holds, sizeof (dmu_tx_hold_t),
                offsetof(dmu_tx_hold_t, txh_node));
            list_create(&tx->tx_callbacks, sizeof (dmu_tx_callback_t),
                offsetof(dmu_tx_callback_t, dcb_node));
            tx->tx_start = gethrtime();
            return (tx);
    }
    
    dmu_tx_t *
    dmu_tx_create(objset_t *os)
    {
            dmu_tx_t *tx = dmu_tx_create_dd(os->os_dsl_dataset->ds_dir);
            tx->tx_objset = os;
            return (tx);
    }
    
    dmu_tx_t *
    dmu_tx_create_assigned(struct dsl_pool *dp, uint64_t txg)
    {
            dmu_tx_t *tx = dmu_tx_create_dd(NULL);
    
            TXG_VERIFY(dp->dp_spa, txg);
            tx->tx_pool = dp;
            tx->tx_txg = txg;
            tx->tx_anyobj = TRUE;
    
            return (tx);
    }
    
    int
   dmu_tx_is_syncing(dmu_tx_t *tx)
   {
           return (tx->tx_anyobj);
   }
   
   int
   dmu_tx_private_ok(dmu_tx_t *tx)
   {
           return (tx->tx_anyobj);
   }
   
   static dmu_tx_hold_t *
   dmu_tx_hold_dnode_impl(dmu_tx_t *tx, dnode_t *dn, enum dmu_tx_hold_type type,
       uint64_t arg1, uint64_t arg2)
   {
           dmu_tx_hold_t *txh;
   
           if (dn != NULL) {
                   (void) zfs_refcount_add(&dn->dn_holds, tx);
                   if (tx->tx_txg != 0) {
                           mutex_enter(&dn->dn_mtx);
                           /*
                            * dn->dn_assigned_txg == tx->tx_txg doesn't pose a
                            * problem, but there's no way for it to happen (for
                            * now, at least).
                            */
                           ASSERT(dn->dn_assigned_txg == 0);
                           dn->dn_assigned_txg = tx->tx_txg;
                           (void) zfs_refcount_add(&dn->dn_tx_holds, tx);
                           mutex_exit(&dn->dn_mtx);
                   }
           }
   
           txh = kmem_zalloc(sizeof (dmu_tx_hold_t), KM_SLEEP);
           txh->txh_tx = tx;
           txh->txh_dnode = dn;
           zfs_refcount_create(&txh->txh_space_towrite);
           zfs_refcount_create(&txh->txh_memory_tohold);
           txh->txh_type = type;
           txh->txh_arg1 = arg1;
           txh->txh_arg2 = arg2;
           list_insert_tail(&tx->tx_holds, txh);
   
           return (txh);
   }
   
   static dmu_tx_hold_t *
   dmu_tx_hold_object_impl(dmu_tx_t *tx, objset_t *os, uint64_t object,
       enum dmu_tx_hold_type type, uint64_t arg1, uint64_t arg2)
   {
           dnode_t *dn = NULL;
           dmu_tx_hold_t *txh;
           int err;
   
           if (object != DMU_NEW_OBJECT) {
                   err = dnode_hold(os, object, FTAG, &dn);
                   if (err != 0) {
                           tx->tx_err = err;
                           return (NULL);
                   }
           }
           txh = dmu_tx_hold_dnode_impl(tx, dn, type, arg1, arg2);
           if (dn != NULL)
                   dnode_rele(dn, FTAG);
           return (txh);
   }
   
   void
   dmu_tx_add_new_object(dmu_tx_t *tx, dnode_t *dn)
   {
           /*
            * If we're syncing, they can manipulate any object anyhow, and
            * the hold on the dnode_t can cause problems.
            */
           if (!dmu_tx_is_syncing(tx))
                   (void) dmu_tx_hold_dnode_impl(tx, dn, THT_NEWOBJECT, 0, 0);
   }
   
   /*
    * This function reads specified data from disk.  The specified data will
    * be needed to perform the transaction -- i.e, it will be read after
    * we do dmu_tx_assign().  There are two reasons that we read the data now
    * (before dmu_tx_assign()):
    *
    * 1. Reading it now has potentially better performance.  The transaction
    * has not yet been assigned, so the TXG is not held open, and also the
    * caller typically has less locks held when calling dmu_tx_hold_*() than
    * after the transaction has been assigned.  This reduces the lock (and txg)
    * hold times, thus reducing lock contention.
    *
    * 2. It is easier for callers (primarily the ZPL) to handle i/o errors
    * that are detected before they start making changes to the DMU state
    * (i.e. now).  Once the transaction has been assigned, and some DMU
    * state has been changed, it can be difficult to recover from an i/o
    * error (e.g. to undo the changes already made in memory at the DMU
    * layer).  Typically code to do so does not exist in the caller -- it
    * assumes that the data has already been cached and thus i/o errors are
    * not possible.
    *
    * It has been observed that the i/o initiated here can be a performance
    * problem, and it appears to be optional, because we don't look at the
    * data which is read.  However, removing this read would only serve to
    * move the work elsewhere (after the dmu_tx_assign()), where it may
    * have a greater impact on performance (in addition to the impact on
    * fault tolerance noted above).
    */
   static int
   dmu_tx_check_ioerr(zio_t *zio, dnode_t *dn, int level, uint64_t blkid)
   {
           int err;
           dmu_buf_impl_t *db;
   
           rw_enter(&dn->dn_struct_rwlock, RW_READER);
           db = dbuf_hold_level(dn, level, blkid, FTAG);
           rw_exit(&dn->dn_struct_rwlock);
           if (db == NULL)
                   return (SET_ERROR(EIO));
           /*
            * PARTIAL_FIRST allows caching for uncacheable blocks.  It will
            * be cleared after dmu_buf_will_dirty() call dbuf_read() again.
            */
           err = dbuf_read(db, zio, DB_RF_CANFAIL | DB_RF_NOPREFETCH |
               (level == 0 ? DB_RF_PARTIAL_FIRST : 0));
           dbuf_rele(db, FTAG);
           return (err);
   }
   
   static void
   dmu_tx_count_write(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
   {
           dnode_t *dn = txh->txh_dnode;
           int err = 0;
   
           if (len == 0)
                   return;
   
           (void) zfs_refcount_add_many(&txh->txh_space_towrite, len, FTAG);
   
           if (dn == NULL)
                   return;
   
