zfs: allow large block/gzip/raidz for boot pools

[unleashed.git] / usr / src / uts / common / fs / zfs / vdev.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or 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) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
 * Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
 * Copyright (c) 2014 Integros [integros.com]
 * Copyright 2016 Toomas Soome <tsoome@me.com>
 */

#include <sys/zfs_context.h>
#include <sys/fm/fs/zfs.h>
#include <sys/spa.h>
#include <sys/spa_impl.h>
#include <sys/dmu.h>
#include <sys/dmu_tx.h>
#include <sys/vdev_impl.h>
#include <sys/uberblock_impl.h>
#include <sys/metaslab.h>
#include <sys/metaslab_impl.h>
#include <sys/space_map.h>
#include <sys/space_reftree.h>
#include <sys/zio.h>
#include <sys/zap.h>
#include <sys/fs/zfs.h>
#include <sys/arc.h>
#include <sys/zil.h>
#include <sys/dsl_scan.h>

/*
 * Virtual device management.
 */

static vdev_ops_t *vdev_ops_table[] = {
        &vdev_root_ops,
        &vdev_raidz_ops,
        &vdev_mirror_ops,
        &vdev_replacing_ops,
        &vdev_spare_ops,
        &vdev_disk_ops,
        &vdev_file_ops,
        &vdev_missing_ops,
        &vdev_hole_ops,
        NULL
};

/* maximum scrub/resilver I/O queue per leaf vdev */
int zfs_scrub_limit = 10;

/*
 * When a vdev is added, it will be divided into approximately (but no
 * more than) this number of metaslabs.
 */
int metaslabs_per_vdev = 200;

/*
 * Given a vdev type, return the appropriate ops vector.
 */
static vdev_ops_t *
vdev_getops(const char *type)
{
        vdev_ops_t *ops, **opspp;

        for (opspp = vdev_ops_table; (ops = *opspp) != NULL; opspp++)
                if (strcmp(ops->vdev_op_type, type) == 0)
                        break;

        return (ops);
}

/*
 * Default asize function: return the MAX of psize with the asize of
 * all children.  This is what's used by anything other than RAID-Z.
 */
uint64_t
vdev_default_asize(vdev_t *vd, uint64_t psize)
{
        uint64_t asize = P2ROUNDUP(psize, 1ULL << vd->vdev_top->vdev_ashift);
        uint64_t csize;

        for (int c = 0; c < vd->vdev_children; c++) {
                csize = vdev_psize_to_asize(vd->vdev_child[c], psize);
                asize = MAX(asize, csize);
        }

        return (asize);
}

/*
 * Get the minimum allocatable size. We define the allocatable size as
 * the vdev's asize rounded to the nearest metaslab. This allows us to
 * replace or attach devices which don't have the same physical size but
 * can still satisfy the same number of allocations.
 */
uint64_t
vdev_get_min_asize(vdev_t *vd)
{
        vdev_t *pvd = vd->vdev_parent;

        /*
         * If our parent is NULL (inactive spare or cache) or is the root,
         * just return our own asize.
         */
        if (pvd == NULL)
                return (vd->vdev_asize);

        /*
         * The top-level vdev just returns the allocatable size rounded
         * to the nearest metaslab.
         */
        if (vd == vd->vdev_top)
                return (P2ALIGN(vd->vdev_asize, 1ULL << vd->vdev_ms_shift));

        /*
         * The allocatable space for a raidz vdev is N * sizeof(smallest child),
         * so each child must provide at least 1/Nth of its asize.
         */
        if (pvd->vdev_ops == &vdev_raidz_ops)
                return (pvd->vdev_min_asize / pvd->vdev_children);

        return (pvd->vdev_min_asize);
}

void
vdev_set_min_asize(vdev_t *vd)
{
        vd->vdev_min_asize = vdev_get_min_asize(vd);

        for (int c = 0; c < vd->vdev_children; c++)
                vdev_set_min_asize(vd->vdev_child[c]);
}

vdev_t *
vdev_lookup_top(spa_t *spa, uint64_t vdev)
{
        vdev_t *rvd = spa->spa_root_vdev;

        ASSERT(spa_config_held(spa, SCL_ALL, RW_READER) != 0);

        if (vdev < rvd->vdev_children) {
                ASSERT(rvd->vdev_child[vdev] != NULL);
                return (rvd->vdev_child[vdev]);
        }

        return (NULL);
}

vdev_t *
vdev_lookup_by_guid(vdev_t *vd, uint64_t guid)
{
        vdev_t *mvd;

        if (vd->vdev_guid == guid)
                return (vd);

        for (int c = 0; c < vd->vdev_children; c++)
                if ((mvd = vdev_lookup_by_guid(vd->vdev_child[c], guid)) !=
                    NULL)
                        return (mvd);

        return (NULL);
}

static int
vdev_count_leaves_impl(vdev_t *vd)
{
        int n = 0;

        if (vd->vdev_ops->vdev_op_leaf)
                return (1);

        for (int c = 0; c < vd->vdev_children; c++)
                n += vdev_count_leaves_impl(vd->vdev_child[c]);

        return (n);
}

int
vdev_count_leaves(spa_t *spa)
{
        return (vdev_count_leaves_impl(spa->spa_root_vdev));
}

void
vdev_add_child(vdev_t *pvd, vdev_t *cvd)
{
        size_t oldsize, newsize;
        uint64_t id = cvd->vdev_id;
        vdev_t **newchild;
        spa_t *spa = cvd->vdev_spa;

        ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
        ASSERT(cvd->vdev_parent == NULL);

        cvd->vdev_parent = pvd;

        if (pvd == NULL)
                return;

        ASSERT(id >= pvd->vdev_children || pvd->vdev_child[id] == NULL);

        oldsize = pvd->vdev_children * sizeof (vdev_t *);
        pvd->vdev_children = MAX(pvd->vdev_children, id + 1);
        newsize = pvd->vdev_children * sizeof (vdev_t *);

        newchild = kmem_zalloc(newsize, KM_SLEEP);
        if (pvd->vdev_child != NULL) {
                bcopy(pvd->vdev_child, newchild, oldsize);
                kmem_free(pvd->vdev_child, oldsize);
        }

        pvd->vdev_child = newchild;
        pvd->vdev_child[id] = cvd;

        cvd->vdev_top = (pvd->vdev_top ? pvd->vdev_top: cvd);
        ASSERT(cvd->vdev_top->vdev_parent->vdev_parent == NULL);

        /*
         * Walk up all ancestors to update guid sum.
         */
        for (; pvd != NULL; pvd = pvd->vdev_parent)
                pvd->vdev_guid_sum += cvd->vdev_guid_sum;
}

void
vdev_remove_child(vdev_t *pvd, vdev_t *cvd)
{
        int c;
        uint_t id = cvd->vdev_id;

        ASSERT(cvd->vdev_parent == pvd);

        if (pvd == NULL)
                return;

        ASSERT(id < pvd->vdev_children);
        ASSERT(pvd->vdev_child[id] == cvd);

        pvd->vdev_child[id] = NULL;
        cvd->vdev_parent = NULL;

        for (c = 0; c < pvd->vdev_children; c++)
                if (pvd->vdev_child[c])
                        break;

        if (c == pvd->vdev_children) {
                kmem_free(pvd->vdev_child, c * sizeof (vdev_t *));
                pvd->vdev_child = NULL;
                pvd->vdev_children = 0;
        }

        /*
         * Walk up all ancestors to update guid sum.
         */
        for (; pvd != NULL; pvd = pvd->vdev_parent)
                pvd->vdev_guid_sum -= cvd->vdev_guid_sum;
}

/*
 * Remove any holes in the child array.
 */
void
vdev_compact_children(vdev_t *pvd)
{
        vdev_t **newchild, *cvd;
        int oldc = pvd->vdev_children;
        int newc;

        ASSERT(spa_config_held(pvd->vdev_spa, SCL_ALL, RW_WRITER) == SCL_ALL);

        for (int c = newc = 0; c < oldc; c++)
                if (pvd->vdev_child[c])
                        newc++;

        newchild = kmem_alloc(newc * sizeof (vdev_t *), KM_SLEEP);

        for (int c = newc = 0; c < oldc; c++) {
                if ((cvd = pvd->vdev_child[c]) != NULL) {
                        newchild[newc] = cvd;
                        cvd->vdev_id = newc++;
                }
        }

        kmem_free(pvd->vdev_child, oldc * sizeof (vdev_t *));
        pvd->vdev_child = newchild;
        pvd->vdev_children = newc;
}

/*
 * Allocate and minimally initialize a vdev_t.
 */
vdev_t *
vdev_alloc_common(spa_t *spa, uint_t id, uint64_t guid, vdev_ops_t *ops)
{
        vdev_t *vd;

        vd = kmem_zalloc(sizeof (vdev_t), KM_SLEEP);

        if (spa->spa_root_vdev == NULL) {
                ASSERT(ops == &vdev_root_ops);
                spa->spa_root_vdev = vd;
                spa->spa_load_guid = spa_generate_guid(NULL);
        }

        if (guid == 0 && ops != &vdev_hole_ops) {
                if (spa->spa_root_vdev == vd) {
                        /*
                         * The root vdev's guid will also be the pool guid,
                         * which must be unique among all pools.
                         */
                        guid = spa_generate_guid(NULL);
                } else {
                        /*
                         * Any other vdev's guid must be unique within the pool.
                         */
                        guid = spa_generate_guid(spa);
                }
                ASSERT(!spa_guid_exists(spa_guid(spa), guid));
        }

        vd->vdev_spa = spa;
        vd->vdev_id = id;
        vd->vdev_guid = guid;
        vd->vdev_guid_sum = guid;
        vd->vdev_ops = ops;
        vd->vdev_state = VDEV_STATE_CLOSED;
        vd->vdev_ishole = (ops == &vdev_hole_ops);

        mutex_init(&vd->vdev_dtl_lock, NULL, MUTEX_DEFAULT, NULL);
        mutex_init(&vd->vdev_stat_lock, NULL, MUTEX_DEFAULT, NULL);
        mutex_init(&vd->vdev_probe_lock, NULL, MUTEX_DEFAULT, NULL);
        for (int t = 0; t < DTL_TYPES; t++) {
                vd->vdev_dtl[t] = range_tree_create(NULL, NULL,
                    &vd->vdev_dtl_lock);
        }
        txg_list_create(&vd->vdev_ms_list,
            offsetof(struct metaslab, ms_txg_node));
        txg_list_create(&vd->vdev_dtl_list,
            offsetof(struct vdev, vdev_dtl_node));
        vd->vdev_stat.vs_timestamp = gethrtime();
        vdev_queue_init(vd);
        vdev_cache_init(vd);

        return (vd);
}

/*
 * Allocate a new vdev.  The 'alloctype' is used to control whether we are
 * creating a new vdev or loading an existing one - the behavior is slightly
 * different for each case.
 */
int
vdev_alloc(spa_t *spa, vdev_t **vdp, nvlist_t *nv, vdev_t *parent, uint_t id,
    int alloctype)
{
        vdev_ops_t *ops;
        char *type;
        uint64_t guid = 0, islog, nparity;
        vdev_t *vd;

        ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);

        if (nvlist_lookup_string(nv, ZPOOL_CONFIG_TYPE, &type) != 0)
                return (SET_ERROR(EINVAL));

        if ((ops = vdev_getops(type)) == NULL)
                return (SET_ERROR(EINVAL));

        /*
         * If this is a load, get the vdev guid from the nvlist.
         * Otherwise, vdev_alloc_common() will generate one for us.
         */
        if (alloctype == VDEV_ALLOC_LOAD) {
                uint64_t label_id;

                if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_ID, &label_id) ||
                    label_id != id)
                        return (SET_ERROR(EINVAL));

                if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_GUID, &guid) != 0)
                        return (SET_ERROR(EINVAL));
        } else if (alloctype == VDEV_ALLOC_SPARE) {
                if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_GUID, &guid) != 0)
                        return (SET_ERROR(EINVAL));
        } else if (alloctype == VDEV_ALLOC_L2CACHE) {
                if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_GUID, &guid) != 0)
                        return (SET_ERROR(EINVAL));
        } else if (alloctype == VDEV_ALLOC_ROOTPOOL) {
                if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_GUID, &guid) != 0)
                        return (SET_ERROR(EINVAL));
        }

        /*
         * The first allocated vdev must be of type 'root'.
         */
        if (ops != &vdev_root_ops && spa->spa_root_vdev == NULL)
                return (SET_ERROR(EINVAL));

        /*
         * Determine whether we're a log vdev.
         */
        islog = 0;
        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_IS_LOG, &islog);
        if (islog && spa_version(spa) < SPA_VERSION_SLOGS)
                return (SET_ERROR(ENOTSUP));

        if (ops == &vdev_hole_ops && spa_version(spa) < SPA_VERSION_HOLES)
                return (SET_ERROR(ENOTSUP));

        /*
         * Set the nparity property for RAID-Z vdevs.
         */
        nparity = -1ULL;
        if (ops == &vdev_raidz_ops) {
                if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_NPARITY,
                    &nparity) == 0) {
                        if (nparity == 0 || nparity > VDEV_RAIDZ_MAXPARITY)
                                return (SET_ERROR(EINVAL));
                        /*
                         * Previous versions could only support 1 or 2 parity
                         * device.
                         */
                        if (nparity > 1 &&
                            spa_version(spa) < SPA_VERSION_RAIDZ2)
                                return (SET_ERROR(ENOTSUP));
                        if (nparity > 2 &&
                            spa_version(spa) < SPA_VERSION_RAIDZ3)
                                return (SET_ERROR(ENOTSUP));
                } else {
                        /*
                         * We require the parity to be specified for SPAs that
                         * support multiple parity levels.
                         */
                        if (spa_version(spa) >= SPA_VERSION_RAIDZ2)
                                return (SET_ERROR(EINVAL));
                        /*
                         * Otherwise, we default to 1 parity device for RAID-Z.
                         */
                        nparity = 1;
                }
        } else {
                nparity = 0;
        }
        ASSERT(nparity != -1ULL);

        vd = vdev_alloc_common(spa, id, guid, ops);

        vd->vdev_islog = islog;
        vd->vdev_nparity = nparity;

        if (nvlist_lookup_string(nv, ZPOOL_CONFIG_PATH, &vd->vdev_path) == 0)
                vd->vdev_path = spa_strdup(vd->vdev_path);
        if (nvlist_lookup_string(nv, ZPOOL_CONFIG_DEVID, &vd->vdev_devid) == 0)
                vd->vdev_devid = spa_strdup(vd->vdev_devid);
        if (nvlist_lookup_string(nv, ZPOOL_CONFIG_PHYS_PATH,
            &vd->vdev_physpath) == 0)
                vd->vdev_physpath = spa_strdup(vd->vdev_physpath);
        if (nvlist_lookup_string(nv, ZPOOL_CONFIG_FRU, &vd->vdev_fru) == 0)
                vd->vdev_fru = spa_strdup(vd->vdev_fru);

