fs/zfs/dmu_traverse.c

	dmu_traverse.c revision fa9e4066f08beec538e775443c5be79dd423fcab
/*
 * 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"

#include <sys/zfs_context.h>
#include <sys/dmu_objset.h>
#include <sys/dmu_traverse.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_pool.h>
#include <sys/dnode.h>
#include <sys/spa.h>
#include <sys/zio.h>
#include <sys/dmu_impl.h>

#define BP_SPAN_SHIFT(level, width) ((level) * (width))

#define BP_EQUAL(b1, b2)                \
    (DVA_EQUAL(BP_IDENTITY(b1), BP_IDENTITY(b2)) && \
    (b1)->blk_birth == (b2)->blk_birth)

/*
 * Compare two bookmarks.
 *
 * For ADVANCE_PRE, the visitation order is:
 *
 *  objset 0, 1, 2, ..., ZB_MAXOBJSET.
 *  object 0, 1, 2, ..., ZB_MAXOBJECT.
 *  blkoff 0, 1, 2, ...
 *  level ZB_MAXLEVEL, ..., 2, 1, 0.
 *
 * where blkoff = blkid << BP_SPAN_SHIFT(level, width), and thus a valid
 * ordering vector is:
 *
 *  < objset, object, blkoff, -level >
 *
 * For ADVANCE_POST, the starting offsets aren't sequential but ending
 * offsets [blkoff = (blkid + 1) << BP_SPAN_SHIFT(level, width)] are.
 * The visitation order is:
 *
 *  objset 1, 2, ..., ZB_MAXOBJSET, 0.
 *  object 1, 2, ..., ZB_MAXOBJECT, 0.
 *  blkoff 1, 2, ...
 *  level 0, 1, 2, ..., ZB_MAXLEVEL.
 *
 * and thus a valid ordering vector is:
 *
 *  < objset - 1, object - 1, blkoff, level >
 *
 * Both orderings can be expressed as:
 *
 *  < objset + bias, object + bias, blkoff, level ^ bias >
 *
 * where 'bias' is either 0 or -1 (for ADVANCE_PRE or ADVANCE_POST)
 * and 'blkoff' is (blkid - bias) << BP_SPAN_SHIFT(level, wshift).
 *
 * Special case: an objset's osphys is represented as level -1 of object 0.
 * It is always either the very first or very last block we visit in an objset.
 * Therefore, if either bookmark's level is -1, level alone determines order.
 */
static int
compare_bookmark(zbookmark_t *szb, zbookmark_t *ezb, dnode_phys_t *dnp,
    int advance)
{
    int bias = (advance & ADVANCE_PRE) ? 0 : -1;
    uint64_t sblkoff, eblkoff;
    int slevel, elevel, wshift;

    if (szb->zb_objset + bias < ezb->zb_objset + bias)
        return (-1);

    if (szb->zb_objset + bias > ezb->zb_objset + bias)
        return (1);

    slevel = szb->zb_level;
    elevel = ezb->zb_level;

    if ((slevel | elevel) < 0)
        return ((slevel ^ bias) - (elevel ^ bias));

    if (szb->zb_object + bias < ezb->zb_object + bias)
        return (-1);

    if (szb->zb_object + bias > ezb->zb_object + bias)
        return (1);

    if (dnp == NULL)
        return (0);

    wshift = dnp->dn_indblkshift - SPA_BLKPTRSHIFT;

    sblkoff = (szb->zb_blkid - bias) << BP_SPAN_SHIFT(slevel, wshift);
    eblkoff = (ezb->zb_blkid - bias) << BP_SPAN_SHIFT(elevel, wshift);

    if (sblkoff < eblkoff)
        return (-1);

    if (sblkoff > eblkoff)
        return (1);

    return ((elevel ^ bias) - (slevel ^ bias));
}

#define SET_BOOKMARK(zb, objset, object, level, blkid)  \
{                           \
    (zb)->zb_objset = objset;           \
    (zb)->zb_object = object;           \
    (zb)->zb_level = level;             \
    (zb)->zb_blkid = blkid;             \
}