           /*
            * For i/o error checking, read the blocks that will be needed
            * to perform the write: the first and last level-0 blocks (if
            * they are not aligned, i.e. if they are partial-block writes),
            * and all the level-1 blocks.
            */
           if (dn->dn_maxblkid == 0) {
                   if (off < dn->dn_datablksz &&
                       (off > 0 || len < dn->dn_datablksz)) {
                           err = dmu_tx_check_ioerr(NULL, dn, 0, 0);
                           if (err != 0) {
                                   txh->txh_tx->tx_err = err;
                           }
                   }
           } else {
                   zio_t *zio = zio_root(dn->dn_objset->os_spa,
                       NULL, NULL, ZIO_FLAG_CANFAIL);
   
                   /* first level-0 block */
                   uint64_t start = off >> dn->dn_datablkshift;
                   if (P2PHASE(off, dn->dn_datablksz) || len < dn->dn_datablksz) {
                           err = dmu_tx_check_ioerr(zio, dn, 0, start);
                           if (err != 0) {
                                   txh->txh_tx->tx_err = err;
                           }
                   }
   
                   /* last level-0 block */
                   uint64_t end = (off + len - 1) >> dn->dn_datablkshift;
                   if (end != start && end <= dn->dn_maxblkid &&
                       P2PHASE(off + len, dn->dn_datablksz)) {
                           err = dmu_tx_check_ioerr(zio, dn, 0, end);
                           if (err != 0) {
                                   txh->txh_tx->tx_err = err;
                           }
                   }
   
                   /* level-1 blocks */
                   if (dn->dn_nlevels > 1) {
                           int shft = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
                           for (uint64_t i = (start >> shft) + 1;
                               i < end >> shft; i++) {
                                   err = dmu_tx_check_ioerr(zio, dn, 1, i);
                                   if (err != 0) {
                                           txh->txh_tx->tx_err = err;
                                   }
                           }
                   }
   
                   err = zio_wait(zio);
                   if (err != 0) {
                           txh->txh_tx->tx_err = err;
                   }
           }
   }
   
   static void
   dmu_tx_count_dnode(dmu_tx_hold_t *txh)
   {
           (void) zfs_refcount_add_many(&txh->txh_space_towrite,
               DNODE_MIN_SIZE, FTAG);
   }
   
   void
   dmu_tx_hold_write(dmu_tx_t *tx, uint64_t object, uint64_t off, int len)
   {
           dmu_tx_hold_t *txh;
   
           ASSERT0(tx->tx_txg);
           ASSERT3U(len, <=, DMU_MAX_ACCESS);
           ASSERT(len == 0 || UINT64_MAX - off >= len - 1);
   
           txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
               object, THT_WRITE, off, len);
           if (txh != NULL) {
                   dmu_tx_count_write(txh, off, len);
                   dmu_tx_count_dnode(txh);
           }
   }
   
   void
   dmu_tx_hold_write_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off, int len)
   {
           dmu_tx_hold_t *txh;
   
           ASSERT0(tx->tx_txg);
           ASSERT3U(len, <=, DMU_MAX_ACCESS);
           ASSERT(len == 0 || UINT64_MAX - off >= len - 1);
   
           txh = dmu_tx_hold_dnode_impl(tx, dn, THT_WRITE, off, len);
           if (txh != NULL) {
                   dmu_tx_count_write(txh, off, len);
                   dmu_tx_count_dnode(txh);
           }
   }
   
   /*
    * This function marks the transaction as being a "net free".  The end
    * result is that refquotas will be disabled for this transaction, and
    * this transaction will be able to use half of the pool space overhead
    * (see dsl_pool_adjustedsize()).  Therefore this function should only
    * be called for transactions that we expect will not cause a net increase
    * in the amount of space used (but it's OK if that is occasionally not true).
    */
   void
   dmu_tx_mark_netfree(dmu_tx_t *tx)
   {
           tx->tx_netfree = B_TRUE;
   }
   
   static void
   dmu_tx_hold_free_impl(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
   {
           dmu_tx_t *tx = txh->txh_tx;
           dnode_t *dn = txh->txh_dnode;
           int err;
   
           ASSERT(tx->tx_txg == 0);
   
           dmu_tx_count_dnode(txh);
   
           if (off >= (dn->dn_maxblkid + 1) * dn->dn_datablksz)
                   return;
           if (len == DMU_OBJECT_END)
                   len = (dn->dn_maxblkid + 1) * dn->dn_datablksz - off;
   
           dmu_tx_count_dnode(txh);
   
           /*
            * For i/o error checking, we read the first and last level-0
            * blocks if they are not aligned, and all the level-1 blocks.
            *
            * Note:  dbuf_free_range() assumes that we have not instantiated
            * any level-0 dbufs that will be completely freed.  Therefore we must
            * exercise care to not read or count the first and last blocks
            * if they are blocksize-aligned.
            */
           if (dn->dn_datablkshift == 0) {
                   if (off != 0 || len < dn->dn_datablksz)
                           dmu_tx_count_write(txh, 0, dn->dn_datablksz);
           } else {
                   /* first block will be modified if it is not aligned */
                   if (!IS_P2ALIGNED(off, 1 << dn->dn_datablkshift))
                           dmu_tx_count_write(txh, off, 1);
                   /* last block will be modified if it is not aligned */
                   if (!IS_P2ALIGNED(off + len, 1 << dn->dn_datablkshift))
                           dmu_tx_count_write(txh, off + len, 1);
           }
   
           /*
            * Check level-1 blocks.
            */
           if (dn->dn_nlevels > 1) {
                   int shift = dn->dn_datablkshift + dn->dn_indblkshift -
                       SPA_BLKPTRSHIFT;
                   uint64_t start = off >> shift;
                   uint64_t end = (off + len) >> shift;
   
                   ASSERT(dn->dn_indblkshift != 0);
   
                   /*
                    * dnode_reallocate() can result in an object with indirect
                    * blocks having an odd data block size.  In this case,
                    * just check the single block.
                    */
                   if (dn->dn_datablkshift == 0)
                           start = end = 0;
   
                   zio_t *zio = zio_root(tx->tx_pool->dp_spa,
                       NULL, NULL, ZIO_FLAG_CANFAIL);
                   for (uint64_t i = start; i <= end; i++) {
                           uint64_t ibyte = i << shift;
                           err = dnode_next_offset(dn, 0, &ibyte, 2, 1, 0);
                           i = ibyte >> shift;
                           if (err == ESRCH || i > end)
                                   break;
                           if (err != 0) {
                                   tx->tx_err = err;
                                   (void) zio_wait(zio);
                                   return;
                           }
   
                           (void) zfs_refcount_add_many(&txh->txh_memory_tohold,
                               1 << dn->dn_indblkshift, FTAG);
   