        /*
         * Set the whole_disk property.  If it's not specified, leave the value
         * as -1.
         */
        if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_WHOLE_DISK,
            &vd->vdev_wholedisk) != 0)
                vd->vdev_wholedisk = -1ULL;

        /*
         * Look for the 'not present' flag.  This will only be set if the device
         * was not present at the time of import.
         */
        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_NOT_PRESENT,
            &vd->vdev_not_present);

        /*
         * Get the alignment requirement.
         */
        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_ASHIFT, &vd->vdev_ashift);

        /*
         * Retrieve the vdev creation time.
         */
        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_CREATE_TXG,
            &vd->vdev_crtxg);

        /*
         * If we're a top-level vdev, try to load the allocation parameters.
         */
        if (parent && !parent->vdev_parent &&
            (alloctype == VDEV_ALLOC_LOAD || alloctype == VDEV_ALLOC_SPLIT)) {
                (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_METASLAB_ARRAY,
                    &vd->vdev_ms_array);
                (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_METASLAB_SHIFT,
                    &vd->vdev_ms_shift);
                (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_ASIZE,
                    &vd->vdev_asize);
                (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_REMOVING,
                    &vd->vdev_removing);
                (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_VDEV_TOP_ZAP,
                    &vd->vdev_top_zap);
        } else {
                ASSERT0(vd->vdev_top_zap);
        }

        if (parent && !parent->vdev_parent && alloctype != VDEV_ALLOC_ATTACH) {
                ASSERT(alloctype == VDEV_ALLOC_LOAD ||
                    alloctype == VDEV_ALLOC_ADD ||
                    alloctype == VDEV_ALLOC_SPLIT ||
                    alloctype == VDEV_ALLOC_ROOTPOOL);
                vd->vdev_mg = metaslab_group_create(islog ?
                    spa_log_class(spa) : spa_normal_class(spa), vd);
        }

        if (vd->vdev_ops->vdev_op_leaf &&
            (alloctype == VDEV_ALLOC_LOAD || alloctype == VDEV_ALLOC_SPLIT)) {
                (void) nvlist_lookup_uint64(nv,
                    ZPOOL_CONFIG_VDEV_LEAF_ZAP, &vd->vdev_leaf_zap);
        } else {
                ASSERT0(vd->vdev_leaf_zap);
        }

        /*
         * If we're a leaf vdev, try to load the DTL object and other state.
         */

        if (vd->vdev_ops->vdev_op_leaf &&
            (alloctype == VDEV_ALLOC_LOAD || alloctype == VDEV_ALLOC_L2CACHE ||
            alloctype == VDEV_ALLOC_ROOTPOOL)) {
                if (alloctype == VDEV_ALLOC_LOAD) {
                        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_DTL,
                            &vd->vdev_dtl_object);
                        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_UNSPARE,
                            &vd->vdev_unspare);
                }

                if (alloctype == VDEV_ALLOC_ROOTPOOL) {
                        uint64_t spare = 0;

                        if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_IS_SPARE,
                            &spare) == 0 && spare)
                                spa_spare_add(vd);
                }

                (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_OFFLINE,
                    &vd->vdev_offline);

                (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_RESILVER_TXG,
                    &vd->vdev_resilver_txg);

                /*
                 * When importing a pool, we want to ignore the persistent fault
                 * state, as the diagnosis made on another system may not be
                 * valid in the current context.  Local vdevs will
                 * remain in the faulted state.
                 */
                if (spa_load_state(spa) == SPA_LOAD_OPEN) {
                        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_FAULTED,
                            &vd->vdev_faulted);
                        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_DEGRADED,
                            &vd->vdev_degraded);
                        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_REMOVED,
                            &vd->vdev_removed);

                        if (vd->vdev_faulted || vd->vdev_degraded) {
                                char *aux;

                                vd->vdev_label_aux =
                                    VDEV_AUX_ERR_EXCEEDED;
                                if (nvlist_lookup_string(nv,
                                    ZPOOL_CONFIG_AUX_STATE, &aux) == 0 &&
                                    strcmp(aux, "external") == 0)
                                        vd->vdev_label_aux = VDEV_AUX_EXTERNAL;
                        }
                }
        }

        /*
         * Add ourselves to the parent's list of children.
         */
        vdev_add_child(parent, vd);

        *vdp = vd;

        return (0);
}

void
vdev_free(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;

        /*
         * vdev_free() implies closing the vdev first.  This is simpler than
         * trying to ensure complicated semantics for all callers.
         */
        vdev_close(vd);

        ASSERT(!list_link_active(&vd->vdev_config_dirty_node));
        ASSERT(!list_link_active(&vd->vdev_state_dirty_node));

        /*
         * Free all children.
         */
        for (int c = 0; c < vd->vdev_children; c++)
                vdev_free(vd->vdev_child[c]);

        ASSERT(vd->vdev_child == NULL);
        ASSERT(vd->vdev_guid_sum == vd->vdev_guid);

        /*
         * Discard allocation state.
         */
        if (vd->vdev_mg != NULL) {
                vdev_metaslab_fini(vd);
                metaslab_group_destroy(vd->vdev_mg);
        }

        ASSERT0(vd->vdev_stat.vs_space);
        ASSERT0(vd->vdev_stat.vs_dspace);
        ASSERT0(vd->vdev_stat.vs_alloc);

        /*
         * Remove this vdev from its parent's child list.
         */
        vdev_remove_child(vd->vdev_parent, vd);

        ASSERT(vd->vdev_parent == NULL);

        /*
         * Clean up vdev structure.
         */
        vdev_queue_fini(vd);
        vdev_cache_fini(vd);

        if (vd->vdev_path)
                spa_strfree(vd->vdev_path);
        if (vd->vdev_devid)
                spa_strfree(vd->vdev_devid);
        if (vd->vdev_physpath)
                spa_strfree(vd->vdev_physpath);
        if (vd->vdev_fru)
                spa_strfree(vd->vdev_fru);

        if (vd->vdev_isspare)
                spa_spare_remove(vd);
        if (vd->vdev_isl2cache)
                spa_l2cache_remove(vd);

        txg_list_destroy(&vd->vdev_ms_list);
        txg_list_destroy(&vd->vdev_dtl_list);

        mutex_enter(&vd->vdev_dtl_lock);
        space_map_close(vd->vdev_dtl_sm);
        for (int t = 0; t < DTL_TYPES; t++) {
                range_tree_vacate(vd->vdev_dtl[t], NULL, NULL);
                range_tree_destroy(vd->vdev_dtl[t]);
        }
        mutex_exit(&vd->vdev_dtl_lock);

        mutex_destroy(&vd->vdev_dtl_lock);
        mutex_destroy(&vd->vdev_stat_lock);
        mutex_destroy(&vd->vdev_probe_lock);

        if (vd == spa->spa_root_vdev)
                spa->spa_root_vdev = NULL;

        kmem_free(vd, sizeof (vdev_t));
}

/*
 * Transfer top-level vdev state from svd to tvd.
 */
static void
vdev_top_transfer(vdev_t *svd, vdev_t *tvd)
{
        spa_t *spa = svd->vdev_spa;
        metaslab_t *msp;
        vdev_t *vd;
        int t;

        ASSERT(tvd == tvd->vdev_top);

        tvd->vdev_ms_array = svd->vdev_ms_array;
        tvd->vdev_ms_shift = svd->vdev_ms_shift;
        tvd->vdev_ms_count = svd->vdev_ms_count;
        tvd->vdev_top_zap = svd->vdev_top_zap;

        svd->vdev_ms_array = 0;
        svd->vdev_ms_shift = 0;
        svd->vdev_ms_count = 0;
        svd->vdev_top_zap = 0;

        if (tvd->vdev_mg)
                ASSERT3P(tvd->vdev_mg, ==, svd->vdev_mg);
        tvd->vdev_mg = svd->vdev_mg;
        tvd->vdev_ms = svd->vdev_ms;

        svd->vdev_mg = NULL;
        svd->vdev_ms = NULL;

        if (tvd->vdev_mg != NULL)
                tvd->vdev_mg->mg_vd = tvd;

        tvd->vdev_stat.vs_alloc = svd->vdev_stat.vs_alloc;
        tvd->vdev_stat.vs_space = svd->vdev_stat.vs_space;
        tvd->vdev_stat.vs_dspace = svd->vdev_stat.vs_dspace;

        svd->vdev_stat.vs_alloc = 0;
        svd->vdev_stat.vs_space = 0;
        svd->vdev_stat.vs_dspace = 0;

        for (t = 0; t < TXG_SIZE; t++) {
                while ((msp = txg_list_remove(&svd->vdev_ms_list, t)) != NULL)
                        (void) txg_list_add(&tvd->vdev_ms_list, msp, t);
                while ((vd = txg_list_remove(&svd->vdev_dtl_list, t)) != NULL)
                        (void) txg_list_add(&tvd->vdev_dtl_list, vd, t);
                if (txg_list_remove_this(&spa->spa_vdev_txg_list, svd, t))
                        (void) txg_list_add(&spa->spa_vdev_txg_list, tvd, t);
        }

        if (list_link_active(&svd->vdev_config_dirty_node)) {
                vdev_config_clean(svd);
                vdev_config_dirty(tvd);
        }

        if (list_link_active(&svd->vdev_state_dirty_node)) {
                vdev_state_clean(svd);
                vdev_state_dirty(tvd);
        }

        tvd->vdev_deflate_ratio = svd->vdev_deflate_ratio;
        svd->vdev_deflate_ratio = 0;

        tvd->vdev_islog = svd->vdev_islog;
        svd->vdev_islog = 0;
}

static void
vdev_top_update(vdev_t *tvd, vdev_t *vd)
{
        if (vd == NULL)
                return;

        vd->vdev_top = tvd;

        for (int c = 0; c < vd->vdev_children; c++)
                vdev_top_update(tvd, vd->vdev_child[c]);
}

/*
 * Add a mirror/replacing vdev above an existing vdev.
 */
vdev_t *
vdev_add_parent(vdev_t *cvd, vdev_ops_t *ops)
{
        spa_t *spa = cvd->vdev_spa;
        vdev_t *pvd = cvd->vdev_parent;
        vdev_t *mvd;

        ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);

        mvd = vdev_alloc_common(spa, cvd->vdev_id, 0, ops);

        mvd->vdev_asize = cvd->vdev_asize;
        mvd->vdev_min_asize = cvd->vdev_min_asize;
        mvd->vdev_max_asize = cvd->vdev_max_asize;
        mvd->vdev_ashift = cvd->vdev_ashift;
        mvd->vdev_state = cvd->vdev_state;
        mvd->vdev_crtxg = cvd->vdev_crtxg;

        vdev_remove_child(pvd, cvd);
        vdev_add_child(pvd, mvd);
        cvd->vdev_id = mvd->vdev_children;
        vdev_add_child(mvd, cvd);
        vdev_top_update(cvd->vdev_top, cvd->vdev_top);

        if (mvd == mvd->vdev_top)
                vdev_top_transfer(cvd, mvd);

        return (mvd);
}

/*
 * Remove a 1-way mirror/replacing vdev from the tree.
 */
void
vdev_remove_parent(vdev_t *cvd)
{
        vdev_t *mvd = cvd->vdev_parent;
        vdev_t *pvd = mvd->vdev_parent;

        ASSERT(spa_config_held(cvd->vdev_spa, SCL_ALL, RW_WRITER) == SCL_ALL);

        ASSERT(mvd->vdev_children == 1);
        ASSERT(mvd->vdev_ops == &vdev_mirror_ops ||
            mvd->vdev_ops == &vdev_replacing_ops ||
            mvd->vdev_ops == &vdev_spare_ops);
        cvd->vdev_ashift = mvd->vdev_ashift;

        vdev_remove_child(mvd, cvd);
        vdev_remove_child(pvd, mvd);

        /*
         * If cvd will replace mvd as a top-level vdev, preserve mvd's guid.
         * Otherwise, we could have detached an offline device, and when we
         * go to import the pool we'll think we have two top-level vdevs,
         * instead of a different version of the same top-level vdev.
         */
        if (mvd->vdev_top == mvd) {
                uint64_t guid_delta = mvd->vdev_guid - cvd->vdev_guid;
                cvd->vdev_orig_guid = cvd->vdev_guid;
                cvd->vdev_guid += guid_delta;
                cvd->vdev_guid_sum += guid_delta;
        }
        cvd->vdev_id = mvd->vdev_id;
        vdev_add_child(pvd, cvd);
        vdev_top_update(cvd->vdev_top, cvd->vdev_top);

        if (cvd == cvd->vdev_top)
                vdev_top_transfer(mvd, cvd);

        ASSERT(mvd->vdev_children == 0);
        vdev_free(mvd);
}

int
vdev_metaslab_init(vdev_t *vd, uint64_t txg)
{
        spa_t *spa = vd->vdev_spa;
        objset_t *mos = spa->spa_meta_objset;
        uint64_t m;
        uint64_t oldc = vd->vdev_ms_count;
        uint64_t newc = vd->vdev_asize >> vd->vdev_ms_shift;
        metaslab_t **mspp;
        int error;

        ASSERT(txg == 0 || spa_config_held(spa, SCL_ALLOC, RW_WRITER));

        /*
         * This vdev is not being allocated from yet or is a hole.
         */
        if (vd->vdev_ms_shift == 0)
                return (0);

        ASSERT(!vd->vdev_ishole);

        /*
         * Compute the raidz-deflation ratio.  Note, we hard-code
         * in 128k (1 << 17) because it is the "typical" blocksize.
         * Even though SPA_MAXBLOCKSIZE changed, this algorithm can not change,
         * otherwise it would inconsistently account for existing bp's.
         */
        vd->vdev_deflate_ratio = (1 << 17) /
            (vdev_psize_to_asize(vd, 1 << 17) >> SPA_MINBLOCKSHIFT);

        ASSERT(oldc <= newc);

        mspp = kmem_zalloc(newc * sizeof (*mspp), KM_SLEEP);

        if (oldc != 0) {
                bcopy(vd->vdev_ms, mspp, oldc * sizeof (*mspp));
                kmem_free(vd->vdev_ms, oldc * sizeof (*mspp));
        }

        vd->vdev_ms = mspp;
        vd->vdev_ms_count = newc;

        for (m = oldc; m < newc; m++) {
                uint64_t object = 0;

                if (txg == 0) {
                        error = dmu_read(mos, vd->vdev_ms_array,
                            m * sizeof (uint64_t), sizeof (uint64_t), &object,
                            DMU_READ_PREFETCH);
                        if (error)
                                return (error);
                }

                error = metaslab_init(vd->vdev_mg, m, object, txg,
                    &(vd->vdev_ms[m]));
                if (error)
                        return (error);
        }

        if (txg == 0)
                spa_config_enter(spa, SCL_ALLOC, FTAG, RW_WRITER);

        /*
         * If the vdev is being removed we don't activate
         * the metaslabs since we want to ensure that no new
         * allocations are performed on this device.
         */
        if (oldc == 0 && !vd->vdev_removing)
                metaslab_group_activate(vd->vdev_mg);

        if (txg == 0)
                spa_config_exit(spa, SCL_ALLOC, FTAG);

        return (0);
}

void
vdev_metaslab_fini(vdev_t *vd)
{
        uint64_t m;
        uint64_t count = vd->vdev_ms_count;

        if (vd->vdev_ms != NULL) {
                metaslab_group_passivate(vd->vdev_mg);
                for (m = 0; m < count; m++) {
                        metaslab_t *msp = vd->vdev_ms[m];

