fs/zfs/zap.c

	zap.c revision 87e5029a3226958edab1512d6182bc74d8d80c9a
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2005 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"


/*
 * 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/zap.h>
#include <sys/zap_impl.h>
#include <sys/zap_leaf.h>

#define MIN_FREE (ZAP_LEAF_NUMCHUNKS*9/10)

static void zap_grow_ptrtbl(zap_t *zap, dmu_tx_t *tx);
static int zap_tryupgradedir(zap_t *zap, dmu_tx_t *tx);
static zap_leaf_t *zap_get_leaf_byblk(zap_t *zap, uint64_t blkid,
    dmu_tx_t *tx, krw_t lt);
static void zap_leaf_pageout(dmu_buf_t *db, void *vl);


void
fzap_byteswap(void *vbuf, size_t size)
{
    uint64_t block_type;

    ASSERT(size == (1<<ZAP_BLOCK_SHIFT));
    block_type = *(uint64_t *)vbuf;

    switch (block_type) {
    case ZBT_LEAF:
    case BSWAP_64(ZBT_LEAF):
        zap_leaf_byteswap(vbuf);
        return;
    case ZBT_HEADER:
    case BSWAP_64(ZBT_HEADER):
    default:
        /* it's a ptrtbl block */
        byteswap_uint64_array(vbuf, 1<<ZAP_BLOCK_SHIFT);
        return;
    }
}

void
fzap_upgrade(zap_t *zap, dmu_tx_t *tx)
{
    dmu_buf_t *db;
    zap_leaf_t *l;
    int i;
    zap_phys_t *zp;

    ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
    zap->zap_ismicro = FALSE;

    (void) dmu_buf_update_user(zap->zap_dbuf, zap, zap,
        &zap->zap_f.zap_phys, zap_pageout);

    mutex_init(&zap->zap_f.zap_num_entries_mtx, 0, 0, 0);

    zp = zap->zap_f.zap_phys;
    /*
     * explicitly zero it since it might be coming from an
     * initialized microzap
     */
    ASSERT3U(sizeof (zap_phys_t), ==, zap->zap_dbuf->db_size);
    bzero(zp, sizeof (zap_phys_t));
    zp->zap_block_type = ZBT_HEADER;
    zp->zap_magic = ZAP_MAGIC;

    zp->zap_ptrtbl.zt_shift = ZAP_PTRTBL_MIN_SHIFT;

    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;

    for (i = 0; i < (1<<ZAP_PTRTBL_MIN_SHIFT); i++)
        zp->zap_leafs[i] = 1;   /* block 1 will be the first leaf */

    /*
     * set up block 1 - the first leaf
     */
    db = dmu_buf_hold(zap->zap_objset, zap->zap_object,
        1<<ZAP_BLOCK_SHIFT);
    dmu_buf_will_dirty(db, tx);

    l = kmem_zalloc(sizeof (zap_leaf_t), KM_SLEEP);
    l->l_dbuf = db;
    l->l_phys = db->db_data;

    zap_leaf_init(l);

    kmem_free(l, sizeof (zap_leaf_t));
    dmu_buf_rele(db);
}

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 void
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 b, newblk;
    dmu_buf_t *db_old, *db_new;
    int hepb = 1<<(ZAP_BLOCK_SHIFT-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, tx);
        tbl->zt_nextblk = newblk;
        ASSERT3U(tbl->zt_blks_copied, ==, 0);
        dmu_prefetch(zap->zap_objset, zap->zap_object,
            tbl->zt_blk << ZAP_BLOCK_SHIFT, tbl->zt_numblks <<
            ZAP_BLOCK_SHIFT);
    }

    /*
     * Copy the ptrtbl from the old to new location, leaving the odd
     * entries blank as we go.
     */

    b = tbl->zt_blks_copied;
    db_old = dmu_buf_hold(zap->zap_objset, zap->zap_object,
        (tbl->zt_blk + b) << ZAP_BLOCK_SHIFT);
    dmu_buf_read(db_old);