                           err = dmu_tx_check_ioerr(zio, dn, 1, i);
                           if (err != 0) {
                                   tx->tx_err = err;
                                   (void) zio_wait(zio);
                                   return;
                           }
                   }
                   err = zio_wait(zio);
                   if (err != 0) {
                           tx->tx_err = err;
                           return;
                   }
           }
   }
   
   void
   dmu_tx_hold_free(dmu_tx_t *tx, uint64_t object, uint64_t off, uint64_t len)
   {
           dmu_tx_hold_t *txh;
   
           txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
               object, THT_FREE, off, len);
           if (txh != NULL)
                   (void) dmu_tx_hold_free_impl(txh, off, len);
   }
   
   void
   dmu_tx_hold_free_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off, uint64_t len)
   {
           dmu_tx_hold_t *txh;
   
           txh = dmu_tx_hold_dnode_impl(tx, dn, THT_FREE, off, len);
           if (txh != NULL)
                   (void) dmu_tx_hold_free_impl(txh, off, len);
   }
   
   static void
   dmu_tx_hold_zap_impl(dmu_tx_hold_t *txh, const char *name)
   {
           dmu_tx_t *tx = txh->txh_tx;
           dnode_t *dn = txh->txh_dnode;
           int err;
           extern int zap_micro_max_size;
   
           ASSERT(tx->tx_txg == 0);
   
           dmu_tx_count_dnode(txh);
   
           /*
            * Modifying a almost-full microzap is around the worst case (128KB)
            *
            * If it is a fat zap, the worst case would be 7*16KB=112KB:
            * - 3 blocks overwritten: target leaf, ptrtbl block, header block
            * - 4 new blocks written if adding:
            *    - 2 blocks for possibly split leaves,
            *    - 2 grown ptrtbl blocks
            */
           (void) zfs_refcount_add_many(&txh->txh_space_towrite,
               zap_micro_max_size, FTAG);
   
           if (dn == NULL)
                   return;
   
           ASSERT3U(DMU_OT_BYTESWAP(dn->dn_type), ==, DMU_BSWAP_ZAP);
   
           if (dn->dn_maxblkid == 0 || name == NULL) {
                   /*
                    * This is a microzap (only one block), or we don't know
                    * the name.  Check the first block for i/o errors.
                    */
                   err = dmu_tx_check_ioerr(NULL, dn, 0, 0);
                   if (err != 0) {
                           tx->tx_err = err;
                   }
           } else {
                   /*
                    * Access the name so that we'll check for i/o errors to
                    * the leaf blocks, etc.  We ignore ENOENT, as this name
                    * may not yet exist.
                    */
                   err = zap_lookup_by_dnode(dn, name, 8, 0, NULL);
                   if (err == EIO || err == ECKSUM || err == ENXIO) {
                           tx->tx_err = err;
                   }
           }
   }
   
   void
   dmu_tx_hold_zap(dmu_tx_t *tx, uint64_t object, int add, const char *name)
   {
           dmu_tx_hold_t *txh;
   
           ASSERT0(tx->tx_txg);
   
           txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
               object, THT_ZAP, add, (uintptr_t)name);
           if (txh != NULL)
                   dmu_tx_hold_zap_impl(txh, name);
   }
   
   void
   dmu_tx_hold_zap_by_dnode(dmu_tx_t *tx, dnode_t *dn, int add, const char *name)
   {
           dmu_tx_hold_t *txh;
   
           ASSERT0(tx->tx_txg);
           ASSERT(dn != NULL);
   
           txh = dmu_tx_hold_dnode_impl(tx, dn, THT_ZAP, add, (uintptr_t)name);
           if (txh != NULL)
                   dmu_tx_hold_zap_impl(txh, name);
   }
   
   void
   dmu_tx_hold_bonus(dmu_tx_t *tx, uint64_t object)
   {
           dmu_tx_hold_t *txh;
   
           ASSERT(tx->tx_txg == 0);
   
           txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
               object, THT_BONUS, 0, 0);
           if (txh)
                   dmu_tx_count_dnode(txh);
   }
   
   void
   dmu_tx_hold_bonus_by_dnode(dmu_tx_t *tx, dnode_t *dn)
   {
           dmu_tx_hold_t *txh;
   
           ASSERT0(tx->tx_txg);
   
           txh = dmu_tx_hold_dnode_impl(tx, dn, THT_BONUS, 0, 0);
           if (txh)
                   dmu_tx_count_dnode(txh);
   }
   
   void
   dmu_tx_hold_space(dmu_tx_t *tx, uint64_t space)
   {
           dmu_tx_hold_t *txh;
   
           ASSERT(tx->tx_txg == 0);
   
           txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
               DMU_NEW_OBJECT, THT_SPACE, space, 0);
           if (txh) {
                   (void) zfs_refcount_add_many(
                       &txh->txh_space_towrite, space, FTAG);
           }
   }
   
   #ifdef ZFS_DEBUG
   void
   dmu_tx_dirty_buf(dmu_tx_t *tx, dmu_buf_impl_t *db)
   {
           boolean_t match_object = B_FALSE;
           boolean_t match_offset = B_FALSE;
   
           DB_DNODE_ENTER(db);
           dnode_t *dn = DB_DNODE(db);
           ASSERT(tx->tx_txg != 0);
           ASSERT(tx->tx_objset == NULL || dn->dn_objset == tx->tx_objset);
           ASSERT3U(dn->dn_object, ==, db->db.db_object);
   
           if (tx->tx_anyobj) {
                   DB_DNODE_EXIT(db);
                   return;
           }
   
           /* XXX No checking on the meta dnode for now */
           if (db->db.db_object == DMU_META_DNODE_OBJECT) {
                   DB_DNODE_EXIT(db);
                   return;
           }
   
           for (dmu_tx_hold_t *txh = list_head(&tx->tx_holds); txh != NULL;
               txh = list_next(&tx->tx_holds, txh)) {
                   ASSERT3U(dn->dn_assigned_txg, ==, tx->tx_txg);
                   if (txh->txh_dnode == dn && txh->txh_type != THT_NEWOBJECT)
                           match_object = TRUE;
                   if (txh->txh_dnode == NULL || txh->txh_dnode == dn) {
                           int datablkshift = dn->dn_datablkshift ?
                               dn->dn_datablkshift : SPA_MAXBLOCKSHIFT;
                           int epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
                           int shift = datablkshift + epbs * db->db_level;
                           uint64_t beginblk = shift >= 64 ? 0 :
                               (txh->txh_arg1 >> shift);
                           uint64_t endblk = shift >= 64 ? 0 :
                               ((txh->txh_arg1 + txh->txh_arg2 - 1) >> shift);
                           uint64_t blkid = db->db_blkid;
   
