FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/zap.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 (c) 2012, 2018 by Delphix. All rights reserved.
     * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
     */
    
    /*
     * This file contains the top half of the zfs directory structure
     * implementation. The bottom half is in zap_leaf.c.
     *
     * The zdir is an extendable hash data structure. There is a table of
     * pointers to buckets (zap_t->zd_data->zd_leafs). The buckets are
     * each a constant size and hold a variable number of directory entries.
     * The buckets (aka "leaf nodes") are implemented in zap_leaf.c.
     *
     * The pointer table holds a power of 2 number of pointers.
     * (1<<zap_t->zd_data->zd_phys->zd_prefix_len).  The bucket pointed to
     * by the pointer at index i in the table holds entries whose hash value
     * has a zd_prefix_len - bit prefix
     */
    
    #include <sys/spa.h>
    #include <sys/dmu.h>
    #include <sys/zfs_context.h>
    #include <sys/zfs_znode.h>
    #include <sys/fs/zfs.h>
    #include <sys/zap.h>
    #include <sys/zap_impl.h>
    #include <sys/zap_leaf.h>
    
    /*
     * If zap_iterate_prefetch is set, we will prefetch the entire ZAP object
     * (all leaf blocks) when we start iterating over it.
     *
     * For zap_cursor_init(), the callers all intend to iterate through all the
     * entries.  There are a few cases where an error (typically i/o error) could
     * cause it to bail out early.
     *
     * For zap_cursor_init_serialized(), there are callers that do the iteration
     * outside of ZFS.  Typically they would iterate over everything, but we
     * don't have control of that.  E.g. zfs_ioc_snapshot_list_next(),
     * zcp_snapshots_iter(), and other iterators over things in the MOS - these
     * are called by /sbin/zfs and channel programs.  The other example is
     * zfs_readdir() which iterates over directory entries for the getdents()
     * syscall.  /sbin/ls iterates to the end (unless it receives a signal), but
     * userland doesn't have to.
     *
     * Given that the ZAP entries aren't returned in a specific order, the only
     * legitimate use cases for partial iteration would be:
     *
     * 1. Pagination: e.g. you only want to display 100 entries at a time, so you
     *    get the first 100 and then wait for the user to hit "next page", which
     *    they may never do).
     *
     * 2. You want to know if there are more than X entries, without relying on
     *    the zfs-specific implementation of the directory's st_size (which is
     *    the number of entries).
     */
    static int zap_iterate_prefetch = B_TRUE;
    
    int fzap_default_block_shift = 14; /* 16k blocksize */
    
    static uint64_t zap_allocate_blocks(zap_t *zap, int nblocks);
    
    void
    fzap_byteswap(void *vbuf, size_t size)
    {
            uint64_t block_type = *(uint64_t *)vbuf;
    
            if (block_type == ZBT_LEAF || block_type == BSWAP_64(ZBT_LEAF))
                    zap_leaf_byteswap(vbuf, size);
            else {
                    /* it's a ptrtbl block */
                    byteswap_uint64_array(vbuf, size);
            }
    }
    
    void
    fzap_upgrade(zap_t *zap, dmu_tx_t *tx, zap_flags_t flags)
   {
           ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
           zap->zap_ismicro = FALSE;
   
           zap->zap_dbu.dbu_evict_func_sync = zap_evict_sync;
           zap->zap_dbu.dbu_evict_func_async = NULL;
   
           mutex_init(&zap->zap_f.zap_num_entries_mtx, 0, MUTEX_DEFAULT, 0);
           zap->zap_f.zap_block_shift = highbit64(zap->zap_dbuf->db_size) - 1;
   
           zap_phys_t *zp = zap_f_phys(zap);
           /*
            * explicitly zero it since it might be coming from an
            * initialized microzap
            */
           memset(zap->zap_dbuf->db_data, 0, zap->zap_dbuf->db_size);
           zp->zap_block_type = ZBT_HEADER;
           zp->zap_magic = ZAP_MAGIC;
   
           zp->zap_ptrtbl.zt_shift = ZAP_EMBEDDED_PTRTBL_SHIFT(zap);
   
           zp->zap_freeblk = 2;            /* block 1 will be the first leaf */
           zp->zap_num_leafs = 1;
           zp->zap_num_entries = 0;
           zp->zap_salt = zap->zap_salt;
           zp->zap_normflags = zap->zap_normflags;
           zp->zap_flags = flags;
   
           /* block 1 will be the first leaf */
           for (int i = 0; i < (1<<zp->zap_ptrtbl.zt_shift); i++)
                   ZAP_EMBEDDED_PTRTBL_ENT(zap, i) = 1;
   
           /*
            * set up block 1 - the first leaf
            */
           dmu_buf_t *db;
           VERIFY0(dmu_buf_hold(zap->zap_objset, zap->zap_object,
               1<<FZAP_BLOCK_SHIFT(zap), FTAG, &db, DMU_READ_NO_PREFETCH));
           dmu_buf_will_dirty(db, tx);
   
           zap_leaf_t *l = kmem_zalloc(sizeof (zap_leaf_t), KM_SLEEP);
           l->l_dbuf = db;
   
           zap_leaf_init(l, zp->zap_normflags != 0);
   
           kmem_free(l, sizeof (zap_leaf_t));
           dmu_buf_rele(db, FTAG);
   }
   
   static int
   zap_tryupgradedir(zap_t *zap, dmu_tx_t *tx)
   {
           if (RW_WRITE_HELD(&zap->zap_rwlock))
                   return (1);
           if (rw_tryupgrade(&zap->zap_rwlock)) {
                   dmu_buf_will_dirty(zap->zap_dbuf, tx);
                   return (1);
           }
           return (0);
   }
   
   /*
    * Generic routines for dealing with the pointer & cookie tables.
    */
   
   static int
   zap_table_grow(zap_t *zap, zap_table_phys_t *tbl,
       void (*transfer_func)(const uint64_t *src, uint64_t *dst, int n),
       dmu_tx_t *tx)
   {
           uint64_t newblk;
           int bs = FZAP_BLOCK_SHIFT(zap);
           int hepb = 1<<(bs-4);
           /* hepb = half the number of entries in a block */
   
           ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
           ASSERT(tbl->zt_blk != 0);
           ASSERT(tbl->zt_numblks > 0);
   
           if (tbl->zt_nextblk != 0) {
                   newblk = tbl->zt_nextblk;
           } else {
                   newblk = zap_allocate_blocks(zap, tbl->zt_numblks * 2);
                   tbl->zt_nextblk = newblk;
                   ASSERT0(tbl->zt_blks_copied);
                   dmu_prefetch(zap->zap_objset, zap->zap_object, 0,
                       tbl->zt_blk << bs, tbl->zt_numblks << bs,
                       ZIO_PRIORITY_SYNC_READ);
           }
   
