fs/zfs/dsl_scan.c

	dsl_scan.c revision 3f9d6ad73e45c6823b409f93b0c8d4f62861d2d5
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
 */

#include <sys/dsl_scan.h>
#include <sys/dsl_pool.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_prop.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_synctask.h>
#include <sys/dnode.h>
#include <sys/dmu_tx.h>
#include <sys/dmu_objset.h>
#include <sys/arc.h>
#include <sys/zap.h>
#include <sys/zio.h>
#include <sys/zfs_context.h>
#include <sys/fs/zfs.h>
#include <sys/zfs_znode.h>
#include <sys/spa_impl.h>
#include <sys/vdev_impl.h>
#include <sys/zil_impl.h>
#include <sys/zio_checksum.h>
#include <sys/ddt.h>
#include <sys/sa.h>
#include <sys/sa_impl.h>
#ifdef _KERNEL
#include <sys/zfs_vfsops.h>
#endif

typedef int (scan_cb_t)(dsl_pool_t *, const blkptr_t *, const zbookmark_t *);

static scan_cb_t dsl_scan_defrag_cb;
static scan_cb_t dsl_scan_scrub_cb;
static scan_cb_t dsl_scan_remove_cb;
static dsl_syncfunc_t dsl_scan_cancel_sync;
static void dsl_scan_sync_state(dsl_scan_t *, dmu_tx_t *tx);

int zfs_scan_min_time_ms = 1000; /* min millisecs to scrub per txg */
int zfs_resilver_min_time_ms = 3000; /* min millisecs to resilver per txg */
boolean_t zfs_no_scrub_io = B_FALSE; /* set to disable scrub i/o */
boolean_t zfs_no_scrub_prefetch = B_FALSE; /* set to disable srub prefetching */
enum ddt_class zfs_scrub_ddt_class_max = DDT_CLASS_DUPLICATE;
int dsl_scan_delay_completion = B_FALSE; /* set to delay scan completion */

#define DSL_SCAN_IS_SCRUB_RESILVER(scn) \
    ((scn)->scn_phys.scn_func == POOL_SCAN_SCRUB || \
    (scn)->scn_phys.scn_func == POOL_SCAN_RESILVER)

extern int zfs_txg_timeout;

/* the order has to match pool_scan_type */
static scan_cb_t *scan_funcs[POOL_SCAN_FUNCS] = {
    NULL,
    dsl_scan_scrub_cb,  /* POOL_SCAN_SCRUB */
    dsl_scan_scrub_cb,  /* POOL_SCAN_RESILVER */
};

int
dsl_scan_init(dsl_pool_t *dp, uint64_t txg)
{
    int err;
    dsl_scan_t *scn;
    spa_t *spa = dp->dp_spa;
    uint64_t f;

    scn = dp->dp_scan = kmem_zalloc(sizeof (dsl_scan_t), KM_SLEEP);
    scn->scn_dp = dp;

    err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
        "scrub_func", sizeof (uint64_t), 1, &f);
    if (err == 0) {
        /*
         * There was an old-style scrub in progress.  Restart a
         * new-style scrub from the beginning.
         */
        scn->scn_restart_txg = txg;
        zfs_dbgmsg("old-style scrub was in progress; "
            "restarting new-style scrub in txg %llu",
            scn->scn_restart_txg);

        /*
         * Load the queue obj from the old location so that it
         * can be freed by dsl_scan_done().
         */
        (void) zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            "scrub_queue", sizeof (uint64_t), 1,
            &scn->scn_phys.scn_queue_obj);
    } else {
        err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_SCAN, sizeof (uint64_t), SCAN_PHYS_NUMINTS,
            &scn->scn_phys);
        if (err == ENOENT)
            return (0);
        else if (err)
            return (err);

        if (scn->scn_phys.scn_state == DSS_SCANNING &&
            spa_prev_software_version(dp->dp_spa) < SPA_VERSION_SCAN) {
            /*
             * A new-type scrub was in progress on an old
             * pool, and the pool was accessed by old
             * software.  Restart from the beginning, since
             * the old software may have changed the pool in
             * the meantime.
             */
            scn->scn_restart_txg = txg;
            zfs_dbgmsg("new-style scrub was modified "
                "by old software; restarting in txg %llu",
                scn->scn_restart_txg);
        }
    }

    spa_scan_stat_init(spa);
    return (0);
}

void
dsl_scan_fini(dsl_pool_t *dp)
{
    if (dp->dp_scan) {
        kmem_free(dp->dp_scan, sizeof (dsl_scan_t));
        dp->dp_scan = NULL;
    }
}

/* ARGSUSED */
static int
dsl_scan_setup_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
    dsl_scan_t *scn = arg1;

    if (scn->scn_phys.scn_state == DSS_SCANNING)
        return (EBUSY);

    return (0);
}

/* ARGSUSED */
static void
dsl_scan_setup_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
    dsl_scan_t *scn = arg1;
    pool_scan_func_t *funcp = arg2;
    dmu_object_type_t ot = 0;
    dsl_pool_t *dp = scn->scn_dp;
    spa_t *spa = dp->dp_spa;

    ASSERT(scn->scn_phys.scn_state != DSS_SCANNING);
    ASSERT(*funcp > POOL_SCAN_NONE && *funcp < POOL_SCAN_FUNCS);
    bzero(&scn->scn_phys, sizeof (scn->scn_phys));
    scn->scn_phys.scn_func = *funcp;
    scn->scn_phys.scn_state = DSS_SCANNING;
    scn->scn_phys.scn_min_txg = 0;
    scn->scn_phys.scn_max_txg = tx->tx_txg;
    scn->scn_phys.scn_ddt_class_max = DDT_CLASSES - 1; /* the entire DDT */
    scn->scn_phys.scn_start_time = gethrestime_sec();
    scn->scn_phys.scn_errors = 0;
    scn->scn_phys.scn_to_examine = spa->spa_root_vdev->vdev_stat.vs_alloc;
    scn->scn_restart_txg = 0;
    spa_scan_stat_init(spa);

    if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
        scn->scn_phys.scn_ddt_class_max = zfs_scrub_ddt_class_max;

        /* rewrite all disk labels */
        vdev_config_dirty(spa->spa_root_vdev);

        if (vdev_resilver_needed(spa->spa_root_vdev,
            &scn->scn_phys.scn_min_txg, &scn->scn_phys.scn_max_txg)) {
            spa_event_notify(spa, NULL, ESC_ZFS_RESILVER_START);
        } else {
            spa_event_notify(spa, NULL, ESC_ZFS_SCRUB_START);
        }

        spa->spa_scrub_started = B_TRUE;
        /*
         * If this is an incremental scrub, limit the DDT scrub phase
         * to just the auto-ditto class (for correctness); the rest
         * of the scrub should go faster using top-down pruning.
         */
        if (scn->scn_phys.scn_min_txg > TXG_INITIAL)
            scn->scn_phys.scn_ddt_class_max = DDT_CLASS_DITTO;

    }

    /* back to the generic stuff */

    if (dp->dp_blkstats == NULL) {
        dp->dp_blkstats =
            kmem_alloc(sizeof (zfs_all_blkstats_t), KM_SLEEP);
    }
    bzero(dp->dp_blkstats, sizeof (zfs_all_blkstats_t));

    if (spa_version(spa) < SPA_VERSION_DSL_SCRUB)
        ot = DMU_OT_ZAP_OTHER;

    scn->scn_phys.scn_queue_obj = zap_create(dp->dp_meta_objset,
        ot ? ot : DMU_OT_SCAN_QUEUE, DMU_OT_NONE, 0, tx);

    dsl_scan_sync_state(scn, tx);

    spa_history_log_internal(LOG_POOL_SCAN, spa, tx,
        "func=%u mintxg=%llu maxtxg=%llu",
        *funcp, scn->scn_phys.scn_min_txg, scn->scn_phys.scn_max_txg);
}