                        if (msp != NULL)
                                metaslab_fini(msp);
                }
                kmem_free(vd->vdev_ms, count * sizeof (metaslab_t *));
                vd->vdev_ms = NULL;
        }
}

typedef struct vdev_probe_stats {
        boolean_t       vps_readable;
        boolean_t       vps_writeable;
        int             vps_flags;
} vdev_probe_stats_t;

static void
vdev_probe_done(zio_t *zio)
{
        spa_t *spa = zio->io_spa;
        vdev_t *vd = zio->io_vd;
        vdev_probe_stats_t *vps = zio->io_private;

        ASSERT(vd->vdev_probe_zio != NULL);

        if (zio->io_type == ZIO_TYPE_READ) {
                if (zio->io_error == 0)
                        vps->vps_readable = 1;
                if (zio->io_error == 0 && spa_writeable(spa)) {
                        zio_nowait(zio_write_phys(vd->vdev_probe_zio, vd,
                            zio->io_offset, zio->io_size, zio->io_data,
                            ZIO_CHECKSUM_OFF, vdev_probe_done, vps,
                            ZIO_PRIORITY_SYNC_WRITE, vps->vps_flags, B_TRUE));
                } else {
                        zio_buf_free(zio->io_data, zio->io_size);
                }
        } else if (zio->io_type == ZIO_TYPE_WRITE) {
                if (zio->io_error == 0)
                        vps->vps_writeable = 1;
                zio_buf_free(zio->io_data, zio->io_size);
        } else if (zio->io_type == ZIO_TYPE_NULL) {
                zio_t *pio;

                vd->vdev_cant_read |= !vps->vps_readable;
                vd->vdev_cant_write |= !vps->vps_writeable;

                if (vdev_readable(vd) &&
                    (vdev_writeable(vd) || !spa_writeable(spa))) {
                        zio->io_error = 0;
                } else {
                        ASSERT(zio->io_error != 0);
                        zfs_ereport_post(FM_EREPORT_ZFS_PROBE_FAILURE,
                            spa, vd, NULL, 0, 0);
                        zio->io_error = SET_ERROR(ENXIO);
                }

                mutex_enter(&vd->vdev_probe_lock);
                ASSERT(vd->vdev_probe_zio == zio);
                vd->vdev_probe_zio = NULL;
                mutex_exit(&vd->vdev_probe_lock);

                while ((pio = zio_walk_parents(zio)) != NULL)
                        if (!vdev_accessible(vd, pio))
                                pio->io_error = SET_ERROR(ENXIO);

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

/*
 * Determine whether this device is accessible.
 *
 * Read and write to several known locations: the pad regions of each
 * vdev label but the first, which we leave alone in case it contains
 * a VTOC.
 */
zio_t *
vdev_probe(vdev_t *vd, zio_t *zio)
{
        spa_t *spa = vd->vdev_spa;
        vdev_probe_stats_t *vps = NULL;
        zio_t *pio;

        ASSERT(vd->vdev_ops->vdev_op_leaf);

        /*
         * Don't probe the probe.
         */
        if (zio && (zio->io_flags & ZIO_FLAG_PROBE))
                return (NULL);

        /*
         * To prevent 'probe storms' when a device fails, we create
         * just one probe i/o at a time.  All zios that want to probe
         * this vdev will become parents of the probe io.
         */
        mutex_enter(&vd->vdev_probe_lock);

        if ((pio = vd->vdev_probe_zio) == NULL) {
                vps = kmem_zalloc(sizeof (*vps), KM_SLEEP);

                vps->vps_flags = ZIO_FLAG_CANFAIL | ZIO_FLAG_PROBE |
                    ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_AGGREGATE |
                    ZIO_FLAG_TRYHARD;

                if (spa_config_held(spa, SCL_ZIO, RW_WRITER)) {
                        /*
                         * vdev_cant_read and vdev_cant_write can only
                         * transition from TRUE to FALSE when we have the
                         * SCL_ZIO lock as writer; otherwise they can only
                         * transition from FALSE to TRUE.  This ensures that
                         * any zio looking at these values can assume that
                         * failures persist for the life of the I/O.  That's
                         * important because when a device has intermittent
                         * connectivity problems, we want to ensure that
                         * they're ascribed to the device (ENXIO) and not
                         * the zio (EIO).
                         *
                         * Since we hold SCL_ZIO as writer here, clear both
                         * values so the probe can reevaluate from first
                         * principles.
                         */
                        vps->vps_flags |= ZIO_FLAG_CONFIG_WRITER;
                        vd->vdev_cant_read = B_FALSE;
                        vd->vdev_cant_write = B_FALSE;
                }

                vd->vdev_probe_zio = pio = zio_null(NULL, spa, vd,
                    vdev_probe_done, vps,
                    vps->vps_flags | ZIO_FLAG_DONT_PROPAGATE);

                /*
                 * We can't change the vdev state in this context, so we
                 * kick off an async task to do it on our behalf.
                 */
                if (zio != NULL) {
                        vd->vdev_probe_wanted = B_TRUE;
                        spa_async_request(spa, SPA_ASYNC_PROBE);
                }
        }

        if (zio != NULL)
                zio_add_child(zio, pio);

        mutex_exit(&vd->vdev_probe_lock);

        if (vps == NULL) {
                ASSERT(zio != NULL);
                return (NULL);
        }

        for (int l = 1; l < VDEV_LABELS; l++) {
                zio_nowait(zio_read_phys(pio, vd,
                    vdev_label_offset(vd->vdev_psize, l,
                    offsetof(vdev_label_t, vl_pad2)),
                    VDEV_PAD_SIZE, zio_buf_alloc(VDEV_PAD_SIZE),
                    ZIO_CHECKSUM_OFF, vdev_probe_done, vps,
                    ZIO_PRIORITY_SYNC_READ, vps->vps_flags, B_TRUE));
        }

        if (zio == NULL)
                return (pio);

        zio_nowait(pio);
        return (NULL);
}

static void
vdev_open_child(void *arg)
{
        vdev_t *vd = arg;

        vd->vdev_open_thread = curthread;
        vd->vdev_open_error = vdev_open(vd);
        vd->vdev_open_thread = NULL;
}

boolean_t
vdev_uses_zvols(vdev_t *vd)
{
        if (vd->vdev_path && strncmp(vd->vdev_path, ZVOL_DIR,
            strlen(ZVOL_DIR)) == 0)
                return (B_TRUE);
        for (int c = 0; c < vd->vdev_children; c++)
                if (vdev_uses_zvols(vd->vdev_child[c]))
                        return (B_TRUE);
        return (B_FALSE);
}

void
vdev_open_children(vdev_t *vd)
{
        taskq_t *tq;
        int children = vd->vdev_children;

        /*
         * in order to handle pools on top of zvols, do the opens
         * in a single thread so that the same thread holds the
         * spa_namespace_lock
         */
        if (vdev_uses_zvols(vd)) {
                for (int c = 0; c < children; c++)
                        vd->vdev_child[c]->vdev_open_error =
                            vdev_open(vd->vdev_child[c]);
                return;
        }
        tq = taskq_create("vdev_open", children, minclsyspri,
            children, children, TASKQ_PREPOPULATE);

        for (int c = 0; c < children; c++)
                VERIFY(taskq_dispatch(tq, vdev_open_child, vd->vdev_child[c],
                    TQ_SLEEP) != NULL);

        taskq_destroy(tq);
}

/*
 * Prepare a virtual device for access.
 */
int
vdev_open(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        int error;
        uint64_t osize = 0;
        uint64_t max_osize = 0;
        uint64_t asize, max_asize, psize;
        uint64_t ashift = 0;

        ASSERT(vd->vdev_open_thread == curthread ||
            spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);
        ASSERT(vd->vdev_state == VDEV_STATE_CLOSED ||
            vd->vdev_state == VDEV_STATE_CANT_OPEN ||
            vd->vdev_state == VDEV_STATE_OFFLINE);

        vd->vdev_stat.vs_aux = VDEV_AUX_NONE;
        vd->vdev_cant_read = B_FALSE;
        vd->vdev_cant_write = B_FALSE;
        vd->vdev_min_asize = vdev_get_min_asize(vd);

        /*
         * If this vdev is not removed, check its fault status.  If it's
         * faulted, bail out of the open.
         */
        if (!vd->vdev_removed && vd->vdev_faulted) {
                ASSERT(vd->vdev_children == 0);
                ASSERT(vd->vdev_label_aux == VDEV_AUX_ERR_EXCEEDED ||
                    vd->vdev_label_aux == VDEV_AUX_EXTERNAL);
                vdev_set_state(vd, B_TRUE, VDEV_STATE_FAULTED,
                    vd->vdev_label_aux);
                return (SET_ERROR(ENXIO));
        } else if (vd->vdev_offline) {
                ASSERT(vd->vdev_children == 0);
                vdev_set_state(vd, B_TRUE, VDEV_STATE_OFFLINE, VDEV_AUX_NONE);
                return (SET_ERROR(ENXIO));
        }

        error = vd->vdev_ops->vdev_op_open(vd, &osize, &max_osize, &ashift);

        /*
         * Reset the vdev_reopening flag so that we actually close
         * the vdev on error.
         */
        vd->vdev_reopening = B_FALSE;
        if (zio_injection_enabled && error == 0)
                error = zio_handle_device_injection(vd, NULL, ENXIO);

        if (error) {
                if (vd->vdev_removed &&
                    vd->vdev_stat.vs_aux != VDEV_AUX_OPEN_FAILED)
                        vd->vdev_removed = B_FALSE;

                vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                    vd->vdev_stat.vs_aux);
                return (error);
        }

        vd->vdev_removed = B_FALSE;

        /*
         * Recheck the faulted flag now that we have confirmed that
         * the vdev is accessible.  If we're faulted, bail.
         */
        if (vd->vdev_faulted) {
                ASSERT(vd->vdev_children == 0);
                ASSERT(vd->vdev_label_aux == VDEV_AUX_ERR_EXCEEDED ||
                    vd->vdev_label_aux == VDEV_AUX_EXTERNAL);
                vdev_set_state(vd, B_TRUE, VDEV_STATE_FAULTED,
                    vd->vdev_label_aux);
                return (SET_ERROR(ENXIO));
        }

        if (vd->vdev_degraded) {
                ASSERT(vd->vdev_children == 0);
                vdev_set_state(vd, B_TRUE, VDEV_STATE_DEGRADED,
                    VDEV_AUX_ERR_EXCEEDED);
        } else {
                vdev_set_state(vd, B_TRUE, VDEV_STATE_HEALTHY, 0);
        }

        /*
         * For hole or missing vdevs we just return success.
         */
        if (vd->vdev_ishole || vd->vdev_ops == &vdev_missing_ops)
                return (0);

        for (int c = 0; c < vd->vdev_children; c++) {
                if (vd->vdev_child[c]->vdev_state != VDEV_STATE_HEALTHY) {
                        vdev_set_state(vd, B_TRUE, VDEV_STATE_DEGRADED,
                            VDEV_AUX_NONE);
                        break;
                }
        }

        osize = P2ALIGN(osize, (uint64_t)sizeof (vdev_label_t));
        max_osize = P2ALIGN(max_osize, (uint64_t)sizeof (vdev_label_t));

        if (vd->vdev_children == 0) {
                if (osize < SPA_MINDEVSIZE) {
                        vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_TOO_SMALL);
                        return (SET_ERROR(EOVERFLOW));
                }
                psize = osize;
                asize = osize - (VDEV_LABEL_START_SIZE + VDEV_LABEL_END_SIZE);
                max_asize = max_osize - (VDEV_LABEL_START_SIZE +
                    VDEV_LABEL_END_SIZE);
        } else {
                if (vd->vdev_parent != NULL && osize < SPA_MINDEVSIZE -
                    (VDEV_LABEL_START_SIZE + VDEV_LABEL_END_SIZE)) {
                        vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_TOO_SMALL);
                        return (SET_ERROR(EOVERFLOW));
                }
                psize = 0;
                asize = osize;
                max_asize = max_osize;
        }

        vd->vdev_psize = psize;

        /*
         * Make sure the allocatable size hasn't shrunk.
         */
        if (asize < vd->vdev_min_asize) {
                vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                    VDEV_AUX_BAD_LABEL);
                return (SET_ERROR(EINVAL));
        }

        if (vd->vdev_asize == 0) {
                /*
                 * This is the first-ever open, so use the computed values.
                 * For testing purposes, a higher ashift can be requested.
                 */
                vd->vdev_asize = asize;
                vd->vdev_max_asize = max_asize;
                vd->vdev_ashift = MAX(ashift, vd->vdev_ashift);
        } else {
                /*
                 * Detect if the alignment requirement has increased.
                 * We don't want to make the pool unavailable, just
                 * issue a warning instead.
                 */
                if (ashift > vd->vdev_top->vdev_ashift &&
                    vd->vdev_ops->vdev_op_leaf) {
                        cmn_err(CE_WARN,
                            "Disk, '%s', has a block alignment that is "
                            "larger than the pool's alignment\n",
                            vd->vdev_path);
                }
                vd->vdev_max_asize = max_asize;
        }

        /*
         * If all children are healthy and the asize has increased,
         * then we've experienced dynamic LUN growth.  If automatic
         * expansion is enabled then use the additional space.
         */
        if (vd->vdev_state == VDEV_STATE_HEALTHY && asize > vd->vdev_asize &&
            (vd->vdev_expanding || spa->spa_autoexpand))
                vd->vdev_asize = asize;

        vdev_set_min_asize(vd);

        /*
         * Ensure we can issue some IO before declaring the
         * vdev open for business.
         */
        if (vd->vdev_ops->vdev_op_leaf &&
            (error = zio_wait(vdev_probe(vd, NULL))) != 0) {
                vdev_set_state(vd, B_TRUE, VDEV_STATE_FAULTED,
                    VDEV_AUX_ERR_EXCEEDED);
                return (error);
        }

        /*
         * Track the min and max ashift values for normal data devices.
         */
        if (vd->vdev_top == vd && vd->vdev_ashift != 0 &&
            !vd->vdev_islog && vd->vdev_aux == NULL) {
                if (vd->vdev_ashift > spa->spa_max_ashift)
                        spa->spa_max_ashift = vd->vdev_ashift;
                if (vd->vdev_ashift < spa->spa_min_ashift)
                        spa->spa_min_ashift = vd->vdev_ashift;
        }