           /*
            * Copy the ptrtbl from the old to new location.
            */
   
           uint64_t b = tbl->zt_blks_copied;
           dmu_buf_t *db_old;
           int err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
               (tbl->zt_blk + b) << bs, FTAG, &db_old, DMU_READ_NO_PREFETCH);
           if (err != 0)
                   return (err);
   
           /* first half of entries in old[b] go to new[2*b+0] */
           dmu_buf_t *db_new;
           VERIFY0(dmu_buf_hold(zap->zap_objset, zap->zap_object,
               (newblk + 2*b+0) << bs, FTAG, &db_new, DMU_READ_NO_PREFETCH));
           dmu_buf_will_dirty(db_new, tx);
           transfer_func(db_old->db_data, db_new->db_data, hepb);
           dmu_buf_rele(db_new, FTAG);
   
           /* second half of entries in old[b] go to new[2*b+1] */
           VERIFY0(dmu_buf_hold(zap->zap_objset, zap->zap_object,
               (newblk + 2*b+1) << bs, FTAG, &db_new, DMU_READ_NO_PREFETCH));
           dmu_buf_will_dirty(db_new, tx);
           transfer_func((uint64_t *)db_old->db_data + hepb,
               db_new->db_data, hepb);
           dmu_buf_rele(db_new, FTAG);
   
           dmu_buf_rele(db_old, FTAG);
   
           tbl->zt_blks_copied++;
   
           dprintf("copied block %llu of %llu\n",
               (u_longlong_t)tbl->zt_blks_copied,
               (u_longlong_t)tbl->zt_numblks);
   
           if (tbl->zt_blks_copied == tbl->zt_numblks) {
                   (void) dmu_free_range(zap->zap_objset, zap->zap_object,
                       tbl->zt_blk << bs, tbl->zt_numblks << bs, tx);
   
                   tbl->zt_blk = newblk;
                   tbl->zt_numblks *= 2;
                   tbl->zt_shift++;
                   tbl->zt_nextblk = 0;
                   tbl->zt_blks_copied = 0;
   
                   dprintf("finished; numblocks now %llu (%uk entries)\n",
                       (u_longlong_t)tbl->zt_numblks, 1<<(tbl->zt_shift-10));
           }
   
           return (0);
   }
   
   static int
   zap_table_store(zap_t *zap, zap_table_phys_t *tbl, uint64_t idx, uint64_t val,
       dmu_tx_t *tx)
   {
           int bs = FZAP_BLOCK_SHIFT(zap);
   
           ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
           ASSERT(tbl->zt_blk != 0);
   
           dprintf("storing %llx at index %llx\n", (u_longlong_t)val,
               (u_longlong_t)idx);
   
           uint64_t blk = idx >> (bs-3);
           uint64_t off = idx & ((1<<(bs-3))-1);
   
           dmu_buf_t *db;
           int err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
               (tbl->zt_blk + blk) << bs, FTAG, &db, DMU_READ_NO_PREFETCH);
           if (err != 0)
                   return (err);
           dmu_buf_will_dirty(db, tx);
   
           if (tbl->zt_nextblk != 0) {
                   uint64_t idx2 = idx * 2;
                   uint64_t blk2 = idx2 >> (bs-3);
                   uint64_t off2 = idx2 & ((1<<(bs-3))-1);
                   dmu_buf_t *db2;
   
                   err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
                       (tbl->zt_nextblk + blk2) << bs, FTAG, &db2,
                       DMU_READ_NO_PREFETCH);
                   if (err != 0) {
                           dmu_buf_rele(db, FTAG);
                           return (err);
                   }
                   dmu_buf_will_dirty(db2, tx);
                   ((uint64_t *)db2->db_data)[off2] = val;
                   ((uint64_t *)db2->db_data)[off2+1] = val;
                   dmu_buf_rele(db2, FTAG);
           }
   
           ((uint64_t *)db->db_data)[off] = val;
           dmu_buf_rele(db, FTAG);
   
           return (0);
   }
   
   static int
   zap_table_load(zap_t *zap, zap_table_phys_t *tbl, uint64_t idx, uint64_t *valp)
   {
           int bs = FZAP_BLOCK_SHIFT(zap);
   
           ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
   
           uint64_t blk = idx >> (bs-3);
           uint64_t off = idx & ((1<<(bs-3))-1);
   
           /*
            * Note: this is equivalent to dmu_buf_hold(), but we use
            * _dnode_enter / _by_dnode because it's faster because we don't
            * have to hold the dnode.
            */
           dnode_t *dn = dmu_buf_dnode_enter(zap->zap_dbuf);
           dmu_buf_t *db;
           int err = dmu_buf_hold_by_dnode(dn,
               (tbl->zt_blk + blk) << bs, FTAG, &db, DMU_READ_NO_PREFETCH);
           dmu_buf_dnode_exit(zap->zap_dbuf);
           if (err != 0)
                   return (err);
           *valp = ((uint64_t *)db->db_data)[off];
           dmu_buf_rele(db, FTAG);
   
           if (tbl->zt_nextblk != 0) {
                   /*
                    * read the nextblk for the sake of i/o error checking,
                    * so that zap_table_load() will catch errors for
                    * zap_table_store.
                    */
                   blk = (idx*2) >> (bs-3);
   
                   dn = dmu_buf_dnode_enter(zap->zap_dbuf);
                   err = dmu_buf_hold_by_dnode(dn,
                       (tbl->zt_nextblk + blk) << bs, FTAG, &db,
                       DMU_READ_NO_PREFETCH);
                   dmu_buf_dnode_exit(zap->zap_dbuf);
                   if (err == 0)
                           dmu_buf_rele(db, FTAG);
           }
           return (err);
   }
   