#define SET_BOOKMARK_LB(zb, level, blkid)       \
{                           \
    (zb)->zb_level = level;             \
    (zb)->zb_blkid = blkid;             \
}

static int
advance_objset(zseg_t *zseg, uint64_t objset, int advance)
{
    zbookmark_t *zb = &zseg->seg_start;

    if (advance & ADVANCE_PRE) {
        if (objset >= ZB_MAXOBJSET)
            return (ERANGE);
        SET_BOOKMARK(zb, objset, 0, -1, 0);
    } else {
        if (objset >= ZB_MAXOBJSET)
            objset = 0;
        SET_BOOKMARK(zb, objset, 1, 0, 0);
    }

    if (compare_bookmark(zb, &zseg->seg_end, NULL, advance) > 0)
        return (ERANGE);

    return (EAGAIN);
}

static int
advance_object(zseg_t *zseg, uint64_t object, int advance)
{
    zbookmark_t *zb = &zseg->seg_start;

    if (advance & ADVANCE_PRE) {
        if (object >= ZB_MAXOBJECT) {
            SET_BOOKMARK(zb, zb->zb_objset + 1, 0, -1, 0);
        } else {
            SET_BOOKMARK(zb, zb->zb_objset, object, ZB_MAXLEVEL, 0);
        }
    } else {
        if (zb->zb_object == 0) {
            SET_BOOKMARK(zb, zb->zb_objset, 0, -1, 0);
        } else {
            if (object >= ZB_MAXOBJECT)
                object = 0;
            SET_BOOKMARK(zb, zb->zb_objset, object, 0, 0);
        }
    }

    if (compare_bookmark(zb, &zseg->seg_end, NULL, advance) > 0)
        return (ERANGE);

    return (EAGAIN);
}

static int
advance_from_osphys(zseg_t *zseg, int advance)
{
    zbookmark_t *zb = &zseg->seg_start;

    ASSERT(zb->zb_object == 0);
    ASSERT(zb->zb_level == -1);
    ASSERT(zb->zb_blkid == 0);

    if (advance & ADVANCE_PRE) {
        SET_BOOKMARK_LB(zb, ZB_MAXLEVEL, 0);
    } else {
        if (zb->zb_objset == 0)
            return (ERANGE);
        SET_BOOKMARK(zb, zb->zb_objset + 1, 1, 0, 0);
    }

    if (compare_bookmark(zb, &zseg->seg_end, NULL, advance) > 0)
        return (ERANGE);

    return (EAGAIN);
}

static int
advance_block(zseg_t *zseg, dnode_phys_t *dnp, int rc, int advance)
{
    zbookmark_t *zb = &zseg->seg_start;
    int wshift = dnp->dn_indblkshift - SPA_BLKPTRSHIFT;
    int maxlevel = dnp->dn_nlevels - 1;
    int level = zb->zb_level;
    uint64_t blkid = zb->zb_blkid;

    if (advance & ADVANCE_PRE) {
        if (level > 0 && rc == 0) {
            level--;
            blkid <<= wshift;
        } else {
            blkid++;

            if ((blkid << BP_SPAN_SHIFT(level, wshift)) >
                dnp->dn_maxblkid)
                return (ERANGE);

            while (level < maxlevel) {
                if (P2PHASE(blkid, 1ULL << wshift))
                    break;
                blkid >>= wshift;
                level++;
            }
        }
    } else {
        if (level >= maxlevel || P2PHASE(blkid + 1, 1ULL << wshift)) {
            blkid = (blkid + 1) << BP_SPAN_SHIFT(level, wshift);
            level = 0;
        } else {
            blkid >>= wshift;
            level++;
        }

        while ((blkid << BP_SPAN_SHIFT(level, wshift)) >
            dnp->dn_maxblkid) {
            if (level == maxlevel)
                return (ERANGE);
            blkid >>= wshift;
            level++;
        }
    }
    SET_BOOKMARK_LB(zb, level, blkid);

    if (compare_bookmark(zb, &zseg->seg_end, dnp, advance) > 0)
        return (ERANGE);

    return (EAGAIN);
}

static int
traverse_callback(traverse_handle_t *th, zseg_t *zseg, traverse_blk_cache_t *bc)
{
    /*
     * Before we issue the callback, prune against maxtxg.
     *
     * We prune against mintxg before we get here because it's a big win.
     * If a given block was born in txg 37, then we know that the entire
     * subtree below that block must have been born in txg 37 or earlier.
     * We can therefore lop off huge branches of the tree as we go.
     *
     * There's no corresponding optimization for maxtxg because knowing
     * that bp->blk_birth >= maxtxg doesn't imply anything about the bp's
     * children.  In fact, the copy-on-write design of ZFS ensures that
     * top-level blocks will pretty much always be new.
     *
     * Therefore, in the name of simplicity we don't prune against
     * maxtxg until the last possible moment -- that being right now.
     */
    if (bc->bc_errno == 0 && bc->bc_blkptr.blk_birth >= zseg->seg_maxtxg)
        return (0);

    if (bc->bc_errno == 0) {
        zbookmark_t *zb = &bc->bc_bookmark;
        zbookmark_t *szb = &zseg->seg_start;
        zbookmark_t *ezb = &zseg->seg_end;
        zbookmark_t *lzb = &th->th_lastcb;
        dnode_phys_t *dnp = bc->bc_dnode;