        /*
         * If a leaf vdev has a DTL, and seems healthy, then kick off a
         * resilver.  But don't do this if we are doing a reopen for a scrub,
         * since this would just restart the scrub we are already doing.
         */
        if (vd->vdev_ops->vdev_op_leaf && !spa->spa_scrub_reopen &&
            vdev_resilver_needed(vd, NULL, NULL))
                spa_async_request(spa, SPA_ASYNC_RESILVER);

        return (0);
}

/*
 * Called once the vdevs are all opened, this routine validates the label
 * contents.  This needs to be done before vdev_load() so that we don't
 * inadvertently do repair I/Os to the wrong device.
 *
 * If 'strict' is false ignore the spa guid check. This is necessary because
 * if the machine crashed during a re-guid the new guid might have been written
 * to all of the vdev labels, but not the cached config. The strict check
 * will be performed when the pool is opened again using the mos config.
 *
 * This function will only return failure if one of the vdevs indicates that it
 * has since been destroyed or exported.  This is only possible if
 * /etc/zfs/zpool.cache was readonly at the time.  Otherwise, the vdev state
 * will be updated but the function will return 0.
 */
int
vdev_validate(vdev_t *vd, boolean_t strict)
{
        spa_t *spa = vd->vdev_spa;
        nvlist_t *label;
        uint64_t guid = 0, top_guid;
        uint64_t state;

        for (int c = 0; c < vd->vdev_children; c++)
                if (vdev_validate(vd->vdev_child[c], strict) != 0)
                        return (SET_ERROR(EBADF));

        /*
         * If the device has already failed, or was marked offline, don't do
         * any further validation.  Otherwise, label I/O will fail and we will
         * overwrite the previous state.
         */
        if (vd->vdev_ops->vdev_op_leaf && vdev_readable(vd)) {
                uint64_t aux_guid = 0;
                nvlist_t *nvl;
                uint64_t txg = spa_last_synced_txg(spa) != 0 ?
                    spa_last_synced_txg(spa) : -1ULL;

                if ((label = vdev_label_read_config(vd, txg)) == NULL) {
                        vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_BAD_LABEL);
                        return (0);
                }

                /*
                 * Determine if this vdev has been split off into another
                 * pool.  If so, then refuse to open it.
                 */
                if (nvlist_lookup_uint64(label, ZPOOL_CONFIG_SPLIT_GUID,
                    &aux_guid) == 0 && aux_guid == spa_guid(spa)) {
                        vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_SPLIT_POOL);
                        nvlist_free(label);
                        return (0);
                }

                if (strict && (nvlist_lookup_uint64(label,
                    ZPOOL_CONFIG_POOL_GUID, &guid) != 0 ||
                    guid != spa_guid(spa))) {
                        vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_CORRUPT_DATA);
                        nvlist_free(label);
                        return (0);
                }

                if (nvlist_lookup_nvlist(label, ZPOOL_CONFIG_VDEV_TREE, &nvl)
                    != 0 || nvlist_lookup_uint64(nvl, ZPOOL_CONFIG_ORIG_GUID,
                    &aux_guid) != 0)
                        aux_guid = 0;

                /*
                 * If this vdev just became a top-level vdev because its
                 * sibling was detached, it will have adopted the parent's
                 * vdev guid -- but the label may or may not be on disk yet.
                 * Fortunately, either version of the label will have the
                 * same top guid, so if we're a top-level vdev, we can
                 * safely compare to that instead.
                 *
                 * If we split this vdev off instead, then we also check the
                 * original pool's guid.  We don't want to consider the vdev
                 * corrupt if it is partway through a split operation.
                 */
                if (nvlist_lookup_uint64(label, ZPOOL_CONFIG_GUID,
                    &guid) != 0 ||
                    nvlist_lookup_uint64(label, ZPOOL_CONFIG_TOP_GUID,
                    &top_guid) != 0 ||
                    ((vd->vdev_guid != guid && vd->vdev_guid != aux_guid) &&
                    (vd->vdev_guid != top_guid || vd != vd->vdev_top))) {
                        vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_CORRUPT_DATA);
                        nvlist_free(label);
                        return (0);
                }

                if (nvlist_lookup_uint64(label, ZPOOL_CONFIG_POOL_STATE,
                    &state) != 0) {
                        vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_CORRUPT_DATA);
                        nvlist_free(label);
                        return (0);
                }

                nvlist_free(label);

                /*
                 * If this is a verbatim import, no need to check the
                 * state of the pool.
                 */
                if (!(spa->spa_import_flags & ZFS_IMPORT_VERBATIM) &&
                    spa_load_state(spa) == SPA_LOAD_OPEN &&
                    state != POOL_STATE_ACTIVE)
                        return (SET_ERROR(EBADF));

                /*
                 * If we were able to open and validate a vdev that was
                 * previously marked permanently unavailable, clear that state
                 * now.
                 */
                if (vd->vdev_not_present)
                        vd->vdev_not_present = 0;
        }

        return (0);
}

/*
 * Close a virtual device.
 */
void
vdev_close(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        vdev_t *pvd = vd->vdev_parent;

        ASSERT(spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);

        /*
         * If our parent is reopening, then we are as well, unless we are
         * going offline.
         */
        if (pvd != NULL && pvd->vdev_reopening)
                vd->vdev_reopening = (pvd->vdev_reopening && !vd->vdev_offline);

        vd->vdev_ops->vdev_op_close(vd);

        vdev_cache_purge(vd);

        /*
         * We record the previous state before we close it, so that if we are
         * doing a reopen(), we don't generate FMA ereports if we notice that
         * it's still faulted.
         */
        vd->vdev_prevstate = vd->vdev_state;

        if (vd->vdev_offline)
                vd->vdev_state = VDEV_STATE_OFFLINE;
        else
                vd->vdev_state = VDEV_STATE_CLOSED;
        vd->vdev_stat.vs_aux = VDEV_AUX_NONE;
}

void
vdev_hold(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;

        ASSERT(spa_is_root(spa));
        if (spa->spa_state == POOL_STATE_UNINITIALIZED)
                return;

        for (int c = 0; c < vd->vdev_children; c++)
                vdev_hold(vd->vdev_child[c]);

        if (vd->vdev_ops->vdev_op_leaf)
                vd->vdev_ops->vdev_op_hold(vd);
}

void
vdev_rele(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;

        ASSERT(spa_is_root(spa));
        for (int c = 0; c < vd->vdev_children; c++)
                vdev_rele(vd->vdev_child[c]);

        if (vd->vdev_ops->vdev_op_leaf)
                vd->vdev_ops->vdev_op_rele(vd);
}

/*
 * Reopen all interior vdevs and any unopened leaves.  We don't actually
 * reopen leaf vdevs which had previously been opened as they might deadlock
 * on the spa_config_lock.  Instead we only obtain the leaf's physical size.
 * If the leaf has never been opened then open it, as usual.
 */
void
vdev_reopen(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;

        ASSERT(spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);

        /* set the reopening flag unless we're taking the vdev offline */
        vd->vdev_reopening = !vd->vdev_offline;
        vdev_close(vd);
        (void) vdev_open(vd);

        /*
         * Call vdev_validate() here to make sure we have the same device.
         * Otherwise, a device with an invalid label could be successfully
         * opened in response to vdev_reopen().
         */
        if (vd->vdev_aux) {
                (void) vdev_validate_aux(vd);
                if (vdev_readable(vd) && vdev_writeable(vd) &&
                    vd->vdev_aux == &spa->spa_l2cache &&
                    !l2arc_vdev_present(vd))
                        l2arc_add_vdev(spa, vd);
        } else {
                (void) vdev_validate(vd, B_TRUE);
        }

        /*
         * Reassess parent vdev's health.
         */
        vdev_propagate_state(vd);
}

int
vdev_create(vdev_t *vd, uint64_t txg, boolean_t isreplacing)
{
        int error;

        /*
         * Normally, partial opens (e.g. of a mirror) are allowed.
         * For a create, however, we want to fail the request if
         * there are any components we can't open.
         */
        error = vdev_open(vd);

        if (error || vd->vdev_state != VDEV_STATE_HEALTHY) {
                vdev_close(vd);
                return (error ? error : ENXIO);
        }

        /*
         * Recursively load DTLs and initialize all labels.
         */
        if ((error = vdev_dtl_load(vd)) != 0 ||
            (error = vdev_label_init(vd, txg, isreplacing ?
            VDEV_LABEL_REPLACE : VDEV_LABEL_CREATE)) != 0) {
                vdev_close(vd);
                return (error);
        }

        return (0);
}

void
vdev_metaslab_set_size(vdev_t *vd)
{
        /*
         * Aim for roughly metaslabs_per_vdev (default 200) metaslabs per vdev.
         */
        vd->vdev_ms_shift = highbit64(vd->vdev_asize / metaslabs_per_vdev);
        vd->vdev_ms_shift = MAX(vd->vdev_ms_shift, SPA_MAXBLOCKSHIFT);
}

void
vdev_dirty(vdev_t *vd, int flags, void *arg, uint64_t txg)
{
        ASSERT(vd == vd->vdev_top);
        ASSERT(!vd->vdev_ishole);
        ASSERT(ISP2(flags));
        ASSERT(spa_writeable(vd->vdev_spa));

        if (flags & VDD_METASLAB)
                (void) txg_list_add(&vd->vdev_ms_list, arg, txg);

        if (flags & VDD_DTL)
                (void) txg_list_add(&vd->vdev_dtl_list, arg, txg);

        (void) txg_list_add(&vd->vdev_spa->spa_vdev_txg_list, vd, txg);
}

void
vdev_dirty_leaves(vdev_t *vd, int flags, uint64_t txg)
{
        for (int c = 0; c < vd->vdev_children; c++)
                vdev_dirty_leaves(vd->vdev_child[c], flags, txg);

        if (vd->vdev_ops->vdev_op_leaf)
                vdev_dirty(vd->vdev_top, flags, vd, txg);
}

/*
 * DTLs.
 *
 * A vdev's DTL (dirty time log) is the set of transaction groups for which
 * the vdev has less than perfect replication.  There are four kinds of DTL:
 *
 * DTL_MISSING: txgs for which the vdev has no valid copies of the data
 *
 * DTL_PARTIAL: txgs for which data is available, but not fully replicated
 *
 * DTL_SCRUB: the txgs that could not be repaired by the last scrub; upon
 *      scrub completion, DTL_SCRUB replaces DTL_MISSING in the range of
 *      txgs that was scrubbed.
 *
 * DTL_OUTAGE: txgs which cannot currently be read, whether due to
 *      persistent errors or just some device being offline.
 *      Unlike the other three, the DTL_OUTAGE map is not generally
 *      maintained; it's only computed when needed, typically to
 *      determine whether a device can be detached.
 *
 * For leaf vdevs, DTL_MISSING and DTL_PARTIAL are identical: the device
 * either has the data or it doesn't.
 *
 * For interior vdevs such as mirror and RAID-Z the picture is more complex.
 * A vdev's DTL_PARTIAL is the union of its children's DTL_PARTIALs, because
 * if any child is less than fully replicated, then so is its parent.
 * A vdev's DTL_MISSING is a modified union of its children's DTL_MISSINGs,
 * comprising only those txgs which appear in 'maxfaults' or more children;
 * those are the txgs we don't have enough replication to read.  For example,
 * double-parity RAID-Z can tolerate up to two missing devices (maxfaults == 2);
 * thus, its DTL_MISSING consists of the set of txgs that appear in more than
 * two child DTL_MISSING maps.
 *
 * It should be clear from the above that to compute the DTLs and outage maps
 * for all vdevs, it suffices to know just the leaf vdevs' DTL_MISSING maps.
 * Therefore, that is all we keep on disk.  When loading the pool, or after
 * a configuration change, we generate all other DTLs from first principles.
 */
void
vdev_dtl_dirty(vdev_t *vd, vdev_dtl_type_t t, uint64_t txg, uint64_t size)
{
        range_tree_t *rt = vd->vdev_dtl[t];

        ASSERT(t < DTL_TYPES);
        ASSERT(vd != vd->vdev_spa->spa_root_vdev);
        ASSERT(spa_writeable(vd->vdev_spa));

        mutex_enter(rt->rt_lock);
        if (!range_tree_contains(rt, txg, size))
                range_tree_add(rt, txg, size);
        mutex_exit(rt->rt_lock);
}

boolean_t
vdev_dtl_contains(vdev_t *vd, vdev_dtl_type_t t, uint64_t txg, uint64_t size)
{
        range_tree_t *rt = vd->vdev_dtl[t];
        boolean_t dirty = B_FALSE;

        ASSERT(t < DTL_TYPES);
        ASSERT(vd != vd->vdev_spa->spa_root_vdev);

        mutex_enter(rt->rt_lock);
        if (range_tree_space(rt) != 0)
                dirty = range_tree_contains(rt, txg, size);
        mutex_exit(rt->rt_lock);

        return (dirty);
}

boolean_t
vdev_dtl_empty(vdev_t *vd, vdev_dtl_type_t t)
{
        range_tree_t *rt = vd->vdev_dtl[t];
        boolean_t empty;

        mutex_enter(rt->rt_lock);
        empty = (range_tree_space(rt) == 0);
        mutex_exit(rt->rt_lock);

        return (empty);
}

/*
 * Returns the lowest txg in the DTL range.
 */
static uint64_t
vdev_dtl_min(vdev_t *vd)
{
        range_seg_t *rs;

        ASSERT(MUTEX_HELD(&vd->vdev_dtl_lock));
        ASSERT3U(range_tree_space(vd->vdev_dtl[DTL_MISSING]), !=, 0);
        ASSERT0(vd->vdev_children);

        rs = avl_first(&vd->vdev_dtl[DTL_MISSING]->rt_root);
        return (rs->rs_start - 1);
}

/*
 * Returns the highest txg in the DTL.
 */
static uint64_t
vdev_dtl_max(vdev_t *vd)
{
        range_seg_t *rs;

        ASSERT(MUTEX_HELD(&vd->vdev_dtl_lock));
        ASSERT3U(range_tree_space(vd->vdev_dtl[DTL_MISSING]), !=, 0);
        ASSERT0(vd->vdev_children);

        rs = avl_last(&vd->vdev_dtl[DTL_MISSING]->rt_root);
        return (rs->rs_end);
}

/*
 * Determine if a resilvering vdev should remove any DTL entries from
 * its range. If the vdev was resilvering for the entire duration of the
 * scan then it should excise that range from its DTLs. Otherwise, this
 * vdev is considered partially resilvered and should leave its DTL
 * entries intact. The comment in vdev_dtl_reassess() describes how we
 * excise the DTLs.
 */
static boolean_t
vdev_dtl_should_excise(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        dsl_scan_t *scn = spa->spa_dsl_pool->dp_scan;

        ASSERT0(scn->scn_phys.scn_errors);
        ASSERT0(vd->vdev_children);

        if (vd->vdev_resilver_txg == 0 ||
            range_tree_space(vd->vdev_dtl[DTL_MISSING]) == 0)
                return (B_TRUE);

        /*
         * When a resilver is initiated the scan will assign the scn_max_txg
         * value to the highest txg value that exists in all DTLs. If this
         * device's max DTL is not part of this scan (i.e. it is not in
         * the range (scn_min_txg, scn_max_txg] then it is not eligible
         * for excision.
         */
        if (vdev_dtl_max(vd) <= scn->scn_phys.scn_max_txg) {
                ASSERT3U(scn->scn_phys.scn_min_txg, <=, vdev_dtl_min(vd));
                ASSERT3U(scn->scn_phys.scn_min_txg, <, vd->vdev_resilver_txg);
                ASSERT3U(vd->vdev_resilver_txg, <=, scn->scn_phys.scn_max_txg);
                return (B_TRUE);
        }
        return (B_FALSE);
}