   /*
    * Routines for growing the ptrtbl.
    */
   
   static void
   zap_ptrtbl_transfer(const uint64_t *src, uint64_t *dst, int n)
   {
           for (int i = 0; i < n; i++) {
                   uint64_t lb = src[i];
                   dst[2 * i + 0] = lb;
                   dst[2 * i + 1] = lb;
           }
   }
   
   static int
   zap_grow_ptrtbl(zap_t *zap, dmu_tx_t *tx)
   {
           /*
            * The pointer table should never use more hash bits than we
            * have (otherwise we'd be using useless zero bits to index it).
            * If we are within 2 bits of running out, stop growing, since
            * this is already an aberrant condition.
            */
           if (zap_f_phys(zap)->zap_ptrtbl.zt_shift >= zap_hashbits(zap) - 2)
                   return (SET_ERROR(ENOSPC));
   
           if (zap_f_phys(zap)->zap_ptrtbl.zt_numblks == 0) {
                   /*
                    * We are outgrowing the "embedded" ptrtbl (the one
                    * stored in the header block).  Give it its own entire
                    * block, which will double the size of the ptrtbl.
                    */
                   ASSERT3U(zap_f_phys(zap)->zap_ptrtbl.zt_shift, ==,
                       ZAP_EMBEDDED_PTRTBL_SHIFT(zap));
                   ASSERT0(zap_f_phys(zap)->zap_ptrtbl.zt_blk);
   
                   uint64_t newblk = zap_allocate_blocks(zap, 1);
                   dmu_buf_t *db_new;
                   int err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
                       newblk << FZAP_BLOCK_SHIFT(zap), FTAG, &db_new,
                       DMU_READ_NO_PREFETCH);
                   if (err != 0)
                           return (err);
                   dmu_buf_will_dirty(db_new, tx);
                   zap_ptrtbl_transfer(&ZAP_EMBEDDED_PTRTBL_ENT(zap, 0),
                       db_new->db_data, 1 << ZAP_EMBEDDED_PTRTBL_SHIFT(zap));
                   dmu_buf_rele(db_new, FTAG);
   
                   zap_f_phys(zap)->zap_ptrtbl.zt_blk = newblk;
                   zap_f_phys(zap)->zap_ptrtbl.zt_numblks = 1;
                   zap_f_phys(zap)->zap_ptrtbl.zt_shift++;
   
                   ASSERT3U(1ULL << zap_f_phys(zap)->zap_ptrtbl.zt_shift, ==,
                       zap_f_phys(zap)->zap_ptrtbl.zt_numblks <<
                       (FZAP_BLOCK_SHIFT(zap)-3));
   
                   return (0);
           } else {
                   return (zap_table_grow(zap, &zap_f_phys(zap)->zap_ptrtbl,
                       zap_ptrtbl_transfer, tx));
           }
   }
   
   static void
   zap_increment_num_entries(zap_t *zap, int delta, dmu_tx_t *tx)
   {
           dmu_buf_will_dirty(zap->zap_dbuf, tx);
           mutex_enter(&zap->zap_f.zap_num_entries_mtx);
           ASSERT(delta > 0 || zap_f_phys(zap)->zap_num_entries >= -delta);
           zap_f_phys(zap)->zap_num_entries += delta;
           mutex_exit(&zap->zap_f.zap_num_entries_mtx);
   }
   
   static uint64_t
   zap_allocate_blocks(zap_t *zap, int nblocks)
   {
           ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
           uint64_t newblk = zap_f_phys(zap)->zap_freeblk;
           zap_f_phys(zap)->zap_freeblk += nblocks;
           return (newblk);
   }
   
   static void
   zap_leaf_evict_sync(void *dbu)
   {
           zap_leaf_t *l = dbu;
   
           rw_destroy(&l->l_rwlock);
           kmem_free(l, sizeof (zap_leaf_t));
   }
   
   static zap_leaf_t *
   zap_create_leaf(zap_t *zap, dmu_tx_t *tx)
   {
           zap_leaf_t *l = kmem_zalloc(sizeof (zap_leaf_t), KM_SLEEP);
   
           ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
   
           rw_init(&l->l_rwlock, NULL, RW_NOLOCKDEP, NULL);
           rw_enter(&l->l_rwlock, RW_WRITER);
           l->l_blkid = zap_allocate_blocks(zap, 1);
           l->l_dbuf = NULL;
   
           VERIFY0(dmu_buf_hold(zap->zap_objset, zap->zap_object,
               l->l_blkid << FZAP_BLOCK_SHIFT(zap), NULL, &l->l_dbuf,
               DMU_READ_NO_PREFETCH));
           dmu_buf_init_user(&l->l_dbu, zap_leaf_evict_sync, NULL, &l->l_dbuf);
           VERIFY3P(NULL, ==, dmu_buf_set_user(l->l_dbuf, &l->l_dbu));
           dmu_buf_will_dirty(l->l_dbuf, tx);
   
           zap_leaf_init(l, zap->zap_normflags != 0);
   
           zap_f_phys(zap)->zap_num_leafs++;
   
           return (l);
   }
   
   int
   fzap_count(zap_t *zap, uint64_t *count)
   {
           ASSERT(!zap->zap_ismicro);
           mutex_enter(&zap->zap_f.zap_num_entries_mtx); /* unnecessary */
           *count = zap_f_phys(zap)->zap_num_entries;
           mutex_exit(&zap->zap_f.zap_num_entries_mtx);
           return (0);
   }
   
   /*
    * Routines for obtaining zap_leaf_t's
    */
   
   void
   zap_put_leaf(zap_leaf_t *l)
   {
           rw_exit(&l->l_rwlock);
           dmu_buf_rele(l->l_dbuf, NULL);
   }
   
   static zap_leaf_t *
   zap_open_leaf(uint64_t blkid, dmu_buf_t *db)
   {
           ASSERT(blkid != 0);
   
           zap_leaf_t *l = kmem_zalloc(sizeof (zap_leaf_t), KM_SLEEP);
           rw_init(&l->l_rwlock, NULL, RW_DEFAULT, NULL);
           rw_enter(&l->l_rwlock, RW_WRITER);
           l->l_blkid = blkid;
           l->l_bs = highbit64(db->db_size) - 1;
           l->l_dbuf = db;
   
           dmu_buf_init_user(&l->l_dbu, zap_leaf_evict_sync, NULL, &l->l_dbuf);
           zap_leaf_t *winner = dmu_buf_set_user(db, &l->l_dbu);
   
           rw_exit(&l->l_rwlock);
           if (winner != NULL) {
                   /* someone else set it first */
                   zap_leaf_evict_sync(&l->l_dbu);
                   l = winner;
           }
   
           /*
            * lhr_pad was previously used for the next leaf in the leaf
            * chain.  There should be no chained leafs (as we have removed
            * support for them).
            */
           ASSERT0(zap_leaf_phys(l)->l_hdr.lh_pad1);
   
           /*
            * There should be more hash entries than there can be
            * chunks to put in the hash table
            */
           ASSERT3U(ZAP_LEAF_HASH_NUMENTRIES(l), >, ZAP_LEAF_NUMCHUNKS(l) / 3);
   