        /*
         * Debugging: verify that the order we visit things
         * agrees with the order defined by compare_bookmark().
         */
        ASSERT(compare_bookmark(zb, ezb, dnp, th->th_advance) <= 0);
        ASSERT(compare_bookmark(zb, szb, dnp, th->th_advance) == 0);
        ASSERT(compare_bookmark(lzb, zb, dnp, th->th_advance) < 0 ||
            lzb->zb_level == ZB_NO_LEVEL);
        *lzb = *zb;
    }

    th->th_callbacks++;
    return (th->th_func(bc, th->th_spa, th->th_arg));
}

static int
traverse_read(traverse_handle_t *th, traverse_blk_cache_t *bc, blkptr_t *bp,
    dnode_phys_t *dnp)
{
    zbookmark_t *zb = &bc->bc_bookmark;
    int error;

    th->th_hits++;

    bc->bc_dnode = dnp;
    bc->bc_errno = 0;

    if (BP_EQUAL(&bc->bc_blkptr, bp))
        return (0);

    bc->bc_blkptr = *bp;

    if (bc->bc_data == NULL)
        return (0);

    if (BP_IS_HOLE(bp)) {
        ASSERT(th->th_advance & ADVANCE_HOLES);
        return (0);
    }

    if (compare_bookmark(zb, &th->th_noread, dnp, 0) == 0) {
        error = EIO;
    } else if (arc_tryread(th->th_spa, bp, bc->bc_data) == 0) {
        error = 0;
        th->th_arc_hits++;
    } else {
        error = zio_wait(zio_read(NULL, th->th_spa, bp, bc->bc_data,
            BP_GET_LSIZE(bp), NULL, NULL, ZIO_PRIORITY_SYNC_READ,
            th->th_zio_flags | ZIO_FLAG_DONT_CACHE));

        if (BP_SHOULD_BYTESWAP(bp) && error == 0)
            (zb->zb_level > 0 ? byteswap_uint64_array :
                dmu_ot[BP_GET_TYPE(bp)].ot_byteswap)(bc->bc_data,
                BP_GET_LSIZE(bp));
        th->th_reads++;
    }

    if (error) {
        bc->bc_errno = error;
        error = traverse_callback(th, NULL, bc);
        ASSERT(error == EAGAIN || error == EINTR || error == ERESTART);
        bc->bc_blkptr.blk_birth = -1ULL;
    }

    dprintf("cache %02x error %d <%llu, %llu, %d, %llx>\n",
        bc - &th->th_cache[0][0], error,
        zb->zb_objset, zb->zb_object, zb->zb_level, zb->zb_blkid);

    return (error);
}

static int
find_block(traverse_handle_t *th, zseg_t *zseg, dnode_phys_t *dnp, int depth)
{
    zbookmark_t *zb = &zseg->seg_start;
    traverse_blk_cache_t *bc;
    blkptr_t *bp = dnp->dn_blkptr;
    int i, first, level;
    int nbp = dnp->dn_nblkptr;
    int minlevel = zb->zb_level;
    int maxlevel = dnp->dn_nlevels - 1;
    int wshift = dnp->dn_indblkshift - SPA_BLKPTRSHIFT;
    int bp_shift = BP_SPAN_SHIFT(maxlevel - minlevel, wshift);
    uint64_t blkid = zb->zb_blkid >> bp_shift;
    int do_holes = (th->th_advance & ADVANCE_HOLES) && depth == ZB_DN_CACHE;
    int rc;

    if (minlevel > maxlevel || blkid >= nbp)
        return (ERANGE);

    for (level = maxlevel; level >= minlevel; level--) {
        first = P2PHASE(blkid, 1ULL << wshift);

        for (i = first; i < nbp; i++)
            if (bp[i].blk_birth > zseg->seg_mintxg ||
                BP_IS_HOLE(&bp[i]) && do_holes)
                break;

        if (i != first) {
            i--;
            SET_BOOKMARK_LB(zb, level, blkid + (i - first));
            return (ENOTBLK);
        }

        bc = &th->th_cache[depth][level];