/* ARGSUSED */
static void
dsl_scan_done(dsl_scan_t *scn, boolean_t complete, dmu_tx_t *tx)
{
    static const char *old_names[] = {
        "scrub_bookmark",
        "scrub_ddt_bookmark",
        "scrub_ddt_class_max",
        "scrub_queue",
        "scrub_min_txg",
        "scrub_max_txg",
        "scrub_func",
        "scrub_errors",
        NULL
    };

    dsl_pool_t *dp = scn->scn_dp;
    spa_t *spa = dp->dp_spa;
    int i;

    /* Remove any remnants of an old-style scrub. */
    for (i = 0; old_names[i]; i++) {
        (void) zap_remove(dp->dp_meta_objset,
            DMU_POOL_DIRECTORY_OBJECT, old_names[i], tx);
    }

    if (scn->scn_phys.scn_queue_obj != 0) {
        VERIFY(0 == dmu_object_free(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, tx));
        scn->scn_phys.scn_queue_obj = 0;
    }

    /*
     * If we were "restarted" from a stopped state, don't bother
     * with anything else.
     */
    if (scn->scn_phys.scn_state != DSS_SCANNING)
        return;

    if (complete)
        scn->scn_phys.scn_state = DSS_FINISHED;
    else
        scn->scn_phys.scn_state = DSS_CANCELED;

    spa_history_log_internal(LOG_POOL_SCAN_DONE, spa, tx,
        "complete=%u", complete);

    if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
        mutex_enter(&spa->spa_scrub_lock);
        while (spa->spa_scrub_inflight > 0) {
            cv_wait(&spa->spa_scrub_io_cv,
                &spa->spa_scrub_lock);
        }
        mutex_exit(&spa->spa_scrub_lock);
        spa->spa_scrub_started = B_FALSE;
        spa->spa_scrub_active = B_FALSE;

        /*
         * If the scrub/resilver completed, update all DTLs to
         * reflect this.  Whether it succeeded or not, vacate
         * all temporary scrub DTLs.
         */
        vdev_dtl_reassess(spa->spa_root_vdev, tx->tx_txg,
            complete ? scn->scn_phys.scn_max_txg : 0, B_TRUE);
        if (complete) {
            spa_event_notify(spa, NULL, scn->scn_phys.scn_min_txg ?
                ESC_ZFS_RESILVER_FINISH : ESC_ZFS_SCRUB_FINISH);
        }
        spa_errlog_rotate(spa);

        /*
         * We may have finished replacing a device.
         * Let the async thread assess this and handle the detach.
         */
        spa_async_request(spa, SPA_ASYNC_RESILVER_DONE);
    }

    scn->scn_phys.scn_end_time = gethrestime_sec();
}

/* ARGSUSED */
static int
dsl_scan_cancel_check(void *arg1, void *arg2, dmu_tx_t *tx)
{
    dsl_scan_t *scn = arg1;

    if (scn->scn_phys.scn_state != DSS_SCANNING)
        return (ENOENT);
    return (0);
}

/* ARGSUSED */
static void
dsl_scan_cancel_sync(void *arg1, void *arg2, dmu_tx_t *tx)
{
    dsl_scan_t *scn = arg1;

    dsl_scan_done(scn, B_FALSE, tx);
    dsl_scan_sync_state(scn, tx);
}

int
dsl_scan_cancel(dsl_pool_t *dp)
{
    boolean_t complete = B_FALSE;
    int err;

    err = dsl_sync_task_do(dp, dsl_scan_cancel_check,
        dsl_scan_cancel_sync, dp->dp_scan, &complete, 3);
    return (err);
}

static void dsl_scan_visitbp(blkptr_t *bp,
    const zbookmark_t *zb, dnode_phys_t *dnp, arc_buf_t *pbuf,
    dsl_dataset_t *ds, dsl_scan_t *scn, dmu_objset_type_t ostype,
    dmu_tx_t *tx);
static void dsl_scan_visitdnode(dsl_scan_t *, dsl_dataset_t *ds,
    dmu_objset_type_t ostype,
    dnode_phys_t *dnp, arc_buf_t *buf, uint64_t object, dmu_tx_t *tx);

void
dsl_free(dsl_pool_t *dp, uint64_t txg, const blkptr_t *bp)
{
    zio_free(dp->dp_spa, txg, bp);
}

void
dsl_free_sync(zio_t *pio, dsl_pool_t *dp, uint64_t txg, const blkptr_t *bpp)
{
    ASSERT(dsl_pool_sync_context(dp));
    zio_nowait(zio_free_sync(pio, dp->dp_spa, txg, bpp, pio->io_flags));
}

int
dsl_read(zio_t *pio, spa_t *spa, const blkptr_t *bpp, arc_buf_t *pbuf,
    arc_done_func_t *done, void *private, int priority, int zio_flags,
    uint32_t *arc_flags, const zbookmark_t *zb)
{
    return (arc_read(pio, spa, bpp, pbuf, done, private,
        priority, zio_flags, arc_flags, zb));
}

int
dsl_read_nolock(zio_t *pio, spa_t *spa, const blkptr_t *bpp,
    arc_done_func_t *done, void *private, int priority, int zio_flags,
    uint32_t *arc_flags, const zbookmark_t *zb)
{
    return (arc_read_nolock(pio, spa, bpp, done, private,
        priority, zio_flags, arc_flags, zb));
}

static boolean_t
bookmark_is_zero(const zbookmark_t *zb)
{
    return (zb->zb_objset == 0 && zb->zb_object == 0 &&
        zb->zb_level == 0 && zb->zb_blkid == 0);
}

/* dnp is the dnode for zb1->zb_object */
static boolean_t
bookmark_is_before(const dnode_phys_t *dnp, const zbookmark_t *zb1,
    const zbookmark_t *zb2)
{
    uint64_t zb1nextL0, zb2thisobj;

    ASSERT(zb1->zb_objset == zb2->zb_objset);
    ASSERT(zb2->zb_level == 0);

    /*
     * A bookmark in the deadlist is considered to be after
     * everything else.
     */
    if (zb2->zb_object == DMU_DEADLIST_OBJECT)
        return (B_TRUE);

    /* The objset_phys_t isn't before anything. */
    if (dnp == NULL)
        return (B_FALSE);

    zb1nextL0 = (zb1->zb_blkid + 1) <<
        ((zb1->zb_level) * (dnp->dn_indblkshift - SPA_BLKPTRSHIFT));

    zb2thisobj = zb2->zb_object ? zb2->zb_object :
        zb2->zb_blkid << (DNODE_BLOCK_SHIFT - DNODE_SHIFT);

    if (zb1->zb_object == DMU_META_DNODE_OBJECT) {
        uint64_t nextobj = zb1nextL0 *
            (dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT) >> DNODE_SHIFT;
        return (nextobj <= zb2thisobj);
    }

    if (zb1->zb_object < zb2thisobj)
        return (B_TRUE);
    if (zb1->zb_object > zb2thisobj)
        return (B_FALSE);
    if (zb2->zb_object == DMU_META_DNODE_OBJECT)
        return (B_FALSE);
    return (zb1nextL0 <= zb2->zb_blkid);
}

static uint64_t
dsl_scan_ds_maxtxg(dsl_dataset_t *ds)
{
    uint64_t smt = ds->ds_dir->dd_pool->dp_scan->scn_phys.scn_max_txg;
    if (dsl_dataset_is_snapshot(ds))
        return (MIN(smt, ds->ds_phys->ds_creation_txg));
    return (smt);
}

static void
dsl_scan_sync_state(dsl_scan_t *scn, dmu_tx_t *tx)
{
    VERIFY(0 == zap_update(scn->scn_dp->dp_meta_objset,
        DMU_POOL_DIRECTORY_OBJECT,
        DMU_POOL_SCAN, sizeof (uint64_t), SCAN_PHYS_NUMINTS,
        &scn->scn_phys, tx));
}

static boolean_t
dsl_scan_check_pause(dsl_scan_t *scn, const zbookmark_t *zb)
{
    uint64_t elapsed_nanosecs;
    int mintime;