                           /* XXX txh_arg2 better not be zero... */
   
                           dprintf("found txh type %x beginblk=%llx endblk=%llx\n",
                               txh->txh_type, (u_longlong_t)beginblk,
                               (u_longlong_t)endblk);
   
                           switch (txh->txh_type) {
                           case THT_WRITE:
                                   if (blkid >= beginblk && blkid <= endblk)
                                           match_offset = TRUE;
                                   /*
                                    * We will let this hold work for the bonus
                                    * or spill buffer so that we don't need to
                                    * hold it when creating a new object.
                                    */
                                   if (blkid == DMU_BONUS_BLKID ||
                                       blkid == DMU_SPILL_BLKID)
                                           match_offset = TRUE;
                                   /*
                                    * They might have to increase nlevels,
                                    * thus dirtying the new TLIBs.  Or the
                                    * might have to change the block size,
                                    * thus dirying the new lvl=0 blk=0.
                                    */
                                   if (blkid == 0)
                                           match_offset = TRUE;
                                   break;
                           case THT_FREE:
                                   /*
                                    * We will dirty all the level 1 blocks in
                                    * the free range and perhaps the first and
                                    * last level 0 block.
                                    */
                                   if (blkid >= beginblk && (blkid <= endblk ||
                                       txh->txh_arg2 == DMU_OBJECT_END))
                                           match_offset = TRUE;
                                   break;
                           case THT_SPILL:
                                   if (blkid == DMU_SPILL_BLKID)
                                           match_offset = TRUE;
                                   break;
                           case THT_BONUS:
                                   if (blkid == DMU_BONUS_BLKID)
                                           match_offset = TRUE;
                                   break;
                           case THT_ZAP:
                                   match_offset = TRUE;
                                   break;
                           case THT_NEWOBJECT:
                                   match_object = TRUE;
                                   break;
                           default:
                                   cmn_err(CE_PANIC, "bad txh_type %d",
                                       txh->txh_type);
                           }
                   }
                   if (match_object && match_offset) {
                           DB_DNODE_EXIT(db);
                           return;
                   }
           }
           DB_DNODE_EXIT(db);
           panic("dirtying dbuf obj=%llx lvl=%u blkid=%llx but not tx_held\n",
               (u_longlong_t)db->db.db_object, db->db_level,
               (u_longlong_t)db->db_blkid);
   }
   #endif
   
   /*
    * If we can't do 10 iops, something is wrong.  Let us go ahead
    * and hit zfs_dirty_data_max.
    */
   static const hrtime_t zfs_delay_max_ns = 100 * MICROSEC; /* 100 milliseconds */
   
   /*
    * We delay transactions when we've determined that the backend storage
    * isn't able to accommodate the rate of incoming writes.
    *
    * If there is already a transaction waiting, we delay relative to when
    * that transaction finishes waiting.  This way the calculated min_time
    * is independent of the number of threads concurrently executing
    * transactions.
    *
    * If we are the only waiter, wait relative to when the transaction
    * started, rather than the current time.  This credits the transaction for
    * "time already served", e.g. reading indirect blocks.
    *
    * The minimum time for a transaction to take is calculated as:
    *     min_time = scale * (dirty - min) / (max - dirty)
    *     min_time is then capped at zfs_delay_max_ns.
    *
    * The delay has two degrees of freedom that can be adjusted via tunables.
    * The percentage of dirty data at which we start to delay is defined by
    * zfs_delay_min_dirty_percent. This should typically be at or above
    * zfs_vdev_async_write_active_max_dirty_percent so that we only start to
    * delay after writing at full speed has failed to keep up with the incoming
    * write rate. The scale of the curve is defined by zfs_delay_scale. Roughly
    * speaking, this variable determines the amount of delay at the midpoint of
    * the curve.
    *
    * delay
    *  10ms +-------------------------------------------------------------*+
    *       |                                                             *|
    *   9ms +                                                             *+
    *       |                                                             *|
    *   8ms +                                                             *+
    *       |                                                            * |
    *   7ms +                                                            * +
    *       |                                                            * |
    *   6ms +                                                            * +
    *       |                                                            * |
    *   5ms +                                                           *  +
    *       |                                                           *  |
    *   4ms +                                                           *  +
    *       |                                                           *  |
    *   3ms +                                                          *   +
    *       |                                                          *   |
    *   2ms +                                              (midpoint) *    +
    *       |                                                  |    **     |
    *   1ms +                                                  v ***       +
    *       |             zfs_delay_scale ---------->     ********         |
    *     0 +-------------------------------------*********----------------+
    *       0%                    <- zfs_dirty_data_max ->               100%
    *
    * Note that since the delay is added to the outstanding time remaining on the
    * most recent transaction, the delay is effectively the inverse of IOPS.
    * Here the midpoint of 500us translates to 2000 IOPS. The shape of the curve
    * was chosen such that small changes in the amount of accumulated dirty data
    * in the first 3/4 of the curve yield relatively small differences in the
    * amount of delay.
    *
    * The effects can be easier to understand when the amount of delay is
    * represented on a log scale:
    *
    * delay
    * 100ms +-------------------------------------------------------------++
    *       +                                                              +
    *       |                                                              |
    *       +                                                             *+
    *  10ms +                                                             *+
    *       +                                                           ** +
    *       |                                              (midpoint)  **  |
    *       +                                                  |     **    +
    *   1ms +                                                  v ****      +
    *       +             zfs_delay_scale ---------->        *****         +
    *       |                                             ****             |
    *       +                                          ****                +
    * 100us +                                        **                    +
    *       +                                       *                      +
    *       |                                      *                       |
    *       +                                     *                        +
    *  10us +                                     *                        +
    *       +                                                              +
    *       |                                                              |
    *       +                                                              +
    *       +--------------------------------------------------------------+
    *       0%                    <- zfs_dirty_data_max ->               100%
    *
    * Note here that only as the amount of dirty data approaches its limit does
    * the delay start to increase rapidly. The goal of a properly tuned system
    * should be to keep the amount of dirty data out of that range by first
    * ensuring that the appropriate limits are set for the I/O scheduler to reach
    * optimal throughput on the backend storage, and then by changing the value
    * of zfs_delay_scale to increase the steepness of the curve.
    */
   static void
   dmu_tx_delay(dmu_tx_t *tx, uint64_t dirty)
   {
           dsl_pool_t *dp = tx->tx_pool;
           uint64_t delay_min_bytes, wrlog;
           hrtime_t wakeup, tx_time = 0, now;
   