    /* first half of entries in old[b] go to new[2*b+0] */
    db_new = dmu_buf_hold(zap->zap_objset, zap->zap_object,
        (newblk + 2*b+0) << ZAP_BLOCK_SHIFT);
    dmu_buf_will_dirty(db_new, tx);
    transfer_func(db_old->db_data, db_new->db_data, hepb);
    dmu_buf_rele(db_new);

    /* second half of entries in old[b] go to new[2*b+1] */
    db_new = dmu_buf_hold(zap->zap_objset, zap->zap_object,
        (newblk + 2*b+1) << ZAP_BLOCK_SHIFT);
    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);

    dmu_buf_rele(db_old);

    tbl->zt_blks_copied++;

    dprintf("copied block %llu of %llu\n",
        tbl->zt_blks_copied, tbl->zt_numblks);

    if (tbl->zt_blks_copied == tbl->zt_numblks) {
        dmu_free_range(zap->zap_objset, zap->zap_object,
            tbl->zt_blk << ZAP_BLOCK_SHIFT,
            tbl->zt_numblks << ZAP_BLOCK_SHIFT, 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 (%lluk entries)\n",
            tbl->zt_numblks, 1<<(tbl->zt_shift-10));
    }
}

static uint64_t
zap_table_store(zap_t *zap, zap_table_phys_t *tbl, uint64_t idx, uint64_t val,
    dmu_tx_t *tx)
{
    uint64_t blk, off, oldval;
    dmu_buf_t *db;

    ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    ASSERT(tbl->zt_blk != 0);

    dprintf("storing %llx at index %llx\n", val, idx);

    blk = idx >> (ZAP_BLOCK_SHIFT-3);
    off = idx & ((1<<(ZAP_BLOCK_SHIFT-3))-1);

    db = dmu_buf_hold(zap->zap_objset, zap->zap_object,
        (tbl->zt_blk + blk) << ZAP_BLOCK_SHIFT);
    dmu_buf_will_dirty(db, tx);
    oldval = ((uint64_t *)db->db_data)[off];
    ((uint64_t *)db->db_data)[off] = val;
    dmu_buf_rele(db);

    if (tbl->zt_nextblk != 0) {
        idx *= 2;
        blk = idx >> (ZAP_BLOCK_SHIFT-3);
        off = idx & ((1<<(ZAP_BLOCK_SHIFT-3))-1);

        db = dmu_buf_hold(zap->zap_objset, zap->zap_object,
            (tbl->zt_nextblk + blk) << ZAP_BLOCK_SHIFT);
        dmu_buf_will_dirty(db, tx);
        ((uint64_t *)db->db_data)[off] = val;
        ((uint64_t *)db->db_data)[off+1] = val;
        dmu_buf_rele(db);
    }

    return (oldval);
}

static uint64_t
zap_table_load(zap_t *zap, zap_table_phys_t *tbl, uint64_t idx)
{
    uint64_t blk, off, val;
    dmu_buf_t *db;

    ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));

    blk = idx >> (ZAP_BLOCK_SHIFT-3);
    off = idx & ((1<<(ZAP_BLOCK_SHIFT-3))-1);

    db = dmu_buf_hold(zap->zap_objset, zap->zap_object,
        (tbl->zt_blk + blk) << ZAP_BLOCK_SHIFT);
    dmu_buf_read(db);
    val = ((uint64_t *)db->db_data)[off];
    dmu_buf_rele(db);
    return (val);
}

/*
 * Routines for growing the ptrtbl.
 */

static void
zap_ptrtbl_transfer(const uint64_t *src, uint64_t *dst, int n)
{
    int i;
    for (i = 0; i < n; i++) {
        uint64_t lb = src[i];
        dst[2*i+0] = lb;
        dst[2*i+1] = lb;
    }
}

static void
zap_grow_ptrtbl(zap_t *zap, dmu_tx_t *tx)
{
    if (zap->zap_f.zap_phys->zap_ptrtbl.zt_shift == 32)
        return;

    if (zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks == 0) {
        /*
         * The ptrtbl can no longer be contained in the
         * header block.  Give it its own entire block, which
         * will quadruple the size of the ptrtbl.
         */
        uint64_t newblk;
        dmu_buf_t *db_new;