/*
 * Reassess DTLs after a config change or scrub completion.
 */
void
vdev_dtl_reassess(vdev_t *vd, uint64_t txg, uint64_t scrub_txg, int scrub_done)
{
        spa_t *spa = vd->vdev_spa;
        avl_tree_t reftree;
        int minref;

        ASSERT(spa_config_held(spa, SCL_ALL, RW_READER) != 0);

        for (int c = 0; c < vd->vdev_children; c++)
                vdev_dtl_reassess(vd->vdev_child[c], txg,
                    scrub_txg, scrub_done);

        if (vd == spa->spa_root_vdev || vd->vdev_ishole || vd->vdev_aux)
                return;

        if (vd->vdev_ops->vdev_op_leaf) {
                dsl_scan_t *scn = spa->spa_dsl_pool->dp_scan;

                mutex_enter(&vd->vdev_dtl_lock);

                /*
                 * If we've completed a scan cleanly then determine
                 * if this vdev should remove any DTLs. We only want to
                 * excise regions on vdevs that were available during
                 * the entire duration of this scan.
                 */
                if (scrub_txg != 0 &&
                    (spa->spa_scrub_started ||
                    (scn != NULL && scn->scn_phys.scn_errors == 0)) &&
                    vdev_dtl_should_excise(vd)) {
                        /*
                         * We completed a scrub up to scrub_txg.  If we
                         * did it without rebooting, then the scrub dtl
                         * will be valid, so excise the old region and
                         * fold in the scrub dtl.  Otherwise, leave the
                         * dtl as-is if there was an error.
                         *
                         * There's little trick here: to excise the beginning
                         * of the DTL_MISSING map, we put it into a reference
                         * tree and then add a segment with refcnt -1 that
                         * covers the range [0, scrub_txg).  This means
                         * that each txg in that range has refcnt -1 or 0.
                         * We then add DTL_SCRUB with a refcnt of 2, so that
                         * entries in the range [0, scrub_txg) will have a
                         * positive refcnt -- either 1 or 2.  We then convert
                         * the reference tree into the new DTL_MISSING map.
                         */
                        space_reftree_create(&reftree);
                        space_reftree_add_map(&reftree,
                            vd->vdev_dtl[DTL_MISSING], 1);
                        space_reftree_add_seg(&reftree, 0, scrub_txg, -1);
                        space_reftree_add_map(&reftree,
                            vd->vdev_dtl[DTL_SCRUB], 2);
                        space_reftree_generate_map(&reftree,
                            vd->vdev_dtl[DTL_MISSING], 1);
                        space_reftree_destroy(&reftree);
                }
                range_tree_vacate(vd->vdev_dtl[DTL_PARTIAL], NULL, NULL);
                range_tree_walk(vd->vdev_dtl[DTL_MISSING],
                    range_tree_add, vd->vdev_dtl[DTL_PARTIAL]);
                if (scrub_done)
                        range_tree_vacate(vd->vdev_dtl[DTL_SCRUB], NULL, NULL);
                range_tree_vacate(vd->vdev_dtl[DTL_OUTAGE], NULL, NULL);
                if (!vdev_readable(vd))
                        range_tree_add(vd->vdev_dtl[DTL_OUTAGE], 0, -1ULL);
                else
                        range_tree_walk(vd->vdev_dtl[DTL_MISSING],
                            range_tree_add, vd->vdev_dtl[DTL_OUTAGE]);

                /*
                 * If the vdev was resilvering and no longer has any
                 * DTLs then reset its resilvering flag.
                 */
                if (vd->vdev_resilver_txg != 0 &&
                    range_tree_space(vd->vdev_dtl[DTL_MISSING]) == 0 &&
                    range_tree_space(vd->vdev_dtl[DTL_OUTAGE]) == 0)
                        vd->vdev_resilver_txg = 0;

                mutex_exit(&vd->vdev_dtl_lock);

                if (txg != 0)
                        vdev_dirty(vd->vdev_top, VDD_DTL, vd, txg);
                return;
        }

        mutex_enter(&vd->vdev_dtl_lock);
        for (int t = 0; t < DTL_TYPES; t++) {
                /* account for child's outage in parent's missing map */
                int s = (t == DTL_MISSING) ? DTL_OUTAGE: t;
                if (t == DTL_SCRUB)
                        continue;                       /* leaf vdevs only */
                if (t == DTL_PARTIAL)
                        minref = 1;                     /* i.e. non-zero */
                else if (vd->vdev_nparity != 0)
                        minref = vd->vdev_nparity + 1;  /* RAID-Z */
                else
                        minref = vd->vdev_children;     /* any kind of mirror */
                space_reftree_create(&reftree);
                for (int c = 0; c < vd->vdev_children; c++) {
                        vdev_t *cvd = vd->vdev_child[c];
                        mutex_enter(&cvd->vdev_dtl_lock);
                        space_reftree_add_map(&reftree, cvd->vdev_dtl[s], 1);
                        mutex_exit(&cvd->vdev_dtl_lock);
                }
                space_reftree_generate_map(&reftree, vd->vdev_dtl[t], minref);
                space_reftree_destroy(&reftree);
        }
        mutex_exit(&vd->vdev_dtl_lock);
}

int
vdev_dtl_load(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        objset_t *mos = spa->spa_meta_objset;
        int error = 0;

        if (vd->vdev_ops->vdev_op_leaf && vd->vdev_dtl_object != 0) {
                ASSERT(!vd->vdev_ishole);

                error = space_map_open(&vd->vdev_dtl_sm, mos,
                    vd->vdev_dtl_object, 0, -1ULL, 0, &vd->vdev_dtl_lock);
                if (error)
                        return (error);
                ASSERT(vd->vdev_dtl_sm != NULL);

                mutex_enter(&vd->vdev_dtl_lock);

                /*
                 * Now that we've opened the space_map we need to update
                 * the in-core DTL.
                 */
                space_map_update(vd->vdev_dtl_sm);

                error = space_map_load(vd->vdev_dtl_sm,
                    vd->vdev_dtl[DTL_MISSING], SM_ALLOC);
                mutex_exit(&vd->vdev_dtl_lock);

                return (error);
        }

        for (int c = 0; c < vd->vdev_children; c++) {
                error = vdev_dtl_load(vd->vdev_child[c]);
                if (error != 0)
                        break;
        }

        return (error);
}

void
vdev_destroy_unlink_zap(vdev_t *vd, uint64_t zapobj, dmu_tx_t *tx)
{
        spa_t *spa = vd->vdev_spa;

        VERIFY0(zap_destroy(spa->spa_meta_objset, zapobj, tx));
        VERIFY0(zap_remove_int(spa->spa_meta_objset, spa->spa_all_vdev_zaps,
            zapobj, tx));
}

uint64_t
vdev_create_link_zap(vdev_t *vd, dmu_tx_t *tx)
{
        spa_t *spa = vd->vdev_spa;
        uint64_t zap = zap_create(spa->spa_meta_objset, DMU_OTN_ZAP_METADATA,
            DMU_OT_NONE, 0, tx);

        ASSERT(zap != 0);
        VERIFY0(zap_add_int(spa->spa_meta_objset, spa->spa_all_vdev_zaps,
            zap, tx));

        return (zap);
}

void
vdev_construct_zaps(vdev_t *vd, dmu_tx_t *tx)
{
        if (vd->vdev_ops != &vdev_hole_ops &&
            vd->vdev_ops != &vdev_missing_ops &&
            vd->vdev_ops != &vdev_root_ops &&
            !vd->vdev_top->vdev_removing) {
                if (vd->vdev_ops->vdev_op_leaf && vd->vdev_leaf_zap == 0) {
                        vd->vdev_leaf_zap = vdev_create_link_zap(vd, tx);
                }
                if (vd == vd->vdev_top && vd->vdev_top_zap == 0) {
                        vd->vdev_top_zap = vdev_create_link_zap(vd, tx);
                }
        }
        for (uint64_t i = 0; i < vd->vdev_children; i++) {
                vdev_construct_zaps(vd->vdev_child[i], tx);
        }
}

void
vdev_dtl_sync(vdev_t *vd, uint64_t txg)
{
        spa_t *spa = vd->vdev_spa;
        range_tree_t *rt = vd->vdev_dtl[DTL_MISSING];
        objset_t *mos = spa->spa_meta_objset;
        range_tree_t *rtsync;
        kmutex_t rtlock;
        dmu_tx_t *tx;
        uint64_t object = space_map_object(vd->vdev_dtl_sm);

        ASSERT(!vd->vdev_ishole);
        ASSERT(vd->vdev_ops->vdev_op_leaf);

        tx = dmu_tx_create_assigned(spa->spa_dsl_pool, txg);

        if (vd->vdev_detached || vd->vdev_top->vdev_removing) {
                mutex_enter(&vd->vdev_dtl_lock);
                space_map_free(vd->vdev_dtl_sm, tx);
                space_map_close(vd->vdev_dtl_sm);
                vd->vdev_dtl_sm = NULL;
                mutex_exit(&vd->vdev_dtl_lock);

                /*
                 * We only destroy the leaf ZAP for detached leaves or for
                 * removed log devices. Removed data devices handle leaf ZAP
                 * cleanup later, once cancellation is no longer possible.
                 */
                if (vd->vdev_leaf_zap != 0 && (vd->vdev_detached ||
                    vd->vdev_top->vdev_islog)) {
                        vdev_destroy_unlink_zap(vd, vd->vdev_leaf_zap, tx);
                        vd->vdev_leaf_zap = 0;
                }

                dmu_tx_commit(tx);
                return;
        }

        if (vd->vdev_dtl_sm == NULL) {
                uint64_t new_object;

                new_object = space_map_alloc(mos, tx);
                VERIFY3U(new_object, !=, 0);

                VERIFY0(space_map_open(&vd->vdev_dtl_sm, mos, new_object,
                    0, -1ULL, 0, &vd->vdev_dtl_lock));
                ASSERT(vd->vdev_dtl_sm != NULL);
        }

        mutex_init(&rtlock, NULL, MUTEX_DEFAULT, NULL);

        rtsync = range_tree_create(NULL, NULL, &rtlock);

        mutex_enter(&rtlock);

        mutex_enter(&vd->vdev_dtl_lock);
        range_tree_walk(rt, range_tree_add, rtsync);
        mutex_exit(&vd->vdev_dtl_lock);

        space_map_truncate(vd->vdev_dtl_sm, tx);
        space_map_write(vd->vdev_dtl_sm, rtsync, SM_ALLOC, tx);
        range_tree_vacate(rtsync, NULL, NULL);

        range_tree_destroy(rtsync);

        mutex_exit(&rtlock);
        mutex_destroy(&rtlock);

        /*
         * If the object for the space map has changed then dirty
         * the top level so that we update the config.
         */
        if (object != space_map_object(vd->vdev_dtl_sm)) {
                zfs_dbgmsg("txg %llu, spa %s, DTL old object %llu, "
                    "new object %llu", txg, spa_name(spa), object,
                    space_map_object(vd->vdev_dtl_sm));
                vdev_config_dirty(vd->vdev_top);
        }

        dmu_tx_commit(tx);

        mutex_enter(&vd->vdev_dtl_lock);
        space_map_update(vd->vdev_dtl_sm);
        mutex_exit(&vd->vdev_dtl_lock);
}

/*
 * Determine whether the specified vdev can be offlined/detached/removed
 * without losing data.
 */
boolean_t
vdev_dtl_required(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        vdev_t *tvd = vd->vdev_top;
        uint8_t cant_read = vd->vdev_cant_read;
        boolean_t required;

        ASSERT(spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);

        if (vd == spa->spa_root_vdev || vd == tvd)
                return (B_TRUE);

        /*
         * Temporarily mark the device as unreadable, and then determine
         * whether this results in any DTL outages in the top-level vdev.
         * If not, we can safely offline/detach/remove the device.
         */
        vd->vdev_cant_read = B_TRUE;
        vdev_dtl_reassess(tvd, 0, 0, B_FALSE);
        required = !vdev_dtl_empty(tvd, DTL_OUTAGE);
        vd->vdev_cant_read = cant_read;
        vdev_dtl_reassess(tvd, 0, 0, B_FALSE);

        if (!required && zio_injection_enabled)
                required = !!zio_handle_device_injection(vd, NULL, ECHILD);

        return (required);
}

/*
 * Determine if resilver is needed, and if so the txg range.
 */
boolean_t
vdev_resilver_needed(vdev_t *vd, uint64_t *minp, uint64_t *maxp)
{
        boolean_t needed = B_FALSE;
        uint64_t thismin = UINT64_MAX;
        uint64_t thismax = 0;

        if (vd->vdev_children == 0) {
                mutex_enter(&vd->vdev_dtl_lock);
                if (range_tree_space(vd->vdev_dtl[DTL_MISSING]) != 0 &&
                    vdev_writeable(vd)) {

                        thismin = vdev_dtl_min(vd);
                        thismax = vdev_dtl_max(vd);
                        needed = B_TRUE;
                }
                mutex_exit(&vd->vdev_dtl_lock);
        } else {
                for (int c = 0; c < vd->vdev_children; c++) {
                        vdev_t *cvd = vd->vdev_child[c];
                        uint64_t cmin, cmax;

                        if (vdev_resilver_needed(cvd, &cmin, &cmax)) {
                                thismin = MIN(thismin, cmin);
                                thismax = MAX(thismax, cmax);
                                needed = B_TRUE;
                        }
                }
        }

        if (needed && minp) {
                *minp = thismin;
                *maxp = thismax;
        }
        return (needed);
}

void
vdev_load(vdev_t *vd)
{
        /*
         * Recursively load all children.
         */
        for (int c = 0; c < vd->vdev_children; c++)
                vdev_load(vd->vdev_child[c]);

        /*
         * If this is a top-level vdev, initialize its metaslabs.
         */
        if (vd == vd->vdev_top && !vd->vdev_ishole &&
            (vd->vdev_ashift == 0 || vd->vdev_asize == 0 ||
            vdev_metaslab_init(vd, 0) != 0))
                vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
                    VDEV_AUX_CORRUPT_DATA);

        /*
         * If this is a leaf vdev, load its DTL.
         */
        if (vd->vdev_ops->vdev_op_leaf && vdev_dtl_load(vd) != 0)
                vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
                    VDEV_AUX_CORRUPT_DATA);
}