           /* Calculate minimum transaction time for the dirty data amount. */
           delay_min_bytes =
               zfs_dirty_data_max * zfs_delay_min_dirty_percent / 100;
           if (dirty > delay_min_bytes) {
                   /*
                    * The caller has already waited until we are under the max.
                    * We make them pass us the amount of dirty data so we don't
                    * have to handle the case of it being >= the max, which
                    * could cause a divide-by-zero if it's == the max.
                    */
                   ASSERT3U(dirty, <, zfs_dirty_data_max);
   
                   tx_time = zfs_delay_scale * (dirty - delay_min_bytes) /
                       (zfs_dirty_data_max - dirty);
           }
   
           /* Calculate minimum transaction time for the TX_WRITE log size. */
           wrlog = aggsum_upper_bound(&dp->dp_wrlog_total);
           delay_min_bytes =
               zfs_wrlog_data_max * zfs_delay_min_dirty_percent / 100;
           if (wrlog >= zfs_wrlog_data_max) {
                   tx_time = zfs_delay_max_ns;
           } else if (wrlog > delay_min_bytes) {
                   tx_time = MAX(zfs_delay_scale * (wrlog - delay_min_bytes) /
                       (zfs_wrlog_data_max - wrlog), tx_time);
           }
   
           if (tx_time == 0)
                   return;
   
           tx_time = MIN(tx_time, zfs_delay_max_ns);
           now = gethrtime();
           if (now > tx->tx_start + tx_time)
                   return;
   
           DTRACE_PROBE3(delay__mintime, dmu_tx_t *, tx, uint64_t, dirty,
               uint64_t, tx_time);
   
           mutex_enter(&dp->dp_lock);
           wakeup = MAX(tx->tx_start + tx_time, dp->dp_last_wakeup + tx_time);
           dp->dp_last_wakeup = wakeup;
           mutex_exit(&dp->dp_lock);
   
           zfs_sleep_until(wakeup);
   }
   
   /*
    * This routine attempts to assign the transaction to a transaction group.
    * To do so, we must determine if there is sufficient free space on disk.
    *
    * If this is a "netfree" transaction (i.e. we called dmu_tx_mark_netfree()
    * on it), then it is assumed that there is sufficient free space,
    * unless there's insufficient slop space in the pool (see the comment
    * above spa_slop_shift in spa_misc.c).
    *
    * If it is not a "netfree" transaction, then if the data already on disk
    * is over the allowed usage (e.g. quota), this will fail with EDQUOT or
    * ENOSPC.  Otherwise, if the current rough estimate of pending changes,
    * plus the rough estimate of this transaction's changes, may exceed the
    * allowed usage, then this will fail with ERESTART, which will cause the
    * caller to wait for the pending changes to be written to disk (by waiting
    * for the next TXG to open), and then check the space usage again.
    *
    * The rough estimate of pending changes is comprised of the sum of:
    *
    *  - this transaction's holds' txh_space_towrite
    *
    *  - dd_tempreserved[], which is the sum of in-flight transactions'
    *    holds' txh_space_towrite (i.e. those transactions that have called
    *    dmu_tx_assign() but not yet called dmu_tx_commit()).
    *
    *  - dd_space_towrite[], which is the amount of dirtied dbufs.
    *
    * Note that all of these values are inflated by spa_get_worst_case_asize(),
    * which means that we may get ERESTART well before we are actually in danger
    * of running out of space, but this also mitigates any small inaccuracies
    * in the rough estimate (e.g. txh_space_towrite doesn't take into account
    * indirect blocks, and dd_space_towrite[] doesn't take into account changes
    * to the MOS).
    *
    * Note that due to this algorithm, it is possible to exceed the allowed
    * usage by one transaction.  Also, as we approach the allowed usage,
    * we will allow a very limited amount of changes into each TXG, thus
    * decreasing performance.
    */
   static int
   dmu_tx_try_assign(dmu_tx_t *tx, uint64_t txg_how)
   {
           spa_t *spa = tx->tx_pool->dp_spa;
   
           ASSERT0(tx->tx_txg);
   
           if (tx->tx_err) {
                   DMU_TX_STAT_BUMP(dmu_tx_error);
                   return (tx->tx_err);
           }
   
           if (spa_suspended(spa)) {
                   DMU_TX_STAT_BUMP(dmu_tx_suspended);
   
                   /*
                    * If the user has indicated a blocking failure mode
                    * then return ERESTART which will block in dmu_tx_wait().
                    * Otherwise, return EIO so that an error can get
                    * propagated back to the VOP calls.
                    *
                    * Note that we always honor the txg_how flag regardless
                    * of the failuremode setting.
                    */
                   if (spa_get_failmode(spa) == ZIO_FAILURE_MODE_CONTINUE &&
                       !(txg_how & TXG_WAIT))
                           return (SET_ERROR(EIO));
   
                   return (SET_ERROR(ERESTART));
           }
   
           if (!tx->tx_dirty_delayed &&
               dsl_pool_need_wrlog_delay(tx->tx_pool)) {
                   tx->tx_wait_dirty = B_TRUE;
                   DMU_TX_STAT_BUMP(dmu_tx_wrlog_delay);
                   return (SET_ERROR(ERESTART));
           }
   
           if (!tx->tx_dirty_delayed &&
               dsl_pool_need_dirty_delay(tx->tx_pool)) {
                   tx->tx_wait_dirty = B_TRUE;
                   DMU_TX_STAT_BUMP(dmu_tx_dirty_delay);
                   return (SET_ERROR(ERESTART));
           }
   
           tx->tx_txg = txg_hold_open(tx->tx_pool, &tx->tx_txgh);
           tx->tx_needassign_txh = NULL;
   
           /*
            * NB: No error returns are allowed after txg_hold_open, but
            * before processing the dnode holds, due to the
            * dmu_tx_unassign() logic.
            */
   
           uint64_t towrite = 0;
           uint64_t tohold = 0;
           for (dmu_tx_hold_t *txh = list_head(&tx->tx_holds); txh != NULL;
               txh = list_next(&tx->tx_holds, txh)) {
                   dnode_t *dn = txh->txh_dnode;
                   if (dn != NULL) {
                           /*
                            * This thread can't hold the dn_struct_rwlock
                            * while assigning the tx, because this can lead to
                            * deadlock. Specifically, if this dnode is already
                            * assigned to an earlier txg, this thread may need
                            * to wait for that txg to sync (the ERESTART case
                            * below).  The other thread that has assigned this
                            * dnode to an earlier txg prevents this txg from
                            * syncing until its tx can complete (calling
                            * dmu_tx_commit()), but it may need to acquire the
                            * dn_struct_rwlock to do so (e.g. via
                            * dmu_buf_hold*()).
                            *
                            * Note that this thread can't hold the lock for
                            * read either, but the rwlock doesn't record
                            * enough information to make that assertion.
                            */
                           ASSERT(!RW_WRITE_HELD(&dn->dn_struct_rwlock));
   