    /* we never skip user/group accounting objects */
    if (zb && (int64_t)zb->zb_object < 0)
        return (B_FALSE);

    if (scn->scn_pausing)
        return (B_TRUE); /* we're already pausing */

    if (!bookmark_is_zero(&scn->scn_phys.scn_bookmark))
        return (B_FALSE); /* we're resuming */

    /* We only know how to resume from level-0 blocks. */
    if (zb && zb->zb_level != 0)
        return (B_FALSE);

    mintime = (scn->scn_phys.scn_func == POOL_SCAN_RESILVER) ?
        zfs_resilver_min_time_ms : zfs_scan_min_time_ms;
    elapsed_nanosecs = gethrtime() - scn->scn_sync_start_time;
    if (elapsed_nanosecs / NANOSEC > zfs_txg_timeout ||
        (elapsed_nanosecs / MICROSEC > mintime &&
        txg_sync_waiting(scn->scn_dp)) ||
        spa_shutting_down(scn->scn_dp->dp_spa)) {
        if (zb) {
            dprintf("pausing at bookmark %llx/%llx/%llx/%llx\n",
                (longlong_t)zb->zb_objset,
                (longlong_t)zb->zb_object,
                (longlong_t)zb->zb_level,
                (longlong_t)zb->zb_blkid);
            scn->scn_phys.scn_bookmark = *zb;
        }
        dprintf("pausing at DDT bookmark %llx/%llx/%llx/%llx\n",
            (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_class,
            (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_type,
            (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_checksum,
            (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_cursor);
        scn->scn_pausing = B_TRUE;
        return (B_TRUE);
    }
    return (B_FALSE);
}

typedef struct zil_scan_arg {
    dsl_pool_t  *zsa_dp;
    zil_header_t    *zsa_zh;
} zil_scan_arg_t;

/* ARGSUSED */
static int
dsl_scan_zil_block(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
{
    zil_scan_arg_t *zsa = arg;
    dsl_pool_t *dp = zsa->zsa_dp;
    dsl_scan_t *scn = dp->dp_scan;
    zil_header_t *zh = zsa->zsa_zh;
    zbookmark_t zb;

    if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
        return (0);

    /*
     * One block ("stubby") can be allocated a long time ago; we
     * want to visit that one because it has been allocated
     * (on-disk) even if it hasn't been claimed (even though for
     * scrub there's nothing to do to it).
     */
    if (claim_txg == 0 && bp->blk_birth >= spa_first_txg(dp->dp_spa))
        return (0);

    SET_BOOKMARK(&zb, zh->zh_log.blk_cksum.zc_word[ZIL_ZC_OBJSET],
        ZB_ZIL_OBJECT, ZB_ZIL_LEVEL, bp->blk_cksum.zc_word[ZIL_ZC_SEQ]);

    VERIFY(0 == scan_funcs[scn->scn_phys.scn_func](dp, bp, &zb));
    return (0);
}

/* ARGSUSED */
static int
dsl_scan_zil_record(zilog_t *zilog, lr_t *lrc, void *arg, uint64_t claim_txg)
{
    if (lrc->lrc_txtype == TX_WRITE) {
        zil_scan_arg_t *zsa = arg;
        dsl_pool_t *dp = zsa->zsa_dp;
        dsl_scan_t *scn = dp->dp_scan;
        zil_header_t *zh = zsa->zsa_zh;
        lr_write_t *lr = (lr_write_t *)lrc;
        blkptr_t *bp = &lr->lr_blkptr;
        zbookmark_t zb;

        if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
            return (0);

        /*
         * birth can be < claim_txg if this record's txg is
         * already txg sync'ed (but this log block contains
         * other records that are not synced)
         */
        if (claim_txg == 0 || bp->blk_birth < claim_txg)
            return (0);

        SET_BOOKMARK(&zb, zh->zh_log.blk_cksum.zc_word[ZIL_ZC_OBJSET],
            lr->lr_foid, ZB_ZIL_LEVEL,
            lr->lr_offset / BP_GET_LSIZE(bp));

        VERIFY(0 == scan_funcs[scn->scn_phys.scn_func](dp, bp, &zb));
    }
    return (0);
}

static void
dsl_scan_zil(dsl_pool_t *dp, zil_header_t *zh)
{
    uint64_t claim_txg = zh->zh_claim_txg;
    zil_scan_arg_t zsa = { dp, zh };
    zilog_t *zilog;

    /*
     * We only want to visit blocks that have been claimed but not yet
     * replayed (or, in read-only mode, blocks that *would* be claimed).
     */
    if (claim_txg == 0 && spa_writeable(dp->dp_spa))
        return;

    zilog = zil_alloc(dp->dp_meta_objset, zh);

    (void) zil_parse(zilog, dsl_scan_zil_block, dsl_scan_zil_record, &zsa,
        claim_txg);

    zil_free(zilog);
}

/* ARGSUSED */
static void
dsl_scan_prefetch(dsl_scan_t *scn, arc_buf_t *buf, blkptr_t *bp,
    uint64_t objset, uint64_t object, uint64_t blkid)
{
    zbookmark_t czb;
    uint32_t flags = ARC_NOWAIT | ARC_PREFETCH;

    if (zfs_no_scrub_prefetch)
        return;

    if (BP_IS_HOLE(bp) || bp->blk_birth <= scn->scn_phys.scn_min_txg ||
        (BP_GET_LEVEL(bp) == 0 && BP_GET_TYPE(bp) != DMU_OT_DNODE))
        return;

    SET_BOOKMARK(&czb, objset, object, BP_GET_LEVEL(bp), blkid);

    /*
     * XXX need to make sure all of these arc_read() prefetches are
     * done before setting xlateall (similar to dsl_read())
     */
    (void) arc_read(scn->scn_prefetch_zio_root, scn->scn_dp->dp_spa, bp,
        buf, NULL, NULL, ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
        &flags, &czb);
}

static boolean_t
dsl_scan_check_resume(dsl_scan_t *scn, const dnode_phys_t *dnp,
    const zbookmark_t *zb)
{
    /*
     * We never skip over user/group accounting objects (obj<0)
     */
    if (!bookmark_is_zero(&scn->scn_phys.scn_bookmark) &&
        (int64_t)zb->zb_object >= 0) {
        /*
         * If we already visited this bp & everything below (in
         * a prior txg sync), don't bother doing it again.
         */
        if (bookmark_is_before(dnp, zb, &scn->scn_phys.scn_bookmark))
            return (B_TRUE);

        /*
         * If we found the block we're trying to resume from, or
         * we went past it to a different object, zero it out to
         * indicate that it's OK to start checking for pausing
         * again.
         */
        if (bcmp(zb, &scn->scn_phys.scn_bookmark, sizeof (*zb)) == 0 ||
            zb->zb_object > scn->scn_phys.scn_bookmark.zb_object) {
            dprintf("resuming at %llx/%llx/%llx/%llx\n",
                (longlong_t)zb->zb_objset,
                (longlong_t)zb->zb_object,
                (longlong_t)zb->zb_level,
                (longlong_t)zb->zb_blkid);
            bzero(&scn->scn_phys.scn_bookmark, sizeof (*zb));
        }
    }
    return (B_FALSE);
}

/*
 * Return nonzero on i/o error.
 * Return new buf to write out in *bufp.
 */
static int
dsl_scan_recurse(dsl_scan_t *scn, dsl_dataset_t *ds, dmu_objset_type_t ostype,
    dnode_phys_t *dnp, const blkptr_t *bp,
    const zbookmark_t *zb, dmu_tx_t *tx, arc_buf_t **bufp)
{
    dsl_pool_t *dp = scn->scn_dp;
    int err;

    if (BP_GET_LEVEL(bp) > 0) {
        uint32_t flags = ARC_WAIT;
        int i;
        blkptr_t *cbp;
        int epb = BP_GET_LSIZE(bp) >> SPA_BLKPTRSHIFT;

        err = arc_read_nolock(NULL, dp->dp_spa, bp,
            arc_getbuf_func, bufp,
            ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
        if (err) {
            scn->scn_phys.scn_errors++;
            return (err);
        }
        for (i = 0, cbp = (*bufp)->b_data; i < epb; i++, cbp++) {
            dsl_scan_prefetch(scn, *bufp, cbp, zb->zb_objset,
                zb->zb_object, zb->zb_blkid * epb + i);
        }
        for (i = 0, cbp = (*bufp)->b_data; i < epb; i++, cbp++) {
            zbookmark_t czb;