           /* The chunks should begin at the end of the hash table */
           ASSERT3P(&ZAP_LEAF_CHUNK(l, 0), ==, (zap_leaf_chunk_t *)
               &zap_leaf_phys(l)->l_hash[ZAP_LEAF_HASH_NUMENTRIES(l)]);
   
           /* The chunks should end at the end of the block */
           ASSERT3U((uintptr_t)&ZAP_LEAF_CHUNK(l, ZAP_LEAF_NUMCHUNKS(l)) -
               (uintptr_t)zap_leaf_phys(l), ==, l->l_dbuf->db_size);
   
           return (l);
   }
   
   static int
   zap_get_leaf_byblk(zap_t *zap, uint64_t blkid, dmu_tx_t *tx, krw_t lt,
       zap_leaf_t **lp)
   {
           dmu_buf_t *db;
   
           ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
   
           /*
            * If system crashed just after dmu_free_long_range in zfs_rmnode, we
            * would be left with an empty xattr dir in delete queue. blkid=0
            * would be passed in when doing zfs_purgedir. If that's the case we
            * should just return immediately. The underlying objects should
            * already be freed, so this should be perfectly fine.
            */
           if (blkid == 0)
                   return (SET_ERROR(ENOENT));
   
           int bs = FZAP_BLOCK_SHIFT(zap);
           dnode_t *dn = dmu_buf_dnode_enter(zap->zap_dbuf);
           int err = dmu_buf_hold_by_dnode(dn,
               blkid << bs, NULL, &db, DMU_READ_NO_PREFETCH);
           dmu_buf_dnode_exit(zap->zap_dbuf);
           if (err != 0)
                   return (err);
   
           ASSERT3U(db->db_object, ==, zap->zap_object);
           ASSERT3U(db->db_offset, ==, blkid << bs);
           ASSERT3U(db->db_size, ==, 1 << bs);
           ASSERT(blkid != 0);
   
           zap_leaf_t *l = dmu_buf_get_user(db);
   
           if (l == NULL)
                   l = zap_open_leaf(blkid, db);
   
           rw_enter(&l->l_rwlock, lt);
           /*
            * Must lock before dirtying, otherwise zap_leaf_phys(l) could change,
            * causing ASSERT below to fail.
            */
           if (lt == RW_WRITER)
                   dmu_buf_will_dirty(db, tx);
           ASSERT3U(l->l_blkid, ==, blkid);
           ASSERT3P(l->l_dbuf, ==, db);
           ASSERT3U(zap_leaf_phys(l)->l_hdr.lh_block_type, ==, ZBT_LEAF);
           ASSERT3U(zap_leaf_phys(l)->l_hdr.lh_magic, ==, ZAP_LEAF_MAGIC);
   
           *lp = l;
           return (0);
   }
   
   static int
   zap_idx_to_blk(zap_t *zap, uint64_t idx, uint64_t *valp)
   {
           ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
   
           if (zap_f_phys(zap)->zap_ptrtbl.zt_numblks == 0) {
                   ASSERT3U(idx, <,
                       (1ULL << zap_f_phys(zap)->zap_ptrtbl.zt_shift));
                   *valp = ZAP_EMBEDDED_PTRTBL_ENT(zap, idx);
                   return (0);
           } else {
                   return (zap_table_load(zap, &zap_f_phys(zap)->zap_ptrtbl,
                       idx, valp));
           }
   }
   
   static int
   zap_set_idx_to_blk(zap_t *zap, uint64_t idx, uint64_t blk, dmu_tx_t *tx)
   {
           ASSERT(tx != NULL);
           ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
   
           if (zap_f_phys(zap)->zap_ptrtbl.zt_blk == 0) {
                   ZAP_EMBEDDED_PTRTBL_ENT(zap, idx) = blk;
                   return (0);
           } else {
                   return (zap_table_store(zap, &zap_f_phys(zap)->zap_ptrtbl,
                       idx, blk, tx));
           }
   }
   
   static int
   zap_deref_leaf(zap_t *zap, uint64_t h, dmu_tx_t *tx, krw_t lt, zap_leaf_t **lp)
   {
           uint64_t blk;
   
           ASSERT(zap->zap_dbuf == NULL ||
               zap_f_phys(zap) == zap->zap_dbuf->db_data);
   
           /* Reality check for corrupt zap objects (leaf or header). */
           if ((zap_f_phys(zap)->zap_block_type != ZBT_LEAF &&
               zap_f_phys(zap)->zap_block_type != ZBT_HEADER) ||
               zap_f_phys(zap)->zap_magic != ZAP_MAGIC) {
                   return (SET_ERROR(EIO));
           }
   
           uint64_t idx = ZAP_HASH_IDX(h, zap_f_phys(zap)->zap_ptrtbl.zt_shift);
           int err = zap_idx_to_blk(zap, idx, &blk);
           if (err != 0)
                   return (err);
           err = zap_get_leaf_byblk(zap, blk, tx, lt, lp);
   
           ASSERT(err ||
               ZAP_HASH_IDX(h, zap_leaf_phys(*lp)->l_hdr.lh_prefix_len) ==
               zap_leaf_phys(*lp)->l_hdr.lh_prefix);
           return (err);
   }
   
   static int
   zap_expand_leaf(zap_name_t *zn, zap_leaf_t *l,
       const void *tag, dmu_tx_t *tx, zap_leaf_t **lp)
   {
           zap_t *zap = zn->zn_zap;
           uint64_t hash = zn->zn_hash;
           int err;
           int old_prefix_len = zap_leaf_phys(l)->l_hdr.lh_prefix_len;
   
           ASSERT3U(old_prefix_len, <=, zap_f_phys(zap)->zap_ptrtbl.zt_shift);
           ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
   