        ASSERT3U(zap->zap_f.zap_phys->zap_ptrtbl.zt_shift, ==,
            ZAP_PTRTBL_MIN_SHIFT);
        ASSERT3U(zap->zap_f.zap_phys->zap_ptrtbl.zt_blk, ==, 0);

        newblk = zap_allocate_blocks(zap, 1, tx);
        db_new = dmu_buf_hold(zap->zap_objset, zap->zap_object,
            newblk << ZAP_BLOCK_SHIFT);

        dmu_buf_will_dirty(db_new, tx);
        zap_ptrtbl_transfer(zap->zap_f.zap_phys->zap_leafs,
            db_new->db_data, 1 << ZAP_PTRTBL_MIN_SHIFT);
        dmu_buf_rele(db_new);

        zap->zap_f.zap_phys->zap_ptrtbl.zt_blk = newblk;
        zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks = 1;
        zap->zap_f.zap_phys->zap_ptrtbl.zt_shift++;

        ASSERT3U(1ULL << zap->zap_f.zap_phys->zap_ptrtbl.zt_shift, ==,
            zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks <<
            (ZAP_BLOCK_SHIFT-3));
    } else {
        zap_table_grow(zap, &zap->zap_f.zap_phys->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->zap_f.zap_phys->zap_num_entries >= -delta);

    zap->zap_f.zap_phys->zap_num_entries += delta;

    mutex_exit(&zap->zap_f.zap_num_entries_mtx);
}

uint64_t
zap_allocate_blocks(zap_t *zap, int nblocks, dmu_tx_t *tx)
{
    uint64_t newblk;
    ASSERT(tx != NULL);
    if (!RW_WRITE_HELD(&zap->zap_rwlock)) {
        dmu_buf_will_dirty(zap->zap_dbuf, tx);
    }
    newblk = atomic_add_64_nv(&zap->zap_f.zap_phys->zap_freeblk, nblocks) -
        nblocks;
    return (newblk);
}


/*
 * This function doesn't increment zap_num_leafs because it's used to
 * allocate a leaf chain, which doesn't count against zap_num_leafs.
 * The directory must be held exclusively for this tx.
 */
zap_leaf_t *
zap_create_leaf(zap_t *zap, dmu_tx_t *tx)
{
    void *winner;
    zap_leaf_t *l = kmem_alloc(sizeof (zap_leaf_t), KM_SLEEP);

    ASSERT(tx != NULL);
    ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));
    /* hence we already dirtied zap->zap_dbuf */

    rw_init(&l->l_rwlock, 0, 0, 0);
    rw_enter(&l->l_rwlock, RW_WRITER);
    l->l_blkid = zap_allocate_blocks(zap, 1, tx);
    l->l_next = NULL;
    l->l_dbuf = NULL;
    l->l_phys = NULL;

    l->l_dbuf = dmu_buf_hold(zap->zap_objset, zap->zap_object,
        l->l_blkid << ZAP_BLOCK_SHIFT);
    winner = dmu_buf_set_user(l->l_dbuf, l, &l->l_phys, zap_leaf_pageout);
    ASSERT(winner == NULL);
    dmu_buf_will_dirty(l->l_dbuf, tx);

    zap_leaf_init(l);

    return (l);
}

/* ARGSUSED */
void
zap_destroy_leaf(zap_t *zap, zap_leaf_t *l, dmu_tx_t *tx)
{
    /* uint64_t offset = l->l_blkid << ZAP_BLOCK_SHIFT; */
    rw_exit(&l->l_rwlock);
    dmu_buf_rele(l->l_dbuf);
    /* XXX there are still holds on this block, so we can't free it? */
    /* dmu_free_range(zap->zap_objset, zap->zap_object, */
        /* offset,  1<<ZAP_BLOCK_SHIFT, tx); */
}

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->zap_f.zap_phys->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)
{
    zap_leaf_t *nl = l->l_next;
    while (nl) {
        zap_leaf_t *nnl = nl->l_next;
        rw_exit(&nl->l_rwlock);
        dmu_buf_rele(nl->l_dbuf);
        nl = nnl;
    }
    rw_exit(&l->l_rwlock);
    dmu_buf_rele(l->l_dbuf);
}