            SET_BOOKMARK(&czb, zb->zb_objset, zb->zb_object,
                zb->zb_level - 1,
                zb->zb_blkid * epb + i);
            dsl_scan_visitbp(cbp, &czb, dnp,
                *bufp, ds, scn, ostype, tx);
        }
    } else if (BP_GET_TYPE(bp) == DMU_OT_USERGROUP_USED) {
        uint32_t flags = ARC_WAIT;

        err = arc_read_nolock(NULL, dp->dp_spa, bp,
            arc_getbuf_func, bufp,
            ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
        if (err) {
            scn->scn_phys.scn_errors++;
            return (err);
        }
    } else if (BP_GET_TYPE(bp) == DMU_OT_DNODE) {
        uint32_t flags = ARC_WAIT;
        dnode_phys_t *cdnp;
        int i, j;
        int epb = BP_GET_LSIZE(bp) >> DNODE_SHIFT;

        err = arc_read_nolock(NULL, dp->dp_spa, bp,
            arc_getbuf_func, bufp,
            ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
        if (err) {
            scn->scn_phys.scn_errors++;
            return (err);
        }
        for (i = 0, cdnp = (*bufp)->b_data; i < epb; i++, cdnp++) {
            for (j = 0; j < cdnp->dn_nblkptr; j++) {
                blkptr_t *cbp = &cdnp->dn_blkptr[j];
                dsl_scan_prefetch(scn, *bufp, cbp,
                    zb->zb_objset, zb->zb_blkid * epb + i, j);
            }
        }
        for (i = 0, cdnp = (*bufp)->b_data; i < epb; i++, cdnp++) {
            dsl_scan_visitdnode(scn, ds, ostype,
                cdnp, *bufp, zb->zb_blkid * epb + i, tx);
        }

    } else if (BP_GET_TYPE(bp) == DMU_OT_OBJSET) {
        uint32_t flags = ARC_WAIT;
        objset_phys_t *osp;

        err = arc_read_nolock(NULL, dp->dp_spa, bp,
            arc_getbuf_func, bufp,
            ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
        if (err) {
            scn->scn_phys.scn_errors++;
            return (err);
        }

        osp = (*bufp)->b_data;

        if (DSL_SCAN_IS_SCRUB_RESILVER(scn))
            dsl_scan_zil(dp, &osp->os_zil_header);

        dsl_scan_visitdnode(scn, ds, osp->os_type,
            &osp->os_meta_dnode, *bufp, DMU_META_DNODE_OBJECT, tx);

        if (OBJSET_BUF_HAS_USERUSED(*bufp)) {
            /*
             * We also always visit user/group accounting
             * objects, and never skip them, even if we are
             * pausing.  This is necessary so that the space
             * deltas from this txg get integrated.
             */
            dsl_scan_visitdnode(scn, ds, osp->os_type,
                &osp->os_groupused_dnode, *bufp,
                DMU_GROUPUSED_OBJECT, tx);
            dsl_scan_visitdnode(scn, ds, osp->os_type,
                &osp->os_userused_dnode, *bufp,
                DMU_USERUSED_OBJECT, tx);
        }
    }

    return (0);
}

static void
dsl_scan_visitdnode(dsl_scan_t *scn, dsl_dataset_t *ds,
    dmu_objset_type_t ostype, dnode_phys_t *dnp, arc_buf_t *buf,
    uint64_t object, dmu_tx_t *tx)
{
    int j;

    for (j = 0; j < dnp->dn_nblkptr; j++) {
        zbookmark_t czb;

        SET_BOOKMARK(&czb, ds ? ds->ds_object : 0, object,
            dnp->dn_nlevels - 1, j);
        dsl_scan_visitbp(&dnp->dn_blkptr[j],
            &czb, dnp, buf, ds, scn, ostype, tx);
    }

    if (dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) {
        zbookmark_t czb;
        SET_BOOKMARK(&czb, ds ? ds->ds_object : 0, object,
            0, DMU_SPILL_BLKID);
        dsl_scan_visitbp(&dnp->dn_spill,
            &czb, dnp, buf, ds, scn, ostype, tx);
    }
}

/*
 * The arguments are in this order because mdb can only print the
 * first 5; we want them to be useful.
 */
static void
dsl_scan_visitbp(blkptr_t *bp, const zbookmark_t *zb,
    dnode_phys_t *dnp, arc_buf_t *pbuf,
    dsl_dataset_t *ds, dsl_scan_t *scn, dmu_objset_type_t ostype,
    dmu_tx_t *tx)
{
    dsl_pool_t *dp = scn->scn_dp;
    arc_buf_t *buf = NULL;
    blkptr_t bp_toread = *bp;

    /* ASSERT(pbuf == NULL || arc_released(pbuf)); */

    if (dsl_scan_check_pause(scn, zb))
        return;

    if (dsl_scan_check_resume(scn, dnp, zb))
        return;

    if (bp->blk_birth == 0)
        return;

    scn->scn_visited_this_txg++;

    dprintf_bp(bp,
        "visiting ds=%p/%llu zb=%llx/%llx/%llx/%llx buf=%p bp=%p",
        ds, ds ? ds->ds_object : 0,
        zb->zb_objset, zb->zb_object, zb->zb_level, zb->zb_blkid,
        pbuf, bp);

    if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
        return;

    if (BP_GET_TYPE(bp) != DMU_OT_USERGROUP_USED) {
        /*
         * For non-user-accounting blocks, we need to read the
         * new bp (from a deleted snapshot, found in
         * check_existing_xlation).  If we used the old bp,
         * pointers inside this block from before we resumed
         * would be untranslated.
         *
         * For user-accounting blocks, we need to read the old
         * bp, because we will apply the entire space delta to
         * it (original untranslated -> translations from
         * deleted snap -> now).
         */
        bp_toread = *bp;
    }

    if (dsl_scan_recurse(scn, ds, ostype, dnp, &bp_toread, zb, tx,
        &buf) != 0)
        return;

    /*
     * If dsl_scan_ddt() has aready visited this block, it will have
     * already done any translations or scrubbing, so don't call the
     * callback again.
     */
    if (ddt_class_contains(dp->dp_spa,
        scn->scn_phys.scn_ddt_class_max, bp)) {
        ASSERT(buf == NULL);
        return;
    }

    /*
     * If this block is from the future (after cur_max_txg), then we
     * are doing this on behalf of a deleted snapshot, and we will
     * revisit the future block on the next pass of this dataset.
     * Don't scan it now unless we need to because something
     * under it was modified.
     */
    if (bp->blk_birth <= scn->scn_phys.scn_cur_max_txg) {
        scan_funcs[scn->scn_phys.scn_func](dp, bp, zb);
    }
    if (buf)
        (void) arc_buf_remove_ref(buf, &buf);
}

static void
dsl_scan_visit_rootbp(dsl_scan_t *scn, dsl_dataset_t *ds, blkptr_t *bp,
    dmu_tx_t *tx)
{
    zbookmark_t zb;