/*
 * The special vdev case is used for hot spares and l2cache devices.  Its
 * sole purpose it to set the vdev state for the associated vdev.  To do this,
 * we make sure that we can open the underlying device, then try to read the
 * label, and make sure that the label is sane and that it hasn't been
 * repurposed to another pool.
 */
int
vdev_validate_aux(vdev_t *vd)
{
        nvlist_t *label;
        uint64_t guid, version;
        uint64_t state;

        if (!vdev_readable(vd))
                return (0);

        if ((label = vdev_label_read_config(vd, -1ULL)) == NULL) {
                vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                    VDEV_AUX_CORRUPT_DATA);
                return (-1);
        }

        if (nvlist_lookup_uint64(label, ZPOOL_CONFIG_VERSION, &version) != 0 ||
            !SPA_VERSION_IS_SUPPORTED(version) ||
            nvlist_lookup_uint64(label, ZPOOL_CONFIG_GUID, &guid) != 0 ||
            guid != vd->vdev_guid ||
            nvlist_lookup_uint64(label, ZPOOL_CONFIG_POOL_STATE, &state) != 0) {
                vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                    VDEV_AUX_CORRUPT_DATA);
                nvlist_free(label);
                return (-1);
        }

        /*
         * We don't actually check the pool state here.  If it's in fact in
         * use by another pool, we update this fact on the fly when requested.
         */
        nvlist_free(label);
        return (0);
}

void
vdev_remove(vdev_t *vd, uint64_t txg)
{
        spa_t *spa = vd->vdev_spa;
        objset_t *mos = spa->spa_meta_objset;
        dmu_tx_t *tx;

        tx = dmu_tx_create_assigned(spa_get_dsl(spa), txg);
        ASSERT(vd == vd->vdev_top);
        ASSERT3U(txg, ==, spa_syncing_txg(spa));

        if (vd->vdev_ms != NULL) {
                metaslab_group_t *mg = vd->vdev_mg;

                metaslab_group_histogram_verify(mg);
                metaslab_class_histogram_verify(mg->mg_class);

                for (int m = 0; m < vd->vdev_ms_count; m++) {
                        metaslab_t *msp = vd->vdev_ms[m];

                        if (msp == NULL || msp->ms_sm == NULL)
                                continue;

                        mutex_enter(&msp->ms_lock);
                        /*
                         * If the metaslab was not loaded when the vdev
                         * was removed then the histogram accounting may
                         * not be accurate. Update the histogram information
                         * here so that we ensure that the metaslab group
                         * and metaslab class are up-to-date.
                         */
                        metaslab_group_histogram_remove(mg, msp);

                        VERIFY0(space_map_allocated(msp->ms_sm));
                        space_map_free(msp->ms_sm, tx);
                        space_map_close(msp->ms_sm);
                        msp->ms_sm = NULL;
                        mutex_exit(&msp->ms_lock);
                }

                metaslab_group_histogram_verify(mg);
                metaslab_class_histogram_verify(mg->mg_class);
                for (int i = 0; i < RANGE_TREE_HISTOGRAM_SIZE; i++)
                        ASSERT0(mg->mg_histogram[i]);

        }

        if (vd->vdev_ms_array) {
                (void) dmu_object_free(mos, vd->vdev_ms_array, tx);
                vd->vdev_ms_array = 0;
        }

        if (vd->vdev_islog && vd->vdev_top_zap != 0) {
                vdev_destroy_unlink_zap(vd, vd->vdev_top_zap, tx);
                vd->vdev_top_zap = 0;
        }
        dmu_tx_commit(tx);
}

void
vdev_sync_done(vdev_t *vd, uint64_t txg)
{
        metaslab_t *msp;
        boolean_t reassess = !txg_list_empty(&vd->vdev_ms_list, TXG_CLEAN(txg));

        ASSERT(!vd->vdev_ishole);

        while (msp = txg_list_remove(&vd->vdev_ms_list, TXG_CLEAN(txg)))
                metaslab_sync_done(msp, txg);

        if (reassess)
                metaslab_sync_reassess(vd->vdev_mg);
}

void
vdev_sync(vdev_t *vd, uint64_t txg)
{
        spa_t *spa = vd->vdev_spa;
        vdev_t *lvd;
        metaslab_t *msp;
        dmu_tx_t *tx;

        ASSERT(!vd->vdev_ishole);

        if (vd->vdev_ms_array == 0 && vd->vdev_ms_shift != 0) {
                ASSERT(vd == vd->vdev_top);
                tx = dmu_tx_create_assigned(spa->spa_dsl_pool, txg);
                vd->vdev_ms_array = dmu_object_alloc(spa->spa_meta_objset,
                    DMU_OT_OBJECT_ARRAY, 0, DMU_OT_NONE, 0, tx);
                ASSERT(vd->vdev_ms_array != 0);
                vdev_config_dirty(vd);
                dmu_tx_commit(tx);
        }

        /*
         * Remove the metadata associated with this vdev once it's empty.
         */
        if (vd->vdev_stat.vs_alloc == 0 && vd->vdev_removing)
                vdev_remove(vd, txg);

        while ((msp = txg_list_remove(&vd->vdev_ms_list, txg)) != NULL) {
                metaslab_sync(msp, txg);
                (void) txg_list_add(&vd->vdev_ms_list, msp, TXG_CLEAN(txg));
        }

        while ((lvd = txg_list_remove(&vd->vdev_dtl_list, txg)) != NULL)
                vdev_dtl_sync(lvd, txg);

        (void) txg_list_add(&spa->spa_vdev_txg_list, vd, TXG_CLEAN(txg));
}

uint64_t
vdev_psize_to_asize(vdev_t *vd, uint64_t psize)
{
        return (vd->vdev_ops->vdev_op_asize(vd, psize));
}

/*
 * Mark the given vdev faulted.  A faulted vdev behaves as if the device could
 * not be opened, and no I/O is attempted.
 */
int
vdev_fault(spa_t *spa, uint64_t guid, vdev_aux_t aux)
{
        vdev_t *vd, *tvd;

        spa_vdev_state_enter(spa, SCL_NONE);

        if ((vd = spa_lookup_by_guid(spa, guid, B_TRUE)) == NULL)
                return (spa_vdev_state_exit(spa, NULL, ENODEV));

        if (!vd->vdev_ops->vdev_op_leaf)
                return (spa_vdev_state_exit(spa, NULL, ENOTSUP));

        tvd = vd->vdev_top;

        /*
         * We don't directly use the aux state here, but if we do a
         * vdev_reopen(), we need this value to be present to remember why we
         * were faulted.
         */
        vd->vdev_label_aux = aux;

        /*
         * Faulted state takes precedence over degraded.
         */
        vd->vdev_delayed_close = B_FALSE;
        vd->vdev_faulted = 1ULL;
        vd->vdev_degraded = 0ULL;
        vdev_set_state(vd, B_FALSE, VDEV_STATE_FAULTED, aux);

        /*
         * If this device has the only valid copy of the data, then
         * back off and simply mark the vdev as degraded instead.
         */
        if (!tvd->vdev_islog && vd->vdev_aux == NULL && vdev_dtl_required(vd)) {
                vd->vdev_degraded = 1ULL;
                vd->vdev_faulted = 0ULL;

                /*
                 * If we reopen the device and it's not dead, only then do we
                 * mark it degraded.
                 */
                vdev_reopen(tvd);

                if (vdev_readable(vd))
                        vdev_set_state(vd, B_FALSE, VDEV_STATE_DEGRADED, aux);
        }

        return (spa_vdev_state_exit(spa, vd, 0));
}

/*
 * Mark the given vdev degraded.  A degraded vdev is purely an indication to the
 * user that something is wrong.  The vdev continues to operate as normal as far
 * as I/O is concerned.
 */
int
vdev_degrade(spa_t *spa, uint64_t guid, vdev_aux_t aux)
{
        vdev_t *vd;

        spa_vdev_state_enter(spa, SCL_NONE);

        if ((vd = spa_lookup_by_guid(spa, guid, B_TRUE)) == NULL)
                return (spa_vdev_state_exit(spa, NULL, ENODEV));

        if (!vd->vdev_ops->vdev_op_leaf)
                return (spa_vdev_state_exit(spa, NULL, ENOTSUP));

        /*
         * If the vdev is already faulted, then don't do anything.
         */
        if (vd->vdev_faulted || vd->vdev_degraded)
                return (spa_vdev_state_exit(spa, NULL, 0));

        vd->vdev_degraded = 1ULL;
        if (!vdev_is_dead(vd))
                vdev_set_state(vd, B_FALSE, VDEV_STATE_DEGRADED,
                    aux);

        return (spa_vdev_state_exit(spa, vd, 0));
}

/*
 * Online the given vdev.
 *
 * If 'ZFS_ONLINE_UNSPARE' is set, it implies two things.  First, any attached
 * spare device should be detached when the device finishes resilvering.
 * Second, the online should be treated like a 'test' online case, so no FMA
 * events are generated if the device fails to open.
 */
int
vdev_online(spa_t *spa, uint64_t guid, uint64_t flags, vdev_state_t *newstate)
{
        vdev_t *vd, *tvd, *pvd, *rvd = spa->spa_root_vdev;
        boolean_t postevent = B_FALSE;

        spa_vdev_state_enter(spa, SCL_NONE);

        if ((vd = spa_lookup_by_guid(spa, guid, B_TRUE)) == NULL)
                return (spa_vdev_state_exit(spa, NULL, ENODEV));

        if (!vd->vdev_ops->vdev_op_leaf)
                return (spa_vdev_state_exit(spa, NULL, ENOTSUP));

        postevent =
            (vd->vdev_offline == B_TRUE || vd->vdev_tmpoffline == B_TRUE) ?
            B_TRUE : B_FALSE;

        tvd = vd->vdev_top;
        vd->vdev_offline = B_FALSE;
        vd->vdev_tmpoffline = B_FALSE;
        vd->vdev_checkremove = !!(flags & ZFS_ONLINE_CHECKREMOVE);
        vd->vdev_forcefault = !!(flags & ZFS_ONLINE_FORCEFAULT);

        /* XXX - L2ARC 1.0 does not support expansion */
        if (!vd->vdev_aux) {
                for (pvd = vd; pvd != rvd; pvd = pvd->vdev_parent)
                        pvd->vdev_expanding = !!(flags & ZFS_ONLINE_EXPAND);
        }

        vdev_reopen(tvd);
        vd->vdev_checkremove = vd->vdev_forcefault = B_FALSE;

        if (!vd->vdev_aux) {
                for (pvd = vd; pvd != rvd; pvd = pvd->vdev_parent)
                        pvd->vdev_expanding = B_FALSE;
        }

        if (newstate)
                *newstate = vd->vdev_state;
        if ((flags & ZFS_ONLINE_UNSPARE) &&
            !vdev_is_dead(vd) && vd->vdev_parent &&
            vd->vdev_parent->vdev_ops == &vdev_spare_ops &&
            vd->vdev_parent->vdev_child[0] == vd)
                vd->vdev_unspare = B_TRUE;

        if ((flags & ZFS_ONLINE_EXPAND) || spa->spa_autoexpand) {

                /* XXX - L2ARC 1.0 does not support expansion */
                if (vd->vdev_aux)
                        return (spa_vdev_state_exit(spa, vd, ENOTSUP));
                spa_async_request(spa, SPA_ASYNC_CONFIG_UPDATE);
        }

        if (postevent)
                spa_event_notify(spa, vd, ESC_ZFS_VDEV_ONLINE);

        return (spa_vdev_state_exit(spa, vd, 0));
}

static int
vdev_offline_locked(spa_t *spa, uint64_t guid, uint64_t flags)
{
        vdev_t *vd, *tvd;
        int error = 0;
        uint64_t generation;
        metaslab_group_t *mg;

top:
        spa_vdev_state_enter(spa, SCL_ALLOC);

        if ((vd = spa_lookup_by_guid(spa, guid, B_TRUE)) == NULL)
                return (spa_vdev_state_exit(spa, NULL, ENODEV));

        if (!vd->vdev_ops->vdev_op_leaf)
                return (spa_vdev_state_exit(spa, NULL, ENOTSUP));

        tvd = vd->vdev_top;
        mg = tvd->vdev_mg;
        generation = spa->spa_config_generation + 1;

        /*
         * If the device isn't already offline, try to offline it.
         */
        if (!vd->vdev_offline) {
                /*
                 * If this device has the only valid copy of some data,
                 * don't allow it to be offlined. Log devices are always
                 * expendable.
                 */
                if (!tvd->vdev_islog && vd->vdev_aux == NULL &&
                    vdev_dtl_required(vd))
                        return (spa_vdev_state_exit(spa, NULL, EBUSY));

                /*
                 * If the top-level is a slog and it has had allocations
                 * then proceed.  We check that the vdev's metaslab group
                 * is not NULL since it's possible that we may have just
                 * added this vdev but not yet initialized its metaslabs.
                 */
                if (tvd->vdev_islog && mg != NULL) {
                        /*
                         * Prevent any future allocations.
                         */
                        metaslab_group_passivate(mg);
                        (void) spa_vdev_state_exit(spa, vd, 0);

                        error = spa_offline_log(spa);

                        spa_vdev_state_enter(spa, SCL_ALLOC);

                        /*
                         * Check to see if the config has changed.
                         */
                        if (error || generation != spa->spa_config_generation) {
                                metaslab_group_activate(mg);
                                if (error)
                                        return (spa_vdev_state_exit(spa,
                                            vd, error));
                                (void) spa_vdev_state_exit(spa, vd, 0);
                                goto top;
                        }
                        ASSERT0(tvd->vdev_stat.vs_alloc);
                }

                /*
                 * Offline this device and reopen its top-level vdev.
                 * If the top-level vdev is a log device then just offline
                 * it. Otherwise, if this action results in the top-level
                 * vdev becoming unusable, undo it and fail the request.
                 */
                vd->vdev_offline = B_TRUE;
                vdev_reopen(tvd);

                if (!tvd->vdev_islog && vd->vdev_aux == NULL &&
                    vdev_is_dead(tvd)) {
                        vd->vdev_offline = B_FALSE;
                        vdev_reopen(tvd);
                        return (spa_vdev_state_exit(spa, NULL, EBUSY));
                }

                /*
                 * Add the device back into the metaslab rotor so that
                 * once we online the device it's open for business.
                 */
                if (tvd->vdev_islog && mg != NULL)
                        metaslab_group_activate(mg);
        }

        vd->vdev_tmpoffline = !!(flags & ZFS_OFFLINE_TEMPORARY);

        return (spa_vdev_state_exit(spa, vd, 0));
}

int
vdev_offline(spa_t *spa, uint64_t guid, uint64_t flags)
{
        int error;

        mutex_enter(&spa->spa_vdev_top_lock);
        error = vdev_offline_locked(spa, guid, flags);
        mutex_exit(&spa->spa_vdev_top_lock);

        return (error);
}

/*
 * Clear the error counts associated with this vdev.  Unlike vdev_online() and
 * vdev_offline(), we assume the spa config is locked.  We also clear all
 * children.  If 'vd' is NULL, then the user wants to clear all vdevs.
 */
void
vdev_clear(spa_t *spa, vdev_t *vd)
{
        vdev_t *rvd = spa->spa_root_vdev;

        ASSERT(spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);

        if (vd == NULL)
                vd = rvd;

        vd->vdev_stat.vs_read_errors = 0;
        vd->vdev_stat.vs_write_errors = 0;
        vd->vdev_stat.vs_checksum_errors = 0;

        for (int c = 0; c < vd->vdev_children; c++)
                vdev_clear(spa, vd->vdev_child[c]);