_NOTE(ARGSUSED(0))
static void
zap_leaf_pageout(dmu_buf_t *db, void *vl)
{
    zap_leaf_t *l = vl;

    rw_destroy(&l->l_rwlock);
    kmem_free(l, sizeof (zap_leaf_t));
}

static zap_leaf_t *
zap_open_leaf(uint64_t blkid, dmu_buf_t *db)
{
    zap_leaf_t *l, *winner;

    ASSERT(blkid != 0);

    l = kmem_alloc(sizeof (zap_leaf_t), KM_SLEEP);
    rw_init(&l->l_rwlock, 0, 0, 0);
    rw_enter(&l->l_rwlock, RW_WRITER);
    l->l_blkid = blkid;
    l->l_next = NULL;
    l->l_dbuf = db;
    l->l_phys = NULL;

    winner = dmu_buf_set_user(db, l, &l->l_phys, zap_leaf_pageout);

    rw_exit(&l->l_rwlock);
    if (winner != NULL) {
        /* someone else set it first */
        zap_leaf_pageout(NULL, l);
        l = winner;
    }

    return (l);
}

static zap_leaf_t *
zap_get_leaf_byblk_impl(zap_t *zap, uint64_t blkid, dmu_tx_t *tx, krw_t lt)
{
    dmu_buf_t *db;
    zap_leaf_t *l;

    ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));

    db = dmu_buf_hold(zap->zap_objset, zap->zap_object,
        blkid << ZAP_BLOCK_SHIFT);

    ASSERT3U(db->db_object, ==, zap->zap_object);
    ASSERT3U(db->db_offset, ==, blkid << ZAP_BLOCK_SHIFT);
    ASSERT3U(db->db_size, ==, 1 << ZAP_BLOCK_SHIFT);
    ASSERT(blkid != 0);

    dmu_buf_read(db);
    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 l->l_phys 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);
    ASSERT3P(l->l_phys, ==, l->l_dbuf->db_data);
    ASSERT3U(l->lh_block_type, ==, ZBT_LEAF);
    ASSERT3U(l->lh_magic, ==, ZAP_LEAF_MAGIC);

    return (l);
}

static zap_leaf_t *
zap_get_leaf_byblk(zap_t *zap, uint64_t blkid, dmu_tx_t *tx, krw_t lt)
{
    zap_leaf_t *l, *nl;

    l = zap_get_leaf_byblk_impl(zap, blkid, tx, lt);

    nl = l;
    while (nl->lh_next != 0) {
        zap_leaf_t *nnl;
        nnl = zap_get_leaf_byblk_impl(zap, nl->lh_next, tx, lt);
        nl->l_next = nnl;
        nl = nnl;
    }

    return (l);
}

static uint64_t
zap_idx_to_blk(zap_t *zap, uint64_t idx)
{
    ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));

    if (zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks == 0) {
        ASSERT3U(idx, <,
            (1ULL << zap->zap_f.zap_phys->zap_ptrtbl.zt_shift));
        return (zap->zap_f.zap_phys->zap_leafs[idx]);
    } else {
        return (zap_table_load(zap, &zap->zap_f.zap_phys->zap_ptrtbl,
            idx));
    }
}

static void
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->zap_f.zap_phys->zap_ptrtbl.zt_blk == 0) {
        zap->zap_f.zap_phys->zap_leafs[idx] = blk;
    } else {
        (void) zap_table_store(zap, &zap->zap_f.zap_phys->zap_ptrtbl,
            idx, blk, tx);
    }
}

static zap_leaf_t *
zap_deref_leaf(zap_t *zap, uint64_t h, dmu_tx_t *tx, krw_t lt)
{
    uint64_t idx;
    zap_leaf_t *l;

    ASSERT(zap->zap_dbuf == NULL ||
        zap->zap_f.zap_phys == zap->zap_dbuf->db_data);
    ASSERT3U(zap->zap_f.zap_phys->zap_magic, ==, ZAP_MAGIC);
    idx = ZAP_HASH_IDX(h, zap->zap_f.zap_phys->zap_ptrtbl.zt_shift);
    l = zap_get_leaf_byblk(zap, zap_idx_to_blk(zap, idx), tx, lt);