    SET_BOOKMARK(&zb, ds ? ds->ds_object : DMU_META_OBJSET,
        ZB_ROOT_OBJECT, ZB_ROOT_LEVEL, ZB_ROOT_BLKID);
    dsl_scan_visitbp(bp, &zb, NULL, NULL,
        ds, scn, DMU_OST_NONE, tx);

    dprintf_ds(ds, "finished scan%s", "");
}

void
dsl_scan_ds_destroyed(dsl_dataset_t *ds, dmu_tx_t *tx)
{
    dsl_pool_t *dp = ds->ds_dir->dd_pool;
    dsl_scan_t *scn = dp->dp_scan;
    uint64_t mintxg;

    if (scn->scn_phys.scn_state != DSS_SCANNING)
        return;

    if (scn->scn_phys.scn_bookmark.zb_objset == ds->ds_object) {
        if (dsl_dataset_is_snapshot(ds)) {
            /* Note, scn_cur_{min,max}_txg stays the same. */
            scn->scn_phys.scn_bookmark.zb_objset =
                ds->ds_phys->ds_next_snap_obj;
            zfs_dbgmsg("destroying ds %llu; currently traversing; "
                "reset zb_objset to %llu",
                (u_longlong_t)ds->ds_object,
                (u_longlong_t)ds->ds_phys->ds_next_snap_obj);
            scn->scn_phys.scn_flags |= DSF_VISIT_DS_AGAIN;
        } else {
            SET_BOOKMARK(&scn->scn_phys.scn_bookmark,
                ZB_DESTROYED_OBJSET, 0, 0, 0);
            zfs_dbgmsg("destroying ds %llu; currently traversing; "
                "reset bookmark to -1,0,0,0",
                (u_longlong_t)ds->ds_object);
        }
    } else if (zap_lookup_int_key(dp->dp_meta_objset,
        scn->scn_phys.scn_queue_obj, ds->ds_object, &mintxg) == 0) {
        ASSERT3U(ds->ds_phys->ds_num_children, <=, 1);
        VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds->ds_object, tx));
        if (dsl_dataset_is_snapshot(ds)) {
            /*
             * We keep the same mintxg; it could be >
             * ds_creation_txg if the previous snapshot was
             * deleted too.
             */
            VERIFY(zap_add_int_key(dp->dp_meta_objset,
                scn->scn_phys.scn_queue_obj,
                ds->ds_phys->ds_next_snap_obj, mintxg, tx) == 0);
            zfs_dbgmsg("destroying ds %llu; in queue; "
                "replacing with %llu",
                (u_longlong_t)ds->ds_object,
                (u_longlong_t)ds->ds_phys->ds_next_snap_obj);
        } else {
            zfs_dbgmsg("destroying ds %llu; in queue; removing",
                (u_longlong_t)ds->ds_object);
        }
    } else {
        zfs_dbgmsg("destroying ds %llu; ignoring",
            (u_longlong_t)ds->ds_object);
    }

    /*
     * dsl_scan_sync() should be called after this, and should sync
     * out our changed state, but just to be safe, do it here.
     */
    dsl_scan_sync_state(scn, tx);
}

void
dsl_scan_ds_snapshotted(dsl_dataset_t *ds, dmu_tx_t *tx)
{
    dsl_pool_t *dp = ds->ds_dir->dd_pool;
    dsl_scan_t *scn = dp->dp_scan;
    uint64_t mintxg;

    if (scn->scn_phys.scn_state != DSS_SCANNING)
        return;

    ASSERT(ds->ds_phys->ds_prev_snap_obj != 0);

    if (scn->scn_phys.scn_bookmark.zb_objset == ds->ds_object) {
        scn->scn_phys.scn_bookmark.zb_objset =
            ds->ds_phys->ds_prev_snap_obj;
        zfs_dbgmsg("snapshotting ds %llu; currently traversing; "
            "reset zb_objset to %llu",
            (u_longlong_t)ds->ds_object,
            (u_longlong_t)ds->ds_phys->ds_prev_snap_obj);
    } else if (zap_lookup_int_key(dp->dp_meta_objset,
        scn->scn_phys.scn_queue_obj, ds->ds_object, &mintxg) == 0) {
        VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds->ds_object, tx));
        VERIFY(zap_add_int_key(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj,
            ds->ds_phys->ds_prev_snap_obj, mintxg, tx) == 0);
        zfs_dbgmsg("snapshotting ds %llu; in queue; "
            "replacing with %llu",
            (u_longlong_t)ds->ds_object,
            (u_longlong_t)ds->ds_phys->ds_prev_snap_obj);
    }
    dsl_scan_sync_state(scn, tx);
}

void
dsl_scan_ds_clone_swapped(dsl_dataset_t *ds1, dsl_dataset_t *ds2, dmu_tx_t *tx)
{
    dsl_pool_t *dp = ds1->ds_dir->dd_pool;
    dsl_scan_t *scn = dp->dp_scan;
    uint64_t mintxg;

    if (scn->scn_phys.scn_state != DSS_SCANNING)
        return;

    if (scn->scn_phys.scn_bookmark.zb_objset == ds1->ds_object) {
        scn->scn_phys.scn_bookmark.zb_objset = ds2->ds_object;
        zfs_dbgmsg("clone_swap ds %llu; currently traversing; "
            "reset zb_objset to %llu",
            (u_longlong_t)ds1->ds_object,
            (u_longlong_t)ds2->ds_object);
    } else if (scn->scn_phys.scn_bookmark.zb_objset == ds2->ds_object) {
        scn->scn_phys.scn_bookmark.zb_objset = ds1->ds_object;
        zfs_dbgmsg("clone_swap ds %llu; currently traversing; "
            "reset zb_objset to %llu",
            (u_longlong_t)ds2->ds_object,
            (u_longlong_t)ds1->ds_object);
    }

    if (zap_lookup_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
        ds1->ds_object, &mintxg) == 0) {
        int err;

        ASSERT3U(mintxg, ==, ds1->ds_phys->ds_prev_snap_txg);
        ASSERT3U(mintxg, ==, ds2->ds_phys->ds_prev_snap_txg);
        VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds1->ds_object, tx));
        err = zap_add_int_key(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds2->ds_object, mintxg, tx);
        VERIFY(err == 0 || err == EEXIST);
        if (err == EEXIST) {
            /* Both were there to begin with */
            VERIFY(0 == zap_add_int_key(dp->dp_meta_objset,
                scn->scn_phys.scn_queue_obj,
                ds1->ds_object, mintxg, tx));
        }
        zfs_dbgmsg("clone_swap ds %llu; in queue; "
            "replacing with %llu",
            (u_longlong_t)ds1->ds_object,
            (u_longlong_t)ds2->ds_object);
    } else if (zap_lookup_int_key(dp->dp_meta_objset,
        scn->scn_phys.scn_queue_obj, ds2->ds_object, &mintxg) == 0) {
        ASSERT3U(mintxg, ==, ds1->ds_phys->ds_prev_snap_txg);
        ASSERT3U(mintxg, ==, ds2->ds_phys->ds_prev_snap_txg);
        VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds2->ds_object, tx));
        VERIFY(0 == zap_add_int_key(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds1->ds_object, mintxg, tx));
        zfs_dbgmsg("clone_swap ds %llu; in queue; "
            "replacing with %llu",
            (u_longlong_t)ds2->ds_object,
            (u_longlong_t)ds1->ds_object);
    }

    dsl_scan_sync_state(scn, tx);
}

struct enqueue_clones_arg {
    dmu_tx_t *tx;
    uint64_t originobj;
};

/* ARGSUSED */
static int
enqueue_clones_cb(spa_t *spa, uint64_t dsobj, const char *dsname, void *arg)
{
    struct enqueue_clones_arg *eca = arg;
    dsl_dataset_t *ds;
    int err;
    dsl_pool_t *dp = spa->spa_dsl_pool;
    dsl_scan_t *scn = dp->dp_scan;

    err = dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds);
    if (err)
        return (err);

    if (ds->ds_dir->dd_phys->dd_origin_obj == eca->originobj) {
        while (ds->ds_phys->ds_prev_snap_obj != eca->originobj) {
            dsl_dataset_t *prev;
            err = dsl_dataset_hold_obj(dp,
                ds->ds_phys->ds_prev_snap_obj, FTAG, &prev);

            dsl_dataset_rele(ds, FTAG);
            if (err)
                return (err);
            ds = prev;
        }
        VERIFY(zap_add_int_key(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds->ds_object,
            ds->ds_phys->ds_prev_snap_txg, eca->tx) == 0);
    }
    dsl_dataset_rele(ds, FTAG);
    return (0);
}

static void
dsl_scan_visitds(dsl_scan_t *scn, uint64_t dsobj, dmu_tx_t *tx)
{
    dsl_pool_t *dp = scn->scn_dp;
    dsl_dataset_t *ds;

    VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));

    /*
     * Iterate over the bps in this ds.
     */
    dmu_buf_will_dirty(ds->ds_dbuf, tx);
    dsl_scan_visit_rootbp(scn, ds, &ds->ds_phys->ds_bp, tx);

    char *dsname = kmem_alloc(ZFS_MAXNAMELEN, KM_SLEEP);
    dsl_dataset_name(ds, dsname);
    zfs_dbgmsg("scanned dataset %llu (%s) with min=%llu max=%llu; "
        "pausing=%u",
        (longlong_t)dsobj, dsname,
        (longlong_t)scn->scn_phys.scn_cur_min_txg,
        (longlong_t)scn->scn_phys.scn_cur_max_txg,
        (int)scn->scn_pausing);
    kmem_free(dsname, ZFS_MAXNAMELEN);

    if (scn->scn_pausing)
        goto out;

    /*
     * We've finished this pass over this dataset.
     */

    /*
     * If we did not completely visit this dataset, do another pass.
     */
    if (scn->scn_phys.scn_flags & DSF_VISIT_DS_AGAIN) {
        zfs_dbgmsg("incomplete pass; visiting again");
        scn->scn_phys.scn_flags &= ~DSF_VISIT_DS_AGAIN;
        VERIFY(zap_add_int_key(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds->ds_object,
            scn->scn_phys.scn_cur_max_txg, tx) == 0);
        goto out;
    }

    /*
     * Add descendent datasets to work queue.
     */
    if (ds->ds_phys->ds_next_snap_obj != 0) {
        VERIFY(zap_add_int_key(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, ds->ds_phys->ds_next_snap_obj,
            ds->ds_phys->ds_creation_txg, tx) == 0);
    }
    if (ds->ds_phys->ds_num_children > 1) {
        boolean_t usenext = B_FALSE;
        if (ds->ds_phys->ds_next_clones_obj != 0) {
            uint64_t count;
            /*
             * A bug in a previous version of the code could
             * cause upgrade_clones_cb() to not set
             * ds_next_snap_obj when it should, leading to a
             * missing entry.  Therefore we can only use the
             * next_clones_obj when its count is correct.
             */
            int err = zap_count(dp->dp_meta_objset,
                ds->ds_phys->ds_next_clones_obj, &count);
            if (err == 0 &&
                count == ds->ds_phys->ds_num_children - 1)
                usenext = B_TRUE;
        }

        if (usenext) {
            VERIFY(zap_join_key(dp->dp_meta_objset,
                ds->ds_phys->ds_next_clones_obj,
                scn->scn_phys.scn_queue_obj,
                ds->ds_phys->ds_creation_txg, tx) == 0);
        } else {
            struct enqueue_clones_arg eca;
            eca.tx = tx;
            eca.originobj = ds->ds_object;

            (void) dmu_objset_find_spa(ds->ds_dir->dd_pool->dp_spa,
                NULL, enqueue_clones_cb, &eca, DS_FIND_CHILDREN);
        }
    }

out:
    dsl_dataset_rele(ds, FTAG);
}

/* ARGSUSED */
static int
enqueue_cb(spa_t *spa, uint64_t dsobj, const char *dsname, void *arg)
{
    dmu_tx_t *tx = arg;
    dsl_dataset_t *ds;
    int err;
    dsl_pool_t *dp = spa->spa_dsl_pool;
    dsl_scan_t *scn = dp->dp_scan;

    err = dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds);
    if (err)
        return (err);

    while (ds->ds_phys->ds_prev_snap_obj != 0) {
        dsl_dataset_t *prev;
        err = dsl_dataset_hold_obj(dp, ds->ds_phys->ds_prev_snap_obj,
            FTAG, &prev);
        if (err) {
            dsl_dataset_rele(ds, FTAG);
            return (err);
        }

        /*
         * If this is a clone, we don't need to worry about it for now.
         */
        if (prev->ds_phys->ds_next_snap_obj != ds->ds_object) {
            dsl_dataset_rele(ds, FTAG);
            dsl_dataset_rele(prev, FTAG);
            return (0);
        }
        dsl_dataset_rele(ds, FTAG);
        ds = prev;
    }

    VERIFY(zap_add_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
        ds->ds_object, ds->ds_phys->ds_prev_snap_txg, tx) == 0);
    dsl_dataset_rele(ds, FTAG);
    return (0);
}

/*
 * Scrub/dedup interaction.
 *
 * If there are N references to a deduped block, we don't want to scrub it
 * N times -- ideally, we should scrub it exactly once.
 *
 * We leverage the fact that the dde's replication class (enum ddt_class)
 * is ordered from highest replication class (DDT_CLASS_DITTO) to lowest
 * (DDT_CLASS_UNIQUE) so that we may walk the DDT in that order.
 *
 * To prevent excess scrubbing, the scrub begins by walking the DDT
 * to find all blocks with refcnt > 1, and scrubs each of these once.
 * Since there are two replication classes which contain blocks with
 * refcnt > 1, we scrub the highest replication class (DDT_CLASS_DITTO) first.
 * Finally the top-down scrub begins, only visiting blocks with refcnt == 1.
 *
 * There would be nothing more to say if a block's refcnt couldn't change
 * during a scrub, but of course it can so we must account for changes
 * in a block's replication class.
 *
 * Here's an example of what can occur:
 *
 * If a block has refcnt > 1 during the DDT scrub phase, but has refcnt == 1
 * when visited during the top-down scrub phase, it will be scrubbed twice.
 * This negates our scrub optimization, but is otherwise harmless.
 *
 * If a block has refcnt == 1 during the DDT scrub phase, but has refcnt > 1
 * on each visit during the top-down scrub phase, it will never be scrubbed.
 * To catch this, ddt_sync_entry() notifies the scrub code whenever a block's
 * reference class transitions to a higher level (i.e DDT_CLASS_UNIQUE to
 * DDT_CLASS_DUPLICATE); if it transitions from refcnt == 1 to refcnt > 1
 * while a scrub is in progress, it scrubs the block right then.
 */
static void
dsl_scan_ddt(dsl_scan_t *scn, dmu_tx_t *tx)
{
    ddt_bookmark_t *ddb = &scn->scn_phys.scn_ddt_bookmark;
    ddt_entry_t dde = { 0 };
    int error;
    uint64_t n = 0;

    while ((error = ddt_walk(scn->scn_dp->dp_spa, ddb, &dde)) == 0) {
        ddt_t *ddt;

        if (ddb->ddb_class > scn->scn_phys.scn_ddt_class_max)
            break;
        dprintf("visiting ddb=%llu/%llu/%llu/%llx\n",
            (longlong_t)ddb->ddb_class,
            (longlong_t)ddb->ddb_type,
            (longlong_t)ddb->ddb_checksum,
            (longlong_t)ddb->ddb_cursor);

        /* There should be no pending changes to the dedup table */
        ddt = scn->scn_dp->dp_spa->spa_ddt[ddb->ddb_checksum];
        ASSERT(avl_first(&ddt->ddt_tree) == NULL);

        dsl_scan_ddt_entry(scn, ddb->ddb_checksum, &dde, tx);
        n++;

        if (dsl_scan_check_pause(scn, NULL))
            break;
    }

    zfs_dbgmsg("scanned %llu ddt entries with class_max = %u; pausing=%u",
        (longlong_t)n, (int)scn->scn_phys.scn_ddt_class_max,
        (int)scn->scn_pausing);