        /*
         * If we're in the FAULTED state or have experienced failed I/O, then
         * clear the persistent state and attempt to reopen the device.  We
         * also mark the vdev config dirty, so that the new faulted state is
         * written out to disk.
         */
        if (vd->vdev_faulted || vd->vdev_degraded ||
            !vdev_readable(vd) || !vdev_writeable(vd)) {

                /*
                 * When reopening in reponse to a clear event, it may be due to
                 * a fmadm repair request.  In this case, if the device is
                 * still broken, we want to still post the ereport again.
                 */
                vd->vdev_forcefault = B_TRUE;

                vd->vdev_faulted = vd->vdev_degraded = 0ULL;
                vd->vdev_cant_read = B_FALSE;
                vd->vdev_cant_write = B_FALSE;

                vdev_reopen(vd == rvd ? rvd : vd->vdev_top);

                vd->vdev_forcefault = B_FALSE;

                if (vd != rvd && vdev_writeable(vd->vdev_top))
                        vdev_state_dirty(vd->vdev_top);

                if (vd->vdev_aux == NULL && !vdev_is_dead(vd))
                        spa_async_request(spa, SPA_ASYNC_RESILVER);

                spa_event_notify(spa, vd, ESC_ZFS_VDEV_CLEAR);
        }

        /*
         * When clearing a FMA-diagnosed fault, we always want to
         * unspare the device, as we assume that the original spare was
         * done in response to the FMA fault.
         */
        if (!vdev_is_dead(vd) && vd->vdev_parent != NULL &&
            vd->vdev_parent->vdev_ops == &vdev_spare_ops &&
            vd->vdev_parent->vdev_child[0] == vd)
                vd->vdev_unspare = B_TRUE;
}

boolean_t
vdev_is_dead(vdev_t *vd)
{
        /*
         * Holes and missing devices are always considered "dead".
         * This simplifies the code since we don't have to check for
         * these types of devices in the various code paths.
         * Instead we rely on the fact that we skip over dead devices
         * before issuing I/O to them.
         */
        return (vd->vdev_state < VDEV_STATE_DEGRADED || vd->vdev_ishole ||
            vd->vdev_ops == &vdev_missing_ops);
}

boolean_t
vdev_readable(vdev_t *vd)
{
        return (!vdev_is_dead(vd) && !vd->vdev_cant_read);
}

boolean_t
vdev_writeable(vdev_t *vd)
{
        return (!vdev_is_dead(vd) && !vd->vdev_cant_write);
}

boolean_t
vdev_allocatable(vdev_t *vd)
{
        uint64_t state = vd->vdev_state;

        /*
         * We currently allow allocations from vdevs which may be in the
         * process of reopening (i.e. VDEV_STATE_CLOSED). If the device
         * fails to reopen then we'll catch it later when we're holding
         * the proper locks.  Note that we have to get the vdev state
         * in a local variable because although it changes atomically,
         * we're asking two separate questions about it.
         */
        return (!(state < VDEV_STATE_DEGRADED && state != VDEV_STATE_CLOSED) &&
            !vd->vdev_cant_write && !vd->vdev_ishole);
}

boolean_t
vdev_accessible(vdev_t *vd, zio_t *zio)
{
        ASSERT(zio->io_vd == vd);

        if (vdev_is_dead(vd) || vd->vdev_remove_wanted)
                return (B_FALSE);

        if (zio->io_type == ZIO_TYPE_READ)
                return (!vd->vdev_cant_read);

        if (zio->io_type == ZIO_TYPE_WRITE)
                return (!vd->vdev_cant_write);

        return (B_TRUE);
}

/*
 * Get statistics for the given vdev.
 */
void
vdev_get_stats(vdev_t *vd, vdev_stat_t *vs)
{
        spa_t *spa = vd->vdev_spa;
        vdev_t *rvd = spa->spa_root_vdev;

        ASSERT(spa_config_held(spa, SCL_ALL, RW_READER) != 0);

        mutex_enter(&vd->vdev_stat_lock);
        bcopy(&vd->vdev_stat, vs, sizeof (*vs));
        vs->vs_timestamp = gethrtime() - vs->vs_timestamp;
        vs->vs_state = vd->vdev_state;
        vs->vs_rsize = vdev_get_min_asize(vd);
        if (vd->vdev_ops->vdev_op_leaf)
                vs->vs_rsize += VDEV_LABEL_START_SIZE + VDEV_LABEL_END_SIZE;
        vs->vs_esize = vd->vdev_max_asize - vd->vdev_asize;
        if (vd->vdev_aux == NULL && vd == vd->vdev_top && !vd->vdev_ishole) {
                vs->vs_fragmentation = vd->vdev_mg->mg_fragmentation;
        }

        /*
         * If we're getting stats on the root vdev, aggregate the I/O counts
         * over all top-level vdevs (i.e. the direct children of the root).
         */
        if (vd == rvd) {
                for (int c = 0; c < rvd->vdev_children; c++) {
                        vdev_t *cvd = rvd->vdev_child[c];
                        vdev_stat_t *cvs = &cvd->vdev_stat;

                        for (int t = 0; t < ZIO_TYPES; t++) {
                                vs->vs_ops[t] += cvs->vs_ops[t];
                                vs->vs_bytes[t] += cvs->vs_bytes[t];
                        }
                        cvs->vs_scan_removing = cvd->vdev_removing;
                }
        }
        mutex_exit(&vd->vdev_stat_lock);
}

void
vdev_clear_stats(vdev_t *vd)
{
        mutex_enter(&vd->vdev_stat_lock);
        vd->vdev_stat.vs_space = 0;
        vd->vdev_stat.vs_dspace = 0;
        vd->vdev_stat.vs_alloc = 0;
        mutex_exit(&vd->vdev_stat_lock);
}

void
vdev_scan_stat_init(vdev_t *vd)
{
        vdev_stat_t *vs = &vd->vdev_stat;

        for (int c = 0; c < vd->vdev_children; c++)
                vdev_scan_stat_init(vd->vdev_child[c]);

        mutex_enter(&vd->vdev_stat_lock);
        vs->vs_scan_processed = 0;
        mutex_exit(&vd->vdev_stat_lock);
}

void
vdev_stat_update(zio_t *zio, uint64_t psize)
{
        spa_t *spa = zio->io_spa;
        vdev_t *rvd = spa->spa_root_vdev;
        vdev_t *vd = zio->io_vd ? zio->io_vd : rvd;
        vdev_t *pvd;
        uint64_t txg = zio->io_txg;
        vdev_stat_t *vs = &vd->vdev_stat;
        zio_type_t type = zio->io_type;
        int flags = zio->io_flags;

        /*
         * If this i/o is a gang leader, it didn't do any actual work.
         */
        if (zio->io_gang_tree)
                return;

        if (zio->io_error == 0) {
                /*
                 * If this is a root i/o, don't count it -- we've already
                 * counted the top-level vdevs, and vdev_get_stats() will
                 * aggregate them when asked.  This reduces contention on
                 * the root vdev_stat_lock and implicitly handles blocks
                 * that compress away to holes, for which there is no i/o.
                 * (Holes never create vdev children, so all the counters
                 * remain zero, which is what we want.)
                 *
                 * Note: this only applies to successful i/o (io_error == 0)
                 * because unlike i/o counts, errors are not additive.
                 * When reading a ditto block, for example, failure of
                 * one top-level vdev does not imply a root-level error.
                 */
                if (vd == rvd)
                        return;

                ASSERT(vd == zio->io_vd);

                if (flags & ZIO_FLAG_IO_BYPASS)
                        return;

                mutex_enter(&vd->vdev_stat_lock);

                if (flags & ZIO_FLAG_IO_REPAIR) {
                        if (flags & ZIO_FLAG_SCAN_THREAD) {
                                dsl_scan_phys_t *scn_phys =
                                    &spa->spa_dsl_pool->dp_scan->scn_phys;
                                uint64_t *processed = &scn_phys->scn_processed;

                                /* XXX cleanup? */
                                if (vd->vdev_ops->vdev_op_leaf)
                                        atomic_add_64(processed, psize);
                                vs->vs_scan_processed += psize;
                        }

                        if (flags & ZIO_FLAG_SELF_HEAL)
                                vs->vs_self_healed += psize;
                }

                vs->vs_ops[type]++;
                vs->vs_bytes[type] += psize;

                mutex_exit(&vd->vdev_stat_lock);
                return;
        }

        if (flags & ZIO_FLAG_SPECULATIVE)
                return;

        /*
         * If this is an I/O error that is going to be retried, then ignore the
         * error.  Otherwise, the user may interpret B_FAILFAST I/O errors as
         * hard errors, when in reality they can happen for any number of
         * innocuous reasons (bus resets, MPxIO link failure, etc).
         */
        if (zio->io_error == EIO &&
            !(zio->io_flags & ZIO_FLAG_IO_RETRY))
                return;

        /*
         * Intent logs writes won't propagate their error to the root
         * I/O so don't mark these types of failures as pool-level
         * errors.
         */
        if (zio->io_vd == NULL && (zio->io_flags & ZIO_FLAG_DONT_PROPAGATE))
                return;

        mutex_enter(&vd->vdev_stat_lock);
        if (type == ZIO_TYPE_READ && !vdev_is_dead(vd)) {
                if (zio->io_error == ECKSUM)
                        vs->vs_checksum_errors++;
                else
                        vs->vs_read_errors++;
        }
        if (type == ZIO_TYPE_WRITE && !vdev_is_dead(vd))
                vs->vs_write_errors++;
        mutex_exit(&vd->vdev_stat_lock);

        if (type == ZIO_TYPE_WRITE && txg != 0 &&
            (!(flags & ZIO_FLAG_IO_REPAIR) ||
            (flags & ZIO_FLAG_SCAN_THREAD) ||
            spa->spa_claiming)) {
                /*
                 * This is either a normal write (not a repair), or it's
                 * a repair induced by the scrub thread, or it's a repair
                 * made by zil_claim() during spa_load() in the first txg.
                 * In the normal case, we commit the DTL change in the same
                 * txg as the block was born.  In the scrub-induced repair
                 * case, we know that scrubs run in first-pass syncing context,
                 * so we commit the DTL change in spa_syncing_txg(spa).
                 * In the zil_claim() case, we commit in spa_first_txg(spa).
                 *
                 * We currently do not make DTL entries for failed spontaneous
                 * self-healing writes triggered by normal (non-scrubbing)
                 * reads, because we have no transactional context in which to
                 * do so -- and it's not clear that it'd be desirable anyway.
                 */
                if (vd->vdev_ops->vdev_op_leaf) {
                        uint64_t commit_txg = txg;
                        if (flags & ZIO_FLAG_SCAN_THREAD) {
                                ASSERT(flags & ZIO_FLAG_IO_REPAIR);
                                ASSERT(spa_sync_pass(spa) == 1);
                                vdev_dtl_dirty(vd, DTL_SCRUB, txg, 1);
                                commit_txg = spa_syncing_txg(spa);
                        } else if (spa->spa_claiming) {
                                ASSERT(flags & ZIO_FLAG_IO_REPAIR);
                                commit_txg = spa_first_txg(spa);
                        }
                        ASSERT(commit_txg >= spa_syncing_txg(spa));
                        if (vdev_dtl_contains(vd, DTL_MISSING, txg, 1))
                                return;
                        for (pvd = vd; pvd != rvd; pvd = pvd->vdev_parent)
                                vdev_dtl_dirty(pvd, DTL_PARTIAL, txg, 1);
                        vdev_dirty(vd->vdev_top, VDD_DTL, vd, commit_txg);
                }
                if (vd != rvd)
                        vdev_dtl_dirty(vd, DTL_MISSING, txg, 1);
        }
}

/*
 * Update the in-core space usage stats for this vdev, its metaslab class,
 * and the root vdev.
 */
void
vdev_space_update(vdev_t *vd, int64_t alloc_delta, int64_t defer_delta,
    int64_t space_delta)
{
        int64_t dspace_delta = space_delta;
        spa_t *spa = vd->vdev_spa;
        vdev_t *rvd = spa->spa_root_vdev;
        metaslab_group_t *mg = vd->vdev_mg;
        metaslab_class_t *mc = mg ? mg->mg_class : NULL;

        ASSERT(vd == vd->vdev_top);

        /*
         * Apply the inverse of the psize-to-asize (ie. RAID-Z) space-expansion
         * factor.  We must calculate this here and not at the root vdev
         * because the root vdev's psize-to-asize is simply the max of its
         * childrens', thus not accurate enough for us.
         */
        ASSERT((dspace_delta & (SPA_MINBLOCKSIZE-1)) == 0);
        ASSERT(vd->vdev_deflate_ratio != 0 || vd->vdev_isl2cache);
        dspace_delta = (dspace_delta >> SPA_MINBLOCKSHIFT) *
            vd->vdev_deflate_ratio;

        mutex_enter(&vd->vdev_stat_lock);
        vd->vdev_stat.vs_alloc += alloc_delta;
        vd->vdev_stat.vs_space += space_delta;
        vd->vdev_stat.vs_dspace += dspace_delta;
        mutex_exit(&vd->vdev_stat_lock);

        if (mc == spa_normal_class(spa)) {
                mutex_enter(&rvd->vdev_stat_lock);
                rvd->vdev_stat.vs_alloc += alloc_delta;
                rvd->vdev_stat.vs_space += space_delta;
                rvd->vdev_stat.vs_dspace += dspace_delta;
                mutex_exit(&rvd->vdev_stat_lock);
        }

        if (mc != NULL) {
                ASSERT(rvd == vd->vdev_parent);
                ASSERT(vd->vdev_ms_count != 0);

                metaslab_class_space_update(mc,
                    alloc_delta, defer_delta, space_delta, dspace_delta);
        }
}

/*
 * Mark a top-level vdev's config as dirty, placing it on the dirty list
 * so that it will be written out next time the vdev configuration is synced.
 * If the root vdev is specified (vdev_top == NULL), dirty all top-level vdevs.
 */
void
vdev_config_dirty(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        vdev_t *rvd = spa->spa_root_vdev;
        int c;

        ASSERT(spa_writeable(spa));

        /*
         * If this is an aux vdev (as with l2cache and spare devices), then we
         * update the vdev config manually and set the sync flag.
         */
        if (vd->vdev_aux != NULL) {
                spa_aux_vdev_t *sav = vd->vdev_aux;
                nvlist_t **aux;
                uint_t naux;

                for (c = 0; c < sav->sav_count; c++) {
                        if (sav->sav_vdevs[c] == vd)
                                break;
                }

                if (c == sav->sav_count) {
                        /*
                         * We're being removed.  There's nothing more to do.
                         */
                        ASSERT(sav->sav_sync == B_TRUE);
                        return;
                }

                sav->sav_sync = B_TRUE;

                if (nvlist_lookup_nvlist_array(sav->sav_config,
                    ZPOOL_CONFIG_L2CACHE, &aux, &naux) != 0) {
                        VERIFY(nvlist_lookup_nvlist_array(sav->sav_config,
                            ZPOOL_CONFIG_SPARES, &aux, &naux) == 0);
                }