                           mutex_enter(&dn->dn_mtx);
                           if (dn->dn_assigned_txg == tx->tx_txg - 1) {
                                   mutex_exit(&dn->dn_mtx);
                                   tx->tx_needassign_txh = txh;
                                   DMU_TX_STAT_BUMP(dmu_tx_group);
                                   return (SET_ERROR(ERESTART));
                           }
                           if (dn->dn_assigned_txg == 0)
                                   dn->dn_assigned_txg = tx->tx_txg;
                           ASSERT3U(dn->dn_assigned_txg, ==, tx->tx_txg);
                           (void) zfs_refcount_add(&dn->dn_tx_holds, tx);
                           mutex_exit(&dn->dn_mtx);
                   }
                   towrite += zfs_refcount_count(&txh->txh_space_towrite);
                   tohold += zfs_refcount_count(&txh->txh_memory_tohold);
           }
   
           /* needed allocation: worst-case estimate of write space */
           uint64_t asize = spa_get_worst_case_asize(tx->tx_pool->dp_spa, towrite);
           /* calculate memory footprint estimate */
           uint64_t memory = towrite + tohold;
   
           if (tx->tx_dir != NULL && asize != 0) {
                   int err = dsl_dir_tempreserve_space(tx->tx_dir, memory,
                       asize, tx->tx_netfree, &tx->tx_tempreserve_cookie, tx);
                   if (err != 0)
                           return (err);
           }
   
           DMU_TX_STAT_BUMP(dmu_tx_assigned);
   
           return (0);
   }
   
   static void
   dmu_tx_unassign(dmu_tx_t *tx)
   {
           if (tx->tx_txg == 0)
                   return;
   
           txg_rele_to_quiesce(&tx->tx_txgh);
   
           /*
            * Walk the transaction's hold list, removing the hold on the
            * associated dnode, and notifying waiters if the refcount drops to 0.
           */
          for (dmu_tx_hold_t *txh = list_head(&tx->tx_holds);
              txh && txh != tx->tx_needassign_txh;
              txh = list_next(&tx->tx_holds, txh)) {
                  dnode_t *dn = txh->txh_dnode;
  
                  if (dn == NULL)
                          continue;
                  mutex_enter(&dn->dn_mtx);
                  ASSERT3U(dn->dn_assigned_txg, ==, tx->tx_txg);
  
                  if (zfs_refcount_remove(&dn->dn_tx_holds, tx) == 0) {
                          dn->dn_assigned_txg = 0;
                          cv_broadcast(&dn->dn_notxholds);
                  }
                  mutex_exit(&dn->dn_mtx);
          }
  
          txg_rele_to_sync(&tx->tx_txgh);
  
          tx->tx_lasttried_txg = tx->tx_txg;
          tx->tx_txg = 0;
  }
  
  /*
   * Assign tx to a transaction group; txg_how is a bitmask:
   *
   * If TXG_WAIT is set and the currently open txg is full, this function
   * will wait until there's a new txg. This should be used when no locks
   * are being held. With this bit set, this function will only fail if
   * we're truly out of space (or over quota).
   *
   * If TXG_WAIT is *not* set and we can't assign into the currently open
   * txg without blocking, this function will return immediately with
   * ERESTART. This should be used whenever locks are being held.  On an
   * ERESTART error, the caller should drop all locks, call dmu_tx_wait(),
   * and try again.
   *
   * If TXG_NOTHROTTLE is set, this indicates that this tx should not be
   * delayed due on the ZFS Write Throttle (see comments in dsl_pool.c for
   * details on the throttle). This is used by the VFS operations, after
   * they have already called dmu_tx_wait() (though most likely on a
   * different tx).
   *
   * It is guaranteed that subsequent successful calls to dmu_tx_assign()
   * will assign the tx to monotonically increasing txgs. Of course this is
   * not strong monotonicity, because the same txg can be returned multiple
   * times in a row. This guarantee holds both for subsequent calls from
   * one thread and for multiple threads. For example, it is impossible to
   * observe the following sequence of events:
   *
   *          Thread 1                            Thread 2
   *
   *     dmu_tx_assign(T1, ...)
   *     1 <- dmu_tx_get_txg(T1)
   *                                       dmu_tx_assign(T2, ...)
   *                                       2 <- dmu_tx_get_txg(T2)
   *     dmu_tx_assign(T3, ...)
   *     1 <- dmu_tx_get_txg(T3)
   */
  int
  dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how)
  {
          int err;
  
          ASSERT(tx->tx_txg == 0);
          ASSERT0(txg_how & ~(TXG_WAIT | TXG_NOTHROTTLE));
          ASSERT(!dsl_pool_sync_context(tx->tx_pool));
  
          /* If we might wait, we must not hold the config lock. */
          IMPLY((txg_how & TXG_WAIT), !dsl_pool_config_held(tx->tx_pool));
  
          if ((txg_how & TXG_NOTHROTTLE))
                  tx->tx_dirty_delayed = B_TRUE;
  
          while ((err = dmu_tx_try_assign(tx, txg_how)) != 0) {
                  dmu_tx_unassign(tx);
  
                  if (err != ERESTART || !(txg_how & TXG_WAIT))
                          return (err);
  
                  dmu_tx_wait(tx);
          }
  
          txg_rele_to_quiesce(&tx->tx_txgh);
  
          return (0);
  }
  
  void
  dmu_tx_wait(dmu_tx_t *tx)
  {
          spa_t *spa = tx->tx_pool->dp_spa;
          dsl_pool_t *dp = tx->tx_pool;
          hrtime_t before;
  
          ASSERT(tx->tx_txg == 0);
          ASSERT(!dsl_pool_config_held(tx->tx_pool));
  
          before = gethrtime();
  
          if (tx->tx_wait_dirty) {
                  uint64_t dirty;
  