        SET_BOOKMARK(&bc->bc_bookmark, zb->zb_objset, zb->zb_object,
            level, blkid);

        if (rc = traverse_read(th, bc, bp + i, dnp)) {
            if (rc != EAGAIN) {
                SET_BOOKMARK_LB(zb, level, blkid);
            }
            return (rc);
        }

        if (BP_IS_HOLE(&bp[i])) {
            SET_BOOKMARK_LB(zb, level, blkid);
            th->th_lastcb.zb_level = ZB_NO_LEVEL;
            return (0);
        }

        nbp = 1 << wshift;
        bp = bc->bc_data;
        bp_shift -= wshift;
        blkid = zb->zb_blkid >> bp_shift;
    }

    return (0);
}

static int
get_dnode(traverse_handle_t *th, uint64_t objset, dnode_phys_t *mdn,
    uint64_t *objectp, dnode_phys_t **dnpp, uint64_t txg, int type, int depth)
{
    zseg_t zseg;
    zbookmark_t *zb = &zseg.seg_start;
    uint64_t object = *objectp;
    int i, rc;

    SET_BOOKMARK(zb, objset, 0, 0, object / DNODES_PER_BLOCK);
    SET_BOOKMARK(&zseg.seg_end, objset, 0, 0, ZB_MAXBLKID);

    zseg.seg_mintxg = txg;
    zseg.seg_maxtxg = -1ULL;

    for (;;) {
        rc = find_block(th, &zseg, mdn, depth);

        if (rc == EAGAIN || rc == EINTR || rc == ERANGE)
            break;

        if (rc == 0 && zb->zb_level == 0) {
            dnode_phys_t *dnp = th->th_cache[depth][0].bc_data;
            for (i = 0; i < DNODES_PER_BLOCK; i++) {
                object = (zb->zb_blkid * DNODES_PER_BLOCK) + i;
                if (object >= *objectp &&
                    dnp[i].dn_type != DMU_OT_NONE &&
                    (type == -1 || dnp[i].dn_type == type)) {
                    *objectp = object;
                    *dnpp = &dnp[i];
                    return (0);
                }
            }
        }

        rc = advance_block(&zseg, mdn, rc, ADVANCE_PRE);

        if (rc == ERANGE)
            break;
    }

    if (rc == ERANGE)
        *objectp = ZB_MAXOBJECT;

    return (rc);
}

static int
traverse_segment(traverse_handle_t *th, zseg_t *zseg, blkptr_t *mosbp)
{
    zbookmark_t *zb = &zseg->seg_start;
    traverse_blk_cache_t *bc;
    dnode_phys_t *dn, *dn_tmp;
    int worklimit = 1000;
    int rc;

    dprintf("<%llu, %llu, %d, %llx>\n",
        zb->zb_objset, zb->zb_object, zb->zb_level, zb->zb_blkid);

    bc = &th->th_cache[ZB_MOS_CACHE][ZB_MAXLEVEL - 1];
    dn = &((objset_phys_t *)bc->bc_data)->os_meta_dnode;

    SET_BOOKMARK(&bc->bc_bookmark, 0, 0, -1, 0);

    rc = traverse_read(th, bc, mosbp, dn);

    if (rc)     /* If we get ERESTART, we've got nowhere left to go */
        return (rc == ERESTART ? EINTR : rc);

    ASSERT(dn->dn_nlevels < ZB_MAXLEVEL);

    if (zb->zb_objset != 0) {
        uint64_t objset = zb->zb_objset;
        dsl_dataset_phys_t *dsp;

        rc = get_dnode(th, 0, dn, &objset, &dn_tmp, 0,
            DMU_OT_DSL_OBJSET, ZB_MOS_CACHE);

        if (objset != zb->zb_objset)
            rc = advance_objset(zseg, objset, th->th_advance);

        if (rc != 0)
            return (rc);

        dsp = DN_BONUS(dn_tmp);

        bc = &th->th_cache[ZB_MDN_CACHE][ZB_MAXLEVEL - 1];
        dn = &((objset_phys_t *)bc->bc_data)->os_meta_dnode;