                ASSERT(c < naux);

                /*
                 * Setting the nvlist in the middle if the array is a little
                 * sketchy, but it will work.
                 */
                nvlist_free(aux[c]);
                aux[c] = vdev_config_generate(spa, vd, B_TRUE, 0);

                return;
        }

        /*
         * The dirty list is protected by the SCL_CONFIG lock.  The caller
         * must either hold SCL_CONFIG as writer, or must be the sync thread
         * (which holds SCL_CONFIG as reader).  There's only one sync thread,
         * so this is sufficient to ensure mutual exclusion.
         */
        ASSERT(spa_config_held(spa, SCL_CONFIG, RW_WRITER) ||
            (dsl_pool_sync_context(spa_get_dsl(spa)) &&
            spa_config_held(spa, SCL_CONFIG, RW_READER)));

        if (vd == rvd) {
                for (c = 0; c < rvd->vdev_children; c++)
                        vdev_config_dirty(rvd->vdev_child[c]);
        } else {
                ASSERT(vd == vd->vdev_top);

                if (!list_link_active(&vd->vdev_config_dirty_node) &&
                    !vd->vdev_ishole)
                        list_insert_head(&spa->spa_config_dirty_list, vd);
        }
}

void
vdev_config_clean(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;

        ASSERT(spa_config_held(spa, SCL_CONFIG, RW_WRITER) ||
            (dsl_pool_sync_context(spa_get_dsl(spa)) &&
            spa_config_held(spa, SCL_CONFIG, RW_READER)));

        ASSERT(list_link_active(&vd->vdev_config_dirty_node));
        list_remove(&spa->spa_config_dirty_list, vd);
}

/*
 * Mark a top-level vdev's state as dirty, so that the next pass of
 * spa_sync() can convert this into vdev_config_dirty().  We distinguish
 * the state changes from larger config changes because they require
 * much less locking, and are often needed for administrative actions.
 */
void
vdev_state_dirty(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;

        ASSERT(spa_writeable(spa));
        ASSERT(vd == vd->vdev_top);

        /*
         * The state list is protected by the SCL_STATE lock.  The caller
         * must either hold SCL_STATE as writer, or must be the sync thread
         * (which holds SCL_STATE as reader).  There's only one sync thread,
         * so this is sufficient to ensure mutual exclusion.
         */
        ASSERT(spa_config_held(spa, SCL_STATE, RW_WRITER) ||
            (dsl_pool_sync_context(spa_get_dsl(spa)) &&
            spa_config_held(spa, SCL_STATE, RW_READER)));

        if (!list_link_active(&vd->vdev_state_dirty_node) && !vd->vdev_ishole)
                list_insert_head(&spa->spa_state_dirty_list, vd);
}

void
vdev_state_clean(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;

        ASSERT(spa_config_held(spa, SCL_STATE, RW_WRITER) ||
            (dsl_pool_sync_context(spa_get_dsl(spa)) &&
            spa_config_held(spa, SCL_STATE, RW_READER)));

        ASSERT(list_link_active(&vd->vdev_state_dirty_node));
        list_remove(&spa->spa_state_dirty_list, vd);
}

/*
 * Propagate vdev state up from children to parent.
 */
void
vdev_propagate_state(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        vdev_t *rvd = spa->spa_root_vdev;
        int degraded = 0, faulted = 0;
        int corrupted = 0;
        vdev_t *child;

        if (vd->vdev_children > 0) {
                for (int c = 0; c < vd->vdev_children; c++) {
                        child = vd->vdev_child[c];

                        /*
                         * Don't factor holes into the decision.
                         */
                        if (child->vdev_ishole)
                                continue;

                        if (!vdev_readable(child) ||
                            (!vdev_writeable(child) && spa_writeable(spa))) {
                                /*
                                 * Root special: if there is a top-level log
                                 * device, treat the root vdev as if it were
                                 * degraded.
                                 */
                                if (child->vdev_islog && vd == rvd)
                                        degraded++;
                                else
                                        faulted++;
                        } else if (child->vdev_state <= VDEV_STATE_DEGRADED) {
                                degraded++;
                        }

                        if (child->vdev_stat.vs_aux == VDEV_AUX_CORRUPT_DATA)
                                corrupted++;
                }

                vd->vdev_ops->vdev_op_state_change(vd, faulted, degraded);

                /*
                 * Root special: if there is a top-level vdev that cannot be
                 * opened due to corrupted metadata, then propagate the root
                 * vdev's aux state as 'corrupt' rather than 'insufficient
                 * replicas'.
                 */
                if (corrupted && vd == rvd &&
                    rvd->vdev_state == VDEV_STATE_CANT_OPEN)
                        vdev_set_state(rvd, B_FALSE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_CORRUPT_DATA);
        }

        if (vd->vdev_parent)
                vdev_propagate_state(vd->vdev_parent);
}

/*
 * Set a vdev's state.  If this is during an open, we don't update the parent
 * state, because we're in the process of opening children depth-first.
 * Otherwise, we propagate the change to the parent.
 *
 * If this routine places a device in a faulted state, an appropriate ereport is
 * generated.
 */
void
vdev_set_state(vdev_t *vd, boolean_t isopen, vdev_state_t state, vdev_aux_t aux)
{
        uint64_t save_state;
        spa_t *spa = vd->vdev_spa;

        if (state == vd->vdev_state) {
                vd->vdev_stat.vs_aux = aux;
                return;
        }

        save_state = vd->vdev_state;

        vd->vdev_state = state;
        vd->vdev_stat.vs_aux = aux;

        /*
         * If we are setting the vdev state to anything but an open state, then
         * always close the underlying device unless the device has requested
         * a delayed close (i.e. we're about to remove or fault the device).
         * Otherwise, we keep accessible but invalid devices open forever.
         * We don't call vdev_close() itself, because that implies some extra
         * checks (offline, etc) that we don't want here.  This is limited to
         * leaf devices, because otherwise closing the device will affect other
         * children.
         */
        if (!vd->vdev_delayed_close && vdev_is_dead(vd) &&
            vd->vdev_ops->vdev_op_leaf)
                vd->vdev_ops->vdev_op_close(vd);

        /*
         * If we have brought this vdev back into service, we need
         * to notify fmd so that it can gracefully repair any outstanding
         * cases due to a missing device.  We do this in all cases, even those
         * that probably don't correlate to a repaired fault.  This is sure to
         * catch all cases, and we let the zfs-retire agent sort it out.  If
         * this is a transient state it's OK, as the retire agent will
         * double-check the state of the vdev before repairing it.
         */
        if (state == VDEV_STATE_HEALTHY && vd->vdev_ops->vdev_op_leaf &&
            vd->vdev_prevstate != state)
                zfs_post_state_change(spa, vd);

        if (vd->vdev_removed &&
            state == VDEV_STATE_CANT_OPEN &&
            (aux == VDEV_AUX_OPEN_FAILED || vd->vdev_checkremove)) {
                /*
                 * If the previous state is set to VDEV_STATE_REMOVED, then this
                 * device was previously marked removed and someone attempted to
                 * reopen it.  If this failed due to a nonexistent device, then
                 * keep the device in the REMOVED state.  We also let this be if
                 * it is one of our special test online cases, which is only
                 * attempting to online the device and shouldn't generate an FMA
                 * fault.
                 */
                vd->vdev_state = VDEV_STATE_REMOVED;
                vd->vdev_stat.vs_aux = VDEV_AUX_NONE;
        } else if (state == VDEV_STATE_REMOVED) {
                vd->vdev_removed = B_TRUE;
        } else if (state == VDEV_STATE_CANT_OPEN) {
                /*
                 * If we fail to open a vdev during an import or recovery, we
                 * mark it as "not available", which signifies that it was
                 * never there to begin with.  Failure to open such a device
                 * is not considered an error.
                 */
                if ((spa_load_state(spa) == SPA_LOAD_IMPORT ||
                    spa_load_state(spa) == SPA_LOAD_RECOVER) &&
                    vd->vdev_ops->vdev_op_leaf)
                        vd->vdev_not_present = 1;

                /*
                 * Post the appropriate ereport.  If the 'prevstate' field is
                 * set to something other than VDEV_STATE_UNKNOWN, it indicates
                 * that this is part of a vdev_reopen().  In this case, we don't
                 * want to post the ereport if the device was already in the
                 * CANT_OPEN state beforehand.
                 *
                 * If the 'checkremove' flag is set, then this is an attempt to
                 * online the device in response to an insertion event.  If we
                 * hit this case, then we have detected an insertion event for a
                 * faulted or offline device that wasn't in the removed state.
                 * In this scenario, we don't post an ereport because we are
                 * about to replace the device, or attempt an online with
                 * vdev_forcefault, which will generate the fault for us.
                 */
                if ((vd->vdev_prevstate != state || vd->vdev_forcefault) &&
                    !vd->vdev_not_present && !vd->vdev_checkremove &&
                    vd != spa->spa_root_vdev) {
                        const char *class;

                        switch (aux) {
                        case VDEV_AUX_OPEN_FAILED:
                                class = FM_EREPORT_ZFS_DEVICE_OPEN_FAILED;
                                break;
                        case VDEV_AUX_CORRUPT_DATA:
                                class = FM_EREPORT_ZFS_DEVICE_CORRUPT_DATA;
                                break;
                        case VDEV_AUX_NO_REPLICAS:
                                class = FM_EREPORT_ZFS_DEVICE_NO_REPLICAS;
                                break;
                        case VDEV_AUX_BAD_GUID_SUM:
                                class = FM_EREPORT_ZFS_DEVICE_BAD_GUID_SUM;
                                break;
                        case VDEV_AUX_TOO_SMALL:
                                class = FM_EREPORT_ZFS_DEVICE_TOO_SMALL;
                                break;
                        case VDEV_AUX_BAD_LABEL:
                                class = FM_EREPORT_ZFS_DEVICE_BAD_LABEL;
                                break;
                        default:
                                class = FM_EREPORT_ZFS_DEVICE_UNKNOWN;
                        }

                        zfs_ereport_post(class, spa, vd, NULL, save_state, 0);
                }

                /* Erase any notion of persistent removed state */
                vd->vdev_removed = B_FALSE;
        } else {
                vd->vdev_removed = B_FALSE;
        }

        if (!isopen && vd->vdev_parent)
                vdev_propagate_state(vd->vdev_parent);
}

/*
 * Check the vdev configuration to ensure that it's capable of supporting
 * a root pool. We do not support partial configuration.
 * In addition, only a single top-level vdev is allowed.
 */
boolean_t
vdev_is_bootable(vdev_t *vd)
{
        if (!vd->vdev_ops->vdev_op_leaf) {
                char *vdev_type = vd->vdev_ops->vdev_op_type;

                if (strcmp(vdev_type, VDEV_TYPE_ROOT) == 0 &&
                    vd->vdev_children > 1) {
                        return (B_FALSE);
                } else if (strcmp(vdev_type, VDEV_TYPE_MISSING) == 0) {
                        return (B_FALSE);
                }
        }

        for (int c = 0; c < vd->vdev_children; c++) {
                if (!vdev_is_bootable(vd->vdev_child[c]))
                        return (B_FALSE);
        }
        return (B_TRUE);
}

/*
 * Load the state from the original vdev tree (ovd) which
 * we've retrieved from the MOS config object. If the original
 * vdev was offline or faulted then we transfer that state to the
 * device in the current vdev tree (nvd).
 */
void
vdev_load_log_state(vdev_t *nvd, vdev_t *ovd)
{
        spa_t *spa = nvd->vdev_spa;

        ASSERT(nvd->vdev_top->vdev_islog);
        ASSERT(spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);
        ASSERT3U(nvd->vdev_guid, ==, ovd->vdev_guid);

        for (int c = 0; c < nvd->vdev_children; c++)
                vdev_load_log_state(nvd->vdev_child[c], ovd->vdev_child[c]);

        if (nvd->vdev_ops->vdev_op_leaf) {
                /*
                 * Restore the persistent vdev state
                 */
                nvd->vdev_offline = ovd->vdev_offline;
                nvd->vdev_faulted = ovd->vdev_faulted;
                nvd->vdev_degraded = ovd->vdev_degraded;
                nvd->vdev_removed = ovd->vdev_removed;
        }
}

/*
 * Determine if a log device has valid content.  If the vdev was
 * removed or faulted in the MOS config then we know that
 * the content on the log device has already been written to the pool.
 */
boolean_t
vdev_log_state_valid(vdev_t *vd)
{
        if (vd->vdev_ops->vdev_op_leaf && !vd->vdev_faulted &&
            !vd->vdev_removed)
                return (B_TRUE);

        for (int c = 0; c < vd->vdev_children; c++)
                if (vdev_log_state_valid(vd->vdev_child[c]))
                        return (B_TRUE);

        return (B_FALSE);
}

/*
 * Expand a vdev if possible.
 */
void
vdev_expand(vdev_t *vd, uint64_t txg)
{
        ASSERT(vd->vdev_top == vd);
        ASSERT(spa_config_held(vd->vdev_spa, SCL_ALL, RW_WRITER) == SCL_ALL);

        if ((vd->vdev_asize >> vd->vdev_ms_shift) > vd->vdev_ms_count) {
                VERIFY(vdev_metaslab_init(vd, txg) == 0);
                vdev_config_dirty(vd);
        }
}

/*
 * Split a vdev.
 */
void
vdev_split(vdev_t *vd)
{
        vdev_t *cvd, *pvd = vd->vdev_parent;

        vdev_remove_child(pvd, vd);
        vdev_compact_children(pvd);

        cvd = pvd->vdev_child[0];
        if (pvd->vdev_children == 1) {
                vdev_remove_parent(cvd);
                cvd->vdev_splitting = B_TRUE;
        }
        vdev_propagate_state(cvd);
}

void
vdev_deadman(vdev_t *vd)
{
        for (int c = 0; c < vd->vdev_children; c++) {
                vdev_t *cvd = vd->vdev_child[c];

                vdev_deadman(cvd);
        }

        if (vd->vdev_ops->vdev_op_leaf) {
                vdev_queue_t *vq = &vd->vdev_queue;

                mutex_enter(&vq->vq_lock);
                if (avl_numnodes(&vq->vq_active_tree) > 0) {
                        spa_t *spa = vd->vdev_spa;
                        zio_t *fio;
                        uint64_t delta;

                        /*
                         * Look at the head of all the pending queues,
                         * if any I/O has been outstanding for longer than
                         * the spa_deadman_synctime we panic the system.
                         */
                        fio = avl_first(&vq->vq_active_tree);
                        delta = gethrtime() - fio->io_timestamp;
                        if (delta > spa_deadman_synctime(spa)) {
                                zfs_dbgmsg("SLOW IO: zio timestamp %lluns, "
                                    "delta %lluns, last io %lluns",
                                    fio->io_timestamp, delta,
                                    vq->vq_io_complete_ts);
                                fm_panic("I/O to pool '%s' appears to be "
                                    "hung.", spa_name(spa));
                        }
                }
                mutex_exit(&vq->vq_lock);
        }
}