           ASSERT3U(ZAP_HASH_IDX(hash, old_prefix_len), ==,
               zap_leaf_phys(l)->l_hdr.lh_prefix);
   
           if (zap_tryupgradedir(zap, tx) == 0 ||
               old_prefix_len == zap_f_phys(zap)->zap_ptrtbl.zt_shift) {
                   /* We failed to upgrade, or need to grow the pointer table */
                   objset_t *os = zap->zap_objset;
                   uint64_t object = zap->zap_object;
   
                   zap_put_leaf(l);
                   zap_unlockdir(zap, tag);
                   err = zap_lockdir(os, object, tx, RW_WRITER,
                       FALSE, FALSE, tag, &zn->zn_zap);
                   zap = zn->zn_zap;
                   if (err != 0)
                           return (err);
                   ASSERT(!zap->zap_ismicro);
   
                   while (old_prefix_len ==
                       zap_f_phys(zap)->zap_ptrtbl.zt_shift) {
                           err = zap_grow_ptrtbl(zap, tx);
                           if (err != 0)
                                   return (err);
                   }
   
                   err = zap_deref_leaf(zap, hash, tx, RW_WRITER, &l);
                   if (err != 0)
                           return (err);
   
                   if (zap_leaf_phys(l)->l_hdr.lh_prefix_len != old_prefix_len) {
                           /* it split while our locks were down */
                           *lp = l;
                           return (0);
                   }
           }
           ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
           ASSERT3U(old_prefix_len, <, zap_f_phys(zap)->zap_ptrtbl.zt_shift);
           ASSERT3U(ZAP_HASH_IDX(hash, old_prefix_len), ==,
               zap_leaf_phys(l)->l_hdr.lh_prefix);
   
           int prefix_diff = zap_f_phys(zap)->zap_ptrtbl.zt_shift -
               (old_prefix_len + 1);
           uint64_t sibling =
               (ZAP_HASH_IDX(hash, old_prefix_len + 1) | 1) << prefix_diff;
   
           /* check for i/o errors before doing zap_leaf_split */
           for (int i = 0; i < (1ULL << prefix_diff); i++) {
                   uint64_t blk;
                   err = zap_idx_to_blk(zap, sibling + i, &blk);
                   if (err != 0)
                           return (err);
                   ASSERT3U(blk, ==, l->l_blkid);
           }
   
           zap_leaf_t *nl = zap_create_leaf(zap, tx);
           zap_leaf_split(l, nl, zap->zap_normflags != 0);
   
           /* set sibling pointers */
           for (int i = 0; i < (1ULL << prefix_diff); i++) {
                   err = zap_set_idx_to_blk(zap, sibling + i, nl->l_blkid, tx);
                   ASSERT0(err); /* we checked for i/o errors above */
           }
   
           ASSERT3U(zap_leaf_phys(l)->l_hdr.lh_prefix_len, >, 0);
   
           if (hash & (1ULL << (64 - zap_leaf_phys(l)->l_hdr.lh_prefix_len))) {
                   /* we want the sibling */
                   zap_put_leaf(l);
                   *lp = nl;
           } else {
                   zap_put_leaf(nl);
                   *lp = l;
           }
   
           return (0);
   }
   
   static void
   zap_put_leaf_maybe_grow_ptrtbl(zap_name_t *zn, zap_leaf_t *l,
       const void *tag, dmu_tx_t *tx)
   {
           zap_t *zap = zn->zn_zap;
           int shift = zap_f_phys(zap)->zap_ptrtbl.zt_shift;
           int leaffull = (zap_leaf_phys(l)->l_hdr.lh_prefix_len == shift &&
               zap_leaf_phys(l)->l_hdr.lh_nfree < ZAP_LEAF_LOW_WATER);
   
           zap_put_leaf(l);
   
           if (leaffull || zap_f_phys(zap)->zap_ptrtbl.zt_nextblk) {
                   /*
                    * We are in the middle of growing the pointer table, or
                    * this leaf will soon make us grow it.
                    */
                   if (zap_tryupgradedir(zap, tx) == 0) {
                           objset_t *os = zap->zap_objset;
                           uint64_t zapobj = zap->zap_object;
   
                           zap_unlockdir(zap, tag);
                           int err = zap_lockdir(os, zapobj, tx,
                               RW_WRITER, FALSE, FALSE, tag, &zn->zn_zap);
                           zap = zn->zn_zap;
                           if (err != 0)
                                   return;
                   }
   
                   /* could have finished growing while our locks were down */
                   if (zap_f_phys(zap)->zap_ptrtbl.zt_shift == shift)
                           (void) zap_grow_ptrtbl(zap, tx);
           }
   }
   
   static int
   fzap_checkname(zap_name_t *zn)
   {
           if (zn->zn_key_orig_numints * zn->zn_key_intlen > ZAP_MAXNAMELEN)
                   return (SET_ERROR(ENAMETOOLONG));
           return (0);
   }
   
   static int
   fzap_checksize(uint64_t integer_size, uint64_t num_integers)
   {
           /* Only integer sizes supported by C */
           switch (integer_size) {
           case 1:
           case 2:
           case 4:
           case 8:
                   break;
           default:
                   return (SET_ERROR(EINVAL));
           }
   
           if (integer_size * num_integers > ZAP_MAXVALUELEN)
                   return (SET_ERROR(E2BIG));
   
           return (0);
   }
   
   static int
   fzap_check(zap_name_t *zn, uint64_t integer_size, uint64_t num_integers)
   {
           int err = fzap_checkname(zn);
           if (err != 0)
                   return (err);
           return (fzap_checksize(integer_size, num_integers));
   }
   
   /*
    * Routines for manipulating attributes.
    */
   int
   fzap_lookup(zap_name_t *zn,
       uint64_t integer_size, uint64_t num_integers, void *buf,
       char *realname, int rn_len, boolean_t *ncp)
   {
           zap_leaf_t *l;
           zap_entry_handle_t zeh;
   
           int err = fzap_checkname(zn);
           if (err != 0)
                   return (err);
   
           err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, NULL, RW_READER, &l);
           if (err != 0)
                   return (err);
           err = zap_leaf_lookup(l, zn, &zeh);
           if (err == 0) {
                   if ((err = fzap_checksize(integer_size, num_integers)) != 0) {
                           zap_put_leaf(l);
                           return (err);
                   }
   
                   err = zap_entry_read(&zeh, integer_size, num_integers, buf);
                   (void) zap_entry_read_name(zn->zn_zap, &zeh, rn_len, realname);
                   if (ncp) {
                           *ncp = zap_entry_normalization_conflict(&zeh,
                               zn, NULL, zn->zn_zap);
                   }
           }
   
           zap_put_leaf(l);
           return (err);
   }
   
   int
   fzap_add_cd(zap_name_t *zn,
       uint64_t integer_size, uint64_t num_integers,
       const void *val, uint32_t cd, const void *tag, dmu_tx_t *tx)
   {
           zap_leaf_t *l;
           int err;
           zap_entry_handle_t zeh;
           zap_t *zap = zn->zn_zap;
   
           ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
           ASSERT(!zap->zap_ismicro);
           ASSERT(fzap_check(zn, integer_size, num_integers) == 0);
   
           err = zap_deref_leaf(zap, zn->zn_hash, tx, RW_WRITER, &l);
           if (err != 0)
                   return (err);
   retry:
           err = zap_leaf_lookup(l, zn, &zeh);
           if (err == 0) {
                   err = SET_ERROR(EEXIST);
                   goto out;
           }
           if (err != ENOENT)
                   goto out;
   
           err = zap_entry_create(l, zn, cd,
               integer_size, num_integers, val, &zeh);
   
           if (err == 0) {
                   zap_increment_num_entries(zap, 1, tx);
           } else if (err == EAGAIN) {
                   err = zap_expand_leaf(zn, l, tag, tx, &l);
                   zap = zn->zn_zap;       /* zap_expand_leaf() may change zap */
                   if (err == 0) {
                           goto retry;
                   } else if (err == ENOSPC) {
                           /*
                            * If we failed to expand the leaf, then bailout
                            * as there is no point trying
                            * zap_put_leaf_maybe_grow_ptrtbl().
                            */
                           return (err);
                   }
           }
   
   out:
           if (zap != NULL)
                   zap_put_leaf_maybe_grow_ptrtbl(zn, l, tag, tx);
           return (err);
   }
   
   int
   fzap_add(zap_name_t *zn,
       uint64_t integer_size, uint64_t num_integers,
       const void *val, const void *tag, dmu_tx_t *tx)
   {
           int err = fzap_check(zn, integer_size, num_integers);
           if (err != 0)
                   return (err);
   
           return (fzap_add_cd(zn, integer_size, num_integers,
               val, ZAP_NEED_CD, tag, tx));
   }
   
   int
   fzap_update(zap_name_t *zn,
       int integer_size, uint64_t num_integers, const void *val,
       const void *tag, dmu_tx_t *tx)
   {
           zap_leaf_t *l;
           int err;
           boolean_t create;
           zap_entry_handle_t zeh;
           zap_t *zap = zn->zn_zap;
   
           ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
           err = fzap_check(zn, integer_size, num_integers);
           if (err != 0)
                   return (err);
   
           err = zap_deref_leaf(zap, zn->zn_hash, tx, RW_WRITER, &l);
           if (err != 0)
                   return (err);
   retry:
           err = zap_leaf_lookup(l, zn, &zeh);
           create = (err == ENOENT);
           ASSERT(err == 0 || err == ENOENT);
   
           if (create) {
                   err = zap_entry_create(l, zn, ZAP_NEED_CD,
                       integer_size, num_integers, val, &zeh);
                   if (err == 0)
                           zap_increment_num_entries(zap, 1, tx);
           } else {
                   err = zap_entry_update(&zeh, integer_size, num_integers, val);
           }
   
           if (err == EAGAIN) {
                   err = zap_expand_leaf(zn, l, tag, tx, &l);
                   zap = zn->zn_zap;       /* zap_expand_leaf() may change zap */
                   if (err == 0)
                           goto retry;
           }
   
           if (zap != NULL)
                   zap_put_leaf_maybe_grow_ptrtbl(zn, l, tag, tx);
           return (err);
   }
   
   int
   fzap_length(zap_name_t *zn,
       uint64_t *integer_size, uint64_t *num_integers)
   {
           zap_leaf_t *l;
           int err;
           zap_entry_handle_t zeh;
   
           err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, NULL, RW_READER, &l);
           if (err != 0)
                   return (err);
           err = zap_leaf_lookup(l, zn, &zeh);
           if (err != 0)
                   goto out;
   
           if (integer_size != NULL)
                   *integer_size = zeh.zeh_integer_size;
           if (num_integers != NULL)
                   *num_integers = zeh.zeh_num_integers;
   out:
           zap_put_leaf(l);
           return (err);
   }
   
   int
   fzap_remove(zap_name_t *zn, dmu_tx_t *tx)
   {
           zap_leaf_t *l;
           int err;
           zap_entry_handle_t zeh;
   
           err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, tx, RW_WRITER, &l);
           if (err != 0)
                   return (err);
           err = zap_leaf_lookup(l, zn, &zeh);
           if (err == 0) {
                   zap_entry_remove(&zeh);
                   zap_increment_num_entries(zn->zn_zap, -1, tx);
           }
           zap_put_leaf(l);
           return (err);
   }
   
   void
   fzap_prefetch(zap_name_t *zn)
   {
           uint64_t blk;
           zap_t *zap = zn->zn_zap;
   
           uint64_t idx = ZAP_HASH_IDX(zn->zn_hash,
               zap_f_phys(zap)->zap_ptrtbl.zt_shift);
           if (zap_idx_to_blk(zap, idx, &blk) != 0)
                   return;
           int bs = FZAP_BLOCK_SHIFT(zap);
           dmu_prefetch(zap->zap_objset, zap->zap_object, 0, blk << bs, 1 << bs,
               ZIO_PRIORITY_SYNC_READ);
   }
   
   /*
    * Helper functions for consumers.
    */
   
   uint64_t
   zap_create_link(objset_t *os, dmu_object_type_t ot, uint64_t parent_obj,
       const char *name, dmu_tx_t *tx)
   {
          return (zap_create_link_dnsize(os, ot, parent_obj, name, 0, tx));
  }
  
  uint64_t
  zap_create_link_dnsize(objset_t *os, dmu_object_type_t ot, uint64_t parent_obj,
      const char *name, int dnodesize, dmu_tx_t *tx)
  {
          uint64_t new_obj;
  
          new_obj = zap_create_dnsize(os, ot, DMU_OT_NONE, 0, dnodesize, tx);
          VERIFY(new_obj != 0);
          VERIFY0(zap_add(os, parent_obj, name, sizeof (uint64_t), 1, &new_obj,
              tx));
  
          return (new_obj);
  }
  
  int
  zap_value_search(objset_t *os, uint64_t zapobj, uint64_t value, uint64_t mask,
      char *name)
  {
          zap_cursor_t zc;
          int err;
  
          if (mask == 0)
                  mask = -1ULL;
  
          zap_attribute_t *za = kmem_alloc(sizeof (*za), KM_SLEEP);
          for (zap_cursor_init(&zc, os, zapobj);
              (err = zap_cursor_retrieve(&zc, za)) == 0;
              zap_cursor_advance(&zc)) {
                  if ((za->za_first_integer & mask) == (value & mask)) {
                          (void) strlcpy(name, za->za_name, MAXNAMELEN);
                          break;
                  }
          }
          zap_cursor_fini(&zc);
          kmem_free(za, sizeof (*za));
          return (err);
  }
  
  int
  zap_join(objset_t *os, uint64_t fromobj, uint64_t intoobj, dmu_tx_t *tx)
  {
          zap_cursor_t zc;
          int err = 0;
  