        SET_BOOKMARK(&bc->bc_bookmark, objset, 0, -1, 0);

        rc = traverse_read(th, bc, &dsp->ds_bp, dn);

        if (rc != 0) {
            if (rc == ERESTART)
                rc = advance_objset(zseg, zb->zb_objset + 1,
                    th->th_advance);
            return (rc);
        }

        if (th->th_advance & ADVANCE_PRUNE)
            zseg->seg_mintxg =
                MAX(zseg->seg_mintxg, dsp->ds_prev_snap_txg);
    }

    if (zb->zb_level == -1) {
        ASSERT(zb->zb_object == 0);

        if (bc->bc_blkptr.blk_birth > zseg->seg_mintxg) {
            rc = traverse_callback(th, zseg, bc);
            if (rc) {
                ASSERT(rc == EINTR);
                return (rc);
            }
        }

        return (advance_from_osphys(zseg, th->th_advance));
    }

    if (zb->zb_object != 0) {
        uint64_t object = zb->zb_object;

        rc = get_dnode(th, zb->zb_objset, dn, &object, &dn_tmp,
            zseg->seg_mintxg, -1, ZB_MDN_CACHE);

        if (object != zb->zb_object)
            rc = advance_object(zseg, object, th->th_advance);

        if (rc != 0)
            return (rc);

        dn = dn_tmp;
    }

    if (zb->zb_level == ZB_MAXLEVEL)
        zb->zb_level = dn->dn_nlevels - 1;

    for (;;) {
        rc = find_block(th, zseg, dn, ZB_DN_CACHE);

        if (rc == EAGAIN || rc == EINTR || rc == ERANGE)
            break;

        if (rc == 0) {
            bc = &th->th_cache[ZB_DN_CACHE][zb->zb_level];
            ASSERT(bc->bc_dnode == dn);
            ASSERT(bc->bc_blkptr.blk_birth <= mosbp->blk_birth);
            rc = traverse_callback(th, zseg, bc);
            if (rc) {
                ASSERT(rc == EINTR);
                return (rc);
            }
            if (BP_IS_HOLE(&bc->bc_blkptr)) {
                ASSERT(th->th_advance & ADVANCE_HOLES);
                rc = ENOTBLK;
            }
        }

        rc = advance_block(zseg, dn, rc, th->th_advance);

        if (rc == ERANGE)
            break;

        /*
         * Give spa_sync() a chance to run.
         */
        if (spa_traverse_wanted(th->th_spa)) {
            th->th_syncs++;
            return (EAGAIN);
        }

        if (--worklimit == 0)
            return (EAGAIN);
    }

    if (rc == ERANGE)
        rc = advance_object(zseg, zb->zb_object + 1, th->th_advance);

    return (rc);
}

/*
 * It is the caller's responsibility to ensure that the dsl_dataset_t
 * doesn't go away during traversal.
 */
int
traverse_dsl_dataset(dsl_dataset_t *ds, uint64_t txg_start, int advance,
    blkptr_cb_t func, void *arg)
{
    spa_t *spa = ds->ds_dir->dd_pool->dp_spa;
    traverse_handle_t *th;
    int err;

    th = traverse_init(spa, func, arg, advance, ZIO_FLAG_MUSTSUCCEED);

    traverse_add_objset(th, txg_start, -1ULL, ds->ds_object);

    while ((err = traverse_more(th)) == EAGAIN)
        continue;

    traverse_fini(th);
    return (err);
}

int
traverse_more(traverse_handle_t *th)
{
    zseg_t *zseg = list_head(&th->th_seglist);
    uint64_t save_txg;  /* XXX won't be necessary with real itinerary */
    krwlock_t *rw = spa_traverse_rwlock(th->th_spa);
    blkptr_t *mosbp = spa_get_rootblkptr(th->th_spa);
    int rc;

    if (zseg == NULL)
        return (0);

    th->th_restarts++;

    save_txg = zseg->seg_mintxg;

    if (!(th->th_advance & ADVANCE_NOLOCK))
        rw_enter(rw, RW_READER);

    rc = traverse_segment(th, zseg, mosbp);
    ASSERT(rc == ERANGE || rc == EAGAIN || rc == EINTR);

    if (!(th->th_advance & ADVANCE_NOLOCK))
        rw_exit(rw);

    zseg->seg_mintxg = save_txg;

    if (rc == ERANGE) {
        list_remove(&th->th_seglist, zseg);
        kmem_free(zseg, sizeof (*zseg));
        return (EAGAIN);
    }

    return (rc);
}

/*
 * Note: (mintxg, maxtxg) is an open interval; mintxg and maxtxg themselves
 * are not included.  The blocks covered by this segment will all have
 * mintxg < birth < maxtxg.
 */
static void
traverse_add_segment(traverse_handle_t *th, uint64_t mintxg, uint64_t maxtxg,
    uint64_t sobjset, uint64_t sobject, int slevel, uint64_t sblkid,
    uint64_t eobjset, uint64_t eobject, int elevel, uint64_t eblkid)
{
    zseg_t *zseg;