    ASSERT3U(ZAP_HASH_IDX(h, l->lh_prefix_len), ==, l->lh_prefix);

    return (l);
}


static zap_leaf_t *
zap_expand_leaf(zap_t *zap, zap_leaf_t *l, uint64_t hash, dmu_tx_t *tx)
{
    zap_leaf_t *nl;
    int prefix_diff, i, err;
    uint64_t sibling;

    ASSERT3U(l->lh_prefix_len, <=,
        zap->zap_f.zap_phys->zap_ptrtbl.zt_shift);
    ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));

    ASSERT3U(ZAP_HASH_IDX(hash, l->lh_prefix_len), ==, l->lh_prefix);

    if (zap_tryupgradedir(zap, tx) == 0) {
        /* failed to upgrade */
        int old_prefix_len = l->lh_prefix_len;
        objset_t *os = zap->zap_objset;
        uint64_t object = zap->zap_object;

        zap_put_leaf(l);
        zap_unlockdir(zap);
        err = zap_lockdir(os, object, tx, RW_WRITER, FALSE, &zap);
        ASSERT3U(err, ==, 0);
        ASSERT(!zap->zap_ismicro);
        l = zap_deref_leaf(zap, hash, tx, RW_WRITER);

        if (l->lh_prefix_len != old_prefix_len)
            /* it split while our locks were down */
            return (l);
    }
    ASSERT(RW_WRITE_HELD(&zap->zap_rwlock));

    if (l->lh_prefix_len == zap->zap_f.zap_phys->zap_ptrtbl.zt_shift) {
        /* There's only one pointer to us. Chain on another leaf blk. */
        (void) zap_leaf_chainmore(l, zap_create_leaf(zap, tx));
        dprintf("chaining leaf %x/%d\n", l->lh_prefix,
            l->lh_prefix_len);
        return (l);
    }

    ASSERT3U(ZAP_HASH_IDX(hash, l->lh_prefix_len), ==, l->lh_prefix);

    /* There's more than one pointer to us. Split this leaf. */
    nl = zap_leaf_split(zap, l, tx);

    /* set sibling pointers */
    prefix_diff =
        zap->zap_f.zap_phys->zap_ptrtbl.zt_shift - l->lh_prefix_len;
    sibling = (ZAP_HASH_IDX(hash, l->lh_prefix_len) | 1) << prefix_diff;
    for (i = 0; i < (1ULL<<prefix_diff); i++) {
        ASSERT3U(zap_idx_to_blk(zap, sibling+i), ==, l->l_blkid);
        zap_set_idx_to_blk(zap, sibling+i, nl->l_blkid, tx);
        /* dprintf("set %d to %u %x\n", sibling+i, nl->l_blkid, nl); */
    }

    zap->zap_f.zap_phys->zap_num_leafs++;

    if (hash & (1ULL << (64 - l->lh_prefix_len))) {
        /* we want the sibling */
        zap_put_leaf(l);
        l = nl;
    } else {
        zap_put_leaf(nl);
    }

    return (l);
}

static void
zap_put_leaf_maybe_grow_ptrtbl(zap_t *zap,
    zap_leaf_t *l, dmu_tx_t *tx)
{
    int shift, err;

again:
    shift = zap->zap_f.zap_phys->zap_ptrtbl.zt_shift;

    if (l->lh_prefix_len == shift &&
        (l->l_next != NULL || l->lh_nfree < MIN_FREE)) {
        /* this leaf will soon make us grow the pointer table */

        if (zap_tryupgradedir(zap, tx) == 0) {
            objset_t *os = zap->zap_objset;
            uint64_t zapobj = zap->zap_object;
            uint64_t blkid = l->l_blkid;

            zap_put_leaf(l);
            zap_unlockdir(zap);
            err = zap_lockdir(os, zapobj, tx,
                RW_WRITER, FALSE, &zap);
            ASSERT3U(err, ==, 0);
            l = zap_get_leaf_byblk(zap, blkid, tx, RW_READER);
            goto again;
        }

        zap_put_leaf(l);
        zap_grow_ptrtbl(zap, tx);
    } else {
        zap_put_leaf(l);
    }
}