    ASSERT(error == 0 || error == ENOENT);
    ASSERT(error != ENOENT ||
        ddb->ddb_class > scn->scn_phys.scn_ddt_class_max);
}

/* ARGSUSED */
void
dsl_scan_ddt_entry(dsl_scan_t *scn, enum zio_checksum checksum,
    ddt_entry_t *dde, dmu_tx_t *tx)
{
    const ddt_key_t *ddk = &dde->dde_key;
    ddt_phys_t *ddp = dde->dde_phys;
    blkptr_t bp;
    zbookmark_t zb = { 0 };

    if (scn->scn_phys.scn_state != DSS_SCANNING)
        return;

    for (int p = 0; p < DDT_PHYS_TYPES; p++, ddp++) {
        if (ddp->ddp_phys_birth == 0 ||
            ddp->ddp_phys_birth > scn->scn_phys.scn_cur_max_txg)
            continue;
        ddt_bp_create(checksum, ddk, ddp, &bp);

        scn->scn_visited_this_txg++;
        scan_funcs[scn->scn_phys.scn_func](scn->scn_dp, &bp, &zb);
    }
}

static void
dsl_scan_visit(dsl_scan_t *scn, dmu_tx_t *tx)
{
    dsl_pool_t *dp = scn->scn_dp;
    zap_cursor_t zc;
    zap_attribute_t za;

    if (scn->scn_phys.scn_ddt_bookmark.ddb_class <=
        scn->scn_phys.scn_ddt_class_max) {
        scn->scn_phys.scn_cur_min_txg = scn->scn_phys.scn_min_txg;
        scn->scn_phys.scn_cur_max_txg = scn->scn_phys.scn_max_txg;
        dsl_scan_ddt(scn, tx);
        if (scn->scn_pausing)
            return;
    }

    if (scn->scn_phys.scn_bookmark.zb_objset == DMU_META_OBJSET) {
        /* First do the MOS & ORIGIN */

        scn->scn_phys.scn_cur_min_txg = scn->scn_phys.scn_min_txg;
        scn->scn_phys.scn_cur_max_txg = scn->scn_phys.scn_max_txg;
        dsl_scan_visit_rootbp(scn, NULL,
            &dp->dp_meta_rootbp, tx);
        spa_set_rootblkptr(dp->dp_spa, &dp->dp_meta_rootbp);
        if (scn->scn_pausing)
            return;

        if (spa_version(dp->dp_spa) < SPA_VERSION_DSL_SCRUB) {
            VERIFY(0 == dmu_objset_find_spa(dp->dp_spa,
                NULL, enqueue_cb, tx, DS_FIND_CHILDREN));
        } else {
            dsl_scan_visitds(scn,
                dp->dp_origin_snap->ds_object, tx);
        }
        ASSERT(!scn->scn_pausing);
    } else if (scn->scn_phys.scn_bookmark.zb_objset !=
        ZB_DESTROYED_OBJSET) {
        /*
         * If we were paused, continue from here.  Note if the
         * ds we were paused on was deleted, the zb_objset may
         * be -1, so we will skip this and find a new objset
         * below.
         */
        dsl_scan_visitds(scn, scn->scn_phys.scn_bookmark.zb_objset, tx);
        if (scn->scn_pausing)
            return;
    }

    /*
     * In case we were paused right at the end of the ds, zero the
     * bookmark so we don't think that we're still trying to resume.
     */
    bzero(&scn->scn_phys.scn_bookmark, sizeof (zbookmark_t));

    /* keep pulling things out of the zap-object-as-queue */
    while (zap_cursor_init(&zc, dp->dp_meta_objset,
        scn->scn_phys.scn_queue_obj),
        zap_cursor_retrieve(&zc, &za) == 0) {
        dsl_dataset_t *ds;
        uint64_t dsobj;

        dsobj = strtonum(za.za_name, NULL);
        VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
            scn->scn_phys.scn_queue_obj, dsobj, tx));

        /* Set up min/max txg */
        VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
        if (za.za_first_integer != 0) {
            scn->scn_phys.scn_cur_min_txg =
                MAX(scn->scn_phys.scn_min_txg,
                za.za_first_integer);
        } else {
            scn->scn_phys.scn_cur_min_txg =
                MAX(scn->scn_phys.scn_min_txg,
                ds->ds_phys->ds_prev_snap_txg);
        }
        scn->scn_phys.scn_cur_max_txg = dsl_scan_ds_maxtxg(ds);
        dsl_dataset_rele(ds, FTAG);

        dsl_scan_visitds(scn, dsobj, tx);
        zap_cursor_fini(&zc);
        if (scn->scn_pausing)
            return;
    }
    zap_cursor_fini(&zc);
}

void
dsl_scan_sync(dsl_pool_t *dp, dmu_tx_t *tx)
{
    dsl_scan_t *scn = dp->dp_scan;
    spa_t *spa = dp->dp_spa;

    /*
     * Check for scn_restart_txg before checking spa_load_state, so
     * that we can restart an old-style scan while the pool is being
     * imported (see dsl_scan_init).
     */
    if (scn->scn_restart_txg != 0 &&
        scn->scn_restart_txg <= tx->tx_txg) {
        pool_scan_func_t func = POOL_SCAN_SCRUB;
        dsl_scan_done(scn, B_FALSE, tx);
        if (vdev_resilver_needed(spa->spa_root_vdev, NULL, NULL))
            func = POOL_SCAN_RESILVER;
        zfs_dbgmsg("restarting scan func=%u txg=%llu",
            func, tx->tx_txg);
        dsl_scan_setup_sync(scn, &func, tx);
    }

    if (dp->dp_spa->spa_load_state != SPA_LOAD_NONE ||
        spa_shutting_down(spa) ||
        spa_sync_pass(dp->dp_spa) > 1 ||
        scn->scn_phys.scn_state != DSS_SCANNING)
        return;

    scn->scn_visited_this_txg = 0;
    scn->scn_pausing = B_FALSE;
    scn->scn_sync_start_time = gethrtime();
    spa->spa_scrub_active = B_TRUE;

    if (scn->scn_phys.scn_ddt_bookmark.ddb_class <=
        scn->scn_phys.scn_ddt_class_max) {
        zfs_dbgmsg("doing scan sync txg %llu; "
            "ddt bm=%llu/%llu/%llu/%llx",
            (longlong_t)tx->tx_txg,
            (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_class,
            (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_type,
            (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_checksum,
            (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_cursor);
        ASSERT(scn->scn_phys.scn_bookmark.zb_objset == 0);
        ASSERT(scn->scn_phys.scn_bookmark.zb_object == 0);
        ASSERT(scn->scn_phys.scn_bookmark.zb_level == 0);
        ASSERT(scn->scn_phys.scn_bookmark.zb_blkid == 0);
    } else {
        zfs_dbgmsg("doing scan sync txg %llu; bm=%llu/%llu/%llu/%llu",
            (longlong_t)tx->tx_txg,
            (longlong_t)scn->scn_phys.scn_bookmark.zb_objset,
            (longlong_t)scn->scn_phys.scn_bookmark.zb_object,
            (longlong_t)scn->scn_phys.scn_bookmark.zb_level,
            (longlong_t)scn->scn_phys.scn_bookmark.zb_blkid);
    }

    scn->scn_prefetch_zio_root = zio_root(dp->dp_spa, NULL,
        NULL, ZIO_FLAG_CANFAIL);
    dsl_scan_visit(scn, tx);
    (void) zio_wait(scn->scn_prefetch_zio_root);
    scn->scn_prefetch_zio_root = NULL;

    zfs_dbgmsg("visited %llu blocks in %llums",
        (longlong_t)scn->scn_visited_this_txg,
        (longlong_t)(gethrtime() - scn->scn_sync_start_time) / MICROSEC);

    if (!scn->scn_pausing) {
        /* finished with scan. */
        zfs_dbgmsg("finished scan txg %llu", (longlong_t)tx->tx_txg);
        dsl_scan_done(scn, B_TRUE, tx);
    }