    zseg = kmem_alloc(sizeof (zseg_t), KM_SLEEP);

    zseg->seg_mintxg = mintxg;
    zseg->seg_maxtxg = maxtxg;

    zseg->seg_start.zb_objset = sobjset;
    zseg->seg_start.zb_object = sobject;
    zseg->seg_start.zb_level = slevel;
    zseg->seg_start.zb_blkid = sblkid;

    zseg->seg_end.zb_objset = eobjset;
    zseg->seg_end.zb_object = eobject;
    zseg->seg_end.zb_level = elevel;
    zseg->seg_end.zb_blkid = eblkid;

    list_insert_tail(&th->th_seglist, zseg);
}

void
traverse_add_dnode(traverse_handle_t *th, uint64_t mintxg, uint64_t maxtxg,
    uint64_t objset, uint64_t object)
{
    if (th->th_advance & ADVANCE_PRE)
        traverse_add_segment(th, mintxg, maxtxg,
            objset, object, ZB_MAXLEVEL, 0,
            objset, object, 0, ZB_MAXBLKID);
    else
        traverse_add_segment(th, mintxg, maxtxg,
            objset, object, 0, 0,
            objset, object, 0, ZB_MAXBLKID);
}

void
traverse_add_objset(traverse_handle_t *th, uint64_t mintxg, uint64_t maxtxg,
    uint64_t objset)
{
    if (th->th_advance & ADVANCE_PRE)
        traverse_add_segment(th, mintxg, maxtxg,
            objset, 0, -1, 0,
            objset, ZB_MAXOBJECT, 0, ZB_MAXBLKID);
    else
        traverse_add_segment(th, mintxg, maxtxg,
            objset, 1, 0, 0,
            objset, 0, -1, 0);
}

void
traverse_add_pool(traverse_handle_t *th, uint64_t mintxg, uint64_t maxtxg)
{
    if (th->th_advance & ADVANCE_PRE)
        traverse_add_segment(th, mintxg, maxtxg,
            0, 0, -1, 0,
            ZB_MAXOBJSET, ZB_MAXOBJECT, 0, ZB_MAXBLKID);
    else
        traverse_add_segment(th, mintxg, maxtxg,
            1, 1, 0, 0,
            0, 0, -1, 0);
}

traverse_handle_t *
traverse_init(spa_t *spa, blkptr_cb_t func, void *arg, int advance,
    int zio_flags)
{
    traverse_handle_t *th;
    int d, l;

    th = kmem_zalloc(sizeof (*th), KM_SLEEP);

    th->th_spa = spa;
    th->th_func = func;
    th->th_arg = arg;
    th->th_advance = advance;
    th->th_lastcb.zb_level = ZB_NO_LEVEL;
    th->th_noread.zb_level = ZB_NO_LEVEL;
    th->th_zio_flags = zio_flags;

    list_create(&th->th_seglist, sizeof (zseg_t),
        offsetof(zseg_t, seg_node));

    for (d = 0; d < ZB_DEPTH; d++) {
        for (l = 0; l < ZB_MAXLEVEL; l++) {
            if ((advance & ADVANCE_DATA) ||
                l != 0 || d != ZB_DN_CACHE)
                th->th_cache[d][l].bc_data =
                    zio_buf_alloc(SPA_MAXBLOCKSIZE);
        }
    }

    return (th);
}

void
traverse_fini(traverse_handle_t *th)
{
    int d, l;
    zseg_t *zseg;

    for (d = 0; d < ZB_DEPTH; d++)
        for (l = 0; l < ZB_MAXLEVEL; l++)
            if (th->th_cache[d][l].bc_data != NULL)
                zio_buf_free(th->th_cache[d][l].bc_data,
                    SPA_MAXBLOCKSIZE);

    while ((zseg = list_head(&th->th_seglist)) != NULL) {
        list_remove(&th->th_seglist, zseg);
        kmem_free(zseg, sizeof (*zseg));
    }

    list_destroy(&th->th_seglist);

    dprintf("%llu hit, %llu ARC, %llu IO, %llu cb, %llu sync, %llu again\n",
        th->th_hits, th->th_arc_hits, th->th_reads, th->th_callbacks,
        th->th_syncs, th->th_restarts);

    kmem_free(th, sizeof (*th));
}