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 (EINVAL);
    }

    /* Make sure we won't overflow */
    if (integer_size * num_integers < num_integers)
        return (EINVAL);
    if (integer_size * num_integers > DMU_MAX_ACCESS)
        return (EINVAL);

    return (0);
}

/*
 * Routines for maniplulating attributes.
 */
int
fzap_lookup(zap_t *zap, const char *name,
    uint64_t integer_size, uint64_t num_integers, void *buf)
{
    zap_leaf_t *l;
    int err;
    uint64_t hash;
    zap_entry_handle_t zeh;

    err = fzap_checksize(integer_size, num_integers);
    if (err != 0)
        return (err);

    hash = zap_hash(zap, name);
    l = zap_deref_leaf(zap, hash, NULL, RW_READER);
    err = zap_leaf_lookup(l, name, hash, &zeh);
    if (err != 0)
        goto out;
    err = zap_entry_read(&zeh, integer_size, num_integers, buf);
out:
    zap_put_leaf(l);
    return (err);
}

int
fzap_add_cd(zap_t *zap, const char *name,
    uint64_t integer_size, uint64_t num_integers,
    const void *val, uint32_t cd, dmu_tx_t *tx, zap_leaf_t **lp)
{
    zap_leaf_t *l;
    uint64_t hash;
    int err;
    zap_entry_handle_t zeh;

    ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    ASSERT(!zap->zap_ismicro);
    ASSERT(fzap_checksize(integer_size, num_integers) == 0);

    hash = zap_hash(zap, name);
    l = zap_deref_leaf(zap, hash, tx, RW_WRITER);
retry:
    err = zap_leaf_lookup(l, name, hash, &zeh);
    if (err == 0) {
        err = EEXIST;
        goto out;
    }
    ASSERT(err == ENOENT);

    /* XXX If this leaf is chained, split it if we can. */
    err = zap_entry_create(l, name, hash, cd,
        integer_size, num_integers, val, &zeh);

    if (err == 0) {
        zap_increment_num_entries(zap, 1, tx);
    } else if (err == EAGAIN) {
        l = zap_expand_leaf(zap, l, hash, tx);
        goto retry;
    }

out:
    if (lp)
        *lp = l;
    else
        zap_put_leaf(l);
    return (err);
}

int
fzap_add(zap_t *zap, const char *name,
    uint64_t integer_size, uint64_t num_integers,
    const void *val, dmu_tx_t *tx)
{
    int err;
    zap_leaf_t *l;

    err = fzap_checksize(integer_size, num_integers);
    if (err != 0)
        return (err);

    err = fzap_add_cd(zap, name, integer_size, num_integers,
        val, ZAP_MAXCD, tx, &l);

    zap_put_leaf_maybe_grow_ptrtbl(zap, l, tx);
    return (err);
}

int
fzap_update(zap_t *zap, const char *name,
    int integer_size, uint64_t num_integers, const void *val, dmu_tx_t *tx)
{
    zap_leaf_t *l;
    uint64_t hash;
    int err, create;
    zap_entry_handle_t zeh;

    ASSERT(RW_LOCK_HELD(&zap->zap_rwlock));
    err = fzap_checksize(integer_size, num_integers);
    if (err != 0)
        return (err);

    hash = zap_hash(zap, name);
    l = zap_deref_leaf(zap, hash, tx, RW_WRITER);
retry:
    err = zap_leaf_lookup(l, name, hash, &zeh);
    create = (err == ENOENT);
    ASSERT(err == 0 || err == ENOENT);

    /* XXX If this leaf is chained, split it if we can. */

    if (create) {
        err = zap_entry_create(l, name, hash, ZAP_MAXCD,
            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) {
        l = zap_expand_leaf(zap, l, hash, tx);
        goto retry;
    }

    zap_put_leaf_maybe_grow_ptrtbl(zap, l, tx);
    return (err);
}

int
fzap_length(zap_t *zap, const char *name,
    uint64_t *integer_size, uint64_t *num_integers)
{
    zap_leaf_t *l;
    int err;
    uint64_t hash;
    zap_entry_handle_t zeh;

    hash = zap_hash(zap, name);
    l = zap_deref_leaf(zap, hash, NULL, RW_READER);
    err = zap_leaf_lookup(l, name, hash, &zeh);
    if (err != 0)
        goto out;