          zap_attribute_t *za = kmem_alloc(sizeof (*za), KM_SLEEP);
          for (zap_cursor_init(&zc, os, fromobj);
              zap_cursor_retrieve(&zc, za) == 0;
              (void) zap_cursor_advance(&zc)) {
                  if (za->za_integer_length != 8 || za->za_num_integers != 1) {
                          err = SET_ERROR(EINVAL);
                          break;
                  }
                  err = zap_add(os, intoobj, za->za_name,
                      8, 1, &za->za_first_integer, tx);
                  if (err != 0)
                          break;
          }
          zap_cursor_fini(&zc);
          kmem_free(za, sizeof (*za));
          return (err);
  }
  
  int
  zap_join_key(objset_t *os, uint64_t fromobj, uint64_t intoobj,
      uint64_t value, dmu_tx_t *tx)
  {
          zap_cursor_t zc;
          int err = 0;
  
          zap_attribute_t *za = kmem_alloc(sizeof (*za), KM_SLEEP);
          for (zap_cursor_init(&zc, os, fromobj);
              zap_cursor_retrieve(&zc, za) == 0;
              (void) zap_cursor_advance(&zc)) {
                  if (za->za_integer_length != 8 || za->za_num_integers != 1) {
                          err = SET_ERROR(EINVAL);
                          break;
                  }
                  err = zap_add(os, intoobj, za->za_name,
                      8, 1, &value, tx);
                  if (err != 0)
                          break;
          }
          zap_cursor_fini(&zc);
          kmem_free(za, sizeof (*za));
          return (err);
  }
  
  int
  zap_join_increment(objset_t *os, uint64_t fromobj, uint64_t intoobj,
      dmu_tx_t *tx)
  {
          zap_cursor_t zc;
          int err = 0;
  
          zap_attribute_t *za = kmem_alloc(sizeof (*za), KM_SLEEP);
          for (zap_cursor_init(&zc, os, fromobj);
              zap_cursor_retrieve(&zc, za) == 0;
              (void) zap_cursor_advance(&zc)) {
                  uint64_t delta = 0;
  
                  if (za->za_integer_length != 8 || za->za_num_integers != 1) {
                          err = SET_ERROR(EINVAL);
                          break;
                  }
  
                  err = zap_lookup(os, intoobj, za->za_name, 8, 1, &delta);
                  if (err != 0 && err != ENOENT)
                          break;
                  delta += za->za_first_integer;
                  err = zap_update(os, intoobj, za->za_name, 8, 1, &delta, tx);
                  if (err != 0)
                          break;
          }
          zap_cursor_fini(&zc);
          kmem_free(za, sizeof (*za));
          return (err);
  }
  
  int
  zap_add_int(objset_t *os, uint64_t obj, uint64_t value, dmu_tx_t *tx)
  {
          char name[20];
  
          (void) snprintf(name, sizeof (name), "%llx", (longlong_t)value);
          return (zap_add(os, obj, name, 8, 1, &value, tx));
  }
  
  int
  zap_remove_int(objset_t *os, uint64_t obj, uint64_t value, dmu_tx_t *tx)
  {
          char name[20];
  
          (void) snprintf(name, sizeof (name), "%llx", (longlong_t)value);
          return (zap_remove(os, obj, name, tx));
  }
  
  int
  zap_lookup_int(objset_t *os, uint64_t obj, uint64_t value)
  {
          char name[20];
  
          (void) snprintf(name, sizeof (name), "%llx", (longlong_t)value);
          return (zap_lookup(os, obj, name, 8, 1, &value));
  }
  
  int
  zap_add_int_key(objset_t *os, uint64_t obj,
      uint64_t key, uint64_t value, dmu_tx_t *tx)
  {
          char name[20];
  
          (void) snprintf(name, sizeof (name), "%llx", (longlong_t)key);
          return (zap_add(os, obj, name, 8, 1, &value, tx));
  }
  
  int
  zap_update_int_key(objset_t *os, uint64_t obj,
      uint64_t key, uint64_t value, dmu_tx_t *tx)
  {
          char name[20];
  
          (void) snprintf(name, sizeof (name), "%llx", (longlong_t)key);
          return (zap_update(os, obj, name, 8, 1, &value, tx));
  }
  
  int
  zap_lookup_int_key(objset_t *os, uint64_t obj, uint64_t key, uint64_t *valuep)
  {
          char name[20];
  
          (void) snprintf(name, sizeof (name), "%llx", (longlong_t)key);
          return (zap_lookup(os, obj, name, 8, 1, valuep));
  }
  
  int
  zap_increment(objset_t *os, uint64_t obj, const char *name, int64_t delta,
      dmu_tx_t *tx)
  {
          uint64_t value = 0;
  
          if (delta == 0)
                  return (0);
  
          int err = zap_lookup(os, obj, name, 8, 1, &value);
          if (err != 0 && err != ENOENT)
                  return (err);
          value += delta;
          if (value == 0)
                  err = zap_remove(os, obj, name, tx);
          else
                  err = zap_update(os, obj, name, 8, 1, &value, tx);
          return (err);
  }
  
  int
  zap_increment_int(objset_t *os, uint64_t obj, uint64_t key, int64_t delta,
      dmu_tx_t *tx)
  {
          char name[20];
  
          (void) snprintf(name, sizeof (name), "%llx", (longlong_t)key);
          return (zap_increment(os, obj, name, delta, tx));
  }
  
  /*
   * Routines for iterating over the attributes.
   */
  
  int
  fzap_cursor_retrieve(zap_t *zap, zap_cursor_t *zc, zap_attribute_t *za)
  {
          int err = ENOENT;
          zap_entry_handle_t zeh;
          zap_leaf_t *l;
  
          /* retrieve the next entry at or after zc_hash/zc_cd */
          /* if no entry, return ENOENT */
  