    if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
        mutex_enter(&spa->spa_scrub_lock);
        while (spa->spa_scrub_inflight > 0) {
            cv_wait(&spa->spa_scrub_io_cv,
                &spa->spa_scrub_lock);
        }
        mutex_exit(&spa->spa_scrub_lock);
    }

    dsl_scan_sync_state(scn, tx);
}

/*
 * This will start a new scan, or restart an existing one.
 */
void
dsl_resilver_restart(dsl_pool_t *dp, uint64_t txg)
{
    if (txg == 0) {
        dmu_tx_t *tx;
        tx = dmu_tx_create_dd(dp->dp_mos_dir);
        VERIFY(0 == dmu_tx_assign(tx, TXG_WAIT));

        txg = dmu_tx_get_txg(tx);
        dp->dp_scan->scn_restart_txg = txg;
        dmu_tx_commit(tx);
    } else {
        dp->dp_scan->scn_restart_txg = txg;
    }
    zfs_dbgmsg("restarting resilver txg=%llu", txg);
}

boolean_t
dsl_scan_resilvering(dsl_pool_t *dp)
{
    return (dp->dp_scan->scn_phys.scn_state == DSS_SCANNING &&
        dp->dp_scan->scn_phys.scn_func == POOL_SCAN_RESILVER);
}

/*
 * scrub consumers
 */

static void
count_block(zfs_all_blkstats_t *zab, const blkptr_t *bp)
{
    int i;

    /*
     * If we resume after a reboot, zab will be NULL; don't record
     * incomplete stats in that case.
     */
    if (zab == NULL)
        return;

    for (i = 0; i < 4; i++) {
        int l = (i < 2) ? BP_GET_LEVEL(bp) : DN_MAX_LEVELS;
        int t = (i & 1) ? BP_GET_TYPE(bp) : DMU_OT_TOTAL;
        zfs_blkstat_t *zb = &zab->zab_type[l][t];
        int equal;

        zb->zb_count++;
        zb->zb_asize += BP_GET_ASIZE(bp);
        zb->zb_lsize += BP_GET_LSIZE(bp);
        zb->zb_psize += BP_GET_PSIZE(bp);
        zb->zb_gangs += BP_COUNT_GANG(bp);

        switch (BP_GET_NDVAS(bp)) {
        case 2:
            if (DVA_GET_VDEV(&bp->blk_dva[0]) ==
                DVA_GET_VDEV(&bp->blk_dva[1]))
                zb->zb_ditto_2_of_2_samevdev++;
            break;
        case 3:
            equal = (DVA_GET_VDEV(&bp->blk_dva[0]) ==
                DVA_GET_VDEV(&bp->blk_dva[1])) +
                (DVA_GET_VDEV(&bp->blk_dva[0]) ==
                DVA_GET_VDEV(&bp->blk_dva[2])) +
                (DVA_GET_VDEV(&bp->blk_dva[1]) ==
                DVA_GET_VDEV(&bp->blk_dva[2]));
            if (equal == 1)
                zb->zb_ditto_2_of_3_samevdev++;
            else if (equal == 3)
                zb->zb_ditto_3_of_3_samevdev++;
            break;
        }
    }
}

static void
dsl_scan_scrub_done(zio_t *zio)
{
    spa_t *spa = zio->io_spa;

    zio_data_buf_free(zio->io_data, zio->io_size);

    mutex_enter(&spa->spa_scrub_lock);
    spa->spa_scrub_inflight--;
    cv_broadcast(&spa->spa_scrub_io_cv);

    if (zio->io_error && (zio->io_error != ECKSUM ||
        !(zio->io_flags & ZIO_FLAG_SPECULATIVE))) {
        spa->spa_dsl_pool->dp_scan->scn_phys.scn_errors++;
    }
    mutex_exit(&spa->spa_scrub_lock);
}

static int
dsl_scan_scrub_cb(dsl_pool_t *dp,
    const blkptr_t *bp, const zbookmark_t *zb)
{
    dsl_scan_t *scn = dp->dp_scan;
    size_t size = BP_GET_PSIZE(bp);
    spa_t *spa = dp->dp_spa;
    uint64_t phys_birth = BP_PHYSICAL_BIRTH(bp);
    boolean_t needs_io;
    int zio_flags = ZIO_FLAG_SCRUB_THREAD | ZIO_FLAG_RAW | ZIO_FLAG_CANFAIL;
    int zio_priority;

    if (phys_birth <= scn->scn_phys.scn_min_txg ||
        phys_birth >= scn->scn_phys.scn_max_txg)
        return (0);

    count_block(dp->dp_blkstats, bp);

    ASSERT(DSL_SCAN_IS_SCRUB_RESILVER(scn));
    if (scn->scn_phys.scn_func == POOL_SCAN_SCRUB) {
        zio_flags |= ZIO_FLAG_SCRUB;
        zio_priority = ZIO_PRIORITY_SCRUB;
        needs_io = B_TRUE;
    } else if (scn->scn_phys.scn_func == POOL_SCAN_RESILVER) {
        zio_flags |= ZIO_FLAG_RESILVER;
        zio_priority = ZIO_PRIORITY_RESILVER;
        needs_io = B_FALSE;
    }

    /* If it's an intent log block, failure is expected. */
    if (zb->zb_level == ZB_ZIL_LEVEL)
        zio_flags |= ZIO_FLAG_SPECULATIVE;

    for (int d = 0; d < BP_GET_NDVAS(bp); d++) {
        vdev_t *vd = vdev_lookup_top(spa,
            DVA_GET_VDEV(&bp->blk_dva[d]));

        /*
         * Keep track of how much data we've examined so that
         * zpool(1M) status can make useful progress reports.
         */
        scn->scn_phys.scn_examined += DVA_GET_ASIZE(&bp->blk_dva[d]);
        spa->spa_scan_pass_exam += DVA_GET_ASIZE(&bp->blk_dva[d]);

        /* if it's a resilver, this may not be in the target range */
        if (!needs_io) {
            if (DVA_GET_GANG(&bp->blk_dva[d])) {
                /*
                 * Gang members may be spread across multiple
                 * vdevs, so the best estimate we have is the
                 * scrub range, which has already been checked.
                 * XXX -- it would be better to change our
                 * allocation policy to ensure that all
                 * gang members reside on the same vdev.
                 */
                needs_io = B_TRUE;
            } else {
                needs_io = vdev_dtl_contains(vd, DTL_PARTIAL,
                    phys_birth, 1);
            }
        }
    }

    if (needs_io && !zfs_no_scrub_io) {
        void *data = zio_data_buf_alloc(size);

        mutex_enter(&spa->spa_scrub_lock);
        while (spa->spa_scrub_inflight >= spa->spa_scrub_maxinflight)
            cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
        spa->spa_scrub_inflight++;
        mutex_exit(&spa->spa_scrub_lock);

        zio_nowait(zio_read(NULL, spa, bp, data, size,
            dsl_scan_scrub_done, NULL, zio_priority,
            zio_flags, zb));
    }

    /* do not relocate this block */
    return (0);
}

int
dsl_scan(dsl_pool_t *dp, pool_scan_func_t func)
{
    spa_t *spa = dp->dp_spa;

    /*
     * Purge all vdev caches and probe all devices.  We do this here
     * rather than in sync context because this requires a writer lock
     * on the spa_config lock, which we can't do from sync context.  The
     * spa_scrub_reopen flag indicates that vdev_open() should not
     * attempt to start another scrub.
     */
    spa_vdev_state_enter(spa, SCL_NONE);
    spa->spa_scrub_reopen = B_TRUE;
    vdev_reopen(spa->spa_root_vdev);
    spa->spa_scrub_reopen = B_FALSE;
    (void) spa_vdev_state_exit(spa, NULL, 0);

    return (dsl_sync_task_do(dp, dsl_scan_setup_check,
        dsl_scan_setup_sync, dp->dp_scan, &func, 0));
}