    if (integer_size)
        *integer_size = zeh.zeh_integer_size;
    if (num_integers)
        *num_integers = zeh.zeh_num_integers;
out:
    zap_put_leaf(l);
    return (err);
}

int
fzap_remove(zap_t *zap, const char *name, dmu_tx_t *tx)
{
    zap_leaf_t *l;
    uint64_t hash;
    int err;
    zap_entry_handle_t zeh;

    hash = zap_hash(zap, name);
    l = zap_deref_leaf(zap, hash, tx, RW_WRITER);
    err = zap_leaf_lookup(l, name, hash, &zeh);
    if (err == 0) {
        zap_entry_remove(&zeh);
        zap_increment_num_entries(zap, -1, tx);
    }
    zap_put_leaf(l);
    dprintf("fzap_remove: ds=%p obj=%llu name=%s err=%d\n",
        zap->zap_objset, zap->zap_object, name, err);
    return (err);
}

int
zap_value_search(objset_t *os, uint64_t zapobj, uint64_t value, char *name)
{
    zap_cursor_t zc;
    zap_attribute_t *za;
    int err;

    za = kmem_alloc(sizeof (zap_attribute_t), 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 == value) {
            (void) strcpy(name, za->za_name);
            break;
        }
    }
    zap_cursor_fini(&zc);
    kmem_free(za, sizeof (zap_attribute_t));
    return (err);
}


/*
 * 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 (zc->zc_leaf &&
        (ZAP_HASH_IDX(zc->zc_hash, zc->zc_leaf->lh_prefix_len) !=
        zc->zc_leaf->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) {
        zc->zc_leaf = zap_deref_leaf(zap, zc->zc_hash, NULL, RW_READER);
    } 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) {
        uint64_t nocare = (1ULL << (64 - l->lh_prefix_len)) - 1;
        zc->zc_hash = (zc->zc_hash & ~nocare) + nocare + 1;
        zc->zc_cd = 0;
        if (l->lh_prefix_len == 0 || 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(&zeh,
            sizeof (za->za_name), za->za_name);
        ASSERT(err == 0);
    }
    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)
{
    int i;
    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 (i = 0; i < len; i++) {
        zap_leaf_t *l;

        if (tbl[i] == lastblk)
            continue;
        lastblk = tbl[i];

        l = zap_get_leaf_byblk(zap, tbl[i], NULL, RW_READER);

        zap_stats_leaf(zap, l, zs);
        zap_put_leaf(l);
    }
}

void
fzap_get_stats(zap_t *zap, zap_stats_t *zs)
{
    zs->zs_ptrtbl_len = 1ULL << zap->zap_f.zap_phys->zap_ptrtbl.zt_shift;
    zs->zs_blocksize = 1ULL << ZAP_BLOCK_SHIFT;
    zs->zs_num_leafs = zap->zap_f.zap_phys->zap_num_leafs;
    zs->zs_num_entries = zap->zap_f.zap_phys->zap_num_entries;
    zs->zs_num_blocks = zap->zap_f.zap_phys->zap_freeblk;

    if (zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks == 0) {
        /* the ptrtbl is entirely in the header block. */
        zap_stats_ptrtbl(zap, zap->zap_f.zap_phys->zap_leafs,
            1 << ZAP_PTRTBL_MIN_SHIFT, zs);
    } else {
        int b;

        dmu_prefetch(zap->zap_objset, zap->zap_object,
            zap->zap_f.zap_phys->zap_ptrtbl.zt_blk << ZAP_BLOCK_SHIFT,
            zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks <<
            ZAP_BLOCK_SHIFT);

        for (b = 0; b < zap->zap_f.zap_phys->zap_ptrtbl.zt_numblks;
            b++) {
            dmu_buf_t *db;

            db = dmu_buf_hold(zap->zap_objset, zap->zap_object,
                (zap->zap_f.zap_phys->zap_ptrtbl.zt_blk + b) <<
                ZAP_BLOCK_SHIFT);
            dmu_buf_read(db);
            zap_stats_ptrtbl(zap, db->db_data,
                1<<(ZAP_BLOCK_SHIFT-3), zs);
            dmu_buf_rele(db);
        }
    }
}