          /*
           * If we are reading from the beginning, we're almost certain to
           * iterate over the entire ZAP object.  If there are multiple leaf
           * blocks (freeblk > 2), prefetch the whole object (up to
           * dmu_prefetch_max bytes), so that we read the leaf blocks
           * concurrently. (Unless noprefetch was requested via
           * zap_cursor_init_noprefetch()).
           */
          if (zc->zc_hash == 0 && zap_iterate_prefetch &&
              zc->zc_prefetch && zap_f_phys(zap)->zap_freeblk > 2) {
                  dmu_prefetch(zc->zc_objset, zc->zc_zapobj, 0, 0,
                      zap_f_phys(zap)->zap_freeblk << FZAP_BLOCK_SHIFT(zap),
                      ZIO_PRIORITY_ASYNC_READ);
          }
  
          if (zc->zc_leaf &&
              (ZAP_HASH_IDX(zc->zc_hash,
              zap_leaf_phys(zc->zc_leaf)->l_hdr.lh_prefix_len) !=
              zap_leaf_phys(zc->zc_leaf)->l_hdr.lh_prefix)) {
                  rw_enter(&zc->zc_leaf->l_rwlock, RW_READER);
                  zap_put_leaf(zc->zc_leaf);
                  zc->zc_leaf = NULL;
          }
  
  again:
          if (zc->zc_leaf == NULL) {
                  err = zap_deref_leaf(zap, zc->zc_hash, NULL, RW_READER,
                      &zc->zc_leaf);
                  if (err != 0)
                          return (err);
          } else {
                  rw_enter(&zc->zc_leaf->l_rwlock, RW_READER);
          }
          l = zc->zc_leaf;
  
          err = zap_leaf_lookup_closest(l, zc->zc_hash, zc->zc_cd, &zeh);
  
          if (err == ENOENT) {
                  if (zap_leaf_phys(l)->l_hdr.lh_prefix_len == 0) {
                          zc->zc_hash = -1ULL;
                          zc->zc_cd = 0;
                  } else {
                          uint64_t nocare = (1ULL <<
                              (64 - zap_leaf_phys(l)->l_hdr.lh_prefix_len)) - 1;
  
                          zc->zc_hash = (zc->zc_hash & ~nocare) + nocare + 1;
                          zc->zc_cd = 0;
  
                          if (zc->zc_hash == 0) {
                                  zc->zc_hash = -1ULL;
                          } else {
                                  zap_put_leaf(zc->zc_leaf);
                                  zc->zc_leaf = NULL;
                                  goto again;
                          }
                  }
          }
  
          if (err == 0) {
                  zc->zc_hash = zeh.zeh_hash;
                  zc->zc_cd = zeh.zeh_cd;
                  za->za_integer_length = zeh.zeh_integer_size;
                  za->za_num_integers = zeh.zeh_num_integers;
                  if (zeh.zeh_num_integers == 0) {
                          za->za_first_integer = 0;
                  } else {
                          err = zap_entry_read(&zeh, 8, 1, &za->za_first_integer);
                          ASSERT(err == 0 || err == EOVERFLOW);
                  }
                  err = zap_entry_read_name(zap, &zeh,
                      sizeof (za->za_name), za->za_name);
                  ASSERT(err == 0);
  
                  za->za_normalization_conflict =
                      zap_entry_normalization_conflict(&zeh,
                      NULL, za->za_name, zap);
          }
          rw_exit(&zc->zc_leaf->l_rwlock);
          return (err);
  }
  
  static void
  zap_stats_ptrtbl(zap_t *zap, uint64_t *tbl, int len, zap_stats_t *zs)
  {
          uint64_t lastblk = 0;
  
          /*
           * NB: if a leaf has more pointers than an entire ptrtbl block
           * can hold, then it'll be accounted for more than once, since
           * we won't have lastblk.
           */
          for (int i = 0; i < len; i++) {
                  zap_leaf_t *l;
  
                  if (tbl[i] == lastblk)
                          continue;
                  lastblk = tbl[i];
  
                  int err = zap_get_leaf_byblk(zap, tbl[i], NULL, RW_READER, &l);
                  if (err == 0) {
                          zap_leaf_stats(zap, l, zs);
                          zap_put_leaf(l);
                  }
          }
  }
  
  void
  fzap_get_stats(zap_t *zap, zap_stats_t *zs)
  {
          int bs = FZAP_BLOCK_SHIFT(zap);
          zs->zs_blocksize = 1ULL << bs;
  
          /*
           * Set zap_phys_t fields
           */
          zs->zs_num_leafs = zap_f_phys(zap)->zap_num_leafs;
          zs->zs_num_entries = zap_f_phys(zap)->zap_num_entries;
          zs->zs_num_blocks = zap_f_phys(zap)->zap_freeblk;
          zs->zs_block_type = zap_f_phys(zap)->zap_block_type;
          zs->zs_magic = zap_f_phys(zap)->zap_magic;
          zs->zs_salt = zap_f_phys(zap)->zap_salt;
  
          /*
           * Set zap_ptrtbl fields
           */
          zs->zs_ptrtbl_len = 1ULL << zap_f_phys(zap)->zap_ptrtbl.zt_shift;
          zs->zs_ptrtbl_nextblk = zap_f_phys(zap)->zap_ptrtbl.zt_nextblk;
          zs->zs_ptrtbl_blks_copied =
              zap_f_phys(zap)->zap_ptrtbl.zt_blks_copied;
          zs->zs_ptrtbl_zt_blk = zap_f_phys(zap)->zap_ptrtbl.zt_blk;
          zs->zs_ptrtbl_zt_numblks = zap_f_phys(zap)->zap_ptrtbl.zt_numblks;
          zs->zs_ptrtbl_zt_shift = zap_f_phys(zap)->zap_ptrtbl.zt_shift;
  
          if (zap_f_phys(zap)->zap_ptrtbl.zt_numblks == 0) {
                  /* the ptrtbl is entirely in the header block. */
                  zap_stats_ptrtbl(zap, &ZAP_EMBEDDED_PTRTBL_ENT(zap, 0),
                      1 << ZAP_EMBEDDED_PTRTBL_SHIFT(zap), zs);
          } else {
                  dmu_prefetch(zap->zap_objset, zap->zap_object, 0,
                      zap_f_phys(zap)->zap_ptrtbl.zt_blk << bs,
                      zap_f_phys(zap)->zap_ptrtbl.zt_numblks << bs,
                      ZIO_PRIORITY_SYNC_READ);
  
                  for (int b = 0; b < zap_f_phys(zap)->zap_ptrtbl.zt_numblks;
                      b++) {
                          dmu_buf_t *db;
                          int err;
  
                          err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
                              (zap_f_phys(zap)->zap_ptrtbl.zt_blk + b) << bs,
                              FTAG, &db, DMU_READ_NO_PREFETCH);
                          if (err == 0) {
                                  zap_stats_ptrtbl(zap, db->db_data,
                                      1<<(bs-3), zs);
                                  dmu_buf_rele(db, FTAG);
                          }
                  }
          }
  }
  
  /* CSTYLED */
  ZFS_MODULE_PARAM(zfs, , zap_iterate_prefetch, INT, ZMOD_RW,
          "When iterating ZAP object, prefetch it");

Cache object: eaa87cf4eb1e87193d81869b75ea4dcd