                  /*
                   * dmu_tx_try_assign() has determined that we need to wait
                   * because we've consumed much or all of the dirty buffer
                   * space.
                   */
                  mutex_enter(&dp->dp_lock);
                  if (dp->dp_dirty_total >= zfs_dirty_data_max)
                          DMU_TX_STAT_BUMP(dmu_tx_dirty_over_max);
                  while (dp->dp_dirty_total >= zfs_dirty_data_max)
                          cv_wait(&dp->dp_spaceavail_cv, &dp->dp_lock);
                  dirty = dp->dp_dirty_total;
                  mutex_exit(&dp->dp_lock);
  
                  dmu_tx_delay(tx, dirty);
  
                  tx->tx_wait_dirty = B_FALSE;
  
                  /*
                   * Note: setting tx_dirty_delayed only has effect if the
                   * caller used TX_WAIT.  Otherwise they are going to
                   * destroy this tx and try again.  The common case,
                   * zfs_write(), uses TX_WAIT.
                   */
                  tx->tx_dirty_delayed = B_TRUE;
          } else if (spa_suspended(spa) || tx->tx_lasttried_txg == 0) {
                  /*
                   * If the pool is suspended we need to wait until it
                   * is resumed.  Note that it's possible that the pool
                   * has become active after this thread has tried to
                   * obtain a tx.  If that's the case then tx_lasttried_txg
                   * would not have been set.
                   */
                  txg_wait_synced(dp, spa_last_synced_txg(spa) + 1);
          } else if (tx->tx_needassign_txh) {
                  dnode_t *dn = tx->tx_needassign_txh->txh_dnode;
  
                  mutex_enter(&dn->dn_mtx);
                  while (dn->dn_assigned_txg == tx->tx_lasttried_txg - 1)
                          cv_wait(&dn->dn_notxholds, &dn->dn_mtx);
                  mutex_exit(&dn->dn_mtx);
                  tx->tx_needassign_txh = NULL;
          } else {
                  /*
                   * If we have a lot of dirty data just wait until we sync
                   * out a TXG at which point we'll hopefully have synced
                   * a portion of the changes.
                   */
                  txg_wait_synced(dp, spa_last_synced_txg(spa) + 1);
          }
  
          spa_tx_assign_add_nsecs(spa, gethrtime() - before);
  }
  
  static void
  dmu_tx_destroy(dmu_tx_t *tx)
  {
          dmu_tx_hold_t *txh;
  
          while ((txh = list_head(&tx->tx_holds)) != NULL) {
                  dnode_t *dn = txh->txh_dnode;
  
                  list_remove(&tx->tx_holds, txh);
                  zfs_refcount_destroy_many(&txh->txh_space_towrite,
                      zfs_refcount_count(&txh->txh_space_towrite));
                  zfs_refcount_destroy_many(&txh->txh_memory_tohold,
                      zfs_refcount_count(&txh->txh_memory_tohold));
                  kmem_free(txh, sizeof (dmu_tx_hold_t));
                  if (dn != NULL)
                          dnode_rele(dn, tx);
          }
  
          list_destroy(&tx->tx_callbacks);
          list_destroy(&tx->tx_holds);
          kmem_free(tx, sizeof (dmu_tx_t));
  }
  
  void
  dmu_tx_commit(dmu_tx_t *tx)
  {
          ASSERT(tx->tx_txg != 0);
  
          /*
           * Go through the transaction's hold list and remove holds on
           * associated dnodes, notifying waiters if no holds remain.
           */
          for (dmu_tx_hold_t *txh = list_head(&tx->tx_holds); txh != NULL;
              txh = list_next(&tx->tx_holds, txh)) {
                  dnode_t *dn = txh->txh_dnode;
  
                  if (dn == NULL)
                          continue;
  
                  mutex_enter(&dn->dn_mtx);
                  ASSERT3U(dn->dn_assigned_txg, ==, tx->tx_txg);
  
                  if (zfs_refcount_remove(&dn->dn_tx_holds, tx) == 0) {
                          dn->dn_assigned_txg = 0;
                          cv_broadcast(&dn->dn_notxholds);
                  }
                  mutex_exit(&dn->dn_mtx);
          }
  
          if (tx->tx_tempreserve_cookie)
                  dsl_dir_tempreserve_clear(tx->tx_tempreserve_cookie, tx);
  
          if (!list_is_empty(&tx->tx_callbacks))
                  txg_register_callbacks(&tx->tx_txgh, &tx->tx_callbacks);
  
          if (tx->tx_anyobj == FALSE)
                  txg_rele_to_sync(&tx->tx_txgh);
  
          dmu_tx_destroy(tx);
  }
  
  void
  dmu_tx_abort(dmu_tx_t *tx)
  {
          ASSERT(tx->tx_txg == 0);
  
          /*
           * Call any registered callbacks with an error code.
           */
          if (!list_is_empty(&tx->tx_callbacks))
                  dmu_tx_do_callbacks(&tx->tx_callbacks, SET_ERROR(ECANCELED));
  
          dmu_tx_destroy(tx);
  }
  
  uint64_t
  dmu_tx_get_txg(dmu_tx_t *tx)
  {
          ASSERT(tx->tx_txg != 0);
          return (tx->tx_txg);
  }
  
  dsl_pool_t *
  dmu_tx_pool(dmu_tx_t *tx)
  {
          ASSERT(tx->tx_pool != NULL);
          return (tx->tx_pool);
  }
  
  void
  dmu_tx_callback_register(dmu_tx_t *tx, dmu_tx_callback_func_t *func, void *data)
  {
          dmu_tx_callback_t *dcb;
  
          dcb = kmem_alloc(sizeof (dmu_tx_callback_t), KM_SLEEP);
  
          dcb->dcb_func = func;
          dcb->dcb_data = data;
  
          list_insert_tail(&tx->tx_callbacks, dcb);
  }
  
  /*
   * Call all the commit callbacks on a list, with a given error code.
   */
  void
  dmu_tx_do_callbacks(list_t *cb_list, int error)
  {
          dmu_tx_callback_t *dcb;
  
          while ((dcb = list_tail(cb_list)) != NULL) {
                  list_remove(cb_list, dcb);
                  dcb->dcb_func(dcb->dcb_data, error);
                  kmem_free(dcb, sizeof (dmu_tx_callback_t));
          }
  }
  
  /*
   * Interface to hold a bunch of attributes.
   * used for creating new files.
   * attrsize is the total size of all attributes
   * to be added during object creation
   *
   * For updating/adding a single attribute dmu_tx_hold_sa() should be used.
   */
  
  /*
   * hold necessary attribute name for attribute registration.
   * should be a very rare case where this is needed.  If it does
   * happen it would only happen on the first write to the file system.
   */
  static void
  dmu_tx_sa_registration_hold(sa_os_t *sa, dmu_tx_t *tx)
  {
          if (!sa->sa_need_attr_registration)
                  return;
  
          for (int i = 0; i != sa->sa_num_attrs; i++) {
                  if (!sa->sa_attr_table[i].sa_registered) {
                          if (sa->sa_reg_attr_obj)
                                  dmu_tx_hold_zap(tx, sa->sa_reg_attr_obj,
                                      B_TRUE, sa->sa_attr_table[i].sa_name);
                          else
                                  dmu_tx_hold_zap(tx, DMU_NEW_OBJECT,
                                      B_TRUE, sa->sa_attr_table[i].sa_name);
                  }
          }
  }
  
  void
  dmu_tx_hold_spill(dmu_tx_t *tx, uint64_t object)
  {
          dmu_tx_hold_t *txh;
  
          txh = dmu_tx_hold_object_impl(tx, tx->tx_objset, object,
              THT_SPILL, 0, 0);
          if (txh != NULL)
                  (void) zfs_refcount_add_many(&txh->txh_space_towrite,
                      SPA_OLD_MAXBLOCKSIZE, FTAG);
  }
  
  void
  dmu_tx_hold_sa_create(dmu_tx_t *tx, int attrsize)
  {
          sa_os_t *sa = tx->tx_objset->os_sa;
  
          dmu_tx_hold_bonus(tx, DMU_NEW_OBJECT);
  
          if (tx->tx_objset->os_sa->sa_master_obj == 0)
                  return;
  
          if (tx->tx_objset->os_sa->sa_layout_attr_obj) {
                  dmu_tx_hold_zap(tx, sa->sa_layout_attr_obj, B_TRUE, NULL);
          } else {
                  dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_LAYOUTS);
                  dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_REGISTRY);
                  dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, B_TRUE, NULL);
                  dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, B_TRUE, NULL);
          }
  
          dmu_tx_sa_registration_hold(sa, tx);
  
          if (attrsize <= DN_OLD_MAX_BONUSLEN && !sa->sa_force_spill)
                  return;
  
          (void) dmu_tx_hold_object_impl(tx, tx->tx_objset, DMU_NEW_OBJECT,
              THT_SPILL, 0, 0);
  }
  
  /*
   * Hold SA attribute
   *
   * dmu_tx_hold_sa(dmu_tx_t *tx, sa_handle_t *, attribute, add, size)
   *
   * variable_size is the total size of all variable sized attributes
   * passed to this function.  It is not the total size of all
   * variable size attributes that *may* exist on this object.
   */
  void
  dmu_tx_hold_sa(dmu_tx_t *tx, sa_handle_t *hdl, boolean_t may_grow)
  {
          uint64_t object;
          sa_os_t *sa = tx->tx_objset->os_sa;
  
          ASSERT(hdl != NULL);
  
          object = sa_handle_object(hdl);
  
          dmu_buf_impl_t *db = (dmu_buf_impl_t *)hdl->sa_bonus;
          DB_DNODE_ENTER(db);
          dmu_tx_hold_bonus_by_dnode(tx, DB_DNODE(db));
          DB_DNODE_EXIT(db);
  
          if (tx->tx_objset->os_sa->sa_master_obj == 0)
                  return;
  
          if (tx->tx_objset->os_sa->sa_reg_attr_obj == 0 ||
              tx->tx_objset->os_sa->sa_layout_attr_obj == 0) {
                  dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_LAYOUTS);
                  dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_REGISTRY);
                  dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, B_TRUE, NULL);
                  dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, B_TRUE, NULL);
          }
  
          dmu_tx_sa_registration_hold(sa, tx);
  
          if (may_grow && tx->tx_objset->os_sa->sa_layout_attr_obj)
                  dmu_tx_hold_zap(tx, sa->sa_layout_attr_obj, B_TRUE, NULL);
  
          if (sa->sa_force_spill || may_grow || hdl->sa_spill) {
                  ASSERT(tx->tx_txg == 0);
                  dmu_tx_hold_spill(tx, object);
          } else {
                  dnode_t *dn;
  
                  DB_DNODE_ENTER(db);
                  dn = DB_DNODE(db);
                  if (dn->dn_have_spill) {
                          ASSERT(tx->tx_txg == 0);
                          dmu_tx_hold_spill(tx, object);
                  }
                  DB_DNODE_EXIT(db);
          }
  }
  
  void
  dmu_tx_init(void)
  {
          dmu_tx_ksp = kstat_create("zfs", 0, "dmu_tx", "misc",
              KSTAT_TYPE_NAMED, sizeof (dmu_tx_stats) / sizeof (kstat_named_t),
              KSTAT_FLAG_VIRTUAL);
  
          if (dmu_tx_ksp != NULL) {
                  dmu_tx_ksp->ks_data = &dmu_tx_stats;
                  kstat_install(dmu_tx_ksp);
          }
  }
  
  void
  dmu_tx_fini(void)
  {
          if (dmu_tx_ksp != NULL) {
                  kstat_delete(dmu_tx_ksp);
                  dmu_tx_ksp = NULL;
          }
  }
  
  #if defined(_KERNEL)
  EXPORT_SYMBOL(dmu_tx_create);
  EXPORT_SYMBOL(dmu_tx_hold_write);
  EXPORT_SYMBOL(dmu_tx_hold_write_by_dnode);
  EXPORT_SYMBOL(dmu_tx_hold_free);
  EXPORT_SYMBOL(dmu_tx_hold_free_by_dnode);
  EXPORT_SYMBOL(dmu_tx_hold_zap);
  EXPORT_SYMBOL(dmu_tx_hold_zap_by_dnode);
  EXPORT_SYMBOL(dmu_tx_hold_bonus);
  EXPORT_SYMBOL(dmu_tx_hold_bonus_by_dnode);
  EXPORT_SYMBOL(dmu_tx_abort);
  EXPORT_SYMBOL(dmu_tx_assign);
  EXPORT_SYMBOL(dmu_tx_wait);
  EXPORT_SYMBOL(dmu_tx_commit);
  EXPORT_SYMBOL(dmu_tx_mark_netfree);
  EXPORT_SYMBOL(dmu_tx_get_txg);
  EXPORT_SYMBOL(dmu_tx_callback_register);
  EXPORT_SYMBOL(dmu_tx_do_callbacks);
  EXPORT_SYMBOL(dmu_tx_hold_spill);
  EXPORT_SYMBOL(dmu_tx_hold_sa_create);
  EXPORT_SYMBOL(dmu_tx_hold_sa);
  #endif

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